Online monitoring system and method for porosity defects in laser additive manufacturing overlap processing

Abstract

The present invention provides an online monitoring system and method for porosity defects in laser additive manufacturing (AM) overlap processing. The system comprises a laser, a laser head, a displacement device, a material feed device, a coaxial image acquisition unit, an online image processing unit, an online overlap rate processing unit, and an online porosity defect processing unit. The acquired images are processed, including grayscale processing, image filtering and noise reduction, width feature extraction, and overlap melt pool feature extraction. Based on data from the online image processing unit and position information from the pore defect online monitoring system, the acquired overlap features are corrected in real time, and the actual overlap value and overlap rate are derived online. Based on the actual overlap value and overlap rate, as well as the overlap melt pool feature information, it is determined whether the overlap is a porosity defect. Through image calibration, acquisition, preprocessing, correction, and calculation, the present invention achieves rapid and reliable online monitoring of porosity defects in laser additive manufacturing (AM) overlap processing.

Description

Technical Field

[0001] The present invention relates to the technical field of online monitoring of laser additive manufacturing, and in particular to an online monitoring system and method for air hole defects in overlapped processing of laser additive manufacturing. Background Art

[0002] Additive manufacturing, a different type of processing method from traditional equal-material and subtractive manufacturing, offers advantages such as directness, speed, intelligence, and near-net-shape production. It is effective for processing complex structures, intricate materials, and small batches of parts. Laser additive manufacturing, which uses lasers as its energy source, boasts advantages such as wide applicability to a wide range of materials, the absence of a vacuum environment, and relatively low cost.

[0003] Laser additive manufacturing, especially additive manufacturing of metal products in the industrial field, has poor quality uniformity and is affected by many factors. Among them, dimensional accuracy and defect issues have always affected the popularization and application of this technology. In laser additive manufacturing, with the exception of individual thin-walled parts that require single-pass multi-layer processing, other application areas, including forming, repair, coating, etc., require multi-pass overlapping processing. In multi-pass processing, too low an overlap rate will cause the surface of the additive part to be uneven and produce high roughness; too high an overlap rate will cause the height of the additive part to increase abnormally and cause severe deformation; at the same time, due to reasons such as thermal balance and posture changes, the width of each additive manufacturing pass, or even the same pass, is not stable; defects such as pores and slag inclusions often occur at the overlap between passes. Therefore, in order to obtain laser additive parts with high dimensional accuracy and no defects, especially in the processing of complex structures or gradient materials, it is often necessary to spend a lot of resources on the design of the additive manufacturing process.

[0004] In the field of laser additive manufacturing, there has been some progress in the research of obtaining high-quality parts through online monitoring and feedback control methods. However, these advances have not yet found an effective method for online monitoring and feedback adjustment of lap joint processing porosity defects.

[0005] Patent document CN107688028A (application number: CN201710669368.0) discloses a method for online monitoring of overlap rate in laser additive manufacturing. This method utilizes an online monitoring system for overlap rate in laser additive manufacturing, which adds an online image processing unit and an online overlap rate processing unit to the existing online monitoring system. The online image processing unit includes a grayscale processing module, an image filtering and noise reduction module, a width feature extraction module, and an overlap feature extraction module. The online overlap rate processing unit can perform real-time corrections on the acquired overlap rate features based on data from the online image processing unit and the position information of the online monitoring system, and then derive the actual overlap value and overlap rate value online.

[0006] At present, the determination of pore defects in overlap processing in laser additive manufacturing still relies mainly on a large number of preliminary tests, and it is impossible to perform intelligent online monitoring and feedback adjustment according to the processing conditions.

[0007] Therefore, there is currently a lack of effective solutions to the problem that additive manufacturing process design consumes a lot of resources and cannot be monitored online and feedback adjusted. This problem has a significant impact on the processing quality and resource utilization of laser additive manufacturing. Therefore, it is necessary to propose a method for online monitoring of porosity defects in laser additive manufacturing overlap processing to solve the problems of additive manufacturing process design and online monitoring and feedback adjustment. Summary of the Invention

[0008] In view of the defects in the prior art, the purpose of the present invention is to provide an online monitoring system for air hole defects in laser additive manufacturing overlap processing.

[0009] The laser additive manufacturing overlap processing porosity defect online monitoring system provided by the present invention comprises: a laser, a laser head, a displacement device, a material feeding device, an image coaxial acquisition unit, an image online processing unit, an overlap rate online processing unit and a porosity defect online processing unit;

[0010] The laser is connected to a laser head, which is used to generate laser light. The laser light is then transmitted to the laser head through an optical fiber. Finally, through the beam collimation and focusing functions of the laser head, a laser beam is formed and transmitted to the object to be processed.

[0011] The displacement device is connected to the laser head and is used to move the laser head or the processing object to achieve relative movement between the laser head and the processing object;

[0012] The material feeding device is connected to the substrate and is used to transport powder or wire. After the powder or wire is transported to the laser head, it is transported to the processing object simultaneously with the laser beam to complete the melting of the powder or wire.

[0013] The image online processing unit is connected to the image coaxial acquisition unit to process the image acquired by the image coaxial acquisition unit, including grayscale processing, image filtering and noise reduction, width feature extraction and overlap molten pool feature extraction;

[0014] The overlap rate online processing unit corrects the acquired overlap features in real time based on the data from the image online processing unit and the posture information of the pore defect online monitoring system, and obtains the actual overlap value and overlap rate value online;

[0015] The porosity defect online processing unit determines whether the overlap is a porosity defect based on the actual overlap value and overlap rate value and the molten pool characteristic information of the overlap.

[0016] Preferably, the grayscale processing includes: compressing the grayscale distribution range in the grayscale histogram of the original image to at least 1 / 2 of the original image through Gamma transformation and contrast adjustment.

[0017] Preferably, the image filtering and denoising includes: removing powder splash interference outside the molten pool area, and removing powder splash, molten pool slag and molten pool bubble interference with pixel values ​​less than 10 within the molten pool area through Gaussian filtering, median filtering and small pixel target removal.

[0018] Preferably, the width feature extraction includes: obtaining the pixel value L of the maximum width of the molten pool perpendicular to the scanning direction through pixel summation operation.

[0019] Preferably, the extraction of the molten pool features at the overlap includes: performing pixel sum operation and selecting the trough of the pixel sum value of the molten pool parallel to the scanning direction as the overlap position, the pixel value of the position at a vertical distance from the previous processing part is S, and obtaining the molten pool shape contour A, the area of ​​the high grayscale area B at the head of the molten pool, the area C at the top of the molten pool, and the oscillation frequency D at the tail of the molten pool.

[0020] Preferably, the laser includes a semiconductor laser or a Nd:YAG laser, and the laser is connected to the laser head via an optical fiber connection.

[0021] Preferably, the displacement device includes a CNC machine tool or a robot.

[0022] Preferably, the image coaxial acquisition unit comprises a 45° beam splitter, a filter, a lens and a camera built into the laser head. The beam splitter realizes the forward transmission of laser light and the reverse transmission of visible light. The filter filters out strong light and interference light. The lens and camera acquire the image of the laser additive melt pool at every moment.

[0023] The light emitted by the liquid metal pool is filtered by a filter to leave only the required visible light band, then transmitted to the lens through two 45° beam splitters and collected by a camera connected to the lens.

[0024] The method for online monitoring of porosity defects in laser additive manufacturing overlap processing provided by the present invention comprises the following steps:

[0025] Step 1: Adjust the distance between the laser head and the substrate to 2 mm from the powder convergence point, focus the image coaxial acquisition unit through the calibration plate, and calibrate the ratio of the image to the actual size. The ratio of the image pixel value to the actual size is n:1;

[0026] Step 2: The relative displacement between the laser head and the substrate or the previously additive manufactured part is controlled by a displacement device. The pose information of the laser head and the substrate or the previously additive manufactured part is jointly determined by the displacement device and the angle of the substrate or the previously additive manufactured part. Additive manufacturing is performed on the substrate or the previously additive manufactured part, and the laser molten pool image is collected in real time by an image coaxial acquisition unit, and the acquisition frame rate ranges from 20 to 200 fps; wherein, the pose information includes the tilt angle α of the laser head and the tilt angle β of the substrate or the previously additive manufactured part.

[0027] Step 3: The image online processing unit preprocesses the collected image, including grayscale processing, image filtering and noise reduction, width feature extraction module and molten pool feature extraction at the lap joint, and the processing time is 5 to 50 ms.

[0028] Step 4: According to the calibration ratio n:1 in Step 1 and the pose information in Step 2, the previous width feature L1 and the current lap joint feature S extracted in Step 3 are imported into the lap rate online processing unit, and according to the formula the actual lap value D is obtained; according to the formula the actual lap rate η is obtained.

[0029] Step 5: Establish a criterion. The overall criterion consists of the processing state of the first single-layer single-pass and the processing state of the subsequent lap passes. The former is determined by the molten pool shape profile A, and the latter is used to identify the lap state according to the range of the actual lap rate η. The actual lap rate η is as follows: when it is less than the threshold η₁, surface unevenness defects or normal lap occur; when it is between η₁ and η₂, normal lap or pore defects occur; when it is greater than the threshold η₂, pore defects or lap layer stacking defects occur; among them, the pore defects are determined by the porosity P at the lap joint. When the porosity P at the lap joint ≥ p, it is determined that there are pore defects, and when P < p, it is determined that there are no pore defects, and p is the pore defect determination value.

[0030] Preferably, Step 5 includes:

[0031] Step 5.1: Through the first molten pool image, evaluate the state of the single-layer single-pass molten pool. If A is nearly circular, it meets the usage requirements and can directly proceed to the second pass of processing; if A is an irregular circle, it does not meet the usage requirements and the process parameters need to be adjusted to make A nearly circular, otherwise lap pores and surface unevenness defects will occur; if A is nearly trapezoidal, it does not meet the usage requirements and the process parameters need to be adjusted to make A nearly circular, otherwise lap pore defects will occur; after A is adjusted, proceed to the subsequent steps.

[0032] Step 5.2: When 0 ≤ η < η₁ and A is nearly circular, when B < b₁ and D < d₁, it is an unevenness defect, otherwise it is a normal lap.

[0033] Step 5.3: When η1 ≤ η < η2, A is nearly circular, C > c1, and D < d2 are normal lap joints; otherwise, it is a pore defect.

[0034] Step 5.4: When η ≥ η2, B < b2 and C > c2 are pore defects; otherwise, it is a lap layer stacking defect.

[0035] Among them, the porosity value of the pore defect is obtained from a metallographic experiment; η1, η2, b1, b2, c1, c2, d1, and d2 are corresponding parameter thresholds determined by preliminary experiments.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The present invention provides an online monitoring system and method for pore defects in laser additive manufacturing lap processing, which solves the problems that additive manufacturing process design requires a large amount of resources and the online monitoring problem in online monitoring and feedback adjustment. It can obtain the actual lap rate value in real time and determine whether there is a pore defect at the lap joint, and based on this, optimize the design and feedback adjustment of the additive manufacturing process, making the laser additive manufacturing have higher quality and more resource savings.

[0038] (2) The present invention can perform online monitoring of pore defects in laser additive manufacturing lap processing, with a short processing time, stable and reliable method. It can be used not only for the monitoring part in the monitoring of pore defects in lap processing under normal conditions but also for the design and optimization of lap processing under complex structures and gradient materials.

[0039] (3) The present invention has a high degree of integration, can be embedded in the current monitoring system without adding too many new hardware devices, and can collect width data in real time. For the visual image of the molten pool, deeper analysis can be carried out, such as online detection of defects, etc.

[0040] (4) The present invention has strong applicability, is not restricted by problems such as the properties, dimensions, and surface states of the feeding material or the substrate material, and has good adaptability. <0​​​​​​​​​​​​​​(a), (b), (c), (d) and (e) are monitoring images of the Cu-Cr-Zr matrix and Cu-Cr-Zr powder processing process and the molten pool characteristics at the overlap in the embodiment of the present invention;

[0045] In the figure: 1-laser; 2-displacement device; 3-laser head; 4-material feeding device; 5-coaxial image acquisition unit; 6-computer. DETAILED DESCRIPTION

[0046] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0047] Example:

[0048] like Figure 1 The present invention provides an online monitoring system for air hole defects in laser additive manufacturing overlap processing, comprising:

[0049] Laser 1: In this embodiment, the laser 1 is a semiconductor laser;

[0050] Displacement device 2: The displacement device 2 is a six-axis robot in this embodiment;

[0051] Laser head 3: the laser head 3 is a laser cladding head in this embodiment;

[0052] Material feeding device 4: the material feeding device 4 is a powder feeder in this embodiment;

[0053] Image coaxial acquisition unit 5: The visual image acquisition device in the image coaxial acquisition unit is a CMOS camera in this embodiment;

[0054] Computer 6: In this embodiment, the computer 6 includes an image online processing unit, an overlap rate online processing unit, and a pore defect online processing unit.

[0055] The powder and matrix materials used in this embodiment are both Cu-Cr-Zr powders with a powder diameter of 15 to 53 μm; the matrix size is 120×30×10 mm, and is the substrate in the directed energy deposition additive manufacturing process.

[0056] like Figure 2 The present invention provides an online monitoring method for air hole defects in laser additive manufacturing overlap processing, comprising:

[0057] (1) The distance between the laser head 3 and the substrate is adjusted to the powder convergence point, that is, 15 mm. The image coaxial acquisition unit is focused using a calibration plate, and the ratio of the image to the actual size is calibrated. The ratio of the image pixel value to the actual size of 1 mm is 130:1.

[0058] (2) The relative displacement between the laser head 3 and the substrate or the added material part is controlled by the displacement device 2. The position information is determined by the relative angle between the displacement device 2 and the substrate. The relative angle should not exceed 30°. The image coaxial acquisition unit 5 acquires the laser molten pool image in real time. The acquisition frame rate is 100 fps.

[0059] (3) The image online processing unit preprocesses the collected images, including grayscale processing, image filtering and noise reduction, width feature extraction module and overlap molten pool feature extraction. The overall processing time is 10 to 30 ms per frame of image;

[0060] The grayscale processing adjusts the grayscale distribution range of the original image grayscale histogram to 3 to 150 through gamma transformation and contrast adjustment, thereby enhancing image details;

[0061] The image filtering and noise reduction removes powder splash interference outside the molten pool area and removes powder splash, molten pool slag and molten pool bubble interference with pixel values ​​less than 10 within the molten pool area through Gaussian filtering, median filtering and small pixel target removal;

[0062] The width feature extraction is performed by pixel summing operation to obtain the pixel value L of the maximum width of the molten pool perpendicular to the scanning direction;

[0063] The weld pool feature extraction at the overlap is performed by pixel summation and the trough of the weld pool parallel to the scanning direction is selected as the overlap position. Figure 3 The pixel value of the vertical distance from the position to the previous processing part is S, and the molten pool shape outline A, the area of ​​the high grayscale area B at the head of the molten pool, the area C at the top of the molten pool, and the oscillation frequency D at the tail of the molten pool are obtained.

[0064] (4) According to the calibration ratio of 130:1 in step (1) and the posture information in step (2), the posture information includes the tilt angle α (0°) of the laser head and the tilt angle β (0°) of the substrate or the added material part, Figure 3 Taking (d) as an example, the previous width feature L1 (261) and the current overlap feature S (127) extracted in step (3) are imported into the overlap rate online processing unit;

[0065] According to the formula The actual overlap value D is found to be 0.98 mm;

[0066] According to the formula The actual overlap ratio η is 0.49, or 49%.

[0067] (5) The relevant parameters were determined through preliminary experiments, η1 was 16%, η2 was 63%, and b1 was 0.24 mm. 2 , b2 is 0.33mm 2 , c1 is 2.66mm 2 , c2 is 3.18mm 2 , d1 is 19Hz, and d2 is 28Hz.

[0068] (6) Establish the criterion. The overall criterion consists of the processing status of the first single-layer single-pass and the processing status of the subsequent overlapped passes. The former is determined by the molten pool shape profile A, and the latter identifies the overlapped state according to the range of the actual overlap rate η. The actual overlap rate η is: when it is less than 16%, surface unevenness defects or normal overlap may occur; when it is 16-63%, normal overlap or pore defects may occur; when it is greater than 63%, pore defects or overlap layer stacking defects may occur. Among them, the pore defect is determined by the porosity P at the overlap. When the porosity P at the overlap is ≥1%, it is determined that there is a pore defect. When P is <1%, it is determined that there is no pore defect. Figure 3 For example, (d) shows that the molten pool shape A is nearly circular, and the high grayscale area B at the head of the molten pool is 0.23 mm. 2 , the top area of ​​the molten pool C is 2.58mm 2 , the oscillation frequency D of the molten pool tail is 31Hz, and the specific process is as follows:

[0069] 1) The single-layer single-pass molten pool state evaluation is performed through the first molten pool image. A is nearly circular, which meets the use requirements and can be directly processed into the second pass.

[0070] 2) 16% ≤ η = 49% < 63%, A is nearly circular, C = 2.58 mm 2 <2.66mm 2 , D=31Hz>28Hz, it is judged as a pore defect.

[0071] The porosity value of the pore defect is obtained from a metallographic experiment, and the porosity P is 6.4%>1%, indicating that the pore defect exists.

[0072] The method proposed in the present invention can quickly realize the effective monitoring of porosity defects in laser additive manufacturing overlap processing, speed up the overlap process design and optimization, and thus improve the quality and efficiency of laser additive manufacturing.

[0073] In the description of this application, it should be understood 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 accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply 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 this application.

[0074] Those skilled in the art will appreciate that, in addition to implementing the system, device, and various modules provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same program in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, embedded microcontrollers, and the like by logically programming the method steps. Therefore, the system, device, and various modules provided by the present invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; the modules for implementing various functions can also be considered both software programs for implementing the method and structures within the hardware component.

[0075] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. An online monitoring system for porosity defects in laser additive manufacturing overlap processing, characterized in that: include: Laser, laser head, displacement device, material feeding device, image coaxial acquisition unit, image online processing unit, overlap rate online processing unit and porosity defect online processing unit; The laser is connected to a laser head, which is used to generate laser light. The laser light is then transmitted to the laser head through an optical fiber. Finally, through the beam collimation and focusing functions of the laser head, a laser beam is formed and transmitted to the object to be processed. The displacement device is connected to the laser head and is used to move the laser head or the processing object to achieve relative movement between the laser head and the processing object; The material feeding device is connected to the substrate and is used to transport powder or wire. After the powder or wire is transported to the laser head, it is transported to the processing object simultaneously with the laser beam to complete the melting of the powder or wire. The image online processing unit is connected to the image coaxial acquisition unit to process the image acquired by the image coaxial acquisition unit, including grayscale processing, image filtering and noise reduction, width feature extraction and overlap molten pool feature extraction; The overlap rate online processing unit corrects the acquired overlap features in real time based on the data from the image online processing unit and the posture information of the pore defect online monitoring system, and obtains the actual overlap value and overlap rate value online; The porosity defect online processing unit determines whether the overlap is a porosity defect based on the actual overlap value and overlap rate value and the molten pool characteristic information of the overlap.

2. The online monitoring system for porosity defects in laser additive manufacturing overlap processing according to claim 1 is characterized in that: The grayscale processing includes: compressing the grayscale distribution range in the grayscale histogram of the original image to at least 1 / 2 of the original image through Gamma transformation and contrast adjustment.

3. The online monitoring system for porosity defects in laser additive manufacturing overlap processing according to claim 1 is characterized in that: The image filtering and denoising includes: removing powder splash interference outside the molten pool area through Gaussian filtering, median filtering and small pixel target removal, removing powder splash, molten pool slag and molten pool bubble interference with pixel values ​​less than 10 in the molten pool area.

4. The online monitoring system for porosity defects in laser additive manufacturing overlap processing according to claim 1, characterized in that: The width feature extraction includes: obtaining a pixel value L of the maximum width of the molten pool perpendicular to the scanning direction through pixel summation operation.

5. The online monitoring system for porosity defects in laser additive manufacturing overlap processing according to claim 1, characterized in that: The molten pool feature extraction at the overlap includes: performing pixel sum operation and selecting the trough of the pixel sum value of the molten pool parallel to the scanning direction as the overlap position, the pixel value of the position perpendicular to the previous processing part is S, and obtaining the molten pool shape contour A, the high grayscale area B at the head of the molten pool, the top area C of the molten pool, and the oscillation frequency D at the tail of the molten pool.

6. The online monitoring system for porosity defects in laser additive manufacturing overlap processing according to claim 1, characterized in that: The laser includes a semiconductor laser or a Nd:YAG laser, and the laser is connected to the laser head by optical fiber connection.

7. The online monitoring system for porosity defects in laser additive manufacturing overlap processing according to claim 1, characterized in that: The displacement device includes a CNC machine tool or a robot.

8. The online monitoring system for porosity defects in laser additive manufacturing overlap processing according to claim 1, characterized in that: The image coaxial acquisition unit includes a 45° beam splitter, a filter, a lens, and a camera built into the laser head. The beam splitter realizes the forward transmission of laser light and the reverse transmission of visible light. The filter filters out strong light and interference light. The lens and camera acquire the image of the laser additive melt pool at every moment. The light emitted by the liquid metal pool is filtered by a filter to leave only the required visible light band, then transmitted to the lens through two 45° beam splitters and collected by a camera connected to the lens.

9. A method for online monitoring of porosity defects in laser additive manufacturing overlap processing, characterized in that: The online monitoring system for porosity defects in laser additive manufacturing overlap processing according to any one of claims 1 to 8 comprises the following steps: Step 1: Adjust the distance between the laser head and the substrate to 2 mm from the powder convergence point. Focus the image coaxial acquisition unit through a calibration plate and calibrate the ratio of the image to the actual size. The ratio of the image pixel value to the actual size is n:1; Step 2: The relative displacement between the laser head and the substrate or the already additive manufactured part is controlled by a displacement device. The pose information of the laser head and the substrate or the already additive manufactured part is jointly determined by the displacement device and the angle of the substrate or the already additive manufactured part. Perform additive manufacturing on the substrate or the already additive manufactured part, and collect the laser melt pool image in real time through the image coaxial acquisition unit. The acquisition frame rate range is 20 - 200 fps; where the pose information includes the tilt angle α of the laser head and the tilt angle β of the substrate or the already additive manufactured part; Step 3: The image online processing unit preprocesses the collected image, including grayscale processing, image filtering and noise reduction, width feature extraction module and lap joint melt pool feature extraction. The processing time is 5 - 50 ms; Step 4: According to the calibration ratio n:1 in step 1 and the pose information in step 2, the previous width feature L1 extracted in step 3 and the current overlap feature S are imported into the overlap rate online processing unit, and the formula is used. The actual overlap value D is obtained; according to the formula The actual overlap rate η is obtained; Step 5: Establish criteria. The overall criterion consists of the processing state of the first single-layer single-pass and the subsequent lap joints. The former is determined by the melt pool shape profile A, and the latter respectively identifies the lap joint state according to the range of the actual lap rate η. The actual lap rate η is as follows: when it is less than the threshold η1, there are surface concavity and convexity defects or normal lap joints; when it is between η1 and η2, there are normal lap joints or pore defects; when it is greater than the threshold η2, there are pore defects or lap layer stacking defects; among them, the pore defects are determined by the porosity P at the lap joint. When the porosity P at the lap joint ≥ p, it is determined that there are pore defects. When P < p, it is determined that there are no pore defects. p is the pore defect determination value.

10. The online monitoring method for porosity defects in laser additive manufacturing overlap processing according to claim 9, characterized in that: The said Step 5 includes: Step 5.1: Through the first melt pool image, evaluate the single-layer single-pass melt pool state. If A is nearly circular, it meets the usage requirements and can directly proceed to the second pass of processing; if A is an irregular circle, it does not meet the usage requirements and the process parameters need to be adjusted to make A nearly circular, otherwise it will cause lap joint pores and surface concavity and convexity defects; if A is nearly trapezoidal, it does not meet the usage requirements and the process parameters need to be adjusted to make A nearly circular, otherwise it will cause lap joint pore defects; after A is adjusted, proceed to the subsequent link; Step 5.2: When 0 ≤ η < η1 and A is nearly circular, when B < b1 and D < d1, it is a concavity and convexity defect, otherwise it is a normal lap joint; Step 5.3: When η1 ≤ η < η2 and A is nearly circular, when C > c1 and D < d2, it is a normal lap joint, otherwise it is a pore defect; Step 5.4: When η ≥ η2, when B < b2 and C > c2, it is a pore defect, otherwise it is a lap layer stacking defect; Among them, the porosity value of the pore defect is obtained through metallographic experiments; η1, η2, b1, b2, c1, c2, d1, d2 are corresponding parameter thresholds determined by preliminary experiments.

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