It’s Time For Direct Metal 3D-Printing


It’s tough times for 3D-printing. Stratasys got burned on Makerbot, trustful backers got burned on the Peachy Printer meltdown, I burned my finger on a brand new hotend just yesterday, and that’s only the more recent events. In recent years more than a few startups embarked on the challenge of developing a piece of 3D printing technology that would make a difference. More colors, more materials, more reliable, bigger, faster, cheaper, easier to use. There was even a metal 3D printing startup, MatterFab, which pulled off a functional prototype of a low-cost metal-powder-laser-melting 3D printer, securing $13M in funding, and disappearing silently, poof.

This is just the children’s corner of the mall, and the grown-ups have really just begun pulling out their titanium credit cards. General Electric is on track to introduce 3D printed, FAA-approved fuel nozzles into its aircraft jet engines, Airbus is heading for 3D-printed, lightweight components and interior, and SpaceX has already sent rockets with 3D printed Main Oxidizer Valves (MOV) into orbit, aiming to make the SuperDraco the first fully 3D printed rocket engine. Direct metal 3D printing is transitioning from the experimental research phase to production, and it’s interesting to see how and why large industries, well, disrupt themselves.

Direct metal 3D printing fuses metal powder particles layer by layer into dense objects and does not require post-print infusion like binder-based methods. The selective melting of the particles can be achieved through an electron beam (Electron Beam Melting, EBM) or lasers (Direct Metal Laser Melting, DMLM, synonymous to EOS’s trademarked DMLS). Laser-based direct metal 3D-printing is currently experiencing an extreme push since it typically outperforms the previously hyped EBM technology in terms of resolution and surface finish. DMLM saves the need for a vacuum chamber, but since it requires several high power laser units to catch up to the productivity level of a single beam EBM machine, as well as an inert gas atmosphere and post-print heat treatment, it is also more expensive.

metalysis_particles
Image source: Metalysis

This is, obviously, not the kind of push that puts cheap devices on your desktop. DMLM machines cost about $1M and above, and besides the acquisition price of a machine, direct metal 3D-printing is also a process with a ludicrous per-unit-cost. The materials, fine, high purity metal powders have to be generated through gas- or plasma atomization to obtain consistent and spherical particles. Then there is the printing process itself, which fuses the pricey powders into solid shapes utilizing one or more powerful fiber lasers for several days or even weeks. What comes after that is a classic, manual process of cleaning, annealing, support structure removal, subtractive refining and surface treatment. The high per-unit-cost directly reflects the efforts that must go into the processing of each and every individual particle inside a 3D printed product, and while those efforts sum up quickly, they scale rather poorly.

So, does that mean labeling additive manufacturing as an efficient and waste-free manufacturing method is naively wrong? That depends on the application. The Yb-fiber-lasers commonly used in DMLM machines are a surprisingly effective way of fusing metals and can stay in continuous operation for more than a decade due to their very long MTBF. However, even at very high, experimental build rates of up to 500 mm3 (30 inch3) per hour, their advantage mostly unfolds in high complexity and low quantity applications. So on the one side, 3D printing a simple steel component that was formerly mass-manufactured in a casting process will still cost 10 to 100 times more with DMLM. On the other side, a 3D-printed functional group that combines tens to hundreds of cast or subtractively manufactured parts into a single piece can be significantly cheaper than its traditional counterpart. Eventually, what makes companies like SpaceX, GE and Airbus buy into the technology are the non-trivial implications and cost lever effects:

Lightweight Construction

Angular strut based on bionic design principles and mathematical models for structure generation. Source: “Neue Konstruktionsansätze in der additiven Fertigung”, C. Emmelmann, 2013

Additive manufacturing allows for complexity. Its ability to generate arbitrary shapes and structures enables lightweight construction techniques, where excess material is shaved away from a design based on mathematical and natural models, often referred to as „bionic design“. Since in aviation, even minor weight savings accumulate to massive fuel savings over the course of a single long-distance flight, aircraft manufacturers are going to great lengths when it comes to weight reduction.

Compliance And Quality Assurance

Integration_Emmelmann
Comparison of a conventional assembly with an integral 3D printed component. Source: “Disruptiver Change Prozess durch 3 D Druck in der industriellen Wertschöpfungskette”, C. Emmelmann 2015

A single functional group in a passenger airplane can contain hundreds of individual parts, all of which undergo the internal process of quality assurance and must obtain FAA approval going into service. Baking a few dozen functional parts into a single 3D-printed unit helps to reduce costly and time-consuming compliance and QA efforts.

High-Temperature Materials

3D-printed Super Draco rocket engine, source: SpaceX, 2014
3D-printed Super Draco rocket engine, source: SpaceX, 2014

Extreme temperature applications, from cryogenic fuel valves to white-hot engine bodies, require very temperature and corrosion resistant materials, such as cobalt-chromium and nickel-based superalloys or titanium and titanium-based alloys. These materials are very challenging to machine subtractively while they can be almost effortlessly processed via DMLM.

Cooling channels

This power electronics enclosure utilizes 3D-printed cooling plates to maximize cooling efficiency in constrained spaces. Source: Erfolgreiche 3 D Druckindustrialisierung durch hybride Fertigungsmethoden und Bionic Production
Concept study of a power electronics enclosure for EV onboard chargers. 3D-printed cooling plates with fine pitched, internal coolant channels maximize heat dissipation in constrained spaces. Image source: “Erfolgreiche 3 D Druckindustrialisierung durch hybride Fertigungsmethoden und Bionic Production”, C. Emmelmann 2015

3D-printing allows internal cooling channels to be embedded in thermally stressed components, extending part life and improving efficiency in electronics and thermodynamic applications. Internal cooling channels also can also help to increase the throughput of injection molding tools.

It’s what you make of it

There are clearly a number of products, such as implants and prosthesis, efficient cooling solutions for power electronics, and lightweight frame construction in automotive which are uniquely suited for direct 3D-printing in metal. Currently, they aren’t in the cost-effective operating point of direct metal printing. But they will eventually get there, either by piggybacking on larger industries or on a wave of innovation driven by makers and hackers.

Aurora Impeller
3D printed metal impeller, source: E-Brochure 2016, Aurora Labs Ltd. 2016

Just like MatterFab demonstrated, low-cost DMLM machines are – somewhat possible, but need drive, ideas, the the right applications and funding to become productive and viable. Still, others continue where MatterFab seemingly left off. Aurora Labs — a startup team that happened to have invested more time into their technology than into their cancelled Kickstarter campaign — recently released some footage from their DMLM printer, and it looks like they are getting there. I leave you with this short snippet of a scratch built Ti6Al4V printing DMLM machine, printing a quite decent impeller.