How Does Selective Laser Sintering Work?

by Matthew Wellington on March 11, 2014

Selective Laser Sintered ObjectJust like the Stereolithography (SLA) technology, Selective Laser Sintering is an additive manufacturing technique which can be used to turn digital CAD designs into 3-Dimensional objects.

The printing process in Selective Laser Sintering (SLS) is however not quite the same as that used in Stereolithography.

In SLA, an ultraviolet curable photopolyme resin is used instead of powder and an ultraviolet laser is used to cure the liquid into a solid object.

When it comes to SLS on the other hand, powdered  is heated by a high powered laser at just below its melting point. This causes the powders to sinter together forming the solid 3D model which was intended to be made.

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 are said to expire this 2014. With those limiting patents out of the way, many more manufacturers will now be able to access the SLS technology.

The end result will be more players getting into the market and stiffening competition. Consequently cheaper, more improved SLS machines are likely to be developed in the near future which will be affordable to the majority of 3D enthusiasts.

How the SLS Process Works

The Selective Laser Sintering process mainly describes the method through which miniature particles of plastic, glass or ceramics are exposed to heat by high-power laser; in order to fuse them together forming a 3-Dimensional solid object. In the most basic sense, this is exactly what happens in the Selective Laser Sintering process.

The process often starts by creating a CAD file. The CAD file is what will have all the details related to the design of the object which is to be created.

Once the design is complete, the CAD file has to be converted to STL format for easy comprehension of the design by an SLS machine. At this stage, the printing process can begin.

Bear in mind that all the 3D printing materials to be used in the SLS process have to be powdered. Before the printing starts, the powdered materials must be dispersed above the build platform in a thin layer. The build platform is always found inside the SLS machine.

The next step will now be to direct a laser down to the platform. The laser normally is controlled by a computer and therefore through the computer the designer can easily determine what will be fabricated using the laser. When the laser is directed to the platform, it begins tracing cross-sections of the designed digital object onto the powdered material.

The laser’s main purpose is to heat the powder just below its melting point fusing the tiny particles together forming a solid object. Immediately the first layer is created, the platform of the Selective Laser Sintering machine drops by about 0.1mm to expose a new layer of the powdered material for another cross-section of the object to be traced and fused together by the laser.

This process repeats itself over and over again until the entire object has been fabricated. The object will then be allowed some time to properly cool off before being removed from the SLS machine.

Unique Facts about SLS Technology

Firstly, 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.

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.

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.

Can an SLS Machine be Used at Home?

At the moment, no. It is ill-advised to use SLS machine in homes because the high-powered lasers SLS machines use are potentially insidious especially when used in the typical home environment. It is for this reason why you will only find big companies and manufacturing organizations using SLS machines.

Even then, there are many inventors who are stepping up with the sole focus of developing SLS machines which will be safe for home use. When such ‘homemade SLS machines’ (as they are commonly referred to) finally get to homes; consumers will at last have the opportunity of directly accessing and making the most of the Selective Laser Sintering Technology.

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