To cut a sheet metal we need basically two cutting edges, acting against each other or
developing the same effect. In tool making we fulfill the requirement by providing the punch
and die, one of them is stationary and other moving.
The cutting action takes place when the inner cutting edges punch forces the stock (in
between against) the outer cutting edges (die).
This process is divided into different steps:
- The punch starts to penetrate into stock material. The material is subjected to pressure below elastic limit. This means if we would now retract the punch, the so far compressed stock material would come back to original state. The radii formation starts by both the cutting edges. (Fig 1)
- Further penetration, the pressure exceeds the elastic limit. Permanent deformation would now be noted if punch is retracted. The radii is formed and dish shaped deformation is noted. Penetration is completed and the U.T.S. is more or less reached. (Fig 2)
- Fractures starts now to occur at the two cutting edges. Fractures meet and cutting is completed. (Fig 3)
