Fabrication of Miniature Shell Structures of Stainless Steel Foil and Their Forming Limit in Single Point Incremental Microforming
Toshiyuki Obikawa* and Tsutomu Sekine**
*Institute of Industrial Science, the University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
**Department of Precision Engineering, School of Engineering, Tokai University, 4-1-1 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan
Single Point Incremental Microforming (SPIMF) using neither dies nor a backing plate is applied to the fabrication of miniature shell structures of stainless steel foil in meso-scale. A piece of 8 µm-thick blank, which is held in a blank holder on a desktop forming machine, is incrementally formed with a thin, round-tip tool. Three kinds of polygonal pyramids are formed, and their forming limits are compared to those when 12 µm-thick aluminum foil is used. It is found that the forming limit of stainless steel foil in forming pyramids depends only on the tensile strain of a triangular lateral face, whereas that of aluminum foil depends on the sum of two principal tensile strains on the surface of a rounded lateral edge. It is also found that the forming limit of stainless steel foil can be drastically increased by SPIMF.
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