Before machining the straight bevel gear to split the wheel blank, first measure the flatness of the upper and lower surfaces of the straight bevel gear blank, the perpendicularity of the two end faces and the diameter of the inner and outer circles of the wheel blank with a coordinate measuring instrument. During the measurement, take the lower surface of the straight bevel gear blank as the benchmark, select four characteristic lines along the width direction of the straight bevel gear to split the wheel blank, and take points at an interval of 3mm on the selected characteristic line, Then measure the spatial coordinates of each point in turn, and the CMM will automatically calculate the flatness and verticality of each plane relative to the bottom surface of spur bevel gear blank through the coordinate values of these points. Since the indoor temperature during the measurement is maintained at about 20 ℃, the influence of temperature change on the deformation of split spur bevel gear blank is not considered. From multiple spatial coordinate values measured by the CMM, it can be inferred that there is basically no deformation of spur bevel gear blank before machining.
After the measurement of straight bevel gear split wheel blank is completed, place the straight bevel gear split wheel blank on the machine tool workbench for clamping, align and set the tool according to the previously defined programming origin position, import the corresponding NC program into the machine tool, and process the tooth groove in the middle of the straight bevel gear blank according to the process sequence of rough machining first and then finish machining, as shown in Figure 1. After the machining of the tooth groove in the middle of the straight bevel gear blank is completed, the straight bevel gear split blank is unloaded from the workbench and placed naturally for more than one day. At this time, the residual stress in the straight bevel gear split blank is redistributed, and the measurement results are relatively accurate. According to the method of using coordinate measuring instrument to measure the straight bevel gear blank before machining, the corresponding feature point coordinates after machining are measured again, and the position tolerance value of straight bevel gear blank is automatically calculated. From the measured spatial coordinate values, it can be inferred that the middle position of the straight bevel gear blank is concave after machining, and the maximum deformation of the middle position of the straight bevel gear blank along the thickness direction can reach 0.058mm.
After the second measurement by the coordinate measuring instrument, continue to use the previous processing method to process the straight bevel gear split blank with the middle tooth groove cut off. The sequence of processing the tooth groove is to process the straight bevel gear blank from the middle to the right until the right half of the straight bevel gear split blank is processed. After machining, divide the straight bevel gear and place the wheel blank for a period of time, and then conduct the third measurement with a CMM, as shown in Figure 2. From the measured spatial coordinate values of the straight bevel gear blank, it can be concluded that after the right half of the straight bevel gear blank is processed, the processing position is obviously concave downward, and the maximum deformation of the straight bevel gear blank along the thickness direction can reach 0.097mm.
After the third measurement by the coordinate measuring instrument, continue to cut the straight bevel gear blank of the right half from the middle to the left on the NC machine tool until the whole straight bevel gear blank is finished. Place the processed straight bevel gear blank for a period of time, and then put the blank on the CMM for the fourth measurement, as shown in Figure 3. From the measured spatial coordinate value of spur bevel gear blank, it can be inferred that the whole spur bevel gear blank is concave in the middle and warped at both ends after machining, and the maximum deformation of spur bevel gear blank along the thickness direction can reach 0.137mm.
The data such as the position tolerance of the straight bevel gear split blank and the diameter of the inner and outer circles measured by the CMM each time are listed in the table, as shown in the table. The design diameters of the inner and outer circles of the straight bevel gear blank before machining are 1000mm and 1200mm, and the design included angle of the left and right end faces of the straight bevel gear blank is 36 °. From the data in the table, it can be seen that the straight bevel gear blank is not machined during the first measurement, and the dimensional data measured by the coordinate measuring instrument has less deviation from the original design dimensions. At this time, the flatness and perpendicularity tolerance of the straight bevel gear blank are also small. However, with the continuous processing, the position tolerance and inner and outer circle diameter of straight bevel gear have changed significantly.
| Parallelism of upper surface of wheel blank | Perpendicularity of left end face of wheel blank | Perpendicularity of right end face of wheel blank | Outer diameter of wheel blank | Diameter of inner circle of wheel blank | Clamp at left and right ends of wheel blank | |
| First measurement | 0.038 | 0.016 | 0.016 | 1200.001 | 1000.001 | 36.009° |
| Second measurement | 0.077 | 0.019 | 0.017 | 1200.028 | 1000.002 | 36.005° |
| Third measurement | 0.121 | 0.026 | 0.025 | 1200.049 | 1000.049 | 35.996° |
| Fourth measurement | 0.161 | 0.031 | 0.028 | 1200.072 | 1000.071 | 35.989° |