A method for designing a profile of a sheet metal forming die

Abstract

The application discloses a sheet metal forming die surface design method, comprising the following steps: step one, determining a horizontal plane; step two, determining a median plane; step three, constructing a die surface. The application provides a median plane and horizontal plane determination method, ensures that the curvature distribution of the part surface is symmetrical, the normal of each point of the curved surface points to above the horizontal plane, can quickly and accurately confirm the design coordinates of the die, improves the design efficiency, and avoids design errors caused by visual addition of experience. The application uses a surface compensation method, the curvature of the formed curved surface is continuous, the integrity is strong, guide points are added during curved surface fitting, the continuity of the sheet metal part surface after forming is ensured, and the design work efficiency is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of aircraft sheet metal forming technology, specifically a method for designing the profile of a sheet metal forming mold. Background Technology

[0002] Sheet metal parts are typically formed using molds. When designing a mold, the first step is to define the horizontal and central planes of the mold surface to determine the placement of the part. The choice of these planes directly affects the final forming result. This is usually determined by process engineers based on experience and visual observation. After the mold is manufactured, adjustments are made according to actual usage, resulting in a relatively long production cycle.

[0003] Secondly, designers need to extend and compensate the curved surfaces of the parts. The compensated surfaces need to meet the characteristics of smooth streamlines. Designers usually use operations such as surface extension and surface filling in CAD software to assemble the curved surfaces. However, for complex curved surfaces, especially aircraft sheet metal parts, their shapes are usually composed of gradient curves. The small curved surface pieces formed by surface extension cannot be assembled. Applying surface filling will result in the overall mold surface not being smooth, with abrupt curvature points. The parts are prone to breakage during forming, and the operation is complicated and the design cycle is long, which cannot meet the requirements of high-quality manufacturing.

[0004] Therefore, given the shortcomings of existing technologies, there is a need to provide a method that can efficiently and accurately position and extend mold surfaces in order to achieve rapid mold surface design. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for designing the surface of sheet metal forming molds, which can quickly determine the horizontal plane and the mid-plane of the surface during mold design, and extend the curved surface to construct the mold surface, thereby achieving the purpose of rapid mold surface design.

[0006] The technical solution of the present invention is to provide a method for designing the surface profile of a sheet metal forming mold, characterized by the following steps:

[0007] Step 1: Determine the horizontal plane. The specific process is as follows:

[0008] 1-1. Import the part model into the software, extract the outer surface of the part, perform curvature analysis on the edge line of the surface, and take 3 auxiliary points on the edge line with the smallest radius of curvature to make auxiliary planes. Define the vertical direction of the plane as the curvature smoothing direction.

[0009] 1-2. Create n cross-sections along the direction of the gentle curvature of the part's surface, where n is not less than 10, and extract n cross-section lines from the surface.

[0010] 1-3. Perform curvature analysis on each tangent line, calculate the curvature distribution of each tangent line, and obtain the point with the minimum radius of curvature of each tangent line as the curvature inflection point of that tangent line.

[0011] 1-4. Use n curvature inflection points to create a fitting plane using the least squares method, and use this plane as the horizontal plane of the mold surface.

[0012] Step 2: Determine the midplane. The specific process is as follows:

[0013] 2-1. Project n curvature inflection points onto a horizontal plane to obtain n projection points.

[0014] 2-2. Perform linear fitting on n projection points, stretch the fitted line along the horizontal normal direction of the mold surface, and use the resulting plane as the mid-plane.

[0015] Step 3: Construct the mold surface. The specific process is as follows:

[0016] 3-1. Along a direction perpendicular to the direction of the gradual curvature, make n... ′ n cross-sections ′ Not less than 10, and obtain n ′ There are n×n tangent lines. ′ Intersection points.

[0017] 3-2. For n+n ′ Tangential extensions are made at both ends of the tangential line, with an extension length of 60-80mm. The endpoints are taken as guide points for the surface extension, resulting in 2(n+n) ′ ( ) guide points to complete the discretization of the surface.

[0018] 3-3. For n×n ′ 1 intersection point and 2(n+n) ′ The surface equation is obtained by fitting the surface to the guide points.

[0019] 3-4. Compare the coordinates of the guide points, take the maximum and minimum X values ​​among all points as the range of X values ​​in the point cloud, and take the maximum and minimum Y values ​​among all points as the range of Y values ​​in the point cloud. Select values ​​at equal intervals within the ranges of X and Y, with the distance between values ​​not exceeding one-thousandth of the range, to form a two-dimensional matrix of X and Y values. Substitute each two-dimensional point value in the matrix into the surface equation to calculate the corresponding Z value of the two-dimensional point. The two-dimensional point values ​​and their corresponding Z values ​​form a three-dimensional surface point cloud.

[0020] 3-5. Construct a curved surface from the 3D point cloud and use the obtained curved surface as the mold surface.

[0021] The advantages of this invention are as follows: The method for determining the mid-plane and horizontal plane provided by this invention ensures the symmetrical distribution of the curvature of the part's surface, with the normals of each point on the surface pointing above the horizontal plane. This enables rapid and accurate confirmation of the mold's design coordinates, improving design efficiency and avoiding design errors caused by visual inspection and experience. The surface compensation method provided by this invention results in a surface with continuous curvature and strong integrity. The addition of guide points during surface fitting ensures the continuity of the sheet metal part's surface after forming, significantly improving design efficiency.

[0022] The present invention will be further described below with reference to specific accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 Typical product illustration

[0024] Figure 2 Curvature inflection point selection diagram

[0025] Figure 3 Horizontal plane and mid-plane schematic diagram

[0026] Figure 4 Discrete surface diagram

[0027] Figure 5 Point cloud formation diagram

[0028] Numbering in the diagram: 1. Part outer surface; 2. Edge line; 3. Auxiliary point; 4. Auxiliary plane; 5. Curvature inflection point; 6. Horizontal plane; 7. Projection point; 8. Fitted line; 9. Midplane; 10. Intersection point; 11. Guide point; 12. 3D surface point cloud Detailed Implementation

[0029] like Figure 1-5 As shown, a method for designing the profile of a sheet metal forming mold includes the following steps:

[0030] Step 1: Determine the horizontal plane. The specific process is as follows:

[0031] 1. Figure 1 In the part model import software, the outer surface 1 of the part is extracted, and the curvature of the four edge lines of the surface is analyzed to obtain the minimum curvature radius of the four edges. In this embodiment, the minimum curvature radii are 33.25mm, 41.31mm, 246.22mm and 1453000mm respectively. On the edge line with the smallest curvature radius, that is, the edge line 2 with a curvature radius of 33.25mm, three auxiliary points 3 are randomly selected to form an auxiliary plane 4. The vertical direction of the auxiliary plane 4 is defined as the curvature smoothing direction.

[0032] 2. Create 12 facets along the direction of the gentle curvature of the part's surface, and extract 12 facet lines from the surface.

[0033] 3. Perform curvature analysis on each tangent line, calculate the curvature distribution of each tangent line, and obtain the point with the minimum radius of curvature of each tangent line as the curvature inflection point 5 of that tangent line.

[0034] 4. Using 12 curvature inflection points 5, a fitting plane is created using the least squares method, and this plane is used as the horizontal plane of the mold surface 6.

[0035] Step 2: Determine the midplane. The specific process is as follows:

[0036] 1. Project the 12 curvature inflection points 5 onto the horizontal plane 6 to obtain 12 projection points 7.

[0037] 2. Perform linear fitting on the 12 projection points 7, and stretch the fitted line 8 along the normal direction of the horizontal plane 6 of the mold surface to form the plane as the mid-plane 9.

[0038] Step 3: Construct the mold surface. The specific process is as follows:

[0039] 1. Make 16 cuts along a direction perpendicular to the direction of the curvature, and obtain 16 cut lines. At this time, 192 intersection points are formed between the cut lines.

[0040] 2. Extend the tangents at both ends of the 28 tangent lines by 60mm, and take the endpoints as guide points 11 for surface extension to obtain 56 guide points, thus completing the discretization of the surface.

[0041] 3. Perform surface fitting on the 192 intersection points 10 and the 56 guide points 11 to obtain the surface equation.

[0042] 4. Compare the coordinates of the guide points, and take the maximum and minimum X values ​​among all points as the range of point cloud X, and the maximum and minimum Y values ​​among all points as the range of point cloud Y. In this embodiment, the range of X is 0–3596 mm, and the range of Y is 0–1185 mm. Values ​​are selected at equal intervals within the X and Y ranges, with the distance between values ​​not exceeding one-thousandth of the range. In this embodiment, the X distance is 3 mm, and the Y distance is 1 mm, forming a two-dimensional matrix of X and Y values. Each two-dimensional point value in the matrix is ​​substituted into the surface equation to calculate the corresponding Z value. The two-dimensional point values ​​and their corresponding Z values ​​form a three-dimensional surface point cloud 12.

[0043] 5. Construct the 3D point cloud 12 into a curved surface, and use the obtained curved surface as the mold surface.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for designing the profile of a sheet metal forming mold, characterized in that... Includes the following steps: Step 1: Determine the horizontal plane. The specific process is as follows: 1-1. Import the part model into the software, extract the outer surface of the part, perform curvature analysis on the edge line of the surface, and take 3 auxiliary points on the edge line with the smallest radius of curvature to make auxiliary planes. Define the vertical direction of the plane as the curvature smoothing direction. 1-2. Create n cross-sections along the direction of the gentle curvature of the part's surface, where n is not less than 10, and extract n cross-section lines from the surface; 1-3. Perform curvature analysis on each tangent line, calculate the curvature distribution of each tangent line, and obtain the point with the minimum radius of curvature of each tangent line as the curvature inflection point of that tangent line; 1-4. Use n curvature inflection points to create a fitting plane using the least squares method, and use this plane as the horizontal plane of the mold surface; Step 2: Determine the midplane. The specific process is as follows: 2-1. Project n curvature inflection points onto a horizontal plane to obtain n projection points; 2-2. Fit a straight line to n projection points, stretch the fitted straight line along the horizontal normal direction of the mold surface, and use the resulting plane as the mid-plane; Step 3: Construct the mold surface. The specific process is as follows: 3-1. Along the direction perpendicular to the direction of the gentle curvature, make... One cross-section, Not less than 10, and obtain A section line, at this time forming between the section lines One intersection point; 3-2. To Tangential extensions are made at both ends of the tangential line, with an extension length of 60-80mm. The endpoints are taken as guide points for the surface extension, thus obtaining... A guide point is used to complete the discretization of the surface; 3-3. To The intersection points and By fitting a surface to a guide point, the surface equation is obtained; 3-4. Compare the coordinates of the guide points, take the maximum and minimum X values ​​among all points as the range of X values ​​in the point cloud, and take the maximum and minimum Y values ​​among all points as the range of Y values ​​in the point cloud. Select values ​​at equal intervals within the ranges of X and Y, with the distance between values ​​not exceeding one-thousandth of the range, to form a two-dimensional matrix of X and Y values. Substitute each two-dimensional point value in the matrix into the surface equation to calculate the corresponding Z value for that two-dimensional point. The two-dimensional point values ​​and their corresponding Z values ​​form a three-dimensional surface point cloud. 3-5. Construct a curved surface from the 3D point cloud and use the obtained curved surface as the mold surface.

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