Application of Taguchi Method for Optimization of Friction Stir Welding Process Parameters to Joining of Al Alloy

Abstract

In this study, the joining of 6061-T4 Al alloy plates are carried out using friction stir welding (FSW) process and the process parameters are optimized using Taguchi method. The rotational speed, welding speed and axial force are the process parameters taken into consideration. The optimum process parameters are determined with reference to tensile strength of the joint. The results indicate that the rotational speed is highest significant parameter to deciding the tensile strength of the joint. The result shows that optimal values of process parameters are to get a maximum tensile strength of friction stir welded AA 6061 is 162 MPa. Friction stir welding (FSW) is a solid state joining process that invented at The Welding Institute (TWI) United Kingdom in 1991, is a viable technique for joining aluminium alloys that are difficult to fusion welding [1]. No defects are observed in FSW like porosity, alloy segregation and hot cracking, and welds are produced with good surface quality and thus no post weld cleaning is required [2]. There have been a lot of efforts to understand the effect of process parameters on material flow behavior, microstructure formation and mechanical properties of friction stir welded joints. The effect of some important process parameters on weld properties is major area for researchers [3-5]. In order to study the effect of FSW process parameters, most of follow the traditional experimental techniques, i.e. varying one parameter at a time while other parameters are constant, this conventional parametric design of experiment approach is time consuming. Taguchi statistical design is a powerful tool to identify significant factor from many factors by conducting relatively less number of experiments. Though research work applying Taguchi method on various processes have been reported in literatures [6-11], it appears that the optimization of FSW process parameters of 6061-T4 aluminium alloy using Taguchi method has not been reported yet. Considering the above facts, the Taguchi method is adopted to analyse the effect of each processing parameters (i.e. rotational speed, welding speed and axial force) for optimum tensile strength of friction stir welded joints of 6061-T4 aluminium alloy. Taguchi method Taguchi, a Japanese quality engineer widely recognized as the father of quality engineering [12], addresses quality in two main areas: off-line and on-line quality control. Both of these areas are very cost sensitive in the decisions that are made with respect to the activities in each. Off-line quality control refers to the improvement in quality in the product and process development stages. On-line quality control refers to the monitoring of current manufacturing processes to verify the quality levels produced [13]. The most important difference between a classical experimentaldesign and a Taguchi methodbased robust design technique is that the former tends to focus solely on the mean of the quality characteristic, while the later considers the minimization of the variance of the characteristic of interest. Although the Taguchi method has drawn much criticism due to several major limitations, it has been able to solve single response problems effectively.