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#066 Method of Using Standard Components (15) Block Punches

Category : Die Design
January21, 2011
In shapes other than round, the part that is embedded into the punch plate (the shank part) is most often made square or odd shaped. A typical shape of a block punch is shown in Fig. 1.
Fig. (a) is of the straight type. This is the type with the punch cross-section being large and is a type that is easy to produce.
Fig. (b) is one with a small punch cross-section, and is a type used when the strength is not enough in a straight type. The size is still the one in which it is possible to give considerations to machining the punch making straight the parts that are difficult to machine.
Fig. (c) is the shape when the punch cross-section is small and priority is given to the punch strength. This is the shape that makes the punch machining most difficult. As long as there are no problems, it is good to design to the shape of (a).
Fig. 1 Shapes of block punches

The above discussion is about common block punches. Since Misumi presupposes standardization, as shown in Fig. 2, the block punches are limited to shanks parts that are square and tool tips that are either square or oval shaped. Fig. 2 Block punches of Misumi

Among block punches it is also possible to make those that work only at one side (edge cutting punches or L-shape bending punches, etc.). In such cases, a sideward force acts on the punch. Countermeasures for this are necessary in the punches. Fig. 3 shows examples of countermeasures against sideward forces.
A projecting part is prepared in the cutting edge part of the punch. This projecting part is called the back up heel (or simply, heel). Before starting the press forming operations, the heel part is inserted in the die, receives the sideward force during operation, and prevents changes in the clearance, etc. As a countermeasure against sideward force, there is also the method of making the die side projecting relative to the normal shape of the punch.
Fig. 3 Sideward pressure countermeasures

The major methods for preventing a block punch from getting detached are shown in Fig. 4.
Fig. (a) is a flange stopper. In the figure, although a flange is shown only on one side, it is also possible to have flanges on two or three sides. The design of providing a flange on all four sides is very rare as being making the machining of the flange very tedious.
Fig. (b) is a key stopper. Very often the key groove is provided on one side or on two opposite sides. Although the machining of a key groove is easier than the machining of a flange, since it affects the strength of the punch, it is necessary to exercise caution while paying attention to the size of the punch.
Fig. (c) is a screw stopper. This is used very frequently in punches prepared by wire cutting. Apart from the punch detaching prevention methods shown here, there are also other methods with some special techniques adopted. In a single die, as far as possible, the form of punch detaching prevention is made the same, thereby making it easy to assemble and disassemble the punch.
Fig. 4 Preventing the punch from getting detached

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