Among the range of additive manufacturing processes, powder-bed fusion is known for flexibility and design freedom, as well as the efficiency that contrasts AM with metalcasting, machining, or fabricating complex parts. Even so, PBF still is not economically viable for industrial-scale production.
For background, PBF describes various specific technologies – including Selective Laser Sintering (SLS), Laser powder bed fusion (LPBF), Electron beam melting (EBM) – that produce three-dimensional shapes by applying an energy source to powdered materials (metal alloys or ceramic powder), according to a CAD model that defines individual slices of the design that solidify into the finished structure as each layer is converted.
ALD Vacuum Technologies has built what it calls the world’s largest PBF system by optimizing its own capabilities in high-temperature vacuum technologies, electron-beam processing, and powder distribution under vacuum. The resulting the electron beam Powder Bed Fusion process, is able to produce components significantly larger than established PBF-concepts can achieve, including turbine parts or surgical implants in high-value titanium alloys, likeTi64 or titanium aluminide, nickel-based superalloys, copper, or refractory metals.
From powder to parts
Producing prototypes or small volume orders via metal AM is popular with manufacturers and some end-customers due to low material consumption and the flexibility for achieving lightweight complex structures. “Instead of subtracting material through conventional operations such as milling, the desired parts are formed in layers by melting and fusing metal powder using a strong heat source like a laser or electron beam,” explained Dr. Fuad Osmanlic, ALD’s v.p. - Additive Manufacturing. “In general, this allows better control of resources and results in less material waste and lower energy consumption.”
However, the limits on component size and production volumes reduce the range and applications for parts that may be produced by PBF. ALD also noted that because the quality of production process depends on the powder used, meaning that the mechanical properties of the finished component may reduce the process yield.
Also, some PBF processes are so energy-intensive and time-consuming that conventional manufacturing processes may be more effective for some applications.
ALD’s new “EBuild” process is a plant design for electron beam Powder Bed Fusion (E-PBF) processing, and the first system available for both large-scale parts and high-volume production. Among its features are a special powder application system, efficient electron-beam technology, and heat-repellent materials that improve the efficiency for producing some specific products, notably turbines, while significantly reducing material consumption versus conventional manufacturing.
The EBuild system is designed to be completely vacuum-tight for metal additive manufacturing of parts in vacuum or a controlled inert-gas atmosphere. “The synergy between the individual system components and a smart control system leads to cost reduction and lower carbon footprint of production and product life cycle,” according to ALD.
26x larger build volume
In its basic configuration the EBuild® 850 system will convert powder to metal parts with dimensions up to 850x850x1,000 mm³, layer by layer via selective electron-beam melting followed by solidification. The main system components are an electron beam gun, a retractable build chamber, a process chamber connected to a powder-application system, and mobile withdrawal and extraction units. A second build chamber may complement this set-up in order to perform the melt and cool down processes in one chamber, while extracting the parts and powder from the second one and preparing it for the next build.
“In order to overcome the limitations in component size, we have deliberately worked to expand the chamber design to many times the usual dimensions without sacrificing process quality,” Dr. Osmanlic explained. So, the high-precision withdrawal unit can position a powder bed weighing up to 15 mt with an accuracy of approximately 0.01 mm and a total build height of approximately 1,000 mm.
In order to apply the base material, the powder application system fills the build area through a uniform powder distribution. Therefore, the feeder platform is raised to the exact height defined by the operator. This ensures that the powder fed to the rake always remains constant. To prevent the high process temperatures during melting from affecting the powder distribution, the application system is water-cooled.
“It was important to us that our powder application system can also handle powders with low flowability to increase the powder yield, which both saves resources and lowers the price per kilogram,” Osmanlic offered. While the rake feeds new material, layer by layer, the electron beam selectively melts the powder according to the defined component contours until the part is finished and ready to be handed over to the extraction unit for cooldown. All chamber walls and components exposed to high temperatures are equipped with heat shields to moderate energy consumption during melting and avoid heat loss. Also, all valves exposed to powder and metal dust are protected to ensure reliable functionality in severe conditions. “These types of valves have been field-proven in similar applications under production-scale conditions for many years,” he added.
Digital twinning and customization
In order to achieve industrial series production, the system has a high level of automation, as well as advanced process monitoring, closed-loop control, data logging, status indication, fault and alarm functions, and safety interlocks.
One noteworthy capability is EBuild® 850’s back-scattered electron imaging: it offers automatic fault detection through high-contrast layer imaging as well as the option of a 3D-model digital twin. All process preparation, control, and monitoring can be carried out via a PC or the built-in interface. So, all relevant functions are visualized and the production process is intuitive and easy to operate. In addition, several control panels in the operating area allow specific functions to be executed locally. “Even with a high amount of automation we value operational flexibility and control where needed,” Dr. Osmanlic explained.
Some operators may resist metal AM processing because of lack of practical experience – but ALD noted that it considers the EBuild® 850 concept to be a joint venture its customers: the plant design is tailored to the demands of each site, so that each user receives turn-key installation, including process and production support. “Switching to new technologies in one’s production can be daunting and overwhelming without exploiting the full potential. Therefore, the EBuild® 850 is not an off-the-shelf plant, but specifically tailored to fully access the greater design freedom as well as enabling to produce what is needed, when it is needed – without having to fear exploding energy costs and high material waste,” according to Dr. Osmanlic.