阅读说明：本技术 冲压成型方法 (Press molding method ) 是由 松谷健司 秋庭弘克 佐野武司 大宫由武 于 2020-03-03 设计创作，主要内容包括：一种冲压成型方法,包括：第一拉伸工序,其成型第一拉深台阶部(40)；第二拉伸工序,其成型第二拉深台阶部(60)；和精加工工序,其完成台阶部(20)。在第一拉伸工序中,在特征线条(16)的延长区域(PF),在比第二外侧弯曲部(66p)靠外侧的位置成型第一外侧弯曲部(46p),并且以与第二平行部(64p)的拉深深度相同的深度成型第一平行部(44p)。在第二拉伸工序中,成型曲率比第一内侧弯曲部(48p)大的第二内侧弯曲部(68p)。(A method of stamping forming, comprising: a first drawing step for forming a first drawing step section (40); a second drawing step for forming a second drawing step section (60); and a finishing step for finishing the step (20). In the first drawing step, in an extended region (PF) of the character string (16), a first outer bent portion (46p) is formed at a position outside a second outer bent portion (66p), and a first parallel portion (44p) is formed at the same depth as the drawing depth of the second parallel portion (64 p). In the second drawing step, a second inner curved portion (68p) having a curvature greater than that of the first inner curved portion (48p) is formed.)

1. A press forming method for forming a stepped portion (20) at an end portion of a main body portion (14) having a characteristic line (16),

the method comprises the following steps:

a first drawing step of drawing a workpiece having the characteristic line to form a first drawn step portion (40), the first drawn step portion (40) having a first inclined portion (42) and a first parallel portion (44), wherein the first inclined portion (42) is connected to the main body portion via a first outer bent portion (46), and the first parallel portion (44) is connected to the first inclined portion via a first inner bent portion (48) and extends in parallel to the main body portion;

a second drawing step of drawing the first drawing step portion after the first drawing step to form a second drawing step portion (60), the second drawing step portion (60) having a second inclined portion (62) and a second parallel portion (64), wherein the second inclined portion (62) is connected to the main body portion via a second outer bent portion (66), and the second parallel portion (64) is connected to the second inclined portion via a second inner bent portion (68) and extends in parallel to the main body portion; and

a finishing process of finishing the stepped portion after the second drawing process,

in the first drawing step, the first outer bent portion is formed at a position outside the second outer bent portion in an extension region (PF) located on an extension line of the characteristic line, and the first parallel portion is formed at a depth equal to a drawing depth of the second parallel portion,

in the second drawing step, the second inner curved portion having a curvature larger than that of the first inner curved portion is formed in the extension region.

2. The press-forming method according to claim 1,

in the first drawing step, the first outer curved portion is formed at the same position as the second outer curved portion in a peripheral region (AF) located in the periphery in the direction orthogonal to the extending direction of the feature line, and the first parallel portion is formed to be shallower than the drawing depth of the second parallel portion.

3. The press-forming method according to claim 2,

the first outward bent portion of the extension region is formed at a position outside the first outward bent portion of the peripheral region.

4. The press-forming method according to claim 2,

an outer corner (28) is formed at the second outer bent portion of the stepped portion and an inner corner (30) is formed at the second inner bent portion of the stepped portion,

an interval between the second inside bend portion of the extension region and the inside inner peripheral corner portion is shorter than an interval between the second inside bend portion of the peripheral region and the inside inner peripheral corner portion.

5. The press-forming method according to any one of claims 1 to 4,

in the second stretching step, the second inside bent portion of the extension region is moved to a position inside the first inside bent portion in the first stretching step.

6. The press-forming method according to claim 1,

the step portion is provided at an end portion on the front side of an outer panel (10) constituting a rear door of an automobile.

Technical Field

The present invention relates to a press forming method for forming a stepped portion in a workpiece having a characteristic line (character line).

Background

An outer panel of an automobile door is formed by folding an outer peripheral edge portion of a main body portion constituting an external appearance (see japanese patent laid-open publication No. 62-57406). For example, a stepped portion is provided on the front side of the rear door so as to overlap with the boundary portion on the rear side of the front door. The stepped portion is used to suppress the door from entering the cabin (cabin) and becoming unable to open when another vehicle collides with the side surface of the vehicle.

Disclosure of Invention

In addition, in some automobiles, distinctive lines (ridges) are provided on the outer panel of the door. When such a feature line is formed and a stepped portion is formed by pressing, there is a problem that wrinkles are likely to occur because an included angle at which the feature line is sandwiched is small. In order to suppress the wrinkles, it is conceivable to increase the elongation of the plate material during the drawing, but in this case, another problem arises in that cracks are likely to occur in the step portion. Wrinkles or cracks generated in the outer panel may deteriorate the appearance of the outer panel, and thus the outer panel cannot be used as a product.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a press forming method capable of suppressing the occurrence of wrinkles and cracks in forming a stepped portion on a panel having a characteristic line, and of greatly improving the yield in manufacturing.

In order to achieve the above object, one aspect of the present invention provides a press-forming method for forming a stepped portion at an end portion of a body portion having a characteristic line, the press-forming method including: a first drawing step of drawing a workpiece having the characteristic line to form a first drawn step portion having a first inclined portion connected to the main body portion via a first outer bent portion and a first parallel portion connected to the first inclined portion via a first inner bent portion and extending in parallel to the main body portion; a second drawing step of drawing the first drawing step portion after the first drawing step to form a second drawing step portion having a second inclined portion connected to the main body portion via a second outer bent portion and a second parallel portion connected to the second inclined portion via a second inner bent portion and extending in parallel with the main body portion; and a finishing step of finishing the stepped portion after the second drawing step, wherein in the first drawing step, the first outer curved portion is formed at a position outside the second outer curved portion in an extension region located on an extension line of the characteristic line, and the first parallel portion is formed at a depth equal to a drawing depth of the second parallel portion, and in the second drawing step, the second inner curved portion having a curvature larger than that of the first inner curved portion is formed in the extension region.

In the press molding method, the first drawing step and the second drawing step are performed, whereby the stepped portion can be formed satisfactorily without causing wrinkles or cracks even in the end portion of the body portion having the characteristic line. That is, since the first outside bent portion formed in the first stretching step and the second outside bent portion formed in the second stretching step are shifted in position, the plate material at a specific position in the extended region can be suppressed from becoming extremely thin. Therefore, the crack can be suppressed from entering the extension region. Further, the first parallel portion formed in the first drawing step has the same depth as the second parallel portion, and the second inner curved portion formed in the second drawing step has a large curvature, so that the second inner curved portion can be brought close to the step portion in the finished state in the second drawing step. Therefore, the contraction of the second inside bend portion is reduced in the finishing process, thereby suppressing the generation of wrinkles in the extended region. Therefore, the press forming method can greatly improve the yield in manufacturing.

Drawings

Fig. 1A is a plan view showing an outer panel of a rear door formed by a press forming method according to an embodiment of the present invention. FIG. 1B is a cross-sectional view IB-IB of FIG. 1A.

Fig. 2 is a flowchart showing steps of the manufacturing method.

Fig. 3 is a perspective view showing the first drawing step portion formed by the first drawing process (drawing process).

Fig. 4A is a cross-sectional view showing a first drawing step corresponding to a peripheral region IVA-IVA in fig. 3. Fig. 4B is a cross-sectional view showing the first drawing step corresponding to the extended region of IVB-IVB in fig. 3.

Fig. 5 is a perspective view showing a second drawing step portion formed by the second drawing step.

Fig. 6A is a cross-sectional view showing a second stretching step corresponding to the peripheral region VIA-VIA of fig. 5. Fig. 6B is a cross-sectional view showing a second drawing step corresponding to an extended region of VIB-VIB in fig. 5.

Fig. 7A is a cross-sectional view comparing the first drawing step portion, the second drawing step portion, and the step portion of the extended region. Fig. 7B is a schematic view of the arrow X2 direction viewed from the arrow X1 side of fig. 7A.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings by way of examples of preferred embodiments.

In the press forming method according to an embodiment of the present invention, an outer panel 10 of an automobile rear door as shown in fig. 1A is formed. The outer panel 10 is formed in a substantially trapezoidal shape, is long in the front-rear direction of the automobile (the vehicle length direction: the arrow X direction), is short in the height direction of the automobile (the vertical direction: the arrow Y direction), and is inclined at the lower portion on the rear side (the arrow X2 side).

The outer panel 10 has a main body portion 14 exposed to the outside of the automobile (constituting the appearance of a rear door). A door handle arrangement portion 12 for installing a door handle, not shown, is formed in a rear portion of the body portion 14. A clear character line 16 (ridge line) of the automobile is formed on the surface of the body 14 at a predetermined position in the arrow Y direction (at the same height as the door handle arrangement portion 12). The feature line 16 is raised with respect to a smooth surface portion 18 smoothly formed in the arrow Y direction (vertical direction) of the feature line 16, and extends substantially linearly along the arrow X direction. That is, the angle between the back sides of the pair of smooth surface portions 18 sandwiching the feature line 16 is less than 180 °.

The outer panel 10 has a stepped portion 20 at the front end (arrow X1 side in fig. 1A) of the body portion 14. The stepped portion 20 is a portion that is overlapped (covered) on the rear side of the front door in the assembled state of the automobile. The step portion 20 is formed over substantially the entire length in the arrow Y direction, and is also provided at the formation portion of the characteristic line 16. The stepped portion 20 is also curved in a mountain shape in the arrow Y direction and extends with a portion located on the extension line of the characteristic line 16 as a reference line, in conformity with the main body portion 14.

The step portion 20 of the outer panel 10 has, as viewed in a cross section along the arrow X direction shown in fig. 1B: a first orthogonal portion 22 that is bent from the main body portion 14 toward the cabin side; a parallel portion 24 extending in the arrow X direction from the first orthogonal portion 22; and a second orthogonal portion 26 that curves further toward the cabin side from the parallel portion 24. The first orthogonal portion 22 is longer than the second orthogonal portion 26.

The outer corner 28 between the main body portion 14 and the first orthogonal portion 22 forms a boundary between an outer exposed portion of the outer panel 10 and a portion hidden in the front door, and is formed as a rounded corner having a large curvature. On the other hand, the inner peripheral corner 30 between the first orthogonal portion 22 and the parallel portion 24 is formed as a rounded corner having a smaller curvature than the outer corner 28. Further, the inner peripheral corner 32 between the parallel portion 24 and the second orthogonal portion 26 is formed to be rounded to the same degree as the curvature of the outer corner 28.

The outer panel 10 described above is press-formed in the step shown in fig. 2, thereby performing main body portion forming processing for forming the main body portion 14 having the characteristic line 16 and step portion forming processing for forming the step portion 20.

In the body portion forming process, in the first stretching step, an intermediate formed body (not shown) having an intermediate ridge portion having a curvature radius larger than that of the characteristic line 16 to be formed is press-formed from a plate material. Then, in a second stretching step after the first stretching step, the target molded body (main body portion 14) is press-molded from the intermediate molded body.

Here, the intermediate molded body molded in the first stretching step may be molded to have a matching region where the cross-sectional shape coincides with the target molded body on both sides of the intermediate ridge line portion and an intermediate region where the cross-sectional shape does not coincide with the target molded body. Thus, in the second stretching step, the material of the intermediate molded body that is insufficient in the characteristic line 16 can be supplied to the intermediate molded portion from both sides of the intermediate ridge line portion, and scratches and cracks around the characteristic line 16 can be suppressed.

In the step portion forming process, the first drawing step portion 40 is formed by the first drawing step, and the second drawing step portion 60 is formed by the second drawing step. In the step portion forming process, after the second drawing step, a trimming (trim) step of cutting the outer periphery of the second drawn step portion 60 and a finishing step of forming the step portion 20 as a finished state by bending or the like are sequentially performed.

Here, in the conventional press molding method, when the stepped portion 20 is molded on the outer panel 10 having the characteristic line 16 as described above, wrinkles or cracks may occur in the formation portion of the characteristic line 16. In the press-forming method according to the present embodiment, the formation in consideration of the characteristic line 16 is performed in the first stretching step and the second stretching step, thereby suppressing the occurrence of wrinkles and cracks. The following describes in detail the formation of the first drawing stepped portion 40 in the first drawing step and the formation of the second drawing stepped portion 60 in the second drawing step.

In the first drawing step, as shown in fig. 3, 4A, and 4B, the edge side of the plate material (workpiece) for forming the characteristic line 16 (intermediate ridge line) is subjected to drawing work, whereby the first drawn step portion 40 is formed. The first drawing step portion 40 is formed in a shape in which the first inclined portion 42 is continuous with the outer periphery of the main body portion 14 and the first parallel portion 44 is continuous with the outer periphery of the first inclined portion 42.

A first outside curved portion 46 having a curvature much smaller than that of the outside corner portion 28 of the step portion 20 in a finished state is formed between the outer periphery of the main body portion 14 and the inner periphery of the first inclined portion 42. Similarly, a first inside bent portion 48 having a curvature much smaller than that of the inside inner peripheral corner portion 30 of the completed outer panel 10 is formed between the outer periphery of the first inclined portion 42 and the inner periphery of the first parallel portion 44.

In the first drawing step, for example, a first drawing apparatus 56 is used, and the first drawing apparatus 56 includes: a punch (punch; lower die) 50 that supports the back side of the workpiece (main body portion 14); a die (dies; upper die) 52 which presses the surface side of the workpiece; and a die convex portion 54 which presses the workpiece to form the first parallel portion 44. Although not shown, the workpiece located on the opposite side of the body 14 with the die convex portion 54 interposed therebetween is also sandwiched between the die and the punch, not shown.

Then, in the first drawing step, drawing is performed so that the cross-sectional shapes (cross-sections along the arrow X direction) of the extended region PF located on the extension line of the characteristic line 16 and the peripheral region AF located in the periphery shifted in the arrow Y direction with respect to the extended region PF are different from each other. The peripheral area AF corresponds to a portion continuous with the smooth surface portion 18 of the main body portion 14. That is, the planar shapes of the punch 50, the die 52, and the die-convex 54 of the first stretch-producing device 56 and the amount of protrusion of the die-convex 54 are appropriately designed so that the cross-sectional shape of the extended region PF is different from the cross-sectional shape of the peripheral region AF. Hereinafter, the configurations of the step portion 20 located in the peripheral area AF will be described with reference numeral a given to the end of the reference numeral, and the configurations of the step portion 20 located in the extended area PF will be described with reference numeral p given to the end of the reference numeral.

Specifically, the first outside bend 46a of the peripheral area AF is formed at substantially the same position as the outside corner 28 of the completed step portion 20 (slightly closer to the arrow X1 side than the outside corner 28). The first outer bent portion 46a sets the inclination angle of the first inclined portion 42a with respect to the main body portion 14 to be small. The first inside curved portion 48a of the peripheral area AF is formed at substantially the same position as the inside outer peripheral corner portion 32 of the step portion 20 in the finished state. Therefore, the first parallel portion 44a is formed shallow with respect to the drawing depth D1a of the smooth surface portion 18 (body portion 14).

On the other hand, the first outside bend 46p of the extended region PF is formed to be offset toward the arrow X1 side (outside) from the outside corner 28 of the completed step portion 20. That is, the first outside bend 46p of the extended region PF is offset toward the arrow X1 side from the first outside bend 46a of the peripheral region AF. In fig. 4A and 4B, the main body portion 14 (the character line 16) is located below the step portion 20 in the finished state because the main body portion 14 is processed at a shallower position than the character line 16 in the first drawing step, and the main body portion 14 is lifted up to the character line 16 in the second drawing step. The inclination angle of the first inclined portion 42p with respect to the main body portion 14 is set larger than the inclination angle of the first inclined portion 42a by the first outside bent portion 46 p.

The first inside bent portion 48p of the extended region PF is formed at substantially the same position as the inside outer peripheral corner portion 32 of the step portion 20 in the finished state. Therefore, the drawing depth D1p of the first parallel portion 44p with respect to the feature line 16 (body portion 14) is deeper than the drawing depth D1a of the peripheral region AF.

In addition, the curvatures of the first outside curved portion 46p and the first inside curved portion 48p in the extension area PF are formed smaller than those of the first outside curved portion 46a and the first inside curved portion 48a in the peripheral area AF. Further, the distance I1p between the first outside bend 46p and the first inside bend 48p in the extended region PF is formed shorter than the distance I1a between the first outside bend 46a and the first inside bend 48a in the peripheral region AF. Accordingly, when the length L1p of the 1 st inclined part 42p in the extension area PF is compared with the length L1a of the 1 st inclined part 42a in the peripheral area AF, a relationship of L1p < L1a is obtained.

In the 1 st drawn stepped portion 40 molded as described above, the 1 st outer bent portion 46p of the extension region PF and the vicinity thereof extend outward of the body portion 14 with respect to the 1 st outer bent portion 46a of the peripheral region AF. In the 1 st drawing stepped portion 40, the 1 st parallel portion 44p of the extension region PF is slightly recessed from the 1 st parallel portion 44a of the peripheral region AF.

In the second drawing step after the first drawing step, as shown in fig. 5, 6A, and 6B, the first drawing step portion 40 connected to the body portion 14 is further subjected to drawing work to mold the second drawing step portion 60. The second drawing stepped portion 60 is formed such that the second inclined portion 62 is continuous with the outer periphery of the main body portion 14, and the second parallel portion 64 is continuous with the outer periphery of the second inclined portion 62. A second outside curved portion 66 having a curvature much smaller than that of the outside corner portion 28 of the completed step portion 20 is formed between the outer periphery of the main body portion 14 and the inner periphery of the second inclined portion 62. Similarly, a second inside curved portion 68 having a curvature much smaller than that of the inside inner peripheral corner portion 30 of the stepped portion 20 in the finished state is formed between the outer periphery of the second inclined portion 62 and the inner periphery of the second parallel portion 64.

Specifically, in the second drawing step, the intermediate formed body (workpiece) having the first drawing step portion 40 is conveyed to the second drawing device 76, and is drawn by the second drawing device 76. Similarly to the first stretching apparatus 56, the second stretching apparatus 76 includes: a punch 70 that supports the back surface side of the body 14; a die 72 for pressing the surface side of the workpiece (body 14); and a die convex portion 74 for pressing the workpiece to form the second parallel portion 64. Although not shown, the workpiece located on the opposite side of the body 14 with the die convex portion 74 interposed therebetween is also sandwiched between the die and the punch, not shown. In the second stretching step, the planar shapes of the punch 70, the die 72, and the die convex portion 74 and the amount of protrusion of the die convex portion 74 are also appropriately designed, and thus the extended region PF and the peripheral region AF are molded so that their cross sections along the arrow X direction are different from each other.

Specifically, the second outside curved portion 66a of the peripheral area AF is formed at substantially the same position as the outside corner 28 of the completed step portion 20. The second outside bent portion 66a sets the inclination angle of the second inclined portion 62a with respect to the main body portion 14 to be larger than the inclination angle of the first inclined portion 42a in the first stretching step. The second inside bent portion 68a of the peripheral area AF is formed slightly on the arrow X2 side with respect to the inside outer peripheral corner 32 of the step portion 20 in the finished state. The second parallel portion 64a is formed deeper than the drawing depth D1a of the first parallel portion 44a in the first drawing step with respect to the drawing depth D2a of the smooth surface portion 18 (body portion 14).

On the other hand, the second outside bent portion 66p of the extension region PF is formed at substantially the same position as the outside corner portion 28 of the completed stepped portion 20. That is, the first outside bent portion 46p formed in the first stretching step is positioned on the X1 side with respect to the second outside bent portion 66p formed in the second stretching step. Therefore, the position of the vicinity of the first outer bent portion 46p where the plate material of the workpiece is stretched in the first stretching step is shifted from the position of the vicinity of the second outer bent portion 66p where the plate material is stretched in the second stretching step.

In addition, the curvature of the second outside bent portion 66p is formed to be larger than the curvature of the first outside bent portion 46p in the first drawing step. The second outside bent portion 66p also sets the inclination angle of the second slope portion 62p with respect to the main body portion 14 to be larger than the inclination angle of the second slope portion 62a of the peripheral area AF.

The second inside bent portion 68p of the extended region PF is located closer to the arrow X2 than the inside outer peripheral corner 32 of the completed step portion 20. The depth of drawing D2p of the second parallel portion 64p with respect to the feature line 16 (body portion 14) is formed to be slightly deeper than the depth of drawing D2a of the second parallel portion 64a of the peripheral region AF.

In addition, the curvatures of the second outside curved portion 66p and the second inside curved portion 68p in the extension area PF are formed smaller than those of the second outside curved portion 66a and the second inside curved portion 68a in the peripheral area AF. Also, the distance I2p between the second outside bent portion 66p and the second inside bent portion 68p in the extension area PF is set shorter than the distance I2a between the second outside bent portion 66a and the second inside bent portion 68a in the peripheral area AF. When the length L2p of the 2 nd inclined part 62p in the extension area PF is compared with the length L2a of the 2 nd inclined part 62a in the peripheral area AF, a relationship of L2p < L2a is obtained.

Returning to fig. 2, in the trimming process after the second drawing process, the outer periphery of the second drawing stepped portion 60 is cut so as to match the size of the stepped portion 20. That is, the second parallel portion 64 of the second drawn stepped portion 60 protrudes to the outside longer than the stepped portion 20 in the finished state, and by cutting the outside of the second parallel portion 64 in the trimming process, a trimmed molded article having a size corresponding to the stepped portion 20 in the finished state (in view of molding of the second orthogonal portion 26) is obtained.

Then, in a finishing step after the trimming step, the trimmed product is placed on a press device (not shown) and press-formed (bending or the like) to form the stepped portion 20.

The press forming method according to the present embodiment is basically configured as described above, and the operation thereof will be described below.

In the press forming method, as shown in fig. 2, a first drawing step, a second drawing step, a trimming step, and a finishing step are sequentially performed to form the main body portion 14 having the characteristic line 16 and simultaneously form the stepped portion 20 at the tip of the main body portion 14.

As shown in fig. 4A and 6A, in the first stretching step, the first outside bent portion 46A is formed in the peripheral area AF at substantially the same position as the second outside bent portion 66A of the peripheral area AF in the second stretching step. In the first drawing step, the first parallel portion 44a having the drawing depth D1a shallower than the drawing depth D2a of the second parallel portion 64a is formed. The length L1a of the first inclined portion 42a is shorter than the length L2a of the second inclined portion 62 a. Therefore, the portion of the main body 14 that is continuous with the smooth surface portion 18 is processed into the same shape as the first drawing step in manufacturing the normal step portion 20.

On the other hand, as shown in fig. 4B and 7A, in the first stretching step, the first outside bent portion 46p is formed at a position outside (arrow X1 side) the second outside bent portion 66p of the extended region PF of the second stretching step in the extended region PF. In the first drawing step, the first parallel portions 44p of the extended region PF are formed to have the same depth as the drawing depth D2p of the second parallel portions 64p of the second drawing step. More specifically, the first parallel portion 44p is formed to be equal to or less than the depth of the completed step portion 20, and the length L1p of the first inclined portion 42p is similar to the length L2p of the second inclined portion 62 p.

That is, in the extended region PF of the first stretching step, the plate material near the first outside bend portion 46p having a small curvature is stretched, and the second parallel portion 64p is pressed (punch) to a position close to the parallel portion 24 of the step portion 20. Accordingly, the thickness of the portion near the first outer bend portion 46p at the position offset outward gradually becomes thinner (smaller) in the planar direction with respect to the outer corner portion 28 of the completed step portion 20.

In the second drawing step after the first drawing step, the peripheral area AF continuous with the smooth surface portion 18 of the main body portion 14 shown in fig. 6A is processed into the same shape as the second drawing step in the production of the normal step portion 20. That is, in the peripheral area AF, the second outside curved portion 66a is molded at substantially the same position as the outside corner 28 of the step portion 20 in the finished state, and the second parallel portion 64a is molded at a depth close to the parallel portion 24 of the step portion 20 in the finished state.

On the other hand, in the extended region PF of the second stretching step, as shown in fig. 6B and 7A, the second outside bent portion 66p is formed so as to be shifted inward (arrow X2 side) with respect to the first outside bent portion 46 p. In the second stretching step, the second inside bend 68p is formed so as to have a curvature greater than that of the first inside bend 48p in the extended region PF at a position inward (arrow X2 side) of the first inside bend 48p in the first stretching step.

Therefore, in the extended region PF in the second stretching step, the plate material near the second outer bent portion 66p on the inner side of the first outer bent portion 46p in the first stretching step is stretched. Therefore, different portions of the plate material constituting the step portion 20 are stretched in the first stretching step and the second stretching step, and thus it is possible to avoid concentrated stretching of specific portions of the plate material. Therefore, the stepped portion 20 can suppress the occurrence of cracks in the extended region PF.

As shown in fig. 7A and 7B, the second inside bend 68p in the second stretching step is located close to the inside inner peripheral corner 30 of the completed step portion 20 (at a distance Cp shorter than the distance between the second inside bend 68a in the peripheral region AF and the inside inner peripheral corner 30 of the completed step portion 20). That is, the perimeter of the extended region PF around the second inner bend 68p is defined as l₁And the perimeter of the inner peripheral corner 30 of the step part 20 in the finished state is defined as l₀In the case of (2), the circumference length l₁And the circumference l₀The sizes are close to each other (the circumferential lengths are almost not different from each other). The periphery of the second inside curved portion 68p and the periphery of the inside inner peripheral corner portion 30 of the extended region PF are ranges in which the stepped portion 20 is formed by the curved characteristic line 16 of the main body portion 14.

Here, when the linear shrinkage rate S in the extended region PF is expressed by the following formula (1), the linear shrinkage rate S of the extended region PF in the present embodiment is much smaller than that of a normal press molding (for example, the linear shrinkage rate S of the peripheral region AF).

S＝(l₁-l₀)/l₀ …(1)

By thus making the linear shrinkage rate S of the extended region PF small, the sheet material concentration is suppressed as much as possible when the step portion 20 in a finished state is molded using the second drawn step portion 60 (the finished molded product after the finishing process) in the finishing process. Therefore, the stepped portion 20 also suppresses the generation of wrinkles in the extended region PF.

The present invention is not limited to the above embodiments, and various modifications can be made in accordance with the gist of the present invention. For example, the press forming method is not limited to the production of the outer panel 10 applied to the rear door, and can be applied to various molded products having the character string 16 and the step portion 20.

The technical ideas and effects that can be grasped from the above embodiments are described below.

In the press molding method, the first drawing step and the second drawing step are performed, whereby the stepped portion 20 can be formed satisfactorily without generating wrinkles or cracks even in the end portion of the body portion 14 having the characteristic line 16. That is, since the first outside bent portion 46p formed in the first stretching step and the second outside bent portion 66p formed in the second stretching step are shifted in position, the plate material at a specific portion in the extended region PF can be suppressed from becoming extremely thin. Therefore, the crack can be suppressed from entering the extension area PF. Further, the first parallel portion 44p formed in the first drawing step has the same depth as the second parallel portion 64p, and the second inner bent portion 68p can be brought close to the step portion 20 in the finished state by forming the curvature of the second inner bent portion 68p to be large in the second drawing step. Therefore, the second inside bend 68p is less contracted in the finishing process, and the occurrence of wrinkles in the extended region PF is suppressed. Accordingly, the press forming method can greatly improve the yield in manufacturing.

In the first drawing step, the first outside bent portion 46a is formed at the same position as the second outside bent portion 66a in the peripheral area AF located in the periphery in the direction orthogonal to the extending direction of the characteristic line 16 (intermediate ridge line), and the first parallel portion 44a is formed to be shallower than the drawing depth D2a of the second parallel portion 64 a. Accordingly, in the peripheral region AF located around the extension region PF, the shape of the stepped portion 20 can be gradually approximated by two stages of drawing, and the stepped portion 20 can be stably molded.

The first outside bent portion 46p of the extension area PF is formed outside the first outside bent portion 46a of the peripheral area AF. Accordingly, in the first drawing step, the extension region PF (near the first outer bend portion 46p) extends outward with respect to the peripheral region AF, thereby preventing deformation of the shape of the main body portion 14 having the characteristic line 16 (intermediate ridge line).

In addition, in the step portion 20, the outer corner portion 28 is formed at the position of the second outer curved portion 66p and the inner peripheral corner portion 30 is formed at the position of the second inner curved portion 68p by the finishing process, and the interval Cp between the second inner curved portion 68p and the inner peripheral corner portion 30 of the extended region PF is shorter than the interval between the second inner curved portion 68a and the inner peripheral corner portion 30 of the peripheral region AF. This can further suppress the contraction of the extension region PF in the second stretching step, and can more reliably suppress the occurrence of wrinkles in the stepped portion 20.

In the second stretching step, the second inside bend 68p of the extension region PF is moved more inward than the first inside bend 48p in the first stretching step. Accordingly, in the second stretching step, the sheet material in the vicinity of the second inside bend 68p of the extension region PF can be suppressed from being elongated, and the shape of the step portion 20 in the finished state can be approximated.

The stepped portion 20 is provided at the front end of the outer panel 10 constituting the rear door of the automobile. Accordingly, even if the outer panel 10 constituting the rear door has the character line 16, the step portion 20 overlapping the boundary portion of the front door at the front end portion can be molded in a beautiful manner.