30CrMnSiA high-strength steel helicopter undercarriage laser in-situ repair method

Abstract

The invention discloses a laser in-situ repair method for a 30CrMnSiA high-strength steel helicopter undercarriage. The laser in-situ repair method comprises the following specific steps: S1, powder preparation; s2, pretreatment; s3, performing laser cladding repair in an argon environment; s4, polishing is conducted; and S5, laser quenching heat treatment is carried out, the structure, hardness and tensile property of the sample subjected to laser quenching treatment after laser cladding repair are compared with those of an original sample and a sample subjected to laser cladding repair only, and results show that the surface hardness after laser quenching is improved by 14.2% compared with that of the original sample and is improved by about 39.3% compared with that of the sample subjected to laser cladding repair only. After laser quenching, the tensile strength reaches 97.6% of that of an original sample, the yield strength is improved by 8%, and compared with a sample repaired only through laser cladding, the tensile strength is improved by 8%, and the yield strength is improved by 10.7%, so that the surface hardness can be obviously improved, the tensile property of parts can be improved, and the service life can be prolonged by adopting laser quenching treatment after laser cladding.

Description

Technical Field

[0001] The invention relates to the technical field of laser cladding and laser quenching, and in particular to a laser in-situ repair method for a 30CrMnSiA high-strength steel helicopter landing gear. Background Art

[0002] 30CrMnSiA structural steel has good hardenability and comprehensive mechanical properties, such as high strength and excellent toughness, and is widely used in key structural parts of the aerospace industry, construction and mechanical equipment, such as landing gear, propellers, and aircraft engines. During their service, these landing gear parts need to withstand frequent impacts, wear or corrosion, and are prone to microcracks, cracks and other defects, which eventually lead to failure before the end of their service life. In order to avoid the high economic and time costs of replacing parts, using appropriate repair methods to repair and extend the life of damaged parts can avoid material waste and significantly shorten the maintenance cycle of helicopters. It is also an important means to reduce the cost of using such parts.

[0003] Traditional helicopter maintenance technology has many problems. For example, the use of existing welding technology for maintenance will shorten the service life of parts, reduce reliability, or even scrap them due to deformation, cracking, or thermal damage defects. As a new type of remanufacturing repair technology, laser cladding repair technology uses the damaged and failed parts of the parts as the matrix. Under the action of a high-energy laser beam, the cladding powder is melted and deposited layer by layer on the area to be repaired to obtain a surface modification technology that forms a metallurgical bonding coating with the matrix, ultimately achieving the purpose of repairing parts. Laser quenching heat treatment is an advanced surface treatment technology. After treatment, it not only has high hardness and good wear resistance, but also can significantly improve the fatigue strength of parts.

[0004] Therefore, it is still necessary to combine laser cladding with laser quenching to repair damaged landing gear. It can be repaired on-site without disassembly, and can improve work efficiency while ensuring the performance of components. Summary of the invention

[0005] In view of this, in order to solve the above technical problems, the purpose of the present invention is to propose a laser in-situ repair method for 30CrMnSiA high-strength steel helicopter landing gear, which can eliminate the defects of existing repair technology due to deformation, cracking, thermal damage, etc., and solve the problems of cumbersome disassembly, high time and economic costs. It can not only efficiently repair the service fatigue damage of helicopter landing gear components, but also extend the service life.

[0006] The technical solutions adopted are:

[0007] A laser in-situ repair method for a 30CrMnSiA high-strength steel helicopter landing gear of the present invention comprises the following steps:

[0008] S1. Powder making: using a plasma rotating electrode powder making method to obtain 30CrMnSiA metal powder;

[0009] S2. Pretreatment: Use an electric spark wire cutting machine to prefabricate a "U"-shaped notch, use a grinder and polisher to polish the substrate and the notch to remove surface oxides, and use alcohol to ultrasonically clean the substrate;

[0010] S3. Carry out laser cladding repair test under the protection of argon gas, adjust the laser power, scanning speed and powder feeding rate, and repair the substrate under the parameters with good cladding macro effect;

[0011] S4. Polishing: Use a handheld grinder and polisher to polish the cladding repair surface;

[0012] S5. Laser quenching heat treatment: After the laser cladding repair is completed, switch the quenching laser head, perform laser quenching heat treatment on the cladding layer along the cladding direction, and adjust the optimal parameters under different laser powers and scanning speeds.

[0013] Furthermore, the plasma rotating electrode powder making method in S1 has a current of 1000-1600A and a rotation speed of 12000-15000r / min.

[0014] Furthermore, in S2, a groove with a depth of 0.5 mm and a width of 3.6 mm was cut at the damaged part, and the oxide scale on the cladding surface was polished using 400-grit sandpaper.

[0015] Furthermore, in S3, the flow rate of the protective gas is 15 L / min, the laser power is 2040 W, the scanning speed is 300 mm / min, the powder feeding rate is 1.6 g / min, and the spot diameter is 3 mm.

[0016] Furthermore, in S5, the laser quenching heat treatment process parameters are: laser power 1620 W, scanning speed 500 mm / min, spot diameter 12 mm, and defocus amount 288 mm.

[0017] The beneficial effects of the present invention are:

[0018] Through the laser in-situ repair process of the 30CrMnSiA high-strength steel helicopter landing gear of the present invention, the damaged parts can be repaired to a great extent, residual compressive stress can be introduced, the hardness of the material surface can be increased, the fatigue resistance can be enhanced, and the service life can be extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings involved in the description of the embodiments are briefly introduced below.

[0020] Figure 1The figure is a schematic diagram of the process of laser in-situ repair of 30CrMnSiA high-strength steel helicopter landing gear.

[0021] Figure 2 Schematic diagram of laser cladding and laser quenching.

[0022] Figure 3 Figure 2 is a schematic diagram of the cross-sectional morphology of the sample after laser cladding and laser quenching.

[0023] Figure 4 Schematic diagram of the metallographic structure of the quenching zone, molten pool zone and substrate zone.

[0024] Figure 5 Schematic diagram of hardness distribution from the outside to the inside of the cross section.

[0025] Figure 6 Schematic diagram of stress-strain curve and tensile properties of the specimen. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only partial embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] like Figure 1 As shown, a laser in-situ repair method for 30CrMnSiA high-strength steel helicopter landing gear of this embodiment includes the following steps:

[0028] S1. In order to achieve accurate repair of defective parts, first use non-destructive testing equipment to check all positions of the landing gear, determine the area and size of microcracks, and design the size of the prefabricated repair gap. ;

[0029] S2. After the damaged part is identified, use the electric spark wire cutting machine to cut a "U"-shaped notch in the damaged area, remove the microcracks and other defects in the area, and reserve a deposition position for powder feeding laser cladding. Use 400# sandpaper to grind the prefabricated groove to remove the oxide scale and other burrs generated during the wire cutting process, and then use alcohol or acetone to clean the notch and surrounding areas to eliminate the influence of other impurities on the cladding;

[0030] S3. After the notch processing is completed, the 30CrMnSiA metal powder with a diameter of 45-105μm obtained by the plasma rotating electrode powder making method is loaded into the powder feeder. Adjust the protective gas flow rate to 15L / min, the laser head is 15mm away from the notch plane (defocus), and the spot diameter is 3mm. Write the robot arm movement program, set the process parameters: laser power 2040W, scanning speed 300mm / min, powder feeding rate 1.6g / min, and finally perform laser cladding repair;

[0031] S4. After laser cladding, due to excessive surface roughness, a handheld grinder and polisher is required to polish the repaired area. The polished repaired area needs to reach the original surface flatness and roughness.

[0032] S5. Switch the laser cladding head of the equipment to the laser quenching head, adjust the height between the quenching beam emitter and the part to be quenched, and adjust the equipment to 288mm as the standard quenching distance. Set the laser quenching process parameters: laser power 1620W, scanning speed 500mm / min, quenching beam as an elliptical spot with a long diameter of 12mm and a short diameter of 2mm. After setting the process parameters, perform laser quenching heat treatment on the cladding layer along the cladding direction;

[0033] S6. During the laser quenching process, the surface temperature is high, oxidation will occur during the quenching process, and black oxide scale will appear after the quenching is completed. The area needs to be polished again using a grinder and polisher to make the final plane tolerance meet the repair standards;

[0034] S7. Characterize and test the material after a series of laser repair processes, observe the cross-sectional morphology and metallographic structure; test the microhardness in the cross-sectional cladding normal direction; test the tensile properties of the repaired material. Finally, evaluate the repair effect through the above test results.

[0035] Using 30CrMnSiA high-strength steel as the matrix, before laser cladding repair, the damaged parts of the landing gear are detected by non-destructive testing equipment, the repair area is determined, and a "U"-shaped groove with a width of 3.6mm and a depth of 0.5mm is designed.

[0036] Use an electric spark wire cutting machine to cut a "U"-shaped groove at the damaged part of the landing gear according to the above design scheme, reserving deposition space for laser cladding repair.

[0037] Use 400# sandpaper to grind the prefabricated "U"-shaped groove, which is conducive to the adhesion of molten powder, improves the interface bonding strength, and can remove the surface oxide scale to reduce the impact of impurities on cladding repair.

[0038] The ultra-high sphericity 30CrMnSiA powder prepared by the plasma rotating electrode powder making method was selected as the laser cladding powder. The cladding repair was carried out in a protective gas environment with a flow rate of 15L / min. The cladding process parameters were set as follows: spot diameter 3mm, defocus amount 15mm, laser power 2040W, scanning speed 300mm / min, and powder feeding rate 1.6g / min.

[0039] The repaired area of ​​the cladding surface needs to reach the original surface flatness and roughness after grinding and polishing.

[0040] Switch the laser device and use the laser quenching transmitter to quench the repaired part. The process parameters are: laser power 1620W, scanning speed 500mm / min.

[0041] like Figure 2-4 As shown in the figure, 4% nitric acid alcohol is used to corrode the cross section after laser cladding and quenching. It can be seen that the heat input causes different areas to appear in the cross section, where the quenching depth is about 1mm and the width is about 15.3mm. After laser quenching, the quenching zone is a cryptocrystalline martensite structure, the heat-affected zone is a tempered troostite structure that maintains the martensite phase, and the substrate area is a lath-shaped tempered martensite structure.

[0042] like Figure 5 and Figure 6 As shown in the figure, the hardness of the hardened layer after laser quenching reaches 614.72HV0.3, which is 14.2% higher than that of the original sample and 39.3% higher than that of the sample repaired by laser cladding alone. The tensile strength after laser quenching reaches 97.6% of the original sample, and the yield strength increases by 8%, which is 8% higher than that of the sample repaired by laser cladding alone, and the yield strength increases by 10.7%.

[0043] The method of the present invention is also applicable to laser in-situ repair of other parts of a helicopter.

[0044] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A laser in-situ repair method for 30CrMnSiA high-strength steel helicopter landing gear, characterized in that: The steps include: S1. Powder making: using a plasma rotating electrode powder making method to obtain 30CrMnSiA metal powder; S2. Pretreatment: Use an EDM wire cutting machine to preform a "U"-shaped notch, use a grinder and polisher to polish the substrate and the notch to remove surface oxides, and use alcohol to ultrasonically clean the substrate; S3. Carry out laser cladding repair test under the protection of argon gas, adjust the laser power, scanning speed and powder feeding rate, and repair the substrate under the parameters with good cladding macro effect; S4. Polishing: Use a handheld grinder and polisher to polish the cladding repair surface; S5. Laser quenching heat treatment: After the laser cladding repair is completed, switch the quenching laser head, perform laser quenching heat treatment on the cladding layer along the cladding direction, and adjust the optimal parameters under different laser powers and scanning speeds.

2. The laser in-situ repair method for 30CrMnSiA high-strength steel helicopter landing gear according to claim 1 is characterized in that: The plasma rotating electrode powder making method in S1 has a current of 1000-1600A and a rotation speed of 12000-15000r / min.

3. The laser in-situ repair method for 30CrMnSiA high-strength steel helicopter landing gear according to claim 1 is characterized in that: In S2, a groove with a depth of 0.5 mm and a width of 3.6 mm was cut at the damaged part, and the oxide scale on the cladding surface was polished with 400-grit sandpaper.

4. The laser in-situ repair method for 30CrMnSiA high-strength steel helicopter landing gear according to claim 1 is characterized in that: In S3, the flow rate of the shielding gas is 15 L / min, the laser power is 2040 W, the scanning speed is 300 mm / min, the powder feeding rate is 1.6 g / min, and the spot diameter is 3 mm.

5. The laser in-situ repair method for 30CrMnSiA high-strength steel helicopter landing gear according to claim 1 is characterized in that: In S5, the laser quenching heat treatment process parameters are: laser power 1620W, scanning speed 500mm / min, spot diameter 12mm, and defocus 288mm.

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