Effect of Thickness to Grain Size Ratio on Drawability for Micro Deep Drawing of AISI 304 Stainless Steel

Although deep drawing process in the macro scale are well developed, the known concepts cannot be applied to micro deep drawing through directly scale down the specimen and tooling size due to the so-called size effects. Therefore, tensile test and micro deep drawing experiments were conducted to generate the knowledge for the micro deep drawing process. Stainless steel 304 foils with 4 different thicknesses (150μm, 100μm, 50μm and 20μm) were used to investigate the influence of the blank holder forces and T/D ratio (thickness/average grain diameter) on the limit draw ratio (LDR). Four female dies with different die diameters and die shoulder radii and one punch were used for this study. The experimental results show: 1) the required blank holder force increases with increasing of T/D ratio, 2) the limit drawing ratio (LDR) increases with increasing of T/D ratio and increases at a decreasing slope as T/D ratio becomes larger, and 3) the limit drawing ratio (LDR) becomes steady when T/D ratio > 10 for the as-received stainless steel 304 foils. Finally, the authors recommend having at least 10 grains throughout the stainless steel 304 foils thickness for obtaining better formability and steady deep drawing behavior for micro sheet forming.