 Welding is a fabrication or sculptural process that joins materials , usually metals or thermoplastics , by causing fusion , which 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 often added to the joint to form a pool of molten material ( the weld pool ) that cools to form a joint that can be as strong , or even stronger , than the base material . Pressure may also be used in conjunction with heat , or by itself , to produce a weld . 
