Metal Additive Manufacturing. Ehsan Toyserkani

of metal AM in each industry.

Figure 1.13 Most important metal AM processes versus part size, complexity, and resolution needed.

       1.5.1 Medical and Dental

      The medical industry was one of the early adopters of AM for the fabrication of not only metal parts, but also ceramics, polymers, and FGMs. Metal AM has been used to produce medical devices and tools, surgery guides and prototypes, implants, prosthetics, orthotics, dental implants, crowns, and bridges from biocompatible metals such as various titanium, tantalum, and nickel alloys. These are among the main families of metal AM materials with a somewhat well‐established process‐property record that can be leveraged by companies, clinics, and hospitals that will use AM in the future. The design freedom in the production of complex parts with internal pores and cavities facilitating the growth of cells and the production of patient‐specific parts based on the imaging of patients' anatomy are the main reasons that the medical and dental industry has shown such a high interest in AM. With personalized healthcare on the horizon, it is only expected that the scope of using AM in these sectors would increase. Due to the high precision required to produce medical parts, PBF processes are the dominant AM techniques in this sector. In addition, porosity and selective stiffness are of major importance to medical devices. Thus, BJ is playing an important role as it can produce implants with controlled porosity. Next‐generation customized porous implants aim to better integrate with the surrounding bone, as they improve body fluid/cell‐laden permeability. Functionally gradient porous implants/scaffolds are being designed based on interconnected triply periodic minimal surfaces (TPMS); see Chapter 10.

Figure 1.14 depicts multiple dental and orthopedic devices developed by multiple companies and centers as attributed in the figure caption. Behind all these medical devices, there is an incredible story that the authors suggest the reader look at the references provided in the caption too. In summary, metal AM (especially LPBF and E‐PBF) has been an instrumental tool for the realization of these patient‐tailored metal implants mainly made from titanium alloys.

Figure 1.14 (a) Dental crowns printed by LPBF

      (Source: Courtesy of EOS [16]),

      (b) joint implants printed by E‐LPF

      (Source: Courtesy of Orthostream [17]),

      (c) functionally gradient porous titanium load‐bearing hip implant printed by Renishaw's LPBF

      (Source: Courtesy of Betatype [18]),

      (d) customized ribs and sternum printed by E‐PBF

      (Source: Courtesy of Anatomics and Lab22 [19]).

       1.5.2 Aerospace and Defense

      The industrial adoption of metal AM was ramped up when large aviation, aerospace, and defense organizations/agencies such as GE Aviation, Lockheed Martin, SpaceX, the U.S. Department of Defense, and U.S. Air Force joined the race and started to heavily invest in R&D, machine development, advanced materials, and government‐backed AM programs in mid 2010s. AM is uniquely attractive to this sector because of the lower material waste, lightweighting, reduction of the need for assembly through components consolidation, and the capability of production of highly intricate and complex parts that ultimately contribute to less fuel consumption and cost‐saving due to lower level of certification as the number of parts decreases [20].

      Led by safety requirements, this industry is known for having rigorous testing and certification procedures to evaluate the performance of the parts. As such, further improvements in the repeatability, reliability, and control of the metal AM systems are necessary before we can see airplanes or spacecraft with the majority of their components 3D printed. Nevertheless, it is reported by GE Additive that 28 fuel nozzles, 228 stages 5 and 6 blades and, 1 heat exchanger and 16 particles separators of GE9X engine (a new generation of high‐bypass turbofan jet engine developed by GE Aviation exclusively for the Boeing 777X) are additively manufactured [7].

In space applications, the race is even wider. In 2015, the first‐ever communications satellite with a design life of 16 years and weighed 4.7 metric tons satellite (named TurkmenAlem52E) with an aluminum 3D printed component was launched by SpaceX. This component was an antenna horn mounting strut. Thales developed several antenna supports with an envelope dimension of 45 × 40 × 21 cm, made from aluminum. The AM‐made supports have saved 22% weight and a 30% cost and an estimated decrease in the production time of 1–2 months. These brackets are subjected to a wide range of thermal stresses as during normal operation, they see temperatures of −180 to +150 °C. Designing this part for 3D printing allowed a much more efficient part to be developed because fasteners were no longer needed.

On the rocket engine applications, major activities are underway by SpaceX, NASA, and Aerojet Rocketdyn to adopt AM for rocket engine components because the qualification testing and heritage could be transferrable in many situations. SpaceX launched its Falcon 9 rocket with the first time ever AM‐made Main Oxidizer Valve (MOV) in one of its nine Merlin 1D engines. The MOV operated successfully where high‐pressure liquid oxygen under cryogenic temperatures and harmonic and subharmonic vibration levels were used [21]. The printed version of this traditionally casted part actually has superior strength, ductility, and fracture resistance. The 3D printed part has lower variability in material properties vs. the cast version due to uneven cooling of the part during casting. The MOV body was printed from nickel‐based alloys using LPBF in less than 2 days versus the several months it takes to manufacture the cast version [21]. SpaceX also additively manufactured a SuperDraco Engine chamber. The SuperDraco engines are responsible for powering the Dragon Version 2 spacecraft's launch escape system. This system activates in an emergency to carry the astronauts to safety. These engines are also able to enable the spacecraft to land propulsively with the accuracy of a helicopter, making the spacecraft reusable, lowering the cost of space travel. This engine is being qualified. The qualification program includes testing multiple starts, extended firing periods, and extreme propellant flow and temperatures. Figure 1.15 shows AM‐made parts for SpaceX engines.

      Currently, the propulsion system is the primary focus of Lockheed Martin's AM efforts, with a goal to reduce the lead time on the fuel tanks from 18 months to only a few weeks.

      One other major activities are related to the mission to “3D Printing in Space.” While the plastic 3D printing has been tested in the international space station, there are many challenges associated with metal AM in space. The issue of “gravity” must be resolved before AM can be reliably replaced with expensive supply runs to the space stations.

Figure 1.15 LPBF‐made combustion chamber (left) and the engine in finished configuration (right).

      Source: Courtesy of SpaceX [22].

Another development is associated