Additive manufacturing (AM) is a process technology to create objects by subsequent layers of material. It is also commonly called "3D printing" because it is an additive printing process. The materials that can be used varies from polymers (plastic materials), metal materials to composite materials.
There are several 3D printing technologies; among these, those that are used today use a laser beam to sinter the powder of basic material. They are: SLS (Selective Laser Sintering) for the sintering of polymeric materials and the SLM (Selective Laser Melting) for the fusion of metal powders. The latter is also called DMLS (Direct Metal Laser Sintering).
The result of the SLS process with polymeric materials is a solid structure, produced from the information of a 3D software model. The laser moves on the 3D cross-section and it fuses the powder at the predetermined points. The metal dust particles come together, creating a single solid part. The powder that is not hit by the laser remains as it is.
The principles of the Laser Sintering technique are illustrated in this infographic