Troubleshooting guide › Weld defects › Distortion
Distortion is the bending, twisting or shrinking of a job as the weld cools. Every weld shrinks; the question is whether you let it shrink evenly. It is the defect that costs fabricators the most in rework, because a frame that is out of square or a panel that has buckled has to be straightened or scrapped.
Reviewed by the Cruxweld technical team, October 2026. Settings are starting points to confirm on a test piece; acceptance is decided by the code or drawing the job is built to. Checks marked “call” are for our technical team.
Angular distortion: a fillet weld pulls the vertical plate over. Longitudinal bowing: a long bead bends the beam into a banana. Buckling: thin sheet ripples beside the weld. Shrinkage: the job comes out shorter than drawn.
Illustration, not a photo. Orange marks the defect.
Larger welds and slower travel put more heat in, and more heat means more shrinkage.
The weld side shrinks and pulls the job that way.
Welding from one end to the other lets shrinkage accumulate.
The gap opens or closes as the weld moves along.
Parts are free to move.
Heat builds up and buckles the sheet.
| Process | Typical reason on this process | What to do |
|---|---|---|
| MIG / MAG | Over-welding: fillets larger than the drawing asks for, too slow travel, continuous welds where intermittent would do. | Weld the leg size specified and no more, use the fastest travel that still fuses, stagger short welds. |
| ARC / MMA | Many slow passes with large electrodes put more heat in than one faster MIG pass. | Fewer, faster passes; balance welds on both sides of the neutral axis. |
| TIG on stainless | Stainless expands 50 % more than mild steel and holds heat; thin sheet buckles. | Tack every 30-50 mm, use copper backing or chill bars, keep interpass below 150 degrees C. |
| Submerged arc | High heat input on long seams: angular distortion and bowing. | Pre-set the angle, weld from the centre outwards, alternate sides on double-V joints. |
| Welding carriage / automation | Consistent speed actually reduces distortion, but a carriage will faithfully over-weld if the speed is set too low. | Set speed from the leg size table, weld both sides with two carriages or alternate sides. |
MIG / MAG fillet, 1.0 mm wire on 5 mm frame tube. A starting point only; confirm on a test piece of the same plate.
| Fillet size | as drawn, usually 4 mm, not more |
| Current / voltage | about 150-190 A / 20-23 V |
| Travel | as fast as fusion allows |
| Sequence | tack all, then weld opposite corners in turn |
| Fixture | flat table, clamps, check square after tacking |
Typical values for mild steel. Your wire, plate condition and machine will move them. Our technical team can set them with your operator on a video call.
Measure before and after: a straight edge and feeler gauge on plate, a string line on long beams, a square on frames. Record the pull on the first part of a batch and pre-set the opposite way on the rest.
Yes, by flame straightening (local heat on the convex side, then cooling) or by pressing. Both take time and skill, so prevention by sequence and tacking is cheaper.
It removes the variation in speed and arc length that a hand weld has, so heat input is consistent and lower on average. It cannot undo a bad sequence.
It stops movement during welding but locks in stress, which can release as distortion when the clamps come off, or as cracks. Clamp, but also sequence the welds and pre-set where possible.
Mechanised welding (a carriage or a positioner) keeps travel speed constant, which keeps heat input and distortion predictable on long seams. For hand welding, a good fixture matters more than the machine.
Send a photo of the weld or cut, your machine model, consumable and plate thickness. Our technical team replies on WhatsApp with the likely causes and the next checks to make.
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