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Be Green: 'Revert' to Scrap

Aug 16, 2023

What do you think when someone says "scrap" or "revert?" Head to a dictionary and you’ll see synonyms like "useless," "worthless," or "ineffective." These associations run deep, and changing those perceptions is a challenge. But, if the additive manufacturing (AM) industry wants to improve its commercial and environmental sustainability, changing how we think of scrap—indeed refuting the whole concept—is something that we must embrace.

Independent qualification is key to assuaging manufacturers’ concerns about recycled, reworked, or rejuvenated materials. By rigorous testing to real-world production standards, the old associations can be challenged, and AM can confidently adopt a more sustainable path forward.

Manufacturing is inherently impactful to the environment. Taking some part of the natural world—be it stone, wood, minerals, or metals—and turning it into something useful means extracting basic resources and spending energy and further resources converting them.

Simply getting the materials in the right form to be worked is where some of the biggest ecological and economic impacts originate. The extraction, processing, refining, transport, and subsequent waste streams impact sustainability far more than the energy used in the physical manufacturing process.

Metals and alloys pose specific challenges in extraction and processing, requiring huge amounts of energy and resources across multiple processing steps. The steel industry alone is estimated to account for about 7% of carbon emissions globally. On one hand, this is perhaps not surprising, given that in 2021 almost 2 billion metric tons of crude steel was produced worldwide. But it's also indicative of the outsized impacts that reducing carbon emissions from metals and alloys value chains could have in the race to net zero.

Powder-bed processes are by far the most commonly used metal AM technologies, using either laser or electron-beam power sources. While AM makes up a very small percentage of materials used and parts created in the context of the global manufacturing industry, the process is growing rapidly.

The gap between AM's abilities and manufacturing requirements is shrinking as the technologies mature, creating more touchpoints for application development.

More emphasis is being placed on repeatability, quality, qualification, and certification of AM processes. An increasingly holistic view of the AM ecosystem is also driving the technology toward true industrialization.

Additionally, the requirements in manufacturing are changing in a way that brings them closer to AM's capabilities. Shorter runs, just-in-time manufacturing, and spares-on-demand all bring AM into the picture and allow additively manufactured parts to replace traditional manufacturing. It is essential, therefore, that AM pays attention to its sustainability now, so that the impact is compounded through greater adoption in the years to come.

Materials choice is a key component in delivering sustainability goals across manufacturing; nowhere is this more evident than in metal powders. Legacy powder-production technologies such as gas atomization (GA) and plasma atomization (PA) are significantly inefficient and environmentally damaging.

GA, the most common technique for creating metal-AM powders, produces powder particles that typically range from one to 250 microns in size. But laser-powder-bed fusion (LPBF) machines can only process powder particle sizes within a window of 15–63 microns (individual systems or applications often make this window much narrower).

PA shares the same low yields as GA, and, as such, all atomized produced powder is largely unsuitable for AM. This means the useful portion bears the environmental and economic weight of the off-sized powder created. The incorrect size material often gets put back into the revert manufacturing process, using more energy and adding to the carbon footprint without adding any value. Titanium specifically gets incinerated or goes to a landfill, which has its own environmental challenges.

An additional challenge for atomized-produced powder is its feedstock requirement of either ingot for GA or wire for PA. These processes can either use virgin materials, which have an inherent environmental impact associated with extraction, or rely on ingot or wire produced from non-virgin material that has created more carbon and consumed vast amounts of energy even before the atomization process begins. For PA, in particular, this not only makes an additional environmental impact, but significantly limits the workable metal powders that can be created.

6K's UniMelt system is a production-scale, microwave-plasma process that produces advanced materials used in AM, lithium-ion battery material manufacturing, and other industrial markets. Extremely high yields, produced with less energy input, help the UniMelt system address some of the shortcomings of legacy technologies. Additionally, the system can process an almost infinite variety of metals and alloys, including hard-to-process refractories, with highly controlled chemistries and physical characteristics. This is a virtuous circle allowing AM to tackle more of the challenges faced by manufacturers and further accelerate adoption.

Perhaps the biggest commercial and environmental impact of the system is its ability to use "scrap" as a feedstock. Used powders, used support structures, failed prints, machining scrap, end-of-life parts, and more can be used as feedstock for premium metal powders. But can a circular economy for metal powders compete with the quality of virgin stock?

The best way to change an opinion or entrenched association is with independently ascertained evidence. So how does sustainable metal powder stack up against material from legacy production methods in a real-world production environment?

Morf3D is an El Segundo, Calif.-based engineering, advanced manufacturing, and metal-AM leader focused on the aerospace sector. As part of its drive toward sustainability, the company qualified sustainably produced Ni 718 powder from 6K Additive in a production environment at its Metallurgy Center of Excellence and is currently working on Ni 625.

Morf3D compared 6K Additive's sustainably produced powder with data from its legacy GA-produced materials. The test parts showed that 6K Additive's sustainably produced Ni 718 met or outperformed those built with traditional GA-produced powder. CT scanning to examine physical characteristics revealed that 6K Additive's powder demonstrated high consistency at the particle level, with excellent spheroidicity and up to two times less powder porosity than the GA-produced powder. Consistent powders make consistent parts, with less waste as a result.

For mechanical property testing, test coupons were produced on an EOS 400-4, with a 40-µm layer thickness and Morf3D's production parameters. As-printed, machined, non-heat treated, and heat-treated samples were produced in order to assess parts straight from the machine, as well as those more representative of production parts. Heat-treated and machined coupons underwent tensile testing, producing a consistent dataset without outlying results.

The test coupons surpassed Morf3D's minimum requirements and exceeded the legacy material data. Fatigue testing saw sustainable Ni718 exceed expected industry standards and once again outperform legacy data. Parts made with 6K Additive powder showed consistently better surface finish than parts made with legacy powder.

While sustainability rightly sits at the top of every consumer's conscience, every board meeting agenda, and every news cycle, it is essential that AM grapples with the topic. Increasingly, environmental and commercial imperatives are intertwined to the point that the only viable route now is a sustainable one. Added to that, circular economies provide an opportunity to reduce the cost contribution of metals through recycling schemes that facilitate the next batch of material.

We will also save for another day the added value of using scrap for supply chain security in the face of the geopolitical landscape. So let's reconsider what scrap is, what it could be, and what we need it to be in future: not the end of the line, but just another step in a perpetual circular economy.

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