What Is Selective Laser Sintering?

15 Sep 2020
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What Is Selective Laser Sintering?

Selective laser sintering (SLS) is an additive manufacturing process that utilises a laser in order to sinter some form of powdered material such as polyamide or nylon, automatically aiming the laser at points in space that are defined by a 3D model, and fusing the material together in order to create a solid component. It is similar to selective laser melting and is a relatively new technique that is used for low volume production of parts and for quick prototyping.

SLS was developed by Dr Carl Deckard and Dr Joe Beaman at the University of Texas in Austin in the mid 1980’s, and they set up a company – DTM – to design and build the SLS machines. The company was bought out by 3D Systems in 2001. SLS requires the use of very high-powered lasers and as such is not a cheap process but can produce items that are very intricate in design and finished to an extremely high standard.

SLS involves using a high-powered laser, such as a carbon dioxide laser, that fuses powders of plastic, ceramic, glass, or metal into the desired 3D shape. The laser selectively fuses the powder by scanning from a 3D digital description of the part, from a CAD file or similar, on the surface of a bed of powder. After each cross-section is scanned, the powder bed is lowered by one layer of thickness and a new layer of material is applied on top of it. This process is repeated until the desired object is formed.

An SLS machine will typically use a pulsed laser because the finished part density will depend on the peak laser power rather than its’ duration, The machine will heat the powder to somewhere below its’ melting point which makes it simpler for the laser to heat the selected regions to the melting point.

The part that is being constructed is surrounded by unsintered powder at all times and this makes it possible to create geometrical shapes which other machines simply cannot do. Furthermore, because the machine’s chamber is filled with powder at all times, it means that multiple parts  can be positioned to fit within the boundaries of the chamber using a process called nesting, and this has the effect of faster production times and at less cost. However, one thing to consider is that it is not possible to create a hollow but fully enclosed part, because there is nowhere for the unsintered powder inside to drain out.

The nylon powder that we use in selective laser sintering at London 3D Printing is created in a ball mill using cryogenic grinding at temperatures lower than ambient because if not cooled they clog and adhere in lumpy masses. They are chilled using dry ice (dry grinding) or liquid nitrogen or liquid carbon dioxide (wet grinding) which enables thermoplastics to be ground to a very fine powder which can result in particles as small as 5 microns in diameter. Powder particles typically range from 15 microns to 100 microns and can be customised to fit different thicknesses in the SLS process.

The technology of SLS is used widely around the world today in many different industries because of the fact that it can produce extremely complex parts quickly and easily. It is used for the construction of prototype parts during the design cycle in order that they can be assessed regarding their suitability in respect of form and function.

SLS is also being increasingly used for small production runs for parts in the aero-space industry and for hardware for military purposes and electronics. In addition, it is being used in medical research and has been used to create human body parts including ears, arms and legs, and muscles. It has even been used to produce artificial skin in a trial programme between L’Oreal and Organovo.

At London 3D Printing we have a range of different 3D printers and we can produce virtually anything that you want within the maximum size limits. Whether you need a prototype part or parts, or small production runs, we have a fast turnaround time. Depending upon our workload and your exact requirements, we normally produce a finished prototype or parts within 2 – 4 days.

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