VEIM XIAMEN MOTOR MACH CO.LTD Language：中文版
The thinner the motor core material "can be broken by blowing bombs", the better?
Release time: 2023-04-27
How the material used for the rotor or stator laminations is chosen has a fundamental and far-reaching effect in motor design, with core material affecting characteristics such as output, heat rise, weight and cost of the motor (here the term "motor" is used loosely to include generators, tachometers, resolvers, alternators, etc.). Few engineering schools take the time to delve into this material selection, and since various materials come from multiple suppliers, it can be difficult to find an overview of all materials in one place.
The first thing to be clear is that no one material is optimal (or even usable) for every application and there must be trade-offs between cost, weight, size and other factors. In addition, lamination processing after fabrication has a great influence on the performance of the designed core. Criteria for material selection include cost, permeability, electromagnetic loss, and saturation flux density. Permeability and core loss vary with flux reversal frequency (in Hertz) and flux density, and in some applications the shape of the hysteresis curve becomes important. Every available material is optimized for one or more of these properties and less than perfect in others.
Several factors must be considered when selecting the appropriate steel for an electric motor.
Currently, the most commonly used material for electric motor cores is generally cold-rolled laminated steel, which is the lowest-cost material for volume applications, and its ease of stamping and low tool wear help reduce the cost of finished lamination. In applications where higher core losses are acceptable (DC pole piece, low duty cycle, etc.) and low cost end equipment, carbon steel should be considered, although the magnetic and mechanical properties of this material are of course more decisive factors one. The thinner the material, the lower the high-frequency eddy current loss and the higher the efficiency of the motor. This in turn means lower power consumption, resulting in longer transmission distances at the same power capacity level. According to the power formula below, the best material thickness is as thin as possible.
Thinner sheets lead to longer production times and reduced throughput
Taking the example of an electric motor with a stator outer diameter of 250 mm and a stack height of 120 mm, the thinner the sheet thickness, the more laminations are required to achieve the desired overall height. The punching speed varies between 220 strokes/min (for 0.25 mm thick sheet) and 250 strokes/min (for 0.35 mm), depending on the sheet thickness. Taking scrap, downtime and system availability into account, throughput will be between 32 stacks (0.35 mm) and 19 stacks (0.25 mm) per hour, which means a 1.7-fold increase in punching time.
Consider efficiency maximization, but not application independent
Powerful electric motors can be produced in a large number of grades of steel, and the first question when choosing a drive motor for purely electric operation is how much money can be saved by using higher quality, thinner and thus more expensive electrical steel. Even relatively small differences in efficiency can affect the battery's range and thus the required (very expensive) battery capacity.
If the electric motor is only used to support the internal combustion engine in a mild hybrid vehicle, or if the vehicle is intended to operate purely electric over short or medium ranges (as in a hybrid or plug-in hybrid vehicle), then the performance curve is less demanding. In addition to saving material for the engine, the required battery capacity is also significantly reduced, which is why it makes sense to reduce the efficiency of the motor in the thickness range of 0.3 to 0.35 mm.
In addition, extremely thin iron core steel can improve the efficiency of high-speed motors, especially the efficiency of the stator, but in the rotor, it is often necessary to achieve very high strength instead of thinner thickness, special connection process, such as full surface bonding combined so that the rotor design also has a positive effect on efficiency.
Summary: Thin is not always good, from an overall point of view of machinability, cost, application areas, efficiency and other technical factors of motor design, the use of core steel has to be looked at very differently, many conditions clearly Indicates that it is advantageous to use steels of different thicknesses.
