Welding joins metals by melting base materials (and usually a filler) into a fused joint. The four most common processes each solve different problems, and picking the wrong one costs you time, money, or structural integrity.

MIG (GMAW — Gas Metal Arc Welding)

• A continuously-fed wire electrode melts into the joint while shielding gas (typically 75% argon / 25% CO₂ for steel) protects the weld pool from atmospheric contamination.
• Best for: Mild steel, aluminum, and stainless in production environments. It's fast, easy to learn, and works well on material from 24-gauge sheet up to thick plate.
• Limitation: Requires shielding gas, so outdoor use in wind is problematic. Penetration on thick sections is moderate.

TIG (GTAW — Gas Tungsten Arc Welding)

• A non-consumable tungsten electrode creates the arc; filler rod is added by hand. Pure argon shields the pool.
• Best for: Precision work — aerospace tubing, bicycle frames, thin stainless, and exotic alloys (titanium, chromoly). Produces the cleanest, most aesthetic welds.
• Limitation: Slow. A TIG pass might run at 4–8 inches per minute versus 20–40 for MIG. Requires significant operator skill (both hands plus a foot pedal).

Stick (SMAW — Shielded Metal Arc Welding)

• A flux-coated consumable electrode creates both the arc and its own shielding gas as the coating burns off, leaving a protective slag layer.
• Best for: Field work, structural steel, and dirty or rusty material. No external gas bottle needed, so it works outdoors in wind and rain. This is what holds up most bridges and buildings.
• Limitation: Slag must be chipped between passes. Not practical on thin sheet metal (below ~⅛ inch).

Flux-Cored (FCAW)

• Similar to MIG but uses a tubular wire filled with flux. Can run with shielding gas (dual-shield) or without (self-shielded).
• Best for: High deposition rates on heavy structural steel. Self-shielded FCAW is common in outdoor construction — shipyards, pipelines, and heavy equipment.

A practical rule of thumb for joint strength: A properly executed fillet weld's allowable shear load (per inch of length) is approximately 0.707 × weld leg size × allowable shear stress. For example, a ¼-inch fillet weld using E70 electrode (21 ksi allowable shear) carries about 0.707 × 0.25 × 21,000 = 3,712 lbs per inch of weld. So a 3-inch-long ¼" fillet weld on a bracket handles roughly 11,100 lbs in shear — that's real load capacity from a small weld.

Real-world example: A fabrication shop building a steel handrail uses MIG for speed on the mild steel tubes, then switches to TIG for the stainless steel cap rail where appearance matters. The field crew bolts the assemblies in place and stick-welds the base plates to embedded steel — no gas bottles needed on a windy rooftop.