Hello everyone and welcome to the third week of our online course. Theme 1, features of SLS, SLM, and DMLS technologies. SLS, selective laser sintering, is an additive manufacturing method which consists of melting fine powder material we use in a laser. Last week, we already talked about selective laser fusion, but then it was about 3D prototyping and machines using polymeric powder as a raw material. Today, we will talk about machines that work with metal powder, One of the varieties of SLS technology when it is realized using layer by layer laser melting of metal powders is commonly called SLM, selective laser melting. Besides SLM, there is also a method which is also a kind of SLS technology. Direct metal laser sintering, DMLS, selective laser melting, SLM, and direct metal laser sintering, DMLS, are two additive manufacturing processes that belong to the 3D printing group using the powder layering method. These two technologies have much in common. Both use a laser to melt metal powder particles selectively, binding them together and creating a model layer by layer. In addition, the materials used in both processes are metals in granular form. The differences between SLM and DMLS are connected with the basics of the particle ball binding process. SLM uses metal powders with the same melting point and completely melts the particles, whereas in DMLS, the powder consists of materials with variable melting points. SLM produces parts from a single metal while DMLS produces parts from metal alloys. In the case of DMLS, direct laser sintering, laser energy is sufficient to melt fine particles and to melt the surface of large particles partially. Therefore, the fine fraction acts as a binding material when creating the product, and the large fraction is the main structural component of the material. Thus, in DMLS technology, the main mechanisms for joining the particles are solid phase and liquid phase sintering. In contrast to classical liquid phase sintering in the DMLS process, the fusion of particle secures locally during accelerated crystallization of the liquid phase. Both SLM and DMLS technologies are used in industry in order to create final engineering products. They are very widely used in mechanical engineering. This is due to the fact that this technology makes it possible to produce parts with very complex geometry. It is almost impossible to repeat such products using conventional milling or laser machines. They have no glues, joints, or seems, because of that, the part gets better performance characteristics. The principle of operation of SLS and DMLS devices are very similar. The camera in which printing takes place is first filled within inner gas, e.g. argon, to minimize oxidation of metal powder. Then it is heated to the optimum operating temperature. The powder layer is distributed over the platform. A powerful laser makes the process along a given trajectory in the program, fusing the metal particles together and creating the next layer. When the sintering process is complete, the platform moves down by one layer. Then another thin layer of metal powder is applied. The process is repeated until the printing of the entire model is completed. Then the 3D printer camera is cooled down to room temperature. The excess powder is removed manually, for example, with a brush. After that, the parts are usually heat treated while they are still attached to the platform. This is done to relieve any residual stresses. Further processing can be carried out with them. The work piece is removed from the platform by cutting. The main advantage of DMLS compared to SLM is that, it enables to create objects without any residual stresses and internal defects that can effect the traditionally produced metal components. This is extremely important for metal components that will work on the high loads, such as parts in aerospace or automotive industry. SLM is a process with very high energy because each layer of metal powder must be heated to the temperature above the melting point of the metal. The high temperature gradients occurring in the production of SLM can also lead to stresses and dislocations within the final product, which can impair its physical properties. The metal components manufactured traditionally must be heat treated after manufacture in order to relieve internal stresses. However, selective laser melting, namely SLM, also has advantages allowing printing objects extremely densely and thermally.