Isothermal Forming Process of Titanium Alloy Based on Simulation

Abstract

The present invention provides an isothermal forming process for titanium alloy based on simulation, including: S1, establishing a material property database recognizable by Autoform software according to the input variables and output variables of material property tests; S2, determining the isothermal forming process route according to the characteristics of titanium alloy parts, and the isothermal forming process route includes an isothermal deep drawing process and an isothermal shape correction process; S3, performing theoretical analysis according to the material property database and the isothermal forming process route to determine the hot forming parameters that need to be simulated for the isothermal deep drawing process and the isothermal shape correction process; S4, using Autoform software to perform simulation of the isothermal deep drawing process and the isothermal shape correction process on titanium alloy sheet metal; S5, trial-producing parts according to the forming parameters obtained from the simulation, and adjusting the forming parameters of the isothermal deep drawing process and the isothermal shape correction process of the parts according to the forming quality of the trial-produced parts to make them meet the technical requirements of the parts.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy forming, and particularly to an isothermal forming process of titanium alloy based on simulation. Background Technique

[0002] In the application of titanium alloy materials, sheet metal forming, especially thin sheet forming, has always been a difficult point in the forming field. Because the forming performance of titanium alloy at room temperature is poor, in order to improve the forming performance of the material, it is often necessary to heat the titanium alloy sheet before forming, which brings many uncertain factors to the forming of titanium alloy sheet and increases the complexity of the forming process.

[0003] There are generally two ways of hot forming: local hot forming and isothermal forming.

[0004] Local hot forming means that during the forming process, the die is not heated, and the titanium alloy sheet is immediately transferred to the die for forming after heating. During the forming process, heat conduction will occur between the titanium alloy sheet and the die, the titanium alloy sheet will cool down, and the die will heat up. Isothermal forming means that during the forming process, the die and the titanium alloy sheet are heated simultaneously and then formed, and their forming working conditions are different.

[0005] In view of the high sensitivity of the forming performance of titanium alloy to temperature, isothermal forming is suitable for titanium alloy parts. At the same time, the cost of the isothermal forming test of titanium alloy parts is relatively high and the cycle is relatively long. Therefore, at present, the isothermal stamping process on a single-action hot press is widely used in engineering, and the isothermal drawing process on a double-action hot press is only applied to titanium alloy parts with relatively low process difficulty such as rotating bodies and relatively shallow box-shaped parts.

[0006] For parts with relatively high process difficulty (such as box-shaped parts with a relatively large depth), it is necessary to split them into multiple local parts with simple structures and easy forming according to the shape of the parts to be formed. The forming of each local part mostly adopts the isothermal forming process. After forming, the formed local parts are welded together to form the whole part. The process is complex, the accuracy is difficult to control, the consistency of the welding joints is poor, and the overall accuracy of the parts with multi-segment welding is poor due to welding deformation, resulting in poor overall forming accuracy of the parts after forming. A single-action hot press means that only the punch or the die moves, and a double-action hydraulic press means that in addition to the movement of the punch or the die, it can also drive the blank holder to move. And for thin-walled sheet metal parts, an isothermal drawing forming generally requires a blank holder, so a double-action hot press equipment is mostly used.

[0007] To solve the above problems, reliable simulation can be used to obtain the forming parameters of isothermal hot forming, and then the isothermal hot forming trial die is used to verify the simulation results, thereby reducing the test cost and shortening the test cycle. However, the commonly used finite element simulation software is not very suitable for isothermal hot forming simulation. Because the operation cycle of finite element analysis software with thermal field simulation modules such as Abaqus, Deform, MARC, and Pam-Stamp is too long, generally taking several hours to several days, and the convergence of the operation is relatively poor, prone to operation failure. Moreover, there are few settings and optimizations for sheet metal forming, and the interaction is not friendly.

[0008] Autoform software is a dedicated sheet metal finite element analysis software with a short operation cycle, high operation success rate, and high simulation accuracy. It is widely used in the field of hot forming of high-strength steel for automobiles, but it is designed to simulate local hot forming processes.

[0009] Therefore, there is an urgent need for a titanium alloy isothermal hot forming process based on simulation to solve the above technical problems. Summary of the Invention

[0010] The purpose of the present invention is to propose a titanium alloy isothermal hot forming process based on simulation to solve at least one of the above problems.

[0011] The titanium alloy isothermal hot forming process based on simulation includes:

[0012] S1. Conduct a material property test on the titanium alloy material. The input variables of the material property test include temperature, average strain rate, and specimen direction. The output variables of the material property test include elastic modulus, Poisson's ratio, flow stress-strain curve, and sheet thickness directionality coefficient r value. Establish a material property database recognizable by Autoform software based on the input variables and output variables of the material property test;

[0013] S2. Determine the isothermal hot forming process route according to the characteristics of the titanium alloy part. The isothermal hot forming process route includes an isothermal hot drawing process and an isothermal sizing process;

[0014] S3. Conduct a theoretical analysis based on the material property database and the isothermal hot forming process route to determine the hot forming parameters that need to be simulated for the isothermal hot drawing process and the isothermal sizing process. The hot forming parameters of the isothermal hot forming process include temperature, average strain rate, and sheet placement direction;

[0015] S4. Use Autoform software to conduct simulation of the isothermal hot drawing process and the isothermal sizing process on the titanium alloy sheet;

[0016] Obtain the forming parameters of the isothermal deep drawing process and the isothermal shape correction process according to the simulation results of the Autoform software;

[0017] S5: Conduct trial production of the part based on the forming parameters obtained from the simulation, and adjust the forming parameters of the isothermal deep drawing process and the isothermal shape correction process of the part according to the forming quality of the trial-produced part to meet the technical requirements of the part.

[0018] Preferably, in step S3,

[0019] For the simulation of the titanium alloy part, the temperature is sampled linearly, and a simulation temperature value is taken every 50 °C;

[0020] The average strain rate is sampled proportionally, and the value range of the average strain rate is 10 -3 s -1 -10 -1 s -1 ;

[0021] The placement direction of the sheet is the included angle between the sheet length direction and the rolling direction, and 0 °, 45 °, and 90 ° are taken respectively.

[0022] Preferably, in step S3, calculate the average strain rate in the simulations of the isothermal deep drawing process and the isothermal shape correction process of the titanium alloy part respectively ;

[0023] Its calculation formula is:

[0024] ;

[0025] is the maximum deformation of the corresponding process of the titanium alloy part;

[0026] s is the stroke of the corresponding process;

[0027] is the load closing speed of the hot forming equipment used in the corresponding process.

[0028] Preferably, in step S4, the simulation using the Autoform software includes:

[0029] S41. Import the material property database of the titanium alloy obtained in the material property test in step S1;

[0030] S42. Construct the simulation models of the isothermal deep drawing process and the isothermal shape correction process of the titanium alloy sheet, and set boundary conditions for the simulation models of the isothermal deep drawing process and the isothermal shape correction process respectively;

[0031] S43. Simulate the hot forming parameters determined in step S3, obtain the contour map of the optimal thinning rate corresponding to different hot forming parameters, and obtain the forming parameters of the isothermal hot drawing process and the isothermal hot sizing process according to the simulation results.

[0032] Preferably, in step S42, in the isothermal hot drawing process, the simulation model of the titanium alloy part includes a first punch, a first die, and a blank holder. The first punch is arranged above the first die, the titanium alloy sheet is arranged between the first punch and the first die, and the blank holder is arranged between the first punch and the titanium alloy sheet.

[0033] In the isothermal hot sizing process, the simulation model of the titanium alloy part includes a second punch and a second die. The second punch is arranged above the second die, and the preformed part formed in the isothermal hot drawing process is placed between the second punch and the second die.

[0034] The boundary conditions in the isothermal hot drawing process in step S42 include:

[0035] Using the hot forming module in Autoform software, the first punch, the first die, and the titanium alloy sheet are loaded with the thermal field simultaneously, and the heat radiation and heat conduction are set to 0.

[0036] Apply a fixed constraint to the first die.

[0037] Apply a first displacement to the blank holder to ensure the blank holding gap.

[0038] Apply a second displacement to the first punch to ensure the die closing position of the first punch and the first die.

[0039] The friction coefficient of the first die is 0.1 - 0.15; the friction coefficient of the first punch is 0.4 - 0.45.

[0040] The boundary conditions in the isothermal hot sizing process in step S42 include:

[0041] Apply a fixed constraint to the second die.

[0042] Apply a third displacement to the second punch to ensure the die closing position of the second punch and the second die.

[0043] The friction coefficient of the second die is 0.4 - 0.45; the friction coefficient of the second punch is 0.4 - 0.45.

[0044] Preferably, in step S5, trial production of the part is carried out according to the forming parameters obtained from the simulation, including:

[0045] The forming parameters of the isothermal deep drawing process include:

[0046] Adopt the forming parameters of the isothermal deep drawing process obtained in step S43, including temperature, the mold closing speed of the hot forming equipment load, the sheet placement direction, the blank holding gap, the blank holding force, and the mold closing force;

[0047] Use water-based graphite to lubricate the titanium alloy sheet; use boron nitride to prevent oxidation of the titanium alloy sheet;

[0048] The forming parameters of the isothermal shape correction process include:

[0049] Adopt the forming parameters of the isothermal shape correction process obtained in step S43, including temperature, the mold closing speed of the hot forming equipment load, the sheet placement direction, and the mold closing force;

[0050] Use boron nitride to prevent oxidation of the titanium alloy parts formed by the isothermal deep drawing process.

[0051] Preferably, in step S5, when trial-producing parts according to the forming parameters obtained from the simulation, it further includes:

[0052] For the isothermal shape correction process, according to the forming temperature range obtained in step S43, select the intermediate temperature to calculate the thermal expansion compensation and determine the size of the mold surface.

[0053] Preferably, in step S5, when trial-producing parts according to the forming parameters obtained from the simulation, it further includes forming with a double-action hot forming hydraulic press;

[0054] The working parameters of the double-action hot forming hydraulic press include: the forming pressure of the double-action hot forming hydraulic press, which controls the mold closing force of the molds used in the isothermal deep drawing process and the isothermal shape correction process; the ejector rod of the double-action hot forming hydraulic press is connected to the blank holder, and the ejector rod pressure controls the blank holding force of the blank holder used in the isothermal deep drawing process;

[0055] The pressure control accuracy range of the forming pressure of the double-action hot forming hydraulic press is not greater than ±1%;

[0056] The upper workbench is connected to the first punch or the second punch, and the upper workbench is used to control the forming speed of the titanium alloy parts;

[0057] The lower workbench fixedly installs the first die or the second die;

[0058] The maximum heating temperature of the working chamber of the double-action hot forming hydraulic press does not exceed 900 °C.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] Titanium alloy parts are manufactured by isothermal hot forming. Compared with parts manufactured by segmented isothermal hot stamping and welding processes, the generation of weld seams is avoided, and the accuracy and consistency of the parts are better; processes such as welding and shape correction are eliminated, and the forming efficiency is higher; without manual intervention such as shape correction and welding, the surface quality of the parts is better.

[0061] By establishing a material property database, the accuracy of subsequent simulation is effectively improved.

[0062] The hot forming module of Autoform software features accuracy, efficiency, and user-friendliness. Through secondary development of its thermal field loading method, it can accurately simulate hot forming conditions and solve the finite element simulation problem of the isothermal hot forming process of titanium alloy.

[0063] Through Autoform finite element simulation, the forming parameters for trial production of titanium alloy parts are obtained, and based on the influence of the forming parameters on the forming quality, the modification of the forming parameters during the manufacturing process is guided. While avoiding forming failures such as cracking and wrinkling, the forming thinning is optimized to meet the technical requirements of the parts; it can effectively reduce the development cost of the parts, shorten the development cycle of the parts, and also facilitate the rapid determination of the development process of the parts.

[0064] By controlling the forming temperature, the expansion of the parts and the mold is affected, and the deviation of the forming size can be compensated within a certain range, so that the forming size meets the technical requirements of the parts, avoiding a large increase in the development cost and development cycle caused by mold repair. Brief Description of the Drawings

[0065] Figure 1 It is a schematic structural diagram of a titanium alloy box-shaped part provided by the embodiment in the present invention;

[0066] Figure 2 It is a schematic diagram of the forming process route of the embodiment in the present invention;

[0067] Figure 3 It is a simulation model of the isothermal hot drawing process of OP20 in the embodiment of the present invention;

[0068] Figure 4 It is a simulation model of the isothermal hot shape correction process of OP30 in the embodiment of the present invention;

[0069] Figure 5 It is a flowchart of the isothermal hot forming process of titanium alloy based on simulation in the embodiment of the present invention;

[0070] Figure 6 It is when the sheet placement direction is 0° and the average strain rate is 10 -1 s -1 in the embodiment of the present invention, the flow stress-strain curve diagram of Ti6Al4V material at the simulation temperature;

[0071] Figure 7 When the sheet placement direction is 0° and the average strain rate is 10 -2 s -1 in the embodiments of the present invention, it is the flow stress-strain curve of Ti6Al4V material at the simulation temperature;

[0072] Figure 8 When the sheet placement direction is 0° and the average strain rate is 10 -3 s -1 in the embodiments of the present invention, it is the flow stress-strain curve of Ti6Al4V material at the simulation temperature;

[0073] Figure 9 When the average strain rate is 10 -3 s -1 in the embodiments of the present invention, it is the curve of the sheet thickness directionality coefficient r value - temperature of Ti6Al4V material;

[0074] Figure 10 When the temperature is 600 °C in the embodiments of the present invention, it is the curve of the sheet thickness directionality coefficient r value - average strain rate of Ti6Al4V material;

[0075] Figure 11 It is the simulation cloud diagram of working condition 1 in Table 2 of the embodiments of the present invention;

[0076] Figure 12 It is the simulation cloud diagram of working condition 2 in Table 2 of the embodiments of the present invention;

[0077] Figure 13 It is the simulation cloud diagram of working condition 3 in Table 2 of the embodiments of the present invention;

[0078] Figure 14 It is the simulation cloud diagram of working condition 4 in Table 2 of the embodiments of the present invention;

[0079] Figure 15 It is the simulation cloud diagram of working condition 5 in Table 2 of the embodiments of the present invention;

[0080] Figure 16 It is the simulation cloud diagram of working condition 6 in Table 2 of the embodiments of the present invention;

[0081] Figure 17 It is the simulation cloud diagram of working condition 7 in Table 2 of the embodiments of the present invention;

[0082] Figure 18 It is the simulation cloud diagram of working condition 8 in Table 2 of the embodiments of the present invention.

[0083] In the figure: 1. Titanium alloy sheet; 2. First punch; 3. First die; 4. Blank holder; 5. Second punch; 6. Second die. Specific embodiments

[0084] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Additionally, it should be noted that for the convenience of description, only the parts related to the present invention are shown in the drawings, rather than all of them.

[0085] Some orientation terms are defined in the present invention. Without contrary explanations, the orientation terms such as "upper", "lower", "left", "right", "inner", and "outer" are used for convenience of understanding, and thus do not constitute a limitation on the protection scope of the present invention.

[0086] In the present invention, unless otherwise clearly specified and defined, the first feature being "above" or "below" the second feature may include direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but are in contact through other features therebetween. Moreover, the first feature being "above", "over", and "on top of" the second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature has a higher horizontal height than the second feature. The first feature being "below", "beneath", and "underneath" the second feature includes the first feature being directly below and obliquely below the second feature, or simply indicating that the first feature has a lower horizontal height than the second feature.

[0087] In the description of the present invention, unless otherwise clearly specified and defined, the terms "connected", "connected to", and "fixed" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0088] The part formed by the isothermal forming process of titanium alloy based on simulation provided in this embodiment is as Figure 1The rectangular box-shaped part shown. The material of the titanium alloy box-shaped part is Ti6Al4V, and Ti6Al4V contains 6% of the α-stabilizing element Al and 4% of the β-stabilizing element V. Of course, it can also be other titanium alloy materials, which are not limited in this regard. The material thickness is 1.2 mm, the external dimensions are approximately 380 mm × 160 mm × 91 mm, the fillet radius at the transition between the side wall and the flange is 10 mm, the fillet radius of the side wall transition is 20 mm, the fillet radius of the bottom is 8 mm, and the transition of the bottom fillet is made smooth. The maximum thinning rate of the formed Ti6Al4V titanium alloy box-shaped part does not exceed 25%.

[0089] It can be understood that the isothermal hot forming process of titanium alloy based on simulation is not limited to rectangular box-shaped parts, and is also applicable to titanium alloy parts of other shapes.

[0090] In particular, the isothermal hot forming process of titanium alloy based on simulation is also applicable to other isothermal hot forming processes, including but not limited to double-action hot drawing process, single-action hot stamping process, hot bending process, hot sizing process, etc.

[0091] This embodiment is not limited in this regard and can be set according to actual requirements.

[0092] As Figures 1 - 5 shown, the isothermal hot forming process of titanium alloy based on simulation includes the following:

[0093] S1. Conduct material property tests on the titanium alloy material. The input variables of the material property tests include temperature, average strain rate, and specimen direction. The output variables of the material property tests include elastic modulus, Poisson's ratio, flow stress-strain curve, and the r-value of the sheet thickness directionality coefficient; establish a material property database recognizable by Autoform software based on the input variables and output variables of the material property tests;

[0094] S2. Determine the isothermal hot forming process route according to the characteristics of the titanium alloy part. The isothermal hot forming process route includes an isothermal hot drawing process and an isothermal hot sizing process;

[0095] S3. Conduct theoretical analysis according to the material property database and the isothermal hot forming process route to determine the hot forming parameters that need to be simulated for the isothermal hot drawing process and the isothermal hot sizing process. The parameters of the isothermal hot forming process include temperature, average strain rate, and the sheet placement direction;

[0096] S4. Use Autoform software to simulate the isothermal hot drawing process and the isothermal hot sizing process of the titanium alloy sheet 1;

[0097] Obtain the forming parameters of the isothermal hot drawing process and the isothermal hot sizing process according to the simulation results of Autoform software;

[0098] S5: Conduct trial production of the part according to the forming parameters obtained from the simulation, and adjust the forming parameters of the isothermal hot drawing process and the isothermal hot sizing process of the part according to the forming quality of the trial-produced part to meet the technical requirements of the part.

[0099] In step S1, a function curve fitted with multiple data is obtained through the material property test of the titanium alloy material. The Autoform software can recognize the function of the function curve or can recognize a predetermined number of data points selected from the data.

[0100] Preferably, in step S3, the temperature of the simulation of the titanium alloy part adopts linear sampling, and a simulation temperature value is taken every 50 °C. The average strain rate adopts proportional sampling, and the value range of the average strain rate is 10 -3 s -1 -10 -1 s -1 . The placing direction of the sheet metal is 0°, 45° and 90°.

[0101] The elastic modulus of the titanium alloy material is related to the temperature, and different titanium alloy materials have different relationships with the temperature, which can be obtained by querying the existing data. In this embodiment, the relationship between the elastic modulus and the temperature of the Ti6Al4V titanium alloy can be queried according to the prior art. And the Poisson's ratio of the above Ti6Al4V titanium alloy is 0.33.

[0102] The above material property test of the titanium alloy material includes three input variables. When the values of the temperature, the average strain rate and the placing direction of the sheet metal are different, multiple different simulation conditions will be formed.

[0103] Preferably, in this embodiment, the material property test of the Ti6Al4V titanium alloy material in step S1 is a unidirectional tensile high-temperature mechanical property test on the sheet of the Ti6Al4V titanium alloy material, and the test standard conforms to GB / T228.2-2015.

[0104] Through the material property test of the Ti6Al4V titanium alloy material, a material property database applicable to the Autoform software is established. That is, the relationship between the input variables and the output variables of the material property test of the Ti6Al4V titanium alloy material is input into the Autoform software after data processing to construct a material model for the simulation of the titanium alloy sheet metal.

[0105] The input variables of the material property test of the titanium alloy material are temperature, average strain rate and specimen direction. The specimen direction refers to the included angle between the length direction of the specimen and the rolling direction of the sheet metal. The performance indexes in the material property database include elastic modulus, Poisson's ratio, flow stress-strain curve and r value. The r value is the sheet thickness directionality coefficient.

[0106] In step S1, the sampling points of temperature for the variable temperature of the material performance test of the above titanium alloy material are determined by linear sampling. In the range of 20°C to 300°C, the formability of the titanium alloy material is little affected by temperature. Therefore, the titanium alloy material cannot meet the process requirements within the temperature range of 20°C to 300°C. In the range of 300°C to 500°C, with the increase of temperature, the formability of the titanium alloy material gradually improves, but the overall change is not significant.

[0107] The lower limit of the temperature range of isothermal hot forming is the minimum temperature corresponding to forming the titanium alloy material part that meets the predetermined requirements of the forming limit of the isothermal hot forming process of the titanium alloy material. The upper limit of the temperature range of isothermal hot forming is the superplastic forming temperature of the titanium alloy material. And because the performance of the titanium alloy material changes greatly at the recrystallization temperature, therefore, the value of the forming temperature of the titanium alloy part must include the recrystallization temperature. In this embodiment, the recrystallization temperature of the Ti6Al4V titanium alloy material is 700°C, and the superplastic forming temperature is 850°C.

[0108] When the temperature change value of the titanium alloy material is 50°C, it will have a certain impact on the parts formed by the isothermal hot forming process, but it does not reach the level of determining whether the parts formed by the isothermal hot forming process can be formed. In addition, considering the test cost, in this embodiment, the material performance test of the titanium alloy material is selected for linear sampling at intervals of 50°C within the temperature range of 500°C to 850°C, that is, eight temperature sampling points of 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, and 850°C are selected.

[0109] The sampling range of the average strain rate of the titanium alloy material is limited by the forming speed of the hot forming equipment, that is, the load clamping speed of the hot forming equipment.

[0110] Generally, the range of the average strain rate for realizing the isothermal hot forming of the titanium alloy material on a conventional hot forming equipment is 10 -3 s -1 ~ 10 -1 s -1 . Proportional sampling is carried out within this range. Specifically, considering the test difficulty and cost, this embodiment selects the proportional sampling method with an interval of 10 times, and selects 10 -3 s -1 、10 -2 s -1 and 10 -1 s -1 as the sampling points of three average strain rates.

[0111] In other embodiments, for different hot forming equipment and different forming process requirements, the sampling range of the average strain rate of the titanium alloy material will be different. The sampling points of the average strain rate adopt proportional sampling, and the ratio can be adjusted according to actual needs.

[0112] According to the determination specification of the r value (thickness directionality coefficient) of the material performance test of the titanium alloy material, the sheet placement directions of 0°, 45°, and 90° are selected.

[0113] In step S2, a forming process route is designed according to the characteristics of the titanium alloy part. Specifically, the part forming route is as Figure 2 shown:

[0114] The part forming process is completed in two steps: the OP20 isothermal drawing process and the OP30 isothermal sizing process; in the OP20 isothermal drawing process, the features in the original profile that are not suitable for drawing are modified, which is beneficial to the flow of the flange material. In the OP30 isothermal sizing process, the features that are not formed or not formed in place in the previous step are sized. In this embodiment, as Figure 3 shown, for the fillets (at I) on the flange and the fillets (at II) between the flange and the side wall of the Ti6Al4V titanium alloy material, the forming quality of the part is ensured, and at the same time, the dimensional accuracy of the part is ensured.

[0115] In this embodiment, the temperature range, the average strain rate range, and the sheet placement direction of the Ti6Al4V titanium alloy part in the Autoform software simulation are determined.

[0116] In step S3, the temperature range of the Ti6Al4V titanium alloy part simulation is determined according to the material performance database and the requirements of the isothermal hot forming process. The lower limit of the temperature range is the predetermined requirement that meets the forming limit of the isothermal hot forming process of the Ti6Al4V titanium alloy material, which is the minimum temperature corresponding to forming the Ti6Al4V titanium alloy material part. The upper limit of the temperature range is the superplastic forming temperature of the Ti6Al4V titanium alloy material.

[0117] Specifically, according to the technical requirements of the parts in the embodiment, the maximum allowable deformation of the parts is 25%. Therefore, the forming limit of the Ti6Al4V titanium alloy material needs to be above 25% to ensure sufficient forming threshold. Generally speaking, the higher the temperature of the Ti6Al4V titanium alloy material, the greater the forming limit of the Ti6Al4V titanium alloy parts. Therefore, according to the material property database and the technical requirements of the parts, the lower limit of the hot forming temperature range is the temperature corresponding to a forming limit of 25%. In this embodiment, this temperature is 600°C. The forming limit requirement of the box-shaped parts in this embodiment reaches 25%. The hot forming temperature of the parts is related to the forming limit of the parts. For example, when the hot forming temperature of the parts is 600°C, the forming limit that the parts can reach is 10%. After exceeding 10%, the parts may crack if further deep drawing is continued. In other embodiments, the lower limit of the hot forming temperature range needs to be set according to the requirements of the hot forming process, and the forming limit is not limited to 25%.

[0118] In this embodiment, for the variable temperature of the material property test of the above Ti6Al4V titanium alloy material, linear sampling is used to determine the sampling points of the temperature. In the range of 20°C to 300°C, the forming performance of the Ti6Al4V titanium alloy material is little affected by the temperature. Therefore, the Ti6Al4V titanium alloy material cannot meet the process requirements within the temperature range of 20°C to 300°C. In the range of 300°C to 500°C, with the increase of the temperature, the forming performance of the Ti6Al4V titanium alloy material gradually improves, but the overall change is not large. Above 850°C, the Ti6Al4V titanium alloy material exhibits superplasticity, and the material properties change greatly. The material tends to thin rather than deform during the forming process.

[0119] In summary, in this embodiment, the temperature range of the titanium alloy parts simulated in the Autoform software is 600°C to 850°C.

[0120] In step S3, the average strain rate in the simulations of the isothermal hot drawing process and the isothermal hot sizing process of the titanium alloy parts is calculated respectively , and its calculation formula is

[0121] ;

[0122] Among them, is the maximum deformation of the corresponding process of the titanium alloy parts; that is, in the isothermal hot drawing process, is the maximum deformation of the titanium alloy parts in the isothermal hot drawing process; in the isothermal hot sizing process, is the maximum deformation of the titanium alloy parts in the isothermal hot sizing process;

[0123] s is the stroke of the corresponding process; that is, in the isothermal hot drawing process, s is the stroke of the isothermal hot drawing process; in the isothermal hot sizing process, s is the stroke of the isothermal hot sizing process;

[0124] is the load clamping speed of the hot forming equipment used in the corresponding process; that is, in the isothermal hot drawing process, is the load clamping speed of the hot forming equipment used in the isothermal hot drawing process; in the isothermal hot sizing process, is the load clamping speed of the hot forming equipment used in the isothermal hot sizing process.

[0125] Using the above calculation formula, the average strain rate of the isothermal hot drawing process and the isothermal hot sizing process can be calculated respectively .

[0126] Specifically, in this embodiment, the stroke of the OP20 isothermal hot drawing process of the Ti6Al4V titanium alloy part is 100 mm, and the maximum deformation is about 20%. The load clamping speed of the hot forming equipment ranges from 0.5 mm / s to 5 mm / s. According to the calculation formula of the average strain rate ;

[0127] ;

[0128] The hot forming equipment can meet the average strain rate requirements of the parts in this process for 10 -3 s -1 ~10 -2 s -1 .

[0129] Specifically, in this embodiment, the stroke s of the OP30 isothermal hot sizing process of the Ti6Al4V titanium alloy part is about 10 mm, and the maximum deformation is about 20%. The load clamping speed of the hot forming equipment ranges from 0.5 mm / s to 5 mm / s. According to the calculation formula of the average strain rate ;

[0130] ;

[0131] The hot forming equipment can meet the average strain rate requirements of the parts in this process for 10 -2 s -1 ~10 -1 s -1 .

[0132] In summary, in this embodiment, the value range of the average strain rate of the titanium alloy part in the isothermal hot drawing process is 10-3 s -1 ~10 -2 s -1 , the average strain rate in the isothermal hot calibration process ranges from 10 -2 s -1 ~10 -1 s -1 .

[0133] When hot forming the Ti6Al4V titanium alloy material in this embodiment, a sampling method with a ratio of 10 times interval is selected, and 10 -3 s -1 , 10 -2 s -1 and 10 -1 s -1 three sampling points of the average strain rate are selected.

[0134] In step S3, determine the placing direction of the sheet metal, that is, there are three placing states where the rolling direction of the sheet metal forms 0°, 45°, and 90° with a certain specific angle of the mold. The mold in this embodiment is a cuboid, and the length direction of the sheet metal during blanking forms a certain specific angle with the rolling direction of the sheet metal, that is, the rolling direction of the sheet metal forms a certain specific angle with the length direction of the mold.

[0135] In summary, in this embodiment, select the placing direction of the sheet metal, that is, there are three placing states where the rolling direction of the sheet metal forms 0°, 45°, and 90° with the length direction of the mold.

[0136] By analyzing the material properties within the above value range, further determine the simulation hot forming parameters of the part.

[0137] Figure 6 is the flow stress-strain curve at different temperatures under the condition that the average strain rate of the Ti6Al4V titanium alloy material is 10 -1 s -1 . Figure 7 is the flow stress-strain curve at different temperatures under the condition that the average strain rate of the Ti6Al4V titanium alloy material is 10 -2 s -1 . Figure 8 is the flow stress-strain curve at different temperatures under the condition that the average strain rate of the Ti6Al4V titanium alloy material is 10 -3 s -1 . The flow stress is the stress state of the Ti6Al4V titanium alloy material under different temperatures, average strain rates, and strain conditions. It is an important data reflecting the forming performance of the Ti6Al4V titanium alloy material and is also a comprehensive reflection of the evolution of the internal microstructure and property changes of the metal during the deformation process.

[0138] AfterFigures 6 - 8 From the comparison and analysis, it can be seen that: when the average strain rate remains unchanged, in the temperature range of 600°C - 850°C, the flow stress of Ti6Al4V titanium alloy decreases significantly with the increase of temperature, and at the same time, the forming limit increases significantly. When the temperature remains unchanged, in the average strain rate range of 10 -3 s -1 ~10 -1 s -1 range, the flow stress of Ti6Al4V titanium alloy decreases significantly with the decrease of the average strain rate, and at the same time, the forming limit increases significantly.

[0139] Figure 9 is the curve of the change of the sheet thickness directionality coefficient r value - temperature at different angles between the length direction of the sheet and the rolling direction when the average strain rate of Ti6Al4V titanium alloy material is 10 -3 s -1 . The sheet thickness directionality coefficient r value characterizes the difference in the deformation performance in the thickness direction and the sheet plane direction of the sheet under the same stress conditions. The larger the r value, the more difficult the deformation in the thickness direction, and the less likely the part is to tend to thin, which is beneficial to deep drawing forming. Comparison and analysis Figure 9 show that: the r value decreases significantly with the increase of temperature. The higher the temperature, the less significant the directionality difference of the r value, and it tends to be unified above 800°C. The r value of the specimen at a 45° angle to the rolling direction is the largest. Therefore, the lower the temperature, the larger the r value, and the increase degree of the r value in the 0° and 90° directions is much lower than that in the 45° direction.

[0140] Figure 10 is the curve of the change of the sheet thickness directionality coefficient r value - average strain rate at different angles between the forming temperature of Ti6Al4V titanium alloy material is 600°C and the rolling direction. Comparison and analysis Figure 10 show that: the larger the average strain rate, the larger the r value; among them, the increase degree of the r value in the 0° and 90° directions is much lower than that in the 45° direction. In summary, the r value increases with the decrease of temperature and the increase of the average strain rate, and the increase degree of the r value in the 0° and 90° directions is much lower than that in the 45° direction.

[0141] Comprehensively Figure 9 and Figure 10 it can be seen that when the temperature remains unchanged, when the average strain rate changes in the range of 10 -3 s -1 to 10 -1 s -1 , the r value and the average strain rate increase in a positive linear curve.

[0142] Specifically, based on the characteristics of the titanium alloy material itself and according to the above material performance experimental data, the influence of the titanium alloy material performance on the part forming is as follows:

[0143] 1. Influence of Temperature on Part Formability

[0144] ① As the forming temperature increases, the formability limit of the material improves, and the deformation resistance decreases. This is beneficial for drawing forming.

[0145] ② As the forming temperature increases, the friction of the material increases, the work hardening phenomenon weakens, and in the drawing force transmission area, which is the area of the side wall of the box-shaped part, its load-bearing capacity weakens, and the stress concentration phenomenon is obvious. The r value decreases, and the part is more prone to thinning. This is not conducive to drawing forming.

[0146] ③ As the forming temperature increases, the oxidation phenomenon of the part is serious. There is basically no oxidation at 600 °C, and the oxidation is serious above 750 °C.

[0147] ④ Around 700 °C is the recrystallization temperature of TC4 material. Above 700 °C, the material properties change significantly, the springback of part forming decreases significantly, and the sizing effect is significant.

[0148] 2. The average strain rate has the following effects on part formability:

[0149] The smaller the average strain rate, the more beneficial it is for forming.

[0150] 3. The sheet metal placement direction has the following effects on part formability:

[0151] The higher the temperature, the smaller the influence of the sheet metal placement direction on part formability. Above 700 °C, the influence of the sheet metal placement direction on part formability can be ignored.

[0152] For the warm drawing process such as OP20, the stresses in all directions of the box-shaped part are uneven, and the stress concentration phenomenon is obvious. The influence effect of the above factor ② is obvious. Considering the above four factors comprehensively, especially the existence of the above factor ②, it is difficult to directly judge the optimal hot forming parameters of this part and it must be determined through simulation analysis. Therefore, the value range of the simulation temperature is 600 °C to 850 °C, and samples are taken at intervals of 50 °C. From the Figures 6 - 10 curve, the average strain rate in this embodiment can be selected as 10 -3 s -1 . If the forming temperature is lower than 700 °C, it is necessary to determine the influence of the sheet metal placement direction on part forming.

[0153] For the warm sizing process such as OP30, the deformation of the part is mainly local bulging, and the influence of the above factor ② on forming can be ignored. Therefore, in this OP30 warm sizing process, only the above factors ①③④ need to be considered comprehensively. Therefore, from the Figures 6 - 10 curve, the designed forming temperature is 700 °C to 800 °C, and samples are taken at intervals of 50 °C. The average strain rate can be selected as 10 -2 s-1 ; The influence of the sheet metal placement direction on part forming can be ignored.

[0154] In step S4, the isothermal hot forming simulation of the titanium alloy sheet 1 is carried out using Autoform software.

[0155] In step S4, the simulation using Autoform software includes:

[0156] S41. Import the material property database of the titanium alloy obtained in the material property test in step S1;

[0157] S42. Construct the simulation models of the isothermal hot drawing process and the isothermal hot sizing process of the titanium alloy sheet, and set the boundary conditions for the simulation models of the isothermal hot drawing process and the isothermal hot sizing process respectively;

[0158] S43. Carry out the simulation of the hot forming parameters determined in step S3, obtain the optimal thinning rate distribution nephogram corresponding to different hot forming parameters, and obtain the forming parameters of the isothermal hot drawing process and the isothermal hot sizing process according to the simulation results.

[0159] Specifically, for the OP20 isothermal hot drawing process of the embodiment, in step S42, in the isothermal hot drawing process, as Figure 3 shown, the simulation model of the titanium alloy part includes a first punch 2, a first die 3 and a blank holder 4. The first punch 2 is arranged above the first die 3. The titanium alloy sheet 1 is arranged between the first punch 2 and the first die 3. The blank holder 4 is arranged between the first punch 2 and the titanium alloy sheet 1.

[0160] The boundary conditions in the isothermal hot drawing process in step S42 include: using the hot forming module in Autoform software, loading the thermal field on the first punch 2, the first die 3 and the titanium alloy sheet 1 at the same time, and setting the thermal radiation and heat conduction to 0. Applying a fixed constraint to the first die 3; applying a first displacement to the blank holder 4 to ensure a blank holding gap of 1.26 mm to 1.32 mm; applying a second displacement to the first punch 2 to ensure the die closing position of the first punch 2 and the first die 3; the friction coefficient of the first die 3 is 0.1 - 0.15. The friction coefficient of the first punch 2 is 0.4 - 0.45.

[0161] According to step S3, 8 groups of hot forming parameter combinations are selected for the simulation of the OP20 isothermal hot drawing process in step S4, as shown in Table 1.

[0162]

[0163] In step S43, without forming failure, the summary of the best maximum thinning rate results is shown in Table 2.

[0164]

[0165] Such as Figures 11 - 18 The simulation nephogram of the Ti6Al4V titanium alloy parts under the above 1-8 working conditions in the above OP20 warm isothermal drawing process.

[0166] In step S43, the above OP20 warm isothermal drawing process specifically obtains the forming parameters according to the simulation and the influence trend of the change of the forming parameters on the forming effect as follows:

[0167] Comparing the eight groups of working conditions in Table 2 with an average strain rate of 10 -3 s -1 、the blank placement directions of 0°, 45° and 90°, and the forming temperatures of 600°C, 650°C, 700°C, 750°C, 800°C, 850°C respectively, it can be seen that the influence trend of the change of the forming temperature on the forming effect is: the maximum thinning rate of the Ti6Al4V titanium alloy parts shows a significant upward trend with the increase of temperature. When the temperature is above 750°C, the stress concentration phenomenon is serious, and local severe thinning occurs, which cannot meet the forming requirements of the Ti6Al4V titanium alloy parts. Therefore, the forming temperature range of the OP20 warm isothermal drawing process of the parts in this embodiment is 600°C to 700°C.

[0168] Comparing the three groups of hot forming parameters with a forming temperature of 600°C, an average strain rate of 10 -3 s -1 、and the blank placement directions of 0°, 45°, 90° respectively, and performing finite element simulation on the drawing process of the Ti6Al4V titanium alloy parts, it can be seen that the influence trend of the change of the blank placement direction on the forming effect is: the blank placement direction has a significant impact on the maximum thinning rate of the Ti6Al4V titanium alloy parts. The maximum thinning rate of the parts formed with the blank at 0° is the lowest, that is, the best blank placement direction is 0°.

[0169] In summary, the forming parameters of the OP20 warm isothermal drawing process obtained according to the simulation are shown in Table 3:

[0170]

[0171] Among them, the blank holding gap and the blank holding force have the greatest impact on the forming quality among the warm isothermal drawing simulation forming parameters. The size of the blank holding gap largely affects the flow of the blank, resulting in the occurrence of part forming failures (such as cracking, wrinkling, etc.). The blank holding force should not only meet the need to ensure the blank holding gap, but also avoid being too large to cause thickness direction deformation of the die. According to the simulation results, the blank holding gap of 1.25 mm and the blank holding force of 10 t are the best forming parameters.

[0172] For the OP30 warm isothermal sizing process of the embodiment, such as Figure 4As shown, in the isothermal calibration process of OP30 in this embodiment, the simulation model of the titanium alloy part includes a second punch 5 and a second die 6. The second punch 5 is arranged above the second die 6, and the preformed part formed in the isothermal forming process is placed between the second punch 5 and the second die 6.

[0173] The boundary conditions in the isothermal calibration process in step S42 include:

[0174] Apply a fixed constraint to the second die. Apply a third displacement to the second punch to ensure the final die - closing position.

[0175] The friction coefficient of the second die is 0.4 - 0.45; the friction coefficient of the second punch is 0.4 - 0.45.

[0176] The process action is: the second die 6 does not move, the second punch 5 moves downward to close the die, and calibrate the preformed part in the isothermal drawing process of OP20.

[0177] According to step S3, select 3 groups of parameter combinations for the simulation of the isothermal calibration process of OP30, as shown in Table 4.

[0178]

[0179] In step S43, the maximum thinning rates obtained from the isothermal calibration process are summarized as shown in Table 5.

[0180]

[0181] The forming parameters obtained from the simulation and the influence trend of the change of forming parameters on the forming effect are as follows:

[0182] Comparing the three working conditions with an average strain rate of 0.01 s -1 , a blank placement direction of 0°, and forming temperatures of 700°C, 750°C, and 800°C respectively, it can be seen that the influence trend of the change of forming temperature on the forming effect is: the maximum thinning rate of the part shows an upward trend with the increase of temperature, but the difference is not significant. Therefore, the forming temperature range of the isothermal calibration process of the part can be determined to be 700°C - 800°C.

[0183] Since within the temperature range of 700°C - 800°C and at an average strain rate of 10 -2 s -1 , the directional differences of the r - value tend to be consistent under the forming conditions, so there is no requirement for the blank placement direction. In summary, the forming parameters of the isothermal calibration process of OP30 obtained from the simulation are shown in Table 6:

[0184]

[0185] Among them, the clamping force has the greatest impact on the forming quality among the calibration simulation forming parameters. It is necessary to not only meet the requirements of the calibration force of the part, but also avoid excessive force that may cause cracking and thickness-direction deformation of the mold. According to the simulation results, a clamping force of 30t is the optimal forming parameter.

[0186] In step S5, trial production of the part is carried out according to the forming parameters obtained from the simulation; and the forming parameters of the part are adjusted according to the forming quality of the trial-produced part to meet the technical requirements of the part.

[0187] Specifically, in step S5, the trial production of the titanium alloy part is carried out by double-action hot forming hydraulic press. Some parameters of the double-action hot forming hydraulic press are shown in Table 7.

[0188]

[0189] The working parameters of the above double-action hot forming hydraulic press include: the forming pressure of the double-action hot forming hydraulic press, which controls the clamping force of the mold used in the isothermal hot drawing process and the isothermal hot calibration process; the ejector rod of the double-action hot forming hydraulic press is connected to the blank holder 4, and the ejector rod pressure is used to control the blank holding force of the blank holder 4.

[0190] The pressure control accuracy range of the forming pressure of the double-action hot forming hydraulic press is not greater than ±1%. The control accuracy of this double-action hot forming hydraulic press is mainly controlled by the valves on the pipeline.

[0191] The upper worktable is connected to the first punch 2 or the second punch 5, and the upper worktable is used to control the forming speed of the titanium alloy part.

[0192] The lower worktable is fixedly installed with the first die 3 or the second die 6;

[0193] The effective table range of the lower worktable and the upper worktable in the above Table 7, that is, the size of the mold that can be installed on the upper worktable and the lower worktable.

[0194] The maximum heating temperature of the working chamber of the double-action hot forming hydraulic press does not exceed 900°C.

[0195] In step S5, trial production of the part is carried out according to the forming parameters obtained from the simulation, including:

[0196] The forming parameters of the isothermal hot drawing process include:

[0197] Adopt the forming parameters of the isothermal hot drawing process obtained in step S43, including temperature, hot forming equipment load clamping speed, sheet metal placement direction, blank holding gap, blank holding force, clamping force;

[0198] Use water-based graphite to lubricate the titanium alloy sheet; use boron nitride to prevent oxidation of the titanium alloy sheet;

[0199] The forming parameters of the isothermal hot calibration process include:

[0200] Adopt the forming parameters of the isothermal hot calibration process obtained in step S43, including temperature, the mold closing speed of the hot forming equipment load, the sheet metal placement direction, the blank holding force, and the mold closing force;

[0201] Use boron nitride to prevent oxidation of the titanium alloy parts formed by the isothermal hot drawing process.

[0202] Specifically, the forming pressure of the double-action hot forming hydraulic press used in this embodiment is 3150 KN. The ejector rod is connected to the blank holder 4, and the ejecting force of the ejector rod is 500 KN. The pressure control accuracy range of the forming pressure of the double-action hot forming hydraulic press is not greater than ±1%. The lifting speed range of the upper workbench is 0.5 mm / s to 10 mm / s. The effective tabletop range of the workbench is 1600 mm * 1200 mm. The maximum heating temperature of the forming die does not exceed 900 °C.

[0203] In the isothermal hot calibration process, the blank holder 4 is no longer used. The forming pressure of the double-action hot forming hydraulic press is 3150 KN. The pressure control accuracy range of the forming pressure of the double-action hot forming hydraulic press is not greater than ±1%. The speed range of the lifting of the upper workbench is 0.5 mm / s to 10 mm / s.

[0204] In this embodiment, after the parts are first trial-produced according to the forming parameters in the OP20 isothermal hot drawing process, forming failures such as forming wrinkles and fractures occur in the parts. According to the drawing forming experience, the adjustment effect of the blank holding force is the best, indicating that the set blank holding force of 10 t in the isothermal hot drawing process is too small.

[0205] For the second trial production of the parts, the blank holding force is 30 t. The drawing forming effect of the formed parts is good, and there are no forming failures such as fractures and wrinkles.

[0206] In this embodiment, after the parts are first trial-produced according to the forming parameters in the OP30 isothermal hot calibration process, the calibration effect of the parts is good, and there are no forming failures such as fractures and wrinkles. The external dimensions of the parts are detected. The detection results show that the overall dimensions of the parts are approximately 0.16% larger. For the key dimensions of the external shape of the cavity position of the box-shaped parts, it is 370 ± 0.5 mm. The dimensions of this cavity position are fixed after forming and cannot be further precision processed. The actual measured dimension is approximately 370.6 mm, which does not meet the part dimension tolerance requirements.

[0207] In step S5, trial production of the part is carried out according to the forming parameters obtained from simulation. It also includes that in the isothermal hot sizing process, according to the forming temperature range obtained in step S43, the intermediate temperature is selected to calculate the thermal expansion compensation and determine the die surface size. In the trial production, within the forming temperature range, selecting a forming temperature higher than the intermediate temperature can obtain a part with a size larger than the theoretical size; selecting a forming temperature lower than the intermediate temperature can obtain a part with a size smaller than the theoretical size; and the dimensional deviation of the part caused by reasons such as thermal expansion calculation and die manufacturing error can be compensated accordingly.

[0208] Specifically, during the hot forming process, both the die and the part will undergo thermal expansion. The linear expansion coefficient of the material is that for every 1°C increase in the material, the size of the material will increase by a certain value. When the linear expansion coefficients of the die and the part are the same, they will increase proportionally during hot forming, and there is no need to set a compensation amount. When the linear expansion coefficients of the two are different, it is necessary to compensate for the thermal expansion amounts of the two. At the same time, due to die manufacturing errors and errors generated during the part manufacturing process, and after the part is hot formed, springback will occur, and the springback amount cannot be calculated accurately. All the above factors will cause dimensional changes in the overall part. In this embodiment, the dimensional changes of the die and the part during the hot forming process are calculated according to the temperature. Therefore, the linear expansion coefficient of the die is calculated under the condition that the hot forming temperature is 750°C. During actual hot forming production, under the condition of a temperature of 700°C, after the part is formed, the size will be smaller than the theoretical value to overcome the deformation caused by springback.

[0209] After the above die is processed, it is difficult to adjust the die size, and for the blank holding force adjustment of the die, if wrinkling or cracking occurs after the part is formed, the blank holding force of the die can be adjusted, but it has little impact on the external dimensions of the formed part. For the size of the titanium alloy sheet 1 of the part, since the titanium alloy sheet 1 of the part is irregular, after multiple forming adjustments, the titanium alloy sheet 1 is finalized, and the size and shape will not be adjusted. For the influencing factors of temperature and average strain rate on the hot forming of the part, the lower the average strain rate, the better the forming effect of the part, but the hot forming cycle and production cost of the part need to be considered.

[0210] Specifically, according to theoretical calculation, when the forming temperature is adjusted from 750°C to 700°C, due to the difference in the expansion amounts of the die and the part, the size of the formed part will decrease by 0.05%.

[0211] After changing the forming temperature to 700°C, in this embodiment, after the part completes the second trial production of the OP30 isothermal hot sizing process, the sizing effect of the trial-produced part is good, and there are no forming failures such as cracking and wrinkling; the external dimensions of the part are detected. For the key external dimension of the part of 370 ± 0.5 mm, the measured dimension is reduced to 370.4 mm, meeting the part tolerance.

[0212] In this embodiment, the forming parameters of the trial-produced parts are adjusted according to the forming quality of the parts, especially the adjustment of the blank-holder force and temperature, so as to meet the technical requirements of the parts. The final forming parameters are shown in Table 8:

[0213]

[0214] Although the present invention has been described in detail above with general descriptions, specific embodiments and experiments, some modifications or improvements can be made to it on the basis of the present invention, which is obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. The isothermal forming process of Ti6Al4V titanium alloy based on simulation, characterized in that Including: S1. Conduct material property tests on the titanium alloy material. The part formed by the isothermal hot forming process of the titanium alloy based on simulation is a rectangular box-shaped part. The material of the titanium alloy box-shaped part is Ti6Al4V. The input variables of the material property test include temperature, average strain rate, and specimen direction. The output variables of the material property test include elastic modulus, Poisson's ratio, flow stress-strain curve, and sheet thickness directionality coefficient r value. Establish a material property database recognizable by Autoform software according to the input variables and output variables of the material property test. The material property test of the Ti6Al4V titanium alloy material is a unidirectional tensile high-temperature mechanical property test of the Ti6Al4V titanium alloy material. S2. Determine the isothermal hot forming process route according to the characteristics of the Ti6Al4V titanium alloy part. The isothermal hot forming process route includes an isothermal deep drawing process and an isothermal sizing process. S3. Conduct theoretical analysis according to the material property database and the isothermal hot forming process route to determine the hot forming parameters that need to be simulated for the isothermal deep drawing process and the isothermal sizing process. The hot forming parameters of the isothermal hot forming process include temperature, average strain rate, and sheet placement direction. In step S3, The temperature range of the simulation of the Ti6Al4V titanium alloy material is 600°C - 850°C. Linear sampling is adopted, and a simulation temperature value is taken every 50°C. The average strain rate adopts proportional sampling, and the value range of the average strain rate of the titanium alloy material in the isothermal hot stretching process is 10 -3 s -1 ~ 10 -2 s -1 , and the value range of the average strain rate in the isothermal hot sizing process is 10 -2 s -1 ~ 10 -1 s -1 ; The sheet placement direction is the angle between the sheet length direction and the rolling direction, and 0°, 45°, and 90° are taken respectively. S4. Use Autoform software to conduct simulation of the isothermal deep drawing process and the isothermal sizing process on the Ti6Al4V titanium alloy sheet. Obtain the forming parameters of the isothermal deep drawing process and the isothermal sizing process according to the simulation results of Autoform software. In step S4, the simulation using Autoform software includes: S41. Import the material property database of the Ti6Al4V titanium alloy obtained in the material property test in step S1. S42. Construct simulation models of the isothermal deep drawing process and the isothermal sizing process of the Ti6Al4V titanium alloy sheet, and set boundary conditions for the simulation models of the isothermal deep drawing process and the isothermal sizing process respectively. S43. Conduct simulation of the hot forming parameters determined in step S3, obtain the best thinning rate distribution nephogram corresponding to different hot forming parameters, and obtain the forming parameters of the isothermal deep drawing process and the isothermal sizing process according to the simulation results. In step S42, in the isothermal deep drawing process, the simulation model of the Ti6Al4V titanium alloy part includes a first punch, a first die, and a blank holder. The first punch is arranged above the first die. The Ti6Al4V titanium alloy sheet is arranged between the first punch and the first die. The blank holder is arranged between the first punch and the Ti6Al4V titanium alloy sheet. In the isothermal hot shaping process, the simulation model of the Ti6Al4V titanium alloy part includes a second convex die and a second concave die, the second convex die is arranged above the second concave die, and the preformed part formed in the isothermal hot drawing process is placed between the second convex die and the second concave die; The boundary conditions in the isothermal hot drawing process in step S42 include: Using the hot forming module in the Autoform software, the first male die, the first female die and the Ti6Al4V titanium alloy sheet are simultaneously loaded with a thermal force field, and heat radiation and heat conduction are set to 0; S5: trial-produce the parts according to the forming parameters obtained from the simulation, and adjust the forming parameters of the isothermal hot drawing process and the isothermal hot shaping process of the parts according to the forming quality of the trial-produced parts to meet the technical requirements of the parts.

2. The isothermal hot forming process of Ti6Al4V titanium alloy based on simulation according to claim 1, characterized in that, In step S3, calculate the average strain rate in the simulations of the isothermal hot drawing process and the isothermal hot sizing process for the Ti6Al4V titanium alloy part, respectively ; The calculation formula is: ； is the maximum deformation amount of the corresponding process for the Ti6Al4V titanium alloy part; s is the stroke of the corresponding process; The load clamping speed of the hot forming equipment used in the corresponding process.

3. The isothermal hot forming process of Ti6Al4V titanium alloy based on simulation according to claim 1, characterized in that In step S5, trial production of parts is performed according to the forming parameters obtained by simulation, including: The forming parameters of the isothermal hot drawing process include: The forming parameters of the isothermal hot drawing process obtained in step S43 include temperature, hot forming equipment load clamping speed, sheet material placement direction, blank holder gap, blank holder force, and clamping force; Water-based graphite is used to lubricate Ti6Al4V titanium alloy sheets; boron nitride is used to prevent oxidation of Ti6Al4V titanium alloy sheets; The forming parameters of the isothermal heat correction process include: The forming parameters of the isothermal heat correction process obtained in step S43 are used, including temperature, hot forming equipment load clamping speed, sheet material placement direction, and clamping force; Boron nitride is used to prevent oxidation of the Ti6Al4V titanium alloy parts formed by the isothermal hot drawing process.

4. The isothermal hot forming process of Ti6Al4V titanium alloy based on simulation according to claim 1, characterized in that, In step S5, trial production of parts is performed according to the forming parameters obtained by simulation, and the process also includes: The isothermal heat correction process selects an intermediate temperature to calculate thermal expansion compensation and determine the size of the mold surface according to the forming temperature range obtained in step S43.

5. The isothermal hot forming process of Ti6Al4V titanium alloy based on simulation according to claim 1, characterized in that, The boundary conditions in the isothermal hot drawing process in step S42 include: applying a fixed constraint to the first concave die; Applying a first displacement to the blank holder ring to ensure a blank holder gap; Applying a second displacement to the first convex mold to ensure a mold-closing position of the first convex mold and the first concave mold; The friction coefficient of the first concave die is 0.1-0.15; the friction coefficient of the first convex die is 0.4-0.45; The boundary conditions in the isothermal heat correction process in step S42 include: applying a fixed constraint to the second concave die; Applying a third displacement to the second convex mold to ensure the second convex mold and the second concave mold are in a clamping position; The friction coefficient of the second concave mold is 0.4-0.45; the friction coefficient of the second convex mold is 0.4-0.

45.

6. The isothermal hot forming process of Ti6Al4V titanium alloy based on simulation according to claim 1, characterized in that, In step S5, trial production of the parts is performed according to the forming parameters obtained by the simulation, and forming is also performed using a double-action hot forming hydraulic press; The working parameters of the double-action hot forming hydraulic press include: the forming pressure of the double-action hot forming hydraulic press, which controls the clamping force of the molds used in the isothermal hot drawing process and the isothermal hot sizing process; the ejector rod of the double-action hot forming hydraulic press is connected to the blank holder, and the ejector rod pressure controls the blank holding force of the blank holder used in the isothermal hot drawing process. The pressure control accuracy range of the forming pressure of the double-action hot forming hydraulic press is not greater than ±1%. The upper workbench is connected to the first punch or the second punch, and the upper workbench is used to control the forming speed of the Ti6Al4V titanium alloy part. The lower workbench fixedly installs the first die or the second die. The maximum heating temperature of the working chamber of the double-action hot forming hydraulic press does not exceed 900 °C.

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