Welding, soldering, and brazing are fabrication processes that join materials, usually metals or thermoplastics, by causing coalescence. Welding is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, but sometimes pressure is used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting point material between the workpieces to form a bond.