PRESS FORM DEVICE AND METHOD FOR PRODUCING PRESS-FORMED ARTICLES

Abstract

To reduce warping of vertical wall portions without causing buckling during pressing. Press-forming into a hat cross-sectional shape having one linear vertical wall portion and the other curved vertical wall portion and not having a flange portion is performed. A punch and a pad sandwiching a top sheet portion therebetween, bending blades for bend-forming the vertical wall portions, and stoppers facing the bending blades are provided. The punch is supported by a first cushion component. The bending blades each have an upper die component and a lower die component disposed facing each other in the press direction with an interval (D) equal to a set compression amount in the range of 2% or more and 6% or less of the heights of the vertical wall portions and a second cushion component interposed between the upper die component and the lower die component, maintaining the interval (D), and contractible in the press direction. The cushion pressure of the second cushion component is lower than the cushion pressure of the first cushion component and has such cushion pressure that the second cushion component does not contract during the bend-forming of the vertical wall portions.

Claims

1. A press form device for performing a first step of bend-forming a base sheet or a material to be processed obtained by applying bending or drawing to a base sheet beforehand into a hat cross-sectional shape having a top sheet portion and right and left vertical wall portions continuous to both sides in a width direction of the top sheet portion, having one vertical wall portion linearly extending along a longitudinal direction and the other vertical wall portion having a curved portion projecting to a side of the one vertical wall portion along the longitudinal direction, and not having a flange portion and a second step of applying compression by a preset compression amount in a direction along a press direction to the vertical wall portions in a formed state by the first step, the preset compression amount being set in a range of 2% or more and 6% or less of heights of the vertical wall portions, the press form device comprising: a punch and a pad sandwiching the top sheet portion between the punch and the pad in a sheet thickness direction; bending blades disposed on sides of the punch and the pad and bend-forming the vertical wall portions; and stoppers facing the bending blades in the press direction and constraining end portions of the material to be processed, wherein the pad and the bending blades configure an upper die, the punch is supported by a first cushion component elastically expandable and contractible in the press direction, the bending blades each have an upper die component and a lower die component vertically divided in middle of the press direction and disposed facing each other in the press direction with an interval equal to the compression amount to be applied and a second cushion component interposed between the upper die component and the lower die component, maintaining the interval, and contractible in the press direction at a, predetermined pressure or more, and cushion pressure of the second cushion component is lower than cushion pressure of the first cushion component and has such cushion pressure that the second cushion component does not contract during the bend-forming of the vertical wall portions in the first step.

2. A method for producing a press-formed article comprising: a first step of forming a base sheet or a material to be processed obtained by applying bending or drawing to a base sheet beforehand into a hat cross-sectional, shape having a top sheet portion and right and left vertical wall portions continuous to both sides in a width direction of the top sheet portion, having one vertical wall portion linearly extending along a longitudinal direction and the other vertical wall portion having a curved portion projecting to a side of the one vertical wall portion along the longitudinal direction, and not having a flange portion; and a second step of applying compression by a preset compression amount in a direction along a press direction to the vertical wall portions in a formed state by the first step, the preset compression amount being set in a range of 2% or more and 6% or less of heights of the vertical wall portions, wherein, using a die which is provided with a punch and a pad sandwiching the top sheet portion between the punch and the pad in a sheet thickness direction, bending blades, disposed on sides of the punch and the pad and bend-forming the vertical wall portions, and stoppers facing the bending blades in the press direction and constraining end portions of the material to be processed and in which the pad and the bending blades configure an upper die and the bending blades each have an upper die component and a lower die component vertically divided in middle of the press direction and disposed facing each other in the press direction with an interval equal to the compression amount to be applied and a cushion component interposed between the upper die component and the lower die component, maintaining the interval, and contractible in the press direction at a predetermined pressure or more, in the first step, the vertical wall portions are bend-formed by moving the bending blades in the press direction while maintaining a state where the cushion component does not contract by cushion pressure until the end portions of the material to be processed abut on the stoppers and the lower die components abut on the stoppers while sandwiching the top sheet portion with the punch and the pad, and in the second step, the bending blades are further moved in the press direction until the upper die components and the lower die components contact each other following the first step, so that the vertical wall portions are sandwiched between the bending blades and a side surface of the punch, whereby the interval becomes small while preventing buckling, so that the compression is applied to the vertical wall portions.

3. The method for producing a press-formed article according to claim 2, wherein the material to be processed is a metal sheet having tensile strength of 440 MPa or more.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] FIG. 1 is a perspective view illustrating an example of a component which has a hat cross-sectional shape not having a flange portion and in which at least one of vertical wall portions is curved among body frame components;

[0032] FIGS. 2A and 2B are figures explaining a press-formed article according to an embodiment based on the present invention. FIG. 2A is a perspective view and FIG. 2B is a figure viewed from above;

[0033] FIG. 3 is a schematic cross-sectional view explaining a die according to the embodiment based on the present invention;

[0034] FIGS. 4A to 4E are cross-sectional views schematically explaining the movement of the die in press-forming according to the embodiment based on the present invention;

[0035] FIG. 5 is a figure schematically illustrating a developed state of a blank used in Examples;

[0036] FIGS. 6A and 6B are figures illustrating results of measuring the deviation amount from the component shape in the evaluation cross sections of components produced by the press-forming in the longitudinal direction;

[0037] FIG. 7 is a figure illustrating the relationship between the waving amount and the compression ratio applied to the vertical wall portion on the curved side.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0038] Next, an embodiment of the present invention will now be described with reference to the drawings.

[0039] Herein, the following description is directed to a hat cross-sectional shape having a top sheet portion 1A and right and left vertical wall portions 1Ba, 1Bb continuous to both sides in the width direction of the top sheet portion 1A and not having a flange portion as illustrated in FIG. 2 as the shape of a press-formed article 1. In this embodiment, one vertical wall portion 1Bb is linear and the other vertical wall portion 1Ba is curved along the longitudinal direction in a view from above. More specifically, the one vertical wall portion 1Bb linearly extends along the longitudinal direction and the other vertical wall portion 1Ba has a shape having a curved portion projecting to the side of the one vertical wall portion 1Bb along the longitudinal direction. FIG. 2 illustrate an example in which the entire other vertical wall portion 1Ba configures the curved portion. However, a shape may be acceptable in which the curved portion projecting to the side of the one vertical wall portion 1Bb is provided in a part in the longitudinal direction of the other vertical wall portion 1Ba.

[0040] The dimensions illustrated in FIGS. 2A and 2B are examples and the dimensions in Examples are also indicated. The angle formed by the top sheet portion 1A and the vertical wall portions 1Ba, 1Bb is set to 90° or more and 100° or less, for example.

[0041] The present invention in an embodiment particularly exhibits the effects when a material to be processed 2 is a metal sheet having tensile strength of 440 MPa or more and preferably 590 MPa or more.

<Die>

[0042] A press form device of this embodiment is provided with a punch 21 and a pad 11 sandwiching the top sheet portion 1A therebetween in the sheet thickness direction, bending blades 12 disposed on the sides of the punch 21 and the pad 11 and bend-forming the vertical wall portions 1Ba, 1Bb, and stoppers 22 facing the bending blades 12 in the press direction and constraining end portions of the material to be processed 2 (see FIG. 3). The punch 21 is supported by a first cushion component 24 elastically expandable and contractible in the press direction. The bending blades 12 each have an upper die component 12A and a lower die component 12B vertically divided in the middle of the press direction and disposed facing each other in the press direction with an interval D equal to the compression amount to be applied and a second cushion component 14 interposed between the upper die component 12A and the lower die component 12B, maintaining the interval D, and contractible in the press direction at predetermined pressure or more. The cushion pressure of the second cushion component 14 is lower than the cushion pressure of the first cushion component 24 and has such cushion pressure that the second cushion component 14 does not contract in bend-forming of the vertical wall portions 1Ba, 1Bb in a first process.

[0043] Herein, the cushion component is a device provided with a pressure maintaining function to generate reaction force against a formed article by hydraulic pressure, pneumatic pressure, or the like. The reaction force generated by the cushion component serves as the cushion pressure.

[0044] Next, a specific example of the press form device of this embodiment is described with reference to FIG. 3.

[0045] The press form device of this embodiment is provided with an upper die 10 and a lower die 20 as illustrated in FIG. 3.

[0046] The upper die 10 is provided with the pad 11 and the bending blades 12. The pad 11 is attached to the undersurface of a press sheet 13 for upper die through a third cushion component 15. In the third cushion component 15, the axis in the expanding and contracting direction is set in the press direction (vertical direction in FIG. 3). The third cushion component 15 is formed by a gas spring, for example. The cushion pressure thereof is set to 8 ton, for example.

[0047] The bending blades 12 are disposed on the sides of the pad 11 and used for bend-forming the vertical wall portions 1Ba, 1Bb. The bending blades 12 each are divided into the upper die component 12A and the lower die component 12B by a plane crossing the press direction at arbitrary positions among positions facing the vertical wall portions 1Ba, 1Bb. The upper die components 12A have shoulder portions 12Aa having upper end portions fixed to the press sheet 13 for upper die and bend-forming connection portions of the top sheet portion 1A and the vertical wall portions 1Ba, 1Bb.

[0048] The interval D between the upper die component 12A and the lower die component 12B is set to the interval D equal to the preset compression amount. The interval D is maintained by the second cushion component 14 interposed between the upper die component 12A and the lower die component 12B. The interval D is set to a value equal to the compression amount set in the range of 2% or more and 6% or less of the heights of the vertical wall portions 1Ba, 1Bb. Usually, the interval D is set to a size of several millimeters which is less than 10 mm.

[0049] The second cushion component 14 is formed by a gas spring, for example, and is contractible when pressure equal to or higher than the preset predetermined pressure is applied in a direction along the press direction. For example, when the predetermined pressure described above is applied, the second cushion component 14 begins to contract. The interval D decreases by the amount corresponding to the magnitude of the applied pressure. The second cushion component 14 is provided so as to be contractible until the upper die component 12A and the lower die component 12B abut on each other. The cushion pressure of the second cushion component 14 is set to 3 ton, for example.

[0050] The lower die 20 is provided with the punch 21 and the stoppers 22 disposed on the sides of the punch 21.

[0051] The punch 21 is set to face the pad 11 in the press direction and provided through the first cushion component 24 with respect to the upper surface of a press sheet 23 for lower die. The first cushion component 24 is formed by a die cushion, such as a cushion pin, for example, and is elastically expandable and contractible in the press direction. The cushion pressure of the first cushion component 24 is set to 50 ton, for example.

[0052] The stoppers 22 are fixed to the upper surface of the press sheet 23 for lower die. The gap between the punch 21 and the stoppers 22 is set to be less than the thickness of the material to be processed 2, e.g., 0.02 mm or less, as viewed in the press direction.

[0053] Herein, the cushion pressure of each of the first cushion component 24, the second cushion component 14, and the third cushion component 15 is set to satisfy the following relationship.

[0054] First cushion component 24>Third cushion component 15

[0055] Third cushion component 15>Second cushion component 14

[0056] However, the cushion pressure of the second cushion component 14 is set to be equal to or higher than such cushion pressure that the interval D between the upper die component 12A and the lower die component 12B does not vary, i.e., the cushion component does not contract, in a state where the vertical wall portions 1Ba, 1Bb are bend-formed and compressive force in a direction along the press direction is not applied to the vertical wall portions 1Ba, 1Bb.

[0057] By setting the relationship of “Cushion pressure of first cushion component 24>Cushion pressure of third cushion component 15”, the punch 21 placed on the first cushion component 24 can be set so as not to move up and down when bend-forming is advanced by the bending blades 12 while pressing the top sheet portion 1A with the pad 11.

[0058] When the cushion pressure (pressure) of the second cushion component 14 is set to 3 ton or more, the interval D between the upper die component 12A and the lower die component 12B can be maintained constant in bend-forming the vertical wall portions 1Ba, 1Bb.

[0059] Moreover, by setting the relationship of “Cushion pressure of first cushion component 24>Cushion pressure of second cushion component 14”, a desired compression amount can be applied to the vertical wall portions 1Ba, 1Bb by lowering the upper die 10 until the upper die components 12A and the lower die components 12B contact each other in a second process.

<Method for Producing Press-Formed Article 1>

[0060] Next, a method for producing the press-formed article 1 using the above-described press form device is described.

[0061] The method for producing the press-formed article 1 of this embodiment has at least the first process and the second process performed following the first process.

[0062] The first process includes bend-forming the vertical wall portions 1Ba, 1Bb of a base sheet or the material to be processed 2 (blank) obtained by applying bending or drawing to a base sheet beforehand into a hat cross-sectional shape having the top sheet portion 1A and the right and left vertical wall portions 1Ba, 1Bb continuous to both sides in the width direction of the top sheet portion 1A, having the one vertical wall portion 1Bb linearly extending along the longitudinal direction and the other vertical wall portion 1Ba having a curved portion projecting to the side of the one vertical wall portion 1Bb along the longitudinal direction, and not having a flange portion to achieve a first formed state. More specifically, the first process is a process of forming the vertical wall portions 1Ba, 1Bb by setting the material to be processed 2 (blank) in the die, and then sandwiching the top sheet portion 1A of the material to be processed 2 with the punch 21 and the pad 11 and lowering the lower bending blades (lower die components 12B) of the divided bending blades 12 until the undersurfaces of the lower bending blades contact the stoppers 22.

[0063] The second process includes applying compression to the vertical wall portions 1Ba, 1Bb by the preset compression amount in a direction along the press direction in the bend-formed state by the first process to achieve a second formed state. More specifically, the second process is a process in which the upper die 10 is further lowered while maintaining the state where the entire component is sandwiched with the pad 11, the bending blades 12, and the punch 21 after the first formed state by the first process, and then the punch 21 placed on the first cushion component 24 is lowered accompanying the lowering. At this time, the upper die 10 is lowered until the second cushion components 14 (gas spring) set in the divided bending blades 12 contract, so that the upper die components 12A and the lower die components 12B configuring the divided bending blades 12 contact each other. Moreover, end portions (lower end portions of the vertical wall portions 1Ba, 1Bb) of the material to be processed 2 are constrained by being perpendicularly pressed against the surfaces of the stoppers 22 and do not move.

[0064] An operation of the die in the press-forming is described with reference to FIGS. 4A to 4E.

[0065] FIGS. 4A to 4E illustrate an example when a blank (material to be processed 2) deformed by springback after formed once by press-forming, such as foam or draw forming, is press-formed based on embodiments of the present invention to be produced as the press-formed article 1. It is a matter of course that a plate-like base sheet may be used as the blank (material to be processed 2).

[0066] First, the top sheet portion 1A of the blank is placed on the punch bottom as illustrated in FIG. 4A. At this time, the punch 21 is raised by about 10 mm, for example, beforehand so that the punch bottom is higher than the vertical wall height of a component to be formed.

[0067] Next, the upper die 10 is lowered, whereby the top sheet portion 1A of the blank 2 is sandwiched with the punch 21 and the pad 11 as illustrated in FIG. 4B. Subsequently, the bend-forming of the vertical wall portions 1Ba, 1Bb by the bending blades 12 is performed by lowering the bending blades 12 as illustrated in FIG. 4C. Then, the undersurfaces of the lower bending blades (lower die components 12B) of the divided bending blades 12 are brought into contact with the stoppers 22. The operation of the die is set so that, when the undersurfaces of the lower die components 12B contact the stoppers 22, blank end portions contact the stoppers 22. The operation of the die is set so that, until the state above, the second cushion components 14 set in the divided bending blades 12 do not contract. This setting can be performed by the cushion pressure of the second cushion components 14. More specifically, the cushion pressure may be set to be higher than force transmitted to the lower bending blades (lower die components 12B) by friction from the vertical wall portions of the blank 2.

[0068] In this state (see FIG. 4C), the blank 2 is in the state of being sandwiched with the upper die 10 and the lower die 20, and thus is temporarily formed into a target component shape. This state is the first formed state. The above corresponds to the first process.

[0069] Next, after the first formed state, the upper die 10 is further lowered by the preset compression amount as illustrated in FIG. 4D. At this time, the upper die component 12A relatively approaches the lower die component 12B by the contraction of the second cushion component 14, so that both the die components 12A, 12B contact each other. More specifically, the pad 11 and the upper die components 12A of the bending blades 12 are lowered interlocking with the lowering of a slide of a pressing machine. The pressurization force of the pressing machine is higher than the cushion pressure interlocking with the punch 21, and therefore the punch 21 is also lowered. Meanwhile, the stoppers 22 are fixed and do not move, and therefore end portions of the blank 2 are constrained by the stoppers 22. Furthermore, the entire blank 2 is constrained by the pad 11, the bending blades 12, and the punch 21 at this time, and therefore there is no room for the blank 2 to cause out-of-plane deformation. Therefore, compressive force can be applied without causing buckling in the vertical wall portions 1Ba, 1Bb of the blank 2. This state is the second formed state (see FIG. 4D). The above corresponds to the second process.

[0070] Finally, the upper die 10 is raised as illustrated in FIG. 4E to thereby release the press-formed article 1 produced by the press-forming from the die.

[0071] As described above, this embodiment can form the blank (material to be processed 2) into a component of a hat shaped cross section having the one vertical wall portion 1Bb linearly extending along the longitudinal direction and the other vertical wall portion 1Ba having a curved portion projecting to the side of the one vertical wall portion 1Bb along the longitudinal direction and not having a flange portion, apply target compression to the vertical wall portions 1Ba, 1Bb, and reduce the warping of the vertical wall portions 1Ba, 1Bb. occurring in performing the press-forming into the component shape having the top sheet portion 1A and the vertical wall portions 1Ba, 1Bb continuous thereto and not having a flange portion only by lowering the upper die 10. As a result, the press-formed article 1 with good dimensional accuracy can be provided.

EXAMPLES

[0072] Next, Examples based on the embodiments of the present invention are described.

[0073] A 440 MPa grade cold-rolled steel sheet (sheet thickness of 1.0 mm) and a 1180 MPa grade cold-rolled steel sheet (sheet thickness of 1.0 mm) as base sheets were press-formed into the press-formed article 1 of the hat cross-sectional shape having the top sheet portion 1A, the linear vertical wall portion 1Bb, and the curved vertical wall portion 1Ba and not having a flange portion as illustrated in FIG. 2.

[0074] At this time, in order to vary the compression amount to the vertical wall portions 1Ba, 1Bb of the press-formed article 1, blanks in which the blank shapes were individually adjusted so that the blank lengths of the vertical wall portions 1Ba, 1Bb were longer by 1 to 5 mm than the heights of the vertical wall portions 1Ba, 1Bb of a formed article as in the developed blank shape illustrated in FIG. 5 were prepared as the material to be processed 2. Hatched portions in FIG. 5 are lengthened portions.

[0075] Then, each blank above was subjected to usual processing of performing foam forming in a state where the top sheet portion 1A was sandwiched with the pad 11 beforehand, and then sprung back by form release to create a blank (material to be processed 2). Then, the blank was press-formed using the die described in the embodiment.

[0076] The compression amount to be set corresponds to the length made larger than the heights of the vertical wall portions 1Ba, 1Bb of the formed article. More specifically, the compression amount was set in the range of 1 to 5 mm. The compression amount can be adjusted by the lowering amount of the upper die 10.

[0077] The heights of the vertical wall portions 1Ba, 1Bb in the product shape were set to 83 mm as illustrated in FIG. 2A.

[0078] Then, the deviation degree of the cross-sectional shape when each compression ratio was applied from the component shape as a product after the press-forming was measured along the longitudinal direction. FIGS. 6A and 6B illustrate the measurement results in each material. In FIGS. 6A and 6B, “only foam” (corresponding to No. 1 and No. 8 of Table 1) indicates a case where the application of the compression by the second process was not performed. FIG. 6A illustrates a case where the material is the 1180 MPa grade cold-rolled steel sheet. FIG. 6B illustrates a case where the material is the 440 MPa grade cold-rolled steel sheet.

[0079] Table 1 illustrates the amount in which the vertical wall portion 1Ba was lengthened from the component shape and the compression ratio generated in the vertical wall portions 1Ba, 1Bb at this time. The amount obtained by subtracting the minimum value from the maximum value of the deviation amount from the product shape along the longitudinal direction is defined as the waving amount. In the evaluation of this Example, a case where the waving amount was 5 mm or less was determined that the shape fixability was excellent, which was expressed by “◯” in Table 1. Some actual products are passed even when the waving amount is 10 mm or less in some cases. Even when the waving amount determination was “×” in Table 1, some products are passed as a product in some cases. Herein, the compression ratio is a ratio of the compression amount to the height of the vertical wall portion 1Ba (Compression amount/Height of vertical wall portion)×100) in the final product shape.

TABLE-US-00001 TABLE 1 Blank extension Compression Waving amount No. Material amount (mm) ratio (%) Method determination 1 1180 MPa No 0.0 Conventional x steel sheet extension example 2 1180 MPa 1.0 1.2 Present invention x steel sheet example 3 1180 MPa 2.0 2.4 Present invention x steel sheet example 4 1180 MPa 3.0 3.6 Present invention x steel sheet example 5 1180 MPa 4.0 4.8 Present invention ∘ steel sheet example 6 1180 MPa 4.5 5.4 Present invention ∘ steel sheet example 7 1180 MPa 5.0 6.0 Present invention x (Buckling steel sheet example occurred) 8 440 MPa No 0.0 Conventional x steel sheet extension example 9 440 MPa 1.0 1.2 Present invention x steel sheet example 10 440 MPa 2.0 2.4 Present invention ∘ steel sheet example 11 440 MPa 3.0 3.6 Present invention ∘ steel sheet example 12 440 MPa 4.0 4.8 Present invention ∘ steel sheet example 13 440 MPa 4.5 5.4 Present invention ∘ steel sheet example 14 440 MPa 5.0 6.0 Present invention x (Buckling steel sheet example occurred)

[0080] As is understood from FIG. 6, it is found that the warping of the curved vertical wall portion 1Ba is improved with an increase in the compression ratio, so that the cross-sectional shape approaches the component shape. Furthermore, it is found that the deviation amount from the component shape of the cross section decreases accompanying the same.

[0081] FIG. 7 illustrates the relationship between the compression ratio applied to the vertical wall portion 1Ba and the waving amount. As is understood from FIG. 7, it is found that, in the 1180 MPa steel sheet, the warping of the vertical wall portion 1Ba is sharply improved and the waving amount starts to decrease around when about 2.5% of the compression ratio was applied, i.e., 2.5% or more. The waving amount is less than 10 mm when the compression ratio is 3.0% or more and furthermore the waving amount is less than 5 mm when the compression ratio is 4.0% or more, which shows that the waving amount reduction effect starts to converge. Also in the 440 MPa steel sheet, the warping of the vertical wall portion 1Ba is similarly improved with an increase in the compression ratio. The waving amount was less than 5 mm at the compression ratio of 2.0% or more. Moreover, in this example, no material was able to be formed under the conditions where the compression ratio exceeded 6.0% because the material flowed into the gap between the divided bending blades 12 and buckling occurred. In view of the above, in the component shape using the 1180 MPa grade cold-rolled steel sheet, the compression ratio is preferably 3.0% or more and less than 6.0% and more preferably 4.0% or more and less than 6.0%. In the component shape using the 440 MPa grade cold-rolled steel sheet, the compression ratio is preferably 2.0% or more and less than 6.0%.

[0082] As described above, the entire contents of Japanese Patent Application Publication No. 2017-062445 (filed Mar. 28, 2017) to which this application claims priority form part of this disclosure by reference.

[0083] Although the description is given referring to a limited number of embodiments herein, the scope of the present invention is not limited thereto. It is obvious for those skilled in the art to alter and modify the embodiments based on the disclosure above.

REFERENCE SIGNS LIST

[0084] 1 press-formed article

[0085] 1A top sheet portion

[0086] 1Ba vertical wall portion on curved side

[0087] 1Bb vertical wall portion

[0088] 2 material to be processed

[0089] 10 upper die

[0090] 11 pad

[0091] 12 bending blade

[0092] 12A upper die component

[0093] 12B lower die component

[0094] 13 press sheet for upper die

[0095] 14 second cushion component

[0096] 15 third cushion component

[0097] 20 lower die

[0098] 21 punch

[0099] 22 stopper

[0100] 23 press sheet for lower die

[0101] 24 first cushion component

[0102] D interval