Constant Current Density Compression Behavior of 304 Stainless Steel and Ti-6Al-4V During Electrically-Assisted Forming

Abstract

A metal forming technique which has more recently come of interest as an alternative to processes that use elevated temperatures at some stage during manufacturing is Electrically-Assisted Forming (EAF). EAF is a processing technique which applies electrical current through the workpiece concurrently while the material is being formed. At present, this method has only been studied on an experimental level in laboratory settings, and the heuristic results show increased fracture strain, reduced flow stress, and reduced springback; the enhanced process capability is beyond the range that would be expected from pure resistive heating alone. Thus far, when applying the electrical current through the workpiece during deformation, the current magnitude flowing through the workpiece has remained constant. Hence, for a compression loading, the current flux or density decreases as a result of an increasing specimen area. This work examines the effect of a non-constant current density (NCCD) and a constant current density (CCD) on the deformation behavior of 304 Stainless Steel and Ti-6Al-4V during uniaxial compression testing. Additionally, the application of a CCD is used to modify existing empirically-based EAF flow stress models for these materials. From this testing, it is shown that a CCD during forming can significantly reduce the flow stress of the material as compared to the NCCD tests. The reductions in the flow stress were increased at higher strains by approximately 30% and 15% for the 304 Stainless Steel and Ti-6Al-4V, respectively. More importantly, these flow stress curves are better representative of how the material responds to an applied electrical current as the specimen shape change is removed from the results. Also, the NCCD tests were approximated using an existing empirically-based EAF flow stress model and the CCD tests concluded that a new flow stress predictor model be introduced.