Welding joins two or more metal parts by melting both materials, which are then cooled so that the two metals are permanently bonded. Welding services are of two types, spot welding and seam welding, used primarily for sheet metal parts. Welding services include the use of gas flame, an electric arc, a laser and friction among others. Welding is a growing industry, widely used in metalworking and product engineering. Anything made of metal can be welded, from vehicles like cars, trucks and motorcycles to rail cars, ships, aircraft, rockets and space stations; in construction, skyscrapers, bridges and highways, oil and natural-gas pipelines, offshore oil platforms, giant wind turbines and solar panels. Welding services also include installation and maintenance of boilers, antipollution systems and other large structures, as well as piping for industrial, commercial and residential facilities. Welding is even used by artists to create sculptures and decorative items.