How to control distortion in welding?

Distortion is the change in shape of a part caused by uneven thermal expansion and contraction during welding. Here's how to control it:

Types of distortion:

• Longitudinal shrinkage: The weld shortens along its axis
• Transverse shrinkage: Narrowing perpendicular to the weld bead
• Angular distortion: The piece bends around the weld axis
• Buckling: Deformation of thin sheet metal

Control techniques:

• Skip welding (stitch welding): weld in spaced segments, alternating sides and letting the part cool between segments — the segment length is set from the thickness and the expected shrinkage
• Presetting (pre-bending): tilt the pieces against the expected deformation, by an amount calculated from the expected shrinkage
• Clamping: Use rigid clamps to hold pieces in place. However, clamping increases residual stresses
• Welding sequence: For a multi-pass joint, weld symmetrically (pass 1 on left, pass 2 on right)
• Minimal heat input: Use the lowest amperage possible while maintaining fusion. Limit the number of passes

Shrinkage: it is calculated for a given joint from welding energy, thickness and number of passes; no single value applies to every assembly.