High velocity forming of steel sheets and tubes for applications in the automotive industry - HI-VEL : final report

The main objective of the HI-VEL project is to establish the feasibility of high velocity forming methods and to quantify the enhancement achievable with these techniques in the formability of high strength steel (HSS) and stainless steel sheets and tubes for automotive applications. Electromagnetic forming (EMF) and electrohydraulic forming (EHF) processes were studied during the HI-VEL project. After a first mechanical characterisation at strain rates up to 1000s-1, the following materials were selected for the high velocity experimental testing: AISI441 (1.4509), HT800XD (DP800), Dogal800DPX (DPX800), HT700TD (TRIP700) and IF210. The materials constitutive data at high strain rates were obtained for the Johnson Cook material modelling. EMF and EHF simulations were validated with experimental high velocity tests. The fatigue behaviour of high velocity formed samples was similar to the conventionally formed ones. Due to the low electrical conductivity of the HSS and stainless steels, the EMF technology showed its viability for these materials only in the case of small forming grades applications, such as the electromagnetic sizing of U-parts in order to eliminate the elastic recovery. For any other deep drawing operation, EMF technology can be applied to steels using an electrical conductive driver that accelerates the steel part towards the die. Comparing the conventional bulge forming and the multi-impulse EHF, the obtained dome heights increased from 57 to 70 mm for TRIP700 steel and from 48.5 to 54 mm for DPX800 steel. Multi-impulse EHF increased the formability of HSS and has interesting industrial applications, such as forming undercut part designs using a split die.