Powder bed fusion with a laser beam (also called SLM or DMLS) is the most widely used currently in the 3D-printing ecosystem. Here a laser beam melts the metal powder particles, so they connect and form a melt pool. When the powder cools down it solidifies again. The cooling of the melt pool is rapid and leads to very fine crystal grains. After the laser is done with melting one slice, another layer of powder is added to the powder bed and the process of melting begins again. To really achieve a defect free part, there are many parameters to fine tune. A few of these parameters are laser power, laser scan speed, the pattern in which the laser scans, the amount of process gas present, etc. The process gas is a very important part of 3d-printing since the presence of oxygen would lead to contamination and oxidization of the metal.
The process is very versatile, since it can be done with many different materials, like steel, copper, aluminium, titanium, tungsten, nickel and cobalt alloys. Even metallic glasses can be manufactured. Targeted manipulation of the process parameters can even fine tune the mechanical properties of the part.
A big advantage is the possibility of reusing the unused powder. This means its a much more sustainable process than subtractive manufacturing, where up to 70 % of the material can be waste