Abstract
Dieless blanking/punching are useful for piercing microholes because removing the die makes it possible to overcome the difficulty in piercing a small-sized die hole and assembling a die set. However, only cylindrical punches had been employed in previous studies on dieless blanking/punching. Piercing holes using noncylindrical micropunches was therefore attempted. The workpiece was backed up with adhesive tape instead of the die. Stainless-steel sheets were blanked using cemented tungsten carbide micropunches fabricated by electrical discharge machining. Blanking was successfully carried out in a 5-μm-thick sheet using micropunches with a rectangular cross section of 18 μm on the long side and 16 μm on the short side and a semicircular cross section of 20 μm in diameter. Corners of the pierced holes were finely processed, especially at the hole entrances. This result demonstrates that noncircular microholes can be pierced as well as circular ones by dieless blanking. An investigation into the relationships between blanking conditions and blanking characteristics showed that the punch stroke must be at least 30 μm for micropunches to penetrate a 5-μm-thick sheet at a punch feed speed of 50 μm/s. Furthermore, the maximum punch load increased with increasing punch feed speed for semicylindrical micropunches and was almost the same for quadrangular-prism micropunches. Rotating micropunches were also used and circular microholes were successfully pierced, indicating that noncylindrical micropunches can be employed for piercing both circular and noncircular holes. In addition, the punch load decreased with increasing punch rotation speed, likely because the cutting action by the peripheral edges of micropunches facilitated punch penetration.
Published Version
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