JP4631335B2 - Method for determining the shape of a press mold - Google Patents

Description

The present invention relates to the shape determining method of a press mold.

Press molding is a method of processing a material to be formed into a desired shape by sandwiching a material to be molded such as metal or resin with two or more press molds (hereinafter also simply referred to as molds). When the molding material is taken out from the mold after press molding, it may be elastically deformed (spring back) and may be different from the desired shape.
Therefore, there has been an idea to press-mold a material to be molded with a press-molding die that compensates for this elastic deformation.

However, in order to compensate for the elastic deformation of the material to be molded after press molding, if the material to be molded is press-molded and is different from the desired shape, It is necessary to repeat a series of processes of processing and correcting the shape of the material by repeating it manually several times, which requires a lot of time and labor.
In order to solve this problem, for example, a method for determining the shape of a press-molding die by performing a calculation by a three-dimensional finite element method using a computer as shown in Patent Document 1 has been studied. .

  Here, with respect to a method for determining the shape of a press-molding die that compensates for elastic deformation, an example of a conventional general processing flow as in Patent Document 1 will be referred to as appropriate with reference to FIGS. I will explain. FIG. 6 is a flowchart showing an example of a conventional general processing flow. FIG. 7 shows a flow of how the shape of the material to be molded and the mold are predicted, temporarily set, and corrected when the conventional general processing flow is followed. Are shown schematically step by step.

  In this conventional general process, as shown in FIG. 6, first, an initial mold shape is provisionally set on a computer (step S1). Here, the initial mold shape is, for example, when the material to be molded is to be processed into a hat shape as shown in FIG. 7A, the desired shape after press molding of the material to be molded is between the upper and lower molds. Temporary setting is made as shown in FIG.

  Next, press molding is performed with the temporarily set initial mold shape, and the shape of the molding material after detachment from the mold is calculated by a three-dimensional finite element method to predict the entire molding material (step S8). ). That is, as the shape of the material to be molded after press molding, for example, the one in which the spring back is generated as shown in FIG. 7C is predicted by calculation as shown in FIG. 7D.

  Then, a difference between the shape of the material to be molded after the press molding and a desired shape is obtained by calculating by some method using some method. There are various ways of obtaining such an error. For example, each corner portion is taken as a representative portion, and for example, as shown in the example of FIG. Z1), (X2, Y2, Z2), the first angle Θ, the second angle Ψ, etc. are set and expressed as target values, and are calculated and predicted as the shape of the material to be molded after press molding. A method of comparing with the result is conceivable. In this example, the first angle Θ, the first angle as the angle formed with respect to the direction in which the material to be molded is clamped by the mold (the direction in which the line indicated by VL in FIG. 7B extends) is used as a reference. A second angle ψ was set (hereinafter the same in other examples).

  On the other hand, the material to be molded after press molding in which spring back occurs corresponds to the three-dimensional positions (X1, Y1, Z1), (X2, Y2, Z2), the first angle Θ, and the second angle Ψ, respectively. As shown in the example of FIG. 7C, the portion to be processed becomes a predicted value such as the three-dimensional position (x1, y1, z1), (x2, y2, z2), the first angle θ, the second angle ψ, etc. It has become. Therefore, (X1, Y1, Z1), (X2, Y2, Z2) and (x1, y1, z1), (x2, y2, z2), Θ and θ, Ψ and ψ are compared, and the components and values are compared. An error of the predicted value with respect to the target value is obtained by taking a difference between them or taking a ratio, and it is determined whether or not all of these errors are less than an allowable value (step S9).

  If the obtained error is greater than or equal to the allowable value (“No” in step S9), the mold shape is corrected on the computer so that the error is less than the allowable value (step S10), and the process returns to step S8. . Such a series of calculations (by the loop indicated by symbol R in FIG. 6) is performed by, for example, a three-dimensional finite element method as shown by a mesh in FIG. 7D, and the error is less than the allowable value. Repeat as many times as necessary. FIG. 7D shows a divided mesh when the material to be molded is virtually divided into elements, which appears in the calculation by the three-dimensional finite element method.

As a result, when the calculation converges and the above error becomes less than the allowable value (“Yes” in step S9), the mold shape at that time, for example, as shown in FIG. A mold shape that can press-mold the material to be molded into a shape is finally determined (step S11), and the process ends. If press molding is performed using the mold thus determined, for example, as shown in FIG. 7 (f), the material to be molded can be press-molded into a hat shape similar to FIG. 7 (a), that is, a desired shape. It becomes possible.
JP 2003-157299 A

However, as a result of repeated studies by the inventor, as described above, it is very time-consuming to repeatedly perform the calculation by the three-dimensional finite element method until the error becomes less than the allowable value. all right.
An object of the present invention is to overcome this problem and provide a method capable of determining the shape of a press-molding die in a shorter time than in the prior art.

That is, the first invention is used hand in determining the press-mold shape, a press-molding die shape determining method constructed by using a computer, the computer, press First and second prediction means for predicting the amount of springback in the virtual cross section of the molding die are provided, and the first prediction means is selected by one or more pre-set initial mold shapes a step of accepting an input of a virtual cross-section is, and a step of predicting the amount of spring back in the virtual section of the molded material after press molding is performed a two-dimensional calculation by the input virtual cross, the second prediction means includes the steps of receiving an input of temporarily set Karikin shape to compensate for spring back amount within a virtual cross-section based on the prediction in the first prediction means, of its input A step of Karikin shape in by performing calculation by the three-dimensional finite element method to predict the spring back amount of the object to be profiled after press molding were the Karikin shape to compensate for the expected spring back amount And the step of correcting.
The second aspect of the present invention is characterized in that the two-dimensional calculation is based on a two-dimensional finite element method .

  According to the present invention, it is possible to determine the shape of a press-molding die in a shorter time than in the past.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
1 to 3 are diagrams for explaining one embodiment of the present invention.
In the present embodiment, as shown in FIG. 1, a PC (personal computer) 100 is used to determine the shape of a press-molding die by the method for determining the shape of a press-molding die according to the present invention. Is.

The configuration of the internal functions of the PC 100 will be described with reference to FIG.
The PC 100 includes a CPU 30 that controls the operation and the entire system based on the control program, a ROM 32 that stores the control program of the CPU 30, a RAM 34 that temporarily stores data read from the ROM 32 and the operation results of the CPU 30, It is composed of an interface (I / F) 38 that mediates data input / output to / from the device, and these are connected to each other via a bus 39 that is a signal line for transferring data so that data can be exchanged between them. Yes.

The I / F 38 includes, as external devices, an operation panel 40 that allows an operator to input various data, a storage device 42 that stores input data and calculation results, a display 44 that displays input data and calculation results, and the like. It is connected.
The CPU 30 activates a program stored in the ROM 32 and, according to the program, executes a series of processes for determining the shape of the press mold according to the present embodiment, the contents of which are shown in the flowchart of FIG. It has become. In addition, about the content of the process demonstrated below, in order to make an understanding easy, the same code | symbol is attached | subjected and demonstrated for the same thing as the conventional general process mentioned above.

FIG. 2 is a flowchart showing the contents of a series of processes for determining the shape of the press mold according to the present embodiment.
When this series of processes is executed, the process first proceeds to step S1, as shown in FIG.
In step S1, an initial mold shape is provisionally set. As the initial mold shape, for example, the size and angle of a representative portion of the molding material can be temporarily set based on data on the desired shape of the molding material designed by three-dimensional CAD or the like. .

  Next, the process proceeds to step S2, and a representative virtual section of the initial mold shape is selected. As this representative virtual cross section, it is preferable to select a virtual cross section in which the flow of the material to be molded during press molding does not occur across the surface based on experience. In addition, this virtual cross section has one place when the cross-sectional shape of the material to be molded is uniform in the longitudinal direction (normal direction of the cross section) as shown in FIG. 4A, FIG. When changing in the longitudinal direction as in (c), it is preferable to select a plurality of representative locations.

Next, the process proceeds to step S3, where one virtual cross section is first selected from the virtual cross sections, and calculation is performed by the two-dimensional finite element method (two-dimensional calculation) and after press forming (after leaving the mold). ) To predict the shape of the molding material over the entire molding material.
Then, the amount of springback in the virtual cross section of the material to be molded after press molding is obtained with respect to the size and angle of a representative portion in the virtual cross section of the material to be molded after press molding, and step S4. Then, the error of the desired shape is obtained. As for the dimensions and angles of the representative portion of the material to be molded, there are various possible ways other than the example of FIG. 3 described later, but even one of these errors exceeds the allowable value. If (No), the process proceeds to step S5, and if all errors are less than the allowable value (Yes), the process proceeds to step S6.

Next, in step S5, a mold is used so that an error obtained with respect to the dimension and angle of a representative portion in the virtual cross section between the shape of the material to be molded after press molding and the desired shape is less than an allowable value. The shape is corrected on the computer, and the process returns to step S3. Such a series of calculations (by the loop indicated by symbol S in FIG. 2) is first executed as described above.
In step S6, it is determined whether or not the above calculation has been performed for all virtual cross sections. If there is an uncalculated virtual cross section (No), the process returns to step S2, but the uncalculated If there is no virtual cross section (Yes), the process proceeds to step S7.

In step S7, the mold shape when it becomes (Yes) in step S6 is temporarily set as the temporary mold shape. That is, a temporary mold shape is temporarily set by calculation using the two-dimensional finite element method, and the process proceeds to step S8.
In step S8, a three-dimensional finite element method is used to calculate the shape of the molding material after press molding (after removal from the mold) over the entire molding material using the temporary mold shape obtained by the two-dimensional calculation. Predict and seek. Then, the spring back amount of the material to be molded after press molding is obtained for the dimension and angle of the representative portion of the material to be molded after press molding, and the process proceeds to step S9.

In step S9, an error between the shape of the material to be molded after the press molding and a desired shape is obtained for a dimension and an angle of a certain representative portion. In other words, there are various possible ways to determine the dimension and angle of the representative portion of the material to be molded in addition to the example shown in FIG. If it is equal to or greater than the value (No), the process proceeds to step S10, and if all errors are less than the allowable value (Yes), the process proceeds to step S11.
In step S10, the mold shape is corrected on the computer so that these errors are less than the allowable value, and the process returns to step S8.
In step S11, the mold shape at that time is finally determined as a mold shape capable of press-molding the material to be molded into a desired shape, and the process ends.

Next, how to predict, temporarily set, and correct the shape of the material to be molded and the shape of the mold when following the flow of the series of processes for determining the shape of the press-molding mold described above The flow of this will be described with reference to FIG.
In the press molding die shape determining method of the present invention, as described above, first, an initial die shape is temporarily set on the PC 100 (step S1). This initial mold shape is the same as in the case of following the conventional general processing flow described above, when the shape of the material to be molded is press-molded into a hat shape as shown in FIG. May temporarily set a desired shape as an initial mold shape.

Then, a representative virtual cross section of the initial mold shape is selected (step S2). At this time, when the virtual cross section is press-molded into a hat shape, for example, as shown by a symbol J in FIG.
Next, in this virtual cross section, a calculation is performed by a two-dimensional finite element method as shown in FIG. Thereby, as a shape of the molding material after the press molding in the virtual cross section of the molding material, for example, the one having a spring back as shown in FIG. S3).

  Next, an error between the shape of the molding material after press molding and the desired shape is obtained and compared with an allowable value (step S4). There are various methods for obtaining such an error. For example, a part important for the function of the product is taken as a representative part, and, for example, as shown in FIG. The first angle Θ, the second angle ψ, etc. are set as target values, and compared with the results obtained by predicting by calculation as the shape of the material to be molded after press molding (after removal from the mold). In this example, the first angle Θ, the first angle as the angle formed with respect to the direction in which the material to be pressed is clamped with the mold (the direction in which the line indicated by reference numeral VL in FIG. A second angle ψ is set (hereinafter the same in other examples). As the width dimension D, which is the distance between the two points P1 and P2 shown in the figure, for example, if the distance between the positions to be spot welded is set, the dimensional accuracy of the part important for the function of the product is secured. It is preferable to know if it can be done.

  On the other hand, in the material to be molded after the press forming in which the spring back is generated, the portions corresponding to the width dimension D, the first angle Θ, and the second angle Ψ are as shown in the example of FIG. The predicted values are the width dimension d, the first angle θ, the second angle ψ, and the like. For this reason, D and d, Θ and θ, and Ψ and ψ are compared, and the difference between the values or the ratio is calculated to determine the error of the predicted value with respect to the target value. If at least one is not less than the allowable value, the shape of the mold in the two-dimensional virtual section is shown in FIG. Modify on the computer as in example d). In the figure, for example, by forming inclination angles α and β on the hat-shaped flange portion, the material to be molded after the spring back is targeted to make the flange portion as flat as possible. In addition, each predicted value such as the width dimension d, the first angle θ, the second angle ψ, and the like has an error represented by the difference with respect to each target value D, Θ, ψ. Is multiplied by each coefficient c, a, b to compensate for c (d−D), a (Θ−θ), and b (Ψ−ψ) in the direction opposite to the springback direction rather than the desired shape. Therefore, the shape of the mold is corrected. In addition, the code | symbol HL in the same figure shows a horizontal direction, and how many each line which passes along each reference point and the above-mentioned P1 and P2 with respect to the horizontal line which passes through each reference point shown by code | symbol R2, R3. It becomes the reference line which makes the angle of. Reference numerals R1, R2 and R3 are reference points provided for drawing a reference line for deciding what angle to apply to represent the angles θ and ψ used for correcting the mold shape. is there.

  Then, as described above, the dimensions of the respective parts on the mold side in the direction opposite to the direction of springback from the desired shape by c (d−D), a (Θ−θ), and b (Ψ−ψ). Then, the mold shape is corrected to the corrected shape (step S5), and the respective target values D, Θ, Ψ of the respective predicted values such as the aforementioned width dimension d, the first angle θ, the second angle ψ, and the like. The series of calculations described above is repeated many times until the error with respect to becomes less than the allowable value (by the loop indicated by the symbol S in FIG. 2).

For this calculation, a calculation based on the two-dimensional finite element method as shown in FIG. Since it is a two-dimensional calculation, it hardly takes time to converge.
Then, based on the calculation result by the two-dimensional finite element method, a three-dimensional temporary mold shape as shown in FIG. 3 (e) is temporarily set (step S7), and the covering of the temporary mold shape is performed. The amount of springback after press molding of the molding material is estimated and calculated by calculation using a three-dimensional finite element method (step S8).

Here, calculation is performed by a three-dimensional finite element method as shown in FIG. Thereby, as a shape after press molding of the material to be molded, a shape in which a springback occurs as shown in FIG.
Next, an error between the shape of the material to be molded after press molding and a desired shape is obtained (step S9).
There are various methods for obtaining such an error. For example, as in the above-described two-dimensional calculation, a part important for the function of the product is taken as a representative part. For example, as shown in FIG. For the shape, the width dimension D, the first angle Θ, the second angle Ψ, etc. are set as target values, and compared with the results obtained by predicting by calculation as the shape of the material to be molded after press molding. .

  On the other hand, in the material to be molded after press molding in which the spring back is generated, the portions corresponding to the width dimension D, the first angle Θ, and the second angle ψ are as shown in the example of FIG. The predicted values are the width dimension d, the first angle θ, the second angle ψ, and the like. For this reason, D and d, Θ and θ, and Ψ and ψ are compared, and the difference between the values or the ratio is calculated to determine the error of the predicted value with respect to the target value. Determine whether. In this example, the same part dimensions and angles as in the above two-dimensional calculation are calculated by the three-dimensional finite element method to determine whether or not all errors are less than the allowable value. It is not necessary to determine whether or not the error is less than the allowable value for the angle and the angle, and in the calculation by the three-dimensional finite element method, it may be determined for a separate size and angle.

  If at least one of the obtained errors is greater than the allowable value, the mold shape is three-dimensionally corrected on the computer so that the error is less than the allowable value (step S10). Here, the mold shape after correction is obtained by calculating the springback amount of the molding material after press molding obtained by calculation and calculation before correction, with respect to the dimensions and angles of representative parts important for the function of the product. The virtual shape is obtained by calculating the error of the desired shape and compensating the size and angle in the opposite direction to the springback direction of the desired shape. Or an intermediate shape between the virtual shape and a desired shape is preferable. In other words, in the above-described example, when compensating for c (d−D), a (Θ−θ), and b (Ψ−ψ) in the opposite direction to the springback direction rather than the desired shape. 0 <c ≦ 1, 0 <a ≦ 1, and 0 <b ≦ 1.

  Then, the series of calculations described above is repeated many times until the error of each predicted value of the dimensions and angles of the representative portions with respect to each target value is less than the allowable value (according to the loop indicated by T in FIG. 2). ). For this calculation, a calculation based on the three-dimensional finite element method as shown in FIG. Then, when the error becomes less than the allowable value, the mold shape as shown in FIG. 3G capable of press-molding the molding material into a desired shape as shown in FIG. (Step S11).

  As described above, according to the press molding die shape determining method of the present invention, an initial die shape is temporarily set (step S1), and one or more virtual cross sections are selected based on the initial die shape. (Step S2), a calculation by a two-dimensional finite element method, which is a two-dimensional calculation, is performed on the virtual cross section to predict a springback amount in the virtual cross section of the material to be molded after press forming (Step S3). ). Next, a temporary mold shape is provisionally set so as to compensate for the amount of springback in the virtual cross section (step S7), and calculation by the three-dimensional finite element method is performed on the temporary mold shape to perform press molding of the molding material. The subsequent springback amount is predicted (step S8).

  As described above, according to the method for determining the shape of a press molding die of the present invention, first, within the virtual cross section of the material to be molded after press molding, which is obtained by prediction by calculation using the two-dimensional finite element method as two-dimensional calculation. Temporarily set the temporary mold shape so as to compensate for the springback amount at the press, and perform the calculation using the three-dimensional finite element method with the temporary mold shape to compensate for the springback amount of the workpiece after press molding. I am trying to determine the shape of the mold.

  That is, since the calculation for setting the temporary mold shape is a two-dimensional calculation, it hardly takes time to converge, and the temporary mold shape can be temporarily set. Furthermore, the temporary mold shape is a shape that compensates for the amount of springback, although it is a preliminary one by two-dimensional calculation. Therefore, the calculation by the three-dimensional finite element method, which is subsequently performed, starts from a shape that is substantially close to the shape of the final press-molding die that can press-mold the material to a desired shape in advance by the above-described two-dimensional calculation. Since it can be a point, the time required for convergence can be greatly shortened as compared with the case where the calculation is performed by the three-dimensional finite element method from the beginning according to the conventional general processing flow. Thereby, according to the shape determination method of the press-molding die of the present invention, the shape of the press-molding die can be determined in a short time compared with the conventional method.

Also, a method for press-molding a material to be molded using a mold having a shape determined by the method for determining the shape of a press-molding die according to the present invention (hereinafter referred to as “the press-molding method of a material to be molded according to the present invention”). If the material to be molded is press-molded, as shown in FIG. 3 (h), the material to be molded after press molding can be brought as close as possible to the desired shape shown in FIG. 3 (a). Become.
The method for determining the shape of a press molding die and the method for pressing a material to be molded according to the present invention are not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. Is possible.

For example, in the above-described embodiment, the case where the material to be molded is formed into a simple hat shape has been described as an example in order to facilitate understanding, but the present invention is not limited to this, and the cross-sectional shape is in the longitudinal direction. If it is applied to a case where the material to be molded is press-molded into a complex shape that changes, the effect of shortening the time required for calculation can be exhibited.
Alternatively, the ROM described as storing the control program or the like in FIG. 1 may be substituted with, for example, a hard disk or other storage medium.

  Further, for example, in the above embodiment, in the calculation by the three-dimensional finite element method, a part important for the function of the product is taken as a representative part, and the width dimension is obtained for a desired shape as in the example of FIG. D, the first angle Θ, the second angle Ψ, etc. have been set as target values, and explained as an example compared with the results obtained by predicting by calculation as the shape of the material to be molded after press molding, The present invention is not limited to this. For example, a plurality of points are randomly set on a computer-molded material having a desired shape on a computer, and distances between the plurality of points are obtained, The sum of squares obtained by summing squares of the difference in distance between the plurality of points on the molding material may be minimized.

Alternatively, if the calculation by the three-dimensional finite element method has resulted in a large error from the desired shape, the calculation by the three-dimensional finite element method is not repeated and the two-dimensional process of step S3 is performed again. You may make it return to calculation.
Further, for example, in the above-described embodiment, as the two-dimensional calculation, the calculation by the two-dimensional finite element method is performed and the spring back amount in the virtual cross section of the material to be molded after press molding is obtained. The invention is not limited to this, and for the two-dimensional calculation, for example, elasto-plastic tensile bending-bending-unloading calculation by elementary analysis can be used.

Below, the effect by the shape determination method of the press-molding die of the present invention will be verified by Examples.
The method of determining the shape of the press molding die of the present invention (hereinafter referred to as “the method of the present invention”) and the calculation by the conventional three-dimensional finite element method are performed until the error becomes less than the allowable value. Comparison with a method (hereinafter referred to as “conventional method”) repeated repeatedly was performed on a high-strength cold-rolled steel sheet having a tensile strength at a normal temperature of 440 MPa. A commercially available finite element method analysis system was used for the calculation by the three-dimensional finite element method.

  Regarding the shapes of the three types of molding materials shown in FIGS. 4A to 4C, the shapes of the press molding dies were determined by the method of the present invention and the conventional method, respectively. In addition, about the shape of three types of to-be-molded materials, the virtual cross section was each selected like JN shown to the figure. FIG. 4 (d) shows where the dimensions of each part regarding the shape of each virtual cross section represent, and Table 1 shows specific values of these dimensions. Incidentally, W3 represents the dimension in the longitudinal direction as shown in FIGS.

FIG. 5 is a graph showing a comparison of the total time required for completion of calculation in the method of the present invention and the conventional method.
As shown in the figure, it was confirmed that the method of the present invention can determine the shape of the press-molding die in the shape 1 and the shape 2 in a remarkably short time as compared with the conventional method. In the case of shape 3, the calculation did not converge and could not be completed by the conventional method, but could not be completed by the method of the present invention.

It is a block diagram which shows the structure of PC (personal computer) used by one embodiment of this invention. It is a flowchart which shows the content of a series of processes for the shape determination of the metal mold | die for press molding of one embodiment of this invention. How to predict, temporarily set, and correct the shape of the material to be molded and the shape of the mold when following the flow of a series of processes for determining the shape of the mold for press molding of the present invention. It is a figure which shows an example of a flow typically step by step. It is a figure which shows the shape of the to-be-molded material used for the Example for verification of the effect of this invention. It is a graph which shows the effect of the present invention. It is a flowchart which shows an example of the flow of the conventional general process about the shape determination method of the metal mold | die for press molding. How to predict, provisionally set, and correct the shape of the material to be molded and the shape of the mold when following the conventional general processing flow of the method for determining the shape of the mold for press molding It is a figure which shows an example of a flow typically step by step.

Explanation of symbols

30 CPU
32 ROM
34 RAM
38 I / F
39 Bus 40 Operation panel 42 Storage device 44 Display 100 PC (personal computer)

Claims (2)

Used hand in determining the press-mold shape, a has been press-mold shape determining method constructed using computer, the computer is in a virtual cross-section of a press mold Comprising first and second prediction means for predicting the amount of springback of
The first predicting means receives an input of one or more selected virtual sections with a preset initial mold shape, and performs two-dimensional calculation on the input virtual sections and after press forming Predicting the amount of springback in the virtual cross section of the material to be molded,
The second predicting means receives an input of a temporary mold shape temporarily set so as to compensate for a springback amount in a virtual cross section based on the prediction in the first predicting means, and the input a step of Karikin shape in by performing calculation by the three-dimensional finite element method to predict the spring back amount of the object to be profiled after press molding, the Karikin shape to compensate for the expected spring back amount press mold shape determining method which comprises a step of modifying.   The method for determining a shape of a press-molding die according to claim 1, wherein the two-dimensional calculation is based on a two-dimensional finite element method.

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