Abstract
Leakage flux in rotor core bridges is a problem specific to interior permanent-magnet (IPM) motors. It is widely known that the partial non-magnetization of bridges reduces the magnetic flux leakage. In a previous study, a process was proposed whereby a part of the silicon steel sheet that bridges after pressing was non-magnetized by melting and mixing Ni–Cr alloy powder with a silicon steel sheet using a laser, and the rotor core was produced by laminating them. However, because the final solidification part had solidification defects, such as cracks and shrinkage cavity, the process was proposed to leave a homogenous part free of solidification defects. Therefore, the area of the improved portion increased. We focused on developing a new alloy for non-magnetic improvement to suppress solidification defects. The improved portion was melted and mixed using a laser with various B contents to obtain a composition of Fe–(15–20) mass%Ni–(15–20) mass%Cr–(2–3) mass%Si–(0–1.6) mass%B. Large cracks and large shrinkage cavity were observed in the boron-free alloy. The cracks and shrinkage cavity decreased with an increase in the B content. The minimization of the area of non-magnetic improvement is possible by suppressing solidification defects. Consequently, the laser processing speed per piece and the amount of expensive nickel were reduced. These new alloys show promise for practical applications in the partial non-magnetization process.
To reduce the number of solidification defects formed during the nonmagnetic improvement of silicon steel, the development of a new alloy for non-magnetic improvement was carried out. The improved portion was melted and mixed by a laser with Ni–Cr powder with various B contents and silicon steel to obtain a chemical composition of Fe–(15–20) mass%Ni–(15–20) mass%Cr–(2–3) mass%Si–(0–1.6) mass%B. Figure shows the effect of B content (x mass%) in Fe–Cr–Ni–Si on the appearance. The upper photos are the topside view of each sample, and the bottom photos are the enlarged view of the final solidification area. x in Fe–Cr–Ni–Si are (a) 0, (b) 0.2, (c) 0.9 and (d) 1.6. Large cracks and large shrinkage cavity were observed in the boron-free alloy. The cracks and shrinkage cavity became smaller with an increase in the boron content.
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