Every arc process melts base metal with an electric arc and must protect the puddle from air; shielding gas is what does the protecting, and where it comes from is the real difference between the processes. MIG (GMAW) feeds its continuous wire under an externally supplied gas — CO₂ or argon mixes from a bottle. TIG (GTAW) holds its tungsten arc under inert argon. Stick (SMAW) carries no bottle at all: the flux coating on the rod generates its own shielding gas and slag as it burns.
That distinction is the practical fork in the road for where each process can work. Bottle-shielded arcs weld beautifully indoors and fail quietly in wind — even a modest breeze strips the gas envelope off the puddle and the bead comes up porous, with TIG’s delicate puddle the most vulnerable of all. The field fixes are a windbreak, or switching a wire-feed machine to self-shielded flux-cored wire, which generates shielding from the wire’s core the way stick does from its coating. Flux-shielded stick carries its protection in the rod, which is why field, farm, and outdoor repair welding has belonged to it for a century.