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Proceedings of ICAME-2015

15th& 16th of October 2015, UCEV,Villupuram,Tamil Nadu

E-mail:cmghari2004@gmail.com

ICAME264

A Numerical Simulation Study on Drill Bit Point Angle and Helix Angle during

Drilling AISI 1045 STEEL

G. Hariharan

Department of Mechanical Engineering

University College of Engineering, Anna University

Kancheepuram, TamilNadu, India

Cmghari2004@gmail.com

N. Shenbaga Vinayaga Moorthi

Department of Mechanical Engineering

University VOC College of Engineering, Anna University

Thoothukudi, TamilNadu, India

nsvmoorthi@gmail.com

N. Senthilkumar

Department of Mechanical Engineering

Adhiparasakthi Engineering College

Melmaruvathur, TamilNadu, India

nsk@adhiparasakthi.in

Abstract--- In this work, finite element simulation of drilling

process is performed to study the various characteristics of the drill

bit by varying its point angle and helix angle during drilling AISI

1045 steel using tungsten carbide drills. The machining parameters

surface speed and feed rate is kept constant. Variations in effective

stress, effective strain, mean stress, maximum principal stress,

temperature and cutting forces are determined using DEFORM-3D,

Finite Element simulation software. Simulation results obtained for

different drill bits were compared and the best combination of point

angle and helix angle is determined. With the best combination of

point angle and helix angle, both drilling simulation and

experimentation is performed to validate the simulation results.

Results obtained show better output responses than the other

combinations proving the efficiency of the simulation results.

I. INTRODUCTION

Drilling is a hole making process carried out using drill bits,

which has one or more major cutting edges and helical or

straight flutes, used to remove material as chips. The cutting

motion for drill bit is rotational and the feed of the drill is

applied through longitudinal axis. The drill bit is represented by

various geometries such as rake or helix angle, point angle,

relief angle, number of flutes, web thickness and drill bit

diameter. The angle formed by the edge of a flute and a line

parallel to a drill centerline is known as helix angle of a drilling

tool and the angle formed by cutting edges of the drill is called

as point angle. Twist drill is the most common drill. Cutting

speed is the peripheral speed of drill, feed is the movement of

drill along the axis of hole for one revolution and depth of cut is

the radius of the drill. For obtaining minimum cost of

machining and minimum production time these parameters has

to be optimized [1].

Isbilir and Ghassemieh [2] investigated experimentally and

numerically the drilling of Ti6Al4V material, by developing a

3D finite element model based on Lagrangian approach using

ABAQUS/explicit and studied the effects of cutting parameters

on the induced thrust force and torque. Matsumura et al. [3]

presented a numerical model to analyze the cutting temperature

in drilling for carbon steel by dividing the cutting edges into

discrete segments in the cutting area. From the determined chip

flow models, cutting forces were predicted. Lacalle et al. [4]

developed a mechanistic model to predict thrust force and

torque during drilling aluminium alloy Al 7075-T6 with double-

point angle edges, designed to avoid part distortion at the drill

entrance into material and validated the model for wide range of

cutting conditions.

Narasimha et al. [5] investigated the torque-thrust coupling

effect in twist drills to study the influence of helix angle on

torsional and the cross-coupling stiffnesses and found that the

coupling interaction is strongly influenced by the helix angle

and the magnitudes of the coefficients increase parabolically

with drill diameter.Arrazola and Ozel [6] investigate the

influence of limiting shear stress at the tool–chip contact on

frictional conditions using two distinct FE models with

Arbitrary LagrangianEulerian (ALE) fully coupled thermal-

stress analyses. By coupling both sticking and sliding frictions,

friction models at tool-chip and work-tool interface is

studied.Yen et al. [7] developed a methodology to predict tool

wear and tool life using FEM simulations by proposing a model

for the specified tool–workpiece pair and modifying the

commercial FEM code for automatic calculation of tool wear

and updating tool geometry and finally experimental

validation.Usui et al. [8] predicted chip formation and cutting

force for a single point tool of arbitrary geometry using energy

method and developed an equation for carbide tool crater wear

both experimentally and theoretically.

In this work, the drill bit geometries such as point angle and

helix angle are varied with different combinations and the

effects of these combinations such as temperature, effective

stress, effective strain, maximum principal stress, mean stress

and cutting forces were determined by conducting simulations

for each combinations using DEFORM-3D [9] a FEA software

with AISI 1045 steel as a workpiece material [10,11] and High

Speed steel as a tool material. The comparative study has been

made with the results of simulations to find the better

combination of the point and helix angle from the various

combinations taken for the analysis.

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II. METHODOLOGY

A. Deform 3D

Deform-3D is a powerful process simulation system

designed to analyze the three dimensional flow of complex

metal forming processes. Deform-3D is a practical and efficient

tool to predict the material flow in industrial forming operations

without the cost and delay of shop trials. In DEFORM-3D, the

machining simulation capabilities are built upon a powerful

process simulation system designed to analyze the three-

dimensional (3D) flow of complex manufacturing processes

[12-14].

Fig. 1.Modelled drill bit and workpiece

The modelled drill bit and workpiece is shown in Fig. 1.

The drill bit is modeled for a radius of 5 mm, point angle 118°

and helix angle 30°. The workpiece is generated by 100 mm

diameter and 50 mm height with 2 mm and 118° point angle

pre-drilled workpiece. During meshing, a finer mesh gives finer

accuracy, but the simulation time increases exponentially as the

number of elements increases linearly. Tetrahedral elements are

having four nodes the relative mesh method is used for the

meshing of tool as well as workpiece material. Simulations

performed with 20000 elements are sufficient to give an

accurate model of the drill bit. In this study, Cockcroft and

Latham fracture criterion was employed to predict the fracture

criteria. Cockcroft-Latham fracture criterion shown in Eq. (1) is

the integral damage value using the maximum principle stress

and equivalent strain. It needs only one material constant to

express the amount of ductile damage. Therefore material

constant can be determined only by one experiment.

=1

0 (1)

where is the maximum principle stress, is the

equivalent strain,

Is the equivalent strain at which the

fracture occurs, 1 Is the material constant to express the limit

of ductile damage. The integral I showing in Eq.(2) is the

normalized damage value of Eq.(1). This integral is calculated

at each integration points (Gauss points), usingstresses and

strains computed by finite element analysis [15,16]. If

integralI at Gauss point of an element becomes 1, its damage

value in the element reaches fracture criterion and element is

deleted.

=1

1

0. (2)

The flow stress equation proposed by Oxley used in this

analysis is as given in Equ. 4 and Equ. 5, which is expressed as

a work-hardening behavior where σ0 and n are functions of

velocity modified temperature Tmod in which the strain rate and

temperature are combined into a single function.

0n

(3)

mod 0

1- logT T v

(4)

whereσ0 is strength coefficient, n is strain hardening index,

T is temperature, v is a constant,

is strain,

is strain-rate.

The most commonly used boundary conditions are heat

exchange with the environment involving heat transfer [17].

The boundary conditions provided in this analysis are initial

temperature of 30°C, shear friction factor of 0.7 and heat

transfer coefficient at the workpiece-tool interface as 100

N/sec/mm/C. For workpiece, the velocities in all the directions

are fixed and for tool, movement in Y direction is allowed.

The material constitutive law used to model the material

behavior is Oxley’s flow stress equation and for modeling the

contact at the tool–chip interface, a constant shear factor

friction law is employed.

The process of replacing the distorted mesh with a new

undistorted mesh is known as remeshing which interpolates the

variables from the old mesh to the newly developed mesh.

Global remeshing is considered during simulation process, in

which every element of the old mesh gets replaced with new

mesh element, followed by interpolation.

B. Workpiece and Drillbit material

AISI 1045 material is used for experimental investigation,

which is a low cost alloy having adequatetoughness and

strength suitable for most of the engineering and construction

applications, of hardness 181 BHN [18]. Applications include

axles, bolts, connecting rods, studs, spindles, light gears and

guide rods. The typical composition of the AISI 1045 steel is

shown in Table 1. The tool material used for this simulation

analysis is High Speed Steel, which is commonly used in most

of the industries as a tool material. Selecting High speed steel

[HSS] over carbide drill bit is due to its strength to withstand

larger cutting forces and also due to low cost of tools. The

advantage of HSS over carbide is its strength to withstand

cutting forces and the low cost of the tools. HSS performs well

with intermittent cutting and requires low power, but is suitable

only for lower range of cutting speeds when compared to that of

carbide cutting tools.

TABLE I. CHEMICAL COMPOSITION OF AISI 1045 STEEL.

Carbon

Silicon

Manganese

Phosphorous

Sulphur

Iron

0.45%

0.32%

0.693%

0.02%

0.022%

Remainder

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III. RESULTS AND DISCUSSIONS

A. Simulation Results

During the pre-processing stage of simulation, the boundary

conditions for drilling are straight forward. The edges of the

workpiece are fixed in all directions. The rotational speed is

100 rpm and the feed rate is 0.2 mm/rev, which is kept constant

for all simulations. The environment temperature is defined as

30°C. The heat exchange is usually very small because the

drilling process happens very quickly. T After the end of

simulation the values of the parameters as mean stress, effective

stress, effective strain, maximum principal stress and

temperature are determined. Figure 2 shows the simulation of

drilling process.

Fig. 2.Modelled drill bit and workpiece

The effects of 118° point angle and the varying helix angles

are shown in Fig. 3. After performing the drilling simulation,

the maximum temperature lies between 1579°C to 1598°C.

Similarly the effective stress during the simulation will be

varying between 1398 MPa to 1528 MPa , the effective strain is

varying between 33 to 34, the maximum principal stress is

varying between 4370 MPa to 5390 MPa and the mean stress is

varying between 3674 MPa to 4897 MPa. When the drill bit

makes contact with the workpiece, friction increases due to

shearing action and the temperature between the interfacing

area of the tool and workpiece will be increasing. The

temperature distribution over the other areas than the

interfacing area is lesser than that area.

Figure 4 shows the effects of 127° point angle and the

varying helix angles. After performing the simulation, the

maximum temperature lies between 1471°C to 1593°C,

effective stress varies between 1313 MPa to 1610 MPa,

effective strain varies from 23 to 30, maximum principal stress

varies from 4267 MPa to 4561 MPa and the mean stress varies

from 3485 MPa to 3672 MPa.

Figure 5 shows the effect of 136° point angle on variation

of helix angles. After performing the drilling simulation, the

maximum temperature obtained is between 1459°C to 1472°C.

Similarly effective stress varies between 1532MPa to

1645MPa, effective strain variesfrom 32 to 35, maximum

principal stress varies between 4886 MPa to 5311MPa and

mean stress varies between 3937MPa to 4632MPa.

From each simulation, maximum values of the variables are

taken for better comparison of different combinations and

graphs were drawn as shown in Fig. 6. From graph, it is

observed that higher interaction effect is seen for all output

responses with respect to helix angle.

Figure 7 shows the resultant cutting forces acting on the

workpiece during the drilling over for various point angles and

helix angles chosen. From the results obtained, it is observed

that as the point angle increases, the resultant cutting force

acting also increases for all the values of chosen helix angles.

But variation in point angle does not have any impact on

resultant cutting force except decreasing its intensity. For

lower helix angle and point angle, resultant cutting forces are

higher and for higher helix angle and higher point angle,

resultant cutting forces are lower.

Fig. 7.Resultant cutting forces for various drill bit geometry

B. Experimental Validation

With the determined optimum drilling speed 100m/min,

feed rate of 0.2mm/rev, point angle of 127° and helix angle

25°, a confirmation experiment is conducted experimentally

with vertical milling center attached with kistler dynamometer

of model 9257B, to observe the thrust force and torque. The

signals of cutting forces was amplified and fed through a data-

acquisition system on the DYNAWARE 7.511.328

softwareand the measured output responses are given in Table

2. From results, it is obvious that the lower cutting force

which is given from these point angle 127° and helix angle 25°

is the best combination for the effective work.

TABLE II. MEASURED RESPONSES OF CONFIRMATION

EXPERIMENT.

Thrust

force (N)

Torque

(N-m)

Material Removal

Rate (g/min)

Surface roughness

(microns)

106.431

1.542

75.094

4.156

35.032.530.027.525.0

3500

3000

2500

2000

1500

1000

Helix Angle (de g.)

Res ultant Cutting Force (N)

Resultant Cutting Force for 118 deg. Point angle

Resultant Cutting Force for 127 deg. Point angle

Resultant Cutting Force for 136 deg. Point angle

Variation of Resultant Cutting Force over Point Angle

ISBN 978-93-85477-29-4

839

Proceedings of ICAME-2015

15th& 16th of October 2015, UCEV,Villupuram,Tamil Nadu

E-mail:cmghari2004@gmail.com

Fig. 3.Effect of 118° point angle and varying helix angle

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Fig. 4.Effect of 127° point angle and varying helix angle

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Fig. 5.Effect of 136° point angle and varying helix angle

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Fig. 6. Influence of helix angle and point angle over responses

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IV. CONCLUSION

In this work, behavior of twist drill for varying helix and

point angle is studied using Deform-3D during drilling AISI

1045 steel with HSS drill. Temperature distributions, effective

stress, maximum effective stress in drill were analyzed. The

following observations were obtained. author/s of only one

affiliation.

a) The optimum point angle determined is 127° and

optimum helix angle is 25°.

b) With increase in point angle, effective stress, mean

stress, principal stress and effect strain increases. For 127°

point angle, these output responses were lower.

c) Temperature distribution increases with increase in

point angle. For lower point angle temperature is lower,

increases with increase in point angle.

d) Resultant cutting force decreases with increase in point

angle, lower for 127° point angle.

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