Extruded Sheet Metal Hole

Extruded holes very close to the part edge can lead to sheet metal deformation or tearing.

Extruded sheet metal hole.

Creating an extruded hole using a punching process requires extreme pressure force. The following illustration shows the extruded hole geometry. Applications include for self tapping sheet metal screws or in thicker material to permit tapping for machine screws. Alternately the hole could be pre pierced in a separate station and then the edges extruded at a second station.

It is recommended that the minimum distance between two extruded holes should be six times the thickness of sheet metal. If extruded holes are too close it can lead to metal deformation. An extruded hole is one that is generated at one station using a specially stepped punch that first shears a smaller hole and then follows through to deform the local area around the hole into a projection by limited forward extrusion. You can imagine the shape as being a body to the punch of any shape and from this protrudes the punch pin of the diameter you want.

Extruded holes unipunch tooling can be used to simultaneously punch a hole and extrude the material down. Certain distance should be maintained between two extruded holes in sheet metal designs.