Our company is a professional manufacturer of heavy-duty transmissions. In the long-term production, the manufacturing technology of the gear transmission for passenger cars and the shaving process for truck transmissions has been formed. With the increasingly fierce market competition, the company put forward the strategic policy of “combining passengers and goods, reducing costs and increasing efficiencyâ€. For this reason, engineers and technicians have made technical improvements to the grinding process and applied the roll-shaving process. In addition, the recent improvement in heat treatment conditions of the company has created conditions for the implementation of the rolling process.
Rolling shaving scheme
The two-axis first gear in the transmission mainly plays its role in starting and climbing, and the tooth-tooth accuracy of the running teeth is not a decisive factor on the noise of the transmission. According to this situation, it is considered that the process of grinding and shaving the part in the transmission for the passenger car can improve the production efficiency and reduce the production cost.
The rolling shaving process scheme is: forging billet → isothermal normalizing → coarse, fine car → pinning → hobbing → shaving → carburizing cooling / direct quenching / tempering, stress peening → grinding hole and end face machining → meshing noise Inspection → cleaning → final inspection → storage.
Shaving in the roll shaving process
Shaving is a method of finishing gears. Due to the high productivity of the shaving, the good gear quality, the long service life of the shaving cutter and the simple structure and convenient adjustment of the machine tool used, the shaving process has been widely used in gear processing of mass production of automobiles, tractors and machine tools.
1. Processing method of shaving
According to the feeding direction of the shaving, the shaving processing methods include axial shaving, diagonal shaving, tangential shaving, and radial feeding shaving. According to the characteristics of our company, the production batch and the condition of the shaving machine, both axial shaving and radial shaving are adopted in the product processing. In this paper, the shaving of the two-axis first gear is processed by the axial shaving method.
2. Machine tools and tooling
(1) The shaving machine adopts the former West Germany ZSA320 shaving machine, which can process spur and helical gears, and can process drum teeth and small taper gears. It can perform three kinds of shaving in axial, diagonal and tangential directions. The accuracy grade is 5, and the surface roughness value Ra is 0.63 μm.
(2) The shaving cutter selects the disc-shaped shaving cutter, the precision is grade A, and the standard shaving cutter made of W6Mo5Cr4V2 steel is used after the shape modification processing. The basic parameters are diameter 244mm, width 25mm, number of teeth 46, helix angle 2.5°. The axis angle is 10°.
(3) Shaving jig A floating jig is used, which is based on the inner circumference of the product to reduce the clamping error of the workpiece.
(4) Tool and workpiece clamping After the shaving cutter is clamped, its axial circular runout and radial circular runout are both ≤0.01mm. When the product is clamped, the top and bottom radial runout of the machine tool is required to be ≤0.005mm, and the offset between the two top center lines (with a tip pitch of 150mm) on the table movement direction is ≤0.01mm, and the end face and radial runout of the machine tool spindle ≤0.005mm, the parallelism of the end faces of the gasket is ≤0.005mm. At the same time, it ensures that the shaving mandrel has a good fit with the inner hole of the gear and has a minimum fit clearance.
3. Shaving shaving parameter control
(1) Technical parameters of the gear requirements The parameter values ​​of the shaving requirements control are determined by analyzing the changes of the parameters before and after the heat. The control values ​​of the gear shaving parameters are shown in the attached table. Since the shaving is a hot pre-process, considering the pre-heat correction problem, the tooth shape and the tooth direction are specifically determined according to the hot and cold deformation conditions, and the tolerance values ​​of the tooth profile and the tooth direction in the attached table are for reference only.
Shaving control parameter list
(2) Cutting speed When the disc shaver is in operation, the cutting speed at each point on the tooth height changes. The so-called cutting speed refers to the sliding speed at the meshing node. The cutting speed of the alloy steel material was 105 m/min, and the workpiece rotation speed nw was finally calculated to be 141 r/min.
(3) Feeding amount The longitudinal feed amount is related to the tooth surface roughness, tool life and productivity. For gears with fine surface roughness and high material hardness, the gear should be taken to a small value. The longitudinal feed rate is divided into the longitudinal feed amount f (mm/r) per revolution of the workpiece and the longitudinal feed amount v f (mm/min) per minute on the table. The relationship between the two is:
v f = fn w
For a two-axis gear, the f value can be 0.1 to 0.2 mm/r. According to the results of multiple trial shavings, it was determined that the rough and finishing table vf were 35 mm/min and 20 mm/min, respectively.
Radial feed is related to the stiffness of the machine tool, fixture, and the ability to correct pre-shave errors when shaving. According to the long-term production situation of our company, the remaining shaving margin is 0.09~0.12mm according to experience. According to the relevant information, each stroke is 0.02 ~ 0.06mm. The final radial feed amount for the countershaft gear is 0.02 mm, 0.03 mm, 0.03 mm and 0.02 mm for each stroke as a 0.10 mm shaving allowance.
(4) Number of strokes The number of strokes is divided into the number of strokes and the number of strokes. The number of strokes depends on the amount of shaving and the amount of radial feed. When the radial feed amount is small, excessive stroke times can deteriorate the cutting conditions and reduce the tool life. The number of smoothing strokes is related to the roughness of the tooth surface, the number of smoothing strokes increases, and the value of the tooth surface roughness parameter decreases. At the same time, the total number of cutting and finishing strokes should be double. In the two-axis one-speed gear shaving process, the single stroke number of the cutting stroke is four times, and the number of single strokes of the finishing stroke is two times.
(5) Axis angle and cutting fluid? The angle of intersection between the shaving cutter and the workpiece is an important factor affecting the shaving performance. It directly affects the cutting performance of the cutting edge, the quality of the machined surface, the tooth profile accuracy of the shaved workpiece and the service life of the tool. . The range of the angle of the shaft is generally 10 ° ~ 20 °, according to the gear parameters and the parameters of the shaver, the angle of the shaving axis of the gear mentioned in this paper is 10 °. Sufficient, lubricious and fluid cutting fluids should be used in shaving to achieve good shaving.
4. Guarantee of shaving accuracy
During the shaving process, there is no drive chain between the tool and the workpiece, but a free drive. The ability of the shaving to correct the error of the shaved gear is not the same, some errors can be corrected, some errors can not be corrected basically, or converted into other forms of error after correction. Due to the congenital defects in the shaving mechanism, the shaving after the shaving is generally concave, destroying the correct involute profile, and therefore the shaving of the shaving cutter is often corrected. According to the characteristics of the shaving process, it is very important to determine the accuracy of the shaving gear.
(1) The shaving front blank requires control of the quality of the workpiece material, such as uniform hardness, no local defects such as hard impurities and pores, to prevent the shaving cutter from blunt prematurely; to maintain the shaving reference surface and shaving front The reference surface of the cutting tooth processing is consistent; the front tooth surface of the shaving should not have a hard machining mark; the top of the shaving cutter and the root of the workpiece do not interfere; the precision of the shaving processing is improved, the shaving allowance is reduced; and the precision of the shaving gear is ensured. Reach: The first tolerance group (mainly the error items Fw, Fr which affect the accuracy of the transfer motion) is not lower than the shaving requirement. Other error items can be lower than the shaving accuracy by one level; pre-trimming according to the heat treatment deformation can be shaved Pre-cutting tool tooth pre-trimming or tooth direction (spiral angle) pre-trimming.
(2) Shaving requirements? In combination with pre-shaving pre-shaping, the shaving cutter can also be partially pre-trimmed according to the heat treatment deformation; in order to maintain the shaving cutter's ability to correct the workpiece error, the coincidence degree during shaving should be ≤1.5mm; The knife should be sharpened in time to keep the blade sharp. When the shaving cutter is blunt, the tooth surface of the workpiece is squeezed, the tooth shape error is increased, the contact accuracy is lowered, and the noise is increased when shaving; a reasonable cutting amount is selected. The shaving speed has a significant influence on the tooth profile and pitch accuracy of the workpiece. The number of finishing strokes has a great influence on the quality of the machined tooth surface; the appropriate cutting fluid is selected according to the material of the workpiece and needs to be filtered.
5. Shaving process notes
In shaving, the following points must be noted:
1) Unreasonable cutting amount will result in unstable control parameters, abnormal shaving stress on the gears, and finally the gears will be thermally deformed irregularly.
2) After the machine tool is adjusted, the test shaving gear must be tested first. After passing the inspection, the mass production is carried out.
3) If the tooth surface is lost during the shaving process, there is a squeezing pattern, the tooth surface is dull, the toothed end face has a large flash edge, a sickle phenomenon, the tooth shape error increases, and the shaving process If an abnormal sound or the like occurs, the tool must be changed in time.
Shaving cutter
1. Shaving knife sharpening basis
For the gear roll or roll shaving process, the sharpening of the shaving cutter is extremely important. Due to different products and different requirements, the degree of tooth profile correction will be different. There are three main reasons for the shaving of the shaving cutter:
1) According to the principle of gear meshing, when the shaving cutter meshes with the gear to be machined, the instantaneous cutting force is changed due to the change of the instantaneous gear ratio, so that the gear to be machined varies from 0.01 to 0.02 mm around the pitch circle. The concave phenomenon deviates from the theoretical involute, so the shaving cutter must trim the tooth shape by 0.01 to 0.02 mm in its corresponding area to compensate for the concave amount in the gear tooth shape.
2) In fact, when the gear with the theoretical involute is meshed under the load, it can not guarantee the smooth running and no noise in the transmission, so it is necessary to have a reasonable tooth shape to reduce the interference under the load meshing.
3) Since the gear will have tooth-shaped and tooth-tooth deformation during the heat treatment, it is necessary to modify the hot front shaving cutter. Of course, it is very difficult to accurately determine the shape of the shaving cutter, because it is not only related to the final tooth shape and tooth direction of the gear, but also directly related to the quality of the shaving, so it often takes several repeated trials. The best shaving curve can be obtained after the gears.
2. The basic method of shaving cutter tooth shape modification
1) Firstly, the standard involute shaving cutter that meets the design accuracy requirements is used to test the machined gear first. The shaving process must be correct. All the operating factors such as adjusting the machine tool and clamping must strictly implement the cutting specifications and will shave well. The gears are plotted on the involute checker to plot the tooth profile of the tooth profile.
2) Calculate the angle value of the gear concave amount Ïf and the angle value of the additional tilt angle of the shaving cutter Ïf according to the shape of the tooth profile measured by the shaved gear and the concave amount in the curve, and select the angle of the corresponding point of the shaving cutter correction Sample and change the angle value of the grinding installation angle.
3) The gears shaved by the shaving cutter after grinding the tooth shape by the above method can basically meet the requirements of the shape of the tooth profile, but it is also necessary to find out the deformation condition after heat treatment of the product multiple times according to the actual situation, and again the shaving cutter The corresponding grinding is carried out, and then the gear is machined with the resharpened shaving cutter until the acceptable contact and involute shapes are shaved.
When shaving the gear, the pressure of the product shaved by the standard toothed shaving cutter is small, and the tooth profile is corrected by 0.015 to 0.018 mm. According to this tooth shape, we correct the shaving cutter tooth shape to -0.015 mm. Once again, the product is tested and shaved, and finally the tooth shape of the product meets the product design requirements. More than 90% of the products are qualified by the paired noise detection before assembly assembly.
Statistical analysis of data before and after shaving
In the improved shaving control of the two-axis one-speed gear rolling process, the common normal line data was measured, and the total length of the common normal line before and after the heat of 12 pieces of gears was measured. The results show that the common normal line value after gear shaving processing has a tendency of rising heat before and after the existing heat treatment conditions, and the absolute deformation amount is basically concentrated at 0.02 mm, which meets the requirements of the gear common normal length tolerance of 0.06 mm; And after the heat, the common normal value meets the technical requirements of the finished product size and the company's related quality deviation (the finished public normal line value W8=110.82~110.759, Fw≤0.045mm). This also shows that the control of the gear common normal value is focused on the shaving process. In order to more accurately indicate the effect of shaving, the hot tooth front and back tooth contrast curves of the gears were also measured during processing.
The results show that the tooth profile of the tooth after the shaving is consistent with the heat of the curve, the change is relatively small, and the change is relatively stable, which indicates that the gear tooth orientation after the gear is hot is required, and the shaving control is the key.
Conclusion
The example of the rolling shaving process of the two-axis one-speed gear proves that the rolling shaving process is feasible, and the shaving control is the key. Only by closely combining the two, the roll-shaving process can be implemented. The “roll-shaving†process can be reduced to the “roll-shaving†process, which can greatly reduce the grinding time of the product, shorten the manufacturing cycle of the product, and have significant economic benefits.
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