JP2019104051A - Pre-prediction method of crack occurrence existence when molding press-molding body - Google Patents

Abstract

To largely contribute to lead-time shortening of development, by predicting the occurrence of a crack by taking into consideration the winding direction of a coil of a pressed plate.SOLUTION: When defining a molding limit line as y=f(x)(y:a maximum main strain, x:a minimum main strain) when a plate thickness of a pressed plate 2 is (t), in a simple flexure test of a testing plate provided by rolling out of a coil of rolling a steel strip of the plate thickness (t), when a difference of a limit strain when flexurally molding so that a flexure ridge line runs along the winding direction of the coil when flexurally molded so that the flexure ridge line crosses with the winding direction of the coil, is α×t (α:a prescribed factor), a computer calculates a correction molding limit line y=f(x)-α×t, and determines whether or not respective finite elements are positioned on the upper side than the correction molding limit line, and predicts that a crack is caused in a position of a press molding body corresponding to the respective finite elements positioned on the upper side than the correction molding limit line.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method of predicting in advance whether or not a crack is generated in a press-formed product by press-forming simulation in a stage prior to press-forming a plate to be pressed to obtain a press-formed product.

  2. Description of the Related Art Conventionally, when designing a press-formed body used for automobiles, home electric appliances and the like, a press using a computer in order to minimize rework during design and manufacture of a press die for forming the press-formed body. An operation of predicting in advance whether or not a crack occurs during molding of a press-formed product is performed by molding simulation.

  For example, in patent document 1, while creating model data which consists of a plurality of finite elements which modeled a plate to be pressed, and performing numerical analysis by press forming simulation on a computer using the model data concerned, each finite The computer determines whether the maximum principal strain and the minimum principal strain of the element are located above the forming limit line in the forming limit diagram, and the press-formed body corresponding to each finite element located above the forming limit line It is predicted in advance that a crack will occur in the position.

JP, 2006-167766, A

  By the way, as a plate to be pressed before being formed into a press-formed body, a plate obtained by winding a coil formed by winding a steel strip and cutting it at a predetermined length in the unwinding direction is generally used, and a press die The set state (winding direction of the coil) of the plate to be pressed before pressing is naturally determined by material removal for the purpose of improving the material yield. Then, in the press-formed body, the bending-shaped portion is formed along the winding direction of the coil rather than forming the press-formed body by bending the bending-formed portion so that the bending ridge intersects the winding direction of the coil. It is generally known that cracking is more likely to occur at the time of press-forming if the press-formed body is formed by bending.

  However, in the prior evaluation based on the conventional press forming simulation as in Patent Document 1, the set state (winding direction of the coil) of the plate to be pressed with respect to the press die is not taken into consideration. Due to differences in the attitude of the plate before pressing (coil winding direction), there may be variations in evaluation of crack occurrence, which may lead to development repercussions such as having to make design changes that were not originally necessary. there were. Therefore, there is a demand for making a significant contribution to shortening the lead time of development by reflecting the difference in the set state (winding direction of the coil) of the plate to be pressed with respect to the press die before performing prediction in advance. The

  The present invention has been made in view of such a point, and an object of the present invention is to shorten the lead time of development by predicting the occurrence of cracking taking into consideration the winding direction of the coil of the plate to be pressed. It is to contribute greatly.

  In order to achieve the above object, the present invention is characterized in that it is devised to be able to perform preliminary evaluation in consideration of the set state of the plate to be pressed with respect to the press die considered to be difficult to press. Do.

Specifically, in the pre-stage of obtaining a press-formed body by press-molding a plate to be pressed, model data consisting of a large number of finite elements obtained by modeling the plate to be pressed is created and press-formed using the model data A numerical analysis by simulation is performed on a computer to derive the maximum principal strain ε ₁ and the minimum principal strain ε ₂ of each finite element in the model data, and then the maximum principal strain ε ₁ and the minimum principal strain of each finite element The computer determines whether or not ε ₂ is located above the forming limit line, and predicts that a crack will occur at the position of the press-formed body corresponding to each finite element located above the forming limit line The following solutions were taken for the method of predicting the occurrence of cracking during molding of a molded body.

That is, in the present invention, when the thickness of the plate to be pressed is t, the forming limit line experimentally or theoretically derived is y = f (x) (y: maximum principal strain, x: minimum In the simple bending test of a test plate obtained by unrolling a coil of a steel strip having a thickness t and defining it as the main strain), the bending ridge was bent and formed so as to intersect the winding direction of the coil In the case where the difference in critical strain is α × t (α: predetermined coefficient) when the bending ridge line is bent and formed along the winding direction of the coil, the computer corrects and forms from the forming limit line. The limit line y = f (x) −α × t is calculated, and it is determined whether or not the maximum principal strain ε ₁ and the minimum principal strain ε _{2 of} each of the finite elements are located above the modified forming limit line, Each finite element located above the above correction forming limit line It is predicted that a crack will occur at the position of the above-mentioned press-formed product corresponding to.

  In the present invention, the computer calculates the lower limit value of the forming limit line which is previously assumed to be the case where forming is most difficult, such as bending each bending forming portion to obtain a press forming body so that the bending ridge line follows the winding direction of the coil. Since it is predicted in advance whether or not a crack will occur in the press-formed product, if it is predicted that a crack will occur, it is understood that a design change such as a mold is always necessary, while the crack is In the case where it is predicted not to occur, the material removal can be freely examined regardless of the winding direction of the coil for the purpose of improving the yield and the like. Therefore, the time spent on the design change of the mold, the examination of material removal, etc. is reduced, and the number of rework is reduced, which can greatly contribute to the shortening of the development lead time.

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 the press-formed body which performs prior prediction of 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 shaping | molding to this press-formed body. It is a schematic perspective view which each shows the model data of the to-be-pressed board in FIG. 2 which shows the state displayed on the computer, and the model data after the deformation | transformation by press molding simulation. FIG. 3 is a forming limit diagram used to predict in advance whether or not a crack will occur during forming of the press-formed body of FIG. 2, and a maximum principal strain and a minimum of each finite element in model data after deformation by the press-forming simulation of FIG. 3 It is the figure which plotted the principal distortion, respectively. It is a perspective view of the model data after the deformation | transformation by the press molding simulation which showed the position of each finite element corresponding to the point group located in E2 part of FIG. It is general data of limit surface strain at the time of simple bending deformation.

  Hereinafter, embodiments of the present invention will be described in detail based on the drawings. The following description of the preferred embodiments is merely exemplary in nature.

FIG. 1 is a flowchart 1 showing the operation procedure of the prediction method according to the embodiment of the present invention. According to the prediction method of the present invention, as shown in FIG. 2 and FIG. 3, the plate to be pressed 2 is pressed prior to forming the press-formed body 3 having a hat shape in cross section as a target shape. The above press-formed body at the time of forming by creating model data D1 consisting of a large number of modeled finite elements _An (n is a natural number) and performing numerical analysis by press forming simulation using the model data D1 on a computer It is predicted in advance whether or not a crack will occur in 3 and whether or not a crack will occur in forming the press-formed body 3 by sequentially passing through six steps S1 to S6 (see FIG. 1) It comes to understand in advance.

  As shown in FIG. 2, the press-formed body 3 has four bending portions 3 a which extend along the longitudinal direction and have a cross-sectional shape that is bent at about 90 °.

  The plate 2 to be pressed is obtained by unwinding from a coil formed by winding a steel strip having a thickness t and cutting it out at a predetermined interval. Parts having a hat-shaped cross section in which the respective bending portions 3a extend in the same direction, such as the pressing body 3, bend the bending portions 3a so that the ridges intersect the winding direction of the coil to obtain the pressing body 3 (Mold with the plate 2 set in the mold so that the winding direction of the coil is the X1 direction in FIG. 2), or bend the bending section 3a in the winding direction of the coil It is common to obtain a press-formed product 3 by bending along the length (forming in a state where the plate 2 to be pressed is set in a mold so that the winding direction of the coil is the X2 direction in FIG. 2).

  That is, in the case of the press-formed body 3 as shown in FIG. 2, the plate to be pressed 2 is used as a mold so that the winding direction of the coil intersects with the longitudinal direction of the press-formed body 3 (X1 direction). Either molding is performed in the set state, or molding is performed in a state in which the plate to be pressed 2 is set in a mold so that the coil winding direction is parallel to the longitudinal direction of the press molded body 3 (X2 direction). It is supposed to

  A forming limit diagram G as shown in FIG. 4 is used in advance to predict whether or not a crack will occur when forming the press-formed product 3. In this forming limit diagram G, there are a forming limit line L1 having a substantially V shape, and a modified forming limit line L2 located below the forming limit line L1 and having the same shape as the forming limit line L1. Each is displayed.

  The forming limit line L1 is, for example, experimentally or theoretically derived when the thickness of the plate 2 to be pressed is t, and whether or not a crack occurs during press forming is determined on the computer It is used as a general threshold when predicting.

For example, in the case of obtaining the pressed bodies 3, after deriving respectively the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ of each finite element A _n in the model data D1 of FIG. 3 in the computer, each finite element A _n press molding the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ of whether positioned above the forming limit line L1 is determined computer, corresponding to the finite element a _n positioned above the forming limit line L1 It is predicted that a crack will occur at the position of the body 3.

Furthermore, by comparing the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ of each finite element A _n in the model data D1 in FIG. 3 and forming limit line L1, the maximum principal strain epsilon ₁ and the minimum of all the finite elements A _n If principal strain epsilon ₂ is positioned below the forming limit line L1, it predicts that cracking pressed bodies 3 is not generated.

  On the other hand, in the correction forming limit line L2, according to the prediction method of the present invention, cracks are formed at the time of forming on the assumption that the press forming body 3 is obtained by bending the bending forming portion 3a so that the bending ridge line follows the winding direction of the coil. If it is used as a threshold when predicting whether it will occur or not and the forming limit line L1 is defined as y = f (x) (y: maximum principal strain, x: minimum principal strain), y = f (x ) -Α × t (α: predetermined coefficient).

  In the simple bending test of a test plate obtained by unrolling a steel strip having a thickness t by taking out α x t at the modified forming limit line L 2, the bending ridge line intersects the winding direction of the coil This is the difference in critical strain when the bending ridge is bent and formed along the winding direction of the coil as compared to the case of bending and forming.

For example, in the case of obtaining the pressed bodies 3 by bending the molding portion 3a bent to the bending ridge line extends along the winding direction of the coil, the maximum principal strain epsilon ₁ and a minimum of the finite element A _n in the model data D1 of FIG. 3 after the principal strain epsilon ₂ computer derived respectively, determines whether the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ of each finite element a _n is positioned above the modified forming limit line L2, corrected forming limit cracking the position of the pressed bodies 3 is predicted to occur for each finite element a _n on the upper side than the line L2.

Furthermore, by comparing the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ of each finite element A _n in the model data D1 in FIG. 3 and fixes the forming limit line L2, the maximum principal strain epsilon ₁ and all of the finite element A _n If the minimum principal strain epsilon ₂ is positioned below the modified forming limit line L2, it predicts that cracking pressed bodies 3 is not generated.

  As described above, in the prediction method of the present invention, the bending ridge line intersects the winding direction of the coil when the press-formed body 3 is formed by calculating the lower limit value of the assumed forming limit line on the computer. Thus, not only in the case where the press-formed body 3 is formed by bending the bend-formed portion 3a, but also in the case where the press-formed body 3 is obtained by bending the bend-formed portion 3a so that the bending ridge line follows the winding direction of the coil. Can be evaluated.

  The corrected forming limit line L2 was derived as follows.

  In a simple bending test, assuming that a bending radius when a predetermined test plate (980 MPa class) is simple bent is R and a plate thickness is t, the relationship between R / t and the amount of strain of the outer surface is curve C1 of FIG. It is generally known to be. Then, in the simple bending test, the curve C1 is R / t when the bending ridge line is bent along the winding direction of the coil while the bending ridge line is bent so as to cross the coil winding direction. It is also known that the value of the curve C2 deviates by about -1 in the axial direction.

When the simple bending test using a test plate with a plate thickness of 1 mm was performed, the difference between the strain amount when the bending radius R = 3 and the strain amount when the bending radius R = 4 was 0.011. That is, it was found that when the difference in bending radius R is 1, the difference in strain amount is 0.011. Accordingly, when viewed in forming limit diagram G, it shifts the position of the shaping limit line L1 so that the minimum principal strain epsilon ₂ is a limit strain value at 0 becomes downward by -0.011 × t It is considered that if the lower limit value is used, it is possible to evaluate the presence or absence of the most severe occurrence of cracking, and when using the forming limit line L1: y = f (x) for the assessment of the presence or absence of cracking of the press-formed product 3, the correction is made first of all Using the forming limit line L2: y = f (x)-0.011 x t, it was decided to evaluate the presence or absence of the occurrence of cracking. The strain amount 0.011 is a value that changes depending on the material of the plate 2 to be pressed.

  Next, the result of having evaluated the presence or absence of the crack generation using the method of this invention is explained in full detail.

  First, as shown in FIG. 2 and FIG. 3, when obtaining the press-formed product 3 by bending the bending portion 3a so that the bending ridge intersects the winding direction of the coil, no bending occurs. The model data D1 of the press-formed product 3 in which a crack is generated when bending and forming the bend-formed portion 3a along the winding direction of the coil is prepared. In addition, E1 part of FIG. 2 is a crack generation site.

Next, determined by numerical analysis by press-forming simulation of maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ of each finite element A _n in the model data D1 in a computer, were plotted respectively forming limit diagram G. Then, as shown in FIG. 4, although there was no plot above the forming limit line L1, a large number of plots were extracted in the region E2 between the forming limit line L1 and the corrected forming limit line L2.

When displaying each finite element A _n corresponding to the number of plots located in the region E2 in the model data D1 after molding (E3 parts), as shown in FIG. 5, as the bending ridge line extends along the winding direction of the coil It corresponded with the generation | occurrence | production site | part (E1 part) of the crack at the time of bending the bending shaping | molding part 3a and obtaining the press-forming body 3 actually.

  That is, as shown in FIG. 4 and FIG. 5, when forming the press-formed body 3, when the bending forming portion 3a is bent so that the bending ridge line follows the winding direction of the coil, the limit strain which is predicted to be cracked In the forming limit diagram G, it was found that the region is concentrated in the region between the forming limit line L1 and the corrected forming limit line L2.

  Next, the procedure of the prior prediction of the occurrence of cracking at the time of molding of the press-formed product 3 using the prediction method of the present invention will be described in detail.

First, as shown in FIG. 1, in step S1, to create a model data D1 composed of a plurality of finite elements A _n a modeled object pressing plate 2 in a computer.

  Next, in step S2, a forming limit diagram G is obtained when the thickness of the plate 2 to be pressed is t (see FIG. 4).

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

Thereafter, in step S4, whether or not the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ of each finite element A _n is positioned above the modified forming limit line L2 of the forming limit diagram G computer determines.

When the judgment at step S4 is YES, the words, if there is a finite element A _n on the upper side of the modified molding limit line L2, the process proceeds to step S5, the maximum principal strain epsilon ₁ and a minimum of the finite elements A _n principal strain epsilon ₂ determines whether positioned above the forming limit line L1 of forming limit diagram G.

On the other hand, when the determination in step S4 is NO, i.e., when there is no finite element A _n on the upper side of the modified molding limit line L2, it is judged that the crack at the time of molding regardless winding direction of the coil does not occur Thus, the pre-prediction of the occurrence of cracking at the time of molding of the press-formed body 3 is ended.

Then, when the determination in step S5 is YES, i.e., if there is a finite element A _n on the upper side of the forming limit line L1, to review the shape of the press-molded body 3 and the mold proceeds to step S6 .

On the other hand, when the determination in step S5 is NO, i.e., when there is no finite element A _n on the upper side of the forming limit line L1, the bend forming portion 3a as the bending ridge line intersects the winding direction of the coil If the press-formed body 3 is obtained by bending, it is determined that no cracking occurs at the time of forming, and the prior prediction of the occurrence of the occurrence of the crack at the time of forming the press-formed body 3 is ended.

  From the above, according to the embodiment of the present invention, a forming limit line is assumed in advance where it is difficult to form the press-formed product 3 by bending each bend-formed portion 3a so that the bending ridge line follows the winding direction of the coil. Since the computer calculates the corrected forming limit line L2 which is the lower limit value of and makes a preliminary prediction as to whether or not a crack occurs in the press-formed product 3, if it is predicted that a crack will occur, gold is It turns out that design changes such as molds are always necessary, but when it is predicted that cracking will not occur, material removal is freely examined regardless of the winding direction of the coil for the purpose of improving the yield etc. Will be able to Therefore, the time spent on the design change of the mold, the examination of material removal, etc. is reduced, and the number of rework is reduced, which can greatly contribute to the shortening of the development lead time.

In the embodiment of the present invention, first, by comparing the corrected forming limit line L2 of the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ and forming limit diagrams G of each finite element A _n, then corrected Forming Limit and so as to compare the forming limit line L1 of the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ and forming limit diagrams G of each finite element a _n when located finite element a _n above the line L2 maximum but not limited to, for example, by comparing the forming limit line L1 of the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ and forming limit diagrams G of each finite element a _n, for each finite element a _n it may be compared with the corrected forming limit line L2 of the principal strain epsilon ₁ and the minimum principal strain epsilon ₂ and forming limit diagrams G, forming a maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ of each finite element a _n after comparing the corrected forming limit line L2 limit diagram G, of each finite element a _n Maximum may end the principal strain epsilon ₁ and the minimum principal strain epsilon ₂ and advance prediction of occurrence or non-occurrence cracks without comparing the shaping limit line L1 of the forming limit diagram G.

  Further, in the embodiment of the present invention, the presence or absence of the occurrence of a crack in the press-formed product 3 having a hat-shaped cross section is predicted using the method of the prior prediction of the present invention. The presence or absence is also predictable. For example, in the embodiment of the present invention, all the bending ridges of each of the bent portions 3a of the press-formed body 3 extend in the same direction, but all the bending ridges of each of the bent portions 3a extend in the same direction. It is predictable even if it is not a body.

  The present invention is suitable for a method of predicting in advance whether or not a crack will occur in a press-formed product by press-forming simulation at a stage prior to press-forming a plate to be pressed to obtain a press-formed product.

1 flow chart 2 pressed plate 3 press formed body G forming limit line L1 forming limit line L2 correction forming limit line

Claims (1)

In the pre-stage of press-molding a plate to be pressed to obtain a press-formed body, model data consisting of a large number of finite elements obtained by modeling the plate to be pressed is created and numerical analysis by press-forming simulation using the model data is performed. performed by the computer derives each finite elements of the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ and in the model data, then the maximum principal strain epsilon ₁ and the minimum principal strain epsilon ₂ is forming limit of the above finite element At the time of molding of a press-formed product which the above-mentioned computer judges whether or not it is located above the line, and predicts that a crack will occur at the position of the above-mentioned press-formed product corresponding to each finite element located above the above-mentioned forming limit line. Advance prediction method for the occurrence of cracking in
When the thickness of the above-mentioned pressed plate is t, if the forming limit line experimentally or theoretically derived is defined as y = f (x) (y: maximum principal strain, x: minimum principal strain) In a simple bending test of a test plate obtained by unrolling a coil of steel strip having a thickness of t, the bending ridge line is formed as opposed to the bending ridge line so as to cross the coil winding direction. When the difference in critical strain is α × t (α: predetermined coefficient) when bending and forming along the winding direction of the coil, the computer generates a correction forming limit line y = f (from the forming limit line). x)-α x t is calculated, and it is determined whether or not the maximum principal strain ε ₁ and the minimum principal strain ε _{2 of} each of the finite elements are positioned above the corrected forming limit line, according to the corrected forming limit line The above press corresponding to each finite element located on the upper side It predicts that a crack will occur in the position of a form, The prior prediction method of the crack occurrence existence at the time of shaping | molding of the press-formed body characterized by the above-mentioned.