Method for evaluating forming accuracy of an electric arc additive manufactured component

Abstract

A kind of forming precision evaluation method of arc additive manufacturing component, in arc additive platform integration line laser profiler group appearance scanning platform, realize the in-situ measurement of deposition piece appearance;Establish the digital twin model of scanning platform, automatically plan and verify the scanning scheme according to the component STL model, obtain the ideal appearance point cloud after virtual scanning of STL model by point cloud reconstruction;The verified scanning scheme is applied to the deposition piece appearance measurement, and the actual appearance point cloud is reconstructed;Because deposition and scanning use the same positioning reference, the actual and ideal appearance point cloud is naturally aligned without additional registration, and the deviation can be directly compared and cloud chart is generated, the forming error is directly presented, and the forming precision of deposition piece is accurately evaluated.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing technology, specifically to a method for evaluating the forming accuracy of arc additive manufacturing components based on a line laser profilometer and digital twin. Background Technology

[0002] Metal additive manufacturing technology, as one of the core development directions of advanced manufacturing, occupies an important position in the transformation and upgrading of the manufacturing industry. This technology directly drives the formation of components by layer-by-layer material deposition, driven by 3D model data (usually in STL format). Among them, arc additive manufacturing technology, which uses an electric arc as a heat source to melt metal wires, is suitable for high-end equipment manufacturing fields such as aerospace and shipbuilding due to its advantages of high deposition efficiency and low equipment cost.

[0003] The forming accuracy of arc additive manufacturing is a key focus for both academia and industry. However, a complete technical system for measuring the morphology of deposited parts and evaluating forming accuracy in arc additive manufacturing has not yet been established, and existing solutions have many limitations. The current mainstream measurement method involves removing the deposited part from the forming platform and transferring it to an independent measuring device for scanning. This method has two main drawbacks: firstly, the layer-by-layer deposition characteristics of arc additive manufacturing create a significant step effect, and this non-uniform surface feature makes it difficult to register the measured morphology with the STL model; secondly, the morphology data of the deposited part obtained by measurement is usually in point cloud format after processing, while the STL model is surface mesh data. The two data structures are different, making direct comparative analysis impossible. Constrained by the above problems, existing forming accuracy evaluation methods almost all rely solely on the measured morphology, characterizing forming accuracy by extracting statistical quantities such as standard deviation or calculating specific indicators based on custom formulas. The paper "An efficient cooling method to mitigate heat accumulation in wire arcadditive manufacturing" published in *Materials Letters* discloses a method for evaluating the forming accuracy of a deposited part by calculating its surface roughness (Sa, Sq, Sz) based on point clouds measured by a laser 3D scanner. However, such evaluation metrics only reflect the geometric characteristics of the measured morphology itself and cannot intuitively quantify the deviation of the deposited part's morphology from the STL model. Consequently, it is difficult to accurately determine whether the deposited part, after subsequent subtractive processing, can meet the manufacturing requirements of the target component in terms of size, shape, etc.

[0004] In recent years, advancements in optical measurement technology and the introduction of the digital twin concept have made it possible to achieve in-situ measurement of the morphology of deposited parts in arc additive manufacturing, thereby enabling accurate evaluation of forming precision. However, no such combined technology has yet emerged in this field. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a method for evaluating the forming accuracy of arc additive manufacturing components. This method involves using a line laser profilometer to perform in-situ measurements of the deposited part's morphology on a forming platform to obtain actual scanning results. Simultaneously, digital twin technology is used to simulate the scanning process of the corresponding STL model, generating virtual scanning results that are consistent with the actual scanning results and require no additional registration. Deviations can be directly compared and cloud maps generated, intuitively presenting the forming error and achieving accurate evaluation of the forming accuracy of the deposited part.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for evaluating the forming accuracy of arc additive manufacturing components involves integrating a line laser profilometer into an arc additive manufacturing equipment and reusing the original forming platform as a morphology scanning platform. A digital twin model of this scanning platform is constructed, and a scanning scheme is planned based on the STL model corresponding to the deposited part. The STL model is then virtually scanned, and the generated virtual scan results are reconstructed using 3D point cloud data to obtain point cloud data of the ideal morphology. Subsequently, the corresponding scanning scheme is applied to in-situ measurement to scan and reconstruct the morphology of the deposited part, obtaining point cloud data of the actual morphology. Based on this, a deviation analysis method adapted to the layer-by-layer deposition characteristics of arc additive manufacturing is used to process the two types of point cloud data, achieving a quantitative evaluation of the forming accuracy.

[0007] The morphology scanning platform includes a four-axis motion platform 2 and a line laser profilometer assembly. The four-axis motion platform 2 is equipped with a turntable, which has three translational degrees of freedom (X, Y, and Z) and one rotational degree of freedom (C). The deposited part is carried on the turntable. The host computer 5 sends motion commands to the motion control cabinet 1 connected to the four-axis motion platform 2 to drive the turntable to complete the specified motion. The line laser profilometer assembly includes a side profilometer 3 and a top profilometer 4, which are installed in a preset posture on the fixed frame of the four-axis motion platform 2. The line laser emitted by the profilometer forms a fixed measurement area in space. After the deposited part is formed on the turntable, it maintains its initial clamping state with the turntable. During the measurement process, it moves with the turntable and passes through the measurement area formed by the profilometer, realizing in-situ measurement of the morphology of the deposited part. The side profiler (3) and the top profiler (4) are configured to move on the fixed frame to adjust the measurement area.

[0008] The digital twin model is a digital twin model of the topography scanning platform constructed in the host computer 5, used to plan the scanning scheme and perform virtual scanning of the STL model. The four-axis motion platform 2 is mapped to a reference coordinate system and a turntable coordinate system. The reference coordinate system is a fixed coordinate system with the platform zero point as the origin; the turntable coordinate system is a follower coordinate system that moves with the turntable, with its Z-axis as the rotation axis. Its pose in the reference coordinate system is described by a four-dimensional vector (X, Y, Z, C), which represents the homogeneous transformation relationship between the turntable coordinate system and the reference coordinate system. Initially, the two coordinate systems coincide. The STL model is a digital prototype of the deposited part, which maintains a fixed pose in the turntable coordinate system. In the reference coordinate system, each line laser profilometer component is equivalent to a rectangle parallel to the ZOX plane according to its respective measurement area, and its position is determined by calibration. Among them, the field of view and measurement direction of the side profilometer are parallel to the Z-axis and X-axis, respectively, and the field of view and measurement direction of the top profilometer are parallel to the X-axis and Z-axis, respectively. In the reference coordinate system, the motion process of the virtual scan is described by the change of the pose vector of the turntable coordinate system over time. Each time the profilometer triggers a measurement, it calculates the intersection profile of the equivalent rectangle and the STL model at that moment, and takes points at certain intervals along the field of view on the profile. The distance data of each point relative to the center of the rectangle in the measurement direction constitutes the virtual measurement result of that trigger.

[0009] The scanning scheme, based on the constructed digital twin model, generates scanning schemes adapted for side and top surface measurements respectively. Each scanning scheme includes multiple sets of scanning parameters, each set consisting of an initial pose (X...). ST ,Y ST Z ST C ST The scanning process consists of the moving distance d, the moving speed v, and the trigger frequency f. First, the turntable is controlled to reach the initial pose, then it moves at a given speed v along the negative y-axis for a uniform distance d. During the movement, the profilometer triggers measurements at a given frequency. For the side scanning scheme, a layered, multi-angle scanning method is adopted. Within the same layer, the Z-axis of the initial pose is used in each set of scanning parameters. ST The components are equal, while the rotational component C ST Then, the given number of angles is uniformly selected within 0~360°; for the top surface scanning scheme, the C of the initial pose in its scanning parameters... ST The component is fixed at 0°; X in the side scanning scheme ST Y ST , d and X in the top surface scanning scheme ST Y ST Z ST d and d are automatically calculated based on the slice results of the STL model along the corresponding measurement direction in the reference coordinate system, so as to enable more surfaces of the STL model to pass through the equivalent rectangle and realize the morphology measurement of the deposited part.

[0010] The three-dimensional point cloud reconstruction converts the effective values ​​in the original measurement data obtained by the scanning scheme into three-dimensional coordinates in the reference coordinate system. Then, according to the homogeneous transformation matrix between the turntable coordinate system and the reference coordinate system at the corresponding measurement time, the contour points are transformed into the turntable coordinate system, thereby realizing the point cloud reconstruction of the surface morphology in the turntable coordinate system and obtaining the actual morphology point cloud and the ideal morphology point cloud of the deposited part.

[0011] The quantitative evaluation of the forming accuracy is as follows: based on the actual morphology point cloud and the ideal morphology point cloud obtained from the reconstruction, the deviation of the actual morphology from the ideal morphology is calculated, and the side deviation cloud map and the top deviation cloud map are generated respectively.

[0012] The top surface deviation cloud map is generated by calculating the deviation between the actual topographic point cloud and the ideal topographic point cloud at the same X and Y coordinates in the Z direction, and using the ideal topographic point cloud as a reference. The side surface deviation cloud map is generated by utilizing the property that the field of view of the side profiler 3 is parallel to the Z-axis and the profile points are evenly distributed in this direction. The side surface point cloud is processed into layers according to the Z value. After the ideal topographic point cloud is layered according to the Z value, the slice image of the STL model at the corresponding height can be obtained. The actual topographic point cloud at the same height is projected onto the slice image to determine the corresponding projection point of each actual point on the slice image. The side surface deviation cloud map of this layer is generated with the projection point as a reference and the distance between the actual point and the projection point as the deviation.

[0013] The sliced ​​image is subjected to beveled cornering processing, and the deviation cloud maps of each layer are combined to obtain a complete side deviation cloud map.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (A) This invention integrates a line laser profilometer component on the basis of an electric arc additive forming platform to construct an integrated morphology scanning platform, which can perform in-situ measurement of the morphology of the deposited part on the forming platform, making it possible to realize closed-loop control of "deposition-measurement-compensation deposition", and significantly improving the continuity and flexibility of the electric arc additive manufacturing process.

[0015] (B) This invention constructs a digital twin model of a morphology scanning platform, which can automatically plan scanning schemes, significantly improve measurement efficiency, and generate virtual scanning results that are naturally aligned with the actual scanning results. It can be used for deviation analysis without additional registration, effectively solving the problem of registration between measurement data and model data, and providing reliable data support for the evaluation of forming accuracy.

[0016] (C) This invention proposes for the first time a high coverage measurement method that combines side layering, multi-angle scanning and top surface scanning, and develops a three-dimensional point cloud reconstruction process adapted to it, so as to achieve full measurement and accurate reconstruction of the morphology of the arc additive deposition part.

[0017] In summary, this invention proposes for the first time a forming accuracy evaluation method based on the surface topography deviation cloud map of the deposited part relative to the STL model. By using the top surface deviation cloud map and the side surface deviation cloud map, the forming error distribution of the deposited part can be presented intuitively. This allows for a more accurate determination of whether the deposited part meets the manufacturing requirements of the target component in terms of size, shape, etc. after subsequent subtractive processing, significantly improving the visualization and engineering practicality of forming accuracy evaluation. Attached Figure Description

[0018] Figure 1 This is a framework diagram of the present invention.

[0019] Figure 2 This is a schematic diagram of the topography scanning platform of the present invention.

[0020] Figure 3(a) is a schematic diagram of the important measurement parameters of the line laser profilometer of the present invention, and Figure 3(b) is a schematic diagram of the measurement results.

[0021] Figure 4 This is a schematic diagram of the digital twin model of the topography scanning platform according to an embodiment of the present invention.

[0022] Figure 5(a) is an ideal STL model of the deposited part in an embodiment of the present invention, and Figure 5(b) is a three-dimensional point cloud reconstruction result. Detailed Implementation

[0023] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the present invention and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Reference Figure 1 A method for evaluating the forming accuracy of arc additive manufacturing components is proposed. This method utilizes a morphology scanning platform, a digital twin model, a scanning scheme, and 3D point cloud reconstruction to evaluate forming accuracy. Specifically, a line laser profilometer is integrated into the arc additive manufacturing equipment, and the existing forming platform is reused as a morphology scanning platform. A digital twin model of this scanning platform is constructed, and a scanning scheme is planned based on the STL model corresponding to the deposited part. The STL model is then virtually scanned, and the generated virtual scanning results are reconstructed into point cloud data representing the ideal morphology. Subsequently, the validated scanning scheme is applied to in-situ measurement to scan and reconstruct the morphology of the deposited part, obtaining point cloud data representing the actual morphology. Based on this, a deviation analysis method adapted to the layer-by-layer deposition characteristics of arc additive manufacturing is used to process the two types of point cloud data, achieving a quantitative evaluation of forming accuracy.

[0025] Topographic scanning platform: Reference Figure 2The system consists of a four-axis motion platform and a line laser profilometer assembly, enabling functions such as deposition part bearing, motion control, and in-situ measurement. The four-axis motion platform 2 has three translational degrees of freedom (X, Y, Z) and one rotational degree of freedom (C) provided by a 100mm radius cylindrical turntable. The upper surface of the turntable is the direct bearing surface of the deposition part, and its outermost edge point in the positive X-axis direction serves as a key reference for calibrating the absolute installation position of the line laser profilometer assembly in the platform's reference coordinate system. The host computer 5 can send motion commands to the motion control cabinet 1 connected to the four-axis motion platform 2, driving the turntable to complete the specified motion. The line laser profilometer assembly includes a side profilometer 3 and a top profilometer 4, both mounted in a preset posture on the fixed frame of the four-axis motion platform 2. The emitted line laser forms a fixed measurement area in space. After the deposition part is formed on the turntable, it maintains its initial clamping state with the turntable. During the measurement process, it moves with the turntable and passes through the measurement area of ​​the profilometer, achieving in-situ measurement of the deposition part's morphology. Referring to Figure 3(a), in this embodiment, the reference distance of the linear laser profilometer is 73mm, the measurement range is 73±20.5mm, and the near-end field of view width is 30mm. To ensure the validity of the measurement data is not affected by changes in the field of view width, only the profilometer data within the central 20mm field of view is output in subsequent measurements. This range contains 1600 profilometer data points spaced at 0.0125mm intervals in the field of view direction. The trigger frequency f of the profilometer is set in the host computer 5, and each trigger obtains 1600 measurement values, i.e., the aforementioned profilometer data. Referring to Figure 3(b), in one scan, assuming the profilometer is triggered m times, the scan result can be expressed by an m×1600 matrix S, where S... i,j This represents the j-th measurement value obtained from the i-th trigger. After the topography scanning platform is built, the installation positions of the side profiler 3 and the top profiler 4 are calibrated respectively; the calibration process of the side profiler 3 is as follows: control the turntable from the initial pose (X... ST =180mm, Y ST =20mm, Z ST =210mm, C ST =0°) Moves d=40mm in the negative Y-axis direction at v=300mm / min. At the start of the movement, the profilometer is synchronously triggered at a frequency of f=500Hz. The corresponding measured value S of the reference point on the turntable is found in the i=627th row and j=859th column of the scanning result matrix S. 627,859 =3.65mm, calculate the calibration result X of the side profiler 3 according to formula (1). side =276.35mm, Y side =13.74mm, Z side =199.28mm; The calibration process of the top surface profiler 4 is as follows: control the turntable from the initial pose (X ST =-110mm, YST =20mm, Z ST =360mm, C ST =0°) Moves d=40mm in the negative Y-axis direction at v=300mm / min. At the start of the movement, the profilometer is synchronously triggered at a frequency of f=500Hz. The corresponding measured value S of the reference point on the turntable is found in the i=492nd row and j=571st column of the scanning result matrix S. 492,571 =-9.12mm, calculate the calibration result X of the top surface profiler 4 according to formula (2). top =-2.88mm, Y top =15.09mm, Z top =369.12mm.

[0026] (1) (2) The digital twin model: Refer to Figure 4 A digital twin model of the topography scanning platform is constructed in the host computer 5 to plan the scanning scheme and perform virtual scanning of the STL model. The four-axis motion platform 2 is mapped to a reference coordinate system and a turntable coordinate system. The reference coordinate system is a fixed coordinate system with the platform zero point as the origin; the turntable coordinate system is a follower coordinate system that moves with the turntable, with its Z-axis as the rotation axis. The pose in the reference coordinate system is described by a four-dimensional vector (X,Y,Z,C), which can represent the homogeneous transformation relationship between the turntable coordinate system and the reference coordinate system. In the initial state, the two coordinate systems coincide. The STL model, as the digital prototype of the deposited part, maintains a fixed pose in the turntable coordinate system. The side profiler 3 uses its calibration results (X... side ,Y side Z side This is equivalent to Y=Y in the reference coordinate system. side A rectangle on a plane, whose four vertices, in counter-clockwise order, are: (X... side +20.5,Y side Z side ), (X side -20.5,Y side Z side ), (X side -20.5,Y side Z side +20), (X side +20.5,Y side Z side +20), its measurement positive direction is the positive X-axis direction, and its field of view positive direction is the positive Z-axis direction. The short and long sides of the rectangle correspond to the field of view width and measurement range of the line laser profilometer, respectively; the top surface profilometer 4 is based on its calibration results (X top ,Ytop Z top This is equivalent to Y=Y in the reference coordinate system. top A rectangle on a plane, whose four vertices, in counter-clockwise order, are: (X...) top ,Y top Z top +20.5), (X top ,Y top Z top -20.5), (X top -20,Y top Z top -20.5), (X top -20,Y top Z top +20.5), its positive measurement direction is the positive Z-axis direction, and the positive field of view is the negative X-axis direction. The short and long sides of the rectangle correspond to the field of view width and measurement range of the line laser profilometer, respectively. In the reference coordinate system, the motion process of the virtual scan is described by the change of the pose vector of the turntable coordinate system over time; and each triggered measurement of the profilometer corresponds to the calculation of the intersection profile of the equivalent rectangle and the STL model at that moment, and 1600 points are taken sequentially along the positive field of view on the profile at intervals of 0.0125mm. The distance data of each point relative to the center of the rectangle in the measurement direction constitutes the virtual measurement result of that trigger.

[0027] The scanning scheme, based on the constructed digital twin model, generates scanning schemes adapted for side and top surface measurements. The scanning scheme includes multiple sets of scanning parameters, each set consisting of an initial pose (X). ST ,Y ST Z ST C ST The scanning parameters consist of the moving distance d (mm), the moving speed v (mm / min), and the trigger frequency f (Hz). The corresponding scanning process is as follows: first, the turntable is controlled to reach the initial pose, and then it moves at a given speed v along the negative y-axis for a uniform distance d. During the movement, the profilometer triggers the measurement according to the given frequency f. For the side scanning scheme, a layered, multi-angle scanning method is adopted; within the same layer, the Z-axis of the initial pose in each set of scanning parameters... ST The components are equal, while the rotational component C ST Then, select angles uniformly within the range of 0 to 360° according to the given number of angles; Z for each layer ST Forming an arithmetic sequence with the first term Z side -Z min (where Z) min (This refers to the minimum value in the Z direction of the STL model in the turntable coordinate system). The tolerance is 20mm for the short side of the equivalent rectangle of the side profiler 3. The last term of the sequence is less than Z. side -Z max (where Z)max This is the maximum term of the STL model in the Z-direction (maximum value in the turntable coordinate system). For the top surface scanning scheme, the C-value of the initial pose in its scanning parameters... ST The component is fixed at 0°. Furthermore, the X-ray in the side-scan scheme... ST Y ST , d and X in the top surface scanning scheme ST Y ST Z ST d and d are automatically calculated based on the slice results of the STL model along the corresponding measurement direction in the reference coordinate system, so as to enable more surfaces of the STL model to pass through the equivalent rectangle, so as to achieve the morphology measurement of the deposited part with high surface coverage.

[0028] 3D point cloud reconstruction: The valid values ​​(falling within the closed interval [-20.5, +20.5] mm, corresponding to the measurement range of the line laser profilometer) in the original measurement data obtained by the applied scanning scheme are converted into 3D coordinates in the reference coordinate system. Then, according to the homogeneous transformation matrix between the turntable coordinate system and the reference coordinate system at the corresponding measurement time, the contour points are transformed into the turntable coordinate system, thereby realizing the point cloud reconstruction of the surface morphology in the turntable coordinate system. For a single set of scanning parameters in the side scanning scheme, the single measurement value S in the result matrix S is... i,j Convert the reference equation (3) to three-dimensional coordinates (X) in the reference coordinate system. i,j ,Y i,j Z i,j S i,j During the scanning process The pose of the turntable at this moment is measured to be (X). ST ,Y ST -vt / 60,Z ST C ST The homogeneous transformation matrix from the reference coordinate system to the turntable coordinate system is H. S is calculated using equation (4). i,j Three-dimensional coordinates (X) in the turntable coordinate system i,j ',Y i,j ',Z i,j For a single set of scanning parameters in the top-surface scanning scheme, the individual measurement value S in the result matrix S is... i,j Convert the coordinates (X) of the reference equation (5) to three-dimensional coordinates in the reference coordinate system. i,j ,Y i,j Z i,j Since the motion process of top surface scanning is the same as that of side surface scanning, the calculation method of its turntable pose and homogeneous transformation matrix H is the same as that of side surface scanning. Therefore, the S of the top surface scanning result is... i,j Three-dimensional coordinates (X) in the turntable coordinate system i , j ′, Y i, j ′, Z i , j Similarly, referencing equation (4), we obtain the actual and ideal topographic point clouds of the deposited part by reconstructing the actual and virtual scan data respectively using the above method.

[0029] (3) (4) (5).

[0030] The forming accuracy evaluation involves calculating the deviation of the actual topography relative to the ideal topography based on the reconstructed actual and ideal topography point clouds, and generating side deviation cloud maps and top deviation cloud maps respectively. For the top deviation cloud map, the deviation in the Z direction between the actual and ideal topography point clouds can be calculated at the same X and Y coordinates, and the top deviation cloud map is generated based on the ideal topography point cloud. For the side deviation cloud map, due to the use of a layered, multi-angle scanning method, direct comparison cannot obtain a deviation cloud map under a unified reference. Utilizing the property that the field of view of the side profiler is parallel to the Z-axis and the profile points are uniformly distributed in this direction, the side point cloud can be layered according to the Z value. After the ideal topography point cloud is layered according to the Z value, a slice of the STL model at the corresponding height can be obtained. The actual topography point cloud at the same height is projected onto the slice, the corresponding projection point of each actual point on the slice is determined, and the side deviation cloud map of that layer is generated based on the projection point and the distance between the actual point and the projection point. To ensure the uniqueness of the projection relationship, the sliced ​​pattern was rounded with a small radius. The deviation contour maps of each layer were combined to obtain a complete side deviation contour map. The deviation contour map can visually reflect the forming error distribution of the deposited part, and is used to determine whether it can meet the manufacturing requirements of the target component in terms of size, shape, etc., after subsequent subtractive processing.

[0031] Referring to Figure 5, this embodiment describes an arc additively deposited Invar alloy component. A method for evaluating the forming accuracy of arc additively deposited components based on a line laser profilometer and digital twin includes the following steps: Step 1: Deploy and initialize the topography scanning platform and its digital twin model; Step 2: Hang the welding torch vertically at the designated position directly above the center of the turntable, keeping it fixed during the deposition process. Control the four-axis motion platform to complete the component deposition according to the deposition path generated by the path planning software based on the turntable coordinate system and the STL model. After deposition, move the welding torch to a position that will not obstruct subsequent morphology measurements. Step 3: Automatically plan the scanning scheme using the digital twin model and complete the virtual scanning of the component STL model; (3.1) Import the STL model of the component into the digital twin model and make its pose in the turntable coordinate system consistent with the positioning used by the path planning software in step two; (3.2) As shown in Table 1 and Table 2, generate the side scanning scheme and the top scanning scheme respectively; (3.3) The component STL model was virtually scanned according to the scanning scheme, and the virtual scanning result was reconstructed into a three-dimensional point cloud to obtain the ideal topography point cloud shown in Figure 5(b). The shape is basically consistent with the STL model and can fully cover the surface of the component, which verifies the effectiveness of the scanning scheme.

[0032] Table 1 Side Scan Scheme Table 2 Top surface scanning scheme Step 4: Using a validated scanning scheme, the morphology of the deposited part is measured on a morphology scanning platform. The scanning results are then used to reconstruct a 3D point cloud to obtain the actual morphology point cloud of the deposited part.

[0033] Step 5: Evaluate the forming accuracy. By comparing the deviation between the actual topographic point cloud and the ideal topographic point cloud, generate side deviation cloud maps and top deviation cloud maps respectively.

[0034] In summary, this invention provides a method for evaluating the forming accuracy of arc additive manufacturing components based on a line laser profilometer and digital twin. By integrating a line laser profilometer into an arc additive manufacturing platform to construct a topography scanning platform, component deposition and topography measurement can be achieved on the same platform. Simultaneously, a digital twin model of the scanning platform is established. Using this digital twin model, a scanning scheme can be automatically planned based on the STL model of the deposited part, and the effectiveness of the scanning scheme can be verified through virtual scanning, thereby improving measurement efficiency. Applying the scanning scheme, actual scanning results and virtual scanning results of the surface topography of the deposited part and its STL model can be obtained separately. Since the STL model in the digital twin model uses the same positioning reference as when driving the component forming, the actual topography point cloud obtained after 3D point cloud reconstruction of the actual and virtual scanning results is naturally aligned with the ideal topography point cloud, effectively solving the problem of difficulty in accurately registering the arc additively deposited part with the STL model due to the significant surface step effect. Based on this, by comparing and analyzing the deviation between the actual morphology and the ideal morphology, a deviation cloud map is generated, which can intuitively present the forming error distribution of the deposited part, providing a reliable basis for optimizing the arc additive manufacturing process or subsequent subtractive processing.

Claims

1. A method for evaluating the forming accuracy of arc additive manufacturing components, characterized in that, A line laser profilometer is integrated into an arc additive manufacturing equipment, and the original forming platform is reused as a morphology scanning platform. By constructing a digital twin model of this scanning platform, a scanning scheme is planned based on the STL model corresponding to the deposited part. The STL model is then virtually scanned, and the generated virtual scanning results are reconstructed into point cloud data of the ideal morphology through 3D point cloud reconstruction. Subsequently, the corresponding scanning scheme is applied to in-situ measurement to scan and reconstruct the morphology of the deposited part to obtain point cloud data of the actual morphology. Based on this, the two types of point cloud data are processed by a deviation analysis method adapted to the layer-by-layer deposition characteristics of electric arc additive manufacturing, so as to achieve a quantitative evaluation of the forming accuracy.

2. The method for evaluating the forming accuracy of arc additive manufacturing components according to claim 1, characterized in that, The morphology scanning platform includes a four-axis motion platform (2) and a line laser profilometer assembly. The four-axis motion platform (2) is equipped with a turntable, which has three translational degrees of freedom (X, Y, Z) and one rotational degree of freedom (C). The deposited part is carried on the turntable. The host computer (5) sends motion commands to the motion control cabinet (1) connected to the four-axis motion platform (2) to drive the turntable to complete the specified motion. The line laser profilometer assembly includes a side profilometer (3) and a top profilometer (4) installed in a preset posture on the fixed frame of the four-axis motion platform (2). The line laser emitted by the profilometer forms a fixed measurement area in space. After the deposited part is formed on the turntable, it maintains the initial clamping state with the turntable. During the measurement process, it moves with the turntable and passes through the measurement area formed by the profilometer to realize the in-situ measurement of the morphology of the deposited part.

3. The method for evaluating the forming accuracy of arc additive manufacturing components according to claim 2, characterized in that, The side profiler (3) and the top profiler (4) are configured to move on the fixed frame to adjust the measurement area.

4. A method for evaluating the forming accuracy of arc additive manufacturing components according to claim 2 or 3, characterized in that, The digital twin model is a digital twin model of the topography scanning platform constructed in the host computer (5), used to plan the scanning scheme and perform virtual scanning on the STL model. The four-axis motion platform (2) is mapped to a reference coordinate system and a turntable coordinate system. The reference coordinate system is a fixed coordinate system with the platform zero point as the origin. The turntable coordinate system is a follower coordinate system that moves with the turntable. Its Z-axis is the rotation axis. The pose in the reference coordinate system is described by a four-dimensional vector (X,Y,Z,C). This pose vector represents the homogeneous transformation relationship between the turntable coordinate system and the reference coordinate system. In the initial state, the two coordinate systems coincide. The STL model is a digital prototype of the deposited part, which maintains a fixed position in the turntable coordinate system. In the reference coordinate system, the line laser profilometer components are equivalent to rectangles parallel to the ZOX plane according to their respective measurement areas, and their positions are determined by calibration. Among them, the field of view and measurement direction of the side profilometer are parallel to the Z-axis and X-axis, respectively, and the field of view and measurement direction of the top profilometer are parallel to the X-axis and Z-axis, respectively. In the reference coordinate system, the motion process of the virtual scan is described by the change of the pose vector of the turntable coordinate system over time. Each trigger measurement of the profilometer corresponds to the calculation of the intersection profile of the equivalent rectangle and the STL model at that moment, and points are taken at certain intervals along the field of view on the profile. The distance data of each point relative to the center of the rectangle in the measurement direction constitutes the virtual measurement result of that trigger.

5. The method for evaluating the forming accuracy of arc additive manufacturing components according to claim 4, characterized in that, The scanning scheme, based on the constructed digital twin model, generates scanning schemes adapted for side and top surface measurements respectively. Each scanning scheme includes multiple sets of scanning parameters, each set consisting of an initial pose (X...). ST ,Y ST Z ST C ST The scanning process consists of the moving distance d, the moving speed v, and the trigger frequency f. First, the turntable is controlled to reach the initial pose, then it moves at a given speed v along the negative y-axis for a uniform distance d. During the movement, the profilometer triggers measurements at a given frequency. For the side scanning scheme, a layered, multi-angle scanning method is adopted. Within the same layer, the Z-axis of the initial pose is used in each set of scanning parameters. ST The components are equal, while the rotational component C ST Then, the given number of angles is uniformly selected within 0~360°; for the top surface scanning scheme, the C of the initial pose in its scanning parameters... ST The component is fixed at 0°; X in the side scanning scheme ST Y ST , d and X in the top surface scanning scheme ST Y ST Z ST d and d are automatically calculated based on the slice results of the STL model along the corresponding measurement direction in the reference coordinate system, so as to enable more surfaces of the STL model to pass through the equivalent rectangle and realize the morphology measurement of the deposited part.

6. The method for evaluating the forming accuracy of arc additive manufacturing components according to claim 5, characterized in that, The three-dimensional point cloud reconstruction converts the effective values ​​in the original measurement data obtained by the scanning scheme into three-dimensional coordinates in the reference coordinate system. Then, according to the homogeneous transformation matrix between the turntable coordinate system and the reference coordinate system at the corresponding measurement time, the contour points are transformed into the turntable coordinate system, thereby realizing the point cloud reconstruction of the surface morphology in the turntable coordinate system and obtaining the actual morphology point cloud and the ideal morphology point cloud of the deposited part.

7. The method for evaluating the forming accuracy of arc additive manufacturing components according to claim 1, characterized in that, The quantitative evaluation of the forming accuracy is as follows: based on the actual morphology point cloud and the ideal morphology point cloud obtained from the reconstruction, the deviation of the actual morphology from the ideal morphology is calculated, and the side deviation cloud map and the top deviation cloud map are generated respectively.

8. The method for evaluating the forming accuracy of arc additive manufacturing components according to claim 7, characterized in that, The top surface deviation cloud map is generated by calculating the deviation between the actual topographic point cloud and the ideal topographic point cloud in the Z direction at the same X and Y coordinates, and using the ideal topographic point cloud as the reference. The side surface deviation cloud map is generated by using the property that the field of view of the side profiler (3) is parallel to the Z axis and the profile points are evenly distributed in this direction. The side surface point cloud is processed into layers according to the Z value. After the ideal topographic point cloud is layered according to the Z value, the slice graphics of the STL model at the corresponding height are obtained. The actual topographic point cloud at the same height is projected onto the slice graphics to determine the corresponding projection point of each actual point on the slice graphics. The side surface deviation cloud map of this layer is generated with the projection point as the reference and the distance between the actual point and the projection point as the deviation.

9. The method for evaluating the forming accuracy of arc additive manufacturing components according to claim 8, characterized in that, The sliced ​​image is subjected to beveled cornering processing, and the deviation cloud maps of each layer are combined to obtain a complete side deviation cloud map.

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