Shot blasting method for strengthening surface of gear

Abstract

The invention provides a shot blasting method for strengthening the surface of a gear. The shot blasting method mainly comprises the following steps: step 1, determining basic parameters of a gear material and dividing a blasted material area; 2, calculating the shot blasting surface coverage rate based on shot blasting parameters such as the shot size, the crater diameter and the shot number; step 3, randomly generating and calculating the spatial position of the multi-shot peening shot; and 4, shot peening strengthening parameter design with the gear surface roughness and the residual compressive stress as targets is carried out. According to the method, the gear roughness and residual stress calculation method is combined, the influence of various shot blasting parameters on the surface strengthening integrity of the gear is analyzed, the tooth surface performance of the gear is improved, and the fatigue life of the gear is prolonged.

Description

Technical Field

[0001] The invention relates to a gear surface strengthening technology, and in particular to a gear surface strengthening shot peening method. Background Art

[0002] The integrated transmission is an irreplaceable part of the vehicle, and its performance directly affects the vehicle's maneuverability, reliability and other performance. Gears are an important part of the integrated transmission, and how to improve their fatigue performance is crucial.

[0003] Shot peening can change the fatigue strength of metal structural parts by introducing residual compressive stress field on the surface. It is widely used in automobile, aviation and other industries because it significantly improves the fatigue life of mechanical structural parts. At present, there is no shot peening process for 20Cr2Ni4A gears in China, and the unclear law of the influence of shot peening parameters on the surface strengthening integrity of gears needs to be solved urgently. Summary of the invention

[0004] The invention provides a shot peening method for gear surface strengthening, aims at the blank of shot peening strengthening process for 20Cr2Ni4A material gear, solves the problem of unclear influence of shot peening parameters on gear surface strengthening integrity, and improves gear tooth surface performance and fatigue life.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A shot peening method for strengthening the surface of a gear comprises the following steps: Step 1: Determine the basic parameters of gear materials and the area division of sprayed materials; Step 2: Calculation of shot peening surface coverage based on shot peening parameters such as shot size, crater diameter and number of shots; Step 3: Random generation and calculation of spatial positions of multi-shot peening projectiles; Step 4: Shot peening parameter design targeting gear surface roughness and residual compressive stress.

[0006] Furthermore, in step 1, the material used for the gear as a typical rotating component is 20Cr2Ni4A material, and the surface of the shot peening material is mainly divided into three areas: area I is a coarse grid area, area II is a shot peening affected area, and area III is a shot center distribution area.

[0007] Furthermore, in step 2, the coverage calculation is to calculate the shot peening coverage for different shot diameters and crater diameters to determine the number of shots required at different coverage rates.

[0008] Furthermore, in step 3, the random.uniform() function is used to obtain the coordinate point of the center of the random pellet in the space directly above the central distribution area of ​​the plate pellets. To ensure that the positions of any two pellets in the space do not overlap, the distance between all the generated pellet center coordinate points is judged based on the loop statement, and the judgment logic is whether the distance is greater than the pellet diameter.

[0009] Furthermore, in step 4, with the gear surface roughness and residual compressive stress as the target, the influence of shot peening strengthening parameters such as shot size, shot peening speed and shot peening coverage on the surface strengthening integrity parameters of 20Cr2Ni4A material is analyzed to obtain a better residual stress field distribution and surface roughness.

[0010] The beneficial effects of the present invention are: (1) The above shot peening method can enhance the surface integrity of the gear and improve the gear tooth surface performance and fatigue life.

[0011] (2) The proposed method can improve the fatigue life of gears and can be extended to other materials and other typical rotating components to enhance the surface integrity and improve the fatigue life. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a division diagram of the sprayed material area of ​​the present invention; Figure 2 is a flow chart of the surface coverage calculation program of the present invention; Figure 3 It is a flow chart of the random generation calculation program of the projectile position of the present invention; Figure 4 is a graph showing the effect of pellet size on surface roughness and maximum residual compressive stress of the present invention; Figure 5 is the effect diagram of the shot peening speed on the surface roughness and the maximum residual compressive stress of the present invention; Figure 6 This is a graph showing the influence of the shot peening coverage on the surface roughness and the maximum residual compressive stress of the present invention. DETAILED DESCRIPTION

[0013] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the specific implementation methods of the present invention are described in detail below with reference to the accompanying drawings.

[0014] A shot peening method for strengthening the surface of a gear involves the following steps: Step 1: The material of the typical component gear of the present invention is 20Cr2Ni4A material, and the plastic parameters of 20Cr2Ni4A material adopt Johnson-Cook model (select Rate dependent when defining the material). This model is applicable to most materials that deform at high strain rates, and the yield limit of the material is expressed by the following formula: (1) in, is the material yield limit; is the material yield stress; is the material strain power coefficient; is the equivalent plastic strain of the material; is the strain hardening exponent; is the strain rate sensitivity coefficient; is the strain influence factor; is the reference strain rate; is the temperature influence factor, is the temperature sensitivity coefficient. At the same time, the material melting point and reference temperature (generally room temperature) need to be set in Abaqus. Other parameters are shown in Table 1: Table 1 Constitutive model parameters of 20Cr2Ni4A material

[0015]

[0016] Considering the calculation time and the fact that the depth of the layer affected by the residual stress of shot peening is generally within 2mm, the size of the 20Cr2Ni4A plate model is 1.5mm×1.5mm×2mm. In order to improve the efficiency of computer calculation, the plate surface is divided into three areas: Area I is a coarse grid area with a size of 1.5mm×1.5mm, Area II is a shot peening affected area with a size of 1mm×1mm, and Area III is a shot center distribution area (the center of the shot is distributed in this area) with a size of 0.75mm×0.75mm. Figure 1 shown.

[0017] Step 2: First, the diameter of a single crater needs to be calculated, 2ap, where ap represents the radius of a single shot crater. In the single shot peening simulation study, by establishing a single shot impact model, changing the peening speed and diameter, the displacement of the plate impact area along the layer depth direction under different initial conditions is obtained, the crater node displacement curve in the calculation results is extracted, and the distance between the two points with zero displacement along the layer depth direction is taken as the size of the crater diameter.

[0018] After obtaining the diameter of the single-shot impact crater 2ap, in order to calculate the shot peening coverage, the surface of the shot peening affected area of ​​the 20Cr2Ni4A plate is equally divided along the x and y directions to generate Nx and Ny nodes, then a total of Nt=Nx×Ny nodes are generated, and then the distance S from each node to the center of all shot spheres is calculated, where the coordinates of the center of the shot sphere are randomly generated by the Python program within the specified range. If S>ap exists for all S, then the node is in the unpeened area. The number of all nodes in the unpeened area is recorded as M, and the coverage rate C=(1-M / Nt)×100%. The developed Python program flow chart is as follows: Figure 2 shown.

[0019] Step 3: Based on Python, the present invention generates random coordinates of the center of the projectile in space, so that the projectile is randomly distributed just above the 20Cr2Ni4A plate collision research area. The coordinates of the center of any projectile ( , , ) satisfies the following relationship: (2) (3) (4) in,( , , )、( , , ) is the spatial distribution range of the projectiles. The centers of any two projectiles ( , , )、( , , ) satisfy the following relationship: (5) In the above formula, D is the diameter of the projectile. The random.uniform() function is used to obtain the coordinate point of the random projectile center in the space directly above the central distribution area of ​​the plate pellets. Figure 3 The calculation program flow of random generation of projectile positions is to generate a spatially randomly distributed multi-projectile model.

[0020] Step 4: (1) The shot peening speed is 60 m / s, the shot peening coverage is 100%, and the impact of 0.3 mm, 0.4 mm, 0.5 mm, and 0.6 mm projectiles are simulated respectively. The residual stress field distribution and surface roughness under different shot sizes are obtained, such as Figure 4 shown.

[0021] (2) Take the projectile diameter as 0.5mm and the coverage rate as 100%, and simulate the impact of the pellets at 65m / s, 70m / s, 75m / s, and 80m / s. The residual stress distribution and surface roughness at different shot peening speeds are obtained, such as Figure 5 shown.

[0022] (3) The shot peening speed is 70m / s, the shot size is 0.5mm, and the shot impact conditions at coverage rates of 100%, 150%, 200%, 250% and 300% are simulated respectively. The residual stress field distribution and surface roughness under different coverage parameters are obtained, such as Figure 6 shown.

[0023] The increase of shot size and shot peening speed is conducive to the increase of residual compressive stress. However, in actual shot peening, under the premise of ensuring the optimization of residual stress field to meet the requirements, the shot size and shot peening speed should be strictly controlled, and the shot peening coverage should be controlled between 100% and 200% to ensure that the surface roughness is within a reasonable range.

[0024] The parts not elaborated in detail in the present invention belong to the known technologies in the art. Any technical solutions formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the present invention.

Claims

1. A shot peening method for strengthening the surface of a gear, characterized in that: The following steps are involved: Step 1: Determine the basic parameters of gear materials and the area division of sprayed materials; Step 2: Calculation of shot peening surface coverage based on shot size, crater diameter and shot number for each shot peening parameter; Step 3: Random generation and calculation of spatial positions of multi-shot peening projectiles; Step 4: Shot peening parameter design targeting gear surface roughness and residual compressive stress.

2. A shot peening method for strengthening the surface of a gear as claimed in claim 1, characterized in that: The gear material is 20Cr2Ni4A material, and the yield limit of the material is expressed by the following formula: （1） in, is the material yield limit; is the material yield stress; is the material strain power coefficient; is the equivalent plastic strain of the material; is the strain hardening exponent; is the strain rate sensitivity coefficient; is the strain influence factor; is the reference strain rate; is the temperature influence factor, is the temperature sensitivity coefficient; The surface of the peened material is divided into three areas: area I is the coarse grid area, area II is the shot peening affected area, and area III is the shot center distribution area.

3. A shot peening method for strengthening the gear surface as claimed in claim 1, characterized in that: In step 2, firstly, the diameter of a single crater 2ap needs to be calculated, where ap represents the radius of a single shot crater, and a single shot impact model is established. The shot peening speed and diameter are changed to obtain the displacement of the plate impact area along the layer depth direction under different initial conditions. The crater node displacement curve in the calculation result is extracted, and the distance between the two points with zero displacement along the layer depth direction is taken as the size of the crater diameter. After obtaining the diameter of the single projectile impact crater 2ap, in order to calculate the shot peening coverage, the surface of the shot peening affected area of ​​20Cr2Ni4A plate is equally divided along the x and y directions to generate Nx and Ny nodes, then a total of Nt=Nx×Ny nodes are generated, and then the distance S from each node to the center of all projectiles is calculated, where the coordinates of the center of the projectile are randomly generated by the Python program within the specified range. If S>ap exists for all S, then the node is in the unpeened area. The number of all nodes in the unpeened area is recorded as M, and the coverage C=(1-M / Nt)×100%.

4. A shot peening method for strengthening the surface of a gear as claimed in claim 1, characterized in that: In step 3, the projectiles are randomly distributed above the 20Cr2Ni4A plate collision study area. The coordinates of the center of any projectile ( , , ) satisfies the following relationship: （2） （3） （4） in,( , , )、( , , ) is the spatial distribution range of the projectiles. The centers of any two projectiles ( , , )、( , , ) satisfy the following relationship: （5） In the above formula, D is the diameter of the projectile; The random.uniform() function is used to obtain the coordinate point of the center of the random projectile in the space directly above the central distribution area of ​​the plate pellets.

5. A shot peening method for strengthening the surface of a gear as claimed in claim 1, characterized in that: In step 4, the shot peening parameters including shot size, shot peening speed and shot peening coverage are calculated with the gear surface roughness and residual compressive stress as the targets.

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