Simulation and prediction method for high-temperature forming limit curve of medium-thickness plate material

Abstract

The invention relates to the technical field of test simulation, in particular to a method for simulating and predicting a high-temperature forming limit curve of a medium-thickness plate material. The method comprises the following steps: constructing a plate model and a mold model for a bulging test; grid division processing is conducted on the plate model and the mold model; defining a property model and a thermal material model of the plate model and the mold model; wherein the property model comprises a plurality of groups of property parameters, and the thermal material model comprises a plurality of groups of thermal parameters; defining a friction coefficient, an ambient temperature, an initial temperature and a heat conductivity coefficient between the model and the mold model; the necking instability of the material in the thickness direction is recognized through the maximum male die force criterion and the strain path transformation criterion; and representing the temperature field change, the pressing displacement change and the thinning rate change of the plate material model, and carrying out simulation prediction on the high-temperature forming limit curve of the medium-thickness plate material. According to the scheme provided by the invention, the medium-thickness plate material high-temperature forming limit curve can be obtained through simulation prediction.

Description

Technical Field

[0001] The present invention relates to the field of test simulation technology, and in particular to a method for simulating and predicting a high-temperature forming limit curve of a medium-thick plate material. Background Art

[0002] The forming limit diagram (FLD) is an important indicator for describing the formability of sheet metal. It not only assesses the local formability of sheet metal and identifies potential sheet metal instability and fracture in numerical simulations, but also allows for the rationality of stamping processes and die structure design during stamping, providing a foundation for die commissioning. It is widely used in the field of sheet metal stamping. Traditional experimental methods for obtaining FLDs are often time-consuming and costly, consuming large amounts of experimental materials, and therefore inefficient.

[0003] Therefore, in response to the above problems, a method that can predict the experiment is urgently needed. Summary of the Invention

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

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

[0006] Construct sheet metal model and die model for bulging test;

[0007] Performing meshing processing on the sheet metal model and the mold model;

[0008] Defining a property model and a 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] defining a friction coefficient, an ambient temperature, an initial temperature, and a thermal conductivity between the model and the mold model;

[0010] The maximum punch force criterion and the strain path transformation criterion are used to identify the necking instability of the material along the thickness direction.

[0011] The temperature field changes, downward displacement changes and thinning rate changes of the sheet metal model are characterized, and the high-temperature forming limit curve of medium and thick plate materials is simulated and predicted.

[0012] In one possible design, each set of property parameters includes temperature, density, elastic modulus, Poisson's ratio, thermal expansion coefficient, 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 that after the punch force reaches a maximum and then drops to zero, the moment when the punch force is maximum is determined as the instability moment, and the corresponding maximum principal strain value in the sheet plane at this moment is regarded as the limit principal strain value, and the second principal strain value is the limit secondary strain value.

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

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

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

[0018] The temperatures and temperature differences of the sheet metal model and the die model during the stamping process are determined.

[0019] In one possible design, the downward displacement change is characterized by:

[0020] According to the set mold parameters, set the downward displacement;

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

[0022] In a second aspect, an embodiment of the present invention further provides a device for simulating and predicting a high-temperature forming limit curve of a medium and thick plate material, for implementing any of the above methods, the device comprising:

[0023] The first unit is used to build the sheet metal model and die model for bulging test;

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

[0025] A third unit is used to define a property model and a 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] A fourth unit is used to define a friction coefficient, an ambient temperature, an initial temperature, and a thermal conductivity between the model and the mold model;

[0027] Unit 5 is used to identify necking instability along the thickness direction of the material using the maximum punch force criterion and the strain path transition criterion;

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

[0029] In a third aspect, an embodiment of the present invention further provides an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the method described in any embodiment of this specification is implemented.

[0030] In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, enables the computer to execute the method 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 material model and a mold model can be obtained by modeling. By meshing the two models, the models can be divided into multiple grids with certain shapes and positional relationships, which makes it easier to simulate the deformation of the sheet material under the action of the mold. Furthermore, the property models and thermal material models of the two models are defined to determine the mechanical properties and thermodynamic properties of the material. Further, the interaction parameters between the mold and the sheet material are defined, including the friction coefficient, ambient temperature, initial temperature and thermal conductivity. Then, the maximum punch force criterion and the strain path transformation criterion are used to identify the necking instability of the material along the thickness direction. Finally, the test conditions are parameterized, including temperature field changes, downward displacement changes and thinning rate changes, to simulate and predict the sheet material. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 An embodiment of the present invention provides a sheet material image of different shapes and sizes;

[0035] Figure 2 It is a three-dimensional geometric model diagram provided by one embodiment of the present invention;

[0036] Figure 3a This is a finite element mold mesh division diagram provided by an embodiment of the present invention;

[0037] Figure 3bThis is another finite element mold mesh division diagram provided by an embodiment of the present invention;

[0038] Figure 3c This is another finite element mold mesh division diagram provided by an embodiment of the present invention;

[0039] Figure 3d This is another finite element mold mesh division diagram provided by an embodiment of the present invention;

[0040] Figure 4a This is the punch force-time curve corresponding to the 20mm specimen;

[0041] Figure 4b This is the punch force-time curve corresponding to the 40mm specimen;

[0042] Figure 4c This is the punch force-time curve corresponding to the 100mm specimen;

[0043] Figure 4d This is the punch force-time curve corresponding to the 180mm specimen;

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

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

[0047] Figure 7b This is a temperature field cloud diagram corresponding to a sheet material with a friction coefficient of 0.4 provided by one embodiment of the present invention;

[0048] Figure 7c This is a temperature field cloud diagram corresponding to a sheet material with a friction coefficient of 0.45 provided by one embodiment of the present invention;

[0049] Figure 7d This is a temperature field cloud diagram corresponding to a sheet material under a friction coefficient of 0.5 provided by one embodiment of the present invention;

[0050] Figure 8a This is a nephogram of downward displacement corresponding to a sheet material under a friction coefficient of 0.35 provided by one embodiment of the present invention;

[0051] Figure 8b This is a nephogram of downward displacement corresponding to a sheet material under a friction coefficient of 0.4 provided by one embodiment of the present invention;

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

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

[0054] Figure 9a This is a cloud diagram of the thinning rate of a sheet material corresponding to a friction coefficient of 0.35 provided by one embodiment of the present invention;

[0055] Figure 9b This is a cloud diagram of the thinning rate of a sheet material corresponding to a friction coefficient of 0.4 provided by one embodiment of the present invention;

[0056] Figure 9c This is a cloud diagram of the thinning rate of a sheet material corresponding to a friction coefficient of 0.45 provided by one embodiment of the present invention;

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

[0058] Figure 10a This is a temperature field cloud diagram corresponding to a sheet material at a temperature of 850°C provided by an embodiment of the present invention;

[0059] Figure 10b This is a temperature field cloud diagram corresponding to a sheet material at a temperature of 880°C provided by an embodiment of the present invention;

[0060] Figure 10c This is a temperature field cloud diagram corresponding to a sheet material at a temperature of 900°C provided by an embodiment of the present invention;

[0061] Figure 10d This is a temperature field cloud diagram corresponding to a sheet material at a temperature of 920°C provided by an embodiment of the present invention;

[0062] Figure 11a This is a downward displacement cloud diagram corresponding to a sheet material at a temperature of 850° C. provided by one embodiment of the present invention;

[0063] Figure 11b This is a downward displacement cloud diagram corresponding to a sheet material at a temperature of 880°C provided by an embodiment of the present invention;

[0064] Figure 11c This is a downward displacement cloud diagram corresponding to a sheet material at a temperature of 900°C provided by an embodiment of the present invention;

[0065] Figure 11d This is a downward displacement cloud diagram corresponding to a sheet material at a temperature of 920°C provided by an embodiment of the present invention;

[0066] Figure 12a This is a thinning rate cloud diagram corresponding to a sheet material at a temperature of 850° C. provided by one embodiment of the present invention;

[0067] Figure 12b This is a thinning rate cloud diagram corresponding to a sheet material at a temperature of 880°C provided by an embodiment of the present invention;

[0068] Figure 12c This is a thinning rate cloud diagram corresponding to a sheet material at a temperature of 900° C. provided by one embodiment of the present invention;

[0069] Figure 12d This is a thinning rate cloud diagram corresponding to a sheet material at a temperature of 920° C. provided by one embodiment of the present invention;

[0070] Figure 13 It is the principal strain nephogram corresponding to the critical fracture when the sheet width is 20mm and 180mm;

[0071] Figure 14 It is the secondary strain nephogram corresponding to the critical fracture when the sheet width is 20mm and 180mm;

[0072] Figure 15 It is the hot forming limit diagram of TC4 sheet when the initial forming temperature is 850℃;

[0073] Figure 16 It is the forming limit diagram at the same temperature and different strain rates. DETAILED DESCRIPTION

[0074] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

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

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

[0077] S1, construct the sheet metal model and die model for bulging test;

[0078] S2, meshing the sheet metal model and the mold model;

[0079] S3, defining a property model and a 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;

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

[0081] S5, using the maximum punch force criterion and the strain path transformation criterion to identify the necking instability of the material along the thickness direction;

[0082] S6, characterizes the temperature field changes, downward displacement changes and thinning rate changes of the sheet metal model, and simulates and predicts the high-temperature forming limit curve of medium and thick plate materials.

[0083] In this embodiment, a sheet material model and a mold model can be obtained by modeling. By meshing the two models, the models can be divided into multiple grids with certain shapes and positional relationships, which makes it easier to simulate the deformation of the sheet material under the action of the mold. Furthermore, the property models and thermal material models of the two models are defined to determine the mechanical properties and thermodynamic properties of the material. Further, the interaction parameters between the mold and the sheet material are defined, including the friction coefficient, ambient temperature, initial temperature and thermal conductivity. Then, the maximum punch force criterion and the strain path transformation criterion are used to identify the necking instability of the material along the thickness direction. Finally, the test conditions are parameterized, including temperature field changes, downward displacement changes and thinning rate changes, to simulate and predict the sheet material.

[0084] Specifically, for S1:

[0085] The geometric model of the bulging experiment was constructed using the 3D modeling software Solidworks to model the male and female dies, blank holder, and sheet metal. The model should be identical in shape and size to the test die, and the file should be exported in the ".igs" format. The geometric dimensions and process parameters of the male and female dies and blank holder are as follows:

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

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

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

[0089] In order to obtain the strain and stress paths of the specimens under different conditions, the test uses specimens with different geometric dimensions. Figure 1 , the geometric model is shown in Figure 2 The sheet material adopts the method of changing the width of the sample to design 9 groups of different size samples, with a diameter of 180mm and a width range of 20mm to 180mm, with an interval of 20mm, and saved in the "igs" format.

[0090] For S2:

[0091] Meshing

[0092] In DYNAFORM sheet metal forming simulation software, BT shell elements are typically used for finite element simulation. Meshing primarily occurs in three different meshing formats: ToolMesh, PartMesh, and TriangleMesh. The ToolMesh format is the most commonly used. The ToolMesh format features a mix of triangles and quadrilaterals. Surfaces with minimal curvature are primarily quadrilateral, while areas with significant curvature changes and surface transitions have more triangular elements. This ensures a better fit and representation of the tool body's curved surfaces and geometry. DYNAFORM software also utilizes adaptive meshing technology, which allows for improved mesh quality through adjustments such as the maximum element size (Max.Size), minimum element size (Min.Size), element angle (Element Angle), and refinement level. Meshing also includes the option to redefine the mesh, automatically patch voids, and optimize outer edge meshes. Figure 3 shows the sheet metal meshing, with the number of elements gradually increasing as the forming process progresses. The mesh type is BT quadrilateral shell elements, with a mesh size of 5 mm and a minimum size of 1 mm.

[0093] For S3:

[0094] Material model selection

[0095] In sheet metal forming analysis, the mold is usually made of rigid material, and the sheet metal generally adopts rigid-plastic material, elastic-plastic material model, etc. Among them, the power exponential plastic material model, the thickness anisotropic elastic-plastic material model, the three-parameter Barlat material model, etc. are more suitable for thin sheet metal stamping forming analysis. Dynaform software comes with a variety of material models, and commonly used material models include material models 18, 24, 36, 37, and 125. However, they are all suitable for room temperature forming and not for high temperature forming processes. This simulation selected material model 106. The material parameters required for TC4 medium and thick plate were obtained through tensile testing and J-MAT pro simulation software. The parameters required for material model 106 are shown in Table 1. The rheological stress curves corresponding to different temperatures of the sheet metal were fitted using the Vocehardening law saturated stress hardening model.

[0096] Table 1 Parameters required for material model No. 106

[0097]

[0098] During the hot forming process, heat transfer, such as heat conduction, occurs between the sheet and the mold, necessitating the definition of thermal material models for both the sheet and the mold. Dynaform software offers six thermal material models. After comparing the parameters required for each model, thermal material model #6 was selected for both the sheet and the mold. H13 hot work die steel was selected as the mold material. The required thermal physical properties for the TC4 sheet and H13 hot work die steel thermal material models were obtained using J-MAT pro simulation software. The specific parameters are shown in Table 2.

[0099] Table 2 Parameters required for thermal material model

[0100]

[0101] For S4:

[0102] Define boundary and contact conditions

[0103] In the numerical simulation model for predicting the isothermal hot forming limit curve of high-strength steel plates, the die temperature is the same as the initial forming temperature of the sheet, and the effects of radiation and convection heat transfer with the surrounding environment on the sheet temperature are ignored. In cold die bulge forming tests, the limiting strain values under different strain states are typically determined by varying the specimen geometry and the friction coefficient between the sheet and the sheet. However, in the hot stamping process, effective control of the friction between the sheet and the die is difficult, as it depends not only on the forming temperature, the coating materials of the die and sheet, but also on factors such as the die surface roughness. Therefore, this paper adopts a fixed friction coefficient value and predicts the isothermal hot forming limit curve by varying the specimen geometry. The contact interface between the sheet and the die is defined as "surf-to-surf," with initial forming temperatures of 850°C, 880°C, 900°C, and 920°C, respectively, and the ambient temperature is set at 20°C. 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 phase removes a significant amount of heat, so the heat transfer coefficient was set to 2000 W / m²·K based on reference materials. The contact conditions included the friction coefficient and the interfacial contact 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 speed was set to 25 mm / s.

[0104] Table 3 Heat transfer coefficient at different temperatures

[0105]

[0106] For S5:

[0107] Determination of instability criteria

[0108] Dynaform software, a software specifically designed to simulate sheet metal stamping, is 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 recognize the necking of the material along the thickness direction. For elements that have already cracked, the solver will continue to calculate. Therefore, it is necessary to add a sheet metal instability judgment criterion after the solver. For room-temperature stamping of ordinary plastic materials, the program will calculate the corresponding FLD0 (the lowest point of the forming limit diagram) based on the material strain hardening exponent n value, sheet thickness t, and thickness anisotropy index r value entered by the user in the post-processing software using Keeler's formula (as shown in formula (1-1)), and generate the FLD curve according to formula (1-2).

[0109]

[0110]

[0111] However, Keeler's formula is extremely limited and cannot be used to calculate forming limit diagrams (FLDs) for other materials, such as high-strength steel, aluminum alloys, and magnesium alloys. Furthermore, the strain hardening exponent n and the thickness anisotropy index r of the material constantly change during high-temperature forming, resulting in large errors in the FLDs obtained using Keeler's formula. Titanium alloys are significantly affected by strain rate during forming, and the strain rate sensitivity index is crucial for their forming process. Using the software's built-in FLD function can produce significant errors. Therefore, it is necessary to find an appropriate instability criterion to determine the ultimate strain value of the element at 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 numerical simulation software to study the forming limits of materials.

[0112] ① Maximum punch force instability criterion:

[0113] As the punch presses the sheet metal, the punch force eventually reaches a maximum value as the punch displacement increases. The force then rapidly drops to zero. The moment the punch force reaches its maximum can be considered the moment of material instability, which is the maximum punch force instability criterion. The corresponding maximum principal strain value within the sheet metal plane at this moment can be considered the limiting principal strain value, and the second principal strain value is the limiting secondary strain value. Using the Dynaform post-processing software EtaPostProcessor, open the idx file, click on the chart to load the "rcforc" file, select "BLANK / 10_Punch," and select the Z-direction force component. This then derives a curve showing the relationship between the punch's motion time and the Z-direction force acting on the specimen. The moment when the punch force reaches its maximum value is found, and the corresponding primary and secondary strain values are recorded.

[0114] Figure 4 shows the punch force-time curves for specimens with sheet widths of 20 mm and 180 mm. By simulating cupping of sheets with different sheet widths, it was found that the maximum punch force criterion only applies to smaller sheet widths (20 to 80 mm). When the sheet width is relatively large (100 to 180 mm), the specimen exhibits a double-tension state, with the punch force increasing continuously with displacement and no peak value.

[0115] ② Maximum thinning rate judgment criteria

[0116] During the numerical simulation of bulging, when a grid cell in the sheet metal exhibits a thickness reduction rate exceeding 30%, it is considered that the sheet metal has undergone unstable fracture. The strain on the grid cell in the fractured region at this moment is extracted as the limiting strain value for this criterion, known as 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 unstable fracture will vary with different materials and strain paths. Furthermore, in the Dynaform software, it is very difficult to identify a single grid cell in the sheet metal that has reached the required thinning rate. Many researchers believe that in most cases, fracture has already occurred when deformation reaches the maximum thinning rate, making the limiting strain obtained using the maximum thinning rate criterion inaccurate. In summary, the maximum thinning rate criterion has significant limitations in obtaining the limiting strain, and is not used in this paper to determine unstable fracture in the sheet metal. In some embodiments of the present invention, the strain path transition criterion includes determining the limiting strain value as the strain corresponding to the inflection point where the stress state is transformed into a plane stress state based on the path transition diagram.

[0117] ③ Based on the strain path transformation criterion

[0118] like Figure 6 The strain path transition diagram shows that at this point, the stress state has transitioned to a plane stress state, and the strain corresponding to the inflection point of the transition is the ultimate strain value. Simulating nine sheet metal widths, post-processing results show that for sheet metal widths ranging from 20 to 80 mm, the punch force-time curve exhibits a maximum punch force, but the strain path lacks an inflection point. Therefore, the maximum punch force criterion is selected as the instability criterion. For sheet metal widths between 100 and 180 mm, the post-processing results show no maximum force, but the strain path exhibits an inflection point. Therefore, the strain path transition criterion is selected as the instability criterion.

[0119] The specimens were determined using a strain path method. Researchers believe that concentrated instability caused by load is due to the appearance of a plane strain state. Numerical simulation results show that the strain path of the maximum strain unit often undergoes a linear, steady increase to a plane strain state. This process produces a necking point, where the strain suddenly shifts to a plane strain state. As shown in the figure, the maximum principal strain initially rises gently, then suddenly increases rapidly at the point of contraction, while the minimum principal strain increases slowly. The turning point is where the specimen necks and ruptures. This method is only applicable to specimens with relatively wide widths.

[0120] For S6:

[0121] Simulation performance characterization

[0122] 1. Changes in sheet temperature field

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

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

[0125] 2. Changes in downward displacement

[0126] (1) According to the mold parameters we set, 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 intuitively analyzed;

[0128] 3. Changes in thinning rate

[0129] After the result export and analysis, by controlling the time, the change of sheet metal thinning rate in different stamping stages can be obtained.

[0130] Finally, the simulation results are analyzed:

[0131] In order to study the influence of the initial deformation temperature and friction coefficient of the sheet metal on the sheet metal forming quality, a sheet metal with a size of 180×180 mm was selected, and the initial deformation temperature of the sheet metal was set to 850℃, 880℃, 900℃ and 920℃, the mold temperature was 750℃, the forming speed was 25mm / s, and the friction coefficients were 0.35, 0.4, 0.45 and 0.5 respectively. The strain path transformation criterion was used to find the number of steps corresponding to the critical rupture moment of the maximum principal strain unit. The temperature field, downward displacement and thinning rate of the sheet metal under different deformation conditions at the critical rupture moment were compared and analyzed.

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

[0133] The initial forming temperature of the sheet metal was set at 850°C, and different friction coefficients were set: 0.35, 0.4, 0.45, and 0.5. Figure 7 shows the temperature field cloud plots corresponding to the critical fracture moment of the sheet metal under different friction coefficients. Comparing the temperature fields under different friction coefficients reveals that due to heat conduction between the sheet metal and the die and blank holder, the sheet metal temperature under the blank holder is almost always close to 750°C, similar to the die temperature, for different friction coefficients. However, the temperature field in the forming area is affected by the stamping speed, and the stamping time varies significantly. Therefore, the temperature field corresponding to the forming part of the sheet metal in contact with the punch at critical fracture varies significantly. The temperatures at the center of the sheet metal contacting the punch are 770°C, 769°C, and 768°C, respectively, while the temperatures at the parts farther from the punch are 758°C, 756°C, and 754°C, respectively. As the friction coefficient increases, the temperature in the center of the sheet metal contacting the punch is higher, and the temperature decreases with distance from the center. On the one hand, the mold cools the sheet during the forming process. Due to the closer contact between the center of the sheet and the mold and the higher coefficient of friction, the cooling effect in this area is less than that at the edges. On the other hand, the varying thickness of the sheet results in uneven heat dissipation, which creates a non-uniform temperature field. Thinner areas cool faster, while thicker areas cool more slowly, creating a temperature gradient in the transition zone. This temperature change causes changes in internal stress. During thermal deformation, stress is sensitive to temperature changes, so transition zones with large temperature differences produce significant stress concentrations.

[0134] Figure 8 shows a cloud diagram of the sheet metal's downward displacement corresponding to the critical rupture moment for different friction coefficients. The maximum downward displacement corresponding to the critical rupture moment for different friction coefficients is 36.75mm, 36.78mm, 36.79mm, and 36.82mm, respectively. As the friction coefficient increases, the friction between the sheet metal and the die increases. This increased friction requires greater force to overcome friction during the forming process, causing the sheet metal to sink deeper into the die. In other words, the maximum downward displacement increases with the friction coefficient.

[0135] Figure 9 is a cloud diagram of the thinning rate corresponding to the critical rupture moment under different friction coefficients. The maximum thinning rates corresponding to the critical rupture moment 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 rupture moment of the sheet metal gradually increases, the load that the sheet metal can withstand in the thickness direction increases, and the corresponding thinning rate increases. Under the same thickness, the greater the friction coefficient, the easier it is for the workpiece to crack, the greater the material thinning rate, and under the same specifications, the resulting workpiece is lighter. Therefore, during the forming process, we should add lubricant to keep the friction coefficient at an appropriate value as needed.

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

[0137] When studying the effect of the initial forming temperature of the sheet metal on the forming process, sheet metal of the same specifications was selected. To ensure that it was not affected by the forming speed, the friction coefficient was uniformly set to 0.4. The initial deformation temperatures of the sheet metal were 850°C, 880°C, 900°C, and 920°C, respectively. Figure 10 shows the temperature field cloud corresponding to the critical rupture moment 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 rupture moment. However, due to heat transfer and conduction between the sheet metal and the mold and in the cooling system, the temperature field corresponding to the sheet metal at critical rupture does not differ much. The temperature is highest at the center of the contact area between the sheet metal and the punch, and the temperature decreases as it moves away from the center. The temperature distribution is relatively uniform near the center.

[0138] Figure 11 shows the downward displacement contours corresponding to the critical fracture moment of the sheet metal at different initial deformation temperatures. It can be seen that the maximum downward displacements of the sheet metal at the critical fracture moment for different initial deformation temperatures are 31.82 mm, 36.20 mm, 36.39 mm, and 30.87 mm, respectively. The maximum downward displacement increases with increasing initial deformation temperature, reaching a maximum at 900°C, and then decreases with increasing initial deformation temperature.

[0139] Figure 12 shows a cloud plot of the thinning rate corresponding to the critical rupture moment for different initial deformation temperatures. It can be seen that the maximum thinning rates corresponding to different initial forming temperatures at the critical rupture moment are 39.58%, 39.98%, 55.12%, and 49.02%, respectively. Following the same pattern as the downward displacement, the thinning rate increases with increasing initial deformation temperature. The thinning rate reaches its maximum at 900°C. Thereafter, the thinning rate decreases with increasing initial deformation temperature. The area with the highest thinning rate is located at the contact center between the punch and the sheet.

[0140] ③Establishment of hot forming limit diagram of TC4 sheet

[0141] The forming temperature is set to 850℃ and the forming speed is set to 25mm / s. The hemispherical punch bulging simulation is performed on the sheet. The post-processing results are analyzed using the criterion combining the maximum punch force and the strain path transformation. The critical instability moment of different sheet widths is found, and the principal strain and secondary strain cloud diagrams corresponding to this moment are analyzed. Figure 13 The principal strain nephogram corresponding to the critical fracture when the sheet width is 20mm and 180mm. Figure 14 It is the secondary strain cloud corresponding to the critical fracture when the sheet width is 20mm and 180mm.

[0142] The major and minor strain points under different strain paths were extracted through analysis, as shown in Table 4. The data were imported into Origin data processing software and fitted to obtain the hot forming limit diagram of TC4 sheet (see Table 4). Figure 15 The FLD curve is fitted with a quadratic term to show a parabolic shape.

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

[0144]

[0145] An embodiment of the present invention provides a device for simulating and predicting the high-temperature forming limit curve of medium and thick plate materials. The device embodiment can be implemented through software, or through hardware or a combination of software and hardware. From the hardware level, a hardware architecture diagram of an electronic device in which a device for simulating and predicting the high-temperature forming limit curve of medium and thick plate materials is provided in an embodiment of the present invention, in addition to a processor, memory, network interface, and non-volatile memory, the electronic device in the embodiment where the device is located can generally also include other hardware, such as a forwarding chip responsible for processing messages, etc. Taking software implementation as an example, as a device in a logical sense, it is formed by the CPU of the electronic device where it is located reading the corresponding computer program in the non-volatile memory into the memory for execution. A device for simulating and predicting the high-temperature forming limit curve of medium and thick plate materials provided in this embodiment includes:

[0146] The first unit is used to build the sheet metal model and die model for bulging test;

[0147] The second unit is used to perform meshing processing 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; wherein the property model includes multiple sets of property parameters, and the thermal material model includes multiple sets of thermal parameters;

[0149] Unit 4 is used to define the friction coefficient, ambient temperature, initial temperature and thermal conductivity between the model and the mold model;

[0150] Unit 5 is used to identify necking instability along the thickness direction of the material using the maximum punch force criterion and the strain path transition criterion;

[0151] The sixth unit is used to characterize the temperature field changes, downward 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 should be understood that the structure illustrated in the embodiments of the present invention does not constitute a specific limitation on a device for simulating and predicting the forming limit curve of a medium-thick plate material at high temperature. In other embodiments of the present invention, a device for simulating and predicting the forming limit curve of a medium-thick plate material at high temperature may include more or fewer components than illustrated, or may combine or separate certain components, or employ a different component arrangement. The illustrated components may be implemented in hardware, software, or a combination of both.

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

[0154] An embodiment of the present invention also provides 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 a method for simulating and predicting the high-temperature forming limit curve of medium and thick plate materials in any embodiment of the present invention.

[0155] An embodiment of the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the processor executes a method for simulating and predicting a high-temperature forming limit curve of a medium and thick plate material in any embodiment of the present invention.

[0156] Specifically, a system or device equipped with a storage medium can be provided, on which software program codes that implement the functions of any of the above-mentioned embodiments are stored, and a computer (or CPU or MPU) of the system or device can be enabled to read and execute the program codes stored in the storage medium.

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

[0158] Examples of storage media for providing 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, the program code can be downloaded from a server computer via a communication network.

[0159] In addition, it should be clear that the functions of any of the above embodiments can be achieved not only by executing the program code read by the computer, but also by enabling the operating system operating on the computer to complete part or all of the actual operations based on the instructions of the program code.

[0160] In addition, it can be understood that the program code read from the storage medium is written into a memory provided in an expansion board inserted into the computer or into a memory provided in an expansion module connected to the computer, and then based on the instructions of the program code, a CPU installed on the expansion board or expansion module is enabled to perform part or all of the actual operations, thereby realizing the functions of any of the above embodiments.

[0161] It should be noted that, in this article, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprising a ..." do not exclude the presence of other identical factors in the process, method, article or device comprising the elements.

[0162] Those skilled in the art will understand that all or part of the steps of implementing the above-mentioned method embodiment can be completed by hardware related to program instructions, and the aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it executes the steps of the above-mentioned method embodiment; and the aforementioned storage medium includes: ROM, RAM, disk or optical disk, etc. Various media that can store program codes.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for simulating and predicting the high-temperature forming limit curve of medium and thick plate materials, characterized in that: include: Construct sheet metal model and die model for bulging test; Performing meshing processing on the sheet metal model and the mold model; Defining a property model and a 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; defining a friction coefficient, an ambient temperature, an initial temperature, and a thermal conductivity between the model and the mold model; The maximum punch force criterion and the strain path transformation criterion are used to identify the necking instability of the material along the thickness direction. The temperature field changes, downward displacement changes and thinning rate changes of the sheet metal model are characterized, and the high-temperature forming limit curve of medium and thick plate materials is simulated and predicted.

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, thermal expansion coefficient, viscosity parameter and viscous parameter obtained through tensile testing and simulation.

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: The maximum punch force criterion is that after the punch force reaches its maximum and then drops to zero, the moment when the punch force is maximum is determined as the instability moment, and the corresponding maximum principal strain value in the sheet plane at this moment is regarded as the limit principal strain value, and the second principal strain value is the limit secondary strain value.

5. The simulation prediction method according to claim 1, characterized in that: The strain path transformation criterion includes: when the stress state is transformed into the plane stress state according to the path transformation diagram, the strain corresponding to the inflection point where the transformation occurs is determined as the limit strain value.

6. The simulation prediction method according to claim 1, characterized in that: Characterizing the temperature field change of the sheet metal model, including: Setting convection parameters and heat transfer parameters of the sheet metal model and the mold model; The temperatures and temperature differences of the sheet metal model and the die model during the stamping process are determined.

7. The simulation prediction method according to claim 1, characterized in that: The downward displacement change is characterized by the following method: According to the set mold parameters, set the downward displacement; The changes of sheet metal during stamping are analyzed by controlling the downward displacement.

8. A device for simulating and predicting the high-temperature forming limit curve of medium and thick plate materials, characterized in that: For implementing the method according to any one of claims 1 to 7, the apparatus comprises: The first unit is used to build the sheet metal model and die model for bulging test; The second unit is used to perform meshing processing on the sheet metal model and the mold model; A third unit is used to define a property model and a 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; A fourth unit is used to define a friction coefficient, an ambient temperature, an initial temperature, and a thermal conductivity between the model and the mold model; Unit 5 is used to identify necking instability along the thickness direction of the material using the maximum punch force criterion and the strain path transition criterion; The sixth unit is used to characterize the temperature field change, downward displacement change and thinning rate change of the sheet metal model, and to simulate and predict the high-temperature forming limit curve of medium and thick plate materials.

9. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the method according to any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to execute the method according to any one of claims 1 to 7.

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