What is the main purpose of using flux in the brazing process?

Using flux in the brazing process serves the critical function of preventing oxidation during the heating of the metal parts being joined. Oxidation can form a barrier that inhibits the strength and quality of the joint by preventing the braze material from properly wetting and adhering to the base metals. By providing a protective atmosphere, flux ensures that the surfaces remain clean and effective for bond formation, which helps achieve a reliable and strong joint.

The other options present roles that are not applicable in this context; cooling the joint can actually hinder the brazing process instead of aiding it, increasing the melting point is contrary to flux's role since it's intended to facilitate melting, and while support can be a factor after joining, it is not a function of the flux during the brazing process itself. Thus, the primary purpose remains focused on preventing oxidation, ensuring successful brazing.