Defect Troubleshooting Guide

Diagnose laser welding porosity, cracks, undercut, spatter, and incomplete fusion with controlled checks for cleaning, shielding, focus, fit-up, and heat input.

Laser welding troubleshooting quick answer

Start with the observed defect, then check the simplest controlled variables first: surface preparation, shielding coverage, focus position, fit-up, travel speed, and heat input. Change one variable at a time and verify the result with the inspection method defined for the part.

Surface quality calculatorCrack risk calculatorDefect troubleshooting table

Defect Diagnosis Flowchart

Start here → Identify defect type → Follow solution path

Start: Defect FoundVisual inspection:What do you see?PorosityRound cavitiessurface/internal✓ Clean surface✓ Increase gas✓ Reduce speedCracksLinear fracturesReview nowCheck preheatCheck fillerCheck PWHTUndercutGroove atweld toeCheck heat inputCheck speedCheck focusSpatterMetal dropletsaround weldCheck intensityClean surfaceCheck focusIncompleteLack offusionCheck energyCheck speedFix fit-upStill have defects after fixes?Check material-specific factorsMaterial Issue?High Carbon Steel:Check thermal planAl/Cu: check absorptionEquipment Issue?Check beam quality M²Check gas purityCheck calibrationProcess Issue?Joint fit-up toleranceFixturing/clampingImprove prep✓ Problem SolvedDocument solution!

Systematic approach: Start with visible preparation and shielding checks, then change one variable at a time and record the inspection result.

Common Defects Overview

P

Porosity

Check:
Common check item
Severity:
Medium
C

Cracks

Check:
High-priority check item
Severity:
High
U

Undercut

Check:
Geometry check item
Severity:
Medium
S

Spatter

Check:
Process stability item
Severity:
Low
F

Incomplete Fusion

Check:
Fusion check item
Severity:
High

1. Porosity

Identification

  • Appearance: Round cavities on surface or internal (X-ray shows circular dark spots)
  • Location: Random distribution or concentrated at start/stop points
  • Size: Record the measured indication size and compare it with the applicable acceptance level.

Decision Tree

Step 1: Where is the porosity located?
  • → Start end only: Check start parameters (ramp up too fast)
  • → Stop end only: Check stop parameters (crater not filled)
  • → Along entire weld: Go to Step 2
  • → Random spots: Check surface contamination first
Step 2: Is the surface clean?
  • Visible oil or grease: Clean with an approved method, then recheck.
  • Rust or oxidation: Use the specified mechanical or chemical cleaning method.
  • Moisture concern: Check drying or preheat requirements before welding.
  • Surface appears clean: Go to Step 3.
Step 3: Is gas shielding adequate?
  • Flow is unstable: Confirm regulator, nozzle, and fixture interference.
  • Nozzle is poorly positioned: Adjust coverage and repeat the sample check.
  • Gas quality is uncertain: Confirm cylinder, line, and purge condition.
  • Gas checks are acceptable: Go to Step 4.
Step 4: Check welding speed
  • Keyhole appears unstable: adjust speed and heat input in a controlled trial.
  • Still have porosity: check material composition, coating, and hidden contamination.

Solution Priority Table

SolutionEffectivenessDifficultyCostTime
1. Clean surface thoroughly
High
EasyLowShort check
2. Confirm shielding coverage and gas delivery
Moderate
EasyLowShort check
3. Adjust travel speed only after checking keyhole stability
Moderate
EasyLowShort trial
4. Replace gas cylinder (check purity)
Variable
MediumMedium10 min
5. Preheat material to remove moisture
Targeted
MediumMedium20-30 min

2. Cracks

Priority warning

Treat cracks as a stop-and-review condition. Do not release the weld until the cause, inspection method, and acceptance requirement are resolved by the responsible engineering owner.

Identification

  • Types: Hot cracks (intergranular) vs Cold cracks (transgranular)
  • Longitudinal: Along weld centerline (hot cracks, high restraint)
  • Transverse: Across weld (cold cracks, hydrogen embrittlement)
  • Crater cracks: At weld termination (solidification)

Material-Specific Crack Risk

MaterialCrack RiskRisk LevelPrevention Measures
Low Carbon SteelLow
Low
Confirm restraint, thickness, and procedure requirements
Medium Carbon SteelModerate
Medium
Check carbon equivalent, preheat need, and cooling rate
High Carbon SteelElevated
High
Use a controlled thermal plan and procedure-defined inspection
Cast IronVery elevated
Very High
Use metallurgy review, filler selection, and controlled cooling plan
Stainless Steel 304Application dependent
Low
Reduce restraint and confirm HAZ or corrosion requirements
Aluminum 6061Application dependent
Medium
Check filler, heat input, porosity, and cracking tendency
TitaniumShielding dependent
Low
Control shielding, back purge, cleaning, and hot-zone exposure

Solution Priority Table

SolutionEffectivenessDifficultyCostTime
1. Check whether preheat is required for the material and restraint level
High
MediumMediumProcedure dependent
2. Use flexible fixturing (reduce restraint)
Moderate
MediumLow10-20 min
3. Optimize weld sequence
Moderate
MediumLow5 min
4. Add filler material
Targeted
HardMedium10 min
5. Post-weld heat treatment when specified
Application-dependent
HardHighProcedure dependent

Quick Solutions for Other Defects

Undercut

  • Reduce local heat input and verify bead edge shape
  • Increase travel speed cautiously if the weld remains stable
  • Check focus and beam position before changing more variables
  • Add filler material

Spatter

  • Reduce local intensity if keyhole behavior is unstable
  • Check focus and plume behavior before changing more variables
  • Increase gas flow
  • Clean surface thoroughly

Incomplete Fusion

  • Increase delivered energy only after checking fit-up and focus
  • Reduce welding speed
  • Improve joint fit-up against the project tolerance
  • Check focus position against the qualified setup

Troubleshooting Practices

Systematic Approach

  1. Document the defect: Take photos, note location, measure size
  2. Follow decision tree: Check preparation, shielding, focus, fit-up, and heat input in order
  3. Change one variable at a time: Don't adjust multiple parameters simultaneously
  4. Verify the fix: Run test welds before production
  5. Record the solution: Build institutional knowledge

Common Mistakes

  • Adjusting too many parameters: Can't identify root cause
  • Skipping surface cleaning: Often contributes to porosity and unstable weld appearance
  • Ignoring material properties: Carbon equivalent, alloy family, coating, and restraint can change the thermal plan
  • Not documenting gas flow: Record nozzle setup, flow reading, coverage, and repeat-check evidence

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