Mechanism of tooth surface distortion in machining helical gear with profile modification

Worm machining helical gear is mainly realized by changing the center distance between cutter and gear along the tooth width direction, and the machining process is essentially a meshing process of two gears. According to the principle of spatial meshing, the contact points of two tooth surfaces in the meshing process as shown in Fig. 1 (a) form an inclined contact trace on the helical gear with the generating motion, and the cutting amount on the same contact trace is the same. Therefore, the amount of resection on both sides of the symmetrical tooth width center at the same height is inconsistent, resulting in the tooth surface distortion.

In theory, the inclination angle of contact trace between cutter and gear is related to the spiral angle of gear, and the cutting depth is related to the modification amount. Taking the gear with 29 teeth, 3 mm modulus and 15 mm width as an example, the diagonal feed coefficient C is 0, the center distance transformation coefficient a is 0. 001, and the change of helix angle is in turn The relationship between helix angle and tooth surface twist coefficient calculated by 0 °, 10 °, 20 ° and 30 ° is shown in Fig. 2 (a). It can be seen that spur gear has no tooth surface distortion and helical gear has tooth surface distortion, and with the increase of helix angle, the degree of tooth surface distortion is more serious. Taking gears with the same parameters as an example, the diagonal feed coefficient C is 0, the spiral angle is 10 ° and the change coefficient a of center distance is 0, 0. 001, 0. 002, 0. 003 and 0 004. The relationship between the center distance transformation coefficient and the tooth surface distortion coefficient is shown in Fig. 5 (b). The image is horizontal, and the center distance transformation coefficient has no effect on the tooth surface distortion. This is because the modification amount is a Δ 12mm, and Δ 1 is the tooth width of the corresponding point. Changing the center distance transformation coefficient a will change the overall modification amount proportionally. When applied to the distortion coefficient r, the value has no effect, so the modification amount has no effect The degree of distortion of tooth surface.

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