A method for repairing the gears of a helicopter reducer

Abstract

The present invention relates to the technical field of aircraft maintenance, and particularly to a repair method for worn gear tooth surfaces, especially a repair method for worn gear tooth surfaces of a helicopter reducer. The procedures of this method are as follows: judging the tooth surface state, determining the wear range, grinding the working surface of the gear, performing acid etching inspection on the gear, performing stress relief treatment on the ground gear, performing shot peening treatment on the ground tooth surface, performing vibratory finishing on the tooth surface, and inspecting. By using the method proposed by the present invention, the smoothness of the gear movement and the uniformity of the load distribution after repair can be ensured, the bending fatigue strength of the tooth profile is increased, and its load-bearing capacity can be improved. It prevents the crack propagation in the tooth surface layer, reduces the spalling and pitting of the tooth surface, and improves the service life of the gear.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft maintenance, and particularly to a repair method for gear tooth surface wear, especially a repair method for gear tooth surface wear of a helicopter reducer. Background Art

[0002] Gears are one of the most widely used transmission parts in helicopter reducers, with the functions of speed change and direction change, and play a role in transmitting the engine power in the reducer. Among the failure forms of gear transmission, the problem of tooth surface wear is the most prominent.

[0003] Part wear is an important factor affecting the TBO life of the reducer. When tooth surface wear occurs, it will not only affect the transmission accuracy and efficiency of the gear, but also cause the vibration value of the reducer to be too large, and seriously affect the safety of the whole machine. In addition, after the tooth surface of such key gears wears, it will be scrapped according to the traditional repair method, and the "repair by replacement" repair method will be adopted. This repair method will not only increase the overhaul cost of the helicopter reducer, but also occupy a large amount of production equipment resources.

[0004] In summary, there is an urgent need to study a repair method for gear tooth surface wear of a helicopter reducer to ensure that the repaired gear can meet the requirements of the whole machine, while reducing the overhaul cost and releasing production capacity. Summary of the Invention

[0005] The purpose of the present invention is to propose a repair method for gear tooth surface wear of a helicopter reducer, which does not change the performance of the product as much as possible and can meet the use requirements for one overhaul period after repair.

[0006] Most of the gears of the helicopter reducer are carburized, and generally require the final effective carburized layer depth to be 0.6 - 1 mm and the tooth surface hardness HRC ≥ 58. The actual processing technology generally requires the effective carburized layer depth of the tooth surface after heat treatment to be 0.92 - 1.12 mm, and the maximum grinding allowance is about 0.22 mm (the grinding allowance is obtained by converting the tooth thickness values before and after grinding according to the process regulations). After the reducer works for one overhaul period, the actual wear amount of the tooth surface is generally within 0.05 mm. Therefore, for the gears due for overhaul, only 0.05 mm of the tooth thickness of the working tooth surface is ground, and the remaining carburized layer depth can still meet the requirements.

[0007] The technical solution of the present invention is: a repair method for gear tooth surface wear of a helicopter reducer includes the following steps:

[0008] (1) Judge the tooth surface state. If the tooth surface is abrasive wear, repair it according to the next step, otherwise scrap it;

[0009] (2) Determine the wear range. If the unilateral wear amount of the tooth surface does not exceed the wear limit of 0.05 mm, proceed to the next step for repair;

[0010] (3) Grind the working surface of the gear to ensure that the grinding amount is not greater than 0.05 mm, and ensure that the tooth profile and tooth direction after grinding meet the design requirements;

[0011] (4) Conduct acid etching inspection on the gear to ensure no grinding burns;

[0012] (5) Conduct stress relieving treatment on the gear after grinding;

[0013] (6) Conduct shot peening treatment on the ground tooth surface with the intensity greater than or equal to 0.008 A (inch). After passing the inspection, proceed to the next step for repair;

[0014] (7) Conduct vibratory finishing on the tooth surface to ensure that the surface roughness grade of the tooth surface is higher than 0.4 μm;

[0015] (8) For the gear with root relief design at the tooth root, it can be directly assembled and used. For the gear without root relief design at the tooth root, the fatigue life after repair needs to be determined through gear fatigue test before assembly and use.

[0016] Further, No. 230 cast steel shot is used during shot peening treatment.

[0017] Beneficial technical effects: By adopting the repair method proposed by the present invention, the smoothness of the gear movement and the uniformity of the load distribution after repair can be ensured, the bending fatigue strength of the tooth is increased, and its load-bearing capacity can be improved. It can prevent the crack propagation in the tooth surface layer to reduce tooth surface spalling and pitting, and improve the service life of the gear. Specific embodiments

[0018] The present invention determines the range of repairable gears according to the tooth surface condition. Abrasive wear on the tooth surface is mainly caused by metal particles entering the tooth surface with the lubricating oil during the operation of the reducer, resulting in uneven wear on the tooth surface and forming abrasive damage. The depth of such damage generally does not exceed 0.1 mm. Determining the wear range is to ensure that the tooth thickness of the gear is not too thin and to meet the requirements for the case depth of the gear surface, so as to ensure the safety of gear operation. The tooth surface wear is determined to be not more than 0.05 mm of the wear limit, which is mainly based on theoretical calculations and the repair and use conditions of more than 150 reducers. Repairing the tooth surface according to the tooth profile and helix tolerance requirements is to ensure the smoothness of the gear movement and the uniformity of the load distribution after repair. Selecting No. 230 cast steel shot with a strength greater than or equal to 0.008A (inch) for shot peening the tooth surface mainly refers to the "Aviation Manufacturing Engineering Handbook - Gear Technology" and the process requirements of similar new gears. The surface cold hardening layer generated by shot peening increases the bending fatigue strength of the tooth and can improve its load-carrying capacity. At the same time, shot peening can also prevent the crack propagation in the tooth surface layer, reduce tooth surface spalling and pitting, and improve the service life of the gear. Vibration finishing the tooth surface to ensure that the tooth surface roughness value is better than 0.4 μm is to increase the contact area of the tooth surface, thereby improving the contact fatigue strength and wear resistance of the tooth surface.

[0019] Example 1

[0020] Abrasion appears on the tooth surface of the first-stage sun gear of a certain type of helicopter reducer. The repair steps are as follows:

[0021] (1) The tooth surface condition of the first-stage sun gear is abrasive wear, and repair is carried out according to the next step;

[0022] (2) Measure the wear amount. The unilateral wear amount is 0.04 mm, and repair is carried out according to the next step;

[0023] (3) Grind the working surface of the gear by 0.05 mm. The tooth profile and helix conform to the design requirements, and repair is carried out according to the next step;

[0024] (4) The acid etching inspection is qualified, and repair is carried out according to the next step;

[0025] (5) The stress relief treatment is qualified, and repair is carried out according to the next step;

[0026] (6) Use No. 230 cast steel shot to carry out shot peening treatment on the ground tooth surface. The shot peening strength is 0.008A (inch). The shot peening is qualified, and repair is carried out according to the next step;

[0027] (7) Vibration finish the tooth surface. The tooth surface roughness value is 0.32 μm, which is qualified;

[0028] (8) The gear repair is qualified. It has a root-cutting structure design and is installed for use.

[0029] In order to achieve better repair effects, during the specific implementation of the above method, the following optimization improvements can also be carried out. Specifically, in step (3) of the above method, a special mandrel is used for positioning before grinding the gear to ensure the installation accuracy and ensure uniform grinding of the gear.

[0030] In step (3) of the above method, diamond grinding wheels are used for grinding, which has high grinding accuracy and good consistency in tooth profile and tooth direction.

[0031] In step (3) of the above method, the ground tooth surface is a single-sided tooth surface, which reduces the influence of normal gear grinding on the tooth thickness and ensures the strength of the repaired gear.

[0032] In step (3) of the above method, only the involute part of the tooth surface is ground, which has no influence on the bending strength of the gear with a root relief design.

[0033] In step (4) of the above method, the acid etching inspection is only carried out on the ground part of the tooth surface to avoid burns during the grinding process, which may affect the gear strength.

[0034] In step (5) of the above method, stress relief is carried out on the entire gear to avoid the release of residual stress during the subsequent use process caused by the cold working process.

[0035] In step (5) of the above method, the temperature, time and other control parameters for stress relief need to be selected according to the gear material to achieve the required effect under the condition of not affecting the strength.

[0036] In step (6) of the above method, shot peening treatment is carried out on all tooth surfaces and tooth roots, which can increase the compressive stress on the tooth surface and improve the fatigue life.

[0037] In step (6) of the above method, a special fixture needs to be designed for shot peening to ensure that shot peening is completed at one time without allowing interruption for secondary clamping to avoid stress concentration.

[0038] In step (6) of the above method, the shot peening coverage rate is 200%, which ensures the effective shot peening area and uniformity.

[0039] In step (6) of the above method, a shot peening arc height test needs to be carried out before the shot peening process to ensure that the shot peening strength can meet the use requirements.

[0040] In step (6) of the above method, shot peening is carried out in a radial spraying manner, and the spraying distance is not less than 100 mm.

[0041] In step (7) of the above method, vibratory finishing is carried out on the tooth surfaces of the gear teeth, which improves the surface roughness of the ground tooth surface, increases the tooth surface contact area, reduces the wear during the gear meshing process, and improves the contact fatigue strength.

[0042] In step (7) of the above method, the vibratory finishing adopts an integral intrusion method to improve the vibratory finishing efficiency. The gear web part is protected by a tooling, and only the gear tooth part is subjected to vibratory finishing.

[0043] After the above repair method is implemented, the repair quality can be evaluated by measuring the tooth profile, tooth direction, dimension between measuring rods, and magnetic particle inspection.

[0044] If the repaired gear does not have a root relief design, the fatigue life after repair can be determined through a gear fatigue test.

Claims

1. A repair method for tooth surface wear of helicopter reducer gears, characterized in that The method comprises the following steps: Step 1: Determine the tooth surface condition. If the tooth surface is abrasive wear, repair it according to the next step, otherwise scrap it. Step 2: Determine the wear range. If the wear on one side of the tooth surface does not exceed the wear limit of 0.05mm, proceed to the next step for repair. Step 3: Grind the gear working surface. During grinding, ensure that the grinding amount is no more than 0.05mm, and ensure that the tooth shape and tooth direction after grinding meet the design requirements; Step 4: Check the gears by acid etching; Step 5, performing stress relief treatment on the gear after grinding; Step 6: Shot peening is performed on the tooth surface after grinding. The shot peening intensity is greater than or equal to 0.008A inches. If it is qualified, the next step is followed for repair; Step 7: Perform vibration finishing on the tooth surface. The vibration finishing must ensure that the surface roughness level of the tooth surface is higher than 0.4μm; Step 8. For gears with a root-digging design on the tooth root, they can be directly assembled and used. For gears without a root-digging design on the tooth root, a gear fatigue test is required before assembly and use to determine the fatigue life after repair.

2. The repair method for tooth surface wear of helicopter reducer gears according to claim 1, characterized in that, The shot peening process uses No. 230 cast steel shot.

3. The repair method for tooth surface wear of helicopter reducer gears according to claim 2, characterized in that, The shot peening treatment is to perform shot peening treatment on all tooth surfaces and tooth roots.

4. The repair method for the tooth surface wear of the helicopter reducer gear according to claim 3, characterized in that, Before shot peening, a shot peening arc height test should be carried out.

5. The repair method for tooth surface wear of the helicopter reducer gear according to any one of claims 1-4, characterized in that, The shot peening process is completed in one step.

6. The repair method for tooth surface wear of the helicopter reducer gear according to claim 1, characterized in that, In step three, grinding is performed using a diamond grinding wheel.

7. The repair method for tooth surface wear of helicopter reducer gears according to claim 1, characterized in that, The acid etching inspection is only performed on the grinding area of ​​the tooth surface.

8. The repair method for the tooth surface wear of the helicopter reducer gear according to claim 1, characterized in that, Stress relief treatment is performed on the entire gear.

9. The repair method for the tooth surface wear of the helicopter reducer gear according to claim 1, characterized in that, Vibration finishing uses an overall intrusive process.