Weld Shrinkage Prediction Troubleshooting

Shrinkage Prediction vs Reality — Quick Answer

Use this when the calculator said 2 mm shrinkage but you got 8 mm bow, or predicted angular change doesn't match the fixture release. This page is prediction error only — not how to fix bowed plate (see Weld Distortion Troubleshooting).

1. Restraint Not Accounted For in the Estimate

What it looks like: Calculator predicts large angular change; part barely moves because it was fully fixtured. Or opposite: calc assumes free shrinkage but heavy framing actually forced bending into a weaker direction.

Likely causes: Models assume unrestrained joint line shrinkage. Clamps, tack spacing, and adjacent stiff members redistribute shrinkage into bow or twist not captured by a simple volume×coefficient estimate.

Fixes: Classify restraint level (free, partial, fully fixtured) when interpreting the calculator. For fixtured work, expect less visible movement but higher locked-in stress — field symptoms on Weld Distortion Troubleshooting.

2. Multi-Pass Heat Accumulation

What it looks like: First pass matches estimate; distortion accelerates on fill and cap. Angular change non-linear with pass count.

Likely causes: Single-pass shrinkage model applied to multi-pass groove. Interpass temperature raises local compliance; cumulative longitudinal shrinkage on long seams dominates over single-bead calc.

Fixes: Use per-segment or per-pass planning from the guide; stagger welds, back-step, or limit interpass heat input. Compare prediction to field distortion patterns.

3. Material-Specific Shrinkage Factor Errors

What it looks like: Mild steel factor applied to stainless or aluminum; prediction consistently high or low by alloy batch.

Likely causes: Coefficient of thermal expansion and yield strength differ by alloy — shrinkage force and amount scale with material. Using a generic 0.05–0.10% without alloy selection skews results.

Fixes: Select actual base metal in the calculator; record shop measurements to calibrate your process. Aluminum distorts more per unit shrinkage force than steel due to lower modulus.