It is very difficult to deal with the tooth surface defects after finishing. When the precision of large cast steel gears is not very high, the thermal deformation of repair welding after finishing can also be ignored. However, with the progress of science and technology, the requirements for product accuracy are higher and higher. In many cases, large deformation after finishing is not allowed. Even if a margin of 1-2mm is left after tooth milling, and then magnetic particle or penetration flaw detection is carried out, the defects are repaired in time. If the amount of repair welding is too large, there will be large deformation, affecting the accuracy of large cast steel gears, which brings great difficulty to repair welding.
The traditional process is to carry out ultrasonic flaw detection after rough machining the outer circle, then carry out heat treatment, and then turn the outer circle, then mill the teeth and leave a few millimeters of allowance, magnetic particle or penetration flaw detection, and finish milling the teeth after dealing with the flaw detection defects. Sometimes, a rough turning process is added after heat treatment to remove the black skin and create conditions for ultrasonic flaw detection after heat treatment. After ultrasonic flaw detection, it is found that there is room for treatment of delayed defects. Ultrasonic flaw detection is carried out in accordance with the standard. For defects that do not exceed the standard, the ultrasonic flaw detection report cannot be reflected. However, once these defects with small equivalent and small area are exposed on the tooth surface after tooth milling, the visual inspection, magnetic particle and penetration flaw detection cannot pass, and must be removed and repaired.
The key to the problem is how to deal with these defects that do not exceed the standard through ultrasonic testing. Can the surface defects exposed after milling be reduced as much as possible to reduce the amount of repair welding, so as to achieve the purpose of reducing deformation?
Improving the processing technology is the first way people think of. The most common method is to add a milling process before heat treatment. This method is often used in the production of quarter large cast steel gears. The improved process is to turn the outer circle and then mill the teeth before heat treatment, mill the tooth surface to half the tooth height, and then carry out magnetic particle or penetration flaw detection process. The defects detected by surface flaw detection are repaired and welded, and then carry out heat treatment process. This method can repair a large number of welding, is not afraid of deformation, and will not affect the accuracy of cast steel large gears. However, because of the outer circle of milled teeth, the surface shape is complex and the stress is concentrated, it is easy to produce more defects.