Experimental method and experimental device for dynamic forming limit of pipe

Abstract

The invention discloses a pipe dynamic forming limit experiment method and experiment device, and relates to the technical field of pipe forming limit experiments, and the method comprises the following steps: S1, determining which strain path loading state the forming limit experiment is in, and selecting a mold; s2, the mold, the pipe and the spiral pipe coil are concentrically assembled from outside to inside; s3, discharging the coil of the spiral pipe, so that the deformation area of the pipe is freely expanded to a critical fracture state; s4, carrying out strain measurement on the critical fracture part; s5, the strain path loading state is changed, the steps are repeated, and forming limit experiments under different strain paths are completed; s6, establishing a pipe dynamic forming limit diagram; pipe bulging is achieved through discharging of the spiral pipe coil, pipe forming limit experiments are conducted, the experiment efficiency is improved, the experiment device is simplified, the discharging voltage is controllable, the energy utilization rate is high, parameter consistency is good, and the experiment result stability is high; and the dynamic forming limit diagram of the pipe can be obtained by changing the loading state of the strain path.

Description

Technical Field

[0001] The invention relates to the technical field of tube forming limit experiments, and in particular to a tube dynamic forming limit experiment method and an experiment device. Background Art

[0002] Metal pipe fittings with hollow structures are not only light in weight, but also have the advantages of high strength, high toughness, high shock absorption capacity, good forming performance and high material utilization rate. During use, they can meet the requirements of lightweight and toughening products, while reducing product weight, ensuring product strength, and can process products with complex shapes. They are widely used in aerospace, machinery, pressure instruments and other fields; since high-rate forming technology has been proven to improve the forming limit of lightweight and difficult-to-deform materials such as aluminum alloys, magnesium alloys, and titanium alloys, in recent years, in the field of high-end manufacturing, it is not uncommon to use high-rate forming technologies such as electromagnetic forming and electro-hydraulic forming to process thin-walled pipe fittings. Although the high strain rate significantly improves the forming quality of parts, the strain loading path in the deformation zone of the parts in actual production is relatively complex, and instability defects such as rupture are also prone to occur.

[0003] Constructing a forming limit diagram is the most effective and common method for evaluating the comprehensive forming performance of metal tubes. The forming limit experiment of tubes known to the applicant uses a method of causing the tube to rupture by hydraulic bulging. Due to the slow speed of hydraulic bulging, the forming limit diagram construction method is not suitable for the field of high-rate forming, and the entire experimental device is relatively complicated.

[0004] Therefore, people are in urgent need of a dynamic forming limit test method for pipes with high experimental efficiency. Summary of the invention

[0005] The purpose of the present invention is to provide a dynamic forming limit test method and experimental device for tubes, so as to solve the problems existing in the above-mentioned prior art, realize tube bulging by discharging a spiral tube coil, effectively improve the experimental efficiency, and obtain the dynamic forming limit diagram of the tube by changing the strain path loading state.

[0006] To achieve the above object, the present invention provides the following solution: The present invention provides a method for testing the dynamic forming limit of a tube, comprising the following steps:

[0007] S1: Determine the strain path loading state of the forming limit experiment, and select an open die formed by an opening on the annular structure or an open closed die formed by a hole on the annular structure;

[0008] S2: Assemble the selected mold, tube and spiral tube coil concentrically from outside to inside, with the outer surface of the tube close to the inner surface of the mold, and ensure that the gap between the coil and the tube is uniform;

[0009] S3: Setting the discharge voltage, the spiral tube coil discharges, and the deformation zone of the tube corresponding to the opening or hole position of the mold is freely bulged until a critical rupture occurs;

[0010] S4: strain measurement at the critical rupture point;

[0011] S5: changing the strain path loading state, repeating the above steps, and completing the forming limit test under different strain paths;

[0012] S6: Establish the dynamic forming limit diagram of the tube.

[0013] Preferably, in step S1, if the secondary strain ε2≤0, an open mold is selected, and if the secondary strain ε2>0, an open-hole closed mold is selected.

[0014] Preferably, before step S2, a finite element model of the mold, the tube and the spiral tube coil is established for simulation. If the strain state of the tube deformation zone in the finite element simulation result does not meet expectations, the finite element model is continuously optimized. If the strain state of the tube deformation zone meets expectations, the shape of the processed tube 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 deformation zone of the tube is changed so that the deformation zone of the tube is in an arbitrary strain path loading state from single tension to plane strain during dynamic deformation; if the secondary strain ε2>0, the tube length is increased and the shape of the mold opening is changed so that the deformation zone of the tube 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 tube in the processed deformation zone, and in step S4, a grid near the critical rupture point in the deformation zone of the tube is extracted for strain measurement.

[0017] Preferably, the grid is formed by electrochemical etching.

[0018] The present invention also provides a dynamic forming limit test device for pipes applied to the dynamic forming limit test method for pipes, comprising a mold, a pipe and a spiral tube coil, wherein the mold, the pipe and the spiral tube coil are coaxially arranged from outside to inside, the outer diameter of the pipe matches the inner diameter of the mold, a gap is arranged between the outer circumferential wall of the spiral tube coil and the inner circumferential wall of the pipe, and the mold is provided with an opening or hole for deformation of the pipe.

[0019] Preferably, the spiral tube coil is connected to an RLC oscillation circuit.

[0020] Preferably, the cross-section of the spiral tube coil is rectangular.

[0021] Preferably, the inner edges of the openings or holes of the mold are rounded.

[0022] Compared with the prior art, the present invention mainly achieves the following technical effects:

[0023] The tube forming limit experiment is carried out by discharging a spiral tube coil to realize tube bulging. Compared with hydraulic bulging, the tube bulging efficiency is improved, thereby improving the experimental efficiency. At the same time, the spiral tube coil discharge method simplifies the experimental device and reduces the cost. It has the advantages of controllable discharge voltage, high energy utilization rate, good parameter consistency and high stability of experimental results. It can carry out dynamic forming limit experiments more accurately and with high repeatability. On this basis, the dynamic forming limit diagram of the tube is obtained by changing the strain path loading state, which has guiding significance for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 It is an operation flow chart of the dynamic forming limit test method of the pipe in the embodiment of the present invention;

[0026] Figure 2 A cross-sectional view of a dynamic forming limit test device for a tube in an embodiment of the present invention;

[0027] Figure 3 It is a structural schematic diagram of a dynamic forming limit test device for a pipe under a uniaxial tensile strain path in an embodiment of the present invention;

[0028] Figure 4 It is a schematic structural diagram of a dynamic forming limit test device for a tube under a plane strain path in an embodiment of the present invention;

[0029] Figure 5 It is a structural schematic diagram of a dynamic forming limit test device for a pipe under a medium double tensile strain path according to an embodiment of the present invention;

[0030] Figure 6 It is a schematic structural diagram of an open-type mold in an embodiment of the present invention;

[0031] Figure 7 It is a schematic diagram of the structure of an open-hole closed mold in an embodiment of the present invention;

[0032] Figure 8 Schematic diagram of the structure of the spiral tube coil in the embodiment of the present invention;

[0033] Fig. 9 : is a diagram of the shape of the pipe under different strain loading paths in an embodiment of the present invention;

[0034] Among them, 1. mold; 2. pipe; 3. spiral tube coil; 4. RLC oscillation circuit; 5. deformation zone. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The purpose of the present invention is to provide a dynamic forming limit test method and experimental device for tubes, so as to solve the problems existing in the prior art, realize tube bulging by discharging a spiral tube coil, effectively improve the experimental efficiency, and obtain the dynamic forming limit diagram of the tube by changing the strain path loading state.

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Please refer to Figures 1 to 9 As shown, a dynamic forming limit test method for a tube is provided, comprising the following steps:

[0039] S1: Determine the strain path loading state of the forming limit experiment, that is, determine the expected strain path forming limit; select an open die formed by an opening on the annular structure or an open closed die formed by a hole on the annular structure;

[0040] S2: The selected mold 1, tube 2 and spiral tube coil 3 are assembled concentrically from outside to inside, the outer surface of the tube 2 is close to the inner surface of the mold 1, and the gap between the coil and the tube 2 is uniform, so that the tube 2 is bulged only at the opening or hole of the mold 1, and the force is uniform, ensuring the accuracy of the experimental data;

[0041] S3: setting the discharge voltage, the spiral tube coil 3 discharges, and the deformation zone 5 of the tube 2 corresponding to the opening or opening position of the mold 1 is freely bulged until a critical rupture state occurs;

[0042] S4: strain measurement at the critical rupture point;

[0043] S5: changing the strain path loading state, repeating the above steps, and completing the forming limit test under different strain paths;

[0044] S6: Establish a dynamic forming limit diagram for tube 2.

[0045] The tube 2 is expanded by discharging the spiral tube coil 3 to perform a forming limit test on the tube 2. Compared with hydraulic expansion, the expansion efficiency of the tube 2 is improved, thereby improving the experimental efficiency. At the same time, the discharge method of the spiral tube coil 3 simplifies the experimental device and reduces the cost. It has the advantages of controllable discharge voltage, high energy utilization rate, good parameter consistency and high stability of experimental results, and can perform dynamic forming limit experiments more accurately and repeatedly. On this basis, the dynamic forming limit diagram of the tube 2 is obtained by changing the strain path loading state, which has guiding significance for industrial production. In addition, the concentric assembly of the mold 1, the tube 2 and the spiral tube coil 3 makes the tube 2 easy to replace, and the material selection range of the tube 2 is effectively improved.

[0046] In step S1 , the mold 1 is selected according to the following method: if the secondary strain ε2≤0, an open mold is selected; if the secondary strain ε2>0, an open-hole closed mold is selected.

[0047] In order to improve the implementation effect and reduce material waste, before step S2, a finite element model of the mold 1, the tube 2 and the spiral tube coil 3 is established for simulation. If the strain state of the deformation zone 5 of the tube 2 in the finite element simulation result does not meet expectations, the finite element model is continuously optimized. If the strain state of the deformation zone 5 of the tube 2 meets expectations, the shape of the deformation zone 5 of the processed tube 2 and the shape of the mold 1 are consistent with the finite element model.

[0048] When the finite element model is optimized, if the secondary strain ε2≤0, the deformation zone 5 of the tube 2 is placed in an arbitrary strain path loading state from single tension to plane strain during dynamic deformation by changing the aspect ratio of the deformation zone 5; if the secondary strain ε2>0, in order to prevent the circumferential feeding of the deformation zone 5, the length of the tube 2 needs to be increased, and the shape of the opening of the mold 1 needs to be changed (mainly by changing the major-minor axis ratio of the hole), so that the deformation zone 5 of the tube 2 is placed in an arbitrary double-tension strain path loading state during dynamic deformation.

[0049] In order to facilitate the zoning work and improve the accuracy of the measurement data, before step S2, a grid is printed on the surface of the tube 2 in the processed deformation zone 5. In step S4, the grid near the critical rupture of the deformation zone 5 of the tube 2 is extracted for strain measurement.

[0050] In this embodiment, the grid is formed by electrochemical corrosion. In other embodiments, other methods for forming the grid may also be used.

[0051] The present invention also provides a dynamic forming limit test device for a tube, which can be applied to the above-mentioned dynamic forming limit test method for a tube, comprising a mold 1, a tube 2 and a spiral tube coil 3. The mold 1, the tube 2 and the spiral tube coil 3 are coaxially arranged from outside to inside, the outer diameter of the tube 2 matches the inner diameter of the mold 1, a gap is arranged between the outer circumferential wall of the spiral tube coil 3 and the inner circumferential wall of the tube 2, and an opening or a hole is arranged on the mold 1 for the tube 2 to deform. Specifically, two molds 1 can be arranged, one mold 1 is an open mold formed by an opening on an annular structure, and the other mold 1 is an open closed mold formed by an opening on an annular structure. The position of the tube 2 corresponding to the opening or hole of the mold 1 is the deformation zone 5, and the other positions are non-deformation zones.

[0052] In this embodiment, the spiral tube coil 3 is connected to the RLC oscillation circuit 4, and the spiral tube coil 3 is passed with alternating current. The principle of the dynamic forming limit experimental device of the tube 2 is: the spiral tube coil 3 releases the pulse current that is attenuated by oscillation, and the current excites a pulse strong magnetic field around the spiral tube coil 3, thereby generating an induced 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 tube coil 3; since the magnetic lines of force have the characteristic of expansion, the tube wall of the tube 2 is subjected to a magnetic field force of huge amplitude, and the non-deformation zone of the tube 2 is in close contact with the inner surface of the mold 1 and does not move. The deformation zone 5 of the tube 2 is not constrained by the mold 1, and will be driven by the magnetic field force to undergo plastic deformation and move at high speed, and finally rupture, so that the forming limit of the tube 2 under different strain path loadings can be obtained.

[0053] In this embodiment, the cross section of the spiral tube coil 3 is rectangular, the winding process is simpler, and it is easy to install and maintain; in other embodiments, the cross section of the spiral tube 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 of the internal tube 2.

[0055] Combination Figure 3 The implementation method of the dynamic forming limit test method of the tube under the single tensile strain path is specifically described. The tube 2 used in this implementation method is a 5A06 aluminum alloy tube with a structural dimension of 93mm (outer diameter) × 90mm (length) × 1.5mm (wall thickness). An open mold is used, the material is 45# steel, the structural dimension is 93 (inner diameter) × 90mm (length) × 30mm (wall thickness), the fillet at the opening is R10, and the spiral tube coil 3 is wound by a 5mm×7mm rectangular cross-section copper wire with a total of 9 turns. The effective length of the working interval of the spiral tube coil 3 is about 55mm.

[0056] The dynamic forming limit test method for tubes includes the following steps:

[0057] (1) Establishing a finite element model of the mold 1, the tube 2 and the spiral tube coil 3, and changing the aspect ratio of the deformation zone 5 of the tube 2 so that the tube 2 satisfies the single tensile strain path loading state during dynamic deformation;

[0058] (2) Based on the finite element simulation optimization results, it is judged that when the aspect ratio of the deformation zone 5 of the tube 2 is 7 and the width dimension is 15 mm, the single tensile strain path loading state is met;

[0059] (3) Processing the deformation zone 5 of the pipe 2 to be consistent with the finite element model;

[0060] (4) using electrochemical corrosion to print a grid on the surface of the tube 2 in the processed deformation zone 5;

[0061] (5) The mold 1, the tube 2 and the spiral tube coil 3 are assembled concentrically to ensure the coaxiality of the three. The non-deformed area of ​​the tube 2 is close to the inner surface of the mold 1. At the same time, the gap between the coil and the tube 2 is uniform and the gap is 2 mm.

[0062] (6) The discharge voltage is set to 8 kV, and the spiral tube coil 3 is used for discharge, so that the deformation zone 5 of the tube 2 is freely expanded to a critical fracture state;

[0063] (7) The mesh near the rupture of the deformation zone 5 of the tube 2 is extracted for strain measurement, and the forming limit diagram under the single tensile strain path loading condition is established.

[0064] Combination Figure 5 The implementation method of the dynamic forming limit test method of the tube under the equal double tensile strain path is specifically described. The tube 2 used in this implementation method is a 5A06 aluminum alloy tube with a structural dimension of 93mm (outer diameter) × 140mm (length) × 1.5mm (wall thickness). An open-hole closed mold is adopted. The material is 45# steel, and the structural dimension is 93 (inner diameter) × 90mm (length) × 30mm (wall thickness). The spiral tube coil 3 is wound by a 5mm×7mm rectangular cross-section copper wire with a total of 9 turns. The effective length of the working interval of the spiral tube coil 3 is about 55mm.

[0065] The present invention provides a method for testing the dynamic forming limit of a pipe, comprising the following steps:

[0066] (1) Establishing a finite element model of the mold 1, the tube 2 and the spiral tube coil 3, and changing the opening shape of the closed mold 1 so that the tube 2 satisfies the equal double tensile strain path state during dynamic deformation;

[0067] (2) According to the finite element simulation optimization results, it is judged that when the length-short axis ratio of the opening of the closed mold 1 is 1, the hole diameter is 50 mm, and the fillet of the opening is R10, the equal double tensile strain path loading state is met;

[0068] (3) machining the opening shape of the closed mold 1 to be consistent with the finite element model;

[0069] (4) Printing a grid on the surface of the tube 2 by electrochemical etching;

[0070] (5) The mold 1, the tube 2 and the spiral tube coil 3 are assembled concentrically to ensure the coaxiality of the three. The outer surface of the tube 2 is close to the inner surface of the mold 1. At the same time, the gap between the coil and the tube 2 is uniform, and the gap is 2 mm;

[0071] (6) The discharge voltage is set to 10 kV, and the spiral tube coil 3 is used for discharge, so that the deformation zone 5 of the tube 2 is freely expanded to a critical fracture state;

[0072] (7) The mesh near the rupture of the deformation zone 5 of the tube 2 is extracted for strain measurement, and the forming limit diagram under the equal double tensile strain path loading condition is established.

[0073] Adaptive changes made according to actual needs are all within the protection scope of the present invention.

[0074] It should be noted that it is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any reference numerals in the claims should not be regarded as limiting the claims involved.

[0075] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A dynamic forming limit test method for a tube, characterized in that: The following steps are involved: S1: Determine the strain path loading state of the forming limit experiment, and select an open die formed by an opening on the annular structure or an open closed die formed by a hole on the annular structure; S2: Assemble the selected mold, tube and spiral tube coil concentrically from outside to inside, with the outer surface of the tube close to the inner surface of the mold, and ensure that the gap between the coil and the tube is uniform; S3: Setting the discharge voltage, the spiral tube coil discharges, and the deformation zone of the tube corresponding to the opening or hole position of the mold is freely bulged until a critical rupture occurs; S4: strain measurement at the critical rupture point; S5: changing the strain path loading state, repeating the above steps S1-S4, and completing the forming limit test under different strain paths; S6: Establish the dynamic forming limit diagram of the tube.

2. The dynamic forming limit test method for pipes according to claim 1, characterized in that: In step S1, if the secondary strain ε2≤0, an open mold is selected, and if the secondary strain ε2>0, an open-hole closed mold is selected.

3. The dynamic forming limit test method for tubes according to claim 2, characterized in that: Before step S2, a finite element model of the mold, the tube and the spiral tube coil is established for simulation. If the strain state of the tube deformation zone in the finite element simulation result does not meet expectations, the finite element model is continuously optimized. If the strain state of the tube deformation zone meets expectations, the shape of the processed tube deformation zone and the shape of the mold are consistent with the finite element model.

4. The dynamic forming limit test method for tubes according to claim 3, characterized in that: If the secondary strain ε2≤0, the deformation zone of the tube is placed in any strain path loading state from single tension to plane strain during dynamic deformation by changing the aspect ratio of the deformation zone of the tube; if the secondary strain ε2>0, the tube length is increased and the shape of the mold opening is changed so that the deformation zone of the tube is placed in any double tension strain path loading state during dynamic deformation.

5. The dynamic forming limit test method for tubes 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, a grid near the critical rupture point in the deformation zone of the pipe is extracted for strain measurement.

6. The dynamic forming limit test method for tubes according to claim 5, characterized in that: The grid is formed by electrochemical etching.

7. A dynamic forming limit test device for pipes, characterized in that: The method for testing the dynamic forming limit of a tube as claimed in any one of claims 1 to 6 comprises a die, a tube and a spiral tube coil, wherein the die, the tube and the spiral tube coil are coaxially arranged from outside to inside, the outer diameter of the tube matches the inner diameter of the die, a gap is arranged between the outer circumferential wall of the spiral tube coil and the inner circumferential wall of the tube, and the die is provided with an opening or hole for deformation of the tube.

8. The dynamic forming limit test device for tubes according to claim 7, characterized in that: The solenoid coil is connected to an RLC oscillation circuit.

9. The tube dynamic forming limit test device according to claim 7, characterized in that: The cross section of the spiral tube coil is rectangular.

10. The tube dynamic forming limit test device according to claim 7, characterized in that: The inner edge of the opening or hole of the mold is rounded.

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