INVESTIGATIONS ON THE MICRO-SCALE SURFACE INTERACTIONS AND TRIBOLOGICAL SIZE EFFECT IN MICRO-STAMPING OF SS316L SHEETS

Micro-stamping is a convenient sheet-metal forming technology providing small tolerances, surface accuracy, low-cost and fast production of thin metallic sheets. Compared to macro-forming operations, tribological changes in microforming processes are harshened. Tribological size effect should be considered for a better understanding of surface interaction on micro-scale. The objective of this study is to establish numerical and experimental models for micro-stamping of stainless steel blanks regarding the tribological size effect and determine the effects of feature size of the dies and stamping force onto friction, von-Mises stress, plastic strain, part thickness changes. Numerical models of micro-stamping process for the dies with 3 distinct channel sizes (250 µm, 750 µm and 2500 µm) were established in FEA package Ls-Dyna. Several coefficients of friction values were imposed and runs were performed. Micro-stamping were also conducted to verify the established FE models. It was noted that the dies with different channel sizes showed different magnitudes and distributions of von-Mises stress and plastic strain. In addition, different friction coefficients were encountered for the micro-stamping dies with 250 µm, 750 µm and 2500 µm channel sizes. The lower channel size the higher coefficient of friction was observed as a result of tribological size effect.