Problems Encountered in Gear Processing

Gears are very important in our daily life and are an indispensable part, but we often encounter some problems when processing gears. The following are some common problems in the process of gear processing.
1. Tooth profile error
Tooth profile error refers to the normal interval between two ideal tooth profile (involute) profiles that contain the actual tooth profile profile within the tooth profile working department. Gear hob is the most commonly used tool for processing external meshing spur and helical cylindrical involute gears. The axial section of the back blade of this hob is a straight line. If it is used instead of the involute hob to cut teeth, the cut gear tooth profile is not an involute, which theoretically causes a certain tooth profile error, which is called the gear hob shaping error. In addition, it is impossible to obtain a completely accurate involute tooth profile in the actual processing process. There are always various errors, which affect the stability of the transmission. The base circle of the gear is the only parameter that determines the involute tooth profile. If the base circle has an error during hobbing, the tooth profile must also have an error.

2. Incorrect number of teeth
The total number of teeth on the entire circumference of the gear is called the number of teeth. The principles and requirements for determining the number of gear teeth are to first determine the gear module and the transmission shaft diameter in order to meet the structural requirements.
First, the hob is not selected correctly. Since the gear tooth shape is relatively complex, the factors affecting its processing accuracy are also very complex and changeable. In addition to the accuracy of the hobbing equipment itself, the installation and adjustment of the gear blank, the gear material, heat treatment and other factors, the reasonable selection of the gear hob is also very important. The error in the number of teeth will cause an instantaneous change in the transmission ratio during the meshing of each pair of gears.
Second, the workpiece blank size is incorrect. The traditional blank size benchmark design ignores the differences in the process, and uniformly uses the various size benchmarks in the part drawing as the blank size benchmark, resulting in an increase in the margin error of the blank during subsequent processing and waste of materials.
Third, the additional motion direction is incorrect. When the hobbing machine processes helical gears, it is difficult to determine the additional motion direction. In addition, the changes in factors such as milling method, workpiece spiral direction and hob spiral direction increase the difficulty of judgment.

3. Asymmetric tooth shape
First, the hob is not installed in the center. The installation of the hob affects the radial and axial runout of the hob, and ultimately affects the gear cutting accuracy. Generally, before installing the hob, it is advisable to calibrate the cutter shaft first, and control the radial runout of both ends to be less than 0.005mm. The verticality of the step and the nut end face to the axis should be less than 0.01mm, and the washer should be hardened and ground flat. When the hob is installed on the cutter shaft, the radial runout of the bosses on both sides needs to be corrected, and it should be "synchronized" as much as possible, that is, the highest points of the radial runout at both ends are in the same direction.
Secondly, after the hob is sharpened, the helix angle or lead error is large. Commonly used tools for machining external meshing spur and helical cylindrical gears. During machining, the hob is equivalent to a helical gear with a large helix angle, and its number of teeth is the number of heads of the hob. The workpiece is equivalent to another helical gear. They mesh with each other in space according to a pair of helical gears, rotate at a fixed speed ratio, and the tooth profiles of the cutter teeth at adjacent positions cut in sequence are enveloping the gear tooth profile.