The selective laser sintering stations (SLS) use thermoplastic materials or metal powder to create 3D prototype parts. A computer-directed heat laser melts powder layer by layer. More powder is deposited on top of each solidified layer and again sintered.
The selective laser sintering allows for more diversity in the selection of materials. These include nylon, glass-filled nylon, polycarbonate, metals, elastomers, SOMOS (rubber-like) and Truform (investment casting). Hence, the SLS process provides for the most functional rapid prototype available.
A typical selective laser-sintering machine consists of two powder magazines on either side of the work area. The leveling roller spreads the powder from one magazine crossing the designated area to another. Further, the laser outlines the layer intricately. The work platform moves down by the size of one layer and then the roller moves in the opposite direction. The laser beam traces the surface of powder that is tightly compacted to
selectively liquefy and bond it to create a layer on the object. Until the part is complete, whole process is repeated. The temperature of the fabrication chamber is maintained just below melting point of the powder and so the heat of the laser only raises the temperature slightly so as to cause
sintering.
To prevent possible explosion in handling large quantities of powder the fabrication chamber maintains a nitrogen atmosphere, this speeds up the process. When the object is fully formed piston is raised to elevate the
http://www.PrototypeZone.com Page 54 object. The excess powder is simply brushed off and the final finishing of the object is carried out manually. However, the part needs to cool down and hence has to be kept in the machine until that happens. The large parts with thin sections may even require two days as cooling time. The selective laser sintering method is also being used for direct fabrication of metal or ceramic objects and tools.
The materials used in this process are used according to their intended purpose. DuraForm is used for functional plastic parts, DuraForm GF is used for glass-filled functional plastic parts, Somos 21 is used in durable
elastomer parts, LaserForm A6 is used in metal and tooling and CastForm PS is used in casting patterns.
Selective laser sintering offers the advantage of making functional parts in final materials, i.e. the object to be made is made in the material in which it is to be sold. The system is more complex than stereolithography and most other technologies. Also the SLS has the capacity to make metal
prototype parts using Rapid Steel A6 or Laser Form ST-200 materials where metallic powder is used in the laser sintering process. However, the
disadvantages of SLS are that the object is porous and hence it has to be filled with a sealant to make it functional.
Therefore, selective laser sintering has given the world a fast and effective way to make prototypical objects. The advantages of the SLS process are great and it has relatively less disadvantages. SLS is a better way of prototyping than stereolithography.
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Stereolithography
Stereolithography abbreviated as SLA is a process of Rapid prototyping. It is used for the production of three dimensional and physical objects like the conceptual models or the master pattern. It is often referred with the names like 3-D printing or 3-D layering. The three-dimensional or the physical objects are created with the aid of CAD drawings. It uses the method of the CAD drawings that assist the mechanical engineers to verify certain parts and have a visual idea about their products. It is also beneficial for inventors as they can get an estimate for their future inventory products. 3-D printing technology is very useful in the 21st century in all the sectors. With the invention of Stereolithography, workload of several companies has reduced and there is an increase in quality and production of goods. The machine of Stereolithography is aided by the computer to create 3-D parts and is based upon the method of layers.
Stereolithography makes use of liquid UV curable resin. It also uses a UV laser, which is used to build layers over layers. On the surface of the resin, a laser beam traces the part of the cross section pattern. The pattern or part, which is traced, is hardened when exposed to the UV laser light. Once the part or the pattern is solidified, the elevator of Stereolithography descends by single layer. The thickness of the layer is generally between 0.05 mm to 0.15 mm. The resin-filled blade swipes the cross section part and later it is re-coated with new materials. Adhering to the previous layers, the
subsequent layer pattern is traced and this leads to the formation of the 3-D part. The excess resign on the parts is cleaned with chemical bath. Once it is cleaned properly, then it is cured in the UV oven.
http://www.PrototypeZone.com Page 56 There is a drastic increase in the geometric visualization of the product. The complex factors in the product are curbed with the use of this technology, as one can easily understand the layout of the products. The process is time saving and result oriented. It yields quick results and helps to minimize the errors. The support structures that are attached to the elevator platform are used in Stereolithography. This helps to over come the deflection of
geometry due to gravity and also helps to hold the cross section of 2-D. For the use of Stereolithography machine the generation of the supporters is done automatically while preparing the 3-D CAD models. However, the supports are removed manually when the product is ready. In some of the rapid prototyping process, the supports are removed automatically.
Stereolithography is beneficial in all the fields. The biggest advantage of this technology is that functional parts are created within no time and play a vital role in the working environment. They are also used for various
purposes like thermoforming, blow molding, injection molding and provide strong mechanisms. This technology is economical and can be implemented in various sectors at affordable prices.
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