n.
Technique for joining metallic parts, usually through the application of heat.
Discovered in the 1st millennium AD during attempts to manipulate iron into useful shapes, the technique produced a strong, tough blade. Welding traditionally involved interlayering relatively soft and tough iron with high-carbon material, followed by hammer forging . Modern welding processes include gas welding, arc welding, and resistance welding. More recently, electron-beam welding, laser welding, and several solid-phase processes such as diffusion bonding, friction welding, and ultrasonic joining have been developed. See also brazing , soldering .