Draw die tonnage

I thought someone here might know...

We're discussing draw dies in school. When dealing with deep draws, frequently the final shell must be made in two or more drawing operations (redraws).

We have simple formulas to calculate draw tonnage for simple shapes (obviously only predictions).

My question is this: If you calculate the tonnage required to perform, say, a 70% reduction in *one shot* (not ideal, if even possible), would the tonnage required for multiple draws to obtain the same final shell be the same as the single-shot tonnage?

This is mostly just interesting as opposed to important, as far as I'm concerned. It does, however, have very real applications in industry.

Does anyone know the answer for sure? I have the "Die Design Handbook" vol.

3 but the math is over my head, as well as the theory.

Regards,

Robin

Reply to
Robin S.
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Not necessarily...

Since drawing requires plastic flow of the material and you tend to thin one section while thickening another, there are a number of factors that come into play. One is as simple as the speed of the stroke...too slow and the material flow causes increased pressures to be needed, too fast and you end up blowing out the thin sections.

Of course there's always work hardening of the material also...Depending on the material, you may get only one or two pre-form operations before the material is too brittle and needs to be annealed before further draws.

Finally, the stretching of the material in early pre-form draws changes the grain direction and thickness of the material so further draws may be fighting that a bit or may be eased.

Overall, it's too complex to answer your question with a generality. Your statement might be true in certain circumstances but as you already know, the real world doesn't always follow the "book" when things get really complex as in plastic metal flow.

Koz (who makes a note that he is NOT an expert, just taking from some minor experience doing mostly aluminum refrigeration coil fins and such....5 pre-form draws before the final sizing draw by the way)

Reply to
Koz

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