Selective laser melting

Selective laser melting (SLM) is one of many proprietary names for a metal additive manufacturing (AM) technology that uses a bed of powder with a source of heat to create metal parts. Also known as direct metal laser sintering (DMLS), the ASTM standard term is powder bed fusion (PBF). PBF is a rapid prototyping, 3D printing, or additive manufacturing technique designed to use a high power-density laser to melt and fuse metallic powders together.

History Selective laser melting is one of many proprietary powder bed fusion technologies, started in 1995 at the Fraunhofer Institute ILT in Aachen, Germany. A research project run by Wilhelm Meiners, Konrad Wissenbach, and Andres Gasser resulted in the so-called basic ILT SLM patent. The ASTM International F42 standards committee has grouped selective laser melting into the category of "laser sintering", although this is an acknowledged misnomer because the process fully melts the metal into a solid homogeneous fully dense mass, unlike selective laser sintering (SLS) which is a true sintering process. Another name for selective laser melting is direct metal laser sintering (DMLS), a name deposited by the EOS brand, however misleading on the real process because the part is being melted during the production, not sintered, which means the part is fully dense. A similar process is electron beam melting (EBM), which uses an electron beam as the energy source.

Process Selective laser melting is able to process a variety of alloys, allowing prototypes to be functional hardware made out of the same material as production components. Since the components are built layer by layer, it is possible to design complex freeform geometries, internal features and challenging internal passages that could not be produced using conventional manufacturing techniques such as casting or otherwise machined. SLM produces fully dense durable metal parts that work well as both functional prototypes or end-use production parts. The process starts by slicing the 3D CAD file data into layers, usually from 20 to 100 micrometers thick, creating a 2D cross-section of each layer; this file format is the industry standard .stl file used on most layer-based 3D printing or stereolithography technologies. This file is then loaded into a file preparation software package that assigns parameters, values and physical supports that allow the file to be interpreted and built by different types of additive manufacturing machines. With selective laser melting, thin layers of atomized metal powder are evenly distributed using a re-coating mechanism onto a substrate plate, usually metal, that is fastened to an indexing platform that moves in the vertical (Z) axis. This takes place inside a chamber containing a tightly controlled atmosphere of inert gas, either argon or nitrogen at oxygen levels below 1000 parts per million. Once each layer has been distributed, each 2D slice of the part geometry is fused by selectively melting the powder. This is accomplished with a high-power laser beam, usually an ytterbium fiber laser with hundreds of watts. The laser beam is directed in the X and Y directions with two high frequency scanning mirrors and remains in focus along the layer utilising an F-Theta lens arrangement. The laser energy is intense and focused enough to permit full melting (fusion) of the particles to form a solid structure. The process is repeated layer after layer until the part is complete. SLM machines predominantly uses a high-powered Yb-fiber optic laser with standard laser powers ranging from 100–1000 W. Inside the build chamber area, there is a material dispensing platform and a build platform along with a recoater system (blade or roller) used to evenly spread new powder across the build platform. Parts are built up additively layer by layer, typically using layers 30–60 micrometers thick.

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