JP7382913B2 - Numerical simulation defect occurrence risk evaluation method and device - Google Patents

Description

The present invention relates to a defect occurrence risk evaluation method and apparatus using numerical simulation.

As a method for hot rolling a strip, a method is known in which the circumferential compressive strain on the surface of the strip is evaluated to satisfy the defect guarantee (see Patent Document 1). In such a method of hot rolling a strip, a mold called a grooved roll is used, so that deformation of the strip in the width direction is restricted. Therefore, linear flaws occur in the axial direction of the strip. Therefore, in order to guarantee defects, only the compressive strain in the circumferential direction at the portion exiting from the grooved roll needs to be considered.

However, in forging, three-dimensional deformation occurs in response to compression in one direction. Therefore, it is difficult to specify the deformation behavior of the material as described above. In other words, it is difficult to specify what kind of flaw occurs in which part.

On the other hand, there is a known method of simulating the deformation behavior of a material during forging using numerical simulation using the finite element method (see Patent Document 2). This method divides the shape data of the material and mold into multiple elements, calculates the plastic strain energy, and simulates the deformation behavior of the material. This makes it possible to predict the plastic deformation of the material as well as the load that will be applied to the material.

Japanese Patent Application Publication No. 2007-90429 Japanese Patent Application Publication No. 2008-33435

Due to the nature of the finite element method, the method described in Patent Document 2 can predict the occurrence of defects such as flaws that are larger than the element size. However, it is difficult to predict the occurrence of defects such as flaws that are smaller than the element size. Furthermore, if the element size is set smaller in order to predict the occurrence of smaller defects, the calculation time will increase proportionally, and there is a possibility that the calculation will not be completed in a practical time. Furthermore, it is difficult to determine the optimal (minimum) element size that allows the calculation to be completed in a practical amount of time.

An object of the present invention is to predict the occurrence of minute defects in a practical calculation time using a numerical simulation defect occurrence risk evaluation method and apparatus.

A first aspect of the present invention is a defect occurrence risk evaluation method for numerical simulation using the finite element method of a forging process, which comprises: acquiring a numerical simulation model as shape data; dividing the numerical simulation model into a plurality of elements; calculating the initial surface area of each of the plurality of elements, storing the calculated initial surface area, calculating the surface area of each of the plurality of elements while performing a numerical simulation of the forging process, and calculating the surface area of each of the plurality of elements, As the numerical simulation progresses, the degree of decrease in surface area is calculated for each of the plurality of elements, and the portions where the elements exist whose degree of decrease is greater than a predetermined threshold are determined to have a risk of defect occurrence in the numerical simulation model. The present invention provides a method for evaluating the risk of defect occurrence using numerical simulation, which includes evaluating a specific part of a part.

According to this method, the risk of defect occurrence is evaluated based on the degree of reduction in the surface area of each of a plurality of elements of a numerical simulation model. Therefore, even if the size of each of the plurality of elements is larger than the size of a defect such as a flaw that may occur, the risk of defect occurrence can be evaluated. Therefore, the risk of occurrence of minute defects can be evaluated without setting the element size so small. Therefore, the occurrence of minute defects can be predicted within a practical calculation time. Note that the predetermined threshold value may vary depending on the element size of the numerical simulation model and the size of the minute defect to be confirmed.

The degree of reduction may be a ratio of the initial surface area of each of the plurality of elements.

According to this method, the degree of reduction is calculated based on the initial surface area of each of the plurality of elements. Therefore, the degree of decrease can be easily calculated without complicating calculations. The predetermined threshold value in this method may be defined based on the evaluation value SS obtained as SS=(Si-S0)/S0, for example. Here, Si indicates the surface area at i step (i is a natural number), and S0 indicates the initial surface area. The value of the evaluation value SS, which can serve as the above-mentioned predetermined threshold value, is basically set to a value smaller than 0 (when the surface area becomes smaller than the surface area of the previous step), and in this case, it is considered that a minute defect occurs. Furthermore, for defects that are visible to the extent that they can be visually confirmed, a value smaller than this can be the threshold value. Specifically, the predetermined threshold value may be set to about -0.35, for example. However, as described above, this value may change depending on the element size of the numerical simulation model and the size of the minute defect to be confirmed.

The specific region may be displayed on the screen.

According to this method, parts with a high risk of defect occurrence can be visually recognized.

A second aspect of the present invention is a defect occurrence risk evaluation device for numerical simulation using the finite element method of a forging process, which includes a model acquisition unit that acquires a numerical simulation model as shape data, and a model acquisition unit that acquires a numerical simulation model as shape data; an element dividing unit that divides the plurality of elements into elements, an initial surface area calculating unit that calculates an initial surface area of each of the plurality of elements, a storage unit that stores the calculated initial surface area, and a numerical simulation of the forging process. an elapsed surface area calculation unit that calculates the surface area of each of the plurality of elements, and a reduction degree calculation unit that calculates the degree of reduction in surface area of each of the plurality of elements as the numerical simulation of the forging process progresses; Provided is a defect occurrence risk evaluation device for numerical simulation, comprising an evaluation unit that evaluates a part where an element exists whose degree of reduction is larger than a predetermined threshold value as a specific part having a risk of defect occurrence in the numerical simulation model.

According to the present invention, minute defects can be predicted in a practical calculation time using a numerical simulation defect occurrence risk evaluation method and apparatus.

The front view which shows the material before shaping|molding of the forging process. FIG. 3 is a front view showing the material after being formed in the forging process. The front view which shows the numerical simulation model before forming of the forging process. The front view showing a numerical simulation model after forming in the forging process. FIG. 1 is a block diagram of a defect occurrence risk evaluation device 1 for numerical simulation according to an embodiment of the present invention. 1 is a flowchart showing a defect occurrence risk evaluation method using numerical simulation according to an embodiment of the present invention. A photo showing the R5 material before forging. A photo showing the R5 material after forging. A photograph showing an enlarged part of FIG. 8. A contour diagram corresponding to FIG. 9. A photo showing R10 material before forging. A photograph showing the R10 material after forging. A photograph showing an enlarged part of FIG. 12. FIG. 14 is a contour diagram corresponding to FIG. 13.

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

Referring to FIGS. 1 and 2, in the forging process, a material 2 is rolled down and formed into a desired shape. Defects such as flaws F may occur on the surface of the material 2 during molding. In this embodiment, the occurrence of such defects is predicted by numerical simulation using the finite element method.

Referring to FIGS. 3 and 4, in numerical simulation using the finite element method, the numerical simulation model of material 2 is divided into a plurality of elements and calculations are performed for each element. In the forging process, the size of the element is reduced as it is shaped. In general, the smaller the size of the divided elements, the more accurate numerical simulation is possible and the occurrence of minute defects can be predicted. However, the smaller the element size, the more calculation time. Therefore, if the elements are set too small, the calculation may not be completed within a practical calculation time. Focusing on this, in this embodiment, we present a defect occurrence risk evaluation method using numerical simulation that can predict the occurrence of minute defects in a practical calculation time based on a reduction in element size without setting the element size too small. and describe the equipment.

FIG. 5 is a block diagram of a defect occurrence risk evaluation device 1 (hereinafter also simply referred to as evaluation device 1) for numerical simulation according to the present embodiment. The evaluation device 1 is composed of hardware such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), and software installed therein. For example, the evaluation device 1 is configured with an information processing device such as a desktop computer, a notebook computer, a workstation, or a tablet terminal. The evaluation device 1 has a model forming section 10, a calculation section 20, a storage section 30, an evaluation section 40, and an output section 50 as a functional configuration. These are realized through cooperation between a processor, which is a hardware resource, and a program, which is software.

The model forming section 10 includes a model acquiring section 11, an element dividing section 12, and a condition setting section 13. The model acquisition unit 11 is a part that acquires shape data of a material to be forged as a numerical simulation model. The data may be obtained from outside or may be created by the user. The element division section 12 is a section that divides the analytical model acquired by the model acquisition section 11 into a plurality of elements. The size of the plurality of elements may be set larger than the size of defects such as flaws that may occur. The condition setting section 13 is a section for setting various conditions for numerical simulation. In the condition setting section 13, physical property values of the material and various boundary conditions are set.

The calculation section 20 includes an initial surface area calculation section 21 , an elapsed surface area calculation section 22 , and a reduction degree calculation section 23 . The initial surface area calculating section 21 is a section that calculates the initial surface area of each of a plurality of elements by the element dividing section 12. The elapsed surface area calculation unit 22 is a part that calculates the surface area of each of a plurality of elements while executing numerical simulation of a forging process. Therefore, the elapsed surface area calculating section 22 sequentially calculates new surface areas. The reduction degree calculation unit 23 is a part that calculates the degree of reduction in surface area for each of a plurality of elements. In this embodiment, the reduction degree calculation unit 23 calculates the degree of reduction as a ratio of the reduction to the initial surface area of each of the plurality of elements. Alternatively, while new surface areas are being calculated one after another, the degree of decrease in the currently calculated surface area relative to the previously calculated surface area may be calculated. In this way, various methods of calculating the degree of decrease can be considered.

The storage unit 30 stores programs that run on the processor, parameter data necessary for numerical simulation, and the like. In particular, the storage unit 30 stores the initial surface area of each of the plurality of elements calculated by the initial surface area calculation unit 21. Further, the storage unit 30 may store the surface area of each of the plurality of elements calculated by the elapsed surface area calculation unit 22.

The evaluation unit 40 is a part that evaluates a portion in which an element exists whose degree of reduction is greater than a predetermined threshold value as a specific portion with a risk of defect occurrence in the numerical simulation model. The predetermined threshold value may vary depending on the element size of the numerical simulation model and the size of the minute defect to be confirmed.

The output section 50 is a section that outputs the evaluation results from the evaluation section 40. The output unit 50 may be a commercially available display (screen) such as a liquid crystal display, a plasma display, or an organic EL display.

Referring to FIG. 6, a defect occurrence risk evaluation method using numerical simulation according to the present embodiment will be described.

When the evaluation method of this embodiment is started, first, the model acquisition unit 11 acquires shape data of a material to be forged as a numerical simulation model (step S6-1). Next, the element dividing unit 12 divides the numerical simulation model into a plurality of elements (step S6-2). At this time, the condition setting unit 13 sets numerical simulation conditions. Next, the initial surface area calculation unit 21 calculates the initial surface area for each of the plurality of elements and stores it in the storage unit 30 (step S6-3). Then, a simulation of the forging process is executed (step S6-4). At this time, the surface area of each of the plurality of elements is sequentially calculated at the same time. This makes it possible to calculate changes in surface area for each of the plurality of elements as the numerical simulation progresses. In particular, in this embodiment, the degree of decrease calculation unit 23 calculates the degree of decrease in surface area (step S6-5). Then, the evaluation unit 40 evaluates a portion where an element whose degree of reduction is greater than a predetermined threshold exists as a specific portion with a risk of defect occurrence in the numerical simulation model (step S6-6). The evaluation result by the evaluation unit 40 is output by displaying the specific region on the screen (output unit 50) (step S6-7).

7 to 14 show comparison results between numerical simulation and experiment of this embodiment.

Two types of materials 2A and 2B were prepared in numerical simulations and experiments. Materials 2A and 2B were prepared by bending cylindrical materials with a diameter of 20 mm and a length of 150 mm into a V-shape by 120 degrees at the center portion (bending portions 2a and 2b). The materials 2A and 2B are carbon steel for machine structures (S45C). The material 2A has a bending radius of 5 mm (R5) at the bent portion 2a (see FIGS. 7 to 10). The material 2B has a bending radius of 10 mm (R10) at the bent portion 2b (see FIGS. 11 to 14). These two types of materials 2A and 2B were held at 1200° C. for 1 hour and rolled down by forging until the thickness was reduced to about 50%, and the presence or absence of flaws was confirmed.

FIG. 7 shows the R5 material 2A before forging, and FIG. 8 shows the R5 material 2A after forging. Further, FIG. 9 shows an enlarged view of the bent portion 2a of the material 2A in FIG. 8. Referring to FIGS. 7 to 9, a flaw F was generated on the surface of the bent portion 2a of the material 2A due to the forging process. In addition, in FIG. 9, the flaw F is schematically marked in order to facilitate identification of the flaw F. FIG. 10 is a contour diagram showing numerical simulation results corresponding to the experimental results of FIG. 9. In the contour diagram, the degree of reduction in surface area of the plurality of elements is displayed as an evaluation value. In this embodiment, the evaluation value becomes smaller as the degree of decrease becomes larger (since it is a negative value, the absolute value becomes larger). Specifically, the evaluation value SS was evaluated based on the following formula. The predetermined threshold value here is set to -0.35, for example. However, this value changes depending on the element size of the numerical simulation model and the size of the minute defect to be confirmed.

ＳＳ：評価値
Ｓｉ：ｉステップ（ｉは自然数）における表面積
Ｓ０：初期表面積

SS: Evaluation value Si: Surface area at i step (i is a natural number) S0: Initial surface area

By comparing and referring to FIGS. 9 and 10, it can be confirmed that the location where the flaw F in FIG. 9 occurs matches the location where the evaluation value is small (the location where the degree of decrease in surface area is large) in FIG. 10. In addition, in FIG. 10, the evaluation value SS is approximately -0.5 in the center of the figure, which is smaller than the threshold value of -0.35, and the evaluation value SS increases as it moves away from the center. Yes (approaching 0).

Similarly, FIG. 11 shows the R10 material 2B before forging, and FIG. 12 shows the R10 material 2B after forging. Further, FIG. 13 shows an enlarged view of the bent portion 2b of the material 2B in FIG. 12. Referring to FIGS. 11 to 13, no flaws were generated in the material 2B due to the forging process. FIG. 14 is a contour diagram showing numerical simulation results corresponding to the experimental results of FIG. 13. In the contour diagram, the degree of reduction in surface area of the plurality of elements is displayed as an evaluation value.

Comparing and referring to FIGS. 9, 10, 13, and 14, unlike FIG. 9, no flaws have occurred in FIG. 13, and the evaluation value in FIG. 14 is larger than in FIG. 13 (the degree of decrease in surface area is smaller). It was confirmed that there is a correlation between the occurrence of defects and the degree of reduction in the surface area of the element. Note that in FIG. 14, the evaluation value SS is approximately −0.3 in the center of the figure, and the evaluation value SS becomes larger (closer to 0) as the distance from the center increases. As a result, it was confirmed that defects such as scratches are likely to occur in areas where the degree of reduction in the surface area of the element is greater than a predetermined value.

According to the present embodiment, the risk of defect occurrence is evaluated based on the degree of reduction in the surface area of each of the plurality of elements of the numerical simulation model. Therefore, even if the size of each of the plurality of elements is larger than the size of a defect such as a flaw that may occur, the risk of defect occurrence can be evaluated. Therefore, the risk of occurrence of minute defects can be evaluated without setting the element size so small. Therefore, the occurrence of minute defects can be predicted within a practical calculation time.

Furthermore, in this embodiment, the degree of reduction is calculated based on the initial surface area of each of the plurality of elements. Therefore, the degree of decrease can be easily calculated without complicating calculations.

Furthermore, in this embodiment, specific parts with a risk of defect occurrence are displayed on the screen (output unit 50) in the numerical simulation model, so parts with a high risk of defect occurrence can be visually recognized.

Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and can be implemented with various modifications within the scope of the present invention. For example, there are no particular restrictions on the shape or size of the material, and the present invention can be applied to materials of various shapes and sizes.

1 Numerical simulation defect occurrence risk evaluation device 2, 2A, 2B Material 2a, 2b Bending section 10 Model forming section 11 Model acquiring section 12 Element dividing section 13 Condition setting section 20 Calculating section 21 Initial surface area calculating section 22 Elapsed surface area calculating section 23 Decrease degree calculation unit 30 Storage unit 40 Evaluation unit 50 Output unit

Claims (4)

A defect occurrence risk evaluation method for numerical simulation using a finite element method in a forging process, the method comprising:
Obtain a numerical simulation model as shape data,
Divide the numerical simulation model into multiple elements,
calculating the initial surface area of each of the plurality of elements;
storing the calculated initial surface area;
Calculating the surface area of each of the plurality of elements while performing a numerical simulation of the forging process,
Calculating the degree of reduction in surface area for each of the plurality of elements as the numerical simulation of the forging process progresses,
A method for evaluating the risk of defect occurrence in numerical simulation, the method comprising: evaluating, in the numerical simulation model, a portion where an element exists whose degree of reduction is greater than a predetermined threshold value as a specific portion having a risk of defect occurrence. 2. The defect occurrence risk evaluation method using numerical simulation according to claim 1, wherein the degree of reduction is a ratio of the reduction to the initial surface area of each of the plurality of elements. The defect occurrence risk evaluation method for numerical simulation according to claim 1 or 2, wherein the specific portion is displayed on a screen. A defect occurrence risk evaluation device for numerical simulation using the finite element method in a forging process,
a model acquisition unit that acquires a numerical simulation model as shape data;
an element dividing unit that divides the numerical simulation model into a plurality of elements;
an initial surface area calculation unit that calculates an initial surface area of each of the plurality of elements;
a storage unit that stores the calculated initial surface area;
an elapsed surface area calculation unit that calculates the surface area of each of the plurality of elements while executing a numerical simulation of the forging process;
a reduction degree calculation unit that calculates the degree of reduction in surface area for each of the plurality of elements as the numerical simulation of the forging process progresses;
An evaluation device for evaluating the risk of defect occurrence in numerical simulation, comprising: an evaluation unit that evaluates, in the numerical simulation model, a portion in which an element exists whose degree of reduction is greater than a predetermined threshold value as a specific portion with a risk of defect occurrence.