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Ultrasonic vibration-assisted cutting of titanium alloys: A state-of-the-art review

May 2024
Chinese Journal of Aeronautics

DOI:10.1016/j.cja.2024.05.034

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Authors:

Ahmar Khan

Nanjing University of Aeronautics and Astronautics

Xin Wang

Nanjing University of Aeronautics and Astronautics

Biao Zhao

Nanjing University of Aeronautics and Astronautics

Wenfeng Ding

Nanjing University of Aeronautics and Astronautics

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REVIEW

Ultrasonic vibration-assisted cutting of titanium

alloys: A state-of-the-art review

Ahmar KHAN

, Xin WANG

, Biao ZHAO

a,*

, Wenfeng DING

Muhammad JAMIL

, Aqib Mashood KHAN

, Syed Hammad ALI

Sadam HUSSAIN

, Jiong ZHANG

, Raj DAS

National Key Laboratory of Science and Technology on Helicopter Transmission, Nanjing University of Aeronautics and

Astronautics, Nanjing 210016, China

Department of Mechanical Engineering, College of Engineering, City University of Hong Kong, Hong Kong 999077, China

Centre for Additive Manufacturing, School of Engineering, Aerospace Engineering and Aviation, RMIT University, Victoria

3083, Australia

Received 30 January 2024; revised 3 March 2024; accepted 28 April 2024

Available online 31 May 2024

KEYWORDS

Ultrasonic vibration-assisted

cutting;

Titanium alloys;

Material removal mecha-

nism;

Machinability;

Sustainability

Abstract The remarkable ability of titanium alloys to preserve their superior physical and chem-

ical characteristics when subjected to extreme conditions signiﬁcantly enhances their importance in

the aerospace, military, and medical sectors. However, conventional machining of titanium alloys

leads to elevated tool wear, development of surface defects, and reduced machining efﬁciency

due to their low heat conductivity, and chemical afﬁnity. These issues can be somewhat counter-

acted by integrating ultrasonic vibration in the conventional machining of titanium alloys and also

enhance sustainability. This review article offers a holistic evaluation of the inﬂuence of ultrasonic

vibration-assisted milling and turning on cutting forces, temperature, tool wear, and surface integ-

rity, encompassing surface morphology, surface roughness, surface residual stress, surface hardness,

and surface tribological properties during titanium alloys machining. Furthermore, it investigates

the sustainability aspect that has not been previously examined. Studies on the performance of

ultrasonic-assisted cutting revealed several advantages, including decreased cutting forces and cut-

ting temperature, improved tool life, and a better-machined surface during machining. Conse-

quently, the sustainability factor is improved due to minimized energy consumption and residual

waste. In conclusion, the key challenges and future prospects in the ultrasonic-assisted cutting of

titanium alloys are also discussed. This review article provides beneﬁcial knowledge for manufactur-

*Corresponding author.

E-mail address: zhaobiao@nuaa.edu.cn (B. ZHAO).

This article is part of a special issue ‘‘Emerging Materials

Processing Technologies for Aerospace Applications”.

Production and hosting by Elsevier

Peer review under responsibility of Editorial Committee of CJA.

Chinese Journal of Aeronautics, (2025), 38, 103078

Chinese Society of Aeronautics and Astronautics

& Beihang University

Chinese Journal of Aeronautics

cja@buaa.edu.cn

www.sciencedirect.com

https://doi.org/10.1016/j.cja.2024.05.034

1000-9361 Ó2024 Production and hosting by Elsevier Ltd. on behalf of Chinese Society of Aeronautics and Astronautics.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

ers and researchers regarding ultrasonic vibration-assisted cutting of titanium alloy and will play an

important role in achieving sustainability in the industry.

Ó2024 Production and hosting by Elsevier Ltd. on behalf of Chinese Society of Aeronautics and

Astronautics. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

1. Introduction

Titanium alloys possess a number of remarkable characteris-

tics that make them highly desirable in the aerospace industry,

including lightweight, a high strength-to-weight ratio, resis-

tance to corrosion and oxidation, and high fracture durabil-

ity.

1,2

The excellent properties of titanium reduce the weight

of aircraft, increase the structural strength, and improve the

corrosion resistance of aircraft components.

The complex

and specialized design of aircraft components requires good

surface quality and tight tolerance. This is because shape accu-

racy and good surface quality are critical for aircraft to sustain

in harsh environments.

Different machining methods are used

in the aerospace industry to achieve the intended conﬁguration

of aircraft components made from titanium alloys.

Milling

and turning are used in the aerospace industry to produce

the net shape or near net shape parts. However, the excellent

mechanical properties and minimal thermal conductivity of

titanium alloys make their machining considerably difﬁcult.

Ensuring ideal surface quality while machining titanium alloys

presents a signiﬁcant challenge. The tool undergoes increased

wear when machining titanium alloys, predominantly as a

result of the cutting region elevated temperature and the tita-

nium alloys ability to retain excellent mechanical properties

even at extremely high temperatures.

The severe tool wear

increases the cutting forces and produces several defects on

the machined surface.

During the machining of Ti

AlNb,

the cutting temperature can easily reach about 800 °C at high

cutting speed.

Fan et al.

performed turning on titanium

alloy with a cemented carbide tool to investigate the tool wear

behavior. It was determined that elevated cutting temperature

within the cutting zone gives rise to pronounced tool wear. The

cutting forces produced in the milling of titanium alloy were

examined by Zhang et al.

. When machining titanium alloy,

signiﬁcant tool wear resulted in high cutting forces. Shokrani

et al.

investigated the surface condition of Ti–6Al–4V alloy

during conventional milling (CM). Surface imperfections were

produced by the machining process, including abrasion marks,

adhered material, and material dispersion. The conventional

machining of titanium alloy leads to substantial tool wear, ele-

vated cutting forces, and subpar surface integrity.

So, sus-

tainability is a concern in traditional machining of titanium

alloys because of high energy consumption, material waste,

and impact on the environment.

Recently, hybrid machining processes, such as vibration-

assisted machining, thermal-assisted machining (TAM), and

laser-assisted machining (LAM), have become increasingly

popular in the machining industry. Prior studies have noted

that the utilization of hybrid machining processes can substan-

tially enhance the efﬁciency and quality of the machined tita-

nium alloy surfaces.

14–16

Numerous studies have been

undertaken to comprehend the impact of ultrasonic vibrations

during milling and turning of hard-to-cut materials. The ﬁnd-

ings from these studies indicated that integrating vibration into

the milling and turning process can substantially enhance sur-

face quality and minimize the cutting forces and cutting tem-

perature.

17,18

Fig. 1 shows the applications of ultrasonic

vibration-assisted machining.

Ultrasonic vibration-assisted machining is a manufacturing

procedure in which the workpiece or tool is subjected to high

frequency and low amplitude vibrations. With the integration

of vibrations into the machining processes, the tool regularly

disengages from the workpiece at suitable machining and

vibration parameters, consequently resulting in an improved

material removal mechanism.

Jiao et al.

asserted that the

cutting forces produced in the ultrasonic vibration-assisted

milling (UVAM) of titanium alloy were lower as compared

to in the CM process. Chen et al.

formulated the model for

force and temperature prediction during vibration-assisted

machining process. The ﬁndings indicate that machining with

vibration assistance lowers the ploughing forces and tempera-

ture. Kandi et al.

performed simulation and experimental

investigation for ultrasonic vibration-assisted turning (UVAT)

of titanium alloy. The utilization of ultrasonic vibration in the

cutting process serves to mitigate the cutting temperature,

thereby enhancing the overall quality of the machined surface.

To reduce cutting forces and surface roughness while machin-

ing titanium alloys, Lu

¨et al.

suggested the use of UVAM.

According to Pei et al.

, UVAT had an edge when it came

to enhancing Ti–6Al–4V machined surface quality. Li et al.

conducted longitudinal torsional vibration-assisted milling

(LTUAM) on TC18 titanium alloy. The ﬁndings show that

the machining technique improves the machined surface mor-

phology, dramatically lowers the cutting temperature, and

greatly reduces cutting forces. As previously indicated, UVAM

and UAVT procedures offer a number of beneﬁts; neverthe-

less, they also have a number of drawbacks, including signiﬁ-

cant tool wear and, in some situations, decreased surface

quality.

Therefore, to optimize the machining process, a deep

analysis of the effect of process parameters of ultrasonic-

assisted milling and turning on the performance of titanium

alloys’ machining is essential. Fig. 2 depicts the papers pub-

lished on ultrasonic assisted machining of titanium alloys in

the last fourteen years, data from Scopus with search keywords

string: (TITLE-ABS-KEY (ultrasonic assisted machining, tita-

nium alloys)). The vibration-assisted machining of titanium

alloys got researchers’ attention recently due to their applica-

tion in the aerospace industry. The analysis of vibration-

assisted machining will help to improve productivity and

increase the usage of titanium alloys in aerospace applications.

Recently, numerous scholars have investigated the impact

of ultrasonic-assisted machining of hard-to-cut materials on

output parameters. However, this review paper distinguishes

itself by not only synthesizing existing research on

ultrasonic-assisted machining of titanium alloys but also by

addressing the research gaps that have thus far remained rela-

tively unexplored. In recent years, several scholarly publica-

tions have examined ultrasonic vibration-assisted machining.

2 A. KHAN et al.

The existing literature on ultrasonic vibration-assisted machin-

ing mainly explored the vibration system design and applica-

tion effects.

27,28

The review paper by Haﬁz et al.

examined

the effect of process parameters on cutting force, tool life,

and surface integrity during ultrasonic-assisted machining of

Inconel alloys. Similarly, Yang et al.

offered a comprehensive

review of the development trend in vibration-assisted machin-

ing. They analyzed the effect of different vibration-assisted

machining techniques on tool life and surface quality during

the machining of advanced materials. Their analysis over-

looked the speciﬁc challenges unique to vibration-assisted

machining of titanium alloys and sustainability aspects, leav-

ing a research gap regarding the effect of vibration-assisted

machining of titanium alloy on cutting forces and temperature,

tool life, surface quality, and sustainability aspects such as pro-

ductivity, energy consumption, and environmental elements.

The primary objective of this review article is to meticu-

lously analyze the effect of ultrasonic-assisted milling and turn-

ing of titanium alloys (Ti–6Al–4 V, TC4, TC18, Ti

AlNb,

Al, Ti–676–0.9L and Ti–6246) on cutting forces, tool wear,

and surface integrity, and evaluate the effect of ultrasonic-

assisted machining of titanium alloys on sustainability aspects.

This study aims to consolidate a comprehensive collection of

data pertaining to the ultrasonic-assisted machining of

Fig. 1 Applications of ultrasonic vibration-assisted machining.

Fig. 2 Publications on ultrasonic-assisted machining of titanium

alloys.

Ultrasonic vibration-assisted cutting of titanium alloys 3

titanium alloys, thereby establishing a foundational resource

for future investigations in this ﬁeld. The structure of the paper

is shown in Fig. 3.Section 1 explains the need for the machin-

ing of titanium alloys, the challenges related to the machining

of titanium alloys, the effect of vibration-assisted cutting, and

the purpose of the review paper. Section 2 explains the primary

mechanism of vibration-assisted cutting, modes of vibrations

in vibration-assisted machining, vibration system for

vibration-assisted cutting, and limitations of vibration system

are explained. In section 3 and section 4, the effect of process

parameters on cutting forces and temperature, analyzing the

tool wear behaviour and tool life, and examining the effect

of process parameters on the machined surface, including sur-

face morphology, surface roughness, surface hardness, surface

residual stress, and surface tribological properties during the

ultrasonic assisted milling and turning of titanium alloys are

analyzed. Section 5 reviews the effect of vibration-assisted

cutting of titanium alloys on sustainability aspects such as

Fig. 3 Framework of the review paper.

4 A. KHAN et al.

productivity, energy consumption, and environmental aspects.

In section 6, the conclusions of the current research are made

and offer a prospective viewpoint on the expected directions

for future developments.

2. Basic principle of ultrasonic vibration-assisted cutting

The manufacturing industries are currently exploring sustain-

able manufacturing techniques to align with global regulations

and meet the rising expectations of consumers for sustainable

products. Ultrasonic-assisted machining is a manufacturing

technology with great potential to fulﬁll the requirements of

industrialists to produce high-quality products while aligning

with sustainability principles. Ultrasonic vibration-assisted

cutting is a procedure that involves the application of rapid

oscillations with high frequency to either the tool or the work-

piece in a conventional machining process to improve its per-

formance.

The incorporation of ultrasonic vibration into

the machining process of challenging-to-machine materials

effectively mitigates the magnitude of cutting forces,

decreases the cutting temperature, improves the surface qual-

ity, and increases the life of the tool.

25,33

Due to high precision

and capability to produce defect-free surfaces, ultrasonic-

assisted milling, and turning play a pivotal role in the manu-

facturing of different aeronautical components that are usually

made of hard-to-cut materials.

The ultrasonic vibration-assisted cutting can be classiﬁed

into one dimensional (1D),

26,34–38

two dimensional (2D),

39–45

and three dimensional (3D) ultrasonic vibration-assisted cut-

ting based on the vibrations applied in different directions.

46–

The vibration assisted machining was introduced in 1960s,

and in 1980s and 1990s different vibration modes were devel-

oped for vibration assisted machining.

50,51

After 2000, vibra-

tion assisted machining made signiﬁcant progress with the

development of 2D and 3D vibration assisted machining.

52,53

Skelton et al.

performed tangential ultrasonic vibration-

assisted turning (TUVAT) and axial ultrasonic vibration-

assisted turning (AUVAT) by using a hydraulic vibrator, and

they observed a signiﬁcant reduction in the cutting forces.

Moriwaki and Shamoto

carried out radial ultrasonic

vibration-assisted turning (RUVAT) on stainless steel by using

diamond tool, highlighting a decrease in the tool wear as com-

pare to conventional turning (CT). Zhang et al.

suppressed

the tool wear in steel machining by performing tangential axial

ultrasonic vibration-assisted turning (TAUVAT) but the

energy consumption in vibration-assisted machining was

higher than CT. Tangential radial ultrasonic vibration-

assisted turning (TRUVAT) conducted by Shamoto et al.

using synchronized two directional vibrations revealed the

reduction in chip thickness and cutting forces. By utilizing a

piezoelectric actuator, Kim et al.

carried out radial axial

ultrasonic vibration-assisted turning (RAUVAT) to suppress

the burr formation on the machined surface. Compared to

1D UVAT, 2D UVAT enhanced the machining quality, and

the adaptability of 2D UVAT is superior, but it requires

high-standard vibration systems. Fig. 4 depicts different types

of vibration modes in UVAM and UVAT.

26,34–49

Lin et al.

developed a 3D elliptical vibration system to

perform 3D UVAT by using the diamond tool. 3D elliptical

vibrations applied on the tool enhanced the tool life and

improved the machined surface quality. The complex tool

trajectory of 3D UVAT makes it more suitable for machining

freeform surfaces. Through the application of longitudinal

vibrations to the workpiece, Lian et al.

conducted longitudi-

nal ultrasonic vibration-assisted milling (LUVAM) and

demonstrated the substantial effect of longitudinal vibration

in reducing the machined surface roughness. Shen et al.

per-

formed feed direction ultrasonic vibration-assisted milling

(FDUVAM) by using an ultrasonic vibrator that produces

vibration in the feed direction. The intermittent separation

due to feed vibrations generated a uniform surface with fewer

surface defects. But FDUVAM signiﬁcantly increases the sur-

face roughness as compared to CM. Niu et al.

designed a

spindle that produces longitudinal torsional vibration to carry

out LTUAM. The application of longitudinal torsional vibra-

tions in the milling process was beneﬁcial to obtain the com-

pressive residual stress in the machined surface. Haﬁz et al.

utilized a longitudinal-feed direction vibration system to per-

form LFUVAM on Inconel, emphasizing the impact of longi-

tudinal feed vibrations on reducing surface roughness.

Employing a sophisticated 2D vibrating worktable, Chern

et al.

executed bending-bending ultrasonic vibration-

assisted milling (BBVAM) and observed a considerable reduc-

tion in slot surface roughness. Compared to 1D UVAM, 2D

elliptical vibration milling eliminates the problems related to

1D UVAM and also enhances tool life and machining efﬁ-

ciency. Ming et al.

conducted 3D UVAM employing a 3D

ultrasonic vibration system and noted a signiﬁcant reduction

in tangential and radial forces coefﬁcient due to the separation

impact of vibration. However, 3D UVAM caused an increase

in the axial force coefﬁcient due to friction between the tool

and workpiece in the axial direction. 3D vibrations can help

better chip evacuation and increase the tool life and machining

efﬁciency.

In vibration-assisted machining, the material removal

mechanism directly affects the machining efﬁciency, tool life,

and surface quality. The dynamic change in tool and work-

piece engagement due to integrated ultrasonic vibrations

resulted in the transformation of cutting forces, tool wear

behaviour, chip formation process and surface generation

mechanism. Factors such as tool-workpiece interaction condi-

tion, the inﬂuence of vibration parameters, and chip formation

mechanism are essential to evaluate the material removal

mechanism in vibration-assisted machining.

The ultrasonic

vibrations integration into the conventional machining process

changes it to intermittent cutting from continuous cutting.

Many researchers have analyzed that during one vibration

cycle, vibration-assisted machining is divided into two phases:

cutting and separation. The intermittent separation cutting

characteristics change the material removal mechanism and

inﬂuence the cutting forces, temperature, and surface quality.

The intermittent separation cutting characteristics are crucial

for the cutting ﬂuid to effectively access the cutting zone and

offer optimal lubrication performance.

To analyze the peri-

odic separation characteristics during UVAM, Ni et al.

pro-

posed a mathematical model to evaluate the tool-workpiece

contact rate (TWCR). The TWCR is the ratio of cutting time

to the duration of a single vibration cycle. The TWCR rate

depends on the machining and ultrasonic parameters. The cut-

ting process is divided into the cutting and separation phases

during vibration-assisted down-milling and up-milling, respec-

tively, as illustrated in Fig. 5(a) and (b). The complexity of

intermittent machining in UVAM is signiﬁcantly increased

Ultrasonic vibration-assisted cutting of titanium alloys 5

by the non-periodic distribution of contact and separation

locations between the tool and workpiece caused by the con-

tinual variation in critical velocity. The TWCR for vibration-

assisted up-milling and down-milling can be calculated from

Eqs. (1) and (2), respectively.

2Acos pft

4r

fþt2

hi

sin pft

4r

ft2

hi

¼Rt4r

ft2

0vcos /xrt4t2

ðÞþxrt½dt

ð1Þ

2Acos pft

8r

fþt6

hi

sin pft

8r

ft6

hi

¼Rt8r

ft6

0vcos /xrt8t6

ðÞþxrt½dt

ð2Þ

where Aand ris feed vibration amplitude and TWCR. t

and

depicts tool separation time during adjacent vibration cycles

in up-milling. t

and t

depicts tool separation time during

adjacent vibration cycles in down-milling. v, f, £and x

are

Fig. 4 Different vibration modes in UVAM and UVAT.

26,34–49

6 A. KHAN et al.

cutting speed, vibration frequency, cutting angle, and angular

rotation speed, respectively.

The TWCR during UVAM depends on the cutting speed,

vibration frequency, amplitude, and cutting angle. Fig. 5(c)

and (d) depicts the inﬂuence of cutting speed, amplitude, and

frequency on the TWCR during UVAM. With the increase

in amplitude and frequency, the value of TWCR decreased,

and the separation duration became higher. The cutting speed

has a direct correlation with the TWCR during UVAM. The

TWCR increases with the increase in cutting speed because

the contact time between the tool and the workpiece is higher

at a high cutting speed. The cutting angle greatly inﬂuences the

contact rate during UVAM. TWCR decreased with the rise in

cutting angle in up-milling. At the same time in down-milling,

it enlarged with the rise in cutting angle. The performance of

UVAT also highly depends on the contact rate of the tool

and workpiece. The TWCR in UVAT is inﬂuenced by three

essential machining parameters: cutting speed, vibration fre-

quency, and vibration amplitude. The low contact rate at high

amplitude, high frequency, and low cutting speed resulted in

reduced cutting forces, cutting temperature, and improved sur-

face quality.

In summary, the analysis of previous literature indicated

that a low value of TWCR is beneﬁcial for vibration-assisted

machining to obtain good machining performance. Compared

to CM, the decrease in TWCR in UVAM signiﬁes a reduction

in cutting time, ultimately resulting in a decrease in cutting

forces, increased heat dissipation, enhanced surface quality,

and improved tool life. In the conventional vibration-assisted

machining process, the critical cutting speed conﬁnes them to

a low cutting speed because at a cutting speed higher than

the critical cutting speed, the periodic separation characteris-

tics of vibration-assisted machining diminish, resulting in lim-

ited cutting efﬁciency. Consequently, the vibration-assisted

machining processes whose performance is limited by critical

cutting speed are referred to as low-speed vibration-assisted

machining processes and cannot be appropriate for high-

speed machining.

66,67

On the other hand, high-speed ultrasonic

vibration-assisted cutting (HUVC) is the process in which the

cutting performance is not limited by critical cutting speed,

and intermittent separation between tool and workpiece can

be achieved under certain conditions. In HUVC, the vibrations

are applied in the feed direction.

The ability of HUVC to sur-

pass the critical cutting speed of conventional vibration-

assisted machining process signiﬁcantly enhances the machin-

ability of titanium alloys by reducing cutting forces, extending

tool life, and enhancing cutting efﬁciency.

In vibration-assisted machining, the vibration system is an

important part of the machining setup. With the increasing

competition among the manufacturing industries, every indus-

try is looking for methods that are capable of producing the

required parts with good quality and dimensional accuracy.

The design of the vibration system is crucial to applying vibra-

tion at the required frequency and amplitude. Generally, a

vibration system includes a vibration generator, vibration

transducer, vibration ampliﬁer, and control system.

The

selection of a vibration generator, transducer, and horn for

the vibration system is critical to provide the desired output

for the machining process. The role of the vibration generator

in the vibration system is to change the AC energy into pulsat-

ing electrical energy. The transducer converts the high pulsat-

ing electrical energy to mechanical displacement. The horn is

used to amplify the amplitude of mechanical displacement

and transfer it to a tool or workpiece in the form of vibra-

tions.

The vibration systems are divided into two categories:

platform vibration system and spindle vibration system.

The

Fig. 5 Analysis of TWCR during UVAM.

Ultrasonic vibration-assisted cutting of titanium alloys 7

platform vibration systems encompass 1D ultrasonic vibration

platform system,

2D ultrasonic vibration platform system,

and 3D ultrasonic vibration platform system.

The spindle

vibration system is a rotary spindle ultrasonic vibration-

assisted processing system,

such as ULTRASONIC 20 linear

of DMG MORI. Many researchers have utilized different

vibration systems. A vibration system to produce the longitu-

dinal torsional vibration in the UVAM process is shown in

Fig. 6(a).

The transmitting terminal ﬁxed on the spindle

frame transfers electrical energy to the receiving terminal ﬁxed

on the tool frame. The horn ampliﬁes the mechanical displace-

ment and produces longitudinal and torsional vibrations of the

same frequency.

Maurotto et al.

used a longitudinal vibra-

tion system for the milling of AISI 316L and investigated the

surface roughness, surface residual stress, and tool wear behav-

ior. Yuan et al.

designed a vibration platform to vibrate the

workpiece in two dimensions. The slots were present on the

vibration device, which helped in ﬁxing the workpiece at differ-

ent angles. Du et al.

proposed a longitudinal-bending hybrid

vibration system for the milling of titanium alloys. The

longitudinal-bending vibrations system decreased the surface

roughness by 54% compared to the longitudinal vibration-

assisted system. Wei et al.

designed a system to integrate

3D vibration in the turning process. It produces a spatial ellip-

tical vibration by using an organized 1D and 2D vibration sys-

tem together. It was found that a 3D vibration generator

improves the surface quality and generates a uniform texture

on the surface. Fig. 6(b) depicts the vibration system that pro-

duces vibration in three directions.

The vibration assistance in the machining process signiﬁ-

cantly enhances the cutting efﬁciency. However, with the

advantages of vibration-assisted machining, it also has certain

limitations. The material removal mechanism and machining

performance can be affected by difﬁculty in accurate control-

ling the vibration amplitude and frequency.

64,69

The nonlinear-

ity of the piezoelectric transducer and variation in external

load makes the precise control of vibration amplitude very dif-

ﬁcult. Besides, the material used in the manufacturing of vibra-

tion systems is frequently unsuitable for the working

environment. It leads to localized heating at the interface

between the cutting tool and the collet.

27,77

The increased heat

in the localized surface can result in higher energy absorption,

thereby decreasing the amplitude and frequency of vibration.

The widespread use of vibration-assisted machining can be

hindered by several factors, including workpiece geometry

and material properties, thereby reducing its adaptability to

speciﬁc applications. Overcoming these limitations through

advancement in control systems, adaptive machining strate-

gies, development of low-cost materials for vibration system

manufacturing, and focus on sustainability is essential to max-

imize the use of vibration-assisted machining in the manufac-

turing industries.

3. Ultrasonic assisted milling process

The effectiveness of UVAM for titanium alloys is described in

this section. This endeavor entails the meticulous analysis of

the impact of UVAM process parameters on various factors,

including cutting forces, cutting temperature, tool wear behav-

ior, and surface quality. Furthermore, the aim is to delve into

the intricate relationship between these process parameters and

the resultant machining output. The primary objective of this

investigation is to shed light upon the manner in which the out-

put parameters of machining undergo alterations in both CM

and UVAM.

3.1. Cutting forces and temperature

In the UVAM of titanium alloy, analyzing the cutting forces is

crucial for optimizing the machining process. Cutting forces

impact tool wear, energy consumption, and machining efﬁ-

ciency. When UVAM was utilized to machine titanium alloys,

Fig. 6 Tool vibration system utilized in machining processes.

8 A. KHAN et al.

a signiﬁcantly reduced cutting force was generated in compar-

ison to CM.

78–80

Ren et al.

explored the cutting forces pro-

duced during LTUAM of titanium alloy in dry environment.

The intermittent separation between tool and workpiece due

to ultrasonic vibration reduces the friction and decrease cut-

ting forces by 20%–40% in comparison to CM. Zhang et al.

investigated the cutting forces during LTUAM of thin wall

curved surfaces of titanium alloy. The result showed that the

cutting forces in UVAM were lower than in CM due to reduc-

tion in net cutting time because of longitudinal torsional vibra-

tions. The integration of vibration in the milling process leads

to intermittent separation between tool and workpiece and

facilitate in smoother material removal, reduces the friction

and cutting force.

Ying et al.

performed simulation to

investigate the machining efﬁciency during LTUAM process.

When considering the cutting forces generated during the

CM of titanium alloys, the results demonstrated that the cut-

ting forces generated in a vibration-assisted procedure were

signiﬁcantly lower due to periodic cutting mechanism. Xie

et al.

examined the cutting forces during longitudinal tor-

sional vibration-assisted side milling of titanium alloy. They

found that the cutting forces decreased by 16.05% as com-

pared to cutting forces in CM process. Comparative investiga-

tions between CM and longitudinal-bending ultrasonic

vibration-assisted milling (LBUAM) of TC4 in a dry environ-

ment were conducted by Hu et al.

. They demonstrated that

intermittent tool-workpiece separation in the LBUAM process

reduces cutting forces by 43.2%. The irregular separation

between the tool and workpiece results in a state of unstable

cutting forces. The intermittent separation generated by

high-frequency vibration forces the tool cutting edges to disen-

gage from the cutting surface which resulted in ﬂuctuation of

cutting forces and reduced the maximum cutting force in

LBUAM. With the vibration of the tool, the cutting edge cut

in and cut out the material. Because of this phenomenon, the

cutting forces change from high to low level. Therefore, in

the event of tool-workpiece disengagement, the resultant cut-

ting force becomes inconsequential. Fig. 7 depicts the behavior

of the tool under the vibration and the cutting forces analysis

in CM and LBUAM under a dry environment. The applica-

tion of 3D ultrasonic vibration to the milling tool in the 3D-

UVAM process reduced the cutting forces in radial and tan-

gential as compared to CM.

The reduced friction between

the tool and the workpiece due to high-speed separation

caused by high-frequency vibration helps in reducing the cut-

ting forces. However, 3D ultrasonic vibrations lead to

increased axial cutting forces because of increased friction

coefﬁcient in the axial direction.

The cutting force behavior during vibration-assisted

machining is inﬂuenced by periodic separation characteristics.

The analysis of TWCR can help in understanding the dynamic

nature of cutting forces during UVAM. The TWCR depends

on machining and ultrasonic vibration parameters and little

variation in parameters can affect the periodic separation char-

acteristics and behavior of cutting forces.

The low cutting

forces are produced when the value of TWCR is close to zero

because at the low value of TWCR, the separation between

tool and workpiece is maximum. The increase in amplitude

of the vibrations reduces the cutting forces by increasing the

separation period.

During elliptical vibration-assisted milling

(EVAM), Han et al.

investigated the impact of tool-

workpiece separation on the cutting forces. They observed that

in titanium alloy EVAM, the reduction in cutting forces

decreased as the gap between tool and workpiece diminished.

In their study, Tong et al.

examined the impact of duty cycle

variation on cutting forces. An upward trend in the duty cycle

was noted as the cutting speed was increased. The distance

between the tool and the workpiece was reduced as the duty

cycle was increased. As the duty cycle was enhanced, the cut-

ting forces in the UVAM process also increased. Wang et al.

analyzed the cutting forces during the end milling of titanium

alloy. The TWCR increased when the velocity of the tool

vibrations surpassed the velocity of the cutting process, and

higher intermittent separation reduced the cutting force. The

study conducted by Gao et al.

involved a comprehensive

evaluation of the machinability of Ti–6Al–4V alloy by utilizing

the LTUAM technique under dry-cutting conditions.

Researchers conducted an investigation into the inﬂuence of

vibration parameters on the cutting forces. It was discovered

that as the amplitude of the vibrations increased the TWCR

reduced, and caused a reduction in cutting forces. The cutting

forces in the feed direction were decreased by 14.9%, and the

cutting force in the longitudinal direction decreased by 30.2%

with the increase in amplitude from 0 to 6 lm. At large ampli-

tudes, the rate of interaction between the tool and the work-

piece diminishes, resulting in a decline in the cutting forces

generated.

Xie et al.

conducted a comprehensive empirical

investigation to assess cutting speed variations impact on the

cutting forces in absence of cutting ﬂuid while conducting

LTUAM on TC18 titanium alloy. It was noted that the cutting

forces in the vibration-assisted process were 34.1% lower than

in the CM. The cutting forces exhibited direct correlation with

the cutting speed, and escalated with the escalation of the cut-

ting speed. The feed per tooth and width of cut signiﬁcantly

affect the cutting forces in UVAM. With the increase in feed

and width of cut the cutting forces increased due to an increase

in material removal per unit time.

The application of ultra-

sonic vibrations in the titanium alloy milling signiﬁcantly

reduces the cutting forces as long as there exists an intermittent

separation between tool and workpiece due to vibrations. The

periodic separation between the tool and workpiece decreases

with the increase in cutting speed. At the point when the cut-

ting speed increases over critical cutting speed, the TWCR

becomes equal to 1 then no periodic separation occurs which

diminishes the positive effect of UVAM. So, to optimize the

advantage of UVAM the machining and ultrasonic parameters

should fall within the range where periodic separation occurs.

The cutting forces were signiﬁcantly inﬂuenced by the tool

geometry and tool wear. The parameters that inﬂuence the cut-

ting forces in UVAM of Ti–6Al–4 V were investigated by Zhao

et al.

. The tool helix angle and vibration amplitude had neg-

ative relationship with the milling forces. It was observed that

the milling forces exhibited an upward trend as the depth of

cut, cutting speed, and feed per tooth increased. The cutting

speed of 60 m/min, depth of cut of 0.1 mm, feed per tooth

of 0.01 mm/z, vibration amplitude of 4 lm, and tool helix

angle of 40°resulted in the lowest milling force. Niu et al.

performed a simulation to examine the impact of tool geome-

try parameters on cutting forces in the context of LTUAM.

They observed that with the increase in helix angle the cutting

force in x-axis direction signiﬁcantly reduced. The cutting

force in the y-axis direction largely depends on the tool rake

angle. The increased rake angle from 0°to 6°substantially

reduces the cutting force. Liu et al.

examined the impact of

Ultrasonic vibration-assisted cutting of titanium alloys 9

variation in tool wear on cutting forces during UVAM. It was

found that the presence of a direct connection between cutting

forces and tool wear in UVAM, speciﬁcally increased tool

wear, leads to a substantial escalation in cutting forces. Liu

et al.

examined the inﬂuence of tool wear on cutting forces

through experimental means. A direct correlation was

observed between tool degradation and cutting forces. The

friction between the tool rake and the ﬂank face increases in

tandem with tool wear, resulting in elevated cutting forces dur-

ing the machining operation. In addition to the ultrasonic and

machining parameters, the tool geometry and tool wear had a

signiﬁcant inﬂuence on the cutting forces in UVAM.

The integration of ultrasonic vibration in the machining of

titanium alloys reduces the cutting temperature by reducing

friction and improving heat dissipation. Li et al.

conducted

comparative experiments between CM and LUVAM of Ti–

6Al–4V and found that the cutting temperature in LUVAM

was 42% lower than the CM in dry conditions. The integration

of longitudinal vibration in CM changes the linear trajectory

of cutting edges to the sinusoidal waveform. The ultrasonic

vibration intermittently separates the tool and the workpiece,

the frictional effect between them is drastically reduced, and

the cutting temperature falls considerably as a result of

enhanced heat dissipation. The comparison of cutting tool tra-

Fig. 7 Cutting force dynamics analysis in CM and LBUAM.

10 A. KHAN et al.

jectories and temperature variation in CM and LUVAM are

illustrated in Fig. 8. The maximum cutting temperature was

60.2 ℃in LUVAM whereas 102.8 ℃in CM over the same

machining parameters. A study by Ying et al.

examined

and presented the better performance of UVAM as compared

to the CM of Ti–6Al–4V in dry machining environment. Lon-

gitudinal torsional vibrations of 4 lmto5lm amplitude were

applied to the milling tool by using an ultrasonic transducer

and horn. Consequently, a signiﬁcant reduction of temperature

was observed in LTUAM of Ti–6Al–4V as compared to CM at

various levels of machining parameters. In the investigation

performed by Zhang et al.

, it was found that the cutting tem-

perature was reduced by 17.53% in the LTUAM process when

compared to CM of Ti–6Al–4V in a dry machining environ-

ment. The vibration applied to the tool produced a separation

between the tool and the workpiece in the axial and feed direc-

tion, and the intermittent separation suppressed the frictional

effect between the tool, workpiece, and chips and improved

the heat dissipation. The investigation into the relationship

between cutting temperature and machining parameters

revealed that the radial depth of cut contributed the most, at

44.8%, to the variation in cutting temperature.

The reduction in cutting temperature during UVAM

depends on the periodic separation characteristics. Xie et al.

examined the ramiﬁcation of spindle speed on the cutting tem-

perature during LUVAM of TC18 titanium alloy at a constant

amplitude of 2 lm in the absence of cutting ﬂuid. They discov-

ered that the maximal temperature was 19.5% lower in the

UVAM process than in the CM process. The reduction in cut-

ting temperature during UVAM is dependent on the gap

between the tool and the workpiece; air travels through the

crevice between the tool and the workpiece when the tool

vibrates, thereby increasing heat dissipation in the cutting

zone. A reduction in the temperature of cutting area was noted

as the cutting speed increased until it reached 2400 r/min, at

which point it commenced to rise again. In their scholarly

investigation, Gao et al.

conducted a comprehensive exami-

nation to assess the inﬂuence of vibration amplitude on the

cutting temperature of Ti–6Al–4V in dry machining condi-

tions. In contrast to CM, they discovered that the cutting tem-

perature was reduced, and it ﬂuctuated in response to the tool

incisions and excisions from the substrate. Temperature study

indicated that as the amplitude of the vibration increased, the

cutting temperature correspondingly decreased. This is because

greater vibration amplitude helps in heat evacuation from the

cutting area. Hence, in UVAM high heat dissipation can be

achieved at low speed and high amplitude.

In vibration-assisted machining, the intermittent separation

between tool and workpiece due to vibration allows the cutting

ﬂuid to reach the cutting zone, resulting in increased heat dis-

sipation. Niu et al.

explored the cutting temperature in dry

and minimum quantity lubrication (MQL) machining environ-

ments during LTUAM. The application of longitudinal vibra-

tion creates a gap between the tool, workpiece, and chips and

helps the MQL droplet enter the cutting zone. In comparison

to dry machining, it was observed that the incorporation of

MQL into UVAM can further minimize the cutting tempera-

ture because the incorporation of MQL into the cutting zone

Fig. 8 Effect of CM and LUVAM on cutting temperature during machining of Ti-6Al-4V.

Ultrasonic vibration-assisted cutting of titanium alloys 11

facilitates thermal dissipation. The deterioration of the tool in

UVAM leads to an increase in cutting temperature.

This is

because when tool wear is high, there is an increased frictional

effect between the tool and the workpiece. In summary, the

UVAM of titanium alloys signiﬁcantly enhances the machin-

ing efﬁciency by reducing cutting forces and cutting tempera-

ture. The investigation of cutting forces and temperature

expressed the potential for increased precision, decreased tool

wear, and improved overall machining efﬁciency. Further

research in this ﬁeld is crucial for optimizing the process

parameters and realizing the advantages of advanced ultra-

sonic vibration-assisted machining technology in titanium

alloy applications.

3.2. Tool wear behavior

Tool wear is a critical determinant in the machining process,

drastically inﬂuencing output, precision, and overall function-

ality. Additionally, tool wear has a detrimental impact on the

dimensional precision and accuracy of the machined compo-

nent, leading to an escalation in surface irregularity. Defective

machined parts, increased machining expenses, and diminished

productivity resulted from tools that were too worn during the

machining process. Su et al.

observed that PCD tool wear is

exceptionally high in CM titanium alloys as a result of the cut-

ting tool undergoing substantial thermal and mechanical stres-

ses. However, titanium alloy UVAM substantially reduces tool

deterioration. Liu et al.

examined the cemented carbide tool

life in the UVAM of titanium alloy. A signiﬁcant enhancement

in tool longevity was observed when ultrasonic vibration was

integrated into the machining procedure, as opposed to the

CM.

Tool wear typically progresses through several stages as the

cutting tool interacts with the workpiece material during

machining operations. Liu et al.

observed that the tool life

of TiSiN-coated carbide tool was longer in UVAM than in

CM, and there were three types of tool wear associated with

the coated carbide milling tool. These include adhesive wear,

oxidation wear, and diffusion wear. Due to the vibration of

the tool, the chip material did not stick on the tooltip, which

was beneﬁcial for the reduction of tool wear. It was also found

that there were three stages of ﬂank face wear. These include

initial, normal, and severe wear stages, which occurred in 0–

5 min, 5–50 min, and 50–70 min cutting durations, respec-

tively. With the wear of the cutting tool, its cutting edges

become dull. Due to blunt cutting edges, shearing the material

is very difﬁcult. As the cutting tool wears, its cutting edges lose

their shape, and high friction is produced between the tool and

the workpiece. High cutting forces were caused by increased

friction and altered tool geometry. Carbide tool wears behav-

ior during titanium alloy machining is shown in Fig. 9(a).

The tool life during vibration-assisted machining is signiﬁ-

cantly inﬂuenced by the vibration characteristics in each

method. Over the same machining parameters, the cutting tool

experiences different levels of wear in LTUAM and LBUAM

due to different vibration characteristics in each method. In

the investigation performed by Chen et al.

on carbide tool

wear behavior during LTUAM of Ti–6Al–4V, it was observed

that the ﬂank face wear of ball end milling tool in LTUAM

was 30% lower as compared to CM at cutting speed

2000 r/min, feed 0.05 mm/z, depth of cut 0.4 mm, ultrasonic

frequency 35 kHz and vibration amplitude 5 lm over changing

milling area. The intermittent separation between the work-

piece and the tool in UVAM led to the prolongation of tool life

through the mitigation of tool wear. Hu et al.

investigated

the four-ﬂute tungsten steel tool wear during the LBUAM of

TC4 titanium alloy. The experimental investigation showed

that LBUAM reduces the wear of tools as compared to con-

ventional processes. They observed that the tool life was

166% higher in LBUAM as compared to CM when TC4

was machined at a cutting speed of 2000 r/min, feed of

3lm/z, depth of cut of 60 lm, vibration frequency of

18.5 kHz, and vibration amplitude of 5 lm. Whereas the use

of longitudinal-bending vibration suppresses the growth of

edge chipping and adhesion of material, leading to high tool

life. LTUAM and LBUAM over the same cutting speed and

vibration amplitude increased the tool’s life by different levels.

The vibration amplitude and tool geometry notably inﬂu-

ence the tool wear behavior. Gao et al.

100

investigated the con-

sequences of variation in vibration amplitude and the tool

helix angle on the ﬂank face wear of the TiAlN-coated carbide

tool during LTUAM of Ti–6Al–4V. It was observed that

amplitude and tool helix angle signiﬁcantly affect the tool ser-

vice life, and at low amplitude, severe tool wear occurred. With

the increase of amplitude to 3 lm, the ﬂank face wear was sig-

niﬁcantly reduced. However, a further increase in the ampli-

tude suppresses the beneﬁts of tool wear reduction during

UVAM. The inﬂuence of tool ﬂank wear on cutting forces

and the impact of vibration amplitude and tool helix angle

on ﬂank face wear is illustrated in Fig. 9(b)–(d).

100

Edge tip-

ping, coating spallation, and cold weld wear were observed

on the tool ﬂank face during the LTUAM of titanium alloys.

The morphologies of the tool ﬂank face wear during CM

and LTUAM are illustrated in Fig. 10 via scanning electron

microscope (SEM) and Energy dispersive X-ray (EDX) analy-

sis. The utilization of coolant in UVAM substantially enhances

the tool performance. An important investigation on the two-

ﬂute cemented carbide tool wear behavior during FDUVAM

of Ti–6Al–4V was done by Ni et al.

. The wear morphologies

were found to be edge chipping, adhesive wear, fatigue micro-

cracks, peeling off, friction traces, and debris. In UVAM, the

tool underwent severe wear as compared to conventional

milling due to high kinetic energy collision between the vibrat-

ing workpiece and the tool. The high kinetic energy collision

resulted in damage to the tooltip. However, the tool wear

was signiﬁcantly reduced by providing the cooling and lubrica-

tion properties with MQL. The use of MQL in UVAM sup-

pressed the growth of friction traces on the ﬂank face and

microcracks on the tool cutting edge. The TiAlN coating on

the cutting tool increases the hardness and wear resistance,

substantially preventing the cutting tool from damage. Chen

et al.

101

utilized ultrasonic vibration-assisted helical milling

with axial and tangential feed to create holes in Ti–6Al–4V

at varying cutting speeds. The ultrasonic vibration equipment

was utilized to apply vibration on the four-ﬂute cemented car-

bide tool in the axial direction. In vibration-assisted helical

milling, due to axial vibration, the tool bottom collides with

uncut chips of uneven thickness at high speed, resulting in

higher ﬂank wear as compared to conventional helical milling.

However, The TiAlN coating on tool signiﬁcantly improves

the tool’s life. The Ti and Al in the coating increase the hard-

ness, wear resistance, and thermal stability of the tool. The

tool coated with AlTiN showed less ﬂank wear as compared

12 A. KHAN et al.

to tools coated with coatings containing Cr and Si during high-

speed UVAM of titanium alloy.

102

In summary, the tool wear during UVAM titanium alloys is

reduced in comparison to that of CM titanium alloys. The

strategic occurrence of regular gaps between the workpiece

and tool has been empirically demonstrated to effectively mit-

igate the deleterious effects of cutting forces and friction,

thereby enhancing the tool’s longevity. However, in some stud-

ies, it has been observed that during UVAM, the high cutting

load during titanium alloy machining and high-frequency

ultrasonic vibration applications cause severe damage and

demand superior tool performance.

26,30

Therefore, developing

tools suitable for ultrasonic-assisted machining highlights an

important direction for future exploration. In the future, the

tool performance can further be improved by research into

tool cutting-edge, tool materials and coatings, and creative

cooling and lubricating strategies will be essential. Further-

more, with the advancement in ultrasonic-assisted machining

technology, the optimized machining parameters and machin-

ing conditions will contribute to increased tool life and

decreased wear.

3.3. Surface integrity

The preservation of surface integrity in titanium alloys is of

utmost importance during the UVAM process. Consequently,

in order to enhance the surface integrity of titanium alloy, it is

imperative to comprehend the impact that UVAM exerts on

the machined surface. This section presents an assessment of

the inﬂuence of UVAM process parameters on various surface

characteristics, including surface morphology, surface rough-

ness, surface hardness, surface residual stress, and surface tri-

bological properties. The review scope of machined surface

quality in UVAM is shown in Fig. 11.

3.3.1. Surface morphology

The machined surface morphology greatly inﬂuences the func-

tionality and performance of machined components. It has a

direct impact on various parameters, including fatigue life,

wear resistance, corrosion resistance, and friction. The surface

of titanium alloy parts used in the aerospace industry is criti-

cal. During the CM of titanium alloys, different types of sur-

Fig. 9 Assessment of tool performance during vibration assisted machining.

Ultrasonic vibration-assisted cutting of titanium alloys 13

Fig. 10 TiAlN coated carbide tool ﬂank face wear morphologies.

100

Fig. 11 Review scope of machined surface quality in UVAM.

14 A. KHAN et al.

face defects occurred on the surface, such as tool marks, ther-

mal cracks, adhered material, and chatter marks.

103

Titanium

alloys are recognized for their superior corrosion resistance.

However, several surface defects that occur during the CM

of titanium alloys can compromise on corrosion resistance,

making it crucial to sustain a long-term corrosive environment.

In the machining of the Ti

Al intermetallic compound, it was

found that in the absence of tool vibration, the chip material

adhered to the surface, and the defective surface was produced.

However, with the implementation of longitudinal torsional

vibration on the tool, no swarf and material adhered on the

surface. The manifestation of a wavy line texture on a surface

is a direct consequence of vibrational forces acting on the tool.

Notably, the amplitude of vibrations exhibits a positive corre-

lation with the depth of the resulting texture.

104

Fig. 12 illus-

trates the surface morphology of titanium alloys during CM

and LTUAM.

The surface morphology of Ti–6Al–4V alloy

was experimentally examined by Chang et al.

during

ultrasonic-assisted slot milling. The axial vibration of the tool

was utilized to examine the surface morphology at various

depths of cut and with varying amplitudes. It was found that

in UVAM, tool vibration texture and tool trajectory were pre-

sent on the surface, whereas on the surface machined by CM,

width of cut marks and scratches were observed on the bottom

surface. In contrast, the microtexture of the tool vibration pat-

tern was more consistent along the side wall of the cavity.

The nature of the texture produced on machined surface

during UVAM signiﬁcantly altered with the variation in cut-

ting speed and amplitude. Xie et al.

experimentally evaluated

the impact of vibration amplitude and cutting speed on surface

morphology during LUVAM of TC18 titanium alloy. It was

found that the surface morphology of the surface machined

by UVAM was more regular than that of the surface machined

by CM. A surface machined by UVAM initially exhibited a

rib-like micro-texture when the speed of cutting was low. How-

ever, as the cutting speed escalates, the micro-texture becomes

more regular as a result of the ironing effect caused by the tool

cutting edges. With the ampliﬁcation of vibration amplitude,

tool pressing traces due to vibration became more evident on

the surface. Another observation made by Xie et al.

experi-

mentally investigated the surface morphology during the

machining of TC18 at different cutting speeds. The ﬁndings

indicated that the machined surface exhibited axial feed marks

and scratches throughout the CM process. On the machined

surface, a frequency-induced tool motion pattern microtexture

was produced as a result of tool vibration during UVAM. As

the velocity of the cutting process was augmented, the discerni-

bility of tool imprints upon the machined surface progressively

diminished. By means of simulations and experiments, Qin

et al.

proposed a mathematical model to investigate the sur-

face texture generation mechanism during LTUAM of tita-

nium alloys. The tool trajectory and tool 3D geometry were

considered in the development of the model. It was observed

that ultrasonic frequency, tool secondary cutting edge, and

tool clearance angle have a signiﬁcant inﬂuence on the micro-

texture produced on the machined surface. The experimental

results visualized that with the increase of feed the size of

micro dimple texture increases in the feed direction. On the

other hand, when cutting speed increases, phase differences

arise that cause the micro dimples to stagger in the direction

of cutting. Fig. 13 illustrates the effect of cutting speed and

feed rate on microtexture produced during LTUAM. Tong

et al.

105

examined the surface morphology of a thin curved wall

component composed of Ti–6Al–4V in accordance with

LTUAM. It was observed that good surface quality with

smooth and regular micro-texture could be obtained at a small

feed of 0.03 mm/z, medium amplitude of 3 lm, and moderate

spindle speed of 2100 r/min. They noted that with an increase

in feed and spindle speed, the micro-texture became less dense,

and with the further increase in amplitude, the tool ironing

effect on the surface dominated. Through experiments, Zhang

et al.

106

examined the surface morphology of Ti–6Al–4 V in

CM and rotary ultrasonic elliptical vibration-assisted milling

(RUEAM). It was observed that in the CM chip material

adhered to the machined surface. Meanwhile, in RUEAM,

uniform and distinct micro-texture was produced on the sur-

face. As the speed of the cutting process escalates, the size of

the microtextured increases, but surface characteristics deteri-

orate due to ploughing and plastic separation of material

due to the waveform motion of the tool due to the elliptical

vibration of the tool.

In vibration-assisted cutting, low vibration amplitude

caused the chip material to adhere to the machined surface.

Xie et al.

107

explored the impact of vibration amplitude, feed,

and spindle speed on the surface quality of TC18 titanium

alloy after machining by the LTUAM process. The ultrasonic

vibration of the frequency 24.5 kHz was applied by using an

ultrasonic vibration device. It was observed that micro-

Fig. 12 Comparison of machined surface morphology: CM vs LTUAM.

Ultrasonic vibration-assisted cutting of titanium alloys 15

textures were created on the machined surface due to tool

vibration. At low amplitude, the chip material adhered to

the machined surface, and tiny burrs were produced on the

surface. With the increase of amplitude, the micro-texture

became uniform, and no material was adhered to the surface.

At elevated speed and low feed rate, the micro texture on the

machined surface was more consistent and distinct. In sum-

mary, the texture generation mechanism depends on tool

geometry, tool path, and machining parameters. Due to the

complex interaction between the tool and workpiece during

vibration-assisted machining, further investigation of the sur-

face topography is necessary, even though research on this

topic has advanced signiﬁcantly in recent years.

3.3.2. Surface roughness

The presence of functional surfaces can have a positive impact

on the practical application of the component, but it depends

on the speciﬁc requirement, intended use, and materials. The

optimal results for speciﬁc applications can achieved by opti-

mizing the UVAM process parameters. Therefore, the investi-

gation of the surface formation mechanism is important to

enhance the practical applications.

108–110

Numerous investiga-

tions have been undertaken to scrutinize the impact of UVAM

on the surface roughness characteristics of machined compo-

nents composed of titanium alloy.

111

Ren et al.

examined

the surface homogenization and roughness during LTUAM

of Ti–6Al–4 V. The comparative analysis showed that the

Fig. 13 Surface morphologies at different feed and cutting speeds in LTUAM.

16 A. KHAN et al.

LTUAM reduces the surface roughness than the CM. At the

cutting speed of 4000 rpm, the surface roughness in LTUAM

was higher than that of CM. However, the shift in material

removal mode from shearing to squeezing at high speed

resulted in a more uniform and less rough surface in UVAM

at 5000 rpm. Fig. 14 shows the roughness characteristics of

the surface machined by CM and LTUAM. Hu et al.

demon-

strated that 46.7% less surface roughness compared with CM

in a dry environment can be obtained by applying

longitudinal-bending vibration. Han et al.

analyzed the sur-

face roughness in EVAM of Ti-6Al-4 V. It was observed that

the cross-feed motion of the tool due to vibration generated

tool vibration marks on the machined surface also increased

the surface roughness as compared to CM. The surface pro-

duced by various UVAM techniques may display varying

degrees of surface roughness, even when the cutting parame-

ters are the same. Yuan et al.

examined the surface roughness

by using CM, 2D UVAM, and 3D UVAM techniques. It was

observed that over the same machining parameters, different

UVAM methods generate surfaces with varying roughness.

When comparing the CM and 3D UVAM, the 2D UVAM

had superior cutting qualities, at a cutting speed of

1700 rpm, the surface roughness decreased by 54% and 57%

respectively. With an amplitude of 8 lm in the feeding direc-

tion, the surface roughness value of 2DUVC was approxi-

mately 64% and 65.9% less than that of 3DUVC and CC,

respectively. Variations in surface roughness over identical cut-

ting parameters can be attributed to the fact that distinct

UVAM methods produce varying results due to variables such

as vibration characteristics, tool trajectory, and material

removal mechanism. The ironing effect of the tool and its sep-

aration characteristics reduce the surface roughness in 2D

UVAM, whereas 3D UVAM is more suitable for machining

freeform surfaces.

The variation in machining and vibration characteristics

inﬂuenced the roughness of the machined surface in UVAM.

Xia et al.

conducted a study to examine how changes in

vibration amplitude and cutting speed affect the surface rough-

ness of Ti

AlNb intermetallic alloy during UVAM. Analysis

revealed that there was a clear correlation between surface

roughness and amplitude. Furthermore, it was found that

because of the decreased vibration effect, the high cutting

speed leads to an increase in surface roughness. Xie et al.

examined the connection between surface integrity and cutting

speed. The researchers discovered that the LTUAM 45.5%

decreased the surface roughness compared to CM. The surface

roughness in UVAM had a moderate rise when the cutting

speed was raised. This is due to the fact that high cutting

speeds hinder the separation due to vibrations and negate

the advantages of UVAM. In their study, Niu et al.

utilized

multi-objective optimization to determine the most effective

cutting parameters for LTUAM of Ti–6Al–4 V. The variable

that exhibited the most pronounced impact on surface rough-

ness was determined to be the feed per tooth. The surface

Fig. 14 Micrographs illustrating surface roughness at various cutting speeds in CM and LTUAM.

Ultrasonic vibration-assisted cutting of titanium alloys 17

roughness exhibited an upward trend as the depth of cut and

feed per tooth were increased. Feed rate of 0.01–0.011 mm/z,

milling speed of 86.8–88.3 m/min, width of cut of 1.02–

1.17 mm, depth of cut of 0.15–0.16 mm, and vibration ampli-

tude of 2–5 lm are required to achieve a high-quality surface.

Ming et al.

proposed a mathematical model for surface

roughness prediction based on geometric kinematic character-

istics and dynamic factors for 3D UVAM. Compared to CM,

the higher surface roughness was observed due to the forma-

tion of complex texture and tool high-frequency vibrations

mark on the machined surface. Liu et al.

examined the

impact of tool wear on the surface roughness of Ti–6Al–4V

during CM and UVAM. At the initial wear stage, with time,

the surface roughness decreased but at the severe wear stage,

due to the high frictional effect between the tool and the work-

piece, the surface roughness increased as the tool further worn.

The manifestation of pronounced roughness was observed on

the surface due to the generation of texture on the surface

due to the vibration of the tool. The researchers Zou et al.

112

demonstrated that the utilization of MQL in ultrasonic

vibration-assisted helical milling of Ti–6Al–4V effectively

diminished the surface roughness through the enhancement

of lubrication and cooling within the cutting zone. Investiga-

tions have shown that the UVAM of titanium alloys may

increase or decrease the surface roughness. However, desired

results can be achieved through proper control and optimiza-

tion of different parameters to eliminate the harmful effects

such as pits, material adhesion and chatter.

3.3.3. Surface hardness

When the material is removed from the metal part by a

machining process, the surface of the material is plastically

deformed due to high cutting forces acting on the surface.

Consequently, the hardness of the machined component sur-

face becomes higher than that of bulk material.

113

The applica-

tion of CM and UVAM to the machining of Ti–6Al–4V

revealed that the surface hardness of the machined part was

greater in magnitude than that of the bulk material. The

increase in hardness was due to the hammering effect of the

tool due to vibrations and extrusion, as well as frictional

impact between the tool and workpiece, which resulted in

deformation and hardening of the surface.

Niu et al.

inves-

tigated the machined surface hardness during LTUAM. They

noted that the hardness of the machined surface was higher

than that of the machined surface in CM. The hardness of

the surface increases with the increase of vibration amplitude

because, at high amplitude, the tool strikes the workpiece with

high energy. In machining, the surface hardness depends on

the deepness of the plastic deformation layer. Due to the rear-

rangement of material in the plastic deformation layer, the sur-

face hardness of the material is increased. Xie. et al.

investigated the effect of increasing vibration amplitude in

LUVAM of TC18. It was discovered that as the vibration

amplitude grows, so does the thickness of the plastic deforma-

tion layer. The hammering effect of the tool at high amplitude

increases the plastic deformation layer thickness. Fig. 15(a)

show the impact of vibration amplitude on plastic deformation

layer depth.

During machining, the surface hardness is directly inﬂu-

enced by variations in feed rate and cutting speed. The opti-

mized cutting parameters can elevate the surface hardness

while minimizing plastic deformation layer thickness. The

scholarly work conducted by Xie et al.

delved into the intri-

cate ramiﬁcations of varying cutting speeds on the intricate

structure of the plastic deformation layer in the context of

LTUAM. It has been observed that augmenting the cutting

speed yields a substantial increase in the depth of the plastic

deformation layer, as well as elongation of the grain in the cut-

ting direction. This phenomenon arises from the excessive fric-

tion that occurs between the tool and the workpiece when

operating at high cutting speeds. Fig. 15(c) depicts the dis-

cernible inﬂuence of varying cutting speeds on the plastic

deformation layer.

The study conducted by Xie et al.

107

involved a meticulous experimental assessment of the impact

of feed rate on the plastic deformation layer in the processes

of CM and LTUAM. At a high feed rate in CM due to high

mechanical and thermal loads, a larger plastically deformed

layer was produced. However, in LTUAM, the effect of aug-

mentation in the feed rate is not very signiﬁcant because the

impact of high-frequency vibration was more prominent than

that of mechanical thermal load. Fig. 15(b) and (d) shows

the structure of the plastic deformation layer affected by ultra-

sonic vibrations.

107

In another observation, Qin et al.

examined the inﬂuence

of spindle speed and feed on surface hardness in LTUAM of

titanium alloy. Surface hardness decreased with increasing feed

and spindle speed in the UVAM. The highest hardness, 438.61

HV, was noted at a cutting speed of 1000 rpm and feed of

0.01 mm/z. In their study, Zhang et al.

114

conducted experi-

ments to investigate the impact of vibration amplitude and cut-

ting speed on surface hardness during the machining process of

Ti–6Al–4V alloy. During the CM process, it was noted that as

the velocity of the cutting process was augmented, a corre-

sponding elevation in the level of surface hardness was

observed. In RUEAM, it was observed that the surface hard-

ness decreased as the velocity of the cutting process was aug-

mented. The reason for the decrease in hardness was a

reduction in the ultrasonic effect at high speed. At low cutting

speed, with the enhancement of amplitude, the surface hard-

ness signiﬁcantly increased. At higher cutting speeds, the

increase in amplitude had no discernible impact on surface

hardness. Chen et al.

101

observed the subsurface hardness in

ultrasonic vibration-assisted helical milling. They observed

that the hardness along the circumferential direction in the

machined hole was not identical due to the tool-workpiece sep-

aration effect. The value of the surface hardness was increased

with the escalation of tangential and axial feed and spindle

speed. In summary, the analysis of the surface hardness of tita-

nium alloys during UVAM highlights the complex relationship

between material reactions and machining parameters. The

high ultrasonic amplitude and cutting speed led to the ham-

mering effect of the tool and high friction between the tool

and workpiece, resulting in elevated surface hardness and high

plastic deformation layer thickness. By optimizing these

parameters, a controlled plastic deformation layer that affects

surface hardness may be produced. Achieving the ideal balance

is important since too much deformation might have unfavor-

able effects.

3.3.4. Surface residual stress

Residual stresses arise within machined components as a con-

sequence of thermo-mechanical loads incurred during the

18 A. KHAN et al.

machining procedure. The generation of residual stress in

machined objects can exert a substantial effect on both the fati-

gue life and surface integrity of machined parts.

115

Niu et al.

116

created a mathematical model for residual stress prediction

and validated it through experiments. They developed the

model based on the tool’s cutting-edge trajectory in LTUAM.

They found that mechanical and thermal stresses generated by

shear action, as well as the frictional effect between the tool

and workpiece in the cutting zone, induce residual stress. They

noted that the value of compressive stress developed on the

surface changed as the depth of the machined surface changed,

and the experimental value was close to the predicted values.

The high-frequency ultrasonic vibrations can improve the

material removal mechanism and reduce the tensile residual

stress. However, as the vibration amplitude increased, the cut-

ting temperature decreased, and the tensile residual stress

caused by thermal stress decreased. The high amplitude causes

the tool to strike the workpiece with high impact, resulting in

high compressive residual stress in the machined part.

117

Zhang et al.

examined the impact of cutting speed and ampli-

tude on residual stress in LTUAM of a thin, curved titanium

alloy component. The study demonstrated that the magnitude

of vibration had the most signiﬁcant impact on the generation

of compressive residual stress on the surface. The compressive

residual stress ampliﬁed proportionally with the amplitude.

With an increase in amplitude, the separation effect of the tool

increases, which results in the tool hammering on the work-

piece. An increased vibration amplitude causes a severe extru-

sion effect, which increases the residual stress induced on the

surface. With the escalation of cutting speed, the compressive

stress is reduced because high speed suppresses the tool separa-

tion effect. Fig. 16 illustrates the stress generation mechanism

due to mechanical and thermal load. The tensile stress is

induced in the machined surface due to the thermal load dur-

ing the machining process. In the cutting process, a large

amount of heat is produced due to friction and severe plastic

deformation, which produces thermal stresses due to uneven

temperature distribution. The amount of tensile stress pro-

duced is greater in CM than in LTUAM. However, in

LTUAM high compressive stress is induced due to extrusion

and rubbing action of the tool. The utilization of UVAM exhi-

bits a dual effect on the machined material, namely the aug-

mentation of compressive stress and the ampliﬁcation of the

depth of layer of residual stress.

The amount of residual compressive stress induced in the

machined part depends on the duty ratio, cutting speed, and

amplitude. In LTUAM of TC18 titanium alloy, Xie et al.

107

experimentally examined the residual stress of the machined

surface during CM and LTUAM. The surface was found to

have been subjected to compressive residual stress. Compared

to CM, the residual stress value in UVAM is 21.5% greater.

The resultant residual stress value depends on the machining

and ultrasonic parameters. The amount of compressive stress

induced in machining increased with the enlargement of vibra-

tion amplitude. The duty ratio increases as spindle speed and

feed rate increase, reducing tool separation. The increase in

spindle speed resulted in decreased compressive residual

stress.

Chen et al.

investigated the residual stress created

Fig. 15 Microstructural analysis of machined surface plastic deformation layer.

Ultrasonic vibration-assisted cutting of titanium alloys 19

in both the axial and circumferential orientations of the cavity

using ultrasonic-assisted helical milling of Ti–6Al–4V. In the

axial and circumferential direction of the cavity, the induced

compressive stress was enhanced by 85% and 99%, respec-

tively, through the utilization of ultrasonic vibration-assisted

helical milling in comparison to conventional machining. The

increase in compressive stress was due to the hammering effect

of the tool due to vibration. It was observed that the amount

of stress reduced as the distance from the surface increased. In

conclusion, the UVAM of titanium alloys induces beneﬁcial

compressive residual stress in the machined surface. The

induced compressive stress enhanced the material properties

and reduced the chances of fatigue failures. In the future, with

the advancement in ultrasonic machining technology,

researchers should focus on reﬁning the machining parameters

to optimize the compressive stress beneﬁts.

3.3.5. Surface tribological properties

The tribological properties of machined surfaces are very crit-

ical. In the aerospace and automotive industry, signiﬁcant

importance is given to tribological properties because they

affect the component’s life, efﬁciency, and performance.

118

The friction and wear characteristics of the machined surface

are inﬂuenced by the hardness, microtexture, and residual

stress of the surface. The material tribological characteristics

are greatly improved by the presence of a hard surface, high

compressive residual stress, and a precise and well-deﬁned

micro-texture.

119

Different types of surface microtexture can

be produced by using UVAM with different machining ultra-

sonic vibration parameters.

120,121

Zheng et al.

122

explored the

effect of surface microtexture on the tribological characteris-

tics during UVAM of Ti–6Al–4V. The friction and wear exper-

iments were conducted under conditions of oil lubrication.

Observations revealed that the use of UVAM resulted in a sig-

niﬁcant decrease of 35% in the friction coefﬁcient and a sub-

stantial reduction of 67% in the wear volume of the

machined surface in comparison to CM. Chen et al.

experi-

mentally inspected the tribological properties of titanium alloy

machined by CM and LTUAM. It was observed that the sur-

face produced by CM contained tool marks and scratches.

Meanwhile, the UVAM produced micro-textures on the

machined surface. The friction test showed that with identical

machining and ultrasonic vibration parameters, the coefﬁcient

of friction (COF) of the surface machined by UVAM was

lower than that of the surface machined by the CM process.

The vibration-assisted machined surface showed superior tri-

bological properties as compared to conventionally machined

surfaces due to ﬁsh scale microtexture formation on the sur-

face. Xia et al.

examined the tribological properties by per-

forming friction and wear tests on the Ti

AlNb machined

surface. They observed that the micro-texture formed by

UVAM increases and stabilizes the wear resistance of the

machined surface. The microtexture produced on the surface

can store the impurities and wear particles, improving the con-

tact between the friction pair. However, in conventionally

machined surfaces, the worn particle can produce pits on the

surface by extrusion. The COF of the surface machined by

UVAM was 27.8% lower than that of the conventionally

machined surface. The surface obtained by LTUAM at

LA = 3 lm and TA = 1.8 lm exhibits better wear resistance

properties than at other parameters. Fig. 17 illustrates the fric-

tion phenomenon and surface topography after the wear test

with varying amplitude in CM and LTUAM.

Fig. 16 Residual stress generation mechanism during machining.

20 A. KHAN et al.

In their study, Zhang et al.

120

performed experiments to

explore the impact of vibration amplitude and cutting speed

on surface tribological characteristics. They observed that

the COF augmented as the cutting speed escalated. It was dis-

covered that low amplitude or overgrowing amplitude resulted

in poor tribological properties of the machined surface. In

another study, Zhu et al.

123

examined the inﬂuence of UVAM

on the tribological properties of machined Ti–6Al–4V. They

observed surfaces machined by UVAM express excellent tribo-

logical properties. The development of surface uniform micro-

texture improved the surface quality and decreased the COF.

It was found that the vibration amplitude had the most impact

on the COF and that the COF rose as the cutting speed ele-

vated. With the upsurge of amplitude, the surface tribological

properties ﬁrst improved and then deteriorated. The uneven

micro-texture distribution at high amplitude was the main

cause of high friction on the machined surface. In summary,

the generation of microtexture in the UVAM signiﬁcantly

improves the tribological properties of the machined surface.

In the future, by determining the proper machining parame-

ters, vibration parameters, and machining techniques, the tri-

bological properties can be improved further. Table 1 lists

the summary of studies reported on UVAM of titanium

alloys.

23,25,26,74,78,81,83–86,88,89,91–93,95,97,98,100,120,122,124,125

4. Ultrasonic-assisted turning process

This section provides an explanation of the performance char-

acteristics of UVAT as they apply to titanium alloys. In addi-

tion, a thorough investigation was undertaken to evaluate the

inﬂuence of UVAT process parameters on a multitude of crit-

ical variables, including cutting forces, cutting temperature,

tool wear characteristics, and surface quality. The objective

of this analysis was to clarify the dynamic alterations that have

been identiﬁed in CT and UVAT methods.

4.1. Cutting force and temperature

Ultrasonic vibration signiﬁcantly inﬂuences the machining

processes. The UVAT technique offers superior machining

performance over the CT process. The depth of cut, feed rate,

and cutting speed are some of the machining factors that deter-

mine the cutting forces generated in the UVAT process.

126,127

Fig. 17 Analysis of tribological properties of surface machined with CM and LTUAM.

Ultrasonic vibration-assisted cutting of titanium alloys 21

Table 1 Summary of studies reported on UVAM of titanium alloys.

23,25,26,74,78,81,83–86,88,89,91–93,95,97,98,100,120,122,124,125.

Method Material Amplitude

(lm)

Frequency

(kHz)

Output (Compared with CM) Reference

LUVAM TC18 2–4 33.9 S

:"85%; Compressive stress: "50%;

Cutting temperature: ;19.5%;

Cutting force: ;34.1%

Xie et al.

FDUVAM Ti-6Al-

820R

:;30% Ni et al.

LTUAM Ti-6Al-

LA = 1–4;

TA = 0.67–

2.67

35 F

:;7.4%29.1%;

:;34.7%- 40.1%; VB: ;18% after 67.5 m cutting

length

Gao et al.

100

LBUAM Ti-6Al-

0–5 18.5 F

:;32.3%; F

:;31%; F

:;6.6%;

:;35%; Tool life: "166%

Hu et al.

LTUAM Ti-6Al-

5.6 25 Cutting force: ;20%-40%;

Surface roughness ratio: ;74.6%

Ren et al.

LTUAM Ti-6Al-

LA = 4–5;

TA = 3.2–4

35 F

:;36%; Temperature: ;15%-25%;

Compressive residual stress: "25%

Ying et al.

LTUAM Ti-6Al-

5;6 30 Tong et al.

LUVAM Ti-6Al-

5 25 After 40-minutes tool wear

Cutting force: ;55%; R

:;15%;

Cutting temperature: ;17%

Liu et al.

LUVAM Ti-6Al-

630R

:;19-24% Su et al.

124

LTUAM Ti-6Al-

1–9 32.2 Cutting force: ;14%;

Tool wear: ;30%; COF: ;5%-18.3%

Chen et al.

EVAM Ti-6Al-

3–9 19.3 Li et al.

LTUAM Ti-6Al-

3 22.7 COF: ;60%;

:"66%

Zhang

et al.

120

LUVAM Ti-6Al-

20 Compressive residual stress: "6-26%;

COF: ;23.78%;

Wear volume: ;67%

Zheng

et al.

122

LUVAM;

LTUAM

Ti-6Al-

LA = 5.75;

TA = 1.35

(LA)

32.24 Rinck et al.

125

LTUAM TC18 LA = 5;

TA = 0.6(LA)

33 Cutting force: ;16.05%;

Surface roughness: ;45.65%;

Compressive residual stress: "24.35%;

Plastic deformation layer depth: "212%

Xie et al.

LTUAM Ti-6Al-

1–4  Zhao et al.

LTUAM Ti

AlNb LA = 1–4;

TA = 0.67–3.2

35 COF: ;27.08%; R

:;42.5% Xia et al.

LUVAM Ti-6Al-

1.6–3.1 28 Cutting force: ;12.2%;

Plastic deformation layer depth: "27%;

:"27.85%;

Surface hardness: "1.3%

Chang et al.

LUVAM Ti-6Al-

5 32.6 Cutting force: ;3.4%-18.6%;

:;13%-24%;

Cutting temperature: ;10%-15%

Niu et al.

LUVAM TC18 1.5–3.5 Cutting force: ;15%;

Cutting temperature: ;42%;

Compressive residual stress: "40%;

:;44%

Li et al.

LUVAM Ti-6Al-

1–5 24.8 F

:;15%;

:;72% at vibration amplitude of 1 lm

Lu et al.

LTUAM Ti-6Al-

2 21.3 Resultant force: ;3.11%-28.90%;

Axis force: ;12.70% 45.05%;

Surface microhardness: "6.34%-13.22%;

Qin et al.

LUVAM Ti-6Al-

2–4 30 F

:;14.6%; F

:;30.2%;

Cutting temperature: ;25.9%;

:;35.1%; S

:;34.0%

Gao et al.

22 A. KHAN et al.

Sui et al.

128

performed the AUVAT in dry conditions on Ti–

6Al–4V to investigate the cutting forces. The theoretical model

was developed to evaluate the separation characteristics in the

AUVAT. The implementation of vibration in the feed direc-

tion led to periodic separation, resulting in reduced average

cutting forces in AUVAT compared to CT. The depth of cut

showed a higher impact on the cutting forces compared to

machining parameters. The cutting forces of thin wall titanium

alloy during HUVC were studied by Peng et al.

129

in a dry

machining environment. A force sensor with a 36 kHz mea-

surement frequency was utilized to evaluate the cutting forces.

The cutting forces in both CT and UVAT were investigated at

the same machining conditions (feed of 0.005 mm/r and cut-

ting speed of 200 m/min). It was observed that the integration

of vibration of 20 lm amplitude lessens the principal cutting

force by 40% and thrust force by 30%. The decrease in cutting

forces during UVAT was due to the conversion of the process

from continuous cutting to intermittent cutting due to the

vibration of the tool. The experimental mechanism and the

inﬂuence of CT and AVUAT on cutting forces are shown in

Fig. 18. Maurotto et al.

130

examined the impact of depth of

cut and cutting speed on cutting forces during UVAT of tita-

nium alloy in the absence of coolant. The tool was exposed

to radial-direction vibration as the workpiece rotated. The

radial and tangential cutting forces were decreased when vibra-

tion was included in the CT process. The analysis of the behav-

ior of cutting forces showed that as cutting speed and depth of

cut grew, so did the cutting forces. It was found that the rate at

which the cutting forces in UVAT decreased, reduced in tan-

dem with the depth of cut.

The mathematical model to calculate the cutting forces in

2D-UVAT was established by Kurniawan et al.

131

. The effect

of cutting-edge radius and kinematics of the 2D-UVAT pro-

cess was analyzed in the developed mathematical model. The

conventional cutting, static friction, and reverse kinetic mech-

anism were observed in one vibration cycle in 2D-UVAT. The

experimental results demonstrated that compared to tradi-

tional cutting methods, the 2D UVAT generated reduced cut-

ting forces. As a consequence of thermal softening, the cutting

forces in conventional machining diminish as the cutting speed

rises. The cutting forces experienced during 2D-UVAT of Ti–

6Al–4V exhibited variability under tool vibration and further

increased as the cutting speed surged. Cakir et al.

132

evaluated

the cutting force by performing a simulation of UVAT of Ti–

6Al–4V. The tool vibration was generated in the direction par-

allel to the cutting speed direction. They discovered that the

reduced tool-workpiece contact rate due to the application of

vibration on the tool decreased the cutting forces by 56% in

UVAT. The tool-workpiece contact rate increases with the

increase in cutting speed. At high cutting speed the behavior

of cutting forces was similar in UVAT and CT, because at

the high cutting speed no separation occurred between tool

and workpiece. Muhammad et al.

133

carried out turning of

Ti–676–0.9La and Ti–6246 samples for different levels of cut-

Fig. 18 Analysis of impact of cutting parameters and AUVAT on cutting forces.

129

Ultrasonic vibration-assisted cutting of titanium alloys 23

ting speed while maintaining constant depth of cut and feed

rate with the assistance of ultrasonic vibration, characterized

by a 10 lm amplitude. The UVAT was investigated to enhance

the surface characteristics and lessen the cutting forces. The

UVAT process analysis revealed that the cutting forces for

both materials decreased signiﬁcantly. However, the decrease

in cutting forces became less pronounced as the cutting speed

approached the critical speed. Because the duration of the gap

among the tool and the workpiece is minimized at elevated cut-

ting speeds, this leads to increased cutting forces. The intermit-

tent separation of the workpiece and tool is a critical

component of the UVAT procedure. The separation properties

are inﬂuenced by parameters related to machining and vibra-

tion. Alterations in separation properties have an impact on

the effectiveness of the cutting procedure. Llanos et al.

134

stud-

ied the impact of ultrasonic vibration on the cutting forces gen-

erated by Ti–6Al–4 V during UVAT in a dry environment. It

was found that properties of the tool-workpiece separation,

which are impacted by the spindle speed and vibration ampli-

tude, deﬁne the cutting forces generated in UVAT. The separa-

tion between the workpiece and tool increased in tandem with

the amplitude of the vibration, leading to a more pronounced

separation. The reduction in cutting forces was a result of the

increased vibration amplitude, demonstrating an inverse con-

nection between force and vibration amplitude. In the UVAT

process, duty ratio and separation characteristics signiﬁcantly

affect the machining performance. The transient separation

in UVAT results in the decrease of the cutting forces. The tran-

sient separation creates a circumstance in which no material

removal occurs, resulting in a 10 to 40% decrease in cutting

force at a duty ratio of 0.55 to 1.

135

The cutting temperature in the machining of titanium alloys

is an important factor. The low thermal conductivity of tita-

nium alloys led to high temperatures in the cutting area during

CT. The high cutting temperature can increase the tool wear.

Studies have shown that the intermittent cutting mechanism

of UVAT reduces the cutting temperature in comparison with

CT. The separation effect due to vibration enhances the heat

dissipation from the shearing zone.

136

Zhang et al.

investi-

gated the cutting temperature during UVAT of difﬁcult-to-

cut material at high cutting speed in coolant conditions. They

developed a model and performed experiments to observe the

temperature variation in high-speed UVAT. Based on the sep-

aration characteristics of UVAT, heat generation during the

cutting phase and heat dissipation during the separation phase

were calculated using the developed temperature model. The

14% maximum error was noticed during the validation of

the model through experiments. It was observed cutting speed

and duty ratio were identiﬁed as the two primary variables that

have a substantial impact on the cutting temperature. As a

consequence of increasing the duty ratio and speed of cutting,

a rise in cutting temperature was observed due to the reduced

time available for heat transmission from the cutting zone dur-

ing the tool-workpiece separation period at high cutting

speeds. Kurniawan et al.

131

aimed to investigate the cutting

temperature during UVAT of titanium alloy in a dry environ-

ment. Due to the relatively high shearing velocity of the tool in

2D-UVAT, the shear zone temperature was higher in 2D-

UVAT as compared to the conventional machining process.

Whereas the mean value of cutting temperature was lower in

2D-UVAT than in CT. It was noticed that the primary defor-

mation zone temperature in the 2D-UVAT was lower than the

CT over the same cutting speed as illustrated in Fig. 19. Chen

et al.

137

employed a nonuniform moving heat source model to

examine the inﬂuence of ultrasonic vibration parameters on

the temperature of shear zone and machined surface during

UVAT of Ti–6Al–4V. Some important observations were as

follows: the ultrasonic vibrations amplitude and frequency

had a signiﬁcant impact on the temperature gradient in the

depth of cut direction and cutting direction, the lower temper-

ature in the shear zone can be obtained by applying high

amplitude and frequency vibrations, the temperature of the

machined surface can be reduced by raising the amplitude

and lowering the frequency of the vibrations.

The intermittent separation phenomenon in UVAT facili-

tates the lubricant and coolant to reach the cutting zone and

increase heat dissipation. The application of lubricant and

coolant in UVAT signiﬁcantly reduces the cutting tempera-

ture. Cakir et al.

132

experimentally evaluated the cutting tem-

perature in dry conditions during the turning of titanium

alloy. They observed that the UVAT reduces the cutting tem-

perature as compared to CT. The cutting temperature in

UVAT ﬂuctuates, and the peak temperature was higher as

compared to CT. Muhammad et al.

133

evaluated the machin-

ability of Ti–6246 and Ti–676–0.92La during CT and UVAT

in coolant conditions. They determined that the energy

imparted to the instrument by vibrations was the cause of

the elevated temperature in UVAT, a factor that was absent

in CT. Furthermore, the cutting temperature exhibited an

increase in cutting speed from 10 m/min to 60 m/min at a con-

stant amplitude of 10 lm. HUVC of Ti–6Al–4V was per-

formed by Lu et al.

138

to explore the cutting temperature by

applying a high-pressure coolant. Machinability evaluations

were conducted between ﬂood and high-pressure coolant

machining environments. The cutting temperature was

decreased by 55% in HUVC as compared to the CT. The duty

cycle of 0.9 nearly eliminates the detachment effect of high-

speed ultrasonic turning, and the effect of increasing cutting

speed on temperature becomes more pronounced. In sum-

mary, the cutting forces and temperature produced in UVAT

are considerably reduced compared to conventional processes.

From a comprehensive examination of the existing literature, it

became clear that the machining parameters and machining

conditions all had a substantial impact on the cutting forces

and cutting temperature during UVAT. The pursuit of a

dynamic adaptive control system capable of accommodating

evolving machining conditions holds the potential to facilitate

the attainment of optimal cutting forces and temperature pro-

ﬁles in forthcoming times.

4.2. Tool wear behavior

In the machining process the cutting efﬁciency and surface

quality of the machined workpiece depend on the tool wear

behaviour and tool life. Therefore, signiﬁcant efforts have been

made to enhance the service life of the tool by selecting tool

material, by adopting different machining technologies, by

using different machining environments, and by adjusting cut-

ting parameters. Studies indicate that ultrasonic vibration-

assisted technology effectively reduces tool wear.

55,139–141

The UVAT technique showcases a reduction in tool wear

due to the application of high-frequency vibrations to the cut-

ting tool. This phenomenon effectively diminishes the cutting

24 A. KHAN et al.

forces experienced and minimizes the friction encountered

between the tool and the workpiece. Airao et al.

142

investigated

the tungsten carbide tool life behaviour during CT and UVAT

of Ti–6Al–4 V when subjected to dry and ﬂood cooling. The

investigations were conducted with the following constant val-

ues: 70 rpm for cutting speed, 0.2 mm/r for feed rate, 0.3 mm

for depth of cut, 20 kHz for vibration, and 10 lm for vibration

amplitude. It has been observed that UVAT extends the life of

tools in comparison to CT. The tool life was increased by 6%–

12% in UVAT with sustainable cutting ﬂuid as compared to

UVAT in dry conditions. The application of cutting ﬂuid in

UVAT increases the lifespan of the tool by increasing the heat

dissipation and reducing the tool wear. Lu et al.

138

minimized

the cemented carbide tool degradation by using the high-

pressure coolant in UVAT. When titanium alloy was machined

in the absence of a high-pressure coolant, oxidation wear and

adhesive wear were the predominant methodologies of wear. It

was observed that the application of high-pressure coolant in

UVAT increased the tool’s life by 6.3 times compared with

CT. By eliminating adhesive and oxidation wear with high-

pressure coolant, abrasive wear was identiﬁed as the primary

wear mechanism in high-pressure UVAT. Sui et al.

128

stated

that the increase in feed rate increased the duty ratio, which

resulted in enhanced cutting forces and tool wear. Because

with the increase of duty ratio, the periodic gap between tool

and workpiece becomes minimal. During the AUVAT of tita-

nium alloy, it was noted that oxidation, adhesive, and abrasive

wear were the primary wear mechanisms. As the feed rate and

cutting speed were augmented, a corresponding decrease in

tool life was observed. Conversely, an elevation in vibration

amplitude yielded an increase in tool life. The titanium alloy

was machined for a longer distance using a tungsten carbide

tool in a high-pressure cooling environment. Fig. 20(a) illus-

trates the inﬂuence of rotation speed on the TiAlN-coated

tungsten carbide tool and PCBN tool life during CT and

AUVAT.

128

In vibration-assisted machining, the feed rate is the most

critical parameter that affects the tool’s life. During AUVAT,

the separation characteristics of the tool and workpiece are

greatly affected by changes in feed rate. The higher value of

the feed rate signiﬁcantly reduces the separation duration.

Sui et al.

135

investigated the effect of cutting speed, feed rate,

and depth of cut on cemented carbide tool life during

AUVAT. They found that feed rate had more impact on tool

life as compared with cutting speed and depth of cut. The feed

rate directly inﬂuences the duty ratio, and a higher value of the

duty ratio leads to higher tool wear. The optimal combination

for higher tool life was a low feed rate, less depth of cut, and

moderate cutting speed. A higher value of cutting parameters

increases the cutting temperature, resulting in higher tool wear.

The impact of machining variables on TiAlN-coated cemented

carbide tool wear behavior was examined experimentally by

Zhang et al.

143

. It was found that feed rate and spindle speed

had a noteworthy impact on tool wear during the AUVAT

of titanium alloy. The AUVAT parameter, known as the duty

ratio, exhibits dependence on both the feed rate and vibration

amplitude. It is signiﬁcant to point out that a duty ratio of 0.55

resulted in the most prolonged tool life. Using cutting ﬂuid in

Fig. 19 Comparison of cutting temperature with varying cutting speed during CT and 2D-UVAT.

131

Ultrasonic vibration-assisted cutting of titanium alloys 25

the AUVAT greatly extended the tool’s life. Fig. 20(b) illus-

trates how the duty ratio affects tool ﬂank wear during CT

and AUAVT.

143

The utilization of liquid carbon dioxide (LCO

), and MQL

signiﬁcantly improve the tool life in vibration-assisted cutting.

Airao et al.

144

performed an experimental investigation to ana-

lyze the effect of dry, wet, LCO

and MQL machining condi-

tions on TiAlN-coated CNMG120408MS tool service life.

Abrasion, adhesion, and edge ﬂaking were identiﬁed as the pri-

mary mechanisms of deterioration. The application of MQL,

LCO

, and ﬂood coolant in UVAT was found to substantially

decrease tool fatigue. The use of cooling ﬂuid increases the loss

of heat from the cutting area, reduces the cutting temperature,

and improves the tool life. The ﬂank and rake face wear mor-

phologies during CT and UVAT under dry conditions are

shown in Fig. 21(a). In another observation, Yan et al.

145

stud-

ied cemented carbide tool insert wear morphology during CT

and UVAT of titanium alloy. It was found that material adhe-

sion, abrasion, and notch wear were the main wear mecha-

nisms. The ﬂank and rake face wear morphologies are shown

Fig. 20 Effect of tool and UVAT characteristics on tool wear behavior.

Fig. 21 Typical tool rake and ﬂank face wear morphologies after machining titanium alloys.

26 A. KHAN et al.

in Fig. 21(b). Tan et al.

investigated the PCD tool wear

behavior during CT and ultrasonic elliptical vibration-

assisted turning (UEVT) in a dry machining environment. It

was observed that the UEVT process meaningfully reduces

the ﬂank face wear compared to CT. Fig. 21(c) shows the tool

wear morphology during CT and UEVT. The built-up edge

(BUE), adhered material, and chipping were observed in CC.

However, in UEVT, the tool wear was not severe. Overall,

UVAT of titanium alloys suppresses tool wear compared to

CT. Consequently, UVAT improves the tool life, minimizes

the machining cost, and reduces the poor effect of tool wear

on the environment.

4.3. Surface integrity

Titanium alloys are widely used in the aerospace sector due to

their favorable mechanical characteristics and exceptional

resistance to corrosion. The surface integrity of machined tita-

nium alloys is a crucial element that substantially impacts the

characteristics and lifespan of the machined product. Under-

standing the behavior of machined surface quality is necessary

for maximizing the advantages of UVAT in industries where

titanium alloys are extensively used. This section depicts the

impact of UVAT process parameters on surface morphology,

surface roughness, surface hardness, surface residual stress,

and surface tribological characteristics.

4.3.1. Surface morphology

The surface morphology of the machined component is greatly

improved as a result of the high-frequency vibration that is

imparted to the cutting tool during the UVAT of titanium

alloy. Both the chip fragment and the BUE creation are sup-

pressed by the vibrations that are implemented on the cutting

tool. During the UVAT, a titanium alloy with a textured sur-

face was produced. Peng et al.

146

compared the CT and UVAT

and observed that UVAT resulted in a textured surface. Under

the application of vibration in the turning process, the gener-

ated textured surface contains small grooves and valleys.

135

The semi-spherical microtexture was observed on the titanium

alloy surface machined by the 3D UEVT process.

147

Tan

et al.

evaluated the surface characteristics machined by CT

and UVAT. They observed that the surface machined by the

CT process contained defects. These defects include adhered

material, grooves, BUE, tool feed marks, and side ﬂow of

material due to plastic deformation. The surface machined

by the UVAT process was smooth without the presence of

any defects. Tan et al.

148

examined the surface morphology

of machined Ti–6Al–4V. The UEVT process was used to pro-

duce the machined surface. They observed that uniform tool

feed marks were present on the machined surface, similar to

feed marks produced in the CT process. The elliptical oscilla-

tion of the tool generated a consistent vibratory texture on

the surface that was being machined, aligning with the direc-

tion of the cutting process. Fig. 22(a) illustrate the texture pro-

duced in the cutting direction during UEVT. The size of

microtexture during UVAT depend on the cutting speed.

148

With the increase in cutting speed the size of the micro mounts

was increased. Fig. 22(b) illustrate texture size variation with

an increase in cutting speed.

With the passage of time, the

tool cutting edge loses its form as the machining process con-

tinues. Tool wear is caused by strong cutting forces and high

temperatures in the cutting zone. Tool wear had an important

inﬂuence on the machined surface texture. The texture gener-

ated on the surface had obvious boundaries at the start of

the machining. However, as the tool wears, the texture on

the surface begins to fade. The increasing tool wear resulted

in a low-quality machined surface.

128

In UVAT, utilizing cooling and lubrication conditions pre-

vents machined surfaces from damage and material adhesion.

Yan et al.

145

evaluated the surface quality of titanium alloy

machined by the UVAT process. They noted that the applica-

tion of MQL in conjunction with UVAT enhanced the quality

of the surface. The surface became smooth, and there were no

defects or adhered material on the surface. Overall, the UVAT

improves the surface ﬁnish of titanium alloy and makes it suit-

able for aerospace applications where smooth and dimension-

ally accurate parts are required. Nevertheless, the composition

of the surface changes with variations in vibration amplitude,

cutting speed, and input rate. However, by optimizing the

machining techniques and parameters, it is possible to achieve

the desired surface texture.

4.3.2. Surface roughness

The surface roughness of hard-to-cut materials during UVAT

is inﬂuenced by vibration parameters, machining parameters,

and the machining environment.

24,149

Silberschmidt et al.

150

conducted a review of UVAT in an effort to reduce the surface

roughness of titanium alloy during machining. When vibration

was applied to a cutting instrument, the surface roughness was

observed to be reduced by 49% in comparison to the surface

roughness obtained using CT. For optimal surface ﬁnish, the

optimum combination of low feed rate and cutting speed

was utilized in conjunction with other parameters. Patil et al.

151

demonstrated that titanium alloy UVAT resulted in a substan-

tial reduction in surface roughness and an enhancement in sur-

face quality. It has been documented that as cutting speed

increased, the surface roughness value exhibited a further

decline. Wei et al.

assessed the surface roughness during

the machining of challenging-to-cut materials and analyzed

the impact of various conventional and UVAT techniques.

The CT, UVAT, UEVT, and 3D-UVAT processes were per-

formed to study their effect on the surface quality. It was

found that the 3D-UVAT process produced less surface rough-

ness than other machining methods. The inﬂuence of different

machining methods on the surface roughness is illustrated in

Fig. 23. As the cutting speed increased in CT, the surface

roughness was reduced; possible reasons include reduced cut-

ting force from thermal softening and reduced built-up edge.

However, surface roughness rises with higher cutting speeds

during UEVT and 3D-UVAT because increased cutting speed

leads to weaker separation characteristics. The application of

3D elliptical vibration in the turning process eliminates the

feed marks of the tool and reduces the surface roughness in

the feed direction.

147

In UEVT surface roughness greatly inﬂuenced by variation

in amplitude of vibrations in cutting direction and depth of cut

direction. Tan et al.

148

examined the inﬂuence of vibration

amplitude on titanium alloy surface roughness during UEVT.

It was documented that as the amplitude of vibration increased

in the direction of cutting and decreased in the direction of

depth of cut, the surface roughness value decreased. However,

it is critical to implement various cooling techniques during the

Ultrasonic vibration-assisted cutting of titanium alloys 27

machining process to attain the desired surface quality. The

cooling and lubrication decrease the cutting temperature and

aid in minimizing tool wear, resulting in good surface quality.

Airao et al.

144

conducted studies on Ti–6Al–4 V alloys in wet,

dry, MQL, and LCO

environments to examine their impact

on surface roughness. It was observed that the integration of

cooling and lubrication techniques improved the surface qual-

ity. The lowest surface roughness was observed in combination

of LCO

and UVAT. In summary, many variables signiﬁcantly

impact surface roughness, including machining technique,

machining environment, machining parameters, vibration

parameters, and tool condition. In the future, the surface

Fig. 22 Assessment of effect of UVAT and cutting speed on the machined surface microtexture.

Fig. 23 The 3D surface roughness obtained by four different machining methods: CT, UVAT, UEVT and 3D-UVAT.

28 A. KHAN et al.

roughness in UVAT of titanium alloy can further be improved

by exploring advanced tool material, coating, and optimizing

the UVAT process.

4.3.3. Surface hardness

Surface hardness is a critical factor of machining performance,

and it is quite important to comprehend how it changed in tita-

nium alloys during UVAT. Achieving the appropriate hard-

ness of a machined component is a critical priority in the

aerospace industry since surface hardness has a major role in

the effectiveness, longevity, and quality of an aircraft part.

Machined surface hardness depends on vibration parameters,

machining parameters, and machining environment. Many

researchers have done studies on the surface hardness of tita-

nium alloy during UVAT. The research work done by Lotﬁ

et al.

147

indicates the features of 3D-UEVT. An increase in

the machined surface microhardness was observed during

machining of Ti–6Al–4V. The hardness of the surface

machined by 3D-UEVT was higher as compared to the surface

machined by CT and the hardness of bulk material. The sur-

face hardness depends on the nature of the plastic deformation

layer. Peng et al.

152

investigated the complex microstructure of

the deformed plastic layer formed during the machining pro-

cess of Ti–6Al–4V titanium alloy. The typical microstructure

of Ti–6Al–4V is shown in Fig. 24(a): SEM, optical microscope

(OM), and inverse pole ﬁgure (IPF) imaging. It was found that

more severe plastic deformation occurs in UVAT than in CT.

The IPF and kernel average misorientation (KAM) map of

plastic deformation layer in CT and UVAT is shown in

Fig. 24(b). Peng et al.

146

studied the high-speed AUVAT of

Fig. 24 Analysis of the inﬂuence of CT and UVAT on plastic deformation layer characteristics of Ti–6Al–4V.

Ultrasonic vibration-assisted cutting of titanium alloys 29

Ti–6Al–4V alloys. It was discovered that UVAT caused signif-

icant plastic deformation. The intense plastic deformation on

the machined surface was caused by the frictional effect

between the tool and workpiece, as well as the ironing impact

of the tool. This process results in a considerable decrease in

the grain size of the microstructure. The Hall-Petch effect

claims that a reduction in grain size leads to an augmentation

in material hardness. AUVAT exhibited a higher surface hard-

ness compared to CT, which was shown to increase with the

rise in cutting speed. Fig. 24(c) and 24(d) illustrates the

changes in the microstructure of the plastic dAeformation

layer as the velocity of the cutting process escalates in both

CT and AUVAT.

Surface hardness during UVAT, compared to CT, may be

higher or lower depending on the vibration characteristic. In

3D-UEVT and AUVAT, the surface hardness was higher than

that of CT.

146,147

On the other hand, the 2D-UVAT surface

hardness is lower than that of CT. Kurniawan et al.

131

observed the surface microhardness of Ti–6Al–4V during

2D-UVAT. It was discovered that the surface hardness was

lower in the UVAT method compared to the CT procedure.

It was noted that in the normal turning process, the tool con-

sistently stays in connection with the workpiece. Thus, it

causes high deformation of material on the surface as com-

pared to the UVAT process. The high deformation of the

material on the surface increased the hardness of the material.

A study performed by Bai et al.

153

intended to examine the

inﬂuence of CT and UVAT on surface microhardness. It was

found that the machined surface hardness was higher in the

CT process. The hardness value dropped as the depth from

the machined surface increased for both surfaces machined

by CT and UVAT. The application of cutting ﬂuid enhanced

the surface hardness during the machining. Airao et al.

154

examined the surface quality while performing machining on

Ti–6Al–4V. The studies were done both with and without

the addition of sustainable cutting oil. It was observed that

the surface hardness was larger in UVAT than in CT. The

vibrating tool in UVAT produced high plastic deformation

and strain hardening. The value of hardness reduced with

the growth of distance from the top of the surface. Due to

rapid heating and cooling in UVAT with sustainable cutting

ﬂuid enlarges the hardness of the material. In summary, the

machined surface hardness of titanium alloy varies depending

on the vibration modes, machining parameters, and cooling

conditions. The required surface hardness can be attained by

employing optimized cutting parameters and suitable condi-

tions for machining different titanium alloys.

4.3.4. Surface residual stress

The nature of the residual stress produced during the machin-

ing of titanium alloys depends on different factors, including

machining parameters, vibration characteristics, tool geome-

try, and machining environment. The residual stress in the

machined item is caused by the high thermal and mechanical

loads on the component being machined. The phase transfor-

mation of material during machining can also introduce resid-

ual stress in the workpiece material.

155

Sivareddy et al.

115

studied the inﬂuence of vibration and machining parameters

on changes in thermal and mechanical loads on the surface

being machined. They found that compressive circumferential

and axial stress was induced in the machined surface. The shift

from tensile to compressive residual stress in the circumferen-

tial direction occurred as the ultrasonic power increased. In

contrast, its compressive character transformed into a tensile

one when cutting speed, feed, and depth of cut were increased.

The high thermal load at higher values of the machining

parameter leads to the generation of tensile stress in the cir-

cumferential direction. Maroju et al.

156

investigated the resid-

ual stress produced during UVAT of Ti–6Al–4V alloys. The X-

ray diffraction equipment was utilized to examined the residual

stress developed during the machining. The surface showed

signs of being subjected to compressive stress during UVAT

due to the high mechanical action of the tool on the surface.

The compressive stress induced in the machining surface in

the cutting direction was 45% higher than that of tensile stress

in the conventional turning process. Fig. 25(a) shows the resid-

ual stress generation mechanism during vibration-assisted

machining. In 2D UVAT of titanium alloy, the author

observed the compressive stress in the machined surface. High

mechanical load in UVAT due to the vibration impact of the

tool and tool velocity leads to the generation of higher com-

pressive residual stress as compared to residual stress in CT.

131

In a study on how cutting speed affects residual stress, Peng

et al.

146

found that as cutting speed increased, the compressive

stress created in the machined surface decreased. However, in

CT, as cutting speed increased, compressive stress changed to

tensile stress because of the high thermal load at high speed.

Fig. 25(b) illustrates how increasing cutting speed during CT

and high-speed UVAT affects the residual stress created on

the machined surface. In short, during the UVAT of titanium

alloys, compressive residual stress is induced in the processed

component. However, the nature of the stress can change from

compressive stress to tensile stress at higher values of machin-

ing parameters. The high compressive stress induced in tita-

nium alloy during UVAT can increase its fatigue strength,

wear resistance, and dimensional stability. These advantages

can make UVAT a preferred machining method in the aero-

space industry, where titanium alloys are widely used in the

manufacturing of aircraft components.

4.3.5. Surface tribological properties

The aerospace and automotive industries pay great attention

to the tribological qualities of machined surfaces, such as wear

resistance, lubrication, and friction coefﬁcient, because of the

harsh operating environments that these sectors provide.

157

The machining method had a noteworthy inﬂuence on the tri-

bological properties of machined surfaces. Researchers have

investigated the factors that affect the tribological properties

of the surface being machined. Amini et al.

158

investigated

and compared the tribological properties of surface machined

by three different modes of UVAT. It was observed that

UVAT created a uniform microtexture on the surface. The for-

mation of uniform microtextures leads to improvement in the

tribological properties of the material by increasing the wear

resistance and reducing the friction coefﬁcient. In the course

of Ti–6Al–4V high-speed UVAT, Peng et al.

152

examined the

machined surface’s tribological characteristics. The wear test

showed that the wear volume loss of the surface machined

by UVAT was 23% decreased as compared to the surface

machined by CT. They observed that decreased surface rough-

ness, high surface hardness, high wear resistance, and high

compressive stress improved the tribological properties of tita-

30 A. KHAN et al.

nium alloy in UVAT. The wear morphologies of surfaces

machined by CT and AUVAT after the wear test are shown

in Fig. 26.

Summarily, the ultrasonic-assisted turning had a meaning-

ful consequence on the tribological properties of the machined

titanium alloy surface. The UVAT increases the wear resis-

tance of the machined surface. However, very few papers have

been published on the impact of UVAT on the tribological

properties of the machined surface of titanium alloys. In the

future, the researcher should investigate the inﬂuence of differ-

ent machining parameters, vibration parameters, and machin-

ing environments on surface tribological properties during

ultrasonic-assisted machining of titanium alloys. Table 2 lists

the summary of studies reported on UVAT of titanium

alloys.

21,33,41,127,128,131,135,142–145,147,148,150,152,153

5. Sustainability evaluation under ultrasonic vibration-assisted

cutting

Sustainable machining methods play an essential part in the

growth of manufacturing companies. Right now, manufactur-

ing companies are trying hard to ﬁnd new sustainable methods

for machining difﬁcult-to-cut materials. Sustainability covers

three different areas: social, environmental, and eco-

nomic.

159,160

Sustainability has different deﬁnitions for differ-

ent sectors. In the machining industry, sustainability is

evaluated based on energy consumption, tool life, cooling

and lubrication, effect on environment, and quality of the

machined material.

160

The machining process of titanium

alloys is exceedingly difﬁcult owing to their exceptionally high

hardness and limited thermal conductivity. Dry machining of

Fig. 25 Analysis of residual stress during CT and UVAT.

Fig. 26 SEM images of wear morphologies of surface machined by CT and AUVAT at varying cutting speeds.

152

Ultrasonic vibration-assisted cutting of titanium alloys 31

titanium alloys generates substantial cutting forces, which con-

sequently lead to elevated energy consumption.

161

The elevated

temperature in the cutting zone during machining titanium

alloys, which is attributed to their limited thermal conductiv-

ity, results in augmented tool wear.

162,163

The decreased tool

life impacts the environment in terms of high carbon produc-

tion during tool manufacturing, and also tool disposal con-

tributes to solid waste in landﬁlls. The high cutting

temperature and high tool wear in dry machining inﬂuences

the surface ﬁnish, causing high surface roughness and defects

on the surface.

The defective surface produced by dry

machining requires another ﬁnishing process to get the desired

quality and increase the consumption of energy and resources.

Utilizing a coolant or lubricant during titanium alloy machin-

ing substantially decreases the cutting temperature, extends the

tool life, and increases the machining process’s efﬁciency.

164

Nevertheless, environmental and human health are adversely

affected by the lubricant used during machining. The lubri-

cants contain hazardous chemicals, and leakage, inappropriate

disposal, and evaporation of lubricant during machining can

harm the ecosystem, contaminate the water, and harm human

health.

165

The increased energy consumption, impact on the

environment, material waste, and effect on human health make

them unsustainable for titanium alloy machining. In the

machining of titanium alloys, vibration-assisted machining

emerges as a promising machining method that can solve var-

ious sustainability challenges related to conventional machin-

ing of titanium alloys.

The vibration-assisted cutting process generates diminished

cutting forces in comparison to the traditional machining

method employed for titanium alloys.

166

The low cutting

forces generated during vibration-assisted machining of tita-

nium alloys minimize heat generation. The reduced heat pro-

duction in the cutting area increases the tool life and also

prevents the workpiece surface from thermal damage.

86,167

To evaluate the sustainability beneﬁts of vibration assisted cut-

ting, various aspects need to be studied, such as power con-

sumption, tool life, material removal efﬁciency, and

environmental impact. The vibration-assisted cutting process

signiﬁcantly reduces the power consumption during the

Table 2 Summary of studies reported on UVAT of titanium alloys.

21,33,41,127,128,131,135,142–145,147,148,150,152,153

Method Amplitude (lm) Frequency

(kHz)

Output (Compared with CT) Reference

AUVAT 10 22.145 Cutting force: ;10%-40% Sui et al.

135

2D UVAT Radial amplitude (RA) = 5,Tangential

amplitude

(TLA) = 5

16 Cutting temperature: ;12%16%;

Surface hardness: ;12%14%;

Compressive residual stress: "166%

Kurniawan et al.

131

TUVAT 10 20 VB "20% dry and ;70% LCO

condition;

Power consumption ;7%;

;5%18.5%

Airao et al.

144

UEVT RA = 4, Axial amplitude (AA) = 6 29.76 R

:;37%57% Tan et al.

AUVAT 10 22.1 Cutting forces ;30%-50%;

Cutting temperature ;15%;

Tool life "102%

Zhang et al.

143

AUVAT 3–9 22.18 Sui et al.

128

TUVAT 10 20 Tool life: "6%-12%;

Power consumption: ;18%

Airao et al.

142

RUVAT 10 28 VB ;33% in dry condition;

:;47% in dry condition

Yan et al.

145

UEVT RA = 1–5, AA = 1–6 29.75 Tan et al.

148

TUVAT 8 20 R

:;49%, S

:;43.5% Silberschmidt et al.

150

AUVAT 15 21.96 R

:;14.22%, R

:;29.4%;

Plastic deformation layer depth:

"81%;

Surface hardness: "7.17%;

Compressive residual stress: "22.5%;

Wear volume: ;20%-25%

Peng et al.

152

TUVAT 10–20 20 Surface hardness: ;21.21% Bai et al.

153

UEVT TLA = 5–15, RA = 4–12 20,30,40 Xie et al.

127

RAUVAT 5, 15, 20 20 F

:;13.4%–51.1%;

:;5.3%–68.3%;

Temperature: ;4.1%–9.4%;

Surface plastic deformation: ;2.6%–

34.5%

Chen et al.

TUVAT,

EVAT

TLA = 15–25, RA = 10 20 F

:;8%-13%; F

:;6.5%-21.3%; Chen et al.

3D UEVT RA = 14, AA = 10, TLA = 14 17.2 F

:;20%–30%; F

:;50%–70%;

:;55%–65%; R

;;30%

Lotﬁ et al.

147

32 A. KHAN et al.

machining of titanium alloys. Airao et al.

142

examined the

power consumption during conventional and ultrasonic-

assisted machining of titanium alloys. It was noted that

ultrasonic-assisted machining decreases the cutting forces.

The power consumed in ultrasonic-assisted machining was

14%–20% lower than in traditional machining. In another

observation, Airao et al.

144

examined the power consumed

during the machining of titanium alloy under different sustain-

able cooling environments. They found that the vibration-

assisted machining process of titanium alloy consumes less

energy as compared to conventional machining. They also

observed that energy consumption could further decrease by

10% in ultrasonic-assisted machining of titanium alloys under

LCO

as compared to machining in a dry environment. Fig. 27

shows the power consumption under different machining envi-

ronments during CT and UVAT of titanium alloy. During the

of vibration-assisted cutting of titanium alloys, it was detected

that reduced cutting forces and cutting temperature increased

the tool’s life. The rise in tool life reduces the cost of machining

and also minimizes the time required for machining. The heat

generation during vibration-assisted cutting of titanium alloys

is lower as compared to conventional machining, resulting in a

reduction of the dependence on cutting ﬂuid. The decreased

tool wear and lower dependency on cutting ﬂuid during

vibration-assisted cutting reduce the emission of carbon during

tool production and decrease the impact of tool and cutting

ﬂuid disposal on the environment. The good surface ﬁnish pro-

duced by vibration-assisted cutting eliminates the need for

other ﬁnishing processes. UVAT of titanium alloys minimizes

waste material and saves resources and energy. Thus, reduced

power consumption, and decreased residual waste make

vibration-assisted cutting of titanium alloy a sustainable

machining option. In conclusion, vibration-assisted machining

signiﬁcantly reduced the power consumption during titanium

alloy machining. Previous research works have primarily

focused on power consumption during vibration-assisted

machining of titanium alloys. However, research on the costs

and environmental effects of vibration-assisted machining

has not been done. Industries are utilizing ultrasonic

vibration-assisted machining without considering cost and

environmental impact factors. Ignoring sustainability aspects

in vibration-assisted machining of titanium alloys can lead to

environmental degradation, social implications and economic

deﬁciencies. Future research should extend beyond power con-

sumption to encompass the evaluation of environmental

impact and cost in vibration-assisted machining of titanium

alloys. Investigating costs, and environmental impact, and

exploring new materials for tools will contribute to enhancing

machining efﬁciency and sustainability.

6. Conclusion

A comprehensive literature review on the application of

ultrasonic-assisted milling and turning techniques to titanium

alloys is presented in the current article. This study compre-

hensively investigates the fundamental principles that control

vibration-assisted machining. Additionally, it explores the

effects of various process parameters on cutting forces, temper-

ature, tool wear characteristics, and surface quality. The sus-

tainability aspect during vibration-assisted machining of

titanium alloys is evaluated by considering factors including

power usage, material waste, tool lifespan, and environmental

impact. The following are the important ﬁndings:

(1) The ultrasonic vibration system signiﬁcantly impacts the

performance of vibration-assisted machining. The recent

developments in ultrasonic vibration systems have

exceptionally enhanced the effectiveness of ultrasonic-

assisted machining. However, by overcoming the ﬂuctu-

ation in vibration amplitude at a constant frequency,

localized heating between the tool and collet chuck,

and optimizing the design of the ultrasonic vibration

system, the performance of vibration-assisted machining

can be further improved.

(2) The integration of ultrasonic vibration in titanium alloy

machining reveals a prominent impact on the mitigation

of cutting force due to periodic separation and reduction

in friction between tool and workpiece, consequently

enhancing machining efﬁciency. Furthermore, the inte-

gration of ultrasonic vibration throughout the machin-

ing process contributes to a substantial decrease in

cutting temperature. The periodic separation and

reduced frictional heat signiﬁcantly enhance the heat dis-

sipation from the cutting zone. However, the existence

of critical cutting speed restricts the cutting efﬁciency.

In the HUVC method, the separation can be achieved

at a cutting speed higher than the critical cutting speed

of other UVAT and UVAM processes, resulting in low

cutting forces, low cutting temperature and high cutting

efﬁciency.

(3) The efﬁcient damping of cutting forces and reduced fric-

tional effects during ultrasonic vibration-assisted

machining of titanium alloys signiﬁcantly enhance the

cutting tool life. The tool life in vibration-assisted

machining of titanium alloys depends on cutting time,

tool geometry, cutting speed, and TWCR, and in ideal

conditions, vibration-assisted machining enhance the

tool life by 166%. At times, due to high kinetic energy

collision between the vibrating tool and the workpiece,

the tool experience edge chipping, microcracks. The

use of MQL and high-pressure coolant signiﬁcantly sup-

Fig. 27 Power consumption during CT and UVAT.

144

Ultrasonic vibration-assisted cutting of titanium alloys 33

presses the wear of the tool. The reduction in tool wear

due to reduced friction and forces, by substantially

increasing tool functionality duration, improves the efﬁ-

ciency of the machining process.

(4) Compared to conventional machining, ultrasonic-

assisted machining enhances the machined surface char-

acteristics. In conventional machining of titanium

alloys, severe surface damage (pits and scratches) was

observed on the machined surface due to excessive tool

wear. Ultrasonic-assisted machining exhibits promising

potential in mitigating surface defects and roughness.

Vibration-assisted machining of titanium alloys pro-

duced textured surfaces; the nature and the size of the

texture depend on the separation characteristics in dif-

ferent vibration-assisted machining methods and on

the machining and vibration parameters. The

vibration-assisted machining reduced the surface rough-

ness to the micro-nano level. The LUVAM reduced the

machined titanium alloy surface roughness by 72%

compared to CM. However, under the same cutting

parameters, the 1D, 2D, and 3D vibration-assisted

machining generates surfaces with different roughness

levels due to different tool trajectories and vibration

characteristics in each method. The surface texture and

surface roughness depend on the parameters of the

machining process as well as on the characteristics of

the vibration-assisted machining method.

(5) The severe mechanical impact of ultrasonic-assisted

machining on titanium alloys, which causes high plastic

deformation and changes the grain structure, leads to

high surface hardness. The hammering effect of the tool

signiﬁcantly increases the plastic deformation layer

thickness. The increase in cutting speed during

vibration-assisted machining of titanium alloys increases

the hardness of the machined surface due to excessive

friction between the tool and the workpiece. The com-

plex interaction between the workpiece and cutting tool

induces compressive residual stresses in the machined

surface. The vibration-assisted machining increases the

compressive stress by 50% in the machined titanium

alloy surface. The nature of residual stress depends on

the cutting parameters and changes from compressive

to tensile with an increase in cutting speed. The induced

compressive stress in the machined part increases fatigue

resistance and mitigates the fracture risk.

(6) Tribological properties of the machined surface during

vibration-assisted machining sufﬁciently improved by

the presence of a texture, high hardness, and induced

compressive stress in the machined surface. The

vibration-assisted machining of titanium alloys was

found to reduce the COF by 60% and machined surface

wear volume by 67%. The discernible reduction in COF

and the signiﬁcant enhancement in wear resistance serve

to underscore the inherent beneﬁts of employing

vibration-assisted machining techniques in enhancing

the overall effectiveness of titanium alloy components.

(7) The cutting speed, feed rate, depth of cut, vibration

amplitude, and frequency were found to have a signiﬁ-

cant impact on ultrasonic-assisted machining. By appro-

priately adjusting these process parameters, the desired

outcome can be achieved, as each parameter has its

unique effect on the output.

(8) Vibration-assisted machining of titanium alloys offers

several sustainable advantages, such as an 18% reduc-

tion in power consumption and a 300% increase in tool

life compared to traditional machining methods. In the

future, vibration-assisted machining has the potential

to signiﬁcantly contribute to sustainable manufacturing

in the aerospace industry by utilizing more efﬁcient

and cost-effective vibration systems.

7. Future directions

The future prospects (Fig. 28) for ultrasonic vibration-assisted

machining of titanium alloys are as follows:

(1) Vibration system: In recent few years, the development

in technology has transformed the vibration system

characteristics from 1D vibration mode to 3D vibration

mode. However, the nonlinearity of the piezoelectric

transducer and variation in external load makes the pre-

cise control of vibration amplitude very difﬁcult.

Besides, the material used in the manufacturing of vibra-

tion systems is frequently unsuitable for the working

environment and leads to localized heating at the inter-

face between the cutting tool and the collet. The

increased heat in the localized surface can result in

higher energy absorption, thereby decreasing the ampli-

tude and frequency of vibration. The research efforts in

the vibration system will be focused on integrating arti-

ﬁcial intelligence and advanced materials into the ultra-

sonic tool handle to address the challenges of precise

control of vibration amplitude and tool handle heating.

(2) Advanced vibration-assisted machining technology:

Advanced vibration machining techniques such as 3D

vibration-assisted machining have signiﬁcantly

enhanced the machining efﬁciency. But advanced vibra-

tion machining methods have not been universally

applied to machine all types of titanium alloys. This lack

of utilization of advanced vibration machining poten-

tials highlights the area for future investigation. Further-

more, the theoretical analysis of cutting characteristics

in 3D vibration-assisted machining is relatively imma-

ture. In the future, dedicated research efforts will be

required to investigate the material removal mechanism

by considering different aspects such as tool geometry,

the effect of machining and vibration parameters, and

tool trajectory in 3D vibration-assisted machining. It

will help to predict the cutting forces and surface gener-

ation mechanism, enhance the cutting efﬁciency, and

optimize the machining process.

(3) Surface integrity and tool life: To enhance machining

precision and achieve surfaces with superior texture

and low roughness, it is imperative to prioritize research

efforts on the development of a special tool suitable for

vibration-assisted machining to prevent surface damage.

Recently, most of the research was focused on vibration

devices and machining characteristics, but less attention

was given to cutting tools. The high cutting load during

titanium alloy machining and high-frequency ultrasonic

vibration applications to cutting tools demand superior

tool performance. Therefore, developing tools suitable

34 A. KHAN et al.

for ultrasonic-assisted machining highlights an impor-

tant direction for future exploration. Additionally, there

is an urgent need to establish a multifunctional device

capable of producing surfaces with exceptional texture

and minimal roughness. Furthermore, optimizing

machining and vibration parameters will signiﬁcantly

contribute to enhancing surface quality while prolonging

tool life.

(4) Environmental and sustainability aspects: There is a

scarcity of studies reporting on the sustainability aspect

during vibration-assisted machining of titanium alloys.

Additionally, it has been observed that limited research

exists regarding power consumption in vibration-

assisted machining of titanium alloys. Currently, to

machine titanium alloy components industries are utiliz-

ing vibration-assisted machining without considering

sustainability aspects, ignoring factors such as environ-

mental impact and cost implications. Ignoring sustain-

ability aspects in vibration-assisted machining of

titanium alloys can lead to environmental degradation,

social implications and economic deﬁciencies. Future

research should extend beyond power consumption to

encompass the evaluation of environmental impact and

cost in vibration-assisted machining of titanium alloys.

Investigating costs, environmental impact, and explor-

ing new materials for tools will contribute to enhance

machining efﬁciency and sustainability.

(5) Over the past few years, the vibration system has under-

gone numerous modiﬁcations that have signiﬁcantly

enhanced the machining performance. Consequently, it

is imperative to optimize process parameters in order

to further enhance the performance of vibration-

assisted machining for titanium alloys while considering

these advancements.

Fig. 28 Status and future prospects for ultrasonic vibration-assisted machining for titanium alloys.

Ultrasonic vibration-assisted cutting of titanium alloys 35

CRediT authorship contribution statement

Ahmar KHAN: Writing – original draft. Xin WANG: Concep-

tualization. Biao ZHAO: Writing – review & editing, Funding

acquisition. Wenfeng DING: Supervision, Funding acquisition.

Muhammad JAMIL: Investigation. Aqib Mashood KHAN:

Investigation. Syed Hammad ALI: Software. Sadam HUS-

SAIN: Software. Jiong ZHANG: Writing – review & editing.

Raj DAS: Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing

ﬁnancial interests or personal relationships that could have

appeared to inﬂuence the work reported in this paper.

Acknowledgements

This work was ﬁnancially supported by the National Natural

Science Foundation of China (Nos. 92160301, 92060203,

52175415 and 52205475), the Science Center for Gas Turbine

Project (No. P2023-B-IV-003-001), the Natural Science Foun-

dation of Jiangsu Province (No. BK20210295), and the Hua-

qiao University Engineering Research Center of Brittle

Materials Machining (MOE, 2023IME-001).

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Unraveling the influence of vibrations on material removal and surface quality in longitudinal ultrasonic vibration–assisted milling of Ti2AlNb intermetallic alloy

Article

Full-text available

Jan 2025
INT J ADV MANUF TECH

Ti2AlNb intermetallic alloy is a typical high-temperature resistant material with exceptional mechanical properties and is beneficial to enhance the performance of aero-engine components. However, machining of Ti2AlNb intermetallic alloy is extremely difficult, and ensuring the required surface integrity is an ongoing challenge, especially when aiming to preserve surface defects for high-precision applications. The benefits of ultrasonic-assisted machining in enhancing machinability are well documented. However, the precise impact of longitudinal ultrasonic vibration–assisted milling (LUVAM) on the material removal mechanism and surface quality in Ti2AlNb intermetallic alloy machining is yet uncertain, highlighting a crucial area for comprehensive research. Therefore, this work presents in-depth theoretical investigations into the material removal mechanism, surface generation mechanism, and tool-chip separation conditions associated with LUVAM. Then, conventional milling (CM) and LUVAM experiments on Ti2AlNb were performed, and the study encompasses the analysis of cutting forces, chip morphology, surface defects, and texture characteristics using a scanning electron microscope (SEM) and morphological assessment. The results reveal that LUVAM reduces the Fx and Fy cutting forces compared with CM, while the reduction in cutting forces progressively decreases with increasing cutting speed. The longitudinal vibration in LUVAM assists in chip breakage and the formation of thinner lamellae on chip-free surfaces as compared with CM. The utilization of LUVAM leads to the formation of ultrasonic vibration texture on the chip back surface and machined surface and suppresses the formation of grooves and material adhesion, which are prominent in CM. In addition, LUVAM is beneficial in reducing surface roughness and causes a maximum reduction of 21.43% and 20.6% in 3D surface roughness Sa and Sq, respectively, compared with the CM. Furthermore, these insights into material removal mechanism, chip formation, and surface quality in LUVAM of Ti2AlNb intermetallic alloy not only advance the understanding of this process but also lay the groundwork for further optimization in high-performance aerospace and engineering applications, where superior surface integrity is paramount.

Pulsed laser remelting non-resonant vibration assisted grinding Al-Si alloy

Article

Apr 2025
INT J MECH SCI

Resistive thermal fusion interface: A novel additive manufacturing process of titanium alloy

Article

Feb 2025
J MATER PROCESS TECH

Thermal and force simulation modelling of graphene oxide nanosheets as cutting fluid additives during Ti-6Al-4V drilling process

Article

Dec 2024
INT J THERM SCI

Titanium alloys (Ti-6Al-4V) contain mechanical properties and low thermal conductivity that can lead to heat and friction during machining process, which will seriously affect tool wear and surface quality. Currently, titanium alloys are rarely used in industry due to limitations in cooling methods. Two-dimensional materials, known for their excellent thermal properties and hydrophilicity, are suitable additives for improving the properties of base fluids. In this study, graphene oxide (GO) nanosheets, recognized for their exceptional thermal conductivity and lubrication properties, are proposed as promising cutting fluid additives. A force and thermal model for the Ti-6Al-4V drilling process is developed to simulate thermal conductivity with different coolants. Additionally, a related force model under various cutting fluid environments is established. The experimental methodology is designed to measure the drilling temperature and drilling force to investigate the impact on cutting temperature and cutting force at various speeds, feeds, and cooling methods (dry machining, conventional cutting fluid, and GO nanosheets as additives to the conventional coolant). This analysis aims to validate the thermal conductivity, drilling temperature, cutting force, and friction during the drilling process under different coolants, speeds, and feeds. The results indicate that GO nanosheets as additives in cutting fluids during the Ti-6Al-4V drilling process can significantly reduce drilling temperature and cutting force. This improvement is attributed to the enhanced thermal conductivity and lubrication mechanism provided by the GO nanosheets.

Knowledge-based intelligent ensemble monitoring method of grit wear in ultrasonic assisted grinding

Article

Dec 2024
ADV ENG INFORM

Grain Refinement-Induced Machined Surface Quality Promotion in Ultrasonic Vibration-Assisted Polycrystalline Diamond Cutting of Polycrystalline Cu

Article

Nov 2024

The fabrication of ultra-smooth surface of polycrystalline metals with high surface integrity by mechanical cutting is challenging due to the heterogeneous internal microstructures, which lead to anisotropic material removal within individual grain interiors. In the present work, we perform finite element simulations and experiments of ultrasonic vibration-assisted cutting of polycrystalline Cu using PCD tool, with an emphasis on the cutting-induced microstructure evolution and its impact on the machined surface formation. Specifically, a framework of incorporating the strain and stress obtained by finite element simulation into subsequent cellular automata simulation is established, which is capable of predicting microstructure evolution in terms of dislocation density change, grain deformation, grain refinement and grain growth. Furthermore, the predicted grain refinement in subsurface is experimentally validated by electron back-scattering diffraction characterization. The results demonstrate the effectiveness of applying ultrasonic vibration assistance in promoting cutting-induced grain refinement and accompanied integrity of machined surface using PCD tool, as compared to conventional cutting. Furthermore, the influence of vibration amplitude on grain refinement and accompanied surface roughness and cutting force is further evaluated. Finally, a surface roughness of 22 nm is realized in ultrasonic elliptical vibration-assisted PCD cutting of polycrystalline Cu with a large cutting depth of 5 µm and a cutting edge radius of 2 µm. Current findings provide a feasible way of fabrication ultra-smooth surface of polycrystalline metals in low cost and high efficiency by tailoring the microstructure evolution behavior.

Towards Sustainable Grinding of Difficult-to-Cut Alloys—A Holistic Review and Trends

Article

Full-text available

Mar 2024

Grinding, a critical precision machining process for difficult-to-cut alloys, has undergone continual technological advancements to improve machining efficiency. However, the sustainability of this process is gaining heightened attention due to significant challenges associated with the substantial specific grinding energy and the extensive heat generated when working with difficult-to-cut alloys, renowned for their exceptional physical and mechanical properties. In response to these challenges, the widespread application of massive coolant in manufacturing industries to dissipate grinding heat has led to complex post-cleaning and disposal processes. This, in turn, has resulted in issues such as large energy consumption, a considerable carbon footprint, and concerns related to worker health and safety, which have become the main factors that restrict the development of grinding technology. This paper provides a holistic review of sustainability in grinding difficult-to-cut alloys, encompassing current trends and future directions. The examination extends to developing grinding technologies explicitly tailored for these alloys, comprehensively evaluating their sustainability performance. Additionally, the exploration delves into innovative sustainable technologies, such as heat pipe/oscillating heat pipe grinding wheels, minimum quantity lubrication, cryogenic cooling, and others. These groundbreaking technologies aim to reduce dependence on hazardous coolants, minimizing energy and resource consumption and carbon emissions associated with coolant-related or subsequent disposal processes. The essence of these technologies lies in their potential to revolutionize traditional grinding practices, presenting environmentally friendly alternatives. Finally, future development trends and research directions are put forward to pursue the current limitation of sustainable grinding for difficult-to-cut alloys. This paper can guide future research and development efforts toward more environmentally friendly grinding operations by understanding the current state of sustainable grinding and identifying emerging trends.

Nontraditional energy-assisted mechanical machining of difficult-to-cut materials and components in aerospace community: a comparative analysis

Article

Full-text available

Jan 2024

Difficult-to-cut materials such as titanium alloys, high-temperature alloys, metal/ceramic/polymer-matrix composites, hard and brittle materials, as well as geometrically complex components such as thin-walled structures, micro channels and complex surfaces, are widely used in aerospace community. Mechanical machining is the main material removal process and responsible for the vast majority of material removal for aerospace components. Nevertheless, it encounters many problems in terms of severe and rapid tool wear, low machining efficiency, and deteriorated surface integrity. Nontraditional energy-assisted mechanical machining is a hybrid process in which nontraditional energies, e.g., vibration, laser, electric, etc., are applied to improve the machinability of local material and decrease burden of mechanical machining. It provides a feasible and promising way for improving machinability and surface quality, reducing process forces, and prolonging tool life, etc. However, systematic reviews of this technology are lacking with respect to the current research status and development direction. This paper reviews recent progress in nontraditional energy-assisted mechanical machining of difficult-to-cut materials and components in aerospace community. It focuses on the processing principles, material responses under nontraditional energy, resultant forces and temperatures, material removal mechanisms and applications of these processes including vibration-, laser-, electric-, magnetic-, chemical-, cryogenic cooling-, and hybrid nontraditional energies-assisted mechanical machining. Eventually, a comprehensive summary of the principles, advantages and limitations for each hybrid process is provided, and future perspectives on forward design, device development and sustainability of nontraditional energy-assisted mechanical machining processes are discussed.

Multi Objective Parametric Optimization of Ultrasonic Vibration Assisted Turning on TI6AL4V Alloy

Article

Full-text available

Sep 2023

The industrial and engineering applications of Titanium alloys has increased in the recent times particularly in automobile and aerospace industries. Ultrasonic machining of titanium alloys is one of the developments in the recent times to counter the poor machinability characteristics of Ti alloys. In this work, ultrasonic vibration assisted turning is adopted in machining Ti6AL4V with cutting speed, feed rate, depth of cut and amplitude as process parameters. Cutting force, cutting temperature and surface roughness are considered as performance evaluators. The role of each process parameter on each of the responses is evaluated and the optimum parametric combination for multi objective optimization is determined using Grey Relational Analysis. The results are interpreted with respect to tool work contact ratio. It was concluded from the experimental analysis that cutting force, cutting temperature and surface roughness depend on the TWCR which in turn depends on cutting speed and amplitude of vibration. Low TWCR revealed better performance whereas the effect of ultrasonic vibration is found to be reduced with increment in TWCR. In addition, feed rate and depth of cut are found to be significant in effecting the multi response characteristic (GRG).

Optimization Milling Force and Surface Roughness of Ti-6Al-4V Based on Ultrasonic-Assisted Milling (UAM): An Experimental Study

Article

Full-text available

Aug 2023

This study aimed to develop a longitudinal ultrasonic-assisted milling system to investigate the machinability of titanium (Ti) Alloy Ti-6Al-4V (TC4). Aiming at reduced milling force and enhanced surface quality, ultrasonic-assisted milling was investigated taking into account the following processing parameters: spindle speed (cutting rate) n, feed per tooth fz, milling depth ap, and ultrasonic amplitude A. A comparison was made with conventional milling. The results of univariate tests demonstrated that the ultrasonic amplitude had the most significant impact on the milling force along the z-axis, resulting in a reduction of 15.48% compared with conventional milling. The range analysis results of multivariate tests demonstrated that ap and fz were the dominant factors influencing the cutting force. The minimum reduction in the milling force in ultrasonic-assisted milling along the x-, y-, and z-axes was 11.77%, 15.52%, and 17.66%, respectively, compared with that in conventional milling. The ultrasonic-assisted milling led to reduced surface roughness and enhanced surface quality; the maximum surface roughness in ultrasonic-assisted milling was 25.93%, 36.36% and 26.32% in terms of n, fz, and ap, respectively. In longitudinal ultrasonic-assisted milling, the periodic “separation-contact” was accompanied by microimpacts, resulting in even smaller intermittent periodic cutting forces. Hence, regular fish scale machining mesh was observed on the processed surface, and the workpiece surface exhibited high cleanness and smoothness. The reasonable configuration of ultrasonic-assisted milling parameters can effectively improve the milling force and surface quality of Ti alloys and accumulate reference data for the subsequent machining process research.

Micro/nano incremental material removal mechanisms in high-frequency ultrasonic vibration-assisted cutting of 316L stainless steel

Article

Full-text available

Aug 2023
INT J MACH TOOL MANU

Although the intermittent contact by the ultrasonic vibration-assisted cutting explained the machinability advantages, there exists a research gap in concentrating the effects of high-frequency ultrasonic vibration-assisted cutting (HFUVAC). This work clarified the differences of the micro/nano incremental material removal mechanisms between conventional cutting (CC) and high-frequency ultrasonic vibration-assisted cutting of 316L stainless steel. The machinability advantages and microstructure features were compared and analyzed through the ultra-precision cutting experiments. Compared with the continuous contact mode of the conventional cutting, the incremental effect of the high-frequency ultrasonic vibration-assisted cutting achieved superior machinability, which included cutting force decreasing, tool wear reduction, surface defects suppression, and chips undergoing from discontinuous quasi-shear state to continuous multiple-shear state. As the nominal cutting speed increased in the high-frequency ultrasonic vibration-assisted cutting, the surface defects and surface roughness showed an increasing trend, which was indispensable to control the normal cutting speeds below 5 m/min, or the cutting stroke in each vibration cycle less than 800 nm to obtain the defect-free surface. The grain refinement and severe elongation deformation were observed at the chip bottom and machined surface of the conventional cutting due to strong mechanical friction loads. While the microstructure features of chips and the machined surface in the local deformation layer were the results of friction reduction, dynamic recrystallization, and twinning/stacking formation induced by the incremental effects of the high-frequency ultrasonic vibration-assisted cutting. The results help to improve surface quality and optimize the ratio of cutting speed to vibration frequency to enhance the efficiency.

Optimizing Processing Parameters and Surface Quality of TC18 via Ultrasonic-Assisted Milling (UAM): An Experimental Study

Article

Full-text available

May 2023

This study conducted longitudinal ultrasonic-assisted milling (UAM) tests and optimized a combination of milling technological parameters to achieve high-quality machining of TC18 titanium alloy. The motion paths of the cutter under the coupled superposition states of longitudinal ultrasonic vibration and end milling were analyzed. Based on the orthogonal test, the cutting forces, cutting temperatures, residual stresses, and surface topographical patterns of TC18 specimens under different UAM conditions (cutting speeds, feeds per tooth, cutting depths, and ultrasonic vibration amplitudes) were examined. The differences between ordinary milling and UAM in terms of machining performance were compared. Using UAM, numerous characteristics (including variable cutting thickness in the cutting area, variable cutting front angles of the tool, and the lifting of the cuttings by the tool) were optimized, reducing the average cutting force in all directions, lowering the cutting temperature, increasing the surface residual compressive stress, and significantly improving the surface morphology. Finally, fish scale bionic microtextures with clear, uniform, and regular patterns were formed on the machined surface. High-frequency vibration can improve material removal convenience, thus reducing surface roughness. The introduction of longitudinal ultrasonic vibration to the end milling process can overcome the limitations of traditional processing. The optimal combination of UAM parameters for titanium alloy machining was determined through the end milling orthogonal test with compound ultrasonic vibration, which significantly improved the surface quality of TC18 workpieces. This study provides insightful reference data for subsequent machining process optimization.

Ultrasonic Assisted Machining Overview: Accessing Feasibility and Overcoming Challenges for Milling Applications

Article

Full-text available

May 2023

Machinability, along with its associated facets, is a critical parameter that ultimately determines the cost of machining. Its optimization, however, is inherently limited by the current technology. To surmount such limitations, novel alternative machining technologies, such as Ultrasonic Assisted Machining (UAM), have emerged. The present study introduces UAM, the technology’s underlying principles, and general considerations for vibration application (harmonic waves, eigenfrequencies, resonance). The influence of ultrasonic application on the key parameters of conventional machining processes is studied and relevant research data are presented to support UAM benefits. Following, a comprehensive kinematic examination of vibration application to the milling process is conducted, accounting for various possible vibration modes. A detailed analysis of the requisite system components and their technical specifications is presented, followed by identifying common issues within such systems. Solutions for the identified limitations are proposed, acting as design guidelines for future technological advancements. Finally, based on the conducted research, conclusions are drawn and future directions for UAM are suggested.

A critical review of piezoelectric ultrasonic transducers for ultrasonic-assisted precision machining

Article

Aug 2023
ULTRASONICS

Piezoelectric ultrasonic-assisted precision machining (PUAPM) technology is considered to be an efficient and environmentally friendly machining strategy by virtue of cutting force reduction, ductile cutting promotion, tool wear and machining noise reduction. Piezoelectric ultrasonic transducer (PUT) provides ultrasonic energy for PUAPM system, which is the core component to ensure the normal operation of the system. PUTs for PUAPM devices have emerged endlessly in recent decades and have been successfully applied in many fields, such as MEMS, biomedicine, optoelectronics, aerospace, etc. However, there is no comprehensive classification and analysis of the basic configurations, excitation principles, typical structures, performance analyses and control strategies for PUT. This work gives a critical review of research on PUT in recent years, especially the structural optimization, application expansion and ultrasonic energy stabilization in PUAPM. The influence mechanism of excitation mode, modal type, modal combination, horn structure and ceramic arrangement on the optimization of PUT structure is summarized. The improvement effect and mechanism of PUT vibration dimension, amplitude, frequency and structural characteristics on surface roughness, surface texture and cutting force are discussed. In addition, the causes of PUT amplitude fluctuation, and the influence of sensing and control methods on PUT amplitude regulation and system integration are analyzed. This review will help in understanding the current development and diversified applications of PUT and will promote the application of ultrasonic technology in more fields.

Study on force-thermal characteristics and cutting performance of titanium alloy milled by ultrasonic vibration and minimum quantity lubrication

Article

Jun 2023
J Manuf Process

Analysis and modeling of cutting force considering the tool runout effect in longitudinal-torsional ultrasonic vibration-assisted 5 axis ball end milling

Article

May 2023
J MATER PROCESS TECH

Ultrasonic vibration-assisted cutting of titanium alloys: A state-of-the-art review

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