A CAE-based solution method for cam trajectory of profile bending

Abstract

The present invention belongs to the technical field of CAE analysis of automotive parts and provides a CAE-based method for solving cam trajectory lines for profile bending, comprising the following steps: Step 1: Extracting and segmenting bending feature lines; Step 2: Converting 3D bending to 2D; Step 3: Determining the center of rotation; Step 4: Determining the horizontal movement curve of the center of rotation; Step 5: Determining the cam trajectory; Step 6: Correcting the cam trajectory; and Step 7: CAE simulation verification. The present invention is advantageous in that it provides a typical example of CAE simulation software solving practical engineering problems and represents an expansion of CAE applications. CAE software can conveniently calculate the trajectory of various parts of a product during the bending process and the positional relationship between modules. It can also conveniently observe changes in product length, adjust the cam trajectory, and verify the effects of the adjustments.

Description

Technical Field

[0001] The invention belongs to the technical field of CAE analysis of automobile parts and relates to a CAE-based method for solving a cam trajectory line of a profile bending forming process. Background Art

[0002] This invention originates from the bending of door frame moldings. The intermediate framework of the bent door frame moldings is a discontinuous aluminum core. Evaluation of the bent portion reveals that the required tensile force for bending this product is low, making conventional stretch-bent products prone to breaking. To improve the yield rate, a custom-made, dedicated bending machine is used for the bending process. This dedicated bending machine typically uses displacement to control the position of the clamps. Increasing the distance between the two ends creates tension within the product, while decreasing the distance creates compression. Excessive or insufficient tension is detrimental to forming. Therefore, precise control of the clamp position is crucial for the dedicated bending machine. The product in this invention exhibits two primary characteristic radii in terms of curvature. Therefore, it is advisable to perform the bending process in two stages: forming corners I and II, with corner I formed first and then corner II. If the first and second rotation centers remain stationary during the bending process, the product will be continuously lengthened by the movement of the clamps, resulting in thinning or even severe distortion of the cross-section. To maintain a substantially unchanged or slightly elongated length after bending, the rotation center must be moved backward. This movement is controlled by the first and second cams. Therefore, the design of the cam curves in this invention is crucial and a key aspect to be protected. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a CAE-based solution method for the cam trajectory line of profile bending forming, based on the current status of the existing technology. CAD and CAE technologies are used to analyze the forming of profiles in displacement-controlled stretch bending, and the results are used to guide the design of the bending die cam trajectory.

[0004] The technical solution adopted by the present invention to solve the above technical problems is: a CAE-based method for solving the cam trajectory of a profile bending forming process, characterized by comprising the following steps:

[0005] Step 1: Extract and segment the bending feature line: Extract the guide line on the inner mold surface of the product in the bending direction as the bending guide feature line, and set the number of bending segments based on the characteristics of the bending guide line and the bending stroke;

[0006] Step 2: Convert 3D curvature to 2D: Decompose the curvature of the 3D curved product into two directions: height and horizontal. First, form the height curvature, then the horizontal curvature. Project the 3D guide line directly onto the plane, keeping the length of the 3D guide line unchanged and the Y coordinate of the corresponding point unchanged. Project the height curvature onto the plane (Z = 0).

[0007] Step 3: Determine the center of rotation: Position the tangent point of the guide line in the plane state. The guide line is tangent to the horizontal baseline. The tangent point is located at the segment point. The tangent point is the intersection of the corresponding perpendicular bisector and the external angle bisector.

[0008] Step 4: Determine the horizontal movement curve of the rotation center: Assuming the product length remains constant during bending, consider the required movement of the rotation center. In the model, simplify the product as a beam element with a circular cross-section and a radius of 0.1mm. Apply a small auxiliary extension force to the ends to maintain a straight line, limited to a limit that does not cause excessive elongation of the beam element, such as 1N. Each segment is 10mm, for a total of 128 beam elements. After the calculation is completed, the displacement of endpoint N137 in the X direction is obtained.

[0009] Step 5. Obtain the cam trajectory: The curve of the change of the cam radial radius during the bending process is equal to the movement curve of the rotation center. Then, after appropriate extension and correction, the cam trajectory line is obtained;

[0010] Step 6. Cam track correction: Use the EXCEL table to correct the horizontal movement curve of the rotation center, and evenly distribute the product elongation to the bending process;

[0011] Step 7. CAE simulation verification: Marc software is used for simulation verification. EXCEL is used to process the cam radial variation law data and draw the cam trajectory. At the same time, a rotation center movement curve is given to observe whether the cam is close to the fixed wheel.

[0012] In the above-mentioned CAE-based method for solving the cam trajectory line of a profile bending forming process, step 1 uses a guide wire as a bending guide characteristic line, and bends the curve I and curve II in two segments. After the bending characteristic line is segmented, the characteristic line is repositioned so that the tangent line of the segment point is flush with the horizontal line.

[0013] In the above-mentioned CAE-based method for solving the cam trajectory of a profile bending molding, the length of the 3D guide line is set to 1269.3 mm in step 2. Assuming that it is divided into 100 segments, each segment is 12.693 mm long, and any segment has △x i ^2+△y i ^2+△z i ^2=12.693^2, the Y coordinate remains unchanged during projection, so △x i ^2+△z i ^2 is constant, an increase in the X coordinate is equal to a corresponding decrease in the Z coordinate.

[0014] In the above-mentioned CAE-based method for solving the cam trajectory line of profile bending, the two ends of the guide line in step three are tangent to the horizontal baseline before and after bending. The positions of O1 and O2 are determined according to the basic properties of plane geometry, that is, the intersection of the corresponding perpendicular bisector and the external angle bisector. The determined center of rotation is its initial position. Horizontal movement is required during the bending process, and the position is not constant. The horizontal movement curve is controlled by two cams.

[0015] Compared with the existing technology, the advantage of the present invention is that it is a typical case of CAE simulation software solving practical engineering problems. It is an expansion of CAE application. CAE software can easily calculate the running trajectory of various parts of the product during the bending and forming process and the positional relationship between each module. It can also easily observe the change in product length and adjust the cam trajectory line and check the effect after adjustment. The present invention can be combined with Excel to easily perform data processing. For example, the conversion of 3D guide lines into 2D guide lines and the acquisition of cam trajectory lines require the use of Excel data processing functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of segmented bending;

[0017] Figure 2 It is a schematic diagram of the cam trajectory;

[0018] Figure 3 This is a complete flow chart of the CAE profile bending cam trajectory solution method. DETAILED DESCRIPTION

[0019] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] In the description of the present invention, it should be understood that the terms "center", "lateral", "longitudinal", "front", "back", "left", "right", "up", "down", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the scope of protection of the present invention.

[0021] In the figure; curve I100; curve II200.

[0022] This implementation uses Marc software and Excel software to provide a CAE-based solution method for the cam trajectory line of profile bending, which is suitable for displacement-controlled stretch bending. If the bending is three-dimensional, the spatial guide line must be converted into 2D first. If it is already a plane bending, skip step 2 and go directly to step 3. Figure 3 As shown, the main steps are as follows.

[0023] Step 1: Extract and Segment the Bend Feature Line: First, extract the guide line on the inner die surface of the product in the bending direction as the bend guide feature line. The number of bend segments is determined based on the characteristics of the bend guide line and the bending stroke. The principle is to place sections with similar curvatures in the same bend segment as much as possible. The bending stroke should not be too large and should not exceed the equipment's tolerance. The guide line at section a is selected as the bend guide feature line. The curves are divided into two segments, curves I100 and II200, representing bend angles I and II. After segmenting the bend feature line, the feature line is repositioned so that the tangent line at the segment point is aligned with the horizontal line.

[0024] Step 2: Convert 3D Bending to 2D: 3D curved product molding can break down the curvature into two directions: height and horizontal. The height curvature is formed first, followed by the horizontal curvature. This product has a height curvature. Using a dedicated bending machine to achieve this height curvature would require first forming the height curvature and then forming the flat curvature. This would reduce production efficiency, create a complex machine structure, make springback control difficult, and increase debugging difficulties. Given the relatively small height curvature and the greater flexibility of the trim, the height curvature can be achieved through manual bending during assembly. Therefore, the 3D product needs to be simplified to flat bending, and the inspection fixture is also manufactured using this 2D semi-finished product.

[0025] Projecting the 3D guide line directly onto the plane will shorten the guide line length, which is obviously not a reasonable approach. The idea is to keep the length of the 3D guide line unchanged, the Y coordinate of the corresponding point unchanged, and project the arc in the height direction onto the plane (Z=0). From the Z axis, the plane arc will be slightly enlarged. The original 3D guide line length is 1269.3mm. Assuming it is divided into 100 segments, each segment is 12.693mm long, and any segment has △x i ^2+△y i ^2+△z i ^2=12.693^2, since the Y coordinate does not change during projection, △x i ^2+△z i ^2 is constant, and an increase in the X coordinate is equivalent to a corresponding decrease in the Z coordinate. The 2D guide line converted by this method is as follows Figure 2 shown.

[0026] Step 3: Determine the center of rotation: Arrange the guide line in the plane state according to the tangent point position. The guide line is tangent to the horizontal baseline, and the tangent point is located at the segmentation point. Since the two ends of the guide line are tangent to the horizontal baseline before and after bending, it is easy to determine the positions of O1 and O2 according to the basic properties of plane geometry, which are the intersection points of the corresponding perpendicular bisectors and the external angle bisectors. It should be clear that the rotation center determined in this way is its initial position. Since horizontal movement is required during the bending process, the position is not constant. The horizontal movement curve is controlled by two cams. Next, we will introduce how to determine the horizontal movement curve of the rotation center.

[0027] Step 4: Determine the horizontal movement curve of the rotation center: For convenience, first assume that the product length remains unchanged during the bending process to consider the required movement of the rotation center. This problem can be solved by maintaining the rotation center unchanged and observing the movement of the product ends E1 and E2. Taking the modeling of the second bend of curve II200 as an example, the product is simplified into a beam element with a circular cross-section and a radius of 0.1mm. A small auxiliary extension force is applied to the ends to maintain the ends in a straight line, limited to not causing excessive elongation of the beam element, such as 1N.

[0028] To ensure the reliability of the calculation, the mesh should be finer, in this case 10mm per segment, for a total of 128 beam elements. After the calculation is completed, the displacement of endpoint N137 in the X direction is obtained. It can be deduced that when endpoint E2 is fixed, if the product length is to be maintained unchanged, the horizontal movement curve of the rotation center is also the same as Figure 2 , but in the opposite direction. This article uses bend II as an example to illustrate the calculation of horizontal movement during rotation. Angle I can be calculated similarly.

[0029] Step 5: Determination of cam trajectory: Still taking bend angle II as an example to illustrate the method of determining the cam trajectory, it is obvious that the movement of the rotation center is achieved by changing the cam radius. The cam trajectory is determined based on this idea, so that the curve of the change of the cam radial radius during the bending process is equal to the movement curve of the rotation center. Then, appropriate extension and correction are made to obtain the cam trajectory line. Figure 2 In the mold rotation 31.1 o During the angle process, the radial change of the cam, 57.7 mm, is exactly equal to the final distance moved by the rotation center. Therefore, the bending of the cam outer contour is equivalent to the movement of the rotation center. The contour of cam I can be obtained using the same method.

[0030] Step 6: Cam Track Correction: The cam track obtained in Step 5 is a cam shape that doesn't account for product length changes. In practice, to ensure a constant tension during the bending process, minimizing springback and preventing wrinkling and deformation, the product needs to stretch and withstand a certain amount of tension. This stretch is generally determined empirically. Too much stretching will result in excessive stretching and thinning, while too little will lead to product instability, wrinkling, and increased springback. Generally, the product stretches by 0.4% during the pre-stretching phase, 0.6% during the forming phase, and approximately 1% after bending. When factoring in product stretch, the horizontal movement of the rotation center is reduced, which is ultimately reflected in the chuck displacement trajectory for displacement-controlled stretch-bending. In practice, the horizontal movement curve of the rotation center is corrected using an Excel spreadsheet to evenly distribute the product stretch throughout the bending process. In this case, the product stretches by 5mm during pre-stretching, 3mm during the first bend, and 5mm during the second bend. The product blank is 1276mm, and the total length after bending is 1289mm.

[0031] Step 7: CAE simulation verification: In order to check whether the desired cam trajectory is correct, Marc software can be used for simulation verification. EXCEL is used to process the cam radial change law data and draw the cam trajectory. At the same time, a rotation center movement curve is given to observe whether the cam is close to the fixed wheel. From the simulation results, cam I fits very well, and cam II has a slight deviation during the bending process, which is probably caused by calculation error. However, this error can be corrected by manually adjusting the cam profile to obtain a completely covered cam trajectory.

[0032] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them with similar methods without departing from the scope defined by the spirit of the present invention.

Claims

1. A CAE-based method for solving the cam trajectory of a profile bending process, characterized in that: The following steps are involved: Step 1: Extract and segment the bending feature line: Extract the guide line on the inner mold surface of the product in the bending direction as the bending guide feature line, and set the number of bending segments based on the characteristics of the bending guide line and the bending stroke; Step 2: Convert 3D curvature to 2D: Decompose the curvature of the 3D curved product into two directions: height and horizontal. First, form the height curvature, then the horizontal curvature. Project the 3D guide line directly onto the plane, keeping the length of the 3D guide line unchanged and the Y coordinate of the corresponding point unchanged. Project the height curvature onto the plane (Z = 0). Step 3: Determine the center of rotation: Position the tangent point of the guide line in the plane state. The guide line is tangent to the horizontal baseline. The tangent point is located at the segment point. The tangent point is the intersection of the corresponding perpendicular bisector and the external angle bisector. Step 4. Determine the horizontal movement curve of the rotation center: Assuming that the length of the product remains unchanged during the bending process, consider how the rotation center must move. In the model, the product is simplified into a beam element with a circular cross-section and a radius of 0.1mm. A small auxiliary extension force is applied to the end to keep the end straight, but not enough to cause excessive elongation of the beam element. After the calculation is completed, the displacement of the endpoint in the X direction is obtained; Step 5. Obtain the cam trajectory: The curve of the change of the cam radial radius during the bending process is equal to the movement curve of the rotation center. Then, after appropriate extension and correction, the cam trajectory line is obtained; Step 6. Cam track correction: Use the Excel spreadsheet to correct the horizontal movement curve of the rotation center, and evenly distribute the product elongation to the bending process; Step 7. CAE simulation verification: Marc software is used for simulation verification. EXCEL is used to process the cam radial variation law data and draw the cam trajectory. At the same time, a rotation center movement curve is given to observe whether the cam is close to the fixed wheel.

2. The CAE-based method for solving the cam trajectory of a profile bending molding process according to claim 1, characterized in that: Step 1: Use the wire as the bending guide feature line and bend it into two segments, Curve I and Curve II. After the bending feature line is segmented, reposition the feature line so that the tangent line of the segment point is flush with the horizontal line.

3. The CAE-based method for solving the cam trajectory of a profile bending molding process according to claim 1, characterized in that: In the step 2, the length of the 3D guide line is set to 1269.3 mm. Assuming that it is divided into 100 segments, each segment is 12.693 mm long, and any segment has △x i ^2+△y i ^2+△z i ^2=12.693^2, the Y coordinate remains unchanged during projection, so △x i ^2+△z i ^2 is constant, an increase in the X coordinate is equal to a corresponding decrease in the Z coordinate.

4. The CAE-based method for solving the cam trajectory of a profile bending molding process according to claim 1, characterized in that: In the step three, the two ends of the guide wire are tangent to the horizontal baseline before and after bending. The positions of O1 and O2 are determined according to the basic properties of plane geometry, that is, the intersection of the corresponding perpendicular bisector and the external angle bisector. The determined center of rotation is its initial position. Horizontal movement is required during the bending process, and the position is not constant. The horizontal movement curve is controlled by two cams.

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