Stamping forming simulation method based on adaptive equivalent drawbead resistance

Abstract

The present application relates to a kind of stamping forming simulation methods based on adaptive equivalent drawbead resistance, comprising the following steps: establishing the stamping forming die model with drawbead, and the sheet metal to be processed is generated grid and is placed in stamping forming die;The stamping process of sheet metal is simulated by finite element method, and the equivalent drawbead resistance and the equivalent drawbead lifting force of the grid cell of sheet metal and drawbead contact are calculated in each incremental step of the stamping forming, and all the grid cells of sheet metal and drawbead contact are found out.The present application can adaptively predict the resistance of equivalent drawbead in stamping forming simulation, and the simulation result is more accurate compared with fixed equivalent drawbead resistance model.

Description

Technical Field

[0001] This invention relates to a stamping simulation method based on adaptive equivalent drawbead resistance, belonging to the field of stamping simulation technology. Background Technology

[0002] Sheet metal stamping, as an important method of metal forming, is widely used in aerospace, automotive, home appliance, packaging, and other related fields. For parts with complex shapes and high surface quality requirements (such as body panels), uneven material flow during the stamping process often leads to defects such as wrinkling and tearing in certain areas. To reduce the likelihood of these defects, draw beads are typically placed around the die to increase the feeding resistance in those areas, control uniform material deformation, and obtain qualified parts.

[0003] Properly and reasonably arranging draw beads can not only improve the deformation state of the sheet metal, making it more uniform, but also reduce the blank holder force required for forming, improve the surface quality of the formed sheet metal, and extend the service life of the die. The success or failure of the forming process can be directly determined by the design of draw beads; therefore, draw bead design is one of the key technologies in the design of stamping dies for automotive body panels.

[0004] Currently, existing sheet metal forming technologies mostly use equivalent drawbead models to simulate real drawbeads, without considering the work hardening and thickness changes that occur as the sheet metal flows through the drawbeads. Therefore, when using stamping simulation results for actual stamping production, the accuracy of the parts needs to be further improved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a simulation method based on adaptive equivalent drawbead resistance that can improve the stamping accuracy of parts.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is: a stamping simulation method based on adaptive equivalent drawbead resistance, comprising the following steps:

[0007] Step 1: Establish a stamping die model with drawbeads. Generate a mesh from the sheet metal to be processed and place it into the stamping die. Calculate the initial drawbead resistance F of the mesh cells in contact with the sheet metal. R0 and initial drawbeam lifting force F U0 Wherein, the thickness of the sheet material to be processed is t0, the strengthening coefficient is K, and the hardening index is n;

[0008] Step 2: Simulate the stamping process of the sheet metal using the finite element method. For each incremental step of the stamping process, find all m mesh elements in contact with the drawbead and calculate the equivalent drawbead resistance and equivalent drawbead lifting force of the mesh elements in contact with the drawbead.

[0009] The method for calculating the equivalent drawbead resistance and equivalent drawbead lifting force of the i-th grid cell in contact with the drawbead is as follows:

[0010]

[0011]

[0012]

[0013]

[0014] Among them, S i Let be the projected area of ​​the contact portion between the i-th mesh element and the drawbead in the stamping direction.

[0015] F Ri The equivalent drawbead resistance of the i-th grid cell is...

[0016] F Ui The equivalent drawbead lifting force of the i-th mesh element is...

[0017] W db For the width of the ties,

[0018] w is a preset relaxation factor.

[0019] t i Let be the sheet thickness of the i-th grid cell.

[0020] ε i The equivalent strain of the i-th grid cell is...

[0021] 0 < i < m + 1.

[0022] The beneficial effects of this invention are as follows: This invention fully considers the work hardening and thickness changes that occur when sheet metal flows through the drawbeads. It utilizes finite element analysis to calculate the strain and thickness change data of the sheet metal mesh elements during simulation, and uses this data to calculate the drawbead resistance and lift force. This improves upon existing stamping simulation techniques that use fixed drawbead resistance and lift force, by employing variable equivalent drawbead resistance and lift force that are correlated with the sheet metal thickness and equivalent strain. This allows for adaptive iterative optimization of the equivalent drawbead resistance and lift force, and the adaptive results are applied to the stamping simulation forming process. This enables real-time prediction of the equivalent drawbead resistance, better reflecting the actual stamping forming conditions, effectively improving forming quality, and thus obtaining superior stamping simulation results and increasing simulation accuracy. Based on the accurate simulation results, the drawbead settings during actual stamping production can be adjusted, thereby improving the forming quality of the part surface, increasing stamping efficiency, and extending die life. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the stamping die according to an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram showing the distribution of drawbars.

[0025] Figure 3 This is a schematic diagram showing the contact between the sheet metal grid cells and the drawbead boundary line.

[0026] Figure 4 This is a schematic diagram of the thickness distribution of the part after simulation in this embodiment.

[0027] Reference numerals: 1. Die; 2. Blank holder; 3. Punch; 4. Drawbead; 5. Mesh cell of sheet metal; 6. Boundary line of drawbead. Detailed Implementation

[0028] This embodiment is used to simulate sheet metal stamping. The stamped products can be car body, chassis, fuel tank and other parts. The sheet metal can be made of metal sheets such as steel and aluminum.

[0029] The stamping simulation method based on adaptive equivalent drawbead resistance in this embodiment includes the following steps:

[0030] Step 1, such as Figure 1 As shown, a stamping die model with drawbeads is established. The sheet metal to be processed is meshed and placed into the stamping die. The initial drawbead resistance F of the mesh cells in contact with the sheet metal is calculated. R0 and initial drawbeam lifting force F U0 Wherein, the thickness of the sheet material to be processed is t0, the strengthening coefficient is K, and the hardening index is n.

[0031] The stamping die model includes the materials of the punch, die, and blank holder, as well as various stamping parameters during drawing. These stamping parameters include at least the drawing method, tool stroke, blank holder force, and coefficient of friction, which are existing technologies and will not be elaborated further. The sheet metal mesh can be a triangular mesh or a hybrid mesh of triangles and quadrilaterals.

[0032] In this embodiment, the sheet material is galvanized sheet DX53D+Z-0.8, with a strengthening coefficient K of 490.0MPa, a hardening index n of 0.204, and an initial sheet thickness of 2.0mm. The stamping die is used for single-action drawing, with a tool stroke of 85.0mm, a blank holder force of 120.0kN, a friction coefficient of 0.15, and the part to be formed is an N-shaped sheet.

[0033] The setting of draw beads is also existing technology, creating equivalent draw bead lines of different lengths in different areas according to the characteristics of the part to be processed. This embodiment uses circular draw beads, such as... Figure 2 As shown, nine drawing ribs are provided on the pressure ring, with a rib height of 5.0 mm, a rib radius of 5.0 mm, and a groove radius of 3.0 mm.

[0034] The initial drawbead resistance F of the grid cell in contact with the sheet metal R0 and initial drawbeam lifting force F U0 The calculation method is also existing technology, for example, it can be obtained based on the classic Stoughton equivalent drawbeam resistance model.

[0035] Existing technologies, when simulating sheet metal stamping, utilize the initial drawbead resistance F. R0 and initial drawbeam lifting force F U0 As the fixed drawbead resistance and drawbead lifting force in the stamping process.

[0036] Step 2: Simulate the stamping process of the sheet metal using the finite element method. At the start of the stamping process, for each incremental step of the stamping forming (i.e., the die moves forward one incremental step), obtain the equivalent strain of each mesh element. As the sheet metal continuously flows over the drawbead, the number of sheet metal mesh elements in contact with the drawbead gradually increases, and the number of sheet metal mesh elements in contact with the drawbead also changes continuously. Therefore, for each incremental step of the stamping forming, find all m mesh elements of the sheet metal in contact with the drawbead, and calculate the equivalent drawbead resistance and equivalent drawbead lifting force of the mesh elements of the sheet metal in contact with the drawbead.

[0037] Preferably, the method for identifying the grid cells in contact with the drawbead of the sheet metal is as follows: for each grid cell, if not all of its nodes are located on the same side of the drawbead boundary line, then the grid cell is in contact with the drawbead. Figure 3 As shown, the contact between the triangular sheet metal mesh element and the drawbead indicates that not all three nodes of the mesh element are located on the same side of the drawbead boundary line. This is existing technology, and can be found in the 2016 thesis of Yanshan University, "Development and Application of Equivalent Drawbead Model Based on ABAQUS Software" (author: Liu Peng). Alternatively, contact can be determined by observing whether the mesh element's projection in the stamping direction coincides with the drawbead.

[0038] The method for calculating the equivalent drawbead resistance and equivalent drawbead lifting force of the i-th grid cell in contact with the drawbead of the sheet metal is as follows:

[0039]

[0040]

[0041]

[0042]

[0043] Among them, S i Let be the projected area of ​​the contact portion between the i-th mesh element and the drawbead in the stamping direction.

[0044] F Ri The equivalent drawbead resistance of the i-th grid cell is...

[0045] F Ui The equivalent drawbead lifting force of the i-th mesh element is...

[0046] W db For the width of the ties,

[0047] w is a preset relaxation factor.

[0048] t i Let be the sheet thickness of the i-th grid cell.

[0049] ε i The equivalent strain of the i-th grid cell is...

[0050] 0 < i < m + 1.

[0051] The projection of the mesh element of the sheet metal into the drawbead in the stamping direction is usually an irregular quadrilateral. When calculating the projected area S of the i-th mesh element in the stamping direction into the drawbead,... i ,like Figure 3 As shown, assuming the direction perpendicular to the paper and inwards is the stamping direction, the projection of the sheet metal grid cell in contact with the drawbead in this direction is typically an irregular shape with four nodes. Since the drawbead line is relatively small, the irregular shape can be treated as a quadrilateral. The projected area S iIt can be obtained from the coordinates of the four nodes A, B, C, and D.

[0052] The preset relaxation factor w is an empirical value, preferably ranging from [0.0, 2.0]. Generally, it can be implemented according to the following guidelines: w = 0.0 in zero-stretch state, w = 0.15 in weak-stretch state, w = 0.35 in medium-strength stretch state, w = 0.9 in strong-stretch state, and w = 2.0 in locked state. Of course, the preset relaxation factor w can also be fine-tuned within a certain range based on experience.

[0053] This embodiment, based on the sheet metal mesh elements flowing through the drawbead in the current increment step, considers the work hardening and thinning phenomena during material flow. It extracts equivalent strain data and thickness change data during the stamping process, converts the equivalent strain data into equivalent stress data using a power-law hardening curve, and defines the obtained stress and thickness change data as plastic parameters. These parameters are then input into the equivalent drawbead resistance calculation model to obtain the equivalent resistance in the current increment step. The resistance values ​​are then assigned to the sheet metal nodes in contact with the drawbead for stamping simulation. This process is repeated iteratively to adaptively update the equivalent drawbead resistance data until the stamping process simulation ends, thus obtaining more accurate simulation results than existing technologies.

[0054] Figure 4 The diagram shows the thickness distribution of the part after simulation in this embodiment. It can be seen that the forming quality of the part is good, and the thickness value is basically concentrated between 1.60-2.05mm, which meets the expected effect. Therefore, this embodiment can adaptively predict the resistance of the equivalent drawbead in the stamping forming simulation. According to the applicant's comparative test, its simulation results are more accurate than the fixed equivalent drawbead resistance model.

Claims

1. A stamping simulation method based on adaptive equivalent drawbead resistance, comprising the following steps: Step 1: Establish a stamping die model with drawbeads. Generate a mesh from the sheet metal to be processed and place it into the stamping die. Calculate the initial drawbead resistance F of the mesh cells in contact with the sheet metal. R0 and initial drawbeam lifting force F U0 Wherein, the thickness of the sheet material to be processed is t0, the strengthening coefficient is K, and the hardening index is n; Step 2: Simulate the stamping process of the sheet metal using the finite element method. For each incremental step of the stamping process, find all m mesh elements in contact with the drawbead and calculate the equivalent drawbead resistance and equivalent drawbead lifting force of the mesh elements in contact with the drawbead. The method for calculating the equivalent drawbead resistance and equivalent drawbead lifting force of the i-th grid cell in contact with the drawbead is as follows: Among them, S i Let be the projected area of ​​the contact portion between the i-th mesh element and the drawbead in the stamping direction. F Ri Let be the drawbead resistance of the i-th grid cell. F Ui The drawbead lifting force of the i-th grid element. W db For the width of the ties, w is a preset relaxation factor. t i Let be the sheet thickness of the i-th grid cell. ε i The equivalent strain of the i-th grid cell is... 0 < i < m + 1.

2. The stamping simulation method based on adaptive equivalent drawbead resistance according to claim 1, characterized in that: When generating a grid from the sheet material to be processed, use a triangular grid or a mixed grid of triangles and quadrilaterals.

3. The stamping simulation method based on adaptive equivalent drawbead resistance according to claim 1 or 2, characterized in that, The method for finding the grid cells in contact with the drawbead of the sheet metal is as follows: for each grid cell, if not all of its nodes are located on the same side of the drawbead boundary line, then the grid cell is in contact with the drawbead.

4. The stamping simulation method based on adaptive equivalent drawbead resistance according to claim 1 or 2, characterized in that, The preset relaxation factor w has a value range of [0.0, 2.0].

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