TIG welding problem and solution

[etpm]

I needed to make two aluminum door frames for our greenhouse. I have a machine shop so I milled the corners to exact 45 degree angles. The material is 3/16 thick angle with 1.5 inch legs. After milling the material I beveled the corners on the back side for good weld penetration. I left about 3/32 un-beveled so that I could use flat left to keep the corners at 90 degrees. Being out of practice for TIG welding I decided to weld a few practice pieces. So I machined some short pieces and welded them. After welding the corners ended up at less than 90 degrees. Looking at the parts I could see that there was 100% contact at the corners, the outsides had not pulled away, which would have given the less than 90 degree corners. I had clamped the parts well and yet they still pulled. Looking closely at the inside of the angle I noticed that the aluminum was bulged slightly where the weld was. I finally determined that the aluminum had gotten soft during the welding process and when the weld cooled it pulled so hard it bulged the material so that I ended up with the less than 90 degree corners. To fix this problem I welded about halfway from the outside and welded the very outside corner. I did this for all 4 corners. After all the corners were done I came back and welded the last half of each beveled part. This process of letting the aluminum get completely cool as well as having the rest of the corner welded allowed me to lay down the last part of the bead without the aluminum getting soft. Now all the corners are perfect 90 degree angles.
Eric

 

[CalG]

I needed to make two aluminum door frames for our greenhouse. I have a machine shop so I milled the corners to exact 45 degree angles. The material is 3/16 thick angle with 1.5 inch legs. After milling the material I beveled the corners on the back side for good weld penetration. I left about 3/32 un-beveled so that I could use flat left to keep the corners at 90 degrees. Being out of practice for TIG welding I decided to weld a few practice pieces. So I machined some short pieces and welded them. After welding the corners ended up at less than 90 degrees. Looking at the parts I could see that there was 100% contact at the corners, the outsides had not pulled away, which would have given the less than 90 degree corners. I had clamped the parts well and yet they still pulled. Looking closely at the inside of the angle I noticed that the aluminum was bulged slightly where the weld was. I finally determined that the aluminum had gotten soft during the welding process and when the weld cooled it pulled so hard it bulged the material so that I ended up with the less than 90 degree corners. To fix this problem I welded about halfway from the outside and welded the very outside corner. I did this for all 4 corners. After all the corners were done I came back and welded the last half of each beveled part. This process of letting the aluminum get completely cool as well as having the rest of the corner welded allowed me to lay down the last part of the bead without the aluminum getting soft. Now all the corners are perfect 90 degree angles.
Eric

Start with tack welds at the inside and outside of each corner. Straighten everything as you go before welding it all up.

Clamping doesn't help a bit. The HAZ is powerful!

 

[etpm]

Start with tack welds at the inside and outside of each corner

I tried that. The real problem was the aluminum was getting so hot. I needed it to be cooler to prevent it from getting so soft. You are right about the clamping, didn't help. If it had been steel I don't think there would have been a problem.
Eric