Selective Electron Beam Melting (SEBM)

How does SEBM work?

The entire process takes place in a high vacuum, as this is the only way to use the electron beam at all: In a gaseous atmosphere, the electrons would be scattered and slowed down by the gas molecules, making it impossible to maintain a stable, focused beam. As a welcome side effect, the vacuum atmosphere also protects the material from oxidation, which is particularly advantageous when processing reactive materials such as titanium or titanium aluminides.

At the start of the manufacturing process, the substrate plate is heated to the process temperature using the electron beam; depending on the material, this temperature can reach several hundred degrees Celsius. Then the first layer of powder is applied and evenly distributed across the build platform using a recoater or rake. The freshly applied layer can then be preheated again with the electron beam. This so-called »preheat« slightly sinteres the powder, making the powder bed electrically conductive and mechanically stable, and maintaining the part temperature at a consistently high level.

In the actual melting step, a focused electron beam scans the cross-sectional surfaces of the part as derived from the data of a 3D-CAD-model and selectively melts the powder. The beam is deflected electromagnetically, making the process inertia-free and extremely fast, which is why multiple melt pools can be maintained virtually simultaneously. Depending on the process strategy, melting is followed either by a post-heating step (known as »postheat«) to achieve the desired component temperature, or the process proceeds immediately to the next layer. To do this, the build platform lowers by one layer thickness, new powder is deposited, and the cycle of preheating, melting, and, if necessary, postheating begins anew. This is repeated until the part is fully built up.

Since the part is kept at a high temperature throughout the entire process, it is produced under thermal conditions similar to those of a casting process. This largely prevents internal stresses, and subsequent stress-relief annealing is generally not required. The result is high-strength, virtually pore-free parts with excellent mechanical properties.

No smoke events

A key improvement lies in the neutralization of the electron beam by positively charged ions. This prevents the powder particles from becoming electrostatically charged – an important factor in avoiding so-called »smoke events«, in which the powder is stirred up uncontrollably by sudden discharges. At the same time, this charge neutralization enables targeted sintering exclusively in the areas that are actually to be melted. Unlike many conventional systems, this also allows complex geometries with internal channels and cavities to be produced.

Flexible electron beam

Another feature of the system is the high flexibility of the electron beam:

unlike laser processing, it can not only work linearly, but also jump between several points within fractions of a second and create multiple molten pools simultaneously. This »hot part«-process ensures that a high temperature level can be maintained. This allows components with thin and thick wall thicknesses to be manufactured with virtually no distortion.

Vacuum process management

Processing in a vacuum, combined with preheating temperatures of up to 1000 °C, also enables the processing of complex alloys and high-melting or highly reflective materials such as copper or tungsten. In contrast to laser processes, electron beam melting does not generate any significant internal stresses. Due to the simultaneous processing of several melting zones and controlled cooling in a vacuum, the build-up process is metallurgically comparable to a casting process. In addition, the layer-by-layer heating and solidification acts like an integrated heat treatment, resulting in a more homogeneous microstructure and improved mechanical properties.

Open machine architecture

Thanks to its open machine architecture, the system also offers a high degree of flexibility in the development of new material combinations and process parameters – a decisive advantage for research and development and customized manufacturing.