Electron Beam Melting (EBM)
What is Electron Beam Melting?
Electron beam melting (EBM) is an innovative additive manufacturing (AM) process in which metal powder or filament is completely melted by a concentrated beam of electrons. Production in a vacuum chamber ensures that oxidation will not compromise highly reactive materials like titanium. Vacuum production is also required so electrons don’t collide with gas molecules.
Not long ago, most EBM projects merely illustrated the considerable possibilities of the AM process. Today, the potential of electron beam melting technology is more fully realized as it is used to print components used in demanding aerospace, automotive, defense, petrochemical and medical applications.
How Does the Electron Beam Melting Process Work?
A tungsten filament in the electron beam gun is superheated to create a cloud of electrons that accelerate to approximately one-half the speed of light. A magnetic field focuses the beam to the desired diameter. A second magnetic field directs the beam of electrons to the desired spot on the print bed.
Electron beam melting is a high-energy, high-temperature process. This was illustrated by researchers at NASA’s Marshall Space Flight Center when they measured temperatures as high as 2,000 degrees C in the electron beam melting process.
Once a component or prototype has been printed, the build envelope is removed and the build platform and attached object are removed from the loose powder. Powder clinging to the object or remaining in internal cavities is blown or blasted away. Post-processing methods, including hot isostatic pressing (HIP), heat treatment in inert gas or vacuum heat treatment may be employed to release residual stresses and improve mechanical properties.
In some instances, machining may be used to deliver parts with required critical tolerances. CNC machining, sandblasting and shot peening, plating and electropolishing are available to refine the slightly bumpy finish of an EBM-produced part as required.
Electron beam melting technology builds high-strength parts that take advantage of the inherent properties of the metals processed. EBM virtually eliminates impurities that may otherwise intrude when using traditional methods of fabrication.
Electron beam melting includes two technologies -- powder bed fusion (PBF) and fused deposition. The former uses powdered metal to build objects while the latter uses wire filament.
Titanium’s lightweight, superior strength and corrosion resistance have long attracted designers and engineers in the aerospace and defense industries. Lightweight 3D-printed titanium parts retain required strength and durability, a critical advantage in applications where weight considerations are critical.
Titanium’s biocompatibility makes it attractive for producing components for the medical field. For example, many orthopedic implants are often printed from titanium-6aluminium-4vanadium (Ti6Al4V).
Cobalt chrome is a superalloy with excellent mechanical properties. It is a very hard metal highly resistant to high temperatures, pressure and corrosion. Cobalt chrome is used in aerospace and auto racing where parts operate at very high temperatures. In the medical field, it used to fabricate orthopedic implants and instruments requiring sterilization.
Steel powders offer an attractive combination of value, strength and mechanical properties. The 316L stainless steel is known for its excellent corrosion resistance, which is why it is often used to produce automotive parts, medical instruments and industrial spare parts. Maraging steel (MS1) is a high-strength alloy used in the tooling industry. Designers take advantage of the AM process to produce objects with conformal cooling channels in a manner not possible with traditional manufacturing methods.
Inconel 718 is another superalloy with excellent mechanical properties, corrosion resistance and top performance at high temperatures. EBM-printed parts fabricated from Inconel 718 are used in racing and aerospace applications. Valves fabricated from this nickel alloy are used in the petrochemical industry where durability and corrosion resistance are important characteristics.
Applications of EBM Parts
In the right applications, EBM is a cost-efficient way to produce prototypes and low-run production parts. Electron beam melting prints sophisticated and intricate designs. Object dimensions are highly accurate -- similar to those of cast parts.
EBM parts often feature complex geometries offering substantial weight savings, something that is of utmost importance in weight-critical aerospace applications. Launching payloads into low earth orbit (LEO) is expensive, with payload costs at approximately $1000 to $2000 per pound. EBM parts also reduce the weight of satellites launched into geosynchronous orbit.
The U.S. Food and Drug Administration first cleared orthopedic implants created with electron beam melting technology in 2012. Several years later, the FDA approved craniofacial implants printed by EBM machines.
The unmachined rough surface promotes bone growth, making it popular for fabricating hip and knee implants. One study investigated the responses of osteoblasts (cells that secretes the matrix for bone formation) to the surface of EBM implants. When Ra (surface roughness) is below 24.9 µm, researchers identified benefits for the proliferation of osteoblasts.
Electron Beam Melting Advantages and Disadvantages
As with every manufacturing process, there are advantages and disadvantages when creating objects using EBM.
By improving access to emerging high-growth submarkets, electron beam melting technology offers a competitive edge to progressive enterprises. In many electron beam melting applications, designers enjoy unprecedented design flexibility. Electron beam melting produces parts with properties similar to wrought parts and better than those of cast parts. For many applications, EBM is a cost-effective process that reduces inventory requirements and waste. Reduced lead times often Improve customer satisfaction.
Electron beam melting technology offers other key advantages. Build rates are often 3-5 times those of other AM technologies. Multi-beam systems simultaneously maintain multiple melt pools for enhanced productivity. EBM parts usually need fewer support structures than DMLS parts do. The EBM process is approximately 95-percent energy-efficient, which is five to 10 times better than laser-based AM processes.
The electron beam melting process reduces residual stresses in a variety of ways. It is possible to control residual stress during the preparation of CAD data, during printing and in post-processing. During printing, residual stress is reduced by preheating the print bed and by the heating of the material before it is struck by the electron beam. To a degree, lower residual stress is also a function of the process’ high build temperatures and slower cool-down rates compared to laser-based AM processes.
Electron beam melting technology eliminates sintering, enabling users to gain precise control over porosity. EBM operators further minimize porosity issues by adjusting beam parameters.
The surface of a part printed with electron beam melting often requires post-processing, while the smooth surfaces of DMLM-produced parts do not typically require much post-processing.
EBM machines require important preventative maintenance, and the EBM process requires a significant amount of validation.
Electron beam melting requires the use of pure, unadulterated metals. In every instance, a validated supply chain and thorough testing are necessary to ensure the required purity levels.
Although the production of parts using electron beam melting technology requires a significant capital investment, ROI is simultaneously improved through the elimination of certain inefficiencies and design limitations inherent in traditional manufacturing techniques.