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# Optimization of the welding parameters in resistance spot welding

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### Optimization of the welding parameters in resistance spot welding

1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 31 OPTIMIZATION OF THE WELDING PARAMETERS IN RESISTANCE SPOT WELDING 1 B. D. Gurav ME Student ,Department of Mechanical Engineering, Government Engineering College, Aurangabad, Maharashtra, India. 2 S.D. Ambekar Assistant Professor ,Department of Mechanical Engineering, Government Engineering College, Aurangabad, Maharashtra, India. ABSTRACT Resistance spot welding is commonly used in the automotive industry, because it has the advantage which is high speed, high-production assembly lines and suitability for automation. The objective of this paper is to find out the influence of the various process parameters on the tensile shear strength of the resistance spot welded joints for CRCA steel sheets. The experimental studies were conducted under varying welding current, welding time, and electrode force. By doing the analysis, an optimum parameter combination for the maximum tensile shear strength was obtained. The settings of the process parameters were determined by using Taguchi’s experimental design method. Orthogonal arrays of Taguchi, the signal-to-noise (S/N) ratio, the analysis of variance (ANOVA) employed to find the optimal process parameter levels and to analyze the effect of these parameters on tensile shear strength values. Keywords: Resistance spot welding, CRCA steel, Taguchi method, S/N ratio, ANOVA. I. INTRODUCTION Resistance spot welding (RSW) is a process in which metal surfaces are joined in one or more spots by resistance to the flow of electric current through work pieces that are held together under force by electrodes. The weld is made by a combination of heat, pressure, and time. The process is used for joining sheet materials and uses shaped copper alloy electrodes to apply pressure and convey the electrical current through the work piece. Heat is developed mainly at the interface between two sheets, eventually causing the material being welded to melt, forming a molten pool, the INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 4, Issue 5, September - October (2013), pp. 31-36 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 32 weld nugget. The molten pool is contained by the pressure applied by the electrode tip and the surrounding solid metal. The resistance spot welding has the advantage which is high speed and suitability for automation. Ugur Esme [1] has studied optimization of RSW process parameters for SAE 1010 steel using Taguchi method. He investigated that increasing welding current and electrode force are prime factors controlling the weld strength. He concluded that Taguchi method can be effectively used for optimization of spot welding parameters. D.S. Sahota, Ramandeep Singh, Rajesh Sharma, Harpreet Singh [2] has studied the effect of parameters on resistance spot weld of ASS316 material. In order to his study the significance of the process parameters i.e. current, electrode force and weld cycles, towards the percentage improvement in material hardness. From his results it is clear that parameters significantly affect both the mean and the variation in the percentage improvement in Hardness values of the ASS316 material. A.K. Pandey, M.I. Khan. K.M. Moeed [3] investigation indicate the welding current to be the most significant parameter controlling the weld tensile strength as well as the nugget diameter for AISI-1008 steel sheets .Also they effectively use taguchi method for optimization of spot welding parameters[4]. Niranjan Kumar Singh and Dr. Y. Vijayakumar [5] has presented an investigation on the optimization and effect of welding parameters on indentation of spot welded AISI 301L stainless steel. The level of importance of the welding parameters on indentation is determined by ANOVA (main effect plots). Based on ANOVA method, the highly effective parameters on indentation are found as weld cycle, interaction between weld current & weld cycle and interaction between weld current, weld cycle & hold time whereas weld current, hold time and cool time were less effective factors. Spot welding parameters and heat generation The three main parameters in spot welding are current, contact resistance and weld time. In order to produce good quality weld the above parameters must be controlled properly. The amount of heat generated in this process is governed by the formula, Q = I2 R T Where Q = heat generated, Joules I = current, Amperes R = resistance of the work piece, Ohms T = time of current flow, second Taguchi approach The quality engineering methods of Dr. Taguchi is one of the important statistical tools of total quality management for designing high quality systems at reduced cost. Taguchi recommends a three stage process to achieve desirable product quality by system design, parameter design and tolerance design. While system design helps to identify working levels of the design parameters, parameter design seeks to determine levels of parameter that provide the best performance of product or process under study. The optimum condition is selected so that the influence of uncontrollable factors (noise factors) causes minimum variation to system performance. Orthogonal arrays, ANOVA, S/N ratio analysis and F-test are the essential tools for parameter design. Tolerance design is a step to fine-tune the results of parameter design [6].
3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 33 II. EXPERIMENTAL DETAILS The specimens were cut from a sheet of 1..2 m x 2.5 m. The Specimens were cut parallel to the rolling action of the sheets. The dimensions are 100 mm length and 25 mm width, the overlap being equal to the width of the specimen. This overlap was chosen as per AWS recommendation [7]. The material used in the present work is close rolled close annealing steel (Grade IS 513 D) sheet of 2 mm thickness. The chemical composition for each element of the above material is listed below in table 2.1: Table 2.1 Chemical analysis and Mechanical Properties of Work piece Materials Percent Composition(%) C Mn S P Al 0.045 0.21 0.008 0.015 0.05 Mechanical Properties Yield strength (Mpa) Tensile strength (Mpa) % Elongation Hardness (HRB) Ra (micron) 196 322 46 47.7 1.1 2.1 Selection of the welding parameters and their levels Following input and output parameters are considered:Input parameters selected are welding current, weld time, and welding force. Output parameter predicting strength of weld joint is Tensile- shear strength. The input parameters are shown in table 2.2. Table-2.2 Process parameters and Their Levels Level Welding Current (KA) Electrode Force (KN) Welding Time (Cycle) 1 12.0 3 8 2 12.5 4 9 3 13.5 5 10 2.2 Design the Orthogonal array Depending upon number of levels in a factor, a 2 or a 3 level OA can be selected. If some factors are two-level and some are three-level, then whichever is predominant would indicate which kind of OA is to be selected. Once the decision is made about the right OA, then the number of trials for that array would provide the adequate total dof, When required dof fall between the two dof provided by two OAs, the next larger OA must be chosen. 2.2 Overall loss function & its S/N ratio Tensile shear strength of the welded structures belongs to the larger-the-better quality characteristics. The loss function of the larger-the-better quality characteristics can be expressed as [8] where n is the number of tests, and yi the experimental value of the ith quality characteristic, Lj overall loss function, and j ç is the S/N ratio. By applying Equations (1)–(2), the ç corresponding to the overall loss function for each experiment of L9 was calculated and given in Table 2.3 The effect of each welding process parameter on the S/N ratio at different levels can be separated out because the experimental design is orthogonal. The S/N ratio for each level of the welding process
4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 34 parameters is summarized in Table 2.3 The mean S/N ratio for each level of the welding parameters is summarized and called the S/N response table for tensile shear strength (table 2.4) Table 2.3 Experimental data for tensile shear (T- S) strength and S/N ratio Experiment No. Welding Current (KA) Electrode Force (KN) Welding Time (Cycle) T- S (KN) S/N Ratio 1 1 1 1 10.18 20.1550 2 1 2 2 10.10 20.0864 3 1 3 3 10.54 20.4568 4 2 1 2 10.83 20.6926 5 2 2 3 11.55 21.2516 6 2 3 1 10.54 20.4568 7 3 1 3 11.53 21.2366 8 3 2 1 10.94 20.7803 9 3 3 2 10.58 20.4897 Table 2.4 Response table for S/N ratio for T-S strength Level Welding Current Electrode Force Welding Time 1 20.23 20.69 20.46 2 20.80 20.71 20.42 3 20.84 20.47 20.98 Delta 0.60 0.24 0.56 Rank 1 3 2
5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 35 3. ANALYSIS OF VARIANCE A better feel for the relative effect of the different welding parameters on the tensile shear strength (TS) was obtained by decomposition of variance, which is called analysis of variance (ANOVA) . The relative importance of the welding parameters with respect to the TS was investigated to determine more accurately the optimum combinations of the welding parameters by using ANOVA. The results of ANOVA for the welding outputs are presented in Table 3.1 Statistically; F-test provides a decision at some confidence level as to whether these estimates are significantly different. Larger F-value indicates that the variation of the process parameter makes a big change on the performance. Table 3.1 Analysis of variance for SN ratios CF DOF SS MS F Ratio P % C Welding Current 2 0.68681 0.34340 166.36 0.006 49.72 Electrode Force 2 0.10844 0.05422 26.27 0.037 7.85 Welding Time 2 0.58188 0.29094 140.94 0.007 42.13 Error 2 0.00413 0.00206 Total 8 1.38125 R-sq =99.7 % R-Ad=98.8 % Significant at 95% confidence 4. CONCLUSIONS This paper is presented an investigation on the optimization and the effect of welding parameters on the tensile shear strength of spot welded CRCA steel sheets. 1. The experimental results show that the right section of the input parameters are high current ,medium electrode force and high weld time. 2. The response of S/N ratio with respect to tensile strength indicates the welding current to be the most significant parameter that controls the weld time are comparatively less significant in this regard. 3. The contribution of welding current ,weld time and electrode force towards tensile strength is 49.72%,42.19 %,7.85 % respectively as determined by the ANOVA method. 4. Optimal results have been found by taguchi method using high current 134.5 KA, medium electrode force 4 KN, and high welding time of 10 sec. 5. REFERENCES [1] Ugur Esme., Application of Taguchi method for the optimization of resistance spot welding process, The Arabian Journal for Science and Engineering. 2009, 519-528. [2] D.S. Sahota, Ramandeep Singh, Rajesh Sharma, Harpreet Singh, Study of effect of parameters on resistance spot weld of ASS316 material, Mechanica Confab 2013, 67-78. [3] A.K. Pandey, M.I. Khan. K.M. Moeed, Investigation of the effect of current on tensile strength and nugget diameter of spot welds made on AISI-1008 steel sheets, International Journal of Technical Research and Applications,2013, 01-08. [4] A.K. Pandey, M.I. Khan. K.M. moeed, Optimization of the welding parameters in resistance spot welding. International Journal of Engineering Science and Technology,2013,234-240.
6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 36 [5] Niranjan Kumar Singh and Dr. Y. Vijayakumar, Application of Taguchi method for optimization of resistance spot welding of austenitic stainless steel AISI 301L, The International Institute for Science, Technology and Education ,2012,49-61. [6] P.J. Ross. 2005. Taguchi Techniques for Quality Engineering. 2nd Ed. Tata McGraw Hill. [7] Handbook for resistance spot welding, (2005)http://www.millerwelds.com/pdf/Resistance.pdf [8] Montgomery, Design and Analysis of Experiments. Singapore: Wiley, 2001. [9] Aniruddha Ghosh and Somnath Chattopadhyaya, “Submerged Arc Welding Parameters Estimation Through Graphical Technique”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 1, Issue 1, 2010, pp. 95 - 108, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [10] U. D. Gulhane, A. B. Dixit, P. V. Bane and G. S. Salvi, “Optimization of Process Parameters for 316l Stainless Steel using Taguchi Method and Anova”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 67 - 72, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [11] Ravi Butola, Shanti Lal Meena and Jitendra Kumar, “Effect of Welding Parameter on Micro Hardness of Synergic MIG welding of 304l Austenitic Stainless Steel”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 3, 2013, pp. 337 - 343, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.