US-12619069-B2 - Schlieren system for in-situ/online monitoring of spatter in large-area melt pool

US12619069B2US 12619069 B2US12619069 B2US 12619069B2US-12619069-B2

Abstract

A schlieren system for in-situ/online monitoring of spatter in a large-area melt pool is provided, including a parallel light generation part, a parallel light deflection part, and an image acquisition part. The system can monitor spatter and other physical phenomena in the melt pool in a process of multi-layer printing and adjust a monitored area during an experiment to expand a monitored range. A reflector group composed of a plurality of plane mirrors is arranged, such that an optical path can be kept away from powder and dust areas, avoiding interference between the schlieren system and inherent devices inside a build chamber. Communication between a laser path controller and an optical path deflecting mirror galvanometer motor controller is established to automatically control the plane mirrors to change the monitored area, automatically track the melt pool, and realize online monitoring.

Inventors

Xin Lin
Kunpeng ZHU
Haihong Zhu
Xuefeng Chen
Haodong CHEN

Assignees

WUHAN UNIVERSITY OF SCIENCE AND TECHNOLOGY

Dates

Publication Date: 20260505
Application Date: 20241122
Priority Date: 20240407

Claims (12)

1 . A schlieren system for in-situ/online monitoring of a spatter in a large-area melt pool, wherein the schlieren system is configured to monitor spatter phenomena in the large-area melt pool on a selective laser melting build workbench, the selective laser melting build workbench comprising a powder reservoir ( 4 ), a build platform ( 5 ), and a powder collection bin ( 7 ) arranged in sequence on a bottom surface ( 12 a ) of a printing chamber ( 12 ) in a powder scraping direction y, as well as a laser emitter ( 13 ) arranged above the build platform ( 5 ), the laser emitter ( 13 ) is configured to be controlled by a laser galvanometer motor controller ( 22 ), and to project an emitted laser beam ( 21 ) onto a designated position area of the build platform ( 5 ) according to laser scanning path information outputted from a laser path planner ( 23 ), and to scan along a laser scanning path; and the schlieren system comprising an optical source for generating an initial optical beam ( 19 c ), and an optical beam guiding system comprising a plane mirror designated as a fifth plane mirror ( 9 ), an optical path deflecting mirror ( 17 ), and a reflector group; wherein the fifth plane mirror ( 9 ) is configured to guide any of guiding optical beams ( 19 a ) reflected by the reflector group, and after the any of the guiding optical beams reflected by the reflector group has been reflected by the fifth plane mirror ( 9 ), schlieren optical beams ( 19 b ) are formed, wherein the schlieren optical beams pass through a sputtering area in close proximity to an upper surface of the build platform ( 5 ) in a left-right direction x and reach a sixth plane mirror ( 6 ), wherein the left-right direction x is perpendicular to the powder scraping direction y and parallel to the bottom surface; a projection length of the fifth plane mirror ( 9 ) in the powder scraping direction y is denoted as L 1 , wherein L 1 is greater than or equal to a length L 2 of the sputtering area in the powder scraping direction y; the sixth plane mirror ( 6 ) is configured to guide the schlieren optical beams ( 19 b ) to be reflected to a lens group ( 3 ) and focus on a camera ( 2 ), a projection length L 3 of the sixth plane mirror ( 6 ) in the powder scraping direction y is greater than or equal to L 2 , and the fifth plane mirror ( 9 ) and the sixth plane mirror ( 6 ) are respectively arranged on a left/right side of the build platform ( 5 ) in the left-right direction x; the reflector group comprises at least two reflectors configured to pivot to change directions of the at least two reflectors, the at least two reflectors are arranged on a mounting plane, and mirror surfaces of the at least two reflectors are configured to pivot around pivot axes perpendicular to the mounting plane; the at least two reflectors, the optical path deflecting mirror ( 17 ), and the fifth plane mirror ( 9 ) are arranged on an identical side of the build platform ( 5 ), and when the at least two reflectors are pivoted to a guiding angle, the mirror surfaces of the at least two reflectors face the optical path deflecting mirror ( 17 ) and direct reflected optical beams toward the fifth plane mirror ( 9 ), and the guiding optical beams ( 19 a ) reflected by the at least two reflectors to the fifth plane mirror ( 9 ) are parallel; the optical path deflecting mirror ( 17 ) is configured to be pivotable around an axis ( 18 ) perpendicular to the mounting plane to a working position relatively parallel to one of the at least two reflectors in the reflector group, wherein the one of the at least two reflectors in the reflector group has been pivoted to the guiding angle, wherein the initial optical beam ( 19 c ) is reflected to the one of the at least two reflectors in the reflector group, and a projection distance from the axis ( 18 ) of the optical path deflecting mirror ( 17 ) to the build platform ( 5 ) in a direction of the any of the guiding optical beams ( 19 a ) is less than or equal to a projection distance from a pivot axis of any of the at least two reflectors to the build platform ( 5 ); and a synchronous controller ( 24 ), wherein the synchronous controller ( 24 ) is in a signal connection with the laser path planner ( 23 ); after receiving the laser scanning path information, the synchronous controller synchronously sends the laser scanning path information to the laser galvanometer motor controller ( 22 ) and an optical path deflecting mirror galvanometer motor controller ( 25 ), and the optical path deflecting mirror galvanometer motor controller ( 25 ) being configured to pivot a mirror surface of the optical path deflecting mirror ( 17 ) to the working position, wherein the any of the guiding optical beams ( 19 a ) reflected by the at least two reflectors is reflected by the fifth plane mirror ( 9 ) and passes through the designated position area, wherein the at least two reflectors are pivoted to the guiding angle; wherein the at least two reflectors are arranged in a following manner according to a position of the mounting plane: the mounting plane is a side wall ( 12 b ) of the printing chamber ( 12 ) on a left or right side adjacent to the fifth plane mirror ( 9 ) in the powder scraping direction y, the side wall is parallel to the powder scraping direction y and forms an inclination angle greater than 0° but less than 180° with the bottom surface ( 12 a ), wherein the guiding angle is an angle αI of the mirror surface of each of the at least two reflectors pivoted to the powder scraping direction y, wherein the angle αI is greater than 0° but less than or equal to 45°; and an order of the guiding angles of the mirror surfaces of the at least two reflectors is opposite to an order of projection distances from the pivot axes of the at least two reflectors along the guiding optical beams ( 19 a ) to the bottom surface; a projection length of a union set of the guiding optical beams ( 19 a ) in the powder scraping direction y is greater than or equal to L 1 ; when observing in the powder scraping direction y, projection distances from the pivot axes of the at least two reflectors to an extension surface of the powder collection bin ( 7 ) in the left-right direction x are less than projection distances from the axis ( 18 ) to the extension surface of the powder collection bin ( 7 ) in the left-right direction x; when observing in the direction of the any of the guiding optical beams, projection distances from the pivot axes of the at least two reflectors to the build platform ( 5 ) are greater than or equal to the projection distance from the axis ( 18 ) of the optical path deflecting mirror ( 17 ) to the build platform ( 5 ), a mirror surface of the fifth plane mirror ( 9 ) is parallel to the powder scraping direction y, and the guiding optical beams ( 19 a ) and the schlieren optical beams ( 19 b ) are symmetrical relative to a normal vector of the mirror surface of the fifth plane mirror ( 9 ); and the mounting plane is the bottom surface, the mirror surface of the fifth plane mirror ( 9 ) is perpendicular to the bottom surface, and the guiding optical beams ( 19 a ) and the schlieren optical beams ( 19 b ) are symmetrical relative to the normal vector of the mirror surface of the fifth plane mirror ( 9 ), and the direction of the any of the guiding optical beams is identical to the powder scraping direction y, the guiding angle is an angle αII of a mirror surface of each of the at least two reflectors pivoted to the left-right direction x, wherein the angle αII is greater than 0° but less than or equal to 45°; an order of the guiding angles of the mirror surfaces of the at least two reflectors is opposite to an order of projection distances from the pivot axes of the at least two reflectors along the guiding optical beams ( 19 a ) to an extension body of the build platform ( 5 ) in the left-right direction x, and a projection length of a union set of the guiding optical beams ( 19 a ) onto the fifth plane mirror ( 9 ) in the left-right direction x is greater than or equal to a projection length L 4 of the fifth plane mirror ( 9 ) in the left-right direction x; in the direction of the any of the guiding optical beams, a projection distance from the extension body of the build platform ( 5 ) in the left-right direction x to the pivot axes of the at least two reflectors is greater than or equal to a projection distance from the extension body of the build platform ( 5 ) in the left-right direction x to the axis ( 18 ) of the optical path deflecting mirror ( 17 ); when being observed in the left-right direction x, an extension part of the build platform in the powder scraping direction y on the bottom surface is farther away from the reflector group, but the extension part of the build platform ( 5 ) in the powder scraping direction y on the bottom surface is more adjacent to the axis ( 18 ) of the optical path deflecting mirror ( 17 ); or when being observed in the left-right direction x, the extension part of the build platform in the powder scraping direction y on the bottom surface is more adjacent to the reflector group, but the extension part of the build platform ( 5 ) in the powder scraping direction y on the bottom surface is farther away from the axis ( 18 ) of the optical path deflecting mirror ( 17 ); the optical path deflecting mirror galvanometer motor controller ( 25 ) is configured to control a selected one of the at least two reflectors in the reflector group, when being pivoted to the guiding angle, the selected reflector is configured so that the guiding optical beams ( 19 a ) after being reflected by the fifth plane mirror ( 9 ) are directed to pass through the designated position area corresponding to the laser scanning path; the optical path deflecting mirror galvanometer motor controller ( 25 ) controls the selected reflector to be pivoted to the guiding angle, and sends a motor rotation instruction according to a difference between a complementary angle of a guiding angle of the selected reflector and an angle of the mirror surface of the optical path deflecting mirror ( 17 ) relative to a direction of the any of the guiding optical beams, wherein the optical path deflecting mirror ( 17 ) is pivoted to be parallel to a mirror surface of the selected reflector being pivoted to the guiding angle.
2 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein a direction of an initial optical beam ( 19 c ) incident on the optical path deflecting mirror ( 17 ) is parallel to the guiding optical beams ( 19 a ) reflected by the at least two reflectors.
3 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein light from the optical source is provided by an optical source ( 16 ) system consisting of an optical point source, a concave mirror ( 1 ), and a first plane mirror ( 15 ), and light emitted from the optical point source ( 16 ) reaches the optical path deflecting mirror ( 17 ) after being reflected by the concave mirror ( 1 ) and the first plane mirror ( 15 ).
4 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 3 , wherein a straight-line distance between the optical point source ( 16 ) and the concave mirror ( 1 ) is a focal length of the concave mirror ( 1 ).
5 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein the camera ( 2 ) is mounted behind a focal point of the lens group ( 3 ).
6 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein when the side wall is parallel to the powder scraping direction y and perpendicular to the bottom surface, angles between the mirror surface of the fifth plane mirror ( 9 ) relative to the side wall and the bottom surface are both 45°, the fifth plane mirror ( 9 ) is abutted against the side wall, and the guiding optical beams ( 19 a ) are perpendicular to the bottom surface.
7 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein angles between the mirror surface of the fifth plane mirror ( 9 ) relative to the left-right directions x, as well as the powder scraping direction y are both 45°, and the guiding optical beams ( 19 a ) are parallel to the powder scraping direction y.
8 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein the schlieren optical beams ( 19 b ) are distributed continuously in the powder scraping direction y.
9 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein when the angle αI between the mirror surface of the any of the at least two reflectors and the powder scraping direction y is equal to 45°, in the direction of the any of the guiding optical beams ( 19 a ), the projection distance from the axis ( 18 ) of the optical path deflecting mirror ( 17 ) to the build platform ( 5 ) is equal to the projection distance from the pivot axis of the any of the at least two reflectors to the build platform ( 5 ).
10 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein when the angle αI between the mirror surface of the any of the at least two reflectors and the powder scraping direction y is less than 45°, in the direction of the any of the guiding optical beams, a difference between the projection distance from the pivot axis of the any of the at least two reflectors to the build platform and the projection distance from the axis ( 18 ) of the optical path deflecting mirror ( 17 ) to the build platform ( 5 ) is denoted as H; and a difference in distance between the any of the guiding optical beams ( 19 a ) passing through a mirror surface emergent optical path center of the any of the at least two reflectors and the initial optical beam ( 19 c ) passing through a mirror surface emergent optical path center of the optical path deflecting mirror ( 17 ) is denoted as D, wherein H, D, and the angle αI satisfy a following formula: H = D tan ⁢ 2 ⁢ aI .
11 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein when the angle αII between the mirror surface of the any of the at least two reflectors and the powder scraping direction y is equal to 45°, in the powder scraping direction y, the projection distance from the axis ( 18 ) of the optical path deflecting mirror ( 17 ) to the extension body of the build platform ( 5 ) in the left-right direction x is equal to the projection distance from the pivot axis of the any of the at least two reflectors to the extension body of the build platform ( 5 ) in the left-right direction x.
12 . The schlieren system for the in-situ/online monitoring of the spatter in the large-area melt pool according to claim 1 , wherein when the angle αII between the mirror surface of the any of the at least two reflectors and the powder scraping direction y is equal to 45°, in the powder scraping direction y, a difference between the projection distance from the pivot axis of the any of the at least two reflectors to the build platform and the projection distance from the axis ( 18 ) of the optical path deflecting mirror ( 17 ) to the build platform ( 5 ) in the left-right direction x is denoted as H; and a difference in distance between the any of the guiding optical beams ( 19 a ) passing through a mirror surface emergent optical path center of the any of the at least two reflectors and the initial optical beam ( 19 c ) passing through a mirror surface emergent optical path center of the optical path deflecting mirror ( 17 ) is denoted as D, wherein H, D, and the angle αII satisfy a following formula: H = D tan ⁢ 2 ⁢ aII .

Description

CROSS REFERENCE TO THE RELATED APPLICATIONS This application is based upon and claims priority to Chinese Patent Application No. 202410410531.1, filed on Apr. 7, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to the technical field of laser additive manufacturing, and particularly relates to a large-area real-time monitoring schlieren imaging system for observing spatter and plumes in a melt pool formed by multi-layer scanning of selective laser melting. BACKGROUND Selective laser melting (SLM) is laser rapid prototyping technology commonly used in the field of laser additive manufacturing. Using laser as an energy source, the technology scans a metal powder bed layer by layer according to a path predefined in a 3D CAD slice model, and the scanned metal powder is melted and cured to achieve an effect of metallurgical bonding, and finally a metal part designed by the model is formed. When the laser scans the metal powder bed, the metal powder will melt rapidly under the action of the laser to form a melt pool. During this process, many physical phenomena occur, such as heat conduction, heat convection, heat radiation, evaporation, and spatter, among which spatter directly affects the surface quality of a formed melt track. Therefore, it is essential to monitor the spatter occurred during a forming process of selective laser melting. By capturing images of the spatter, the forming process of spatter can be studied intuitively. A forming mechanism of spatter can be obtained through a large number of experiments, and appropriate measures can be taken to reduce or even eliminate the impact of spatter on the forming quality. At present, two methods for monitoring the spatter in the melt pool are available. One is to employ a high-speed camera for direct shooting, followed by image processing and other means to extract spatter-related information. This method is relatively simple and easy-to-operate; however, it is very difficult for the high-speed camera to completely capture the spatter images due to different sizes and brightness of spatter. The other method is to employ a schlieren imaging device, which makes use of different propagation speeds of light in different media to make the spatter in a detection optical path develop at a specific position, and the high-speed camera is then used to capture images of spatter development. This method can clearly capture the forming and movement of spatter, but the conventional schlieren imaging device cannot monitor the spatter in the melt pool formed by multi-layer scanning due to movements of a scraper and spatial constraints, which limits further study on spatter in the melt pool formed through the selective laser melting. Furthermore, a monitored area is relatively narrow, preventing simultaneous observation of a large number of experimental groups. A chamber cannot be opened, a position of the schlieren imaging device cannot be readjusted or a build platform cannot be replaced until one monitoring session is completed, which increases experimental costs and makes it difficult to ensure consistency of conditions between successive experiments. SUMMARY In view of the deficiencies of the prior art, the present disclosure provides a large-area schlieren system for in-situ/online monitoring of spatter in a multi-layer scanning melt pool formed by selective laser melting, the system can capture images, such as spatter, plumes and the like, of the multi-layer scanning forming melt pool of selective laser melting in a printing chamber with limited space. In order to achieve the above objective, the present disclosure adopts the following technical solution: a schlieren system for in-situ/online monitoring of spatter in a large-area melt pool is used to monitor spatter phenomena in a melt pool on a selective laser melting build workbench, where the selective laser melting build workbench includes a powder reservoir, a build platform, and a powder collection bin arranged in sequence on a bottom surface of a printing chamber in a powder scraping direction y, as well as a laser emitter arranged above the build platform, the laser emitter is configured to be controlled by a laser galvanometer motor controller, and to make an emitted laser beam projected onto a designated position area of the build platform according to laser scanning path information outputted from a laser path planner, and then scans along a laser scanning path; and the schlieren system includes an optical source for generating an initial optical beam, and an optical beam guiding system composed of a fifth plane mirror, an optical path deflecting mirror and a reflector group; whereinthe fifth plane mirror is configured to guide any of guiding optical beams reflected by the reflector group that has been reflected by the fifth plane mirror to form schlieren optical beams, which is perpendicular to the powder scraping direction y and a left