Composite strengthening method for carburized surface of high-bearing gear of aero-engine

Abstract

The invention belongs to the technical field of metal part surface modification, and relates to a composite strengthening method for a carburized surface of a high-bearing gear of an aero-engine. According to the method, high-hardness and high-density ceramic shots are adopted as media for high-energy mechanical shot peening strengthening, the advantage that the subsurface strain hardening effect of the contact strengthening technology is good and the barb-shaped distribution characteristic of mechanical shot peening residual compressive stress are utilized, extremely high residual compressive stress is introduced to the subsurface position, and the contact fatigue performance of the tooth surface of the gear is improved. High-frequency laser shot peening strengthening is used for secondary treatment, so that the surface layer of the material is subjected to plastic deformation, high-amplitude residual compressive stress is introduced into the surface layer of the material within the depth range of more than 500 microns by utilizing the advantage of large influence depth of laser-induced shock waves, and the residual compressive stress can inhibit fatigue crack initiation, has a certain depth and inhibits fatigue crack propagation; and the bending fatigue resistance of the root of the gear can be effectively improved. And an abrasive flow process is adopted, so that the roughness is reduced to be more than 0.4 mu m.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface modification of metal parts, and relates to a composite strengthening method for the carburized surface of a high-load gear of an aero-engine. For the carburized tooth root and tooth surface of the gear, a high-energy mechanical shot peening strengthening method is first used to treat the tooth root and tooth surface, and then a high-frequency laser shot peening strengthening method is used to treat the tooth root of the gear, and finally an abrasive flow method is used to treat the tooth root and tooth surface. Background Art

[0002] Gears for aircraft engines have the characteristics of high material strength, high carburized surface hardness and high gear load. They are key components of the entire engine and are of great significance to the long life and high reliability of the engine. The main failure modes of high-load gears for aircraft engines are contact fatigue and bending fatigue. Deformation strengthening methods such as mechanical shot peening are usually used in engineering to introduce residual compressive stress fields on the surface to improve contact fatigue and bending fatigue performance. Due to the different locations and failure modes of gear contact fatigue failure and bending fatigue failure, it is difficult to improve contact and bending fatigue performance at the same time with a single process method. The carburized surface hardness of high-strength gear steel for aircraft engines is extremely high, generally required to reach HRC65 or above. Conventional mechanical shot peening methods are insufficient in energy and have poor strengthening effects. Conventional laser shock strengthening methods are inefficient and effective in improving bending fatigue but poor in contact fatigue performance.

[0003] The domestic databases were searched, but no relevant literature was found. The domestic and foreign patent databases were searched, but no relevant content was found. The method of the present invention can be used for carburizing the surface of high-load gears of aircraft engines, and can also be promoted and applied to high-load gears in other fields, and has good application prospects. Summary of the invention

[0004] Purpose of the invention: The present invention relates to a composite strengthening method, which coordinates the strengthening mechanism, strengthening effect and efficiency of several methods to achieve the effect of 1+1=1≥3, and can effectively and efficiently improve the bending fatigue and contact fatigue performance of the carburized surface of high-load gears of aircraft engines, thereby ensuring the service safety of aircraft engines.

[0005] The technical solution of the present invention is a composite strengthening method for the carburized surface of a high-load bearing gear of an aero-engine, comprising three steps:

[0006] The first step is to use high-energy mechanical shot peening to strengthen the tooth root and tooth surface. Ceramic shot is used as the medium for high-energy shot peening. The parameters are: shot peening intensity 0.15-0.25mmA, coverage 200%, and the residual compressive stress value at a depth of 0.05μm after treatment is not less than 1500MPa;

[0007] In the second step, high-frequency laser shot peening is used to strengthen the gear tooth root. The boundary of the treatment area is 3mm to 8mm into the tooth surface. Deionized water is used as a conductive medium and a water film is formed to become a water constraint layer for laser shot peening. High-frequency laser shot peening is performed. The parameters are: laser pulse frequency F: ≥1000Hz, pulse width W: 10ns, pulse energy E: 50mj~80mj, focus spot diameter D: Ф0.5mm, overlap rate: greater than 50%, impact number 3 times, and high-frequency laser shot peening is performed on the gear tooth root. The margin of the strengthening area is 3mm to 8mm into the non-tooth surface, the impact number is 3 times, and the depth of the residual compressive stress field of the strengthening layer is not less than 500μm;

[0008] The third step is to perform abrasive flow finishing and strengthening on the tooth root and tooth surface. Silicon carbide and cubic boron nitride are used as abrasives to perform abrasive flow finishing and strengthening on the gear tooth surface. The processing time is controlled to obtain a surface roughness of the gear tooth surface and tooth root of less than Ra0.4μm.

[0009] The high-energy mechanical shot peening strengthening adopts pneumatic CNC shot peening machine equipment.

[0010] The hardness of the ceramic projectile is greater than HRC65, the density is greater than 6.2g / cm3, and the nominal diameter is Ф0.3mm to Ф0.60mm.

[0011] The high-frequency laser shot peening treatment adopts a high-frequency solid pulse laser.

[0012] Before the carburizing and composite strengthening of the surface of the high-load gear, alcohol and acetone are used to clean it thoroughly.

[0013] The quality inspection method after high-energy mechanical shot peening treatment comprises the following steps:

[0014] a) Test the shot peening intensity and coverage according to the method specified in HB / Z 26;

[0015] b) Use samples of the same material, hardness and state as the parts, treat the samples with the same process as the high-energy mechanical shot peening of the parts, use X-ray diffraction residual stress analysis combined with electrolytic polishing to detect the residual stress field of the samples after high-energy mechanical shot peening, and obtain the residual compressive stress value at a position 50μm below the surface. If the residual compressive stress value is greater than 1500MPa, the gear high-energy mechanical shot peening process is considered qualified;

[0016] The quality inspection method after high-frequency laser shot peening treatment is as follows: using samples with the same material, hardness and state as the parts, the samples are treated with the same process as the high-frequency laser shot peening of the parts, and X-ray diffraction residual stress analysis is used in conjunction with an electrolytic polishing method to detect the residual stress field of the samples after high-frequency laser shot peening treatment to obtain the depth of the residual compressive stress field. If the depth is greater than 500 μm, the high-frequency laser shot peening process of the gear is determined to be qualified.

[0017] The quality inspection method after the abrasive flow finishing and strengthening treatment is as follows: use a standard comparison block to visually inspect the surface roughness of the gear tooth surface and tooth root, and the surface roughness is less than Ra0.4μm to be qualified.

[0018] The advantages of the present invention are:

[0019] First, for the high-hardness tooth surface and tooth root after carburizing, the present invention first uses high-hardness and high-density ceramic projectiles as the medium to perform high-energy mechanical shot peening strengthening, which can efficiently strengthen a large area, and utilizes the advantages of good subsurface strain hardening effect of the contact strengthening process and the "hook-shaped" distribution characteristics of the residual compressive stress of mechanical shot peening, as shown in the attached Figure 1 , introducing extremely high residual compressive stress at the sub-surface position can more effectively improve the contact fatigue performance of the gear tooth surface.

[0020] Secondly, for the tooth root whose hardness is further improved after high-energy mechanical shot peening, the present invention uses high-frequency laser shot peening for secondary treatment on the basis of high-energy mechanical shot peening. The high frequency uses a solid laser to excite an ultra-high frequency pulse laser. The pulse laser impacts the surface of the high-temperature alloy to induce a plasma explosion. The energy of the plasma explosion wave gradually increases under the constraint of the water layer and exceeds the dynamic yield limit of the material, causing plastic deformation of the surface layer of the material. The advantage of the large impact depth of the laser-induced shock wave is utilized to introduce high-amplitude residual compressive stress within a depth range of more than 500μm on the surface layer of the material. The residual compressive stress can inhibit the initiation of fatigue cracks, and it has a certain depth, which inhibits the propagation of fatigue cracks, and can effectively improve the bending fatigue resistance of the gear root.

[0021] Third, for surfaces with high roughness values ​​after high-energy mechanical shot peening and high-frequency laser shot peening, the abrasive flow process is adopted, using silicon carbide and cubic boron nitride as abrasives to process the tooth surface and tooth root of the gear, reducing the roughness Ra value to above 0.4μm, further improving the bending fatigue and contact fatigue performance of the gear. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the "undercut-type" residual compressive stress field of mechanical shot peening;

[0023] Figure 2 Schematic diagram of the gear composite strengthening area; among them: the areas indicated by the blue and red solid lines are high-energy mechanical shot peening strengthening, the red solid line area is high-frequency laser shot peening strengthening, and the area indicated by the red dotted line is the high-frequency laser strengthening boundary area. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0025] A composite strengthening method for the carburized surface of a high-load gear of an aero-engine. The composite strengthening treatment method for the high-load gear of an aero-engine mainly includes the following steps:

[0026] (1) Parts preparation

[0027] The parts are made of gear steel. Before composite strengthening, the surface of the parts should be thoroughly cleaned with alcohol, acetone or other suitable cleaning agents to ensure that there is no attachment and oil on the surface.

[0028] (2) Implementation of high energy shot peening process

[0029] The cleaned parts are stably installed on the workbench of the high-energy mechanical shot peening equipment using special tooling. The high-energy mechanical shot peening parameters are selected according to the mechanical properties of the material. The parameter selection range is: shot peening intensity 0.15-0.25mmA, coverage rate 200%, and the shot peening medium used should have a hardness greater than HRC65 and a density greater than 6.2g / cm 3 , ceramic projectiles with a nominal diameter of Ф0.3mm to Ф0.60mm are used to perform high-energy mechanical shot peening on the tooth root and tooth surface of the gear.

[0030] (3) High energy mechanical shot peening quality inspection

[0031] a) Test the shot peening intensity and coverage in accordance with the method specified in HB / Z 26.

[0032] b) Use samples with the same material, hardness and state as the parts, and treat the samples with the same process as the high-energy mechanical shot peening of the parts. Use X-ray diffraction residual stress analysis combined with electrolytic polishing to detect the residual stress field of the samples after high-energy mechanical shot peening (distribution of residual stress with depth), and obtain the residual compressive stress value at 50μm below the surface. If the residual compressive stress value is greater than 1500MPa, it can be determined that the gear high-energy mechanical shot peening process is qualified.

[0033] (4) Parts cleaning

[0034] Use alcohol, acetone or other suitable cleaning agents to clean thoroughly and ensure that there is no attachment and oil on the surface.

[0035] (5) Implementation of high-frequency laser shot peening process

[0036] The cleaned parts are stably mounted on a high-frequency laser workbench using special tooling. The gear tooth root is treated with high-frequency laser shot peening. The boundary of the treatment area is 3mm to 8mm into the tooth surface. Deionized water is used as a conductive medium to form a water film as a water constraint layer for laser shot peening. Parameters are selected according to the mechanical properties of the material. The high-energy laser shot peening parameter range is: laser pulse frequency F: 1000Hz, pulse width W: 10ns, pulse energy E: 50mj to 80mj, focusing spot diameter D: Ф0.5mm. Deionized water is used as a high-frequency laser pulse conductive medium to form a water film as a water constraint layer for laser shot peening. The NC numerical control program for laser beam movement is written to obtain a laser spot overlap rate of 50%. The gear tooth root is subjected to high-frequency laser shot peening. The margin of the strengthening area is 3mm to 8mm into the non-tooth surface, and the number of impacts is 3 times. The depth of the residual compressive stress field of the strengthening layer is obtained to be not less than 500μm;

[0037] (6) High-frequency laser shot peening quality inspection

[0038] Use samples with the same material, hardness and state as the parts, and treat the samples with the same high-frequency laser shot peening process as the parts. Use X-ray diffraction residual stress analysis combined with electrolytic polishing to detect the residual stress field of the samples after high-frequency laser shot peening (the residual stress is distributed with depth) and obtain the depth of the residual compressive stress field. If the depth is greater than 500μm, it can be determined that the gear high-frequency laser shot peening process is qualified.

[0039] (7) Parts cleaning

[0040] Clean thoroughly with alcohol, acetone or other suitable cleaning agents to ensure that there is no attachment and oil on the surface.

[0041] (8) Implementation of abrasive flow strengthening process

[0042] The cleaned parts are stably installed in the abrasive flow equipment using special tooling, and the tooth root and tooth surface are treated with abrasive flow finishing and strengthening. Silicon carbide and cubic boron nitride are used as abrasives to perform abrasive flow finishing and strengthening on the gear tooth surface. The processing time is controlled (the time needs to be determined based on characteristic information such as material and part size) to obtain a surface roughness of the gear tooth surface and root of less than Ra0.4μm.

[0043] (9) Abrasive flow strengthening quality inspection

[0044] Use a standard comparison block to visually inspect the surface roughness of the gear tooth surface and tooth root. The surface roughness is qualified if it is less than Ra0.4μm.

[0045] Example 1

[0046] The gear material is 15Cr14Co12Mo5Ni steel, and the gear has completed all cutting, heat treatment and carburizing processes. The method of the present invention is used to perform composite strengthening treatment on the tooth root and tooth surface of the gear after carburizing.

[0047] (1) Workpiece preparation

[0048] The tooth surface and tooth root are ground, and the surface roughness is Ra0.4μm. First, the surface of the part is cleaned with alcohol to remove surface oil and impurities.

[0049] (2) Determination of high energy mechanical shot peening parameters

[0050] According to the mechanical properties of the material, the parameters are determined as follows:

[0051] Medium: hardness greater than HRC68, density greater than 6.2g / cm 3 , Nominal diameter Ф0.3mm;

[0052] Shot peening intensity: 0.20mmA

[0053] Coverage: 200%

[0054] Shot peening area: tooth surface and tooth root

[0055] (3) Implementation of high energy mechanical shot peening process

[0056] The gear is fixed on the turntable of the CNC high-energy mechanical shot peening equipment and subjected to high-energy mechanical shot peening treatment. The equipment parameters are: spray angle: 90°, spray distance 180mm, spray pressure 0.14MPa, shot flow rate 5Kg / min, turntable speed 20rmp / min, and spray gun feed speed along the Z axis 5mm / sec.

[0057] (4) High energy mechanical shot peening quality inspection

[0058] The test results are as follows:

[0059] Shot peening intensity is 0.205mmA

[0060] Coverage is 200%

[0061] The residual compressive stress at a depth of 50 μm is 1650 MPa

[0062] (5) Parts cleaning

[0063] Use alcohol to clean the gear surface thoroughly to ensure that there is no attachment or oil stain on the surface.

[0064] (6) Selection of high-frequency laser shot peening parameters

[0065] According to the mechanical properties of the material, the parameters are determined as follows:

[0066] Laser pulse frequency is 1000Hz

[0067] Pulse width is 10ns

[0068] Pulse energy is 80mj

[0069] Focus spot diameter is Ф0.5mm

[0070] (7) Implementation of high-frequency laser shot peening process

[0071] The cleaned parts are stably mounted on a high-frequency laser workbench using special tooling, and the tooth root of the gear is strengthened by high-frequency laser shot peening. The margin of the strengthened area is 3mm-8mm into the tooth surface, and the number of impacts is 3 times.

[0072] (8) High-frequency laser shot peening quality inspection

[0073] The depth of the residual stress field is 760 μm.

[0074] (9) Parts cleaning

[0075] Use alcohol to clean the scarf thoroughly to ensure that there is no attachment or oil on the surface.

[0076] (10) Selection of abrasive flow strengthening parameters

[0077] Abrasive flow strengthening treatment was carried out using silicon carbide and cubic boron nitride as abrasives, and the treatment time was 8 hours.

[0078] (11) Implementation of abrasive flow strengthening process

[0079] The cleaned parts are stably installed in the abrasive flow equipment using special tooling, and the equipment is started for abrasive flow strengthening treatment.

[0080] (12) Abrasive flow strengthening quality inspection

[0081] The surface roughness of the parts is less than Ra0.4μm.

Claims

1. A composite strengthening method for the carburized surface of a high-load bearing gear of an aircraft engine, characterized in that: There are three steps involved: The first step is to use high-energy mechanical shot peening to strengthen the tooth root and tooth surface. Ceramic shot is used as the medium for high-energy shot peening. The parameters are: shot peening intensity 0.15-0.25mmA, coverage 200%, and the residual compressive stress value at a depth of 0.05μm after treatment is not less than 1500MPa; In the second step, high-frequency laser shot peening is used to strengthen the gear tooth root. The boundary of the treatment area is 3mm to 8mm into the tooth surface. Deionized water is used as a conductive medium and a water film is formed to become a water constraint layer for laser shot peening. High-frequency laser shot peening is performed. The parameters are: laser pulse frequency F: ≥1000Hz, pulse width W: 10ns, pulse energy E: 50mj~80mj, focus spot diameter D: Ф0.5mm, overlap rate: greater than 50%, impact number 3 times, and high-frequency laser shot peening is performed on the gear tooth root. The margin of the strengthening area is 3mm to 8mm into the non-tooth surface, the impact number is 3 times, and the depth of the residual compressive stress field of the strengthening layer is not less than 500μm; The third step is to perform abrasive flow finishing and strengthening on the tooth root and tooth surface. Silicon carbide and cubic boron nitride are used as abrasives to perform abrasive flow finishing and strengthening on the gear tooth surface. The processing time is controlled to obtain a surface roughness of the gear tooth surface and tooth root of less than Ra0.4μm.

2. The composite strengthening method for carburizing the surface of high-load bearing gears of aircraft engines according to claim 1, characterized in that: The high-energy mechanical shot peening strengthening adopts pneumatic CNC shot peening machine equipment.

3. The composite strengthening method for carburizing the surface of high-load bearing gears of aircraft engines according to claim 1, characterized in that: The hardness of the ceramic projectile is greater than HRC65, the density is greater than 6.2g / cm3, and the nominal diameter is Ф0.3mm to Ф0.60mm.

4. The composite strengthening method for the carburized surface of a high-load bearing gear of an aircraft engine according to claim 1, characterized in that: The high-frequency laser shot peening treatment adopts a high-frequency solid pulse laser.

5. The composite strengthening method for carburizing the surface of high-load bearing gears of aircraft engines according to claim 1, characterized in that: Before the carburizing and composite strengthening of the surface of the high-load gear, alcohol and acetone are used to clean it thoroughly.

6. The composite strengthening method for carburizing the surface of high-load bearing gears of aircraft engines according to claim 1, characterized in that: The quality inspection method after high-energy mechanical shot peening treatment comprises the following steps: a) Test the shot peening intensity and coverage according to the method specified in HB / Z 26; b) Use samples with the same material, hardness and state as the parts, and treat the samples with the same process as the high-energy mechanical shot peening of the parts. Use X-ray diffraction residual stress analysis combined with electrolytic polishing to detect the residual stress field of the samples after high-energy mechanical shot peening, and obtain the residual compressive stress value at 50μm below the surface. If the residual compressive stress value is greater than 1500MPa, the gear high-energy mechanical shot peening process is judged to be qualified.

7. The composite strengthening method for carburizing the surface of high-load bearing gears of aircraft engines according to claim 1, characterized in that: The quality inspection method after high-frequency laser shot peening treatment is as follows: using samples with the same material, hardness and state as the parts, the samples are treated with the same process as the high-frequency laser shot peening of the parts, and X-ray diffraction residual stress analysis is used in conjunction with an electrolytic polishing method to detect the residual stress field of the samples after high-frequency laser shot peening treatment to obtain the depth of the residual compressive stress field. If the depth is greater than 500 μm, the high-frequency laser shot peening process of the gear is determined to be qualified.

8. The composite strengthening method for carburizing the surface of high-load bearing gears of aircraft engines according to claim 1, characterized in that: The quality inspection method after the abrasive flow finishing and strengthening treatment is as follows: use a standard comparison block to visually inspect the surface roughness of the gear tooth surface and tooth root, and the surface roughness is less than Ra0.4μm to be qualified.

Images