3D PRINTED TOOLS TO REDUCE RESIDUAL STRESSES, THINNING AND MARTENSITE CONTENT DURING DEEP DRAWING OF METASTABLE AUSTENITIC STEELS

In contrast to the single-stage process, high deformation degrees can be achieved using multi-stage deep drawing strategies. However, the first forming step already leads to significant changes in the sheet metal forming behavior. Temperature changes are caused by friction and plastic deformation in an inhomogeneous behavior, which in turn affect the whole subsequent drawing steps and the final part itself. As worst case, deep drawing components may already fail during the first drawing step due to excessive formation of deformation- induced martensite or delayed cracking, which might happen to the final part even hours or days after production. In this study the influence of the tool temperatures is investigated to reduce the residual stresses and the martensite formation. As a result, the forming forces and sheet metal thinning can be reduced. For this purpose, a special 3D printed tool is tested, which is manufactured by selective laser melting (SLM) and offers the possibility to temper the blank holder, the die and the punch. The results show that an optimized tool temperature strategy reduces the forming forces, residual stresses, formation of martensite and sheet metal thinning for the metastable austenitic steel used.