Welding w/o warping

[doorsRus]

This is the problem I have. I need the advice of experienced welder
I have a project to build an aluminum door for an aircraft. It is an airstair door. Approx. 4 ft by 5 ft. It is made up of many sheetmetal parts all 6061. All the same thickness .063. Some parts will be bent to shape on a brake. Others will be cold formed to shape using a shrinker stretcher. All the parts will then be put in a jig fixture for welding, which will result in essentially a shell. The problem that a previous manufacturer had was warping.
I saw at one time a welder first tacking together, than welding little sections (approx 1 inch) at time at opposing locations. I think it was for allowing even heating of the aluminum. I would think with the addition of "clamping until cooling" that this might reduce the warpage.
Is this correct?
Karl

 

[butelja]

Have you considered riveted construction as is used on most aircraft construction? I realize that aircraft are usually riveted because the alloys used (i.e.-2024) are not weldable. Even though 6061 is readily weldable, I don't think there is anything that would preclude riveting.

On the other hand, if welding is definitely required, then stitch welding, as you have described, will reduce distortion. The key is to make as many small tack welds to tie everything together before welding out the structure. Then, on long beads, skip weld and then go back to fill in the skipped areas. Of course, the heat affected zone around the welds will be weaker than the parent material, unless post weld heat treating is performed. That heat treating opens up more possibility of distortion unless the weldment is rigidly held in a massive jig during the heat treating process.

 

[doorsRus]

Riveting would have been nice, but the door has an STC that says as as originally designed to be welded. to change to rivets would require a redesign and a immense amount of paperwork to satisfy the FAA.
Thanks for your response

 

[quattro]

I am not a welder, but I designed and supervised welding of large 6061-T6 aluminum structures for radiocomm antennas. We successfully used "clamping until cool" method as you described it. It worked well provided parts were properly jigged.
Efraim

 

[mcprofusion]

Copper water cool shoes can be used to control distortion.

 

[chiph]

have you considered pulsing and/or helium to offset the thermal conductivity?