Lightweight design method and system for large stamping equipment based on digital twinning

Abstract

The application discloses a large stamping equipment lightweight design method and system based on digital twinning, and mainly relates to the technical field of large forging and pressing equipment design. The method comprises the following steps: decomposing the whole machine stiffness coupling system based on the series stiffness rule and calculating the stiffness contribution proportion of each component; constructing a rigid-flexible integrated finite element digital twinning model; sequentially performing modal simulation, static mechanics simulation and transient dynamics simulation; superimposing the simulation results of the three types to cross-divide the core sensitive area and the non-sensitive area; carrying out topology optimization on the non-sensitive area and size optimization on the core sensitive area according to the stiffness contribution proportion as the constraint level; and outputting the final scheme after repeating the three types of simulation verification on the optimized structure. The application has the advantages that it realizes the improvement of stiffness design accuracy, full coverage of dynamic working conditions, guarantee of anti-unbalanced load capacity and lightweight of equipment structure, and the whole-process digital iteration does not need physical prototype trial production.

Description

Technical Field

[0001] This invention relates to the field of design technology for large forging and pressing equipment, specifically a lightweight design method and system for large stamping equipment based on digital twins. Background Technology

[0002] Large stamping equipment is the core equipment for forming automotive body panels, aerospace structural components, and home appliance housings. Its load-bearing components, such as the body, cranks, connecting rods, and sliders, bear complex alternating loads under full-load and off-center loading conditions. The overall rigidity of the machine directly determines the stamping accuracy and equipment lifespan. As equipment develops towards larger tonnage, higher speed, and lighter weight, traditional experience-based design methods are no longer sufficient to meet the balance between rigidity prediction accuracy and weight reduction requirements.

[0003] Currently, lightweight design of large stamping equipment mainly relies on two methods: static finite element analysis and empirical topology optimization. Static finite element analysis takes a single full-load condition as input to solve for the deformation and stress distribution of the whole machine, and then carries out local structural reinforcement or material reduction based on this. Empirical topology optimization uses volume fraction as constraint and minimizes flexibility as objective to remove redundant material in non-load-bearing areas.

[0004] The above method has three shortcomings: First, it does not establish a series deconstruction model of stiffness coupling of multiple components such as the fuselage, crank, connecting rod, and slider, and cannot quantify the contribution of each component to the overall stiffness, thus lacking a quantitative basis for optimization direction; Second, it only covers static working conditions and does not carry out modal and transient dynamic simulations, so it cannot capture the transient stiffness fluctuations caused by the coupling of punching force and inertial force near the dead point of stamping, and the identification of dynamic stiffness weak areas and impact sensitive areas is missing; Third, the lightweight optimization does not differentiate between core sensitive areas and non-sensitive areas, and blindly reducing weight can easily lead to a decrease in static stiffness, weakening of resistance to eccentric loads, and stress concentration.

[0005] Therefore, there is an urgent need for a lightweight design method and system for large stamping equipment based on digital twins to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a lightweight design method and system for large stamping equipment based on digital twins. It achieves improved stiffness design accuracy, full coverage of dynamic working conditions, guaranteed anti-eccentric load capacity and lightweight equipment structure, and the whole process is digitally iterated without the need for physical prototype manufacturing.

[0007] To achieve the above objectives, the present invention employs the following technical solution: On the one hand, the present invention provides a lightweight design method for large stamping equipment based on digital twins, comprising the following steps: S1. Based on the series stiffness law, the overall stiffness of large stamping equipment is deconstructed into a series coupling system of key load-bearing components, and the contribution ratio of each component to the overall stiffness is calculated. S2. Construct a geometric model of the entire stamping equipment, refine the mesh of the core area of ​​transmission and load bearing, simplify the mesh of the non-transmission and non-load bearing area of ​​the outer body, and apply differentiated tie rod preload and full-load off-center stamping load to generate a rigid-flexible integrated finite element digital twin model. S3. Perform modal simulation, static mechanical simulation and transient dynamic simulation on the digital twin model in sequence to obtain the inherent vibration mode characteristics, static deformation and stress distribution and transient stiffness evolution law; S4. Superimpose the three types of simulation results, take the overlapping area that is determined to be stiffness sensitive by all three types of simulation as the core sensitive area, and take the area that shows low stress in only single-dimensional simulation and whose stiffness contribution ratio is lower than the threshold as the non-sensitive area. S5. Using the stiffness contribution ratio as the basis for optimization constraint level, and taking the stiffness performance of the core sensitive area as not lower than the original design index as rigid constraint, carry out topology optimization with the goal of minimizing self-weight in the non-sensitive area, and carry out size optimization under stiffness constraint in the core sensitive area. S6. Repeat the three types of simulations on the optimized whole structure to verify that each stiffness index is not lower than the preset design threshold, and output the final lightweight solution.

[0008] Preferably, in step S1, the key load-bearing components include the fuselage, crank, connecting rod, and slider, and the load is transferred from the slider to the fuselage via the connecting rod and crank. The crank is an eccentric shaft structure, and its overall stiffness is composed of torsional stiffness and bending stiffness in parallel. The stiffness contribution ratio of each component is used as the basis for determining the optimization constraint level. The higher the stiffness contribution ratio of a component, the higher the stiffness constraint level during the optimization process.

[0009] Preferably, in step S2, the full-load off-center stamping load is 1.6 times the nominal force of the equipment; The preload of the tie rods on the left and right sides is set differently according to the anti-eccentric load requirements. The preload of a single tie rod on the left side is greater than that of a single tie rod on the right side, in order to counteract the asymmetrical deformation of the fuselage under eccentric load conditions.

[0010] Preferably, in step S3, modal simulation includes: The first six natural frequencies and corresponding mode shapes of the whole machine are extracted, and the weak areas of dynamic stiffness are located by the distribution of mode shapes. The first mode shape is the back-and-forth swing of the whole machine, the second mode shape is the left-right swing, the third mode shape is the torsion of the upper part of the machine in the Y direction, the fourth mode shape is the vertical up-and-down vibration along the Y direction, the fifth mode shape is the local torsion of the machine column in the X direction, and the sixth mode shape is the local torsion of the upper part of the machine.

[0011] Preferably, in step S3, the static mechanical simulation includes: The deformation and equivalent stress distribution of the whole machine and its key components under full load and off-center load conditions are determined. The maximum axial tensile deformation of the tie rod, the maximum deformation of the center of the bottom surface of the slider, the deformation law of the column in each direction, and the stress concentration characteristics at the contact points of the crank and the frame, the contact points of the connecting rod and the connector, and the welding points of the slider and the guide rail are obtained to locate the areas with weak static stiffness.

[0012] Preferably, in step S3, the transient dynamics simulation includes: A four-degree-of-freedom transient stiffness transfer model is constructed by selecting crank angle, slider rigid body displacement, connecting rod elastic deformation, and fuselage elastic deformation as generalized coordinates. Based on the Lagrange dynamics equations and Rayleigh dissipation functions, dynamic equilibrium equations are established for four generalized coordinates. The total kinetic energy of the system consists of the crank rotational kinetic energy, the connecting rod translational kinetic energy, and the slider translational kinetic energy. The system potential energy consists of the connecting rod elastic potential energy and the fuselage elastic potential energy. The transient stiffness of the connecting rod and the transient stiffness of the fuselage are introduced, which vary dynamically with load, deformation, and time. The Rayleigh dissipation function covers the crank rotational damping, the connecting rod elastic deformation damping, and the fuselage elastic deformation damping. The dynamic equilibrium equations are rearranged into standard dynamic equations in matrix form. The standard dynamic equations include a mass matrix, a damping matrix, a time-varying stiffness matrix, and a generalized external load vector. The time-varying stiffness matrix changes dynamically with load, deformation, and time during the stamping process. The transient stiffness of the connecting rod and the fuselage during continuous stamping is solved based on the standard dynamic equations. The stiffness change law caused by the coupling of stamping force and inertial force near the bottom dead point of stamping is captured, and the sensitive area of ​​impact load is located.

[0013] Preferably, in step S4, the core sensitive area is an overlapping area where all three types of simulation results determine that the area is stiffness sensitive, including the center of the bottom surface of the slider, the welding point of the slider guide rail, and the upper part of the tie rod and the column; the non-sensitive area is an area where only a single-dimensional simulation shows that the stress is less than 10% of the yield strength of the corresponding material, and the contribution to the stiffness of the whole machine is less than 5%.

[0014] Preferably, the topology optimization removes redundant materials in non-sensitive areas while retaining the load-bearing structure on the stress transmission path; the size optimization uses the response surface methodology to iteratively adjust the cross-sectional parameters of the core sensitive area, including wall thickness and stiffener layout; throughout the optimization process, the deformation and stress values ​​of the core sensitive area are rigidly constrained to not exceed the corresponding thresholds of the original design.

[0015] Preferably, in step S6: If any core stiffness index in the three types of simulations is lower than the preset design threshold, return to step S5 to adjust the optimization parameters and re-execute step S6; Repeat the above iterations until all core stiffness indices in the three types of simulations are not lower than the preset design thresholds, and output the final lightweight solution.

[0016] On the other hand, the present invention also provides a lightweight design system for large stamping equipment based on digital twins, for implementing the above-mentioned method, comprising: The stiffness decomposition module is used to deconstruct the stiffness coupling system of the whole machine based on the series stiffness law and calculate the stiffness contribution ratio of each component. The digital twin modeling module is used to construct the overall geometric model, complete the differentiated mesh generation and boundary condition loading, and generate a rigid-flexible integrated finite element model. The multi-dimensional simulation module is used to sequentially perform modal simulation, static mechanical simulation, and transient dynamic simulation, and output three types of stiffness performance data. The weak area identification module is used to overlay three types of simulation results and cross-divide the core sensitive area and non-sensitive area; The zoning optimization module is used to perform topology and size optimization in different regions, with the constraint that the stiffness index of the core sensitive area is not lower than the original design. The verification output module is used to perform multi-dimensional simulation verification of the optimization scheme and output the final lightweight design scheme that meets the threshold requirements. When performing transient dynamics simulation, the multi-dimensional simulation module selects crank angle, slider rigid body displacement, connecting rod elastic deformation, and fuselage elastic deformation as generalized coordinates to construct a four-degree-of-freedom transient stiffness transfer model. The model includes a time-varying stiffness matrix that dynamically changes with load, deformation, and time. When the core stiffness index is lower than the preset design threshold, the verification output module triggers the partition optimization module to re-execute the optimization and receives the verification result from the multi-dimensional simulation module again, until all core stiffness indices of the three types of simulations are not lower than the preset design threshold.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention deconstructs the overall stiffness of the machine into a coupled system of key load-bearing components through the series stiffness law and quantifies the stiffness contribution ratio of each component. This contribution ratio is used as the basis for the optimization constraint level, so that the direction of lightweight optimization has a quantitative basis and overcomes the defect of inaccurate stiffness prediction in traditional empirical design methods.

[0018] 2. This invention constructs a rigid-flexible integrated digital twin model, refines the mesh of the core area of ​​the transmission load, simplifies the mesh of the non-load-bearing area of ​​the outer body, and applies differentiated tie rod preload and full-load off-center stamping load to accurately restore the full-load off-center forging boundary conditions, providing a high-fidelity digital base for multi-dimensional stiffness simulation.

[0019] 3. This invention sequentially performs modal simulation, static mechanical simulation and transient dynamic simulation, and constructs a four-degree-of-freedom transient stiffness transfer model to capture the transient stiffness fluctuation caused by the coupling of punching force and inertial force near the dead point of the stamping, thus making up for the deficiency of traditional static analysis in not being able to cover dynamic impact conditions.

[0020] 4. This invention divides the core sensitive area and non-sensitive area by superimposing three types of simulation results, performs topology optimization on the non-sensitive area and size optimization under stiffness constraints on the core sensitive area, and achieves lightweight equipment structure without degrading the static stiffness, dynamic stiffness and anti-eccentric load capacity of the whole machine. Moreover, the whole process is digitally iterated without the need for physical prototype manufacturing. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the overall machine stiffness contribution disassembly mechanism of the present invention; Figure 3 This is a flowchart of the digital twin modeling and simulation process of this invention; Figure 4 This is a flowchart of the modal analysis of the press machine according to the present invention; Figure 5 This is a cloud diagram of the press model of the present invention, wherein... Figure 5 (a) is a deformation cloud diagram of the entire press. Figure 5 (b) is the equivalent stress cloud diagram of the entire press; Figure 6 This is a schematic diagram of the system structure of the present invention. Detailed Implementation

[0022] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined in this application.

[0023] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0024] Example: like Figure 1 As shown, this embodiment provides a lightweight design method for large stamping equipment based on digital twins, including: S1. Decomposition of overall machine stiffness contribution: Based on the series stiffness law, the overall stiffness of large stamping equipment is decomposed into a series coupling system of four key load-bearing components: the machine body, crank, connecting rod, and slider, and the contribution ratio of each component to the overall machine stiffness is calculated. S2. Rigid-Flexible Integrated Digital Twin Modeling: Construct the geometric model of the entire stamping equipment, match the material properties of each component, refine the mesh of the core area of ​​transmission and load bearing composed of crank, connecting rod, slider, and guide rail, simplify the mesh of the non-force transmission and non-load bearing area of ​​the outer body, and complete the finite element modeling; load the differential tie rod preload and full-load off-center stamping load on the left and right sides, set the base fixed constraint, and restore the boundary conditions of full-load off-center forging. S3. Multi-dimensional stiffness performance simulation: Modal simulation, static mechanical simulation and transient dynamic simulation are carried out in sequence to obtain the inherent vibration mode characteristics, static deformation and stress distribution, and transient stiffness evolution law under impact load. S4. Cross-identification of stiffness weak areas: Superimpose the results data of three types of simulations to locate the static stiffness weak areas, dynamic stiffness weak areas and impact sensitive areas respectively, and divide the core sensitive areas where the stiffness performance needs to meet the original design indicators, as well as the non-sensitive areas where weight reduction design can be carried out. S5. Regional lightweight optimization: With the static stiffness, dynamic stiffness, and anti-eccentric load performance of the core sensitive area not lower than the original design index as rigid constraints, topology optimization with the goal of minimizing self-weight is carried out on the non-load-bearing low-stress structure of the non-sensitive area, and dimensional optimization under stiffness constraints is carried out on the key sections of the core sensitive area to complete the lightweight design of the whole machine. S6. Multi-dimensional simulation verification: Repeatedly perform three types of stiffness simulation on the optimized whole structure, verify that the static stiffness, dynamic stiffness and anti-eccentric load performance are not lower than the preset design threshold, and output the final lightweight solution.

[0025] This embodiment is a preferred implementation, using the SPE4-800G servo crank press as the design object. The equipment has a nominal force of 8MN, a slider stroke of 450mm, a stroke frequency of 1-25 times per minute, and the dimensions of the worktable and the bottom surface of the slider are both 2500mm×4500mm. Please refer to Table 1 for the parameters.

[0026] Table 1 Main Technical Parameters of Servo Crank Press

[0027] The entire machine consists of a crossbeam, column, worktable, base, tie rod, and crank-connecting rod motion mechanism, driven by dual servo motors. This embodiment utilizes digital twin technology for lightweight design, ensuring that the overall rigidity and resistance to eccentric loads are not lower than the original design specifications. All parameters and simulation results are derived from actual finite element simulation tests.

[0028] S1. Decomposition of Overall Machine Stiffness Contribution. First, a theoretical decomposition of the overall machine stiffness is conducted to clarify the stiffness composition and coupling relationship during power transmission. For example... Figure 2 As shown, the overall stiffness of the press is composed of four key components connected in series: the press body, crank, connecting rod, and slide block. The load is transmitted from the slide block through the connecting rod and crank to the press body. The elastic deformation of each component under stress is added together to form the total deformation of the entire press. Therefore, the reciprocal of the overall stiffness of the press is equal to the sum of the reciprocals of the stiffness of each component, satisfying the series stiffness coupling formula: ; In the formula, For the overall stiffness of the machine, For fuselage rigidity, For the overall stiffness of the crank, For the stiffness of the connecting rod, Let be the slider stiffness. The crank is an eccentric shaft structure, and its overall stiffness is composed of torsional stiffness and bending stiffness in parallel. These two factors together determine the crank's load-bearing deformation characteristics, satisfying: , , ; In the formula, For crank torsional stiffness, Let G be the crank bending stiffness, G be the material shear modulus, J be the polar moment of inertia, E be the material elastic modulus, and I be the moment of inertia of the cross section. Where is the crank length. The axial stiffness of individual components such as the fuselage, connecting rod, and slider satisfies the general calculation formula: ; In the formula, This refers to the elastic modulus of the material of the corresponding component. The total cross-sectional area of ​​the component. The effective load-bearing length of the component; , , ; In the formula, F is the punching force. This refers to the amount of elastic deformation of the fuselage caused by stamping. The length of the link. Let A be the effective length of the slider, and A be the top region where the upper part of the column connects to the crossbeam. The above formula can quantify the contribution of each component to the overall machine stiffness. Components with higher stiffness contribution ratios will have higher constraint levels in subsequent optimization processes, thus determining optimization priorities.

[0029] S2. Rigid-Flexible Integrated Digital Twin Modeling. This stage constructs a finite element digital twin model with a 1:1 scale to the physical object. The overall modeling process is as follows: Figure 3As shown, the simulation is divided into four stages: geometric model construction, material property matching, differential mesh generation, and boundary condition loading. In the geometric model construction stage, the complete structure of the equipment's beam, column, worktable, base, tie rod, and crank-connecting rod mechanism is analyzed. A three-dimensional geometric model is constructed according to the actual dimensions, and non-critical small structures such as bolt holes and chamfers are reasonably simplified to improve simulation efficiency while ensuring calculation accuracy. In the material property matching stage, corresponding materials were matched according to the function and stress characteristics of different components. For structural components such as beams, columns, sliders, worktables, and bases, Q235-A steel was used, with a density of 7850 kg / m³, Young's modulus of 210 GPa, and Poisson's ratio of 0.3. For core transmission components such as idler shafts and eccentric shafts, 42CrMo steel was used, with a density of 8050 kg / m³, Young's modulus of 210 GPa, and Poisson's ratio of 0.28. For connecting components such as tie rods, tensioning nuts, idler wheels, and eccentric wheels, 45 steel was used, with a density of 7850 kg / m³, Young's modulus of 209 GPa, and Poisson's ratio of 0.31. The parameters are shown in Table 2.

[0030] Table 2. Materials and Material Properties of Various Components of the Press

[0031] In the mesh generation stage, tetrahedral elements were used to mesh the entire machine. The core transmission and load-bearing region, consisting of cranks, connecting rods, sliders, and guide rails, was refined. Element density was increased in stress concentration areas and areas of stiffness variation, while the mesh was simplified in the non-load-bearing, non-transmission areas of the outer fuselage. The final machine model contains 1,036,287 nodes and 591,048 elements, balancing computational accuracy and operational efficiency. In the boundary condition loading stage, the preload of the tie rods was calculated according to the closed-type combined fuselage design requirements. First, the structural stiffness of the tie rods and columns was calculated using the component stiffness formula, where the cross-sectional area of ​​the tie rod S1 = 0.0346 m². 2 The length L1 = 11m, and the cross-sectional area of ​​the column S2 = 0.471m². 2 The length L2 = 5.3m. Substituting this into the axial stiffness formula, we can obtain the stiffness of the tie rod. =6.68×10⁸ N / m, column stiffness =1.94×10¹⁰ N / m. Taking a preload coefficient of 1.5, substituting it into the total preload formula: ; In the formula, z is the preload coefficient. The nominal force of the equipment is given. The total preload is calculated to be 11.6MN. Considering the eccentric load design requirements, different preloads are applied to the tie rods on both sides to satisfy the following conditions: ; In the formula, Preload for the single tie rod on the left side. The preload of the single tie rod on the right is 3.3MN. In this embodiment, the preload of the single tie rod on the left is 3.3MN, and the preload of the single tie rod on the right is 2.5MN. The stamping load is set to 1.6 times the nominal force, i.e., 12.8MN, and is applied vertically to the upper surface of the worktable and the lower surface of the slider, respectively. With the bottom surface of the base as a fully fixed constraint, the full-load off-center forging condition is completely reproduced.

[0032] S3, Multi-dimensional stiffness performance simulation. For example... Figure 4 As shown, after modeling is completed, modal simulation, static mechanical simulation, and transient dynamic simulation are carried out sequentially to comprehensively obtain the stiffness characteristics of the equipment from three dimensions. First, modal simulation analysis is performed to construct the overall dynamic equations under no-load and no-damping conditions, and the natural frequencies and mode shapes are solved using series stiffness theory. In actual motion conditions, given the impact force, the differential equations of motion satisfy: ; In the formula, For the overall quality of the press, For structural damping, Here is the stiffness matrix. For acceleration vectors, For velocity vectors, It is a displacement vector. Let the impact force be 0. When the impact force is 0, the structural damping is 0, and the calculated series stiffness of the entire machine is: ; ; In the formula, It is the inherent frequency of the entire machine. This represents the elastic deformation. Based on this model, the transient stiffness of the connecting rod and the fuselage during continuous stamping can be solved, accurately capturing the stress wave effect and nonlinear transient response under stamping impact loads, clarifying the stiffness change law caused by the coupling of stamping force and inertial force near the bottom dead center, and compensating for static analysis. As shown in Table 3, the first six dominant vibration modes are extracted: The first mode is the back-and-forth oscillation of the whole machine, with a natural frequency of 16.539Hz, corresponding to a crank speed of 992.34r / min. The amplitude of the body gradually increases from the column upwards, which can easily cause slider guidance deviation; The second mode is the left-right oscillation, with a natural frequency of 32.082Hz, which will disturb the structural symmetry and cause stiffness reduction; The third mode is the upper part of the body twisting in the Y direction, with a natural frequency of 44.034Hz, which can easily generate alternating stress and cause fatigue failure; The fourth mode is the vertical up-and-down vibration along the Y direction, with a natural frequency of 72.286Hz, which directly affects the guidance and transmission system; The fifth mode is the local twisting of the body column in the X direction, with a natural frequency of 103.67Hz, which will reduce the stiffness of the column and cause slider wobbling; The sixth mode is the local twisting of the upper part of the body, with a natural frequency of 119.88Hz, which can easily cause stiffness degradation of key transmission components.

[0033] Table 3. First six natural modal frequencies and vibration modes of the entire press machine.

[0034] Modal analysis identifies the resonant frequency range that the equipment needs to avoid, pinpointing areas of weak dynamic stiffness. Next, static mechanical simulation analysis is performed to solve for the overall deformation and stress distribution under full-load and off-center loading conditions. Figure 5 As shown, the largest deformation of the entire machine is concentrated at the tie rod, with a maximum deformation of 2.8415 mm, resulting from the combined effect of preload and impact force, causing axial tensile deformation. The slider, as the direct load-bearing component, exhibits the second largest compressive deformation. The base, subject to fixed constraints, shows the smallest deformation. The overall stress of the machine is at a low level, with stress concentrations mainly distributed at the contact points between the crank and frame, the connecting rod and connector, and the welded joints between the slider body and the guide rail surface. The maximum stress values ​​are 243.59 MPa, 56.934 MPa, and 139.1 MPa, respectively, all below the yield strength of the corresponding materials. The deformation of the column gradually decreases from top to bottom, with the largest deformation along the Y-axis at 0.22851 mm. The total maximum deformation is 0.30527 mm, consistent with the bending deformation trend of the column under stress. The maximum deformation of the slider is concentrated in the central area of ​​the bottom surface, gradually decreasing from the center to both sides. The maximum deformation at the centerline of the bottom surface is 0.67342 mm. Due to the differential preload on both sides, the deformation on the right side is slightly greater than that on the left. The stress distribution also shows a decreasing trend from the center to both sides, with local stress concentration at the internal reinforcing ribs. The connecting rod deformation decreases from 0.4 mm to about 0.15 mm from top to bottom, exhibiting a non-linear decay. The deformation on the inner side of the bottom is significantly greater than that on the outer side, with a maximum deformation of 0.46095 mm and a maximum stress of 56.934 MPa, concentrated at the connection with the connector. Static simulation is used to identify areas with weak static stiffness and stress concentration risk points. Finally, transient dynamic simulation analysis is conducted, selecting the crank angle... Slider rigid body displacement x, connecting rod elastic deformation Airframe elastic deformation Using generalized coordinates, construct a four-degree-of-freedom transient stiffness transfer model. Kinetic energy of the crankshaft rotation in a press for: ; In the formula, J is the moment of inertia. The crank angular velocity; Linkage translational kinetic energy for: ; In the formula, Let be the velocity of the rigid body of the slider. Let be the rate of change of the elastic deformation of the connecting rod with time. The equivalent mass of the connecting rod; Translational kinetic energy of the slider for: ; In the formula, For the mass of the slider, The rate of change of the elastic deformation of the fuselage over time; The total kinetic energy T of the servo press system is: .

[0035] The system's potential energy primarily originates from the elastic potential energy of the connecting rod and the fuselage. This elastic potential energy, along with the stiffness coefficient and elastic deformation, satisfies Hooke's Law. Considering that the stiffness of the connecting rod and fuselage dynamically changes with load, deformation, and time during the stamping process, transient stiffness of the connecting rod is introduced. and the transient stiffness of the connecting rod Then the total potential energy is: ; To account for the influence of system damping on dynamic response, the Rayleigh dissipation function is used to describe the energy dissipation characteristics of the system, covering crank rotation damping, connecting rod elastic deformation damping, and fuselage elastic deformation damping, with damping coefficients defined as follows: , and Then the dissipation function D is: .

[0036] Based on the Lagrange dynamic equations and Rayleigh dissipation functions, dynamic equilibrium equations are established for the four generalized coordinates, and finally the standard dynamic equations in matrix form are derived: 1. Crank rotation dynamics equation: ; In the formula, The moment of inertia of the crank rotation, The crank angular acceleration, The driving torque of the motor varies with time t.

[0037] 2. Equations for the displacement dynamics of the rigid body of the slider: ; In the formula, Let the acceleration of the slider be the rigid body acceleration. The acceleration due to the elastic deformation of the connecting rod. For the elastic deformation acceleration of the fuselage, The force is transmitted from the crank to the slider via the connecting rod. The workpiece stamping resistance is the reaction force generated by the workpiece on the slider during the stamping process, which varies with time t.

[0038] 3. Dynamic equation of elastic deformation of the connecting rod: ; In the formula, The elastic force of the connecting rod is obtained by multiplying the transient stiffness of the connecting rod by its elastic deformation. This is the elastic deformation speed of the connecting rod.

[0039] 4. Equation of elastic deformation dynamics of the fuselage: ; In the formula, The fuselage elasticity is obtained by multiplying the transient stiffness of the fuselage by its elastic deformation. This refers to the elastic deformation speed of the fuselage.

[0040] The above equations are rearranged into standard dynamic equations in matrix form: ; In the formula, M is the mass matrix, C is the damping matrix, K(t) is the time-varying stiffness matrix, and F(t) is the generalized external load vector. It is a generalized acceleration vector. For generalized velocity vectors, It is a generalized coordinate vector.

[0041] By inverse solving the transient stiffness of the connecting rod and the transient stiffness of the fuselage, the transient stiffness of the entire aircraft can be obtained: .

[0042] Based on this model, the transient stiffness of the connecting rod and the fuselage during continuous stamping can be solved. It can accurately capture the stiffness change law caused by the coupling of stamping force and inertial force near the dead point of stamping, and make up for the deficiency of static analysis in not being able to cover dynamic impact conditions.

[0043] S4. Cross-identification of Stiffness Weak Areas. Based on multi-dimensional simulation results, the precise location of three types of stiffness weak areas is achieved. The core sensitive areas are overlapping regions identified as stiffness-sensitive by all three simulation results, including the center of the slider bottom surface, the welded joint of the slider guide rail, and the upper part of the tie rod and column. Static stiffness weak areas are mainly the center of the slider bottom surface, the tie rod, and the upper part of the column. The center of the slider bottom surface exhibits the largest deformation, making it the core sensitive area affecting stamping accuracy. The tie rod, subjected to the combined effects of preload and stamping force, has the highest proportion of axial deformation, a significant factor contributing to overall machine stiffness degradation. Dynamic stiffness weak areas are mainly the upper part of the column and machine body. Forward / backward swinging, left / right swinging, and torsional deformation can cause a decrease in slider guiding accuracy, resulting in dynamic stiffness degradation. Impact-sensitive areas are mainly the welded joint of the slider guide rail, the connecting rod connection, and the crank support. These areas are prone to stress concentration and fatigue damage under impact loads, making them high-risk areas for stiffness degradation during long-term operation. The non-sensitive area is defined as the region where, in single-dimensional simulation, the stress is less than 10% of the corresponding material's yield strength, and its contribution to the overall stiffness is less than 5%. These areas are mainly distributed in the non-load-bearing structures on the outer perimeter of the fuselage and are the primary targets for lightweighting and weight reduction. Cross-identification clarifies the core areas that must be prioritized during the optimization process, thus defining rigid boundaries for lightweighting optimization.

[0044] S5. Regional lightweight optimization. With the static stiffness, dynamic stiffness, and resistance to eccentric loads of the whole machine not lower than the original design specifications as rigid constraints, regional lightweight optimization is carried out.

[0045] For the low-stress areas on the outer perimeter of the fuselage, which are not sensitive, a topology optimization method is used to remove redundant materials while retaining the load-bearing structure along the stress transmission path, thereby reducing the self-weight without affecting the structural stiffness. For the critical cross-sectional dimensions of the beams and columns, a response surface methodology is used to conduct multi-objective dimensional optimization, iteratively adjusting parameters such as wall thickness and stiffener layout to achieve the optimal balance between stiffness and self-weight. During the optimization process, it is strictly ensured that core stiffness indicators such as the deformation of the slider bottom surface, the deformation of the tie rod, and the deformation of the column do not deteriorate, while ensuring that the maximum stress of all components is lower than the material yield strength, thus balancing strength and stiffness requirements.

[0046] S6. Multi-dimensional simulation verification. Modal simulation, static mechanical simulation, and transient dynamic simulation are repeatedly performed on the optimized structural model to verify core performance indicators such as natural frequency, deformation, stress value, and transient stiffness. At the same time, the strength safety factor is checked to confirm that all indicators meet the design requirements. If any indicators fail to meet the standards, the optimization steps are returned to adjust the parameters and iterative verification is performed again to form a complete design process, ensuring the reliability and engineering feasibility of the lightweight solution.

[0047] like Figure 6 As shown, this embodiment also provides a lightweight design system for large stamping equipment based on digital twins, including: The stiffness decomposition module is used to deconstruct the stiffness coupling system of the whole machine based on the series stiffness law and calculate the stiffness contribution ratio of each component. The digital twin modeling module is used to construct the overall geometric model, complete the differentiated mesh generation and boundary condition loading, and generate a rigid-flexible integrated finite element model. The multi-dimensional simulation module is used to sequentially perform modal simulation, static mechanical simulation, and transient dynamic simulation, and output three types of stiffness performance data. The weak area identification module is used to overlay three types of simulation results and cross-divide the core sensitive area and non-sensitive area; The zoning optimization module is used to perform topology and size optimization in different regions, with the constraint that the stiffness index of the core sensitive area is not lower than the original design. The verification output module is used to perform multi-dimensional simulation verification of the optimization scheme and output the final lightweight design scheme that meets the threshold requirements. When performing transient dynamics simulation, the multi-dimensional simulation module selects crank angle, slider rigid body displacement, connecting rod elastic deformation, and fuselage elastic deformation as generalized coordinates to construct a four-degree-of-freedom transient stiffness transfer model. The model includes a time-varying stiffness matrix that dynamically changes with load, deformation, and time. When the core stiffness index of the verification output module is lower than the preset design threshold, the partition optimization module is triggered to re-execute the optimization and receive the verification results of the multi-dimensional simulation module again until all core stiffness indices of the three types of simulations are not lower than the preset design threshold.

[0048] The above is a detailed description of the preferred embodiments of the present invention, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A lightweight design method for large-scale stamping equipment based on digital twins, characterized in that, Includes the following steps: S1. Based on the series stiffness law, the overall stiffness of large stamping equipment is deconstructed into a series coupling system of key load-bearing components, and the contribution ratio of each component to the overall stiffness is calculated. S2. Construct a geometric model of the entire stamping equipment, refine the mesh of the core area of ​​transmission and load bearing, simplify the mesh of the non-transmission and non-load bearing area of ​​the outer body, and apply differentiated tie rod preload and full-load off-center stamping load to generate a rigid-flexible integrated finite element digital twin model. S3. Perform modal simulation, static mechanical simulation and transient dynamic simulation on the digital twin model in sequence to obtain the inherent vibration mode characteristics, static deformation and stress distribution and transient stiffness evolution law; S4. Superimpose the three types of simulation results, take the overlapping area that is determined to be stiffness sensitive by all three types of simulation as the core sensitive area, and take the area that shows low stress in only single-dimensional simulation and whose stiffness contribution ratio is lower than the threshold as the non-sensitive area. S5. Using the stiffness contribution ratio as the basis for optimization constraint level, and taking the stiffness performance of the core sensitive area as not lower than the original design index as rigid constraint, carry out topology optimization with the goal of minimizing self-weight in the non-sensitive area, and carry out size optimization under stiffness constraint in the core sensitive area. S6. Repeat the three types of simulations on the optimized whole structure to verify that each stiffness index is not lower than the preset design threshold, and output the final lightweight solution.

2. The method according to claim 1, characterized in that, In step S1, the key load-bearing components include the fuselage, crank, connecting rod, and slider, and the load is transferred from the slider to the fuselage via the connecting rod and crank. The crank is an eccentric shaft structure, and its overall stiffness is composed of torsional stiffness and bending stiffness in parallel. The stiffness contribution ratio of each component is used as the basis for determining the optimization constraint level. The higher the stiffness contribution ratio of a component, the higher the stiffness constraint level during the optimization process.

3. The method according to claim 1, characterized in that, In step S2, the full-load off-center stamping load is taken as 1.6 times the nominal force of the equipment; The preload of the tie rods on the left and right sides is set differently according to the anti-eccentric load requirements. The preload of a single tie rod on the left side is greater than that of a single tie rod on the right side, in order to counteract the asymmetrical deformation of the fuselage under eccentric load conditions.

4. The method according to claim 1, characterized in that, In step S3, modal simulation includes: The first six natural frequencies and corresponding mode shapes of the whole machine are extracted, and the weak areas of dynamic stiffness are located by the distribution of mode shapes. The first mode shape is the back-and-forth swing of the whole machine, the second mode shape is the left-right swing, the third mode shape is the torsion of the upper part of the machine in the Y direction, the fourth mode shape is the vertical up-and-down vibration along the Y direction, the fifth mode shape is the local torsion of the machine column in the X direction, and the sixth mode shape is the local torsion of the upper part of the machine.

5. The method according to claim 1, characterized in that, In step S3, the static mechanical simulation includes: The deformation and equivalent stress distribution of the whole machine and its key components under full load and off-center load conditions are determined. The maximum axial tensile deformation of the tie rod, the maximum deformation of the center of the bottom surface of the slider, the deformation law of the column in each direction, and the stress concentration characteristics at the contact points of the crank and the frame, the contact points of the connecting rod and the connector, and the welding points of the slider and the guide rail are obtained to locate the areas with weak static stiffness.

6. The method according to claim 1, characterized in that, In step S3, the transient dynamics simulation includes: A four-degree-of-freedom transient stiffness transfer model is constructed by selecting crank angle, slider rigid body displacement, connecting rod elastic deformation, and fuselage elastic deformation as generalized coordinates. Based on the Lagrange dynamics equations and Rayleigh dissipation functions, dynamic equilibrium equations are established for four generalized coordinates. The total kinetic energy of the system consists of the crank rotational kinetic energy, the connecting rod translational kinetic energy, and the slider translational kinetic energy. The system potential energy consists of the connecting rod elastic potential energy and the fuselage elastic potential energy. The transient stiffness of the connecting rod and the transient stiffness of the fuselage are introduced, which vary dynamically with load, deformation, and time. The Rayleigh dissipation function covers the crank rotational damping, the connecting rod elastic deformation damping, and the fuselage elastic deformation damping. The dynamic equilibrium equations are rearranged into standard dynamic equations in matrix form. The standard dynamic equations include a mass matrix, a damping matrix, a time-varying stiffness matrix, and a generalized external load vector. The time-varying stiffness matrix changes dynamically with load, deformation, and time during the stamping process. The transient stiffness of the connecting rod and the fuselage during continuous stamping is solved based on the standard dynamic equations. The stiffness change law caused by the coupling of stamping force and inertial force near the bottom dead point of stamping is captured, and the sensitive area of ​​impact load is located.

7. The method according to claim 1, characterized in that, In step S4, the core sensitive area is the overlapping area where all three types of simulation results determine that it is stiffness sensitive, including the center of the bottom surface of the slider, the welding point of the slider guide rail, and the upper part of the tie rod and column; the non-sensitive area is the area where only a single-dimensional simulation shows that the stress is less than 10% of the corresponding material yield strength, and the contribution to the stiffness of the whole machine is less than 5%.

8. The method according to claim 1, characterized in that, In step S5, the topology optimization removes redundant materials in non-sensitive areas while retaining the load-bearing structure on the stress transmission path; the size optimization uses the response surface methodology to iteratively adjust the cross-sectional parameters of the core sensitive area, including wall thickness and stiffener layout. The entire optimization process is rigidly constrained by ensuring that the deformation and stress values ​​in the core sensitive areas do not exceed the corresponding thresholds of the original design.

9. The method according to claim 1, characterized in that, In step S6: If any core stiffness index in the three types of simulations is lower than the preset design threshold, return to step S5 to adjust the optimization parameters and re-execute step S6; Repeat the above iterations until all core stiffness indices in the three types of simulations are not lower than the preset design thresholds, and output the final lightweight solution.

10. A lightweight design system for large-scale stamping equipment based on digital twins, used to implement the method described in any one of claims 1 to 9, characterized in that, include: The stiffness decomposition module is used to deconstruct the stiffness coupling system of the whole machine based on the series stiffness law and calculate the stiffness contribution ratio of each component. The digital twin modeling module is used to construct the overall geometric model, complete the differentiated mesh generation and boundary condition loading, and generate a rigid-flexible integrated finite element model. The multi-dimensional simulation module is used to sequentially perform modal simulation, static mechanical simulation, and transient dynamic simulation, and output three types of stiffness performance data. The weak area identification module is used to overlay three types of simulation results and cross-divide the core sensitive area and non-sensitive area; The zoning optimization module is used to perform topology and size optimization in different regions, with the constraint that the stiffness index of the core sensitive area is not lower than the original design. The verification output module is used to perform multi-dimensional simulation verification of the optimization scheme and output the final lightweight design scheme that meets the threshold requirements. When performing transient dynamics simulation, the multi-dimensional simulation module selects crank angle, slider rigid body displacement, connecting rod elastic deformation, and fuselage elastic deformation as generalized coordinates to construct a four-degree-of-freedom transient stiffness transfer model. The model includes a time-varying stiffness matrix that dynamically changes with load, deformation, and time. When the core stiffness index is lower than the preset design threshold, the verification output module triggers the partition optimization module to re-execute the optimization and receives the verification result from the multi-dimensional simulation module again, until all core stiffness indices of the three types of simulations are not lower than the preset design threshold.

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