SLS = Selective Laser Sintering Posted on 28 Jan 21:26

SLS and FDM Comparison - Surfaces
SLS and FDM Comparison - Cut Away

SLS = Selective Laser Sintering

The images above are a direct comparison of our SLS Project VII kendama alongside an early prototype we had made using a home/office FDM (Fused Deposition Modeling) 3D printer. Most people envision an FDM type extruder when they think of 3D printing. They are the most common form of printer available to the home/office environment. They are relatively affordable to own and maintain but they also do not produce the most sturdy or refined parts. The extrusion of melted plastic filament in patterned layers has limitations on surface quality, durability and part geometry. Part geometry can fail during prints due to the need for added support braces for undercut/overhanging features as these features can fall-over during extrusion if the nozzle has a buildup and bumps the printed surface. They are great tools, but hardly capable of producing performance parts.

The method of 3D printing we opted to use for our Project VII kendama is referred to as SLS. If you look it up on wikipedia, the first sentence sums it up pretty nicely.

Selective Laser Sintering (SLS) is an additive manufacturing technique that uses a laser as the power source to sinter powdered material (typically metal), aiming the laser automatically at points in space defined by a 3D model, binding the material together to create a solid structure.

Although we haven't done business with them, Solid Concepts is one of the leading providers of additive manufacturing services and has a good overview video walking through what all is involved in the SLS process.

Part geometry is nearly unconstrained with this method of rapid manufacturing as the powdered material that is sintered to make the finished part is also the material that, when not fused, aids to support all part geometry. This means that you can print, say, a whiffle ball, inside another whiffle ball, inside another whiffle ball, as many times as you want and the ball layers will be completely free to bounce around inside each other. The only thing that would have to be cleaned up when the sintering is finished is the excess powder surrounding the finished parts. And any unused powder can be used again for future parts.

Although the cost of printing each kendama by means of SLS is notably more expensive than buying plastic filament and a personal-sized 3D printer, we feel that the added value in performance and appearance are what really matter. That being said, even SLS nylon parts have a breaking point as it is plastic, but that point is much more substantial than any home-printed FDM part. This is due to the fact that the FDM process creates fused wall features that are strong when compressed in one direction, but are extremely brittle when forced along the other direction. SLS, however, sinters/fuses each particle layer inside a heated chamber using a highly calibrated laser to assure that the finished part is equally strong in all directions.