# An Additively Manufactured Fe-3 Si Stator for a High-Performance Electrical Motor
## 3 Results and Discussion
### Measured Back EMF  
The assembled motor was run for back EMF (BEMF) testing where the motor ran without any excitation current when it could be considered performing as an electric generator. In other words, the BEMF zero load condition of the electric motor where induction on stator coils is only due to the magnetic fields of permanent magnets inserted in the rotor. Figure 8 shows the measured BEMF for the assembled brushless permanent magnet motor which reached up to 900 mV at 1400 rpm.  
\begin{table}
\begin{tabular}{c c c} \hline
**Properties** & **Conventionally Processed** & **SLM-Printed and EDM-Cut Ring Samples** \\ \hline \hline \multicolumn{1}{c}{Lamination thickness} & 0.65 mm & 1.4 mm \\ \hline \multicolumn{1}{c}{Measured Induction, B\({}_{\text{m}}\), and Saturation} & \multicolumn{1}{c}{M\({}_{\text{s}}\): 1.46 to 1.98 [31]} & B\({}_{\text{m}}\): 1.72 at 100 Oe fieldB\({}_{\text{m}}\): 1.57 at 30 Oe \\ \multicolumn{1}{c}{Magnetization, M\({}_{\text{s}}\) (T)} & \multicolumn{1}{c}{M\({}_{\text{s}}\): 1.46 to 1.98 [31]} & \multicolumn{1}{c}{B\({}_{\text{m}}\): 1.72 at higher field} \\ \multicolumn{1}{c}{Coercivity, H\({}_{\text{c}}\) (Oe)} & 25 to 50 A m\({}^{-1}\) (0.314 to 0.628 Oe) [36] & 0.5 \\ \multicolumn{1}{c}{Resistivity,} & \multicolumn{1}{c}{-50 [37]} & 50 \\ \multicolumn{1}{c}{Maximum permeability (non-oriented)} & \multicolumn{1}{c}{3000 to 9000 [30]} & 7494 \\ \multicolumn{1}{c}{AC core loss,} & 4.6 to 9.22 (60 Hz, 1.5 T) at 0.65 mm thickness & \multicolumn{1}{c}{-20 (60 Hz, 1.5 T) at 1.4 mm} \\ \multicolumn{1}{c}{(Watts/lb.)} & \multicolumn{1}{c}{[31]} & \multicolumn{1}{c}{-20 (60 Hz, 1.5 T) at 1.4 mm} \\ \multicolumn{1}{c}{Tensile strength (MPa)} & \multicolumn{1}{c}{\(>\)400 [2]} & 555.57 \\ \hline \end{tabular}
\end{table}
Table 4: Comparison of the magnetic and electrical properties of conventionally processed electrical steel and SLM AM Fe3 Si laminates.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Fe-3 Si** & & **As Printed** & **750 \({}^{\circ}\)C-2 h** & **800 \({}^{\circ}\)C-2 h** \\ \hline
**Test** & **B\({}_{\text{m}}\)** & **Core Loss** & **Core Loss** & **Core Loss** \\ \hline \hline Freq, (Hz) & (Gauss) & Watts/lb. & Watts/lb. & Watts/lb. \\
60 & 5000 & 1.72 & 1.11 & 0.911 \\
60 & 10,000 & 8.65 & 6.22 & 5.76 \\
60 & 15,000 & 21.5 & 19.6 & 20.3 \\ \hline
400 & 5000 & 40.2 & 30.1 & 28.2 \\
1000 & 5000 & 173 & 166 & 166 \\
5000 & 2000 & 336 & 268 & 254 \\
10,00 The back EMF is very low for a motor of such size. A possible reason for this is the polymer content of the AM PMs. Back EMF results from the interaction between the electromagnetic field of the stator and the permanent magnetic field of the rotor. The AM PM has PPS filler polymer content, which does not contribute to magnetic field formation, and is itself electromagnetically inert; thus, the PM field is quite weak and is not capable of offering enough resistance to the stator field, hence the low back EMF for the assembled motor. Still, while the back EMF is low, this is a result of the low PM field and will result in a low-efficiency motor. Better AM PM of higher energy products is still necessary for an energy-efficient motor. Our group, and many others in our field, are constantly improving the energy product of AM PMs, so the energy efficiency of AM motors will continue to improve in the near future. The energy product of AM PMs could be improved in many ways. The feedstock could be premixed with a higher loading of magnetic materials before 3D printing, resulting in high magnetic material content, which results in higher energy products for the resulting AM PM. The AM PM could also be post-aligned in a magnetic field at elevated temperatures, which aligns the grains of the material, resulting in higher anisotropy, thus improving the energy product of the AM PM in the aligned direction.