There are certain materials that are better suited to punch presses than others, and can cause problems such as blunt tooling, rough edges and wasted time if used on a CNC punch. Below is a simple guide to materials that can be punched on a CNC punch, and those that should be treated with care.
Mild Steel Is the Natural Fit
Mild steel is the typical material for which CNC Punching Machines are designed. It can be punched cleanly across a wide range of gauges (0.5mm up to 6mm thick material) and produces a neat shear edge when using standard tooling and clearances of around 10% to 15% of material thickness.
Aluminium Needs Correct Clearance
Aluminium can be easily punched using a standard punch set. However, the clearance of the punch with the material is more critical and typically needs to be increased to around 15-20% of the material thickness. A polished punch face is recommended to stop the material sticking to the punch.
Stainless Steel Demands More Tonnage
As you would expect, stainless steel is punachable, but like most materials, it work-hardens very quickly. Hence, the greater tonnage and extremely sharp tooling required for this material. The 304 grade is slightly more forgiving than the 316, and typically we recommend a maximum thickness of half that which could be processed in mild steel of comparable gauge.
A useful reference for CNC Punching Machines is https://www.cotswold-machinery-sales.co.uk/euromac-bending-machines/punching-machines.
Copper and Brass Require Lubrication
The harder materials of Copper and Brass can be punched but must be lubricated to stop galling. The lubrication needs to be applied before each punch and the material needs to be kept clean to stop any sticky patches building up. The clearances for these materials are similar to those of Aluminium work.
Materials to Avoid
Materials that are too hard (i.e. have too high a tensile strength) can crack the tooling or even jam the ram in the punch. You should check the material’s tensile strength against the manufacturer’s punch tonnage chart before attempting to punch unusual materials.
It’s so important to match the material to the machine from the start and to get the best out of your tooling.
