Improve shaft gear hobbing technical precision approach
Posted byadmin  date2009-9-29  click3080

Hobbing gear processing is a commonly used method, high precision hobbing machine, using precision hob, accuracy can be processed out 4-5 teeth. In general level hobbing, with ordinary precision hob, only eight precision machined teeth. Gearbox shaft gear unit required accuracy level of 8-7-7, and when hobbing mainly do two center hole and end positioning reference, so the analysis of sources of error hobbing, master assurance and improve the precision approach is very important.
1 hobbing accuracy analysis
main and pinion precision motion accuracy, smooth precision, accuracy of contact information. Hobbing using control normal length and diameter of the ring gear to ensure movement precision jump, with the control deviation profile error and base sections to ensure smooth working of the precision error of the control gear to ensure the accuracy of contact. Next, hobbing prone to several errors in the analysis of the causes:
1 ring gear runout (ie geometric eccentricity)
ring gear runout refers a transfer within the scope of the probe within the alveolar or teeth on the high school sided with the tooth contact probe relative to the tooth axis of maximum variation. Ring gear is eccentric with respect to the shaft centerline, this is due to the eccentric mounting parts, the part of the center hole and two rotational center of the table coincides or is not installed and cause too much deviation. Or because of poor manufacturing top and top hole, caused by poor surface contact with the positioning eccentric, so jump ring gear diameter above the main cause analysis should be addressed.
2 normal length error (ie sports eccentric)
hobbing principle is generating method of processing gear, gear blanks from the tool to the drive chain between the sub-toothed gear ratio according to a certain relationship to maintain precise movement sex. But the drive chain is a series of components of the transmission.
Their manufacturing and assembly errors in the transmission of movement is bound to focus reflected to the drive end of the chain parts, the relative movement of the unevenness affect tooth machining accuracy. Normal length change is a reflection of the uneven distribution of the gear teeth, the maximum error, this error is mainly rotary precision worm gear hobbing machine table caused by uneven, there is a circular rail wear hobbing table, and the table indexing worm circular guide different axes caused Furthermore hanging tooth surfaces of teeth with severe bump or hang wheel bite too loose or too tight will also affect the normal line change tolerance.
profile error analysis refers to the tooth profile error within the working part, the actual inclusion of two ideal tooth profile tooth (involute) profile between the normal distance. In the actual processing is impossible to obtain exactly the right involute profile, there is always a variety of errors, thus affecting the smooth transmission. Base circle of the gear involute is to determine the only parameter, if the base circle when hobbing produce errors, tooth inevitably there will be errors.
Hob speed / rotary table angular xcosao (ao for the hob original profile angle), the hobbing process depends mainly on the involute hob and gear blank to maintain a certain ratio between the sub- teeth to ensure that, we can see that the error is mainly hob tooth profile error of the decision, hob sharpening poor quality is prone to tooth profile error. Meanwhile hob in the installation resulting runout, axial movement (ie installation error) also affect the profile errors. Common errors asymmetric tooth, tooth angle error (addendum become fat or thickening), resulting in periodic errors.
4 tooth to tooth error analysis
error is indexing cylindrical surface, the whole tooth width range, inclusive actual tooth to tooth design lines two lines end distance. Causing the error is mainly due to tooth machine, tool feed direction and the vertical axis are offset part or on the tailstock center is inconsistent with the rotary table center, as well as helical gear hobbing, hanging round the differential calculation error large, the differential gear manufacturing and transmission chain adjustment error is too large. Another fixture and gear blanks manufacturing, installation, adjustment can also cause teeth to low precision error.
5 tooth surface roughness analysis
bad tooth surface roughness generally have several phenomena: Hairline, gnawing teeth, fish phosphorus, tear.
Cause tooth surface roughness are the main reasons are the following: machine, tool, workpiece overall system less rigid, large gap; hob and the workpiece relative position changes; hob sharpening improper parts uneven material; cutting inappropriate choice of parameters and so on.

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