Experimental investigation of polycarbonate sheets deformed by SPIF: formability, micro-mechanisms of failure and temperature analysis

This article presents an experimental research performed on a polycarbonate sheet deformed by single point incremental forming (SPIF). The analysis is implemented within the framework developed in previous research work for assessing formability and failure by necking and fracture of polymeric sheets in conventional and incremental sheet forming (ISF) processes. The experimental plan is taking into account a series of process parameters, including tool diameter, feed rate, spindle speed and step down. The results allow an evaluation of the influence of these parameters on the formability and their effect on the failure modes. In this regard, three modes of failure were observed: fracture, twisting and crazing. It was shown that most of the typical forming conditions in SPIF lead to failure by fracture in the absence of necking (crack opening in mode I), and all the test conditions presented a combination of twisting and fracture. Higher values of the step down increased the intensity of twisting whereas high values of spindle speed resulted in crazing. A scanning electron microscopy (SEM) evaluation was performed as well as an integral temperature analysis to provide a complete window for understanding the conditions upon which the different failure modes of this thermoplastic material are developed in SPIF.