| 摘要 |
<p>Metal sheet is first provided with a small round hole, which is located concentrically above a counterbored hole in a die; and hole is surrounded by a ring notch in the surface of the die. An upper punch has an axial hole with a conical bottom outlet; and a drawing punch is located in the axial hole in upper punch. Both punches are driven downwards to make a tubular hole in the sheet, the hole being surrounded by a ring recess. The hole is tapped to provide a screw thread for a bolt fitted with a washer, which is driven into the ring recess when the bolt is tightened.</p> |
