A device and method for preparing thin-walled formed parts based on a dual-gradient structure

Abstract

The present invention relates to an incremental forming device and method for preparing thin-walled components with a dual-gradient structure based on thermomechanically coupled cyclic loading. The device comprises: a fixture support tooling, a drive device, and a rotatable tool head. The fixture support tooling is used to clamp the sheet material to be formed, apply a back-force when the sheet material undergoes forward forming, and provide support when the sheet material undergoes reverse forming. The drive control unit adjusts the deformation conditions of the local area of ​​the sheet material based on the motion state (downward pressure, rotational speed) and motion trajectory of the tool head. Under thermomechanically coupled cyclic loading conditions, a high-performance thin-walled formed part with a dual-gradient structure having a positive grain gradient and a reverse dislocation density gradient along the thickness direction is prepared. Compared with the existing technology, the present invention uses thermomechanically coupled incremental forming technology to prepare a new dual-gradient structure and simultaneously prepares a thin-walled formed part, which can significantly improve the strength and toughness of the formed part, effectively reduce processing costs, and improve processing efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of material heterogeneous structure design, and in particular to a device and method for preparing thin-walled formed parts based on a dual-gradient structure. Background Art

[0002] With the continuous development of new material preparation processes and material structure design, the demand for advanced materials with excellent strength and toughness is becoming increasingly urgent in fields such as aerospace, rail transportation, nuclear power, petroleum, and chemical engineering. However, traditional engineering materials have an "inverted" relationship between strength and toughness, that is, the strength-toughness relationship follows a concave "banana" curve. When using traditional methods to improve material strength, toughness is often sacrificed. Therefore, how to achieve a synergistic improvement in the strength and toughness of engineering materials is an urgent problem that needs to be solved.

[0003] Existing research suggests that by regulating the heterogeneity between components, such as by gradient distribution of grain size along a specific scale, it is possible to overcome the "mutually exclusive" relationship between strength and toughness, thereby making the "banana" curve convex. Common processes for preparing grain-graded heterogeneous materials include surface mechanical treatment, surface shot peening, magnetron sputtering, and 3D printing. The main principle is to use surface mechanical treatment or energy deposition to induce gradient deformation from the surface to the core of the material under processing conditions such as gradient distribution of strain, strain rate, or temperature, thereby obtaining heterogeneous materials with gradient grain size structures.

[0004] Among them, surface mechanical treatment and surface shot peening are post-forming processing steps. Compared with the integrated processes of part forming and gradient preparation such as magnetron sputtering and 3D printing, the process is more complicated; methods such as 3D printing and magnetron sputtering have the disadvantages of being expensive and costly. In addition, the grain gradient heterogeneous materials prepared by traditional processes such as surface mechanical grinding will introduce large residual stresses inside the sample. In summary, although the above-mentioned traditional grain gradient structure preparation process can improve the strength and toughness of the material, the improvement is not significant; and the existing research can only be prepared on sheet materials or rods, that is, it has not yet been applied to formed parts, so it does not have engineering application value for the time being. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a device and method for preparing thin-walled formed parts based on a dual-gradient structure. A new dual-gradient structure is prepared through thermomechanical coupling progressive forming technology, and thin-walled formed parts are prepared at the same time, which can effectively improve the strength and toughness of the formed parts.

[0006] The objectives of the present invention can be achieved through the following technical solutions: A device for preparing thin-walled formed parts based on a dual-gradient structure, comprising a fixture support tooling, a support die is provided below the fixture support tooling, a tool head is provided above the fixture support tooling, the tool head is connected to the output end of the spindle motor, the input end of the spindle motor is connected to a drive control unit, the drive control unit is connected to a host computer, and the fixture support tooling is used to clamp the sheet material to be formed;

[0007] The supporting mold is used to apply a back force when the sheet material is formed in the forward direction and to provide a supporting effect when the sheet material is formed in the reverse direction;

[0008] Under the corresponding instructions of the host, the drive control unit adjusts the movement state of the tool head by controlling the working state of the spindle motor, so as to perform thermal-mechanical coupled progressive forming processing on the sheet metal, thereby preparing a dual-gradient structure including a coupled grain positive gradient and a dislocation reverse gradient, and simultaneously obtaining a corresponding thin-walled formed part.

[0009] Furthermore, the host is connected to a temperature detector, which is used to detect the surface temperature data of the sheet metal in real time and transmit it to the host. The host changes the instructions output to the drive control unit in real time according to the surface temperature of the sheet metal.

[0010] Furthermore, the temperature detector is provided with a display device for displaying the current temperature change of the sheet material surface in real time.

[0011] Furthermore, the temperature detector is specifically a thermal imager.

[0012] Furthermore, the fixture support tooling is composed of a combination of detachable "I"-shaped fixtures, which are fixed on the processing plane and can be assembled and disassembled according to the size of the formed part.

[0013] Furthermore, the supporting mold is fixed to the processing plane and is located at the bottom of the sheet material to be formed.

[0014] Furthermore, the tool head is a cylinder, and the transition area between the end face of the tool head and the main body is a transition fillet.

[0015] Furthermore, the tool head is made of non-magnetic tungsten steel or hard alloy.

[0016] A method for preparing a thin-walled formed part based on a dual-gradient structure comprises the following steps:

[0017] S1. Pre-model the target part in 3D and generate the corresponding 3D machining trajectory. Import the 3D machining trajectory into the host computer;

[0018] S2. Utilize the relationship between the material's dynamic recrystallization behavior and deformation conditions (temperature, strain rate, and strain, etc.), and set the spatial gradient distribution of the deformation conditions based on the spatial characteristics of the target dual-gradient structure. Calculate and set the processing parameters based on the analytical model of deformation conditions and processing parameters.

[0019] S3. Fix the support die to the machining plane and clamp the sheet to be formed on the fixture support fixture. Calibrate the tool head initial position and cutting height. The main machine transmits the 3D machining trajectory and machining process parameter instructions to the drive control unit. Combined with real-time feedback on the sheet surface temperature, the spindle motor drives the tool head to perform thermomechanical coupled progressive forming on the sheet. If the sheet temperature does not meet the analytical model prediction results, the analytical model is corrected and the machining process parameters are reset.

[0020] S4. A dual-gradient structure including a coupled grain forward gradient and a dislocation reverse gradient is prepared, and a corresponding thin-walled formed part is obtained at the same time.

[0021] Furthermore, the processing parameters include the pressing amount, the rotation speed of the tool head and the feed speed.

[0022] Furthermore, the specific process of the tool head performing thermal-mechanical coupled progressive forming processing on the sheet material in step S3 is as follows: according to the currently set processing parameters, the tool head rotates at high speed and contacts the sheet material, generates heat by frictional heat generation and transfers the heat to the surface of the sheet material. At the same time, the tool head is connected to the spindle motor to transfer the load required for sheet material forming, so that the sheet material completes local deformation under the point contact of the tool head. Thereafter, the tool head moves according to the three-dimensional processing trajectory to complete the processing layer by layer. During the progressive process, the tool head transfers the heat and forming load to the sheet material surface according to the three-dimensional processing trajectory, completing the simultaneous preparation and processing of the thick-sheet dual-gradient structure and the geometric shape of the formed part.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] The present invention provides a fixture support fixture for clamping the sheet material to be formed. A support die is provided below the fixture support fixture to apply a back-force during forward forming of the sheet material and provide support during reverse forming of the sheet material. Furthermore, a drive control unit is provided to adjust the motion state of the tool head by controlling the operating state of the spindle motor under corresponding instructions from the host computer, thereby performing a thermomechanically coupled progressive forming process on the sheet material, thereby producing a dual-gradient structure and a corresponding thin-walled formed part. The dual-gradient structure includes a heterogeneous structure with a coupled grain forward gradient and a dislocation reverse gradient, which can effectively improve the problem of insufficient core hardening. While producing the dual-gradient structure, it also achieves shape processing and performance optimization of the component, effectively improving the strength and toughness of the thin-walled formed part while effectively reducing processing steps and costs, significantly improving production efficiency.

[0025] The present invention is provided with a temperature detector for detecting the surface temperature data of the sheet metal in real time and transmitting it to the host computer. The host computer changes the instructions output to the drive control unit in real time according to the surface temperature of the sheet metal. If the surface temperature of the sheet metal does not reach the expected level or has exceeded the expected level, the processing parameters are adjusted accordingly, which can ensure the precise adjustment of the processing process, thereby preparing a product that conforms to the target formed part.

[0026] The present invention utilizes the frictional heat generated by the tool head and the sheet material to promote dynamic recrystallization of the sheet material surface due to high temperature and large deformation, thereby forming a dual-gradient structure in which a fine-grained positive gradient and a dislocation reverse gradient coexist along the thickness direction. Compared with traditional processes such as mechanical grinding and laser impact that utilize large surface deformation to obtain a fine-grained gradient structure, the present invention does not introduce additional residual stress, and can effectively improve the stability and reliability of the formed parts during subsequent processing and use, thereby realizing low-cost, high-efficiency, and easy-to-control real-time dual-gradient structure preparation, overcoming the shortcomings of traditional gradient structure preparation methods such as high cost, low efficiency, difficult to control performance, and large residual stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the overall scheme of the present invention;

[0028] Figure 2 Schematic diagram of the device structure of the present invention;

[0029] Figure 3 Schematic diagram of the method flow of the present invention;

[0030] Figure 4 Schematic diagram of the application process of the embodiment;

[0031] Figures 5a-5b The target formed part model and the schematic diagram of the three-dimensional processing trajectory in the embodiment;

[0032] Figure 6 The microstructure diagrams of different dual gradient structures in the embodiments;

[0033] Figures 7a-7b The mechanical properties curves of different dual gradient structures in the embodiment;

[0034] Explanation of the marks in the figure: 1. Fixture support tooling, 2. Support mold, 3. Tool head, 4. Spindle motor, 5. Main machine, 6. Drive control unit, 7. Temperature detector. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Example

[0037] like Figure 1 As shown, the present invention proposes a progressive forming preparation scheme for preparing thin-walled components with a dual-gradient structure based on thermomechanical coupling cyclic loading. On the one hand, a thin-walled component progressive forming device is designed and the thin-walled component preparation is completed; on the other hand, a dual-gradient structure of grains and dislocations is introduced into the thin-walled component to improve the strength and toughness of the thin-walled component. Among them, the device mainly includes a clamp support tool, a drive device, and a rotatable tool head. The clamp support tool is used to clamp the sheet to be formed and apply a back force when the sheet undergoes forward forming and provide support when the sheet undergoes reverse forming. The drive control unit adjusts the deformation conditions (temperature, strain rate, and strain) of the local area of ​​the sheet through the motion state (downward pressure, rotation speed) and motion trajectory of the tool head. Under the conditions of thermomechanical coupling cyclic loading, a high-performance thin-walled formed part with a dual-gradient structure with a positive grain gradient and a reverse dislocation density gradient along the thickness direction is prepared. This scheme mainly uses thermomechanical coupling progressive forming technology to prepare a new dual-gradient structure and simultaneously prepare thin-walled formed parts. The dual-gradient structure includes a heterogeneous structure in which the positive gradient of the grain is coupled with the reverse gradient of the dislocation, which can effectively improve the problem of insufficient hardening of the core, and realize the shape processing and performance optimization of the component while preparing the dual-gradient structure. It can not only effectively improve the strength and toughness of thin-walled formed parts, but also effectively reduce the processing steps and costs, and significantly improve production efficiency.

[0038] like Figure 2 As shown, a thin-walled formed part preparation device based on a dual-gradient structure includes a fixture support tool 1, a support die 2 is provided below the fixture support tool 1, a tool head 3 is provided above the fixture support tool 1, the tool head 3 is connected to the output end of the spindle motor 4, the input end of the spindle motor 4 is connected to the drive control unit 6, and the drive control unit 6 is connected to the host 5. The fixture support tool 1 is used to clamp the sheet material to be formed;

[0039] The supporting die 2 is used to apply a back force when the sheet metal is being formed in the forward direction and to provide support when the sheet metal is being formed in the reverse direction;

[0040] Under the corresponding instructions of the host 5, the drive control unit 6 adjusts the movement state of the tool head 3 by controlling the working state of the spindle motor 4, so as to perform thermomechanical coupled progressive forming treatment on the sheet material, thereby preparing a dual-gradient structure including the coupling of the positive gradient of the grain and the reverse gradient of the dislocation, and obtaining the corresponding thin-walled formed parts.

[0041] It should be noted that the incremental forming technology is a sheet metal processing method based on a milling trajectory generation algorithm, and is widely used in the manufacturing industry. Due to its low processing cost and highly flexible manufacturing process, it is widely used in the field of rapid prototyping of small batches, customization and complex parts. The main process idea of ​​the incremental forming technology is "local deformation, step-by-step accumulation", which is similar to the process and deformation mechanism of mechanical stirring grinding technology. This scheme takes into account that the tool head can be set to a rotation mode on the CNC machine tool, and a large amount of frictional heat will be generated when it contacts the workpiece surface, causing the sheet metal to undergo dynamic recrystallization under the action of the thermal effect, thereby obtaining a fine-grained gradient structure with no residual stress or low residual stress.

[0042] In addition, the host 5 is connected to a temperature detector 7, which is used to detect the surface temperature of the sheet metal in real time and transmit the data to the host 5. The host 5 changes the instructions output to the drive control unit 6 in real time based on the surface temperature of the sheet metal. The temperature detector 7 is provided with a display screen for displaying the current changes in the surface temperature of the sheet metal in real time.

[0043] In this embodiment, the above-mentioned device is constructed in conjunction with a three-axis CNC milling machine. The fixture support tooling 1 is fixed on the processing plane of the milling machine and fixed around the sheet material to clamp the sheet material to be formed. The fixture support tooling 1 is composed of a detachable "I"-shaped fixture and can be assembled and disassembled according to the size of the formed part.

[0044] The support die 2 is also fixed to the milling machine processing plane and to the bottom of the sheet material, so as to apply additional back force when the sheet material undergoes positive deformation and to play a supporting role when the sheet material undergoes reverse forming;

[0045] The tool head 3 is connected to the spindle motor 4, and the motion trajectory of the tool head 3 is controlled by the drive control unit 6 to make contact with the sheet metal. The main body of the tool head 3 is a cylinder with a length of 120mm and a diameter of 20mm. The end face of the tool head is a 10mm circular plane. The transition area between the end face and the main body is a transition fillet with a radius of 5mm. The tool head is made of non-magnetic tungsten steel or cemented carbide, which still maintains high strength and hardness at 800°C. The tool head has two degrees of freedom, namely the vertical coordinate axis translational freedom and the rotational freedom. The two coordinate axis translational freedoms of the formed part in the processing plane are satisfied by the milling machine processing plane.

[0046] In this embodiment, the temperature detector 7 is a thermal imager, which is fixed to the processing plane of the milling machine. The probe is aligned with the contact position between the tool head 3 and the sheet material to record the surface temperature of the sheet material in real time.

[0047] Using the above device, a method for preparing thin-walled formed parts based on a dual gradient structure is realized, such as Figure 3 As shown, the following steps are included:

[0048] S1. Pre-model the target part in 3D and generate the corresponding 3D machining trajectory. Import the 3D machining trajectory into the host computer;

[0049] S2. Utilize the relationship between the material's dynamic recrystallization behavior and deformation conditions (temperature, strain rate, and strain, etc.), and set the spatial gradient distribution of the deformation conditions based on the spatial characteristics of the target dual-gradient structure. Calculate and set the processing parameters based on the analytical model of deformation conditions and processing parameters.

[0050] S3. Fix the support die to the machining plane and clamp the sheet to be formed on the fixture support fixture. Calibrate the tool head initial position and cutting height. The main machine transmits the 3D machining trajectory and machining process parameter instructions to the drive control unit. Combined with real-time feedback on the sheet surface temperature, the spindle motor drives the tool head to perform thermomechanical coupled progressive forming on the sheet. If the sheet temperature does not meet the analytical model prediction results, the analytical model is corrected and the machining process parameters are reset.

[0051] S4. A dual-gradient structure including a coupled grain forward gradient and a dislocation reverse gradient is prepared, and a corresponding thin-walled formed part is obtained at the same time.

[0052] In step S3, the specific process of the tool head performing thermal-mechanical coupled progressive forming processing on the sheet material is as follows: according to the currently set processing parameters, the tool head rotates at high speed and contacts the sheet material, generates heat by frictional heating and transfers the heat to the sheet material surface; at the same time, the tool head is connected to the spindle motor to transfer the load required for sheet material forming, so that the sheet material completes local deformation under the point contact of the tool head; thereafter, the tool head moves according to the three-dimensional processing trajectory to complete the processing layer by layer; in the progressive process, the tool head transfers the heat and forming load to the sheet material surface according to the three-dimensional processing trajectory, completing the simultaneous preparation and processing of the thick-sheet dual-gradient structure and the geometric shape of the formed part.

[0053] The application process of this embodiment is as follows Figure 4 As shown, including:

[0054] Step 1: Pre-treat the sheet to be formed (316L stainless steel sheet), use sandpaper to polish the surface oxide layer of the sheet until a uniform and flat surface with a metallic luster is exposed, and apply a layer of high-temperature lubricating grease about 0.1-0.2mm thick on the surface of the sheet to be formed.

[0055] Step 2: Using the relationship between the dynamic recrystallization behavior of the material and the deformation conditions (temperature, strain rate, strain, etc.), according to the spatial characteristics of the target dual-gradient structure, set the spatial gradient distribution law of the deformation conditions. According to the analytical model of deformation conditions and processing parameters, calculate and set the processing parameters. Figure 5a and 5bAs shown, the geometric shape of the formed part is constructed using 3D modeling software, a 3D CNC milling machine processing trajectory is generated, and the processing trajectory is exported into NC (Numeric Control) code format.

[0056] The processing parameters controlled by the drive control unit generally refer to the forming angle, downward pressure, tool head rotation speed, and feed rate. In this embodiment, the forming angle and feed rate are related to the geometry of the thin-walled part and are set to 40° and 1500 mm / min, respectively. The tool head rotation speed and downward pressure determine the deformation conditions of the sheet material, which in turn affect the spatial distribution of the dual-gradient structure. In this embodiment, the deformation conditions and processing parameters for 316L stainless steel sheet are calculated using the following model:

[0057]

[0058] Where: X DRX is the volume fraction of dynamic recrystallization; T is the deformation temperature; ε is the strain magnitude; is the strain rate; Z is the Zener-Hollomon parameter; ε c is the microstructural critical strain at the starting point of dynamic recrystallization, which is related to the Z parameter; ε * is the strain at the maximum recrystallization rate, which is also related to the Z parameter; Q is the activation energy of thermal deformation; R is the gas constant, and A, n and α are all undetermined material constants.

[0059] In the above model, after removing the undetermined material constants, the free variables are deformation conditions such as deformation temperature, strain, and strain rate. Therefore, the recrystallized volume fraction can be calculated based on the deformation conditions, thereby regulating the spatial distribution of the dual-gradient structure. The deformation conditions are determined by the processing parameters. In this example, based on experience and literature on the thermomechanically coupled incremental forming process for 316L stainless steel sheet, the processing parameters under certain deformation conditions were calculated using the following model.

[0060] The temperature calculation formula is:

[0061]

[0062] Where: T is the processing temperature; T m is the melting point of the material; ω is the tool head speed; v is the feed speed; k and γ are fitting parameters.

[0063] The strain calculation formula is:

[0064]

[0065] Where: ε t is the sum of the bending strain and tensile strain of the sheet; ε sis the shear strain on the sheet surface; R p is the tool head size; t P is the target depth; t g is the final thickness of the sheet; t0 is the original sheet thickness; Δt is the deformation time; h is the width of the surface heat-affected zone; r is the horizontal distance from the center of the tool head; θ is the angle between the calculation point and the horizontal movement direction.

[0066] The strain rate calculation formula is:

[0067] Surface contact area:

[0068] Internal deformation area:

[0069] in: is the strain rate; R t C is the tool head corner radius; t is the thermal conductivity of the sheet; G t is the temperature gradient, which can be calculated based on the temperature measurement value; F z is the forming load, which can be measured; μ is the friction coefficient; β is the forming angle.

[0070] Based on the above formula, a relationship model can be established between processing parameters, deformation conditions, and recrystallized volume fraction when producing a dual-gradient structure using a thermomechanically coupled incremental forming process for 316L stainless steel. It should be noted that this relationship model contains a number of empirical formulas, and the prediction results for the actual dual-gradient structure can only provide a reference for selecting processing parameters.

[0071] Based on the calculation results of the above relationship model, the processing window for 316L stainless steel sheet is: tool head rotation speed of 2000-5000 RPM, downward pressure of 0.1-0.3 mm, forming angle of 40°, and feed rate of 1500 mm / min. During the specific incremental forming process, the tool head rotation speed and downward pressure are adjusted accordingly based on the actual sheet surface temperature.

[0072] Step 3: Import the NC code file into the CNC milling machine host and set the tool head rotation speed and feed speed in the host.

[0073] Step 4: Fix the support mold on the milling machine processing plane and clamp the sheet to be formed on the fixture and support tooling.

[0074] Step 5: Calibrate the initial position of the tool head and the cutting height, import the machining trajectory NC code in the host into the drive control unit, and drive the tool head to start moving according to the machining trajectory.

[0075] Step 6: Turn on the temperature detector and start the machine tool; the tool head performs processing according to the preset motion trajectory, rotation speed, and feed speed, and promptly cleans the cutting debris generated when the tool head contacts the sheet surface;

[0076] During the forming process, the tool head rotates at high speed, making contact with the sheet material. This frictional heating generates heat and transfers it to the sheet material's surface. Simultaneously, the tool head is connected to the spindle motor, transmitting the required forming load. This allows the sheet material to undergo local deformation due to the tool head's point contact. Subsequently, the tool head completes the forming process layer by layer, following the motion trajectory provided by the drive control unit. This progressive process transfers heat and forming loads to the sheet material's surface along a pre-set processing trajectory, enabling the simultaneous creation and processing of the sheet material's through-thickness dual-gradient structure and the resulting part's geometry.

[0077] Step 7: During the processing, use a thermal imager to detect the temperature changes on the sheet metal surface in real time. If the temperature does not reach the expected level or exceeds the expected level, return to step 3 to adjust the tool head rotation speed and downward pressure.

[0078] Step 8: After the processing is completed, turn off the milling machine switch, remove the processed parts, and clean the processing debris and residual lubricating grease on the surface of the parts.

[0079] Step 9: Wire-cut the formed part to obtain tensile specimens and microscopic specimens. After grinding the surface to the relevant experimental standards, electron backscatter diffraction (EBSD) characterization and uniaxial tensile specimens are performed to verify the dual-gradient structure and mechanical properties of the formed part.

[0080] The results of EBSD characterization and uniaxial tensile test are as follows Figure 6 、 Figure 7a 、 Figure 7b As shown. Figure 6 It can be seen that dual-gradient structural parts with different grain positive gradients and dislocation reverse gradients can be prepared according to the thermomechanical coupling incremental forming process. Figures 7a-7b It can be seen that by changing the process parameters such as the pressing amount, tool head rotation speed and feed speed, formed parts with different strength and toughness combinations can be obtained.

[0081] In summary, this solution uses thermomechanical coupling progressive forming technology to produce a dual-gradient structure with high strength and high toughness. This dual-gradient structure includes a heterogeneous structure in which the positive gradient of the grain is coupled with the reverse gradient of the dislocation. It can effectively improve the problem of insufficient core hardening in the traditional fine-grained gradient structure, and its mechanical properties have absolute advantages over other similar materials. This solution only requires the use of a three-axis CNC milling machine and a matching forming fixture. The process is simple and low-cost. The heat generated by friction between the tool head and the sheet surface can be effectively controlled by adjusting the speed, feed speed and pass pressure of the milling machine. That is, by simply adjusting the processing parameters of the milling machine, the spatial random distribution of the output heat can be achieved, and then the precise adjustment of the dual-gradient structure can be completed, and formed parts with different strength and toughness combinations can be obtained.

[0082] At the same time, using this solution to prepare dual-gradient structures can simultaneously achieve shape processing and performance optimization of components, effectively reducing processing steps and costs, and significantly improving production efficiency. Furthermore, when this solution uses thermomechanically coupled incremental forming technology to prepare dual-gradient structures, the main principle of surface grain refinement is dynamic recrystallization. Compared to traditional processes such as mechanical grinding and laser shock blasting that use large surface deformation to achieve fine-grained gradient structures, this method does not introduce additional residual stress and can effectively improve the stability and reliability of the formed parts during subsequent processing and use.

Claims

1. A device for preparing thin-walled formed parts based on a dual gradient structure, characterized in that: The invention comprises a fixture support tool (1), wherein a support die (2) is provided below the fixture support tool (1), a tool head (3) is provided above the fixture support tool (1), the tool head (3) is connected to the output end of a spindle motor (4), the input end of the spindle motor (4) is connected to a drive control unit (6), the drive control unit (6) is connected to a host (5), and the fixture support tool (1) is used for clamping a sheet material to be formed; The support mold (2) is used to apply a back force when the sheet material is formed in the forward direction, and to produce a supporting effect when the sheet material is formed in the reverse direction; The host (5) is connected to a temperature detector (7), which is used to detect the surface temperature data of the sheet metal in real time and transmit the data to the host (5). The host (5) changes the instructions output to the drive control unit (6) in real time according to the surface temperature of the sheet metal; The driving control unit (6) adjusts the motion state of the tool head (3) by controlling the working state of the spindle motor (4) under the corresponding instruction of the host (5), so as to perform a thermomechanical coupled progressive forming process on the sheet material. The tool head (3) rotates at a high speed and contacts the sheet material, generates heat by frictional heating and transfers the heat to the surface of the sheet material, thereby preparing a dual-gradient structure including a coupled grain positive gradient and a dislocation reverse gradient, and simultaneously obtaining a corresponding thin-walled formed part.

2. The device for preparing thin-walled formed parts based on a dual gradient structure according to claim 1, characterized in that: The temperature detector (7) is provided with a display device for displaying the current temperature change of the sheet material surface in real time.

3. The device for preparing thin-walled formed parts based on a dual gradient structure according to claim 1, characterized in that: The fixture support tooling (1) is composed of a combination of detachable "I"-shaped fixtures, fixed on a processing plane, and can be assembled and disassembled according to the size of the formed part.

4. The device for preparing thin-walled formed parts based on a dual gradient structure according to claim 3, characterized in that: The supporting mold (2) is fixed on the processing plane and is located at the bottom of the sheet material to be formed.

5. The device for preparing thin-walled formed parts based on a dual gradient structure according to claim 1, characterized in that: The tool head (3) is a cylinder, and the transition area between the end face of the tool head (3) and the main body is a transition fillet.

6. The device for preparing thin-walled formed parts based on a dual gradient structure according to claim 1, characterized in that: The tool head (3) is made of non-magnetic tungsten steel or hard alloy.

7. A method for preparing thin-walled formed parts based on a dual-gradient structure, applied to the device for preparing thin-walled formed parts based on a dual-gradient structure as claimed in claim 1, characterized in that: The following steps are involved: S1. Pre-modeling the target formed part in three dimensions, generating a corresponding three-dimensional machining trajectory, and importing the three-dimensional machining trajectory into the host computer; S2. Utilizing the relationship between the dynamic recrystallization behavior of the material and the deformation conditions, and based on the spatial characteristics of the target dual-gradient structure, the spatial gradient distribution law of the deformation conditions is set, and the processing parameters are calculated and set based on the analytical model of the deformation conditions and processing parameters; S3. Fix the support die on the processing plane, clamp the sheet to be formed on the fixture support fixture, calibrate the initial position of the tool head and the cutting height, and transmit the three-dimensional processing trajectory and processing parameter instructions to the drive control unit. Combined with the real-time feedback of the sheet surface temperature, the spindle motor drives the tool head to perform thermomechanical coupled progressive forming on the sheet. If the sheet temperature does not meet the prediction results of the analytical model, the analytical model is corrected and the processing parameters are reset. S4. A dual-gradient structure including a coupled grain forward gradient and a dislocation reverse gradient is prepared, and a corresponding thin-walled formed part is obtained at the same time.

8. The method for preparing a thin-walled formed part based on a dual gradient structure according to claim 7, characterized in that: The processing parameters include the pressing amount, the rotation speed of the tool head and the feed speed.

9. The method for preparing a thin-walled formed part based on a dual gradient structure according to claim 7, characterized in that: The specific process of the tool head performing thermal-mechanical coupled progressive forming processing on the sheet material in step S3 is as follows: according to the currently set processing parameters, the tool head rotates at high speed and contacts the sheet material, generates heat by frictional heating and transfers the heat to the surface of the sheet material, and at the same time, the tool head is connected to the spindle motor to transfer the load required for sheet material forming, so that the sheet material completes local deformation under the point contact of the tool head. Thereafter, the tool head moves according to the three-dimensional processing trajectory to complete the processing layer by layer. During the progressive process, the tool head transfers the heat and forming load to the sheet material surface according to the three-dimensional processing trajectory, completing the simultaneous preparation and processing of the thick-section dual-gradient structure of the sheet material and the geometric shape of the formed part.

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