A Numerical-Experimental Investigation of the Wrinkling Defect in Incremental Forming of Thin Polycarbonate Sheets

Incremental forming is a relatively new technology, whose deformation strategy is similar to the layered manufacturing principle of rapid prototyping approach. It promises a flexible, short time and inexpensive way to form sheet products of metals or polymers. Conversely, the process suffers from some peculiars defects, like twisting and wrinkling, which can be particularly evident when forming thin thermoplastic sheets. With the aim to enhance understanding of the wrinkling phenomenon, an experimental campaign on the single point incremental forming of thin polycarbonate sheets and FE analyses were performed. In particular, fixed wall angle square pyramid frusta were incrementally formed by varying two parameters, i.e. their wall angle and the vertical step depth per revolution of the toolpath. The investigation of the forming forces, the deformation states and the sheets thinning highlights the effects of the combined action of the above-mentioned parameters and plans the way to predict the occurrence of the twisting defect.