Jour of Adv Research in Dynamical & Control Systems, 11-Special Issue, July 2017
Statistical Approach on Interaction Effect, Mean Response & S/N Ratio Analysis of Pulsed Current TIG Welding Parameters on Thermal Profile & Mechanical Properties of Al–SiC Composite Sivachidambaram Pichumani, PhD Research Scholar, School of Mechanical Engineering, SASTRA University, Thanjavur, India. E-mail:
[email protected] Raghuraman Srinivasan, Professor, School of Mechanical Engineering, SASTRA University, Thanjavur, India. E-mail:
[email protected].
Abstract--- Al-SiC composite welded using PCTIG welding experiment is designed using Taguchi L9 orthogonal array to reduce the number experiments from 81 to 9 experimental conditions. The parameters considered for PCTIG welding are peak current, base current, pulse frequency and pulse on time. The mechanical properties such as bend strength, weld centre micro hardness and thermal profile for peak temperature & cooling rate are studied in the above experimental conditions. The Interaction effect, signal to noise (S/N) ratio and mean response are developed to find the influence of each pulsed current parameter at various levels & the percentage of influence by pulsed current parameters on bend strength, weld centre micro hardness and thermal profile of peak temperature & cooling rate are analysed. From the statistical analysis, it is observed that pulse frequency has higher effect on weld zone micro hardness and the influencing parameters on bending load are identified as peak current & pulse on time. It is observed that peak temperature is highly influenced by pulse on time and pulse on time & pulse frequency has higher influence on the cooling rate. The slight variation from the desired values of pulsed current TIG welding parameters leads to higher deviation in the response. PCTIG welding parameters of peak current of 160A, base current of 60A, pulse on time as 50% and pulse frequency as 5Hz shows desired optimal results. Keywords--- Al-SiC Composite, PCTIG Welding, Signal to Noise (S/N) Ratio, Mean Response, Interaction Effect, Bend Strength, Micro Hardness.
I.
Introduction
Number of aluminum alloys are being studied intended for research and technological applications [1] and several aspects are considered with regard to the metallic matrix its composition [2], response to heat treatments, mechanical and corrosion behavior [3]. Aluminum has played continuous a key role in the development of metal matrix composites (MMCs) reinforced with a variety of ceramic materials including Al2O3, TiC, B4C, and SiC [3, 4]. This drawn the attention of research scientists and technologists on Al/SiC composite [5]. Stir casting route is more suitable for low wt % (< 20%) for mass production, the infiltration routes and powder metallurgy are more appropriate for wt % of the reinforcement (>40%) with components having lesser L/D ratio ranging from 0.75 to 1.25. This shows that the production of Al-SiC composite using stir casting has been proved economical and most suitable way [6], compared with other manufacturing processes such as powder metallurgy route and spray coating process [5, 6]. TIG welding on aluminum composite gives reduced weld strength because of higher heat generation in weld zone [7] and lesser cooling rate [8] of weld pool which brings coarse grain structure in weld zone and residual stresses developed in heat affected zone [9]. TIG welding of Al-SiC composite produces the Al4C3 phase which is more brittle in nature, leading to inferior weld quality [9]. Eliminating aluminum carbide development in TIG welding on Al-SiC composite is the challenge for enhancement in weld quality [10]. The issue of coarse grain microstructure amid TIG welding on aluminum combinations could be redressed by utilizing surface nucleation [11], microcooler addition [12], arc oscillation [13], impact of pulsed current system on aluminum alloy 6061 fatigue strength [14] and pulsed current on aluminum alloy 7075 tensile strength [15] to acquire fine grain microstructure. Among this pulsed current system has wide acknowledgement [16, 17], as it can be utilized continuously for wide mechanical applications with least changes in the existing system [18].
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Signal to noise (S/N) ratio and mean response are used to find the percentage effect of pulsed current parameters on the micro hardness, bending load and thermal profile. S/N ratio and mean response are compared with each other to validate percentage effect of pulsed current parameters. Interaction effect graphs are plotted to get a overview idea regarding the parameters and levels used in statistical analysis.
II.
Experimentation
To study the mean effect, interaction effect and S/N ratio analysis, the experiments are designed based on Taguchi L9 orthogonal array. PCTIG welding parameters of 4 factors and 3 levels through Taguchi L9 orthogonal array is considered for 9 experimental conditions. Autogenous TIG welding performed on Al-8%SiC composite material with a plate thickness of 5mm using ADOR CHAMPTIG 300AD welding machine as shown in figure 1. During welding, the thermocouple is placed 10mm away from the weld centre and 30mm from the welding starting place, to acquire data for time temperature profile. The data are acquired using Data Acquisition System (DAQ) which consists of LabView software coupled with National Instrument NI cDAQ 9174 kit comprising of temperature acquiring module -NI 9211. Micro hardness measured on weld centre, 1mm below the welded surface and it is measured using Shimadzu micro Vickers hardness tester as shown in figure 2 with according to the standard of ASTM E 384. Bend test is also performed with the standard of ASTM E190 on sub sized sample with dimensions of 100mm x 30mm x 5mm (L x W x T). Samples before and after bend test are shown in figure 3 and figure 4.
Figure 1: PCTIG Welding Machine with DAQ System
Figure 2: Vickers Micro Hardness Tester
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Figure 3: Bend Test Sample – before Bending
Figure 4: Bend Test Sample – after bending
III.
Results
Micro hardness, bend load, cooling rate and peak temperature during thermal profile are tabulated in table 1. These tabulated values are processed using Design Expert® statistical software, to evaluate the effect the peak current, base current, pulse on time and pulse frequency through interaction effect graphs, mean response and S/N ratio studies. Table 1: Results Condition Peak current (A) Base current (A) Pulse on time (%) Micro hardness (HV) Bending load (N) Peak temperature (K) Cooling rate (K/s)
IV.
1 160 40 60 61.2 1320 649 283.6
2 140 60 60 62.9 1380 583 282.1
3 150 60 40 65.3 880 667 292.4
4 140 40 40 71.3 1220 637 291.9
5 150 50 60 67.6 1270 608 282.3
6 140 50 50 67.2 1300 678 286.9
7 160 50 40 60.8 990 615 284.6
8 160 60 50 75.1 1460 747 294.5
9 150 40 50 63.2 880 648 290.4
Discussion
4.1. Micro Hardness Interaction Effect Figure 5 represents Interaction effect plot between peak current, base current, pulse on time and pulse frequency on micro hardness. It shows the combination effect of pulsed current parameters on micro hardness and it also shows the best combination of parameters with their levels in order to get higher micro hardness value. It is inferred that peak current of 160A, base current of 60A, pulse on time of 50% and pulse frequency of
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5Hz shows the maximized hardness value of above 72HV and actual experimental value for this condition is 75HV. This shows that predicted interaction effect values and the experimental results are in good agreement with each other.
Figure 5: Interaction Effect Graph for Micro Hardness S/N Ratio and Mean Response Table 2 shows the S/N ratio analysis and table 3 shows the mean response analysis. From these tables the effect percentage of pulsed current parameters on micro hardness has been evaluated. From table 2, pulse frequency has 50% & pulse on time has 25% influences on the micro hardness value. Peak current has 9.5% & base current has 14% which are comparatively lower effect percentage than the pulse on time and pulse frequency. Hence it is inferred that the slight change in pulse frequency and pulse on time has higher influence on micro hardness at peak current and base current. S/N ratio analysis in table 2 and mean response analysis in table 3 shows more or less same effect percentage of pulsed current parameters on micro hardness. Table 2: S/N Ratio Table for Micro Hardness Level 1 2 3 Delta Rank Percentage
Peak current (A) 36.53 36.30 36.31 0.22 4.00 9.57
S/N ratio Base current (A) 36.27 36.27 36.59 0.32 3.00 13.91
Pulse on time (%) 36.35 36.69 36.10 0.59 2.00 25.65
Pulse frequency (Hz) 35.89 37.06 36.19 1.17 1.00 50.87
Table 3: Mean Response Table for Micro Hardness Level 1 2 3 Delta Rank Percentage
Peak current (A) 67.13 65.37 65.70 1.77 4.00 9.85
Mean response Base current (A) Pulse on time (%) 65.23 65.80 65.20 68.50 67.77 63.90 2.57 4.60 3.00 2.00 14.30 25.60
Pulse frequency (Hz) 62.30 71.33 64.57 9.03 1.00 50.25
4.2. Bending Load Interaction Effect Interaction effect plot for bending load is plotted in figure 6. It shows the effect of pulsed current parameters of peak current, base current, pulse on time and pulse frequency on bending load. It also shows the best combination of parameter with its level of peak current of 160A, base current of 60A, pulse on time of 50% and pulse frequency of 5Hz for the maximum bending load of 1400N. This value is found nearly equal to actual value obtained in this condition of 1460N. This similarity confirmed from interaction effect graph and the
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experimental results proves that the experimental findings and interaction effect values through Minitab statistical software are in good agreement with each other.
Figure 6: Interaction Effect Graph for Bending Load S/N Ratio and Mean Response Table 4 shows the S/N ratio analysis and table 5 shows the mean response analysis for bending load. From these tables effect percentage of pulsed current parameters on bending load has been evaluated. From table 4, peak current of 33%, pulse on time of 32% and pulse frequency of 26% influences on the bending load of the PCTIG welded sample. Base current has only 9.5% effect percentage which was comparatively lower effect percentage than the other pulsed current TIG welding parameters. This shows peak current, pulse on time and pulse frequency has significant influence on bending load. S/N ratio analysis in table 4 and mean response analysis in table 5 shows similar effect percentage of pulsed current parameters on bending load. Table 4: S/N Ratio Table for Bending Load Level 1 2 3 Delta Rank Percentage
Peak current (A) 2.27 -0.05 1.87 2.32 1.00 32.87
S/N ratio Base current (A) 1.01 1.42 1.66 0.65 4.00 9.20
Pulse on time (%) 0.18 1.49 2.43 2.25 2.00 31.96
Pulse frequency (Hz) 0.53 2.36 1.19 1.83 3.00 25.97
Table 5: Mean Response Table for Bending Load Level 1 2 3 Delta Rank Percentage
Peak current (A) 1.30 1.01 1.26 0.29 1.00 32.12
Mean response Base current (A) Pulse on time (%) 1.14 1.03 1.87 1.21 1.24 1.32 0.10 0.28 4.00 2.00 11.07 31.01
Pulse frequency (Hz) 1.08 1.32 1.17 0.23 3.00 25.80
4.3. Peak Temperature Interaction Effect Figure 7 depicts Interaction plot between peak current, base current, pulse on time and pulse frequency on peak temperature near weld zone. It shows the combination effect of pulsed current parameters on peak temperature near weld zone and it also shows best combination of parameter with its level to get higher peak temperature value. It is inferred from the figure that peak current of 160A, base current of 60A, pulse on time of
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50% and pulse frequency of 5Hz shows highest peak temperature of 740K and this interaction effect value is nearly equal to the actual value of 747K found in this condition. This shows that interaction effect predictions is precisely correlating with the experimental value.
Figure 7: Interaction Effect Graph for Peak Temperature S/N Ratio and Mean Response Table 6 showed the S/N ratio analysis and table 7 showed the mean response analysis for the peak temperature. From these tables effect percentage of pulsed current parameters on peak temperature has been evaluated. An evaluation result shows that pulse frequency has 27% & pulse on time has 40% influences on the peak temperature near weld zone. Peak current has 19% & base current has 14% which is comparatively lower percentage effect than the pulse on time and pulse frequency. So the slight change in pulse frequency and pulse on time has higher influence on peak temperature than the peak current and base current. S/N ratio analysis in table 6 and mean response analysis in table 7 shows the effect percentage of pulsed current parameters on peak temperature near weld zone are nearly equal. Table 6: S/N Ratio Table for Peak Temperature S/N ratio Level 1 2 3 Delta Rank Percentage
Peak current (A) 51.07 51.30 51.90 0.83 3.00 18.74
Base current (A) 51.40 51.11 51.75 0.64 4.00 14.45
Pulse on time (%) 51.27 52.38 50.61 1.77 1.00 39.95
Pulse frequency (Hz) 50.66 51.75 51.85 1.19 2.00 26.86
Table 7: Mean response table for peak temperature Level 1 2 3 Delta Rank Percentage
Peak current (A) 359.70 368.00 397.30 37.70 3.00 19.17
Mean response Base current (A) Pulse on time (%) 371.70 366.70 360.70 418.00 392.70 340.30 32.00 77.70 4.00 1.00 16.27 39.50
Pulse frequency (Hz) 342.30 391.00 391.70 49.30 2.00 25.06
4.4. Cooling Rate Interaction Effect Cooling rate’s interaction plot between peak current, base current, pulse on time and pulse frequency is shown in figure 8. Here combination effect of pulsed current parameters on cooling rate near weld zone and it also shows best combination of parameter with its level to achieve maximum cooling rate. It also shows peak
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current of 160A, base current of 60A, pulse on time of 50% and pulse frequency of 5Hz has the maximum cooling rate at 293K/s and actual experimental value found in this condition is 295K/s. This shows that interaction effect predictions and the experimental results are in good agreement with each other.
Figure 8: Interaction Effect Graph for Cooling Rate S/N Ratio and Mean Response Table 8 shows the S/N ratio analysis and table 9 shows the mean response analysis for effect percentage analysis of pulsed current parameters on cooling rate. It is inferred that the pulse on time has highest of 49% influence on the cooling rate. Base current of 25%, pulse frequency of 19% shows that peak current has lowest of 8% effect on cooling rate. So the slight change in pulse on time has higher influence than the peak current, pulse frequency and base current. S/N ratio analysis and mean response analysis shows similar effect percentage of pulsed current parameters on cooling rate. This showed S/N ratio analysis and mean response on above experiments are consistent. Table 8: S/N Ratio Table for Cooling Rate Level 1 2 3 Delta Rank Percentage
Peak current (A) 292.76 302.90 294.84 10.14 4.00 7.61
S/N ratio Base current (A) 307.06 275.34 308.10 32.76 2.00 25.59
Pulse on time (%) 314.34 320.58 255.58 65.00 1.00 48.78
Pulse frequency (Hz) 282.62 307.97 299.78 25.35 3.00 19.02
Table 9: Mean Response Table for Cooling Rate Mean response Level Peak current (A) 13.96 1 15.36 2 14.23 3 1.39 Delta 4.00 Rank Percentage 8.07
V.
Base current (A) 15.63 11.62 16.30 4.69 2.00 27.15
Pulse on time (%) 16.61 17.30 9.64 7.66 1.00 44.37
Pulse frequency (Hz) 12.68 16.21 14.66 3.52 3.00 20.41
Conclusion
Interaction effect, signal to noise ratio (S/N) and mean response are developed to evaluate the influence of each pulsed current parameter at each levels in order to calculate the effect percentage of pulsed current parameters on bend strength, weld centre micro hardness and thermal profiles of peak temperature & cooling rate during PCTIG welding of Al-SiC composite.
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Pulse frequency has 50% & pulse on time has 25% influence on the micro hardness value. Peak current of 9.5% & base current of 14% is comparatively lower percentage effect than the pulse on time and pulse frequency. Peak current has 33%, pulse on time has 32% and pulse frequency has 26% of influence on the bending load of the PCTIG welded sample. Pulse on time has 49% influence on the cooling rate. Base current has 25%, pulse frequency has 19% & peak current has 8% which is comparatively lower effect on cooling rate. Pulse frequency has 27% & pulse on time has 40% influence on the peak temperature near weld zone. Peak current of 19% & base current of 14% is comparatively lower percentage effect than the pulse on time and pulse frequency. It is inferred that the pulse frequency is having higher effect on weld zone micro hardness. For bending load major influencing parameters are peak current & pulse on time. Peak temperature is highly influenced by pulse on time. Pulse on time and pulse frequency is having higher influence on the cooling rate. PCTIG welding parameters such as peak current of 160A, base current of 60A, pulse on time as 50% and pulse frequency as 5Hz shows highly desired results for determining the bending load, micro hardness, thermal profile of peak temperature and cooling rate. The deviation between actual experimental values and desired predicted values using interaction effect, S/N ratio analysis & Mean response analysis proves that the study is statistical significant.
Acknowledgement The authors express their sincere thanks with gratitude to the Vice-Chancellor of SASTRA University for allowing us to pursue our research work in the School Mechanical Engineering.
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