Metal additive manufacturing (AM) has reached an interesting stage in its development as a production technology. It’s certainly not young—the first research on selective laser sintering (SLS) was published in 1986—and yet the idea of 3D printing with metal is nevertheless regarded as a novel one. In short, the technology has reached that awkward phase where it’s mature, but still seen by many as an adolescent: it’s a millennial.
And—like millennials—metal AM is crucial to the future of manufacturing. The best way to understand why is to take a close look at where it’s come from and what it’s doing today.
3D Printing with Metal – Then & Now
Although the first metal 3D printers emerged in the ‘90s, the technological basis for metal AM goes back much farther than that. “In the ‘60s, we started working with wire feedstock and electron beam welding for nuclear applications,” explained Kenn Lachenberg, Director of Operations at Sciaky Inc. “Then in the ‘70s, and more so in the ‘80s, we started building up air seals for jet engine repair using the EB process with wire feed. As we started doing more bulk deposition with the process, we learned that complete components could be fabricated with a reverse-machining approach where we add material, layer by layer, rather than removing it to fabricate the geometries needed. During that transition, to address the need for dynamic energy adjustment in the melt pool and consistently build target components, we developed our patented closed-loop control system; further refined today and known as IRISS (Interlayer Realtime Imaging & Sensing System).
This summary of Sciaky’s entrance into metal additive manufacturing is characteristic of the industry as a whole: the technology began as a limited solution for highly-specialized applications, but over time began to spread out and, as it did, became more and more refined. Within the last decade, there has been rapid and significant growth in both the technologies and the applications for metal AM.
There are numerous ways to delineate the types of metal 3D printing, but one of the most straightforward is in terms of feedstock. Although their techniques for manipulating feedstock differ, all metal 3D printers use either metal powder or metal wire. Both existed prior to the advent of 3D printing as materials for other production processes: coating for powders and welding for wire. However, despite this commonality, metal wire and metal powder offer a very different set of challenges and benefits when it comes to additive manufacturing.
For example, ensuring the quality of a metal powder requires more than checking its chemistry, since the size of the metal particles can also have a significant impact on part density. However, with wire, Lachenberg adds, “As long as they can hold a material spec and it sits within the chemistry range that you need, including traceability documentation, you can be confident with that wire supplier. We’ve been working with a major wire supplier for the aerospace industry for many years, but we’re always researching additional suppliers.”
Another major difference between powder- and wire-based metal AM processes lies in the relative flexibility of these two types of metal 3D printers. There’s a growing consensus among metal AM experts that the best way to avoid defects on powder machines is to limit each machine to a single metal or alloy. This is because even the most thorough post-print cleaning tends to miss at least some powder elements, which can interfere with the next build if it uses a different material with significantly different properties. In contrast, wire-based 3D printing processes, such as Sciaky’s Electron Beam Additive Manufacturing (EBAM), do not suffer from the same restriction.
“With the EBAM process, we can quickly and entirely change the wire feedstock to include the same alloy, a different alloy, or a combination of alloys, if a multiple wirefeed system is employed,” added Lachenberg. “The multiple alloy feed mechanism, with very precise independent control of deposited material, lends itself nicely to the creation of new and very unique alloys. With powder systems, it would be very difficult to control the combination of different materials to produce a special alloy with any degree of precision.”
A Brief Introduction to EBAM
The additive manufacturing industry doesn’t skimp on acronyms—SLS, SLA, PBF, DED, DMLS, etc.—which can make it a challenge to keep all the various technologies straight. Focusing on one example, Electron Beam Additive Manufacturing (EBAM) is Sciaky’s proprietary technique for producing large-scale metal structures much faster than conventional forging or casting. As the name implies, EBAM uses an electron beam to melt a metal wire feedstock and thereby produces near-net shape parts, layer-by-layer. Of course, there’s a lot more to it than that.
“Most people don’t realize that with the electron beam, you’re not just impacting the wire with a single beam directed into the melt pool,” Lachenberg said. “You have a raster scan beam pattern, much like that generated by old cathode ray tube televisions from the ‘50s and ‘60s, producing a rastered image. The rastered pattern of the beam for 3D printing can serve to heat the molten pool, wire and surrounding areas to precisely create pre- and post-heat zones that can impact the metal’s microstructure.”
Most industrial metal 3D printers use an inert shielding gas, such as argon or nitrogen, to minimize the risk of contamination when working with refractory or reactive materials. In contrast, EBAM operates in a pure vacuum environment. According to Lachenberg, this offers a distinct advantage in terms of contaminates. “A shielding gas is only so pure,” he said. “As an example, if you have a shielding gas around a weld—an arc or even a beam—the environment around the molten material may be somewhere around 200-500ppm contaminates. In that vacuum environment we use, you’re at about 0.1ppm.”
EBAM was created with large parts in mind—with an existing build envelope of up to 19’ x 4’ x 4’, Sciaky’s EBAM machines can accommodate round parts exceeding 8’ in diameter. However, the technology can also be applied to parts as small as 8 in3. Common materials used by EBAM machines as wire feedstock include:
- Titanium and Titanium Alloys
- Inconel 718, 625
- Tantalum
- Tungsten
- Niobium
- Stainless Steels (300 series)
- 2319, 4043 Aluminum
- 4340 Steel
- Zircalloy
- 70-30 Copper Nickel
- 70-30 Nickel Copper
“I think what really separates EBAM from other technologies is the deposition rate,” Lachenberg said. “For other processes, you’re typically dealing with maybe five pounds per hour for PBF. We’re typically running over 15 pounds per hour, with some projects running up to 25 pounds per hour. Even then, I think we’re only operating at somewhere around 30 percent of the machine’s capability. The machine axes travel speeds, wire feed rate and power level, can be throttled up to produce even higher deposition rates going forward.”
Metal Additive Applications
By general consensus, the two industries leading the charge in metal additive manufacturing are aerospace and medical devices. It’s easy to understand why: the parts made by aerospace and medical device manufacturers tend to be complex and made of expensive or difficult-to-machine materials. As the saying goes, complexity comes free with AM, and the issues that arise with performing subtractive operations on metals, such as tungsten, are a non-issue in additive.
Lachenberg agreed that the aerospace and medical device industries showed the initial interest in metal AM, but he noted another important commonality between them: strict regulations. “We’re working on a number of programs with major aerospace companies,” he said, “and right now we’re going through the material processing elements. If you want to put a printed part on an aircraft that people are going to fly on, you’re going to have to go through some stringent qualification requirements. As a disruptive process or emerging technology, you are not simply grandfathered to incorporate critical printed metal structures, and understandably so, you must go through all the extensive qualification and certification processes.”
The tight tolerances set by these industries can also be a challenge, which is why many parts made with metal additive processes like EBAM typically go through one or more post-processing operations. For this reason, parts are often 3D printed to near net shape and finish machined.
“What we’ve found is that when we try to go even more near net shape, our finishing supplier will ask us to add a little more material to allow their cutting tools more stock to work with,” said Lachenberg. “The general rule we have is plus or minus three millimeters around the net shape. Of course, for some applications—particularly those in industries with looser tolerances—post-processing may be unnecessary.” Lachenberg pointed to the ballast tanks Sciaky made for a submarine project as an example.
One of the most intriguing applications for wire-based metal additive processes, such as EBAM, is the ability to repair metal parts. Being able to add material onto a damaged part and then machine it back to specifications can save enormous amounts of time and money compared to manufacturing an entirely new replacement. “The premise of this started out years ago, with building those air seals for jet engine components,” Lachenberg explained. “EBAM also allows triple process capability (printing, cladding & welding) in a single machine, as demonstrated by the production of the ballast tanks for ISE’s Arctic Explorer autonomous Unmanned Underwater Vehicles (UUVs). The titanium ballast tank hemispheres were produced with EBAM 3D printing, followed by EB Cladding for additional features, and then EB Welded to join each hemisphere, with all processing done in a pure vacuum environment. With this combination of capabilities, EBAM is the most versatile 3D printing solution in the market today for producing high quality parts.”
Getting Started with Metal AM
Regardless of what you may think of millennials, the simple fact is that we need to work with them—assuming you aren’t already. Much the same can be said for metal additive manufacturing. So, where do you start? In either case, the key is research: learn more about the possibilities and potential. In the case of metal AM, Lachenberg offered some more practical advice:
“Metal AM’s best attributes are adaptability, for specialized part design, and fabrication, which isn’t constrained by legacy manufacturing methods. While keeping in mind all the new approaches with this technology, it is important to understand how its applications are performing in the field. This could springboard the design and build of your part. While there are many high deposition rate AM machines out there, most of them have not built a single part that has made it to production. As for myself, I am a firm believer that real-world experience holds more credibility.”
For more information, visit the Sciaky website.
Sciaky Inc. has sponsored this post. All opinions are mine. --Ian Wright