JP2017100165A - Press wrinkle generation determining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a press wrinkle generation determining method.SOLUTION: The press wrinkle generation determining method related to the present invention determines existence or nonexistence of wrinkle generation at a vertical wall part 5 press-molded by giving a blank 11 of a specified shape when flange-shrinkage-molding a press mold product 1 provided with a top plate part 3 having a convex outer periphery part 3a at least a part of which protrudes outside and a vertical wall part 5 bending from the convex outer periphery part 3a at the top plate part 3 to outside continuously through form-molding of a blank 11 by using a press molding metal die 20 provided with a punch 21 and a die 23. In a case that the compression distortion which is generated at the tip 5b of the vertical wall part 5 by form-molding of the blank 11 and depends on the blank end part radius Rexceeds a wrinkle generation limit distortion εderived without including the blank end part radius R, it is determined that wrinkle generation at the vertical wall part 5 exists.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a press wrinkle generation determination method for determining the presence or absence of wrinkle generation in a press-formed product formed by foam molding.

  In recent years, high-strength steel sheets are being frequently used for automobile parts in order to reduce the weight of automobile bodies due to environmental problems. For the production of automobile parts, press molding with excellent production cost is often used. However, high strength steel sheets used as blanks (press forming materials) are inferior in ductility compared to low strength steel sheets. In forming, a large strain is applied to the steel sheet, so that the material tends to break. Therefore, there are many cases where foam (bending) forming, which is press forming mainly of bending without using a blank holder, is applied. However, since the tension applied to the steel sheet in foam molding is relatively small, the material surplus due to the part shape tends to be a direct factor in generating wrinkles, and there is a problem that it is difficult to obtain a press-formed product with a target shape.

  The conventional method for suppressing the generation of wrinkles (press wrinkles) in press molding is to use a wrinkle pressing pad mechanism that is driven separately from the press machine, and by applying a load to the wrinkle-generating part in advance, the material surplus There is a method for preventing the buckling of the plate material due to. However, with this method, it is possible to suppress wrinkles on the upper surface of the part that can be sandwiched between the punch and the pad in the initial stage of molding, but it cannot be applied to the vertical part of the part that has a large inclination with respect to the driving direction of the press. In particular, when the top plate portion and the vertical wall portion are provided and the vertical wall portion is contracted and flange-formed, wrinkles are likely to occur, which is a problem.

  Accordingly, in order to obtain a press-molded product without wrinkles, it is necessary to clarify the factors of wrinkle generation in the foam molding process and to determine conditions such as the material and the target shape. Furthermore, in recent years, with the advancement of simulation technology by the finite element method, it has been performed to predict the occurrence of wrinkles in advance without actually performing pressing.

  In Patent Document 1, a press forming simulation based on an elasto-plastic finite element method is performed using a computer, a wrinkle evaluation parameter is obtained from equivalent stress and equivalent strain in the press forming process, and wrinkles are generated based on the value of the wrinkle evaluation parameter. A method for predicting the occurrence of wrinkles that determines the presence or absence of a wrinkle is disclosed.

JP-A-11-319971

  The wrinkle occurrence prediction method disclosed in Patent Document 1 performs a finite element analysis using a computer. However, in order to perform highly accurate prediction, a large amount of time and cost are required for calculation. In order to determine the conditions for obtaining a non-pressed product, trial and error are required even for calculation, and there is a problem that further time and cost are required.

  The present invention was made in order to solve the problem of wrinkle generation when the vertical wall portion that is difficult to suppress wrinkles during press molding as described above is formed by flange forming. It is an object of the present invention to provide a press wrinkle occurrence determination method that can easily and accurately determine the presence or absence of wrinkle occurrence.

(1) The method for determining the occurrence of press wrinkles according to the present invention includes a top plate portion having a convex outer peripheral edge portion in which at least a part of the outer peripheral edge protrudes outward, and a convex outer peripheral edge portion in the top plate portion. For a press-molded product having a vertical wall portion that curves continuously outward from a blank using a press-molding die that includes a punch and a die, the blank is formed by flange molding, and a predetermined flange is formed. When a blank having a shape is given, it is determined whether or not wrinkles are generated in the vertical wall after the blank is press-molded, and the compressive strain generated at the tip of the vertical wall determines the blank end radius. exceeding the wrinkle limit strain epsilon _cr is calculated using equation (a) containing no generation there and determine the wrinkles in the vertical wall portion of the press-molded product having a compressive strain is dependent on the blank end radius It is characterized in that.
However,
σ: Blank material strength [MPa]
t: Blank thickness [mm]
R: Curvature radius of curvature in the vertical wall [mm]
r _p : Punch shoulder radius [mm]
r _d : die shoulder radius [mm]
A, B, C, D, E, F: Coefficient

(2) In the above described (1), the compressive strain generated at the tip of the vertical wall portion of the press-molded product is calculated by the equation (b) using the blank end radius. .
However,
ε _E : Compression strain generated at the tip of the vertical wall
R _b : Blank edge radius [mm]

In the present invention, a top plate portion having a convex outer peripheral edge portion in which at least a part of the outer peripheral edge protrudes outward, and continuously outward from the convex outer peripheral edge portion of the top plate portion. When a press-molded product provided with a curved vertical wall portion is subjected to flange forming by shrinking a blank by form molding using a press mold including a punch and a die, it is determined whether or not wrinkles are generated in the vertical wall portion. Whether or not the compressive strain generated at the tip of the vertical wall portion by foam molding of the blank exceeds the wrinkle generation limit strain ε _cr calculated using the formula (a) not including the blank end radius. Therefore, it is possible to determine in advance whether or not there is wrinkle in a press-formed product having a compressive strain that depends on the radius of the blank edge, greatly increasing the time and cost for accurately determining the shape of the blank. It is possible to reduce.

It is a figure explaining the press-formed product made into object in this invention. It is a figure explaining the press-molding die used for shaping | molding of the press-formed product made into object in this invention. It is a figure explaining the shape of the blank for shape | molding the press molded product made into object in this invention. It is a figure explaining the press molding process of the press molded product which concerns on this invention. It is a figure explaining the wrinkles which generate | occur | produce when form-molding the press molded product which concerns on this invention. It is a figure explaining the compressive strain in the press wrinkle generation | occurrence | production determination method which concerns on embodiment of this invention. It is a graph showing the relationship between the tensile strength of a blank and a wrinkle generation | occurrence | production limit distortion in the press wrinkle generation | occurrence | production determination method which concerns on embodiment of this invention. In the press wrinkle generation determination method according to the embodiment of the present invention, it is a graph showing the relationship between the blank plate thickness and the wrinkle generation limit strain. In the press wrinkle generation determination method according to the embodiment of the present invention, it is a graph showing the relationship between the punch shoulder radius and the wrinkle generation limit strain. In the press wrinkle generation determination method according to the embodiment of the present invention, it is a graph showing the relationship between the die shoulder radius and the wrinkle generation limit strain. In the press wrinkle generation determination method according to the embodiment of the present invention, it is a graph showing the relationship between the radius of curvature of the curved portion of the press-formed product and the wrinkle generation limit strain. It is a figure explaining the press-formed product in Example 1 of the present invention. It is a graph showing the correlation of the measured value of wrinkle generation | occurrence | production limit distortion in Example 1 of this invention, and the calculated value by Formula (c). It is a graph showing the correlation of the measured value of wrinkle generation | occurrence | production limit distortion in Example 2 of this invention, and the calculated value by Formula (d).

  The press wrinkle occurrence determination method according to the embodiment of the present invention includes a press-formed product 1 having a top plate portion 3 and a vertical wall portion 5 that curves outwardly as shown in FIG. When compressive flange molding is performed by foam molding, the compressive strain generated at the tip 5b of the vertical wall portion 5 depending on a predetermined blank shape (blank end radius) is calculated, and when the compressive strain exceeds the wrinkle generation limit strain, It is determined that wrinkles are generated in the vertical wall 5.

  Before explaining the method for determining the occurrence of press wrinkles according to the present embodiment, the compressive strain and the wrinkle generation limit strain generated in the press-formed product 1 to be molded in the present invention and the tip 5b of the vertical wall portion 5 will be described below. explain.

<Press-formed product>
As shown in FIG. 1, the press-formed product 1 includes a top plate portion 3 having a convex outer peripheral edge portion 3 a in which at least a part of the outer peripheral edge protrudes outward, and a convex outer peripheral edge in the top plate portion 3. A vertical wall portion 5 having a curved portion 5a which is continuous from the portion 3a through the connecting portion 7 and curves outwardly in an arc shape.

As shown in FIG. 2, the press-formed product 1 is formed by the following procedure using a press-molding die 20 including a punch 21, a die 23, and a pad 25.
First, the blank 11 having a shape as shown in FIG. 3 is placed on the punch 21 so that the arcuate arc portion 11a is substantially parallel to the punch shoulder portion 21a. Then, as shown in FIG. 4, the die 23 and the punch 21 are relatively moved while the blank 11 is pressed by the punch 21 and the pad 25, and the portion corresponding to the vertical wall portion 5 in the blank 11 is contracted and flange-molded. The press-formed product 1 is manufactured.

  In the press-formed product 1 in which the bending process of the vertical wall portion 5 is contracted and the flange is deformed, the contraction deformation is concentrated on the front end 5b of the vertical wall portion 5, and the height h of the vertical wall portion 5 exceeds a certain value. As a result of buckling, wrinkles 9 are generated in the vertical wall portion 5 as shown in FIG.

<Compression strain and wrinkle generation limit strain>
In the present invention, the compression strain generated at the tip 5b in the direction (edge direction) along the tip 5b of the vertical wall portion 5 during the molding of the press-molded product 1 is calculated (see FIG. 6). The presence or absence of wrinkle generation in the wall 5 is determined.

The compressive strain ε _E in the edge direction at the front end 5b of the vertical wall portion 5 is, for example, the curvature radius of curvature in the vertical wall portion 5, that is, the curvature radius R of the curved portion 5a (see FIG. 1), the blank end portion of the blank 11 It can be expressed by the following formula (b) using the radius R _b and the plate thickness t.

However, (epsilon) _E is a value in the center of the plate | board thickness direction of the blank 11, and R is taken as the curvature radius by the side of the punch 21 in the plate | board thickness direction of the vertical wall part 5. FIG.
Further, the blank end radius _Rb is a radius of curvature at the end of the blank 11 corresponding to the front end 5b of the vertical wall portion 5, and is the radius of curvature at the arc portion 11a of the blank 11 in FIG.

In the present invention, as a reference for determining the presence or absence of occurrence of press wrinkles in the vertical wall portion 5 using the value of the compressive strain ε _E depending on the blank end radius R _b , the wrinkles are not generated in the vertical wall portion 5. A compressive strain when the height h of the vertical wall portion 5 is maximum is defined as a wrinkle generation limit strain ε _cr .

The height h of the vertical wall portion 5 which is curved in the press-molded article 1, and the blank edge radius R _b, but determined by the punch shoulder radius r _p of the press molding die 20, bending in a range in which wrinkles are not generated vertical wall The maximum height of the portion 5 is independent of the blank end radius _Rb .
Therefore, the wrinkle generation limit strain ε _cr when forming the maximum height of the curved vertical wall portion 5 in a range where no wrinkles are generated can be obtained without using the blank end radius R _b .

On the other hand, the blank end radius _Rb affects the compressive strain generated at the tip 5b of the vertical wall 5 when the vertical wall 5 is curved in the press-formed product 1.
That is, if the blank end radius R _b is used or the wrinkle generation limit strain ε _cr can be calculated, whether or not wrinkles are generated in the curved vertical wall portion 5 of the press-formed product 1 due to the blank shape (blank end radius R _b ). Can be determined.

The wrinkle generation limit strain ε _cr defined in this way does not include the blank end radius R _b , and changes depending on the material strength of the blank 11 and the shape difference between the press-formed product 1 and the press-molding mold 20. Thus, as the shape of the press molding die 20, the punch shoulder radius r _p in the cross-sectional shape of the punch shoulder portion 21a and the die shoulder radius r _d which is the curvature radius in the cross-sectional shape of the die shoulder portion 23a can be cited (see FIG. 4).

Therefore, in order to investigate the influence of the material strength of the blank 11 on the wrinkle generation limit strain ε _cr in the shrinkage flange deformation, the conditions regarding the shape such as the punch shoulder radius r _p and the die shoulder radius r _{d of} the press mold 20 are as follows. While maintaining the same, foam was formed using blanks 11 having different material strengths, and wrinkle generation limit strain ε _cr at each material strength was obtained.

7, the tensile curvature radius R of the curved portion 5a 90 mm, a punch shoulder radius r _p 8 mm, a die shoulder radius r _d 8 mm, the plate thickness t and 1.2mm blank 11, as different blank 11 of material strength strength The wrinkle generation limit strain ε _cr when σ _TS uses a blank 11 of 270 MPa class, 590 MPa class, and 980 MPa class is shown. From FIG. 7, as the tensile strength σ _TS of the blank 11 increases, the wrinkle generation limit strain decreases, and the relationship between the tensile strength σ _TS of the blank 11 and the wrinkle generation limit strain ε _cr is substantially linear. Therefore, it is considered that the wrinkle generation limit strain ε _cr is substantially proportional to the material strength σ of the blank 11.

Similarly, the influence of the thickness t of the blank 11 on the wrinkle generation limit strain ε _cr was examined.
Figure 8, 90 mm radius of curvature R of curvature in the curved portion 5a, a punch shoulder radius r _p and 8 mm, a die shoulder radius r _d and 8 mm, showing the wrinkle limit strain epsilon _cr of changing the plate thickness t. From FIG. 8, the wrinkle generation limit strain ε _cr increases as the plate thickness t of the blank 11 increases at any tensile strength σ _TS , and the relationship between the plate thickness and the wrinkle generation limit strain is almost linear.

Next, the influence of the shape of the press molding die 20 on the wrinkle generation limit strain ε _cr was examined.
Figure 9, 980 MPa grade tensile strength sigma _TS of the blank 11, 1.2 mm plate thickness t, 90 mm radius of curvature R of curvature in the curved portion 5a, a die shoulder radius r _d and 8 mm, change the punch shoulder radius r _p FIG. 10 shows the results when the blank 11 has a tensile strength σ _TS of 980 MPa class, a sheet thickness t of 1.2 mm, a curvature radius R of the curvature in the vertical wall portion 5 of 90 mm, a punch shoulder radius r _p of 8 mm, The wrinkle generation limit strain ε _cr when the shoulder radius r _d is changed is shown.
The larger the values of both the punch shoulder radius and the die shoulder radius, the larger the wrinkle generation limit strain ε _cr, and the relationship with the wrinkle generation limit strain was almost linear.

Further, the influence of the curvature radius R of the bending portion 5a on the wrinkle generation limit strain ε _cr was examined. 1.2m plate thickness t of the blank 11 in FIG. 11, 2 mm punch shoulder radius r _p, a die shoulder radius r _d to change the curvature radius R of curvature in the curved portion 5a as 8 mm, the tensile strength sigma _TS blank 11 The wrinkle generation limit strain ε _cr in the case of 270 MPa class, 590 MPa class, and 980 MPa is shown.
The smaller the curvature radius R of the curve, the larger the wrinkle generation limit strain ε _cr , and the influence was inversely related. Further, it was found that the influence of the tensile strength σ _TS of the blank 11 is relatively large when the radius of curvature R is small, that is, when the wrinkle generation limit strain ε _cr is large.

From the above results, the wrinkle generation limit strain ε _cr in the vertical wall portion 5 of the press-formed product 1 is the material strength σ and the plate thickness t of the blank 11, the curvature radius R of the curved portion 5a, and the punch shoulder radius r. It was considered that it could be predicted from _p and die shoulder radius r _d, and was formulated as in equation (a).

  The coefficients A to F in the formula (a) can be determined by regression analysis from the results of press molding experiments and molding simulations under at least six conditions.

In the formulation of the formula (a), since the influence of the tensile strength σ _TS of the blank 11 was great when the wrinkle generation limit strain ε _cr was large from the result shown in FIG. The term representing the influence of σ is multiplied by the term representing the influence of the shape of the press-formed product 1 and the press-molding mold 20. In this case, the thickness t of the blank 11 is included in the term representing the shape.

Further, when considering the similar deformation of the press molding object, it is considered that normalization is possible by dividing the influence of the thickness t of the blank 11 and the shape of the press molding die 20 by any one parameter, and wrinkles are generated. The curvature radius R of the curve has an inverse relationship with the limit strain ε _cr , and the plate thickness t, punch shoulder radius r _p , and die shoulder radius r _d are divided.

The formula (a) is formulated based on the result of the compressive strain when the tensile strength σ _TS of the blank 11 is changed, but the material strength σ in the formula (a) is not limited to the tensile strength. For example, the yield strength σ _YS of the blank 11 may be used.

<Press wrinkle generation judgment method>
Next, the press wrinkle occurrence determination method according to the present embodiment will be described below.
First, as conditions for forming the press-molded product 1 using the press-molding die 20, the thickness t and material strength σ of the blank 11 to be subjected to press-molding, the punch shoulder radius r _p of the press-molding die 20, The die shoulder radius r _d and the curvature radius of curvature in the vertical wall portion 5, that is, the curvature radius R of curvature in the curved portion 5a are set.

Using these values, the wrinkle generation limit strain ε _cr is calculated by the equation (a). Further, the blank end radius R _{b of} the blank 11, the plate thickness t, and the curvature radius R on the punch 21 side in the plate thickness direction of the vertical wall portion 5 are used to calculate the vertical wall portion 5 of the press-formed product 1 according to the formula (b). The compressive strain ε _E in the edge direction generated at the tip 5b is calculated.

In calculating the wrinkle generation limit strain ε _cr by the equation (a), it is necessary to determine the values of the coefficients A to F in advance.

When the compression strain value ε _E calculated by the equation (b) is larger than the wrinkle generation limit strain value ε _cr calculated by the equation (a), it is determined that wrinkles are generated in the vertical wall portion 5 of the press-formed product 1. judge.
On the other hand, when the compressive strain value ε _E calculated by the equation (b) is equal to or _smaller than the wrinkle generation limit strain value ε _cr calculated by the equation (a), no wrinkle is generated in the vertical wall portion 5 of the press-formed product 1. Is determined.

As described above, the press wrinkle generation determination method according to the present embodiment determines in advance whether or not wrinkle is generated by using the material strength and thickness of the blank and the shape of the press mold before actually performing press molding. Therefore, the time and cost for determining the shape of the blank (blank end radius R _b ) can be greatly reduced.

  In the above description, the occurrence of wrinkles in the vertical wall portion 5 is determined for the press-formed product 1 formed by the press-molding die 20 provided with the pad 25. Such a press wrinkle generation determination method may be a method in which the press-formed product 1 is foam-formed only by the punch 21 and the die 23 without using the pad 25.

  Further, the above description is intended for the press-formed product 1 having the curved portion 5a in which a part of the vertical wall portion 5 is curved in an arc shape, but the press wrinkle occurrence determination method according to the present invention is illustrated in FIG. As shown in FIG. 12, the presence or absence of occurrence of press wrinkles may be determined for a press-formed product 31 in which all the vertical wall portions 35 are curved in an arc shape.

  An experiment for verifying that the occurrence of press wrinkles in the vertical wall portion of the press-formed product can be determined by the method for determining occurrence of press wrinkles according to the present invention will be described below.

In Example 1, first, for the press-formed product 31 shown in FIG. 12, the tensile strength σ _TS of the blank 11 is 270 MPa to 1180 MPa, the plate thickness t is 0.7 mm to 3.2 mm, and the vertical wall portion 35 25mm~100mm radius of curvature R of the curved, 2 mm to 20 mm punch shoulder radius r _p, a die shoulder radius r _d under the conditions set in the range of 2 mm to 20 mm, the vertical wall portion 35 of the press-molded product 31 high The thickness h was changed and molded, and the wrinkle generation limit strain was measured based on the presence or absence of wrinkle generation in the vertical wall portion 35.

Then, a multiple regression analysis is performed on the equation (a) using the measurement result of the wrinkle generation limit strain ε _cr formed for the press-formed product 31 of FIG. 12, and the coefficients A to F in the equation (a) are calculated. The value was determined.
The formula used for calculating the wrinkle generation limit strain ε _cr in Example 1 is shown below.

FIG. 13 shows the correlation between the measured value of the wrinkle generation limit strain ε _cr and the calculated value calculated by the equation (c).
The correlation coefficient r between them is 0.995, and it can be seen that the equation (c) can satisfactorily represent the wrinkle generation limit strain.

Next, the wrinkle generation limit strain ε _cr calculated by the equation (c) is changed from the disc-shaped top plate portion 33 shown in FIG. 12 and the convex outer peripheral edge portion 33 a of the top plate portion 33 through the connection portion 37. When forming a shallow cylindrical press-formed product 31 having a continuous vertical wall portion 35 that curves outward, it was applied to the determination of wrinkle generation in the vertical wall portion 35.

  In the press-formed product 31, the die was relatively moved to the punch side while the blank was held by the punch and the pad, the vertical wall portion 35 was bent, and the presence or absence of wrinkles at the tip of the vertical wall portion 35 was observed.

The press molded product 31 is formed by changing the tensile strength σ _TS of the blank 11, the plate thickness t, the curvature radius R of the curvature in the vertical wall 35, the punch shoulder radius r _p and the die shoulder radius r _d, and the vertical wall at that time The presence or absence of wrinkle generation in the portion 35 is measured, the wrinkle generation limit strain ε _cr is calculated by the equation (c), and the end of the vertical wall portion 35 is calculated by the equation (b) by changing the blank end radius R _b. It calculates the compression strain epsilon _E, compared with the determination result of the presence or absence of wrinkle generation using the expression (b) wrinkling limit strain epsilon _cr calculated by the calculated compression strain epsilon _E and formula (c) by did.
Table 1 shows the experimental results and determination results for the presence or absence of wrinkle generation under each condition.

From Table 1, the wrinkle limit strain epsilon _cr calculated by Formula (c) which does not use the radius R _b blank end, that the presence or absence of wrinkling of the vertical wall portion 35 by the blank end radius R _b can be accurately determined Proven.

  In Example 2, as in Example 1, an experiment was conducted to verify that the determination of the occurrence of press wrinkles in the vertical wall portion of the press-formed product can be made by the method for determining occurrence of press wrinkles according to the present invention.

In Example 2, first, for the press-formed product 1 shown in FIG. 1, the blank 11 has a tensile strength σ _TS of 980 MPa to 1470 MPa, a plate thickness t of 1.0 mm, and a curvature radius R of the curved portion 5a. the molded 100Mm～2000mm, punch shoulder radius r _p of 8 mm, under the conditions that the die shoulder radius r _d set in a range of 8 mm, a press-molded article 1 by changing the blank end radius R _b, the vertical wall The wrinkle generation limit strain ε _cr was measured based on the presence or absence of wrinkle generation in the part 5.

Then, a multiple regression analysis is performed on the equation (a) using the measurement result of the wrinkle generation limit strain ε _cr formed for the press-formed product 1 of FIG. 1, and the coefficients A to F in the equation (a) are calculated. The value was determined.
The formula used for calculating the wrinkle generation limit strain in Example 2 is shown below.

FIG. 14 shows the relationship between the measured value of the wrinkle generation limit strain ε _cr and the calculated value calculated by the equation (d).
The correlation coefficient r between them is 0.997, and it can be seen that the equation (d) represents the wrinkle generation limit strain ε _cr well.

Next, a top plate portion 3 having a convex outer peripheral edge portion 3a projecting outwardly as shown in FIG. 1 and a wrinkle generation limit strain ε _cr calculated by the formula (d), and the top plate portion 3 was applied to the determination of the occurrence of wrinkles in the vertical wall portion 5 during foam molding of the press-formed product 1 having the vertical wall portion 5 that is continuous from the convex outer peripheral edge portion 3a and curves outward.

The press molded product 1 is formed by changing the tensile strength σ _TS of the blank 11, the plate thickness t, the curvature radius R of the curved portion 5 a, the punch shoulder radius r _p, and the die shoulder radius r _d . Measure wrinkle occurrence, calculate wrinkle generation limit strain ε _cr by equation (d), change blank end radius R _b, and compressive strain at tip of vertical wall 35 by equation (b) ε _E was calculated, and the compression strain ε _E calculated by the equation (b) and the wrinkle generation limit strain ε _cr calculated by the equation (d) were used and compared with the determination result of the occurrence of wrinkles.
Table 2 shows the experimental results and determination results for the presence or absence of wrinkle generation under each condition.

From Table 2, the wrinkle limit strain epsilon _cr calculated by Formula (d) without using a radius R _b blank end, that the presence or absence of wrinkling of the vertical wall portion 35 by the blank end radius R _b can be accurately determined Proven.

DESCRIPTION OF SYMBOLS 1 Press molding 3 Top plate part 3a Convex outer periphery part 5 Vertical wall part 5a Curved part 5b Tip 7 Connection part 9 Wrinkle 11 Blank 11a Arc part 20 Press molding die 21 Punch 21a Punch shoulder part 23 Die 23a Die shoulder part 25 Pad 31 Press-formed product 33 Top plate portion 33a Convex outer peripheral edge portion 35 Vertical wall portion 37 Connection portion

Claims (2)

A top plate portion having a convex outer peripheral edge portion in which at least a part of the outer peripheral edge protrudes outward, and a vertical wall portion that curves continuously outward from the convex outer peripheral edge portion of the top plate portion. When a blank is shrunk by foam molding using a press molding die provided with a punch and a die and given a blank of a predetermined shape, the blank is press molded. It is a press wrinkle occurrence determination method for determining the presence or absence of wrinkle occurrence in the vertical wall portion after
When the compressive strain generated at the tip of the vertical wall portion exceeds the wrinkle generation limit strain ε _cr calculated using the formula (a) not including the blank end radius, the compressive strain depends on the blank end radius. A press wrinkle occurrence determination method, characterized in that it is determined that wrinkles are generated in the vertical wall portion of a press-formed product.
However,
σ: Blank material strength [MPa]
t: Blank thickness [mm]
R: Curvature radius of curvature in the vertical wall [mm]
r _p : Punch shoulder radius [mm]
r _d : die shoulder radius [mm]
A, B, C, D, E, F: Coefficient 2. The method for determining the occurrence of press wrinkles according to claim 1, wherein the compressive strain generated at the tip of the vertical wall portion of the press-formed product is calculated by an equation (b) using a radius of a blank end portion.
However,
ε _E : Compression strain generated at the tip of the vertical wall
R _b : Blank edge radius [mm]