A thick plate arc composite welding method and system based on multi-frequency composite induction

Abstract

The application provides a thick plate arc composite welding method and system based on multi-frequency composite induction, and belongs to the technical field of metal welding. The method comprises the following steps: obtaining the surface temperature and internal temperature of a workpiece to be welded in real time through a multi-depth temperature sensing array; adjusting the power ratio of low-frequency current and high-frequency current based on the difference between the actual temperature gradient and the target temperature gradient through a first closed-loop control loop; adjusting the total output power based on the difference between the average temperature of the workpiece and the target temperature through a second closed-loop control loop; at the same time, the arc parameters are monitored in real time, and the power of the high-frequency current is adjusted compensatively through a feedforward control model. The application also provides a system for executing the method. Through double closed-loop control combined with feedforward compensation, the application realizes decoupling, accurate and adaptive control of the thick plate welding temperature field, can directly control the temperature gradient, and effectively suppresses welding defects.

Description

Technical Field

[0001] This application relates to the field of metal welding technology, and in particular to a method and system for thick plate arc composite welding based on multi-frequency composite induction. Background Technology

[0002] Arc-induction hybrid welding technology is an effective means of improving weld joint performance by intervening in the welding thermal process through the combination of an electric arc as the main heat source and an induction auxiliary heat source. In existing technologies, induction heating is mostly used as an auxiliary process for preheating before welding and post-weld heat treatment, typically employing a single-frequency induction power source, such as a medium-to-high frequency induction power source. Utilizing the skin effect, this method can rapidly heat the surface layer of the workpiece.

[0003] However, existing technologies have inherent drawbacks when applied to welding thick plates (e.g., those thicker than 50 mm). Firstly, achieving both heating depth and uniformity is difficult. High-frequency induction heating, due to the skin effect, concentrates heat highly on the workpiece surface, failing to effectively heat the core area of ​​thick plates. Conversely, while low-frequency induction heating offers greater penetration depth, its surface heating efficiency is low and its response is slow, making rapid and precise control of the overall temperature difficult. Current technologies lack a means to combine the advantages of both methods to achieve simultaneous and efficient heating of thick plates from the surface to the core.

[0004] Secondly, existing technologies lack control over the critical physical quantity of "temperature gradient." The key to high-quality welding of thick plates lies in controlling the temperature gradient along the thickness direction. By slowing the cooling rate of the core relative to the surface, microstructural transformation can be regulated, cold cracking suppressed, and residual stress reduced. Existing technologies typically only target surface temperature, leaving the internal temperature distribution and the temperature gradient along the thickness direction "out of control." This results in inadequate preheating and slow cooling effects, and limited ability to suppress welding defects.

[0005] Furthermore, existing control methods are mostly open-loop control based on preset power or time, or simple feedback control based on single-point surface temperature. These methods cannot adapt to dynamic changes during the welding process. For example, the energy fluctuations of the electric arc itself directly disturb the workpiece surface temperature, and existing sensing systems cannot respond to this disturbance quickly and actively, leading to unstable welding thermal cycles and affecting the final weld quality and consistency. Even assuming simultaneous heating at both high and low frequencies, due to the significant coupling effect between the two heating modes, existing technologies have failed to provide an effective algorithm and control strategy that can decouple control and independently adjust the core and surface temperatures. Summary of the Invention

[0006] The purpose of this application is to provide a method and system for thick plate arc composite welding based on multi-frequency composite induction, in order to solve the technical problem that in the existing technology for thick plate welding, due to the limitations of heating methods and control strategies, it is impossible to perform precise and adaptive closed-loop control of the temperature distribution (especially the temperature gradient) of the thick plate along the thickness direction, and it is easily affected by process disturbances such as arc fluctuations, resulting in unstable welding quality.

[0007] To achieve the above objectives, this application provides a thick plate arc-heated composite welding method based on multi-frequency composite induction, which is applied to a welding apparatus including an arc welding device and a composite induction heating system. The composite induction heating system can output low-frequency current and high-frequency current. The method includes: acquiring at least one surface temperature and at least one internal temperature of the workpiece to be welded in real time through a multi-depth temperature sensing array; adjusting the power ratio of the low-frequency current and the high-frequency current based on the difference between the actual temperature gradient calculated from the surface temperature and the internal temperature and a preset target temperature gradient through a first closed-loop control loop; adjusting the total output power of the low-frequency current and the high-frequency current based on the difference between the average workpiece temperature determined from the surface temperature and the internal temperature and a preset target temperature through a second closed-loop control loop; monitoring the arc parameters of the arc welding device in real time, and compensatingly adjusting the power of the high-frequency current through a feedforward control model; wherein, the compensating adjustment includes superimposing the compensation power output by the feedforward control model onto the power command of the high-frequency current, and synchronously adjusting the power command of the low-frequency current according to the power ratio determined by the first closed-loop control loop.

[0008] Optionally, the method is performed in at least one of the following stages: preheating before welding, heat tracing during welding, and slow cooling after welding.

[0009] Optionally, during the post-weld slow cooling stage, the target temperature is reduced in a programmed manner according to a preset slow cooling curve.

[0010] Optionally, the multi-depth temperature sensing array includes a surface temperature sensor and an internal temperature sensor; wherein the surface temperature sensor is an infrared thermometer; and the internal temperature sensor is selected from a thermocouple or a non-contact temperature probe based on the eddy current detection principle.

[0011] Optionally, the arc parameters include at least one of arc current and arc voltage.

[0012] Optionally, the method further includes a time-domain switching step, employing different control modes at different welding stages; wherein the control modes include at least one of the following: a power ratio mode dominated by low-frequency current is adopted in the overall preheating stage; and a heat preservation mode is adopted in the interlayer heat preservation stage of multi-pass welding, in which low-frequency current is output in a low-frequency, low-power pulse manner while maintaining a basic high-frequency current output for power ratio adjustment.

[0013] Optionally, the target temperature gradient is a preset non-zero value for use in dissimilar metal welding.

[0014] This application also provides a thick plate arc welding system based on multi-frequency composite induction, including an arc welding device and a composite induction heating system. The composite induction heating system includes: a composite induction power supply for outputting low-frequency current and high-frequency current; an inductor connected to the composite induction power supply; a multi-depth temperature sensing array for real-time acquisition of at least one surface temperature and at least one internal temperature of the workpiece to be welded; and a control system connected to the composite induction power supply, the multi-depth temperature sensing array, and the arc welding device. The control system is configured to: calculate the actual temperature gradient of the workpiece along its thickness direction based on the surface temperature and the internal temperature, and compare the actual temperature gradient with a preset target temperature gradient, so as to determine the difference between the two values. The system adjusts the power ratio of the low-frequency current and the high-frequency current; it determines the average temperature of the workpiece based on the surface temperature and internal temperature using a preset calculation method, and compares it with a preset target temperature to adjust the total output power of the low-frequency current and the high-frequency current based on the difference; it monitors the arc parameters of the arc welding equipment, and when the fluctuation amplitude of the arc parameters exceeds a preset threshold, it performs compensatory adjustment of the power of the high-frequency current through a preset feedforward control model; wherein, the control system is further configured to: superimpose the compensation power output by the feedforward control model onto the power command of the high-frequency current, and synchronously adjust the power command of the low-frequency current according to the power ratio determined by the control logic used to adjust the power ratio.

[0015] Optionally, the multi-depth temperature sensing array includes a surface temperature sensor and an internal temperature sensor; wherein the surface temperature sensor is an infrared thermometer; and the internal temperature sensor is selected from a thermocouple or a non-contact temperature probe based on the eddy current detection principle.

[0016] Optionally, the control system is further configured to perform time-domain switching, employing different control modes at different welding stages. The control modes include at least one of a power ratio mode dominated by low-frequency current and a low-frequency low-power pulse mode. In the low-frequency low-power pulse mode, the control system outputs low-frequency current with a preset low duty cycle while maintaining a basic high-frequency current output for power ratio adjustment.

[0017] Compared with the prior art, the technical solution provided in this application has the following beneficial effects: 1. It achieves direct and precise control of the temperature gradient. By taking the "temperature gradient" as the direct control target and adjusting the high and low frequency power ratio in a closed loop, it can accurately create and maintain an ideal internal cooling environment, thereby more effectively suppressing cold cracks that are common in thick plate welding and significantly reducing residual stress.

[0018] 2. The heating function has been decoupled and stabilized. Through the dual closed-loop control strategy of "gradient-ratio" and "uniform temperature-total power", the coupling problem between high-frequency (surface) heating and low-frequency (core) heating has been effectively solved, and the core temperature and surface temperature can be adjusted almost independently, which greatly improves the control accuracy and stability of the temperature field.

[0019] 3. Enhanced process robustness and welding quality consistency: By introducing feedforward compensation control based on arc parameters, the system can actively suppress energy disturbances from the main heat source of the arc, avoiding their impact on the workpiece temperature field, significantly improving the thermal stability of the entire welding process, thereby ensuring a high degree of welding quality consistency.

[0020] 4. It achieves efficient deep-penetration volume heating. Through closed-loop coordinated control of high and low frequency power, it ensures that heat is efficiently and accurately delivered to the required depth, realizing the ideal "moving insulation body" effect, which not only ensures the heating effect of the core, but also avoids surface overheating and unnecessary energy waste. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic diagram of a thick plate arc composite welding system based on multi-frequency composite induction provided in an embodiment of this application; Figure 2A schematic flowchart of a thick plate arc composite welding method based on multi-frequency composite induction provided in an embodiment of this application; Figure 3 This is a schematic diagram of the dynamic response timing of the feedforward compensation control in the embodiments of this application; Explanation of reference numerals in the attached drawings: 10-Arc welding equipment; 20-Workpiece; 30-Composite induction power supply; 31-Low-frequency power module; 32-High-frequency power module; 40-Inductor; 50-Multi-depth temperature sensor array; 51-Surface temperature sensor; 52-Internal temperature sensor; 60-Control system; S100-Parameter setting procedure; S200-Preheating procedure before welding; S300-Heating procedure during welding; S400-Post-weld slow cooling procedure. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0024] Example 1

[0025] This embodiment provides a basic implementation scheme for a thick plate arc composite welding method and system based on multi-frequency composite induction. This scheme achieves precise control of temperature gradient and average temperature throughout the entire process of thick plate butt welding, and can actively suppress arc disturbances.

[0026] Please see Figure 1 This document illustrates a schematic diagram of a thick plate arc-to-metal composite welding system based on multi-frequency composite induction, according to an embodiment of this application. The system includes an arc welding device 10 and a composite induction heating system. The arc welding device 10 can be a conventional gas metal arc welding (GMAW), tungsten inert gas (TIG) welding, or plasma arc welding device, used to provide the primary welding heat source. The composite induction heating system serves as an auxiliary heat source, its core function being to precisely control the temperature field of the workpiece 20 to be welded.

[0027] Specifically, the composite induction heating system includes a composite induction power supply 30, an inductor 40, a multi-depth temperature sensing array 50, and a control system 60 as the core of the system.

[0028] The composite induction power supply 30, as a key hardware component for realizing the technical solution of this application, integrates at least one low-frequency power module 31 and one high-frequency power module 32. The low-frequency power module 31 outputs alternating current at a lower frequency (e.g., in the range of 50Hz to 1kHz), and the alternating magnetic field it generates has a strong penetration depth, primarily used for deep, overall volumetric heating of the workpiece 20. The high-frequency power module 32 outputs alternating current at a higher frequency (e.g., in the range of 10kHz to 100kHz), and the alternating magnetic field it generates is mainly concentrated on the surface of the workpiece 20 due to the skin effect, used for rapid and sensitive temperature regulation of the workpiece surface. These two modules can independently adjust their respective output power according to the instructions of the control system 60, and achieve a composite output of the two frequency currents.

[0029] Inductor 40 is connected to the output of composite induction power supply 30. Inductor 40 is typically customized according to the shape of workpiece 20 and welding process; for example, it can be a C-type or E-type iron core inductor, or a flexible coil surrounding the weld. In one embodiment of this application, inductor 40 is configured to move synchronously with the welding torch of arc welding equipment 10, thereby forming a moving and controllable temperature field in front of, below, and behind the welding area. When the composite current passes through inductor 40, eddy currents are induced in workpiece 20, thereby generating an induction heating effect at a composite frequency.

[0030] The multi-depth temperature sensing array 50 provides crucial feedback information for closed-loop control, enabling real-time and accurate acquisition of key temperature information of the workpiece 20 along its thickness direction. It is understood that this array includes at least one surface temperature sensor 51 and one internal temperature sensor 52. The surface temperature sensor 51 measures the temperature of the workpiece 20's surface; as a preferred implementation, a non-contact infrared thermometer or a dual-color thermometer can be used, with the measurement point aligned with a critical area near the weld bevel. The internal temperature sensor 52 measures the temperature of the core or subsurface layer of the workpiece 20. In some specific applications, the internal temperature sensor 52 can be a sheathed thermocouple, such as a K-type thermocouple, pre-embedded inside the workpiece or closely attached to the back of the weld. Through these two sensors, the control system 60 can obtain the surface temperature in real time. and internal temperature .

[0031] The control system 60, acting as the command center of the entire welding system, establishes signal connections with the arc welding equipment 10, the composite induction power supply 30, and the multi-depth temperature sensor array 50. As an optional implementation, the control system 60 can be a programmable logic controller, an industrial computer, or a dedicated digital signal processor system. This system receives real-time temperature signals from the multi-depth temperature sensor array 50 and simultaneously monitors arc parameter signals (such as arc current or voltage) from the arc welding equipment 10. Based on the acquired input information, the control system 60 executes an advanced multivariate collaborative control strategy, thereby generating precise power control commands and sending these commands to the low-frequency power module 31 and the high-frequency power module 32 of the composite induction power supply 30, thus achieving closed-loop control of the entire welding thermal process.

[0032] The welding object in this embodiment is a butt joint of a 100mm thick EH36 high-strength ship plate steel. The system configuration is as follows: the arc welding equipment 10 is a gas metal arc welding machine; the composite induction power supply 30 is set with a low frequency of 0.5kHz and a high frequency of 30kHz; the inductor 40 is C-type and moves synchronously with the welding torch; the multi-depth temperature sensing array 50 consists of a dual-color infrared thermometer (as a surface temperature sensor 51, measuring the surface temperature of the weld bevel). ) and an armored K-type thermocouple closely attached to the back of the weld (serving as an internal temperature sensor 52, approximating the core temperature) The system consists of a Siemens S7-1500 series programmable logic controller (PLC).

[0033] like Figure 3 As shown, before welding begins, parameter setting step S100 is executed first. The operator can set key process control targets in the control system 60 through the human-machine interface. In this embodiment, the set targets include: target average temperature. And allow a tolerance of ±10°C; target temperature gradient At the same time, an upper limit is set, requiring that the actual gradient should not exceed 20°C at any time. In addition, relevant parameters for feedforward control need to be set, for example, setting the feedforward compensation action to be triggered when the arc current instantaneously increases by more than 5%.

[0034] After the setup is complete, the method proceeds to the preheating step S200. In this step, the arc welding equipment 10 is not yet started; only the composite induction heating system is operational. The control system 60 executes the dual closed-loop control logic cyclically at a high frequency (e.g., every 100 milliseconds). Within one control cycle, the control system 60 first acquires the current surface temperature from the surface temperature sensor 51 and the internal temperature sensor 52. and internal temperature The collected data is then sent to the internal calculation module. The actual temperature gradient calculation module S1 calculates the actual temperature gradient. Meanwhile, the average temperature calculation module S2 calculates the actual average temperature. It should be noted that the calculation method for average temperature is not limited to this; it can also be a weighted average or other calculation methods that can reflect the overall temperature level.

[0035] The calculated actual temperature gradient and actual average temperature They enter two independent closed-loop control loops respectively.

[0036] In the first closed-loop control loop, i.e., the gradient control loop, the actual temperature gradient is... With the preset target temperature gradient Compare to obtain gradient error The error value is input to the gradient controller C1 (e.g., a proportional-integral-derivative controller or a proportional-integral controller). The gradient controller C1 operates based on the gradient error. The magnitude and trend of the change are used to output a power ratio R (for determining the high-frequency power and low-frequency power). The adjustment signal. The core logic of this loop is: when the actual gradient is too large ( This indicates that the surface layer is overheated relative to the core. In this case, the controller will reduce the power ratio R, that is, relatively reduce the high-frequency power or increase the low-frequency power, in order to suppress surface heating and enhance core heating, thereby promoting gradient descent. Conversely, when the actual gradient is too small, the power ratio R will be increased accordingly.

[0037] Accordingly, in the second closed-loop control loop, namely the temperature equalization control loop, the actual average temperature T_avg is compared with the preset target average temperature. The average temperature error was obtained. This error is fed into the temperature equalization controller C2 (which can also be a proportional-integral-derivative controller or a proportional-integral controller), which determines the temperature equalization error based on the error. Output an adjustment signal to determine the total output power of the high-frequency power and the low-frequency power. The control logic for this loop is as follows: when the actual average temperature is lower than the target value, the controller increases the total power. To increase the overall heating rate; conversely, to reduce the overall power.

[0038] Through the two parallel closed-loop control loops described above, the control system 60 obtains the power ratio R and the total power. These two key intermediate control variables are then fed into the power calculation module M1, which calculates the basic high-frequency power command based on the following set of equations. and low-frequency power commands :

[0039] Solving for:

[0040] It should be noted that during the preheating stage before welding, since there is no arc disturbance, the output compensation power of the feedforward controller C3 is [not specified]. It is zero. Therefore, the final high-frequency power command is zero. That is equal to The control system 60 will calculate... and As a digital or analog signal, it is sent to the high-frequency power module 32 and low-frequency power module 31 of the composite inductive power supply 30, instructing them to output power accordingly. This process continues to cycle until... and All temperatures stabilize within the preset target range. At this point, preheating is complete, and the workpiece reaches the ideal state for welding.

[0041] Next, the method proceeds to the welding heat tracing step S300. The operator or automated system starts the arc welding equipment 10, and the welding torch begins to move along the weld seam for welding. During this stage, the control system 60 continuously executes the aforementioned dual closed-loop control strategy to maintain a stable temperature field in the welding area. However, in the welding heat tracing stage, a new technical challenge needs to be addressed: the electric arc itself is a high-energy and fluctuating heat source. Understandably, due to factors such as droplet transfer and arc length changes, the arc current and voltage will experience instantaneous fluctuations. These fluctuations will directly impact the temperature of the workpiece surface (especially near the bevel), thereby disturbing the temperature field carefully maintained through feedback control.

[0042] To address this issue, this application introduces feedforward compensation control based on arc parameters. The control system 60 monitors the arc parameters of the arc welding equipment 10 in real time via a high-speed data acquisition channel at an extremely high sampling rate (e.g., 10ms period), which in this embodiment is the arc current. Continuous analysis of feedforward controller C3 Signal. Once detected If the fluctuation amplitude exceeds a preset threshold (e.g., a momentary increase of 5%), the feedforward controller C3 is triggered and, based on a preset feedforward control model, instantaneously calculates a compensation power. The model can be a simple proportional model, such as... ,in This is the fluctuation in current, and k is a coefficient calibrated experimentally beforehand. In this example, the compensation power... A negative value means that the heat input needs to be reduced instantaneously.

[0043] This compensation power Directly superimposed on the base high-frequency power command calculated by the double closed-loop circuit. This, in turn, forms the final high-frequency power command: Since high-frequency induction primarily acts on the surface and has an extremely fast response speed, this rapid and brief compensatory adjustment of high-frequency power can almost instantly offset the heating effect of increased arc energy on the workpiece surface temperature. Simultaneously, to maintain a constant power ratio R determined by the gradient controller C1, the control system 60 will adjust the power according to the updated high-frequency power command. Synchronous adjustment of low-frequency power command, i.e. In this way, feedforward compensation can be ensured to suppress surface temperature disturbances without disrupting existing control over the temperature gradient. Once the arc current disturbance disappears, Zeroing out, compensation power It also resets to zero, and the system returns to a state controlled solely by dual closed loops.

[0044] After the welding task is completed, the arc welding equipment 10 stops working, and the process enters the post-weld slow cooling step S400. To suppress the initiation of delayed cracks and optimize residual stress distribution, uniform and slow cooling of the thick plate is crucial. During this stage, the composite induction heating system continues to operate, while the control system 60 switches to a programmed cooling mode. Specifically, the target average temperature in the uniform temperature control loop... Instead of a fixed value, it dynamically changes over time based on a preset slow cooling curve (e.g., a linear decrease of 5°C per minute). Simultaneously, the target temperature gradient of the gradient control loop... It is set to a smaller value (e.g., 10°C) to achieve better cooling uniformity. The control system 60 continuously executes dual closed-loop control, constantly adjusting the total power and power ratio of high and low frequencies, driving the actual temperature field of the workpiece to accurately follow this preset slow cooling trajectory until the workpiece temperature drops to a safe temperature (e.g., close to room temperature), at which point the entire welding process ends.

[0045] Using the method provided in this embodiment, during the entire welding process of a 100mm thick EH36 steel plate, the temperature difference between its upper and lower surfaces (which can be approximated as...) The temperature was effectively controlled below 25°C. Post-weld X-ray non-destructive testing of the weld joint revealed a dense internal structure without any cracks or defects. Stress testing using the blind-hole method showed that the residual stress peak of the joint obtained using this method was reduced by more than 60% compared to weld joints obtained using the traditional single preheating method.

[0046] When using conventional high-frequency induction heating along the Z-axis of the workpiece thickness, the temperature distribution exhibits extremely high surface temperatures that rapidly decrease towards the core, resulting in a significant temperature gradient. In contrast, the method described in this application produces a very gentle temperature curve from the workpiece surface to the core, with a minimal temperature gradient. This fully demonstrates the significant advantages of this application in achieving uniform heating across the entire thickness of thick plates and precise control of the temperature gradient.

[0047] Example 2

[0048] This embodiment aims to demonstrate a variant application of the technical solution of this application in an automated robotic welding production line. In order to maximize production cycle time and energy efficiency while ensuring high-quality welding, this embodiment adopts a time-domain switching control mode, which automatically switches different induction heating control strategies at different stages of the welding process.

[0049] In this embodiment, the system configuration is largely similar to that of Embodiment 1, except that the entire welding system, including the arc welding torch and the inductor 40, is integrated into the end effector of a six-axis welding robot. The control system 60 is pre-programmed with control program modules for different process stages.

[0050] The working process is as follows: 1. Overall preheating stage: It is understandable that for large or thick-section workpieces, if the precision dual closed-loop mode in Example 1 is used to preheat from room temperature, it may take a long time. To improve efficiency, this embodiment adopts a "pure low-frequency high-power" mode in this stage. The control system 60 commands the composite induction power supply 30 to mainly output a high-power current (e.g., frequency 1kHz, power 80kW) from the low-frequency power module 31, while the high-frequency power module 32 can be not working or only output a very small amount of power. Accordingly, the control logic of the control system 60 is also simplified, and only the reading of the internal temperature sensor 52 is used. As feedback, single-variable closed-loop control is implemented, with the goal of rapidly raising the core temperature of the entire workpiece to a base preheating temperature, such as 100°C. Due to the strong penetrating power of low-frequency current, this mode enables the most efficient volumetric heating.

[0051] 2. Welding and Heating Stage: Once the overall temperature of the workpiece reaches the base preheating temperature, the robot begins to move and ignites the electric arc to perform welding. At this time, the control system 60 seamlessly switches to the same "gradient-ratio" and "temperature equalization-total power" dual closed-loop control as in Example 1, and superimposes feedforward compensation control based on arc parameters. The goal of this stage is to achieve the most precise temperature field control to ensure welding quality.

[0052] 3. Interlayer Insulation Stage (for Multi-pass Welding): In multi-pass welding of thick plates, after completing one weld, the robot may need to move to the starting point of the next pass or perform auxiliary operations such as root cleaning and grinding. During this period, if insulation is not performed, the workpiece temperature will drop rapidly, requiring reheating before the next weld, which will undoubtedly affect production efficiency and welding quality. In view of this, this embodiment introduces a "low-frequency, low-power pulse insulation" mode. When the control system 60 detects that the arc has been extinguished and the robot is in a moving or waiting state, the system automatically switches to this mode. In this mode, the control system 60 instructs the low-frequency power supply module 31 to output current in a low-power, low-duty-cycle pulse manner, for example, turning on for 200 milliseconds per second and outputting 10kW of power. This method can effectively compensate for the natural heat dissipation of the workpiece with extremely low average power consumption, maintaining the internal temperature of the workpiece near the target insulation temperature. In order to still be able to adjust for possible small temperature gradients during this stage, the high-frequency power supply module 32 can maintain a small base power output, thereby ensuring that the power ratio adjustment function is still effective. At this point, the control system 60 can continue to perform dual closed-loop control, but the total power is limited to a lower insulation level.

[0053] 4. Post-weld slow cooling stage: After all welding passes are completed, the robot stops welding and the control system 60 switches back to the same dual closed-loop programmed slow cooling mode as in Example 1 to precisely control the cooling rate and temperature uniformity of the workpiece.

[0054] By adopting this phased, time-domain switching control strategy, this embodiment ensures the quality of precise temperature field control during the critical welding stages (i.e., welding heat tracing and post-weld slow cooling), while leveraging the rapid heating during the preheating stage and the low-power insulation during the interlayer waiting stage. This significantly optimizes the time and energy consumption of the entire process, thereby greatly improving the overall efficiency and economy of the automated production line.

[0055] Example 3

[0056] This embodiment demonstrates the adaptability of the technical solution of this application in welding components with complex geometries or large dimensions, especially in application scenarios where it is inconvenient to install contact temperature sensors. By adopting a fully non-contact temperature measurement scheme, this embodiment broadens the scope of application of this application.

[0057] The welding object in this embodiment is a saddle-shaped weld on a pipe joint of a large pressure vessel. This type of weld has a complex three-dimensional curved surface shape, is made of high-strength alloy steel, and has a plate thickness of up to 80 mm. It should be noted that embedding or mounting contact sensors such as thermocouples on such workpieces is not only difficult to implement, but the sensors are also extremely prone to damage during the welding process.

[0058] Therefore, this embodiment makes the following adaptive adjustments to the system configuration: First, the sensor 40 uses a flexible, conformal induction coil. This coil can be closely fitted to the complex curved surface of the saddle-shaped weld to ensure that the induced magnetic field can act uniformly on the welding area. Second, as a core feature of this embodiment, the multi-depth temperature sensing array 50 adopts a fully non-contact measurement scheme. The surface temperature sensor 51 still uses an infrared thermometer, with its measurement spot always aligned with the bevel surface in front of the welding torch. The internal temperature sensor 52 uses a non-contact temperature probe based on the eddy current detection principle. This probe itself includes an excitation coil and a detection coil, and is placed on the workpiece surface (e.g., the back or side of the weld). Its working principle is as follows: the excitation coil induces eddy currents in the workpiece, and the distribution depth of the eddy currents is related to the excitation frequency; since the conductivity of the metal changes with temperature, this change will cause a change in the phase and amplitude of the eddy current field; the detection coil is responsible for capturing this change. By analyzing the phase change of the eddy current signal at a specific frequency and combining it with a pre-calibrated "phase-temperature-depth" database, the temperature at a specific depth (e.g., 30-40 mm) of the subsurface layer of the workpiece can be determined.

[0059] During operation, the control system 60 receives surface temperature signals from the infrared thermometer. and the internal temperature signal from the eddy current temperature probe Understandably, although the two sensors have different physical principles, the control system 60 obtains the two key input signals required to achieve dual closed-loop control. Therefore, the control system 60 executes the same core control strategy as in Example 1, that is, by combining "gradient-ratio" and "temperature-total power" dual closed-loop control with arc parameter feedforward compensation, to adjust the high and low frequency power ratio and total power output of the composite induction power supply 30.

[0060] The results of this embodiment demonstrate that even on complex curved joints where traditional contact sensors cannot be used, the technical solution provided in this application can still acquire the required multi-depth temperature information using non-contact sensing technology and achieve effective closed-loop control of the temperature gradient. The ultimate effect is the successful suppression of welding cracks in the high-risk area of ​​the saddle weld, thereby ensuring the manufacturing quality and service safety of the pressure vessel, a critical pressure-bearing component.

[0061] Example 4

[0062] This embodiment aims to demonstrate the high flexibility of the control strategy of this application, namely, that it can not only be used to minimize the temperature gradient to pursue uniform cooling, but also actively create and maintain a specific, non-zero temperature gradient profile according to special process requirements. This capability has important application value in welding dissimilar metals.

[0063] The welding object in this embodiment is a butt joint of dissimilar metal thick plates made of stainless steel and carbon steel. The thermophysical properties (such as thermal conductivity and coefficient of thermal expansion) of these two materials differ significantly. During welding and subsequent cooling, if the temperature field is completely uniform, the significant difference in the coefficients of thermal expansion between the two materials will generate huge structural stress and residual stress at the interface during cooling and contraction, which can easily lead to interface cracking.

[0064] To address this issue, an advanced process concept involves actively maintaining a specific temperature difference between the two materials during the cooling process. The thermal stress generated by this temperature difference partially offsets the structural stress caused by the difference in material properties, thereby reducing the total stress level at the interface.

[0065] The technical solution of this application precisely achieves this precise control objective. The system configuration is similar to that of Embodiment 1; the key lies in setting the control parameters. For example, suppose that finite element simulation or experimental research reveals that, to balance thermal stress, the temperature on the stainless steel side needs to be maintained 30°C higher than that on the carbon steel side during the slow cooling phase. In this case, the surface temperature sensor 51 can be aligned with the surface of the stainless steel side, and the internal temperature sensor 52 can be aligned with a certain depth on the carbon steel side. Accordingly, the target temperature gradient is set in the control system 60. Set to a non-zero value, that is At the same time, a desired overall slow-cooling reference temperature is set, such as the target average temperature. (and decrease according to the slow cooling curve).

[0066] During the subsequent welding and slow cooling process, the control system 60 executes the same dual closed-loop control logic as in Example 1. At this time, the gradient controller C1 will adjust the control logic based on the error... The power ratio R is adjusted accordingly. When the actual temperature difference is less than 30°C, the controller increases R, that is, increases the proportion of high-frequency power, to raise the surface temperature of the stainless steel side; when the actual temperature difference is greater than 30°C, it adjusts in the opposite direction. At the same time, the temperature equalization controller C2 is still responsible for maintaining the overall average temperature near the target value.

[0067] In this way, the control system 60 can dynamically and precisely adjust the output of high and low frequency power, thereby driving the temperature field of the entire welding area to always maintain a specific state where "the average temperature is about 180°C, while the stainless steel side is about 30°C higher than the carbon steel side".

[0068] The intended effect of this embodiment is that by actively maintaining a specific temperature gradient profile that is conducive to balancing thermal stress, the residual stress concentration at the interface of dissimilar metal welded joints can be significantly reduced, and interface cracking or performance degradation caused by thermophysical property mismatch can be effectively avoided, thereby obtaining a sound and reliable dissimilar metal welded joint. This also fully demonstrates the powerful control and flexibility of the technical solution of this application in dealing with complex and special welding problems.

[0069] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A thick plate arc-heated composite welding method based on multi-frequency composite induction, applied to a welding apparatus including arc welding equipment and a composite induction heating system, wherein the composite induction heating system is capable of outputting low-frequency current and high-frequency current, characterized in that, The method includes: The temperature of at least one surface layer and at least one internal temperature of the workpiece to be welded are acquired in real time through a multi-depth temperature sensing array. The power ratio of the low-frequency current and the high-frequency current is adjusted by using the first closed-loop control loop based on the difference between the actual temperature gradient calculated from the surface temperature and the internal temperature and the preset target temperature gradient. The total output power of the low-frequency current and the high-frequency current is adjusted by the second closed-loop control loop based on the difference between the average temperature of the workpiece determined by the surface temperature and the internal temperature and the preset target temperature. The arc parameters of the arc welding equipment are monitored in real time, and the power of the high-frequency current is adjusted compensatorily through a feedforward control model. The compensatory adjustment includes superimposing the compensatory power output by the feedforward control model onto the power command of the high-frequency current, and synchronously adjusting the power command of the low-frequency current according to the power ratio determined by the first closed-loop control loop.

2. The method according to claim 1, characterized in that, The method is performed in at least one of the following stages: preheating before welding, heat tracing during welding, and slow cooling after welding.

3. The method according to claim 2, characterized in that, During the post-weld slow cooling stage, the target temperature is reduced in a programmed manner according to a preset slow cooling curve.

4. The method according to claim 1, characterized in that, The multi-depth temperature sensing array includes a surface temperature sensor and an internal temperature sensor; wherein, the surface temperature sensor is an infrared thermometer; and the internal temperature sensor is selected from a thermocouple or a non-contact temperature probe based on the eddy current detection principle.

5. The method according to claim 1, characterized in that, The arc parameters include at least one of arc current and arc voltage.

6. The method according to claim 1, characterized in that, The method further includes a time-domain switching step, employing different control modes at different welding stages; wherein the control mode includes at least one of the following: During the overall preheating stage, a power ratio mode based on low-frequency current is adopted. During the interlayer insulation stage of multi-pass welding, an insulation mode is adopted. In this insulation mode, a low-frequency current is output in the form of low-frequency, low-power pulses, while maintaining a basic high-frequency current output for power ratio adjustment.

7. The method according to claim 1, characterized in that, The target temperature gradient is a preset non-zero value for use in dissimilar metal welding.

8. A thick plate arc-heating composite welding system based on multi-frequency composite induction, comprising arc welding equipment and a composite induction heating system, characterized in that, The composite induction heating system includes: Composite inductive power supply, used to output low-frequency current and high-frequency current; The sensor is connected to the composite inductive power supply; A multi-depth temperature sensing array is used to acquire at least one surface temperature and at least one internal temperature of the workpiece to be welded in real time. A control system is connected to the composite induction power supply, the multi-depth temperature sensing array, and the arc welding equipment, wherein the control system is configured as follows: The actual temperature gradient along the thickness direction of the workpiece is calculated based on the surface temperature and internal temperature, and the actual temperature gradient is compared with the preset target temperature gradient so as to adjust the power ratio of the low-frequency current and the high-frequency current according to the difference. Based on the surface temperature and internal temperature, the average temperature of the workpiece is determined by a preset calculation method and compared with a preset target temperature, so as to adjust the total output power of the low-frequency current and the high-frequency current according to the difference. The arc parameters of the arc welding equipment are monitored, and when the fluctuation amplitude of the arc parameters exceeds a preset threshold, the power of the high-frequency current is adjusted compensatorily through a preset feedforward control model. The control system is further configured to: superimpose the compensation power output by the feedforward control model onto the power command of the high-frequency current, and synchronously adjust the power command of the low-frequency current according to the power ratio determined by the control logic for adjusting the power ratio.

9. The system according to claim 8, characterized in that, The multi-depth temperature sensing array includes a surface temperature sensor and an internal temperature sensor; wherein, the surface temperature sensor is an infrared thermometer; and the internal temperature sensor is selected from a thermocouple or a non-contact temperature probe based on the eddy current detection principle.

10. The system according to claim 8, characterized in that, The control system is also configured to perform time-domain switching and adopt different control modes at different welding stages. The control modes include at least one of a power ratio mode dominated by low-frequency current and a low-frequency low-power pulse mode. In the low-frequency low-power pulse mode, the control system outputs low-frequency current with a preset low duty cycle while maintaining a basic high-frequency current output for power ratio adjustment.

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