A herringbone gear is a cylindrical gear that has a right-handed tooth on one part of the tooth width and a left-handed tooth on the other part of the tooth width. The herringbone gear is translated into double-helical gear in English. The herringbone gear has the advantages of high load carrying capacity, stable transmission and small axial load, and is widely used in the transmission system of heavy machinery. The herringbone gear shaft can be made separately on the two sides and then combined together; or although the two sides are integrated, the necessary overtravel grooves are left between the effective tooth surfaces on both sides; or the gear shaping is used. Method, but also need to break the flank on both sides. Compared with the processing of ordinary gears, the processing technology of the herringbone teeth is more complicated and difficult, and the commonly used processing methods are generally processed by using a finger gear milling cutter.
First, the processing points of herringbone gear
The intersection of the left and right spirals of the herringbone gear can form a plurality of planes, and the plane symmetrical to the end face of the gear is generally referred to as the center plane of the herringbone. Due to the limitation of the structure of the reducer and the condition of the normal meshing transmission of the gear, the position of the herringbone gear shaft must be placed during assembly, and the position error of the center plane of the herringbone must be controlled within the allowable range of the assembly adjustment.
Second, process analysis
From the assembly point of the herringbone gear, the biggest difficulty in processing the herringbone gear is to control the position of the center plane of the herringbone.
1, processing ideas
In this paper, the main method for controlling the positional tolerance of the center of the herringbone is to firstly machine the tooth profile on one side and then lead the spiral of the tooth to the outer circle of the other side by the scribe line to reduce the deflection of the plane position of the center of the human figure. The error can be processed according to the following processing route: rolling one side gear → fitter scribing → rolling the other side gear, as follows:
2, the choice of equipment and tools
Due to certain restrictions on the processing equipment, the processing equipment used in this paper is the Y320 hobbing machine manufactured by Wuhan Heavy Machine Tool Factory. The hob adopts the m10, a20°, γ4°40' right-handed single-head high-speed steel standard according to the drawings. Hob for processing.
3, the calculation of the split tooth hanging wheel
Calculated by the split tooth hanging wheel:
(where K - the number of hobs - Z - the number of teeth) Y320 has a fixed number of 20 or 40, which is determined according to the parameters of the herringbone in this example.
Then: that is to say, the number of gears of the four gears to be used is a=40, b=30, c=50, d=90; the four gears of abcd are respectively mounted on the carrier to complete the split gear. It is worth noting that when the cutter is in the same direction as the workpiece, there is no need to add the intermediate wheel. In this case, the left-handed part is first processed, and the tool and the workpiece are rotated differently.
4. Calculation of differential hanging wheel
The calculation formula for the differential hanging wheel is:
(where β - workpiece helix angle mn - normal modulus K - number of hob heads) Because the Y320 type hobbing machine has a differential number of 15, so here are:
From the ratio hanging wheel table, it can be found that when i=0.6538351167, a2=89, b2=41, c2=25, d2=83, the error value is:
If the error value is within the allowable range, the differential hanging wheel is:
5, the installation of the hob and the clamping correction of the workpiece
In this paper, we first select the left-handed part of the processing of the herringbone gear. According to the hob rotation direction, the spiral lifting angle and the herringbone spiral angle, the installation diagram of the hob can be determined as shown in Figure 3, and the hob inclination angle is β+γ= 25°. 50' 31"+4°40'= 30°30' 31". The workpiece is clamped using a collet. The workpiece is corrected using a dial gauge, and the accuracy is controlled within 0.05 mm. The main points of the clamp correction: 1 The positioning reference should be accurate and reliable. 2 The tooth core axis coincides with the rotation axis of the table. 3 The bearing end face should be perpendicular to the axis of rotation of the table. 4 The distance between the bearing surface of the tooth blank and the point of the cutting force is as small as possible. 5 It must have sufficient rigidity and clamping force to ensure no deformation during clamping work and no vibration during processing.
6, the number of passes and the choice of feed
In this case, the herringbone gear material is 40Cr. Under the premise of ensuring the quality of the workpiece and the reasonable hob life, the gear processing is processed by 3 passes. The first time the knife was taken, the amount was 1.2m, the second time was 0.7m, and the third time was about 0.3m. Normally, in order to improve the accuracy of the gear and ensure the size of the tooth shape, the common normal length W/k should be measured for the third infeed, and the third infeed amount should be determined from the length of the common normal line. The feed amount ΔL = 1.46 × (W / k - Wk).
The feed amount is selected according to the feed rate table. The feed amount per direction of the hob of the table is 0.38 mm. At this time, the feed gear hanger is B, and the gear position is I.
7, fitter scribing
In this example, after the left-handed gear is machined, the workpiece is unloaded to the scribing machine. According to the pattern and technical requirements, the left-hand gear tooth tip spiral is led to the outer circle of the other right-handed gear tooth blank, and the tooth blank is used for the stroke. The line tool draws the processing boundary. It should be noted here that, unlike other workpiece marking requirements, the center plane of the human character of the gear is basically determined by the scribe line. Therefore, the basic requirement of the scribe line is that the line is clear and symmetrical, and the positioning and positioning dimensions are accurate. Since the line of the scribe line has a certain width, it is necessary to improve the technical requirements, and the scribe line precision is required to be 0.10-0.25 mm.
8. Re-adjust the hob installation angle and clamp the workpiece
The gear processed this time is the right-handed part of the herringbone gear. Therefore, it is necessary to adjust the installation angle of the hob. The adjusted angle should be β-γ=25°50' 31"—4°40'= 21°10' 31 ", as shown in Figure 5. The workpiece clamping correction is the same as that in step 5, and then the hob is corrected so that the position of the hob is as close as possible to the machining boundary drawn by the outer circle of the right-handed gear blank.
9, the choice of the second pass
This time, it should be noted that the first time the tool should be taken, the tool should be tested first. When the length of 2~5mm is processed, the position error of the knife position and the processing boundary is measured, and then the mounting position of the hob is adjusted according to the error amount. (We can use the dial gauge to measure) and continue the machining. This step can be repeated several times until the position error of the center of the herringbone is reduced and controlled within 0.25mm. After the hob installation position is corrected, you can follow the step 6 to complete the machining of the herringbone gear.
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