JP6303815B2 - Forging crack prediction method, forging crack prediction program, and recording medium - Google Patents

Description

  The present invention relates to a forging crack prediction method, a forging crack prediction program, and a recording medium.

  In die forging in which a forged product is manufactured by forming a material with a die, if the plastic deformation of the material exceeds a limit, a crack occurs on the surface or inside of the forged product.

  In relation to this, the following Patent Document 1 proposes a method for predicting cracks in a forged product by performing a forming simulation using a finite element method. According to this method, since the crack of the forged product can be predicted by examination on the desk, the time and cost for product development can be reduced.

Japanese Patent Laid-Open No. 11-191098

  However, in the above method, the occurrence of cracks is predicted using an evaluation formula obtained by multiplying the stress in the material by the equivalent strain increment. For this reason, in the case of the plastic deformation in which the stress direction and the strain direction are different from each other, there is a problem that the crack of the forged product cannot be accurately predicted.

  The present invention has been made to solve the above-described problems. Accordingly, an object of the present invention is to provide a forging crack prediction method, a forging crack prediction program, and a recording medium capable of accurately predicting cracks in a forged product even when plastic deformation is different in stress direction and strain direction. It is to be.

  The above object of the present invention is achieved by the following means.

The present invention predicts cracks in the forged product by deformation analysis when a forged product is produced by forging a material with a mold. The present invention calculates, for each element of the finite element model of the material, the stress component, strain increment component and equivalent stress in each direction in the coordinate system of the model, and the stress component and strain increment component in the same direction are calculated. The predicted value for predicting cracks in the forged product is calculated for each direction. The present invention predicts cracking of the forged product by comparing a time integral value of the predicted value calculated for each direction with a threshold value .

  According to the present invention, forging cracks are evaluated using a predicted value obtained by multiplying a stress component and a strain increment component in the same direction, so that the stress direction and the strain direction are different in plastic deformation. Even if it exists, the crack of a forged product can be estimated correctly.

It is a block diagram which shows schematic structure of the analyzer with which the forge crack prediction method which concerns on one Embodiment of this invention is applied. 2A is a diagram illustrating an example of a material that is forged by a mold, and FIG. 2B is a diagram illustrating an example of a forged product that is obtained by forging a material using a mold. . It is a flowchart which shows the procedure of the forge crack prediction process performed by an analyzer. It is a figure which shows an example of the threshold value stored in the database. It is a figure which shows the analysis result of a forge crack prediction process. It is a photograph of the forged product in which cracking occurred during forging. It is a flowchart which shows the procedure of a general forge crack prediction process. It is a flowchart which shows the procedure of the forge crack prediction process which concerns on a modification. It is a figure which shows transition of the cumulative value of a crack prediction value. It is a figure which shows an example of a tripod type | mold constant velocity joint. It is a figure which shows an example of the metal mold | die used for the forge molding of a constant velocity joint.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of an analysis apparatus 1 to which a forging crack prediction method according to an embodiment of the present invention is applied.

  As shown in FIG. 1, the analysis device 1 includes a main body unit 10, a display unit 20, and an input unit 30. The display unit 20 and the input unit 30 are electrically connected to the main body unit 10. The analysis device 1 is, for example, a general computer.

  The main body unit 10 includes an arithmetic processing unit 11 and a storage unit 12. The arithmetic processing unit 11 includes a CPU and the like, and includes a model generation unit 111, an analysis unit 112, and a display information calculation unit 113. The storage unit 12 includes a ROM, a RAM, a hard disk, and the like, and stores various data such as shape data of a material that is forged by a mold and various programs such as a forging crack prediction program. In addition, the storage unit 12 is provided with a database 121 that stores threshold values that are referred to when determining the presence or absence of cracks in the forged product.

  The model generation unit 111 generates a finite element model of a material that is forged by a mold. The analysis unit 112 performs plastic deformation analysis using a finite element model of the material, and predicts cracks in the forged product. The display information calculation unit 113 performs processing for displaying the analysis result on the display unit 20. The functions of the model generation unit 111, the analysis unit 112, and the display information calculation unit 113 are exhibited when the CPU executes various programs stored in the storage unit 12.

  The display unit 20 is a liquid crystal display, for example, and displays various types of information. The input unit 30 is, for example, a pointing device such as a mouse or a keyboard, and is used for inputting various types of information.

  The analysis apparatus 1 configured as described above predicts cracks in a forged product by deformation analysis when a forged product is manufactured by forging a material with a mold. Hereinafter, the forging crack prediction method according to the present embodiment will be described with reference to FIGS.

  First, with reference to FIG. 2, the forged product which the analysis apparatus 1 estimates a crack is demonstrated. 2A is a diagram illustrating an example of a material 200 that is forged by the mold 300, and FIG. 2B is an example of a forged product that is obtained by forging the material 200 using the mold 300. FIG.

  As shown in FIG. 2A, the material 200 has a cylindrical shape (tube shape). Then, as shown in FIG. 2B, the forged product is manufactured by forward extrusion molding in which the cylindrical material 200 is pushed into the mold 300 to reduce the diameter of the material 200.

  In such forward extrusion molding, stress is generated in the central axis direction of the cylindrical material 200, while compressive strain is generated in the circumferential direction of the material 200. The analysis apparatus 1 predicts cracks in the forged product with respect to plastic deformation in which the stress direction and the strain direction are different.

  FIG. 3 is a flowchart showing a procedure of forging crack prediction processing executed by the analysis apparatus 1. In the forging crack prediction process, plastic deformation analysis is performed to calculate the stress and strain increment of each element of the finite element model of the material 200 at a minute time interval, and the crack of the forged product is predicted. Note that the algorithm shown in the flowchart of FIG. 3 is stored as a program in the storage unit 12 of the analysis apparatus 1 and is executed by the CPU.

First, the analysis apparatus 1 calculates the stress component σ _i and the strain increment component dε _i in each direction in the coordinate system of the finite element model for each element of the finite element model (step S101). Specifically, the analysis apparatus 1 performs deformation analysis using a finite element model of the material 200, and for each element of the finite element model, each direction i (radial direction r, circumferential direction θ, The stress component σ _i and the strain increment component dε _{i in the} height direction z) are respectively calculated. Since the technique itself for calculating the stress component and the strain increment component of each element in the deformation analysis using the finite element model is a known technique, detailed description thereof is omitted.

Next, the analysis apparatus 1 calculates the equivalent stress σ (step S102). Specifically, the analysis apparatus 1 calculates the equivalent stress σ from the stress components σ _{i in} the three directions r, θ, and z of the polar coordinate system calculated in the process shown in step S101. In addition, since the technique itself which calculates equivalent stress from the stress component of each direction of a polar coordinate system is also a well-known technique, detailed description is abbreviate | omitted.

Next, the analysis apparatus 1 calculates the crack prediction value dD _i in each direction (step S103). Specifically, the analysis apparatus 1 multiplies each of the three directions r, θ, and z of the polar coordinate system by the stress component σ _i calculated in the process shown in step S101 and the strain increment component dε _i to forge. A crack prediction value dD _i for predicting a crack of the product is calculated. More specifically, the analysis apparatus 1 calculates the product of the stress component σ _i and the strain increment component dε _i calculated in the process shown in step S101 by the process shown in step S102, as shown in the following equation (1). The crack prediction value dD _i is calculated by dividing by the equivalent stress σ.

Here, σ _i is a stress component in the direction i, σ is an equivalent stress, dε _i is a strain increment component in the direction i, and i is a radial direction r, a circumferential direction θ, and a height direction z in the polar coordinate system. .

Next, the analysis apparatus 1 calculates a cumulative value D _i of crack prediction values dD _{i in} each direction (step S104). Specifically, the analysis apparatus 1 adds the crack prediction value dD _i calculated in the process shown in step S103 to the cumulative value D _i for each of the three directions r, θ, and z of the polar coordinate system, thereby predicting the crack. updating the cumulative value _{D i} value dD _i. In other words, the analysis apparatus 1, as shown in the following equation (2), calculates the time integral value of the crack prediction value dD _i.

  Next, the analyzing apparatus 1 determines whether or not the step has been completed (step S105). Specifically, the analysis apparatus 1 determines whether or not the step corresponding to the minute time of the analysis unit has reached the final step.

  When determining that the step has not ended (step S105: NO), the analysis apparatus 1 returns to the process of step S101. And the analysis apparatus 1 repeats the process of step S101-S104 until a step is complete | finished.

  On the other hand, when determining that the step is completed (step S105: YES), the analysis apparatus 1 refers to the database 121 (step S106). Specifically, the analysis device 1 reads the threshold value stored in the database 121 with reference to the database 121.

  FIG. 4 is a diagram illustrating an example of threshold values stored in the database 121. A plurality of threshold values are stored in the database 121, and each threshold value is associated with the type of the material 200 and the content of pre-processing (such as normalization processing) applied to the material 200. The analysis apparatus 1 reads a threshold value associated with the type of material used for analysis and the content of preprocessing from a plurality of threshold values stored in the database 121. For example, when the type of the material 200 is the type C and the content of the preprocessing is the processing A, the analysis apparatus 1 reads the threshold value 0.43.

And the analysis apparatus 1 judges the presence or absence, direction, and position of a crack (step S107), and complete | finishes a process. Specifically, the analysis apparatus 1 compares the cumulative value D _i of the crack prediction values dD _{i in} each direction calculated in the process shown in step S104 with the threshold value read in the process shown in step S106, and the occurrence of cracks. Determine the presence or absence. In this embodiment, three directions r in a polar coordinate system, theta, of the three cumulative value D _i calculated respectively for z, if at least one of the cumulative value exceeds the threshold value, the analysis apparatus 1, cracks Judge that it occurs. Moreover, the analysis apparatus 1 determines the generation | occurrence | production position of the crack in a forging from the position in the finite element model of the element which shows the cumulative value exceeding the threshold value. Furthermore, the analysis apparatus 1 determines the direction of cracking by comparing the cumulative values D _i in the three directions r, θ, and z.

As described above, according to the processing of the flowchart shown in FIG. 3, the stress component and the strain increment component of each element are calculated for each of the three directions r, θ, z of the polar coordinate system every minute time. . By the incremental component strain in the same direction of the stress components are multiplied, cracking predicted value dD _i in each direction is calculated. Then, the cumulative value D _i of cracks predicted value dD _i in each direction is compared with a predetermined threshold value, occurrence of cracks can be determined. At the same time, the position where the crack occurs and the direction of the crack are also determined.

  FIG. 5 is a diagram showing an analysis result of forging crack prediction processing, and FIG. 6 is a photograph of a forged product in which cracking occurred during forging.

FIG. 5A is a diagram showing a distribution of cumulative values _Dθ of crack prediction values calculated by the forging crack prediction process of the present embodiment. FIG. 5B is a diagram showing a distribution of cumulative value D of crack prediction values calculated by a general forging crack prediction process as shown in the flowchart of FIG. 7 as a comparative example.

As described above, in the forging crack prediction process of the present embodiment, analysis is performed for each of the three directions r, θ, and z in the polar coordinate system. FIG. 5A shows the analysis result in the circumferential direction θ among the analysis results in the three directions. As shown in FIG. 5A, referring to the analysis result in the circumferential direction θ of the polar coordinate system, the element indicating the accumulated value D _θ exceeding the threshold value is surrounded by the tip of the forged product (circled in FIG. 5A). Present).

  Therefore, according to the forging crack prediction process of the present embodiment, it is predicted that a crack will occur from the tip of the cylindrical material 200 so as to tear in the circumferential direction. And this prediction result corresponds with the tendency of the crack which arose in the actual forging shown in FIG. That is, according to the forging crack prediction process of the present embodiment, it is possible to accurately predict cracks in the forged product.

  On the other hand, as shown in FIG. 5B, in a general forging crack prediction process, the element at the tip of the cylindrical material 200 shows a cumulative value D equal to or lower than the threshold value, and the tip of the cylindrical material 200 It is not predicted that cracking will occur. Therefore, a general forging crack prediction process cannot accurately predict cracks in a forged product.

In the general forging crack prediction process shown in the flowchart of FIG. 7, first, the stress component σ _i and strain increment component dε _i in each direction in the polar coordinate system are calculated for each element of the finite element model (step S201). ). Subsequently, the maximum principal stress σ _max , the equivalent stress σ, and the equivalent strain increment dε are calculated from the stress component σ _i and the strain increment component dε _i in each direction (step S202). Then, as shown in the following equation (3), a value obtained by dividing the product of the maximum principal stress σ _max and the equivalent strain increment dε by the equivalent stress σ is calculated as the predicted crack value dD (step S203).

  Then, as shown in the following equation (4), the cumulative value D of the crack prediction value dD is calculated (step S204), and the position where the crack occurs is determined based on the magnitude of the cumulative value D of the crack prediction value dD. (Step S206).

  As described above, in a general forging crack prediction process, the occurrence of cracks is predicted using a calculation formula obtained by multiplying the maximum principal stress and the equivalent strain increment. For this reason, according to a general forging crack prediction process, in the case of plastic deformation in which the direction of the stress and the equivalent strain increment is different, the presence or absence of cracks in the forged product and the occurrence position of the cracks cannot be accurately predicted. Further, since the equivalent strain increment is a non-directional scalar amount, the forging crack prediction direction cannot be predicted according to a general forging crack prediction process.

  On the other hand, in the forging crack prediction process of this embodiment, the occurrence of cracks is predicted using a calculation formula obtained by multiplying the stress component and strain increment component in the same direction. For this reason, even if it is the plastic deformation from which a stress direction and a strain direction differ, the presence or absence of a crack of a forging, the generation | occurrence | production position of a crack, and the direction of a crack can be estimated correctly.

  Furthermore, according to the forging crack prediction process of the present embodiment, the mold specifications can be determined by hooding back the crack prediction results to the mold design.

  FIG. 8 is a flowchart showing a procedure of forging crack prediction processing according to the modification.

  Steps S101 to S107 are the same as the processing of the flowchart shown in FIG.

  After determining whether or not there is a crack in the process shown in step S107, the analysis apparatus 1 determines whether or not there is a crack (step S108). If it is determined that there is no crack (step S108: YES), the analysis apparatus 1 ends the process.

  On the other hand, when determining that there is a crack (step S108: NO), the analysis apparatus 1 changes the specification of the mold 300 (step S109) and returns to the process of step S101. Specifically, the analysis apparatus 1 first changes the specifications such as the inclination angle of the inclined portion and the roundness (R) of the corner portion for reducing the diameter of the material 200 with respect to the shape model of the mold 300 used for the analysis. To do. And the analysis apparatus 1 returns to the process of step S101, applies the new shape model of the metal mold | die 300, and repeats the process of step S101-S107.

  According to such a configuration, it is possible to easily design the mold 300 in which cracks do not occur in the forged product without producing the mold by trial and error.

  Next, with reference to FIG. 9, a method for determining a threshold value that is referred to when determining the presence or absence of a crack will be described. In the present embodiment, the threshold is determined based on the results obtained by actually manufacturing a plurality of forgings having different drawing ratios and the cumulative values of the plurality of predicted crack values calculated for each of the plurality of forgings. To do.

  FIG. 9 is a diagram showing the transition of the cumulative value D of crack prediction values. The horizontal axis in FIG. 9 is the molding time, and the vertical axis is the cumulative value D of the predicted crack value. In FIG. 9, the analysis is performed by changing the aperture ratio of the material 200 in three stages. At the same time, a forged product is manufactured by actually performing forward extrusion molding, and it is confirmed whether or not a crack has occurred in the manufactured forged product.

  As shown in FIG. 9, the cumulative value D of crack prediction values increases as the drawing ratio of the material 200 increases. Then, from the result of actually manufacturing the forged product, no cracking occurs in the forged product whose cumulative value D of the predicted crack value is 0.4, and the forged product whose cumulative value D of the predicted crack value exceeds 0.4. It can be seen that cracking occurs. Therefore, if the threshold is set to 0.4, the presence or absence of cracks can be correctly determined.

  In the present embodiment, by changing the type of material and the content of preprocessing applied to the material and repeating the above threshold determination procedure, a plurality of threshold values that differ depending on the type of material and the content of preprocessing are set. decide. The plurality of threshold values are stored in the database 121 in association with the type of material and the content of preprocessing.

  According to such a configuration, a threshold value common to all forged products can be determined. Therefore, it is possible to omit the correlation work for determining the threshold value by comparing the analysis result and the prototype result for each forged product.

  As described above, in the embodiment described above, the case of predicting cracks in a forged product has been described for forward extrusion molding in which a cylindrical material is pressed into a mold to reduce the diameter of the material. However, the present invention can also be applied to forward extrusion molding that expands the diameter of a cylindrical material. Alternatively, the present invention can also be applied to lateral extrusion.

  FIG. 10 is a view showing an example of a tripod type constant velocity joint 400 of an automobile. As shown in FIG. 10, the constant velocity joint 400 includes a drum-shaped main body portion 410 and three protruding portions 420 that protrude laterally from the main body portion 410.

  FIG. 11 is a view showing an example of a mold 500 used for forging of the tripod constant velocity joint 400. The constant velocity joint 400 is manufactured by pressing a material disposed in the die 510 from above and below with a punch 520 and projecting a part of the material to the side. In such side extrusion molding, depending on the shape of the forged product, the amount of deformation of the raw material increases, and there is a risk that cracks may occur in the forged product.

  According to the forging crack prediction process of the present embodiment, cracks can be accurately predicted for a forged product manufactured by side extrusion molding such as a tripod type constant velocity joint.

  As described above, the described embodiment has the following effects.

  (A) Since the crack of the forged product is evaluated using the predicted value obtained by multiplying the stress component and the strain increment component in the same direction, even if the plastic deformation is different between the stress direction and the strain direction. It is possible to accurately predict cracks in forged products. Specifically, it is possible to accurately predict the presence / absence of a crack, the position where the crack occurs, and the direction of the crack. As a result, it becomes easy to take measures such as mold design change.

  (B) Since the threshold value is associated with the type of material and the content of the pretreatment applied to the material, and different threshold values are used depending on the type of material and the content of the preprocessing, It can be judged accurately.

  (C) Since the threshold value is determined based on a result obtained by actually manufacturing a plurality of forgings having different drawing ratios and a cumulative value of predicted crack values calculated for the plurality of forgings, forging Correlation work for determining the threshold value can be omitted by comparing the analysis result with the prototype result for each product.

  (D) If it is predicted that cracks will occur in the forged product, the analysis is repeated by changing the specifications of the mold, so trial and error mold prototyping can be omitted.

  (E) Since the crack of the forged product manufactured by forward extrusion molding can be accurately predicted, the time and cost required for the development of the forged product manufactured by forward extrusion molding can be reduced.

  (F) Since the crack of the forged product manufactured by the side extrusion molding can be accurately predicted, the time and cost required for the development of the forged product manufactured by the side extrusion molding can be reduced.

  As described above, in the described embodiment, the forging crack prediction method and the forging crack prediction program of the present invention have been described. However, it goes without saying that the present invention can be appropriately added, modified, and omitted by those skilled in the art within the scope of the technical idea.

  For example, in the above-described embodiment, the cumulative value of the predicted crack value is calculated, and it is determined whether or not a crack occurs from the cumulative value of the predicted crack value. However, the cumulative value of the predicted crack value is not necessarily calculated. For example, it may be directly determined from the predicted crack value whether or not a crack will occur.

  In the above-described embodiment, the threshold is associated with the type of material and the content of preprocessing applied to the material, and a different threshold is used depending on the type of material and the content of preprocessing. However, the forging conditions associated with the threshold value are not limited to the type of material and the content of the pretreatment, and the threshold value may be associated with the temperature at which the material is forged.

  In the above-described embodiment, when the threshold value is determined, the aperture ratio of the cylindrical material is changed in three stages, and the analysis result and the prototype result are compared. However, the analysis result and the prototype result may be compared by changing the thickness of the cylindrical material in a plurality of stages.

  In the above-described embodiment, when the predicted crack value is calculated, the product of the stress component in the same direction and the strain increment component is divided by the equivalent stress, and the stress component is made dimensionless. However, the stress component may not be made dimensionless.

  In the above-described embodiment, the case where the plastic deformation analysis is performed using the polar coordinate system is described as an example. However, the coordinate system used for the plastic deformation analysis is not limited to the polar coordinate system, and may be an XYZ orthogonal coordinate system. In this case, the stress component and the strain increment component of each element are calculated for each of the X direction, the Y direction, and the Z direction.

  The means for performing various processes in the analysis apparatus according to the above-described embodiment can be realized by either a dedicated hardware circuit or a programmed computer. The program may be provided by a computer-readable recording medium such as a CD-ROM, or may be provided online via a network such as the Internet. In this case, the program recorded on the computer-readable recording medium is normally transferred to and stored in a storage unit such as a hard disk.

1 analysis equipment,
10 Main body,
11 arithmetic processing unit,
12 storage unit,
20 display section,
30 input section,
111 model generator,
112 analysis unit,
113 Display information calculation unit,
121 database,
200 materials,
300,500 molds,
400 Tripod type constant velocity joint.

Claims (13)

A forging crack prediction method for predicting cracking of the forged product by deformation analysis when forging a material by a die and manufacturing a forged product,
For each element of the finite element model of the material, calculating a stress component, a strain increment component and an equivalent stress in each direction in the coordinate system of the model;
Dividing the product of the stress component and the strain increment component in the same direction by the equivalent stress, and calculating a predicted value for predicting cracks in the forged product for each direction (b);
(C) predicting cracks in the forged product by comparing a time integral value of the predicted value calculated for each direction with a threshold value ;
A forging crack prediction method having If the cumulative value of the predicted value exceeds a predetermined threshold, it is determined that cracks occur in the forged product in the step (c),
The threshold value is associated with at least one forging condition among the type of the material, the content of pretreatment applied to the material, and the temperature during forging of the material, and varies depending on the forging condition. The forging crack prediction method according to claim 1, wherein the threshold value is used.   The threshold value is based on a result obtained by actually manufacturing a plurality of forgings having different dimensions of the specific part, and each cumulative value of the plurality of predicted values respectively calculated for the plurality of forgings. The forging crack prediction method according to claim 2 to be determined. When it is determined in the step (c) that cracks occur in the forged product, the step (d) of changing the specifications of the mold,
The forging crack according to any one of claims 1 to 3, further comprising a step (e) of applying the changed specifications of the mold and repeating the steps (a) to (c). Prediction method.   The forging crack prediction method according to any one of claims 1 to 4, wherein the forged product is manufactured by forward extrusion molding in which a cylindrical material is pushed into a mold to change the diameter of the material.   The said forged product is manufactured by the side extrusion which presses the raw material in a metal mold | die in a 1st direction, and makes a part of said raw material protrude in the 2nd direction different from the said 1st direction. 5. The forging crack prediction method according to any one of 4 above. A forging crack prediction program for predicting cracks of the forged product by deformation analysis when forging is produced by forging a material with a mold,
(A) calculating a stress component, a strain increment component, and an equivalent stress in each direction in the coordinate system of the model for each element of the finite element model of the material;
Dividing the product of the stress component and the strain increment component in the same direction by the equivalent stress and calculating a predicted value for predicting cracks in the forged product for each direction (b);
A step (c) for predicting cracks in the forged product by comparing a time integral value of the predicted value calculated for each direction with a threshold value ;
Forging crack prediction program that makes the computer execute. When the cumulative value of the predicted values exceeds a predetermined threshold, it is determined that cracks occur in the forged product in the procedure (c),
The threshold value is associated with at least one forging condition among the type of the material, the content of pretreatment applied to the material, and the temperature during forging of the material, and varies depending on the forging condition. The forging crack prediction program according to claim 7, wherein the threshold value is used.   The threshold value is based on a result obtained by actually manufacturing a plurality of forgings having different dimensions of the specific part, and each cumulative value of the plurality of predicted values respectively calculated for the plurality of forgings. The forging crack prediction program according to claim 8 to be determined. When it is determined in the step (c) that the forged product is cracked, a step (d) for changing the specifications of the mold,
The procedure (e) of repeating the procedure (a) to the procedure (c) by applying the changed specifications of the mold, and further causing the computer to execute the procedure (10). The forging crack prediction program described.   The forged crack prediction program according to any one of claims 7 to 10, wherein the forged product is manufactured by forward extrusion molding in which a cylindrical material is pushed into a mold to change the diameter of the material.   The said forged product is manufactured by the side extrusion which presses the raw material in a metal mold | die in a 1st direction, and makes a part of said raw material protrude in the 2nd direction different from the said 1st direction. The forging crack prediction program according to any one of 10 above.   The computer-readable recording medium which recorded the forge crack prediction program of any one of Claims 7-12.