Punching is the process of removing material by applying a shearing force. This process requires a punching machine, punch, die and a sheet material to be punched.
A shearing force is produced when an object is subjected to an opposing force.
A sheet of material is placed in the punching machine’s jaws, in between the punch and die.
The punching machine forces the punch through the material and into the corresponding die cavity, punching out a piece of scrap material as it goes through.
It is important that the punch and corresponding die are used together.
The punch is fractionally smaller than the die cavity and the difference in size (which is known as “clearance”) allows the material to bend and fracture as the punch is pushed through it. The material that is forced from the workpiece is called the slug or scrap.
The amount of clearance needs to be less than the thickness of the material being punched. If there is too much clearance (e.g. the die is too big) the material will be rolled over as the punch enters the die and you will not get a cleanly cut hole.
If the punch is larger than the die it will not be able to enter the die and will not punch a hole in the material.
The shape of the punch’s face will affect the amount of force needed during the punching process. The most common shapes for punch faces are: flat, concave, bevelled and double bevelled.
If the surface of the punch face is flat, a greater force is required as the entire surface area of the punch face is trying to push through your material at once.
A bevelled or concave punch will reduce the force needed as less surface area is trying to force its way through your material at any one time.
