A cast-extrusion integrated electric vehicle lower body structure stiffening layout topology optimization method

Abstract

This invention discloses a topology optimization method for the stiffening layout of an integrated die-cast and extruded electric vehicle underbody structure, relating to the field of electric vehicles. The method involves finite element mesh generation for the electric vehicle underbody structure, classifying the mesh into extrusion meshes and casting meshes based on the processing technology used for the components. The finite element mesh within a single component is further subdivided into design domains and non-design domains. For the casting design domain, a mathematical model of casting constraints is established to optimize the stiffening of thin-walled die-cast parts. For the extrusion design domain, an extrusion process constraint is applied to establish a mathematical model to optimize the internal stiffening of the cross-section. The mathematical model is solved to obtain the density distribution of each element, determining the stiffening layout form that satisfies both comprehensive service conditions and dual manufacturing process constraints. Based on the calculated element density distribution and load transfer path, the topology optimization results are reconstructed into a CAD model or mesh model with stiffeners.

Description

Technical Field

[0001] This invention relates to the technical field of electric vehicles, and more specifically, to a topology optimization method for the stiffening layout of the underbody structure of an integrated cast-extruded electric vehicle. Background Technology

[0002] Structural optimization design is one of the most effective means to achieve lightweighting of the entire vehicle chassis. Through structural optimization design, lightweighting can be achieved while ensuring that the chassis and body structure meet strength requirements, thereby improving the driving range of electric vehicles while ensuring the safety of the body structure.

[0003] Using topology optimization for lightweight design of vehicle chassis structures has advantages such as high lightweighting degree, high rigidity and strength, and flexible application. Currently, many studies have proposed lightweight design methods for vehicle body and chassis structures based on topology optimization.

[0004] In summary, while topology optimization for lightweight design of vehicle bodies and chassis is a relatively mature technology, most research focuses on topology optimization for single manufacturing processes, such as forging, sheet metal parts, and bus frames, where beams are typically formed by extrusion. Furthermore, design methods that utilize multiple processes for joint optimization within the same topology optimization design process are still underdeveloped. For components using different manufacturing processes, separate optimization analyses are usually employed, making the entire analysis and design process relatively cumbersome. Summary of the Invention

[0005] The purpose of this invention is to propose a design method for simultaneously performing topology optimization design on extruded and cast components under various load conditions.

[0006] The technical solution of this invention is: to provide a topology optimization method for the stiffening layout of the underbody structure of an integrated cast-extruded electric vehicle, the method comprising:

[0007] S1. Finite Element Model Construction and Working Condition Definition: Finite element mesh generation is performed on the lower body structure of the electric vehicle. Based on the processing technology adopted by the components, the finite element mesh is classified into extrusion mesh and casting mesh. Extrusion parts include door sill beams, and casting parts include front castings and rear castings. Taking into account the service conditions of the whole vehicle, the multi-condition load conditions, weighting coefficients and boundary constraints, including collision, bending, torsion and bottoming out, are determined.

[0008] S2. Construction of Design Domain and Non-Design Domain: The finite element mesh inside a single component in step S1 is divided a second time, and the mesh of each casting and extrusion is subdivided into design domain and non-design domain; among them, the non-design domain is the area that retains the basic outline and function of the component, and the design domain is the area used for stiffening distribution calculation; the extrusion design domain, non-design domain and casting design domain are connected by mesh common nodes.

[0009] S3. Establish and solve the casting-extrusion collaborative topology optimization model: For the casting design domain and the extrusion design domain, establish a mathematical model that includes objective function, volume fraction constraints, and manufacturing process constraints; in the mathematical model, apply casting process constraints to the casting design domain to restrict the material distribution to meet the process requirements along a specific draft direction, so as to optimize the stiffening of thin-walled die castings; apply extrusion process constraints to the extrusion design domain to restrict the material distribution to meet the requirement of consistent cross-section along the extrusion direction, so as to optimize the internal stiffening of the cross-section; by solving the mathematical model, obtain the density distribution of each element, and determine the stiffening layout form that meets the comprehensive service conditions and dual manufacturing process constraints;

[0010] S4. Reconstruction of reinforced structure: Based on the element density distribution and load transfer path calculated in step S3, and combined with the actual processing and installation conditions, the topology optimization results are reconstructed into a CAD model or mesh model with reinforcing ribs.

[0011] In any of the above technical solutions, the mathematical model in step S3 is further defined as follows:

[0012] Find ;

[0013] Min ;

[0014] st ;

[0015] ;

[0016] ;

[0017] ;

[0018] ;

[0019] ;

[0020] ;

[0021] ;

[0022] In the formula, , , , , , , This represents the density of the corresponding unit. The total number of units; This represents the total number of structural load cases. For the first Weighting factors for each working condition; For the first Flexibility under various operating conditions; and The first The load and displacement matrix corresponding to each working condition; The overall stiffness matrix; Let V be the volume of each unit. A function that calculates the sum of the volumes of all elements in the design domain; Design domain volume; For the constrained volume fraction, This represents the density of the cells represented by the entity element. This represents the unit density represented by the void element; This represents the total number of cell rows in the casting design domain. Indicates the row number above the separation surface. Indicates the row number below the separation surface. Indicates the column number along the draft direction. It is the first row above the separation surface. It is a threshold greater than or equal to 1. The total number of elements in a single extrusion design domain section. This represents the element portion occupied by a solid within a single extrusion design domain section. This refers to the element portion that is not occupied by a solid within a single extrusion design domain section.

[0023] In any of the above technical solutions, the specific implementation of the casting process constraints and extrusion process constraints in step S3 is as follows:

[0024] Casting process constraints: restrict the density distribution of a row of units along the draft direction in the casting design domain, so that it meets the requirement of increasing or decreasing distribution along the draft direction and parting surface position, and avoids the occurrence of undercut structures;

[0025] Extrusion process constraints: restrict the element density distribution along the extrusion direction in the extrusion design domain, so that the element portion occupied by the solid in a single extrusion design domain section remains consistent along the extrusion direction, resulting in a beam structure with the same cross-section formed by stretching the cross-section.

[0026] In any of the above technical solutions, the specific rules for dividing the design domain and non-design domain in step S2 are further as follows:

[0027] For castings: The shell envelope area that bears the structural function is the non-design domain. Starting from the outside of this area, along the casting draft direction, a grid of a preset number of layers is stretched outward based on the original contour to serve as the casting design domain.

[0028] For extrusions: extending inward from the outermost single-layer shell contour, the hexahedral mesh filling the shell interior is divided into extrusion design domains, while the outer shell is retained as a non-design domain; and ensuring that adjacent extrusion design domains and casting design domains are separated by a portion of non-design domains.

[0029] In any of the above technical solutions, the multi-condition load conditions and weighting coefficients in step S1 specifically include: front-end collision, rear-end collision, left-side collision, and right-side collision conditions, with a weighting coefficient set to 1; front bending, front torsion, rear bending, and rear torsion conditions, with a weighting coefficient set to 2; and bottoming-out conditions, with a weighting coefficient set to 1.

[0030] In any of the above technical solutions, further, in step S3, when applying manufacturing process constraints, the draft direction is set to the vertical direction for the main design domain of the front and rear castings; the draft direction is set to the horizontal direction for the lower and side design domains of the front and rear castings; the extrusion direction is set to the extension direction along the beam structure at the front and rear of the vehicle body for the sill beam design domain; and minimum size constraints and maximum size constraints are set at the same time to control the width of the generated reinforcing ribs within the machinable range.

[0031] In any of the above technical solutions, further, the stiffened structure reconstruction in step S4 specifically includes:

[0032] For the high-density areas shown in the optimization results, they are transformed into the direction of the reinforcing ribs in the design; based on the topology results of the previous casting, vertical reinforcing ribs are arranged along the edge of the design domain, and diagonal or fork-shaped reinforcing ribs are arranged on the side; based on the extrusion topology results of the threshold beam, the internal reinforcement layout of its cross section is designed as a Z-shaped structure; based on the topology results of the subsequent casting, transverse reinforcing ribs are designed inside, and the bottom structure is modified to an I-shaped state.

[0033] The beneficial effects of this invention are:

[0034] The present invention proposes a stiffening design method for the lower body structure of electric vehicles based on integrated extrusion and casting topology optimization. The process of this method can guide the lightweight design process in vehicle development, enhance the overall structural stiffness, and improve structural reliability.

[0035] This invention proposes a method for simultaneously performing topology optimization on extruded and cast components. It takes into account the connection between the two components and couples the processing constraints of extrusion and casting with the topology optimization method. This avoids the complex process of performing topology optimization separately on extruded and cast components, improves the development speed of the lower body structure, and simplifies the design process for structural optimization of the lower body structure.

[0036] This invention achieves coordinated optimization of stiffening of thin-walled die-cast parts and internal stiffening of cross-sections in electric vehicle bodies under comprehensive service conditions by integrating multi-condition performance analysis of the whole vehicle, topology optimization, casting draft and extrusion process modeling, and so on. This enables high-performance and lightweight design of cast-extruded integrated electric vehicle body structure under complex multi-objective performance requirements. Attached Figure Description

[0037] The advantages of the above and additional aspects of the present invention will become apparent and readily understood in the description of the embodiments in conjunction with the following drawings, wherein:

[0038] Figure 1 This is a schematic diagram of the geometric CAD model of the lower body structure of an electric vehicle underbody structure, based on an embodiment of the cast-extruded integrated electric vehicle underbody structure reinforcement layout topology optimization method according to an embodiment of the present invention.

[0039] Figure 2 This is a schematic diagram of the finite element mesh model of the topology optimization method for the stiffening layout of the underbody structure of an electric vehicle with integrated casting and extrusion according to an embodiment of the present invention.

[0040] Figure 3 This is a load constraint diagram of the collision-related working conditions of the topology optimization method for the stiffened layout of the underbody structure of an electric vehicle with integrated casting and extrusion according to an embodiment of the present invention.

[0041] Figure 4 This is a load constraint diagram of the torsional bending related working conditions of the topology optimization method for the stiffened layout of the cast-extruded integrated electric vehicle body structure according to an embodiment of the present invention.

[0042] Figure 5 This is a schematic diagram of the load constraint under the bottoming condition of the topology optimization method for the stiffened layout of the cast-extruded integrated electric vehicle body structure according to an embodiment of the present invention.

[0043] Figure 6 This is a schematic diagram illustrating the setting of the casting design domain and casting constraints in a topology optimization method for the stiffening layout of the underbody structure of an electric vehicle based on an embodiment of the present invention.

[0044] Figure 7 This is a schematic diagram of the extrusion design domain and extrusion constraint settings in the topology optimization method for the stiffened layout of the underbody structure of an electric vehicle based on an embodiment of the present invention.

[0045] Figure 8 This is a schematic diagram of the topology optimization results and corresponding reinforcement design inside the front casting of the topology optimization method for the stiffening layout of the underbody structure of an electric vehicle according to an embodiment of the present invention.

[0046] Figure 9 This is a topology optimization result and corresponding reinforcement design schematic diagram of the lower part of the front casting of the cast-extruded integrated electric vehicle body structure reinforcement layout topology optimization method according to an embodiment of the present invention.

[0047] Figure 10 This is a topology optimization result and corresponding reinforcement design schematic diagram of the front casting side of the topology optimization method for the stiffening layout of the underbody structure of an electric vehicle according to an embodiment of the present invention.

[0048] Figure 11 This is a topology optimization result and corresponding reinforcement design schematic diagram of the extruded sill beam of the cast-extruded integrated electric vehicle lower body structure reinforcement layout topology optimization method according to an embodiment of the present invention.

[0049] Figure 12 This is a schematic diagram of the topology optimization results and corresponding reinforcement design inside the casting of the cast-extruded integrated electric vehicle body structure reinforcement layout topology optimization method according to an embodiment of the present invention.

[0050] Figure 13 This is a topology optimization result and corresponding reinforcement design schematic diagram of the rear casting side of the cast-extruded integrated electric vehicle body structure reinforcement layout topology optimization method according to an embodiment of the present invention.

[0051] in, Figures 2 to 13 To represent the grouping of the design domain or the optimized density distribution, it needs to be represented as a schematic diagram of the distribution of a colored hexahedral mesh. Detailed Implementation

[0052] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0053] In the following description, many specific details are set forth in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0054] This embodiment provides a topology optimization method for the stiffening layout of the cast-extruded integrated electric vehicle lower body structure. This method is mainly used for the stiffening topology optimization design of cast and extruded parts of the electric vehicle lower body under comprehensive service conditions. By integrating multi-condition performance analysis of the whole vehicle, topology optimization, casting draft, and extrusion process modeling, it achieves coordinated optimization of stiffening of thin-walled die-cast parts and internal stiffening of cross-sections in the electric vehicle lower body. This achieves high-performance and lightweight design of the cast-extruded integrated electric vehicle body structure under complex multi-objective performance requirements. The method includes:

[0055] S1. Construction of the finite element model of the lower vehicle body and definition of working loads:

[0056] First, finite element meshing is performed on existing lower body structures requiring stiffener distribution design. For different extruded and cast parts, the finite element meshes are classified according to the corresponding processing technology. This is based on the existing vehicle model's CAD drawings (such as...). Figure 1 As shown, necessary reductions are made, retaining only components related to the vehicle body structure and requiring structural reinforcement layout design. Finite element mesh generation is performed on the retained components, establishing a mesh as shown... Figure 2 The integrated finite element mesh model shown is composed of multiple components, including the front casting, front longitudinal beam, battery pack housing, sill beam, middle crossbeam, and rear casting.

[0057] To facilitate subsequent adjustments and modifications to the design domain, the overall finite element mesh model was divided using hexahedral meshes with a side length of 5mm. Furthermore, coarse hexahedral meshes were used to replace the original meshes based on the outline of the corresponding parts. The resulting overall finite element model consisted of fully filled hexahedral meshes without any cavities. After meshing, the meshes corresponding to extruded parts and castings using different processing techniques were grouped and categorized from the overall mesh model based on their original part shapes. This determined the mesh boundary positions for extruded and casting parts, facilitating further classification and subdivision in the future.

[0058] Taking into account front-end collision, rear-end collision, side collision, overall bending, overall torsional load, and bottoming-out conditions, the loads and weighting coefficients for each condition are determined based on engineering experience. The methods for setting corresponding boundary constraints under these conditions are also considered. Based on engineering experience, the applicable conditions for the lower vehicle body model are determined, such as... Figure 3 The diagram shows the load constraints for the collision-related conditions. Figure 4 The load constraint diagram for the torsional bending related working conditions is shown below. Figure 5The diagram illustrates the load constraints for the bottoming-out condition. In the collision condition, both front and rear collision loads are evenly distributed to the frontmost (rearmost) element of the front (rear) component through the rbe2 element. The magnitude of the front and rear collision loads is 10000 N, and the magnitude of the side collision load is 5000 N. Fixed constraints are applied at the ends (front ends) in the opposite direction of the loads, constraining degrees of freedom 1, 2, and 3. In the bending and torsional conditions, corresponding bending and torsional loads are applied to the damper mounting points on the front and rear castings, with a magnitude of 5000 N. These loads are connected to the castings through the rbe2 element, and fixed constraints are applied to the castings on the other side, constraining degrees of freedom 1, 2, and 3. In the bottoming-out condition, a horizontal upward load of 5000 N is applied to the bottom of the battery pack. Fixed constraints are applied to the damper mounting points of the four castings, constraining degrees of freedom 1, 2, and 3.

[0059] In multi-condition optimization, the weight coefficients for each condition are set as follows: the weight coefficients for front collision, rear collision, left-side collision, and right-side collision are all 1; the weight coefficients for front bending, front torsion, rear bending, and rear torsion are all 2; and the weight coefficient for bottoming out is 1.

[0060] S2. Division and connection settings of design domain and non-design domain:

[0061] like Figure 6 and Figure 7 As shown, based on the mesh division in step S1, the mesh of each casting and extruded part is further subdivided into design domain and non-design domain. Specifically, the subdivision method involves starting from the outer side of the shell envelope region of the casting part that bears the specific structural function, and stretching 5-6 layers of mesh along the casting draft direction and the original contour. Figure 6 The two colored areas are shown; and the extrusion extends inward from the outermost single-layer shell contour, with all the hexahedral meshes inward from the shell being divided into a stiffened distributed topology optimization computational domain mesh, as shown. Figure 7 The two sets of colored areas shown in the diagram represent the threshold beam. The non-design area is the retained, unreinforced design area, encompassing the shell-like region that bears the specific structural functions of the castings and extrusions. Furthermore, a portion of the non-design area is maintained between adjacent extrusion and casting design areas to ensure the rationality and stability of the structure.

[0062] The connection between the extrusion design domain, non-design domain, and casting design domain adopts a mesh-based shared-node method, and the material is set to aluminum. For components requiring stiffening distribution design, their original stiffening rib layout is deleted, retaining only the parts maintaining the component's function and external contour features. The interior is uniformly filled with hexahedral elements. After filling the design domain, the overall model contains 1,241,388 hexahedral meshes. After mesh classification and partitioning, the overall mesh model will be divided into two parts: design domain and non-design domain. Within the design domain, the roughly grouped components are further subdivided according to the different component manufacturing processes. The design domain mesh is the optimization object of the optimization model proposed below, and its quantity and density will decrease during the optimization process; the non-design domain mesh carries the main external contour and function of the structure, and its quantity and density remain unchanged during the optimization process.

[0063] S3. Establish and solve the mathematical model for topology optimization of the integrated casting and extrusion process:

[0064] For the design domains of casting and extrusion, a mathematical model is established that comprehensively considers multi-condition compliance response, objective function, volume fraction constraints, and manufacturing process constraints. In this embodiment, the optimization objective is to minimize the weighted compliance across all conditions. Overall volume fraction constraints are also considered. The value is set to 0.4. Simultaneously, the minimum feature size constraint is set to 15mm, and the maximum feature size constraint to 30mm, to ensure the formed reinforcing rib structure is machinable and to avoid the checkerboard pattern in the optimization results.

[0065] To achieve synergistic optimization of the casting-extrusion integration, this invention introduces specific constraints for different processes into the mathematical model:

[0066] Casting process constraints: Apply draft direction constraints to the design domains of the front and rear castings. For example... Figure 6 As shown, for the main body of the front and rear castings, the topology optimization forming method is constrained to meet the draft requirements in the vertical direction; for the lower and side parts of the front and rear castings, the draft direction is set to be horizontal. Mathematically, by constraining the element density distributed along the draft direction in the design domain to have an increasing or decreasing distribution (without undercut), and taking an extreme value at the parting surface, the casting demolding requirements are met.

[0067] Extrusion Process Constraints: For extruded structures such as sill beams, extrusion constraints are applied along the extension direction (i.e., the front-to-back direction) of the beam structure. This constraint requires that the element density distribution in a single extrusion design domain section remain consistent along the extrusion direction, ensuring that the optimized structure is formed by stretching the section along the extrusion direction. Figure 7 As shown.

[0068] Based on the above conditions, the following topology optimization mathematical model is established for calculation:

[0069] Find ;

[0070] Min ;

[0071] st ;

[0072] ;

[0073] ;

[0074] ;

[0075] ;

[0076] ;

[0077] ;

[0078] ;

[0079] Simultaneously satisfying the casting process constraint formula (controlling the density gradient along the draft direction) and the extrusion process constraint formula (controlling the consistency of cross-sectional density) mentioned above. By solving this mathematical model, the density distribution of each element is obtained, thereby determining the load transfer path and material distribution form.

[0080] In the formula, , , , , , , This represents the density of the corresponding unit. The total number of units; This represents the total number of structural load cases. For the first Weighting factors for each working condition; For the first Flexibility under various operating conditions; and The first The load and displacement matrix corresponding to each working condition; The overall stiffness matrix; Let V be the volume of each unit. A function that calculates the sum of the volumes of all elements in the design domain; Design domain volume; For the constrained volume fraction, This represents the density of the cells represented by the entity element. This represents the element density indicated by the void element. In this design case, the total number of working conditions for the lower body structure is 9; volume fraction. All are taken as 0.4; among them, the weighting coefficients for front collision, rear collision, left-side collision, and right-side collision are 1, the weighting coefficients for front bending and torsion, rear bending and torsion are 2, and the weighting coefficient for bottoming out is 1.

[0081] Lines 4 to 6 of st are casting process constraints. Within the applied casting process constraints... This represents the total number of cell rows in the casting design domain. Indicates the row number above the separation surface. Indicates the row number below the separation surface. Indicates the column number along the draft direction. It is the first row above the separation surface. It is a threshold greater than or equal to 1, used to control the checkerboard phenomenon. The constraint formula as a whole restricts the element density distribution of a row of elements distributed in the casting direction to conform to an increasing or decreasing distribution along the casting direction and parting surface position, so as to meet the casting process requirements. The seventh and eighth rows of st are extrusion process constraints, in which the applied extrusion constraints are... The total number of elements in a single extrusion design domain section. This represents the element portion occupied by a solid within a single extrusion design domain section. This represents the element portion in a single extrusion design domain section that is not occupied by a solid. Extrusion constraint indicates that the extruded part is entirely stretched from the section along the extrusion direction.

[0082] S4. Post-processing and reconstruction of reinforced layout:

[0083] Based on the topology optimization results (unit density distribution) obtained in step 3, and combined with the actual component processing and installation conditions, the optimization results are transformed into specific CAD models or mesh models. Based on the load transfer path design results of the casting and extrusion parts after topology optimization, the reinforcement layout of the casting and the cross-section of the extrusion parts are conceptually designed, which specifically includes: (1) For the obvious high-density areas in the optimization results, they are transformed into the direction of the reinforcing ribs in the design; (2) Ensure that the reinforcement layout after topology optimization meets the actual processing requirements and the space requirements for the installation of other components; (3) If the original design outline of the component is not retained in the topology optimization results, but has an irreplaceable role in the overall structure, the topology optimization results and the original design should be considered comprehensively, and the original design layout should be retained as appropriate.

[0084] The specific reconstruction result of this embodiment is as follows:

[0085] like Figure 8The topology optimization results and corresponding stiffening design schematic diagram of the front casting in this invention are shown. It can be seen that, along the draft direction, the load transfer path of the front casting design domain is mainly distributed along the edge of the design domain. Therefore, considering the topology optimization results and the rationality of the casting draft direction and structure, three vertical stiffeners are added to the casting, distributed along the edge. Considering structural rationality and processing constraints, the stiffener distribution area at the bottom edge in the topology optimization results is not reflected in the stiffening settings.

[0086] like Figure 9 The topology optimization result and corresponding stiffening design of the lower part of the front casting shown in the present invention are configured such that the draft direction is set to be perpendicular to the draft direction of the front casting, and the direction of the stiffening rib is the same as the transverse direction of the vehicle coordinate system. Considering the topology optimization result, two parallel stiffening ribs are set at the lower end, and stiffening ribs are arranged at the bottom. Since there are fewer distributed structures at the front end in the topology optimization result, only two long ribs are arranged to conform to the characteristics of the rear structure.

[0087] like Figure 10 The topology optimization results and corresponding stiffening design of the front casting side shown in this invention demonstrate that the stiffening form of the front casting side is generally obliquely connected, as can be seen from the topology optimization results. Therefore, the stiffening rib arrangement is set as follows: Figure 10 The distribution shown can be designed as a symmetrical fork structure in a more robust design, taking into account the cross-load conditions that are not addressed.

[0088] like Figure 11 The topology optimization results and corresponding reinforcement design of the sill beam in this invention are shown. Since the sill beam is an extruded part, it is subject to extrusion processing constraints. Its cross-section remains unchanged in the direction of the processing constraints. Therefore, through the topology optimization results, the reinforcement layout of the sill beam cross-section is set to a Z-shape on the original sill beam layout, which further optimizes its load-bearing capacity while ensuring other functions.

[0089] like Figure 12 The topology optimization results and corresponding stiffening designs of the post-cast component in this invention are shown. In the topology optimization results, a clear load transfer path is presented in the upper part of the post-cast component design domain, while the lower part has more clustered elements. Therefore, in the stiffening design, two horizontally oriented and vertically oriented stiffeners are designed. In the lower topology optimization results, the main load transfer path has a horizontal distribution. Therefore, in the stiffening design, a horizontally distributed stiffener is arranged in the lower part, and referring to the topology structure, the bottom is modified into an I-shaped state.

[0090] like Figure 13 The topology optimization results and corresponding stiffening designs of the rear casting side shown in this invention indicate that the force transmission path distribution is mainly lateral. Therefore, the stiffening rib design mainly refers to the rib positions in the topology optimization results.

[0091] Since this invention proposes an integrated topology optimization design method for the lower body structure that simultaneously contains extruded and cast parts, it adopts a simplified finite element model of the lower body and performs topology optimization work on the composite model of casting and extruded parts for the front casting-sill beam-rear casting. This method plays a guiding role in the stiffening layout design of vehicle models in actual development. Specifically, it is necessary to consider the overall spatial layout of the vehicle and the design optimization results for comprehensive judgment.

[0092] Through the above steps, the present invention achieves synergistic optimization of the reinforcement of thin-walled die-cast parts and internal reinforcement of cross-sections of electric vehicle lower body under comprehensive service conditions, and finally obtains a body structure design scheme that meets the requirements of high performance and lightweighting.

[0093] In summary, this invention proposes a topology optimization method for the stiffening layout of the underbody structure of an integrated cast-extruded electric vehicle, comprising:

[0094] S1. Finite Element Model Construction and Working Condition Definition: Finite element mesh generation is performed on the lower body structure of the electric vehicle. Based on the processing technology adopted by the components, the finite element mesh is classified into extrusion mesh and casting mesh. Taking into account the service conditions of the whole vehicle, the multi-condition load conditions, weighting coefficients and boundary constraints, including collision, bending, torsion and bottoming out, are determined.

[0095] S2. Construction of Design Domain and Non-Design Domain: The finite element mesh inside a single component in step S1 is divided into a second part, and the mesh of each casting and extrusion is subdivided into a design domain and a non-design domain. The non-design domain is the area that retains the basic outline and function of the component, and the design domain is the area used for stiffening distribution calculation. The extrusion design domain, non-design domain and casting design domain are connected by mesh sharing nodes.

[0096] S3. Establish and solve the casting-extrusion collaborative topology optimization model: For the casting design domain and the extrusion design domain, establish a mathematical model that includes objective function, volume fraction constraints, and manufacturing process constraints; In the mathematical model, for the casting design domain, impose casting process constraints to restrict the material distribution to meet the process requirements along a specific draft direction, so as to optimize the stiffening of thin-walled die castings; for the extrusion design domain, impose extrusion process constraints to restrict the material distribution to meet the requirement of consistent cross-section along the extrusion direction, so as to optimize the stiffening inside the cross-section; By solving the mathematical model, obtain the density distribution of each element, and determine the stiffening layout form that meets the comprehensive service conditions and dual manufacturing process constraints.

[0097] S4. Reconstruction of reinforced structure: Based on the element density distribution and load transfer path calculated in step S3, and combined with the actual processing and installation conditions, the topology optimization results are reconstructed into a CAD model or mesh model with reinforcing ribs.

[0098] The steps in this invention can be adjusted, combined, or deleted according to actual needs.

[0099] The units in the device of the present invention can be merged, divided, or reduced according to actual needs.

[0100] In this invention, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; "linking" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention according to the specific circumstances.

[0101] The shapes of the components in the accompanying drawings are schematic and may differ from their actual shapes. The drawings are only used to illustrate the principles of the present invention and are not intended to limit the present invention.

[0102] Although the invention has been disclosed in detail with reference to the accompanying drawings, it should be understood that these descriptions are merely exemplary and not intended to limit the application of the invention. The scope of protection of the invention is defined by the appended claims and may include various modifications, alterations, and equivalents made to the invention without departing from the scope and spirit of the invention.

Claims

1. A cast-extrusion integrated electric vehicle underbody structure stiffening layout topology optimization method, characterized in that, The method includes: S1. Finite Element Model Construction and Working Condition Definition: Finite element mesh generation is performed on the lower body structure of the electric vehicle. Based on the processing technology adopted by the components, the finite element mesh is classified into extrusion mesh and casting mesh. Extrusion parts include door sill beams, and casting parts include front castings and rear castings. Taking into account the service conditions of the whole vehicle, the multi-condition load conditions, weighting coefficients and boundary constraints, including collision, bending, torsion and bottoming out, are determined. S2. Construction of Design Domain and Non-Design Domain: The finite element mesh inside a single component in step S1 is divided a second time, and the mesh of each casting and extrusion is subdivided into design domain and non-design domain; among them, the non-design domain is the area that retains the basic outline and function of the component, and the design domain is the area used for stiffening distribution calculation; the extrusion design domain, non-design domain and casting design domain are connected by mesh common nodes. S3. Establish and solve the casting-extrusion collaborative topology optimization model: For the casting design domain and the extrusion design domain, establish a mathematical model that includes objective function, volume fraction constraints, and manufacturing process constraints; in the mathematical model, apply casting process constraints to the casting design domain to restrict the material distribution to meet the process requirements along a specific draft direction, so as to optimize the stiffening of thin-walled die castings; apply extrusion process constraints to the extrusion design domain to restrict the material distribution to meet the requirement of consistent cross-section along the extrusion direction, so as to optimize the internal stiffening of the cross-section; by solving the mathematical model, obtain the density distribution of each element, and determine the stiffening layout form that meets the comprehensive service conditions and dual manufacturing process constraints; S4. Reconstruction of stiffened structure: Based on the element density distribution and load transfer path calculated in step S3, and combined with the actual processing and installation conditions, the topology optimization results are reconstructed into a CAD model or mesh model with stiffeners. The mathematical model in step S3 is as follows: Find ; Min ; s. t. ; ； ； ； ； ； ； ； In the formula, , , , , , , This represents the density of the corresponding unit. The total number of units; This represents the total number of structural load cases. For the first Weighting factors for each working condition; For the first Flexibility under various operating conditions; and The first The load and displacement matrix corresponding to each working condition; The overall stiffness matrix; Let V be the volume of each unit. A function that calculates the sum of the volumes of all elements in the design domain; Design domain volume; For the constrained volume fraction, This represents the density of the cells represented by the entity element. This represents the unit density represented by the void element; This represents the total number of cell rows in the casting design domain. Indicates the row number above the separation surface. Indicates the row number below the separation surface. Indicates the column number along the draft direction. It is the first row above the separation surface. It is a threshold greater than or equal to 1. The total number of elements in a single extrusion design domain section. This represents the element portion occupied by a solid within a single extrusion design domain section. This refers to the element portion that is not occupied by a solid within a single extrusion design domain section.

2. The method for topology optimization of the stiffening layout of the cast-extruded integrated electric vehicle lower body structure as described in claim 1, characterized in that, The specific implementation methods for the casting process constraints and extrusion process constraints in step S3 are as follows: Casting process constraints: restrict the density distribution of a row of units along the draft direction in the casting design domain, so that it meets the requirement of increasing or decreasing distribution along the draft direction and parting surface position, and avoids the occurrence of undercut structures; Extrusion process constraints: restrict the element density distribution along the extrusion direction in the extrusion design domain, so that the element portion occupied by the solid in a single extrusion design domain section remains consistent along the extrusion direction, resulting in a beam structure with the same cross-section formed by stretching the cross-section.

3. The method for topology optimization of the stiffening layout of the underbody structure of an electric vehicle as described in claim 1, characterized in that, The specific rules for dividing the design domain and non-design domain in step S2 are as follows: For castings: The shell envelope area that bears the structural function is the non-design domain. Starting from the outside of this area, along the casting draft direction, a grid of a preset number of layers is stretched outward based on the original contour to serve as the casting design domain. For extrusions: extending inward from the outermost single-layer shell contour, the hexahedral mesh filling the shell interior is divided into extrusion design domains, while the outer shell is retained as a non-design domain; and ensuring that adjacent extrusion design domains and casting design domains are separated by a portion of non-design domains.

4. The method for topology optimization of the stiffening layout of the underbody structure of an electric vehicle as described in claim 1, characterized in that, The multi-condition load conditions and weighting coefficients in step S1 specifically include: front-end collision, rear-end collision, left-side collision, and right-side collision conditions, with a weighting coefficient of 1; front bending, front torsion, rear bending, and rear torsion conditions, with a weighting coefficient of 2; and bottoming-out conditions, with a weighting coefficient of 1.

5. The method for topology optimization of the stiffening layout of the underbody structure of an electric vehicle as described in claim 1, characterized in that, In step S3, when applying manufacturing process constraints, the draft direction is set to the vertical direction for the main design domain of the front and rear castings; the draft direction is set to the horizontal direction for the lower and side design domains of the front and rear castings; and the extrusion direction is set to the extension direction along the beam structure at the front and rear of the vehicle body for the sill beam design domain. At the same time, minimum size constraints and maximum size constraints are set to control the width of the generated reinforcing ribs within the machinable range.

6. The method for topology optimization of the stiffening layout of the underbody structure of an electric vehicle as described in claim 1, characterized in that, The stiffening structure reconstruction in step S4 specifically includes: For the high-density areas shown in the optimization results, they are transformed into the direction of the reinforcing ribs in the design; based on the topology results of the previous casting, vertical reinforcing ribs are arranged along the edge of the design domain, and diagonal or fork-shaped reinforcing ribs are arranged on the side; based on the extrusion topology results of the threshold beam, the internal reinforcement layout of its cross section is designed as a Z-shaped structure; based on the topology results of the subsequent casting, transverse reinforcing ribs are designed inside, and the bottom structure is modified to an I-shaped state.

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