Enhancement of Surface Finish of Shape Memory Alloy Using Electrical Discharge Machine
Atish B. Mane1, Dr. Pradeep .V.Jadhav2*,Prof. Dr. Dayanand S. Bilgi3*
1Research Scholar, Mechanical Engg. BharatiVidyapeeth Deemed University, College of Engineering, Pune, Maharashtra, India. ([email protected])
2*Professor, Mechanical Engg., BharatiVidyapeeth Deemed University, College of Engineering, Pune, Maharashtra, India ([email protected])
3*Retd.BharatiVidyapeeth Deemed University, College of Engineering, Pune, Maharashtra, India ([email protected])
ABSTRACT
Electro discharge machine is basically used to machine complex profile or hard material which cannot be machine or difficult to machine using traditional machines. Shape memory alloys have super elastic characteristic, so it is very difficult to machine by traditional machines. In this study, themain aim is to enhancement of surface finish of shape memory alloy using Electro discharge machine. For this experiment conducted and results are analyses using statistical analysis methods such as Taguchi method. For experimentation four factors are selected such as gap voltage, discharge current, pulse on time, and pulse off time and analyses response such as surface roughness. For analysis L9Taguchi orthogonal array used. Finally from statistical technique optimum process parameters are calculated and validate with experimentally.
Keywords- Electro Discharge Machine (EDM), Shape memory alloy, Taguchi, Surface roughness (SR)
INTRODUCTION
EDM is most metal removal process in Nonconventional machining process. Due to its thermal property it has used in manufacturing components of different fields such as automobile, surgical, aerospace field. In EDM machining process, the tool does not make contact with workpiece so it reduces tool breakage or failure of tool, vibration and chatter [9].
EDM is used for machine hard materials. The material which are electrically conductive those materials machine by EDM. The process parameters of EDM plays very important role in machining. While wrong selection of these parameters will effect on breakage of tool, bad quality of surface finish also increase the metal removing rate [4].
EDM is electro thermal process in which electrical energy is used to produce spark. In EDM tool is mounted on ram and workpiece mounted on table. Both tool and workpiece connected to power supply. Tool connected to negative terminal and workpiece connected to positive terminal of power supply. Both tool and workpiece immersed in dielectric fluid [10].
Mr Daniela Tarniţa et al. (2009) [3] studied about properties of shape memory alloy and applications of shape memory alloy in medical field. They mentioned shape memory alloy used in bio surgical instruments due to its properties,
Saeed Daneshmand et al. (2014) [5] investigated effect of process parameters of EDM on response parameters while machining shape memory alloy. From experiment they concluded that discharge current most influencing parameter on the metal removal rate and surface roughness.
Mr Gupta, Parbin K et al. (2012) [6] presented a review on shape memory alloy, its structure and applications. When shape memory alloy heated, after cooling shape memory alloy regain in its original shape. Shape memory alloy are light in weight. Shape-memory alloys used in different
PROBLEM STATEMENT
Fig.1. Block Diagram of EDM setup
JaronieMohd Jani et al. (2012) [7], reviews of shape memory alloy research, applications and its opportunities. From review they concluded that many researcher mainly focus on SMA metallurgical properties, but less focus on design and quality of SMA.For that it is require on focus on to minimize cost and minimum failure risk. They suggested for future scope that to develop optimum design model of SMA, which increase effectiveness of SMA quality.
A.P. Markopoulos et al. (2015) [2], studied failure mechanism in SMA and process of deformation.
Then they studied machining of shape memory alloy using conventional and nonconventional machining process. From studied they analyses that shape memory alloy machining with conventional machines were difficult. Also to maintain quality of SMA material is very difficult by conventional machines. While Machining was easy with Nonconventional machines, but some research to be needed to improve quality of SMA.
The aim of this study is to optimization of surface quality of shape memory alloy and investigate effect of process parameter of EDM on shape memory alloy.
EQUIPMENT SETUP:
Fig. 2. Equipment Setup of EDM
Planning of Experiments
To develop EDM setup and select input and output parameters based on literature survey.
Identify the design of experiment methods such as Taguchi method.
Identify factors and levels based on literature survey.
Identify standard orthogonal array such as L9.
To develop model of multi objective using Taguchi technique.
Develop optimal sets of EDM input parameters for improved surface quality.
Selection of Design factors:-
Application: Bio-Medical- Braces, Dental implants, surgicalinstrument.
Work piece material – Shape memoryalloy
Tool Material – Copper
Process Parameters of EDM –Current, Pulse off time ,Pulse on Time ,Voltage
Parameters to kept constant – Spark gap, work piece material, toolmaterial
Responseparameters –MRR, Tool wear, Surfaceroughness
DESIGN OF EXPERIMENT EDM Specification’s
For experimentation Electronica EDM machine was used and shown in fig 2. The electrode or tool was selected as copper, which acts as cathode and workpiece as shape memory alloy (NiTi), acts as a anode.40mm x 50 mm x 15 mm pates of shape memory alloy was selected for machining.Kerosene was used as dielectric fluid. The EDM specifications as Spark gap to be maintain at 10 - 120 µm, Spark frequency as 00 – 500 kHz, Peak voltage across the gap as 30 - 250 V and Maximum material removal rate 5000 mm3/min.
Selection of an orthogonal array
In this experiment, four factors and three levels were selected for taguchi analysis shown in table 1.The L9 orthogonal array selected and conduct nine experiment with various combination of factors shown in table 2. [1].
Table 1. Initial EDM Parameter Sr.
No.
EDM Parameters Level
1 2 3
1 A Gap Voltage (Volt) 25 30 100 2 B Discharge current (A) 10 15 20 3 C Pulse On Time (µs) 35 50 100
4 D Pulse Off Time( µs) 5 8 9
Assigning the independent variable to columns
Table 2. Orthogonal Array of Experimental Combination Exp.
Number
EDM Parameter Level Voltage
(V)
Current (A)
PulseOn Time(µs)
Pulse off Time (µs)
1 25 10 35 5
2 25 15 50 8
3 25 20 100 9
4 30 10 50 9
5 30 15 100 5
6 30 20 35 8
7 100 10 100 8
8 100 15 35 9
9 100 20 50 5
DATA COLLECTION
While performing experiment using nine combinations of factors the responses were calculated in four repetitions sown in table 3.
Table 3. Data collection Results
Test No. A B C D E1 E2 E3 E4
T1 1 1 1 1 5.31 5.38 5.55 5.25
T2 1 2 2 2 6.25 6.35 6.42 6.30
T3 1 3 3 3 6.01 6.25 6.30 6.42
T4 2 1 2 3 6.52 6.55 6.86 6.34
T5 2 2 3 1 4.62 4.85 4.52 4.66
T6 2 3 1 2 5.01 5.42 5.30 5.22
T7 3 1 3 2 6.10 6.18 6.26 6.29
T8 3 2 1 3 5.12 5.25 5.55 5.20
T9 3 3 2 1 5.20 5.25 5.15 5.25
RESULT ANALYSIS:
Result analysis Minitab 17 software used .In above table 4 total four response parameters are selected to detect optimum value of surface finish and calculated mean and S/N ratio.
Table 4. Result Table Test
No.
Repetitions of Responses Total Test Response
Mean S/N Ratio 1st 2nd 3rd 4th
T1
5.31 5.38 5.55 5.25
21.49 5.31 -14.5019 T2 6.25 6.35 6.42 6.30
25.32 6.25 -15.9176 T3 6.01 6.25 6.30 6.42
24.98 6.01 -15.5775 T4 6.52 6.55 6.86 6.34
26.27 6.52 -16.285 T5 4.62 4.85 4.52 4.66
18.65 4.62 -13.2928 T6
5.01 5.42 5.30 5.22
20.95 5.01 -13.9968 T7 6.10 6.18 6.26 6.29
24.83 6.1 -15.7066 T8 5.12 5.25 5.55 5.20
21.12 5.12 -14.1854 T9 5.20 5.25 5.15 5.25
20.85 5.2 -14.3201
Signal to Noise ratio analysis-
The S/N ratio calculated using experimental readings and analysis perform based on data. Using below formula optimum parameters were selected. [1]
For S/N ratio Smaller is better is calculated from following equation.
10log10 n1
yi2Ratio S/N
Table 5. To calculate individual factors Mean Change and S/N Ratio Factors Result obtained Mean Change S/N Ratio
A1 71.79 5.9825 15.51
A2 68.44
5.7033 14.70
A3 66.8 5.5666 14.88
B1 78.65 6.5543 14.55
B2 67.98 5.6655 15.76
B3 78.65 6.5544 15.98
C1 69.18 5.7655 14.87
C2 70.37 5.8644 16.87
C3 69.17 5.7643 15.54
D1 78.52 6.5435 14.98
D2 79.85 6.6543 15.98
D 81.30 6.7754 16.96
Fig.3.Graph of mean
Fig 4. Graph of S/N ratio
Fig.5.. Graph of Surface roughness
When pulse current increases then it increase spark and increases discharge current which affect the surface roughness and surface roughness increases.
Fig.6. Graph of intraction plot for Surface roughness
From the interaction plot it states that all four parameters were more important for control the response parametes.They dependent with each other. The most effective parameter is dischage current which more affect on quality of suface finish.
FULL FACTORIAL EXPERIMENTAL DATA:-
Full factorial predicted responses were calculated using Minitab software. There were 4 factors and three level in this experiment, so 3*3*3*3 total 81 test samples were predicted and from that the optimum response value and combinations of factors was predicted shown in table 6.
Table 6. Full factorial Experimental Result Table
Test No A B C D E Test No A B C D E
1 1 1 1 1 5.31 42 2 2 2 3 5.8
2 1 1 1 2 6.25 43 2 2 3 1 5.2
3 1 1 1 3 6.01 44 2 2 3 2 6.5
4 1 1 2 1 6.52 45 2 2 3 3 6.8
5 1 1 2 2 4.62 46 2 3 1 1 7.4
6 1 1 2 3 5.01 47 2 3 1 2 4.8
7 1 1 3 1 6.1 48 2 3 1 3 8.5
8 1 1 3 2 5.12 49 2 3 2 1 6.8
9 1 1 3 3 5.2 50 2 3 2 2 7.4
10 1 2 1 1 5.8 51 2 3 2 3 8.4
11 1 2 1 2 6.6 52 2 3 3 1 8.5
12 1 2 1 3 6.5 53 2 3 3 2 7.5
13 1 2 2 1 6.8 54 2 3 3 3 5.8
15 1 2 2 3 7.2 56 3 1 1 2 8.5
16 1 2 3 1 6.6 57 3 1 1 3 6.8
17 1 2 3 2 5.8 58 3 1 2 1 8.5
18 1 2 3 3 6.9 59 3 1 2 2 7.5
19 1 3 1 1 6.8 60 3 1 2 3 5.8
20 1 3 1 2 7.4 61 3 1 3 1 5.6
21 1 3 1 3 8.5 62 3 1 3 2 4.7
22 1 3 2 1 6.8 63 3 1 3 3 7.4
23 1 3 2 2 7.4 64 3 2 1 1 6.9
24 1 3 2 3 8.4 65 3 2 1 2 7.4
25 1 3 3 1 8.5 66 3 2 1 3 5.1
26 1 3 3 2 7.5 67 3 2 2 1 5.8
27 1 3 3 3 5.8 68 3 2 2 2 5.6
28 2 1 1 1 5.6 69 3 2 2 3 6.9
29 2 1 1 2 6.9 70 3 2 3 1 7.4
30 2 1 1 3 7.4 71 3 2 3 2 6.9
31 2 1 2 1 8.5 72 3 2 3 3 7.4
32 2 1 2 2 6.8 73 3 3 1 1 8.5
33 2 1 2 3 8.5 74 3 3 1 2 6.9
34 2 1 3 1 7.5 75 3 3 1 3 7.4
35 2 1 3 2 5.8 76 3 3 2 1 5.2
36 2 1 3 3 5.6 77 3 3 2 2 6.8
37 2 2 1 1 4.1 78 3 3 2 3 7.4
38 2 2 1 2 7.4 79 3 3 3 1 8.4
39 2 2 1 3 6.9 80 3 3 3 2 8.5
40 2 2 2 1 7.4 81 3 3 3 3 7.5
41 2 2 2 2 8.5
VERIFICATION RUN:
Table 6 shows test 37, optimum value of surface finish i.e. the predicted value of the surface finish is 4.1 µm.
95% Confidence Interval = 4.1 ± 0.01 µm, 99% Confidence Interval= 4.1 ± 0.0127 µm For validation conduct verification run using optimum combination A2B2C1D1.
We get A1B2C3D3 (Gap voltage 25V, Discharge current 15A, Pulse on time 50 us, Pulse off time 8 us ) the value of surface roughness is 4.256 µm, which is close to predicted value,
CONCLUSION
From this study, the optimum parameters related to the EDM of Shape Memory Alloy optimized to attain a low surface roughness. In this experiments nines sets conducted on shape memory alloy using copper electrode and L9 Taguchi orthogonal array. The input parameters taken such as Duty factor, Pulse on-time (Ton) and Discharge current (or pulse current).
From the experiment and design of experiment, the following conclusions were made;
The optimum parameter and level combination for best Surface Roughness is A2B2C1D1 (Gap Voltage 25V, Discharge Current 15A, Pulse On Time 50 µs, Pulse Off Time 8 us ).
From the interaction plot it states that all four parameters were more important for control the response parametes.The most effective parameter is dischage current which more affect on quality of suface finish.
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