Experimental Investigation on Friction-Stir-Assisted Incremental Forming with Synchronous Bonding of Aluminum Alloy and Steel Sheets

A novel incremental sheet forming process, friction-stir-assisted incremental sheet forming with synchronous bonding (FS-ISF&SB) using aluminum alloy and steel sheets was developed. The influences of stacking sequence, wall angle, ratio of rotational speed to feeding rate and step down on the forming and bonding quality, geometric profile, interface morphology and thickness distribution were investigated through a series of experiments. Experimental results demonstrate that FS-ISF&SB is specifically suitable for the fabrication laminated sheet metal parts. The part with good forming and bonding quality can be obtained with the stacking sequence as of S-A, wall angle as of 40°, rotational speed as of 3000 RPM, feeding rate as of 750 mm/min and step down as of 0.4 mm, respectively. Based on the scoring of various failure modes, five factors are listed in descending order of significance in forming and bonding quality as wall angle, step down, stacking sequence, rotational speed and ratio of rotational speed to feeding rate. A special geometric feature named as “bump structure” reveals the heterogeneous deformation. Results also indicate that the thickness distribution of the formed part does not conform to sine law, and the deviation from design model increases with the increasing of wall angle.