Device and process for reducing welding hot crack sensitivity through external magnetic field

Abstract

The invention relates to a device and process for reducing welding hot crack sensitivity by applying a magnetic field, comprising a welding gun, magnetic generating devices fixed on two sides of the welding gun, capable of rotating freely on a horizontal plane and then fixed through buckles, coils wound on the surfaces of the magnetic generating devices, and perpendicular to the central section of a welding seam. The action position of the magnetic generation device is located between the center of a welding pool of a to-be-welded workpiece and the paste area, and the excitation power source controls the first peak current, the second peak current and the current frequency. The device is simple and reliable in structure, small in limitation of welding space and high in efficiency, parameters of an external magnetic field are convenient to adjust, and automation is easy to achieve; the arc is stable; a welding seam is naturally formed and has a good appearance; the change of weld metal structure components cannot be caused; when the welding test plate is pushed, movement of the welding gun is achieved at the same time, programmed control over all assemblies can be achieved, and precision is high; the propelling process can be monitored in real time, control precision is high, and operation is easy and convenient.

Description

Technical Field

[0001] The present invention relates to a device and process for reducing the sensitivity to welding hot cracks, and particularly to a device and process for reducing the sensitivity to welding hot cracks by applying an external magnetic field. Background Art

[0002] Hot cracks are one of the most harmful defects in the welding manufacturing process, seriously affecting the reliability and safety of welded structures. These cracks usually occur in the mushy zone at the rear of the molten weld pool (solid-liquid two-phase zones are prone to form solidification cracks), directly restricting the production and application of welded components. Many materials have problems with hot cracks, such as stainless steel, nickel-based alloys, etc. At present, the means to improve the sensitivity to hot cracks through auxiliary means are relatively limited, and applying an external magnetic field is a method that is relatively easy to implement and has application and promotion prospects. Some studies have shown that applying a magnetic field during welding can greatly improve the quality and heat transfer characteristics of the molten metal pool. These technologies help to refine the grain structure, reduce compositional segregation, promote the homogenization and diffusion of the second phase, and reduce the sensitivity to welding hot cracks. Applying an external magnetic field can improve welding productivity, improve the weld formation, enhance the ductility and toughness of the welded metal, while reducing residual stress and welding defects. Arc deflection under an alternating magnetic field helps to refine the weld structure and minimize the formation of coarse columnar crystals. Enhancing the solidification process of alloys by applying an external magnetic field has the advantages of non-contact operation, less pollution, and low cost. In addition, it is closely related to the factors of hot cracks. Therefore, using an external magnetic field to reduce welding hot cracks has great potential. Summary of the Invention

[0003] Object of the Invention: The object of the present invention is to propose a device and process for reducing the sensitivity to welding hot cracks by applying an external magnetic field to simply, efficiently, and effectively control welding hot cracks.

[0004] Technical Solution: The present invention includes a welding torch, on both sides of which magnetic generating devices are fixed. The magnetic generating devices can rotate arbitrarily in the horizontal plane. Coils are wound around the surfaces of the magnetic generating devices. The magnetic generating devices are perpendicular to the central cross-section of the weld, and the acting position of the magnetic generating devices is between the center of the welding molten pool and the mushy zone of the workpiece to be welded.

[0005] The tip of the welding torch electrode is about 2 mm above the workpiece to be welded, and the magnetic head is about 3 mm above the workpiece to be welded.

[0006] The coil is connected to an exciting power supply.

[0007] The exciting power supply controls the first peak current, the second peak current, and the current frequency to form an alternating magnetic field covering the weld molten pool. By changing the magnitude of the exciting current and the frequency, the magnetic field intensity is changed, and the magnetic field phase can be controlled separately.

[0008] The magnetic generating device is fixed by a buckle.

[0009] Adjust the parameters of the appropriate excitation power supply to make the magnetic field process conform to the predetermined welding scenario, so that the weld formation is good and the sensitivity to hot cracks is low; viewed perpendicular to the welding progress direction, the magnetic field polarity is set to N on the left and S on the right, the excitation frequency is 10 Hz, the excitation current is 10 A, and the magnetic field strength is about 20 mT. The weld formation is beautiful and the sensitivity to welding hot cracks is reduced. The order of the sensitivity to hot cracks under different polarities from high to low is: S on the left and N on the right > S on the left and S on the right > N on the left and N on the right > no magnetic field > N on the left and S on the right.

[0010] The moving speed of the lower test plate in the welded test plate combination is adjusted in two stages: after moving a certain distance at the initial speed V1, it is reduced to the preset speed V, and V is much lower than the initial speed V1. The preset speed V is the moving speed of the lower test plate. After welding is completed, the weld length LW and the hot crack length LC in the area corresponding to the second-stage speed on the surface of the specimen are statistically counted, and the crack rate LC / LW is calculated. If the cracking generated at the first-stage speed propagates at the second-stage speed, the crack length in the area corresponding to the second-stage speed is the length of the hot crack LC; when LC / LW is equal to 0, that is, the crack does not expand; when LC / LW is equal to 1, the weld is completely cracked, and the extended length of the crack at this time is statistically counted as an index of the sensitivity to welding hot cracks.

[0011] By comparing the relationship between the moving speed V (second-stage speed) of the lower plate and the magnetic field parameters and the characteristic parameters of hot cracks; making the speed range of the lower test plate corresponding to the situation where the crack in the weld just does not expand to just completely crack, which is the speed range for evaluating the crack sensitivity basis, that is, the quantitative evaluation of the sensitivity to hot cracks is completed. When the magnetic field polarity is set to N on the left and S on the right, at an excitation frequency of 10 Hz, an excitation current of 10 A, and a magnetic field strength of about 20 mT, the speed range of the lower test plate corresponding to the situation where the stainless steel weld just does not expand to just completely crack is 0.32 - 0.55 mm / s; without applying a magnetic field, the speed range of the lower test plate corresponding to the situation where the stainless steel weld just does not expand to just completely crack is 0.18 - 0.25 mm / s. This means that for the stainless steel weld at an excitation frequency of 10 Hz, an excitation current of 10 A, and a magnetic field strength of about 20 mT, the ability to resist the expansion of hot cracks is strong and the sensitivity to hot cracks is reduced.

[0012] According to the speed range V of the lower test plate corresponding to the weld under different magnetic field conditions (magnetic field polarity, excitation frequency, excitation current, magnetic field strength), obtain the relationship diagram of the magnetic field strength and the moving speed of the lower test plate (sensitivity to hot cracks), and compare the numerical height of the speed range V of the lower test plate corresponding to different magnetic field conditions. The higher the value, the lower the sensitivity to hot cracks, thus realizing the function of the applied magnetic field to reduce the sensitivity to welding hot cracks.

[0013] Beneficial effects: The present invention has the following advantages:

[0014] (1) The invention has a simple and reliable structure, uses a wide range of materials, has a wide range of applicable scenarios, is less restricted by the welding space, has high efficiency, is convenient to adjust the parameters of the applied magnetic field, and is easy to realize automation; the arc is stable; the weld belongs to natural forming and has a good appearance; it belongs to in-situ control during welding and has strong pertinence; it will not cause changes in the composition of the weld metal structure.

[0015] (2) When the welding test plate is pushed, the movement of the welding torch is realized simultaneously, and the programmed control of each component can be achieved with high precision; the propulsion process, the displacement, speed, and control precision of the welding torch movement can be monitored in real time, and the operation is simple and convenient.

[0016] (3) A method for evaluating the effect of reducing the sensitivity of welding hot cracks by an applied magnetic field is proposed, so as to obtain the appropriate magnetic field polarity and magnetic field parameters, realize the refinement of the weld metal grains, change the crystallographic directionality of the grains, make the structure tend to be more uniform, and effectively reduce the sensitivity of welding hot cracks from both metallurgical crystallization and mechanics aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram for verifying the overall structure of the present invention;

[0018] Figure 2 It is a waveform diagram of the exciting current output by the magnetic field power supply of the present invention;

[0019] Figure 3 It is a relationship diagram between the moving speed of the test plate and the crack rate without magnetic field and with magnetic field polarity of the present invention;

[0020] Figure 4 It is a relationship diagram between different magnetic field polarities and the moving speed of the test plate of the present invention;

[0021] Figure 5 It is a relationship diagram between the moving speed of the test plate with different magnetic field parameters and the crack rate of the present invention;

[0022] Figure 6 It is a relationship diagram between the magnetic field strength and the moving speed of the test plate of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be further described below with reference to the accompanying drawings.

[0024] Example 1

[0025] As Figure 1As shown in the figure, the device for reducing the sensitivity of welding hot cracks by applying an external magnetic field in this embodiment includes a workbench 11, which is connected to a controller 10. On the top of the workbench 11, there is an upper test plate 12. A lower test plate 13 is slidably connected to the top of the upper test plate 12. The size of the upper test plate 12 is 126mm×25mm×3mm, and the lower test plate 13 is a stainless steel thin plate with a size of 75mm×75mm×3mm. Cracks are generated by pushing the lower test plate 13 to move. Above the lower test plate 13, there is a welding torch 3. The welding torch can be moved and fixed through a guide rail and a welding torch clamping device, thereby adjusting the relative position between the welding torch 3 and the upper test plate 12. The welding torch 3 is fixed by a welding torch clamp. The welding torch clamp in this embodiment is a straight handle welding torch clamp, which can include a connecting part for connecting to the workbench 11 and a clamping part for clamping the welding torch. The connecting part includes a support directly installed on the workbench 11. There is a through hole on the support. There are two rows of horizontally arranged long grooves on the workbench 11. The size and distance of the long grooves correspond to the position of the through hole on the support. The straight handle welding torch clamp is fixed to the workbench 11 through fixing bolts, and the straight handle welding torch clamp can slide on the horizontal guide rod of the workbench 11. The clamping part is used to directly clamp the welding torch and is locked by fixing bolts. The straight handle welding torch can slide up and down along its own axis. After adjusting the height of the welding torch to the required position, it is fixed with a fastening bolt.

[0026] The workbench 11 includes a frame structure, a counterweight (not shown), etc., which satisfy the positional relationship between the welding torch 3, the magnetic generating device 1, and the upper test plate 12 and the lower test plate 13, and there is no interference phenomenon. Preferably, the height of the workbench 11 is designed to be adjustable. The height of the workbench 11 is adjusted through the controller 10, and it can play a role in maintaining horizontal fixation after reaching the specified height. This method has a simple structure and can achieve the effect of horizontal fixation. There are a chute and a through hole for a guide plate on the workbench 11. The chute provides a certain moving distance for the upper test plate 12 and the lower test plate 13 to ensure that the test plates can move stably. Through holes are drilled on the workbench 11, and the guide plate is fixed to the workbench 11 through bolts and nuts to achieve the purpose of increasing the stability of the workbench. When the distance between the welding torch 3 and the upper test plate 12 is 2mm, stable welding can be achieved without affecting the surface quality of the weld.

[0027] Magnetic generating devices 1 are fixed on both sides of the welding torch 3. The magnetic generating devices 1 are fixed on both sides of the welding torch 3 through clamps 14, and the magnetic generating devices can rotate arbitrarily in the horizontal plane for outputting a magnetic field. The two magnetic generating devices 1 are symmetrically located on both sides of the welding direction. During the welding process, the welding torch 3 and the magnetic generating devices 1 move synchronously and maintain a specific distance until all welding is completed. A coil 2 is wound on the surface of the magnetic generating device 1. The coil 2 is a copper coil with relatively good electrical conductivity. The coil 2 is connected to an excitation power supply 6. The welding torch 3 is connected to a welding power supply 7. The welding power supply 7 is connected to a circulating water cooling device 8 and an argon gas cylinder 9. The welding torch 3 is cooled by the circulating water cooling device 8 in a circulating manner, and the argon gas cylinder 9 provides argon gas to ensure stable welding.

[0028] During the welding process, the magnetic generating device 1 is perpendicular to the central section of the weld seam and moves synchronously with the welding heat source. The acting position of the magnetic generating device 1 is located between the center of the welding molten pool 4 of the workpiece to be welded and the mushy zone 5, applying a transverse extrusion strain to the weld metal in the mushy zone behind the molten pool, offsetting the inherent cracking tensile strain of the weld seam, thereby eliminating the generation of welding hot cracks. At the same time, it can refine the grains of the weld metal and change the directionality of grain crystallization, making the structure tend to be more uniform, effectively controlling the generation of welding hot cracks from both metallurgical and mechanical aspects.

[0029] During the welding process, the upper test plate 12 is kept stationary, and the lower test plate 13 moves under the push of the servo motor, and the moving direction is perpendicular to the welding direction. During the test, the moving speed is adjusted in two stages. The initial speed V1 (the first-stage speed) is relatively large (such as 0.50 mm / s), and it moves a certain distance to ensure the initiation of weld hot cracks. Then, through the control system, it is reduced to the preset speed V (the second-stage speed), and its value is much lower than the initial speed V1 (such as 0.10 mm / s) to make the hot cracks propagate. At this time, the preset speed (the second-stage speed) is regarded as the moving speed of the lower test plate, denoted as V = 0.10 mm / s. Due to the movement of the lower test plate, hot cracks will be generated in the weld seam, and the propagation length of the cracks at this time is statistically analyzed as an index of crack sensitivity. By adjusting parameters such as the excitation frequency and excitation current, the solidification cracking behavior changes accordingly, thus facilitating the study of the relationship between the external magnetic field process parameters and the hot crack sensitivity. Before welding starts, the test plates are cleaned with anhydrous ethanol to mainly remove the oil stains and other surface impurities on the test plate surfaces, avoiding interference with the test and affecting the test results.

[0030] As Figure 1 shown, after welding is completed, under a 10-fold magnifying glass, the weld length LW and the hot crack length LC in the area corresponding to the second-stage speed on the surface of the specimen are statistically analyzed, and LC / LW (crack ratio) is calculated. If the cracking generated at the first-stage speed propagates at the second-stage speed, the crack length in the area corresponding to the second-stage speed is the length of the hot crack LC. When LC / LW is equal to 0, that is, the crack does not expand; when LC / LW is equal to 1, it indicates that the weld has full cracking.

[0031] The excitation power supply 6 controls three parameters, the first peak current (large plug pins 1 and 2), the second peak current (pins 3 and 4), and the current frequency; the dot button below the control panel, press it once to enter the parameter setting, and press it again to enter the display mode; press the rotary button and rotate to set the above three groups of parameters.

[0032] As Figure 2As shown, Pin 1 and Pin 2 are connected to a magnetic head coil (1 in and 2 out), and Pin 3 and Pin 4 are connected to a magnetic head coil (3 out and 4 in). The output current phase difference between these two groups of pins is 180 degrees, and a DC variable-frequency square-wave signal is output. After the magnetic generating device 1 is connected to the excitation power supply 6, by adjusting the connection sequence of Pin 1, Pin 2 and the magnetic head coil, the polarity of the magnetic head can be changed, thereby affecting the magnetic field distribution. After testing, when the magnetic field polarity of the left magnetic head is the N pole and the magnetic field polarity of the right magnetic head is the S pole, that is, in the direction of the magnetic field, the weld width can be shrunk to a certain extent, and the weld depth can be increased to a certain extent, thereby achieving the effect of refining the weld.

[0033] Finally, a relationship diagram between the moving speed V of the lower plate (the second speed) and the hot crack characteristic parameters is drawn. The moving speed range of the lower test plate corresponding to the situation where the crack in the weld just does not expand to just completely crack is the moving speed range required for evaluating the crack sensitivity, that is, the quantitative evaluation of the hot crack sensitivity is completed.

[0034] As shown in Tables 1 and 2, it is a table of different magnetic field polarities, magnetic field parameters and welding process parameters of the device for reducing the sensitivity of welding hot cracks by an external magnetic field. Control all welding process parameters to be the same, change the magnetic field polarity and magnetic field parameters for testing, and quantitatively evaluate the reduction of hot crack sensitivity by an external magnetic field.

[0035] Table 1 Table of different magnetic field polarities and process parameters

[0036]

[0037] Table 2 Table of magnetic field parameters and process parameters

[0038]

[0039]

[0040] As Figure 3 and Figure 4 shown, set the same excitation current and excitation frequency, change the magnetic field polarity by the excitation power supply wiring sequence, and obtain that the optimal magnetic field polarity is N on the left and S on the right, that is, in the direction of the magnetic field. The worst magnetic field polarity is S on the left and N on the right, that is, against the magnetic field direction. The order of the hot crack sensitivity under different polarities from high to low is: S on the left and N on the right > S on the left and S on the right > N on the left and N on the right > no magnetic field > N on the left and S on the right.

[0041] According to adjusting the excitation frequency and excitation current, thereby resulting in the moving speed V range of the lower test plate corresponding to the weld of stainless steel under different magnetic field intensities, draw a relationship diagram between the moving speed of the lower test plate and the crack rate, as Figure 5As shown, when the excitation frequency is 10 Hz, the excitation current is 10 A, and the magnetic field strength is about 20 mT, the velocity range of the moving speed V of the stainless steel lower test plate is significantly higher numerically than that of stainless steel under other magnetic field conditions. This indicates that when the excitation frequency is 10 Hz, the excitation current is 10 A, and the magnetic field strength is about 20 mT, the ability of stainless steel to inhibit crack propagation is stronger than that under other magnetic field conditions.

[0042] As Figure 6 shown, a relationship diagram between the magnetic field strength and the moving speed of the lower test plate is obtained, thus indirectly reflecting the relationship between the magnetic field strength and the hot crack sensitivity. As can be seen from the figure, according to the crack tests of stainless steel with different magnetic field parameters, when the excitation frequency is 10 Hz, the excitation current is 10 A, and the magnetic field strength is about 20 mT, the moving speed range of the lower test plate corresponding to the stainless steel weld just not expanding to just completely cracking is 0.32 - 0.55 mm / s; without applying a magnetic field, the moving speed range of the lower test plate corresponding to the stainless steel weld just not expanding to just completely cracking is 0.18 - 0.25 mm / s. Under other magnetic field applications, the moving speed range of the lower test plate corresponding to the stainless steel weld just not expanding to just completely cracking is less than that under the non - magnetic field condition, meaning that when the excitation frequency is 10 Hz, the excitation current is 10 A, and the magnetic field strength is about 20 mT, the stainless steel weld has the strongest ability to resist hot crack propagation and the lowest hot crack sensitivity, thus realizing the function of adjusting the external magnetic field parameters to reduce the hot crack sensitivity of welding.

[0043] Example 2

[0044] The process of reducing the hot crack sensitivity of welding by applying an external magnetic field in this example includes the following steps:

[0045] After welding is completed, count the weld length LW and the hot crack length LC in the area corresponding to the second - stage speed on the surface of the specimen, and calculate the crack rate LC / LW.

[0046] If the cracking generated at the first - stage speed propagates at the second - stage speed, the crack length in the area corresponding to the second - stage speed is the length of the hot crack LC; when LC / LW is equal to 0, that is, the crack does not expand; when LC / LW is equal to 1, the weld is completely cracked.

[0047] Draw a relationship diagram between the moving speed V (second - stage speed) of the lower plate and the hot crack characteristic parameters. The moving speed range of the lower test plate corresponding to the weld just not expanding to just completely cracking is the moving speed range required for evaluating the crack sensitivity basis, that is, the quantitative evaluation of the hot crack sensitivity is completed.

[0048] Control the same excitation current and excitation frequency, change the magnetic field polarity through the excitation power supply wiring sequence, obtain the high and low hot crack sensitivities under different magnetic field polarities, and thus select the optimal magnetic field polarity.

[0049] Plot the relationship diagram between the moving speed V of the lower plate (the second-stage speed) and different magnetic field polarities. Thus, indirectly reflect the relationship between different magnetic field polarities and the sensitivity to hot cracks, and complete the quantitative evaluation of the sensitivity to hot cracks.

[0050] Determine the optimal magnetic field polarity (left N and right S in this experiment). By changing the exciting current and exciting frequency, obtain the high and low sensitivities to hot cracks under different exciting currents and exciting frequencies, so as to select the optimal magnetic field parameters (exciting frequency 10 Hz, exciting current 10 A, magnetic field strength about 20 mT in this experiment).

[0051] Plot the relationship diagram between the moving speed V of the lower plate (the second-stage speed) and different magnetic field parameters. Thus, indirectly reflect the relationship between different magnetic field parameters and the sensitivity to hot cracks, and complete the quantitative evaluation of the sensitivity to hot cracks.

[0052] Taking the above test plate with dimensions of 126 mm × 25 mm × 3 mm and the lower test plate with dimensions of 75 mm × 75 mm × 3 mm as stainless steel thin plates as an example, the corresponding welding parameters and the optimal magnetic field parameters are as follows:

[0053] Welding speed v: 1.5 mm / s; The best parameters of the exciting power supply: When the magnetic field polarity of the left magnetic head is the N pole and the magnetic field polarity of the right magnetic head is the S pole, that is, in the direction of the magnetic field, the exciting frequency is 10 Hz, the exciting current is 10 A, and the magnetic field strength is about 20 mT; Welding current: 110 A. Gas flow rate: 18 L / min. Cooling method: Water cooling. Distance between the tungsten electrode of the welding torch and the workpiece to be welded: 2 mm.

[0054] Finally, turn off the gas, open the fixture, take out the workpiece, and turn off the circulating water cooling device after the cooling water has circulated for a period of time. Thus, the entire welding process is completed.

Claims

1. A device for reducing the sensitivity of welding thermal cracks by applying an external magnetic field, characterized in that: The invention comprises a welding gun, wherein magnetic generating devices are fixed on both sides of the welding gun, the magnetic generating devices can rotate arbitrarily in a horizontal plane, a coil is wound on the surface of the magnetic generating device, the magnetic generating device is perpendicular to the central section of the weld, and the action position of the magnetic generating device is located between the center of the welding pool and the mushy area of ​​the workpiece to be welded.

2. The device for reducing welding thermal crack sensitivity by applying an external magnetic field according to claim 1, characterized in that: The tip of the welding gun electrode is located about 2 mm above the workpiece to be welded, and the magnetic head is located about 3 mm above the workpiece to be welded.

3. The device for reducing welding thermal crack sensitivity by applying an external magnetic field according to claim 1, characterized in that: The coil is connected to an excitation power source.

4. The device for reducing welding thermal crack sensitivity by applying an external magnetic field according to claim 3, characterized in that: The excitation power supply controls the first peak current, the second peak current and the current frequency to form an alternating magnetic field covering the weld pool.

5. The device for reducing welding thermal crack sensitivity by applying an external magnetic field according to claim 1, characterized in that: The magnetic generating device is fixed by a buckle.

6. A process for reducing the sensitivity of welding thermal cracks by applying an external magnetic field, characterized in that: Adjust the parameters of the excitation power supply to make the magnetic field process conform to the predetermined welding scenario.

7. The process for reducing welding thermal crack sensitivity by applying an external magnetic field according to claim 6, characterized in that: The order of thermal crack sensitivity under different polarities from high to low is: left S and right N>left S and right S>left N and right N>no magnetic field>left N and right S.

8. The process for reducing welding thermal crack sensitivity by applying an external magnetic field according to claim 6, characterized in that: The moving speed adjustment process of the lower test plate in the welded test plate combination is as follows: the initial speed V1 is reduced to the preset speed V after moving a certain distance, and V is much lower than the initial speed V1. The preset speed V is the moving speed of the lower test plate.

9. The process for reducing welding thermal crack sensitivity by applying an external magnetic field according to claim 8, characterized in that: By comparing the relationship between the lower plate moving speed V and the magnetic field parameters and the characteristic parameters of the thermal crack, the lower test plate moving speed range corresponding to the crack in the weld not extending to completely cracking is used to evaluate the movement speed range based on crack sensitivity.

10. The process for reducing welding thermal crack sensitivity by applying an external magnetic field according to claim 9, characterized in that: According to the interval of the lower test plate moving speed V corresponding to the weld under different magnetic field conditions, the relationship between the magnetic field intensity and the lower test plate moving speed is obtained, and the numerical values ​​of the intervals of the lower test plate moving speed V corresponding to different magnetic field conditions are compared.

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