Variable-temperature deep drawing-rapid air expansion composite forming method for thick titanium alloy plate

Abstract

The invention relates to the technical field of die forming, in particular to a variable-temperature deep drawing-rapid air expansion composite forming method for a thick titanium alloy plate. The method comprises the steps that a model of a stamping die of the end socket is established, and the thickness of a to-be-stamped plate is set; limiting conditions in the stamping process are set, and a variable-temperature deep drawing model is obtained; establishing a Backoften constitutive equation, and determining strain rate sensitive indexes and strength coefficients at different temperatures according to the material strength at different temperatures; performing a finite element simulation process according to the strain rate sensitive index and the strength coefficient to obtain a superplastic inflatable model; according to the variable-temperature drawing model and the superplastic air expansion model, a variable-temperature drawing-rapid air expansion model is established; representing the simulation performance of the variable-temperature drawing-rapid air expansion model, and analyzing a drawing result and an air expansion result; and determining a test reference according to an analysis result, and carrying out a variable-temperature drawing-rapid inflation composite forming test. According to the scheme, excessive attempts of experiments can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of die forming, and particularly relates to a variable-temperature drawing-rapid gas inflation composite forming method for thick-plate titanium alloy. Background Art

[0002] During the entire process of hot isothermal drawing forming of traditional titanium alloy head parts, there are defects such as cracking at the bottom of the head and wrinkling at the top edge, and there are also problems such as uneven deformation distribution; while traditional gas inflation forming technology has problems such as excessive wall thickness reduction, poor wall thickness uniformity, and easy deterioration of tissue properties. Since titanium alloy has high strength and elongation at high temperatures, variable-temperature drawing under the condition of non-uniform temperature field and rapid gas inflation forming under the condition of high-pressure inert gas can solve the above problems to a certain extent.

[0003] Currently, to complete the drawing forming, multiple experiments are required, and multiple experiments will bring the problem of too high cost. Therefore, there is an urgent need for a simulation prediction method that can reduce excessive attempts in experiments and minimize the cost, so as to achieve the purpose of cost reduction and efficiency improvement. Summary of the Invention

[0004] An embodiment of the present invention provides a variable-temperature drawing-rapid gas inflation composite forming method for thick-plate titanium alloy, which can reduce excessive attempts in experiments and minimize the cost, so as to achieve the purpose of cost reduction and efficiency improvement.

[0005] An embodiment of the present invention provides a variable-temperature drawing-rapid gas inflation composite forming method for thick-plate titanium alloy, which is characterized by including:

[0006] Establish a model of the stamping die for the head and set the thickness of the blank to be stamped.

[0007] Set the limiting conditions during the stamping process to obtain a variable-temperature drawing model; wherein, the limiting conditions include the punch movement condition, the blank holder load condition, the material properties of the blank to be stamped, the contact condition, the initial condition, the boundary condition, the load working condition, and the operation parameter condition.

[0008] Establish the Backoften constitutive equation and determine the strain rate sensitivity index and strength coefficient at different temperatures according to the material strength at different temperatures.

[0009] Conduct a finite element simulation process according to the strain rate sensitivity index and the strength coefficient to obtain a superplastic gas inflation model.

[0010] Establish a variable-temperature drawing-rapid gas inflation model according to the variable-temperature drawing model and the superplastic gas inflation model.

[0011] Characterize the simulation performance of the variable-temperature deep drawing - rapid gas inflation model, and analyze the deep drawing results and gas inflation results; among them, the simulation performance includes Mises stress change, strain change analysis, thinning rate change, and thinning rate change;

[0012] Determine the test reference according to the analysis results, and conduct the variable-temperature deep drawing - rapid gas inflation composite forming test.

[0013] In a possible design, the punch motion conditions include stamping speed, stamping distance, stamping time, and return time.

[0014] In a possible design, the blank holder load conditions include the initial value of the blank holding force, the initial time for tightly pressing the blank, and reaching the blank holding force.

[0015] In a possible design, the material properties include density, Poisson's ratio, and thermophysical properties.

[0016] In a possible design, the contact conditions define the mutual relationship between contact bodies, including the definition of the punch rigid body and the definition of the blank holder rigid body. The definition of the punch rigid body includes that when defining the punch rigid body contact body, a displacement loading control method is adopted. The definition of the blank holder rigid body includes that when defining the blank holder rigid body contact body, the blank holder adopts a load loading control method, and a control node is required to control the load and displacement of the blank holder.

[0017] In a possible design, the initial conditions include the temperatures of the upper and lower surfaces of the sheet metal to be stamped;

[0018] The boundary conditions include the fixed displacement constraint of the blank holder control node that only allows the node to move along the pressing direction and the load application of the blank holder control node;

[0019] The load condition is used to realize the contact analysis process between the punch, the blank holder, and the die;

[0020] The operation parameter conditions are used to select and call the set initial conditions, contact conditions, and load conditions, and are also used to set the analysis type and define the analysis results.

[0021] In a possible design, establishing the Backoften constitutive equation and determining the strain rate sensitivity index and strength coefficient at different temperatures according to the material strength at different temperatures includes:

[0022] Derive the constitutive equation to obtain

[0023] Among them, the constitutive equation is m is the strain rate sensitivity index, and K is the strength coefficient;

[0024] Collect the stress σ and strain rate in the deep drawing data of the material at different temperatures

[0025] Determine the m value according to lnε and lnσ at different temperatures, and determine the strength coefficient according to the m value and the constitutive equation

[0026] In a possible design, the finite element simulation is performed according to the strain rate sensitivity index and the strength coefficient to obtain a superplastic gas bulging model, including:

[0027] Establish a geometric model according to the strain rate sensitivity index and the strength coefficient

[0028] Apply fixed boundary conditions to the elements outside the deformation area of the geometric model, and perform load condition settings to obtain a superplastic gas bulging model

[0029] In a possible design, the variable temperature deep drawing-rapid gas bulging model is established according to the variable temperature deep drawing model and the superplastic gas bulging model, including:

[0030] Export the analysis state data of the last step of the variable temperature deep drawing model, and use the analysis state data as the previous analysis state of the superplastic gas bulging model to complete all model simulation analyses

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

[0032] During the entire process of hot isothermal deep drawing forming of traditional titanium alloy head parts, there are defects such as cracking at the bottom of the head and wrinkling at the top edge, and there are also problems such as uneven deformation distribution; while traditional gas bulging forming technology has problems such as excessive wall thickness reduction, poor wall thickness uniformity, and easy deterioration of tissue properties. Since titanium alloy has high strength and elongation at high temperatures, variable temperature deep drawing under non-uniform temperature field conditions and rapid gas bulging forming under high-pressure inert gas conditions can solve the above problems to a certain extent. In order to reduce excessive attempts in experiments and minimize costs, so as to achieve cost reduction and efficiency increase and efficiently complete our requirements. On this basis, we use numerical simulation methods to analyze the deep drawing process of non-uniform temperature field and the superplastic bulging process under high-pressure gas, which is of great significance for predicting the form of defects and studying the forming law. In this paper, the finite element software MSC.Marc is used to simulate and analyze the non-uniform temperature deep drawing-rapid gas bulging process of the head part, and the characteristics of the non-uniform temperature deep drawing-rapid gas bulging composite forming of the head part are studied by numerical simulation method, and the wall thickness distribution law, stress and strain distribution law and unit thickness change of the head part under different temperature gradients are analyzed and summarized Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0034] Figure 1 It is a schematic diagram of mold assembly provided by an embodiment of the present invention;

[0035] Figure 2 It is a diagram showing the placement relationship between the sheet metal and the mold after meshing provided by an embodiment of the present invention;

[0036] Figure 3 It is a schematic diagram of boundary conditions provided by an embodiment of the present invention;

[0037] Figure 4 It is a diagram of the results of variable-temperature deep drawing provided by an embodiment of the present invention;

[0038] Figure 5 It is a diagram showing the change of Mises stress during the deep drawing process provided by an embodiment of the present invention;

[0039] Figure 6 It is another diagram showing the change of Mises stress during the deep drawing process provided by an embodiment of the present invention;

[0040] Figure 7 It is a diagram showing the change of the downward displacement during the deep drawing process provided by an embodiment of the present invention;

[0041] Figure 8 It is a diagram showing the change of the unit thickness during the deep drawing process provided by an embodiment of the present invention;

[0042] Figure 9 It is a diagram showing the change process of the equivalent strain during the deep drawing process provided by an embodiment of the present invention;

[0043] Figure 10 It is a diagram showing the change of the displacement in the X direction provided by an embodiment of the present invention;

[0044] Figure 11 It is a diagram showing the change of the unit thickness of superplastic forming provided by an embodiment of the present invention. Detailed implementation manners

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] An embodiment of the present invention provides a variable-temperature drawing-rapid gas inflation composite forming method for thick-plate titanium alloy, which is characterized by including:

[0047] Step 1: Establish a model of the stamping die for the head, and set the thickness of the sheet material to be stamped.

[0048] Step 2: Set the limiting conditions during the stamping process to obtain a variable-temperature drawing model. Among them, the limiting conditions include the punch movement condition, the blank holder load condition, the material properties of the sheet material to be stamped, the contact condition, the initial condition, the boundary condition, the load working condition, and the operation parameter condition.

[0049] Step 3: Establish the Backoften constitutive equation, and determine the strain rate sensitivity index and strength coefficient at different temperatures according to the material strength at different temperatures.

[0050] Step 4: Perform a finite element simulation process according to the strain rate sensitivity index and strength coefficient to obtain a superplastic gas inflation model.

[0051] Step 5: Establish a variable-temperature drawing-rapid gas inflation model according to the variable-temperature drawing model and the superplastic gas inflation model.

[0052] Step 6: Characterize the simulation performance of the variable-temperature drawing-rapid gas inflation model, and analyze the drawing result and the gas inflation result. Among them, the simulation performance includes Mises stress change, strain change analysis, thinning rate change, and thinning rate change.

[0053] Step 7: Determine the test reference according to the analysis result, and conduct a variable-temperature drawing-rapid gas inflation composite forming test.

[0054] Regarding Step 1, the stamping model of the head is as Figure 1 shown, and its basic dimensional parameters are listed in Table 1. The stamping process of the head is a combination of the drawing and bulging processes. The blank undergoes a complex deformation path during the forming process. The bottom is mainly subjected to biaxial tensile stress, generating biaxial tensile strain, and the blank is thinned; the flange part is subjected to circumferential compressive stress and radial compressive stress, generating biaxial compressive strain and thickening. During the flow of the blank, due to the action of the blank holder, repeated bending and reverse bending will occur, and the deformation is relatively severe.

[0055] Table 1 Die Geometric Parameters

[0056]

[0057] In the MARC forming simulation software, since the sheet thickness is relatively thick, we expand the thickness to 14 mm by means of entity expansion. The element type is set as solid elements, the die is a rigid body, and the sheet is a deformable body. Since the thickness change cannot be displayed in the post-processing results of solid elements, we add a three-dimensional solid shell structure on the basis of the sheet solid elements and adopt element type 185 to show the wall thickness change during the warm drawing process. The principle of the non-uniform temperature field is to increase the temperature of the originally thick part to enhance its deformation ability and decrease the temperature of the originally thin part to weaken its deformation ability.

[0058] In some embodiments of the present invention, the punch motion conditions include stamping speed, stamping distance, stamping time, and return time.

[0059] In MSC.Marc, the table definition function is often used in the processes of defining motion characteristics, boundary conditions, material characteristics, etc. The table definition function is often used to represent the function of some variables with respect to other parameters, such as time, increment, temperature, and plastic strain, etc. The function values are defined as the vertical axis of the table, and the independent variables of the function are defined as the horizontal axis. A total of 4 tables are used in the finite element simulation process of the drawing forming of the head part, namely the punch motion table definition, the blank holder load table definition, the 850 - 0.01 plastic strain table definition, and the 880 - 0.01 plastic strain table definition.

[0060] Punch motion table definition

[0061] The speed of the punch motion represents the magnitude of the stamping speed. For the convenience of research, the punch motion is described by the time-displacement table, and the slope in the time-displacement table is the stamping speed. In the actual forming test, the punch motion is carried out slowly. Therefore, usually in the finite element analysis, the motion speed is artificially increased to reduce the simulation time and improve the simulation efficiency. The increased motion speed is called the virtual stamping speed, and the stamping speeds set in this simulation all refer to the virtual stamping speed. The stamping speed is set to 10 mm / s. The punch punches downward by 100 mm and lasts for 10 s, and then returns, lasting for 5 s. Therefore, the punch motion values that can be input and added are: 0 0 1 0 10 100 15 0.

[0062] In some embodiments of the present invention, the blank holder load conditions include the initial value of the blank holding force, the time for initially clamping the blank, and the attainment of the blank holding force.

[0063] Blank holder load table definition

[0064] The magnitude of the binder load is usually obtained by multiplying the corresponding value of the curve in the table by a preset value. The initial value of the blank-holding force is 0. In the simulation, it is specified that the binder can clamp the blank within 0.8 s initially, reaching a blank-holding force of 4000 N. Therefore, the input punch motion values are: 0 0 0.8 4 15 0. The defined binder load curve. Add a node at (300, 65, 0).

[0065] In some embodiments of the present invention, the material properties include density, Poisson's ratio, and thermophysical properties.

[0066] The definition of material properties mainly includes two parts: inputting the content of material characteristics and applying the material properties to the elements. The definition of material properties is to define the physical properties of materials, such as density, Poisson's ratio, etc., and some thermophysical properties. The MSC.Marc numerical simulation software comes with a large number of material properties in the MSC.Mentat database, which can be extracted and used as needed or the material properties can be established independently according to experimental data.

[0067] The key to the definition of material properties is the stress-strain relationship. The stress-strain relationship can be achieved by two methods. The first is to directly define the stress-strain relationship curve through data points; the other is to use the constitutive equation of common materials to represent the stress-strain relationship of materials. During the deep drawing forming process of TC4 medium-thick plates, it is necessary to accurately master the change of the deformation resistance of the material at different temperatures, that is, the flow stress of TC4 medium-thick plates at different temperatures and deformation rates. Based on the experimental data provided by the high-temperature tensile test of TC4 plates, this paper organizes the curve data measured in the high-temperature tensile test of TC4 medium-thick plates and substitutes them into MARC.

[0068] In some embodiments of the present invention, the contact conditions define the mutual relationship between contacting bodies, including the definition of the punch rigid body and the definition of the binder rigid body. The definition of the punch rigid body includes that when defining the punch rigid body contacting body, a displacement loading control method is adopted. The definition of the binder rigid body includes that when defining the binder rigid body contacting body, the binder adopts a load loading control method, and a control node is required to control the load and displacement of the binder.

[0069] During the numerical simulation of the deep drawing forming of the head part, the sheet metal undergoes a loading and unloading process. During loading, the sheet metal deforms, and during unloading, the sheet metal will experience springback, resulting in changes in the shape and size of the sheet. First, define the blank deforming body contact body, and the deforming body contact definition is applied to all elements. Then, define the punch rigid body contact body, the die rigid body contact body, and the blank holder rigid body contact body in sequence. When defining the rigid body contact body, not only the motion form of the rigid body is defined, but also the temperature of the rigid body is defined. The rigid body temperature is the die temperature, which is set to 20 °C. It should be noted that 1) when defining the punch rigid body contact body, the displacement loading control method is adopted. Enter -1 in the corresponding text box in the Y direction, and then select the punch displacement table in the table definition. 2) When defining the blank holder rigid body contact body, the blank holder adopts the load loading control method, and a control node is required to control the load and displacement of the blank holder. Therefore, when setting the blank holder rigid body contact body, a node needs to be added in advance. In this way, when defining the blank holder contact body attributes, the added node is used as the control node, and the node load loading control method is adopted.

[0070] The key to contact definition lies in the contact table definition. The contact table defines the mutual relationship between contact bodies. To avoid contacts that are simply impossible to occur between contact bodies, the contact table is used to determine the contact pairs between multiple contact bodies. In the simulation of the deep drawing forming of the head part, a total of three pairs of contacts are involved: the contact between the punch and the sheet metal, the contact between the blank holder and the sheet metal, and the contact between the die and the sheet metal.

[0071] In some embodiments of the present invention, the initial conditions include the temperatures of the upper and lower surfaces of the sheet metal to be stamped;

[0072] The boundary conditions include the fixed displacement constraint of the blank holder control node that only allows the node to move along the pressing direction and the application of the blank holder control node load;

[0073] The load condition is used to implement the contact analysis process between the punch, the blank holder, and the die;

[0074] The job parameter condition is used to select and call the set initial conditions, contact conditions, and load conditions, and is also used to set the analysis type and define the analysis results.

[0075] Definition of Initial Conditions

[0076] Since the temperature of the sheet metal deformer cannot be defined at the contact part, it needs to be defined in the initial conditions. The definition of the initial conditions includes two parts: what kind of initial conditions to apply and where to apply them. When defining the temperature of the sheet metal deformer, a non-uniform temperature distribution is adopted, with the upper surface set at 850 °C and the lower surface set at 880 °C, and the temperature is directly added to all unit nodes. It should be noted that a control node is added when defining the load loading control method of the blank holder contact body, and this control node for controlling the movement and load of the blank holder needs to be removed after the initial conditions are added to all nodes.

[0077] Definition of Boundary Conditions

[0078] Boundary conditions, also known as support conditions, mainly include two parts: what kind of boundary conditions to apply and how to apply the boundary conditions. A total of 2 boundary conditions are required for the numerical simulation of the deep drawing forming of the head part, which are used for the fixed displacement constraint of the blank holder control node and the load application of the blank holder control node respectively. When defining the boundary condition of the fixed displacement constraint of the blank holder control node, the displacements in the X and Z directions and the rotations in the X, Y, and Z directions are all set to 0, and only the movement in the Y direction is allowed, acting on the control node. When defining the boundary condition of the load application of the blank holder control node, the load in the Y direction is set in the Force Y selection box, the magnitude and direction of the blank holding force are entered in the text box, and the predefined blank holder load table is selected in the Table.

[0079] Definition of Load Conditions

[0080] During the deep drawing forming process of the head part, there is one loading, so a Loadcases can be defined in the load conditions to realize the contact analysis process between the punch, the blank holder, and the die. When loading the boundary conditions, select the predefined fixed displacement constraint and load constraint boundary conditions of the blank holder. When setting the contact, select the predefined interaction contact relationship between the blank deformer and the die. When defining the solution control card, the maximum number of iterations needs to be determined. To ensure the smooth progress of the simulation, some specified regulations also need to be set artificially, such as specifying that the solver forces the solution when non-positive definiteness appears, continuing the next analysis when non-convergence occurs in the increment step, and at the same time selecting the modified Newton-Raphson method for calculation. Finally, the overall load time needs to be set. When determining the stepping program, if a fixed time step is selected, the number of steps needs to be input, and if an adaptive time step is selected, it is not required. It should be noted that the overall load time specifying the working condition definition process should correspond to the time of the punch loading history curve.

[0081] Definition of Job Parameters and Submission for Execution

[0082] As the last step before submitting a job for execution, the job parameters need to be defined. Not only can you choose to call the pre-set initial conditions, contact conditions, load cases, etc., but you also need to set the analysis type and define the analysis results. Set the defined initial conditions and load cases, select the initial contact, specify the friction type as Coulomb Bilinear (Displacment), set it to 0.2. In the calculation result control window, select the analysis results to be output and output them to the Marc post-processing file. After setting all the parameters, check whether there are any errors in the job task. When the prompt check result is: "INFO: Found 0 errors and 0 warnings", it means there are no errors or warnings, and then you can submit the job to start the calculation and perform the simulation.

[0083] In some embodiments of the present invention, the Backoften constitutive equation is established, and according to the material strength at different temperatures, the strain rate sensitivity index and strength coefficient at different temperatures are determined, including:

[0084] Derive the constitutive equation to obtain

[0085] where the constitutive equation is m is the strain rate sensitivity index, and K is the strength coefficient;

[0086] Collect the stress σ and strain rate in the drawing data of the material at different temperatures

[0087] Determine the value of m according to lnε and lnσ at different temperatures, and determine the strength coefficient according to the value of m and the constitutive equation.

[0088] Establishment of the Backoften constitutive equation

[0089] The value of m is the strain rate sensitivity index, which is used to describe the relationship between the deformation resistance and the strain rate during the deformation of the material. It is a very important concept in the field of superplastic forming. The value range of m is generally at least 0.3 and at most 0.9. When the m value of the material is greater than 0.3, the material is generally considered to have superplasticity. The larger the m value, the greater the degree to which the deformation resistance is affected by the strain rate. During the deformation of the material, once local necking occurs, the strain rate at this point will change rapidly. Since the deformation resistance of the material is greatly affected by the strain rate, it will hinder the continued development of the necking at this point and cause the transfer of the necking. Therefore, the material will continue to deform, making the material have superplasticity. The value of m is a parameter in the Backoften constitutive equation. Taking the derivative of both sides of the constitutive equation gives:

[0090]

[0091] The specified true strain is 0.3, and the strengths at various temperatures are collected as shown in Table 2. Take lnσ and As shown in Table 3.

[0092] Table 2 Strengths at a true strain of 0.3

[0093]

[0094]

[0095] Table 3 Take lnσ and

[0096]

[0097] Import the data in Table 3 into the origin software. With as the abscissa and lnσ as the ordinate, plot the data at each temperature in the form of a scatter plot, use data processing software to fit the data points, and solve the slopes of each fitted line as Figure 5 shown. From the fitting results, the m values at each temperature can be obtained. Among them, the m value at 880 °C is the highest, which is 0.32. When the m value is greater than 0.3, we consider that the material has superplasticity. The TC4 high-temperature titanium alloy is a high-temperature titanium alloy for long-term use at high temperatures, and its superplasticity change is consistent with the analysis result of the elongation. When the temperature reaches around 900 °C, the material begins to undergo a phase change, so the superplasticity of the material decreases at this time.

[0098] Next, solve for the K value. Substitute the data in Table 3 into the original analytical formula of the Backoften equation respectively to obtain the K value as shown in Table 4.

[0099] Table 4 m values and K values

[0100]

[0101] Substitute the m value and the K value into the equation respectively to obtain the constitutive equations at each temperature as shown in Table 5.

[0102] Table 5 m values and K values

[0103]

[0104] In some embodiments of the present invention, according to the strain rate sensitivity index and the strength coefficient, a finite element simulation is performed to obtain a superplastic gas bulging model, including:

[0105] Establish a geometric model according to the strain rate sensitivity index and the strength coefficient;

[0106] Apply fixed boundary conditions to the elements outside the deformation region of the geometric model, and set the load conditions to obtain a superplastic gas bulging model.

[0107] Before performing finite element simulation, the model needs to be simplified first. Compared with forming processes such as stamping, the die for superplastic forming is simple and does not require an independent punch. Only a closed space needs to be formed by the sheet and the die. Therefore, before performing finite element simulation, the sheet and the die are constructed in a 3D modeling software as Figure 6 shown.

[0108] Import the model into MARC to divide the mesh. Select the geometric feature of the sheet as a 3D solid shell, and set the thickness of the sheet to 14 mm, which can ensure both the accuracy of the results and the calculation speed. Since the constitutive equation of the metamaterial uses the rigid-plastic constitutive equation, the power-law model is selected for the model. The M value and K value of the material at 880 °C cause a large degree of deformation in the superplastic forming material. Therefore, the elastic-plastic constitutive equation cannot meet the deformation degree of the material, so it is input into Marc.

[0109] Boundary condition setting and load condition setting

[0110] Superplastic forming requires a closed space, and the transmission medium is an inert gas. Therefore, fixed boundary conditions need to be applied to the elements outside the deformation area, and distributed forces on the element surface are applied to the elements in the deformation area to simulate the action of the actual air pressure. The placement of the actual die and the sheet after mesh division is as Figure 2 shown, and the boundary conditions are as Figure 3 shown.

[0111] In some embodiments of the present invention, according to the variable-temperature deep drawing model and the superplastic gas bulging model, a variable-temperature deep drawing - rapid gas bulging model is established, including:

[0112] Export the analysis state data of the last step of the variable-temperature deep drawing model, and use the analysis state data as the previous analysis state of the superplastic gas bulging model to complete the full model simulation analysis.

[0113] The basic process is as follows:

[0114] 1) Scan the results of a certain increment step of a certain result file; 2) Collect the numbers of specified contact body elements and nodes; 3) Collect the corresponding result values according to the numbers of the elements and nodes; 4) Directly copy the collected result values or copy them as initial conditions to the new model according to the two-dimensional to three-dimensional expansion rule.

[0115] ② The specific operation steps are: 1) Run the first working step analysis; 2) Open the result file; 3) Extract the result file from the result file of the previous step analysis and expand it (if necessary, expand from two-dimensional to three-dimensional model) to a three-dimensional mesh; the boundary conditions can also be expanded at the same time; 4) Establish an analysis model for the second working step based on the extracted or expanded new mesh; 5) Define the Pre-State initial conditions in the menu for defining initial conditions; 6) Run the new model. The variable-temperature stretching results are shown in Figure 4 .

[0116] Regarding Step 6, simulate performance characterization

[0117] 1. Mises stress variation

[0118] (1) Select Stress in the analysis task result file in MARC;

[0119] (2) During stamping and bulging, compare the maximum stress with the previous high-temperature tensile data to ensure that the results meet the experimental conditions.

[0120] 2. Strain variation analysis:

[0121] (1) Select overall equivalent plastic strain, Equivalent Inherent Strain, and equivalent plastic strain rate in the MARC analysis task result file;

[0122] (2) Based on strain analysis, determine the changes in the formed part during the drawing process; based on the high-temperature tensile data, ensure that the simulated maximum strain value is within the test range;

[0123] 3. Thinning rate variation:

[0124] (1) Select Thickness of Element in the analysis task result file in MARC;

[0125] (2) Perform forming under the set conditions, observe and analyze the element thickness changes at each increment step to ensure that the thinning rate is within an appropriate range.

[0126] 4. Press-down displacement variation:

[0127] (1) Select displacement in the analysis task result file in MARC;

[0128] (2) By observing the displacement changes at each increment step, determine our press-down depth and bulging depth to ensure that they are within the required depth range.

[0129] Analysis of the results of warm drawing - rapid gas bulging composite forming:

[0130] (1) Analysis of drawing results:

[0131] Through Figure 5 and Figure 6It can be seen that the drawing process mainly focuses on the first 30 steps. The central part of the sheet is the main stress-bearing area, and the maximum stress during the drawing process is about 150 MPa. The tensile strength of the material at 850 degrees Celsius is about 180 MPa. The stress-bearing area in the last 20 increment steps is the wrinkling area of the process section, and the bulging material is gradually flattened. Although there is some supplementary material around the original sheet, the degree is very small. It can be seen that the sheet relies on its own plasticity for deformation. After the drawing is completed, the material has been formed to 97 mm, as Figure 7 shown. Subsequently, it relies on gas pressure bulging. The thinning situation of the material is as Figure 8 shown. It can be found from the figure that the maximum thinning is 12.45 mm, and the thinning rate is less than 30%, and the forming is good. Combining Figure 9 it can be known that the deformation state of the sheet is consistent with the stress change judgment. The middle part of the head part deforms first, and the deformation bulges like a sphere, and then gradually forms. The maximum strain value only appears on both sides of the head. The maximum equivalent plastic strain value is about 0.16. According to the high-temperature tensile experiment, it can be known that when the material is at 850 degrees Celsius and the strain rate is 0.1 s-1, the true strain is 0.78. Within the plastic strain range of the material, through Figure 7 the displacement change, it can be seen that the displacement changes on both sides of the center point are equal, which proves from the side that the medium-thick plate bulges in a perfect circle during the variable-temperature drawing process.

[0132] (2) Analysis of the gas bulging result:

[0133] When performing finite element simulation, it is not very strict to restore the actual processing state. We only need to calculate the required quantities, and can ignore the data with little reference significance for us, and appropriately simplify the calculation model. On the other hand, it can speed up the calculation speed and improve the calculation efficiency. Therefore, the following assumptions need to be made before the calculation:

[0134] (1) It is considered that the volume of the sheet does not change during the forming process;

[0135] (2) It is considered that all contact frictions between the sheet and the die, between the dies, etc. are Coulomb frictions, and the friction coefficient is uniformly set to 0.2;

[0136] Through Figure 10 the X-direction displacement change, it can be seen that the displacement changes on both sides of the center point are equal, which proves from the side that the flat plate bulges in a perfect circle during the superplastic process. The thinning situation of the sheet can be intuitively reflected by the wall thickness distribution. The thickness distribution at each moment during the finite element simulation process is plotted as Figure 11 shown.

[0137] Through Figure 10 and Figure 11It is judged that the thinning state of the material is consistent with the stress change and strain change. As the equivalent plastic strain increases, the sheet gradually thins, and the maximum thinning occurs at the center of the head. The original sheet is 14 mm thick, and the thickness at the maximum thinning is only about 13.55 mm, which also reflects from the side that the bulging process realizes forming through thinning because the forming process is a closed space and no material replenishment can be carried out.

[0138] Through the above simulation analysis, it can be concluded that the material undergoes superplastic gas bulging forming between 880 and 900 °C and 0.001 s-1 to 0.005 s-1. Finally, the obtained forming quality is good, without the occurrence of drawing cracks and wrinkles, and it is applicable to the rapid gas bulging process after our drawing.

[0139] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A variable-temperature deep drawing-rapid gas inflation composite forming method for thick-plate titanium alloy, characterized in that, Including: Establish a model of the stamping die for the head, and set the thickness of the blank to be stamped. Set the limiting conditions during the stamping process to obtain a variable-temperature drawing model; among them, the limiting conditions include punch movement conditions, blank-holder load conditions, material properties of the blank to be stamped, contact conditions, initial conditions, boundary conditions, load case conditions, and operation parameter conditions. Establish the Backoften constitutive equation, and determine the strain rate sensitivity index and strength coefficient at different temperatures according to the material strength at different temperatures. Carry out a finite element simulation process according to the strain rate sensitivity index and the strength coefficient to obtain a superplastic gas bulging model. Establish a variable-temperature drawing-rapid gas bulging model according to the variable-temperature drawing model and the superplastic gas bulging model. Characterize the simulation performance of the variable-temperature drawing-rapid gas bulging model, and analyze the drawing result and the gas bulging result; among them, the simulation performance includes Mises stress change, strain change analysis, thinning rate change, and thinning rate change. Determine the test reference according to the analysis result, and carry out a variable-temperature drawing-rapid gas bulging composite forming test.

2. The method according to claim 1, wherein The punch movement conditions include stamping speed, stamping distance, stamping time, and return time.

3. The method according to claim 1, wherein The blank-holder load conditions include the initial value of the blank-holder force, the initial blank-holding time, and reaching the blank-holder force.

4. The method according to claim 1, wherein The material properties include density, Poisson's ratio, and thermophysical properties.

5. The method according to claim 1, wherein The contact conditions define the mutual relationship between contact bodies, including the definition of the punch rigid body and the definition of the blank-holder rigid body. The definition of the punch rigid body includes that when defining the punch rigid body contact body, a displacement loading control method is adopted. The definition of the blank-holder rigid body includes that when defining the blank-holder rigid body contact body, the blank-holder adopts a load loading control method, and a control node is required to control the load and displacement of the blank-holder.

6. The method according to claim 1, wherein The initial conditions include the temperatures of the upper and lower surfaces of the blank to be stamped. The boundary conditions include the fixed displacement constraint of the blank-holder control node that only allows the node to move along the pressing direction and the load application of the blank-holder control node. The load case conditions are used to realize the contact analysis process between the punch, the blank-holder, and the die. The operation parameter conditions are used to select and call the set initial conditions, contact conditions, and load cases, and are also used to set the analysis type and define the analysis results.

7. The method according to claim 1, wherein The establishment of the Backoften constitutive equation and the determination of the strain rate sensitivity index and strength coefficient at different temperatures according to the material strength at different temperatures include: Derive the constitutive equation to obtain Among them, the constitutive equation is σ = Kε m , where m is the strain rate sensitivity index and K is the strength coefficient; Collect the stress σ and strain rate ε in the deep drawing data of the material at different temperatures · ; Determine the m value according to lnε and lnσ at different temperatures, and determine the strength coefficient according to the m value and the constitutive equation.

8. The method according to claim 1, characterized in that, The finite element simulation according to the strain rate sensitivity index and the strength coefficient to obtain a superplastic gas bulging model includes: Establish a geometric model according to the strain rate sensitivity index and the strength coefficient. Apply fixed boundary conditions to the elements outside the deformation area of the geometric model, and carry out load case settings to obtain a superplastic gas bulging model.

9. The method according to claim 1, characterized in that The establishment of a variable-temperature drawing-rapid gas bulging model according to the variable-temperature drawing model and the superplastic gas bulging model includes: Export the analysis status data of the last step of the variable-temperature drawing model, and use the analysis status data as the previous analysis status of the superplastic bulging model to complete the simulation analysis of all models.

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