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Post Processing Methods used to Improve Surface Finish of Products which are Manufactured by Additive Manufacturing Technologies: A Review

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Abstract

The Additive Manufacturing (AM) processes open the possibility to go directly from Computer-Aided Design (CAD) to a physical prototype. These prototypes are used as test models before it is finalized as well as sometimes as a final product. Additive Manufacturing has many advantages over the traditional process used to develop a product such as allowing early customer involvement in product development, complex shape generation and also save time as well as money. Additive manufacturing also possess some special challenges that are usually worth overcoming such as Poor Surface quality, Physical Properties and use of specific raw material for manufacturing. To improve the surface quality several attempts had been made by controlling various process parameters of Additive manufacturing and also applying different post processing techniques on components manufactured by Additive manufacturing. The main objective of this work is to document an extensive literature review in the general area of post processing techniques which are used in Additive manufacturing.
ARTICLE OF PROFESSIONAL INTEREST
Post Processing Methods used to Improve Surface Finish
of Products which are Manufactured by Additive Manufacturing
Technologies: A Review
N. N. Kumbhar
1
A. V. Mulay
1
Received: 31 August 2015 / Accepted: 16 August 2016
The Institution of Engineers (India) 2016
Abstract The Additive Manufacturing (AM) processes
open the possibility to go directly from Computer-Aided
Design (CAD) to a physical prototype. These prototypes
are used as test models before it is finalized as well as
sometimes as a final product. Additive Manufacturing has
many advantages over the traditional process used to
develop a product such as allowing early customer
involvement in product development, complex shape gen-
eration and also save time as well as money. Additive
manufacturing also possess some special challenges that
are usually worth overcoming such as Poor Surface quality,
Physical Properties and use of specific raw material for
manufacturing. To improve the surface quality several
attempts had been made by controlling various process
parameters of Additive manufacturing and also applying
different post processing techniques on components man-
ufactured by Additive manufacturing. The main objective
of this work is to document an extensive literature review
in the general area of post processing techniques which are
used in Additive manufacturing.
Keywords Additive manufacturing
Post processing technique Surface finish
Laser surface finishing
Introduction
Additive manufacturing was born as a rapid prototyping
technology with the process of joining materials in suc-
cessive layer by layer to make objects. It allows designers
to produce accurate physical prototypes directly from 3D-
CAD model in few hours.
The processes are best suited to parts which are gener-
ally complex in design with freeform curves and features,
possessing only a limited percentage of plane surfaces.
However, a major problem to commercial use is the poor
surface finish caused by ‘Stair Casing Effect’, which is
shown in Fig. 1d[1].
Figure 1gives idea about manufacturing steps in AM.
Steps are listed below,
1. Generation of 3D CAD model by any commercial
CAD software (Fig. 1a).
2. Slicing of a 3D CAD model in 2D layers (Fig. 1b).
3. Generation of physical output by stacking those 2D
layers one by one (Fig. 1c).
Due to stacking of 2D layers the generated model having
with poor surface finish because of the ‘Stair Casing
Effect’ shown in Fig. 1d.
To minimize the Stair casing effect several researchers
worked on different process parameters related with
Additive manufacturing such as part orientation, layer
thickness and orientation of material deposition as well as
to get the best results many researchers worked on different
post-processing techniques.
There are different types of post processing techniques,
which are used to improve surface quality depending upon
the application and the model material.
&N. N. Kumbhar
kumbharnn88@gmail.com
1
Department of Production Engineering, College of
Engineering, Pune 411005, India
123
J. Inst. Eng. India Ser. C
DOI 10.1007/s40032-016-0340-z
Additive Manufacturing Methods
There are many different Additive manufacturing pro-
cesses, all with their specific benefits, drawbacks and
application areas. The available Additive manufacturing
processes are classified on the bases of various character-
istics such as type of raw material used, form of raw
material and principle used [1].
The classification based on raw materials carried out is
given in Table 1and 2.
Classification Based on Principle Used
In 2010, the American Society for Testing and Materials
(ASTM) group ‘‘ASTM F42—Additive Manufacturing’
formulated a set of standards that classify the range of
Additive Manufacturing processes into seven categories
(Standard Terminology for Additive Manufacturing Tech-
nologies, 2012) [2]
1. VAT Photopolymerisation
2. Material Jetting
3. Binder Jetting
4. Material Extrusion
5. Powder Bed Fusion
6. Sheet Lamination
7. Directed Energy Deposition.
Table 3shows various principles used for different
types of Additive manufacturing processes.
These methods are having some capabilities such as,
Unbounded geometric freedom,
To control the local geometric (micro-structure)
Avoid the use of tooling
Lowered inventory requirements
Waste-less fabrication
Unattended operation (allowed fully automated
operation)
Customer-driven design.
As there are many advantages of AM, however there are
some disadvantages also such as,
Demand for better materials.
Existing CAD systems.
Data management (Size of STL file)
Low-volume production
Financial overheads
Surface Quality of Products
Compared with other conventional AM method having
low surface quality because of layer by layer manufactur-
ing and stair casing effect on surface. As a result, the
surface finish of the parts is not satisfactory and hence
surface roughness is a key issue in AM. The different AM
processes have yielded varying surface roughness results
with respect to their layer thickness. The researchers have
[3] investigated surface roughness values of parts which are
generated by different AM processes. Table 4below shows
roughness values for different AM processes. As compared
to other processes FDM gives a poor surface finish band
(9–40 lm).
To obtain the required surface finish several attempts
have been made by optimizing process parameters such as
part orientation, built orientation, layer thickness and using
post processing operation such as machining operation
(turning, milling, CNC machining), abrasive machining,
chemical machining, laser surface finishing operations and
abrasive flow machining. As there is much more work is
carried on optimizing the process parameters such as
Fig. 1 An illustration of the
layer-based additive
manufacturing processes and
related stair-stepping effect.
aCAD Model, bSlicing
cActual output by AM dStair
casing effect
Table 1 Classification based on raw material used
Raw material used Additive manufacturing process
Polymer Stereolithography (SLA)
Fused Deposition Modeling (FDM)
Three-dimensional Printing (3DP)
Selective Laser Sintering (SLS)
Laminated-Object Manufacturing (LOM)
Metal FDM
3DP
SLS
Direct Metal Laser Sintering (DMLS)
Ceramic 3DP
SLS
J. Inst. Eng. India Ser. C
123
controlling the part orientation at initial stage by different
combinations with respect to STL file to get required out-
put. Controlling the built orientation of parts in machine
and controlling the layer thickness.
As discussed earlier, the ‘Stair Casing Effect’, which is
non-removable by parameter optimization. It has to be
minimized by post-processing operation.
Post Processing Techniques
Additive manufacturing technique helps to develop a pro-
duct from the basic design of the component and to
optimize the iterative product development time. Although
AM provides many advantages over other manufacturing
technologies, it still has some major drawbacks such as the
staircase effect, surface quality and dimensional accuracy.
Most of the researchers worked on various post processing
techniques to overcome the drawbacks.
Some of the researchers have [4] investigated two
automated finishing techniques which are, Vibratory Bowl
Abrasion Finishing and Ultrasonic Abrasion Finishing. By
using these techniques, the experiments are carried out on
components made from Ciba-Geigy XB5081-1 (durable
resin) and XB 5143 (general purpose resin) resins with the
aim of producing an acceptable surface roughness. After
experimentation results from Scanning Electron Micro-
scopy (SEM) and surface topography analyses suggested
that both techniques are capable of improving the model
surfaces. Compared with Ultrasonic abrasion finishing,
Vibratory Bowl abrasion finishing process has achieved a
good surface finish in a reasonable amount of time with
improvements of around 74 % (Initial R
a
value is
5.71 lm—after processing 1.68 lm).
The investigators have [5] worked on vibratory grinding,
which is used to refine SLS parts from the surfaces. In this
method, the suitable ceramic bodies were investigated and
process times were determined. By using optical variance
analysis researcher were demonstrated that parts without
complex structures are readily amenable to vibratory
grinding (removal \0.1 mm) and the R
a
value of surface
is changed from 11 to 2 lm.
Some of the researchers have [6] conducted the exper-
iments on parts built by FDM process using HCM (Hot
Cutter Machining) processes is successfully attempt for
enhancing surface finish. This machining process provides
a layer by layer machining and it is observed that surface
roughness is in the order of 0.3 lm with 87 % confidence
level. But this method is restricted up to flat surfaces.
The investigators have [7,8] studied the influence of a
chemical post-processing treatment on FDM models which
are manufactured from Acrylonitrile Butadiene Styrene
(ABS) plastic. The experiment is carried out in chemical
bath with dimethylketone (acetone), ester and chloride
solvents. Dimethylketone was chosen due to its low cost,
Table 2 Classification based on form of raw material used
Supply phase Additive manufacturing process Materials
Liquid SLA Photopolymers (acrylates, epoxies, colorable resins, filled resins)
FDM Polymers (ABS, polyacrylate, etc.), wax, metals and ceramics with binder
Powder 3DP
DMLS
Ceramic, polymer and metal powders with binder
Solid SLS Polymers, metals with binder, metals, ceramics and sand with binder
LOM Paper, polymers
Table 3 Classification based on principle used
Principle used Additive manufacturing process
VAT photopolymerisation
Material jetting Drop on Demand (DOD)
Binder jetting
Material extrusion FDM
Powder bed fusion DMLS
Electron Beam Melting (EBM)
Selective Heat Sintering (SHS)
Selective Laser Melting (SLM)
SLS
3DP
Sheet lamination LOM
Directed energy deposition
Table 4 Surface roughness of AM technique [3]
Sl.
no.
Name of
process
Minimum layer
thickness, mm
Surface roughness
(Ra), lm
1 SLA 0.10 2–40
2 SLS 0.125 5–35
3 FDM 0.254 9–40
4 3D printing
(3DP)
0.175 12–27
5 LOM 0.114 6–27
6 Poly jetting
process
0.10 3–30
J. Inst. Eng. India Ser. C
123
very low toxicity and very high diffusion rate. At the time
of experimentation model is immersed in a volume of 90 %
dimethylketone and 10 % water for 300 Sec. The model
has been analysed and yields a significant improvement of
the R
a
value. The chemical post treatment does not require
human intervention and has led to a significant improve-
ment in surface finish at the expense of a negligible change
in the prototype size. After post-processing R
a
value varies
in between 2–4 lm.
The researchers have [9] discussed various methods
which are used to improve the surface roughness of the
parts which are generated by DMLS. DMLS gives a raw
finish on model surface compare to a medium turned sur-
face with a surface roughness of approximately R
a
as
8.75 lm. This surface roughness can be improved all the
way up to R
a
0.025 lm, qualifying as a super mirror finish.
There are several processes available that can be used to
achieve the desired surface roughness or finish of DMLS
built models which are Abrasive Blast (Grit and Ceramic),
Shot Peen, Polishing, Electrochemical Polishing, Optical
Polish (Hand Finishing), CNC Finishing/Machining,
Abrasive Flow Machining (Extrude Hone) Polishing,
Electroplating, Micro Machining Process (MMP).
The investigators have [10] worked on a simple post
processing method for improving surface quality of parts
generated from AM. In this case study, aluminium filled
epoxy resin is used as a filler to improve the surface quality
of model fabricated by fused FDM. The average surface
roughness of wax pattern can be drastically reduced from
17.10 to 2.76 lm. Surface roughness improvement up to
83.85 % can be achieved.
Some researchers have [11] carried out the experiments
on SLS built parts to improve surface finish by using CO
2
and Nd:YAG lasers. On the basis of experiments,
researchers observed that partial-melting of surface with an
increase in R
a
values and decrease in over-melting. The
results obtained indicate that a reduction in R
a
roughness
has been achieved in 420 stainless steel—bronze infiltrated
SLS parts by means of CO
2
and Nd: YAG laser polishing.
The best results are: (1) R
a
reduction from 2.1 to 1.6 lmat
220 W and 2.2 mm/s (2) R
a
reduction from 2.38 to
1.65 lm at 320 W and 1.19 mm/s and (3) R
a
reduction
from 2.38 to 0.8 lm at 420 W and 4.5 mm/s. By means of
Nd: YAG laser polishing the best result is a R
a
reduction
from 9.0 to 2.40 lm at 220 W and 1.7 mm/s.
The researchers have [12] performed experiments on
Laser-polishing tests for lines, planar surfaces and inclined
planes. The experimental tests were carried out on the parts
which are generated from the SLS process with an initial
roughness of 7.5–7.8 lm Ra. After conducting Experi-
mental results present final surface roughness below
1.49 lm Ra, which represent an 80.1 % reduction of the
mean roughness.
It has been found that the surface finish can also be
improved by using post processing techniques. Various
post processing techniques are listed below in Table 5on
the bases of conventional and non-conventional
approaches.
Also the same methods are categorized on the bases of
raw material used in Additive manufacturing in Table 6.
Looking at Table 6, laser micromachining is common
technique used as post processing operation on polymer,
Metal and Ceramic. Therefore, this work is focused on
laser surface finishing.
Laser Surface Finishing
The quality attributes of LASER combined with a high
degree of flexibility, contact-less machining and the
Table 5 Post processing methods with respect to nature
Conventional Non-conventional
a. Vibratory bowl abrasion/abrasive blast
(grit and ceramic)/shot peen vibratory
grinding
b. HCM (hot cutter machining)
c. Optical polish (Hand finishing)
d. CNC Finishing/machining
e. Micro machining process (MMP)
f. Filling the gaps by epoxy resin/part
painting
a. Ultrasonic abrasion
b. Chemical post-
processing treatment
c. Electrochemical
polishing,
d. Electroplating
e. Laser micro
machining
Table 6 Post processing methods with respect to raw material
Raw material used Post processing method
Polymer Vibratory bowl abrasion
Hot Cutter Machining (HCM)
Optical polish (Hand Finishing)
Micro Machining Process (MMP)
Filling the gaps by epoxy resin/Part painting
Chemical post-processing treatment
Electroplating
Laser micro machining
Metal Vibratory bowl abrasion
HCM (Hot cutter machining)
Optical polish (hand finishing)
MMP
Chemical post-processing treatment
Electroplating
Laser micro machining
Ceramic Vibratory bowl abrasion
Optical polish (hand finishing)
MMP
Laser micro machining
J. Inst. Eng. India Ser. C
123
possibility of high automation as well as easy integration
allows us to use this tool in a wide field of macro
machining processes on many materials including silicon,
ceramics, metal and polymer.
The researchers have [13,14] utilised laser microma-
chining that includes a number of different processes which
are differentiated on the bases of feature geometry and the
manner in which material is removed from the surface. In
laser micromachining a beam is used to slice the substrate
material, leaving behind a kerf which extends completely
through to the opposite side of the substrate. As is com-
monly the case in laser cutting of sheet metal, the material
removed from the kerf is predominantly ejected out the
opposite side. Figure 2Shows laser cutting operation.
When a material removal is carried out from only one
side i.e. called ablation process and the removed material
must necessarily be ejected from the same side as which
the laser is incident. Figure 3Shows laser ablation process.
In both cases, the removed material is ejected primarily
through the kerf which has been cut by laser beam and
which trails along behind the laser beam as it is moved
along the tool path. The material removal process involves
both thermal and chemical processes, depending upon how
the laser radiation interacts with the substrate. At longer
wavelengths, the photon energy is insufficient to provide
anything more than a simple heating of the substrate. At
sufficiently high intensities, however, the heating can be
concentrated enough to first melt the substrate material
within a localized zone, and then vaporize it in those areas
where the laser intensity and subsequent heating is higher.
Then the substrate material is transition to the gas phase,
although the vaporized material is often subsequently
ionized by the laser radiation, leading to a plasma and
plume that can have the effect of occluding the incident
beam.
It is customary to identify three zones around the inci-
dent beam:
1. The heat-affected zone or HAZ
2. The melt zone
3. The vaporization zone.
Some materials can pass directly from the solid phase to
vapour phase by sublimation, and thus melt zone is absent.
Both melting followed by vaporization or direct sublima-
tion that is purely thermal ablation processes. At shorter
wavelengths, the photon energy may reach the level of the
chemical bond strength of the substrate. Laser radiation
may then break those chemical bonds through direct pho-
ton absorption, leading to volatilisation of the substrate into
simpler compounds.
The investigators have [15] worked on short laser which
are used for machining. In this process the photon energy is
lost to chemical bond scission, the heating effects of the
beam are greatly reduced, and this region is sometimes
referred to as ‘‘cold laser machining,’’ or photochemical
ablation. This greatly reduces the transient thermal stresses
that occur as part of thermal ablation, and thus result shows
less bowing, warping, and delamination of the substrate, as
well as fewer edge melting effects which degrade feature
accuracy. Since the peak temperature rise is greatly
reduced, conductive heat flow away from the irradiation
area is also reduced, and better dimensional control of the
micro machined structure is obtained. There has been a
general trend toward using shorter wavelength lasers for
micromachining over the past two decades of development.
Currently, UV lasers in the range of 350 to 250 nm which
are used in industrial market because of cold laser
machining.
Lasers for Post-processing (Laser Micromachining)
There are different types of lasers are available in market
for material processing. The researchers [1618] have
worked on lasers and discussed that by far the most com-
mon laser used for industrial processing is the carbon
dioxide (CO
2
) gas laser. This popularity comes from its
unique combination of high average power, high effi-
ciency, and rugged construction. CO
2
lasers are used
extensively for marking, engraving, drilling, cutting,
Fig. 2 Laser cutting operation
Fig. 3 Laser ablation process
J. Inst. Eng. India Ser. C
123
welding, annealing, and heat treating an enormous variety
of industrial materials. For micromachining applications,
the long wavelength translates into a fairly large spot
diameter of *50–150 lm with a corresponding kerf width.
The most common solid-state laser used in the industry
is the neodymium-doped yttrium aluminium-garnet, or
Nd:YAG [19,20]. For micromachining purposes there are
four types of Nd:YAG lasers are used which gives different
wavelength output which are 1064 nm, 532 nm (Green
output), 355 nm (near ultraviolet-UVA band) and 266 nm
(deep ultraviolet- UVC band).
Copper vapour lasers have also proven their use in high
accuracy micromachining [21,22]. Copper vapour lasers
also have excellent beam quality and can usually produce a
diffraction-limited spot on the substrate with only simple
external beam steering optics. The disadvantage of copper
vapor lasers is that they tend to have a shorter service life
and require more maintenance than Nd: YAG lasers
Excimer lasers have also found wide use in materials
processing applications [23]. Commonly used excimer
lasers are the XeF which emits at 351 nm, the KrF which
emits at 249 nm, the ArF which emits at 193 nm, and the
diatomic F2 which emits at 157 nm. Like other laser sys-
tems this types of lasers are used in materials processing as
per application.
The researchers [24] told us, at higher beam intensities
laser can be used for surface ablation of materials and due
to the short wavelength and short pulse width, laser typi-
cally produce clean, crisp features in metals, ceramics,
glasses, polymers, and composites making them adapt-
able for numerous micromachining applications.
Conclusion
In this work, the literature related to various surface finish
techniques has been reviewed. It has been found that there
are various methods to improve surface finish of parts
manufactured by Additive manufacturing. The surface
finish can be improved by selecting suitable method as per
the requirement of surface finish. The study of various
works indicates that systematic implementation of post
processing technique can improve the R
a
value of parts.
Most authors have put in efforts in designing the processes
for post processing operations. In doing so, many
assumptions such as the Abrasive size, feed rate in HCM,
concentration of chemical, flow rate of abrasives, Laser
power were assumed.
From this survey it is found that the surface finish can
also be improved by using some post processing tech-
niques. Out of post processing techniques, on-going
research focused on chemical treatment on polymer and
metal printed parts and Laser micro machining on polymer,
metal and ceramic.
Acknowledgment This paper is a revised and expanded version of
the article entitled, ‘‘Post processing methods used to improve surface
finish of products which are manufactured by Additive Manufacturing
(AM) technologies—A review’’ was presented in ‘‘International
Conference on Additive Manufacturing and 3D Printing’’ held at
Chennai, India during February 6–7, 2015.
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... However, substantive eforts have been made to address these challenges. Heat treatment strategies to alleviate process-related macroresidual stresses, as well as the attainment of equilibrium microstructures for Ti6Al4V and therefore, improving the mechanical properties of the alloy, are available in the open literature [10][11][12][13][14]. Various methods of improving the surface quality of AM parts have been studied, some of which have been shown to reduce the surface roughness to as low as R a � 0.025 μm [15] from typical values of R a ≈ 5 μm and R z ≈ 25 μm [16], which qualifes as a superior mirror fnish. Te use of optimal AM process parameters has been shown to reduce and mitigate the formation of pores in the produced parts. ...
... During heat treatment, α′ martensite transforms into a mixture of equilibrium α and β phases. Te α laths in the mixture have an average width that varies depending on the heat treatment temperature and cooling rate [11][12][13][14][15][16][17][18][19][20][21] applied. Te subtransus heat treatment does not lead to changes in the morphology of the prior-β grains. ...
... Te subtransus heat treatment does not lead to changes in the morphology of the prior-β grains. However super-transus heat treatment leads to decomposition and subsequent growth of columnar prior-β grains into equiaxed prior-β grains [15][16][17][18][19][20][21]. A combination of both subtransus and super-transus heat treatments and diferent cooling rates can be used to optimise the microstructure of the alloy. ...
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Heat treatment of direct metal laser sintering (DMLS) Ti6Al4V (ELI) generates different mechanical properties of the alloy depending on the heat treatment cycle adopted. This is due to the different aspects of the microstructure, such as phase fraction, grain size, texture, and dislocation density, which vary with heat treatment. Other external factors, such as the prevailing level of strain, strain rate, and temperature, also affect the mechanical properties of the material. This paper presents the development of a theoretical model that couples the effects of strain rate, temperature, strain, grain size, and initial dislocation density to describe the flow properties of DMLS Ti6Al4V (ELI). According to the model, higher initial dislocation density results in higher yield stress, low strain hardening, and earlier saturation of flow stress. The model shows that the parabolic shape of the stress-strain curve of the alloy is dictated by the initial dislocation density, which is generally a factor of grain size.
... Therefore, for precision engineering applications, which require both tight dimensional and surface finish tolerances, LPBF parts are often machined or finished using post-processing [6,7]. A particular challenge is the finishing of complex and inaccessible geometries, such as internal noncylindrical cooling channels and undercut surfaces. ...
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In this paper, we present the first known experimental results in using hybrid additive-subtractive laser powder bed fusion (h-LPBF) to make a type of passive radio frequency component called a quarter wave resonator (QWR). The h-LPBF process uses in-situ, interlayer vertical milling to machine certain inaccessible, critical internal features of the QWR device during printing. Using h-LPBF, the as-built surface roughness of functionally important features improved to Ra ~ 2 µm compared to Ra ~ 8 to 20 µm for conventional (additive only) LPBF-processed QWRs. Additionally, the dimensions of certain critical features were closer to their intended design. These metrological improvements resulting from h-LPBF reduced RF losses by a factor of almost 2. Consequently, the RF performance (Q-factor) of h-LPBF-processed QWR components were 1.5 to 2 times superior compared to their conventional LPBF counterparts, and the performance advantage was sustained on stress relief and chemical etching. These results were verified with theoretical electromagnetic simulations.
... Nowadays it is used for mass production in different field, for example in the medical industry (Regis et al., 2015), thanks to the high variety of materials and the post processes applicable. Such post processes can increase the mechanical properties of parts at an higher cost (Liu and Shin, 2019) and are associated with specific operating conditions (Kumbhar and Mulay, 2018). At the same time several obstacles limit the spread of AM for spare parts management. ...
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Additive Manufacturing (AM) is a promising technology for producing spare parts, due to the wide variety of forms and materials that can be used and their enhanced mechanical properties. Given these features and the low lead times compared to classical manufacturing (CM), AM is now being investigated for the management of spare parts. This literature stream is relatively new, with many works based on different hypotheses (e.g., the reliability of AM parts) and with different conclusions. This critical literature review provides practitioners with information on the models available, their findings, and their limitations. Further research directions are also identified.
... On the other hand, parts produced by AM have process-inherent defects, and one of the most important is the surface roughness. Because of layered manufacturing and the stair-step effect, the surface finish of the parts produced by AM is poorer compared to the traditional manufacturing methods [1,2]. This is especially true for the inclined and curved surfaces. ...
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The traditional manufacturing industry has been revolutionized with the introduction of additive manufacturing which is based on layer-by-layer manufacturing. Due to these tool-free techniques, complex shape manufacturing becomes much more convenient in comparison to traditional machining. However, additive manufacturing comes with its inherent process characteristics of high surface roughness, which in turn effect fatigue strength as well as residual stresses. Therefore, in this paper, common post-processing techniques for additive manufactured (AM) parts were examined. The main objective was to analyze the finishing processes in terms of their ability to finish complicated surfaces and their performance were expressed as average surface roughness (Sa and Ra). The techniques were divided according to the materials they applied to and the material removal mechanism. It was found that chemical finishing significantly reduces surface roughness and can be used to finish parts with complicated geometry. Laser finishing, on the other hand, cannot be used to finish intricate internal surfaces. Among the mechanical abrasion methods, abrasive flow finishing shows optimum results in terms of its ability to finish complicated freeform cavities with improved accuracy for both polymer and metal parts. However, it was found that, in general, most mechanical abrasion processes lack the ability to finish complex parts. Moreover, although most of post-processing methods are conducted using single finishing processes, AM parts can be finished with hybrid successive processes to reap the benefits of different post-processing techniques and overcome the limitation of individual process.
... So numerous pre-processing techniques used the controlling different AM process parameters have been developed to improve the surface quality of AM parts. Several post-processing techniques are also developed to improve the surface0quality of an AM part [43][44][45]. The most frequent phenomenon that occurs during the AM process is the stair-stepping/stair-casing effect, which results in surface roughness in 3D printed products, as shown in Figs. 5 and 6 below [46][47][48][49][50][51]. ...
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... And after the printing process, the product is removed from the printing bed platform, and the supporting materials are removed and then started the post processing. According to Kumbhar et al., [10], post-processing procedures are typically utilized to increase surface smoothness. Ahmad et al., [11][12] has discovered the optimum parameters of FDM using ABS material and used PolyJet 3D printer to print 30 samples of molar teeth. ...
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In the development and manufacturing industries, fused deposition modeling (FDM) receives the greatest attention. It is the most important additive manufacturing (AM) technique, which refers to the process of depositing multiple layers of material in a computer-controlled environment to form a three-dimensional product. Research is presently focusing on the development of 3D printed bio-composite polymers with improved performance. Many studies on the development of new composite materials using natural fiber as a feedstock filament for FDM have recently been published. As a result, conducting a rheology characteristics analysis of new composite materials made from natural resources is required. Its major purpose is to describe the flow behavior of the fiber composite material and determine the optimal melting temperature for the extrusion process of producing wire filament. Thus, this paper focuses on rheological properties of fiber-reinforced thermoplastic composite for FDM.
... As-sintered parts normally possess a relatively high surface roughness, especially on vertical surfaces due to the effect of the distinct powder layers they are made of [23]. Postprocessing operations involving vibratory abrasion and chemical treatments [24] may be required to achieve a good surface finish in components with complex geometry and internal features. The flowchart of the binder jetting process is illustrated in Figure 4. ...
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The opportunity to process pure copper through additive manufacturing has been widely explored in recent years, both in academic research and for industrial uses. Compared to well-established fabrication routes, the inherent absence of severe design constraints in additive manufacturing enables the creation of sophisticated copper components for applications where excellent electrical and thermal conductivity is paramount. These include electric motor components, heat management systems, heat-treating inductors, and electromagnetic devices. This chapter discusses the main additive manufacturing technologies used to fabricate pure copper products and their achievable properties, drawing attention to the advantages and the challenges they have to face considering the peculiar physical properties of copper. An insight on the topic of recycling of copper powders used in additive manufacturing is also provided. Finally, an overview of the potential areas of application of additively manufactured pure copper components is presented, highlighting the current technological gaps that could be filled by the implementation of additive manufacturing solutions.
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The characterization of Ni-based superalloy Inconel® 718 fabricated by powder-based laser fusion process was performed to study microstructural evolution and accompanying mechanical properties of as-deposited and post-heat-treated material. The current effort employs a low laser volumetric energy density during the deposition. X-ray diffraction, optical, and scanning electron microscopy were done for microstructural characterization. Examination of hardness values, tensile properties, and fractography based on sample orientation was also performed. X-ray diffraction studies facilitated qualitative confirmation of as-deposited samples possessing cube texture. The optical and scanning electron micrographs aided in examining the evolution of microscopic features after each post-processing stage. The as-deposited material possessed columnar grain morphology along with melt-pool marks, which on further magnification showed cellular-dendritic sub-grains along with Laves phases in the interdendritic grain boundaries. Solution heat treatment resulted in reducing these detrimental Laves phases and relief of thermal residual stresses caused by non-homogeneous recrystallization. Solution treatment also led to the formation of equiaxed grain clusters at various sample locations along with the existing columnar grains. The incoherent δ phase was formed at the grain boundaries along with coherent γ″ precipitates. The mechanical properties of as-deposited Inconel 718 alloy were near-isotropic in specimens oriented parallel and perpendicular to the build direction which is ascribed to low laser volumetric energy density. Micrographs of fractured surfaces taken for both directions of all sample conditions showed a ductile mode of fracture.
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Additive Manufacturing (AM) has recently emerged as a promising technique in spare parts manufacturing. Unlike conventional manufacturing (CM) techniques, AM can lead to a reduction in inventory levels, particularly when insourced, through manufacturing spare parts on demand. However, due to the high production costs, the economic benefits of manufacturing spare parts through AM are unclear to managers and practitioners. Recent studies aimed at assisting in this decision have two main limitations: (i) they assume that AM spare parts typically have higher failure rates than CM parts: and (ii) they do not consider the AM machinery investment costs and parts are assumed to be externally supplied. We have developed a model that overcomes these limitations, first by assessing the failure rates of AM spare parts through an interdisciplinary approach rather than making arbitrary assumptions, which enables a comparison with the failure rates through CM reported in the literature. Second, we considered that the manufacturing of AM spare parts can be insourced and thus the investment costs for AM printers are also included, while the manufacturing of CM spare parts is considered to be outsourced. The model was tested with unconstrained and constrained stock systems, and clearly demonstrates the advantages of an insourced 3D printer for on-demand printing under constrained stock systems. Neither is AM preferable under an unconstrained system, due to the high costs of purchasing the printer and of production.
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In literature several studies have been performed to analyze the surface finish of rapid prototyped parts. These researches have been mainly aimed to the optimal build direction of prototypes to obtain the best possible surface finish on specific surfaces. Very diffuse technologies that suffers considerably of low surface quality are Fused Deposition Modeling (FDM) and extrusion based Rapid Prototyping machines in general. Hand finishing for even the most basic levels of part quality are often required by the customers, forcing the geometrical features of the prototypes to be controlled by the skill level of the operator. This study completes past researches performed by the authors on tensile and flexural properties of chemical dipped specimens after immersion in a dimethyl ketone-water solution. The authors aim to gain a more in-depth knowledge of this process, by analyzing and comparing the compressive properties of finished and non-finished FDM parts through the use of an experimental approach, totalizing about 100 tests.
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Rapid prototyping (RP) process is inherently performed by layered manufacturing. The surface finish of the RP part is inevitably excessively rough. In this study, aluminum filled epoxy resin is used as a filler to improve surface quality of wax injection tool fabricated by fused deposition modeling. The average surface roughness of wax patterns can be drastically reduced from 1710 μm to 276 μm. Surface roughness improvement of up to 83.85% can be achieved. Expected advantages of this technique include simple manufacturing process, low manufacturing cost, flexible process capability and good dimensional accuracy.
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Laser polishing by means of shallow surface melting of indirect-SLS metal parts was achieved using high power CO 2 and Nd:YAG lasers raster scanned at high speed. This was an effective technique for reducing surface roughness. The fast moving laser beam provides just enough heat energy to cause melting of the surface peaks. The molten mass then flows into the surface valleys by surface tension, gravity and laser pressure, thus diminishing the roughness. Surface roughness R a data were obtained by profilometry measurements of the polished samples. An analytical model was developed based on the assumption that the surface of an SLS part consists of semi-spherical caps. The model was used to predict the R a values as a function of laser power, scan speed and precursor powder particle size. The modeled results fit the empirical data within a 15% error.
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Plastic parts are often coated to fulfill the desired functional requirements during product life. This may be for decorative purposes only, but also for functions such as improved tribology, wear and humidity resistance, UV-and light stability, hygienic and biofilm resistance. Moving SLS towards Rapid Manufacturing (RM) and making those parts competitive with parts produced by other techniques (e.g. injection molding) implies the adoption of a new quality of part finishing and coating strategy for SLS. This paper provides a survey of current finishing methods used for RM-SLS parts in our institute and highlights the manually-driven process steps. The need for, and first trials with, a more automated finishing process (e.g. vibratory grinding) are discussed, as is the need for innovative supporting software tools.
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Measurements are reported of the steady-state ablation rates and surface temperatures of aluminum alloys 2024 and 7075 caused by a CW CO2 laser assisted by a gas flow of variable composition. The effects of surface layers of oxides and nitrides on the absorptances at 10.6 microns were investigated. Absorptances for these alloys were found to be substantially lower than those measured earlier for steels and titanium alloys.
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This paper describes the characteristics of the heat-affected zone (HAZ) of a UV YAG laser-drilled hole in glass fiber reinforced plastic (GFRP) printed circuit boards. The structures of the HAZ produced by different laser parameters were analyzed. When drilled with lower power and repetition rate, a clear hole wall with very little black charred material was obtained. On the other hand, when drilled with high power and repetition rate, matrix recession and fiber protrusion were observed, also a loose coating was found covering the protruded glass fibers. The results also show that for a given repetition rate, the size of the HAZ increases with increase in average laser power. As for the effect of the pulse repetition rate, a peak value of HAZ width is reached at about 7kHz for each given laser power, and beyond which the HAZ width decreases. A novel evaluation parameter, defined as the quotient of total area of the HAZ and the profile length, is suggested to quantify the size of the laser-induced HAZ in fiber reinforced composites.
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In this work, a surface finish method for parts built-up by selective laser sintering (SLS) is presented. One of the main drawbacks of the SLS technique is the high surface roughness of resulting parts. Therefore, parts have to be polished to be valid for operation conditions. Polishing processes are usually based on manual abrasive techniques. However, in the present paper, a surface polishing method based on laser irradiation is presented. The laser beam melts a microscopic layer on the surface, which re-solidifies under shielding gas protective conditions, resulting in a smoother surface.Laser-polishing tests for lines, planar surfaces and inclined planes have been performed, with satisfactory results in all the cases. The experimental tests were carried out on sintered test parts with an initial roughness of 7.5–7.8 μm Ra. The tested material is a commercial alloy denominated LaserForm ST-100©, composed by sintered stainless steel and infiltrated bronze that it is used mainly for the constitution of injection moulds. Experimental results present final surface roughness below 1.49 μm Ra, which represent an 80.1% reduction of the mean roughness. Finally, a complete analysis of test probes and its metallurgical composition is presented. Considering that the material presents a non-homogeneous structure, the polished surfaces present slightly higher hardness values and are more homogeneous than the initial ones. Thus, polished surfaces do not present any heat affected zone or cracks, which could cause failure during the part operation.