Slide 001: Introduction to Welding Processes¶
Slide Visual¶
Slide Overview¶
This slide introduces the two arc welding processes covered in this unit — MIG (GMAW) and TIG (GTAW) — and establishes the foundational science of how metal is joined by fusion welding. Students will understand the core physics before learning specific techniques.
Instruction Notes¶
What is Fusion Welding?¶
Fusion welding joins metals by melting the base materials at the joint, allowing them to solidify together. An electrical arc provides the heat source — temperatures reach 6,000-10,000°F at the arc center, far exceeding the melting points of steel (~2,750°F), aluminum (~1,220°F), and stainless steel (~2,550°F).
MIG Welding (GMAW — Gas Metal Arc Welding)¶
MIG uses a continuously fed consumable wire electrode that serves as both the arc source and the filler metal. An external shielding gas (typically 75% Argon/25% CO₂ for steel, or 100% Argon for aluminum) protects the weld pool.
| Feature | Detail |
|---|---|
| Process | Semi-automatic — machine feeds wire, operator guides torch |
| Arc type | Short-circuit, globular, spray, or pulsed transfer |
| Filler delivery | Automatic — wire feeds through the torch |
| Shielding | External gas from cylinder |
| Learning curve | Moderate — often called "the glue gun of welding" |
| Best for | Production, thick sections, long runs |
| Polarity | DCEP (electrode positive) |
TIG Welding (GTAW — Gas Tungsten Arc Welding)¶
TIG uses a non-consumable tungsten electrode to create the arc. The operator manually feeds a separate filler rod into the weld pool. Pure argon provides shielding.
| Feature | Detail |
|---|---|
| Process | Manual — operator controls torch, filler, and foot pedal simultaneously |
| Arc type | Continuous, stable, controllable |
| Filler delivery | Manual — operator dips rod into pool |
| Shielding | Pure argon (argon/helium for some applications) |
| Learning curve | High — requires exceptional hand coordination |
| Best for | Precision, thin material, critical joints, visible welds |
| Polarity | DCEN for steel/stainless, AC for aluminum |
The Welding Triangle¶
Three variables control every weld: 1. Current (amperage): Controls heat input — more amps = more heat = deeper penetration 2. Voltage: Controls arc length and bead shape — higher voltage = wider, flatter bead 3. Travel speed: Controls heat input per unit length — faster = less heat per inch = narrower bead
These three must be balanced for every material, thickness, and joint configuration.
Why Both MIG and TIG?¶
MIG and TIG have complementary strengths. A well-rounded welder uses MIG for production speed and thick sections, and TIG for precision, thin material, and aesthetic welds. Many real-world projects require both processes.
Key Talking Points¶
- All fusion welding melts the base metal — this is what distinguishes it from brazing and soldering
- MIG feeds filler automatically; TIG requires manual filler rod control — fundamentally different skills
- Both processes require shielding gas to protect the molten weld pool
- The welding triangle (current, voltage, travel speed) governs every weld
- Neither process is "better" — they are tools for different situations
Learning Objectives (Concept Check)¶
- [ ] Explain the fundamental principle of fusion welding
- [ ] Compare MIG and TIG welding across 5 key characteristics
- [ ] Define the three variables of the welding triangle
Last Updated: 2026-03-19