Welding is the joining together of materials (typically metals or thermoplastics), usually by a fusion process.
Most commonly, workpieces are welded by melting both of them and adding more molten metal or plastic to form a pool that cools to form a strong joint. The energy to form the joint between metal workpieces most often comes from a flame (e.g. oxy-acetylene) or an electric arc, but welding by laser beam, electron beam and friction processes is well established. Energy for fusion welding of thermoplastics typically comes from direct contact with a heated tool or a hot gas.
Types of welding
Welding differs from soldering and brazing in that enough heat is applied to melt the materials to be joined. Soldering uses solder, a lower melting-point material.