How is weld overlay done?

Weld overlay, cladding or sometimes known as hardfacing is a procedure in which the base metal is built up layer by layer with weld material (of appropriate chemical characteristics), usually to a dimensional specification for later machining processes to produce a final part. For example we used to run hardfacing electrodes on starter bar assemblies for the steel mill next door, and we built a special sub arc for the mill rollers, which would then get machined down and sent back to the client. This was much cheaper for the customer than buying new ones every time.