A pipe dynamic forming limit experiment method and experiment device
The tube bulging is achieved by discharging a spiral coil, which solves the problem of slow hydraulic bulging speed, simplifies the experimental setup, and improves the efficiency and accuracy of tube forming limit tests, making it suitable for high-speed forming applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2025-02-20
- Publication Date
- 2026-07-21
AI Technical Summary
In existing technologies, hydraulic bulging is slow, resulting in low efficiency of tube forming limit tests. Furthermore, the test equipment is complex and not suitable for high-speed forming applications, and is prone to instability defects such as cracking.
The tube bulging method is adopted by using spiral tube coil discharge. By changing the strain path loading state, a dynamic forming limit diagram of the tube is established, which simplifies the experimental setup and improves efficiency.
It improves the efficiency of pipe bulging, simplifies the experimental setup, reduces costs, and provides high stability, high energy utilization, and good parameter consistency in experimental results. It can accurately and repeatedly conduct dynamic forming limit experiments.
Smart Images
Figure CN119985051B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of pipe forming limit testing technology, and in particular to a method and apparatus for dynamic forming limit testing of pipes. Background Technology
[0002] Hollow metal tubing is not only lightweight but also boasts advantages such as high strength, high toughness, high shock absorption, good formability, and high material utilization. During use, it can meet the requirements of both lightweighting and strength enhancement, reducing product weight while maintaining strength. It can also process products with complex shapes and is widely used in aerospace, machinery, and pressure instruments. Since high-speed forming technology has been proven to improve the forming limits of lightweight, difficult-to-deform materials such as aluminum alloys, magnesium alloys, and titanium alloys, in recent years, the use of high-speed forming technologies such as electromagnetic forming and electro-hydraulic forming to process thin-walled tubing has become increasingly common in high-end manufacturing. Although high strain rates significantly improve the forming quality of parts, the complex strain loading paths in the deformation zone during actual production can easily lead to instability defects such as cracking.
[0003] Constructing a forming limit diagram is the most effective and common method for evaluating the overall forming performance of metal tubes. The forming limit test known to the applicant uses hydraulic bulging to cause the tube to break. Since the hydraulic bulging speed is relatively slow, the forming limit diagram construction method is not suitable for high-rate forming fields, and the entire experimental setup is relatively complex.
[0004] Therefore, there is an urgent need for a high-efficiency experimental method for dynamic forming limit testing of pipes. Summary of the Invention
[0005] The purpose of this invention is to provide a method and apparatus for dynamic forming limit testing of pipes, in order to solve the problems existing in the prior art. The pipe bulging is achieved by discharging a spiral coil, which effectively improves the experimental efficiency. Furthermore, the dynamic forming limit diagram of the pipe can be obtained by changing the strain path loading state.
[0006] To achieve the above objectives, the present invention provides the following solution: The present invention provides a method for dynamic forming limit testing of pipes, comprising the following steps:
[0007] S1: Determine the strain path loading state of the forming limit test and select either an open mold formed by an opening on a ring structure or an open-hole closed mold formed by a hole on a ring structure.
[0008] S2: Assemble the selected mold, tubing and spiral coil concentrically from the outside to the inside, with the outer surface of the tubing tightly against the inner surface of the mold, while ensuring that the gap between the coil and the tubing is uniform.
[0009] S3: Set the discharge voltage, discharge the spiral tube coil, and allow the deformation zone of the tube corresponding to the opening or orifice of the mold to expand freely until it reaches the critical rupture state.
[0010] S4: Perform strain measurement at the critical rupture point;
[0011] S5: Change the strain path loading state and repeat the above steps to complete the forming limit test under different strain paths;
[0012] S6: Establish the limit diagram for dynamic forming of pipes.
[0013] Preferably, in step S1, if the secondary strain ε2≤0, an open mold is selected; if the secondary strain ε2>0, a closed mold with an opening is selected.
[0014] Preferably, before step S2, a finite element model of the mold, pipe and spiral coil is established for simulation. If the strain state of the pipe deformation zone in the finite element simulation results does not meet expectations, the finite element model is further optimized. If the strain state of the pipe deformation zone meets expectations, the shape of the processed pipe deformation zone and the shape of the mold are consistent with the finite element model.
[0015] Preferably, if the secondary strain ε2≤0, the aspect ratio of the pipe deformation zone is changed so that the pipe deformation zone is in an arbitrary strain path loading state from single tension to plane strain during dynamic deformation; if the secondary strain ε2>0, the pipe length is increased and the mold opening shape is changed so that the pipe deformation zone is in an arbitrary double tension strain path loading state during dynamic deformation.
[0016] Preferably, before step S2, a grid is printed on the surface of the pipe in the processed deformation zone, and in step S4, the grid near the critical rupture point of the pipe deformation zone is extracted for strain measurement.
[0017] Preferably, the mesh is formed by electrochemical corrosion.
[0018] The present invention also provides a dynamic forming limit test device for pipes, which is applied to the dynamic forming limit test method of pipes, including a mold, a pipe and a spiral coil. The mold, the pipe and the spiral coil are coaxially arranged from the outside to the inside. The outer diameter of the pipe matches the inner diameter of the mold. A gap is provided between the outer peripheral wall of the spiral coil and the inner peripheral wall of the pipe. The mold is provided with an opening or hole for the deformation of the pipe.
[0019] Preferably, the helical coil is connected to an RLC oscillation circuit.
[0020] Preferably, the cross-section of the helical coil is rectangular.
[0021] Preferably, the inner edge of the opening or aperture of the mold is rounded.
[0022] The present invention achieves the following main technical effects compared to the prior art:
[0023] The tube forming limit test is conducted by using spiral coil discharge to achieve tube bulging. Compared with hydraulic bulging, this method improves the tube bulging efficiency and thus the experimental efficiency. At the same time, the spiral coil discharge method simplifies the experimental setup, reduces costs, and has the advantages of controllable discharge voltage, high energy utilization, good parameter consistency, and high experimental result stability. It can conduct dynamic forming limit tests more accurately and with higher repeatability. Based on this, the dynamic forming limit diagram of the tube can be obtained by changing the strain path and loading state, which has guiding significance for industrial production. Attached Figure Description
[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0025] Figure 1 This is a flowchart illustrating the operation of the pipe dynamic forming limit test method in an embodiment of the present invention.
[0026] Figure 2 This is a cross-sectional view of the pipe dynamic forming limit test device in an embodiment of the present invention;
[0027] Figure 3 This is a schematic diagram of the structure of the tube dynamic forming limit test device under uniaxial tensile strain path in an embodiment of the present invention;
[0028] Figure 4 This is a schematic diagram of the structure of the dynamic forming limit test device for tubular materials under plane strain path in an embodiment of the present invention;
[0029] Figure 5 This is a schematic diagram of the structure of the tube dynamic forming limit test device under the equal bitensile strain path in an embodiment of the present invention;
[0030] Figure 6 This is a schematic diagram of the structure of the open-type mold in an embodiment of the present invention;
[0031] Figure 7 This is a schematic diagram of the structure of the open-type closed mold in an embodiment of the present invention;
[0032] Figure 8 This is a schematic diagram of the structure of the helical coil in an embodiment of the present invention;
[0033] Figure 9 These are diagrams showing the pipe shape under different strain loading paths in embodiments of the present invention;
[0034] Among them, 1. mold; 2. pipe; 3. spiral coil; 4. RLC oscillation circuit; 5. deformation zone. Detailed Implementation
[0035] 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.
[0036] The purpose of this invention is to provide a method and apparatus for dynamic forming limit testing of pipes to solve the problems existing in the prior art. The pipe bulging is achieved by discharging a spiral coil, which effectively improves the experimental efficiency. Furthermore, the dynamic forming limit diagram of the pipe can be obtained by changing the strain path loading state.
[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0038] Please refer to the following: Figures 1-9 As shown, a method for dynamic forming limit testing of pipes is provided, including the following steps:
[0039] S1: Determine the strain path loading state of the forming limit test, that is, determine the strain path forming limit to be obtained; select an open mold formed by an opening on a ring structure or an open-hole closed mold formed by a hole on a ring structure.
[0040] S2: Assemble the selected mold 1, tube 2 and spiral coil 3 concentrically from the outside to the inside. The outer surface of tube 2 is in close contact with the inner surface of mold 1. At the same time, ensure that the gap between the coil and tube 2 is uniform, so that tube 2 only expands at the opening or hole of mold 1 and the force is uniform, ensuring the accuracy of experimental data.
[0041] S3: Set the discharge voltage, discharge the spiral coil 3, and allow the deformation zone 5 of the tube 2 corresponding to the opening or hole position of the mold 1 to freely expand until it reaches the critical rupture state.
[0042] S4: Perform strain measurement at the critical rupture point;
[0043] S5: Change the strain path loading state and repeat the above steps to complete the forming limit test under different strain paths;
[0044] S6: Establish the dynamic forming limit diagram of pipe 2.
[0045] The forming limit test of tube 2 is carried out by discharging the spiral coil 3 to achieve tube 2 bulging. Compared with hydraulic bulging, the forming efficiency of tube 2 is improved, thereby improving the experimental efficiency. At the same time, the discharge method of spiral coil 3 simplifies the experimental device, reduces costs, and has the advantages of controllable discharge voltage, high energy utilization, good parameter consistency, and high experimental result stability. It can conduct dynamic forming limit tests more accurately and with higher repeatability. On this basis, the dynamic forming limit diagram of tube 2 is obtained by changing the strain path loading state, which has guiding significance for industrial production. In addition, the concentric assembly of mold 1, tube 2 and spiral coil 3 makes tube 2 easy to replace and effectively expands the selection range of tube 2 materials.
[0046] In step S1, the selection of mold 1 is based on the following method: if the secondary strain ε2≤0, then an open mold is selected; if the secondary strain ε2>0, then an open-hole closed mold is selected.
[0047] To improve the implementation effect and reduce material waste, before step S2, a finite element model of mold 1, pipe 2 and spiral coil 3 is established for simulation. If the strain state of the deformation zone 5 of pipe 2 does not meet the expectations in the finite element simulation results, the finite element model is further optimized. If the strain state of the deformation zone 5 of pipe 2 meets the expectations, the shape of the deformation zone 5 of pipe 2 and the shape of mold 1 are consistent with the finite element model.
[0048] During finite element model optimization, if the secondary strain ε2≤0, the aspect ratio of the deformation zone 5 of pipe 2 is changed so that the deformation zone 5 of pipe 2 is in an arbitrary strain path loading state from single tension to plane strain during dynamic deformation; if the secondary strain ε2>0, in order to hinder the circumferential feeding of the deformation zone 5, the length of pipe 2 needs to be increased and the opening shape of mold 1 needs to be changed (mainly changing the length-to-short axis ratio of the hole) so that the deformation zone 5 of pipe 2 is in an arbitrary double tension strain path loading state during dynamic deformation.
[0049] To facilitate zoning and improve the accuracy of measurement data, a grid is printed on the surface of the pipe 2 in the pre-processed deformation zone 5 before step S2. In step S4, the grid near the critical rupture point of the deformation zone 5 of the pipe 2 is extracted for strain measurement.
[0050] In this embodiment, the mesh is formed by electrochemical corrosion. In other embodiments, other methods for forming meshes may also be used.
[0051] This invention also provides a dynamic forming limit test device for pipes, which can be applied to the above-mentioned dynamic forming limit test method for pipes. It includes a mold 1, a pipe 2, and a spiral coil 3. The mold 1, the pipe 2, and the spiral coil 3 are coaxially arranged from the outside to the inside. The outer diameter of the pipe 2 matches the inner diameter of the mold 1. A gap is provided between the outer peripheral wall of the spiral coil 3 and the inner peripheral wall of the pipe 2. The mold 1 is provided with an opening or hole for the deformation of the pipe 2. Specifically, two molds 1 can be provided. One mold 1 is an open mold formed by an opening on a ring structure, and the other mold 1 is an open-hole closed mold formed by an opening on a ring structure. The position of the pipe 2 corresponding to the opening or hole of the mold 1 is the deformation zone 5, and other positions are non-deformation zones.
[0052] In this embodiment, the spiral coil 3 is connected to an RLC oscillation circuit 4, and the spiral coil 3 is energized with alternating current. The principle of the dynamic forming limit test device for the tube 2 is as follows: the pulse current that is attenuated by oscillation is released by the spiral coil 3. The current excites a strong pulse magnetic field around the spiral coil 3, thereby inducing a current on the surface of the tube 2. According to Lenz's law, the magnetic lines of force are constrained in the gap between the surface of the target part and the spiral coil 3. Due to the expansion characteristic of the magnetic lines of force, the tube wall of the tube 2 is subjected to a magnetic force with a huge amplitude. The non-deformable area of the tube 2 does not move because it is in close contact with the inner surface of the mold 1. The deformable area 5 of the tube 2 is not constrained by the mold 1 and will be driven by the magnetic force to undergo plastic deformation and move at high speed, eventually resulting in rupture. Thus, the forming limit of the tube 2 under different strain path loading can be obtained.
[0053] In this embodiment, the cross-section of the helical coil 3 is rectangular, which simplifies the winding process and makes it easier to install and maintain. In other embodiments, the cross-section of the helical coil 3 can also be other shapes, such as circular.
[0054] In this embodiment, the inner edge of the opening or hole of the mold 1 is rounded to prevent the sharp inner edge from affecting the expansion of the tube 2 during the expansion process.
[0055] Combination Figure 3 This document describes the implementation method of the dynamic forming limit test method for tubular materials under a single tensile strain path. The tubular material 2 used in this implementation method is a 5A06 aluminum alloy cylinder with structural dimensions of 93mm (outer diameter) × 90mm (length) × 1.5mm (wall thickness). An open mold is used, made of 45# steel with structural dimensions of 93 (inner diameter) × 90mm (length) × 30mm (wall thickness). The fillet radius at the opening is R10. The spiral coil 3 is made of copper wire with a rectangular cross-section of 5mm × 7mm, wound with a total of 9 turns. The effective length of the working range of the spiral coil 3 is approximately 55mm.
[0056] The dynamic forming limit test method for pipes includes the following steps:
[0057] (1) Establish a finite element model of mold 1, pipe 2 and spiral coil 3. By changing the aspect ratio of the deformation zone 5 of pipe 2, pipe 2 can meet the single tensile strain path loading state during dynamic deformation.
[0058] (2) Based on the finite element simulation optimization results, it is determined that when the length-to-width ratio of the deformation zone 5 of pipe 2 is 7 and the width is 15mm, it meets the single tensile strain path loading state.
[0059] (3) The deformation zone 5 of the pipe 2 is machined to be consistent with the finite element model;
[0060] (4) Electrochemical etching is used to print a grid on the surface of the pipe 2 in the processed deformation zone 5;
[0061] (5) Assemble the mold 1, tube 2 and spiral coil 3 concentrically to ensure the coaxiality of the three. The non-deformation area of tube 2 is in close contact with the inner surface of mold 1. At the same time, ensure that the gap between the coil and tube 2 is uniform and the gap is 2mm.
[0062] (6) Set the discharge voltage to 8kV and use the spiral tube coil 3 to discharge, so that the deformation zone 5 of the tube 2 can freely expand until it reaches the critical rupture state;
[0063] (7) Extract the mesh near the fracture point of the deformation zone 5 of the pipe 2 for strain measurement, and establish the forming limit diagram under the single tensile strain path loading condition.
[0064] Combination Figure 5 The specific implementation method of the dynamic forming limit test method of the tube under the equal bitensile strain path is described. The tube 2 used in this implementation method is a 5A06 aluminum alloy cylinder with structural dimensions of 93mm (outer diameter) × 140mm (length) × 1.5mm (wall thickness). An open-type closed mold is used, and the material is 45# steel with structural dimensions of 93 (inner diameter) × 90mm (length) × 30mm (wall thickness). The spiral tube coil 3 is made of copper wire with a rectangular cross section of 5mm × 7mm, with a total of 9 turns. The effective length of the working range of the spiral tube coil 3 is about 55mm.
[0065] The method for dynamic forming limit test of pipes provided by this invention includes the following steps:
[0066] (1) Establish finite element models of mold 1, pipe 2 and spiral coil 3. By changing the opening shape of the closed mold 1, the pipe 2 can satisfy the equal bitensile strain path state during dynamic deformation.
[0067] (2) Based on the finite element simulation optimization results, it is determined that when the ratio of the major axis to the minor axis of the opening of the closed mold 1 is 1, the diameter of the opening is 50mm, and the fillet at the opening is R10, the loading state of the equal double tensile strain path is satisfied.
[0068] (3) The shape of the opening of the closed mold 1 is machined to be consistent with the finite element model;
[0069] (4) Electrochemical etching is used to print a grid on the surface of pipe 2;
[0070] (5) Assemble the mold 1, tube 2 and spiral coil 3 concentrically to ensure the coaxiality of the three. The outer surface of tube 2 is in close contact with the inner surface of mold 1. At the same time, ensure that the gap between the coil and tube 2 is uniform and the gap is 2mm.
[0071] (6) Set the discharge voltage to 10kV and use the spiral tube coil 3 to discharge, so that the deformation zone 5 of the tube 2 can freely expand until it reaches the critical rupture state;
[0072] (7) Extract the mesh near the fracture point of the deformation zone 5 of the pipe 2 for strain measurement, and establish the forming limit diagram under the condition of equal double tensile strain path loading.
[0073] Any adaptive changes made according to actual needs are within the scope of protection of this invention.
[0074] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0075] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.
Claims
1. A method for dynamic forming limit testing of pipes, characterized in that, Includes the following steps: S1: Determine the strain path loading state of the forming limit test and select either an open mold formed by an opening on the annular structure or an open-hole closed mold formed by an opening on the annular structure, wherein the opening completely cuts off the annular structure; if the secondary strain ε2≤0, then the open mold is selected, and if the secondary strain ε2>0, then the open-hole closed mold is selected. S2: Assemble the selected mold, tubing and spiral coil concentrically from the outside to the inside, with the outer surface of the tubing tightly against the inner surface of the mold, while ensuring that the gap between the coil and the tubing is uniform. S3: Set the discharge voltage, discharge the spiral coil, and allow the deformation zone of the tube corresponding to the opening or orifice of the mold to freely expand until it reaches a critical rupture state. Specifically, the spiral coil releases an oscillating and decaying pulse current, which generates a strong pulsed magnetic field around the spiral coil, thereby inducing a current on the surface of the tube. The magnetic lines of force are constrained within the gap between the target surface and the spiral coil. Due to the expansion characteristic of the magnetic lines of force, the tube wall is subjected to magnetic force. The non-deformable area of the tube does not move because it is in close contact with the inner surface of the mold. The deformable area of the tube is not constrained by the mold and will undergo plastic deformation driven by the magnetic force. S4: Perform strain measurement at the critical rupture point; S5: Change the strain path loading state and repeat the above steps S1-S4 to complete the forming limit test under different strain paths. S6: Establish the limit diagram for dynamic forming of pipes.
2. The method for dynamic forming limit test of pipes according to claim 1, characterized in that, Before step S2, finite element models of the mold, pipe and spiral coil are established for simulation. If the strain state of the pipe deformation zone in the finite element simulation results does not meet expectations, the finite element model is further optimized. If the strain state of the pipe deformation zone meets expectations, the shape of the pipe deformation zone and the shape of the mold are processed to be consistent with the finite element model.
3. The method for dynamic forming limit test of pipes according to claim 2, characterized in that, If the secondary strain ε2≤0, by changing the aspect ratio of the pipe deformation zone, the pipe deformation zone is placed in an arbitrary strain path loading state from single tension to plane strain during dynamic deformation; if the secondary strain ε2>0, the pipe length is increased and the mold opening shape is changed, so that the pipe deformation zone is placed in an arbitrary double tension strain path loading state during dynamic deformation.
4. The method for dynamic forming limit test of pipes according to claim 1, characterized in that, Before step S2, a grid is printed on the surface of the pipe in the processed deformation zone. In step S4, the grid near the critical rupture point of the pipe deformation zone is extracted for strain measurement.
5. The method for dynamic forming limit test of pipes according to claim 4, characterized in that, The mesh is formed by electrochemical corrosion.
6. A dynamic forming limit test device for pipes, characterized in that, The method for dynamic forming limit test of tubing as described in any one of claims 1-5 includes a mold, a tubing, and a spiral coil. The mold, the tubing, and the spiral coil are coaxially arranged from the outside to the inside. The outer diameter of the tubing matches the inner diameter of the mold. A gap is provided between the outer peripheral wall of the spiral coil and the inner peripheral wall of the tubing. The mold is provided with an opening or aperture for the deformation of the tubing.
7. The pipe dynamic forming limit test apparatus according to claim 6, characterized in that, The spiral coil is connected to an RLC oscillation circuit.
8. The pipe dynamic forming limit test apparatus according to claim 6, characterized in that, The cross-section of the helical coil is rectangular.
9. The pipe dynamic forming limit test apparatus according to claim 6, characterized in that, The inner edge of the opening or aperture of the mold is rounded.