Student Material 001: Welding Fundamentals Quick Reference
Material ID: U6M1-MAT-001
Purpose: Quick reference for welding terminology, joint types, filler/gas selection, and defect identification
Updated: 2026-03-19
MIG vs. TIG Comparison
| Feature |
MIG (GMAW) |
TIG (GTAW) |
| Electrode |
Consumable wire (feeds automatically) |
Non-consumable tungsten (stays in torch) |
| Filler Metal |
Same as electrode wire |
Separate hand-fed rod |
| Shielding Gas |
Ar/COβ mix (steel), pure Ar (Al/SS) |
Pure Argon (all metals) |
| Polarity |
DCEP |
DCEN (steel/SS), AC (aluminum) |
| Speed |
Fast β high deposition rate |
Slow β precision control |
| Learning Curve |
Moderate |
High |
| Best For |
Production, thick material, long welds |
Precision, thin material, visible welds |
| Typical Helmet Shade |
10-12 |
8-10 (lower amps) |
Joint Types Quick Reference
BUTT JOINT LAP JOINT T-JOINT
βββββββββββ βββββββββββ βββββββββββ
β gap βββββββββββ β
βββββββββββ βββββββββββ
CORNER JOINT EDGE JOINT
β βββββββββββ
βββββββββββ βββββββββββ
Shielding Gas Selection
| Base Metal |
MIG Gas |
TIG Gas |
Flow Rate |
| Mild Steel |
C25 (75% Ar / 25% COβ) |
100% Argon |
20-25 CFH |
| Stainless Steel |
100% Argon or Tri-mix |
100% Argon |
15-20 CFH |
| Aluminum |
100% Argon |
100% Argon |
20-30 CFH |
| Copper/Bronze |
100% Argon |
Argon or Ar/He |
20-25 CFH |
| Base Metal |
MIG Wire |
TIG Rod |
Common Sizes |
| Mild Steel (A36, 1018) |
ER70S-6 |
ER70S-2 |
0.030", 0.035" (MIG); 1/16", 3/32" (TIG) |
| Stainless 304 |
ER308L |
ER308L |
0.030", 0.035" (MIG); 1/16", 3/32" (TIG) |
| Stainless 316 |
ER316L |
ER316L |
Same as above |
| Aluminum 6061 |
ER4043 |
ER4043 |
0.030", 0.035" (MIG); 1/16", 3/32" (TIG) |
| Aluminum 5052/5083 |
ER5356 |
ER5356 |
Same as above |
| Carbon steel to Stainless |
ER309L |
ER309L |
Specialty β consult spec |
Weld Defect Quick Reference
| Defect |
Appearance |
Cause |
Fix |
| Porosity |
Small holes/pits in weld |
Contamination, moisture, gas issues |
Clean metal, check gas flow, dry filler |
| Undercut |
Groove at weld toe |
Too much heat, poor angle |
Reduce amps/speed, adjust angle |
| Lack of Fusion |
Weld not bonded to base metal |
Low heat, poor angle, contamination |
Increase amps, direct heat to joint root |
| Burn-Through |
Hole melted through material |
Too much heat, too slow travel |
Reduce amps, increase travel speed |
| Excessive Spatter |
Balls of metal around weld |
Wire speed/voltage mismatch (MIG) |
Adjust voltage, check wire feed |
| Cracking |
Cracks in or near weld |
High carbon, rapid cooling, restraint |
Preheat, slow cool, reduce restraint |
| Overlap/Cold Lap |
Weld metal on surface without fusion |
Cold weld, too much filler |
Increase heat, reduce wire speed/filler |
| Excessive Reinforcement |
Weld bead too tall/convex |
Too much filler, too slow travel |
Increase travel speed, reduce wire feed |
| Incomplete Penetration |
Weld doesn't reach root |
Low amps, wrong gap, poor fit-up |
Increase amps, widen root gap |
Welding Triangle Reference
AMPERAGE
(Heat Input)
/ \
/ \
/ WELD \
/ QUALITY \
/ \
VOLTAGE ββββββββ TRAVEL SPEED
(Arc Length/ (Heat per
Bead Shape) Unit Length)
| Change |
Effect on Bead |
| β Amperage |
Deeper penetration, wider bead |
| β Amperage |
Shallower penetration, narrower bead |
| β Voltage |
Wider, flatter bead, longer arc |
| β Voltage |
Narrower, taller bead, shorter arc |
| β Travel Speed |
Narrower bead, less penetration, less heat input |
| β Travel Speed |
Wider bead, more penetration, more heat input |
Material Thickness to Filler Size Guide
| Base Metal Thickness |
MIG Wire Diameter |
TIG Rod Diameter |
Approx. Amperage Range |
| 24-20 gauge (0.025-0.036") |
0.023" |
1/16" |
30-60A |
| 18-16 gauge (0.048-0.060") |
0.023-0.030" |
1/16" |
40-90A |
| 14-12 gauge (0.075-0.105") |
0.030" |
1/16-3/32" |
70-130A |
| 10 gauge (0.135") |
0.030-0.035" |
3/32" |
90-150A |
| β
" (0.125") |
0.030-0.035" |
3/32" |
100-150A |
| 3/16" (0.1875") |
0.035" |
3/32" |
130-200A |
| ΒΌ" (0.250") |
0.035-0.045" |
3/32-β
" |
170-250A |
Pre-Weld Checklist
[ ] Material identified β base metal type confirmed
[ ] Joint surfaces ground to bright metal
[ ] Joint surfaces degreased (acetone)
[ ] Correct filler metal selected and verified
[ ] Correct shielding gas connected and flow verified
[ ] Machine settings (amps, voltage, wire speed) appropriate
[ ] Work clamp making solid metal-to-metal contact
[ ] Ventilation/fume extraction positioned and running
[ ] Fire extinguisher within 15 feet
[ ] PPE complete β helmet, FR jacket, gloves, boots, respirator
[ ] 35-foot combustible clearance
[ ] Welding screens deployed
Last Updated: 2026-03-19