We produce 3 20 D full-box gearbox with 900 type pumping unit for export to the United States. The quality requirement is that the overall noise is ≤87 dB after the pumping unit is installed, the gear meshing length is 100%, and the appearance is flawless.
We use horizontal boring machine for roughing, gantry machining center for fine boring; gears for vertical car processing; shafts are generally processed with 30 or 40 lathes, and then grinding is carried out by grinding machine. The machining method of the gear tooth is the forming hob hobbing. On the ordinary hobbing machine, only the 8-level precision gear can be machined with the ordinary precision hob. The precision of the gearbox gearing requirements of the full-box gearbox is 8-7-7, and the hobbing process is mainly based on the two center holes and the end faces. Therefore, the error source of the hobbing is analyzed, and the guarantee and improvement are mastered. The method of machining accuracy is very important.
1. Improve the processing accuracy of the box
Since we use the machining center to machine the box, the final finishing is performed according to the program after one setup, so the accuracy of the machine can guarantee the machining accuracy. At the same time, the operator must check the accuracy of the machine tool before processing every day. Then, after processing 5 pieces of box, check one box with the joint arm coordinate measuring instrument to ensure stable accuracy.
2. Improve the accuracy of hobbing
(1) Factors affecting hobbing accuracy The hobbing accuracy 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 are controlled to ensure the motion accuracy. The tooth profile error and the base circle deviation are used to ensure the smoothness of the work. The tooth pitch error is controlled to ensure the contact accuracy. The following is an analysis of several error causes that are prone to hobbing.
1 ring gear radial round runout error (ie geometric eccentricity) The ring gear radial runout means that the measuring rod placed in the tooth gap is measured by using a dial gauge probe within the range of the gear rotation. The maximum amount of change in the axis of the tooth is also the eccentricity of the ring gear relative to the centerline of the shaft. It is caused by the fact that when the parts are installed, the two central holes of the parts do not overlap or the deviation of the rotation center of the worktable is too large, or the top and the top holes are not properly manufactured, and the contact surface is not well contacted to cause eccentricity.
2 Common normal length error (ie, motion eccentricity) The hobbing is to be processed by the exhibition principle. The gear transmission chain from the tool to the tooth blank should maintain the accuracy of the movement according to a certain transmission ratio.
However, these transmission chains are composed of a series of transmission components. Their manufacturing and assembly errors must be concentratedly reflected 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 teeth of the gear. It is mainly the uneven rotation precision of the worm gear of the hobbing machine table, the circular guide rail of the hobbing machine table wears, the indexing worm wheel and the circular guide of the table are different axes. There is a serious bump on the tooth surface of the tooth exchange gear, and the bite is too loose or too tight when the gear is exchanged.
3 Tooth shape error Tooth shape error refers to the normal distance between two ideal involutes that accommodate the actual tooth profile within the tooth working range. It is impossible to obtain a completely correct involute profile in the actual machining process, and there are always various errors that affect the smoothness of the transmission. The base circle of the gear is the only parameter that determines the involute profile. If the base circle produces an error during hobbing, the tooth situation must also have errors. In the hobbing process, the involute tooth shape is mainly ensured by maintaining a certain speed ratio between the hob and the tooth blank. It can be seen that the tooth profile error is mainly determined by the hob tooth shape error, and the hob blade The quality of the grinding is not good, and the radial runout and axial turbulence generated by the hob during installation have an effect on the tooth profile error. Common tooth shape errors are asymmetry, tooth angle error (feet topping or thickening) and cycle error.
4 Tooth direction error The tooth direction 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 cylinder 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 part axis, 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 exchange gear when rolling the helical gear. Large, differential drive chain gear manufacturing and adjustment errors are too large. In addition, the accuracy of manufacturing, mounting, and adjustment of the jig and the blank can also cause a tooth misalignment.
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