Laser Powder Bed Fusion polymer is a widely used Additive manufacturing technology. But considerably high-system costs and major patents expired just a few years ago most systems are in the professional sector.
Laser Powder Bed Fusion polymer is better known as Laser Sintering (LS) / Selective Laser Sintering (SLS). SLS systems usually use a CO₂-Laser as an energy source. An XY-scanner system, featuring of two mirrors, directs the laser beam in the XY-plane on the powder bed. A flat field aka f-theta-lens compensates for the focal height in the z axis. The build material is in powder form, where a hopper, rake or rollers distributed the material in thin layers. The build chamber is filled Nitrogen as a shielding gas. Compared to metal laser powder bed fusion systems, the laser power is of SLS systems is significantly lower. Typically used are CO2 laser with around 50 Watts. As the chamber is heated, the laser has to contribute only 3-5 Kelvin to melt the material. In combination with a high absorption rate of the SLS powder, this allows significantly higher scan/processing speeds, compared to metal systems.
Professional SLS/LS machines
Prices of pro machines starting at about 200 000 dollars but they can reach up to one to two million dollars for large and high-temperature systems.
Prosumer SLS/LS systems
Patents for LS/SLS technology expired in 2014.
Several start-up companies announced to release prosumer systems at a fraction of the cost of pro machines. One of those companies, called Norge LTD, got acquired through the French Groupe Gorgé in March 2015 [link to press release]
The Swiss SINTRATEC GmbH
Build space sizes
Small systems have build envelopes of about 250 mm x 200 mm x 330 mm
Medium size systems have build envelopes of about 350 mm x 350 mm x 600 mm
Large size systems have build envelopes of about 600 mm x 600 mm x 1200 mm The machine with by far the largest build envelopes is the Binhu SLS 1400 with build space dimensions of about1400 x 700 x 500 mm.
As SLS does not require support structures, the build space can be fully utilised. Nesting software allows to position up to hundreds of parts the most efficient way.
Materials typically used are Polyamides (PA11, PA12), Polystyrene but also PEEK can be processed in special high temperature machines. The powder not fused in the process can be recycled to a certain percentage. The ratio of virgin and recycled material affects the material properties of the parts build. An exceptions is PEEK as the material gets thermally damaged in the process and cannot be reused.
Materials can be filled or mixed with other materials to improve thermal and mechanical properties. Glas beats, aluminium and chopped carbon fibers are common additives.
The layer thickness can vary typically from 0,04 mm – 0,15 mm. Due to the high-position accuracy of the XY-laser scan systems used the geometrical accuracy of the parts is more affected by warpage of the parts. Experienced machine operators know how to prevent and mitigate these issues.
SL/SLS has been used for prototyping and part production since decades. Material properties and geometrical accuracy are a good trade-off to create robust parts which can be sanded, died, glued or welded and coated. This is why SLS is often used for prototyping. But machines have gained more productivity, material skept improving and post processing technologies have evolved. This is why more and more end-us applications have come up in recent years. However, HPs Multi Jet Fuision technology has grown into teh SLS market
Here a few examples from different industries using SLS
Prototyping for 0 series, custom parts for luxury vehicles
SLS is a great technology to generate intricate and freeform shape models.
Anatomical models, drill guides and cutting jigs for surgeries. Implants like scull plates made of PEEK to replace bone-structure.
On platforms like Shapeways.com end consumers an upload and share designs and get theses manufactured with LS/SLS technology. From student projects to jewellery to spare parts and improvements for commercial products.
These are still niche applications but LS/SLS is used for low batch production from sunglasses to 3D printed bikinis made 3D fabrics.