A gear shaft is a mechanical part that supports rotating parts and rotates with them to transmit motion, torque, or bending moment.It is generally in the shape of a metal rod, and each segment can have different diameters.The rotating parts of the machine are mounted on the shaft.
According to the different shape of the axis, the axis can be divided into crankshaft and straight axis.According to the bearing condition of the shaft, it can also be divided into: ① Rotating shaft, which bears both bending moment and torque when working, is the most common shaft in machinery, such as the shaft in various reducers. ②Mandrels are used to support rotating parts that only bear bending moment but not transmit torque. Some mandrels rotate, such as the axle of railway vehicles, while others do not rotate, such as the axle supporting pulley. ③The transmission shaft is mainly used to transmit torque without bearing bending moment, such as the long smooth shaft in the crane moving mechanism, the driving shaft of the car, etc.
Design and application
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In design, the application of gear shaft generally involves the following situations:
1. The gear shaft is usually a pinion (a gear with few teeth).
2. The gear shaft is generally at the high speed stage (that is, the low torque stage).
3. The gear shaft is rarely used as a sliding gear for speed change, and is generally a fixed running gear. First, because it is at the high speed stage, its high speed is not suitable for sliding speed change.
4. The gear shaft is a combination of shaft and gear. However, during the design, the length of the shaft should be shortened as much as possible. The length is too long, which is not conducive to the upper gear hobbing machining. The length of the shaft support causes the shaft to be thickened and increases the mechanical strength (such as rigidity, deflection, bending resistance, etc.).
Analysis of processing technology
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Selection of positioning datum
The machining sequence of the main surface of the gear shaft largely depends on the selection of the positioning datum.Shaft partsThe structural characteristics of itself and the position accuracy requirements of the main surfaces of the spindle determine that the axis is the most ideal positioning benchmark.This not only ensures the unity of the datum, but also makes the positioning datum coincide with the design datum.Generally, the outer circle is the coarse datum, and the nape holes at both ends of the shaft are the fine datum.Pay attention to the following points when selecting.
(1) When the mutual position accuracy between the processing surfaces is required to be high, it is better to complete the processing of each surface in one clamping.
(2) When rough machining or positioning cannot be performed with the center holes at both ends (such as machining the taper hole of the spindle), in order to improve the rigidity of the process system during workpiece processing, only the cylindrical surface can be used for positioning or the cylindrical surface and the center hole at one end can be used as the positioning reference.In the process of processing, the outer circle of the shaft and the center hole at one end shall be alternately used as the positioning reference to meet the requirements of mutual position accuracy.
(3) If the shaft is a part with a through hole, the original center hole will disappear after the through hole is drilled.In order to still be able to locate with the center hole, the taper plug or taper sleeve mandrel with the center hole is generally used.When the taper of the shaft hole is large (such asMilling machineSpindle), taper sleeve spindle can be used;When the taper of the spindle taper hole is small (such as the spindle of CA6140 machine tool), the taper plug can be used.It must be noted that the taper sleeve mandrel and taper plug used should have high accuracy and minimize their installation times.The central hole on the taper plug and taper sleeve mandrel is not only the positioning benchmark for its own manufacturing, but also the finishing benchmark for the outer circle of the spindle. Therefore, it is necessary to ensure that the taper surface on the taper plug or taper sleeve mandrel has a high coaxiality with the central hole.In case of medium and small batch production, the workpiece will not be replaced halfway after being installed on the taper plug.If the outer circle and the taper hole need to be processed repeatedly and repeatedly as a benchmark, the center hole must be aligned or reground according to the outer circle when reinstalling the taper plug or the spindle of the shaft sleeve.
From the above analysis, the selection of positioning reference in the gear shaft processing process should consider the following process arrangement: at the beginning, the outer circle should be used as the rough reference to drill the end face center hole, and prepare the positioning reference for rough turning;The rough turning of the outer circle is the positioning reference for subsequent processing: after that, in order to prepare the positioning reference for the semi finish machining and finish machining of the outer circle, the front and rear center holes are processed first as the positioning reference;The gear tooth profile processing also uses the center hole as the positioning benchmark, which well reflects the principle of datum unification and the principle of datum coincidence.[1]
Arrangement of heat treatment process
During the whole process of shaft machining, sufficientheat treatmentProcess to ensure the mechanical properties and machining accuracy requirements of the gear shaft, and improve the machining performance of the workpiece.
Generally, normalizing treatment is arranged first after forging of shaft blanks to eliminate the internal stress of forging, refine grains and improve the cutting performance during machining.
Arrange quenching and tempering treatment after rough machining.In the rough machining stage, after rough turning, drilling and other processes, most of the machining allowance of the gear shaft is removed.In the rough machining process, the cutting force and heat are very large. Under the action of force and heat, the shaft produces a large internal stress. The internal stress can be eliminated through quenching and tempering treatment, instead of aging treatment, and the required toughness can be obtained at the same time.
After semi machining, except for important surfaces, other surfaces have reached the design size.Only finishing allowance is left on the important surface. At this time, local quenching treatment shall be arranged on the tooth to make it reach the designedhardnessRequirements to ensure the wear resistance of these surfaces.The subsequent finishing process can eliminate quenching deformation.
Arrangement of processing sequence
The machining sequence shall be arranged according to the principle of base plane first, rough first and fine second, primary first and secondary second.For general parts of gear shaft, after the center hole is prepared, the excircle shall be processed first, and then other parts shall be processed, and the rough and finish machining shall be conducted separately.In the process of gear shaft machining, heat treatment is taken as the sign, rough machining is performed before quenching and tempering treatment, semi finish machining is performed before quenching treatment, and finish machining is performed after quenching.In this way, after the stages are separated, the final finishing of the main surface is ensured, and the main surface accuracy will not be affected by the stress of other surface processing.
The following points should also be noted when arranging the sequence of gear shaft processes.
(1) The rough machining of the gear profile of the shaft should be arranged after the semi finish machining of each outer circle of the gear shaft is completed, because as a gear shaft, the gear profile machining is the processing content of the part with large workload and processing difficulty, and its processing position can be properly placed back to improve the positioning height of the positioning reference,The tooth profile finish machining should be arranged after all the outer circles and other surfaces of the part are machined, so as to eliminate the heat treatment deformation caused by local quenching of the tooth profile.
(2) The processing sequence of the cylindrical surface should first process the large diameter cylindrical surface, and then process the small diameter cylindrical surface, so as not to reduce therigidity。
(3) The machining of secondary surfaces such as keyways on the gear shaft shall generally be arranged after finishing turning or rough grinding of the outer circle and before finishing grinding the outer circle.If the keyway is milled before finishing, on the one hand, the vibration caused by intermittent cutting before finishing affects the machining quality and easily damages the tool;On the other hand, it is difficult to guarantee the size of keyway.These surface processing should not be arranged after the main surface is finely ground to avoid damaging the main surface precision.[1]
