Abstract
Depending on the stator lamination manufacturing processes (e.g., punching, laser cutting, clamping, welding, interlocking, and bonding), the motor’s magnetic performance parameters, such as cogging torque, hysteresis torque, and iron losses, can vary significantly. In sub-fractional horsepower (SFHP) permanent magnet motors, the manufacturing influence is typically even more severe because, due to their small dimensions, practically, the whole stator material is likely to be affected. This article analyzes the magnetic performance parameters cogging torque, hysteresis torque, and iron losses of three different stator lamination stacks (i.e., M250-35A punched with interlocking, M250-35A laser cut with bonding, and NO10 laser cut with bonding) of an SFHP single-phase brushless permanent magnet motor often found in automotive fan applications. A rheometer is used for extremely accurate torque measurements in the sub-millinewton meter range, and electron backscatter diffraction measurements are performed to visualize changes in the grain morphology and crystal orientation. The findings reveal that the punched stator with interlocking is affected the most by the manufacturing process, showing the lowest cogging torque yet the highest average hysteresis torque and thus up to 40% higher iron losses. The results presented in this article allow for both making basic stator lamination design choices and translating the iron losses, as well as the hysteresis torque and cogging torque waveforms, of a laser cut and bonded prototype into those of its punched and interlocked mass-produced counterpart.
Highlights
T HE magnetic performance parameters of non-oriented steel sheets, often used for the stator of permanent magnet motors, can strongly be affected by manufacturing influences such as cutting and stacking techniques, e.g., [1]–[6]
While punched lamination stacks with interlocking are commonly used for the lowcost high-volume production of sub-fractional horsepower (SFHP) motors [8], laser cut variants with bonding are mostly utilized in prototypes for cost reasons. (Yet, in certain cases, the punched laminations are bonded to avoid the interlocking and thereby improve the motor performance [9].) Mechanical cutting typically causes plastic grain deformation near the cut edge, while laser cutting induces thermal stress due to temperature gradients [10]
The results provided in this paper can help translate the magnetic performance parameters of a prototype to those of its massproduced version
Summary
T HE magnetic performance parameters of non-oriented steel sheets, often used for the stator of permanent magnet motors, can strongly be affected by manufacturing influences such as cutting (e.g., punching, laser cutting) and stacking (e.g., interlocking, bonding, clamping, welding) techniques, e.g., [1]–[6]. (Yet, in certain cases, the punched laminations are bonded to avoid the interlocking and thereby improve the motor performance [9].) Mechanical cutting typically causes plastic grain deformation near the cut edge, while laser cutting induces thermal stress due to temperature gradients [10]. Both cutting techniques shear the hysteresis loop to some extent, decreasing the permeability and, eventually, increasing the iron losses. Performance improvements can be quantified and judged when using different steel grades and implementing bonded lamination stacks of varying thickness instead of interlocked ones
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