A composite fiber laser for laser welding

Abstract

The application discloses a composite fiber laser for laser welding and belongs to the technical field of fiber lasers, which comprises a shell and an optical chamber in the shell, the center of the optical chamber is provided with a fiber winding area, the input end of the fiber winding area is provided with a seed source, the output end is provided with an output connector, a high-reflection grating, a low-reflection grating, an isolator, a pre-amplification stage, a pump beam combiner, a main amplification stage, a cladding light stripper and an optical forging module are sequentially arranged between the seed source and the output connector. By arranging the optical forging module, the fundamental mode laser can be converted into a vortex beam carrying orbital angular momentum by using an acoustic-induced grating, active regulation of the molten pool flow is realized to improve the welding quality, and the vortex light proportion and the topological charge number can be adjusted in real time according to the welding process requirements, so that the output laser beam can match the heat input and stirring intensity required by welding, and the welding requirements of different materials and working conditions can be met.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and more particularly to a composite fiber laser for laser welding. Background Technology

[0002] Laser welding, as a high-precision joining technology, is widely used in fields such as automobile manufacturing. It has advantages such as small heat-affected zone, fast welding speed, and small deformation. Existing fiber lasers mostly output a Gaussian beam in the fundamental mode. In most cases, the output laser beam relies solely on the laser thermal effect to melt and weld the metal material. The weld pool is driven only by natural forces such as thermocapillary force and buoyancy. The internal liquid metal flow is turbulent and the heat and mass transfer efficiency is low, which easily leads to defects such as pores, cracks, and inclusions in the weld. This results in coarse grains and uneven structure in the final weld, and the weld density is difficult to meet the stringent requirements of high-end equipment.

[0003] Furthermore, some existing equipment employs external auxiliary control methods, such as external magnetic field stirring, mechanical oscillation welding torches, and mechanical beam oscillation. It is further pointed out that magnetic fields are easily affected by the welding environment and workpiece material, making precise control of the stirring intensity difficult, and the magnetic field penetration depth is limited, failing to achieve uniform stirring throughout the molten pool. Mechanical oscillation and beam oscillation devices increase the size and weight of the welding head, making it difficult to perform high-frequency dynamic control and easily causing beam deviation.

[0004] Therefore, this invention proposes a composite fiber laser for laser welding to solve the existing problems. Summary of the Invention

[0005] Purpose of the invention: To address the problem that existing fiber lasers can only output a fundamental Gaussian beam, which is insufficient to meet the requirements of high-end precision welding, this invention aims to provide a composite fiber laser for laser welding.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A composite fiber laser for laser welding includes a housing, an optical chamber inside the housing, a fiber winding area at the center of the optical chamber, a seed source at the input end of the fiber winding area, an output connector at the output end of the fiber winding area, and a high-reflection grating, a low-reflection grating, an isolator, a pre-amplification stage, a pump combiner, a main amplification stage, a cladding stripper, and an optical forging module arranged sequentially between the seed source and the output connector, with the above components connected by optical fibers; The optical forging module includes a housing, and inside the housing, from the input end to the output end, there are sequentially arranged a long-period grating, a polarization controller, an acoustic grating, and a graded refractive index optical fiber. The acousto-optic grating converts the incident fundamental mode laser into a vortex beam carrying orbital angular momentum. It includes a ring-core fiber, an aluminum cone below the ring-core fiber, a piezoelectric ceramic actuator and a drive module below the aluminum cone, and the piezoelectric ceramic actuator and the drive module are electrically connected.

[0007] Furthermore, the aforementioned composite fiber laser employs an acousto-optic grating combined with a ring-core fiber to achieve fundamental mode to vortex beam (OAM) conversion. Structurally, the vortex beam generated by the acousto-optic grating is integrated into the fiber laser for active control of the laser welding molten pool. On the other hand, the composite fiber laser provided by this invention can achieve non-contact active stirring control of the welding molten pool, suppressing porosity, cracks, and spatter, refining weld grains, and improving welding quality. It can adjust the proportion and topological charge of the vortex beam in real time, adapting to various materials and working conditions. It has three working modes: pure thermal welding, optical forging, and dynamic composite. It has a stable structure, high conversion efficiency, and strong engineering feasibility, making it suitable for high-end precision laser welding scenarios.

[0008] Beneficial effects: Compared with existing technologies, this invention, by setting an acousto-induced grating, can convert the fundamental mode laser into a vortex beam carrying orbital angular momentum. The output vortex beam can apply a non-contact tangential stirring force to the weld pool, achieving active control of the weld pool flow, thus refining weld grains, reducing porosity and spatter, and controlling residual stress. Second, this invention uses a sinusoidal drive signal to excite a piezoelectric ceramic actuator, forming a curved traveling wave field with a single spatial period in the ring-core fiber. Through the photoelastic effect, a sinusoidal dynamic refractive index grating is generated, achieving high-efficiency and high-purity mode conversion of the fundamental mode laser into a single topological charge vortex beam. This avoids the multi-mode aliasing problem caused by square wave or pulse drive, ensuring the directional controllability and stability of optical forging. Third, through the combined action of a long-period grating, a polarization controller, an acousto grating, and a graded-index optical fiber, this invention can achieve stable generation and collimated output of a vortex beam. It also features three working modes: pure thermal welding, optical forging, and dynamic composite. The proportion of vortex beam and topological charge can be adjusted in real time according to the welding process requirements, so that the output laser beam can match the heat input and stirring intensity required for welding, adapting to the welding requirements of different materials and working conditions. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the overall structure of the composite fiber laser described in this invention; Figure 2 This is a schematic diagram of the external structure of the optical forging module in the composite fiber laser of the present invention. Figure 3 This is a cross-sectional view of the internal structure of the housing in the composite fiber laser described in this invention; Figure 4This is a schematic diagram of the acousto-optic grating in the composite fiber laser of the present invention; Figure 5 This is a schematic diagram of the long-period grating in the composite fiber laser described in this invention; Figure 6 This is a structural assembly diagram of the aluminum cone, piezoelectric ceramic actuator, and isolation ring in the composite fiber laser described in this invention; Figure 7 This is a schematic diagram of the ring-core fiber in the composite fiber laser described in this invention.

[0010] In the diagram: 1. Housing; 101. Optical chamber; 2. Fiber optic winding area; 3. Seed source; 4. Output connector; 5. High-reflection grating; 6. Low-reflection grating; 7. Isolator; 8. Pre-amplification stage; 9. Pump combiner; 10. Main amplification stage; 11. Cladding optical stripper; 12. Housing; 13. Long-period grating; 14. Polarization controller; 15. Graded-index fiber; 16. Ring-core fiber; 1601. Etched area; 17. Aluminum taper; 18. Piezoelectric ceramic actuator; 19. Drive module; 20. Isolation ring. Detailed Implementation

[0011] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0012] Reference Figures 1 to 7A composite fiber laser for laser welding includes a housing 1, an optical chamber 101 inside the housing 1, a fiber winding region 2 at the center of the optical chamber 101, a seed source 3 at the input end of the fiber winding region 2, and an output connector 4 at the output end of the fiber winding region 2. Between the seed source 3 and the output connector 4, a high-reflection grating 5, a low-reflection grating 6, an isolator 7, a pre-amplification stage 8, a pump combiner 9, a main amplification stage 10, a cladding stripper 11, and an optical forging module are sequentially arranged, and the above components are connected by optical fibers. The optical forging module includes a housing 12, and within the housing 12, from the input end to the output end, a long-period grating 13, a polarization grating 14, a polarization grating 15, a polarization grating 16, a polarization grating 17, a polarization grating 18, a polarization grating 19, a polarization grating 10, a polarization grating 11, and an optical forging module are sequentially arranged. The system includes a vibration controller 14, an acousto-optic grating, and a graded-index fiber 15. A long-period grating 13 is used to filter out higher-order noise modes. The polarization controller 14 converts linearly polarized light into circularly polarized light. The acousto-optic grating is used to achieve mode conversion from the fundamental mode to vortex light. The graded-index fiber 15 and the coreless fiber end cap are used to maintain the purity of the vortex light and collimate the output. The acousto-optic grating converts the incident fundamental mode laser into a vortex beam carrying orbital angular momentum. It includes a ring-core fiber 16, with an aluminum cone 17 below the ring-core fiber 16. Below the aluminum cone 17 are a piezoelectric ceramic actuator 18 and a drive module 19, with the piezoelectric ceramic actuator 18 electrically connected to the drive module 19.

[0013] Specifically, a cover plate is provided on the top of the housing 12. The inner sidewall of the housing 12 and the bottom surface of the cover plate are provided with a nickel-plated electromagnetic shielding layer to suppress the electromagnetic radiation generated by the high-frequency drive signal of the piezoelectric ceramic actuator 18, avoid interference with other electronic components of the laser, and ensure stable vortex light output. The piezoelectric ceramic actuator 18 is fixed to the bottom plate surface of the housing 12 by an independent base, and an isolation ring 20 is provided between the independent base and the main body of the housing 12. The ring-core fiber 16 is wet-etched in the acousto-optic grating region to a diameter of 30 μm and a length of 15 mm for the etched region 1601, in order to reduce bending stiffness and make the micron-level amplitude generated by the tip of the aluminum cone 17 sufficient to excite a significant traveling wave acoustic field. The two ends of the etched region 1601 are connected to the unetched fiber through a tapered transition region to avoid optical power leakage and mode conversion efficiency reduction caused by abrupt changes in fiber size.

[0014] It should be noted that, during use, acoustic damping silicone rubber needs to be fitted onto the outer periphery of the ring-core fiber 16 to absorb reflected sound waves and improve the quality of the traveling wave field in the ring-core fiber 16. The bottom opening of the acoustic damping silicone rubber prevents obstruction of the connection between the ring-core fiber 16 and the aluminum taper 17. Acoustic damping silicone rubber is existing technology and will not be described in detail here. This design significantly enhances the sensitivity of the etched, narrow-diameter optical fiber to acoustic waves, enabling the generation of sufficient refractive index modulation depth with a lower driving voltage. This ensures high conversion efficiency of the vortex light, creating conditions for outputting high-power vortex light for welding pool stirring.

[0015] In the above structure, the aluminum cone 17 is arranged in a pyramidal shape. The bottom of the aluminum cone 17 is bonded to the piezoelectric ceramic actuator 18 with epoxy resin, and the tip of the aluminum cone 17 is bonded to the surface of the etched ring-core optical fiber 16 with UV adhesive, so that the pyramidal tip and the optical fiber form a stable contact and prevent displacement under long-term vibration. The long-period grating 13 is written into the optical fiber at the input end of the optical forging module to filter out high-order noise modes, ensuring that the mode entering the polarization controller 14 is a pure fundamental mode, avoiding multi-mode aliasing that causes disorder of the force direction of the molten pool, and ensuring the directional controllability of optical forging.

[0016] Furthermore, the piezoelectric ceramic actuator 18 is fixed to the bottom plate of the housing 12 via an independent base, and is used to form a periodic bending traveling wave field in the ring-core optical fiber 16, generating a dynamic refractive index grating through the photoelastic effect. The period of the dynamic refractive index grating is... Phase matching condition is met:

[0017] in, Let be the fundamental mode propagation constant. Let be the propagation constant of the target vortex light mode. , For the effective refractive index of the mode, The wavelength is denoted as λ, and the propagation constant is obtained by solving the wave equation based on the refractive index distribution and operating wavelength of the ring-core fiber 16.

[0018] In this invention, the driving module 19 generates a sinusoidal driving signal, which is then amplified and applied to the piezoelectric ceramic actuator 18. This causes the piezoelectric ceramic actuator 18 to generate simple harmonic vibrations at a single frequency. These vibrations are transmitted through the aluminum cone 17 and form a curved traveling wave field with a single spatial period in the ring-core fiber 16. Through the photoelastic effect, a sinusoidal dynamic refractive index grating is generated, achieving mode conversion from the fundamental mode laser to a single topological charge vortex beam. It should be noted that the sinusoidal driving signal has a pure spectrum without higher harmonics, resulting in an ideal sinusoidal distribution of the refractive index grating. The diffraction efficiency is concentrated in a single diffraction order, resulting in high mode conversion efficiency. Furthermore, the output vortex beam has a single topological charge and high purity, ensuring a stable and directional tangential stirring force on the molten pool during welding, thus achieving controllable optical forging.

[0019] Specifically, the frequency of the driving signal in this invention With grating period satisfy:

[0020] in This refers to the acoustic wave propagation speed in the ring-core fiber 16. The laser described in this invention can be controlled by adjusting the driving frequency. The grating period can be changed linearly. This allows the phase matching conditions to be covered sequentially. to The mode enables rapid switching of vortex topological charge, providing controllable physical parameters for real-time adjustment of the molten pool stirring intensity during welding.

[0021] To help those skilled in the art better understand the practical effects of this laser, the following further describes its usage setup and working principle: Orbital angular momentum set When: it produces low-order vortex light, suitable for gentle stirring, and is used to refine grains and promote bubble escape.

[0022] Orbital angular momentum set When: it produces intermediate-order vortex light and moderate stirring force, which is used to suppress splashing and regulate the flow of the molten pool.

[0023] Orbital angular momentum set Time: High-order vortex light generates strong vortices, which are used to break up coarse dendrites and forcibly eliminate residual stress.

[0024] When this invention is used, the seed source 3 is first activated to generate a fundamental mode laser. After frequency selection by the high-reflection grating 5 and the low-reflection grating 6, a stable seed light is formed. After passing through the isolator 7, the laser enters the pre-amplification stage 8 and the pump combiner 9 to inject pump light. Then, the laser enters the main amplification stage 10 for power amplification. The amplified laser passes through the cladding light stripper 11 to remove residual pump light and enters the optical forging module. In the optical forging module, the long-period grating 13 filters out higher-order miscellaneous modes, the polarization controller 14 adjusts the linearly polarized light to circularly polarized light, and then the drive module 19 generates a sinusoidal drive signal to excite the piezoelectric ceramic actuator 18 to generate simple harmonic vibration. Through the aluminum cone 17, a single spatial period curved traveling wave field is formed in the etched ring-core fiber 16. The elasto-optic effect is used to generate a sinusoidal dynamic refractive index grating. After satisfying the phase matching condition, the fundamental mode laser is converted into a vortex beam carrying orbital angular momentum. After being converted to adiabatic mode by graded refractive index fiber 15 and expanded and collimated by coreless fiber end cap, the vortex beam is focused onto the workpiece surface by the welding head. The output vortex beam realizes non-contact mechanical stirring of the molten pool, which can refine the weld grains, reduce porosity and spatter, and regulate residual stress, thereby greatly improving the quality of laser welding. During the welding process, the following three working modes can be selected according to process requirements: 1. Pure heat welding mode: acousto-optic grating is off, and the fundamental mode laser is output; 2. Optical forging mode: The acousto-optic grating is turned on and the frequency is fixed, outputting a single topological charge vortex light to apply a tangential stirring force to the molten pool; 3. Composite mode: Real-time adjustment of drive frequency and amplitude, changing the proportion of vortex light and topological charge, dynamically matching heat input and stirring intensity.

[0025] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite fiber laser for laser welding, comprising a housing (1) and an optical chamber (101) therein, characterized in that, The optical chamber (101) has a fiber optic winding area (2) at its center. The input end of the fiber optic winding area (2) has a seed source (3). The output end of the fiber optic winding area (2) has an output connector (4). Between the seed source (3) and the output connector (4), there are sequentially arranged a high-reflection grating (5), a low-reflection grating (6), an isolator (7), a pre-amplification stage (8), a pump combiner (9), a main amplification stage (10), a cladding light stripper (11), and an optical forging module. The above components are connected by optical fibers. The optical forging module includes a housing (12), and the housing (12) is provided with a long-period grating (13), a polarization controller (14), an acousto grating and a graded refractive index fiber (15) in sequence from the input end to the output end. The acousto-optic grating converts the incident fundamental mode laser into a vortex beam carrying orbital angular momentum, including a ring-core fiber (16), an aluminum cone (17) below the ring-core fiber (16), a piezoelectric ceramic actuator (18) and a drive module (19) below the aluminum cone (17), and the piezoelectric ceramic actuator (18) and the drive module (19) are electrically connected.

2. The composite fiber laser for laser welding according to claim 1, characterized in that, A cover plate is provided on the top of the housing (12). The inner sidewall of the housing (12) and the bottom surface of the cover plate are provided with a nickel-plated electromagnetic shielding layer. The piezoelectric ceramic actuator (18) is fixed to the bottom plate surface of the housing (12) by an independent base. An isolation ring (20) is provided between the independent base and the main body of the housing (12).

3. The composite fiber laser for laser welding according to claim 1, characterized in that, The ring-core fiber (16) is wet-etched to a diameter of 30 μm in the acousto-grating region to form an etched region (1601). The length of the etched region (1601) is 15 mm. The two ends of the etched region (1601) are connected to the unetched ring-core fiber (16) through a tapered transition region.

4. The composite fiber laser for laser welding according to claim 1, characterized in that, The aluminum cone (17) is arranged in a pyramidal shape. The bottom of the aluminum cone (17) is bonded to the piezoelectric ceramic actuator (18) with epoxy resin, and the tip of the aluminum cone (17) is bonded to the surface of the etched ring-core optical fiber (16) with ultraviolet glue.

5. The composite fiber laser for laser welding according to claim 1, characterized in that, The long-period grating (13) is written into the optical fiber at the input end of the optical forging module to filter out higher-order noise modes and ensure that the mode entering the polarization controller (14) is a pure fundamental mode.

6. The composite fiber laser for laser welding according to claim 1, characterized in that, The piezoelectric ceramic actuator (18) is used to form a periodic bending traveling wave field in the ring-core fiber (16), generating a dynamic refractive index grating through the photoelastic effect, wherein the period of the dynamic refractive index grating is... Phase matching condition is met: in, Let be the fundamental mode propagation constant. Let be the propagation constant of the target vortex light mode. , For the effective refractive index of the mode, The wavelength of the laser. The orbital angular momentum is given by the propagation constant, which is obtained by solving the wave equation based on the refractive index distribution and operating wavelength of the ring-core fiber (16).

7. The composite fiber laser for laser welding according to any one of claims 1-6, characterized in that, The driving module (19) generates a sinusoidal driving signal and applies the amplified sinusoidal driving signal to the piezoelectric ceramic actuator (18), causing the piezoelectric ceramic actuator (18) to generate a simple harmonic vibration of a single frequency. The simple harmonic vibration is transmitted through the aluminum cone (17) and forms a curved traveling wave field with a single spatial period in the ring core fiber (16). A sinusoidal dynamic refractive index grating is generated through the photoelastic effect, realizing the mode conversion of the fundamental mode laser to a single topological charge vortex beam.

8. The composite fiber laser for laser welding according to any one of claims 1-6, characterized in that, The frequency of the drive signal With grating period satisfy: in is the acoustic wave propagation speed in the ring-core fiber (16).

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