Electron Beam Melting (EBM)
Electron beam melting is similar to laser melting, but working with an electron beam instead of a laser. The machine distributes a layer of metal powder onto a build platform, which is melted by the electron beam. The build platform is then lowered and the next layer of metal powder will be coated on top. The process of coating powder and melting where needed is repated and the parts are built up layer by layer in the powder bed.
Electron beam melting requires support structures, which anchor parts and overhanging structures to the build platform. This enables the heat transfer away from where the powder is melted. Therefore, it reduces thermal stresses and prevents wrapping. The build envelope can be filled by several parts which are built in parallel as long as they are all attached to the build platform. Parts are built under vacuum.
Advantages / disadvantages
The technology manufactures parts in standard metals with high density (above 99%) and good mechanical properties (comparable to traditional production technologies). Compared to laser melting, EBM produces less thermal stress in parts and therefore requires less support structure. Further, it builds parts faster.
Electron beam melting is still a slow and expensive process that only works with a limited set of metals. Parts usually require quite a lot of post-processing. Compared to laser melting, the technology does not achieve equally good surface finishes.
- Small series parts down to one of a kind are produced directly by electron beam melting (post-processing to achieve better tolerances and surface finish might be required)
- Prototypes are produced for form / fit and functional testing
- Support parts (jigs, fixtures, helps) are produced directly by EBM
Characteristics / restrictions
- Maximal build envelope: 350 x 350 x 380mm3
- Minimum feature size: 0.1 mm
- Typical tolerance: +/- 0.2 mm (can be improved through machining)
- Minimum layer thickness: 0.05 mm
- Typical surface finish: 20.3 – 25.4microns RA (can be improved through post-processing)
- Density: Up to 99.9%
Characteristics are only indicative, as there are different types of machines available.
When planning an EBM build, critical tolerances, surface finishes and overhangs need to be taken into consideration. After the build, parts often need to be thermally processed and support structure needs to be mechanically removed. Electron beam melting parts can be further post-processed as any welding part. Read more
The production of parts is planned in a build preparation software. One or several parts are placed in the build using the digital 3D files (typically in the STL file format). Important decision during the set-up phase is the orientation of the part in the build envelope and what support structures are required. This depends on:
- Geometry, overhangs and inclination
- Location of most critical tolerances and surface finishes
- Areas where post-processing is required and additional material needs to be added
- Removal of build envelope: The build cylinder is removed from the machine
- Remove powder: Build platform with the parts attached is taken out of the loose powder. Excess loose powder is removed by sand balsting. This is usually straight forward, however might require some extra effort for parts with complex geometric features (e.g. trapped powder)
- Thermal processing: After the build parts, are often thermally processed to release residual stresses and improve part characteristics and metallurgical structure. Which regime is best depends on the application, desired part characteristics and the material used. Typical processes include vacuum heat treatment, heat treatment under inert gas or hot isostatic pressing (HIP).
- Removal of supports and post-machining: Afterwards, parts are taken off the build platform, typically through wire cutting EDM or machining. Further, support structures are mechanically removed. Parts might be partially post-machined in order to fulfil critical tolerances.
- Surface finish: Often parts need to be further processed to improve surface finish – either mechanically (e.g. polishing, grinding, peening) or chemically (e.g. plating, electro polishing).