Laser removal method of aircraft surface stealth coating responsive to recognizable substrate damage

Abstract

The present application relates to the field of aircraft surface laser advanced manufacturing technology, and discloses a laser removal method of aircraft surface stealth coating capable of identifying substrate damage response, comprising the following steps: 1) fixing a thermocouple on the bottom surface of the aircraft skin sample to be removed, and connecting the thermocouple with a temperature collector and a control end to record the temperature change of the bottom surface of the sample in real time; 2) placing the aircraft skin sample on a workbench with the stealth coating facing the laser; 3) turning on the laser, adjusting parameters, and removing the stealth coating; 4) observing the temperature change of the bottom surface of the sample in real time at the control end, and stopping the laser removal immediately when the temperature curve shows a steep increase trend. The present application links the substrate damage and the visual temperature change by using the temperature response caused by the laser directly acting on the substrate, converts the unobservable removal effect into the temperature curve change that can be monitored in real time, solves the pain point that the substrate damage cannot be identified in the laser removal process, and is convenient to operate and low in price.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser advanced manufacturing technology of aircraft surface, in particular to a laser removal method of aircraft surface stealth coating capable of identifying substrate damage response. BACKGROUND

[0002] Stealth technology is the world's cutting-edge technology, and the stealth coating is the key to aircraft stealth technology. The damage of the aircraft stealth coating can significantly deteriorate its stealth performance. In the process of repairing the stealth coating, the removal of the damaged coating is a key link. For the special coating on the aircraft surface, the commonly used chemical removal method has fatal hazards of substrate damage and penetration corrosion, which can significantly reduce the safety performance of the aircraft skin. The mechanical manual polishing removal has problems of inconsistent removal effect in a large area. The plastic medium jetting technology can cause stress damage on the surface and generate a large amount of waste, which is poor in environmental friendliness. At present, researchers focus on laser removal technology, hoping to use the advantages of non-contact and high control precision of the technology to realize the rapid removal of the stealth coating without damaging the substrate.

[0003] The main function of the aircraft surface stealth coating is the wave absorption performance. The functional requirements of strong electromagnetic wave absorption capacity and wide coverage frequency band determine that the coating thickness is mm level, which brings challenges to the goal of realizing non-damage substrate in the removal process. Since the coating has high laser absorption rate and contains a large amount of metal components, when the laser removes the stealth coating, obvious ablation and gasification phenomena occur, accompanied by sharp high temperature. The mm-level stealth coating needs to be removed by laser for multiple times. When the coating is almost completely removed, it is difficult to judge whether the surface substrate is directly affected by the laser by visual inspection. The laser heating effect can weaken the mechanical properties of the substrate material, thereby causing a significant decrease in the secondary service performance and seriously endangering the flight safety of the aircraft. SUMMARY

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a laser removal method of aircraft surface stealth coating capable of identifying substrate damage response.

[0005] In the research process, the inventors found that the change of temperature can determine whether the stealth coating on the surface of the sample is completely removed and the substrate is not damaged.

[0006] Therefore, the present application provides a laser removal method of stealth coating capable of identifying substrate damage response, comprising the following steps:

[0007] 1) fixing a thermocouple on the bottom surface of the aircraft skin sample to be removed, and connecting the thermocouple with a temperature collector and a control end to record the temperature change of the bottom surface of the sample in real time;

[0008] 2) placing the aircraft skin sample on a workbench, and the stealth coating faces the laser;

[0009] 3) Turn on the laser, adjust the parameters, and remove the stealth coating;

[0010] 4) Real-time observe the temperature change of the sample bottom surface at the control end, and stop the laser removal immediately when the temperature curve shows a steep increase tendency;

[0011] There is no special requirement for the high-precision thermocouple type used in the present application. The thermocouple can be a T-type, E-type, J-type, N-type, K-type, S-type, R-type, B-type, etc. thermocouple, or a general thermocouple, an armored thermocouple, a thin film thermocouple, various special thermocouples, etc.

[0012] Preferably, the thermocouple range in step 1) is -200-1800℃.

[0013] Preferably, the temperature collector in step 1) has a collection frequency of 1-1000Hz and a temperature measurement accuracy of ±0.5℃ or less. The collection frequency in the present application can be any value within 1-1000Hz and the range between any values, such as 10Hz, 100Hz, 200Hz, 300Hz, 400Hz, 500Hz, 600Hz, 700Hz, 800Hz, 900Hz, 10Hz-100Hz, 10Hz-200Hz, 10Hz-500Hz, 10Hz-1000Hz, 100Hz-500Hz, 100Hz-1000Hz, etc.

[0014] Preferably, the pulse laser in step 3) is a CO2 laser, a Nd:YAG laser or a fiber laser, the pulse laser has a power range of 10W-1000W, a laser wavelength range of 200nm-10.6μm, an output power range of 5%-100%, a pulse width range of 1ns-500ns, a pulse frequency range of 10Hz-2000kHz, a laser scanning speed range of 100mm / s-8000mm / s, and a line spacing range of 0.001mm-5mm.

[0015] Preferably, the average power density of the laser in step 3) is 10W / cm 2 -500W / cm 2 .

[0016] Preferably, a circular laser spot or a square laser spot is selected for laser processing in step 3), the diameter of the circular laser spot in step 3) is 10μm-20mm, and the side length of the square laser spot is 10μm-25mm.

[0017] Preferably, the stealth coating is removed 1-20 times according to the thickness of the stealth coating in step 3).

[0018] Preferably, the temperature abrupt increase in step 4) tends to be an order of magnitude change, including from two digits to three digits, and from three digits to four digits.

[0019] Preferably, the temperature abrupt increase in step 4) tends to be an order of magnitude change, including from two digits to three digits, and from three digits to four digits.

[0020] Preferably, when two digits ≤ 50℃, the order of magnitude change includes from two digits to ≥ 100℃; when two digits n is greater than 50℃, the order of magnitude change includes from two digits n to ≥ 2n℃.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] (1) The present application links the damage of the substrate to the visual temperature change caused by the temperature response of the laser directly acting on the substrate, and ingeniously converts the unmeasurable removal effect into a real-time monitorable temperature curve change, thereby solving the pain point of being unable to identify the damage of the substrate during laser removal.

[0023] (2) The present application proposes a strategy for monitoring temperature changes on the bottom surface of the sample, and temperature monitoring can be realized through a thermocouple, a collector and a control end, which is simple in structure, convenient to operate and low in price. Since the laser removal of the stealth coating will produce obvious flames, the present application avoids the problem of being unable to monitor the surface temperature of the sample due to the flames. At the same time, the problem of high cost and complex operation of the existing laser removal online monitoring devices such as laser-induced breakdown spectroscopy technology is solved.

[0024] (3) The present application can also be applied to other laser removal occasions, including composite cleaning, pre-welding treatment, etc., which can ensure that the surface of the sample can be removed cleanly, and has important significance for laser removal of non-destructive substrates. BRIEF DESCRIPTION OF DRAWINGS

[0025] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0026] Figure 1 Figure 1 is a schematic diagram of the laser removal method of the present application for the stealth coating with identifiable substrate damage response;

[0027] Figure 2 (a) is the cross-sectional morphology of the stealth before and after removal in Example 1, Figure 2 (b) is the hardness of the surface of the sample before and after treatment;

[0028] In the figure, 1 - aircraft skin sample, 2 - stealth coating, 3 - laser beam, 4 - laser, 5 - high-precision thermocouple, 6 - temperature collector, 7 - control end. DETAILED DESCRIPTION

[0029] The application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that for those skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made. These are within the scope of the application.

[0030] Example 1

[0031] The laser removal method of the aircraft surface stealth coating which can identify the damage response of the substrate is as follows:

[0032] First, fix the K-type high-precision thermocouple 5 on the bottom surface of the 2024 aluminum alloy aircraft skin sample to be removed, and connect it with the temperature collector 6 and the control end 7. The frequency of the temperature collector 6 is 100 Hz, and the temperature change of the bottom surface of the sample is recorded in real time;

[0033] Second, place the 2024 aluminum alloy aircraft skin sample on the workbench, and the thickness of the 1.05mm stealth coating 2 faces the laser 4;

[0034] Third, turn on the laser, and use a 100W fiber laser to remove the stealth coating. The high-speed movement of the X and Y galvanometer will apply laser energy to the coating surface in the form of two-dimensional arrangement. A 50μm circular laser spot is selected for laser processing, the laser wavelength is 10.6μm, and the output power is 40%. The pulse width is set to 100ns, and the pulse frequency is set to 100kHz. The stealth coating is removed by laser scanning point by point, line by line, and surface by surface. The scanning speed of the laser spot is set to 1500mm / s, the line spacing is set to 0.05mm, and the average laser power density is 50W / cm 2 ;

[0035] Fourth, observe the temperature change of the bottom surface of the sample in real time at the control end 7. After 5 times of laser removal, the temperature suddenly rises from 30℃ to 110℃, and the laser removal is immediately stopped;

[0036] Fifth, turn off the laser 4 and the temperature collection device 5-7, and clean the workbench. Take out the aircraft skin sample 1, and the removal work is completed.

[0037] As Figure 1The temperature acquisition device includes a high-precision thermocouple 5, a temperature collector 6 and a control end 7. The control end 7 can monitor the temperature change of the bottom surface of the sample 1 in real time. When the temperature increases sharply, the laser 4 is stopped immediately. The cross-sectional morphology before and after removal is shown in Figure 2 (a). At this time, the stealth coating has been completely removed. The hardness of the surface of the untreated sample and the sample after different treatments is shown in Figure 2 (b). It can be seen that the hardness of the sample whose laser is stopped immediately after the temperature increases sharply is equivalent to that of the untreated sample, and the substrate is basically not damaged, and the surface hardness is maintained at more than 130 HV. However, after the laser acts again after the temperature increases sharply, the hardness of the surface of the sample decreases to different degrees. After the laser acts once again, the surface hardness decreases to 113 HV, and after the laser acts twice, the surface hardness decreases to 104 HV. Therefore, the higher the scanning frequency, the more the mechanical properties are lost, and the substrate is damaged.

[0038] Example 2

[0039] In the first step, the bottom surface of the aircraft skin sample TC4 titanium alloy to be removed is fixed with a high-precision R-type thermocouple 5, which is connected with a temperature collector 6 and a control end 7. The frequency of the temperature collector 6 is 100 Hz, and the temperature change of the bottom surface of the sample is recorded in real time.

[0040] In the second step, the aircraft skin sample TC4 titanium alloy is placed on a workbench, and the stealth coating 2 with a thickness of 1.50 mm faces the laser 4.

[0041] In the third step, a 300W Nd:YAG laser is used to remove the stealth coating. The high-speed movement of the X and Y galvanometer mirrors causes the laser energy to act on the coating surface in a two-dimensional arrangement. A 5mm circular laser spot is selected for laser processing, and the laser wavelength is 1064nm and the output power is 80%. The pulse width is set to 70ns and the pulse frequency is set to 200kHz. The stealth coating is removed by laser scanning point by point, line by line and surface by surface. The scanning speed of the laser spot is set to 2000mm / s, the line spacing is set to 0.5mm, and the average laser power density is 200W / cm 2 .

[0042] In the fourth step, the temperature change of the bottom surface of the sample is observed in real time at the control end 7. After laser removal for 4 times, the temperature suddenly increases from 60℃ to 150℃, and the laser removal is stopped immediately.

[0043] In the fifth step, the laser 4 and the temperature acquisition device 5-7 are turned off, the workbench is cleaned, the aircraft skin sample 1 is taken out, and the removal work is completed.

[0044] Example 3

[0045] The first step is to fix an S-type high-precision thermocouple 5 on the bottom surface of the 316LN stainless steel sample of the aircraft skin to be removed, and connect it to the temperature acquisition device 6 and the control terminal 7. The temperature acquisition device 6 has a frequency of 10Hz and records the temperature change of the bottom surface of the sample in real time.

[0046] The second step is to place the aircraft skin sample made of 316LN stainless steel on the workbench, with the 3.05mm thick stealth coating 2 facing the laser 4.

[0047] The third step involves removing the stealth coating using a 500W Nd:YAG laser. The high-speed motion of the X and Y mirrors distributes the laser energy onto the coating surface in a two-dimensional arrangement. A 2mm square laser spot is used for laser processing, with a wavelength of 1030nm and an output power of 50%. The pulse width is set to 200ns, and the pulse frequency to 150kHz. The stealth coating is removed through point-by-point, line-by-line, and surface-by-surface laser scanning. The laser spot scanning speed is set to 2500mm / s, the line spacing to 0.02mm, and the average laser power density to 250W / cm². 2 ;

[0048] The fourth step is to observe the temperature change of the bottom surface of the sample in real time at the control terminal 7. After the laser removal is performed 7 times, the temperature suddenly rises from 80℃ to 300℃, and the laser removal is stopped immediately.

[0049] Step 5: Turn off laser 4 and temperature acquisition devices 5-7, clean the workbench, remove aircraft skin sample 1, and the removal work is complete.

[0050] Example 4

[0051] The first step is to fix a K-type high-precision thermocouple 5 to the bottom surface of the 7075 aluminum alloy sample of the aircraft skin to be removed, and connect it to the temperature acquisition device 6 and the control terminal 7. The temperature acquisition device 6 has a frequency of 10Hz and records the temperature change of the bottom surface of the sample in real time.

[0052] The second step is to place the aircraft skin sample 7075 aluminum alloy on the worktable, with the 2.15mm thick stealth coating 2 facing the laser 4.

[0053] The third step involves removing the stealth coating using a 100W CO2 laser. The high-speed motion of the X and Y mirrors distributes the laser energy onto the coating surface in a two-dimensional arrangement. A 20mm square laser spot is used for laser processing, with a wavelength of 200nm and an output power of 60%. The pulse width is set to 400ns, and the pulse frequency to 1000kHz. The stealth coating is removed through point-by-point, line-by-line, and surface-by-surface laser scanning. The laser spot scanning speed is set to 3000mm / s, the line spacing to 5mm, and the average laser power density to 100W / cm². 2 ;

[0054] Fourth step, in the control end 7 real-time observation sample bottom surface temperature change, laser removes 6 times, temperature from 40 ℃ suddenly increases to 120 ℃, immediately stop laser removal;

[0055] Fifth step, close laser 4 and temperature acquisition device 5-7, and clean the workbench, take out the aircraft skin sample 1, and the removal work is finished.

[0056] The specific embodiments of the application are described above. It should be understood that the application is not limited to the specific implementation described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the application.

Claims

1. A method of laser removal of a stealth coating that is responsive to recognition of damage to a substrate, characterized by, The method comprises the following steps: 1) fixing a thermocouple on the bottom surface of a sample piece of aircraft skin to be removed, and connecting the thermocouple with a temperature collector and a control terminal, and recording the temperature change of the bottom surface of the sample piece in real time; 2) placing the sample piece of aircraft skin on a workbench, with the stealth coating facing the laser; 3) turning on the laser, adjusting parameters, and removing the stealth coating; 4) observing the temperature change of the bottom surface of the sample piece in real time at the control terminal, and stopping the laser removal immediately when the temperature curve shows a steep increase tendency, wherein the steep increase tendency in step 4) is a magnitude change, including a change from two digits to three digits, and a change from three digits to four digits; when two digits ≤ 50 ℃, the magnitude change includes a change from two digits to ≥ 100 ℃; when two digits n is greater than 50 ℃, the magnitude change includes a change from two digits n to ≥ 2n ℃.

2. The stealth coating laser removal method of discernible substrate damage response according to claim 1, wherein, The thermocouple in step 1) has a range of -200~1800 ℃.

3. The stealth coating laser removal method of discernible substrate damage response according to claim 1, wherein, The temperature collector in step 1) has a collection frequency of 1~1000 Hz, and a temperature measurement accuracy of ±0.5 ℃ or less.

4. The stealth coating laser removal method of discernible substrate damage response according to claim 1, wherein, The pulsed laser in step 3) is a CO2 laser, an Nd:YAG laser or a fiber laser, the pulsed laser has a power range of 10 W~1000 W, a wavelength range of 200 nm~10.6 μm, a pulse width range of 1 ns~500 ns, a pulse frequency range of 10 Hz~2000 kHz, a laser scanning speed range of 100 mm / s~8000 mm / s, and a line spacing range of 0.001 mm~5 mm.

5. The stealth coating laser removal method of discernible substrate damage response according to claim 1, wherein, The average laser power density in the step 3) is in the range of 10 W / cm 2 500 W / cm 2 .

6. The stealth coating laser removal method of discernible substrate damage response according to claim 1, wherein, The circular laser spot or the square laser spot is selected for laser processing in step 3), the diameter of the circular laser spot in step 3) is 10 μm~20 mm, and the side length of the square laser spot is 10 μm~25 mm.

7. The stealth coating laser removal method of discernible substrate damage response according to claim 1, wherein, The stealth coating is removed for 1~20 times according to the thickness of the stealth coating in step 3).

8. The stealth coating laser removal method of discernible substrate damage response according to claim 1, wherein, The temperature steep increase tendency in step 4) is a magnitude change, including a magnitude change from 10 ℃ to 100 ℃, and a magnitude change from 100 ℃ to 1000 ℃.

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