Perhaps the most common procedure done in a stamping die is cutting. In this process, metal is cut off by placing it in the small gap between the two bypassing tool steel sections. This gap is also known as the cutting clearance. The metal cutting process does not only require a great amount of force, but it creates a great deal of shock as well. That is why metal cutting is among the most severe stamping operations. Too much shock can result to die sections that break, punches that snap and presses that fail.
Imagine the situation wherein you are holding a hammer and were told to set it on a nail, then put it into a piece of wood; you are not likely to achieve anything. However, if you were instructed to raise the hammer then strike the nail, it would surely go into the piece of wood with not much effort. The power of the hammer as it falls, together with the shock, carries out the required work.
If ever you have been in a stamping plant where thick, high-strength steel is being cut, you could literally feel the floor vibrate each time the press cycled. Presses that are designed for cutting high-strength or heavy materials often come with additional heavy-duty frames plus components that can endure incredible shock. Some presses are incorporated with special dampening units to help absorb and dissipate the shock.
What Occurs During Metal Cutting?
As a start, you have to be aware that at times, you have to change the way you see sheet metal. In spite of its physical appearance, strength, weight and density, it is an elastomer. This means that, when it is exposed to a great amount of force, it behaves just like rubbery plastic. It is comparable to Silly Putty, the rubbery stuff inside a red egg, which you may have played with during your childhood. There are metals that are a lot more rubbery than others. On the other hand, high-strength steel and other harder metal are far from what Silly Putty looks like.
In many cutting processes, the metal is stressed until it fails between two components or bypassing die sections. In order for metal to be cut, the die needs a cutting punch, as well as mating section to which the punch goes through. The cutting clearance or distance between cutting sections differs as regards to the type of metal, hardness, thickness and desired edge quality.
Too much or too little clearance between cutting sections can create excessive burr on the part. To reduce the burr height, there must be a sufficient cutting clearance between the cutting sections, and these should be ground from time to time to keep a perfectly square edge. The process of grinding die sections is simply called “sharpening the section” by diemakers and technicians.
Once the mating and punch sections have been ground, they have to be regularly shimmed back up to their operational height. Shimming refers to the process through which thin sheets of stainless steel or other material are placed below the ground section to compensate for what has been ground off. Grinding and shimming are the common tasks performed in a basic maintenance procedure.