Blanking and piercing are both shearing operation. The difference is only in the scrap. In blanking what you cut out is of interest. In punching what you cut from is of interest. For example: You cut a hole in a sheet metal. If you are interested in the disc that is cut out, then the process is called blanking. The sheet metal with a hole through it is the scrap. If you are interested in the sheet metal that now has a hole through it, then the process is called piercing.