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Electron Beam Melting (EBM) is a new alternative for both rapid manufacturing and prototyping metal components, with direct benefits to the aerospace industry.
This technology is fast gaining attention for its ability to deliver fully dense parts with properties equal to wrought materials, at a cost and speed substantially less than metal-based additive-fabrication methods.
EBM not only creates unprecedented strength-to-weight and buy-to-fly ratios, reducing the cost of raw materials and the weight of the component, it also opens the door to new design configurations.
Prior to EBM, combining speed and desired material properties was unattainable. EBM technology stands out for its ability to produce titanium parts in hours versus days. For industries like aerospace, this technology creates new opportunities for prototyping and low-volume production of components.
The time, cost and challenges of machining or investment casting are eliminated, making titanium parts readily available for functional testing or installation on the aircraft. EBM is patented by Arcam AB and distributed in the U.S. by Stratasys.
How it Works
As the name implies, EBM uses an electron beam to melt a titanium powder. The additive fabrication processes builds parts on a layer-by-layer basis. After melting and solidifying one layer of titanium powder, the process is repeated for subsequent layers.
Within the electron beam gun, a tungsten filament incandesces and "boils off" a cloud of electrons (figure 1). These electrons stream through the gun at approximately half the speed of light.
Figure 1: Electron Beam Melting process diagram.
Two magnetic fields organize and direct the fast moving electrons. The first one acts as a magnetic lens, which focuses the beam to the desired diameter. The second magnetic field deflects the focused beam to the target point on the powder bed.
When the high-speed electrons strike the metal powder, the kinetic energy is instantly converted into thermal energy. Raising the temperature above the melting point, the electron beam rapidly liquefies the titanium powder.
Figure 2: Electrons traveling at half the speed of light creates temperatures that melt titanium powders.
The electron beam gun is stationary, and there are no moving mechanical parts for beam deflection. This delivers very high scanning speeds—up to 1,000 m/sec. (3,280 ft/sec)— and fast build rates—up to 60 cm3/hour (3.7 in3/hour). Compared to other metal-additive fabrication technologies, the process is three to five times faster.
The EBM process is performed in a vacuum to prevent a loss of energy that would be caused by the fast moving electrons colliding with air or gas molecules. The vacuum has two advantages.
First, the process is 95 percent efficient in its use of energy, which is 5 to 10 times greater that laser technology. Second, the vacuum supports processing of reactive metal alloys like titanium.
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