On the scale dependence of micro hydromechanical deep drawing
Tooling feature size to minimum thickness becomes small in micro scale products and its ratio affects the deformation behavior and formability in micro sheet forming significantly. Hydroforming technology has been originated and utilized in macro scale sheet forming to enhance the formability. In this study, the effect of relative tooling feature size on drawing characteristics and effects to improve the drawability, such as friction holding effect, hydrodynamic lubrication effect and compression effect by blank edge radial pressure, in micro hydromechanical deep drawing (MHDD) are investigated using plasticity theory and numerical simulation. The results show that the micro drawing characteristics in MHDD can be improved by applying counterpressure. However, the required fluid pressures for friction holding and hydrodynamic lubrication effects increase as the relative punch diameter and/or die shoulder radius to thickness decrease, although the compression effect by radial pressure on blank edge is independent of the relative tooling feature size.