阅读说明：本技术 激光粉末床熔融增材制造过程中的熔池监测方法及装置 (Molten pool monitoring method and device in laser powder bed melting additive manufacturing process ) 是由 魏正英 李俊峰 薛凌峰 来旭辉 王材桦 于 2021-08-13 设计创作，主要内容包括：本发明公开了一种激光粉末床熔融增材制造过程中的熔池监测方法及装置,包括密封模块,密封模块设置在激光粉末床熔融机器的顶部,密封模块内部设置有监测模块,监测模块能够捕捉激光与粉床相互作用下形成的熔池图像；监测模块包括高速相机,高速相机设置在直线滑台上,高速相机和直线滑台分别与电源和控制模块连接,控制模块能够控制直线滑台的移动。本发明对熔池监测更加方便,能获得更加清晰的熔池,可靠性更高。(The invention discloses a molten pool monitoring method and device in a laser powder bed melting additive manufacturing process, which comprises a sealing module, wherein the sealing module is arranged at the top of a laser powder bed melting machine, and a monitoring module is arranged in the sealing module and can capture a molten pool image formed under the interaction of laser and a powder bed; the monitoring module comprises a high-speed camera, the high-speed camera is arranged on the linear sliding table, the high-speed camera and the linear sliding table are respectively connected with the power supply and the control module, and the control module can control the movement of the linear sliding table. The invention is more convenient to monitor the molten pool, can obtain clearer molten pool and has higher reliability.)

1. The molten pool monitoring device in the laser powder bed melting additive manufacturing process is characterized by comprising a sealing module, wherein the sealing module is arranged at the top of a laser powder bed melting machine, a monitoring module is arranged in the sealing module, and the monitoring module can capture a molten pool image formed under the interaction of laser and a powder bed; the monitoring module comprises a high-speed camera (5), the high-speed camera (5) is arranged on the linear sliding table (1), the high-speed camera (5) and the linear sliding table (1) are respectively connected with a power supply (9) and a control module, and the control module can control the movement of the linear sliding table (1).

2. The molten pool monitoring device in the laser powder bed melting additive manufacturing process is characterized in that the sealing module comprises a sealing cover (3), an end cover (2) is arranged at the bottom of the sealing cover (3), and the end cover (2) is arranged at the top of the laser powder bed melting machine.

3. The molten pool monitoring device in the laser powder bed melting additive manufacturing process is characterized in that a square hole is formed in the top of a laser powder bed melting machine, and an end cover (2) is arranged in the square hole and is in sealing connection with the laser powder bed melting machine.

4. The molten pool monitoring device in the laser powder bed melting additive manufacturing process is characterized in that the high-speed camera (5) is connected with the linear sliding table (1) through the support (4).

5. The molten pool monitoring device in the laser powder bed melting additive manufacturing process is characterized in that a microscope (7) is arranged at the lens of the high-speed camera (5), and an optical filter (8) is arranged at the lens of the microscope (7).

6. Molten pool monitoring device in the laser powder bed melting additive manufacturing process according to claim 5, characterized in that the optical filter (8) has a wavelength of 808nm and is arranged inside the microscope (7).

7. Molten pool monitoring device in the laser powder bed melting additive manufacturing process according to claim 5, characterized in that an auxiliary light source (6) is further arranged at the lens of the microscope (7).

8. The molten pool monitoring device in the laser powder bed melting additive manufacturing process is characterized in that the high-speed camera (5) is connected with the computer (10) of the control module through an Ethernet interface and a USB3.0 interface.

9. A molten pool monitoring method in a laser powder bed melting additive manufacturing process is characterized in that the molten pool monitoring device in the laser powder bed melting additive manufacturing process is used, and comprises the following steps:

s1, adjusting the resolution, frame rate and shutter of the high-speed camera, and collecting the molten pool evolution images at different scanning speeds;

s2, filtering the image collected in the step S1 to eliminate noise, carrying out image enhancement processing on the image, and then carrying out threshold segmentation on the image to obtain a binary image;

s3, outputting the binary image obtained in the step S2 as pictures, determining a time line of each picture according to the speed of a set shutter, counting the total number of pixels in a molten pool area, and determining the size of the molten pool according to the size of a calibration object and the number of pixels;

and S4, saving the characteristics of the molten pool at the current moment according to the size of the molten pool and the time of the molten pool in the step S3, and realizing on-line monitoring.

10. The method of claim 9, wherein the full-frame resolution of the high-speed camera is 1024 x 1024pixels, the single-edge resolution is greater than or equal to 1000 pixels, the shooting speed under million pixels is greater than or equal to 13500fps, and the fastest shutter speed is greater than or equal to 1 microsecond.

Technical Field

The invention belongs to the technical field of laser powder bed melting forming, and particularly relates to a molten pool monitoring method and device in a laser powder bed melting material increase manufacturing process.

Background

Laser Powder Bed Fusion (LPBF) is one of additive manufacturing technologies, which is relatively mature and has high forming accuracy, and is also the focus of research in the field of additive manufacturing, and is widely used in aerospace, medical, automotive and other fields. However, since the LPBF process is a very complicated process involving heat and mass transfer, many defects such as spheroidization, cracks, and pores occur in the forming, and in order to improve the forming quality of the LPBF process, an on-line monitoring method may be employed to suppress the defects.

In the LPBF process, the three-dimensional model is imported into Magics software and sliced. After the powder feeding cylinder sends out a certain mass of powder, the powder laying arm lays a layer of powder on the substrate, and then the laser selectively scans the powder on the substrate to form a section of the part. After the scan is completed, the substrate is lowered by one layer of powder and the powder arm is again laid one layer of powder. After a series of cycles, layer-by-layer build-up manufacturing of the part is achieved.

In the fusion forming of the laser powder bed, the observation of the interaction process of laser and powder is crucial to the forming of parts, if the size and the fusion width of a molten pool can be controlled in a stable range when each single channel is printed on the powder bed by the laser, a layer with better quality can be formed, and each layer can play a role in repairing and correcting the defects of the previous layer, so that the whole manufacturing process converges to a good result. If the single-channel or multi-channel printing process in the LPBF process cannot be observed, a data source cannot be provided by subsequent feedback control, so that the quality of a formed part is not optimized. Therefore, high forming effect can be obtained as long as the quality control of each single channel by the molten pool monitoring method and the molten pool monitoring device is ensured.

The existing molten pool monitoring system is generally divided into a side shaft monitoring system and a coaxial monitoring system, and the problems of small available space and tightness of a forming cavity of an LPBF machine cannot be solved, so that most researchers at home and abroad can only shoot outside the forming cavity and cannot monitor the overall appearances of a molten pool and a molten channel, and the traditional monitoring mode can not observe a clear molten channel and a molten pool and can not accurately express the interaction between laser and powder, so that the error of acquired data becomes very large.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a molten pool monitoring method and device in the laser powder bed melting material increase manufacturing process aiming at the defects in the prior art, wherein a high-speed camera, a long working distance microscope, an auxiliary light source and an optical filter are adopted to capture the dynamic changes of a molten channel and a molten pool in real time, and the characteristics of the molten pool are counted by means of an algorithm of data processing and image processing, so that a data basis is provided for the forming quality control and the feedback regulation and control of process parameters.

The invention adopts the following technical scheme:

the molten pool monitoring device in the laser powder bed melting additive manufacturing process comprises a sealing module, wherein the sealing module is arranged at the top of a laser powder bed melting machine, and a monitoring module is arranged in the sealing module and can capture a molten pool image formed under the interaction of laser and a powder bed; the monitoring module comprises a high-speed camera, the high-speed camera is arranged on the linear sliding table, the high-speed camera and the linear sliding table are respectively connected with the power supply and the control module, and the control module can control the movement of the linear sliding table.

Specifically, the sealing module comprises a sealing cover, an end cover is arranged at the bottom of the sealing cover, and the end cover is arranged at the top of the laser powder bed melting machine.

Furthermore, a square hole is formed in the top of the laser powder bed melting machine, and an end cover is arranged in the square hole and is connected with the laser powder bed melting machine in a sealing mode.

Specifically, the high-speed camera is connected with the linear sliding table through a support.

Specifically, a microscope is arranged at the lens of the high-speed camera, and an optical filter is arranged at the lens of the microscope.

Further, the filter has a wavelength of 808nm and is disposed inside the microscope.

Furthermore, an auxiliary light source is arranged at the lens of the microscope.

Specifically, the high-speed camera is connected with the computer of the control module through an Ethernet interface and a USB3.0 interface.

The invention also provides a molten pool monitoring method in the laser powder bed melting additive manufacturing process, which utilizes a molten pool monitoring device in the laser powder bed melting additive manufacturing process and comprises the following steps:

s1, adjusting the resolution, frame rate and shutter of the high-speed camera, and collecting the molten pool evolution images at different scanning speeds;

s2, filtering the image collected in the step S1 to eliminate noise, carrying out image enhancement processing on the image, and then carrying out threshold segmentation on the image to obtain a binary image;

s3, outputting the binary image obtained in the step S2 as pictures, determining a time line of each picture according to the speed of a set shutter, counting the total number of pixels in a molten pool area, and determining the size of the molten pool according to the size of a calibration object and the number of pixels;

and S4, saving the characteristics of the molten pool at the current moment according to the size of the molten pool and the time of the molten pool in the step S3, and realizing on-line monitoring.

Specifically, the full-frame resolution of the high-speed camera is 1024 × 1024pixels, the single-side resolution is not lower than 1000 pixels, the shooting speed under million pixels is more than or equal to 13500fps, and the fastest shutter speed is more than or equal to 1 microsecond.

Compared with the prior art, the invention has at least the following beneficial effects:

the invention relates to a molten pool monitoring device in the melting additive manufacturing process of a laser powder bed, wherein a high-speed camera is assembled on a linear sliding table through a camera support, the high-speed camera can approximately vertically observe a forming plane, and meanwhile, the long-distance focusing of the high-speed camera in a sealed environment can be realized; a module consisting of a long working distance microscope, an optical filter, an auxiliary light source and a high-speed camera can capture a high-speed moving molten pool amplified by 10-30 times, and coupled stray light is filtered at a lens; the micro molten pool moving at high speed can be clearly captured, and a data basis is provided for subsequent image processing and feedback control; the real-time transmission of real-time images is guaranteed, the problem that the position of a light source needs to be adjusted frequently during experiments at each time is avoided, and the consistency of the position of the light source is guaranteed.

Furthermore, the sealing module can support the sliding table and the high-speed camera, so that the high-speed camera can approximately observe a laser scanning plane at a vertical angle, the opening of the device can be sealed, and the whole device is in a sealed state during gas washing.

Further, a square hole needs to be formed in the top of the machine before the sealing module is installed, so that a high-speed camera and a sliding table can be installed conveniently. An end cover is arranged at the square hole, and a sealing ring is arranged at the top of the end cover to seal the whole device.

Further, the high-speed camera is connected with the linear sliding table through the support, the sliding table can indirectly drive the high-speed camera to move in the direction perpendicular to the substrate through the support, the angle of the support can be adjusted, and the adjusted angle is 2-7 degrees so as to achieve shooting at an approximate vertical angle.

Furthermore, a long working distance microscope is arranged at the lens of the high-speed camera, the working focal length of the microscope is about 80mm, the maximum magnification is 30 times, the observed field of view is about 1.4mm multiplied by 1.4mm, the width of the molten pool in the melting forming process of the laser powder bed is 100-300 mu m, and the device is adopted to realize the amplification of the tiny molten pool.

Furthermore, the 808nm narrow-band filter can enable light with specific wavelength to pass through, and light with other wavelengths to be reflected or attenuated. The 808nm filter plate can separate the light of the molten pool from the light of processing laser, illumination laser, molten pool light and the like so as to realize paraxial monitoring.

Furthermore, an auxiliary light source with stable power is arranged at the position of the microscope lens, the maximum power is about 200W, the size of a light spot at the position of 5-10 cm after integration is 2-3 cm, and stable illumination can be provided for a high-speed camera shooting experiment so as to obtain a clear molten pool image.

Furthermore, the actual transmission speed of the USB3.0 interface can reach 100MB/s, so that the pictures collected by the high-speed camera can quickly reach the computer, and are stored in the solid state disk for subsequent data processing.

In conclusion, the invention has the advantages of more convenient monitoring of the molten pool, clearer molten pool acquisition and higher reliability.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

FIG. 1 is a schematic diagram of a molten pool monitoring method and apparatus implemented in the present invention;

FIG. 2 is a schematic diagram of a molten pool monitoring method and apparatus implemented in the present invention;

FIG. 3 is a schematic view of an optical scheme of a molten pool monitoring method and device implemented by the invention

FIG. 4 is a control flow diagram of a molten pool monitoring method and apparatus implemented by the present invention;

FIG. 5 is a captured image of the molten pool monitoring method and apparatus of the present invention under different process parameters, wherein (a) is the image captured at the laser power of 300W and the scanning speed of 200mm/s, and (b) is the image captured at the laser power of 350W and the scanning speed of 200 mm/s.

Wherein: 1. a linear sliding table; 2. an end cap; 3. a sealing cover; 4. a support; 5. a high-speed camera; 6. an auxiliary light source; 7. a microscope; 8. an optical filter; 9. a power source; 10. a computer; 11. a beam splitter.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "one side", "one end", "one side", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It should be further understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, according to actual needs.

Referring to fig. 1 and 2, the present invention provides a molten pool monitoring device in a laser powder bed melting additive manufacturing process, including a linear sliding table 1, an end cover 2, a sealing cover 3, a bracket 4, a high-speed camera 5, an auxiliary light source 6, a microscope 7, a filter 8, a power supply 9, and a computer 10.

Molten bath monitoring system installs on the LPBF machine, high-speed camera 5 passes through support 4 to be installed on the slider of 3 inboard sharp slip tables 1 of sealed cowling, the bottom and the end cover 2 of sealed cowling are in the same place through threaded connection, the control scheme of sharp slip table 1 and the control scheme of high-speed camera 10 are connected with computer 10, computer 10 passes through the removal of motor control program control sharp slip table 1, indirectly drive the removal of high-speed camera 5, thereby realize the remote focusing of high-speed camera under sealed environment, molten bath monitoring system connects the back that finishes, install it at the top of LPBF machine, and use sealed glue to seal the processing.

Referring to fig. 2, the molten pool monitoring system comprises a monitoring module, a sealing module and a control module according to functional division, wherein the monitoring module is arranged in the sealing module and is respectively connected with a power supply 9 and the control module.

The monitoring module comprises a high-speed camera 5, an auxiliary light source 6, a microscope 7 and an optical filter 8, wherein the high-speed camera 5 adopts an NAC high-speed camera ACS-3, the auxiliary light source 6 adopts FC-30W with the wavelength of 808nm, the microscope 7 adopts a long working distance microscope 75X, the wavelength of the optical filter 8 is 808 +/-10 nm, the optical filter 8 with the wavelength of 808nm is installed in the microscope when the system is designed, a light filling head of the auxiliary light source 6 is fixed on a lens of the microscope 7 through a clamping mechanism, the parts do not need to be changed in the subsequent shooting, and then the communication is established with the computer 10 through an Ethernet interface and a USB3.0 interface;

the control module comprises a motor driving program and an Mlink software on the computer 10, controls the forward and reverse rotation of the motor through the motor control program to adjust the focal length, and filters stray light during the melting forming of the laser selection area by means of the auxiliary light source 6 and the optical filter 8 so as to ensure that a high-quality image is obtained. Parameters of the high-speed camera 5 such as resolution, frame rate and shutter are controlled through Mlink software, and a melting channel printed on a powder bed by laser is automatically captured in an AR working mode of the high-speed camera 5.

The sealing module comprises a sealing cover 3, an end cover 2 and sealing gloves and is used for line sealing and air tightness requirements.

The support 4 is connected with the high-speed camera 5 through a pair of inner hexagonal screws with specification of 3/8-16X 1-1/2 (manufactured by English), the linear sliding table 1 is connected with the support 4, the end cover 2 and the sealing cover 3 through M5X 14 or M5X 20 screws, meanwhile, the top of the end cover 2 is sealed through sealing gloves, the bottom of the end cover 2 is embedded into a square hole with the size of 158X 253mm formed in the top of the LPBF machine, finally, sealing glue is used for sealing treatment, and after field assembly and testing, normal operation of the system can be guaranteed.

Referring to fig. 3, the wavelength of the scanning laser is 1070nm, the light emitted from the laser passes through the galvanometer and selectively forms a molten pool on the substrate and interacts with the powder bed, the wavelength of the auxiliary light source 6 is 808 ± 10nm, the light of the left side is the light of the auxiliary light source, the light of the right side is the scanning laser, and the light of the dark color is the light coupling the molten pool light, the natural light, the light of the auxiliary light source and the scanning laser together. The coupled light passes through a filter of 808nm to separate light with specific wavelength, and then is captured by an optical sensor of the high-speed camera 5 to obtain images of the molten pool and the molten channel.

Referring to fig. 4, the present invention is a molten pool monitoring method in a laser powder bed melting additive manufacturing process, including the following steps:

s1, adjusting the resolution, frame rate and shutter of the high-speed camera, and collecting the molten pool evolution images at different scanning speeds;

the lens that high-speed camera adopted is the tight shot, and the working focal length is 80mm, through the removal of computer control straight line slip table, makes high-speed camera reach the working focal length indirectly.

The full-frame resolution of the high-speed camera is 1024 multiplied by 1024pixels, the single-side resolution is not lower than 1000 pixel points, the shooting speed under million pixels is more than or equal to 13500fps, and the fastest shutter speed is more than or equal to 1 microsecond.

The resolution and the frame rate are set in the control software, so that the size of an imaging frame can be adjusted, and the frequency of image acquisition can be adjusted. The scanning speed of the LPBF laser is generally 300-1000 mm/s, the size of a molten pool is generally 100-300 mu m, the frame rate is set to be not less than 10000 frames, and the maximum resolution is selected as far as possible under the condition that the memory of a camera allows so as to ensure that a clear picture is obtained. The shutter size is adjusted to adjust the exposure time, and in order to capture a fast moving tiny puddle, the shutter speed should not be slower than 25 mus to ensure the brightness of the frame and the capture speed of the camera.

After laser power and scanning speed are set in control software of the LPBF machine, laser emitted by a laser has certain energy density, and the laser passes through a scanning galvanometer and then scans on a powder bed according to a preset path, so that a rapidly moving micro molten pool is formed.

S2, filtering the image collected in the step S1 to eliminate noise, carrying out image enhancement processing on the image, and then carrying out threshold segmentation on the image to obtain a binary image;

s3, outputting the binary image obtained in the step S2 as pictures, determining a time line of each picture according to the speed of a set shutter, counting the total number of pixels in a molten pool area, and determining the size of the molten pool according to the size of a calibration object and the number of pixels;

and S4, saving the characteristics of the molten pool at the current moment according to the size of the molten pool and the time of the molten pool in the step S3, and realizing on-line monitoring.

Images captured by a high-speed camera need to satisfy the following conditions:

(1) the picture cannot be blurred, and the image is judged to be unqualified once blurring occurs.

(2) And selecting 5 time points (for example, 20us, 120us, 220us, 320us and 420us) in the output picture, observing from each time point, and judging that the image is qualified if the change of the gray value of the molten pool area, the oscillation of the molten pool and the flow of the powder can be obviously observed within 4 times of the shutter time from the time point.

(3) The laser scanning is often accompanied by white storm, and the image is judged to be unqualified if the area of the white storm is larger than that of the molten pool in the later image processing.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 5, the pictures captured under the conditions of different process parameters (frame rate of (a) and (b) is 3000fps, resolution is 1280 × 800) when shooting), the adopted material is pure tungsten powder, and the dynamic change of the molten pool, powder splashing and powder flowing behavior can be observed through the captured video; (a) laser power: 300W, scan speed 200mm/s, melt width 238um (b) laser power 350W, scan speed 200mm/s, melt width 254 um.

In summary, the present invention provides a molten pool monitoring method and apparatus in the laser powder bed melting additive manufacturing process, which adopts an observation method combining a long working distance microscope, an optical filter, an auxiliary light source and a high-speed camera to realize the on-line monitoring of a rapidly moving micro molten pool. In the installation scheme, the high-speed camera is connected with the linear sliding table through the camera support, so that the approximately vertical observation and the remote focusing of the high-speed camera in a sealed environment are realized. The acquired molten pool morphology information is combined with a later-stage image processing method and molten pool characteristic calculation, and a data basis is provided for optimization of forming quality and selection of process parameters.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.