Gear hob is one of the most widely used high-efficiency gear machining tools. As shown in Figure 1, it is the basic structure diagram of gear hob. The basic worm of gear hob is on the spiral surface where the hob blade is located. The tooth structure of gear hob is worm shape. According to the principle of generating method, the basic worm of gear hob can be divided into the following three types:
(1) Involute worm
The thread surface of involute basic worm is involute spiral surface. The tooth profile of involute worm end section is involute, and the tooth profile of axial section is convex curve. The intersection of any plane tangent to the base cylinder and the involute helical surface is a straight line. As shown in Figure 2, when turning involute worm with a tool, the linear cutting edge shall be placed in the cutting plane of the base cylinder. Although the processing technology of involute worm is complex and difficult to manufacture, the gear hob made of this basic worm has no tooth profile design error and has high precision. Because there is no tooth profile design error and high machining accuracy, it is more convenient to do the theoretical simulation research of gear hobbing process. Therefore, the gear hob selected in this subject is involute worm hob.
(2) Archimedes worm
The thread surface of Archimedes basic worm is Archimedes spiral surface. The tooth profile of the end section of Archimedean worm is Archimedean helix, and the tooth profile of the shaft section is straight line. The tooth profile of the gear processed by the gear hob made of Archimedes basic worm is not involute, and there is a small amount of tooth profile error. Using Archimedes basic worm as gear hob, if the tooth shape angle of Archimedes basic worm is modified, a gear hob similar to involute basic worm can be obtained. The processing technology of Archimedes worm is simpler than that of involute worm. Therefore, Archimedes gear hob is most often used in actual processing and production.
(3) Normal straight profile worm
The thread surface of the normal straight profile basic worm is formed by the helical movement of a straight generatrix around its axis. The normal section tooth profile of the normal straight profile worm is a straight line, and the end section tooth profile is an extended involute. If the tooth profile angle of the normal straight profile basic worm is modified, the gear hob similar to the involute basic worm can also be obtained. However, due to the low accuracy of the gear processed by the gear hob manufactured by the normal straight profile basic worm, the normal straight profile worm hob is generally used for rough machining and large module gear hob.