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Piercing is the operation of cutting internal features (holes or slots) in stock. Piercing can also be combined with other operations such as lance and form (to make a small feature such as tab), pierce and extrude (to make an extruded hole). All these operations can be combined with blanking.

Piercing of all the holes is best done together to ensure good hole-to-hole tolerance and part repeatability. However if the material distorts, the method described below can be done.

When there are large numbers of holes, in a tight pitch, there could be distortions, due to the high amount of tension on the upper surface due to stretching and compression on the bottom surface. This causes the material not to lay flat. This can be avoided/lessened by staggering the piercing of the holes. Holes are punched in a staggered pattern; then the other holes are punched in the alternate staggered pattern.

Design Considerations
  • Minimum hole diameter should be at least 20 % greater than stock thickness. In the case of stainless steels, it should be 2 times the material thickness.
  • Minimum wall thickness (distance from hole to edge or hole to hole) should be at least 2 times stock thickness.
  • For non-round slots, the minimum wall thickness should be 2 times thickness for short slots < 10 thicknesses long; and 4 times thickness for long slots > 10 thicknesses long.

  • Minimum hole (and short slot) to bend distance should be 2.5 × the stock thickness + bend radius.
  • For long slots, the distance should be 4 × the stock thickness + bend radius.