How do metal 3D printers work?

Like all other 3D printing processes, metal 3D printers build parts by adding material one layer at a time based on a digital 3D design - hence the name additive manufacturing.

In this way, parts with geometries that cannot be produced by "traditional" subtractive (CNC machining) or forming (metal casting) techniques can be manufactured without the need for specialized tooling (e.g. molds).