Selective Laser Sintering – Its advantages and disadvantages.
Despite being one of the first 3D printing technologies around, SLS is still one of the best options for many prototyping and low volume production projects. Here we take a brief look at its advantages and disadvantages to see if it could be the right choice for you.
But first it helps to understand the process because this explains why for some projects it could be an ideal choice, but for others you may want to choose an alternative technology.
SLS the process
The SLS machine begins sintering each layer of part geometry into a heated bed of nylon-based powder using a laser. After each layer is fused, a roller moves across the bed to distribute the next layer of powder. The process is repeated layer by layer until the build is complete.
Advantages of using SLS
SLS is reliable, precise and one of the fastest ways of producing prototypes and small volume batches of parts. It has some distinct advantages over other processes:
No support structures
Unlike some other 3D printing processes, the part does not need any support structures since empty spaces are filled with unused loose powder making it self-supporting.
This allows you the freedom to design empty hollow spaces, overhanging features and very thin features. It means you can design parts with complex internal components or channels without the fuss of support structures (be sure to consider design guidelines though, to ensure proper removal of remaining powder). If you need a complex design, it is a good option and you don’t need to produce multiple parts to achieve this.
The process is one of the fastest 3D printing technologies since the lasers have a fast-scanning speed and the powders used only need a short exposure for fusing. In addition, we can tightly arrange multiple parts in the chamber with minimal clearance to maximise the available build space – so you get more parts produced faster.
Excellent mechanical properties
The SLS process produces very strong adhesion between layers so parts have good isotropic properties. This means that their tensile strength, hardness and elongation to break are similar across the x, y and z axes.
These properties mean that the printed parts are often a good alternative to injection moulded parts – whether for prototyping or to produce low volumes. Because of the materials used, generally Nylon, the parts also offer good chemical resistance.
Ideal for dying and colouring
Parts produced by SLS tend to have a porous surface – which could be an advantage or a disadvantage depending on your application. What it does mean is that they are an excellent choice for dying or colouring.
Reduced product development time
Like all 3D printing technologies selective laser sintering allows engineers to prototype parts cost effectively early in the design cycle, since it does not require tooling and involves minimal set up.
For low volume production you may even choose to use the same machine to produce end use parts. It means that you can test and alter prototypes quickly over the course of just a few days and move to production rapidly.
Disadvantages of SLS printing
Like any production technology SLS does have its disadvantages and there are occasions when it may be better to consider alternatives – whether that’s another 3D printing process, CNC machining or injection moulding.
You will probably find that some of the disadvantages are not too much of an issue when you dig a bit deeper and others can be overcome through postprocessing.
You don’t get a wide choice of materials for SLS. At Protolabs for example we offer a full range of materials, from flexible TPU and PA 12 Flex to tough PA 12 40% Glass Filled and PA12 Carbon Filled, while having a great general purpose material, PA 12 White. We find that most projects use nylon-based materials, or polyamides, which are excellent engineering grade plastics that can be used across a wide range of applications.
Nylon is also freely available and relatively cost effective.
Rough surface and porosity
The same porosity that makes SLS printed parts so great for colouring, also means that they have a relatively rough surface, are not leak proof and have a low impact strength, or brittleness.
If these factors are important, then it’s worth noting that they can be overcome using a post processing technique called vapour smoothing. As the name suggests this process produces a smooth surface, that is leak proof and it even improves mechanical properties such as impact strength and elongation at break.
High shrink rate
Because the print powder is subjected to high temperatures for it to sinter, this does mean that as it starts to cool it shrinks which can produce a dimensionally less accurate part than other additive manufacturing technologies. Depending on the design, the shrinkage rate can be as high as 3 to 4%.
It means that you will need to allow for this in your design and adjust the volume of the part accordingly. The stress caused by this contraction can also warp or distort sharp edges and corners.
Take a look at our blog “7 mistakes to avoid when designing 3D printed parts” to help avoid such problems.
Higher waste than other additive manufacturing
One of the key advantages with additive manufacturing is the minimal waste of material using the technology. Unfortunately, SLS does produce some waste since the powder in the chamber is preheated so that it will sinter with minimal exposure to the laser.
This can cause particle grains in the loose powder bed to partially fuse which compromises its quality for reuse. In practice while you can recycle some of the unused powder, some will be waste.
Typical applications for SLS printed parts
Selective laser sintering (SLS) is an industrial 3D printing process that is ideal for rapid prototyping and for manufacturing functional production parts. We offer a number of nylon-based materials and a thermoplastic polyurethane.
If you need highly durable parts that are resistant to heat and chemicals and are flexible with good dimensional stability then it’s a great choice. It’s also a good option when you need a cost-effective solution for higher volumes of 3D printed parts.
A number of different industries use parts produced by SLS, with common applications including; jigs and fixtures, housings and snap fits and living hinges.
Depending on your exact needs it might or might not be the right choice for your next project. At Protolabs we provide five (?) different additive manufacturing processes plus injection moulding and CNC machining so we can advise you on which technology would best meet your specific needs.