A study of influence of hydraulic pressure on micro-hydromechanical deep drawing considering size effects and surface roughness

Micro-hydromechanical deep drawing (MHDD) is a promising micro-manufacturing technology to fabricate micro-metallic products in batch scale. Size effects significantly affect MHDD regarding both material properties and friction. Hydraulic pressure on the blank and its development differ from that in conventional hydromechanical deep drawing. Combined influence of fluid pressure, surface roughness and material inhomogeneity of the blank was investigated in this study via MHDD experiments and advanced FE simulation considering strong fluid-solid interaction (FSI) and size effects. The MHDD experiments under different hydraulic pressures were conducted using the annealed foil followed by the advanced FE simulation. The foil can be successfully drawn into micro-cups, however, wrinkles occurred under high hydraulic pressures. Wrinkle height and number are affected by hydraulic pressure and size effects. Average hydraulic pressure on the blank is lower than the inlet pressure, and pressure development on the blank depends on location and is complex, due to transition of sealing between the blank and die. The maximum drawing force increases, while the contact forces and pressures on the blank holder and die decrease with an increase of hydraulic pressure. Optimal hydraulic pressure for MHDD should be determined with consideration of size effects and MHDD tool geometry.