Welding Distortion Prevention

[Matlsguy]

Hello,

I am familiar with the common practices in welding distortion prevention - i.e. preheating, using opposing welds, or using fixuring to restrict plastic deformation to the fusion zone. A fully restrained weld will still contract elastically when the clamps are removed. I was wondering if its possible to weld in a fully restraining fixture and do a stress relief while the material is still in the fixture. This way all residual elastic strains will be relieved via creep. Once when the assembly is cooled and clamps removed there shouldn't be any elastic "springback". I looked through the ASM Welding Handbook for this practice, but could not find any evidence of it. It it possible to do this technique? Any insite would be much appeciated.

Regards

Matlsguy

 

[metengr]

I was wondering if its possible to weld in a fully restraining fixture and do a stress relief while the material is still in the fixture. This way all residual elastic strains will be relieved via creep.

Reply; I would not recommend it. Strongbacks or other methods of restraint are designed to reduce or prevent distortion in or along a particular direction (transverse, longitudinal or angular), wile still allowing the component to move in other, less critical, directions to avoid over-stressing the base or weld metal (in a fully restrained joint). Stress relief will reduce any residual stresses that were generated as a result of restraint along a preferred direction.

 

[unclesyd]

I concur with metengr about picking only one direction for restraint. Depending on your configuration you could end up with everything just a little out. This is not saying that jigs want help you in some cases. We used jigs all the time to control surfaces where we will have to machine. Most of the time will leave the component tied to jig and stress relieve prior to machining. At times the free floating components have to be coaxed into their proper position after all is said and done.

Distortion Control

The first site list the books by John P. Stewart. The book on distortion control is very good.

The second site has a book "Design of Weldments" by Omer Blodgett that you can't afford to be without. It has a very good section on distortion control.

http://www.aws.org/cgi-bin/mwf/topic_show.pl?tid=8491

https://ssl.lincolnelectric.com/lincoln/apdirect/store.asp?PID=16&cat=8