JP7396550B1 - Press molding method and method for manufacturing press molded products - Google Patents

Abstract

The press molding method and the method for manufacturing a press molded product according to the present invention provide a press molded product having a top plate portion 211, a vertical wall portion 215, a flange portion 219, and a concave curved portion 221 that is curved concavely in a top view. 210 as a target shape, a step (S1) of creating a blank 100 provided with a concave shape 101 corresponding to the curvature of the concave curved portion 221; It has a vertical wall portion 115 and a flange portion 119, and has a concave curved portion 121 that curves concavely in a top view, and a portion of the flange portion 119 and the vertical wall portion 115 is chipped at the curved center portion 121a of the concave curved portion 121. The process includes a step (S3) of press-molding the intermediate-shaped press-formed product 110 provided with the portion 125, and a step (S5) of press-molding the intermediate-shaped press-formed product 110 into a target shape.

Description

The present invention provides a press-forming method for press-forming a press-formed product into a target shape, which has a top plate portion and a vertical wall portion continuous from the top plate portion, and has a concave curved portion that is concavely curved in a top view. and a method for producing a press-molded product.

Automobiles and home appliances have many press-formed products as constituent members, and these press-formed products are manufactured by press-molding blanks that are metal plates. In recent years, high-strength metal plates such as high-strength steel plates and aluminum alloy plates with a tensile strength of 590 MPa or higher have been used for press forming. However, since such a metal plate has low ductility and low Lankford value, there is a problem that cracks are likely to occur during press forming.

As an example of the shape of a press-formed product that is prone to cracking, it has a top plate part and a vertical wall part continuous from the top plate part via a ridgeline part, and when viewed from above, the top plate part, the ridgeline part and the vertical wall part are continuous. There is a press-molded product having a concave curved portion where the wall portion is concavely curved. When such a press-formed product is press-formed from a metal plate blank, cracks (stretch flange cracks) are likely to occur due to tensile deformation in the direction along the curve of the blank during the press-forming process, causing molding defects.

Therefore, conventionally, techniques have been proposed for suppressing the occurrence of stretch flange cracking during the press forming process of a press-formed product having a concave curved portion when viewed from above.

For example, in Patent Document 1, a sheet metal molded product including a top plate portion having a concave outer peripheral edge portion and a flange portion (corresponding to the vertical wall portion of the present application) continuously curved from the concave outer peripheral edge portion is press-formed. In this case, a technique has been disclosed for suppressing the occurrence of stretch flange cracking in the flange portion. In this technique, a preformed product is obtained by first forming a flange portion in a blank, which is composed of a large curvature portion having a large curvature and a small curvature portion having a small curvature sandwiched therebetween. Here, the curvature of the large curvature part is greater than the curvature part that makes up the flange part of the sheet metal molded product, and the curvature of the small curvature part is smaller than the curvature part that makes up the flange part of the sheet metal molded product. do. Furthermore, the flange portion of the preformed product has a shorter line length in plan view compared to the line length of the flange portion of the sheet metal molded product in plan view. It is said that cracking of the flange portion can be suppressed by restriking the preformed product obtained in this way into a target shape.

Further, Patent Document 2 describes a top plate portion and a vertical wall portion that is connected to the top plate portion via a bent portion having an arcuate curved portion and has a flange portion on the opposite side of the bent portion. A technique is disclosed in which a component including a top plate portion, a vertical wall portion, and a flange portion is formed from a raw metal plate. In this technique, while at least a part of the part of the raw metal plate corresponding to the top plate is pressurized by a pad, the end of the part of the raw metal plate corresponding to the lower side of the L-shape is pressed into the die mold. The vertical wall portion and the flange portion are formed while sliding on the portion corresponding to the top plate portion. It is said that this makes it possible to suppress cracks in the flange portion.

Japanese Patent Application Publication No. 2021-159951 Patent No. 5168429

However, with the technology disclosed in Patent Document 1, a press that has a top plate part and a vertical wall part continuous from the top plate part via a ridgeline part, and has a concave curved part that is concavely curved in a top view. When press forming a molded product, stretch flange cracking was likely to occur. In particular, if the radius of curvature of the concave curved part is small (the curvature is large), the line length of the vertical wall part of the intermediate-shaped press-formed product (the flange part of the preformed product of Patent Document 1) is too short, and the concave curved part It was not possible to sufficiently reduce the tensile strain that concentrates on the vertical wall. As a result, the ends of the vertical wall portions in the concave curved portions are molded under large tensile deformation in the direction along the curve, resulting in concentration of tensile strain and a problem in that stretch flange cracks are likely to occur.

In addition, in the technology disclosed in Patent Document 2, the end portion of the portion of the raw metal plate corresponding to the lower side of the L-shape is slid vertically over the portion of the die mold that corresponds to the top plate portion. The raw metal plate moved during press forming to form the wall and flange parts. As a result, there is a problem in that the shape of the press-formed part greatly changes, the dimensional accuracy fluctuates, and the effect of suppressing stretch flange cracking also fluctuates.

The present invention has been made to solve the above-mentioned problems, and provides a stretch flange of a press-formed product having a top plate portion and a vertical wall portion, and a concave curved portion that is concavely curved when viewed from above. It is an object of the present invention to provide a press molding method and a method for manufacturing a press molded product that can sufficiently suppress cracking.

In order to solve the above-mentioned problems and achieve the objectives,
(1) The press forming method according to the present invention has a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, which is curved in a concave shape when viewed from above. a press-molded product having a concave curved portion having a shape as a target shape, the step of producing a blank having a concave shape corresponding to the curvature of the concave curved region of the target shape; The created blank has a top plate part, a vertical wall part continuous from the top plate part, and a flange part continuous from the vertical wall part, and has a concave curved part that curves concavely in a top view, An intermediate-shaped press in which a notch is provided in a part of the flange part and the vertical wall part, or a part of the flange part, the vertical wall part, and the top plate part at the center of the curve of the concave curved part. The intermediate shape forming step includes an intermediate shape forming step of press forming a molded product, and a target shape forming step of press forming the intermediate shape press molded product into the target shape. It is characterized in that press molding is performed so that a part of the shape becomes the chipped part.

(2) The press molding method according to the present invention provides a press molded product having a top plate portion, a vertical wall portion continuous from the top plate portion, and a concave curved portion that is concavely curved when viewed from above. A blank creating step of creating a blank that is press-molded as a target shape and is provided with a concave shape corresponding to the curvature of the concave curved portion; and a concave curved portion that is concavely curved in a top view, and a chipped portion is provided in a part of the vertical wall portion and the top plate portion at a curved center portion of the concave curved portion. An intermediate shape forming step of press-molding the intermediate-shaped press-formed product provided, and a target-shape forming step of press-molding the intermediate-shaped press-formed product into the target shape, and the intermediate shape forming step includes: It is characterized in that press molding is performed so that a part of the concave shape provided on the blank becomes the notch.

(3) In the press forming method according to the present invention, in the above-mentioned invention (1) or (2), in the intermediate shape forming step, the radius of curvature R _E at the curved end of the concave curved portion of the intermediate shape is The radius of curvature of the concave curved portion of the target shape is larger than _R0 .

(4) The method for manufacturing a press-formed product according to the present invention includes a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion. A blank production step of producing a press-molded product having a concave curved portion having a target shape, the blank having a concave shape corresponding to the curvature of the concave curved portion of the target shape; , the created blank has a top plate part, a vertical wall part continuous from the top plate part, and a flange part continuous from the vertical wall part, and has a concave curved part that curves concavely in a top view. an intermediate shape in which a portion of the flange portion and the vertical wall portion or a portion of the flange portion, the vertical wall portion, and the top plate portion are provided in a central portion of the curve of the concave curved portion; an intermediate shape forming step of press-forming the press-formed product into a press-formed product; and a target-shape forming step of press-forming the intermediate-shaped press-formed product into the target shape, and the intermediate shape forming step includes the step of press-forming the press-formed product of the intermediate shape into the target shape. The present invention is characterized in that a part of the concave shape is press-molded so as to become the notched part.

(5) The method for manufacturing a press-formed product according to the present invention includes a press having a top plate portion, a vertical wall portion continuous from the top plate portion, and a concave curved portion that is concavely curved in a top view. A blank producing step of producing a blank having a concave shape corresponding to the curvature of the concave curved portion, and a step of producing a blank with a concave shape corresponding to the curvature of the concave curved portion, and a step of producing a blank having a concave shape corresponding to the curvature of the concave curved portion; a vertical wall part continuous from the plate part, and a concave curved part that curves concavely in a top view, and a part of the vertical wall part and the top plate part is chipped at a curved center part of the concave curved part. an intermediate shape forming step of press-forming an intermediate-shaped press-formed product provided with a part, and a target-shape forming step of press-forming the intermediate-shaped press-formed product into the target shape, the intermediate-shape forming step The method is characterized in that the blank is press-molded so that a part of the concave shape becomes the notch.

(6) In the method for manufacturing a press-formed product according to the present invention, in the invention (4) or (5) above, in the intermediate shape forming step, a radius of curvature R at a curved end of the concave curved portion of the intermediate shape is provided. The present invention is characterized in that _E is press-molded so as to be larger than the radius of curvature R ₀ at the concave curved portion of the target shape.

In the press-forming method and the method for manufacturing a press-formed product according to the present invention, a blank having a concave shape corresponding to the curvature of the concave curved portion is created, and the created blank has a chip at the center of the curve of the concave curved region. Press-form the product into an intermediate-shaped press-formed product having a section. At this time, press molding is performed so that the concave shape provided on the blank becomes a notch. This makes it possible to reduce the tensile stress acting in the vicinity of the chipped portion and to disperse the tensile stress to both ends of the curve in the concave curved portion. As a result, when an intermediate-shaped press-formed product is press-formed into the target shape, stretch flange cracking can be sufficiently suppressed, enabling stable press-forming without cracking, and improving productivity and yield. can be achieved.

FIG. 1 is a flowchart showing the process flow in the press molding method according to the embodiment. FIG. 2 is a perspective view showing an example of a press-formed product to be molded in this embodiment ((a) Z-shaped cross-sectional shape, (b) U-shaped cross-sectional shape, (c) hat cross-sectional shape). FIG. 3 is a diagram illustrating a conventional technique for press-forming a press-formed product having a concave curved portion when viewed from above in one step. FIG. 4 is a contour diagram showing an example of the results of the plate thickness reduction rate of a press-formed product press-formed in one step using the conventional technique. FIG. 5 is a diagram illustrating a preformed product (an intermediate-shaped press-formed product) that is press-formed in the method under comparative conditions. Figure 6 shows an example of the results of the plate thickness reduction rate of a preformed product (an intermediate-shaped press-formed product) and a sheet metal formed product (a target-shaped press-formed product) that were press-formed using the method under the comparative conditions. FIG. FIG. 7 is a diagram illustrating a press-formed product having an intermediate shape and a target shape that are press-formed by the press-forming method according to the embodiment. FIG. 8 is a diagram illustrating a process of press-forming a press-formed product having a concave curved portion when viewed from above by the press-forming method according to the embodiment ((a) intermediate shape forming process, (b) target shape forming process). FIG. 9 is a contour diagram showing an example of the results of the plate thickness reduction rate of a press-formed product having an intermediate shape and a target shape, which were press-formed by the press-forming method according to the embodiment. FIG. 10 is a diagram illustrating a suitable position of a ridgeline portion in a concave curved portion of an intermediate-shaped press-formed product that is press-formed in the press-forming method according to the present invention. FIG. 11 is a diagram illustrating a specific example of a chipped portion in a concave curved portion of an intermediate-shaped press-formed product that is press-formed in the press-forming method according to the present invention. FIG. 12 is a diagram showing a target shape of a press-formed product having a hat cross-sectional shape as a molding target in the example. FIG. 13 is a diagram illustrating the steps of press-forming press-formed products having an intermediate shape and a target shape by the method according to the present invention in an example ((a) intermediate shape forming step, (b) target shape molding process). FIG. 14 is a diagram illustrating a conventional example in which a press-formed product having a target shape is press-formed in one step in an example. FIG. 15 is a contour diagram of the plate thickness reduction rate determined for a press-formed product of a target shape in a conventional example in an example. FIG. 16 is a contour diagram of the plate thickness reduction rate determined for press-formed products with an intermediate shape and a target shape in a comparative example in Examples ((a) a press-formed product with an intermediate shape, (b) a press-formed product with a target shape). Molding). FIG. 17 is a contour diagram of the plate thickness reduction rate determined for the press-formed product with the intermediate shape and the target shape in Invention Example 1 ((a) the press-formed product with the intermediate shape, (b) the press-formed product with the target shape). press molded product). FIG. 18 is a contour diagram of the plate thickness reduction rate determined for the press-formed product with the intermediate shape and the target shape in Invention Example 2 ((a) the press-formed product with the intermediate shape, (b) the press-formed product with the target shape). press molded product).

EMBODIMENT OF THE INVENTION Below, embodiment of the press molding method and the manufacturing method of a press molded article based on this invention is described. Note that the present invention is not limited to this embodiment.

Before explaining the press-forming method and the method for manufacturing a press-formed product according to an embodiment of the present invention, the press-formed product to be molded in the present invention and the circumstances that led to the present invention will be described.

<Press molded product>
FIG. 2 is a perspective view showing a specific example of a press-formed product to be molded in the present invention.

The press-formed product 210 in FIG. 2(a) includes a top plate portion 211, a vertical wall portion 215 continuous from the top plate portion 211 via a ridgeline portion 213, and a vertical wall portion 215 continuous from the vertical wall portion 215 via a die shoulder portion 217. This is an example of a press-molded product having a Z-shaped cross section. The press-formed product 210 has a concave curved portion 221 in which the ridgeline portion 213, the vertical wall portion 215, the die shoulder portion 217, and the flange portion 219 side are concavely curved, and a straight line from both ends of the curve of the concave curved portion 221. A straight line portion 223 extending to.

Further, the press-formed product 230 in FIG. 2(b) is a press-formed product with a U-shaped cross section, which has a top plate portion 231 and a vertical wall portion 235 that continues from both ends of the top plate portion 231 via a ridgeline portion 233. This is an example. The press-formed product 230 includes a concave curved part 241 in which the ridgeline part 233a and the vertical wall part 235a side are concavely curved when viewed from above, and a straight part 243 extending linearly from both curved ends of the concave curved part 241. It is equipped with

Further, the press-formed product 250 in FIG. 2(c) includes a top plate portion 251, a vertical wall portion 255 that continues from both ends of the top plate portion 251 via a ridgeline portion 253, and a vertical wall portion 255 that extends from the vertical wall portion 255 via a die shoulder portion 257. This is an example of a press-molded product having a hat cross-sectional shape and having a continuous flange portion 259. The press-formed product 250 has a concave curved portion 261 in which the ridge portion 253a, the vertical wall portion 255a, the die shoulder portion 257a, and the flange portion 259a side are curved in a concave shape, and a straight line from both ends of the curve of the concave curved portion 261. A straight line portion 263 extending to.

As described above, the press-formed product to be molded in the present invention has a top plate part and a vertical wall part continuous from the top plate part via the ridgeline part, as illustrated in FIG. Any material may be used as long as it has a concave curved portion that curves concavely when viewed. Therefore, the press-formed product to be molded is not limited to other specific shapes, such as the cross-sectional shape, the radius of curvature of the concave curved portion, the length of the straight portion, etc.

Hereinafter, a case where a press-formed product 210 having a Z-shaped cross-section shown in FIG. 2(a) is press-formed into a target shape will be described as an example.

<How the present invention was achieved>
Conventionally, a press-formed product 210 having a Z-shaped cross section and having a concave curved portion 221 when viewed from above as shown in FIG. It was press-molded into the target shape in one step using the provided mold 21. At this time, the concave curved portion 221 formed by the die side concave curved portion molding portion 23a and the punch side concave curved portion molding portion 25a is formed by stretch flange forming.

Regarding the press-formed product 210 that has been press-formed into the target shape in one step, the present inventor conducted a finite element method analysis (FEM analysis) of the press-forming process using the mold 21 shown in FIG. The plate thickness reduction rate of the press-formed product 210 was determined. Here, the plate thickness reduction rate is a value obtained by subtracting the plate thickness of each portion after press forming from the plate thickness of the blank 100, which is a metal plate before press forming, and dividing the result by the plate thickness of the blank 100.

As shown in FIG. 4, in the conventional press-formed product 210 that was press-formed in one step, the plate thickness reduction rate at the end of the flange portion 219 at the concave curved portion 221 was the largest at 21.5%, and the stretch flange It can be seen that cracks are likely to occur during molding.

In order to suppress the occurrence of cracks due to such stretch flange forming, the above-mentioned Patent Document 1 proposes a method of performing press forming in two steps: a flange up step (preforming step) and a restriking step. It had been.

In the method of Patent Document 1, first, in a flange-up step, as shown in FIG. 5, a press-formed product 170 having an intermediate shape, which is a preformed product, is obtained. Then, in the subsequent restriking step, the preformed product is restriked into a press-formed product 210 having a target shape, which is a sheet metal molded product.

In the method of Patent Document 1, an intermediate-shaped press-formed product 170 has two curved ends 181b with a large curvature (with a small radius of curvature _R ), and a curved end portion 181b with a small curvature (with a large radius of curvature _R) sandwiched therebetween. ) A curved central portion 181a.

Here, for the intermediate-shaped press-formed product 170, the length of the curved ridgeline (curvature efgh) at the concave curved portion 181 shown in FIG. Consider a condition where the length is shorter than the length (curvature pq). This condition is disclosed in Patent Document 1: "The flange portion of the preformed product has a line length shorter in plan view compared to the line length of the flange portion of the sheet metal molded product in plan view." The conditions are met. At this time, the curved ridge length (curved efgh) in the concave curved portion 181 of the intermediate-shaped press-formed product 170 refers to the length from the starting point e to the ending point h in the direction along the curved ridge portion 173. say. Further, the ridge line length (curvature pq) of the curve in the concave curved portion 221 of the press-formed product 210 having the target shape is the length from the starting point p to the ending point q in the direction along the curve of the ridge portion 213 indicated by the broken line. It refers to

Then, the inventor of the present application conducted a finite element method analysis for each process under the conditions shown in FIG. 5, and determined the plate thickness reduction rate of each of the intermediate-shaped press-formed product 170 and the target-shaped press-formed product 210.

As shown in FIG. 6, the thickness reduction rate of the intermediate-shaped press-formed product 170 under the conditions shown in FIG. 5 was 24.4% at maximum. Furthermore, the plate thickness reduction rate of the press-formed product 210 having the target shape was 25.4% at maximum. As described above, under the conditions shown in FIG. 5, the plate thickness reduction rate was higher than in the case of conventional press forming in one step (FIG. 4), leading to a situation where stretch flange cracking occurred frequently. That is, it was found that under the conditions shown in FIG. 5, there was almost no effect of suppressing stretch flange cracking.

Therefore, the inventors of the present application have intensively studied means for suppressing such stretch flange cracking. In the study, the inventors of the present application focused on areas where stretch flange cracking occurs in conventional methods. That is, in the press-formed product 210 press-formed into the target shape by the conventional method, as shown in FIGS. 4 and 6, the plate thickness reduction rate is reduced at or near the curved center portion 221a of the flange portion 219 of the concave curved portion 221. was a great result. Therefore, we focused on the fact that stretch flange cracking is likely to occur in this area.

Therefore, in stretch flange forming in which tensile stress acts on a concave curved part, the inventor of the present application has devised a method of reducing the tensile stress acting on or near the concave curved part and dispersing the tensile stress to both ends of the curve in the concave curved part. I considered it carefully. As a result, in intermediate-shaped press-formed products, by forming a shape in which a part of the concave curved part is cut out, the tensile stress acting on the part or its vicinity is reduced, and both ends of the curve in the concave curved part are This led to the idea of dispersing tensile stress. Furthermore, it has been found that by reducing the tensile stress at the concave curved portion, it is possible to suppress stretch flange cracking in press-formed products having intermediate shapes and target shapes.

The present invention has been made based on the results of such studies, and its configuration is as follows.

<Press molding method>
The press-forming method according to the embodiment is a method in which a press-formed product 210 having a concave curved portion 221 that is concavely curved in a top view is press-formed as a target shape, as shown in FIG. 2A as an example. It is. As shown in FIG. 1, the press forming method includes a blank producing step S1, an intermediate shape forming step S3, and a target shape forming step S5. Note that since the press-formed product 210 is manufactured by executing the above-described press-forming method, the invention of the press-forming method can be constituted as the invention of the method of manufacturing a press-formed product. Therefore, the embodiment of the press molding method described below is common to the embodiment of the method of manufacturing a press molded product. Each of the above steps will be described below with reference to FIGS. 7 and 8.

≪Blank creation process≫
The blank creation step S1 is a step of creating a blank 100 (see FIG. 8(a)) provided with a concave shape 101 corresponding to the curvature of the concave curved portion 221 of the press-formed product 210 having the target shape. The curvature of the concave curved portion 221 refers to, for example, the curvature of the ridgeline portion 213 in the concave curved portion 221.

≪Intermediate shape forming process≫
The intermediate shape forming step S3 is a step of press forming the blank 100 into an intermediate shape press molded product 110 shown in FIG. 7(a). Here, the intermediate-shaped press-formed product 110 includes a top plate part 111, a vertical wall part 115 that is continuous from the top plate part 111 via a ridgeline part 113, and a vertical wall part 115 that is continuous from the top plate part 111 via a die shoulder part 117. and a continuous flange portion 119. Further, the intermediate-shaped press-formed product 110 includes a concave curved portion 121 that is concavely curved when viewed from above, and linear portions 123 that extend linearly from both curved ends of the concave curved portion 121. Furthermore, a chipped part 125 in the shape of a chipped part of the flange part 119 and a part of the vertical wall part 115 is provided in the curved center part 121a of the concave curved part 121. Then, in the intermediate shape forming step S3, press molding is performed so that a part of the concave shape 101 provided in the blank 100 becomes a notched portion 125. The notched portion 125 provided in the vertical wall portion 115 of the concave curved portion 121 is a portion that should originally become the vertical wall portion 115, but is a portion in which there is no material. The length of the notched portion 125 in the height direction is shorter than the length of the vertical wall portion 115 other than the concave curved portion 121 in the height direction.

In the intermediate shape forming step S3, for example, as shown in FIG. It is possible to press-form the intermediate-shaped press-formed product 110 by using the press-formed product 110.

The intermediate shape forming die 3 includes a die side intermediate shape concave curved part forming part 3a that forms an intermediate shaped concave curved part 121, and a die side intermediate shape linear part forming part 3b that forms an intermediate shaped straight part 123. has.

The intermediate shape forming punch 5 has a punch side intermediate shape concave curved part forming part 5a and a punch side intermediate shape linear part forming part 5b. The punch side intermediate shape concave curved portion forming section 5a cooperates with the die side intermediate shape concave curved section forming section 3a to form the intermediate shaped concave curved section 121. The punch-side intermediate-shaped linear portion forming section 5b cooperates with the die-side intermediate-shaped linear portion forming section 3b to form an intermediate-shaped linear portion 123.

The pad 7 presses the blank 100 toward the intermediate shape forming punch 5 side and holds the blank 100. In addition, in the intermediate shape forming process S3, the intermediate shape molding die 1 does not necessarily require the pad 7, and the intermediate shape forming die 3 may have a top plate forming part.

≪Target shape forming process≫
The target shape forming step S5 is a step of press forming the intermediate-shaped press-formed product 110 press-formed in the intermediate-shape forming step S3 into a target-shaped press-formed product 210 shown in FIG. 7(b).

In the target shape forming step S5, for example, as shown in FIG. 8(b), a target shape forming die 11 including a target shape forming die 13, a target shape forming punch 15, and a pad 17 is used. It can be press-molded using

The target shape forming die 13 includes a die side target shape concave curved part forming part 13a that forms a concave curved part 221 of the target shape, and a die side target shape linear part forming part 13b that forms a straight line part 223 of the target shape. has.

The target shape forming punch 15 includes a punch side target shape concave curved part forming part 15a and a punch side target shape linear part forming part 15b. The punch side target shape concave curved portion forming section 15a cooperates with the die side target shape concave curved section forming section 13a to form a concave curved section 221 having the target shape. The punch-side target-shape straight-line part forming section 15b cooperates with the die-side target-shape straight-line part forming section 13b to form a straight-line part 223 having the target shape.

The pad 17 presses the top plate portion 111 of the intermediate-shaped press-formed product 110 toward the punch 15 for forming the target shape, thereby holding the press-formed product 110 down. In the target shape forming step S5, the target shape forming die does not necessarily require the pad 17, and the target shape forming die 13 may have a top plate forming part.

<Effect>
In the press forming method according to the embodiment, first, in a blank creating step S1, a blank 100 is created in which a concave shape 101 corresponding to the curvature of the concave curved portion 221 of a press molded product 210 having a target shape is provided. Next, in the press forming method according to the embodiment, in an intermediate shape forming step S3, the created blank 100 is formed into an intermediate shape press molded product 110 in which a notched portion 125 is provided in the curved center portion 121a of the concave curved portion 121. Press mold.

In the intermediate-shaped press-formed product 110 press-formed in this manner, the tensile stress acting in the vicinity of the notched portion 125 is reduced. Furthermore, tensile stress is dispersed at both ends of the curve in the concave curved portion 121. As a result, in the process of press-forming the intermediate-shaped press-formed product 110 into the target-shaped press-formed product 210, stretch flange cracking can be suppressed, and the press-formed product with the target shape can be press-formed.

This is verified by finite element analysis (FEM analysis) of the press forming process in the press forming method according to the embodiment shown as an example in FIG. In this verification, the process of press-forming a blank 100 provided with a concave shape 101 into a press-formed product 110 with an intermediate shape, and the process of press-forming the press-formed product 110 with an intermediate shape into a press-formed product 210 with a target shape, respectively. Finite element method analysis was performed. Then, the plate thickness reduction rate was calculated for each of the intermediate-shaped press-formed product 110 and the target-shaped press-formed product 210.

FIG. 9 is a contour diagram of the plate thickness reduction rate of the press-formed product 110 having the intermediate shape and the press-forming product 210 having the target shape. Here, as shown in FIG. 10, the intermediate-shaped press-formed product 110 is made such that the ridgeline part 113 of the intermediate-shaped concave curved part 121 is outside the ridgeline part 213 of the target-shaped concave curved part 221. did. Note that the outer side of the ridgeline portion 213 of the target shape refers to the center side of the curve of the concave curved portion 221 of the target shape with respect to the curve pq. Furthermore, the ridgeline length of the ridgeline portion 113 at the concave curved portion 121 (for example, 300 mm) was made longer than the ridgeline length (for example, 250 mm) of the ridgeline portion 213 at the concave curved portion 221 of the target shape.

As shown in FIG. 9, the maximum value of the thickness reduction rate of the press-formed product 110 with an intermediate shape is 14.8%, and the maximum value of the thickness reduction rate of the press-formed product 210 with the target shape is 18.5%. Met. This result was smaller than the maximum value (=21.5%) of the plate thickness reduction rate of the press-formed product 210 obtained by the conventional one-step press-forming method shown in FIG. Similarly, the result was smaller than the maximum value (=25.4%) of the plate thickness reduction rate of the press-formed product 210 by the method of Patent Document 1 shown in FIG.

These results suggest that according to the press forming method according to the embodiment, it is possible to suppress the occurrence of stretch flange cracking in the concave curved portion 221 during the press forming process, and to press form the press formed product 210 in the target shape. .

As described above, in the press forming method according to the embodiment, first, a blank 100 (FIG. 8(a)) is created which is provided with a concave shape 101 corresponding to the curvature of the concave curved portion 221 of a press-formed product 210 having a target shape. do. Next, in the press-forming method according to the embodiment, the created blank 100 is press-formed into an intermediate-shaped press-formed product 110 in which a notch 125 is provided in the curved center portion 121a of the concave curved portion 121 (FIG. 9 (a)). Furthermore, in the press molding method according to the embodiment, the press molded product 110 having an intermediate shape is press molded into a press molded product 210 having a target shape (FIG. 9(b)).

As a result, in the process of press forming the intermediate-shaped press-formed product 110, the tensile stress acting in the vicinity of the chipped portion 125 in the concave curved portion 121 is reduced, and the tensile stress is reduced at both ends of the curve in the concave curved portion 121. can be dispersed.

As a result, when the press-formed product 110 with an intermediate shape is press-formed into the press-formed product 210 with the target shape, stretch flange cracking can be sufficiently suppressed, making it possible to perform stable press-forming without cracking, thereby increasing productivity. It is possible to improve the performance and yield.

Furthermore, the press forming method according to the embodiment does not require moving the blank 100 during press forming, unlike the method described in Patent Document 2. Therefore, according to the press molding method according to the embodiment, it is possible to obtain a press molded product 210 having a good target shape while suppressing fluctuations in dimensional accuracy, and it is possible to improve productivity and yield.

In addition, in the above explanation, the ridgeline part 113 of the intermediate-shaped concave curved part 121 is located outside the ridgeline part 213 of the target-shaped concave curved part 221, as shown in FIG. 10 mentioned above. However, the present invention is not limited to this.

However, in the present invention, as shown in FIG. 10, it is preferable that the ridgeline part 113 of the intermediate-shaped concave curved part 121 be located outside the ridgeline part 213 of the target-shaped concave curved part 221. In this case, when compared with the concave curved portion 221 of the target shape, there will be excess material in the top plate portion 111, the ridgeline portion 113, and the vertical wall portion 115 in the concave curved portion 121. As a result, even if a portion of the intermediate-shaped vertical wall portion 115 and flange portion 119 are missing, the press-formed product 210 having the target shape, which includes the top plate portion 211, the vertical wall portion 215, and the flange portion 219, can be reliably formed. Can be press molded.

Furthermore, if the ridgeline part 113 in the concave curved part 121 of the intermediate shape is located outside the ridgeline part 213 of the target shape, local stretch flange deformation is caused by forming the concave curved part 121 in the intermediate shape forming step S3. Material can be secured to follow the material flow that occurs. Then, in the subsequent target shape forming step S5, the strain generated at the end of the flange portion 219 of the concave curved portion 221 of the target shape to be press-formed can be dispersed over a wide range and reduced, further suppressing stretch flange cracking. becomes possible.

Further, when the ridgeline portion 113 of the intermediate-shaped concave curved portion 121 is located outside the target-shaped ridgeline portion 213, the concave curved portion 121 may have a constant radius of curvature. . Alternatively, as shown in FIG. 10, the intermediate-shaped concave curved portion 121 may include a curved center portion 121a (curvature radius R _C ) and a curved end portion 121b (curvature radius R _E ) having different radii of curvature. good. Further, the radius of curvature R _E at the curved end 121b of the intermediate-shaped concave curved portion 121 is not limited to the radius of curvature R ₀ at the target-shaped concave curved portion 221, and R ₀ <R _E and R ₀ >R _E Both are possible. It is also possible that R ₀ =R _E.

Furthermore, in the above case, the length of the ridgeline part 113 at the concave curved part 221 of the intermediate shape (ridgeline length) is compared with the length of the ridgeline part 213 at the concave curved part 221 of the target shape (ridgeline length). It is better to make it longer. Thereby, by forming the concave curved portion 121 in the intermediate shape forming process, it is possible to secure more material that follows the material flow caused by local stretch flange deformation, which is preferable.

In the above embodiment, a press-formed product 210 having a Z-shaped cross section is to be molded, and as shown in FIG. It has a shape with a part of it missing. However, in the present invention, as shown in (ii) of FIG. A chipped portion 127 having a chipped shape may be provided. In this way, the "chipped part" of the intermediate-shaped press-formed product 110 having the flange part 119 is the part that should originally become the vertical wall part 115 or the top plate part 111, but is the part where there is no material. It refers to

Further, as described above, the present invention can be applied to a press-formed product 230 with a U-shaped cross section (FIG. 2(b)), a press-formed product with an L-shaped cross-section, and a press-formed product 250 with a hat cross-section (FIG. 2B). (c)) may be molded.

When a press-formed product with an L-shaped cross section is to be molded, first, a press-formed product 130 as illustrated in FIG. Press mold. In this case, the intermediate-shaped press-formed product 130 has a top plate portion 131 and a vertical wall portion 135 continuous from the top plate portion 131 via a ridgeline portion 133, as shown in FIG. 11(b). Further, the intermediate-shaped press-formed product 130 is provided with a concave curved portion 141 that is concavely curved when viewed from above.

Then, a part of the concave shape 101 (FIG. 8(a)) provided on the blank 100 becomes a chipped portion 147 in the curved center portion 141a of the concave curved portion 141, as shown in FIG. 11(b). It can be press-molded. Here, the chipped portion 147 shown in FIG. 11(b) has a shape in which a portion of the vertical wall portion 135 and the top plate portion 131 at the curved center portion 141a of the concave curved portion 141 are chipped. In this way, in the molding of a press-formed product with an L-shaped cross-section, the "chipped part" in the intermediate-shaped press-formed product 130 is the part that should originally become the top plate part 131, but is in a state where there is no material. It refers to the part where there is.

In addition, when the press-formed product 250 with a hat cross-sectional shape is to be molded, the press-formed product with an intermediate shape is such that a part of the concave shape provided in the blank becomes a chipped part at the center of the curve of the concave curved part. It may be press-molded. In this case, the chipped part in the intermediate-shaped press-formed product is a chipped part of the flange part and vertical wall part at the center of the curve of the concave curved part, or part of the flange part, vertical wall part, and top plate part. It may be of any shape.

In order to obtain an intermediate-shaped press-molded product having such a chipped part, the radius of curvature of the concave shape 101 provided in the blank 100 may be appropriately adjusted in the blank production process (see FIG. 8(a)). Specifically, for example, if the radius of curvature of the concave shape of the blank is made smaller than the radius of curvature of the ridgeline portion of the concave curved portion in the top view of the press-formed product having the target shape (see radius of curvature R ₀ in FIG. 10), good.

Alternatively, the position at which the blank 100 is placed in the intermediate-shape mold may be adjusted in the intermediate-shape molding process so that the intermediate-shape press-molded product has a chipped part. In addition, by performing each step of the above-mentioned press forming method, the target press-formed product can be manufactured, and the manufactured press-formed product will be one in which stretch flange cracking is sufficiently suppressed.

An analysis was conducted to demonstrate the effects of the press molding method and press molded product manufacturing method according to the present invention, and this will be described below.

In this example, a press-formed product 250 having a hat cross-sectional shape shown in FIG. 12 was used as a molding object. Here, in the press-formed product 250, as shown in FIG. 12, the molding height is 50 mm, the radius of curvature of the concave curved portion 261 is 150 mm, and the bending R of the ridge line portion 253 and die shoulder portion 257 is both 10 mm. And so. Furthermore, in the press-formed product 250, the length of the curved portion of the ridgeline portion 253 in the concave curved portion 261 was 236 mm.

First, a blank 100 was created in which a concave shape 101 corresponding to the curvature of the concave curved portion 261 was provided (see FIG. 13(a)). Here, the radius of curvature of the concave shape 101 was 80 mm.

Next, as shown in FIG. 13(a), the blank 100 is formed into an intermediate shape using an intermediate shape molding die 31 that includes an intermediate shape molding die 33, an intermediate shape molding punch 35, and a pad 37. This was press-molded into a press-formed product 150 (see FIG. 13(b)). Here, regarding the intermediate-shaped concave curved portion 161, a case where the curved center portion 161a is linear and the radius of curvature _RE of the curved end portion 161b is 80 mm is referred to as Invention Example 1. In Invention Example 1, the length of the ridgeline of the intermediate-shaped concave curved portion 161 was 273 mm. Further, regarding the intermediate-shaped concave curved portion 161, a case where the curved center portion 161a was made straight and the radius of curvature _RE of the curved end portion 161b was set to 160 mm was defined as Invention Example 2. Inventive example 2 is under the condition that the radius of curvature R _E of the curved end portion 161b of the intermediate-shaped concave curved portion 161 is larger than the radius of curvature R ₀ of the concave curved portion 261 of the target shape. In Invention Example 2, the length of the ridgeline of the intermediate-shaped concave curved portion 161 was 322 mm. As shown in FIG. 13(b), the intermediate-shaped press-formed product 150 has a concavely curved portion 161 that is concavely curved when viewed from above, and linear portions 163 extending from both ends of the concavely curved portion 161. Further, the press-formed product 150 having an intermediate shape is provided with a notch 165 in a portion of the flange portion 159 and the vertical wall portion 155 at the curved center portion 161a of the concave curved portion 161.

Subsequently, as shown in FIG. 13(b), a press-formed product having an intermediate shape is produced using a target shape molding die 41 that includes a target shape molding die 43, a target shape molding punch 45, and a pad 47. 150 was press-molded into a press-formed product 250 having a target shape.

Further, in this example, as a comparison target, a blank 100 is press-formed into the target shape shown in FIG. A conventional example is a case in which a product 250 is press-formed in one step. Furthermore, a comparative example was prepared in which a press-formed product 250 having a target shape was press-formed in two steps under the conditions using the mold having the shape shown in FIG. 5 described above. In the comparative example, regarding the intermediate-shaped concave curved portion 181, the curved center portion 181a was made straight, and the radius of curvature R _E of the curved end portion 181b was set to 80 mm. In the comparative example, the length of the ridgeline of the intermediate-shaped concave curved portion 181 was 211 mm. Then, a finite element method analysis of the press forming process was performed for each of the conventional example and the comparative example, and the plate thickness reduction rate was determined.

FIG. 15 is a contour diagram of the plate thickness reduction rate of a press-formed product 250 having a target shape in a conventional example. FIG. 16 is a contour diagram of the plate thickness reduction rate of a press-formed product 150 with an intermediate shape and a press-formed product 250 with a target shape in a comparative example. FIG. 17 is a contour diagram of the plate thickness reduction rate of the intermediate-shaped press-formed product 150 and the target-shaped press-formed product 250 in Invention Example 1. FIG. 18 is a contour diagram of the plate thickness reduction rate of the intermediate-shaped press-formed product 150 and the target-shaped press-formed product 250 in Invention Example 2. Note that in the conventional example, since press molding was performed in one step, only the results of the press molded product 250 having the target shape are shown.

In the conventional example, as shown in FIG. 15, the part where the plate thickness decreased the most was the end of the flange part 259 in the concave curved part 261, and the maximum value of the plate thickness reduction rate was 20.5%.

In the comparative example, as shown in FIG. 16, since the curved line length of the ridgeline portion 193 of the intermediate-shaped press-formed product 190 is short, the plate thickness reduction rate of the curved center portion 201a of the concave curved portion 201 is relatively small. . However, the maximum value of the plate thickness reduction rate of the curved end portions 201b on both end sides of the concave curved portion 201 is 24.4%, and the maximum value of the plate thickness reduction rate of the press-formed product 250 of the target shape according to the conventional example ( = 20.5%). Furthermore, in the press-formed product 250 obtained by press-forming the intermediate-shaped press-formed product 190 into the target shape, the maximum value of the plate thickness reduction rate at the end of the curve in the concave curved portion 261 is 25.4%. The result was that tensile strain was concentrated and stretch flange cracking was likely to occur.

On the other hand, in Invention Example 1, as shown in FIG. 17, the maximum value of the plate thickness reduction rate in the intermediate-shaped press-formed product 150 is 14.8%, compared to the conventional example and the comparative example. By providing the chipped portion 165, the plate thickness reduction rate could be lowered. Furthermore, in Invention Example 1, the maximum value of the plate thickness reduction rate in the press-formed product 250 having the target shape was 18.3%. This plate thickness reduction rate was a value lower than the maximum value of the plate thickness reduction rate in the target-shaped press-formed product 250 according to the conventional example and the target-shaped press-formed product 250 according to the comparative example.

In addition, in the invention example 2, as shown in FIG. 18, the maximum value of the plate thickness reduction rate in the intermediate-shaped press-formed product 150 is 13.9%, and compared to the conventional example and the comparative example, the chipped part 165 By providing this, it was possible to reduce the plate thickness reduction rate. Furthermore, in Invention Example 2, the maximum value of the plate thickness reduction rate in the press-formed product 250 having the target shape was 18.8%. This plate thickness reduction rate was a value lower than the maximum value of the plate thickness reduction rate in the target-shaped press-formed product 250 according to the conventional example and the target-shaped press-formed product 250 according to the comparative example. Further, the maximum plate thickness reduction rate at both ends of the concave curved portion 261 in Invention Example 2 is 14.2%, and the maximum plate thickness reduction rate at both ends of the concave curved portion 261 in Invention Example 1 is 16%. The plate thickness reduction rate could be further reduced than .2%.

As described above, according to the press forming method of the present invention, the condition is such that the radius of curvature R _E of the curved end 161b of the intermediate-shaped concave curved portion 161 is larger than the radius of curvature R ₀ of the concave curved portion 261 of the target shape. It becomes possible to do this. Further, by appropriately setting the radius of curvature _RE of the curved end portion 161b, it is possible to suppress a decrease in the plate thickness at both ends of the concave curved portion 261 having the target shape.

As described above, it has been suggested that according to the press forming method according to the present invention, stretch flange cracking at the concave curved portion can be reduced in the process of press forming a press molded product having a target shape having the concave curved portion.

The present invention provides a press-forming method and a press-forming method capable of sufficiently suppressing stretch flange cracking of a press-formed product having a top plate portion and a vertical wall portion and having a concave curved portion that is concavely curved when viewed from above. It is possible to provide a method for manufacturing a product.

1 Intermediate shape molding die 3 Intermediate shape molding die 3a Die side intermediate shape concave curved part molding part 3b Die side intermediate shape linear part molding part 5 Intermediate shape molding punch 5a Punch side intermediate shape concave curved part molding part 5b Punch Side intermediate shape linear part forming part 7 Pad 11 Target shape forming mold 13 Target shape forming die 13a Die side target shape concave curved part forming part 13b Die side target shape linear part forming part 15 Target shape forming punch 15a Punch side Target shape concave curved part molding part 15b Punch side target shape straight part molding part 17 Pad 21 Mold 23 Die 23a Die side concave curved part molding part 25 Punch 25a Punch side concave curved part molding part 27 Pad 31 Intermediate shape molding mold 33 Intermediate shape molding die 35 Intermediate shape molding punch 37 Pad 41 Target shape molding die 43 Target shape molding die 45 Target shape molding punch 47 Pad 51 Mold 53 Die 55 Punch 57 Pad 100 Blank 101 Concave shape 110 Press-formed product 111 Top plate portion 113 Ridgeline portion 115 Vertical wall portion 117 Die shoulder portion 119 Flange portion 121 Concave curved portion 121a Curved central portion 121b Curved end portion 123 Straight portion 125 Notch portion 127 Notch portion 130 Press-formed product 131 Top plate portion 133 Ridgeline portion 135 Vertical wall portion 141 Concave curved portion 141a Curved center portion 147 Notch portion 150 Press-formed product 153 Ridgeline portion 155 Vertical wall portion 157 Die shoulder portion 159 Flange portion 161 Concave curved portion 161a Curved center portion 161b Curved end portion 163 Straight line Part 165 Notched portion 170 Press-formed product 173 Ridgeline portion 181 Concave curved portion 181a Curved center portion 181b Curved end portion 190 Press-formed product 193 Ridgeline portion 201 Concave curved portion 201a Curved center portion 201b Curved end portion 210 Press-formed product 211 Top plate portion 213 Ridgeline section 215 Vertical wall section 217 Die shoulder section 219 Flange section 221 Concave curved section 221a Curved central section 223 Straight section 230 Press-formed product 231 Top plate section 233 Ridgeline section 233a Ridgeline section 235 Vertical wall section 235a Vertical wall section 241 Concave curve Part 243 Straight part 250 Press-formed product 251 Top plate part 253 Ridge part 253a Ridge part 255 Vertical wall part 255a Vertical wall part 257 Die shoulder part 257a Die shoulder part 259 Flange part 259a Flange part 261 Concave curved part 263 Straight part

Claims (6)

The aim is to create a press-formed product that has a top plate, a vertical wall continuous from the top plate, and a flange continuous from the vertical wall, and has a concave curved part that curves concavely when viewed from above. A press forming method for press forming a shape,
a blank creation step of creating a blank provided with a concave shape corresponding to the curvature of the concave curved portion of the target shape;
The produced blank has a top plate part, a vertical wall part continuous from the top plate part, and a flange part continuous from the vertical wall part, and has a concave curved part that curves concavely in a top view. , an intermediate shape in which a notch is provided in a part of the flange part and the vertical wall part, or a part of the flange part, the vertical wall part, and the top plate part in the central part of the curve of the concave curved part; an intermediate shape forming process of press forming into a press-formed product;
a target shape forming step of press forming the intermediate-shaped press-formed product into the target shape,
The press forming method is characterized in that in the intermediate shape forming step, press forming is performed so that a part of the concave shape provided on the blank becomes the chipped part. A press-forming method for press-forming a press-formed product into a target shape, which has a top plate portion and a vertical wall portion continuous from the top plate portion, and has a concave curved portion that is concavely curved when viewed from above. ,
a blank creation step of creating a blank provided with a concave shape corresponding to the curvature of the concave curved portion;
The produced blank has a top plate portion, a vertical wall portion continuous from the top plate portion, and a concave curved portion that is concavely curved in a top view, and the above-mentioned portion at the curved center portion of the concave curved portion. an intermediate shape forming step of press forming an intermediate shape press molded product having a notch in a portion of the vertical wall portion and the top plate portion;
a target shape forming step of press forming the intermediate-shaped press-formed product into the target shape,
The press forming method is characterized in that in the intermediate shape forming step, press forming is performed so that a part of the concave shape provided on the blank becomes the chipped part. In the intermediate shape forming step, a radius of curvature _RE at a curved end of the concave curved portion of the intermediate shape is made larger than a radius of curvature _R0 of the concave curved portion of the target shape. Item 2. Press molding method according to item 1 or 2. The aim is to create a press-formed product that has a top plate, a vertical wall continuous from the top plate, and a flange continuous from the vertical wall, and has a concave curved part that curves concavely when viewed from above. A method for manufacturing a press-formed product in a shape, the method comprising:
a blank creation step of creating a blank provided with a concave shape corresponding to the curvature of the concave curved portion of the target shape;
The produced blank has a top plate part, a vertical wall part continuous from the top plate part, and a flange part continuous from the vertical wall part, and has a concave curved part that curves concavely in a top view. , an intermediate shape in which a notch is provided in a part of the flange part and the vertical wall part, or a part of the flange part, the vertical wall part, and the top plate part in the central part of the curve of the concave curved part; an intermediate shape forming process of press forming into a press-formed product;
a target shape forming step of press forming the intermediate-shaped press-formed product into the target shape,
The method for manufacturing a press-formed product, wherein the intermediate shape forming step includes press-forming so that a part of the concave shape provided on the blank becomes the chipped part. A method for producing a press-formed product having a target shape, which includes a top plate portion, a vertical wall portion continuous from the top plate portion, and a concave curved portion that curves concavely when viewed from above. There it is,
a blank creation step of creating a blank provided with a concave shape corresponding to the curvature of the concave curved portion;
The produced blank has a top plate portion, a vertical wall portion continuous from the top plate portion, and a concave curved portion that is concavely curved in a top view, and the above-mentioned portion at the curved center portion of the concave curved portion. an intermediate shape forming step of press forming an intermediate shape press molded product having a notch in a portion of the vertical wall portion and the top plate portion;
a target shape forming step of press forming the intermediate-shaped press-formed product into the target shape,
The method for manufacturing a press-formed product, wherein the intermediate shape forming step includes press-forming so that a part of the concave shape provided on the blank becomes the chipped part. In the intermediate shape forming step, the radius of curvature _RE at the curved end of the concave curved portion of the intermediate shape is press-molded to be larger than the radius of curvature _R0 at the concave curved portion of the target shape. The method for manufacturing a press-formed product according to claim 4 or 5, characterized in that:

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