WO2018030240A1 - Method of manufacturing press-formed article - Google Patents

Abstract

Provided is a method of manufacturing a press-formed article capable of greatly reducing spring-back which occurs in a press-formed article having a longitudinal shape, such as an article in which adjacent straight-line portions are linked by a curved portion. A metal sheet is press-formed into a product shape which has a hat-shaped or U-shaped cross-sectional shape, and which has a longitudinal shape provided with a plurality of straight-line portions and a curved portion linking adjacent straight-line portions. The method includes: a first step of forming an intermediate component in which, if the curved portion has a convex curve on a top sheet portion side, the radius of curvature of the curved portion is made smaller than the radius of curvature in the product shape, such that the linear length of the curved portion in the longitudinal direction of the top sheet portion is greater than the linear length in the product shape, and if the curved portion has a concave curve on the top sheet portion side, the radius of curvature of the curved portion is made larger than the radius of curvature in the product shape, such that the linear length of the curved portion in the longitudinal direction of the top sheet portion is less than the linear length in the product shape; and a second step of press-forming the intermediate component into the product shape.

Description

Manufacturing method of press-molded products

The present invention forms a metal plate into a cross-sectional U-shaped or hat-shaped product shape having a longitudinal shape that is partially curved at one or two locations along the longitudinal direction, such as a side view or a U-shape. The present invention relates to a method for manufacturing a press-formed product.

In recent years, high-tensile materials of 590 MPa or higher have been applied to vehicle body structural parts in order to achieve both improved collision safety and weight reduction of automobile bodies. However, since high tensile strength materials have high yield strength and tensile strength, defective molding such as springback becomes a problem when performing press molding.
One of the press-molded products used for vehicle body structural parts is a part such as a member front side inner. This press-molded product is a hat-shaped cross-sectional component having a square shape in a side view in which two linear portions arranged in the longitudinal direction are connected by a curved portion that is convexly curved toward the top plate portion. When a metal plate is press-molded in such a part shape, tensile stress is generated in the top plate part and compressive stress is generated in the flange part at the bottom dead center of the molding. (Camberback) occurs.
When a high-tensile material is applied to such a component, there is a problem that the stress difference at the bottom dead center is further increased and the spring back is increased.

As conventional techniques for countermeasures against springback, for example, there are techniques described in Patent Documents 1 to 3.
The press molding method described in Patent Document 1 is a method of molding into a pressed part having a shape curved in the longitudinal direction so as to be convex toward the top plate portion side. In Patent Document 1, embossing is formed on the surface of the top plate portion in the first molding step, and the second molding is performed after molding so that the line length of the entire length in the longitudinal direction is longer than the line length in the longitudinal direction of the final product. By press-molding into a product shape so that the embossing is eliminated in the process, a compression stress is applied to the top plate portion to reduce spring back.

The press molding method described in Patent Document 2 is a method of molding a part having a shape curved in the longitudinal direction. In Patent Document 2, a convex part is partially formed on the surface of the top plate part in the middle of molding by a punch in which pins are arranged, and the pin is lowered by a press load in the latter stage of molding to compress the surface of the top plate part. In this method, stress is applied to reduce springback.
The press molding method described in Patent Document 3 is a method for molding a product having a hat-shaped or U-shaped cross-sectional shape and a longitudinal shape having a curved portion at an intermediate portion and straight portions adjacent to the middle portion. . Patent Document 3 uses a blank material longer than the length of the product, and gives compressive stress to the top plate surface by forming the blank material corresponding to the curved portion with respect to the length of the curved portion. This is a method for reducing springback.

Japanese Patent No. 4709659 JP 2008-200709 A Japanese Patent No. 5812312

However, when the press molding method described in Patent Document 1 is applied to the press molding of a part having a U-shape in a side view such as a member front side inner, a locally existing curved portion is applied. It is possible to concentrate and form embossing. However, since the curved portion is small, there is a possibility that cracking may occur in the curved portion and wrinkles may remain after compression by providing a plurality of convex protrusions. For this reason, arrangement | positioning of a protrusion and other designs may become complicated.

Moreover, in the press molding method described in Patent Document 2, since it is necessary to have a press structure in which the pins are arranged in the punch and the pins move during the press molding, the mold has a complicated shape. In addition, when trying to apply to a part having a U-shape, such as a member front side inner, since the curved portion is small, cracking may occur when the material is lifted with a pin.
Moreover, in the press molding method described in Patent Document 3, a mold that is divided into a curved portion and a straight portion existing on both sides thereof is used, so that the structure of the mold becomes complicated. Furthermore, since it is necessary to mold using a blank longer than the product, the compressive stress further increases in the flange part etc. where compressive stress is applied in the original shape, and in some cases there is a possibility that spring back and wrinkles increase. .

The above problems become more prominent when applied to a high tensile strength material having a high tensile strength.
The present invention has been made paying attention to the above points, and greatly reduces the spring back generated in a press-formed product having a longitudinal shape such that adjacent straight portions are connected by a curved portion. An object of the present invention is to provide a method for producing a press-formed product that can be used.

In order to solve the problems, a method for manufacturing a press-formed product according to one aspect of the present invention includes a hat-shaped or U-shaped cross-sectional shape having side wall portions on both sides in the width direction of the top plate portion, and a plurality of cross-sectional shapes. A metal plate is press-molded into a product shape having a longitudinal shape that includes one or two or more curved portions that are convexly or concavely curved toward the top plate portion by connecting the straight portions adjacent to the straight portion. When
When the curved portion is curved convex toward the top plate portion side, the curvature radius of the curved portion is set so that the line length in the longitudinal direction of the top plate portion in the curved portion is longer than the line length in the product shape. When the curvature is smaller than the radius of curvature in the product shape and the bending portion is concave on the top plate portion side, the line length in the longitudinal direction of the top plate portion in the bending portion is the wire length in the product shape. A first step of forming an intermediate part having a radius of curvature of the curved portion larger than the curvature radius of the product shape so as to be shorter, and a second step of press-molding the intermediate part into the product shape It is characterized by having.

According to one aspect of the present invention, after performing a simple preliminary molding (first step) in which the radius of curvature of the curved portion connecting adjacent straight portions is smaller than the product shape, the main molding (second step) is performed. By performing the step, it is possible to reduce the spring back of the hat-shaped or U-shaped cross-section component having a curved portion that is partially curved with a predetermined curvature along the longitudinal direction.
As a result, according to one embodiment of the present invention, a part with high dimensional accuracy can be obtained, which leads to an improvement in yield. Furthermore, since the springback is reduced, for example, when a vehicle body structural component is formed using a component having a hat cross-sectional shape, it is possible to easily assemble the component.

It is a figure which shows the example of the product shape which concerns on embodiment based on this invention, (a) is a side view, (b) is a perspective view. It is the schematic which shows the example of the stress generation | occurrence | production area | region of the tensile stress by the top plate side in the longitudinal direction stress distribution which generate | occur | produces by press molding, and the stress generation | occurrence | production area | region of the compressive stress by the flange side. It is a conceptual diagram explaining the case where a pre-wall is shape | molded in a punch bottom curved part and a line length is earned (a curvature radius is made small). It is the schematic which shows the press molding which concerns on embodiment based on this invention, Comprising: (a) is a figure which illustrates a 1st process and (b) is a 2nd process. It is a schematic side view which shows another example of the product shape which can apply this invention.

Next, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, the product shape 1 of the press-formed product to be manufactured is a hat-shaped crossing in which both sides in the width direction of the top plate portion 1a are continuous with the flange portion 1c via the side wall portion 1b as shown in FIG. It has a surface shape and has a curved portion 11 that is convexly curved toward the top plate portion 1a with respect to one place in the longitudinal direction (a position closer to the right side in FIG. 1). As shown in FIG. An example of the shape of a press-formed product having a U-shaped longitudinal direction will be described. That is, the press-formed product of the present embodiment is a case in which the two linear portions 10 are connected to the top plate portion 1a side by the convex curved portion 11 along the longitudinal direction.

When press-molding into a press-molded product having the above-described shape, a tensile residual stress is generated on the surface of the top plate portion 1a of the bending portion 11 around the apex portion of the U-shape (the apex of the bending portion 11), and the flange portion A compressive residual stress is generated on the surface 1c (see FIG. 2). Then, when these stresses are released, a spring back is generated in the direction (the top plate portion side) in which the adjacent straight portions 10 connected by the bending portion 11 are separated (see FIG. 1). As the material strength increases, this residual stress increases and the amount of springback increases. That is, when a high tensile material of 590 MPa or more is adopted, the spring back becomes large.

In the method for manufacturing a press-formed product of the present embodiment, in order to reduce this spring back, as a press forming step, a first step (preliminary forming step) and a second step performed after the first step are performed. At least a process (main forming process).
In the first step, the metal plate 20 (blank material) is pressed with the upper die 16 and the lower die 15 (see FIG. 4A), and the line length in the longitudinal direction of the top plate portion 1a in the curved portion 11 is determined. The curvature radius of the curved portion 11 is formed into an intermediate part 21 smaller than the curvature radius in the product shape 1 so as to be longer than the line length in the product shape 1.

At this time, when the product shape is a hat-shaped cross-sectional shape having flange portions 1c on both sides in the width direction of the top plate portion 1a via the side wall portions 1b as shown in FIG. It is preferable to set the line length in the longitudinal direction of the flange portion 1c to be shorter than the line length in the product shape.
As the line length in the longitudinal direction of the top plate portion 1a at the curved portion 11, for example, the length of a curved portion connecting the top plate portions 1a of the linear portions 10 on both sides in the longitudinal direction may be adopted (see FIG. 2). Further, as the line length in the longitudinal direction of the flange portion 1c at the curved portion 11, for example, the line length of a curved portion connecting the linear portions on both sides in the longitudinal direction in the flange portion 1c may be adopted (see FIG. 2). .

When the line length in the longitudinal direction of the top plate portion 1a at the curved portion 11 is set with higher accuracy, CAE analysis for forming the metal plate 20 into the product shape 1 is performed, and based on the result, the top plate portion 1a. A stress generation region in which a longitudinal tensile stress is generated is set at a longitudinal position of the bending portion 11, and a line length at that position is employed. Similarly, when the line length in the longitudinal direction of the flange portion 1c at the curved portion 11 is set with higher accuracy, CAE analysis for forming the metal plate 20 into the product shape 1 is performed, and the flange portion is based on the result. A stress generation region in which a longitudinal compressive stress is generated in 1c is set at a longitudinal position at the flange portion 1c, and a line length at that position is adopted.

Here, when the line length in the longitudinal direction of the top plate portion 1a in the bending portion 11 is defined as L1o in the product shape 1 and defined as L1 ′ in the intermediate part 21, the following expression (1) is satisfied. It is preferable to design as follows.
L1o <L1 ′ ≦ 1.01 × L1o (1)
Here, when L1 ′ is larger than (1.01 × L1o), in the first step, the tension generated at the apex of the top plate portion 1a in the bending portion 11 becomes excessive, and this is applied to a super high tensile material. In addition, the possibility of cracking increases. On the other hand, when L1 ′ is smaller than L1o, the springback may not be sufficiently reduced because sufficient compressive stress is not applied to the surface of the top plate portion 1a in the second step.

Moreover, when the length of the longitudinal direction of the flange portion 1c in the curved portion 11 is defined as L2o in the product shape and defined as L2 ′ in the intermediate part, it is preferable to design so as to satisfy the following expression (3). .
L2o> L2 ′ ≧ 0.99 × L2o (3)
In the first step, as a method of making the radius of curvature of the top plate portion 1 a in the curved portion 11 smaller than that of the product shape 1, the intersection angle itself between the long axes of the two linear portions 10 is smaller than that of the product shape 1. There is also a method in which a mold is used to form a value longer than the line length of the bending portion 11 in the longitudinal direction of the top plate portion 1a.

In the present embodiment, when the first step is formed under the condition that the intersection angle of the line obtained by extending the axes of two adjacent linear portions 10 is the same as or substantially the same as the intersection angle in the product shape 1 Will be described as an example.
That is, as shown in FIG. 3, in a side view, the imaginary line L11 obtained by extending the top plate portion 1a of the two linear portions 10 located across the target bending portion 11 toward the vertex WP0 side of the bending portion 11, Consider L12. The intersection of the two virtual lines L11 and L12 is LP. 3 is a profile of the top plate portion 1 a of the curved portion 11 in the product shape 1, and a sign W <b> 1 is a profile of the top plate portion 1 a of the curved portion 11 in the intermediate part 21. As shown in FIG. 3, the distance ΔH <b> 1 between the top plate portion 1 a of the curved portion 11 and the intersection point LP in the intermediate part 21 is larger than the distance ΔH <b> 0 between the top plate portion 1 a of the curved portion 11 and the intersection point LP in the product shape 1. Is set to be small.

That is, the molding in the first step is performed so that the interval ΔH0 between the intersection LP of the imaginary lines L11 and L12 and the vertex WP0 of the curved portion 11 in the product shape 1 is reduced, that is, the preliminary meat Y is given. Thus, the line length of the top plate portion 1a at the curved portion 11 in the intermediate part 21 is set to be longer than the product shape 1, and the curvature radius at the curved portion 11 in the intermediate part 21 is set to the product shape 1. It is formed so that the radius of curvature is smaller than that.
In the first step, with respect to the top plate portion 1a, the metal plate 20 (blank material) is pressed with the upper and lower molds 15 and 16 in which the shape of the curved portion 11 becomes the profile of WP1 as shown in FIG. The intermediate part 21 is molded (see FIG. 4A).

Next, in the second step, the intermediate part 21 is pressed with the upper and lower molds 17 and 18 in which the shape of the curved part 11 becomes the outline of WP0 as shown in FIG. Manufacture to shape 1.
In the first step, by shaping the pre-mesh Y as described above, the shape of the previous step can be designed more easily than arranging a plurality of convex shapes as described in Patent Document 1, and the second step The wire length obtained by extending the preliminary meat Y at the time of molding in this step becomes difficult to flow to other parts, and it becomes easy to apply compressive stress.

At the same time, in the first step, by designing the length of the flange portion 1c at the curved portion 11 to be short, it is easy to apply a tensile stress to the flange portion 1c.
Here, for example, draw molding or foam molding is applied in the first process, and the second process is a wrist-like process in which the product shape 1 is molded. In addition, the metal plate 20 to be formed is applicable as long as it is a metal plate 20 made of a press-moldable metal material such as a steel plate or an aluminum alloy, but depending on the case of an ultra-high tensile material having a material strength of 590 MPa or more. The spring back along the longitudinal direction can be effectively reduced.

In the above embodiment, as illustrated in FIG. 1, the case where the product is formed into a product shape 1 having a hat-shaped cross section in a side view as illustrated in FIG. 1 is illustrated. The present invention can be applied even when it is formed into a U-shaped cross-sectional component. However, the present invention is particularly effective for the product shape 1 having a hat-shaped cross section.
Moreover, the product shape 1 is not limited to the product shape 1 in which the curved part 11 exists in only one place along a longitudinal direction like FIG. For example, as shown in FIG. 5, a product having a longitudinal shape in which the curved portions 11 are provided at two or more locations along the longitudinal direction, and the adjacent straight portions 10 are connected by the curved portions 11. Even if it is a shape, this invention is applicable.

At this time, as shown in FIG. 5B, in the case where each curved portion 11 has a curved shape that is convex toward the top plate portion 1a, as described above, What is necessary is just to design the metal mold | die of a 1st process so that the line length of the top-plate part 1a in an intermediate part may become long rather than a shape, and the curvature radius in an intermediate part may become small rather than a product shape.
Further, as shown in FIG. 5 (a), in the first step, the length of the curved portion 11 having a concave shape on the top plate portion 1a side is the line length in the longitudinal direction of the top plate portion 1a in the curved portion 11. Is set so that the curvature radius of the curved portion 11 becomes an intermediate part larger than the curvature radius of the product shape 1 so as to be shorter than the line length in the product shape. In a curved portion where the curved portion 11 is concave on the top plate portion 1a side, for example, the curvature of the product shape 1 is shortened by forming the concave portion that forms the curvature so as to give a pre-wall. Adjust the radius of curvature to be larger than the radius.

At this time, when the longitudinal length of the top plate portion 1a in the curved portion 11 is defined as L1o in the product shape and defined as L1 'in the intermediate part, it is set so as to satisfy the following expression (2). It is preferable to do.
L1o> L1 ′ ≧ 0.99 × L1o (2)
Further, with respect to the curved shape portion where the curved portion 11 is concave on the top plate portion 1a side, the longitudinal length of the flange portion 1c in the curved portion 11 is defined as L2o in the product shape, and L2 ′ in the intermediate part. When defined, it is preferable to design so as to satisfy the following expression (4).
L2o <L2 ′ ≦ 1.01 × L2o (4)

In order to confirm the effect of reducing the springback by the press molding method according to the present invention, a press molding analysis and a springback analysis by a finite element method (FEM) were performed.
In the present embodiment, the product shape 1 is a square shape in a side view shown in FIG. 1, and is a hat-shaped cross-sectional component that is curved with a predetermined curvature in the longitudinal direction at the apex portion of the round shape. Set to conditions. The metal plate 20 used for press forming was a steel plate having a plate thickness t = 2.0 mm and a tensile strength of 590 MPa to 1180 MPa.
Table 1 shows the analysis conditions and the evaluation results at that time.

Sample No. 1-3 are comparative examples in which the springback analysis was performed under the condition that the metal plate 20 was press-formed into the product shape 1 by the second step without performing the first step. This sample No. In the cases of 1 to 3, it can be seen that the maximum deviation from the product shape is 5.7 mm or more, and that the maximum deviation from the product shape increases as the material strength increases. It can be seen that the maximum deviation from the product shape is 10.4 mm for the 1180 MPa material.

Sample No. Nos. 4 to 12 are analyzed under press conditions based on the present invention. In this sample example, the line length L1 ′ in the longitudinal direction of the top plate portion 1a at the curved portion 11 in the intermediate part is (1.005 × L1o) or (1.01) with respect to the line length L1o in the product shape 1. × L1o) is set under the condition that the first step is performed and then the product shape 1 is press-molded in the second step.
Sample No. In Nos. 4 to 6, in the first step, the line length L1 ′ of the top plate portion 1a of the bending portion 11 is changed to 1.005 times the product shape 1, and then the product shape 1 is changed to the second step. This was analyzed under the condition of press forming. However, the line length L2 ′ of the flange portion 1c of the curved portion 11 in the first step was set to the same length as the line length L2o in the product shape 1. When the springback analysis is performed under these conditions, the maximum springback amount is 2.9 mm for the 1180 MPa material. It can be seen that the springback is greatly reduced as compared with FIG.

Sample No. 7 to 9, sample No. As in 4 to 6, after the line length L1 ′ of the top plate portion 1a of the bending portion 11 is deformed to 1.005 times the product shape 1 in the first step, the product shape is obtained in the second step. 1 was analyzed under the condition of press molding. However, the line length L2 ′ of the flange portion 1c of the curved portion 11 in the first step was set to 0.995 times the line length L2o in the product shape 1. When the springback analysis is performed under these conditions, the maximum springback amount is −1.3 mm for the 1180 MPa material. Springback is greatly reduced compared to Sample No. 3, and Sample No. It can be seen that the absolute value of the springback is smaller than 6.

Furthermore, sample no. 10 to 12, in the first step, the line length L1 ′ of the top plate portion 1a of the bending portion 11 is deformed to 1.01 times the product shape 1, and then the product shape 1 is changed to the second step. This was analyzed under the condition of press forming. However, the line length L2 ′ of the flange portion 1c of the curved portion 11 in the first step was set to the same length as the line length L2o in the product shape 1. When the springback analysis is performed under these conditions, the maximum springback amount is 1.2 mm for the 1180 MPa material. It can be seen that the springback is greatly reduced as compared with FIG.

As described above, the entire contents of Japanese Patent Application No. 2016-156816 (filed on Aug. 9, 2016), from which this application claims priority, form part of this disclosure by reference.
Although the present invention has been described with reference to a limited number of embodiments, the scope of rights is not limited thereto, and modifications of each embodiment based on the above disclosure are obvious to those skilled in the art.

DESCRIPTION OF SYMBOLS 1 Product shape 1a Top plate part 1b Side wall part 1c Flange part 10 Straight line part 11 Curved part 15, 16 Mold 17 and 18 in 1st process 20 Mold 20 in 2nd process Metal plate 21 Intermediate part
Line length of the top plate in L1o product shape
L1 'Line length of the top plate at the intermediate part
L2o product shape flange length
L2 'Line length of flange part at intermediate part L11, L12 Virtual line LP Intersection WP0 Vertex Y Precarnation

Claims (10)

It has a side wall portion on both sides in the width direction of the top plate portion, has a hat-shaped or U-shaped cross-sectional shape, and connects the straight portions adjacent to a plurality of straight portions to be convex or concave on the top plate portion side. When manufacturing by pressing a metal plate into a product shape having a longitudinal shape with one or more curved portions curved,
When the curved portion is curved convex toward the top plate portion side, the curvature radius of the curved portion is set so that the line length in the longitudinal direction of the top plate portion in the curved portion is longer than the line length in the product shape. When the curvature is smaller than the radius of curvature in the product shape and the bending portion is concave on the top plate portion side, the line length in the longitudinal direction of the top plate portion in the bending portion is the wire length in the product shape. A first step of forming an intermediate part in which the curvature radius of the curved portion is larger than the curvature radius in the product shape so as to be shorter;
And a second step of press-molding the intermediate part into the product shape. When the line length in the longitudinal direction of the top plate portion in the curved portion is defined as L1o in the product shape and defined as L1 ′ in the intermediate part,
2. The method for manufacturing a press-formed product according to claim 1, wherein the following equation (1) is satisfied when the curved portion is convex toward the top plate portion side.
L1o <L1 ′ ≦ 1.01 × L1o (1) When the line length in the longitudinal direction of the top plate portion in the curved portion is defined as L1o in the product shape and defined as L1 ′ in the intermediate part,
2. The method for manufacturing a press-formed product according to claim 1, wherein when the curved portion is concave on the top plate side, the following expression (2) is satisfied.
L1o> L1 ′ ≧ 0.99 × L1o (2) The range of the curved portion is set in a stress generation region where longitudinal tensile stress or longitudinal compressive stress is generated in the top plate portion based on the result of CAE analysis for forming the metal plate into the product shape. The method for producing a press-formed product according to claim 2 or 3. In the first step, when the curved portion is convex on the top plate portion side, the top plate portions of the two linear portions located across the target curved portion are extended toward the apex side of the curved portion. 5. The method according to claim 1, wherein a pre-curve is formed so that an interval between the intersection of the imaginary lines and the apex of the curved portion is small, and the curvature radius of the curved portion is reduced. The manufacturing method of the press-formed product described in the item. The product shape is a hat-shaped cross-sectional shape having flange portions on both sides in the width direction of the top plate portion via side wall portions,
In the first step, when the curved portion is curved convex toward the top plate portion, the longitudinal length of the flange portion in the curved portion is set to be shorter than the length of the product shape. When the curved part is concavely curved toward the top plate part side, the longitudinal length of the flange part in the curved part is set so as to be longer than the line length in the product shape. The method for producing a press-formed product according to any one of claims 1 to 5, wherein the press-formed product is molded into a shape. When the line length in the longitudinal direction of the flange portion in the curved portion is defined as L2o in the product shape and defined as L2 ′ in the intermediate part,
7. The method for manufacturing a press-formed product according to claim 6, wherein when the curved portion is convex toward the top plate portion, the following expression (3) is satisfied.
L2o> L2 ′ ≧ 0.99 × L2o (3) When the line length in the longitudinal direction of the flange portion in the curved portion is defined as L2o in the product shape and defined as L2 ′ in the intermediate part,
The method for manufacturing a press-formed product according to claim 6 or 7, wherein when the curved portion is concave on the top plate portion side, the following expression (4) is satisfied.
L2o <L2 ′ ≦ 1.01 × L2o (4) The press according to any one of claims 1 to 8, wherein the first step is a re-strike step in which draw molding or foam molding is applied, and the second step is molding into a product shape. Manufacturing method of molded products. The method for producing a press-formed product according to any one of claims 1 to 9, wherein the metal plate is a steel plate having a material strength of 590 MPa or more.

Images