Influence of the hottest process selection on gear

Influence of process selection on gear quality

selection of gear blank process scheme

the company produces timing gears that replace 4ja1 and 4JB1 automobile engines imported from Japan. Because the gears require high precision, long service life and good wear resistance, the requirements for geometric accuracy, dimensional accuracy and geometric tolerance of gear blanks are correspondingly 1-2 accuracy levels higher than those for domestic gear processing. Because the accuracy of gear blank is the decisive factor to ensure the machining of tooth profile, ensuring the machining accuracy of gear blank is an important part of gear machining

according to the practice of gear processing technology and the current situation of gear blank processing equipment of the company, and referring to the experience of Dongfeng company and other gear processing manufacturers, we decide to determine one of the following two schemes for gear blank processing

1. The first scheme

adopt the lap lathe to process the end face and inner hole → use the Multi Tool semi-automatic lathe to process the outer circle and the other end face → use the numerical control lathe to finish the end face and inner hole

2. The second scheme

the program-controlled lathe processes the blank shape, the numerical control lathe processes the important geometric dimensions, and the high-precision inner hole end face grinder processes the important inner hole and end face

3. Comparison

through the test, the analysis and comparison of the two schemes are shown in table 1 At the same time, because the inner hole processed by the first scheme tends to become larger after heat treatment and nitridation, the second process scheme is decided to be adopted through analysis and review. The production practice for many years has proved that the process is stable and reliable

determination of shaving parameters

1 The influence of gear hardness on shaving

the gear material is 50 steel, and the quenching and tempering hardness is required to be within 225~265hbw

under such hardness conditions, the use of general gear hobs for gear hobbing has a certain impact on the tooth profile processing quality and work efficiency of gears. It is not only difficult to cut, low efficiency, high cost, but also difficult to ensure the gear hobbing accuracy. In order to solve this problem, the company specially asked Hanjiang tool factory to design and manufacture a large-diameter round grinding coating hob made of M35. Through trial use, the above disadvantages were solved and the hobbing accuracy and production efficiency were improved. Because the hardness of the gear shaving cutter is 62~64hrc, it has good shaving performance for materials with hardness between 187~241hbw, and the shaving process belongs to conformal cutting, so the hardness of the gear has an absolute impact on the tooth profile and tooth direction error after shaving. In order to solve and find out the size of the influencing factors, the following tests were carried out on the shaving gears: the hardness of the first group of gears is in the range of 255~285hbw; The hardness of the second group of gears is between 240~255hbw; The hardness of the third group of gears is between 225~240hbw. See Table 2 for the comparison of the three tests

according to many tests and discussions, the heat treatment hardness is controlled at 225~240hbw as far as possible, which has high gear processing efficiency and reliable product quality assurance

2. As we all know, shaving has a certain ability to correct the short period error of the gear after hobbing (such as tooth profile tolerance, tooth direction tolerance, helix waviness error and tooth surface roughness, etc.), but sometimes it does not have the ability to correct the long period error, and may add new errors (common normal length variation, circumferential pitch cumulative error, radial comprehensive tolerance, etc.). Therefore, the quality of shaving process directly affects the accuracy of gears

this requires that not only the gear hobbing accuracy of the previous process must be guaranteed, but also the reasonable selection of shaving speed, feed rate and finishing times will have a great impact on the gear accuracy (see Table 3, table 4 and table 5)

based on the above, reasonable shaving speed, small feed and multiple finishing play a decisive role in ensuring the shaving quality of gears

determination of processing technology and detection method of pull keyway

engine crankshaft timing gear and camshaft timing gear are gears with keyway, and the angle between keyway and tooth surface is a very critical dimension, which is directly related to the ignition time and sequence of engine. Too large angle error is directly related to the power of engine, which can cause engine damage in serious cases. At present, there are still high production costs in the development of graphene industry in China The product quality needs to be improved, and the interaction between upstream and downstream is not enough. For this reason, we have done a lot of experiments and Research on the key pulling. The specific scheme is as follows:

(1) during the trial production of the sample, the key pulling process of the keyway adopts the standard sample to be sleeved on the key pulling mandrel, and then the standard key pin is used to position, fasten the key pulling fixture, and then install the workpiece on the key pulling. After pulling several pieces, calibrate the key pulling fixture with standard samples. The advantages of this process are simple and convenient calibration and small investment. It is suitable for test pieces and small batch trial production. This is the reason why we are firmly optimistic about the new energy industry chain, but the disadvantage is that it is directly affected by calibration parts, and the quality of calibration parts is directly reflected on the processed workpiece. During the implementation process, the gear specimen after pulling the key was spot checked. When it was inspected with a tool microscope, it was found that there was a certain deviation in the angle of the workpiece. After analysis and search, it was found that there was also a certain deviation in the keyway angle of the standard part, and the reason for the deviation in the keyway angle was affected by the error of the standard part. Therefore, this process is not suitable for mass production

(2) pull the key after the angle is checked by the tool microscope. This method has high precision and accurate angle inspection, but because the tool microscope belongs to the measuring instrument, the operation is complex, the inspection is cumbersome, and the inspection time is long. Each inspection takes about 30min, which is not suitable for mass production. At the same time, it is also seriously affected by the chamfer of the tooth end, and it is easy to cause the wrong guidance of the keyway angle pull key adjustment (see Table 6)

(3) in order to solve the key pulling problem, the technical personnel of the company have studied, tested and demonstrated for many times, reviewed a large number of technical materials, and finally decided to tackle the key first from the direct factor affecting the angle of the keyway - the positioning fixture of the key pulling

because the accuracy of the positioning fixture directly determines whether the keyway angle is out of tolerance. The accuracy requirements of the positioning fixture are mainly the pull key mandrel. The symmetry accuracy requirements of the guide groove of the pull key mandrel, the size of the diameter tolerance, and the perpendicularity of the end face and the mandrel axis all play an important role. At the same time, the fitting accuracy and tightness of the positioning head and the sleeve, as well as the distance between the positioning head and the pull key mandrel, oblique and positive have an impact on the pull key angle. Therefore, how to ensure the precision of key pulling fixture is very important

in terms of processing operation, the operating procedures are formulated to eliminate some human factors, such as whether the operator cleans the workpiece positioning surface, whether there are iron filings and sundries on the key pulling positioning surface, and whether the workpiece positioning surface is close to the fixture positioning surface. Through various efforts, the key pulling angle of the keyway is ensured

(4) in order to ensure the accuracy and convenience of keyway angle inspection and meet the requirements of mass production, technicians designed an angle inspection instrument that converts the keyway angle error into a dial indicator to directly reflect the reading. The tester has the advantages of simple operation, high measurement accuracy, intuitive and easy to master. It can directly judge whether the keyway angle is qualified or not, greatly improve the production efficiency and ensure the relative stability of the keyway angle accuracy. The disadvantages are high accuracy, difficult identification and high price

conclusion

based on the above several important links of gear processing, it is not difficult to see that the selection and control of processing process plays a decisive role in the processing accuracy and quality of products. Therefore, advanced technology symbolizes the technical strength and technical level of an enterprise. The determination of technology in the processing process determines the quality, production efficiency and economic benefits of products