Optimized power-to-weight ratio achieved by partnership and a new alloy
Since 2011, Vacuumschmelze has partnered AMK as a sponsor of Formula Student Electric with the aim of optimizing electric motors with specific attention to their power-to-weight ratio. In line with the company's slogan, "Advanced Materials – The Key to Progress", Vacuumschmelze produces rotor and stator assemblies from their CoFe alloys VACOFLUX and VACODUR. These materials exhibit significantly higher induction than classic electrical steel; for example, at 2.3 T their saturation magnetization is 13 percent higher than that of electrical steel.
Table 1: Typical material properties of VACODUR 49 compared with electrical steel M270-50A.
This year, Vacuumschmelze completed the development of its new alloy, VACODUR 49. Specific heat treatments can be applied to this high-induction CoFe material, increasing its strength in order to handle the requirements of an electric motor or generator. For example, stator assemblies, which are exposed to lower mechanical stress, can be produced from an alloy with optimum magnetic properties but a relatively low yield strength of 210 MPa. However, higher-strength materials are frequently required for high-speed rotors and an appropriate heat treatment can increase the yield strength to up to 390 MPa, significantly higher than that of electrical steel (see chart 1
). Independent of the strength of the material chosen, induction values dramatically outperform those of electrical steel, especially at lower field strengths. M270-50A electrical steel has an induction value of 1.49 T at a magnetic field strength of 2.5 kA/m, but at the same field strength, both variants of VACODUR 49 outperform electrical steel by about 50 percent, with values of 2.23 and 2.27 T respectively (see Figure 1
Figure 1: Comparison of static initial magnetisation curves for VACODUR 49 and M270-50A electrical steel.
(Induktion = Induction / magnetisch optimiert = magnetically optimised / mechanisch optimiert = mechanically optimised / Electroblech = Electrical steel / magnetische Feldstärke = Magnetic field strength)
Motors with an extremely high power-to-weight ratio can therefore be built using Co-Fe alloys. Used by the aerospace industry for decades to save weight, these Co-Fe materials are now commonly adopted for applications in automation technology and high-end motor sports.
This is also the final link in the chain for the use of VACODUR 49 in the AMK motors for Formula Student Electric: starting with a Hightorque DT series liquid-cooled synchronous servo motor, the M270-50A electrical steel stator assemblies were replaced by assemblies made by Vacuumschmelze from VACODUR 49 (see Figure 2
Figure 2: DT5-26-10-POW liquid-cooled synchronous motor by AMK with four stator assemblies of VACODUR 49.