Does friction contribute to formability improvement using servo press?

Abstract Servo press forming machines are advanced systems that capable of imparting interrupted punch motion, resulting in enhanced room temperature formability. The exact mechanism the formability improvement is not yet established. contribution motion ductility has been studied through stress relaxation phenomena uniaxial tensile (UT) tests. However, reason for improved observed when employing servo complicated due to additional from frictional effects. In present work, an attempt made decouple friction effect on numerically. using a hole expansion test (HET). limit during modeled Hosford-Coulomb (HC) damage criteria, which implemented as user subroutine commercial explicit finite element (FE) software. Only accounted evolution variable loading. Therefore, difference between simulation and experimental ratio (HER) can be used overall expansion. HER different. study showed model effectively captures deformation process both monotonic loading conditions. Compared relaxation, played major role HET.