Which shielding gas is primarily used for its ability to produce a stable arc?

Argon is primarily used as a shielding gas in MIG welding due to its ability to produce a stable arc. This stability is crucial for achieving clean and consistent welds. Argon is an inert gas, which means it does not react with the molten metal, minimizing contamination and providing a clean welding atmosphere.

The stability of the arc is enhanced by argon's physical properties, such as its high ionization potential, which allows it to maintain a steady plasma state during the welding process. This results in better control over the weld pool and helps in producing smoother weld beads with minimal spatter.

Additionally, argon's low density allows it to envelop the weld area effectively, protecting the molten weld pool from atmospheric gases that could lead to defects. While helium can also provide a stable arc and enhance heat input, argon is more commonly used because it offers a more stable and controllable arc for most applications.

Using oxygen or carbon dioxide as a shielding gas is not ideal for maintaining a stable arc in MIG welding; these gases can react with molten metal and introduce impurities, leading to poor weld quality.