#157 Design of Compound Punching Dies (6) Design of a Knockout - 1
As shown in Fig. 1, a knockout is assembled inside the die. A compound die has the inverted placement structure in which the die for outer shape punching is the top die (goes up and down along with the slide of the press machine) and the punch for outer shape punching is the bottom die (fixed on the bolster plate side of the press machine). A knockout is a characteristic part of this structure.
A knockout has two roles, that is, the role of a stripper of a hole punching punch and the role of ejecting the product that has entered inside the die. Normally, a knockout is prepared with the same shape as that of the product. As shown in Fig. 2, the surface of the knockout is either made level with the die surface or is made to project slightly beyond it. The amount of projection is about 0.5 mm to 1.0 mm. Contrary to common assumption, it is very rare that its surface is made level with the surface of the die.
When the knockout has moved by the maximum amount inside the die, as shown in Fig. 3(a), care should be taken so that the cutting edge of the die does not get separated, or the stepped part of the hole punching punch does not hit against the reverse side of the knockout. As shown in Fig. 3(b), when the knockout gets separated from the cutting edge of the die, in some rare cases, the knockout can become immovable because it has got stuck to the underside of the cutting edge of the die, and hence causing the die to break. In addition, the interference between the stepped part of the hole punching punch and the hole of the knockout can lead to breakage of the knockout or of the punch.


- #167 Problems in Punching and their Countermeasures (6) Scrap Processing in Punching
- #166 Problems in Punching and their Countermeasures (5) Trimming of Drawn and Shaped Parts
- #165 Problems in Punching and their Countermeasures (4) Scrap Clogging in Punching
- #164 Problems in Punching and their Countermeasures (3) Bending and Twisting of Narrow Punched Parts
- #163 Problems in Punching and their Countermeasures (2) Bending due to Punching

