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.

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.

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. Fully Dense Titanium
The EBM machine produces components from Ti6Al4V (Ti64) and Ti6Al4V ELI, two commonly used alloys in the aerospace industry. The Ti64 parts exhibit properties (figure 3) that match those of wrought materials and exceed those of investment castings.

The parts are 100 percent dense directly from the EBM machine, so there is no need for a secondary infiltration processes. If desired, the Ti64 parts can be HIP (hot isostatic pressing) treated.

Parts produced with EBM are near-net shape like those made with metal casting processes. Since the electron beam fully melts the titanium, the liquefied metal conforms to the surrounding metal powder, which yields a surface finish similar to a precision sand casting. So, some light secondary machining or grinding may be required.

With material properties that match, or exceed, those of conventional manufacturing processes, EBM allows aerospace companies to produce prototypes and production parts without the inherent cost and challenges (figure 4).

Titanium is difficult to machine, cast and weld. This leads to long lead times and high cost when machining or investment casting titanium aircraft components.

Opportunities Created

Working directly from 3D CAD data, EBM builds titanium components in hours. With conventional processes, production of titanium parts can take days or weeks.

The ease and speed of producing titanium parts with the EBM machine makes functional prototypes readily accessible to the design and manufacturing team. This means that functional evaluations can be completed earlier and more frequently in the design cycle.

Since EBM produces true titanium parts, these advantages can be applied to components for commercial and military aircraft. EBM creates an opportunity to employ rapid manufacturing of flight-ready titanium structures.

Although titanium is often the best material for certain aircraft component applications, costs, challenges and time prevent its use. In these instances, machined or investment cast aluminum is used for weight reduction.

When aluminum is not satisfactory, steel may be used in spite of its weight. With EBM, manufacturers have an effective alternative that combines the advantages of aluminum and steel while overcoming the obstacles of making titanium parts.

Another advantage is that the additive process can make a multi-piece assembly as one component. In those cases where the limits of machining and casting force a designer to create an assembly, EBM can reduce production costs. By combining two or more individual components into a single piece, assembly is eliminated, and the cost of manufacturing may be reduced.

Replacing aluminum and steel parts with titanium and making a single part instead of an assembly are significant benefits to aerospace manufacturers. However, EBM offers an even greater benefit. It creates an opportunity to design and manufacture aircraft components with unprecedented strength-to-weight and buy-to-fly ratios.

Besides making solid titanium parts, the additive EBM process can also produce hollow parts with an internal strengthening scaffold. Impossible with any other method, EBM can deliver the required mechanical strength with much less mass. This reduces the cost of raw materials and the weight of the component.

Aerospace companies, like Boeing Phantom Works, have recognized the benefits of EBM for prototyping and manufacturing. Directly from CAD, it is producing metal parts for functional testing and creating new designs that capitalize on the design freedom that the additive process offers.

Electron Beam Melting is a unique prototyping and manufacturing process that can simultaneously reduce costs, reduce weight, and reduce time. It offers the material properties of machined titanium, expands the design complexity possible with casting and eliminates the challenges and time of both.

About the author

Joe Hiemenz is a technical communications manager for Stratasys Inc., in Minneapolis. Arcam AB is headquartered in Molndal, Sweden.