Shop-floor diagnosis

Defect Troubleshooting Table

Common symptoms, likely causes, and first checks for weld defect troubleshooting.

Start withThe symptom

Use the visible defect to choose the first check instead of changing every setting.

First ruleChange one variable

Avoid changing power, speed, focus, and gas all at once.

Stop pointSection or escalate

Hidden defects, cracks, and repeated failures need sectioned evidence before release.

Defect triage table

Symptom	Likely causes	First checks
Porosity	Oil, oxide, moisture, poor shielding, unstable keyhole, or excessive speed.	Clean surface, verify gas flow/nozzle angle, reduce speed, and section a sample.
Cracking	High carbon equivalent, restraint, fast cooling, brittle phase formation, or filler mismatch.	Check CE, preheat range, weld sequence, restraint, and post-weld heat-treatment need.
Undercut	High speed, excessive power density, focus error, edge gap, or poor beam alignment.	Reduce speed, adjust focus, verify fit-up, and inspect the weld toe.
Spatter / expulsion	Excess peak power, contaminated surface, tight vapor channel, or unstable absorption.	Clean surface, lower peak power, adjust pulse shape, and verify clamping.
Incomplete fusion	Low heat input, poor focus, excessive gap, oxide barrier, or high thermal conductivity.	Increase heat input carefully, improve joint prep, and confirm penetration by sectioning.

Sequence	Action	Result to compare
1. Surface and fit-up	Clean the same way, reclamp, and confirm gap/mismatch before changing settings.	If the defect disappears, keep the process row and tighten preparation controls.
2. Shielding	Verify gas type, purity, flow, nozzle distance, angle, and backside/trailing coverage.	If oxidation or porosity changes, document the gas setup as a process variable.
3. Focus and path	Check focus height, spot position, beam alignment, robot path, and acceleration zones.	If the defect follows corners or starts/stops, tune path control before heat input.
4. Power-speed pair	Adjust power or speed in small steps while holding all previous checks constant.	Compare bead shape, penetration, HAZ, and defect frequency after each step.
5. Thermal strategy	Review preheat, interpass temperature, heat sinking, weld sequence, and restraint.	Use when cracks, distortion, hardness, or HAZ width remain the limiting issue.

Signal	Reason	Action
Cracks appear	A surface crack can indicate metallurgical or restraint failure, not a cosmetic issue.	Stop release, section the sample, and review material/preheat/restraint assumptions.
Porosity persists after cleaning and gas checks	The pore source may be trapped contamination, keyhole instability, or material condition.	Section representative samples and compare pore location to the weld pool geometry.
Penetration varies along the same seam	Path height, fixture movement, or heat buildup may be changing during the weld.	Cut start, middle, end, and any corner or speed-transition location.
A correction fixes one defect and creates another	The process is at a window boundary, not a stable center point.	Build a smaller matrix around the last passing setting and record rejected edges.

Confirm final requirements against the current standard text, workplace procedure, and project specification before releasing production settings.