A cooling weld moves the assembly
A frame can be square on the bench yet pull inward, bow or twist after welding. Uneven heating and contraction change its geometry.
TWI and Lincoln Electric treat distortion as a combined design, assembly and sequence problem. The approved welding procedure and design remain decisive.
1. Define finished dimensions
State outside dimensions, diagonals, holes, joint form and weld symbols. Mitred and butt-jointed frames need different cut calculations.
Confirm actual section and wall thickness, test the saw and remove burrs without enlarging joint gaps.
2. Establish a flat reference
Check the bench, stops and squares, and remove debris beneath the work. Clamp firmly without crushing thin walls.
A fixture provides repeatable references; approve the first part before batching all cuts and tacks.
3. Treat tacks as welds
Tacks carry stress and may remain within the final weld. They need clean surfaces, compatible filler and sound fusion.
Tack critical references first, distribute the remaining tacks and recheck diagonals. TWI lists tack welding, paired assemblies and stiffening among distortion-control techniques.
4. Verify diagonals and plane
Equal side lengths do not prove squareness. Compare diagonals and check all corners against a reference plane.
Adjust tacks and clamps in a controlled manner. Presetting requires trials and an approved procedure.
5. Balance the welding sequence
Completing one side can concentrate heat. Where the procedure allows, alternate sides or distribute shorter runs. Lincoln Electric notes that welding only one side causes more distortion than alternating sides.
Do not reduce required weld quality. Good joint design can limit unnecessary weld-metal volume, but weld size comes from engineering.
6. Control heat input
Current, voltage, travel speed, consumable and interpass temperature all matter. Excessively slow travel can overheat thin sections.
Do not quench hot steel without an approved procedure. Allow balanced cooling and measure final geometry at a suitable temperature.
7. Correct only with control
Recheck dimensions, holes and weld acceptance after releasing clamps. Clean spatter without thinning the parent metal.
Pressing or flame straightening requires expertise, especially for structural work. Record and remove the upstream cause instead of repeatedly forcing parts straight.
8. Prepare a fabrication record
Specify grade, wall thickness, cut list, tolerances, welds, plates, holes, coating and quantity. Structural work may require qualified procedures and inspection.
Record tack sequence, parameters and before-and-after dimensions on the first article to make repeat production consistent.