Additive methods of manufacturing (3D-Printing) for technical component development are on a fast-track to becoming the key technology for future production. This trend is clearly visible in sectors that emphasis sustainability and lightweight construction like medical engineering, aviation and automotive. In these fields, the economization of material and weight have an especially high impact on performance and costs. The medical engineers value the high degrees of freedom and biocompatibility of these novel techniques. Loadcase-adapted constructions usually lead to very complex geometries that combine low weight and high stability–perfect match for the nature-inspired bionic lightweight design, which benefits greatly from the flexibility provided by the additive methods.
3D-Printing processes for functional components
Functional 3D-Printing components are printed in powder-based processes that utilize metal, ceramics or sand. In the build-up procedure, distinct layers are selectively and successively melted in a powder bed to form the final component. The most popular method is the Selective Laser Melting (SLM), where a high-powered laser melts the particles in a protective atmosphere. Although the freedom of design and the complexity of possible geometries of additive manufacturing methods is unrivalled, certain boundary conditions and rules of construction have to be met for optimal printing results. If a complex design fails to meet these 3D-Printing restrictions, additional supporting structures have to be inserted. These structures are not exclusively of structural necessity but are often used as heatsinks for thin-walled profiles. After the printing process these supporting structures have to be removed mechanically and cannot be recycled directly. So, even if the constructed component meets highly material saving standards, the production process reduces the efficiency to a varying degree. To counteract these losses, the Electron Beam Melting (EBM) has been introduced as an attractive alternative technique.
The EBM Procedures
The basic procedure in EBM – powder bed and selective melting of layers – resembles the SLM technique. In contrast to the laser, an electron beam operates under vacuum conditions. The energy input of the electron beam is increased 10 fold as compared to the laser which reduces production time by 40%. Due to the higher energy intake, the raw material has to be chosen accordingly. Titan-aluminum or cobalt-chrome alloys meet the requirements in terms of higher melting points but are more cost-intensive than the popular aluminum alloys in other methods. On the other hand these new materials are capable to advance into areas of highly stressed components that are traditionally occupied by moulding or forging technologies. The option of raw material substitution and component re-design in regards to high-strength materials is of considerable interest. One main advantage of EBM (besides the highly versatile materials) is the capacity of printing highly complex geometries without supporting structures. We assessed this technology in cooperation with the company AIM SWEDEN by the example of the bottom bracket bearing of our Bionic Bike (see right hand image). The surface roughness of the titan made component has not been post processed. In large-scale applications with subsequent paintwork this would be recommended however. Overall we are enthusiastic about the flexibility of this technique.
EBM refrains from supporting structures
At the outset of the procedure, the powder bed is pre-heated, so that the particles melt lightly to one another. This strengthens the component in the making sufficiently with regards to mechanical support and temperature drainage. A subsequent sandblast with the very same raw powder cleans the finished component and allows a direct recycling of the remaining particles – a wear of about 3% is achieved. The pre-heating and linking in the powder bed results in a higher surface roughness (Ra>10 µm) as compared to SLM. Both processes, EBM and SLM require a mechanical post-treatment for highly defined drilling holes and interfaces. For higher surface qualities of EBM manufactured components a hydro-erosive treatment with grinding particles embedded in a fluid is recommended. A surface roughness of down to Ra=0,08 µm is thus possible.
In addition to the absence of supporting structures, the self-stabilizing powder-bed of EBM offers great advantages of component “Packing”. Components can be placed freely in the design space and even be stacked, thus allowing an increased number of units per cycle.
Conclusion: The EBM technique offers advantages with regards to material consumption, production time and exceptionally high freedom of design. Specific applications require a detailed selection of raw materials and careful analysis of achievable and required surface roughness.