NUMBER OF PASSES-

The number of passes required to form a given shape is dependent on several variables:

1. Formability of the material

2. Thickness of the material

3. Complexity of the product shape

4. Tolerances of the product shape

5. The tool designers judgment, which is ultimately based on his experience, and his access to past successful tool designs.

There have been a couple of attempts to show a mathematical relationship that could be used to determine the number of passes. One of these was published in 1994 by the Fabricators & Manufacturers Association in a paperback called Roll Forming, subtitled Collected Articles and Technical Papers. On page 6 the author

(unnamed) suggests a relationship , where P=number of passes, L = bending distance as illustrated in Fig. 4.1, and e=Admissible bending distance. Fig. 4.1 repeats the essential elements of the author s original drawing which defined L and e . The equation implies that e is a constant increment between the successive passes of the progression. The author s drawing shows pass 10 to be a duplicate of pass 9 which means that the value of e between those two passes must necessarily be zero. Similarly, the increment between pass 8 and pass 9 must be much smaller than that between pass 4 and pass 5. In the author s accompanying text, he states The bending distance, e, is an empirical value which depends on the geometry of the machine being used, which means that e only has a meaningful...