JP6908078B2 - Manufacturing method of pressed parts and design method of lower die - Google Patents

Description

The present invention relates to a technique for suppressing material edge cracking at an elongated flange portion due to press molding.

As measures to prevent material edge cracking at the flange by press working, conventional measures such as extending the blank line length within the tolerance of product dimensions and adding a preforming process for pre-walling have been taken. Proposed. Here, Patent Document 1 describes a stretch flange crack prediction technique. Patent Document 2 describes that expansion flange cracking is suppressed by specifying the shape of the outer peripheral edge of the flange portion. Patent Documents 3 and 4 describe that flange cracking is suppressed by providing a preformed portion or the like in the vicinity of the maximum elongation deformation portion in the preforming step.

Japanese Patent No. 4935713 JP-A-2009-160655 Japanese Patent No. 5979164 JP 2015-139783

By the known technique described in Patent Document 1 and the like, it is possible to determine whether or not molding is possible, such as the presence or absence of flange cracks, in press molding. However, the technique described in Patent Document 2 may limit the shape of parts. Further, in Patent Documents 3 and 4, it is necessary to provide a preformed portion or the like to the blank in advance.
The present invention has been made by paying attention to the above points, and is generated at the stretched flange portion during pressing without necessarily increasing the number of pressing steps and without changing the shape of the pressed part or the shape of the blank. The purpose is to suppress material edge cracking.

In press molding, there is a concern that cracks may occur at the tensile deformed portion of the flange portion. Cracking of the flange portion occurs when the breaking limit is exceeded during stretch flange processing. In addition, the plate thickness reduction rate of the fracture-risk portion increases before the fracture occurs. On the other hand, the inventors have studied a technique capable of suppressing bending cracks in the flange portion without necessarily increasing the number of steps without taking the above-mentioned general crack countermeasures. Then, the inventors have found that by changing the restraint condition of the flange portion by the lower mold, the restriction on the material flow to the position where the crack may occur is relaxed and the crack can be suppressed.

In order to solve the problem, one aspect of the present invention is to press a blank with an upper die and a lower die, and to perform a vertical wall portion continuous with the top plate portion and a flange portion continuous with the vertical wall portion. In a method for manufacturing a pressed part having a bending molding step of bending and molding, the lower die is set to a shape that is not in contact with the entire lower surface or a part of the lower surface of the flange region to be the flange portion of the blank, and the bending molding is performed. The gist is to do.

Further, in another aspect of the present invention, the blank is pressed with the upper die and the lower die, and the vertical wall portion continuous with the top plate portion and the flange portion continuous with the vertical wall portion are bent and molded. Simulation of the bending molding process under the condition that the lower mold is set to be in contact with the entire lower surface of the flange region and the bending molding is performed in the method for designing the lower mold used in the above. When the analysis is performed by a computer and it is determined that the flange edge of the flange portion after bending molding is cracked, the lower mold is set to a shape that is not in contact with the entire lower surface or a part of the lower surface of the flange region. Is the gist.

According to one aspect of the present invention, it is possible to suppress material edge cracking that occurs in the stretched flange portion during pressing without necessarily increasing the number of pressing steps and without changing the shape of the pressed part or the shape of the blank. It becomes.

It is a figure which shows the example of the cross-sectional shape of the pressed part which concerns on 1st Embodiment based on this invention. It is a figure explaining an example of a pressed part. It is a figure explaining the structural example of the manufacturing method. It is a figure explaining the non-contact area, (a) is the side view along the flange edge, (b) (c) is the figure which shows the example of the non-contact area. It is a figure explaining the schematic diagram of the mold, (a) is the mold shape at the cross-sectional view position of AA'in FIG. 2, and (b) is the shape of the mold at the cross-sectional view position of B-B'in FIG. It is a figure which shows the mold shape. It is a figure which shows the modification of the lower mold shape.

Next, an embodiment of the present invention will be described with reference to the drawings.
The shape of the pressed part targeted by the present embodiment is, for example, as shown in FIG. 1, a top plate portion 10, a vertical wall portion 11 continuous with the top plate portion 10, and a flange portion continuous with the vertical wall portion 11. Has 12 and. FIG. 1A shows a cross-sectional hat shape, and FIG. 1B shows an example of a cross-sectional shape in which the vertical wall portion 11 and the flange portion 12 are continuous only in the width direction of the top plate portion 10. It is shown in the figure.

The part shape of the press part 1 which is the object of the present invention is a shape in which material edge cracks may occur in the flange portion 12 when bending and molding are performed with a general die. Here, there is a possibility that material edge cracks may occur in the flange portion 12 during press working such that tensile deformation occurs in the flange portion 12 along the flange edge 12a. The material edge crack of the flange portion 12 is also described as a flange edge crack.

In the present embodiment, as shown in FIG. 2, a case where the outer edge of the flange portion 12 partially projects in the width direction of the top plate portion 10 with respect to the shape of the top plate portion 10 in a plan view is taken as an example. Will be explained. The present invention is not limited to the shape of the pressed parts shown in FIG. The present invention is applicable as long as it has a bending forming step of performing bending forming in which tensile deformation occurs in the flange portion 12 along the flange edge 12a.

Here, when the blank 13 is bent and molded into the shape of the pressed part 1 as shown in FIG. 2 by the upper die and the lower die, the lower die is a flange region of the flange portion 12 of the blank 13. When a normal mold in contact with the entire lower surface was used, cracks 15 were generated on the flange edge 12a and wrinkles were generated on both sides of the cracks 15. Reference numeral 14 is a region of the wrinkle generation portion. A high-strength steel plate having a tensile strength of 590 MPa was used as the blank 13. The higher the tensile strength of the blank 13, the more likely it is that cracks 15 will occur. Therefore, the present invention is suitable for, for example, a high-tensile steel plate having a tensile strength of 590 MPa or more.

However, the present invention can be applied not only to steel but also to iron alloys such as stainless steel, and also to non-ferrous materials and non-metal materials. Further, the pressed part 1 manufactured in the present embodiment is suitable as, for example, an automobile part, but the present invention can be applied not only to an automobile part but also to all processes for press-molding a plate material.
In the present specification, the wrinkle generation region (range) is, for example, a wrinkle generation region (range in the direction along the flange edge 12a) in which the plate loss due to press working is 5% or more. The wrinkle generating portion 14 is a portion that is strongly restrained by the mold by abutting on the lower mold relatively earlier than the positions of the other flange portions 12.

As shown in FIG. 3, the method for manufacturing the pressed part 1 of the present embodiment includes a crack / wrinkle evaluation unit 20A, a lower die determining unit 20B, and a bending forming step 20C. The crack / wrinkle evaluation unit 20A and the lower mold determination unit 20B constitute a design method for the lower mold 31.
The portion of the blank 13 that becomes the flange portion 12 by pressing the blank 13 into the shape of the desired pressed component 1 is referred to as a “flange region”.

The crack / wrinkle evaluation unit 20A is a mold including the upper mold 30 and the lower mold 31 used in the bending molding step 20C, and the lower mold 31 is set to be in contact with the entire lower surface of the flange region for bending molding. Is a step of determining whether or not cracks 15 or wrinkles are generated in the flange edge 12a of the flange portion 12 after bending and forming. Further, the crack / wrinkle evaluation unit 20A performs a process of specifying the position of the crack 15 and the wrinkle generation region (wrinkle generation unit 14) where the crack 15 or the wrinkle occurs when the crack 15 or the wrinkle occurs. Here, when the lower mold 31 is in contact with the entire lower surface of the flange region, it means that the lower mold 31 is substantially in contact with the entire lower surface of the flange region. For example, the lower mold 31 is in contact with the entire lower surface of the flange region. Is in contact with the lower surface of the flange region by 90% or more, preferably 95% or more.

The crack / wrinkle evaluation unit 20A creates a prototype using the mold to be used in the bending molding process 20C, and determines whether or not cracks 15 and wrinkles are generated at the flange edge 12a, and the position of the wrinkle generation unit 14. May be specified. Further, the crack / wrinkle evaluation unit 20A performs the bending molding step 20C under the condition that the lower mold 31 is set to be in contact with the entire lower surface of the flange region to be the flange portion 12 of the blank 13 and the bending molding is performed. By performing the simulation analysis of the above, the presence / absence and range of cracks 15 and wrinkles in the flange portion 12 may be estimated. In this case, the crack / wrinkle evaluation unit 20A obtains the distribution of the plate thickness reduction rate and the stress / strain distribution at the portion where the stretch flange is deformed by, for example, simulation analysis by CAE, so that the crack 15 and the wrinkle as described above can be obtained. Make an evaluation.

Here, when the shape of the mold used in the bending molding step 20C has already been determined, the condition is that "the lower mold 31 comes into contact with the entire lower surface of the flange region serving as the flange portion 12 in the blank 13". A prototype may be created or a CAE analysis may be performed to evaluate the cracks 15 and wrinkles as described above, without providing the mold shape that has already been determined.
The lower mold determining unit 20B determines whether or not the crack / wrinkle evaluation unit 20A has determined that the crack 15 and wrinkles do not occur, and if it determines that the crack 15 and wrinkles do not occur, the crack / wrinkle evaluation unit 20B evaluates the crack / wrinkle. The mold shape used for evaluation in part 20A is determined to be the mold used in the bending molding step 20C.

On the other hand, if it is determined that cracks 15 and wrinkles are generated, the lower mold determining unit 20B is located on both sides of the lower mold 31 with the crack 15 generation positions in the direction along the flange edge 12a. The region including at least one wrinkle generating portion 14 in the wrinkle generating portion 14 is referred to as a non-contact region 21. Then, the lower mold determining unit 20B specifies the position of the non-contact region 21 in the flange region of the blank 13 and the shape of the lower mold 31 such that the lower mold 31 is non-contact. Then, the lower mold 31 having the specified shape is used as the lower mold 31 of the mold used in the bending forming step 20C. It is not necessary to change the shape of the upper mold 30 used for evaluation in the crack / wrinkle evaluation unit 20A.

Here, as shown in FIG. 4, the region including the wrinkle generating portion 14, which is the non-contact region 21, includes the wrinkle generating portion 14 and the wrinkle generation lengths L1 and L2 in the direction along the flange edge 12a. Set the length to 3 times or more of. Preferably, as shown in FIG. 4B, it is preferable to set the non-contact region 21 on both sides of the wrinkle generating portion 14 and the wrinkle generating portion 14 in a region equal to or more than 1 times the wrinkle generation lengths L1 and L2.

It has been confirmed that if the length of the non-contact region 21 is three times as long as the wrinkle generation lengths L1 and L2, the crack 15 at the position closest to the wrinkle generation portion 14 is suppressed. .. There is no particular upper limit to the length of the non-contact region 21 as long as the length of the non-contact region 21 is three times or more the wrinkle generation lengths L1 and L2 for suppressing cracks 15. As shown in FIG. 4C, the entire flange region may be the non-contact region 21. In the case of an elongated flange shape in which the flange portion 12 is cracked 15 or wrinkled, the flange portion 12 is bent and formed even if the lower mold 31 does not restrain the flange portion 12.

However, considering the accuracy of press molding of the flange portion 12, the length of the region including the wrinkle-generating portion 14 is preferably 10 times or less the wrinkle-generating lengths L1 and L2, for example. Further, the non-contact region 21 is preferably a region of 2/3 or less of the flange length in the direction along the flange edge 12a, and more preferably a region of 1/2 or less.

In the bending forming step 20C, as shown in FIG. 5, the blank 13 is pressed by the upper die 30 and the lower die 31 using the die determined by the lower die determining portion 20B, and the top plate is pressed. The vertical wall portion 11 continuous with the portion 10 and the flange portion 12 continuous with the vertical wall portion 11 are bent and molded to manufacture the target pressed part 1. At this time, in the bending molding step 20C, it is preferable to adopt foam molding that does not use a wrinkle retainer. 5 (a) is a cross section at the AA'position of FIG. 2, and an example of the shape of the lower mold 31 other than the non-contact region 21 is shown. FIG. 5 (b) is B of FIG. It is a cross section at the −B'position, and an example of the shape of the lower mold 31 in the non-contact region 21 is shown.

Here, in the lower mold determining portion 20B, the region including at least one wrinkle generating portion 14 of the wrinkle generating portion 14 located on both sides of the crack 15 is specified as the non-contact region 21, but on both sides of the crack 15. The region including the wrinkle-generating portion 14 in all the wrinkle-generating portions 14 may be simply set as the non-contact region 21 without being limited to the located wrinkle-generating portion 14.

Further, in the above description, the region including the wrinkle generating portion 14 along the flange edge 12a is defined as the non-contact region 21, but the flange region portion of the non-contact region 21 is lower than the portion on the vertical wall portion 11 side. Even if the mold 31 is set to be in contact (see FIG. 6) and the bending line (ridge line) between the vertical wall portion 11 and the flange portion 12 is more reliably bent and formed in the bending forming step 20C. good. In this case, 1/3 or less of the length from the boundary line with the vertical wall portion 11 to the flange edge 12a is set as the area where the lower mold 31 contacts.

The pressed part 1 press-molded in the bending molding step 20C does not have to have the final product shape. As a subsequent step of the bending molding step 20C, there may be a step of press molding into the product shape.
According to the method of the present embodiment, the material edge crack 15 generated in the stretch flange portion 12 during press working does not necessarily increase the number of pressing steps and does not change the shape of the pressed part 1 or the shape of the blank 13. Can be suppressed.

Here, when the manufacturing method of the present embodiment was adopted when manufacturing the pressed part 1 of FIG. 2, the material edge crack 15 at the flange portion 12 was suppressed without changing the shape of the pressed part 1. I have confirmed that.
Further, as confirmed by CAE analysis, it was analyzed that bending molding was performed under the condition that the entire lower surface of the flange region was in contact with the lower mold 31, and the maximum plate thickness reduction rate at the stretched flange portion 12 was 21.6. %Met.

On the other hand, with respect to the wrinkle-generating portions 14 located on both sides of the crack 15, the wrinkle-generating portions 14 and the wrinkle-generating portions 14 have wrinkle-generating portions 14 and wrinkle-generating portions 14 on both sides, respectively. When CAE analysis was performed by setting the non-contact region 21 with the lower mold 31 (three times the growth), the maximum plate thickness reduction rate at the extension flange portion 12 was 10.7%, which was a plate thickness reduction rate. Was halved.
Further, when CAE analysis was performed with the entire surface of the flange portion 12 as the non-contact region 21 with the lower mold 31, the maximum plate thickness reduction rate at the extension flange portion 12 was 1.7%, and the plate thickness reduction rate was high. It was confirmed that it was significantly smaller.

1 Pressed parts 10 Top plate part 11 Vertical wall part 12 Flange part 12a Flange edge 13 Blank 14 Wrinkle generation part 15 Crack 20A Crack / wrinkle evaluation part 20B Lower mold determination part 20C Bending forming process 21 Non-contact area 30 Upper mold 31 Lower mold L1, L2 Wrinkle generation length

Claims (6)

A method for manufacturing a pressed part having a bending step of pressing a blank with an upper die and a lower die to bend a vertical wall portion continuous with the top plate portion and a flange portion continuous with the vertical wall portion. In
The lower mold is set to a shape that is not in contact with a part of the lower surface of the flange region to be the flange portion of the blank , and the bending molding is performed.
When it is determined that cracks occur in the flange edge of the flange portion after bending molding when the lower mold is set to be in contact with the entire lower surface of the flange region and the bending molding is performed, the lower mold is used. Is set to a shape that is not in contact with a part of the lower surface of the flange region, and the bending molding is performed.
A method of manufacturing a pressed part, which is characterized in that. At least one wrinkle-generating portion of the wrinkle-generating portion located on both sides of the lower mold in a region that is not in contact with the lower surface of the flange region with the cracking occurrence position in between in the direction along the flange edge. The length of the region including the wrinkled portion is set to be three times or more the length of the wrinkled portion in the direction along the flange edge. Item 1. The method for manufacturing a pressed part according to Item 1. The method for manufacturing a pressed part according to claim 1 or 2 , wherein the pressing step of molding into a product shape is provided as a subsequent step of the bending molding step. The method for manufacturing a pressed part according to any one of claims 1 to 3 , wherein the bending molding in the bending molding step is a foam molding. The lower die used when the blank is pressed with the upper die and the lower die to bend and form the vertical wall portion continuous with the top plate portion and the flange portion continuous with the vertical wall portion. It ’s a design method,
Bending molding is performed by performing a simulation analysis of the bending molding process on a computer under the condition that the lower mold is set to be in contact with the entire lower surface of the flange region serving as the flange portion of the blank and the bending molding is performed. The lower mold is characterized in that the shape of the lower mold is set to a shape that is not in contact with a part of the lower surface of the flange region when it is determined that the flange edge of the flange portion is cracked later. Design method. Under the condition that the lower mold is set to be in contact with the entire lower surface of the flange region and the bending molding is performed, a simulation analysis of the bending molding process is performed by a computer to crack the flange edge of the flange portion. When it is determined that wrinkles will occur,
At least one wrinkle-generating portion of the wrinkle-generating portion located on both sides of the lower mold in a region that is not in contact with the lower surface of the flange region with the cracking occurrence position in between in the direction along the flange edge. 5. The region according to claim 5, wherein the region including the wrinkled portion is set to a length of three times or more the length of the wrinkled portion in the direction along the flange edge. How to design the lower mold.

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