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#037 Basics of Die Structure (19) Structure of Drawing Dies: First Drawing Dies for Upward Drawing

Category : Drawing and Forming Work
April16, 2010

This is a drawing die structure in which the placement of punch and die is inverted. This die structure is shown in Fig. 1.

Fig. 1

This die structure is used extremely frequently for drawing operations. The wrinkle suppressor is very often called the blank holder. This is because the blank positioning part has been prepared in the wrinkle suppressor. The material to be formed is placed on the blank holder, the drawing is done upwards from below, and the product enters the die. The product that has entered the die is ejected from the die by the knock out at the top dead point, and is blown away to outside the die by compressed air, etc.

The method of knocking out is shown in Fig. 2

Fig. 2 Relationship between the press machine and the die

The state at the bottom dead point after completion of drawing is shown in Fig. 2(a). The product that has been drawn by the punch of the bottom die is present inside the die. The knock out is pushed up by the product. Along with the knock out, the knock out rod and the needle of the press machine are pushed up together. From this condition, although the slide of the press machine rises towards the top dead point, the product that has entered the die remains as it is in the die. After rising to near the top dead point, the needle hits against the needle adjustment screw. When this happens, the needle is lowered and lowers the knock out via the knock out rod, and ejects the product to outside the die. Fig. 2(b) shows the condition when the product ejection has been completed. The fearsome thing in this knock out structure is that of adjusting the needle. If the needle adjustment screw is lowered too much by mistake, the knock out rod will get bent. In the worst case, the top die gets detached from the slide and falls down thereby leading to accidents. When the knock out is not used or before adjusting the knock out, the needle adjustment screw should always be unscrewed up to the topmost position.

Returning to Fig. 1 let us pay attention to the die cushion in the bottom die. (This figure is showing a small die. In a large die, the die cushion will become an accessory apparatus of the press machine.) The die cushion is extending downwards after passing through the bolster hole of the press machine. Therefore, a considerably long spring can be used. This implies that it is possible to carry out the forming of even a considerably long drawn product. This makes it possible to form difficult products that can not be formed using downward drawing. Since it is sufficient to merely place the blank on the blank holder, the operability of press operation is much better than that of downward drawing. This can be used for forming shapes from blanks even when the product has a flange as well as when the product does not have a flange.

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