Some Details Needing Attention in Machining Shaft Parts

Shaft parts are a common type of parts. Its structure is a rotating body, and its length is generally larger than the diameter. It is widely used in various mechanical equipment to support transmission parts, transmit torque and bear load. The processing of shaft parts should follow certain rules. This paper will come to the specific processing steps and some problems that need attention.

Basic machining route of shaft parts
The main machining surfaces of shaft parts are cylindrical surfaces and common special surfaces. Therefore, the most appropriate machining methods should be selected according to various accuracy levels and surface roughness requirements. The basic processing routes can be summarized into four.
1. The processing route from rough turning to semi finish turning and then to finish turning is also the main process route selected for the needle excircle processing of shaft parts with common materials.
2. From rough turning to semi finish turning, then to rough grinding, and finally to finish grinding, this processing route is the best choice for parts with high requirements on ferrous materials and precision, small requirements on surface roughness, and need to be hardened, because grinding is the most ideal subsequent processing procedure.
3. From rough turning to semi finish turning, then to finish turning and diamond turning, this processing route is specially used for processing non-ferrous materials. Because the non-ferrous metals have low hardness and are easy to block the gap between sand grains, it is usually not easy to obtain the required surface roughness by grinding, so the processes of finish turning and diamond turning must be used; The last processing route is from rough turning to semi fine turning, and then to rough grinding and fine grinding.
4. It is a frequently used processing route for parts that have been hardened with ferrous materials and require high precision and low surface roughness.

Pre machining of shaft parts
Before turning the excircle of shaft parts, some preparation procedures must be carried out, which is the pre processing process of shaft parts. The most important preparation process is straightening. Because the workpiece is often bent and deformed in the process of manufacturing, transportation and storage. In order to ensure reliable clamping and even distribution of machining allowance, various presses or straightening machines are used for straightening in cold state.

Positioning datum for machining shaft parts
1. The center hole of the workpiece is used as the positioning datum for processing. In the processing of shaft parts, the coaxiality of each external circular surface, taper hole and thread surface, and the perpendicularity of the end face to the rotation axis are important manifestations of position accuracy. These surfaces are generally designed on the basis of the centerline of the shaft and positioned with the central hole, which conforms to the principle of datum coincidence. The center hole is not only the positioning reference for turning, but also the positioning reference and inspection reference for other processing procedures, which conforms to the principle of unified reference. When two central holes are used for positioning, a plurality of outer circles and end faces can be machined to the maximum extent in one clamping.
2. The outer circle and the center hole are used as the positioning datum for processing. This method effectively overcomes the disadvantage of poor rigidity of center hole positioning, especially when machining heavy workpieces, the center hole positioning will cause unstable clamping, and the cutting amount cannot be too large. It is unnecessary to worry about this problem if the outer circle and the central hole are used as the positioning datum. In rough machining, the method of using the cylindrical surface of the shaft and a central hole as the positioning datum can bear a large cutting torque during machining, which is the most common positioning method for shaft parts.
3. The two cylindrical surfaces are used as the positioning datum for processing. When machining the inner hole of the hollow shaft, the central hole cannot be used as the positioning datum, so the two outer circular surfaces of the shaft should be used as the positioning datum. When machining the spindle of the machine tool, the two supporting journals are often used as the positioning reference, which can effectively ensure the coaxiality requirement of the taper hole relative to the supporting journal, and eliminate the error caused by the non coincidence of the reference.
4. The taper plug with the central hole is used as the positioning datum for processing. This method is most commonly used in the machining of the outer surface of hollow shafts.

Clamping of shaft parts
The processing of taper plug and taper sleeve mandrel must have high processing accuracy. The center hole is not only the positioning reference for manufacturing itself, but also the reference for finishing the outer circle of the hollow shaft. It must ensure that the taper surface on the taper plug or taper sleeve mandrel has a high coaxiality with the center hole. Therefore, when selecting the clamping method, attention should be paid to reducing the installation times of the cone plug as far as possible, so as to reduce the repeated installation error of the parts. In actual production, after the installation of the cone plug, generally speaking, before the completion of processing, it will not be removed or replaced during processing.