Experimental study on the limit test method of polypropylene sheet incremental forming

Incremental forming can satisfy the requirement of small batch and individual production of polymer sheet. The forming limit is the main basis for judging the incremental forming properties. At present, the incremental forming limit of sheet metal usually uses crack as the failure criterion. Polypropylene (PP) sheet is sensitive to the incremental forming temperature, and the thickness variation does not follow the cosine theorem. There is a lack of systematic research on the incremental forming limit test method so far. For the first time, this paper proposes a limit test method of PP sheet incremental forming, where the wrinkling is proposed as failure criterion. The method to fast determine the wrinkling forming limit angle θmax is given by utilizing the combination of the revolving body with circular surface and conic workpiece and the interpolation iterative approximation of forming angle. PP sheet with 2.85-mm thickness is selected as the experimental object. The wrinkling forming limit angle θmax is 64° according to the above process method.