JP5210085B2 - Deformation forecasting method - Google Patents

Description

  The present invention relates to a deformation occurrence prediction method. More specifically, the present invention relates to a deformation occurrence prediction method for predicting the occurrence of deformation (such as wrinkles and surface distortion generated in a flat portion) in a product manufactured by press molding.

  Panel products such as automobile door panels and roof panels are formed by preparing a mold having a desired product shape and press-molding a plate material with a predetermined molding force.

  Here, when the mold is actually manufactured, prior to this, a process of manufacturing a product by press molding is simulated. That is, based on a model shape of a mold designed by CAD (Computer Aided Design), simulation is performed by CAE (Computer Aided Engineering), and the quality of a product manufactured based on the model shape is evaluated. Basically, the mold is actually manufactured after the result of the evaluation by the simulation is determined to be a non-defective product.

  In such a simulation, it is particularly important whether or not it is possible to predict the occurrence of deformation in a product in order to improve the quality of the product and reduce the cost for manufacturing the mold.

Therefore, a method for predicting the occurrence of deformation by simulation has been proposed. For example, in the method disclosed in Patent Document 1, the bending stress distributed in the cross section in the thickness direction of the plate material when the mold reaches bottom dead center, that is, when a predetermined forming force is applied to the plate material, is calculated. Integrate the bending stress along the thickness direction. Further, the curvature of the plate material is calculated according to the integrated bending stress and the elastic coefficient and thickness of the plate material, thereby predicting the occurrence of deformation in the product.
JP 2007-229761 A

  By the way, when the mold is released and the molding force applied to the plate material is unloaded, the plate material is elastically recovered, so that the shape changes from the shape at the time when the mold reaches the bottom dead center. For this reason, the shape and occurrence position of the deform also change before and after the unloading of the forming force. However, in the method disclosed in Patent Document 1, since the occurrence of deformation is predicted based on the bending stress of the plate material before unloading, the influence of such elastic recovery of the plate material is sufficiently taken into consideration. I can't say.

  The present invention is a deformation occurrence prediction method for predicting the occurrence of deformation in a press-molded product, and a deformation occurrence prediction method capable of predicting the occurrence of deformation in a product in consideration of the effect of elastic recovery of a plate material. The purpose is to provide.

  The deformation occurrence prediction method of the present invention is a deformation occurrence prediction method for predicting the occurrence of deformation in a product by performing a simulation of a process of manufacturing a product from a plate material by press molding, and is a molding that acts on a plate material from the outside A first step (for example, steps S1 to S3 in FIG. 3 described later) for calculating a stress (for example, an internal stress σ described later) acting on the plate deformed under the forming force based on the force; Based on the stress calculated in the first step, a second step (for example, a later-described figure) that calculates a stress (for example, an internal stress σ ′ described later) that acts on the plate after elastic recovery under the stress. 3 of steps S4 and S5), and the stress acting on the plate after elastic recovery calculated in the second step, the stress on one side of the neutral plane along the plate thickness direction (example) For example, a deformation determination amount (for example, a back-to-back stress difference Δσ to be described later) that is defined including a difference between an internal stress σ1 to be described later and a stress on the other side (for example, an internal stress σ2 to be described later) is calculated. Steps (for example, steps S4 to S6 in FIG. 3 described later) and a fourth step (for example, step S7 in FIG. 3 described later) for displaying the distribution of the deformation determination amount calculated in the third step, It is characterized by including.

According to the present invention, the stress acting on the plate material deformed under a predetermined forming force is calculated, and the stress acting on the plate material after elastic recovery under this stress is calculated. Further, among these stresses, a deformation determination amount defined including a difference between stresses on one side and the other side of the neutral surface along the plate thickness direction is calculated, and the distribution of the deformation determination amount is displayed. .
As described above, in the process of manufacturing a product by press molding, when the mold reaches the bottom dead center, that is, when a predetermined molding force is applied by the mold, the deformation is unloaded. As a result, the shape and generation position change. In this invention, by calculating the deformation determination amount based on the stress acting on the plate material after elastic recovery, it is possible to accurately predict the occurrence of deformation in the product in consideration of the effect of elastic recovery of the plate material. it can.

  According to the present invention, the deformation determination amount is calculated based on the stress acting on the plate material after the elastic recovery, thereby accurately predicting the occurrence of the deformation in the product in consideration of the influence of the elastic recovery of the plate material. be able to.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a simulation system 1 to which a deforming occurrence prediction method according to an embodiment of the present invention is applied.

  The simulation system 1 includes an input device 4 through which an operator inputs various data and commands, an arithmetic device 6 that executes various arithmetic processes in response to input from the input device 4, a display device 2 that displays an image, It predicts the occurrence of deformation in press-molded products.

The display device 2 is configured by hardware such as a CRT or a liquid crystal display capable of displaying an image. On the display unit of the display device 2, for example, an image related to a simulation result described later (see FIGS. 6 to 8 described later) or the like is displayed as a calculation result by the calculation device 6.
The input device 4 includes hardware such as a keyboard and a mouse that can be operated by an operator. Data and commands input by operating the input device 4 are input to the arithmetic device 6.
The arithmetic device 6 includes a molding simulation execution unit 61, a springback simulation execution unit 62, a deformation determination amount calculation unit 63, and a storage device 65.

  The forming simulation execution unit 61 and the springback simulation executing unit 62 each perform a simulation of a process for manufacturing a product from a plate-like work by press forming, and analyze a stress acting on the work. Here, for example, a finite element method is used for simulation of a process of manufacturing a product from a workpiece. That is, the workpiece shape is subdivided into three-dimensional unit components, and various data are input to calculate the stress acting on each unit component based on a predetermined finite element calculation formula.

The molding simulation execution unit 61 calculates internal stress acting on the workpiece deformed under the molding force based on the three-dimensional shape data of the mold model and the molding force acting on the workpiece from the outside.
Based on the internal stress calculated by the forming simulation execution unit 61, the springback simulation execution unit 62 calculates the internal stress that acts on the workpiece after elastic recovery under the internal stress.

Based on the internal stress calculated by the springback simulation execution unit 62, the deformation determination amount calculation unit 63 calculates a deformation determination amount that is a measure for the occurrence of deformation in the product.
The storage device 65 stores three-dimensional shape data of a mold model for manufacturing a product by press molding. As the three-dimensional shape data of this model, for example, data designed by a CAD system is used.

  Note that the molding simulation execution unit 61, the springback simulation execution unit 62, the deformation determination amount calculation unit 63, and the storage device 65 of the arithmetic device 6 have a hardware configuration such as a CPU, a ROM, a RAM, and a hard disk, respectively. Realized.

FIG. 2 is a diagram showing an example of a press-molded product, and specifically shows a door panel 9 of an automobile.
The door panel 9 has a substantially rectangular shape, and line character lines 91 and 92 extending in a substantially horizontal direction are formed on the upper end side and the lower end side, respectively. On the character line 91 on the upper end side of the door panel 9, a concave portion 93 to which an outer handle (not shown) gripped by the driver is attached is formed. In addition, the periphery of the recess 93 is substantially flat, but when manufactured by press molding, deformation is particularly likely to occur.
In the present embodiment, a door panel 9 as shown in FIG. 2 will be described as an example of an object to be simulated by the simulation system 1, that is, a press-molded product, but the present invention is not limited to this.

FIG. 3 is a flowchart showing a simulation procedure by the simulation system 1.
In step S1, various data necessary for executing the molding simulation in step S2 are input. Here, the various data includes three-dimensional shape data of a mold model, data on forming force, data on material characteristics of a workpiece, and the like. The three-dimensional shape data of the model is designed in advance by a CAD system and stored in the storage device 65. The molding force indicates the pressure applied to the workpiece from the mold. The workpiece material property data includes, for example, the workpiece material, the workpiece plate thickness, the workpiece tensile strength, and the workpiece elastic coefficient.

  In step S2, a forming simulation is executed based on the various input data. In step S3, an internal stress σ acting on the workpiece is calculated from the result of the forming simulation. In particular, in these steps S2 and S3, the mold reaches the bottom dead center, the above-mentioned forming force is applied to the workpiece, and the internal stress σ acting on each component of the workpiece deformed under this forming force is calculated.

FIG. 4 is a cross-sectional view along the thickness direction of the workpiece deformed under the forming force.
When a forming force along the thickness direction is applied to the workpiece by pressurizing with a mold, deformation may occur in a part of the workpiece. At this time, as shown in FIG. 4, an internal stress σ that varies along the thickness direction is generated in the workpiece. More specifically, in the cross section along the thickness direction of the workpiece, a tensile stress indicated by a positive sign is generated in a portion where the workpiece is compressed (above the neutral plane O in FIG. 4). A compressive stress indicated by a negative sign is generated in the pulled portion (lower side than the neutral plane O in FIG. 4).

  Returning to FIG. 3, in step S4, based on the internal stress σ calculated in step S3, the shape of the workpiece after pressing (the shape of the workpiece before elastic recovery), and the data on the material properties of the workpiece after pressing. Execute the spring back simulation of the workpiece. In step S5, an internal stress σ ′ acting on the workpiece after elastic recovery is calculated from the result of the springback simulation. In step S6, based on the calculated internal stress σ ′, a later-described front / back stress difference Δσ is calculated as a deformation determination amount in each part of the workpiece. In step S7, the calculated front / back stress difference Δσ distribution is calculated. (Refer to the distribution diagram of the front-back stress difference Δσ shown in FIG. 6 described later).

FIG. 5 is a cross-sectional view along the thickness direction of the work after elastic recovery. More specifically, FIG. 5 is a cross-sectional view along the thickness direction of the portion shown in FIG. 4 after elastic recovery.
As described above, when the work is deformed by applying a predetermined forming force, an internal stress σ is generated in each part of the work. For this reason, when the mold is released and the forming force applied to the workpiece is unloaded, the workpiece is elastically recovered and deformed under the internal stress σ. In steps S4 and S5, the process of deformation of the workpiece elastically recovering under the internal stress σ is simulated in this way, and the internal stress σ ′ acting on the workpiece after elastic recovery is calculated.

  In step S6, a cross section T extending along the plate thickness direction is defined in each part of the workpiece, and the internal stress on the front surface side and the internal stress on the back surface side from the neutral plane O of the cross section T A front-back stress difference Δσ defined including the difference is calculated. Further, in step S7, a three-dimensional distribution of the calculated front / back stress difference Δσ is displayed.

In this embodiment, as the front-back stress difference Δσ, as shown in the following formula (1), among the internal stress σ ′ calculated in step S5, the internal stress σ1 on the surface of the workpiece and the internal stress on the back surface of the workpiece The one defined by the difference from σ2 is used.
Δσ = σ1-σ2 (1)

The execution result of the simulation by the simulation system 1 as described above will be described.
FIG. 6 is a distribution diagram of the front-back stress difference Δσ. In the stress difference distribution diagram shown in FIG. 6, the absolute value of the front / back stress difference Δσ around the concave portion 93 of the product is divided into three levels, and is expressed by hatching. That is, a portion where the absolute value of the front / back stress difference Δσ is the smallest is indicated by thin hatching, and as the absolute value of the front / back stress difference Δσ increases, it is indicated by darker hatching.

As shown in FIG. 6, a portion having a large absolute value of the front-back stress difference Δσ is distributed in the vicinity of the recess 93.
7 is a diagram showing the distribution of the front / back stress difference Δσ along the line VIII-VIII in FIG. 6, and FIG. 8 is a diagram showing the distribution of the front / back stress difference Δσ along the line IX-IX in FIG. is there. The line VIII-VIII and the line IX-IX extend through substantially flat portions above and below the recess 93, respectively.

  7 and 8, the front-back stress difference Δσ calculated by the simulation system is indicated by a solid line. Further, the displacement between the shape of the product actually manufactured by the mold and the ideal shape of the product manufactured by this mold is defined as a displacement amount, and this displacement amount is indicated by a broken line.

As shown in FIGS. 7 and 8, the distribution of the front / back stress difference Δσ and the amount of displacement are substantially the same. In other words, the region where the front-back stress difference Δσ is large and the region where the displacement amount is large generally coincide.
Since the displacement amount is an amount indicating a deviation between the actual product shape and the ideal product shape, the actual product is deformed in a portion where the absolute value of the displacement amount is large. Therefore, the front / back stress difference Δσ that reproduces the behavior substantially equal to the displacement amount can be used as the deformation determination amount, and it can be predicted that the deformation occurs in the portion where the absolute value of the front / back stress difference Δσ is large.

According to the deformation occurrence prediction method of the present embodiment, there are the following effects.
First, an internal stress σ acting on a workpiece deformed under a predetermined forming force is calculated, and an internal stress σ ′ acting on the workpiece after elastic recovery under the internal stress σ is calculated. Further, of the internal stress σ ′, in the cross section T extending along the plate thickness direction, it is defined by the difference between the internal stress σ1 on the surface side with respect to the neutral plane O and the internal stress σ2 on the back surface side. The front / back stress difference Δσ is calculated, and the distribution of the front / back stress difference Δσ is displayed.

FIG. 9 is a diagram showing a configuration around the concave portion 93 of the work after elastic recovery. In FIG. 9, the deformed 97 generated on the workpiece when the mold reaches bottom dead center is indicated by a broken line, and the deformed 98 generated on the workpiece after the mold is released and elastically recovered is indicated by a solid line. .
As shown in FIG. 9, in the process of manufacturing a product by press molding, the deformation and the position of the deformation generated in the workpiece change before and after elastic recovery. In the present embodiment, by calculating the front-back stress difference Δσ based on the internal stress σ ′ acting on the workpiece after elastic recovery, the deformation due to the elastic recovery of the workpiece is taken into account, and the occurrence of deformation in the product is accurately performed. Can be predicted.

  It should be noted that the present invention is not limited to the above-described embodiment, but includes modifications and improvements as long as the object of the present invention can be achieved.

For example, in the above embodiment, the front / back stress difference Δσ defined by the above formula (1) is used as the deformation determination amount, but the present invention is not limited to this. Any amount that includes the difference between the internal stress on the front surface side and the internal stress on the back surface side from the neutral surface along the plate thickness direction can be used as the deformation determination amount. For example, the amount corresponding to the bending moment in each part of the workpiece, that is, the product of the internal stress σ ′ and the distance from the origin, with the neutral plane O as the origin, is changed from the surface of the workpiece to the back surface along the cross section T. You may use the amount integrated over the deformation determination amount. In this case, although it takes a calculation time compared to the above embodiment, the occurrence of deformation can be predicted with higher accuracy.
Further, either the shell element or the solid element may be selected as the simulation analysis target.

1 is a block diagram showing a schematic configuration of a simulation system according to an embodiment of the present invention. It is a figure which shows an example of the model of the metal mold | die which concerns on the said embodiment. It is a flowchart which shows the procedure of the simulation performed by the simulation system which concerns on the said embodiment. It is sectional drawing along the thickness direction of the workpiece | work deform | transformed under the forming force which concerns on the said embodiment. It is sectional drawing along the thickness direction of the workpiece | work after the elastic recovery which concerns on the said embodiment. It is a distribution map of the front-back stress difference which concerns on the said embodiment. It is a figure which shows distribution of the front-back stress difference along line VIII-VIII extended above the recessed part which concerns on the said embodiment. It is a figure which shows distribution of the front-back stress difference along line IX-IX extended below the recessed part which concerns on the said embodiment. It is a figure which shows the structure around the recessed part of the workpiece | work after the elastic recovery which concerns on the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Simulation system 6 ... Arithmetic unit 61 ... Molding simulation execution part 62 ... Springback simulation execution part 63 ... Deform judgment amount calculation part 65 ... Memory | storage device 9 ... Door panel 93 ... Recessed part 98 ... Deformation

Claims (1)

A method for predicting the occurrence of deformation by performing a simulation of a process for producing a product from a plate material by press molding, and predicting the occurrence position and size of the deformation in the product,
A first step of calculating a stress acting on the plate deformed under the forming force based on a forming force acting on the plate from outside;
Based on the stress calculated in the first step, a second step of calculating a stress acting on the plate material after elastic recovery under the stress;
Of the stresses acting on the plate material after elastic recovery calculated in the second step, a data defined including the difference between the stress on one side of the neutral surface and the stress on the other side along the plate thickness direction. A third step of calculating a form determination amount;
And a fourth step of displaying the distribution of the deformation determination amount calculated in the third step.

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