METHOD FOR MANUFACTURING MOLDED PRODUCT

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2024-109877 filed on Jul. 8, 2024 with the Japan Patent Office, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to a method for manufacturing a molded product.

BACKGROUND

Japanese Unexamined Patent Application Publication No. 2006-142341 discloses a method of press molding a tailored blank. According to this press molding method, a press molded product including a top plate, a vertical wall, and a flange and having a depth is formed. More specifically, a deep-draw molding is performed by a punch and a counter punch descending while holding a portion of the tailored blank where the top plate is to be formed. The tailored blank includes a welded portion, where different steel plates are welded to the tailored blank. The welded portion is situated at a position held by the punch and the counter punch, that is, in the top plate. The press molding advances with the punch and the counter punch holding the top plate so as to reduce in-plane displacement of materials in the top plate. This inhibits the welded portion from moving away from a desired position.

SUMMARY

However, if the deep-draw molding is performed while the displacement of the welded portion is excessively inhibited in a case where the welded portion of the tailored blank is situated in the flange, a problem has been found that the tailored blank breaks. In other words, in a case where the in-plane displacement of the material in the flange is excessively inhibited, it is difficult for the material to flow from the flange towards the top plate when the top plate is formed by the deep-draw molding. Accordingly, there has been a possibility of a breakage of the tailored blank, the displacement of the material of which is excessively inhibited.

One aspect of the present disclosure provides a technique to inhibit a breakage of a tailored blank when forming a press molded product having a welded portion in a flange.

One mode of the present disclosure is a method for manufacturing a molded product in which a tailored blank is pressed to obtain the molded product. The tailored blank is a steel plate formed by joining a first steel plate and a second steel plate together by welding. The second steel plate has a plate thickness and/or a strength different from those of the first steel plate. The tailored blank includes at least one welded portion that is formed by welding an end surface of the first steel plate and an end surface of the second steel plate to each other. The molded product includes a top plate, a vertical wall, and a flange. The vertical wall is a plate-like portion that stands from an end of the top plate so as to surround the top plate. The flange is a plate-like portion that extends from the vertical wall in a direction intersecting the vertical wall and is situated to surround the top plate in a plan view perpendicular to the top plate. The tailored blank includes a top plate corresponding portion, a vertical wall corresponding portion, and a flange corresponding portion. The top plate corresponding portion is a portion corresponding to the top plate. The vertical wall corresponding portion is a portion corresponding to the vertical wall. The flange corresponding portion is a portion corresponding to the flange. The top plate corresponding portion is situated in the first steel plate. The at least one welded portion is situated in the flange corresponding portion.

The method includes situating the tailored blank between a first metallic mold and a second metallic mold arranged apart from each other; achieving a held state in which the flange corresponding portion is held between the first metallic mold and a holder; and forming the top plate, the vertical wall, and the flange by pressing the tailored blank with the first metallic mold and the second metallic mold by bringing the first metallic mold and the second metallic mold close to each other while maintaining the held state. The holder is a member that is situated between the first metallic mold and the second metallic mold and that holds the flange corresponding portion in coordination with the first metallic mold. In the held state, the first metallic mold and the holder hold the flange corresponding portion such that the at least one welded portion is movable towards the top plate corresponding portion.

Such a configuration enables the at least one welded portion to move towards the top plate corresponding portion in the held state, which makes it easier for the material to flow from the flange corresponding portion to the top plate corresponding portion. Accordingly, the plate thickness of the first steel plate is less likely to decrease, and the at least one welded portion can be displaced smoothly. As a consequence, it is possible to inhibit the tailored blank from breaking when forming the press molded product having the at least one welded portion in the flange.

In one aspect of the present disclosure, a pressure applied to the tailored blank by the holder in the held state may be set to satisfy the following mathematical formula (Formula 1).

X [ ton ] < Ts [ MPa ] × 0.005 × A [ mm 2 ] 9.8 [ Formula ⁢ 1 ]

X is a pressure applied to the tailored blank by the holder. Ts is a tensile strength of the first steel plate. A is a contact area of the holder and the tailored blank before the tailored blank is pressed by the first metallic mold and the second metallic mold.

Such a configuration enables the held state to be maintained in a state where the displacement of the at least one welded portion towards the top plate corresponding portion is not easily inhibited. Accordingly, it becomes easier for the material to flow from the flange corresponding portion towards the top plate corresponding portion.

In one aspect of the present disclosure, the plate thickness of the first steel plate may be less than the plate thickness of the second steel plate. An adjusting member for adjusting the distance between the tailored blank and the first metallic mold in the held state may be disposed between the first metallic mold and the second metallic mold. The distance between the tailored blank and the first metallic mold in the held state may be adjusted to greater than or equal to 5% and less than 20% of the plate thickness of the first steel plate by the adjusting member.

According to such a configuration, the tailored blank does not excessively adhere to the first metallic mold and the holder in the held state due to a gap created between the tailored blank and the first metallic mold. Thus, the held state can be maintained while keeping it difficult to inhibit the at least one welded portion from being displaced towards the top plate corresponding portion. Accordingly, it is easier for the material to flow from the flange corresponding portion towards the top plate corresponding portion.

In one aspect of the present disclosure, in the forming, an amount of displacement of the at least one welded portion towards the top plate corresponding portion may be designed in advance. A portion of the first metallic mold and/or the holder that can contact the at least one welded portion in the held state may have a hardness greater than a hardness of the at least one welded portion.

Such a configuration can inhibit the first metallic mold and/or the holder from being shaved or chipped even when the at least one welded portion is displaced in a displacement area while contacting the first metallic mold and/or the holder. This can reduce deformation of the first metallic mold and/or the holder, and therefore, the held state can be stably maintained.

In one aspect of the present disclosure, in a plan view perpendicular to a plate thickness direction of the tailored blank, the top plate corresponding portion may include an end portion of the tailored blank on a first side. The top plate corresponding portion may be situated in a part of the first side. The at least one welded portion may extend from an end portion of the tailored blank on a second side, which is situated opposite from the first side, towards the first side so as to avoid the top plate corresponding portion.

According to such a configuration, the distance from the top plate corresponding portion to the at least one welded portion is different between the first side, where the amount of deformation of the tailored blank is relatively large, and the second side, where the amount of deformation of the tailored blank is relatively small. In other words, the at least one welded portion is situated in the tailored blank in view of the amount of displacement of the at least one welded portion during the press working. Accordingly, when the press molded product is formed, the at least one welded portion can be situated at a desired position. Specifically, it is possible to obtain a press molded product in which the at least one welded portion extends roughly parallel to a ridgeline between the vertical wall and the flange.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 is a schematic partial perspective view of a press molded product;

FIG. 2A is a schematic plan view of the press molded product;

FIG. 2B is a schematic plan view of a tailored blank;

FIG. 3A is a cross-sectional view taken along a line IIIA-IIIA of FIG. 2A;

FIG. 3B is a cross-sectional view taken along a line IIIB-IIIB of FIG. 2A;

FIG. 4A is a schematic cross-sectional view of a weld bead that rises upward and downward;

FIG. 4B is a schematic cross-sectional view of a weld bead that rises downward;

FIG. 5 is a schematic partial cross-sectional view of a press molding device;

FIG. 6A is a cross-sectional view taken along a line VIA-VIA of FIG. 6B;

FIG. 6B is a plan view of the press molding device in a holding step;

FIG. 6C is a cross-sectional view taken along a line VIC-VIC of FIG. 6D;

FIG. 6D is a plan view of the press molding device during pressing;

FIG. 6E is a cross-sectional view taken along a line VIE-VIE of FIG. 6F;

FIG. 6F is a plan view of the press molding device when the pressing is completed;

FIG. 7 is a flowchart for explaining a method for manufacturing the press molded product;

FIG. 8 is a schematic diagram for explaining a displacement area; and

FIG. 9 is a schematic cross-sectional view of a press molding device in a second embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

1. First Embodiment

1-1. Press Molded Product

A press molded product 1 shown in FIG. 1 and FIG. 2A is formed by press molding a tailored blank 10 shown in FIG. 2B. Hereinafter, in explanations of the press molded product 1 and the tailored blank 10, plate thickness directions of the press molded product 1 and the tailored blank 10 are referred to as upward-downward directions. Directions in which a second steel plate 12, which will be mentioned below, is situated with respect to a first steel plate 11, which will also be mentioned below, are referred to as right-left directions. Longitudinal directions of the second steel plate 12 are referred to as front-rear directions. A direction from the second steel plate 12 towards the first steel plate 11 may be referred to as an inner direction (a direction towards inner side). A direction from the first steel plate 11 towards the second steel plate 12 may be referred to as an outer direction (a direction towards outer side). These directions are defined for convenience of explanation and do not limit modes of use of the press molded product 1.

The press molded product 1 is used as a rear floor pan mounted to a vehicle, as an example. FIG. 1 is a diagram showing the right half of the press molded product 1. The left half of the press molded product 1, which is not shown in the drawing, is designed to be right-left symmetric with the right half of the press molded product 1. The press molded product 1 may be a component of a vehicle other than the rear floor pan, such as a rocker outer panel and other floor pans. The press molded product 1 may be a component for something other than a vehicle.

The press molded product 1 includes a top plate 2, a vertical wall 3, and a flange 4. The top plate 2 is a plate-like portion spreading on a single plane. Specifically, the top plate 2 has a roughly rectangular shape in a plan view. The top plate 2 may include any unevenness. For example, the top plate 2 may include a recess which forms an upward projection when looking at the top plate 2 from below or may include a recess which forms a downward projection when looking at the top plate 2 from above.

The vertical wall 3 is a plate-like portion standing from an end of the top plate 2 so as to surround the top plate 2. Specifically, the vertical wall 3 is a wall that extends downward from a front edge, a left edge, and a right edge of the top plate 2. In other words, the vertical wall 3 is a wall surrounding the top plate 2 in three directions. That is, the top plate 2 and the vertical wall 3 of the press molded product 1 have a bag-like outer shape. The bag-like shape is a shape that allows an object to be housed in its inner space and that has an opening for the object to be housed and removed. In the press molded product 1, an object can be housed in the inner space surrounded by the top plate 2 and the vertical wall 3. In addition, an object can be housed and removed from an opening formed on a side opposite from the top plate 2 across the vertical wall 3. In the present embodiment, the vertical wall 3 extends from the bottom towards the top so as to slightly slant towards the top plate 2. In other words, as shown in FIG. 3A, a cross-section of the top plate 2 and the vertical wall 3 perpendicular to the front-rear directions is trapezoidal. In addition, a cross-section of the vertical wall 3 perpendicular to the upward-downward directions is roughly U-shaped.

The flange 4 is a plate-like portion extending from the vertical wall 3 in a direction intersecting the vertical wall 3 and is a portion situated so as to surround the top plate 2 in a plan view perpendicular to the top plate 2. Specifically, the flange 4 is a plate extending roughly parallel to the top plate 2 from an edge of the vertical wall 3 opposite from an edge contacting the top plate 2 in a direction away from the top plate 2. In other words, the flange 4 is a plate surrounding the top plate 2 from three directions in a plan view.

For example, the size of the press molded product 1 is as follows: the width in the right-left directions is about 1500 mm; the length in the front-rear directions is about 700 mm; and the depth in the upward-downward directions is about 180 mm. For example, the size of the bag-like portion of the press molded product 1 is as follows: the width in the right-left directions is about 600 mm; the length in the front-rear directions is about 200 mm; and the depth in the upward-downward directions is about 180 mm.

As shown in FIG. 2A, the press molded product 1 includes a first steel plate 11, a second steel plate 12, a third steel plate 13, a first welded portion 14, and a second welded portion 15. Each of these will be explained below in detail.

1-2. Tailored Blank

The tailored blank 10 shown in FIG. 2B is a steel plate formed by joining the first steel plate 11, two second steel plates 12, and two third steel plates 13 to each other by welding. In other words, the tailored blank 10 is a blank prepared by integrating the first steel plate 11, the two second steel plates 12, and the two third steel plates 13 into one plate by joining them by welding. The two second steel plates 12 are separately situated on the right side and the left side of the first steel plate 11 so as to interpose the first steel plate 11 between the two second steel plates 12. The two third steel plates 13 are situated to interpose the first steel plate 11 and the second steel plates 12. The tailored blank 10 is right-left symmetric.

The first steel plate 11 is a roughly trapezoidal plate-like member. Specifically, the first steel plate 11 is a steel plate formed such that its rear end portion is longer than its front end portion and such that its width in the right-left directions decreases from the rear side towards the front side. As one example, the plate thickness of the first steel plate 11 is 0.6 mm, and the tensile strength of the first steel plate 11 is 270 MPa.

The second steel plate 12 is a plate-like member having a length. Specifically, the second steel plate 12 has a roughly rectangular outline with a longer side disposed in the front-rear directions. The second steel plate 12 has a plate thickness and/or a strength different from those of the first steel plate 11. In the present embodiment, the second steel plate 12 has a plate thickness that is greater than the plate thickness of the first steel plate 11, and a tensile strength that is greater than the tensile strength of the first steel plate 11. The second steel plate 12 is a high tensile steel material. As an example, the plate thickness of the second steel plate 12 is 1.0 mm, and the tensile strength of the second steel plate 12 is 780 MPa. The ratio of strength between the first steel plate 11 and the second steel plate 12 is 4.8. This ratio of strength is calculated by dividing the value obtained by multiplying the tensile strength and the plate thickness of the second steel plate 12 by the value obtained by multiplying the tensile strength and the plate thickness of the first steel plate 11.

The third steel plate 13 is a plate-like member having an outline with a longer side disposed in the front-rear directions. A central area of the third steel plate 13 in the front-rear directions slightly expands in the outer direction. The third steel plate 13 has a plate thickness and/or a strength different from those of the first steel plate 11 and the second steel plate 12. In the present embodiment, the third steel plate 13 has a plate thickness greater than the plate thickness of the first steel plate 11. In addition, the third steel plate 13 has a plate thickness smaller than the plate thickness of the second steel plate 12 and has a tensile strength smaller than the tensile strength of the second steel plate 12. As one example, the plate thickness of the third steel plate 13 is 0.65 mm, and the tensile strength of the third steel plate 13 is 270 MPa.

The tailored blank 10 includes the first welded portion 14 formed therein. The first welded portion 14 is where an end surface of the first steel plate 11 and an end surface of the second steel plate 12 are welded together. Specifically, the first welded portion 14 is a weld bead formed by welding between and along an edge of the first steel plate 11 on a side of the second steel plate 12 and an edge of the second steel plate 12 on a side of the first steel plate 11. In other words, the tailored blank 10 includes a welding line formed along the edge of the first steel plate 11 on the side of the second steel plate 12 and the edge of the second steel plate 12 on the side of the first steel plate 11.

The tailored blank 10 also includes the second welded portion 15 formed therein. The second welded portion 15 is where an end surface of the second steel plate 12 and an end surface of the third steel plate 13 are welded to each other. Specifically, the second welded portion 15 is a weld bead formed by welding between and along an edge of the second steel plate 12 on a side of the third steel plate 13 and an edge of the third steel plate 13 on a side of the second steel plate 12. In other words, the tailored blank 10 includes a welding line formed along the edge of the second steel plate 12 on the side of the third steel plate 13 and the edge of the third steel plate 13 on the side of the second steel plate 12.

The tailored blank 10 is formed by joining the first steel plate 11, the second steel plates 12, and the third steel plates 13, each of which has a different plate thickness. In the present embodiment, the first steel plate 11, the second steel plates 12, and the third steel plates 13 are joined such that top surfaces of these plates are disposed on the same plane. The first steel plate 11, the second steel plates 12, and the third steel plates 13 may be joined such that bottom surfaces of these plates are disposed on the same plane. The surface of each of these steel plates has some unevenness due to the nature of the material. The said same plane is not limited to be a smooth plane.

As shown in FIG. 4A, the first welded portion 14 and the second welded portion 15 (in other words, the weld beads) may be formed to rise higher than the top surface of the tailored blank 10 in the upward direction or may be formed to rise higher than the bottom surface of the tailored blank 10 in the downward direction. The first welded portion 14 and the second welded portion 15 may be formed with its lower side recessed and its upper side risen in the upward direction, or as shown in FIG. 4B, with its upper side recessed and its lower side risen in the downward direction. FIG. 4A and FIG. 4B show the first welded portion 14. In FIG. 4A and FIG. 4B, the difference in plate thickness between the first steel plate 11 and the second steel plate 12 is omitted.

As shown in FIG. 2B, the tailored blank 10 includes a top plate corresponding portion 2A, a vertical wall corresponding portion 3A, and a flange corresponding portion 4A.

The top plate corresponding portion 2A represents a portion corresponding to the top plate 2 of the press molded product 1. In other words, the top plate corresponding portion 2A is an area in the tailored blank 10 where the top plate 2 is formed when the press molded product 1 is molded. The top plate corresponding portion 2A is a roughly rectangular area.

The vertical wall corresponding portion 3A represents a portion corresponding to the vertical wall 3 of the press molded product 1. In other words, the vertical wall corresponding portion 3A is an area in the tailored blank 10 where the vertical wall 3 is formed when the press molded product 1 is molded. The vertical wall corresponding portion 3A is a roughly U-shaped area surrounding the top plate corresponding portion 2A in three directions.

The flange corresponding portion 4A represents a portion corresponding to the flange 4 of the press molded product 1. In other words, the flange corresponding portion 4A is an area in the tailored blank 10 where the flange 4 is formed when the press molded product 1 is molded. The flange 4 is an area in the tailored blank 10 other than the top plate corresponding portion 2A and the vertical wall corresponding portion 3A.

The top plate corresponding portion 2A and the vertical wall corresponding portion 3A are situated in the first steel plate 11. Specifically, in a plan view, the top plate corresponding portion 2A is situated in a rear portion of the tailored blank 10 including the rear end portion of the tailored blank 10. More specifically, the top plate corresponding portion 2A and the vertical wall corresponding portion 3A are situated in a roughly central area of the tailored blank 10 in the right-left directions which is a rear area of the tailored blank 10 in the front-rear directions.

The flange corresponding portion 4A is situated in a portion of the first steel plate 11, in the second steel plates 12, and in the third steel plates 13. Specifically, in a plan view, the flange corresponding portion 4A is situated in the entire front portion of the tailored blank 10 including the front end portion of the tailored blank 10 and in the entire right-left portions of the tailored blank 10 including the end portions on the right side and the left side.

The first welded portion 14 and the second welded portion 15 are situated in the flange corresponding portion 4A. Specifically, the first welded portion 14 extends from the front end portion of the tailored blank 10 towards the rear side so as to avoid the top plate corresponding portion 2A. More specifically, the first welded portion 14 extends slantwise away from a boundary between the vertical wall corresponding portion 3A and the flange corresponding portion 4A, which extends in the front-rear directions, from the front side to the rear side. The first welded portion 14 is situated in a vicinity of the vertical wall corresponding portion 3A. Specifically, in the right half of the tailored blank 10, the first welded portion 14 is situated at a position which is less than about one-third of the distance from the boundary between the vertical wall corresponding portion 3A and the flange corresponding portion 4A, which extends in the front-rear directions, to a right edge of the flange corresponding portion 4A. The second welded portion 15 extends roughly parallel to the first welded portion 14.

1-3. Press Molding Device

A press molding device 100 shown in FIG. 5 is a device for pressing the tailored blank 10 to obtain the press molded product 1. FIG. 5 and FIG. 6A to 6F are diagrams showing the right half of the press molding device 100. The left half of the press molding device 100 which is not illustrated is right-left symmetric with the right half. In FIGS. 6B, 6D, and 6F, metallic molds and tailored blank are transparently shown.

The press molding device 100 includes a die 101, a punch 102, and a blank holder 103. The die 101 and the punch 102 are metallic molds arranged to face each other in the upward-downward directions. In the present embodiment, the die 101 is situated above the punch 102, and the punch 102 is situated below the die 101. Press working using the die 101 and the punch 102 is performed by moving the die 101 in the upward-downward directions. The die 101 and the blank holder 103 are configured to be displaceable in the upward-downward directions by an unillustrated drive mechanism.

The die 101 is situated above the tailored blank 10 so as to cover the entirety of the tailored blank 10. The punch 102 is situated below the tailored blank 10.

The die 101 and the punch 102 are each shaped after the shape of the press molded product 1. Specifically, the die 101 includes a top plate forming portion 2C and a vertical wall forming portion 3C, and the punch 102 includes a top plate forming portion 2D and a vertical wall forming portion 3D. The top plate forming portions 2C and 2D are portions for forming the top plate 2. The vertical wall forming portions 3C and 3D are portions for forming the vertical wall 3. The die 101 has a shape with its central portion in the right-left directions recessed upward. The punch 102 has a shape with an upward projection.

The blank holder 103 is a member situated to face the die 101, and is a member that can hold the flange corresponding portion 4A in coordination with the die 101. As shown in FIG. 9, the blank holder 103 is situated between the die 101 and a pedestal of the punch 102. The area of the blank holder 103 is greater than the area of the flange corresponding portion 4A so that the blank holder 103 can hold the entirety of the bottom surface of the flange corresponding portion 4A. A part of the first steel plate 11, the second steel plates 12, and the third steel plates 13 can be mounted on the blank holder 103. In other words, the blank holder 103 is a member that spreads from the boundary between the vertical wall corresponding portion 3A and the flange corresponding portion 4A to the front, to the right, and to the left.

In a held state which will be mentioned below, portions of the die 101 and the blank holder 103 that can come in contact with the first welded portion 14 and the second welded portion 15 are formed of a material having a hardness greater than the hardness of the first welded portion 14 and the second welded portion 15. In other words, portions of the die 101 and the blank holder 103 that face with a displacement area, which will be mentioned below, in the held state are formed of a material having a hardness greater than the hardness of the first welded portion 14 and the second welded portion 15. For example, the portions of the die 101 and the blank holder 103 that face with the displacement area in the held state may be formed of a material whose carbon content is greater than the carbon content of the first welded portion 14 and the second welded portion 15.

1-4. Method for Manufacturing Press Molded Product

A method for manufacturing the press molded product 1 through which the press molded product 1 is obtained by pressing the tailored blank 10 will be explained with reference to the flowchart in FIG. 7. The method for manufacturing the press molded product 1 includes a blank producing step S1, a first molding step S2, a trimming step S3, and a second molding step S4. The method for manufacturing the press molded product 1 is performed in the following order: the blank producing step S1; the first molding step S2; the trimming step S3; and the second molding step S4.

In the blank producing step S1, the tailored blank 10 is produced. Specifically, the first steel plate 11, the second steel plates 12, and the third steel plates 13 are joined by welding to produce the tailored blank 10. The shape of the tailored blank 10 is determined based on an amount of deformation of the tailored blank 10 in a pressing step which will be mentioned below. The amount of deformation of the tailored blank 10 can be alternatively referred to as an amount of displacement of the material of the tailored blank 10. For example, the amount of displacement of the material of the tailored blank 10 is calculated by a simulator. In other words, the amount of displacement of the first welded portion 14 and the second welded portion 15 towards the top plate corresponding portion 2A in the pressing step is pre-designed. That is, the first welded portion 14 and the second welded portion 15 are displaced in the displacement area, which is a pre-designed area, in the tailored blank 10 towards the top plate corresponding portion 2A. More specifically, it is predicted that the amount of displacement of the first welded portion 14 and the second welded portion 15 increases in a portion where the amount of deformation is relatively large as shown in FIG. 3A compared to a portion where the amount of deformation is relatively small as shown in FIG. 3B. Specifically, when the top plate 2 is formed, it is predicted that the amount of displacement of the first welded portion 14 and the second welded portion 15 is relatively large at a location where the amount of the material of the tailored blank 10 that flows towards the top plate 2 is relatively large. Accordingly, in the blank producing step S1, the steel plates are each welded at predicted locations of the first welded portion 14 and the second welded portion 15 in the tailored blank 10 obtained by calculating backwards from the locations of the first welded portion 14 and the second welded portion 15 of the press molded product 1 considering the amount of deformation of the tailored blank 10. The displacement of the first welded portion 14 and the second welded portion 15 will be explained below in detail.

The first molding step S2 is a step to obtain an intermediate molded product by drawing the tailored blank 10 using the press molding device 100. The first molding step S2 includes a positioning step S21, a holding step S22, and a pressing step S23.

In the positioning step S21, the tailored blank 10 is situated between the die 101 and the punch 102 disposed away from each other. Specifically, the flange corresponding portion 4A of the tailored blank 10 is mounted on a top surface of the blank holder 103.

In the holding step S22, as the die 101 descends, the die 101 and the blank holder 103 move relatively closer to each other, and the tailored blank 10 is fixed while being held between the die 101 and the blank holder 103. Specifically, the state of the tailored blank 10 is transitioned to the held state where the flange corresponding portion 4A is held between the die 101 and the blank holder 103. In the held state, the die 101 and the blank holder 103 hold the flange corresponding portion 4A therebetween such that the first welded portion 14 and the second welded portion 15 can be displaced towards the top plate corresponding portion 2A.

In the present embodiment, a pressure applied to the tailored blank 10 by the blank holder 103 in the held state is set to satisfy the following mathematical formula (Formula 1).

X [ ton ] < Ts [ MPa ] × 0.005 × A [ mm 2 ] 9.8 [ Formula ⁢ 1 ]

In Formula 1, X is a pressure applied to the tailored blank 10 by the blank holder 103. Ts is a tensile strength of the steel plate whose value obtained by multiplying its tensile strength and its plate thickness is the smallest (the first steel plate 11 in the present embodiment). A is a contact area of the blank holder 103 and the tailored blank 10 before the tailored blank 10 is pressed by the die 101 and the punch 102. Due to the nature of the material, the surface of the tailored blank 10 has some unevenness. Thus, the tailored blank 10 does not necessarily adhere to the blank holder 103 over the entire surface. The contact area includes the area where the blank holder 103 and the tailored blank 10 overlap each other in the upward-downward directions in addition to the area where the blank holder 103 and the tailored blank 10 contact each other.

In the pressing step S23, the tailored blank 10 is pressed by the die 101 and the punch 102 by moving the die 101 and the punch 102 close to each other in the held state to form the top plate 2, the vertical wall 3, and the flange 4. Specifically, the die 101 and the blank holder 103 are descended in the held state. When the die 101 and the blank holder 103 reach a bottom dead center, the top plate 2 is formed in a portion of the tailored blank 10 held between the top plate forming portions 2C and 2D, and the vertical wall 3 is formed in a portion of the tailored blank 10 held between the vertical wall forming portions 3C and 3D. The flange 4 is formed in a portion of the tailored blank 10 held between the die 101 and the blank holder 103.

The trimming step S3 is a step for trimming the intermediate molded product formed in the first molding step S2. In the trimming step S3, an unnecessary part is removed from the intermediate molded product.

The second molding step S4 is a step for performing optional processing on the intermediate molded product processed in the trimming step S3. For example, processing such as bending and creating a hole is performed.

The press molded product 1 is formed through the aforementioned steps S1 to S4.

1-5. Displacement of First Welded Portion and Second Welded Portion

Since the transition to the held state until the completion of the press working, the first welded portion 14 and the second welded portion 15 are held between the die 101 and the blank holder 103 so as to be displaced in the pre-designed displacement area towards the top plate corresponding portion 2A.

As shown in FIG. 2B, in the tailored blank 10, the first welded portion 14 and the second welded portion 15 extends at an angle with respect to the boundary between the vertical wall corresponding portion 3A and the flange corresponding portion 4A which extends in the front-rear directions. Here, “at an angle” means that the angle between the welding line and an imaginary straight line extended from the boundary in the front-rear directions is about 5 degrees or more.

Meanwhile, as shown in FIG. 2A, the first welded portion 14 and the second welded portion 15 extend roughly parallel to the ridgeline between the vertical wall 3 and the flange 4 in the press molded product 1. Specifically, the first welded portion 14 and the second welded portion 15 extend roughly parallel to the ridgeline between the vertical wall 3 and the flange 4 that extends in the front-rear directions. More specifically, the first welded portion 14 and the second welded portion 15 extend at an angle with respect to the ridgeline from the front end portion to a corner portion where a wall of the vertical wall 3 that spreads in the upward-downward directions and the front-rear directions intersects with a wall of the vertical wall 3 that spreads in the upward-downward directions and the right-left directions.

The first welded portion 14 and the second welded portion 15 extend roughly parallel to the ridgeline from the corner portion to the rear end portion. In other words, the material of the tailored blank 10 is displaced so as to rotate about the corner portion towards the top plate corresponding portion 2A during the press working. In the area where the amount of deformation is relatively large, in other words, in the area on the rear side of the corner portion, the material of the tailored blank 10 is displaced so as to rotate largely compared to the rotation in the area where the amount of deformation is relatively small, in other words, in the area on the front side of the corner portion.

The first welded portion 14 and the second welded portion 15 are also displaced so as to rotate about the corner portion towards the top plate corresponding portion 2A. In other words, the angle formed by the first welded portion 14 and the ridgeline between the vertical wall 3 and the flange 4 in the press molded product 1 is smaller than the angle formed by the first welded portion 14 and the boundary between the vertical wall corresponding portion 3A and the flange corresponding portion 4A in the tailored blank 10. As a consequence, the first welded portion 14 and the ridgeline are roughly parallel to each other. Specifically, the angle formed by the first welded portion 14 and the ridgeline between the vertical wall 3 and the flange 4 in the press molded product 1 is approximately less than 5 degrees. As shown in FIG. 8, an area surrounded by a broken line 14A (that is, the first welded portion 14 before the press working) and a broken line 14B (that is, the first welded portion 14 after the press working) is the displacement area of the first welded portion 14. An area surrounded by a broken line 15A (that is, the second welded portion 15 before the press working) and a broken line 15B (that is, the second welded portion 15 after the press working) is the displacement area of the second welded portion 15. The displacement area has a roughly triangular shape with a position at the height of the corner portion in the front-rear directions being the apex, and with the width in the right-left directions increasing towards the rear side.

1-6. Effects

According to the first embodiment that has been explained in detail above, the following effects can be obtained.

• • (1a) In the aforementioned embodiment, the die 101 and the blank holder 103 hold the flange corresponding portion 4A such that the first welded portion 14 and the second welded portion 15 can be displaced towards the top plate corresponding portion 2A in the held state. In the press working, the plate thickness of the first steel plate 11 becomes smaller than its original plate thickness since the amount of deformation of the top plate corresponding portion 2A and the vertical wall corresponding portion 3A is relatively large. If the die 101 and the blank holder 103 hold the flange corresponding portion 4A so as to excessively inhibit the displacement of the first welded portion 14 and the second welded portion 15, it is difficult for the material to flow from the flange corresponding portion 4A toward the top plate corresponding portion 2A. Thus, a breakage easily occurs in the first steel plate 11 having a smaller plate thickness or in the vicinity of the first welded portion 14 and the second welded portion 15 whose displacement is excessively inhibited. However, according to the configuration mentioned above, the first welded portion 14 and the second welded portion 15 can be displaced towards the top plate corresponding portion 2A, and therefore, the material easily flows from the flange corresponding portion 4A towards the top plate corresponding portion 2A. Thus, the plate thickness of the first steel plate 11 is less likely to become smaller. In addition, the first welded portion 14 and the second welded portion 15 can also be displaced smoothly. Accordingly, a breakage of the tailored blank 10 can be inhibited when forming the press molded product 1 having the first welded portion 14 and the second welded portion 15 in the flange 4.

If the tailored blank 10 is pressed without being held by the die 101 and the blank holder 103, a crease is easily generated on the press molded product 1 due to an excessive flow of the material from the flange corresponding portion 4A towards the top plate corresponding portion 2A. However, according to the configuration mentioned above, such an excessive flow of the material from the flange corresponding portion 4A towards the top plate corresponding portion 2A can be inhibited since the flange corresponding portion 4A is held between the die 101 and the blank holder 103. Thus, generation of a crease on the press molded product 1 can be reduced.

• • (1b) In the aforementioned embodiment, the pressure applied to the tailored blank 10 by the blank holder 103 in the held state is set to satisfy Formula 1. Such a configuration enables the held state to be maintained in a state where the displacement of the first welded portion 14 and the second welded portion 15 towards the top plate corresponding portion 2A is not easily inhibited. Accordingly, it becomes easier for the material to flow from the flange corresponding portion 4A towards the top plate corresponding portion 2A.
  • (1c) In the aforementioned embodiment, the portions of the die 101 and the blank holder 103 that can come in contact with the first welded portion 14 and the second welded portion 15 in held state are formed of a material having a hardness greater than the hardness of the first welded portion 14 and the second welded portion 15. Such a configuration can inhibit the die 101 and the blank holder 103 from being shaved or chipped even when the weld bead that is formed to be risen is displaced in the displacement area while contacting the die 101 and the blank holder 103. This can reduce deformation of the die 101 and the blank holder 103, and therefore, the held state can be stably maintained.
  • (1d) In the aforementioned embodiment, in a plan view, the top plate corresponding portion 2A is situated in a rear portion of the tailored blank 10 including the rear end portion of the tailored blank 10. In addition, the first welded portion 14 extends from the front end portion of the tailored blank 10 towards the rear side so as to avoid the top plate corresponding portion 2A. Due to such a configuration, the distance from the top plate corresponding portion 2A to a portion of the first welded portion 14 where the amount of deformation of the tailored blank 10 is relatively large is different from the distance from the top plate corresponding portion 2A to a portion of the first welded portion 14 where the amount of deformation of the tailored blank 10 is relatively small. In other words, the first welded portion 14 is situated in the tailored blank 10 considering the amount of displacement of the first welded portion 14 during the press working. Accordingly, when the production of the press molded product 1 is finished, the first welded portion 14 can be situated at a desired location. Specifically, it is possible to obtain the press molded product 1 in which the first welded portion 14 extends roughly parallel to the ridgeline between the vertical wall 3 and the flange 4.

1-7. Correspondence

In the aforementioned embodiment, the die 101 corresponds to a first metallic mold, the punch 102 corresponds to a second metallic mold, and the blank holder 103 corresponds to a holder. In addition, the rear side corresponds to a first side, and the front side corresponds to a second side.

2. Second Embodiment

2-1. Configuration

Explanations of the configuration of the second embodiment that is common with the configuration of the first embodiment will be omitted, and the second embodiment will be explained focusing on differences from the first embodiment. The same reference numerals as in the first embodiment represent the same configurations, and the preceding descriptions will be referred to.

In the first embodiment, the first welded portion 14 and the second welded portion 15 are configured to be displaceable towards the top plate corresponding portion 2A in the held state. In other words, a configuration was illustrated in which the pressure applied to the tailored blank 10 by the blank holder 103 in the held state is set to satisfy Formula 1 so that the die 101 and the blank holder 103 hold the flange corresponding portion 4A.

In the second embodiment, another configuration will be illustrated in which the die 101 and the blank holder 103 hold the flange corresponding portion 4A so that the first welded portion 14 and the second welded portion 15 are displaceable towards the top plate corresponding portion 2A in the held state.

In the second embodiment, the press molding device 100 includes an adjusting member. The adjusting member is for adjusting the distance between the tailored blank 10 and the die 101 in the held state. As shown in FIG. 9, the press molding device 100 includes a first adjusting member 21 and a second adjusting member 22 as the adjusting members.

The first adjusting member 21 is a cylindrical metal. As an example, the first adjusting member 21 is a distance block. The shape of the first adjusting member 21 is not limited thereto. For example, the shape of the first adjusting member 21 may be a polygonal prism.

The second adjusting member 22 is a disk-shaped metal. As an example, the second adjusting member 22 is a shim. The shape of the second adjusting member 22 is not limited thereto. For example, the shape of the second adjusting member 22 may be rectangular. The thickness of the second adjusting member 22 is configured to be less than the thickness of the first adjusting member 21.

The first adjusting member 21 and the second adjusting member 22 are situated outside of the third steel plate 13. The first adjusting member 21 and the second adjusting member 22 are placed on one another and situated between the blank holder 103 and the die 101. In the present embodiment, the second adjusting member 22 is placed on the top surface of the blank holder 103, and the first adjusting member 21 is placed on the top surface of the second adjusting member 22. Specifically, at least two sets of the first adjusting member 21 and the second adjusting member 22 placed on one another are situated outside of the outer circumference of the tailored blank 10. The at least two sets of the first adjusting member 21 and the second adjusting member 22 are arranged along the outer circumference of the tailored blank 10 at a given interval. In other words, the at least two sets of the first adjusting member 21 and the second adjusting member 22 are situated around the tailored blank 10 and arranged in a way that covers the front, rear, right, and left of the tailored blank 10.

As such, in the second embodiment, the first adjusting member 21 and the second adjusting member 22 are arranged in the press molding device 100 such that the distance between the tailored blank 10 and the die 101 in the held state is adjusted to be greater than or equal to 5% and less than 20% of the plate thickness of the thinnest steel plate among the steel plates forming the tailored blank 10. In the present embodiment, the first adjusting member 21 and the second adjusting member 22 are arranged such that the distance between the top surface of the tailored blank 10 and the bottom surface of the die 101 in the held state is adjusted to be greater than or equal to 5% and less than 20% of the plate thickness of the first steel plate 11.

2-2. Effects

According to the second embodiment that has been explained in detail above, the following effects can be obtained in addition to the effects (1a), (1c), and (1d) of the first embodiment described above.

• • (2a) The distance between the tailored blank 10 and the die 101 in the held state is adjusted to be greater than or equal to 5% and less than 20% of the plate thickness of the first steel plate 11 by placing the first adjusting member 21 and the second adjusting member 22. Such a configuration enables the held state to be maintained in a state where the displacement of the first welded portion 14 and the second welded portion 15 towards the top plate corresponding portion 2A is not easily inhibited. Accordingly, it becomes easier for the material to flow from the flange corresponding portion 4A towards the top plate corresponding portion 2A. In other words, excessive adhesion of the tailored blank 10 to the die 101 and the blank holder 103 in the held state can be avoided by creating a gap between the tailored blank 10 and the die 101. In addition, since the surface of the tailored blank 10 includes some unevenness due to the nature of the material, the die 101 and the blank holder 103 can hold the tailored blank 10 by partially contacting the tailored blank 10 if the gap between the tailored blank 10 and the die 101 is greater than or equal to 5% and less than 20% of the plate thickness of the first steel plate 11.
  • (2b) The first adjusting member 21 and the second adjusting member 22 are placed on one another and situated between the die 101 and the punch 102, and the thickness of the second adjusting member 22 is configured to be less than the thickness of the first adjusting member 21. Such a configuration makes it easier to perform fine adjustments of the distance between the tailored blank 10 and the die 101.

2-3. Modified Example of Second Embodiment

In the aforementioned second embodiment, a configuration was illustrated in which the press molding device 100 includes two adjusting members, namely the first adjusting member 21 and the second adjusting member 22. However, the number of the adjusting members included in the press molding device 100 is not limited thereto. For example, the press molding device 100 may include one adjusting member or may use three or more adjusting members placed on one another.

OTHER EMBODIMENTS

The embodiments of the present disclosure have been explained above; however, it is needless to say that the present disclosure is not limited to the above-described embodiments and may be implemented in various forms.

• • (3a) In the aforementioned embodiments, a configuration was illustrated in which the tailored blank 10 is a steel plate formed by joining the first steel plate 11, the second steel plate 12, and the third steel plate 13 by welding. However, the configuration of the tailored blank 10 is not limited thereto. For example, the tailored blank 10 may be a steel plate formed by joining the first steel plate 11 and two second steel plates 12 by welding. The number of the steel plates to be joined can be appropriately determined depending on the shape of the desired press molded product.
  • (3b) In the aforementioned embodiments, a configuration was illustrated in which the plate thickness of the second steel plate 12 is greater than the plate thickness of the first steel plate 11, and the tensile strength of the second steel plate 12 is greater than the tensile strength of the first steel plate 11. However, the quality of the material of the second steel plate 12 is not limited thereto. The plate thickness of the second steel plate 12 may be less than the plate thickness of the first steel plate 11, and/or, the tensile strength of the second steel plate 12 may be less than the tensile strength of the first steel plate 11. The ratio of strength between the first steel plate 11 and the second steel plate 12 may be less than or equal to 1.0. The method for manufacturing the press molded product 1 of the aforementioned embodiments may be applied to various kinds of the tailored blank 10 prepared by combining steel plates having different plate thicknesses and/or strengths.
  • (3c) In the aforementioned embodiments, a configuration was illustrated in which the first welded portion 14 extends from the front end portion of the tailored blank 10 towards the rear side of the tailored blank 10 so as to avoid the top plate corresponding portion 2A. However, the location of the first welded portion 14 in the tailored blank 10 is not limited thereto. For example, the first welded portion 14 may be situated to extend roughly parallel to the top plate corresponding portion 2A also in the tailored blank 10. The first welded portion 14 and the second welded portion 15 in the tailored blank 10 may vary depending on the shape of the press molded product 1 and may be situated at any locations estimated by calculating backwards from the locations of the first welded portion 14 and the second welded portion 15 of the press molded product 1.
  • (3d) In the method for manufacturing the press molded product 1, the configuration of the aforementioned first embodiment and the configuration of the aforementioned second embodiment may be simultaneously implemented. In other words, the press molding device 100 may include the adjusting member, and at the same time, the pressure applied to the tailored blank 10 by the blank holder 103 in the held state may be set to satisfy Formula 1.
  • (3e) Functions of one element in the aforementioned embodiments may be distributed to two or more elements. Functions of two or more elements may be integrated into one element. A part of the configuration of the aforementioned embodiments may be omitted. At least a part of the configuration of the aforementioned embodiments may be added to or replaced with other configurations of the aforementioned embodiments.