Weld sequence for this part?

[Trboatworks]

All.

I need to weld up two of these struts.
They are about ten feet long and four high.

What is the best weld sequence to minimize warping?

The larger pipe is 1-1/2” SCH 40 and the smaller 1” SCH 40.
The cross parts are 1.25”x1-1/2” ovals.

BD anodized.

What say you?
I am thinking this will want to curl a bit tighter as the larger pipe will overcome the smaller with welding.

 

[magneticanomaly]

I do not think sequence will have much effect. Both chords will tend to warp toward the welded side. so the smaller one will open its curve and the larger will tighten it. Since the larger one is stronger, and welds are a slightly lesser % of its length, I agree that the whole structure will tend to curl.

You migh be able to balance it by using a process with more heat input (like SMAW) for the inner chord-to-strut welds, and less heat input for the outer, (like GMAW).

But for a short run without the luxury of lots of parts to experiment on, I would make a rigid fixture to hold critical features in the correct relative position, weld it, then do a litle heat-shrinking as needed until the part comes freely out of the fixture.

OR, you could try vibrating the part as you weld, with part in alignment fixture, which IME greatly reduces warping

 

[climb-101]

i would tank every thing together with 4 tacks on each joint. i would preheat it with a weed burner torch and weld the ends and work from one end to the other. i don’t think it will warp too much with some preheat since the tubes will be trying to warp into each other.

the other thing you could do is run some water through the tube while you weld to help control the heat. i would also make sure to weld both the same way so if the do move they will still match.

 

[Trboatworks]

Ok thanks guys.

I need to get these done today so will just run with it.
I have the first one clamped up in a fixture to lock it up but honestly I am not sure if that is much help in controlling how much it moves.

Anchoring the ends makes sense.
The only thing I was thinking was welding the small pipe first thinking it had a better chance of balancing the warp that way.

 

[BT Fabrication]

Ok thanks guys.

I need to get these done today so will just run with it.
I have the first one clamped up in a fixture to lock it up but honestly I am not sure if that is much help in controlling how much it moves.

Anchoring the ends makes sense.
The only thing I was thinking was welding the small pipe first thinking it had a better chance of balancing the warp that way.

being tubing, it won't warp much as long as you don't sit in one spot and cook it. get in, get out. as the structure will prevent it from moving much.

 

[Trboatworks]

Thanks all.
I have the first one fully welded up.
Essentially no change in shape.

The strut squirmed around a bit in the fixture as I was running through it but in the end I suppose the weld distortion on those two pipes balanced out.