The machining of motor shafts involves many critical dimensional elements, such as the dimensions of the shaft extension, bearing positions, and core positions, which are related to fit and installation. The center hole, which is crucial for the uniqueness of the reference datum, is also a significant concern. Any non-compliance or deviation from design expectations in any of these areas will pose a serious risk. To prevent non-compliance or deviations from design expectations, Ms. [Name], drawing on the experience of various manufacturers, discusses shaft machining issues.
Control of key dimensional elements of motor shaft
The shaft has higher precision and surface roughness than other parts, and the fit between the shaft and other components is also tighter. The following factors must be considered during machining.
● Coaxiality of working surfaces. The main working surfaces are the bearing seat (the surface that mates with the bearing) and the shaft extension (the surface that mates with the drive wheel). If the radial runout (eccentricity) of the shaft extension surface relative to the bearing seat surface is too large, vibration and noise will occur during motor operation. In addition, if the radial runout of the parts where the rotor core, slip rings, commutator, and fan are installed is too large, although the outer diameter of these components can be corrected during rotor precision machining, it will cause a large initial imbalance. If the rotor core, slip rings, commutator, and fan are assembled onto the shaft after precision machining, then excessive radial runout of these components will greatly affect the reliability of motor operation.
● Control of dimensional accuracy and cylindricity of mating parts. The dimensional and positional accuracy of shaft extensions, bearing positions, and core positions must be accurate; otherwise, assembly difficulties may occur, or even damage to parts, loose or inflexible bearings, and excessive bearing temperature rise may result.
● Shaft roughness control. Low roughness on mating surfaces leads to easy wear and loosening of the mating parts. Conversely, excessively low roughness on non-mating surfaces reduces the shaft's fatigue strength.
● The fillet radius and wheel runout groove at the shaft shoulder must be machined according to the specified dimensions. An excessively small fillet radius and an excessively deep wheel runout groove will reduce the strength of the shaft; an excessively large fillet radius will cause uneven contact between the end faces of the mating parts. The wheel runout groove is necessary to prevent the side of the grinding wheel from rubbing against the shaft shoulder during grinding. The dimensions of the runout groove should be selected according to mechanical industry standards.
● The symmetry of the keyway relative to the axis of the reference surface should not exceed the tolerance; otherwise, it will cause assembly difficulties. For keyways in hot-pressed mating parts, the keyway must conform to the drawing requirements. Otherwise, during hot-pressing assembly, due to symmetry deviations, the workpiece cannot be installed in the correct position. Hot-pressed assembled workpieces are difficult to disassemble after installation, often resulting in scrap.
● The distance between the two bearing bearings must be accurate. Otherwise, it will cause problems such as axial displacement of the rotor core or bearing jamming after assembly.
Basic machining process of shaft
The machining process of a shaft can be divided into two stages: pre-machining and forming. Pre-machining includes straightening the round steel, blanking, end face finishing, and drilling center holes. The purpose of pre-machining is to provide a qualified blank and establish process positioning references for forming. Forming includes rough turning, semi-finish turning, finish turning, grinding the outer diameter, and milling keyways. The purpose of forming is to machine the blank into the shape and dimensions of the structural design.
Straightening and blanking of round steel are carried out before the blanks enter the machining process to facilitate in-plant transportation and reduce the footprint of the machining area. End faceting, center hole drilling, and forming are all performed during the machining process to facilitate assembly line operations.
Different motor manufacturers and different organizational models are all set according to their own product characteristics and factory characteristics, but they all follow the same principle: grasping the key elements and simplifying the process is the essence of mass lean production.
