Chapter 6: Blanking and Piercing Operations
6-1 METAL-CUTTING PROCESS
Metal cutting is a process used for separating a piece of material of predetermined shape and size from the remaining portion of a strip or sheet of metal. It is one of the most extensively used processes throughout die and sheet-metal work. It consists of several different material-parting operations, such a piercing, perforating, shearing, notching, cutoff, and blanking.
In blanking, the piece is cut off from the sheet, and it becomes a finished part. In piercing, the cutout portion is scrap which gets disposed off while the product part travels on through the remainder of the die. The terminology is different here, though both processes are basically the same and therefore belong to the same category, which is the process of metal cutting (Fig. 6-1).
Figure 6-1: Blanking and piercing differentiation.
The actual task of cutting is subject to many concerns. The quality of surface of the cut, condition of the remaining part, straightness of the edge, amount of burr, dimensional stability-all these are quite complex areas of interest, well known to those involved in sheet-metal work.
Most of these concerns are based upon the condition of the tooling and its geometry, material thickness per metal-cutting clearance, material composition, amount of press force, accurate locating under proper tooling, and a host of additional minor criteria. These all may affect the production of thousands and thousands of metal-stamped parts.
With correct clearances between the punch and die, almost perfect edge surface may be obtained. This, however, will...