The Cleveland Punch and Die tip for the day is knowing the hardness of the material being punched. Punches and dies used to pierce holes in A-36 steel structural beams, plate, or sheet metal should be confined to and used only on these types of materials. Attempting to punch certain materials such as armor plate or spring steel will often exceed the capabilities of the tooling, causing it to fail.
When dealing with material hardness, factors involving the thickness and diameter limitations must be considered. The diameter of the punch must be such that the punch's compressive strength is greater than the force required to pierce the hole. This punching force can be found by multiplying the material thickness by its shear strength in PSI, then multiplying by the length of the cut. The general rule of thumb is to never punch a hole where the punch dimension is less than the material thickness. (ie, 1/4" punch through 1/2" material)
The maximum allowable compressive stress depends on the type of tool steel from which the punch is made, and its hardness. For example, oil-hardened, shock resistant tool steel will withstand 300,000 PSI compressive stress before breaking and can be used at 250,000 PSI with good tool life. Other tool steels can also be considered, depending on the material to be punched. When ordering punches and dies, the user is responsible for advising Cleveland Punch and Die of the type of material, the hardness and the thickness of material being punched. Having this knowledge will allow your CPD customer service representative to provide the highest quality tool for your specific application.