## 3 Numerical Modeling and Novel Technologies and Materials
### 3D Printed Electrical Machines
Furthermore, there is much work on conductive materials [247; 248; 249], where the main aim is to achieve the highest conductivity, and the main concerns are how to create the electric isolation around the wire. Not only the material characteristics are important, but also there are concerns with printing quality itself [250]. Most 3D printed objects need post-processing because of printing supports and  
Figure 10: A model (**a**) and the geometry (**b**) of a 3D printed electrical machine. (**c**) shows one step from the design process, and (**d**) shows the printed, optimized heat exchanger. surface quality, but also to enhance the material properties. To produce a full electrical machine with 3D printing, there is a need for a multi-material metal printer. At the moment, the best quality is achieved with selective laser melting (SLM), but this method allows printing only one material at a time. Other metal printing methods like binder jetting or direct energy deposition allow printing several materials at the same time, but with reduced material quality. There is an effort to reduce the post-processing (turning, milling, etc. ); the surface quality can be worse than conventional manufacturing. Therefore, there is a higher concern about the manufacturing tolerances here. The earliest examples of using a 3D printer in electrical machine manufacturing was printing the housing of the machine from Fused Deposition Modeling (FDM) and plastic [251]. This solution does not give much advantages to the machines, but it can show the possibilities of what can be done. In [252], a similar solution was used, but instead of using pure plastic, some parts were printed with iron powder. There are several possibilities to increase the cooling capability of the electrical machine through 3D printing. One possibility is to produce a special frame for the machine, where the cooling channels are printed inside the frame [253; 254; 255]. This allows improving the overall thermal performance of the machine. Instead of cooling the machine through the machine frame, it has been proposed to directly cool the machine windings. For this, printing a hollow winding or using direct winding heat exchangers has been proposed [256]. For example, in [257], a 3D printed direct winding heat exchanger was proposed that was installed in direct contact with the concentrated winding of a flux-switching permanent magnet machine. For this, they used the FDM printing method, and different polymers were used to print the heat exchanger. This allowed improving the power density of the machine. In [258], a similar heat exchanger was proposed, but printed with ceramic material. The advantages of AM to produce thin layers and 3D shapes make it a good solution for producing lightweight machines. It allows reducing the weight by reducing the material used for machine supports [259]. For example, in [260], the authors presented a lightweight steel powder rotor where a lattice structure was used. Through this, they managed to reduce the machine weight by 25 %, as well as a 23 % inertia reduction. Furthermore, it is possible to produce the machine frame with a lattice structure, resulting in weight reduction. In [261], the authors reduced the volume of the magnetic core of a 3D printed magnetic clutch by 24% by increasing the magnetic force by more than 10% with the application of multiobjective robust design optimization methodologies (Figure 11). The possibility to produce complex 3D shapes allows more comprehensive optimization of the magnetic circuit, i.e., the stator and rotor cores of the machine, without the limitations of conventional subtractive and formative manufacturing methods, which can result in designs with significantly enhanced performance and notably lower material consumption and costs. For example in [262; 263], the shape optimization of the reluctance machine rotor was presented, resulting in the minimization of the torque ripple and mass of the rotor.