Preparation process for optimizing residual stress of metal nickel stamping connecting piece for new energy battery

Abstract

The invention belongs to the technical field of preparation of high-quality metallic nickel connecting strips for new energy batteries, and provides a preparation process for optimizing residual stress of a metallic nickel stamping connecting sheet for a new energy battery, which specifically comprises the steps of material selection, striping, continuous die stamping, inert atmosphere protection annealing, and residual stress detection and control. The range of corners and chamfers of a stamping die adopted in the progressive die stamping is 0.2 mm-1 mm, and the fit dimensional tolerance of a female die and a male die of the stamping die is controlled to be + / -0.05 mm; and the stamping surface in contact with the metal nickel strip is processed by adopting an electrochemical corrosion milling method, the roughness Ra of the stamping surface is less than 0.4 mu m, and the hardness HRC is more than or equal to 55. The metal nickel connecting strip prepared through the method is low in residual stress and small in size deformation after being used, the service life of the metal nickel connecting strip is prolonged, safety and reliability of the metal nickel connecting strip are improved, and the application prospect is wide.

Description

Technical Field

[0001] This invention belongs to the technical field of high-quality nickel alloy connecting pieces for new energy batteries, and relates to a stamping process that optimizes the residual stress distribution of connecting pieces and improves the service life of nickel metal products. Background Technology

[0002] The background technology of this project is the field of stamping preparation technology for nickel metal connecting pieces used in new energy battery power systems.

[0003] With the rapid development of the national new energy vehicle and new energy unmanned aerial vehicle industries, the demand for supporting power battery materials has increased significantly. Nickel, with its advantages of high conductivity, oxidation resistance, corrosion resistance, high strength, and high temperature resistance, is widely used in new energy batteries and other fields. However, with the expansion of application areas and the increase in demand, the requirements for the surface quality and service life of nickel connecting pieces prepared by stamping processes are becoming increasingly stringent. Stamping is a processing method that applies pressure to nickel plates or strips using a die, causing them to separate or plastically deform to obtain the desired shape and size. It features high speed, high efficiency, and high precision, making it suitable for mass production. However, the high speed of the stamping process results in a high energy conversion of kinetic energy into distortion energy, forming residual stress stored inside the nickel parts. This stress can lead to deformation, stress corrosion, and shortened product lifespan during use. Therefore, optimizing the magnitude and distribution of residual stress inside nickel connecting pieces is crucial for improving the reliability of new energy batteries and ensuring the safety of new energy vehicles and electric aircraft.

[0004] Residual stress refers to a force that maintains self-equilibrium within a metal component after external factors such as additional stress, temperature, and load are removed. The fundamental cause of residual stress formation is the change in interatomic interaction forces caused by the inhomogeneity of material composition or structure at the microscale due to different arrangements of different atoms or the same atoms. The presence of residual stress will change the stress state of the metal component during use. It is related to the residual elastic strain in local areas of the material and is a response to the elastic anisotropy or plastic anisotropy of the material. It affects the fatigue strength, corrosion resistance, and dimensional stability of the material. It has been reported that residual stress directly or indirectly causes up to 50% of mechanical part failures, thus becoming a technical issue of increasing concern in the engineering field. Statistical analysis of the test results suggests that controlling the residual stress within 15% of the material's yield strength during the stamping process of nickel metal connecting pieces can prevent deformation or cracking of metal components. The effects of residual stress on nickel metal connecting pieces mainly include four aspects: (1) shortening fatigue life. When metal parts with complex stress states (such as discs) are subjected to compressive stress, the fatigue strength of the components can be improved. However, when the residual stress is in the tensile stress state, the fatigue life of the metal components is reduced; (2) It causes deformation of the parts. Residual stress will cause deformation of the parts. For example, the stamping process affects the original stress balance state of the alloy itself, causing stress concentration. Stress concentration further increases the actual tensile stress value of the surface layer of the connecting strip, which manifests as deformation and dimensional instability of the parts, affecting the reliability of use; (3) It accelerates stress corrosion. Studies have shown that stress and corrosion are necessary conditions for stress corrosion. Tensile stress accelerates stress corrosion. Therefore, residual tensile stress will accelerate the stress corrosion problem of high temperature alloy parts, which has a particularly significant impact on parts used in humid and hot environments; (4) It damages the mechanical properties of the parts. Residual stress affects the yield strength, brittleness value, etc. of metal materials. For example, if there is a high residual tensile stress in the nickel connecting strip, it is equivalent to raising the origin of the stress-strain curve, which is equivalent to lowering the tensile yield limit of the material.

[0005] Studies suggest that residual stress persists throughout the entire manufacturing process of nickel-plated connecting strips in the new energy field, affecting not only the service life of parts but also their reliability. Methods for eliminating or reducing residual stress in metal parts include natural aging, vibration aging, and stress-relief annealing. However, the issue of residual stress control in nickel-plated stamped connecting strips used in new energy vehicles and aircraft power systems has not been addressed in relevant domestic and international literature.

[0006] The invention patents related to this invention are: (1) Residual stress relief device (patent number: CN201910566288.1), which discloses a device for eliminating residual stress in metal parts by using ultrasound. It utilizes the characteristics of ultrasound propagation in liquid to make the workpiece immersed in the liquid vibrate at ultrasonic frequency, obtain excitation force to cause micro-plastic deformation inside the material, and realize the release of the overall residual stress of the workpiece without damaging the surface and internal structure of the workpiece; (2) A method and device for eliminating stress deformation in the process of electric arc additive manufacturing of large components (CN202210142217.0), which belongs to the field of electric arc additive manufacturing and specifically involves a method and device for eliminating stress deformation in the process of electric arc additive manufacturing of large components. The above patents are very different from the process innovation points proposed in this invention. At present, there is an urgent need for a solution to the problems of high residual stress, easy deformation of parts, and impact on service life of metal nickel stamping connecting pieces used in new energy batteries. Summary of the Invention

[0007] The purpose of this invention is to address the problems of high residual stress, easy deformation of parts, and reduced service life of nickel stamped connectors for new energy batteries. It proposes an optimized preparation process for residual stress in nickel stamped connectors to meet the requirements of new energy batteries for high-performance nickel connectors.

[0008] The objective of this invention is achieved through the following means: A process for optimizing the residual stress of nickel stamped connecting pieces is disclosed. This process specifically includes material selection, slitting, progressive die stamping, inert atmosphere annealing, and residual stress detection and control. The progressive die stamping uses stamping dies with corner and chamfer ranges of 0.2mm-1mm, and the dimensional tolerance of the mating dimensions of the female and male dies is controlled to ±0.05mm. The surface roughness Ra of the stamping surface in contact with the nickel strip is <0.4μm, and the hardness HRC≥55. The stamping die includes conventional female and male dies, bolts, nuts, and locating pins, connected by bolts or locating pins. The stamping surface in contact with the nickel strip is machined using conventional electrochemical etching milling methods.

[0009] Preferably, the continuous die stamping is a multi-stage continuous die stamping process for preparing nickel connecting sheets; wherein the bending angle of each stamping stage is ≤50° and the stretching depth is ≤4mm.

[0010] Preferably, the specific steps of the multi-process continuous die stamping are as follows: the first step of stamping deformation reaches 20% of the final deformation amount, the second step reaches 80%, and the third step reaches 100% of the final deformation amount.

[0011] Preferably, the inert atmosphere protected annealing is carried out in an electric furnace with an argon protective atmosphere to continuously anneal the stamped nickel connecting strip to reduce residual stress. The temperature control accuracy of the annealing furnace is ±5℃. The purity of the argon gas is ≥99.8%. The annealing temperature of the nickel stamping is 650℃-680℃, and the holding time is 2min-5min.

[0012] Preferably, the residual stress detection and control involves randomly selecting three pieces from each batch of annealed nickel stampings at the stamping bending location where the residual stress is greatest, and detecting the residual stress values ​​at these three points. Based on the residual stress on the surface of qualified products, the average value and normal distribution are calculated and analyzed using EXCEL software. The average residual stress of the annealed nickel stampings is controlled to be ≤200MPa.

[0013] Preferably, the slitting process involves using a slitting machine to cut the nickel strip into nickel strips with a width that meets the design requirements of the new energy battery connector.

[0014] Preferably, the nickel strip is selected to meet the requirements of new energy battery connectors, and the nickel plate or strip is selected to meet the product requirements in terms of chemical composition, thickness and mechanical properties.

[0015] The advantages of this invention compared with the prior art are as follows: This invention addresses the problems of high residual stress, easy deformation of parts, and reduced service life of nickel stamped connecting pieces for new energy batteries by proposing a preparation process method to optimize the residual stress of nickel stamped connecting pieces.

[0016] (1) Design and process control of progressive stamping dies: taking into account the usage requirements and material properties of nickel connecting pieces, The design of progressive stamping dies requires that the corners and chamfers of the stamping dies be within the range of 0.2mm-1mm to avoid stress concentration and reduce residual stress during stamping. Specifically, the dimensional tolerance of the mating dies (male and female) is controlled to ±0.05mm. The stamping surfaces in contact with the nickel strip can be machined using electrochemical etching milling to ensure a smooth surface finish. The surface roughness Ra < 0.4μm and hardness HRC ≥ 55 are achieved. Compared with traditional manufacturing processes, this not only improves product quality and maintains production efficiency but also reduces residual stress. (2) Stress-relief annealing process design: By using high-purity argon as the protective atmosphere for annealing the nickel metal connecting piece, the oxidation of the material surface is avoided, and the surface quality is guaranteed.

[0017] Therefore, the nickel metal connecting strip prepared by this invention has low residual stress and small dimensional deformation after use, which helps to improve the service life and safety reliability of the nickel metal connecting strip, and has broad application prospects. Attached Figure Description

[0018] Figure 1 The nickel metal connector sheet prepared in Example 1.

[0019] Figure 2 The nickel metal connector was prepared for Comparative Example 1.

[0020] Figure 3 The nickel metal connector was prepared for Comparative Example 2. Detailed Implementation

[0021] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0022] In the specific embodiments of the present invention, unless otherwise specified, the reagents and materials used are all conventional commercially available products in the art and can be obtained through commercial channels. Example 1

[0023] According to the requirements for new energy battery connectors, the following materials are selected: chemical composition (Ni+Co (wt%, the same below) ≥99.5%, C<0.1%, S<0.005%, P<0.002%, total impurity elements not exceeding 0.5%), thickness 0.5mm, and mechanical properties (σ). b =350MPa, δ 10A nickel metal strip meeting the requirements (Ni + Co (wt%, the same below) ≥ 99.5, C < 0.1, S < 0.005, P < 0.002, total impurity elements not exceeding 0.5), with a thickness of 1 mm and mechanical properties (σ≥ 3480 MPa, δ) is selected according to the requirements of the new energy battery connection piece. The nickel metal strip is slit and cut into nickel metal strips with a width meeting the requirements of the new energy battery connection piece, with a width of 20 mm. The surface of the strip after slitting is smooth, without cracks and bubbles. In view of the characteristics of nickel metal, the stamping die includes a conventional female die, male die, bolts, nuts and positioning pins, and is connected by bolts or positioning pins. The edges and chamfers of the stamping die are 1 mm respectively to avoid stress concentration and reduce the stamping residual stress. Among them, the mating dimensional tolerance of the female die and male die is controlled at ±0.05 mm; the stamping surface contacting the nickel metal strip is processed by the method of electrochemical corrosion milling, the surface roughness Ra of the stamping surface is 0.2 μm, and the hardness HRC is 56; the nickel metal connection piece is prepared by the method of multi-process continuous die stamping: in the first step, the stamping deformation reaches 20% of the final deformation amount, in the second step it reaches 80%, and in the third step it reaches 100% of the final deformation amount. Using this continuous stamping die can reduce the accumulation of residual stress inside the stamping parts and avoid cracking of the product surface caused by excessive one-time forming amount. Among them, the bending angle of each stamping process is 30°, and the drawing depth is 3 mm; an electric furnace with an argon (Ar) protective atmosphere is used to continuously anneal the nickel metal connection strip after stamping to reduce the residual stress, and the temperature control accuracy of the annealing furnace is ±5°C. Among them, the purity requirement of argon is 99.8%; the annealing process of the nickel metal stamping parts is 650°C, and the holding time is 2 min; for each batch of annealed nickel metal stamping parts, 3 pieces are randomly inspected to measure the residual stress. At the stamping and bending part with the maximum residual stress of the stamping parts, a portable X-ray residual stress tester is used to detect the residual stress values at 3 points, which are 20 MPa, 35 MPa and 40 MPa respectively; the surface quality of the nickel metal connection piece qualified for annealing and residual stress detection is inspected by visual observation, without surface defects such as cracks, folds and pits, and is judged as a qualified product. Example 2

[0024] According to the requirements of the new energy battery connection piece, select chemical composition (Ni + Co (wt%, the same below) ≥ 99.5, C < 0.1, S < 0.005, P < 0.002, total impurity elements not exceeding 0.5), thickness 1 mm and mechanical properties (σ b ≥ 3480 MPa, δ 10=16% ( ) of metallic nickel strip. The metallic nickel strip is slit into strips with a width of 30mm, meeting the requirements for new energy battery connecting pieces. The surface finish of the slit strip is smooth, free from defects such as cracks and bubbles that affect the appearance and quality of the stamped parts. Considering the characteristics of metallic nickel, the stamping dies include conventional female and male dies, as well as bolts, nuts, and locating pins, connected by bolts or locating pins. The corners and chamfers of the stamping dies are 0.5mm to avoid stress concentration and reduce residual stamping stress. The dimensional tolerance of the female and male dies is controlled at ±0.05mm. The stamping surface in contact with the metallic nickel strip is machined by electrochemical etching milling, achieving a surface roughness Ra=0.1μm and a hardness HRC=59. A multi-stage progressive die stamping method is used to prepare the metallic nickel connecting pieces: the first step achieves 20% of the final deformation, the second step achieves 80%, and the third step achieves 100% of the final deformation. This continuous stamping die reduces the accumulation of residual stress inside the stamped parts, preventing surface cracking caused by excessive forming volume in a single pass. Each stamping operation involves a 40° bending angle and a 4mm drawing depth. An electric furnace with an argon (Ar) protective atmosphere is used for continuous annealing of the stamped nickel connecting strips to reduce residual stress. The annealing furnace temperature control accuracy is ±5℃. The argon purity is 99.9%. The annealing process for the nickel stamped parts is at 650℃ with a holding time of 2 minutes. Three pieces from each batch of annealed nickel stamped parts are randomly selected for residual stress measurement. At the stamping bending area with the highest residual stress, a portable X-ray residual stress tester is used to measure the residual stress values ​​at three points: 43MPa, 32MPa, and 30MPa, meeting the requirements. Visual inspection is used to check the surface quality of the annealed and residual stress-tested nickel connecting strips. The absence of surface defects such as cracks, folds, and pits indicates a qualified product. Comparative Example 1

[0025] The process differs from that in Example 1 in that multi-stage continuous die stamping is replaced by a single stamping method (one stamping to 100% of the final deformation). Due to the excessive deformation, the residual stress generated in the product is large, leading to product deformation. Comparative Example 2

[0026] The process differs from that in Example 1 in that nitrogen is used as the protective atmosphere for annealing the nickel connecting pieces in the stress-relief annealing process. Products obtained with nitrogen as the protective atmosphere develop brittle nitrides on the surface at high temperatures, resulting in high hardness, high stress, and surface microcracks.

Claims

1. A manufacturing process for optimizing the residual stress of nickel stamped connecting pieces, characterized in that... The process specifically includes material selection, slitting, progressive die stamping, inert atmosphere protective annealing, residual stress detection and control. The progressive die stamping uses stamping dies with corner and chamfer ranges of 0.2mm-1mm. The dimensional tolerance of the mating of the female and male dies is controlled at ±0.05mm. The surface roughness Ra of the stamping surface in contact with the nickel strip is <0.4μm, and the hardness HRC≥55.

2. The preparation process for optimizing the residual stress of nickel stamped connecting pieces according to claim 1, characterized in that... The continuous die stamping process is used to prepare nickel connecting sheets by multi-stage continuous die stamping; wherein the bending angle of each stamping stage is ≤50° and the stretching depth is ≤4mm.

3. The preparation process for optimizing the residual stress of the nickel stamping connecting piece according to claim 2, characterized in that... The specific steps of the multi-process continuous die stamping are as follows: the first step is to stamp and deform to reach 20% of the final deformation amount, the second step is to reach 80%, and the third step is to reach 100% of the final deformation amount.

4. The preparation process for optimizing the residual stress of nickel stamped connecting pieces according to claim 1, characterized in that... The inert atmosphere protected annealing is carried out in an electric furnace with an argon protective atmosphere to continuously anneal the stamped nickel connecting strip to reduce residual stress. The temperature control accuracy of the annealing furnace is ±5℃. The purity of the argon gas is ≥99.8%. The annealing temperature of the nickel stamping is 650℃-680℃, and the holding time is 2min-5min.

5. The preparation process for optimizing the residual stress of nickel stamped connecting pieces according to claim 1, characterized in that... The aforementioned Residual stress detection and control involves randomly selecting three pieces from each batch of annealed nickel stampings at the stamping bending point where residual stress is greatest, and measuring the residual stress values ​​at these three points. Based on statistical analysis of the residual stress values ​​on the surface of qualified products, the average residual stress of annealed nickel stampings is controlled to be ≤200MPa.

6. The preparation process for optimizing the residual stress of nickel stamped connecting pieces according to claim 1, characterized in that... The slitting process involves using a slitting machine to cut and slice nickel strips into nickel strips.

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