Method for controlling wall thickness uniformity of large-size aluminum alloy cylindrical battery shell by continuous extrusion

Abstract

This application relates to the field of precision forming technology for aluminum alloys, and in particular to a method for controlling the uniformity of wall thickness in continuously extruded large-size aluminum alloy cylindrical battery casings. This method is based on the law of constant volume in metal plastic forming, and achieves uniform wall thickness control by establishing a flow balance model between the upper and lower flow cavities. The core technologies address three main causes: asymmetric bending shear resistance (75%), asymmetric vertical temperature gradient (15%), and asymmetric wall adhesion resistance (10%). To address the wall thickness deviation caused by the high flow velocity in the upper cavity and the slow flow velocity in the lower cavity, an asymmetric flow-promoting angle compensation scheme is adopted. The lower flow-promoting angle equals the upper flow-promoting angle plus an adjustment δ, with the effective engineering range of δ being 1° to 15°. Through six dimensionless correction factors combined with calculation formulas, quantitative adaptation is achieved for all operating conditions. This method has a scientific mechanism, is quantitatively controllable, and has strong mass production feasibility, applicable to full-size battery casing production, and completely solves the deviation problem of thinner upper walls and thicker lower walls.

Description

Technical Field

[0001] This invention relates to a method for controlling the uniformity of wall thickness of large-size aluminum alloy cylindrical battery casings through continuous extrusion, belonging to the technical field of precision plastic processing of non-ferrous metals and manufacturing of power battery components for new energy vehicles. Background Technology

[0002] Conclad's single-round, double-groove continuous extrusion process is currently the mainstream production process for large-size aluminum alloy cylindrical battery casings, offering advantages such as continuous operation, high efficiency, low energy consumption, and high material utilization. However, under conditions of perfectly symmetrical left and right feeding, existing symmetrical mold designs still exhibit directional wall thickness deviations, with the upper wall being thinner and the lower wall being thicker. The deviation is typically 0.05–0.12 mm, which cannot meet the precision requirement of a wall thickness deviation of ≤0.02 mm for new energy power battery casings.

[0003] Existing solutions mainly rely on manual experience in mold repair, gravity correction theory, grinding of sizing cavities, and temperature compensation. For example, Chinese patent CN112355042A discloses a continuous extrusion aluminum alloy battery casing mold that adopts a symmetrical flow guide cavity design and adjusts the wall thickness by grinding the sizing cavity. However, it still has the following defects: many trial molding times (usually 3-5 times), high material loss, long development cycle, uncontrollable accuracy (wall thickness deviation 0.05~0.12mm), and discrepancies between theory and actual measurement, which cannot meet the accuracy requirement of wall thickness deviation ≤0.02mm for new energy power battery casings.

[0004] In view of the above-mentioned shortcomings, the present invention aims to create a method for controlling the uniformity of wall thickness of large-size aluminum alloy cylindrical battery casings through continuous extrusion, so as to make it more valuable for industrial application. Summary of the Invention

[0005] To address the aforementioned technical problems, the purpose of this invention is to provide a method for controlling the uniformity of wall thickness in continuously extruded large-size aluminum alloy cylindrical battery casings that has a clear mechanism, is quantitatively controllable, achieves first-time mold trial qualification, and is compatible with all specifications. By quantitatively compensating for the difference in flow resistance between the upper and lower guide cavities through asymmetric flow-promoting angles, this method completely solves the common industry problem of thin upper walls and thick lower walls, achieving a wall thickness deviation of ≤0.02mm, a material utilization rate of ≥93%, and a first-time mold trial qualification rate of 100%.

[0006] The present invention provides a method for controlling the uniformity of wall thickness of large-size aluminum alloy cylindrical battery shells in continuous extrusion. In the continuous extrusion molding process, the metal flow rate in the upper guide cavity of the die is faster than that in the lower guide cavity, resulting in a thinner upper wall and a thicker lower wall. The method adopts an asymmetric flow-promoting angle quantitative compensation strategy. By increasing the flow-promoting angle of the lower guide cavity, its flow resistance is reduced, so that the metal volume flow rate of the upper and lower guide cavities is equal, thereby achieving uniform wall thickness control.

[0007] The asymmetric flow-promoting angle quantitative compensation strategy calculates the flow-promoting angle adjustment δ according to the following formula: ; in: K is the comprehensive coefficient for flow resistance asymmetry; This is the size normalization factor; This is a temperature correction factor; This is the speed correction factor; For lubrication correction factor; For the sizing length factor, This is the material flowability factor.

[0008] Furthermore, the effective engineering range of the flow angle adjustment δ is 1°≤δ≤15°.

[0009] Furthermore, each dimensionless correction factor is determined as follows: The size normalization factor Where D is the outer diameter of the battery casing and t is the target wall thickness. D ref =21mm, t ref =0.6mm; The temperature correction factor Where T is the mold temperature. T ref =480℃, m =0.006; The speed correction factor Where n is the rotational speed of the extrusion roller, n ref =8rpm; The lubrication correction factor Where μ is the coefficient of lubrication friction. μ ref =0.2; The sizing length factor Where L is the length of the fixed-diameter cavity, L ref =60mm; The material fluidity factor Where σ is the high-temperature flow stress, σ ref =90MPa.

[0010] Furthermore, the comprehensive coefficient K for flow resistance asymmetry is a process setpoint, with an engineering value range of 1.5 to 8.0.

[0011] Furthermore, the effective flow height h of the guide cavity is determined according to the following formula: In the formula, t is the wall thickness of the finished battery case, and 0.1mm is the compensation amount for high-temperature metal rheological expansion.

[0012] Further, the initial symmetric flow-promoting angle α0 is selected according to the wall thickness specification: when the thin-walled case has t≤0.4mm, the value range of α0 is 50° to 60°; when the conventional case has 0.4mm<t≤0.8mm, the value range of α0 is 30° to 50°; when the thick-walled case has t>0.8mm, the value range of α0 is 20° to 30°.

[0013] Further, the final machining angle is determined in the following manner: the lower flow-promoting angle α↓ = α0 + δ, and the upper flow-promoting angle α↑ = α0 - δ; where α0 is the initial symmetric flow-promoting angle, and δ is the adjustment amount of the flow-promoting angle.

[0014] Further, it is applicable to cylindrical battery cases with an outer diameter of 18mm to 60mm, including 18650 type, 21700 type, 4680 type and custom specifications thereof.

[0015] Further, a left-right symmetrical feeding condition is adopted, the extrusion equipment adopts a one-wheel double-groove continuous extruder, the die material is H13 hot work die steel, the lubrication method is graphite emulsion lubrication, and the cooling method is a die closed-loop water cooling system; the method enables the upper and lower wall thickness deviation to be controlled within 0.02mm, and the qualified standard can be achieved through one trial die.

[0016] With the above solutions, the present invention has at least the following advantages: (1) The accuracy meets the standard, the upper and lower wall thickness deviations of battery cases of all specifications are controlled within 0.02mm, which meets the mandatory accuracy requirements of new energy power battery cases; (2) One-time trial die, all embodiments achieve qualification after one trial die, which greatly reduces the trial die cost and development cycle; (3) Stable mass production, good consistency in batch production, and small deviation between batches; (4) Guaranteed production capacity, maintaining high-efficiency production capacity, with a material utilization rate of over 94%; (5) Strong universality, applicable to the full specification size range from 18650 to 4680, as well as conventional aluminum alloy materials.

[0017] The above description is only an overview of the technical solutions of the present invention. In order to clearly understand the technical means of the present invention and implement them according to the content of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Description of the Drawings

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show a certain embodiment of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a three-dimensional structural schematic diagram of the combined extrusion die of the present invention; Figure 2 This is a front view of the combined extrusion die of the present invention; Figure 3 This is a front cross-sectional view of the combined extrusion die of the present invention; Figure 4 This is a left view of the female die in the combined extrusion die of the present invention; Figure 5 This is a cross-sectional view of the female die in the combined extrusion die of the present invention; Figure 6 This is a cross-sectional view of the female die in the combined extrusion die of the present invention.

[0020] In the figure: 1. Male mold; 2. Female mold; 3. Upper guide cavity; 4. Lower guide cavity; 5. Upper guide surface; 6. Lower guide surface; 21. Sizing cavity; 22. Guide cavity inlet fillet. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0022] See Figures 1 to 6 A preferred embodiment of the present invention provides a combined extrusion die, comprising a male die 1 and a female die 2. The male die 1 is connected to the extrusion roller shoe and has two symmetrical feed ports that are respectively connected to the two die openings of the extrusion roller. The rear end of the male die 1 cooperates with the female die 2 to form an upper guide cavity 3 and a lower guide cavity 4. The female mold 2 has a horizontal sizing cavity at its center for forming the final size of the battery casing; the front end of the female mold 2 cooperates with the male mold 1 to form the outer wall of the upper guide cavity 3 and the lower guide cavity 4. The upper guide cavity 3 is inclined downwards, and the lower guide cavity 4 is inclined upwards, converging towards each other at the sizing cavity 21; The lower wall of the upper guide cavity 3 is the upper guide surface 5, the upper wall of the lower guide cavity 4 is the lower guide surface 6, and the flow angle α is the angle between the guide surface and the radial direction of the sizing cavity 21. The upper guide cavity 3 and the lower guide cavity 4 have equal volumes to ensure uniform metal filling; The upper guide surface 5 and the lower guide surface 6 adopt a straight line design to avoid uneven flow caused by curved surfaces; The sizing cavity 21 has a flow guide cavity inlet fillet 22 on one side of the male mold 1. The radius of the flow guide cavity inlet fillet 22 is R=2~3mm to avoid the generation of eddies in the metal flow. A method for controlling the uniformity of wall thickness in continuously extruded large-size aluminum alloy cylindrical battery casings, specifically including the following steps: Based on the Conclad single-round dual-groove symmetrical feeding process, an asymmetric flow-promoting angle quantitative compensation strategy is adopted: In response to the directional defects caused by the metal flow rate of the upper guide cavity 3 being faster than that of the lower guide cavity 4 during continuous extrusion molding, an asymmetric flow-promoting angle quantitative compensation strategy is adopted. By increasing the flow-promoting angle of the lower guide cavity 4 and decreasing the flow-promoting angle of the upper guide cavity 3, the metal volume flow rate of the upper and lower guide cavities is made equal, thus achieving uniform wall thickness.

[0023] Based on the parallel channel flow formula, the volumetric flow rate of metal is directly proportional to the driving force and inversely proportional to the flow resistance: In the formula: For equipment constants, As the driving force of extrusion pressure, This represents the total flow resistance.

[0024] Make the flow rates of the upper and lower guide cavities equal. By introducing six dimensionless correction factors—size, temperature, rotational speed, lubrication, sizing length, and material flowability—the formula for calculating the flow angle adjustment was finally derived: ; Table 1 General Baseline Operating Conditions

[0025] Table 2 Definition of all parameters of dimensionless factor

[0026] Standardized calibration method for the overall coefficient K of flow resistance asymmetry Flow resistance coefficient These are the core parameters of this invention, which are fixed values ​​under the same mold structure and aluminum alloy material, and are calibrated using the following method: (1) Manufactured using the standard operating conditions (21700 type 3003 aluminum alloy battery case); (2) Initial selection Calculate the adjustment angle And process the molds; (3) Measured deviation of upper and lower wall thickness ; (4) Correct according to the following formula :

[0027] (5) Repeat steps 2 to 4 until the wall thickness deviation is ≤0.02mm. This refers to the calibration values ​​for the mold structure and materials; (6) The calibrated K value can be reused in batch production of all specifications of battery cases with the same mold structure (guide flow cavity cross-sectional shape, inlet fillet radius R=2~3mm, male and female mold fitting clearance ≤0.005mm, and consistent sizing cavity inlet transition form) and the same aluminum alloy grade, without the need for recalibration; when crossing mold structures or materials, it is necessary to recalibrate according to this method.

[0028] Key geometric parameter constraints Effective flow height of the guide cavity: ; The finished battery casing has a thick wall. 0.1mm: High-temperature metal rheological expansion compensation amount, used for accurate correction of flow resistance model; Physical meaning: The actual flow height of the metal in the guide cavity is not the assembly gap or expansion clearance; Initial symmetrical flow angle Selection Thin-walled shell ( 50°~60° (A larger angle reduces flow resistance and avoids molding difficulties); Conventional housing ( ): 30°~50°; Thick-walled shell ( ): 20°~30° (Small angle increases flow resistance and ensures molding accuracy) Flow angle adjustment amount Classification; Small-sized housing (18650): ; Standard size housing (21700): ; Large housing (4680): ; Extra-large custom-made housing: ; Standardized implementation process This method can be standardized and automated throughout the entire process, without human intervention. The steps are as follows: (1) Parameter acquisition Collect the following parameters: Product parameters: Battery casing outer diameter Wall thickness ; Material parameters: Aluminum alloy grade, high-temperature flow stress ; Process parameters: mold temperature Extrusion roller speed coefficient of friction Length of sizing cavity ; (2) Calculation of dimensionless factors Substitute into the formula to calculate the 6 dimensionless correction factors:

[0029] (3) Calibration of flow resistance coefficient K Select the flow resistance coefficient based on the mold structure and aluminum alloy grade. (The same mold and materials are fixed values; once calibrated, they can be used for a lifetime.) (4) Calculation of flow angle adjustment Substitute into the core formula to calculate the adjustment amount ,make sure Within the range of 1° to 15°; (5) Determination of final machining angle (6) Precision machining of molds The upper and lower guide surfaces are machined using a five-axis CNC machining center to ensure angular accuracy and surface quality. (7) Mold assembly and debugging Assemble the male and female molds according to the specifications, and check the coaxiality and fit clearance; (8) Mass production of installed equipment Two aluminum alloy billets are fed simultaneously for continuous extrusion production, directly producing high-precision finished products. Precision machining and assembly requirements for molds: Processing equipment: A five-axis CNC machining center is used to ensure angular accuracy; Angular tolerance: Machining tolerance for upper and lower flow angles ≤ ±0.02°; Surface quality: The polishing degree of the guide surface Ra≤0.4μm, reducing the frictional resistance of the wall surface; Coaxiality: The coaxiality of the male and female molds during assembly is ≤0.01mm; Fitting clearance: The fitting clearance between male and female molds is ≤0.005mm to avoid metal flash; Heat treatment: The mold is made of H13 hot work die steel, with a quenching hardness of HRC48~52, and tempering to fully eliminate internal stress.

[0030] Example Example 1 (1) Input parameters Product parameters: , ; Material parameters: 5052 aluminum alloy ; Process parameters: , , , ; Mold parameters: , ; (2) Factor calculation

[0031]

[0032]

[0033]

[0034]

[0035] ; (3) Calculation of adjustment amount (Effective within the range of 1° to 15°) (4) Final machining angle Lower flow angle: ; Upper flow angle: ; (5) Mass production verification results Upper and lower wall thickness deviation: 0.012mm (≤0.02mm, compliant); Roundness: 0.03mm (≤0.06mm, meets standard); Number of trial moldings: 1 successful attempt; Production capacity: 132 pieces / minute; Material utilization rate: 94%.

[0036] Example 2: Type 21700 conventional battery casing (3003 aluminum alloy) (1) Input parameters Product parameters: , ; Material parameters: 3003 aluminum alloy ; Process parameters: , , , ; Mold parameters: , ; (2) Factor calculation All factors are 1.0. ; (3) Calculation of adjustment amount (4) Final machining angle Lower flow angle: ; Upper flow angle: ; (5) Mass production verification results Upper and lower wall thickness deviation: 0.010mm; Number of trial moldings: 1 successful attempt; Production capacity: 140 pieces / minute.

[0037] Example 3: 18650 type small-size battery case (3003 aluminum alloy); (1) Input parameters Product parameters: , ; Process parameters: , , ; Mold parameters: , ; (2) Calculation of adjustment amount (3) Verification results Upper and lower wall thickness deviation: 0.011mm; The trial molding was successful on the first attempt; Example 4: Oversized custom battery casing (extreme operating conditions). (1) Input parameters Product parameters: , ; Material parameters: 5052 aluminum alloy ; Process parameters: , , μ=0.22, L=90mm; Mold parameters: α0=52°, K=2.25 (values ​​calibrated using the calibration method of this invention); (2) Factor calculation: ， ， ， ， ， ； (3) Calculation of adjustment amount: (Effective within the range of 1° to 15°) (4) Verification results Upper and lower wall thickness deviation: 0.015mm; Completely solve the defect of being thin at the top and thick at the bottom.

[0038] Comparative Example Comparative Example 1: Symmetrical flow angle design without compensation (blank control) (1) Test conditions: Same as in Example 1, using a 55° symmetrical flow-inducing angle, without flow resistance compensation; (2) Measured results: Upper wall thickness: 0.27mm; Bottom wall thickness: 0.33mm; Upper and lower wall thickness deviation: 0.06mm (out of tolerance by 3 times); Number of trial moldings: 5; 1200 shells were scrapped. Production costs increased by 18%.

[0039] The symmetrical flow-inducing angle design cannot solve the systemic defect of the upper wall being too thin and the lower wall being too thick, thus verifying the necessity and technical effect of the asymmetric compensation design of the present invention.

[0040] Comparative Example 2: Traditional manual experience-based mold repair method (standard industry solution) (1) Test conditions: Same as in Example 1, without a quantitative model, the guide surface was manually ground by an engineer with more than 10 years of experience; (2) Measured results: Upper and lower wall thickness deviation: 0.12mm (severely out of tolerance); Number of trial moldings: 6; Production capacity has been reduced to 90 pieces per minute; Mass production consistency is extremely poor, with batch-to-batch deviations ≥0.03mm.

[0041] Traditional manual experience-based mold repair methods rely heavily on the individual abilities of engineers and cannot guarantee the stability and consistency of mass production. This verifies the technical advantages of the quantitative and controllable method of this invention.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the uniformity of wall thickness in continuously extruded large-size aluminum alloy cylindrical battery casings, characterized in that, Aiming at the directional defect that the metal flow velocity in the upper flow guiding cavity of the die is faster than that in the lower flow guiding cavity during the continuous extrusion forming process, which leads to the upper wall being too thin and the lower wall being too thick, a quantitative compensation strategy with asymmetric flow promoting angles is adopted, which reduces the flow resistance by increasing the flow promoting angle of the lower flow guiding cavity, so that the metal volume flow rates of the upper and lower flow guiding cavities are equal, and the wall thickness uniformity control is realized; The method comprises the following steps: S1. Calibration of the comprehensive coefficient K for flow resistance asymmetry: Production is carried out using the benchmark operating condition (21700 type 3003 aluminum alloy battery case). Initially, K=4.

0. The flow angle adjustment δ is calculated, and the mold is machined. The actual deviation of the upper and lower wall thickness Δt is measured. Correct the K value and repeat the above steps until the wall thickness deviation is ≤0.02mm, to obtain the K value corresponding to the mold structure and material; S2. Collect product parameters, material parameters and process parameters, and calculate 6 dimensionless correction factors; S3. Calculate the flow angle adjustment amount δ according to the following formula: ; Where: K is the comprehensive coefficient of flow resistance asymmetry calibrated in step S1; This is the size normalization factor; This is a temperature correction factor; This is the speed correction factor; For lubrication correction factor; For the sizing length factor, For material flowability factor; S4. Adjust the flow promoting angles of the upper and lower flow guiding cavities according to δ.

2. The method for controlling the uniformity of wall thickness of continuously extruded large-size aluminum alloy cylindrical battery casing according to claim 1, characterized in that: The engineering effective range of the flow promoting angle adjustment amount δ is 1°≤δ≤15°.

3. The method for controlling the uniformity of wall thickness of continuously extruded large-size aluminum alloy cylindrical battery casing according to claim 1, characterized in that, Each dimensionless correction factor is determined in the following manner: The size normalization factor Where D is the outer diameter of the battery casing and t is the target wall thickness. D ref =21mm, t ref =0.6mm; The temperature correction factor Where T is the mold temperature. T ref =480℃, m =0.006; The speed correction factor Where n is the rotational speed of the extrusion roller, n ref =8rpm; The lubrication correction factor Where μ is the coefficient of lubrication friction. μ ref =0.2; The sizing length factor Where L is the length of the fixed-diameter cavity, L ref =60mm; The material fluidity factor Where σ is the high-temperature flow stress, σ ref =90MPa.

4. The method for controlling the uniformity of wall thickness of continuously extruded large-size aluminum alloy cylindrical battery casings according to claim 1, characterized in that, The flow resistance asymmetry comprehensive coefficient K is a fixed process value, and its engineering value range is 1.5 to 8.

0.

5. The method for controlling the uniformity of wall thickness of continuously extruded large-size aluminum alloy cylindrical battery casings according to claim 1, characterized in that, The effective flow passage height h of the flow guiding cavity is determined by the following formula: h=t+Δh, where t is the wall thickness of the finished battery case, Δh is the high-temperature metal rheological expansion compensation amount, and its value range is 0.08mm to 0.12mm.

6. The method for controlling the uniformity of wall thickness of continuously extruded large-size aluminum alloy cylindrical battery casings according to claim 1, characterized in that, Select the initial symmetric flow promoting angle α0 according to the wall thickness specification: when the thin-walled case has t≤0.4mm, the value range of α0 is 50° to 60°; when the conventional case has 0.4mm<t≤0.8mm, the value range of α0 is 30° to 50°; when the thick-walled case has t>0.8mm, the value range of α0 is 20° to 30°.

7. The method for controlling the uniformity of wall thickness of continuously extruded large-size aluminum alloy cylindrical battery casings according to any one of claims 1-6, characterized in that, The final processing angle is determined based on the principle that the metal volume flow rates of the upper and lower guide cavities are equal: the flow-promoting angle α↓ of the lower guide cavity is greater than the flow-promoting angle α↑ of the upper guide cavity, and α↓ = α0 + δ1, α↑ = α0 - δ2, where δ1 and δ2 are positive real numbers, satisfying the following conditions: δ is the flow angle adjustment amount as described in claim 1.

8. The method for controlling the uniformity of wall thickness of continuously extruded large-size aluminum alloy cylindrical battery casings according to any one of claims 1-6, characterized in that, It is applicable to cylindrical battery cases with an outer diameter of 18mm to 60mm, including 18650 type, 21700 type, 4680 type and custom specifications thereof.

9. The method for controlling the uniformity of wall thickness of continuously extruded large-size aluminum alloy cylindrical battery casings according to any one of claims 1-8, characterized in that, A left-right symmetrical feeding condition is adopted, the extrusion equipment adopts a single-wheel double-groove continuous extruder, the die material is H13 hot work die steel, the quenching hardness is HRC48 to 52, the lubrication method is graphite emulsion lubrication, and the cooling method is a die closed-loop water cooling system; during die processing, the machining tolerance of the upper and lower flow promoting angles is ≤±0.02°, the polishing degree of the flow guiding surface Ra≤0.4μm, the assembly coaxiality of the male and female dies is ≤0.01mm, and the fitting clearance is ≤0.005mm.

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