What is a Gear Shaft?

Gear shaft refers to a mechanical part that supports and rotates with a rotating part to transmit motion, torque or bending moment. Generally round metal rods, each section can have different diameters. The parts in the machine that perform rotary motion are mounted on the shaft.

According to the shape of the axis, the shaft can be divided into two types: crankshaft and straight shaft. According to the bearing capacity of the shaft, it can be divided into: The rotating shaft, which bears both bending moment and torque during work, is the most common shaft in machinery, such as the shaft in various reducers. Mandrels are used to support rotating parts that only bear bending moments without transmitting torque. Some mandrels rotate, such as the axles of railway vehicles, and some mandrels do not rotate, such as the shafts that support pulleys. The drive shaft is mainly used to transmit torque without bearing bending moments, such as the long light shaft in the crane moving mechanism, the drive shaft of the car, etc.

In the design, the application of the gear shaft is generally nothing more than the following situations:

1. The gear shaft is usually a pinion (gear with few teeth).

2. The gear shaft is generally in the high-speed stage (that is, the low-torque stage).

3. Gear shafts are rarely used as variable-speed sliding gears. They are generally fixed-speed gears. First, because they are at high speeds, their high speeds are not suitable for sliding speed changes.

4. The gear shaft is a combination of the shaft and the gear. However, when designing, the length of the shaft must be shortened as much as possible. One is too long to be conducive to hobbing machining. The other is that the shaft is too long and the shaft is thickened. And increase the mechanical strength (such as rigidity, deflection, bending resistance, etc.).

Selection of gear shaft positioning reference

The processing sequence of the main surface of the gear shaft largely depends on the selection of the positioning reference. The structural characteristics of the shaft parts and the positional accuracy requirements of the main surfaces of the main shaft determine that the axis is the ideal positioning reference. This not only guarantees uniform benchmarks, but also makes positioning benchmarks and design benchmarks coincide. Generally, the outer circle is used as a rough reference, and the item sharp holes at both ends of the shaft are used as a fine reference. Please also pay attention to the following points when making specific choices.

(1) When the accuracy of the mutual position between the processed surfaces is high, it is best to complete the processing of the surfaces in one clamping.

(2) When rough machining or positioning cannot be performed with the center hole at both ends (such as the taper hole of the spindle), in order to improve the rigidity of the process system during workpiece processing, only the outer surface or the outer surface and the central hole at one end can be used Benchmark. In the process of machining, the outer circle of the shaft and the central hole at one end should be used alternately as the positioning reference to meet the mutual position accuracy requirements.

(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 a tip hole, a cone plug or cone sleeve mandrel with a tip hole is generally used. When the taper of the shaft hole is large (such as the spindle of a milling machine), a taper sleeve can be used; when the taper of the spindle hole is small (such as a CA6140 machine tool spindle), a taper can be used. It must be noted that the taper sleeve mandrel and taper used should have high accuracy and minimize the number of installations. The center hole on the taper plug and taper sleeve mandrel is not only the positioning reference manufactured by itself, but also the finishing reference of the spindle outer circle. Therefore, it is necessary to ensure that the taper surface of the taper plug or taper sleeve and the central hole have a high Concentricity. For small and medium batch production, the workpiece is generally not replaced halfway after installation on the cone plug. If the outer circle and the tapered hole need to be processed repeatedly as a reference to each other, the center hole must be aligned or re-ground in accordance with the outer circle when reinstalling the tapered plug or sleeve mandrel.

From the above analysis, when selecting the positioning datum during the gear shaft machining process, we should consider arranging the process as follows: at the beginning, the outer circle is used as the rough datum to drill the center hole on the end face to prepare the positioning datum for the rough turning; Processing preparation positioning reference: In order to prepare positioning reference for semi-finishing and finishing outer circle, the front and rear center holes are processed as positioning reference. The gear tooth processing also uses center holes as positioning reference, which is very good. It embodies the principle of unification of benchmarks and fully reflects the principle of coincidence of benchmarks. ^[1]

Arrangement of gear shaft heat treatment process

In the entire process of shaft processing, sufficient heat treatment procedures should be arranged to ensure the mechanical properties and processing accuracy requirements of the gear shaft and improve the workability of the workpiece.

Normally, after the shaft blank is forged, a normalizing treatment is first arranged to eliminate the forging internal stress, refine the grains, and improve the cutting performance during machining.

After roughing, quenching and tempering is arranged. In the rough machining stage, after rough turning, drilling and other processes, most of the machining allowance of the gear shaft is cut off. During the rough machining process, the cutting force and heat are very large. Under the action of force and heat, the shaft generates a large internal stress. The internal stress can be eliminated through the quenching and tempering process, instead of the aging process, and the required toughness can be obtained.

After semi-machining, all surfaces have reached the design dimensions except the important surfaces. Only the finishing allowance is left on the important surfaces. At this time, local hardening treatment is arranged on the teeth, etc., so that it meets the designed hardness requirements to ensure the wear resistance of these surfaces. The subsequent finishing process can eliminate quenching deformation.

Arrangement of gear shaft processing sequence

Arrangement of machining sequence is based on the principle of base first, rough first and then fine first, then master first. For the general parts of the gear shaft, after preparing the center hole, first process the outer circle, then process the other parts, and pay attention to the rough and finish machining separately. In the gear shaft processing technology, heat treatment is used as the mark, before the quenching treatment is rough machining, before the quenching treatment is semi-finishing, and after quenching, it is finishing. After the stages are separated in this way, the finishing of the main surface is ensured at the end, and the precision of the main surface is not affected by the stress of other surface processing.

When arranging the sequence of gear shaft processes, the following points should also be noted.

(1) The roughing of the tooth profile of the shaft should be arranged after the semi-finishing of the outer circumference of the gear shaft, because as a gear shaft, the tooth profile machining is a relatively large amount of work and a difficult process in the processing of this part. The processing content, after the processing position is appropriately placed, can increase the positioning height of the positioning reference, and the tooth profile finishing should be arranged after all the outer circles and other surfaces of the part have been processed, thereby eliminating the heat treatment deformation caused by the local quenching of the tooth profile. .

(2) The machining sequence of the outer circle surface should be processed first with a large diameter outer circle, and then with a small diameter outer circle, so as not to reduce the stiffness of the workpiece at the beginning.

(3) The machining of secondary surfaces such as keyways on gear shafts should generally be arranged after finishing or rough grinding on the outer circle and before finishing grinding on the outer circle. If the keyway is milled before finishing, on the one hand, before the finishing, vibration due to intermittent cutting will affect the machining quality and damage the tool; on the other hand, the size of the keyway is difficult to guarantee. These surface processing should not be arranged after the main surface is ground, so as not to damage the main surface accuracy. ^[1]