Pipe expansion method and device using double-loop magnetic concentrator

Abstract

The application relates to a pipe expanding method using a double-ring magnetic concentrator, which comprises the following steps: manufacturing a double-ring magnetic concentrator; placing an expanding coil, the double-ring magnetic concentrator and a pipe to be expanded from inside to outside on an expanding base, aligning the pipe to be expanded with the center of the expanding base and fixing the pipe; connecting the expanding coil to a pulse power supply, electrifying the expanding coil, controlling the discharge time of the pulse power supply and electromagnetically expanding the pipe to be expanded; judging whether the expanding effect of the pipe meets the forming specification of the pipe; if the expanding effect meets the forming specification, the process is ended; otherwise, the pipe is electromagnetically expanded again. The expanding method uses the bidirectional loading mode of the inner and outer walls of the double-ring magnetic concentrator, improves the axial uniformity of pipe expanding, and effectively inhibits the wall thickness reduction in the pipe expanding process.

Description

Technical Field

[0001] This invention belongs to the field of aerospace tube forming control, specifically relating to a tube bulging method and apparatus using a double-ring magnet collector. Background Technology

[0002] Technological innovations in electromagnetic forming are often marked by new drive coil structures that produce a more rational distribution of electromagnetic force.

[0003] The existing tube bulging system consists of a charging system, a discharge capacitor, a switch, a drive coil, and the tube. The charging system first charges the capacitor, then closes the switch. The energy stored in the capacitor is transferred to the drive coil in the form of pulsed current. The magnetic field generated by the coil itself and the induced eddy currents on the tube combine to generate the electromagnetic force that drives the tube bulging. However, the current drive coil loading system results in an uneven convex shape for the tube, and a significant reduction in the tube's wall thickness.

[0004] The invention patent CN103406418B, entitled "Radial and Axial Bidirectional Loading Electromagnetic Forming Method and Apparatus for Metal Tubes," provides a radial and axial bidirectional loading electromagnetic forming method and apparatus for metal tubes. It mainly includes an eddy current coil for generating induced eddy currents, a magnetic field coil for generating a radial magnetic field, and a power supply system for powering the eddy current coil and the magnetic field coil. This invention also provides a radial and axial bidirectional loading electromagnetic forming method for metal tubes, which can provide high-speed deformation experimental conditions for metal tubes under different load forms, offering a new experimental means for studying the high-speed deformation mechanism of materials. However, while this patent can provide bidirectional electromagnetic force loading for tubes, it requires a large number of coils, resulting in complex tooling and insufficient economic efficiency.

[0005] The invention patent CN110210116A, entitled "A Two-Dimensional Axisymmetric Simulation Model and Modeling Method for Electromagnetic Forming of Pipe Fittings with Magnets," provides a two-dimensional axisymmetric simulation model and modeling method suitable for the electromagnetic forming of pipe fittings with magnets. Compared with existing three-dimensional models, the simulation model and method provided by this invention have a faster calculation speed; compared with existing two-dimensional axisymmetric models, the simulation model and method provided by this invention are closer to physical reality and have higher calculation accuracy. However, this patent does not design a magnetic field converter to be suitable for applying bidirectional electromagnetic forces to the pipe fittings. Summary of the Invention

[0006] The technical problem of this invention is that the radial electromagnetic force provided by the forming coil in existing pipe forming methods is much greater than the axial electromagnetic force, resulting in a reduction in the wall thickness of the pipe after forming. Because the radial electromagnetic force is unevenly distributed along the axial direction of the pipe, the formed pipe exhibits an axially uneven convex shape.

[0007] The purpose of this invention is to address the aforementioned problems by providing a method and apparatus for tube bulging using a double-ring magnet collector. A double-ring magnet collector is placed between the bulging coil and the tube to be bulged, thereby altering the magnetic field distribution between them. The induced eddy currents generated on the inner wall of the double-ring magnet collector, in the opposite direction to the outer wall, reduce the radial electromagnetic force in the middle of the tube outside the magnet collector, resulting in better axial uniformity during tube forming. The total longitudinal length of the double-ring magnet collector is greater than the length of the tube to be bulged, increasing the ratio of axial to radial electromagnetic forces on the tube, promoting axial material flow, and suppressing wall thinning during tube bulging.

[0008] The technical solution of this invention is a tube bulging method using a double-ring magnet collector, comprising the following steps: Step 1: Construct a double-ring magnet; Step 2: Place the expansion coil, double-ring magnet collector, and tube to be expanded on the expansion base from the inside out, and align and fix the central axis of the expansion coil, double-ring magnet collector, and tube to be expanded with the center line of the expansion base. Step 3: Connect the expansion coil to the pulse power supply, energize the expansion coil, control the discharge time of the pulse power supply, and perform electromagnetic expansion of the tube to be expanded; Step 4: Determine whether the bulging effect of the pipe fitting meets the forming specifications of the pipe fitting. If it meets the forming specifications, the process ends; otherwise, proceed to step 3 to perform electromagnetic bulging on the pipe fitting again.

[0009] Preferably, before fabricating the double-ring magnet collector, an electromagnetic forming model of the workpiece, including the double-ring magnet collector, the drive coil, and the tube to be formed, is established using finite element analysis software. A pulse current is applied to the drive coil of the electromagnetic forming model of the workpiece to simulate the bulging effect of the tube. The shape and parameters of the double-ring magnet collector are adjusted, and the simulation experiment is repeated to achieve the best axial uniformity of the tube and the minimum reduction in tube wall thickness. The shape and parameters of the double-ring magnet collector are determined by simulation.

[0010] Preferably, in step 3, the discharge pulse width of the pulse power supply is 50~1000us.

[0011] Preferably, the difference between the inner diameter of the pipe to be formed and the outer diameter of the double-ring magnet collector is no more than 12 mm.

[0012] Preferably, the difference between the inner diameter of the double-ring magnet collector and the outer diameter of the expansion coil is no greater than 2 mm.

[0013] The convex double-ring magnet collector consists of an upper ring and a lower ring, both of which have outward protrusions. The distance between the lower ring and the upper ring is 6mm.

[0014] A stepped double-ring magnet collector, comprising an upper ring and a lower ring, both with stepped inner walls.

[0015] Compared with the prior art, the beneficial effects of the present invention include: 1) The bulging method of the present invention uses a combination of a double-ring magnet collector and a bulging coil to apply bidirectional electromagnetic force to the bulging tube, which improves the axial uniformity of the tube bulging and effectively suppresses the wall thickness reduction during the tube bulging process.

[0016] 2) The present invention uses the inner and outer wall structures of the magnet collector designed with different parameters to achieve electromagnetic force loading with different ratios of radial electromagnetic force and axial electromagnetic force, which can meet the needs of different pipe forming specifications.

[0017] 3) Improved service life of the drive coil. The double-ring magnet collector of the present invention withstands the electromagnetic force of the tube and the drive coil during the tube expansion process, which greatly reduces the electromagnetic force on the drive coil and thus extends the service life of the drive coil. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 This is a schematic diagram of the pipe forming device in Embodiment 1.

[0020] Figure 2 This is a schematic diagram of the induced current distribution of the double-ring magnet in Example 1 during the expansion of the tube.

[0021] Figure 3 This is a schematic diagram of the radial and axial electromagnetic forces acting on the pipe fitting during the bulging process of the pipe fitting in Example 1.

[0022] Figure 4 This is a schematic diagram of the pipe forming device in Embodiment 2.

[0023] Figure 5 This is a schematic diagram of the induced current distribution of the double-ring magnet in Example 2 during the tube expansion process.

[0024] Figure 6 This is a schematic diagram of the radial and axial electromagnetic forces acting on the pipe during the pipe bulging process in Example 2. Detailed Implementation

[0025] Example 1 In this embodiment, an electromagnetic forming model of a workpiece, including a double-ring magnet collector, a drive coil, and the tube to be formed, is established using finite element analysis software. A pulse current is applied to the drive coil of the electromagnetic forming model of the workpiece to simulate the bulging effect of the tube. The shape and parameters of the double-ring magnet collector are adjusted, and the simulation experiment is repeated to achieve the best axial uniformity of the tube and the minimum reduction in tube wall thickness. The shape and parameters of the double-ring magnet collector are determined by simulation.

[0026] The tube bulging method using a double-ring magnet collector includes the following steps: Step 1: Construct a double-ring magnet; Step 2: Place the expansion coil, double-ring magnet collector, and tube to be expanded on the expansion base from the inside out, and align and fix the central axis of the expansion coil, double-ring magnet collector, and tube to be expanded with the center line of the expansion base. Step 3: Connect the forming coil to the pulse power supply, energize the forming coil, control the discharge time of the pulse power supply, and perform electromagnetic forming of the tube to be formed; the discharge pulse width of the pulse power supply is 50~1000us.

[0027] Step 4: Determine whether the bulging effect of the pipe fitting meets the forming specifications of the pipe fitting. If it meets the forming specifications, the process ends; otherwise, proceed to step 3 to perform electromagnetic bulging on the pipe fitting again.

[0028] The length of the tube to be expanded in the embodiment is 80mm.

[0029] like Figure 1 As shown, the embodiment employs a convex double-ring magnet collector 1, comprising an upper ring 1a and a lower ring 1b. The outer wall 101 of the upper ring 1a has an outward protrusion, while the inner wall of the upper ring 1a is axially flat. The lower ring 1b has the same structure as the upper ring 1a. The distance between the upper ring 1a and the lower ring 1b is 6mm.

[0030] like Figure 1-3 As shown, the pipe forming device of this embodiment includes a forming base 4, a forming coil 2, a convex double-ring magnet collector 1, a top cover 5, and a pulse power supply 6. The forming base 4 has an annular forming area 401. The forming coil 2, the convex double-ring magnet collector 1, and the pipe to be formed 3 are placed from the inside out in the annular forming area 401 of the forming base. The central axes of the forming coil 2 and the convex double-ring magnet collector 1 are aligned with the center line of the forming base 4. The forming coil 2 is electrically connected to the pulse power supply 6. The top cover 5 presses the pipe to be formed 3. The upper ring 1a of the convex double-ring magnet collector 1 is fixedly connected to the top cover 5.

[0031] In this embodiment, symmetrical double-ring magnet collectors are located at both ends of the tube. The currents on the outer and inner walls of the double-ring magnet collectors are equal in magnitude but opposite in direction. Because the current direction on the inner wall of the double-ring magnet collector is opposite to the coil current direction, the current direction on the outer wall of the double-ring magnet collector is the same as the coil current direction. This causes the electromagnetic force on the tube to shift from the middle of the tube to the ends, weakening the radial electromagnetic force on the middle of the tube. Due to the end effect during the tube's expansion process, the symmetrical double-ring magnet collectors can effectively suppress the end effect, ensuring a uniform distribution of the radial electromagnetic force along the tube's axial direction. The outer wall of the double-ring magnet collector is embedded in the top cover, and the portion protruding above the tube provides axial electromagnetic force, effectively suppressing the thinning of the tube wall.

[0032] The convex double-ring magnet collector enhances the radial electromagnetic force at the pipe end, greatly improving the uniformity of pipe expansion, and effectively suppresses wall thinning at the end of the magnet collector. The introduction of the magnet collector protects the drive coil and extends the service life of the drive coil and itself.

[0033] Example 2 like Figure 4 As shown, the embodiment employs a stepped double-ring magnet collector, including an upper ring 1A and a lower ring 1B. The outer wall 101 of the upper ring 1A has an outward protrusion, and the inner wall of the upper ring 1B is stepped. The lower ring 1B has the same structure as the upper ring 1A. The distance between the upper ring 1A and the lower ring 1B is 6mm.

[0034] The tube bulging method using a double-ring magnet collector includes the following steps: Step 1: Construct a double-ring magnet; Step 2: Place the expansion coil, double-ring magnet collector, and tube to be expanded on the expansion base from the inside out, and align and fix the central axis of the expansion coil, double-ring magnet collector, and tube to be expanded with the center line of the expansion base. Step 3: Connect the expansion coil to the pulse power supply, energize the expansion coil, control the discharge time of the pulse power supply, and perform electromagnetic expansion of the tube to be expanded; Step 4: Determine whether the bulging effect of the pipe fitting meets the forming specifications of the pipe fitting. If it meets the forming specifications, the process ends; otherwise, proceed to step 3 to perform electromagnetic bulging on the pipe fitting again.

[0035] like Figure 4-6 As shown, the pipe forming device of this embodiment includes a forming base 4, a forming coil 2, a stepped double-ring magnet collector 1, a top cover 5, and a pulse power supply 6. The forming base 4 has an annular forming area 401. The forming coil 2, the stepped double-ring magnet collector 1, and the pipe to be formed 3 are placed from the inside out in the annular forming area 401 of the forming base. The central axes of the forming coil 2 and the convex double-ring magnet collector 1 are aligned with the center line of the forming base 4. The forming coil 2 is electrically connected to the pulse power supply 6. The top cover 5 presses the pipe to be formed 3. The upper ring 1A of the stepped double-ring magnet collector 1 is fixedly connected to the top cover 5.

[0036] In this embodiment, symmetrical stepped double-ring magnet collectors are located at both ends of the tube. The current magnitudes at the outer and inner walls are equal, but the directions are opposite. The current direction on the outer wall of the stepped double-ring magnet collector is the same as the coil current direction, causing the electromagnetic force on the tube to shift from the middle of the tube to the ends, thus weakening the radial electromagnetic force on the middle of the tube. The convex shape of the outer wall of the stepped double-ring magnet collector effectively suppresses the end effect of electromagnetic expansion of the tube, making the radial electromagnetic force evenly distributed along the axial direction of the tube. The portion of the magnet collector's outer wall embedded in the top cover, protruding above the tube, provides axial electromagnetic force, effectively suppressing the thinning of the tube wall.

[0037] The stepped double-ring magnet collector can concentrate the electromagnetic force of the pipe fitting at the end, and the convex shape of the outer wall of the magnet collector can concentrate the electromagnetic force, effectively suppressing the end effect in the electromagnetic expansion of the pipe fitting, and its end can effectively suppress the wall thickness reduction.

Claims

1. A method for bulging tubular fittings using a double-ring magnet collector, characterized in that, The double-ring magnet collector includes an upper ring and a lower ring with the same structure. The total longitudinal length of the double-ring magnet collector is greater than the length of the tube to be expanded. The inner walls of the upper ring and the lower ring are both stepped, and both the upper ring and the lower ring include outward protrusions. The tube bulging method includes the following steps: Step 1: Construct a double-ring magnet; Step 2: Place the expansion coil, double-ring magnet collector, and tube to be expanded on the expansion base from the inside out, and align and fix the central axis of the expansion coil, double-ring magnet collector, and tube to be expanded with the center line of the expansion base. Step 3: Connect the expansion coil to the pulse power supply, energize the expansion coil, control the discharge time of the pulse power supply, and perform electromagnetic expansion of the tube to be expanded; Step 4: Determine whether the bulging effect of the pipe fitting meets the forming specifications of the pipe fitting. If it meets the forming specifications, the process ends; otherwise, proceed to step 3 to perform electromagnetic bulging on the pipe fitting again.

2. The tube bulging method using a double-ring magnet collector according to claim 1, characterized in that, Before fabricating the double-ring magnet collector, an electromagnetic forming model of the workpiece, including the double-ring magnet collector, the expansion coil, and the tube to be expanded, was established using finite element analysis software. A pulse current was applied to the expansion coil of the electromagnetic forming model of the workpiece to simulate the expansion effect of the tube. The shape and parameters of the double-ring magnet collector were adjusted, and the simulation experiment was repeated to achieve the best axial uniformity of the tube and the minimum reduction in tube wall thickness. The shape and parameters of the double-ring magnet collector were determined by simulation.

3. The tube bulging method using a double-ring magnet collector according to claim 1 or 2, characterized in that, The difference between the inner diameter of the tube to be expanded and the outer diameter of the double-ring magnet should not exceed 12mm.

4. The tube bulging method using a double-ring magnet collector according to claim 3, characterized in that, The difference between the inner diameter of the double-ring magnet collector and the outer diameter of the expansion coil is no more than 2mm.

5. The tube bulging method using a double-ring magnet collector according to claim 4, characterized in that, In step 3, the discharge pulse width of the pulse power supply is 50~1000µs.

Images