Lithium strip extrusion forming finite element simulation method and system

Abstract

The invention provides a lithium strip extrusion forming finite element simulation method and system. The method comprises the steps that S1, a model is built based on a Lagrange description method and an Euler description method, and grid division is conducted; s2, defining material attributes of the lithium metal and the model, and setting a viscoplastic constitutive relation of the lithium metal; s3, establishing a dynamic display analysis step, setting a contact mode and a constraint condition, and simulating an extrusion process; and S4, evaluating the stress distribution uniformity and fluctuation characteristics of lithium strip forming according to the stress nephogram output by the model and the stress fluctuation data of the preset fixed point of the extrusion port. Based on the coupling Euler-Lagrange method, the plastic deformation behavior of the lithium metal in the mold and the internal stress distribution and fluctuation characteristics of the lithium strip are simulated; material attributes are defined by introducing a viscoplastic constitutive model, and the hardening behavior of the lithium strip in a mold runner is described; a symmetric modeling method is adopted and a local mesh refinement technology is combined, so that the model calculation efficiency and the simulation precision are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material forming, in particular to a lithium strip extrusion forming finite element simulation method and system, and especially to a lithium strip extrusion forming finite element simulation method and system based on a coupled Euler-Lagrange method. BACKGROUND

[0002] As a very important metal material in the energy storage industry, lithium strip has a small density, a low standard electrode potential, and an ultra-high theoretical specific capacity (3860 mAh / g), which greatly helps the development of high specific energy batteries. As a battery negative material, lithium strip is not only applied to high specific energy lithium primary batteries and lithium metal secondary batteries, but also widely used in all-solid-state batteries and semi-solid-state batteries.

[0003] Metal lithium is soft and has good ductility. The production of lithium strip usually consists of lithium strip extrusion process and lithium strip calendering process. The lithium strip extrusion process is a lithium strip forming process in which a high-purity lithium ingot is placed in a die cavity of an extrusion machine, a plunger or a screw provides a pressure of 10-15 MPa, the metal lithium ingot is plastically deformed in the die cavity, and finally the lithium strip is extruded from the die outlet in the form of lithium strip. The thickness of the lithium strip prepared by the lithium strip extrusion process is usually between 0.5-5 mm. The calendering process of lithium strip is a further thinning and spreading of the lithium strip produced by the extrusion process. The current lithium strip calendering process can produce ultra-thin lithium strip with a thickness of 2 μm.

[0004] During the lithium strip extrusion process, due to the different structures of the die and process parameters, different degrees of stress concentration and stress fluctuation defects usually occur. These defects can cause local cracking, thickness fluctuation and organization distortion of the extruded lithium strip, and in the subsequent calendering process, the lithium strip is more likely to be broken during calendering, and the thickness uniformity of the lithium strip is difficult to control. Therefore, controlling the stress distribution and stress fluctuation of the lithium strip during the extrusion process is crucial to the forming quality of the lithium strip.

[0005] The extrusion process of lithium strip belongs to one of profile extrusion processes. At present, the finite element analysis of profile extrusion process has been studied by engineers and technicians at home and abroad, but the research objects are concentrated on light alloy materials such as aluminum profiles and magnesium profiles, and the analysis methods mainly depend on two types: the updated Lagrangian method based on DEFORM-3D and the arbitrary Lagrangian-Euler method based on HyperXtrude. The updated Lagrangian method based on DEFORM-3D divides the grid on the material, and adopts dynamic grid redivision in the analysis process to control the grid distortion problem caused by large deformation. However, compared with the profile extrusion process of aluminum alloy and magnesium alloy, the extrusion ratio of the lithium strip extrusion process is extremely large, and the grid will still be extremely severely twisted. The arbitrary Lagrangian-Euler method based on HyperXtrude can reduce the grid distortion to a certain extent by making the grid and the material independent of each other, and using the Lagrangian description method for the material boundary and the Euler description method for the material interior. However, for the lithium strip forming process with extremely large extrusion ratio and simple flow channel structure, this method will still cause significant grid distortion due to the violent material flow, resulting in the decrease of calculation accuracy and stability.

[0006] The coupled Euler-Lagrangian method uses the Euler description method for the material flow area and the Lagrangian description method for the rigid part. The simulation of the flowability of lithium metal material fundamentally solves the grid twisting problem of the material in the extreme deformation. However, the contact of this method is only triggered between the rigid body and the material (non-grid), which is easy to cause non-physical penetration or contact failure due to the flow in and out of the boundary material. The calculation amount of this method is also significantly higher than that of the updated Lagrangian method and the arbitrary Lagrangian-Euler method during the calculation process, and about 3-5 times of calculation resources are usually required.

[0007] Patent document CN207414043U discloses a lithium strip extrusion structure with cleaning medium output function, but it is mainly used to clean the lithium strip residues generated in the extrusion process, which is completely different from the technical problems to be solved by the present application. SUMMARY

[0008] In view of the defects in the prior art, the purpose of the present application is to provide a lithium strip extrusion forming finite element simulation method and system.

[0009] According to the lithium strip extrusion forming finite element simulation method provided by the present application, the following steps are included:

[0010] Step S1: constructing a model based on the Lagrangian description method and the Euler description method, and dividing the grid of the model;

[0011] Step S2: defining the material properties of lithium metal and the model, and setting the viscoplastic constitutive relation of lithium metal;

[0012] The material properties include elastic properties, plastic properties and density;

[0013] Step S3: based on the constructed model and the defined material properties, establishing a dynamic display analysis step, setting the contact mode and the constraint condition, defining the initial position of the lithium metal, and simulating the extrusion process;

[0014] Step S4: according to the stress nephogram output by the model and the stress fluctuation data of the preset fixed point of the extrusion port, evaluating the stress distribution uniformity and fluctuation characteristics of the lithium strip forming.

[0015] Preferably, the step S1 comprises:

[0016] The geometric model of the extrusion die, the barrel and the extrusion head defined by the Lagrange description method, and the lithium metal blank flow area model defined by the Euler description method are constructed; the irregular structure of the extrusion port area in the extrusion die is divided by the tetrahedral mesh with the minimum edge length, the lithium metal blank flow area model within a certain range in the height direction of the extrusion port area is divided by the hexahedral mesh, and the structure of the extrusion head, the lithium metal blank flow area and the regular structure area of the extrusion die are divided by the hexahedral mesh.

[0017] Preferably, the step S1 further comprises:

[0018] The barrel and the extrusion die are combined into an integral geometric model, the planar connection and the bolt connection between them are removed, and the outward stripping feature at the extrusion port of the extrusion die is removed, and only the structure of the barrel, the extrusion port of the extrusion die along the axial direction within a certain length and the structure of the bottom of the extrusion head along the axial direction are constructed into a geometric model; in the construction of the Euler domain symmetric geometric model of the lithium metal flow range, the size of the Euler domain geometric model completely wraps the assembly model of the extrusion die, the barrel and the extrusion head, and a certain space along the axial direction is reserved as the outflow range of the metal lithium strip.

[0019] Preferably, the hardening characteristic in the viscoplastic constitutive relation of the lithium metal is introduced by introducing the Cowper-Symonds model as the theoretical basis of the strain rate effect, and the power law equation is adopted as follows:

[0020]

[0021] Wherein, σ is the rheological stress, A represents the quasi-static yield strength, B is the strain rate strengthening coefficient, is the strain rate, and n is the strain rate sensitivity index.

[0022] Preferably, the step S3 comprises:

[0023] The dynamic explicit analysis is used, and the analysis step setting of the geometric nonlinear calculation is started;

[0024] The contact mode comprises normal contact defined by coupling tangential contact and hard contact constraint mechanism of isotropic friction model by using penalty function method.

[0025] The setting of the constraint condition comprises:

[0026] The rigid body constraint is used for the structure of the extrusion die, the barrel and the extrusion head; the velocity range constraint is set for the reference point of the extrusion head, and all the degrees of freedom except the extrusion direction are all constrained, and the fixed constraint is set for the reference point of the extrusion die;

[0027] The field predefinition setting is used to couple the geometric model of the initial lithium metal region and the lithium material attribute, and to define the initial position of the lithium metal.

[0028] Preferably, the constraint condition further comprises the constraint of the Euler domain of lithium metal flow, and the normal velocity of the contact area of the Euler domain with the center surface of the length direction and the width direction of the assembly is set to 0.

[0029] Preferably, the fixed point positions of the model stress sampling are three groups, which are respectively located at the two sections of the width direction of the extrusion port, the center line of the extrusion port and the midpoint of the two ends, and the center line of the width direction of the extrusion port; the stress of the lithium strip in the thickness direction and the width direction is sampled.

[0030] Preferably, the data collection of the fluctuation characteristics comprises setting all the grids in the width direction of the lithium strip as stress sampling points, collecting all the stress data in the width direction in a single frame and drawing a stress curve, and judging the stress fluctuation degree of the width direction of the lithium strip by comparing the stress curves of different frames.

[0031] According to the lithium strip extrusion forming finite element simulation system provided by the application, the lithium strip extrusion forming finite element simulation system comprises:

[0032] Module M1: constructing a model based on the Lagrange description method and the Euler description method, and performing grid division on the model;

[0033] Module M2: defining the material attribute of the lithium metal and the model, and setting the viscoplastic constitutive relation of the lithium metal;

[0034] The material attribute comprises an elastic attribute, a plastic attribute and a density;

[0035] Module M3: establishing a dynamic display analysis step based on the constructed model and the defined material attribute, setting a contact mode and a constraint condition, defining the initial position of the lithium metal, and simulating an extrusion process;

[0036] Module M4: evaluating the stress distribution uniformity and the fluctuation characteristics of the lithium strip forming according to the stress nephogram output by the model and the stress fluctuation data of the preset fixed point positions of the extrusion port.

[0037] Preferably, the module M1 comprises:

[0038] Constructing the geometric model of the extrusion die, the barrel and the extrusion head defined by the Lagrange description method, and the lithium metal billet flow area model defined by the Euler description method; using the minimum edge length tetrahedral mesh to divide the irregular structure of the extrusion port area in the extrusion die, using the hexahedral mesh to divide the lithium metal billet flow area model within a certain range in the height direction of the extrusion port area, and using the hexahedral mesh to divide the regular structure of the extrusion head, the lithium metal billet flow area and the extrusion die.

[0039] Preferably, the module M1 further comprises:

[0040] Combining the barrel and the extrusion die into an integral geometric model, removing the planar connection and bolt connection therebetween, and removing the outward stripping feature at the extrusion port of the extrusion die, and only constructing the geometric model of the barrel, the extrusion port of the extrusion die along the axial direction within a certain length, and the structure of the bottom of the extrusion head along the axial direction; in the construction of the Euler domain symmetric geometric model of the lithium metal flow range, the size of the Euler domain geometric model completely wraps the assembly model of the extrusion die, the barrel and the extrusion head, and a certain space is reserved along the axial direction as the outflow range of the metal lithium strip.

[0041] Preferably, the hardening characteristic in the viscoplastic constitutive relationship of the lithium metal is introduced by introducing the Cowper-Symonds model as the theoretical basis of the strain rate effect, and the power law equation is:

[0042]

[0043] wherein σ is the rheological stress, A represents the quasi-static yield strength, B is the strain rate strengthening coefficient, is the strain rate, and n is the strain rate sensitivity index.

[0044] Preferably, the module M3 comprises:

[0045] Using dynamic explicit analysis, setting the analysis step of geometric nonlinear calculation to be open;

[0046] The contact mode comprises the normal contact defined by the tangential contact and the hard contact constraint mechanism of the isotropic friction model coupled by the penalty function method;

[0047] The setting of the constraint condition comprises:

[0048] Using rigid body constraint for the structure of the extrusion die, the barrel and the extrusion head; setting the velocity range constraint for the reference point of the extrusion head, and fully constraining all degrees of freedom except the extrusion direction, and setting the fixed constraint for the reference point of the extrusion die;

[0049] The geometry model of the lithium metal initial region is coupled with the lithium material attribute by using field predefinition setting to define the position of the lithium metal initial region.

[0050] Preferably, the constraint condition further comprises a constraint of an Euler domain of lithium metal flow, and the normal velocity of the contact area between the length direction and the width direction center surface of the assembly and the Euler domain is set to 0.

[0051] Preferably, the fixed point positions of the model stress sampling are three groups, which are located at the two width direction of the extrusion port, the center line of the extrusion port and the midpoint of the two ends, and the center line of the width direction of the extrusion port; the stress of the lithium strip two ends, the thickness direction of the lithium strip and the width direction of the lithium strip is sampled.

[0052] Preferably, the data collection of the fluctuation characteristics comprises setting all the grids in the width direction of the lithium strip as stress sampling points, collecting all the stress data in the width direction in a single frame and drawing a stress curve, and judging the stress fluctuation degree of the width direction of the lithium strip by comparing the stress curves of different frames.

[0053] Compared with the prior art, the present application has the following beneficial effects:

[0054] 1. The present application is based on the coupled Euler-Lagrange method, realizes the simulation of the plastic deformation behavior of lithium metal in the mold, the internal stress distribution and the fluctuation characteristics of the lithium strip, introduces the viscoplastic constitutive model to define the material attribute, describes the hardening behavior of the lithium strip in the mold flow channel, and uses the symmetric modeling method combined with the local grid refinement technology to improve the calculation efficiency and simulation accuracy of the model.

[0055] 2. The finite element simulation method provided by the present application can systematically analyze the stress distribution characteristics and fluctuation rules of the lithium strip extrusion process, provides a theoretical basis for the structure optimization of the extrusion die and the selection of the best process parameter combination, and further provides an important technical reference for the actual production of the lithium strip extrusion forming.

[0056] 3. The present application uses the coupled Euler-Lagrange method, uses the Euler description method for the extruded lithium metal, regards it as a fluid for simulation according to its fluidity in deformation, establishes the Euler domain of the stress deformation of the lithium metal, so that the grid remains fixed while the lithium metal deforms, fundamentally eliminates the grid distortion caused by the large deformation of the lithium metal, and uses the Lagrange description method for the rigid parts and defines the contact surface of the lithium metal to limit the deformation range of the lithium metal.

[0057] 4. The present application describes the hardening phenomenon of the flowing lithium metal in the extrusion process, simulates the pressure rise of the extrusion head in the extrusion process, introduces the Cowper-Symonds model to provide the relationship between the strain rate and the stress, so that the extrusion speed and the extrusion pressure are matched in the extrusion process.

[0058] 5、The present application reduces the total amount of grid by 3 / 4 through the use of symmetric model for calculation, and the calculation amount is greatly reduced compared with the complete model; the saved computing power is concentrated on the calculation of the extrusion port grid refinement, which can improve the calculation accuracy of the extrusion port grid and prevent the penetration behavior of the coupled Euler-Lagrange method at the extrusion port. BRIEF DESCRIPTION OF DRAWINGS

[0059] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments thereof, read in conjunction with the accompanying drawings:

[0060] Figure 1 A schematic diagram of a lithium strip extrusion assembly geometry model containing an Euler domain in an embodiment of the present application.

[0061] Figure 2 A schematic diagram of a grid division model of an extrusion die in an embodiment of the present application.

[0062] Figure 3 A cross-sectional view of an extrusion die and an extrusion stress distribution cloud map in an embodiment of the present application.

[0063] Figure 4 A stress distribution and fluctuation characteristic map of a lithium strip in the thickness direction under stable extrusion state in an embodiment of the present application.

[0064] Figure 5 A stress distribution and fluctuation characteristic map of lithium strip at both ends under stable extrusion state in an embodiment of the present application.

[0065] Figure 6 A stress distribution and fluctuation characteristic map of a lithium strip in the width direction under stable extrusion state in an embodiment of the present application.

[0066] Figure 7 A flow chart of the method of the present application. DETAILED DESCRIPTION

[0067] The present application will be described in detail below with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of changes and improvements can be made. These all belong to the protection scope of the present application.

[0068] As shown in Figure 7 A lithium strip extrusion forming finite element simulation method based on coupled Euler-Lagrange method, comprising the following steps:

[0069] S1, geometric model and grid division based on coupled Euler-Lagrange method:

[0070] The Euler-Lagrange coupling model is established by using the coupled Euler-Lagrange (CEL) method of ABAQUS; wherein, the Lagrangian domain is set as the geometric model of the extrusion die, the barrel and the extrusion head, and the Euler domain is set as the model of the lithium metal blank flow area.

[0071] In the coupled Euler-Lagrange (CEL) method

[0072] 1. Momentum equation of Lagrangian method

[0073]

[0074] Wherein, ρ L is the Lagrangian material density, is the material derivative, v L is the Lagrangian material point velocity, is the spatial derivative operator based on the Lagrangian material coordinates, σ L is the Lagrangian stress tensor, and b is the body force.

[0075] 2. Momentum equation of Euler method (fixed control volume perspective)

[0076]

[0077] Wherein, ρ E is the Euler domain density, v E is the Euler domain velocity field, is the local time derivative of the fixed spatial point, is the spatial derivative operator based on the Euler spatial coordinates, ρ E v E v E is the momentum flux tensor, σ E is the Euler stress tensor, and b is the body force.

[0078] 3. Force balance condition of the coupling interface

[0079] σ E ·n=-σ L ·n

[0080] The integral form is

[0081]

[0082] Wherein, n is the unit normal vector of the interface, Γ is the coupling interface of the Euler domain and the Lagrangian domain, σ E ·n is the surface force density of the Euler domain acting on the coupling interface, f L,i is the force received by the i-th Lagrangian material point at the coupling interface, and dΓ is the microelement area of the coupling interface.

[0083] 4. Velocity equilibrium conditions at the coupling interface

[0084] v E =v L

[0085] 5. Displacement equilibrium condition of the coupling interface

[0086]

[0087] Among them, u E For the Eulerian domain displacement field, u L Let t be the Lagrange displacement of the material point, and t be the time variable.

[0088] Geometric models of the extrusion die, barrel, and extrusion head, defined using the Lagrange method, and a lithium metal billet flow region model, defined using the Eulerian method, were constructed. For the irregularly structured extrusion orifice region in the extrusion die, a tetrahedral mesh with a minimum side length of 0.1mm-0.25mm (1 / 20-1 / 8 of the lithium strip thickness) was used. For the lithium metal billet flow region model located near the height of the extrusion orifice region, a hexahedral mesh with small height, width, and length (0.1mm-0.5mm) (1 / 20-1 / 4 of the lithium strip thickness) was used. For the structurally regular regions of the extrusion head, lithium metal billet flow region, and extrusion die, a hexahedral mesh with a larger side length (2mm-8mm) was used.

[0089] When constructing the geometric model, the barrel and extrusion die are merged into a single geometric model. The planar and bolted connections between the two are removed, as are the outward draft features at the extrusion outlet of the extrusion die. The geometric model is constructed only for a certain length of the barrel and the extrusion outlet along the axial direction, and for a shorter length of the bottom of the extrusion head along the axial direction. In constructing the Eulerian domain symmetric geometric model of the lithium metal flow range, the size of the Eulerian domain geometric model must completely enclose the assembly model of the extrusion die, barrel, and extrusion head, and a certain space is reserved along the axial direction as the outflow range of the lithium metal strip.

[0090] S2. Define the material model based on lithium metal and hardening behavior: Define the conventional material properties (elasticity, plasticity and density) of lithium metal and extrusion die, and set the viscoplastic constitutive relation of lithium metal based on the Cowper-Symonds model.

[0091] The hardening characteristics in the viscoplastic constitutive relation of lithium metal are based on the Cowper-Symonds model as the theoretical basis for the strain rate effect, using a power-law equation: Where σ is the rheological stress, A represents the quasi-static yield strength, and B is the strain rate hardening coefficient. Let be the strain rate, and n be the strain rate sensitivity index.

[0092] S3, Analysis step setting, interaction and constraint of extrusion forming: The analysis step setting is adopted with short simulation time length, using dynamic explicit analysis, opening geometric nonlinear calculation. The contact type is defined by normal contact with tangential contact and hard contact constraint mechanism of isotropic friction model coupled by penalty function method. The rigid body constraint is used for the structure of extrusion die, barrel and extrusion head. The reference point of the extrusion head is set to a low speed range constraint, and all degrees of freedom except the extrusion direction are all constrained, and the reference point of the extrusion die is set to a fixed constraint. The constraint of the lithium metal flow Euler domain is set to 0 for the normal velocity of the contact area between the center surface of the assembly length direction and the width direction in the Euler domain. The field predefinition is used to couple the geometric model of the initial region of lithium metal with the lithium material properties, and to define the position of the initial lithium metal.

[0093] S4, Model analysis: According to the stress cloud and the stress fluctuation data of the preset fixed point of the extrusion outlet, the stress distribution uniformity and fluctuation characteristics of the lithium strip forming are evaluated.

[0094] The evaluation process includes: if the stress cloud shows that the maximum stress value of the extrusion outlet inward region exceeds the preset threshold value 12-14 MPa, it is determined that there is serious stress concentration in this region. In the stress data of the fixed point, the difference between the maximum stress value and the minimum stress value is > 0.5 MPa, then it is determined that there is serious stress fluctuation in this region.

[0095] The fixed point of the model stress sampling has three groups, which are located in the two width directions of the extrusion outlet, the center and the midpoint of the vertical line of the two ends of the extrusion outlet, and the center line of the width direction of the extrusion outlet. The stress of the lithium strip at both ends, the thickness direction and the width direction of the lithium strip is sampled.

[0096] Fluctuation data collection refers to: setting all the grids in the width direction of the lithium strip as stress sampling points, collecting all the stress data in the width direction in a single frame and drawing a stress curve, and judging the stress fluctuation degree of the lithium strip in the width direction by comparing the stress curves of different frames.

[0097] In one embodiment, the mesh division, material parameter definition, analysis step setting and stress data collection and evaluation of the above simulation method are realized by ABAQUS finite element analysis software.

[0098] The finite element simulation analysis method quantifies the stress distribution and fluctuation characteristics in the extrusion process of lithium strip, and provides data basis for the optimization of extrusion die geometry and process parameters. This method is suitable for the simulation of soft and ductile metal strip extrusion forming technology, especially for the preparation simulation of alkali metal strip, including lithium strip, sodium strip, potassium strip, rubidium strip and other alkali metal strip extrusion simulation.

[0099] The present application aims at the deficiencies existing in the prior art, and provides a lithium strip extrusion forming finite element simulation method based on a coupled Euler-Lagrange method, which aims to provide a new reference for the lithium strip extrusion forming process.

[0100] The lithium strip extrusion forming finite element simulation method based on the coupled Euler-Lagrange method provided by the present application breaks through the above bottleneck through the following innovative mechanisms:

[0101] 1. Coping with grid distortion: using the coupled Euler-Lagrange method, applying Euler description method in the lithium metal flow area, and applying Lagrange description method in the rigid parts such as extrusion die, barrel and extrusion head area.

[0102] 2. Coping with contact penetration: using local grid refinement, and encrypting the grid of the extrusion port and the fluid-structure coupling contact boundary.

[0103] 3. Coping with the calculation requirement: using a symmetric model to ensure grid refinement while controlling the amount of calculation.

[0104] 4. Coping with material definition: using the viscoplastic constitutive relation according to the power law model to represent the flowability of lithium metal under high stress and the hardening phenomenon under low stress in the extrusion process.

[0105] The purpose of the present application is achieved by the following technical solutions:

[0106] <First aspect>

[0107] The present application provides a lithium strip extrusion forming finite element simulation method based on a coupled Euler-Lagrange method, which adopts a coupled Euler-Lagrange model in a multi-physical field coupling algorithm, adopts a viscoplastic constitutive model in a material model, adopts a symmetric model design strategy in the simplification of geometry and boundary conditions, and adopts grid refinement at the extrusion port and the contact surface in the optimization of grid discretization.

[0108] In one embodiment, the coupled Euler-Lagrange method uses Euler description method for lithium metal flow area and Lagrange description method for rigid parts such as extrusion die, barrel and extrusion head.

[0109] In one embodiment, the viscoplastic model sets the material constitutive model of lithium metal according to the power law model, reflecting the hardening behavior of lithium metal under high stress in the extrusion process.

[0110] In one embodiment, the geometry and boundary condition simplification uses a symmetric model, divides the whole model into four symmetric monomer models according to the two symmetric surfaces of the lithium strip extrusion forming assembly model, and performs finite element simulation analysis on the monomer model.

[0111] In one embodiment, the mesh discretization optimization reduces the contact penetration phenomenon at the extrusion port caused by the use of the coupled Euler-Lagrange method by refining the mesh in the range where lithium metal contacts the extrusion port in the Eulerian domain.

[0112] <Second aspect>

[0113] This invention provides a method for designing an extrusion nozzle structure based on a finite element model of lithium strip extrusion process, which can reduce stress concentration in lithium strips and mitigate extrusion stress fluctuations. The method includes the following steps:

[0114] S1. Original model finite element model construction: Complete the geometric model drawing of the model to be optimized, mesh model generation, material constitutive model definition, analysis step setting, contact property setting, and constraint setting.

[0115] S2. Analysis of the original finite element model: Analyze the stress distribution and stress fluctuation results obtained from the calculation of the original finite element model.

[0116] S3. Optimization Model Finite Element Model Construction: Based on the stress concentration and strong stress fluctuation locations of the original finite element model, optimize the design of similar structures in different directions.

[0117] S4. Determine the optimization direction: Based on the comparison of the finite element analysis results of the optimization models in different directions, select the model with the best stress distribution and stable stress fluctuation, and determine the next optimization direction.

[0118] like Figure 1 As shown, in one embodiment, step S1, the geometric model drawing includes rigid components and Eulerian domains. The rigid components include a barrel, an extrusion die, and an extrusion head, wherein the barrel and extrusion die are drawn as a single geometric body. The Eulerian domain is required to encompass the entire rigid component, and its structure is required to be cubic.

[0119] like Figure 2 As shown, in one embodiment, in step S1, the mesh model is divided using a hexahedral mesh for the Eulerian domain and 4-10 meshes for the extrusion port portion in the thickness direction. For rigid components with regular structures, such as the extrusion head, a hexahedral mesh is used; for rigid components with complex structures, such as the barrel and extrusion die, a tetrahedral mesh is used, and the extrusion port portion is divided into 3-10 meshes on each short side.

[0120] In one embodiment, in step S1, the constitutive model of the material is defined as a power-law model for the density, elasticity, plasticity, and viscoplasticity of lithium metal.

[0121] In one embodiment, the stress concentration and stress fluctuation related data are obtained in step S2 as follows:

[0122] As shown in Figure 3 and shown in Figure 4 , first based on the stress cloud of the lithium strip extrusion process, and sampling is taken in the Euler domain where the extrusion port is located in the thickness direction of the lithium strip to obtain the basic stress data; to master the stress distribution characteristics of the lithium strip edge, fine sampling points need to be taken in the range of 4-10mm from the outside to the inside of the two side edges, and the stress data of each sampling point changing with time is collected, as shown in Figure 5 ; for the judgment of the stress fluctuation degree in the width direction of the lithium strip, the specific operation is to set all the grids in this direction as stress sampling points, collect all the stress data in a single frame and draw a stress curve, and complete the judgment by comparing the stress curves of different frames, as shown in Figure 6 .

[0123] In one embodiment, in the S3 step, the optimization design in different directions is to add transition planes with different angles to the extrusion port structure according to the stress distribution and stress fluctuation of the original model.

[0124] In one embodiment, in the S3 step, the optimization model finite element model has the same material constitutive model definition, analysis step setting, contact attribute setting, and constraint setting as the original model finite element model.

[0125] In one embodiment, in the S4 step, the finite element analysis result comparison compares the stress analysis data of the three models. The stress analysis method is the same as the analysis method in the S2 step.

[0126] The above is the basic embodiment of the present application, and the scheme of the present application will be further described through four preferred embodiments.

[0127] Embodiment 1

[0128] This embodiment relates to a lithium strip extrusion forming finite element simulation method based on a coupled Euler-Lagrange method. The method is used to analyze the stress distribution and stress fluctuation of the lithium strip extrusion process in a square extrusion port extrusion die. The finite element simulation method adopts the coupled Euler-Lagrange method in the multi-physical field coupling algorithm, adopts the viscoplastic model in the material constitutive model, adopts the symmetric model design strategy in the geometry and boundary condition simplification, and adopts the grid refinement at the extrusion port and the contact surface in the grid discretization optimization.

[0129] The model design steps are as follows:

[0130] S1, geometry model and grid design: as shown in Figure 1The geometric model of the extrusion die, the barrel, and the extrusion head of the square extrusion port is drawn, and the geometric model of the Euler domain of lithium metal deformation is drawn. The tetrahedral mesh is used for the extrusion die and the barrel, and the mesh is refined to 5 units in the thickness direction of the extrusion port of the symmetric model of the extrusion die. Figure 2 The hexahedral mesh is used for the extrusion head and the Euler domain, and the hexahedral mesh with a size of 0.2*1*2 mm is used for the extrusion port range.

[0131] S2, material property setting: the density, elastic property, plastic property, and power law model of work hardening of lithium metal are set, wherein the strain rate strengthening coefficient is 1.2E8, and the strain rate sensitivity index is 4.5.

[0132] S3, interaction setting: the extrusion die, the barrel, and the extrusion head are set as rigid bodies, and the reference points are determined. The contact mode is set, the tangential contact behavior adopts a penalty function algorithm coupled with an isotropic friction model, the friction coefficient is 0.15, and the normal contact adopts a hard contact constraint mechanism.

[0133] S4, analysis step and constraint setting: the simulation time of the analysis step is 0.03 s, dynamic explicit analysis is adopted, and geometric nonlinear calculation is performed. The reference points of the extrusion die and the barrel are fixedly constrained, the reference point of the extrusion head is set to have a loading speed of 0.3 m / s, and the normal velocities of the two faces of the lithium metal Euler domain that coincide with the model symmetry plane are set to 0.

[0134] S5, model analysis: the finite element model is calculated, the data of the stress change of the sampling points with time are collected according to the stress cloud map of the results, the sampling points are collected in the Euler domain of the extrusion port in the thickness direction and the width direction of the lithium strip. At the same time, in order to obtain the detailed distribution of the stress of the lithium strip edge, the sampling points are collected in detail from the end point to the internal 5 mm range on both sides of the lithium strip.

[0135] The corresponding finite element model is designed for the lithium strip extrusion forming process of the square extrusion port of the extrusion die. It can be seen from the stress distribution cloud map of the finite element model results that the lithium metal inside the extrusion port has a serious stress concentration, and the maximum stress can reach 15.36 MPa, as shown in Figure 3 In the thickness direction of the lithium strip, the surface layer has the maximum stress, which always exceeds 11.75 MPa, and the internal stress is smaller and maintained below 11.2 MPa, as shown in Figure 4 It can be seen from the stress collection diagram of the 5 mm internal point from the center point of the narrow edge that the stress of the edge of the lithium strip is the largest, which is between 11.2-11.3 MPa, and the stress of the edge of the lithium strip close to the internal is smaller, which is between 10.75-11.0 MPa, as shown in Figure 5It can be seen from the lithium ribbon width direction sampling diagram at different times that the stress distribution in the width direction of the lithium ribbon is relatively uniform, and most of them remain between 10.95-11.1 MPa, such as Figure 6 .

[0136] According to the finite element simulation results, it can be seen that in the process of producing lithium ribbon by square extrusion die, the stress difference between the surface and the inside of the lithium ribbon at the extrusion port is large, which is easy to cause different internal and external organizational structures and uneven residual stress distribution. At the same time, the stress gradient of the lithium ribbon edge is large, the edge crack rate is large, and the uniformity of the width is high.

[0137] Example 2

[0138] This embodiment relates to a lithium ribbon extrusion forming finite element simulation method based on coupled Euler-Lagrange method. The method is used to analyze the stress distribution and stress fluctuation of lithium ribbon extrusion process when using 4mm chamfer transition extrusion port of extrusion die. The finite element simulation method adopts coupled Euler-Lagrange method in multi-physical field coupling algorithm, adopts viscoplastic model in material constitutive model, adopts symmetric model design strategy in geometry and boundary condition simplification, and adopts mesh refinement at extrusion port and contact surface in mesh discretization optimization.

[0139] The model design steps are as follows:

[0140] S1, geometry model and mesh design: as shown in Figure 1 , draw the geometry model of the extrusion die, barrel and extrusion head of the 4mm chamfer transition extrusion port, and draw the Euler domain geometry model of lithium metal deformation. The tetrahedral mesh is used for the extrusion die and barrel, and the mesh is refined to 5 in the thickness direction of the symmetric model of the extrusion die. As shown in Figure 2 , hexahedral mesh is used for the extrusion head and Euler domain, and hexahedral mesh with size of 0.2x1x2mm is used for the extrusion port range.

[0141] S2, material property setting: set the density, elastic property, plastic property of lithium metal material, and power law model of work hardening of lithium metal , in which the strain rate strengthening coefficient Multiplier is 1.2E8, and the strain rate sensitive index Exponent is 4.5.

[0142] S3, interaction setting: set the extrusion die, barrel and extrusion head as rigid body, and determine the reference point. Set the contact mode, adopt penalty function algorithm to couple isotropic friction model for tangential contact behavior, and the friction coefficient is 0.15. The normal contact adopts hard contact constraint mechanism.

[0143] S4, analysis step and constraint setting: the simulation time of the analysis step is 0.03 s, dynamic explicit analysis is adopted, and geometric nonlinear calculation is performed. The reference points of the extrusion die and the barrel are fixedly constrained, the reference point of the extrusion head is set to have a loading speed of 0.3 m / s, and the normal velocities of the two faces of the lithium metal Euler domain that are coincident with the model symmetry plane are set to 0.

[0144] S5, model analysis: the finite element model is calculated, the data of the stress of the sampling points changing with time are collected according to the stress nephogram of the result, and the sampling points are collected in the Euler domain where the extrusion port is located in the thickness direction and the width direction of the lithium strip. Meanwhile, in order to obtain the detailed distribution of the stress of the lithium strip edge, the sampling points are collected in the range of 5 mm from the end point to the inside of the lithium strip on both sides.

[0145] The finite element model corresponding to the lithium strip extrusion forming process of the extrusion die with a 4mm chamfer transition extrusion port is designed in this embodiment. It can be seen from the stress distribution nephogram of the result of the finite element model that, compared with the square extrusion port model described in embodiment 1, the stress concentration of the lithium metal inward of the extrusion port of the 4mm chamfer transition extrusion port model is obviously relieved, the maximum stress is 12.35 MPa, as shown in Figure 3 In the thickness direction of the lithium strip, the surface layer has a larger stress, which is smaller than the stress of the square extrusion port model of embodiment 1, about 11.6 MPa, the inside has a smaller stress, maintained at 10.75-11.20 MPa, as shown in Figure 4 Compared with the stress of the square extrusion port model, the stress is more uniform. It can be seen from the stress collection diagram of the center point of the narrow side to the inside 5mm that the stress of the outermost edge of the lithium strip is the largest, between 11.0-11.26 MPa, the stress of the edge close to the inside of the lithium strip is smaller, between 10.75-11.0 MPa, as shown in Figure 5 Compared with the stress of the square extrusion port model, the stress is more uniform. According to the sampling diagram of the lithium strip in the width direction at different times, it can be seen that the stress distribution in the width direction of the inside of the lithium strip fluctuates greatly, most of which is maintained at 10.75-11.2 MPa, as shown in Figure 6 At the same time, the stress of the outermost sampling point drops sharply, which is related to the fact that the introduction of the transition chamfer causes the width of the lithium strip to decrease, resulting in incomplete collection of data.

[0146] According to the result of the finite element simulation, it can be seen that, in the process of producing the lithium strip by the extrusion die with a 4mm chamfer transition extrusion port structure, compared with the extrusion die with a square extrusion port structure, the stress concentration is relieved, the stress difference between the surface and the inside of the lithium strip at the extrusion port is reduced. The stress fluctuation in the thickness direction of the lithium strip is small, and the distribution is uniform. In the width direction, the overall stress fluctuation is small, but due to the introduction of the transition chamfer, the local stress distribution is uneven. The stress gradient of the edge of the lithium strip is smaller, the edge cracking rate is reduced, and the width unevenness is reduced.

[0147] Example 3

[0148] This embodiment relates to a finite element simulation method of lithium ribbon extrusion based on coupled Euler-Lagrange method. The method is used to analyze the stress distribution and stress fluctuation of lithium ribbon extrusion process in an extrusion die with 30° bi-planar transition and total size of 4mm extrusion outlet. The finite element simulation method adopts coupled Euler-Lagrange method in the multi-physical field coupling algorithm, adopts viscoplastic model in the material constitutive model, adopts symmetric model design strategy in the simplification of geometry and boundary conditions, and adopts mesh refinement at the extrusion outlet and contact surface in the mesh discretization optimization.

[0149] The model design steps are as follows:

[0150] S1, geometry model and mesh design: draw the geometry model of the extrusion die, barrel and extrusion head of the 30° bi-planar transition extrusion outlet with total size of 4mm, and draw the Euler domain geometry model of lithium metal deformation, as shown in Figure 1 The extrusion die and barrel are divided by tetrahedral mesh, and the symmetric model of the extrusion die is refined to 5 in the thickness direction of the extrusion outlet. The extrusion head and Euler domain are divided by hexahedral mesh, and the extrusion outlet range is divided by hexahedral mesh with size of 0.2x1x0.5mm, as shown in Figure 2 .

[0151] S2, material property setting: set the density, elastic property, plastic property of lithium metal material, and the power law model of lithium metal work hardening wherein the strain rate strengthening coefficient Multiplier is 1.2E8, and the strain rate sensitivity index Exponent is 4.5.

[0152] S3, interaction setting: set the extrusion die, barrel and extrusion head as rigid body and determine the reference points. Set the contact mode, adopt penalty function algorithm to couple isotropic friction model for tangential contact behavior, and take friction coefficient value as 0.15, and adopt hard contact constraint mechanism for normal contact.

[0153] S4, analysis step and constraint setting: the simulation time of analysis step is 0.03s, dynamic explicit analysis is adopted, and geometric nonlinear calculation is performed. The reference points of the extrusion die and barrel are fixedly constrained, the reference point of the extrusion head is set to loading speed of 0.3m / s, and the normal velocity of the two faces of the lithium metal Euler domain coinciding with the model symmetry surface is set to 0.

[0154] S5. Model Analysis: The finite element model is calculated, and based on the stress cloud diagram of the results, data on the stress variation of sampling points over time are collected. Sampling points are taken in the Euler region where the extrusion port is located in both the thickness and width directions of the lithium strip. At the same time, in order to obtain a detailed distribution of the stress at the edge of the lithium strip, detailed sampling points are taken from the endpoints to within 5 mm on both sides of the lithium strip.

[0155] This embodiment designs a finite element model for the lithium strip extrusion process using an extrusion die with a 30° double-plane transition and a total extrusion orifice size of 4mm. According to the stress distribution cloud map of the finite element model results, compared to the square extrusion orifice model described in Embodiment 1, this model alleviates the stress concentration of lithium metal inwards from the extrusion orifice. However, compared to the 4mm chamfered transition extrusion orifice model described in Embodiment 2, the model in this embodiment exhibits a higher degree of stress concentration of lithium metal inwards from the extrusion orifice, with a maximum stress reaching 13.77MPa. Figure 3 As shown, in the thickness direction of the lithium strip, the surface layer experiences the highest stress, at 11.75 MPa, while the internal stress distribution is uniform, ranging from 10.95 to 11.15 MPa. Figure 4 As shown in the image, the stress distribution at a point 5mm inward from the center of the narrow edge reveals a relatively uniform stress distribution from the edge to the interior of the lithium strip, ranging from 10.90 to 11.20 MPa. Figure 5 As shown in the sampling images of the lithium strip width direction at different times, the stress distribution inside the lithium strip fluctuates significantly in the width direction, ranging from 10.30 to 10.8 MPa. Figure 6 As shown.

[0156] The finite element simulation results show that during the production of lithium strip using an extrusion die with a 30° double-plane transition and a total extrusion orifice size of 4mm, the stress difference between the surface and interior of the lithium strip at the extrusion orifice is small, and the stress gradient at the edge of the lithium strip is also small. Compared with an extrusion die with a square extrusion orifice structure, stress concentration is alleviated. The stress fluctuation in the thickness direction of the lithium strip is small, and the distribution is more uniform. In the width direction, the stress fluctuation increases, which is due to the introduction of a small-angle transition plane, leading to uneven distribution of lithium metal stress at the extrusion orifice. The stress gradient at the edge of the lithium strip is lower, reducing the incidence of edge cracking and the non-uniformity of width spread.

[0157] Example 4

[0158] The embodiment relates to a lithium strip extrusion finite element simulation method based on a coupled Euler-Lagrange method. The method is used for analyzing stress distribution and stress fluctuation of a lithium strip extrusion process in a 60-degree double-plane transition extrusion die with a total size of 7 mm. The finite element simulation method adopts the coupled Euler-Lagrange method in a multi-physical field coupling algorithm, adopts a viscoplastic model in a material constitutive model, adopts a symmetric model design strategy in geometry and boundary condition simplification, and adopts mesh refinement at an extrusion port and a contact surface in mesh discretization optimization.

[0159] The model design steps are as follows:

[0160] S1, geometry model and mesh design: draw a geometry model of a 60-degree double-plane transition extrusion die with a total size of 7 mm, a cylinder and an extrusion head, and draw an Euler domain geometry model of lithium metal deformation, as shown in the drawing. Figure 1 The extrusion die and the cylinder are divided by a tetrahedron mesh, and the symmetric model of the extrusion die is refined to 5 in the thickness direction of the extrusion port. The extrusion head and the Euler domain are divided by a hexahedron mesh, and the extrusion port range is divided by a hexahedron mesh with a size of 0.2*1*0.5 mm, as shown in the drawing. Figure 2

[0161] S2, material attribute setting: set the density, elastic attribute, plastic attribute and power law model of lithium metal work hardening of the lithium metal material wherein a strain rate strengthening coefficient Multiplier is 1.2E8, and a strain rate sensitive index Exponent is 4.5.

[0162] S3, interaction setting: the extrusion die, the cylinder and the extrusion head are set as rigid bodies, and reference points are determined. The contact mode is set, a penalty function algorithm is coupled with an isotropic friction model for tangential contact behavior, a friction coefficient is 0.15, and a hard contact constraint mechanism is adopted for normal contact.

[0163] S4, analysis step and constraint setting: the simulation time length of the analysis step is 0.03 s, a dynamic explicit analysis is adopted, and geometric nonlinear calculation is performed. The reference points of the extrusion die and the cylinder are fixedly constrained, the reference point of the extrusion head is set to have a loading speed of 0.3 m / s, and the normal velocities of two faces of the lithium metal Euler domain that coincide with the model symmetric face are set to be 0.

[0164] S5, model analysis: the finite element model is calculated, data of point stress changes with time are collected according to a stress cloud map of the result, and points are sampled in the Euler domain where the extrusion port is located in the thickness direction and the width direction of the lithium strip. Meanwhile, in order to obtain detailed distribution of lithium strip edge stress, points are carefully sampled on both sides of the lithium strip from the end point to the inside 5 mm.

[0165] ​The embodiment designs a corresponding finite element model for the lithium strip extrusion forming process of the extrusion die with a 60° biplane transition total size of 7mm extrusion outlet. According to the stress distribution cloud map of the finite element model result, compared with the square extrusion outlet model described in embodiment 1, the stress concentration of the model inwardly to the extrusion outlet is greatly reduced. The maximum stress is below 11.00MPa, as shown in the figure. Figure 3 In the thickness direction of the lithium strip, the stress difference between the surface layer and the internal layer is further reduced, the surface layer stress fluctuates between 10.9-11.1MPa, the internal stress distribution is uniform, and is between 10.65-10.80MPa, as shown in the figure. Figure 4 According to the stress collection diagram at the center point of the narrow edge inwardly to 5mm, the stress distribution of the lithium strip from the edge to the internal layer is more uniform, between 10.50-10.75MPa, as shown in the figure. Figure 5 According to the sampling diagram in the width direction of the lithium strip at different times, the stress distribution in the width direction of the internal layer of the lithium strip fluctuates less, is uniform, and is between 10.50-10.8MPa, as shown in the figure. Figure 6 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

[0166] According to the finite element simulation result, in the process of producing the lithium strip by the extrusion die with a 60° biplane transition total size of 7mm extrusion outlet, the stress difference between the surface and the internal layer of the lithium strip at the extrusion outlet is small, and the stress gradient of the lithium strip edge is small, compared with the extrusion die with a square extrusion outlet structure, the stress concentration is greatly relieved. The stress fluctuation in the thickness direction of the lithium strip is small and the distribution is uniform. In the width direction, the stress fluctuation is small and the distribution is uniform.

[0167] The application also provides a lithium strip extrusion forming finite element simulation system, which can be realized by executing the flow steps of the lithium strip extrusion forming finite element simulation method, that is, the lithium strip extrusion forming finite element simulation method can be understood by those skilled in the art as the preferred embodiment of the lithium strip extrusion forming finite element simulation system.

[0168] Specifically, a lithium strip extrusion forming finite element simulation system comprises:

[0169] Module M1: constructing a model based on Lagrange description method and Euler description method, and performing grid division on the model;

[0170] Module M2: defining the material properties of lithium metal and the model, and setting the viscoplastic constitutive relation of lithium metal;

[0171] The material properties include elastic properties, plastic properties and density;

[0172] ​Module M3: Based on the constructed model and the defined material properties, establish dynamic display analysis steps, set contact methods and constraint conditions, define the initial position of lithium metal, and simulate the extrusion process;

[0173] Module M4: According to the stress nephogram output by the model and the stress fluctuation data of the preset fixed point of the extrusion port, evaluate the stress distribution uniformity and fluctuation characteristics of the lithium strip forming.

[0174] The module M1 comprises:

[0175] The geometric model of the extrusion die, the barrel and the extrusion head defined by the Lagrange description method, and the lithium metal blank flow area model defined by the Euler description method are constructed; the extrusion port area with irregular structure in the extrusion die is divided by the minimum edge length tetrahedral grid, the lithium metal blank flow area model within a certain range in the height direction of the extrusion port area is divided by the hexahedral grid, and the extrusion head, the lithium metal blank flow area and the regular structure area of the extrusion die are divided by the hexahedral grid.

[0176] The module M1 further comprises:

[0177] The barrel and the extrusion die are combined into an integral geometric model, the planar connection and bolt connection between them are removed, and the outward stripping feature at the extrusion port of the extrusion die is removed, only the structure of the barrel, the extrusion port of the extrusion die along the axial direction within a certain length and the structure of the bottom of the extrusion head along the axial direction are constructed into a geometric model; in the construction of the Euler domain symmetric geometric model of the lithium metal flow range, the size of the Euler domain geometric model completely wraps the assembly model of the extrusion die, the barrel and the extrusion head, and a certain space along the axial direction is reserved as the outflow range of the metal lithium strip.

[0178] The hardening characteristic in the viscoplastic constitutive relation of the lithium metal is introduced by introducing the Cowper-Symonds model as the theoretical basis of the strain rate effect, and the power law equation is used:

[0179]

[0180] Wherein, σ is the rheological stress, A represents the quasi-static yield strength, B is the strain rate strengthening coefficient, is the strain rate, and n is the strain rate sensitivity index.

[0181] The module M3 comprises:

[0182] Dynamic explicit analysis is used, and the analysis step setting of geometric nonlinear calculation is opened;

[0183] The contact method comprises normal contact defined by the tangential contact and hard contact constraint mechanism of the isotropic friction model coupled by the penalty function method;

[0184] The setting of the constraint condition comprises:

[0185] A rigid body constraint is used for the extrusion die, the barrel and the extrusion head structure; a velocity range constraint is set for the reference point of the extrusion head, and all degrees of freedom except the extrusion direction are fully constrained, and a fixed constraint is set for the reference point of the extrusion die;

[0186] The field is predefined to couple the geometric model of the initial lithium metal region with the lithium material properties, and to define the initial position of the lithium metal.

[0187] The constraint condition further comprises a constraint of the lithium metal flow Euler domain, and the normal velocity of the contact area between the length direction and the width direction center surface of the assembly in the Euler domain is set to 0.

[0188] The fixed point positions of the model stress sampling are three groups, respectively located at the two width directions of the extrusion port, the center line of the extrusion port and the midpoint of the two ends, and the center line of the extrusion port width direction; the stress of the lithium ribbon two ends, the thickness direction of the lithium ribbon and the width direction of the lithium ribbon is sampled.

[0189] The data collection of the fluctuation characteristics comprises setting all the grids in the width direction of the lithium ribbon as stress sampling points, collecting all the stress data in the width direction in a single frame and drawing a stress curve, and comparing the stress curves of different frames to judge the stress fluctuation degree of the width direction of the lithium ribbon.

[0190] Those skilled in the art know that, in addition to implementing the system provided by the present application and each device, module and unit thereof in the form of pure computer readable program code, the same functions can also be realized by logically programming the method steps to make the system provided by the present application and each device, module and unit thereof in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for realizing various functions can also be considered as structures within the hardware component; the devices, modules and units for realizing various functions can also be considered as both software modules realizing methods and structures within hardware components.

[0191] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the present application. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A finite element simulation method for lithium strip extrusion molding, characterized in that, include: Step S1: Construct a model based on the Lagrange and Eulerian description methods, and then mesh the model. Step S2: Define the material properties of lithium metal and the model, and set the viscoplastic constitutive relation of lithium metal; The material properties include elastic properties, plastic properties, and density; Step S3: Based on the constructed model and defined material properties, establish a dynamic display analysis step, set the contact mode and constraint conditions, define the initial location of lithium metal, and simulate the extrusion process; Step S4: Based on the stress cloud map output by the model and the stress fluctuation data of the preset fixed point at the extrusion port, evaluate the stress distribution uniformity and fluctuation characteristics of lithium strip forming.

2. The finite element simulation method for lithium strip extrusion molding according to claim 1, characterized in that, Step S1 includes: Geometric models of the extrusion die, barrel, and extrusion head, defined by the Lagrange method, and a lithium metal billet flow region model defined by the Eulerian method are constructed. The irregular extrusion port region in the extrusion die is divided into tetrahedral meshes with the minimum side length, the lithium metal billet flow region model within a certain range of the height direction of the extrusion port region is divided into hexahedral meshes, and the structurally regular regions of the extrusion head, lithium metal billet flow region, and extrusion die are divided into hexahedral meshes.

3. The finite element simulation method for lithium strip extrusion molding according to claim 2, characterized in that, Step S1 further includes: The barrel and extrusion die are merged into a single geometric model, removing the planar and bolted connections between them, and removing the outward draft feature at the extrusion die outlet. Geometric models are constructed only for a certain length of the barrel, the extrusion die outlet along the axial direction, and the structure at the bottom of the extrusion head along the axial direction. In the construction of the Eulerian domain symmetric geometric model of the lithium metal flow range, the dimensions of the Eulerian domain geometric model completely enclose the assembly model of the extrusion die, barrel, and extrusion head, and a certain space is reserved along the axial direction as the outflow range of the lithium metal strip.

4. The finite element simulation method for lithium strip extrusion molding according to claim 1, characterized in that, The hardening characteristics in the viscoplastic constitutive relation of lithium metal are based on the Cowper-Symonds model as the theoretical basis for the strain rate effect, and the power-law equation used is: Where σ is the rheological stress, A represents the quasi-static yield strength, and B is the strain rate hardening coefficient. Let be the strain rate, and n be the strain rate sensitivity index.

5. The finite element simulation method for lithium strip extrusion molding according to claim 1, characterized in that, Step S3 includes: Use dynamic explicit analysis to enable the analysis step settings for geometric nonlinear calculations; The contact methods include tangential contact and normal contact defined by a hard contact constraint mechanism that couples an isotropic friction model using the penalty function method. The constraints are set as follows: Rigid body constraints are applied to the extrusion die, barrel, and extrusion head structure; a velocity range constraint is set for the reference point of the extrusion head, and all degrees of freedom except the extrusion direction are constrained; a fixed constraint is set for the reference point of the extrusion die. By using field predefined settings, the geometric model of the initial lithium metal region is coupled with the properties of lithium material to define the initial location of lithium metal.

6. The finite element simulation method for lithium strip extrusion molding according to claim 5, characterized in that, The constraints also include constraints on the lithium metal flow Eulerian domain, where the normal velocity of the contact area between the Eulerian domain and the center plane of the assembly in the length and width directions is set to 0.

7. The finite element simulation method for lithium strip extrusion molding according to claim 1, characterized in that, There are three sets of fixed points for model stress sampling, located at the two width sections of the extrusion port, the perpendicular bisector between the center of the extrusion port and the midpoints of both ends, and the centerline of the width direction of the extrusion port; the stress at both ends of the lithium strip, in the thickness direction of the lithium strip, and in the width direction of the lithium strip are sampled.

8. The finite element simulation method for lithium strip extrusion molding according to claim 1, characterized in that, Data acquisition of fluctuation characteristics includes setting all grids in the width direction of the lithium strip as stress sampling points, collecting all stress data in that width direction in a single frame and plotting it as a stress curve, and judging the degree of stress fluctuation in the width direction of the lithium strip by comparing the stress curves of different frames.

9. A finite element simulation system for lithium strip extrusion molding, characterized in that, include: Module M1: Constructs a model based on the Lagrange and Eulerian description methods, and performs mesh generation on the model; Module M2: Defines the material properties of lithium metal and the model, and sets the viscoplastic constitutive relation of lithium metal; The material properties include elastic properties, plastic properties, and density; Module M3: Based on the constructed model and defined material properties, a dynamic display analysis step is established, contact methods and constraints are set, the initial position of lithium metal is defined, and the extrusion process is simulated; Module M4: Based on the stress cloud map output by the model and the stress fluctuation data of the preset fixed point at the extrusion port, evaluate the stress distribution uniformity and fluctuation characteristics of lithium strip forming.

10. The lithium strip extrusion molding finite element simulation system according to claim 9, characterized in that, The module M1 includes: Geometric models of the extrusion die, barrel, and extrusion head, defined by the Lagrange method, and a lithium metal billet flow region model defined by the Eulerian method are constructed. The irregular extrusion port region in the extrusion die is divided into tetrahedral meshes with the minimum side length, the lithium metal billet flow region model within a certain range of the height direction of the extrusion port region is divided into hexahedral meshes, and the structurally regular regions of the extrusion head, lithium metal billet flow region, and extrusion die are divided into hexahedral meshes.

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