JP2002336913A - Press forming simulation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simulation method in which restrictive conditions necessary in the beginning of press forming simulation are automatically set according to the shape of a formed article, and the simulation need not be interrupted in the middle thereof. SOLUTION: This press forming simulation method comprises a step (S4) of deciding whether or not the shape of the completed article is symmetrical, a step (S11) of setting the restrictive conditions in X-direction and Y-direction at the position of the center of gravity of a plate model with the pressing direction as Z-direction and the plane orthogonal thereto being an X-Y plane if the shape is not symmetrical, and setting either restrictive condition in X- direction or Y-direction at the position away from the position of the center of gravity by the predetermined distance, a step (S21 or S22) of setting the restrictive conditions on the symmetrical line part of the plate model if the shape is symmetrical, a step (S8) of releasing the set restrictions at the time when the plate is brought into contact with a die.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for simulating press forming.

[0002]

2. Description of the Related Art In recent years, simulation of a press-formed product using a finite element method has been used in designing a press-formed product and a press-forming die for forming the same.

[0003] In this simulation, before entering the forming process, a plate material (blank material) model to which a finite element mesh is applied is placed in a mold to which a finite element mesh (or point cloud data) is applied, and a plate material model is applied. Is calculated by calculation. In addition, after the bending deformation is completed, the plate material model is not mechanically stable enough to fit into the tool. In other words, in the simulation calculation, there is no constraint by the tool, so the numerically sufficient freedom constraint cannot be obtained and the calculation is performed. Is calculated by calculating the blank hold deformation under a situation where the bank is easily broken.

Here, an outline of the actual pressing process will be described.

FIG. 8 is a drawing showing an outline of an actual pressing process.

In the actual pressing step, first, a plate material (plank material) 100 is placed on a lower die (die) 101 (FIG. 8A). At this time, the plate 100 bends and deforms due to its own weight. Thereafter, the blank hole portion 102 is lowered to form a blank hold (FIG. 8B). Subsequently, the upper die (punch) 103 is lowered and pressed to perform punch forming (FIG. 8C). Pressing is completed when the upper die 103 reaches the bottom dead center (FIG. 8D).

As described above, in actual press forming, plank hold for holding a plate material is performed before the upper die is lowered. However, in the simulation by the finite element method program of static analysis, bending deformation and blanking are performed. When calculating the hold deformation, the translation and the rotation on the XY plane (the pressing direction of the upper die (punch) is defined as the Z direction, and the plane orthogonal to the Z direction is defined as the XY plane) are defined. Modeling of a special tool is not usually performed. Therefore, it is necessary to set a constraint state as a boundary condition instead to create a mechanically stable state. The boundary conditions for creating such a constraint state include a condition that the plate should not be deformed differently from reality. For this reason, the boundary conditions set at the time of execution of the analysis are set to a displacement constraint and a rotation constraint that do not give unnatural forced deformation while maintaining mechanical stability in the XY plane.

FIG. 9 is a view showing a plate material model in a state where boundary conditions are entered by a conventional method. As shown in the figure, by setting the constraint condition in the X direction and the Y direction with respect to the plate material model 10, the boundary condition is set so that the rotation constraint is simultaneously applied.

[0009]

Heretofore, in the above-described press forming simulation, an analyst has manually input a boundary condition for restricting displacement or rotation. For this reason, a lot of work is required before starting the analysis, and there is a problem that much labor and time are required.

Also, the boundary condition to be given first differs depending on the shape of the product to be simulated or the level of skill of the analyst, and in some cases, there is a problem that the calculation cannot be satisfied with the set boundary condition.
There is also a problem that the setting of the boundary condition is redone by trial and error many times, which takes much time.

After the forming process has progressed and the contact area with the tool has increased and sufficient mechanical stability has been obtained, it is necessary to remove the initially applied displacement constraint and rotation constraint.
At that point, it is necessary to temporarily stop the simulation to remove the constraint conditions and the like, and there is a problem that the simulation cannot be performed efficiently.

Accordingly, an object of the present invention is to provide a press forming simulation in which the constraint conditions to be given at the beginning of the simulation are automatically set in accordance with the shape of the molded article to be simulated, and the simulation needs to be interrupted halfway. There is no press forming simulation method.

[0013]

The object of the present invention is achieved by the following constitution.

(1) A step of judging whether or not the completed shape of the molded article has symmetry. If the result of the judgment is that there is no symmetry, the pressing direction is set to the Z direction, and the pressing direction is orthogonal to the Z direction. With the plane being the XY plane, the constraint conditions in the X direction and the Y direction are set at the center of gravity of the plate material model, and either the X direction or the Y direction is set at a position away from the center of gravity by a predetermined position. And a step of setting a constraint condition on a symmetrical line portion of the plate material model if the result of the determination indicates that there is symmetry, a simulation method of press forming.

(2) In the step of setting a constraint condition on a symmetrical line portion of the plate material model, when there are a plurality of symmetrical lines, the constraint condition is set on any one of the symmetrical lines. 2. The press molding simulation method according to 1.

(3) The simulation method according to claim 1 or 2, wherein the simulation method is a simulation using a finite element method, and the constraint condition is provided on a node of a finite element mesh on the plate material model. Simulation method of press molding.

(4) The constraint condition is released when a press mold comes into contact with the plate material model in the course of the simulation.
3. The press molding simulation method according to any one of 3.

[0018]

The present invention configured as described above has the following effects in each claim.

According to the first aspect of the present invention, the symmetry of the press-formed product to be simulated is detected. If there is no symmetry, the constraint condition is set at the center of gravity of the plate material and at a position away from the center of gravity by a predetermined distance. On the other hand, when there is symmetry, the constraint condition is set at the line of symmetry, so that the constraint condition is automatically set at or near a static mechanically balanced portion. Therefore, when calculating the deflection or blank hold due to the weight of the plate material, the plate material model does not become unstable, and an accurate simulation can be performed.

According to the second aspect of the invention, when there are a plurality of symmetry lines, the constraint condition is set to any one of the symmetry lines, so that the constraint condition can be set more easily.

According to the third aspect of the present invention, the simulation is executed by the finite element method, and the constraint conditions are set at the nodes of the finite element mesh.
A constraint condition can be set on the plate material model.

According to the fourth aspect of the present invention, in the course of the simulation, when the press die comes into contact with the plate material model, the set restraint conditions are released. An efficient simulation can be performed without the need.

[0023]

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a flowchart showing the procedure of a press forming simulation method to which the present invention is applied.

Here, a simulation program based on the finite element method is used. As is well known, the finite element method simulation program performs calculations by dividing the press forming process into steps of, for example, thousands to tens of thousands of hours, and at each time step, at each node of the plate material model divided into the finite element mesh. It is calculated by reducing the problem to solve the linear equation of nodal force increment versus nodal displacement increment.

For this reason, also in the present embodiment, in order to perform the simulation by the finite element method, first, the finite element mesh data is applied to the plate material (blank material) model, and the point data is allocated to the press forming die model. Settings are made (S1).

Next, as the boundary conditions of the plate model, boundary conditions such as dimensions and rigidity of the plate are read (S2). The reading of the boundary conditions is based on the physical characteristics of the plate material, and does not include the constraint conditions arbitrarily set by the analyst as in the related art.

Subsequently, symmetry is detected from the completed shape of the molded article to be simulated (S3). In addition,
The completed shape uses, for example, design data (CAD data) of a molded product.

If there is no symmetry as a result of the detection (S4, N
In o), the center of gravity of the plate material model is calculated, the constraint condition in the X direction and the Y direction is set at the node closest to the position of the center of gravity, and the center of gravity is set on the node closest to the position away from the center of gravity by a predetermined distance. A constraint condition in the Y direction is set (S11).

For a node closest to the position separated by a predetermined distance, for example, a position at a predetermined distance in the X-axis + direction is determined from the position of the center of gravity. Move gradually until a node exists, and when a node exists, a constraint condition is set for that node.

FIG. 2 is a drawing showing a plate material model in which the constraint conditions are set as described above.

As shown in the drawing, constraints in the X and Y directions are placed on the node closest to the position of the center of gravity of the plate material model 10, and here, a constraint in the Y direction is placed at a position 50 mm away from the center of gravity. As a result, conditions for restricting the translation and rotation of the plate are set.

Note that the constraint set at a node near a position at a predetermined distance from the center of gravity may be a constraint in the Y direction instead of the constraint in the X direction.

In step S4, if there is symmetry (S4, Yes), it is determined whether the symmetry is 対 称 or １ ／ (S5).

As shown in FIG. 3, "1/2 symmetry" refers to a shape having a line of symmetry that divides into 1/2 at the center of one plate. As shown in FIG. 2, a shape having a symmetry line that divides one plate material into quarters.

Examples of symmetric products include a floor panel, a roof panel, a bonnet panel, and a trunk panel, for example, in the case of an automobile body. Also, even if one product does not have symmetry, if two or more of the same products are press-formed at once, there is a half symmetry if two products are press-formed at once. ,
Press molding four at once has a quarter symmetry.

In step S5, in the case of 1/2 symmetry, a constraint condition is set along the symmetry line (S21).
In the case of molding a product having 1/2 symmetry, for example, as shown in FIG. 5, a constraint in the X direction is set in the plate material model 10 in a direction along the X axis which is a line of symmetry. When the symmetry line is along the Y-axis direction, a constraint in the Y direction is set.

On the other hand, if the symmetry is 1/4 symmetry, the constraint condition is set along any one of the symmetry lines (S22). In the case of molding a molded product having 1/4 symmetry, for example, as shown in FIG. 6, the symmetry lines are in the X-axis direction and the Y-axis direction. Set constraints along. Of course, the constraint may be set along a line of symmetry in the Y-axis direction.

Thereafter, a simulation is executed (S6), and it is determined whether or not any of the point data of the upper model has contacted any of the nodes of the plate material model (S6).
7). Here, if there is no contact, the simulation is continued as it is. On the other hand, when the plate material model and the upper mold model are in contact with each other, at that time, the above-described step S11,
The constraint conditions set in S21 or S22 are released (S8). This makes it possible to automatically remove the constraint conditions provided on the plate material model immediately before the punch forming by the press forming die starts.

Thereafter, similarly to the ordinary simulation, the simulation of the press forming is continued until the upper die reaches the bottom dead center (S9, S10).

FIG. 7 shows an example of a graphic display of the result of a simulation performed according to the above processing procedure.

FIG. 7 is a drawing showing only half of the plane of symmetry when a plate material having a half symmetry in the completed shape is placed on the lower mold model 11, and FIG.
FIG. 7B is a perspective view showing a state immediately after placing the camera.
FIG. 7C is a side view showing a state immediately after the plate material model 10 is placed, FIG. 7C is a perspective view showing a state of the plate material model 10 after its own weight deflection deformation, and FIG.
It is a side view which shows the state after zero weight deflection deformation.

In the simulation of a molded product having such a half symmetry, as shown in FIGS. 7A and 7B, first, the plate material model 10 is placed on the lower mold model 11 and the symmetrical line portion is formed. An X-direction constraint condition is set.
Thereafter, as shown in FIG. 7C and FIG. 7D, the deflection calculation of the plate material model 10 by its own weight is performed. At this time, since the present embodiment is applied, the constraint condition is automatically set in the part that is mechanically balanced,
Accurate simulation can be performed even at a stage where the plate material model 10 is not restricted by the press die.

As described above, according to the present embodiment, a node close to the center of gravity is selected from the nodes in the plate material model, and the displacement constraint is automatically made in that part in both the X and Y directions. It is set, and the cancellation is automatically performed. Therefore, it is not necessary to set boundary conditions including constraint conditions for deflection calculation and blank hold calculation, which were conventionally performed manually, and it is not necessary to stop the simulation halfway to release the set constraint conditions. Thus, it is possible to perform a more efficient and accurate press forming simulation.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of a press forming simulation method to which the present invention is applied.

FIG. 2 is a diagram showing an example of a constraint condition set for a plate material model having no symmetry.

FIG. 3 is a drawing for explaining 1/2 symmetry.

FIG. 4 is a drawing for explaining quarter symmetry.

FIG. 5 is a diagram showing an example of a constraint condition set for a plate material model having half symmetry.

FIG. 6 is a diagram illustrating an example of a constraint condition set for a plate material model having a quarter symmetry.

FIG. 7 is a diagram illustrating a graphic display example of a result of performing a simulation method to which the present invention is applied.

FIG. 8 is a schematic view showing an actual pressing step.

FIG. 9 is a diagram illustrating an example of setting a boundary condition including a set constraint that has been conventionally performed manually.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Plate material (blank material) model 11 ... Lower mold model 100 ... Plate material (blank material) 101 ... Lower mold 102 ... Blank hole part 103 ... Upper mold

Claims (4)

[Claims] 1. A step of determining whether or not the finished shape of a molded product has symmetry. If the result of the determination is that there is no symmetry, the pressing direction is changed to Z.
Direction and the plane orthogonal to the Z direction is defined as the XY plane, and the constraint conditions in the X direction and the Y direction are set at the center of gravity of the plate material model. Setting any one of the constraint conditions; and, as a result of the determination, if there is symmetry, setting a constraint condition on a symmetrical line portion of the plate material model. Simulation method. 2. The step of setting a constraint condition on a symmetrical line portion of the plate material model, wherein, when there are a plurality of symmetrical lines, the constraint condition is set on any one of the symmetrical lines. The press molding simulation method described in the above. 3. The press according to claim 1, wherein the simulation method is a simulation based on a finite element method, and wherein the constraint condition is provided on a node of a finite element mesh on the plate material model. Simulation method of molding. 4. The press according to claim 1, wherein the constraint condition is released when a press mold comes into contact with the plate material model during a simulation process. Simulation method of molding.