A coil structure for increasing the length of electromagnetic pulse welding of copper tube to steel rod

Abstract

This invention discloses a coil structure for increasing the length of electromagnetic pulse welding of copper tubes / steel bars. The structure involves first machining a bevel at a certain angle on the coil, specifically by machining inclined surfaces on both sides of the coil. Then, the copper tube and steel bar are coaxially assembled and aligned, ensuring the welding area is within the bevel of the coil. Finally, electromagnetic pulse welding is applied to the copper tube and steel bar. This method effectively expands the axial magnetic field area, optimizes the axial magnetic field distribution of the weld, and enhances the magnetic field strength and electromagnetic force of the copper tube within the bevel area. This avoids problems such as a small effective weld connection area and uneven interface waveform caused by insufficient magnetic field strength and a small effective area, thereby improving the mechanical properties of the copper / steel electromagnetic pulse welded joint.

Description

Technical Field

[0001] This invention belongs to the field of applied welding technology, specifically relating to a coil structure for increasing the length of electromagnetic pulse welding of copper tubes / steel bars. Background Technology

[0002] Currently, the welding of copper tubes and steel bars mainly relies on diffusion welding and continuous-drive friction welding, both of which have significant limitations. Diffusion welding requires heating the copper to over 1000 ℃ and holding it at that temperature for over 1 minute. Prolonged exposure to high temperatures significantly softens the heat-affected zone on the steel side, leading to a decrease in joint strength and hardness. Furthermore, the significant thermophysical differences between copper and steel easily generate residual interfacial stress, porosity, and brittle intermetallic compounds, resulting in poor joint stability. While friction welding has a lower heat input, it is difficult to achieve uniform pressure along the circumference of the copper tube during the upsetting stage, easily leading to uneven circumferential bonding, localized incomplete welding, and the formation of vortex-like defects and stress concentrations at the interface, resulting in large joint strength dispersion and insufficient reliability. Even with electromagnetic pulse welding, the high-speed impact of the copper tube with the steel bar creates a jet of metal particles within a narrow gap. Large-diameter particles are prone to becoming trapped at the interface, converting kinetic energy into internal energy and causing localized instantaneous melting and resolidification, leading to defects such as porosity and microcracks, thus hindering the improvement of joint performance.

[0003] Regarding the welding of copper tubes and steel bars, Chinese patent CN116275451A discloses a welding method for connecting copper tubes and steel bars using electromagnetic pulse waveforms. Specifically, it discloses an electromagnetic pulse welding method to weld the copper tube onto the steel bar, which improves the joint strength to some extent. However, in the actual welding process, the copper tube impacts the steel bar at high speed under electromagnetic force, forming a high-speed jet of metal particles within the extremely narrow overlap gap. Small-diameter particles can be smoothly discharged from the interface with the jet, while large-diameter particles rapidly decay their kinetic energy along the welding direction and remain at the interface trough. Their kinetic energy is converted into internal energy, causing a sudden increase in local interface temperature, triggering a local melting-rapid resolidification phenomenon. This easily leads to the formation of pores, microcracks, inclusions, and vortex-like melting defects at the interface, resulting in discontinuous interface bonding and stress concentration, severely affecting the joint strength and service life. Simultaneously, the conventional coil structure has a narrow axial magnetic field area and uneven magnetic field distribution, easily leading to a small effective weld connection area and uneven interface waveform. Therefore, to avoid the above problems, this patent changes the coil structure and expands the magnetic field area, which can effectively expand the axial magnetic field area, optimize the axial magnetic field distribution of the weld, and improve the magnetic field strength and electromagnetic force of the copper tube in the welding zone, thereby effectively improving the mechanical properties of the copper / steel electromagnetic pulse welding joint. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a coil structure for increasing the length of electromagnetic pulse welding of copper tubes / steel bars. This method effectively expands the axial magnetic field's effective area, optimizes the axial magnetic field distribution in the weld, and enhances the magnetic field strength and electromagnetic force of the copper tube within the welding zone. This avoids the problems of a small effective weld connection area and uneven interface waveform caused by insufficient magnetic field strength and a small effective area, thereby increasing the connection length of copper / steel electromagnetic pulse welding.

[0005] Compared with the prior art, the present invention has the following beneficial effects: This invention, by processing magnetic collecting surfaces at different angles (30°, 35°, 40°, 45°, 50°) at both ends of the coil and placing the welding area within the inclined surface region of the coil, expands the range of the axial magnetic field generated by the coil during the welding process due to the inclined surface structure of the coil. This results in a larger distribution range of the magnetic field required for welding along the weld axial direction, significantly improving the uniformity of stress and the intensity of the copper tube in the welding area. This enables a longer and more stable effective connection interface, improves the uniformity of the interface waveform, and avoids defects such as insufficient effective connection area of ​​the weld and interface waveform distortion, thereby improving the overall mechanical properties of the copper / steel welded joint. Attached Figure Description

[0006] Figure 1 Schematic diagram of the welding assembly of copper tubes and steel bars Figure 2 Schematic diagram of inclined plane structure coil Figure 3 Schematic diagrams of different coil structures Figure 4 Comparison of magnetic field strength at different coil angles Figure 5 Comparison of copper-steel welded interface connection lengths; (a) 45° inclined coil (e) straight coil Figure 6 Tensile specimen diagram Figure 7 Tensile load-displacement curve in Figure 1 1- Welding coil with a 45° bevel structure; 2- Copper tube; 3- Steel rod Detailed Implementation

[0007] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, taking a 45° coil structure as an example.

[0008] A coil structure for increasing the length of electromagnetic pulse welding of copper tubes / steel rods involves first machining 45° bevels on both ends of the coil using a milling machine to form a beveled welding coil, ensuring that the axial coverage length of the beveled area is greater than the length of the area to be welded; then, the copper tube is fitted onto the steel rod, aligning it with the surface to be welded, and assembled into a welding fixture, ensuring that the area to be welded is within the axial coverage range of the beveled area of ​​the coil; finally, electromagnetic pulse welding is used to complete the connection between the copper tube and the steel rod.

[0009] As the welding discharge process proceeds, the 45° inclined coil can effectively break the axial distribution limitation of the magnetic field of conventional coils, expand the effective area of ​​the axial magnetic field, optimize the axial magnetic field uniformity of the weld, and significantly improve the amplitude and circumferential and axial uniformity of the electromagnetic force on the copper tube in the inclined groove coverage area. This allows the copper tube to achieve synchronous and uniform high-speed impact over a longer axial range, thereby greatly increasing the effective connection length of the welding interface, improving the uniformity and continuity of the interface waveform, avoiding defects such as local incomplete welding and interface waveform distortion, and thus improving the overall mechanical properties of the copper / steel electromagnetic pulse welding joint.

[0010] In practice, the 45° inclined plane on the coil is a symmetrical structure, with the direction of the inclined plane forming a 45° angle with the coil axis. The height of the inclined plane is set according to the effective working length of the coil and the length of the area to be welded, ensuring that the welding area is completely within the magnetic field enhancement range of the inclined plane.

[0011] In specific implementation, a coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods includes the following steps: (1) Determine the length of the copper tube to be welded and the length of the steel rod to be welded. Process a through inclined surface at a 45° angle to the axial direction on the outer circumference of the effective working section of the coil. The axial coverage length of the inclined surface is greater than the length of the area to be welded. The width of the working coil is less than or equal to the welding length and can only be less than or equal to 0.2~0.3 mm.

[0012] (2) Before joining the copper tube and steel rod on the welding fixture, clean the inner wall of the copper tube and the surface of the steel rod to be welded with acetone to remove surface oil, impurities and other adhering substances to avoid surface metal oxidation, and dry them quickly with cold air; assemble the copper tube and steel rod on the welding fixture, with the copper tube sleeved on the steel rod, the surfaces of the copper tube and the steel rod to be welded facing each other, and leave a uniform welding gap of 1~1.2 mm between the copper tube and the steel rod to ensure that the axial position of the area to be welded is completely corresponding to the axial position of the coil groove area, and the workpiece axis coincides with the coil axis.

[0013] (3) The capacitor is turned on to discharge the coil with a 45° inclined plane. A time-varying high-intensity current with a very short period is passed through the coil. Under the action of the 45° inclined plane of the coil, the copper tube is made to strike the steel rod at high speed and synchronously under uniform electromagnetic force, so as to realize the electromagnetic pulse welding of the copper tube and the steel rod.

[0014] In practice, to ensure the strengthening effect of the coil magnetic field and the stability of the structure, the surface roughness of the inclined surface is controlled to be <3.2μm, and the edge of the groove is free of burrs and deformation to avoid tip discharge and magnetic field distortion during the discharge process.

[0015] In practice, to ensure uniform circumferential and axial force on the copper tube and achieve effective welding across the entire circumference and length, the axial length of the inclined area of ​​the control coil is greater than 1.2 times the length to be welded, ensuring that the welding area is within the strongest uniform magnetic field range.

[0016] In practice, to ensure the uniformity of the welding gap and avoid asynchronous impacts and incomplete welding due to uneven gaps, the circumferential deviation of the welding gap between the copper tube and the steel bar should be controlled to be no more than 0.2 mm, and the axial gap fluctuation should be no more than 0.3 mm.

[0017] In specific implementation, in step (3), under the control of the above-mentioned coil inclined structure and assembly process, the electromagnetic pulse discharge voltage is selected to be 21.5KV, the capacitance is 240μF, the inductance is 300 nH, and the resistance is 3 mΩ.

[0018] This invention employs a welding coil with a 45° bevel for electromagnetic pulse welding of copper tubes and steel bars. First, a uniformly distributed 45° bevel structure is machined within the effective working section of the coil. The inner wall of the copper tube and the surfaces of the steel bar to be welded are then cleaned with acetone and rapidly dried with cold air. Subsequently, the workpiece and welding system are assembled on the welding fixture. A schematic diagram of the welding process is shown below. Figure 1 As shown.

[0019] To better verify the feasibility of the coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods in this patent, such as Figure 2 As shown, this paper conducts a series of simulations on the connection system of copper tube and steel rod using different coil structures, compares and analyzes the simulation results, and selects the angle with the largest magnetic induction intensity for experimental verification.

[0020] Implementation Case 1 (1) Simulation optimization Create coils with five inclined plane angles of 30°, 35°, 40°, 45°, and 50°, such as... Figure 3 As shown, this is a simulation model of electromagnetic pulse welding of a straight coil, with a uniform discharge voltage of 21.5kV, a capacitance of 240μF, a welding gap of 1.0mm, an inductance of 300nH, and a resistance of 3mΩ.

[0021] (2) Simulation data such as magnetic induction intensity, electromagnetic force, and magnetic field range in key areas were extracted, and the results are as follows: Straight coil: Magnetic flux density is approximately 42.21 tesla 30° inclined plane: magnetic induction intensity is approximately 36.00 tesla, a decrease of 14.71% compared to a flat surface; 35° inclined plane: magnetic flux density is approximately 37.54 tesla, which is 11.06% lower than that of a flat surface; 40° inclined plane: magnetic flux density is approximately 39.29 tesla, a decrease of 6.92% compared to a flat surface; 45° inclined plane: magnetic induction intensity is approximately 52.25 tesla, an increase of 23.79% compared to a flat plane; 50° inclined plane: magnetic flux density is approximately 40.42 tesla, a decrease of 4.24% compared to a flat surface;

[0022] The magnetic flux density obtained in this implementation case Figure 4 It can be clearly seen that the 45° inclined coil can provide better electromagnetic drive conditions for electromagnetic pulse welding.

[0023] Implementation Case 2 (1) Experimental testing (2) Experimental preparation: copper tube (Φ12 mm×2 mm), 304 steel rod (Φ10 mm), welding area length 5 mm; clean the welding surface with acetone, dry with cold air, assembly gap 1.0 mm. Welding parameters: welding energy 36 kJ, discharge voltage 17 kV, discharge frequency 23 kHz.

[0024] This implementation case yielded Figure 5A comparison of the joint length at the copper / steel weld interface, as shown in low-magnification morphology (a) and (e), reveals that the straight coil weld has 8 weld peaks and an effective weld length of 1.8 mm, while the 45° inclined coil weld has 15 weld peaks and an effective weld length increased to 2.47 mm. The diameter of the coil was 28.7 mm, which is 28.7% higher than the former. The optimized coil structure can significantly expand the effective bonding range of the joint and improve the continuity of the welding interface. High magnification morphology (b) and (f) quantitative comparison show that: for straight coil welding, the average wavelength of the interface wave is 113.49 μm and the average peak height is 42.80 μm; for 45° inclined coil welding, the average wavelength of the interface wave is 171.47 μm and the average peak height is 61.76 μm. The latter has higher interface collision energy and more intense plastic deformation. TEM (c) and (g) show that the interface regions of both groups of joints undergo dynamic recrystallization due to intense plastic deformation, forming a significantly refined equiaxed crystal structure. Compared with straight coil welding, the recrystallized grains of the 45° inclined coil welding interface are finer and more uniformly distributed, and the refinement effect is more significant. High-resolution TEM morphology (d) and (h) and corresponding selected area electron diffraction results show that clear lattice fringes and a large number of dislocation defects were observed at both interfaces, and the diffraction patterns showed typical polycrystalline ring characteristics, which verified the occurrence of dynamic recrystallization at the interface. Among them, the 45° inclined coil welding interface has a higher dislocation density and a greater degree of lattice distortion, which further confirms that the interface collision energy is higher under this coil structure and the joint metallurgical bonding effect is better.

[0025] Implementation Case 3 (1) Mechanical property testing (2) Experimental Preparation: After completing the electromagnetic pulse welding, in order to ensure that the test results of the tensile specimens accurately reflect the optimal mechanical properties of the joint, the composite specimens need to be directionally cut. Based on the magnetic field simulation results, the magnetic induction intensity reaches its peak at the 90° position of the coil. Taking the joint center as the reference, according to... Figure 6 Tensile specimens were prepared with the following dimensions: the copper tube wall thickness was 2 mm, and the overlap length between the steel rod and the copper tube was 10 mm, ensuring that the effective test section of the specimen completely covered the peak area of ​​magnetic induction intensity. After processing, quasi-static tensile tests were conducted on the specimens, and the load-displacement curves were recorded to evaluate the tensile load-bearing capacity of the joint under optimal magnetic field conditions.

[0026] The results of this experiment Figure 7 Tensile mechanical properties, from Figure 7 As can be seen, the ultimate tensile load of the joint made with a straight coil is 1601 N; while the ultimate tensile load of the joint made with a 45° inclined coil is increased to 2226 N, which is about 39.0% higher than that of the straight coil. This shows that the 45° inclined coil can significantly improve the tensile load capacity of the joint.

[0027] Finally, it should be noted that the above embodiments of the present invention are merely illustrative examples and not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods, characterized in that, First, a certain angled bevel is machined on both ends of the coil using a milling machine to form a beveled welding coil, ensuring that the axial coverage length of the beveled area of ​​the coil is greater than the length of the area to be welded. Then, a copper tube is fitted onto a steel rod and aligned with the surface of the steel rod to be welded, and assembled into a welding fixture, ensuring that the area to be welded is within the axial coverage range of the beveled area of ​​the coil. Finally, electromagnetic pulse welding is used to complete the connection between the copper tube and the steel rod.

2. The coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods according to claim 1, characterized in that, The coil's inclined surface has a symmetrical structure, and the axial coverage length of the inclined surface is greater than the length of the area to be welded, but not less than 1.2 times the length to be welded.

3. The coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods according to claim 1, characterized in that, Includes the following steps: (1) Determine the length of the copper tube to be welded and the length of the steel rod to be welded. Process a through inclined surface at a certain angle to the axis on the outer circumference of the effective working section of the coil. The axial coverage length of the inclined surface is greater than the length of the area to be welded. The width of the working coil is less than or equal to the welding length and can only be less than or equal to 0.2~0.3 mm. (2) Before joining the copper tube and steel rod on the welding fixture, clean the inner wall of the copper tube and the surface of the steel rod to be welded with acetone to remove surface oil, impurities and other adhering substances to avoid surface metal oxidation, and dry them quickly with cold air; assemble the copper tube and steel rod on the welding fixture, with the copper tube sleeved on the steel rod, the surfaces of the copper tube and the steel rod to be welded facing each other, and leave a uniform welding gap of 1~1.2 mm between the copper tube and the steel rod to ensure that the axial position of the area to be welded is completely corresponding to the axial position of the coil groove area, and the workpiece axis coincides with the coil axis. (3) The capacitor is turned on to discharge the inclined coil at a certain angle. A time-varying high-intensity current with a very short period is passed through the coil. Under the action of the inclined coil, the copper tube is made to strike the steel rod at high speed and synchronously under uniform electromagnetic force, so as to realize the electromagnetic pulse welding of the copper tube and the steel rod.

4. The coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods according to claim 3, characterized in that, The width of the working coil should be less than or equal to the welding length, and should be controlled within 0.2~0.3 mm.

5. A coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods according to claim 4, characterized in that, The width of the coil bevel is 13-15 mm, and the depth of the coil on one side is 20 mm.

6. A coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods according to claim 3, characterized in that, The beveled edge is free of burrs and deformation.

7. A coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods according to claim 6, characterized in that, The surface roughness of the beveled coil is <3.2μm.

8. A coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods according to claim 3, characterized in that, The welding gap between the copper tube and the steel bar is 1~1.2 mm, the circumferential deviation is no more than 0.2 mm, and the axial gap fluctuation is no more than 0.3 mm.

9. A coil structure for increasing the electromagnetic pulse welding length of copper tubes / steel rods according to claim 3, characterized in that, In step (3), the electromagnetic pulse welding parameters are: discharge voltage 21.5kV, capacitance 240μF, inductance 300 nH, and resistance 3mΩ.

10. This invention discloses a coil structure for increasing the length of electromagnetic pulse welding of copper tubes / steel rods. This structure first processes magnetic collecting surfaces at different angles at both ends of the coil, placing the welding area within the inclined region of the coil. Then, a copper tube is fitted onto a steel rod, aligning it with the surface to be welded. Finally, electromagnetic pulse welding is used to connect the copper tube and the steel rod. This structure effectively expands the axial magnetic field area, optimizes the axial magnetic field distribution of the weld, and enhances the magnetic field strength and electromagnetic force of the copper tube within the welding area. This avoids problems such as a small effective connection area and uneven interface waveform caused by insufficient magnetic field strength and a small effective area, thereby effectively improving the connection length and overall mechanical properties of the copper / steel electromagnetic pulse weld.

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