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Metal Milestones in 3D Printing

Kip Hanson
By Kip Hanson Contributing Editor, SME Media

Tracing the not-so-distant roots of metal 3D printing, its development, and where it’s headed

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The RenAM 500Q from Renishaw printing parts for a Renishaw optical system.

Compared to machining and other traditional metalworking processes, additive manufacturing (AM) is a newcomer. Most industry experts trace its birth to 1987, when Chuck Hull of 3D Systems fame introduced the first commercially available stereolithography machine, the SLA-1. Two years later, Stratasys co-founder Scott Crump and his wife Lisa developed FDM (fused deposition modeling), and two years after that, Electro Optical Systems (EOS) founder Hans Langer delivered the STEREOS 400, a direct competitor to the SLA-1. The rapid prototyping industry was born.

There was just one problem with these early systems, though: they only printed plastic. If you wanted metal parts, you’d have to machine, stamp, form, or cast them. Granted, EOS did develop what many consider the first 3D metal printer—the EOSINT M250—in 1994, but this machine used a blend of metal powders—bronze and nickel, for example—one of which provided the low melting point needed to form the binding matrix. The name of this metal printing technology? DMLS, or direct metal laser sintering.

Sinter No More

As a result, the first fully-dense metal 3D-printed parts wouldn’t arrive until 2004 or so. It was then that EOS introduced the EOSINT M270, a powder bed system equipped with a 200-W, diode-pumped fiber laser boasting sufficient power to actually melt the individual metal particles. Fortunately, the company didn’t have to change its trademark moniker—the S in DMLS now stands for solidification or “schmelzen” (German for “to melt”), even though most in the industry still refer to it as sintering.

A great deal has changed since then. Though the underlying “one layer at a time, working from the bottom up” methodology common to virtually all 3D printers hasn’t changed over the past three decades, DMLS and its cousin, electron beam melting (EBM), have continued to grow more accurate and capable, to the point that the parts now coming off these machines are routinely used for flight-critical applications, as well as in the human body. At the same time, there are several new metal additive technologies. These include metal binder jet, direct energy deposition (DED) systems employing metal powder or wire feedstock, and FDM’s metallic counterpart, bound powder extrusion (BPE). More on these shortly.

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A new feature available in 3DXpert 15 allows full automation of the support generation process for different geometries while maintaining a high level of optional manual control.

With these developments comes the extensive knowledge base and support infrastructure needed to fully utilize metal AM, chief among them an entire industry built around the processing of high-quality metal powders. “Back in 1994, nobody was making powder,” said Ankit Saharan, manager of applications development and R&D at EOS North America, Pflugerville, Texas. “We were forced to use what was basically scrap material from other manufacturing processes and develop blends that would accomplish our goals. By 2004, we had nine metals, and today, practically all of the major alloys are available, as well as a number of newer, often proprietary materials.”

Not Your Parents’ 3D-Printer

Aside from leveraging this metallic rainbow of powders, EOS and others have worked hard to improve their wares. Laser power has increased five-fold or more, with some production systems boasting dual or even quad lasers. The use of vacuum or inert gases like argon, together with tightly-sealed build chambers, has led to more metallurgically-sound workpieces. Recoater technology continues to advance, as does laser control and the use of inline metrology systems to monitor build processes. Simply put, metal 3D printing is poised to become a mainstream process, one able to produce parts never before possible in the history of manufacturing.

A big chunk of this success is due to modern CAD software. AM product designers have had to set aside decades-old design for manufacturability (DFM) principles in favor of design for additive manufacturing (DfAM), much of which revolves around the creation of the unconventional shapes and geometries that 3D printing is known for. One might argue that without generative design software, 3D printing is like a finely-tuned engine forced to run on low octane fuel. But there’s also build preparation software, process control and monitoring software, simulation software, and these tools are just as important to metal AM as are high-quality powders and feedstock.

Mark Cook, vice president of product management for the metals business unit at 3D Systems Inc., Rock Hill, S.C., agreed. He said the company’s 3DXpert combines these functions and more into a single parametric package, providing AM operators with a CAD-based platform that covers the initial file import through to post-processing. “Every company has resident machine software to do the build prep and manage the process parameters, but we developed 3DXpert to be a single solution for the entire metal AM workflow.”

Though 3D Systems has been a pioneer in polymer-based additive manufacturing. It played a vital role in the development of SLS (selective laser sintering) with its 2001 acquisition of inventor Carl Deckard’s company DTM. However, it didn’t enter the metal AM space until 2013. That’s when it added DMP (direct metal printing) to its product portfolio, working with and then acquiring a controlling share of Phenix Systems, Riom, France, followed one year later with its acquisition of Leuven, Belgium-based LayerWise.

Since then, 3D Systems has continued to improve upon those two DMP technologies, starting with the introduction of an oxygen-free build environment. “By placing the entire chamber under vacuum, we’re able to eliminate oxygen and nitrogen from the powder while reducing the uptake of other contaminants,” Cook said. “This is a key feature for customers producing aircraft and medical parts, particularly those made of titanium, which is oxygen-reactive. We’ve also extended this level of environmental control to our removable print module. Not only does this assure consistent powder quality and therefore more consistent parts, it also simplifies material handling and reduces machine downtime. We see each of these attributes as critical for productive metal additive manufacturing.”

Rock Hill to Leuven (and Back Again)

Cook noted that the seeds of this vacuum technology came from LayerWise, a DMP equipment manufacturer located close to another AM pioneer, Materialise NV. Ironically, Materialise founder Fried Vancraen and his wife Hilde bought one of the early iterations of 3D Systems’ stereolithography machines—the SLA-250. That was in 1990 and it was their first 3D printer. Also ironic is the fact that around this same time, Bart Van der Schueren, chief technical officer for Materialise, was busy working on a prototype laser-based metal printer as part of his master’s thesis at KU Leuven’s Department of Mechanical Engineering. Van der Schueren would go on to join Materialise several years later, but his early work on electron beam melting was picked up by others at the university, and eventually led to LayerWise’s formation in 2008. The 3D printing world is tight-knit indeed.

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Like all manufacturing processes, metal 3D printer operation requires adherence to relevant safety guidelines, including worker protection.

Though an early adopter of polymer 3D printing, Materialise NV, Plymouth Mich., is another company new to the metal AM party, though not in the way you might think. Materialise began commercializing 3D-printed metal parts through a series of acquisitions and partnerships, primarily in the orthopedic sector, as far back as 2008. This work came in-house in 2014 after Materialise invested in DMLS and LaserCUSING machines from EOS and Concept Laser, respectively.

“It didn’t make economic sense for us to invest in our own hardware, not at first,” Van der Schueren explained. “We’ve watched as the performance of 3D metal printers has increased steadily year after year, but obsolescence was of particular concern in those early days. At the same time, we had to develop the knowledge necessary to operate a metal printer in an economical way, while also creating the revenue stream necessary to support such an investment.”

Today, Materialise has nearly 200 3D printers, with roughly twenty of them able to print metal. The company is also recognized as a leader in 3D printing services and software. The Materialise Magics platform is a brand-agnostic suite of utilities covering everything from the build preparation discussed earlier to process and quality control functions to the virtual planning tools needed for craniomaxillofacial (CMF)surgery, a medical field Materialise specializes in.

From Implants to Aircraft Parts

So, too, does Renishaw PLC. Since 2009, the UK-based metrology manufacturer has delved deeply into the CMF and dental sectors, beginning with its purchase of a metal 3D printer. “Our chairman wasn’t too happy with the results we were getting and decided we would develop our own machine,” said Mark Kirby, additive manufacturing business manager for Renishaw Canada. “We started by purchasing MTT Technologies in 2011, a company that already had a line of additive manufacturing equipment, which we used as a starting point.”

That equipment was quickly retooled and rebranded to deliver the 200-W, single-laser machine known as the Renishaw AM 250, a machine that has since been superseded by the AM 400. More recently, however, Renishaw introduced its multi-laser RenAM 500Q. “We’ve continued to improve our additive platform by developing our own optical train—which we 3D-print on our equipment, by the way—as well as a powder recirculation and filtration system,” Kirby said. “The 500Q is a culmination of all these advances, together with four independent 500-W lasers for maximum throughput and build speeds.”

More so than speed, Kirby said the AM industry as a whole is driven by the need for process repeatability. This means printing parts with the same metallurgical and physical characteristics today as you printed last year, which is why most machine builders’ development efforts (Renishaw’s included) continue to focus on control of the build environment, powder and laser management, and advanced processing software. Renishaw is one of the many machine builders that supports integration with the Materialise Magics suite, although Kirby noted that the company has also developed its own QuantAM build preparation and InfiniAM brand of process monitoring software. Other machine builders have followed suit with similar systems.

Ultimately, process control means the ability to print parts on any machine, whether it’s from Renishaw or another maker. This becomes even more relevant with higher production volumes, like those seen in the automotive industry, or distributed manufacturing scenarios. Machine builders must therefore provide robust metal printing solutions, Kirby suggested, but predictable enough that all of the machines in a build farm will perform the same way. “If we were talking about machining, no one would ever say, ‘Well, you can only do that on a Mazak or an Okuma or a Matsuura.’ That would be completely unacceptable to any manufacturer, whatever they produce,” said Kirby.

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This heat exchanger, 3D-printed out of Inconel 718, demonstrates VELO3D’s support-less capabilities when printing internal cooling channels and fine features.

Sans Supports

The need for temporary support structures that must be removed post-build have been a thorn in the 3D printing industry’s side. Is there a solution? Zach Murphree thinks we’re getting close. The vice president of technical partnerships at additive manufacturing solutions provider VELO3D Inc., Campbell, Calif. is quick to point out that the company’s Sapphire printer is breaking metal AM norms by reducing and in some cases eliminating those support structures. “We continue to push the finite limits of the LPBF (laser powder bed fusion) process and have been able to successfully print zero-degree angles, i.e. horizontal surfaces, without any support structures at all,” he said.

Support-free printing provides several advantages, Murphree explained. There is the reduction in post-processing costs, often a significant portion of the total piece price. There is also less support-related redesign needed, making the process of transitioning parts from traditional manufacturing to additive easier. The entire build chamber can be used when parts don’t have to be anchored to the build plate, significantly increasing machine capability. Perhaps most importantly, designers achieve greater freedom with support-free printing, opening the door to previously un-manufacturable structures—such as internal fluid channels and heat exchangers—and delicate details that secondary machining processes might destroy.

Despite these successes, Murphree suggested that the AM industry overall has a ways to go before going completely mainstream. “I think the quality assurance side of 3D printing is still underdeveloped,” he said. “The dearth of conclusive in-situ data on part quality is a pervasive problem that all end users are dealing with. Because of this, customers tend to lack confidence in the parts they get out of additive systems, something we’ve addressed with our new Assure Quality Assurance and Control System, which weaves machine calibration together with metrology to provide a comprehensive build report that gives the user detailed insights into what occurred during the build.

“There’s also the cost of 3D-printed parts, which is generally greater than those produced with conventional manufacturing processes and therefore has limited the technology’s use somewhat to high-value aerospace and medical parts,” Murphree continued. “To bring costs down, you’re seeing systems with larger build platforms and multiple lasers, as well as the quality improvements needed for higher-volume manufacturing applications.”

Meet ADAM

Thus far, we’ve only discussed metal powder bed fusion (PBF) printers, which use a laser or in some cases an electron beam to join tiny bits of metal into fully dense products. Yet there are some new kids on the additive block, systems that promise build speeds 100 times faster than PBF printers with far lower investment costs to boot. What’s more, most of these systems are aimed at office or light industrial use, bringing the printer directly alongside and at the disposal of product designers and engineers.

One of these systems comes from Markforged Inc., Watertown, Mass., where director of materials Joe Roy-Mayhew described how the company has leveraged its expertise in the 3D printing of composite materials as an entry into metal AM. “We launched our first metal 3D printer—the Metal X—in February 2019 under the premise of democratizing metal 3D printing with an intrinsically safe and cost-effective method of part production,” he said.

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The Markforged Print Farm is said to be an economic, scalable solution for carbon fiber and metal 3D printing needs.

The Metal X printer uses metal powder bound in a plastic matrix as a feedstock (what many refer to as bound powder extrusion [BPE]). At the time of the initial product launch, that material was limited to 17-4 PH stainless steel, although the company has since expanded its offering to include Inconel 625 and several grades of tool steel. The system works by extruding the metal feedstock in a manner akin to FDM printing, but leaves behind a “green” part that is then washed to remove most of the binder material. The now “brown” part is moved to a sintering furnace, burning away the remaining binder and fusing the workpiece into a fully-dense metal component.

This process is what Markforged calls atomic diffusion additive manufacturing (ADAM). Roy-Mayhew said it offers several advantages over PBF systems, starting with the powder. “With laser sintering, you typically have a bed of metal powder and the parts coming out of that bed are dependent on its properties,” he said. “There are also handling considerations with metal powder, such as waste and recycling, as well as support structures and post-processing requirements. We don’t have any of that with ADAM. It’s an easy-to-use system that gives you consistent, reliable parts and can be deployed practically anywhere.”

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Volkswagen intends to use HP’s Metal Jet to 3D print a variety of parts for its next generation of vehicles.

Crank Up The Volume

Another alternative to metal PBF is binder jet, or more specifically, HP Metal Jet. Uday Yadati, responsible for product management, strategy, business development, and application engineering at Palo Alto, Calif.-based HP Inc., explained that the system works like a traditional paper printer in that it uses wide-area processing to build an entire layer at one time. “HP Metal Jet can place up to 630 million nanogram-sized drops per second of a liquid binding agent onto a metal powder bed, which helps to quickly and precisely build a part layer by layer,” he said. “The result is build speeds up to 50 times faster than other metal additive manufacturing technologies on the market, but [binder jet] is also less expensive and more reliable.”

As with Markforged’s ADAM process, binder jet parts undergo various secondary processes—in the case of HP Metal Jet, these include decaking to remove loose powder, followed by sintering in a furnace. Machining might also be needed for close-tolerance features, as well as polishing to meet surface finish requirements. HP Metal Jet is currently limited to industry-standard stainless-steel powders, although the company is working with material partners to expand its portfolio. What’s not limited, however, is its throughput—Yadati said the technology targets high-volume manufacturing of production-grade metal parts, especially those used in the automotive and consumer products space.

“Our technology represents a huge opportunity for automakers as they shift toward electric vehicles (EVs) and away from internal combustion engines,” he said. “Volkswagen, for instance, has completed a successful execution of the first step in its strategic roadmap for Metal Jet through the production of more than 10,000 high-quality parts produced by HP and GKN Powder Metallurgy to support the visionary ID.3 electric vehicle launch event. In subsequent phases, Volkswagen intends to integrate Metal Jet printed structural parts into the next generation of vehicles as quickly as possible and is targeting a continuous increase in part size and accuracy, with the future goal of soccer-ball size parts made in production runs of 50,000 to 100,000 per year.”

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