A local negative pressure laser welding dynamic regulation system and welding method

Abstract

The present application relates to the technical field of laser welding, and specifically discloses a kind of local negative pressure laser welding dynamic control system and welding method.System includes local negative pressure welding cabin, support and drive unit, lens barrel adjusting unit, negative pressure generating unit and control unit;Cabin upper and lower openings are sealedly connected with the cylinder wall of the cylinder to be welded;Lens barrel adjusting unit includes length adjusting module consisting of a plurality of detachable annular cylinders and protective lens module provided with air blowing needle valve;Control unit adjusts negative pressure degree in real time according to molten pool temperature gradient, smoke concentration, laser power attenuation three-way signal through fuzzy PID controller.Welding method includes: clamping positioning, vacuumizing and completing negative pressure-optical collaborative compensation, setting parameters, driving cylinder rotation and starting laser welding, dynamically regulating negative pressure degree, estimating penetration in real time through acoustic emission signal and small hole radiation spectrum and adjusting, finally restoring normal pressure and detecting weld quality.

Description

Technical Field

[0001] This invention relates to the field of laser welding technology, specifically to a local negative pressure laser welding dynamic control system and welding method. Background Technology

[0002] In aerospace, nuclear power, and heavy equipment manufacturing, high-quality welding of large, thick-walled cylindrical structural components is a critical manufacturing process. Research shows that under vacuum or low-pressure conditions, the coupling efficiency between the laser beam and the metal material is significantly improved, plasma plumes are effectively suppressed, laser welding penetration depth can be increased by 2-3 times compared to atmospheric pressure conditions, weld porosity is significantly reduced, and joint mechanical properties are greatly improved. However, for ultra-large cylindrical structures with diameters of several meters and lengths of tens of meters, using an integrated vacuum chamber requires constructing a massive vacuum chamber capable of accommodating the entire workpiece, resulting in equipment investments of tens of millions of yuan, vacuuming times of several hours, and extremely inconvenient workpiece loading and unloading, exhibiting very poor flexibility and making it difficult to promote its application in engineering practice.

[0003] To overcome the drawbacks of the overall vacuum chamber solution, local vacuum laser welding technology has emerged. Its core idea is to create a low-pressure sealed environment only in a local area of ​​the weld, thereby significantly reducing equipment costs and vacuuming time. Existing partial vacuum laser welding technology has made some progress: Chinese patent CN110293313A discloses a laser welding partial vacuum sealing fixture, which achieves partial vacuum by setting sealing covers on both sides of the plate to be welded and using vacuum grooves and vents, thus overcoming the limitations of equipment on workpiece size. However, this solution is mainly designed for butt welds of plate plates and does not address the rotary sealing problem of cylindrical circumferential welds. Chinese patent CN116551181A discloses a semi-enclosed partial low vacuum laser welding device, which forms a partial low vacuum environment in the welding area through a multi-stage vacuum chamber structure and dynamic sealing module, effectively suppressing the attenuation of laser energy by plasma plumes. However, this solution is also geared towards plate welding conditions, and the compatibility between the sealing structure and the curved surface of the cylinder is not resolved. Chinese patents CN117123920A and CN117283128A disclose a series of partial vacuum sealing devices, which have improved the design of the local sealing structure and the fume protection components, achieving a titanium alloy joint strength coefficient of over 0.95 and a vacuum degree of 10. -2While the above solutions achieve better welding performance, the fume protection components in these solutions only passively block fumes through air resistance structures, lacking an active air curtain protection mechanism for the high-density metal vapor plumes generated by high-power laser welding. Chinese patent CN119634983A discloses a multi-axis linkage local vacuum laser welding device for longitudinal and circumferential seams of a cylinder. It achieves compatible welding of circumferential and longitudinal seams of the cylinder through rotating support components and sliding sealing components, and introduces a secondary current acquisition and control system to dynamically adjust the pumping speed based on the secondary current signal. This improves upon the aforementioned solutions in terms of negative pressure control, but its regulation still relies on a single signal feedback and cannot cope with the complex working conditions of multi-physical field coupling such as molten pool temperature field, fume concentration, and laser power attenuation during high-power laser welding.

[0004] After in-depth research, the inventors discovered that the existing local vacuum laser welding solutions still have the following significant drawbacks when applied to circumferential welding of large, thick-walled cylinders: First, existing solutions lack effective active protection measures for the optical system under local negative pressure environments with high-power lasers (30kW and above). The intense metal vapor plumes and spatter generated during welding easily contaminate the protective lenses, leading to heat absorption failure and affecting the continuity of the welding process. Second, existing solutions do not provide a precise adjustable mechanism for the distance between the laser welding head and the workpiece surface, making it impossible to flexibly adapt to the focal length requirements when welding cylinders with different wall thicknesses. Third, the negative pressure control in existing solutions relies on a single sensor signal. First, the existing solutions lack intelligent dynamic control capabilities based on the fusion of multiple sensors, such as molten pool temperature gradient, fume concentration, and laser power attenuation, leading to unstable welding quality. Second, the existing solutions do not reveal the influence of gas refractive index changes on the laser beam focal position under local negative pressure, and lack a quantitative correspondence and collaborative compensation mechanism between negative pressure and focal length offset. Third, the existing solutions lack real-time online detection methods for weld penetration, making it impossible to achieve linkage adjustment of laser power, welding speed, and negative pressure, resulting in insufficient welding quality assurance capabilities. Fourth, the existing solutions do not consider the influence of the internal and external pressure difference on the molten pool morphology during the welding of large thick-walled cylinders, and lack an active control mechanism for dynamic balance of internal and external pressure differences. Summary of the Invention

[0005] The purpose of this invention is to provide a local negative pressure laser welding dynamic control system and welding method to solve the technical problems existing in the prior art, such as insufficient protection of optical components, inflexible focal length adjustment, single dimension of negative pressure control, poor coordination of fume treatment, lack of negative pressure-optical collaborative compensation mechanism, and lack of real-time detection and feedback control of penetration depth.

[0006] The present invention adopts the following technical solution: The first aspect of the present invention provides a local negative pressure laser welding dynamic control system, comprising: a local negative pressure welding chamber, which is open at both the upper and lower ends, and the upper and lower parts are sealed to the cylinder wall of the cylinder to be welded, forming a closed space in the local area of ​​the weld; The support and drive unit is located below the local negative pressure welding chamber and is used to support and drive the cylinder to be welded to rotate. The lens barrel adjustment unit, located outside the local negative pressure welding chamber as a laser incident interface, includes a length adjustment module and a protective lens module. The length adjustment module consists of multiple sealed and detachably connected annular cylinders to adjust the laser focal length. The protective lens module is equipped with an air blowing needle valve. The air passage of the air blowing needle valve is parallel to the plane where the protective lens is located and intersects the optical axis. The air passage outlet faces the surface of the protective lens to form an air curtain on the surface of the protective lens to suppress metal vapor plume contamination. The negative pressure generating unit is sealed to the interior of the local negative pressure welding chamber and is used to regulate the negative pressure inside the chamber, including a vacuum sensor. The control unit is electrically connected to each unit and adjusts the negative pressure inside the chamber in real time through a fuzzy PID controller based on the molten pool temperature gradient signal, the dust concentration signal, and the laser power attenuation signal.

[0007] Furthermore, the local negative pressure welding chamber includes two identical arc-shaped cavity walls, which are symmetrically and detachably connected. An annular first sealing element is provided at the upper and lower parts of the cavity walls. The first sealing element is sleeved on the outer wall of the cylinder to be welded and cooperates with the cavity wall to form a dynamic seal. A second sealing element is provided at the connection between the two cavity walls.

[0008] Furthermore, the support and drive unit includes a support base, a support base, and a drive mechanism, with the top of the support base connected to the bottom of the local negative pressure welding chamber; The support base is located below the support base, and the drive mechanism is installed on the support base to support the cylinder to be welded and drive the cylinder to be welded to rotate along its own axis. The driving mechanism includes a circular support plate, multiple support rollers, and a driving device. The multiple support rollers are rotatably mounted on the circular support plate along multiple axes of symmetry on the surface of the circular support plate. The output end of the driving device is connected to two support rollers on one of the axes of symmetry through a reduction mechanism.

[0009] Furthermore, the lens barrel adjustment unit also includes a welding chamber, a cooling unit, and a negative pressure module. The welding chamber is located outside the local negative pressure welding chamber and communicates with the interior of the local negative pressure welding chamber. The protective lens module, the length adjustment module, and the negative pressure module are sequentially and sealed together along the optical axis. The negative pressure module is provided with an air extraction hole for connection to the negative pressure generating unit. The cooling unit is a spiral cooling water channel surrounding the protective lens module, the length adjustment module, and the negative pressure module. The protective lens module includes a ring lens mounting module and a protective lens. The protective lens is embedded in the ring lens mounting module. The air blowing needle valve is set on the outer peripheral wall of the ring lens mounting module. A laser power monitoring sensor is set on the side of the protective lens near the welding chamber. The length adjustment module consists of multiple identical annular cylinders that are detachably connected in sequence via sealing rings and bolts or threads.

[0010] Furthermore, the local negative pressure welding chamber includes two identical semi-circular arc-shaped cavity walls, which are symmetrically and detachably connected. The upper and lower ends of the opposite side walls of the two cavity walls are slidably sealed with semi-circular arc-shaped plates. A third sealing element is provided on the inner arc of the semi-circular arc-shaped plate. The two semi-circular arc-shaped plates are detachably connected, and a fourth sealing element is provided at the connection between the two semi-circular arc-shaped plates.

[0011] Furthermore, it also includes a preheating and cooling unit and a fume treatment unit, both of which are electrically connected to the control unit; The preheating and cooling unit includes a heating device, a cooling device, and temperature sensing units located at the upper and lower parts of the local negative pressure welding chamber. The heating device and the cooling device are respectively connected to the upper and lower parts of the local negative pressure welding chamber. The fume treatment unit is connected to the interior of the local negative pressure welding chamber and works in conjunction with the negative pressure generating unit to treat the fume inside the local negative pressure welding chamber.

[0012] Furthermore, the negative pressure generating unit also includes an electromagnetic regulating valve; The control unit collects data from three sensors in real time: the molten pool temperature gradient signal, the fume concentration signal, and the laser power attenuation signal. The molten pool temperature gradient signal is acquired through multiple sets of infrared temperature sensors arranged along the welding direction, and the temperature gradient value G between the front and rear zones of the molten pool is calculated. T =(T 后区 -T 前区 The smoke and dust concentration signal is monitored in real time by a laser transmission smoke and dust concentration sensor, which detects the mass concentration of smoke and dust in the cabin. d and its rate of change dC d / dt; The laser power attenuation signal is used to calculate the power attenuation rate η in real time through the laser power monitoring sensor; The control unit inputs three signals to the fuzzy PID controller, and uses the main vacuum pump group working frequency and the opening degree of the electromagnetic regulating valve as output variables to adjust the negative pressure in the chamber in real time. The weighting coefficient is automatically retrieved by the control unit from the process parameter library according to the material type and wall thickness.

[0013] Furthermore, the control unit is also used to perform negative pressure-optical coordinated control, specifically including: Based on the target negative pressure, the correspondence between negative pressure and focal length offset is queried. The laser beam focal point drift caused by the change in gas refractive index due to the local negative pressure environment is calculated. The total length of the lens tube adjustment unit is compensated by increasing or decreasing the number of annular cylinders in the length adjustment module, so that the laser beam focal point position is compensated to the target position.

[0014] Furthermore, it also includes an inner ring negative pressure chamber disposed inside the cylinder to be welded, the inner ring negative pressure chamber having an independent air extraction pipe. The control unit performs dynamic balance control of internal and external pressure difference, specifically including: Real-time acquisition of external chamber pressure P in the local negative pressure welding chamber 外 The inner chamber pressure P of the inner negative pressure chamber 内 Calculate the real-time internal and external pressure difference ΔP; when the pressure difference exceeds the upper limit of the optimal pressure difference range, increase the internal venting rate Q. 内 And appropriately reduce the external venting rate Q. 外 When the pressure differential is below the lower limit of the optimal pressure differential range, reduce the internal venting rate Q. 内 And appropriately increase the external venting rate Q. 外 To maintain the internal and external pressure difference within the optimal range to ensure the stability of the molten pool morphology and suppress the spread of spatter; The local negative pressure laser welding dynamic control system also includes an acoustic emission sensor and a fiber optic spectrometer, both of which are electrically connected to the control unit. The acoustic emission sensor is installed on the cavity wall of the local negative pressure welding chamber to collect acoustic emission signals during the welding process in real time and extract characteristic parameters. The fiber optic spectrometer is installed on the side wall of the lens tube adjustment unit, and its fiber optic probe is optically coupled to the welding area inside the chamber through the observation window of the welding chamber to collect spectral radiation signals in the pinhole area. The control unit performs weighted fusion of the signals from the acoustic emission sensor and the fiber optic spectrometer to estimate the weld penetration depth in real time. Based on the deviation between the estimated penetration depth and the target penetration depth, the control unit controls the rotation speed of the support and drive units and the pumping rate of the negative pressure generating unit, as well as sends power adjustment commands to the external laser, to achieve closed-loop regulation of the welding speed, the negative pressure inside the chamber, and the laser power.

[0015] A second aspect of the present invention provides a method for local negative pressure laser welding of large thick-walled cylinders, based on the system described above, comprising the following steps: S1. Hoist the cylinder to be welded to the support and drive unit, and adjust the height of the cylinder to be welded so that the weld position matches the working height of the local negative pressure welding chamber; S2. Move the local negative pressure welding chamber to the weld start position, first start the negative pressure generating unit to assist the sealing, and then draw the negative pressure in the chamber to the target value of the preheating stage. S3. Based on the wall thickness of the cylinder to be welded and the welding process requirements, adjust the length adjustment module to make the total length of the lens barrel adjustment unit match the focal length requirement, and query the correspondence between the negative pressure and the focal length offset according to the target negative pressure to complete the negative pressure-optical collaborative compensation. S4. Set the welding process parameters and the operating parameters of each unit in the control unit; S5. Seal the area to be welded inside the cylinder to be welded; start the support and drive unit to drive the cylinder to be welded to rotate, start the external laser to output the laser beam to irradiate the weld area, and the control unit dynamically adjusts the negative pressure in the chamber through a fuzzy PID controller based on three signals: molten pool temperature gradient, fume concentration, and laser power attenuation. The control unit estimates the melt depth in real time through acoustic emission signal and pinhole radiation spectrum and adjusts the laser power, welding speed and negative pressure to complete the circumferential weld. S6. After welding is completed, turn off the laser, gradually restore the internal pressure of the local negative pressure welding chamber to normal pressure, shut down the welding system and check the weld quality.

[0016] The core principle of the above technical solution lies in the fact that under local negative pressure, the number density of gas molecules inside the chamber decreases, and the plasma plume density and metal vapor concentration along the laser beam propagation path decrease significantly, thereby reducing the scattering, absorption, and refraction losses of laser energy, increasing laser power density, and enhancing deep penetration welding capability. Simultaneously, the low-pressure environment relatively increases the surface tension of the molten pool, improves keyhole stability, reduces the driving force for porosity nucleation, and improves the metallurgical quality of the weld. Based on the above fundamental principles, this invention further achieves dynamic and precise control through the following three key technological breakthroughs: First, multi-sensor fusion fuzzy PID control couples the three physical quantities—molten pool temperature gradient, dust concentration, and laser power attenuation—into a unified control input, identifying and dynamically responding to abnormal conditions such as plasma bursts, molten pool overheating, and keyhole instability in real time, upgrading negative pressure control from single-dimensional threshold control to multi-dimensional adaptive control; Second, negative pressure-optical synergistic compensation, based on the physical law of gas refractive index changing with pressure, establishes a quantitative model of negative pressure degree-focal length offset-lens compensation. The correspondence was established, and a quantitative correspondence between negative pressure, focal length offset, and lens barrel compensation was established. By adjusting the length of the lens barrel adjustment unit before welding, focus drift compensation was completed to ensure that the high-power laser beam is always accurately focused on the target depth of the weld. Thirdly, the acoustic emission-spectral dual-mode penetration depth estimation utilizes the complementary characteristics of the acoustic signal of the molten pool vibration and the spectral signal of the pinhole radiation during welding to achieve real-time online estimation of penetration depth. A feedback control system linking three parameters of laser power, welding speed, and negative pressure was constructed to ensure the consistency of weld penetration depth.

[0017] The present invention has at least the following advantages over the prior art: (1) The present invention provides a protective lens module with a blowing needle valve in a local negative pressure welding chamber to form a stable air curtain on the surface of the protective lens, actively blocking metal vapor plumes and welding spatter, effectively extending the service life of the protective lens under high-power laser welding conditions and ensuring the continuity of the welding process.

[0018] (2) The present invention adopts a length adjustment module composed of multiple detachable annular cylinders. The laser focus position can be adjusted by increasing or decreasing the number of annular cylinders, which can flexibly adapt to the focal length requirements of cylinders with different wall thicknesses. The focal length adjustment method is simple and reliable.

[0019] (3) The control unit of the present invention adopts a fuzzy PID control strategy that integrates three signals: molten pool temperature gradient signal, fume concentration signal and laser power attenuation signal. This upgrades the negative pressure regulation from single-dimensional threshold control to multi-dimensional adaptive regulation, which significantly improves the welding stability under complex working conditions.

[0020] (4) This invention establishes a quantitative correspondence between the change in gas refractive index and the amount of laser beam focus drift under local negative pressure. Through the negative pressure-optical synergistic compensation mechanism, the focus drift caused by the change in gas refractive index under the target negative pressure is eliminated, ensuring that the high-power laser beam is always accurately focused on the target depth.

[0021] (5) This invention achieves real-time online estimation of weld depth by dual-mode fusion of acoustic emission signal and pinhole radiation spectrum, and constructs a three-parameter linkage feedback control system of laser power, welding speed and negative pressure, which effectively ensures the consistency of weld depth and weld quality of circumferential welding of large thick-walled cylinders.

[0022] (6) The present invention maintains the pressure difference between the inner and outer rings within the optimal range through the inner and outer ring coordinated negative pressure control logic, effectively suppressing the collapse of the molten pool and the diffusion of spatter, and improving the back forming quality of the weld seam of the thick-walled cylinder. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments are briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope of protection. Those skilled in the art can obtain other related drawings based on these drawings.

[0024] Figure 1 This is a schematic diagram of the overall structure of the local negative pressure laser welding dynamic control system provided in an embodiment of the present invention.

[0025] Figure 2 This is a structural explosion diagram of a local negative pressure welding chamber provided in an embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram of the structure of a partially negative pressure welding chamber in another embodiment of the present invention.

[0027] Figure 4 This is a schematic diagram of the internal structure of the local negative pressure laser welding dynamic control system provided in an embodiment of the present invention.

[0028] Figure 5 This is a schematic diagram of the lens barrel adjustment unit provided in an embodiment of the present invention.

[0029] Figure 6 This is a metallographic comparison of two stainless steel welded joints under different environmental pressures and the same laser power conditions.

[0030] Figure 7 This is a schematic diagram showing the experimental results of local negative pressure laser welding of different materials.

[0031] Figure 8 A schematic diagram showing the variation of average weld depth of titanium alloys obtained when different laser powers are matched with the optimal welding process under negative pressure conditions.

[0032] Figure 9 This is a schematic flowchart of a local negative pressure laser welding method for large thick-walled cylinders provided in an embodiment of the present invention.

[0033] In the diagram: 10. Local negative pressure welding chamber; 11. Chamber wall; 12. First seal; 13. Second seal; 14. Semi-circular arc plate; 15. Third seal; 20. Support and drive unit; 21. Support base; 22. Support base; 23. Drive mechanism; 30. Lens tube adjustment unit; 31. Welding chamber; 311. Observation window; 32. Protective lens module; 33. Length adjustment module; 34. Negative pressure module; 200. Cylinder to be welded; 231. Circular bearing plate; 232. Support roller; 321. Annular lens mounting module; 322. Protective lens; 323. Air needle valve; 331. Annular cylinder; 341. Air extraction port. Detailed Implementation

[0034] Overall, the technical solution adopted in this invention is as follows: A method for localized negative pressure laser welding of large, thick-walled cylinders includes the following steps: hoisting the cylinder to be welded to the support and drive unit, adjusting the height of the cylinder to match the weld position with the working height of the localized negative pressure welding chamber; moving the localized negative pressure welding chamber to the weld start position, first activating the negative pressure generating unit for auxiliary sealing, and then drawing the negative pressure inside the chamber to the target value of the preheating stage; adjusting the length adjustment module according to the wall thickness of the cylinder to be welded and the welding process requirements to match the total length of the lens barrel adjustment unit with the focal length requirement, and querying the correspondence between the negative pressure and the focal length offset according to the target negative pressure to complete the negative pressure-optical coordinated compensation; and in the control unit... Set the welding process parameters and the operating parameters of each unit; seal the area to be welded inside the cylinder to be welded; start the support and drive unit to drive the cylinder to be welded to rotate; start the external laser to output a laser beam to irradiate the weld area; the control unit dynamically adjusts the negative pressure inside the chamber through a fuzzy PID controller based on three signals: the temperature gradient of the molten pool, the concentration of dust, and the laser power attenuation; at the same time, it estimates the penetration depth in real time and adjusts the laser power, welding speed, and negative pressure through acoustic emission signals and pinhole radiation spectra to complete the circumferential weld; after welding is completed, turn off the laser, gradually restore the pressure inside the local negative pressure welding chamber to normal pressure, shut down the welding system, and check the weld quality.

[0035] Overall, the dynamic control system and method for local negative pressure laser welding of cylindrical bodies provided by this invention, by setting a length adjustment module in the lens barrel adjustment unit, can precisely adjust the length of the laser incident interface, thereby matching the focal length requirements when welding cylindrical bodies with different wall thicknesses. This solves the problem in the prior art where the distance between the welding head and the workpiece is fixed and cannot adapt to different wall thicknesses, thus expanding the applicability of the system. The lens barrel adjustment unit is equipped with a protective lens module with a blowing needle valve and an independently operating cooling unit, which can form an air curtain to protect the protective lens and effectively dissipate heat under local negative pressure, significantly reducing the risk of contamination and thermal damage to optical components from the metal vapor plume and spatter generated by ultra-high power laser welding, thus solving the problem of optical component protection. Through the coordination of the control unit and the negative pressure generating unit, the negative pressure inside the chamber can be dynamically adjusted according to a preset program or real-time monitoring data, achieving intelligent control of the negative pressure environment. In addition, the system includes a fume treatment unit connected to the local negative pressure welding chamber, which works in conjunction with the negative pressure generating unit. Through the control unit coordinating the vacuum rate and fume treatment parameters, it effectively handles welding fumes whose diffusion characteristics change in the local negative pressure environment, preventing their accumulation or blockage of the vacuum system within the chamber, thus ensuring the stability of the negative pressure environment and the cleanliness of the welding process. The local negative pressure welding chamber adopts a structure with openings at the top and bottom and sealed connections to the cylindrical wall, eliminating the need for a large overall vacuum chamber and greatly improving the equipment's economy and flexibility. The support and drive unit can stably support and drive the rotation of the ultra-large cylindrical body, cooperating with the fixed local negative pressure welding chamber to achieve circumferential welding, improving the level of welding automation and efficiency.

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0037] The negative pressure degree referred to in this invention refers to the amount of reduction (in kPa) in the absolute pressure of the gas inside the local negative pressure welding chamber relative to atmospheric pressure. The greater the negative pressure degree, the lower the absolute gas pressure inside the chamber.

[0038] Example 1 This embodiment provides a dynamic control system for local negative pressure laser welding of large, thick-walled cylinders. (See also...) Figure 1 The system includes a local negative pressure welding chamber 10, a support and drive unit 20, a lens barrel adjustment unit 30, a negative pressure generating unit, and a control unit.

[0039] The local negative pressure welding chamber 10 has openings at both the top and bottom, and its upper and lower parts are sealed to the cylinder wall of the cylinder 200 to be welded, forming a closed space in the local area of ​​the weld, allowing laser welding to be performed in a local low-pressure environment. See also Figure 2 The local negative pressure welding chamber 10 includes two identical arc-shaped cavity walls 11, which are symmetrically and detachably connected. Annular first sealing elements 12 are provided at the upper and lower parts of each cavity wall 11. During assembly, the first sealing elements 12 are fitted onto the outer wall of the cylinder 200 to be welded, forming a dynamic seal with the cavity walls 11, allowing the cylinder 200 to rotate in a sealed state. A second sealing element 13 is provided at the connection point of the two cavity walls 11 to ensure airtightness when the two cavity walls 11 are closed. This split, detachable structure allows the local negative pressure welding chamber 10 to be directly installed around the cylinder 200 at any axial position, without needing to be fitted from the end, thus offering strong adaptability.

[0040] The support and drive unit 20 is located below the local negative pressure welding chamber 10 and includes a support base 21, a support base 22, and a drive mechanism 23. The top of the support base 21 is connected to the bottom of the local negative pressure welding chamber 10, fixing the local negative pressure welding chamber 10 and the support base 22 together. The support base 22 is located below the support base 21, providing bottom support for the entire system. The drive mechanism 23 is mounted on the support base 22 and contacts the outer wall of the cylinder 200 to be welded. It is used to support the cylinder 200 to be welded and drive it to rotate uniformly around its own axis to achieve circumferential welding. The drive mechanism 23 includes a circular support plate 231, multiple support rollers 232, and a drive device. Multiple support rollers 232 are arranged to rotate along multiple symmetrical axes on the surface of the circular bearing disk 231. The output end of the drive device is connected to two support rollers 232 on one of the symmetrical axes through a reduction mechanism, so as to uniformly transmit the driving torque to the two active rollers. The remaining support rollers 232 serve as driven rollers to provide auxiliary support, ensuring the stability and coaxiality of the cylinder 200 to be welded during the rotation process.

[0041] See Figure 4 and Figure 5 The lens barrel adjustment unit 30 includes a welding chamber 31, a protective lens module 32, a length adjustment module 33, a negative pressure module 34, and a cooling unit. The welding chamber 31 is located on the outer periphery of the cavity wall 11, and a sealing ring is installed between the welding chamber 31 and the cavity wall 11 for sealing. The welding chamber 31 is connected to the interior of the local negative pressure welding chamber 10, and the laser beam enters the weld area inside the chamber through the welding chamber 31. An observation window 311 is provided on the welding chamber 31 for the operator to observe the status of the welding area in real time.

[0042] The protective lens module 32, length adjustment module 33, and negative pressure module 34 are sequentially and sealed together along the optical axis, forming a complete laser transmission channel. The protective lens module 32 includes an annular lens mounting module 321 and a protective lens 322, with the protective lens 322 embedded and fixed within the annular lens mounting module 321. An air-blowing needle valve 323 is provided on the outer peripheral wall of the annular lens mounting module 321. The air passage of the air-blowing needle valve 323 is parallel to the plane containing the protective lens 322, and its extension line intersects the optical axis in space. The air passage outlet faces the inner surface of the protective lens 322. During welding, high-purity argon gas is continuously injected into the surface of the protective lens 322 through the air-blowing needle valve 323, forming a stable gas curtain on the surface of the protective lens 322, effectively preventing contamination and thermal damage to the protective lens 322 from metal vapor plumes and welding spatter. A laser power monitoring sensor is installed on the side of the protective lens 322 near the welding chamber 31 to monitor the actual laser power transmitted through the protective lens 322 in real time, providing a data source for the acquisition of power attenuation signals. The annular lens mounting module 321 is equipped with multiple welding head adapter interfaces, which can quickly replace different types of welding heads according to process requirements.

[0043] The length adjustment module 33 consists of multiple identical annular cylinders 331, which are detachably connected by sealing rings and bolts or threads. By increasing or decreasing the number of annular cylinders 331, the overall length of the lens barrel adjustment unit 30 can be linearly changed, thereby precisely adjusting the position of the laser focus relative to the workpiece surface to adapt to the defocusing requirements during welding of cylinders with different wall thicknesses. The negative pressure module 34 is installed on the welding chamber 31 and is equipped with an evacuation port 341. It is sealed to the negative pressure generating unit through a vacuum pipe. During evacuation, the internal optical path space of the protective lens module 32, the length adjustment module 33, and the negative pressure module 34 can be synchronously maintained at the same negative pressure state as the chamber, eliminating the influence of internal and external pressure differences on the optical path system. The cooling unit is a spiral cooling water channel surrounding the protective lens module 32, the length adjustment module 33, and the negative pressure module 34. Circulating cooling water is introduced to forcibly cool the lens barrel adjustment unit 30, preventing damage to the components due to heat accumulation during high-power laser transmission.

[0044] The negative pressure generating unit is sealed to the evacuation port 341 via a vacuum pipe and includes a main vacuum pump assembly, an auxiliary vacuum pump, and a vacuum sensor. The main vacuum pump assembly is responsible for rapidly evacuating the air pressure in the local negative pressure welding chamber 10 to the target negative pressure level and maintaining a stable negative pressure environment during the welding process; the auxiliary vacuum pump is used for auxiliary evacuation during the initial sealing stage; the vacuum sensor monitors the negative pressure level inside the chamber in real time and transmits the monitoring data to the control unit.

[0045] The control unit is electrically connected to the support and drive unit 20, the lens barrel adjustment unit 30, the negative pressure generating unit, and each auxiliary unit, and is responsible for coordinating the operation of each unit in the system. The control unit has a built-in process parameter library, which stores the optimal welding process parameters and negative pressure control parameters for different material grades and wall thicknesses. It can automatically retrieve the corresponding parameters according to the workpiece information set by the operator. During the welding process, the control unit dynamically adjusts the pumping speed of the negative pressure generating unit based on real-time feedback data from each sensor, thereby achieving intelligent control of the negative pressure inside the chamber.

[0046] See Figure 3 In another modified embodiment of this invention, the local negative pressure welding chamber 10 includes two identical semi-circular arc-shaped cavity walls 11, which are symmetrically and detachably connected, with a second sealing element 13 at the connection point. Semi-circular arc-shaped plates 14 are slidably and sealingly provided at the upper and lower ends of the opposite sidewalls of the two cavity walls 11. A third sealing element 15 is provided on the inner arc of the semi-circular arc plate 14. The two semi-circular arc plates 14 are detachably connected, with a fourth sealing element at the connection point. In this modified embodiment, the semi-circular arc plate 14 can slide relative to the cavity wall 11, allowing the local negative pressure welding chamber 10 to complete circumferential welding by rotating the chamber itself while the cylinder 200 to be welded remains fixed. This is suitable for special working conditions where the cylinder size is extremely large and rotational drive is difficult.

[0047] This embodiment also includes a preheating and cooling unit and a fume treatment unit, both electrically connected to the control unit. The preheating and cooling unit includes a heating device, a cooling device, and temperature sensing units located at the upper and lower parts of the local negative pressure welding chamber 10. The heating and cooling devices are respectively connected to the upper and lower parts of the local negative pressure welding chamber 10. Before welding, the heating device preheats the weld area to reduce welding thermal stress and prevent cold cracking; after welding, the cooling device performs controlled cooling of the weld to optimize the weld metallographic structure. The temperature sensing units monitor the temperature of the front, middle, and rear zones of the weld in real time and transmit the data to the control unit to achieve precise control of the welding thermal cycle. The fume treatment unit is connected to the interior of the local negative pressure welding chamber 10 and works in conjunction with the negative pressure generating unit to collect and purify the welding fumes generated inside the chamber, preventing fumes from accumulating and contaminating optical components or clogging the vacuum pump assembly.

[0048] See Figure 9 This embodiment also provides a local negative pressure laser welding method for large thick-walled cylinders. This method is based on the above system and specifically includes the following steps: S1. Hoist the cylinder 200 to be welded to the support and drive unit 20, adjust the height of the cylinder 200 to match the position of the weld with the working height of the local negative pressure welding chamber 10; close the two cavity walls 11 so that the local negative pressure welding chamber 10 surrounds the cylinder 200 to be welded, and check the sealing status of each seal.

[0049] S2. Move the local negative pressure welding chamber 10 to the starting position of the weld. First, start the auxiliary vacuum pump to perform auxiliary sealing and air extraction. After confirming that the chamber is sealed, start the main vacuum pump group to extract the negative pressure in the chamber to the target value of the preheating stage. Start the preheating and cooling unit to preheat the weld area.

[0050] S3. Based on the wall thickness of the cylinder 200 to be welded and the welding process requirements, the total length of the lens barrel adjustment unit 30 is adjusted by increasing or decreasing the number of annular cylinders 331 in the length adjustment module 33, so that the laser focus position meets the focal length requirements; at the same time, the corresponding relationship table between negative pressure and focal length offset is consulted according to the target negative pressure, the amount of focus drift caused by the change in gas refractive index due to the local negative pressure environment is determined, and the negative pressure-optical collaborative compensation is completed by further adjusting the number of annular cylinders 331, so that the laser beam focus position is accurately aligned with the target depth of the weld.

[0051] S4. Set welding process parameters in the control unit, including laser power, welding speed, and defocusing amount; set the operating parameters of each unit, including the phased target negative pressure of the negative pressure generating unit (preheating stage, arc initiation stage, stable welding stage, arc termination stage), the rotation speed of the support and drive unit 20, and the weighting coefficient of multi-sensor fusion control.

[0052] S5. Seal the area to be welded inside the cylinder 200; start the support and drive unit 20 to drive the cylinder 200 to rotate at a uniform speed, and simultaneously start the external laser to output a laser beam, which is transmitted through the lens barrel adjustment unit 30 and irradiates the weld area to begin circumferential welding. During the welding process, the control unit dynamically adjusts the negative pressure in the chamber in real time according to the molten pool temperature gradient signal, the fume concentration signal and the laser power attenuation signal, so that the negative pressure in the chamber changes sequentially according to the target values ​​of the preheating stage, the arc initiation stage, the stable welding stage and the arc termination stage; at the same time, the penetration depth is estimated in real time through the acoustic emission signal and the keyhole radiation spectrum (i.e., the optical radiation spectrum emitted by the keyhole area formed by laser deep penetration welding, whose spectral characteristics are related to the molten pool temperature and the melting depth), and the laser power, welding speed and negative pressure are adjusted to ensure that the weld penetration depth meets the design requirements and the circumferential welding is completed.

[0053] S6. After welding is completed, turn off the laser and stop the rotation of the support and drive unit 20; gradually open the air valve to slowly restore the internal pressure of the local negative pressure welding chamber 10 to normal pressure to prevent the weld quality from being affected by sudden pressure changes; after the pressure inside the chamber is restored to normal pressure, turn off the welding system, disassemble the local negative pressure welding chamber 10, and perform visual inspection and non-destructive testing on the weld quality.

[0054] Figure 6 The figures show a metallographic comparison of two stainless steel welded joints under different environmental pressures and the same laser power. The comparison results show that the penetration ability of laser welding is significantly increased under negative pressure conditions, and the penetration depth is significantly improved compared with normal pressure conditions. Figure 7 The results of the local negative pressure laser welding experiment on different materials show that by using local negative pressure to weld different materials and matching the corresponding process parameters, a large penetration depth can be obtained and the weld formation is good. Figure 8 The diagram shows the variation of average weld depth of titanium alloys obtained when different laser powers are matched with the optimal welding process under negative pressure conditions, which verifies the achievability of high-power laser welding capability under local negative pressure conditions.

[0055] Example 2 This embodiment provides a real-time adaptive negative pressure control method based on multi-sensor fusion. Based on the system described in Embodiment 1, the control unit further constructs a multi-sensor fusion signal system on the basis of the multi-sensor arrangement described in Embodiment 1, realizing intelligent dynamic control of the cabin negative pressure. The control unit collects data from the following three types of sensors in real time.

[0056] (1) Melt pool temperature gradient signal: Multiple sets of infrared temperature sensors are equidistantly arranged along the welding direction in the local negative pressure welding chamber 10. The response wavelength is 8~14μm and the response time is no more than 1ms. The temperature of the front area of ​​the molten pool (-5mm from the center of the spot), the center area of ​​the molten pool (center of the spot), and the rear area of ​​the molten pool (+5mm and +10mm from the center of the spot) are monitored respectively. The control unit calculates the temperature gradient value according to the following formula: G T =(T 后区 -T 前区 ) / L, where L is the sensor spacing, and the first and second order characteristic parameters of the molten pool temperature field are extracted as control inputs.

[0057] (2) Smoke concentration signal: A laser transmission type smoke concentration sensor is installed in the local negative pressure welding chamber 10. The measurement wavelength is 650nm and the optical path is 150mm to monitor the smoke mass concentration C in the chamber in real time. d (Unit: mg / m³) 3 ) and its rate of change dC d / dt.

[0058] (3) The laser power attenuation signal is monitored in real time by the laser power monitoring sensor in the protective lens module 32. The actual laser power Pactual (unit: W) after passing through the protective lens 322 is monitored and the power attenuation rate is calculated by the following formula: η = (Pactual) 设定 -P 实际 ) / P 设定 ×100%.

[0059] Where P 设定 The operator inputs the target laser output power (rated power, unit: W) to the control unit in step S4, which remains constant during a single welding process. η comprehensively reflects the transmission loss of the protective lens and the scattering and absorption of the laser by the plasma plume and dust in the welding chamber. The control unit also extracts the rate of change of η, dη / dt, as a supplementary feature of the control input to distinguish between two types of operating conditions: slow accumulation of lens contamination (smaller dη / dt) and sudden enhancement of the plasma plume (larger dη / dt), triggering different negative pressure regulation responses for each.

[0060] The control unit uses the above three signals as input variables for the fuzzy PID controller, takes the weighted sum of the three signals as the control deviation, and outputs the operating frequency f of the main vacuum pump unit in the negative pressure generating unit. 泵 (Adjustment range 20~50Hz) and the opening degree V of the solenoid regulating valve 阀 (Adjustment range 0~100%). The weighting coefficients α, β, and γ satisfy α+β+γ=1, and are automatically retrieved from the process parameter database by the control unit based on the material type and wall thickness. The fuzzy PID control rules are shown in the table below: Experiments have verified that the optimal negative pressure control parameters for different material grades under different wall thicknesses are shown in the table below, which can be directly accessed from the control unit's process parameter library: This embodiment upgrades the negative pressure regulation dimension from a single sensor and single signal feedback to a fusion of three sensors: molten pool temperature gradient, dust concentration, and laser power attenuation. It also upgrades the control method from simple threshold control to fuzzy PID adaptive control, realizing precise dynamic regulation of negative pressure under complex working conditions with multi-physics coupling.

[0061] Example 3 In a localized negative pressure environment, the refractive index n of the gas inside the chamber decreases as the absolute pressure P decreases, and the relationship satisfies the Gladstone-Dale linear relationship: n(P)-1=(n0-1)×(P / P0) Where n0 is the gas refractive index at standard atmospheric pressure P0 (101.325 kPa) (for air, n0≈1.000279 at a wavelength of 1064 nm), P is the actual absolute pressure inside the chamber (kPa), and T is considered as constant temperature treatment (the contribution of temperature change in the welding area to the path refractive index is relatively small compared to pressure change and can be ignored within the engineering accuracy range).

[0062] When the negative pressure (the decrease in cabin pressure relative to atmospheric pressure) is ΔP = P0 - P, the change in refractive index Δn is: Δn = (n0 - 1) × ΔP / P0 ≈ 2.79 × 10 -4 ×(ΔP / P0) For a laser system in which a parallel beam is incident through a focusing lens, when there is a medium layer with a uniformly varying refractive index in the optical path, the relationship between the laser beam focal shift Δf, the refractive index change Δn, and the optical path length L is as follows: Δf≈-Δn×L path / (n0 2 ) Where L path L is the propagation path length of the laser beam in the negative pressure medium (in mm). For the system of this invention, L path Taking the distance from the protective lens to the workpiece surface, which is the sum of the total length of the lens barrel adjustment unit 30 and the depth of the welding chamber 31, under the condition of a nominal focal length of 500mm, L path It is approximately 500mm.

[0063] Since the order of Δn is approximately 10 -5 The focal shift Δf caused solely by changes in refractive index is on the order of approximately 10. -3 On the order of mm (i.e., μm), for high-power laser welding (where the focal depth is typically several hundred μm), this theoretical drift is insufficient to cause a significant impact. However, under high-power laser welding conditions (≥30kW), the thermal lensing effect (resulting in a refractive index gradient due to increased temperature at the lens center) of the protective lens module 32, along with changes in plasma plume density distribution in a negative pressure environment, introduce additional equivalent focal length shifts on top of the aforementioned theoretical drift. Experimental measurements show that the combined focal drift is typically 0.2–2.0 mm, far exceeding the theoretical prediction of a simple refractive index change.

[0064] Therefore, this invention employs a method combining experimental calibration and theoretical correction to establish a quantitative correspondence between negative pressure and focal length offset: Before formal welding, the actual offset Δf of the laser beam focal position is measured at different negative pressures (gradually pumped from atmospheric pressure to the target negative pressure, measured every 5 kPa) using the knife-edge method or a CCD focal point measurement device. 实测The measured data is stored in the process parameter database of the control unit to form a lookup table. During experimental calibration, the laser power should be consistent with the actual welding power (or a power condition equivalent to the thermal lensing effect under the actual power should be used) to ensure the validity of the calibration results.

[0065] During the welding preparation stage (corresponding to step S3), the correspondence between negative pressure and focal length offset is consulted based on the target negative pressure level. The laser beam focus drift Δf caused by the change in gas refractive index due to the local negative pressure environment is calculated. Based on Δf, the required barrel length compensation is determined. By increasing or decreasing the number of annular cylinders 331 in the length adjustment module 33, the total length of the barrel adjustment unit 30 is compensated and adjusted to ensure that the laser beam focus position is accurately compensated to the target position. The above compensation adjustment is completed once before welding starts, and the barrel length remains unchanged during welding. The small fluctuations in negative pressure during welding have an impact on the focus drift within the allowable accuracy range and do not require further adjustment.

[0066] Based on systematic experiments, the laser beam focus drift and the required lens barrel length compensation under different negative pressure levels in the local negative pressure welding chamber 10 are shown in the table below (taking a nominal focal length of 500mm as an example): The data in the table above uses a nominal focal length of 500mm (i.e., the total length of the lens barrel adjustment unit 30 is 500mm) as an example. Experiments have verified that the focal drift Δf is related to the total length of the lens barrel L. total Approximately proportional: Δf(L total )≈Δf(500mm)×L total / 500 For other working conditions with nominal focal lengths of 300mm, 400mm, 600mm, etc., the compensation amount for the lens barrel length can be calculated using the above formula, or the parameters can be independently calibrated and stored in the process parameter library.

[0067] This embodiment establishes a quantitative correspondence between the change in gas refractive index and the laser beam focal drift under local negative pressure, and directly maps this relationship to the length compensation of the lens barrel adjustment unit 30, realizing the coordinated pre-compensation of negative pressure and focal length, which significantly improves the focal control accuracy of high-power laser welding.

[0068] Example 4 This embodiment provides a method for dynamic balance control of internal and external pressure difference. Based on the system described in Embodiment 1, for the welding of cylinders with large wall thickness, an inner ring negative pressure chamber is added inside the cylinder 200 to be welded. This chamber works in conjunction with the local negative pressure welding chamber 10 in Embodiment 1 to create a double-sided negative pressure environment at the welding site. The control unit then executes the dynamic balance control logic of internal and external pressure difference.

[0069] The structure of the inner negative pressure chamber is similar to the design concept of the local negative pressure welding chamber 10. It adopts a split and detachable structure, including two semi-circular arc-shaped inner chamber walls. The two inner chamber walls are symmetrically and detachably connected, and a fifth sealing element is set at the connection to ensure airtightness. The curvature of the inner chamber wall matches the inner diameter of the cylinder 200 to be welded. Inner arc-shaped sealing elements are provided at both the upper and lower ends of the outer arc surface of the inner chamber wall (i.e., the contact surface with the inner wall of the cylinder 200 to be welded). The inner arc-shaped sealing elements fit tightly against the inner wall of the cylinder, forming a sealed inner cavity in a local area inside the weld.

[0070] The inner ring negative pressure chamber is fixedly installed on the inner wall of the cylinder 200 to be welded via an inner cavity support frame, and rotates synchronously with the cylinder 200. An inner chamber evacuation port is provided at one end of the inner ring negative pressure chamber. A vacuum hose is led out through a rotary joint at the end of the cylinder 200 to connect to the inner chamber vacuum pump controlled by the control unit, enabling independent vacuum control of the inner ring negative pressure chamber. The vacuum hose must be a negative pressure resistant flexible hose (pressure resistance rating not lower than -0.1MPa), and the leakage rate of the rotary joint should not exceed 1×10⁻⁶. -3 Pa·m 3 / s, to ensure the airtightness of the inner cavity.

[0071] An inner chamber pressure sensor (range 0~101.325 kPa, accuracy ±0.05 kPa) is installed inside the inner negative pressure chamber to monitor the inner chamber pressure P in real time and transmit the signal to the control unit through a rotating conductive slip ring.

[0072] The circumferential coverage of the inner ring negative pressure chamber is not less than 50mm on each side of the weld area, and the axial width is not less than 40mm, to ensure that the back area of ​​the molten pool is completely within the negative pressure protection range.

[0073] Internal and external pressure difference ΔP=P 内 -P 外 It has a significant impact on the behavior of the molten pool and the quality of the weld: when ΔP is too large (greater than +500Pa), the molten pool bulges towards the inner wall, which can easily cause the molten pool to collapse and the back of the weld to be concave; when ΔP is too small (less than -200Pa), the molten pool bulges towards the outer wall, and the spatter spreads towards the inner wall intensifies; when ΔP is maintained within the optimal range, the molten pool morphology is stable and the spread of spatter is effectively suppressed.

[0074] The control unit executes the dynamic balance control logic of internal and external pressure difference: real-time acquisition of the external pressure P of the local negative pressure welding chamber 10. 外 The inner chamber pressure P of the inner negative pressure chamber 内 Calculate the real-time internal and external pressure difference ΔP; when the pressure difference exceeds the upper limit of the optimal pressure difference range, increase the internal venting rate Q. 内 And appropriately reduce the external venting rate Q. 外 When the pressure differential is below the lower limit of the optimal pressure differential range, reduce the internal venting rate Q. 内And appropriately increase the external venting rate Q. 外 The linkage between the inner and outer chamber air extraction rates is as follows: Q 内 (t)=Q 内0 +K 内 ·[ΔP(t)-ΔP 目标 ], Q 外 (t)=Q 外0 -K 外 ·[ΔP(t)-ΔP 目标 The optimal pressure differential ranges for different wall thicknesses are shown in the table below: By adjusting the extraction rates of the inner and outer chambers in a coordinated manner, the pressure difference between the inner and outer chambers is maintained within the optimal range, ensuring the stability of the molten pool shape and suppressing the spread of spatter, thereby improving the back-side forming quality of welds in the welding of thick-walled cylinders.

[0075] Example 5 This embodiment provides a method for online detection and feedback control of weld quality. Based on the system described in Embodiment 1, and building upon the sensor systems described in Embodiments 1 and 2, an acoustic emission sensor and a fiber optic spectrometer are further introduced to construct a real-time weld depth estimation and feedback control system, achieving an upgrade from open-loop preset to adaptive control.

[0076] Acoustic emission sensors are installed on the cavity wall 11 of the local negative pressure welding chamber 10 to collect acoustic emission signals during the welding process in real time, and to extract three characteristic parameters: root mean square value, peak frequency, and spectral centroid. Through experimental calibration, a quantitative relationship between the weld penetration and the aforementioned acoustic emission characteristic parameters is established.

[0077] The quantitative relationship between acoustic emission characteristic parameters and melting depth was established using a multiple linear regression model: D AE =a1×RMS+a2×f peak +a3×f centroid +a4×(RMS×f peak )+b Where DAE is the estimated melt depth (mm) for acoustic emission, RMS is the root mean square value of the acoustic emission signal (mV), and f peak f is the peak frequency (kHz). centroidLet be the centroid of the spectrum (kHz), a1, a2, a3, and a4 be the regression coefficients, and b be the intercept. Each coefficient was determined through the following calibration experiments: Under target material, target wall thickness, and target negative pressure conditions, at least 30 sets of calibration weld tests were conducted with different laser powers (divided into 20%, 40%, 60%, 80%, and 100% of rated power) and different welding speeds (combinations of 60%, 80%, 100%, and 120% of rated speed). The actual weld penetration depth was measured using metallographic sections, and least-squares regression was performed with the acoustic emission characteristic parameters of the corresponding time period to obtain the coefficient values. A holdout set was used for validation (the validation set proportion was no less than 20%). The model was considered valid when the root mean square error (RMSE) of the validation set was no greater than 1.5 mm.

[0078] Since the acoustic properties of different material grades differ, the regression coefficients mentioned above are calibrated separately according to the material grade and then uniformly stored in the process parameter library of the control unit. During welding, the control unit automatically retrieves the corresponding parameter group based on the material grade input by the operator.

[0079] The accuracy of the melt depth estimation reaches ±1.5mm (confidence level 95%). A fiber optic spectrometer is set on the side wall of the lens barrel adjustment unit 30. The spectral radiation signal of the aperture region is collected through the observation window 311, and the continuous spectrum slope and the intensity of the characteristic spectral lines of metal elements are extracted for spectral verification of the acoustic emission estimation results.

[0080] The control unit performs a weighted fusion of the melt depth estimated by acoustic emission and the melt depth verified by spectroscopy to obtain the real-time melt depth estimate D. 实时 The control unit will D 实时 With target melting depth D 目标 The comparison is performed, and the following feedback control logic is executed: (1) When D 实时 Below D 目标 At the same time, the control unit gradually increases the laser power and appropriately reduces the rotation speed of the support and drive unit 20 in order to prolong the laser action time and increase the melting depth; (2) When D 实时 When the pressure remains low and the laser power is close to its upper limit, the control unit further reduces the negative pressure inside the chamber, using the enhanced plasma plume suppression effect under a lower pressure environment to improve the laser's melting penetration ability. (3) When an abnormal jump in the characteristic frequency appears in the acoustic emission signal, the control unit automatically determines it as a precursor to keyhole instability or molten pool collapse, and triggers speed reduction and pressure increase intervention measures to prevent the expansion of welding defects.

[0081] Through the above feedback control, a complete feedback control system was constructed that links the penetration depth estimation with the laser power, welding speed, and negative pressure adjustment, realizing real-time online control of weld penetration depth and effectively ensuring the welding quality of circumferential welds for large thick-walled cylinders.

[0082] In practice, the pinhole radiation spectrum signal acquired by the fiber optic spectrometer is processed according to the following steps: (1) Calculation of continuous spectrum slope: The spectral intensity-wavelength curve is linearly fitted in the 500-650nm band, and the slope value k is used as the slope value. spec (Unit: counts / nm) Characterizes the molten pool temperature level, kJ spec A larger value indicates a higher molten pool temperature and a larger equivalent molten volume, and is positively correlated with the depth of molten metal. (2) Characteristic spectral line intensity extraction: Characteristic spectral lines of typical metallic elements are extracted for commonly used materials (austenitic stainless steel: iron characteristic line 373.5nm, chromium characteristic line 425.4nm; titanium alloy: titanium characteristic lines 453.4nm, 499.1nm), and the integral intensity I of the characteristic spectral lines is calculated. spec I spe c is positively correlated with the amount of molten metal evaporated, and consequently with the melting depth; (3) Spectral penetration depth estimation: A univariate calibration curve is used, and the I value is obtained by pre-establishing a calibration weld. spec -D measured curve (cubic polynomial fitting), real-time I spec Values ​​mapped to spectra to estimate melt depth D spec .

[0083] In practice, the control unit fuses the acoustic emission penetration depth estimate D using the following dynamic weighting method. AE And the estimated value of spectral melting depth D spec : D 实时 =w AE ×D AE +w pec ×D spec Fusion weight w AE and w spec The system is dynamically adjusted based on the real-time confidence level of each signal, with the following specific rules: (1) When the root mean square (RMS) value of the acoustic emission signal is lower than the effective threshold (more than 3 times the background noise), the acoustic emission signal is deemed invalid, and w is set to w. AE =0, w spec =1; (2) When the signal-to-noise ratio (SNR) is lower than the set threshold (SNR < 10 dB) due to smoke and dust pollution inside the cabin, the spectral signal is deemed invalid, and w is set to w. AE =1, w spec =0; (3) Under normal operating conditions where both signals are valid, the standard deviation σ of the most recent 10 estimation points for each signal is used as the basis for the calculation. AE and σ spec Calculate the confidence weights: w AE =(1 / σ AE ) / (1 / σ AE +1 / σspec), w spec =1-w AE A smaller standard deviation indicates a more stable signal, and a larger corresponding weight. The above dynamic weighting strategy ensures the robustness of the system under complex operating conditions (such as a sudden increase in smoke or acoustic interference).

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A local negative pressure laser welding dynamic control system, characterized in that, include: The local negative pressure welding chamber (10) has openings at both the top and bottom, and the upper and lower parts are sealed to the cylinder wall of the cylinder to be welded (200), forming a closed space in the local area of ​​the weld. The support and drive unit (20) is located below the local negative pressure welding chamber (10) and is used to support and drive the cylinder to be welded (200) to rotate. The lens barrel adjustment unit (30) is located outside the local negative pressure welding chamber (10) as a laser incident interface. It includes a length adjustment module (33) and a protective lens module (32). The length adjustment module (33) is composed of multiple sealed and detachably connected annular cylinders (331) to adjust the laser focal length. The protective lens module (32) is equipped with an air blowing needle valve (323). The air passage of the air blowing needle valve (323) is parallel to the plane where the protective lens (322) is located and intersects the optical axis. The air passage outlet faces the surface of the protective lens (322) to form an air curtain on the surface of the protective lens (322) to suppress metal vapor plume contamination. The negative pressure generating unit is sealed to the interior of the local negative pressure welding chamber (10) and is used to adjust the negative pressure inside the chamber, including a vacuum sensor. The control unit is electrically connected to each unit and adjusts the negative pressure inside the chamber in real time through a fuzzy PID controller based on the molten pool temperature gradient signal, the dust concentration signal, and the laser power attenuation signal.

2. The local negative pressure laser welding dynamic control system according to claim 1, characterized in that, The local negative pressure welding chamber (10) includes two identical arc-shaped cavity walls (11). The two cavity walls (11) are symmetrically and detachably connected. An annular first sealing element (12) is provided at the upper and lower parts of the cavity wall (11). The first sealing element (12) is sleeved on the outer wall of the cylinder (200) to be welded and cooperates with the cavity wall (11) to form a dynamic seal. A second sealing element (13) is provided at the connection of the two cavity walls (11).

3. The local negative pressure laser welding dynamic control system according to claim 1, characterized in that, The support and drive unit (20) includes a support base (21), a support base (22), and a drive mechanism (23). The top of the support base (21) is connected to the bottom of the local negative pressure welding chamber (10). The support base (22) is located below the support base (21), and the drive mechanism (23) is installed on the support base (22) to support the cylinder to be welded (200) and drive the cylinder to be welded (200) to rotate along its own axis; The drive mechanism (23) includes a circular support disk (231), multiple support rollers (232) and a drive device. The multiple support rollers (232) are rotatably mounted on the circular support disk (231) along multiple symmetrical axes on the disk surface. The output end of the drive device is connected to two support rollers (232) on one of the symmetrical axes through a reduction mechanism.

4. The local negative pressure laser welding dynamic control system according to claim 1, characterized in that, The lens barrel adjustment unit (30) also includes a welding chamber (31), a cooling unit and a negative pressure module (34). The welding chamber (31) is located outside the local negative pressure welding chamber (10) and communicates with the interior of the local negative pressure welding chamber (10). The protective lens module (32), the length adjustment module (33) and the negative pressure module (34) are sequentially and sealed together along the optical axis. The negative pressure module (34) is provided with an air extraction hole (341) for connecting to the negative pressure generating unit. The cooling unit is a spiral cooling water channel surrounding the protective lens module (32), the length adjustment module (33) and the negative pressure module (34). The protective lens module (32) includes an annular lens mounting module (321) and a protective lens (322). The protective lens (322) is embedded in the annular lens mounting module (321). The air blowing needle valve (323) is set on the outer peripheral wall of the annular lens mounting module (321). A laser power monitoring sensor is set on the side of the protective lens (322) near the welding chamber (31). The length adjustment module (33) is composed of multiple annular cylinders (331) with the same structure, which are detachably connected in sequence by sealing rings and bolts or threads.

5. The local negative pressure laser welding dynamic control system according to claim 1, characterized in that, The local negative pressure welding chamber (10) includes two identical semi-circular arc-shaped cavity walls (11). The two cavity walls (11) are symmetrically and detachably connected. The upper and lower ends of the opposite side walls of the two cavity walls (11) are slidably sealed with semi-circular arc plates (14). A third sealing element (15) is provided on the inner arc of the semi-circular arc plate (14). The two semi-circular arc plates (14) are detachably connected. A fourth sealing element is provided at the connection of the two semi-circular arc plates (14).

6. The local negative pressure laser welding dynamic control system according to claim 1, characterized in that, It also includes a preheating and cooling unit and a dust treatment unit, both of which are electrically connected to the control unit; The preheating and cooling unit includes a heating device, a cooling device, and a temperature sensing unit located at the upper and lower parts of the local negative pressure welding chamber (10). The heating device and the cooling device are respectively connected to the upper and lower parts of the local negative pressure welding chamber (10). The fume treatment unit is connected to the interior of the local negative pressure welding chamber (10) and works in conjunction with the negative pressure generating unit to treat the fume inside the local negative pressure welding chamber (10).

7. The local negative pressure laser welding dynamic control system according to claim 1, characterized in that, The negative pressure generating unit also includes an electromagnetic regulating valve; The control unit collects data from three sensors in real time: the molten pool temperature gradient signal, the fume concentration signal, and the laser power attenuation signal. The molten pool temperature gradient signal is acquired through multiple sets of infrared temperature sensors arranged along the welding direction, and the temperature gradient value G between the front and rear zones of the molten pool is calculated. T =(T 后区 -T 前区 The smoke and dust concentration signal is monitored in real time by a laser transmission smoke and dust concentration sensor, which detects the mass concentration of smoke and dust in the cabin. d and its rate of change dC d / dt; The laser power attenuation signal is used to calculate the power attenuation rate η in real time through the laser power monitoring sensor; The control unit inputs three signals to the fuzzy PID controller, and uses the main vacuum pump group working frequency and the opening degree of the electromagnetic regulating valve as output variables to adjust the negative pressure in the chamber in real time. The weighting coefficient is automatically retrieved by the control unit from the process parameter library according to the material type and wall thickness.

8. The local negative pressure laser welding dynamic control system according to claim 1, characterized in that, The control unit is also used to perform negative pressure-optical coordinated control, specifically including: Based on the target negative pressure, the correspondence between negative pressure and focal length offset is queried. The laser beam focal point drift caused by the change in gas refractive index due to the local negative pressure environment is calculated. The total length of the lens tube adjustment unit (30) is compensated by increasing or decreasing the number of annular cylinders (331) in the length adjustment module (33), so that the laser beam focal point position is compensated to the target position.

9. The local negative pressure laser welding dynamic control system according to claim 1, characterized in that, It also includes an inner ring negative pressure chamber located inside the cylinder body (200) to be welded, the inner ring negative pressure chamber having an independent air extraction pipe. The control unit performs dynamic balance control of internal and external pressure differences, specifically including: Real-time acquisition of the external chamber pressure P of the local negative pressure welding chamber (10) 外 The inner chamber pressure P of the inner negative pressure chamber 内 Calculate the real-time internal and external pressure difference ΔP; when the pressure difference exceeds the upper limit of the optimal pressure difference range, increase the internal venting rate Q. 内 And appropriately reduce the external venting rate Q. 外 When the pressure differential is below the lower limit of the optimal pressure differential range, reduce the internal venting rate Q. 内 And appropriately increase the external venting rate Q. 外 To maintain the internal and external pressure difference within the optimal range to ensure the stability of the molten pool morphology and suppress the spread of spatter; The local negative pressure laser welding dynamic control system also includes an acoustic emission sensor and a fiber optic spectrometer, both of which are electrically connected to the control unit. The acoustic emission sensor is set on the cavity wall (11) of the local negative pressure welding chamber (10) to collect acoustic emission signals during the welding process in real time and extract characteristic parameters. The fiber optic spectrometer is set on the side wall of the lens tube adjustment unit (30), and its fiber optic probe is optically coupled to the welding area inside the chamber through the observation window (311) of the welding chamber (31) to collect the spectral radiation signal of the pinhole area. The control unit performs weighted fusion of the signals from the acoustic emission sensor and the fiber optic spectrometer, estimates the weld penetration depth in real time, and, based on the deviation between the estimated penetration depth and the target penetration depth, controls the rotation speed of the support and drive unit (20) and the pumping rate of the negative pressure generating unit, as well as sends power adjustment commands to the external laser, to achieve closed-loop adjustment of the welding speed, the negative pressure inside the chamber, and the laser power.

10. A method for local negative pressure laser welding of large thick-walled cylinders, implemented based on the system described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Hoist the cylinder to be welded (200) to the support and drive unit (20), and adjust the height of the cylinder to be welded (200) so that the weld position matches the working height of the local negative pressure welding chamber (10); S2. Move the local negative pressure welding chamber (10) to the weld start position, first start the negative pressure generating unit to assist the sealing, and then draw the negative pressure in the chamber to the target value of the preheating stage. S3. According to the wall thickness of the cylinder (200) to be welded and the welding process requirements, adjust the length adjustment module (33) so that the total length of the lens barrel adjustment unit (30) matches the focal length requirement, and query the correspondence between the negative pressure and the focal length offset according to the target negative pressure to complete the negative pressure-optical collaborative compensation. S4. Set the welding process parameters and the operating parameters of each unit in the control unit; S5. Seal the weld area on the inside of the cylinder (200) to be welded; The support and drive unit (20) is started to drive the cylinder to be welded (200) to rotate. The external laser is started to output a laser beam to irradiate the weld area. The control unit dynamically adjusts the negative pressure in the chamber through a fuzzy PID controller based on three signals: the temperature gradient of the molten pool, the concentration of dust, and the laser power attenuation. The melting depth is estimated in real time through acoustic emission signal and pinhole radiation spectrum, and the laser power, welding speed and negative pressure are adjusted to complete the circumferential weld. S6. After welding is completed, turn off the laser, gradually restore the internal pressure of the local negative pressure welding chamber (10) to normal pressure, shut down the welding system and check the weld quality.

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