A method of joining two metals by fusing them by one or another solid-state process.

Since most metal surfaces are covered by a layer of oxide or a similar material, the first step in welding is to remove that layer or to form a new surface by cutting or deforming the metal to be welded.

In gas welding, an oxyacetylene or oxyhydrogen torch is used to create the weld. Arc welding uses the heat that is generated by an electric arc to join the metals. Atomic-hydrogen arc welding combines gas welding and arc welding.