SLA (stereolithography laser) and SLS (selective laser sintering)

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Theme three, SLA stereolithography laser and SLS Selective Laser Sintering. Laser stereolithography, SLA 3D printing technology based on layer by layer curine of liquid material under the action of a laser beam. Photopolymer is a substance that changes its properties under the influence of ultraviolet light. In normal condition, the photopolymer is supplied. When exposed to UV radiation of electromagnetic range, it becomes strong. Irradiation, duration and wavelength are calculated depending on the specific material, object size and environmental conditions. A mesh platform is placed in a container with liquid photopolymer on which the prototype will be grown. Initially, the platform is placed at such a depth that it is covered by the thinnest layer of material, only 0.05 to 0.13 millimeter thick. In fact, this is the thickness of the layer in laser stereolithography. Next, the laser is turned on, effecting those polymer parts that correspond to the walls of a given object causing their harding. After that, the whole platform is submerged exactly on one layer, ie, on the depth of 0.05 to 0.13 millimeters. Upon completion of construction, the object is immersed in a bath with a special composition to remove excess elements and complete cleaning. Eventually the final irradiation with light for curing. As well as many other 3D prototyping methods, SLA laser stereolithography requires the construction of supporting structures, which are manually removed after construction. Advantages are features of the technology. Manufacturing of models of any complexity, thin-walled parts, small parts. Easy pulsation of the manufactured prototype, high construction accuracy and high surface quality. Properties of applied polymers allow using the grown prototype as a finished product. Larger working chamber, they mentions in comparison with other 3D printers. Low percentage of consumables for support. Low production noise level of parts. Models obtained by this method have sufficient strength, as well as transparency. It is possible to visualize the gas and hydrodynamic flaws inside the models. Such models are also widely applicable for precision casting of metals in mechanical engineering. The SLA model is cast in the molding sand. Then it is a new at a high temperatures up to 1,000 degrees of Celsius. In this case, the plastic is completely burned out and the metal is poured in its place in the formed mold on their vacuum. After the metal hardening, the form is destroyed and the part is removed. Most of the 3D printers working with SLA technology create objects with the size of about 500 by 500 by 600 millimeters, but there are exceptions. The American company has created a device capable of creating objects much larger than the classical ones. 1,500 by 750 by 550 millimeters, which opens up new horizons of this technology. The principle of SLS operation is powder sintering with the help of infrared laser at elevated temperature, which helps powder grains, consolidate during contact with the laser beam. In a conventional SLS printer, there is a so-called [inaudible] on which the roller distributes a thin layer of powder, and then the laser sinters the particles according to the 3D model, creating a detail layer by layer. Then the platform moves down in a small step and the process repeats until the last layer is formed. At the end of the process, a part appears and it is needed to remove the model from the mass of unsintered powder and optionally to perform sandblasting. This is the real advantage of the SLS. Unlike the FDM, SLS can produce 3D printing without any supporting structures, which is important for the models with complex geometries. They are suspended in powder and do not require support. It also allows printing the entire volume of the working chamber by placing any number of parts. It is necessary to distinguish two main categories of materials. Metal and non-metallic powders. The first group is mostly used in the automotive and aviation industries, they will be discussed later. But the second covers prototyping. Poly sterile, poly amide and nylon can be used as polymeric powders. In addition, the SLS method allows printing theramics, glass and sand mixtures. The SLS method has disadvantages, as well as other additive technologies. Firstly, grown models usually require post-processing because of the are rough or poor structure. Secondly, there are special requirements to the room and operating conditions of the printer. The main thing is air filtration during conditioning as the powder is harmful.