One method of gear machining is the forming method, that is, cutting the teeth by forming a milling cutter that exactly matches the shape of the groove to be cut, such as milling teeth; and the other is forming, that is, using the meshing motion between the cutter and the driven gear. Cutting teeth, such as hobbing and forming teeth (demonstra). Machined with a hob and forming tool).
The method of milling a gear with a milling machine is described below. Cylindrical spur gears can be machined on horizontal milling machines with disc milling cutters or with finger milling cutters on vertical milling machines. In this paper, the cylindrical spur gear of Z=16 (that is, the number of teeth is 16) and M=2 (that is, the modulus is 2) is taken as an example to introduce the milling process of the gear.
1, check the size of the blank
The diameter of the top circle is mainly checked so that the thickness of the indexing scallop is correct according to the actual diameter of the top circle when adjusting the cutting depth.
2, bad clamping and correction
The spur gear has shaft teeth and disc blanks. If it is a shaft type blank, one end can be directly clamped by the three-jaw chuck of the indexing head, and the other end can be tightly pressed by the tip of the tailstock; if it is a disc-shaped blank, the blank is first placed on the mandrel, the heart One end of the shaft is clamped on the three-jaw chuck of the indexing head, and the other end is tightly pressed by the tip of the tail.
Correcting the blank is important. First correct the roundness. If the roundness is not good, it will affect the indexing circle tooth thickness; then correct the straightness, that is, the line connecting the center of the three-jaw chuck and the center of the tailstock must be longitudinally walked with the table. The direction of the knife is parallel, otherwise the milled teeth are inclined; the final correction height, that is, the distance from the center of the indexing head three-jaw chuck to the work surface and the distance from the center of the tailstock to the work surface should be the same. If the height is too poor, the milling The teeth that come out are shallow.
Accuracy analysis of tooth machining: The accuracy of shaft teeth is mainly related to motion accuracy, stationarity accuracy and contact accuracy. In the hobbing process, the length of the common normal line and the ring diameter jump are used to ensure the motion accuracy. The control tooth profile error and the base curve deviation are used to ensure the smoothness of the work, and the tooth pitch error is controlled to ensure the contact accuracy.
The following are some of the causes of error in the hobbing process: ring gear radial jump ring radial jump ring radial jump ring radial runout error dynamic error dynamic error dynamic error (ie geometric eccentricity or geometry Eccentricity, ie geometric eccentricity, ie geometric eccentricity) The radial runout of the ring gear means that the probe is in the tooth groove or on the gear teeth in the range of one revolution of the gear, and the double-sided contact with the middle of the tooth height, the maximum of the probe relative to the axis of the tooth The amount of change.
It is also the eccentricity of the gear ring relative to the centerline of the shaft. This eccentricity is caused by the fact that the two central holes of the part do not coincide or deviate too much from the center of rotation of the table when the parts are mounted.
Or due to poor manufacturing of the top and top holes, the positioning surface is not well contacted, resulting in eccentricity, so the ring diameter jump should be mainly solved from the above reasons.
Hobbing is to use the principle of the forming method to machine the gear. The gear transmission chain from the tool to the tooth blank should maintain the accuracy of the movement according to a certain transmission ratio.
But these drive chains are made up of a series of transmission components. Their manufacturing and assembly errors must be concentrated on the end parts of the transmission chain during the transmission movement, resulting in non-uniformity of relative motion and affecting the machining accuracy of the gear teeth.
The change of the length of the common normal line is the maximum error that reflects the uneven distribution of the gear teeth. This error is mainly caused by the uneven rotation accuracy of the worm gear table of the hobbing machine, as well as the circular guide rail wear of the hobbing machine table, the indexing worm wheel and the circular guide of the table. Caused by different axes, in addition, there are severe bumps on the tooth surface of the split gear or the bite is too loose or too tight when the hanging wheel will affect the change of the common normal.
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