Coaxial composite light spot heat source regulation and control system and method for metal additive manufacturing

Abstract

The invention relates to the field of metal additive manufacturing, and discloses a coaxial composite light spot heat source regulation and control system and method for metal additive manufacturing, and the system comprises a main melting laser used for generating a main melting laser beam; the VCSEL heating laser module is used for coaxially overlapping the main melting laser beam and the annular heating laser beam in space and can form a composite light spot on the surface of the workpiece, and the composite light spot comprises a central high-energy melting area and a peripheral annular heating area; the scanning execution module is used for driving the composite light spot to synchronously move along a preset scanning path; and the control module is used for controlling the power of the main melting laser and the power of each VCSEL array of the VCSEL heating laser module according to the scanning path and the process parameters. The method is particularly suitable for LPBF forming of materials such as high-temperature alloy sensitive to residual stress, nickel-based alloy difficult to weld, titanium alloy and the like and large-size, thick-wall and complex geometric structural parts.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing, and in particular to a coaxial composite spot heat source control system and method for metal additive manufacturing. Background Technology

[0002] With the increasing demand for high-performance complex metal components in aerospace, gas turbine, and mold manufacturing industries, LPBF (Layer-by-Layer Blasting) has become one of the most widely used processes in metal additive manufacturing due to its ability to fabricate thin-walled structures, complex internal flow channels, topology-optimized support structures, and large-size integrated components. LPBF achieves layer-by-layer stacking by melting and solidifying metal powder point-by-point using a high-power laser. Because of the high power density, concentrated energy, and small spot size of the main melting laser, the temperature at the center of the molten pool can instantly reach the material's melting point or even the overheated zone, while the edges and surrounding unmelted areas remain at significantly lower temperatures. This localized extreme temperature gradient leads to the following typical problems: 1. Intense and uneven thermal shrinkage occurs during the melting / solidification process, resulting in high residual stress; 2. Inducing thermal cracks in high-temperature alloys with high hardness or high γ' content, difficult-to-weld nickel-based alloys, Ti alloys, and other materials; 3. Causes warping, edge collapse, and dimensional shifts in large-area scanning or thick-walled areas; 4. Molten pool splashing and powder bounce affect surface quality and density.

[0003] Similar high thermal gradient problems also exist in other metal laser additive manufacturing processes such as directional energy deposition, especially in the deposition of large-size components and the remanufacturing and repair of complex surfaces, which can easily cause significant residual stress concentration and macroscopic deformation.

[0004] Traditional thermal management approaches mainly include: overall platform heating, forming cavity heating, scanning strategy optimization, and reducing single-cycle energy input, but these methods have inherent limitations: 1. Overall heating can only uniformly raise the temperature of the entire field, and cannot provide directional heating to the "peripheral ring" of the molten pool within the same time window during the formation of the molten pool; 2. Existing coaxial auxiliary heating is usually collinear with the main melting laser, but it still exhibits single-point heating or linear tail-following heating, and cannot establish a stable and continuous medium temperature field in the circumferential direction of the molten pool.

[0005] 3. At the moment of melting, the temperature difference between the center of the molten pool and its boundary is still very large, the radial temperature gradient is still steep, and the cooling is still a strong contraction field of "extremely hot at the center and extremely cold at the edge".

[0006] In summary, existing technologies are unable to actively smooth out the transient temperature gradient inside and around the molten pool at the critical moment of melting, and in particular, they cannot meet the stringent requirements for residual stress and shape stability of easily deformable components such as thin-walled, complex, and large-sized components.

[0007] Therefore, there is an urgent need for a composite beam scheme that is fully coaxially coupled with the main melting laser beam during the scanning process. This would allow the high-power main beam to be responsible for melting the powder in the central region at the same spot location, while a ring-shaped, relatively low-power heating energy field would surround and stabilize the surrounding area of ​​the molten pool. This would enable simultaneous melting and local thermal management, thereby suppressing residual stress and component deformation at the source. Summary of the Invention

[0008] The main objective of this invention is to solve the technical problem that existing technologies cannot meet the stringent requirements for residual stress and shape stability in easily deformable components such as thin-walled, complex, and large-sized parts. A coaxial composite spot heat source control system for metal additive manufacturing includes: The main melting laser is used to generate the main melting laser beam. VCSEL heating laser module, comprising multiple independently addressable VCSEL arrays for outputting a ring-shaped heating laser beam; A beam coupling module is used to coaxially superimpose the main melting laser beam and the ring heating laser beam in space to form a composite spot on the surface of the workpiece. The composite spot includes a central high-energy melting zone and an outer ring heating zone. The scanning execution module is used to drive the composite light spot to move synchronously along a preset scanning path; The control module, connected to the main melting laser and the VCSEL heating laser module, is used to control the power of the main melting laser according to the scanning path and process parameters, and to independently control each VCSEL array of the VCSEL heating laser module. It generates and updates the illumination matrix of the peripheral heating zone to selectively illuminate one or more VCSEL sub-arrays / chips and allocate power, thereby adjusting the effective heating coverage pattern and range of the peripheral heating zone. It also performs closed-loop control of the temperature of the peripheral heating zone to maintain it at the target temperature. Within the corresponding allowable range, the coverage shape and coverage area of ​​the peripheral heating zone are adjustable and the temperature is controllable.

[0009] This invention also provides a method for controlling the heat source of a coaxial composite laser spot suitable for metal laser additive manufacturing, the method comprising the following steps: It provides a main melting laser beam and a ring heating laser beam output from multiple independently addressable VCSEL arrays; The main melting laser beam and the ring heating laser beam are coaxially superimposed in space by beam coupling to form a composite spot on the workpiece surface. The composite spot includes a central high-energy melting zone and an outer ring heating zone. Drive the composite light spot to move synchronously along the preset scanning path; During the scanning process, the power of the main melting laser beam is controlled so that the central high-energy melting zone melts the metal powder to form a molten pool; simultaneously... Based on the scanning path and process parameters, the power distribution of the multiple VCSEL arrays is independently controlled, so that the outer annular heating zone synchronously heats the edge, semi-melted zone and solidified zone of the molten pool, thereby directly reducing the radial temperature gradient of the molten pool and suppressing residual stress and hot cracks.

[0010] The present invention has the following beneficial effects: (1) Adjustable effective coverage area of ​​the annular heating zone: By configuring and updating the lighting matrix of the VCSEL array, selective start-up and shutdown, power allocation and sector allocation of the VCSEL subarray / chip can be realized, thereby adjusting the effective heating coverage shape and coverage range of the outer annular heating zone (including the radial range and azimuth range of the coverage area); in some embodiments, the beam shape can also be adjusted by the annular beam shaping component to further expand the adjustability of the coverage range, thereby enabling the configuration of the required effective heating coverage range for different materials and different geometric feature areas.

[0011] (2) The target temperature of the annular heating zone is adjustable and can be stabilized in a closed loop: By modulating the output power and / or PWM duty cycle of each VCSEL array (or sector) and combining it with temperature or radiation feedback to achieve closed-loop regulation, the target temperature of the annular heating zone can be stabilized. (Or radiation intensity) can be set and controlled within the set range.

[0012] (3) Coaxial composite spot achieves synchronous thermal management: the main melting laser beam and the peripheral ring heating beam are coaxially superimposed to form a composite spot, and move synchronously with the scan, so that the melting zone and the surrounding heat-affected zone can achieve coordinated heating and thermal field adjustment in the same spatial position, thereby helping to reduce the defect risk caused by radial temperature gradient and thermal stress concentration around the molten pool.

[0013] (4) Sector-based zone adjustment to achieve differentiated control of path direction: By independently setting and controlling different sectors of the annular heating zone, differentiated thermal management such as preheating of the scanning front area and slow cooling / heat preservation of the scanning tail area can be achieved, thereby improving the forming consistency of thermally sensitive areas such as start and end points, corners, thin walls and support.

[0014] (5) Reduce ghosting interference in beam combining and improve the controllability of energy action: In the implementation of coaxial beam combining using wave splitting / combining optical elements, by setting up structures such as wedge angle dichroic mirrors, the ghost beam formed by multiple reflections is deviated from the main optical axis and isolated / absorbed, thereby reducing the impact of undesired light spots on processing and monitoring, and improving system stability and repeatability.

[0015] (6) Easy to integrate and implement in engineering: VCSEL arrays have the characteristics of addressable, partitionable control and fast response speed. The control module can output control commands such as array lighting and power / duty cycle modulation based on the scanning path and process parameters, which is easy to integrate or modify with existing LPBF optomechanical systems and has good modularity and scalability.

[0016] (7) Applicable scenarios cover complex geometry and stress-sensitive materials: This invention can be used for laser powder bed melting forming of residual stress-sensitive materials (such as high-temperature alloys, nickel-based alloys, titanium alloys, etc.) and large-size, thick-walled or complex geometric components, and can be extended to deposition manufacturing and remanufacturing repair scenarios such as directional energy deposition. Attached Figure Description

[0017] Figure 1 This is a block diagram of the overall system structure of the present invention.

[0018] Figure 2 This is a schematic diagram of the beam combining optical path.

[0019] Figure 3 This is a schematic diagram of power zone control.

[0020] Figure 4 This is a schematic diagram of the spatial superposition and scanning of coaxial composite light spots.

[0021] Figure 5 This is a top-view schematic diagram of the coverage pattern of the coaxial composite light spot.

[0022] The attached figures are labeled as follows: 1. Master melting laser; 2. Collimating lens; 3. VCSEL heating laser; 4. XY galvanometer; 5. Beam coupler; 6. f-θ lens; 7. Protective window; 8. Build surface; 9. Workpiece; 10. Substrate; 11. Distributor movement direction; 12. Distributor; 13. Powder supply; 14. Powder supply hopper; 15. Piston; 16. Build stage movement direction; 17. Build stage; 18. Excess powder hopper; 19. Excess powder; 20. Atmosphere control system; 21. Electrical and / or digital signals; 22. Controller; 23. LPBF system; 24. Master laser beam; 25. VCSEL heating laser ring beam; 26. Composite spot; 27. Lateral displacement; 28. Optical trap; 29. ​​Dichroic mirror; 30. Wedge angle; 311, 312, ... 31 i VCSEL chips; 321, 322, ... 32 iVCSEL fan array laser. Detailed Implementation

[0023] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” or “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0024] For ease of understanding, the specific process of the embodiments of the present invention is described below. Please refer to [link / reference]. Figure 1 The first embodiment of the coaxial composite spot heat source control system for metal additive manufacturing in this invention includes: The main melting laser is used to generate the main melting laser beam. The VCSEL heating laser module includes multiple independently addressable VCSEL arrays for outputting a ring-shaped heating laser beam, wherein the multiple VCSEL arrays are configured to form a ring or multi-segment arc arrangement to form a ring-shaped heating area on the workpiece surface. A beam coupling module is used to coaxially superimpose the main melting laser beam and the ring heating laser beam in space to form a composite spot on the surface of the workpiece. The composite spot includes a central high-energy melting zone and an outer ring heating zone. The scanning execution module is used to drive the composite light spot to move synchronously along a preset scanning path; such as Figure 4 As shown, this is a schematic diagram of the spatial superposition and scanning of the coaxial composite spot of the present invention. The main melting laser beam and the peripheral ring heating laser beam are coaxially superimposed in space to form a composite spot, and move synchronously on the surface of the powder bed along a preset scanning path under the drive of the scanning execution module.

[0025] The control module, connected to the main melting laser and the VCSEL heating laser module, is used to control the power of the main melting laser according to the scanning path and process parameters, and to independently control each VCSEL array of the VCSEL heating laser module. It generates and updates the illumination matrix of the peripheral heating zone to selectively illuminate one or more VCSEL sub-arrays / chips and allocate power, thereby adjusting the effective heating coverage pattern and range of the peripheral heating zone. It also performs closed-loop control of the temperature of the peripheral heating zone to maintain it at the target temperature. Within the corresponding allowable range, the coverage shape and range of the peripheral heating zone are adjustable and the temperature is controllable. During the scanning process, the central high-energy melting zone is used to melt metal powder to form a molten pool, while the peripheral annular heating zone is used to simultaneously heat the edge of the molten pool, the semi-molten zone, and the just-solidified zone to reduce the radial temperature gradient and residual stress of the molten pool.

[0026] Specifically, the structure of the coaxial composite spot heat source control system for metal additive manufacturing is as follows: 1. Main melting laser 1, used to melt metal powder on a powder bed to form a molten pool; the output power of the main melting laser can typically range from hundreds of watts to kilowatts, and the focused spot diameter is in the range of tens of micrometers to hundreds of micrometers; 2. VCSEL heated laser 3, comprising multiple VCSEL fan-shaped array lasers 321, 322, ... 32 n Each sector array laser comprises multiple VCSEL chips 311, 312, ... 31 n Each VCSEL chip can be addressed and adjusted independently, and the output power of a single VCSEL chip can range from several watts to tens of watts. 3. Beam combining module 5, used to spatially coaxially couple the main melting laser beam with multiple sub-beams output from the VCSEL heating laser 3, so that the combined composite beam forms a composite spot with a central high-energy region and an outer ring heating region on the powder bed surface; 4. Scanning execution component: The galvanometer scanning head 4 drives the composite light spot to move along a predetermined scanning path; 5. Control module 22 is used to send power distribution commands, duty cycle commands, and start / stop commands to each array of VCSEL heating laser 3 in real time according to process parameters such as scanning path, scanning speed, and main melting laser power setting, so as to dynamically shape the power distribution of the annular heat field.

[0027] During operation, the central high-energy region of the main melting laser 1 is responsible for rapidly melting the powder at the target point to form a molten pool. Simultaneously, the annular or near-annular heat zone formed by the VCSEL heating laser 3 via the beam combining module 5 simultaneously irradiates the boundary region, semi-molten region, and the metal region where the wake is solidifying within the molten pool, providing controlled moderate heat input to this region. Since the central beam and the annular beam are spatially coaxial and move synchronously through the scanning execution component and the galvanometer scanning head 4, the melting behavior and the thermal gradient alignment are completed synchronously.

[0028] Formation of the thermal field of a toroidal VCSEL The VCSEL heated laser 3 can be multiple discrete VCSEL chips / arrays arranged in a ring or multiple segments of annular arc, or a planar VCSEL array shaped by microlenses / uniform plates / annular apertures to output a ring-shaped power distribution. For example... Figure 3 The diagram shows a power zoning control schematic of the annular VCSEL heating zone of the present invention. By dividing the annular heating zone into multiple sectors along the azimuth direction and independently addressing and setting the power of the VCSEL array or VCSEL subarray within each sector, differentiated thermal management such as scanning front preheating and scanning trail slow cooling can be achieved. In some embodiments, the VCSEL chips in each VCSEL subarray can also be selectively lit or have their power adjusted independently according to control requirements, thereby further improving the spatial control accuracy of the annular heating zone.

[0029] 1. The control module 22 can set the sector (0°~120° angle range) in front of the forward direction to a higher power to promote the preheating of the powder at the scanning front; 2. At the same time, the backward sector (180°~300° angle range) is set to medium power to slowly cool and keep the newly solidified metal at the molten pool tail, reduce the quenching rate, and suppress the peak value of thermal tensile stress.

[0030] like Figure 5 The diagram shows a top-view schematic of the coaxial composite beam pattern covering the powder bed surface according to the present invention. The composite beam pattern includes a high-energy-density melting zone at the center and an annular heating zone surrounding it. The annular heating zone can be divided into one or more sectors along the azimuth direction, with the sector coverage angle denoted by θ. In this invention, the coverage pattern of the outer heating zone is not limited to a continuous and complete annular structure, but can be formed by selectively lighting and discontinuous annular or sectoral patterns or combinations thereof through the selective lighting and power allocation of the VCSEL subarray / chip. The different filling textures in the figure are only used to illustrate the heating coverage pattern and spatial distribution characteristics and do not constitute a limitation on specific temperature values ​​or continuity.

[0031] In some embodiments of the present invention, the radial position of the annular heating zone can be adjusted by an optical shaping element so that it mainly covers the edge of the molten pool and the just solidified area, thereby avoiding remelting or excessive disturbance to the central molten zone, which is beneficial to maintaining the stability of the molten pool and reducing thermal stress concentration.

[0032] Beam coupling / combining methods The beam combining module 5 may include, but is not limited to: coaxial mirror group, wave splitting / combining optical elements, concentric lens group, etc.

[0033] One approach is to omit the wave-splitter / combiner mirror in the beam coupling module 5. The main melting laser, after collimation, propagates along the main optical path axis (+X direction) through the central channel of the beam coupling module 5. Multiple VCSEL emitting chips are fixed to the inner wall mounting surface of the beam coupling module 5, arranged in a ring around the main optical path axis, with their emitting surfaces facing the +X direction. The VCSEL emitted light is shaped into a ring beam parallel to the main optical path by a ring collimating / uniform optics located at the entrance of the beam coupling module 5. This ensures that at the exit end of the beam coupling module 5, the central main melting beam and the peripheral ring heating beam share the same optical aperture and are jointly incident on the XY galvanometer assembly 4 and the f-θ lens 6, thereby forming a composite light spot on the powder bed surface with a central high-power region and a ring low-power region coaxially distributed.

[0034] Another approach is to use different wavelengths for the main melting laser and the VCSEL. For example, the main melting laser could be in the near-infrared band, and the VCSEL in another near-infrared or mid-infrared band. Wavelength multiplexing is achieved through a wavelength splitter / combiner (dichroic mirror 29) located inside the beam coupling module 5, allowing the energy of different wavelengths to be focused on the same focal plane but exhibiting a central + annular spatial power distribution. In a preferred embodiment of the invention, this second wavelength multiplexing scheme is preferred. The specific structure is as follows... Figure 2 As shown: The near-infrared laser beam 24 output by the main melting laser 1 is transmitted through the dichroic plate 29 to form a central spot, and the ring beam 25 of another band output by the VCSEL heating laser 3 is reflected by the dichroic plate 29 to form an outer ring. The two are focused on the powder bed surface by the same XY galvanometer 4 and f-θ lens 6 to form a composite spot 26 with a central high-power region and an annular low-power region.

[0035] Ghosting elimination mechanism in beam coupling: In the coaxial optical path, the main melting laser beam 24 and the VCSEL ring beam 25 need to be superimposed through a wave splitter / combiner mirror 29. Even with an anti-reflection coating on the back surface of a traditional flat dichroic mirror, a small amount of secondary reflection will still occur. If the dichroic mirror is an ideal flat plate, this reflected light will be parallel to the main optical path and produce a slight lateral shift, ultimately forming a slightly offset ghost spot on the workpiece surface, leading to decreased machining accuracy or sensor misreading.

[0036] This invention completely eliminates ghosting interference through the following optical design (see...) Figure 2 ): The substrate of the wave splitter / combiner 29 is not a parallel flat plate, but is machined with a specific wedge angle α (α ≤ 0.5° in this invention). The main beam 24 enters through the front surface and exits after refraction through the rear surface. The VCSEL beam 25 is reflected by the front surface into the main optical path. Any ghost beam generated from the rear surface of the dichroic mirror will have a significant angular deviation from the principal optical axis due to the presence of the wedge angle.

[0037] Because the ghost beam has an angular deviation, it will spatially separate from the main beam after propagating a certain distance. The system has an optical trap 28 at a specific position on the side wall of the optical path. The optical trap 28 is made of a high-absorption material, such as anodized black aluminum or lined with a labyrinth-like light-absorbing structure, to physically intercept and absorb this part of the stray light that deviates from the main optical path.

[0038] Through the above beam combining, the composite spot that finally reaches the powder bed surface is not simply two separate spots, but rather a central high-power region and an annular low-power region that are highly overlapping in space.

[0039] Process control and closed-loop regulation The control module 22 performs the following steps during the scanning process: 1. Based on the preset scanning path, obtain the coordinates of the current scanning landing point and the scanning speed; 2. Set the energy input to match the main melting laser power and scanning speed to ensure stable formation of the molten pool; 3. Calculate the required target temperature distribution of the annular thermal field, and provide the target power, duty cycle, and operating sector angle for each VCSEL array; 4. Send control commands to VCSEL heating laser 3 to maintain the target heat level at the edge of the molten pool in the annular heating element; 5. Obtain the actual thermal field feedback signal from the temperature / radiation monitoring unit, compare the feedback with the target thermal field, and if overcooling or overheating is detected, adjust the VCSEL power of certain azimuth sector in real time to achieve closed-loop control.

[0040] The control module 22 acquires the current temperature around the molten pool within a preset sampling period and compares it with the target temperature. The deviation is compared, and the PWM duty cycle output of the VCSEL array is calculated using closed-loop control strategies such as PID. The PWM duty cycle (or output power) is then limited to dynamically adjust the power of the annular heating zone to keep the temperature around the molten pool stable near the set value.

[0041] The control strategy of this invention is as follows: based on the process / material library and online monitoring feedback, determine and dynamically adjust the effective heating coverage shape and coverage range of the peripheral heating zone, and adjust it in relation to the target temperature. The system is designed to adapt to the thermal management requirements of different materials and regions with different geometric features. The effective heating coverage pattern can be achieved by selectively lighting and distributing power to multiple VCSEL subarrays / chips. The resulting heating area can be a continuous or discontinuous ring, sector, or combination thereof.

[0042] (i) Process / Material Library: The control module has a built-in or external process / material library. The process / material library includes at least the following information: material type, powder characteristics, layer thickness, scanning speed, main laser power or energy density, substrate preheating temperature, and geometric category of the forming area (thin-walled, thick-walled, corner, start and end points, near support, etc.). The above information is then compared with the recommended peripheral heating zone illumination matrix, sector coverage angle θ and / or sector boundary (azimuth range), and target temperature. The correspondence between (and / or the corresponding VCSEL power limit and / or duty cycle range); wherein, the lighting matrix is ​​used to characterize the start / stop status and / or power level of each VCSEL subarray / chip.

[0043] (ii) Timing of Coverage Pattern Update: When a change in material or process parameters is detected, the scanning path enters a region of different geometric categories, continuous scanning causes a change in the thermal accumulation state, or the deviation of the monitored temperature / radiation signal relative to the target value exceeds a preset threshold (e.g., temperature deviation threshold ε and duration threshold τ), the control module triggers an update of the illumination matrix and / or the sector coverage angle θ and / or the sector boundary. Reselection or fine-tuning.

[0044] (III) Implementation of Coverage Pattern: The control module can update the illumination matrix and allocate sectors to form the required effective heating coverage pattern and coverage range; in some embodiments, the beam pattern can also be adjusted by driving the variable annular aperture, variable magnification or adjustable focus shaping component, thereby forming an outer heating coverage area on the powder bed surface that is compatible with the heat-affected zone of the molten pool edge.

[0045] (iv) Temperature controllability and closed-loop correction: After determining the lighting matrix (and the sector coverage angle θ and / or sector boundary), the control module uses... To control the target, power and / or duty cycle modulation (e.g., PWM current modulation) is applied to each VCSEL subarray / chip based on temperature and / or radiation monitoring signals to control the temperature of the peripheral heating zone. Within the corresponding allowable range; when the feedback deviation continues to exceed the limit, in addition to power adjustment, the lighting matrix and / or the sector coverage angle θ and / or sector boundary can be updated in conjunction to achieve coordinated control of the peripheral heating zone with "adjustable coverage shape + controllable temperature", thereby helping to reduce the radial temperature gradient of the molten pool and reduce residual stress.

[0046] This invention also relates to a method for controlling the heat source of a coaxial composite laser spot suitable for metal laser additive manufacturing, the method comprising the following steps: It provides a main melting laser beam and a ring heating laser beam output from multiple independently addressable VCSEL arrays; The main melting laser beam and the ring heating laser beam are coaxially superimposed in space by beam coupling to form a composite spot on the workpiece surface. The composite spot includes a central high-energy melting zone and an outer ring heating zone. Drive the composite light spot to move synchronously along the preset scanning path; During the scanning process, the power of the main melting laser beam is controlled so that the central high-energy melting zone melts the metal powder to form a molten pool. At the same time, according to the scanning path and process parameters, the power distribution of the multiple VCSEL arrays is independently controlled so that the outer annular heating zone synchronously heats the edge, semi-melted zone and solidified zone of the molten pool to directly reduce the radial temperature gradient of the molten pool, thereby suppressing residual stress and hot cracks.

[0047] In this invention, the main melting laser beam and the annular or near-annular heating light band formed by multiple VCSEL arrays are coaxially superimposed in space through the beam coupling module, forming a composite light spot of "central high-energy melting beam + peripheral annular VCSEL thermal field" on the powder bed surface, so as to realize the synchronous action of melting and temperature control at the same landing point and the same time scale.

[0048] VCSEL arrays are arranged in a ring or multi-segment arc pattern, or formed into a ring-shaped light field through optical shaping such as uniform light / ring aperture; multiple VCSEL arrays can be addressed and individually adjusted to realize multi-sector zone control of the ring thermal field in the azimuth angle of 0° to 360°, and support differentiated thermal management strategies such as forward preheating and backward slow cooling.

[0049] The combined beam is projected onto the powder bed surface through the same galvanometer or coaxial scanning optical system, ensuring that the main melting beam and the annular heating band are highly aligned in space and move synchronously as a whole during the scanning process. This forms an "in-situ, synchronous" molten pool temperature control mechanism, rather than the traditional trajectory-following heating.

[0050] The annular VCSEL thermal field covers the edge of the molten pool, the semi-molten zone, and the just-solidified zone. By controlling the radius, width, and power level of the annular zone, it directly weakens the radial temperature gradient from the center of the molten pool to the boundary at the moment of molten pool formation, reduces the quenching rate and peak thermal tensile stress in the boundary zone, and suppresses hot cracking, warping, and dimensional deviation from the source.

[0051] The control module adjusts the power distribution, duty cycle and working sector of each VCSEL array in real time based on process parameters such as scanning path, scanning speed, main melting laser power and geometric features of the forming area, so as to realize differentiated and programmable thermal management for different areas.

[0052] The system can be configured with molten pool infrared radiation monitoring, surface height difference or other temperature / radiation feedback modules to obtain real-time thermal field information of the molten pool edge and wake region; the control module makes closed-loop adjustments to the power distribution, duty cycle or ring radius of the VCSEL ring based on the feedback, so that the cooling rate of the molten pool boundary is maintained within the preset range, thereby improving process stability and forming consistency.

[0053] The beam coupling module can use main melting lasers of different wavelengths and VCSEL arrays to achieve coaxial beam combining of the central beam and the ring beam through wave splitting / combining optical elements, coaxial mirror groups or concentric lens groups, which not only ensures the spatial structure of the beam spot, but also takes into account the system integration and engineering feasibility.

[0054] This invention is particularly applicable to LPBF forming of materials such as high-temperature alloys sensitive to residual stress, difficult-to-weld nickel-based alloys, and titanium alloys, as well as large-size, thick-walled, and complex geometric components. It is also applicable to the deposition and remanufacturing repair of complex components in processes such as directional energy deposition, which uses laser as the main melting heat source and drives the deposition head to move along a three-dimensional trajectory through CNC motion axes or robots. It can significantly reduce the risk of cracks and warping while maintaining consistent density, and improve dimensional accuracy and forming success rate.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A coaxial composite spot heat source control system for metal additive manufacturing, characterized in that, The system includes: The main melting laser is used to generate the main melting laser beam. VCSEL heating laser module, comprising multiple independently addressable VCSEL arrays for outputting a ring-shaped heating laser beam; A beam coupling module is used to coaxially superimpose the main melting laser beam and the ring heating laser beam in space to form a composite spot on the surface of the workpiece. The composite spot includes a central high-energy melting zone and an outer ring heating zone. The scanning execution module is used to drive the composite light spot to move synchronously along a preset scanning path; The control module, connected to the main melting laser and the VCSEL heating laser module, is used to control the power of the main melting laser according to the scanning path and process parameters, and to independently control each VCSEL array of the VCSEL heating laser module. It generates and updates the illumination matrix of the peripheral heating zone to selectively illuminate one or more VCSEL sub-arrays / chips and allocate power, thereby adjusting the effective heating coverage pattern and range of the peripheral heating zone. It also performs closed-loop control of the temperature of the peripheral heating zone to maintain it at the target temperature. Within the corresponding allowable range, the coverage shape and coverage area of ​​the peripheral heating zone are adjustable and the temperature is controllable.

2. The coaxial composite spot heat source control system for metal additive manufacturing according to claim 1, characterized in that, The multiple VCSEL arrays are configured to form a ring or a multi-segment ring arc arrangement.

3. The coaxial composite spot heat source control system for metal additive manufacturing according to claim 1, characterized in that, The VCSEL array is a planar VCSEL array, which outputs a heating laser beam with a ring-shaped power distribution after being shaped.

4. The coaxial composite spot heat source control system for metal additive manufacturing according to claim 1, characterized in that, The control module sets a power for the sector ahead in the forward direction to promote early heating of the powder at the scanning front; and sets a power for the sector behind in the forward direction to slowly cool and keep the newly solidified metal at the molten pool tail.

5. The coaxial composite spot heat source control system for metal additive manufacturing according to claim 1, characterized in that, The beam combining module includes a central channel and multiple VCSEL array lasers arranged in a ring. The main melting laser beam is collimated and propagates through the central channel along the main optical path axis. The emitting surfaces of the VCSEL array lasers face the direction of the main optical path axis, and the emitted light is formed into a ring beam parallel to the main optical path by a ring collimating / uniform optical element disposed at the entrance of the beam combining module. This allows the main melting laser beam and the ring beam to share the same optical aperture and be incident together on the scanning execution component at the output end of the beam combining module.

6. The coaxial composite spot heat source control system for metal additive manufacturing according to claim 1, characterized in that, The beam combining module includes a wave splitter / combiner. The main melting laser outputs a laser beam of a first wavelength, and the VCSEL heating laser outputs a ring beam of a second wavelength. The wave splitter / combiner is configured to transmit the laser beam of the first wavelength and reflect the ring beam of the second wavelength, so that the laser beam of the first wavelength forms a central high-power region, and the ring beam of the second wavelength forms an outer ring. The two beams are combined into a composite spot on the powder bed surface through the same focusing optical system.

7. A method for controlling the heat source of a coaxial composite laser spot suitable for metal laser additive manufacturing, characterized in that, The method includes the following steps: It provides a main melting laser beam and a ring heating laser beam output from multiple independently addressable VCSEL arrays; The main melting laser beam and the ring heating laser beam are coaxially superimposed in space by a beam coupling module to form a composite spot on the workpiece surface. The composite spot includes a central high-energy melting zone and an outer ring heating zone. Drive the composite light spot to move synchronously along the preset scanning path; During the scanning process, the power of the main melting laser beam is controlled so that the central high-energy melting zone melts the metal powder to form a molten pool; simultaneously... Based on the scanning path and process parameters, the power distribution of the multiple VCSEL arrays is independently controlled, so that the outer annular heating zone synchronously heats the edge, semi-melted zone and solidified zone of the molten pool, thereby directly reducing the radial temperature gradient of the molten pool and suppressing residual stress and hot cracks.

8. The coaxial composite spot heat source control system for metal additive manufacturing according to claims 1-6 is applied to LPBF forming of high-temperature alloys, nickel-based alloys, titanium alloys, and other difficult-to-form materials and large-size / thick-walled components.

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