Electromagnetic induction heating assisted laser shock peening method suitable for complex curved surface

Abstract

The invention particularly relates to an electromagnetic induction heating-assisted laser shock peening method suitable for a complex curved surface, which comprises the following steps: evaluating a surface to be processed, and carrying out block division and path planning according to the curvature of the surface to be processed; determining technological parameters of laser shock peening and electromagnetic induction heating; selecting and installing an induction heating coil; adjusting the posture of the device to enable the laser outlet and the coil to adapt to the surface of the processing area; coating an absorbing layer, and starting an electromagnetic induction device to preheat a processing area; carrying out laser shock peening assisted by electromagnetic induction heating; part surface state real-time monitoring and device posture adjustment; and checking the processing effect until all the blocks are processed. According to the processing method for block division, path planning and surface condition real-time monitoring to guide attitude adjustment, surface temperature uniformity can be ensured when curved surfaces with irregular shapes are processed, and three types of scanning strategies are provided for different types of curved surfaces, so that the processing effect is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of laser processing technology, specifically relating to an electromagnetic induction heating-assisted laser shock strengthening method suitable for complex curved surfaces. Background Technology

[0002] In the aerospace field, critical hot-end components such as high-pressure turbine blades, combustion chamber walls, and nozzle guides are subjected to extremely harsh high-temperature and high-pressure service environments for extended periods. To improve the fatigue resistance and corrosion resistance of these components and extend their service life, various surface strengthening processes such as laser shock peening (LSP), shot peening, and rolling are typically used to treat their surfaces and introduce a residual compressive stress layer.

[0003] Laser shock peening, also known as laser shot peening, is a novel surface strengthening technology characterized by high pressure, high energy, and high strain rate. Compared to other surface strengthening technologies, laser shot peening can significantly improve the microstructure and residual stress distribution of material surfaces while maintaining relatively low surface roughness, thereby greatly extending the fatigue life of parts. This technology is currently widely used in aerospace, shipbuilding, and rail transportation fields to enhance the performance of core components.

[0004] However, traditional laser shock peening has significant limitations. Parts treated with laser shock peening are often subjected to long-term high-temperature service environments, and rapid stress release can lead to a rapid weakening or even disappearance of the strengthening effect, shortening the service life of the parts and potentially causing major safety accidents. Therefore, improving the thermal stability of residual compressive stress in the strengthened layer and delaying its stress release in high-temperature environments is a crucial technical challenge currently facing laser shock peening.

[0005] Building upon laser peening technology, thermo-coupling techniques have been combined to propose warm peening, which involves laser shock peening under specific temperature conditions. This thermal activation promotes the interaction between dislocations, solute atoms, and precipitated phases, effectively suppressing dislocation recovery and migration at high temperatures and enhancing the thermal stability of residual stress and the microstructure's resistance to recovery. While this technology can delay stress release to some extent, existing warm peening equipment and processes are not yet mature. Heating methods primarily rely on heat conduction, resulting in a shallow heat-affected zone, slow energy transfer efficiency, and imprecise temperature control. Furthermore, for parts with complex geometries and irregular curved surfaces, existing heating methods suffer from uneven heating and uncontrollable heat-affected zone and depth. This significantly increases the difficulty of implementing warm peening, leading to uneven and unreliable residual stress, thus limiting its practical application in component strengthening and repair.

[0006] Existing technologies such as CN114737044A and CN114603252B disclose methods for electromagnetic induction heating-assisted laser shock strengthening, and limit parameters such as spot size and pulse frequency. However, when processing workpieces with complex curved surfaces or non-uniform surface morphology, technical challenges exist, such as difficulty in real-time control of coupling distance and uneven heating and strengthening. CN115755081A proposes to monitor and adjust the working distance and path of laser shock strengthening in real time through an image measurement system and a laser rangefinder, but it does not address the spatial layout of the electromagnetic induction heating coil and its deep integration and control with the laser process.

[0007] To address the aforementioned challenges, this invention proposes a novel method that combines workpiece surface segmentation with laser shock peening path planning, real-time surface condition monitoring, and electromagnetic induction heating coil design. The core technology lies in acquiring real-time three-dimensional information of the workpiece surface through a vision system and multiple temperature and distance sensors. The strengthening path is automatically optimized by segmenting according to surface curvature, and the collaborative attitude adaptive control of the electromagnetic induction heating coil and the laser head is achieved. During processing, the system automatically adjusts the spatial position and coupling distance of the electromagnetic induction heating coil and the laser head based on the surface condition and real-time temperature, achieving uniform and precise strengthening and heating distribution.

[0008] This method significantly improves the adaptability and uniformity of the strengthening process for complex curved surfaces or irregularly shaped parts, and overcomes the problems of existing technologies that can only strengthen simple surfaces or local areas and are prone to overheating or heating dead zones. It has high engineering practical value and promising prospects for promotion. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention provides a method for electromagnetic induction heating-assisted laser shock strengthening. The aim is to enhance the machinability of materials by introducing electromagnetic induction heating into the laser shock strengthening process, thereby implementing precise, inside-out heat transfer on various parts to be processed at the processing site, and enhancing the thermal stability of the residual compressive stress introduced by laser shock strengthening, thus preventing stress release during the service of materials in high-temperature environments.

[0010] To achieve the above objectives, the present invention provides the following solution:

[0011] An electromagnetic induction heating-assisted laser shock strengthening method applicable to complex curved surfaces, the method comprising:

[0012] S1. Evaluate the surface morphology, material, and processing requirements of the workpiece to be processed. Divide the surface of the workpiece to be processed into n processing blocks according to the curvature of the surface and plan the laser shock scanning path for each processing block.

[0013] S2. Select the process parameters for laser shock strengthening and electromagnetic induction heating, determine the energy, spot size, and overlap rate of laser shock strengthening, and preliminarily determine the range of electromagnetic induction heating current parameters.

[0014] S3. Select a modular electromagnetic induction heating coil that meets the preset adaptation requirements of the processing block and install it. Adjust the spatial position of the motion control module connected to the light outlet and the motion end of the electromagnetic induction heating coil so that the central axis of the electromagnetic induction heating coil on the winding plane is coaxial with the laser light outlet and perpendicular to the surface of the workpiece to be processed.

[0015] S4. Coat the surface of the workpiece to be processed with an absorption layer, turn on the temperature monitoring sensor, and pass current into the electromagnetic induction heating coil based on the electromagnetic induction heating current parameter range to locally preheat the initial impact position of the workpiece surface.

[0016] S5. Open the constraint layer spraying system and laser. Based on the three-dimensional morphology and local temperature distribution of the electromagnetic induction heating coil and the surface of the workpiece to be processed, adjust the frequency of the current flowing through the electromagnetic induction heating coil and fine-tune the spatial orientation of the electromagnetic induction heating coil so that the electromagnetic induction heating coil is parallel to the surface of the workpiece to be processed.

[0017] S6. After completing the laser shock strengthening of one path, position the shock device as a whole at the starting position of the next path, repeat the processing steps of S3-S5 n times until all laser shock strengthening paths are completed, turn off the laser and the constraint layer spraying system, disconnect the induction heating power supply, and the vision monitoring system collects the surface information of the processed workpiece.

[0018] Preferably, the electromagnetic induction heating coil is made of a circular copper tube with a wire diameter of 1 mm, and the surface is covered with an asbestos insulation layer. The number of turns is 3 to 6, and the turn spacing is less than half the diameter of the copper tube.

[0019] Preferably, the inner and outer diameter parameters of the electromagnetic induction heating coil are determined based on the designed inductance value L and the preset current frequency, wherein:

[0020]

[0021] Where N is the number of turns of the electromagnetic induction heating coil, and μ0 is the free permeability. d avg d1 is the average diameter of the electromagnetic induction heating coil, α is a dimensionless parameter representing the relative difference in diameter, d2 is the outer diameter of the electromagnetic induction heating coil, and d2 is the inner diameter of the electromagnetic induction heating coil.

[0022] Preferably, the electromagnetic induction heating coil adopts a modular design:

[0023] Multiple sets of modular electromagnetic induction heating coils with different numbers of turns, diameters, and turn spacings are prepared. Before laser impacting each processing block, the overall control system automatically selects and replaces the modular electromagnetic induction heating coil that meets the preset adaptation requirements of the current processing block based on the visual monitoring system and surface partition detection results.

[0024] Preferably, the laser shock scanning path planning for each processing block in S1 includes:

[0025] The laser shock strengthening path is determined according to the curved shape of the workpiece surface and is selected from XY path, YX path and spiral path. During the processing, the laser shock strengthening path is divided into several parts, and preheating and laser shock strengthening are performed in stages after the electromagnetic induction heating coil posture is adjusted.

[0026] Preferred,

[0027] The XY and YX paths are suitable for curved surfaces that approximate cylinders. During the laser shock process, each preheating process impacts a straight trajectory along the preset curvature direction.

[0028] Spiral paths are suitable for parabolic surfaces with similar protrusions or depressions. For protruding parabolic surfaces, after preheating, the impact starts from the center of the protruding parabolic surface. For concave parabolic surfaces, the impact starts from the outer edge of the concave parabolic surface.

[0029] Preferably, the electromagnetic induction heating current parameter range in S2 is 1kHz to 5kHz.

[0030] Preferred,

[0031]

[0032] Where T is the preset steady-state temperature, T0 is the ambient temperature, δ is the current penetration depth, h is the convective heat transfer coefficient, P0 is the volume power density of the induced current inside the conductive material, and P 电 Let η be the total output power of the power supply, η be the system thermal efficiency, and A be the projected area of ​​the electromagnetic induction coil.

[0033] Preferred,

[0034] The laser shock strengthening parameters are selected according to the material properties. The specific parameters are as follows: pulse energy 5-10J, pulse width 10-15ns, wavelength 1064nm, spot diameter 2-3mm, and overlap rate 50%.

[0035] The absorbent layer is made of high-temperature resistant black paint;

[0036] The constraint layer is made of high-temperature resistant glycerin.

[0037] Preferably, the temperature monitoring sensor is used to monitor the temperature of the workpiece surface during preheating and processing, wherein the temperature of the workpiece surface is determined according to the type of material of the workpiece during processing.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] 1. The processing method for block division, path planning, and real-time monitoring of surface condition to guide attitude adjustment provided by the present invention can ensure uniform surface temperature when processing irregular curved surfaces, and provides three major categories of scanning strategies for different types of curved surfaces to enhance the processing effect.

[0040] 2. This invention employs a combination of non-contact electromagnetic induction heating and laser shock, which can be adapted to the surface treatment of high-temperature service components with different morphologies and alloy systems. The processing temperature is precisely adjustable, and it provides guidance for the design and manufacturing of electromagnetic induction heating coils.

[0041] 3. The processing method provided by the present invention can improve the thermal stability of the compressive stress layer formed by laser shock strengthening, promote the coupling effect between dislocations and solute atoms, enhance the dislocation pinning effect, prevent stress release of hot-end components during service, improve stress retention rate, and extend the effective period of strengthening effect.

[0042] 4. The processing method provided by this invention can enhance the physical and mechanical properties of various parts surfaces, reduce the problem of insufficient plasticity caused by localized thermal hardening of materials, and enable more complete transmission of laser shock energy on the material surface, thereby improving the thickness and uniformity of the residual compressive stress layer and achieving a deeper and more stable strengthening effect. It can generate a deeper residual compressive stress layer and a heat-treated hardened layer on the surface of parts, improving the material's hardness, fatigue resistance, high-temperature resistance, and stress corrosion resistance. Attached Figure Description

[0043] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the process flow of an electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to an embodiment of the present invention;

[0045] Figure 2 This is a schematic diagram of the overall structure of the electromagnetic induction heating-assisted laser shock stress strengthening system according to an embodiment of the present invention;

[0046] Figure 3This is a schematic diagram of the laser shock scanning path according to an embodiment of the present invention, wherein (a) is a schematic diagram of the XY path, (b) is a schematic diagram of the YX path, and (c) is a schematic diagram of the spiral path;

[0047] Figure 4 This is a schematic diagram of the scanning path for two types of curved surfaces according to an embodiment of the present invention;

[0048] Figure captions: 1-Surface of workpiece to be processed, 2-Constraint layer spraying system, 3-Induction coil support arm, 4-Pulsed laser, 5-Laser output port, 6-Temperature monitoring sensor, 7-Electromagnetic induction heating coil, 8-Vision monitoring system. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] Example 1

[0052] Single laser shock peening faces the problems of shallow plastic layer and excessively rapid stress release under high temperature environment. Existing laser shot peening processes have complex heating methods, limited application scenarios, and are prone to uneven heating when processing curved surfaces.

[0053] To solve the above problems, such as Figure 1 As shown, this invention provides an electromagnetic induction heating-assisted laser shock strengthening method suitable for complex curved surfaces, the method comprising:

[0054] S1. Evaluate the surface morphology, material, and processing requirements of the workpiece to be processed. Divide the surface of the workpiece to be processed into n processing blocks according to the curvature of the surface and plan the laser shock scanning path for each processing block.

[0055] S2. Select the process parameters for laser shock peening and electromagnetic induction heating, determine the energy, spot size, and overlap rate of laser shock peening, and determine the range of electromagnetic induction heating current parameters.

[0056] S3. Select a modular electromagnetic induction heating coil that meets the preset adaptation requirements of the processing block and install it. Adjust the spatial position of the motion control module connected to the light outlet and the motion end of the electromagnetic induction heating coil so that the central axis of the electromagnetic induction heating coil on the winding plane is coaxial with the laser light outlet and perpendicular to the surface of the workpiece to be processed.

[0057] S4. Coat the surface of the workpiece to be processed with an absorption layer, turn on the temperature monitoring sensor, and pass current into the electromagnetic induction heating coil based on the electromagnetic induction heating current parameter range to locally preheat the initial impact position of the workpiece surface.

[0058] S5. Open the constraint layer spraying system and laser. Based on the three-dimensional morphology and local temperature distribution of the electromagnetic induction heating coil and the surface of the workpiece to be processed, adjust the frequency of the current flowing through the electromagnetic induction heating coil and fine-tune the spatial orientation of the electromagnetic induction heating coil so that the electromagnetic induction heating coil is parallel to the surface of the workpiece to be processed.

[0059] S6. After completing the laser shock strengthening of one path, position the shock device as a whole at the starting position of the next path, repeat the processing steps of S3-S5 n times until all laser shock strengthening paths are completed, turn off the laser and the constraint layer spraying system, disconnect the induction heating power supply, and the vision monitoring system collects the surface information of the processed workpiece.

[0060] like Figure 2 As shown, the overall structure of the electromagnetic induction heating assisted laser shock stress strengthening system of this invention includes: 1-the surface of the workpiece to be processed, 2-the constraint layer spraying system, 3-the induction coil support arm, 4-the pulsed laser, 5-the laser light outlet, 6-the temperature monitoring sensor, 7-the electromagnetic induction heating coil, and 8-the visual monitoring system.

[0061] This invention provides a reference-type laser shock peening device, which mainly comprises four parts: a motion control module, a laser generator, a laser spatial transmission device, and a device platform. The motion control module is primarily a robotic arm, with a laser output port and an electromagnetic induction heating coil mounting interface at its moving end for adjusting their spatial position during processing. The laser generator produces high-peak-power pulsed laser light, with programmable parameters such as laser output frequency, pulse energy, and pulse width. The laser spatial transmission device, composed of a series of lenses and optical fibers, transmits the pulsed laser light generated by the laser generator to the laser output port in the motion control module without affecting the robotic arm's movement. The device platform, supporting the three modules, has motor-driven rollers and a locking device installed underneath. When the entire shock peening device needs to be positioned and moved, the rollers move the platform. After reaching the predetermined processing position, the platform locks, ensuring the stability of the device during laser shock peening.

[0062] Furthermore, the specific implementation process of this invention is as follows:

[0063] A visual monitoring system is set up to determine the material, shape, and size of the workpiece surface. Based on these parameters, the shape, size, and working coupling distance of the electromagnetic induction heating coil relative to the workpiece are initially determined.

[0064] Based on the surface material of the workpiece to be processed and the processing requirements, the laser shock strengthening path, spot size and overlap rate are planned, and the curvature and roughness parameters of the workpiece surface to be processed are collected along the path. The overall laser shock strengthening path is divided into several paths according to the surface curvature information of the material to be processed, so as to ensure that the surface curvature fluctuation within each path is small. Based on the above parameters and processing requirements, the corresponding working environment is built in the programming software.

[0065] Based on real-time acquired surface three-dimensional data, key parameters of the electromagnetic induction heating coil (such as number of turns, diameter, and turn spacing) are optimized, and based on this, the coil is selected and installed in a preset modular coil to ensure that the selected coil structure and layout are precisely matched with the surface morphology of each zone, thereby maximizing local heating efficiency.

[0066] Adjust the spatial position of the device so that the electromagnetic induction heating coil and the light outlet are coaxial and perpendicular to the surface of the workpiece to be processed, and ensure the initial coupling distance of the electromagnetic induction heating coil.

[0067] An absorbent layer is coated on the surface of the workpiece to be processed.

[0068] Turn on the temperature monitoring sensor and pass current into the electromagnetic induction heating coil to preheat the initial impact position on the surface of the workpiece to be processed.

[0069] Turn on the constraint layer spraying system.

[0070] The laser is turned on to implement the laser shock peening process assisted by electromagnetic induction heating. During the processing, the system continuously monitors the three-dimensional morphology and local temperature distribution of the heating coil and the workpiece surface, and automatically adjusts the spatial orientation, coupling distance and excitation current of the electromagnetic induction heating coil to achieve closed-loop optimization control of the heating process, ensuring that the temperature of the processing area is kept near the preset steady-state temperature, and that the laser incident angle is always perpendicular to the position to be processed.

[0071] After completing the impact enhancement of one path, the impact device is positioned at the starting position of the next path, and the above processing process is repeated.

[0072] After completing all processes, the laser and constraint layer spraying system are turned off, the induction heating power supply is disconnected, and the vision monitoring system collects surface information after processing to ensure the processing effect.

[0073] Furthermore, the electromagnetic induction heating coil can be replaced according to the specific process conditions. It is made of a circular copper tube with a wire diameter of 1mm, and the surface is covered with an asbestos heat insulation layer. The number of turns is 3 to 6, and the turn spacing is less than half the diameter of the copper tube.

[0074] The inner and outer diameter parameters of the electromagnetic induction heating coil are determined based on the designed inductance value L (μH) and the preset current frequency, wherein:

[0075]

[0076] Where N is the number of turns of the electromagnetic induction heating coil, and μ0 is the free permeability (H / m). d avg d1 is the average diameter of the electromagnetic induction heating coil, α is a dimensionless parameter representing the relative difference in diameter, d1 is the outer diameter (m) of the electromagnetic induction heating coil, and d2 is the inner diameter (m) of the electromagnetic induction heating coil. L should be in the range of 0.2 to 1 μH.

[0077] The electromagnetic induction heating coil adopts a modular design, with multiple sets of modular electromagnetic induction heating coils having different numbers of turns, diameters, and turn spacings. Before laser impact treatment of each processing area, the overall control system can automatically select and replace the electromagnetic induction heating coil that meets the preset adaptation requirements of the current processing area based on the visual monitoring system and surface zoning detection results. For areas with different curvatures, surface features, and strengthening requirements, the installation is automatically switched through the system control platform.

[0078] Furthermore, the coupling distance is determined during processing by the surface shape data of the workpiece, the laser shock strengthening path, and the material type collected by the vision monitoring system. It is adjusted by the motion control device, and its approximate range is determined by the type of material being processed. For ferromagnetic materials such as nickel-based alloys, the coupling distance is controlled between 6 and 9 mm, while for non-ferromagnetic materials such as titanium alloys, the coupling distance is controlled between 4 and 7 mm.

[0079] Furthermore, such as Figure 3 , Figure 4 As shown, in order to ensure that the surface of the workpiece is heated evenly during the impact strengthening process, the impact path should be determined according to the shape of the curved surface. Specifically, three trajectories can be selected: XY path, YX path, and spiral path. During the processing, the path can be divided into several parts, and preheating and impact strengthening are performed in stages after the posture adjustment, thereby ensuring that the processed surface is heated evenly.

[0080] Among them, the XY path and YX path are suitable for curved surfaces that are approximately cylindrical. During the laser shock process, each preheating process impacts a straight trajectory along the preset curvature direction (the direction with smaller curvature), and then the attitude is adjusted to ensure that the electromagnetic induction heating coil is parallel to the current impact path tangential before repeating the processing process.

[0081] Spiral paths are suitable for parabolic surfaces with protrusions or depressions. For protruding parabolic surfaces, after preheating, the impact starts from the center of the protruding parabolic surface. After processing a certain area, the attitude is adjusted according to the working conditions to reduce the coupling distance so that the surrounding lower positions are fully heated before continuing the impact to strengthen the process. This process is repeated until the entire surface of the workpiece is processed. For concave parabolic surfaces, the impact starts from the outer edge of the concave parabolic surface.

[0082] Furthermore, the frequency of the current flowing through the electromagnetic induction heating coil should ensure that the current penetration depth δ of the electromagnetic induction heating coil is greater than the depth of the laser shock reinforced residual stress layer. Where δ is the current penetration depth (mm), ρ is the workpiece resistivity (Ω), μ is the relative permeability of the workpiece, f is the AC electric field frequency (Hz), the current penetration depth is greater than or equal to 1.5mm, and the current frequency range is 1kHz to 5kHz.

[0083] Furthermore, during the electromagnetic induction heating-assisted laser shock enhancement process for each processing block, a steady-state temperature is preset to obtain the best processing effect, which is calculated as follows:

[0084]

[0085] Where T is the preset steady-state temperature, T0 is the ambient temperature, δ is the current penetration depth, h is the convective heat transfer coefficient, and P0 is the volume power density of the induced current inside the conductive material (W / m³). 3 ), P 电 Let η be the total output power of the power supply (kW), η be the system thermal efficiency, which can be approximated as 0.7, and A be the projected area of ​​the electromagnetic induction coil.

[0086] Furthermore, the laser shock enhancement parameters are: pulse energy 5-10J, pulse width 10-15ns, wavelength 1064nm, spot diameter 2-3mm, and overlap rate 50%.

[0087] The absorbent layer is made of high-temperature resistant black paint;

[0088] The constraint layer is made of high-temperature resistant glycerin.

[0089] Furthermore, a temperature monitoring sensor is used to monitor the surface temperature of the workpiece during preheating and processing. During processing, the surface temperature of the workpiece is determined based on the material type of the workpiece, ensuring it remains within 0.4T. m , among which, T m This is the melting temperature of the material to be processed.

[0090] Temperature monitoring sensors are embedded in the process path, enabling closed-loop temperature control of each zone during processing. If the temperature in a certain area is insufficient, the system automatically increases the heating current or extends the local heating time. For areas with large curvature and high heat loss, high-turn electromagnetic induction heating coils or increased induced current are preferentially used to achieve compensatory heating and ensure consistent overall strengthening effect.

[0091] In summary, this invention, during laser shock peening, comprehensively utilizes multi-source monitoring information such as surface three-dimensional morphology and real-time temperature and distance to automatically optimize the processing area based on surface curvature, and adaptively adjusts the laser shock path and electromagnetic induction heating parameters accordingly, achieving precise matching of peening to different morphological regions. By implementing closed-loop optimization control of the electromagnetic induction heating coil parameters (such as number of turns, diameter, turn spacing, and spatial orientation) and its coupling distance with the workpiece surface, each region is kept in an optimal heating and strengthening state throughout the entire strengthening process. This method can effectively promote stable coupling between dislocations and alloying elements in the strengthened layer, delay stress relaxation and microstructure recovery under high-temperature service conditions, significantly improve the thermal stability of residual compressive stress inside the part, thereby enhancing the long-term service reliability and failure resistance of key components.

[0092] This invention introduces electromagnetic induction heating into the laser shock strengthening process to precisely heat various parts to be processed from the inside out on the processing site, thereby enhancing the machinability of the material and improving the thermal stability of the residual compressive stress introduced by laser shock strengthening, thus preventing stress release during the service of the material in a high-temperature environment.

[0093] Example 2

[0094] This embodiment illustrates the implementation process of the electromagnetic induction heating-assisted laser shock strengthening method applicable to complex curved surfaces in the aforementioned embodiment using specific data, as follows:

[0095] This embodiment takes the repair of damage to the root of an aircraft turbine blade made of nickel-based superalloy (IN718) as an example. The area to be processed is a rectangular area with a size of approximately 40mm*20mm on the outer surface of the root.

[0096] First, based on the processing requirements, a suitable modular electromagnetic induction heating coil was selected. The coil was made of a circular copper tube with a wire diameter of 1mm, and the surface was covered with a 0.5mm thick asbestos insulation layer to prevent heat radiation damage to the coil. Considering the structural characteristics of the turbine blade root, a circular planar coil with an inner diameter of 18mm and an outer diameter of 22mm was selected, with 4 turns and a turn spacing of 0.4mm.

[0097] The electromagnetic induction heating process parameters were determined, and the temperature required for electromagnetic pulse induction heating assisted by laser shock peening should be maintained at 0.4T. m , among which, T m This refers to the melting temperature of the metal material to be processed. The pulse power supply frequency is selected according to the process requirements. Based on the operating conditions in this embodiment, medium-frequency induction heating is used, with the current frequency set to 3kHz, corresponding to an effective current value of 650A and a power density of approximately 0.62W / mm². 2 This ensures a heating depth of approximately 2.5 mm, covering the thickness of the residual stress layer strengthened by laser shock.

[0098] The coupling distance during the processing is automatically controlled by the surface three-dimensional morphology data measured by the vision monitoring system. For nickel-based alloys such as IN718, the coupling distance is set to 6mm ± 0.5mm. In areas with large curvature, the distance can be increased to 8mm to avoid local overheating.

[0099] The second step is to set up a device so that the electromagnetic induction heating coil and the light outlet are coaxial and perpendicular to the surface of the turbine blade processing position. The temperature monitoring device can acquire the surface temperature of the workpiece in real time, and the visual monitoring system can acquire the surface morphology information of the material.

[0100] The third step involves the visual monitoring system acquiring information such as the surface shape and roughness of the workpiece to be processed. In this embodiment, the area to be processed is a rectangular region with dimensions of approximately 40mm x 20mm on the outer surface of the root. Due to the curvature differences in the root morphology, the processing area is first divided into four near-rectangular blocks with smaller curvatures based on the curvature distribution, and an XY-type scanning path is selected to achieve localized uniform heating and strengthening. The corresponding working environment is then built in the programming software based on the above parameters.

[0101] The fourth step is to coat the turbine blades with high-temperature resistant black paint as an absorbent layer at the locations to be machined.

[0102] The fifth step involves passing current through the electromagnetic induction heating coil to preheat the area near the first path. Temperature monitoring is used to wait for the surface temperature of the turbine blade to be repaired to reach approximately 500°C. Throughout the entire processing, this area should be kept stable at this temperature.

[0103] Step 6: Turn on the flow-guiding and spraying robot to form a uniformly thick constraint layer on the surface of the workpiece to be processed. Preferably, the selected constraint layer is a clear, high-temperature resistant glycerin.

[0104] Step 7: Perform electromagnetic induction heating-assisted laser shock blasting on the first path. Turn on the laser and implement the electromagnetic induction heating-assisted laser shock blasting process. During processing, the system continuously monitors the three-dimensional morphology and local temperature distribution of the electromagnetic induction heating coil and the workpiece surface, automatically adjusting the spatial orientation, coupling distance, and excitation current of the electromagnetic induction heating coil to achieve closed-loop optimized control of the heating process. This ensures that the temperature in the processing area remains near the preset steady-state temperature, and the laser incident angle is always perpendicular to the position to be processed. The laser shock blasting parameters are: pulse energy 5J, pulse width 10ns, wavelength 1064nm, spot diameter 3mm, and overlap rate 50%.

[0105] In the eighth step, after completing the processing of the first path, the visual monitoring system collects the surface morphology information of the part and inputs these parameters into a preset program for analysis and calculation. Based on the results, the system guides the overall device to adjust its position so that the electromagnetic induction heating coil can effectively heat the surface where the second path is located.

[0106] Step 9: Repeat steps 5 through 8 until all four blocks are effectively processed.

[0107] Finally, the laser is turned off, the electromagnetic induction heating power supply is disconnected, and the constraint layer injection system is shut down to end the process. The repair and remanufacturing effect of the turbine blade root is then evaluated.

[0108] In summary, by introducing electromagnetic induction heating into the laser shock strengthening process, this invention can effectively and uniformly heat various curved surface parts from the inside out on the processing site, with precise control over the affected area and processing temperature, thereby enhancing the machinability of the material and improving the thermal stability of the residual compressive stress introduced by laser shock strengthening, thus preventing stress release during the service of the material in a high-temperature environment.

[0109] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for electromagnetic induction heating assisted laser shock strengthening suitable for complex curved surfaces, characterized in that, The method includes: S1. Evaluate the surface morphology, material, and processing requirements of the workpiece to be processed. Divide the surface of the workpiece to be processed into n processing blocks according to the curvature of the surface and plan the laser shock scanning path for each processing block. S2. Select the process parameters for laser shock peening and electromagnetic induction heating, determine the energy, spot size, and overlap rate of laser shock peening, and determine the range of electromagnetic induction heating current parameters. S3. Select a modular electromagnetic induction heating coil that meets the preset adaptation requirements of the processing block and install it. Adjust the spatial position of the motion control module connected to the light outlet and the motion end of the electromagnetic induction heating coil so that the central axis of the electromagnetic induction heating coil on the winding plane is coaxial with the laser light outlet and perpendicular to the surface of the workpiece to be processed. S4. Coat the surface of the workpiece to be processed with an absorption layer, turn on the temperature monitoring sensor, and pass current into the electromagnetic induction heating coil based on the electromagnetic induction heating current parameter range to locally preheat the initial impact position of the workpiece surface. S5. Open the constraint layer spraying system and laser. Based on the three-dimensional morphology and local temperature distribution of the electromagnetic induction heating coil and the surface of the workpiece to be processed, adjust the frequency of the current flowing through the electromagnetic induction heating coil and fine-tune the spatial orientation of the electromagnetic induction heating coil so that the electromagnetic induction heating coil is parallel to the surface of the workpiece to be processed. S6. After completing the laser shock strengthening of one path, position the shock device as a whole at the starting position of the next path, repeat the processing steps of S3-S5 n times until all laser shock strengthening paths are completed, turn off the laser and the constraint layer spraying system, disconnect the induction heating power supply, and the vision monitoring system collects the surface information of the processed workpiece.

2. The electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to claim 1, characterized in that, The electromagnetic induction heating coil is made of a circular copper tube with a wire diameter of 1 mm, and the surface is covered with an asbestos insulation layer. The number of turns is 3 to 6, and the spacing between the turns is less than half the diameter of the copper tube.

3. The electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to claim 2, characterized in that, The inner and outer diameter parameters of the electromagnetic induction heating coil are determined based on the designed inductance value L and the preset current frequency, wherein: Where N is the number of turns of the electromagnetic induction heating coil, and μ0 is the free permeability. d avg d1 is the average diameter of the electromagnetic induction heating coil, α is a dimensionless parameter representing the relative difference in diameter, d2 is the outer diameter of the electromagnetic induction heating coil, and d2 is the inner diameter of the electromagnetic induction heating coil.

4. The electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to claim 3, characterized in that, The electromagnetic induction heating coil adopts a modular design: Multiple sets of modular electromagnetic induction heating coils with different numbers of turns, diameters, and turn spacings are prepared. Before laser impacting each processing block, the overall control system automatically selects and replaces the modular electromagnetic induction heating coil that meets the preset adaptation requirements of the current processing block based on the visual monitoring system and surface partition detection results.

5. The electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to claim 1, characterized in that, The laser shock scanning path planning for each processing block in S1 includes: The laser shock strengthening path is determined according to the curved shape of the workpiece surface and is selected from XY path, YX path and spiral path. During the processing, the laser shock strengthening path is divided into several parts, and preheating and laser shock strengthening are performed in stages after the electromagnetic induction heating coil posture is adjusted.

6. The electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to claim 5, characterized in that, The XY and YX paths are suitable for curved surfaces that approximate cylinders. During the laser shock process, each preheating process impacts a straight trajectory along the preset curvature direction. Spiral paths are suitable for parabolic surfaces with similar protrusions or depressions. For protruding parabolic surfaces, after preheating, the impact starts from the center of the protruding parabolic surface. For concave parabolic surfaces, the impact starts from the outer edge of the concave parabolic surface.

7. The electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to claim 1, characterized in that, The electromagnetic induction heating current parameter range in S2 is 1kHz to 5kHz.

8. The electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to claim 1, characterized in that, Where T is the preset steady-state temperature, T0 is the ambient temperature, δ is the current penetration depth, h is the convective heat transfer coefficient, P0 is the volume power density of the induced current inside the conductive material, and P 电 Let η be the total output power of the power supply, η be the system thermal efficiency, and A be the projected area of ​​the electromagnetic induction coil.

9. The electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to claim 1, characterized in that, The laser shock strengthening parameters are selected according to the material properties. The specific parameters are as follows: pulse energy 5-10J, pulse width 10-15ns, wavelength 1064nm, spot diameter 2-3mm, and overlap rate 50%. The absorbent layer is made of high-temperature resistant black paint; The constraint layer is made of high-temperature resistant glycerin.

10. The electromagnetic induction heating-assisted laser shock strengthening method for complex curved surfaces according to claim 1, characterized in that, Temperature monitoring sensors are used to monitor the surface temperature of the workpiece during preheating and processing. The surface temperature of the workpiece is determined according to the type of material of the workpiece during processing.

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