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stress relieving 6061-T651
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Posted by: paul.apprill

06/07/2007, 10:13:31

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We need to stress relieve a large machined aluminum part before final machining to relieve residual machining stresses to ensure flatness. Our machine shop recommends 350F for 2 hrs.Is this sufficient? Can you cite a reference (ASM Handbook, other)?







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Re: stress relieving 6061-T651
Re: stress relieving 6061-T651 -- paul.apprill Post Reply Top of thread Forum
Posted by: randykimball

06/07/2007, 10:43:49

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Ok, here is what I did for many years with excellent results.
I was known for planning thin round parts of 6061 with window cuts and odd shape removals. What I did was put them outside for a few days so they took the evening cool and noon sun cycles. They relaxed and made us famous with several vendors for being able to produce those magical round thin parts that had a history of failure before we got our hands on them. Of coarse we did the final machine work in pots and on mandrels with three point contacts... not in a chuck. ...AND some parts required a second trip outside with .01 diameter stock left.

To do this we left about .032 to .1 stock on the diameter depending on the size of the blank and how much movement we expected during the relax period.

Well, anyway, it worked... and worked well!





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Modified by randykimball at Thu, Jun 07, 2007, 10:46:58


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Re: stress relieving 6061-T651
Re: stress relieving 6061-T651 -- paul.apprill Post Reply Top of thread Forum
Posted by: Kelly Bramble

06/07/2007, 10:26:55

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I don't remember the specification, however I have done this before on a particularly tough to manufacture part.

The challenge was that we had an aggressive flatness requirement and due to the internal stresses of the part following machining operations, the part warped us out of tolerance after the manufacturing restraining loads where removed. I believe our solution was to rough cut the part leaving about .015" extra material on the critical surface before heat treating. The heat treating consisted of placing the part in an oven at about 350F for several hours. Then the part was final machine cut to the desired size and flatness. The heat treating process reduced the internal stresstes in the material.

Keep in mind that the heat treat process will reduce the working loads and other strength characteristics of the material.

Ultimately, I believe the right solutions in our application were to either specify the flatness with the part in a restrained condition or back off of the aggressive tolerance specification.

I will look around and see if I can find the relevant specification.








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Re: Re: stress relieving 6061-T651
Re: Re: stress relieving 6061-T651 -- Kelly Bramble Post Reply Top of thread Forum
Posted by: Kelly Bramble

06/07/2007, 10:37:28

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OK, I found the document, however there is not a specification.

We used this process on a spacecraft component and handled it with a engineering drawing note.

The note was: Prior to final machining, stress relieve at 350 degress F for 8 to 10 hours. Cool in still air.

There was a description within an email that also gave a maximum exposure time for the different aluminum alloys. For 6061 the maximum exposure time was 100 hours a 350F, 10 hours at 375F and 1/2 hour at 400F.








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