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Knife Gear accuracy

Update:21 Jul 2018

1 common normal length error (ie motion eccentricity)   […]

1 common normal length error (ie motion eccentricity)
Hobbing is to use the principle of the forming method to process 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, affecting the machining accuracy of the teeth. The change of the length of the common normal line is the maximum error that reflects the uneven distribution of the teeth of the gear. This error is mainly caused by the uneven rotation accuracy of the worm gear of the hobbing machine table, as well as the wear of the circular guide of the hobbing machine table, the indexing worm wheel and the circular guide of the table. Caused by different axes, in addition to the severe tooth bump on the tooth surface of the split tooth or the loose or too tight bite of the hanging wheel will also affect the variation of the common normal line.
2 tooth shape error analysis
Tooth shape error refers to the normal distance between two ideal toothed (involute) profiles that accommodate the actual tooth profile in the toothed working portion. It is impossible to obtain a completely correct involute profile in the actual machining process, and there are always various errors, thereby affecting the smoothness of the transmission. The base circle of the gear is the only parameter that determines the shape of the involute tooth. If there is an error in the base circle during hobbing, the tooth situation must also have errors. Base circle radius R=
Hob moving speed / table slewing angular speed xcosao (ao is the original tooth angle of the hob). During the hobbing process, the involute tooth shape is mainly ensured by maintaining a certain speed ratio between the hob and the blank. It can be seen that the tooth shape error is mainly determined by the hob tooth shape error, and the hob edge grinding quality is not good and the tooth shape error is easy to occur. At the same time, the radial runout and axial turbulence (ie installation error) generated by the hob during installation also have an effect on the tooth profile error. Common tooth shape errors are asymmetrical, tooth angle error (tooth top or thick), cycle error, and so on.
3 tooth error analysis
The tooth tooth error is the end face distance of the two design tooth lines that accommodate the actual tooth line in the range of the full tooth width on the indexing cylindrical surface. The main cause of the tooth misalignment is that the vertical feed direction of the machine tool and the tool holder is offset from the axis of the part, or the center of the top end of the tailstock is inconsistent with the center of rotation of the table, and the calculation error of the differential hanging wheel when rolling the helical gear Large, differential drive chain gear manufacturing and adjustment errors are too large. In addition, the accuracy of the manufacturing, installation and adjustment of the jig and the blank can also cause the tooth misalignment.
4 tooth surface roughness analysis
There are several phenomena in the tooth surface roughness: hairline, caries, fish phosphorus, tear.