Workpiece forming method based on controlling the conduction state of the coil by the energizing coefficient

Abstract

This invention relates to a workpiece forming method based on controlling the conduction state of coils using an energizing coefficient. Each turn of the drive coil group is connected to a power supply via an individual switch. During the sheet metal forming process, the conduction state of each turn of the drive coil group is individually controlled according to the real-time forming position of the sheet metal, i.e., the energized area of ​​the drive coil group is adjusted in real time, ensuring that the electromagnetic field direction at the sheet metal is parallel to the sheet metal surface, and the electromagnetic force on the sheet metal is always perpendicular to the sheet metal surface. This invention improves the flatness of the metal sheet surface, thus improving the forming quality of the metal sheet, and enhances the heat dissipation effect of each turn of the coil; it also increases the convenience of inspection and maintenance of each turn of the drive coil group.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic forming control of metal workpieces, and specifically relates to a workpiece forming method based on controlling the conduction state of the coil according to the energizing coefficient. Background Technology

[0002] With the development of technologies in China's aerospace and automotive industries, the demand for lightweight technologies is constantly increasing. The realization of lightweight technologies depends on the lightweight design of key components. Currently, there are two main approaches to lightweight design: one is to use lightweight structural designs such as hollow, thin-walled, ribbed, and biomimetic structures; the other is to use lightweight, high-strength materials such as magnesium alloys, aluminum alloys, titanium alloys, and high-performance composite materials. The second approach is the primary method for achieving lightweight design. However, lightweight, high-strength materials have poor formability at room temperature. Traditional forming methods such as stamping and hydraulic forming are prone to wrinkling and cracking, and they exhibit low plasticity and severe springback. Traditional forming methods are not ideal. Given the current severe energy shortages and environmental damage, the automotive industry is undergoing significant industrial upgrading and transformation. Research shows that if the total weight of a vehicle is reduced by 10%, fuel efficiency can be improved by 6%–8%, and exhaust emissions can be reduced by 4%. Lightweighting in the automotive industry is gradually becoming a research hotspot, but traditional forming methods limit the industrial application of lightweight, high-strength materials. Electromagnetic forming provides a new technical means for lightweight metal processing.

[0003] Electromagnetic forming (EMF) is a high-speed forming technology that uses electromagnetic force as the driving force. This technology not only improves the forming performance of materials but also has the advantage of reducing costs, making it one of the forming methods for improving the industrial application of lightweight and efficient materials. In the EMF process, a capacitor is first charged, and then the capacitor discharges to a drive coil. A strong pulsed current is generated within the drive coil, which produces a changing magnetic field. The metal workpiece near the drive coil generates induced eddy currents under this changing magnetic field. Under the superimposed electromagnetic force between the coil current and the workpiece eddy currents, the metal workpiece undergoes accelerated deformation, first producing elastic deformation and then plastic deformation, thus achieving the material forming process. Compared with traditional forming methods, EMF has the following main advantages: First, it improves the forming limit, as it is a high strain rate forming process, which can increase the material's strain rate sensitivity and strain hardening rate; second, it applies force non-contactly, which can improve the stress concentration problem during the forming process, resulting in high surface quality of the formed workpiece.

[0004] Existing electromagnetic forming patents mainly focus on changing the position of the drive coil to alter the distribution of electromagnetic force, thereby improving workpiece forming performance. Chinese invention patent CN108080483B, "An Electromagnetic Forming Device and Method," discloses an electromagnetic forming device. The drive coil module includes multiple drive coils arranged dispersedly above the forming area of ​​the sheet metal; multiple edge-pressing coil modules are used to generate edge-pressing force by interacting the magnetic field they produce in space during discharge with the eddy currents induced in the flange area of ​​the sheet metal; when a single discharge fails to achieve the target shape, the forming coil is moved, and discharge is performed again using timing control. This patent solves the problems of unidirectional electromagnetic force and difficulty in winding forming coils for large-size materials in traditional electromagnetic forming methods. However, during the movement of the forming coil, the displacement control of the forming coil requires very high precision, and the problem of wrinkling in the formed sheet metal is severe. In 2017, Xiong Qi's paper "Design and Implementation of Electromagnetic Forming for Large-Size Aluminum Alloy Sheets"... [1] "A multi-pole coil axial movement forming is proposed. Its basic principle is to use a relatively small coil with a high magnetic field strength for multi-step forming. During the forming process, the driving coil is gradually moved downward. This method solves the problem of the relatively singular main direction of the magnetic field in space and provides a good solution for the forming depth of the sheet metal, but it cannot improve the forming effect in the lateral direction."

[0005] In summary, there is a lack of better methods and devices for improving the electromagnetic forming performance of sheet metal in the existing technology.

[0006] References:

[0007] [1] Xiong Qi. Electromagnetic forming design and implementation of large-size aluminum alloy plates [D]. Huazhong University of Science and Technology, 2017. Summary of the Invention

[0008] The purpose of this invention is to provide a workpiece forming method based on controlling the conduction state of a coil using an energizing coefficient. This method aims to solve the problem of uneven surface finishes in existing metal workpiece forming methods, such as sheet metal bulging, which negatively impacts workpiece quality. By replacing the traditional monolithic coil group with a coil group composed of individually energized single-turn coils, the invention addresses the problems of large size, difficulty in winding, and poor heat dissipation associated with monolithic coils. Each turn of the coil is controlled by a different switch to drive its conduction. By controlling the energized area of ​​the driving coil group in real time, the metal workpiece is subjected only to electromagnetic forces perpendicular to its surface, thus improving the flatness of the workpiece surface and consequently, enhancing the forming quality of the metal workpiece.

[0009] The technical solution of the present invention is a workpiece forming method based on controlling the conduction state of the coil by the energizing coefficient, comprising the following steps:

[0010] Step 1: Secure the sheet metal using the edge clamping device;

[0011] Step 2: Based on the material and forming specifications of the plate to be formed, determine the parameters of the drive coil group, including the number of coil layers and the coil spacing, and model the drive coil using the finite element analysis software Comsol Ansys.

[0012] Step 3: Power each coil of the drive coil group independently. Each coil is connected to the power supply via a switch. At time t0, control the coil switch to energize each coil. The plate begins to deform under the electromagnetic field of the drive coil group. t0 represents the initial moment of plate forming.

[0013] Step 4: Use a high-speed camera to photograph the forming process of the plate, and calculate the maximum vertical deformation of the plate at time t and the angle between the plate and the horizontal plane, i.e., the tilt angle.

[0014] Step 5: Determine the first and second conical boundary surfaces parallel to the plate surface at time t by using the top, bottom left, and right edge lines of the coil group. The first conical boundary surface passes through the first turn of the outermost coil of the top layer of the coil group, and the second conical boundary surface passes through the center point of the bottom coil of the coil group. The area enclosed by the first and second conical boundary surfaces and the outer cylindrical surface of the coil group is the energized region. Construct the energized region at time t using the finite element analysis software Comsol Ansys.

[0015] Step 6: Calculate the current carrying coefficient of each coil based on the volume of each coil in the energized area, determine whether a single coil is conducting based on the current carrying coefficient, and control the coil switch based on the determination result of each coil.

[0016] Step 7: Let t = t + Δt, that is, add a time step to time t, where Δt represents the time step, and determine if t ≤ t end Is the condition true? If the result is yes, proceed to step 4; otherwise, end the process. end Indicates the forming deadline.

[0017] Preferably, in step 6, the current carrying coefficient C i,j The value of is coil X i,j The area within the cross-section of the energized region and the coil X i,j The ratio of the cross-sectional areas, C i,j Let i = 1, 2…M and j = 1, 2…N represent the energizing coefficient of the j-th turn of the i-th layer. The driving coil group is numbered sequentially from top to bottom, and sequentially from outside to inside, with M being the number of coil layers in the driving coil group and N being the number of turns in each layer.

[0018] Preferably, a threshold T for the current conduction coefficient is set, if

[0019] C i,j ≥T

[0020] Then control coil X i,j The switch causes coil X to... i,j power ups.

[0021] Furthermore, the threshold T is determined based on the value of the coil spacing L. When 0mm≤L<5mm, the threshold T is 1 / 2; when 5mm≤L≤10mm, the threshold T is 2 / 3.

[0022] Preferably, the time step Δt ranges from 10 to 1000 μs.

[0023] Preferably, a capacitor power supply is used to power each turn of the drive coil group, and the discharge voltage of the capacitor power supply is 0.35-35kV.

[0024] Preferably, the capacitance of the capacitor power supply is 32-3200μF.

[0025] An electromagnetic forming apparatus includes a drive coil assembly, a capacitor power supply, a pressing device, a high-speed camera, and a computer. The drive coil assembly includes multi-turn coils arranged in layers, with each coil connected to the capacitor power supply via a separate air switch. The high-speed camera is communicatively connected to the computer, and its lens is aimed at the drive coil assembly and the workpiece to be formed. The high-speed camera is used to capture the forming process of the workpiece.

[0026] Under the action of pulsed current, the drive coil assembly generates a pulsed magnetic field. Eddy currents are generated in the workpiece under the pulsed magnetic field, and the interaction between the eddy currents and the magnetic field generates an electromagnetic force, thus providing conditions for workpiece deformation. The coils provided by this invention are represented as an array in a spatial cross-sectional view. After the workpiece deforms to a certain extent, the energized area of ​​the drive coil assembly will change according to the workpiece deformation. When the energized area of ​​the drive coil assembly is different, that is, when different energized coils are used, the direction of the generated pulsed magnetic field is different. Under the interaction between the eddy currents and the magnetic field, an electromagnetic force perpendicular to the current shape of the workpiece is generated.

[0027] Compared with the prior art, the beneficial effects of the present invention include:

[0028] 1) The present invention uses a drive coil group composed of discrete coils. Each turn of the drive coil group is connected to the power supply via a separate switch. By controlling the energized area of ​​the drive coil group in real time, the metal plate is only subjected to electromagnetic force in the direction perpendicular to the surface of the plate, thereby improving the flatness of the surface of the metal plate and thus improving the forming quality of the metal plate.

[0029] 2) This invention uses a coil group composed of discrete, individually energized single-turn coils to replace the traditional integral coil group, which facilitates precise control of the energizing time, energizing duration, and current magnitude of each coil, and also improves the heat dissipation effect of each coil. In addition, it also increases the convenience of inspection and maintenance of each coil in the drive coil group. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Figure 1 This is a schematic flowchart of a workpiece forming method based on controlling the conduction state of a coil using an energizing coefficient, as an example.

[0032] Figure 2 The equivalent circuit diagram of each turn of the drive coil group in the embodiment is connected to the power supply.

[0033] Figure 3 This is a schematic diagram of the force direction of the plate and the driving coil in the initial state of Embodiment 1.

[0034] Figure 4 This is a schematic diagram of the energized area of ​​the drive coil when the plate tilt angle is 10.7° in Example 1.

[0035] Figure 5 This is a schematic diagram of the energized area of ​​the drive coil when the plate tilt angle is 20.3° in Example 1.

[0036] Figure 6 This is a schematic diagram of the force direction of the plate and the driving coil in the initial state in Example 2.

[0037] Figure 7 This is a schematic diagram of the energized area of ​​the drive coil when the plate tilt angle is 19.2° in Example 2.

[0038] Figure 8 This is a schematic diagram of the energized area of ​​the drive coil when the plate tilt angle is 36.3° in Example 2.

[0039] Explanation of reference numerals in the attached drawings: Plate 1, Edge pressing device 2. Detailed Implementation

[0040] Example 1

[0041] like Figure 1 As shown, a workpiece forming method based on controlling the conduction state of a coil using an energizing coefficient includes:

[0042] Step 1: Fix plate 1 using edge pressing device 2.

[0043] Step 2: Based on the material and forming specifications of the plate to be formed, determine the parameters of the drive coil group, including the number of coil layers and the coil spacing, and model the drive coil group using the finite element analysis software Comsol Ansys.

[0044] Step 3: Power each turn of the drive coil group independently, with each turn connected to the power supply via a switch, such as... Figure 2As shown. At time t0, the control coil switch energizes each turn of the coil, and the plate begins to deform under the electromagnetic field of the drive coil group. t0 represents the initial time of workpiece forming.

[0045] In this embodiment, the discharge voltage of the capacitor power supply is 3.5kV, and the capacitance of the capacitor power supply is 320μF.

[0046] Step 4: Use a high-speed camera to photograph the forming process of the plate, and calculate the maximum vertical deformation of the plate at time t and the angle between the plate and the horizontal plane, i.e., the tilt angle.

[0047] Step 5: Determine the first and second conical boundary surfaces parallel to the plate surface at time t by passing through the top, bottom left, and right edge lines of the drive coil group. The first conical boundary surface passes through the first turn of the outermost coil of the top layer of the coil group, and the second conical boundary surface passes through the center point of the bottom coil of the coil group. The area enclosed by the first and second conical boundary surfaces and the outer cylindrical surface of the coil group is the energized region. Construct the energized region at time t in the finite element analysis software Comsol Ansys.

[0048] Step 6: Calculate the current carrying coefficient of each coil based on the area of ​​each coil in the energized region, determine whether a single coil is conducting based on the current carrying coefficient, and control the coil switch based on the determination result of each coil.

[0049] Current carrying coefficient C i,j The value of is coil X i,j The area within the cross-section of the energized region and the coil X i,j The ratio of the cross-sectional areas, C i,j Let i = 1, 2…M and j = 1, 2…N represent the energizing coefficient of the j-th turn of the i-th layer. The driving coil group is numbered sequentially from top to bottom, and sequentially from outside to inside, with M being the number of coil layers in the driving coil group and N being the number of turns in each layer.

[0050] In the embodiment, M=4, N=6, meaning the drive coil group has 4 layers, each layer has 6 turns of coil, such as... Figure 3 As shown.

[0051] Set a threshold T for the current carrying capacity.

[0052] If C i,j ≥T,

[0053] Then control coil X i,j The switch causes coil X to... i,j power ups.

[0054] In this embodiment, the coil spacing L is 0 mm and T = 1 / 2.

[0055] Step 7: Let t = t + Δt, that is, add a time step to time t, where Δt represents the time step, and determine if t ≤ t end Is the condition true? If the result is yes, proceed to step 4; otherwise, end the process. end Indicates the forming deadline.

[0056] Figure 4 The diagram shows a schematic of a plate with a conical surface forming an angle of 10.7° with the horizontal plane. Based on an image of the plate taken by a high-speed camera at the current moment, the computer determines the energized area of ​​the drive coils in a drive coil group model created using the finite element analysis software Comsol Ansys. Based on the area of ​​each coil turn within the energized area, the energizing coefficient of each coil turn is calculated, and it is determined whether the energizing coefficient is greater than or equal to 1 / 2. If the energizing coefficient is not less than 1 / 2, the switch of that coil turn is controlled to make it conduct; otherwise, the switch of that coil turn is turned off. Specifically, the determination result is: First layer coil X... 1,1 X 1,2 When energized, the second layer coil X 2,1 X 2,2 X 2,3 X 2,4 X 2,5 X 2,6 When energized, the third layer coil X 3,1 X 3,2 X 3,3 X 3,4 X 3,5 X 3,6 Power on, fourth layer coil X 4,5 X 4,6 When energized, the electromagnetic field generated by the coil and the eddy current induced on the plate work together to produce an electromagnetic force F perpendicular to the surface of the plate.

[0057] When the angle between the tapered surface of the sheet and the horizontal plane is 20.3°, such as Figure 5 As shown, based on the image of the board taken by a high-speed camera at the current moment, the computer determines the energized area of ​​the drive coil in the drive coil group model established by the finite element analysis software Comsol Ansys, calculates the energization coefficient of each turn of the coil, and compares it with a threshold of 1 / 2 to determine whether the turn of the coil is energized. The specific determination result is: First layer coil X 1,1 When energized, the second layer coil X 2,1 X 2,2 X 2,3 X 2,4 When energized, the third layer coil X 3,2 X 3,3 X 3,4 X 3,5 Power on, fourth layer coil X 4,6When energized, the magnetic field generated by the energized coil interacts with the eddy currents induced on the board to produce an electromagnetic force F perpendicular to the surface of the board.

[0058] The electromagnetic forming apparatus for the above-mentioned workpiece forming method includes a drive coil assembly, a capacitor power supply, a pressing device, a high-speed camera, and a computer. The drive coil assembly comprises multi-turn coils arranged in layers, with each coil connected to the capacitor power supply via a separate air switch. The high-speed camera is communicatively connected to the computer, and its lens is aimed at the drive coil assembly and the workpiece to be formed. The high-speed camera is used to capture the forming process of the workpiece. The drive coil assembly uses a circular ring coil.

[0059] Example 2

[0060] The workpiece forming method in Example 2 is the same as in Example 1. The difference between the electromagnetic forming device in Example 2 and Example 1 is that the drive coil group includes 6 layers of coils, each layer having 3 turns, i.e., M=6, N=3, as shown below. Figure 6 As shown.

[0061] In this embodiment, the coil spacing L is 5mm and the threshold T = 2 / 3.

[0062] The time step Δt is 10us.

[0063] Figure 7 The diagram shows a schematic of a plate with a conical surface forming an angle of 19.2° with the horizontal plane. Based on an image of the plate taken by a high-speed camera at the current moment, the computer determines the energized region of the drive coils in a drive coil assembly model created using the finite element analysis software Comsol Ansys. Based on the volume of each coil turn within the energized region, the energizing coefficient of each coil turn is calculated, and it is determined whether the energizing coefficient is greater than or equal to 2 / 3. If the energizing coefficient is not less than 2 / 3, the switch of that coil turn is controlled to make it conduct; otherwise, the switch of that coil turn is turned off. Specifically, the determination result is: First layer coil X... 1,1 When energized, the second layer coil X 2,1 X 2,2 X 2,3 When energized, the third layer coil X 3,1 X 3,2 X 3,3 Power on, fourth layer coil X 4,1 X 4,2 X 4,3 Power on, fifth layer coil X 5,1 X 5,2 X 5,3 Power on, sixth layer coil X 6,3 When energized, the electromagnetic field generated by the coil and the eddy current induced on the plate work together to produce an electromagnetic force F perpendicular to the surface of the plate.

[0064] When the angle between the tapered surface of the sheet and the horizontal plane is 36.3°, such as Figure 8 As shown, based on the image of the board taken by a high-speed camera at the current moment, the computer determines the energized area of ​​the drive coil in the drive coil group model established by the finite element analysis software Comsol Ansys, calculates the energization coefficient of each turn of the coil, and compares it with the threshold of 2 / 3 to determine whether the turn of the coil is energized. The specific judgment result is: First layer coil X 1,1 When energized, the second layer coil X 2,1 X 2,2 When energized, the third layer coil X 3,1 X 3,2 X 3,3 Power on, fourth layer coil X 4,1 X 4,2 X 4,3 Power on, fifth layer coil X 5,2 X 5,3 Power on, sixth layer coil X 6,3 When energized, the magnetic field generated by the energized coil interacts with the eddy currents induced on the board to produce an electromagnetic force F perpendicular to the surface of the board.

Claims

1. A workpiece forming method based on a coil conduction state control using a conduction coefficient, characterized by, The workpiece is a plate. Each turn of the drive coil group is connected to the power supply via a separate switch. During the plate forming process, the workpiece forming method controls the conduction state of each turn of the drive coil group individually according to the real-time plate forming position, that is, adjusts the energized area of ​​the drive coil group in real time, so that the direction of the electromagnetic field at the plate is parallel to the plate surface, and the electromagnetic force on the plate is always perpendicular to the plate surface, thereby improving the forming effect and quality of the plate. The workpiece forming method includes the following steps: Step 1: Secure the sheet metal using the edge clamping device; Step 2: Based on the material and forming specifications of the plate to be formed, determine the parameters of the drive coil group, including the number of coil layers and the coil spacing, and model the drive coil using the finite element analysis software ComsolAnsys. Step 3: Power each coil of the drive coil group independently. Each coil is connected to the power supply via a switch. At time t0, control the coil switch to energize each coil. The plate begins to deform under the electromagnetic field of the drive coil group. t0 represents the initial moment of plate forming. Step 4: Use a high-speed camera to photograph the forming process of the plate, and calculate the maximum vertical deformation of the plate at time t and the angle between the plate and the horizontal plane, i.e., the tilt angle. Step 5: Determine the first and second conical boundary surfaces parallel to the plate surface at time t by using the top, bottom left, and right edge lines of the coil group. The first conical boundary surface passes through the outermost first turn of the top layer coil group, and the second conical boundary surface passes through the center point of the bottom layer coil group. The area enclosed by the first and second conical boundary surfaces and the outer cylindrical surface of the coil group is the energized region. Construct the energized region at time t in the finite element analysis software Comsol Ansys. Step 6: Calculate the current carrying coefficient of each coil based on the volume of each coil in the energized area, determine whether a single coil is conducting based on the current carrying coefficient, and control the coil switch based on the determination result of each coil. Step 7: Let t = t + Δt, i.e. increase the time t by a time step Δt, and determine whether t ≤ t end is true. If the result is true, execute Step 4, otherwise end, t end represents the forming deadline time.

2. The workpiece forming method of claim 1, wherein, In step 6, the energization coefficient C i,j is the ratio of the area of the coil X i,j located in the cross section of the energization region to the cross-sectional area of the coil X i,j , C i,j , i = 1, 2…M, j = 1, 2…N represents the energization coefficient of the i-th layer and the j-th turn coil, and the driving coil group is numbered in sequence from top to bottom layer by layer and from outside to inside turn by turn, M is the number of layers of the driving coil group, and N is the number of turns per layer of coil.

3. The workpiece forming method based on controlling the coil conduction state according to claim 2, characterized in that, Set a threshold T for the current carrying capacity. If C i,j ≥ T The control coil X i,j switches the coil X i,j on.

4. The workpiece forming method based on controlling the coil conduction state according to claim 3, characterized in that, The threshold T is determined based on the value of the coil distance L. When 0mm≤L<5mm, the threshold T is 1 / 2; when 5mm≤L≤10mm, the threshold T is 2 / 3.

5. The workpiece forming method based on controlling the coil conduction state according to claim 4, characterized in that, The time step Δt ranges from 10 to 1000 μs.

6. The workpiece forming method based on controlling the coil conduction state according to claim 3, 4, or 5, characterized in that, A capacitor power supply is used to power each turn of the drive coil group, and the discharge voltage of the capacitor power supply is 0.35-35kV.

7. The workpiece forming method based on controlling the coil conduction state according to claim 6, characterized in that, The capacitance of the capacitor power supply is 32-3200μF.

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