In order to fulfill the promise of additive manufacturing of eliminating material waste, the AM industry needs to stop wasting materials. In metal powder bed 3D printing this issue has become more relevant as the technology targets larger production batches. And a viable solution to end material waste now exists: it starts with powder rejuvenation. 6K Additive’s UniMelt microwave plasma technology is promising recycled metal powders for PBF with quality even superior to traditionally atomized materials from ingots. Reducing metal powder waste emerged as a key demand during 3dpbm’s AM Focus on Sustainability so we reached out to 6K’s Chairman and CEO, Aaron Bent, Ph.D. to learn how the Boston-based company is addressing this issue.
Not only has 6K developed a method to efficiently recycle metals – even the toughest refractory ones – to turn them into ready-to-use AM powders, its UniMelt technology also promises near 100% yield of powders ranging from 15 to 45 micron (which can be used in metal laser PBF) as well as the 45-106 micron range (for e-beam PBF processes), or any determined size for a particular application or technology. To put this into context, standard gas atomization processes get about 30%. 6K also claims to produce truly spherical particles, void of porosity and satellites, and with better flowability than powders made with competing technologies.
As the company prepares to enter the market with its first Inconel 718 material, the impact from this approach could be huge for both cost-effectiveness (which is a major factor) and for establishing AM as a fully environmentally sustainable process, which – let’s be honest – it isn’t yet.
Building industry trust
One of the reasons why large quantities of metal powders are wasted in AM processes is that adopters of advanced manufacturing processes worry about even minimal deviations in powder quality. “The truth is that there are zero issues with rejuvenation,” Dr. Bent assures us. “We add no contamination in our UniMelt process. There is no combustion, no electrodes that wear: we are capable of synthesizing much more demanding materials – highly stoichiometrically accurate lithium-ion battery cathode and anode materials for the energy storage market.”
Following his Aeronautics Ph.D. at MIT, Dr. Bent has built up over 20 years of experience founding and running companies in various disruptive technologies across a broad range of markets including defense, automotive, energy efficiency, solar, clean metals production, and telecommunications. Thus he understands these industries’ demands.
“As a baseline, we’ve conducted studies where we process best-in-class gas atomization powders in our UniMelt system, and we substantially improve their properties: flow, sphericity, satellite removal, apparent density – this gave us strong confidence that not only can we provide acceptable rejuvenation results but also dramatically improve properties of the virgin powders.” 6K is able to reprocess used powder, which has deteriorated due to unavoidable factors such as oxygen levels (gains oxygen each time powder is used), loss of morphology (i.e. becoming less spherical) preventing flow in an AM system, restoring to its premium state.
This is actually already a relatively standard practice, even among aerospace companies and it is referred to as “Revert”. Rolls Royce has a Revert program for closed-loop recycling of nearly 20,000 tonnes of metal alloys it uses every year. Almost 95% of a used aero-engine can now be recycled and around half of the recovered material can be safely used again to make a new engine. 6K can help make closed-loop recycling several orders of magnitude more efficient for AM adopters. “Rejuvenation is a dramatic reduction in energy demands compared to producing new powders from ingot or wire,” Dr. Bent points out. “Even if other atomization processes had comparable yield rates, UniMelt only uses one third to one-fifth of the argon gas in production, and has twice the electrical efficiency of an inductively coupled plasma.” Dr. Bent highlights that UniMelt is routinely 99% efficient from microwave to plasma, versus 40% – 45% for inductively coupled plasma (ICP).
Because of the efficiency of its microwave plasma process, the most significant benefits of UniMelt technology extend beyond powder rejuvenation, “6K can approach near 100% yield in its plasma process because we engineer the feedstock for the final powder size distribution required by the 3D printer.” Dr. Bent says. In contrast, typically only 30% of a gas atomized powder falls into the PSD required by laser powder bed fusion systems. The remainder is waste. In titanium, only a very small portion of the under-sized or over-sized powders can be re-melted and most are just landfilled. For other alloys, a portion can be remelted, but not all. The waste from a 30% yield includes the energy and expense of creating an ingot for atomization, the transportation to the atomizer, and the energy to atomize. Another aspect to consider – no less important – is the economic sustainability of AM: today materials represent about 10%-15% of the overall part cost. However, the progressive reduction in the cost of equipment and production processes is driving down overall part cost. Within five years, powders could grow to represent as much as 40% of the overall part cost in certain industrial segments.
Ready to market
6K is now ready to go to market with its first product, Inconel 718, followed by Ti64 later this year. The company is currently commissioning a new production facility in Pittsburgh that comprises 40,000 sq ft of new state-of-the-art capacity including multiple UniMelt production systems for producing various alloys, both reactive and non-reactive. The facility is already ISO9001 and will be AS9100 by the end of the year.
This location already upcycles over 1 million pounds of titanium a year, for use in alloying high-quality aluminum for the automotive, defense, and medical products sectors. Research- and sustainability-centric AM services such as Castheon and Sintavia have conducted print runs with 6K powders on a limited basis. Now several more leading AM service bureaus, as well as major AM adopters in aerospace & defense, oil & gas, and medical implant verticals are receiving samples.
Dr. Bent admits the team is excited about the availability of powders on a much broader scale. Last year the company demonstrated a whole host of materials including tungsten, tantalum, SS 17-4, AlSi10Mg, Inconel 625, molybdenum and rhenium. The mining and extracting processes for these materials are often extremely toxic to the environment: reducing their waste is even more of an imperative for the additive manufacturing industry.
The possibilities offered by 6K’s technology go beyond refractories. The company has demonstrated a High Entropy Alloy (HEA) made with 5 separate elements, two of which had almost a 900°C degree difference in melting temperature. Castheon used it to produce the world’s first HEA AM printed part. “Our mantra is ‘If you can think it, we can produce it!’, which is why many of the defense companies are speaking to us about creation of materials and new HEA’s that have never been available in conventional manufacturing, let alone in powder form for additive manufacturing,” says Dr. Bent.
No material limits
And 6K is not limiting itself to the metal powders market. Ceramics and advanced polymers are also on the list. “We produced our first ceramic powders 5 years ago, and are waiting for the technology for direct sintering to catch up,” Dr. Bent confirms. 6K has produced powders from garnets, nitrides, alumina and zirconia, in sizes ranging from 50 nm to 150 micron. One thing to note is that the company’s focus is exclusively set on laser-based or e-beam, direct sintering technologies, so it may be some time before we’ll see ceramics. Polymers may be closer, though. “We are very interested in polymer-based spherical powders” Dr. Bent confirms. “While we have yet to formally begin a program, we have been approached by several customers for advanced thermoplastics, PEEK, and various impregnated polymers.”
The UniMelt’s process capabilities can expand beyond metal into ceramic and even plastics and 6K is open and looking to partner with companies developing AM applications that require a unique material, in order to leverage the capabilities of UniMelt vs what can be made today. One thing that 6K is not looking to do at this point is to focus on other powder-based processes, such as binder jetting and cold spray, which generally have lower requirements for either materials or powder sphericity and size. “Our first objective is to enable additive manufacturing of the most advanced materials with the most advanced properties, by making it both economically and environmentally sustainable,” says Dr. Bent. “We believe this is possible, and in fact, believe that the industry will demand it, once solutions become available.”
If 6K will be able to deliver on this promise, the AM industry will be able to realize its own promise of dramatically reducing waste in comparison to subtractive manufacturing, and achieve ideal buy-to-fly ratio objectives by ensuring that much of the original source material becomes a final part.
Today this promise is objectively not being realized. The powder manufacturing process is 70% waste. The printing itself can result in an additional 30%-40% waste of materials, from supports, used powder, and non-conforming parts post-print. By leveraging sustainable sources for powder rejuvenation and producing powder with 100% yield production processes – which are the two pillars of 6K’s strategy – the company is now starting to pilot its “zero loss” model, whereby it can take the waste streams from 3D printing sites and close the loop to premium powders. There could not be a better time.