Question regarding drawn shells

Hello,

On draw dies, I was taught that when designing a cup draw strip with anything under a 40% draw, a ‘dog bone’ type strip design should be used, and that if it is over 40% it should be designed as an ‘onion cut’ (lanced) type strip (Some call it a cookie cut), & if it is really thick material or the draw depth is equal to or deeper than 2x the cup diameter. Then you should design using a stretch web type strip design. My question is:
A: Is this accurate
B: If so, how thick does material have to be to justify switching to the stretch web type carrier?

Very interested in this topic as well. I would love to know what rules of thumb apply.

Designing dies for drawn shells

D.Minnich said:

Hello,

On draw dies, I was taught that when designing a cup draw strip with anything under a 40% draw, a ‘dog bone’ type strip design should be used, and that if it is over 40% it should be designed as an ‘onion cut’ (lanced) type strip (Some call it a cookie cut), & if it is really thick material or the draw depth is equal to or deeper than 2x the cup diameter. Then you should design using a stretch web type strip design. My question is:
A: Is this accurate
B: If so, how thick does material have to be to justify switching to the stretch web type carrier?

Click to expand...

It may be helpful to refer to a copy of "Die Design And Die-making Practices" Published by the Industrial Press the same publishers that prints the "Machinery's Handbook".
Forty percent is a good general rule with #4 temper sheet for the first draw. It's hard to pin down the best first draw depending on the material temper but for the most part your good to go. It makes a difference depending on the diameter of the shell and the draw radii. There is a best draw radii to use depending on the material thickness and the diameter of the shell.
In reference to web design. I can only suggest that when the stock strip distortion interferes with the stock strip progression; it is a judgement call. There are few hard fast rule when building draw dies.

Roger