The machining of the motor base is an extremely important step in the motor manufacturing process. Many inexplicable or bizarre malfunctions, resembling "dancing" or "disco," are related to the motor base. Here, Ms. Zhu compares different machining schemes for the motor base, illustrating the advantages and disadvantages of different processing methods.
Comparative Analysis of Different Machine Base Machining Schemes
The machining of the machine base is closely related to the manufacturing of the iron core and the stator. When determining the machining scheme, the manufacturing of iron core laminations and the precision machining of the stator must be considered simultaneously. Schemes that ensure the coaxiality of the inner circle of the stator iron core and the two end stops can be divided into five types: smooth stop, smooth inner circle of the stator iron core, smooth outer circle of the stator iron core, "two non-smooth" and "two smooth".
● In the smooth stator core design, the inner and outer diameters of the stator core are not machined. After being pressed into the machine base, the machine base stop is precision machined using the inner diameter of the core as a positioning reference. In the smooth stator core inner diameter design, the inner diameter of the core is precision machined or rough ground using the machine base stop as a reference. In the smooth stator core outer diameter design, the outer diameter of the core is precision machined using the inner diameter of the core as a reference. After being pressed into the machine base, no further machining is performed. In the "two-no-smooth" design, the inner and outer diameters of the stator core are not machined, and the machine base stop is also not machined after being pressed into the machine base. In the "two-smooth" design, the inner diameter of the core and the machine base stop at the other end are precision machined using the machine base stop that has been precision machined at one end as a reference.
●Depending on the different positioning reference surfaces, the machining of the machine base can be divided into two different machining schemes. The first scheme uses the stop and end face as the positioning reference surfaces; the second scheme uses the base plane and base hole as the positioning reference surfaces.
During machining, the reference surface is machined first, and then other parts are machined using the reference surface for positioning. In the smooth stop design, the stop is deformed due to the core being pressed into the machine base. After precision machining of the stop, the roundness of the stop is better. Precision machining of the stop eliminates the errors generated during machine base machining, core manufacturing, and assembly, thereby achieving the required coaxiality. Therefore, the coaxiality of the stator mainly depends on the accuracy and positioning error of the expansion tool used during precision machining of the stop. When machining the machine base parts, the coaxiality and accuracy of the stop and the inner circle can be lowered, which is beneficial for using combination machine tools or automatic lines. However, this adds an extra smooth stop process, thus occupying an extra machine tool. Furthermore, when precision machining the stop, appropriate measures should be taken to prevent iron filings from falling into the winding ends and damaging the windings.
● In the optical stator core inner diameter design, the coaxiality of the stator is achieved by precision turning or grinding the inner diameter of the core using a stop-edge positioning method. This relaxes the requirements for the coaxiality of the machine base inner diameter and the stop-edge, as well as the accuracy of the lamination inner diameter and the coaxiality of the inner and outer diameters. However, precision turning or grinding the inner diameter of the core will increase iron loss and reduce performance. Except in special cases where this design is still retained, it is generally no longer used.
●In the optical stator core outer diameter design, the accuracy of the core's outer diameter and the coaxiality of its inner and outer diameters are achieved by precision machining the outer diameter using the inner diameter as a reference after the core is press-fitted. This relaxes the requirements for the accuracy of the lamination's outer diameter and the coaxiality of its inner and outer diameters. However, the cutting conditions are poor during core outer diameter machining, requiring a single-edged turning tool with a short tool life. Since no further machining is performed after the core is pressed into the machine base, the accuracy and coaxiality requirements for the machine base are also high.
● In the "two-no-light" scheme, the accuracy and coaxiality of the stator depend entirely on the machining quality of the parts, requiring high machining quality for the laminations, core, and frame. However, by eliminating a finishing process after the core is pressed into the frame, the assembly line eliminates backtracking and facilitates the rational layout of workshop routes.
● In the "two-light" scheme, the coaxiality of the stator is achieved by precision machining the inner circle of the core and the other end of the core using a stop-and-position method. This relaxes the requirements for the accuracy of the inner circle of the laminations and the coaxiality of the inner and outer circles, but precision machining of the inner circle of the core will also increase iron loss. This scheme is sometimes used in the stator machining of medium-sized asynchronous motors.
Two different machining reference surface schemes are analyzed and compared.
●The advantages of the first processing scheme are that the main processes (processing of end face, stop and inner circle) are processed by general horizontal or vertical lathes, the equipment is highly versatile; clamping is convenient and processing efficiency is high; the process method is easy to master; the thickness of the machine base circumference is uniform; the center height dimension is easy to guarantee. Its disadvantages are three: (1) The two ends of the stop and the inner circle are not processed in one clamping. The errors generated in positioning and clamping make the coaxiality of one end of the stop and the other end of the stop and the inner circle low. Especially when the stop jig is worn to the point that it cannot be kept clean, the form and position tolerance will exceed the tolerance. (2) Drill the bottom hole after machining the stop and the inner circle. Since the positioning of the bottom hole drilling jig is inconvenient, the distance between the bottom hole and the center line of the machine base is easy to produce left and right asymmetry. (3) The positioning area of the stop is small, and the stop and the inner circle are easy to be deformed due to clamping when machining.
●The advantages of the second processing scheme are that it uses a plane as the positioning reference surface, which is stable and reliable; the two ends of the machine base and the inner circle can be clamped and processed at one time, with high coaxiality; it saves loading and unloading time, and the inner circle can be precision turned after machining the base first, which can reduce clamping deformation. Its disadvantages are four: (1) It has high precision requirements for the base plane; (2) Since the inner circle has not been processed when the base plane is processed, the amount of processing of the base plane will affect the processing of the inner circle. It is not easy to ensure the uniformity of the machine base wall thickness and the precision of the center height at the same time; (3) It has high requirements for equipment and processing technology; (4) It increases the time and cost.
As can be seen, the first processing method is easy to master, has high processing efficiency, and can guarantee quality, therefore it is the most commonly used in factories. However, as machine base processing develops towards automated lines, it is required that the clamping state of the workpiece remain unchanged at each station.
This is easier to achieve when positioning with the base plane, so the second machining scheme tends to be adopted. On the entire automated line, in order to ensure the accuracy of the machine base center height, the machining process of the base plane is usually divided into two processes: rough milling and finish milling, which are arranged before and after the machining processes of the stop and the inner circle, respectively.
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