Welding is a fabrication process that joins materials, typically metals or thermoplastics, by causing coalescence (fusion). This is usually achieved by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong, permanent joint. Key applications (virtually everywhere! ) are : construction (buildings, bridges),manufacturing (cars, ships, airplanes, trains, appliances),energy (pipelines, power plants, oil rigs, wind turbines),infrastructure (repairs, maintenance),art and sculpture, microelectronics (ultra-precise welding).