Electron-beam additive manufacturing

Electron-beam additive manufacturing, or electron-beam melting (EBM) is a type of additive manufacturing, or 3D printing, for metal parts. The raw material (metal powder or wire) is placed under a vacuum and fused together from heating by an electron beam. This technique is distinct from selective laser sintering as the raw material fuses having completely melted.

By means of an electron beam as an energy source, a metal powder is purposefully melted, whereby compact components of almost any geometry can be produced directly from the design data. For this purpose, similar to the selective laser melting, alternately applied a powder layer with a doctor blade to the previous and selectively melted by electron beam. In this way, the desired component is generated in layers.

In selective laser melting (SLM), the melt jet is mechanically controlled, whereas in electron beam melting, the melt jet is deflected in a vacuum via a magnetic field (and thus without inertia). As a result, theoretically higher process speeds are possible with the EBM in comparison to the SLM.

Compared to traditional manufacturing processes such as casting, sintering or forging, there are several advantages. These include:

Great geometric freedom of design
Shortening the time between development and market introduction
Higher material efficiency
No costs for component-specific tools, molds, cores or the like
Economic production of prototypes and / or small series

Compared to the traditional additive manufacturing processes, the following disadvantages arise, among others:

Relatively high initial investment
Relatively slow production of components
No economic production of large series
The relatively small volume of the device limits the maximum possible dimensions of the component
The EBM process creates a higher density of material defects, which may be due to e.g. B. leads to lower material strength
Largest supplier of EBM systems and owner of the EBM brand is the Swedish company Arcam AB.

Technology
This process, which starts directly from the pure metal to the powder state, makes it possible to produce finished and void-free parts (the last characteristic feature of this technology until at least 2011 when the SLM models (metal-based 3D printers) “Selective Laser Melting”) still could not achieve such high-density performance, now the SLM technology has achieved performance approaching the EBM process). The production process involves placing the powder layers of the material to be melted under vacuum, starting from thicknesses of about 0.1 mm and with a casting capacity up to 80 cm 3/ h. Working under vacuum, and therefore in the absence of air, also allows working on materials that would otherwise react immediately with oxygen producing unwanted compounds.

The machine, which reads data from a 3D CAD model, is divided into 4 sectors:

Command (PC)
Power (high voltage)
Cannon (cathode tube) where the electron beam is generated
Chamber (maintained at constant pressure (3 * 10 -5))
The melting process takes place at temperatures typically between 700 and 1,000 ° C and allows to obtain parts substantially free of residual stresses and which therefore do not require post-heat treatments after production.

The EBM technique was developed by the Swedish company Arcam.

Metal powder-based systems
Metal powders can be consolidated into a solid mass using an electron beam as the heat source. Parts are manufactured by melting metal powder, layer by layer, with an electron beam in a high vacuum.

This powder bed method produces fully dense metal parts directly from metal powder with characteristics of the target material. The EBM machine reads data from a 3D CAD model and lays down successive layers of powdered material. These layers are melted together utilizing a computer-controlled electron beam. In this way it builds up the parts. The process takes place under vacuum, which makes it suited to manufacture parts in reactive materials with a high affinity for oxygen, e.g. titanium. The process is known to operate at higher temperatures (up to 1000 °C), which can lead to differences in phase formation though solidification and solid-state phase transformation.

The powder feedstock is typically pre-alloyed, as opposed to a mixture. That aspect allows classification of EBM with selective laser melting (SLM), where competing technologies like SLS and DMLS require thermal treatment after fabrication. Compared to SLM and DMLS, EBM has a generally superior build rate because of its higher energy density and scanning method.

Research developments
Recent work has been published by ORNL, demonstrating the use of EBM technology to control local crystallographic grain orientations in Inconel. Other notable developments have focused on the development of process parameters to produce parts out of alloys such as copper, niobium, Al 2024, bulk metallic glass, stainless steel, and titanium aluminide. Currently commercial materials for EBM include commercially pure Titanium, Ti-6Al-4V, CoCr, Inconel 718, and Inconel 625.

Metal wire-based systems
Another approach is to use an electron beam to melt welding wire onto a surface to build up a part. This is similar to the common 3D printing process of fused deposition modeling, but with metal, rather than plastics. With this process, an electron-beam gun provides the energy source used for melting metallic feedstock, which is typically wire. The electron beam is a highly efficient power source that can be both precisely focused and deflected using electromagnetic coils at rates well into thousands of hertz. Typical electron-beam welding systems have high power availability, with 30- and 42-kilowatt systems being most common. A major advantage of using metallic components with electron beams is that the process is conducted within a high-vacuum environment of 1×10−4 Torr or greater, providing a contamination-free work zone that does not require the use of additional inert gases commonly used with laser and arc-based processes. With EBDM, feedstock material is fed into a molten pool created by the electron beam. Through the use of computer numeric controls (CNC), the molten pool is moved about on a substrate plate, adding material just where it is needed to produce the near net shape. This process is repeated in a layer-by-layer fashion, until the desired 3D shape is produced.

Depending on the part being manufactured, deposition rates can range up to 200 cubic inches (3,300 cm3) per hour. With a light alloy, such as titanium, this translates to a real-time deposition rate of 40 pounds (18 kg) per hour. A wide range of engineering alloys are compatible with the EBDM process and are readily available in the form of welding wire from an existing supply base. These include, but are not limited to, stainless steels, cobalt alloys, nickel alloys, copper nickel alloys, tantalum, titanium alloys, as well as many other high-value materials.

Market
Titanium alloys are widely used with this technology, which makes it a suitable choice for the medical implant market.

CE-certified acetabular cups are in series production with EBM since 2007 by two European orthopedic implant manufacturers, Adler Ortho and Lima Corporate.

The U.S. implant manufacturer Exactech has also received FDA clearance for an acetabular cup manufactured with the EBM technology.

Aerospace and other highly demanding mechanical applications are also targeted, see Rutherford rocket engine.

The EBM process has been developed for manufacturing parts in gamma titanium aluminide and is currently being developed by Avio S.p.A. and General Electric Aviation for the production of turbine blades in γ-TiAl for gas-turbine engines.

Source from Wikipedia