16 GMAW Distortion Control
Distortion is the same thing as warping. In the past, the terms “warpage” or ‘warping” were typically used. Nowadays, people tend to say “distortion.” When metal gets hot it expands, when it cools down it shrinks. If metal heats and cools unevenly, it will expand and contract unevenly (distortion). Metal will always distort towards the heat.
Not all metals distort the same way. How much metal distorts depends on how well it conducts heat and how fast it expands. Under the same circumstances, stainless steel will distort more than carbon steel because stainless has lower thermal conductivity (it conducts less heat) and it expands faster.
You cannot totally prevent distortion, but it can be controlled to an “acceptable level”. An acceptable level of distortion will not compromise the integrity of the weld.
Methods of Distortion Control
- Restraint: physically hold the metal in place as you weld.
- Sequencing: start with offset plates, then weld in a sequence in which the plates straighten out as you weld.
- Finding the proper sequencing order is often done by trial and error.
- Minimizing welding: use staggered instead of intermittent welds.
- Why does this work? Welding creates heat. Heat causes distortion. If you can weld less, there will be less heat and distortion.
- Proper joint preparation: put tack welds in the right places.
- Best fit-up: measure before you weld.
- Higher welding speed: don’t let heat get concentrated.
- This is especially useful and important when welding with aluminum!
- Make fewer passes.
- Offset parts: start crooked so it straightens out as you weld.
- Some welds you cannot tack multiple sides.
- Peen the weld metal: this causes the metal to stretch, offsetting contractions.
- Heat sinks: use water or an aluminum block to cool your metal
- Flame bending: apply heat to a distorted section to reverse distortion.
