Arc and wire synergic control method and system for variable gap groove TIG welding

Abstract

The application discloses a kind of arc and wire feeding collaborative control method and system of variable gap groove TIG welding, to solve the problem of uneven arc coverage, the weld quality defect caused by the mismatch between the amount of wire feeding and the groove width in variable gap groove welding.The method applies a directional magnetic field to the TIG arc through a sharp corner magnetic field generating device, achieving active regulation of the arc cross-sectional width; real-time acquisition of arc images is achieved using a vision sensor, and the maximum width of the arc is extracted; through closed-loop control logic, when the arc does not contact the two sides of the groove, the sharp corner magnetic field strength is increased to expand the arc coverage; when the arc contacts the two sides of the groove, the magnetic field strength is kept stable, and the wire feeding speed is dynamically adjusted according to the groove width, so that the amount of wire feeding and the groove gap are accurately matched.The application realizes the collaborative adaptive control of arc morphology and wire feeding speed, effectively deals with the assembly error and welding deformation of variable gap groove, ensures the uniformity of weld formation, reduces the defect rate of incomplete penetration, incomplete fusion and excessive reinforcement, and improves the level of welding automation and production efficiency.

Description

Technical Field

[0001] This invention relates to the field of welding automation and process control technology, specifically to a TIG welding method and system suitable for variable gap bevels (such as V-grooves, U-grooves, etc.), and particularly to a technology that achieves coordinated adaptive control of the arc shape and wire feed speed by actively adjusting the arc shape and wire feed speed. Background Technology

[0002] In the field of thick plate structure welding (such as shipbuilding, pressure vessels, and nuclear power pipeline docking), the precision of beveling and assembly directly determines the weld quality. Due to the rigid deformation of large workpieces, beveling machining errors (typically ±0.5~2mm), and the dynamic influence of thermal deformation of the molten pool during welding, the actual weld bevel gap often exhibits non-uniform and dynamically changing characteristics, i.e., variable gap bevel. Traditional TIG welding and existing control technologies face significant bottlenecks in addressing this problem. 1. Imbalance between arc coverage and bevel gap: The arc shape of traditional TIG welding is fixed. When the bevel gap suddenly increases, the arc cannot cover both sides of the bevel at the same time, which easily leads to defects such as incomplete fusion and incomplete penetration of the sidewalls. When the gap decreases sharply, the arc energy is excessively concentrated, resulting in burn-through or excessive weld height. Especially in space-constrained scenarios such as circumferential welding of small-diameter pipes, the defect rate is as high as 15% or more.

[0003] 2. Asynchronous wire feeding adjustment and gap change: Existing technologies mostly adopt the "constant speed wire feeding + welding current feedforward adjustment" mode. The wire feeding amount is only related to the preset current and is not directly coupled with the real-time bevel gap. For example, when the bevel gap increases from 3mm to 5mm, constant speed wire feeding will lead to insufficient filling, requiring manual pause for adjustment, which seriously reduces welding efficiency (automated line downtime rate exceeds 20%).

[0004] 3. Lag in process perception and control response: Existing gap detection technologies are divided into pre-weld laser scanning and in-weld mechanical contact detection. The former cannot cope with dynamic gap changes during welding (such as gap shrinkage caused by thermal deformation), while the latter is easily damaged by high temperature of the molten pool and spatter. The detection delay is usually more than 100ms, which is much greater than the solidification time of the molten pool (about 30~50ms), leading to control failure.

[0005] Existing related technologies, such as CN118926658A which discloses a magnetically controlled oscillating indirect arc ultra-narrow gap welding device and method, only widen the arc through a transverse magnetic field and adopt an open-loop control mode. It does not adjust the magnetic field strength according to the actual state of the bevel, nor does it achieve coordination with the wire feeding speed. CN117066655A proposes a pipeline robot argon arc intelligent root pass welding system and method, which only adjusts the wire feeding through image recognition of the bevel width, failing to solve the fundamental problem of insufficient arc coverage. Therefore, there is an urgent need for a technical solution that integrates active arc control, real-time state perception, and dual-parameter collaborative closed-loop control to overcome the limitations of single control in existing technologies. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method and system for coordinated control of arc and wire feed in variable gap TIG welding. This method actively adjusts the arc width through a sharp-angle magnetic field and uses visual sensing to monitor the contact state between the arc and the bevel in real time, using this as a criterion for switching control modes. Ultimately, it achieves seamless coordination between the arc width expansion mode and the wire feed speed following mode, ensuring that the arc effectively covers both sides of the bevel under any bevel gap, and that the amount of filler metal is precisely matched to the gap.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The system comprises a welding system, an excitation system, a vision inspection system, a wire feeding execution system, and a central control system. First, the welding power source ignites the arc. The excitation system outputs current to four magnetic induction coils to generate a sharp-angle magnetic field to regulate the shape of the arc. The vision inspection system acquires and processes welding images in real time to obtain the maximum arc width. The central control system controls the arc cross-sectional area by adjusting the current. When the maximum arc width is detected to be no longer changing, a wire feeding speed control signal is output to the wire feeding execution system to adjust the wire feeding speed, thereby achieving precise matching between the filler metal amount and the bevel gap.

[0008] The excitation system is an actuator for adjusting the arc shape. It includes a support bracket, four magnetic poles, and an excitation power supply. Four magnetic poles are fixedly connected to the inner wall of the support bracket. Each magnetic pole consists of a magnetic rod and an excitation coil wound on the magnetic rod, and the welding torch is located at the center of the support bracket. By passing a current of a specific magnitude and direction through these coils, a sharp-angle magnetic field with controllable intensity can be generated. This magnetic field interacts with the arc plasma to generate a Lorentz force, thereby laterally compressing or expanding the arc and effectively adjusting the width and energy distribution of the arc.

[0009] The vision inspection system is a sensing mechanism for acquiring real-time status information of the welding process. It includes an industrial camera and an image processing unit. The camera is preferably arranged laterally at an angle of 30° to 60° near the welding area and equipped with a narrow-bandpass filter. The center wavelength of the narrow-bandpass filter matches the strong characteristic spectrum of the TIG arc. The image processing unit performs preprocessing, threshold segmentation, and edge extraction on the acquired arc image, and finally accurately calculates and outputs the maximum arc width value Wᵥ as a key feedback signal for the system.

[0010] The wire feeding system is an actuator that controls the amount of filler metal fed. It uses a servo motor with high dynamic response to drive the wire feeding wheel, which can accurately and quickly adjust the wire feeding speed according to the control signal to ensure that the wire feeding amount matches the bevel gap and the arc state in real time.

[0011] The central control system is the control center of the entire system, communicating with the aforementioned three system modules. It receives arc width data from the vision inspection system and makes decisions based on preset dual-mode collaborative control logic. Its core function is to determine whether to enter arc width expansion mode or wire feeding speed following mode based on the relationship between real-time arc width and bevel width, and accordingly output magnetic field adjustment signals (such as adjusting excitation current) to the sharp-angle magnetic field generation system and wire feeding speed control signals to the wire feeding execution system, thereby achieving closed-loop control.

[0012] Compared with the prior art, the inventiveness and advantages of this invention are reflected in: 1. Directionality and precision of arc control: Using a sharp-angle magnetic field instead of a traditional planar magnetic field, the magnetic field gradient effect of the sharp poles is utilized to make the arc directionally widen along the bevel width direction, avoiding energy waste caused by the arc diverging in the upward and downward directions; 2. Innovation of dual-mode coordination: Automatic mode switching is achieved by using the arc-groove contact state as the criterion, which solves the timing coordination problem of controlling the arc first and then adjusting the wire. Compared with the existing "independent arc and wire control", the weld non-fusion defect rate is greatly reduced. 3. Rapid response capability: The total delay of visual inspection and control response is ≤60ms, which is much lower than the solidification time of the molten pool. It can cope with gap changes of ±2mm / s and adapt to the dynamic welding requirements of large structures such as ships and pressure vessels. 4. Increased automation: Variable gap adaptation can be completed without manual intervention, significantly reducing welding downtime for adjustment. Attached Figure Description

[0013] Figure 1This is a schematic diagram of the overall structure and signal connection of the collaborative control system of the present invention, wherein the welding gun (1), welding power supply (2), bearing bracket (3), copper coil (4), magnetic rod (5), excitation power supply (6), CCD camera (7), welding wire (8), wire feeding wheel (9), central controller (10), and U-shaped bevel workpiece (11). Figure 2 It is the cross-section of an electric arc under the action of a sharp-angled magnetic field; Figure 3 This is the arc width image after image preprocessing; Figure 4 Figure 5 and Figure 6 This is a diagram showing the shape of the electric arc filling the U-shaped bevel under different sharp-angle magnetic field intensities according to the present invention; Figure 7 This is a flowchart of the dual-mode collaborative control logic of the present invention. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. See also Figure 1 The collaborative control system of this invention mainly comprises the following parts: a welding system, a sharp-angle magnetic field excitation system, a vision inspection system, a wire feeding execution system, and a central control system. The welding system consists of a TIG welding torch and a welding power source. The welding power source provides the welding torch with welding current and arc-starting high frequency. The welding torch is fixedly installed at the center of the support frame. The sharp-angle magnetic field excitation system, as the actuator for adjusting the arc shape, mainly consists of a support frame, four sets of electromagnetic coils, magnetic rods, and an excitation power source. Four magnetic rods made of high magnetic permeability material are symmetrically and vertically fixed to the inner wall of the non-magnetic support frame. Each magnetic rod is wound with an excitation coil. The wiring method of the four coils causes the magnetic field directions generated to be superimposed in the arc region, forming a magnetic field... Figure 2 The directional sharp-angle magnetic field shown The excitation power supply provides a continuously adjustable DC excitation current to the coil. By changing the current magnitude, a continuously varying magnetic field strength within the range of 0~500mT can be generated in the center region of the arc. The vision inspection system, acting as the system's eye, consists of an industrial camera and its image processing unit. The camera is mounted at a side angle and equipped with a narrow-band filter whose center wavelength matches the strong characteristic spectral lines of the TIG arc to effectively filter out background stray light interference, clearly capture the arc shape, and measure the maximum width of the arc, such as... Figure 3As shown, the wire feeding system, as the conveying mechanism for the filler metal, includes a wire feeding wheel, welding wire, a drive motor, and a wire guide tube. The drive motor is preferably a high-precision servo motor to ensure that the wire feeding speed control accuracy is not less than ±0.01 mm / s. The welding wire is pushed to the leading edge of the molten pool through the wire feeding wheel. The central control system, as the brain of the system, is implemented by an industrial computer. It communicates bidirectionally with the excitation power supply, camera, and wire feeding servo driver through a data line, coordinates the work of each module, and executes the core dual-mode collaborative control algorithm.

[0015] Please see Figure 7 , Figure 7 The core control logic flow of this invention is implemented in the following steps: Before welding, the operator sets basic process parameters, including welding current, welding speed, and shielding gas flow rate; sets the control cycle T, initializes the excitation current, and calibrates the coefficients k and b in the wire feed speed mapping relationship v = k × Wᵥ + b through process experiments based on the bevel form and welding material; the welding power source ignites the TIG arc, and the central controller simultaneously starts the continuous acquisition and timed control cycle of the vision detection module; at the beginning of each control cycle, the camera acquires an image of the arc, which is transmitted to the image processing unit in the central controller for processing, as follows: Gaussian filtering is applied to the image to reduce noise caused by arc flicker and spatter; an adaptive threshold segmentation algorithm is used to separate the bright arc area from the dark background; the Canny edge detection algorithm is applied to accurately extract the contour of the arc area; the arc contour is analyzed on the cross-section perpendicular to the welding direction, its maximum width pixel value is calculated, and the actual physical width Wᵥ is obtained through the pre-calibrated pixel-physical size conversion relationship, such as... Figure 3 As shown.

[0016] The central controller is based on the current width Wᵥ and the width Wᵥ of the previous cycle. -1 Comparison, execution Figure 7 The decision-making logic shown is as follows: Mode 1: Arc width expansion control mode; if Wᵥ>Wᵥ -1 If the arc is still in the expansion process and has not yet made stable contact with both sides of the bevel, the central controller sends a command to the excitation power supply to increase the excitation current by a preset step size. The enhanced sharp-angle magnetic field exerts a greater Lorentz force on the arc plasma, causing the arc cross-section to widen further to both sides, as shown in the comparison. Figure 4 and Figure 5 .

[0017] Mode 2: Wire feed speed follow-up control mode; if Wᵥ = Wᵥ -1, it is determined that the arc width has reached the physical limit under the current groove gap, that is, the arc has simultaneously and stably contacted or is very close to both side walls of the groove. The central controller sends an instruction to keep the current excitation current constant, thereby stabilizing the arc shape, as Figure 5 , 6 shown; the central controller substitutes the current maximum arc width Wᵥ into the formula v = k × Wᵥ + b to calculate the target wire feeding speed v required to accurately match the current gap; immediately, the controller sends an instruction to the wire feeding servo driver to drive the wire feeding wheel to feed the welding wire at the speed v.

[0018] After the loop execution and dynamic adaptation, after completing the control of the current cycle, the next control cycle starts. During the entire welding process, this closed-loop of perception - decision - execution continuously runs; when the groove gap changes: if the gap becomes larger, in the next cycle, the vision system will detect Wᵥ -1 <Wᵥ, the system will automatically switch back to Mode 1, first enhance the magnetic field to broaden the arc, and then switch back to Mode 2 and increase the wire feeding speed after the arc stably contacts both sides again; if the gap becomes smaller, the arc will contact the side wall in advance and the width will stop growing Wᵥ -1 >Wᵥ=Wᵥ +1 , the system remains in Mode 2 and automatically reduces the wire feeding speed according to the decreased Wᵥ value.

Claims

1. A method for coordinated control of arc and wire feeding in variable gap bevel TIG welding, characterized in that, Includes the following steps: S1: Sharp-angle magnetic field generating devices are symmetrically arranged on both sides of the TIG welding torch. By adjusting the excitation current of the device, an adjustable sharp-angle magnetic field is generated to actively control the cross-sectional width of the TIG arc. S2: Real-time acquisition of welding area images using a vision sensor, extraction of arc contours using image processing algorithms, and calculation of the maximum arc width Wᵥ; S3: Based on the changing trend of the maximum arc width Wᵥ and its relationship with the bevel width, a dual-mode collaborative control decision is executed: when it is determined that the arc has not stably contacted both sides of the bevel, the arc width expansion control mode is entered to increase the magnetic field strength at the sharp corner to widen the arc; when it is determined that the arc has stably contacted both sides of the bevel, the wire feeding speed following control mode is entered to maintain the magnetic field strength stable and dynamically adjust the wire feeding speed according to the real-time arc width Wᵥ. S4: During the welding process, steps S2 and S3 are continuously executed to achieve dynamic closed-loop coordinated control of arc width and wire feed speed for variable gap bevels.

2. The method according to claim 1, characterized in that, In step S3, the criterion for "determining that the electric arc has not stably contacted both sides of the bevel" is: within a fixed control period T, the maximum width Wᵢ of the electric arc collected in the current period is greater than the width Wᵢ₋1 collected in the previous period.

3. The method according to claim 1, characterized in that, In step S3, the criterion for determining that the electric arc has stably contacted both sides of the bevel is: within a fixed control period T, the maximum arc width Wᵢ collected in the current period is equal to the width Wᵢ₋1 collected in the previous period.

4. The method according to claim 1, characterized in that, In step S3, under the wire feed speed following control mode, the target wire feed speed v and the real-time arc width Wᵥ are calculated through the linear mapping relationship v = k × Wᵥ + b, where k is the wire feed coefficient, b is the basic wire feed speed, and k and b are calibrated through welding process tests.

5. The method according to claim 1, characterized in that, In step S2, the image processing algorithm includes at least: image filtering and noise reduction, arc region and background segmentation, edge contour extraction, and calculation of maximum width based on contour geometric features.

6. An arc and wire feeding coordinated control system for implementing the method of any one of claims 1-5 in variable gap bevel TIG welding, characterized in that, include: A sharp-angle magnetic field excitation system is used to generate a sharp-angle magnetic field with controllable intensity to adjust the arc width; A visual inspection system is used to acquire and process welding images in real time to obtain the maximum arc width Wᵥ; A wire feeding execution system is used to control the wire feeding speed with high precision; a central control system is communicatively connected to the sharp-angle magnetic field generating system, the vision detection system, and the wire feeding execution module; the central control system is configured to: receive arc width data from the vision detection module, and output a magnetic field adjustment signal to the sharp-angle magnetic field generating system and / or output a wire feeding speed control signal to the wire feeding execution system according to the dual-mode collaborative control logic described in claims 1-5.

7. The system according to claim 6, characterized in that, The sharp-angle magnetic field generating system includes four symmetrically arranged electromagnetic poles and an excitation power supply. The magnetic poles are made of high-permeability material and are sharp-angled, with the distance between the sharp end and the center line of the electric arc being 5~15mm. The excitation power supply can provide a continuously adjustable current to the electromagnetic coil, and the magnetic field strength generated can be adjusted within the range of 0~500mT.

8. The system according to claim 6, characterized in that, The visual inspection module includes an industrial CCD camera, a narrowband filter, and an image processing unit. The center wavelength of the narrowband filter matches the strong characteristic spectrum of the TIG arc. The image processing unit has a built-in program for executing the image processing algorithm of claim 5.

9. The system according to claim 6, characterized in that, The wire feeding execution module includes a servo motor, a wire feeder driven by the servo motor, and wire feeding rollers, and its wire feeding speed control accuracy is not less than ±0.01 mm / s.

10. The system according to claim 6, characterized in that, The central control module has a built-in dual-mode closed-loop control logic unit, which is programmed to perform mode switching and control decisions based on the criteria described in claims 2 and 3.

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