Welding is a process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together creating fusion. Welding is distinct from lower temperature metal-joining techniques such as brazing and soldering, which do not melt the base metal.
In addition to melting the base metal, a filler material is typically added to the joint to form a pool of molten material (the weld pool) that cools to form the joint that, based on the weld configuration - which can be stronger than the base material (parent metal). Welding also requires a form of shield to protect the filler metals or melted metals from being contaminated or oxidized.
While often an industrial process, welding may be performed in many different environments, including in open air, under water, and in outer space. Welding is a hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation.