Abstract
The dieless punching of ultrasmall-diameter holes was attempted because it is difficult to punch such holes by conventional punching methods. Removing the die made it possible to solve the problem of difficulty in piercing an ultrasmall-diameter die hole and assembling a die set. The workpiece was backed up with adhesive tape instead of the die. Stainless-steel sheets were punched using cemented tungsten carbide small-diameter punches fabricated by electrical discharge machining. As a result, an 8.5-μm-diameter hole was successfully punched in a 5-μm-thick sheet using a 10-μm-diameter punch. A hole with a diameter smaller than 6 μm was also punched in a 3-μm-thick sheet using a 6-μm-diameter punch. Furthermore, the punch load evolution was measured using a load cell, and the punch load was shown to reach a positive peak when the punch penetrated the workpiece. An investigation into the relationships between punching conditions and punching characteristics showed that the punch stroke must be at least 30 μm for a 10-μm-diameter punch to penetrate a 5-μm-thick workpiece at a punch feed speed of 50 μm/s. In addition, the maximum punch load decreased with increasing punch feed speed. When the punch was rotated, the hole diameter increased, likely because of the cutting action of the punch peripheral surface. The cutting action facilitated punch penetration, resulting in a reduced punch load. Ultrasonic oscillation was also employed by oscillating the workpiece in the punch axial direction. The punch load was considerably reduced, demonstrating that ultrasonic oscillation is effective even when the workpiece is oscillated instead of the punch.
Published Version
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