EXPERIMENTAL INVESTIGATION ON RESISTANCE SPOT WELDING OF ALUMINIUM ALLOY 6082T651 USING INTERLAYER OF SS304

Transcription

1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 7, July 2018, pp , Article ID: IJMET_09_07_036 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed EXPERIMENTAL INVESTIGATION ON RESISTANCE SPOT WELDING OF ALUMINIUM ALLOY 6082T651 USING INTERLAYER OF SS304 Arick. M. Lakhani Faculty of Technology and Engineering, C.U Shah University, Wadhwan, Gujarat, India Assistant Professor, Department of Mechanical Engineering, V.V.P Engineering College, Rajkot, Gujarat, India Dr. P.H. Darji Professor and Principal, C.U. Shah College of Engineering and Technology, C.U Shah University, Wadhwan, Gujarat, India ABSTRACT It is the need of current automotive industries towards economical fabrication with improved mechanical properties of aluminium thin sheets. This paper summarize comparative work on the resistance spot welding of aluminium alloy 6082T651, without interlayer and with interlayer of SS304 having 0.3 mm thickness. Welding current (AMP), electrode force (N) and welding time (Cycle) were studied as input parameters. Range of Electrode Force was 2300 N, 3600 N and 4900 N, Welding Time was 1 cycle, 3 cycles and 5 cycles, Welding Current was 23 KA, 26 KA and 29 KA. Taguchi method is used to generate design matrix for experimental work. Failure load and nugget diameter were output parameters for this work. Effect of interlayer on the failure load is area of interest in this work and how thickness of interlayer will affect the failure load is observed during experiments. It was observed that formation of inter-metallic compounds between aluminium alloy 6082T651 and SS304 significantly affects the failure load of joints. Key words: Resistance spot welding, Taguchi Method, Interlayer, Optimization. Cite this Article: Arick. M. Lakhani and Dr. P.H. Darji, Experimental Investigation on Resistance Spot Welding of Aluminium Alloy 6082T651 using Interlayer of SS304, International Journal of Mechanical Engineering and Technology 9(7), 2018, pp editor@iaeme.com

2 Arick. M. Lakhani and Dr. P.H. Darji 1. INTRODUCTION Optimized design of the vehicle is the need of automobile industry to achieve better performance with lower manufacturing cost. However light weight car bodies for the reduction in consumption of natural sources of energy is also an important factor [1]. If aluminium is used for entire car structure because of its light weight characteristics, the overall cost increases drastically [2]. Also, universal replacement of aluminium to steel is difficult due to formability, weldability and corrosion resistance. The above criterion is achieved by using different material along with aluminium so that functionalities of materials can be utilized to the fullest extent [3]. Steel and aluminium are widely used as construction materials for automotive industries. Hence hybrid structural body of aluminium and steel is required as steel is less expensive than aluminium [4]. Conventional joining processes applied for joining of steel to aluminium were non- fusion joining methods such as adhesive bonding and mechanical fastening done [5]. Resistance spot welding process is a boon for automotive industries, there are approximately 5000 spot welds in every car, susceptible to various loading conditions. Thus, high strength of spot weld is must in order to sustain various loads. RSW process utilizes the concentrated Joule heat on sheets to be welded. These sheets are firmly held together through which current flows for particular time duration and hence heat is produced [6]. Thus a good quality spot weld joint is obtained by providing the optimum combination of electrode force, welding time and welding current which are our input parameters for the present study. RSW of aluminium is difficult because sufficient heat is not produced due to its low specific heat. High thermal conductivity of aluminium is responsible for the diffusion of heat into electrodes and the area surrounding nugget (welded joint). There are inherent differences in electrical, mechanical and thermal properties of aluminium and steel [7]. It is difficult to achieve strong metallurgical bonds (Inter-metallic compounds) of Fe-Al between them with low current for direct fusion welding process such as Resistance Spot Welding process. Due to low heat generation and high heat conduction of aluminium alloy high electric current is required which will form coalescence in the faying surfaces [8]. Taguchi method is quick and cost effective when applied to statistics of experiments for optimizing products and processes, by which there is an enhancement of performance and capabilities [9]. Taguchi techniques have been extensively used in engineering design suggested [10]. Thus quality characteristics or responses of RSW process based on the effect of various parameters can be studied through Taguchi method. This method consists of various sub-design procedure such as system design, parameter design and tolerance design procedure for obtaining accurate results. System design is applied to produce a prototype design by identifying the working levels of process parameters to improve performance characteristics [11]. Parameter design is applied to achieve best quality output at lower cost(less number of experiments) by appropriate selection of Orthogonal Array (OA) which depends on the number of process parameters and their range of values. The performance of experiment is carried out as per the sequence of OA. The calculated difference between experimental value and desired value is known as loss function. Taguchi method used this value of loss function to measure the deviation of response from desired value. In Taguchi method Signal means desired value which represents mean of output characteristics and Noise means the undesired value which represents squared deviation of output characteristics. This Signal to Noise (S/N) ratio analysis will receive the value of overall loss function as input to transform editor@iaeme.com

3 Experimental Investigation on Resistance Spot Welding of Aluminium Alloy 6082T651 using Interlayer of SS304 S/N ratio is having three types of quality characteristics in its analysis Lower the better, Larger the better, and Nominal the best. For each level of process parameters, S/N ratio is calculated on the basis of S/N ratio analysis. Larger S/N ratio suggests more appropriate quality characteristics regardless of its type (Lower the better, Larger the better, and Nominal the best. The highest value of S/N ratio gives the process parameters of optimum level. Furthermore, to see which process parameters are statistically significant, statistical Analysis Of Variance (ANOVA) is performed and hence process parameters can be predicted for optimal combination. Thus there are three important tools for parameter design- OA, S/N ratio analysis, ANOVA. In the end, confirmation runs are performed to validate the obtained optimum process parameters from parameter design. Tolerance design is used to filter the results obtained from parameter design. In this paper, Taguchi method is applied to RSW process to recognize process parameters which affect variability in output parameters like failure load and nugget diameter while using the interlayer of SS304. Computation of S/N ratio from the parametric combination of spot welding process gives performance characteristics whose base is experimental data. A set of optimum welding parameters was obtained from S/N ratio analysis. Also, investigation of predominant process parameters was done by applying ANOVA. 2. WELDING PROCESS PARAMETERS Key welding parameters for the RSW are welding time, welding current and electrode force. Electrode force is the result of the compressive effect of electrodes which apply to the base metal prepared for the welding. This electrode force divides into two parts, squeeze force and actual force for welding. Squeeze force stands for the holding of base metal and actual force is welding force which influences the heat generated during welding. This applied force is inversely proportional to the heat energy. Low electrode force cannot make good quality weld thus excessive welding force can lead to expulsion. The optimum value of the electrode force is required for the sound weld. Welding current is essential for heat generation. Welding current plays the major role in the RSW process and also gives vital effect on the failure load and nugget diameter. Welding current should be as low as possible to reduce excessive heat input and high enough to get sound welding of material as per weldability. Optimum control of heat input is very important for the qualitative joint. Welding time is directly proportional with heat generation. As welding time increases, the heat input will increases. For AC power source unit time measurement is in cycle with 50 cycle/seconds for the typical 50 Hertz (Hz) Indian machine. Figure 1, shows the input and output parameters considered for this study. Figure 1 Selected input and output parameters for RSW process editor@iaeme.com

4 Arick. M. Lakhani and Dr. P.H. Darji 3. MATERIALS AND EXPERIMENTAL PROCEDURE Two sets of designed experiments were performed, to investigate the effect of SS304 interlayer (20mm x 25mm x 0.3mm) with aluminium alloy 6082T651 (100mm x 25 mm x 1mm) in RSW process on strength of weld joint having a lap over of 20mm in both case. Various experiments were conducted, to find out appropriate thickness of interlayer. 0.1 mm, 0.2 mm and 0.3 mm of interlayer thicknesses were studied. Based on these experiments, appropriate quality of weld was obtained with use of 0.3 mm interlayer thickness of SS304. Chemical and mechanical properties for both aluminium alloy 6082T651 and SS304 is shown in Table 1 and Table 2 respectively. Aluminium alloy 6082T651 is extensively used in aerospace industries, automobiles, and other applications. Surfaces of sheets were abraded randomly with silicon carbide P220 grade (Emery paper) [12].Further, it was cleaned by dry air jet, prior to welding. Figure 2 and figure 3, shows the arrangement of experimental set up for (i) Al/Al weld without interlayer (ii) Al/Al weld with 0.3mm interlayer of SS304 respectively. Figure 2 Test coupons dimensions for Al/Al weld without interlayer (not to scale, dimensions are in mm). Figure 3 Test coupons dimensions for Al/Al weld with 0.3mm interlayer of SS304 (not to scale, dimensions are in mm). Table 1 Chemical (wt %) and mechanical properties of aluminium alloy 6082T651. Tensile Strength (MPa) Yield strength (MPa) Alloying elements Si Mn Mg Fe Cu Al Tensile Strength (MPa) Yield Strength (MPa) Table 2 Chemical (mass %) properties of SS304. Alloying Elements Si Mn C P S Ni Cr Fe Bal. Single values are maximum 3.1. Design of Orthogonal Array (OA) Orthogonal array gives the systematic sequence of experiments which can be further statistically analyzed [13,14]. Also, it is used to see the effect of various process parameters on characteristics (Output parameters Failure load and Nugget diameter). The control over editor@iaeme.com

5 Experimental Investigation on Resistance Spot Welding of Aluminium Alloy 6082T651 using Interlayer of SS304 process parameters at various levels to observe the effect is possible by this method. Moreover, which process parameters are needed to control at which levels can be determined, by OA [15]. For which their maximum and minimum values of process parameters must be known through in-depth research of process and its process parameters. Larger the range of values more values can be tested and vice versa. Process parameters selected for RSW were electrode force (N), welding current (KA), and welding time (Cycle). For each process parameter levels were identified to obtain best characteristics of weld joint from the available range of spot welding. L9 OA was selected through Taguchi method for 3 levels and 3 process parameters having 8 degrees of freedom. Total 9 experiments were performed for each set (i) Al/Al weld without interlayer (ii) Al/Al weld with 0.3 mm interlayer of SS304 using L9 Orthogonal Array (OA). Table 3 shows the design matrix used for the experimental work which is generated by the L9 orthogonal array. Table 4 shows the experimental layout by which experiments were conducted. Table 1 Design of Experiment for both the sets (i) Al/Al weld without interlayer (ii) Al/Al weld with 0.3mm interlayer of SS304. Process Parameters Level Output Parameters Electrode Force (N) Welding Time (Cycle) Nugget Diameter (mm) Welding Current (KA) Failure Load (N) Table 4 Experimental layout Using L9 Orthogonal Array for both the sets (i) Al/Al weld without interlayer (ii) Al/Al weld with 0.3mm interlayer of SS304. Experiment number A Electrode Force (N) Levels of process parameters B Welding Time (Cycle) C Welding Current (KA) Squeeze time second, hold time second and off time second was kept constant during all experiments. The geometry and material (copper) of the electrode was kept constant throughout the experiments for both the sets. Figure 4 and figure 5, shows the sample coupons for the inspection of Failure load (KN) and Nugget diameter (mm) respectively for (i) Al/Al weld without interlayer (ii) Al/Al weld with 0.3mm interlayer of SS304 respectively editor@iaeme.com

6 Arick. M. Lakhani and Dr. P.H. Darji 4. RESULT AND DISCUSSION Table 5 shows the results of experiments for failure load and nugget diameter. Nugget diameter was measured with the help of digital Vernier caliper and failure load was tested on universal testing machine. Figure 4 Sample coupons for the inspection of Failure load (KN) and Nugget diameter (mm) for Al/Al weld without interlayer. Figure 5 Sample coupons for the inspection of Failure load (KN) and Nugget diameter (mm) for Al/Al weld with 0.3mm interlayer of SS304. Table 5 Results of experiments for failure load and nugget diameter for both the sets (i) Al/Al weld without interlayer (ii) Al/Al weld with 0.3mm interlayer of SS304. Without With interlayer of Process Parameters No. Of interlayer 0.3 mm SS304 Exp. Electrode force (N) Welding time (Cycle) Welding Current (KA) F.L (N) N.D (mm) F.L (N) N.D (mm) S/N Ratio Analysis The goal of this investigation was to maximize the failure load and optimize the nugget diameter. Thus larger is better for and nominal is best was applied to failure load and nugget diameter respectively. Equation (1) and (2) represents expressions for calculation of S/N ratio for larger is better and nominal are best characteristics [16] editor@iaeme.com

7 Experimental Investigation on Resistance Spot Welding of Aluminium Alloy 6082T651 using Interlayer of SS304 Where, x i is S/N ratio, y ij is the i th quality characteristics value at the j th test ( i = 1,2, m; j = 1,2, n) Where, is i th average quality characteristics experimental value; ( ) is the corresponding deviation and n is the total number of tests. Figure 6, represents the S/N ratio graphs of Al/Al weld without interlayer. For 9 experiments of Al/Al weld without interlayer total mean of S/N ratio was calculated and is shown in table 6. Figure 6 S/N ratio graphs of Al/Al weld without interlayer, for nugget diameter and failure load respectively. Table 6 S/N response for failure load and nugget diameter for Al/Al weld without interlayer. Output Parameter Nugget Diameter Failure Load S/N Ratio Process Total Mean Max- Units Level Level Level Parameters S/N Min Electrode Force N Welding Time Cycle Welding Current KA Electrode Force N Welding Time Cycle Welding Current KA editor@iaeme.com

8 Arick. M. Lakhani and Dr. P.H. Darji S/N Ratio for Nugget Diameter S/N Ratio for Failure Load Figure 1 S/N ratio graphs of Al/Al weld with 0.3mm interlayer of SS304, for failure laod and nugget diameter. Table 7 S/N response for failure load and nugget diameter for Al/Al weld with 0.3mm interlayer of SS304. Output Parameter Nugget Diameter Failure Load S/N Ratio Process Total Mean Max- Units Level Level Level Parameters S/N Min Electrode Force N Welding Time Cycle Welding Current KA Electrode Force N Welding Time Cycle Welding Current KA Figure 7, represents the S/N ratio graphs of Al/Al weld with 0.3mm interlayer of SS304. For 9 experiments of Al/Al weld with 0.3mm interlayer of SS304, total mean of S/N ratio was calculated and is shown in table 7. From Table 5 and S/N ratio analysis it was found that failure load of Al/Al weld with 0.3mm interlayer of SS304 is greater, and hence further analysis ANOVA was carried out for the same Analysis of Variance (ANOVA) Mean squares against experimental errors are compared with specific confidence levels by ANOVA to see the significance of all factors [17,18]. ANOVA is applied to observe the sensitivity of process and their significance on quality characteristics of failure load and nugget diameter of the weld joint. In both cases, welding without interlayer and welding with the interlayer of 0.3mm SS304, the confidence level was constant at 95%. Large F-value of process parameter indicates that it affects the responses more significantly. Table 8 and table 9, shows the ANOVA table failure load and nugget diameter for Al/Al weld with 0.3mm interlayer of SS304. Welding time (cycle) have more effect on the output parameters as its F-value is larger than other parameters. Also, P-values are less than 0.05 so it is significant to the output. The value of the R-square is also near to 1 and matching with the confidence level of 95% editor@iaeme.com

9 Source DF Seq. SS Value Contributio n Adj SS Adj MS F-Value P-Value S R-sq R-sq (adj) R-sq (pred) Source DF Seq SS Value Contributio n Adj SS Adj MS F Value P Value S R-Sq R-sq (adj) R-sq (pred) Experimental Investigation on Resistance Spot Welding of Aluminium Alloy 6082T651 using Interlayer of SS304 Values of R-Square and P-Values are appropriate as per ANOVA standards. Hence it proves that the model is significant and selection of process parameters is appropriate for the resistance spot welding process. Table 8 ANOVA table of failure load Al/Al weld with 0.3mm interlayer of SS304. N % % % Cycle % KA % % Error % Total % Table 9 ANOVA table of nugget diameter Al/Al weld with 0.3mm interlayer of SS304. N % Cycle % KA % Error % Total % % % % 4.3. Empirical Relation A regression equation is presented here to develop the empirical relation between the input and output parameters for all the experiments. With the help of regression, it can be possible to develop the model for any range of the input, between the levels selected for the experiments. It is developed with the help of ANOVA. Equation (3) and (4) are the Advance regression equations which gives the values failure load and nugget diameter for Al/Al weld with 0.3mm interlayer of SS304. N.D. = N_ N_ N_ Cycle_ Cycle_ Cycle_ KA_ KA_ KA_29 (3) F.L. = N_ N_ N_ Cycle_ Cycle_ Cycle_ KA_ KA_ KA_29 (4) By this equations, it is clearly seen that every level have its significant effect on the output parameter with specific efficiency. Every level of the experiment is mentioned in the equation so that difference between effect of every level can be obtained directly. The empirical relation developed on the basis of the maximum and minimum range selected, and these equations predict the result for welding of aluminium alloy 6082T251 with Al/Al weld with 0.3mm interlayer of SS editor@iaeme.com

10 Arick. M. Lakhani and Dr. P.H. Darji With the help of ANOVA response and S/N response, all the results are appropriate with each other which proves that the input parameters are authentic for the quality welding. ANOVA graph also verifies the results of S/N response. Figure 7, shows the S/N ratio graph for Al/Al weld with 0.3mm interlayer of SS304. Peak values in the graph show the optimize value obtained from the Taguchi analysis. Thus, following values are obtained as an optimum value for Al/Al weld with 0.3mm interlayer of SS304. Nugget Diameter 3600 N, 3 Cycle, 29 KA and Failure Load 2300 N, 5 Cycle, 29 KA. These values are used in the confirmatory test to validate the process parameter with software output. In the case of failure load, maximum value obtained in the output in optimized value and in nugget diameter, the optimal values are optimized value by Taguchi method. Figure 8, shows the contribution of input process parameters on nugget diameter and failure load. 5. CONFIRMATION TEST Based on the values obtained by Taguchi optimization, confirmation test was carried out and following results were confirmed as shown in Table 10. Results reflects the error less is than 10 % which shows that optimized value gives the best result and indicates of it being fit for selection. Figure 2 Significance of RSW process parameters for nugget diameter and failure load. Table 10 Confirmation test result. Output Factors Electrode Force (N) Welding Time (Cycle) Welding Current (KA) 3600 N 3 Cycle 29 KA Values 2300 N 5 Cycle Experimental Software Error % Nugget diameter (mm) Failure load (N) Nugget diameter (mm) Failure load (N) Nugget diameter (mm) Failure load (N) % 1.03 % % 0.85 % 29 KA % 0.10 % editor@iaeme.com

11 Experimental Investigation on Resistance Spot Welding of Aluminium Alloy 6082T651 using Interlayer of SS CONCLUSIONS Combine effect of interlayer thickness and welding parameters were studied on aluminium 6082T651. The conclusion obtained is as follows. 1. Using interlayer of SS304 of 0.3mm thickness, properties of resistance spot welding can be increased and also optimum nugget diameter and failure load can be obtained which is 5.61 mm and N respectively. 2. Welding time has more significant effect on response compared to electrode force and welding current. Due to high current, there is degradation in electrode because of this phenomenon welding time have a more significant effect than welding current and electrode force. 3. Interlayer thickness has its own significant effect for qualitative Al/Al weld with 0.3mm interlayer of SS It has been concluded that failure load is affected by welding time which constitutes 92% compared to other input parameters. ACKNOWLEDGMENT The present study was supported by the C.U Shah University, Gujarat, India. REFERENCES [1] X. Sun, E. V Stephens, M. A. Khaleel, H. Shao, and M. Kimchi, Resistance Spot Welding of Aluminum Alloy to Steel with Transition Material - From Process to Performance - Part 1: Experimental Study, Welding Journal, Vol. 83, No. 6, 2004, 188S 195S. [2] Ranfeng Qiu, Hongxin Shi, Hua Yu and Keke Zhang, Joining phenomena of stainless steel / aluminium alloy joint welded by thermal compensation resistance spot welding International Journal of Materials and Production Technology, Vol. 49, No. 4, 2014, [3] H. Oikawa and T. Saitoh, Resistance spot welding of steel and aluminium sheet using insert metal, Welding International, Vol. 13, No. 5, 1999, [4] S. M. Darwish and M. S. Soliman, Variables of spot welding commercial aluminium sheets having different thickness, International Journal of Materials and Product Technology, Vol. 9, No. 4-6, 1994, [5] H. Oikawa, S. Ohmiya, T. Yoshimura, and T. Saitoh, Resistance spot welding of steel and aluminium sheet using insert metal, Science and Technology of Welding and Joining, Vol. 4, No. 2, 1999, [6] S. K. Khanna,. He, and H. N. grawal, Residual Stress Measurement in Spot Welds and the Effect of Fatigue Loading on Redistribution of Stresses Using High Sensitivity Moir Interferometry, Journal of Engineering Materials and Technology, Vol. 123, No. 1, 2001, [7] S. Satonaka,. Iwamoto, R. Qui, and T. Fujioka, Trends and new applications of spot welding for aluminium alloy sheets, Welding International, Vol. 20, No. 11, 2006, [8] R. Qiu, C. Iwamoto, and S. Satonaka, Interfacial microstructure and strength of steel/aluminum alloy joints welded by resistance spot welding with cover plate, Journal of Materials Processing Technology, Vol. 209, No. 8, 2009, editor@iaeme.com

12 Arick. M. Lakhani and Dr. P.H. Darji [9] V.Ramakoteswara Rao, N.Ramanaiah, M.M.M.Sarcar, Optimization of volumetric wear rate of AA7075-Ti metal matrix composite by using taguchi technique, Jordan Journal of Mechanical and Industrial Engineering, Vol. 10, No. 3, 2016, [10] H. Rowlands and J. ntony, pplication of design of experiments to a spot welding process, ssembly utomation, Vol. 23, No. 3, 2003, [11] Sivaraos, K. R. Milkey,. R. Samsudin,. K. Dubey, and P. Kidd, omparison between taguchi method and response surface methodology (RSM) in modelling CO2 laser machining, Jordan Journal of Mechanical and Industrial Engineering, Vol. 8, No. 1, 2014, [12]. M. Pereira, J. M. Ferreira,. Loureiro, J. D. M. osta, and P. J. Bártolo, Effect of process parameters on the strength of resistance spot welds in 6082-T6 aluminium alloy, Materials and Design, Vol. 31, No. 5, 2010, [13] U. Eşme, pplication of Taguchi Method for the Optimization of Resistance Spot Welding Process, The rabian Journal for Science and Engineering, Vol. 34, No. 2, 2009, [14] S. Shafee, B. B. Naik, and K. Sammaiah, Resistance Spot Weld Quality haracteristics Improvement By Taguchi Method, Materials Today: Proceedings, Vol. 2, No. 4-5, 2015, [15] A. Al-refaie, T. Wu, and M. Li, n Effective pproach for Solving The Multi-Response Problem in Taguchi Method, Jordan Journal of Mechanical and Industrial Engineering, Vol. 4, No. 2, 2010, [16] J. ntony, Multi-response optimization in industrial experiments using Taguchi s quality loss function and principal component analysis, Quality and Reliability Engineering International, Vol. 16, No. 1, 2000, 3-8. [17] S.. Juang and Y. S. Tarng, Process parameter selection for optimizing the weld pool geometry in the tungsten inert gas welding of stainless steel, Journal of Materials Processing Technology, Vol. 122, No. 1, 2002, [18] N. Tosun,. ogun, and G. Tosun, study on kerf and material removal rate in wire electrical discharge machining based on Taguchi method, Journal of Materials Processing Technology, Vol. 152, No. 3, 2004, editor@iaeme.com