A heavy forging die residual stress self-compensation design method and system

Abstract

The application discloses a heavy forging die residual stress self-compensation design method and system, relates to the technical field of industrial mother machine manufacturing, and aims to solve the technical problems that the prior art cannot actively control residual stress in the forging process, the compensation structure design lacks quantitative basis, and there is no verification optimization mechanism after compensation. The heavy forging die residual stress self-compensation design method comprises the following steps: performing thermal-mechanical coupling simulation on a target forging under initial die conditions to extract residual stress distribution after cooling to room temperature; identifying stress concentration areas, evaluating the danger level, and calculating compensation compressive stress; selecting elastic grooves, asymmetric stiffness cavity walls or pre-deformation curved surface compensation units according to the area characteristics to design, establishing a quantitative mapping between the structure parameters and the compensation stress; constructing a die model containing the compensation unit and implementing coupling simulation, if the compensation effect does not meet the standard, adjusting the parameters through multi-objective function iteration until convergence; and outputting the optimized die design.

Description

Technical Field

[0001] This invention relates to the field of industrial machine tool manufacturing technology, and more specifically, to a self-compensating design method and system for residual stress in heavy forging dies. Background Technology

[0002] The precision retention and service life of industrial machine tools depend primarily on the manufacturing quality of key transmission components such as spindles, gears, lead screws, and guide rails, with the forging process being the core factor determining the internal structure and mechanical properties of these parts. During forging, due to uneven plastic deformation within the material and the phase transformation effect during subsequent cooling, residual stresses are generated within the forging, existing in a self-balancing state. These residual stresses are the root cause of warping deformation during subsequent heat treatment, exceeding precision tolerances after machining, and premature fatigue fracture or even low-stress brittle fracture during service.

[0003] Currently, industry-wide technologies for controlling residual stress in forgings primarily focus on post-forming treatments. These often employ post-treatment processes such as quenching followed by cold pressing, cold stretching, vibration aging, cryogenic treatment, and localized tempering to reduce existing residual stress, or surface strengthening processes like shot peening and rolling to improve surface stress conditions. However, these post-treatment methods all have inherent drawbacks. Firstly, all post-treatment processes can only intervene after residual stress has already formed, failing to prevent stress formation at its source, and their effectiveness in reducing deep residual stress within the forging is extremely limited. Secondly, post-treatment processes typically increase processing time by more than 30% and manufacturing costs by more than 25%, significantly reducing production efficiency and economic benefits. Furthermore, mechanical straightening methods like cold pressing can easily introduce new stress concentrations or surface damage into the forging, potentially leading to a decrease in the fatigue resistance of the parts. More importantly, existing mold design methods only focus on the geometric forming accuracy of the forging and the service life of the mold itself, completely ignoring the influence of the mold cavity structure on the distribution of residual stress inside the forging. When the forging is formed in the mold cavity, the distribution of residual stress is uncontrollable, which means that subsequent expensive post-processing processes must be used to remedy the situation. Summary of the Invention

[0004] The purpose of this invention is to provide a self-compensating design method and system for residual stress in heavy-duty forging dies, which solves the technical problems of existing technologies that cannot actively control residual stress during forging, lack quantitative basis for compensation structure design, and lack of verification and optimization mechanisms after compensation. In view of this, this invention achieves this through the following solution.

[0005] In a first aspect, the present invention provides a self-compensating design method for residual stress in heavy forging dies, comprising: Thermo-mechanical coupled numerical simulation was performed on the entire forging process of the target forging under initial mold conditions, and the residual stress distribution data after the forging cooled to room temperature was extracted. Based on the residual stress distribution data, stress concentration areas on the forging are identified, the hazard level of each stress concentration area is assessed and classified, and the required compressive stress compensation is obtained. Based on the characteristics of the stress concentration area, one or more of the following can be selected for structural design: elastic groove compensation unit, asymmetric stiffness cavity wall compensation unit, and pre-deformed curved surface compensation unit. A quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress is established. An improved mold model containing the selected compensation unit is established, and coupled simulation verification of the forging and the mold is performed. When the compensation effect does not meet the preset requirements, the structural parameters of the compensation unit are iteratively adjusted through a multi-objective optimization function until the convergence criterion is met. The final mold design result is output based on the optimized structural parameters.

[0006] Compared with existing technologies, the self-compensation design method for residual stress in heavy forging dies of this invention uses thermo-mechanical coupling numerical simulation of the entire forging process of the target forging under initial die conditions. This allows the magnitude and distribution of residual stress inside the forging to be accurately predicted during the die design stage, providing a quantitative basis for subsequent compensation design. Based on this, stress concentration areas are accurately identified and hazard assessments and classifications are performed according to the residual stress distribution data, transforming the compensation design from experience-driven to data-driven, effectively avoiding insufficient or excessive compensation. Then, based on the characteristics of the stress concentration areas, one or more of the following structural design units—elastic groove compensation units, asymmetric stiffness cavity wall compensation units, or pre-deformed curved surface compensation units—are selected. A quantitative mapping relationship between the structural parameters of the compensation units and the compensation stress is established, transforming the die cavity from a rigid structure to a structure with active compensation capabilities, achieving precise matching between compensation stress and structural parameters. Finally, a coupled simulation verification is performed by establishing an improved die model containing compensation units, and a multi-objective optimization function is used to iteratively adjust the structural parameters until the convergence criterion is met, effectively ensuring the compensation effect while also considering the die's service life. The above-mentioned technical solution of the invention solves the technical problems of existing technologies being unable to actively control residual stress during forging, lacking quantitative basis for compensation structure design, and lacking verification and optimization mechanisms after compensation.

[0007] Furthermore, in the self-compensation design method for residual stress of heavy forging dies of the present invention, in the thermo-mechanical coupling numerical simulation, the constitutive model of the forging material is described by a constitutive model that simultaneously considers the temperature softening effect, strain hardening effect and strain rate strengthening effect, and the comprehensive heat transfer coefficient is composed of the superposition of the convective heat transfer coefficient, the radiative heat transfer coefficient and the contact heat transfer coefficient; the residual stress is obtained by the superposition of elastic stress, plastic stress and phase transformation stress.

[0008] Furthermore, in the heavy-duty forging die residual stress self-compensation design method of the present invention, identifying the stress concentration area on the forging includes: The stress gradient method is used to identify local areas of stress variation, and the stress concentration factor method is used to quantify the degree of stress concentration. When the stress gradient exceeds a preset stress gradient threshold and the stress concentration factor exceeds a preset stress concentration factor threshold, the area is determined to be a stress concentration area.

[0009] Furthermore, in the self-compensation design method for residual stress of heavy forging dies of the present invention, the hazard assessment is based on the third strength theory. The equivalent stress is obtained by obtaining the difference between the first principal stress and the third principal stress. The hazard level is determined according to the ratio of the equivalent stress to the yield strength of the forging material. When the ratio is greater than or equal to 0.45, it is the first hazard area; when the ratio is between 0.35 and 0.45, it is the second hazard area; and when the ratio is less than 0.35, it is the third hazard area. The first hazard area is subject to mandatory stress compensation, the second hazard area is compensated as needed, and the third hazard area is exempt from compensation.

[0010] Furthermore, in the self-compensation design method for residual stress of heavy forging dies of the present invention, the elastic groove compensation unit is applicable to local stress concentration areas, and an elastic groove with a bottom arc transition is set at the corresponding position of the die cavity; the asymmetric stiffness cavity wall compensation unit is applicable to areas with uneven stress distribution, and an asymmetric stiffness distribution is formed by the difference in cavity wall thickness in different areas; the pre-deformed surface compensation unit is applicable to areas of overall bending or torsional deformation, and the die cavity surface is designed as a pre-deformed surface opposite to the deformation direction of the forging.

[0011] Furthermore, in the self-compensation design method for residual stress of heavy forging dies of the present invention, the coupled simulation simultaneously considers the elastic deformation of the die and the elastoplastic deformation of the forging. The compensation effect is quantitatively evaluated by stress deviation and deformation deviation. When both stress deviation and deformation deviation are less than the preset threshold, the compensation effect is determined to meet the requirements.

[0012] Furthermore, in the self-compensation design method for residual stress in heavy forging dies of the present invention, the groove depth, groove width, and bottom fillet radius of the elastic groove compensation unit are determined by the following formula: ; ; ; in, Indicates the depth of the groove. This indicates the required compressive stress compensation. Indicates the thickness of the mold cavity wall. Indicates the Poisson's ratio of the mold material. Indicates the elastic modulus of the mold material. This represents the stress concentration correction factor. Indicates the width of the groove. Indicates the radius of the fillet at the bottom of the groove. This represents the first optimization coefficient. This represents the second optimization coefficient.

[0013] Furthermore, in the self-compensation design method for residual stress of heavy forging dies of the present invention, the local stiffness of the die cavity in the asymmetric stiffness cavity wall compensation unit is expressed as: ;in, Indicates the elastic modulus of the mold material. Indicates the thickness of the cavity wall. Indicates the Poisson's ratio of the mold material. Indicates the span of the cavity wall support; The cavity wall thickness in different regions is expressed as follows: ;in, Indicates the cavity wall thickness of the reference region. Indicates the first The area requires compensation for compressive stress. Indicates the required compressive stress compensation in the reference area; The maximum pre-deformation amount in the pre-deformed surface compensation unit is expressed as: ;in, Indicates the deformation compensation coefficient. This indicates the predicted maximum deformation of the forging. This indicates the preset correction function. Indicates the coefficient of thermal expansion of the forging material. This represents the average temperature difference during the cooling process of the forging. This indicates the total length of the forging.

[0014] Furthermore, in the self-compensation design method for residual stress of heavy forging dies of the present invention, the multi-objective optimization function is expressed as: ; in, Represents the objective function value. This represents the first preset weighting coefficient. This represents the maximum residual stress in the forging obtained from the simulation. Indicates the maximum residual stress of the target. This represents the second preset weighting coefficient. This represents the maximum deformation of the forging obtained from the simulation. This indicates the maximum deformation of the target. This represents the third preset weighting coefficient. Indicates the maximum working stress of the mold. This indicates the yield strength of the mold material.

[0015] Secondly, the present invention provides a self-compensating system for residual stress in heavy forging dies, comprising: The simulation prediction module is used to perform thermo-mechanical coupling numerical simulation of the entire forging process of the target forging under the initial mold conditions, and to extract the residual stress distribution data after the forging is cooled to room temperature; The stress identification module is used to identify stress concentration areas on the forging based on the residual stress distribution data, assess the hazard level of each stress concentration area and classify it into levels, and obtain the required compressive stress compensation. The compensation design module is used to select one or more of the following structural design units—elastic groove compensation unit, asymmetric stiffness cavity wall compensation unit, and pre-deformed curved surface compensation unit—based on the characteristics of the stress concentration area, and to establish a quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress. The coupling optimization module is used to build an improved mold model containing the selected compensation unit and to perform coupled simulation verification of the forging and the mold. When the compensation effect does not meet the preset requirements, the structural parameters of the compensation unit are iteratively adjusted through a multi-objective optimization function until the convergence criterion is met.

[0016] Compared with the prior art, the beneficial effects of the heavy forging die residual stress self-compensation system of the present invention are the same as those of the heavy forging die residual stress self-compensation design method described in the above technical solution, and will not be repeated here. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a flowchart illustrating the self-compensation design method for residual stress in heavy-duty forging dies according to the present invention. Figure 2 This is a schematic diagram of the initial model of the forging, upper die, and lower die in this invention; Figure 3 This is a schematic diagram of the simulation results of forgings under conventional mold conditions in this invention; Figure 4 This is a schematic diagram of the logic for identifying stress concentration areas and determining hazard levels in this invention.

[0018] Figure label: 1. Upper die; 2. Lower die; 3. Forging blank; A. High-risk area; B. Medium-risk area. Detailed Implementation

[0019] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0020] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0022] Currently, industry-wide technologies for controlling residual stress in forgings primarily focus on post-forming treatments. These often employ post-treatment processes such as quenching followed by cold pressing, cold stretching, vibration aging, cryogenic treatment, and localized tempering to reduce existing residual stress, or surface strengthening processes like shot peening and rolling to improve surface stress conditions. However, these post-treatment methods all have inherent drawbacks. Firstly, all post-treatment processes can only intervene after residual stress has already formed, failing to prevent stress formation at its source, and their effectiveness in reducing deep residual stress within the forging is extremely limited. Secondly, post-treatment processes typically increase processing time by more than 30% and manufacturing costs by more than 25%, significantly reducing production efficiency and economic benefits. Furthermore, mechanical straightening methods like cold pressing can easily introduce new stress concentrations or surface damage into the forging, potentially leading to a decrease in the fatigue resistance of the parts. More importantly, existing mold design methods only focus on the geometric forming accuracy of the forging and the service life of the mold itself, completely ignoring the influence of the mold cavity structure on the distribution of residual stress inside the forging. When the forging is formed in the mold cavity, the distribution of residual stress is uncontrollable, which means that subsequent expensive post-processing processes must be used to remedy the situation.

[0023] To address the above technical problems, this invention provides a self-compensating design method for residual stress in heavy-duty forging dies, comprising: Thermo-mechanical coupled numerical simulation was performed on the entire forging process of the target forging under initial mold conditions, and the residual stress distribution data after the forging cooled to room temperature was extracted. Based on the residual stress distribution data, stress concentration areas on the forging are identified, the hazard level of each stress concentration area is assessed and classified, and the required compressive stress compensation is obtained. Based on the characteristics of the stress concentration area, one or more of the following can be selected for structural design: elastic groove compensation unit, asymmetric stiffness cavity wall compensation unit, and pre-deformed curved surface compensation unit. A quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress is established. An improved mold model containing the selected compensation unit is established, and coupled simulation verification of the forging and the mold is performed. When the compensation effect does not meet the preset requirements, the structural parameters of the compensation unit are iteratively adjusted through a multi-objective optimization function until the convergence criterion is met. The final mold design result is output based on the optimized structural parameters.

[0024] With the above technical solution, the self-compensation design method for residual stress in heavy forging dies of the present invention, through thermo-mechanical coupling numerical simulation of the entire forging process of the target forging under initial die conditions, allows the magnitude and distribution of residual stress inside the forging to be accurately predicted during the die design stage, providing a quantitative basis for subsequent compensation design. Based on this, stress concentration areas are accurately identified and hazard assessments and classifications are performed according to the residual stress distribution data, transforming the compensation design from experience-driven to data-driven, effectively avoiding insufficient or excessive compensation. Then, based on the characteristics of the stress concentration areas, one or more of the following structural design units are selected: elastic groove compensation unit, asymmetric stiffness cavity wall compensation unit, or pre-deformed curved surface compensation unit. A quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress is established, transforming the die cavity from a rigid structure to a structure with active compensation capability, achieving precise matching between compensation stress and structural parameters. Subsequently, a coupled simulation verification is performed by establishing an improved die model containing compensation units, and a multi-objective optimization function is used to iteratively adjust the structural parameters until the convergence criterion is met, effectively ensuring the compensation effect while also considering the die's service life. The above-mentioned technical solution of the invention solves the technical problems of existing technologies being unable to actively control residual stress during forging, lacking quantitative basis for compensation structure design, and lacking verification and optimization mechanisms after compensation.

[0025] To better understand the present invention, the following specific embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0026] Example 1 This embodiment provides a self-compensating design method for residual stress in heavy forging dies, including: Step 1: Perform thermo-mechanical coupling numerical simulation on the entire forging process of the target forging under the initial mold conditions, and extract the residual stress distribution data after the forging is cooled to room temperature; Step 2: Based on the residual stress distribution data, identify the stress concentration areas on the forging, assess the hazard level of each stress concentration area and classify the level, and obtain the required compressive stress compensation. Step 3: Select one or more of the following structural design units based on the characteristics of the stress concentration area: elastic groove compensation unit, asymmetric stiffness cavity wall compensation unit, and pre-deformed curved surface compensation unit; and establish a quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress. Step 4: Establish an improved mold model containing the selected compensation unit, and perform coupled simulation verification of the forging and the mold. If the compensation effect does not meet the preset requirements, adjust the structural parameters of the compensation unit iteratively through a multi-objective optimization function until the convergence criterion is met. Step 5: Output the final mold design results based on the optimized structural parameters.

[0027] Example 2 Firstly, this embodiment provides a self-compensating design method for residual stress in heavy forging dies, including: Step 1: Perform thermo-mechanical coupling numerical simulation on the entire forging process of the target forging under the initial mold conditions, and extract the residual stress distribution data after the forging is cooled to room temperature; In the thermo-mechanical coupling numerical simulation, the constitutive model of the forging material is described by a constitutive model that simultaneously considers the temperature softening effect, strain hardening effect and strain rate strengthening effect. The comprehensive heat transfer coefficient is composed of the superposition of the convective heat transfer coefficient, the radiative heat transfer coefficient and the contact heat transfer coefficient. The residual stress is obtained by the superposition of elastic stress, plastic stress and phase transformation stress.

[0028] Step 2: Based on the residual stress distribution data, identify the stress concentration areas on the forging, assess the hazard level of each stress concentration area and classify the level, and obtain the required compressive stress compensation.

[0029] Furthermore, identifying the stress concentration region on the forging includes: using the stress gradient method to identify local areas with drastic stress changes, using the stress concentration coefficient method to quantify the degree of stress concentration, and determining that the region is a stress concentration region when the stress gradient exceeds a preset stress gradient threshold and the stress concentration coefficient exceeds a preset stress concentration coefficient threshold.

[0030] The hazard assessment is based on the third strength theory. The equivalent stress is obtained by measuring the difference between the first principal stress and the third principal stress. The hazard level is determined by the ratio of the equivalent stress to the yield strength of the forging material. When the ratio is greater than or equal to 0.45, it is the first hazard area (i.e., the high-hazard area); when the ratio is between 0.35 and 0.45, it is the second hazard area (i.e., the medium-hazard area); and when the ratio is less than 0.35, it is the third hazard area (i.e., the low-hazard area). The first hazard area is subject to mandatory stress compensation, the second hazard area is compensated as needed, and the third hazard area is exempt from compensation.

[0031] Step 3: Select one or more of the following structural design units based on the characteristics of the stress concentration area: elastic groove compensation unit, asymmetric stiffness cavity wall compensation unit, and pre-deformed curved surface compensation unit; and establish a quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress.

[0032] Furthermore, the elastic groove compensation unit is suitable for areas of localized stress concentration, with an elastic groove featuring a bottom arc transition set at the corresponding position of the mold cavity; the asymmetric stiffness cavity wall compensation unit is suitable for areas with uneven stress distribution, forming an asymmetric stiffness distribution through differences in cavity wall thickness in different areas; the pre-deformed surface compensation unit is suitable for areas of overall bending or torsional deformation, designing the mold cavity surface as a pre-deformed surface opposite to the deformation direction of the forging. The coupled simulation simultaneously considers the elastic deformation of the mold and the elastoplastic deformation of the forging.

[0033] Furthermore, the groove depth, groove width, and bottom fillet radius of the elastic groove compensation unit are determined by the following formulas: ; ; ; in, Indicates the depth of the groove. This indicates the required compressive stress compensation. Indicates the thickness of the mold cavity wall. Indicates the Poisson's ratio of the mold material. Indicates the elastic modulus of the mold material. This represents the stress concentration correction factor. Indicates the width of the groove. Indicates the radius of the fillet at the bottom of the groove. This represents the first optimization coefficient. This represents the second optimization coefficient.

[0034] Furthermore, the local stiffness of the mold cavity in the asymmetric stiffness cavity wall compensation unit is expressed as: ;in, Indicates the elastic modulus of the mold material. Indicates the thickness of the cavity wall. Indicates the Poisson's ratio of the mold material. Indicates the span of the cavity wall support; The cavity wall thickness in different regions is expressed as follows: ;in, Indicates the cavity wall thickness of the reference region. Indicates the first The area requires compensation for compressive stress. Indicates the required compressive stress compensation in the reference area; The maximum pre-deformation amount in the pre-deformed surface compensation unit is expressed as: ;in, Indicates the deformation compensation coefficient. This indicates the predicted maximum deformation of the forging. This indicates the preset correction function. Indicates the coefficient of thermal expansion of the forging material. This represents the average temperature difference during the cooling process of the forging. This indicates the total length of the forging.

[0035] Step 4: Establish an improved mold model containing the selected compensation unit, and perform coupled simulation verification of the forging and the mold. If the compensation effect does not meet the preset requirements, adjust the structural parameters of the compensation unit iteratively through a multi-objective optimization function until the convergence criterion is met. The compensation effect is quantitatively evaluated by stress deviation and deformation deviation. When both stress deviation and deformation deviation are less than the preset threshold, the compensation effect is determined to meet the requirements. The multi-objective optimization function is expressed as: ; in, Represents the objective function value. This represents the first preset weighting coefficient. This represents the maximum residual stress in the forging obtained from the simulation. Indicates the maximum residual stress of the target. This represents the second preset weighting coefficient. This represents the maximum deformation of the forging obtained from the simulation. This indicates the maximum deformation of the target. This represents the third preset weighting coefficient. Indicates the maximum working stress of the mold. This indicates the yield strength of the mold material.

[0036] Step 5: Output the final mold design results based on the optimized structural parameters.

[0037] Secondly, this embodiment provides a self-compensation system for residual stress in heavy forging dies, comprising: The simulation prediction module is used to perform thermo-mechanical coupling numerical simulation of the entire forging process of the target forging under the initial mold conditions, and to extract the residual stress distribution data after the forging is cooled to room temperature; The stress identification module is used to identify stress concentration areas on the forging based on the residual stress distribution data, assess the hazard level of each stress concentration area and classify it into levels, and obtain the required compressive stress compensation. The compensation design module is used to select one or more of the following structural design units—elastic groove compensation unit, asymmetric stiffness cavity wall compensation unit, and pre-deformed curved surface compensation unit—based on the characteristics of the stress concentration area, and to establish a quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress. The coupling optimization module is used to build an improved mold model containing the selected compensation unit and to perform coupled simulation verification of the forging and the mold. When the compensation effect does not meet the preset requirements, the structural parameters of the compensation unit are iteratively adjusted through a multi-objective optimization function until the convergence criterion is met.

[0038] Example 3 Please see Figure 1 This embodiment further illustrates the self-compensation design method for residual stress in heavy forging dies of the present invention based on Embodiment 2 above. Specifically: S100 is used for numerical simulation of the forging process and stress distribution prediction of forging parts; among which: S101. Establish a three-dimensional geometric model of the target forging and the initial mold, import it into the finite element simulation software, and use the Johnson-Cook equation, which considers temperature softening, strain hardening and strain rate strengthening, as the constitutive model of the forging material, expressed as: ; ; ; in, Indicates flow stress, This represents the yield strength at the reference temperature and reference strain rate. Indicates hardening modulus, Represents equivalent plastic strain. Indicates the hardening index. Represents the strain rate sensitivity coefficient. To normalize the strain rate, Indicates the temperature sensitivity coefficient. Indicates the normalized temperature. Indicates strain rate. Indicates the reference strain rate. Indicates the instantaneous temperature of the material. Indicates room temperature. Indicates the melting point of the material.

[0039] S102 sets the multi-physics coupling boundary conditions for the forging process. The comprehensive heat transfer coefficient includes three parts: convective heat transfer, radiative heat transfer, and contact heat transfer, which correspond to the heat exchange between the forging and air, the forging and the environment, and the forging and the die, respectively, and are expressed as follows: ; in, Indicates the overall heat transfer coefficient. The convective heat transfer coefficient is determined based on the air velocity. This represents the radiative heat transfer coefficient, calculated based on the material's emissivity and the Stefan-Boltzmann law. This represents the contact heat transfer coefficient, which is determined based on the contact pressure. The friction boundary adopts the Coulomb friction model, and the friction coefficient is selected based on the mold lubrication conditions.

[0040] S103, a thermo-mechanical coupling simulation of the conventional forging process is performed. Using a preset simulation step size, the transient heat conduction equation is solved. This equation describes the temperature variation with time and space during the forging process, expressed as: ;

[0041] in, Indicates the density of the material. Indicates specific heat capacity. Indicates the instantaneous temperature of the material. Indicates time, Indicates the thermal conductivity coefficient. This represents the intensity of the internal heat source, which is derived from the work done by plastic deformation. During the simulation, a preset convergence criterion is used to control the calculation accuracy.

[0042] S104, extract the residual stress distribution data of the forging at the final forging moment and during the cooling to room temperature process. The residual stress consists of three parts: elastic stress, plastic stress, and phase transformation stress. Among them, the phase transformation stress is generated by the volume change caused by the phase transformation of the material, and is expressed as: ; in, Indicates residual stress. Represents elastic stress. Indicates plastic stress, The phase transformation stress is represented by the following formula: , Indicates the elastic modulus; This represents the rate of change of phase transition volume; This represents Poisson's ratio. The maximum residual stress, average residual stress, and residual stress distribution non-uniformity coefficient of the forging are statistically determined, and residual stress distribution contour maps and stress curves along key sections are plotted.

[0043] S200, stress concentration area identification and feature analysis are performed; among which: S201 uses a dual approach—the stress gradient method and the stress concentration factor method—to identify stress concentration areas on forgings. The stress gradient method identifies localized areas of drastic stress changes, while the stress concentration factor method quantifies the degree of stress concentration. (Stress gradient...) Calculation formula and stress concentration factor The calculation formula is as follows: ; ; in, Indicates stress, Indicates the local maximum stress. This represents the nominal stress in the corresponding region, when ( (Preset stress gradient threshold) and stress concentration factor ( When the preset stress concentration factor threshold is used, the region is determined to be a stress concentration region.

[0044] S202, based on the third strength theory, assesses the hazard level of each stress concentration region, classifying them into three levels: high hazard, medium hazard, and low hazard; the equivalent stress is expressed as: ;in, Indicates the first principal stress. This represents the third principal stress. The hazard level is determined based on the ratio of equivalent stress to the yield strength of the forging material. High-hazard areas require stress compensation, medium-hazard areas may require compensation depending on the actual situation, and low-hazard areas do not require compensation.

[0045] S203 involves a characteristic analysis of each high-risk stress concentration region to determine its geometry, area, maximum stress value, and principal stress direction. The basic compensation coefficient for each region is calculated and corrected based on material properties, forging temperature, and deformation rate to ensure more accurate stress compensation, expressed as follows: ; in, This represents the comprehensive compensation coefficient. This indicates the preset basic compensation coefficient. This represents the material correction factor, which is determined based on the yield strength of the forging material. This represents the temperature correction factor, which is determined based on the forging temperature. This represents the strain rate correction factor, which is determined based on the forging deformation rate.

[0046] The required compressive stress compensation is: ; This represents the maximum stress value in the region.

[0047] S300 involves selecting the type of stress compensation unit and designing the structure. Based on the characteristics of the stress concentration area, one or more combinations of the following three standardized stress compensation units are selected to establish a quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress. Specifically: S301, in areas of localized stress concentration such as journals, tooth roots, and fillet transitions, elastic grooves are designed at the corresponding stress concentration points in the die cavity of the forging. The bottom of the grooves uses a rounded transition to prevent stress concentration from occurring within the grooves themselves. When multiple consecutive stress concentration points exist, multiple grooves are arranged at preset intervals to ensure that the compensation effects of each groove do not interfere with each other. The groove depth is calculated based on the required compressive stress compensation. This formula is derived from the thin-plate bending theory of elasticity and is expressed as: ; To ensure sufficient deformation space for the groove, the formula for calculating the groove width is: ; To minimize stress concentration while ensuring machining feasibility, the optimization formula for the fillet radius at the bottom of the groove is: Among them, among them, Indicates the depth of the groove. This indicates the required compressive stress compensation. Indicates the thickness of the mold cavity wall. Indicates the Poisson's ratio of the mold material. Indicates the elastic modulus of the mold material. This represents the stress concentration correction factor, taking into account the stress concentration effect at the bottom of the groove. Indicates the width of the groove. Indicates the radius of the fillet at the bottom of the groove. This represents the first optimization coefficient. This represents the second optimization coefficient.

[0048] S302: In areas with uneven stress distribution, such as guide surfaces and flanges, cavity walls of different thicknesses can be designed in different areas of the mold cavity to create an asymmetric stiffness distribution. Areas with high stiffness experience less deformation, while areas with low stiffness experience greater deformation, thus generating differentiated compensating stresses.

[0049] The local stiffness of a mold cavity is defined as the force required per unit deformation: ; The cavity wall thickness is adjusted according to the magnitude of the required compressive stress compensation. The formula for calculating the cavity wall thickness in different regions is as follows: ; To further ensure a balance between the overall strength and compensation effect of the mold, the stiffness ratio optimization formula is as follows: ; in, Indicates the elastic modulus of the mold material. Indicates the thickness of the cavity wall. Indicates the Poisson's ratio of the mold material. Indicates the span of the cavity wall support. Indicates the cavity wall thickness of the reference region. Indicates the first The area requires compensation for compressive stress. This indicates the compressive stress that needs to be compensated in the reference area. Indicates the maximum local stiffness. Indicates the minimum local stiffness. Indicates the maximum stress. This indicates the minimum stress.

[0050] S303, when dealing with areas of overall bending or torsional deformation in long shaft or plate-type parts, the mold cavity surface is designed as a pre-deformation surface opposite to the forging deformation direction, fitted with a smooth, continuous curve to avoid sharp edges and abrupt changes. The distribution of the pre-deformation amount along the length of the forging uses a preset function, conforming to the deformation patterns of most forgings, and is expressed as: ; in, This represents the distribution function of the pre-deformation amount along the length of the forging. Indicates the maximum pre-deformation amount. Represents the preset distribution function. Indicates the distance from the end face of the forging. This indicates the total length of the forging.

[0051] Taking both forging deformation and cooling deformation into account, the formula for calculating the maximum pre-deformation is as follows: ; in, Indicates the maximum pre-deformation amount. Indicates the deformation compensation coefficient. This indicates the predicted maximum deformation of the forging. Indicates the coefficient of thermal expansion of the forging material. This represents the average temperature difference during the cooling process of the forging. This indicates the preset correction function.

[0052] To ensure the continuity of the first and second derivatives of the surface at the segmentation points, the smooth fitting formula for the pre-deformed surface is as follows: ; in, The smooth fitting function represents the pre-deformed surface. Indicates the first The first coefficient of the fitted curve, Indicates the first The second coefficient of the fitted curve, Indicates the first The third coefficient of the fitted curve. Indicates the first The fourth coefficient of the fitted curve. Indicates the first The coordinates of the starting point of the fitted curve segment. Indicates the first The coordinates of the endpoint of the fitted curve segment are determined by using preset boundary conditions.

[0053] S400 was used for mold-forging coupling simulation verification and parameter optimization; specifically: S401. Establish a three-dimensional model of the mold containing stress compensation units, and perform thermo-mechanical-structural coupling simulation of the forging and the mold. The simulation considers both the elastic deformation of the mold and the elastoplastic deformation of the forging.

[0054] S402, extract the residual stress distribution and deformation data of the forging obtained from the simulation, calculate the stress deviation and deformation deviation, and evaluate the compensation effect, as shown below: ; ; in, Indicates stress deviation, This represents the maximum residual stress in the forging obtained from the simulation. Indicates the maximum residual stress of the target. Indicates deformation deviation. This represents the maximum deformation of the forging obtained from the simulation. This represents the target maximum deformation. When both stress deviation and deformation deviation are less than the preset threshold, the compensation effect is considered to meet the design requirements.

[0055] S403 establishes a multi-objective optimization function that comprehensively considers three objectives: residual stress, deformation, and mold life. The importance of each objective is balanced using weighting coefficients, and is expressed as follows: ; in, Represents the objective function value. This represents the first preset weighting coefficient. This represents the maximum residual stress in the forging obtained from the simulation. Indicates the maximum residual stress of the target. This represents the second preset weighting coefficient. This represents the maximum deformation of the forging obtained from the simulation. This indicates the maximum deformation of the target. This represents the third preset weighting coefficient. Indicates the maximum working stress of the mold. This indicates the yield strength of the mold material.

[0056] S404 employs an optimization algorithm to iteratively optimize the structural parameters of the stress compensation element. A preset optimization step size is used, and the simulation and optimization process is repeated until the convergence criterion is met. The iterative convergence criterion is: ;in, Indicates the first The objective function value of the next iteration. This indicates the preset convergence accuracy.

[0057] S500, final mold design output; specifically: S501 generates mold engineering drawings based on the optimized parameters. The final mold design scheme includes an elastic groove compensation unit, a stiffness compensation structure, and a reverse pre-deformation surface.

[0058] S502 establishes the mold manufacturing process specifications, clarifying the machining accuracy requirements for stress compensation units, including surface roughness and geometric tolerances. A tolerance allocation formula is used to determine the machining tolerances of each compensation unit; areas with higher compensation stress require higher machining accuracy, expressed as: ;in, Indicates the first Machining tolerances of each compensation unit, Indicates the datum tolerance. This indicates the compensating stress in the region. This represents the maximum compressive stress that is compensated.

[0059] S503 establishes a mold use and maintenance guide, specifying the mold's preheating temperature range, maximum permissible forging pressure, and periodic inspection cycle. It also clarifies the mold's lubrication methods, cooling requirements, and wear repair standards to ensure the mold maintains stable compensation effects throughout its service life. The mold preheating temperature calculation formula, ensuring no thermal cracks occur during operation, is expressed as: ;in, Indicates the mold preheating temperature. Indicates the reference preheating temperature. Indicates the preset temperature coefficient. This indicates the yield strength of the mold material.

[0060] Example 4 Please see Figures 1 to 4 This embodiment further illustrates the self-compensation design method for residual stress in heavy forging dies of the present invention, based on Embodiment 3 above. Specifically:

[0061] This embodiment uses a forging die for a heavy forging of a machine tool structural component as the design object for illustration. This forging is a typical machine tool structural component with a central groove, two side bosses, and a rounded transition area. During the forging process, it is prone to generating significant equivalent and residual stresses in the central transition area, at the root of the bosses, and on both sides of the groove; including: S100, performing numerical simulation and stress distribution prediction of the forging process; specifically: S101. Establish the three-dimensional geometric models of the target forging and the initial die. Based on the external dimensions of the target machine tool structural components, establish models of the forging blank, upper die, lower die, and constraint boundaries. The initial forging blank is set as a rectangular slab structure, and the die cavities on both sides are equipped with forming surfaces that match the forging bosses and grooves. Import the models into Abaqus for thermo-mechanical coupling simulation. The forging material is selected as 42CrMo steel, and the die material is selected as H13 hot work die steel. The constitutive model of the forging material adopts the Johnson-Cook equation, which considers temperature softening, strain hardening, and strain rate strengthening. ; ; ; In this embodiment, the parameters of 42CrMo steel are set as follows: , , , , Reference strain rate room temperature Material melting point .

[0062] S102 sets the multi-physics coupling boundary conditions for the forging process. The initial heating temperature of the forging is set to 1150℃, the initial preheating temperature of the upper and lower dies is set to 250℃, and the ambient temperature is set to 20℃. The upper die moves vertically downwards at a pressing speed of 80mm / s, with a total pressing time of 1s. Convective heat transfer is implemented between the forging and the air, radiative heat transfer between the forging and the environment, and contact heat transfer in the contact area between the forging and the die. The convective heat transfer coefficient is... Radiative heat transfer coefficient Contact heat transfer coefficient Substitute into the formula for the comprehensive heat transfer coefficient to calculate; The friction boundary adopts the Coulomb friction model, the mold lubrication condition is graphite lubrication, and the friction coefficient is... .

[0063] S103 is used for thermo-mechanical coupling simulation of the forging process under conventional mold conditions. The forging is meshed using C3D8R three-dimensional eight-node reduced integral elements, with local mesh refinement focusing on the central groove, the roots of the two side bosses, and the rounded transition area. The minimum mesh size is set to 2mm. An automatic stabilization time step is used for the simulation to solve for the temperature field, stress field, and plastic strain field during the forging process. Figure 2 The figure shows the initial state before forging. At this time, the forging blank 3 has not yet been pressed down by the mold (upper mold 1 and lower mold 2), the equivalent stress is close to 0MPa, and the forging is in an undeformed state. Figure 3 The image shows the forging state, which has a high-risk zone A and a medium-risk zone B. Under the action of the upper and lower dies, the forging completes the formation of the central groove and the two side bosses. The equivalent stress increases significantly at the bottom of the central groove, the root of the bosses and the transition fillet, with the maximum equivalent stress being approximately 600 MPa.

[0064] S104, extracting residual stress distribution data at the final forging time and after cooling to room temperature. Elastic modulus of 42CrMo steel. Poisson's ratio Phase change volume change rate Substitute into the phase transformation stress calculation formula: ; Simulation results show that, under the initial mold conditions without stress compensation units, the maximum residual stress of the forging after cooling to room temperature is 286 MPa, the average residual stress is 172 MPa, and the residual stress distribution non-uniformity coefficient is 0.38. The bottom of the central groove and the roots of the two side bosses are the main areas of residual stress concentration, requiring stress compensation design.

[0065] S200, perform stress concentration area identification and feature analysis; specifically:

[0066] S201 identifies stress concentration regions based on the stress gradient method and stress concentration factor method. Residual stress curves are extracted along the middle section, the root section of the left boss, and the root section of the right boss of the forging, respectively, with a preset stress gradient threshold. Stress concentration factor threshold The simulation data is as follows: ① Bottom region of the central groove: local maximum stress nominal stress Substitute into the stress concentration factor formula to calculate: Stress gradient in this region ,satisfy and It was determined to be a stress concentration area.

[0067] ②Local maximum stress in the root region of the left boss nominal stress Substitute into the stress concentration factor formula to calculate: Stress gradient in this region ,satisfy and It was determined to be a stress concentration area.

[0068] ③ The root region of the right-side boss: local maximum stress nominal stress Substitute into the stress concentration factor formula to calculate: Stress gradient in this region ,satisfy and It was determined to be a stress concentration area.

[0069] S202, risk assessment based on the third strength theory. Yield strength of 42CrMo steel forgings at room temperature. .

[0070] ① First principal stress in the bottom region of the central groove Third principal stress Substitute into the equivalent stress calculation formula: ; ; ② First principal stress in the root region of the left boss Third principal stress Substitute into the equivalent stress calculation formula: ; ; ③ First principal stress in the root region of the right-side boss Third principal stress Substitute into the equivalent stress calculation formula: ; ; The hazard level criterion is set as follows: It was a high-risk area at the time. It was then a medium-risk area. The area at the bottom of the central groove is considered a low-risk area. Therefore, the area at the bottom of the central groove is a high-risk area, and the areas at the roots of the left and right bosses are medium-risk areas. Stress compensation must be performed on the area at the bottom of the central groove, and auxiliary compensation should be performed simultaneously on the areas at the roots of the left and right bosses based on the effectiveness of the initial compensation.

[0071] S203, calculate the stress compensation coefficient and the required compressive stress compensation. For the bottom region of the central groove, set the basic compensation coefficient. Material correction factor Temperature correction factor Strain rate correction factor Maximum stress Substitute the comprehensive compensation coefficient and the compensation compressive stress formula to calculate: ; For the dangerous areas at the base of the left and right protrusions, an auxiliary compensation coefficient is used. Substitute into the compressive stress compensation formula to calculate: ; .

[0072] S300 involves selecting the type of stress compensation unit and designing the structure; specifically:

[0073] S301, an elastic groove compensation unit is designed for the local stress concentration area at the bottom of the central groove. Since the bottom of the central groove is a local stress concentration area with a high stress peak, an elastic groove is designed at the corresponding position of the mold cavity. This allows the mold to undergo localized controllable elastic deformation during forging loading, thereby applying compensating compressive stress to the corresponding area of ​​the forging in the opposite direction to the residual stress.

[0074] In this embodiment, the mold cavity wall thickness H13 mold steel elastic modulus Poisson's ratio Stress concentration correction factor Compensation for compressive stress required in the central region Substitute into the groove depth formula to calculate: Therefore, the depth is set on the inner surface of the mold cavity corresponding to the bottom of the central groove. The elastic groove.

[0075] To ensure the groove has sufficient deformation space, substitute the values ​​into the groove width formula for calculation: ;

[0076] Considering machining allowance and fillet transition, this embodiment uses the groove width. .

[0077] Substitute the fillet radius at the bottom of the groove into the formula to calculate: ; Therefore, the radius of the bottom fillet of the central elastic groove is taken as... This ensures that there is no stress concentration at the bottom of the groove.

[0078] S302, a rigid cavity wall compensation unit is designed for the root areas of the left and right bosses. These areas are considered medium-risk zones with a banded stress distribution; therefore, a rigid cavity wall is used for auxiliary compensation. The central area of ​​the mold is used as the reference compensation zone, with a reference wall thickness... Reference compressive stress The compressive stress to be compensated at the root of the left-side boss. The compressive stress to be compensated at the root of the right-side boss Substitute into the cavity wall thickness calculation formula: ; ;

[0079] Therefore, in this embodiment, the cavity wall thickness corresponding to the root of the left boss is designed to be 72mm, and the cavity wall thickness corresponding to the root of the right boss is designed to be 71mm. The difference in cavity wall thickness on both sides creates a stiffness distribution, allowing the mold to apply differentiated compressive stress to the root areas of the two bosses during the forging process.

[0080] S303 is a pre-deformation surface compensation unit designed to address the overall bending deformation trend. Based on conventional mold simulation results, the forging exhibits a slight upward warping trend along its length after final forging, predicting the maximum bending deformation. To suppress overall bending deformation, the die cavity surface is designed as a pre-deformed curved surface opposite to the deformation direction of the forging. Deformation compensation coefficient. Correction function Substitute into the formula for calculating the maximum pre-deformation: ; Take the maximum pre-deformation amount The length of the forging follows a parabolic distribution. ,when Substitute the values ​​into the calculation: ;

[0081] The maximum reverse pre-deformation amount is set at the middle of the forging, which is 0.39 mm, and gradually transitions to 0 mm at both ends. To avoid abrupt changes in the pre-deformed surface at the segmentation points, a cubic spline function is used to smoothly fit the cavity surface, ensuring the continuity of the first and second derivatives of the surface.

[0082] S400 was used for mold-forging coupling simulation verification and parameter optimization; specifically: S401. Establish a 3D model of the mold including stress compensation units. Based on the above calculation results, add a central elastic groove compensation unit, left / right stiffness cavity wall compensation units, and an overall pre-deformation surface compensation unit to the initial mold model to form an improved mold model. Re-simulate the improved mold and the forging model, considering the mold's elastic deformation, the forging's elastoplastic deformation, contact friction, and contact heat transfer during the simulation.

[0083] S402, extracts residual stress and deformation data of forgings under compensated die conditions. Sets the target maximum residual stress. Target maximum deformation After the first compensation simulation, the maximum residual stress of the forging after cooling to room temperature was... Maximum deformation m. Substitute into the formulas for stress deviation and deformation deviation to calculate: ; ;

[0084] The stress deviation threshold and deformation deviation threshold were set to 10%. In the first compensation simulation, the stress deviation met the requirements, but the deformation deviation exceeded the threshold. Therefore, it is necessary to further optimize the pre-deformed surface parameters.

[0085] S403, Establish a multi-objective optimization function. Taking into account residual stress, deformation, and mold life, a weighting coefficient for residual stress is set. Deformation weighting coefficient Mold life weighting coefficient The yield strength of H13 mold steel after quenching and tempering is taken. The maximum working stress of the mold in the first compensation simulation Substitute into the multi-objective optimization function to calculate: ; S404, iterative optimization of compensation unit parameters. Based on the first simulation results, the maximum pre-deformation was adjusted from 0.39mm to 0.43mm, while the depth of the central elastic groove was slightly adjusted from 2.8mm to 3.0mm. The wall thicknesses of the stiffness cavities on the left and right sides were maintained at 72mm and 71mm, respectively. After the second compensation simulation, the maximum residual stress of the forging was extracted. Maximum deformation Maximum working stress of the mold Substitute into the deviation formula to calculate: ; ; All values ​​are less than the preset threshold, thus meeting the compensation effect requirements.

[0086] The second objective function value is: ; Set convergence precision Calculate the change in the objective function between two consecutive intervals: ; A third fine-tuning was performed, maintaining the depth of the central elastic groove at 3.0 mm and adjusting the maximum pre-deformation to 0.42 mm. After the third compensation simulation, the maximum residual stress of the forging was... Maximum deformation Maximum working stress of the mold Substitute into the objective function to calculate: ; ; Since the iterative convergence criterion is satisfied, the parameters for the third optimization are determined to be the optimal design scheme.

[0087] By comparison, the maximum residual stress of forgings under conventional die conditions is 286 MPa. After using the die compensation method of this invention, the maximum residual stress is reduced to 176 MPa. Substituting into the formula for the reduction rate, the following calculation is performed: ; Under conventional die conditions, the maximum bending deformation of the forging is 0.42 mm. After using the compensation die of this invention, the maximum bending deformation is reduced to 0.2 mm. Substituting into the reduction formula, the following calculation is performed: ; This demonstrates that the present invention can effectively reduce residual stress in forgings and improve post-forging deformation.

[0088] S500, final mold design output; specifically: S501 generates mold engineering drawings based on the optimized parameters. The final mold design includes: setting an elastic groove compensation unit at the bottom of the central groove corresponding to the cavity area, with a groove depth of... Groove width Bottom corner radius A local wall thickness is set in the cavity area corresponding to the root of the left boss. Stiffness compensation structure; local wall thickness is set in the cavity area corresponding to the root of the right boss. A stiffness compensation structure; the maximum pre-deformation amount is set along the overall length of the mold cavity. The reverse pre-deformed surface.

[0089] S502, determine the machining tolerance of the compensation unit. Reference tolerance. Maximum compressive stress The compressive stress compensation in the central elastic groove region is 164 MPa, the compressive stress compensation in the root region of the left boss is 117 MPa, and the compressive stress compensation in the root region of the right boss is 114 MPa. Substituting these values ​​into the tolerance distribution formula, the following calculations are performed: ; ; ; Therefore, the engineering drawings indicate that the machining tolerance for the depth of the central elastic groove is ±0.03mm, the machining tolerance for the wall thickness of the rigid cavities on the left and right sides is ±0.02mm, and the tolerance for the profile of the pre-deformed curved surface is 0.03mm.

[0090] S503 specifies the mold manufacturing process specifications and usage and maintenance requirements. During mold manufacturing, the central elastic groove is machined using CNC milling, and the bottom fillet is precision machined using a ball end mill. The surface roughness of the groove is controlled within [specific parameters]. The cavity wall is formed by integral machining, and the local wall thickness is detected by a coordinate measuring machine; the pre-deformed surface is machined by five-axis CNC, and the surface contour accuracy is checked by three-dimensional scanning.

[0091] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0092] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A self-compensating design method for residual stress in heavy-duty forging dies, characterized in that, include: Thermo-mechanical coupled numerical simulation was performed on the entire forging process of the target forging under initial mold conditions, and the residual stress distribution data after the forging cooled to room temperature was extracted. Based on the residual stress distribution data, stress concentration areas on the forging are identified, the hazard level of each stress concentration area is assessed and classified, and the required compressive stress compensation is obtained. Based on the characteristics of the stress concentration area, one or more of the following can be selected for structural design: elastic groove compensation unit, asymmetric stiffness cavity wall compensation unit, and pre-deformed curved surface compensation unit. A quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress is established. An improved mold model containing the selected compensation unit is established, and coupled simulation verification of the forging and the mold is performed. When the compensation effect does not meet the preset requirements, the structural parameters of the compensation unit are iteratively adjusted through a multi-objective optimization function until the convergence criterion is met. The final mold design result is output based on the optimized structural parameters.

2. The self-compensation design method for residual stress in heavy forging dies according to claim 1, characterized in that, In the thermo-mechanical coupling numerical simulation, the constitutive model of the forging material is described by a constitutive model that simultaneously considers the temperature softening effect, strain hardening effect and strain rate strengthening effect. The comprehensive heat transfer coefficient is composed of the superposition of the convective heat transfer coefficient, the radiative heat transfer coefficient and the contact heat transfer coefficient. The residual stress is obtained by the superposition of elastic stress, plastic stress and phase transformation stress.

3. The self-compensation design method for residual stress in heavy forging dies according to claim 1, characterized in that, Identifying the stress concentration areas on the forging includes: The stress gradient method is used to identify local areas of stress variation, and the stress concentration factor method is used to quantify the degree of stress concentration. When the stress gradient exceeds a preset stress gradient threshold and the stress concentration factor exceeds a preset stress concentration factor threshold, the area is determined to be a stress concentration area.

4. The self-compensation design method for residual stress in heavy forging dies according to claim 1, characterized in that, The hazard assessment is based on the third strength theory. The equivalent stress is obtained by measuring the difference between the first principal stress and the third principal stress. The hazard level is determined according to the ratio of the equivalent stress to the yield strength of the forging material. A ratio greater than or equal to 0.45 indicates the first hazard zone, a ratio between 0.35 and 0.45 indicates the second hazard zone, and a ratio less than 0.35 indicates the third hazard zone. Stress compensation is mandatory in the first hazard zone, compensation is required in the second hazard zone, and compensation is exempted in the third hazard zone.

5. The self-compensation design method for residual stress in heavy forging dies according to claim 1, characterized in that, The elastic groove compensation unit is suitable for areas with localized stress concentration, and an elastic groove with a bottom arc transition is set at the corresponding position of the mold cavity; the asymmetric stiffness cavity wall compensation unit is suitable for areas with uneven stress distribution, and an asymmetric stiffness distribution is formed by the difference in cavity wall thickness in different areas; the pre-deformed surface compensation unit is suitable for areas with overall bending or torsional deformation, and the surface of the mold cavity is designed as a pre-deformed surface opposite to the deformation direction of the forging.

6. The self-compensation design method for residual stress in heavy forging dies according to claim 1, characterized in that, The coupled simulation simultaneously considers the elastic deformation of the mold and the elastoplastic deformation of the forging. The compensation effect is quantitatively evaluated by stress deviation and deformation deviation. When both stress deviation and deformation deviation are less than the preset threshold, the compensation effect is determined to meet the requirements.

7. The self-compensation design method for residual stress in heavy forging dies according to claim 5, characterized in that, The groove depth, groove width, and bottom fillet radius of the elastic groove compensation unit are determined by the following formulas: ； ； ； in, Indicates the depth of the groove. This indicates the required compressive stress compensation. Indicates the thickness of the mold cavity wall. Indicates the Poisson's ratio of the mold material. Indicates the elastic modulus of the mold material. This represents the stress concentration correction factor. Indicates the width of the groove. Indicates the radius of the fillet at the bottom of the groove. This represents the first optimization coefficient. This represents the second optimization coefficient.

8. The self-compensation design method for residual stress in heavy forging dies according to claim 5, characterized in that, The local stiffness of the mold cavity in the asymmetric stiffness cavity wall compensation unit is expressed as follows: ;in, Indicates the elastic modulus of the mold material. Indicates the thickness of the cavity wall. Indicates the Poisson's ratio of the mold material. Indicates the span of the cavity wall support; The cavity wall thickness in different regions is expressed as follows: ;in, Indicates the cavity wall thickness of the reference region. Indicates the first The area requires compensation for compressive stress. Indicates the required compressive stress compensation in the reference area; The maximum pre-deformation amount in the pre-deformed surface compensation unit is expressed as: ;in, Indicates the deformation compensation coefficient. This indicates the predicted maximum deformation of the forging. This indicates the preset correction function. Indicates the coefficient of thermal expansion of the forging material. This represents the average temperature difference during the cooling process of the forging. This indicates the total length of the forging.

9. The self-compensation design method for residual stress in heavy forging dies according to claim 1, characterized in that, The multi-objective optimization function is expressed as: ； in, Represents the objective function value. This represents the first preset weighting coefficient. This represents the maximum residual stress in the forging obtained from the simulation. Indicates the maximum residual stress of the target. This represents the second preset weighting coefficient. This represents the maximum deformation of the forging obtained from the simulation. This indicates the maximum deformation of the target. This represents the third preset weighting coefficient. Indicates the maximum working stress of the mold. This indicates the yield strength of the mold material.

10. A self-compensating system for residual stress in heavy-duty forging dies, characterized in that, include: The simulation prediction module is used to perform thermo-mechanical coupling numerical simulation of the entire forging process of the target forging under the initial mold conditions, and to extract the residual stress distribution data after the forging is cooled to room temperature; The stress identification module is used to identify stress concentration areas on the forging based on the residual stress distribution data, assess the hazard level of each stress concentration area and classify it into levels, and obtain the required compressive stress compensation. The compensation design module is used to select one or more of the following structural design units—elastic groove compensation unit, asymmetric stiffness cavity wall compensation unit, and pre-deformed curved surface compensation unit—based on the characteristics of the stress concentration area, and to establish a quantitative mapping relationship between the structural parameters of the compensation unit and the compensation stress. The coupling optimization module is used to build an improved mold model containing the selected compensation unit and to perform coupled simulation verification of the forging and the mold. When the compensation effect does not meet the preset requirements, the structural parameters of the compensation unit are iteratively adjusted through a multi-objective optimization function until the convergence criterion is met.

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