GTAW Fundamentals: Equipment and Setup
Gas Tungsten Arc Welding (GTAW), universally known as TIG (Tungsten Inert Gas) welding, uses a non-consumable tungsten electrode to create an arc that melts the base metal; a separate filler rod is fed into the molten pool by the welder's free hand. TIG produces the highest quality, cleanest welds of any arc welding process — the inert gas shield (argon or helium) and the absence of flux mean no slag, no spatter, and exceptional control over bead appearance and penetration. This control comes at the cost of speed and skill — TIG is the slowest common arc welding process and requires the highest level of hand-eye coordination. Equipment setup for stainless steel TIG: Tungsten electrode — use 2% thoriated (red band, gray color) or 2% ceriated (gray band) tungsten, which maintains a sharp pointed tip for the DC electrode negative (DCEN) current used on stainless. Keep the tungsten ground to a sharp point; the pointed tip concentrates the arc precisely. Polarity: DCEN (direct current electrode negative = direct current straight polarity) — current flows from the workpiece through the arc to the tungsten. DCEN concentrates approximately 70% of the arc heat in the weld pool (in the base metal) and 30% at the electrode. Shielding gas: pure argon at 15–20 CFH (cubic feet per hour). Filler rod: for 304 stainless, use ER308L filler rod (the 'L' indicates low carbon content, critical for avoiding carbide precipitation sensitization discussed below). Equipment setup for aluminum TIG: Polarity — AC (alternating current) is required for aluminum. During the electrode-positive (reverse polarity) half-cycle of AC, the arc blasts the aluminum oxide layer off the base metal surface (the oxide layer has a melting point of 3,700°F vs. aluminum's 1,220°F — it must be removed or it prevents fusion). During the electrode-negative half-cycle, the arc heats the base metal for fusion. Tungsten: pure tungsten (green band) or zirconiated (white band) — AC's electrode-positive half-cycles cause the tip to ball up; a balled tungsten concentrates the heat of the EP cycle effectively for oxide cleaning. Shielding gas: pure argon (helium or argon/helium mix for increased heat input on thick aluminum). Filler rod: ER4043 (general purpose aluminum) or ER5356 (higher strength, anodizes better).