Influence of Global Forced-air Warming on the Bulge Formation in Shallow Sloped SPIF Parts

Shallow sloped single point incrementally formed (SPIF) parts typically show undesirable geometric deviations from the designed shape due to accumulated unwanted bulging. In this study, the effect of global heating by forced-air warming on the geometric accuracy of low-angled parts with a conical geometry is investigated. A finite element (FE) model was developed to simulate the SPIF process at elevated temperatures. The simulation results show that the sheet metal is subjected to significantly higher levels of stress in cold forming condition with respect to parts formed at elevated temperatures. Due to the increase in strength caused by strain hardening, a larger area of the sheet (both in the wall and bulge regions) is affected by the tool during forming at room temperature. Softening of the material by heat-assisted forming reduces the strain hardening and extended straining of the part which results in a reduction of the bulge height and of the under-forming of the cone base.