Method and apparatus for simultaneous observation of a cladding layer and a melt pool in an electric arc additive manufacturing

Abstract

The present application relates to the technical field of additive manufacturing, in particular to a method and device for simultaneously observing cladding layer and molten pool in electric arc additive manufacturing. In the device, the first CCD camera is set to low exposure and small gain mode, and a high-pass infrared filter is added in front of the first CCD camera to effectively reduce the influence of electric arc light; the second CCD camera is set to high exposure and large gain mode, and imaging is performed by relying on the reflected electric arc light of the cladding layer. Based on Poisson fusion algorithm, the present application performs selected area splicing on the molten pool image captured by the first CCD camera and the cladding layer image captured by the second CCD camera, and realizes the simultaneous observation of the cladding layer and the molten pool in the additive manufacturing process. The present application has simple structure and can be widely applied in the field of electric arc additive manufacturing automation.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology. More specifically, it relates to a method and apparatus for simultaneously observing the cladding layer and the molten pool in arc additive manufacturing. Background Technology

[0002] Additive manufacturing technology is rapidly developing as a highly efficient method for quickly forming parts with complex geometries. Arc additive manufacturing, which uses an electric arc as a heat source and metal wire as a filler material to form a workpiece, is an extremely important technology in additive manufacturing. Simultaneous monitoring of the cladding layer and the molten pool in the additive region during arc additive manufacturing provides operators with more visual information. This not only helps operators judge the quality of additive forming but also allows them to observe the deviation between the actual additive path and the predetermined path, thereby enabling real-time adjustments to additive process parameters and the additive path. This is of great significance to the field of automation in arc additive manufacturing.

[0003] However, due to the intense arc light generated during arc additive manufacturing, conventional monocular cameras have limited sensitivity, making it impossible to image the molten pool area after imaging the cladding layer region; similarly, it is impossible to image the cladding layer region after imaging the molten pool area. This invention provides a method and apparatus for simultaneous observation of the cladding layer and molten pool in arc additive manufacturing, based on a binocular CCD camera. This enables simultaneous observation of both the cladding layer and the molten pool, providing crucial guidance for operators to judge additive manufacturing quality and path in real time, and can be widely applied in the field of additive manufacturing automation.

[0004] The existing solution to the problem of simultaneously observing the cladding layer and the molten pool during additive manufacturing is to use an external active light source to continuously or indirectly illuminate the additive manufacturing area, thereby greatly increasing the brightness of the surrounding environment, reducing the contrast between the arc light and the surrounding environment, and making the cladding layer and the molten pool visible. However, because the arc light is too strong, the external light source used needs to meet certain conditions, such as forming a certain angle with the optical axis of the lens; the wavelength of the external light source needs to be selected according to different materials, etc. The lighting source and equipment are complex, which greatly increases the usage conditions and is not conducive to the development of automation in arc additive manufacturing. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method and apparatus for simultaneous observation of the cladding layer and the molten pool. This method enables dynamic observation of the molten pool while also enabling real-time observation of the cladding layer.

[0006] To achieve the above objectives, the present invention provides a specific technical solution:

[0007] A device for simultaneously observing the cladding layer and molten pool in arc additive manufacturing includes a PC, a first CCD camera, a second CCD camera, signal cables, a network cable, a beam splitter, a total reflection mirror, a switch, a data acquisition card, and an 850nm high-pass infrared filter. The PC is connected to the switch via a network cable and to the data acquisition card via a signal cable. The switch is connected to both the first and second CCD cameras via network cables; the data acquisition card is connected to both the first and second CCD cameras via signal cables.

[0008] Furthermore, adding an 850nm high-pass filter in front of the first CCD camera can greatly reduce arc light interference.

[0009] Furthermore, a beam splitter with a transmittance-to-reflection ratio of 1:1 is placed in front of the first CCD camera, and a total reflection mirror is placed in front of the second CCD camera. The plane of the beam splitter is at an angle of 45° to the lens plane of the first CCD camera, and the beam splitter and the total reflection mirror are placed parallel to each other at equal intervals.

[0010] Furthermore, the first CCD camera and the second CCD camera are placed parallel to each other at equal intervals and on the same horizontal plane. The first CCD camera features low exposure and low gain, which is beneficial for clear imaging of the fused pool; the second CCD camera features high exposure and high gain, which is beneficial for clear imaging of the cladding layer.

[0011] A method for simultaneously observing the cladding layer and the molten pool in arc additive manufacturing specifically includes the following steps:

[0012] Step 1: The PC sends a shooting command, and the data acquisition card sends out TTL high and low level signals;

[0013] Step 2: The first CCD camera and the second CCD camera simultaneously trigger the shooting in response to the high-level signal, thus obtaining the first raw image and the second raw image.

[0014] Step 3: Based on Zhang Zhengyou's calibration method, calibrate the first CCD camera and the second CCD camera to obtain their internal and external parameters.

[0015] Step 4: Based on the intrinsic and extrinsic parameters of the first CCD camera and the second CCD camera obtained in Step 3, calibrate the first original image and the second original image respectively to obtain the first image and the second image.

[0016] Step 5: Extract the Region of Interest (ROI) from the molten pool region in the first image;

[0017] By selectively stitching together the molten pool portion in the first image and the cladding layer portion in the second image, simultaneous observation of the cladding layer and the molten pool can be achieved during the additive manufacturing process.

[0018] Step 6: Based on the Poisson fusion algorithm, fuse the ROI regions in the first image with the second image.

[0019]

[0020] In the formula, Ω represents the ROI region in the fused image; f and f * These represent the pixel values ​​of the fused image inside and outside Ω, respectively. This represents the outer boundary region of Ω; For the gradient operator of the image; These are the gradient vector fields of the second image and the ROI image, respectively; These are constraints.

[0021] Furthermore, in step five, the steps for selecting a splicing scheme are as follows:

[0022] The first step is to perform median filtering on the first and second images;

[0023] The second step involves adaptive thresholding of the image after median filtering in the first step, based on Otsu's algorithm, to obtain a binarized image.

[0024] Step 3: Perform edge detection on the binarized image from the above steps based on the Canny algorithm.

[0025] Step 4: Perform morphological dilation processing. In the final processed image, the area enclosed by the edges is the melt pool. Extract the ROI from this area.

[0026] Step 5: Based on the Poisson fusion algorithm, select and fuse the ROI regions in the first image with the second image after median filtering. The calculation formula is:

[0027]

[0028] In the formula, Ω represents the ROI region in the fused image; f and f * These represent the pixel values ​​of the fused image inside and outside Ω, respectively. This represents the outer boundary region of Ω; For the gradient operator of the image; These are the gradient vector fields of the second image and the ROI image, respectively; These are constraints.

[0029] Compared with the prior art, the significant advantages of this invention are:

[0030] (1) By designing a beam splitting optical path system, this invention greatly reduces the impact of arc light on camera imaging, which is beneficial for the equipment to clearly image the molten pool and cladding layer. On the other hand, since the light received by the first CCD camera and the second CCD camera both come from the beam splitter, it ensures that the shooting area and field of view between the images formed by the first CCD camera and the second CCD camera are completely the same, and there is no need to perform image registration, which effectively ensures the quality of image fusion in the later stage.

[0031] (2) This invention uses different imaging methods for different regions, which effectively increases the visible area in the imaging of the first CCD camera and the second CCD camera. The first CCD camera is set to a low exposure and low gain mode and is equipped with an 850nm infrared high-pass filter, which can greatly filter the arc light and achieve clear imaging of the molten pool; while for the light transmitted through the beam splitter, a total reflection mirror is used to reflect the transmitted light for imaging of the second CCD camera. The second CCD camera is set to a high exposure and high gain mode, which achieves clear imaging of the cladding layer.

[0032] (3) By using the Poisson fusion algorithm, the ROI of the molten pool area image captured by the first CCD camera is extracted and fused into the image captured by the second CCD camera, thus realizing clear imaging of the cladding layer and the molten pool at the same time during the arc additive manufacturing process, providing more visual information for the operator. At the same time, the device of the present invention has a simple structure and is easy to install, and can be widely used in the field of arc additive manufacturing automation. Attached Figure Description

[0033] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0034] Figure 1 This is a schematic diagram of the structure of a device for simultaneously observing the cladding layer and the molten pool in arc additive manufacturing according to the present invention.

[0035] Figure 2 This is a flowchart of a method for simultaneously observing the cladding layer and the molten pool in arc additive manufacturing.

[0036] The components include: molten pool area (1), beam splitter (2), total reflection mirror (3), 850nm high-pass infrared filter (4), camera lens (5), first CCD camera (6), second CCD camera (7), network cable (8), signal line (9), switch (10), data acquisition card (11), and PC terminal (12). Detailed Implementation

[0037] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0038] like Figure 1 As shown, this invention discloses a device for simultaneously observing the cladding layer and the molten pool in arc additive manufacturing. Specifically, it includes a beam splitter 2, a total reflection mirror 3, an 850nm high-pass infrared filter 4, a camera lens 5, a first CCD camera 6, a second CCD camera 7, a network cable 8, a signal line 9, a switch 10, a data acquisition card 11, and a PC terminal 12; 1 is a schematic diagram of the molten pool area. The PC terminal 12 is connected to the switch via the network cable 8 and to the data acquisition card 11 via the signal line 9. The switch 10 is connected to the first CCD camera 6 and the second CCD camera 7 via the network cable 8; the data acquisition card is connected to the first CCD camera and the second CCD camera 7 via the signal line. A beam splitter with a transmittance-to-reflection ratio of 1:1 is placed in front of the first CCD camera, and a total reflection mirror is placed in front of the second CCD camera. The angle between the plane of the beam splitter and the plane of the first CCD camera lens is 45°, and the beam splitter and the total reflection mirror are placed parallel and equidistantly. The first CCD camera is set to low exposure and low gain mode; the second CCD camera is set to high exposure and high gain mode. During the additive manufacturing process, the arc light and the reflected light from the molten pool are split in two by a beam splitter. One portion passes through an 850nm high-pass infrared filter and is received by a first CCD camera for imaging the molten pool region; the other portion passes through a total reflection mirror and is received by a second CCD camera for imaging the cladding layer region. The image acquired by the first CCD camera is used to extract the Region of Interest (ROI) for the molten pool region. A Poisson fusion algorithm is then used to fuse the ROI image acquired by the first CCD camera with the image acquired by the second CCD camera, ultimately resulting in an image where both the molten pool region and the cladding layer region can be observed simultaneously.

[0039] This invention provides a method for simultaneously observing the cladding layer and the molten pool in arc additive manufacturing, specifically including the following steps:

[0040] (1) When the PC sends a shooting command, the data acquisition card will send a TTL level signal in response to the command.

[0041] (2) The first CCD camera and the second CCD camera receive the TTL high-level signal and simultaneously take pictures. The image acquired by the first CCD camera is the first original image; the image acquired by the second CCD camera is the second original image.

[0042] (3) Using a checkerboard calibration board, the first CCD camera and the second CCD camera were calibrated based on Zhang Zhengyou's calibration method to obtain the internal and external parameters of the first and second CCD cameras.

[0043] (4) The camera intrinsic and extrinsic parameters obtained in step three are used to correct the first original image and the second original image respectively. The corrected images are the first image and the second image.

[0044] (5) Extract the Region of Interest (ROI) from the molten pool region in the first image. This includes the following steps:

[0045] Step 1: Perform median filtering on the first and second images;

[0046] Step 2: Based on Otsu's algorithm, perform adaptive thresholding on the image after median filtering in Step 1 to obtain a binarized image.

[0047] Step 3: Perform edge detection on the binarized image from the above steps based on the Canny algorithm.

[0048] Step 4: Perform morphological dilation processing. In the final processed image, the area enclosed by the edges is the melt pool. Extract the ROI from this area.

[0049] (6) Based on the Poisson fusion algorithm, the ROI regions in the first image are fused with those in the second image. The calculation formula is as follows:

[0050]

[0051] In the formula, Ω represents the ROI region in the fused image; f and f * These represent the pixel values ​​of the fused image inside and outside Ω, respectively. This represents the outer boundary region of Ω; For the gradient operator of the image; These are the gradient vector fields of the second image and the ROI image, respectively; These are constraints.

Claims

1. A method for simultaneously observing the cladding layer and the molten pool in arc additive manufacturing, characterized in that, Includes the following steps: (1) When the PC sends a shooting command, the data acquisition card will send a TTL level signal in response to the command; (2) The first CCD camera and the second CCD camera receive the TTL high-level signal and take pictures simultaneously; the image acquired by the first CCD camera is the first original image; the image acquired by the second CCD camera is the second original image; the first CCD camera is used for imaging the molten pool area, and the second CCD camera is used for imaging the cladding layer area. (3) Using a checkerboard or dot calibration plate, the first CCD camera and the second CCD camera are calibrated respectively based on Zhang Zhengyou's calibration method to obtain the intrinsic and extrinsic parameters of the first and second CCD cameras; (4) The camera intrinsic and extrinsic parameters obtained in step three are used to correct the first original image and the second original image respectively. The corrected images are the first image and the second image. (5) Extract the Region of Interest (ROI) from the molten pool region in the first image; specifically, this includes the following steps: Step 1: Perform median filtering on the first image; Step 2: Based on Otsu's algorithm, adaptive threshold segmentation is performed on the image after median filtering in Step 1 to obtain a binarized molten pool region image; Step 3: Perform edge detection on the binarized image from the above steps using the Canny algorithm; Step 4: Perform morphological dilation processing. In the final processed image, the area enclosed by the edges is the melt pool. Extract the ROI from this area. (6) Based on the Poisson fusion algorithm, the ROI region in the first image is fused with the second image; In the formula, The ROI region in the fused image; and The fused images are respectively in Pixel values ​​inside and outside; for The outer boundary region; For the gradient operator of the image; These are the gradient vector fields of the second image and the ROI image, respectively; These are constraints.

2. An observation device for the method of simultaneously observing the cladding layer and the molten pool in arc additive manufacturing as described in claim 1, characterized in that, Including data acquisition cards; The data acquisition card is connected in parallel with the switch, and the two ends of the data acquisition card and the switch are respectively connected to the PC and the dual CCD camera. The data acquisition card emits high and low level signals (TTL). Upon receiving a shooting command from the PC, the data acquisition card emits a TTL signal to simultaneously control the dual CCD cameras to take a picture. The first CCD camera is equipped with a beam splitter and a high-pass filter. A total reflection mirror is installed in front of the second CCD camera so that all the light passing through the beam splitter is captured by the second CCD camera for imaging the cladding layer.

3. The device for simultaneously observing the cladding layer and the molten pool in arc additive manufacturing according to claim 2, characterized in that, The two CCD cameras are placed parallel to each other at equal intervals and on the same horizontal plane.

4. The device for simultaneous observation of the cladding layer and the molten pool in arc additive manufacturing according to claim 2, characterized in that, The first CCD camera has a first exposure time and a first gain amplitude; the second CCD camera has a second exposure time and a second gain amplitude.

5. The device for simultaneous observation of the cladding layer and the molten pool in arc additive manufacturing according to claim 4, characterized in that, During the additive manufacturing process, the first exposure time is shorter than the second exposure time, and the first gain amplitude is shorter than the second gain amplitude.

6. The device for simultaneous observation of the cladding layer and the molten pool in arc additive manufacturing according to claim 2, characterized in that, The first CCD camera has a beam splitter in front of it, and the transmittance-to-reflection ratio is 1:1 (transmitted light: reflected light).

7. The device for simultaneous observation of the cladding layer and the molten pool in arc additive manufacturing according to claim 2, characterized in that, The high-pass filter is an 850nm high-pass filter.

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