Titanium alloy laser welding pore control method and system based on molten pool state feedback

Abstract

The application discloses a kind of based on molten pool state feedback's titanium alloy laser welding pore control method and system, by design adjustable electromagnetic stirring power and frequency electromagnetic generating module connection magnetic field exerting component, establish the matching process parameter library of electromagnetic stirring and laser welding, cooperative adjustment infrared blue light composite laser welding process parameter, including infrared laser power, blue light laser power, welding speed and defocusing amount.Again using high-speed camera device carries infrared thermal imaging monitoring molten pool state, simultaneously construct real-time monitoring and feedback control system, to realize titanium alloy welding overall closed-loop control.Adopt the method of the application can realize the stirring of molten pool in laser welding process, make pore effectively escape, avoid the pore defect caused by gas not in time to escape under the condition that laser welding cooling speed is faster.Titanium alloy laser welding pore rate is reduced to 2% and below, compared with traditional laser welding method reduces more than 80%, significantly improves welding quality stability.

Description

Technical Field

[0001] This invention relates to the field of laser welding technology, and in particular to a method and system for controlling porosity in titanium alloy laser welding based on molten pool state feedback. Background Technology

[0002] Titanium alloys, with their high specific strength, excellent corrosion resistance, good fracture toughness, and good biocompatibility, have become indispensable materials in aerospace, marine engineering, petrochemical, and medical device fields. Their corrosion resistance far exceeds that of stainless steel, resisting long-term corrosion from seawater, chlorides, and acidic / alkaline media, making them suitable for submarine pressure hulls, deep-sea drilling components, and chemical reaction vessels. Specific strength is a crucial factor in achieving lightweight aircraft and improving fuel efficiency and load capacity, leading to their widespread use in aircraft frames, engine compressor blades, and rocket casings. In particular, their excellent fracture toughness ensures structural safety and reliability under extreme loads, and their biocompatibility and non-toxicity make them an ideal choice for human implants, allowing for long-term stable coexistence with human tissue. Therefore, in practical applications, titanium alloys are often welded to manufacture various components.

[0003] In the laser welding of titanium alloys, porosity is a critical issue that seriously affects weld quality. During laser welding of titanium alloys, due to their high affinity for gases such as hydrogen, oxygen, and nitrogen, these gases are easily drawn in. Furthermore, the rapid cooling rate of the molten pool during laser welding prevents the gases from escaping, leading to the formation of porosity. The presence of porosity reduces the strength, toughness, and sealing properties of the weld joint, severely impacting the reliability and service life of titanium alloy components.

[0004] Currently, solutions to the porosity problem in titanium alloy laser welding are limited. Conventional process parameter optimization, such as adjusting laser power, welding speed, and defocusing amount, can improve porosity to some extent, but the effects are not significant. Other complex welding techniques, such as vacuum welding and dual-beam welding, are also employed. While these can reduce porosity formation, they suffer from high equipment costs and complex processes, hindering large-scale application. Furthermore, the application of infrared-blue light composite laser welding equipment combined with electromagnetic stirring technology for porosity control in titanium alloy laser welding is not yet mature, lacking effective methods to fully leverage the advantages of electromagnetic stirring in porosity control.

[0005] Therefore, there is an urgent need for a method and system for controlling porosity in titanium alloy laser welding based on molten pool state feedback, so as to effectively control the porosity generated during laser welding and further improve the welding quality. Summary of the Invention

[0006] The summary section of this application is intended to provide a brief overview of the concepts, which will be described in detail in the detailed description section below. This summary section is not intended to identify key or essential features of the claimed technical solutions, nor is it intended to limit the scope of the claimed technical solutions.

[0007] To address the problems and shortcomings of existing technologies, this invention aims to provide a method and system for controlling porosity in titanium alloy laser welding based on molten pool state feedback. By introducing electromagnetic stirring, the flow state of the molten pool during titanium alloy laser welding is effectively improved, promoting gas escape and thus significantly reducing porosity defects and improving welding quality. Furthermore, this invention offers advantages such as simple operation and low cost, facilitating its widespread application in actual production. This addresses the problems mentioned in the background section.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] As a first aspect of this application, the present invention discloses a method for controlling porosity in titanium alloy laser welding based on molten pool state feedback, comprising the following steps:

[0010] Step S1: Perform a thorough surface cleaning of the welding area of ​​the workpiece to be welded, removing impurities such as oil and oxide scale from the surface;

[0011] Step S2: Place the base material and the part of the workpiece to be welded below the magnetic field application component and as close as possible to the weld pool. The base material is selected from welding materials that are the same material as the workpiece to be welded.

[0012] Step S3: Establish a matching process parameter library that includes electromagnetic stirring parameters and laser welding parameters;

[0013] Step S4: Based on the material and thickness of the workpiece to be welded, and according to the matching process parameter library, the laser power of the infrared blue light composite laser welding head is set by adjusting the control module, and then simultaneously turned on to melt the workpiece to be welded to form a molten pool and stabilize the thermal field.

[0014] Step S5: During the welding process, the base material is used as the filler material and the inert gas is used as the protective gas. Welding is carried out according to the preset welding path. At the same time, the monitoring feedback module monitors the state of the molten pool in real time during the welding process and sends the data to the host computer.

[0015] Step S6: In the host computer, the real-time molten pool status monitored is compared with the preset ideal molten pool status. When the abnormality occurs for the first time, the power and frequency of the electromagnetic stirring are set by the control module in combination with the preliminary diagnosis rules and the matching process parameter library. The electromagnetic generation module is turned on to apply electromagnetic force to the magnetic field component to achieve molten pool stirring, which is used to promote the rise of gas in the molten pool and suppress porosity.

[0016] Step S7: Continuously compare the real-time molten pool state with the preset ideal molten pool state. If an abnormality occurs again, adjust the magnetic field parameters of the electromagnetic stirring and the process parameters of laser welding through PID feedback control.

[0017] Preferably, the electromagnetic generation module generates an alternating magnetic field and outputs it to the magnetic field application component. The output power is adjustable in the range of 0.5~2.5kW and the frequency is adjustable in the range of 4~15Hz. The power of the electromagnetic generation module determines the magnitude of the generated electromagnetic force and is proportionally matched with the laser power of the infrared-blue light composite laser welding head.

[0018] Preferably, the infrared laser is used to provide thermal energy input to heat the workpiece to be welded and the base material to melt and form a molten pool. The power of the infrared laser increases with the increase of the thickness of the workpiece plate to be welded, and the power range of the infrared laser is 1~20kW.

[0019] Preferably, the blue laser is used to assist the infrared laser in improving the absorption rate of titanium alloy welding and stabilizing the thermal field distribution to reduce porosity formation. The power of the blue laser increases with the increase of the thickness of the workpiece plate being welded, and the power of the blue laser ranges from 0.3 to 2.4 kW.

[0020] Preferably, when the thickness of the workpiece plate is constant, the welding speed increases with the increase of the laser power of the infrared blue light composite laser welding head; the absolute value of the defocusing amount decreases with the increase of the laser power, so that the size of the spot irradiated on the surface of the workpiece is smaller; and the welding swing amplitude decreases accordingly as the thickness of the workpiece plate increases with the increase of the laser power.

[0021] Preferably, in step 6, the monitoring feedback module is used to monitor in real time whether the molten pool state parameters are in an ideal molten pool state, including molten pool size, temperature field distribution, and flow field state; when the local temperature of the temperature field distribution is abnormal and / or the flow field state is turbulent and the duration is longer than 2 seconds, it is determined to be an unideal molten pool state. The adjustment amount of the control is calculated and feedback control is initiated. Then the defocusing amount and the distance between the magnetic field application component and the workpiece being welded are adjusted. If the molten pool state cannot be returned to the ideal molten pool state range within 3 seconds after the adjustment, the welding is suspended.

[0022] Preferably, the ideal molten pool size has a length of 1-30 mm and a width of 0-12 mm. For every 2 mm increase in the thickness of the workpiece plate, the length of the ideal molten pool increases by 0-5 mm and the width increases by 0-2 mm. The ideal molten pool has a center temperature of 1800-2200℃, a temperature difference of no more than 500℃ between the edge and center, and no local overheating or undercooling areas. The ideal molten pool has a flow rate of 5-15 cm / s, and no eddies or turbulence occur during unidirectional or bidirectional stirring.

[0023] Preferably, in step S6, the ideal molten pool state is first quantified as follows: The state of the molten pool monitored in real time by the high-speed camera device is represented as... Calculate the deviation from the ideal molten pool state. If deviation occurs Then, based on the preliminary diagnostic rules, determine whether to adjust the power of the infrared-blue light composite laser welding head or start the power and frequency of electromagnetic stirring.

[0024] Preferably, in step S7, if the molten pool state monitored in real time by the high-speed camera device after the initial intervention still has a deviation... Independent PID control loops are set up, including temperature field control loop, flow field control loop, and geometry control loop. The laser power adjustment is calculated based on temperature deviation and flow velocity deviation. Power adjustment of electromagnetic stirring Then, the influence between laser power and electromagnetic stirring is eliminated by a decoupling compensation network to obtain the final laser power command and the final electromagnetic stirring power command, which are then sent to the adjustment and control module to realize the adjustment of the infrared blue light composite laser welding head and the electromagnetic generation module.

[0025] As a second aspect of this application, the present invention also discloses a titanium alloy laser welding porosity control system based on molten pool state feedback, comprising a power generation module, an adjustment and control module, an electromagnetic generation module, a magnetic field application component, and a monitoring and feedback module. The power generation module is connected to the adjustment and control module to provide driving power for the entire system. The adjustment and control module is connected to a host computer to transmit electromagnetic stirring and laser welding parameters. The adjustment and control module, through the electromagnetic generation module, connects to the magnetic field application component to control the generation of an adjustable alternating magnetic field output to stir the welding molten pool of the workpiece being welded. The adjustment and control module is also connected to the laser generation module to control the output power of the laser gun within the laser generation module, simultaneously performing welding of the workpiece and molten pool porosity control. The monitoring and feedback module monitors the welding molten pool of the workpiece in real time, sending the monitored molten pool parameters to the host computer for comparison with a matching process parameter library to determine if it is in an ideal molten pool state. If it is in an irrational state, the parameters are adjusted and output. The shape and size of the magnetic field application component are optimized and adjusted according to the common shapes and sizes of titanium alloy welding workpieces.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention provides a method and system for controlling porosity in titanium alloy laser welding based on molten pool state feedback. First, the welding area of ​​the workpiece is rigorously cleaned to remove surface impurities such as oil and oxide scale. The base material and the area to be welded on the workpiece are placed directly below the center of the magnetic field application component, which is positioned as close as possible to the molten pool to ensure effective application. A matching process parameter library is established, including electromagnetic stirring parameters and laser welding parameters. Based on the material and thickness of the workpiece, the laser power of the infrared-blue composite laser welding head is adjusted using the control module according to the matching process parameter library, and then simultaneously activated to melt the workpiece, forming a molten pool and stabilizing the thermal field. During welding, the base material is used as the filler material, and an inert gas is used as the protective gas. Welding is performed according to a preset welding path, while a monitoring and feedback module monitors the temperature and flow field information of the molten pool in real time and sends it to the host computer. The real-time molten pool status monitored in the host computer is compared with the preset ideal molten pool status. When an anomaly first occurs, the power and frequency of the electromagnetic stirring are set by the control module based on preliminary diagnostic rules and the matching process parameter library. The electromagnetic generator module is activated to apply electromagnetic force to the magnetic field component to achieve molten pool stirring, which promotes gas buoyancy and suppresses porosity. The real-time molten pool status is continuously compared with the preset ideal molten pool status. When an anomaly occurs again, PID feedback control is used to adjust the magnetic field parameters of the electromagnetic stirring and the laser welding process parameters. This invention promotes gas diffusion and escape in the molten pool through the strong stirring effect of electromagnetic stirring, which can reduce the porosity of titanium alloy laser welding to below 2%, which is more than 80% lower than that of traditional welding methods, greatly improving the quality and performance of the welded joint. The real-time monitoring and feedback control system can adjust parameters in a timely manner according to the actual situation in the welding process, effectively responding to various interference factors in the welding process, making the welding quality more stable and reliable, reducing the scrap rate, and improving production efficiency. Compared with some complex and expensive welding technologies, the electromagnetic stirring-assisted method of the present invention only requires the addition of a relatively simple magnetic field application component and monitoring and control system to the laser welding equipment. The equipment modification cost is low, the operation is simple and easy to master, and it has good cost-effectiveness and market promotion prospects. Attached Figure Description

[0028] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application.

[0029] In the attached diagram:

[0030] Figure 1 This is a structural block diagram of the titanium alloy laser welding porosity control system based on molten pool state feedback in an embodiment of the present invention;

[0031] Figure 2 This is a flowchart illustrating the steps of the titanium alloy laser welding porosity control method based on molten pool state feedback in an embodiment of the present invention.

[0032] Figure 3 This is a connection structure diagram of the titanium alloy laser welding porosity control system based on molten pool state feedback in an embodiment of the present invention;

[0033] Figure 4 This is a connection structure diagram of the electromagnetic generation module and the magnetic field application component in the porosity control system for titanium alloy laser welding based on molten pool state feedback, as described in this embodiment of the invention.

[0034] Figure 5 This is an illustration of the effect of a 2.5 mm thick titanium alloy welding test plate in an embodiment of the present invention.

[0035] Figure 6 The figure shows the tensile property test results of a 2.5 mm thick titanium alloy welded test plate in an embodiment of the present invention.

[0036] Figure 7 This is a fracture morphology diagram of a tensile specimen of a 2.5 mm thick titanium alloy welded test plate in an embodiment of the present invention.

[0037] Figure 8 Metallographic image of a 2.5 mm thick titanium alloy welding test plate in an embodiment of the present invention;

[0038] Figure 9 This is a comparison diagram showing the effect of using the titanium alloy laser welding porosity control method based on molten pool state feedback on thin plates in an embodiment of the present invention;

[0039] Figure 10 This is a comparison diagram showing the effect of using the titanium alloy laser welding porosity control method based on molten pool state feedback for thick plates in an embodiment of the present invention.

[0040] The following are the labels in the attached diagram: 1. Infrared laser welding head; 2. Blue laser welding head; 3. Magnetic field application component; 4. Workpiece to be welded; 5. Welding robot. Detailed Implementation

[0041] Embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings. While some embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the accompanying drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0042] It should also be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. Unless otherwise specified, the embodiments and features described in this disclosure can be combined with each other.

[0043] Example 1

[0044] In this embodiment of the invention, a porosity control system for titanium alloy laser welding based on molten pool state feedback is disclosed, referring to... Figure 1 and Figure 3 The system includes a power generation module, an adjustment and control module, an electromagnetic generation module, a magnetic field application component, a laser generation module, a workpiece to be welded, and a monitoring and feedback module. The power generation module, connected to the adjustment and control module, provides the driving power for the entire system. The adjustment and control module, connected to a host computer, transmits parameters for electromagnetic stirring and laser welding. Through the electromagnetic generation module, the adjustment and control module connects to the magnetic field application component to control the generation of an adjustable alternating magnetic field, driving the component to stir the weld pool of the workpiece. The adjustment and control module also connects to the laser generation module to control the output power of the infrared-blue composite laser welding head within the laser generation module, simultaneously performing welding of the workpiece and control of weld pool porosity. The monitoring and feedback module monitors the weld pool of the workpiece in real time, sending the monitored weld pool parameters to the host computer for comparison with a matching process parameter library to determine if it is in an ideal weld pool state. If it is not in an ideal weld pool state, adjustments are made before output.

[0045] Specifically, the host computer is connected to both the regulation and control module and the monitoring and feedback module. The regulation and control module uses a PLC programmable logic controller, and its connection to the host computer is achieved through a communication interface, optionally using a real-time industrial Ethernet protocol. The host computer transmits the power setpoint, magnetic field frequency, laser power, and start / stop commands from the electromagnetic generator module to the regulation and control module. The regulation and control module transmits parameters such as the actual output power and frequency of the electromagnetic generator module and the actual output laser power of the laser generator module to the host computer. The monitoring and feedback module transmits real-time monitored welding pool feedback data to the host computer. The regulation and control module maintains communication with the host computer to ensure synchronization of the magnetic field parameters with the laser welding process parameters. The electromagnetic generator module and the magnetic field application component are electrically connected via a high-power output terminal. The electromagnetic generator module integrates a power amplifier and impedance matching circuit, and can be connected to the regulation and control module via a shielded twisted-pair cable or an industrial Ethernet cable to drive the magnetic field application component to generate a sufficiently strong stirring magnetic field. The connection between the control module and the laser generator module can be achieved through a combination of serial Ethernet or digital I / O interfaces. Serial Ethernet is used to achieve continuous and precise control of the laser welding head power, while digital I / O interfaces are used to control the laser welding head's on / off state, light emission, and shut-off. The control module can simultaneously control the electromagnetic generator module and the laser generator module via the same real-time industrial Ethernet cable (such as EtherCAT), ensuring that all devices use the same system clock.

[0046] In this embodiment, the power generation module can be a three-phase controllable rectifier industrial power supply module with PFC function, which converts the AC power from the grid into stable DC power to provide drive power for the entire system. The electromagnetic generation module can use existing magnetic field generation and control devices to generate an alternating magnetic field. Through inversion, the input DC power is converted into low-frequency AC power with a frequency of 4~15 Hz and a power of 0.5~2.5 kW that is continuously adjustable, and output to the magnetic field application component to adapt to different welding process requirements. The host computer has a built-in data processing unit and parameter adjustment unit. The data processing unit uses data analysis algorithms to process the sensor data, and the parameter adjustment unit controls the parameter adjustment of the electromagnetic generation module and the laser generation module according to the processing results. It should be noted that the power generation module and the electromagnetic generation module both use known devices in the prior art, and therefore will not be described in detail in this application.

[0047] like Figure 3 and Figure 10As shown, the shape and size of the magnetic field applying component 3 are optimized based on the common shapes and sizes of titanium alloy welding workpieces to ensure that the magnetic field can act uniformly and effectively on the weld pool area. Specifically, the inner diameter of the electromagnetic coil of the magnetic field applying component is adjusted according to the shape and size of the titanium alloy welding workpiece. The laser generating module is an infrared-blue composite laser welding head, including an infrared laser welding head 1 and a blue laser welding head 2. The magnetic field applying component 3 is connected to the infrared laser welding head 1 and the blue laser welding head 2 via connectors, and the infrared laser welding head 1 is connected to the execution end of the welding robot 5 via connectors. During welding, the electromagnetic coil of the magnetic field applying component 3 must be placed directly above the workpiece 4 to be welded, and both the infrared laser welding head 1 and the blue laser welding head 2 must be aligned with the workpiece 4.

[0048] The adjustment and control module connects to a host computer for intelligent control. The monitoring and feedback module includes a high-speed camera equipped with an infrared thermal imaging component, which sends real-time weld pool data of the workpiece to the host computer. Simultaneously, we have established a matching process parameter library for electromagnetic stirring parameters and laser welding parameters, stored in the host computer. Through the host computer's built-in data analysis algorithm, based on the weld pool geometry and flow characteristics extracted by the high-speed camera and the temperature field distribution obtained by infrared thermal imaging, the monitored data is compared with the preset ideal weld pool state. If a deviation is found, indicating a non-ideal weld pool state, parameters such as the electromagnetic stirring frequency, current intensity, dual-band laser power ratio, and scanning speed are adjusted in real time to suppress porosity, reduce spatter, and ensure stable welding quality.

[0049] like Figure 5 The image shows a 2.5 mm thick titanium alloy welded test plate. The tensile property test results of the welded joint are as follows: Figure 6 As shown, the fracture location is at the fusion line between the weld and the base metal. This is because the fusion line region after welding is extremely sensitive to temperature gradients and cooling rates. Excessive cooling leads to martensitic phase transformation, resulting in low tensile strength at this location, causing fracture during tensile testing. Figure 7 As shown, the fracture surface clearly exhibits a porous and reticulated loose structure, with large-sized pores and a fibrous / sheet-like interwoven morphology. Under stress, these pores expand, coalesce, and interconnect, forming a microporous aggregate-type ductile fracture. Therefore, the tensile strength is relatively low at only 806 MPa. This process consumes a large amount of energy, thus exhibiting high toughness and a fracture elongation of 15%. Figure 8 As shown, a typical three-zone structure is clearly presented: the two sides are the parent material zone, with a uniform and fine equiaxed α+β phase microstructure; the narrow band adjacent to the parent material is the heat-affected zone, where coarsening and acicular microstructure are visible. Martensite; the intermediate weld zone is characterized by coarse columnar crystals and numerous acicular crystals. Characterized by martensite and the presence of a small amount of welding porosity, this reflects the typical microstructure of rapid solidification in laser welding.

[0050] Therefore, this invention also discloses a method for controlling porosity in titanium alloy laser welding based on molten pool state feedback, which can effectively solve the porosity problem of the welded joint. Figure 2 As shown, the specific steps include:

[0051] Step S1: Perform a thorough surface cleaning of the welding area of ​​the workpiece to be welded, removing impurities such as oil and oxide scale from the surface;

[0052] Step S2: Place the base material and the part of the workpiece to be welded below the magnetic field application component and as close as possible to the weld pool. The base material is selected from welding materials that match the material of the workpiece to be welded.

[0053] Step S3: Establish a matching process parameter library that includes electromagnetic stirring parameters and laser welding parameters;

[0054] Step S4: Based on the material and thickness of the workpiece to be welded, and according to the matching process parameter library, the laser power of the infrared blue light composite laser welding head is set by adjusting the control module, and then simultaneously turned on to melt the workpiece to be welded to form a molten pool and stabilize the thermal field.

[0055] Step S5: During the welding process, the base material is used as the filler material and the inert gas is used as the protective gas. Welding is carried out according to the preset welding path. At the same time, the monitoring feedback module monitors the state of the molten pool in real time during the welding process and sends the data to the host computer.

[0056] Step S6: In the host computer, the real-time molten pool status monitored is compared with the preset ideal molten pool status. When the abnormality occurs for the first time, the power and frequency of the electromagnetic stirring are set by the control module in combination with the preliminary diagnosis rules and the matching process parameter library. The electromagnetic generation module is turned on to apply electromagnetic force to the magnetic field component to achieve molten pool stirring, which is used to promote the rise of gas in the molten pool and suppress porosity.

[0057] Step S7: Continuously compare the real-time molten pool state with the preset ideal molten pool state. If an abnormality occurs again, adjust the magnetic field parameters of the electromagnetic stirring and the process parameters of laser welding through PID feedback control.

[0058] Specifically, the welding area of ​​the workpiece to be welded is first subjected to rigorous surface cleaning and drying to remove oil, scale, and impurities. This is primarily achieved through a combination of alkaline cleaning to remove oil and acid cleaning to remove scale. Alkaline cleaning involves immersing or spraying with an alkaline degreasing agent at 60-80°C, or cleaning with solvents such as trichloroethylene. Acid cleaning is performed using a mixed acid solution of HF (hydrofluoric acid) + HNO3 (nitric acid). Finally, the workpiece is rinsed thoroughly with plenty of water and dried. This process significantly reduces gas generation. Before welding, the area to be welded is placed directly below the center of the magnetic field application component. A matching process parameter library is established, containing electromagnetic stirring parameters and laser welding process parameters, to provide parameter references for the welding process. This matching process parameter library is based on preset process parameters after multiple experiments. In this embodiment, a TC4 titanium alloy sheet with a thickness of 2.5~20mm is used as an example, as shown in Table 1 below.

[0059]

[0060] Table 1

[0061] Table 1 above shows the electromagnetic stirring and laser welding process parameters for some TC4 titanium alloy welded plates with thicknesses ranging from 2.5mm to 20mm. Since the thickness range of TC4 titanium alloy welded plates is very wide, the matching process parameter library is not limited to the contents of Table 1. Specifically, as shown in Table 1, the power of the electromagnetic stirring determines the magnitude of the generated electromagnetic force and is directly proportional to the laser power of the infrared-blue light composite laser welding head. That is, the greater the power of the electromagnetic force, the greater the laser power of the infrared-blue light composite laser welding head. A greater electromagnetic force results in stronger electromagnetic stirring, promoting gas buoyancy in the molten pool and thus suppressing porosity. Furthermore, as the thickness of the welded plate increases, a greater electromagnetic force results in stronger electromagnetic stirring. Therefore, frequency control can improve the uniformity of electromagnetic stirring. The infrared laser mainly provides thermal energy input and is positively matched to the electromagnetic stirring intensity; higher power requires stronger stirring to suppress overheating and shrinkage in the molten pool. The infrared laser power increases accordingly with the plate thickness. Blue lasers primarily assist infrared lasers in enhancing the absorptivity of titanium alloys (blue light absorptivity is 15%-20% higher than infrared) and stabilizing the thermal field distribution. The power of the blue laser increases accordingly with the increase of the plate thickness. The welding speed reflects the duration of the thermal field action and is related to both the plate thickness and the laser power.

[0062] When the workpiece thickness is constant, increasing the laser power allows for a suitable increase in welding speed. Changes in defocusing amount alter the spot size and power density; a larger absolute value of defocusing amount results in a larger spot size irradiating the workpiece surface. At the same laser power, a larger spot size leads to a significant decrease in power density (power density is inversely proportional to spot area). Defocusing amount must be optimized in conjunction with parameters such as laser power, welding speed, and material thickness. Therefore, as laser power increases, the absolute value of defocusing amount should be reduced to minimize the spot size irradiating the workpiece surface. The welding amplitude in laser welding parameters refers to the periodic lateral oscillation of the laser beam along a preset trajectory during welding. To ensure weld penetration, the welding amplitude should be reduced accordingly with increasing plate thickness to prevent excessive energy density dispersion; conversely, increasing the amplitude requires a simultaneous increase in laser power. Specifically, the welding robot is controlled by a host computer to control the magnetic field application component and the laser welding head, thereby adjusting the defocusing amount, welding amplitude, welding speed, and oscillation frequency.

[0063] Depending on the material and thickness of the workpiece being welded, the electromagnetic generator module provides the power and frequency for electromagnetic stirring to the magnetic field application component. The electromagnetic generator module produces an alternating magnetic field, with its power adjustable from 0.5 to 2.5 kW to control the magnetic field strength, and the frequency adjustable from 4 to 15 Hz to adapt to different welding process requirements. The magnetic field application component generates electromagnetic force to achieve electromagnetic stirring, promoting gas buoyancy in the molten pool and suppressing porosity. The distance between the magnetic field application component and the workpiece being welded is adjustable; this distance determines the strength of the electromagnetic force acting on the molten pool, meaning the closer the distance, the stronger the effect.

[0064] During the welding process, the laser welding head power of the laser generator module is set according to the adjustment and control module settings. Simultaneously, both the infrared and blue laser welding heads are activated and aligned with the workpiece. The infrared-blue composite laser welding head comprises an infrared laser welding head and a blue laser welding head. The infrared laser from the infrared welding head heats the workpiece and base material to melt and form a molten pool, while the blue laser from the blue laser welding head assists the infrared laser in improving the absorption rate during titanium alloy welding. The infrared laser power adjustment range is 1~20kW, the blue laser power adjustment range is 0.3~2.4kW, the welding speed range is 20~50 mm / s, and the defocusing distance range is 0~2 mm. The power adjustment range of the magnetic field application component is 0.5~2.5kW, and the frequency adjustment range is 4~15 Hz.

[0065] During the welding process, the base material is used as the filler material, and the welding consumable is selected from the same material as the workpiece. For example, if the workpiece is TC4 titanium alloy, the welding consumable should be ERTC4ELI. This ensures that the weld joint strength is comparable to that of the base material after melting. The shielding gas used during welding is stored in a gas cylinder, and an inert gas (high-purity argon) is applied to the area to be welded to prevent the weld joint from becoming brittle and developing cracks or porosity. Simultaneously, during the welding process, a high-speed camera and infrared thermography are used to monitor the temperature and flow fields of the molten pool in real time. The high-speed camera acquires the temperature and flow field information of the molten pool, and the monitored data is compared with the preset ideal molten pool state. If a deviation is found, the magnetic field parameters of the electromagnetic stirring and the laser welding process parameters are automatically adjusted to achieve closed-loop control of the welding process and ensure the stability of the welding quality.

[0066] The high-speed camera device is equipped with an infrared thermal imaging component to simultaneously acquire the temperature field distribution, flow state, and surface morphology of the molten pool. If the deviation exceeds a threshold, a feedback control command is triggered promptly. The ideal molten pool parameters acquired include: ① Molten pool dimensions: length 1~30mm, width 0~12mm (proportionally adapted to the plate thickness; for every 2mm increase in thickness, the length increases by 0~5mm and the width by 0~2mm); ② Temperature field distribution: center temperature 1800-2200℃, temperature difference between edge and center ≤500℃, with no localized overheating (temperature ≥2300℃) or undercooling (temperature ≤1600℃) areas; ③ Flow field state: flow velocity 5-15cm / s, flow pattern symmetrical circulating flow (bidirectional stirring) or directional stable flow (unidirectional stirring), without eddies or turbulence, and no significant fluctuations on the molten pool surface. If the molten pool exhibits localized overheating / undercooling or turbulent flow, and the duration is ≥2 seconds, it is determined to be a non-ideal molten pool state. Feedback control is immediately initiated. If the molten pool cannot return to the sub-ideal range within 3 seconds after control, welding is suspended.

[0067] Next, we will quantify the above ideal molten pool state parameters as follows: The ideal molten pool length is expressed as... The reference length is 1mm. This is expressed as a growth factor ranging from 0 to 2.5 mm. The ideal molten pool width is expressed as... The base width is 0mm. The range is 0~1mm. The center temperature of the molten pool is expressed as... Its maximum temperature difference is expressed as The prohibited area is represented as Flow rate in the flow field The flow field and flow regime are represented as The state of the molten pool monitored in real time by the high-speed camera is represented as... Calculate the deviation from the ideal molten pool state. Any parameter exceeding the ideal range is flagged as abnormal. This is when the deviation is first detected. If the value is not 0, the possible causes are determined based on the preliminary diagnostic rules, and the preliminary intervention measures that have the least impact on the welding process and are most targeted are initiated.

[0068] The above preliminary diagnostic rules include: if the symptoms are as follows Local turbulence or eddies occur and The flow is still within the ideal range, but weak bubbles were detected. This indicates instability in the molten pool flow. In this case, the electromagnetic generator module is activated to apply electromagnetic force to the magnetic field components. The power and frequency of the electromagnetic stirring are set according to the matching process parameter library based on the plate thickness. If the behavior is as follows... and If the stirring becomes stagnant, it indicates insufficient electromagnetic force; in this case, increase the electromagnetic stirring power by 20-30%. If it exhibits... and If the stirring exhibits a jetting motion, it indicates that the electromagnetic force is too strong and protective gas is easily drawn in. In this case, reduce the electromagnetic stirring power by 15-25%. If it manifests as... but This is normal, indicating that the temperature gradient is too large, and electromagnetic stirring needs to be strengthened to promote heat diffusion; if it manifests as but This is normal, indicating that the heat input is slightly high but not yet overheated. Reduce the power of the infrared-blue light composite laser welding head by 3-5%. If it manifests as... but Normal, indicating that the heat input is slightly low but has not yet solidified, so the power of the infrared blue light composite laser welding head should be increased by 3~5%.

[0069] If the molten pool state monitored in real time by the high-speed camera still shows deviations after the initial intervention... Simultaneously, adjustment commands are sent to the electromagnetic generator module and the infrared-blue light composite laser welding head. For step 7, the real-time molten pool state is continuously compared with the preset ideal molten pool state. If any abnormalities occur, PID feedback control is used to adjust the magnetic field parameters of the electromagnetic stirring and the process parameters of the laser welding. We categorize the abnormalities into three types and design independent PID control loops for each: a temperature field control loop, a flow field control loop, and a geometry control loop. The temperature field control loop uses the molten pool center temperature as the control factor. and temperature gradient As the controlled variable, infrared laser power Main control variable, blue light power As a secondary control variable, the PID algorithm is used to adjust the thermal input in real time, which is expressed as: .in, This is expressed as the laser power adjustment amount. This is expressed as temperature deviation. , and These are represented as proportional coefficient, integral coefficient, and derivative coefficient, respectively. The flow field control loop is based on the molten pool flow velocity. and flow patterns The controlled variable is the power of the electromagnetic stirring. and the frequency of electromagnetic stirring As the manipulated variable, the adjustment amount of the electromagnetic parameter is calculated using PID control, and expressed as follows: .in, This represents the power adjustment amount for the electromagnetic stirring. This is expressed as flow rate deviation. The geometry control loop is based on the molten pool length. and width The controlled variable is welding speed and decoking amount, which are used as manipulated variables to form a slow-speed adjustment loop that is cascaded with the former two.

[0070] However, to address the strong coupling between laser power and electromagnetic parameters, a decoupling compensation network is used to eliminate the influence between laser power and electromagnetic stirring. This is represented as follows:

[0071] ;

[0072] ;

[0073] in, This refers to the laser power adjustment amount output by the temperature field PID controller. This refers to the adjustment amount of the electromagnetic stirring power output by the flow field PID controller. This indicates the degree of coupling effect of electromagnetic power changes on laser power demand. This indicates the degree of coupling effect of laser power variation on electromagnetic power demand. Together, they form a decoupling compensation network to eliminate mutual interference between the laser and electromagnetic systems. This is determined through experimental calibration. and First, define the temperature control gain. The change in temperature at the center of the molten pool caused by a 1kW change in laser power; flow rate control gain. The change in molten pool flow velocity caused by a 1kW change in electromagnetic power was measured using a pre-conducted step experiment. This calibrated the degree of electromagnetic-laser coupling. While keeping the laser power constant, a step change is applied to the electromagnetic stirring power. Measure the temperature change at the center of the molten pool calculate Then calibrate the degree of laser-electromagnetic coupling. While maintaining a constant electromagnetic stirring power, the laser power is reduced by variation. Measure the change in molten pool flow rate calculate According to decoupling control theory, the decoupling matrix should be a static approximation of the inverse of the coupling matrix, which yields... , Finally, the final laser power command will be given. and final electromagnetic stirring power command The signal is sent to the adjustment and control module to adjust the infrared blue light composite laser welding head and the electromagnetic generation module.

[0074] Example 2

[0075] In this embodiment, the welding of a certain titanium alloy thin plate for aviation is taken as an example.

[0076] Workpiece and material preparation: A 2.5 mm thick titanium alloy sheet for aviation use was selected as the welding workpiece. The welding area of ​​the workpiece was strictly cleaned to remove impurities such as oil and oxide scale, so as to effectively avoid the decomposition of impurities during the welding process and generate gases such as hydrogen and carbon monoxide, and reduce welding defects such as porosity, cracks and slag inclusions.

[0077] Equipment installation and commissioning: Install the magnetic field application component according to the attached... Figure 3 The device is mounted using a mechanical clamp below the infrared and blue laser welding heads, as close as possible to the weld pool to ensure the magnetic field application component effectively acts on the weld pool. The electromagnetic generation module and power generation module are connected, and the power and frequency of the generated electromagnetic field are adjusted to ensure stable operation within the preset range. Simultaneously, the real-time monitoring feedback module is tested to ensure accurate data acquisition by each sensor, proper data reception and processing by the control system, and parameter adjustments based on the feedback results.

[0078] Welding process parameter settings: Based on the experimental experience during the preliminary preparation, a matching process parameter library for electromagnetic stirring parameters and laser welding parameters was established. By referring to tables, the infrared laser power was set to 3000 W, the blue laser power to 600 W, the welding speed to 28 mm / s, and the defocusing amount to 2 mm. Additionally, the power of the electromagnetic generator module was adjusted to 0.5 kW and the frequency to 6 Hz, and the distance between the magnetic field application component and the workpiece being welded was set to 8 mm.

[0079] Welding Process and Monitoring: The infrared-blue light composite laser welding head and electromagnetic generator module are activated to apply a magnetic field to the components, initiating welding. During the welding process, the monitoring and feedback module collects real-time temperature and flow field information of the molten pool using sensors such as high-speed cameras. If the molten pool condition deviates from the preset ideal molten pool condition standard, the electromagnetic stirring and laser welding process parameters are automatically adjusted immediately.

[0080] Welding result inspection: After welding, the weld joint is subjected to metallographic analysis, radiographic testing, and other inspections. For example... Figure 9 As shown in (b), the porosity of the welded joint is 0, which is far lower than the porosity without the method of this invention, and the mechanical properties of the welded joint are good, meeting the quality requirements of titanium alloy structural components for aerospace applications. Figure 9 As shown in (a), the welding results obtained by other methods using existing technology show that more pores appeared after welding.

[0081] Example 3

[0082] In this embodiment, the welding of a titanium alloy thick plate for a ship is taken as an example.

[0083] Workpiece and material preparation: A 20 mm thick titanium alloy plate for aviation use was selected as the welding workpiece. The welding area of ​​the workpiece was also strictly cleaned to remove impurities such as oil and oxide scale to effectively avoid the decomposition of impurities during the welding process and generate gases such as hydrogen and carbon monoxide, thereby reducing welding defects such as porosity, cracks and slag inclusions.

[0084] Equipment installation and commissioning: Repeat the equipment installation and commissioning steps in Example 2 to ensure that the whole system can operate normally.

[0085] Welding process parameter settings: Based on the characteristics of welding thick titanium alloy plates, the matching process parameter library was consulted, and the infrared laser power was adjusted to 15000 W, the blue laser power to 2000 W, the welding speed to 12 mm / s, and the defocusing amount to 0 mm. The power of the electromagnetic generator module was adjusted to 2 kW and the frequency to 12 Hz by adjusting the control module, and the distance between the magnetic field application component and the workpiece being welded was set to 3 mm.

[0086] Welding Process and Monitoring: Welding begins with the activation of the infrared-blue light composite laser welding head and the electromagnetic generator module. During welding, the monitoring and feedback module closely monitors changes in various parameters and the state of the molten pool in real time. Due to the large volume of the molten pool and slow heat dissipation during thick plate welding, different porosity formation may occur. The system adjusts parameters promptly based on actual monitoring data, such as appropriately increasing the magnetic field strength of the electromagnetic stirring during welding to enhance the stirring effect on the large-volume molten pool, while optimizing the laser energy input to ensure a good metallurgical state of the molten pool.

[0087] Welding result inspection: Metallographic analysis, radiographic testing, and other inspections are performed on the welded joints. For example... Figure 10 As shown in (b), the porosity was reduced to 0, and the strength, toughness, and other mechanical properties of the welded joint met the relevant standards for titanium alloy structural components for ships, effectively verifying the effectiveness and reliability of the method and system of this invention in thick plate welding. Figure 10As shown in (a), the welding results obtained by other methods using existing technology show that more pores appeared after welding.

[0088] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0089] Furthermore, in this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0090] The above are merely preferred embodiments of the present invention, and the present invention may have other embodiments. Those skilled in the art can still modify the technical solutions described in the above embodiments, or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling porosity in laser welding of titanium alloys based on molten pool state feedback, characterized in that, Includes the following steps: Step S1: Perform a thorough surface cleaning of the welding area of ​​the workpiece to be welded, removing impurities such as oil and oxide scale from the surface; Step S2: Place the base material and the part of the workpiece to be welded below the magnetic field application component and as close as possible to the weld pool. The base material is selected from welding materials that are the same material as the workpiece to be welded. Step S3: Establish a matching process parameter library that includes electromagnetic stirring parameters and laser welding parameters; Step S4: Based on the material and thickness of the workpiece to be welded, and according to the matching process parameter library, the laser power of the infrared blue light composite laser welding head is set by adjusting the control module, and then simultaneously turned on to melt the workpiece to be welded to form a molten pool and stabilize the thermal field. Step S5: During the welding process, the base material is used as the filler material and the inert gas is used as the protective gas. Welding is carried out according to the preset welding path. At the same time, the monitoring feedback module monitors the state of the molten pool in real time during the welding process and sends the data to the host computer. Step S6: In the host computer, the real-time molten pool status monitored is compared with the preset ideal molten pool status. When the abnormality occurs for the first time, the power and frequency of the electromagnetic stirring are set by the control module in combination with the preliminary diagnosis rules and the matching process parameter library. The electromagnetic generation module is turned on to apply electromagnetic force to the magnetic field component to achieve molten pool stirring, which is used to promote the rise of gas in the molten pool and suppress porosity. Step S7: Continuously compare the real-time molten pool state with the preset ideal molten pool state. If an abnormality occurs again, adjust the magnetic field parameters of the electromagnetic stirring and the process parameters of laser welding through PID feedback control.

2. The method for controlling porosity in titanium alloy laser welding based on molten pool state feedback according to claim 1, characterized in that: The electromagnetic generation module generates an alternating magnetic field and outputs it to the magnetic field application component. The output power is adjustable from 0.5 to 2.5 kW, and the frequency is adjustable from 4 to 15 Hz. The power of the electromagnetic generation module determines the magnitude of the generated electromagnetic force and is proportionally matched with the laser power of the infrared-blue light composite laser welding head.

3. The method for controlling porosity in titanium alloy laser welding based on molten pool state feedback according to claim 2, characterized in that: The infrared laser is used to provide thermal energy input to heat the workpiece and the base material to melt and form a molten pool. The power of the infrared laser increases with the increase of the thickness of the workpiece plate and the power range of the infrared laser is 1~20kW.

4. The method for controlling porosity in titanium alloy laser welding based on molten pool state feedback according to claim 3, characterized in that: The blue laser is used to assist the infrared laser in improving the absorption rate of titanium alloy welding and stabilizing the thermal field distribution to reduce porosity formation. The power of the blue laser increases with the thickness of the workpiece plate being welded, and the power range of the blue laser is 0.3~2.4kW.

5. The method for controlling porosity in titanium alloy laser welding based on molten pool state feedback according to claim 4, characterized in that: When the thickness of the workpiece plate is constant, the welding speed increases with the increase of the laser power of the infrared blue light composite laser welding head; the absolute value of the defocusing amount decreases with the increase of the laser power, so that the size of the spot irradiated on the surface of the workpiece is smaller; as the thickness of the workpiece plate increases, the welding swing amplitude also increases accordingly with the increase of the laser power.

6. The method for controlling porosity in titanium alloy laser welding based on molten pool state feedback according to claim 5, characterized in that: In step 6, the monitoring feedback module is used to monitor in real time whether the molten pool state parameters are in an ideal molten pool state, including molten pool size, temperature field distribution, and flow field state. When the temperature field distribution shows local temperature anomalies and / or the flow field state shows turbulence for a duration of more than 2 seconds, it is determined to be a non-ideal molten pool state. The adjustment amount is calculated and feedback control is initiated. The defocusing amount and the distance between the magnetic field application component and the workpiece being welded are then adjusted. If the molten pool state cannot be returned to the ideal molten pool state range within 3 seconds after adjustment, welding is suspended.

7. The method for controlling porosity in titanium alloy laser welding based on molten pool state feedback according to claim 6, characterized in that: The ideal molten pool has a length of 1-30 mm and a width of 0-12 mm. For every 2 mm increase in the thickness of the workpiece plate, the length of the ideal molten pool increases by 0-5 mm and the width increases by 0-2 mm. The ideal molten pool has a center temperature of 1800-2200℃, and the temperature difference between the edge and center is no higher than 500℃ with no local overheating or undercooling areas. The ideal molten pool has a flow rate of 5-15 cm / s, and the flow pattern is free of eddies and turbulence during unidirectional or bidirectional stirring.

8. The method for controlling porosity in titanium alloy laser welding based on molten pool state feedback according to claim 7, characterized in that: In step S6, the ideal molten pool state is first quantified as follows: The state of the molten pool monitored in real time by the high-speed camera device is represented as... Calculate the deviation from the ideal molten pool state. If deviation occurs Then, based on the preliminary diagnostic rules, determine whether to adjust the power of the infrared-blue light composite laser welding head or start the power and frequency of the electromagnetic stirring.

9. The method for controlling porosity in titanium alloy laser welding based on molten pool state feedback according to claim 8, characterized in that: In step S7, if the molten pool state monitored in real time by the high-speed camera after the initial intervention still has a deviation... Independent PID control loops are set up, including temperature field control loop, flow field control loop, and geometry control loop. The laser power adjustment is calculated based on temperature deviation and flow velocity deviation. Power adjustment of electromagnetic stirrer Then, the influence between laser power and electromagnetic stirring is eliminated by a decoupling compensation network to obtain the final laser power command and the final electromagnetic stirring power command, which are then sent to the adjustment and control module to realize the adjustment of the infrared blue light composite laser welding head and the electromagnetic generation module.

10. A porosity control system for titanium alloy laser welding based on molten pool state feedback, characterized in that: The system includes a power generation module, an adjustment and control module, an electromagnetic generation module, a magnetic field application component, and a monitoring and feedback module. The power generation module is connected to the adjustment and control module to provide drive power for the entire system. The adjustment and control module is connected to a host computer to transmit parameters for electromagnetic stirring and laser welding. The adjustment and control module, through the electromagnetic generation module, connects to the magnetic field application component to control the generation of an adjustable alternating magnetic field output to drive the magnetic field application component, thereby stirring the weld pool of the workpiece being welded. The adjustment and control module is also connected to a laser generation module to control the output power of the infrared-blue light composite laser welding head within the laser generation module, simultaneously performing welding of the workpiece and control of the porosity of the weld pool. The monitoring and feedback module monitors the weld pool of the workpiece in real time, sending the monitored weld pool parameters to the host computer for comparison with a matching process parameter library to determine if it is in an ideal weld pool state. If it is not in an ideal weld pool state, adjustments are made before output. The shape and size of the magnetic field application component are optimized and adjusted according to the common shapes and sizes of titanium alloy welded workpieces.

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