JP4344375B2 - Springback occurrence cause identifying method, apparatus thereof, and program thereof - Google Patents

Description

  The present invention is a method for identifying a cause part of a springback generated in a press-formed product when press-molding a member for an automobile such as a steel plate or a steel bar from a metal such as aluminum, magnesium, titanium, The present invention relates to the apparatus and the program.

Many automotive parts such as doors and bumpers, household electrical appliances, and building materials are manufactured by press forming of steel plates. In recent years, demands for weight reduction of these members have increased, and measures such as thinning the steel material by using a steel material having high strength in order to realize the demand have been attempted.
However, with the strengthening of steel sheets, strict management is required to secure the product shape by press forming, and one of the important items in the management is driving residual stress generated in the steel sheet during press forming. As a force, a spring back is a deformation in which the elastic deformation of the steel plate is elastically recovered.

  In recent years, in order to reduce the development man-hours and costs of automobiles, etc., there is a tendency to start a design stage at the same time as the design stage to examine the molding method of the molded member. Therefore, the man-hours and costs at the design stage for examining the molding method of the molded member have become a bigger problem in the development process and development cost of automobiles and the like.

  FIG. 1 is a schematic cross-sectional view of a molded member showing correspondence to a conventional spring back. (A) shows the shape cross section of the molded product, (b) shows the spring back generated in the molded product after cold press-molding the steel plate with the same mold as the molded product shown in (a), ( c) shows the cross section of the mold shape corrected for spring back. As described above, in order to obtain the molded product shown in (a), there is a correspondence to obtain a desired molded product by using a “prospect” mold that anticipates spring back as shown in (c).

  As a method of forming a mold that anticipates such springback, the residual stress of the steel plate at the bottom dead center pressed to the mold is analyzed by the finite element method, and deformation caused by the residual stress in the opposite direction to the residual stress There has been proposed a method of simply forming a mold in consideration of springback by numerically analyzing a (spring forward) mold (Patent Document 1, Non-Patent Document 1).

  However, since it is very difficult to design a die that fully considers springback by numerical analysis, it is very difficult, so the proposed method simply considers springback by the finite element method. It is to mold a mold. For this reason, it is difficult to numerically analyze what measures are required when the mold does not satisfy the allowable amount of springback. Not.

  For this reason, a mold that easily considers springback, and if the allowable amount of springback is not satisfied, what measures are taken to obtain the desired molded product depends on the experience of engineers. become. Eventually, a trial-and-error test using a mold by the forming method and an actual steel plate is required.

In addition, a method has been proposed in which the springback is reduced by modifying the shape of the steel material or molded product, not the mold shape, to remove residual stress.
FIG. 2 is a perspective view illustrating a conventional method for searching for a site that causes deformation due to springback. (A) shows the shape of the molded product, (b) shows the case where part 1 of the product is cut and removed, (c) shows the case where a hole 2 is made in the product, (d) shows The case where the slit 3 is given to a part of the product is shown. By taking such measures, an attempt has been made to observe the behavior of the springback and to reduce the springback.

  Even if the residual stress that causes the springback is reduced by measures against the springback occurrence site, the rigidity of the member itself decreases due to cutting and drilling, etc. This causes the problem that the problem will occur, and the root cause cannot be investigated. Furthermore, since such a measure actually requires a test using a test mold and a steel plate, there arises a problem of an increase in man-hours and costs at the design stage.

JP 2003-33828 A Mitsubishi Motors Technical Review (2006 No.18, pages 126-131)

  In view of the above-mentioned problems, the present invention specifies a part that causes springback of a press-molded product by numerical analysis, thereby efficiently and economically considering a molding member molding method. It is an object to provide a method for shortening.

  Moreover, this invention makes it a subject to provide the molded product which makes a springback amount below an allowable value by numerical analysis, maintaining product strength.

  In order to solve the above problems, the springback occurrence cause identifying method according to the present invention (program: hereinafter, the parentheses correspond to the program invention) is a numerical analysis of the molding conditions of press molding, and press molding Press molding analysis step (procedure) for obtaining product molding data, and a first spring back amount calculating step for calculating physical property values and physical quantity data for each of a plurality of regions after spring back based on the molding data of the press molded product (Procedure) and an arithmetic processing step (procedure) for performing arithmetic processing on at least one of the physical property value and the physical quantity data in the area when at least one of the physical property value and the physical quantity is larger than a predetermined value; A second springback amount for calculating physical property values and physical quantity data for each of a plurality of areas after the springback based on the result of the arithmetic processing Out and a step (procedure).

  In addition, when there is an area where at least one difference between the physical property value and physical quantity data of the press-formed product before and after the spring back is larger than a predetermined value, the arithmetic processing step (procedure) is the physical property value and physical quantity data of the area. The physical property value and the physical quantity may be a plate thickness, an elastic coefficient, a plastic coefficient, a stress component value, or a strain component value.

  In addition, the device for identifying the cause of the occurrence of springback according to the present invention includes a press molding analysis unit that numerically analyzes the molding conditions of press molding and obtains molding data of the press molded product, and numerically analyzes the molding data to perform spring back. When there is a region where at least one of the physical property value and the physical quantity is greater than a predetermined value, and a spring back analysis unit that calculates the amount, an arithmetic processing that performs arithmetic processing on at least one of the physical property value and physical quantity data of the region And an arithmetic processing unit that causes the springback analysis unit to calculate a springback amount for each of a plurality of regions after the springback based on a result of the arithmetic processing.

Further, when there is an area where at least one difference between the physical property value and the physical quantity data of the press-formed product before and after the spring back is larger than a predetermined value, the arithmetic processing unit has at least one of the physical property value and the physical quantity data of the area. The physical property values and physical quantities may be plate thicknesses, elastic coefficients, plastic coefficients, stress component values, and strain component values.
In addition to the program described above, the program of the present invention is a press molding analysis program for numerically analyzing press molding molding conditions to calculate molding data of a press molded product, physical property values and physical quantity data for each of a plurality of regions, and The springback analysis program for calculating the physical property value and the physical quantity data for each of the plurality of areas after the springback amount and the numerical value analysis by numerically analyzing the molding data and the physical property values and the physical quantity data for each of the plurality of areas is a commercially available program. A program for identifying the cause of the occurrence of springback that can be used to input and output data from these programs, and obtains physical property data and physical quantity data for each of the plurality of areas after the springback from the springback analysis program. Procedure and a region where at least one of the physical property value and the physical quantity is larger than a predetermined value In some cases, a calculation processing procedure for performing calculation processing on at least one of the physical property value and physical quantity data in the region, and a procedure for causing the computer to execute a procedure for outputting a result of the calculation processing to the springback analysis program. good. A commercially available springback analysis program recalculates the amount of springback based on the arithmetic processing data output from the program of the present invention.

  According to the present invention, the specific part to be analyzed is changed as a cause of the occurrence of springback in the press-molded product, and the springback amount is minimized while numerically calculating the physical property value / physical quantity of the specific part. It is possible to identify the cause part of the occurrence of springback and to accurately derive the physical property value / physical quantity of the cause part, or to check them by analytical trial and error. The present invention provides a method for economically and efficiently shortening a study time of a molding method of a molded member.

  Furthermore, the present invention allows the amount of springback change without cutting and punching the actual molded product by changing the specific part and / or the physical property value and physical quantity of the specific part. It is possible to determine a specific portion that is less than or equal to the value, its physical property value and physical quantity. Therefore, since the molded product analyzed in this way can be confirmed to maintain the quality of the product, such as rigidity, at the same time that the spring back variation is less than the allowable value, the predetermined spring back variation required for the molded product Therefore, it is possible to eliminate the need for measures such as cutting and removing a specific part of the molded product and making holes, which sacrifice product quality.

FIG. 3 is a functional configuration diagram of the springback occurrence cause identifying apparatus according to the embodiment of the present invention.
The springback generation cause identifying apparatus 10A includes a press molding analysis unit 11, a springback analysis unit 12, a physical property value / physical quantity calculation processing unit 14, a file storage unit 16, a molding condition input unit 18, and a springback amount output screen 19. Have.

  The forming condition input unit 18 includes shape data (plate thickness, length, width, curvature, strain, etc.) and properties (strength, elongation, etc.) of a steel plate to be analyzed by the press forming analysis unit 11 and the springback analysis unit 12 described later. Material, shape such as plate thickness), mold shape (die (die) and punch shape, curvature, diameter, clearance, lubrication condition), press condition (wrinkle holding load, pad load, bead tension, press pressure, temperature) ) And other molding conditions. Alternatively, a data area in the molding analysis, a data area in the physical property value / physical quantity calculation processing unit 14, a divided area when the screen is displayed on the springback amount output screen 19, and the like can be set separately.

  The press molding analysis unit 11 uses an elastic-plastic finite element method, a rigid-plastic finite element method, a one-step finite element method, a boundary element method, an elementary analysis, etc., with the molding conditions input by the molding condition input unit 18 as input information. Then, numerical analysis is performed to obtain stress, strain, plate thickness and the like of a press-formed workpiece such as a steel plate. The press forming analysis unit 11 outputs a numerical analysis result in the form of variables such as a plate thickness of the workpiece, a stress component value, a strain component value, and a distribution of the variables. The output data is output, for example, as a file “P org.k” to the springback analysis unit 12, a physical property value / physical quantity calculation processing unit 14 and a file storage unit 16 described later.

Numerical analysis by the press forming analysis unit 11 is performed by a finite element method (for example, commercially available software PAM-STAMP, LS-DYNA, Autoform, OPTRIS, ITAS-3D, ASU / P-FORM, ABAQUS, ANSYS, MARC, HYSTAMP, Hyperform. , SIMEX, Fastform3D, Quikstamp) shape data (plate thickness, length, width, curvature, strain, etc.) of the product to be press-molded and properties of the metal plate used (strength, elongation, etc., material thickness) If necessary, set molding conditions such as die shape (die and punch shape, curvature, diameter, clearance, lubrication conditions), press conditions (temperature, pressure), etc., and perform molding analysis. In addition, the distribution of stress and strain values after molding can be obtained numerically.
Further, the press forming analysis unit 11 can display the analysis results such as stress distribution and curvature by the finite element method on the springback amount output screen 19 using post processing software.

  The springback analysis unit 12 uses an output data file “P org.k” of the press forming analysis unit 11 and an output data file “P rem.casen.k” of a physical property value / physical quantity calculation processing unit 14 described later as input data. To perform springback analysis. The springback analysis is an elastic finite element method, elastoplasticity, based on variables such as the plate thickness of the workpiece, the stress component value, the strain component value, and the variable distribution, which are output results of the press forming analysis unit 11. The unloading process is calculated by a finite element method, a one-step finite element method, an elementary analysis, and the like, and a springback amount that is a deformation amount generated in a workpiece is numerically analyzed. The springback amount is calculated for each element of the three-dimensional data coordinates by dividing the workpiece by the finite element method or the like. The amount of springback, which is the amount of deformation that occurs in the workpiece, includes the amount of deformation at an arbitrary point of the workpiece, the amount of deformation at the maximum or minimum displacement point within the specified area of the workpiece, There are an angle formed by a plurality of arbitrary surfaces or lines, or a curvature formed by an arbitrary surface or line of the workpiece.

  The output data that is the result of the springback analysis by the springback analysis unit 12 includes the springback amount, shape such as distortion at the time of springback, properties, stress, etc., and is output to the springback amount output screen 19 and input data. Springback as numerical analysis result output data file “SB org.k” by file “P org.k” or numerical analysis result output data file “SB rem.casen.k” by “Prem.casen.k” The data is output to the analysis unit 12, a physical property value / physical quantity calculation processing unit 14 and a file storage unit 16 which will be described later.

  The physical property value / physical quantity calculation processing unit 14 outputs the output data file “P org.k” of the press forming analysis unit 11, the numerical analysis result output data file “SB org.k” of the springback analysis unit 12, or “SB rem”. .Casen.k ”is input, the calculation process is performed, and“ P rem.casen.k ”is output to the springback analysis unit 12 as a result. Note that the arithmetic processing referred to here includes multiplying at least one of the above variables by a coefficient, making a constant value including zero, performing four arithmetic operations, calculating based on a function, and any non-constant arbitrary It means replacing with a value. The physical property value / physical quantity calculation processing unit 14 makes it possible to determine a variable and a specific part that reduce the springback amount by such calculation processing.

  When the physical property value / physical quantity calculation processing unit 14 acquires data of a press-molded product that is one of the workpieces from the input data, the physical property value / physical quantity calculation processing unit 14 finds a specific part from the part of the press-molded product. It is necessary to divide the data into a plurality of areas. One of the region dividing methods is to divide the region of the workpiece by uniform dimensions.

  For uniform dimensions, it is desirable to consider measures for specific parts. That is, even if a specific part is found, the analysis result may not be used effectively in a very small area where an effective measure cannot be taken for the specific part. For example, when the countermeasure for a specific part is to add a bead of 20 mm × 100 mm, the divided area may be 20 mm square.

As one method for determining a divided area of a molded product, there is a method of determining a divided area based on curvature and elements.
The press forming analysis unit 11 can obtain the coordinate value of each node as geometric information of the workpiece after the forming analysis by numerical analysis, and objectively calculate the curvature of each element and the angle between the elements. Is possible. In the case of a press-formed product, the deformed workpiece has a very large curvature in the bending ridge line portion such as the punch shoulder R and the die shoulder R in the direction perpendicular to the bending ridge line compared to other parts.
Here, if the maximum curvature of each element is calculated and the element having a curvature greater than a certain threshold value is hidden, the parts other than the punch shoulder R and die shoulder R (web surface, vertical wall portion, flange portion) are continuous. It is possible to discriminate and separate as separate areas that are not.

4 to 8 show examples of steps from press forming analysis to calculation processing.
FIG. 4 shows the press forming analysis result, and the stress distribution is displayed in a contour diagram. FIG. 5 shows the curvature of each element as a result of the press forming analysis, and FIG. 6 shows the element with a large curvature hidden. Since the stepped portion has a very large curvature, it can be separated into a plurality of regions with the ridgeline portion of the step as a boundary by hiding elements that have a curvature greater than the threshold value in the vertical wall portion, A region based on the feature shape can be selected by extracting or selecting the region. From FIG. 6, it can be seen that the stepped side wall can be divided into three surfaces, a web, a vertical wall portion with no step (hidden from the figure), and each flange portion on both sides. The areas A15 to A17 shown in FIG. 7 are determined to be subjected to the arithmetic processing for the high stress areas based on the molding data (stress distribution) shown in FIG. . In the determination step, it is determined on the basis of the molding data whether the calculation described later is performed on the region divided based on the curvature and / or the angle. For example, the determination is made based on the stress level after press molding analysis of each divided area.

For the areas A15 to A17, FIG. 8 shows a state in which, for example, a calculation process for setting the stress to zero is performed on all the elements in the respective areas.
Although the maximum curvature of the element is used here, the same region division can be performed using the angle between the elements.
Further, when considering a member member having a hat cross-sectional shape without a step, a web surface, vertical wall portions on both sides, and flange portions on both sides can be selected as separated regions. Further, when the selected region is not a plane, it is possible to select a more characteristic region by repeating the same method.
In this way, the physical property value / physical quantity calculation processing unit 14 can determine the divided region based on the curvature and the elements based on the analysis result of the press forming analysis unit 11.

  The springback analysis unit 12 uses a finite element method (for example, commercially available software PAM-STAMP, LS-DYNA, Autoform, OPTRIS, ITAS-3D, ASU / P-FORM, ABAQUS, ANSYS, MARC, HYSTAMP). The stress distribution described in “P org.k” obtained by the forming analysis unit 11 is input, and the springback analysis is performed. The calculation of the springback in the software is, for example, calculated based on the basic equation of finite elasto-plastic deformation and the content according to the discretization method. However, the springback calculation may be an elastic analysis or an elasto-plastic analysis.

  Further, the springback analysis unit 12 can display the result of the springback analysis by the finite element method on the springback amount output screen 19 using post processing software. Further, the physical property value / physical quantity calculation processing unit 14 standardizes by dividing the spring back amount by the divided area, the representative length of the press-formed product, the representative width, the representative height, the representative plate thickness, the tensile strength, and the like. It is possible to output the data by making it easier to discriminate between the divided variable and the influence degree of the springback, and use the output data to display the contour by post processing software. Such normalization makes it easy to visually grasp the relationship between the physical property value / physical quantity of the workpiece and the springback amount.

  Furthermore, the physical property value / physical quantity calculation processing unit 14 obtains a normalized value by dividing the springback amount by a press molding condition such as a punch speed or a wrinkle holding force, and displays the contour by post processing software. The relationship between the press molding conditions and the amount of springback can be easily grasped visually. This standardization of the amount of springback and the contour display of the numerical value shorten the identification of the cause of the occurrence of springback economically and efficiently, and economically consider the molding method of molded products. And it is possible to shorten it efficiently.

  The file storage unit 16 includes data files “P org.k”, “SB org.k”, “SB”, which are output results of the press forming analysis unit 11, the springback analysis unit 12, and a physical property value / physical quantity calculation processing unit 14 described later. A storage unit for storing “P rem.casen.k”, “SB rem.casen.k”, “P trim.casen.k”, and the like. However, when these data files are directly input / output between the press forming analysis unit 11, the springback analysis unit 12, and the physical property value / physical quantity calculation unit 14, the file storage unit 16 is not necessarily provided. Not necessary.

  The physical property value / physical quantity calculation processing unit 14 selects a partial region in the output data file “P org.k” of the press forming analysis unit 11, and the plate thickness, elastic modulus, plasticity coefficient, An arithmetic process is performed on at least one of the stress component value and the strain component value. Then, an output data file “P rem.case1.k” after the arithmetic processing is generated and output to the springback analysis unit 12. This data file transmission / reception can be repeated, can be stored in the file storage unit 16 sequentially, and can be exchanged in the form of data input / output of the execution process or thread instead of the file format. good.

  The region data for determining the springback specific part or cause used in the finite element method is the calculation of one or more elements in the finite element method, a micro area consisting of a plurality of elements, or a collection of continuous elements. Integral points that are part of points for calculating stress and strain in the unit of calculation, unit of numerical integration by the finite element method (some points in the thickness direction, both points in the plane) Including). “One or more elements” refers to an element that is a region division unit of the finite element method, and “calculation unit classification” refers to one or a continuous set of minute regions that are calculation units in primary analysis. The “integration point” is a point at which approximate integration is generally performed by the finite element method. “Partial integration point” refers to a part of the points where stress and strain are calculated in the calculation unit of the numerical integration method based on the finite element method. Both points are included.

  In addition, “at least one variable of plate thickness, elastic modulus, plasticity coefficient, stress component value, and strain component value” means the plate thickness, elastic modulus (Young's modulus, Poisson's ratio) of a part of the workpiece. ), Plastic coefficient (yield stress, plastic coefficient, work hardening index), stress or strain in x, y, z direction (each of three components), when a three-dimensional coordinate system (x, y, z) is analyzed. It means at least one of a total of 18 factors including the xy plane, the yz plane, and the shear stress or shear strain (each of three components) in the zx plane.

FIG. 9 is a diagram showing a coordinate system used in the finite element method. (A) shows the coordinate system of the whole three-dimensional, (b) shows a local coordinate system.
At this time, as shown in FIG. 9A, in addition to the component values on the (x, y, z) coordinate axes, for example, as shown in FIG. 9B, the plane of the element 31 is regarded as the xy plane. It is assumed to include a total of 12 components of stress, strain, shear stress, and shear strain in the local coordinate system (x1, x2, x3). Also, variables obtained using each stress component and strain component such as equivalent stress, equivalent plastic strain, elastic energy (elastic work), plastic energy (plastic work), and increment of each component value such as stress increment and strain increment It also includes component values calculated in the form.

  In general, in a finite element method analysis using a steel plate as an analysis target, the physical property value / physical quantity of the steel plate is divided into 2 mm to 4 mm square finite elements. However, the division unit of the element is not necessarily limited to 2 mm to 4 mm square because it is divided by a length that approximates that the physical property value / physical quantity is constant. In other words, it may be necessary to limit the finite element to be smaller in a region where the residual stress is large. Each element is defined by a three-dimensional coordinate plane, and the angle and curvature of the plane of the finite element are defined by comparison with other planes.

  Thus, in order to identify the springback occurrence cause part, the member is divided into regions based on the angle and the curvature, and by calculating the portion having a high residual stress level, the calculation amount is greatly reduced, It is possible to identify the cause of the occurrence of springback more quickly.

As an example of arithmetic processing, a method of multiplying the σ _x component value by a coefficient will be described.
The stress component before calculation at the integration point of the selected region is (σ _x0 , σ _y0 , σ _z0 , τ _xy0 , τ _yz0 , τ _zx0 ), and the strain component is (ε _x0 , ε _y0 , ε _z0 , γ _xy0 , γ _yz0 , γ _zx0 ), the stress components (σ _x , σ _y , σ _z , τ _xy , τ _yz , τ _zx ), strain components (ε _x , ε _y , ε _z , γ _xy , γ _yz , γ _zx ) is as follows.
_{σ x = K × σ x0,} σ y = σ y0, σ z = σ z0, τ xy = τ xy0, τ yz = τ yz0, τ zx = τ zx0
ε _x = ε _x0 , ε _y = ε _y0 , ε _z = ε _z0 , γ _xy = γ _xy0 , γ _yz = γ _yz0 , γ _zx = γ _zx0
Here, K is calculated in a range of −1000 to 1000, the value before the processing is used as it is for the plate thickness, and the elastic coefficient and the plastic coefficient are values input by the molding condition input unit 18. It is common to use it. For illustration, K is shown only for σ _x , but other components may be varied as well.

In addition, material characteristics (plate thickness, elastic modulus, plasticity coefficient) can be calculated. For example, the physical property value / physical quantity calculation processing unit 14 selects a partial region of the workpiece obtained from the press forming analysis unit 11 and multiplies the selected region, for example, Young's modulus by a coefficient in the calculation processing. In that case, the thickness t ₀ before calculation of the selected region, Young's modulus E ₀ , Poisson's ratio ν ₀ , plastic coefficients F ₀ , a ₀ , n ₀ (when σ = F ₀ (ε + a ₀ ) ⁿ⁰ ) Then, the thickness t, Young's modulus E, Poisson's ratio ν, plastic coefficient F, a, n (when σ = F (ε + a) ⁿ ) after calculation are as follows.
t = t ₀ , E = K × E ₀ , ν = ν ₀ , F = F ₀ , a = a ₀ , n = n ₀
Here, K can be changed in the range of −1000 to 1000. For illustration, K is shown only for E, but other material properties may be varied as well.

Further, the physical property value / physical quantity calculation processing unit 14 can also select and perform calculation processing by selecting a region by directly editing the file that outputs the state variable obtained from the press forming analysis unit 11. For example, the contents of the file are displayed by software having a text editing function such as word pad, and the component value of the area to be processed is directly rewritten by operating the molding condition input unit 18, or the component value is replaced by cut and paste. Also good.
Thereby, it is possible to quantitatively evaluate how much the variable (component) calculated in the selected region affects the springback.

  For example, when the displacement distribution of a finite element node is displayed in a contour diagram (contour map) or a deformed cut surface is displayed in the springback analysis unit 12, the result of each calculated variable (component) in the selected region is displayed. It is possible to compare the figures side by side on the springback amount output screen 19 or output them to a printer (not shown) for comparison. In addition, when the coordinate value (X, Y, Z) of the node at any specified position is confirmed on the software or by file output, the numerical value for each calculated variable (component) in the selected area is compared, It is possible to make a graph and compare using calculation software or the like.

  The contour diagram displayed on the springback amount output screen 19 shows the springback while repeating the physical property value / physical quantity calculation processing by the physical property value / physical quantity calculation processing unit 14 and the springback amount calculation by the springback analysis unit 12. It is possible to strictly identify the parts and variables that cause the problem.

  Further, the specific region of the physical property value / physical quantity calculation processing unit 14 is changed by selection, or the component value of the selected region is multiplied not only by σx but also by component coefficients such as σy and τxy as calculation processing, The springback analysis unit 12 performs the springback analysis, displays the portion and variables that cause the springback on the springback amount output screen 18, and compares the amount of change in the displacement due to the springback, thereby causing the cause of the springback. It is possible to specify exactly the parts and variables that become.

  In addition, the physical property value / physical quantity calculation processing unit 14 selects a plurality of areas in a part of the workpiece, and performs the calculation process on each selected area at the same time, which is necessary for specifying the cause. It is possible to reduce the number of analysis steps.

FIG. 10 is a perspective view showing an example of region selection of a hat-shaped cross-sectional component according to an embodiment of the present invention.
For example, when the workpiece obtained by the press molding analysis unit 11 is a hat-shaped cross-sectional part as shown in FIG. 5, the physical property value / physical quantity calculation processing unit 14 has a stress after molding as shown in FIG. A plurality of areas A1 and A2 that are larger than a predetermined value are simultaneously selected, a calculation process for multiplying σx by a factor is performed on the selected areas A1 and A2, and a spring using the calculation process result in the springback analysis unit 12 Perform back analysis.

  From the result of the springback analysis, the amount of change in displacement caused by the springback is examined, and it is possible to determine how much the stress component value σx applied to the regions A1 and A2 has an influence on the springback without performing calculation processing for each side. It can be evaluated with only one calculation process.

  Further, after the springback analysis of the springback analysis unit 12 is performed, the region where the amount of springback changes the most is subdivided, and determination is performed until the size of the subdivided region becomes a predetermined value or less. For each divided area, the physical property value / physical quantity calculation processing unit 14 performs calculation processing, and the springback analysis unit 12 performs the springback analysis again. Can be identified, and efficient cause identification is possible. The physical property value / physical quantity calculation processing unit 14 can perform convergence calculation so that the physical property value and the physical quantity are changed as manipulated variables so that the springback change amount is equal to or less than the allowable value, and at the same time, Convergence calculation may be performed so that the divided area is changed as an operation variable.

  In addition, when the press forming analysis unit 11 performs forming analysis using, for example, a finite element method and numerically obtains the stress and strain value distribution after forming, the physical property value / physical quantity calculation processing unit 14 selects a region. In this case, one or more elements can be selected as a calculation target area. The finite element method, which is an analysis method for solving field problems, is characterized by dividing the continuum into finite elements, and the elements are connected at a finite number of nodes located on their sides. The displacement field in the element is uniquely determined from the shape function defined for each element and the displacement of the node. For example, the distribution of the stress component σx obtained by the press forming analysis unit 11 is displayed, and an element having the largest σx value is selected as a selected area, or a group of elements having the largest σx and elements in contact with the element is selected. be able to.

  In addition, when the press forming analysis unit 11 performs forming analysis using, for example, an elementary analysis method and numerically obtains the stress and strain value distribution after forming, the physical property value / physical quantity calculation processing unit 14 selects a region. In this case, one or more calculation unit sections can be selected as a calculation target area.

  In addition, when the press forming analysis unit 11 performs forming analysis using, for example, a finite element method and numerically obtains the stress and strain value distribution after forming, the physical property value / physical quantity calculation processing unit 14 selects a region. In this case, one or more integration points can be selected as a calculation target region. For example, in the finite element analysis of the press forming analysis unit 11, the workpiece is analyzed with a shell element having five integration points (1, 2, 3, 4, 5 from the back surface to the front surface) in the thickness direction. In addition, it is possible to set only 1 integration point closest to the plate back surface of the element selected in the physical property value / physical quantity calculation processing unit 14 and 5 integration points closest to the plate surface as a calculation target region. Thereby, the evaluation which isolate | separated the influence of the bending deformation received when contacting and deform | transforming the part which has a curvature of a metal mold | die can be performed.

  FIG. 11 is a flowchart of the springback generation cause specifying process of the springback cause site specifying process according to the embodiment of the present invention.

  In step S <b> 101, molding conditions are input to the molding condition input unit 18. Next, the process proceeds to step S102.

  In step S102, the press molding analysis unit 11 performs numerical analysis processing on the workpiece defined by the molding conditions, and calculates the distribution of stress and strain values after molding of the product to be press molded. Next, the process proceeds to step S103.

  In step S <b> 103, the physical property value / physical quantity calculation processing unit 14 determines a specific part to be a conversion target region. The specific part is calculated by calculating the curvature and / or angle of the press-molded product, dividing the region of the molded product based on the curvature and / or angle, and determining each divided region based on the molding data. Then, an area for performing arithmetic processing described later is determined. Next, the process proceeds to step S104.

  In step S104, the above-described arithmetic processing for converting at least one of the physical property value and the physical quantity in the partial area determined to be arithmetic processing in S103 is performed. Next, the process proceeds to step S105.

  In step S105, the springback amount is calculated based on the physical property value and the physical quantity subjected to the conversion processing of the workpiece during press molding. Next, the process proceeds to step S106, and at the same time, the result of the springback amount is displayed on the screen by a contour display or the like in step S107.

  In step S106, it is determined whether the allowable value of springback is within the allowable value. If it is within the allowable value, this process is terminated. If it is equal to or greater than the allowable value, the process proceeds to step S108. In step S106 and step S108, a human may manually designate a specific part while watching the amount of change in springback.

  In step S108, the physical property value / physical quantity of the specific part and the workpiece are changed. Here, only a specific part may be changed, only the physical property value / physical quantity may be changed, or both of them may be simultaneously performed. Then, the process returns to step S105. The processing of step S105, step S106, and step S108 can be performed by a convergence calculation such that the amount of change in springback is less than or equal to an allowable value, and is repeated until it becomes less than or equal to a threshold value.

  Note that the number of repetitions of this process is limited, and the process may be terminated when the limited number of repetitions is exceeded. In that case, the human examines the output data file “SB rem.casen.k” of the springback analysis unit 12 stored in the file storage unit 16, and the person looks at the springback amount output screen 19 to determine the optimum specific part. Can be obtained by searching.

  FIG. 12 is a flowchart of the springback occurrence cause specifying process of the springback cause site specifying process according to the embodiment of the present invention.

  In step S <b> 201, the first molding condition is input to the molding condition input unit 18. Next, the process proceeds to step S202.

  In step S202, the press molding analysis unit 11 performs numerical analysis processing on the press-molded product specified by the first molding condition, and calculates the distribution of stress and strain values after molding of the product to be press-molded. Further, the press molding analysis unit 11 performs numerical analysis on the workpiece defined by the second molding condition in which at least one of the first molding conditions is changed, and after the molding of the product to be press molded The distribution of stress and strain values (physical properties and physical quantities) is calculated. Next, the process proceeds to step S203.

  In step S <b> 203, the physical property value / physical quantity calculation processing unit 14 determines a specific part to be a conversion target region. This specific part is the difference between the physical property value and physical quantity for each area of the press-molded product calculated under the first molding condition, and the physical property value and physical quantity for each area of the press-molded product calculated under the second molding condition. Is calculated, and it is determined whether or not the difference value is larger than a predetermined value. If there is a difference value greater than the predetermined value, the region having the difference value is determined as a specific part, and the process proceeds to step S204.

  In step S204, a calculation process for converting at least one of the physical property value and the physical quantity in the region determined in S203 is performed. Next, the process proceeds to step S205.

  In step S205, the springback amount is calculated based on the physical property value and the physical quantity that have been subjected to the calculation process. Next, the process proceeds to step S206, and at the same time, the result of the springback amount is displayed on the screen by a contour display or the like in step S207.

  In step S206, it is determined whether the allowable value of springback is within the allowable value. If it is within the allowable value, this process is terminated. If it is equal to or greater than the allowable value, the process proceeds to step S208.

  In step S208, when the second molding condition in step S202 is changed to a condition that is different from the first molding condition, the process returns to step S202, and the physical property value / physical quantity and determination for determining the specific part in step S203 are determined. When changing the predetermined value for step S204, the process returns to step S203, and when changing the calculation process of step S204, the process returns to step S204. Note that step S208 may be performed by human beings while observing the result of screen output or the like. The processes in steps S202 to S208 may be repeated until the springback change amount is less than the allowable value by the convergence calculation so that the springback change amount is less than the allowable value.

  Note that the number of repetitions of this process is limited, and the process may be terminated when the limited number of repetitions is exceeded. In that case, the human examines the output data file “SB rem.casen.k” of the springback analysis unit 12 stored in the file storage unit 16, and the person looks at the springback amount output screen 19 to determine the optimum specific part. You may seek by searching.

  FIG. 13 shows a flowchart of the springback cause site specifying process according to the embodiment of the present invention.

  In step S <b> 301, molding conditions are input to the molding condition input unit 18. Next, the process proceeds to step S302.

  In step S302, the press molding analysis unit 11 performs numerical analysis processing on the workpiece defined by the molding conditions, and calculates physical property values and physical quantities after molding of the product to be press molded. Next, the process proceeds to step S303.

  In step S303, the springback analysis unit 12 analyzes the press-molded workpiece and calculates a first springback amount. Next, the process proceeds to step S304.

  In step S304, it is determined whether or not there is a region where at least one of the physical property value and physical quantity after the spring back of the press-formed product is larger than a predetermined value. If there is such a region, the region is determined as a specific region. Alternatively, it is determined whether or not there is an area where the difference between the physical property value and the physical quantity before and after the springback is larger than a predetermined value. If there is the area, the area is determined as the specific area. Next, the process proceeds to step S305.

  In step S305, arithmetic processing is performed on at least one of the physical property value and physical quantity data of the determined specific part. Next, the process proceeds to step S306.

  In step S306, the second springback amount is calculated based on the calculated substance amount and physical quantity data of the specific part. Next, the process proceeds to step S307, and at the same time, the result of the first or second springback amount is displayed on the screen by a contour display or the like in step S308.

  In step S307, it is determined whether the second springback amount is within an allowable value. If it is within the allowable value, this process is terminated. If it is equal to or greater than the allowable value, the process proceeds to step S309.

  In step S309, the physical property value and physical quantity variable for determining the specific part, and the arithmetic processing are changed. When changing the specific part determining method, the physical property value and the physical quantity variable to be determined are changed, and the process returns to step S304 to change the predetermined value. When changing a variable or the like performed in the calculation process, the process returns to step S305. Note that step S309 may be performed by human beings while observing the result of screen output or the like. The processing in steps S304 to S309 may be repeated until the springback allowable value is reached or less by convergence calculation.

  If a convergent solution cannot be obtained in relation to the allowable springback value, the number of repetitions of this process may be limited, and the process may be terminated with the limited number of repetitions. Even in such a case, the human examines the output data file “SB UVC.casen.k” of the springback analysis unit 12 stored in the file storage unit 16, and the human looks at the springback amount output screen 19. It is possible to search for and find the optimum specific part.

  FIG. 14 is a hardware configuration diagram of a springback occurrence cause identifying apparatus according to an embodiment of the present invention. The processes in the press forming analysis unit 11, the spring back analysis unit 12, the physical property value / physical quantity calculation processing unit 14, and the partial residual stress removal processing unit 21 described above are defined in the program 100, and the program 100 is executed by the computer 90. You may let them. The computer 90 includes a CPU 91 for executing necessary processing, a memory 92 for storing processing results (for example, RAM (Random Access Memory)), a display 93, for example, an input device 94 such as a keyboard and a mouse, a hard disk 95, a CD / CD An external storage device 96 such as a DVD drive, a NIC (network interface card) 97, and a printer 98 are provided. The computer 90 can be connected to another computer 90 </ b> A via a network 99 configured by an Ethernet (registered trademark) cable connected to the NIC 97.

  The program 100 is stored in a recording medium, loaded from the external storage device 96, or downloaded from another computer 90A via the network 99, and stored in the hard disk 95 of the computer 90 under the control of the CPU 91. Next, the saved program 100 is executed by the CPU 91 and stored in the memory 92 as an execution process or thread. For example, each process in the press forming analysis unit 11, the springback analysis unit 12, the physical property value / physical quantity calculation processing unit 14, or the partial residual stress removal processing unit 21 becomes an execution process or thread, and between each execution process or thread The data file or data described above is input / output. Each of these execution processes or threads may be distributed in the other computer 90A, and each process may be distributed by the computer 90 and the other computer 90A.

  Further, the molding condition input unit 18 and the springback amount output screen 19 shown in FIG. 3 may be an input device 94 and a display 93, respectively. The file storage unit 16 described above may be a hard disk 95. The program 100 may be stored in the hard disk 95. The above contour map output to the display 93 can be output to the printer 98.

  Hereinafter, the present invention will be specifically described with reference to examples.

  FIGS. 15A and 15B are diagrams showing a hat-shaped cross-sectional component subject to springback analysis according to an embodiment of the present invention, wherein FIG. 15A is a perspective view thereof, and FIG. 15B is a cross-sectional view thereof. It consists of side walls W1, W2 and flanges F1, F2.

  For the numerical analysis performed by the press forming analysis unit 11 and the spring back analysis unit 12, commercially available plate forming simulation analysis software PAM-STAMP based on the finite element method was used. The springback analysis used the elastic analysis by the static implicit method.

  As the forming conditions, data of a high-strength steel plate having a plate thickness of 1.6 mm and a tensile strength of 780 MPa was used as the properties of the metal plate. The shape of the die (die, punch, holder) was modeled with shell elements and analyzed assuming a rigid body. The clearance between the die and the punch was 1.6 mm, the same as the plate thickness. A friction coefficient of 0.15 was input and 600 kN was set as the wrinkle holding load.

FIGS. 16A and 16B are diagrams showing a cross-sectional position and a twist angle of a hat-shaped cross-sectional component according to an embodiment of the present invention, where FIG. 16A is a perspective view and FIG. 16B is a cross-sectional view thereof.
The coordinate values of the points constituting the cross section at the positions A and B shown in FIG. 11 were obtained from the obtained results by post processing software, and the angle θ formed by the web surface of the cross section was obtained. Here, the springback amount is a twist angle θ.

  FIG. 17 is a diagram showing the stress distribution after the spring back of the workpiece. The physical property value / physical quantity calculation processing unit 14 selects a region having a high stress level of 5% based on the stress distribution obtained from the springback analysis unit 12 shown in FIG.

FIG. 18 is a diagram illustrating a region selected based on the stress distribution after the workpiece is spring-backed. FIG. 18 shows the region R10 selected at the high stress level of 5%.
The physical property value / physical quantity calculation processing unit 14 performed the following calculation on all integration points of the elements belonging to the region thus selected.
σ _x = 0, σ _y = 0, σ _z = 0, τ _xy = 0, τ _yz = 0, τ _zx = 0
ε _x = ε _x0 , ε _y = ε _y0 , ε _z = ε _z0 , γ _xy = γ _xy0 , γ _yz = γ _yz0 , γ _zx = γ _zx0

Here, the stress component before calculation at the integration point of the selected region is (σ _x0 , σ _y0 , σ _z0 , τ _xy0 , τ _yz0 , τ _zx0 ), and the strain component is (ε _x0 , ε _y0 , ε _z0 , γ _xy0 , γ _yz0 , γ _zx0 ), the stress components after the calculation processing are (σ _x , σ _y , σ _z , τ _xy , τ _yz , τ _zx ), and the strain components are (ε _x , ε _y , ε _z , γ _xy , γ _yz , γ _zx ). For the plate thickness, the value before the calculation processing is used as it is, and the value input to the software PAM-STAMP in the press analysis processing is used as it is for the elastic coefficient and plasticity coefficient. The calculated stress and strain values were output as a calculation result file by the file output means.

  The above-mentioned software PAM-STAMP was used as the springback analysis process. The output result of the physical property value / physical quantity calculation processing execution program was input to software PAM-STAMP to perform a springback analysis. For the springback analysis, an elastic analysis by a static implicit method was used.

  FIG. 19 is a diagram comparing the springback amount when the arithmetic processing is not performed and the springback amount when the arithmetic processing is performed. From this, it is clear that the amount of springback has been reduced by the calculation process for the region R10 selected in FIG. 18, and the selected region R10 shown in FIG. 18 can be identified as the site causing the springback.

20A and 20B are views showing the cross-sectional position and flange spring amount of the hat-shaped cross-sectional component according to the embodiment of the present invention, wherein FIG. 20A is a perspective view and FIG. 20B is a cross-sectional view thereof. The amount of spring back was the displacement of the end point of the cross section A before and after the spring back, that is, the amount of spring splash.
For the numerical analysis performed by the press forming analysis unit 11 and the spring back analysis unit 12, commercially available plate forming simulation analysis software PAM-STAMP based on the finite element method was used. The springback analysis used the elastic analysis by the static implicit method.

  As the forming conditions, data of a high-strength steel plate having a plate thickness of 1.6 mm and a tensile strength of 780 MPa was used as the properties of the metal plate. The shape of the die (die, punch, holder) was modeled with shell elements and analyzed assuming a rigid body. The clearance between the die and the punch was 1.6 mm, the same as the plate thickness. A friction coefficient of 0.15 was input and 600 kN was set as the wrinkle holding load.

FIG. 21 is a diagram showing the stress distribution before and after the spring back of the workpiece. FIG. 22 is a diagram showing a stress difference before and after the workpiece is spring-backed and a region selected based on the stress difference. FIG. 22 shows a region R11 selected at a high 5% stress level.
Based on the stress distribution obtained from the springback analysis unit 12 shown in FIG. 21, the physical property value / physical quantity calculation processing unit 14 selects a region R11 having a high stress level of 5% shown in FIG.

The physical property value / physical quantity calculation processing unit 14 performed the following calculation on all integration points of the elements belonging to the region thus selected.
σ _x = 0, σ _y = 0, σ _z = 0, τ _xy = 0, τ _yz = 0, τ _zx = 0
ε _x = ε _x0 , ε _y = ε _y0 , ε _z = ε _z0 , γ _xy = γ _xy0 , γ _yz = γ _yz0 , γ _zx = γ _zx0

Here, the stress component before calculation at the integration point of the selected region is (σ _x0 , σ _y0 , σ _z0 , τ _xy0 , τ _yz0 , τ _zx0 ), and the strain component is (ε _x0 , ε _y0 , ε _z0 , γ _xy0 , γ _yz0 , γ _zx0 ), the stress components after the calculation processing are (σ _x , σ _y , σ _z , τ _xy , τ _yz , τ _zx ), and the strain components are (ε _x , ε _y , ε _z , γ _xy , γ _yz , γ _zx ). For the plate thickness, the value before the calculation processing is used as it is, and the value input to the software PAM-STAMP in the press analysis processing is used as it is for the elastic coefficient and plasticity coefficient. The calculated stress and strain values were output as a calculation result file by the file output means.

  The above-mentioned software PAM-STAMP was used as the springback analysis process. The output result of the physical property value / physical quantity calculation processing execution program was input to software PAM-STAMP to perform a springback analysis. For the springback analysis, an elastic analysis by a static implicit method was used. The amount of spring back was the displacement of the end point of the cross section A before and after the spring back, that is, the amount of spring splash.

  FIG. 23 is a diagram comparing the springback amount when the arithmetic processing according to one embodiment of the present invention is not performed and the springback amount when the arithmetic processing is performed. From this, it is clear that the amount of springback has been reduced by the calculation process for the region R11 selected in FIG. 22, and the selected region R11 shown in FIG. 22 can be identified as the site causing the springback.

As shown in the examples above, the cause of the springback can be easily identified by quantitatively analyzing the degree of influence of the workpiece on the springback and displaying the information visually. It becomes possible to do.
As described above, the device for identifying the cause of the occurrence of springback according to the present invention can identify the cause of the occurrence of springback by numerical analysis by using the conventional device to examine the springback, so that the test at the design stage of the molded member can be performed. It reduces man-hours and costs. Further, such a device for identifying the cause of occurrence of springback is expected to be applied to all workpieces, and thus brings great benefits to the industry.

  The embodiments described above are merely given as typical examples, and it is obvious to those skilled in the art to combine the components of each embodiment, and variations and variations thereof. Those skilled in the art will understand the principles and claims of the present invention. It is obvious that various modifications of the above-described embodiment can be made without departing from the scope of the invention described in the above.

It is a cross-sectional schematic diagram of a molded member showing correspondence to a conventional spring back. It is a perspective view which illustrates the conventional method which searches the site | part which becomes the generation | occurrence | production of a deformation | transformation by a springback. The functional block diagram of the spring back generation | occurrence | production cause site | part identification apparatus by one Embodiment of this invention is shown. It is a contour figure which shows the stress distribution of the press molding analysis result by the example of this invention. It is a contour figure which shows the curvature of each element by the example of this invention. FIG. 6 is a contour diagram in which elements having a large curvature according to an example of the present invention are not displayed. It is a figure which shows having divided into areas based on the curvature by the example of this invention. It is the contour figure which made the stress of the one part area | region by the example of this invention zero. It is a figure which shows the coordinate system used by the finite element method by one Embodiment of this invention. It is a perspective view which shows the example of the area | region selection of the workpiece by one Embodiment of this invention. It is a flowchart of the spring back generation | occurrence | production cause site | part identification process by one Embodiment of this invention. The functional block diagram of the spring back generation | occurrence | production cause site | part identification apparatus by one Embodiment of this invention is shown. It is a flowchart of the springback generation | occurrence | production cause identification process of the springback cause site | part identification apparatus by one Embodiment of this invention. It is a hardware block diagram of the springback cause site | part identification process by one Embodiment of this invention. It is the perspective view and sectional drawing which show the example of the workpiece by one Example of this invention. It is a figure which shows the cross-sectional position and twist angle of the hat-shaped cross-sectional shape part by the Example of this invention. It is a figure which shows the stress distribution after the springback of the workpiece by one Example of this invention. It is a figure which shows the area | region selected based on the stress distribution after the spring back of the workpiece by one Example of this invention. It is a figure which compares the springback amount when not performing the arithmetic processing by one Example of this invention with one Example of this invention, and the springback amount when performing an arithmetic processing. It is a figure which shows the cross-sectional position and flange spring amount of the hat-shaped cross-sectional shape part by the Example of this invention. It is a figure which shows the stress distribution before and after the springback of the workpiece by one Example of this invention. It is a figure which shows the area | region selected based on distribution of the stress difference before and behind the springback of the workpiece by one Example of this invention, and a stress difference. It is a figure which compares the springback amount when not performing the arithmetic processing by one Example of this invention with the springback amount when performing the arithmetic processing.

Explanation of symbols

10A, 10B Springback occurrence cause identifying device 11 Press molding analysis unit 12 Springback analysis unit 14 Physical property value / physical quantity calculation processing unit 16 File storage unit 18 Molding condition input unit 19 Springback amount output screen

Claims (9)

A press molding analysis step in which a computer numerically analyzes press molding molding conditions to obtain molding data of a press molded product,
A first springback amount calculating step in which a computer calculates stress and / or strain for each of a plurality of regions after springback based on molding data of the press-formed product;
When there is an area where the stress and / or strain is greater than a predetermined value , the computer performs an arithmetic processing step for performing arithmetic processing on the stress and / or strain in the area;
A second spring back amount calculating step in which the computer further calculates stress and / or strain for each of the plurality of regions after the spring back based on the result of the arithmetic processing;
A method for identifying a springback occurrence cause site. The arithmetic processing step, when the difference of stress and / or strain of the spring-back before and after the press-molded article, there is a region larger than a predetermined value, according to claim 1 for performing arithmetic processing to stress and / or strain of the area The method for identifying the cause of the occurrence of springback as described in 1. A press molding analysis unit that numerically analyzes the molding conditions of press molding and obtains molding data of the press molded product,
A numerical analysis of the molding data, a springback amount for each of a plurality of regions , and a springback analysis unit for calculating stress and / or strain ;
When there is a region where the stress and / or strain for each of the plurality of regions after the calculation of the springback amount is larger than a predetermined value, an arithmetic process is performed on the stress and / or strain of the region, and the springback analysis unit Based on the result of the arithmetic processing, further, an arithmetic processing unit for calculating the amount of spring back and the stress and / or strain for each of the plurality of regions after the spring back,
An apparatus for identifying a springback generation cause site, comprising: The arithmetic processing unit, the difference between the stress and / or strain of the spring-back before and after the press-molded product, if there is a region larger than a predetermined value, according to claim 3 for processing to stress and / or strain of the area The device for identifying the site of occurrence of springback as described in 1. A press molding analysis procedure for numerically analyzing press molding molding conditions to obtain molding data of a press molded product,
A first springback amount calculation procedure for calculating stress and / or strain for each of a plurality of regions after springback based on molding data of the press-molded product;
When there is a region where the stress and / or strain is larger than a predetermined value, an arithmetic processing procedure for performing arithmetic processing on the stress and / or strain of the region,
A second springback amount calculating procedure for further calculating stress and / or strain for each of the plurality of regions after springback based on the result of the arithmetic processing;
A computer program for identifying the cause of the occurrence of springback, characterized in that a computer is executed. The arithmetic processing step, when the difference between the stress and / or strain of the spring-back before and after the press-molded article, there is a region larger than a predetermined value, claim performs arithmetic processing to stress and / or strain of the region 5 The program for identifying the cause of the occurrence of springback described in 1. Press forming analysis program for executing the steps of the molding condition of the press molding by numerical analysis to calculate the stress and / or strain of the molding data and a plurality of regions each of the press-molded product in a computer, and, molding data and a plurality of regions each of springback cause sites springback analysis program, city cooperate to perform the steps of calculating in a computer a stress and / or strain of each of a plurality of regions after stress and / or the spring back amount by numerical analysis strain and springback A specific program,
Obtaining a stress and / or strain for each of a plurality of regions after the springback output by a computer executing the springback analysis program;
When there is a region where the stress and / or strain is larger than a predetermined value, an arithmetic processing procedure for performing arithmetic processing on the stress and / or strain of the region,
A procedure for outputting the result of the arithmetic processing to a computer that executes the springback analysis program,
A computer program for identifying the cause of the occurrence of springback, characterized in that a computer is executed. From the press molding analysis program, further comprising a procedure of acquiring stress and / or strain for each of a plurality of regions before the spring back,
In the calculation processing procedure, when there is a region where the difference in stress and / or strain of the press-formed product before and after the spring back is larger than a predetermined value, the calculation processing is performed on the stress and / or strain in the region. 7. The program for identifying the cause of the occurrence of springback according to 7 . A computer-readable recording medium on which the computer program according to any one of claims 5 to 8 is recorded.