A method for locally coupling control of springback in sheet metal stamping forming

Abstract

The application discloses a kind of plate stamping forming springback local coupling control methods, comprising the following steps: according to workpiece structure design workpiece stamping process scheme, using finite element simulation analysis technique analysis and predict workpiece springback amount;According to finite element simulation springback result, draw die surface is compensated for springback;Analysis workpiece occurs large amplitude bending springback area, determine local heating area, in heating device electromagnetic induction heating gun movement path is set;While using local coining method controls bending area springback, coining area is heating area, and grid coining rib is set in the area;In stamping production shaping procedure, local hot forming method and local coining method are simultaneously used to couple control workpiece springback.The springback control method provided by the application solves the problem of large amplitude springback of the product, ensures the quality of the product, and does not need to purchase large heating furnace equipment, reduces the number of die repairing and adjusting, greatly reduces the production cost, and improves the workpiece production efficiency.

Description

Technical Field

[0001] This invention relates to the field of stamping production technology, and in particular to a method for local coupling control of springback in sheet metal stamping. Background Technology

[0002] In the field of automotive body panel stamping, springback causes discrepancies between the formed part's shape and dimensions and the actual die dimensions, thus limiting the overall quality of the body-in-white. Springback is an unavoidable defect in stamping, causing the final dimensions of parts to deviate from the design dimensions. Severe springback can lead to difficulties in subsequent assembly and welding, and may even result in part scrap. Therefore, strict control of springback is essential in the development of automotive stamping dies. Springback research has always been a hot topic and a key focus in the field of sheet metal forming.

[0003] Methods for controlling springback can be divided into springback compensation methods and process methods. When large body panels experience bending springback, and the curvature of the bending surface is small, the springback amount is particularly large. It is difficult to completely control the springback deformation of such products using only finite element simulation technology for prediction and compensation. It is necessary to construct a mathematical model of each process parameter and the springback amount to achieve controlled springback (Yang Yong, Cai Jin, Yang Tiannan. A method and system for predicting and controlling springback in the forming of high-temperature alloy thin-walled parts, 2022.). The construction of this mathematical model is complex. In the process method, the integral hot forming method is more suitable for large automotive body panel parts (Sun Honglei. A device and method for controlling the springback of sheet metal forming, 2020.), but it is not suitable for large structural parts such as anti-collision beams. Although such workpieces are large in size, the forming amount is small, and the plastic deformation only occurs in a small local area. Heating the entire area where no plastic deformation occurs will actually cause unnecessary heat energy loss. Moreover, heating large parts requires a large investment in large heating furnace equipment, which significantly increases production costs. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this invention is to provide a method for local coupling control of springback in sheet metal stamping.

[0005] The present invention is achieved by at least one of the following technical solutions.

[0006] A method for locally coupled control of springback in sheet metal stamping includes the following steps:

[0007] Step 10: Select the stamping direction according to the workpiece structure, design the blank holder surface and process supplement surface, design the workpiece stamping process scheme, and use finite element simulation analysis technology to analyze and predict the springback amount of the workpiece.

[0008] Step 20: Perform springback compensation on the drawing die surface based on the springback results of the finite element simulation. The compensation die surface is divided into three regions: fixed compensation region, direct compensation region, and transition region.

[0009] Step 30: Analyze the area where the workpiece bends and springs back significantly, determine the local heating area, and set the movement path of the electromagnetic induction heating gun in the heating device;

[0010] Step 40: Use local imprinting to control the springback of the bending area. The imprinting area is the heating area. Set grid imprinting ribs in this area.

[0011] Step 50: In the stamping production shaping process, the workpiece springback is controlled by coupling the local hot forming method and the local embossing method.

[0012] Furthermore, the finite element simulation is a full-process springback prediction. Springback simulation is set after each process to obtain the springback value of the workpiece for the entire process.

[0013] Furthermore, the fixed compensation area remains stationary during compensation, and the blank holder surface in the drawing process die is selected as the fixed compensation area;

[0014] The direct compensation area is compensated directly in the anti-normal direction based on the springback simulation analysis results, and the part itself is selected as the direct compensation area.

[0015] The transition zone is the area between the direct compensation zone and the fixed compensation zone. The transition zone and the mold surface before compensation have similar curved surface features, which ensures the quality of the mold surface after compensation and good drawing forming performance.

[0016] Furthermore, the region experiencing significant bending and springback is a region with relatively small curvature, specifically a surface curvature of less than 0.01 mm. -1 .

[0017] Furthermore, the heating area of ​​the heating device is larger than the bending springback area to ensure sufficient local thermoforming.

[0018] Furthermore, the heating device includes an electromagnetic induction heating gun and a robotic arm, the robotic arm holding the electromagnetic induction heating gun and controlling the movement path of the electromagnetic induction gun.

[0019] Furthermore, the electromagnetic induction heating gun moves in a horizontal reciprocating motion, and then moves longitudinally by one unit each time it reaches an end point.

[0020] Furthermore, the grid embossing ribs are arranged in a cross pattern of horizontal and vertical directions, with the spacing between embossing ribs in the same direction being 2 to 3 mm; the height of the embossing ribs is 0.2 to 0.4 mm, and the radius of the embossing ribs is 0.3 to 0.5 mm.

[0021] Furthermore, in the localized hot forming method, the localized heating temperature is 880–950°C, and rapid cooling is required after heating. Rapid cooling is a fast quenching cooling at a cooling rate of 20–300°C / s, and the cooling should be performed before cutting and punching.

[0022] Furthermore, in the local embossing method, the embossing ribs are arranged on the forming punch, and the forming process first uses a heating device to locally heat the part before stamping.

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

[0024] 1. This springback control method improves the springback stability of the product through local thermoforming and local imprinting, solving the problem of large-scale product springback and ensuring product quality. Compared with overall thermoforming, there is no need to purchase large heating furnace equipment, which can greatly reduce production costs, and the product precision is higher through coupling control.

[0025] 2. This method can quickly control springback, reducing the frequency of die repair in mold maintenance, reducing the workload of workers in mold maintenance, reducing the time for processing, assembling and debugging molds, lowering production costs, improving production efficiency, and enhancing the economy and practicality of molds. Attached Figure Description

[0026] Figure 1 This is a flowchart of the local coupling control process for springback during sheet metal stamping in this invention.

[0027] Figure 2a This is a front view of the anti-collision beam drawn part according to an embodiment of the present invention;

[0028] Figure 2b This is a side view of the anti-collision beam drawing component according to an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the grid embossing arrangement of the present invention. Detailed Implementation

[0030] 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 an embodiment of a car model's anti-collision beam and accompanying drawings.

[0031] like Figure 1 The diagram illustrates a method for locally coupled control of springback during sheet metal stamping. This method includes:

[0032] Step 10: Select the stamping direction according to the workpiece structure, design the blank holder surface and process supplement surface, and design the workpiece stamping process scheme. Use finite element simulation analysis technology to analyze and predict the springback amount of the workpiece. The finite element simulation is a full-process springback prediction. Springback simulation is set after each process to obtain the springback value of the workpiece for the whole process.

[0033] The stamping direction not only affects the quality of the drawing result but also determines the design of the subsequent drawing die surface. Furthermore, the rationality of the stamping direction determines whether the entire forming process can proceed smoothly. The most important prerequisite for selecting the stamping direction is to avoid negative stamping angles, as these can damage the die. The angle between the stamping direction and the die surface must be greater than 3°. Secondly, it is essential to ensure that the punch and die can close smoothly, drawing the part in one pass. Additionally, the minimum drawing depth and the basic principle of balanced material feeding around the die cavity must be considered. Since the bumper beam is a symmetrical component, the stamping direction is chosen to be perpendicular to the bottom plane of the bumper beam.

[0034] The pressing surface can be divided into two categories:

[0035] Category 1: The flange edge is not used as part of the blank holder surface. In this case, the blank holder surface needs to be about 20mm away from the bottom of the part. Then, additional processes are used to connect the part to the blank holder surface so that the part can be successfully drawn.

[0036] Category 2: The flange edge can be used as part of the blank holder surface. In this case, the flange edge is both part of the main body of the part and the blank holder surface. For this situation, the flange edge width should not be too large, the shape should be as simple as possible without drastic changes, and it is best to be perpendicular to the stamping direction. Most importantly, as part of the blank holder surface, the flange edge must ensure that the drawing depth does not have large fluctuations to avoid uneven feeding, cracking, or wrinkling during the drawing process. The planes containing the flange edges at both ends of the anti-collision beam are not approximately perpendicular to the stamping direction, so the flange edges cannot be used as part of the blank holder surface. The blank holder surface is set 15mm from the bottom of the part. The plane containing the flange edge is extended to intersect with the blank holder surface using the external extension command, and both sides are rounded with a radius of 10mm.

[0037] There are two types of process supplements:

[0038] One method is to fill in the internal windows and holes of the parts.

[0039] Another method is to connect two parts in the production of two parts from one mold, or to add a supplementary surface to achieve a smooth bottom surface.

[0040] The following points should be considered when supplementing the design process:

[0041] 1) Seal internal holes and windows. If deformation exceeds the limit after filling holes, pre-punching can be performed to avoid stress concentration;

[0042] 2) Extend the surface to fill in the gaps based on the curvature of the part's own surface. All internal surfaces need to be tangentially connected, and sharp corners need to be rounded.

[0043] 3) When it can be drawn into shape in one step and has good formability, the process supplement surface should be as small as possible in order to reduce the generation of waste.

[0044] 4) The design of the process supplementary surface should ensure that it does not affect the smooth progress of subsequent production processes and simplifies them, avoiding side punching and side trimming. Based on the above principles, the process supplementary surface of the crash beam should be designed as follows: Figure 2a and Figure 2b As shown.

[0045] Taking a crash beam product as an example, based on its structural characteristics, the following six-step stamping process is designed. After the material is blanked, the first step is drawing to form the basic shape of the part; the second and third steps are both blanking steps, gradually removing the side scrap and punching out the holes on the main surface of the workpiece; the fourth step is a shaping process to reduce springback deformation; the fifth and sixth steps are both blanking steps, gradually removing all remaining side scrap. The complete stamping process for the crash beam is: D10 drawing → T20 trimming + punching → T30 trimming + punching → F40 shaping → T50 trimming + punching → T60 trimming + punching.

[0046] The springback prediction for the crash beam is a full-process springback prediction using finite element simulation. Springback simulations are set after each process. The full-process springback prediction simulation is set as follows: D10 drawing → M20 springback → T30 trimming + punching → M40 springback → T50 trimming + punching → M60 springback → F70 shaping → M80 springback → T90 trimming + punching → M1000 springback → T110 trimming + punching → M120 springback. The profiles, trimming and punching curves, and original digital models of each process are imported into Autoform. The physical properties of the materials used, such as yield strength, tensile strength, hardening factor, and anisotropy factor, are input into Autoform to construct a new material card. After setting up each process according to the designed full-process springback, springback calculations are performed. Simulation analysis results show that the material drawing process is insufficient. Gray represents almost no plastic deformation, while green represents the range of plastic deformation. In the simulation results, the green range is very small, indicating that the range of plastic deformation is limited and the forming is insufficient. The springback prediction contour map shows that the maximum springback is about 248mm, and the springback deformation is very large, with the workpiece almost springing back into a flat plate shape.

[0047] Step 20: Perform springback compensation on the drawing die surface based on the finite element simulation springback results. The compensation die surface is divided into three regions: a fixed compensation region, a direct compensation region, and a transition region. The fixed compensation region remains stationary during compensation and does not undergo any changes. Typically, the blank holder surface in the drawing process die surface is selected as the fixed compensation region. The direct compensation region is generally compensated directly in the reverse normal direction based on the springback simulation analysis results. According to the compensation characteristics, the part itself is usually selected as the direct compensation region. The transition region is the area between the direct compensation region and the fixed compensation region. This region has similar curved surface features to the die surface before compensation, ensuring the quality of the die surface after compensation and good drawing forming performance.

[0048] As a preferred embodiment, after determining the compensation scheme, the mold is compensated step-by-step using the Autoform compensation module according to the process. The Autoform compensation principle is based on the geometric node displacement compensation method. During compensation, the amount of springback compensation can be controlled by the compensation coefficient, which has a default value of 1. For springback compensation of high-strength steel, this value is generally greater than 1. The material grade used for the anti-collision beam is S700MC, with a yield strength of 835MPa and a tensile strength of 878.8MPa. It belongs to high-strength thick plate parts, and the compensation coefficient is set to 1.2. At the same time, the smoothness coefficient can be used to control whether the surface after compensation is smooth or accurate. The smaller the smoothness coefficient, the smoother the surface generated; the larger the smoothness coefficient, the more accurate the surface generated. The default value is selected as 0.5.

[0049] Using M120 springback compensation for the D10 drawing die surface, the direct compensation area is generally the product surface, with a compensation coefficient of 1.2 and a smoothness coefficient of 0.5. The fixed compensation area is generally the blank holder surface. The reason for not compensating the blank holder surface is that after compensation, the blank holder surface will change from the original horizontal blank holder surface to an irregularly shaped curved surface. In this case, the blank holder surface will not play its original blank holder role, which may cause forming defects in the part. The transition area is generally the process supplement surface. After the compensation is completed, the negative angle of the newly generated drawing die surface needs to be checked. The anti-collision beam drawing die surface has no negative angle after compensation, which meets the production requirements.

[0050] Step 30: Analyze the area of ​​significant bending and springback in the workpiece, determine the local heating area, and set the movement path of the electromagnetic induction heating gun in the control system of the heating device; the area of ​​significant bending and springback is a region with small curvature, with the maximum surface curvature less than 0.01mm. -1The heating area of ​​the heating device is slightly larger than the bending and springback area to ensure sufficient local thermoforming. The heating device consists of an electromagnetic induction heating gun, a robotic arm, and a control system. The robotic arm holds the electromagnetic induction heating gun. The control system controls the movement path of the electromagnetic induction gun by inputting a program to control the robotic arm, and controls the heating temperature of the electromagnetic induction gun by inputting a value. The movement path of the electromagnetic induction heating gun is a lateral reciprocating motion, and it moves longitudinally one unit every time it reaches the endpoint.

[0051] In CATIA, use the measurement command to measure the curvature of each surface of the drawn profile of the crash beam, and identify surfaces with curvature less than 0.01 mm. -1 The analysis, based on the full-process springback simulation results, identifies the area where the workpiece undergoes significant bending and springback. CATIA analysis of the anti-collision beam's drawn surface reveals that the curvature of the rounded corner areas between the bottom surface and the two side slopes of the anti-collision beam is less than 0.01mm. -1 Furthermore, the springback simulation results show that significant springback occurs on both sides of the inclined surface and in the rounded corner area. Therefore, both rounded corner areas are the areas that cause significant springback of the workpiece. Local heating is required in these two rounded corner areas to control the springback. These two rounded corner areas are designated as the heating areas. To ensure sufficient local thermoforming, the heating areas extend 10mm along the boundaries of each area. The heating area of ​​the anti-collision beam is as follows: Figure 2a As shown in A and B, the heating area is programmed in the heating device control system to determine the relative position of the robot and the surface during production. The program is set to achieve the following effect: control the robot to hold the battery induction gun and move it to the initial heating position, start the electromagnetic induction heating gun, and the robot and the battery induction gun move laterally back and forth until the endpoint moves one unit longitudinally along the heating surface until heating is completed.

[0052] Step 40: Simultaneously control the springback of the bending area using a local imprinting method. The imprinted area is the heating area, and a grid of imprinting ribs is set in this area. The grid of imprinting ribs is arranged in a cross pattern of horizontal and vertical directions, as shown in the diagram. Figure 3 As shown;

[0053] As a preferred embodiment, a grid of stamped ribs is provided in the heating area of ​​the anti-collision beam, with the ribs in the same direction spaced 2mm apart, the height of the stamped ribs being 0.3mm, and the radius of the stamped ribs being 0.4mm.

[0054] Step 50: In the stamping production shaping process, the workpiece springback is controlled by simultaneously using local hot forming and local embossing methods.

[0055] In a preferred embodiment, the local heating temperature in the local thermoforming method is 880-950°C, and rapid cooling is required after heating. Rapid cooling is a fast quenching cooling at a cooling rate of 20-300°C / s, and cooling should be performed before trimming and punching. In the local embossing method, embossing ribs are arranged on the forming punch, and the forming process first uses a heating device for local heating before stamping.

[0056] According to the designed process plan, molds for each process are produced. In particular, the drawing die surface adopts the springback compensation surface, the grid imprint ribs in the forming die are located in the forming die punch, and the forming die does not have drawing rib grooves. The molds for each process are installed on the press, the sheet is fed into the drawing die to start processing, after completing the processes D10 drawing, T20 trimming + punching and T30 trimming + punching, the heating device is started to locally heat the anti-collision beam workpiece before the F40 forming process stamping. After heating is completed, the F40 forming process stamping is quickly carried out. After forming and stamping, the workpiece is quickly cooled, and then the subsequent stamping processes T50 trimming + punching and T60 trimming + punching are completed.

[0057] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for localized coupling control of springback in sheet metal stamping, characterized in that, Includes the following steps: Step 10: Select the stamping direction according to the workpiece structure, design the blank holder surface and process supplement surface, design the workpiece stamping process scheme, and use finite element simulation analysis technology to analyze and predict the springback amount of the workpiece. Step 20: Perform springback compensation on the drawing die surface based on the springback results of the finite element simulation. The compensation die surface is divided into three regions: fixed compensation region, direct compensation region, and transition region. The fixed compensation area remains stationary during compensation, and the blank holder surface in the drawing process die is selected as the fixed compensation area; The direct compensation area is compensated directly in the anti-normal direction based on the springback simulation analysis results, and the part itself is selected as the direct compensation area. The transition zone is the area between the direct compensation zone and the fixed compensation zone. The transition zone has similar curved surface features to the mold surface before compensation, which ensures the quality of the mold surface after compensation and good drawing forming performance. Step 30: Analyze the area where the workpiece bends and springs back significantly, determine the local heating area, and set the movement path of the electromagnetic induction heating gun in the heating device; Step 40: Use local imprinting to control the springback of the bending area. The imprinting area is the heating area. Set grid imprinting ribs in this area. Step 50: In the stamping production shaping process, the workpiece springback is controlled by coupling the local hot forming method and the local embossing method.

2. The sheet metal stamping springback local coupling control method as described in claim 1, characterized in that, The finite element simulation is a full-process springback prediction. Springback simulation is set after each process to obtain the springback value of the workpiece for the entire process.

3. The sheet metal stamping springback local coupling control method as described in claim 1, characterized in that, The area where significant bending and springback occur is a region with relatively small curvature, with a surface curvature of less than 0.01 mm. -1 .

4. The sheet metal stamping springback local coupling control method as described in claim 1, characterized in that, The heating area of ​​the heating device is larger than the bending springback area to ensure sufficient local thermoforming.

5. The sheet metal stamping springback local coupling control method as described in claim 1, characterized in that, The heating device includes an electromagnetic induction heating gun and a robotic arm. The robotic arm holds the electromagnetic induction heating gun and controls the movement path of the electromagnetic induction gun.

6. The sheet metal stamping springback local coupling control method as described in claim 1, characterized in that, The electromagnetic induction heating gun moves in a horizontal reciprocating motion, and then moves longitudinally by one unit each time it reaches an end point.

7. The sheet metal stamping springback local coupling control method as described in claim 1, characterized in that, The grid embossing ribs are arranged in a cross pattern of horizontal and vertical directions, with the spacing between embossing ribs in the same direction being 2~3mm; the height of the embossing ribs is 0.2~0.4mm, and the radius of the embossing ribs is 0.3~0.5mm.

8. The sheet metal stamping springback local coupling control method as described in claim 1, characterized in that, The localized hot forming method involves heating at a temperature of 880~950℃, followed by rapid cooling. Rapid cooling is achieved by quenching at a rate of 20~300℃ / s, and should occur before edge trimming and punching.

9. The sheet metal stamping springback local coupling control method as described in claim 1, characterized in that, In the local embossing method, the embossing ribs are arranged on the forming punch, and the forming process first uses a heating device to locally heat the part before stamping.

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