A method for simulating and predicting high temperature forming limit curve of plate material

Abstract

The present application relates to the technical field of test simulation, in particular to a kind of simulation prediction method of high temperature forming limit curve of medium plate material.The method comprises: constructing sheet model and die model for bulging test;The sheet model and the die model are carried out grid division processing;The property model and thermal material model of the sheet model and the die model are defined;Wherein, the property model includes multiple sets of property parameters, and the thermal material model includes multiple sets of thermal parameters;The friction coefficient between the model and the die model, the ambient temperature, the initial temperature and the thermal conductivity are defined;The maximum convex die force criterion and strain path transition criterion are used to identify the necking instability of material along the thickness direction;The temperature field change, the pressing displacement change and the thinning rate change of the sheet model are characterized, and the high temperature forming limit curve simulation prediction of medium plate material is carried out.The scheme provided by the present application can obtain the high temperature forming limit curve of medium plate material by simulation prediction.

Description

Technical Field

[0001] This invention relates to the field of experimental simulation technology, and in particular to a method for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials. Background Technology

[0002] Forming limit diagrams are important indicators describing the formability of sheet metal. They can not only assess the local formability of sheet metal and predict sheet instability and fracture in numerical simulations, but also evaluate the rationality of stamping processes and die structure design, providing a basis for die debugging. They are widely used in the stamping and forming of sheet metal. Traditional experimental methods for obtaining forming limit diagrams are often time-consuming, costly, and consume large amounts of experimental materials, making them inefficient.

[0003] Therefore, in order to address the above problems, there is an urgent need for a method that can predict experiments. Summary of the Invention

[0004] This invention provides a method, apparatus, electronic device, and storage medium for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials, which can obtain the high-temperature forming limit curve of medium-thick plate materials through simulation and prediction.

[0005] In a first aspect, embodiments of the present invention provide a method for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials, comprising:

[0006] Construct sheet metal models and mold models for bulging tests;

[0007] The sheet metal model and the mold model are meshed.

[0008] Define the property model and thermal material model of the sheet metal model and the mold model; wherein, the property model includes multiple sets of property parameters, and the thermal material model includes multiple sets of thermal parameters;

[0009] Define the friction coefficient, ambient temperature, initial temperature, and thermal conductivity between the model and the mold model;

[0010] The maximum punch force criterion and strain path transition criterion are used to identify necking instability in materials along the thickness direction.

[0011] The temperature field change, pressure displacement change and thinning rate change of the sheet material model are characterized to simulate and predict the high temperature forming limit curve of medium and thick plate materials.

[0012] In one possible design, each set of property parameters includes temperature, density, elastic modulus, Poisson's ratio, coefficient of thermal expansion, viscosity parameter, and viscous parameter obtained through tensile testing and simulation.

[0013] In one possible design, each set of thermal parameters includes temperature, specific heat capacity, and thermal conductivity.

[0014] In one possible design, the maximum punch force criterion is to determine the moment when the punch force is at its maximum and then decreases to zero, and the moment when the punch force is at its maximum is the moment of instability. The maximum principal strain value in the plane of the sheet at this moment is regarded as the ultimate principal strain value, and the second principal strain value is the ultimate secondary strain value.

[0015] In one possible design, the strain path transition criterion includes: according to the path transition diagram, the strain corresponding to the inflection point of the transition when the stress state is transformed into a plane stress state is determined as the ultimate strain value.

[0016] In one possible design, characterizing the temperature field changes of the sheet metal model includes:

[0017] Set the convection parameters and heat transfer parameters of the sheet metal model and the mold model;

[0018] Determine the temperature and temperature difference of the sheet metal model and the die model during the stamping process.

[0019] In one possible design, the change in downward displacement is characterized as follows:

[0020] Set the downward displacement amount according to the mold parameters;

[0021] The changes in the sheet metal during the stamping process are analyzed by controlling the downward displacement.

[0022] Secondly, embodiments of the present invention also provide a device for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials, used to implement any of the above methods, the device comprising:

[0023] The first unit is used to construct the sheet metal model and mold model for bulging tests;

[0024] The second unit is used to perform mesh generation processing on the sheet metal model and the mold model;

[0025] The third unit is used to define the property model and thermal material model of the sheet metal model and the mold model; wherein, the property model includes multiple sets of property parameters, and the thermal material model includes multiple sets of thermal parameters;

[0026] The fourth unit is used to define the friction coefficient, ambient temperature, initial temperature, and thermal conductivity between the model and the mold model;

[0027] The fifth unit is used to identify necking instability of materials along the thickness direction using the maximum punch force criterion and the strain path transition criterion.

[0028] The sixth unit is used to characterize the temperature field changes, pressure displacement changes, and thinning rate changes of the sheet material model, and to simulate and predict the high-temperature forming limit curve of medium and thick plate materials.

[0029] Thirdly, embodiments of the present invention also provide an electronic device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, it implements the method described in any embodiment of this specification.

[0030] Fourthly, embodiments of the present invention also provide a computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to perform the methods described in any embodiment of this specification.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] In this embodiment, a sheet metal model and a die model are obtained through modeling. Meshing the two models divides them into multiple meshes with specific shapes and positional relationships, facilitating the simulation of sheet metal deformation under the action of the die. Furthermore, a property model and a thermal material model are defined for both models to determine the mechanical and thermodynamic properties of the materials. Further, the interaction parameters between the die and the sheet metal are defined, including the coefficient of friction, ambient temperature, initial temperature, and thermal conductivity. Then, the maximum punch force criterion and the strain path transition criterion are used to identify necking instability along the thickness direction of the material. Finally, the experimental conditions are parameterized, including changes in temperature field, compression displacement, and thinning rate, to simulate and predict the sheet metal deformation. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is an image of sheet metal of different shapes and sizes provided in one embodiment of the present invention;

[0035] Figure 2 This is a three-dimensional geometric model diagram provided in an embodiment of the present invention;

[0036] Figure 3a This is a finite element mold mesh generation diagram provided in one embodiment of the present invention;

[0037] Figure 3bThis is another finite element mold mesh generation diagram provided in one embodiment of the present invention;

[0038] Figure 3c This is another finite element mold mesh generation diagram provided in one embodiment of the present invention;

[0039] Figure 3d This is another finite element mold mesh generation diagram provided in one embodiment of the present invention;

[0040] Figure 4a This is the punch force-time curve for a 20mm sample.

[0041] Figure 4b This is the punch force-time curve for a 40mm sample;

[0042] Figure 4c This is the punch force-time curve for a 100mm sample.

[0043] Figure 4d This is the punch force-time curve for a 180mm sample.

[0044] Figure 5 This is the result of numerical simulation of sheet metal thinning rate;

[0045] Figure 6 This is a schematic diagram of strain path transformation provided in an embodiment of the present invention;

[0046] Figure 7a This is a temperature field cloud diagram corresponding to a sheet material with a friction coefficient of 0.35, provided in an embodiment of the present invention.

[0047] Figure 7b This is a temperature field cloud diagram corresponding to a sheet metal with a friction coefficient of 0.4, provided in an embodiment of the present invention.

[0048] Figure 7c This is a temperature field cloud diagram corresponding to a sheet metal with a friction coefficient of 0.45, provided in an embodiment of the present invention.

[0049] Figure 7d This is a temperature field cloud diagram corresponding to a sheet metal with a friction coefficient of 0.5, provided in an embodiment of the present invention.

[0050] Figure 8a This is a compression displacement cloud diagram corresponding to a sheet material with a friction coefficient of 0.35 provided in an embodiment of the present invention;

[0051] Figure 8b This is a compression displacement cloud diagram corresponding to a sheet material with a friction coefficient of 0.4 provided in an embodiment of the present invention;

[0052] Figure 8cThis is a compression displacement cloud diagram corresponding to a sheet material with a friction coefficient of 0.45 provided in an embodiment of the present invention;

[0053] Figure 8d This is a compression displacement cloud diagram corresponding to a sheet material with a friction coefficient of 0.5 provided in an embodiment of the present invention;

[0054] Figure 9a This is a thinning rate cloud diagram corresponding to a sheet metal with a friction coefficient of 0.35, provided in an embodiment of the present invention.

[0055] Figure 9b This is a thinning rate cloud diagram corresponding to a sheet metal with a friction coefficient of 0.4 provided in an embodiment of the present invention;

[0056] Figure 9c This is a thinning rate cloud diagram corresponding to a sheet material with a friction coefficient of 0.45, provided in an embodiment of the present invention.

[0057] Figure 9d This is a thinning rate cloud diagram corresponding to a sheet material with a friction coefficient of 0.5 provided in an embodiment of the present invention;

[0058] Figure 10a This is a temperature field cloud map of a sheet metal at 850°C, provided by an embodiment of the present invention.

[0059] Figure 10b This is a temperature field cloud map of a sheet metal at 880°C, provided by an embodiment of the present invention.

[0060] Figure 10c This is a temperature field cloud map of a sheet metal at 900°C, provided by an embodiment of the present invention.

[0061] Figure 10d This is a temperature field cloud map of a sheet metal at 920°C, provided by an embodiment of the present invention.

[0062] Figure 11a This is a compression displacement cloud diagram of a sheet metal at 850°C, provided by an embodiment of the present invention.

[0063] Figure 11b This is a compression displacement cloud diagram of a sheet metal at 880°C, provided by an embodiment of the present invention.

[0064] Figure 11c This is a compression displacement cloud diagram of a sheet metal at 900°C, provided by an embodiment of the present invention.

[0065] Figure 11d This is a compression displacement cloud diagram of a sheet metal at 920°C provided in one embodiment of the present invention;

[0066] Figure 12a This is a thinning rate cloud diagram of a sheet metal at 850°C provided in one embodiment of the present invention;

[0067] Figure 12b This is a thinning rate cloud diagram of a sheet metal at 880°C provided in one embodiment of the present invention;

[0068] Figure 12c This is a thinning rate cloud diagram of a sheet metal at 900°C, provided by an embodiment of the present invention.

[0069] Figure 12d This is a thinning rate cloud diagram of a sheet metal at 920°C provided in one embodiment of the present invention;

[0070] Figure 13 These are the principal strain contour maps corresponding to the critical fracture when the plate width is 20mm and 180mm;

[0071] Figure 14 These are secondary strain contour maps corresponding to critical fracture when the sheet width is 20mm and 180mm;

[0072] Figure 15 This is a thermoforming limit diagram of TC4 sheet metal with an initial forming temperature of 850℃.

[0073] Figure 16 It is a forming limit diagram under different strain rates at the same temperature. Detailed Implementation

[0074] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0075] The specific implementation of the above concept is described below.

[0076] This invention provides a method for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials, comprising:

[0077] S1, Construct the sheet metal model and mold model for the bulging test;

[0078] S2, perform mesh generation on the sheet metal model and the mold model;

[0079] S3 defines the property model and thermal material model for the sheet metal model and the mold model; the property model includes multiple sets of property parameters, and the thermal material model includes multiple sets of thermal parameters.

[0080] S4 defines the friction coefficient, ambient temperature, initial temperature, and thermal conductivity between the model and the mold model;

[0081] S5 uses the maximum punch force criterion and strain path transition criterion to identify necking instability of materials along the thickness direction;

[0082] S6 characterizes the temperature field changes, pressure displacement changes, and thinning rate changes of the sheet material model, and performs high-temperature forming limit curve simulation and prediction for medium-thick plate materials.

[0083] In this embodiment, a sheet metal model and a die model are obtained through modeling. Meshing the two models divides them into multiple meshes with specific shapes and positional relationships, facilitating the simulation of sheet metal deformation under the action of the die. Furthermore, a property model and a thermal material model are defined for both models to determine the mechanical and thermodynamic properties of the materials. Further, the interaction parameters between the die and the sheet metal are defined, including the coefficient of friction, ambient temperature, initial temperature, and thermal conductivity. Then, the maximum punch force criterion and the strain path transition criterion are used to identify necking instability along the thickness direction of the material. Finally, the experimental conditions are parameterized, including changes in temperature field, compression displacement, and thinning rate, to simulate and predict the sheet metal deformation.

[0084] Specifically, regarding S1:

[0085] The geometric model for the bulging experiment was constructed using the 3D modeling software Solidworks to create models of the punch and die, blank holder, and sheet metal. The models should perfectly match the shape and dimensions of the experimental mold, and be exported as ".igs" format files. The geometric dimensions and process parameters of the punch and die, blank holder, and sheet metal are as follows:

[0086] Punch radius: rp = 50mm; Die inner diameter: rd1 = 52.5mm

[0087] Die outer diameter: rd = 112.5 mm; Die fillet radius: rd = 8 mm

[0088] Inner diameter of the blank holder: rb = 60mm; Outer diameter of the blank holder: rb2 = 112.5mm

[0089] To obtain the strain and stress paths of the specimens under different conditions, specimens with different geometric dimensions were used in the experiment. See specimen diagram below. Figure 1 Geometric model see Figure 2 Nine sets of samples of different sizes were designed for the sheet metal by varying the sample width. The diameter was 180 mm, and the width ranged from 20 mm to 180 mm with intervals of 20 mm. The samples were saved in "igs" format.

[0090] For S2:

[0091] Grid division

[0092] In DYNAFORM sheet metal forming simulation software, finite element simulation is typically performed using BT shell elements. There are three main mesh generation methods: ToolMesh, Part Mesh, and Triangle Mesh, with ToolMesh being the most commonly used. ToolMesh uses a mix of triangles and quadrilaterals; surfaces with lower curvature are mostly quadrilateral elements, while areas with greater curvature changes and surface transitions have more triangular elements. This is to better fit and describe the surface and geometry of the tool body. Furthermore, DYNAFORM employs adaptive meshing technology, allowing for improvements in mesh quality by adjusting the maximum element size (Max.Size), minimum element size (Min.Size), element angle, and refinement level. Users can also redefine the mesh, automatically repair voids, and optimize outer edge meshes. The sheet metal mesh generation is shown in Figure 3. The number of mesh elements gradually increases as the forming process progresses. The mesh type is BT quadrilateral shell elements, with a mesh size of 5mm and a minimum size of 1mm.

[0093] For S3:

[0094] Material Model Selection

[0095] In sheet metal forming analysis, the mold is typically made of rigid material, while the sheet metal itself is generally modeled using rigid-plastic or elasto-plastic materials. Among these, the power-law plastic material model, the thickness-anisotropic elasto-plastic material model, and the 3-parameter Barlat material model are particularly suitable for thin sheet metal stamping analysis. Dynaform software includes several built-in material models, such as models 18, 24, 36, 37, and 125, but these are all suitable for room-temperature forming and not for high-temperature forming processes. This simulation selected material model 106. The required material parameters for TC4 medium-thick sheet metal were obtained through tensile testing and J-MAT Pro simulation software. The required parameters for material model 106 are shown in Table 1. The flow stress curves of the sheet metal at different temperatures were fitted using the Vocehardening law saturated stress hardening model.

[0096] Table 1 Required parameters for material model No. 106

[0097]

[0098] During the hot forming process, heat exchange phenomena such as heat conduction occur between the sheet metal and the die, requiring the definition of thermal material models for both the sheet metal and the die. Dynaform software offers six thermal material models; after comparing the required parameters of each model, model number 6 was selected for both the sheet metal and the die. H13 hot work die steel was chosen as the die material. The required thermophysical parameters for the TC4 sheet metal and H13 hot work die steel thermal material models were obtained using J-MAT pro simulation software, as shown in Table 2.

[0099] Table 2 Parameters required for the thermal material model

[0100]

[0101] For S4:

[0102] Define boundary conditions and contact conditions

[0103] In the numerical simulation prediction model of the isothermal hot forming limit curve of high-strength steel sheet, the temperature of the die is the same as the initial forming temperature of the sheet, and the influence of thermal radiation heat transfer and convection heat transfer with the surrounding environment on the sheet temperature is ignored. In cold die bulging tests, it is usually necessary to change the geometric dimensions of the specimen and the friction coefficient between the sheets to obtain the limit strain values ​​under different strain states. However, in the hot stamping process, considering that the friction between the sheet and the die is not only related to the forming temperature, the coating materials of the die and the sheet, but also to factors such as the surface roughness of the die, it is difficult to control effectively. Therefore, this paper uses a fixed friction coefficient value and changes the geometric dimensions of the specimen to predict the isothermal hot forming limit curve. The contact interface between the sheet and the die is defined as Form surf to surf, and the initial forming temperatures of the sheet are 850℃, 880℃, 900℃, and 920℃, respectively, and the ambient temperature is set to 20℃. To define the boundary conditions, the heat transfer coefficients at different temperatures are calculated according to the natural convection heat transfer criterion, as shown in Table 3. The cooling stage removes a significant amount of heat. Based on research, the heat transfer coefficient was set to 2000 W / m²·K. The contact conditions included the friction coefficient and the interfacial heat transfer coefficient. The friction coefficient was set to 0.46, the blank holder force during contact was set to 20 KN, and the initial slab velocity was 25 mm / s.

[0104] Table 3 Heat transfer coefficients at different temperatures

[0105]

[0106] For S5:

[0107] Instability Criteria Determined

[0108] Dynaform software, as a software specifically designed for simulating sheet metal stamping, has been very successful in simulating stamping forming. To save simulation time and accelerate the research cycle, shell elements are generally used for simulation. However, when using shell elements for simulation, the software cannot identify necking along the thickness direction of the material. The solver will continue calculating even for elements that have already fractured. Therefore, a sheet metal instability criterion needs to be added after the solver. For room temperature stamping of ordinary plastic materials, the program calculates the corresponding FLD0 (lowest point of the forming limit diagram) using Keeler's formula (as shown in formula (1-1)) based on the material strain hardening index n, sheet thickness t, and thickness anisotropy index r input by the user in the post-processing software, and generates the FLD curve according to formula (1-2).

[0109]

[0110]

[0111] However, Keeler's formula has significant limitations; it cannot be used to calculate the forming limit diagrams of other materials such as high-strength steel, aluminum alloys, and magnesium alloys. Furthermore, the strain hardening exponent *n* and the thickness anisotropy exponent *r* of materials change continuously during high-temperature forming, resulting in large errors in the forming limit diagrams obtained using Keeler's formula. Titanium alloys are significantly affected by strain rate during forming, and the strain rate sensitivity index is crucial to their forming process; using the built-in FLD function in software yields very large errors. Therefore, it is necessary to find a suitable instability criterion to determine the limit strain value of the element corresponding to the moment when necking fracture occurs in the sheet metal. The maximum punch force criterion and the strain path transition criterion have been widely used in studying the forming limits of materials using numerical simulation software.

[0112] ① Maximum punch force instability criterion:

[0113] During the stamping process of the punch on the sheet metal, as the punch displacement increases, the punch force eventually reaches a maximum value, and then rapidly drops to zero. The moment when the punch force reaches its maximum can be considered the moment of material instability; this is the maximum punch force instability criterion. The maximum principal strain value corresponding to this moment in the sheet metal plane can be considered the ultimate principal strain value, and the second principal strain value is the ultimate secondary strain value. Using the Dynaform post-processing software EtaPostProcessor, open the idx file, click on the graph to load the "rcforc" file, select "BLANK / 10_Punch" for contact, and select the force in the Z direction as the component. Then, export the curve showing the relationship between the punch's motion time and the force in the Z direction acting on the specimen, find the moment when the punch force reaches its maximum value, and record the corresponding principal and secondary strain values.

[0114] Figure 4 shows the punch force-time curves for specimens with sheet widths of 20 mm and 180 mm. Through cup-bulging simulations of sheet metals with different widths, it was found that the maximum punch force criterion only applies when the sheet width is small (20–80 mm). When the sheet width is relatively large (100–180 mm), the specimen experiences a bi-tension state, with the punch force continuously increasing with displacement without reaching a peak value.

[0115] ② Criteria for determining the maximum thinning rate

[0116] In numerical simulations of bulging, when there are mesh elements in the sheet metal with a thickness reduction rate exceeding 30%, the sheet metal can be considered to have undergone instability and fracture at this point. The strain on the mesh element in the fracture region at this moment is extracted as the ultimate strain value of this criterion, which is called the maximum thinning rate criterion. Since the maximum thinning rate of 30% in this criterion is not an experimentally verified value, the thinning rate used to determine instability and fracture will change with different materials and different strain paths. Furthermore, in Dynaform software, it is very difficult to obtain a single mesh element on the sheet metal that reaches the thinning rate. Many scholars believe that in most cases, the sheet metal has already fractured when the deformation reaches the maximum thinning rate; therefore, the ultimate strain obtained through the maximum thinning rate criterion is not accurate. In summary, the maximum thinning rate criterion has significant limitations in obtaining the ultimate strain, and this criterion is not used in this paper to determine the instability and fracture of sheet metal. In some embodiments of this invention, the strain path transition criterion includes: according to the path transition diagram, when the stress state is transformed into a plane stress state, the strain corresponding to the inflection point of the transition is determined as the ultimate strain value.

[0117] ③ Based on the strain path transformation criterion

[0118] like Figure 6 The strain path transition diagram shows that the stress state has now transitioned to a plane stress state, and the strain corresponding to the inflection point of the transition is the ultimate strain value. After simulating nine different sheet widths, the post-processing results show that: when the sheet width is 20–80 mm, the maximum punch force appears in the punch force-time curve, but no inflection point appears in the strain path. Therefore, the maximum punch force criterion is selected as the instability criterion. When the sheet width is between 100–180 mm, no maximum force appears in the post-processing results, but an inflection point appears in the strain path. Therefore, the strain path transition criterion is selected as the instability criterion.

[0119] The strain path determination method was used for the specimens. Researchers believe that concentrated instability caused by the occurrence of a plane strain state is the reason for this. Numerical simulation results show that the strain path of the element with the maximum strain often undergoes a linear, stable increase before transitioning to a plane strain state. This process produces a necking point, where the strain suddenly shifts to the plane strain state. As shown in the figure, the maximum principal strain initially rises gently, then increases rapidly at the necking point, while the minimum principal strain increases slowly. The inflection point is where the specimen necks or fractures. This method is only suitable for specimens with a relatively wide width.

[0120] For S6:

[0121] Simulation performance characterization

[0122] 1. Temperature field changes in sheet metal

[0123] (1) First, set the temperature conditions of the sheet metal and the mold. After setting the convection and heat exchange in Dynaform, the sheet metal will be heated to the predetermined temperature.

[0124] (2) Due to the temperature difference between the mold and the sheet metal, as well as other conditions that hinder the stamping process, the temperature field of the sheet metal will change. Therefore, we need to determine the temperature during the stamping process.

[0125] 2. Changes in downward displacement

[0126] (1) Based on the mold parameters we set, we directly set the downward displacement in Dynaform.

[0127] (2) By controlling the downward displacement, the changes in the sheet metal during the stamping process can be analyzed intuitively;

[0128] 3. Changes in thinning rate

[0129] After exporting and analyzing the results, the changes in sheet thinning rate at different stamping stages can be obtained by controlling the time.

[0130] Finally, the simulation results are analyzed:

[0131] To investigate the effects of initial deformation temperature and friction coefficient on sheet metal forming quality, a sheet metal with dimensions of 180×180mm was selected. The initial deformation temperatures of the sheet metal were set to 850℃, 880℃, 900℃, and 920℃, the mold temperature to 750℃, the forming speed to 25mm / s, and the friction coefficients to 0.35, 0.4, 0.45, and 0.5, respectively. The number of steps corresponding to the critical fracture moment of the maximum principal strain unit was found using the strain path transformation criterion. The sheet metal temperature field, compression displacement, and thinning rate under different deformation conditions at the critical fracture moment were compared and analyzed.

[0132] ① The effect of friction coefficient on the forming process

[0133] The initial forming temperature of the sheet metal was set to 850℃, and different friction coefficients were set: 0.35, 0.4, 0.45, and 0.5. Figure 7 shows the temperature field contour maps corresponding to the critical fracture moment of the sheet metal under different friction coefficients. Comparing the temperature fields under different friction coefficients, it was found that due to heat conduction between the sheet metal and the die and blank holder, the sheet metal temperature under the blank holder was almost close to 750℃ under different friction coefficients, similar to the die temperature. However, the temperature field of the forming area was affected by the stamping speed, and the stamping time varied greatly. Therefore, the temperature field corresponding to the forming part of the sheet metal in contact with the punch at the critical fracture point varied considerably. The temperatures at the center of the contact between the sheet metal and the punch were 770℃, 769℃, and 768℃, respectively, while the temperatures of the parts farther from the punch were 758℃, 756℃, and 754℃, respectively. As the friction coefficient increased, the temperature in the center area of ​​the sheet metal and the punch was high, and the temperature decreased with increasing distance from the center. On the one hand, during the forming process, the mold cools the sheet metal. Because the central area of ​​the sheet metal is in closer contact with the mold and has a higher coefficient of friction, the cooling effect in this area is less effective than at the edges. On the other hand, the varying thickness of the sheet metal leads to uneven heat dissipation, creating a non-uniform temperature field. Thinner areas cool down faster than thicker areas, creating a temperature gradient in the transition zone. This temperature change causes variations in internal stress. Since stress is highly sensitive to temperature changes during hot deformation, significant stress concentration occurs in the transition zone with a large temperature difference.

[0134] Figure 8 shows the sheet metal compression displacement contour plots corresponding to the critical fracture time under different friction coefficients. The maximum compression displacements corresponding to the critical fracture time under different friction coefficients are 36.75 mm, 36.78 mm, 36.79 mm, and 36.82 mm, respectively. As the friction coefficient increases, the frictional force between the sheet metal and the mold increases. This increased frictional force requires more force to overcome the friction during the forming process, thus causing the sheet metal to sink deeper into the mold. In other words, the maximum compression displacement increases with the increase of the friction coefficient.

[0135] Figure 9 shows the thinning rate contour plots corresponding to the critical fracture time under different friction coefficients. The maximum thinning rates corresponding to the critical fracture time under different friction coefficients are 37.6%, 38.64%, 48.84%, and 41.57%, respectively. As the friction coefficient increases, the downward displacement corresponding to the critical fracture time of the sheet gradually increases, the load that the sheet can withstand in the thickness direction increases, and the corresponding thinning rate increases. At the same thickness, the higher the friction coefficient, the easier the workpiece is to crack, and the greater the material thinning rate. Under the same specifications, the resulting workpiece is lighter. Therefore, during the forming process, we should add lubricant to keep the friction coefficient at a suitable level as needed.

[0136] ② The effect of the initial deformation temperature of the sheet metal on the forming process

[0137] In studying the influence of the initial forming temperature of sheet metal on the forming process, sheet metal of the same specification was selected. To ensure that it was not affected by the forming speed, the coefficient of friction was uniformly set to 0.4, and the initial deformation temperatures of the sheet metal were 850℃, 880℃, 900℃, and 920℃, respectively. Figure 10 shows the temperature field cloud map corresponding to the critical fracture time at different initial deformation temperatures. It can be observed that when the initial forming temperature of the sheet metal is different, the higher the initial forming temperature of the sheet metal, the higher the temperature corresponding to the critical fracture time. However, due to heat transfer and conduction between the sheet metal and the mold and the cooling system, the temperature field corresponding to the critical fracture time of the sheet metal is not significantly different. The temperature is highest at the center of the contact area between the sheet metal and the punch, and the temperature decreases with distance from the center. The temperature distribution is relatively uniform at locations not far from the center.

[0138] Figure 11 shows the compression displacement cloud diagrams corresponding to the critical fracture moment of the sheet metal at different initial deformation temperatures. It can be found that the maximum compression displacement of the sheet metal at different initial deformation temperatures at the critical fracture moment is 31.82 mm, 36.20 mm, 36.39 mm, and 30.87 mm, respectively. The maximum compression displacement increases with the increase of the initial deformation temperature of the sheet metal, reaching a maximum at 900℃, and then decreases with the increase of the initial deformation temperature.

[0139] Figure 12 shows the thinning rate contour plots corresponding to the critical fracture time at different initial deformation temperatures. It can be observed that the maximum thinning rates corresponding to different initial forming temperatures at the critical fracture time are 39.58%, 39.98%, 55.12%, and 49.02%, respectively. Similar to the downward displacement pattern, these rates increase with increasing initial deformation temperature of the sheet metal; the larger the downward displacement, the greater the thinning rate. The thinning rate is highest at 900℃. Afterward, the thinning rate decreases with increasing initial deformation temperature. The region with the largest sheet metal thinning rate is located at the contact center between the punch and the sheet metal.

[0140] ③Establishment of the thermoforming limit diagram for TC4 sheet metal

[0141] The forming temperature was set to 850℃ and the forming speed to 25mm / s. The sheet metal was simulated by hemispherical punch bulging. The post-processing results were analyzed by combining the maximum punch force with the strain path transformation criterion. The critical instability moment for different sheet widths was found, and the principal strain and secondary strain cloud diagrams corresponding to that moment were analyzed. Figure 13 These are the principal strain contour plots corresponding to the critical fracture point when the selected plate widths are 20mm and 180mm. Figure 14 These are secondary strain contour maps corresponding to critical fracture when the sheet width is 20mm and 180mm.

[0142] The primary and secondary strain points under different strain paths were extracted through analysis, as shown in Table 4. The data was imported into Origin data processing software and fitted to obtain the thermoforming limit diagram of TC4 sheet (e.g., ...). Figure 15 (As shown). The FLD curve uses a quadratic fitting to represent the shape of a parabola.

[0143] Table 4. Major and minor strain points under different strain paths

[0144]

[0145] This invention provides a device for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials. The device can be implemented through software, hardware, or a combination of both. From a hardware perspective, the hardware architecture diagram of the electronic device housing the device for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials provided in this invention includes, in addition to the processor, memory, network interface, and non-volatile memory, other hardware such as a forwarding chip responsible for processing messages. Taking software implementation as an example, as a logical device, it is formed by the CPU of the electronic device reading the corresponding computer program from the non-volatile memory into memory and running it. The device for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials provided in this embodiment includes:

[0146] The first unit is used to construct the sheet metal model and mold model for bulging tests;

[0147] The second unit is used to perform mesh generation on the sheet metal model and the mold model;

[0148] The third unit is used to define the property model and thermal material model of the sheet metal model and the mold model; the property model includes multiple sets of property parameters, and the thermal material model includes multiple sets of thermal parameters.

[0149] The fourth unit is used to define the friction coefficient, ambient temperature, initial temperature, and thermal conductivity between the model and the mold model;

[0150] The fifth unit is used to identify necking instability of materials along the thickness direction using the maximum punch force criterion and the strain path transition criterion.

[0151] The sixth unit is used to characterize the temperature field changes, pressure displacement changes, and thinning rate changes of the sheet metal model, and to simulate and predict the high-temperature forming limit curve of medium and thick plate materials.

[0152] It is understood that the structures illustrated in the embodiments of the present invention do not constitute a specific limitation on a device for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials. In other embodiments of the present invention, a device for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials may include more or fewer components than illustrated, or combine some components, or split some components, or have different component arrangements. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.

[0153] The information interaction and execution process between the modules in the above-mentioned device are based on the same concept as the method embodiment of the present invention, and the specific details can be found in the description of the method embodiment of the present invention, and will not be repeated here.

[0154] This invention also provides an electronic device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements a method for simulating and predicting the high-temperature forming limit curve of medium-thick plate material according to any embodiment of this invention.

[0155] This invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform a method for simulating and predicting the high-temperature forming limit curve of a medium-thick plate material according to any embodiment of this invention.

[0156] Specifically, a system or apparatus equipped with a storage medium may be provided, on which software program code implementing the functions of any of the embodiments described above is stored, and the computer (or CPU or MPU) of the system or apparatus may read and execute the program code stored in the storage medium.

[0157] In this case, the program code read from the storage medium can itself implement the function of any of the above embodiments, and therefore the program code and the storage medium storing the program code constitute part of the present invention.

[0158] Examples of storage media used to provide program code include floppy disks, hard disks, magneto-optical disks, optical disks (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW), magnetic tapes, non-volatile memory cards, and ROMs. Alternatively, program code can be downloaded from a server computer via a communication network.

[0159] Furthermore, it should be clear that not only can the program code read by the computer be executed, but also the operating system or other components operating on the computer can be instructed based on the program code to perform some or all of the actual operations, thereby realizing the function of any of the embodiments described above.

[0160] Furthermore, it is understood that the program code read from the storage medium is written to the memory set in the expansion board inserted into the computer or to the memory set in the expansion module connected to the computer. Then, based on the instructions of the program code, the CPU or other components installed on the expansion board or expansion module execute some and all of the actual operations, thereby realizing the function of any of the above embodiments.

[0161] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0162] Those skilled in the art will understand that all or part of the steps of the above method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps of the above method embodiments. The aforementioned storage medium includes various media that can store program code, such as ROM, RAM, magnetic disk, or optical disk.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials, characterized in that, include: Construct sheet metal models and mold models for bulging tests; The sheet metal model and the mold model are meshed. Define the property model and thermal material model of the sheet metal model and the mold model; wherein, the property model includes multiple sets of property parameters, and the thermal material model includes multiple sets of thermal parameters; Define the coefficient of friction, ambient temperature, initial temperature, and thermal conductivity between the sheet metal model and the mold model; The maximum punch force criterion and strain path transition criterion are used to identify necking instability in materials along the thickness direction. The temperature field change, pressure displacement change, and thinning rate change of the sheet material model are characterized to simulate and predict the high-temperature forming limit curve of medium and thick plate materials. When the sheet width is 20~80mm, the maximum punch force criterion is selected. The maximum punch force criterion is to determine the moment when the punch force is at its maximum and then reduced to zero, and the moment when the punch force is at its maximum is the moment of instability. The maximum principal strain value in the sheet plane at this moment is regarded as the ultimate principal strain value, and the second principal strain value is the ultimate secondary strain value. When the sheet width is 100~180mm, the strain path transformation criterion is selected. The strain path transformation criterion includes: according to the path transformation diagram, when the stress state is transformed into a plane stress state, the strain corresponding to the inflection point of the transformation is determined as the ultimate strain value.

2. The simulation prediction method according to claim 1, characterized in that, Each set of property parameters includes temperature, density, elastic modulus, Poisson's ratio, coefficient of thermal expansion, viscosity parameter C, and viscosity parameter P, obtained through tensile tests and simulations.

3. The simulation prediction method according to claim 1, characterized in that, Each set of thermal parameters includes temperature, specific heat capacity, and thermal conductivity.

4. The simulation prediction method according to claim 1, characterized in that, Characterizing the temperature field changes of the sheet metal model includes: Set the convection parameters and heat transfer parameters of the sheet metal model and the mold model; Determine the temperature and temperature difference of the sheet metal model and the die model during the stamping process.

5. The simulation prediction method according to claim 1, characterized in that, The change in downward displacement is characterized in the following way: Set the downward displacement amount according to the mold parameters; The changes in the sheet metal during the stamping process are analyzed by controlling the downward displacement.

6. A device for simulating and predicting the high-temperature forming limit curve of medium-thick plate materials, characterized in that, The apparatus for implementing the method as described in any one of claims 1-5 comprises: The first unit is used to construct the sheet metal model and mold model for bulging tests; The second unit is used to perform mesh generation processing on the sheet metal model and the mold model; The third unit is used to define the property model and thermal material model of the sheet metal model and the mold model; wherein, the property model includes multiple sets of property parameters, and the thermal material model includes multiple sets of thermal parameters; The fourth unit is used to define the friction coefficient, ambient temperature, initial temperature, and thermal conductivity between the model and the mold model; The fifth unit is used to identify necking instability of materials along the thickness direction using the maximum punch force criterion and the strain path transition criterion. The sixth unit is used to characterize the temperature field change, pressure displacement change and thinning rate change of the sheet material model, and to simulate and predict the high temperature forming limit curve of medium and thick plate materials. When the sheet width is 20~80mm, the maximum punch force criterion is selected. The maximum punch force criterion is to determine the moment when the punch force is at its maximum and then reduced to zero, and the moment when the punch force is at its maximum is the moment of instability. The maximum principal strain value in the sheet plane at this moment is regarded as the ultimate principal strain value, and the second principal strain value is the ultimate secondary strain value. When the sheet width is 100~180mm, the strain path transformation criterion is selected. The strain path transformation criterion includes: according to the path transformation diagram, when the stress state is transformed into a plane stress state, the strain corresponding to the inflection point of the transformation is determined as the ultimate strain value.

7. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, and the processor, when executing the computer program, implements the method as described in any one of claims 1-5.

8. A computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to perform the method of any one of claims 1-5.

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