Electromagnetic stirring assisted resistance spot welding electrode device and welding method

Abstract

The application relates to a vortex electromagnetic stirring assisted resistance spot welding electrode device and a welding method, and belongs to the field of welding process control. The coils and magnetometers of upper and lower electrodes are connected with a controller through cables; the excitation coil of the lower electrode induces a constant magnetic field in a workpiece, and the vortex excitation coil of the upper electrode induces a gradient distributed vortex field in the workpiece; during the growth of a resistance spot welding nugget, the liquid metal flowing through the vortex in the interior is subjected to strong and controllable Lorentz force electromagnetic stirring, so that the high-temperature metal in the center of the nugget flows to the edge, the heat in the center of the nugget is forced to spread in the transverse direction of the plate in a convection mode, the nugget diameter is increased while the nugget thickness is reduced, and the purpose of controlling the geometric shape of the nugget under the condition of not changing the basic welding parameters is achieved. While improving the bearing capacity of the resistance spot welding joint, the post-weld deformation can be reduced, and the welding quality is significantly improved. The heat input is significantly reduced, and the energy-saving and emission-reducing advantages are obvious.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of welding process control, in particular to a kind of nugget morphology regulation and control technology in resistance spot welding process, especially a kind of vortex electromagnetic stirring assisted resistance spot welding electrode device and welding method. BACKGROUND

[0002] In the field of equipment manufacturing such as automobile, rail passenger car, resistance spot welding is widely used in the lap welding structure of sheet as a kind of welding process with high welding efficiency, low cost and stable welding quality. In the spot welding process, the workpiece is assembled into a lap structure and placed between the upper and lower electrodes; the upper and lower electrodes exert a certain pressure on the workpiece, and pass through a large current for a short time. The internal workpiece compression area forms a certain molten metal under the action of resistance heat, which forms an isolated circular spot weld (nugget) after cooling to connect the plate layer.

[0003] The geometric size of spot welding nugget determines the mechanical properties of the welded joint. The geometric size (diameter, thickness, etc.) of spot welding nugget not only depends on the heat generation inside the workpiece during welding, but also is affected by heat transfer and its equilibrium state. In the conventional resistance spot welding process, due to the balance of material heat generation and heat dissipation, the nugget thickness and diameter have a strong positive relationship. Under fixed welding conditions, increasing the nugget diameter will inevitably lead to an increase in its thickness, and the two are difficult to adjust independently. Therefore, when the spot welding nugget diameter is large, the post-weld deformation of the part is large due to the large amount of metal melting in the thickness direction, and the surface quality is poor. How to reduce the nugget thickness as much as possible while ensuring sufficient nugget diameter has become a key problem in the field of resistance spot welding nugget regulation. SUMMARY

[0004] The purpose of the present application is to provide a vortex electromagnetic stirring assisted resistance spot welding electrode device and welding method, which solves the above-mentioned problems existing in the prior art. By means of external magnetic field and eddy current excitation, the liquid metal inside the resistance spot welding nugget is subjected to strong and controllable electromagnetic stirring during the growth process, so that the high temperature metal at the center of the nugget flows to the edge, and the heat at the center of the nugget is forced to spread laterally through convection, thereby increasing the nugget diameter while reducing the nugget thickness, and achieving the purpose of controlling the nugget geometry without changing the basic welding parameters.

[0005] The above-mentioned purpose of the present application is achieved by the following technical solutions:

[0006] The vortex electromagnetic stirring assisted resistance spot welding electrode device comprises an upper electrode 1, a lower electrode 2 and a controller 3, the coils and magnetometers of the upper and lower electrodes are connected with the controller 3 through cables; the upper electrode 1 is composed of an electrode body one 11, a coil retaining sleeve one 12, a vortex excitation coil 13 and a three-axis magnetometer one 14; the lower electrode 2 is composed of an electrode body two 21, a coil retaining sleeve two 22, an excitation coil 23 and a three-axis magnetometer two 24; during the welding process, the excitation coil 23 of the lower electrode 2 induces a constant magnetic field inside the workpiece, and the vortex excitation coil 13 of the upper electrode 1 induces a gradient distributed vortex field inside the workpiece; during the growth of the resistance spot welding nugget, the liquid metal flowing through the vortex inside is subjected to strong and controllable Lorentz force electromagnetic stirring, so that the high-temperature metal at the center of the nugget flows to the edge, the heat at the center of the nugget is forced to spread laterally in a convection manner, the nugget diameter is increased while the nugget thickness is reduced, and the purpose of controlling the nugget geometry under the condition of not changing the basic welding parameters is achieved.

[0007] The upper electrode 1 is installed in the upper electrode handle of the spot welding equipment through the frustum at the rear end of the electrode body one 11, the electrode cap is arranged at the front end of the electrode body one 11, the inside is a hollow structure, threads are arranged on the outer cylindrical surface, and the electrode cap is responsible for transmitting current, pressure and cooling water during the welding process; the coil retaining sleeve one 12 is installed outside the electrode body one 11 through threads, the vortex excitation coil 13 is embedded in the inside, and the three-axis magnetometer one 14 is arranged at the end.

[0008] The lower electrode 2 is installed in the lower electrode handle of the spot welding equipment through the frustum at the rear end of the electrode body two 21; the electrode cap is arranged at the front end of the electrode body two 21, the inside is a hollow structure, threads are arranged on the outer cylindrical surface, and the electrode cap is responsible for transmitting current, pressure and cooling water during the welding process; the coil retaining sleeve two 22 is installed outside the electrode body two 21 through threads, the vortex excitation coil 23 is embedded in the inside, and the three-axis magnetometer two 24 is arranged at the end.

[0009] The coil retaining sleeve one 12 and the coil retaining sleeve two 22 of the upper electrode 1 and the lower electrode 2 can adjust the relative positions of the coil retaining sleeve one 12 and the coil retaining sleeve two 22 and the electrode body one 11 and the electrode body two 21 through threads, so as to adjust the distance between the coil and the surface of the workpiece, and meet the adjustment needs of the induced magnetic field and the vortex field.

[0010] Another object of the present application is to provide a vortex electromagnetic stirring assisted resistance spot welding method, when resistance spot welding is performed, the upper and lower electrodes 1, 2 are respectively installed in the electrode holding rod of the spot welding device, the electrode body one and two bear the function of the conventional electrode, and are responsible for providing welding current and pressure to the workpiece; the excitation coil 23 of the lower electrode 2 induces a space magnetic field under the action of the constant voltage output by the controller 3, part of the magnetic force lines of the space magnetic field are perpendicular to the surface of the workpiece, penetrate the workpiece and point to the upper electrode 1; the vortex excitation coil 13 of the upper electrode 1 induces a vortex field in the workpiece under the action of the high-frequency alternating voltage output by the controller 3, the vortex takes the electrode axis as the center and is distributed in a ring shape, and the current direction is perpendicular to the magnetic force line in the workpiece;

[0011] The liquid metal in the fusion zone of the resistance spot welding joint forms a overturning flow under the action of the resultant force of the Lorentz force, flows from the center to the edge on the side of the fusion zone close to the upper electrode, and flows from the edge to the center on the side of the fusion zone close to the lower electrode, and macroscopically exhibits the electromagnetic stirring effect; the liquid metal flow caused by the vortex electromagnetic stirring causes the high-temperature metal at the center of the fusion zone to diffuse to the edge, forcibly conducts heat to the periphery of the fusion zone, and changes the temperature distribution of the welding zone under the condition that the basic welding parameters remain unchanged, and as a result, the thickness of the fusion zone is reduced and the diameter is increased, thereby achieving the purpose of controlling the geometric shape of the fusion zone.

[0012] The duration of the induced magnetic field and the vortex field is set by the controller 3, the controller 3 is provided with a constant voltage output circuit, a high-frequency voltage output circuit, a synchronous control and interface circuit, can control the synchronization of the magnetic field, the vortex field and the welding current on-off process, or the synchronization with the welding pressure loading process, and is flexible to set to meet the needs of different spot welding quality control; when the induced magnetic field and the vortex field are synchronized with the welding current on-off process, the vortex electromagnetic stirring is only performed during the generation and growth of the fusion zone, and mainly affects the geometric shape of the fusion zone; when the induced magnetic field and the vortex field are synchronized with the welding pressure loading process, the vortex electromagnetic stirring is performed during the generation, growth and cooling crystallization process of the fusion zone, and on the basis of the size control of the fusion zone, the crystallization process of the liquid metal can also be affected, the grain is refined, and the welding defects are reduced.

[0013] The vortex electromagnetic stirring assisted resistance spot welding method of the present application can effectively increase the diameter of the fusion zone and reduce the thickness of the fusion zone under the condition that the heat input remains unchanged, can improve the carrying capacity of the resistance spot welding joint while reducing the post-weld deformation, and can significantly improve the welding quality. Or, under the premise of ensuring the same fusion zone diameter, the heat input is significantly reduced, and the energy saving and emission reduction advantages are obvious. BRIEF DESCRIPTION OF DRAWINGS

[0014] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. The detailed description of the application is set forth in connection with the accompanying drawings.

[0015] Figure 1 The schematic diagram of the electrode device of the vortex electromagnetic stirring assisted resistance spot welding of the application;

[0016] Figure 2 The schematic diagram of the upper electrode device structure of the application;

[0017] Figure 3 The schematic diagram of the lower electrode device structure of the application;

[0018] Figure 4 The working schematic diagram of the electrode device of the vortex electromagnetic stirring assisted resistance spot welding of the application;

[0019] Figure 5 The schematic diagram of the distribution of the induced magnetic field, the vortex field and the Lorentz force in the spot welding joint of the application;

[0020] Figure 6 The fluidity of the liquid metal in the nugget of the spot welding of the application;

[0021] Figure 7 The comparative schematic diagram of the geometry and the surface indentation of the nugget of the conventional resistance spot welding and the vortex stirring assisted spot welding of the application.

[0022] In the figure: 1, upper electrode; 2, lower electrode; 3, controller; 11, electrode body one; 12, coil retaining sleeve one; 13, vortex excitation coil; 14, three-axis magnetometer one; 21, electrode body two; 22, coil retaining sleeve two; 23, excitation coil; 24, three-axis magnetometer two. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0024] In order to make the above object, characteristics and advantages of the application more obvious and easy to understand, the application will be further described in detail below with reference to the drawings and specific embodiments.

[0025] Reference is made to Figures 1 to 7As shown, the vortex electromagnetic stirring assisted resistance spot welding electrode device and welding method of the present application, through the means of external magnetic field, vortex excitation, makes the liquid metal inside the resistance spot welding nugget in the growth process to be subjected to strong, controllable electromagnetic stirring effect, thereby causing the high temperature metal at the center of the nugget to flow to the edge, and the heat at the center of the nugget to be forced to spread laterally in the plate through convection, while increasing the nugget diameter, reducing the nugget thickness, and achieving the purpose of controlling the nugget geometry without changing the basic welding parameters.

[0026] Referring to Figures 1 to 3 As shown, the vortex electromagnetic stirring assisted resistance spot welding electrode device of the present application is composed of an upper electrode 1, a lower electrode 2 and a controller 3. The coils and magnetometers of the upper and lower electrodes 1 and 2 are connected to the corresponding interfaces of the controller 3 through cables. The upper electrode 1 is composed of an electrode body 11, a coil retaining sleeve 12, a vortex excitation coil 13 and a three-axis magnetometer 14. The lower electrode 2 is composed of an electrode body 21, a coil retaining sleeve 22, an excitation coil 23 and a three-axis magnetometer 24.

[0027] The upper electrode 1 is installed in the upper electrode holder of the spot welding equipment through the taper at the rear end of the electrode body 11. The electrode cap is provided at the front end of the electrode body 11, which is hollow inside and has threads on the outer cylindrical surface, and is responsible for transmitting current, pressure and cooling water during welding. The coil retaining sleeve 12 is installed on the outside of the electrode body 11 through threads, and the vortex excitation coil 13 is embedded in the inside of the coil retaining sleeve 12, and the three-axis magnetometer 14 is provided at the end.

[0028] The lower electrode 2 is installed in the lower electrode holder of the spot welding equipment through the taper at the rear end of the electrode body 21. The electrode cap is provided at the front end of the electrode body 21, which is hollow inside and has threads on the outer cylindrical surface, and is responsible for transmitting current, pressure and cooling water during welding. The coil retaining sleeve 22 is installed on the outside of the electrode body 21 through threads, and the vortex excitation coil 23 is embedded in the inside of the coil retaining sleeve 22, and the three-axis magnetometer 24 is provided at the end.

[0029] The coil retaining sleeves 1 and 2 of the upper and lower electrodes 1 and 2 can adjust the relative position of the coil and the electrode body 1 and 2 through threads, so as to adjust the distance between the coil and the surface of the workpiece, and meet the adjustment needs of the induced magnetic field and the vortex field.

[0030] Referring to Figure 4 and Figure 5As shown, the vortex electromagnetic stirring assisted resistance spot welding method of the present application, when resistance spot welding is performed, the upper and lower electrodes are respectively installed in the electrode holder of the spot welding equipment, the electrode body one and two bear the function of the conventional electrode, responsible for providing welding current and pressure to the workpiece. The excitation coil 23 of the lower electrode 2 induces a spatial magnetic field under the action of the constant voltage output by the controller 3, part of the magnetic force lines of the magnetic field are perpendicular to the surface of the workpiece, penetrate the workpiece and point to the upper electrode 1, as shown. Figure 5 As shown, the vortex excitation coil 13 of the upper electrode 1 induces a vortex field inside the workpiece under the action of the high-frequency alternating voltage output by the controller 3. The vortex is circularly distributed with the electrode axis as the center, and the current direction is perpendicular to the magnetic force line inside the workpiece, as shown. Figure 5

[0031] Referring to Figure 6 As shown, after the upper and lower electrodes are electrified and welded, a nugget is formed inside the workpiece due to the accumulation of heat. With the continuation of electrification, the nugget continues to grow. In this process, the molten metal inside the nugget is always in the magnetic field and vortex excited by the upper and lower electrodes. The current direction of the vortex is perpendicular to the direction of the magnetic field, and the metal material flowing through the vortex is subjected to the action of the Lorentz force, and the force direction points from the center of the nugget to its edge. Because the distribution of the vortex in the thickness direction of the workpiece is not uniform, the vortex near the surface of the workpiece is the largest, and the vortex gradually decreases as it penetrates into the interior of the workpiece, so the Lorentz force received by the liquid metal of the nugget is also not uniform. The liquid metal near the upper electrode is subjected to the largest force, and the force gradually decreases as the distance from the upper electrode increases. Under the combined action of this non-uniform force, the liquid metal of the nugget produces a kind of overturning flow, which flows from the center to the edge on the side of the nugget near the upper electrode, and flows from the edge to the center on the side of the nugget near the lower electrode, which macroscopically exhibits the effect of electromagnetic stirring.

[0032] The liquid metal flow caused by the vortex electromagnetic stirring leads to the diffusion of high-temperature metal at the center of the nugget to the edge, forcing the heat to conduct to the periphery of the nugget, resulting in a change in the temperature distribution of the welding zone under the condition that the basic welding parameters remain unchanged. The result is that the thickness of the nugget is reduced and the diameter is increased, thereby achieving the purpose of controlling the geometry of the nugget.

[0033] ​The duration of the induced magnetic field and the eddy current field is set by the controller 3, which can be synchronized with the welding current on-off process or the welding pressure loading process, and is flexible to meet the needs of different spot welding quality control. When the induced magnetic field and the eddy current field are synchronized with the welding current on-off process, the eddy current electromagnetic stirring is only carried out during the generation and growth of the nugget, mainly affecting the geometry of the nugget; when the induced magnetic field and the eddy current field are synchronized with the welding pressure loading process, the eddy current electromagnetic stirring is carried out during the generation, growth and cooling crystallization of the nugget, which can affect the crystallization process of the liquid metal on the basis of nugget size control, refine the grains and reduce welding defects.

[0034] According to the quality control requirements of different welding joints, the eddy current electromagnetic stirring assisted resistance spot welding electrode device of the present application can adjust the distance between the eddy current excitation coil 13, the excitation coil 23 and the surface of the welded workpiece through the coil retaining sleeve, control the distribution and size of the induced magnetic field and the eddy current field in the workpiece, and thus realize the regulation of different nugget geometries. When adjusting the height of the coil, the three-axis magnetometers one and two installed on the coil retaining sleeve one and two can quickly measure the space magnetic field, and the value is transmitted to the controller 3 through the cable and displayed, which is convenient for the operator to observe and record intuitively.

[0035] Example 1

[0036] The following takes the resistance spot welding process for rail passenger car body components as an example to illustrate:

[0037] (1) The welding material is SUS301L stainless steel, and the plate thickness combination is 1mm+1mm. The electrode cap diameter is Φ14mm, the welding current is 12kA, and the welding time is 400ms. The excitation current is direct current 5A; the eddy current excitation signal source is square wave alternating current with peak voltage 120V and frequency 1KHz.

[0038] (2) Before welding, the eddy current electromagnetic stirring assisted resistance spot welding electrode device of the present application is first installed at the end of the electrode guide rod of the spot welding equipment, and the eddy current excitation coil 13, the excitation coil 23 and the magnetometer are respectively connected with the controller through the cable.

[0039] (3) Before power welding, the controller 3 outputs the excitation current and the eddy current excitation voltage as required to generate the corresponding induced magnetic field and eddy current field in the welding workpiece.

[0040] (4) After starting power welding, the nugget is formed in the spot welding joint under the action of heat accumulation. The liquid metal in the nugget flows and transfers heat under the action of eddy current electromagnetic stirring, changes the distribution of heat, forms a nugget with larger diameter and smaller thickness compared with the conventional spot welding process, thereby achieving the purpose of nugget geometry regulation, and the electrode indentation on the joint surface is smaller than that of the conventional spot welding process, and the joint surface quality is improved, as shown in Figure 7 .

[0041] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made to the present application shall be included in the protection scope of the present application.

Claims

1. A method of eddy current electromagnetic stirring assisted resistance spot welding, characterized by: The vortex electromagnetic stirring assisted resistance spot welding electrode device is realized by the device, which comprises an upper electrode (1), a lower electrode (2) and a controller (3), the coils and magnetometers of the upper and lower electrodes are connected with the controller (3) through cables; the upper electrode (1) is composed of an electrode body one (11), a coil retaining sleeve one (12), a vortex excitation coil (13) and a three-axis magnetometer one (14); the lower electrode (2) is composed of an electrode body two (21), a coil retaining sleeve two (22), an excitation coil (23) and a three-axis magnetometer two (24); the excitation coil (23) of the lower electrode (2) induces a constant magnetic field inside the workpiece, and the vortex excitation coil (13) of the upper electrode (1) induces a gradient distributed vortex field inside the workpiece; during the growth of the resistance spot welding nugget, the liquid metal flowing through the vortex inside is subjected to strong and controllable Lorentz force electromagnetic stirring, so that the high temperature metal at the center of the nugget flows to the edge, and the heat at the center of the nugget is forced to spread laterally in a convection manner, thereby increasing the diameter of the nugget while reducing the thickness of the nugget, so as to achieve the purpose of controlling the geometry of the nugget under the condition of not changing the basic welding parameters; The method is that when resistance spot welding is performed, the upper and lower electrodes (1, 2) are respectively installed in the electrode holding rods of the spot welding equipment, the electrode body one and two bear the functions of the conventional electrode, and are responsible for providing the welding current and pressure to the workpiece; the excitation coil (23) of the lower electrode (2) induces a space magnetic field under the action of the constant voltage output by the controller (3), the space magnetic field has part of magnetic lines perpendicular to the surface of the workpiece, penetrates the workpiece and points to the upper electrode (1); the vortex excitation coil (13) of the upper electrode (1) induces a vortex field inside the workpiece under the action of the high-frequency alternating voltage output by the controller (3); the vortex is circularly distributed with the electrode axis as the center, and the current direction is perpendicular to the magnetic lines inside the workpiece; the two external physical quantities form a controllable Lorentz force field with definite size and direction, which acts on the internal molten pool of the spot welding joint; The liquid metal inside the nugget of the resistance spot welding joint forms a reverse flow under the action of the resultant force of the Lorentz force, flows from the center of the nugget to the edge on the side of the nugget close to the upper electrode, and flows from the edge to the center of the nugget on the side of the nugget close to the lower electrode, which macroscopically shows the electromagnetic stirring effect; the liquid metal flow caused by the vortex electromagnetic stirring causes the high temperature metal at the center of the nugget to diffuse to the edge, forcibly conducts the heat to the periphery of the nugget, and changes the temperature distribution of the welding zone under the condition that the basic welding parameters are unchanged, and the result is that the thickness of the nugget is reduced and the diameter of the nugget is increased, thereby achieving the purpose of nugget geometry control; The duration of the induced magnetic field and the vortex field is set by the controller (3), the induced magnetic field and the vortex field are continuously synchronized with the welding pressure loading process, the vortex electromagnetic stirring is performed during the generation, growth and cooling crystallization process of the nugget, and on the basis of nugget size control, the crystallization process of the liquid metal can also be affected, the grain is refined, and the welding defects are reduced.

2. The eddy current electromagnetic stir-assisted resistance spot welding method of claim 1, wherein: The upper electrode (1) is installed in the upper electrode holder of the spot welding equipment through the taper of the rear end of the electrode body one (11), the front end of the electrode body one (11) is provided with an electrode cap, the inside is a hollow structure, the outer cylindrical surface is provided with threads, and the electrode cap transmits current, pressure and cooling water in the welding process; the coil retaining sleeve one (12) is installed on the outside of the electrode body one (11) through threads, the inside is inlaid with the eddy current excitation coil (13), and the end is provided with the three-axis magnetometer one (14); The lower electrode (2) is installed in the lower electrode holder of the spot welding equipment through the taper of the rear end of the electrode body two (21); the front end of the electrode body two (21) is provided with an electrode cap, the inside is a hollow structure, the outer cylindrical surface is provided with threads, and the electrode cap transmits current, pressure and cooling water in the welding process; the coil retaining sleeve two (22) is installed on the outside of the electrode body two (21) through threads, the inside is inlaid with the eddy current excitation coil (13), and the end is provided with the three-axis magnetometer two (24).

3. The eddy current electromagnetic stir-assisted resistance spot welding method of claim 1, wherein: The coil retaining sleeve one (12) and the coil retaining sleeve two (22) of the upper electrode (1) and the lower electrode (2) can adjust the relative position of the coil retaining sleeve one (12) and the coil retaining sleeve two (22) and the electrode body one (11) and the electrode body two (21) through threads, so that the distance between the coil and the surface of the workpiece is adjusted, and the adjustment needs of the induced magnetic field and the eddy current field are met.

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