MATERIALS
THE LIFE AND TIMES OF AN SLS POWDER WORDS: DANIEL O’CONNOR
D
o you know what the first selective laser sintering (SLS) materials were?
Sugar, salt and sand. At least that’s according to the Godfather of SLS, Carl Deckard, who told TCT last year that he knew SLS powders would need to be granular, so he started playing with what he had to hand. Fast-forward 30 years, and we’re processing Nylons, PEEK, TPUs, flame-retardant polymers, anti-static polymers. SLS technology can leverage thousands of specific mechanical property needs, depending on both the material and sintering process. The most commonly used powder in SLS is Polymide 12 (PA 12) - a robust and resilient nylon material that’s as good for end-use parts as it is for prototypes. Over the years the compound, the milling, the process, the refresh rates have been refined to a point where one can call SLS a mass production process. The steps involved in making a powder before it even sees an SLS machine are complex; it starts with the chemical compounding. “There are many different processes to manufacture polymers,” explains Moritz Kügler, the Product Manager for Polymers at EOS. “The main source is often crude oil that gets refined and made into monomers. Through
the polymerisation process, these monomers are made up into polymers.” At this point, the chemistry can be altered to add mechanical properties like flame retardancy or elasticity. Post-polymerisation the raw material takes many guises - pellets or extruded wire but either way at this point in the chain, for use in SLS the polymer must be ground and milled into a powder.
BACK TO THE GRIND
Many chemical firms choose to mill themselves. However, there are companies like the Dressler Group who specialise in producing the highest-quality powders for additive manufacturing from some of the toughest materials to grind. “Normally a customer comes to us when they have a material with unique properties for additive manufacturing and tells us that they have a problem turning it into a powder,” says Axel Dressler, joint CEO (alongside brother Jan) at Dressler Group. “We try to figure out what their material requirements truly are and then show them how to achieve that specification using our technology.”
Dressler Group has both an Innovation Lab and Technical Centre, where for the past five years, the company has developed processes for grinding previously difficult materials like TPUs and PEEKs into usable powders for SLS. A customer journey at the Dressler Group usually involves exploration in the lab and technical centre, where they can take small trials of the powder for testing, before returning for production quantities. “We have a lot of machines in both our technical centre and on our production line,” explains Jan Dressler. “It is important that we select the right machine to make the right powder. Trying to make powder when you have compounded a material filled with glass or carbonfibre is a challenging process. It has taken us more than three years to develop a process which can be used for previously ungrindable materials.” The Dressler Group will be showing the world this technological development for the preparation of additive powders at both K Show and the upcoming Formnext event in November. The sibling management team are very excited about the possibilities; after all, new materials equal new applications.4
SHOWN:
SLS PROCESS BY EOS
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