Working Principle and Structure of Commutator
The commutator is an important component of the motor, usually made of copper and in an open ring shape. Each segment of the commutator is connected to both ends of the armature coil. When there are multiple coils in the armature, the commutator contains multiple corresponding segments, one segment is connected to each end of each coil.
When the motor is working, the spring brush contacts the commutator and transmits voltage through the commutator segments and armature coil. When the brush passes through the gap of the commutator, the charge switches the commutator segments, thereby changing the polarity of the armature coil, ensuring that the armature rotates continuously and stably in one direction.
Key Requirements for Commutator Surface Quality
The quality of the commutator surface directly affects the running stability of the carbon brush. To ensure that the carbon brush runs smoothly on the commutator surface, the surface must maintain a certain peak-to-valley height. The optimal peak-to-valley height range is 6-10 microns, and the number of lathe patterns should be large to reduce the friction coefficient.
Characteristics and Requirements of Commutator Finishing
The finishing quality of the commutator surface is the key to ensuring the running performance of the brushed motor. The main quality requirements include: the outer diameter and length meet the process standards, the outer circle runout does not exceed 0.006mm, the roundness error does not exceed 0.003mm, the height difference between the sheets does not exceed 0.0015mm, the surface roughness must reach Ra0.1μm to Ra0.8μm, and there is no flash or stretching. The surface texture of the commutator should be clear, smooth, and uniform, and there should be no copper chips sticking.
Commutator materials and their processing characteristics
The materials of the commutator usually include oxygen-free copper (or electrolytic copper) and silver copper alloy. These materials have the characteristics of high toughness, low hardness, and large linear expansion coefficient. They are easy to heat up during processing, making it difficult to control the dimensional accuracy. In addition, there are engraved insulation grooves on the surface of the commutator. The fine-turning process is intermittent cutting, and the edges of the grooves are prone to flash or stretching.
During the cutting process, appropriate tool materials, geometric parameters, and cutting parameters should be selected to control the cutting temperature rise and ensure the processing quality.
Commutator finishing tool selection and processing technology
When selecting tool materials, polycrystalline diamond composites (PCD) are ideal choices due to their high hardness, excellent wear resistance, low friction coefficient, and high thermal conductivity.
The disadvantage of PCD material is its high brittleness, which can be overcome by reasonably selecting tool angles and formulating corresponding processing technologies.
During the finishing process, the geometry and angle of the tool head are particularly important. Usually, the tooltip shape of R0.1mm and the geometric parameters of the front angle γ=12° and the back angle α=14° are selected to reduce friction, control cutting temperature and avoid the formation of built-up edge.
Advantages and challenges of PCD tools in commutator processing
The sharp edge of PCD tools makes them perform well in the cutting process, and can effectively discharge chips and ensure processing quality. However, due to the special structure of the commutator, chips are easy to splash or adhere to the surface during cutting, which will affect the final processing quality.
To solve this problem, it is recommended to use a high-negative-pressure exhaust chip removal system, with high-speed airflow to clean the chips in time and cool the commutator and tool at the same time to improve processing efficiency and quality.
Conclusion
Using PCD tool finishing turning commutator can effectively improve product quality, meet the requirements of surface roughness and wear resistance, avoid the problem of incomplete notch cleaning in traditional processing technology, and thus significantly improve the commutation performance of the motor.
