MIG Welding

MIG welding creates an arc between a continuously fed wire electrode and the workpiece:

Process Components:
- Power Source: Provides constant voltage DC power
- Wire Feeder: Delivers electrode wire at controlled speed
- Welding Gun: Directs wire, gas, and current to the weld
- Shielding Gas: Protects molten metal from atmospheric contamination
- Ground Clamp: Completes the electrical circuit

Transfer Modes:
- Short-Circuit Transfer: Wire touches puddle, creating short circuits. Low heat, good for thin materials and out-of-position welding.
- Globular Transfer: Large droplets transfer across arc. Higher heat, limited to flat and horizontal positions.
- Spray Transfer: Fine droplets stream across arc. High deposition, requires higher parameters and typically flat/horizontal positions.
- Pulsed Spray: Power source alternates between high and low current. Combines spray transfer quality with short-circuit versatility.

Shielding Gases:
- 75% Argon / 25% CO2: Most common for steel, good penetration and bead appearance
- 100% CO2: Deeper penetration, more spatter, lower cost
- 90% Helium / 7.5% Argon / 2.5% CO2: Aluminum applications
- 98% Argon / 2% O2: Stainless steel, clean welds

Wire Types:
- ER70S-6: General purpose mild steel
- ER308L: 304 stainless steel
- ER4043: Aluminum (general purpose)
- ER5356: Aluminum (higher strength)

Proper setup is crucial for quality MIG welds:

Voltage and Wire Feed Speed:
The relationship between voltage (arc length) and wire feed speed (amperage) determines weld characteristics:
- Too Low Voltage: Narrow, ropy bead with poor tie-in
- Too High Voltage: Wide, flat bead with potential undercut
- Too Slow Wire Feed: Insufficient penetration, burn-back
- Too Fast Wire Feed: Excessive spatter, stubbing

Parameter Guidelines (Steel with 75/25 gas):
| Material Thickness | Wire Size | Voltage | Wire Feed (ipm) |
|-------------------|-----------|---------|-----------------|
| 1/8" (3mm) | .030" | 17-19 | 200-250 |
| 3/16" (5mm) | .035" | 19-22 | 250-350 |
| 1/4" (6mm) | .035" | 21-24 | 300-400 |
| 3/8" (10mm) | .045" | 24-28 | 350-450 |

Contact Tip to Work Distance (CTWD):
Maintain 3/8" to 1/2" (10-13mm) from contact tip to work. Too close causes burn-back; too far creates unstable arc.

Gun Angle:
- Push (Forehand): 10-15° from vertical, pushing into weld direction. Flatter bead, less penetration.
- Drag (Backhand): 10-15° from vertical, dragging away from direction. More penetration, higher crown.

Travel Speed:
Affects bead width and penetration. Watch the puddle—travel fast enough to stay on the leading edge, slow enough for proper fill.

Mastering various joints and techniques expands your capabilities:

Common Joint Types:

Butt Joint:
Two pieces joined edge-to-edge. May require beveling for thicker materials. Root opening and backing affect penetration.

Lap Joint:
Overlapping pieces joined with fillet weld. Common in sheet metal. Watch for burn-through on top piece.

T-Joint:
Perpendicular pieces forming a T. Fillet welds on one or both sides. Critical for structural applications.

Corner Joint:
Two pieces meeting at an angle. Inside corner, outside corner, and edge variations. Position affects technique.

Welding Positions:
- 1G/1F (Flat): Easiest, gravity helps. Highest travel speeds and deposition.
- 2G/2F (Horizontal): Gravity pulls puddle down. Adjust gun angle and travel speed.
- 3G/3F (Vertical): Weld up or down depending on process/material. Requires significant technique adjustment.
- 4G/4F (Overhead): Most challenging. Lower parameters, tighter arc, faster travel.

Multi-Pass Welding:
Thick materials require multiple passes:
- Root Pass: First pass establishing penetration
- Fill Passes: Build up joint, may use weave patterns
- Cap Pass: Final pass for appearance and profile

Weave Patterns:
- Stringer bead: Straight travel, minimal weaving
- Crescent weave: Side-to-side motion for fill
- Box weave: Rectangular pattern for wide coverage

MIG welding skills open doors across manufacturing:

Industries Hiring MIG Welders:
- Automotive: Production welding, fabrication, repair
- Structural Steel: Buildings, bridges, heavy equipment
- Manufacturing: General fabrication, machinery, enclosures
- Shipbuilding: Hull construction, outfitting
- Agriculture: Equipment manufacturing and repair
- HVAC: Ductwork fabrication

Career Progression:
1. Entry-Level Welder: Production welding, following WPS. $35,000-$45,000
2. Skilled Welder: Multiple processes, positions. $45,000-$60,000
3. Welder/Fitter: Layout and fit-up plus welding. $55,000-$75,000
4. Lead Welder: Supervise team, quality responsibility. $60,000-$80,000
5. Welding Supervisor/Inspector: Management, certification. $70,000-$100,000

Certifications:
- AWS D1.1 Structural Welding
- AWS D1.3 Sheet Metal Welding
- ASME Section IX for pressure vessels
- API 1104 for pipelines

Advancement Paths:
- Specialize: Robotic welding programming, exotic materials
- Inspect: CWI (Certified Welding Inspector)
- Engineer: Welding engineering technology degree
- Own: Start fabrication or repair business

Physical Considerations:
Welding is physically demanding:
- Standing for extended periods
- Awkward positions for out-of-position work
- Heat exposure
- PPE requirements (helmet, gloves, jacket)

Proper ergonomics and conditioning extend career longevity.