Press-forming device

Abstract

This press-forming device comprises: a preforming die for forming a preformed product (1) having a hat-shaped cross section; and a main forming die (17) for forming a formed product having a final shape from the preformed product. The main forming die includes: a fixed die (32) having a wall (36) against which a tip end surface of a flange portion of the formed product abuts; a first movable die (38) for forming a hat portion (5) of the formed product; and a second movable die (39) for sandwiching the preformed product between the second movable die (39) and a recessed portion of the fixed die to perform forming of the preformed product. The first movable die forms the preformed product into the final shape in a state in which the second movable die is pressing the preformed product against the recessed portion. The pressing force of the second movable die is smaller than the pressing force of the first movable die. A chamfered portion (37) is formed on a tip end portion of the wall of the fixed die. The chamfered portion is formed outside a movement path of the flange portion that moves during forming.　It is thus possible to provide a press-forming device capable of preventing spring-back by imparting compressive stress to a workpiece using simple equipment.

Description

Press forming equipment

[0001] The present invention relates to a press-forming device for bending a steel sheet into a hat-shaped cross section.

[0002] In recent years, ultra-high tensile steel, which has a tensile strength exceeding 1000 MPa and is stronger than high tensile steel, has come to be used as the steel material for automobile bodies. This type of ultra-high tensile steel is cold-bent to form a desired shape. Ultra-high tensile steel has a larger amount of springback after bending than ordinary high tensile steel. For this reason, in the past, molds were re-machined to anticipate springback and obtain the target dimensional accuracy.

[0003] Re-machining a die requires a significant amount of labor, and if re-machining is not sufficient, the die may need to be remade. This increases the amount of iron used due to die re-machining, which is unhealthy for the environment. To minimize such die modifications, a press-forming method has been developed in which forming is performed multiple times to correct springback and achieve the final shape. A conventional press-forming method for correcting springback is described, for example, in Patent Document 1. The press-forming method described in Patent Document 1 is a method for forming a steel sheet 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 consisting of a top plate and vertical plates on both sides. The press-forming method described in Patent Document 1 employs a configuration in which, when forming a steel sheet into a hat-shaped cross section, the formed product is formed into the final shape through two processes: a pre-forming process and a main forming process.

[0004] In the preforming process, a hat-shaped cross-section preform is formed while allowing springback to occur. This forming process involves pressing the vertical walls and flanges on both ends of the preform from the side against a punch, which is a fixed mold, using a horizontally movable die, while the hat portion is sandwiched between a pad and the punch to form the preform, compressing it into its final shape. Compressing the preform suppresses springback. The horizontally movable die is driven in conjunction with the pad that forms the hat portion, converting the vertical movement of the upper mold including the pad into horizontal movement using a cam mechanism.

[0005] Japanese Patent Application Laid-Open No. 2022-39327

[0006] The molding method disclosed in Patent Document 1 requires a cam mechanism to drive the laterally moving die, which causes problems in that the mold becomes complicated and large in size.

[0007] An object of the present invention is to provide a press-forming device that can apply compressive stress to a workpiece and prevent springback using simple equipment.

[0008] In order to achieve this object, the press forming apparatus according to the present invention comprises a preforming die for forming a hat-shaped cross-sectioned product having a flange at the opening end of a hat portion consisting of a top plate and vertical plates on both sides, with forming allowances remaining on both shoulders of the hat portion, and a main forming die for compressing the preform formed by the preforming die to form a final shaped product, the main forming die having a wall against which the tip surface of the flange abuts, a convex portion that fits into the hat portion, and a concave portion formed between the wall and the convex portion, and a fixed die having a forming surface for forming the inner surface of the final shaped product, and a front side die configured to be movable in the height direction of the hat portion, The molding machine includes a first movable mold which sandwiches the top plate side of the hat portion between it and the convex portion of the fixed mold to mold it into a final shape, and a second movable mold which is configured to be movable in the height direction of the hat portion and sandwiches the preform including the open end side of the hat portion between it and the concave portion of the fixed mold to mold it into a final shape, wherein the first movable mold presses the preform against the convex portion of the fixed mold to mold it into a final shape while the second movable mold presses the preform against the concave portion of the fixed mold, and the pressing force used by the second movable mold to press the preform is smaller than the pressing force used by the first movable mold to press the preform, and a chamfered portion is formed at the tip of the wall of the fixed mold, and the chamfered portion is formed outside the moving trajectory of the flange portion which moves when the second movable mold presses the preform against the fixed mold.

[0009] According to the present invention, it is possible to provide a press-forming device that can apply compressive stress to a workpiece and prevent springback using simple equipment.

[0010] FIG. 1 is a flowchart illustrating a press forming method performed by a press forming apparatus according to the present invention. FIG. 2 is a cross-sectional view of a preformed product. FIG. 3 is a cross-sectional view of a molded product in its final shape. FIG. 4 is a cross-sectional view of a preformed mold. FIG. 5 is a cross-sectional view showing an enlarged portion of the preformed mold. FIG. 6 is a cross-sectional view of a mold for main forming. FIG. 7 is a cross-sectional view showing a punch of the main forming mold. FIG. 8 is a cross-sectional view showing an enlarged portion of a fixed mold of the main forming mold. FIG. 9 is a cross-sectional view showing an enlarged portion of a first movable mold. FIG. 10 is a cross-sectional view showing an enlarged portion of one of the second movable molds. FIG. 11 is a cross-sectional view of a main forming mold showing a first main forming step. FIG. 12 is a cross-sectional view of a main forming mold showing an initial stage of a second main forming step. FIG. 13 is a cross-sectional view of a main forming mold showing a state in which the second movable mold is pressing a vertical plate in the second main forming step. FIG. 14 is a cross-sectional view of a main forming mold showing a state in which the second main forming step has been completed. Fig. 15 is a cross-sectional view showing an enlarged portion of the mold for main molding. Fig. 16 is a cross-sectional view of the mold for main molding showing an early stage of the third main molding step. Fig. 17 is a cross-sectional view showing an enlarged portion of the mold for main molding. Fig. 18A is a cross-sectional view of a portion of a molded product schematically showing tensile stress and compressive stress. Fig. 18B is a cross-sectional view of a portion of a molded product schematically showing tensile stress and compressive stress. Fig. 19 is a cross-sectional view of the mold for main molding showing a state after the third main molding step has been completed.

[0011] An embodiment of a press-forming apparatus according to the present invention will now be described in detail with reference to FIGS. 1 to 19 . The press-forming method performed by the press-forming apparatus of the present invention involves a preforming step S1 and a main forming step S2, performed in this order, as shown in the flowchart of FIG. 1 . In the preforming step S1, a preform 1, as shown in FIG. 2 , is formed from a flat plate (not shown) made of high-tensile steel or ultra-high-tensile steel. The preform 1 has a generally hat-shaped cross section, including a hat portion 5 formed by connecting a pair of vertical plates 4 to both sides of a top plate 2 via pad portions 3, and flange portions 6 connected to the open ends of the hat portion 5. The pad portions 3 are formed so that shoulder portions 5 a on both sides of the hat portion 5 partially bulge outward from the hat portion 5. This preforming step S1 is performed using a preforming mold 11 (see FIG. 4 ), which will be described later.

[0012] The main forming step S2, which will be described in detail later, is a step in which the preform 1 is formed into a formed product 12 of the final shape shown in Fig. 3 by carrying out first to third main forming steps S2A to S2C. The formed product 12 of the final shape is formed by correcting deformation of the preform 1 due to springback, and is formed into a hat-shaped cross section having a hat portion 15 consisting of a flat top plate 13 and vertical plates 14 extending linearly on both sides, and a pair of flange portions 16 connected to the open end of the hat portion 15.

[0013] In the final shaped molded product 12, the shoulder portion 15a, which is the connection portion between the top plate 13 and the vertical plate 14 of the hat portion 15, is formed into an arc-shaped cross section by crushing the excess pad portion 3 that was provided in the preformed product 1. In addition, the connection portion 15b between the vertical plate 14 and the flange portion 16 of the hat portion 15 is formed so as to have a concave curved surface when viewed from the front side of the molded product. The main molding step S2 is performed using a main molding die 17 shown in Figures 6 and 7. The main molding die 17 and the above-mentioned preforming die 11 constitute a press molding apparatus 18 according to the present invention.

[0014] As shown in Fig. 4, the preforming die 11 includes a preforming punch 21 having a mountain-shaped cross section for forming the inner surface of the preform 1, a pair of preforming dies 22 and 23 for forming the outer surface of the preform 1, and a preforming pad 24. The preforming punch 21 is fixed to a preforming lower die 25. The preforming lower die 25 is fixed to a base member 26. As shown in Fig. 5, the tip of the preforming punch 21 is formed with a flat plate portion 21a for forming the top plate 2 of the preform 1 and a bulge portion 21b for forming the excess pad portion 3.

[0015] The preforming dies 22, 23 are used to form both side portions including the outer half of the excess pad 3 of the preform 1, and the preforming pad 24 is used to form the inner half of the excess pad 3 and the top plate 2 of the preform 1. The preforming dies 22, 23 and the preforming pad 24 are formed with recesses 22a, 23a, 24a that sandwich the preform 1 between them and the bulging portion 21b of the preforming punch 21.

[0016] The preforming dies 22, 23 and the preforming pad 24 are fixed to a preforming upper die 27. The preforming upper die 27 is configured to be movable in the height direction of the hat portion 5 of the preform 1 (vertical direction in FIG. 4 , that is, the thickness direction of the top plate 2 and flange portion 6) and is driven by a preforming pressure device (not shown). During preforming, the preforming upper die 27 is driven downward by the preforming pressure device, and the preforming dies 22, 23 and the preforming pad 24 press the steel plate (not shown) against the preforming punch 21.

[0017] In the preform 1 formed by this preforming mold 11, as shown in FIG. 2, the forming allowances in the form of excess pads 3 remain on both shoulders 5a of the hat portion 5, and springback occurs, causing the opening sides of the hat portion 5 to expand outward in both directions.

[0018] As shown in FIG. 6, the mold 17 for final molding includes a fixed mold 32 including a lower mold 31 for final molding, which is depicted at the bottom in FIG. 6, and a movable mold 34 including an upper mold 33 for final molding, which is depicted at the top in FIG. 6. The fixed mold 32 includes a punch 35 for final molding formed with a mountain-shaped cross section and a pair of restraining pieces 36 arranged on either side of the punch 35 for final molding. The punch 35 for final molding is a mold that forms the inner surface 15c (see FIG. 3) of the cap portion 15 of the molded product 12 in its final shape and one surface 16a of the flange portion 16 connected to this inner surface 15c. The punch 35 and the restraining pieces 36 are fixed to the lower mold 31 for final molding. In other words, the fixed mold 32 is composed of the lower mold 31 for final molding, the punch 35, and the restraining pieces 36. The lower mold 31 for final molding is configured so as not to be movable.

[0019] As shown in Figure 7, the forming punch 35 has a first flat surface 35a (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 rounded portion 35d, and a second flat surface 35e. The first flat surface 35a is a forming surface that forms the inner surface of the top plate 13 of the hat portion 15 of the final formed product 12. The convex curved surface 35b is a forming surface that forms the inner surfaces of both shoulder portions 15a of the hat portion 15. The outer surface 35c is a forming surface that forms the inner surface of the vertical plate 14. The first rounded portion 35d is a forming surface that forms the inner surface of the connecting portion 15b between the vertical plate 14 of the hat portion 15 and the flange portion 16. The second flat surface 35e is a forming surface that forms the lower surface (one surface 16a) of the flange portion 16. In this embodiment, the portion of the main forming punch 35 extending from the first flat surface 35a to the outer surface 35c corresponds to the "protrusion of the fixed die" of the present invention.

[0020] The first rounding portion 35d is formed by a concave surface that forms a curved cross-sectional shape. In the final-forming punch 35, the first flat surface 35a, the convex curved surface 35b, the outer surface 35c, the first rounding portion 35d, and the second flat surface 35e form the forming surfaces that form the inner surface of the final-shaped product 12. The restraining piece 36 serves as a wall against which the tip surface 16b (see FIG. 3) of the flange portion 16 abuts in the final-forming step S2. It is formed as a mold component separate from the rest of the fixed mold 32 and protrudes toward the final-forming upper mold 33 beyond the second flat surface 35e of the final-forming punch 35. The restraining piece 36 is detachably attached to the final-forming lower mold 31. A chamfered portion 37 is formed at the tip (protruding end) of the restraining piece 36 adjacent to the final-forming punch 35, as shown in FIG. 8.

[0021] As shown in Fig. 6, the movable mold 34 is constructed by assembling a first movable mold 38 and a pair of second movable molds 39 to a main-forming upper mold 33. The main-forming upper mold 33 is configured to be movable in the height direction of the hat portion 15 of the molded product 12 in its final shape (up and down direction in Fig. 6), and is connected to a main-forming pressure device (not shown). The first movable mold 38 is used to sandwich the top plate 13 side of the hat portion 15 between itself and the fixed mold 32 (main-forming punch 35) to mold it into its final shape. The first movable mold 38 is fixed to the main-forming upper mold 33 and can move integrally with the main-forming upper mold 33 in the height direction of the hat portion 15. As shown in Figure 9, the first movable mold 38 is formed with a third flat surface 38a that sandwiches the molded product between itself and the first flat surface 35a of the main molding punch 35, a concave curved surface 38b that sandwiches the molded product between itself and the convex curved surface 35b of the main molding punch 35, and an inner surface 38c that sandwiches the molded product between itself and the outer surface 35c of the main molding punch 35.

[0022] The second movable mold 39 sandwiches the open end of the hat portion 15 and the flange portion 16 between itself and the fixed mold 32 to form the final shape. 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 vertically movable relative to the first movable mold 38. A keeper plate (not shown) may be used instead of the spool retainers 43. The second movable mold 39 is connected to the main molding upper mold 33 via a gas spring 40. The gas spring 40 has a cylinder 40a fixed to the main molding upper mold 33 and a piston rod 40b protruding from the cylinder 40a toward the main molding lower mold 31. The piston rod 40b is urged toward the main molding lower mold 31 by the pressure of compressed gas in the cylinder 40a. The second movable mold 39 is attached to the tip of the piston rod 40b. The gas spring 40 according to this embodiment is attached to the main-forming upper die 33 with its cylinder 40a passing through the first movable die 38. The spring force of the gas spring 40, i.e., the pressing force with which the second movable die 39 is pressed toward the main-forming punch 35, is smaller than the pressing force with which the main-forming pressure device presses the main-forming upper die 33 toward the main-forming punch 35 in the main-forming step S2.

[0023] As shown in FIG. 10 , the second movable mold 39 has a convex portion 41 protruding away from the main-forming upper mold 33 and an inner surface 39a that sandwiches the vertical plate 14 of the final-shaped molded product 12 between itself and the outer surface 35c of the main-forming punch 35. The convex portion 41 is shaped to fit into a groove 42 (see FIG. 8 ) formed by the main-forming punch 35 and the restraining piece 36. That is, the convex portion 41 has a second rounding portion 41a that sandwiches the molded product between itself and the first rounding portion 35d of the main-forming punch 35, and a fourth flat surface 41b that sandwiches the molded product between itself and the second flat surface 35e of the main-forming punch 35. The second rounding portion 41a is formed by a convex curved surface that has a curved cross-sectional shape. In this embodiment, the groove 42 corresponds to the “recess” defined in the present invention. The fourth flat surface 41b is shaped to be smaller than the flange portion 6 of the preform 1.

[0024] One side wall of the groove 42 is formed by a restraining piece 36 that is separate from the main-forming lower die 31 and the main-forming punch 35. This allows a right-angled shape to be formed at the boundary between the bottom surface of the groove 42 and one side wall. That is, the groove 42 can be formed so that no gap is generated between the restraining wall 36 and the flange portion 6 of the preformed product 1 when obtaining the final shaped molded product 12 from the preformed product 1; in other words, so that the leading end surface of the flange portion 6 properly abuts against the restraining wall 36. Furthermore, because the main-forming lower die 31 is configured to be immovable, the leading end surface of the flange portion 6 properly abuts against the restraining wall 36 more stably.

[0025] Next, the main forming step S2 for obtaining the final shaped molded product 12 from the preform 1 using the main forming mold 17 will be described. To form the final shaped molded product 12, a first main forming step S2A is first carried out. In the first main forming step S2A, the preform 1 is placed on a main forming punch 35, as shown in Fig. 11 . At this time, the main forming punch 35 is inserted into the cap portion 5 of the preform 1. The step of placing the preform 1 on the main forming punch 35 is the first main forming step S2A of the main forming step S2.

[0026] Due to springback of the preform 1, the flange portion 6 is separated significantly from the outer surface 35c of the main-forming punch 35. After the preform 1 is placed on the main-forming punch 35, the main-forming pressure device is operated to move the movable die 34 toward the fixed die 32, as shown in FIG. 12. As the movable die 34 moves in this manner, the second movable die 39 first comes into contact with the vertical plate 4 of the cap portion 5 of the preform 1. As the movable die 34 moves further, the second movable die 39 presses the vertical plate 4 of the preform 1 against the outer surface 35c of the main-forming punch 35, as shown in FIG. 13. At this time, the second rounding portion 41a of the second movable die 39 slides in contact with the vertical plate 4, pushing the vertical plate 4 toward the outer surface 35c of the main-forming punch 35.

[0027] As the vertical plate 4 is pressed against the final-forming punch 35, the flange portion 6 approaches the final-forming punch 35. Then, as shown in Fig. 14, the convex portion 41 of the second movable mold 39 is inserted into the groove 42 between the final-forming punch 35 and the restraining piece 36 and reaches the forming end position, whereby the opening of the cap portion 5 and the flange portion 6 are accommodated in the groove 42. The movement trajectory of the tip of the flange portion 6 at this time is shown by the two-dot chain line L in Fig. 15. That is, the tip of the flange portion 6 passes near the chamfered portion 37 on the groove side of the restraining piece 36 and enters the groove 42 without coming into contact with the restraining piece 36. The tip surface (fourth flat surface 41b) of the convex portion 41 of the second movable mold 39 is formed to be smaller than the flange portion 6. Therefore, when the convex portion 41 presses the flange portion 6, the tip side 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 slides on the chamfered portion 37 while bending.

[0028] The main molding upper mold 33 continues to move toward the fixed mold 32 even after the second movable mold 39 has entered the groove 42. At this time, the second movable mold 39 presses the opening portion and flange portion 6 of the cap portion 5 against the fixed mold 32 by the spring force of the gas spring 40. By sandwiching the opening portion and flange portion 6 of the cap portion 5 between the second movable mold 39 and the fixed mold 32 in this way, they are molded into a shape close to the final shape. The process in which the opening portion and flange portion 6 of the cap portion 5 are sandwiched between the fixed mold 32 and the second movable mold 39 in this way constitutes the second main molding step S2B of the main molding step S2.

[0029] When the second movable mold 39 presses the preform 1 against the fixed mold 32 in the second main molding step S2B, part of the vertical plate 4 moves toward the excess pad 3. As a result, as shown in Fig. 14, the top plate 2 of the cap portion 5 is pressed from both sides, and the central portion of the top plate 2 is deformed and curved so as to be convex upward.

[0030] Thereafter, as the main-forming upper die 33 moves further, the first movable die 38 comes into contact with the excess pad 3 of the preform 1 and presses it toward the main-forming punch 35, as shown in Fig. 16. When the first movable die 38 comes into contact with the preform 1 in this manner, the third main-forming step S2C of the main-forming step S2 is initiated. When the excess pad 3 is pressed by the first movable die 38, it is deformed so as to be flat, and presses the vertical plate 4 toward the opening of the cap portion 5, as shown by arrow A in Fig. 17. When the vertical plate 4 is pressed in this manner, the flange portion 6 connected to the vertical plate 4 is also pressed toward the tip side, as shown by arrow B.

[0031] Because the spring force of the gas spring 40 is smaller than the force with which the first movable mold 38 presses the excess pad 3, the flange 6 can be displaced toward the restraining piece 36 while being pressed by the second movable mold 39. When the flange 6 is displaced by being pressed from the vertical wall side, the tip surface 6a of the flange 6 abuts against the restraining piece 36, restricting further displacement of the flange 6. In other words, the opening of the cap portion 5 and the flange 6 are restrained by the fixed mold 32 and the second movable mold 39. With the tip of the flange 6 abutting against the restraining piece 36 in this manner, the second movable mold 39 sandwiches and presses the preform 1 between itself and the fixed mold 32. When the excess pad 3 of the preform 1 is compressed by the first movable mold 38 in this state, the material flow from the excess pad 3 reaches the flange 6, and the preform 1 can be molded so that the open shape of the preform 1 is straight.

[0032] Just before the preformed article 1 is pressed by the first movable mold 38, tensile stress P1 and compressive stress P2 remain inside the top plate 2 and excess pad 3 of the preformed article 1, as shown by the arrows in Fig. 18A. That is, tensile stress P1 remains in the portion that has been stretched by molding, and compressive stress P2 remains in the portion that has been compressed by molding. When the first movable mold 38 presses the preformed article 1 in this state toward the fixed mold 32, a portion of the excess pad 3 is moved toward the center of the top plate 2, causing the central portion of the top plate 2 to bend even more significantly, and the top plate 2 and excess pad 3 of the preformed article 1 are compressed while being deformed into a corrugated shape.

[0033] 19, the first movable die 38 further presses the preformed product 1, and while the preformed product 1 is being pressed against the fixed die 32 by the second movable die 39, the entire molding surface (third flat surface 38a, concave curved surface 38b, and inner surface 38c) of the first movable die 38 comes into close contact with the preformed product 1 and presses it against the main molding punch 35. By the first movable die 38 coming into close contact with the preformed product 1, the portions of the top plate 2 and excess pad 3 of the preformed product 1 that had been stretched to generate tensile stress P1 are compressed (compressive stress P2 acts on them) as shown in FIG. 18B. Furthermore, the portions that had been compressed to generate compressive stress P2 are stretched (tensile stress P1 acts on them). During this process in which the top plate 2 and excess pad 3 are deformed into a corrugated shape and compressed into their final shape, i.e., during the deformation and compression process, the tensile stress P1 and compressive stress P2 cancel each other out, thereby suppressing springback.

[0034] By closely contacting the first movable mold 38 with the preform 1 in this manner, the hat portion 5 and flange portion 6 of the preform 1 are molded into the final hat portion 15 and flange portion 16 while compressive stress is generated in the surface direction in the hat portion 5 and flange portion 6 of the preform 1. The "surface direction" here refers to a direction perpendicular to the thickness direction, i.e., the left-right direction in the top plate 2 and flange portion 6 of the hat portion 5, and the up-down direction in the vertical plate 4. The third main molding step S2C ends when the first movable mold 38 can no longer move. After the third main molding step S2C is completed, the movable mold 34 moves away from the fixed mold 32, and the final molded product 12 is obtained. Tensile stress generated on the outer periphery of the curved portion is reduced in the shoulder portion 15a of the final molded product 12 and in the connection portion 15b between the vertical plate 14 and flange portion 16 of the hat portion 15. Therefore, the final molded product 12 has significantly reduced springback.

[0035] Therefore, according to the press-forming method and press-forming apparatus 18 of this embodiment, the preform 1 can be compressed to form the final shaped formed product 12 by moving the first and second movable dies 38, 39 only in the height direction of the hat portion 15. The press-forming apparatus 18 of this embodiment does not use the cam mechanism used in conventional press-forming apparatuses, and therefore has a simple structure. Therefore, according to this embodiment, it is possible to provide a press-forming method and press-forming apparatus that can apply compressive stress to the workpiece and prevent springback with simple equipment.

[0036] In this embodiment, the portions of the fixed mold 32 and the second movable mold 39 that form the connection portion 15b between the vertical plate 14 of the hat portion 15 and the flange portion 16 are formed by a first rounded portion 35d and a second rounded portion 41a, each of which has a curved cross-sectional shape. In the second main forming step S2B, as the second movable mold 39 moves to the forming end position, the second rounded portion 41a of the second movable mold 39 presses the vertical plate 4 of the preform 1 toward the fixed mold 32. Therefore, the preform 1, which has expanded due to springback, can be formed by the second movable mold 39 so as to be squeezed toward the flange portion 6.

[0037] In this embodiment, a chamfered portion 37 is formed at the tip of the restraining piece 36. In the second main forming step S2B, the tip of the flange portion 6 passes close to the chamfered portion 37. This allows the restraining piece 36 to be positioned so that the flange portion 6 fits between the main forming punch 35 while avoiding interference between the flange portion 6 and the restraining piece 36. This ensures that the final shape of the formed product 12 is compressed reliably when the third main forming step S2C is performed, further reducing the occurrence of springback.

[0038] In this embodiment, the restraining piece 36 is formed as a mold part separate from the other parts of the fixed mold 32 and is configured to be detachable. The boundary between the bottom surface of the groove 42 and the restraining piece 36 is right-angled. The leading end surface of the flange portion 16 of the molded product 12 in its final shape abuts the restraining wall 36 without any gap. If a protrusion corresponding to the restraining piece 36 were integrally formed on the lower mold for final molding 31, a rounded portion would be formed at the boundary between the bottom surface of the groove 42 and the protrusion. In this case, the leading end surface of the flange portion 16 would not be able to abut the wall in the third final molding step S2C, and the flange portion 16 of the molded product 12 in its final shape would not be formed in the correct shape. However, by forming the restraining piece 36 separately from the other parts of the fixed mold 32 as shown in this embodiment, the right-angled portion makes it easy to form a wall (workpiece abutment surface) against which the leading end surface of the flange portion 16 abuts without any gap.

[0039] (Additional Note) The features of the press-forming method and press-forming apparatus according to the above-described embodiment can be described in the form of claims as follows.(Feature 1) The method comprises a preforming step in which a molded product having a hat-shaped cross section and a flange portion at the opening end of a hat portion consisting of a top plate and vertical plates on both sides is molded using a preforming mold so that molding allowances remain on both shoulders of the hat portion; and a main molding step in which the preform molded in the preforming step is compressed using a main molding mold to mold a molded product in a final shape, the main molding mold comprising: a fixed mold having a wall against which the tip surface of the flange portion abuts, a convex portion that fits into the hat portion, and a concave portion formed between the wall and the convex portion, and having a molding surface that molds the inner surface of the molded product in the final shape; a first movable mold configured to be movable in the height direction of the hat portion, and for sandwiching the top plate side of the hat portion between it and the convex portion of the fixed mold to mold it into the final shape; and a second movable mold configured to be movable in the height direction of the hat portion, and for sandwiching the preform including the opening end side of the hat portion between it and the concave portion of the fixed mold to mold it into the final shape, the main molding step comprising: the first movable mold and the second movable mold are configured to have a first main molding step of placing the preform on the convex portion of the fixed mold; a second main molding step of sandwiching the preform between the concave portion of the fixed mold and the second movable mold; and a third main molding step of molding the preform into a final shape by the convex portion of the fixed mold and the first movable mold while the preform is pressed against the concave portion of the fixed mold by the second movable mold, wherein the pressing force when the second movable mold presses the preform in the second main molding step is smaller than the pressing force when the first movable mold presses the preform in the third main molding step, and the portions of the fixed mold and the second movable mold that form the connection between the vertical plate and the flange portion of the hat portion are each formed by a rounded portion with a curved cross-sectional shape, and during the second main molding step, the rounded portion of the second movable mold presses the vertical plate of the preform toward the fixed mold as the second movable mold moves to a molding completion position, a chamfered portion is formed at the tip of the wall of the fixed mold, and in the second main forming step, the tip of the flange portion passes through a position close to the chamfered portion.

[0040] (Feature 2) The method comprises a preforming step in which a molded product having a hat-shaped cross section and a flange portion at the opening end of a hat portion consisting of a top plate and vertical plates on both sides is molded using a preforming mold so that molding allowances remain on both shoulders of the hat portion; and a main molding step in which the preform molded in the preforming step is compressed using a main molding mold to mold a molded product in a final shape, the main molding mold comprising: a fixed mold having a wall against which the tip surface of the flange portion abuts, a convex portion that fits into the hat portion, and a concave portion formed between the wall and the convex portion, and having a molding surface that molds the inner surface of the molded product in the final shape; a first movable mold configured to be movable in the height direction of the hat portion, and for sandwiching the top plate side of the hat portion between it and the convex portion of the fixed mold to mold it into the final shape; and a second movable mold configured to be movable in the height direction of the hat portion, and for sandwiching the preform including the opening end side of the hat portion between it and the concave portion of the fixed mold to mold it into the final shape, the main molding step comprising: the second movable mold is fixed to the lower mold for main forming, and the wall against which the tip end surface of the flange abuts; and the third movable mold is fixed to the lower mold for main forming, and the second movable mold is fixed to the lower mold for main forming, and the third movable mold is fixed to the lower mold for main forming, and the second movable mold is fixed to the lower mold for main forming, and the wall against which the tip end surface of the flange abuts; the third movable mold is fixed to the lower mold for main forming, and the second movable mold is fixed to the lower mold for main forming, and the wall is fixed to the lower mold for main forming, and the third movable mold is formed into a final shape by the convex portion of the fixed mold and the first movable mold. the second movable mold is configured to be movable only in a height direction of the hat portion, which is parallel to the moving direction of the first movable mold, and the second movable mold has the protrusion fixed to the lower mold for main molding and fitted into the hat portion, and the recess formed between the wall and the protrusion;a press-molding method characterized in that, in the third main-molding step, the excess metal portion of the preform is compressed by the first movable mold while the opening portion of the hat portion and the flange portion are constrained by the fixed mold and the second movable mold to restrict displacement.

[0041] (Feature 3) The method comprises: a preforming step in which a preformed product having a hat-shaped cross section and a flange portion at the opening end of a hat portion having a pair of vertical plates connected to both sides of a top plate via excess pad portions protruding upward on both sides of the top plate is formed using a preforming mold so that a forming allowance consisting of excess pad portions remains on both shoulders of the hat portion; and a main forming step in which the preformed product formed in the preforming step is compressed using a main forming mold different from the preforming mold to form a molded product in a final shape, the main forming mold comprising: a fixed mold having a wall against which the tip surface of the flange portion abuts, a convex portion that enters the hat portion, and a groove recess formed between the wall and the convex portion, integrally formed, and having a molding surface that molds the inner surface of the molded product in the final shape; and a first movable mold configured to be movable in the height direction of the hat portion, and that sandwiches the top plate side of the hat portion between the fixed mold and the convex portion to mold it into the final shape. and a second movable mold configured to be movable in the height direction of the hat portion, and sandwiching the preform including the open end side of the hat portion between it and the grooved recess of the fixed mold to mold it into a final shape, the main molding process comprising: a first main molding process in which the preform is placed on the protruding portion of the fixed mold; a second main molding process in which the preform is sandwiched between the grooved recess of the fixed mold and the second movable mold; and a third main molding process in which the top plate of the preform is molded into a final shape by the protruding portion of the fixed mold and the first movable mold with the flange and the vertical plate of the preform pressed against the grooved recess of the fixed mold by the second movable mold, The third main molding process is a press molding method characterized in that the first movable mold presses the preform toward the fixed mold, thereby moving a portion of the excess material toward the center of the top plate, causing the center of the top plate to curve even more significantly, and the top plate and the excess material of the preform are compressed while being deformed into a corrugated shape.

[0042] (Feature 4) In the press molding method described in Feature 2 or Feature 3, the portions of the fixed mold and the second movable mold that mold the connection between the vertical plate and the flange portion of the hat portion are each formed by a rounded portion with a curved cross-sectional shape, and in the second main molding step, the rounded portion of the second movable mold pushes the vertical plate of the preform toward the fixed mold as the second movable mold moves to a molding end position.

[0043] (Feature 5) The press molding method according to Feature 4, wherein a chamfered portion is formed at the tip of the wall of the fixed mold, and in the second main molding step, the tip of the flange passes through a position close to the chamfered portion.

[0044] (Feature 6) In the press molding method described in any one of Features 1 to 3, the wall of the fixed mold is formed by a mold part that is 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 has a right-angle shape, and in the third main molding process, the tip surface of the flange portion abuts against the wall without any gap.

[0045] (Feature 7) A mold for preforming is provided for molding a molded product having a hat-shaped cross section and a flange portion at the opening end of a hat portion consisting of a top plate and vertical plates on both sides, so that molding allowances remain on both shoulders of the hat portion; and a mold for main molding is provided for compressing the preform molded by the mold for preforming to mold a molded product in a final shape, wherein the mold for main molding comprises: a fixed mold having a wall against which the tip surface of the flange portion abuts, a convex portion that fits into the hat portion, and a concave portion formed between the wall and the convex portion, and having a molding surface for molding the inner surface of the molded product in the final shape; a first movable mold configured to be movable in the height direction of the hat portion, and for sandwiching the top plate side of the hat portion between it and the convex portion of the fixed mold to mold it into the final shape; and a second movable mold configured to be movable in the height direction of the hat portion, and for sandwiching the preform including the opening end side of the hat portion between it and the concave portion of the fixed mold to mold it into the final shape. a press molding device characterized in that the first movable mold presses the preform against the convex portion of the fixed mold to form the preform into a final shape while the second movable mold presses the preform against the concave portion of the fixed mold, the pressing force of the second movable mold pressing the preform is smaller than the pressing force of the first movable mold pressing the preform, a chamfered portion is formed at the tip of the wall of the fixed mold, and the chamfered portion is formed outside the moving trajectory of the flange portion that moves as the second movable mold presses the preform against the fixed mold.

[0046] (Feature 8) A mold for preforming is provided which molds a molded product having a hat-shaped cross section and a flange portion at the opening end of a hat portion consisting of a top plate and vertical plates on both sides, so that molding allowances remain on shoulders on both sides of the hat portion; and a mold for main molding which compresses the preform molded by the mold for preforming to mold a molded product in a final shape, the mold for main molding comprising: a fixed mold having a wall against which the tip surface of the flange portion abuts, a convex portion that fits into the hat portion, and a concave portion formed between the wall and the convex portion, and having a molding surface which molds the inner surface of the molded product in the final shape; a first movable mold configured to be movable in the height direction of the hat portion, and which sandwiches the top plate side of the hat portion between itself and the convex portion of the fixed mold to mold it into the final shape; and a second movable mold configured to be movable in the height direction of the hat portion, and which sandwiches the preform including the opening end side of the hat portion between itself and the concave portion of the fixed mold to mold it into the final shape. the first movable mold presses the preform against the convex portion of the fixed mold while the second movable mold presses the preform against the concave portion of the fixed mold to form it into a final shape; the pressing force of the second movable mold when pressing the preform is smaller than the pressing force of the first movable mold when pressing the preform; the forming allowance is constituted by excess padding formed so that shoulders on both sides of the hat portion partially bulge outward from the hat portion; the fixed mold has: a main forming lower mold that cannot move; the wall that is fixed to the main forming lower mold and against which the tip surface of the flange portion abuts; the convex portion that is fixed to the main forming lower mold and enters the hat portion; and the concave portion formed between the wall and the convex portion; the second movable mold is configured to be movable only in a height direction of the hat portion that is parallel to the moving direction of the first movable mold; a first movable die configured to compress the excess material portion of the preform while restricting displacement of the opening portion of the hat portion and the flange portion by the fixed die and the second movable die;

[0047] (Feature 9) A mold for preforming is provided for molding a molded product having a hat-shaped cross section and a flange portion at the opening end of a hat portion having a pair of vertical plates connected to both sides of a top plate via excess pad portions protruding upward, so that molding allowances consisting of excess pad portions remain on both shoulders of the hat portion; and a mold for main molding, which is different from the mold for preforming, for compressing the preform molded by the mold for preforming to mold a molded product in a final shape, wherein the mold for main molding is a fixed mold that integrally forms a wall against which the tip surface of the flange portion abuts, a convex portion that enters the hat portion, and a groove recess formed between the wall and the convex portion, and has a molding surface that molds the inner surface of the molded product in the final shape; and a first movable mold that is configured to be movable in the height direction of the hat portion, and that molds the hat portion into the final shape by sandwiching the top plate side of the hat portion between the fixed mold and the convex portion of the first movable mold. and a second movable mold configured to be movable in the height direction of the hat portion, and sandwiching the preform including the open end side of the hat portion between it and the groove recess of the fixed mold to form it into a final shape, wherein the first movable mold presses the top plate of the preform against the convex portion of the fixed mold while the second movable mold presses the flange and the vertical plate of the preform against the groove recess of the fixed mold to form it into a final shape, wherein the pressing force used by the second movable mold to press the preform is smaller than the pressing force used by the first movable mold to press the preform, and wherein when the first movable mold presses the preform toward the fixed mold, a portion of the excess metal portion is brought closer to the center of the top plate, causing the center portion of the top plate to curve even more significantly, so that the top plate and the excess metal portion of the preform are compressed while being deformed into a corrugated shape.

[0048] (Feature 10) In the press molding apparatus described in any one of Features 7 to 9, the portions of the fixed mold and the second movable mold that form the connection between the vertical plate of the hat portion and the flange portion are each formed by a rounded portion that has a curved cross-sectional shape.

[0049] (Feature 11) The press molding apparatus according to Feature 8 or Feature 9, wherein a chamfered portion is formed at the tip of the wall of the fixed die, and the chamfered portion is formed outside a moving trajectory of the flange portion that moves as the second movable die presses the preform against the fixed die.

[0050] (Feature 12) In the press molding apparatus described in any one of Features 7 to 9, the wall of the fixed mold is formed by a mold part that is 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 forms a right angle, and the tip surface of the flange portion of the molded product in its final shape abuts against the wall without any gap.

[0051] 1...preliminary formed product, 2, 13...top plate, 3...excess material portion, 4, 14...vertical plate, 5, 15...cap portion, 6, 16...flange portion, 11...mold for preliminary forming, 12...final shaped formed product, 15a...shoulder portion, 15c...inner surface of cap portion, 17...mold for actual forming, 18...press forming device, 32...fixed mold, 35d, 41a...rounding portion, 36...restraining piece (wall), 37...chamfered portion, 38...first movable mold, 39...second movable mold.

Claims

1. A mold for preforming, which molds a hat-shaped cross-sectioned product having a flange at the opening end of a hat part consisting of a top plate and vertical plates on both sides, so that molding allowances remain on both shoulders of the hat part; and a mold for main molding, which compresses the preform molded by the mold for preforming to mold a molded product in a final shape, the mold for main molding comprising: a fixed mold having a wall against which the tip face of the flange comes into contact, a convex part that fits into the hat part, and a concave part formed between the wall and the convex part, and having a molding surface for molding the inner surface of the molded product in the final shape; a first movable mold configured to be movable in the height direction of the hat part, which sandwiches the top plate side of the hat part between the fixed mold and the convex part to mold it into the final shape; and a second movable mold configured to be movable in the height direction of the hat part, which sandwiches the preform including the opening end side of the hat part between the fixed mold and the concave part to mold it into the final shape, a press molding device in which the first movable die presses the preformed product against the convex portion of the fixed die while the second movable die presses the preformed product against the concave portion of the fixed die, the pressing force with which the second movable die presses the preformed product is smaller than the pressing force with which the first movable die presses the preformed product, a chamfered portion is formed at the tip portion of the wall of the fixed die, and the chamfered portion is formed outside the movement trajectory of the flange portion that moves as the second movable die presses the preformed product against the fixed die.

2. A press molding apparatus as described in claim 1, wherein the molding allowance is constituted by excess material formed by forming shoulders on both sides of the hat portion into a shape that partially bulges outward from the hat portion, the fixed mold has: a lower mold for main molding that cannot be moved; the wall fixed to the lower mold for main molding and against which the tip surface of the flange portion abuts; the convex portion fixed to the lower mold for main molding and entering the hat portion; and the concave portion formed between the wall and the convex portion, the second movable mold being configured to be movable only in the height direction of the hat portion and in a direction parallel to the movement direction of the first movable mold, and the first movable mold compresses the excess material of the preformed product while the opening portion of the hat portion and the flange portion are restrained by the fixed mold and the second movable mold to restrict displacement.

3. A press molding apparatus as defined in claim 1, wherein the hat portion is formed by a pair of vertical plates connected to both sides of the top plate via excess metal portions protruding upward, the molding allowance consisting of the excess metal portions, the die for main molding is different from the die for preforming, the recess is formed by a groove, and the first movable die presses the top plate of the preformed product against the convex portion of the fixed die while the second movable die is pressing the flange and the vertical plates of the preformed product against the recess consisting of the groove of the fixed die to form it into a final shape, and wherein, as the first movable die presses the preformed product towards the fixed die, a portion of the excess metal portions is brought closer to the center of the top plate, the center of the top plate curves even more significantly, and the top plate and the excess metal portions of the preformed product are compressed while being deformed into a corrugated shape.

4. A press molding apparatus as claimed in any one of claims 1 to 3, wherein the portions of the fixed die and the second movable die which form the connection between the vertical plate of the hat portion and the flange portion are each formed by a rounded portion which has a curved cross-sectional shape.

5. A press molding apparatus as claimed in claim 2 or 3, wherein a chamfered portion is formed at the tip of the wall of the fixed die, and the chamfered portion is formed outside the movement trajectory of the flange portion which moves as the second movable die presses the preform against the fixed die.

6. A press molding apparatus according to any one of claims 1 to 3, wherein 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 forms a right angle, and the tip surface of the flange portion of the molded product in its final shape abuts against the wall without any gap.

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