JP2019038005A - Method for previously estimating occurrence of crack when forming press-formed body - Google Patents

Abstract

To provide a method for previously estimating whether or not cracks occur when forming a press-formed body efficiently and at low cost.SOLUTION: A forming limit diagram G when a work-hardening exponent of a pressed plate 2 is n and a plate thickness is t is obtained. A value X of the maximum principal strain εof the forming limit line S1 when the smallest principal strain εof a forming limit line S1 in the forming limit diagram G is 0 is derived. A numerical analysis by the press forming simulation is performed, and the maximum principal strain εof each finite element Band the smallest principal strain εcorresponding to an outer peripheral edge in model data D1 are derived, respectively. Also, the maximum principal strain εis compared with the value X. Estimation is made that cracks occur in the forming in an area of the outer peripheral edge of the press-formed body 3 corresponding to each finite element Bsatisfying the maximum principal strain ε≥X in each finite element Bderived.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for predicting in advance whether or not a crack occurs in a press-formed body by press-forming simulation in a stage before press forming a pressed plate to obtain a press-formed body.

Conventionally, when designing a press-molded body for use in automobiles, home appliances, etc., press molding is performed by press-molding simulation in order to minimize rework during the design and production of the mold for molding the press-molded body. An operation for predicting in advance whether or not a crack will occur during the molding of the body is performed.
For example, in Patent Document 1, after creating model data composed of a plurality of finite elements that model a plate to be pressed, and performing numerical analysis by press molding simulation using the model data, each finite element in the model data It is predicted in advance whether cracks will occur or not by checking whether the maximum principal strain and the minimum principal strain value are above the forming limit line in the forming limit diagram.

  By the way, the forming limit diagram used in the press forming simulation as described above is obtained by ball head punch overhanging or cylindrical punch overhang forming. Therefore, when performing the advance prediction of crack occurrence by press forming simulation using the forming limit diagram, the accuracy of advance prediction is high for crack occurrence in the region excluding the outer peripheral edge of the press formed body. There was a problem that the accuracy of prior prediction was low with respect to the occurrence of cracks at the peripheral edge.

  In order to avoid this, for example, in Patent Document 2, with respect to a material used for a press-formed body that predicts the occurrence of cracking, the shear plane ratio γ, the strain gradient Δεθ in the end ridge line direction, and the strain gradient in the vertical direction of the end ridge line The relationship between Δεr and the limit equivalent plastic strain εcr is obtained in advance by experiment, and these relationships are approximated, and the position of the forming limit line in the forming limit diagram is corrected by using the approximated expression. The accuracy of prior prediction of the occurrence of cracks at the outer peripheral edge of the molded body is increased.

JP 2006-167766 A JP 2010-69533 A

  However, in the case of Patent Document 2, it is necessary to perform an experiment in advance on a material used for a press-formed body that predicts the occurrence of a crack and calculate an approximate expression, which increases the work time of the worker who performs the prediction work. As a result, the work cost increases.

  In addition, when making a prior prediction, by using the value of the forming limit line of the forming limit diagram used for predicting the occurrence of cracks in the region other than the outer peripheral portion of the press formed body, the outer peripheral portion of the press formed body There is also a demand for predicting in advance whether or not cracking will occur during molding.

  The present invention has been made in view of such points, and the object of the present invention is to predict in advance whether or not cracking will occur during the molding of a press-molded body, and at a low cost. It is to provide a way to do.

In order to achieve the above-mentioned object, the present invention uses a value of the maximum principal strain ε ₁ of the forming limit line when the minimum principal strain ε ₂ in the forming limit line of the forming limit diagram is 0. It is characterized in that it is predicted whether or not a crack will occur at the time of molding at the outer peripheral edge portion.

  Specifically, in the stage before press forming the pressed plate to obtain a press-formed body, model data composed of a plurality of finite elements modeling the pressed plate is created and press forming using the model data is performed. By conducting numerical analysis by simulation, predict whether or not cracks will occur at the outer peripheral edge of the above-mentioned press-formed product during press molding. The solution was taken.

That is, in the first invention, after obtaining the forming limit diagram when the work hardening index of the pressed plate is n and the plate thickness is t, the maximum forming limit line when the minimum principal strain ε ₂ is 0 is obtained. The value X of the principal strain ε ₁ is derived, and then numerical analysis is performed by press forming simulation to derive the maximum principal strain ε ₁ and the minimum principal strain ε ₂ of each finite element corresponding to the outer peripheral edge in the model data. In addition, the maximum principal strain ε ₁ and the value X are compared, and then the outer peripheral edge portion of the press-formed body corresponding to each finite element satisfying the maximum principal strain ε ₁ ≧ X regardless of the value of the minimum principal strain ε ₂ . It is predicted that a crack will occur in the region.

  In the present invention, when a worker performs a prediction work of occurrence of cracks in a press-formed body, in addition to obtaining a normal forming limit diagram, an experiment is performed in advance to calculate an approximate expression. There is no need. In addition, in the prediction method of the present invention, a preliminary prediction as to whether or not a crack occurs at the time of molding in the outer peripheral edge of the press-formed body is made as to whether or not a crack occurs in a region other than the outer peripheral edge of the press-formed body. A part of the value of the forming limit line of the forming limit diagram used when performing the process can be used as it is. Therefore, the operator can efficiently predict the occurrence of cracks in the entire press-formed body without taking time, and the cost for the work of predicting cracks can be suppressed.

It is a flowchart which shows the procedure of the prediction method which concerns on embodiment of this invention. It is a schematic perspective view which shows an example of the press molding which performs prior prediction whether a crack generate | occur | produces at the time of shaping | molding using the prediction method of this invention, and the to-be-pressed board before shape | molding to this press molding. It is a schematic perspective view which shows the model data of the to-be-pressed board in FIG. 2, and the model data after a deformation | transformation by press molding simulation, respectively. FIG. 3 is a forming limit diagram used when predicting in advance whether or not a crack has occurred during forming of the press-formed body of FIG. 2. It is a figure which shows one of the three different press-molded bodies used for the verification for deriving an outer peripheral edge crack determination line. It is a figure which shows one of the three different press-molded bodies used for the verification for deriving an outer peripheral edge crack determination line. It is a figure which shows one of the three different press-molded bodies used for the verification for deriving an outer peripheral edge crack determination line. It is a shaping | molding limit diagram created when the plate | board thickness of each press molding for verification is 0.9 mm. It is a forming limit diagram created when the plate thickness of each verification press-formed body is 1.6 mm. It is a forming limit diagram created when the plate thickness of each verification press-formed body is 2.3 mm.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiment is merely exemplary in nature.

  FIG. 1 is a flowchart 1 showing a work procedure of a prediction method according to an embodiment of the present invention. As shown in FIGS. 2 and 3, the prediction method of the present invention has a plurality of models in which the pressed plate 2 is modeled in the previous stage of press forming the pressed plate 2 into a press-formed body 3 having a target shape. A method for predicting in advance whether or not a crack will occur in the press-formed body 3 during forming by creating model data D1 composed of finite elements of the above and performing numerical analysis by press forming simulation using the model data D1 As shown in FIG. 1, it is possible to know in advance whether or not a crack occurs during the molding of the press-molded body 3 by sequentially performing the seven steps S1 to S7.

  A molding limit diagram G as shown in FIG. 4 is used in advance prediction as to whether or not a crack will occur when the press-molded body 3 is molded. In this forming limit diagram G, a forming limit line S1 having a substantially V shape and an outer peripheral edge crack determination line S2 positioned below the forming limit line S1 and extending in the horizontal direction are displayed. ing.

  The forming limit line S1 is, for example, widely and generally recognized by experiments or theoretically when the work hardening index of the pressed plate 2 is n and the plate thickness is t. In the prediction method of the present invention, it is used as a threshold when predicting whether or not a crack will occur during molding in a region other than the outer peripheral portion of the press-formed body 3.

For example, the maximum principal strain ε ₁ and the minimum principal strain ε ₂ of the finite element A _P1 of the model data D1 corresponding to the position P1 in the press-formed body 3 in FIG. ₂ are above the forming limit line S1, as shown in FIG. If it is located, it is predicted that a crack will occur during molding at the position P1 in the press-molded body 3. On the other hand, the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ finite element A _P2 of the model data D1 corresponding to the position P2 in pressed bodies 3 in FIG. 2, below the forming limit line S1 as shown in FIG. 4 When it is located at the position P2, it is predicted that no crack will occur during molding at the position P2 in the press-molded body 3.

The outer peripheral edge crack judgment line S2, in forming limit line S1, and those minimum principal strain epsilon ₂ is obtained to derive the maximum principal strain epsilon ₁ of the value X at the time of 0, in the prediction method of the present invention It is used as a threshold when predicting whether or not a crack will occur during molding at the outer peripheral edge of the press-formed body 3.

For example, the maximum principal strain ε ₁ and the minimum principal strain ε ₂ of the finite element B _Q1 of the model data D1 corresponding to the position Q1 in the press-formed body 3 of FIG. ₂ are the outer peripheral edge crack determination line S2 as shown in FIG. When located on the upper side, it is predicted that a crack will occur at the time of forming at the position Q1 in the press-formed body 3 even if it is located below the forming limit line S1. On the other hand, the maximum principal strain ε ₁ and the minimum principal strain ε ₂ of the finite element B _Q2 of the model data D1 corresponding to the position Q2 in the press-formed body 3 in FIG. When located on the lower side, it is predicted that no crack will occur during molding at the position Q2 in the press-molded body 3.

  As described above, according to the prediction method of the present invention, in the molding limit diagram G, the outer peripheral edge portion of the press molded body 3 in which the presence or absence of cracks during molding cannot be predicted on the molding limit line S1 is formed. An outer peripheral edge crack determination line S2 used only for predicting whether or not an outer peripheral edge crack has occurred is set based on the forming limit line S1. The outer peripheral edge crack determination line S2 was derived by performing the following verification.

First, three different press-formed bodies 3a to 3c (see FIGS. 5 to 7) having different types of cracks generated in the outer peripheral edge when actually performing press-molding are selected, and each press-formed body 3a is selected. The maximum principal strain ε ₁ and the minimum principal strain ε ₂ at the crack occurrence sites C1 to C3 of ˜3c were determined by numerical analysis by press molding simulation. In addition, the material of the press-molded bodies 3a to 3c was a cold rolled steel sheet of 980 MPa class.

Next, the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ in the cracking sites C1~C3 by changing the molding conditions of each pressed bodies 3a~3c calculated by numerical analysis by the press forming simulation. The molding conditions are such that the friction coefficient is changed between 0.12 and 0.15, which is said to be close to the state of the actual mold, and the plate thickness is 0.9 mm for each of the press molded bodies 3a to 3c. The maximum principal strain ε ₁ and the minimum principal strain ε ₂ at the crack occurrence sites C1 to C3 were calculated by changing to 1.6 mm and 2.3 mm. Then, the maximum principal strain ε ₁ and the minimum principal strain ε ₂ in the crack generation sites C1 to C3 calculated are plotted in the forming limit diagram G. Then, as shown in FIG. 8 to FIG. 10, the limit strain that is predicted to crack at the outer peripheral edge during molding of the press-formed bodies 3 a to 3 c is the minimum principal strain ε ₂ in the molding limit diagram G. It has been found that there is a tendency to concentrate on a region below the value X of the maximum principal strain ε ₁ of the forming limit line S1 when the value is 0 and below the forming limit line S1.

That is, numerical analysis by press molding simulation is performed to derive the maximum principal strain ε ₁ and the minimum principal strain ε ₂ of each finite element B _{n at} the outer peripheral edge in the model data D1, and the maximum principal strain ε ₁ and the value X are obtained. In comparison, regardless of the value of the minimum principal strain ε ₂ , it is possible to predict that a crack will occur during molding in the outer peripheral edge region of the press-formed body 3 corresponding to each finite element B _n satisfying the maximum principal strain ε ₁ ≧ X. It turns out that.

  Next, detailed description will be given of a procedure for pre-prediction of the presence / absence of cracks during the molding of the press-formed body 3 using the prediction method of the present invention.

  First, as shown in FIG. 1, in step S1, model data D1 composed of a plurality of finite elements obtained by modeling the pressed plate 2 on CAD is created.

  Next, in step S2, a forming limit diagram G when the work hardening index of the pressed plate 2 is n and the plate thickness is t is obtained (see FIG. 4).

Next, in step S3, a press molding simulation is performed using the model data D1. Then, obtain the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ of each finite element in the model data D1 reaches the target shape by numerical analysis by press-forming simulation.

Thereafter, in step S4, each finite element A _n (n is a natural number) corresponding to a region other than the outer peripheral portion of the press-formed body 3 among the finite elements of the analyzed model data D1 is extracted.

In step S5, with plotting maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ in forming limit diagram G in each finite element A _n extracted, plotted is above the forming limit line S1 position of each finite element A _n It is compared whether it is located in. Then, while the position of each finite element A _n is when positioned above the forming limit line S1 predicts that its corresponds to the position of the finite element A _n cracking during forming the area of the pressed bodies 3 is generated, when the position of each finite element a _n is positioned below the forming limit line S1 predicts that its corresponds to the position of the finite element a _n cracking during forming the area of the pressed bodies 3 is not generated.

Thereafter, in step S6, finite elements B _n (n is a natural number) corresponding to the outer peripheral portion of the press-formed body 3 among the finite elements of the analyzed model data D1 are extracted.

In step S7, with plotting maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ in forming limit diagram G in each finite element B _n extracted, the outer peripheral edge crack judgment line position of each finite element B _n of plotting It is compared whether or not it is located above S2. And when the position of each finite element _Bn is located above the outer peripheral edge crack determination line S2, it cracks at the time of molding in the region of the outer peripheral edge of the press-formed body 3 corresponding to the position of the finite element _Bn. When the position of each finite element _Bn is located below the outer peripheral edge crack determination line S2, the outer peripheral edge of the press-formed body 3 corresponding to the position of the finite element _Bn is predicted. It is predicted that no cracks will occur during molding in this area, and the preliminary prediction of whether or not cracks have occurred during molding of the press-molded body 3 is completed.

  As described above, according to the embodiment of the present invention, when an operator performs a prediction operation of occurrence of cracks in the press-formed body 3, an approximate expression is calculated by conducting an experiment in advance in addition to obtaining a normal forming limit diagram. There is no need for such work as in Patent Document 2. Further, in the prediction method of the present invention, whether or not a crack is generated in a region other than the outer peripheral edge portion of the press molded body 3 is determined in advance as to whether or not a crack is generated at the outer peripheral edge portion of the press molded body 3 during molding. A part of the value of the forming limit line S1 of the forming limit diagram G used for making the prediction can be used as it is. Therefore, the operator can efficiently predict the occurrence of cracks in the entire area of the press-formed body 3 without taking time, and the cost for the work of predicting cracks can be suppressed.

  The present invention is suitable for a method for predicting in advance whether or not a crack occurs in a press-formed body by press-forming simulation in a stage before a press plate is press-formed to obtain a press-formed body.

DESCRIPTION OF SYMBOLS 1 Flowchart 2 Plate to be pressed 3 Press molded body G Forming limit diagram S1 Forming limit line S2 Outer peripheral edge crack judgment line

Claims (1)

Before the press plate is press-molded to obtain a press-molded body, model data consisting of a plurality of finite elements modeling the press plate is created and numerical analysis is performed by press molding simulation using the model data. It is a prior prediction method for the presence or absence of cracking at the time of molding of a press-molded body for predicting whether or not cracking occurs at the outer peripheral edge of the press-molded body during press molding,
After obtaining the forming limit diagram when the work hardening index of the pressed plate is n and the plate thickness is t, the value X of the maximum principal strain ε ₁ of the forming limit line when the minimum principal strain ε ₂ is 0 is obtained. Derived,
Thereafter, numerical analysis by press molding simulation is performed to derive the maximum principal strain ε ₁ and the minimum principal strain ε ₂ of each finite element corresponding to the outer peripheral edge in the model data, and the maximum principal strain ε ₁ and the value X And then predicting that cracks will occur in the region of the outer peripheral edge of the press-formed body corresponding to each finite element satisfying the maximum principal strain ε ₁ ≧ X regardless of the value of the minimum principal strain ε _2. A method for predicting the presence or absence of cracks during molding of a featured press-molded body.