A coaxial online monitoring lighting device and additive manufacturing equipment for laser selective melting

Abstract

The present application discloses a coaxial online monitoring lighting device and additive manufacturing equipment for laser selective melting. The device includes a printing chamber including a powder bed, and the powder bed is used to form a molten pool and print samples. A laser emits a laser beam, and a galvanometer and a field mirror are arranged in coordination. A dichroic mirror reflects the retrospective light source of the molten pool to a light source module. A high-speed camera and the light source module are coaxially arranged. The light source module includes a primary mirror, a concave lens, a secondary mirror, and a plane reflector. The secondary mirror is a half-reflective half-mirror with a hyperbolic structure. The plane reflector reflects the light gathered at the concave focus of the secondary mirror to the high-speed camera. A coaxial lighting light source is used to ensure that the lighting area and the dynamic monitoring area are highly overlapped. The secondary mirror adopts a hyperbolic half-reflective half-mirror surface structure. The retrospective radiation signal light passes through the primary mirror and the hyperbolic secondary mirror, and finally converges and reflects at the concave focus of the secondary mirror, realizing image acquisition and continuous dynamic shooting of a large area. The lighting light source is arranged in a compact structure, effectively reducing structural limitations and space requirements.

Description

Technical Field

[0001] The present application relates to the field of additive manufacturing technology, and in particular to a coaxial online monitoring lighting device for selective laser melting and additive manufacturing equipment. Background Art

[0002] Selective laser melting belongs to the laser powder bed fusion additive manufacturing technology. It adopts the "discrete-accumulation" forming principle and can achieve the rapid forming of complex structural parts. Various structural defects that are difficult to avoid in additive manufacturing samples have seriously limited the application reliability and applicability of this technology in high-end fields. Online optical signal acquisition is a relatively common monitoring technology that can complete real-time monitoring of the process during additive manufacturing. At present, coaxial image acquisition mainly focuses on the number of spatters, melt pool area and temperature distribution, but lacks intuitive monitoring of melt pool droplets and powder particles. This is mainly limited by the difficulty in designing the lighting source for coaxial monitoring. Summary of the Invention

[0003] The present application aims to address at least one of the technical problems existing in the prior art. To this end, the present application proposes a coaxial online monitoring lighting device for selective laser melting. By employing a coaxial integrated illumination source, the present application avoids variations in image sampling due to differences in illumination intensity at different locations along the scanning path, overcomes the depth of field limitations of the camera, and enables continuous dynamic capture of large areas.

[0004] The present application also proposes an additive manufacturing device including the above-mentioned coaxial online monitoring lighting device for selective laser melting.

[0005] The coaxial online monitoring lighting device for laser selective melting according to the embodiment of the first aspect of the present application comprises: a laser, a dichroic mirror, a galvanometer, a field lens, a light source module, a high-speed camera, and a printing cavity;

[0006] The printing chamber includes a powder bed, and the powder bed is used to form a molten pool and print a sample;

[0007] The laser is used to emit a laser beam, the galvanometer and the field lens are arranged in coordination, and the dichroic mirror, the galvanometer, the field lens, and the molten pool are arranged in sequence along the direction of the beam;

[0008] The dichroic mirror is used to reflect the retrospective light source of the molten pool to the light source module;

[0009] The high-speed camera and the light source module are coaxially arranged, and the light source module includes a primary mirror, a concave lens, a secondary mirror and a plane reflector, and the primary mirror, the concave lens and the secondary mirror are arranged in sequence along the direction in which the light source enters the light source module;

[0010] The secondary mirror is configured as a half-reflective half-mirror with a hyperbolic structure, and the plane reflector is used to reflect the light gathered at the concave focus of the secondary mirror to the high-speed camera.

[0011] The coaxial online monitoring lighting device for laser selective melting according to the embodiment of the first aspect of the present application has at least the following beneficial effects: by designing a coaxial lighting light source, it can be ensured that the lighting area and the dynamic monitoring area are highly overlapped, reducing the required power, and the tracing light source based on the molten pool and the working laser have the same path. In the lighting module, the secondary mirror innovatively adopts a hyperbolic semi-reflective and semi-mirror surface structure design. The traced radiation signal light passes through the main mirror and the hyperbolic secondary mirror, and finally converges at the concave focus of the secondary mirror, and is focused on the focusing plane of the high-speed camera through a plane reflector, thereby realizing the final clear molten pool image acquisition and continuous dynamic shooting of a large area, and the lighting light source is arranged in a compact structure, and does not need to be built into a sealed printing chamber, which can effectively reduce structural limitations and space requirements.

[0012] According to the coaxial online monitoring lighting device for laser selective melting described in the embodiment of the first aspect of the present application, it also includes a convex lens and a filter. The convex lens and the filter are arranged between the plane reflector and the high-speed camera. The plane reflector is used to reflect the light converged by the secondary mirror, and after passing through the convex lens and the filter in sequence, it is focused on the focusing plane of the high-speed camera.

[0013] According to the coaxial online monitoring lighting device for selective laser melting described in the embodiment of the first aspect of the present application, the bandpass wavelength of the filter is 450nm±5nm.

[0014] According to the coaxial online monitoring lighting device for selective laser melting described in the embodiment of the first aspect of the present application, the dichroic mirror is suitable for reflecting light in the wavelength band of 750nm-950nm and transmitting light in the wavelength band of 1050nm-1500nm.

[0015] According to the coaxial online monitoring lighting device for laser selective melting described in the embodiment of the first aspect of the present application, the secondary mirror adopts a hyperbolic half-reflective half-mirror structure with a reflection-transmission ratio R:T of 7:3.

[0016] According to the coaxial online monitoring lighting device for selective laser melting described in the embodiment of the first aspect of the present application, the laser adopts an adjustable 5W-450nm laser lighting light source.

[0017] The coaxial online monitoring lighting device for selective laser melting according to the embodiment of the first aspect of the present application further includes a collimator arranged on the laser, and the laser emits laser light through the collimator.

[0018] According to the coaxial online monitoring lighting device for selective laser melting described in the embodiment of the first aspect of the present application, it is assumed that the focal length of the primary mirror is f, the diameter of the primary mirror is D1, and the relative aperture is q;

[0019] Then the diameter D2 of the secondary mirror is:

[0020]

[0021] Assume that the near point focal length of the secondary mirror is l, the distance between the primary mirror and the secondary mirror is d, and the distance from the light source to the primary mirror is Δ; the focal length of the concave lens is f0, and in terms of spatial distribution, the focus of the concave lens coincides with the focus of the distal end of the secondary mirror;

[0022] Then the shading ratio α of the secondary mirror is:

[0023]

[0024] At this time, the magnification a of the light source is the ratio of the diameter of the outgoing illumination laser light source to the diameter of the light spot when it enters the laser working light path:

[0025]

[0026] The cone coefficient of the optical device is selected according to the above optical path design, and the imaging effects such as aberration are analyzed.

[0027] According to the coaxial online monitoring lighting device for selective laser melting described in the embodiment of the first aspect of the present application, the focal length f of the primary mirror is 160 mm, the diameter D1 of the primary mirror is 30 mm, the relative aperture q is 3, and the diameter D2 of the secondary mirror is 10 mm;

[0028] The near point focal length l of the secondary mirror is 30 mm, the distance d between the primary mirror and the secondary mirror is 110 mm, the distance Δ from the light source to the primary mirror is 40 mm, the shading ratio α of the secondary mirror is 0.187, and the magnification a of the light source is 5.

[0029] According to the embodiment of the second aspect of the present application, the additive manufacturing equipment includes: the coaxial online monitoring lighting device for laser selective melting as described in the embodiment of the first aspect of the present application.

[0030] It is not difficult to understand that the additive manufacturing equipment in the embodiment of the second aspect of the present application has the technical effect of the coaxial online monitoring lighting device for laser selective melting in the embodiment of the first aspect, so it will not be repeated here.

[0031] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present application is further described below with reference to the accompanying drawings and embodiments;

[0033] Figure 1 This is a schematic structural diagram of an embodiment of the present application;

[0034] Figure 2 This is a light path design diagram of an embodiment of the present application.

[0035] Reference numerals:

[0036] 1. Laser; 2. Collimator; 3. Dichroic mirror; 4. Galvanometer; 5. Light source module; 6. High-speed camera; 7. Print sample; 8. Molten pool; 9. Powder bed; 10. Print chamber;

[0037] 51. Primary mirror; 52. Concave lens; 53. Secondary mirror; 54. Plane reflector;

[0038] 61. Convex lens; 62. Filter. DETAILED DESCRIPTION

[0039] The following describes in detail embodiments of the present application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and are not to be construed as limiting the present application.

[0040] In the description of this application, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this application.

[0041] In the description of this application, "several" means one or more, "more" means at least two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The terms "first" and "second" are used solely to distinguish technical features and are not to be construed as indicating or implying relative importance, or as implicitly specifying the number or order of the technical features.

[0042] In the description of this application, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense. Technical personnel in the relevant technical field can reasonably determine the specific meanings of the above terms in this application after combining the specific content of the technical solution.

[0043] Reference Figures 1 to 2The coaxial online monitoring lighting device for selective laser melting according to the first aspect of the present application is specifically related to the optical path design of a light source for coaxial monitoring illumination of a molten pool 8 of additive manufacturing by selective laser melting. The coaxial online monitoring lighting device for selective laser melting includes a laser 1, a dichroic mirror 3, a galvanometer 4, a field lens, a light source module 5, a high-speed camera 6, and a printing chamber 10.

[0044] The printing chamber 10 includes a powder bed 9, which is used to form a molten pool 8 and a printed sample 7; the laser 1 is used to emit a laser beam, and the galvanometer 4 and the field lens are arranged in conjunction with each other. The dichroic mirror 3, the galvanometer 4 and the field lens, and the molten pool 8 are arranged in sequence along the direction of the beam; the dichroic mirror 3 is used to reflect the retrospective light source of the molten pool 8 to the light source module 5; the high-speed camera 6 and the light source module 5 are coaxially arranged, and the light source module 5 includes a main mirror 51, a concave lens 52, a secondary mirror 53 and a plane reflector 54. The main mirror 51, the concave lens 52, and the secondary mirror 53 are arranged in sequence along the direction in which the light source enters the light source module 5; wherein the secondary mirror 53 is set as a half-reflective half-mirror with a hyperbolic structure, and the plane reflector 54 is used to reflect the light gathered at the concave focus of the secondary mirror 53 to the high-speed camera 6.

[0045] It's understandable that during rangefinder monitoring, both the camera and light source are rangefinder mounted, and the illuminated area is the portion of the scan area to be observed and photographed (typically a few to tens of millimeters square). The camera's position and viewing angle are fixed during capture and do not change with the scanning laser path. The resulting image of the melt pool 8 is affected by the illumination, camera depth of field, and observation angle. Furthermore, the resulting image of the melt pool 8 is an oblique side view, requiring measurement and algorithmic correction to obtain a precise top-down view of the melt pool 8.

[0046] During coaxial imaging, the camera is mounted on top of the device to capture the radiation from the melt pool 8, along the same path as the active laser. In this case, the illumination source can be a rangefinder. However, rangefinder mounting can result in uneven illumination, necessitating high-speed continuous sampling during image acquisition. To obtain clear features of the melt pool 8, the camera's viewing angle must be kept as uniform as possible. A coaxial illumination source, combined with a coaxial high-speed camera 6, effectively meets the aforementioned requirements, achieving superior imaging results.

[0047] Reference Figures 1 to 2The coaxial online monitoring lighting device for laser selective melting of the first aspect of the present application can ensure a high degree of overlap between the illumination area and the dynamic monitoring area by designing a coaxial illumination light source, thereby reducing the required power. The tracing light source based on the molten pool 8 and the working laser have the same path. In the illumination module, the secondary mirror 53 innovatively adopts a hyperbolic semi-reflective semi-lens surface structure design. The traced radiation signal light passes through the main mirror 51 and the hyperbolic secondary mirror 53, and finally converges at the concave focus of the secondary mirror 53, and is focused on the focusing plane of the camera 6 through the plane reflector 54, thereby realizing the final clear image acquisition of the molten pool 8 and continuous dynamic shooting of a large area. In addition, the illumination light source is arranged in a compact structure and does not need to be built into the sealed printing cavity 10, which can effectively reduce structural limitations and space requirements.

[0048] In some embodiments of the present application, a convex lens 61 and a filter 62 are further included. The convex lens 61 and the filter 62 are arranged between the plane reflector 54 and the high-speed camera 6. The plane reflector 54 is used to reflect the light concentrated by the secondary mirror 53, and after passing through the convex lens 61 and the filter 62 in sequence, it is focused on the focusing plane of the high-speed camera 6. In some embodiments of the present application, a collimator 2 is also included on the laser 1, and the laser 1 emits laser light through the collimator 2. In some embodiments of the present application, the bandpass wavelength of the filter 62 is 450nm±5nm. In some embodiments of the present application, the laser 1 uses an adjustable 5W-450nm laser illumination light source.

[0049] It is understandable that when sampling images of the laser selective melting process, the retracement light source of the molten pool 8 follows the same path as the working laser with a wavelength of 1075 nm, passing through the field lens and the galvanometer 4 before reaching the dichroic mirror 3. Total reflection occurs at the dichroic mirror 3 (reflection band 750 nm-950 nm) and enters the light source module 5. In the light source module 5, the secondary mirror 53 innovatively adopts a hyperbolic semi-reflective semi-mirror surface structure design. The retracement radiation signal light passes through the primary mirror 51 and the hyperbolic secondary mirror 53, and finally converges at the concave focus of the secondary mirror 53. The converged light is further focused on the focusing plane of the camera 6 through the plane reflector 54, the convex lens 61, and the filter 62, achieving the final clear image acquisition of the molten pool 8. In order to maintain good observability of the molten pool 8 and the surrounding area during the field of view observation during the sampling process, a coaxial illumination light source mode that moves with the laser scanning path is adopted, and an adjustable 5W-450nm laser illumination light source is used. Maintain better illumination and reduce illumination difference. The hyperbolic half-mirror has two focal points and can reflect all light (excluding transmitted light) passing through one of the focal points to the other focal point. Since the focal points of the plano-concave lens 52 and the secondary mirror 53 coincide with each other, the nearly parallel illumination light source can be equivalent to emitting from the focal position and Figure 2The light path shown is reflected by the secondary mirror 53 and the primary mirror 51 before converging into the working laser path, precisely illuminating the molten pool 8 at every moment during the scanning process. The curved mirror employed is a semi-reflective, semi-transmissive structure. 30% of the illumination light source's energy is lost after being transmitted through the secondary mirror 53 and then diverging. However, compared to the large-format illumination requirements of rangefinder illumination (power consumption exceeding 30W), this loss is negligible.

[0050] In some embodiments of the present application, the secondary mirror 53 adopts a hyperbolic half-reflective half-mirror structure with a reflection-transmittance ratio R:T of 7:3. In some embodiments of the present application, the dichroic mirror 3 is suitable for reflecting light in the wavelength band of 750nm-950nm and transmitting light in the wavelength band of 1050nm-1500nm. It can be understood that the core components in the designed optical structure include a dichroic mirror 3 (reflection of 750nm-950nm, transmission of 1050nm-1500nm) and an illumination module, including a parabolic mirror-primary mirror 51, a hyperbolic mirror-secondary mirror 53 and a plano-concave lens 52. Among them, the hyperbolic mirror adopts a half-reflective half-mirror structure with R:T=7:3, and finally converges on the camera's photosensitive surface by focusing and filtering the optical fiber at the focal position of the concave surface (Cassegrain focus), and the illumination light source is installed on the rear side of the primary mirror 51. The space required for imaging is small and the structure is compact.

[0051] In some embodiments of the present application, in order to ensure a structure as compact as possible, the focal length of the primary mirror 51 is f, the diameter of the primary mirror 51 is D1, and the relative aperture is q;

[0052] Then the diameter D2 of the secondary mirror 53 is:

[0053]

[0054] Assume that the near-point focal length of the secondary mirror 53 is l, the distance between the primary mirror 51 and the secondary mirror 53 is d, and the distance from the light source to the primary mirror 51 is Δ; the focal length of the concave lens 52 is f0, and in terms of spatial distribution, the focus of the concave lens 52 coincides with the focus of the distal end of the secondary mirror 53;

[0055] Then the shading ratio α of the secondary mirror 53 is:

[0056]

[0057] At this time, the magnification a of the light source is the ratio of the diameter of the outgoing illumination laser light source to the diameter of the light spot when it enters the laser working light path:

[0058]

[0059] The cone coefficient of the optical device is selected according to the above optical path design, and the imaging effects such as aberration are analyzed.

[0060] In some embodiments, the focal length f of the primary mirror 51 is 160 mm, the diameter D1 of the primary mirror 51 is 30 mm, the relative aperture q is 3, and the diameter D2 of the secondary mirror 53 is 10 mm;

[0061] The near point focal length l of the secondary mirror 53 is 30 mm, the distance d between the main mirror 51 and the secondary mirror 53 is 110 mm, the distance Δ from the light source to the main mirror 51 is 40 mm, the shading ratio α of the secondary mirror 53 is 0.187, and the magnification a of the light source is 5.

[0062] Specifically, after completing the preliminary optical path design, the cone coefficient of the optical device is further selected, and then the imaging effects such as aberrations can be analyzed based on ZEMAX.

[0063] Understandably, to avoid the influence of laser light sources, rangefinder cameras often use short-wavelength, narrow-bandwidth laser illumination sources. At the same time, the illumination intensity must be significantly greater than the stimulated emission of radiation from the molten pool 8 to clearly capture the dynamics of the droplets in the molten pool 8 and the surrounding powder. However, rangefinder image acquisition requires the illumination laser source to cover a large scanning path and possess high illumination power.

[0064] Based on this, refer to Figures 1 to 2 In the coaxial online monitoring lighting device for selective laser melting of the present invention, the target retracement light source for coaxial image monitoring and acquisition is coaxial with the working laser. This maintains the target melt pool 8 in the center of the camera's field of view and avoids image distortion issues that occur during paraxial image acquisition. By designing a coaxial illumination source, the illumination area and the dynamic monitoring area are highly aligned, reducing the required power. Furthermore, the coaxial illumination source is compactly arranged and does not need to be built into the sealed print chamber 10, effectively reducing structural limitations and space requirements.

[0065] Reference Figures 1 to 2 The additive manufacturing equipment of the second embodiment of the present application may be a laser powder bed fusion additive manufacturing device 9, and the additive manufacturing equipment includes the coaxial online monitoring lighting device for laser selective melting of the first embodiment of the present application. By designing a coaxial lighting source, it is possible to ensure that the illumination area and the dynamic monitoring area are highly overlapped, thereby reducing the required power. The coaxial lighting source is compactly arranged and does not need to be built into the sealed printing chamber 10, which can effectively reduce structural limitations and space requirements.

[0066] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0067] The embodiments of the present application are described in detail above in conjunction with the accompanying drawings, but the present application is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in the technical field without departing from the purpose of the present application.

Claims

1. A coaxial online monitoring lighting device for selective laser melting, characterized in that: include: Laser, dichroic mirror, galvanometer, field lens, light source module, high-speed camera and printing cavity; The printing chamber includes a powder bed, and the powder bed is used to form a molten pool and print a sample; The laser is used to emit a laser beam. The galvanometer and the field lens are arranged in coordination. The dichroic mirror, the galvanometer, the field lens, and the molten pool are arranged in sequence along the direction of the beam. The laser adopts a coaxial illumination light source mode that moves along the laser scanning path. The laser adopts an adjustable 5W-450nm laser illumination light source. The dichroic mirror is used to reflect the retrospective light source of the molten pool to the light source module; The high-speed camera and the light source module are coaxially arranged, and the light source module includes a primary mirror, a concave lens, a secondary mirror and a plane reflector, and the primary mirror, the concave lens and the secondary mirror are arranged in sequence along the direction in which the light source enters the light source module; The secondary mirror is configured as a half-reflective half-mirror with a hyperbolic structure, and the plane reflector is used to reflect the light gathered at the concave focus of the secondary mirror to the high-speed camera.

2. The coaxial online monitoring lighting device for selective laser melting according to claim 1, characterized in that: It also includes a convex lens and a filter, which are arranged between the plane reflector and the high-speed camera. The plane reflector is used to reflect the light concentrated by the secondary mirror, and after passing through the convex lens and the filter in sequence, it is focused on the focusing plane of the high-speed camera.

3. The coaxial online monitoring lighting device for selective laser melting according to claim 2, characterized in that: The bandpass wavelength of the filter is 450nm±5nm.

4. The coaxial online monitoring lighting device for selective laser melting according to claim 1, characterized in that: The dichroic mirror is suitable for reflecting light in a wavelength band of 750nm-950nm and transmitting light in a wavelength band of 1050nm-1500nm.

5. The coaxial online monitoring lighting device for selective laser melting according to claim 1, characterized in that: The secondary mirror adopts a hyperbolic half-reflective half-mirror structure with a reflection-transmission ratio R:T of 7:

3.

6. The coaxial online monitoring lighting device for selective laser melting according to claim 1, characterized in that: The invention also includes a collimator arranged on the laser, and the laser emits laser light through the collimator.

7. The coaxial online monitoring lighting device for selective laser melting according to any one of claims 1 to 6, characterized in that: Assume the focal length of the primary mirror is f , the diameter of the primary mirror is D1, and the relative aperture is q; Then the diameter D2 of the secondary mirror is: Assume that the near-point focal length of the secondary mirror is l , the distance between the primary mirror and the secondary mirror is d, the distance from the light source to the primary mirror is ∆; the focal length of the concave lens is f 0, the focus of the concave lens coincides with the focus of the distal end of the secondary mirror in terms of spatial distribution; Then the shading ratio α of the secondary mirror is: At this time, the magnification a of the light source is the ratio of the diameter of the outgoing illumination laser light source to the diameter of the light spot when it enters the laser working light path: The cone coefficient of the optical device is selected according to the above optical path design, and the aberration is analyzed.

8. The coaxial online monitoring lighting device for selective laser melting according to claim 7, characterized in that: The focal length f of the primary mirror is 160 mm, the diameter D1 of the primary mirror is 30 mm, the relative aperture q is 3, and the diameter D2 of the secondary mirror is 10 mm; Near point focal length of the secondary mirror l is 30 mm, the distance d between the primary mirror and the secondary mirror is 110 mm, the distance ∆ from the light source to the primary mirror is 40 mm, the shading ratio α of the secondary mirror is 0.187, and the magnification a of the light source is 5.

9. An additive manufacturing device, characterized in that: include: The coaxial online monitoring lighting device for selective laser melting according to any one of claims 1 to 8.

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