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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
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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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