PRESS FORMING MACHINE AND METHOD FOR MANUFACTURING PRESS-FORMED PRODUCT

Abstract

A press forming machine includes a holding structure configured to hold a workpiece, and a metallic die for press forming the workpiece. The workpiece is a member made by joining a first steel plate and a second steel plate together by butt welding. The butt welding is a welding of an end face of the first steel plate and an end face of the second steel plate at a boundary between the first steel plate and the second steel plate. The holding structure is configured to hold a first region including both the first steel plate and the second steel plate adjacent to the boundary as a specific region in the workpiece, and not to hold a second region that is farther from the boundary than the first region and includes at least one of the first steel plate and the second steel plate adjacent to the first region.

Claims

1. A press forming machine comprising: a holding structure configured to hold a workpiece; and a metallic die for press forming the workpiece, the workpiece being a member in which a first steel plate and a second steel plate are joined together by butt welding, the butt welding being a welding of an end face of the first steel plate and an end face of the second steel plate at a boundary between the first steel plate and the second steel plate, the holding structure being configured to hold a first region including both the first steel plate and the second steel plate adjacent to the boundary as a specific region in the workpiece, and not to hold a second region that is farther from the boundary than the first region and includes at least one of the first steel plate and the second steel plate adjacent to the first region.

2. The press forming machine according to claim 1, wherein the holding structure holds the workpiece along the boundary.

3. The press forming machine according to claim 1, wherein the holding structure is configured to hold an end of a weld line, which is a butt-welded portion of the workpiece.

4. The press forming machine according to claim 1, wherein the first steel plate and the second steel plate differ from each other in at least one of plate thickness and strength.

5. The press forming machine according to claim 4, wherein the first steel plate and the second steel plate have different plate thicknesses, the holding structure has a step corresponding to a difference in plate thickness between the first steel plate and the second steel plate so as to be able to hold surfaces of both the first steel plate and the second steel plate, and the step is provided along a plate thickness direction of the first steel plate and the second steel plate.

6. The press forming machine according to claim 1, wherein the first region is smaller than the second region.

7. A method for manufacturing a press-formed product, the method comprising: holding a workpiece, the workpiece being a member in which a first steel plate and a second steel plate are joined together by butt welding; and press forming at least one of the first steel plate and the second steel plate in its plate thickness direction, the butt welding being a welding of an end face of the first steel plate and an end face of the second steel plate at a boundary between the first steel plate and the second steel plate, the holding the workpiece including holding a first region including both the first steel plate and the second steel plate adjacent to the boundary as a specific region in the workpiece, and not holding a second region that is farther from the boundary than the first region and includes at least one of the first steel plate and the second steel plate adjacent to the first region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Example embodiments of the present disclosure will be described hereinafter with reference to the accompanying drawings, in which:

[0021] FIG. 1 is a perspective view of a press-formed product;

[0022] FIG. 2 is a top view of the press-formed product;

[0023] FIG. 3A is a cross-sectional view of a press forming machine and a tailored blank in an arrangement process, and FIG. 3B is a cross-sectional view of the press forming machine and the tailored blank in a recess forming process;

[0024] FIG. 4A is a cross-sectional view of the press forming machine and the tailored blank in a holding process, and FIG. 4B is a cross-sectional view of the press forming machine and the tailored blank in a wall forming process;

[0025] FIG. 5 is a flowchart illustrating a method for manufacturing the press-formed product;

[0026] FIG. 6 is a cross-sectional view of a second punch with a step and a tailored blank in a wall forming process of another embodiment;

[0027] FIG. 7 is a cross-sectional view of a pad with a step and a tailored blank in a wall forming process of another embodiment;

[0028] FIG. 8 is a cross-sectional view of the second punch with a step, a pad with a step and a tailored blank in a wall forming process of another embodiment; and

[0029] FIG. 9 explains that an end of a weld line is held in another embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0030] Embodiments of the present disclosure are not limited to the embodiments below, and may take various forms as long as they fall within the technical scope of the present disclosure.

1. First Embodiment

1-1. Configuration

[1-1-1. Configuration of Press-Formed Product]

[0031] A press-formed product 1 shown in FIGS. 1 and 2 is formed by press forming a tailored blank 2 shown in FIG. 3A. The tailored blank 2 is a blank material in which a first steel plate 21 and second steel plates 22a, 22b with different plate thicknesses are joined together by butt welding. Press forming includes bending forming, drawing forming, and the like. The press-formed product 1 is a component that constitutes a part of a center floor pan of an automobile. The press-formed product 1 may be a component of other than the center floor pan of the automobile, for example, a component of a rocker outer panel or other floor panels. The press-formed product 1 may be a component mounted on a machine other than the automobile.

[0032] The press-formed product 1 includes a first plate section 11 and second plate sections 12a, 12b.

[0033] The first plate section 11 is an approximately rectangular plate. The first plate section 11 corresponds to the first steel plate 21 in the tailored blank 2 before being press-formed. The first plate section 11 has a first end face and a second end face extending in a first direction perpendicular to its plate thickness direction, on opposite sides of the first plate section 11 in a second direction perpendicular to both the first direction and the plate thickness direction. The first direction and the second direction are indicated in FIGS. 1 and 2 by double-headed arrows. The opposite sides of the first plate section 11 in a second direction refer to first and second sides of the first plate section 11 in the second direction. The first and second sides in the second direction correspond to first and second end sides of the double-headed arrow.

[0034] The second plate sections 12a, 12b are joined to the opposite end faces of the first plate section 11 by butt welding. The second plate sections 12a, 12b have shapes symmetrical about the first plate section 11. The second plate section 12a has an end face extending in the first direction. The end face is joined to the first end face of the first plate section 11 by butt welding. The second plate section 12b has an end face extending in the first direction. The end face is joined to the second end face of the first plate section 11 by butt welding. That is, the butt welding is provided at a boundary 13a between the first plate section 11 and the second plate section 12a and at a boundary 13b between the first plate section 11 and the second plate section 12b. In the press-formed product 1, a portion where the first plate section 11 and the second plate section 12a are butt-welded is referred to as a weld line 14a, and a portion where the first plate section 11 and the second plate section 12b are butt-welded is referred to as a weld line 14b. The second plate sections 12a, 12b correspond to the second steel plates 22a, 22b in the tailored blank 2 before being press-formed.

[0035] The second plate sections 12a, 12b have butted areas 121a, 121b, walls 122a, 122b, and plate ends 123a, 123b, respectively. The butted areas 121a, 121b, the walls 122a, 122b, and the plate ends 123a, 123b are obtained by press forming the second steel plates 22a, 22b.

[0036] The butted areas 121a, 121b expand in a plate shape in the first direction and the second direction. The butted areas 121a, 121b each have a portion joined to the first plate section 11 by butt welding.

[0037] The walls 122a, 122b respectively protrude from ends of the butted areas 121a, 121b opposite to the portions joined to the first plate section 11 in the second direction towards a plate thickness direction of the second plate sections 12a, 12b, and extend in the first direction. The walls 122a, 122b are respectively provided near the weld lines 14a, 14b.

[0038] The plate ends 123a, 123b respectively expand in a direction away from the first plate section 11 in the second direction from ends of the walls 122a, 122b opposite to the ends coupled to the butted areas 121a, 121b.

[0039] In a surface of the first plate section 11, one or more recesses 15 recessed in the plate thickness direction of the first plate section 11 are formed. The recesses 15 have a smaller depth than a length of the walls 122a, 122b protruding from the butted areas 121a, 121b and smaller than the plate thickness of the first plate section 11. The recesses 15 may be at least partially formed in surfaces of the second plate sections 12a, 12b across the boundaries 13a, 13b. There is no specific limitation in shape of the recesses 15 in a cross section perpendicular to the plate thickness direction. For example, the recesses 15 may have an approximately circular shape or an approximately rectangular shape. The recesses 15 do not have to be formed in the first plate section 11 and the second plate sections 12a, 12b.

[1-1-2. Configuration of Tailored Blank]

[0040] The press-formed product 1 is formed when press forming machines 5a, 5b (see FIGS. 3A, 3B, 4A, and 4B) press form the tailored blank 2.

[0041] The tailored blank 2 is a blank material in which the first steel plate 21 and the second steel plates 22a, 22b with different plate thicknesses are joined together by butt welding.

[0042] The first steel plate 21 is an approximately rectangular plate-shaped member. As an example, the first steel plate 21 has a plate thickness of 0.6 mm, and a tensile strength of 270 MPa. The first steel plate 21 has a first end face and a second end face extending in the first direction, on opposite sides of the first steel plate 21 in the second direction. The opposite sides of the first steel plate 21 in the second direction refer to first and second sides of the first steel plate 21 in the second direction.

[0043] The second steel plates 22a, 22b are plate-shaped members. The second steel plates 22a, 22b are made of high tensile materials. The second steel plates 22a, 22b have a plate thickness larger than the first steel plate 21. For example, the second steel plates 22a, 22b have more than twice the plate thickness of the first steel plate 21. As an example, the second steel plates 22a, 22b have a plate thickness of 1.8 mm, and a tensile strength of 780 MPa. The second steel plates 22a, 22b are joined to respective end faces of the first steel plate 21 by butt welding. The second steel plates 22a, 22b have shapes symmetrical about the first steel plate 21. The second steel plate 22a has an end face extending in the first direction. The end face is joined to the first end face of the first steel plate 21 by butt welding. The second steel plate 22b has an end face extending in the first direction. The end face is joined to the second end face of the first steel plate 21 by butt welding. That is, the butt welding is provided at the boundary 13a between the first steel plate 21 and the second steel plates 22a and the boundary 13b between the first steel plate 21 and the second steel plates 22b. In the tailored blank 2, a butt-welded portion of the first steel plate 21 and the second steel plate 22a corresponds to the weld line 14a in the press-formed product 1, and a butt-welded portion of the first steel plate 21 and the second steel plate 22b corresponds to the weld line 14b of the press-formed product 1.

[1-1-3. Configuration of Press Forming Machine]

[0044] A method for manufacturing the press-formed product 1 comprises: forming the recesses 15 in the tailored blank 2 by the press forming machine 5a; and forming the walls 122a, 122b on the tailored blank 2 by the press forming machine 5b.

[0045] As shown in FIGS. 3A and 3B, the press forming machine 5a comprises a first punch 51a, a first die 52a, and holders 53. The press forming machine 5a is positioned to hold the tailored blank 2 from both sides in a plate thickness direction of the tailored blank 2. Hereinafter, the plate thickness direction of the tailored blank 2 is referred to as an up-down direction. The plate thickness direction is not limited to the up-down direction, and may be read as a right-left direction or a front-rear direction. The terms up and down in the up-down direction may be read interchangeably. In the present embodiment, the up-down direction in FIG. 1 is referred to as a vehicle up-down direction since it is the up-down direction when the press-formed product 1 is mounted on a vehicle. The up-down direction in FIGS. 3, 4, 6, 7, and 8 is referred to as a press up-down direction since it is the up-down direction in the press forming. The press up-down direction is opposite to the vehicle up-down direction. That is, the press forming is performed with the tailored blank 2 forming the press-formed product 1 upside down, as opposed to a state in which the press-formed product 1 is mounted on the vehicle.

[0046] The first punch 51a is a punch of a metallic die in the press forming. The first punch 51a is located below the tailored blank 2. An upper surface of the first punch 51a faces the boundaries 13a, 13b of the tailored blank 2, the entire first steel plate 21, and part of the respective second steel plates 22a, 22b.

[0047] The first punch 51a has first punch-side recess forming members 511 for forming the recesses 15 in the tailored blank 2. The first punch-side recess forming members 511 are provided on a surface of the first punch 51a facing the tailored blank 2. The first punch-side recess forming members 511 protrude upward. The first punch-side recess forming members 511 are provided in the same number as the recesses 15 formed in the tailored blank 2.

[0048] The first die 52a is a die of the metallic die in the press forming. The first die 52a is located above the tailored blank 2 so as to cover the entire tailored blank 2.

[0049] The first die 52a has first die-side recess forming members 521 for forming the recesses 15 in the tailored blank 2. The first die-side recess forming members 521 are provided on a surface of the first die 52a facing the tailored blank 2. The first die-side recess forming members 521 are recessed upward so as to fit in the first punch-side recess forming members 511. The first die-side recess forming members 521 are provided in the same number as the recesses 15 formed in the tailored blank 2.

[0050] The holders 53 support the tailored blank 2. The holders 53 are positioned below the tailored blank 2. The holders 53 are located on opposite sides of the first punch 51a in the second direction. Upper surfaces of the holders 53 partially face the second steel plates 22a, 22b.

[0051] The holders 53 are configured so that the holders 53 can move downward together with the first die 52a by being pressed downward by the first die 52a located above the holders 53.

[0052] As shown in FIGS. 4A and 4B, the press forming machine 5b comprises a second punch 51b, a second die 52b, and pads 54. The press forming machine 5b is positioned to sandwich the tailored blank 2 from both sides of the tailored blank 2 in the up-down direction. The tailored blank 2 arranged on the press forming machine 5b is the tailored blank 2 after being press-formed by the press forming machine 5a.

[0053] The second punch 51b is a punch of the metallic die in the press forming. The second punch 51b is positioned below the tailored blank 2. An upper surface of the second punch 51b faces the entire tailored blank 2.

[0054] The second punch 51b has second punch-side wall forming members 512a, 512b for forming the walls 122a, 122b on the tailored blank 2. The second punch-side wall forming members 512a, 512b are provided on a surface of the second punch 51b facing the tailored blank 2, and each have a step in the up-down direction.

[0055] The second die 52b is a die of the metallic die in the press forming. The second die 52b is positioned above the tailored blank 2 so as to cover the entire tailored blank 2.

[0056] The second die 52b has second die-side wall forming members 522a, 522b for forming the walls 122a, 122b on the tailored blank 2. The second die-side wall forming members 522a, 522b are provided on a surface of the second die 52b facing the tailored blank 2. The second die-side wall forming members 522a, 522b each have a step in the up-down direction so as to fit in the second punch-side wall forming members 512a, 512b.

[0057] The pads 54 are used to hold the tailored blank 2 in the press forming. The pads 54 are arranged through the second die 52b. The pads 54 are located above the tailored blank 2. Lower surfaces of the pads 54 face the boundaries 13a, 13b, part of the first steel plate 21, and part of the respective second steel plates 22a, 22b in the tailored blank 2. A not shown gas cushion is arranged above the pads 54. The pads 54 are configured to be able to apply a pressure received from the gas cushion to hold the tailored blank 2.

1-2. Manufacturing Method of Press-Formed Product

[0058] A method for manufacturing the press-formed product 1 comprises an arrangement process S10, a recess forming process S20, a holding process S30, and a wall forming process S40, as shown in FIG. 5. In the method, the arrangement process S10, the recess forming process S20, the holding process S30, and the wall forming process S40 are performed in this order.

[1-2-1. Formation of Recesses]

[0059] The method for manufacturing the press-formed product 1 will be described with reference to FIGS. 3A, 3B, 4A, and 4B.

[0060] The arrangement process S10 and the recess forming process S20 are processes of forming the recesses 15 in the tailored blank 2 by the press forming machine 5a shown in FIGS. 3A and 3B.

[0061] As shown in FIG. 3A, in the arrangement process S10, the tailored blank 2 is arranged on the upper surfaces of the holders 53. The second steel plates 22a, 22b in the tailored blank 2 are supported by the holders 53 by partially contacting the upper surfaces of the holders 53. The first steel plate 21 in the tailored blank 2 is spaced apart from both the first punch 51a and the holders 53. The first steel plate 21 may have a portion that contacts the upper surface of the first punch 51a. The tailored blank 2 is spaced apart from the first die 52a located above the tailored blank 2.

[0062] In the recess forming process S20, the first die 52a moves downward, and contacts an upper surface of the tailored blank 2. Thereafter, the first die 52a, the tailored blank 2, and the holders 53 move downward in an integrated fashion.

[0063] After moving downward until contacting the first punch 51a, the tailored blank 2 is deformed along the first punch-side recess forming members 511 of the first punch 51a and the first die-side recess forming members 521 of the first die 52a due to a pressure received from the first die 52a further moving downward. This press forming forms the recesses 15 in the tailored blank 2 to obtain the first plate section 11 with the recesses 15 (see FIG. 3B).

[1-2-2. Formation of Walls]

[0064] The holding process S30 and the wall forming process S40 are processes of forming the walls 122a, 122b on the tailored blank 2 by the press forming machine 5b shown in FIGS. 4A and 4B.

[0065] As shown in FIG. 4A, in the holding process S30, the tailored blank 2 is held by the second punch 51b located below the tailored blank 2 and the pads 54 located above the tailored blank 2. The tailored blank 2 is spaced apart from the second die 52b located above the tailored blank 2.

[0066] The pads 54 hold first regions 26a, 26b in the tailored blank 2 along the boundaries 13a, 13b. The first regions 26a, 26b are respectively adjacent to the boundaries 13a, 13b including the weld lines 14a, 14b in the tailored blank 2.

[0067] The pads 54 do not hold second regions 27 in the first steel plate 21 and the second steel plates 22a, 22b of the tailored blank 2. The second regions 27 are farther from the boundaries 13a, 13b than the first regions 26a, 26b with respect to the tailored blank 2. The second regions 27 are adjacent to the first regions 26a, 26b. Each of the first regions 26a, 26b is smaller than each of the second regions 27.

[0068] In the present embodiment, the pads 54 hold vicinities of the boundaries 13a, 13b in the tailored blank 2 as the first regions 26a, 26b. In the present embodiment, the pads 54 do not hold regions other than the vicinities of the boundaries 13a, 13b in the tailored blank 2 as the second regions 27.

[0069] In the wall forming process S40, in a state in which the tailored blank 2 is held by the second punch 51b and the pads 54, the second die 52b moves downward, and contacts upper surfaces of the second steel plates 22a, 22b of the tailored blank 2. Thereafter, due to a pressure received from the second die 52b further moving downward, the tailored blank 2 is deformed along the second punch-side wall forming members 512a, 512b of the second punch 51b and the second die-side wall forming members 522a, 522b of the second die 52b. This press forming forms the walls 122a, 122b on the tailored blank 2 to obtain the second plate sections 12a, 12b with the butted areas 121a, 121b, the walls 122a, 122b, and the plate ends 123a, 123b (see FIG. 4B).

[0070] In the wall forming process S40, the second punch 51b, the pads 54, and the first steel plate 21 of the tailored blank 2 do not move.

1-3. Operation and Effect

[0071] According to the embodiment detailed above, the following operations and effects can be obtained.

[0072] (1a) In the wall forming process S40, when the tailored blank 2 is deformed along the second punch-side wall forming members 512a, 512b and the second die-side wall forming members 522a, 522b due to the pressure received from the second die 52b, a force is applied to the weld lines 14a, 14b in a direction to separate the first steel plate 21 and the second steel plates 22a, 22b in the second direction. In this case, stress may concentrate on one of the first steel plate 21 and the second steel plates 22a, 22b, resulting in cracking and deformation. Particularly, the stress is likely to concentrate on the first steel plate 21 that is a material having a smaller plate thickness or a lower tensile strength, and cause cracking and deformation.

[0073] In contrast, in the above-described embodiment, the pads 54 hold the first regions 26a, 26b in the tailored blank 2 along the boundaries 13a, 13b. The first regions 26a, 26b are adjacent to the boundaries 13a, 13b including the weld lines 14a, 14b in the tailored blank 2.

[0074] Further, the pads 54 do not hold the second regions 27 in the first steel plate 21 and the second steel plates 22a, 22b of the tailored blank 2. The second regions 27 are farther from the boundaries 13a, 13b than the first regions 26a, 26b with respect to the tailored blank 2. The second regions 27 are adjacent to the first regions 26a, 26b.

[0075] With the process as above, the areas where the pads 54 hold the tailored blank 2 are smaller than in a case where the pads 54 hold both the first regions 26a, 26b and the second regions 27, especially in a case where the pads 54 hold the whole region of the tailored blank 2 unnecessary for the press forming. Thus, by the pads 54 holding the tailored blank 2, a pressure applied from the pads 54 to the tailored blank 2 (hereinafter, referred to as holding pressure) increases. If the holding pressure is large, movements of the first steel plate 21 and the second steel plates 22a, 22b in the tailored blank 2 are inhibited during the press forming like the wall forming process S40, and the rate of decrease in plate thickness of the tailored blank 2 due to the press forming is reduced. Particularly, in the first regions 26a, 26b including the vicinities of the weld lines 14a, 14b, it is possible to inhibit deformation and cracking of the first steel plate 21 and the second steel plates 22a, 22b. Thus, it is possible to inhibit unnecessary deformation of the tailored blank 2.

[0076] (1b) In the holding process S30 and the wall forming process S40, the pads 54 hold both the first steel plate 21 and the second steel plates 22a, 22b.

[0077] With the configuration as above, it is possible to inhibit the stress from concentrating on either one of the first steel plate 21 and the second steel plates 22a, 22b during the press forming. Thus, compared to a case where the pads 54 hold either the first steel plate 21 or the second steel plates 22a, 22b, it is possible to inhibit deformation or cracking of the tailored blank 2.

[0078] (1c) Each of the first regions 26a, 26b where the pads 54 hold the tailored blank 2 is smaller than each of the second regions 27 where the pads 54 do not hold the tailored blank 2.

[0079] With the configuration as above, it is possible to further reduce the area where the pads 54 hold the tailored blank 2, and further increase the holding pressure of the pads 54. Thus, it is possible to further inhibit unnecessary deformation of the tailored blank 2.

[0080] (1d) In the above-described method for manufacturing the press-formed product 1, after the recesses 15 are formed in the tailored blank 2 in the arrangement process S10 and the recess forming process S20, the walls 122a, 122b are formed on the tailored blank 2 in the holding process S30 and the wall forming process S40.

[0081] According to the processes as above, the recesses 15 are formed in the tailored blank 2 in the holding process S30 and the wall forming process S40. Thus, in the holding process S30 and the wall forming process S40, the pads 54 have to only hold the first regions 26a, 26b of the tailored blank 2 that are prone to deformation and cracking, and do not need to hold any regions other than the first regions 26a, 26b. Accordingly, it is possible to further reduce the area where the pads 54 hold the tailored blank 2, and increase the holding pressure of the pads 54. Accordingly, it is possible to further inhibit unnecessary deformation of the tailored blank 2.

1-4. Correspondence Between Terms

[0082] In the above-described embodiment, the tailored blank 2 corresponds to one example of a workpiece, the pads 54 and the second punch 51b correspond to one example of a holding structure, and the second punch 51b and the pads 54 correspond to a metallic die for press forming the workpiece.

2. Other Embodiments

[0083] An embodiment of the present disclosure has been described in the above. However, the present disclosure is not limited to the above-described embodiment, and may take various forms.

[0084] (2a) In the above-described embodiment, the pads 54 hold the vicinities of the boundaries 13a, 13b in the tailored blank 2, as the first regions 26a, 26b.

[0085] However, the first regions 26a, 26b where the pads 54 hold the tailored blank 2 are not limited to the vicinities of the boundaries 13a, 13b. That is, the first regions 26a, 26b may be extended beyond the vicinities of the boundaries 13a, 13b.

[0086] (2b) In the above-described embodiment, the pads 54 do not hold regions in the tailored blank 2 other than the vicinities of the boundaries 13a, 13b, as the second regions 27.

[0087] However, the regions where the pads 54 do not hold the tailored blank 2 are not limited to the above-described example.

[0088] The pads 54 may be arranged so as not to hold a part of the region of the tailored blank 2 on an opposite side of a side where deformation due to the press forming occurs with respect to the boundaries 13a, 13b, as the second regions 27. For example, in the wall forming process S40, the pads 54 may be arranged so as not to hold part of the region between the boundary 13a and the boundary 13b as a region on the opposite side of the side where the walls 122a, 122b are formed by the press forming with respect to the boundaries 13a, 13b.

[0089] (2c) In the above-described embodiment, the first regions 26a, 26b where the pads 54 hold the tailored blank 2 are smaller than the second regions 27 where the pads 54 do not hold the tailored blank 2. However, each of the first regions 26a, 26b where the pads 54 hold the tailored blank 2 may be greater than or equal to each of the second regions 27 in area. The pads 54 at least hold the vicinities of the weld lines 14a, 14b in both the first steel plate 21 and the second steel plates 22a, 22b, and should have portions where the pads 54 do not hold the tailored blank 2 other than the vicinities of the weld lines 14a, 14b.

[0090] (2d) As in the above-described embodiment, if the first steel plate 21 and the second steel plates 22a, 22b of the tailored blank 2 have different plate thicknesses, at least one of the pads 54 and the second punch 51b may have steps or a step in accordance with a difference in plate thickness. Specifically, at least one of the pads 54 and the second punch 51b may have steps or a step in the plate thickness direction of the first steel plate 21 and the second steel plates 22a, 22b in accordance with the difference in plate thickness between the first steel plate 21 and the second steel plates 22a, 22b so that the respective surfaces of the first steel plate 21 and the second steel plates 22a, 22b can be held.

[0091] For example, as shown in FIG. 6, if there is a step on a lower surface of the tailored blank 2 at the boundary 13b, a second punch 251b may have a punch-side step 261 corresponding to the difference in plate thickness between the first steel plate 21 and the second steel plate 22b at the boundary 13b.

[0092] Alternatively, as shown in FIG. 7, if there is a step on an upper surface of the tailored blank 2 at the boundary 13b, a pad 354 may have a pad-side step 362 corresponding to the difference in plate thickness between the first steel plate 21 and the second steel plate 22b at the boundary 13b.

[0093] Alternatively, as shown in FIG. 8, if there is a step on both the upper and lower surfaces of the tailored blank 2 at the boundary 13b, the second punch 251b and the pad 354 may respectively have the punch-side step 261 and the pad-side step 362 corresponding to the differences in plate thickness between the first steel plate 21 and the second steel plate 22b at the boundary 13b.

[0094] With the configuration as above, even if the two steel plates of the tailored blank 2 have a large difference in plate thickness, the second punch 251b and the pads 354 can hold the both surfaces of the first steel plate 21 and the second steel plates 22a, 22b. Accordingly, it is possible to inhibit cracking and deformation of the tailored blank 2.

[0095] (2e) In the above-described embodiment, the first steel plate 21 and the second steel plates 22a, 22b are different in plate thickness and tensile strength. However, at least one of the plate thickness and the tensile strength of the first steel plate 21 and the second steel plates 22a, 22b may be the same.

[0096] As an example, the first steel plate 21 and the second steel plates 22a, 22b may have the same plate thickness and the same tensile strength, and the tensile strength of both the first steel plate 21 and second steel plates 22a, 22b may be 780 MPa or more. In this case, the vicinities of the weld lines 14a, 14b are prone to softening due to heat caused by the welding, and stress is likely to concentrate in the vicinities of the weld lines 14a, 14b. Thus, by holding the vicinities of the weld lines 14a, 14b with the pads 54, it is possible to inhibit cracking and deformation of the tailored blank 2.

[0097] As an example, the first steel plate 21 and the second steel plates 22a, 22b may have the same plate thickness and the same tensile strength, and both the first steel plate 21 and second steel plates 22a, 22b may be stainless steel. In this case, in the wall forming process S40, the weld lines 14a, 14b of the tailored blank 2 are prone to breakage. Thus, by holding the vicinities of the weld lines 14a, 14b with the pads 54, it is possible to inhibit cracking and deformation of the tailored blank 2.

[0098] (2f) In the above-described embodiment, the pads 54 hold the boundaries 13a, 13b including the weld lines 14a, 14b in the tailored blank 2 along the boundaries 13a, 13b in the holding process S30. However, the pads 54 do not have to hold the whole of the boundaries 13a, 13b and the weld lines 14a, 14b, and may partially hold the boundaries 13a, 13b and the weld lines 14a, 14b. The pads 54 do not have to directly hold the weld lines 14a, 14b as long as the pads 54 hold the vicinities of the weld lines 14a, 14b in the tailored blank 2. For example, the pads 54 may partially hold portions such as ends of the weld lines 14a, 14b where cracking is likely to occur, and not the whole weld lines 14a, 14b.

[0099] As an example, as shown in FIG. 9, the first region 26a held by the pad 54 may be a part of the boundary 13a including a part of the weld line 14a in the first steel plate 21 and the second steel plate 22a. In FIG. 9, a shaded region indicates the first region 26a held by the pad 54. Solid lines indicate ridge lines of the first steel plate 21 and the second steel plate 22a and the boundary 13a. A bold line indicates the weld line 14a. A dot-dash line indicates a ridge line of the press-formed product 1 after virtual press forming. A dashed line indicates a portion where the wall 122a is formed during the press forming.

[0100] With the configuration as above, it is possible to further reduce the area where the pads 54 hold the tailored blank 2, and the holding pressure of the pads 54 can be further increased. Therefore, unnecessary deformation of the tailored blank 2 can be further inhibited.

[0101] (2g) In the above-described embodiment, in the method for manufacturing the press-formed product 1, the arrangement process S10, the recess forming process S20, the holding process S30, and the wall forming process S40 are performed in this order. However, the arrangement process S10 and the recess forming process S20 do not have to be performed before the holding process S30 and the wall forming process S40. Particularly, if the press-formed product 1 does not have recesses 15, the arrangement process S10 and the recess forming process S20 do not have to be performed.

[0102] (2h) Two or more functions achieved by one element of the above-described embodiments may be achieved by two or more elements. One function achieved by one element may be achieved by two or more elements. Two or more functions achieved by two or more elements may be achieved by one element. One function achieved by two or more elements may be achieved by one element. Part of the configurations in the above-described embodiments may be omitted. At least part of the configurations in one of the above-described embodiments may be added to or replaced with the configuration in another one of the above-described embodiments.

Technical Idea Disclosed in Present Specification

[Item 1]

[0103] A press forming machine comprising: [0104] a holding structure configured to hold a workpiece; and [0105] a metallic die for press forming the workpiece, [0106] the workpiece being a member in which a first steel plate and a second steel plate are joined together by butt welding, [0107] the butt welding being a welding of an end face of the first steel plate and an end face of the second steel plate at a boundary between the first steel plate and the second steel plate, [0108] the holding structure being configured to hold a first region including both the first steel plate and the second steel plate adjacent to the boundary as a specific region in the workpiece, and not to hold a second region that is farther from the boundary than the first region and includes at least one of the first steel plate and the second steel plate adjacent to the first region.

[Item 2]

[0109] The press forming machine according to Item 1, wherein the holding structure holds the workpiece along the boundary.

[Item 3]

[0110] The press forming machine according to Item 1 or 2, wherein the holding structure is configured to hold an end of a weld line, which is a butt-welded portion of the workpiece.

[Item 4]

[0111] The press forming machine according to any one of Items 1 to 3, wherein the first steel plate and the second steel plate differ from each other in at least one of plate thickness and strength.

[Item 5]

[0112] The press forming machine according to Item 4, wherein [0113] the first steel plate and the second steel plate have different plate thicknesses, [0114] the holding structure has a step corresponding to a difference in plate thickness between the first steel plate and the second steel plate so as to be able to hold surfaces of both the first steel plate and the second steel plate, and [0115] the step is provided along a plate thickness direction of the first steel plate and the second steel plate.

[Item 6]

[0116] The press forming machine according to any one of Items 1 to 5, wherein [0117] the first region is smaller than the second region.

[Item 7]

[0118] A method for manufacturing a press-formed product, the method comprising: [0119] holding a workpiece, the workpiece being a member in which a first steel plate and a second steel plate are joined together by butt welding; and [0120] press forming at least one of the first steel plate and the second steel plate in its plate thickness direction, [0121] the butt welding being a welding of an end face of the first steel plate and an end face of the second steel plate at a boundary between the first steel plate and the second steel plate, [0122] the holding the workpiece including holding a first region including both the first steel plate and the second steel plate adjacent to the boundary as a specific region in the workpiece, and not holding a second region that is farther from the boundary than the first region and includes at least one of the first steel plate and the second steel plate adjacent to the first region.

EXPLANATION OF REFERENCE NUMERALS

[0123] 1 . . . press-formed product, 2 . . . tailored blank, 5a, 5b . . . press forming machine, 13a, 13b . . . boundary, 21 . . . first steel plate, 22a, 22b . . . second steel plate, 26a, 26b . . . first region, 27 . . . second region, 51b, 251b . . . second punch, 54, 354 . . . pad, S30 . . . holding process, S40 . . . wall forming process.