Selective laser melting

Selective laser melting (SLM), also known as direct metal laser sintering (DMLS) or laser powder bed fusion (LPBF), is a rapid prototyping, 3D printing, or additive manufacturing (AM) technique designed to use a high power-density laser to melt and fuse metallic powders together. To many SLM is considered to be a subcategory of selective laser sintering (SLS). The SLM process has the ability to fully melt the metal material into a solid three-dimensional part unlike SLS. Selective laser melting (SLM), also known as direct metal laser sintering (DMLS) or laser powder bed fusion (LPBF), is a rapid prototyping, 3D printing, or additive manufacturing (AM) technique designed to use a high power-density laser to melt and fuse metallic powders together. To many SLM is considered to be a subcategory of selective laser sintering (SLS). The SLM process has the ability to fully melt the metal material into a solid three-dimensional part unlike SLS. Selective laser melting, one of the several 3D printing technologies, started in 1995 at the Fraunhofer Institute ILT in Aachen, Germany, with a German research project, resulting in the so-called basic ILT SLM patent DE 19649865. Already during its pioneering phase Dr. Dieter Schwarze and Dr. Matthias Fockele from F&S Stereolithographietechnik GmbH located in Paderborn collaborated with the ILT researchers Dr. Wilhelm Meiners and Dr. Konrad Wissenbach. In the early 2000s F&S entered into a commercial partnership with MCP HEK GmbH (later on named MTT Technology GmbH and then SLM Solutions GmbH) located in Lübeck in northern Germany. Today Dr. Dieter Schwarze is with SLM Solutions GmbH and Dr. Matthias Fockele founded Realizer GmbH. 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 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. This process is in all points very similar to other SLM processes, and is often considered as a SLM process. A similar process is electron beam melting (EBM), which uses an electron beam as energy source. DMLS uses 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 organic geometries, internal features and challenging passages that could not be cast or otherwise machined. DMLS produces strong, 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 image 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 fine metal powder are evenly distributed using a coating mechanism onto a substrate plate, usually metal, that is fastened to an indexing table 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 500 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. The laser energy is intense enough to permit full melting (welding) of the particles to form solid metal. The process is repeated layer after layer until the part is complete. The DMLS machine uses a high-powered 200 watt Yb-fiber optic laser. Inside the build chamber area, there is a material dispensing platform and a build platform along with a recoater blade used to move new powder over the build platform. The technology fuses metal powder into a solid part by melting it locally using the focused laser beam. Parts are built up additively layer by layer, typically using layers 20 micrometers thick. Many selective laser melting (SLM) machines operate with a work space up to 400 mm (15.748 in) in X & Y and they can go up to 400 mm (15.748 in) Z. Some of the materials being used in this process can include copper, aluminium, stainless steel, tool steel, cobalt chrome, titanium and tungsten. SLM is especially useful for producing tungsten parts because of the high melting point and high ductile-brittle transition temperature of this metal. In order for the material to be used in the process it must exist in atomized form (powder form). Currently available alloys used in the process include 17-4 and 15-5 stainless steel, maraging steel, cobalt chromium, inconel 625 and 718, aluminum AlSi10Mg, and titanium Ti6Al4V.The mechanical properties of samples produced using direct metal laser sintering differ from those manufactured using casting. AlSiMg samples produced using direct metal laser sintering exhibit a higher yield(engineering) then those constructed of commercial as-cast A360.0 alloy by 43% when constructed along the xy-plane and 36% along the z-plane . While the yield strength of AlSiMg has been shown to increase in both the xy-plane and z-plane, the elongation at break decreases along the build direction . The improvement of the mechanical properties of the direct metal laser sintering samples has been attributed to a very fine microstructure.