Presentation on my undergraduate thesis work at DPLC 2016 Conference

Optimization of Process Parameters in CNC
Wire Cut EDM using Taguchi Method for
Effective Machining of STAVAX ESR
BITS Pilani Hyderabad Campus
Chennu Vinodh Reddy

20/03/16 2nd National Conference DPLC 2016 2
EDM Wire Cut is a thermo-electrical process in which
material is removed by a series of sparks between work
piece and wire electrode (tool).

In Wire EDM process, there is no direct contact between workpiece and
tool(wire). Therefore materials of any hardness can be machined which is
electrically conducting can be machined easily with minimum clamping pressure
is required to hold the workpiece.

Input Process Parameters in WEDM
The effectiveness of the whole EDM process depends on number of input
process parameters such as
1) Pulse on Time
2) Pulse off Time
3) Wire Feed Rate
4) Peak Current
5) Servo Voltage
6) Wire Tension
7) Spark Gap Set Voltage
8) Dielectric Fluid Flow
9) Cutting Speed Overide %

TON : Pulse ON Time.
During the pulse on time, the voltage is applied in the gap between workpiece
and the electrode thereby producing discharge.
Range : 100 - 131 (in step of 1) e-Pulse (Equi-energy Pulse)
TOFF : Pulse OFF Time.
TOFF the time between discharges. Off Time has no effect on discharge
energy.
Range : 00 - 63 (in step of 1) e-Pulse (Equi-energy Pulse).
IP : Peak current (A)
Peak current is the amount of power used in discharge machining.
Range : 010 - 230 (in step of 10)

WF : Wire Feed rate setting.
This is a feed rate at which the fresh wire is fed continuously for sparking.
Range : 01 - 15 (in step of 1)
SV : Spark Gap Set Voltage
Gap voltage, also called open circuit voltage specifies the supply voltage to
be placed on the gap.
Range : 00 - 99 (in step of 1) Volt
Dielectric Fluid flow
Dielectric flow rate is the rate at which the dielectric fluid is circulated
Range : 0 to 15 (For 16 step programmable flushing)

VP : Pulse Peak Voltage setting
This is for selection of open gap voltage.
Range : 1 or 2
SF : Servo Feed Setting
This parameter decides the servo speed; the servo speed, at the set value of
SF, can vary in proportion with the gap voltage (normal feed mode) or can be
held constant while machining (with constant feed mode).
Range : 0000 - 0990 for Normal feed
1000 - 1999 for Constant feed
2000 - 2999 for Constant voltage

CS% : Cutting Speed Over-ride %.
CS %overide parameter is provided to reduce the cutting speed to
set CS% value without modifying the set machining condition
parameters or the E-code tables.
This parameter is mainly used to reduce the cutting speed in order to
avoid wire breakages in the following rough machining conditions.
CS% = 100 = Normal cutting speed as per selected machining
condition.
WT : Wire Tension setting.
This is a gram-equivalent load with which the continuously fed wire is
kept under tension so that it remains straight between the wire
guides.
Range : 01 - 15 (in step of 1)

Wire Tension 8 machine units
Pulse Peak Voltage 2 Machine units
Spark Gap Set Voltage 20 V
Servo Feed 2149 machine unit
Cutting Speed Overide % 65%
Jog Height 15 mm
Flushing Pressure 1 machine unit
Cutting Tool Brass wire of Dia 0.25mm
Constant Parameters During Machining

Choosen Parameters and Levels for Exp.
Level 1 Level 2 Level 3
P1 Pulse on Time 105 115 125
P2 Pulse off Time 50 55 60
P3 Peak Current 170 190 210
P4 Wire Feed 3 5 7
● No. of parameters = 4
● No. of levels = 3

Design of Experiments
Taguchi Method:
Taguchi methods are statistical methods developed by
Genichi Taguchi to improve the quality of manufactured
goods and more recently also applied to engineering,
biotechnology, marketing and advertising.
Taguchi's work includes three principal contributions to
statistics:
• A specific loss function
• The philosophy of off-line quality control; and
• Innovations in the design of experiments

Parameter Design Orthogonal Array
● No. of parameters = 4
● No. of levels = 3

EXP P1 P2 P3 P4
1 L 1 L 1 L 1 L 1
2 L 1 L 2 L 2 L 2
3 L 1 L 3 L 3 L 3
4 L 2 L 1 L 2 L 3
5 L 2 L 2 L 3 L 1
6 L 2 L 3 L 1 L 2
7 L 3 L 1 L 3 L 2
8 L 3 L 2 L 1 L 3
9 L 3 L 3 L 2 L 1
Taguchi Orthogonal array = L9
P1: Pulse On Time; P2: Pulse Off Time; P3: Peak Current; P4: Wire Feed

Design of Experiments
Experiment P1 P2 P3 P4
1 105 50 170 3
2 105 55 190 5
3 105 60 210 7
4 115 50 190 7
5 115 55 210 3
6 115 60 170 5
7 125 50 210 5
8 125 55 170 7
9 125 60 190 3

Workpieces
Workpiece Material: Stavax ESR (mould Steel)
Workpiece Dimension: 65mm*10mm*10mm

Stavax ESR
Element Composition %
C 0.38
Si 0.9
Mn 0.5
Cr 13.6
V 0.3
Fe Balance

Setting up workpiece in Wire EDM

CNC EDM WIRE CUT Machine
Operation
Code for making straight cuts on Workpieces
G01 X-40

Response Results
The important machining responses in WEDM
process include
1)Surface Roughness
2)Cutting Speed
3)Kerf Width
4) Material Removal Rate (MRR)

Cutting Speed

Exp P1 P2 P3 P4 Cutting speed
1 105 50 170 3 0.79
2 105 55 190 5 0.71
3 105 60 210 7 0.56
4 115 50 190 7 1.73
5 115 55 210 3 2.32
6 115 60 170 5 1.51
7 125 50 210 5 3.35
8 125 55 170 7 2.21
9 125 60 190 3 2.54
Cutting Speed

Kerf Width
Kerf is the measure of the amount
of the material that is wasted
during machining.
For Measuring Kerf Width of
EDMed workpieces Olympus
STM6 Measuring Microscope is
used with 5x lens.

Kerf Width

Kerf Width
Exp P1 P2 P3 P4 Kerf Width
1 105 50 170 3 315.871
2 105 55 190 5 268.159
3 105 60 210 7 210.915
4 115 50 190 7 703.418
5 115 55 210 3 913.326
6 115 60 170 5 569.2549
7 125 50 210 5 1675.412
8 125 55 170 7 919.779
9 125 60 190 3 1095.883

Material Removal Rate
In WEDM the material erodes from the workpiece by a series of discrete
sparks between the work and the tool electrode immersed in the liquid
dielectric medium.
These electrical discharges melt and vaporize minute amounts of the
work material, which are then ejected and flushed away by the dielectric
fluid.
MRR = (Height of Workpiece)*Kerf Width*(Cutting Speed)
MRR = 10mm*Kerf Width*(Cutting Speed)

MRR
Exp P1 P2 P3 P4 MRR
1 105 50 170 3 315.871625
2 105 55 190 5 268.1599
3 105 60 210 7 210.9156
4 115 50 190 7 703.418
5 115 55 210 3 913.326
6 115 60 170 5 569.2549
7 125 50 210 5 1675.41205
8 125 55 170 7 919.7799
9 125 60 190 3 1095.883

Surface Roughness
Surface Roughness of workpiece is measured using Mithuya
Surftest Sj 410 Machine.

Surface Roughness Tester Machine

Surface Roughness

Surface Roughness
Exp P1 P2 P3 P4 Surface Roughness
1 105 50 170 3 1.478
2 105 55 190 5 1.501
3 105 60 210 7 1.455
4 115 50 190 7 3.501
5 115 55 210 3 3.551
6 115 60 170 5 2.902
7 125 50 210 5 4.501
8 125 55 170 7 3.791
9 125 60 190 3 3.877

After Performing 9 experiments based on Taguchi L9
orthogongal array methodology to obtain response
parameter values Surface Roughness, Cutting Rate,
Kerf Width and MRR.
All the graphs, charts, plots and analysis for surface
roughness parameter have been carried out using
Minitab 17.0 statistical software.
Analysis Using Minitab Software

Surface Roughness
Exp TON TOFF IP W.F S.R SN ratio Means
1 105 50 170 3 1.478 3.3934886812 1.478
2 105 55 190 5 1.501 3.5276138449 1.501
3 105 60 210 7 1.455 3.2572598664 1.455
4 115 50 190 7 3.501 10.8838422153 3.501
5 115 55 210 3 3.551 11.007013446 3.551
6 115 60 170 5 2.902 9.253948162 2.902
7 125 50 210 5 3.84 11.6866244874 3.84
8 125 55 170 7 3.791 11.5750756885 3.791
9 125 60 190 3 3.877 11.7699160201 3.877
Surface Roughness SN ratios, Means values

Pooled Analysis of Variance for
Surface Roughness(S/N Data)
Level TON TOFF IP WF
1 3.393 8.655 8.074 8.723
2 10.382 8.703 8.727 8.156
3 11.677 8.094 8.650 8.572
Delta 8.284 0.610 0.653 0.567
Rank 1 3 2 4

Surface rougness interaction plots

Cutting Speed
Exp TON TOFF IP W.F C.S SN ratio Means
1 105 50 170 3 0.79 -2.0474 0.79
2 105 55 190 5 0.71 -2.9748 0.71
3 105 60 210 7 0.56 -5.0362 0.56
4 115 50 190 7 1.73 4.7609 1.73
5 115 55 210 3 2.32 7.3097 2.32
6 115 60 170 5 1.51 3.5795 1.51
7 125 50 210 5 3.55 11.0045 3.55
8 125 55 170 7 2.21 6.8878 2.21
9 125 60 190 3 2.54 8.0966 2.54

ANOVA Cutting Speed
Level TON TOFF IP W.F
1 -3.353 4.573 2.807 4.453
2 5.217 3.741 3.294 3.870
3 8.663 2.213 4.426 2.204
Delta 12.016 2.359 1.619 2.249
Rank 1 2 4 3

Analysis of Kerf width
Exp TON TOFF IP W.F Kerf
Width
SN ratio Means
1 105 50 170 3 399.8375 52.0376704
669
399.8375
2 105 55 190 5 377.69 51.5427097
256
377.69
3 105 60 210 7 376.635 51.5184135
149
376.635
4 115 50 190 7 406.6 52.1833474
86
406.6
5 115 55 210 3 393.675 51.9027567
232
393.675
6 115 60 170 5 376.99 51.5265966
061
376.99
7 125 50 210 5 541.35 54.6695628
223
541.35
8 125 55 170 7 416.19 52.3858328
199
416.19
9 125 60 190 3 431.45 52.6986094
665
431.45

ANOVA kerf width
1 51.70 52.96 51.98 52.21
2 51.87 51.94 52.14 52.58
3 53.25 51.91 52.70 52.03
Delta 1.55 1.05 0.71 0.55
Rank 1 2 3 4

Analysis of MRR results
Exp TON TOFF IP W.F MRR SN ratio Means
1 105 50 170 3 315.871 49.9902 315.871625
2 105 55 190 5 268.159 48.5678 268.1599
3 105 60 210 7 210.915 46.48217 210.9156
4 115 50 190 7 703.418 56.94426 703.418
5 115 55 210 3 913.326 59.2125 913.326
6 115 60 170 5 569.254 55.1061 569.2549
7 125 50 210 5 1921.792 65.6741 1921.7925
8 125 55 170 7 919.779 59.2736 919.7799
9 125 60 190 3 1095.883 60.7952 1095.883

ANOVA MRR
Level TON TOFF IP W.F
1 48.35 57.54 54.79 56.67
2 57.09 55.68 55.44 56.45
3 61.91 54.13 57.12 54.23
Delta 13.57 3.41 2.33 2.43
Rank 1 2 4 3

Conclusion
Experiments have been designed using Taguchi L9 orthogonal array.
For the performed experiments the following data and plots are included:
●Signal to Noise (S/N) ratio
●Analysis of variance (ANOVA)
●Main effect plots Residual plots
●Interaction plots Counter Plots
●3D Surface Plots
for response parameters Surface roughness, Cutting speed, Gap current, Kerf Width
and Material Removal Rate.
The results presented in this research work will be useful to make CNC wire cut system
to effectively utilized in the present day die and tool manufacturing units.

References
1. Design of experiments via taguchi methods: orthogonal arrays
https://controls.engin.umich.edu/wiki/index.php/Design_of_experiments_via_taguchi_methods:_or
ogonal_arrays
2. Notes on UDDEHOLM STAVAX ESR :
http://www.uddeholm.com/files/PB_Uddeholm_stavax_esr_english.pdf
3. Influence of Process parameters on the Wire EDM process
http://coep.vlab.co.in/?sub=34&brch=105&sim=1028&cnt=1
4. Technology Manual For Pulse Generator : ELPULS 40 DLX (AU) Product : SPRINTCUT (AU)
5. Sprintcut EDM pdf http://www.electronicagroup.com/download/sprintcut.pdf
6. Drawing Main Effects Plots on Minitab http://support.minitab.com/en-us/minitab/17/topic-
library/modeling-statistics/anova/basics/what-is-a-main-effects-plot/

References
7. Drawing Interaction Plots on Minitab
http://support.minitab.com/en-us/minitab/17/topic-library/modeling-statistics/anova/anova-
models/what-is-an-interaction/
8. Drawing Residual Plots on minitab
http://support.minitab.com/en-us/minitab/17/topic-library/modeling-statistics/regression-and
-correlation/residuals-and-residual-plots/residual-plots-in-minitab/
9. Drawing Counter Plots on Minitab
http://support.minitab.com/en-us/minitab/17/topic-library/modeling-statistics/using-fitted
-models/graphs/contour-plots-and-3d-surface-plots/
10. Review on Wire-Cut EDM Process Sreenivasa Rao M, Venkaiah N
11. Taguchi Method and ANOVA: An Approach for Selection of Process Parameters of
EDM of EN-353 Steel

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Presentation on my undergraduate thesis work at DPLC 2016 Conference