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#039 Basics of Die Structure (21) Structure of Drawing Dies: Redrawing Die - 1

Category : Drawing and Forming Work
May 7, 2010

In drawing work, there is a limit to the extent to which drawing can be done in one operation. Therefore, the desired diameter is obtained by repeating drawing several times. Such repeated drawing is called "redrawing". A die that is used for redrawing is called a "redrawing die". Since the drawing diameter difference is large in the step next to first drawing, a die with a structure shown in Fig. 1 or in Fig. 2 is used.

[Fig. 1][Fig. 2]

The product to be formed from now on is formed after placing a guide (inner diameter guide) in the gap between the punch and the inner diameter difference part of the drawn product by the blank holder (wrinkle suppressor in the case of a downward drawing die). Although wrinkles appear in the flange part during first drawing, in redrawing in which the difference between the diameters before and after drawing is large, wrinkles appear as vertical wrinkles in the side wall part. The inner diameter guide supports so that the side wall part does not buckle.

Next the relationship between the inner diameter guide and the rounded part of the die is explained here. The material of the product is gripped between the inner diameter guide and the rounded part of the die, slides over the inner diameter guide, moves to the rounded part of the die, and the drawing is done as the product moves to the interior of the die. At this time, the pressing force on the material held between the inner diameter guide and the rounded part of the die is determined either by the pressure of the die cushion or by the pressure of the spring. If this force is too strong, the deformation resistance becomes large causing breakage defects of the product or breakage of the inner diameter guide. If this force is too weak, it will lead to wrinkles. It is desirable to maintain a fixed gap between the inner diameter guide and the rounded part of the die. To do this, techniques are used such as placing a pin in the die, etc., and also a stopper is provided so that the gap between the inner diameter guide and the rounded part of the die is fixed.

This can be said to be the basic structure of a redrawing die.

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