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#065 Method of Using Standard Components (14) Round Punches - 3

Category : Die Design
December17, 2010

In round hole blanking operation, there is the problem of slug pulling. The easiest method of countermeasure for this is forcibly pushing down the slug that is trying to come up. A punch prepared for this purpose is the ejector punch shown in Fig. 1 (Jector punch in Misumi). Although using the punch is good as a countermeasure against slug pulling, the ejector pin becomes an obstruction while regrinding the punch. Disassembling and removing the ejector pin is very cumbersome. As a countermeasure for this, a hole has been opened at the side of the punch. As shown in Fig. 2, if a pin is inserted in the side hole with the pin pushed down, the ejector pin will remain in the pulled in condition, and hence grinding becomes easy.

[Fig. 1] Ejector punch[Fig. 2] At the time of regrinding the punch

A round punch is used for forming shapes other a round shape. This method is used for the purpose of hole punching of punch plates easy. However, since the orientation will be important if the shape is not round, a rotation stopper will be necessary as shown in Fig. 3. The shapes of rotation stoppers are shown in Fig. 4. The shape (e) can be said to be the basic shape of a rotation stopper. A groove is machined using an end mill, and a pin is inserted in it to make it into a rotation stopper. Adjustments can be made by handling the pin. The shape (d) is one in which the rotation stopper is formed directly using an end mill. The accuracy of the rotation stopper is determined by the accuracy of machining the hole. Although positioning using a rotation stopper looks simple, it is actually quite difficult.

[Fig. 3] Odd shaped hole punch[Fig. 4] Shapes of rotation stopper holes

As a special method of using a round punch, there is the ball lock punch. This is a punch in which the attaching and detaching of the punch can be made with one touch. This is a punch having a groove on the side surface of the punch in which a steel spheres (ball) has been inserted.

[Fig. 5] Ball lock punch

See Fig. 5(a). This punch is used as shown in Fig. 5(b). The punch is set using a dedicated holder called a retainer with a ball held by a spring incorporated in it. When a tensile force acts on the punch, the ball enters into the groove of the ball receiving part of the punch thereby preventing the punch from getting detached. When wanting to detach the punch due to the wear, etc., if a pin is inserted in the hole in the retainer and the ball is pushed up, the punch can be detached easily. The background of creating this kind of structure is that, during the hole punching operations of large components of cars, etc., since it is difficult to take down a large die from the press machine for regrinding the punch, etc., the punch replacement has been made possible in the condition in which the die has been installed in the press machine.

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