First, the difficulty in processing the herringbone teeth
The intersection of the left and right handed teeth of the herringbone gear can form a plurality of planes, and the plane symmetrical to both ends of the gear is generally referred to as the center plane of the herringbone tooth. In order to meet the transmission conditions of the normal meshing of the gear, the position error of the herringbone gear during assembly must be controlled within the allowable range of the adjustment amount.
It can be seen that the maximum processing difficulty of the herringbone gear lies in the control of the medium error. If the master is not good, there will be accumulated error. In the tooth-finishing stage, the case cannot be polished. When hobbing, both the upper and lower sides should be taken into consideration. The minimum margin for individual teeth.
In addition, gears driven by heavy machinery do not allow residual bosses at the root of the root after machining. Because the deformation of the large gear after carburizing and quenching is generally difficult to control, it is easy to appear a boss at the root of the tooth after finishing, so measures must be taken to reduce and control the deformation of the carburized and quenched gear.
Second, the common processing method of herringbone teeth
In order to facilitate the cutting process, the herringbone gear leaves the necessary overtravel groove between the effective tooth surfaces on both sides as needed. The hobbing processing precision and efficiency are relatively high, and the tool has good versatility. Therefore, the gear pre-processing uses hobbing as much as possible to quickly remove most of the tooth shape margin, and the finishing uses grinding teeth to ensure the overall precision of the gear.
1. Tooth processing route.
The main method to control the moderate error is to firstly machine the one tooth shape and then guide the spiral of the tooth to the outer circle of the other side by the method of the fitter scribing to determine the processing boundary and minimize the center plane of the herringbone. Position offset error.
The processing route is: rolling one side gear fitter to scribe and roll the other side gear.
Hobbing is divided into three steps:
According to the pattern and process requirements, the left-handed teeth are rolled.
According to the left-handed tooth line, the cogging contour of the right-handed tooth is drawn (see Fig. 3), including the bottom-to-cut line, and the shape is traversed along the contour track.
Once again, the right hand is rolled and the four teeth are divided.
The first knife: the cutting edge of the cutter tooth, the radial feed is about 0.3 times the full tooth height, and the vernier caliper is used to measure the margin of the rolling groove and the two contour lines. The half of the difference is the value of the file, the direction of the file. a side with a large margin;
The second knife: After the file is cut according to the value of the file and the direction of the file, the radial feed is about 0.4 times the full tooth height. After the roll cutting, after the roll cutting, the value of the file is measured and calculated to determine the direction of the file. Pre-processing alignment method;
The third knife: after the boring tool and the boring tool direction, the radial feed is about 0.15 times the full tooth height, the hobbing, repeating the second knife measurement process, and performing the boring tool.
The fourth knife: After the file is cut according to the value of the file and the direction of the file, roll to the left-handed common normal size value. After the roll-cutting, re-check the centering accuracy and make a record.
2. Hobbing tool selection.
Due to the heavy-duty mechanical transmission of the gear, it is not allowed to leave residual bosses at the root of the tooth after machining. It should have proper surface roughness, especially for hard-toothed gears. The root is the weakest link. There is less grinding in the roots, leaving the bosses to cause stress concentration. If the grinding is more, it is equivalent to destroying the surface strength. Both cases will affect the life of the gears.
3, tooth blank clamping tooling.
In order to reduce the auxiliary time for workpiece clamping and alignment and improve production efficiency, the hobbing tooling (see Figure 5) has been specially designed, which consists of a base, a backing plate, a positioning ring, a locking screw and a pressure plate.
