JP4524573B2 - Press molded product shape prediction method, prediction program, recording medium recording the program, and press molding method - Google Patents

Description

  The present invention relates to a prediction method for predicting the shape of a press-formed product, a program for the prediction, a computer-readable recording medium recording the program, and a press-molding method using the prediction method.

  In the case of manufacturing a molded product (workpiece) of a predetermined shape by press molding a plate-shaped material, conventionally, the mold prototype and trial placement are repeated, and the mold model is corrected each time and finally designed. Conventionally, it is common to complete a press die so that a predetermined shape can be stably obtained.

In recent years, in order to reduce as much time and labor as possible in such a prototype process, molding is performed by applying the elasto-plastic finite element method to predict the shape of a press-formed product and performing analysis using a computer. A simulation method for predicting the shape of a product (see, for example, Patent Document 1) has attracted attention.
However, the conventional shape prediction methods generally have a problem that the prediction accuracy is not yet sufficient for practical use, and the analysis takes time.

  By the way, for example, a flat metal material is fixed between a die and a holder, and a punch is advanced into a concave portion of the die, whereby a molded product (workpiece) having a concave portion in a part of the flat plate (for example, a central portion). In this case, the material is bent at the corner R portion at the entrance of the concave portion of the die, and is bent along the radius of curvature of the corner R portion. The metal material sandwiched between the holders is formed so as to be narrowed down.

That is, a part (upper part) of the vertical wall of the concave portion is formed such that the metal material between the die and the holder is plastically flowed and flows through the corner R portion of the die. The upper part of the vertical wall formed in this way is molded while compressive stress is acting in the plate thickness direction when passing the corner R part of the die, bending occurs when it is taken out from the die after molding, and warpage due to elastic recovery Becomes larger. This phenomenon is one of the major factors that reduce the shape prediction accuracy.
JP 2003-33828 A

In order to improve the shape prediction accuracy at the part that is molded while compressive stress acts in the plate thickness direction like the upper part of the vertical wall in the above-mentioned workpiece, it is elastic-plastic considering the stress in the plate thickness direction as well. The finite element method may be applied, but conventionally, when applying the elasto-plastic finite element method to predict the shape of a thin plate-like workpiece such as a press-formed product, a method using a planar so-called shell element is generally used. In this case, the stress in the in-plane direction is calculated, but usually the plate thickness is virtually ignored, so the stress in the plate thickness direction cannot be calculated.
As a method for calculating the stress in the plate thickness direction, there is a method using a so-called solid element instead of the shell element. In this case, however, it is difficult to obtain an analysis result. there were.

  The present invention has been made in view of such technical problems, and it is an object of the present invention to perform more accurate prediction in a relatively short time when predicting the shape of a plate-like press-formed product. .

  For this reason, the method for predicting the shape of a press-formed product according to the present invention is a method in which a part of a plate-like material is passed through a corner R portion of a die by pressurization of a die punch part, so that a part of the material has a plate thickness. A method for predicting the shape of a press-molded product obtained by performing press molding while applying a compressive stress in a direction, wherein the corner R portion is determined for a material model of the press-molded product. Set material models with different characteristics for the parts that pass and parts that do not pass, and calculate the stress for each part that occurs in the material movement process with the progress of pressurization of the die punch as needed And a step of predicting and calculating the shape of the press-formed product after elastic recovery by solving the balance of the calculated stress for each part.

  In addition, the press-formed product shape prediction program according to the present invention allows a part of the plate-shaped material to pass through the corner R portion of the mold by pressurizing the mold punch part, so that a part of the material is in the plate thickness direction. A press-molded product shape prediction program for causing a computer to predict the shape of a press-molded product obtained by performing press molding while applying the compressive stress of the computer, about the material model of the press-molded product, A material model having different characteristics is set for a portion that passes through the corner R portion and a portion that does not pass through the portion, and the stress at each part generated in the material movement process accompanying the progress of pressurization of the die punch portion is determined by the material movement. The function to calculate at any time along with the above, and the function to predict and calculate the shape of the press-formed product after elastic recovery by solving the balance of the calculated stress for each part It is intended.

Furthermore, a computer-readable recording medium according to the present invention records the press-formed product shape prediction program.
As this recording medium, for example, various known recording media such as an optical disk medium such as a compact disk (CD) and a DVD, and a magnetic tape medium can be applied.

  Furthermore, in the press molding method according to the present invention, a compression stress in the thickness direction is applied to a part of the material by passing a part of the plate-like material through the corner R part of the die by pressing the die punch part. A method of forming a press-molded product obtained by performing press-molding while acting on the shape of the molded product predicted by the press-molded product shape prediction method according to claim 1, and the molding The method includes a step of calculating a shape difference from the normal shape of the product, and a step of performing press forming so as to obtain the normal shape based on the calculation result.

In this case, it is preferable to correct the press mold based on the calculation result of the shape difference and perform press molding using the corrected mold.
Alternatively, press molding may be performed using the press molding die used for the shape prediction calculation of the press molded product, and then post press molding may be performed with a press working amount based on the calculation result of the shape difference. good.

  According to the method for predicting the shape of a press-formed product according to the present invention, a material model having different characteristics is set for a material model of the press-formed product in a portion that passes through the corner R portion of the die and a portion that does not pass through the die punch portion. Compression in the plate thickness direction that acts on the material by passing through the corner R portion by calculating the stress at each part that occurs in the material movement process with the progress of pressurization as needed along with the material movement Calculations that take stress into account can be performed. That is, more accurate prediction can be performed by a relatively simple method and in a relatively short time.

  Further, according to the press-formed product shape prediction program according to the present invention, the material model of the press-formed product has a function of setting a material model having different characteristics depending on whether the part passes through the corner R portion of the mold or not. By passing through the corner R portion by causing a computer to realize the function of calculating the stress of each part generated during the material movement process accompanying the pressurization of the die punch portion as needed with the material movement. By doing so, it is possible to perform calculation in consideration of the compressive stress in the thickness direction acting on the material. That is, more accurate prediction can be performed by a relatively simple method and in a relatively short time.

  Furthermore, according to the computer-readable recording medium according to the present invention, by causing the computer to read the press-molded product shape prediction program, the material model of the press-molded product has a portion that passes through the corner R portion of the mold. A function to set a material model with different characteristics depending on the part that does not pass through, and to calculate the stress of each part of the material generated in the material movement process accompanying the pressurization of the die punch part as needed along with the material movement. The calculation can be performed in consideration of the compressive stress in the thickness direction acting on the material by passing through the corner R. That is, more accurate prediction can be performed by a relatively simple method and in a relatively short time.

  Further, according to the press molding method according to the present invention, based on the calculation result of calculating the shape difference between the shape of the molded product predicted by the shape prediction method of the press molded product and the regular shape of the molded product. In addition, by performing press molding so as to have the regular shape, the shape accuracy is higher based on the calculation result considering the compressive stress in the thickness direction acting on the material by passing through the corner R portion of the mold Press molding can be performed.

  In this press molding method, it is possible to perform press molding with higher shape accuracy by correcting the press molding die based on the calculation result of the shape difference and performing press molding using the corrected die. it can.

  Alternatively, in the press molding method, press molding is performed using the press molding die used for the shape prediction calculation of the press molded product, and then post press molding is performed with a press working amount based on the calculation result of the shape difference. By performing this, it is possible to obtain a press-formed product with higher shape accuracy.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional explanatory view showing an example of a press mold used for the press molding method according to the present embodiment and a molding material. FIG. 2 is an explanatory cross-sectional view showing an enlarged main part of FIG. These press molds and molding materials are the same as those conventionally known.
As shown in these drawings, the press mold includes a die 2 having a concave portion 2c having a predetermined depth in a central portion, and a holder 4 that sandwiches and fixes a flat metal material M in combination with the die 2. The outer peripheral portion 6d is guided by the inner peripheral surface 4d of the holder 4 so as to be slidable in the vertical direction.

A corner 2k at the entrance of the recess 2c of the die 2 (that is, a corner formed by intersecting the upper surface 2f of the die 2 and the vertical wall 2d of the recess 2c) is formed in a curved surface having a predetermined radius of curvature. ing. Hereinafter, this corner portion 2k is referred to as “corner R portion 2k”. The corner 2j at the periphery of the bottom surface 2b of the recess 2c (that is, the corner formed by the intersection of the bottom surface 2b of the recess 2c and the vertical wall 2d) is also formed in a curved surface having a predetermined radius of curvature. Yes.
When performing press molding using the press mold, the flat metal material M is sandwiched and fixed between the upper surface 2f of the die 2 and the lower surface 4f of the holder 4, and the punch 6 is recessed in the die 2. By proceeding toward 2c, as shown by a two-dot chain line in FIG. 1, a central portion of the flat plate portion Wf has a concave portion Wc formed by a vertical wall Wd and a bottom wall Wb (the cross-sectional shape is substantially the same). A hat-shaped press-formed product W (workpiece) is obtained.

  At this time, the material M is bent at the corner R portion 2k at the entrance of the concave portion 2c of the die 2 so as to follow the curved surface of the corner R portion 2k. At this time, the vertical wall Wd of the workpiece concave portion Wc is The portion to be formed is formed such that the metal material M sandwiched between the die 2 and the holder 4 is narrowed down. That is, the metal material M sandwiched between the upper surface 2f of the die 2 and the lower surface 4f of the holder 4 plastically flows in a part (upper part) of the workpiece vertical wall Wd and flows through the corner R portion 2k of the die 2 and flows in. In this way, it is formed.

  In the upper part of the workpiece vertical wall Wd formed in this manner, the die 2 is molded while compressive stress is acting in the plate thickness direction when passing through the corner R portion 2k, and when the die 2 is taken out from the die 2 after molding, it is bent back. And warpage due to elastic recovery increases. This phenomenon is one of the major factors that reduce the shape prediction accuracy of the workpiece W.

FIG. 3 is a partial explanatory view schematically showing a region where the workpiece W (press-molded product) is molded while receiving the action of compressive stress in the plate thickness direction. As shown in this figure, the metal material M sandwiched between the upper surface 2f of the die 2 and the lower surface 4f of the holder 4 is plastically flowed in the upper region Lu up to substantially the upper half of the concave vertical wall Wd of the workpiece W. By forming the die 2 so as to pass through the corner R portion 2k (see the dashed line arrow in FIG. 3), a compressive stress acts in the plate thickness direction when the die 2 passes the corner R portion 2k. Will be molded.
On the other hand, the lower region Ls of the concave vertical wall Wd of the workpiece W is formed without such compressive stress acting in the plate thickness direction.

A prediction method for predicting the shape of the press-formed product W as described above will be described.
Here, shape prediction is performed by forming simulation using a nonlinear finite element method. In such forming simulation, the stress for each part of the workpiece generated in the forming process is calculated by elastic-plastic calculation, and then the balance of stress is solved by using elastic calculation, so that after elastic recovery (so-called spring back). The workpiece shape can be predicted.
FIG. 4 is an explanatory diagram schematically showing the predicted shape of the main part of the work before elastic recovery based on the elastic-plastic calculation result, and FIG. 5 schematically shows the predicted shape of the main part of the work after elastic recovery based on the elastic calculation result. It is explanatory drawing shown in. FIG. 6 is an explanatory diagram schematically showing the predicted shape of the main part of the work before elastic recovery (see the dashed curve) and after elastic recovery (see the solid curve).

  In the present embodiment, in order to further improve the shape prediction accuracy of the forming simulation, a region Lu (that is, a portion passing through the corner R portion 2k of the die 2) in which a compressive stress in the thickness direction acts when forming the workpiece W, and forming At times, a material model having different characteristics is set in the region Ls where the compressive stress in the thickness direction does not act (that is, the portion not passing through the corner R portion 2k of the die 2).

FIG. 11 is a graph showing the stress-strain characteristics of the material metal M used for forming the workpiece W, and the curve N1 shows the original stress-strain characteristics of the material to which no compressive stress is applied, and its hardening. The formula (curing formula 1) is represented by σ = ε ⁿ¹ (σ: stress, ε: strain, n1: constant). On the other hand, the curve N2 shows the stress-strain characteristic when compressive stress is applied. In this case, as is well known, the actual yield point is lowered, and the hardening formula (hardening formula 2) is represented by σ = ε ⁿ² (σ: stress, ε: strain, n2: constant).

In the present embodiment, a material model (hereinafter referred to as a material model 1) having characteristics represented by a curve N1 (curing formula 1) is applied to a region Ls where a compressive stress in the thickness direction does not act during molding. ) And a material model (hereinafter referred to as a material model 2) having a characteristic represented by a curve N2 (curing formula 2) for a region Lu in which a compressive stress in the thickness direction acts during molding. ) Applied.
This makes it possible to perform calculations in consideration of compressive stress in the plate thickness direction even with methods using shell elements that can be analyzed in a relatively short time, without relying on methods using solid elements that require a long time for analysis. Can do.

The presence or absence of the action of compressive stress in the plate thickness direction at the time of molding, that is, the presence or absence of passing through the corner R portion 2k of the die 2 at the time of molding, is determined in the mesh model of the finite element method. The contact is determined by the contact determination method for determining the presence or absence of contact with the node.
As schematically shown in FIG. 10, this contact determination method calculates the distance between the mesh Dm of the die corner R portion and the node F of the material mesh Wm, and when this distance becomes zero (zero: 0), It is determined that there was.

Next, a method for predicting the shape of a press-formed product according to this embodiment will be described with reference to the flowchart of FIG.
When the prediction system starts, first, the material model 1 is set and inputted as the material model of the molding material M (step # 1), and then the elastoplastic calculation is started (step # 2). In step # 3, it is determined whether or not the corner R portion 2k of the die 2 has passed (die R passage). This determination is performed by the aforementioned contact determination method. As a result of the determination at step # 3, when there is no passage, the material model 1 is applied as it is (step # 4), and when there is passage, the material model 2 is applied instead of the material model 1. (Step # 5). In step # 6, elastoplastic calculation is executed.

Next, in step # 7, it is determined whether the stroke of the punch 6 has reached a predetermined amount (excessive) or not reached (not reached), and if not, the process returns to step # 3. Thereafter, the same steps (steps # 3 to # 7) are repeatedly executed. On the other hand, if the stroke is excessive, the elastic-plastic calculation is completed (step # 8).
The series of steps # 3 to # 7 described above constitutes an optional calculation area that is executed as needed while the stroke of the punch 6 is in progress, whereby the stress state of each shell element accompanying the material movement in the molding process. Calculation, selection of an appropriate material model (hardening equation), and stress history can be taken into consideration.

  After that, more preferably, the residual stress value of the material is calculated (step # 9), and the elasticity calculation is executed in consideration of this residual stress value (step # 10). By performing an operation for solving the balance of stress by this elastic calculation, a prediction of the shape after elastic recovery can be obtained.

FIG. 7 is an explanatory diagram of a main part of the work showing the predicted shape (see the dashed curve) according to the conventional shape prediction method and the predicted shape (see the solid curve) according to the present embodiment in comparison with each other. FIG. 8 is an enlarged explanatory view showing the main part Y8 of FIG. 7 in an enlarged manner.
As shown in these figures, in the conventional shape prediction method, since the compressive stress in the thickness direction is not taken into account, the deformation (warp) is predicted to be relatively small, but the shape prediction method according to the present embodiment is According to this, since the compressive stress in the thickness direction is taken into account, deformation (warping) is predicted to be relatively large.

  All of the above shape prediction steps are programmed as a shape prediction program, and are performed by causing a computer to execute this program. Such a shape prediction program can be recorded on various known computer-readable recording media such as an optical disk medium and a magnetic tape medium, and the program is read by attaching the recording medium to a computer reading device. Can be executed.

After the prediction calculation is performed as described above, the shape difference between the shape of the workpiece W predicted and calculated here and the normal shape (design shape) of the workpiece W is calculated. Based on the calculation result, The workpiece W is press-molded so as to have the regular shape.
Specifically, the press mold is corrected based on the calculation result of the shape difference, and press molding is performed using the corrected mold. By performing press molding using such a corrected mold, press molding with higher shape accuracy can be performed.

  Alternatively, press molding may be performed using the press mold used for the prediction calculation, and then post-press molding may be performed with a press working amount based on the calculation result of the shape difference. . By performing such post-press molding, a press-molded product with higher shape accuracy can be obtained.

  As described above, according to the method for predicting the shape of a press-formed product according to this embodiment, the material model of the workpiece W differs between the portion Lu that passes through the corner R portion 2k of the die 2 and the portion Ls that does not pass through. By setting a characteristic material model and calculating the stress for each part of the workpiece generated in the material movement process accompanying the pressurization of the punch 6 as needed with the material movement, the corner R portion The calculation considering the compressive stress in the thickness direction acting on the material by passing 2k can be performed. That is, more accurate prediction can be performed in a relatively simple method and in a relatively short time.

  Needless to say, the present invention is not limited to the above-described embodiments, and various modifications and improvements can be added without departing from the scope of the present invention.

It is a section explanatory view showing the press mold and molding material used for the press molding method concerning the embodiment of the present invention. It is sectional explanatory drawing which expanded and showed the principal part of FIG. It is a partial explanatory view showing typically the principal part of a press-formed product. It is explanatory drawing which shows typically the prediction shape of the workpiece | work principal part before elastic recovery based on the elastoplastic calculation result. It is explanatory drawing which shows typically the estimated shape of the workpiece | work principal part after the elastic recovery based on an elastic calculation result. It is explanatory drawing which shows typically the prediction shape of the workpiece | work principal part before elastic recovery and after elastic recovery collectively. It is explanatory drawing of the principal part of a workpiece | work which shows and compares the prediction shape by the conventional shape prediction method with the prediction shape by the shape prediction method which concerns on this embodiment. FIG. 8 is an enlarged explanatory view showing a main part Y8 of FIG. 7 in an enlarged manner. It is a flowchart for demonstrating the prediction method of the press molded product shape which concerns on this embodiment. It is explanatory drawing of the contact determination method which determines the presence or absence of the contact of the mesh of a die angle | corner R part, and the node of a material mesh. It is a graph which shows the stress-strain characteristic of raw material metal.

Explanation of symbols

2 Dies 2k Corner R part 4 Holder 6 Punch W Press molded product Wc Concave part Wd Vertical wall Lu Upper part of vertical wall Ls Lower part of vertical wall M Plate material

Claims (6)

By pressing the mold punch part, a part of the plate-shaped material is passed through the corner R part of the mold, so that it can be obtained by press forming while applying a compressive stress in the sheet thickness direction to a part of the material. A method for predicting the shape of a press-formed product, which predicts the shape of a press-formed product,
With respect to the material model of the press-formed product, a material model having different characteristics is set for a portion that passes through the corner R portion and a portion that does not pass through, and each of the materials generated in the material movement process accompanying the pressurization of the die punch portion Calculating the stress for each part as needed with the material movement;
Predicting the shape of the press-formed product after elastic recovery by solving the balance of the calculated stress for each of the above-mentioned parts;
A method for predicting the shape of a press-formed product, comprising: By pressing the mold punch part, a part of the plate-shaped material is passed through the corner R part of the mold, so that it can be obtained by press forming while applying a compressive stress in the sheet thickness direction to a part of the material. A press-formed product shape prediction program for causing a computer to predict the shape of a press-formed product,
In the above computer,
With respect to the material model of the press-formed product, a material model having different characteristics is set for a portion that passes through the corner R portion and a portion that does not pass through, and each of the materials generated in the material movement process accompanying the pressurization of the die punch portion. A function to calculate stress for each part as needed along with the material movement;
A function for predicting and calculating the shape of the press-formed product after elastic recovery by solving the balance of the stress for each of the calculated parts,
For predicting the shape of a press-formed product to achieve this.   A computer-readable recording medium on which the press-formed product shape prediction program according to claim 2 is recorded. By pressing the mold punch part, a part of the plate-shaped material is passed through the corner R part of the mold, so that it can be obtained by press forming while applying a compressive stress in the sheet thickness direction to a part of the material. A method of forming a press-molded product,
A step of calculating a shape difference between the shape of the molded product predicted and calculated by the method for predicting the shape of the press-formed product according to claim 1 and a normal shape of the molded product;
Based on the calculation result, performing press molding so as to have the regular shape;
A press molding method characterized by comprising: In the press molding method according to claim 4,
A press molding method, comprising: correcting a press mold based on the calculation result of the shape difference, and performing press molding using the corrected mold. In the press molding method according to claim 4,
A press characterized in that press molding is performed using the press molding die used for the shape prediction calculation of the press molded product, and then post press molding is performed with a press working amount based on the calculation result of the shape difference. Molding method.

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