Thick plate space curved surface forming method based on multi-point mold

Abstract

The invention belongs to the technical field of plate curved surface forming, and particularly relates to a thick plate space curved surface forming method based on a multi-point die, which comprises the steps of S1, reduction schedule design, S2, self-adaptive feeding positioning, S3, dynamic die shape adjustment, S4, gradient coarse reduction, S5, gradual fine reduction, S6, online springback monitoring and S7, closed-loop correction. The optimal reduction regulation is generated through joint calculation of finite element simulation and a springback prediction model, real-time visualization of springback three-dimensional distribution is achieved based on a 1kHz high-frequency sampling force-displacement coupling monitoring system, out-of-tolerance springback is automatically corrected through a reverse compensation algorithm, meanwhile, a multi-sensor cooperative monitoring system and a prediction model constructed based on the mechanics theory are used for monitoring the springback three-dimensional distribution, and the real-time visualization of the springback three-dimensional distribution is achieved. Rebound distribution pre-judgment under different curvatures is achieved, and the shape precision stability of batch production is ensured through a closed-loop correction system.

Description

Technical Field

[0001] This invention relates to the field of sheet metal curved surface forming technology, specifically to a method for forming a thick plate spatial curved surface based on a multi-point mold. Background Technology

[0002] Three-dimensional curved sheet metal parts are characterized by their light weight, material saving, good stress distribution, and smooth shapes, and are widely used in both civilian and military fields. Traditional sheet metal processing methods mainly involve cold stamping on a press using molds, which offers advantages such as high production efficiency and suitability for mass production. However, with increasingly fierce market competition and the accelerating pace of product updates, the existing technology of processing sheet metal using integral molds has shown shortcomings such as long production preparation time, poor processing flexibility, high mold costs, and high manufacturing costs. Therefore, many scholars at home and abroad have devoted themselves to the research of new sheet metal plastic forming technologies, proposing the concept of multi-point mold forming to adapt to the market competition needs of modern manufacturing industries with rapidly changing products.

[0003] Currently, there are various types of multi-point mold forming devices; however, traditional thick plate spatial curved surface forming technology faces the following technical bottlenecks:

[0004] Springback control challenge: Springback is a serious problem during the forming of thick plates due to the elastic recovery of the material. Traditional methods rely on experience to compensate, making it difficult to guarantee accuracy.

[0005] Poor mold adaptability: Fixed molds cannot adapt to the needs of multi-variety, small-batch production, resulting in high mold change costs and long cycles;

[0006] Forming quality defects: Large deformation in a single pass can easily lead to problems such as surface indentation and stress concentration, which affect the fatigue performance of the product. Furthermore, there is a lack of real-time monitoring and closed-loop correction capabilities, and the adjustment of process parameters relies on trial and error. Therefore, there is an urgent need to provide a method for forming thick plate spatial curved surfaces based on multi-point molds. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] Therefore, the purpose of this invention is to provide a method for forming thick plate spatial curved surfaces based on multi-point molds. The optimal compression procedure is generated by finite element simulation and springback prediction model. Based on a force-displacement coupling monitoring system with 1kHz high-frequency sampling, the three-dimensional distribution of springback is visualized in real time. The reverse compensation algorithm automatically corrects excessive springback. At the same time, a multi-sensor collaborative monitoring system and a prediction model based on mechanical theory can predict the springback distribution under different curvatures. Finally, a closed-loop correction system ensures the shape accuracy and stability of mass production.

[0009] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0010] A method for forming a thick plate spatial curved surface based on a multi-point mold includes the following steps:

[0011] S1. Forming procedure design: Based on the three-dimensional point cloud data of the target surface, the forming procedure is generated by combining finite element simulation and springback prediction model, which includes a rough forming stage (single pass) and a fine forming stage (N≥3 passes), with the rough forming deformation accounting for 60-70% of the total.

[0012] S2. Adaptive feeding and positioning: The initial position of the sheet material is confirmed by laser scanning, and it is automatically adjusted to the center of the forming area with a positioning error of ≤0.5mm;

[0013] S3. Dynamic mold shaping: According to the procedure generated by S1, the discrete basic units of the lower mold are synchronously adjusted with an accuracy of 0.01mm to form an intermediate surface with a curvature gradient transition zone.

[0014] S4. Gradient coarse pressing: The upper die adopts zoned pressure control, with the pressure in the central area being 15-20% higher than that in the edge area, to complete the single-pass large deformation forming. After forming, the radius of curvature R1 and the target radius R satisfy: R = 0.92R1 ± 2%.

[0015] S5. Progressive fine pressing: carried out in 3-5 passes, with the deformation amount of each pass decreasing exponentially, and the deformation amount of the last pass ≤ 30% of the first pass, and satisfying: R = 1.05R2-N ± 1% (N is the current pass);

[0016] S6. Online rebound monitoring: During unloading, data is collected in real time through a force-displacement coupling sensor group (sampling frequency ≥ 1kHz). When the contact force decays to 0.1±0.02N, displacement recording is triggered, and a three-dimensional rebound distribution map is generated simultaneously.

[0017] S7. Closed-loop correction: If the springback error exceeds the limit, the reverse compensation algorithm will be automatically started: the optimal compensation surface will be solved in reverse based on the measured springback data, the mold surface will be updated, and S3-S6 will be repeated.

[0018] As a preferred embodiment of the thick plate spatial curved surface forming method based on multi-point mold described in this invention, in order to reduce the friction coefficient, ultrasonic vibration with an amplitude ≤5μm is used to assist the entire forming process.

[0019] As a preferred embodiment of the thick plate spatial curved surface forming method based on multi-point mold described in this invention, wherein: in step S5, the fine pressing process is divided into multiple passes, and the relationship between the radius of curvature R2-N of the formed surface in each pass and the target radius of curvature R satisfies:

[0020] R = (0.95~1.1)R2-N, and R2-N is uniformly or decreasingly distributed with increasing number of passes.

[0021] As a preferred embodiment of the thick plate spatial curved surface forming method based on multi-point mold described in this invention, in step S6, the force-displacement coupling sensor group is integrated into each pressure head of the upper mold to monitor the forming force in real time. The force-displacement coupling sensors work together to measure the springback amount during the unloading stage. The displacement sensor records the displacement data when the plate separates from the mold and is used to calculate the springback error.

[0022] As a preferred embodiment of the thick plate spatial curved surface forming method based on multi-point mold described in this invention, in step S6, the springback monitoring is based on a mathematical model constructed by mechanical theory, and the springback distribution under different curvatures is predicted by equilibrium differential equations and constitutive equations to optimize the design of coarse and fine pressing procedures.

[0023] As a preferred embodiment of the thick plate spatial curved surface forming method based on multi-point mold described in this invention, in step S7, during the springback error detection step, when the force sensor displays the force value F, the displacement sensor is triggered to record data. F is a preset minimum value, and the minimum value range is 0.05 to 0.5, to ensure measurement accuracy.

[0024] As a preferred embodiment of the thick plate spatial curved surface forming method based on multi-point mold described in this invention, the forming mold is composed of discretely arranged basic body units, the height of which can be independently adjusted to form a target envelope surface, and the ends of the basic body units are spherical cap structures to reduce indentations on the plate surface.

[0025] As a preferred embodiment of the thick plate spatial curved surface forming method based on multi-point mold described in this invention, the height of the basic unit is determined by compensating for springback deformation, specifically including:

[0026] Based on the material parameters of the sheet metal and the target curvature, the curvature of the springback compensation surface in the x / y directions is calculated.

[0027] B-spline interpolation is used to generate a springback compensation surface, which is then mapped onto the mold surface.

[0028] As a preferred embodiment of the thick plate spatial curved surface forming method based on multi-point mold described in this invention, the ultrasonic vibration frequency is 20-40kHz, the axial vibration and transverse feed form an elliptical motion trajectory, and the major axis forms an angle of 15-30° with the plate surface.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] High-precision forming control:

[0031] The process employs a multi-pass forming process of "coarse pressing + fine pressing" combined with an exponentially decreasing fine pressing procedure to effectively control springback error and improve the accuracy of the final radius of curvature. Furthermore, the discrete mold adjustment capability with an accuracy of 0.01mm, combined with the design of a curvature gradient transition zone, avoids sudden stress changes.

[0032] Process optimization:

[0033] The optimal compression procedure is generated by combining finite element simulation and springback prediction model. Based on a force-displacement coupling monitoring system with 1kHz high-frequency sampling, the real-time visualization of the three-dimensional distribution of springback is realized. At the same time, the reverse compensation algorithm automatically corrects the excessive springback.

[0034] Enhanced equipment adaptability:

[0035] Discrete basic unit structure (spherical cap end design) can quickly reconstruct mold surface, and B-spline interpolation algorithm realizes accurate mapping of springback compensation surface, thus supporting 3-5 curvature radius distribution modes (uniform / decreasing, 0.95 to 1.1 times the target value);

[0036] Quality consistency assurance:

[0037] A multi-sensor collaborative monitoring system, based on a prediction model constructed from mechanical theory, enables the prediction of springback distribution under different curvatures. A closed-loop correction system then ensures the shape accuracy and stability of mass production. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0039] Figure 1 This is a schematic block diagram illustrating the molding method steps of the present invention. Detailed Implementation

[0040] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0041] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0042] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0044] This invention provides a method for forming thick plate spatial curved surfaces based on multi-point molds. It generates the optimal compression procedure through joint calculation of finite element simulation and springback prediction model, and achieves real-time visualization of the three-dimensional springback distribution based on a force-displacement coupling monitoring system with 1kHz high-frequency sampling. An inverse compensation algorithm automatically corrects excessive springback. Please refer to [link to relevant documentation]. Figure 1 It includes the following steps:

[0045] S1. Forming procedure design: Based on the three-dimensional point cloud data of the target surface, the forming procedure is generated by combining finite element simulation and springback prediction model, which includes a rough forming stage (single pass) and a fine forming stage (N≥3 passes), with the rough forming deformation accounting for 60-70% of the total.

[0046] S2. Adaptive feeding and positioning: The initial position of the sheet material is confirmed by laser scanning, and it is automatically adjusted to the center of the forming area with a positioning error of ≤0.5mm;

[0047] S3. Dynamic mold shaping: According to the procedure generated by S1, the discrete basic units of the lower mold are synchronously adjusted with an accuracy of 0.01mm to form an intermediate surface with a curvature gradient transition zone.

[0048] S4. Gradient coarse pressing: The upper die adopts zoned pressure control, with the pressure in the central area being 15-20% higher than that in the edge area, to complete the single-pass large deformation forming. After forming, the radius of curvature R1 and the target radius R satisfy: R = 0.92R1 ± 2%.

[0049] S5. Progressive fine pressing: carried out in 3-5 passes, with the deformation amount of each pass decreasing exponentially, and the deformation amount of the last pass ≤ 30% of the first pass, and satisfying: R = 1.05R2-N ± 1% (N is the current pass);

[0050] S6. Online rebound monitoring: During unloading, data is collected in real time through a force-displacement coupling sensor group (sampling frequency ≥ 1kHz). When the contact force decays to 0.1±0.02N, displacement recording is triggered, and a three-dimensional rebound distribution map is generated simultaneously.

[0051] S7. Closed-loop correction: If the springback error exceeds the limit, the reverse compensation algorithm will be automatically started: the optimal compensation surface will be solved in reverse based on the measured springback data, the mold surface will be updated, and S3-S6 will be repeated.

[0052] Furthermore, to reduce the coefficient of friction, ultrasonic vibration with an amplitude of ≤5μm is used throughout the forming process. The ultrasonic vibration frequency is 20-40kHz. The axial vibration and transverse feed form an elliptical motion trajectory, with the major axis forming an angle of 15-30° with the surface of the sheet.

[0053] Furthermore, in step S5, the fine pressing process is divided into multiple passes, and the relationship between the radius of curvature R2-N of the formed surface in each pass and the target radius of curvature R satisfies:

[0054] R = (0.95~1.1)R²-N, and R²-N is uniformly or decreasingly distributed with increasing number of passes;

[0055] Furthermore, in step S6, the force-displacement coupling sensor group is integrated into each pressure head of the upper mold to monitor the forming force in real time. The force-displacement coupling sensors work together to measure the springback during the unloading stage. The displacement sensor records the displacement data when the sheet separates from the mold, which is used to calculate the springback error.

[0056] Furthermore, in step S6, the rebound monitoring constructs a mathematical model based on mechanical theory, predicts the rebound distribution under different curvatures through equilibrium differential equations and constitutive equations, and optimizes the design of coarse and fine compression procedures.

[0057] Furthermore, in step S7, during the rebound error detection step, when the force sensor displays the force value F, the displacement sensor is triggered to record data. F is a preset minimum value, with a minimum value range of 0.05 to 0.5, to ensure measurement accuracy.

[0058] Furthermore, the forming mold is composed of discretely arranged basic units, the height of which can be independently adjusted to form the target envelope surface, and the ends of the basic units are spherical cap structures to reduce indentations on the sheet surface;

[0059] Furthermore, the height of the basic unit is determined by compensating for springback deformation, specifically including:

[0060] Based on the material parameters of the sheet metal and the target curvature, the curvature of the springback compensation surface in the x / y directions is calculated.

[0061] B-spline interpolation is used to generate a springback compensation surface, which is then mapped onto the mold surface.

[0062] Working principle: When in use, this invention adopts a multi-pass forming process of "coarse pressing + fine pressing" and a fine pressing procedure with exponentially decreasing speed to effectively control springback error, improve the accuracy of the final radius of curvature, and has a discrete mold adjustment capability with an accuracy of 0.01mm. Combined with the design of a curvature gradient transition zone, it avoids sudden stress changes.

[0063] The optimal compression procedure is generated by combining finite element simulation and springback prediction model. Based on a force-displacement coupling monitoring system with 1kHz high-frequency sampling, the real-time visualization of the three-dimensional distribution of springback is realized. At the same time, the reverse compensation algorithm automatically corrects the excessive springback.

[0064] Meanwhile, a multi-sensor collaborative monitoring system, based on a prediction model constructed from mechanical theory, enables the prediction of springback distribution under different curvatures, and a closed-loop correction system ensures the shape accuracy and stability of mass production.

[0065] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, as long as there is no structural conflict, the features in the disclosed embodiments can be combined with each other in any manner. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for forming a thick plate spatial curved surface based on a multi-point mold, characterized in that, Includes the following steps: S1. Forming procedure design: Based on the three-dimensional point cloud data of the target surface, the forming procedure is generated by combining finite element simulation and springback prediction model. It includes a single pass of rough forming and N≥3 passes of fine forming. The rough forming deformation accounts for 60-70% of the total. S2. Adaptive feeding and positioning: The initial position of the sheet material is confirmed by laser scanning, and it is automatically adjusted to the center of the forming area with a positioning error of ≤0.5mm; S3. Dynamic mold shaping: According to the procedure generated by S1, the discrete basic units of the lower mold are synchronously adjusted with an accuracy of 0.01mm to form an intermediate surface with a curvature gradient transition zone. S4. Gradient coarse pressing: The upper die adopts zoned pressure control, with the pressure in the central area being 15-20% higher than that in the edge area, to complete the single-pass large deformation forming. After forming, the radius of curvature R1 and the target radius R satisfy: R = 0.92R1 ± 2%. S5. Progressive fine pressing: carried out in 3-5 passes, with the deformation amount decreasing exponentially in each pass, and the deformation amount of the last pass ≤ 30% of that of the first pass; S6. Online rebound monitoring: During unloading, a force-displacement coupling sensor group with a sampling frequency of ≥1kHz is used to collect data in real time. When the contact force decays to 0.1±0.02N, displacement recording is triggered, and a three-dimensional rebound distribution map is generated simultaneously. S7. Closed-loop correction: If the springback error exceeds the limit, the reverse compensation algorithm will be automatically started: the optimal compensation surface will be solved in reverse based on the measured springback data, the mold surface will be updated, and S3-S6 will be repeated.

2. The method for forming a thick plate spatial curved surface based on a multi-point mold according to claim 1, characterized in that, To reduce the coefficient of friction, ultrasonic vibration with an amplitude of ≤5μm is used throughout the forming process.

3. The method for forming a thick plate spatial curved surface based on a multi-point mold according to claim 1, characterized in that, In step S5, the fine pressing process is divided into multiple passes, and the relationship between the radius of curvature R2-N of the formed surface in each pass and the target radius of curvature R satisfies: R = (0.95~1.1)R2-N, and R2-N is uniformly or decreasingly distributed with increasing number of passes.

4. The method for forming a thick plate spatial curved surface based on a multi-point mold according to claim 1, characterized in that, In step S6, the force-displacement coupling sensor group is integrated into each pressure head of the upper mold to monitor the forming force in real time. The force-displacement coupling sensors work together to measure the springback during the unloading stage. The displacement sensor records the displacement data when the sheet separates from the mold to calculate the springback error.

5. The method for forming a thick plate spatial curved surface based on a multi-point mold according to claim 1, characterized in that, In step S6, the rebound monitoring is based on a mathematical model constructed from mechanical theory. The rebound distribution under different curvatures is predicted by using equilibrium differential equations and constitutive equations, thereby optimizing the design of coarse and fine compression procedures.

6. The method for forming a thick plate spatial curved surface based on a multi-point mold according to claim 1, characterized in that, In step S7, during the rebound error detection step, when the force sensor displays the force value F, the displacement sensor is triggered to record data. F is a preset minimum value, with a minimum value range of 0.05 to 0.5, to ensure measurement accuracy.

7. The method for forming a thick plate spatial curved surface based on a multi-point mold according to claim 1, characterized in that, The forming mold is composed of discretely arranged basic units, the height of which can be independently adjusted to form the target envelope surface, and the ends of the basic units are spherical cap structures to reduce indentations on the sheet surface.

8. The method for forming a thick plate spatial curved surface based on a multi-point mold according to claim 7, characterized in that, The height of the basic unit is determined by compensating for springback deformation, specifically including: Based on the material parameters of the sheet metal and the target curvature, the curvature of the springback compensation surface in the x / y directions is calculated. B-spline interpolation is used to generate a springback compensation surface, which is then mapped onto the mold surface.

9. The method for forming a thick plate spatial curved surface based on a multi-point mold according to claim 2, characterized in that, The ultrasonic vibration frequency is 20-40kHz, and the axial vibration and transverse feed form an elliptical motion trajectory, with the major axis forming an angle of 15-30° with the surface of the plate.

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