Defect Troubleshooting Guide

Systematic diagnosis and solutions for common laser welding defects. Follow decision trees to identify root causes and prioritize fixes.

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 speed💔 CracksLinear fracturesCRITICAL!⚠ Preheat 300°C⚠ Add filler⚠ PWHT⚡ UndercutGroove atweld toe↓ Reduce power 10%↑ Increase speedDefocus +0.5mm💥 SpatterMetal dropletsaround weld↓ Reduce powerClean surfaceDefocus +0.5mm❌ IncompleteLack offusion↑ Increase power 20%↓ Reduce speedFix fit-upStill have defects after fixes?Check material-specific factorsMaterial Issue?High Carbon Steel:→ Preheat 200-300°CAl/Cu: Need 2-3× powerEquipment Issue?Check beam quality M²Check gas purity→ Calibrate laserProcess Issue?Joint fit-up toleranceFixturing/clamping→ Improve prep✓ Problem SolvedDocument solution!

💡 Systematic Approach: Always start with simplest fixes (cleaning, gas flow). Material and equipment issues are rare (~5-10% of cases). Change ONE variable at a time.

Common Defects Overview

⚪

Porosity

Occurrence:
30%
Severity:
Medium
💔

Cracks

Occurrence:
10%
Severity:
Critical
⚡

Undercut

Occurrence:
15%
Severity:
Medium
💥

Spatter

Occurrence:
20%
Severity:
Low
❌

Incomplete Fusion

Occurrence:
12%
Severity:
High

1. Porosity (30% Occurrence)

Identification

  • Appearance: Round cavities on surface or internal (X-ray shows circular dark spots)
  • Location: Random distribution or concentrated at start/stop points
  • Size: Typically 0.1-2mm diameter

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/grease: Clean with acetone → Re-weld
  • ✅ Rust/oxidation: Mechanical cleaning → Re-weld
  • ✅ Moisture: Preheat to 100°C → Re-weld
  • → Surface appears clean: Go to Step 3
Step 3: Is gas shielding adequate?
  • ✅ Flow rate <15 L/min: Increase to 20 L/min
  • ✅ Nozzle distance >20mm: Adjust to 10-15mm
  • ✅ Gas purity <99.99%: Replace cylinder
  • → Gas seems OK: Go to Step 4
Step 4: Check welding speed
  • ✅ Speed >80mm/s: Reduce to 50-60mm/s
  • → Still have porosity: Material-specific issue (check composition)

Solution Priority Table

SolutionEffectivenessDifficultyCostTime
1. Clean surface thoroughly
85%
EasyLow5-10 min
2. Increase gas flow to 20 L/min
70%
EasyLow1 min
3. Reduce welding speed
60%
EasyLow1 min
4. Replace gas cylinder (check purity)
50%
MediumMedium10 min
5. Preheat material to remove moisture
40%
MediumMedium20-30 min

2. Cracks (10% Occurrence, Most Critical)

Critical Warning

Cracks are the most serious defect - they compromise structural integrity and can lead to catastrophic failure. Never ignore cracks, even small ones.

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 Steel⭐
Very Low
No special measures needed
Medium Carbon Steel⭐⭐⭐
Medium
Preheat 100-200°C
High Carbon Steel⭐⭐⭐⭐⭐
Very High
Preheat 300°C + post-heat
Cast Iron⭐⭐⭐⭐⭐
Extreme
Preheat 500°C + Ni filler
Stainless Steel 304⭐⭐
Low
Reduce restraint
Aluminum 6061⭐⭐⭐
Medium
Avoid 5xxx filler
Titanium⭐⭐
Low
Strict gas shielding

Solution Priority Table

SolutionEffectivenessDifficultyCostTime
1. Preheat to 300°C (high carbon steel)
90%
MediumMedium30-60 min
2. Use flexible fixturing (reduce restraint)
70%
MediumLow10-20 min
3. Optimize weld sequence
60%
MediumLow5 min
4. Add filler material
80%
HardMedium10 min
5. Post-weld heat treatment
95%
HardHigh1-2 hours

Quick Solutions for Other Defects

Undercut (15%)

  • Reduce power by 10-15%
  • Increase speed by 10-20%
  • Defocus beam +0.5mm
  • Add filler material

Spatter (20%)

  • Reduce power by 10%
  • Defocus beam +0.5mm
  • Increase gas flow
  • Clean surface thoroughly

Incomplete Fusion (12%)

  • Increase power by 15-20%
  • Reduce welding speed
  • Improve joint fit-up (gap <0.1mm)
  • Check focus position (0 or -0.5mm)

Troubleshooting Best Practices

Systematic Approach

  1. Document the defect: Take photos, note location, measure size
  2. Follow decision tree: Check most likely causes first (by probability)
  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: Accounts for 60% of porosity
  • Ignoring material properties: High carbon steel needs preheat, period
  • Not using gas flow meter: "Looks OK" is not sufficient

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