A study on size effects for stainless steel foil during micro deep drawing process

In this study, the influencing mechanism of processing parameters, such as lubrication conditions, grain size and foil thickness, on stainless steel 304 (SUS304) foil has been investigated systematically during the micro deep drawing (MDD) process. The dry lubrication condition and glycerin-based nano-additive TiO2 lubricant with different concentrations were selected as a benchmark to study their effects on MDD process. Four stainless steel foils with different thicknesses of 20, 30, 40 and 50 μm were used in the MDD process, and each foil was treated by annealing processes at 950, 980 and 1050 ℃ respectively, in order to obtain different grain sizes. The formed cups qualities in terms of surface roughness, wrinkle and ear defects were analysed, and the punch force-stroke curves and the stress-strain curves were studied during MDD process. The experimental results show that 4.0 wt.% glycerin-based nano-additive TiO2 lubricant has the best lubrication effects due to its lowest drawing force and the better surface quality, and the SUS304 foil with thinner thickness required smaller punch force, while the surface is more uneven in comparison with the thicker SUS304 foil. Moreover, the SUS304 foils annealed at lower temperature had smaller grains, and subsequently had smoother surface textures than those of SUS304 foils with larger grains annealed at higher temperature. The findings of size effects from lubrication, grain size and foil thickness obtained in this study will enhance the mechanism research of SUS304 foil deformation in MDD.