Coils are crucial in motor manufacturing. The quality of a coil depends on both the quality of the electromagnetic wire and the coil's manufacturing process, which mainly includes winding, forming, and insulation. While coil manufacturing methods vary considerably due to factors such as voltage capacity, voltage level, operating environment, equipment conditions, and production volume, their common requirements can be summarized as follows.
Accuracy of number of turns
Errors in the number of turns can affect electromagnetic parameters and make installation difficult. Errors in the number of turns are more likely to occur in loosely wound coils with a large number of turns; therefore, necessary turn counting and testing methods should be used when winding such coils. Motor manufacturers commonly use turn counters. For multi-turn windings, the first turn is generally measured manually and with a turn counter. Subsequent windings of the same coil are mostly checked using a weight comparison method.
When using the weight comparison method, it is essential to ensure the accuracy of the sample coil data. Secondly, consistency in the winding process control is crucial, including requirements for tightness and the length of the winding head. For continuously wound coils, the accuracy of the data for each individual coil must also be guaranteed. Experiments have shown that for the same coil, even with the same number of turns, the weight can vary significantly due to differences in operator strength. For example, coils wound by male and female operators differ considerably. Male operators tend to produce neater coils, which are more conducive to later winding, while female operators, due to relatively weaker strength, produce looser and less neat coils, which are less ideal for later winding.
For motor manufacturers that have already adopted automatic winding machines, both the number of turns control and consistency issues can be easily resolved.
Coil shape control
The coil shape is based on the conformity of theoretical dimensions. It is very important to ensure the shape of the coil when it is formed. Otherwise, it is impossible to complete the subsequent winding, or the insulation of the coil may be damaged due to forced operation, or the forming effect may be poor, affecting other performance of the motor.
The distance between the two edges of the formed coil and the angle they form must be accurate; otherwise, it will cause installation difficulties or direct damage to the insulation. Another important factor is the length of the straight edge. If it is too short, it cannot be installed; if it is too long, the winding end will be too long, affecting the installation of the motor and other components (such as the wind deflector), and may even lead to non-compliance with creepage distance. In more serious cases, it may affect the motor's loss value.
Insulation performance
The inter-turn and ground insulation of the coil must be good and reliable. For high-voltage motor coils, in addition to sufficient electrical strength, low dielectric loss and good corona resistance are also essential. In actual production, improper post-processing control can damage the outer insulation layer or corona resistance band of the coil, posing significant quality risks to motor performance.
Inter-turn insulation in multi-turn coils is a weak point in the winding insulation structure. Therefore, it is crucial to select appropriate magnet wire and suitable processing techniques and tooling to prevent damage to the inter-turn insulation. For any defects in inter-turn insulation, remedial measures must be taken; otherwise, it can lead to catastrophic consequences for the motor. Most motor manufacturers conduct individual checks using an inter-turn withstand voltage tester during semi-finished product testing. If this check is not performed, and verification is only done after the motor is fully tested or released to the market, the resulting losses, especially for customers, will be incalculable.
Special requirements that water-cooled coils should meet
For water-cooled coils, it is also required that the flow resistance of the internal cooling liquid should not increase excessively after processing, and that there be no cracks or pinholes to prevent the internal cooling liquid from penetrating and damaging the insulation.
Coil structure and manufacturing process selection
The materials selected for the coil should be readily available and reasonably priced. Oversaturated materials should not be chosen in pursuit of reliability. In terms of processing technology, necessary process improvements should be made to meet quality requirements and improve efficiency. It is particularly important to emphasize that the operability of the coil manufacturing process is very important, and the safety of workers during operation must be taken into account.
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