Gear precision forging technology – die manufacturing and gear measurement

The precision of cold forming die is the key of gear precision forging technology. At present, the analysis method has developed to a certain level, which can consider a variety of influencing factors and accurately design the mold. However, there are still many difficulties in manufacturing high-precision dies, especially the teeth of gear precision forging dies. Because of the elastic recovery of the gear and the elastic deformation of the die, the gear profile of the die is no longer a standard involute.

Therefore, the data provided to the mold manufacturer is not the standard parameters of the gear, but the data coordinates describing the contour, which usually requires an accuracy of 5 μ Within M. The die of spur gear can be processed by wire cutting; However, the die of helical gear needs electrochemical machining. Wire cutting processing can be close to 5 μ M, but this exceeds the accuracy of general ECM. It must be noted that the profile is not a standard gear. In the mentioned research topic, the mold manufacturing has been processed and modified more than twice.

Another key of gear precision forging technology is measurement, including die and gear measurement. Because the teeth of the die are non-standard gears, a standard gear cannot be used for comparison and measurement, and there are errors in modulus and other parameters. The key difficulty in measuring forged gears is the lack of accurate reference. The inner hole of gear is used as the benchmark for gear machining and measurement. However, the accuracy of gear inner hole obtained by gear forging method is limited and can not be used as the benchmark for measurement. In fact, only gear teeth have precise characteristics. Therefore, if the standard gear measuring equipment is used to measure the forged gear, it is difficult to avoid the positioning error. There is often a case that the contour can be measured accurately and meet the accuracy requirements, but it is difficult to determine its accuracy level.

After years of experience in gear forging and recent experiments with warm forging and cold treatment, we have the following experience:

1) A set of universal dies can be used for precision forging of various gears and proved to be effective in single action single crank press;

2) There are mature design methods to ensure the accuracy and consistency of gear hot and warm forging, such as making the contour size have a cold machining allowance of 0 ∙ 1mm ~ 0 ∙ 2mm;

3) The cold forming (finishing) process can be analyzed in detail by modern means, and a variety of influencing factors, including material, geometry and size, die deformation and lubrication, can be considered, so as to accurately design the die;

4) After cold forming treatment, hot and warm forged gears can reach the accuracy of iso6 ~ 5;

5) There is still a lot of work to be done in die processing and die and gear measurement.

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