Bimetallic tube electro-hydraulic composite forming device and forming method

Abstract

The present invention discloses a bimetallic tube electro-hydraulic composite forming device and forming method, relating to the field of bimetallic tube composite technology. The forming device includes an upper plug, a lower plug, electrodes, and a discharge device. The top and bottom of the bimetallic tube are sealed by the upper plug and the lower plug, respectively. Electrodes are respectively inserted into the upper plug and the lower plug, and a metal wire is connected between the two electrodes. The inner tube of the bimetallic tube is filled with a liquid medium, and the ends of the two electrodes and the metal wire are immersed in the liquid medium. The other ends of the two electrodes are respectively connected to the positive and negative poles of the discharge device. The present invention proposes a bimetallic tube electro-hydraulic composite process device and process method, and proposes material matching criteria for the electro-hydraulic composite process, so as to confirm whether the tube blanks of two materials can be composited through this process before the experiment, thereby reducing trial and error costs.

Description

Technical Field

[0001] The present invention relates to the technical field of bimetallic tube composite technology, in particular to a bimetallic tube electro-hydraulic composite forming device and a forming method. Background Art

[0002] Bimetallic pipes are constructed from two different metal tubes, tightly bonded together using a specific bonding technique. These pipes combine the best properties of both metals, leveraging their superior performance. They offer not only high strength but also excellent high-temperature and corrosion resistance. This extends the pipe's service life, conserves material, and reduces production costs. Consequently, bimetallic pipes are widely used in fields such as petrochemicals, marine development, mechanical engineering, and aerospace. Bimetallic pipes can be categorized as lined or clad, depending on the relative position of the base and cladding tubes. Lined composite pipes are currently primarily produced using quasi-static bonding processes, such as hydraulic bonding. However, the hydraulic expansion process for thin-layer bimetallic tubes requires high pressure, resulting in strict sealing requirements and the need for high-voltage internal equipment, which is costly. While electromagnetic bonding processes do not require expensive specialized equipment, they are not suitable for forming bimetallic tubes with low-conductivity cladding materials. Furthermore, due to coil size and strength limitations, the coil life is limited by the ability to sustain multiple, stable discharges when forming small-diameter lined bimetallic composite tubes. The explosive composite process has safety hazards during forming. Due to the limitations of its process principles, it cannot be mass-produced. In addition, the inner surface quality of the formed bimetallic tube is poor and easily produces ablation marks.

[0003] Electrohydraulic expansion technology is an advanced connection technology based on the principles of electrohydraulic forming. Electrohydraulic forming involves the instantaneous release of electrical energy stored in a discharge device. The energy at the positive and negative electrode ends explodes in water, generating a strong shock wave. The liquid medium (usually water) acts as an energy transmission medium to drive the plastic deformation of metal sheets or pipes. Controlling process parameters such as wire diameter, length, and discharge voltage can increase the impact load of the liquid, thereby achieving a formed connection. However, for high-rate composites, there is currently a lack of matching criteria for composite metal tubes made of two materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a bimetallic tube electro-hydraulic composite forming device and forming method to solve the problems existing in the above-mentioned prior art. The device is suitable for the forming process of small-diameter bimetallic composite tubes with thin lining and coating. The method is not limited by the electrical conductivity of the material on the basis of safety and energy saving. The formed bimetallic tube does not require secondary processing and provides material matching criteria corresponding to the process.

[0005] To achieve the above-mentioned objectives, the present invention provides the following solution: The present invention provides a bimetallic tube electro-hydraulic composite forming device, comprising an upper plug, a lower plug, electrodes and a discharge device, the top and bottom of the bimetallic tube being sealed by the upper plug and the lower plug respectively; electrodes are respectively passed through the upper plug and the lower plug, and a metal wire is connected between the two electrodes; the inner tube of the bimetallic tube is filled with a liquid medium, and the ends of the two electrodes and the metal wire are immersed in the liquid medium; the other ends of the two electrodes are respectively connected to the positive and negative poles of the discharge device.

[0006] In one embodiment, both ends of the upper plug and the lower plug are connected by fastening bolts respectively.

[0007] In one embodiment, a liquid filling interface is provided on the upper plug, and the liquid filling interface is communicated with the inner tube cavity of the bimetallic tube. The liquid filling interface is used to fill the inner tube cavity of the bimetallic tube with liquid medium.

[0008] In one embodiment, the electrodes include a positive electrode and a negative electrode, and the positive electrode and the negative electrode are respectively sealed and installed in the middle position of the upper plug and the lower plug through threaded steel sleeves.

[0009] In one embodiment, an insulating sleeve is provided on the outer side of the electrode, and the upper outer side of the insulating sleeve is sealed and assembled inside the threaded steel sleeve.

[0010] In one embodiment, the insulating sleeve includes an insulating sleeve main body and a protrusion, the protrusion is integrally formed in the middle part of the insulating sleeve main body, the upper shoulder of the protrusion is arranged in contact with the inner wall of the threaded steel sleeve; the bottom of the protrusion is assembled in the opening of the upper plug or the lower plug, and a No. 1 sealing ring is provided between the bottom of the protrusion and the upper plug or the lower plug.

[0011] In one embodiment, the electrode includes an integrated first connecting end, an electrode body, and a second connecting end, the first connecting end is connected to the charging capacitor of the discharge device, the second connecting end is connected to the metal wire, a shoulder is provided between the electrode body and the second connecting end, and the shoulder of the electrode body and the second connecting end is immersed in the liquid medium, and a No. 3 sealing ring is provided at the shoulder of the electrode body and the second connecting end.

[0012] In one embodiment, a No. 2 sealing ring is provided between the top and bottom of the bimetallic tube and the upper plug; a No. 4 sealing ring is provided between the upper and lower ends of the inner tube of the bimetallic tube and the upper and lower plugs; the inner tube and outer tube of the bimetallic tube are assembled together through a gap ring.

[0013] In one embodiment, a vacuum joint is provided on the bottom side wall of the bimetallic tube, and the vacuum joint is connected to a vacuum device.

[0014] The present invention also provides a bimetallic tube electro-hydraulic composite forming method, which is applied to the above-mentioned bimetallic tube electro-hydraulic composite forming device, comprising:

[0015] Under the quasi-static material matching judgment condition, the material strain rate hardening parameter C is introduced, and the material matching criterion of the bimetallic tube electro-hydraulic composite needs to satisfy the following formula:

[0016]

[0017] Where: σ s - yield strength of the outer tube under quasi-static conditions;

[0018] σ - flow stress of the inner wall of the inner tube when the inner wall of the outer tube reaches the yield strength under quasi-static conditions;

[0019] Δ——gap between tubes;

[0020] d——outer diameter of inner tube;

[0021] E1——elastic modulus of outer tube;

[0022] E2——elastic modulus of inner tube;

[0023] C1 - outer tube strain rate strengthening parameter;

[0024] C2 - inner tube strain rate strengthening parameter;

[0025] ——The ratio of the strain rate when the inner and outer tubes are deformed to the strain rate under quasi-static conditions;

[0026] The electro-hydraulic composite forming process of bimetallic tube is as follows:

[0027] Step 1: Cut quasi-static tensile specimens and high-speed tensile specimens from the inner and outer tubes to be composited, and conduct quasi-static and high-speed tensile tests. Record the yield strength of the material at different strain rates and substitute Obtain the material's strain rate strengthening coefficient; substitute the obtained material performance parameters and tube blank geometric parameters into the material matching criterion formula, and determine whether the criterion is valid at different strain rates based on the inter-tube gap;

[0028] Step 2: Use finite element simulation software to simulate the composite process, change the discharge parameters until the inner and outer tubes remain in contact after the shock wave ends, and record the discharge parameters;

[0029] Step 3: Install the metal tube to be formed. First, place the No. 2 sealing ring in the gap ring groove, assemble the inner and outer tubes coaxially through the gap ring, place the No. 4 sealing ring in the plug groove, and fix the inner and outer tubes between the upper and lower plugs. Then tighten the fastening bolts to complete the installation of the metal tube.

[0030] Step 4: Assemble the electrodes. Connect the metal wires between the electrodes. Pass the connected electrodes through the middle of the tube blank. Place the No. 3 sealing ring between the insulating sleeve and the electrode, and the No. 1 sealing ring between the insulating sleeve and the plug. Insert the insulating sleeve from the tail of the electrode, then install the threaded steel sleeve and the nut on the electrode to complete the assembly and fixation of the electrode.

[0031] Step 5: Open the liquid supply device and fill a fixed amount of liquid into the liquid storage chamber of the inner tube;

[0032] Step 6: Turn on the vacuum equipment so that the gap between the inner and outer tubes reaches the set vacuum state;

[0033] Step 7: Check the connection status of the discharge circuit. If the circuit is connected, you can perform the charge and discharge operation.

[0034] Step 8: Close the charging switch of the high-energy pulse discharge device, and the high-voltage power supply charges the charging capacitor through the high-voltage rectifier bridge and the current-limiting resistor. After the preset voltage is reached, the charging switch is disconnected, and the discharge trigger switch is opened to connect the auxiliary discharge gap and start discharging the metal wire;

[0035] Step 9: After the discharge is completed, open the liquid reflux interface to recycle the waste liquid;

[0036] Step 10: Remove the formed bimetallic tube to complete the forming process;

[0037] Step 11: Cut a ring specimen and place it in a shear strength testing device. Use a universal testing machine to apply gradually increasing pressure to the upper punch until the inner and outer tubes are sheared. Record the maximum pressure value and the ratio of the contact area between the inner and outer tubes of the bimetallic tube to obtain the shear strength of the bimetallic tube.

[0038] Compared with the prior art, the present invention has achieved the following beneficial technical effects:

[0039] The present invention discloses an electro-hydraulic composite forming device and method for bimetallic tubes. The forming device comprises an upper plug, a lower plug, electrodes, and a discharge device. The top and bottom of the bimetallic tube are sealed by the upper and lower plugs, respectively. Electrodes are inserted into the upper and lower plugs, with a metal wire connected between the two electrodes. The inner tube of the bimetallic tube is filled with a liquid medium, and the ends of the two electrodes and the metal wire are immersed in the liquid medium. The other ends of the two electrodes are connected to the positive and negative poles of the discharge device, respectively. The present invention proposes an electro-hydraulic composite process device and method for bimetallic tubes, as well as material matching criteria for the electro-hydraulic composite process. This facilitates pre-experimental confirmation of whether two tube blanks of different materials can be composited using this process, reducing trial-and-error costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. 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 any creative work.

[0041] Figure 1 This is a structural diagram of a bimetallic tube electro-hydraulic composite forming device;

[0042] Figure 2 It is the uniaxial tensile curve of the inner tube at different strain rates;

[0043] Figure 3 It is the uniaxial tensile curve of the outer tube at different strain rates;

[0044] Figure 4 This is a schematic diagram of a bimetallic tube shear strength test device;

[0045] Figure 5 This is the uniaxial tensile curve of 304 stainless steel at different strain rates;

[0046] Figure 6 This is the uniaxial tensile curve of Q345 steel at different strain rates;

[0047] Among them, 1. Upper plug; 2. Fastening bolt; 3. Lower plug; 4. Electrode; 5. Insulation sleeve; 6. Threaded steel sleeve; 7. No. 1 sealing ring; 8. Liquid filling interface; 9. No. 2 sealing ring; 10. Inner tube; 11. Metal wire; 12. Outer tube; 13. No. 3 sealing ring; 14. Vacuum joint; 15. No. 4 sealing ring; 16. Gap ring; 17. Charging capacitor; 18. Discharge gap. DETAILED DESCRIPTION

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0049] The purpose of the present invention is to provide a bimetallic tube electro-hydraulic composite forming device and forming method to solve the problems existing in the above-mentioned prior art. The device is suitable for the forming process of small-diameter bimetallic composite tubes with thin lining and coating. The method is not limited by the electrical conductivity of the material on the basis of safety and energy saving. The formed bimetallic tube does not require secondary processing and provides material matching criteria corresponding to the process.

[0050] 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.

[0051] like Figures 1-6 As shown, the present invention provides a bimetallic tube electro-hydraulic composite forming device, including an upper plug 1, a lower plug 3, electrodes 4 and a discharge device. The top and bottom of the bimetallic tube are respectively sealed by the upper plug 1 and the lower plug 3; the upper plug 1 and the lower plug 3 are respectively penetrated by electrodes 4, and a metal wire 11 is connected between the two electrodes 4. The inner tube 10 of the bimetallic tube is filled with a liquid medium, and the ends of the two electrodes 4 and the metal wire 11 are immersed in the liquid medium; the other ends of the two electrodes 4 are respectively connected to the positive and negative poles of the discharge device.

[0052] In one embodiment, both ends of the upper plug 1 and the lower plug 3 are connected by fastening bolts 2 .

[0053] In one embodiment, a liquid filling interface 8 is provided on the upper plug 1, and the liquid filling interface 8 is connected to the cavity of the inner tube 10 of the bimetallic tube. The liquid filling interface 8 is used to fill the cavity of the inner tube 10 of the bimetallic tube with liquid medium.

[0054] In one embodiment, the electrode 4 includes a positive electrode and a negative electrode, and the positive electrode and the negative electrode are respectively sealed and installed in the middle position of the upper plug 1 and the lower plug 3 through the threaded steel sleeve 6.

[0055] In one embodiment, an insulating sleeve 5 is provided on the outer side of the electrode 4 , and the upper outer side of the insulating sleeve 5 is sealed and assembled inside the threaded steel sleeve 6 .

[0056] In one embodiment, the insulating sleeve 5 includes an insulating sleeve main body and a protrusion, the protrusion is integrally formed in the middle part of the insulating sleeve main body, and the upper shoulder of the protrusion is fitted with the inner wall of the threaded steel sleeve 6; the bottom of the protrusion is assembled in the opening of the upper plug 1 or the lower plug 3, and a No. 1 sealing ring 7 is provided between the bottom of the protrusion and the upper plug 1 or the lower plug 3.

[0057] In one embodiment, the electrode 4 includes an integrated first connecting end, an electrode body and a second connecting end. The first connecting end is connected to the charging capacitor 17 of the discharge device, and the second connecting end is connected to the metal wire 11. A shoulder is provided between the electrode body and the second connecting end, and the shoulder of the electrode body and the second connecting end is immersed in the liquid medium. A No. 3 sealing ring 13 is provided at the shoulder of the electrode body and the second connecting end.

[0058] In one embodiment, a No. 2 sealing ring 9 is provided between the top and bottom of the bimetallic tube and the upper plug 1; a No. 4 sealing ring 15 is provided between the upper and lower ends of the inner tube 10 of the bimetallic tube and the upper and lower plugs; the inner tube 10 and the outer tube 12 of the bimetallic tube are assembled together by a gap ring 16.

[0059] In one embodiment, a vacuum joint 14 is provided on the bottom side wall of the bimetallic tube, and the vacuum joint 14 is connected to a vacuum device.

[0060] The technical problem to be solved by the present invention is to propose a forming process suitable for small-diameter thin-lined bimetallic composite pipes. This method is not limited by the electrical conductivity of the material on the basis of safety and energy saving, and the formed bimetallic pipe does not require secondary processing, and provides corresponding material matching criteria for the process.

[0061] In order to solve the above technical problems, the present invention proposes to apply electrohydraulic forming technology to the field of bimetallic tube composite, and drives the inner tube 10 and the outer tube 12 to collide at high speed through the shock wave generated by the discharge of the underwater metal wire 11 to achieve the composite of the inner and outer tubes, and proposes the material matching criteria of this method.

[0062] In order to realize the composite of the two metal tubes, the outer tube 12 needs to have a greater rebound than the inner tube 10 after unloading. When the material is deformed at a high rate, the stress will increase compared to the quasi-static condition, such as Figure 2 and Figure 3 As shown in the figure, the material matching criterion for hydraulic expansion joints under quasi-static conditions is not applicable. At the same time, the impact hydraulic strength generated by the electric explosion of the metal wire 11 is difficult to predict using a formula. Therefore, in order to make a preliminary judgment on the material matching before the experiment, the strain rate strengthening parameter C of the material is introduced under the quasi-static material matching judgment condition. The material is regarded as an ideal line-strengthened elastic-plastic material. The material matching of the bimetallic tube electro-hydraulic composite needs to satisfy the following formula:

[0063]

[0064] Where: σ s - yield strength of the outer tube under quasi-static conditions;

[0065] σ - flow stress of the inner wall of the inner tube when the inner wall of the outer tube reaches the yield strength under quasi-static conditions;

[0066] Δ——gap between tubes;

[0067] d——outer diameter of inner tube;

[0068] E1——elastic modulus of outer tube;

[0069] E2——elastic modulus of inner tube;

[0070] C1 - outer tube strain rate strengthening parameter;

[0071] C2 - inner tube strain rate strengthening parameter;

[0072] ——The ratio of the strain rate during deformation of the inner and outer tubes to the strain rate under quasi-static conditions.

[0073] The composite process of bimetallic tube is as follows:

[0074] Step 1: Cut quasi-static tensile specimens and high-speed tensile specimens from the inner and outer tubes to be composited, and conduct quasi-static and high-speed tensile tests. Record the yield strength of the material at different strain rates and substitute Obtain the material's strain rate strengthening coefficient. Substitute the obtained material performance parameters and tube geometric parameters into the material matching criterion, and determine whether the criterion is valid at different strain rates based on the gap between tubes.

[0075] Step 2: Use finite element simulation software to simulate the composite process, change the discharge parameters until the inner and outer tubes remain in contact after the shock wave ends, and record the discharge parameters.

[0076] Step 3: Install the metal tube to be formed. First, place the No. 2 sealing ring 9 in the groove of the gap ring 16. Then, coaxially assemble the inner and outer tubes through the gap ring 16 with a certain gap. Place the No. 4 sealing ring 15 in the groove of the plug. Then, fix the inner and outer tubes between the upper and lower plugs. Then, tighten the fastening bolts 2 to complete the installation of the metal tube.

[0077] Step 4: Assemble the electrodes 4. Connect a certain length of metal wire 11 between the electrodes 4. Pass the connected electrodes 4 through the middle of the tube blank. Place the No. 3 sealing ring 13 between the insulating sleeve 5 and the electrode 4, and the No. 1 sealing ring 7 between the insulating sleeve 5 and the plug. Insert the insulating sleeve 5 from the tail end of the electrode 4, then install the threaded cylinder sleeve and the nut on the electrode 4 to complete the assembly and fixation of the electrode 4.

[0078] Step 5: Open the liquid supply device and fill the liquid storage chamber with a certain amount of liquid;

[0079] Step 6: Turn on the vacuum equipment to make the gap between the inner and outer tubes reach a certain vacuum state.

[0080] Step 7: Check the connection status of the discharge circuit. If the circuit is in the "on" state, you can perform charging and discharging operations.

[0081] Step 8: Close the charging switch of the high-energy pulse discharge device, and the high-voltage power supply charges the charging capacitor 17 through the high-voltage rectifier bridge and the current-limiting resistor. After the preset voltage is reached, the charging switch is disconnected, and the discharge trigger switch is opened to connect the auxiliary discharge gap 18, and the metal wire 11 begins to be discharged;

[0082] Step 9: After the discharge is completed, open the liquid reflux interface to recycle the waste liquid;

[0083] Step 10: Remove the formed bimetallic tube to complete the forming work.

[0084] Step 11: Cut a ring specimen and place it in a shear strength testing device. Use a universal testing machine to apply gradually increasing pressure to the upper punch until the inner and outer tubes are sheared. Record the maximum pressure value and the ratio of the contact area between the inner and outer tubes of the bimetallic tube to obtain the shear strength of the bimetallic tube.

[0085] The working principle of the above-mentioned bimetallic tube electro-hydraulic composite process is as follows:

[0086] The electro-hydraulic forming machine instantly releases the electrical energy stored in the capacitor to generate a strong pulse current. When the current passes through the metal wire 11 between the positive and negative electrodes, it heats up and vaporizes it, and eventually breaks it down and causes an electric explosion. Due to the incompressibility of the liquid medium, the electric explosion generates a strong shock wave. The shock wave is transmitted to the inner tube 10 through the liquid medium and drives the inner tube 10 to undergo high-speed plastic expansion and collide with the inner wall of the outer tube 12. Subsequently, the inner and outer tubes expand at the same time. After the shock wave ends (or the speed of the inner tube 10 drops to 0), the inner and outer tubes rebound at the same time. Due to the difference in the elasticity of the inner and outer tubes, residual contact force is generated at the contact interface of the inner and outer tubes, thereby realizing the compounding of the bimetallic tube.

[0087] The purpose of the present invention is to provide an economical, safe, and practical method for the bonding of small-diameter, thin-walled bimetallic tubes. Compared with existing bimetallic tube bonding methods, the electro-hydraulic bonding method proposed in the present invention achieves the following beneficial effects:

[0088] 1. Compared with the hydraulic bulging composite process, it does not require large hydraulic equipment, and only requires one discharge device and corresponding tooling to complete the forming, which is much cheaper;

[0089] 2. Compared with the electromagnetic composite process, the electro-hydraulic expansion process is not limited by the material conductivity and can be used to prepare bimetallic tubes with a variety of matching materials. For small-diameter bimetallic tubes, the electromagnetic composite process requires higher strength of the coil and is difficult to achieve multiple stable forming, while the electro-hydraulic expansion process does not have this problem.

[0090] 3. Compared with the explosive composite process, the electro-hydraulic expansion process is safer, the inner surface quality of the prepared bimetallic tube is better, and the deformation of the tube is controlled by voltage, the discharge energy is easy to accurately control, and the experimental results are highly stable.

[0091] Example 1

[0092] Outer tube 12 material: 345 seamless steel pipe, length 100mm, outer diameter 62mm, wall thickness 5.6mm, strain rate strengthening parameter is 0.07, yield strength 380MPa, elastic modulus 210GPa; inner tube 10 material: 304 stainless steel seamless pipe, length 90mm, outer diameter 50, wall thickness 1mm, yield strength 255MPa, strain rate strengthening parameter is 0.0855, elastic modulus 194GPa. Processing requirements: Complete the composite of 304 stainless steel seamless pipe and 345 seamless steel pipe lining. When the pipe fitting is formed by methods such as hydraulic bulging, the tooling hydraulic sealing requirements are high. At the same time, the electromagnetic composite method cannot be used due to the limitation of material conductivity. After calculation, it meets the matching criteria of electro-hydraulic composite materials.

[0093] The method for forming a metal pipe using an electric pulse to trigger an energetic material provided by the present invention:

[0094] Step 1: Cut quasi-static tensile specimens and high-speed tensile specimens from stainless steel tubes and Q345 steel tubes, and perform 0.002s -1 , 2500s -1 , 4500s -1 The tensile test under the strain rate is carried out to obtain the stress-strain curve, such as Figure 5 and Figure 6 As shown, the yield strength of 304 stainless steel at three strain rates is 255MPa, 516MPa and 544MPa respectively, and the yield strength of Q345 steel at three strain rates is 381MPa, 618MPa and 651MPa respectively. The strain rate hardening parameter of 304 stainless steel is 0.086, and the strain rate hardening parameter of Q345 steel is 0.046. The gap between the tubes to be composited is 0.2mm. According to experience, the strain rate is less than 2000s. -1 , after calculation, the criterion always holds true under this strain rate condition.

[0095] Step 2: Use finite element simulation software to simulate the composite process. The capacitance of the pulse current device is 200 μF. The relevant parameters of the metal wire 11 are as follows: the diameter of the metal aluminum wire is 0.5 mm and the length is 20 mm. The simulation found that when the discharge voltage is 8 kV, the inner and outer tubes always remain in contact during the unloading process.

[0096] Step 3: Install the metal tube to be formed, assemble the electrode 4, fill the liquid and evacuate the space between the tubes, and perform the discharge operation after inspection.

[0097] Step 4: Remove the formed bimetallic tube, cut the ring sample and use Figure 4 The method shown measures the shear strength between the inner and outer tubes, and the shear strength is 0.6 MPa.

[0098] According to the standard CJ / T 192-2017, for lined stainless steel composite pipes not larger than DN250, the inter-pipe bonding strength between the base pipe and the composite pipe should not be less than 0.3MPa. Therefore, the stainless steel pipe made by electro-hydraulic composite can meet the requirements.

[0099] 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 characteristics of the present invention. Therefore, from all perspectives, the embodiments should be regarded as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the foregoing description. It is intended that all changes that fall within the meaning and range of equivalents of the claims be included in the present invention, and any reference signs in the claims should not be construed as limiting the claims to which they relate.

[0100] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A bimetallic tube electro-hydraulic composite forming method, characterized in that: include: A bimetallic tube electro-hydraulic composite forming device for use in a bimetallic tube electro-hydraulic composite forming method comprises an upper plug, a lower plug, electrodes, and a discharge device. The top and bottom of the bimetallic tube are sealed by the upper plug and the lower plug, respectively. Electrodes are respectively inserted into the upper plug and the lower plug, with a metal wire connected between the two electrodes. The inner tube of the bimetallic tube is filled with a liquid medium, and the ends of the two electrodes and the metal wire are immersed in the liquid medium. The other ends of the two electrodes are respectively connected to the positive and negative poles of the discharge device. An insulating sleeve is provided on the outside of the electrode, and the upper outer side of the insulating sleeve is sealed and assembled inside the threaded steel sleeve. Under the quasi-static material matching judgment condition, the material strain rate hardening parameter C is introduced, and the material matching criterion of the bimetallic tube electro-hydraulic composite must satisfy the following formula: Where: σ s - yield strength of the outer tube under quasi-static conditions; σ - flow stress of the inner wall of the inner tube when the inner wall of the outer tube reaches the yield strength under quasi-static conditions; Δ——gap between tubes; d——outer diameter of inner tube; E1——elastic modulus of outer tube; E2——elastic modulus of inner tube; C1 - outer tube strain rate strengthening parameter; C2 - inner tube strain rate strengthening parameter; ——The ratio of the strain rate when the inner and outer tubes are deformed to the strain rate under quasi-static conditions; The electro-hydraulic composite forming process of bimetallic tube is as follows: Step 1: Cut quasi-static tensile specimens and high-speed tensile specimens from the inner and outer tubes to be composited, and conduct quasi-static and high-speed tensile tests. Record the yield strength of the material at different strain rates and substitute Obtain the material's strain rate strengthening coefficient; substitute the obtained material performance parameters and tube blank geometric parameters into the material matching criterion formula, and determine whether the criterion is valid at different strain rates based on the inter-tube gap; Step 2: Use finite element simulation software to simulate the composite process, change the discharge parameters until the inner and outer tubes remain in contact after the shock wave ends, and record the discharge parameters; Step 3: Install the metal tube to be formed. First, place the No. 2 sealing ring in the gap ring groove, assemble the inner and outer tubes coaxially through the gap ring, place the No. 4 sealing ring in the plug groove, and fix the inner and outer tubes between the upper and lower plugs. Then tighten the fastening bolts to complete the installation of the metal tube. Step 4: Assemble the electrodes. Connect the metal wires between the electrodes. Pass the connected electrodes through the middle of the tube blank. Place the No. 3 sealing ring between the insulating sleeve and the electrode, and the No. 1 sealing ring between the insulating sleeve and the plug. Insert the insulating sleeve from the tail of the electrode, then install the threaded steel sleeve and the nut on the electrode to complete the assembly and fixation of the electrode. Step 5: Open the liquid supply device and fill a fixed amount of liquid into the liquid storage chamber of the inner tube; Step 6: Turn on the vacuum equipment so that the gap between the inner and outer tubes reaches the set vacuum state; Step 7: Check the connection status of the discharge circuit. If the circuit is connected, you can perform the charge and discharge operation. Step 8: Close the charging switch of the high-energy pulse discharge device, and the high-voltage power supply charges the charging capacitor through the high-voltage rectifier bridge and the current-limiting resistor. After the preset voltage is reached, the charging switch is disconnected, and the discharge trigger switch is opened to connect the auxiliary discharge gap and start discharging the metal wire; Step 9: After the discharge is completed, open the liquid reflux interface to recycle the waste liquid; Step 10: Remove the formed bimetallic tube to complete the forming process; Step 11: Cut a ring specimen and place it in a shear strength testing device. Use a universal testing machine to apply gradually increasing pressure to the upper punch until the inner and outer tubes are sheared. Record the maximum pressure value and the ratio of the contact area between the inner and outer tubes of the bimetallic tube to obtain the shear strength of the bimetallic tube.

2. The electro-hydraulic composite forming method of a bimetallic tube according to claim 1, characterized in that: The two ends of the upper plug and the lower plug are connected by fastening bolts respectively.

3. The bimetallic tube electro-hydraulic composite forming method according to claim 1, characterized in that: The upper plug is provided with a liquid filling interface, which is communicated with the inner tube cavity of the bimetallic tube. The liquid filling interface is used to fill the inner tube cavity of the bimetallic tube with liquid medium.

4. The electro-hydraulic composite forming method of a bimetallic tube according to claim 1, characterized in that: The electrodes include a positive electrode and a negative electrode, and the positive electrode and the negative electrode are respectively sealed and installed in the middle position of the upper plug and the lower plug through threaded steel sleeves.

5. The electro-hydraulic composite forming method of a bimetallic tube according to claim 1, characterized in that: The insulating sleeve includes an insulating sleeve main body and a raised portion. The raised portion is integrally formed in the middle of the insulating sleeve main body. The upper shoulder of the raised portion is fitted with the inner wall of the threaded steel sleeve. The bottom of the raised portion is assembled in the opening of the upper plug or the lower plug, and a No. 1 sealing ring is provided between the bottom of the raised portion and the upper plug or the lower plug.

6. The electro-hydraulic composite forming method of a bimetallic tube according to claim 1, characterized in that: The electrode includes an integrated first connecting end, an electrode body, and a second connecting end. The first connecting end is connected to the charging capacitor of the discharge device, and the second connecting end is connected to the metal wire. A shoulder is provided between the electrode body and the second connecting end, and the shoulder of the electrode body and the second connecting end is immersed in the liquid medium. A No. 3 sealing ring is provided at the shoulder of the electrode body and the second connecting end.

7. The electro-hydraulic composite forming method of a bimetallic tube according to claim 1, characterized in that: No. 2 sealing rings are provided between the top and bottom of the bimetallic tube and the upper plug; No. 4 sealing rings are provided between the upper and lower ends of the inner tube of the bimetallic tube and the upper and lower plugs; the inner tube and outer tube of the bimetallic tube are assembled together through a gap ring.

8. The electro-hydraulic composite forming method of a bimetallic tube according to claim 1, characterized in that: A vacuum joint is provided on the bottom side wall of the bimetallic tube, and the vacuum joint is connected to the vacuum equipment.

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