Welding is a procedure that allows for solid parts to be permanently joined while ensuring the continuity of the material where the weld is applied.
Welding requires the application of localized heat in order to melt the material in question. While this material can be the same as that of the parts to be joined together, it can also be a foreign material (also known as a filler material): the first case is referred to as autogenous welding, while the second case is referred to as heterogeneous welding or brazing.
Welding creates a permanent bond that's different from other permanent bonds (such as nailing or gluing, for example), which do not ensure the material's continuity.
If performed properly and according to certain principles, some autogenous welding processes can even guarantee the near total continuity of the joined materials' characteristics.
Welding operations produce fumes that can generate fine dusts with a particle size of even less than 1 micron when cooled, thus requiring extremely low filtration speeds.