Variable-curvature bidirectional reverse concave type titanium alloy skin progressive hot pressing forming method

Abstract

The invention provides a variable-curvature bidirectional reverse concave type titanium alloy skin progressive hot pressing forming method, belongs to the technical field of digital intelligent skins, and solves the problems that surface quality defects such as wrinkles and cracks are prone to occurring during existing variable-curvature titanium alloy skin progressive hot pressing forming, and the forming period is long. According to the method, the optimal incremental forming times of the part are calculated through a python secondary development method, and the problem of surface wrinkles after the part is formed is effectively solved by optimizing the mold structure and improving the part hot pressing mode. And the optimal incremental forming frequency is calculated, so that the problem that the mechanical property of the part is damaged due to excessive hot pressing frequency is effectively solved, and the forming efficiency of the part is greatly improved.

Description

Technical Field

[0001] The present application belongs to the technical field of titanium alloy precision forming, and specifically relates to a method for progressive hot pressing of a variable curvature bidirectional reverse concave titanium alloy skin. Background Art

[0002] In recent years, titanium alloy materials have been widely used in the field of aircraft skins. Complex variable curvature titanium alloy skins have become the main form of aircraft. The structural characteristics are that the curvature radius is greater than 50mm, the part size is more than 1 meter, and it presents a bidirectional concave structure. Due to the material properties of titanium alloys, they cannot be plastically deformed in a cold state and cannot meet the shape requirements of parts.

[0003] Titanium alloys are conventionally formed by hot forming. If such parts are directly formed by traditional one-time hot pressing, the material cannot be discharged in the limited space during the hot pressing process, and the material has poor fluidity, which will inevitably lead to large-area wrinkles and overlapping defects in the center of the part. As a result, the part qualification rate can only reach 5%, and the maximum degree of adhesion is 5mm, which is difficult to meet the surface quality requirements of skin parts. Summary of the invention

[0004] Purpose of the invention: In combination with the process characteristics of titanium alloy hot forming, the number of hot pressing cycles is predicted in the form of simulation, which effectively reduces the impact of thermal cycles on material properties. At the same time, the progressive hot pressing forming process method is used to complete the two processes of transition forming and final forming. Only one set of forming models is needed, which has the characteristics of low cost and good forming effect. The qualified rate reaches more than 95%. Therefore, it is very necessary to provide a variable curvature bidirectional reverse concave titanium alloy skin progressive hot pressing forming method.

[0005] The present application provides a variable curvature bidirectional reverse concave titanium alloy skin progressive hot pressing forming method, the method comprising the following steps:

[0006] Step 1, establishing the first skin progressive hot pressing model;

[0007] Step 2, establishing the second skin progressive hot pressing model;

[0008] Step 3, build a skin progressive hot pressing cycle program: After the second skin progressive hot pressing cycle analysis is completed, use the python scripting language to add a loop to it to achieve a continuous automatic modeling and analysis process.

[0009] Preferably, the step 1 comprises:

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

[0011] Preferably, the step 2 comprises:

[0012] Due to the first progressive thermal compression shock of the skin, stress and strain exist in the skin. The establishment of the second progressive thermal compression model of the skin should be based on the result data of the first progressive thermal compression analysis. The ABAQUS / Explicit solver is also used to establish the second progressive thermal compression analysis model of the skin.

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

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

[0015] Preferably, the specific operation process of establishing the first skin progressive hot pressing model is: establishing a selection set to realize parameterized selection; when establishing an analysis step, turning on the restart setting; when defining the contact type, selecting general contact.

[0016] Preferably, the cyclic progressive hot pressing mold is preheated to a temperature of 800° C., and the preheating time is 15 minutes.

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

[0018] This application has the following technical effects:

[0019] 1. The present invention designs a reasonable titanium alloy hot forming process method, and calculates the step length according to the design of the part's outer curvature. The accuracy of the step length setting directly determines the accuracy of part forming and the material properties, which can effectively solve the forming problem of double concave skins. The degree of adhesion after forming accuracy can reach within 0.3mm, and the qualified rate can reach more than 95%, which can be applied to related fields such as fuselage skins.

[0020] 2. A progressive forming algorithm for rough materials is designed. This algorithm can effectively control the flow and accumulation of materials on the one hand, and save costs on the other hand, greatly reduce the material size, low production cost, and achieve higher batch production economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of a skin part provided in an embodiment of the present application;

[0022] Figure 2 It is a flow chart of a variable curvature bidirectional reverse concave titanium alloy skin progressive hot pressing forming method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0023] The present invention discloses a method for progressive hot pressing of complex variable curvature bidirectional inverse concave titanium alloy skins based on python secondary development, and belongs to the field of digital skin technology. The present invention solves the problem that surface quality defects such as wrinkles and cracks are prone to occur during the progressive hot pressing of existing variable curvature titanium alloy skins, and the forming cycle is long. The present invention calculates the optimal progressive forming times of parts through the method of python secondary development, and effectively solves the problem of surface wrinkles after part forming by optimizing the mold structure and higher part hot pressing methods. And the optimal progressive forming times calculated by the present application effectively gets rid of the problem of damaged mechanical properties of parts caused by too many hot pressing times, and greatly improves the forming efficiency of the parts.

[0024] See also Figure 1-Figure 2 , the technical solution of the present invention:

[0025] Provided is a method for incremental hot pressing of a variable curvature bidirectional reverse concave titanium alloy skin, the operating steps of which are as follows:

[0026] Step 1: Determine the incremental step length of the material in the hot forming process according to the curvature, material thickness and shape of the part; during the forming process, the incremental forming process is used to realize the pre-forming of the part. The step length is the length of each forming process in the incremental forming process. Since the normal direction directly affects the fluidity of the material, the curvature L in the normal direction is set. m In order to ensure the accuracy of the molding surface, the calculation method of the progressive forming dimension D is shown in formula (1) based on the previous experience data accumulation:

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

[0028] D—incremental forming step length;

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

[0030] Step 2, conduct simulation analysis in combination with the step length setting of the part during the forming process;

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

[0032] The skin progressive hot pressing process is a dynamic process. The size of the first step 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 skin progressive hot pressing model

[0034] The final state of the first skin progressive hot pressing forming is used as input. The establishment of the second skin progressive hot pressing model is based on the result data of the first progressive hot pressing analysis. The ABAQUS / Explicit solver is also used to establish the second skin progressive hot pressing analysis model.

[0035] Step 2-3: Establish the skin progressive hot pressing cycle program according to the step length

[0036] After the nth skin progressive hot-pressing cycle analysis is completed, the python scripting language is used to add a loop to it to realize the continuous automatic modeling and analysis process.

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

[0038] Step 3, conducting a progressive hot pressing process test;

[0039] Step 3-1 Calculate the length of the progressive hot pressing raw material. First, expand it according to the size of the digital model. Combined with the step size setting in step 1, calculate the overall length L of the raw material. z The calculation is performed, and the formula is shown as (2).

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

[0041] Lz—Total length of the raw material

[0042] L—Unfolded rough material length of the part

[0043] D—Incremental forming step length

[0044] t—Thickness of the part

[0045] Step 3-2 Follow 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 hot forming mold into the hot forming equipment, level the tooling and start heating to 650℃-700℃, and start hot pressing when the temperature stabilizes. First, push the first step into the equipment with a pressure of 500KN and a holding time of 3 minutes. Then, gradually perform hot pressing according to the step length calculated in the early stage, set the pressure to 500KN, and hold the pressure for 3-5 minutes. After all the parts are in the furnace, hold the pressure for 7-10 minutes.

[0047] Step 3-4: Take out the parts and cut them according to the mold outline.

[0048] Steps 3-5 are tested to ensure that the digital model is consistent with the design requirements.

[0049] In other embodiments of the present application, a variable curvature bidirectional reverse concave titanium alloy skin progressive hot pressing forming method is provided. The aircraft fuselage skin provided by the embodiment shown is 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 direction is 600, its material is Ti6Al4V, the material thickness δ=1.5mm, and its normal curvature is 300mm.

[0050] Step 1: Determine the progressive step length of the material in the hot forming process according to the curvature, material thickness and shape of the part;

[0051] D=5.78L m -1.022 x10 4 =5.78x300 -1.022 x10 4 =170mm (1)

[0052] Step 2: Combined with the step length of 170 mm during the forming process, the number of incremental forming is 600÷170=3.5 times, and 4 incremental forming simulation analyses are set;

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

[0054] The skin progressive hot pressing process is a dynamic process. The size of the first step 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 skin progressive hot pressing model

[0056] The final state of the first skin progressive hot pressing forming is used as input. The establishment of the second skin progressive hot pressing model is based on the result data of the first progressive hot pressing analysis. The ABAQUS / Explicit solver is also used to establish the second skin progressive hot pressing analysis model.

[0057] Step 2-3: Establish the third skin progressive hot pressing model

[0058] The final state of the second skin progressive hot pressing forming is used as input. The establishment of the third skin progressive hot pressing model is based on the result data of the second progressive hot pressing analysis. The ABAQUS / Explicit solver is also used to establish the third skin progressive hot pressing analysis model.

[0059] Step 2-4, establish the fourth skin progressive hot pressing model

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

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

[0062] Step 3, conducting a progressive hot pressing process test;

[0063] Step 3-1 Calculate the length of the progressive hot pressing raw material. First, expand it according to the size of the digital model. Combined with the step size setting in step 1, calculate the overall length L of the raw material. z The calculation is performed, and the formula is shown as (2).

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

[0065] Lz—Total length of the raw material

[0066] L—Unfolded rough material length of the part

[0067] D—Incremental forming step length

[0068] t—Thickness of the part

[0069] Step 3-2 Follow 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 hot forming mold into the hot forming equipment, level the tooling and start heating to 650℃-700℃, and start hot pressing when the temperature stabilizes. First, put the first step of 170mm into the equipment with a pressure of 500KN and a holding time of 3 minutes, then carry out the second step of gradual forming 170mm inspection, the pressure is set to 500KN, the holding time is 3 minutes, the third step of gradual forming 170mm inspection, the pressure is set to 500KN, the holding time is 4 minutes, the fourth step of gradual forming 90mm inspection, the pressure is set to 500KN, the holding time is 4 minutes, and after all the parts are put into the furnace, the pressure is held for 8 minutes.

[0071] Step 3-4: Take out the parts and cut them according to the mold outline with a cutting accuracy of 0.5mm.

[0072] After the inspection in steps 3-5, the part adhesion can reach 0.2mm and the shape accuracy can be within 0.5mm.

Claims

1. A variable curvature bidirectional reverse concave titanium alloy skin progressive hot pressing forming method, characterized in that: The method comprises the following steps: Step 1, establishing the first skin progressive hot pressing model; Step 2, establishing the second skin progressive hot pressing model; Step 3, build a skin progressive hot pressing cycle program: After the second skin progressive hot pressing cycle analysis is completed, use the python scripting language to add a loop to it to achieve a continuous automatic modeling and analysis process.

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

3. The method according to claim 2, characterized in that The step 2 comprises: Due to the first progressive thermal compression shock of the skin, stress and strain exist in the skin. The establishment of the second progressive thermal compression model of the skin should be based on the result data of the first progressive thermal compression analysis. The ABAQUS / Explicit solver is also used to establish the second progressive thermal compression analysis model of the skin.

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

5. The method according to claim 4, characterized in that In the 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 the analysis efficiency.

6. The method according to claim 5, characterized in that The specific operation process of establishing the first skin progressive thermal compression model is: establish a selection set to realize parameterized selection; turn on the restart setting when establishing the analysis step; select general contact when defining the contact type.

7. The method according to claim 6, characterized in that The cyclic progressive hot pressing mold is preheated to a temperature of 800°C, and the preheating time is 15 minutes.

8. The method according to claim 7, characterized in that The cyclic progressive hot pressing mold holding treatment conditions are: temperature 800℃, pressure 1500N, and holding time 15min.

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