## 2 Additive Manufacturing for Electrical Machines Windings  
Additive manufacturing (AM) of electrical machines has been explored in different studies [5; 6; 7; 8; 9]. New families of electrical machines are manufactured, which were difficult to be built using conventional methods [10; 11; 12; 13]. Yet, utilizing AM in building the active parts, such as core or windings, is still limited. In such parts, not only improving the mechanical properties is required, but also the electromagnetic properties' enhancement is mandatory. This technology can also allow printing different conducting materials using different AM techniques [14; 15; 16]. This includes electron beam melting (EBM) of copper powder [17], the selective laser melting (SLM) of copper [18], aluminum [19; 20], and silver [21], and 3D micro-extrusion of copper and aluminum [22; 23]. However, in most of these attempts, only thin conductors are built without considering complete coil structures. Typically, copper is the common choice for electrical machine windings because of its high electrical and thermal conductivities. On the counterpart, aluminum has relatively lower electrical and thermal conductivities, but it has only 30% of the weight of copper. Additionally, the higher resistivity of aluminum can be beneficial to limit high frequency eddy current losses. So,aluminum can be an effective alternative to copper for high speed electrical machines and weight sensitive applications. Using AM technology, it is also possible to integrate direct cooling channels inside the slot for better thermal performance. Hollow conductors can also be printed with imbedded cooling path for liquid in each turn. An example is investigated in [24]. In this study, 3D printed coils are prototyped using different material alloys (copper and aluminum). Both cases have the exact same design with integrated direct cooling channels. With the proposed approach, the maximum current density is boosted to high levels. Accordingly, the machine power density has also improved significantly. In [25], the AM of shaped profile windings is introduced for minimal AC loss in electrical machines. The main concept is to print the conductors with a profile that is parallel to the slot leakage flux. As a result, minimum interaction between the conductor and the flux is achieved and the losses is minimized. According to the authors, these shaped profile coils have the potential for improving efficiency in different applications such as electric vehicle traction, automotive applications, and aerospace propulsion. In [26], a new design of complete coil is introduced with uneven layers as shown in Figure 1. In this design, the turns near the slot opening have lower height compared to the turns at the slot bottom. As a results, the impact of the cross slot leakage flux is limited and the losses in the upward turns is effectively reduced. Additionally, the cross section area has a z-shaped profile to guarantee a uniform distribution of the current density. The aforementioned coil is printed using aluminum alloy to provide additional limitation to eddy current losses at high speed operation. The coil has also 74% lower weight compared to a conventional copper coil. Despite its good performance at high frequency, this coil is printed with single strand turns. To consider a multi strand coil, more degrees of freedom are required. To conclude, the adoption of advanced techniques such as 3D printing expands the design space available and could afford significant performance improvements and enhanced thermal management. In this paper, one of the targets is to enable AM technology to print a complete 3D coil with a more sophisticated design. In this design, the dimensional freedom of AM can allow for a multi strand coil with low AC losses. Additionally, the strands' locations are transposed to minimize the eddy current losses at high frequency. Figure 1: Shape profiled 3D printed coil with uneven turns [26]. The only one problem of a fully stranded coil is that it has a low fill factor and a higher DC resistance.