Press forming method and press forming apparatus

Abstract

To provide a press molding method that can apply compressive stress to a work-piece to prevent spring back with a simple facility.SOLUTION: The press molding method comprises a preliminary molding step of molding a preliminary molded product 1 with a hat-shape cross section, while leaving a molding margin (an excess thickness part) on a shoulder part, and a main molding step of molding the product into a final shape. In the press molding method, a first movable mold is pressed against a top plate side of a hat part to mold the product, while making a second movable mold 39 that moves in a height direction of the hat part constrain an opening-side end part of the preliminary molded product 1. In the main molding step, a tip portion of a flange part 6 of the preliminary molded product 1 passes on a position adjacent to a chamfered part 37 on a wall (a constraining piece 36) constraining the opening-side end part of the preliminary molded product 1.SELECTED DRAWING: Figure 15

Description

Technical Field

[0001] The present invention relates to a press forming method and a press forming apparatus for bending a steel plate into a hat-shaped cross section.

Background Art

[0002] In recent years, as a steel material used for automobile bodies, ultra-high strength steel having a higher strength than high-tensile steel and a tensile strength exceeding 1000 MPa has been increasingly used. This type of ultra-high strength steel is cold-bent and formed into a predetermined shape. The ultra-high strength steel has a larger springback amount after bending than general high-tensile steel. For this reason, conventionally, in order to obtain the target dimensional accuracy in anticipation of springback, the mold has been re-machined.

[0003] Re-machining the mold requires a great deal of man-hours, and if it cannot be dealt with by re-machining, the mold may be remade. Then, the amount of iron used increases due to remaking the mold, which is not good for the environment. In order to minimize such mold corrections, a press forming method has been considered in which forming is performed a plurality of times to correct springback and form the final shape. As a conventional press forming method for correcting springback, for example, there is a method described in Patent Document 1. The press forming method shown in Patent Document 1 is a method of forming a steel plate into a hat-shaped cross section while suppressing the occurrence of springback. The hat-shaped cross section is a shape in which a flange portion is provided at the open end of a hat portion composed of a top plate and vertical plates on both sides. The press forming method shown in Patent Document 1 adopts a configuration in which a formed product is formed into a final shape in two steps, a preliminary forming step and a main forming step, when forming a steel plate into a hat-shaped cross section.

[0004] In the pre-forming process, a pre-formed part with a hat-shaped cross-section is formed, allowing for springback. In this forming process, the vertical walls on both sides of the pre-formed part and the flanges on both ends are pressed from the side by a lateral-moving die against a fixed mold, which is a punch, while the hat portion is sandwiched between the pad and the punch and formed, so that the pre-formed part is compressed and formed into its final shape. The compression of the pre-formed part suppresses the occurrence of springback. The lateral-moving die is driven by converting the vertical movement of the upper die, which includes the pad, into horizontal movement using a cam mechanism, so as to work in conjunction with the pad that forms the hat portion. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-39327 [Overview of the project] [Problems that the invention aims to solve]

[0006] The molding method shown in Patent Document 1 has the problem of making the mold complex and large because a cam mechanism is required to drive the lateral-moving die.

[0007] The object of the present invention is to provide a press forming method and press forming apparatus that can apply compressive stress to a workpiece using simple equipment to prevent springback. [Means for solving the problem]

[0008] To achieve this objective, the press forming method according to the present invention comprises a pre-forming step in which a molded product with a hat-shaped cross section having a flange portion at the open end of a hat portion consisting of a top plate and vertical plates on both sides is formed by a pre-forming die so that molding allowance remains on the shoulder portions on both sides of the hat portion, and a main forming step in which the pre-formed product formed in the pre-forming step is compressed by a main forming die to form a molded product with a final shape, the main forming die having a wall to which the tip surface of the flange portion abuts, a protrusion that enters into the hat portion, and a recess formed between the wall and the protrusion, and having a molding surface for forming the inner surface of the final molded product, a first movable die configured to move in the height direction of the hat portion and to form the top plate side of the hat portion into the final shape by sandwiching it between the protrusion of the fixed die, and a second movable die configured to move in the height direction of the hat portion and to form the pre-formed product, including the open end side of the hat portion, between the recess of the fixed die, and The molding process comprises a first molding step of placing the pre-molded product on the protrusion of the fixed mold, a second molding step of sandwiching the pre-molded product between the recess of the fixed mold and the second movable mold, and a third molding step of molding the pre-molded product into its final shape by the protrusion of the fixed mold and the first movable mold while the pre-molded product is pressed against the recess of the fixed mold by the second movable mold. The portions of the fixed mold and the second movable mold that form the connection between the vertical plate and the flange of the cap are each formed by rounded portions with a curved cross-sectional shape. In the second molding step, as the second movable mold moves to the molding completion position, the rounded portion of the second movable mold pushes the vertical plate of the pre-molded product toward the fixed mold, forming a chamfered portion at the tip of the wall of the fixed mold. In the second molding step, the tip of the flange passes in close proximity to the chamfered portion.

[0009] Furthermore, the press molding method according to the present invention comprises a pre-molding step in which a molded product with a hat-shaped cross section having a flange portion at the open end of the hat portion, which consists of a top plate and vertical plates on both sides, is molded using a pre-molding die so that molding allowance remains on the shoulder portions on both sides of the hat portion, and a main molding step in which the pre-molded product formed in the pre-molding step is compressed using a main molding die to form a molded product with the final shape, wherein the main molding die has a wall against which the tip surface of the flange portion abuts, a protrusion that enters into the hat portion, and a recess formed between the wall and the protrusion, The molding process comprises a fixed mold having a molding surface for molding the inner surface of the final molded product, a first movable mold configured to be movable in the height direction of the hat portion and molding the top plate side of the hat portion into the final shape by sandwiching it between the fixed mold and the protrusion, and a second movable mold configured to be movable in the height direction of the hat portion and molding the pre-molded product, including the open end side of the hat portion, into the final shape by sandwiching it between the fixed mold and the recess, and the molding process comprises a first molding process in which the pre-molded product is placed on the protrusion of the fixed mold, and the pre-molded product is moved by the fixed mold The molding process includes a second main molding step in which the pre-molded product is sandwiched between the recess of the fixed mold and the second movable mold, and a third main molding step in which the pre-molded product is pressed against the recess of the fixed mold by the second movable mold and molded into the final shape by the convex portion of the fixed mold and the first movable mold, wherein the molding allowance is composed of excess material formed in such a way that the shoulder portions on both sides of the cap portion partially bulge outwards from the cap portion, and the fixed mold includes a lower mold for main molding that cannot be moved and a flange fixed to the lower mold for main molding. The second movable mold has a wall against which the tip surface of the part abuts, a convex portion fixed to the lower mold for the main molding and entering the hat portion, and a recess formed between the wall and the convex portion, wherein the second movable mold is configured to move only in the height direction of the hat portion and parallel to the direction of movement of the first movable mold, and in the third main molding step, the opening portion of the hat portion and the flange portion are constrained and their displacement restricted by the fixed mold and the second movable mold, and the excess material portion of the pre-molded product is compressed by the first movable mold.

[0010] Furthermore, the press forming method according to the present invention comprises a pre-forming step in which a pre-formed product having a hat-shaped cross-section with a flange portion at the open end of a hat portion, in which a pair of vertical plates are connected on both sides of the top plate via upwardly rising excess material portions, is formed by a pre-forming die so that molding allowances consisting of excess material portions remain on the shoulder portions on both sides of the hat portion; and a main forming step in which the pre-formed product formed in the pre-forming step is compressed by a main forming die different from the pre-forming die to form a final-shaped molded product, wherein the main forming die has a fixed die having a molding surface that integrally forms a wall against which the tip surface of the flange portion abuts, a protrusion that enters into the hat portion, and a groove recess formed between the wall and the protrusion, and forms the inner surface of the final-shaped molded product; a first movable die configured to be movable in the height direction of the hat portion, which sandwiches the top plate side of the hat portion between itself and the protrusion of the fixed die to form the final shape; and a second movable die configured to be movable in the height direction of the hat portion. The molding process includes a first molding step of placing the pre-molded product, including the open end side of the cap portion, between the groove recess of the fixed mold and a second movable mold for molding it into its final shape, and the molding process includes a first molding step of placing the pre-molded product on the protrusion of the fixed mold, a second molding step of sandwiching the pre-molded product between the groove recess of the fixed mold and the second movable mold, and a third molding step of molding the top plate of the pre-molded product into its final shape by the protrusion of the fixed mold and the first movable mold while the flange and vertical plate of the pre-molded product are pressed against the groove recess of the fixed mold by the second movable mold, the third molding step is a method in which the first movable mold pushes the pre-molded product toward the fixed mold, so that a part of the excess material is moved toward the center of the top plate, the central part of the top plate is curved more significantly, and the top plate and the excess material of the pre-molded product are compressed while deforming into a corrugated shape.

[0011] In the press forming method described above, the portions of the fixed die and the second movable die that form the connection between the vertical plate and the flange portion of the hat portion are each formed by rounded portions having a curved cross-sectional shape, and in the second main forming step, as the second movable die moves to the forming completion position, the rounded portion of the second movable die may push the vertical plate of the preform toward the fixed die. In the press forming method described above, a chamfered portion is formed at the tip of the wall of the fixed die, and in the second main forming step, the tip of the flange portion may pass in close proximity to the chamfered portion. In the press forming method described above, the wall of the fixed die is formed by a die component separate from the other parts of the fixed die and is detachably configured, the boundary between the bottom surface of the recess and the wall is at a right angle, and the tip surface of the flange portion may contact the wall without any gap during the third main forming step.

[0012] The press molding apparatus according to the present invention comprises a pre-molding die for molding a hat-shaped molded product having a flange portion at the open end of a hat portion consisting of a top plate and vertical plates on both sides, such that molding allowance remains on the shoulder portions on both sides of the hat portion; and a final molding die for compressing the pre-molded product formed by the pre-molding die to form a final molded product. The final molding die has a wall against which the tip surface of the flange portion abuts, a protrusion that enters into the hat portion, and a recess formed between the wall and the protrusion, and a fixed die having a molding surface for molding the inner surface of the final molded product; and a movable part configured to move in the height direction of the hat portion, between the top plate side of the hat portion and the protrusion of the fixed die. The present invention comprises a first movable mold that molds the pre-molded product into its final shape by sandwiching it between two parts, and a second movable mold configured to be movable in the height direction of the cap portion, which molds the pre-molded product, including the open end side of the cap portion, into its final shape by sandwiching it between the fixed mold and the recess of the fixed mold, wherein the first movable mold molds the pre-molded product into its final shape by pressing it against the protrusion of the fixed mold while the second movable mold is pressing the pre-molded product against the recess of the fixed mold, and a chamfered portion is formed at the tip of the wall of the fixed mold, and the chamfered portion may be formed outside the movement trajectory of the flange portion that moves as the second movable mold presses the pre-molded product against the fixed mold.

[0013] Furthermore, the press molding apparatus according to the present invention comprises a pre-molding die for molding a hat-shaped molded product having a flange portion at the open end of a hat portion consisting of a top plate and vertical plates on both sides, such that molding allowances remain on the shoulder portions on both sides of the hat portion, and a main molding die for compressing the pre-molded product formed by the pre-molding die to form a molded product in the final shape, wherein the main molding die has a wall against which the tip surface of the flange portion abuts, a protrusion that enters into the hat portion, and a recess formed between the wall and the protrusion, and has a molding surface for forming the inner surface of the final molded product, a first movable die configured to move in the height direction of the hat portion, and molds the top plate side of the hat portion into the final shape by sandwiching it between the protrusion of the fixed die, and a second movable die configured to move in the height direction of the hat portion, and molds the pre-molded product, including the open end side of the hat portion, into the final shape by sandwiching it between the recess of the fixed die, and the first movable die is The second movable mold presses the pre-molded product against the recess of the fixed mold and then presses the pre-molded product against the protrusion of the fixed mold to form the final shape. The molding allowance consists of excess material formed so that the shoulder portions on both sides of the cap portion partially bulge outwards from the cap portion. The fixed mold has a lower mold for the main molding that cannot be moved, a wall fixed to the lower mold for the main molding that the tip surface of the flange portion abuts against, a protrusion fixed to the lower mold for the main molding that enters the cap portion, and a recess formed between the wall and the protrusion. The second movable mold is configured to move only in the height direction of the cap portion and parallel to the direction of movement of the first movable mold. The first movable mold may compress the excess material of the pre-molded product while the opening portion of the cap portion and the flange portion are constrained and their displacement restricted by the fixed mold and the second movable mold.

[0014] Furthermore, the press molding apparatus according to the present invention comprises a pre-molding die for molding a hat-shaped molded product having a flange portion at the open end of a hat portion, in which a pair of vertical plates are connected on both sides of a top plate via upwardly protruding excess material portions, such that molding allowances consisting of excess material portions remain on the shoulders on both sides of the hat portion; and a main molding die, different from the pre-molding die, for compressing the pre-molded product formed by the pre-molding die to form a molded product in the final shape, wherein the main molding die has a fixed die having a molding surface that integrally forms a wall against which the tip surface of the flange portion abuts, a protrusion that enters into the hat portion, and a groove recess formed between the wall and the protrusion, and molds the inner surface of the molded product in the final shape; and a fixed die configured to be movable in the height direction of the hat portion, with the top plate side of the hat portion being supported by the protrusion of the fixed die. The system includes a first movable mold that sandwiches the pre-molded product between itself and the fixed mold to form the final shape, and a second movable mold that is movable in the height direction of the hat portion and sandwiches the pre-molded product, including the open end side of the hat portion, between itself and the groove recess of the fixed mold to form the final shape. The first movable mold presses the top plate of the pre-molded product against the protrusion of the fixed mold while the second movable mold is pressing the flange and vertical plate of the pre-molded product against the groove recess of the fixed mold to form the final shape. As the first movable mold pushes the pre-molded product toward the fixed mold, a portion of the excess material may be moved toward the center of the top plate, causing the central part of the top plate to curve even more significantly, and the top plate and the excess material of the pre-molded product may be compressed while deforming into a corrugated shape.

[0015] In the present invention, in the press forming apparatus, the portions that form the connection between the vertical plate and the flange portion of the hat portion in the fixed die and the second movable die may each be formed by a rounded portion having a curved cross-sectional shape. In the present invention, in the press forming apparatus, a chamfered portion is formed at the tip of the wall of the fixed die, and the chamfered portion may be formed outside the movement trajectory of the flange portion that moves when the second movable die presses the pre-molded product against the fixed die. In the press molding apparatus of the present invention, the wall of the fixed mold is formed by a mold part separate from other parts of the fixed mold and is configured to be detachable, the boundary between the bottom surface of the recess and the wall is a right-angled shape, and the tip surface of the flange portion of the molded product of the final shape may be in contact with the wall without a gap.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a press molding method and a press molding apparatus capable of applying compressive stress to a workpiece with simple equipment to prevent springback.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a flowchart for explaining the press molding method according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a preformed product. [Figure 3] FIG. 3 is a cross-sectional view of a molded product of the final shape. [Figure 4] FIG. 4 is a cross-sectional view showing a mold for preforming. [Figure 5] FIG. 5 is an enlarged cross-sectional view showing a part of the mold for preforming. [Figure 6] FIG. 6 is a cross-sectional view showing a mold for main forming. [Figure 7] FIG. 7 is a cross-sectional view showing a punch of the mold for main forming. [Figure 8] FIG. 8 is an enlarged cross-sectional view showing a part of the fixed mold of the mold for main forming. [Figure 9] FIG. 9 is an enlarged cross-sectional view showing a part of the first movable mold. [Figure 10] FIG. 10 is an enlarged cross-sectional view showing one of the second movable molds. [Figure 11] FIG. 11 is a cross-sectional view of the mold for main forming showing the first main forming step. [Figure 12] FIG. 12 is a cross-sectional view of the mold for main forming showing the initial stage of the second main forming step. [Figure 13] Figure 13 is a cross-sectional view of the mold used for the main molding process, showing the state in which the second movable mold is pressing against the vertical plate during the second main molding process. [Figure 14] Figure 14 is a cross-sectional view of the mold used for the main molding process, showing the state after the second main molding process has been completed. [Figure 15] Figure 15 is a cross-sectional view showing an enlarged portion of the mold used for this molding process. [Figure 16] Figure 16 is a cross-sectional view of the mold used for the main molding process, showing the initial stage of the third main molding process. [Figure 17] Figure 17 is a cross-sectional view showing an enlarged portion of the mold used for this molding process. [Figure 18] Figure 18 is a schematic cross-sectional view of a molded product showing tensile and compressive stresses. [Figure 19] Figure 19 is a cross-sectional view of the mold used for the main molding process, showing the state after the third main molding process has been completed. [Modes for carrying out the invention]

[0018] Hereinafter, an embodiment of the press forming method and press forming apparatus according to the present invention will be described in detail with reference to Figures 1 to 19. The press forming method according to the present invention is a method in which a preforming process S1 and a main forming process S2 are carried out in this order, as shown in the flowchart of Figure 1. In the preforming process S1, a preformed product 1 as shown in Figure 2 is formed from a flat plate (not shown) made of high-tensile steel or ultra-high-tensile steel. The preformed product 1 is formed in a substantially hat shape in cross-section, having a cap portion 5 in which a pair of vertical plates 4 are connected to both sides of a top plate 2 via excess material portions 3, and flange portions 6 connected to the open ends of the cap portion 5. The excess material portions 3 are formed in a shape in which the shoulder portions 5a on both sides of the cap portion 5 partially bulge outwards from the cap portion 5. This preforming process S1 is carried out by a preforming die 11 (see Figure 4), which will be described later.

[0019] The molding process S2, as will be described in detail later, is a process in which the first to third molding processes S2A to S2C are carried out to form the final molded product 12 shown in Figure 3 from the pre-molded product 1. The final molded product 12 is a pre-molded product 1 whose deformation due to springback has been corrected, and is molded in a hat shape in cross-section, having a cap portion 15 consisting of a flat top plate 13 and linearly extending vertical plates 14 on both sides, and a pair of flange portions 16 connected to the open end of the cap portion 15.

[0020] In the final molded product 12, the shoulder portion 15a, which is the connection point between the top plate 13 and the vertical plate 14 of the cap portion 15, is formed in a circular arc shape in cross-section by crushing the excess material 3 that was provided in the pre-molded product 1. In addition, the connection point 15b between the vertical plate 14 and the flange portion 16 of the cap portion 15 is formed to have a concave curved surface when viewed from the front side of the molded product. The main molding process S2 is carried out using the main molding die 17 shown in Figures 6 and 7. The main molding die 17 and the pre-molding die 11 described above constitute the press molding apparatus 18 according to the present invention.

[0021] As shown in Figure 4, the pre-forming mold 11 includes a pre-forming punch 21 with a mountain-shaped cross-section for forming the inner surface of the pre-formed product 1, and a pair of pre-forming dies 22, 23 and a pre-forming pad 24 for forming the outer surface of the pre-formed product 1. The pre-forming punch 21 is fixed to the pre-forming lower die 25. The pre-forming lower die 25 is fixed to the base member 26. As shown in Figure 5, the tip of the pre-forming punch 21 has a flat portion 21a for forming the top plate 2 of the pre-formed product 1 and a bulging portion 21b for forming the excess material portion 3.

[0022] The pre-forming dies 22 and 23 form both sides of the excess material portion 3 of the pre-formed product 1, including the outer half, while the pre-forming pad 24 forms the inner half of the excess material portion 3 of the pre-formed product 1 and the top plate 2. The pre-forming dies 22, 23 and the pre-forming pad 24 have recesses 22a, 23a, and 24a formed between them and the bulging portion 21b of the pre-forming punch 21, which sandwich the pre-formed product 1.

[0023] The pre-forming dies 22, 23 and the pre-forming pad 24 are fixed to the pre-forming upper die 27. The pre-forming upper die 27 is configured to be movable in the height direction (up and down direction in Figure 4, and in the thickness direction of the top plate 2 and flange portion 6) of the cap portion 5 of the pre-formed product 1, and is driven by a pre-forming pressurizing device (not shown). During pre-forming, the pre-forming upper die 27 is driven downward by the pre-forming pressurizing device, and the pre-forming dies 22, 23 and the pre-forming pad 24 press the steel plate (not shown) against the pre-forming punch 21.

[0024] As shown in Figure 2, the pre-molded product 1 formed by this pre-molding mold 11 has excess material 3 remaining on both shoulder portions 5a of the hat portion 5, and springback occurs, causing the opening side of the hat portion 5 to expand outwards on both sides.

[0025] As shown in Figure 6, the mold 17 for this molding process includes a fixed mold 32, which includes the lower mold 31 shown at the bottom of Figure 6, and a movable mold 34, which includes the upper mold 33 shown at the top of Figure 6. The fixed mold 32 has a main forming punch 35 formed in a mountain-shaped cross-section, and a pair of restraining pieces 36 positioned on both sides of the main forming punch 35. The main forming punch 35 is a mold that forms the inner surface 15c (see Figure 3) of the cap portion 15 of the final molded product 12 and one surface 16a of the flange portion 16 connected to this inner surface 15c. The main forming punch 35 and the restraining pieces 36 are fixed to the lower forming mold 31. In other words, the fixed mold 32 is composed of the lower forming mold 31, the main forming punch 35, and the restraining pieces 36. The lower forming mold 31 is configured so that it cannot be moved.

[0026] As shown in Figure 7, the forming punch 35 has a first flat surface 35a, which is shown at the top in Figure 7, convex curved surfaces 35b connected to both sides of the flat surface 35a, an outer surface 35c, a first rounding portion 35d, a second flat surface 35e, and so on. The first plane 35a is a molding surface that forms the inner surface of the top plate 13 of the cap portion 15 of the final molded product 12. The convex curved surface 35b is a molding surface that forms the inner surfaces of both shoulder portions 15a of the cap portion 15. The outer surface 35c is a molding surface that forms the inner surface of the vertical plate 14. The first rounded portion 35d is a molding surface that forms the inner surface of the connection portion 15b between the vertical plate 14 and the flange portion 16 of the cap portion 15. The second plane 35e is a molding surface that forms the lower surface (one side 16a) of the flange portion 16. In this embodiment, the portion of the molding punch 35 from the first plane 35a to the outer surface 35c corresponds to the "convex portion of the fixed mold" as referred to in the present invention.

[0027] The first rounded portion 35d is formed by a concave curved surface with a curved cross-sectional shape. In this main forming punch 35, the first flat surface 35a, the convex curved surface 35b, the outer surface 35c, the first rounded portion 35d, and the second flat surface 35e form the forming surfaces that shape the inner surface of the final molded product 12. The restraining piece 36 is a wall against which the tip surface 16b (see Figure 3) of the flange portion 16 abuts during the molding process S2. It is formed as a separate mold component from the restraining piece 32 and protrudes from the second plane 35e of the molding punch 35 toward the upper molding die 33. The restraining piece 36 is detachably attached to the lower molding die 31. As shown in Figure 8, a chamfered portion 37 is formed on the tip (protruding end) of the restraining piece 36 adjacent to the main forming punch 35.

[0028] As shown in Figure 6, the movable mold 34 is constructed by assembling a first movable mold 38 and a pair of second movable molds 39 onto the main molding upper mold 33. The main molding upper mold 33 is configured to be movable in the height direction (up and down direction in Figure 6) of the cap portion 15 of the final molded product 12 and is connected to a molding pressurizing device (not shown). The first movable mold 38 forms the final shape of the hat portion 15 by sandwiching the top plate 13 side between it and the fixed mold 32 (main forming punch 35). It is fixed to the main forming upper mold 33 and can move in the height direction of the hat portion 15 together with the main forming upper mold 33. As shown in Figure 9, the first movable mold 38 has a third surface 38a that sandwiches the molded product between it and the first surface 35a of the main forming punch 35, a concave surface 38b that sandwiches the molded product between it and the convex curved surface 35b of the main forming punch 35, and an inner surface 38c that sandwiches the molded product between it and the outer surface 35c of the main forming punch 35.

[0029] The second movable mold 39 forms the final shape by sandwiching the open end of the cap portion 15 and the flange portion 16 between it and the fixed mold 32. In this embodiment, the second movable mold 39 is suspended from the first movable mold 38 by a plurality of spool retainers 43 so as to be movable vertically relative to the first movable mold 38. Note that a keeper plate (not shown) can be used instead of the spool retainers 43. The second movable mold 39 is also connected to the upper mold 33 via a gas spring 40. The gas spring 40 has a cylinder 40a fixed to the upper mold 33 and a piston rod 40b protruding from the cylinder 40a toward the lower mold 31. The piston rod 40b is biased toward the lower mold 31 by the pressure of the compressed gas in the cylinder 40a. The second movable mold 39 is attached to the tip of the piston rod 40b. In this embodiment, the gas spring 40 is attached to the main molding upper mold 33 with the cylinder 40a passing through the first movable mold 38. The spring force of the gas spring 40, that is, the pressing force that pushes the second movable mold 39 toward the main forming punch 35, is smaller than the pressing force that the main forming pressurizing device presses toward the main forming upper mold 33 toward the main forming punch 35 in the main forming process S2.

[0030] As shown in Figure 10, the second movable die 39 has a protrusion 41 that projects on the opposite side from the main upper mold 33, and an inner surface 39a that sandwiches the vertical plate 14 of the final molded product 12 between itself and the outer surface 35c of the main punch 35. The protrusion 41 is shaped to fit into a groove 42 (see Figure 8) formed by the main punch 35 and the restraining die 36. Specifically, the protrusion 41 has a second rounding portion 41a that sandwiches the molded product between itself and the first rounding portion 35d of the main punch 35, and a fourth flat surface 41b that sandwiches the molded product between itself and the second flat surface 35e of the main punch 35. The second rounding portion 41a is formed by a convex curved surface with a curved cross-sectional shape. In this embodiment, the groove 42 corresponds to the "recess" as referred to in the present invention. The fourth plane 41b is formed to be smaller than the flange portion 6 of the pre-molded product 1.

[0031] One side wall of the groove 42 is formed by a restraining die 36, which is separate from the main molding lower die 31 and the main molding punch 35. This allows a right-angle shape to be formed at the boundary between the bottom surface of the groove 42 and one side wall. In other words, the groove 42 can be formed so that there is no gap between the restraining wall 36 and the flange portion 6 of the pre-molded product 1 when obtaining the final molded product 12 from the pre-molded product 1, or in other words, so that the tip surface of the flange portion 6 abuts correctly against the restraining wall 36. Furthermore, since the main molding lower die 31 is configured not to move, the tip surface of the flange portion 6 abuts correctly against the restraining wall 36 more stably.

[0032] Next, the main molding process S2 for obtaining the final molded product 12 from the pre-molded product 1 using the main molding die 17 will be described. In order to mold the final molded product 12, first, the first main molding process S2A is performed. In the first main molding process S2A, as shown in Figure 11, the pre-molded product 1 is placed on the main molding punch 35. At this time, the main molding punch 35 is inserted into the cap portion 5 of the pre-molded product 1. The process of placing the pre-molded product 1 on the main molding punch 35 is the first main molding process S2A in the main molding process S2.

[0033] Due to springback, the flange portion 6 of the pre-molded product 1 separates significantly from the outer surface 35c of the main molding punch 35. After placing the pre-molded product 1 on the main molding punch 35, the main molding pressurizing device is operated to move the movable mold 34 toward the fixed mold 32, as shown in Figure 12. When the movable mold 34 moves in this manner, the second movable mold 39 first comes into contact with the vertical plate 4 of the cap portion 5 of the pre-molded product 1. As the movable mold 34 moves further, as shown in Figure 13, the second movable mold 39 begins to press the vertical plate 4 of the pre-molded product 1 against the outer surface 35c of the main molding punch 35. At this time, the second rounding portion 41a of the second movable mold 39 comes into contact with the vertical plate 4 and slides, pushing the vertical plate 4 toward the outer surface 35c of the main molding punch 35.

[0034] As the vertical plate 4 is pressed against the main forming punch 35, the flange portion 6 approaches the main forming punch 35. Then, as shown in Figure 14, the protrusion 41 of the second movable mold 39 is inserted into the groove 42 between the main forming punch 35 and the restraining die 36 and reaches the molding completion position, so that the opening portion of the cap portion 5 and the flange portion 6 are housed in the groove 42. The movement trajectory of the tip of the flange portion 6 at this time is shown by the dashed line L in Figure 15. That is, the tip of the flange portion 6 passes near the chamfered portion 37 on the groove side of the restraining die 36 and enters the groove 42 without contacting the restraining die 36. The tip surface of the protrusion 41 of the second movable mold 39 (the fourth plane 41b) is formed to be smaller than the flange portion 6. Therefore, when the protrusion 41 presses against the flange portion 6, the tip of the flange portion 6 is not supported by anything, and even if the flange portion 6 comes into contact with the chamfered portion 37 of the restraining piece 36, the tip of the flange portion 6 will slide on the chamfered portion 37 while bending.

[0035] The upper molding die 33 continues to move toward the fixed die 32 even after the second movable die 39 enters the groove 42. At this time, the second movable die 39 presses the opening portion of the cap portion 5 and the flange portion 6 against the fixed die 32 with the spring force of the gas spring 40. In this way, the opening portion of the cap portion 5 and the flange portion 6 are sandwiched between the second movable mold 39 and the fixed mold 32, thereby forming them into a shape close to the final shape. This process in which the opening portion of the cap portion 5 and the flange portion 6 are sandwiched between the fixed mold 32 and the second movable mold 39 constitutes the second main molding process S2B within the main molding process S2.

[0036] In the second main molding process S2B, when the second movable mold 39 presses the pre-molded product 1 against the fixed mold 32, a portion of the vertical plate 4 moves away towards the excess material portion 3. As a result, as shown in Figure 14, the top plate 2 of the cap portion 5 is pressed from both sides, and the central part of the top plate 2 deforms and curves upwards.

[0037] Subsequently, as the main molding upper die 33 moves further, the first movable die 38 comes into contact with the excess material 3 of the pre-molded product 1, as shown in Figure 16, and pushes it toward the main molding punch 35. This contact between the first movable die 38 and the pre-molded product 1 initiates the third main molding process S2C within the main molding process S2. The excess material portion 3 is deformed to become flat by being pressed by the first movable mold 38, and pushes the vertical plate 4 toward the opening side of the cap portion 5, as shown by arrow A in Figure 17. As the vertical plate 4 is pressed in this manner, the flange portion 6 connected to the vertical plate 4 is also pushed toward the tip side, as shown by arrow B.

[0038] Since the spring force of the gas spring 40 is less than the force with which the first movable mold 38 pushes the excess material 3, the flange portion 6 can be displaced toward the restraining piece 36 while being pushed by the second movable mold 39. When the flange portion 6 is displaced by being pushed from the vertical wall side, the tip surface 6a of the flange portion 6 comes into contact with the restraining piece 36, and further displacement of the flange portion 6 is restricted. In other words, the opening portion of the cap portion 5 and the flange portion 6 are restrained by the fixed mold 32 and the second movable mold 39. With the tip of the flange portion 6 in contact with the restraining piece 36, the second movable mold 39 sandwiches the pre-molded product 1 between itself and the fixed mold 32 and presses it. In this state, when the first movable mold 38 compresses the excess material portion 3 of the pre-molded product 1, the material flow from the excess material portion 3 extends to the flange portion 6, and the pre-molded product 1 can be molded so that its open shape becomes straight.

[0039] In the state immediately before the pre-molded product 1 is pressed by the first movable mold 38, tensile stress P1 and compressive stress P2 remain inside the top plate 2 and excess material 3 of the pre-molded product 1, as indicated by the arrows in Figure 18(A). That is, tensile stress P1 remains in the part that has been stretched by molding, and compressive stress P2 remains in the part that has been compressed by molding. When the first movable mold 38 pushes the pre-molded product 1 in this state toward the fixed mold 32, a part of the excess material 3 is moved toward the center of the top plate 2, and the central part of the top plate 2 is further curved, causing the top plate 2 and excess material 3 of the pre-molded product 1 to deform into a corrugated shape and be compressed.

[0040] Subsequently, as shown in Figure 19, the first movable mold 38 further pushes the pre-molded product 1, and with the pre-molded product 1 pressed against the fixed mold 32 by the second movable mold 39, the entire molding surface of the first movable mold 38 (the third flat surface 38a, the concave curved surface 38b, and the inner surface 38c) comes into close contact with the pre-molded product 1 and presses it against the main molding punch 35. As the first movable mold 38 comes into close contact with the premolded product 1, as shown in Figure 18(B), the portion of the premolded product 1's top plate 2 and excess material 3 that was stretched to generate tensile stress P1 is compressed (compressive stress P2 is applied). Conversely, the portion that was compressed to generate compressive stress P2 is stretched (tensile stress P1 is applied). In this process, as the top plate 2 and excess material 3 are deformed into a corrugated shape and compressed into their final shape, the tensile stress P1 and compressive stress P2 cancel each other out, and springback is suppressed.

[0041] In this way, the first movable mold 38 comes into close contact with the pre-molded product 1, causing compressive stress in the planar direction on the cap portion 5 and flange portion 6 of the pre-molded product 1, and the cap portion 5 and flange portion 6 are molded into the final cap portion 15 and flange portion 16. Here, "surface direction" refers to a direction perpendicular to the thickness direction, which is the left-right direction for the top plate 2 and flange portion 6 of the cap portion 5, and the up-down direction for the vertical plate 4. The third main molding process S2C ends when the first movable mold 38 can no longer move. After the third main molding process S2C is completed, the movable mold 34 moves away from the fixed mold 32, and the molded product 12 in its final shape is obtained. In the shoulder portion 15a of the molded product 12 in its final shape, and in the connection portion 15b between the vertical plate 14 and flange portion 16 of the cap portion 15, the tensile stress generated on the outer circumference of the curved portion is reduced. As a result, the occurrence of springback in the molded product 12 in its final shape is significantly suppressed.

[0042] Therefore, according to the press forming method and press forming apparatus 18 of this embodiment, the pre-molded product 1 can be compressed and the final molded product 12 formed by moving the first and second movable molds 38 and 39 only in the height direction of the hat portion 15. The press forming apparatus 18 of this embodiment does not use a cam mechanism that was used in conventional press forming apparatuses, so its structure is simplified. Therefore, according to this embodiment, it is possible to provide a press forming method and press forming apparatus that can apply compressive stress to a workpiece with simple equipment to prevent springback.

[0043] In this embodiment, the portion forming the connection 15b between the vertical plate 14 and the flange portion 16 of the cap portion 15 in the fixed mold 32 and the second movable mold 39 is formed by a first rounded portion 35d and a second rounded portion 41a, which have curved cross-sectional shapes. In the second main molding process S2B, as the second movable mold 39 moves to the molding completion position, the second rounded portion 41a of the second movable mold 39 pushes the vertical plate 4 of the pre-molded product 1 toward the fixed mold 32. As a result, the pre-molded product 1, which has expanded due to springback, can be molded by the second movable mold 39 so that it is narrowed toward the flange portion 6.

[0044] In this embodiment, a chamfered portion 37 is formed at the tip of the restraining piece 36. In the second main molding process S2B, the tip of the flange portion 6 passes in close proximity to the chamfered portion 37. Therefore, the restraining piece 36 can be positioned so that the flange portion 6 fits between it and the main molding punch 35, while avoiding interference between the flange portion 6 and the restraining piece 36. As a result, when the third main molding process S2C is performed, the final molded product 12 is reliably compressed, and the occurrence of springback can be further reduced.

[0045] In this embodiment, the restraining piece 36 is formed by a mold component separate from the restraining mold 32 and is configured to be detachable. The boundary between the bottom surface of the groove 42 and the restraining piece 36 is at a right angle. The tip surface of the flange portion 16 of the final molded product 12 abuts against the restraining wall 36 without any gaps. If the projection corresponding to the restraining piece 36 is formed integrally with the lower mold 31 for the main molding process, a rounded portion will be created at the boundary between the bottom surface of the groove 42 and the projection. In this case, the tip surface of the flange portion 16 cannot be brought against the wall in the third main molding process S2C, and the flange portion 16 of the final molded product 12 cannot be formed in the correct shape. However, as shown in this embodiment, by forming the restraining piece 36 separately from the other parts of the fixed mold 32, a wall (workpiece contact surface) that the tip surface of the flange portion 16 can contact without gaps can be easily formed by the right-angle forming portion. [Explanation of Symbols]

[0046] 1...Pre-molded product, 2,13...Top plate, 3...Excess material, 4,14...Vertical plate, 5,15...Cap part, 6,16...Flange part, 11...Die for pre-molding, 12...Final shaped molded product, 15a...Shoulder part, 15c...Inner surface of cap part, 17...Die for main molding, 18...Press molding device, 32...Fixed die, 35d,41a...Rounding part, 36...Constraining piece (wall), 37...Chamfered part, 38...First movable die, 39...Second movable die, S1...Pre-molding process, S2...Main molding process, S2A...First main molding process, S2B...Second main molding process, S2C...Third main molding process.

Claims

1. A pre-forming step involves forming a hat-shaped molded product, which has a flange portion at the open end of the hat portion consisting of a top plate and vertical plates on both sides, using a pre-forming die so that molding allowance remains on the shoulder portions on both sides of the hat portion. The process includes a main molding step in which the pre-molded product formed in the aforementioned pre-molding step is compressed by a mold for main molding to form a molded product in the final shape. The aforementioned mold for this molding process is A fixed mold having a wall against which the tip surface of the flange portion abuts, a protrusion that fits into the cap portion, and a recess formed between the wall and the protrusion, and having a molding surface for forming the inner surface of the final shaped molded product, A first movable mold is configured to be movable in the height direction of the hat portion, and the top plate side of the hat portion is sandwiched between the protrusion of the fixed mold to form the final shape, The system includes a second movable mold which is configured to be movable in the height direction of the hat portion and which molds the pre-molded product, including the open end side of the hat portion, into its final shape by sandwiching it between the fixed mold and the recess, The aforementioned molding process is, A first molding step involves placing the pre-molded product on the protrusion of the fixed mold, A second main molding step in which the pre-molded product is sandwiched between the recess of the fixed mold and the second movable mold, The process includes a third molding step in which, while the premolded product is pressed against the recess of the fixed mold by the second movable mold, the premolded product is molded into its final shape by the protrusion of the fixed mold and the first movable mold, In the fixed mold and the second movable mold, the portion that forms the connection between the vertical plate and the flange portion of the cap is formed by a rounded portion having a curved cross-sectional shape. In the second molding process described above, as the second movable mold moves to the molding completion position, the rounding portion of the second movable mold pushes the vertical plate of the pre-molded product toward the fixed mold, A chamfered portion is formed at the tip of the wall of the fixed mold. A press molding method characterized in that, in the second molding step described above, the tip portion of the flange portion passes a position close to the chamfered portion.

2. A pre-forming step involves forming a hat-shaped molded product, which has a flange portion at the open end of the hat portion consisting of a top plate and vertical plates on both sides, using a pre-forming die so that molding allowance remains on the shoulder portions on both sides of the hat portion. The process includes a main molding step in which the pre-molded product formed in the aforementioned pre-molding step is compressed by a mold for main molding to form a molded product in the final shape. The aforementioned mold for this molding process is A fixed mold having a wall against which the tip surface of the flange portion abuts, a protrusion that fits into the cap portion, and a recess formed between the wall and the protrusion, and having a molding surface for forming the inner surface of the final shaped molded product, A first movable mold is configured to be movable in the height direction of the hat portion, and the top plate side of the hat portion is sandwiched between the protrusion of the fixed mold to form the final shape, The system includes a second movable mold which is configured to be movable in the height direction of the hat portion and which molds the pre-molded product, including the open end side of the hat portion, into its final shape by sandwiching it between the fixed mold and the recess, The aforementioned molding process is, A first molding step involves placing the pre-molded product on the protrusion of the fixed mold, A second main molding step in which the pre-molded product is sandwiched between the recess of the fixed mold and the second movable mold, The process includes a third molding step in which, while the premolded product is pressed against the recess of the fixed mold by the second movable mold, the premolded product is molded into its final shape by the protrusion of the fixed mold and the first movable mold, The molding allowance is composed of excess material formed in such a way that the shoulder portions on both sides of the hat portion partially bulge outwards from the hat portion. The aforementioned fixed mold is The lower mold for this molding process cannot be moved, The wall fixed to the aforementioned lower mold for molding, and the tip surface of the flange portion abuts against the wall, The protrusion that is fixed to the lower mold and enters the hat portion, The wall and the protrusion have the recess formed between them, The second movable mold is configured to be movable only in the height direction of the hat portion and parallel to the movement direction of the first movable mold. A press molding method characterized in that, in the third main molding step, the opening portion of the cap portion and the flange portion are constrained and their displacement restricted by the fixed mold and the second movable mold, and the excess material portion of the pre-molded product is compressed by the first movable mold.

3. A pre-molding process in which a hat-shaped pre-molded product having a flange portion at the open end of a hat portion, in which a pair of vertical plates are connected via upwardly protruding excess material portions on both sides of the top plate, is formed using a pre-molding mold so that molding allowances consisting of excess material portions remain on the shoulders on both sides of the hat portion, The process includes a main molding step in which the pre-molded product formed in the pre-molding step is compressed using a main molding die different from the pre-molding die to form a molded product in the final shape. The aforementioned mold for this molding process is A fixed mold having a molding surface that integrally forms a wall against which the tip surface of the flange portion abuts, a protrusion that fits into the cap portion, and a recess formed between the wall and the protrusion, and which forms the inner surface of the final molded product, A first movable mold is configured to be movable in the height direction of the hat portion, and the top plate side of the hat portion is sandwiched between the protrusion of the fixed mold to form the final shape, The system includes a second movable mold which is configured to be movable in the height direction of the hat portion and which molds the pre-molded product, including the open end side of the hat portion, into its final shape by sandwiching it between the fixed mold and the recess, The aforementioned molding process is, A first molding step involves placing the pre-molded product on the protrusion of the fixed mold, A second main molding step in which the pre-molded product is sandwiched between the recess of the fixed mold and the second movable mold, The process includes a third molding step in which, while the flange portion and the vertical plate of the premolded product are pressed against the recess of the fixed mold by the second movable mold, the top plate of the premolded product is molded into its final shape by the convex portion of the fixed mold and the first movable mold. The third molding step is a press molding method characterized in that the first movable die pushes the pre-molded product toward the fixed die, thereby causing a portion of the excess material to be moved toward the center of the top plate, the central part of the top plate to curve even more, and the top plate and the excess material of the pre-molded product to be compressed while deforming into a corrugated shape.

4. In the press forming method according to claim 2 or claim 3, In the fixed mold and the second movable mold, the portion that forms the connection between the vertical plate and the flange portion of the cap is formed by a rounded portion having a curved cross-sectional shape. A press molding method characterized in that, in the second main molding step, the rounding portion of the second movable mold pushes the vertical plate of the pre-molded product toward the fixed mold as the second movable mold moves to the molding completion position.

5. In the press forming method described in claim 4, A chamfered portion is formed at the tip of the wall of the fixed mold. A press molding method characterized in that, in the second molding step described above, the tip portion of the flange portion passes a position close to the chamfered portion.

6. In the press forming method according to any one of claims 1 to 3, The wall of the fixed mold is formed by a mold component separate from the other parts of the fixed mold and is configured to be detachable. A press molding method characterized in that the boundary between the bottom surface of the recess and the wall is at a right angle, and in the third main molding step, the tip surface of the flange portion abuts against the wall without any gaps.

7. A pre-molding mold for forming a hat-shaped molded product with a flange portion at the open end of the hat portion, which consists of a top plate and vertical plates on both sides, such that a molding allowance remains on the shoulder portions on both sides of the hat portion, The system includes a main molding die that compresses a pre-molded product formed by the aforementioned pre-molding die to form a final-shaped molded product. The aforementioned mold for this molding process is A fixed mold having a wall against which the tip surface of the flange portion abuts, a protrusion that fits into the cap portion, and a recess formed between the wall and the protrusion, and having a molding surface for forming the inner surface of the final shaped molded product, A first movable mold is configured to be movable in the height direction of the hat portion, and the top plate side of the hat portion is sandwiched between the protrusion of the fixed mold to form the final shape, The system includes a second movable mold which is configured to be movable in the height direction of the hat portion and which molds the pre-molded product, including the open end side of the hat portion, into its final shape by sandwiching it between the fixed mold and the recess, The first movable mold presses the pre-molded product against the convex portion of the fixed mold while the second movable mold is pressing the pre-molded product against the concave portion of the fixed mold to form the final shape. A chamfered portion is formed at the tip of the wall of the fixed mold. The press molding apparatus is characterized in that the chamfered portion is formed outside the movement trajectory of the flange portion, which moves when the second movable mold presses the pre-molded product against the fixed mold.

8. A pre-molding mold for forming a hat-shaped molded product with a flange portion at the open end of the hat portion, which consists of a top plate and vertical plates on both sides, such that a molding allowance remains on the shoulder portions on both sides of the hat portion, The system includes a main molding die that compresses a pre-molded product formed by the aforementioned pre-molding die to form a final-shaped molded product. The aforementioned mold for this molding process is A fixed mold having a wall against which the tip surface of the flange portion abuts, a protrusion that fits into the cap portion, and a recess formed between the wall and the protrusion, and having a molding surface for forming the inner surface of the final shaped molded product, A first movable mold is configured to be movable in the height direction of the hat portion, and the top plate side of the hat portion is sandwiched between the protrusion of the fixed mold to form the final shape, The system includes a second movable mold which is configured to be movable in the height direction of the hat portion and which molds the pre-molded product, including the open end side of the hat portion, into its final shape by sandwiching it between the fixed mold and the recess, The first movable mold presses the pre-molded product against the convex portion of the fixed mold while the second movable mold is pressing the pre-molded product against the concave portion of the fixed mold to form the final shape. The molding allowance is composed of excess material formed in such a way that the shoulder portions on both sides of the hat portion partially bulge outwards from the hat portion. The aforementioned fixed mold is The lower mold for this molding process cannot be moved, The wall fixed to the aforementioned lower mold for molding, and the tip surface of the flange portion abuts against the wall, The protrusion that is fixed to the lower mold and enters the hat portion, The wall and the protrusion have the recess formed between them, The second movable mold is configured to be movable only in the height direction of the hat portion and parallel to the movement direction of the first movable mold. A press molding apparatus characterized in that the first movable die compresses the excess material portion of the pre-molded product while the opening portion of the cap portion and the flange portion are constrained and their displacement is restricted by the fixed die and the second movable die.

9. A pre-molding mold for forming a hat-shaped molded product having a flange portion at the open end of a hat portion, in which a pair of vertical plates are connected on both sides of the top plate via upwardly protruding excess material portions, such that a molding allowance consisting of excess material portions remains on the shoulders on both sides of the hat portion, The system includes a main molding die, which is different from the pre-molding die, for compressing a pre-molded product formed by the aforementioned pre-molding die to form a final-shaped molded product. The aforementioned mold for this molding process is A fixed mold having a molding surface that integrally forms a wall against which the tip surface of the flange portion abuts, a protrusion that fits into the cap portion, and a recess formed between the wall and the protrusion, and which forms the inner surface of the final molded product, A first movable mold is configured to be movable in the height direction of the hat portion, and the top plate side of the hat portion is sandwiched between the protrusion of the fixed mold to form the final shape, The system includes a second movable mold which is configured to be movable in the height direction of the hat portion and which molds the pre-molded product, including the open end side of the hat portion, into its final shape by sandwiching it between the fixed mold and the recess, The first movable mold presses the top plate of the premolded product against the protrusion of the fixed mold while the second movable mold is pressing the flange portion and the vertical plate of the premolded product against the recess of the fixed mold to form the final shape. A press molding apparatus characterized in that the first movable die pushes the preformed product toward the fixed die, thereby causing a portion of the excess material to be moved toward the center of the top plate, the central part of the top plate to curve even more, and the top plate and the excess material of the preformed product to be compressed while deforming into a corrugated shape.

10. In a press molding apparatus according to any one of claims 7 to 9, A press molding apparatus characterized in that the portions that form the connection between the vertical plate and the flange portion of the hat portion in the fixed mold and the second movable mold are each formed by rounded portions having a curved cross-sectional shape.

11. In the press molding apparatus according to claim 8 or claim 9, A chamfered portion is formed at the tip of the wall of the fixed mold. The press molding apparatus is characterized in that the chamfered portion is formed outside the movement trajectory of the flange portion, which moves when the second movable mold presses the pre-molded product against the fixed mold.

12. In a press molding apparatus according to any one of claims 7 to 9, The wall of the fixed mold is formed by a mold component separate from the other parts of the fixed mold and is configured to be detachable. A press molding apparatus characterized in that the boundary between the bottom surface of the recess and the wall is at a right angle, and the leading surface of the flange portion of the final molded product abuts the wall without any gap.

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