What shielding gases to use for MIG/MAG and TIG welding?

The choice of shielding gas is crucial for weld quality. Here are the gases used for each process:

MIG/MAG (GMAW) welding on carbon steel:

• 75% Argon + 25% CO₂ — The usual mix for steel, sold as “C25”: the exact composition and flow rate are on the gas supplier's data sheet, and the WPS sets the one that applies to the joint
• Pure CO₂ — Cheaper than the mix, deeper penetration, but more spatter and a rougher arc
• 98% Argon + 2% O₂ — For very stable spray arc transfer

MIG welding on aluminum:

• Pure argon — The usual gas; the flow rate is the one on the supplier's data sheet and in the WPS

TIG (GTAW) welding:

• Steel/stainless: pure argon, at the flow rate set by the WPS
• Aluminum: 100% Argon or 80% Argon + 20% Helium (helium increases heat input for thick pieces)
• Copper and alloys: helium (hotter than argon for conducting heat)

Gas cost: the platform publishes no price — it depends on the supplier, the cylinder size and the rental agreement (deposit, delivery). Ask your supplier for the rate card.