A progressive hot pressing method for variable curvature bidirectional anti-concave titanium alloy skin

Abstract

This application provides a progressive hot pressing method for variable curvature bidirectional concave titanium alloy skin, belonging to the field of digital skin technology. This invention solves the problems of surface quality defects such as wrinkles and cracks, and long forming cycles, inherent in existing progressive hot pressing methods for variable curvature titanium alloy skin. This invention calculates the optimal number of progressive forming cycles for the part using a Python secondary development method, and effectively solves the surface wrinkling problem after forming by optimizing the mold structure and using a more efficient hot pressing method. Furthermore, the optimal number of progressive forming cycles calculated in this application effectively avoids the problem of damaged mechanical properties caused by excessive hot pressing cycles, greatly improving the forming efficiency of the part.

Description

Technical Field

[0001] This application belongs to the field of precision forming technology of titanium alloys, specifically relating to a progressive hot pressing forming method for a variable curvature bidirectional anti-concave titanium alloy skin. Background Technology

[0002] In recent years, titanium alloys have been widely used in aircraft skins. Complex variable curvature titanium alloy skins have become the main form of aircraft, characterized by a curvature radius greater than 50mm, part sizes exceeding 1 meter, and exhibiting a bidirectional concave structure. However, due to the material properties of titanium alloys, they cannot undergo plastic deformation in a cold state, thus failing to meet the shape requirements of the parts.

[0003] Titanium alloy forming is conventionally done by hot forming. When these parts are directly formed by traditional one-time hot pressing, the material cannot be discharged in a limited space during the hot pressing process. The poor material fluidity inevitably leads to defects such as large-area wrinkles and material stacking in the center of the part. As a result, the part qualification rate can only reach 5%, and the maximum fit to the tire is 5mm, which is difficult to meet the surface quality requirements of skin parts. Summary of the Invention

[0004] Purpose of the invention: Combining the process characteristics of titanium alloy hot forming, this invention uses simulation to predict the number of hot pressing cycles, effectively reducing the impact of hot cycling on material properties. Simultaneously, it employs a progressive hot pressing process to complete both the transition forming and final forming processes, requiring only one forming model. This method is characterized by low cost and excellent forming effect, with a yield rate exceeding 95%. Therefore, it is essential to provide a progressive hot pressing method for variable curvature bidirectional concave titanium alloy skin.

[0005] This application provides a method for progressive hot pressing of a variable curvature bidirectional concave titanium alloy skin, the method comprising the following steps:

[0006] Step 1: Establish the first progressive hot pressing model for the skin;

[0007] Step 2: Establish the second progressive hot pressing model for the skin;

[0008] Step 3, build the progressive hot pressing cycle program for the skin: After the second progressive hot pressing cycle analysis of the skin is completed, the Python scripting language is used to add a loop to it in order to realize the continuous automatic modeling and analysis process.

[0009] Preferably, step 1 includes:

[0010] The skin progressive hot pressing process is a dynamic process. The ABAQUS / Explicit solver was used to establish the first skin progressive hot pressing model.

[0011] Preferably, step 2 includes:

[0012] Due to the stress and strain of the skin during the first progressive hot pressing impact, the establishment of the second progressive hot pressing model of the skin must be based on the results of the first progressive hot pressing analysis. Similarly, the ABAQUS / Explicit solver is used to establish the second progressive hot pressing analysis model of the skin.

[0013] Preferably, the part is a complex variable curvature bidirectional concave titanium alloy skin, the middle part of the part is bidirectionally concave, the total length of the part is 800-900mm, and the maximum depth of the part along the hot pressing direction is 200mm.

[0014] Preferably, in step 1, the ABAQUS / Explicit solver is used to establish the first skin progressive hot pressing model, and the 1 / 2 model is used for analysis to improve analysis efficiency.

[0015] Preferably, the specific operation process for establishing the first progressive hot pressing model of the skin is as follows: establish a selection set to achieve parameterized selection; enable restart settings when establishing the analysis step; select general contact when defining the contact type.

[0016] Preferably, the cyclic progressive hot pressing mold is preheated to 800°C for 15 minutes.

[0017] Preferably, the cyclic progressive hot pressing mold closing and pressure holding conditions are: temperature 800℃, pressure 1500N, and holding time 15min.

[0018] This application has the following technical advantages:

[0019] 1. This invention, through a rationally designed titanium alloy hot forming process, calculates the step length based on the curvature of the part's shape. The accuracy of the step length setting directly determines the accuracy of the part's forming and the material properties. It can effectively solve the forming problem of double concave skins. The forming accuracy and the fit to the tire can reach within 0.3mm, and the pass rate can reach over 95%. It can be applied to fuselage skins and other related fields.

[0020] 2. A progressive forming algorithm for raw materials was designed. This algorithm can effectively control the flow and accumulation of materials, save costs, significantly reduce material size, reduce production costs, and achieve high economic benefits in batch production. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a skin part structure provided in an embodiment of this application;

[0022] Figure 2 This is a flowchart of a progressive hot pressing method for a variable curvature bidirectional concave titanium alloy skin provided in an embodiment of this application. Detailed Implementation

[0023] This invention discloses a progressive hot pressing method for complex variable curvature bidirectional concave titanium alloy skin based on Python secondary development, belonging to the field of digital skin technology. This invention solves the problems of surface quality defects such as wrinkles and cracks, and long forming cycles, inherent in existing progressive hot pressing methods for variable curvature titanium alloy skin. This invention calculates the optimal number of progressive forming cycles for the part using Python secondary development and effectively solves the surface wrinkling problem after forming by optimizing the mold structure and using a more efficient hot pressing method. Furthermore, the optimal number of progressive forming cycles calculated in this application effectively avoids the problem of damaged mechanical properties caused by excessive hot pressing cycles, greatly improving the forming efficiency of the part.

[0024] Please see Figures 1-2 The technical solution of the present invention:

[0025] A progressive hot pressing method for forming a variable curvature bidirectional anti-concave titanium alloy skin is provided. The operation steps of this method are as follows:

[0026] Step 1: Determine the incremental step length of the material during the thermoforming process based on the curvature, material thickness, and shape of the part. During the forming process, the part is pre-formed using an incremental forming process, with the step length being the length of each forming step in the incremental forming process. Since the normal direction directly affects the material's flowability, the curvature L in the normal direction is set. m In order to ensure the accuracy of the profile, based on the accumulation of previous experience data, the progressive forming dimension D is calculated using the following formula (1):

[0027] D = 5.78L m -1.022 x10 4 (1)

[0028] D—Incremental forming step length;

[0029] L m —Curvature in the normal direction of the part

[0030] Step 2: Conduct simulation analysis based on the step length settings of the part during the forming process;

[0031] Step 2-1: Establish the first progressive hot pressing model for the skin.

[0032] The skin progressive hot pressing process is a dynamic process. The first step size is selected and the ABAQUS / Explicit solver is used to establish the first skin progressive hot pressing model.

[0033] Step 2-2: Establish the second progressive hot pressing model for the skin.

[0034] Using the final state of the first progressive hot pressing of the skin as input, the establishment of the second progressive hot pressing model of the skin is based on the results data of the first progressive hot pressing analysis. Similarly, the ABAQUS / Explicit solver is used to establish the second progressive hot pressing analysis model of the skin.

[0035] Steps 2-3: Develop a progressive hot pressing cycle program for the skin based on the step size.

[0036] After the nth progressive hot pressing cycle analysis of the skin is completed, a loop is added using the Python scripting language to achieve a continuous and automatic modeling and analysis process.

[0037] The accuracy of the step size setting and the location of the defect can be determined based on the stress cloud map and stress distribution in the simulation results.

[0038] Step 3: Conduct progressive hot pressing process experiments;

[0039] Step 3-1: Calculate the length of the progressive hot-pressed blank. First, unfold the blank according to the dimensions of the digital model. Combined with the step size setting in Step 1, calculate the overall blank length L. z The calculation is shown in formula (2).

[0040] L z =L+(L / D)x100t (2)

[0041] Lz—Total length of the wool fabric

[0042] L—Length of the unfolded material of the part

[0043] D—Incremental forming step length

[0044] t — thickness of the part

[0045] Step 3-2 according to L z The calculated length is used for precise cutting, and the parts are coated with boron nitride lubricant for anti-oxidation protection.

[0046] Step 3-3: Install the thermoforming mold into the thermoforming equipment, level the tooling, and start heating to 650℃-700℃. Once the temperature stabilizes, begin hot pressing. First, push the first step length into the equipment at a pressure of 500KN and hold the pressure for 3 minutes. Gradually increase the hot pressing according to the previously calculated step length, setting the pressure to 500KN and holding the pressure for 3-5 minutes. After all parts are in the furnace, hold the pressure for 7-10 minutes.

[0047] Steps 3-4: Remove the parts and cut them according to the outline of the mold.

[0048] Steps 3-5 are performed to ensure consistency with the digital model as required by the design.

[0049] In other embodiments of this application, a progressive hot pressing method for variable curvature bidirectional anti-concave titanium alloy skin is shown, and the illustrated implementation provides aircraft fuselage skin as follows: Figure 1 As shown, the middle part of the part is bidirectionally concave. The total length of the part is 1100mm, the width is 600mm, the material is Ti6Al4V, the material thickness is δ=1.5mm, and the normal curvature is 300mm.

[0050] Step 1: Determine the step size of the material during the thermoforming process according to the curvature, material thickness, and shape of the part;

[0051] D = 5.78L m -1.022 x10 4 =5.78 x 300 -1.022 x10 4 =170mm (1)

[0052] Step 2: Based on the step size of 170mm during the part forming process, the number of progressive forming times is 600÷170=3.5 times, and 4 progressive forming simulation analyses are set.

[0053] Step 2-1: Establish the first progressive hot pressing model for the skin.

[0054] The skin progressive hot pressing process is a dynamic process. The first step size is selected and the ABAQUS / Explicit solver is used to establish the first skin progressive hot pressing model.

[0055] Step 2-2: Establish the second progressive hot pressing model for the skin.

[0056] Using the final state of the first progressive hot pressing of the skin as input, the establishment of the second progressive hot pressing model of the skin is based on the results data of the first progressive hot pressing analysis. Similarly, the ABAQUS / Explicit solver is used to establish the second progressive hot pressing analysis model of the skin.

[0057] Steps 2-3: Establish the third progressive hot pressing model for the skin.

[0058] Using the final state of the second progressive hot pressing of the skin as input, the establishment of the third progressive hot pressing model of the skin is based on the results data of the second progressive hot pressing analysis. Similarly, the ABAQUS / Explicit solver is used to establish the third progressive hot pressing analysis model of the skin.

[0059] Steps 2-4: Establish the fourth progressive hot pressing model for the skin.

[0060] Using the final state of the third progressive hot pressing of the skin as input, the establishment of the third progressive hot pressing model of the skin is based on the result data of the third progressive hot pressing analysis. Similarly, the ABAQUS / Explicit solver is used to establish the fourth progressive hot pressing analysis model of the skin.

[0061] The accuracy of the step size setting and the location of the defect can be determined based on the stress cloud map and stress distribution in the simulation results.

[0062] Step 3: Conduct progressive hot pressing process experiments;

[0063] Step 3-1: Calculate the length of the progressive hot-pressed blank. First, unfold the blank according to the dimensions of the digital model. Combined with the step size setting in Step 1, calculate the overall blank length L. z The calculation is shown in formula (2).

[0064] L z =L+(L / D)x100t=600+(600 / 170)x100x1.5=529mm (2)

[0065] Lz—Total length of the wool fabric

[0066] L—Length of the unfolded material of the part

[0067] D—Incremental forming step length

[0068] t — thickness of the part

[0069] Step 3-2 according to L z The calculated length is used for precise cutting, and the parts are coated with boron nitride lubricant for anti-oxidation protection.

[0070] Step 3-3: Install the thermoforming mold into the thermoforming equipment, level the tooling, and start heating to 650℃-700℃. Once the temperature stabilizes, begin hot pressing. First, insert the first 170mm section into the equipment at a pressure of 500KN for 3 minutes. Then, perform the second progressive forming step of 170mm, setting the pressure to 500KN and holding it for 3 minutes. Next, perform the third progressive forming step of 170mm, setting the pressure to 500KN and holding it for 4 minutes. Finally, perform the fourth progressive forming step of 90mm, setting the pressure to 500KN and holding it for 4 minutes. After all parts are in the furnace, maintain the pressure for 8 minutes.

[0071] Steps 3-4: Remove the parts and cut them according to the outer contour of the mold, with a cutting accuracy of 0.5mm.

[0072] After the inspection in steps 3-5, the part's fit to the mold can be as close as 0.2mm, and the dimensional accuracy is within 0.5mm.

Claims

1. A method for progressive hot pressing of a variable curvature bidirectional concave titanium alloy skin, characterized in that, The method includes the following steps: Step 1: Determine the incremental step length of the material during the thermoforming process based on the curvature, material thickness, and shape of the part. During the forming process, the part is pre-formed using an incremental forming process, with the step length being the length of each forming step in the incremental forming process. Since the normal direction directly affects the material's flowability, the curvature L in the normal direction is set. m In order to ensure the accuracy of the profile, based on the accumulation of previous experience data, the calculation method of the progressive forming dimension D is as shown in formula (1): Where D represents the incremental forming step length; L m —Curvature in the normal direction of the part; Step 2: Conduct simulation analysis based on the step length settings during the part forming process: Step 2-1: Establish the first progressive hot pressing model for the skin; Step 2-2: Establish the second progressive hot pressing model for the skin; Steps 2-3: Develop a progressive hot pressing cycle program for the skin based on the step size; Step 3: Conduct progressive hot pressing process experiments; Step 3-1: Calculate the length of the progressive hot-pressed blank. First, unfold the blank according to the dimensions of the digital model. Combined with the step size setting in Step 1, calculate the overall blank length L. z The calculation is performed, and the formula is shown in (2); L z — Total length of the raw material; L — Length of the raw material when the part is unfolded; D — Progressive forming step length; t — Thickness of the part; Step 3-2 According to L z The calculated length is used for precise cutting, and the parts are coated with boron nitride lubricant for anti-oxidation protection; Step 3-3 Install the thermoforming mold into the thermoforming equipment, level the tooling, and start heating to 650℃-700℃. Once the temperature stabilizes, begin hot pressing. First, push the first step length into the equipment at a pressure of 500KN and hold the pressure for 3 minutes. Gradually hot press according to the previously calculated step length, setting the pressure to 500KN and holding the pressure for 3-5 minutes. After all parts are in the furnace, hold the pressure for 7-10 minutes. Steps 3-4: Remove the parts and cut them according to the outline of the mold. Steps 3-5 are performed to ensure consistency with the digital model as required by the design.

2. The method according to claim 1, characterized in that, Step 2-1 includes: The skin progressive hot pressing process is a dynamic process. The ABAQUS / Explicit solver was used to establish the first skin progressive hot pressing model.

3. The method according to claim 2, characterized in that, Step 2-2 includes: Due to the stress and strain of the skin during the first progressive hot pressing impact, the establishment of the second progressive hot pressing model of the skin must be based on the results of the first progressive hot pressing analysis. Similarly, the ABAQUS / Explicit solver is used to establish the second progressive hot pressing analysis model of the skin.

4. The method according to claim 3, characterized in that, The part is a complex variable curvature bidirectional concave titanium alloy skin. The middle part of the part is bidirectionally concave. The total length of the part is 800~900mm, and the maximum depth of the part along the hot pressing direction is 200mm.

5. The method according to claim 4, characterized in that, In step 2-1, the ABAQUS / Explicit solver is used to establish the first skin progressive hot pressing model. The 1 / 2 model is used for analysis to improve analysis efficiency.

6. The method according to claim 5, characterized in that, The specific operation process for establishing the first progressive hot pressing model of the skin is as follows: establish a selection set to achieve parameterized selection; enable restart settings when establishing the analysis step; select general contact when defining the contact type.

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