The shaft is a crucial component of motor products, and its presence varies to different degrees depending on the specifications and operating conditions of the motor. A distinctive feature of the shaft is its highly concentrated set of steps, which facilitate the conversion between electrical and mechanical energy. From a purely functional perspective, the shaft directly mates with the rotor core, bearings, and end covers of the motor itself; similarly, it serves as the link between the motor and the equipment. Given the shaft's essential functions, its design, manufacturing, and maintenance are of paramount importance.
Shaft turning is generally divided into two processes: rough turning and finish turning. Under normal circumstances, these processes are carried out on two lathes with different precision, which is a more economical arrangement.
While the rough machining of the shaft may seem unimportant at first glance, some problems are often caused by improper handling of this step, such as the inability to machine the black skin during the production process or damage to the center hole.
Finish turning is used to achieve the required dimensional accuracy and surface roughness of a shaft. Finish turning demands high precision and should be performed by skilled workers on high-precision lathes. If the center hole of the shaft is worn after rough turning, it must be re-corrected to obtain a precise machining datum before finish turning can proceed.
Introduction to rough turning of motor shaft
Rough turning removes most of the machining allowance from the shaft blank, obtaining a contour shape similar to the shaft and the machining allowance required for finish turning. To improve productivity, the goal is to remove the maximum number of chips per unit time. Therefore, rough turning involves large cutting volumes, high operating temperatures, and requires a powerful lathe with robust clamping.
There are many clamping methods used during rough turning. Generally, one end of the shaft is clamped with a four-jaw chuck, and the other end is held in place by a center (usually a movable center). This method provides a secure clamping with minimal vibration, but requires turning the shaft around. If a chuck is used, one end of the shaft is fitted onto the fixed center on the lathe head, and the chuck is used to clamp the shaft firmly; the other end is held in place by a movable center on the tailstock. Chucks are convenient for clamping, but have a limited adjustment range and are only suitable for small-diameter shafts.
When producing large batches, pneumatic or hydraulic chucks can be used to clamp small and medium-sized shafts. On single-axis semi-automatic lathes, automatic clamping chucks are often used to clamp the shafts to save auxiliary time.
During rough machining, the shaft extension end is usually machined first, and this must be done step by step and section by section. In mass production, especially when machining multi-step small and medium-sized motor shafts, multi-tool machining or contour machining is often used. Multi-tool machining can be performed on multi-tool semi-automatic lathes or ordinary lathes.
In multi-tool machining, several cutting tools simultaneously machine multiple surfaces of the workpiece, reducing machining and auxiliary time and significantly improving productivity. However, this method has the disadvantage of requiring adjustments.
The cutting tools take a long time to work and have a large cutting force, so the machine tools also require a large amount of power.
Shaft contouring can be performed on a hydraulic contouring semi-automatic lathe or on a conventional lathe using a hydraulic contouring tool post. The advantages of hydraulic contouring include reducing worker workload, minimizing auxiliary time spent measuring parts, and increasing productivity.
Roughing often employs heavy-duty or high-speed cutting, resulting in deep cuts and fast feed rates. Therefore, the cutting tool must be robust and have a large heat dissipation surface.
Precautions when roughing out
The shaft must be clamped tightly to prevent the chuck from loosening and damaging the cutting tool during turning.
● Do not tighten or loosen the center too much. When using a dead center, apply lubricant frequently to prevent the center from getting stuck in the center hole and to avoid wear on both the center and the center hole.
● A certain margin should be left for precision machining.
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