Plate three-point incremental forming track design and forming method

Abstract

The invention relates to a plate three-point incremental forming track designing and forming method. The method comprises the following steps that S100, a two-point incremental forming track is generated according to a three-dimensional model of a target part; s200, the track is divided into two areas, the two parts of the track are achieved through two forming tools (2 and 3) respectively, and the connecting line of cutter location points of the two forming tools at the same moment always passes through the same central symmetry axis; s300, a simple support (7) is installed, the periphery of the plate (8) is clamped, a forming tool is installed, and tool setting is conducted; s400, pre-stretching is applied to the plate, and then the two execution tail ends of the machining equipment are made to run according to the tracks of the two forming tools correspondingly to machine the plate; and S500, after machining is completed, the clamping force is removed, and the formed workpiece is taken down. Three-point constraint is formed on the plate through the simple support and the two forming tools, the overall deflection and shaking of the plate during forming are remarkably reduced, and then the geometric accuracy of a final part is improved.

Description

Technical Field

[0001] The present invention relates to sheet metal CNC incremental forming technology, specifically a three-point incremental forming trajectory design and forming method, which is particularly suitable for small-batch high-precision manufacturing of complex curved thin-walled components, such as but not limited to precise and efficient forming of aircraft skins, small-batch trial production of covering parts in the automobile development stage, and customized production of handicrafts. Background Art

[0002] Sheet metal CNC incremental forming is a forming technology with few or no dies. Point loads are applied locally to the sheet metal through the forming tool. As the forming tool continues to move along a predetermined trajectory, deformation accumulates to obtain the final part.

[0003] The development of incremental forming currently focuses on three types of forming processes: single-point, double-point, and double-sided incremental forming. Single-point incremental forming uses only one forming tool and is the earliest proposed incremental forming method. It is the simplest form, but has poor forming accuracy. Double-point incremental forming, based on the single point, applies a simple local or global support on the opposite side of the sheet metal, and pre-stretches the sheet metal by applying downward pressure to the sheet metal clamping frame or upward force to the mold. This process has higher forming accuracy than single-point incremental forming. Double-sided incremental forming uses two forming tools to process both sides of the sheet metal simultaneously. The forming tool on the other side imposes an additional point constraint on the sheet metal, so the accuracy of double-sided incremental forming is also higher than that of single-point incremental forming.

[0004] Although the existing double-point incremental forming and double-sided incremental forming have improved the geometric accuracy compared to the single-point incremental forming, due to the characteristics of the incremental forming point loading, the sheet metal will be deflected as a whole due to uneven force during the forming process, which will lead to the non-adherence to the mold during and after the forming process (see Figure 5 (a)); In addition, as the tool position changes, the sheet metal will experience periodic shaking. The above phenomena lead to the serious lack of precision of incrementally formed parts compared with stamping, drawing and other processes.

[0005] Through the investigation of existing technologies, it is found that the current research on incremental forming is still limited to the above three types of process methods, such as:

[0006] 1. The Chinese invention patent with invention publication number CN102554007A uses a supporting die and uses a cylinder to apply deep drawing deformation to the sheet before performing incremental forming. This is a double-point incremental forming method with a large drawing force.

[0007] 2. The Chinese invention patent with invention publication number CN100447690C uses electromagnetic coils instead of general hemispherical incremental forming tools to apply force to the sheet metal. There is a simple support underneath the sheet metal. This method also belongs to double-point incremental forming.

[0008] 3. The incremental forming methods or devices disclosed in Chinese invention patents with invention publication numbers CN111872222A, CN103639249A, CN102172698A, and CN213496776U all belong to double-sided incremental forming, differing only in the equipment and devices (e.g., whether the equipment configuration is horizontal or vertical, whether the loading unit is driven by a CNC machine tool, a serial robot, or a parallel robot, and whether the clamping mechanism is fixed or movable, etc.);

[0009] 4. In particular, Chinese invention patent publication number CN116116978A proposes a device and method for active two-point incremental forming of blanks. This method, essentially a multi-point spinning process, is applicable only to the forming of axisymmetric rotating parts. Furthermore, this method does not utilize localized supports, using only two forming tools. This may not effectively suppress bending distortion of the blank near the clamping end. Therefore, this method differs significantly from the three-point incremental forming proposed in this invention.

[0010] In summary, in the existing incremental forming methods suitable for non-axisymmetric complex curved surface parts, the sheet metal forming area is weakly constrained. During the forming process, the sheet metal deflects and periodically shakes as the loading position of the forming tool changes continuously, resulting in the part not fitting the mold and the geometric accuracy needs to be improved. Summary of the Invention

[0011] In order to solve the problem of poor geometric accuracy in the existing incremental forming process, the present invention provides a three-point incremental forming trajectory design and forming method for sheet metal, which uses a simple support and two forming tools located on the same side of the sheet metal to perform incremental forming on the flat material. During the forming process, the line connecting the two tool position points at the same time always passes through the same central symmetry axis, which can improve the incremental forming geometric accuracy of non-axisymmetric complex surface parts.

[0012] The technical solution of the sheet metal three-point progressive forming trajectory design and forming method of the present invention is:

[0013] A three-point incremental forming trajectory design and forming method for sheet metal, using a simple support and two forming tools located on the same side of the sheet metal to perform incremental forming on the sheet metal, including the following steps:

[0014] S100: generating a double-point incremental forming trajectory according to a three-dimensional model of a target part;

[0015] S200: Divide the trajectory obtained in S100 into two regions, wherein the two parts of the trajectory are respectively realized by two forming tools, and the line connecting the tool positions of the two forming tools at the same time always passes through the same central symmetry axis;

[0016] S300: Install simple supports, clamp the sheet metal around, install forming tools and align the tools;

[0017] S400: The driving device causes the clamping mechanism and the simple support to move relative to each other, applying pre-stretching to the sheet metal, and then causes the two execution ends of the processing device to move along the trajectories of the two forming tools to process the sheet metal;

[0018] S500: After processing is completed, the clamping force is released and the formed workpiece is removed.

[0019] This technical solution supports the sheet metal by setting up simple supports and maintaining the connection line between the two tool position points at the same time always passing through the same central symmetry axis. It can avoid the deflection, periodic shaking and non-adherence of the sheet metal, thereby improving the geometric accuracy of the progressive forming of non-axisymmetric complex surface parts.

[0020] Furthermore, the trajectory in step S100 is a contour trajectory, consisting of multiple layers of trajectories, each layer having the same Z coordinate, where the Z coordinate is the Z-axis coordinate in a three-dimensional rectangular coordinate system, representing the height.

[0021] Optionally, in step S200, the tool trajectory is post-processed manually or by programming so that the relative positions of the two forming tools meet design requirements, one of which is that the line connecting the tool positions of the two forming tools at the same time always passes through the same central symmetry axis.

[0022] Optionally, in step S300, the simplified support can be a full support with the same shape as the target part, or a partial support with only some of the target part's features. For simple flat-top, sloping-walled cones or square pyramids, partial columnar supports can be used to further reduce costs; for complex free-form surface parts, full supports can be used to improve accuracy.

[0023] Furthermore, in step S300, the raw material for the simple support is high-density wood substitute or rigid PVC. High-density wood substitute is low-cost, but it causes more pollution during milling and has a lower surface hardness. Rigid PVC has high strength and hardness, but the raw material height is limited, and it usually requires bonding multiple layers of thick plates to form the mold blank.

[0024] Optionally, in step S300 , the forming tool is configured as a universal ball head tool.

[0025] Optionally, in step S400, a simple support top is driven by an oil cylinder or a pneumatic cylinder to apply a pre-tensioning force to the sheet material.

[0026] Optionally, in step S400, the two actuators are driven by a serial robot, and the actuators provide power and running trajectory for the forming tool.

[0027] Furthermore, in step S400, the two actuators coordinately control the forming rate through a matching control system to achieve synchronous loading of the two forming tools.

[0028] The advantages of this invention over existing incremental forming technology are:

[0029] 1. The simple support and two forming tools form a three-point constraint on the sheet metal, which can effectively suppress the deflection and periodic shaking of the sheet metal caused by single-tool point loading during traditional incremental forming, greatly improving the forming accuracy of local features and thus significantly improving the forming accuracy of the final part.

[0030] 2. The two forming tools perform simultaneous processing on the same side of the sheet metal. Each tool processes a portion of the target part, greatly shortening the single-side trajectory length. This significantly improves the efficiency of incremental forming and solves the problem of long single-piece forming time when processing large-size parts in traditional incremental forming.

[0031] 3. Compared with the double-sided incremental forming process, the trajectory design method of the present invention is simple and feasible, and does not require the development of special trajectory design software. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the equipment layout adopted in one embodiment of the three-point incremental forming of the present invention.

[0033] Figure 2 It is a schematic diagram of the contour trajectory of the traditional double-point incremental forming tool, where Figure 2 (a) is the XY plane view, Figure 2 (b) Shows that the lines connecting the corresponding trajectory points of each layer pass through the same center point.

[0034] Figure 3 It is a schematic diagram of the trajectories of two forming tools in the three-point incremental forming of the present invention.

[0035] Figure 4 It is a schematic diagram of the relative positions of two forming tools during the three-point progressive forming process of the present invention.

[0036] Figure 5 This is a schematic diagram comparing the deformation of parts during the three-point incremental forming of the present invention and the traditional two-point incremental forming. Figure 5 (a) is a schematic diagram of part deformation during traditional two-point incremental forming. Figure 5 (b) is a schematic diagram of the three-point progressive forming deformation of the present invention.

[0037] The reference numbers in the figure are: 1. Robot 1; 2. Forming tool A; 3. Forming tool B; 4. Sheet material clamping mechanism; 5. Sheet material clamping frame; 6. Robot 2; 7. Simple support; 8. Sheet material; 9. Tool trajectory of the Nth layer; 10. Tool trajectory of the N+1th layer; 11. Tool trajectory of the N+2th layer; 12. Starting point of the Nth layer trajectory of a single tool; 13. Starting point of the N+1th layer trajectory of a single tool; 14. Starting point of the N+2th layer trajectory of a single tool; 15-20. The starting and ending points of the N, N+1 and N+2th layer trajectories of forming tool A respectively; 21-26. The starting and ending points of the N, N+1 and N+2th layer trajectories of forming tool B respectively, where N is a natural number. DETAILED DESCRIPTION

[0038] The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are intended to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention. That is, the present invention is not limited to the preferred embodiments described, and the scope of the present invention is defined by the claims.

[0039] In the description of the present invention, it should be noted that, unless otherwise specified, “plurality” means two or more; the terms “first”, “second”, “A”, “B”, etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance; for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0040] like Figure 1 The figure shows a schematic diagram of the equipment layout adopted in an embodiment of the three-point progressive forming trajectory design and forming method of the present invention. The forming equipment includes two robots (1, 6), two forming tools (2, 3), a clamping mechanism 4, a clamping frame 5 and a simple support 7.

[0041] The serial robot 1 and the robot 2 6 are used as driving devices for the incremental forming tool A 2 and the forming tool B 3. The four sides of the sheet material 8 are fixed to the clamping frame 5 by the clamping mechanism 4. The downward pressure F can be applied to the clamping frame 5 by a hydraulic cylinder or a pneumatic cylinder. The mold is used as a simple support 7 to provide support for the sheet material 8.

[0042] Figure 2 The figure shows a schematic diagram of the contour line trajectory of the traditional single-tool double-point incremental forming (XY plane view in a three-dimensional rectangular coordinate system, the Z coordinate representing the height is not shown), and the lines connecting the corresponding trajectory points of each layer pass through the same center point O (see Figure 2(b)) lays the foundation for the subsequent generation of dual tool trajectories. After the tool moves to the Nth layer trajectory 9, it starts from the starting point 12 of the Nth layer, runs a circle and returns to the starting point 12, and then feeds along the Z direction to the starting point 13 of the N+1th layer trajectory 10; similarly, after running a circle, it feeds to the starting point 14 of the N+2th layer trajectory 11 (see Figure 2 (a)).

[0043] Figure 3 The figure shows the double-tool three-point incremental forming trajectory proposed by the present invention, which can be Figure 2 The trajectory is obtained through manual or programming processing. Figure 3 The left side shows the trajectory of forming tool A. Figure 3 The right side shows the trajectory of forming tool B. The operating order of the two forming tools is:

[0044] At the Nth layer, forming tool A starts from point 15, while forming tool B starts from point 21. Forming tool A moves clockwise to point 16, while forming tool B moves clockwise to point 22.

[0045] Then forming tool A is fed to the starting point 17 of the N+1 layer, while forming tool B is fed to the starting point 23 of the N+1 layer;

[0046] At the N+1th layer, forming tool A moves counterclockwise to point 18, while forming tool B moves counterclockwise to point 24;

[0047] Then forming tool A is fed to the starting point 19 of the N+2 layer, while forming tool B is fed to the starting point 25 of the N+2 layer;

[0048] At layer N+2, forming tool A moves clockwise to point 20, while forming tool B moves clockwise to point 26.

[0049] It should be noted that Figure 2 、 3 Points 12, 15, and 22 are at the same position in space. Similarly, points 13, 18, and 23 are at the same position in space, and points 14, 19, and 26 are at the same position in space. Based on the above ideas, the three-point forming trajectory design of non-axisymmetric complex surface parts is completed.

[0050] Figure 4 Schematic diagram of the relative positions of the two forming tools during the processing.

[0051] By coordinating the speed control of the ends of the two serial robots (1, 6), the synchronous operation of the two forming tools A2 and the forming tool B3 in the present invention can be achieved, so that the line connecting the tool positions of the two always passes through the same central axis O, thereby always generating three-point constraints on the sheet material 8 together with the simple support 7 serving as the mold, thereby effectively reducing the deflection and shaking of the sheet material 8 and significantly improving the geometric accuracy.

[0052] Figure 5 The figure shows a comparison of part deformation between the three-point incremental forming method of the present invention and the conventional two-point incremental forming method. In conventional two-point incremental forming, the eccentric load exerted by a single forming tool 2 on the sheet material 8 causes overall part deflection, causing the final part shape to deviate from the original design and the sheet material 8 to significantly not fit the mold. In contrast, the present invention utilizes two forming tools (2, 3) for simultaneous processing. The mold and the two forming tools (2, 3) apply three-point constraints to the sheet material 8 in real time, eliminating part deflection caused by eccentric loading and significantly improving forming accuracy.

[0053] It should be emphasized that the three points in the three-point progressive forming of the present invention are not randomly selected points, but three points with specific requirements. They are a point C1 where the forming tool A2 contacts the sheet material 8, a point C3 where the forming tool B3 contacts the sheet material 8, and a support point C2 between the sheet material 8 and the top of the simple support 7 during forming. In addition, the line connecting the two points C1 and C3 where the two forming tools contact the sheet material during the forming process always intersects with a central axis O line passing through point C2 (see Appendix). Figure 5 (b)).

[0054] In the three-point incremental forming of the present invention, the pressure applied by forming tool A2 on point C1 will cause deformation of sheet metal 8 at point C3. However, because forming tool B3 also applies pressure to sheet metal 8 at point C3 at the same time, the influence of forming tool A2 on point C3 is reduced or even ignored. Similarly, the pressure applied by forming tool B3 on point C3 will cause deformation of sheet metal 8 at point C1. However, because forming tool A2 also applies pressure to sheet metal 8 at point C1 at the same time, the influence of forming tool B3 on point C1 is reduced or even ignored. It is precisely because the two forming tools (2, 3) can suppress each other's adverse effects on sheet metal 8 that the geometric accuracy of the workpiece after the three-point incremental forming of the present invention is very high.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of implementation of the present invention. Any equivalent changes and modifications made within the scope of protection of the present invention should be considered to fall within the scope of protection of the present invention.

Claims

1. A three-point progressive forming trajectory design and forming method for a sheet material, wherein a simple support (7) and two forming tools (2, 3) located on the same side of the sheet material (8) are used to progressively form the sheet material (8), characterized in that: The steps include: S100: generating a double-point incremental forming trajectory according to a three-dimensional model of a target part; S200: Divide the trajectory obtained in S100 into two regions. The two parts of the trajectory are respectively realized by two forming tools (2, 3). The line connecting the tool positions of the two forming tools (2, 3) at the same time always passes through the same central symmetry axis. S300: Install the simple support (7), clamp the sheet (8) around, install the forming tool (2, 3) and align the tool; S400: The driving device causes the clamping mechanism (4) and the simple support (7) to move relative to each other, applying pre-stretching to the sheet material (8), and then causes the two execution ends of the processing device to run according to the trajectories of the two forming tools (2, 3) to process the sheet material (8); S500: After processing is completed, the clamping force is released and the formed workpiece is removed.

2. The sheet metal three-point progressive forming trajectory design and forming method according to claim 1, characterized in that: The trajectory in step S100 is a contour trajectory, which is composed of multiple layers of trajectories, and each layer has the same Z coordinate.

3. The sheet metal three-point progressive forming trajectory design and forming method according to claim 1, characterized in that: In step S200, the tool trajectory is post-processed manually or by programming so that the relative positions of the two forming tools (2, 3) meet the design requirements.

4. The sheet metal three-point progressive forming trajectory design and forming method according to claim 1, characterized in that: In step S300, the simple support (7) is a full support having the same shape as the target part, or a partial support having only some features of the target part.

5. The sheet metal three-point progressive forming trajectory design and forming method according to claim 1, characterized in that: In step S300, the raw material of the simple support (7) is high-density wood substitute or hard PVC.

6. The sheet metal three-point progressive forming trajectory design and forming method according to claim 1, characterized in that: In step S300 , the forming tool ( 2 , 3 ) is configured as a universal ball-end tool.

7. The sheet metal three-point progressive forming trajectory design and forming method according to claim 1, characterized in that: In step S400, a simple support (7) is driven upward by an oil cylinder or an air cylinder to apply a pre-tensioning force to the sheet material (8).

8. The sheet metal three-point progressive forming trajectory design and forming method according to claim 1, characterized in that: In step S400 , two actuators are driven by a serial robot.

9. The sheet metal three-point incremental forming trajectory design and forming method according to claim 1, characterized in that: In step S400, the two actuators coordinately control the forming rate through a matching control system to achieve synchronous loading of the two forming tools (2, 3).

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