Patent Application
20240109114
This application is based upon and claims the benefit of priority from Chinese Patent Application No. 202211209960.X filed on Sep. 30, 2022, the contents of which are incorporated herein by reference.
The present invention relates to a press forming method for forming a plate material into a predetermined shape.
Outer panels such as a bonnet, a side panel and a door panel of an automobile are generally produced by press-forming a metal plate material. The outer panel is a component part that determines the design of an automobile. For example, a design having a ridge line portion with a small radius of curvature, which is referred to as a character line, is used. In order to form the ridge line portion having such a small radius of curvature by press-forming, an advanced technique is required. For example, WO 2020/195591 A1 discloses a press forming method in which a ridge line portion having a small radius of curvature is formed by pressing.
In the press forming method disclosed in WO 2020/195591 A1, an intermediate formed body having an intermediate ridge line portion having a larger radius of curvature than a ridge line portion is formed in a first pressing step, and then the intermediate ridge line portion is formed into a ridge line portion having a small radius of curvature in a second pressing step. In this press forming method, the intermediate formed body is provided with a slack portion (outer region) in the vicinity of the intermediate ridge line portion so as to be deviated from a target formed body (target formed body 20). Such a slack portion serves as an elongation allowance of the plate material when the ridge line portion having a small radius of curvature is formed, and enables the ridge line portion having a small radius of curvature to be formed by two pressing steps while preventing cracks in the vicinity of the ridge line portion.
However, in the above-described press forming method, as the angle between a pair of flat portions that are located on both sides of the ridge line portion (hereinafter referred to as a dihedral angle θ) decreases, the elongation of the ridge line portion increases. Thus, a larger elongation allowance is required. In the above-described press forming method, if the slack portion is increased in order to provide an elongation allowance required for forming the ridge line portion, the intermediate formed body interferes with an upper die when the intermediate formed body is held between the upper die and a blank holder. As a result, the conventional press forming method has a problem that the formed product is scratched when the dihedral angle θ is reduced.
In order to prevent the occurrence of scratches due to interference between the intermediate formed body and the upper die, it is conceivable to increase the height of the step portion at the boundary between the product portion and the discarded portion of the upper die. In the case of using such an upper die, it is possible to prevent interference between the upper die and the intermediate formed body having the slack portion greatly expanded in the press stroke direction.
However, when the height of the step portion at the boundary between the product portion and the discarded portion of the upper die is increased, the elongation of the discarded portion increases, and as a result, local elongation occurs at the boundary between the product portion and the discarded portion. In order to prevent such local elongation, it is conceivable to provide a slack portion serving as an elongation allowance in the discarded portion. However, it has been found that when the slack portion is provided in the discarded portion, wrinkles arise in the vicinity of the boundary between the product portion and the discarded portion.
It is an object of the present invention to solve the above problems.
According to an aspect of the present invention, there is provided a press forming method for forming a plate material into a target formed body, the plate material including a product portion and a discarded portion located on an outer periphery of the product portion, the discarded portion being to be separated from the product portion after forming, the target formed body including a ridge line portion in the product portion, the press forming method including: a first step of forming an intermediate formed body including an intermediate ridge line portion with an edge radius larger than an edge radius of the ridge line portion; and a second step of forming the target formed body from the intermediate formed body, wherein the product portion of the intermediate formed body includes: an inner portion deviated inward in an edge radial direction of the ridge line portion from the target formed body; and a slack portion deviated outward in the edge radial direction from the target formed body, and the discarded portion of the intermediate formed body includes: a separation portion which is spaced apart from an upper die at an initial stage of the second step to provide an elongation allowance for the discarded portion; and a contact portion configured to come into contact with the upper die to prevent movement of the plate material at the initial stage of the second step.
In the press forming method of the above aspect, since the intermediate formed body of the discarded portion has the separation portion spaced apart from the upper die, an elongation allowance for the discarded portion can be provided. In addition, in the above-described press forming method, since the discarded portion comes into contact with the upper die, it is possible to prevent the excessive supply of the material at the initial stage of the forming step and to prevent the occurrence of wrinkles. Therefore, the press forming method of the above aspect can achieve both prevention of local elongation of the discarded portion and prevention of occurrence of wrinkles.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example.
The press forming method of the present embodiment is applied to, for example, an outer panel 10 of a roof panel or of a trunk portion, of an automobile. This press forming method is suitably used for forming an outer panel 10 having a ridge line portion 16 between flat portions 14 that form the internal angle (dihedral angle) of 90° or less, such as a spoiler 12. In this embodiment, an example of forming a rectangular plate material 18 shown in
The target formed body 20 has a ridge line portion 16 in a product portion 22. The ridge line portion 16 has a small radius of curvature (edge radius) of, for example, 2.5 mm to 9 mm, and has a sharp blade-shaped appearance. The ridge line portion 16 is, for example, a portion of the spoiler 12 and is integrally formed with the outer panel 10. The target formed body 20 has a first slope face 14a on one side of the ridge line portion 16 and a second slope face 14b on the other side of the ridge line portion 16. The ridge line portion 16 is sandwiched between the first slope face 14a and the second slope face 14b. An angle between the first slope face 14a and the second slope face 14b is referred to as a dihedral angle (internal angle or included angle) θ. The press forming method of the present embodiment can form a target formed body 20 in which the dihedral angle θ is relatively small, for example, 30° to 90°.
The plate material 18 used in the press forming method of the present embodiment is formed of, for example, a thin metal plate such as steel or aluminum alloy having a thickness of 0.3 mm to 3 mm. The plate material 18 has a product portion 22 and a discarded portion 24. The product portion 22 is positioned on the central portion of the plate material 18 and is formed into a product shape. The discarded portion 24 is a band-shaped portion located at the peripheral edge portion of the plate material 18 and surrounding the product portion 22.
The discarded portion 24 is positioned at the peripheral portion of the plate material 18 and surrounds the outside of the product portion 22. As shown in
The press forming method of the present embodiment includes a first step and a second step. The first step is a step of forming the flat plate material 18 into an intermediate formed body 30 shown in
Hereinafter, the intermediate formed body 30 will be described. The intermediate formed body 30 includes an intermediate ridge line portion 32, step portions 36, and fixing structures 38. The intermediate ridge line portion 32 is located in the product portion 22 and has an inner portion 33 and a slack portion 34. On the other hand, the step portion 36 and the fixing structure 38 are located in the discarded portion 24.
The intermediate ridge line portion 32 is a ridge-line-shaped portion provided in a portion where the ridge line portion 16 of the target formed body 20 is to be formed. The intermediate ridge line portion 32 has an edge radius larger than the edge radius of the ridge line portion 16. The inner portion 33 of the intermediate ridge line portion 32 deviates downward from the shape of the target formed body 20. The slack portion 34 is located on a side (second slope face 14b side) of the inner portion 33, and is continuously connected to the inner portion 33 with a smooth edge radius. The slack portion 34 deviates so as to bulge outward (upward) in the direction of the edge radius from the second slope face 14b of the target formed body 20. The product portion 22 other than the intermediate ridge line portion 32 of the intermediate formed body 30 is a matching portion 35 that matches the shape of the target formed body 20. The matching portion 35 is formed respectively on both sides of the intermediate ridge line portion 32.
As shown in the enlarged view of
The fixing structure 38 includes a lock bead 40 and an adjustment bead 42. The lock bead 40 and the adjustment bead 42 extend in a groove shape along the outer periphery of the plate material 18. The adjustment bead 42 is located on the inner peripheral side, and the lock bead 40 is located on the outer peripheral side. The lock bead 40 is sandwiched between a lock recess 46 of the blank holder 44 and a lock convex portion 50 of the upper die 48 to prevent positional deviation of the plate material 18. The lock bead 40 is deformed into a rectangular concave shape by the blank holder 44 and the upper die 48 in the holding process. Although not particularly limited, the lock bead 40 may be a round bead having a semicircular cross-sectional shape with an upward concave shape.
The adjustment bead 42 is located between the lock bead 40 and the step portion 36. The adjustment bead 42 has a semicircular cross-sectional shape with a concave upper side so as to form a portion apart from the upper die 48. The adjustment bead 42 is accommodated in an adjustment recess 52 of the blank holder 44. The adjustment bead 42 appears in the intermediate formed body 30 but disappears in the target formed body 20. The adjustment bead 42 serves as an elongation allowance for the discarded portion 24 in the second step. When the second step is completed, the adjustment bead 42 is fully stretched (elongated) and deformed into the shape of the target formed body 20 along the upper die 48.
An end portion on the inner peripheral side (inner end portion) of the adjustment bead 42 serves as a first contact portion 54 that comes into line contact with the blank holder 44 and the upper die 48 in the holding step of
As shown in the drawing, the second contact portion 58 is a portion which comes into line contact with the upper die step portion 60 of the upper die 48 in the holding step. The first contact portion 54 and the second contact portion 58 prevent movement of the discarded portion 24 by friction force, during a process from the holding step to the initial stage of the forming step. As a result, the first contact portion 54 and the second contact portion 58 prevent excessive supply of the elongation allowance and prevent occurrence of wrinkles 31.
The second step is a step performed after the first step. The second step is a step of press-forming the intermediate formed body 30 into the target formed body 20. As shown in
The blank holder 44 supports the fixing structure 38 of the discarded portion 24 of the plate material 18 from below. The blank holder 44 extends annularly along the outer periphery of the plate material 18. The blank holder 44 has the lock recess 46 and the adjustment recess 52 formed in an upper surface 44a. The lock recess 46 is a recessed groove that accommodates the lock bead 40 of the intermediate formed body 30. The lock recess 46 is disposed at a position corresponding to the lock bead 40 and extends annularly in a plan view. After the holding step, the lock convex portion 50 of the upper die 48 is fitted into the lock recess 46. The lock bead 40 of the intermediate formed body 30 is sandwiched and held between the lock recess 46 and the lock convex portion 50.
The adjustment recess 52 is a recessed groove that accommodates the adjustment bead 42 of the intermediate formed body 30. The adjustment recess 52 is positioned on the inner peripheral side of the lock recess 46. The adjustment recess 52 is disposed at a position corresponding to the adjustment bead 42 and extends annularly in a plan view. The adjustment recess 52 has a semicircular cross section and has the same shape as the semicircular adjustment bead 42 of the intermediate formed body 30. As shown in
The blank holder 44 can be elevated and lowered. In the holding step of the second step, the blank holder 44 clamps the intermediate formed body 30 in cooperation with the upper die 48 as the upper die 48 is lowered. When the blank holder 44 is pressed downward by the upper die 48, it descends together with the upper die 48. In the holding step, the first contact portion 54 at the inner end of the adjustment bead 42 is pressed against the upper die 48 by the edge of the adjustment recess 52 of the blank holder 44. The blank holder 44 has a guide portion 53 on the inner peripheral side of the adjustment recess 52. The guide portion 53 has an inclination for guiding the adjustment bead 42 to the adjustment recess 52. The guide portion 53 is separated from the upper die 48 in the holding step. The guide portion 53 forms a gap in which the elongation allowance of the discarded portion 24 can be displaced in the second step.
As shown in
As shown in
The upper die 48 has, on the outer peripheral side of the upper die step portion 60, a clamping portion 74 that holds and sandwiches the plate material 18 between itself and the blank holder 44. The clamping portion 74 has the lock convex portion 50. The lock convex portion 50 is located at a position corresponding to the lock recess 46 of the blank holder 44, and has a convex shape that fits into the lock recess 46. The lock convex portion 50 sandwiches the lock bead 40 of the intermediate formed body 30 between the lock convex portion 50 and the lock recess 46. The lock convex portion 50 and the lock recess 46 prevent displacement of the intermediate formed body 30 relative to the upper die 48. A portion of the upper die 48 that is located right above the adjustment recess 52 of the blank holder 44 is formed flat.
Hereinafter, a specific step of the second step of the press forming method of the present embodiment will be described.
First, as shown in
Next, as shown in
As shown in
As the dihedral angle θ between the first slope face 14a and the second slope face 14b adjacent to the ridge line portion 16 decreases, the elongation allowance required for forming the ridge line portion 16 increases. As the dihedral angle θ becomes smaller, it is necessary to increase the bulge of the slack portion 34. However, if the bulge of the slack portion 34 is large, when the intermediate formed body 30 is held between the upper die 48 and the blank holder 44, the slack portion 34 interferes with the upper die 48, and as a result, the intermediate formed body 30 is scratched or dented.
Therefore, in the present embodiment, as described above, the upper die 48 having the upper die step portion 60 having a height larger than the height of the step portion 36 of the intermediate formed body 30 is used. Such an upper die 48 can increase the distance H2nd between the matching portion 35 of the intermediate formed body 30 and the upper die 48. Therefore, in the press forming method of the present embodiment, the intermediate formed body 30 having the slack portion 34 that bulges more greatly can be fixed to the upper die 48 without interfering with the upper die 48.
When the height of the step portion 36 of the intermediate formed body 30 is made smaller than the height of the upper die step portion 60, the difference in the length of the discarded portion 24 between the intermediate formed body 30 and the target formed body 20 becomes large.
As described with reference to
Next, in the second step, as shown in
In the initial stage of the forming step, the separation portion 56 and the adjustment bead 42 are also deformed in the discarded portion 24 of the intermediate formed body 30. As a result, movement of the sheet material 18 in the direction of the forming surface 66 occurs in the discarded portion 24. At this time, the first contact portion 54 and the second contact portion 58 prevent occurrence of wrinkles 31 in the discarded portion 24.
The press forming method of a comparative example shown in
On the other hand, as shown in
Next, as shown in
As shown in
By the above steps, the plate material 18 is formed into the target formed body 20, and the press forming method of the present embodiment is completed. As described above, according to the press forming method of the present embodiment, the target formed body 20 having the ridge line portion 16 with the small dihedral angle (internal angle) 0 can be efficiently manufactured in the two-stage forming process. In addition, since interference between the slack portion 34 of the intermediate formed body 30 and the upper die 48 can be prevented, the product portion 22 can be prevented from scratching. Thus, it is possible to manufacture a formed product having excellent design properties. Furthermore, this press forming method can prevent local elongation and occurrence of wrinkles 31 of the discarded portion 24, and can prevent degradation in quality of the product portion 22 caused by the discarded portion 24.
The above disclosure is summarized as follows.
One aspect of the present invention is characterized by the press forming method for forming the plate material 18 into the target formed body 20, the plate material including the product portion 22 and the discarded portion 24 located on the outer periphery of the product portion, the discarded portion being to be separated from the product portion after forming, the target formed body including the ridge line portion 16 in the product portion, the press forming method including: the first step of forming the intermediate formed body 30 including the intermediate ridge line portion 32 with the edge radius larger than the edge radius of the ridge line portion; and the second step of forming the target formed body from the intermediate formed body, wherein the product portion of the intermediate formed body includes: the inner portion 33 deviated inward in the edge radial direction of the ridge line portion from the target formed body; and the slack portion 34 deviated outward in the edge radial direction from the target formed body, and the discarded portion of the intermediate formed body includes: the separation portion 56 which is spaced apart from the upper die 48 at the initial stage of the second step to provide the elongation allowance for the discarded portion; and the contact portion 54, 58 which comes into contact with the upper die to prevent movement of the plate material at the initial stage of the second step.
In the press forming method described above, since the intermediate formed body of the discarded portion has the separation portion separated from the upper die, an elongation allowance for the discarded portion can be provided. In addition, in the above-described press forming method, since the discarded portion comes into contact with the upper die, it is possible to prevent the excessive supply of the material at the initial stage of the forming step and to prevent the occurrence of wrinkles. Therefore, the press forming method of the above aspect can achieve both prevention of local elongation of the discarded portion and prevention of occurrence of wrinkles.
In the above press forming method, the forming die 62 used in the second step may include the upper die having a shape of the target formed body, the lower die 64 facing the upper die, and the blank holder 44 disposed on the outer peripheral side of the lower die and configured to hold the discarded portion of the intermediate formed body between the blank holder and the upper die, the second step may include: the holding step of holding the discarded portion between the blank holder and the upper die; and the forming step of pressing the intermediate formed body with the upper die and the lower die to form the intermediate formed body into the target formed body, the upper die may include the upper die step portion 60 at the boundary portion between the product portion and the discarded portion, and the separation portion of the intermediate formed body may be disposed at a position facing the upper die step portion. In this press forming method, the discarded portion is provided with an elongation allowance, and the occurrence of wrinkles due to inward movement (excessive supply) of the plate material can be prevented.
In the above-described press forming method, the intermediate formed body may include the adjustment bead 42 at a position between the blank holder and the upper die, the adjustment bead being spaced apart from the upper die to provide the elongation allowance. In this press forming method, since the intermediate formed body further includes the adjustment bead as an elongation allowance for the discarded portion, excessive tension due to local elongation of the discarded portion can be relaxed.
In the above-described press forming method, the blank holder may include the adjustment recess 52 configured to accommodate the adjustment bead to thereby space the intermediate formed body apart from the upper die. With this press forming method, a large elongation allowance can be provided in a narrow space by providing the elongation allowance in a portion that abuts against the blank holder.
In the above press forming method, the contact portion may include: the first contact portion 54 configured to be in line contact with the upper die at an inner end portion of the adjustment bead; and the second contact portion 58 configured to be in line contact with the upper die step portion, and the separation portion may be located between the first contact portion and the second contact portion. In this press forming method, the first contact portion between the adjustment bead and the upper die and the second contact portion between the step portion and the upper die can prevent movement of the material in the initial stage of the forming step. As a result, the press forming method can prevent the occurrence of wrinkles in the discarded portion.
In the press forming method, in the forming step, the separation portion and the adjustment bead of the intermediate formed body may elongate (stretch) to thereby deform the discarded portion into a shape that causes the discarded portion to be in close contact with the upper die. In this press forming method, the separation portion and the adjustment bead stretch so as to be in close contact with the upper die in the forming step, and thus it is possible to suppress generation of excessive tension in the discarded portion.
Note that the present invention is not limited to the embodiment described above, and various configurations can be adopted therein without departing from the essence and gist of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202211209960.X | Sep 2022 | CN | national |
