Study on size effects in micro deep drawing of stainless steel foil

In this paper, the mechanism of processing parameters, such as lubrication conditions, grain size and foil thickness, on micro deep drawing (MDD) of stainless steel 304 (SUS304) foil has been investigated. The dry and glycerin-based nano-additive TiO₂ lubricant with different concentrations were selected to study the effects of lubrication on MDD process. Four stainless steel samples with different thicknesses of 20, 30, 40 and 50 μm were employed in this study. Each foil was annealed under 950, 980 and 1050 °C respectively to obtain different grain sizes of the samples. The formed cups qualities in terms of surface roughness, wrinkling and earing defects were analysed, and the punch force-stroke curves and the stress-strain curves were studied in MDD. 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 obtained, 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 understanding of SUS304 foil deformation in MDD.