RV reducer has the advantages of high precision, small return difference, good rigidity, wide range of transmission ratio, etc., and is an ideal choice for robot joint reducer. As the core component of the RV reducer, the processing quality and accuracy of the cycloidal wheel directly determine the transmission accuracy of the RV reducer. Scholars at home and abroad have made some research results on the tooth profile of RV reducer cycloidal wheel. Ke Qingxun et al. conducted a first-class and experimental study on the distribution of the temperature field of the cycloid gear in the forming and grinding processWang Jianing et al. studied the relationship between the basic tooth shape parameters of the cycloidal wheel and the meshing stiffness of the RV reducerWang Wentao and Xu Honghai studied the influence of various parameters of cycloid tooth profile on its transmission performanceZhang Yueming et al. studied the optimization and parametric design of the cycloidal gear tooth shape in the RV reducer, and carried out the research on the grinding process of the cycloidal wheel of the RV reducer.
For the grinding of gears, Ming Xingzu et al. studied the optimization of the grinding process parameters of face gearsGuo Hui et al. expounded the method of using a six-axis CNC worm grinding wheel gear grinding machine to grind face gears. There are not many studies related to cycloidal gear processing. In recent years, with the rapid application and development of robot equipment in China, the high-precision motion requirements of the equipment have put forward higher requirements for the machining accuracy of the cycloidal wheel, so the author of this paper studies the surface quality of the cycloid wheel after precision machining, especially the influencing factors of surface roughness.
At present, there are generally two grinding methods for cycloidal tooth profiles: forming method and expansion method. Forming grinding is a method of grinding the tooth surface of the gear tooth after trimming the cross-section profile of the grinding wheel shaft to have the same profile as the single-tooth coaring of the cycloidal wheel, and is widely used for gear tooth surface finishing because of its machining accuracy of more than 4 years. The authors of this paper used the forming method to grind the cycloidal tooth profile and studied the effect of grinding parameters on the surface integrity of the 20crmnti cycloidal tooth profile grinding process.
1.Experimental design.
The material of the cycloidal wheel used in the test is 20crmnti, its chemical composition is shown in Table 1, the corresponding mechanical properties are shown in Table 2, and the geometric parameters and structural diagram of the cycloidal wheel are shown in Table 3 and Figure 1 respectively. The test machine tool is a universal cylindrical grinder M1432B-1000, the grinding test site is shown in Figure 2, the grinding method is reverse grinding, cooling by water-based emulsion, and the grinding wheel adopts a single crystal corundum grinding wheel, the particle size numbers are respectively, medium soft grade, ceramic bond, single crystal corundum is widely used in the surface processing of materials with high toughness and high hardness due to its strong crushing resistance and toughness.
The author used the orthogonal test method, selected the orthogonal table L16 45, and studied the influence of four factors on the surface integrity, such as the linear speed of the grinding wheel, the grinding depth, the axial feed rate of the cycloidal wheel and the particle size of the grinding wheel, and selected the orthogonal test factors and levels of grinding as shown in Table 4, the grinding wheel speed n range was 2000 3200 r min, and the grinding depth ap range was 002 ～0.12mm, cycloidal feed speed vf range is 12～2.8m/min。The orthogonal test results are shown in Table 5. In the test, the OUGHSCAN high-precision surface structure measuring instrument was used to measure the surface roughness of the cycloidal wheel after processing, and five parts were selected at equal distances along the axial feed direction, and the sampling length was 10mm, the assessed length is 50 mm, the measurements are recorded in Table 5.
2.Analysis of test results.
As can be seen from Table 5, the surface roughness is obtained from 023~0.A series of cycloidal wheels of 55 m machined surfaces. From the extremely poor results, it can be seen that the grinding wheel particle size has the greatest influence on roughness, followed by the grinding wheel speed and grinding depth. The least affected is the cycloidal feed rate. Further analysis of the orthogonal test results showed that the relationship between the surface roughness of the 20crmnti steel cycloid wheel and the linear speed of the grinding wheel, the feed rate of the cycloidal wheel, the grinding depth and the particle size of the grinding wheel after grinding was obtained.
The effect of grinding wheel speed on the roughness of the cycloidal tooth profile is plotted in Figure 3 in the orthogonal test, which can be seen from the orthogonal table and Figure 3: In general, with the increase of the grinding wheel speed n, the grinding surface roughness A value will decrease. The main reason is that with the improvement of the grinding ability of the grinding wheel on the tooth surface profile of the cycloidal wheel, the friction between the grinding wheel and the tooth surface contact trace decreases, and the trajectory distance between adjacent contact traces becomes smaller, resulting in the increase of the density of the trace and the reduction of the roughness of the cycloidal tooth surface. And the roughness obtained when the grinding wheel grain size is 60 mesh is generally greater than that of the grain size of 220 mesh, because the larger the particle size number, the more abrasive grains pass through the screen hole per unit length of the grinding wheel, the smaller the abrasive particle size, and the more favorable the surface roughness.
In Fig. 3, when the grinding wheel grain size is 60 mesh, the surface roughness slowly decreases with the increase of rotational speed, and when the grain size is 220 mesh, the surface roughness A value fluctuates and decreases with the increase of rotational speed, that is, it increases slightly at 2800 r min and then decreases, and a smaller surface roughness of 023μm。This is because the increase in the linear speed of the grinding wheel will increase the number of cuts per unit time of the abrasive cutting edge, that is, reduce the single cutting time of the abrasive cutting edge, thereby reducing the residual protrusion height left on the machined surface after the material is removed by the two adjacent grinding cutting edges, which also helps the diffusion of grinding heat, so it will lead to a decrease in the surface roughness value.
Effect of cycloidal feed rate on cycloidal tooth profile roughness.
The results of the influence of the cycloidal feed rate on the roughness in the orthogonal test are plotted as Figure 4, and it can be seen that the value of surface roughness a increases with the increase of the axial feed rate of the cycloidal wheel, regardless of the particle size of 100 mesh or 150 mesh. The reason for this is that with the increase in the feed rate of the cycloidal wheel. The number of abrasive cutting edges on the grinding tooth surface per unit time decreases, so that the grinding residual height formed on the tooth surface per unit area increasesIn addition, with the increase of axial feed rate, the flutter of the grinding machine also increases, which will also have a certain impact on the roughness of the cycloidal wheel, so that the roughness value has a tendency to increase.
Increasing the feed rate of the cycloidal wheel has the opposite effect of increasing the linear speed of the grinding wheel, which will increase the amount of material removed between the two adjacent abrasive cutting edges, and increase the height of the residual bump left on the machined surface, resulting in an increase in the surface roughness value.
Effect of grinding depth on cycloidal profile roughness.
The effect of the cycloidal feed rate on the roughness in the orthogonal test is plotted as Figure 5, and it can be seen that the cycloidal tooth surface becomes coarser as the grinding depth increases. This is due to the fact that the increase in grinding depth will increase the maximum cutting thickness of a single abrasive grain, thereby increasing the plastic deformation of the cycloidal tooth surface, so that the depth of the cut marks left on the gear surface when the abrasive grain cutting edge passes through the grinding work area will also increase, so the tooth surface roughness value will also increase.
At the same time, from the analysis of the grinding principle, the increase of grinding depth will increase the number of cutting edges of abrasive grains involved in grinding at the same time, resulting in an increase in grinding force and a rapid increase in grinding temperature, which will reduce the grinding surface quality. However, from the above test results, although the overall surface roughness value increases with the increase of grinding depth, the effect of the change of grinding depth on the surface roughness is not very obvious. This is due to the fact that in the actual grinding process, the grinding amount is slowly fed to the final grinding depth, rather than directly grinding at the grinding depth at one time.
The effect of grinding wheel grain size on the roughness of cycloidal tooth profile.
As can be seen from Table 5, the grinding wheel particle size has the greatest influence on the surface roughness, and Figure 6 shows the relationship between the grinding wheel particle size and the surface roughness drawn according to the test results.
From the experimental results, it can be seen that the tooth roughness of the cycloid wheel decreases with the increase of the grinding wheel particle size. This is because the larger the grinding wheel particle size, the smaller the diameter size of the abrasive grains, the more abrasive grains per unit area on the grinding wheel surface, the number of abrasive grains actually participating in grinding increases, and the cutting height of the abrasive grains decreases, so that the surface roughness value is reducedAt the same time, the larger the grinding wheel particle size, the smaller the spacing of the cutting marks on the machined surface, the shallower the scratches, thus also reducing the surface roughness;In addition, the greater the number of abrasive grains involved in grinding at the same time, the smaller the grinding force is on each abrasive grain, which reduces the surface roughness value and contributes to the improvement of the machined surface quality.
3.The first model and test verification of grinding surface roughness.
From the above analysis, it can be seen that when the grinding wheel particle size is larger, the better the finishing effect, the grinding wheel with a particle size of 150 mesh is selected and tested with different grinding parameters to obtain the grinding surface roughness data of cycloidal gears, and the test results are regressed and the roughness model is modeled in the form of power function.
where: k, , are all undetermined constants.
By regression of multiple linear equations, the 4 undetermined constants in Equation (1) can be obtained, resulting in a model of the grinding surface roughness of the Cycloidal Tooth Surface at a grinding wheel grain size of 150 mesh**, as shown in Equation (2).
The model range is the range of 3 experimental factors in the orthogonal test.
In order to further verify the effect of the surface roughness model, the test measurements were compared with the values, and the results are shown in Table 6.
As can be seen from Table 6, the relative error between the surface roughness of the cycloid tooth surface ** and the measured value is 195%~5.1%, the maximum relative error is 51%, illustrating that the model of grinding surface roughness of the cycloid tooth surface in the text has a good effect. Therefore, the surface roughness model established by the author of this paper can provide a theoretical reference for the analysis of the surface quality of the precision machining of the cycloid tooth surface.
Through the orthogonal test of grinding of 20crmnti steel cycloid tooth surface, the influence of grinding wheel linear speed, cycloidal feed rate, grinding depth and grinding wheel particle size on the surface roughness of cycloidal wheel tooth surface was analyzed, and the first-class model of cycloidal tooth surface roughness was established on the basis of the test. The conclusion is as follows:
1) The grinding wheel particle size is the biggest factor affecting the grinding surface roughness of the tooth surface of the cycloidal wheel, the influence of the rotation speed of the grinding wheel is secondary, the influence of the grinding depth is small, and the influence of the axial feed rate of the cycloidal wheel is the smallest.
2) The surface roughness can be reduced by selecting the grinding wheel with larger particle size, increasing the rotation speed of the grinding wheel and reducing the grinding depth, and the increase of the feed rate of the cycloidal wheel makes the surface roughness show a tendency to increase as a whole, but the effect of enlargement is not obvious.
3) When grinding with a 150 mesh grit grinding wheel, the grinding wheel speed n = 3200r min and the cycloidal wheel feed rate vf = 12m min, grinding depth ap = 0At 12 mm, the cycloidal tooth surface has a lower surface roughness and better surface quality.
4) The model has a high effect, and the maximum relative error between the model and the measured value affected by surface roughness is 51%, which provides a test basis and reference for the reasonable selection of grinding parameters for actual machining.
References omitted.