Deformation control of carburized gear heat treatment

The heat treatment deformation of carburized gear directly affects the accuracy, strength, noise and life of the gear. There are many factors affecting the deformation of carburizing heat treatment, and only controlling the factors can control the deformation to a small degree. Controlling gear deformation must also be addressed throughout the manufacturing process.

(1) the influence of metallurgical factors of gear material on deformation tests show that the higher the hardenability of steel, the greater the deformation. When the hardness of the part is higher than 40HRC, the deformation will increase significantly. Therefore, there are certain requirements on the hardenability of steel, the narrower the hardenability belt, the more stable the deformation, to the steel mill to provide "low, stable deformation" steel. A1/N content ratio is controlled within the range of 1 ~ 2.5, which can narrow the quenchability zone and reduce deformation (mitsubishi steel plant type assembly). In addition, the box segregation and banded structure of the material affect the uneven deformation and carburizing of gear spline holes.

(2) effect of preparation heat treatment on gear deformation normalizing hardness too high, mixed crystal, a large number of sostenitic or weidner structure will increase the deformation of the inner hole, so we should use temperature-controlled normalizing or isothermal annealing to deal with forging.

(3) influence of carburizing process on deformation temperature uniformity: the uniformity of the carbon layer and the temperature uniformity of the cooling medium affect gear deformation; meanwhile, the higher the carburizing temperature, the thicker the carburizing layer; the lower the oil temperature, the greater the gear deformation. Therefore, it is necessary to improve the equipment, optimize the process and improve the quality of gear heat treatment.

Quenching cooling behavior is the most important factor affecting gear deformation. The quenching deformation of hot oil is smaller than that of cold oil, generally controlled at 100℃±120℃. The mixing mode and intensity both affect the deformation, and the plate gear quenched by the top quenching press shall be adjusted according to the deformation of various gears. The parameters of the blanking press shall be adjusted to reduce the deformation, and the pressure of the inner and outer pressing dies and expanding core blocks, the oil injection amount of each section and the top table shall be adjusted to control the deformation.

(5) the clamping methods and fixture purpose to make uniform heating cooling, work uniform workpiece parts carburized layer, in order to reduce the thermal stress, organizational stress, to reduce the deformation, can change the way the clamping, plate parts and the oil level of the vertical shaft parts made, using the compensation washer, bearing washer, stack washer and so on, spline parts available carburized spindle etc.

(6) cooperation in mechanical processing: first, master the deformation law of heat treatment and the position of moving tolerance zone to improve the pass rate of products; Second, according to the law of deformation, apply anti-deformation, shrinkage end pre-expansion hole, improve the qualified rate of deformation after quenching. Third, for the asymmetric or non-uniform thickness parts to use the method of reserved processing. Fourthly, after heat treatment, spline hole is refined with push knife, or fine grinding spline hole through electrochemical machining, or after carburizing, the mandrel is heated and quenched, and the mandrel is pressed out to ensure the size of spline hole and other means to reduce deformation.

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