Metal Spinning Deformation 1

[Shahyan]

This shell made by metal spinning keeps deforming and I do not know why. There is no problem in the tooling. It is an issue with the material. I do not which mechanical property is the root cause. % elongation 38.4%, maximum tensile strength 426 MPa and yield strength 266.9 MPa. All three properties concur with the standard values. Any help in this matter will be highly appreciated.

 

[btrueblood]

Ok, something is still not right with the tensile modulus numbers you are quoting. 15.9 GPa to 22 GPa is equivalent to roughly 2.3 e6 to 3.2 e6 psi, i.e. about a factor of 10 below typical steels.
Assuming your numbers are off by a factor of 10, something is still not right with the first, "good" material modulus, as again, no alloy (not steel, not titanium, not brass or bronze) has a modulus anywhere near that value even when it is multiplied by 10. From the photo, your material looks to be stainless steel, but you've never explicity stated the alloy so we are just guessing.

0. What material (steel, stainless steel, alloy steel?), what alloy (304?), what condition (as rolled, annealed?)
1. Who did the material testing, and in what form was the alloy when the test was done?
2. Looks like you are starting from a tube - was material testing done on the as-received tube?
3. What tolerance variations exist in the as-received product? Does the "good" material run a bit thicker or thinner than the others?
4. Are you doing any in-process anneals, and if not why not?

 

[EdStainless]

What strain rate did you use for tensile testing? What did the samples look like?
What do the curves look like?
I agree, you modulus vales are wrong. And the modulus does not change for a given alloy. If you are reporting different values it is an artifact of how you are interpreting the tensile curves. There may be some clues in those curve shapes.
What specification is the material purchased to?
You need to add a lot of info before we can help you figure out where to look.

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P.E. Metallurgy