A patent on the principles of EBM were filed in 1993 by the Swedish company, Arcam and the Chalmers University of Technology in Gothenburg. Arcam AB was founded in 1997 to develop and commercialise EBM technologies, although they were bought by GE Additive in 2016.
As discussed above, EBM is a form of metal 3D printing that is used to produce parts with the same characteristics and mechanical property as the metal powder being used.
The process can be broken down into steps, as follows:
- 3D Modelling: Before you can produce anything, you need to create a 3D model of the part you want to build. This is often done using CAD software, but it is also possible to scan a part or download an existing model
- Slicing: Once the 3D model is complete it is sent to be cut into layers by slicing software. The slicer then sends this information across to the 3D printer ready for manufacturing
- Add Feedstock: Before you can start manufacturing, you need to add your chosen metal powder feedstock to your printer. The powders tend to be pre-alloyed rather than a mixture
- Deposition and Melting: Thin layers of your chosen material are deposited and pre-heated before being fused by the high power electron beam. The preheating offers more support to cantilevered areas of your final object. The process occurs in a vacuum and can operate at temperatures as high as up to 1000 °C. However, higher temperatures can create differences in phase formation as a result of solidification and solid-state phase transformation. The deposition and melting step is repeated layer-by-layer until the entire part is built
- Remove Unmelted Powder: Following manufacture, the finished object is removed from the vacuum chamber and any unmelted powder is brushed or blown away with a blowgun
- Post-Processing: Finally, post processing can take place; removing any printing supports and detaching the part from the build plate. Surfaces can also be machined and polished, while it may also be necessary to post-heat the part in an oven to release any manufacturing-induced stresses
The manufacturing must take place in a vacuum to not only ensure the metal powder doesn’t oxidise when heated, but also so that the electron beam operates properly.
Once the process is finished, unmelted powder can be gathered and reused, while the minimal machining required also saves material costs. Taking the aerospace industry as an example, these savings can be sizeable, where machining after other manufacturing processes can mean that just 20% of the material used is left on the actual part.
Electron beam melting has a number of benefits, although there are also some challenges with the process.
1. Advantages
The main advantage of EBM is the manufacturing speed it affords due to the high energy density. Production is further sped up by the electron beam’s capacity to heat several areas of powder simultaneously. By contrast, a laser-based additive manufacturing technique, such as selective laser melting (SLM) is slower as it scans the surface one point at a time, although this does lead to smoother and more accurate parts.
Pre-heating the powder before melting using EBM limits deformations and reduces the need for supports or reinforcements that have to be removed after manufacturing.
2. Disadvantages
- Because electron beams are slightly wider than laser beams, EBM is less accurate than an additive process like SLM.
- Much of the available technology limits the size of the parts that can be created with EBM, whereas laser machines can manufacture parts of over twice their height.
- EBM printers require skilled technicians to operate.
The materials need to be conductive in order for the electron beam to affect them, this means that electron beams cannot be used with ceramics or polymers. The main metals that are used for EBM are titanium and chromium cobalt alloys.
Applications for EBM include within the aerospace and medical industries. This is, for example, because titanium is biocompatible and has desirable mechanical properties. While EBM can produce parts quickly, the lower accuracy and granular finish means it is not suitable for all applications. However, despite the drawbacks, it used to quickly print parts for aerospace, automotive, defence and medical purposes.
A similar process that is worth mentioning here is electron beam deposition modelling (EBDM). With this process, a metal wire is used as the feedstock rather than metal powders, as with EBM. The process works in a similar manner to fused deposition modelling, an additive manufacturing method, but with metal rather than plastics and with the use of an electron beam as an energy source.
The electron beam creates a molten pool into which the metal wire feedstock is fed. This molten pool is moved with the use of computer numeric controls (CNC) so that material can be added where required across a substrate plate. This process is repeated to build the near net shape of a 3D part layer-by-layer.
The electron beam allows for a fast deposition rate of up to 200 cubic inches (3,300 cm3) per hour. The beam is focused and deflected with electromagnetic coils to the desired place to melt the feedstock. Operating in a high-vacuum provides a contamination-free environment for the deposition modelling, and means that additional inert gases, as used with arc or laser based processes, are not required.
EBDM can be used on a range of metals including stainless steel, cobalt alloys, copper nickel alloys, nickel alloys, tantalum, titanium alloys, and more.
Electron beam melting (EBM), or electron beam additive manufacturing, is a technique for 3D printing metal parts from powder. The feedstock is fused together on a powder bed, layer-by-layer, in a vacuum by an electron beam. The electron beam melts the metal powder as guided by a CAD design and the vacuum environment prevents the metal parts from oxidising. EBM creates non-porous or dense microstructures, free from cracks, even from some brittle, intermetallic materials. It is also a relatively fast deposition process.
However, there are some drawbacks with EBM, as it can be difficult to optimise the process parameters, can only be used for certain materials and has limitations on the size of parts that can be created.
However, by melting metal powder using the high temperature electron beam in a high vacuum and building 3D objects in layers, it is possible to produce metal parts that include the characteristics of the materials used. These benefits, as well as the fast deposition rates, have made the EBM process popular for producing parts in a range of different industries.