What is the primary purpose of gas welding?

The primary purpose of gas welding is to join two pieces of metal by melting their edges. In this process, a flame produced by burning a mixture of fuel gas (like acetylene) and oxygen is used to heat the metal until it reaches a molten state. As the edges of the metal pieces melt, a filler material may also be added to ensure a strong bond between the two pieces when they cool and solidify. This method is widely used in fabrication and repair work for creating strong, reliable joints in a variety of metal types and thicknesses.

The other choices describe processes that are not related to the primary goal of gas welding. For instance, cleaning metal surfaces by oxidation pertains to surface preparation rather than joining, tinning involves coating metals to prepare them for soldering, and shaping metal by hammering refers to a forging process, which is a different type of metalworking altogether.