Taking the 80mm thick straight bevel gear blank model as an example, the x-direction stress nephogram of the upper surface during the processing of straight bevel gear blank is shown in Figure 1. In Figure 1, the picture on the left represents the stress change of straight bevel gear blank when mode 1 is selected, and the picture on the right represents the stress change of straight bevel gear blank when mode 2 is selected. It can be seen from the figure that the compressive stress on the upper surface of the straight bevel gear blank before processing is about – 15MPa. After processing, the machined tooth top in the upper surface processing area of the straight bevel gear blank with two processing methods is subjected to about 2MPa tensile stress. The position of the upper surface close to the left and right ends of the straight bevel gear blank is almost free from stress, and the stress on both sides of the tooth groove and the position of the upper surface close to the processing area is almost reduced to 0, The compressive stress on the upper surface far from the machining position decreases slightly. After the two processing methods are selected, the stress distribution on the upper surface of the straight bevel gear blank is the same, and the bottom of each tooth groove is subjected to a compressive stress of about – 15MPa.
When two different processing methods are selected, the stress nephogram in X direction on the bottom surface of straight bevel gear blank is shown in Figure 2. It can be seen from the figure that before machining, the bottom and upper surfaces of straight bevel gear blank are subject to compressive stress of about – 15MPa. After processing, although the bottom surface of the wheel blank in mode 1 is not processed, the compressive stress on the bottom surface is released from left to right in the process of processing. When mode 2 is selected for processing, when the tooth groove in the middle of the straight bevel gear blank is cut off, the stress in the middle and left and right ends of the bottom surface of the straight bevel gear blank is almost completely released, and the compressive stress on the bottom surface of the straight bevel gear blank gradually begins to release as the processing continues. After processing, the stress state of the bottom surface of the straight bevel gear blank corresponding to the two processing methods is the same. In the figure, the yellow green area at the left and right ends of the bottom surface of the straight bevel gear blank is subjected to a tensile stress of about 2MPa, and the stress at other positions on the bottom surface approaches zero.
In order to more clearly analyze the stress change inside the straight bevel gear blank during the machining process, the straight bevel gear blank is cut along the x-axis direction. The stress nephogram of the straight bevel gear blank section before machining is shown in Figure 3, and the stress of the straight bevel gear blank section during the machining process is shown in Figure 4. It can be seen from Fig. 4 that the stress in the material before processing of the split straight bevel gear blank is only related to the thickness of the straight bevel gear blank, the surface compressive stress of the straight bevel gear blank and the internal material tensile stress. When the processing starts, the compressive stress near the bottom of the processed tooth groove is about – 15MPa, the stress at the position originally subject to the maximum tensile stress inside the processed tooth decreases from about 15MPa to about 8Mpa, the position originally subject to the large tensile stress under the tooth groove moves down slightly, and the number of tensile stress decreases slightly, and the compressive stress near the dark blue area near the lower surface of the straight bevel gear blank is released, From about – 15MPa to about – 8Mpa. In the whole machining process, there is no obvious change in the internal stress of the straight bevel gear blank section in the unprocessed area, and the stress on the green part of the section is very small. From this point of view, the stress distribution after processing in two different ways is the same.
Cut the straight bevel gear blank along the width direction to observe the stress distribution of the blank from another angle. The x-direction stress nephogram of the section is shown in Figure 5. Among them, figure a shows the stress nephogram of the straight bevel gear blank section before machining, figure B shows the sectional stress nephogram from the top of the tooth, the blue-green area near the top and root of the tooth in Figure B shows the compressive stress of about – 5MPa, and the yellow area between the top and root of the tooth shows the tensile stress of about 6Mpa. Compared with before machining, the compressive stress of the top of the tooth is reduced by 10MPa, and the tensile stress between the top and root of the tooth is reduced by 9Mpa, The position of the tooth root is subject to a small tensile stress before machining and becomes subject to a large compressive stress after machining. The position of the straight bevel gear blank close to the lower surface is subject to a compressive stress of about – 15MPa before machining and the compressive stress is reduced to – 8Mpa after machining. The red area in Figure B indicates that the tensile stress of about 14.8mpa is little different from that before machining. Figure C shows the sectional stress nephogram from the bottom of the tooth groove. The area near the tooth groove shown in blue indicates that it is subjected to a compressive stress of about – 8Mpa. The material inside the straight bevel gear blank near the lower surface shown in red is subjected to a tensile stress of about 14.8mpa. The area shown in green in the figure is subjected to a small stress.
After processing in mode 2, the straight bevel gear blank is cut along the width direction. The stress of the straight bevel gear blank section during processing is shown in Figure 5. Comparing Figure 6 with figure 5, the stress distribution of straight tooth section and cogging section in the two figures are basically the same.
From the above analysis, it can be concluded that no matter which processing method is adopted, the internal stress in the X direction of the material adjacent to the gear cutting area of the straight bevel gear blank changes greatly during the processing. The maximum degree of stress change is that the processed tooth groove bottom is subject to a small tensile stress before processing, while after processing, it is subject to a compressive stress of about – 15MPa. The compressive stress on the surface of the split wheel blank is almost completely released during the processing. The compressive stress of the material close to the lower surface of the straight bevel gear blank decreases from about – 15MPa to about – 8Mpa, and the tensile and compressive stress inside the processed tooth decreases significantly; Before machining, the part of the material with the maximum tensile stress between the tooth groove bottom and the lower surface of the straight bevel gear blank changes little after machining, and the compressive stress on the surface of the straight bevel gear blank is almost completely released in the machining process.
