#117 Terminology and Surroundings (11) Relative Plate Thickness (Drawing Operation)
While investigating the process of a drawing operation (consider cylindrical drawing), although the number of drawings is determined from the development of the blank and the drawing ratio, it is also possible to continue investigations even if the plate thickness is omitted. However, when we consider the actual drawing, if we assume that the blank diameter obtained during blank calculations is 100 mm, nobody will think that the ease of drawing is the same when the plate thickness is 1 mm as when it is 0.1 mm. "Relative plate thickness" is an attempt to judge the state of drawing from the relationship between the blank diameter and the plate thickness. The relative plate thickness (see Fig. 1) is expressed as follows.
Relative plate thickness = t / D�100(%)
The result of calculation will be in the range of 0.1 to 2.0 in the case of usual products. A product with a smaller value is more difficult to draw, and a product with a larger value is easier to draw.
When the blank diameter is 100 mm and the plate thickness is 0.1 mm, the relative plate thickness becomes 0.1 and is difficult to draw. The meaning of this is that, wrinkles or cracks appear when a small change is made in the conditions such as the wrinkle suppression force, etc.
When the blank diameter is 100 mm and the plate thickness is 1.0 mm, the relative plate thickness becomes 1.0, and with this value, it is possible to draw without much difficulty using a die with a wrinkle suppressor.
When the relative thickness is 3.0 or more, it is possible to draw without a wrinkle suppressor.
When the relative thickness becomes still larger, the plate cracks and it becomes difficult to draw the product.
Using relative thickness, it becomes possible to make judgments in this manner. It is possible to know still more detailed conditions when combined with the drawing ratio.


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