Warping when Welding 2

As you do not describe the joint more precisely, I would presume that you are talking of a T joint, with the thin piece standing on the wide side of the thick piece, fillet welded. The deformation is caused by residual tension stresses along the weld.
One way to reduce stresses and deformation is to weld a short length and immediately after that to peen the weld with a hammer to lengthen the weld bead. Then proceed the same way by short stretches not contiguous, until the whole piece is welded.
Otherwise you could try to bend the thick piece in the opposite direction (from that rainbow you see now), again welding short stretches that will finally straighten the piece to the original shape.

The control of warpage is an arduous task.
Controls include:
1. The use of restraining fixture, strong tiebacks, or many tack welds.
2. The use of heat sinks or rapid of welds.
3. The pre-distortion or pre-bending of the parts prior to welding.
4. Balancing welds about the neutral axis or using wandering sequences, back step welding, or stitch welding.
5. Proper joint design selection and minimum size.
6. Preheat.
7. Peeing.

In your application, attempt stitch welding, weld 2 inches 5cm) skip 12 inches (30 cm) and repeta until the joint is completed.


Vita sine litteris mors est.

Rich,
I hope you meant "peening" in option 7. Noise we can deal with, the smell probably not!

Griffy

You didn't indicate which process you are using, but, process selection can have a significant impact on distortion levels. For the application you described, GMAW in the short circuit mode sounds like a good fit. Back stepping can also be a useful technique in the quest to minimize distortion.

You will never eliminate welding distortion as your weld puddle is about 2000 degrees F and cools meaning the material will shrink. The shrinkage will pull the material. Controlling weld pull is one of the major tasks of a welding engineer.

Some people will tell you to use many small tacks and the it won't pull. In actuality you will get poor penetrating and subpar welds.

Better joint design or mechanical fastening is probabaly your best solution but one approach is to put a bow into the part before welding which will be corrected by the welding.

I know a fellow who used to construct high end custom bicycle frames. He would tack the alloy steel frame tubing with TIG and then fillet braze. This avoids the weld warp of the tubes. It also makes a pretty looking joint.

Every once in a while, I like to refer to the web site below for additional information on welding. Regarding control of distortion, go to the "How To" welding tips section on this web site and scroll down to the article on "Prevention and Control of Weld Distortion". The articles are well written and provide good “hands-on” information.