Damaged part quick response additive repair method based on scanning track closed-loop regulation and control

Abstract

The invention provides a damaged part quick response additive repair method based on scanning track closed-loop regulation and control. Damage types of damaged parts include surface damage such as pits, cracks and spalling, the corresponding additive repairing process is completed by adjusting a laser beam scanning track in a real-time closed-loop mode based on the three-dimensional outline of a to-be-repaired area and the stability degree of a molten pool, and the method has the advantages of being rapid in repairing, few in post-processing procedure and wide in application range. According to the specific means, a high-speed camera coaxially arranged on the basis of a powder feeding cladding head observes the flowing condition of a molten pool on the repaired surface in real time, and closed-loop regulation and control over the moving path of the cladding head are conducted in combination with scanning track planning; the corresponding process comprises the steps of damaged area three-dimensional contour scanning, scanning repairing track planning, molten pool stability observation through a high-speed camera, marginal recognition and parameter track dynamic correction and damaged surface high-flatness repairing. Based on the method, efficient and accurate repairing of the service damaged part can be achieved, rapid response additive repairing can be conducted on multiple damage forms, and the method is particularly suitable for complex environments such as an external field.

Description

Technical Field

[0001] The invention relates to a fast-response additive repair method for damaged parts based on closed-loop control of scanning trajectories, and belongs to the technical field of additive repair. Background Art

[0002] Metal additive manufacturing technology is becoming more and more mature, and its key technologies are constantly making breakthroughs. It has been applied to the research and development, trial production and repair of damaged parts in the aviation field. The repair of damaged aircraft parts is part of the maintenance and support work. Repairing and remanufacturing aircraft based on additive manufacturing technology has solved the problem of high maintenance costs to a certain extent. The application of metal additive manufacturing in the repair of damaged parts has the advantages of not requiring a large number of spare parts, strong emergency support, and a short repair and remanufacturing cycle. It can repair the failed parts, worn parts or defective local areas to the shape, dimensional accuracy and performance status of the original parts, and meet the personalized repair needs of each part. For surface defects such as scratches, abrasions, wear and local deformation, the first step of additive repair and remanufacturing is to reverse the damaged area, obtain the spatial three-dimensional point cloud data of the parts with the help of certain data acquisition technology, and then convert it into a grid and fit it into surface, plane and solid features. After completing the contour scanning and feature reconstruction of the damaged part, the corresponding data is input into the additive manufacturing equipment processing system to plan the scanning path of the cladding head. After the additive repair is turned on, the laser power and scanning rate are the core process parameters that determine the quality of the repair while the cladding head moves along the preset path, and often determine the internal quality and surface flatness of the repaired part. Increasing the laser power and scanning speed can help accelerate the additive repair of the damaged part in the manufacturing process. However, the high laser power causes a violent impact on the melt, which often leads to deterioration of the stability of the molten pool and is easy to spheroidize and splash droplets, deteriorating the surface quality of the repaired area and increasing the subsequent processing steps. In addition, for additive repair of wear and cracking-type concave defects, the edge of the defect is more "sharp" than the bottom of the defect, and the amount of material required is less. The same additive repair process parameters for all parts of the defect tend to form a surface undulation that arches along the periphery of the damaged part. Therefore, the repaired and remanufactured parts obtained by generating a scanning trajectory based solely on the three-dimensional contour of the damaged area require subsequent secondary surface machining and flattening processes, which is not conducive to the efficient and rapid repair of damaged parts.

[0003] At present, the optimization methods for the surface undulations and poor forming quality of additively repaired parts are mainly regional forming, low-power forming and secondary machining. Regional forming is to divide the damaged area into deep and shallow areas according to the distance between the depth of the damaged area and the outer surface, and use high additive forming efficiency and low forming efficiency to fill and repair the deep and shallow areas respectively. Low-power forming technology is mainly aimed at shallow surface damage, such as surface corrosion, pitting, etc., and the overall repair and remanufacturing is carried out with relatively low heat source power. The specific method of secondary machining is to smooth the surface of the additive manufacturing site by manual grinding or mechanical milling technology.

[0004] However, most of the existing optimization methods for repairing damaged areas with poor forming quality sacrifice repair efficiency in exchange for improved repair flatness and precision, and cannot fundamentally achieve efficient, rapid, and accurate repair of damaged areas. Regional forming is only suitable for regularly shaped damage morphologies, and is not suitable for complex feature surfaces such as curved structures. Although low-power forming can improve surface flatness to a certain extent, it increases the time required for additive manufacturing repairs and weakens its rapid response advantage in complex environments. The secondary machining process increases labor costs and causes material waste. Therefore, it is urgent to develop a new type of rapid response additive repair technology for damaged areas to improve the surface quality of remanufacturing forming from the root. Summary of the invention

[0005] The purpose of the present invention is to provide a fast-response additive repair method for damaged parts based on closed-loop control of scanning trajectories, which is suitable for surface damage types such as pits, wear, local cracks, and peeling. The core technology is to use a high-speed camera to perform feature recognition on the three-dimensional contour and stability of the molten pool of the area to be repaired, and to control the movement trajectory of the cladding head based on a built-in algorithm in a closed loop. At the same time, key parameters are independently controlled to promote the rapid and precise flattening of the area to be repaired. The use of this technology can optimize the efficient, precise, and rapid repair of parts with various types of damage, reduce subsequent secondary machining, and is particularly suitable for complex usage scenarios.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A fast-response additive repair method for damaged parts based on closed-loop control of scanning trajectories, wherein the fast-response additive repair refers to the rapid identification, accurate and efficient repair of various types of damage forms in various environments. The means to achieve fast-response repair is to perform feature recognition of the three-dimensional contour and molten pool stability of the repaired area based on a high-speed camera, rely on built-in algorithms for judgment, and close-loop control of the cladding head movement trajectory and parameters such as laser power and powder feeding rate. The specific process is: three-dimensional contour scanning of the damaged area - cladding head movement trajectory planning - high-speed camera observation of molten pool stability - identification of margins and dynamic correction of parameter trajectories - stable solidification of the molten pool - high-flatness repair of the damaged surface.

[0008] The damaged component rapid response repair technology comprises the following steps:

[0009] Step 1: Pre-treatment preparation stage. Perform surface finishing on the damaged area to remove obvious burrs and other defects, and obtain the contour information of the area to be repaired by fast 3D contour scanning to plan the movement trajectory of the cladding head. Preset parameters such as laser power, scanning rate, powder feeding rate, etc., and set the high-speed filter recognition system to align the laser beam focus position. Start the molten pool monitoring-trajectory / parameter closed-loop control system.

[0010] Step 2: Start laser additive repair of the damaged area. After the laser beam melts the powder to form a molten pool on the surface of the substrate, a high-speed camera observes the surface of the molten pool and identifies the edge of the damaged area. It also performs feature recognition on the flow of the molten pool surface and the edge of the damaged area.

[0011] Step 3: Dynamic correction of cladding head trajectory and closed-loop parameters. Abnormal flow on the molten pool surface, splashing droplets and sharp edges of damaged areas are used as identification features, and corresponding thresholds are set. During the movement of the cladding head, when the high-speed camera captures abnormal reflective features on the molten pool surface caused by splashing and other factors, it is determined that the stability of the molten pool is poor at this time. The control system immediately reduces the laser power and powder feeding rate to improve the flow stability of the molten pool and promote surface smoothing. When the monitoring system observes that the molten pool surface is relatively stable, it is determined that the repair rate can be appropriately increased at this time, and the parameters are adjusted accordingly. At the same time, when the cladding head approaches the edge of the damaged area, the filter monitoring system simultaneously identifies the edge of the molten pool and the damaged area, and appropriately reduces the scanning rate and laser power when approaching the edge to ease the edge fluctuations. Through edge / molten pool monitoring-scanning trajectory / parameter closed-loop control, the damaged area is ensured to be smoothed.

[0012] Step 4: The molten pool solidifies and forms stably, and the repair is completed according to the preset procedure.

[0013] Furthermore, the typical types of repairable damage failure of aircraft parts include surface coating and shape and size overrun, which are manifested in scratches, abrasions, shallow pitting, wear, and local pits. The metal powder used for laser additive repair can be stainless steel powder, titanium powder, aluminum powder, etc.

[0014] Furthermore, the purpose of the three-dimensional contour scanning of the damaged area is to obtain the three-dimensional contour of the damaged area, and the scanning and contour reconstruction methods are handheld contour scanning, three-coordinate measurement, white light interferometry scanning and laser confocal scanning, etc. For the repair of centimeter-level damaged areas, rapid scanning technology is mainly used, and for the repair of millimeter-level fine damage, high-precision scanning is performed by white light interferometry.

[0015] Furthermore, the high-speed camera of the high-speed filter recognition system is coaxially fixed to the periphery of the laser additive cladding head, the angle between the lens optical path and the laser optical path does not exceed 5°, and the high-speed camera capture area range exceeds 1.5 times the diameter of the molten pool. At the same time, the high-speed camera has a spatial resolution of not less than 20μm within the capture area, so as to achieve the ability to identify abnormal reflective sites caused by splashing droplets, etc.

[0016] Furthermore, the high-quality capture of the abnormal flow characteristics on the molten pool surface is the basis for the closed-loop dynamic correction of the movement trajectory of the cladding head and the parameters. The molten pool radiates intensely under the rapid heating of the laser beam, which makes it difficult to observe the high-quality surface. The molten pool shooting and high-quality capture involved in the present invention are based on a high-speed camera, and can adopt an overall filtering solution or a filtering-infrared compensation solution.

[0017] Furthermore, considering the high-speed melting and solidification rate characteristics of the molten pool caused by high laser power in laser additive manufacturing, the recording frame rate of the high-speed camera and filtering system is at least 2000fps.

[0018] Furthermore, the "margin / molten pool monitoring-scanning trajectory / parameter closed-loop control" specifically includes monitoring and closed-loop control processes for the margin of the area to be repaired and the stability of the molten pool. As far as molten pool monitoring is concerned, the main objects captured are surface undulations, droplet splashing, local boiling, etc. caused by abnormal flow, which are reflected as abnormal high-brightness reflective point features in the filtered field of view. In the parameter setting link of step one, a reference value A of the molten pool surface brightness is preset. When an abnormal point (such as 1.2A) with a brightness higher than the reference is recorded in a local area of ​​the molten pool, the system determines that a molten pool fluctuation has occurred and performs statistics.

[0019] Furthermore, the monitoring of the edge to be repaired mainly captures the edge of the repair area, which is reflected in the linear reflection feature appearing in the filter field of view. When the cladding head moves to the vicinity of the edge to be repaired, the molten pool approaches the edge accordingly, and the repair edge shows a linear reflection under the radiation of the molten pool. When the high-speed filter capture system records the linear reflection feature, it is determined that the cladding head has approached the edge of the area to be repaired.

[0020] Furthermore, the closed-loop control of the repair parameters is based on the feedback of the monitoring system on the stability of the molten pool. When abnormal reflective features are recorded, the control system determines that the stability of the molten pool is poor at this time, and accordingly reduces the laser power and powder feeding rate to improve the stability of the molten pool; when the monitoring system records stable molten pool features, the system determines that the repair rate can be appropriately increased and the parameter combination can be adjusted. In this way, the closed-loop dynamic control of the repair parameters based on the identification of the molten pool stability features is completed.

[0021] Furthermore, the closed-loop control of the scanning trajectory is based on the recognition feedback of the edge to be repaired by the monitoring system. When the edge of the molten pool is recorded, the control system issues instructions to reduce the scanning rate and laser power to reduce the arching deformation of the edge area.

[0022] Furthermore, the damaged component additive repair system based on scanning trajectory closed-loop control is based on powder / wire-feeding directed energy deposition additive equipment, and the high-energy beam heat source can be laser or arc. After further packaging and integration into the carrier, it can form a mobile rapid additive repair platform to expand the scope of application.

[0023] Compared with the existing damaged component additive repair technology, the present invention has the following advantages:

[0024] 1) Convenient operation and less manual intervention. Using the scanning trajectory closed-loop control additive repair technology for damaged parts involved in the present invention, the control system autonomously identifies the stability of the molten pool and the repair margin based on the preset algorithm, and instantly adjusts the additive repair parameter combination without manual intervention in the additive repair process.

[0025] 2) Effectively reduce post-processing procedures. The closed-loop repair control involved in the series of steps of the present invention can effectively promote the surface flattening of the damaged area, especially the edge part, reduce the secondary machining process after repair, and accelerate the timeliness of emergency repair in complex environments.

[0026] 3) Applicable to a wide range of damage types. Compared with existing additive repair technologies, this invention is flexible and convenient and can be applied to a variety of damage types. It is suitable for both superficial damage and deep damage such as cracks and pits. At the same time, the corresponding repair technology has good portability and can be developed into fixed and mobile repair platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1( a ) is a schematic diagram of preliminary surface finishing of a damaged area;

[0028] Figure 1(b) is a schematic diagram of the initial laser additive repair of the damaged area;

[0029] Figure 1(c) is a schematic diagram of the deepest part of the additive repair process;

[0030] Figure 1(d) is a schematic diagram of the edge of the additive repair process;

[0031] Figure 2 The overall morphology of the repaired component is obtained by adopting the scanning trajectory closed-loop control scheme;

[0032] Figure 3(a) is a schematic diagram of laser additive repair of the initially damaged crack area;

[0033] Figure 3(b) is a schematic diagram of the central part of the area to be repaired;

[0034] Figure 3(c) is a schematic diagram of the additive repair process using only the manual parameter control scheme;

[0035] Figure 4(a) is a schematic diagram of a repaired part based on manually controlled parameters;

[0036] Figure 4(b) shows the metallographic structure of the repair area interface after repair based on artificially controlled parameters.

[0037] In the figure: 1-additive cladding head, 2-high-speed filter recognition system, 3-laser beam convergence focus position, 4-integrated control system, 5-damaged area margin, 6-repaired area, 7-unrepaired area. DETAILED DESCRIPTION

[0038] Figure 1 is a schematic diagram of the additive repair process for damaged components using a scanning trajectory closed-loop control scheme. Figure 2 The overall morphology of the repaired component is obtained by adopting the closed-loop control scheme of the scanning trajectory. Figure 3 is a schematic diagram of the additive repair process using only the manual control parameter scheme. Figure 4 is a schematic diagram of the part after repair based on the manual control parameters and the metallographic structure of the repair area interface.

[0039] like Figure 1a As shown, the damaged area is initially surface-finished to remove obvious defects such as warping and burrs, and the contour information of the area to be repaired is obtained by rapid three-dimensional contour scanning. The movement trajectory of the cladding head (1) in the damaged area is planned based on the three-dimensional contour information. The laser power, scanning rate, powder feeding rate and other parameters are set simultaneously, and the high-speed filter recognition system (2) is set to align with the laser beam convergence focus position (3). The molten pool monitoring-trajectory / parameter closed-loop control system is turned on.

[0040] Start laser additive repair of damaged areas, such as Figure 1a As shown in Figure 1b, after the laser beam melts the powder and forms a molten pool on the substrate surface, the high-speed camera observes the molten pool surface and identifies the edge of the damaged area, and performs feature recognition on the flow of the molten pool surface and the edge of the damaged area. In the center of the area to be repaired, where the damage depth is large, the control system adjusts the laser power and powder feeding rate to a larger value to increase the repair filling rate.

[0041] Cladding head trajectory and parameter closed-loop dynamic correction. When the molten pool flow shows abnormal fluctuations, such as droplet splashing, spraying, spheroidization, etc., the high-speed filter observation system will identify the reflective features caused by the abnormal molten pool fluctuations in the field of view and feed them back to the control system (4), which will then reduce the laser power and powder feeding rate to improve the stability of the molten pool. In addition, when the laser additive repair reaches the edge of the damaged area (5), such as Figure 1c As shown, the high-speed filtering system also identifies edge boundaries and adjusts parameters such as laser power to avoid defects such as arching and warping.

[0042] During the overall repair process of the damaged area, this solution always ensures the flatness of the damaged area through margin / melt pool monitoring-scanning trajectory / parameter closed-loop control.

[0043] In this embodiment, the damaged component failed due to surface cracking during use, with a crack length of 10 cm and a depth of 4 mm. After the crack was properly polished, it was repaired using a powder feeding laser additive device with a scanning trajectory closed-loop control system. Stainless steel powder was used as the repair material, with a powder particle size of 35 to 105 μm. Before additive repair, the laser power was preset to 1500 W, the scanning rate to 10 mm / s, the spot diameter to 2 mm, and the overlap rate to 25%. The image acquisition frame rate of the high-speed filter capture system was set to 2500 fps, the filter capture range to 3.5 mm, and the margin / molten pool monitoring-scanning trajectory / parameter closed-loop control system was turned on.

[0044] The laser additive repair of the damaged crack area begins. After the laser beam melts and feeds stainless steel powder to form a molten pool on the surface of the substrate, a high-speed camera observes the surface of the molten pool and identifies the edge of the damaged area. The flow of the molten pool surface and the edge of the damaged area are identified. In the center of the area to be repaired, where the damage depth is large, the control system adjusts the laser power and powder feeding rate to a larger value to increase the repair filling rate. When the molten pool flow fluctuates abnormally, such as droplet splashing, spraying, and spheroidization, the high-speed filter observation system will identify the reflective features caused by abnormal molten pool fluctuations in the field of view and feed them back to the control system, which then lowers the laser power and powder feeding rate to improve the stability of the molten pool. In addition, when the laser additive repair reaches the edge of the damaged area, the high-speed filter system identifies the edge line and lowers parameters such as the laser power to avoid defects such as arching and warping.

[0045] After the crack area is repaired, the morphology of the overall additively manufactured component is as follows: Figure 2 As shown, the repaired surface exhibits high flatness features and does not require subsequent secondary machining.

[0046] Comparative Example 1

[0047] The damage type, laser additive repair equipment and powder system in this comparative example are consistent with those in the embodiment. In this example, no closed-loop control scheme of the scanning trajectory is adopted, and only the operator manually determines the repair position to adjust the parameters such as laser power and powder feeding rate.

[0048] like Figure 3a As shown in the figure, the laser additive repair of the damaged crack area begins. After the laser beam melts the stainless steel powder to form a molten pool on the surface of the substrate, the center of the repaired area ( Figure 3b ), that is, where the damaged depth is greater, the operator uses higher laser power and powder feeding rate.

[0049] When the laser additive repair reaches the edge of the damaged area, the operator reduces the laser power and powder feeding rate based on experience. However, due to the intense luminous radiation of the molten pool during the laser additive process, it is difficult for the naked eye to accurately identify the boundary of the area to be repaired, resulting in a lag in the adjustment of the laser power and powder feeding rate, which easily leads to warping and arching at the edge of the repair area. Accordingly, a subsequent secondary machining correction process is added.

[0050] Components that are repaired simply by manually controlling additive parameters, such as Figure 4a As shown in Figure 2, the cladding material is obviously arched at the end, and the cross-sectional optical metallographic structure of the repaired surface is observed. Figure 4b As shown, it can be found that the surface is convex upwards, and there is a difference in contour between the repaired area (6) and the unrepaired area (7).

Claims

1. A fast-response additive repair method for damaged parts based on closed-loop control of scanning trajectories, characterized in that: The following steps are involved: Step 1: Pre-treatment preparation stage; Perform surface finishing on the damaged area to remove burrs and defects, and obtain the contour information of the area to be repaired by fast 3D contour scanning to plan the movement trajectory of the cladding head; preset the laser power, scanning rate, and powder feeding rate parameters, and set the high-speed filter recognition system to align with the laser beam focus position; start the molten pool monitoring-trajectory / parameter closed-loop control system; Step 2: Start laser additive repair of the damaged area. After the laser beam melts the powder to form a molten pool on the substrate surface, a high-speed camera observes the molten pool surface and identifies the edge of the damaged area. The flow of the molten pool surface and the edge of the damaged area are characterized. Step 3: Dynamic correction of cladding head trajectory and closed-loop parameters; abnormal flow on the molten pool surface, splashing droplets and sharp edges of damaged areas are used as identification features, and corresponding thresholds are set; during the movement of the cladding head, when the high-speed camera captures abnormal reflective features on the molten pool surface caused by splashing factors, it is determined that the stability of the molten pool is poor at this time, and the control system immediately reduces the laser power and powder feeding rate to improve the flow stability of the molten pool and promote surface smoothing; when the monitoring system observes that the molten pool surface is relatively stable, it is determined that the repair rate can be appropriately increased at this time, and the parameters are adjusted in coordination; at the same time, when the cladding head approaches the edge of the damaged area, the filter monitoring system simultaneously identifies the edge of the molten pool and the damaged area, and appropriately reduces the scanning rate and laser power when approaching the edge to ease the edge fluctuations; through edge / molten pool monitoring-scanning trajectory / parameter closed-loop control, ensure the flatness of the damaged area; Step 4: The molten pool solidifies and forms stably, and the repair is completed according to the preset procedure.

2. The method for rapid response additive repair of damaged parts based on closed-loop control of scanning trajectory according to claim 1, characterized in that: The three-dimensional contour scanning is used to obtain the three-dimensional contour of the damaged area. The scanning and contour reconstruction methods are handheld contour scanning, three-coordinate measurement, white light interferometry scanning and laser confocal scanning. For the repair of centimeter-level damaged areas, rapid scanning technology is mainly used, and for the repair of millimeter-level fine damage, high-precision scanning is performed using white light interferometry.

3. The method for rapid response additive repair of damaged parts based on closed-loop control of scanning trajectory according to claim 1 or 2, characterized in that: The high-speed camera of the high-speed filtering recognition system is coaxially fixed to the outer periphery of the laser additive cladding head, the angle between the lens optical path and the laser optical path does not exceed 5°, and the capture area of ​​the high-speed camera exceeds 1.5 times the diameter of the molten pool; at the same time, the high-speed camera has a spatial resolution of not less than 20μm within the capture area.

4. The method for rapid response additive repair of damaged parts based on closed-loop control of scanning trajectory according to claim 1 or 2, characterized in that: The recording frame rate of the high-speed camera and the filtering system of the high-speed filtering recognition system is at least 2000fps.

5. The method for rapid response additive repair of damaged parts based on closed-loop control of scanning trajectory according to claim 3, characterized in that: The recording frame rate of the high-speed camera and the filtering system of the high-speed filtering recognition system is at least 2000fps.

6. The method for rapid response additive repair of damaged parts based on closed-loop control of scanning trajectory according to claim 1, 2 or 5, characterized in that: The "margin / molten pool monitoring-scanning trajectory / parameter closed-loop control" specifically includes the monitoring and closed-loop control process for the margin of the area to be repaired and the stability of the molten pool; in the parameter setting link of step one, a reference value A of the molten pool surface brightness is preset. When it is recorded that the local molten pool is higher than the reference brightness by 1.2A, the system determines that a molten pool fluctuation occurs and performs statistics.

7. The method for rapid response additive repair of damaged parts based on closed-loop control of scanning trajectory according to claim 3, characterized in that: The "margin / molten pool monitoring-scanning trajectory / parameter closed-loop control" specifically includes the monitoring and closed-loop control process for the margin of the area to be repaired and the stability of the molten pool; in the parameter setting link of step one, a reference value A of the molten pool surface brightness is preset. When it is recorded that the local molten pool is higher than the reference brightness by 1.2A, the system determines that a molten pool fluctuation occurs and performs statistics.

8. The method for rapid response additive repair of damaged parts based on closed-loop control of scanning trajectory according to claim 4, characterized in that: The "margin / molten pool monitoring-scanning trajectory / parameter closed-loop control" specifically includes the monitoring and closed-loop control process for the margin of the area to be repaired and the stability of the molten pool; in the parameter setting link of step one, a reference value A of the molten pool surface brightness is preset. When it is recorded that the local molten pool is higher than the reference brightness by 1.2A, the system determines that a molten pool fluctuation occurs and performs statistics.

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