Post Processing of AM components
Additive Manufacturing allows the integration of precisely placed internal cooling channels into components. With the focus on automated post processing — removal of residual powder and surface smoothing of these channels — the mechanical and chemical engineering departments of the Politecnico Milano (Italy) together with Rösler Italiana S.r.l. conducted a study with the surface treatment methods mass finishing, shot blasting and chemically supported mass finishing. The results clearly demonstrated that with all three methods a significant improvement of the overall surface quality could be achieved.
With Additive Manufacturing (AM) extremely precise component geometries can be produced that are not possible with conventional manufacturing technologies. Among other things it allows the creation of highly complex components with integrated functional features such as precisely placed cooling channels. These unique AM characteristics are of great interest for tool and die making, hydraulic components and the aerospace industry.
Selective Laser Melting – Perfect shape but high surface roughness For the production of tooling components “Selective Laser Melting” (SLM) is the primary manufacturing method. The creation of a component by selective melting of the powder in defined layers by a laser beam results in an extremely dense work piece. The downsides of this manufacturing method are that residual powder must be removed from the cooling channels and the high initial surface roughness of the components with Ra values between 10 and 20 µm. A high surface roughness as well as the powder deposits in the channels negatively impact the functionality of the work pieces resulting in reduced flow rates due to high friction, turbulences, pressure loss in the system and loose particles that can damage other equipment. Since the internal surface areas of complex components with integrated cavities cannot be treated with conventional finishing technologies, new, innovative post processing methods are required.
Mass finishing allows the efficient smoothing of internal channel surface areas To evaluate different treatment methods, among them mass finishing, for smoothing of the external and internal surface areas of AM components, the mechanical and chemical engineering departments of the Politecnico Milano (Italy) together with Rösler Italiana S.r.l. conducted a comprehensive study. This involved the treatment of parts with different shapes and internal passages with different diameters (3, 5, 7.5 and 10 mm) with mass finishing, shot blasting and chemically supported mass finishing. All three surface treatment systems produced surprisingly similar results.
The work pieces had the smoothest surface, as shown in comparatively lower surface roughness readings, and displayed the typical chemically accelerated finish. With Ra values of 0.7 µm the chemically supported mass finishing method produced not only the lowest surface roughness values, but it also required the shortest cycle time. The results also showed that the final roughness values were more or less identical in the vertical and horizontal internal passages.
Fully automatic processing in one machine The tests were conducted on a further development of a M3 machine from AM Solutions. The latter is a brand name of the Rösler group that has specialized in the post processing of 3D printed components and offers a range of suitable equipment solutions. These include the complete spectrum of post processing functions like unpacking, removal of support structures, removal of residual powder, surface cleaning and smoothing, edge radiusing, high gloss polishing and surface preparation for subsequent coating of AM components.
The further development of the existing M3 system will not only allow the effective and targeted treatment of internal passages in the future, but it will also be a fully automated system for consistent finishing of 3D printed components without any manual work requirements. Of course, the loading and unloading of the work pieces can also be automated with a robot. The precise dosing of grinding media and compound with a special replenishment, respectively, dosing system and the equipment “Start”
function are also fully automated.
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