Stress regulation and control method for improving fatigue strength of titanium alloy rotor blade after welding repair

Abstract

The invention relates to the technical field of aero-engine titanium alloy rotor blade repair, in particular to a stress regulation and control method for improving fatigue strength of a titanium alloy rotor blade after welding repair, which comprises the following steps: vacuum heat treatment, self-adaptive machining, first vibration finishing, laser shock peening, shot peening and second vibration finishing. Performing vacuum heat treatment on the blade subjected to electron beam welding repair; a machining program is compiled, machining is conducted on the patch repairing area, and the blade with the profile size meeting the use requirement is obtained; and after the first time of vibration finishing, laser strengthening equipment is used for carrying out laser strengthening on the blade area needing to be strengthened, shot blasting is carried out, then second time of vibration finishing is carried out, and the stress regulation and control method is completed. The vibration fatigue strength of the repaired blade is improved by 30% compared with that of a welding heating treatment process, the service life of the blade is effectively prolonged, the use performance requirement of parts is met, the maintenance and part replacement cost of an aero-engine is reduced, and the method has large economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of repairing titanium alloy rotor blades of aircraft engines, and in particular to a stress control method for improving the fatigue strength of titanium alloy rotor blades after welding repair. Background Art

[0002] The titanium alloy compressor blades and integral blade disk parts of aircraft engines are made of TC17. After use, they will have problems such as wear, foreign object damage (FOD), corrosion, and fatigue damage. In order to reduce manufacturing costs and increase the service life of the blades, welding patches are usually used for repair. Since the parts need to withstand high speeds and centrifugal loads during use, the fatigue life of the material and structure is very high.

[0003] Although electron beam welding technology is relatively mature in the field of metal component repair, problems such as microstructure growth will occur after welding remanufacturing, and large residual tensile stress will be introduced. These factors will lead to reduced fatigue performance of the material and affect the performance of the blade. During the re-service process, the rotor blades of an aircraft engine must not only withstand the effects of alternating loads, but also the coupling effect of high residual tensile stress induced by the remanufacturing process, which will seriously affect the performance and re-service life of the blade. Therefore, in order to meet the needs of high-reliability repair and remanufacturing of key components of aircraft engines, improve the fatigue performance of the entire blade disk after welding repair, and ensure reliability, there is an urgent need for a method that can effectively regulate the residual stress of the blade after welding repair. Summary of the invention

[0004] In view of the problem that residual stress and structural transformation are introduced after electron beam welding patch repair of aircraft engines, which leads to reduced fatigue performance of blades, the present invention provides a stress control method for improving the fatigue strength of titanium alloy rotor blades after welding repair, so as to solve the problem of reduced blade performance after welding repair, ensure the reliability of blade use, meet the repair needs of aircraft engine blades or integral blade disks after use due to damage and misprocessing, and improve the safe operation and maintenance capabilities of aircraft engines.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] A stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair comprises the following steps:

[0007] S1: Vacuum heat treatment

[0008] The blades repaired by electron beam welding are placed in a vacuum heat treatment furnace for vacuum heat treatment;

[0009] S2: Adaptive Machining

[0010] The blades after heat treatment were measured by a three-coordinate measuring machine. The measured data were imported into UG software to reconstruct the blade model. Then, a machining program was compiled. The five-axis CNC machining center equipment was used to perform adaptive milling and grinding on the patch repair area to obtain a blade whose surface dimensions met the use requirements.

[0011] S3: First vibration finishing

[0012] S3.1: Use a special protective cover to protect the blade area obtained in S2 that does not need vibration finishing;

[0013] S3.2: Install the blade on a special fixture, load abrasive into the vibration finishing machine, set processing parameters, and perform the first vibration finishing;

[0014] S3.3: After the first vibration finishing, use a roughness measuring instrument to check the surface roughness of the blade body;

[0015] S4: Laser Shock Strengthening

[0016] S4.1: Prepare laser strengthening procedures for laser strengthening equipment;

[0017] S4.2: Install the blade obtained in S3 into a special fixture for alignment and positioning;

[0018] S4.3: Stick the absorbent layer evenly to the position that needs to be strengthened;

[0019] S4.4: Use special protective tape to protect the blade parts that do not need to be strengthened;

[0020] S4.5: Run the program to perform laser shock peening processing;

[0021] S5: Shot peening

[0022] S5.1: Use special tape for shot peening to protect non-shot peening areas;

[0023] S5.2: Install the blade obtained in S4 into a special fixture and fix it;

[0024] S5.3: Shot peening is performed according to the processing parameters set by the CNC shot peening machine;

[0025] S6: Second vibration finishing

[0026] S6.1: For the blades obtained in S5, the blade areas that do not need to be vibrated are protected by special protective covers;

[0027] S6.2: Install the blade on a special fixture and load abrasive into the vibration finishing machine; set processing parameters and perform the second vibration finishing;

[0028] S6.3: After the second vibration finishing, the surface roughness of the blade body is checked using a roughness measuring instrument to complete the stress control method.

[0029] Furthermore, in S1, the vacuum heat treatment process is to place the blade into the vacuum heat treatment furnace when the temperature is ≤150°C, heat it to (600±10)°C, keep it warm for 4h~4h15min, fill the furnace with argon gas, control the pressure at 0.18~0.2MPa, cool it to below 80°C and take it out of the furnace to complete the vacuum heat treatment.

[0030] Furthermore, in S3.2, the abrasive is a side-cut cylindrical abrasive, the abrasive covers the blade part by at least 30 mm, and the processing parameters are: vibration finishing for 4 hours, water spray flow rate of 150-200 / h, water spray time of 20s, and water spray interval of 300s.

[0031] Furthermore, in S3.3, the surface roughness of the blade body should be no greater than 0.4 μm.

[0032] Furthermore, in S4.1, the laser spot is set to be circular with a diameter of 2.8 mm, and the laser energy is set to 18 J.

[0033] Furthermore, in S4.3, the absorption layer is a black tape with a specification of 25 mm in width and 0.25 mm in thickness.

[0034] Furthermore, in S5.3, the processing parameters are: shot specification is Z300, nozzle diameter is φ12 mm, air pressure is 1 Bar, saturation time is 1 time, nozzle to workpiece distance: 20 ± 10 mm, nozzle moving speed is 50 mm / min, and flow rate is 950 g / min.

[0035] Furthermore, in S6.2, the abrasive is a spherical abrasive, and the abrasive covers the blade part by at least 30 mm. The processing parameters are: vibration finishing for 1 hour; water spray flow rate of 150-200 l / h, water spray time of 20 s, and water spray interval time of 300 s.

[0036] Furthermore, in S6.3, the surface roughness of the blade body should not be greater than 0.4 μm.

[0037] The beneficial effects of the present invention are:

[0038] The present invention has been applied in the repair of titanium alloy rotor blades of internal aircraft engines. The vibration fatigue strength of the repaired blades is increased by 30% compared with the process of welding and heating treatment alone, which effectively increases the service life of the blades, ensures the performance requirements of the parts, reduces the cost of aircraft engine maintenance and replacement, and has great economic benefits.

[0039] The present invention can be directly applied to the welding patch repair of titanium alloy blades and integral blade disk parts of aircraft engines and gas turbines, improve the performance of the repaired blades, and ensure the safety and reliability of the blades. At the same time, the present invention can be extended to the welding repair of rotor parts made of other materials, and has a broad application space.

[0040] The present invention pre-sets a compressive stress layer in the repair area and the weak area of ​​the blade, which can effectively improve the fatigue life of the blade, ensure the service reliability of the blade after welding repair, and meet the repair needs of aviation engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the structure of a titanium alloy rotor blade after being repaired by electron beam welding in the present invention;

[0042] Figure 2 This is a schematic diagram of the blade structure processed by the first vibration finishing process of the present invention;

[0043] Figure 3 This is a schematic diagram of the blade structure processed by the laser shock strengthening process of the present invention;

[0044] Figure 4 It is a schematic diagram of the laser shock peening spot overlap structure of the present invention;

[0045] Figure 5 This is a schematic diagram of the blade structure processed by the mechanical shot peening process and the second vibration finishing process of the present invention. DETAILED DESCRIPTION

[0046] In order to better explain the present invention, so as to facilitate understanding, the following Figure 1-5 , the technical scheme and effects of the present invention are described in detail through specific implementation methods.

[0047] The embodiment of the present invention proposes a stress control method for improving the fatigue strength of titanium alloy rotor blades after welding repair, and comprehensively utilizes the advantages of processes such as heat treatment, laser shock strengthening, mechanical shot peening and vibration finishing to comprehensively improve the performance of the blades after welding repair.

[0048] In this embodiment, the material of the titanium alloy rotor blade is TC17, and the specific steps are as follows:

[0049] Step 1: Vacuum heat treatment

[0050] The blades repaired by electron beam welding are placed in a vacuum heat treatment furnace. Figure 1As shown, vacuum heat treatment is carried out. The heat treatment process is as follows: when the temperature in the vacuum heat treatment furnace is ≤150°C, the blades are loaded into the furnace, heated to (600±10)°C, kept warm for 4h~4h15min, argon is filled into the furnace, the pressure is controlled at 0.18~0.2Mpa, cooled to below 80°C and taken out of the furnace to complete the vacuum heat treatment.

[0051] The vacuum heat treatment process has been verified in long-term production and can effectively reduce the peak value of residual stress, improve the plasticity of weld metal, and reduce the hardness of the heat-affected zone. Therefore, the welded repaired blades are first annealed. The heat treatment system selects TC17 material, and the standard heat treatment system is: 600℃, and the heat preservation is 4 hours.

[0052] Step 2: Adaptive Machining

[0053] A three-coordinate measuring machine is used to measure the blades after heat treatment. After the measurement data is imported into UG software to reconstruct the blade model, a processing program is compiled. A five-axis CNC machining center is used to perform adaptive milling and grinding on the patch repair area to obtain a blade whose surface dimensions meet the use requirements.

[0054] Step 3: First vibration polishing

[0055] 1) According to Figure 2 As shown, the blade area that does not need vibration finishing, that is, the range of 3mm between the vibration finishing and the weld, is protected by a special protective cover;

[0056] 2) Install the blade on a special fixture, and load RMB D1 04 / 05ZS side-cut cylindrical abrasive into the vibration finishing machine. The abrasive should cover the blade by at least 30 mm, which is 35 mm in this embodiment. The specific processing parameters are: vibration finishing for 4 hours, water spraying flow rate of 150-200 / h, water spraying time of 20 seconds, and water spraying interval of 300 seconds;

[0057] 3) Use a roughness measuring instrument to check the surface roughness of the blade body, which should be no greater than 0.4μm.

[0058] After the patch is machined, there will be traces of the blade, which will affect the fatigue performance of the blade. Therefore, the vibration finishing process is selected to remove the traces of the machining. After experimental verification, RMB D1 04 / 05ZS side-cut cylindrical abrasive is selected, and the vibration finishing process is performed for 4 hours, which can restore the surface roughness of the blade to less than 0.4μm.

[0059] Step 4: Laser shock peening

[0060] 1) According to Figure 3 , Figure 4As shown in the figure, a laser strengthening program is compiled for the laser strengthening equipment. The spot is circular with a diameter of 2.8mm, and the laser energy is set to 18J. The width of the edge of the strengthened blade is 8mm, covering the weak position of the edge of the blade. The width of both sides of the strengthened weld is 10mm each, covering the weld and the heat-affected zone.

[0061] 2) Install the blade into a special fixture for alignment and positioning;

[0062] 3) Use a 25mm wide and 0.25mm thick black tape (imported sandblasting tape P306) as an absorption layer and stick it evenly on the position that needs to be strengthened;

[0063] 4) Use black tape to protect the parts of the blade that do not need to be strengthened to prevent laser reflection and scattered light from affecting the surface quality of the blade;

[0064] 5) Run the program to perform laser shock peening processing.

[0065] Although heat treatment can reduce the peak value of residual stress, it cannot completely eliminate it. Tensile stress will still exist in the blade after repair. Laser shock peening is a new type of material surface strengthening technology that can obtain a high-amplitude residual compressive stress layer on the surface of metal parts, thereby improving the fatigue life of the parts. Therefore, the laser shock peening process is selected to process the weld area and the heat-affected zone to change the tensile stress in the blade repair area into compressive stress. At the same time, the inlet and exhaust edges of the blade are the weak areas of the blade and are prone to damage. Therefore, the inlet and exhaust edges of the blade are laser shock peening processed at the same time. After testing, the laser spot is circular with a diameter of 2.8mm, the laser energy is set to 18J, the overlap rate of adjacent spots in each row is 50% (that is, the distance the spot moves each time is the radius of the spot), and the overlap rate of spots between two rows is 30% (that is, 30% of the spot diameter).

[0066] Step 5: Shot Peening

[0067] 1) Use special shot peening tape to protect the non-shot peening area;

[0068] 2) Install the blade into a special fixture and fix it;

[0069] 3) Shot peening was performed according to the processing parameters set by the CNC shot peening machine: shot specification: Z300, nozzle diameter φ12mm, air pressure 1Bar, saturation time 1 time, distance from nozzle to workpiece: 20±10mm, nozzle moving speed 50mm / min, flow rate 950g / min.

[0070] In order to comprehensively improve the damage resistance of the blade and further improve the fatigue performance of the blade as a whole, the blade body is strengthened by shot peening. After testing, the shot specification is selected as Z300, the nozzle diameter is φ12mm, the air pressure is 1Bar, the saturation time is 1 time, the distance from the nozzle to the workpiece is: 20±10mm, the nozzle moving speed is 50mm / min, and the flow rate is 950g / min.

[0071] Step 6: Second vibration polishing

[0072] 1) According to Figure 5 As shown, the blade areas that do not require vibration finishing are protected with special protective covers;

[0073] 2) Install the blade on a special fixture, and load RM 4G spherical abrasive into the vibration finishing machine. The abrasive should cover the blade by at least 30 mm, which is 35 mm in this embodiment. The specific processing parameters are: vibration finishing for 1 hour. Water spraying flow rate 150-200 l / h, water spraying time 20 s, and water spraying interval time 300 s;

[0074] 3) Use a roughness measuring instrument to check the surface roughness of the blade body, which should be no greater than 0.4μm.

[0075] Since shot peening affects the surface roughness of the blade, a second vibration finishing process is performed. After testing, the second vibration finishing uses RM 4G spherical abrasive and the vibration finishing lasts for 1 hour.

[0076] In order to verify the effect of the above process method, the present invention uses an electromagnetic vibration test bench to verify the vibration fatigue test method, setting the test conditions: N f (Number of vibration fatigue cycles) = 3 × 10 7 , vibration frequency: 1120Hz, test fatigue strength limit, the verification result is that the vibration fatigue strength limit reaches 320Mpa, which meets the design vibration fatigue stress use requirements.

Claims

1. A stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair, characterized in that: The steps include: S1: Vacuum heat treatment The blades repaired by electron beam welding are placed in a vacuum heat treatment furnace for vacuum heat treatment; S2: Adaptive Machining The blades after heat treatment were measured by a three-coordinate measuring machine. The measured data were imported into UG software to reconstruct the blade model. Then, a machining program was compiled. The five-axis CNC machining center equipment was used to perform adaptive milling and grinding on the patch repair area to obtain a blade whose surface dimensions met the use requirements. S3: First vibration finishing S3.1: Use a special protective cover to protect the blade area obtained in S2 that does not need vibration finishing; S3.2: Install the blade on a special fixture, load abrasive into the vibration finishing machine, set processing parameters, and perform the first vibration finishing; S3.3: After the first vibration finishing, use a roughness measuring instrument to check the surface roughness of the blade body; S4: Laser Shock Strengthening S4.1: Prepare laser strengthening procedures for laser strengthening equipment; S4.2: Install the blade obtained in S3 into a special fixture for alignment and positioning; S4.3: Stick the absorbent layer evenly to the position that needs to be strengthened; S4.4: Use special protective tape to protect the blade parts that do not need to be strengthened; S4.5: Run the program to perform laser shock peening processing; S5: Shot peening S5.1: Use special tape for shot peening to protect non-shot peening areas; S5.2: Install the blade obtained in S4 into a special fixture and fix it; S5.3: Shot peening is performed according to the processing parameters set by the CNC shot peening machine; S6: Second vibration finishing S6.1: For the blades obtained in S5, the blade areas that do not need to be vibrated are protected by special protective covers; S6.2: Install the blade on a special fixture and load abrasive into the vibration finishing machine; set processing parameters and perform the second vibration finishing; S6.3: After the second vibration finishing, the surface roughness of the blade body is checked using a roughness measuring instrument to complete the stress control method.

2. The stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair according to claim 1, characterized in that: In S1, the vacuum heat treatment process is to place the blade into the vacuum heat treatment furnace when the temperature is ≤150°C, heat it to (600±10)°C, keep it warm for 4h~4h15min, fill the furnace with argon gas, control the pressure at 0.18~0.2MPa, cool it to below 80°C and take it out of the furnace to complete the vacuum heat treatment.

3. The stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair according to claim 1, characterized in that: In S3.2, the abrasive is a side-cut cylindrical abrasive, and the abrasive covers the blade part by at least 30 mm. The processing parameters are: vibration finishing for 4 hours, water spray flow rate of 150-200 / h, water spray time of 20s, and water spray interval of 300s.

4. The stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair according to claim 1, characterized in that: In S3.3, the surface roughness of the blade body should not be greater than 0.4 μm.

5. The stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair according to claim 1, characterized in that: In S4.1, the laser spot is set to be circular with a diameter of 2.8 mm and the laser energy is set to 18 J.

6. The stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair according to claim 1, characterized in that: In S4.3, the absorption layer is a black tape with a specification of 25 mm in width and 0.25 mm in thickness.

7. The stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair according to claim 1, characterized in that: In S5.3, the processing parameters are: shot specification is Z300, nozzle diameter is φ12mm, air pressure is 1Bar, saturation time is 1 time, nozzle to workpiece distance: 20±10mm, nozzle moving speed is 50mm / min, and flow rate is 950g / min.

8. The stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair according to claim 1, characterized in that: In S6.2, the abrasive is a spherical abrasive, and the abrasive covers the blade part by at least 30 mm. The processing parameters are: vibration finishing for 1 hour; water spray flow rate of 150-200 l / h, water spray time of 20 s, and water spray interval time of 300 s.

9. The stress control method for improving fatigue strength of titanium alloy rotor blades after welding repair according to claim 1, characterized in that: In S6.3, the surface roughness of the blade body should not be greater than 0.4 μm.

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