In earlier decades, emphasize was given to the traditional ways of manufacturing any product. But as the technology evolved day by day, a new approach is developed in the manufacturing industry sector where prototyping became one of the important stage in the overall process of designing any part. Additive manufacturing technology is the foremost technology used now a days to make the prototypes of the designed parts. Variety of materials can be processed by using different technologies such as stereo lithography, SLS, Fused deposition method etc. Unlike a subtractive process rapid prototyping is in additive process where the layers of material are added over each other to produce the final part which simplifies the process and enables it to be automated very easily.
Selective laser sintering (SLS) is an intelligent additive manufacturing process based on the use of powder coated metal additives, a process generally used for rapid prototyping and instrumentation. A continuous Laser beams are used or pulsating as heating source for scanning and aligning particles in predetermined sizes and shapes of the layers. The geometry of the scanned layers corresponds to various sections of the models established by computer-aided design (CAD) or from files produced by stereo-lithography (STL). After scanning the first layer, the scanning continues with the second layer which is placed over the first, repeating the process from the bottom to the top until the product is complete.
SLS is known also as solid free and open shape manufacturing process, as a layer fabrication technology, rapid prototyping technology, a selective sintering of metal powders. SLS is reactive when using a chemical reaction of mixing components in the presence of a laser and a selective laser melting (SLM), a direct metal laser sintering (DMLS) or direct metal laser re-melting, when the complete melting of powders is pervasive over the solid state dust sintering. This process was also used in manufacturing moulds, rapid handling of electrodes manufactured, polymer moulds, die casting, die casting of titanium zirconium, bio-medical applications, pieces of zirconium-titanium (PZT) and sheet metal parts.
Selective Laser Sintering technology was developed by Carl Deckard back in the 1980s. At that time Deckard was a student at the University of Texas and with the help of his Mechanical Engineering professor, he was able to not only develop but patent the SLS process. In 1989, together they founded one of the first additive manufacturing companies: Desk Top Manufacturing (DTM) Corp.
12 years down the line (2001) nevertheless, they sold DTM to 3D Systems. However, ever since they discovered this unique additive manufacturing technique, they covered it with major patents which have been one of the main reasons why a lot of companies have not been able to access the technology even after so many years.
The key patents covering SLS have also played a part in making Selective Laser Sintering machines so expensive, because of lack of competition. Averagely, an SLS machine can cost up to $250,000 making such machines expensive to both businesses and homeowners. The good news though is that the core patents for SLS expired in 2014.
How SLS Works?
Sintering has been used for thousands of years to create everyday objects like bricks, porcelain and jewelry.
Like all methods of 3D printing, an object printed with an SLS machine starts as a computer-aided design (CAD) file. CAD files are converted to .STL format, which can be understood by a 3D printing apparatus.
Objects printed with SLS are made with powder materials, most commonly plastics, such as nylon, which are dispersed in a thin layer on top of the build platform inside an SLS machine.
A laser, which is controlled by a computer that tells it what object to “print,” pulses down on the platform, tracing a cross-section of the object onto the powder.
The laser heats the powder either to just below its boiling point (sintering) or above its boiling point (melting), which fuses the particles in the powder together into a solid form.
Once the initial layer is formed, the platform of the SLS machine drops — usually by less than 0.1mm — exposing a new layer of powder for the laser to trace and fuse together. This process continues again and again until the entire object has been printed.
When the object is fully formed, it is left to cool in the machine before being removed.
Unlike other methods of 3D printing, SLS requires very little additional tooling once an object is printed, meaning that objects don’t usually have to be sanded or otherwise altered once they come out of the SLS machine.
SLS doesn’t require the use of additional supports to hold an object together while it is being printed. Such supports are often necessary with other 3D printing methods, such as stereolithography or fused deposition modeling, making these methods more time-consuming than SLS.
What gets made?
SLS machines can print objects in a variety of materials, such as plastics, glass, ceramics and even metal (which is a related process known as direct metal laser sintering). This makes it a popular process for creating both prototypes as well as final products.
SLS has proved to be particularly useful for industries that need only a small quantity of objects printed in high quality materials. One example of this is the aerospace industry, in which SLS is used to build prototypes for airplane parts.
Because airplanes are built in small quantities and remain in service for many years, it isn’t cost-effective for companies to produce physical molds for airplane parts. These molds would be too expensive to make and would then need to be stored for long periods of time without being damaged or corroded.
Using SLS, companies can create prototypes that are stored digitally as .STL files, which they can redesign or reprint as needed.
Because SLS machines can print in a range of high-quality materials, from flexible plastic to food-grade ceramic, SLS is also a popular method for 3D printing customized products, such as hearing aids, dental retainers and prosthetics.
And because objects printed with SLS don’t rely on molds or require additional tooling, this method of manufacturing is also useful for anyone that wishes to print a highly complex or particularly delicate object.
Selective Laser Sintering is a more affordable additive manufacturing technology than many other 3D printing techniques such as Stereolithography and Fused Deposition Modelling (FDM). Therefore widespread use of the technology will bring us closer to making 3D printing a mainstream technology because the costs involved will be greatly mitigated.
Secondly, unlike quite a number of additive manufacturing technologies which are only reliable for making prototypes; SLS can be used for making both Quality Prototypes and final products. This is why with the major patents expiring this year hence many more companies being allowed access to the technology, it will be only a matter of time before real and worthy final products made Using Additive Manufacturing can begin to be sold directly to consumers.
Selective Laser Sintering additionally is a more time efficient technique unlike Stereolithography and FDM. The reason being it does not necessarily require additional supports to hold the object in position as it is being printed. Moreover, SLS often requires negligible additional tooling if any, so any objects coming out of the SLS machine do not have to be prepared any further for selling or presentation.
The unparalleled ability of this technology in making final products can also be attributed to the fact that it is capable of using a rather diverse array of printing materials. While most technologies only rely on plastic materials; Selective Laser Sintering can use plastic, glass, ceramics and even metal. This also makes it easier for SLS to be used in creating customized consumer final products.
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