JP2011218389A - Method of evaluating installation position of detection sensor for detecting breaking of blank - Google Patents

Abstract

The present invention provides a method capable of evaluating the installation position of a blank material breakage detection sensor so as to reliably detect a molding abnormality in which a blank material is broken during press molding.
A molding bottom dead center that is equal to or greater than a predetermined threshold value among contact surface pressures P ₀ when reaching a molding bottom dead center when a press molding tool reaches a molding bottom dead center, calculated for each blank material element. extract the blank elements of the blank element and its surroundings showing an arrival time of the contact surface pressure P _0, among the extracted blank element separates the binding of the blank element adjacent to one another, again, a finite By applying the element method, the contact surface pressure P _i when reaching the bottom dead center for reference is calculated for each blank element, and ΔP that is the absolute value | P ₀ −P _i | of the difference between P ₀ and P _{i i} is examined and evaluated for each press-forming tool element corresponding to the blank material element.
[Selection] Figure 1

Description

  The present invention relates to a method for evaluating the position of a sensor that detects that a blank has been damaged during press molding. Specifically, the present invention relates to a blank material breakage detection sensor installation position evaluation method using a finite element method.

  When a blank material is press-molded using a press-molding tool composed of punches, dies, wrinkle holding molds, etc., the curved convex shape formed on the surface (molding surface) of the press-molding tool, especially small When transferring beads or protrusions with a radius of curvature to the blank material, cracks, wrinkles, and necking that causes plastic deformation on the specific cross-section of the blank material to cause necking, etc., will cause the blank material to break. Becomes a problem.

  Such cracks, wrinkles, necking, etc. are small in size and not so high in frequency, so it is difficult to find these molding abnormalities in the manufacturing process.

  The breakage of the blank material is caused by an increase in contact surface pressure generated by the frictional force between the blank material and the press molding tool during press molding.

  Some of the present inventors have proposed in Patent Document 1 and Non-Patent Document 1 to detect such an increase in contact surface pressure with a piezoelectric sensor installed inside a press-forming tool.

  This is based on the principle that a piezoelectric sensor detects that the press molding tool slightly elastically deforms due to an increase in contact surface pressure.

JP 2009-12043 A

“Development of integrated high-strength steel sheet forming technology (development of mold friction sensor)”, Proceedings of the 57th Joint Conference on Plasticity Processing (October 31 to November 2, 2006, Takaoka Chamber of Commerce and Industry Building) ), Published by the Japan Society for Technology of Plasticity (October 17, 2006), pp. 165-166

  The method described in Patent Document 1 and Non-Patent Document 1 in which a piezoelectric sensor is installed inside a press molding tool breaks the blank material such as cracks, wrinkles, and necking in the blank material during press molding. When a molding abnormality occurs, if the installation location of the piezoelectric sensor is appropriate, the molding abnormality can be detected even if the blank material is slightly damaged.

  Therefore, the piezoelectric sensor installed inside the press molding tool can be used as a blank material breakage detection sensor during press molding.

  However, the determination of the installation location of the blank material breakage detection sensor often depends on the experience and knowledge of the designer of the press-formed product and the press-forming tool.

  In recent years, especially in automobiles, the shape of press-molded products tends to become complicated, and it is difficult to accurately determine the installation position of the blank material breakage detection sensor only with the experience and knowledge of the designer. It has become to.

  In view of the above circumstances, the present invention ensures that a molding abnormality is detected when a blank material breakage detection sensor for detecting a molding abnormality in which a blank material is damaged during press molding is installed inside a press molding tool. It aims at providing the blank material breakage detection sensor installation position evaluation method which can examine and evaluate the installation position of a blank material breakage detection sensor so that it can detect.

  In order to achieve the above object, the present inventors applied a finite element method to an analytical model having a press forming tool element defining a press forming tool and a blank material element defining a blank material, Various analyzes were conducted and studies were repeated.

  As a result, using a model having a press forming tool element that defines a tool for press forming and a blank material element that defines a blank material, the press forming tool is formed after contacting the blank material. The finite element method is applied to press forming until reaching the bottom dead center, and occurs between the press forming tool and the blank when the press forming tool reaches a predetermined position before the bottom dead center. The contact surface pressure when reaching a predetermined position before forming the bottom dead center is calculated, and the portion of the blank material where the contact surface pressure when reaching the predetermined position before forming bottom dead center is a predetermined threshold or more is extracted, and the blank of the portion A modified model that restricts the exchange of numerical values in the finite element method between the blank material elements adjacent to each other among the material elements is created, and the finite element method is applied again to the modified model to make the reference molding dead Pointed hand The contact surface pressure when reaching a predetermined position is calculated, and the difference between the contact surface pressure when reaching a predetermined position before the molding bottom dead center and the contact surface pressure when reaching a predetermined position before the molding bottom dead center for reference is greater than a predetermined value It was predicted that the blank material would be damaged, and the idea was to determine the installation position of the blank material breakage detection sensor on the press-forming tool.

And, when the forming bottom dead center is reached at a predetermined threshold value or more of the contact surface pressure P ₀ when reaching the forming bottom dead center when the press forming tool reaches the forming bottom dead center, calculated for each blank material element The blank material element indicating the contact surface pressure P ₀ and the surrounding blank material elements are extracted, and among the extracted blank material elements, the adjacent blank material elements are separated from each other, and the finite element method is performed again. Is applied to calculate the contact surface pressure P _i when reaching the reference forming bottom dead center for each blank element, and ΔP _i which is the absolute value | P ₀ −P _i | of the difference between P ₀ and P _i is calculated. The present inventors have found that the optimum installation position of the sensor for detecting breakage of the blank material can be selected by examining each press forming tool element corresponding to the blank material element.

  The present invention has been completed with further improvements based on the above findings, and the gist thereof is as follows.

(1) Using a model having a press forming tool element that defines a press forming tool and a blank material element that defines a blank material, the press forming tool comes into contact with the blank material and then is molded. Forming that occurs between the press-forming tool and the blank material when the finite element method is applied to the press-forming process until reaching the dead point and the predetermined position before the bottom dead center of the press-forming tool is reached The contact surface pressure when reaching a predetermined position before the bottom dead center is calculated, and the portion of the blank material where the contact surface pressure when reaching the predetermined position before the formed bottom dead center is a predetermined threshold or more is extracted, and the blank material of the portion Among the elements, create a modified model that restricts the exchange of numerical values in the finite element method between the blank material elements adjacent to each other, and apply the finite element method to the modified model again to form the reference bottom dead center for reference. Pre-specified The contact surface pressure when reaching the position is calculated, and the difference between the contact surface pressure when reaching the predetermined position before the molding bottom dead center and the contact surface pressure when reaching the predetermined position before the molding bottom dead center for reference is greater than a predetermined value. The blank material breakage detection sensor installation position evaluation method, wherein the blank material breakage detection sensor is predicted to be broken, and the installation position of the blank material breakage detection sensor on the press forming tool is determined.

(2) a primary analysis model creation step for creating a primary analysis model for a finite element method having a press molding tool element defining a press molding tool and a blank material element defining a blank material; ,
The finite element method using the first analysis model is applied to the press molding process from when the press molding tool contacts the blank material until reaching the molding bottom dead center, and the press molding tool When the predetermined position before the bottom dead center is reached, the contact surface pressure P _f when the predetermined position before the bottom bottom point is generated between the press molding tool and the blank, and the bottom dead center of the press molding tool is formed. When reaching a point, the contact surface pressure P ₀ at the time of forming bottom dead center arrival generated between the blank material and the press molding tool is calculated for each press molding tool element and for each blank material element, A first analysis step;
Wherein one of the molding bottom dead center reaches when the contact surface pressure P ₀ is calculated the blank elements, the blank elements when the contact surface pressure predetermined threshold or more of the forming bottom dead center reaches P ₀ is calculated, extracting a high P ₀ blank elements, and the high P ₀ blank element extracting step,
The blank elements existing within a predetermined range from the high P ₀ blank element is extracted as the peripheral blank elements, and a peripheral blank element extracting step,
The extraction blank element made of the high P ₀ blank element and the peripheral blank elements, two of the extraction blank elements configured i set adjacent to each other (where, i is the 1~n integer) of and the blank element sets a _i, and the blank element sets a _i generation step,
For nodes N _{i, 1} and N _{i, 2} shared by the extraction blank material element S _{Ai, 1} and the extraction blank material element S _{Ai, 2} constituting the blank material element group A _i , N _{i, 1} is represented by N _{i. , 1a} and _{Ni, 1b, Ni , 2} are separated into _{Ni , 2a} and _{Ni, 2b,} and the blank material element group _Ai is extracted with the extracted blank material element S _{Bi, 1} and the extracted blank material. A blank material element set A _i → B _i conversion step for converting into a blank material element set B _i composed of the elements S _{Bi, 2} ;
The blank element sets A _i of the first-order analysis model, the (i + 1) is replaced with the blank element sets B _i to create a model for the next analysis, the (i + 1) th model creation step for the next analysis When,
Based on the contact surface pressure P _f when reaching a predetermined position before the molding bottom dead center, the press molding process until the press molding tool reaches the bottom molding bottom dead center after contacting the blank material, A finite element method using the (i + 1) th order analysis model is applied, and the contact surface pressure P _i when reaching the reference bottom dead center relative to the contact surface pressure P ₀ when reaching the bottom bottom dead center is determined as the _value for the press molding. (I + 1) order analysis step for calculating each tool element and each blank material element after converting the blank material element set A _i to the blank material element set B _i ;
ΔP _i which is an absolute value | P ₀ −P _i | of the difference between the contact surface pressure P ₀ when reaching the forming bottom dead center and the reference forming bottom dead center contact surface pressure P _i is the forming tool element for pressing. And ΔP _i calculating step for calculating each blank material element after converting the blank material element set A _i to the blank material element set B _i ;
For the integer i of 1 to n, the blank material element group A _i → B _i conversion step, the (i + 1) th order analysis model creation step, the (i + 1) th order analysis step, and the ΔP _i calculation step are repeated. run, for each of the press-molding tool element, summing basis of [Delta] P _i in the following equation (1), and [Delta] P _i sum calculation step,
Wherein among the [Delta] P _i sum, the press-molding tool elements each [Delta] P _i sum which defines the molding surface of the press-molding tool, and outputs the index strain press molding tool molding surface, press molding tool molding surface A strain index output step;
The installation position of the sensor for detecting breakage of the blank material during press forming is determined to be within a predetermined depth from the press forming tool element having a press forming tool forming surface strain index of a predetermined value or more. , Blank material breakage detection sensor installation position determination step,
The blank material breakage detection sensor installation position evaluation method according to (1) above, characterized by comprising:

(3) The blank material breakage detection sensor installation position evaluation method according to (1) or (2) above, wherein the predetermined position before the molding bottom dead center is 5 mm before the molding bottom dead center.

(4) The blank material breakage according to any one of the above (1) to (3), wherein the press molding tool element is a rigid element, and the blank material element is an elastic-plastic deformable shell element. Detection sensor installation position evaluation method.

(5) The press-forming tool forming surface strain index is output as a contour map (contour diagram) of the press-forming tool forming surface, according to any one of (1) to (4) above. Blank material breakage sensor installation position evaluation method.

(6) The blank material breakage detection sensor installation position evaluation method according to any one of (1) to (5), wherein the blank material breakage detection sensor is a piezoelectric sensor.

(7) The blank material breakage detection sensor installation position evaluation method according to any one of (1) to (6), wherein the predetermined depth is 15 mm.

  According to the present invention, even if the press molding tool has a three-dimensionally complicated shape, the installation position of the sensor that detects the molding abnormality that causes the blank material to be damaged during press molding can be determined. In the design stage before production, it is possible to examine, evaluate and determine in advance by numerical analysis, and it is possible to easily find a press-formed product in which a forming abnormality has occurred.

It is a flowchart explaining the blank material breakage detection sensor installation position evaluation method of this invention. Is a view for explaining the blank element sets A _i → B _i conversion step, (a) shows the nodal structure of the blank element sets A _i before the conversion, (b) the blank element pair B _i conversion after the conversion The node composition of is shown. One of the two extraction blank adjacent each other, in the case of three nodes, to convert the blank element sets A _i in the blank element group B _i, the blank element sets A _i → B _i conversion It is a view for explaining the steps, indicating (a) shows a node structure of the blank element sets a _i before the conversion, (b) the nodal structure of the blank element sets B _i after the conversion. It is a figure which shows the external appearance of the vehicle body member for motor vehicles which applies the blank material breakage detection sensor installation position evaluation method of this invention. Is a diagram showing the distribution of the extracted high P ₀ blank elements and peripheral blank elements. 2 shows a distribution of press forming tool elements defining a forming surface of a press forming tool having a press forming tool forming surface strain index of 5% or more and less than 10% of a contact surface pressure P ₀ when forming bottom dead center is reached. FIG. It is a figure which shows distribution of the tool element for press molding which defined the molding surface of the tool for press molding whose press molding tool surface distortion index is 10% or more of the contact surface pressure P ₀ at the time of forming bottom dead center arrival. .

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart illustrating a blank material breakage detection sensor installation position evaluation method according to the present invention. Hereinafter, each step shown in FIG. 1 will be described.

(Step S1)
First, a model for applying the finite element method is created. The created model for the finite element method has a press forming tool element that defines a press forming tool such as a punch, a die, and a wrinkle holding die, and a blank material element that defines a blank material. This is used for the primary analysis executed in step S2, and is referred to as a primary analysis model.

  During actual press forming, the press forming tool is also slightly elastically deformed. However, the amount of elastic deformation of the press forming tool is much smaller than the amount of elastic plastic deformation of the blank material. The press forming tool is preferably defined by a rigid element that does not consider elastic deformation.

  During press forming, the same force is applied to both the press forming tool and the blank due to the law of action and reaction, but it is calculated by the finite element method by defining the press forming tool as a rigid element. The difference in the force acting on the press molding tool depending on the part of the press molding tool becomes clear and convenient.

  Since the blank material is usually a thin plate having a thickness of 1.5 to 5.0 mm, the blank material element is preferably defined as a shell element. Further, since the blank material is not only elastically deformed by press molding, but also greatly plastically deformed, it is preferable to define the blank material element as a shell element that can be elastically plastically deformed.

(Step S2)
In the first analysis, the analysis starts when the press-forming tool comes into contact with the blank material, and the analysis ends when the press-forming tool reaches the forming bottom dead center. For the analysis, a commercially available elastic-plastic analysis solver can be used.

  Data calculated as a result of the primary analysis is a contact surface pressure generated between the blank material and the press molding tool, and is output for each press molding tool element and each blank material element. In the following description, when simply referred to as “contact surface pressure”, it means “contact surface pressure generated between the blank material and the press molding tool” unless otherwise specified. .

The contact surface pressure is output at each time step set before starting the first analysis, but the contact surface pressure when the press molding tool reaches a predetermined position before the molding bottom dead center is determined by the molding bottom dead center. It is stored in the output file of the finite element method as the contact surface pressure P _f when reaching a predetermined position before the dot. Similarly, the contact surface pressure when the press forming tool reaches the forming bottom dead center is stored in the output file of the finite element method as the contact surface pressure P ₀ when the forming bottom dead center is reached.

(Step S3)
The contact surface pressure P ₀ when reaching the forming bottom dead center is output to all the press forming tool elements and the blank material elements, and among them, the contact surface pressure when reaching the forming bottom dead center equal to or more than a predetermined threshold value. The blank material element for which P ₀ is output is extracted. Extracted blank element is referred to as a high P ₀ blank elements.

The predetermined threshold value is described in the input file of the finite element method before the analysis is started, or the contact surface pressure P ₀ when reaching the forming bottom dead center is a contour diagram on the forming surface of the press forming tool ( The threshold value may be determined after confirming the distribution of the contact surface pressure P ₀ when reaching the forming bottom dead center.

There is a correlation between the contact surface pressure P ₀ when reaching the molding bottom dead center and the tension acting on the blank material. Generally, when the contact surface pressure P ₀ when reaching the molding bottom dead center increases, the tension acting on the blank material also increases, This means that the blank is damaged.

When the contact surface pressure P ₀ when reaching the bottom dead center of the molding exceeds a predetermined threshold value, if the tension acting on the blank material greatly exceeds the tensile strength, a large breakage occurs during press molding, and the frequency of occurrence is also Very expensive.

  The blank material breakage detection sensor installation position evaluation method of the present invention is intended to detect a forming abnormality caused by a minute breakage of a blank material that occurs during press forming, and the occurrence frequency is not so high.

Therefore, when a blank material element showing the contact surface pressure P ₀ at the time of reaching the forming bottom dead center greatly exceeding a predetermined threshold is recognized, the shape of the press-formed product (the shape of the press-forming tool) and the forming conditions are changed. The threshold value is determined after performing the primary analysis again.

  The threshold is determined based on the tensile strength of the blank material, taking into account the molding conditions such as the shape of the press-molded product, molding pressure, molding speed, type of lubricant (lubricating oil), etc. It is preferable to set it as 10% of the contact surface pressure P calculated from the following formula (2).

ここで、ｔ：ブランク材の板厚、Ｔ_B：ブランク材の引張強さ、ｒ：ブランク材とプレス成形用工具との接触部の曲率半径である。

Here, t is the thickness of the blank material, T _{B is} the tensile strength of the blank material, and r is the radius of curvature of the contact portion between the blank material and the press molding tool.

For example, when t = 0.7 mm, T _B = 280 MPa, and r = 10 mm, the contact surface pressure P = 17.6 MPa is calculated, so 1.76 MPa, which is 10%, is set as the threshold value.

  In addition, when several r (the curvature radius of the contact part of a blank material and the tool for press molding) exists in a press molded product, the smallest value is employ | adopted as r among them.

  The smaller the r, the higher the contact surface pressure P and the more easily the blank material breaks. Therefore, by adopting the smallest value among r as the r, the threshold value is set at the most easily damaged portion of the entire blank material. It will be decided.

(Step S4)
In the actual press molding, the periphery of the portion corresponding to the high P ₀ blank material element of the blank material is due to variations in molding conditions, etc., even if the contact surface pressure P ₀ when reaching the bottom dead center of molding is less than the threshold It is often damaged. Therefore, a blank material element existing within a predetermined range from the high P ₀ blank material element is extracted as a peripheral blank material element and handled in the same manner as the high P ₀ blank material element.

Here, the predetermined range may be, for example, “within the shape of the press-formed product within the range from the high P ₀ blank material element to the surrounding 10 blank material element or from the high P ₀ blank material element to the surrounding 20 blank material element. When there is a deep drawing shape of R5 or less or corner R5 or less (angle R5 or less or corner R5 or less in the shape of the press forming tool), it corresponds to a portion where the deep drawing shape exists from the high P ₀ blank material element. of blank element to the blank elements, the blank element except high P ₀ blank element can be set to. "said peripheral blank elements.

The predetermined range is described in the input file of the finite element method before the analysis is started, or the contact surface pressure P ₀ when reaching the forming bottom dead center is expressed on a contour diagram on the forming surface of the press forming tool. For example, the predetermined range may be determined after confirming the distribution of the contact surface pressure P ₀ when the molded bottom dead center is reached.

(Step S5)
And high P ₀ blank elements extracted in step S3, the peripheral blank elements extracted in step S4 convenience, will be referred to as extraction blank elements. Of the extracted blank material elements, two adjacent extracted blank material elements are combined to generate a blank material element set A _i .

The number of blank material element groups A _i differs depending on the threshold value setting in step S3 and the distribution of high P ₀ blank material elements. For example, when 100 combinations of two extraction blank material elements adjacent to each other are possible (when there are 100 sets of two extraction blank material elements adjacent to each other), the blank material element groups A ₁ , A ₂ ,. ... _A100 is generated. In this case, the blank material element group A _i (i = 1 to 100) is described.

(Step S6)
In step S5, the blank material element group A _{i obtained} by combining two blank material elements adjacent to each other is converted into a blank material element group B _i as described below.

FIG. 2 is a diagram illustrating a blank material element group A _i → B _i conversion step for converting the blank material element group A _i into a blank material element group B _i , and (a) is a blank material element group before conversion. A node configuration of A _i , (b) shows a node configuration of the blank material element group B _i after conversion.

The blank material element set A _i is composed of two adjacent blank material elements S _{Ai, 1} and S _{Ai, 2} . The blank material element S _{Ai, 1} is composed of nodes N _{i, 1} , N _{i, 2} , N _{i, 3} , N _{i, 4} . The blank material element S _{Ai, 2} is composed of nodes N _{i, 1} , N _{i, 2} , N _{i, 5} , N _{i, 6} .

Node _{N i, 1, N i,} 2 is blank element S _{Ai, 1} and the blank element S _{Ai, 2} and are shared with a blank element S _{Ai, 1} and the blank element S _{Ai, 2} Is restrained.

In step S6, for N _{i, 1} and N _{i, 2} which are shared nodes, N _{i, 1 is changed} to N _{i, 1a} and N _{i, 1b} and N _{i, 2 is changed} to N _{i, 2a} and N _{i, 2b} . Separate and release the restraint between the blank material element S _{Ai, 1} and the blank material element S _{Ai, 2} .

Then, the blank material element S _{Ai, 1} is converted into a blank material element S _{Bi, 1} consisting of nodes N _{i, 1a} , N _{i, 2a} , N _{i, 3} , N _{i, 4} , and blank material element S _{Ai, 1 2} is converted into a blank material element S _{Bi, 2} composed of nodes N _{i, 1b} , N _{i, 2b} , N _{i, 5} , N _{i, 6} .

In this way, the blank material element group A _i composed of _{the two} constrained blank material elements S _{Ai, 1} and S _{Ai, 2} is the blank material element S _{Bi, 1} , S _Bi whose two constraints are released. _{It is} converted to the blank element group B _i consists of _2.

  When the restraint of the two blank elements is released, the stress is not transmitted between the two blank elements, and the stress that the two blank elements share before the restraint is released Since blank material elements existing around the elements are shared instead, it is possible to express a state in which minute damage has occurred in the blank material by numerical analysis.

Note that one or both of the blank material elements S _{Ai, 1} and S _{Ai, 2} constituting the blank material element set A _i are also converted in the same manner when they are composed of three nodes. .

For example, FIG. 3, when the blank element S _{Ai, 2} is composed of three nodes, to convert the blank element sets A _i in the blank element group B _i, the blank element sets A _i → B _i conversion step (A) shows the node configuration of the blank material element set A _i before conversion, and (b) shows the node configuration of the blank material element set B _i after conversion.

As shown in FIG. 3, the blank material element S _{Ai, 1} is composed of nodes N _{i, 1} , N _{i, 2} , N _{i, 3} , N _{i, 4} . The blank material element S _{Ai, 2} is composed of nodes N _{i, 1} , N _{i, 2} and N _{i, 5} . Node _{N i, 1, N i,} 2 is blank element S _{Ai, 1} and the blank element S _{Ai, 2} and are shared with a blank element S _{Ai, 1} and the blank element S _{Ai, 2} Is restrained.

In step S6, for N _{i, 1} and N _{i, 2} which are shared nodes, N _{i, 1 is changed} to N _{i, 1a} and N _{i, 1b} and N _{i, 2 is changed} to N _{i, 2a} and N _{i, 2b} . Separate and release the restraint between the blank material element S _{Ai, 1} and the blank material element S _{Ai, 2} .

The blank material element S _{Ai, 1} is converted into a blank material element S _{Bi, 1} composed of nodes N _{i, 1} , N _{i, 2} , N _{i, 3a} , N _{i, 4a} , and blank material element S _{Ai, 1 2} is converted into a blank material element S _{Bi, 2} composed of nodes N _{i, 1b} , N _{i, 2b} , N _{i, 5} .

FIG. 3 shows the case where the blank material element S _{Ai, 2} is composed of three nodes. However, when the blank material element S _{Ai, 1} is composed of three nodes, the blank material element S _{Ai, 1} and the blank material are illustrated. The same conversion is performed when both of the elements S _{Ai, 2} are composed of three nodes.

(Step S7)
In the primary analysis model created in step S1, only a portion of the blank element sets A _i is replaced with the blank element B _i, (i + 1) th to create a model for the next analysis.

For example, when i = 1, the primary analysis model, to replace only part of the blank element sets A ₁ to blank elements B _1, creating a second-order analysis model. As will be described later, in the next step S8, the (i + 1) th analysis is executed, but since the analysis has already been executed once (primary analysis) in step S1, the (i + 1) th analysis is performed in step S8. ) Next analysis is executed, and the (i + 1) th order analysis model is created in step S7.

Note that all the models for the (i + 1) th order analysis (where i = 1 to n (n is an integer of 1 or more)) are the models for the first order analysis. For example, the fifth-order analysis model, the first-order analysis model is a model obtained by replacing only the part of the blank element group A ₄ in the blank element B _4, the model for the 13th order analysis is first in the model for the next analysis is a model obtained by replacing only the part of the blank element group a ₁₂ in the blank element B _12.

(Step S8)
The (i + 1) th order analysis is executed using the (i + 1) th order analysis model created in step S7. In the (i + 1) th order analysis, the analysis starts when the press forming tool comes into contact with the blank, and the analysis ends when the press forming tool reaches the bottom dead center. However, the press forming tool is blank. The contact surface pressure when reaching the predetermined position before the forming bottom dead center stored in the output file of the finite element method in step S2 until the press forming tool reaches the predetermined position before the forming bottom dead center after the contact with the material. Numerical analysis is performed using P _f data.

  In other words, from the time when the press-forming tool contacts the blank material until the press-forming tool reaches a predetermined position before the forming bottom dead center, numerical analysis is performed using the primary analysis model. become.

  This is because the contact surface pressure after the press molding tool reaches the predetermined position before the bottom dead center of molding is important for breakage of the blank material, especially minute breakage, which occurs during press molding. From the time when the working tool comes into contact with the blank material until the press forming tool reaches a predetermined position before the bottom dead center of forming, it is sufficient to perform the analysis once in the first analysis, and it is not necessary to repeat the analysis. It is.

In this way, by using the contact surface pressure P _f when reaching the predetermined position before the bottom dead center, the analysis time of the (i + 1) th order analysis can be greatly shortened.

The calculated contact surface pressure is output at each time step set before starting the (i + 1) th analysis, but refer to the contact surface pressure when the press forming tool reaches the bottom dead center for forming. Is stored in the output file of the finite element method as the contact surface pressure P _i at the time of reaching the molding bottom dead center. The contact surface pressure P _i at the time of arrival of the molding bottom dead center for reference calculated in step S8 is compared with the contact surface pressure P ₀ at the time of arrival of molding bottom dead center calculated in step S2 in the next step S9. Since it is executed, it is set as “For reference”

Incidentally, when the reference molding bottom dead center reaches the contact surface pressure P _i is outputted to all the press-molding tool elements and the blank elements, for blank elements, the blank element set A at step S6 _This is output for all blank material elements after _i is converted to the blank material element group B _i .

  In addition, the predetermined position before the bottom dead center of the molding, that is, the position at which the repeated analysis is started in order to reproduce the minute breakage of the blank material by numerical analysis is different depending on the shape of the press molded product, but is 5 mm before the bottom dead center of the molding. It is preferable.

  If the analysis is repeatedly performed from a position distant from 5 mm before the molding bottom dead center, for example, 8 mm before the molding bottom dead center, the time step analysis time that is not related to the minute breakage of the blank material increases.

  On the other hand, if the analysis is repeatedly performed from a position closer to the molding bottom dead center than 5 mm before the molding bottom dead center, for example, 3 mm before the molding bottom dead center, a time step where the micro breakage of the blank material is likely to occur, for example, molding bottom dead center. It is difficult to reproduce the minute breakage of the blank material by numerical analysis by not performing precise analysis, that is, repeated analysis, between 5 mm and 3 mm before the point.

  Therefore, it is empirically known in actual press molding, and the blank material is likely to be damaged very little, and it is repeatedly analyzed from 5 mm before the molding bottom dead center to the molding bottom dead center, that is, 5 mm before the molding bottom dead center. Is preferably a predetermined position before molding bottom dead center.

(Step S9)
The absolute value | P ₀ −P _i | of the difference between the contact surface pressure P ₀ when reaching the molding bottom dead center calculated in step S2 and the contact surface pressure P _i when reaching the molding bottom dead center for reference calculated in step S8. A certain ΔP _i is calculated.

Incidentally, [Delta] P _i is outputted to all the press-molding tool elements and the blank elements, for blank elements, and converts the blank element sets A _i in the blank element group B _i in step S6 Output for all subsequent blank elements.

Here, ΔP _i is large when forming bottom dead center obtained by the first analysis model modeled by the blank material element group A _i (two constrained adjacent blank material elements). Molding for reference for reference obtained by the (i + 1) th-order analysis model modeled by the contact surface pressure P ₀ and the blank material element group B _i (two blank material elements adjacent to each other with the constraint released). the difference between the time of the contact surface pressure P _i the point reached represents a greater.

  The difference in contact surface pressure when reaching the bottom dead center of molding is greatly different between before and after expressing the occurrence of micro-breakage of the blank material by numerical analysis. This means that the influence of restraint between two adjacent blank material elements is great.

When the restraint between two blank material elements adjacent to each other is released, stress is not transmitted between the two blank material elements. And before the restraint is released, the stress shared by the two blank material elements is distributed to the elements existing around the two blank material elements, thereby changing the stress distribution. Therefore, when the restriction between two blank material elements adjacent to each other is released, a portion where the contact surface pressure increases or decreases (that is, a portion where ΔP _i is large) occurs.

The portion showing a large ΔP _i is greatly affected by the release of the restraint between two blank material elements adjacent to each other. This means that in actual press molding, when a micro breakage of a blank material occurs, the phenomenon is easily detected by a change in contact surface pressure. Therefore, a blank material breakage detection sensor may be installed at a portion showing a large ΔP _i .

(Step S10)
In order to obtain the distribution of ΔP _i , Steps S6 to S9 are repeatedly executed with respect to the integer i of 1 to n, and are totaled for each press forming tool element based on the following equation (1), and ΔP _i total Calculate the value.

That is, the blank material element group A _i → B _i conversion (step S6) is executed for all the blank material element groups A _i . For example, in the case of the blank material element set A _i (i = 1 to 100), the process is executed for 100 sets of A _i .

Blank of the blank element sets A _{i (i} = 1~100), for example, the case of the blank element set A _43, the node _{N 43,1, N 43,2, N 43,3} , consisting of N _43,4 a wood element S _A43,1, node _{N 43,1, N 43,2, N 43,5} , a blank element S _A43,2 consisting _{N 43,6, N 43,1a, N 43,2a} , N _43,3, a blank element S _B43,1 consisting N _43,4, node _{N 43,1b, N 43,2b, N 43,5} , a blank element S _B43,2 consisting N _43,6 It is converted into a blank material element set B ₄₃ composed of

Then, for all i (i = 1 to 100), the (i + 1) The following analysis and [Delta] P _i calculated is executed for the (i + 1) following the analysis model blank element sets of conversion has been performed (step S6 Step S9 is repeatedly executed for integers 1 to n), so that the press forming tool forms the first (i + 1) th analysis model generated in all blank material element sets generated in Step S5. The analysis was performed from the predetermined position before the bottom dead center until reaching the molded bottom dead center.

(Step S11)
In step S10, among the summed [Delta] P _i sum for each tool for press molding element, the press-molding tool elements each [Delta] P _i sum which defines the molding surface of the press-molding tool, the tool molding surface for press molding Output as strain index.

Since the ΔP _i total value is the amount of change in the contact surface pressure, the magnitude of the ΔP _i total value can be an index representing the size of the strain generated in the press forming tool generated by the contact surface pressure. .

Of the total ΔP _i values of the press forming tool elements, the total ΔP _i value of each press forming tool element that defines the forming surface of the press forming tool is expressed as a press forming tool forming surface strain index. It can be an index indicating the distribution of strain generated on the molding surface of the molding tool.

(Step S12)
If the press-forming tool forming surface strain index output in step S11 is greater than or equal to a predetermined value, a blank material breakage detection sensor is installed within a predetermined depth from the press-forming tool element indicating the predetermined value or more. Judge that it is good to do.

  When the tool forming surface strain index for press forming is output as a contour map (contour diagram) on the forming surface of the press forming tool, the distribution of the press forming tool forming surface strain index on the forming surface of the press forming tool is clear. Therefore, it is possible to easily evaluate where the blank material breakage detection sensor is installed in the press molding tool.

  As the blank material breakage detection sensor is installed in a deeper place (a place away from the forming surface) from the forming surface of the press forming tool, the detection sensitivity decreases. Therefore, the predetermined numerical value of the press forming tool forming surface strain index may be determined in consideration of the depth from the forming surface of the press forming tool in which the blank material breakage detection sensor is installed.

  However, if the installation depth of the blank material breakage detection sensor exceeds 15 mm in depth from the molding surface, the detection sensitivity is extremely lowered. Therefore, it is preferable that the installation depth of the blank material breakage detection sensor from the molding surface of the press molding tool is 15 mm or less.

The press forming tool surface distortion index is a relative value of the strain generated by the contact surface pressure caused by the frictional force between the press forming tool and the blank material during the press forming. Since it shows a distribution, it is preferable to set it to 10% or more of the contact surface pressure P ₀ when reaching the molding bottom dead center.

Site This showing more than 10% of the press when the molding tool forming surface strain index is at least 10% of the contact surface pressure P ₀ molding bottom dead center reaches the molding bottom dead center reaches when the contact surface pressure P _0, Alternatively, when the blank material is damaged due to an excessive tensile stress acting on the blank material in the surrounding area, the phenomenon is installed at a site showing 10% or more of the contact surface pressure P ₀ when reaching the bottom dead center. This is because it can be detected by the blank material breakage detection sensor.

  Moreover, as a blank material breakage detection sensor, as long as it can detect the distortion | strain of the tool for press molding, all can be used, For example, there exist a strain gauge and a piezoelectric sensor. A piezoelectric material sensor is preferable as the blank material breakage detection sensor because the strain detection sensitivity is good.

  Next, the present invention will be further described with reference to examples. Conditions in the examples are one example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is examples of these one condition. It is not limited to. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  FIG. 4 shows the appearance of an automobile body member to which the blank material breakage detection sensor installation position evaluation method of the present invention is applied. In FIG. 4, the code | symbol 10 shows the vehicle body member for motor vehicles.

  The finite element method was applied to the automobile body member 10 to execute Steps S1 to S12 shown in FIG. The press forming tool was defined by a rigid element, and the blank material was defined by a shell element capable of elastic-plastic deformation. The predetermined position before the molding bottom dead center was 5 mm before the molding bottom dead center.

Figure 5 shows at the end of steps S3 and S4, the distribution of the extracted high P ₀ blank elements and peripheral blank elements. In FIG. 5, reference numeral 20 (hatched portion) is a high P ₀ blank element, reference numeral 30 (the vertical line portion) shows the peripheral blank elements.

The high P ₀ blank material is a blank material element that exhibits a contact surface pressure P ₀ at the time of reaching the forming bottom dead center that is 10% or more of the contact surface pressure P calculated by the above-described formula 1.

The plate | board thickness and material of the blank material of the vehicle body member 10 for motor vehicles are as follows.
t (blank thickness): 2.0 mm
S _B (Blank material tensile strength): 780 MPa

  Further, in the punch and die used when press-molding the vehicle body member 10 for an automobile, the punch shoulder R = 8 mm, the die shoulder R = 10 mm, and the curvature radius in the axial length direction = 100 mm. = 8 mm was adopted as the radius of curvature r of the contact portion between the blank material and the press molding tool. At this time, since the contact surface pressure P = 175.6 MPa is calculated from the above-described formula 1, 1056%, which is 17.56 MPa, was set as the threshold value.

Further, the peripheral blank material element is “within the shape of the press molded product within the corner R5 or less within the range from the high P ₀ blank material element to the surrounding 10 blank material element or from the high P ₀ blank material element to the surrounding 20 blank material element. When there is a deep drawing shape with an angle R5 or less (the shape of the press molding tool is an angle R5 or less or a corner R5 or less), a blank material element corresponding to a portion where a deep drawing shape exists from a high P ₀ blank material element of blank element to the blank element except high P ₀ blank elements, and extracted by setting the condition that. "said peripheral blank elements.

FIG. 6 shows a press forming tool element defining a forming surface of a press forming tool whose press forming tool surface distortion index is 5% or more and less than 10% of the contact surface pressure P ₀ when the forming bottom dead center is reached. Show the distribution.

FIG. 7 shows the distribution of press forming tool elements defining the forming surface of the press forming tool, wherein the press forming tool forming surface strain index is 10% or more of the contact surface pressure P ₀ when the forming bottom dead center is reached. .

A piezoelectric sensor is installed at a depth position of 12 mm from the molding surface of the part shown in FIG. 7 where the press molding tool molding surface strain index is 10% or more of the contact surface pressure P ₀ when the molding bottom dead center is reached, As a result of actual press molding, it was confirmed that molding abnormalities in which the blank material was damaged due to cracks, wrinkles, necking, etc. could be detected reliably.

  Since the installation position of the piezoelectric sensor determined according to FIG. 7 further narrows down the parts indicated by reference numerals 20 and 30 in FIG. 5, the blank material breakage detection sensor installation position evaluation method of the present invention is a piezoelectric sensor ( It was confirmed that the installation position of the blank material breakage detection sensor) was accurately determined.

  In addition, the place mentioned above is only what illustrated embodiment of this invention, and this invention can add a various change within the description range of a claim.

  As described above, according to the present invention, even when the press molding tool has a three-dimensionally complicated shape, the installation position of the sensor that detects the molding abnormality that causes the blank material to be damaged during press molding, In the design stage before the production of the press forming tool, it is possible to examine, evaluate and determine in advance by numerical analysis, and it is possible to easily find a press formed product in which a forming abnormality has occurred. The present invention has high utility value industrially.

10 body member for an automobile 20 high P ₀ blank element 30 around the blank element A _i before conversion of the blank element group B after _i conversion of the blank element sets _{S Ai, 1, S Ai,} 2 mutually two adjacent Extract blank element (before conversion)
Two extracted blank elements adjacent to S _{Bi, 1} and S _{Bi, 2} (after conversion)
N _{i, 1} , N _{i, 2} , N _{i, 3} , N _{i, 4} S _{Ai, 1} Nodes N _{i, 1} , N _{i, 2} , N _{i, 5} , (N _{i, 6} ) S _{Ai , 2} nodes N _{i, 1} , N _{i, 2} S _{Ai, 1} and S _{Ai, 2} share nodes N _{i, 1a} , N _{i, 1b} N _{i, 1} separated nodes N _{i, 2a} , N _{i, 2b} N _{i, 2} separated nodes

Claims (7)

  Using a model having a press forming tool element that defines a press forming tool and a blank material element that defines a blank material, the press forming tool comes into contact with the blank material before forming the bottom dead center. The bottom dead center formed between the press molding tool and the blank material when the finite element method is applied to the press molding process until reaching the predetermined position before the bottom bottom dead center of the press molding tool. Calculate the contact surface pressure when reaching the predetermined position before the front, and extract the portion of the blank material where the contact surface pressure when reaching the predetermined position before the bottom bottom of the molding is a predetermined threshold value or more, out of the blank material elements of the portion A change model that restricts the exchange of numerical values in the finite element method between the blank material elements adjacent to each other is created, and the finite element method is applied again to the change model so that a predetermined position before the bottom dead center for reference is formed. To The contact surface pressure is calculated, and the blank at a portion where the difference between the contact surface pressure when reaching a predetermined position before the molding bottom dead center and the contact surface pressure when reaching a predetermined position before the molding bottom dead center for reference is greater than a predetermined value. A blank material breakage detection sensor installation position evaluation method, wherein the blank material breakage detection sensor is predicted to be broken and an installation position of the blank material breakage detection sensor on the press forming tool is determined. A primary analysis model creation step for creating a primary analysis model for the finite element method having a press molding tool element defining a press molding tool and a blank material element defining a blank;
The finite element method using the first analysis model is applied to the press molding process from when the press molding tool contacts the blank material until reaching the molding bottom dead center, and the press molding tool When the predetermined position before the bottom dead center is reached, the contact surface pressure P _f when the predetermined position before the bottom bottom point is generated between the press molding tool and the blank, and the bottom dead center of the press molding tool is formed. When reaching a point, the contact surface pressure P ₀ at the time of forming bottom dead center arrival generated between the blank material and the press molding tool is calculated for each press molding tool element and for each blank material element, A first analysis step;
Wherein one of the molding bottom dead center reaches when the contact surface pressure P ₀ is calculated the blank elements, the blank elements when the contact surface pressure predetermined threshold or more of the forming bottom dead center reaches P ₀ is calculated, extracting a high P ₀ blank elements, and the high P ₀ blank element extracting step,
The blank elements existing within a predetermined range from the high P ₀ blank element is extracted as the peripheral blank elements, and a peripheral blank element extracting step,
The extraction blank element made of the high P ₀ blank element and the peripheral blank elements, two of the extraction blank elements configured i set adjacent to each other (where, i is the 1~n integer) of and the blank element sets a _i, and the blank element sets a _i generation step,
For nodes N _{i, 1} and N _{i, 2} shared by the extraction blank material element S _{Ai, 1} and the extraction blank material element S _{Ai, 2} constituting the blank material element group A _i , N _{i, 1} is represented by N _{i. , 1a} and _{Ni, 1b, Ni , 2} are separated into _{Ni , 2a} and _{Ni, 2b,} and the blank material element group _Ai is extracted with the extracted blank material element S _{Bi, 1} and the extracted blank material. A blank material element set A _i → B _i conversion step for converting into a blank material element set B _i composed of the elements S _{Bi, 2} ;
The blank element sets A _i of the first-order analysis model, the (i + 1) is replaced with the blank element sets B _i to create a model for the next analysis, the (i + 1) th model creation step for the next analysis When,
Based on the contact surface pressure P _f when reaching a predetermined position before the molding bottom dead center, the press molding process until the press molding tool reaches the bottom molding bottom dead center after contacting the blank material, A finite element method using the (i + 1) th order analysis model is applied, and the contact surface pressure P _i when reaching the reference bottom dead center relative to the contact surface pressure P ₀ when reaching the bottom bottom dead center is determined as the _value for the press molding. (I + 1) order analysis step for calculating each tool element and each blank material element after converting the blank material element set A _i to the blank material element set B _i ;
ΔP _i which is an absolute value | P ₀ −P _i | of the difference between the contact surface pressure P ₀ when reaching the forming bottom dead center and the reference forming bottom dead center contact surface pressure P _i is the forming tool element for pressing. And ΔP _i calculating step for calculating each blank material element after converting the blank material element set A _i to the blank material element set B _i ;
For the integer i of 1 to n, the blank material element group A _i → B _i conversion step, the (i + 1) th order analysis model creation step, the (i + 1) th order analysis step, and the ΔP _i calculation step are repeated. run, for each of the press-molding tool element, summing basis of [Delta] P _i in the following equation (1), and [Delta] P _i sum calculation step,
Wherein among the [Delta] P _i sum, the press-molding tool elements each [Delta] P _i sum which defines the molding surface of the press-molding tool, and outputs the index strain press molding tool molding surface, press molding tool molding surface A strain index output step;
The installation position of the sensor for detecting breakage of the blank material during press forming is determined to be within a predetermined depth from the press forming tool element having a press forming tool forming surface strain index of a predetermined value or more. , Blank material breakage detection sensor installation position determination step,
The blank material breakage detection sensor installation position evaluation method according to claim 1, wherein:

  The blank material breakage detection sensor installation position evaluation method according to claim 1 or 2, wherein the predetermined position before the molding bottom dead center is 5 mm before the molding bottom dead center.   The blank material breakage detection sensor installation position according to any one of claims 1 to 3, wherein the press forming tool element is a rigid element, and the blank material element is a shell element that can be elastically plastically deformed. Evaluation methods.   The blank material breakage according to any one of claims 1 to 4, wherein said press forming tool forming surface distortion index is outputted as a contour map (contour drawing) of said press forming tool forming surface. Sensor installation position evaluation method.   The blank material breakage detection sensor installation position evaluation method according to any one of claims 1 to 5, wherein the blank material breakage detection sensor is a piezoelectric sensor.   The said predetermined depth is 15 mm, The blank material breakage detection sensor installation position evaluation method of any one of Claims 1-6 characterized by the above-mentioned.

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