Punching is a process of producing hole in a flat sheet while blanking is a process of cutting out an intricate shape from the sheet which is known as blank (Figure 21.23). The main difference between punching and blanking is that the main ambition in punching is to hole but in blanking is to cut out intricate shape from the sheet. Generally punching is also called piercing but in piercing the hole is produced in the sheet without removing the metal. Following are the points which must be considered during the design of punching and blanking.
Figure 21.23 (a) Punching and (b) Blanking
- Clearance provided on die or punch = 10% of the strip thickness.
- In punching clearance is provided on die while in blanking clearance is provided on punch.
- The shear angle is provided on die in blanking, and on punch in punching.
Perforating: This is a process of punching a number of holes in a sheet.
Parting: This is a process of shearing the sheet into two or more pieces.
Notching: This is a process of removing pieces from the edges.
Lancing: This is a process of leaving a tab without removing any material.
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