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#033 Basics of Die Structure (8) Cutting Off Die

Category : Shearing work
March19, 2010

Cutting off work is a method of blanking work in which the material is cut by shearing into two parts without generating any scrap. If this method is used, the rate of utilization of the material (yield) can be increased to the maximum possible extent.

The basic structure of a cutting off die is shown in Fig. 1. The cutting is done in the condition in which the material is passed through the tunnel part of a fixed stripper and has butted against a block. This work is shown in Fig. 2.

 [Fig. 1][Fig. 2]

Since the burrs at the left and at the right after cutting are in opposite directions, they remain as they are in the products (see Fig. 2). This is the first problem. Another problem comes because the cutting off is done along a single line. The material on the die jumps up due to the bending moment generated during the operation, and on the contrary the tip of the material of the cut part falls down. Since the cutting off is not done with the flat condition maintained, the cut edge surface becomes inclined. This is the second problem.

There are no countermeasures possible for the different directions of the burrs.

As a countermeasure for the cutting edge surface becoming inclined, it is essential to set the cutting clearance smaller than normal. Even when the clearance is small, if the punch moves away because of being pushed by a lateral force during working, the clearance becomes large and the problem only gets worse. It is necessary to take measures to prevent the punch from moving away by providing a back up heel or a back up block so that the punch does not move away.

As a positive measure to prevent the inclination of the material during cutting off, it is important to provide a material pressing member inside the die (inverted pressing member) thereby gripping the material between the punch and the inverted pressing member thereby ensuring that the material does not get inclined during cutting off. In addition to putting an inverted pressing member on the die side, even changing the stripper from a fixed stripper to a movable stripper is a good countermeasure. However, this increases the cost.

Although the cutting off operation appears simple, it is quite difficult when the work has to be done neatly. Although the operating force becomes balanced if the cutting is done with a certain width such as in parting, since the cutting is made on one side, there is the problem that the operating force becomes unbalanced. It is necessary to consider this aspect at the time of designing the structure.

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