Through the analysis of the gear hobbing machining accuracy of shaft gears, find out the factors that affect the gear hobbing machining accuracy, so as to improve the gear hobbing machining quality. In a professional manufacturer of heavy-duty vehicle gearboxes, the shaft gear is the most important part of the gearbox, and its machining accuracy directly affects the overall quality of the gearbox. At present, the gear tooth processing method adopted by the factory is the hobbing-shaving method. To manufacture high-precision gears through the rolling and shaving process, the level of the rolling and shaving process must be brought into full play. The accuracy of shaving depends to a large extent on the accuracy of saddle hobbing, so some error items in hobbing must be strictly controlled to produce high-quality gears. Hobbing is a commonly used gear processing method. On gear hobbing machines with high precision, precision hobs can be used to process gear teeth with 4-5 precision. On ordinary gear hobbing machines, only 8-grade precision gear teeth can be processed with ordinary precision hobs. The accuracy required by the gear gear part of the gearbox shaft is 8-7-7 grades, and the two central holes and the end face are mainly used as the positioning reference during gear hobbing. Therefore, it is very important to analyze the source of the error of gear hobbing and master the method to ensure and improve the machining accuracy.
1 Gear hobbing machining accuracy analysis
Shaft gear accuracy is mainly related to motion accuracy, stability accuracy and contact accuracy. In gear hobbing, control of the length of the common normal and the diameter jump of the ring gear is used to ensure the motion accuracy, control of the tooth shape error and the deviation of the base section is used to ensure the work stability accuracy, and control of the tooth direction error is used to ensure the contact accuracy. The following is an analysis of several error reasons that are prone to occur in gear hobbing:
1.1 Radial runout error of ring gear (ie geometric eccentricity)
The radial runout of the ring gear refers to the maximum variation of the probe relative to the axis of the tooth when the probe is in contact with the middle and middle parts of the tooth on both sides within the first rotation range of the gear. It is also the eccentricity of the ring gear relative to the center line of the shaft. This eccentricity is caused by the fact that the two center holes of the part do not coincide with the rotation center of the worktable when installing the part or the deviation is too large. Or due to poor manufacturing of the top and top holes, the eccentricity is caused by poor contact with the positioning surface, so the diameter jump of the ring gear should be mainly solved from the above reasons.
1.2 Common normal length error (ie motion eccentricity)
Gear hobbing is machined with the principle of extended forming method, and the gear-splitting transmission chain from the tool to the tooth blank must maintain the accuracy of movement according to a certain transmission ratio relationship. But these transmission chains are composed of a series of transmission elements. Their manufacturing and assembly errors must be reflected on the end parts of the transmission chain in the process of transmission movement, resulting in non-uniformity of relative movement, which affects the machining accuracy of the gear teeth. The variation of the length of the common normal is the largest error reflecting the uneven distribution of the gear teeth. This error is mainly caused by the uneven rotation accuracy of the worm gear pair of the gear hobbing machine worktable. The circular guide rails of the gear hobbing machine worktable are worn, and the indexing worm gear and the worktable The circular guide rails are not coaxial. In addition, there is a serious bump on the tooth surface of the gear hanging wheel or the bite is too loose or too tight when the gear is hanging will also affect the variation of the common normal line
