Gear material and processing process
|Gear material and processing process The gear made of 20CrMo steel material is hardened and hardened after carburizing and quenching. The internal hardness of the gear is low, it can withstand large contact stress and bending stress, and has small deformation after quenching. advantage. It is widely used in the manufacture of gears for gears in automobiles and high-precision machine tools.|
In view of the current situation, this experiment uses 20CrMo steel as experimental material for simulation experiments.
The process route is: heat treatment (carburizing and quenching), hot rolling (heat preservation) cooling of tooth roughing (hobbing, gear shaping). The specific process is as follows: after pre-machining and hobbing of 20CrMo gears, carburizing, high-frequency induction heating to AC3 (875) austenitizing temperature, rapid oil cooling to 150-250, precision in hot oil, extrusion The wheel plastically deforms the surface of the tooth to the final size, and the roll is over. When the workpiece is still in the austenitic state, the workpiece is taken out and rapidly cooled to form a hard martensite structure on the tooth surface.
First, the relationship between the tooth angle and the position of the meshing is derived.
The rolling die and the workpiece gear are set to be standard installation, and the gear teeth are rotated counterclockwise under the driving of the rolling die teeth. The position of the broken line of the teeth in the figure is set to the neutral position, and an off angle j1 is generated when the teeth deviate from this position.
At the neutral position j1 = 0, j1 is a positive value when the teeth are deflected counterclockwise with respect to the neutral position, and a negative value when the clockwise is deflected.
The case of the meshing point on the left flank is similar.
Can write the relationship between each position parameter
Right flank: j1=j1/20-j1(1)
Left flank: j1=i1-0-j1/2(2)
Further derivation jj1=j1-j1/2(5)
According to the value range of the tooth rotation angle, it can be known from the above formula that the relationship between j1 and jj1 and rj1 is uniquely determined.
By the same method, the relationship between i1 and ii1, ri1 on the left tooth surface can also be obtained. In fact, i1=j1. Therefore, as long as j1 is given, the positions of the meshing points i and j of the workpiece teeth on the left and right meshing lines are completely determined. In addition, the j-point on the rolling die tooth has a meshing circle radius rj2=rb22j22 (7) where rb2 is the base circle radius of the rolling die tooth;
J2 is the radius of curvature at point j on the rolling die teeth.
Therefore, the position of the j point on the rolling mold teeth can be determined by the formula, and the corresponding position parameters such as jj2, xj2 and j2 are obtained.
According to the Hertz elastic contact deformation theory, the elastic deformation amount at the meshing point j e=115FfBE(10) The plastic deformation amount Sp of the workpiece tooth surface at the contact point can be calculated by the slip line field theory. Sp103=jFjkB2bjFjkBcj(11) Where is the combined radius of curvature of the two flank surfaces at the point of engagement j.
Then the total deformation amount j at the j point on the tooth can be expressed as the following formula j=jjijeSp2 (12) where 2 is the elastic deformation at the j point of the tooth surface of the rolling die, and the calculation method and the elastic deformation of the workpiece tooth The same amount; there is an internal transmission chain between the rolling mold and the workpiece gear, and in the case of a constant center distance pressing method, the normal total deformation amount j=S0 is a fixed value, where S0 is the extrusion along the meshing line direction.
Taking the 20CrMo carburized gear widely used in the automotive industry and precision machine tools as an example, this paper proposes a fine roll deformation heat treatment process that combines heat treatment, fine rolling and quenching into a single online processing process, and establishes a roll. The double-sided meshing force model of the teeth during the extrusion process is used to derive the calculation formulas of elastic bending deformation, elastic contact deformation and total tooth deformation of the rolling die and the workpiece.
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