When machining and manufacturing gear hobs, there is an error between the generating surface of gear hobs and the theoretical position due to the manufacturing and grinding error of the generating surface of gear hobs. Therefore, for the gear hob with generating surface error, the processed gear will produce tooth profile error. The factors causing the profile error of gear hob include: manufacturing error of gear hob, machining error of gear hobbing machine tool and installation error of gear hob.
Through the above analysis of gear hobbing machining error, it is concluded that the main factors causing gear hobbing machining error are:
1) Geometric eccentricity. It is caused by the non coincidence of the rotation axis during gear hobbing and the rotation center when the gear is used.
2) Eccentric motion. It is caused by the inconsistency between the rotation center of the indexing worm gear of the gear hobbing machine tool and the rotation center of the worktable.
3) Short period error of transmission chain of gear hobbing machine tool. The error is mainly caused by the error of indexing chain and differential chain of gear hobbing machine.
4) Manufacturing and installation errors of gear hobs. The error is mainly composed of manufacturing error or approximate modeling of hob tooth profile, radial and axial movement of hob and intersection angle error of hob installation axis.
The gear motion error caused by the geometric eccentricity and motion eccentricity in the above gear hobbing error. The error takes the gear rotation 2 π as the cycle, which is called the long-period error, as shown in Figure 1.
The gear motion error caused by the short period error of the transmission chain of gear hobbing machine tool and the manufacturing and installation error of hob is called short period error, as shown in Figure 2. This error will change the transmission ratio of the gear, resulting in unstable gear transmission.
In fact, the gear motion error is produced by the superposition of various factors. This error is a complex periodic error, as shown in Figure 3, including long and short periodic errors.