Nut projection welding pressurizing method

Abstract

This application relates to the field of projection welding technology for nuts, and discloses a method for applying pressure during projection welding of nuts, including the following steps: Step 1: The welding controller outputs AC voltage to the welding transformer to generate the welding current required for welding. The welding time, 50-1000ms, is also controlled by the welding controller. Step 2: The servo controller controls the movement of the servo cylinder, pushing the moving electrode to a position one workpiece thickness and one projection nut thickness away from the fixed electrode, but without outputting pressure. The distance between the moving electrode and the fixed electrode is 10mm-30mm. The magnitude of the magnetic force generated by the electromagnet is controlled by controlling the magnitude of the excitation current, and the repulsive force generated by the electromagnet and the permanent magnet is used to apply pressure to the nut and workpiece during projection welding. This achieves rapid pressure changes and tracking within a short time, reduces welding spatter during projection welding of nuts, and improves welding quality.

Description

Technical Field

[0001] This invention relates to the field of projection welding technology for nuts, specifically a method for applying pressure during projection welding of nuts. Background Technology

[0002] Projection welding is a special form of spot welding. It involves welding a part to another part with a larger area by using the existing chamfer, bottom surface, or prefabricated projection. Currently, in the design of metal structures in automobiles and home appliances, it is widely used to directly project metal parts, nuts, or bolts onto another part. This is especially true in the design of automotive frame structures, where it has begun to be widely adopted to improve production efficiency and reduce labor intensity.

[0003] Projection welding of nuts places higher demands on the welding pressure, one of the three essential elements of resistance welding. The response speed and control precision of the welding pressure directly determine the quality of the weld.

[0004] During projection welding, at the moment the projection point collapses, due to the static inertia of traditional pressurization systems (pneumatic pressurization or servo electric cylinder pressurization), a "pressure loss" phenomenon occurs, where the actual pressure drops instantaneously. Since the pressure is not compensated in time, spatter is generated under the action of welding current, reducing the strength of the weld. To address this, this invention proposes a pressure application method for projection welding of nuts. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a pressure application method for projection welding of nuts, which solves the problems of slow pressure following speed, easy generation of welding spatter, and thus affecting welding quality in existing projection welding processes.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for pressurizing nut projection welding: A nut projection welding pressurizing device is used, including a welding transformer, a servo cylinder, a welding controller, and a servo controller. Two conductive strips are fixedly connected to one side of the welding transformer. One conductive strip has a fixed electrode fixedly connected to its end away from the welding transformer, and the other conductive strip has a fixed movable electrode fixedly connected to its end away from the welding transformer. A pressure sensor is installed on the outside of the movable electrode, and a permanent magnet is fixedly connected to the side of the movable electrode away from the fixed electrode. An output shaft is installed at the output end of the servo cylinder, and a locking device is installed on the outside of the output shaft. An electromagnet is fixedly connected to one end of the output shaft. The welding controller and the welding transformer are electrically connected.

[0008] The projection welding pressure method includes the following steps:

[0009] Step 1: The welding controller outputs AC voltage to the welding transformer to generate the welding current required for welding. The welding time of 50-1000ms is also controlled by the welding controller.

[0010] Step 2: The servo controller controls the movement of the servo electric cylinder, pushing the moving electrode to a position one workpiece thickness and one projection weld nut thickness away from the fixed electrode, but without outputting pressure. The distance between the moving electrode and the fixed electrode is 10mm to 30mm.

[0011] Step 3: The locking device activates to lock the output shaft of the servo electric cylinder, preparing for subsequent pressurization;

[0012] Step 4: Since the magnitude of the electromagnetic force is proportional to the square of the current passing through the electromagnet, the electromagnet control system outputs the corresponding DC current according to the required welding pressure. The electromagnet generates the corresponding electromagnetic force, which drives the moving electrode to move, thereby applying the corresponding welding pressure to the workpiece.

[0013] Step 5: The pressure sensor installed behind the moving electrode collects the actual pressure value in real time and feeds it back to the electromagnet control system to form a pressure feedback system.

[0014] Step 6: After the pressure output stabilizes, the welding controller outputs the corresponding current. Under the combined action of current and pressure, the welding nut protrusion experiences pressure feedback. At this time, the pressure drops. The pressure sensor feeds back the pressure change to the electromagnet control system. The control system adjusts the electromagnet current input to achieve rapid pressure tracking.

[0015] Step 7: After welding is completed, the welding controller sends a signal indicating that welding is complete to the electromagnet control system. Upon receiving the completion signal, the electromagnet control system controls the electromagnet to generate an attractive force, causing the electromagnet and the permanent magnet to attract each other.

[0016] Step 8: The locking device releases the output shaft of the servo electric cylinder, causing the servo electric cylinder to move in the opposite direction, driving the moving electrode, permanent magnet, and electromagnet to rise together, completing the entire welding process.

[0017] Preferably, the input AC voltage in step one is a three-phase AC 380V voltage, which is rectified and converted into an AC square wave with a frequency of 1000-2000Hz by a bridge inverter unit composed of IGBTs, and then output to the welding transformer.

[0018] Preferably, in step two, the positions of the moving electrode and the fixed electrode are such that the fixed electrode is in contact with the plate and the moving electrode is in contact with the nut.

[0019] Preferably, the pressure repeatability accuracy in step four is ±10 to ±30 Newtons, and the pressure response speed is 20 to 30 kN / milliseconds.

[0020] Preferably, in step four, by controlling the direction of the current flowing through the electromagnet, the direction of the magnetic field generated by the electromagnet is the same as the polarity of the permanent magnet, thereby generating electromagnetic repulsion.

[0021] Preferably, the pressure feedback system in step five is used to adjust the actual pressure output value to match the set value.

[0022] Preferably, in step six, the welding controller outputs a welding current of 10,000 to 30,000 A and an output heating time of 5 to 8 ms.

[0023] Preferably, in step seven, the direction of the electromagnet current is adjusted so that the polarities of the electromagnet and the permanent magnet are opposite.

[0024] Preferably, in step eight, the permanent magnet and electromagnet drive the moving electrode to move and detach from the workpiece through the principle of attraction between opposite polarities of the electrodes.

[0025] This invention provides a method for applying pressure during projection welding of nuts. It has the following beneficial effects:

[0026] This invention controls the magnitude of the magnetic force generated by an electromagnet by controlling the magnitude of the excitation current. The repulsive force between the electromagnet and a permanent magnet is then used to apply pressure to the nut and workpiece during projection welding. This allows for rapid pressure changes and tracking within a short timeframe (typically tens of milliseconds), reducing welding spatter and improving weld quality. Attached Figure Description

[0027] Figure 1 This is a measured waveform diagram of the projection welding pressure change of the pneumatic pressure nut in Embodiment 1 of the present invention;

[0028] Figure 2 This is a schematic diagram of the pressurization device in Embodiment 2 of the present invention;

[0029] Figure 3 This is a system architecture diagram of the pressurization device in Embodiment 2 of the present invention.

[0030] The components include: 1. Welding transformer; 2. Conductive strip; 3. Servo electric cylinder; 4. Locking device; 5. Electromagnet; 6. Permanent magnet; 7. Pressure sensor; 8. Fixed electrode; 9. Moving electrode; and 10. Welding controller. Detailed Implementation

[0031] The technical solutions in 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.

[0032] Example 1:

[0033] Please see the appendix Figure 1 In the existing technology, there are generally two ways to apply pressure during projection welding: cylinder pressure and servo motor pressure.

[0034] The pressure change waveform during the pneumatic pressurization process is shown in the attached figure. Figure 1 As shown, attached Figure 1 The curve in the middle represents the pressure curve during the welding process. The pressure curve shows that the pressure changes during welding mainly occur in the following stages:

[0035] Stage 1: At the moment of energization, the current flows through the end of the protrusion, and the protrusion expands due to heat. At this time, the protrusion has not yet melted. Due to the volume expansion, it pushes the electrode upward, so the electrode force increases.

[0036] Phase 2: The protrusion is rapidly crushed, and the electrode descends rapidly. Due to the slow response of the cylinder, the electrode pressure drops rapidly. At this point, the displacement value drops to its lowest point, and the electrode descent height for this nut is 0.67mm. After the cylinder pressure is replenished, the pressure begins to recover to the set pressure.

[0037] Stage 3: This stage is the weld nugget growth stage. The weld joint is heated and melts to form a weld nugget. Due to its volume expansion, it tries to push the electrode upward. However, the frictional resistance in the pressure structure of the electrode welding machine prevents the weld nugget from expanding, and the electrode force increases instead.

[0038] In the second stage of pneumatic pressurization, in order to achieve high-quality nut projection welding, extremely high requirements are placed on the speed at which the welding pressure follows.

[0039] When servo pressurization is used, the servo control system needs 6-10ms to re-establish the pressure process when the bump is crushed under the combined action of welding current and pressure. Therefore, welding spatter also exists under the pressure loss state, and stable and consistent welding quality cannot be achieved.

[0040] Example 2:

[0041] Please see the appendix Figure 2 - Appendix Figure 3This invention provides a nut projection welding pressure device, including a welding transformer 1, a servo cylinder 3, a welding controller 10, and a servo controller. The welding transformer 10 is fixed to the frame body of the device via a bracket. Two conductive strips 2 are fixedly connected to one side of the welding transformer 1. One conductive strip 2, away from the welding transformer 1, is fixedly connected to a fixed electrode 8, which is installed on the lower side of the frame body. The other conductive strip 2, away from the welding transformer 1, is fixedly connected to a movable electrode 9, which has a slider corresponding to a slide rail on the frame body. This slider guides the movement of the movable electrode 9. A pressure sensor 7 is installed on the outside of the movable electrode 9, and a permanent magnet 6 is fixedly connected to the side of the movable electrode 9 away from the fixed electrode 8. An output shaft is installed at the output end of the servo cylinder 3, which is installed on the upper part of the frame body. A locking device 4 is installed on the outside of the output shaft, and an electromagnet 5 is fixedly connected to one end of the output shaft. The welding controller 10 and the welding transformer 1 are electrically connected.

[0042] A method for applying pressure during projection welding of nuts includes the following steps:

[0043] Step 1: The welding controller 10 outputs AC voltage to the welding transformer 1 to generate the welding current required for welding. The welding time of 50-1000ms is also controlled by the welding controller 10. The input AC voltage is a three-phase AC 380V voltage, which is rectified and converted into an AC square wave with a frequency of 1000-2000Hz by a bridge inverter unit composed of IGBTs, and then output to the welding transformer 1.

[0044] Step 2: The servo controller controls the servo cylinder 3 to move, pushing the moving electrode 9 to a position one workpiece thickness and one projection weld nut thickness away from the fixed electrode 8. This position is where the fixed electrode 8 contacts the material, and the moving electrode 9 contacts the nut. However, no pressure is output. The distance between the moving electrode 9 and the fixed electrode 8 is 10mm to 30mm.

[0045] Step 3: The locking device 4 is activated to lock the output shaft of the servo electric cylinder 3, preparing for subsequent pressurization;

[0046] Step 4: Since the magnitude of the electromagnetic force is proportional to the square of the current flowing through electromagnet 5, the control system of electromagnet 5 outputs a corresponding DC current according to the required welding pressure, and electromagnet 5 generates a corresponding electromagnetic force. By controlling the direction of the current flowing through electromagnet 5, the direction of the magnetic field generated by electromagnet 5 is made the same as the polarity of permanent magnet 6, generating electromagnetic repulsion, which pushes the moving electrode 9 to move, thereby applying the corresponding welding pressure to the workpiece. The pressure repeatability is ±10 to ±30 Newtons, and the pressure response speed is 20 kN to 30 kN / ms.

[0047] Step 5: The pressure sensor 7 installed after the movable electrode 9 collects the actual pressure value in real time and feeds it back to the control system of the electromagnet 5, thus forming a pressure feedback system. The pressure feedback system is used to adjust the actual pressure output value to match the set value.

[0048] Step Six: After the pressure output stabilizes, the welding controller 10 outputs a corresponding current. The welding current output by the welding controller 10 is 10000~30000A, and the heating time is 5~8ms. Under the combined action of current and pressure, the welding nut protrusion experiences pressure feedback. At this time, pressure loss occurs. The pressure sensor 7 feeds back the pressure change to the electromagnet 5 control system. The control system adjusts the current input of the electromagnet 5 to achieve rapid pressure tracking.

[0049] Step 7: After welding is completed, the welding controller 10 sends a welding completion signal to the electromagnet 5 control system. Upon receiving the completion signal, the electromagnet 5 control system controls the electromagnet 5 to generate an attractive force. By adjusting the direction of the current in the electromagnet 5, the polarities of the electromagnet 5 and the permanent magnet 6 are made opposite, causing the electromagnet 5 and the permanent magnet 6 to attract each other.

[0050] Step 8: The locking device 4 releases the output shaft of the servo cylinder 3, causing the servo cylinder 3 to move in the opposite direction, driving the moving electrode 9, permanent magnet 6, and electromagnet 5 to rise together. The permanent magnet 6 and electromagnet 5 move the moving electrode 9 by means of the attraction between opposite poles, thus detaching it from the workpiece. This completes the entire welding process.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for applying pressure during projection welding of a nut, characterized in that, The nut projection welding pressure device includes a welding transformer (1), a servo cylinder (3), a welding controller (10), and a servo controller. Two conductive strips (2) are fixedly connected to one side of the welding transformer (1). One of the conductive strips (2) is fixedly connected to a fixed electrode (8) at the end away from the welding transformer (1), and the other conductive strip (2) is fixedly connected to a moving electrode (9) at the end away from the welding transformer (1). A pressure sensor (7) is installed on the outside of the moving electrode (9), and a permanent magnet (6) is fixedly connected to the side of the moving electrode (9) away from the fixed electrode (8). An output shaft is installed at the output end of the servo cylinder (3), and a locking device (4) is installed on the outside of the output shaft. An electromagnet (5) is fixedly connected to one end of the output shaft. The welding controller (10) and the welding transformer (1) are electrically connected. The welding pressure method includes the following steps: Step 1: The welding controller (10) outputs AC voltage to the welding transformer (1) to generate the welding current required for welding. The welding time of 50 to 1000 ms is also controlled by the welding controller (10). Step 2: The servo controller controls the movement of the servo electric cylinder (3) to push the moving electrode (9) to a position one workpiece thickness and one projection weld nut thickness away from the fixed electrode (8), but does not output pressure. The distance between the moving electrode (9) and the fixed electrode (8) is 10mm to 30mm. Step 3: The locking device (4) is activated to lock the output shaft of the servo electric cylinder (3), preparing for subsequent pressurization; Step 4: Since the magnitude of the electromagnetic force is proportional to the current passing through the electromagnet (5), the electromagnet (5) control system outputs the corresponding DC current according to the required welding pressure. The electromagnet (5) generates the corresponding electromagnetic force, which drives the moving electrode (9) to move, thereby applying the corresponding welding pressure to the workpiece. Step 5: The pressure sensor (7) installed after the moving electrode (9) collects the actual pressure value in real time and feeds it back to the electromagnet (5) control system to form a pressure feedback system. Step 6: After the pressure output stabilizes, the welding controller (10) outputs the corresponding current. Under the combined action of current and pressure, the welding nut protrusion will be crushed. At this time, the pressure will be lost. The pressure sensor (7) will feed back the pressure change to the electromagnet (5) control system. The control system will adjust the current input of the electromagnet (5) to achieve rapid pressure tracking. Step 7: After welding is completed, the welding controller (10) sends the welding completion signal to the electromagnet (5) control system. After receiving the completion signal, the electromagnet (5) control system controls the electromagnet (5) to generate attraction, so that the electromagnet (5) and the permanent magnet (6) attract each other. Step 8: The locking device (4) releases the output shaft of the servo cylinder (3), and the servo cylinder (3) moves in the opposite direction, driving the moving electrode (9), permanent magnet (6), and electromagnet (5) to rise together, completing the entire welding process; In step two, the positions of the movable electrode (9) and the fixed electrode (8) are such that the fixed electrode (8) is in contact with the plate and the movable electrode (9) is in contact with the nut. In step four, by controlling the direction of the current flowing through the electromagnet (5), the direction of the magnetic field generated by the electromagnet (5) is the same as the polarity of the permanent magnet (6), thus generating electromagnetic repulsion.

2. The method for applying pressure during projection welding of a nut according to claim 1, characterized in that, The input AC voltage in step one is a three-phase AC 380V voltage, which is rectified and converted into an AC square wave with a frequency of 1000-2000Hz by a bridge inverter unit composed of IGBTs, and output to the welding transformer (1).

3. The method for applying pressure during projection welding of a nut according to claim 1, characterized in that, The pressure repeatability accuracy in step four is ±10 to ±30 Newtons, and the pressure response speed is 20 to 30 kN / milliseconds.

4. The method for applying pressure during projection welding of a nut according to claim 1, characterized in that, The pressure feedback system in step five is used to adjust the actual pressure output value to match the set value.

5. The method for applying pressure during projection welding of a nut according to claim 1, characterized in that, The welding controller (10) in step six outputs a welding current of 10,000 to 30,000 A and an output heating time of 5 to 8 ms.

6. The method for applying pressure during projection welding of a nut according to claim 1, characterized in that, In step seven, the direction of the current in the electromagnet (5) is adjusted so that the polarities of the electromagnet (5) and the permanent magnet (6) are opposite.

7. The method for applying pressure during projection welding of a nut according to claim 1, characterized in that, In step eight, the permanent magnet (6) and electromagnet (5) drive the moving electrode (9) to move and detach from the workpiece by means of the principle of attraction between opposite electrodes.

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