A constant pressure welding head for a pressure actively adjusted precision spot welding machine

Abstract

This invention discloses a constant pressure welding head for a pressure-actively adjustable precision spot welding machine, relating to the technical field of spot welding machine bodies. It includes a welding head, a main body disposed inside and above the welding head, an upper electrode disposed in the middle of the welding head, a lower electrode disposed below the welding head, a drive module disposed between the welding head and the main body for controlling the lifting and lowering of the main body, and a control unit disposed inside the main body and connected to the upper electrode. This invention, through the collaboration of the control unit and the drive module, enables the welding pressure to precisely follow the physical process of weld nugget formation, growth, and solidification, forming a saddle-shaped pressure curve that effectively suppresses spatter, reduces shrinkage cavities and cracks, and significantly improves weld density and joint strength.

Description

Technical Field

[0001] This invention relates to the technical field of spot welding machine body, specifically a constant pressure welding head for a pressure-actively adjustable precision spot welding machine. Background Technology

[0002] Resistance spot welding is a process that uses the resistance heat generated when current flows through the contact surface of workpieces to melt local metals and form a weld nugget. After cooling, the metals are joined together. The process is generally divided into four stages: pre-pressurization, heating, holding (pressure holding), and cooling and crystallization. The formation and growth of the weld nugget are affected by a combination of factors, including welding current, heating time, electrode pressure, and the material properties of the workpiece.

[0003] In the initial stage of welding, if the low pressure of the pre-pressing stage is used, the contact resistance between the workpieces is insufficient, heat generation is slow, and it is difficult to form a stable weld nugget, which easily leads to incomplete welds. When the weld nugget grows, the liquid metal expands rapidly. If the pressure remains high, it is very easy to squeeze the high-temperature molten metal out of the plate seam, resulting in severe spatter. This not only causes the weld nugget to lose volume and strength, but also contaminates the electrodes and shortens the tooling life. In the cooling and solidification stage, the liquid metal shrinks in volume. If the pressure is not replenished in time, the voids caused by solidification shrinkage cannot be filled, leaving shrinkage cavities and microcracks in the center of the weld joint, and the joint's load-bearing capacity and fatigue resistance will be greatly reduced. Summary of the Invention

[0004] The purpose of this invention is to provide a constant pressure welding head for a pressure-actively adjustable precision spot welding machine to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a constant pressure welding head for a pressure-actively-adjustable precision spot welding machine, comprising:

[0006] Welding joint;

[0007] The main body is located inside and above the welding head;

[0008] The upper electrode is located in the middle of the welding head;

[0009] The lower electrode is located below the welding head;

[0010] A drive module, located between the welding head and the main body, is used to control the lifting and lowering of the main body;

[0011] The control unit is located inside the main body and connected to the upper electrode. It is used to cooperate with the drive module to control the pressure applied by the upper electrode to the workpiece so that the pressure value during the welding process forms a saddle curve.

[0012] Furthermore, the control unit includes:

[0013] A permanent magnet is disposed inside the main body;

[0014] An excitation coil is positioned below the permanent magnet and connected to the upper electrode.

[0015] Furthermore, the control unit also includes:

[0016] The lateral coils have the same structure as the excitation coils and are disposed on both sides of the permanent magnet;

[0017] A limiting plate is disposed on the side opposite to the lateral coil and the permanent magnet, and one end of the limiting plate penetrates the inner wall of the main body. The movement direction of the limiting plate is perpendicular to the side wall of the welding head.

[0018] Furthermore, several rubber pads are disposed on the side of the limiting plate facing the welding head. The vertical cross-section of the rubber pad is trapezoidal. The limiting plate is provided with a groove that matches the rubber pad. The rubber pad protrudes relative to the side wall of the limiting plate.

[0019] Furthermore, the welding head also includes:

[0020] An ultrasonic generator is located on one side of the lower electrode and is used to detect the position of the molten pool, refine the grains in the molten pool, and expel the air inside the molten pool.

[0021] Furthermore, the upper electrode and the lower electrode have the same structure, both adopting a multi-layer concentric ring-shaped stacked structure, with an insulating pad provided between two adjacent ring-shaped layers.

[0022] Furthermore, a measuring unit is disposed between the upper electrode and the main body, the measuring unit comprising:

[0023] Two electrodes are arranged opposite each other and are respectively attached to the upper electrode and the wall of the main body. The two electrodes form a capacitor structure, and the two electrodes are triangular and rectangular respectively.

[0024] An insulating layer is disposed between the two electrode plates.

[0025] Furthermore, a pressure sensor is provided between the excitation coil and the upper electrode. The pressure sensor has the same structure as the measuring unit, and the electrode plate inside the pressure sensor is rectangular.

[0026] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0027] By coordinating the control unit and the drive module, the welding pressure precisely follows the physical process of weld nucleus formation, growth, cooling and solidification, forming a saddle curve of "high pressure nucleation - low pressure anti-splashing - high pressure compaction", which effectively suppresses spatter, reduces shrinkage cracks, and significantly improves weld density and joint strength.

[0028] The electromagnetic spring structure, composed of a permanent magnet and an excitation coil, has a fast response speed and high control precision. It can adjust the output force in real time. With the help of the lateral coil and the limit plate with trapezoidal rubber pad, it ensures that the main body and the welding head are relatively fixed, avoids pressure back transmission and insufficient force, and ensures accurate execution of the pressure curve.

[0029] An ultrasonic generator is integrated on the lower electrode side, which has three functions: real-time detection of the molten pool position, grain refinement by acoustic flow, and bubble removal. This significantly reduces porosity, obtains a fine axial grain structure, and improves the toughness and reliability of the welded area.

[0030] The electrode adopts a multi-layer concentric ring stacked structure. Combined with ultrasonic detection, the area of ​​the current-carrying ring can be adjusted in sections to dynamically compensate for the offset of the molten pool caused by differences in workpiece thickness and conductivity, so that the molten nugget is always centered on the contact surface and the welding consistency is guaranteed.

[0031] The measuring unit and pressure sensor adopt a variable area capacitor structure to detect the minute displacement of the upper electrode and the actual pressure in a non-contact manner, providing accurate feedback for closed-loop control, ensuring constant pressure output, and effectively improving the stability and online controllability of welding quality. Attached Figure Description

[0032] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0033] Figure 1 This is a three-dimensional structural schematic diagram of the present invention;

[0034] Figure 2 This is a schematic diagram of the main three-dimensional structure of the present invention;

[0035] Figure 3 This is a three-dimensional structural diagram of the internal mechanism of the main body of the present invention;

[0036] Figure 4 This is a schematic diagram of the main internal structure of the present invention;

[0037] Figure 5 This is the invention Figure 4 Enlarged structural diagram at point A in the middle;

[0038] Figure 6 This is a three-dimensional structural diagram of the upper electrode and connected electrode plates of the present invention;

[0039] Figure 7 This is a schematic diagram of the three-dimensional structure of the lower electrode of the present invention;

[0040] Figure 8 This is a schematic diagram of the annular stacked structure viewed from the bottom side of the upper electrode of the present invention.

[0041] In the picture:

[0042] 1. Welding head; 101. Main body; 102. Upper electrode; 103. Lower electrode;

[0043] 2. Control unit; 201. Permanent magnet; 202. Excitation coil; 203. Lateral coil; 204. Limiting plate; 205. Rubber pad;

[0044] 3. Measuring unit; 301. Electrode plate; 302. Insulating layer;

[0045] 4. Pressure sensor;

[0046] 5. Driver module;

[0047] 6. Ultrasonic generator. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Please see Figures 1-7 The present invention provides a technical solution: a constant pressure welding head for a pressure-actively-adjustable precision spot welding machine, comprising:

[0050] Welding head 1;

[0051] The main body 101 is disposed above the interior of the welding head 1;

[0052] The upper electrode 102 is disposed in the middle of the welding head 1;

[0053] The lower electrode 103 is disposed below the welding head 1;

[0054] The drive module 5 is disposed between the welding head 1 and the main body 101, and is used to control the lifting and lowering of the main body 101;

[0055] The control unit 2 is located inside the main body 101 and connected to the upper electrode 102. It is used to cooperate with the drive module 5 to control the pressure applied by the upper electrode 102 to the workpiece so that the pressure value during the welding process forms a saddle curve.

[0056] The main body 101 is connected to the welding head 1 through the drive module 5. A control unit 2 is provided between the main body 101 and the upper electrode 102, and the upper electrode 102 is slidably connected to the welding head 1. The constant pressure means that the welding voltage is constant. During the welding process, the pressure generated by the upper electrode 102 on the workpiece is mainly adjusted.

[0057] The drive module 5 includes a stepper motor and a ball screw. The stepper motor controls the body 101 and the upper electrode 102 to move up and down through the ball screw. The drive module 5 controls the upper electrode 102 to contact the workpiece. In the initial stage of welding, the two workpieces contact the upper electrode 102 and the lower electrode 103 respectively. The control unit 2 applies an initial pressure to the upper electrode 102. The initial pressure is relatively high, and the contact surface of the two workpieces (i.e., in the direction of the pressure applied to the upper electrode 102) retains a high contact resistance, so that sufficient heat can be generated at the moment of power-on to quickly form a stable initial weld nugget.

[0058] When the molten nucleus begins to form and enters the rapid growth stage, the molten liquid metal expands rapidly due to heat, generating huge internal pressure. At this time, the control unit 2 reduces the pressure applied to the workpiece by the upper electrode 102 to facilitate the growth and expansion of the molten nucleus and avoid excessive pressure, which would cause the molten metal to splash.

[0059] During the cooling of the melt nugget, the control unit 2 increases the pressure applied to the workpiece by the upper electrode 102, and the volume of the liquid metal begins to shrink. If sufficient external pressure is not applied, solidification shrinkage will leave internal defects such as shrinkage cavities and cracks in the center of the melt nugget. Filling the tiny voids generated by shrinkage ensures that the weld joint is dense and has high strength. The saddle curve perfectly matches the physical process of the melt nugget from formation, growth to solidification through a series of continuous pressure changes of "high pressure nucleation, low pressure anti-splashing, and high pressure compaction".

[0060] See Figures 2-4 The control unit 2 includes:

[0061] A permanent magnet 201 is disposed inside the main body 101;

[0062] The excitation coil 202 is located below the permanent magnet 201 and is connected to the upper electrode 102.

[0063] The drive module 5 mainly controls the upper electrode 102 to contact the workpiece. The main effect of the control unit 2 is to apply pressure of different intensities to the workpiece through the upper electrode 102. The control unit 2 is composed of a permanent magnet 201 and an excitation coil 202. The permanent magnet 201 and the excitation coil 202 cooperate to form an electromagnetic spring structure. When the excitation coil 202 is energized, a controllable electromagnetic field is generated around the excitation coil 202. This electromagnetic field interacts with the constant magnetic field of the permanent magnet 201. According to Lenz's law, the electromagnetic field generated by the excitation coil 202 will generate an axial pushing force or attraction force on the permanent magnet 201, thereby changing the overall output force of the control unit 2. When a positive current is passed through the excitation coil 202, the magnetic field generated by the excitation coil 202 is in the same direction as the magnetic field of the permanent magnet 201. The two repel each other, and the permanent magnet 201 drives the upper electrode 102 to move downward and press the workpiece.

[0064] During the welding process, the control unit 2 adjusts the current intensity supplied to the excitation coil 202 in real time according to the preset pressure curve, so as to achieve precise control of the welding pressure from pre-pressing, welding, holding pressure to unloading. This makes the pressure value change according to the saddle curve, thereby ensuring the stability and consistency of the welding quality. The electromagnetic spring structure has a fast response speed and high control precision, which can meet the stringent requirements of dynamic pressure control for precision spot welding.

[0065] See Figures 2-4 The control unit 2 also includes:

[0066] The lateral coil 203 has the same structure as the excitation coil 202 and is disposed on both sides of the permanent magnet 201;

[0067] A limiting plate 204 is disposed on the side opposite to the lateral coil 203 and the permanent magnet 201, and one end of the limiting plate 204 penetrates the inner wall of the main body 101. The movement direction of the limiting plate 204 is perpendicular to the side wall of the welding head 1.

[0068] The side coil 203 has the same structure as the excitation coil 202, and the working principle of the side coil 203 is the same as that of the excitation coil 202. Before the control unit 2 applies pressure to the workpiece, the side coils 203 on both sides of the permanent magnet 201 are energized first. The magnetic field generated by the side coil 203 repels the magnetic field generated by the permanent magnet 201. At the same time, the side coil 203 is connected to the limiting plate 204. The limiting plate 204 is slidably connected to the main body 101. Under the action of magnetic field repulsion, the limiting plate 204 contacts the inner wall of the welding head 1. Then, through the friction between the limiting plate 204 and the inner wall of the welding head 1, the main body 101 and the welding head 1 are kept relatively stationary, so as to avoid the control unit 2 generating reverse pressure on the ball screw, which would cause the main body 101 to rise relative to the welding head 1, resulting in insufficient welding pressure generated by the upper electrode 102 on the molten pool area of ​​the workpiece.

[0069] See Figure 3 A plurality of rubber pads 205 are disposed on the side of the limiting plate 204 facing the welding head 1. The vertical cross section of the rubber pad 205 is trapezoidal. The limiting plate 204 has a groove that matches the rubber pad 205. The rubber pad 205 protrudes from the side wall of the limiting plate 204.

[0070] By replacing the limiting plate 204 with a rubber pad 205, which directly contacts the inner wall of the welding head 1, the friction coefficient of the rubber pad 205 is greater than that of the limiting plate 204. At the same time, the lateral coil 203 exerts pressure on the rubber pad 205 through the limiting plate 204, causing the protruding part of the rubber pad 205 relative to the limiting plate 204 to deform. The deformed rubber pad 205 has a larger contact area with the inner wall of the welding head 1, thus improving the fixing effect between the main body 101 and the welding head 1.

[0071] See Figure 7 It also includes:

[0072] An ultrasonic generator 6 is disposed on one side of the lower electrode 103 and is used to detect the position of the molten pool, refine the grains in the molten pool, and expel the air inside the molten pool.

[0073] During the welding process, the ultrasonic generator 6 integrated in the electrode continuously emits high-frequency pulses and receives echo signals from the weld nugget boundary through a dedicated monitoring device. This enables precise real-time detection of the weld pool position, allowing for the tracking of the weld nugget formation and growth process, as well as monitoring its solidification process during the cooling stage. This provides a reliable basis for online evaluation of welding quality.

[0074] When ultrasound enters the molten pool, its propagation attenuation creates a sound pressure gradient, driving the melt to generate forced convection (i.e., acoustic flow effect). At the same time, the periodic collapse of cavitation bubbles generates local high-pressure shock waves. These two effects work together to break the growing primary dendrites and disperse the fragments evenly. Furthermore, the solidification mode changes from layer-by-layer progression to simultaneous nucleation of the entire structure, ultimately resulting in a fine and uniform equiaxed crystal structure, which significantly improves the joint strength and toughness.

[0075] Acoustic agitation accelerates the collision and merging of bubbles, increases their rising speed, and promotes their rapid escape from the liquid metal. This effectively reduces the porosity of the weld to an extremely low level, resulting in a dense welded joint without internal defects. It also promotes the escape of bubbles from the liquid metal, reducing porosity defects in the weld and obtaining a dense molten pool.

[0076] See Figure 8 The upper electrode 102 and the lower electrode 103 have the same structure, both adopting a multi-layer concentric ring stacked structure, with an insulating pad between two adjacent ring layers.

[0077] After the upper electrode 102 and the lower electrode 103 are energized, a molten pool can be generated in the contact area of ​​the two metal plates. Due to the inconsistency in the thickness, thermal conductivity and electrical conductivity of the upper and lower metal plates, the molten pool may not be distributed vertically with the contact surface of the two metal plates as the interface. That is, the molten pool is biased towards one of the metal plates. In severe cases, most of the molten pool may be located on one of the metal plates, while only a small melting area appears on the other metal plate. After the molten pool cools down, the welding strength does not meet the production standards.

[0078] By cooperating with the ultrasonic generator 6 through the upper electrode 102 and the lower electrode 103, the ultrasonic generator 6 can detect the contact surface position of two metals, which is consistent with the principle of ultrasonic metal flaw detection and the position of the melt nugget. The upper electrode 102 and the lower electrode 103 are multi-layer concentric ring stacked structures, and an insulating pad is provided between two adjacent ring stacks.

[0079] The ultrasonic generator 6 monitors the position of the two metal contact surfaces in real time. When the molten pool is biased to one side due to the difference in thermal conductivity and thickness between the two plates, the control system adjusts the area of ​​the conductive rings of the multi-layer concentric ring electrodes in different zones. Each ring layer is independent due to the insulating pad. The current density and heat generation in this area can be adjusted by selectively activating more conductive rings closer to the thinner plate side and reducing the number of conductive rings on the thicker plate side: the conductive area on the thinner plate side increases, the current density decreases, and the heat decreases; the conductive area on the thicker plate side decreases, the current density increases, and the heat increases. Through this area control, the heat generation on both sides tends to be balanced, and the center of the molten pool is dynamically "pulled back" to the contact surface between the two plates. The position of the molten pool shifts due to the conductivity and thermal conductivity. The adjustment method of the conductive area of ​​the upper electrode 102 and the lower electrode 103 is the same as the principle of the thickness difference adjustment method.

[0080] See Figure 6 A measuring unit 3 is disposed between the upper electrode 102 and the main body 101. The measuring unit 3 includes:

[0081] Two electrode plates 301 are arranged opposite to each other and are respectively attached to the upper electrode 102 and the wall surface of the main body 101. The two electrode plates 301 form a capacitor structure, and the two electrode plates 301 are triangular and rectangular respectively.

[0082] An insulating layer 302 is disposed between two electrode plates 301.

[0083] The measuring unit 3 adopts the variable area capacitive displacement sensing principle to realize the real-time detection of the small displacement of the upper electrode 102 during the welding process. The measuring unit 3 consists of two oppositely arranged electrode plates 301 and an insulating layer 302 disposed between the two electrode plates 301 to form a capacitor structure. The two electrode plates 301 are respectively attached to the upper electrode 102 and the wall surface of the main body 101, and the geometric shapes of the two electrode plates 301 are triangular and rectangular, respectively.

[0084] When welding enters the nucleus formation stage, the molten metal expands and generates an upward lifting force, which pushes the upper electrode 102 to make a slight upward displacement relative to the main body 101. Since there is a relative movement between the upper electrode 102 and the main body 101, the two electrode plates 301 attached to the walls of the two respectively will move out of place, resulting in a change in the overlapping area between the two electrode plates 301.

[0085] According to the capacitance formula, when the overlapping area S changes with the displacement of the upper electrode 102, the capacitance value of the measuring unit 3 changes synchronously. Since the two plates 301 adopt asymmetrical designs of triangle and rectangle respectively, there is a definite correspondence between their relative displacement and the change in overlapping area. This makes it easy for the subsequent signal processing unit to accurately convert the capacitance change into the displacement of the upper electrode 102, thereby indirectly reflecting the degree of weld nugget expansion and providing real-time feedback for welding quality control.

[0086] See Figure 6 A pressure sensor 4 is provided between the excitation coil 202 and the upper electrode 102. The pressure sensor 4 has the same structure as the measuring unit 3, and the electrode plate 301 inside the pressure sensor 4 is rectangular.

[0087] Pressure sensor 4 is positioned between excitation coil 202 and upper electrode 102. Its structure is the same as that of measuring unit 3. Both internal electrodes 301 are rectangular, forming a variable-area capacitive sensing structure. When welding enters the molten nugget expansion stage, the expansion of the molten nugget volume pushes the upper electrode 102 upward. At this time, the electromagnetic repulsion between excitation coil 202 and permanent magnet 201 remains constant, while the reaction force exerted by upper electrode 102 on the workpiece increases with the increase of displacement, that is, the actual pressure on the molten nugget increases. Pressure sensor 4 detects this pressure change in real time. The upward displacement of upper electrode 102 changes the distance between the two rectangular electrodes 301 inside pressure sensor 4, causing the capacitance value to change synchronously. This capacitance signal is converted and output to the control system. Based on this feedback signal, the control system reduces the current intensity flowing into excitation coil 202 accordingly, reduces the magnitude of electromagnetic repulsion, and causes the pressure of upper electrode 102 on the molten nugget to fall back to the set value, thereby achieving constant pressure control throughout the molten nugget expansion process and avoiding a decrease in welding quality due to pressure fluctuations.

[0088] Working principle of the invention:

[0089] The main body 101 is connected to the welding head 1 through the drive module 5. A control unit 2 is provided between the main body 101 and the upper electrode 102, and the upper electrode 102 is slidably connected to the welding head 1. The constant pressure means that the welding voltage is constant. During the welding process, the pressure generated by the upper electrode 102 on the workpiece is mainly adjusted.

[0090] The drive module 5 includes a stepper motor and a ball screw. The stepper motor controls the body 101 and the upper electrode 102 to move up and down through the ball screw. The drive module 5 controls the upper electrode 102 to contact the workpiece. In the initial stage of welding, the two workpieces contact the upper electrode 102 and the lower electrode 103 respectively. The control unit 2 applies an initial pressure to the upper electrode 102. The initial pressure is relatively high, and the contact surface of the two workpieces (i.e., in the direction of the pressure applied to the upper electrode 102) retains a high contact resistance, so that sufficient heat can be generated at the moment of power-on to quickly form a stable initial weld nugget.

[0091] When the molten nucleus begins to form and enters the rapid growth stage, the molten liquid metal expands rapidly due to heat, generating huge internal pressure. At this time, the control unit 2 reduces the pressure applied to the workpiece by the upper electrode 102 to facilitate the growth and expansion of the molten nucleus and avoid excessive pressure, which would cause the molten metal to splash.

[0092] During the cooling of the melt nugget, the control unit 2 increases the pressure applied to the workpiece by the upper electrode 102, and the volume of the liquid metal begins to shrink. If sufficient external pressure is not applied, solidification shrinkage will leave internal defects such as shrinkage cavities and cracks in the center of the melt nugget. Filling the tiny voids generated by shrinkage ensures that the weld joint is dense and has high strength. The saddle curve perfectly matches the physical process of the melt nugget from formation, growth to solidification through a series of continuous pressure changes of "high pressure nucleation, low pressure anti-splashing, and high pressure compaction".

[0093] The drive module 5 mainly controls the upper electrode 102 to contact the workpiece. The main effect of the control unit 2 is to apply pressure of different intensities to the workpiece through the upper electrode 102. The control unit 2 is composed of a permanent magnet 201 and an excitation coil 202. The permanent magnet 201 and the excitation coil 202 cooperate to form an electromagnetic spring structure. When the excitation coil 202 is energized, a controllable electromagnetic field is generated around the excitation coil 202. This electromagnetic field interacts with the constant magnetic field of the permanent magnet 201. According to Lenz's law, the electromagnetic field generated by the excitation coil 202 will generate an axial pushing force or attraction force on the permanent magnet 201, thereby changing the overall output force of the control unit 2. When a positive current is passed through the excitation coil 202, the magnetic field generated by the excitation coil 202 is in the same direction as the magnetic field of the permanent magnet 201. The two repel each other, and the permanent magnet 201 drives the upper electrode 102 to move downward and press the workpiece.

[0094] During the welding process, the control unit 2 adjusts the current intensity supplied to the excitation coil 202 in real time according to the preset pressure curve, so as to achieve precise control of the welding pressure from pre-pressing, welding, holding pressure to unloading. This makes the pressure value change according to the saddle curve, thereby ensuring the stability and consistency of the welding quality. The electromagnetic spring structure has a fast response speed and high control precision, which can meet the stringent requirements of dynamic pressure control for precision spot welding.

[0095] The side coil 203 has the same structure as the excitation coil 202, and the working principle of the side coil 203 is the same as that of the excitation coil 202. Before the control unit 2 applies pressure to the workpiece, the side coils 203 on both sides of the permanent magnet 201 are energized first. The magnetic field generated by the side coil 203 repels the magnetic field generated by the permanent magnet 201. At the same time, the side coil 203 is connected to the limiting plate 204. The limiting plate 204 is slidably connected to the main body 101. Under the action of magnetic field repulsion, the limiting plate 204 contacts the inner wall of the welding head 1. Then, through the friction between the limiting plate 204 and the inner wall of the welding head 1, the main body 101 and the welding head 1 are kept relatively stationary, so as to avoid the control unit 2 generating reverse pressure on the ball screw, which would cause the main body 101 to rise relative to the welding head 1, resulting in insufficient welding pressure generated by the upper electrode 102 on the molten pool area of ​​the workpiece.

[0096] By replacing the limiting plate 204 with a rubber pad 205, which directly contacts the inner wall of the welding head 1, the friction coefficient of the rubber pad 205 is greater than that of the limiting plate 204. At the same time, the lateral coil 203 exerts pressure on the rubber pad 205 through the limiting plate 204, causing the protruding part of the rubber pad 205 relative to the limiting plate 204 to deform. The deformed rubber pad 205 has a larger contact area with the inner wall of the welding head 1, thus improving the fixing effect between the main body 101 and the welding head 1.

[0097] During the welding process, the ultrasonic generator 6 integrated in the electrode continuously emits high-frequency pulses and receives echo signals from the weld nugget boundary through a dedicated monitoring device. This enables precise real-time detection of the weld pool position, allowing for the tracking of the weld nugget formation and growth process, as well as monitoring its solidification process during the cooling stage. This provides a reliable basis for online evaluation of welding quality.

[0098] When ultrasound enters the molten pool, its propagation attenuation creates a sound pressure gradient, driving the melt to generate forced convection (i.e., acoustic flow effect). At the same time, the periodic collapse of cavitation bubbles generates local high-pressure shock waves. These two effects work together to break the growing primary dendrites and disperse the fragments evenly. Furthermore, the solidification mode changes from layer-by-layer progression to simultaneous nucleation of the entire structure, ultimately resulting in a fine and uniform equiaxed crystal structure, which significantly improves the joint strength and toughness.

[0099] Acoustic agitation accelerates the collision and merging of bubbles, increases their rising speed, and promotes their rapid escape from the liquid metal. This effectively reduces the porosity of the weld to an extremely low level, resulting in a dense welded joint without internal defects. It also promotes the escape of bubbles from the liquid metal, reducing porosity defects in the weld and obtaining a dense molten pool.

[0100] After the upper electrode 102 and the lower electrode 103 are energized, a molten pool can be generated in the contact area of ​​the two metal plates. Due to the inconsistency in the thickness, thermal conductivity and electrical conductivity of the upper and lower metal plates, the molten pool may not be distributed vertically with the contact surface of the two metal plates as the interface. That is, the molten pool is biased towards one of the metal plates. In severe cases, most of the molten pool may be located on one of the metal plates, while only a small melting area appears on the other metal plate. After the molten pool cools down, the welding strength does not meet the production standards.

[0101] By cooperating with the ultrasonic generator 6 through the upper electrode 102 and the lower electrode 103, the ultrasonic generator 6 can detect the contact surface position of two metals, which is consistent with the principle of ultrasonic metal flaw detection and the position of the melt nugget. The upper electrode 102 and the lower electrode 103 are multi-layer concentric ring stacked structures, and an insulating pad is provided between two adjacent ring stacks.

[0102] The ultrasonic generator 6 monitors the position of the two metal contact surfaces in real time. When the molten pool is biased to one side due to the difference in thermal conductivity and thickness between the two plates, the control system adjusts the area of ​​the conductive rings of the multi-layer concentric ring electrodes in different zones. Each ring layer is independent due to the insulating pad. The current density and heat generation in this area can be adjusted by selectively activating more conductive rings closer to the thinner plate side and reducing the number of conductive rings on the thicker plate side: the conductive area on the thinner plate side increases, the current density decreases, and the heat decreases; the conductive area on the thicker plate side decreases, the current density increases, and the heat increases. Through this area control, the heat generation on both sides tends to be balanced, and the center of the molten pool is dynamically "pulled back" to the contact surface between the two plates. The position of the molten pool shifts due to the conductivity and thermal conductivity. The adjustment method of the conductive area of ​​the upper electrode 102 and the lower electrode 103 is the same as the principle of the thickness difference adjustment method.

[0103] The measuring unit 3 adopts the variable area capacitive displacement sensing principle to realize the real-time detection of the small displacement of the upper electrode 102 during the welding process. The measuring unit 3 consists of two oppositely arranged electrode plates 301 and an insulating layer 302 disposed between the two electrode plates 301 to form a capacitor structure. The two electrode plates 301 are respectively attached to the upper electrode 102 and the wall surface of the main body 101, and the geometric shapes of the two electrode plates 301 are triangular and rectangular, respectively.

[0104] When welding enters the nucleus formation stage, the molten metal expands and generates an upward lifting force, which pushes the upper electrode 102 to make a slight upward displacement relative to the main body 101. Since there is a relative movement between the upper electrode 102 and the main body 101, the two electrode plates 301 attached to the walls of the two respectively will move out of place, resulting in a change in the overlapping area between the two electrode plates 301.

[0105] According to the capacitance formula, when the overlapping area S changes with the displacement of the upper electrode 102, the capacitance value of the measuring unit 3 changes synchronously. Since the two plates 301 adopt asymmetrical designs of triangle and rectangle respectively, there is a definite correspondence between their relative displacement and the change in overlapping area. This makes it easy for the subsequent signal processing unit to accurately convert the capacitance change into the displacement of the upper electrode 102, thereby indirectly reflecting the degree of weld nugget expansion and providing real-time feedback for welding quality control.

[0106] Pressure sensor 4 is positioned between excitation coil 202 and upper electrode 102. Its structure is the same as that of measuring unit 3. Both internal electrodes 301 are rectangular, forming a variable-area capacitive sensing structure. When welding enters the molten nugget expansion stage, the expansion of the molten nugget volume pushes the upper electrode 102 upward. At this time, the electromagnetic repulsion between excitation coil 202 and permanent magnet 201 remains constant, while the reaction force exerted by upper electrode 102 on the workpiece increases with the increase of displacement, that is, the actual pressure on the molten nugget increases. Pressure sensor 4 detects this pressure change in real time. The upward displacement of upper electrode 102 changes the distance between the two rectangular electrodes 301 inside pressure sensor 4, causing the capacitance value to change synchronously. This capacitance signal is converted and output to the control system. Based on this feedback signal, the control system reduces the current intensity flowing into excitation coil 202 accordingly, reduces the magnitude of electromagnetic repulsion, and causes the pressure of upper electrode 102 on the molten nugget to fall back to the set value, thereby achieving constant pressure control throughout the molten nugget expansion process and avoiding a decrease in welding quality due to pressure fluctuations.

[0107] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0108] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A constant pressure welding head for a pressure-actively adjustable precision spot welding machine, characterized in that, include: Welding head (1); The main body (101) is disposed above the interior of the welding head (1); The upper electrode (102) is disposed in the middle of the welding head (1); The lower electrode (103) is disposed below the welding head (1); A drive module (5) is disposed between the welding head (1) and the main body (101) for controlling the lifting and lowering of the main body (101); The control unit (2) is located inside the main body (101) and connected to the upper electrode (102). It is used to cooperate with the drive module (5) to control the pressure applied by the upper electrode (102) to the workpiece so that the pressure value during the welding process forms a saddle curve.

2. The constant pressure welding head for a pressure-actively adjustable precision spot welding machine according to claim 1, characterized in that: The control unit (2) includes: A permanent magnet (201) is disposed inside the main body (101); An excitation coil (202) is disposed below the permanent magnet (201) and connected to the upper electrode (102).

3. The constant pressure welding head for a pressure-actively adjustable precision spot welding machine according to claim 2, characterized in that: The control unit (2) further includes: The lateral coil (203) has the same structure as the excitation coil (202) and is disposed on both sides of the permanent magnet (201); A limiting plate (204) is disposed on the side opposite to the lateral coil (203) and the permanent magnet (201), and one end of the limiting plate (204) penetrates the inner wall of the main body (101). The movement direction of the limiting plate (204) is perpendicular to the side wall of the welding head (1).

4. The constant pressure welding head for a pressure-actively adjustable precision spot welding machine according to claim 3, characterized in that: Several rubber pads (205) are disposed on the side of the limiting plate (204) facing the welding head (1). The vertical cross section of the rubber pad (205) is trapezoidal. The limiting plate (204) has a groove that matches the rubber pad (205). The rubber pad (205) protrudes from the side wall of the limiting plate (204).

5. The constant pressure welding head for a pressure-actively adjustable precision spot welding machine according to claim 1, characterized in that: The welding head (1) also includes: An ultrasonic generator (6) is disposed on one side of the lower electrode (103) and is used to detect the position of the molten pool, refine the grains in the molten pool, and expel the air inside the molten pool.

6. The constant pressure welding head for a pressure-actively-adjustable precision spot welding machine according to claim 1, characterized in that: The upper electrode (102) and the lower electrode (103) have the same structure, both adopting a multi-layer concentric ring stacked structure, with an insulating pad between two adjacent ring layers.

7. The constant pressure welding head for a pressure-actively adjustable precision spot welding machine according to claim 1, characterized in that: A measuring unit (3) is disposed between the upper electrode (102) and the main body (101), the measuring unit (3) comprising: Two electrode plates (301) are arranged opposite to each other and are respectively attached to the upper electrode (102) and the wall surface of the main body (101). The two electrode plates (301) form a capacitor structure, and the two electrode plates (301) are triangular and rectangular respectively. An insulating layer (302) is disposed between the two electrode plates (301).

8. The constant pressure welding head for a pressure-actively adjustable precision spot welding machine according to claim 7, characterized in that: A pressure sensor (4) is provided between the excitation coil (202) and the upper electrode (102). The pressure sensor (4) has the same structure as the measuring unit (3), and the electrode plate (301) inside the pressure sensor (4) is rectangular.

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