Yes, there is one way to use a MIG welder without gas: Use flux-cored wire, rather than argon/CO2 or helium, to shield the weld puddle.
MIG Welding Without Gas Using Flux-Cored Wire
Creating a protective gas layer doesn’t necessarily require an expensive gas cylinder. Flux-cored wire creates its own shielding gas around the weld puddle without the need for an external gas supply. The wire is hollow with flux inside that vaporizes in the arc and creates an expanding gas bubble to protect the molten puddle. The carbon in the flux core bonds with the oxygen in the environment and prevents oxidation.
If you’re a beginner to MIG welding, it’s easier to learn and create basic welds using flux-cored wire. This simplifies the process and eliminates one of the factors in creating good welds. It is also cheaper, since you don’t need an expensive cylinder, regulator and cart to transport them.
Flux-cored wire is also used in high volume production MIG welding. Flux-cored wire delivers a constant supply of shielding gas without the need to change out gas cylinders, which ensures high production speed.
This video shows how flux-cored wire is used to MIG weld without gas:
What Happens When You MIG Weld Without Gas?
MIG welding requires good protection for the molten weld pool from environmental contaminants. Using shielding gas with a MIG welder protects the weld pool from oxidation and porosity.
If you MIG weld using pure metal wire without gas shielding it will cause a problem called porosity — small inclusions or bubbles of oxygen, nitrogen and hydrogen trapped in the metal. This significantly weakens the weld.
In addition, oxidation occurs when the molten steel reacts with oxygen in the atmosphere at high temperatures. This replaces iron in the weld with iron oxide, a substantially weaker material.
In a nutshell, MIG welding without some way to protect the weld puddle from the environment is a bad idea that will inevitably lead to weld failure.
Does a MIG Welder Work Without Gas in a Vacuum?
You might think “well, if the weld puddle reacts with atmospheric gases to cause porosity and oxidation problems, then why not MIG weld in a vacuum chamber?”
Electron beam welding and cold welding can both be done in a vacuum. However, MIG welding without gas cannot be done in a vacuum because some form of gas pressure is required for the arc to behave correctly. In fact, TIG welding requires a gas supply even when welding in a vacuum for this reason.
Does a MIG Welder Work Underwater Without Gas?
In short, no. A MIG welder (GMAW) will not work underwater. For arc welding to work it requires the arc and molten metal to form in an area surrounded by gas, not liquid. MIG welding does work underwater because the gas pressure is insufficient to overcome the surrounding water pressure, so a gas bubble cannot form around the arc to allow the metal to melt and form a puddle.
Underwater welding must be done with a stick welder (SMAW). With stick arc welding the flux core vaporizes and expands, creating a gas bubble that pushes the water away and allows the metal to melt and form a weld puddle.