JP7226382B2 - Method for manufacturing pressed parts, die for unbending, and method for forming pressed parts - Google Patents

Description

TECHNICAL FIELD The present invention relates to a technique for manufacturing a pressed part having an L-shaped portion comprising a top plate portion and vertical wall portions formed on both sides or one side of the top plate portion by press-molding a metal plate with a mold. .
The present invention is particularly suitable when using a metal plate that tends to have a large amount of springback, such as a high-strength steel plate, which is a steel plate having a tensile strength of 980 MPa or more.

In recent years, high-strength steel sheets have been widely used for automobile parts in order to reduce the weight of automobile bodies due to environmental problems. Automobile parts are often manufactured using press molding, which is excellent in terms of manufacturing costs. However, high-strength steel sheets have a greater elastic recovery (springback) after forming than low-strength steel sheets. It is often difficult. Therefore, there is a strong demand for the development of a method for manufacturing pressed parts for suppressing springback of automobile parts using high-strength steel sheets.

Here, when forming a metal plate into a press part shape having an L-shaped portion with an L-shaped cross section in which the top plate portion and the vertical wall portion are connected by the first bending portion, the vertical wall portion (flange) is formed into two parts. Press molding may be performed in stages. In this case, the part to be the L-shaped part consisting of the top plate part and the vertical wall part is once formed into a preformed shape with a crank-shaped cross section (a shape in which the vertical wall part is bent to the opposite side to the first bending part in the middle). It is formed by a preforming step of forming and a bending back step of bending back the middle portion of the vertical wall portion that has been bent in the preforming step. Note that the two-stage molding described above is performed for the purpose of, for example, suppressing the occurrence of wrinkles.

In such a part where the flange with an L-shaped cross section is formed in two stages, in addition to the angle change due to the springback of the punch shoulder ridge of the mold, the die in the first process (preforming process) The bent back portion of the shoulder ridge also undergoes an angle change due to springback. Therefore, the amount of dimensional change at the tip of the flange increases compared to the case where the desired L-shaped cross section is formed in one step.

As a countermeasure against angle change due to springback of the pressed parts obtained by the above method, there is a molding method in which the shape of the mold is changed from the correct size in advance so that the tip of the flange becomes the correct size after releasing the mold. be. However, in this molding method, if the actual amount of springback cannot be accurately predicted, deviation occurs in the actual machine, and it takes time and cost to correct the mold. In addition, when high-strength steel sheets are used, there is a possibility that dimensional accuracy failure due to material strength fluctuations cannot be avoided.

As countermeasures against this problem, there are a work bending method described in Patent Document 1 and a metal plate bending method described in Patent Document 2. However, all of these are countermeasures against angle change due to springback of the punch shoulder ridge (first bent portion), and are not effective against angle change due to springback of the bent back portion of the die shoulder ridge.

Japanese Patent No. 4766084 Japanese Patent No. 4015398

When manufacturing an L-shaped portion consisting of a top plate portion and a vertical wall portion (flange) by two-step molding, the method described in Patent Document 1 and Patent Document 2 has a spring-go component near the ridgeline of the punch shoulder, that is, the surface layer A compressive stress is applied to the back layer, and a tensile stress is applied to the back layer to cancel the springback component, thereby suppressing the angle change due to the springback of the above-mentioned bent back portion.

The present invention has been made by focusing on such a point, and when manufacturing an L-shape consisting of a top plate portion and a vertical wall portion (flange) by two-step molding, the vertical wall portion can be formed by a simple means. The purpose is to reduce the dimensional change of the tip.

The authors targeted a press part with a top plate and vertical walls (flanges) formed on both sides and one side of the top plate, and suppressed the angle change of the vertical wall with respect to the top plate. The following findings (1) and (2) were obtained as a result of examination of a pressing method that can be performed and that does not require a complicated mold configuration.
(1) A convex shape is given to the unbent part of the bent die shoulder ridge line, and in the next process, the difference in stress between the front and back of the unbent part is reduced by bending and stretching to a regular shape, and the angle change of the unbent part is reduced. become smaller.
(2) By giving a convex shape to the bent back part of the die shoulder ridge line and bending and stretching it into a regular shape in the next process, the spring back component and the spring go component coexist in the bent back part, and when the material strength fluctuates Angular variation is reduced (material strength sensitivity is reduced).
Here, material strength sensitivity is an index of change in dimensional accuracy with respect to change in material strength of the metal plate, and small material strength sensitivity means that change in dimensional accuracy is small with respect to change in material strength.
The present invention was made based on such findings.

That is, one aspect of the present invention is to manufacture a pressed part by press forming a metal plate into a pressed part shape having a top plate portion and a vertical wall portion continuous to the top plate portion via a first bent portion. In the method of manufacturing a pressed part, the metal plate is bent at the first bending portion, and a plate material serving as the vertical wall portion, when the direction of the vertical wall portion separating from the top plate portion is defined as the separation direction. a preforming step of bending in a direction opposite to the first bending portion at a second bending portion located midway in the separation direction of the portion; and a bending back step of bending back the second bending portion after the preforming step. and, when bending back in the bending back step, the cross section in the separation direction of the plate material portion to be the vertical wall portion is in the opposite direction to the convex direction of the second bent portion in the preforming step. The gist of the invention is that a protruding portion is provided, and the position of the maximum protruding portion of the protruding portion is arranged within the region that was the second bent portion.

In another aspect of the present invention, the metal plate is press-molded into a press part shape having a top plate portion and a vertical wall portion continuous to the top plate portion via a first bent portion. is bent at the first bent portion and bent in a direction opposite to the first bent portion at a second bent portion, which is an intermediate position of the plate material portion to be the vertical wall portion, into a preformed shape. and a bending back step of bending back the second bent portion after the preforming step, a die used in the bending back step, wherein the die is in contact with the plate material to be the vertical wall portion. The molding surface of the mold has a cross section in a direction away from the first bent portion with respect to the plate material portion to be the vertical wall portion, and the cross section is convex in the direction opposite to the convex direction of the second bent portion in the preforming step. Further, the gist of the present invention is that the position of the maximum projecting portion of the projection has a shape capable of providing a projecting portion disposed within the region that becomes the second bent portion.

According to the aspect of the present invention, when the once bent second bent portion (unbent portion) is bent back, the vertical wall portion is provided with a convex portion at a position overlapping with the unbent portion, whereby the top plate is Even in the case of two-step molding of an L-shape consisting of a portion and a vertical wall portion (flange), it is possible to reduce the dimensional change at the tip of the vertical wall portion by a simple means.
In addition, when the vertical wall portion is subsequently bent and stretched into the intended regular shape, it is possible to further reduce the dimensional change at the tip of the vertical wall portion.
Note that, as the target component shape, if the vertical wall portion can allow the bulge formed by the above-described convex shape portion, that shape may be used as the final shape.

It is a figure showing an example of a press part concerning an embodiment based on the present invention. It is a figure explaining the process of 1 time molding. It is a figure explaining the process of the manufacturing method concerning embodiment based on this invention. It is a figure explaining the process of two-stage molding. It is a figure explaining the process of the two-stage molding which concerns on 1st Embodiment based on this invention. It is a figure explaining shaping|molding of the metal mold|die in the bending process which concerns on embodiment based on this invention. It is a figure explaining the stress state of the vertical wall part surface layer in one molding. It is a figure explaining the stress state of the vertical wall part surface layer in the conventional two-stage molding. FIG. 5 is a diagram for explaining the stress state of the surface layer of the vertical wall portion in the two-stage molding of the example of the present invention. It is a schematic diagram explaining the convex shape provided in the molding surface in an Example. It is a figure which compares the amount of springbacks. FIG. 3 compares material strength sensitivity. It is a figure which shows the state of springback after a bending return process. It is a figure which shows the state of springback after a restrike process.

Next, embodiments of the present invention will be described with reference to the drawings.
<Press part shape>
The pressed part shape of the pressed part 2 targeted by the present embodiment is at least a partial part shape as shown in FIG. It has an L-shaped portion 1 having an L-shaped cross section and a vertical wall portion 1B. That is, the present embodiment is applicable to any pressed part 2 having an L-shaped portion 1 at least partially. A flange portion may be formed at the tip of the vertical wall portion 1B. If there is no flange portion, the vertical wall portion 1B constitutes a flange.
Note that the dimensions shown in FIG. 1 are also the dimensions in the example, and do not limit the present invention.

In the following, a description will be given of the case where the L-shaped portion 1 is press-formed, focusing only on the L-shaped portion 1 when the metal plate 10 is press-formed into the press-formed pressed component 2 .

<When forming the L-shaped portion 1 by one-time molding (reference example)>
When the flat metal plate 10 is pressed once to form the L-shaped portion 1, for example, as shown in FIG. , the die 52 (upper mold) is lowered toward the punch 50 to perform the operation. By this forming, the metal plate 10 is bent along the shoulder ridgeline of the punch 50, so that the top plate portion 1A and the vertical wall portion 1B form an L-shaped cross section through the first bent portion 1C (portion that abuts on the punch shoulder ridgeline). It is molded into a shape and shape.
After that, the vertical wall portion 1B is shaped by appropriately performing a restriking process using molds 53 and 54 as shown in FIG. 2(b).

<When forming the L-shaped portion 1 by two-step forming (construction method on which the present embodiment is based)>
On the other hand, when forming the L-shaped portion 1 by two-stage press forming (also referred to as double forming) of the flat metal plate 10, as shown in FIG. Performed in two moldings.
In this embodiment, a restrike process 3D for performing a restrike process is provided after the bendback process 3C.
Moreover, in this embodiment, the trimming process 3B is provided between the preforming process 3A and the bending back process 3C. In the trimming step 3B, for example, trim processing is performed on the region that will be the leading end of the vertical wall portion 1B in the metal plate 10 after the preforming step 3A, to adjust the shape of the end portion of the vertical wall portion 1B. The reason why trimming is performed after bending in the preforming step 3A is to improve the shape accuracy of the product.
Here, the direction in which the vertical wall portion 1B separates from the top plate portion 1A and the first bent portion 1C (the direction toward the tip of the vertical wall portion 1B) is referred to as the separation direction (vertical direction in FIGS. 4 and 5). .

[Preforming step 3A]
In the preforming step 3A, the metal plate 10 is bent at the first bent portion 1C, and the plate portion forming the vertical wall portion 1B is bent at a second bent portion 1D, which is located midway in the direction of separation from the first bent portion 1C. This is a step of forming an intermediate part having a crank-shaped preform 4 (see FIG. 4(b)) by press forming by bending in the opposite direction.
In the preforming step 3A, for example, as shown in FIGS. 4A and 5A, a die 55 ( The upper die) is lowered toward the punch 56 to execute. By this forming, the metal plate 10 is bent along the shoulder ridge of the punch 56 to form the first bent portion 1C (portion in contact with the punch shoulder ridge) between the top plate portion 1A and the vertical wall portion 1B. At the same time, a second bent portion 1D is formed by bending an intermediate position of the plate material to be the vertical wall portion 1B at the shoulder ridgeline of the die 55 in a direction opposite to the first bent portion 1C, thereby forming a crank-shaped preforming shape 4. becomes (see FIG. 4(b)).

The second bent portion 1D extends in a direction intersecting the separation direction. For example, the second bent portion 1D extends in a direction parallel to the first bent portion 1C.
In the above description, pad foam molding was exemplified as the press molding in the preforming step 3A, but foam molding, draw molding, or the like may be employed as the press molding in the preforming step 3A.

[Bending back process 3C]
In the bending back process 3C, press forming is performed to bend back the second bent portion 1D of the preformed shape 4 formed in the preforming process 3A.
In the bending back process 3C, for example, as shown in FIG. Execute by lowering toward At the time of this molding, as shown in FIG. By sandwiching between the side molding surfaces 59A, the second bent portion 1D is bent back to form the vertical wall portion 1B.

Here, conventionally, the shape of the vertical wall portion 1B is formed into the shape of the vertical wall portion of the target pressed part 2 by bending back forming. Normally, the cross-sectional shape of the base of the vertical wall portion 1B is set to a flat shape (linear cross-sectional shape) toward the tip.
Therefore, conventionally, the forming surfaces (punch-side forming surface 58A and die-side forming surface 59A) for forming the vertical wall portion 1B in the mold for the bending-back step 3C are the target L-shaped portion 1. is set as a flat plane that is the same as the surface of the vertical wall portion 1B.
Here, this flat surface (equivalent to the surface of the vertical wall portion 1B in the target L-shaped portion 1) is referred to as a reference surface H.
On the other hand, in the present embodiment, as shown in FIG. 5(c), when bending back in the bending back step 3C, the cross section in the separation direction of the plate material portion to be the vertical wall portion 1B is bent back in the preforming step 3A. A convex portion 5 that is convex in the opposite direction to the convex direction of the second bent portion 1D is provided. At this time, the position of the maximum protruding portion of the protruding portion 5 is designed to be located within the region that was the second bent portion 1D.

In this embodiment, as shown in FIGS. 5 and 6, the punch-side molding surface 58A and the die-side molding surface 59A, which are in contact with the vertical wall portion 1B, are separated from the reference plane H by the preforming process 3A. The convex shape part 5 which is convex in the opposite direction to the convex direction of the second bending part 1D in and is arranged in the area where the position of the maximum protrusion part of the convex is the second bending part 1D. .
Specifically, as shown in FIGS. 5 and 6, the punch-side forming surface 58A is provided with a bulging portion following the convex portion 5 at a position corresponding to the convex portion 5 with respect to the reference plane H. The die-side forming surface 59A is formed with a concave shape 59Aa following the convex portion 5 at a position corresponding to the convex portion 5 with respect to the reference plane H.

It is preferable that the position of the maximum protruding portion of the convex portion 5 be positioned in the central region of the third division of the position of the second bent portion 1D (unbent portion 1E). More preferably, the position of the maximum protruding portion of the convex portion 5 is arranged so as to abut on the top portion of the second bent portion 1D.
It is preferable that the line length of the convex portion 5 in the separation direction is equal to or longer than the line length of the second bent portion 1D. Further, the line length of the convex portion 5 in the separation direction is, for example, less than twice the line length of the second bent portion 1D.

It is preferable that the radius of curvature at the position of the maximum protruding portion of the convex portion 5 is wider than the radius of curvature at the central position of the second bent portion 1D.
Moreover, it is preferable that the height of the convex portion 5 at the position of the maximum protruding portion is 1 mm or more. Further, the height of the convex portion 5 at the position of the maximum protruding portion is, for example, greater than or equal to the plate thickness and less than or equal to 10 times the plate thickness.
In the unbending step 3C, a mold having a molding surface is used to give the convex portion 5 to the region (bent back portion 1E) of the vertical wall portion 1B which was the second bent portion 1D.
The height of the convex portion 5 may be obtained based on the reference plane H, for example.

Here, if the vertical wall portion 1B is partially provided with the convex portion 5 in the separation direction, the concave portions 6 are also formed on both left and right sides of the convex portion 5 in the separation direction. In the above description, the concave portion 6 is provided by partially forming the convex portion 5, but the base position of the concave portion 6 is in the negative direction with respect to the reference plane H. You can also set In this case, for example, the depth of the concave portion 6 is formed shallower than that of the convex portion 5 .
The concave portion 6 may be provided on at least one of the left and right sides of the convex portion 5 . The concave portion 6 can adjust the compressive stress of the surface layer after bending back by adjusting the curvature radius and the like. The recessed portion 6 has a cross section in the separating direction that protrudes on the side opposite to the projecting portion 5 .

[Restrike process 3D]
In the restrike step 3D, as shown in FIGS. 4(c) and 5(c), the vertical wall portion 1B is shaped into the desired shape of the vertical wall portion 1B by molds 59 to 61. Like processing.

(Other operations)
<For one-time molding>
When the flat metal plate 10 is press-molded once to form the L-shaped portion 1, tensile stress is generated in the surface layer (convex side) of the bending ridge line (first bent portion 1C), and the back layer (concave side ) generates compressive stress. When these stresses are released at the time of mold release, springback occurs and the angle of the bent ridge line changes. In this way, when the L-shaped portion 1 is formed by one-time forming, the bending ridgeline given to the metal plate 10 is only the punch shoulder portion.

<In the case of conventional two-stage molding>
Here, the L-shaped portion 1 is formed in two stages as described above, that is, the vertical wall portion 1B is formed halfway in the preforming step 3A, and the second bent portion 1D is flattened in the bending back step 3C of the next step. A case is assumed in which the target L-shaped portion 1 is formed by bending back to a position where

In this case, along with the bending ridgeline forming the first bending portion 1C, the bending ridgeline (the second bending portion bent in the opposite direction to the first bending portion 1C) is also provided at the position where the shoulder portion of the die 59 in the preforming step 3A abuts. 2 bends 1D) are provided. The ridgeline forming the second bent portion 1D is bent back to the target shape (flat shape), so that the surface layer of the bent back portion 1E (the position that was the second bent portion 1D) A tensile stress is generated in the concave side of the second bent portion 1D), and a compressive stress is generated in the back layer (convex side of the second bent portion 1D).
In this way, when the molding is performed in two steps, in addition to the first bent portion 1C, the unbent portion 1E, which was the second bent portion 1D, also undergoes an angle change due to springback in the same direction.
Therefore, the amount of dimensional change at the tip of the vertical wall portion 1B is greater than in the one-time molding.

<In the case of two-stage molding of the present embodiment>
On the other hand, in the present embodiment, the punch-side forming surface 58A and the die-side forming surface 59A that contact the vertical wall portion 1B during bending back forming are formed with the convex shape 58Aa or the concave shape 59Aa on the vertical wall portion 1B. The second bent portion 1D is subjected to bending back forming using a die formed at a position overlapping the area where the bending back portion 1E of the plate material is to be brought into contact.
As a result, in the present embodiment, during this bending back, the cross section of the vertical wall portion 1B in the separation direction with respect to the region overlapping the bending back portion 1E is in the direction opposite to the convex direction of the second bent portion 1D. A protruding portion 5 is provided so as to protrude upward.

By providing the vertical wall portion 1B with the convex portion 5 during the bending back in the bending back process 3C,
Although the tensile stress of the surface layer at the bent-back portion 1E slightly increases, by partially forming the convex portion 5, the compressive stress is applied to the portions to be the two concave portions 6 formed on both sides of the convex portion 5. is generated, and the compressive stress generated in the two recessed portions 6 offsets the tensile stress generated in the bent back portion 1E. As a result, it was confirmed that the amount of springback at the tip of the vertical wall portion 1B is reduced as compared with the conventional method in which the convex portion 5 is not formed.

As described above, in the present embodiment, both compression and tension are applied to the vertical wall portion 1B, thereby reducing the amount of springback and reducing the material strength sensitivity.
Here, the longer the linear length of the protruded portion 5 in the separation direction, the wider the range of both the compressive stress and the tensile stress.
Further, in the present embodiment, the recessed portion 6 is arranged so as not to overlap the unbent portion 1E, but it may partially overlap the unbent portion 1E.

Furthermore, in the present embodiment, the restrike process 3D is performed as a process after the bend-back process 3C.
By restrike processing, bending and stretching are performed so as to crush the convex portion 5 and the convex portion 5 .
The effect of this restriking process is different from the effect of the conventional restriking process, in that the tensile stress in the surface layer of the unbent portion 1E is canceled out, and the compressive stress generated in the recessed portions 6 on both sides is also canceled out. . As a result, the amount of springback is reduced more effectively.

As described above, according to the present embodiment, when the once-bent second bent portion 1D (unbent portion 1E) is bent back, the vertical wall portion 1B is bent so as to overlap the region of the unbent portion 1E. By providing the convex portion 5, even when manufacturing an L-shape consisting of the top plate portion 1A and the vertical wall portion 1B (flange) by two-step molding, the dimension of the tip of the vertical wall portion 1B can be adjusted by a simple means. Change can be reduced.
Further, after that, by bending and stretching the vertical wall portion 1B into a target component shape, it is possible to further reduce the dimensional change at the tip of the vertical wall portion 1B.
If the vertical wall portion 1B can allow the bulge formed by the convex portion 5 as the desired shape of the component, the shape may be used as the final shape.

(effect)
This embodiment has the following effects, for example.
(1) In the present embodiment, a metal plate 10 is press-molded into a pressed part shape having a top plate portion 1A and a vertical wall portion 1B continuous with the top plate portion 1A via a first bent portion 1C. In the method of manufacturing a pressed part 2 for manufacturing a part 2, when the direction away from the top plate portion 1A in the vertical wall portion 1B is defined as the separation direction, the metal plate 10 is bent at the first bent portion 1C. A preforming step 3A of bending and bending in a direction opposite to the first bent portion 1C at a second bent portion 1D, which is a midway position in the separating direction in the plate material portion to be the vertical wall portion 1B, and the preforming step After 3A, a bending-back step 3C for bending back the second bent portion 1D is provided, and when bending back in the bending-back step 3C, the cross section in the separation direction is taken with respect to the plate material portion that will become the vertical wall portion 1B. gives a convex portion 5 that is convex in a direction opposite to the convex direction of the second bent portion 1D in the preforming step 3A, and the position of the maximum protruding portion in the convex portion 5 is set to the second bent portion Place in the region that was 1D.

For example, in order to press-form the metal plate 10 into a pressed part shape having a top plate portion 1A and a vertical wall portion 1B continuous with the top plate portion 1A via a first bent portion 1C, the metal plate 10 is: A preformed shape 4 is formed by bending at the first bending portion 1C and bending in a direction opposite to the first bending portion 1C at a second bending portion 1D, which is an intermediate position of the plate material portion to be the vertical wall portion 1B. In the method of manufacturing the pressed part 2 having the forming step 3A and the bending-back step 3C of bending back the second bent portion 1D after the pre-forming step 3A, the vertical wall is used as a mold used in the bending-back step 3C. The molding surface of the mold that abuts on the plate material to be the portion 1B has a cross section in a direction away from the first bent portion 1C with respect to the plate material portion to be the vertical wall portion 1B. It has a shape capable of providing a convex portion 5 which is convex in the direction opposite to the convex direction of the bent portion 1D and is arranged in a region where the position of the maximum protrusion of the convex is the second bent portion 1D. Use a mold for unbending characterized by

According to this configuration, even if the L-shaped portion 1 is formed by two-step molding, when the plate portion that becomes the vertical wall portion 1B that has been bent into the L shape is bent back, the plate portion that becomes the vertical wall portion 1B is unfolded. By providing the convex portion 5 in the vertical wall portion 1B and specifying the area where the convex portion 5 is provided, both compression and tension are applied to the vertical wall portion 1B, thereby reducing the springback amount and also lowering the material strength sensitivity. becomes possible.

(2) At this time, when bending back in the bending-back step 3C, along with the convex portion 5, the concave portion 6 is positively provided to at least one of both sides of the convex portion 5 in the separating direction. good too.
For example, the molding surface of the mold that abuts on the plate member forming the vertical wall portion 1B is formed on both sides of the plate member forming the vertical wall portion 1B together with the convex portion 5 in the separation direction. A mold for unbending, which has a shape capable of providing the concave portion 6 to at least one of the .
According to this configuration, it is possible to adjust the compressive stress applied by the concave portion 6 formed on at least one of both sides of the convex portion 5 during unbending.

(3) In the present embodiment, after the bend-back process 3C, there is a restrike process 3D in which the plate material portion to be the vertical wall part 1B is restrike-processed into the plate shape of the target vertical wall part 1B.
According to this configuration, it is possible to further reduce the amount of springback at the tip of the vertical wall portion 1B.

(4) The height of the convex portion 5 at the maximum protruding portion position is set to 1 mm or more.
With this configuration, it is possible to reliably reduce the amount of springback.

(5) The metal plate 10 used in the method for manufacturing the pressed part 2 of the present embodiment may be a high-strength steel plate having a tensile strength of 980 MPa or more.
It is possible to reliably reduce the amount of springback even with a high-strength steel sheet that tends to cause springback.

Next, examples based on this embodiment will be described.
Simulation analysis (press forming analysis and springback) was performed for one-step forming, conventional two-step forming, and two-step forming of the example of the present invention under analysis conditions for forming into a part shape model as shown in FIG.
In the conventional two-step molding, the molding surface of the mold for molding the vertical wall portion 1B in the bending-back process 3C is set to have a linear cross section (reference plane H).
On the other hand, in the two-step molding of the invention example, as the molding surface of the mold for molding the vertical wall portion 1B in the bending back process 3C, the cross-sectional linear shape (reference surface H) is used as a base, and the molding surfaces 58A and 59A are A convex shape 58Aa or a recessed shape 59Aa following the convex portion 5 according to the present invention is provided.
Moreover, the high-strength steel plate shown in Table 1 was used as the metal plate 10 to be molded.

The plate thickness of the metal plate 10 was set to 1.6 mm, and the coefficient of friction μ between the mold and the metal plate 10 was set to 0.12.
Then, the amount of springback at the tip of the vertical wall portion 1B and the stress state in the vertical wall portion 1B were compared and evaluated.

Next, the evaluation results will be explained.
(Comparison of stress states)
<For one-time molding>
In the case of one-time molding, as shown in FIG. 7, tensile stress was generated in the surface layer of the first bent portion 1C.
By performing the subsequent restrike step 3D, the tensile stress generated in the surface layer of the first bent portion 1C was slightly reduced.

<In the case of conventional two-stage molding>
In the case of the conventional two-stage molding, as shown in FIG. 8, the preforming step 3A generated tensile stress in the surface layer of the first bent portion 1C and compressive stress in the surface layer of the second bent portion 1D. Next, by the unbending process 3C, tensile stress was generated in the surface layer of the first bent portion 1C, and tensile stress was generated in the surface layer of the unbent portion 1E (second bent portion 1D). Furthermore, the tensile stress of the unbent portion 1E (second bent portion 1D) was slightly reduced by the subsequent restrike step 3D. However, the reduction is significantly smaller than the inventive example.

<In the case of two-stage molding of the invention example>
On the other hand, in the case of the two-stage molding of the invention example, as shown in FIG. A tensile stress was generated, but a compressive stress was generated at the upper and lower positions of the unbent portion 1E (the position of the concave shape 58Ab).
Further, in the restrike step 3D that follows, as shown in FIG. 9, the tensile stress generated in the surface layer of the first bent portion 1C is slightly reduced, and the tensile stress of the unbent portion 1E (second bent portion 1D) is reduced. found to have been erased. In addition, the compressive stress generated at the vertical position of the unbent portion 1E was also reduced.

(Regarding springback amount and material strength sensitivity)
In the one-time molding, the conventional two-stage molding, and the two-stage molding of the example of the present invention, the amount of springback and the material strength sensitivity after the bending back process 3C and the restrike process 3D were obtained. , and the results of FIG. 12 were obtained. At this time, as shown in FIG. 10, a convex shape 58Aa was partially provided along the isolation direction on the forming surface 58A in the bending-back process 3C.
As can be seen from FIG. 11, it was found that the amount of springback in the two-stage molding of the example of the present invention was close to the amount of springback before restrike processing in one-time molding. In addition, it was found that the amount of springback in the two-step molding of the present invention example can be suppressed to a smaller value than in the conventional two-step molding both after the unbending process 3C and after the restrike process 3D.

Also, as can be seen from FIG. 12, it was found that the two-stage molding of the present invention can reduce the sensitivity to material strength as compared with the conventional two-stage molding.
Here, in FIG. 12, the absolute value of the difference in the amount of springback between a metal plate with a tensile strength of 1180 MPa and a metal plate with a tensile strength of 980 MPa is used as an index of material strength sensitivity.
FIG. 13 shows the springback state of the vertical wall portion 1B after the bending-back process 3C in the conventional two-step molding and the two-step molding of the example of the present invention. This is the case where the curvature radius of the convex shape 58Aa provided on the molding surface in the two-step molding of the present invention example is 20 mm (R20), 40 mm (R40), and 60 mm (R60), and the conventional two-step molding (curvature Radius = 0 mm).

As can be seen from FIG. 13, in the two-step molding of the example of the present invention, the amount of springback is reduced compared to the conventional two-step molding, and regardless of the curvature radius of the convex shape 58Aa provided on the molding surface, it is almost the same. It was found that the amount of springback was
Further, FIG. 14 shows the state of springback in the conventional two-step molding and the two-step molding of the example of the present invention after the restrike step 3D.
As can be seen from FIG. 14, in the two-step molding of the example of the present invention, the amount of springback is reduced compared to the conventional two-step molding, and regardless of the curvature radius of the convex shape 58Aa provided on the molding surface, it is almost the same. It was found that the amount of springback was

Here, for the two-step molding of the example of the present invention, the curvature radius of the convex shape 58Aa formed on the molding surface is fixed at 40 mm, and the curvature radius of the concave shape portion 6 is set to 20 mm (R20), 40 mm (R40), 60 mm (R60). ), the amount of springback was obtained. Also in this case, when the amount of springback at the tip of the vertical wall portion 1B was determined, the amount of springback was reduced compared to the conventional two-step molding, and regardless of the radius of curvature of the concave shape provided on the molding surface, It was found that the amount of springback was approximately the same.

Furthermore, the amount of springback was obtained when the height of the maximum protruding portion of the convex shape 58Aa formed on the molding surface was 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, and 2.8 mm.
Also in this case, when the amount of springback at the tip of the vertical wall portion 1B was obtained, the amount of springback was reduced compared to the conventional two-step molding, and regardless of the height of the convex shape 58Aa provided on the molding surface. , the amount of springback is almost the same.

The radius of curvature of the convex shape 58Aa is set to the radius of curvature at the vertex of the convex shape 58Aa.
Further, the convex portion 5 following the convex shape 58Aa provided on the molding surface was formed on the vertical wall portion 1B by the bending-back process 3C.
As described above, it was found that by adopting the two-stage molding based on the present invention, the amount of springback can be suppressed even if the vertical wall portion 1B is formed by the two-stage molding.

1 L-shaped portion 1A Top plate portion 1B Vertical wall portion 1C First bent portion 1D Second bent portion 1E Unbent portion 2 Pressed part 3A Preforming process 3B Trimming process 3C Unbending process 3D Restrike process 4 Preformed shape 5 Convex portion 6 Concave portion 10 Metal plate 58A Punch-side forming surface 59A Die-side forming surface 58Aa Convex shape 58Ab Concave shape 59A Die-side forming surface H Reference surface

Claims (7)

A method for manufacturing a pressed part by press-molding a metal plate into a pressed part shape having a top plate portion and a vertical wall portion continuous with the top plate portion via a first bent portion, the method comprising:
When the vertical wall portion is separated from the top plate portion as a separation direction,
Preforming in which the metal plate is bent at the first bending portion and bent in a direction opposite to the first bending portion at a second bending portion which is an intermediate position in the separation direction of the plate material portion to be the vertical wall portion. process and
After the preforming step, a bending back step of bending back the second bent portion,
When bending back in the bending back step, the cross section of the plate member forming the vertical wall portion has a convex shape in which the cross section in the separation direction is convex in a direction opposite to the convex direction of the second bent portion in the preforming step. give the part
Arranging the position of the maximum protruding portion in the convex portion in the region that was the second bending portion,
A method of manufacturing a pressed part, characterized by: 2. The press part according to claim 1, wherein, when bending back in the bending and returning step, a concave portion is provided on at least one of both sides of the convex portion in the separation direction together with the convex portion. Production method. 3. The method according to claim 1 or 2, further comprising a restriking step of restrike-processing the plate material portion to be the vertical wall portion into a desired plate shape of the vertical wall portion after the bending-back step. A method for manufacturing pressed parts. 4. The method of manufacturing a pressed part according to any one of claims 1 to 3, wherein the height of the convex portion at the position of the maximum protruding portion is 1 mm or more. In order to press-form a metal plate into a press part shape having a top plate portion and a vertical wall portion continuous to the top plate portion via a first bending portion, the metal plate is bent at the first bending portion and a preforming step of forming into a preformed shape bent in a direction opposite to the first bending portion at a second bending portion that is an intermediate position of the plate material portion that becomes the vertical wall portion; and the second bending after the preforming step. A mold used in the bending-back step in a method for manufacturing a pressed part having a bending-back step of bending back the part,
The molding surface of the mold, which contacts the plate material that will form the vertical wall portion, has a cross section in a direction away from the first bending portion with respect to the plate material portion that will form the vertical wall portion. A shape that can provide a convex portion that is convex in the opposite direction to the convex direction of the portion and that the position of the maximum protrusion of the convex is located in the region that becomes the second bent portion.
A mold for unbending, characterized by: The molding surface of the mold that abuts on the plate member forming the vertical wall portion can be provided with the convex portion and the concave portion on at least one of both sides of the convex portion with respect to the plate member portion forming the vertical wall portion. 6. The mold for unbending according to claim 5, characterized in that the mold has a shape of . In the mold according to claim 5 or 6, after bending back the plate material portion to be the vertical wall portion, restriking is applied to the plate shape of the vertical wall portion intended for the vertical wall portion. A molding method for press parts.

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