Validation of FE simulation based on surface roughness model in micro-deep drawing

Metal forming technology has been paid great attention as one of the most economical mass production methods for sub-millimeter-scale microparts as well as macro-scale parts. Although tools and dies are essential for the manufacture of microformed parts, the fundamental knowledge and technological data on their fabrication have not been accumulated. Therefore, establishing design manuals and codes for tools, dies and blank materials for microforming is important for realizing high-precision forming. Particularly for miniaturization in sheet metal forming, the surface roughness of tools and blanks are thought to largely affect the processing characteristics and accuracy of products. From the standpoint of the design of tools and blank materials, this study was focused on the surface roughness of tools and blanks in the micro-deep-drawing process, and aimed at clarifying the effect of surface roughness on microforming characteristics. In our previous study, by finite element (FE) simulation considering surface roughness, the effect of tool surface asperity on the drawn cup surface quality in the two-stage micro-deep-drawing process was simulated. In this study, to verify the validity of the FE model of surface roughness in the micro-deep-drawing process, a new high-precision sequential blanking and drawing setup was developed for the experiment and a microcup with 500 μm diameter was fabricated from stainless steel (SUS304) ultrathin foil of 20 μm thickness. For the evaluation of the drawn cup, the cup geometry, thickness strain distribution, and surface roughness were measured. By comparisons of the FE simulation and the experimental results, the validation of the surface roughness model was studied, and the notable influential factors at the microscale were discussed.