Beam expansion system for laser additive manufacturing

Abstract

This invention relates to a beam expanding system for laser additive manufacturing, belonging to the technical field of laser additive manufacturing equipment. It solves the technical problem that current beam expanding systems in the optical systems of laser additive manufacturing equipment cannot change the shape and size of the output beam. The beam expanding system for laser additive manufacturing includes a first beam expanding module and a second beam expanding module arranged sequentially along the optical path. Both the first and second beam expanding modules include a fixed group, a zoom group, and a compensation group, arranged sequentially along the optical path and composed of multiple cylindrical mirrors. The cylindrical generatrices of the cylindrical mirrors in the first and second beam expanding modules are perpendicular to each other, and the optical axes of the cylindrical mirrors in the first and second beam expanding modules coincide with or are parallel to each other. Therefore, this beam expanding system for laser additive manufacturing can achieve output beams of different sizes (circular) or different ellipticities to meet different processing requirements.

Description

Technical Field

[0001] This invention belongs to the technical field of laser additive manufacturing equipment, and specifically relates to a beam expansion system for laser additive manufacturing. Background Technology

[0002] Currently, the most commonly used technology in the optical systems of laser additive manufacturing equipment is a fixed-magnification circular spot beam expander system. This system consists of a set of spherical lenses in fixed positions, whose function is to expand the incident circular collimated beam into a larger circular collimated beam, which is then focused onto the processing surface by a galvanometer and a field lens to form a fixed circular focused spot. However, because the shape and size of the output beam are fixed, this technology has inherent technical drawbacks in application: First, a single circular spot cannot adjust its ellipticity, making it difficult to adapt to the specific spot shape requirements of different processing strategies such as contour scanning and solid filling, resulting in insufficient process flexibility. Second, when pursuing high-efficiency printing and increasing the spot size, it directly leads to a decrease in energy density, creating an inherent contradiction between scanning efficiency and energy density, which may result in incomplete powder melting. In addition, a symmetrical circular spot makes it difficult to actively control the thermal gradient of the molten pool in the scanning direction, easily causing defects such as spatter and porosity, which restricts further improvement in molding quality. Finally, this technology cannot directionally influence the molten pool solidification process by changing the spot shape, thus lacking the ability to actively control the microstructure of the part. Summary of the Invention

[0003] This invention provides a beam expanding system for laser additive manufacturing, which solves the technical problem that beam expanding systems in the optical systems of current laser additive manufacturing equipment cannot change the shape and size of the output beam.

[0004] The present invention is achieved through the following technical solution: a beam expanding system for laser additive manufacturing, comprising a first beam expanding module and a second beam expanding module arranged sequentially along the optical path. Both the first beam expanding module and the second beam expanding module include a fixed group, a zoom group, and a compensation group, arranged sequentially along the optical path and composed of multiple cylindrical mirrors. The cylindrical generatrices of the cylindrical mirrors of the first beam expanding module and the second beam expanding module are perpendicular to each other, and the optical axes of the cylindrical mirrors of the first beam expanding module and the second beam expanding module coincide or are parallel.

[0005] Optionally, the fixed assembly includes a plano-convex cylindrical lens for receiving and focusing the laser beam to balance aberrations.

[0006] Optionally, the zoom group includes a biconcave cylindrical lens, which is disposed between the fixed group and the compensation group to diverge the laser beam and achieve zoom.

[0007] Optionally, the zoom group further includes a meniscus lens, which is disposed on the light-emitting side of the biconcave cylindrical lens to correct aberrations.

[0008] Optionally, the compensation group includes a plano-convex cylindrical lens group consisting of a plano-concave cylindrical lens and a plano-convex cylindrical lens, for correcting divergence angle and spherical aberration.

[0009] Optionally, a reflector is also included, which is disposed between the first beam expander module and the second beam expander module to make the laser beams passing through the first beam expander module and the second beam expander module parallel.

[0010] Optionally, it also includes a galvanometer, which is disposed on the light-emitting side of the second beam expander module to control the emission direction of the laser beam.

[0011] Optionally, it also includes a field lens, which is disposed on the light-emitting side of the second beam expander module to focus and emit the laser beam.

[0012] Optionally, it also includes a linear slide table, on which the zoom group and the compensation group are mounted.

[0013] Optionally, the aperture of each lens in the fixed group, the variable magnification group, and the compensation group is greater than twice the diameter of the incident laser beam.

[0014] Compared with the prior art, the present invention has the following advantages: The present invention provides a beam expanding system for laser additive manufacturing, comprising a first beam expanding module and a second beam expanding module arranged sequentially along the optical path. Both the first and second beam expanding modules include a fixed group, a zoom group, and a compensation group, arranged sequentially along the optical path and composed of multiple cylindrical mirrors. The cylindrical generatrices of the cylindrical mirrors of the first and second beam expanding modules are perpendicular to each other, and the optical axes of the cylindrical mirrors of the first and second beam expanding modules coincide with or are parallel to each other.

[0015] Through the above steps, the laser beam in the laser additive manufacturing beam expansion system provided by the present invention sequentially passes through the fixed group, variable magnification group, and compensation group in the first beam expansion module, and the fixed group, variable magnification group, and compensation group in the second beam expansion module. The cylindrical mirrors of the first beam expansion module and the second beam expansion module act on the light rays in two perpendicular directions respectively. The laser beam is magnified and expanded by the perpendicular cylindrical mirrors in the first and second beam expansion modules. When the spot of the incident laser beam is circular or elliptical, the cylindrical mirrors in the first and second beam expansion modules can be independently adjusted to achieve the output of circular or elliptical spots of different sizes. This allows the laser beam to adjust the shape of the focused spot acting on the powder bed according to different processing requirements such as contour scanning and solid filling during the processing, thereby effectively balancing scanning efficiency and energy density, improving the stability of the molten pool, and realizing active control of the microstructure of the material. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of a beam expanding system for laser additive manufacturing provided by the present invention; Figure 2 This is a schematic diagram of the internal structure of a beam expanding system for laser additive manufacturing provided by the present invention; Figure 3 This is a top view of a beam expanding system for laser additive manufacturing provided by the present invention; Figure 4 This is a front view of a beam expanding system for laser additive manufacturing provided by the present invention; Figure 5 This is a schematic diagram of a circular light spot before shaping in an embodiment of the present invention; Figure 6-11 This is a schematic diagram of a circular light spot after shaping in an embodiment of the present invention; Figure 12 This is a schematic diagram of an elliptical light spot before shaping in an embodiment of the present invention; Figure 13 This is a schematic diagram of an elliptical light spot after shaping in an embodiment of the present invention.

[0018] In the picture: 1-First beam expander module, 2-Second beam expander module, 3-Planto-convex cylindrical lens, 4-Biconcave cylindrical lens, 5-Meniscus lens, 6-Planto-convex cylindrical lens group, 7-Reflector, 8-Galvanometer, 9-Field lens, 10-Linear slide. Detailed Implementation

[0019] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship 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, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0020] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0023] This invention provides a beam expanding system for laser additive manufacturing, solving the technical problem that current beam expanding systems in the optical systems of laser additive manufacturing equipment cannot change the shape and size of the output beam. The beam expanding system for laser additive manufacturing includes a first beam expanding module 1 and a second beam expanding module 2, wherein: Reference Figures 1-4As shown, the first beam expander module 1 and the second beam expander module 2 are arranged sequentially along the optical path. That is, the laser beam first passes through the first beam expander module 1 and then through the second beam expander module 2. Both the first beam expander module 1 and the second beam expander module 2 include a fixed group, a zoom group, and a compensation group, arranged sequentially along the optical path and composed of multiple cylindrical mirrors. Specifically, the laser beam first passes through the fixed group, zoom group, and compensation group of the first beam expander module 1, and then through the fixed group, zoom group, and compensation group of the second beam expander module 2. The fixed group is used to receive the laser beam and convert the diverging laser beam into a collimated beam. This facilitates subsequent processing by other components; the zoom group is used to adjust the size of the output laser spot; the compensation group is used to correct the divergence angle and spherical aberration; the cylindrical generatrices of the cylindrical mirrors of the first beam expander module 1 and the second beam expander module 2 are perpendicular to each other. Since the cylindrical mirrors converge or diverge the incident light in only one direction, the cylindrical mirrors of the first beam expander module 1 and the second beam expander module 2 act on light rays in two perpendicular directions respectively. By controlling the cylindrical mirrors in the first beam expander module 1 and the second beam expander module 2, the change of the output spot is achieved; (Refer to...) Figures 5-11 As shown, when the incident laser beam spot is circular, it is possible to output circular spots with different ellipticity or different sizes. Figure 5 The image shows the beam spot before shaping, with radii of 2.5 mm in the x-direction and 2.5 mm in the y-direction, and a focusing ellipticity of 99.9%. Figure 6 The image shows the shaped light spot, with radii of 3.5 mm and 4.5 mm in the x and y directions, respectively, and a focusing ellipticity of 77.8%. Figure 7 The image shows the shaped light spot, with radii of 3.7 mm and 4.2 mm in the x and y directions, respectively, and a focusing ellipticity of 88.1%. Figure 8 The image shows the shaped light spot, with radii of 3.25 mm and 3.85 mm in the x and y directions, respectively, and a focusing ellipticity of 84.4%. Figure 9 The image shows the shaped light spot, with radii of 3.55 mm in the x and y directions, and a focusing ellipticity of 99.9%. Figure 10 The image shows the shaped light spot, with radii of 4.5 mm in the x and 4.5 mm in the y directions, and a focusing ellipticity of 99.9%. Figure 11 The shaped light spot has radii of 3 mm in the x-direction and 4.5 mm in the y-direction, with a focusing ellipticity of 66.7%. (Refer to...) Figures 12-13 As shown, when the incident laser beam spot is elliptical, it is also possible to output a circular spot as a circular spot or a spot with different degrees of ellipticity. Figure 12 The image shows the beam spot before reshaping, with radii of 2mm in the x-direction and 2.5mm in the y-direction, and a focusing ellipticity of 80%. Figure 13The image shows the shaped light spot. The radii in the x and y directions are 3.6 mm and 3.6 mm respectively, with a focusing ellipticity of 99.9%. The x-direction is the horizontal direction in the image, and the y-direction is the vertical direction. For details, please refer to [reference needed]. Figure 5 As shown.

[0024] The cylindrical mirrors of the first beam expander module 1 and the second beam expander module 2 have their optical axes aligned or parallel. Specifically, the cylindrical generatrix of the first beam expander module 1 can be rotated along the optical axis to align or parallel with the cylindrical generatrix of the second beam expander module 2. This ensures that the directions of the laser beam's action by the first and second beam expander modules 1 and 2 are perpendicular, facilitating adjustment of the ellipticity of the emitted laser spot. This allows the laser beam to adjust the shape of the focused spot acting on the powder bed according to different processing requirements such as contour scanning and solid filling, effectively balancing scanning efficiency and energy density, improving molten pool stability, and achieving active control over the material's microstructure.

[0025] An optional implementation of this embodiment is as follows: Refer to... Figures 1-4 As shown, the fixed assembly includes a plano-convex cylindrical lens 3, which receives, collects, and converges the light beam to convert the laser beam emitted towards the plano-convex cylindrical lens 3 into a laser beam, so as to facilitate further processing by other components and provide greater freedom for subsequent aberration balancing.

[0026] An optional implementation of this embodiment is as follows: Refer to... Figures 1-4 As shown, the zoom group includes a biconcave cylindrical lens 4, which is positioned between the plano-convex cylindrical lens 3 and the compensation group. It is worth noting that the position of the biconcave cylindrical lens 4 between the plano-convex cylindrical lens 3 and the compensation group corresponds to the lens in the same beam expanding module. That is, the biconcave cylindrical lens 4 in the first beam expanding module 1 is positioned between the plano-convex cylindrical lens 3 and the compensation group in the first beam expanding module 1. Similarly, the biconcave cylindrical lens 4 in the second beam expanding module 2 is positioned between the plano-convex cylindrical lens 3 and the compensation group in the second beam expanding module 2. The biconcave cylindrical lens 4 is used to diverge the laser beam. By moving the position of the biconcave cylindrical lens 4, zoom can be achieved.

[0027] An optional implementation of this embodiment is as follows: Refer to... Figures 1-4 As shown, the zoom group also includes a meniscus negative lens, which is set on the light-emitting side of the double concave cylindrical lens 4. Similarly, the position of the meniscus negative lens on the light-emitting side of the double concave cylindrical lens 4 corresponds to the lens in the same beam expander module. The meniscus negative lens is used for aberration correction to correct the influence of spherical aberration on the light spot.

[0028] An optional implementation of this embodiment is as follows: Refer to... Figures 1-4As shown, the compensation group includes a plano-convex cylindrical lens group 6, which is a combination of a plano-concave cylindrical lens and a plano-convex cylindrical lens. The plano-concave cylindrical lens is located on the light-emitting side of the meniscus negative lens, and the plano-convex cylindrical lens is located on the light-emitting side of the plano-concave cylindrical lens. Similarly, the positions of the plano-concave cylindrical lens and the plano-convex cylindrical lens correspond to the lenses in the same beam expander module. The plano-convex cylindrical lens group 6, which is composed of plano-concave cylindrical lenses and plano-convex cylindrical lenses, is separated by an air gap to correct the divergence angle of the diverging beam and also to correct spherical aberration.

[0029] In this technical solution, the plano-convex cylindrical lens 3 of the first beam expander module 1 and the plano-convex cylindrical lens 3 of the second beam expander module 2 have the same size, focal length, material, etc., that is, they are the same lens, only different in installation position angle. Similarly, the plano-convex cylindrical lens 3 of the first beam expander module 1 and the biconcave cylindrical lens 4 of the second beam expander module 2, the plano-convex cylindrical lens 3 of the first beam expander module 1 and the meniscus lens 5 of the second beam expander module 2, and the plano-convex cylindrical lens group 6 of the first beam expander module 1 and the second beam expander module 2 which is composed of plano-concave cylindrical lens and plano-convex cylindrical lens all have the same size, focal length, material, etc.

[0030] An optional implementation of this embodiment is as follows: Refer to... Figures 1-4 As shown, to extend the length of this beam-expanding system, the laser additive manufacturing beam-expanding system also includes a reflector 7. The reflector 7 is installed between the first beam-expanding module 1 and the second beam-expanding module 2. The reflector 7 is used to change the direction of the laser beam after it passes through the first beam-expanding module 1, so that the laser beam passing through the second beam-expanding module 2 is parallel to the laser beam passing through the first beam-expanding module 1. In this way, by reflecting the laser beam back, the length of this beam-expanding system can be shortened. The number of reflectors 7 can be set according to specific circumstances. In one embodiment provided in this example, there are four reflectors 7. The two reflectors 7 reflect the laser beam four times, so that the laser beam passing through the first beam-expanding module 1 and the laser beam of the second beam-expanding module 2 are emitted in the same direction in parallel.

[0031] An optional implementation of this embodiment is as follows: Refer to... Figures 1-4 As shown, in order to facilitate the control of the position of the emitted laser spot, the beam expanding system for laser additive manufacturing also includes a galvanometer 8. The galvanometer 8 is disposed on the light-emitting side of the second beam expanding module 2. The galvanometer 8 controls the position of the laser spot by controlling the direction of the laser beam. In this embodiment, after the laser beam passes through the galvanometer 8, the laser beam is emitted towards the first beam expanding module 1, and the direction of the laser beam emitted through the galvanometer 8 is perpendicular to the direction of the laser beam in the first beam expanding module 1. This allows for better use of the space between the first beam expanding module 1 and the second beam expanding module 2, reducing the occupation of other areas.

[0032] An optional implementation of this embodiment is as follows: Refer to... Figures 1-4 As shown, it also includes a field lens 9, which is disposed on the light-emitting side of the second beam expander module 2. The field lens 9 is used to focus and emit the laser beam emitted from the galvanometer 8.

[0033] An optional implementation of this embodiment is as follows: Refer to... Figures 2-4 As shown, in order to facilitate the control of the movement of the cylindrical mirrors in the first beam expander module 1 and the second beam expander module 2, the beam expander system for laser additive manufacturing also includes a linear slide 10. The biconcave cylindrical lens 4, the meniscus lens 5, and the plano-convex cylindrical lens group 6 are all mounted on the linear slide 10. The linear slide 10 has a resolution of up to 20μm, a unidirectional positioning accuracy of ≤30μm, and a repeatability of ≤±3μm. Specifically, the beam expander system for laser additive manufacturing is provided with an optical chamber and an electrical chamber. The first beam expander module 1, the second beam expander module 2, the reflector 7, the galvanometer 8, and the field lens 9 are set in the optical chamber. The electrical chamber is equipped with a power supply, a control board, and a driver, etc. The electrical chamber can supply power to the optical chamber and control the linear slide 10 and the galvanometer 8.

[0034] An optional implementation of this embodiment is as follows: the apertures of the plano-convex cylindrical lens 3, the biconcave cylindrical lens 4, the meniscus lens 5, and the plano-convex cylindrical lens group 6 are all greater than twice the diameter of the incident laser beam, thereby better receiving the laser beam and reducing the influence of limited diffraction on the size of the focusing beam waist.

[0035] The incident laser parameters in this embodiment are: center wavelength 1080nm, collimated incident laser beam diameter 5mm. The overall length of the beam expansion system along the optical axis is less than 250mm, and the length perpendicular to the optical axis is less than 80mm.

[0036] The relevant parameters of the lenses used in the beam expanding system for laser additive manufacturing are shown in Table 1. All lenses are made of fused silica to suit high-power laser applications. In the first beam expanding module 1, 31 magnifications of beam expansion can be achieved by fixing the position of the plano-convex cylindrical lens 3 and moving the positions of the biconcave cylindrical lens 4, the meniscus lens, and the plano-convex cylindrical lens group 6. The lens spacing, corresponding beam divergence angle, and wavefront aberration for each magnification are shown in Table 1. The maximum divergence angle is 4.2850E-005°, and the maximum wavefront aberration is 6.0093E-005λ. For an incident beam with a radius of 2.5 mm, the output beam after unidirectional beam expansion satisfies formula a. n =3+(n-1)×0.05, where n is an integer in the range [1,31]. This gives us radii a1=3, a2=3.05, a3=3.1…a n－1 =4.45、a n The emitted beam has a diameter of 4.5 mm. The first beam expander module 1 and the second beam expander module 2 act on the laser beam in two directions, with a total magnification of 31 times in one direction, satisfying formula a.n =a1+(n-1)×1, by combining the multiples in both directions in a pairwise non-overlapping manner, we can finally obtain S. n =n×(a1+a n ) / 2=496 types of light spot shapes, including 31 types of circular light spot beam expansion output and 465 types of elliptical light spot shaping output.

[0037] Table 1. Relevant parameters of each lens in the system

[0038] Table 2. Parameters and performance indicators of the system at various magnifications for single-direction beam expansion.

[0039] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope described in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A beam expander system for laser additive manufacturing, characterized in that, include: A first beam expander module and a second beam expander module are arranged sequentially along the optical path. Both the first beam expander module and the second beam expander module include a fixed group, a zoom group, and a compensation group, which are arranged sequentially along the optical path and composed of multiple cylindrical mirrors. The cylindrical generatrices of the cylindrical mirrors of the first beam expander module and the second beam expander module are perpendicular to each other, and the optical axes of the cylindrical mirrors of the first beam expander module and the second beam expander module are coincident or parallel.

2. The beam expanding system for laser additive manufacturing according to claim 1, characterized in that, The fixed group includes: A plano-convex cylindrical lens is used to receive and converge a laser beam and balance aberrations.

3. The beam expanding system for laser additive manufacturing according to claim 1, characterized in that, The zoom group includes: A biconcave cylindrical lens is disposed between the fixed group and the compensation group to diverge the laser beam and achieve zoom.

4. The beam expanding system for laser additive manufacturing according to claim 3, characterized in that, The zoom group also includes: A meniscus lens is disposed on the light-emitting side of the biconcave cylindrical lens to correct aberrations.

5. The beam expanding system for laser additive manufacturing according to claim 1, characterized in that, The compensation group includes: A plano-convex cylindrical lens group, consisting of a plano-concave cylindrical lens and a plano-convex cylindrical lens, is used to correct divergence angle and spherical aberration.

6. The beam expanding system for laser additive manufacturing according to claim 1, characterized in that, Also includes: A reflector is disposed between the first beam expander module and the second beam expander module to make the laser beams passing through the first beam expander module and the second beam expander module parallel.

7. The beam expanding system for laser additive manufacturing according to claim 1, characterized in that, Also includes: A galvanometer is positioned on the light-emitting side of the second beam expander module to control the emission direction of the laser beam.

8. A beam expander system for laser additive manufacturing according to claim 7, characterized in that, Also includes: A field mirror is positioned on the light-emitting side of the galvanometer to focus and emit the laser beam.

9. A beam expanding system for laser additive manufacturing according to claim 1, characterized in that, Also includes: A linear slide table, wherein the zoom group and the compensation group are mounted on the linear slide table.

10. A beam expanding system for laser additive manufacturing according to claim 1, characterized in that, The aperture of each lens in the fixed group, the variable magnification group, and the compensation group is greater than twice the diameter of the incident laser beam.

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