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3D printing could produce lighter, more powerful motors

25 September, 2017

German researchers are using a multi-material 3D printing technology to create parts for electric motors which, they predict, will lead to lighter motors with increased power densities and greater overload capabilities.

Johannes Rudolph and Fabian Lorenz, from the department for Electrical Power Conversion Systems and Drives at the Technical University of Chemnitz, believe that their technique of combining layers of conductive metal materials and insulating ceramics could lead to new types of motor. “We are able to manufacture machine types that naturally have a very high power density,” says Lorenz.

For example, transverse flux motors, which have so far proved too complex to manufacture in volume could be produced using the new techniques, resulting in machines with much higher force densities than existing radial-flux machines, without needling costly rare-earth magnets.

The conductive and insulating layers are produced using metallic and ceramic pastes, which are formed into layers by an extrusion process and then sintered. The different materials can be printed in a single operation.

“The ceramic insulation of the conductors allows for significantly higher application temperatures, with improved heat conduction, which increases the power density,” explains Lorenz. “In addition, cooling ducts can be integrated, where waste heat is generated to further increase the power density.

Prof Dr Ralf Werner, head of the department, points out that it is very difficult to achieve much improvement in motor efficiencies using conventional construction techniques. “At most, increases of up to 1% are possible – but this usually entails increases in production and material costs,” he says.

The Chemnitz researchers, who have been working on their technology since 2015, have already produced ceramic-insulated coils, and believe that they could fabricate complete motors using their techniques. They are working on integrating a third component – magnetically active iron – into the printing process.

The 3D printing process avoids the need for the complex packing of sheets of electrical steel and the introduction of windings into conventional electric motors. The technique can be used to guide the magnetic flux in three dimensions to generate torque. It is also possible to incorporate cooling channels into a motor’s coils or laminated core, and to incorporate windings into parts of a motor which would not be accessible using conventional manufacturing methods.

As a result, it should be possible to manufacture motors that are optimised for their operating conditions. The ability to reduce motor weights could be of particular interest for aerospace applications.

Initially, the researchers experimented using their own hand-made extruder. However, they were not able to achieve the desired precision in the dosing of the highly viscous metallic and ceramic pastes.

“The biggest hurdle to overcome on the way to the printed electric motor is that the pairing of ceramics and copper is a particular problem due to their very different physical properties,” Werner explains.

Fabian Lorenz (left) and Johannes Rudolph working on their multi-material 3D printer, which can process up to three materials in a single operation.
Photo: Bildarchiv der Pressestelle / Uwe Meinhold

The challenge was to optimally coordinate the mechanical and physical properties of the pair of materials. In addition, the paste had to “flowable”  for the materials to be printed using an extrusion process. Shape stability was also essential to achieve the required design after extrusion.

The additive production process developed by the German researchers allows different material combinations of ceramics and metals to be used together in a way that cannot be achieved using conventional production methods. Through a series of experiments, they say they have succeeded in developing the metallic and ceramic materials that can be used in the form of pastes for the printing process.

As well as optimising the material properties for 3D printing, the researchers had to control the shrinkage of the materials during the drying and sintering process. They report that this has “proven to be very difficult”. But, by setting the temperature in the sintering oven to match the paste properties, they were able to overcome the problem. Furthermore, the temperature changes can be used to optimise the properties of the materials to achieve even higher power densities.

Dosing accuracy and precision are extremely important for the motor-printing process. Rudolph and Lorenz found that the ViscoTec extruder print-heads – which are designed to handle viscous pastes – improved the start and end points of each line, resulting in even printing. The heads also allow volume flows to be adjusted during the printing process to achieve the required characteristics.

The German researchers suggest that their multi-material printing technology could have other applications, such as the manufacturing of heat exchangers. This could open up new possibilities because the process allows cooling geometries to be integrated which could not be produced by any other manufacturing technology.

Rudolph and Lorenz are planning to spin-off their technology from Chemnitz University of Technology in the future.

3D printing a ceramic insulating coil
Photo: Johannes Rudolph

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