Forming Limit Investigation of AA6061 Friction Stir Welded Blank in a Single Point Incremental Forming Process: RSM Approach

In the present work, an experimental study was made to identify formability characteristics of aluminum 6061 fiction stir welded blank in an incremental forming process. Forming limit diagram, bowl height, minimum thickness and thickness distribution were studied to find formability of tailored welded blank. Firstly, series of experiments were carried out to find which joining direction caused higher formability and desired forming limit curve. For this purpose, joints with three different directions (i.e. rolling direction, transverse direction and diagonal direction) were prepared and formability i.e. formed bowl height until failure along with forming limit curves were compared. After finding the best joining direction, effect of welding process parameters i.e. rotational speed, plunge depth and travel speed on formability of welded blanks were analyzed by using response surface methodology (RSM). The results were discussed according to microstructure and fractography analysis obtained by scanning electron microscopy. After finding the effects, welded blanks with optimal parameter combination were fabricated and effect of incremental forming parameters i.e. spindle speed, feeding rate and axial step on thickness distribution were analyzed. Here, RSM was also used to find parametric and optimum setting of parameters. From the results, it was obtained that joints with diagonal direction caused higher value of bowl height. Also, tool rotary speed of 1600 RPM, travel speed of 40 mm/min and plunge depth of 0.15 mm caused higher value of bowl height implying high formability. Furthermore, it was found that selection of 0 RPM spindle speed, 600 mm/min feeding rate and axial depth of 0.6 mm resulted in higher thickness distribution.