A method for preparing a plurality of fine and dense groove-shaped copper bars by using a copper extruder

Abstract

The application discloses a preparation method of a copper bar with multiple fine and dense groove types by an extrusion copper machine, and belongs to the technical field of copper material extrusion molding. The method comprises the following steps: step one, blank pretreatment: selecting high-conductivity oxygen-free copper cast blanks, and performing multi-stage stepped heating to make the temperature gradient inside and outside the blank be less than or equal to 15 DEG C; adopting a sectional combined extrusion die, wherein the multiple-groove finishing and shaping area is provided with parallel fine and dense grooves with a groove bottom with a micro-convex circular arc transition structure; feeding the blank into the extrusion copper machine, and adopting a three-stage variable-speed extrusion process of low-speed pressure building, medium-speed filling and high-speed fine extrusion, and applying a transient pressure boost pulse at the end of the high-speed stage. Through the synergistic effect of blank pretreatment, die design, variable-speed pulse extrusion, online protection and multi-stage aging, the application can stably extrude the copper bar with multiple fine and dense groove types, the groove width of which is less than or equal to 0.5 mm, and the depth-width ratio of which is greater than 2. The product has high size precision and excellent comprehensive performance, and the die has a long service life and a high yield, and is suitable for new energy, power transmission and other fields.

Description

Technical Field

[0001] This invention relates to the field of copper extrusion molding technology, specifically to a method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine. Background Technology

[0002] Copper busbars, as key conductor components in power transmission and distribution systems, are widely used in switchgear, busbar trunking, transformers, and battery connection systems for new energy vehicles. As electrical equipment evolves towards higher integration, miniaturization, and efficient heat dissipation, higher demands are placed on the structural design of copper busbars—they not only need excellent conductivity but also require multiple fine grooves on their surface or sides to enhance heat dissipation, reduce weight, and ensure precise connection with other components.

[0003] Traditional copper busbar processing methods mainly include: 1. Milling or broaching: This process involves machining grooves into the surface of ordinary copper busbars. However, it has problems such as low material utilization (approximately 10% to 20% loss), low processing efficiency, and the easy generation of burrs and residual stress concentration at the edges of the grooves.

[0004] 2. Conventional hot extrusion molding: Although it can be formed in one step, it is difficult to stably extrude a fine multi-groove structure with a width of less than 3mm and a depth-to-width ratio of more than 2mm due to limitations in mold design and extrusion process. Common defects include incomplete filling of the groove bottom, tearing of the groove sidewalls, uneven groove spacing, and groove deformation due to cooling and shrinkage after extrusion.

[0005] 3. Precision cold drawing: For fine grooves, cold drawing has extremely high friction, severe die wear, and obvious work hardening of copper material, which easily leads to cracking.

[0006] Therefore, developing a process that can stably, efficiently, and with high quality extrude copper busbars with multiple fine grooves has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] Technical problems to be solved The purpose of this invention is to overcome the shortcomings of the existing technology and to propose a method for preparing copper busbars by extruding multiple fine grooves using a copper extrusion machine.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine includes the following steps: Step 1: Billet pretreatment: Select high-conductivity oxygen-free copper billets and heat them in a multi-stage stepped manner to 750℃~920℃, and hold them at the temperature so that the temperature gradient between the inside and outside of the billet is ≤15℃. Step 2, Mold Design and Assembly: A segmented combined extrusion mold is adopted, which includes at least an inlet guiding area, a compression deformation area, a multi-groove finishing and shaping area, and an outlet air-cooling shaping section; the multi-groove finishing and shaping area has 3 to 12 parallel fine groove structures with a groove width of 0.5mm to 3.0mm, a groove depth of 2mm to 10mm, and a groove spacing ≥ 1.2 times the groove width, and the bottom of the groove has a slightly convex arc transition structure; Step 3, variable temperature and speed extrusion: The pretreated billet is fed into the copper extruder, the temperature of the extrusion barrel is controlled at 600℃~750℃, and a three-stage variable speed extrusion process including low speed, medium speed and high speed is adopted, and an instantaneous pressure pulse is applied at the end of the high speed section. Step 4: Online tension straightening and groove protection: The extruded grooved copper busbar first enters the air-float non-contact guiding device, and then enters the multi-roll staggered tension straightener. The straightening tension is controlled at 30% to 50% of the material yield strength. At the same time, low-temperature nitrogen gas flow is introduced into each fine groove. Step 5, Multi-stage aging treatment: The straightened copper busbar is placed in a protective atmosphere furnace and first subjected to stress-relief annealing at 180℃~220℃, then heated to 280℃~320℃ for precipitation strengthening treatment, and finally cooled with the furnace to obtain a copper busbar with multiple fine grooves.

[0009] As a further aspect of the present invention: the multi-stage stepped heating in step one is specifically divided into: the first stage heating to 400℃~500℃ and holding for 20min~40min, the second stage heating to 600℃~700℃ and holding for 15min~30min, and the third stage heating to 750℃~920℃ and holding until the internal and external temperature difference meets the standard.

[0010] As a further aspect of the present invention: the radius of the arc of the micro-convex arc transition structure at the bottom of the multi-groove finishing and shaping area is 0.05mm to 0.15mm, and the micro-convex arc is formed by precision electrical discharge machining, with a surface roughness Ra≤0.2μm.

[0011] As a further aspect of the present invention: the inlet guide area of ​​the segmented combined extrusion die is provided with honeycomb-shaped diversion holes, the number of diversion holes being 2 to 4 times the number of slots, and the outlet flow velocity deviation of each diversion hole being controlled within ±5%. The outlet air-cooling and shaping section is equipped with an annular air-cooling channel surrounding the extrusion channel, through which compressed air at a pressure of 0.1MPa to 0.3MPa is introduced to initially cool the extruded copper busbar to 500℃ to 600℃.

[0012] As a further aspect of the present invention: the core material of the multi-groove finishing and shaping area is a cemented carbide or a ceramic matrix composite material, and the surface of the core is provided with a TiAlN or CrAlN coating with a coating thickness of 2μm to 5μm and a hardness ≥35GPa.

[0013] As a further aspect of the present invention: in the three-stage variable speed extrusion process of step three, the speed of the low-speed segment is 0.5mm / s to 1.5mm / s, the speed of the medium-speed segment is 2mm / s to 5mm / s, and the speed of the high-speed segment is 6mm / s to 12mm / s; the pressure increase amplitude of the instantaneous pressure boosting pulse is 5% to 10% of the normal extrusion pressure, and the pulse duration is 0.2s to 0.5s; The instantaneous boost pulse is achieved by a hydraulic servo impact device linked to the copper extrusion machine control system, with a pulse frequency of 10Hz to 50Hz and a pulse width of 20ms to 80ms. The triggering condition at the end of the high-speed section is: the remaining extrusion stroke is detected by the displacement sensor, and a pulse is automatically triggered when the remaining stroke is ≤10mm.

[0014] As a further aspect of the present invention: the air-floating non-contact guiding device in step four includes a plurality of annular air holes arranged at intervals, from which compressed air of 0.2MPa to 0.5MPa is ejected, so that the copper busbar is suspended and moves forward before the groove is completely hardened. The pressure of the low-temperature nitrogen gas flow into each fine-grained tank is 0.1MPa to 0.3MPa, and the flow rate is 5 to 8 L / min per tank; the temperature of the low-temperature nitrogen gas is -15℃ to 0℃.

[0015] As a further aspect of the present invention: the surface of the straightening rollers of the multi-roller staggered tension straightener in step four that contacts the copper busbar is covered with a polyurethane coating, and only contacts the back plane of the copper busbar, not the groove surface.

[0016] As a further aspect of the present invention: the holding time for stress-relief annealing in step five is 0.5h to 1h, and the holding time for precipitation strengthening treatment is 2h to 4h; The protective atmosphere is a mixture of nitrogen and hydrogen, with hydrogen accounting for 3% to 8% of the volume, and a dew point ≤ -40℃.

[0017] As a further aspect of the present invention: the fine groove width tolerance of the prepared copper busbar is ±0.05mm, the groove depth tolerance is ±0.08mm, the cumulative error of the groove spacing is ≤0.1mm / 100mm, the tensile strength of the copper busbar is ≥320MPa, and the conductivity is ≥98%IACS.

[0018] Compared with the prior art, the present invention has the following significant advantages: (1) High precision of groove: Through the synergistic effect of micro-convex arc groove bottom mold and three-stage variable speed pulse extrusion, the width, depth and spacing tolerance of fine groove are strictly controlled to meet the requirements of high precision assembly.

[0019] (2) Material utilization and production efficiency are greatly improved: one-time extrusion molding avoids post-processing losses, and with the optimized speed curve, green manufacturing with high efficiency and high material utilization is achieved.

[0020] (3) Excellent overall performance of the product: Multi-stage aging treatment enables the copper busbar to obtain high strength and high conductivity at the same time, breaking the contradiction between the two in the traditional process, and can meet the application scenarios of high current carrying capacity and high reliability.

[0021] (4) Significantly extended mold life: The reasonable mold structure design combined with the wear-resistant coating greatly reduces wear and cracks during the extrusion process and reduces production interruptions caused by frequent mold changes.

[0022] (5) High yield and good process stability: The online non-contact protection scheme effectively prevents the deformation of the groove. Batch production verification shows that the process has high repeatability and the overall cost is lower than the existing technology. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process flow of the method of the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] I. Example: See Figure 1 This embodiment is used to illustrate the specific implementation process of the method of the present invention, but it is not intended to limit the scope of protection of the present invention.

[0026] This embodiment aims to prepare a copper busbar with 8 parallel fine grooves. The busbar is 60 mm wide and 8 mm thick, with grooves 1.5 mm wide, 4.5 mm deep, and 2.0 mm apart. The billet used is a TU1 grade oxygen-free copper casting billet with a diameter of 120 mm and a length of 300 mm.

[0027] The main equipment includes: a multi-stage stepped heating furnace (controllable atmosphere), a 4000kN horizontal copper extrusion machine (equipped with a hydraulic servo pulse device and PLC control system), a segmented combined extrusion die, an air-float guide device, a multi-roll staggered tension straightener, and a protective atmosphere multi-stage aging furnace.

[0028] Step 1: Pre-treatment of billet: The TU1 oxygen-free copper billet was placed in a controlled atmosphere furnace, with nitrogen gas purging the furnace to prevent oxidation of the billet surface. The following three-stage stepped heating and holding procedure was employed: ① First stage heating: The furnace temperature is raised to 500℃ at a heating rate of ≤10℃ / min, and then held for 30 minutes. This stage ensures that the surface temperature of the billet rises evenly, avoiding thermal stress cracks caused by excessively rapid heating.

[0029] ② Second stage heating: Continue heating at a rate of ≤8℃ / min to 680℃, and hold for 20 minutes. This stage allows heat to be gradually conducted to the core of the billet, reducing the temperature difference between the inside and outside.

[0030] ③ Third stage heating: The temperature is then increased to 880℃ at a rate of ≤6℃ / min and held for 40 minutes. After the holding period, the surface and center (through pre-drilled holes) of the billet are measured using a contact thermocouple thermometer. The surface temperature is recorded as 882℃ and the center temperature as 870℃. The temperature difference between the inside and outside is 12℃, which meets the design requirement of ≤15℃.

[0031] After heating is complete, the billet is transferred from the heating furnace to the copper extrusion machine feed inlet by an automatic robotic arm. The transfer time is controlled within 30 seconds to reduce heat loss.

[0032] Step Two: Mold Design and Assembly This embodiment employs a segmented, modular extrusion die, which is cylindrical in shape with a total length of approximately 280mm and an outer diameter matching the outlet diameter of the copper extruder barrel (φ160mm). The die is coaxially assembled with four functional sections from the feed end (rear end) to the discharge end (front end): an inlet guiding zone, a compression deformation zone, a multi-groove finishing and shaping zone, and an outlet air-cooling shaping section. These sections are connected as a single unit via locating pins and end-face clamping bolts, facilitating the disassembly and replacement of worn parts.

[0033] From its external appearance, the rear end of the mold is the inlet guide zone, shaped like a short cylinder with a flared feed inlet at the center of the end face; the middle is the compression deformation zone, shaped like a frustum cone, with its outer diameter gradually narrowing from back to front; the front is the multi-groove finishing and shaping zone, shaped like a disc, with a hard alloy mold core embedded inside, the end face of which is machined with fine grooves; the very front is the outlet air-cooling and shaping section, shaped like a sleeve, with an air pipe connector on the side wall. After the entire mold is assembled, the internal flow channel smoothly transitions from a circular cross-section to a rectangular grooved cross-section, and the metal undergoes four stages in sequence as it passes through: diversion, compression, shaping, and cooling. The specific structure is as follows: Inlet flow guide area: It is equipped with 24 honeycomb-shaped flow diversion holes (3 times the number of slots). The flow diversion holes are arranged in concentric circles, and the diameter of the holes gradually increases from the center to the outer edge. Through computational fluid dynamics simulation optimization, the flow velocity deviation at the outlet of each flow diversion hole is controlled within ±5%. The function of the flow diversion holes is to evenly distribute the single copper material to the corresponding area of ​​each slot.

[0034] Compression deformation zone: tapered flow channel, with a compression ratio designed to be 8:1, allowing the metal to gradually aggregate and increase pressure.

[0035] Multi-groove finishing and shaping area: The mold core is made of WC-Co cemented carbide (6% cobalt content), with a TiAlN coating applied by physical vapor deposition (PVD) to a thickness of 3.5 μm. Nanoindentation testing shows the coating hardness to be 36 GPa. This area features eight parallel fine grooves, each 1.5 mm wide, 4.5 mm deep, and 2.0 mm apart. Each groove has a slightly convex, rounded transition structure at its bottom with a radius of 0.10 mm. This structure is formed by precision electrical discharge machining, achieving a surface roughness Ra ≤ 0.2 μm.

[0036] Exit air-cooling and shaping section: An annular air-cooling channel is provided on the exit side of the mold core, through which 0.2MPa compressed air is introduced to initially cool the newly extruded groove-shaped copper busbar in order to maintain the groove shape profile.

[0037] After the mold is assembled, it is preheated to 450℃~500℃ and held for 30 minutes to reduce thermal shock during the initial extrusion stage.

[0038] Step 3: Variable temperature and speed extrusion: The pretreated billet is fed into the copper extrusion machine barrel, which is heated to 700℃ and held for 20 minutes to ensure uniform barrel temperature. The extrusion shaft is hydraulically driven, and its displacement and pressure are monitored in real time by a programmable logic controller (PLC). The extrusion process employs a three-stage speed-changing curve, as detailed below: 0.3 seconds before the end of the high-speed operation (the remaining stroke is calculated in real time by a displacement sensor), the PLC sends a trigger signal to the hydraulic servo impact device. This device superimposes an instantaneous pressure boosting pulse onto the existing extrusion pressure: the boosting amplitude is 8% of the normal extrusion pressure (normal extrusion pressure is approximately 420 MPa, pulse peak is approximately 454 MPa), the pulse frequency is 30 Hz, the pulse width is 50 ms, and the pulse waveform is an approximately rectangular wave. At this time, a brief spike can be observed on the extrusion pressure curve, which then quickly recovers.

[0039] The function of this pulse is to force the metal to completely fill the micro-corners of the groove tip and bottom just as it is about to leave the mold's shaping zone, while simultaneously compacting the tiny pores inside the material. After extrusion, the copper busbar passes through the outlet air-cooling shaping section, where it is initially cooled to approximately 500°C.

[0040] Step 4: Online tension straightening and groove protection: The extruded grooved copper busbar (temperature approximately 500℃, not yet fully hardened) first enters the air-float non-contact guide device.

[0041] Air-floating guide: This device consists of three rows of annular air holes arranged along the direction of copper busbar movement, with six air holes in each row, evenly surrounding the copper busbar. Room temperature compressed air (dew point -20℃) at 0.35MPa is ejected from the air holes, forming a uniform air cushion layer, allowing the copper busbar to float and move forward before the slot is fully hardened, without contact with any solid parts; the air-floating distance (the gap between the copper busbar surface and the inner wall of the guide device) is approximately 1-2mm.

[0042] Nitrogen blowing within the tank: Following the air flotation guide section, a tank-shaped blowing manifold is installed. The manifold has eight micro-nozzles, each aimed at the inlet of a fine-grained tank. Low-temperature nitrogen (temperature -10℃ to 0℃, supplied by a liquid nitrogen evaporator) is introduced into each fine-grained tank at a pressure of 0.2 MPa and a flow rate of approximately 5–8 L / min per tank. The low-temperature nitrogen has three functions: ① Directional cooling of the weakest areas of the tank shape, accelerating tank shaping; ② Forming a micro-positive pressure cushion, supporting the tank sidewalls from the inside and preventing deformation of the tank openings during subsequent straightening; ③ Displacing hot air within the tank, reducing oxidation.

[0043] Multi-roll staggered tension straightening: After air flotation and nitrogen blowing, the copper busbar temperature drops to approximately 150℃~200℃ before entering a seven-roll staggered tension straightener. Before straightening, the yield strength of the copper busbar is measured to be approximately 110MPa using an online portable hardness tester (Webster hardness tester). The straightening tension is set to 40% of this strength, i.e., 44MPa. The straightening rollers are polyurethane-coated rollers, with no protrusions on the part that contacts the groove, only contacting the back plane (no groove surface) of the copper busbar to avoid damaging the groove opening; after straightening, the curvature per meter of the copper busbar is ≤0.5mm.

[0044] Step 5: Multi-level timeliness processing: The straightened copper busbars are cut into 2-meter lengths and placed in a multi-stage aging furnace under a protective atmosphere. The furnace atmosphere is a mixture of nitrogen and hydrogen, with hydrogen accounting for 5% by volume and a dew point of -45°C, to prevent oxidation of the copper busbar surface and to reduce the trace oxide film.

[0045] A two-stage aging process is adopted: 1. Stress-relief annealing: Heat to 200℃ at a rate of ≤15℃ / min, hold for 45 minutes, and maintain a slightly positive atmosphere pressure (1.05~1.1 atm) in the furnace during this stage. After holding, do not rush to raise the temperature, but let the furnace transition naturally (about 15 minutes) to the next stage.

[0046] 2. Precipitation enhancement treatment: Continue heating to 300℃ (heating rate ≤10℃ / min), and hold for 3 hours. During the holding period, the temperature fluctuation inside the furnace should be controlled within ±5℃.

[0047] 3. Cooling: After the heat preservation is completed, turn off the heating power, keep the protective atmosphere circulating, and let it cool with the furnace to ≤60℃ before removing it and allowing it to cool naturally to room temperature. Detection and Results The finished copper busbars are subjected to systematic testing, and all testing methods comply with national or industry standards.

[0048] (1) Dimensional inspection of the channel The groove width, groove depth, and groove spacing were measured using a coordinate measuring machine (ZEISS CONTURA G2, accuracy ±0.003mm). Sampling locations: Five sections were randomly selected from each batch, each 200mm in length, and three cross-sections (ends and midpoint) were measured on each section. Measurement results: Groove width: average value 1.50mm, maximum value 1.52mm, minimum value 1.47mm, tolerance range +0.02 / -0.03mm, meeting the ±0.05mm requirement.

[0049] Groove depth: average value 4.48mm, maximum value 4.52mm, minimum value 4.44mm, tolerance range +0.04 / -0.06mm, meeting the ±0.08mm requirement.

[0050] Cumulative error of slot spacing: The theoretical value of the total span of 8 slots (from the center of the 1st slot to the center of the 8th slot) is 16.0mm, and the measured average value is 15.98mm, with an error of 0.02mm. Converted to a cumulative error per unit length of 0.02mm / 100mm, it is far better than ≤0.1mm / 100mm.

[0051] (2) Microstructure of the trough The tank bottom and sidewalls were observed using a super depth-of-field 3D microscope (KEYENCE VHX-6000, 200× magnification). Observation results: The tank bottom was fully filled, with no microcracks, pores, or missing material; the tank sidewalls were straight, without burrs or tears. The surface roughness of the tank bottom was measured using a white light interferometer, with an Ra value of 0.83 μm (better than the design requirement of ≤1.0 μm).

[0052] (3) Mechanical property testing Tensile specimens were prepared according to GB / T 228.1-2010 "Metallic materials, tensile testing—Part 1: Tests at room temperature". Due to the non-uniform cross-section of the copper busbar (including grooves), non-proportional specimens were used, with a parallel length containing complete grooves, a gauge length of 50 mm, and a width of 12 mm (containing at least two complete grooves). Tensile testing was performed using a universal testing machine (Zwick Z100) at a tensile rate of 1 mm / min. Five specimens were tested. Results: Tensile strength Rm: 336MPa, 338MPa, 334MPa, 337MPa, 335MPa, average value 336MPa, standard deviation 1.5MPa.

[0053] Percentage elongation after fracture A: 11.8%, 12.2%, 12.0%, 12.1%, 11.9%, with an average value of 12.0%.

[0054] (4) Conductivity test An eddy current conductivity meter (Foerster SIGMATEST 2.069, calibrated to the International Annealed Copper Standard IACS) is used. Measurement position: the back plane (groove-free surface) of the copper busbar. One measurement is taken every 500 mm along the length direction, and a total of 10 points are measured. Each point is measured repeatedly 3 times and the average value is taken. The ambient temperature is 20℃±1℃. Results: the maximum value is 98.6% IACS, the minimum value is 98.2% IACS, the average value is 98.4% IACS, and the standard deviation is 0.12%.

[0055] (5) Yield statistics The total extrusion length of this batch is 502 meters. Defect judgment criteria: the width or depth of any groove exceeds the tolerance range by more than 0.03 mm; there are cracks or insufficient filling with a length of ≥10 mm in the groove; the overall curvature of the copper busbar is >1 mm / m; there are scratches with a depth of ≥0.1 mm on the surface. After inspection meter by meter (using laser profile scanner + manual re-inspection), the qualified length is 483 meters, and the finished product yield is 96.5%.

[0056] Conclusion of Embodiment 1: all the technical indicators claimed in the present invention have been fully achieved, and the effectiveness of the process chain has been verified.

[0057] II. Experiment To verify the feasibility and superiority of the process of the present invention, multiple sets of comparative experiments were carried out. Each set of experiments took Embodiment 1 as the benchmark, changed a single parameter or cancelled a certain feature, and kept the rest unchanged. The detailed experimental data are as follows.

[0058] Experiment 1. Comparison of billet heating methods Three-stage stepped heating significantly reduces the temperature gradient and improves metal fluidity, increasing the groove integrity rate from 71.2% to 94.6%.

[0059] Experiment 2. Comparison of mold groove bottom structures The micro-convex arc structure greatly reduces the stress concentration coefficient, reduces the cracking rate by more than 90%, and significantly reduces the extrusion pressure fluctuation.

[0060] Experiment 3. Optimization of extrusion speed curve Three-stage variable speed配合 end pulse achieves the optimal combination of filling quality and production efficiency.

[0061] Experiment 4. Comparison of Online Slot Protection Schemes The present invention provides online protection with zero contact, low deformation, and high straightness.

[0062] Experiment 5. Comparison of Multi-stage Aging Processes The preferred aging process of this invention results in fine and dispersed precipitates, achieving an optimal match between strength and conductivity.

[0063] Experiment 6. Batch Stability Verification Ten batches were produced consecutively, each 500 meters long, using the process described in Example 1. Summary of test results: All batches met design requirements, demonstrating excellent process stability.

[0064] Experiment 7. Comparison of mold lifespan On the same copper extrusion machine, different die materials and coatings are used to continuously extrude until failure (failure is defined as groove width exceeding tolerance or the appearance of irreparable cracks).

[0065] The mold life of this invention reaches more than 5400 meters, which is about 70% higher than that of ordinary cemented carbide molds, and the failure mode is repairable uniform wear rather than catastrophic cracks.

[0066] Experiment 8. Comprehensive comparison with existing technologies The above data shows that the present invention is significantly superior to the prior art in terms of material utilization, production efficiency, micro-groove processing capability, mechanical and electrical properties, and overall cost.

[0067] III. Comparative Example To verify the overall superiority of the technical solution of the present invention, the following comparative example is set up: the same blank and mold as in Example 1 are used, but the following comparative process is adopted: Single-stage heating: 880℃×2.5h (internal and external temperature difference 32℃); Constant speed extrusion: 5mm / s, without pulse boosting; It features no air flotation guidance, no in-tank nitrogen blowing, and uses traditional roller contact guidance. Single-stage aging: 300℃×3h.

[0068] Results: The integrity rate of the groove shape was only 72%, and a large number of products had bottom cracks, missing material at the groove tips, and uneven groove spacing. The groove width deviation reached ±0.18mm, exceeding the design requirements. The yield rate was 62%, and the mold life was only 1500 meters (failure due to the propagation of microcracks); the tensile strength was 312MPa, and the conductivity was 96.2% IACS.

[0069] This comparative example further verifies the overall effect of the synergistic interaction and indispensability of the various technical features of the present invention.

[0070] In summary, the method for preparing multiple fine-groove copper busbars using a copper extrusion machine provided by this invention, through the synergistic effect of billet pretreatment, die design, variable-speed pulse extrusion, online protection, and multi-stage aging, can stably extrude multiple fine-groove copper busbars with a groove width ≤0.5mm and a depth-to-width ratio >2. Furthermore, this method can be directly applied to existing copper extrusion equipment, requiring only the replacement of a dedicated die, the addition of an air flotation guide device, an in-groove nitrogen blowing pipeline, and a hydraulic servo pulse control system, resulting in low modification costs and strong applicability. The prepared fine-groove copper busbars can be widely used in fields such as battery connectors for new energy vehicles, high-power busbar trunking, rail transit conductive rails, and wind power converter busbars. The implementation of this invention can significantly reduce copper busbar manufacturing costs and improve material utilization, possessing extremely high economic value and environmental benefits.

[0071] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine, comprising the following steps: Step 1: Billet pretreatment: Select high-conductivity oxygen-free copper billets and heat them in a multi-stage stepped manner to 750℃~920℃, and hold them at the temperature so that the temperature gradient between the inside and outside of the billet is ≤15℃. Step 2, Mold Design and Assembly: A segmented combined extrusion mold is adopted, which includes at least an inlet guiding area, a compression deformation area, a multi-groove finishing and shaping area, and an outlet air-cooling shaping section; the multi-groove finishing and shaping area has 3 to 12 parallel fine groove structures with a groove width of 0.5mm to 3.0mm, a groove depth of 2mm to 10mm, and a groove spacing ≥ 1.2 times the groove width, and the bottom of the groove has a slightly convex arc transition structure; Step 3, variable temperature and speed extrusion: The pretreated billet is fed into the copper extruder, the temperature of the extrusion barrel is controlled at 600℃~750℃, and a three-stage variable speed extrusion process including low speed, medium speed and high speed is adopted, and an instantaneous pressure pulse is applied at the end of the high speed section. Step 4: Online tension straightening and groove protection: The extruded grooved copper busbar first enters the air-float non-contact guiding device, and then enters the multi-roll staggered tension straightener. The straightening tension is controlled at 30% to 50% of the material yield strength. At the same time, low-temperature nitrogen gas flow is introduced into each fine groove. Step 5, Multi-stage aging treatment: The straightened copper busbar is placed in a protective atmosphere furnace and first subjected to stress-relief annealing at 180℃~220℃, then heated to 280℃~320℃ for precipitation strengthening treatment, and finally cooled with the furnace to obtain a copper busbar with multiple fine grooves.

2. The method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine according to claim 1, characterized in that: The multi-stage stepped heating in step one is specifically divided into: the first stage heating to 400℃~500℃ and holding for 20min~40min, the second stage heating to 600℃~700℃ and holding for 15min~30min, and the third stage heating to 750℃~920℃ and holding until the internal and external temperature difference meets the standard.

3. The method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine according to claim 1, characterized in that: The radius of the arc of the micro-convex arc transition structure at the bottom of the multi-groove finishing and shaping area is 0.05mm to 0.15mm. The micro-convex arc is formed by precision electrical discharge machining, and the surface roughness Ra≤0.2μm.

4. The method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine according to claim 1, characterized in that: The segmented combined extrusion die has a honeycomb-shaped flow divider in the inlet guide area. The number of flow dividers is 2 to 4 times the number of slots, and the outlet flow velocity deviation of each flow divider is controlled within ±5%. The outlet air-cooling and shaping section is equipped with an annular air-cooling channel surrounding the extrusion channel, through which compressed air at a pressure of 0.1MPa to 0.3MPa is introduced to initially cool the extruded copper busbar to 500℃ to 600℃.

5. The method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine according to claim 1, characterized in that: The core material of the multi-groove finishing and shaping area is a cemented carbide or ceramic matrix composite material. The core surface is coated with TiAlN or CrAlN, with a coating thickness of 2μm to 5μm and a hardness of ≥35GPa.

6. The method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine according to claim 1, characterized in that: In the three-stage variable speed extrusion process in step three, the low-speed segment has a speed of 0.5 mm / s to 1.5 mm / s, the medium-speed segment has a speed of 2 mm / s to 5 mm / s, and the high-speed segment has a speed of 6 mm / s to 12 mm / s; the instantaneous pressure boosting pulse has a pressure boosting amplitude of 5% to 10% of the normal extrusion pressure, and the pulse duration is 0.2 s to 0.5 s; The instantaneous boost pulse is achieved by a hydraulic servo impact device linked to the copper extrusion machine control system, with a pulse frequency of 10Hz to 50Hz and a pulse width of 20ms to 80ms. The triggering condition at the end of the high-speed section is: the remaining extrusion stroke is detected by the displacement sensor, and a pulse is automatically triggered when the remaining stroke is ≤10mm.

7. The method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine according to claim 1, characterized in that: The air-floating non-contact guiding device in step four includes multiple annular air holes arranged at intervals, from which compressed air of 0.2MPa to 0.5MPa is ejected, causing the copper busbar to float and move forward before the groove is completely hardened. The pressure of the low-temperature nitrogen gas flow introduced into each fine-grained tank is 0.1MPa to 0.3MPa, and the flow rate is 5 to 8 L / min per tank; the temperature of the low-temperature nitrogen gas is -15℃ to 0℃.

8. The method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine according to claim 1, characterized in that: In step four, the surface of the straightening rollers of the multi-roller staggered tension straightener that contacts the copper busbar is covered with a polyurethane coating, and they only contact the back plane of the copper busbar, not the groove surface.

9. The method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine according to claim 1, characterized in that: The holding time for stress-relief annealing in step five is 0.5h to 1h, and the holding time for precipitation strengthening treatment is 2h to 4h. The protective atmosphere is a mixture of nitrogen and hydrogen, with hydrogen accounting for 3% to 8% by volume, and a dew point ≤ -40℃.

10. A method for preparing copper busbars with multiple fine grooves extruded by a copper extrusion machine according to any one of claims 1-9, characterized in that: The prepared copper busbar has a fine groove width tolerance of ±0.05mm, a groove depth tolerance of ±0.08mm, a cumulative error of groove spacing ≤0.1mm / 100mm, a tensile strength of ≥320MPa, and a conductivity of ≥98% IACS.

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