Narrow-gap horizontal position welding process based on asymmetric alternating magnetic field and molten pool control method

Abstract

The invention discloses a narrow-gap horizontal position welding process based on an asymmetric alternating magnetic field and a molten pool control method, and relates to the technical field of welding processes and control, and the narrow-gap horizontal position welding process comprises the following steps that in the welding process, the alternating magnetic field is applied to a welding arc area, and the magnetic field is generated by a magnetic control system; the magnetic field intensity of the magnetic field in the upward swinging stage of the electric arc is larger than that in the downward swinging stage by adjusting the waveform and amplitude of the current input to the magnetic control coil; asymmetric swing of an electric arc is accurately regulated and controlled through an asymmetric alternating magnetic field, the swing amplitude of the electric arc on the groove wall of the upper side is larger than that of the lower side by 1-2 mm, the residence time of the electric arc on the groove wall of the upper side is 0.3-0.5 s longer than that of the lower side, heat input distribution accurately matched with the horizontal position welding gravity characteristic is formed, and therefore active intervention on the flowing direction of a molten pool is achieved, and directional electromagnetic force is generated based on the asymmetric magnetic field gradient; and upward magnetic levitation force is formed, the magnetic levitation force and the gravity of the molten pool form force field balance, 30%-50% of the gravity influence of the molten pool is counteracted, and downward flowing of the molten pool is inhibited from the source.

Description

Technical Field

[0001] This invention relates to the field of welding technology and control, specifically to a narrow-gap horizontal welding process based on an asymmetric alternating magnetic field and a method for controlling the molten pool. Background Technology

[0002] Narrow gap welding technology is widely used in welding thick plate structures due to its advantages such as low heat input, small deformation, and high efficiency. However, in transverse welding (non-horizontal position), the molten pool is prone to downward flow due to gravity, resulting in defects such as weld asymmetry, poor sidewall wetting, and lack of fusion, which seriously affect the joint quality.

[0003] Traditional magnetron welding with narrow gaps typically employs a symmetrical alternating magnetic field to cause the arc to oscillate symmetrically on both sides of the bevel, achieving uniform heat input. However, in the horizontal welding position, the symmetrical heat input cannot overcome the downward flow of the molten pool caused by gravity, leading to metal accumulation on the lower side of the weld and potential lack of fusion on the upper side.

[0004] A search revealed a Chinese patent publication, CN118720332A, which discloses a closed-loop control method for the temperature field of narrow-gap welds based on a magnetically controlled GTAW arc. This method addresses the adverse effects of improper heat input distribution on weld formation during the GTAW process, specifically addressing the issue of uneven heat input distribution across the narrow gap. The method utilizes a GTAW robot to control the welding motion; a magnetic field generator to control the weld temperature field distribution by adjusting the magnetic field parameters; and a left-right temperature detection system to monitor the temperature on both sides of the weld.

[0005] However, the aforementioned existing technologies still have significant limitations. Their core design focuses on balancing heat input on both sides of the weld, and their magnetic field control logic and temperature field closed-loop control are based on flat welding or symmetrical bevel scenarios, without specific optimization for the gravity characteristics of horizontal welding positions. During horizontal welding, the molten pool metal naturally tends to flow downwards due to gravity. The symmetrical heat input distribution and magnetic field application methods of the existing technologies cannot create an effective constraint force opposite to the direction of gravity; they can only slightly improve heat distribution and cannot counteract the dominant influence of gravity on the molten pool flow, leading to downward flow of the molten pool.

[0006] Therefore, there is an urgent need for a welding process that can actively regulate the arc oscillation behavior and heat input distribution in order to achieve stable control of the molten pool and optimize the weld formation in the horizontal welding position. Summary of the Invention

[0007] The purpose of this invention is to provide a narrow-gap horizontal welding process and a molten pool control method based on an asymmetric alternating magnetic field, so as to solve the problem of asymmetric flow of the molten pool caused by gravity in the prior art during horizontal welding.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a narrow-gap horizontal welding process based on an asymmetric alternating magnetic field, comprising the following steps:

[0009] S1: During the welding process, an alternating magnetic field is applied to the welding arc area, and the magnetic field is generated by a magnetic control system;

[0010] S2: By adjusting the waveform and amplitude of the current input to the magnetic control coil, the ratio of the magnetic field strength during the upward swing phase of the electric arc to the magnetic field strength during the downward swing phase is ≥1.5;

[0011] S3: The asymmetrical alternating magnetic field is used to drive the electric arc to oscillate asymmetrically within the narrow gap groove, so that the oscillation amplitude of the electric arc in the upper side wall region of the groove is 1-2 mm larger than that in the lower side wall region, in order to counteract the downward flow of the molten pool caused by gravity and optimize the weld formation.

[0012] Furthermore, in step S2, the magnetic field strength during the upward swing phase is 3-5 mT, and the magnetic field strength during the downward swing phase is 1-2 mT.

[0013] When the base material is a low thermal conductivity material such as titanium alloy or aluminum alloy, a magnetic field strength combination of 3-4 mT / 1-1.5 mT is preferred; when the base material is a high thermal conductivity material such as stainless steel, a magnetic field strength combination of 4-5 mT / 1.5-2 mT is preferred.

[0014] Furthermore, the low-frequency range of the asymmetric alternating magnetic field is 0.5 Hz to 1 Hz;

[0015] The frequency of the asymmetric alternating magnetic field can be adjusted within the range of 0.5Hz to 10Hz. When it is suitable for welding conventional thick plates and the base material is a low thermal conductivity material such as titanium alloy or aluminum alloy, 1Hz is selected; when it is suitable for welding thicker plates or the base material is a high thermal conductivity material such as stainless steel, 0.5Hz is selected.

[0016] Furthermore, the current waveform in step S2 adopts an asymmetric square wave with an upper two-lower or upper three-lower duration, wherein the duration of the positive half-cycle of the square wave corresponds to the upward swinging phase of the arc, and the duration of the negative half-cycle corresponds to the downward swinging phase of the arc. The pulse width duty cycle of the asymmetric square wave is adjustable in the range of 2:1-4:1.

[0017] Furthermore, the magnetic control system includes an alternating magnetic control power supply, a magnetic control coil, and magnetic poles. The magnetic control power supply is used to input an adjustable current and frequency alternating current into the magnetic control coil to generate an alternating magnetic field. The magnetic poles are used to guide the magnetic field to the arc and molten pool areas.

[0018] Furthermore, the magnetron coil is wound with 500 turns of high-temperature resistant enameled wire with a diameter of 1.2mm, and silicon steel sheets are embedded inside the magnetron coil to enhance the magnetic field focusing effect and reduce hysteresis loss.

[0019] Furthermore, it also includes a monitoring unit, which includes a high-speed camera system positioned above the welding area and an arc pressure sensor mounted on the welding torch;

[0020] Among them, the high-speed camera system has a frame rate of ≥1000fps, which is used to clearly capture the shape of the molten pool and the arc oscillation trajectory; the arc pressure sensor has a measurement accuracy of ±10Pa, which is used to collect arc pressure data in real time. The two work together to achieve accurate monitoring of arc behavior and molten pool flow.

[0021] A method for controlling the molten pool to achieve the above-mentioned narrow gap horizontal welding process includes the following steps:

[0022] M1: Set the magnetic field parameters so that the magnetic field strength during the upward swing phase is greater than that during the downward swing phase, forming a magnetic field strength gradient distribution that is high on the upper side and low on the lower side.

[0023] M2: Through the magnetic field strength gradient distribution, an upward magnetic levitation force greater than that on the lower side is generated on the upper side of the molten pool to counteract the downward flow of gravity on the molten pool.

[0024] M3: Controls the magnetic field frequency to be in the low-frequency range and works in conjunction with the magnetic field strength to optimize the temperature gradient between the molten pool and the bevel sidewall, thereby reducing defects in poor fusion of the lower sidewall.

[0025] M4: The asymmetric alternating magnetic field is used to drive the electric arc to oscillate asymmetrically, so that the residence time and heat input of the electric arc in the upper side wall region of the bevel are greater than those in the lower side wall region, thereby increasing the temperature of the upper side wall and reducing the temperature gradient between the upper and lower sides of the weld.

[0026] M5: By controlling the heat input and arc oscillation in step M4, the upper sidewall is subjected to greater arc pressure and fluid shear force, pushing the molten pool metal upwards and forming an auxiliary force field opposite to the direction of gravity. This auxiliary force, combined with the magnetic levitation force of M2, can achieve comprehensive suppression of the molten pool's downward flow. When the magnetic levitation force of M2 can stabilize the molten pool, the auxiliary force can be finely adjusted by regulating the arc oscillation amplitude. When the molten pool collapse exceeds the standard, the magnetic levitation force of M2 is increased first, and then the auxiliary force is enhanced by extending the arc's dwell time on the upper side.

[0027] M6: By increasing the heat input to the upper sidewall, the solid-liquid interfacial tension in this area is reduced, which promotes the wetting and spreading of the molten pool metal on the upper sidewall of the bevel and improves the weld formation.

[0028] Compared with the prior art, the narrow gap horizontal welding process and molten pool control method based on asymmetric alternating magnetic field provided by the present invention have the following beneficial effects:

[0029] 1. By precisely controlling the asymmetric oscillation of the electric arc through an asymmetric alternating magnetic field, the oscillation amplitude and dwell time of the arc on the upper bevel wall are made greater than those on the lower side, forming a magnetic field intensity gradient and heat input distribution that is stronger at the top and weaker at the bottom. This allows for active intervention in the flow direction of the molten pool, using upward magnetic levitation to offset part of the molten pool's gravity, fundamentally suppressing the downward flow of the molten pool caused by gravity at the horizontal welding position, and solving the problems of metal accumulation on the lower side of the weld and insufficient heat input on the upper side in traditional symmetrical magnetic field welding.

[0030] 2. The asymmetric magnetic field drives the arc in an up-large, down-small oscillation pattern, combined with a square wave current waveform of "two up, one down" or "three up, one down," resulting in symmetrical weld formation on both the upper and lower sides and significantly improved sidewall wettability. After welding, the weld contact angle is less than 90°, effectively avoiding defects such as incomplete fusion and poor sidewall wetting. Furthermore, the molten pool collapse is close to zero, resulting in a full and uniform weld formation, significantly improving the joint quality and appearance consistency of narrow-gap horizontal welds.

[0031] 3. The magnetic field parameters and current waveforms of this process can be flexibly switched according to the bevel size and base material characteristics, adapting to the narrow gap horizontal welding requirements of 20-25mm thick plates, and are especially suitable for high-strength materials such as titanium alloys, aluminum alloys, and stainless steel. Whether it is stainless steel with high thermal conductivity or easily oxidized titanium alloys, stable welding can be achieved through parameter optimization without significant adjustments to the system structure, making the process highly versatile.

[0032] 4. The magnetic control system, welding system and detection system of the present invention can be seamlessly integrated and can be docked with a six-axis robotic arm and a robotic welding system to achieve automated welding. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0034] Figure 1 This is a schematic diagram of the narrow gap horizontal welding system provided in an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the structure of the magnetic control system provided in an embodiment of the present invention;

[0036] Figure 3 This is a flowchart of the narrow-gap horizontal welding process provided in an embodiment of the present invention;

[0037] Figure 4 The flowchart of the molten pool control logic provided in the embodiment of the present invention.

[0038] Explanation of reference numerals in the attached figures:

[0039] 1. Welding system; 2. Magnetically controlled system; 201. Magnetically controlled coil; 202. Magnetic pole. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] As attached Figure 1 To be continued Figure 4 As shown:

[0042] Example 1:

[0043] This invention provides a narrow-gap horizontal welding system based on an asymmetric alternating magnetic field, comprising a welding system 1, a magnetic control system 2, and a detection system;

[0044] Welding system 1 includes a GTAW welding power source, a wire feeding system, a six-axis robotic arm, and a shielding gas system. The welding power source uses a DC pulse GTAW power supply with an adjustable output current range of 200-260A to provide a stable welding current. The wire feeding system is used to feed filler wire with an adjustable wire feeding speed range of 2.0-2.2m / min. The six-axis robotic arm is used to precisely control the position and attitude of the welding torch. The shielding gas system outputs high-purity argon gas to prevent oxidation of the molten pool.

[0045] The magnetic control system 2 includes an alternating magnetic control power supply, a magnetic control coil 201, and magnetic poles 202. The magnetic control power supply is used to input adjustable current and frequency alternating current into the magnetic control coil 201 to generate an alternating magnetic field. The magnetic control coil 201 is made of 1.2mm diameter high-temperature resistant enameled wire wound with 500 turns, and silicon steel sheets are embedded inside the magnetic control coil 201 to enhance the magnetic field focusing effect and reduce hysteresis loss. The magnetic poles 202 are symmetrically arranged on both sides of the welding torch to guide the alternating magnetic field to the arc and molten pool area.

[0046] The detection system includes a monitoring unit and a current measuring device. The monitoring unit comprises a high-speed camera system positioned above the welding area and an arc pressure sensor mounted on the welding torch, used for real-time monitoring of arc behavior and molten pool flow. The current measuring device is a Hall effect current sensor, used to acquire current signals in the welding circuit in real time and transmit the data to the control system. The high-speed camera system has a frame rate ≥1000fps to clearly capture the molten pool morphology and arc oscillation trajectory; the arc pressure sensor has a measurement accuracy of ±10Pa, used to acquire arc pressure data in real time. Together, they achieve accurate monitoring of arc behavior and molten pool flow.

[0047] Working Principle: Example 1 constructs a complete asymmetric magnetic field horizontal welding hardware platform. During welding, the magnetic control system 2, based on instructions from the central controller, outputs an asymmetric square wave current to the magnetic control coil 201, generating an alternating magnetic field that is stronger at the top and weaker at the bottom. This magnetic field is precisely applied to the arc zone through the magnetic poles 202. This asymmetric magnetic field drives the arc to oscillate asymmetrically within the narrow gap groove, with the magnetic field strength being 5mT during the upward oscillation and 2mT during the downward oscillation. This significantly increases the residence time and heat input of the arc in the upper sidewall region, thereby actively suppressing the downward flow of the molten pool caused by gravity. Simultaneously, the monitoring unit collects real-time data on molten pool flow and arc pressure, providing a basis for real-time monitoring and feedback for process stability and weld formation quality.

[0048] Example 2:

[0049] This embodiment provides a narrow-gap horizontal welding process based on an asymmetric alternating magnetic field, including the following steps:

[0050] S1: During the welding process, an alternating magnetic field is applied to the welding arc area, and the magnetic field is generated by the magnetic control system 2;

[0051] S2: By adjusting the waveform and amplitude of the current input to the magnetic control coil 201, the ratio of the magnetic field strength during the upward swing phase of the arc to the magnetic field strength during the downward swing phase is ≥1.5.

[0052] S3: The asymmetrical alternating magnetic field is used to drive the electric arc to oscillate asymmetrically within the narrow gap groove, so that the oscillation amplitude of the electric arc in the upper side wall region of the groove is 1-2mm larger than that in the lower side wall region, in order to counteract the downward flow of the molten pool caused by gravity and optimize the weld formation.

[0053] In one embodiment of the present invention, in step S2, the magnetic field strength during the upward swing phase is 3-5 mT, and the magnetic field strength during the downward swing phase is 1-2 mT.

[0054] When the base material is a low thermal conductivity material such as titanium alloy or aluminum alloy, a magnetic field strength combination of 3-4 mT / 1-1.5 mT is preferred; when the base material is a high thermal conductivity material such as stainless steel, a magnetic field strength combination of 4-5 mT / 1.5-2 mT is preferred.

[0055] In one embodiment of the present invention, the low-frequency range of the asymmetric alternating magnetic field is 0.5 Hz to 1 Hz;

[0056] The frequency of the asymmetric alternating magnetic field can be adjusted from 0.5Hz to 10Hz. When welding conventional thick plates and the base material is a low thermal conductivity material such as titanium alloy or aluminum alloy, 1Hz is selected; when welding thicker plates or when the base material is a high thermal conductivity material such as stainless steel, 0.5Hz is selected.

[0057] In one embodiment of the present invention, the current waveform in step S2 adopts an asymmetric square wave with an upper two-lower or upper three-lower duration, wherein the duration of the positive half-cycle of the square wave corresponds to the upward swinging phase of the arc, and the duration of the negative half-cycle corresponds to the downward swinging phase of the arc. Furthermore, the pulse width duty cycle of the asymmetric square wave is adjustable within the range of 2:1 to 4:1.

[0058] In one embodiment of the present invention, the magnetic control system 2 supports one-key switching of magnetic field waveforms, which is achieved through the duty cycle adjustment module of the magnetic control power supply. It can be set by a knob or digital interface, and can quickly switch between upper two-lower and upper three-lower square waves according to the bevel size and the characteristics of the base material, adapting to the welding requirements of different thicknesses (20-25mm) and materials (titanium alloy, stainless steel).

[0059] In one embodiment of the present invention, in step S3, the arc oscillation trajectory is precisely constrained by the guiding effect of the magnetic pole 202. The magnetic pole 202 is made of low carbon steel and its surface is insulated to avoid electrical coupling interference with the arc. The magnetic pole 202 is 15mm away from the center line of the bevel and 10mm away from the bevel surface to ensure that the magnetic field is accurately applied to the arc and molten pool area.

[0060] In one embodiment of the present invention, high-purity argon gas is used for protection during the welding process, and the protective gas nozzle is close to the top of the bevel to prevent the molten pool from contacting air and causing oxidation defects.

[0061] In one embodiment of the present invention, the bevel adopts a U-shaped structure, and the surface of the bevel is mechanically polished to remove oxide scale and oil stains.

[0062] Working Principle: Example 2 proposes an arc oscillation control process based on an asymmetric alternating magnetic field. The core lies in constructing a magnetic field environment with a strong upper layer and a weak lower layer, along with an asymmetric current waveform, through the magnetic control system 2, to achieve precise control of the arc oscillation trajectory and heat input distribution. By utilizing the magnetic field strength gradient (5mT / 2mT) to generate a stable upward magnetic levitation force on the upper side of the molten pool, the gravitational force of the molten pool is directly counteracted, forming a basic force field balance between gravity and magnetic levitation. Combined with the duty cycle design of the asymmetric square wave, the residence time of the arc on the upper bevel wall is extended, resulting in a significant increase in heat input on the upper side compared to the lower side, effectively reducing the temperature gradient between the upper and lower sides and improving the wettability of the molten pool. Meanwhile, the low-frequency magnetic field (0.5Hz to 1Hz) avoids the dispersion of heat input caused by high-frequency oscillation, ensuring that the arc energy is concentrated on the bevel sidewall, promoting the spread of molten pool metal on the sidewall, and suppressing the downward flow of molten pool from both force field and thermal field dimensions. This solves the core defects in horizontal welding such as weld asymmetry and sidewall incomplete fusion, and significantly improves the forming quality and process stability of narrow gap horizontal welding.

[0063] Example 3:

[0064] In conjunction with Embodiments 1 and 2 above, the present invention also provides a method for controlling the molten pool to implement the above-mentioned narrow gap horizontal welding process, comprising the following steps:

[0065] M1: Set the magnetic field parameters so that the magnetic field strength during the upward swing phase is greater than that during the downward swing phase, forming a magnetic field strength gradient distribution that is high on the upper side and low on the lower side.

[0066] M2: Through the gradient distribution of magnetic field strength, an upward magnetic levitation force greater than that on the lower side is generated on the upper side of the molten pool to counteract the downward flow of gravity on the molten pool.

[0067] M3: Controls the magnetic field frequency to be in the low-frequency range and works in conjunction with the magnetic field strength to optimize the temperature gradient between the molten pool and the bevel sidewall, reducing defects in poor fusion of the lower sidewall.

[0068] M4: The arc is driven to oscillate asymmetrically by an asymmetric alternating magnetic field, so that the residence time and heat input of the arc in the upper side wall region of the bevel are greater than those in the lower side wall region, thereby increasing the temperature of the upper side wall and reducing the temperature gradient between the upper and lower sides of the weld.

[0069] M5: By controlling the heat input and arc oscillation in step M4, the upper sidewall is subjected to greater arc pressure and fluid shear force, pushing the molten pool metal upwards and forming an auxiliary force field opposite to the direction of gravity. This auxiliary force, combined with the magnetic levitation force of M2, can achieve comprehensive suppression of the molten pool's downward flow. When the magnetic levitation force of M2 can stabilize the molten pool, the auxiliary force can be finely adjusted by regulating the arc oscillation amplitude. When the molten pool collapse exceeds the standard, the magnetic levitation force of M2 is increased first, and then the auxiliary force is enhanced by extending the arc's dwell time on the upper side.

[0070] M6: By increasing the heat input to the upper sidewall, the solid-liquid interfacial tension in this area is reduced, which promotes the wetting and spreading of the molten pool metal on the upper sidewall of the bevel and improves the weld formation.

[0071] Example 4:

[0072] As attached Figure 3-4 As shown, this process uses narrow-gap horizontal welding of 20mm thick TA2 titanium alloy as a typical application scenario, realizing standardized operation of the entire process from groove preparation to welding completion, as detailed below:

[0073] I. Preparatory Stage

[0074] 1) Workpiece and bevel preparation

[0075] Workpiece specifications: Select TA2 titanium alloy plate with a thickness of 500mm×300mm×20mm, adopt the butt joint form, and the bevel is machined into a U-shaped structure with an upper width of 10mm, a lower width of 8mm, a depth of 20mm, a bevel angle of 60°, and a side wall verticality error of ≤0.1mm to ensure that the influence of bevel geometric accuracy on the welding formation is minimized.

[0076] Bevel pretreatment: First, use a 120-grit grinding wheel to mechanically grind the bevel surface and the area within 20mm on both sides to remove oxide scale, rust and processing burrs. After grinding, the surface roughness of the bevel Ra≤1.6μm; then wipe it repeatedly 3 times with gauze soaked in anhydrous ethanol to remove residual oil and impurities. After wiping, let it air dry naturally. Start welding within 30 minutes to avoid secondary oxidation of the bevel.

[0077] 2) Preparation of welding materials and tools

[0078] Filler wire: ERTi-2 titanium alloy welding wire with a diameter of 1.2mm is selected. The wire surface is free of oxide scale, cracks and oil stains. Before use, it is dried at 200℃ for 2 hours to remove surface adsorbed moisture and prevent porosity defects during welding.

[0079] Protective gas: High-purity argon gas with a purity of ≥99.99% is used, and the cylinder pressure is ≥10MPa. Before use, impurities in the bottom of the cylinder should be released for 30 seconds to ensure gas purity. Equipped with a flow meter with an accuracy of ±0.1L / min to ensure stable protective gas flow.

[0080] Auxiliary tools: A graphite pad is used to support the bottom of the workpiece. The surface of the pad is machined with grooves that match the bevel to prevent the loss of molten metal. The two sides of the workpiece are fixed with pneumatic clamping devices to prevent the workpiece from deforming or shifting during welding.

[0081] 3) Equipment debugging and parameter preset

[0082] System assembly: The magnetron coil 201 is fixed to the front end of the welding torch with a clamp, and the magnetic poles 202 are symmetrically arranged on both sides of the welding torch, with a distance of 15mm from the center line of the bevel and a distance of 10mm from the surface of the bevel, to ensure that the magnetic field accurately covers the arc and molten pool area; the six-axis robotic arm is rigidly connected to the welding platform, with a levelness error of ≤0.1mm / m, to ensure the accuracy of the welding torch movement.

[0083] Electrical calibration: The magnetically controlled power supply outputs an asymmetrical square wave current with "three upper and one lower" configuration. The coil current is calibrated using a Hall current sensor to ensure that the upper magnetic field strength reaches 5mT and the lower magnetic field strength reaches 2mT, with a magnetic field strength error of ≤±0.1mT. The high-speed camera system focuses on the center of the molten pool, and the exposure parameters are adjusted until the image is clear. The arc pressure sensor is zero-point calibrated to ensure accurate data acquisition.

[0084] Parameter settings: welding current 230A, welding speed 90mm / min, wire feed speed 2.0m / min; shielding gas flow rate 20L / min, gas inlet time 3s, gas shut-off time 5s; magnetic field frequency 1Hz, square wave positive half-cycle duration 0.6s, negative half-cycle duration 0.2s.

[0085] II. Welding Execution Phase

[0086] 1) Magnetic field application and arc ignition

[0087] The magnetic control system 2 is started. The magnetic control power supply outputs an asymmetrical square wave current according to the preset parameters. The magnetic control coil 201 generates an alternating magnetic field, which is focused by the magnetic pole 202 and acts on the arc area. A miniature probe-type gaussmeter is used to measure the magnetic field strength. Five measurement points are evenly distributed from top to bottom along the center line of the bevel (spaced 4mm apart) to avoid obstruction by the side wall of the bevel and to ensure the feasibility of the measurement operation. The measured magnetic field strength distribution meets the design requirements of 5mT / 2mT.

[0088] The six-axis robotic arm moves the welding torch to the welding start position, with the welding torch axis at a 3° angle to the bevel centerline and the nozzle 5mm away from the bevel surface. The welding power is turned on, and the arc is ignited using a high-frequency arc ignition method with an arc ignition current of 250A and an arc ignition time of 0.5s. After successful arc ignition, the current is automatically switched to the set welding current of 230A.

[0089] 2) Arc oscillation and synchronous wire feeding

[0090] Once the arc stabilizes, the wire feeding system starts synchronously, feeding the welding wire at a constant speed of 2.0 m / min. The wire extension length is kept at 4 mm to avoid arc instability caused by excessive extension or short circuit defects caused by excessively short extension.

[0091] Driven by an asymmetric magnetic field, the electric arc oscillates periodically with a larger amplitude at the top and a smaller amplitude at the bottom: when oscillating upwards, the magnetic field strength is 5mT, the oscillation amplitude is 3mm, and it stays on the upper sidewall of the bevel for 0.6s to ensure sufficient heat input to the upper sidewall; when oscillating downwards, the magnetic field strength is 2mT, the oscillation amplitude is 1mm, and it stays on the lower sidewall of the bevel for 0.2s to avoid excessive metal accumulation on the lower sidewall; the oscillation period is 1s, and the cycle continues until the welding is completed.

[0092] 3) Process monitoring and dynamic adjustment

[0093] Monitoring data acquisition: The high-speed camera system captures the molten pool morphology in real time at a frame rate of 1000fps, and extracts the molten pool collapse amount and the contact angle of the upper and lower sidewalls through image recognition algorithms; the arc pressure sensor collects arc pressure data in real time, with a sampling frequency of 1kHz and a data range controlled within 500-600Pa; the Hall current sensor continuously monitors the current of the magnetron coil to ensure the stability of the magnetic field parameters.

[0094] Dynamic adjustment logic: If the molten pool collapse is greater than 0.2mm, the central controller instructs the magnetic power supply to increase the upper magnetic field strength by 0.3mT and simultaneously increase the wire feeding speed by 0.1m / min to suppress the molten pool from flowing downwards; if the upper contact angle is greater than or equal to 90°, the positive half-cycle time of the square wave is extended by 0.1s to increase the upper heat input and improve wettability; if the arc pressure fluctuation exceeds ±50Pa, the welding power supply is fine-tuned with a current of ±5A to maintain stable arc combustion.

[0095] III. Welding Termination and Post-processing Stage

[0096] When the welding reaches the end position, the welding current is reduced from 50A / s to 100A, maintained for 3s, and then cut off to avoid the formation of arc crater defects; the wire feeding system stops feeding wire after a delay of 2s to ensure that the arc crater is fully filled; the shielding gas continues to be introduced for 5s to prevent the high-temperature molten pool from oxidizing due to contact with air.

[0097] After welding was completed, a special test was conducted on the weld formation quality and performance. The results are as follows:

[0098] Weld contact angle detection: The weld cross-section was observed using an optical microscope, and the contact angle between the weld and the bevel sidewall was measured using image analysis software. The upper contact angle was 70°-80°, and the lower contact angle was 65°-75°, both less than 90°, which meets the core judgment criteria for good wettability, proving that the molten pool metal has excellent wetting and spreading effect on the bevel sidewall.

[0099] Detection of weld pool collapse: The vertical deviation between the weld surface and the center line of the groove was measured by a laser rangefinder. The measured collapse of the weld pool was 0.1-0.2mm, which is much lower than the 1.2-1.5mm of the traditional symmetrical magnetic field welding process, achieving the control target of "collapse close to zero".

[0100] Defect detection: Ultrasonic testing (UT) was used to inspect the inside of the weld. No defects such as incomplete fusion, incomplete penetration, or porosity were found, and the weld pass rate reached 100%. Macroscopic observation of the weld surface showed that the weld was full and uniform, with a symmetry error of ≤0.3mm on the upper and lower sides, and no undercut or incomplete fusion marks on the sidewall.

[0101] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A narrow-gap horizontal welding process based on an asymmetric alternating magnetic field, characterized in that, Includes the following steps: S1: During the welding process, an alternating magnetic field is applied to the welding arc area, and the magnetic field is generated by the magnetic control system (2); S2: By adjusting the waveform and amplitude of the current input to the magnetic control coil (201), the ratio of the magnetic field strength during the upward swing phase of the arc to the magnetic field strength during the downward swing phase is ≥1.5; S3: The asymmetrical alternating magnetic field is used to drive the electric arc to oscillate asymmetrically within the narrow gap groove, so that the oscillation amplitude of the electric arc in the upper side wall region of the groove is 1-2 mm larger than that in the lower side wall region, in order to counteract the downward flow of the molten pool caused by gravity and optimize the weld formation.

2. The narrow-gap horizontal welding process based on an asymmetric alternating magnetic field according to claim 1, characterized in that, In step S2, the magnetic field strength during the upward swing phase is 3-5 mT, and the magnetic field strength during the downward swing phase is 1-2 mT. When the base material is a low thermal conductivity material such as titanium alloy or aluminum alloy, a magnetic field strength combination of 3-4 mT / 1-1.5 mT is preferred; when the base material is a high thermal conductivity material such as stainless steel, a magnetic field strength combination of 4-5 mT / 1.5-2 mT is preferred.

3. The narrow-gap horizontal welding process based on an asymmetric alternating magnetic field according to claim 1, characterized in that, The low-frequency range of the asymmetric alternating magnetic field is 0.5 Hz to 1 Hz; The frequency of the asymmetric alternating magnetic field can be adjusted within the range of 0.5Hz to 10Hz. When it is suitable for welding conventional thick plates and the base material is a low thermal conductivity material such as titanium alloy or aluminum alloy, 1Hz is selected; when it is suitable for welding thicker plates or the base material is a high thermal conductivity material such as stainless steel, 0.5Hz is selected.

4. The narrow-gap horizontal welding process based on an asymmetric alternating magnetic field according to claim 1, characterized in that, The current waveform in step S2 adopts an asymmetric square wave with two cycles up and one cycle down or three cycles up and one cycle down. The duration of the positive half-cycle of the square wave corresponds to the upward swinging phase of the arc, and the duration of the negative half-cycle corresponds to the downward swinging phase of the arc. The pulse width duty cycle of the asymmetric square wave is adjustable in the range of 2:1-4:

1.

5. The narrow-gap horizontal welding process based on an asymmetric alternating magnetic field according to claim 1, characterized in that, The magnetic control system (2) includes an alternating magnetic control power supply, a magnetic control coil (201) and a magnetic pole (202). The magnetic control power supply is used to input an adjustable current and frequency alternating current into the magnetic control coil (201) to generate an alternating magnetic field. The magnetic pole (202) is used to guide the magnetic field to the arc and molten pool area.

6. The narrow-gap horizontal welding process based on an asymmetric alternating magnetic field according to claim 5, characterized in that, The magnetron coil (201) is wound with 500 turns of high-temperature resistant enameled wire with a diameter of 1.2 mm, and silicon steel sheets are embedded inside the magnetron coil (201) to enhance the magnetic field focusing effect and reduce hysteresis loss.

7. The narrow-gap horizontal welding process based on an asymmetric alternating magnetic field according to claim 1, characterized in that, It also includes a monitoring unit, which includes a high-speed camera system positioned above the welding area and an arc pressure sensor mounted on the welding torch; Among them, the high-speed camera system has a frame rate of ≥1000fps, which is used to clearly capture the shape of the molten pool and the arc oscillation trajectory; the arc pressure sensor has a measurement accuracy of ±10Pa, which is used to collect arc pressure data in real time. The two work together to achieve accurate monitoring of arc behavior and molten pool flow.

8. A method for controlling the molten pool in implementing the narrow-gap horizontal welding process according to any one of claims 1-7, characterized in that, Includes the following steps: M1: Set the magnetic field parameters so that the magnetic field strength during the upward swing phase is greater than that during the downward swing phase, forming a magnetic field strength gradient distribution that is high on the upper side and low on the lower side, laying the foundation for subsequent force field and thermal field control. M2: Through the magnetic field strength gradient distribution, an upward magnetic levitation force greater than that on the lower side is generated on the upper side of the molten pool to counteract the downward flow of gravity on the molten pool. M3: Controls the magnetic field frequency to be in the low-frequency range, and works in conjunction with the magnetic field strength to optimize the temperature gradient between the molten pool and the bevel sidewall, providing a temperature environment support for subsequent arc oscillation and heat input distribution. M4: The asymmetric alternating magnetic field is used to drive the electric arc to oscillate asymmetrically, so that the residence time and heat input of the electric arc in the upper side wall region of the bevel are greater than those in the lower side wall region, thereby increasing the temperature of the upper side wall and reducing the temperature gradient between the upper and lower sides of the weld. M5: By controlling the heat input and arc oscillation in step M4, the upper sidewall is subjected to greater arc pressure and fluid shear force, pushing the molten pool metal upwards and forming an auxiliary force field opposite to the direction of gravity. This auxiliary force, combined with the magnetic levitation force of M2, can achieve comprehensive suppression of the molten pool's downward flow. When the magnetic levitation force of M2 can stabilize the molten pool, the auxiliary force can be finely adjusted by regulating the arc oscillation amplitude. When the molten pool collapse exceeds the standard, the magnetic levitation force of M2 is increased first, and then the auxiliary force is enhanced by extending the arc's dwell time on the upper side. M6: By increasing the heat input to the upper sidewall through step M4, the solid-liquid interfacial tension in this area is reduced, which promotes the wetting and spreading of the molten pool metal on the upper sidewall of the bevel, and ultimately improves the weld formation.

Images