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.