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Discussion on Arc Gear Manufacturing Process Fan Shaotang, Wang Qiaoying (Taiyuan Heavy Machinery (Group) Co., Ltd., Taiyuan 030024) In the past, the company has formed its own process and characteristics in the process of manufacturing 67-type orphan gears, whether it is convex or concave. Tooth, our manufacturing points are: (1) strictly control the outer diameter dimensional accuracy and positional accuracy of the blank; (2) the gear with the modulus m<12 is processed by the same modulus circular ore cutter; the gear with the modulus m>2 In the case of rough cutting, the involute gear hob can be used to improve the machining efficiency; to control the rough cutting depth, it is necessary to leave sufficient cutting allowance, and then use the round ore hob to cut the cutting tool to improve the tool life. The common normal method for measuring the orphan gear technology is more accurate and reliable.
Arc gears have more advantages than involute gears, high contact strength, stable transmission, and high efficiency. These are well known.
Conversely, if the involute gear transmission is to achieve the same effect as the arc gear transmission, then the design must be changed from the structure, large modulus, large volume, or hard toothed gear transmission. All of this adds manufacturing costs and makes it difficult to manufacture, and in some cases it can't replace arc gears. Therefore, arc gear transmission is widely used.
After years of comparative practice, China has designated the 67 type as the reference tooth profile of the circular gear, which has more advantages than other types of tooth shape. Uniform tooth shape is conducive to tool manufacturing and production technology management and standardization, overcoming the cumbersome drawbacks of other tooth parameters.
1Technical characteristics Arc gear transmission is a pair of convex teeth and concave teeth. The convex tooth or concave tooth is formed by the arc tooth shape instead of the involute gear. The blade of the original rack tool is in the exhibition. In the process of formation, it is enveloped by different continuous positions, but is a forming surface of a blade. Therefore, the tooth profile of the gear and the tool are consistent in any section. The entire process of cutting the tool into the tooth profile of the part (such as the convex tooth) can only completely cut out the tooth shape at the moment when the center of the toothed arc of the tool coincides with the part line of the part. For the concave teeth, although the center of the curvature radius of the tooth shape is slightly offset from the pitch line (0.075 m - 0.025 m), it can be approximated as the convex tooth formation, and the normal direction is also approximately circular.
In the processing of arc gears, except for the different tools used, the other process and equipment selections are not much different from the involute gears, but pay attention to the following points during the machining process: (1) Arc gears in theory It is a helical surface meshing transmission, so the pair of gears that mesh with each other must have the same axial pitch, and the overlap coefficient Z must be greater than 1, that is, the tooth bevel must be large enough.
In order to ensure that the axial pitch reaches a certain precision, the hob machining is the only correct way. In addition, the helix angle error will be the main cause of the unequal axial pitch. It will reduce the contact length in the direction of the tooth width and affect the work balance. Therefore, the smaller the spiral angle error, the better, preferably no more than 4 seconds, and try to be consistent. The intermeshing gears are machined as much as possible on the same machine with the same set of hanging wheels.
(2) When machining circular arc gears, the center distance and the depth of the cutting teeth will directly affect the contact position of the gears, resulting in lower bearing capacity and affecting its service life.
As described above, the arc tooth gear meshing in the end face is the same as the tool tooth profile curve, which is not exactly the envelope of the blade motion track. Therefore, the tooth profile of the part Accuracy and tooth surface roughness are directly related to tool accuracy, especially for finished parts after tool regrind, and the quality of the sharpening should be controlled. In addition, when machining a pair of conjugate gears, two hobs are required to be convex and concave, and since the arc teeth have no undercut phenomenon, the minimum number of teeth of the gears may be slightly smaller. Secondly, the arc gear has good running performance, so the manufacturing error caused by the tool can be quickly extended from the initial point contact to the face joint by the proper loading and unloading after assembly. When making billets, be sure to control the dimensional accuracy and positional accuracy of the outer diameter. For final forming, the grinding method should be used and the actual size should be marked on the top of the tooth to be used for cutting teeth.
2.2 Selection of rough-cutting tools The circular-arc gears are generally machined with the same modulus of the gears with a modulus of <12, but for the larger-modulus gears, due to the special tooth profile, It is unreasonable to use it to remove a large amount of metal, both in terms of processing efficiency and tool life. Practice has repeatedly proved that the use of involute gear hobs for rough cutting is a good method of processing.
Due to the tooth shape of the involute hob and the arc tooth hob, there are differences in shape and various parameters. It is very important to know how to master the depth of the cutting teeth and to have sufficient precision.
It can be seen that when the involute hob rough cuts the teeth, the amount of the teeth is relatively uniform. In the case of rough-cut concave teeth, the residual value at the root radius is particularly small. When the coarse-cut convex teeth are small, the tooth height is small. When the concave teeth are cut, the root is high, which is close to or slightly larger than the teeth of the involute hob. The top is high, so there must be sufficient retention in the depth of cut. Both of these cases are equivalent to machining a positive displacement involute gear.
The calculation of the depth of cut when rough-cut concave arc gear: It can be seen that as long as Si>Sx, it means that the tooth surface has left a fine cutting margin. The touch reached the use of this blessing in the use of CWishing Zhi 17 arc tooth roots in the S-cut depth balance where the arc is wide.
As long as Si2 is larger than Sx2, there is a fine cut.
In order to find Sx2, we must first find X2. For the 67-arc gear x2= After knowing Z2, we can find Sx2 in the following order to find the number of imaginary teeth. Z'2 P arc gear indexing circle spiral angle is r 2, R base 2 points 2 to find the pressure angle a at r root 2+ from which we can see that r root 2+ is the r point 2hu+x2 at the arc groove width h2 concave tooth full depth hu involute gear hob The height of the crest height rg2 concave tooth root fillet radius x2 is equivalent to the tool displacement amount when rolling the involute gear. As described above, Si>Sx can ensure that the tooth root has a fine pair of 67 type rg2. Knowing the A2, you can find the Si2 rough-cut convex tooth, the calculation of the depth of cut: It can be seen that there is a fine cutting allowance when Sxi>Sn, which is equivalent to the rolling-cutting gear in order to satisfy the above formula.
For the 67-arc gear, x1=0. =x1/mn After knowing Z, the number of imaginary teeth Z can be obtained in the following order: Wh1 and W1 are cut by 4, and 0 is cut by the hob at the root. Excessive WishingHouse, the precise cutting capacity of the gear can be selected according to Table 1.
Gear module l2-l4l6l820222527 tooth type 67 involute hob modulus l2- machining with involute hob convex arc gear balance r root 2i 18丨 pressure angle a + gossip is r Divided into 1 known number 'When A is determined, it can be found that Sil passes through multiple practice and calculations, and the residual value A on the depth of cut is normal.) The control of the incision hob with the involute hob rough cutting arc 2.3 As mentioned above, the influence of the cutting depth on the arc gear is very important. If the operation is not correct, the processed gear will not meet the requirements.
The actual depth of cut, in addition to considering the theoretical depth h of the tooth, the actual deviation A2 of the radius of the tooth and the depth of the file A when cutting the depth of the tool, in addition to the machine scale, should also be in the bed Use the dial gauge positioning method on the column or table slide.
In the machining, the cutting depth of the tool is adjusted according to the difference of the measured tooth thickness.
Legal line length difference A Chamfer depth difference 2.4 hobbing tool arc gear machining is different from involute machining. When machining convex teeth, the center of the tooth groove of the hob should coincide with the center of the table. When machining a concave tooth, the center of the tooth should coincide with the center of the table. Due to the instantaneous shaping in the tooth profile machining, the correct orientation of the tool position is ensured only to keep the two sides of the cut tooth shape symmetrical.
(a) Machining the convex gear to machine the concave gear to machine the circular gear. 3 Technical measurement of the circular arc. b. Calculation of the chord depth. In general, there are two ways to measure the circular gear: It is a tooth depth measurement method that controls the depth of the string teeth and the root diameter. The other is a tooth thickness measurement method with a string thickness and a common normal.
3.1 Chord depth, tooth depth measurement method a, the root diameter measurement method (see) is more intuitive and stable, but subject to the size and size of the part, the general measurement range does not exceed 1m. If the part is tested When the number of teeth is an odd number, the slant diameter should be calculated as follows instead of the root circle size.
Type 67 concave teeth When mn is x-30, H1 and H2 are the convex teeth of the convex and concave teeth, respectively, which are two parallel spatial spirals. The calculation of the string tooth thickness can be attributed to the shortest distance between the two spirals. When using accurate calculation, it is very complicated. In engineering, the maximum helix angle of the arc gear is about 30, and the number of teeth of the convex tooth is more than 10, which can be calculated by the approximation method.
The steps are as follows: find the equivalent tooth number to obtain the declination S De1 real, Der is the actual outer circle size of the convex and concave gear respectively 3.2 string tooth thickness, the common normal line measurement tooth center center shift amount b tooth contour center distance distance s, h value: 3.2.2 Calculation of the common normal The common normal of the circular gear is the shortest distance line between the normal of the theoretical meshing point and the track of the intersection of the cylinders plus their distance to the theoretical meshing point.
The following is only a description of the convex tooth calculation method: the P-tooth profile radius and the chord thickness of the convex-concave tooth can be measured by the tooth thickness caliper. When measuring the common normal line, the vernier caliper can be used (the claw is required to be round when measuring the concave tooth) Just fine.
The several measurement methods described above can be determined according to the actual situation. In comparison, the common normal method is accurate and reliable, because it is not affected by the processing size of the outer circumference of the tooth.