Method for forming a blank and apparatus for forming a blank

Abstract

The present invention prevents wrinkles and cracks from occurring in thin areas when drawing a blank having multiple thicknesses. The blank forming method of the present invention comprises a blank holder which is provided on the outside of the punch and includes a first holder part that clamps the thick-walled parts of the blank between itself and the die, and a second holder part that clamps the thin-walled parts of the blank, which are thinner than the thick-walled parts, between itself and the die. The multiple holder parts are capable of individually applying a pressing force to the blank to clamp it between itself and the die by an independent operating mechanism. The first holder part clamps the thin-walled parts when, due to the material flow during drawing, the thick-walled parts clamped by the die and the first holder part are pulled out of the area clamped by the die and the first holder part, and at the same time the thin-walled parts are drawn into that area.

Description

Technical Field

[0001] The present invention relates to a method for forming a blank and a blank forming apparatus.

Background Art

[0002] Automobile body frames are required to have collision safety performance such as absorbing energy during a collision and suppressing deformation of the vehicle body. As a method for improving collision safety performance, for example, a method of overlapping and joining reinforcing parts to a reinforcing portion of the vehicle body frame can be cited. In this method, since it is necessary to separately produce the vehicle body frame and the reinforcing parts, there is a concern that the manufacturing cost will increase.

[0003] As a method for manufacturing a reinforced vehicle body frame, for example, there is a method using a patchwork blank (laminated blank) or a tailored welded blank. A patchwork blank is obtained by overlapping and joining a plurality of blanks. A tailored welded blank is obtained by joining a plurality of blanks having different plate thicknesses or strengths in an adjacent state. Although it is necessary to manufacture such a blank having a plurality of plate thicknesses, since the labor for manufacturing the above-described reinforcing parts can be saved, an increase in the manufacturing cost of the vehicle body frame can be suppressed.

[0004] By the way, in the die for performing the above-described drawing forming, it has been proposed to dispose a movable block that sandwiches the blank between the die and the blank holder and the pinch (see Patent Document 1). In the die disclosed in Patent Document 1, even after the outer edge portion of the blank has passed through between the die and the blank holder, the outer edge portion of the blank can be appropriately pinched between the die and the movable block.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, the method described in Patent Document 1 has a problem in that when drawing a blank that has parts with different thicknesses, if there are parts with relatively thinner thicknesses before the outer edge of the blank passes through the gap between the die and the blank holder, it becomes impossible to maintain an appropriate clamping state for those parts, resulting in wrinkles or cracks.

[0007] The present invention has been made in view of the above problems, and aims to provide a technology that can suppress the occurrence of wrinkles and cracks when drawing a blank having parts with different plate thicknesses, by maintaining an appropriate clamping state for the parts with relatively thinner plate thicknesses. [Means for solving the problem]

[0008] One method for forming a blank is a forming method in which, while maintaining a state in which the outer edge of the blank is clamped between opposing dies and a blank holder, a punch facing the die is brought close to the die and pressed against the blank to perform deep drawing of the blank, wherein the blank has a thick-walled portion where the thickness is greater than other parts, and the blank holder is provided on the outside of the punch and includes a first holder portion that clamps the thick-walled portion of the blank between itself and the die, and a second holder portion that clamps the thin-walled portion of the blank where the thickness is thinner than the thick-walled portion between itself and the die, It is composed of several holder sections, each of which has an independent operating mechanism that allows it to individually apply a pressing force to the blank to narrow it between itself and the die. The first holder section is characterized in that, when the material flow caused by the blank being drawn in during deep drawing pulls out the thick-walled portion that has been narrowed by the die and the first holder section, and at the same time a thin-walled portion is drawn into that region, it is biased toward the die by an operating mechanism independent of the second holder section to narrow the thin-walled portion of the blank.

[0009] Furthermore, the blank is preferably either a patchwork blank, in which multiple metal sheets are overlapped and joined together, and thin-walled and thick-walled sections are formed due to the difference in the number of overlapping metal sheets, or a tailored weld blank, in which multiple metal sheets with different thicknesses or strengths are joined adjacent to each other.

[0010] Furthermore, a blank forming apparatus from another perspective is a forming apparatus that performs deep drawing of a blank by bringing a punch and a die close together so as to press the blank against a punch facing the die, while maintaining a state in which the outer edge of the blank is clamped between an opposing die and a blank holder, wherein the blank has a thick-walled portion where the plate thickness is greater than other parts, and the blank holder is provided on the outside of the punch and includes a first holder portion that clamps the thick-walled portion of the blank between itself and the die, and a second holder portion that clamps the thin-walled portion of the blank where the plate thickness is thinner than the thick-walled portion between itself and the die, It is composed of several holder sections, each of which has an independent operating mechanism that allows it to individually apply a pressing force to the blank to narrow it between itself and the die. The first holder section is characterized in that, when the material flow caused by the blank being drawn in during deep drawing pulls out the thick-walled portion that has been narrowed by the die and the first holder section, and at the same time a thin-walled portion is drawn into that region, it is biased toward the die by an operating mechanism independent of the second holder section to narrow the thin-walled portion of the blank.

[0011] Furthermore, the blank is preferably either a patchwork blank, in which multiple metal sheets are overlapped and joined together, and thin-walled and thick-walled sections are formed due to the difference in the number of overlapping metal sheets, or a tailored weld blank, in which multiple metal sheets with different thicknesses or strengths are joined adjacent to each other.

[0012] Furthermore, it is preferable that the clamping surface of the first holder portion protrudes more towards the die than the clamping surface of the second holder portion, thereby increasing the clamping load of the first holder portion when the blank is compressed between the die and the blank holder. [Effects of the Invention]

[0013] According to this disclosure, it is possible to provide a technology that can prevent wrinkles and cracks from occurring in the thinner parts of a blank when deep drawing is performed on a blank having multiple thicknesses. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic perspective view showing an example of a molded product in this embodiment. [Figure 2] This is a schematic perspective view showing an example of a blank space. [Figure 3] Figure 1 shows a cross-sectional view illustrating an example of the configuration of a molding apparatus corresponding to planar PL1. [Figure 4] Figure 4(a) is a plan view comparing the sizes of the blank holder and the patchwork blank, and Figure 4(b) is a cross-sectional view taken along line A-A' in (a). [Figure 5] This is a cross-sectional view showing the blank being compressed between the die and the subholder. [Figure 6] This is a cross-sectional view showing the blank compressed between the die and the blank holder. [Figure 7] This is a cross-sectional view showing the blank, compressed between the die and the blank holder, in contact with the punch. [Figure 8] Figure 8(a) is a cross-sectional view showing the blank compressed between the die and the blank holder and pressed against the punch, and Figure 8(b) is a magnified cross-sectional view showing the state near the punch. [Figure 9] Figure 9(a) is a cross-sectional view showing the die in the bottom dead center position, and Figure 9(b) is a magnified cross-sectional view showing the state near the punch. [Figure 10] This is a cross-sectional view showing an example of the configuration of a molding apparatus that can be used as a comparative example. [Figure 11] FIG. 11(a) is a perspective view showing the state of a molded product generated by the molding apparatus shown in the present embodiment, and FIG. 11(b) is a perspective view showing the state of a molded product generated by a molding apparatus as a comparative example. [Figure 12] In the molding apparatus as a comparative example, it is a cross-sectional view showing a state in which the outer edge portion of the patchwork blank is drawn between the convex portion of the punch and the concave portion of the die. [Figure 13] It is a perspective view showing an example of the configuration of a tailored welded blank. [Figure 14] FIG. 14(a) is a perspective view showing the state of a molded product obtained by performing ironing on a tailored welded blank using the molding apparatus shown in the present embodiment, and FIG. 14(b) is a perspective view showing the state of a molded product obtained by performing ironing on a tailored welded blank using a molding apparatus as a comparative example. [Figure 15] It is a cross-sectional view showing an example of the configuration of a molding apparatus having a lower mold in which a main holder and a sub-holder can be individually moved.

MODE FOR CARRYING OUT THE INVENTION

[0015] Hereinafter, the blank molding method and molding apparatus shown in the present embodiment will be described with reference to the drawings. The blank molding method shown in the present embodiment is a method of performing ironing on a blank having a thick portion with a plate thickness thicker than other portions.

[0016] As shown in FIG. 1, the molded product 10 is a member having a substantially hat-shaped cross-sectional shape with a top plate portion 11, vertical wall portions 12, 12, and flange portions 13, 13. Further, the molded product 10 has a mountain-shaped shape in which the central portion in the longitudinal direction of the molded product 10 is bent upward, and the bent portion and its vicinity are reinforced. In FIG. 1, the main portion of the molded product 10 is formed by a blank B1 described later, and the reinforcing portion is formed by a blank B2 described later. The angle θ formed by the straight line L1 indicating the extending direction of one end portion 11a of the top plate portion 11 and the straight line L2 indicating the extending direction of the other end portion 11b, that is, the bending angle θ of the molded product 10 is, for example, θ = 30°.

[0017] In this embodiment, the cross-sectional shape of the molded product 10 is approximately hat-shaped, but it may also be approximately crank-shaped, for example.

[0018] The blank used to produce the molded product 10 will be described below. In the following description, the short direction of blank B will be referred to as the X-axis direction, the long direction of blank B as the Y-axis direction, and the direction perpendicular to the X-axis direction and the Y-axis direction as the Z-axis direction.

[0019] As shown in Figure 2, blank B is, for example, a patchwork blank. In the following description, the patchwork blank will be denoted by the symbol B. Patchwork blank B is made by overlapping two rectangular blanks B1 and B2 with different thicknesses or strengths and joining them by spot welding or the like. That is, in the patchwork blank B shown in this embodiment, the part where blank B2 is overlapped and joined to blank B1 becomes the thick part of patchwork blank B.

[0020] In Figure 2, spot welding is performed at two locations (e.g., indicated by symbols P1 and P2) on a straight line L3 that passes through the midpoint of the blank B1 in the longitudinal direction and extends in the transverse direction of the blank B1. However, the locations where spot welding is performed are not limited to these.

[0021] Of the two blanks B1 and B2 that make up patchwork blank B shown in Figure 2, blank B1 is made of, for example, a steel plate with a tensile strength of 980 MPa and a thickness of 1.4 mm. The length of the long side W1 and the length of the short side D1 of blank B1 are, for example, W1 = 760 mm and D1 = 350 mm.

[0022] For example, blank B2 is made of steel plate with a tensile strength of 1470 MPa and a thickness of 1.6 mm. The length of the long side W2 and the length of the short side D2 of blank B2 are, for example, W2 = 260 mm and D2 = 180 mm.

[0023] The example shown uses steel plates with different thicknesses and tensile strengths as the two blanks B1 and B2 that make up patchwork blank B, but it is also possible to use metal sheet materials other than steel plates.

[0024] Next, the configuration of the molding apparatus 20 that performs deep drawing on the patchwork blank B shown in Figure 2 will be explained using Figures 3 and 4. Figure 3 is a cross-sectional view showing an example of the configuration of the molding apparatus in plan PL1 shown in Figure 1. Figure 4(a) is a plan view comparing the sizes of the blank holder and the blank, and Figure 4(b) is a cross-sectional view taken along A-A' shown in Figure 4(a). Note that in Figure 3, only the configuration of the mold 21 provided in the molding apparatus 20 is shown, and other configurations are omitted.

[0025] As shown in Figure 3, the molding apparatus 20 is a device that performs deep drawing on a blank B by relatively moving the positions of the upper mold 22 or the lower mold 23 that constitute the mold 21. In this embodiment, an example is given in which the upper mold 22 is moved in a direction toward or toward the lower mold 23.

[0026] The mold 21 consists of an upper mold 22 and a lower mold 23. The upper mold 22 is capable of moving between the top dead center and the bottom dead center. When the upper mold 22 moves from the top dead center towards the bottom dead center, the upper mold 22 moves closer to the lower mold 23. When the upper mold 22 moves from the bottom dead center towards the top dead center, the upper mold 22 moves further away from the lower mold 23.

[0027] The upper mold 22 has a die 25 and a mold body 26 that holds the die 25. As the upper mold 22 moves from the top dead center to the bottom dead center, the die 25 compresses the outer edge of the patchwork blank B between itself and the blank holder 27. A recess 25b is provided on the lower surface 25a of the die 25. During deep drawing, a protrusion 28a formed on the punch 28 is inserted into the recess 25b.

[0028] The lower die 23 includes a blank holder 27, a punch 28, and a die body 29 that holds the blank holder 27 and the punch 28. The blank holder 27 is a member that clamps the outer edge of the patchwork blank B between itself and the die 25. The blank holder 27 is composed of main holders 31, 32 and sub-holders 33, 34. Here, the main holders 31, 32 correspond to the second holder portion described in the claim, and the sub-holders 33, 34 correspond to the first holder portion described in the claim.

[0029] In this embodiment, a blank holder 27 having two main holders 31 and 32 is shown as an example, but it is also possible to use a blank holder having only one main holder.

[0030] The main holders 31 and 32 are supported by the mold body 29 so as to be movable in the vertical direction by cushion pins 35 and 36. In the central part of the longitudinal direction of the main holder 31, a rectangular storage recess 31c is provided, which is cut out from the upper surface 31a to the inner surface 31b of the main holder 31. A sub-holder 33 is provided in the storage recess 31c so as to be movable in the vertical direction via a spring mechanism 37.

[0031] Similarly, a storage recess 32c is provided in the central portion of the main holder 32 in the longitudinal direction, which is cut out in a rectangular shape from the upper surface 32a to the inner surface 32b of the main holder 32. A sub-holder 34 is provided in the storage recess 32c so as to be movable in the vertical direction via a spring mechanism 38. Here, the spring mechanisms 37 and 38 correspond to the biasing means described in the claim.

[0032] Sub-holders 33 and 34 are components that compress the patchwork blank B separately from the main holders 31 and 32. The sub-holders 33 and 34 are provided to be movable in the vertical direction (Z-axis direction in Figure 4(b)) by spring mechanisms 37 and 38 provided in the storage recesses 31c and 32c.

[0033] The spring mechanisms 37 and 38 consist of, for example, three gas springs and bias the sub-holders 33 and 34 upward. The gas springs used as spring mechanisms 37 and 38 have, for example, an initial load of 9.2 kN, a maximum load of 14.8 kN, and a stroke of 80 mm. By biasing the sub-holders 33 and 34 upward with spring mechanisms 37 and 38, the sub-holders 33 and 34 apply, for example, a load of 72 kN to the patchwork blank B.

[0034] When the upper die 22 is at top dead center, the sub-holders 33 and 34 are held with parts of them inserted into the respective storage recesses 31c and 32c of the main holders 31 and 32. At this time, the upper surfaces 33a and 34a of the sub-holders 33 and 34 protrude, for example, by about 40 mm from the upper surfaces 31a and 32a of the main holders 31 and 32. Then, as the upper die 22 moves from top dead center to bottom dead center, the sub-holders 33 and 34 are pressed by the die 25 and stored in the storage recesses 31c and 32c until the upper surfaces 33a and 34a of the sub-holders 33 and 34 are at the same height as the upper surfaces 31a and 32a of the main holders 31 and 32.

[0035] Furthermore, by having the upper surfaces 33a and 34a of the sub-holders 33 and 34 protrude from the upper surfaces 31a and 32a of the main holders 31 and 32, the load on the patchwork blank B when it is pressed between the die 25 and the blank holder 27 can be increased.

[0036] As shown in Figure 4(a), in the width direction of patchwork blank B (X-axis direction in Figure 4(a)), both ends of blank B1 are located inward from the outer ends of main holders 31 and 32. Also, in the extension direction of patchwork blank B (Y-axis direction in Figure 4(a)), both ends of blank B1 are located inward from both ends of main holders 31 and 32.

[0037] Similarly, in the width direction of patchwork blank B (X-axis direction in Figure 4(a)), both ends of blank B2 are located inward from the outer ends of sub-holders 33 and 34. Also, in the extension direction of patchwork blank B (Y-axis direction in Figure 4(a)), both ends of blank B2 are located inward from the both ends of main holders 31 and 32.

[0038] When the deep drawing process begins and the die 25 descends, the outer edge of the patchwork blank B is compressed between the die 25 and the main holders 31 and 32. Additionally, the thicker portion of the patchwork blank B is compressed between the die 25 and the sub-holders 33 and 34. Here, the outer edge of the patchwork blank B is the outer edge of blank B1. The thicker portion of the patchwork blank B is the area where blank B1 and blank B2 are joined.

[0039] The punch 28 has a protrusion 28a against which the central part of the patchwork blank B is pressed. The protrusion 28a is provided with an insertion portion 28b into which the blank B2 joined to the blank B1 enters when the patchwork blank B is pressed against the protrusion 28a.

[0040] Next, the process of forming the molded product 10 using the molding apparatus 20 shown in Figure 3 will be described. As shown in Figure 3, the patchwork blank B is placed between the upper mold 22 and the lower mold 23 such that blank B1 faces the upper mold 22 and blank B2 faces the lower mold 23.

[0041] When deep drawing begins, the upper die 22 of the mold 21, which is at top dead center, moves toward bottom dead center. As shown in Figure 5, as the upper die 22 moves toward bottom dead center, the die 25 clamps the thick-walled portion located in the center of the patchwork blank B between the sub-holders 33 and 34 of the blank holder 27.

[0042] Subsequently, the die 25 presses the sub-holders 33 and 34 of the blank holder 27 downwards while maintaining a state in which the thick-walled portion located in the center of the patchwork blank B is clamped between the die 25 and the sub-holders 33 and 34 of the blank holder 27. As a result, the sub-holders 33 and 34 are pushed into the storage recesses 31c of the main holder 31 and 32c of the main holder 32, respectively, against the biasing force of the spring mechanisms 37 and 38. During the process in which the sub-holders 33 and 34 are being pressed by the die 25, a predetermined load is applied to the patchwork blank B by the biasing force of the spring mechanisms 37 and 38.

[0043] As shown in Figure 6, the sub-holders 33 and 34 are pressed against the die 25 and pushed into the storage recesses 31c of the main holder 31 and 32c of the main holder 32, respectively. At this time, the die 25 clamps the outer edge of the patchwork blank B between itself and the main holders 31 and 32.

[0044] The die 25 moves toward the bottom dead center while pressing against the main holders 31 and 32, as well as the sub-holders 33 and 34. Consequently, the thicker portion of the patchwork blank B, which is sandwiched between the die 25 and the blank holder 27, is pressed against the punch 28 (see Figure 7).

[0045] Even after the thick portion of patchwork blank B is pressed against punch 28, die 25 continues to press the blank holder 27 downward. This causes the convex portion 28a of punch 28 to engage with the concave portion 25b of die 25 (see Figure 8(a)). At this time, the thick portion of patchwork blank B pressed against punch 28 is pulled between the punch shoulders 28c, 28d of punch 28 and the die shoulders 25c, 25d of die 25. As a result, the material in the thick portion of patchwork blank B, which is sandwiched between subholders 33, 34 and die 25, is pulled towards the die shoulders 25c, 25d of die 25 and drawn between the convex portion 28a of punch 28 and the concave portion 25b of die 25 (see Figure 8(b)).

[0046] The action of pulling the material in the thicker portion of the patchwork blank B, which is compressed between the sub-holders 33, 34 and the die 25, toward the die shoulders 25c, 25d of the die 25 continues until the die 25 reaches its bottom dead center. As a result, the thicker portion of the patchwork blank B is squeezed out from between the die 25 and the sub-holders 33, 34 and moves between the convex portion 28a of the punch 28 and the concave portion 25b of the die 25.

[0047] At this time, the outer edge of patchwork blank B is pulled toward the die shoulders 25c and 25d, similar to the thicker portion of patchwork blank B, but is compressed between the die 25 and the main holders 31 and 32.

[0048] As the thicker portion of the patchwork blank B moves between the convex portion 28a of the punch 28 and the concave portion 25b of the die 25, the sub-holders 33 and 34 move upward due to the biasing force of the spring mechanisms 37 and 38. At this time, the sub-holders 33 and 34 clamp the portion of the patchwork blank B that is on the outer edge and inside the portion that is compressed between the main holders 31 and 32 and the die 25. As a result, the sub-holders 33 and 34 apply a predetermined load to that portion (see Figures 9(a) and 9(b)). This state is maintained until the upper die 22 moves to the bottom dead center. This produces a molded product 10 with a top plate portion 11, vertical wall portions 12, 12 and flange portions 13, 13, and a mountain-shaped form with a bent central portion.

[0049] In this way, during the process of producing the mountain-shaped molded product 10, the sub-holders 33 and 34 apply a predetermined load to the patchwork blank B while clamping it between themselves and the die 25. This makes it possible to prevent wrinkles and cracks from occurring in the flange portion 13 of the molded product 10, in molded products where the central part in the longitudinal direction is bent upward.

[0050] Below, we simulated whether wrinkles or cracks occur in the molded product 10 formed from the patchwork blank B shown in this embodiment using the molding apparatus 20. As a comparative example, we simulated whether wrinkles or cracks occur in the molded product 60 produced by deep drawing using the molding apparatus 50 shown in Figure 10.

[0051] As shown in Figure 10, the molding apparatus 50 has a mold 51 composed of an upper mold 52 and a lower mold 53. The upper mold 52 has a die 54 and a mold body 55 that holds the die 54. The lower mold 53 has blank holders 56, 57, a punch 58, and a mold body 59 that holds them. The die 54 of the upper mold 52 and the punch 58 of the lower mold 53 have the same configuration as the die 25 of the upper mold 22 and the punch 28 of the lower mold 23 in this embodiment. Therefore, the description of the die 54 and the punch 58 is omitted.

[0052] The blank holders 56 and 57 used in the lower mold 53 are held in place by the mold body 59 so as to be movable in the vertical direction by cushion pins 61 and 62. The upper surfaces 56a and 57a of the blank holders 56 and 57 are provided with insertion portions 56b and 57b, respectively, into which the blank B2 of the patchwork blank B is inserted. Preferably, the depth of the insertion portions 56b and 57b is equal to or greater than the thickness of the blank B2.

[0053] As shown in Figure 11(a), for example, in a simulation of deep drawing using the molding apparatus 20 described in this embodiment, it was found that when a molded product 10 having a top plate portion 11, vertical wall portions 12, 12 and flange portions 13, 13, with the central portion bent upward, no wrinkles or cracks occurred in the flange portion 13 located near the bent portion 10a of the molded product 10.

[0054] On the other hand, as shown in Figure 11(b), in a simulation of deep drawing using the molding apparatus 50 described in the comparative example, it was found that when a molded product 60 having a top plate portion 64, vertical wall portions 65, 65 and flange portions 66, 66, with the central portion bent upward, wrinkles were generated in the flange portion 66 near the bent portion 60a of the molded product 60 (four locations indicated by ellipses).

[0055] As shown in Figure 12, in the molding apparatus 50, the thick-walled portion of the patchwork blank B is inserted into the insertion portion 56b of the blank holder 56 and the insertion portion 57b of the blank holder 57, respectively, and is then pressed between the die 54 and the blank holders 56 and 57. As the thick-walled portion of the patchwork blank B is pressed against the convex portion 58a of the punch 58, the thick-walled portion of the patchwork blank B that was inserted into the insertion portion 56b of the blank holder 56 and the insertion portion 57b of the blank holder 57 is squeezed out from between the die 54 and the blank holders 56 and 57. The squeezed-out thick-walled portion of the patchwork blank B moves between the concave portion 54b of the die 54 and the convex portion 58a of the punch 58. At this time, the outer edge of the patchwork blank B that faces the insertion portion 56b of the blank holder 56 and the insertion portion 57b of the blank holder 57 is not pressed between the die 54 and the blank holders 56 and 57. As a result, it was found that the above region becomes curved.

[0056] Thus, it was found that in the deep drawing of the patchwork blank B using the molding apparatus 20 shown in this embodiment, the occurrence of wrinkles in the flange portion 13 near the bent portion 10a of the molded product 10 can be suppressed.

[0057] In this embodiment, a patchwork blank, which is made by overlapping multiple blanks, was described as an example of a blank used in deep drawing. However, it is not limited to a patchwork blank as long as the blank has a thicker section than other parts. As shown in Figure 13, for example, it is also possible to use a tailored welded blank B', which is formed by welding a blank B3 and blanks B4, B5, B6, and B7, which have different thicknesses from the blank B3, so that the blanks B4, B5, B6, and B7 are arranged around the outer circumference of the blank B3.

[0058] In the tailored welded blank B' shown in Figure 13, blank B3 is made of steel plate with a tensile strength of 1470 MPa and a thickness of 2.0 mm. The length of the long side W3 and the length of the short side D3 of blank B3 are, for example, W3 = 260 mm and D3 = 180 mm.

[0059] Furthermore, blanks B4, B5, B6, and B7 are made of steel plate with a tensile strength of 980 MPa and a thickness of 1.0 mm. For blanks B4 and B5, the length of the long side W4 and the length of the short side D4 are, for example, W4 = 760 mm and D4 = 85 mm. For blanks B6 and B7, the length of the long side W5 and the length of the short side D5 are, for example, W5 = 250 mm and D5 = 180 mm.

[0060] In this case as well, simulations of deep drawing using the molding apparatus 20 shown in this embodiment showed that when producing a molded product 70 having a top plate portion 71, vertical wall portions 72, 72 and flange portions 73, 73, and a bent portion 70a in the center that is bent upward, no wrinkles or cracks occurred in the flange portion 73 (see Figure 14(a)). On the other hand, simulations of deep drawing using the molding apparatus 50 shown as a comparative example showed that when producing a molded product 80 having the same shape as the molded product 70, i.e., a molded product 80 having a top plate portion 81, vertical wall portions 82, 82 and flange portions 83, 83, and a bent portion 80a in the center that is bent upward, wrinkles occurred in the flange portion 83 in the vicinity of the bent portion 80a (four locations shown by ellipses) (see Figure 14(b)).

[0061] Thus, even when a tailored welded blank is used as the blank, the molding apparatus 20 shown in this embodiment can be used to appropriately clamp blanks B of different thicknesses during deep drawing. As a result, the occurrence of wrinkles in the flange portion 73 near the bent portion 70a of the molded product 70 can be suppressed.

[0062] In this embodiment, an example is shown in which the blank holder 27 is composed of main holders 31, 32 and sub-holders 33, 34 that can be stored in storage recesses 31c, 32c provided in the main holders 31, 32, respectively. However, as shown in Figure 15, it is also possible to use a lower die 90 composed of a punch 91, main holders 92, 93, sub-holders 94, 95 positioned between the punch 91 and the main holders 92, 93, and a die body 96 that individually supports these so as to be movable. The main holders 92, 93 and the sub-holders 94, 95 are each supported by a cushion holder 97. In this case, the main holders 92, 93 and the sub-holders 94, 95 function as a blank holder 98. Note that in Figure 15, the upper die can be configured in the same way as in this embodiment, and therefore uses the same reference numerals as shown in Figure 3.

[0063] <Summary of effects> According to the blank forming method and forming apparatus of this embodiment, when deep drawing is performed on a blank having a thick-walled portion that is thicker than other parts, even if the blank material is drawn between the die and the pinch and the position of the thick-walled portion of the blank changes, an appropriate load can be applied to the blank. As a result, wrinkles and cracks in the flange portion of the molded product are prevented. [Explanation of Symbols]

[0064] 20,50 Molding equipment 21,51 molds 22,52 Upper mold 23,53 Lower mold 25.55 di 27.57 Blank holder 28.58 punches 31,32 Main holder (second holder part) 33,34 Sub-holder (first holder part) 37,38 Spring mechanism (biasing means) B Blank (Patchwork Blank) B' Blank (Tailored Welded Blank)

Claims

1. A molding method for performing deep drawing of a blank by maintaining a state in which the outer edge of the blank is clamped between opposing dies and a blank holder, and then bringing a punch facing the die closer to the die and pressing the punch against the blank, The blank has a thicker section than other sections, The blank holder is provided on the outside of the punch and is composed of a plurality of holder parts, including a first holder part that clamps the thicker portion of the blank between itself and the die, and a second holder part that clamps the thinner portion of the blank, which is thinner than the thicker portion, between itself and the die. The plurality of holder portions can individually apply a pressing force to the blank for narrowing the gap between them and the die, through their independent operating mechanisms. A method for forming a blank, wherein the first holder portion is biased toward the die by an operating mechanism independent of the second holder portion when, due to material flow resulting from the drawing of the blank during the drawing process, the thick-walled portion compressed by the die and the first holder portion is pulled out of the region compressed by the die and the first holder portion, and at the same time the thin-walled portion is drawn into that region, thereby compressing the thin-walled portion of the blank.

2. The method for forming a blank according to claim 1, wherein the blank is either a patchwork blank formed by overlapping and joining multiple metal sheet materials, with thin-walled and thick-walled portions formed by differences in the number of overlapping metal sheet materials, or a tailored weld blank formed by adjacently joining multiple metal sheet materials with different thicknesses or strengths.

3. A molding apparatus that performs deep drawing of a blank by bringing a punch and a die close together so as to press the blank against a punch facing the die, while maintaining a state in which the outer edge of the blank is clamped between an opposing die and a blank holder, The blank has a thicker section than other sections, The blank holder is provided on the outside of the punch and is composed of a plurality of holder parts, including a first holder part that clamps the thicker portion of the blank between itself and the die, and a second holder part that clamps the thinner portion of the blank, which is thinner than the thicker portion, between itself and the die. The plurality of holder portions can individually apply a pressing force to the blank for narrowing the gap between them and the die, through their independent operating mechanisms. The first holder portion is biased toward the die by an operating mechanism independent of the second holder portion to compress the thin-walled portion of the blank when, due to material flow resulting from the drawing of the blank during the drawing process, the thick-walled portion compressed by the die and the first holder portion is pulled out of the region compressed by the die and the first holder portion, and at the same time the thin-walled portion is drawn into that region.

4. The blank forming apparatus according to claim 3, wherein the blank is either a patchwork blank formed by overlapping and joining multiple metal sheet materials, with thin-walled and thick-walled portions formed by differences in the number of overlapping metal sheet materials, or a tailored weld blank formed by adjacently joining multiple metal sheet materials with different thicknesses or strengths.

5. The blank molding apparatus according to claim 3 or 4, wherein the clamping surface of the first holder portion protrudes toward the die side more than the clamping surface of the second holder portion, thereby increasing the clamping load of the first holder portion when the blank is compressed by the die and the blank holder.

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