Nondestructive laser cleaning method and cleaning device for surface of aluminum alloy workpiece

Abstract

The invention discloses a nondestructive laser cleaning method and device for the surface of an aluminum alloy workpiece. The cleaning method comprises the ten steps of fixing a workpiece, determining a cleaning area, planning a flat-topped laser scanning path, setting parameters of the flat-topped laser, starting cleaning of the flat-topped laser, planning a scanning path of the Gaussian laser, setting parameters of the Gaussian laser, starting cleaning of the Gaussian laser, judging the cleaning effect and completing cleaning. The cleaning device comprises a workbench, an image acquisition device, a flat-top laser, a Gaussian laser and a dynamic focusing optical system, wherein the workbench is connected with a computer control system and can move a platform in a 3D mode. The laser paint removing method has the beneficial effects that under the double-pulse laser action of the flat-top laser and the Gaussian laser, the thermal elastic expansion between the paint layer and the substrate generated by the flat-top laser is larger than the adhesive force effect between the paint layer and the substrate, the edge of the expanded paint layer is accurately cut by the Gaussian laser, and the efficient and lossless laser paint removing technology is obtained. And a more efficient, uniform and safe cleaning effect is achieved.

Description

Technical Field

[0001] The invention relates to a cleaning method and a cleaning device, in particular to a non-destructive laser cleaning method and a cleaning device for the surface of an aluminum alloy workpiece, belonging to the technical field of laser cleaning. Background Art

[0002] Aluminum alloy materials have the advantages of light weight and outstanding mechanical properties, and are widely used in the aviation industry. In order to meet the requirements of aircraft flight safety performance and extend the service life of aircraft, aircraft need to be thoroughly depainted every 5-6 years. Traditional removal methods are time-consuming and labor-intensive, and seriously pollute the environment. Laser cleaning technology has unique advantages such as high efficiency, environmental protection, wide application, and high cleaning accuracy. It is a promising way to remove paint.

[0003] At present, laser paint removal in the aviation industry mainly studies high-power laser cleaning devices and methods. Due to the inevitable thermal effect of the laser action process, the paint removal process can easily damage the surface of the aluminum alloy substrate. Reasonable configuration of laser process parameters can reduce the damage to the aluminum alloy substrate, but the laser cleaning efficiency cannot be guaranteed.

[0004] Chinese patent CN 118616422 A discloses a multi-wavelength laser composite cleaning device, system and method thereof. Lasers of different wavelengths can be combined into a combined laser beam through an optical path composite mechanism to shoot at the same location of the object to be cleaned, or multiple laser beams can be formed to shoot at different locations of the object to be cleaned; the production effects are respectively to improve the cleaning quality and cleaning efficiency. However, when combining into a combined laser beam for cleaning, the power parameters of different wavelengths cannot be accurately controlled, which will cause damage to the surface of the workpiece; multiple laser beams to different locations of the object to be cleaned will cause inconsistent cleaning effects and quality. This technical solution cannot take into account both cleaning quality and cleaning efficiency at the same time. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to address the problems of relatively low cleaning efficiency and severe thermal damage in the prior art, and to propose a non-destructive laser cleaning method and cleaning device for the surface of an aluminum alloy workpiece. Under the action of a double-pulse laser, the flat-top laser produces a thermal elastic expansion of the paint layer and the substrate that is greater than the adhesion between the two. The second laser beam accurately cuts the edge of the expanded paint layer, obtaining an efficient and non-destructive laser paint removal technology, and achieving a more efficient, uniform and safe cleaning effect.

[0006] Technical solution: A non-destructive laser cleaning method for the surface of an aluminum alloy workpiece, comprising the following steps:

[0007] Step 1: Fix the workpiece on the workbench with a 3D movable platform;

[0008] Step 2: Determine the cleaning area, determine the starting position for measurement and cleaning, and set the measurement parameters of the contour measurement system according to the working environment;

[0009] Step 3: Plan the flat-top laser scanning path. Plan the scanning path of the flat-top laser beam according to the size and shape of the area to be cleaned acquired in step 2, and store the starting, process and end point coordinate parameters. The scanning path matches the shape and size of the area to be cleaned. If the area to be cleaned is square, the path adopts a square shape. If the area to be cleaned is smaller than the large spot diameter, a single large spot is used.

[0010] Step 4: Setting the flat-top laser parameters according to the physicochemical properties of the paint layer, the physicochemical properties of the substrate and the laser parameters;

[0011] Step 5: Start the flat-top laser cleaning, and start the flat-top laser to complete the scanning of the entire cleaning area according to the scanning path planned in step 3;

[0012] Step 6: planning the Gaussian laser scanning path, planning a Gaussian laser scanning path with an outer closed loop according to the shape formed by the flat-top laser scanning in step 3 and the image collected after the flat-top laser cleaning; further correcting the Gaussian laser scanning path by collecting the image after the flat-top laser cleaning;

[0013] Step 7: Setting Gaussian laser parameters: Setting Gaussian laser parameters according to the physicochemical properties of the paint layer, the physicochemical properties of the substrate and the laser parameters;

[0014] Step 8: Start the Gaussian laser for cleaning. Start the Gaussian laser to scan the entire cleaning area according to the scanning path planned in step 6.

[0015] Step 9: Determine the cleaning effect. If the test result shows that there is still a residual paint layer on the surface of the workpiece, the system will re-execute from step 2 until the cleaning effect meets the set requirements; if the test result shows that the surface of the workpiece meets the cleaning requirements, go to step 10;

[0016] Step 10: After cleaning is completed, shut down and maintain the laser cleaning device.

[0017] The present invention can achieve lossless high cleaning quality through the flat-top laser beam emitted by the flat-top laser and the Gaussian laser beam emitted by the Gaussian laser. According to the combination of force effect and thermal effect, the paint layer expands and bulges after the flat-top laser beam performs preliminary treatment on the surface of the workpiece, and the Gaussian laser beam accurately cuts the paint layer on the surface of the workpiece, and finally the surface paint layer falls off directly. Compared with the traditional single-beam laser cleaning device, the cleaning quality is significantly improved. The flat-top laser beam emitted by the flat-top laser in the present invention has a uniform distribution of the energy of the flat-top laser beam on the surface of the workpiece, making the cleaning process more uniform and effectively avoiding the phenomenon of incomplete cleaning or local over-cleaning. The present invention greatly improves the laser cleaning efficiency through the combination of rapid laser endothermic expansion and edge cutting. The performance requirements of the two lasers used are not high, and compared with the single-beam laser paint removal that requires high energy and high power lasers, the cost of the equipment is greatly reduced.

[0018] Preferably, in order to separate the paint layer from the aluminum alloy while avoiding thermal damage to the aluminum alloy substrate, the flat-top laser emits a flat-top beam, the spot of the flat-top beam is a large spot, and the diameter of the large spot ranges from 50um to 5cm;

[0019] The flat-top laser parameter in step 4 is the flat-top laser energy density W1, which is calculated as follows:

[0020]

[0021] Where W1 is the flat-top laser energy density of the flat-top laser, K is the thermal conductivity, δ is the reflectivity of the material to the laser, τ is the pulse width, α is the thermal diffusivity, d is the distance between the two parallel planes of the primer and the substrate, and H 12 is the Hamaker coefficient of the contact between the substrate and the paint layer, with the unit of N·m, σ is the thermal expansion coefficient of the paint layer, with the unit of 1 / °C or 1 / °F, and E is the Young's modulus of elasticity of the paint layer, with the unit of Pascal or psi.

[0022] After the laser energy of the large spot is absorbed by the paint layer, due to the different physical and chemical properties of the aluminum alloy and the paint layer, the surface paint layer expands or bulges due to the thermal effect of the flat-top laser, and the connection between the paint layer and the substrate is greatly weakened. Since the melting point of the aluminum alloy substrate is much higher than the set temperature generated by the laser, thermal damage to the aluminum alloy substrate is avoided.

[0023] The flat-top laser uses a large spot of flat-top light, because the energy distribution of the flat-top light is relatively uniform, which guarantees consistent energy density over a large area. The laser energy is quickly absorbed by the surface material, and the laser energy density is low. At this time, the temperature is not enough to melt the surface paint layer, but only cause expansion or bubbling. Therefore, the mechanism is not traditional ablation vaporization. The large spot flat-top beam provides a relatively uniform low energy density in a larger area, which can cause the paint layer to be physically separated and peeled off in a larger range, and the paint layer is pushed away or expanded as a whole through this softer force effect.

[0024] Preferably, in order to accurately control the laser energy density of the flat-top laser to achieve separation of the paint layer from the aluminum alloy while avoiding thermal damage to the aluminum alloy substrate, the laser energy density of the flat-top laser is less than the laser removal threshold of the paint layer and less than the laser damage threshold of the aluminum alloy.

[0025] Preferably, in order to improve the cleaning efficiency, the scanning path of the flat-top laser is planned in step 3 as a single spot or a scanning superimposed spot; the spot size and the scanning mode are set according to the shape and size of the area to be cleaned;

[0026] When the area to be cleaned is large, the spot diameter used is 50um-1cm, and a scanning beam is used to form a large spot. The scanning method is "bow" shape or "spiral" shape or other scanning methods; when the diameter of the area to be cleaned is less than 5cm and relatively scattered, a spot diameter of 1cm-5cm is used, and a large spot of a single beam is used.

[0027] Preferably, in order to improve efficiency while avoiding affecting cleaning quality, the superposition rate of the scanning superimposed light spots is -20%<η1<10%.

[0028] Preferably, in order to achieve efficient and non-destructive removal of the paint layer, the Gaussian laser emits a Gaussian beam, and the spot of the Gaussian beam is a small spot, and the diameter of the spot ranges from 1um to 50um, because the energy distribution center of the Gaussian beam is the strongest, and the farther away from the center, the weaker the energy. The small spot can concentrate the laser energy in a very small area, generating an extremely high laser energy density. After the laser is absorbed, the surface temperature of the paint layer rises, exceeding the vaporization temperature of the paint layer, resulting in the edge of the paint layer being cut, so that the paint layer is quickly peeled off in a large area, achieving efficient and non-destructive removal of the paint layer.

[0029] The Gaussian laser parameter in step 7 is the Gaussian laser energy density W2, which is calculated as follows:

[0030]

[0031] Among them, T s is the vaporization temperature of the paint layer, K is the thermal conductivity, α is the thermal diffusivity, δ is the reflectivity of the material to the laser, and τ is the pulse width.

[0032] Preferably, in order to precisely control the laser energy density of the Gaussian laser to achieve separation of the paint layer from the aluminum alloy while avoiding thermal damage to the aluminum alloy substrate, the laser energy density of the Gaussian laser is greater than the laser removal threshold of the paint layer but less than the laser damage threshold of the aluminum alloy.

[0033] Preferably, in order to improve efficiency while avoiding affecting cleaning quality, when planning the Gaussian laser scanning path in step six, the laser beam scanning path of the Gaussian laser covers the outer edge of the laser beam of the flat-top laser, and the superposition rate of the scanning superimposed light spots is 0.1%<η2<30%.

[0034] There are many ways to combine the two laser beams. The contour scanned by the flat-top laser acting on the surface of the material can be square, rectangular, circular, etc., which is specifically set according to the shape and size of the area to be cleaned. The Gaussian laser acting on the surface of the material scans along the edge of the contour scanned by the flat-top laser, and is corrected in combination with the collected contour image scanned by the flat-top laser to cover the edge of the flat-top laser contour.

[0035] The scanning path of the flat-top laser is in the shape of a "bow", forming a filled square figure. The scanning starting point of the Gaussian laser is the same as that of the flat-top laser. The path scans clockwise or counterclockwise along the edge of the square figure to form a closed "mouth" shape.

[0036] A non-destructive laser cleaning device for the surface of an aluminum alloy workpiece, comprising a computer control system, a workbench with a 3D movable platform, an image acquisition device, a flat-top laser, a Gaussian laser and a dynamic focusing optical system, wherein the computer control system is respectively connected to the workbench with a 3D movable platform, the image acquisition device, the flat-top laser, the Gaussian laser and the dynamic focusing optical system by signals;

[0037] The dynamic focusing optical system includes a flat-top laser scanning galvanometer, a Gaussian laser scanning galvanometer, a beam combiner and an adjustable focusing lens system;

[0038] The flat-top laser emitted by the flat-top laser is sequentially focused to the workpiece surface by a flat-top laser scanning galvanometer, a beam combiner and an adjustable focusing lens system;

[0039] The Gaussian laser emitted by the Gaussian laser is sequentially focused to the surface of the workpiece by a Gaussian laser scanning galvanometer, a beam combiner and an adjustable focusing lens system;

[0040] The function of the adjustable focusing lens is to adjust the focal length of the laser beam so that the laser energy can be accurately focused on the workpiece surface to achieve efficient laser cleaning effect. The function of the flat-top laser scanning galvanometer, Gaussian laser scanning galvanometer and beam combiner is to quickly move the path of the laser beam, thereby achieving high-speed and high-precision laser scanning on the workpiece surface to ensure uniform cleaning and processing.

[0041] The workpiece to be cleaned is fixed on a workbench with a 3D movable platform, and the movement of the workbench enables the setting of the cleaning trajectory;

[0042] The workbench of the 3D movable platform is suitable for moving in three directions, X, Y and Z, to ensure that the surface of the workpiece can be accurately aligned with the laser beam output by the laser, and the pulse laser cooperates with the workbench of the 3D movable platform. The workbench of the 3D movable platform is controlled by a computer control system, and the moving accuracy of the workbench of the 3D movable platform is 5μm.

[0043] The image acquisition device acquires images of the size and shape of the area to be cleaned on the surface of the workpiece and the cleaning effect and feeds them back to the computer control system.

[0044] The shooting direction of the image acquisition device is consistent with the irradiation direction of the pulse laser, so as to acquire the image of the workpiece located on the workbench of the 3D mobile platform.

[0045] Preferably, in order to avoid environmental pollution, a dust suction device is further included, the dust suction device is connected to the computer control system, and the dust suction device is turned on at the same time as the flat-top laser and the Gaussian laser. The dust suction device of the present invention is started synchronously with the laser cleaning process, can absorb the peeled coating or pollutants in real time, and prevent secondary pollution through a high-efficiency filter, so as to keep the working environment clean and meet environmental protection requirements.

[0046] Beneficial effects: Under the dual-pulse laser action of the flat-top laser and the Gaussian laser, the flat-top laser produces a thermoelastic expansion effect that is greater than the adhesion between the paint layer and the substrate, and the Gaussian laser accurately cuts the edge of the expanded paint layer, thereby obtaining a highly efficient and non-destructive laser paint removal technology. The device and method proposed in the present invention overcome the limitations of single-beam laser paint removal and achieve a more efficient, uniform and safe cleaning effect. The laser energy used in the present invention is far less than the energy requirement of existing single-beam laser paint removal, which is beneficial to reducing costs. The dust suction device of the present invention is started synchronously with the laser cleaning process, and can remove the stripped coating or contaminants in real time, and prevent secondary pollution through a high-efficiency filter, thereby keeping the working environment clean and meeting environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0048] Figure 1 is a flow chart of the cleaning method of the present invention;

[0049] Figure 2 It is a structural schematic diagram of the cleaning device of the present invention;

[0050] Figure 3 Schematic diagram of the laser cleaning path of the present invention Figure 1 ;

[0051] Figure 4 Schematic diagram of the laser cleaning path of the present invention Figure 2 ;

[0052] Figure 5 Schematic diagram of the laser cleaning path of the present invention Figure 3 ;

[0053] Figure 6 Schematic diagram of the laser cleaning path of the present invention Figure 4 ;

[0054] Figure 7 This is a scanning electron microscope image of the laser cleaning effect of the present invention. DETAILED DESCRIPTION

[0055] 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 part of the embodiments of the present invention, not all of the 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.

[0056] In the description of the present invention, it is necessary to understand that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0057] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0058] like Figure 1 and 2 As shown, a non-destructive laser cleaning method for the surface of an aluminum alloy workpiece comprises the following steps:

[0059] Step 1: Fix the workpiece. Fix the aluminum alloy workpiece to be cleaned on the workbench 2 with a 3D movable platform to ensure that the surface of the workpiece is flat. Start the image acquisition device 3 to capture the surface image of the aluminum alloy workpiece. The image acquisition device 3 transmits the image to the computer control system 1 for storage.

[0060] Step 2: Determine the cleaning area, determine the starting position for measurement and cleaning, and set the measurement parameters of the contour measurement system according to the working environment;

[0061] Step 3: Plan the flat-top laser scanning path. Plan the scanning path of the flat-top laser beam according to the size and shape of the area to be cleaned acquired in step 2, and store the starting, process and end point coordinate parameters. The scanning path matches the shape and size of the area to be cleaned. If the area to be cleaned is square, the path adopts a square shape. If the area to be cleaned is smaller than the large spot diameter, a single large spot is used.

[0062] like Figure 3-6 As shown, in order to improve the cleaning efficiency, the scanning path of the flat-top laser is planned in step 3 as a single spot or a scanning superimposed spot; the spot size and scanning mode are set according to the shape and size of the area to be cleaned;

[0063] When the area to be cleaned is large, the spot diameter used is 50um-1cm, and a scanning beam is used to form a large spot. The scanning method is "bow" shape or "spiral" shape or other scanning methods; when the diameter of the area to be cleaned is less than 5cm and relatively scattered, a spot diameter of 1cm-5cm is used, and a large spot of a single beam is used.

[0064] Step 4: Setting the flat-top laser parameters according to the physicochemical properties of the paint layer, the physicochemical properties of the substrate and the laser parameters;

[0065] In order to separate the paint layer from the aluminum alloy and avoid thermal damage to the aluminum alloy substrate, the flat-top laser emits a flat-top beam, the spot of the flat-top beam is a large spot, and the diameter of the large spot ranges from 50um to 5cm;

[0066]

[0067] Where W1 is the flat-top laser energy density of the flat-top laser, K is the thermal conductivity, δ is the reflectivity of the material to the laser, τ is the pulse width, α is the thermal diffusivity, d is the distance between the two parallel planes of the primer and the substrate, and H 12is the Hamaker coefficient of the contact between the substrate and the paint layer, with the unit of N·m, σ is the thermal expansion coefficient of the paint layer, with the unit of 1 / °C or 1 / °F, and E is the Young's modulus of elasticity of the paint layer, with the unit of Pascal or psi.

[0068] Calculations show that when the flat-top laser energy density is 4.456 J / cm2, the surface will expand or bulge. When the flat-top laser energy density is greater than 4.456 J / cm2, the surface primer will be ablated and vaporized.

[0069] The flat-top laser parameters of the flat-top laser 4 are set as follows: the flat-top laser energy density is 3.819 J / cm2-4.456 J / cm2, the scanning speed is 1500 mm / s-2000 mm / s and the frequency is 80 kHz-100 kHz (a pulsed laser with a laser power parameter range of 0 W-100 W is selected). In order to protect the aluminum alloy substrate, the computer control system 1 will ensure that the laser parameters are within a safe range to avoid damage to the substrate. At the same time, the adjustable focusing lens system 64 in the dynamic focusing optical system accurately positions the laser beam focus on the paint layer on the surface of the aluminum alloy.

[0070] The flat-top laser beam of the flat-top laser 4 is started, and the computer control system 1 instructs the workbench 2 with a 3D movable platform to move the aluminum alloy workpiece under the laser beam. The flat-top laser beam causes the surface of the paint layer to expand rapidly due to heat, resulting in bulging or loosening, thereby reducing the bonding strength between the paint layer and the aluminum alloy substrate.

[0071] After the laser energy of the large spot is absorbed by the paint layer, due to the different physical and chemical properties of the aluminum alloy and the paint layer, the surface paint layer expands or bulges due to the thermal effect of the flat-top laser, and the connection between the paint layer and the substrate is greatly weakened. Since the melting point of the aluminum alloy substrate is much higher than the temperature generated by the laser, thermal damage to the aluminum alloy substrate is avoided.

[0072] The flat-top laser 4 uses a flat-top light with a large spot, because the energy distribution of the flat-top laser is relatively uniform, which ensures that a consistent energy density is provided over a large area. The laser energy is quickly absorbed by the surface material, and the laser energy density is low. At this time, the temperature is not enough to melt the surface paint layer, but only causes expansion or bubbling. Therefore, the mechanism is not the traditional ablation vaporization. The flat-top laser beam with a large spot provides a relatively uniform low energy density in a large area, which can cause the paint layer to be physically separated and peeled off in a large range, and the paint layer is pushed away or expanded as a whole through this softer force effect.

[0073] In order to accurately control the laser energy density of the flat-top laser 4 to achieve separation of the paint layer and the aluminum alloy while avoiding thermal damage to the aluminum alloy substrate, the laser energy density of the flat-top laser 4 is less than the laser removal threshold of the paint layer and less than the laser damage threshold of the aluminum alloy.

[0074] In order to improve the efficiency and avoid affecting the cleaning quality, the superposition rate of the scanning superimposed light spots is -20%<η1<10%.

[0075] Step 5: Start the flat-top laser cleaning, and start the flat-top laser to complete the scanning of the entire cleaning area according to the scanning path planned in step 3;

[0076] Step 6: Plan the scanning path of the Gaussian laser 5. According to the shape formed by the flat-top laser scanning in step 3 and the image collected after the flat-top laser 4 is cleaned, plan the scanning path of the Gaussian laser 5 with a peripheral closed loop; further correct the scanning path of the Gaussian laser 5 by collecting the image after the flat-top laser 4 is cleaned;

[0077] like Figure 3-6 As shown, in order to improve efficiency while avoiding affecting the cleaning quality, when planning the scanning path of the Gaussian laser 5 in step six, the laser beam scanning path of the Gaussian laser 5 covers the outer edge of the laser beam of the flat-top laser 4, and the superposition rate of the scanning superimposed light spots is 0.1%<η2<30%.

[0078] Step 7, setting the parameters of the Gaussian laser 5, according to the physicochemical properties of the paint layer, the physicochemical properties of the substrate and the laser parameters;

[0079] In order to achieve efficient and non-destructive removal of the paint layer, the Gaussian laser emits a Gaussian beam, and the spot of the Gaussian beam is a small spot with a diameter range of 1um-50um, because the energy distribution center of the Gaussian beam is the strongest, and the farther away from the center, the weaker the energy. The small spot can concentrate the laser energy in a very small area, generating an extremely high laser energy density. After the laser is absorbed, the surface temperature of the paint layer rises, exceeding the vaporization temperature of the paint layer, resulting in the edge of the paint layer being cut, so that the paint layer is quickly peeled off in a large area, achieving efficient and non-destructive removal of the paint layer.

[0080] The parameter of the Gaussian laser 5 in step 7 is the Gaussian laser energy density W2, which is calculated as follows:

[0081]

[0082] Among them, T s is the vaporization temperature of the paint layer, K is the thermal conductivity, α is the thermal diffusivity, δ is the reflectivity of the material to the laser, and τ is the pulse width.

[0083] After the preliminary treatment is completed, the computer control system 1 starts the Gaussian laser of the Gaussian laser 5 again, and the Gaussian laser parameters are energy density of 9.549J / cm2-11.459J / cm2, scanning speed of 1200mm / s-2000mm / s and frequency of 80kHz-100kHz, and controls the workbench 2 with a 3D movable platform to move the aluminum alloy workpiece to the irradiation area of ​​the flat-top laser. The Gaussian laser accurately cuts and peels off the loosened edge of the paint layer to ensure that the paint layer is completely removed from the aluminum alloy surface while avoiding damage to the substrate. The Gaussian laser scanning galvanometer 62 ensures that the laser beam accurately removes the edge of the paint layer.

[0084] In order to accurately control the laser energy density of the Gaussian laser 5 to achieve separation of the paint layer from the aluminum alloy while avoiding thermal damage to the aluminum alloy substrate, the laser energy density of the Gaussian laser 5 is greater than the laser removal threshold of the paint layer but less than the laser damage threshold of the aluminum alloy.

[0085] Step 8: Start the Gaussian laser 5 for cleaning. Start the Gaussian laser 5 to complete the scanning of the entire cleaning area according to the scanning path planned in step 6;

[0086] Step 9: Determine the cleaning effect. If the test result shows that there is still a residual paint layer on the surface of the workpiece, the system will re-execute from step 2 until the cleaning effect meets the set requirements; if the test result shows that the surface of the workpiece meets the cleaning requirements, go to step 10;

[0087] Step 10: After cleaning is completed, shut down and maintain the laser cleaning device.

[0088] The present invention can achieve lossless high cleaning quality through the flat-top laser beam emitted by the flat-top laser and the Gaussian laser beam emitted by the Gaussian laser. According to the combination of force effect and thermal effect, the paint layer expands and bulges after the flat-top laser beam performs preliminary treatment on the surface of the workpiece, and the Gaussian laser beam accurately cuts the paint layer on the surface of the workpiece, and finally the surface paint layer falls off directly. Compared with the traditional single-beam laser cleaning device, the cleaning quality is significantly improved. The flat-top laser beam emitted by the flat-top laser in the present invention has a uniform distribution of the energy of the flat-top laser beam on the surface of the workpiece, making the cleaning process more uniform and effectively avoiding the phenomenon of incomplete cleaning or local over-cleaning. The present invention greatly improves the laser cleaning efficiency through the combination of rapid laser endothermic expansion and edge cutting. The performance requirements of the two lasers used are not high, and compared with the single-beam laser paint removal that requires high energy and high power lasers, the cost of the equipment is greatly reduced.

[0089] like Figure 2As shown, a non-destructive laser cleaning device for the surface of an aluminum alloy workpiece comprises a computer control system 1, a workbench 2 with a 3D movable platform, an image acquisition device 3, a flat-top laser 4, a Gaussian laser 5 and a dynamic focusing optical system 6, wherein the computer control system 1 is respectively connected to the workbench 2 with a 3D movable platform, the image acquisition device 3, the flat-top laser 4, the Gaussian laser 5 and the dynamic focusing optical system 6 by signals;

[0090] The dynamic focusing optical system 6 includes a flat-top laser scanning galvanometer 61, a Gaussian laser scanning galvanometer 62, a beam combiner 63 and an adjustable focusing lens system 64;

[0091] The function of the adjustable focusing lens 64 is to adjust the focal length of the laser beam so that the laser energy can be accurately focused on the workpiece surface to achieve an efficient laser cleaning effect.

[0092] The flat-top laser emitted by the flat-top laser 4 is focused to the workpiece surface through the flat-top laser scanning galvanometer 61, the beam combiner 63 and the adjustable focusing lens system 64 in sequence;

[0093] The Gaussian laser emitted by the Gaussian laser 5 is sequentially focused to the workpiece surface by passing through the Gaussian laser scanning galvanometer 62, the beam combiner 63 and the adjustable focusing lens system 64;

[0094] The function of the flat-top laser scanning galvanometer 61, Gaussian laser scanning galvanometer 62 and beam combiner 63 is to quickly move the path of the laser beam, thereby achieving high-speed and high-precision laser scanning on the surface of the workpiece to ensure uniform cleaning and processing.

[0095] The workpiece to be cleaned is fixed on the workbench 2 of the 3D movable platform, and the workbench 2 moves to set the cleaning trajectory; the workbench 2 of the 3D movable platform is suitable for moving in the three directions of X, Y, and Z to ensure that the surface of the workpiece can be accurately aligned with the laser beam output by the laser, and the pulse laser cooperates with the workbench 2 of the 3D movable platform. The workbench 2 of the 3D movable platform is controlled by a computer control system 1, and the moving accuracy of the workbench 2 of the 3D movable platform is 5μm.

[0096] The image acquisition device 3 collects images of the size and shape of the area to be cleaned on the surface of the workpiece and the cleaning effect and feeds them back to the computer control system 1. The shooting direction of the image acquisition device 3 is consistent with the irradiation direction of the pulse laser to collect images of the workpiece on the workbench 2 of the 3D mobile platform.

[0097] The cleaning system further comprises a dust collecting device 7, which is connected to the computer control system 1 and is turned on simultaneously with the flat-top laser 4 and the Gaussian laser 5. The dust collecting device 7 is started synchronously during the cleaning process to ensure that the stripped coating or pollutants are removed immediately to prevent secondary pollution.

[0098] like Figure 3 As shown, in this embodiment, Figure 3 (a) is the large spot scanning path of the first flat-top laser beam of the flat-top laser 4. The first flat-top light beam relies on a large spot (diameter range of 1mm-5mm) with a large area and uniform energy distribution according to the force effect to expand or bubble the paint layer, and the "bow" shape can effectively reduce the superposition of heat, so that the material can be heated more evenly and reduce thermal damage; Figure 3 (b) is the small spot scanning path of the second Gaussian laser emitted by the Gaussian laser 5. The second Gaussian light needs to concentrate energy in a small spot (diameter range 0.2mm-0.5mm) according to the thermal effect, and realizes material cutting through high-temperature melting or gasification. The cleaning path starting points of the first flat-top light and the second Gaussian light are the same.

[0099] like Figure 4 As shown, in this embodiment, Figure 4 (a) is the large spot scanning path of the first flat-top laser beam emitted by the flat-top laser 4. The large spot of the first flat-top light beam is rectangular (side length range is 1m-5mm), and the scanning path is a "bow" shape, which can effectively reduce thermal damage; Figure 4 (b) is the small spot scanning path of the second Gaussian laser emitted by the Gaussian laser 5. The second Gaussian light needs to concentrate energy in a small spot (diameter range 0.2mm-0.5mm) according to the thermal effect, and realizes material cutting through high-temperature melting or gasification. The cleaning path starting points of the first flat-top light and the second Gaussian light are the same.

[0100] like Figure 5 As shown, in this embodiment, Figure 5 (a) is a scanning path of a large spot (diameter range 0.2mm-0.5mm) of the first flat-top light beam emitted by the flat-top laser 4, and the spiral scanning path can reduce repeated ablation and effectively avoid ineffective movement of the laser beam; Figure 5 (b) is the scanning path of the second Gaussian light beam emitted by the Gaussian laser 5. The second Gaussian light beam needs to concentrate energy in a small spot (diameter range 0.2mm-0.5mm) according to the thermal effect, and realizes material cutting through high-temperature melting or gasification. The cleaning path of the second Gaussian light beam is along the edge of the large spot of the first flat-top light beam.

[0101] like Figure 6 As shown, in this example, Figure 6 (a) is a large spot of the first flat-top laser of the flat-top laser 4. When the diameter of the area to be cleaned is less than 5 cm and is relatively dispersed, a spot diameter of 1 cm-5 cm is used, and a large spot of a single beam is used. Figure 6(b) is the scanning path of the small spot of the second Gaussian laser emitted by the Gaussian laser. The direct range of the small spot is 0.2mm-0.5mm. The cleaning path of the second Gaussian light is along the edge of the large spot of the first flat-top light.

[0102] like Figure 7 As shown, in this embodiment, the laser energy density of the second Gaussian laser emitted by the fixed Gaussian laser 5 is 11.459 J / cm2, the frequency is 100 kHz and the scanning speed is 1500 mm / s, and the frequency of the first Gaussian laser emitted by the fixed flat-top laser 4 is 100 kHz and the scanning speed is 1500 mm / s. Figure 7 These are scanning electron microscope images at different laser energy densities. The flat-top laser energy density in the leftmost electron microscope image is 3.183J / cm2, and it can be seen that the paint layer on the surface of the aluminum alloy is slightly melted, but due to insufficient energy density, the expansion and bulging effect cannot be achieved, so it is not cleaned thoroughly; the flat-top laser energy density in the middle electron microscope image is 3.565J / cm2, and the surface is relatively smooth and the cleaning path can be seen, with only a small amount of contaminants on the surface, and the cleaning effect is best at this time; the flat-top laser energy density on the rightmost is 4.074J / cm2, and due to the high laser energy density, it can be seen that the surface is blackened and damages the substrate, resulting in excessive cleaning.

[0103] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0104] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined in this specification may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A non-destructive laser cleaning method for the surface of an aluminum alloy workpiece, characterized in that: The following steps are involved: Step 1: Fix the workpiece on the workbench with a 3D movable platform; Step 2: Determine the cleaning area, determine the starting position for measurement and cleaning, and set the measurement parameters of the contour measurement system according to the working environment; Step 3: Plan the flat-top laser scanning path, plan the scanning path of the flat-top laser beam according to the size and shape of the area to be cleaned acquired in step 2, and store the starting, process and end point coordinate parameters; Step 4: Setting the flat-top laser parameters according to the physicochemical properties of the paint layer, the physicochemical properties of the substrate and the laser parameters; Step 5: Start the flat-top laser cleaning, and start the flat-top laser to complete the scanning of the entire cleaning area according to the scanning path planned in step 3; Step 6: planning a Gaussian laser scanning path, and planning a Gaussian laser scanning path to form an outer closed loop according to the shape formed by the flat-top laser scanning in step 3 and the image collected after the flat-top laser cleaning; Step 7: Setting Gaussian laser parameters: Setting Gaussian laser parameters according to the physicochemical properties of the paint layer, the physicochemical properties of the substrate and the laser parameters; Step 8: Start the Gaussian laser for cleaning. Start the Gaussian laser to scan the entire cleaning area according to the scanning path planned in step 6. Step 9: Determine the cleaning effect. If the test result shows that there is still a residual paint layer on the surface of the workpiece, the system will re-execute from step 2 until the cleaning effect meets the set requirements; if the test result shows that the surface of the workpiece meets the cleaning requirements, go to step 10; Step 10: After cleaning is completed, shut down and maintain the laser cleaning device.

2. The non-destructive laser cleaning method for the surface of an aluminum alloy workpiece according to claim 1, characterized in that: The flat-top laser emits a flat-top beam, the spot of the flat-top beam is a large spot, and the diameter of the large spot ranges from 50um to 5cm; The flat-top laser parameter in step 4 is the flat-top laser energy density W1, which is calculated as follows: Where W1 is the flat-top laser energy density of the flat-top laser, K is the thermal conductivity, δ is the reflectivity of the material to the laser, τ is the pulse width, α is the thermal diffusivity, d is the distance between the two parallel planes of the primer and the substrate, and H 12 is the Hamaker coefficient of the contact between the substrate and the paint layer, with the unit of N·m, σ is the thermal expansion coefficient of the paint layer, with the unit of 1 / °C or 1 / °F, and E is the Young's modulus of elasticity of the paint layer, with the unit of Pascal or psi.

3. The non-destructive laser cleaning method for the surface of an aluminum alloy workpiece according to claim 2, characterized in that: The laser energy density of the flat-top laser is less than the laser removal threshold of the paint layer and less than the laser damage threshold of the aluminum alloy.

4. The non-destructive laser cleaning method for the surface of an aluminum alloy workpiece according to claim 1, characterized in that: In the step 3, the scanning path of the flat-top laser is planned to be a single light spot or a scanning superimposed light spot; When the spot diameter is 50um-1cm, a scanning beam is used to form a large spot, and the scanning method is "bow" or "spiral"; when the spot diameter is 1cm-5cm, a single beam large spot is used.

5. The non-destructive laser cleaning method for the surface of an aluminum alloy workpiece according to claim 4, characterized in that: The superposition rate of the scanning superimposed light spots is -20%<η1<10%.

6. The non-destructive laser cleaning method for the surface of an aluminum alloy workpiece according to claim 1, characterized in that: The Gaussian laser emits a Gaussian beam, the spot of the Gaussian beam is a small spot, and the diameter of the spot ranges from 1um to 50um. The Gaussian laser parameter in step 7 is the Gaussian laser energy density W2, which is calculated as follows: Among them, T s is the vaporization temperature of the paint layer, K is the thermal conductivity, α is the thermal diffusivity, δ is the reflectivity of the material to the laser, and τ is the pulse width.

7. The non-destructive laser cleaning method for the surface of an aluminum alloy workpiece according to claim 6, characterized in that: The laser energy density of the Gaussian laser is greater than the laser removal threshold of the paint layer, but less than the laser damage threshold of the aluminum alloy.

8. The non-destructive laser cleaning method for the surface of an aluminum alloy workpiece according to claim 1, characterized in that: When planning the scanning path of the Gaussian laser in step 6, the scanning path of the laser beam of the Gaussian laser covers the outer edge of the laser beam of the flat-top laser, and the superposition rate of the scanning superimposed light spots is 0.1%<η2<30%.

9. A cleaning device for implementing the non-destructive laser cleaning method for the surface of an aluminum alloy workpiece according to claim 1, characterized in that: The invention comprises a computer control system (1), a workbench (2) with a 3D movable platform, an image acquisition device (3), a flat-top laser (4), a Gaussian laser (5) and a dynamic focusing optical system (6), wherein the computer control system (1) is respectively connected to the workbench (2) with a 3D movable platform, the image acquisition device (3), the flat-top laser (4), the Gaussian laser (5) and the dynamic focusing optical system (6) by signals; The dynamic focusing optical system (6) comprises a flat-top laser scanning galvanometer (61), a Gaussian laser scanning galvanometer (62), a beam combiner (63) and an adjustable focusing lens system (64); The flat-top laser emitted by the flat-top laser (4) is focused onto the surface of the workpiece through a flat-top laser scanning galvanometer (61), a beam combiner (63) and an adjustable focusing lens system (64) in sequence; The Gaussian laser emitted by the Gaussian laser (5) is focused onto the surface of the workpiece through a Gaussian laser scanning galvanometer (62), a beam combiner (63) and an adjustable focusing lens system (64) in sequence; The workpiece to be cleaned is fixed on a workbench (2) which is a 3D movable platform, and the workbench (2) moves to achieve the setting of the cleaning trajectory; The image acquisition device (3) acquires images of the size and shape of the area to be cleaned on the surface of the workpiece and the cleaning effect and feeds them back to the computer control system (1).

10. The cleaning device of the non-destructive laser cleaning method for the surface of an aluminum alloy workpiece according to claim 9, characterized in that: It also comprises a dust suction device (7), wherein the dust suction device (7) is connected to the computer control system (1) for control, and the dust suction device (7) is turned on simultaneously with the flat-top laser (4) and the Gaussian laser (5).

Images