CN112304870A - Point-to-point laser ultrasonic PBF additive manufacturing online detection system and method - Google Patents
Point-to-point laser ultrasonic PBF additive manufacturing online detection system and method Download PDFInfo
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Abstract
The invention discloses a point-to-point laser ultrasonic PBF additive manufacturing online detection system and a point-to-point laser ultrasonic PBF additive manufacturing online detection method.A laser ultrasonic receiver and a printing laser share a printing laser vibrating mirror and a transflective mirror and are used in a time-sharing manner, wherein the transflective mirror combines the printing laser and the receiving laser to the same optical path, and the optical path axis of the printing laser vibrating mirror and the laser ultrasonic shared laser vibrating mirror is vertical to a working surface; the exciting laser galvanometer is obliquely arranged on one side of the printing laser galvanometer, and the axes of the exciting and receiving laser light paths are converged at the center of the printing area on the working surface. The invention gives consideration to detection precision and detection efficiency, can realize the cooperative work of additive manufacturing and online detection, and is particularly suitable for the application requirement of PBF additive manufacturing online detection.
Description
Technical Field
The invention relates to a nondestructive testing system and a nondestructive testing method, in particular to a point-to-point laser ultrasonic PBF additive manufacturing online testing system and a point-to-point laser ultrasonic PBF additive manufacturing online testing method.
Background
Additive Manufacturing (AM) technology, which is known as "3D printing technology", is based on the principle of discrete-stacking, and is a technology for layering three-dimensional parts by software and accumulating materials layer by layer to manufacture solid parts, and is generally classified into two main process categories, namely pbf (powder Bed fusion) and ded (direct Energy deposition). Compared with the traditional material manufacturing method (material reduction manufacturing), the additive manufacturing has the characteristics of high material utilization rate, high part design freedom degree, capability of producing various mechanical parts with complex structures and the like, and is widely applied to various industrial manufacturing fields of automobiles, aerospace, medical treatment, war industry and the like. However, due to the principle of long-time 'point-by-point scanning/layer-by-layer accumulation' reciprocating circulation, process defects such as air holes, cracks, non-fusion and the like are difficult to avoid, and the quality of the component is damaged. The lack of quality monitoring means in the additive manufacturing process on the global scale has become a significant bottleneck restricting the development, popularization and application of the technology.
The existing nondestructive testing of the additive manufactured part is mainly divided into on-line testing and off-line testing. The off-line detection technology performed after the additive manufacturing is finished is relatively mature, but the off-line characteristic of the off-line detection technology makes the defects of deep burying type and small size in the product not detectable. The online detection is a method for detecting the formed part in real time in the additive manufacturing process, can timely find defects, reflect the current printing quality, and can realize timely adjustment of the additive process when combined with feedback control, so that the defects are eliminated and the continuous occurrence of the defects is reduced.
Disclosure of Invention
The purpose of the invention is as follows: one of the purposes of the invention is to provide a point-to-point laser ultrasonic PBF additive manufacturing online detection system, which can realize the cooperative work of additive manufacturing and online detection; the invention also aims to provide a point-to-point laser ultrasonic PBF additive manufacturing online detection method, which can ensure the detection efficiency and high precision at the same time.
The technical scheme is as follows: the invention discloses a point-to-point laser ultrasonic PBF additive manufacturing online detection system, which comprises an excitation laser, a laser ultrasonic receiver, an optical system, a control system and a data processing system, wherein the laser ultrasonic receiver and a printing laser share a printing laser vibrating mirror and a trans-mirror, and the trans-mirror combines the printing laser and the receiving laser to the same optical path and uses the same in a time-sharing manner, so that the printing system and the detection system are staggered, and the action of an optical switch is avoided; the axis of the light path of the printing laser galvanometer is vertical to the working surface; the exciting laser galvanometer is obliquely arranged on one side of the printing laser galvanometer, and the axes of the exciting and receiving laser light paths are converged at the center of the printing area on the working surface, so that the cooperative detection of constant distance between exciting laser and detection laser is ensured.
The detection system of the invention combines the printing laser and the receiving laser to the same optical path for time-sharing use through the transflective mirror, thereby avoiding the action of an optical switch and enabling an optical component to bear the high power of the printing laser. The laser ultrasonic receiver and the printing laser share a vibrating mirror which can be recorded as a printing/receiving shared vibrating mirror, the printing/receiving shared vibrating mirror is a light path axis vertical working surface, the exciting laser vibrating mirror is obliquely arranged, and the light path axis and the exciting laser vibrating mirror are superposed in the center of a printing area of the working surface.
The existing optical on-line detection technology does not directly detect defects in parts, and is characterized in that an optical sensor is additionally arranged on a printing light path, printing light laser is applied to a molten pool, reflected light rays are split by a transflective lens after passing through a field lens and a galvanometer, and the reflected light rays are recorded and processed by a computer through photoelectric conversion and image video conversion of the optical sensor, so that the printing quality is indirectly reflected.
In the online detection system, the excitation laser emits pulse laser to the detection surface to excite to generate ultrasonic waves, the laser ultrasonic receiver emits detection laser and receives reflected light from the detection surface, and the vibration of the surface to be detected is detected by an optical interference principle and is used for receiving surface waves generated by laser excitation; the control system controls the exciting and receiving galvanometer to enable exciting and receiving laser to be accurately projected to the designated position of the detection surface, and the data processing system collects ultrasonic detection data from the laser ultrasonic receiver and performs data processing, so that a detection result is obtained.
The excitation laser emits pulse laser, the pulse width of the laser is 1-10 nm, the repetition pulse frequency of the laser is less than 30kHz, and the energy of a single laser pulse is 1-2 mJ; for exciting the generation of ultrasonic waves at the detection surface.
The laser ultrasonic receiver emits detection laser and receives reflected light from the detection surface, detects the vibration of the surface to be detected through an optical interference principle, and the vibration detection frequency range is 100MHz at most and is used for receiving surface waves generated by laser excitation;
the optical system includes corresponding optical elements such as optical fibers, optical devices, galvanometer systems, and the like. Receiving laser and the additive manufacturing equipment share light paths such as a collimator and a printing laser galvanometer; the excitation laser is obliquely arranged, so that the axes of the laser light paths for excitation and reception are converged at the center of the printing area of the powder bed;
the computer control system consists of a control computer, a corresponding motion controller and a control cable, and controls the excitation and receiving galvanometer to accurately project excitation and receiving laser to a specified position on the detection surface; the control signal of the laser is excited and received to control the light emission of the laser;
the computer data processing system consists of a data processing computer with a data acquisition function, collects ultrasonic detection data from the laser ultrasonic receiver, and performs data processing to obtain a detection result. The data processing computer and the control computer are connected by Ethernet to transmit feedback control signal.
When the on-line detection of additive manufacturing is realized, the on-line detection is not completely and synchronously realized in the printing process in order to accurately detect the defect condition in the printing layer, but the printing of a plurality of layers and one-time detection are alternately carried out. The added detection link interrupts the original continuous printing process, influences the printing process to a certain extent and reduces the printing efficiency. In order to reduce the influence of the alternate detection process on printing, each detection time is required to be as short as possible, but the traditional laser ultrasonic scanning detection method is difficult to realize high-precision and high-efficiency detection at the same time. The invention provides a point-to-point laser ultrasonic detection method, which comprehensively utilizes the traditional ultrasonic scanning strategy, thereby realizing the good effect of considering both the detection precision and the detection efficiency and being particularly suitable for the application requirement of PBF additive manufacturing on-line detection.
The invention provides a point-to-point laser ultrasonic PBF additive manufacturing online detection method, which comprises the steps of alternately carrying out the additive manufacturing process and the laser ultrasonic detection process of a part, scanning defects in the formed thickness by an online detection system when the overall thickness of each additive manufacturing process is within the range which can be covered by the next laser ultrasonic detection, and displaying the defect condition of the current layer; and reconstructing the defect distribution in the finished part by analyzing the laser ultrasonic detection data of all layers until the whole part is formed.
The method adopts a scheme that a laser ultrasonic detection (LUT) and an Additive Manufacturing (AM) system work cooperatively, the whole AM process and the online detection of the invention are realized by alternating an AM process and a laser ultrasonic detection (LUT) process, and after printing is finished, data reconstruction is carried out on all obtained detection layer defect information according to a spatial position relation, so that the information of defect three-dimensional distribution in the part with the effect like tomography can be obtained. During each AM process, the powder is melted by the heat source and built up layer by layer to form, with the possibility of defects forming during the powder consolidation process. For additive manufacturing and in-line inspection to be effective, the overall shape thickness of each AM process should be within the range that can be covered by the next LUT inspection, typically no more than 0.7 mm. The AM thickness of each layer is generally around 20-50 μm depending on the particle size of the powder used. Taking the AM process as 10 layers as an example, the thickness is about 200 and 500 μm, which satisfies the range requirement that LUT detection can cover. Therefore, after 10 layers of AM is formed (if the particle size of the powder is small, such as D50 is about 20 μm, the particle size can be set to be 20-25 layers), a LUT system test is carried out once to test the defects in the formed thickness, and the defects of the current layer can be displayed in the scanning process. And (4) alternating the AM process and the LUT process until the whole part is formed, and reconstructing the defect distribution in the finished part by analyzing the LUT data of all layers.
The detection method of the invention is a step and a method for realizing an online detection function by applying the detection hardware system, is completely different from the principle of optical online detection, and is also different from the detection execution of the traditional A, B, C scanning mode of laser ultrasound. The invention combines the online detection system, innovatively provides a point-to-point detection process, when the laser ultrasonic detection method is implemented, A, B, C scanning and data processing are utilized to realize defect detection, and the scanning interval between B and C is invariable. The scanning interval is large, the speed is high, but the detection precision is low; the scanning interval is small, the speed is slow, but the detection precision is high. When the material increase manufacturing on-line detection is implemented, two aspects of time efficiency and detection precision need to be considered simultaneously. The invention provides a point-to-point LUT detection method, which adopts two scanning intervals of coarse scanning and fine scanning through effective matching of B scanning and C scanning, thereby improving the detection efficiency on the premise of considering the accuracy. That is, the present invention employs C-scans that are based on a coarse grid as a whole, and B-scans that employ a local fine grid in accurately identifying the defect contours. Thus, not only can the high efficiency of the coarse grid be obtained, but also the high accuracy of the defect outline position identification can be obtained.
The invention is suitable for metal additive manufacturing of PBF type, and implements a detection layer after a plurality of printing layers are finished, and printing and detection are alternately carried out, thereby finishing the processes of additive manufacturing and online detection. The method comprises the steps of detecting defects contained in a just finished printing layer in a quasi-real-time online mode, determining printing quality, and providing position, size and shape information of the defects for feedback control. Compared with the existing laser ultrasonic nondestructive detection method, the point-to-point laser ultrasonic scanning defect detection method provided by the invention has the advantages of high time efficiency and high space detection precision, and can be used for considering both thick and thin scanning space dimensions through the optimization of the scanning path.
Preferably, the laser ultrasonic testing comprises the following steps:
(1) reading a slice file for additive manufacturing to obtain the regional geometric information of the current detection layer;
(2) setting grid parameters of C scanning and B scanning, generating scanning grids in the region according to the grid parameters of C scanning, and generating corresponding B scanning grids in each C grid;
(3) c grid scanning is carried out: during scanning, the distance between the projection points of the excitation laser and the laser receiving galvanometer is kept unchanged and is kept as a C grid parameter by utilizing the excitation laser galvanometer and the laser receiving galvanometer, a point-to-point detection signal of a detection surface is obtained after each projection, and whether a defect exists in a detection area is judged by utilizing the peak value of the obtained point-to-point detection signal;
(4) and judging whether the B scanning is required according to the detection precision.
In the step (3), a reference signal is set before C grid scanning is carried out, when the peak-to-peak value of a point-to-point detection signal is equal to the peak-to-peak value of the reference signal, the current grid is marked as 0, and when obvious enhancement occurs, the current grid is marked as 1; marked-1 when significantly attenuated; a significant increase or decrease in the peak-to-peak value of the signal indicates a defect between the two projected points.
Wherein the setting of the reference signal comprises: before testing, a reference sample which is made of the same material and is free of defects is excited under the same laser to calibrate the amplitude of the reference signal, and calibration data are stored in a data processing system.
After completing the C-scan of the detection surface, the data processing system searches for a grid in which the absolute value of the sum of the adjacent grid mark values is 1 and the grid mark value is not 0 among the recorded grid mark values, and records the grid number as a boundary grid.
When B scanning is required, on a B scanning grid in each C grid marked as a boundary grid, utilizing two galvanometers to keep the distance between the excitation laser and the projection point of the received laser as a B grid parameter, and carrying out B scanning, wherein the distance is unchanged in the scanning process; and marking according to the marking of C scanning and the method of processing data during and after scanning, and finding out boundary grids to realize accurate detection of the defect outline.
Specifically, the laser ultrasonic testing includes the following testing procedures:
(1) reading a slice file of additive manufacturing to obtain the area geometric information of the current detection layer;
(2) setting grid parameters of C scanning and B scanning, wherein the grid parameters of C scanning are coarse grids and are used for improving the detection efficiency; and the B scanning grid parameter is a fine grid and is used for improving the detection precision of the defects. Based on the C-scan grid parameters, scan grids are generated within the region, and a corresponding B-scan grid is generated within each C-grid.
(3) First, a C-grid scan is performed: during scanning, the distance between the projection points of the excitation laser and the receiving laser is kept unchanged by utilizing the two galvanometers, the distance is kept as a C grid parameter, a point-to-point detection signal is obtained after each projection, and the single detection signal can be called an A scanning signal. Before testing, the signal amplitude is calibrated by using a reference sample which is made of the same material, has approximate surface roughness and is free of defects, and the calibrated value is stored in a computer so as to be convenient to read and use. When the peak value of the point-to-point detection signal of the obtained detection surface is equal to the peak value of the reference signal, marking the current grid as 0; labeled 1 when significant enhancement occurred; the time of significant attenuation is marked as-1. A significant increase or decrease in the peak-to-peak value of the signal indicates a defect between the two projected points.
After the C-scan of the surface is completed, the data processing computer searches for a grid in which the absolute value of the sum of the grid mark values adjacent thereto is 1 and the grid mark value is not 0 among the recorded grid mark values, and records the grid number as a boundary grid.
B-scan may or may not be performed depending on the detection accuracy requirements. When B scanning is carried out, on the B scanning grids in the C grids marked as boundary grids, in a similar mode to C grid scanning, the distance between the excitation laser and the projection point of the receiving laser is kept as a B grid parameter by using two galvanometers, and the distance is unchanged in the scanning process, so that B scanning is carried out. And marking is carried out according to the marking of C scanning and the method for processing data in the scanning process and after the scanning, and a boundary grid is found out, so that the defect outline is accurately detected.
The online detection function of the existing commercial PBF metal additive manufacturing is not popularized yet, and the commercial online detection technology is applied more frequently to the optical analysis of a molten pool by using the reflected light of printing light while printing. Its advantages are synchronous printing; the defect that the defect condition at the position can be observed and predicted only through a molten pool, and the defect is not direct and not accurate enough; in addition, the detection principle also determines that the method can only be used for detecting the defects on the surface and cannot reflect the defect condition in a certain depth. Other on-line detection techniques are still basically in the research stage, such as a method of fixing a contact ultrasonic probe on a substrate, and the method has limited precision and is not suitable for detecting large complex parts; the method for realizing dynamic real-time monitoring of the molten pool by adopting the X-ray synchrotron radiation technology has huge equipment cost, needs a specially-made powder bin as a sample box, cannot realize printing and online detection of real parts, and is not suitable for research and engineering application. The detection system and the detection method provided by the invention realize the fusion of the laser ultrasonic online detection and the additive manufacturing process effectively, and the point-to-point laser ultrasonic detection (scanning) method provided by the invention considers the contradiction problem of the detection spatial resolution and the time efficiency, and realizes the unification of the 3D printing and the online detection process effectively.
Has the advantages that:
(1) the invention provides a laser ultrasonic point-to-point online defect detection system and method suitable for metal additive manufacturing of a PBF type, aiming at the problem that the metal additive manufacturing of the PBF type does not have an online defect detection technology. After a plurality of printing layers are completed, implementing a detection layer, and alternately performing printing and detection so as to complete the processes of additive manufacturing and online detection; the method comprises the steps of detecting defects contained in a just finished printing layer in a quasi-real-time online mode, determining printing quality, and providing position, size and shape information of the defects for feedback control.
(2) Aiming at the conditions that when the traditional laser ultrasonic nondestructive testing technology scans the tested material in large area with equal precision, massive processing data is generated, and the testing efficiency is low, the invention considers two scanning space dimensions of thickness and thickness, and has the advantages of high time efficiency and high space testing precision, and the data processing amount of a computer is greatly reduced.
(3) The invention can effectively improve the scanning speed and the scanning precision near the defect, and judge the information such as the position, the size profile and the like of the defect more accurately; the method is simple to operate, good in repeatability and independent of the technical level of detection personnel.
(4) When the online detection of the additive manufacturing process is realized, additive manufacturing is performed in multiple layers and laser ultrasonic detection is performed in one layer alternately, the characteristic that the surface wave of ultrasonic waves can cover a certain depth is utilized during each detection, the thickness coverage detection of just finished printing is realized, the printing and detection processes are repeatedly and alternately performed, and finally the whole process of integrated manufacturing and online detection is completed. Because the printing process can not be synchronized to realize the online detection completely in real time, the detection link is added to interrupt the original continuous printing process, the printing process is influenced to a certain extent, and the printing efficiency is reduced. In order to reduce the influence of the alternate detection process on printing, the invention provides a point-to-point laser ultrasonic detection method, which comprehensively utilizes the traditional ultrasonic scanning strategy, thereby realizing the good effect of considering both the detection precision and the detection efficiency and being particularly suitable for the application requirement of PBF additive manufacturing online detection.
Drawings
FIG. 1 is a schematic block diagram of an additive manufacturing and in-line inspection system of the present invention;
FIG. 2 is a flow chart of the steps of the on-line detection method of the present invention;
FIG. 3 is a schematic illustration of the integration and cooperation of additive manufacturing and online detection;
FIG. 4 is a schematic diagram of a scanning inspection method of the present invention;
FIG. 5 is a graph of the peak variation during laser ultrasound A-scan;
fig. 6 is a schematic diagram of the scanning detection result.
Wherein: 1. a fiber coupler; 2. a transflective mirror; 3. a collimating mirror; 4. printing a galvanometer shared by laser and a laser ultrasonic receiver; 5. exciting a laser galvanometer; 6. a printing work cavity; 7. a printing and inspection surface of the powder bed; 8. printing a powder cylinder; 9. an optical fiber; 10. a motion control signal; 11 sharing a galvanometer motion controller; 12 galvanometer motion controller; 13 exciting the laser; 14 a printing laser; 15 laser ultrasonic receiver; 16 detecting a data line; 17 control signal lines; 18 detecting data display; 19 a data processing computer; 20. and a control computer.
Detailed Description
The present invention will be described in further detail with reference to examples.
The invention relates to a point-to-point laser ultrasonic PBF additive manufacturing online detection system, which comprises an excitation laser 13, a laser ultrasonic receiver 15, an optical system, a control system and a data processing system.
As shown in fig. 1, the structure of the additive manufacturing and on-line detection system is schematically illustrated, the detection system includes an optical fiber coupler 1, a transflective mirror 2, a collimating mirror 3, a vibrating mirror 4 shared by a printing laser and a laser ultrasonic receiver, an excitation laser vibrating mirror 5, a printing working cavity 6, a printing powder cylinder 8, an optical fiber 9, a shared vibrating mirror motion controller 11, a vibrating mirror motion controller 12, an excitation laser 13, a printing laser 14, a laser ultrasonic receiver 15, a detection data display 18, a data processing computer 19, and a control computer 20, the laser ultrasonic receiver 15 and the printing laser 14 share the printing laser vibrating mirror 4, the collimator 3, and the transflective mirror 2, the shared vibrating mirror can be recorded as the printing/receiving shared vibrating mirror 4, the transflective mirror 2 combines the printing laser and the receiving laser into the same optical path and uses the same time-sharing laser, the optical path axis of the printing laser vibrating mirror 4 is perpendicular to the working surface, the printing and detection surface 7 of the powder bed; the exciting laser galvanometer 5 is obliquely arranged on one side of the printing laser galvanometer 4, and the axes of the exciting and receiving laser light paths are converged at the center of the printing area of the working surface. The computer 20 controls the corresponding motion controller and the excitation laser 13, the printing laser 14 and the laser ultrasonic receiver 15 through the control signal line 17, and the shared galvanometer motion controller 11 and the galvanometer motion controller 12 control the excitation and receiving galvanometers through the motion control signal 10 so that the excitation and receiving laser can be accurately projected to the designated position of the detection surface. Wherein, the principle schematic diagram of the transflective mirror is shown in the upper left circle of fig. 1.
The excitation laser emits pulse laser, the pulse width of the laser is 1-10 nm, the repetition pulse frequency of the laser is less than 30kHz, and the energy of a single laser pulse is 1-2 mJ, and the excitation laser is used for exciting and generating ultrasonic waves on the detection surface.
The laser ultrasonic receiver emits detection laser and receives reflected light from the detection surface, detects the vibration of the surface to be detected through an optical interference principle, the vibration detection frequency range is 100MHz at most, and the laser ultrasonic receiver is used for receiving surface waves generated by laser excitation and transmitting detection data to a computer through a detection data line 16 for data processing.
The optical system includes corresponding optical elements such as optical fibers, optical devices, galvanometer systems, and the like. Receiving laser and the additive manufacturing equipment share light paths such as a collimator and a printing laser galvanometer; the excitation laser is obliquely arranged, so that the axes of the laser light paths for excitation and reception are converged at the center of the printing area of the powder bed;
the control system consists of a control computer, a corresponding motion controller and a control cable, and controls the excitation and receiving galvanometers to accurately project excitation and receiving laser to a specified position on the detection surface; the control signal of the laser is excited and received to control the light emission of the laser;
the data processing system is composed of a data processing computer with a data acquisition function, collects ultrasonic detection data from the laser ultrasonic receiver, and performs data processing to obtain a detection result. The data processing computer and the control computer are connected by Ethernet to transmit feedback control signal.
As shown in fig. 2 and 3, which are a flow chart and a schematic diagram of steps of the online detection method of the present invention, the present embodiment provides an online detection method of PBF additive manufacturing by point-to-point laser ultrasound, which includes the following steps:
(1) determining a detection geometry region
Reading the slice file of additive manufacturing to obtain the shape of the current region of the detection layer is shown in fig. 4, the geometric information of the minimum circumscribed rectangle is 10 × 10mm, and it can be known that the maximum feature length is 10 mm.
(2) The grid parameters of the C scan and the B scan are set with reference to Table 1 based on the geometric information of the detection region (FIG. 4)
Δ X: the distance between the projection points of the excitation laser and the receiving laser during C scanning is shown, and the moving distance of the two points in the x direction is also shown;
Δ Y: the moving distance of two points in the y direction in the C scan is shown.
dx: the distance between the two laser beams when B-scanning is performed is also the distance moved in the x direction.
dy: indicating that the distance between the two lasers when B-scanning is performed is also the distance moved in the y-direction.
TABLE 1 reference table for empirical selection of scan parameters
From table 1, the C scan parameters are known: Δ X ═ 1mm Δ Y ═ 1 mm;
b, scanning parameters: dx is 0.1mm dy is 0.1 mm.
Where maximum feature length refers to the maximum feature size of a single scan area on the part. A scanning is point-to-point one-time detection; the B scanning is that a plurality of A scanning forms a line (generally a straight line, the extension is a linear profile in the invention); the C scanning is a surface formed by a plurality of A scanning points in an array mode.
(3) Generating scan grids within the region based on the C-scan grid parameters, and generating a corresponding B-scan grid within each C-scan grid; as shown in fig. 4.
(4) Before testing, a reference sample which is made of the same material, has approximate surface roughness and is free of defects is excited under the same laser to calibrate the signal amplitude, and calibration data are stored in a computer in advance for ready calling. First, a C-grid scan is performed: during scanning, the distance between the projection points of the excitation laser and the receiving laser is kept to be constant at delta X by using the two galvanometers, a next line is scanned by moving delta Y in the Y direction after one line is scanned, and a point-to-point detection signal is obtained after each projection. When the peak value of the point-to-point detection signal of the obtained detection surface is equal to the peak value of the reference signal, marking the current grid as 0; labeled 1 when significant enhancement occurred; the time of significant attenuation is marked as-1. A significant increase or decrease in the peak-to-peak value of the signal indicates that a boundary of a defect of a certain size exists between the two projected points, as shown in fig. 5. The invention can detect the minimum size of the defect, which is related to the type of material, the surface roughness and the frequency of laser.
(5) After the C-scan of the surface is completed, the data processing computer searches for a grid in which the absolute value of the sum of the grid mark values adjacent thereto is 1 and the grid mark value is not 0 among the recorded grid mark values, and records the grid number as a boundary grid.
(6) B-scan may or may not be performed depending on the detection accuracy requirements. And B scanning is required when the performance requirement of the workpiece is high or the size is small, grid division is carried out in each C grid marked as a boundary grid according to B scanning parameters, the distance between the projection points of the excitation laser and the received laser is kept as dx by using two galvanometers in a mode similar to C grid scanning, and the B scanning is carried out when the distance is unchanged in the scanning process. And marking is carried out according to the marking of C scanning and the method for processing data in the scanning process and after the scanning, and a boundary grid is found out, so that the defect outline is accurately detected. The results are schematically shown in FIG. 6.
The laser repetition frequency used in the detection system of the embodiment is 500Hz, and the point-to-point laser ultrasonic detection time of the invention is adopted: (10 × 10+10 × 19)/500 ═ 4 s; (a 1 x 1mm rough scan was first performed, followed by a 0.1 x 0.1mm fine scan for the defect).
If the same detection precision is obtained by adopting the conventional defect scanning in the prior art, the scanning time of 0.1 x 0.1mm is as follows: 10 × 100/500 ═ 20 s; i.e. 0.1 x 0.1mm for each point.
By comparison, the experimental method has the advantage that the relatively accurate scanning time is shortened to 1/5.
The invention provides an integrated system scheme, and integrates the on-line detection and the additive manufacturing process, wherein the additive manufacturing process and the laser ultrasonic detection process are alternately carried out, and finally the whole process of integrated manufacturing and on-line detection is completed. Wherein the number of layers in the additive manufacturing process is related to the particle size of the powder particles, and the total layer thickness is generally not more than 0.7 mm. The detection layer adopts a laser ultrasonic method, and the invention refines the detection strategy combining the respective advantages of A, B, C scanning. The detection method can give consideration to both detection precision and efficiency. The integrated system can realize integration of manufacturing and online quality monitoring, and provides important help for determining printing quality, providing position, size and shape information of defects for feedback control and realizing non-defective additive manufacturing.
Claims (10)
1. A point-to-point laser ultrasonic PBF additive manufacturing online detection system is characterized in that: the laser ultrasonic receiver and the printing laser share a printing laser vibrating mirror and a trans-reflecting mirror, the trans-reflecting mirror combines the printing laser and the receiving laser to the same light path and uses the same in a time-sharing manner, and the light path axis of the printing laser vibrating mirror is vertical to the working surface; the exciting laser galvanometer is obliquely arranged on one side of the printing laser galvanometer, and the axes of the exciting and receiving laser light paths are converged at the center of the printing area on the working surface.
2. The point-to-point laser ultrasonic PBF additive manufacturing online detection system according to claim 1, wherein: the excitation laser emits pulse laser to the detection surface to be excited to generate ultrasonic waves, the laser ultrasonic receiver emits detection laser and receives reflected light from the detection surface, and the vibration of the surface to be detected is detected through an optical interference principle and is used for receiving surface waves generated by laser excitation; the control system controls the exciting and receiving galvanometer to enable exciting and receiving laser to be accurately projected to the designated position of the detection surface, and the data processing system collects ultrasonic detection data from the laser ultrasonic receiver and performs data processing, so that a detection result is obtained.
3. The point-to-point laser ultrasonic PBF additive manufacturing online detection system according to claim 1, wherein: the laser pulse width emitted by the excitation laser is 1-10 nm, the laser repetition pulse frequency is less than 30kHz, and the energy of a single laser pulse is 1-2 mJ.
4. A point-to-point laser ultrasonic PBF additive manufacturing online detection method is characterized by comprising the following steps: the additive manufacturing process and the laser ultrasonic detection process of the part are alternately carried out, the assembly-shaped thickness of each additive manufacturing process is in the range which can be covered by the next laser ultrasonic detection, and the online detection system scans the defects in the formed thickness and displays the defect condition of the current layer; and reconstructing the defect distribution in the finished part by analyzing the laser ultrasonic detection data of all layers until the whole part is formed.
5. The point-to-point laser ultrasonic online detection method for PBF additive manufacturing according to claim 4, wherein the laser ultrasonic detection comprises the following steps:
(1) reading a slice file for additive manufacturing to obtain the regional geometric information of the current detection layer;
(2) setting grid parameters of C scanning and B scanning, generating scanning grids in the region according to the grid parameters of C scanning, and generating corresponding B scanning grids in each C grid;
(3) c grid scanning is carried out: during scanning, the distance between the projection points of the excitation laser and the laser receiving galvanometer is kept unchanged and is kept as a C grid parameter by utilizing the excitation laser galvanometer and the laser receiving galvanometer, a point-to-point detection signal of a detection surface is obtained after each projection, and whether a defect exists in a detection area is judged by utilizing the peak value of the obtained point-to-point detection signal;
(4) and judging whether the B scanning is required according to the detection precision.
6. The point-to-point laser ultrasonic PBF additive manufacturing online detection method according to claim 5, characterized in that: in the step (3), a reference signal is set before C grid scanning is carried out, when the peak-to-peak value of a point-to-point detection signal is equal to the peak-to-peak value of the reference signal, the current grid is marked as 0, and when obvious enhancement occurs, the current grid is marked as 1; marked-1 when significantly attenuated; a significant increase or decrease in the peak-to-peak value of the signal indicates a defect between the two projected points.
7. The point-to-point laser ultrasonic PBF additive manufacturing online detection method according to claim 5, characterized in that: in the step (3), after the C-scan of the detection surface is completed, the data processing system searches for a grid in which the absolute value of the sum of the adjacent grid mark values is 1 and the grid mark value is not 0 among the recorded grid mark values, and records the grid number as a boundary grid.
8. The point-to-point laser ultrasonic online PBF additive manufacturing detection method according to claim 7, characterized in that: when B scanning is required, on a B scanning grid in each C grid marked as a boundary grid, utilizing two galvanometers to keep the distance between the excitation laser and the projection point of the received laser as a B grid parameter, and carrying out B scanning, wherein the distance is unchanged in the scanning process; and marking according to the marking of C scanning and the method of processing data during and after scanning, and finding out boundary grids to realize accurate detection of the defect outline.
9. The point-to-point laser ultrasonic online PBF additive manufacturing detection method according to claim 6, wherein the setting of the reference signal comprises: before testing, a reference sample which is made of the same material and is free of defects is excited under the same laser to calibrate the amplitude of the reference signal, and calibration data are stored in a data processing system.
10. The point-to-point laser ultrasonic PBF additive manufacturing online detection method according to claim 5, characterized in that: the thickness of the assembly shape in each additive manufacturing process is less than or equal to 0.7 mm.
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