A new hybrid stretch forming and double-layer two-point incremental sheet forming process

This research presents a new hybrid stretch forming and double-layer two-point incremental sheet forming (hybrid stretch forming and DL-TPIF). The novelty of the proposed hybrid process is first to employ double-layer blank sheets in the conventional two-point incremental sheet forming (TPIF) process, which allows the material in the flange region to flow into the deformation region for achieving more uniform thickness distribution and less thinning. The use of an upper dummy sheet prevents the forming tool from direct contact the target blank sheet to improve the surface quality. Secondly, the combination of the stretch forming and the DL-TPIF processes enables seamless integration of the two forming processes to take advantages of both processes. The proposed new hybrid process was evaluated by two case studies through experimental testing and finite element (FE) simulation. Three pre-stretching conditions were examined to evaluate the effect of the prior stretching operation. The results showed that the maximum thickness reduction of the dome shape produced by the new stretch forming and DL-TPIF process was less than one third of that obtained from the conventional TPIF process. The geometrical accuracy and surface quality were also improved by using this new hybrid forming process.