Welding is the union of pieces of metal by fusing the opposing
surfaces that have been made molten by heat. Processes similar to
welding include brazing and soldering. Allied processes include the
removal and cutting of metals. Common heat sources are the electric
arc and oxy - gas flames. Gas welding/cutting entails heat being
applied to the metal by the flame from a torch in which a gas, such
as acetylene, is burnt with a supply of oxygen or air