PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Internal Spline Gears Heat Treatment Process

1.Technical parameters and processing technology of internal spline gears

1.1 Technical parameters and structure of internal spline gear

Gear internal spline parameters: module: m=1.25, number of teeth: z=30, pressure angle: α=20°, major diameter: D=40, major diameter: d=37.5, measuring rod diameter: dp=2.61, span Bar distance diameter: M=34.657-34.753, material: 20CrMnTi, heat treatment: carburizing and quenching S0.7～C59.

2. Internal spline gear heat treatment process

2.1 Normalizing process and control

For the internal spline gear of 20CrMnTi, the isothermal normalizing process is required, and the normalizing temperature is required to be 880°C higher than the final heat treatment carburizing temperature, and the normalizing temperature is controlled to 930°C, which can effectively control the heat treatment deformation. In order to fully eliminate the residual stress of the forging billet, refine the grains and reduce the deformation of the internal spline gear during the final heat treatment, the normalizing holding time is controlled at 1 hour. The control of the normalizing cooling rate is to obtain suitable normalized hardness and more uniform normalized structure and improve cutting performance. And it is required to adjust the cooling method according to the weather and season, control the normalizing hardness HB160-207 and the hardness difference, and control the normalizing metallographic structure level 3.

2.2 Cold working drawing spline process and control

Through multiple broaching tests, in the horizontal broaching machine, no matter the positioning of the large end face of the gear or the end face of the small lap, due to the thin wall thickness of the small lap end, plastic deformation occurs, and the span M value of the small lap end should be small 0.01 ~ 0.02mm, resulting in axial taper. In vertical broaching, the axial taper of the internal spline is smaller, and the consistency of the M value across the rod distance is more stable. Through multiple cold and hot coordination tests and re-adjustment of the size of the broach, it is ensured that the requirements of the drawings are met after heat treatment. Specified broaching process: use a vertical broaching machine to pull the internal spline, adjust the size of the broach to M=34.78-34.81, select the broaching speed of 1.5-1.8m/min, pay close attention to the surface quality of the internal spline during the broaching process, and promptly regrind or replace the broach.

2.3 Heat treatment process and control

The heat treatment process of the internal spline gear is processed on the SIMUWU vacuum heat treatment furnace equipment. The heat treatment adopts the process of carburizing and direct quenching after cooling. Low temperature tempering is performed after quenching.

Carburizing and quenching, as the final heat treatment process of internal spline gears, is the most important part of gear deformation and a crucial process to control gear heat treatment deformation. Therefore, on the basis of the conventional carburizing and quenching process for the internal spline gear, the following process improvement measures are taken:

(1) Carburizing temperature.

The thermal stress is caused by the temperature difference between the inside and outside of the gear. During the carburizing process, the temperature of the outer surface of the gear is the highest, and the temperature of the inner spline is the lowest, and the temperature difference can reach 200 °C. Due to the high temperature of the outer surface of the gear, the volume expands, resulting in compressive stress on the core; while the core temperature is low, the expansion is small, and tensile stress is generated on the surface. Therefore, in order to reduce the deformation carburizing temperature, the original 900°C was adjusted to 880°C.

(2) Quenching temperature.

The higher the quenching temperature, the greater the structural stress and the greater the deformation during the quenching process. Therefore, in order to reduce the deformation, when selecting the quenching temperature, it is necessary to ensure that there is no non-martensitic structure in the infiltrated layer. On the premise of ensuring the hardness of the gear, try to choose a lower quenching temperature. A quenching temperature of 840°C was chosen for this purpose.

(3) Furnace loading method.

When other process parameters are stable, the furnace loading method and compensation measures are very important. The traditional stacking method is adopted: due to the large contact surface of the gear, the uniformity of the temperature of each workpiece in the furnace and the fluidity of the carburizing atmosphere are reduced. At the same time, when quenching, it is difficult for the quenching oil to penetrate uniformly, so this way of loading the furnace, the deformation of the spline in the gear is large. Adopt “X” mandrel hanging: change the stacking to hanging to ensure the uniformity of the temperature of each workpiece and the smooth flow of the carburizing atmosphere, so that the infiltration layer on the surface of the gear is more uniform. During quenching, the quenching oil can also penetrate more uniformly, and the test results show that the deformation of the hanging installation is smaller than that of the stacked installation. Adopt “X” mandrel hanging and compensation sleeve: due to the asymmetry between the large end of the internal spline gear and the lap end, the wall thickness of the small lap end is thinner, the cooling speed is fast during quenching, and the internal spline at the corresponding end shrinks greatly. Axial taper is caused. In response to this phenomenon, a compensation sleeve is placed on the outer circle of the small lap of the gear, and the “X” mandrel is used to hang it, so that the shrinkage of the internal spline is effectively controlled during carburizing and quenching. It also slows down the quenching and cooling speed of the splines in the small lap end and reduces the axial taper. Through multi-batch production, the improvement of the process has achieved satisfactory results: the variation of the M value of the internal spline is controlled within 0.08mm, which meets the requirements of the drawing; the axial taper of the internal spline is controlled within 0.05mm. The detection pass rate of the spline comprehensive plug gauge is over 98%. Meet the product quality requirements.