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3D Printing Increases the Benefit of Gearwheels

| Editor: Alexander Stark

3D printing of metallic components makes it possible to create completely new functions of smart products. Only post-processing is not yet ideal. That is why a university is looking for a suitable solution.

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Markus Merkel can monitor the printing process through a glass panel. In the 3D printer, laser light melts a metallic powder. Thus, layer by layer, complex products can be made of metal.
( Source: MM MaschinenMarkt / Thomas Klink )

Gearwheels are one of the essential drive components — nothing would run without them. Therefore, gearwheels are quite commonplace. However, what lies on the table in front of Prof. Markus Merkel stands out from this mass of gears. This is because it has cavities in it. "We create added value, so to speak, with holes," Merkel explains. The engineer and professor at the University of Aalen and his team print these gears with metal powders. Among the applications for this process, which Merkel and his team have in mind, are electric drives and transmissions, which are exposed to strong speed changes. With 3D printing, it is possible to create cavities in the component in a single process step. "This is impossible with established production processes," says Merkel.

Thanks to the cavities, the gearwheel is lighter and has lower moments of inertia, which results in less energy requirements for acceleration and deceleration. In addition, a coolant can be conducted through these cavities, eliminating the need for external cooling. This reduces the space requirement. "But sensors or actuators can also be integrated into the cavities," Merkel spins the idea further. "Then the gearwheel could communicate with the higher-level components and, for example, report a problematic rise in temperature in real time — so that the entire system can react before the gearwheel or gearbox is damaged.

Complex structures can be easily realized with additive processes. Problems only occurre on the surface of the components.
Complex structures can be easily realized with additive processes. Problems only occurre on the surface of the components.
( Source: MM MaschinenMarkt / Thomas Klink )

Additive manufacturing processes are a hot topic at many research institutes and in the industry. Merkel explains the interesting aspects of his university’s approach as follows: "At the university we deal with the complete cycle of the process — from the raw material and the printing technology to the surface finishing of the components. This approach is based on an overall philosophy. "Those who study and do research with us should be able to understand complex processes and think in a networked way," emphasizes Merkel. The construction of the component is computer-aided and digital, as is the analysis of its mechanical properties. The actual 3D printing is based exclusively on digital data. Tools or molds are not necessary. Even the quality analysis of the resulting component delivers comprehensive digital 3D data that can then be used for the improvement of materials and technology.

Finishing Coat with Laser Pulses

However, the surface of a gearwheel has a much rougher surface after printing than it would have, had it been milled. This is where Simon Ruck, research assistant and doctoral student in Prof. Harald Riegel's team, comes in. Together with his colleagues, Ruck is researching laser processes that can be used to smooth a rough surface. "We have to be very careful with this type of finishing, otherwise the printed component would become unusable," he explains. After printing, there remain many particles of residual powder on the surface of the gearwheel, which have adhered to it during production. To get rid of them, the surface is heated with laser pulses that are shorter than one microsecond. "This removes unwanted particles and oxide layers," says Ruck."If we were to supply more energy, however, the particles would tear tiny craters into the surface, which is undesirable, of course." The cleaning is followed by laser polishing follows, which reduces the surface roughness by 75 %, i.e. an "arithmetic mean roughness value" of less than 0.2 µm. Laser polishing, which involves the remelting of a wafer-thin edge layer of the surface, requires a high-purity material just like 3D printing does, which is why conventionally manufactured metal components often cause problems.

The surface finishing of 3D contours in industry has so far only been done manually. "In order to mechanize this process, we have to use a robot for laser polishing that can follow the contour precisely, i.e. a robot that does not just move on three spatial axes," explains Ruck. The researchers from Aalen will continue to work on further improving this method as part of the Smart-Pro project.

Optimizing Metal Powder for the Printer

The starting material used to print the gearwheel is an aluminum alloy, which is commercially available as a powder. But it has to be adapted to the 3D printer used in order to deliver an adequate quality. The materials scientist and doctoral student Tim Schubert at the Institute for Materials Research (IMFAA), together with Dr. Timo Bernthaler and Rector Prof. Gerhard Schneider, takes on this task. "There were simple reasons why printing did not produce satisfactory results at first — such as varying residual moisture in different batches of the powder," explains Schubert. Using different devices, he and his colleagues analyze the properties of the powders and of the printed products in order to align them with the process parameters selected for the 3D printing process. Through teamwork in research it was possible to establish the ideal settings.

This article was first published by MM Maschinen Markt.

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