Shanghai Tractor internal combustion engine Co., Ltd. studied the spline hole distortion of xf-125 primary transmission gear, carried out tests from the aspects of raw materials, heat treatment process and cold working stress, explored many influencing factors of spline hole shrinkage, and took corresponding technical measures to solve this technical key. Research shows:
1) The banded and widmanstatten structure of raw material tooth blank directly affect the distortion of gear spline hole after carburizing and quenching. The absolute distortion of gear spline hole with banded structure of grade 4-5 and widmanstatten structure of grade 3 is about 0.08mm. Therefore, among the factors causing distortion, the microstructure level of raw material tooth blank is one of the important factors.
2) Cold working stress is particularly sensitive to the distortion of spline hole of primary traditional gear after carburizing and quenching. Press and print on the gear end face to double the distortion of the spline hole, and the absolute distortion is about 0.1mm.
3) Quenching temperature, quenching oil, cooling mode and clamping method all affect the spline distortion of primary transmission gear, but the influence is smaller than that of raw materials and cold working stress. Quenching temperatures of 880 ℃ and 910 ℃ have no obvious effect on the distortion of spline hole of primary transmission gear. CMH clamping method based on thermal stress makes the spline hole of primary transmission gear swell; Ch method clamping based on tissue stress can reduce the spline hole of primary transmission gear.
4) the best carburizing and quenching process to reduce or control the distortion of spline hole of primary transmission gear is as follows: carburizing at 910 ℃, isothermal at 8 20 ℃ and oil quenching at 35 ℃.
The tooth blank shall ensure that the banded structure is ≤ grade 1; Widmanstatten tissue grade 0; The grain grade is 5-8. Without additional increase of cold working stress, the absolute distortion of spline hole is about 0.04mm at 35 ℃ oil quenching and about 0.05mm at G oil quenching.