Laser additive manufacturing optical system of circular polarization point ring composite light spot

Abstract

The invention is suitable for the technical field of laser additive manufacturing, and provides a laser additive manufacturing optical system of a circular polarization point ring composite light spot, which comprises a linear polarization laser lambda1, a linear polarization laser lambda2, an adjustable linear polarizer 1, an adjustable linear polarizer 2, an axicon 1, an axicon 2, a 1 / 4 wave plate 1-5, a polarization beam combiner (PBC) and a beam expanding scanning focusing system, a light-emitting optical axis of a laser lambda1 is coaxial with an adjustable linear polaroid 1, a 1 / 4 wave plate 1 and a 1 / 4 wave plate 3, a light-emitting optical axis of a laser lambda2 is coaxial with an axicon 1, an axicon 2, an adjustable linear polaroid 2, a 1 / 4 wave plate 2 and a 1 / 4 wave plate 4 and is perpendicular to the optical axis of the lambda1, a transmission axis and a reflection axis of a polarization beam combiner PBC are coaxial with the optical axes of the lambda1 and the lambda2 respectively, and two beams of light are coaxial with a 1 / 4 wave plate 5 after being combined through the PBC. Finally, entering a beam-expanding scanning focusing system; according to the method, circular polarization regulation and control and point-ring composite light spot characteristics are integrated, light spot parameter dynamic adjustment and high-reflection metal reflection suppression are achieved, and the forming quality is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of laser additive manufacturing technology, and particularly relates to a laser additive manufacturing optical system with a circularly polarized dot ring composite spot. Background Technology

[0002] Existing spot generation schemes mainly rely on multi-clad fiber structures or multi-component optical systems, which suffer from high costs and poor adjustment flexibility. Among them, the ring fiber scheme forms a central spherical spot and an edge ring spot through special fibers, but the center-to-ring diameter ratio, ring width, and energy distribution ratio of the spot are fixed by the inherent characteristics of the fiber. They cannot be dynamically adjusted according to the thermal conductivity differences of highly reflective metal materials or the forming requirements of components. This makes it difficult for the same system to adapt to the melting parameters of different materials, increasing the manufacturing difficulty of high-end components. Traditional laser additive manufacturing systems mostly use linearly polarized or unpolarized light, which results in significant energy loss when dealing with highly reflective metals such as copper, aluminum, and gold. The absorption rate of highly reflective metals to linearly polarized light is strongly angle-dependent, leading to uneven energy distribution within the molten pool and making it prone to defects such as spheroidization and porosity. Although circularly polarized light can reduce angle-sensitive reflection, existing systems have not integrated circularly polarized light with a dotted ring composite spot, making it impossible to simultaneously utilize the advantages of "polarization-suppressed reflection" and "spot-optimized energy distribution," thus making it difficult to solve the problem of thermal stress concentration in highly reflective metals. The existing system lacks the ability to coordinate the energy distribution and polarization state of the light spot. For the interface bonding requirements of heterogeneous materials, it cannot match the melting temperature difference of the two materials by adjusting the light spot parameters, resulting in insufficient interface bonding strength and difficulty in meeting the thermal conductivity requirements of the heat dissipation structure of electronic devices. Therefore, a laser additive manufacturing optical system with a circularly polarized dot ring composite spot is needed to solve the above problems. Summary of the Invention

[0003] The purpose of this invention is to provide a laser additive manufacturing optical system for a circularly polarized dot ring composite spot, in order to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A laser additive manufacturing optical system for a circularly polarized dot ring composite spot includes a linearly polarized laser λ1, a linearly polarized laser λ2, an adjustable linearly polarizer 1, an adjustable linearly polarizer 2, an axial cone mirror 1, an axial cone mirror 2, a quarter-wave plate 1, a quarter-wave plate 2, a quarter-wave plate 3, a quarter-wave plate 4, a quarter-wave plate 5, a polarization beam combiner PBC, and a beam expander scanning focusing system. The output optical axis of laser λ1 is collinear with the central axis of adjustable linear polarizer 1, quarter-wave plate 1, and quarter-wave plate 3. The output optical axis of laser λ2 is collinear with the central axis of axial conical mirror 1, axial conical mirror 2, adjustable linear polarizer 2, quarter-wave plate 2, and quarter-wave plate 4. The output optical axes of laser λ1 and laser λ2 are perpendicular to each other. The transmission axis of the polarization combiner PBC is collinear with the output optical axis of the laser λ1, and the reflection axis of the polarization combiner PBC is collinear with the output optical axis of the laser λ2. The beams output from lasers λ1 and λ2 are combined by a polarization beam combiner (PBC) to form a beam whose optical axis is collinear with the central axis of the quarter-wave plate 5. The output end of the quarter-wave plate 5 is collinear with the input end of the beam expander scanning focusing system. The output power of lasers λ1 and λ2 is 500-1000W, the output wavelength is 1030-1090nm and the wavelengths are different, and the beam divergence angle is less than 0.05rad. The distance between the axial cone mirror 1 and the axial cone mirror 2 can be adjusted within the range of 30-80mm, and the beam expanding scanning focusing system can adjust the width of the annular spot within the range of 70-150μm and the outer ring diameter within the range of 180-330μm; The dual-laser wavelength difference design can match the absorption peaks of different highly reflective metals, avoiding energy waste caused by a single wavelength; the adjustable axis-cone mirror spacing design breaks through the limitations of the traditional fixed fiber spot. For different needs of aerospace precision components and large aluminum shells, parameter adjustment can be achieved without replacing optical components, reducing equipment costs, reducing changeover time, and improving manufacturing efficiency.

[0005] In a further technical solution, the adjustable linear polarizer 1 is used to filter stray light from the linearly polarized light output by the laser λ1, so as to improve the extinction ratio of the linearly polarized light. The adjustable linear polarizer 2 is used to filter stray light from the annular linearly polarized light output by the axial cone mirror 2, so as to improve the extinction ratio of the annular linearly polarized light. Stray light filtering can increase the extinction ratio of linearly polarized light from 100:1 in traditional systems to over 1000:1, reducing energy loss caused by stray light. For highly reflective copper, pure linearly polarized light can ensure the integrity of subsequent polarization conversion, avoid local reflectivity fluctuations caused by impure polarization, and thus improve the uniformity of molten pool energy distribution by 15%, effectively suppressing spheroidization defects.

[0006] In a further technical solution, the phase delay accuracy of the quarter-wave plate 1, quarter-wave plate 2, quarter-wave plate 3, quarter-wave plate 4, and quarter-wave plate 5 is all less than 1 / 500λ, and the light-transmitting aperture is all greater than 12.7mm. The quarter-wave plate 1 is used to convert the linearly polarized light purified by the adjustable linear polarizer 1 into left-hand circularly polarized light (LCP), and the quarter-wave plate 2 is used to convert the annular linearly polarized light purified by the adjustable linear polarizer 2 into right-hand circularly polarized light (RCP). A high-precision phase delay of 1 / 500λ ensures complete polarization state conversion, avoiding reflection loss caused by residual linear polarization components; a large aperture can adapt to the transmission requirements of 500-1000W high-power lasers, preventing beam truncation due to insufficient aperture; independent generation of LCP and RCP can match the differences in light-matter interaction on highly reflective metal surfaces. For example, the absorption rate of LCP on copper surfaces is higher than that of linearly polarized light, and the absorption rate of RCP on aluminum surfaces is higher than that of linearly polarized light. Differentiated polarization states further improve energy utilization efficiency, while enhancing the symmetry of molten pool flow and reducing compositional segregation.

[0007] In a further technical solution, the quarter-wave plate 3 is used to convert left-handed circularly polarized light (LCP) into p-polarized linearly polarized light, and the polarization direction of the p-polarized linearly polarized light matches the transmission direction of the polarization beam combiner (PBC). The quarter-wave plate 4 is used to convert right-hand circularly polarized light (RCP) into s-polarized linearly polarized light, and the polarization direction of the s-polarized linearly polarized light matches the reflection direction of the polarization beam combiner PBC. The quarter-wave plate 5 is used to convert the linearly polarized point ring spot after beam combining by the polarization beam combiner PBC into a circularly polarized point ring spot. Precise matching of the p / s polarization state with the transmission / reflection direction of the PBC can improve the beam combining efficiency to over 98% and reduce energy loss; the final polarization conversion of the 1 / 4 wave plate 5 can reduce the angle-sensitive reflection fluctuation of highly reflective metals from 30%-50% to below 5%, ensuring energy absorption stability; the circular polarization state can also suppress the "directional reflection" phenomenon of metal powder, improve the energy utilization rate of the powder bed by 12%, and reduce the amount of splashing.

[0008] In a further technical solution, the cone angle of the axial cone mirror 1 is -10°, which is used to convert the linearly polarized light output by the laser λ2 into a ring-shaped diverging beam; The cone angle of the axial cone mirror 2 is 10°, which is used to convert the annular diverging beam into a parallel annular beam. The light transmission wavelength range of both the axial conical mirror 1 and the axial conical mirror 2 is 1030-1090nm; The combination of -10° and 10° positive and negative cone angles enables precise control of the "divergence-collimation" of the ring beam, ensuring the radial energy uniformity of the ring spot and avoiding the energy attenuation at the edge of the spot caused by traditional single-axis conical lens schemes. The fixed transmission wavelength range is perfectly matched with the laser output wavelength to prevent spot deformation caused by wavelength shift. For example, the ring spot formed by a 1090nm laser after passing through the axial conical lens can have its ring width deviation controlled within ±3μm, providing a stable beam foundation for subsequent focusing and shaping, and ensuring the dimensional accuracy of the component.

[0009] In a further technical solution, the polarization beam combiner (PBC) transmits incident p-polarized linearly polarized light while maintaining its polarization state, and reflects incident s-polarized linearly polarized light while maintaining its polarization state. After being combined by a polarization beam combiner (PBC), an unfocused dot-ring spot is formed, and the polarization state of the dot spot is orthogonal to that of the ring spot. The polarization-maintaining design avoids polarization state disorder during beam combining and prevents beam energy interference caused by polarization mixing. The orthogonal polarization state ensures that the point beam and the ring beam have no energy coupling during propagation, ensuring a stable energy distribution between the high-energy central region and the low-energy outer ring region. The central region can achieve deep melting of highly reflective metals, while the outer ring region can provide preheating and slow cooling, thus suppressing thermal stress concentration from the source.

[0010] In a further technical solution, the beam expanding scanning focusing system integrates a beam expander, an XY scanning galvanometer, and a focusing lens group; The beam expander is used to expand the unfocused circularly polarized ring spot output by the 1 / 4 wave plate 5. The focusing lens group is used to focus the expanded spot. The XY scanning galvanometer can swing along the XY direction to move the focused circularly polarized ring spot within the working plane. The beam expander can adjust the magnification of the light spot according to the working area requirements, adapting to the manufacturing needs of components of different sizes; the focal length design of the focusing lens group can ensure that the energy density of the focused light spot meets the requirements of high-reflectivity metal melting, and the focusing accuracy can ensure the forming of component details; the swing speed and path accuracy of the XY scanning galvanometer can match the forming path of complex components, reducing defects caused by path deviation.

[0011] A further technical solution is that by adjusting the distance between the axial conical mirror 1 and the axial conical mirror 2, the width of the annular spot can be continuously adjusted within the range of 70-150μm, and the outer ring diameter of the annular spot can be continuously adjusted within the range of 180-330μm. The continuously adjustable design can adapt to the thermal requirements of different high-reflectivity metals. For example, for copper with high thermal conductivity, adjusting the ring width to 70μm can reduce the rapid cooling of the molten pool caused by heat diffusion and ensure that the molten pool flows fully. For aluminum with low melting point, adjusting the ring width to 150μm can increase the preheating area and avoid burn-off caused by local overheating. The outer ring diameter can be adjusted to match the size of the forming area of ​​the component.

[0012] Compared with the prior art, the beneficial effects of the present invention are: This invention achieves a synergistic polarization-energy control effect: through the coordinated operation of quarter-wave plates 1-5 and the polarization combiner (PBC), integrated control of circularly polarized light and point-ring composite light spots is realized. The quarter-wave plates 1-4 convert linearly polarized light into LCP / RCP and then adapt it to the transmission / reflection direction of the PBC to ensure efficient beam combining. The quarter-wave plate 5 ultimately unifies the polarization state, eliminating the angle-sensitive reflection of highly reflective metals. The high-energy region at the center of the point-ring light spot (λ1 optical path) achieves deep melting, while the low-energy region on the outer ring (λ2 optical path) provides preheating and slow cooling, reducing the molten pool temperature gradient from 500K / mm to 200K / mm. This fundamentally solves the problem of "uniform molten pool energy leading to spheroidization and porosity" in the background technology. The porosity of copper components is reduced from 8% to below 2%, and the spheroidization rate of aluminum components is reduced from 15% to below 3%. This invention provides a dynamically adjustable light field topology effect: by adjusting the distance between axial conical mirror 1 and axial conical mirror 2 (range 30-80mm), the ring width (70-150μm) and outer ring diameter (180-330μm) of the annular light spot can be directly changed. This allows for adaptation to different high-reflectivity metals and components without replacing optical components. When the distance is adjusted to 30mm, the ring width is 70μm and the outer ring diameter is 180μm, suitable for molding aerospace precision brackets (detail size 0.1mm), ensuring detail accuracy (±0.01mm). When the distance is adjusted to 80mm, the ring width is 150μm and the outer ring diameter is 330μm, suitable for manufacturing large aluminum shells (size 280mm×280mm), improving molding efficiency by 30%. This solves the problem of "unadjustable light spot structure and poor adaptability" in the prior art, reducing equipment changeover costs and time. This invention achieves multi-physics field coupling optimization by coordinating the components of the beam expanding and scanning focusing system (beam expander adjusting the amplitude, focusing lens group controlling energy density, and XY scanning galvanometer moving the light spot), simultaneously regulating the thermal field, flow field, and stress field. The stable energy distribution of the circularly polarized ring light spot ensures a uniform temperature gradient in the thermal field, suppressing thermal stress concentration. Precise path control of the XY scanning galvanometer stabilizes the flow direction of the molten pool, reducing component segregation. For copper-aluminum composite heat dissipation structures, adjusting the light spot parameters to match the melting temperature difference between the two materials improves interfacial bonding strength and reduces interfacial thermal resistance, solving the problems of "numerous molding defects in high-reflectivity materials and poor interfacial bonding between heterogeneous materials" in the prior art, thus meeting the performance requirements of high-end components.

[0013] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the optical path layout of the present invention; Figure 2 This is a simulation diagram of the dot ring spot of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0017] Example 1 like Figures 1-2 As shown, this embodiment of the invention provides a laser additive manufacturing optical system for a circularly polarized dot ring composite spot, including a linearly polarized laser λ1, a linearly polarized laser λ2, an adjustable linearly polarizer 1, an adjustable linearly polarizer 2, an axial cone mirror 1, an axial cone mirror 2, a quarter-wave plate 1, a quarter-wave plate 2, a quarter-wave plate 3, a quarter-wave plate 4, a quarter-wave plate 5, a polarization beam combiner PBC, and a beam expander scanning focusing system; The output optical axis of laser λ1 is collinear with the central axis of adjustable linear polarizer 1, quarter-wave plate 1, and quarter-wave plate 3. The output optical axis of laser λ2 is collinear with the central axis of axial conical mirror 1, axial conical mirror 2, adjustable linear polarizer 2, quarter-wave plate 2, and quarter-wave plate 4. The output optical axes of laser λ1 and laser λ2 are perpendicular to each other. The transmission axis of the polarization combiner PBC is collinear with the output optical axis of the laser λ1, and the reflection axis of the polarization combiner PBC is collinear with the output optical axis of the laser λ2. The beams output from lasers λ1 and λ2 are combined by a polarization beam combiner (PBC) to form a beam whose optical axis is collinear with the central axis of the quarter-wave plate 5. The output end of the quarter-wave plate 5 is collinear with the input end of the beam expander scanning focusing system.

[0018] The laser λ1 has an output power of 500W, an output wavelength of 1030nm, and a beam divergence angle of 0.04rad. The laser λ2 has an output power of 600W, an output wavelength of 1050nm, and a beam divergence angle of 0.03rad. The cone angle of the axial cone mirror 1 is -10°, the cone angle of the axial cone mirror 2 is 10°, the distance between the two is set to 30mm, and the light transmission wavelength range of both the axial cone mirror 1 and the axial cone mirror 2 is 1030-1090nm. The phase delay accuracy of the quarter-wave plate 1, quarter-wave plate 2, quarter-wave plate 3, quarter-wave plate 4, and quarter-wave plate 5 is all 1 / 600λ (satisfying the limitation of "less than 1 / 500λ" in the claim), and the light-transmitting aperture is all 15mm (satisfying the limitation of "greater than 12.7mm" in the claim). The beam expanding scanning focusing system integrates a beam expander, an XY scanning galvanometer, and a focusing lens group. The initial magnification of the beam expander is set to 1x, the focal length of the focusing lens group is set to 100mm, and the maximum swing speed of the XY scanning galvanometer is set to 300mm / s.

[0019] In this embodiment, the adjustable linear polarizer 1 filters stray light from the linearly polarized light output by the laser λ1, increasing the extinction ratio of the linearly polarized light to 1200:1. The adjustable linear polarizer 2 filters stray light from the annular linearly polarized light output by the axial cone mirror 2, increasing the extinction ratio of the annular linearly polarized light to 1100:1. The quarter-wave plate 1 converts the linearly polarized light purified by the tunable linear polarizer 1 into left-handed circularly polarized light (LCP). The quarter-wave plate 3 further converts the left-handed circularly polarized light (LCP) into p-polarized linearly polarized light. The polarization direction of the p-polarized linearly polarized light is perfectly matched with the transmission direction of the polarization combiner PBC, ensuring that the transmittance of the polarization combiner PBC to it reaches 98.5%. The quarter-wave plate 2 converts the annular linearly polarized light purified by the adjustable linear polarizer 2 into right-hand circularly polarized light (RCP). The quarter-wave plate 4 further converts the right-hand circularly polarized light (RCP) into s-polarized linearly polarized light. The polarization direction of this s-polarized linearly polarized light is perfectly matched with the reflection direction of the polarization combiner PBC, ensuring that the reflectivity of the polarization combiner PBC reaches 98.2%. The polarization combiner (PBC) transmits incident p-polarized linearly polarized light while maintaining its polarization state, and reflects incident s-polarized linearly polarized light while maintaining its polarization state. After the two beams are combined by the PBC, they form an unfocused dot-ring spot. The polarization state of the dot spot (from the laser λ1 optical path) is orthogonal to the polarization state of the ring spot (from the laser λ2 optical path), with no energy coupling loss. The quarter-wave plate 5 converts the unfocused linearly polarized ring spot into a circularly polarized ring spot, eliminating the sensitivity of the highly reflective metallic material to the laser incident angle. After the beam expander of the beam expanding scanning focusing system expands the circularly polarized ring spot by 1x, it is focused onto the surface of the copper powder bed by the focusing lens group. The width of the ring spot after focusing is 70μm and the outer ring diameter is 180μm. The XY scanning galvanometer swings in the XY direction along the preset precision component path (such as micro electronic connector), which drives the focused circularly polarized ring spot to move. In this embodiment, the system is used for additive manufacturing of copper powder (a highly reflective metal with a reflectivity of approximately 90%). The circularly polarized ring spot increases the energy absorption rate of the copper powder from 35% to 62% in the traditional linearly polarized light system, effectively avoiding spheroidization defects caused by uneven energy distribution in the molten pool (the spheroidization rate is reduced from 15% to 2.8%). The high energy density of the central circular spot (1.1×10⁻⁶) 6 Achieving deep melting of copper powder (melting depth 0.4 mm, melting depth deviation <4%) with W / cm², and low energy density of the annular spot (5.2 × 10⁻⁶ W / cm²). 5 The area around the molten zone is preheated and slowly cooled by W / cm², reducing the thermal stress value from 500MPa to 190MPa. The dimensional accuracy of the molded micro-electronic connector reaches ±0.008mm, meeting the assembly requirements of micro-electronic devices.

[0020] Example 2 The difference between this embodiment and Embodiment 1 is that: Laser parameters: The output power of linearly polarized laser λ1 is adjusted to 700W and the output wavelength is adjusted to 1060nm; the output power of linearly polarized laser λ2 is adjusted to 800W and the output wavelength is adjusted to 1070nm. Axial cone parameters: The distance between axial cone 1 and axial cone 2 is adjusted to 55mm; 1 / 4 wave plate parameters: The phase delay accuracy of 1 / 4 wave plates 1-5 is adjusted to 1 / 550λ; Parameters of the beam expander scanning focusing system: the magnification of the beam expander is adjusted to 1.5x, the focal length of the focusing lens group is adjusted to 150mm, and the maximum swing speed of the XY scanning galvanometer is adjusted to 500mm / s.

[0021] In this embodiment, after the distance between the axial cone mirror 1 and the axial cone mirror 2 is adjusted to 55mm, the beam expander scanning focusing system focuses the light, and the width of the annular spot is adjusted to 110μm and the outer ring diameter is adjusted to 255μm (still satisfying the limitation in the claim that "the width of the annular spot is in the range of 70-150μm and the outer ring diameter is in the range of 180-330μm"). The phase delay accuracy of the quarter-wave plates 1-5 is improved to 1 / 550λ, which increases the polarization state conversion efficiency from 98% in Example 1 to 98.8%, and reduces the reflection loss caused by residual linear polarization components (reflection loss is reduced from 1.5% to 0.9%).

[0022] After the magnification of the beam expander is adjusted to 1.5x, the working area is expanded from 100mm×100mm in Example 1 to 150mm×150mm, which is suitable for the manufacturing needs of medium-sized components. With the focal length of the focusing lens group adjusted to 150mm and the laser power increased, the energy density of the central circular spot after focusing reaches 1.3×10⁻⁶. 6 W / cm², the energy density of the annular light spot reaches 6.1×10⁻⁶. 5 W / cm²; The maximum oscillation speed of the XY scanning galvanometer is increased to 500 mm / s, which improves the molding efficiency by 66.7% compared to Example 1.

[0023] In this embodiment, the system is used for additive manufacturing of aluminum powder (high reflectivity metal, approximately 88% reflectivity), and the target component is aluminum fins (fin spacing 0.12 mm) of a copper-aluminum composite heat dissipation structure for electronic devices. The 110μm annular spot width is precisely matched with the fin spacing, avoiding defects such as incomplete fusion or over-fusion caused by the mismatch between the spot size and the component characteristics; Circularly polarized light reduced the angle-sensitive reflection fluctuation of aluminum powder from ±30% to ±4%, and stabilized the energy absorption rate at over 58%. The central circular spot ensures that the aluminum powder is fully melted (melt depth 0.35mm), and the preheating effect of the annular spot reduces the melting temperature gradient of the aluminum powder from 450K / mm to 220K / mm, effectively suppressing thermal stress cracking that easily occurs in aluminum components (cracking rate reduced from 8% to 1.2%). The formed aluminum fins exhibit a perpendicularity deviation of <0.4°, a surface roughness Ra of <2.8μm, and an interfacial bonding strength with the copper substrate of 120MPa, meeting the thermal conductivity and structural strength requirements of the composite heat dissipation structure (interfacial thermal resistance <8×10⁻⁻⁴). 5 m²・K / W).

[0024] Example 3 The difference between this embodiment and Embodiment 2 is that: Laser parameters: The output power of linearly polarized laser λ1 is adjusted to 1000W and the output wavelength is adjusted to 1090nm; the output power of linearly polarized laser λ2 is adjusted to 500W and the output wavelength is adjusted to 1080nm. Axial cone parameters: The distance between axial cone 1 and axial cone 2 is adjusted to 80mm; 1 / 4 wave plate parameters: The aperture of 1-5 of the 1 / 4 wave plate is adjusted to 18mm; Parameters of the beam expander scanning focusing system: the magnification of the beam expander is adjusted to 2x, the focal length of the focusing lens group is adjusted to 200mm, and the maximum swing speed of the XY scanning galvanometer is adjusted to 800mm / s.

[0025] In this embodiment, after the distance between the axial cone mirror 1 and the axial cone mirror 2 is adjusted to 80mm, the beam expander scanning focusing system focuses the light, and the width of the annular spot is adjusted to 150μm and the outer ring diameter is adjusted to 330μm (which meets the limitation in the claim that "the width of the annular spot is in the range of 70-150μm and the outer ring diameter is in the range of 180-330μm"). The aperture of the quarter-wave plate 1-5 is increased to 18mm to meet the transmission requirements of 1000W high-power laser, avoiding beam cutoff due to insufficient aperture (beam cutoff loss is reduced from 0.8% in Example 2 to 0.3%), and ensuring the full utilization of high-power laser energy.

[0026] After the magnification of the beam expander is adjusted to 2x, the working area is further expanded to 200mm×200mm, which can form large components in one go. With the focal length of the focusing lens group adjusted to 200mm, combined with the 1000W high power of the laser λ1, the energy density of the central circular spot after focusing reaches 1.5×10⁻⁶. 6 W / cm², meeting the deep melting requirements of thick-walled components; The maximum oscillation speed of the XY scanning galvanometer is increased to 800 mm / s, which improves the molding efficiency by 60% compared to Example 2, making it suitable for the mass production needs of large components.

[0027] In this embodiment, the system is used for additive manufacturing of large aluminum brackets (200mm×150mm×80mm) in the aerospace field; The 150μm annular spot width provides large-area preheating, which improves the preheating temperature uniformity of aluminum powder bed to over 95%, reducing the temperature gradient difference during the forming process of large components. The high energy density of the central circular spot ensures full melting of the thick-walled area of ​​the support, while the slow cooling effect of the annular spot makes the residual stress of the support uniformly distributed, avoiding deformation that is prone to occur in large components. After mechanical testing, the formed aluminum bracket has a tensile strength of 280MPa and an elongation of 8%, meeting the mechanical performance requirements of the aerospace industry for structural components. Moreover, the forming cycle is shortened by 40% compared with the traditional linear polarized light system, and the manufacturing cost is reduced by 25%.

[0028] Working principle and usage process of this invention: High-quality additive manufacturing of highly reflective metallic materials is achieved through a collaborative process of "dual-path polarization modulation - spatial beam combining - beam focusing and scanning". The specific steps are as follows: Laser emission and polarization purification: Linearly polarized laser λ1 (power 500-1000W, wavelength 1030-1090nm, divergence angle <0.05rad) outputs linearly polarized light, which enters tunable linear polarizer 1; Adjustable linear polarizer 1 filters stray light in the beam, increasing the extinction ratio to over 1000:1, ensuring the accuracy of subsequent polarization conversion; Meanwhile, the linearly polarized laser λ2 (with a different wavelength than λ1, but the same parameters as λ1) outputs linearly polarized light, which directly enters the axis conical mirror 1; Axicon 1 (cone angle -10°) converts linearly polarized light into a ring-shaped diverging beam, which enters axicon 2 (cone angle 10°, distance from axicon 1 adjustable from 30-80mm). The axial cone mirror 2 changes the divergence angle of the annular diverging beam by adjusting the spacing, converting it into a parallel annular beam, which then enters the adjustable linear polarizer 2. Adjustable linear polarizer 2 filters stray light in the ring beam, and also increases the extinction ratio to over 1000:1, thus completing the polarization purification of the dual optical paths. Polarization state conversion and beam combining adaptation: The linearly polarized light purified by the adjustable linear polarizer 1 enters the 1 / 4 wave plate 1 (phase delay accuracy <1 / 500λ, light-passing aperture >12.7mm). The quarter-wave plate 1 converts linearly polarized light into left-hand circularly polarized light (LCP) through a phase delay of λ / 4, and the LCP enters the quarter-wave plate 3; the quarter-wave plate 3 applies another phase delay of λ / 4 to convert the LCP into p-polarized linearly polarized light, and the p-polarization direction is precisely matched with the transmission direction of the polarization beam combiner PBC. Meanwhile, the annular linearly polarized light purified by the adjustable linear polarizer 2 enters the quarter-wave plate 2 (with the same parameters as the quarter-wave plate 1). 1 / 4 wave plate 2 converts the annular linearly polarized light into right-hand circularly polarized light (RCP), and the RCP enters 1 / 4 wave plate 4; The 1 / 4 wave plate 4 converts RCP into s-polarized linearly polarized light, and the s-polarization direction is precisely matched with the reflection direction of the polarization combiner PBC, thus completing the polarization state conversion and beam combining adaptation of the two optical paths. Spatial beam combining and circular polarization unification: p-polarized linearly polarized light is incident along the transmission axis of the polarization beam combiner (PBC), and the PBC transmits it while maintaining its polarization state. s-polarized linearly polarized light is incident along the reflection axis of the PBC, and the PBC reflects it at 90° while maintaining its polarization state (reflectivity ≥ 98%). The two beams of light are spatially combined inside the PBC to form an unfocused dot-ring spot (the central circular spot comes from the λ1 optical path, and the ring spot comes from the λ2 optical path; their polarization states are orthogonal and there is no energy coupling). The linearly polarized ring spot after beam combining enters the 1 / 4 wave plate 5 (parameters are the same as 1 / 4 wave plate 1). The 1 / 4 wave plate 5, through λ / 4 phase delay, transforms the orthogonal linearly polarized point ring spot into a circularly polarized point ring spot, eliminating the sensitivity of the highly reflective metal to the laser incident angle and completing the polarization state unification. Beam expanding and focusing with dynamic scanning shaping: The circularly polarized dot ring beam enters the beam expander of the beam expanding and focusing system; The beam expander adjusts the magnification of the beam (adjustable from 1 to 5 times) according to the working area requirements (such as 100mm×100mm to 300mm×300mm) to achieve the matching of the beam size and the working area. The expanded beam enters the focusing lens group; the focusing lens group, through precise focal length control (e.g., 100-200mm), focuses the beam onto the surface of the metal powder bed, achieving a power density of 5×10⁻⁶ for the central circular beam. 5 -1.2×10 6 W / cm² (meets the requirements for high-reflectivity metal melting), and the power density of the annular spot reaches 2.5×10⁻⁶. 5 -6×10 5 W / cm² (to achieve preheating and slow cooling); The focused light spot enters the XY scanning galvanometer; the XY scanning galvanometer oscillates along the XY direction at a speed of 0-1000 mm / s according to the preset component forming path (such as the cooling channel of the precision bracket, the fin array of the heat dissipation structure), driving the light spot to move within the working area; During the movement, the central circular spot dominates the deep melting of the metal powder, while the annular spot preheats (reduces the temperature gradient) and slowly cools (suppresses thermal stress) the periphery of the molten area, ultimately completing the additive manufacturing of the high-reflectivity metal component; Throughout the entire process, by adjusting the distance between axial conical mirror 1 and axial conical mirror 2, the width (70-150μm) and outer ring diameter (180-330μm) of the annular light spot can be changed in real time to adapt to the forming requirements of different materials and components. The high-precision phase delay of each quarter wave plate and the efficient beam combining of the polarization combiner PBC ensure the stability of the circular polarization state and the energy utilization rate, fundamentally solving the problems of reflection, defects and efficiency in additive manufacturing of high reflective metal materials.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser additive manufacturing optical system for a circularly polarized dot-ring composite light spot, comprising a linearly polarized laser λ1, a linearly polarized laser λ2, an adjustable linearly polarizer 1, an adjustable linearly polarizer 2, an axial conical mirror 1, an axial conical mirror 2, a quarter-wave plate 1, a quarter-wave plate 2, a quarter-wave plate 3, a quarter-wave plate 4, a quarter-wave plate 5, a polarization beam combiner (PBC), and a beam expander, scanning, and focusing system, characterized in that, The output optical axis of laser λ1 is collinear with the central axis of adjustable linear polarizer 1, quarter-wave plate 1, and quarter-wave plate 3. The output optical axis of laser λ2 is collinear with the central axis of axial conical mirror 1, axial conical mirror 2, adjustable linear polarizer 2, quarter-wave plate 2, and quarter-wave plate 4. The output optical axes of laser λ1 and laser λ2 are perpendicular to each other. The transmission axis of the polarization combiner PBC is collinear with the output optical axis of the laser λ1, and the reflection axis of the polarization combiner PBC is collinear with the output optical axis of the laser λ2. The beams output from lasers λ1 and λ2 are combined by a polarization beam combiner (PBC) to form a beam whose optical axis is collinear with the central axis of the quarter-wave plate 5. The output end of the quarter-wave plate 5 is collinear with the input end of the beam expander scanning focusing system. The output power of lasers λ1 and λ2 is 500-1000W, the output wavelength is 1030-1090nm and the wavelengths are different, and the beam divergence angle is less than 0.05rad. The distance between the axial conical mirror 1 and the axial conical mirror 2 can be adjusted within the range of 30-80mm. The beam expanding scanning focusing system can adjust the width of the annular spot within the range of 70-150μm and the outer ring diameter within the range of 180-330μm.

2. The laser additive manufacturing optical system for a circularly polarized dot-ring composite light spot according to claim 1, characterized in that, The adjustable linear polarizer 1 is used to filter stray light from the linearly polarized light output by the laser λ1, so as to improve the extinction ratio of the linearly polarized light. The adjustable linear polarizer 2 is used to filter stray light from the annular linearly polarized light output by the axial cone mirror 2, so as to improve the extinction ratio of the annular linearly polarized light.

3. The laser additive manufacturing optical system for a circularly polarized dot-ring composite light spot according to claim 1, characterized in that, The phase delay accuracy of the quarter-wave plate 1, quarter-wave plate 2, quarter-wave plate 3, quarter-wave plate 4, and quarter-wave plate 5 is all less than 1 / 500λ, and the light-transmitting aperture is all greater than 12.7mm. The quarter-wave plate 1 is used to convert the linearly polarized light purified by the adjustable linear polarizer 1 into left-handed circularly polarized light (LCP), and the quarter-wave plate 2 is used to convert the annular linearly polarized light purified by the adjustable linear polarizer 2 into right-handed circularly polarized light (RCP).

4. The laser additive manufacturing optical system for a circularly polarized dot-ring composite spot according to claim 1, characterized in that, The quarter-wave plate 3 is used to convert left-hand circularly polarized light (LCP) into p-polarized linearly polarized light, and the polarization direction of the p-polarized linearly polarized light matches the transmission direction of the polarization combiner PBC. The quarter-wave plate 4 is used to convert right-hand circularly polarized light (RCP) into s-polarized linearly polarized light, and the polarization direction of the s-polarized linearly polarized light matches the reflection direction of the polarization beam combiner PBC. The quarter-wave plate 5 is used to convert the linearly polarized point ring spot after beam combining by the polarization beam combiner (PBC) into a circularly polarized point ring spot.

5. The laser additive manufacturing optical system for a circularly polarized dot-ring composite spot according to claim 1, characterized in that, The cone angle of the axial cone mirror 1 is -10°, which is used to convert the linearly polarized light output by the laser λ2 into a ring-shaped diverging beam. The cone angle of the axial cone mirror 2 is 10°, which is used to convert the annular diverging beam into a parallel annular beam. The light transmission wavelength range of both the axial conical mirror 1 and the axial conical mirror 2 is 1030-1090nm.

6. The laser additive manufacturing optical system for a circularly polarized dot-ring composite spot according to claim 1, characterized in that, The polarization beam combiner (PBC) transmits incident p-polarized linearly polarized light while maintaining its polarization state, and reflects incident s-polarized linearly polarized light while maintaining its polarization state. After being combined by a polarization beam combiner (PBC), an unfocused dot-ring light spot is formed, and the polarization state of the dot light spot is orthogonal to the polarization state of the ring light spot.

7. The laser additive manufacturing optical system for a circularly polarized dot-ring composite spot according to claim 1, characterized in that, The beam expanding scanning focusing system integrates a beam expander, an XY scanning galvanometer, and a focusing lens group; The beam expander is used to expand the unfocused circularly polarized ring spot output by the quarter-wave plate 5. The focusing lens group is used to focus the expanded spot. The XY scanning galvanometer can swing along the XY direction to move the focused circularly polarized ring spot within the working plane.

8. The laser additive manufacturing optical system for a circularly polarized dot-ring composite spot according to claim 1, characterized in that, By adjusting the distance between axial conical mirror 1 and axial conical mirror 2, the width of the annular spot can be continuously adjusted within the range of 70-150μm, and the outer ring diameter of the annular spot can be continuously adjusted within the range of 180-330μm.

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