Crimp Die for 45 Primer and Cartridge -- FEA non-linear Analysis not matching with Real life results

[MechEngineerNT]

Hey Guys,

I'm running a quasi-static non-linear FEA in Ansys trying to simulate crimping a primer into the cartridge using a die crimp tool. In short, the crimping operation works in real life (80 units tested), to which I've decided to try to simulate. However, the results of the simulation aren't matching up with the real life results. I've put in all the right material properties of a 7075-T6 aluminum, and have also put in the bi-linear curve to simulate strain hardening. In the attachment, you can see I'm above the ultimate strength of the material, although it is in compression. Why does it work in real life, but the simulation isn't showing it? This has been giving me hell!

Thanks!

 

[ornerynorsk]

First of all, FEA is not a strength of mine, but let me point out that your set-up does not appear to represent what is happening in a typical primer crimp. It looks much more like tube-end swaging. The punch will be interacting with the cartridge base end-of-tool rather than side-of-tool. The 2 types of primer pocket crimp I am most familiar with is the "stab" type or annular ring type, neither of which perform an operation similar to tube end swaging.

My only other though is are you sure your cartridge casings are 7075-T6?


It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[dgallup]

I'm with ornerynorsk, I've never see an aluminum 45 ACP casing. Brass or nickel plated steel.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[ornerynorsk]

There are aluminum casings, sold under "Blazer" trade name by CCI, but I'm not sure if 7075-T6 is an alloy used. I remember the 30mm DoD project for what would eventually be used in the GAU-8, I think it was an alloy specifically designed by Alcoa for that project. 7075 seems a little too hard.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[btrueblood]

I'm wondering why you want to crimp the primer in the first place?

 

[ornerynorsk]

It's usually a military thing. It's to prevent back pressure of the igniting round from blowing the primer out, potentially jamming the action of a semi-or full auto gun. I've actually had this happen on a semi-auto 50 BMG rifle that did not have the primers crimped while shooting reloads. On a high cyclic rate gun it can really muck up things.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.