Influences of micro-friction on surface finish in micro deep drawing of SUS304 cups

Surface asperities take a large part of a thin blank in micro-sheet forming processes. Contact and friction significantly affect micro-sheet forming and cannot be simplified as homogeneous in simulation. Material heterogeneity of the blank further affects the friction and its impact becomes significant in micro-scale. In this study, a FE model representing surface morphology of SUS304 sheets was built for micro deep drawing simulation. Each node on the blank model had the same height as an asperity. Key surface morphological characters of the blank can be presented with a proper mesh density. The material size effects were presented via refined material properties assignment based on sheets' microstructures. Due to the initial surface morphology, wear accumulation and thickness distribution were significantly affected. Experimental results well validated prediction of worst worn area on drawn cup mouth in simulation. Surface roughening which affects shape accuracy in the micro-scale was affected by the wear behaviour during the drawing process. Thus, different roughening behaviours at three divided areas on the drawn cup were wall explained.