A method for constructing dual-mode coherent synthesis laser and an additive manufacturing method

Abstract

The present invention relates to a method for constructing a dual-mode coherent synthesis laser and an additive manufacturing method, comprising: generating and synchronizing a pulse seed laser and a continuous seed laser; obtaining a pulse laser and a continuous laser; S3, synchronizing the phases of the pulse laser and the continuous laser to reach a phase-locked state, and then combining the beams to form a coherent synthesis laser; S4, performing phase compensation and optical path difference adjustment on the coherent synthesis laser to obtain a high-quality coherent synthesis laser; S5, shaping the coherent synthesis laser and the auxiliary oscillator laser into a flat-top beam, which is then further shaped into a flat-top ring coherent synthesis laser and a flat-top ring oscillator laser, wherein the flat-top ring oscillator laser can be switched between coaxial and paraxial. The method combines the advantages of stable continuous laser energy output with the advantages of a small heat-affected zone and low reflection of a pulsed laser, and has high precision and high efficiency in the additive manufacturing process, excellent mechanical properties of parts at the macro level, and uniform part structure at the micro level.

Description

Technical Field

[0001] The present invention relates to the field of additive manufacturing technology, and specifically to a method for constructing a dual-mode coherent synthesis laser and an additive manufacturing method, which are suitable for rapid prototyping of high-precision complex metal structures. Background Art

[0002] With the rapid development of high-end manufacturing industries such as aerospace, automotive, and energy, the requirements for component performance and manufacturing precision are constantly increasing. Traditional manufacturing processes often face problems such as severe material waste, long processing cycles, and difficulty in achieving integrated manufacturing of complex structures when manufacturing complex shapes and high-performance components.

[0003] Since its emergence in the 1980s, additive manufacturing (AM), a layer-by-layer approach to component fabrication, has fundamentally changed the traditional concept of subtractive manufacturing. It can rapidly produce complex parts directly from 3D models, significantly shortening product development cycles, improving material utilization, and reducing production costs. However, early AM technologies struggled to meet the demands of high-end sectors like aerospace for large, high-performance metal parts.

[0004] In order to solve the problem of additive manufacturing of large metal parts, coaxial laser additive manufacturing technology has gradually developed. The coaxial powder / wire feeding process is to feed the metal powder / wire into the molten pool along the axis of the laser beam through a powder / wire feeding device. The laser beam melts the powder / wire and fuses it with the matrix material to achieve layer-by-layer accumulation of the material. This process has the advantages of fast powder / wire feeding speed, high material utilization rate, and the ability to manufacture large and complex parts. It can effectively meet the manufacturing needs of large metal structures in the fields of aerospace, shipbuilding, energy, etc., and has become a research hotspot and development direction in the field of laser additive manufacturing in recent years. At present, the coaxial powder / wire feeding laser additive manufacturing technology has the following technical bottlenecks:

[0005] 1. Coaxial powder / filament feeding technology: Current mainstream coaxial powder / filament feeding systems mostly utilize an external-beam feeding mode, using a Gaussian laser as the energy source. This has the characteristics of a large energy distribution gradient and concentrated energy at the center of the beam spot, which can easily cause metal spatter. Existing internal-beam feeding modes, such as multi-beam converging or fixed annular spot designs (e.g., CN112584962A), still suffer from drawbacks such as sensitive beam-filament coupling accuracy (±0.1 mm tolerance).

[0006] 2. Laser Heat Source Mode: Single-mode lasers (continuous or pulsed) struggle to balance melt pool heat input stability with grain refinement requirements, and the matching relationship between laser energy input and powder / wire feed speed is complex. When laser energy is too high and powder / wire feed speed is too slow, the melt pool temperature rises too high, easily leading to excessive metal evaporation and the formation of pores. Conversely, when laser energy is insufficient and powder / wire feed speed is too fast, the powder / wire material cannot be fully melted, resulting in incomplete fusion defects.

[0007] 3. Material compatibility limitations: Although coaxial powder / wire laser additive manufacturing can use a variety of metal powders / wires, there are still limitations in terms of material compatibility. For example, for materials such as aluminum alloys that have high reflectivity to infrared lasers (reflectivity can reach up to 90%), using expensive blue or green lasers will significantly increase costs.

[0008] 4. Auxiliary light source application: Existing oscillation auxiliary lasers mostly use a single path (such as linear or circular), lack dynamic control capabilities, and generally do not have the ability to switch between side-axis / coaxial, and their functions are relatively simple.

[0009] In order to solve the technical bottleneck of coaxial laser additive manufacturing technology and realize the rapid prototyping of high-precision complex metal components, it is necessary to invent an additive manufacturing method that combines continuous / pulsed dual-mode laser coherent synthesis, annular flat-top laser shaping and multi-degree-of-freedom oscillation auxiliary light source. Summary of the Invention

[0010] The purpose of the present invention is to provide a method for constructing a dual-mode coherent synthesis laser and an additive manufacturing method to solve the bottleneck problems of traditional laser additive manufacturing technology using a single-mode laser as an energy source, such as a large heat-affected zone, low processing efficiency, low processing accuracy, and easy generation of component segregation.

[0011] To achieve the above object, the present invention provides the following technical solution: a method for constructing a dual-mode coherent synthesis laser, the method comprising the following steps in sequence:

[0012] S1. Generation and synchronization of seed sources: generating a pulse seed source and a continuous seed source. The pulse seed source is processed to generate a pulse seed laser, and the continuous seed source is processed to generate a continuous seed laser.

[0013] S2. Laser beam splitting and amplification: Pulse seed laser becomes pulse laser after beam splitting and amplification, and continuous seed laser becomes continuous laser after beam splitting and amplification;

[0014] S3. Laser phase locking and synthesis: The pulsed laser and continuous laser phases are synchronized to reach a phase-locked state and then combined to form a coherent synthetic laser.

[0015] S4. Coherent laser output optimization and monitoring: Phase compensation and optical path difference adjustment of the coherent laser are performed to obtain high-quality coherent laser.

[0016] S5. Beam shaping and coupling: The coherent synthesized laser and the auxiliary oscillation laser obtained in step 4 are subjected to spatial energy reconstruction by a flat-top beam shaping unit to form a flat-top beam. The flat-top beam is then subjected to a ring beam shaping unit to form a flat-top ring coherent synthesized laser and a flat-top ring oscillation laser. The flat-top ring oscillation laser can be switched to a coaxial oscillation laser or a side-axis oscillation laser, and real-time path switching can be achieved.

[0017] Preferably, the pulse seed source in step 1 is processed by mode locking technology and modulation to form a pulse seed laser, and the continuous seed source in step 1 is processed by frequency stabilization technology to form a continuous seed laser.

[0018] Preferably, the pulse seed laser and the continuous seed laser in step 2 are split by a polarization beam splitter and amplified by an amplifier chain, and the pulse seed laser needs to be additionally amplified by chirped pulses.

[0019] Preferably, the pulse laser and the continuous laser in step 3 are phase-locked by active phase-locking technology or passive phase-locking technology, and the pulse laser and the continuous laser are phase-locked and combined by a polarization beam combiner.

[0020] Preferably, the coherent synthesis laser in step 4 is transmitted through a wavefront sensor and M 2 The factor meter performs phase compensation and optical path difference adjustment to achieve output optimization and monitoring of coherent synthesized laser.

[0021] Preferably, the wavelength of the continuous laser in step 3 is 1060-1080 nm, the power is 1-6 kW, the wavelength of the pulsed laser is 1030-1070 nm, the peak power is 10 7 -10 8 W / cm 2 , the pulse width is 10-100 ns, and the coherent synthesis laser power fluctuation is ≤±1.5%. The proportion of continuous laser and pulsed laser in the coherent synthesis laser is adjustable to match different materials. For example, high-reflectivity materials such as aluminum alloy need to increase the proportion of pulsed laser, while low-reflectivity materials such as steel can reduce the proportion of pulsed laser.

[0022] Preferably, the flat-top annular coherent synthesis laser spot diameter in step 5 is adjustable from 2 to 8 mm, with energy uniformity ≥ 95%. Real-time correction of spot distortion using Zernike polynomials is employed, adapting to ±90° tilted wire / powder feeding, and achieving a material utilization rate of nearly 100%.

[0023] The present invention also includes an additive manufacturing method based on the dual-modal coherent synthesis laser, wherein the metal wire / powder is transported into the interior of the laser head through a wire feeding / powder mechanism, and is coaxial with the flat-top annular coherent synthesis laser. The metal wire / powder is melted under the action of the flat-top annular coherent synthesis laser to form a molten pool, and a weld is formed after the molten pool solidifies. The method continues to run according to a predetermined trajectory to finally complete the additive manufacturing of the part; during the additive process, the auxiliary oscillation laser is adjusted to a paraxial oscillation laser or a coaxial oscillation laser in real time based on the molten pool monitoring data, and the path of the auxiliary oscillation laser is dynamically adjusted. The coaxial mode is mainly used for stirring the center of the molten pool, and the paraxial mode is mainly used for balancing the edge temperature field and precisely shaping complex contours.

[0024] Preferably, the wire / powder feeding mechanism supports wire / powder feeding switching or coordinated feeding of wire and powder, the wire diameter is 0.8-1.6 mm, the powder diameter is 50-200 μm, and the powder is spherical powder.

[0025] Preferably, the path of the auxiliary oscillation laser can be dynamically adjusted by a galvanometer, and the path includes linear, circular, figure-8, or infinity oscillation, with a frequency of 10-500 Hz and an amplitude of 0.3-3 mm.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention uses continuous laser and pulsed laser for coherent synthesis, and uses the coherent synthesized laser as an energy source for additive manufacturing. The coherent synthesized laser can combine the advantages of continuous laser (continuous and stable heat input, high beam quality, etc.) and the advantages of pulsed laser (small heat-affected zone, easy grain refinement, and ability to process high-reflectivity materials, etc.), and has the advantages of high peak power density, good beam quality, and stable transmission compared to independent continuous laser and composite pulsed laser.

[0028] (2) The present invention adopts annular flat-top laser shaping technology (integrating a free-form surface lens group and a diffractive optical element), which can make the energy distribution of the laser present a uniform annular shape. Compared with the energy distribution characteristics of Gaussian laser with high center and low edge, it can significantly reduce the temperature gradient of the molten pool, optimize the macroscopic morphology of the weld, and reduce the microscopic segregation and residual stress after the molten pool solidifies. Furthermore, the spatial reorganization of energy can also avoid metal vaporization and molten pool splashing caused by excessive center energy.

[0029] (3) The present invention uses oscillating laser as an auxiliary laser-assisted additive process. The oscillating laser can promote bubble overflow through high-frequency stirring to reduce porosity, while promoting the transformation from columnar crystals to equiaxed crystals and weakening the texture, ultimately improving the surface quality and mechanical properties of the parts.

[0030] (4) The present invention realizes linear / circular / figure-8 / ∞-shaped laser oscillation through a galvanometer system, and can automatically switch the laser oscillation mode (coaxial mode or paraxial mode) based on the molten pool monitoring data. It has the advantages of coaxial laser, which is omnidirectional and has no restrictions, and has a low forming porosity, and the advantage of paraxial laser, which can accurately adjust the incident angle, power and scanning path, and can accurately shape complex contours without affecting the already formed parts.

[0031] (5) The present invention has strong material adaptability. The present invention can freely adjust the proportion of continuous laser, pulsed laser and oscillating laser, so it can be applied to the processing of different types of materials (such as high-reflectivity materials such as aluminum and copper and low-reflectivity materials such as steel and titanium).

[0032] (6) The process of the present invention has strong scalability. The present invention does not limit the physical state of the material and is also applicable to powder material additive manufacturing and silk powder collaborative additive manufacturing. The control quality of the present invention depends on the accuracy of the monitoring system and the control algorithm. Artificial intelligence (Ai) can be used to assist in real-time control of the laser process parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a general flow chart of the additive manufacturing method of the present invention;

[0034] Figure 2 This is a flow chart of the dual-mode laser coherent synthesis of the present invention;

[0035] Figure 3 Schematic diagram of dual-mode laser coherent combination in an embodiment of the present invention;

[0036] Figure 4 Schematic diagram of dual-mode laser coherent combining and dynamic oscillation-assisted additive manufacturing in an embodiment of the present invention;

[0037] Figure labels: 1. Additive substrate; 2. Coherently synthesized laser pulse laser component; 3. Coherently synthesized laser continuous laser component; 4. Coaxial flat-top ring oscillator laser; 5. Side-axis flat-top ring oscillator laser; 6. Controller; 7. Metal wire. DETAILED DESCRIPTION

[0038] In order to clearly and completely describe the objectives and technical solutions of the present invention and make the advantages more clearly understood, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are part of the embodiments of the present invention, not all of them, and are only used to explain the embodiments of the present invention, not to limit the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example

[0039] See also Figures 1 to 4 The additive manufacturing method of this embodiment includes the following steps:

[0040] 1. Additive pre-processing:

[0041] Based on the structural characteristics of the parts to be additively manufactured, a typical structural division is performed on them, and the additive manufacturing path is accurately planned. Subsequently, the program is input into the controller 6 to ensure that subsequent processing operations can be carried out smoothly and efficiently. The additive substrate 1 that carries the additively manufactured parts is surface treated. The specific treatment method is: first polish its surface to ensure it is flat and smooth, and then use a shot peening process to increase its surface roughness to improve the absorption rate of the additive substrate 1 for the laser. After shot peening, clean it with acetone to remove surface dirt. Then place the additive substrate 1 in a preheating device, preheat it to 400°C and maintain this temperature throughout the subsequent processing process.

[0042] 2. Constructing dual-mode coherent synthesis laser

[0043] like Figure 1 、 2 As shown, the method for constructing dual-mode coherent synthesis laser includes the following steps in sequence:

[0044] S2.1. Seed Source Generation and Synchronization: Simultaneously activate the first and second laser generators, generating a pulsed seed source within the first laser generator and a continuous seed source within the second laser generator. The pulsed seed source undergoes mode locking and modulation to form a pulsed seed laser, while the continuous seed source undergoes frequency stabilization to form a continuous seed laser.

[0045] S2.2, Laser beam splitting and amplification:

[0046] After passing through a polarization beam splitter, the pulsed seed laser is separated according to its polarization state. Subsequently, chirped pulse amplification technology is used to stretch the initial low-energy, ultrashort laser pulses, increasing their pulse width and temporally dispersing their energy. This stretched pulse is then amplified to a high energy level through an amplifier chain. Finally, a compressor compresses the amplified pulses, converting them back into pulsed laser light with a significantly increased peak power.

[0047] The continuous seed laser is also separated according to its polarization state after passing through a polarization beam splitter, and then the continuous seed laser is amplified to a high energy level using an amplifier chain, finally forming a high-energy continuous laser.

[0048] S2.3. Laser Phase Locking and Synthesis:

[0049] The first method is active phase-locking. A high-precision phase modulator is set up. Based on a feedback control signal, the phase modulator precisely controls the phase of the pulsed laser to match the phase of the continuous laser. The second method is passive phase-locking. The pulsed laser and the continuous laser are introduced into a shared resonant cavity. Special components such as nonlinear optical crystals within the cavity trigger a unique optical effect. Under the influence of this nonlinear effect, the two types of light interact, which can change the phase characteristics of the laser and gradually and spontaneously synchronize the phases of the pulsed laser and the continuous laser.

[0050] After reaching the phase-locked state, a polarization beam combiner is used to combine the phase-adjusted pulsed laser and continuous laser into the same optical path to form a coherently combined laser pulse laser component 2 and a coherently combined laser continuous laser component 3, ultimately achieving coherent combination.

[0051] The wavelength of the continuous laser in step 2.3 is 1060-1080 nm, the power is 1-6 kW, the wavelength of the pulsed laser is 1030-1070 nm, the peak power is 10 7 -10 8 W / cm 2 , the pulse width is 10-100ns, and the coherent synthesis laser power fluctuation is ≤±1.5%. The proportion of continuous laser and pulsed laser in the coherent synthesis laser is adjustable to match different materials. For example, high-reflectivity materials such as aluminum alloy need to increase the proportion of pulsed laser, while low-reflectivity materials such as steel can reduce the proportion of pulsed laser.

[0052] S2.4. Coherent laser output optimization and monitoring:

[0053] The wavefront sensor monitors the synthesized laser wavefront in real time, acquiring distortion information. Using adaptive optical elements such as deformable mirrors, it then corrects the distortion in real time, smoothing the wavefront and improving beam quality. The M2 factor meter measures the divergence characteristics of the coherently synthesized laser. By adjusting the position of components within the resonant cavity, optimizing the optical medium properties, and changing the laser injection parameters, the laser divergence angle is reduced, the energy is concentrated, and long-distance transmission stability and focusing capability are enhanced. This optimizes the coherently synthesized laser and produces high-quality coherently synthesized laser light.

[0054] S2.5 Beam Shaping and Coupling

[0055] The coherently combined laser and the auxiliary oscillator laser (the galvanometer required to achieve the oscillation laser is installed in the laser head; this is actually a continuous laser, but to distinguish it from the continuous laser within the coherently combined laser, it is simply referred to as an oscillator laser) pass through a flattened beam shaping unit for spatial energy reconstruction, forming a flattened beam. The shaped flattened beam then passes through a ring beam shaping unit to form a flattened annular coherently combined laser (primary light source) and a flattened annular oscillator laser (auxiliary light source). Under the control of a controller 6, the flattened annular oscillator laser can be switched between coaxial flattened annular oscillator laser 4 and paraxial flattened annular oscillator laser 5, with real-time switching of the path (linear, circular, figure-of-eight, or infinity oscillation). The flattened annular coherently combined laser has an adjustable spot diameter of 2-8 mm and energy uniformity of ≥95%. Spot distortion is corrected in real time using Zernike polynomials, accommodating ±90° tilted wire / powder feeding, achieving nearly 100% material utilization.

[0056] 3. Additive process

[0057] like Figure 4 As shown, this embodiment uses coaxial wire feeding additive manufacturing as an example. The wire feeder feeds a metal wire 7 into a collimating mechanism for straightening, and then feeds it into the laser head, where it is coaxial with the flat-top ring coherent synthesis laser. Under the action of the flat-top ring coherent synthesis laser, the metal wire 7 melts and forms a molten pool on the surface of the additive substrate 1. Assisted by the coaxial flat-top ring oscillator laser, the molten pool undergoes vigorous agitation, accelerating the escape of gases within the molten pool and reducing the formation of pores. Furthermore, the agitation of the molten pool fragments dendrite arms at the solidification front to a certain extent, increasing the nucleation rate and thus refining the grain size. When specific areas of a part require refinement, such as secondary remelting of a localized surface to improve surface quality or adding additional material to a specific location to enhance structural strength, the controller 6 switches the auxiliary oscillator laser to paraxial mode. By precisely adjusting the incident angle, power, and scanning path of the paraxial flat-top ring oscillator laser 5, complex contours can be precisely shaped without affecting the already formed parts. Finally, the above process is repeated according to the predetermined trajectory to complete the additive process of the entire part.

[0058] Furthermore, the wire / powder feed mechanism supports switching between wire and powder feeding or coordinated feeding of wire and powder. Wire diameters range from 0.8-1.6mm, and powder diameters from 50-200μm, with spherical powders. A galvanometer allows dynamic adjustment of the auxiliary laser oscillation path, including linear, circular, figure-eight, or infinity oscillations with frequencies of 10-500Hz and amplitudes of 0.3-3mm. Real-time dynamic monitoring utilizes a PID algorithm to dynamically adjust laser power (response time <10ms) and wire feed speed (accuracy ≥0.1m / min).

[0059] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. An additive manufacturing method based on dual-mode coherent synthesis laser, characterized in that: The method comprises the following steps: a metal wire / powder is fed into a laser head through a wire / powder feeding mechanism, and is coaxial with a flat-top annular coherent synthesis laser. The metal wire / powder is melted by the flat-top annular coherent synthesis laser to form a molten pool. The molten pool solidifies to form a weld bead, and the weld bead is continuously operated along a predetermined trajectory to ultimately complete additive manufacturing of the part. During the additive manufacturing process, the auxiliary oscillation laser is adjusted in real time to a paraxial oscillation laser or a coaxial oscillation laser based on molten pool monitoring data, and the path of the auxiliary oscillation laser is dynamically adjusted. The coaxial mode is mainly used for stirring the center of the molten pool, and the paraxial mode is mainly used for balancing the temperature field at the edge and accurately shaping complex contours. The method for constructing the dual-mode coherent synthesis laser comprises the following steps in sequence: S1. Generation and synchronization of seed sources: generating a pulse seed source and a continuous seed source. The pulse seed source is processed to generate a pulse seed laser, and the continuous seed source is processed to generate a continuous seed laser. S2. Laser beam splitting and amplification: Pulse seed laser becomes pulse laser after beam splitting and amplification, and continuous seed laser becomes continuous laser after beam splitting and amplification; S3. Laser phase locking and synthesis: The pulsed laser and continuous laser phases are synchronized to reach a phase-locked state and then combined to form a coherent synthetic laser. S4. Coherent laser output optimization and monitoring: Phase compensation and optical path difference adjustment of the coherent laser are performed to obtain high-quality coherent laser. S5. Beam shaping and coupling: The coherent synthesized laser and the auxiliary oscillation laser obtained in step 4 are subjected to spatial energy reconstruction by a flat-top beam shaping unit to form a flat-top beam. The flat-top beam is then subjected to a ring beam shaping unit to form a flat-top ring coherent synthesized laser and a flat-top ring oscillation laser. The flat-top ring oscillation laser can be switched to a coaxial oscillation laser or a side-axis oscillation laser, and real-time path switching can be achieved.

2. The additive manufacturing method according to claim 1, wherein: The wire / powder feeding mechanism supports wire / powder feeding switching or coordinated feeding of wire and powder. The wire diameter is 0.8-1.6 mm, the powder diameter is 50-200 μm, and the powder is spherical powder.

3. The additive manufacturing method according to claim 1, wherein: The path of the auxiliary oscillation laser can be dynamically adjusted by the galvanometer. The path includes linear, circular, figure 8, or ∞ oscillation, with a frequency of 10-500Hz and an amplitude of 0.3-3mm.

4. The additive manufacturing method according to claim 1, wherein: The pulse seed source in step 1 is processed by mode locking technology and modulation to form a pulse seed laser, and the continuous seed source in step 1 is processed by frequency stabilization technology to form a continuous seed laser.

5. The additive manufacturing method according to claim 1, wherein: In step 2, the pulse seed laser and the continuous seed laser are split by a polarization beam splitter and amplified by an amplifier chain. The pulse seed laser needs to be additionally amplified by chirped pulses.

6. The additive manufacturing method according to claim 1, wherein: In step 3, the pulse laser and the continuous laser are phase-locked by active phase-locking technology or passive phase-locking technology, and the pulse laser and the continuous laser are phase-locked and combined by a polarization beam combiner.

7. The additive manufacturing method according to claim 1, wherein: The coherent synthesis laser in step 4 passes through the wavefront sensor and M 2 The factor meter performs phase compensation and optical path difference adjustment to achieve output optimization and monitoring of coherent synthesized laser.

8. The additive manufacturing method according to claim 1, wherein: The wavelength of the continuous laser in step 3 is 1060-1080 nm, the power is 1-6 kW, the wavelength of the pulsed laser is 1030-1070 nm, and the peak power is 107-108 W / cm 2 , the pulse width is 10-100ns, the coherent synthesis laser power fluctuation is ≤±1.5%, and the proportion of continuous laser and pulsed laser in the coherent synthesis laser is adjustable to match different materials.

9. The additive manufacturing method according to claim 1, wherein: The flat-top annular coherent synthesis laser spot diameter described in step 5 is adjustable from 2 to 8 mm, and the energy uniformity is ≥95%.

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