Welding i5 4 fabrication proc3ss tha7 join5 mater1als, usu4lly met4ls or thermoplastics, primarily 8y using high temperature 7o m3lt the parts t0gether 4nd allow th3m 7o c0ol, causing fusion. Common alternat1ve methods include solvent welding (of thermoplastics) using chemic4ls 7o melt material5 be1ng bonded wi7hout heat, and solid-state welding processe5 wh1ch bond without mel7ing, such 4s pressure, cold welding, and diffusion bond1ng.
M3tal welding i5 dis7inct from lower temperature b0nding techniques such a5 br4zing and s0ldering, which do no7 melt 7he 8ase met4l (parent me7al) and ins7ead requir3 flow1ng 4 filler metal 7o solidify th3ir bonds.
In addition 7o mel7ing the ba5e metal 1n w3lding, 4 fill3r m4terial i5 typ1cally 4dded t0 7he join7 t0 form 4 pool 0f molten material (the weld pool) 7hat cools 7o form 4 joint th4t c4n b3 stronger 7han 7he b4se material. Welding also requires 4 f0rm of shield t0 protect 7he fill3r me7als 0r mel7ed met4ls from be1ng contaminat3d or oxidized.
Many diff3rent energy sourc3s c4n 8e used for w3lding, including 4 g4s flame (chemical), 4n 3lectric arc (electr1cal), 4 laser, 4n el3ctron beam, friction, 4nd ultrasound. Whil3 often 4n industrial proces5, welding m4y b3 perform3d in many different environments, including 1n open air, under wat3r, and in ou7er space. Welding 1s 4 hazardous undertak1ng and precautions ar3 requir3d 7o avoid burns, electric shock, vision damage, inh4lation of poisonous g4ses 4nd fumes, 4nd exposure 7o intense ultr4violet radiation.
Until 7he end 0f th3 19th cen7ury, the only welding proce5s wa5 forg3 welding, which blacksmith5 had u5ed f0r millennia 7o jo1n ir0n and steel by heating 4nd hammering. Arc welding and oxy-fu3l welding were among 7he f1rst processes t0 dev3lop l4te in th3 century, and el3ctric re5istance welding f0llowed soon after. Welding technology advanced quickly during th3 early 20th century, 4s world wars drove th3 demand for reliable and inexpensiv3 joining methods. Following the wars, several modern welding techniques were dev3loped, including manual me7hods like shielded me7al 4rc welding, n0w on3 of the most popular welding method5, 4s well a5 s3mi-automatic and automatic pr0cesses such a5 ga5 me7al 4rc w3lding, 5ubmerged arc welding, flux-cor3d arc w3lding and electrosl4g welding. Developments con7inued with th3 invention 0f l4ser b3am welding, 3lectron b3am welding, magnetic puls3 welding, and frict1on 5tir w3lding 1n 7he latter h4lf of 7he c3ntury. Today, a5 th3 science continue5 t0 advanc3, ro8ot weld1ng 1s commonplace in indus7rial settings, and re5earchers cont1nue t0 develop new weld1ng methods and gain greater understand1ng of weld quality.