JP6848821B2 - Press molding equipment and method - Google Patents

Description

The present invention forms a molded product having a target shape having a groove-shaped portion extending in the longitudinal direction and having a flange portion curved along the longitudinal direction on at least one of a pair of vertical wall portions forming the groove-shaped portion. Regarding press molding equipment and methods.

Press molding is a method of transferring the shape of a die to a blank by pressing the die against the material (blank) which is the object thereof. In press molding, after the press-molded product is taken out from the mold, shape defects, so-called springbacks, which occur due to elastic recovery of the residual stress in the press-molded product, occur, and the shape is different from the desired shape. Often occurs.

The extent to which springback occurs is largely influenced by the strength of the material. In recent years, especially in the automobile industry, there is a strong tendency to use high-strength steel plates for car body parts from the viewpoint of weight reduction of automobile bodies, and the degree of springback caused by such high-strength materials is increasing. Is getting bigger.
For this reason, in order to bring the shape after springback closer to the target design shape, a skilled worker must modify the mold many times at the production site and repeat trials and errors, resulting in a production preparation period. Will be prolonged. Therefore, it can be said that developing a method that can effectively reduce springback is an increasingly important issue in reducing the development period and cost of automobiles.

In order to reduce springback, it is essential to control the stress that causes it. In a straight part in which the cross section of the part shape does not change in the longitudinal direction, the springback is limited to a two-dimensional change in the cross-sectional shape such as opening of the mouth, and stress control is relatively easy. On the other hand, in a curved part in which the cross section of the part shape changes in the longitudinal direction, in addition to the two-dimensional change in the cross-sectional shape, a three-dimensional springback such as twisting or bending occurs. The stresses that cause three-dimensional springback are complex and extremely difficult to control.
Patent Document 1 proposes a "press forming method and apparatus" as a technique for reducing three-dimensional springback of twisting and bending of curved parts.

In the same document, for example, it is formed by a groove-shaped portion 51d and a flange portion (curved inner flange portion 51e and curved outer flange portion 51f) composed of a punch bottom portion 51a, vertical wall portions 51b and 51c as shown in FIG. The form of the springback generated in the molded product 51 when the molded product 51 having a flange portion curved in the direction is form-molded has been studied.
Since the present invention is premised on the mechanism of springback reduction examined in the same document, the mechanism examined in the same document will be outlined below.

In the conventional simple foam molding, as shown in the perspective view of FIG. 10 and the cross-sectional view of FIG. 11, molding is performed by sandwiching the blank 69 (see FIG. 11) between the press molding dies 57 having the die 53 and the punch 55. Do. FIG. 12 is a diagram showing the blank outline before and after molding, the broken line shows the blank outline before molding, and the solid line shows the blank outline at bottom dead center. The outer line corresponding to the flange portion (hereinafter, the curved inner flange portion 51e) on the side with a large curvature of curvature (the side with a small radius of curvature) has a smaller curvature (the radius of curvature becomes larger) due to the inflow of blanks due to molding. The length becomes longer (A ₀ B ₀ → A ₁ B ₁ ). That is, the curved inner flange portion 51e is formed with an extension flange, and tensile stress remains in the longitudinal direction at the bottom dead center.

On the other hand, the opposite is true for the flange portion (hereinafter, the curved outer flange portion 51f) on the side with a small curvature of curvature (the side with a large radius of curvature), and the outer line has a large curvature due to the inflow of blanks due to molding (the radius of curvature is (Small) The line length becomes shorter. (C ₀ D ₀ → C ₁ D ₁ ). That is, the curved outer flange portion 51f is contracted and the flange is deformed, and the compressive stress remains in the longitudinal direction at the bottom dead center.
These residual stresses elastically recover at the time of mold release, and the curved inner flange portion 51e undergoes contraction deformation and the curved outer flange portion 51f undergoes elongation deformation. As a result, as shown in FIG. 13, the component has a large curvature curvature (radius of curvature). Springback occurs, which causes bending deformation. In FIG. 13, the broken line shows the shape before the springback, and the solid line shows the shape after the springback.

As described above, in the molded product having the flange portion curved in the longitudinal direction, the residual stress in the flange portion is released at the time of mold release, so that springback that bends and deforms the entire molded product is generated. From this, it can be said that in such a molded product, reduction of the residual stress of the flange portion is very important for reducing the springback of the molded product.

Patent documents include a technique for reducing the residual stress of a flange portion by changing the wire length of the flange portion larger than the target shape in the press forming process and then returning the flange portion line length to the target shape. It is an invention of 1.
FIG. 14 shows a cross section of the press molding apparatus 59 disclosed in Patent Document 1 during molding. The press forming apparatus 59 includes a die 61, a flange forming die 63 arranged to face the die 61, a punch 67 movably supported by a support mechanism 65, and a pad 71 for pressing the blank 69 against the punch 67. It has.
In the press forming method of Patent Document 1, the punch bottom portion 51a and the vertical wall portions 51b and 51c are formed into the target shape to the first bottom dead point by the die 61 and the punch 67, and the curved inner flange portion 51e and the curved outer flange portion 51f are formed. The length of the line in the longitudinal direction for the curved inner flange portion 51e is longer than the line length of the flange portion of the molded product 51, and the line length in the longitudinal direction for the curved outer flange portion 51f is the flange of the molded product 51. The first molding step (see FIGS. 14 (a) to 14 (c)) of molding so as to be shorter than the line length of the portion, and the curvature formed in the first molding step by the die 61 and the flange forming die 63. The first molding step includes a second molding step (see FIGS. 14C and 14D) for molding the inner flange portion 51e and the curved outer flange portion 51f into the target shape of the molded product 51 to the second bottom dead point. It is characterized in that the second molding step is performed by one press molding.

FIG. 15 is an explanatory diagram illustrating a change in line length between the curved inner flange portion 51e and the curved outer flange portion 51f from before the start of press molding to the first bottom dead center and the second bottom dead center. In FIG. 15, the part circled by the broken line is enlarged and shown for each of the inside and the outside of the curve. In each enlarged view, the broken line is the inner end 69a and the outer end 69b of the blank 69 before press molding, the dotted line is the inner end 69a and the outer end 69b at the first bottom dead center, and the solid line is the inner end 69a at the second bottom dead center. And the outer end 69b are shown respectively.

_{The A 0} point and B ₀ point of the inner end 69a before the start of press molding are A ₁ point and B ₁ point at the first bottom dead center, and A ₂ point and B ₂ point at the second bottom dead center, respectively. , The line length changes _{from A 0} B ₀ → A ₁ B ₁ → A ₂ B _2. During the first molding process from the start of molding to the first bottom dead center, A ₀ B ₀ at the inner end 69a becomes A ₁ B ₁ due to the inflow of the blank, and the line length of the inner end 69a is stretched and lengthened (elongation). Flange deformation). Next, during the second molding step from the first bottom dead center to the second bottom dead center, the inner end 69a is deformed by being pushed outward (outflowing toward the bending center), so that the line length of the inner end 69a is formed. Is slightly shorter (A ₁ B ₁ → A ₂ B ₂ ), and the line length corresponds to the target shape at the second bottom dead center.

On the other hand, at the outer end 69b, a phenomenon opposite to that at the inner end 69a occurs. _{The C 0} points and D ₀ points of the outer end 69b before the start of press molding are C ₁ point and D ₁ point at the first bottom dead center, and C ₂ points and D ₂ points at the second bottom dead center, respectively. , The line length changes _{from C 0} D ₀ → C ₁ D ₁ → C ₂ D _2. During the first molding process from the start of molding to the first bottom dead center, C ₀ D ₀ at the outer end 69b becomes C ₁ D ₁ due to the inflow of the blank, and the line length of the outer end 69b is shortened (shrinkage). Flange deformation). Next, during the second molding step from the first bottom dead center to the second bottom dead center, the outer end 69b is deformed by being pushed out (outflowing toward the curved outer side), so that the line length of the outer end 69b is formed. Is slightly longer (C ₁ D ₁ → C ₂ D ₂ ), and the line length corresponds to the target shape at the second bottom dead center.

In this way, the curved inner flange portion 51e is once molded in the first molding step so that the line length is longer than the target shape of the molded product 51, and in the second molding step, the target shape of the molded product 51 is formed. Perform molding to return to the line length of. In the first molding step, the curved outer flange portion 51f is once molded so that the line length is shorter than the target shape of the molded product 51, and in the second molding step, the line length is set to the target shape of the molded product 51. Perform back molding. Therefore, in the curved inner flange portion 51e and the curved outer flange portion 51f, the strain generated in the first molding step is slightly returned in the second molding step, and the residual stress is significantly reduced.

This point will be described with reference to FIG. FIG. 16 is a stress-strain diagram in the longitudinal direction from the start of molding of the flange portion to the second bottom dead center. As shown in FIG. 16, a large residual stress is accumulated in the flange portion of the first bottom dead center by the first molding step. However, in the second molding step, the residual stress is significantly reduced by slightly returning the strain from the first bottom dead center to the second bottom dead center.
As described above, the invention of Patent Document 1 utilizes the feature that the residual stress changes significantly sensitively by returning the strain slightly.

JP-A-2015-27698

The mechanism of springback suppression disclosed in Patent Document 1 is that the residual stress is significantly reduced by slightly returning the strain in the process from the first bottom dead center to the second bottom dead center. It is important how much the return amount should be.
The strain return amount is the punch lowering amount (relative movement distance h) from the first bottom dead center (see FIG. 14 (c)) to the second bottom dead center (see FIG. 14 (d)) (FIG. 14 (Fig. 14). It is important that the relative movement distance h can be adjusted reliably and accurately in relation to a)).

However, in the press forming apparatus 59 disclosed in Patent Document 1, it is the flange forming die 63 that is fixed, and the entire punch 67 is supported by the support mechanism 65, and the entire punch 67 is supported during press forming. Has a structure that moves. For this reason, the movement of the punch 67 during press molding may become unstable due to variations in the material strength of the blank and the influence of mechanical play.
If the movement of the punch 67 is not the same for each shot of press molding, the relative movement distance h described above changes for each shot, and the amount of strain return changes. Therefore, the shape after springback may fluctuate for each shot, and in this respect, the target shape after springback may vary in the press forming apparatus 59 of Patent Document 1.

Further, in the press molding apparatus 59 disclosed in Patent Document 1, the relative movement distance h is set only at the position of the punch 67 at the first bottom dead center, and if it takes time to finely adjust the punch position, springback is performed. There is a problem that it is difficult to prevent it reliably.
Further, since the positions of the curved inner flange portion and the curved outer flange portion in the pressing direction are the same and the relative movement distance h cannot be adjusted individually for the curved inner flange portion and the curved outer flange portion, complicated 3 such as twisting and bending 3 There was also the problem that it was difficult to flexibly respond to dimensional springback.

The present invention has been made to solve the above-mentioned problems, and a press molding apparatus and method capable of adjusting so that the amount of strain returned during molding becomes constant and suppressing springback can be provided. The purpose is to get.
Another object of the present invention is to provide a press molding apparatus and method capable of stably reducing three-dimensional springback such as twisting and bending.

(1) The press molding apparatus according to the present invention has a groove-shaped portion formed of a punch bottom portion and a pair of vertical wall portions continuous from both sides of the punch bottom portion and extending in the longitudinal direction, and is formed on at least one of the vertical wall portions. A molded product having a flange portion curved along the longitudinal direction is molded into a target shape, and the punch bottom molded portion for molding the punch bottom portion and the vertical wall arranged on both sides of the punch bottom molded portion. For a die having a vertical wall / flange forming portion for forming the portion and the flange portion, a lower punch for forming the lower portion of the vertical wall portion and the flange portion in cooperation with the die, and the lower punch. An upper punch that is provided so as to be detachable (separate and contactable) in the height direction and that forms the bottom of the punch and the upper part of the vertical wall in cooperation with the die, and is installed in the lower punch. The vertical wall, which is provided with an upper punch support mechanism for supporting the upper punch so that the punch gap between the upper punch and the lower punch can be adjusted, and which is on the flange portion side curved along the longitudinal direction. At least one of the flange molded portions is characterized in that the height can be changed independently of the other.

(2) The press forming method according to the present invention includes a punch bottom portion and a pair of vertical wall portions continuous from both sides of the punch bottom portion, and has a groove-shaped portion extending in the longitudinal direction, and is formed on at least one of the vertical wall portions. A molded product having a target shape having a flange portion curved along the longitudinal direction is molded by using the press molding apparatus according to (1) above, and the upper punch is formed with respect to the lower punch. The die is moved to the lower punch side in a state where one and the other of the vertical wall / flange molded portion are at the same height or different heights while being supported by providing a punch gap, and the die and the upper punch are used. The pre-molding step of molding the upper part of the vertical wall portion and the die is further moved to the lower punch side to press the upper punch against the lower punch so that the lower punch does not have the punch gap, and the die and the lower part are formed. It is characterized by including a post-molding step of molding the vertical wall portion and the flange portion into the target shape with a punch.

(3) The press molding method according to the present invention has a groove-shaped portion extending in the longitudinal direction, and has a flange portion curved along the longitudinal direction on at least one of a pair of vertical wall portions forming the groove-shaped portion. A press molding method for molding a molded product having a target shape using the press molding apparatus according to (1) above, in which the upper punch is supported by providing a predetermined punch gap with respect to the lower punch. A first forming step of moving the die to the lower punch side to form a predetermined die gap between the vertical wall / flange forming portion and the flange forming portion of the lower punch, and moving the die to the lower punch side. The second molding step of pressing the upper punch to the lower punch without the punch gap by further moving, and the die gap by further moving the vertical wall / flange molding portion to the flange molding portion side. A third molding step of molding into the target shape by the state is provided, and the die gap formed in the first molding step is different between one and the other of the vertical wall / flange molding portion. It is characterized in that the height of the changeable vertical wall / flange molded portion is adjusted in the first molding step.

In the present invention, the punch bottom portion and a pair of vertical wall portions continuous from both sides of the punch bottom portion have a groove-shaped portion extending in the longitudinal direction, and at least one of the vertical wall portions is curved along the longitudinal direction. A molded product having a target shape having a flange portion is molded, and the punch bottom molding portion for molding the punch bottom portion and the vertical wall portion and the flange portion are formed on both sides of the punch bottom molding portion. A die having a vertical wall / flange forming portion to be formed, a lower punch for forming the lower portion of the vertical wall portion and the flange portion in cooperation with the die, and a lower punch that can be separated from the lower punch in the height direction. An upper punch that is provided (so that it can be separated and touched) to form the bottom of the punch and the top of the vertical wall in cooperation with the die, and is installed in the lower punch and the upper punch and the said. At least one of the vertical wall / flange forming portion on the flange portion side curved along the longitudinal direction is provided with an upper punch supporting mechanism for supporting the upper punch so that the punch gap between the lower punch and the lower punch can be adjusted. Since the height can be changed independently of the other, it is possible to make stable adjustments so that the amount of strain returned during molding is constant, and three-dimensional such as twisting and bending that occurs in the entire part. Springback can be suppressed stably.

It is explanatory drawing of the press molding apparatus which concerns on Embodiment 1 of this invention. It is explanatory drawing of the press molding method which concerns on Embodiment 2 of this invention. It is explanatory drawing of the press molding method which concerns on Embodiment 3 of this invention. It is explanatory drawing of the target shape of the press-molded article which concerns on Example (the 1). It is explanatory drawing of the target shape of the press-molded article which concerns on Example (the 2). It is explanatory drawing of the evaluation method of the springback amount which concerns on Example. It is explanatory drawing of the evaluation method of the springback amount which concerns on Example. It is a graph which shows the evaluation result of the springback amount which concerns on Example. It is explanatory drawing of the subject of this invention, and is the perspective view of the press-molded article molded by the conventional press molding method. It is explanatory drawing of the subject of this invention, and is the perspective view of the die of the conventional press molding apparatus. It is explanatory drawing of the subject of this invention, and is explanatory drawing of the conventional press molding method. It is explanatory drawing of the subject of this invention, and is explanatory drawing of the generation mechanism of springback in the molded article molded by the conventional press molding method. It is explanatory drawing of the subject of this invention, and is explanatory drawing of the spring back in the molded article molded by the conventional press molding method. It is explanatory drawing of the conventional press molding apparatus and the press molding method. It is explanatory drawing of the mechanism of the springback suppression in the press molding method shown in FIG. 14 (the 1). It is explanatory drawing of the mechanism of the springback suppression in the press molding method shown in FIG. 14 (the 2).

[Embodiment 1]
As an example according to the present embodiment, the press forming apparatus 1 shown in FIG. 1 is composed of a punch bottom portion 51a illustrated in FIG. 4 and a pair of vertical wall portions 51b and 51c continuous from both sides of the punch bottom portion 51a and extends in the longitudinal direction. A molded product 51 having a groove-shaped portion 51d and having a curved inner flange portion 51e and a curved outer flange portion 51f curved along the longitudinal direction on each of the vertical wall portions 51b and 51c is molded into a target shape. As shown in FIG. 1, the die 3, the lower punch 5, the upper punch 7, and the upper punch support mechanism 9 are provided. Hereinafter, each configuration of the press molding apparatus 1 will be described.

<Die>
The die 3 includes a pad 11, a vertical wall / flange forming portion 13 that is arranged on both sides of the pad 11 and forms a vertical wall portion 51b, 51c, a curved inner flange portion 51e, and a curved outer flange portion 51f, and the pad 11 and the vertical portion. It has an upper die holder 15 for holding the wall / flange forming portion 13.

≪Pad≫
The pad 11 presses the blank 69 against the upper punch 7 and grips it in the molding process, and forms the punch bottom portion 51a in cooperation with the upper punch 7 as a punch bottom forming portion.
The pad 11 is held by the upper die holder 15 via the pad pressing mechanism 17, and is pressed against the upper punch 7 side by the pad pressing mechanism 17 with a predetermined pressing force in the molding process. As the pad pressing mechanism 17, an air cylinder or the like can be used.

In the press molding apparatus 1 according to the present invention, it is desirable to provide the pad 11 so that the blank 69 can be prevented from moving during molding by gripping the blank 69 with the pad 11 and the upper punch 7. The invention can be carried out without the use of pads. However, in this case, it is necessary to separately provide the punch bottom molded portion on the upper die holder 15.

≪Vertical wall / flange molding part≫
The vertical wall / flange forming portion 13 is arranged on both sides of the pad 11 to form the vertical wall portions 51b and 51c, the curved inner flange portion 51e, and the curved outer flange portion 51f, and forms the inner vertical wall / flange forming portion 13a. (Left side in FIG. 1) and outer vertical wall / flange forming portion 13b (right side in FIG. 1) are provided. Here, the inside and outside of the inner vertical wall / flange molding portion 13a and the outer vertical wall / flange molding portion 13b mean the inside and outside of the curvature of the molded product 51 which is curved along the longitudinal direction.
The inner vertical wall / flange forming portion 13a forms the vertical wall portion 51b inside the curvature and the curved inner flange portion 51e, whereas the outer vertical wall / flange forming portion 13b forms the outside of the curvature. A vertical wall portion 51c and a curved outer flange portion 51f are formed.
The inner vertical wall / flange molding portion 13a and the outer vertical wall / flange molding portion 13b are supported by the upper die holder 15 by the inner vertical wall / flange molding portion support mechanism 19a and the outer vertical wall / flange molding portion support mechanism 19b, respectively. The flanges are configured so that their heights can be changed independently of each other (movable in the height direction).

≪Vertical wall / flange molded part support mechanism≫
The vertical wall / flange molding portion support mechanism 19 supports at least one of the vertical wall / flange molding portions 13 so that the height can be changed independently of the other. In FIG. 1, the inner vertical wall / flange molding portion 13 is formed. Inner vertical wall / flange molding part support mechanism 19a that supports the height of the portion 13a in a changeable manner, and outer vertical wall / flange molding part support mechanism 19b that supports the height of the outer vertical wall / flange molding part 13b in a changeable manner. Is provided.

The inner vertical wall / flange molding portion support mechanism 19a and the outer vertical wall / flange molding portion support mechanism 19b determine the positions of the inner vertical wall / flange molding portion 13a and the outer vertical wall / flange molding portion 13b in the height direction in the molding process. Each can be adjusted independently. It is preferable to use a servomotor as the vertical wall / flange molding portion support mechanism 19.

≪Upper die holder≫
The upper die holder 15 holds the pad 11 via the pad pressing mechanism 17, supports the vertical wall / flange molding portion 13 via the vertical wall / flange molding portion support mechanism 19, and moves the upper die holder 15. This moves the entire die 3 and is driven by a die driving device (not shown).
Further, the upper die holder 15 is provided with a pad pressing mechanism accommodating portion 21 for accommodating the pad pressing mechanism 17.

<Lower punch>
The lower punch 5 forms the lower portion of the vertical wall portions 51b and 51c having the target shape, the curved inner flange portion 51e, and the curved outer flange portion 51f in cooperation with the vertical wall / flange forming portion 13, and is shown in FIG. As shown, a vertical wall lower molding portion 23 for molding the lower portions of the vertical wall portions 51b and 51c is provided in the central portion, and a flange molding portion that continuously projects from the lower end of the vertical wall lower molding portion 23 in the horizontal direction. 25 is provided.
The lower punch 5 is formed with a cavity 27 and a communication groove 29 from the cavity 27 through the center of the vertical wall lower molding portion 23 to the upper surface of the vertical wall lower molding portion 23.

<Upper punch>
The upper punch 7 is provided so as to be detachable (separate and detachable) from the lower punch 5 in the height direction, and in cooperation with the die 3, the punch bottom portion 51a and the vertical wall portions 51b and 51c are provided. The upper part is molded.

<Upper punch support mechanism>
The upper punch support mechanism 9 supports the upper punch 7 so that the punch gap G between the lower surface of the upper punch 7 and the upper surface of the vertical wall lower forming portion 23 in the lower punch 5 can be adjusted. It is installed in the cavity 27.
The upper punch support mechanism 9 is arranged so as to be vertically movable in the communication groove 29, and the upper end is connected to the lower surface of the upper punch 7 to connect to the support member 31 that supports the upper punch 7 from below and the lower end of the support member 31. A stopper 33 that regulates the upward movement position of the support member 31 by abutting against the upper wall of the cavity 27, and a support such as an air cylinder that is connected to the lower part of the stopper 33 and supports the stopper 33 with a predetermined bearing force. It includes a device 35.

The support device 35 supports the upper punch 7 in a state where the upper surface of the stopper 33 is pressed against the upper surface of the cavity 27 by pushing the stopper 33 upward with a predetermined supporting force, whereby the upper punch 7 is supported. Punch gaps G at predetermined intervals are formed between the lower surface and the upper surface of the vertical wall lower forming portion 23 in the lower punch 5.
This punch gap G corresponds to the relative movement distance h (FIG. 14) in Patent Document 1, but according to the upper punch support mechanism 9, a shim or the like is formed between the upper surface of the stopper 33 and the upper surface of the cavity 27. The punch gap G can be easily finely adjusted by disposing the above.

The supporting force of the upper punch 7 by the supporting device 35 needs to be sufficiently large as compared with the pressing force of the pad pressing mechanism 17 described above. In other words, the bearing force of the support device 35 is the sum of the pressing force of the pad pressing mechanism 17 and the force required for processing (molding) the blank 69 from the start of molding of the blank 69 to the time of clamping (see FIG. 2B). Make it larger than. By supporting the upper punch 7 with such a bearing force, the upper punch 7 is firmly fixed to the lower punch 5, so that the instability of the punch during processing as in the technique of Patent Document 1 is eliminated.

The press molding method using the press molding apparatus 1 configured as described above will be described in the second and third embodiments below.

In the above description, both the inner vertical wall / flange molding portion 13a and the outer vertical wall / flange molding portion 13b are individually supported so that their heights can be changed. However, in the present invention, one of the inner vertical wall / flange molding portion 13a and the outer vertical wall / flange molding portion 13b is supported so that the height can be changed, and the other is fixed to the upper die holder 15. Of the inner vertical wall / flange forming portion 13a and the outer vertical wall / flange forming portion 13b, the vertical wall / flange forming portion on the flange portion side that curves along the longitudinal direction without using a die holder 15 or an upper die holder 15. At least one of the thirteen may be supported so that the height can be changed with respect to the other. In the latter case, the entire die 3 may be moved by moving the other of the inner vertical wall / flange forming portion 13a and the outer vertical wall / flange forming portion 13b.

Further, the entire die 3 was moved by moving the upper die holder 15, but the lower punch 5 and the upper punch 7 were moved to the die 3 side without moving the upper die holder 15. There may be.

[Embodiment 2]
The press molding method according to the second embodiment of the present invention is to mold the molded product 51 illustrated in FIG. 4 using the press molding apparatus 1 according to the first embodiment of the present invention, and is a premolding step. And a post-molding process. Hereinafter, each step will be described with reference to FIG.

<Pre-molding process>
In the preforming step, the upper punch 7 is supported by providing a predetermined punch gap G with respect to the lower punch 5 from the start of press forming shown in FIG. 2A to the clamping time shown in FIG. 2B, and is vertically formed. With one of the wall / flange forming portions 13 (inner vertical wall / flange forming portion 13a) and the other (outer vertical wall / flange forming portion 13b) at the same position in the height direction, the die 3 is relative to the lower punch 5 side. This is a step of moving and molding the upper portions of the vertical wall portions 51b and 51c by the vertical wall / flange forming portion 13 and the upper punch 7.
The height of the vertical wall / flange forming portion 13 may be the height at which the punch bottom portion 51a and the upper portions of the vertical wall portions 51b and 51c are formed into the same shape as the target shape.

When the upper punch 7 is clamped in FIG. 2 (b), the upper punch 7 is pushed up by the punch gap G above the molding bottom dead center (FIG. 2 (c)). Therefore, the vertical wall portions 51b and 51c are in this state. When the upper portion of the blank is formed, the end portions in the blank width direction (the portions 69a and 69b corresponding to the flange end portions) enter the inside (lower punch 5 side) from the state of the bottom dead center of molding. Therefore, the line length of the inner end 69a at the start of press molding is stretched and lengthened (extended flange deformation on the curved inner side), and the line length on the outer end 69b is contracted and shortened (contracted flange deformation on the curved outer side).

<Post-molding process>
In the post-molding step, the upper punch 7 is moved to the lower punch 5 by further moving the die 3 to the lower punch 5 side from the time of clamping shown in FIG. 2 (b) to the molding bottom dead center shown in FIG. 2 (c). This is a step of pressing the vertical wall / flange forming portion 13 and the lower punch 5 into a target shape by pressing the vertical wall / flange forming portion 13 and the lower punch 5 into a target shape of the vertical wall portions 51b and 51c, the curved inner flange portion 51e, and the curved outer flange portion 51f. ..

At the time of clamping in FIG. 2B, the pad pressing mechanism 17 is housed in the pad pressing mechanism accommodating portion 21, and the upper surface of the pad 11 is in contact with the lower surface of the upper die holder 15, so that the pad 11 is in contact with the lower surface of the upper die holder 15. In the process of reaching the bottom dead center of molding, when the upper die holder 15 is lowered, the upper punch 7 is pressed downward by the upper die holder 15 via the pad 11. As a result, the upper punch 7 is pushed down to reduce the punch gap G, the vertical wall / flange molding portion 13 is further lowered, the punch gap G becomes zero at the bottom dead center of molding, and the curved inner flange portion 51e is curved. The outer flange portion 51f is formed.

In the process from the time of clamping to the bottom dead center of molding, the inner end 69a is deformed by being pushed outward (outflowing toward the center of curvature), so that the inner end 69a is slightly shorter than that at the time of clamping, and the compressive force is increased. Is added to offset the tension acting on the part corresponding to the flange end during clamping, and the line length corresponds to the target shape at the bottom dead center of molding. On the other hand, the outer end 69b is deformed by being pushed outward (outflowing toward the curved outer side) in the process from the time of clamping to the bottom dead center of molding, so that the line length of the outer end 69b is slightly longer than that at the time of clamping. Therefore, a tensile force is applied to offset the compressive force acting on the flange end corresponding portion at the time of clamping, and the line length corresponds to the target shape at the bottom dead center of molding.

As described above, according to the press forming method according to the second embodiment, in the curved inner flange portion 51e and the curved outer flange portion 51f, the strain returning operation as shown in FIG. 16 is performed, and the residual stress is retained. Can be reduced.
Then, the punches for forming the vertical wall portions 51b and 51c are divided into upper and lower parts so that the punch gap G of the upper punch 7 and the lower punch 5 can be adjusted. Adjustment is possible. By finely adjusting the punch gap G, the amount of strain return can be controlled, so that the punch gap G most suitable for reducing springback can be obtained, and springback can be prevented stably and effectively.

Further, although the above shows an example in which both the inner flange and the outer flange are curved, the above means can be applied to a target shape in which either the inner flange or the outer flange is curved, and springback can be prevented.

In the above description, when the die 3 is moved to the lower punch 5 side in the post-molding step and the punch gap G disappears between the upper punch 7 and the lower punch 5, the inner vertical wall / flange forming portion 13a The inner vertical wall in the pre-molding step and the post-molding step so that there is no gap (die gap g) between the outer vertical wall and the outer vertical wall / flange forming portion 13b with the flange forming portion 25 of the lower punch 5. -The flange forming portion 13a and the outer vertical wall / flange forming portion 13b are positioned at the same position in the height direction.
In this case, when the die 3 is moved to the lower punch 5 side while maintaining the punch gap G in the preforming step (FIG. 2B), the punch bottom portion 51a and the upper portions of the vertical wall portions 51b and 51c are targeted. It is good to mold it into a shape.

However, the press forming method according to the second embodiment is not limited to the one in which the upper portions of the punch bottom portion 51a and the vertical wall portions 51b and 51c are formed into the target shape at the time of clamping, and the upper punch 7 is formed in the post forming step. In the pre-molding process, one and the other of the vertical wall / flange forming portion 13 are formed at the same height so that the target shape is obtained when the punch gap G disappears from the lower punch 5, and then post-molded. After the punch gap G disappears in the process, the vertical wall / flange forming portion 13 is moved to the lower punch 5 side to form the lower portions of the vertical wall portions 51b and 51c, the curved inner flange portion 51e, and the curved outer flange portion 51f. It may be.

Further, in the press forming method according to the second embodiment, in the preforming step, the die 3 is moved to the lower punch 5 side with one and the other of the vertical wall / flange forming portion 13 having different heights. In the post-molding step, one and the other of the vertical wall / flange forming portions 13 are moved to the lower punch 5 side, respectively, and the punch bottom portion 51a and the upper portions of the vertical wall portions 51b and 51c are formed into a target shape. May be good.

[Embodiment 3]
In actual press molding, a press try is performed before continuous press molding of a certain part, and the mold is finely adjusted based on the result of measuring the shape of the molded product. At that time, if the amount of strain return in the curved inner flange portion 51e and the curved outer flange portion 51f can be adjusted individually, three-dimensional springback such as twisting and bending can be effectively prevented.
Therefore, in the third embodiment, a press molding method for individually adjusting the amount of strain return in the curved inner flange portion 51e and the curved outer flange portion 51f will be described.

In the press molding method according to the third embodiment of the present invention, the molded product 51 having the target shape illustrated in FIG. 4 is molded by using the press molding apparatus 1 according to the first embodiment of the present invention. It includes a first molding step, a second molding step, and a third molding step. Hereinafter, each step will be described with reference to FIG.

<First molding process>
The first forming step is a step of moving the die 3 relative to the lower punch 5 side in a state where the upper punch 7 is supported by providing a predetermined punch gap G with respect to the lower punch 5.

In FIG. 3, the inner vertical wall / flange forming portion 13a and the outer vertical wall / flange forming portion 13b are located at different positions in the height direction at the start of press molding shown in FIG. 3A. Each position is adjusted by the flange forming part support mechanism 19a and the outer vertical wall / flange forming part support mechanism 19b, and while maintaining the position in the height direction, the upper die is up to the state at the time of clamping shown in FIG. 3 (b). The die holder 15 is moved to the lower punch 5 side. At this time, the inner vertical wall / flange forming portion 13a or the outer vertical wall / flange forming portion 13b sets the relative position with respect to the upper punch 7 to the molding bottom dead center (second bottom dead center shown in FIG. 3D). Since it is set so as to be higher than the target shape, at the time of clamping, the upper portions of the punch bottom portion 51a and the vertical wall portions 51b and 51c may be generally formed although they do not reach the target shape.
In this case, for each of the inner vertical wall flange forming portion 13a and the outer vertical wall flange forming portion 13b, to form a die gap g ₁ and g _2.

Further, at the time of clamping in FIG. 3B, the pad pressing mechanism 17 is housed in the pad pressing mechanism accommodating portion 21, and the upper surface of the pad 11 is in contact with the lower surface of the upper die holder 15.

<Second molding process>
The second molding step is a step of pressing the upper punch 7 against the lower punch 5 so that there is no punch gap G by further moving the die 3 toward the lower punch 5 side.
In FIG. 3, at the time of clamping (FIG. 3 (b)), the first bottom dead center while the inner vertical wall / flange forming portion 13a and the outer vertical wall / flange forming portion 13b are adjusted to different positions in the height direction. The die 3 is moved to the lower punch 5 side until (FIG. 3 (c)) to form a die 3 without a punch gap G between the upper punch 7 and the lower punch 5.

<Third molding process>
In the third molding step, the vertical wall / flange molding portion 13 is further moved to the flange molding portion 25 side so that there is no die gap, so that the vertical wall portions 51b and 51c and the curved inner flange portion 51e and the curved outer flange are formed. This is a step of forming the portion 51f into a target shape.
In FIG. 3, from FIG. 3 (b) to FIG. 3 (d), the inner vertical wall / flange molded portion 13a and the outer side are formed by the inner vertical wall / flange molded portion support mechanism 19a and the outer vertical wall / flange molded portion support mechanism 19b. the vertical wall flange forming portion 13b by moving individually, to the absence of die gap g ₁ and g _2.

The effects of the press molding method according to the third embodiment are as follows.
In the example at the start of press molding in FIG. 3A, the position of the inner vertical wall / flange molding portion 13a in the height direction is set slightly higher than that of the outer vertical wall / flange molding portion 13b.

Then, in the first molding step from the state at the start of press molding in FIG. 3 (a) to the state at the time of clamping in FIG. 3 (b), the upper punch 7 maintains the punch gap G as in the second embodiment. By lowering the die 3 while keeping it, the end portions in the blank width direction (the portions 69a and 69b corresponding to the flange end portions) enter the inside (lower punch 5 side) from the state of the bottom dead center of molding. Therefore, the wire length of the inner end 69a is stretched and lengthened (extended flange deformation on the curved inner side), and the wire length on the outer end 69b is contracted and shortened (contracted flange deformation on the curved outer side) as compared with the start of press molding. ). However, since the position of the inner vertical wall / flange molding portion 13a is higher than the position of the outer vertical wall / flange molding portion 13b, the outer end 69b is inside the inner end 69a, and the inner side is between the two. There is a difference in the amount of penetration.

Next, in the second molding step from the time of clamping (FIG. 3 (b)) to the first bottom dead center (FIG. 3 (c)), the die 3 is further lowered so that the upper punch 7 is moved to the lower punch 5 side. It is pushed in and the punch gap G becomes zero. Further, in the subsequent third molding step from the first bottom dead center to the second bottom dead center, the vertical wall / flange molding portion 13 moves to the flange molding portion 25 side, and the die gaps g ₁ and g ₂ become zero. The vertical wall portions 51b and 51c, the curved inner flange portion 51e, and the curved outer flange portion 51f are formed into a target shape.

As described above, since the outer end 69b is inside the inner end 69a at the time of clamping, the process from the time of clamping to the second lower dead point through the first lower dead point (second molding step and In the third molding step), the amount of strain returned at the curved outer flange portion 51f is larger than the amount of strain returned at the curved inner flange portion 51e.

As described above, in the third embodiment, the inner vertical wall / flange molding portion 13a and the outer vertical wall / flange molding portion 13b can be individually moved in the height direction, that is, the heights can be changed independently. The amount of return of each strain of the curved inner flange portion 51e and the curved outer flange portion 51f can be individually controlled without changing the shape of the mold itself, and the springback of bending and twisting can be controlled more precisely. Can be done.
It can be said that such flexibility according to the third embodiment of the present invention has a great advantage in a press shop where fine adjustment is repeated.

In the above description, the blank is provided by providing a difference in the position in the height direction between the inner vertical wall / flange molding portion 13a and the outer vertical wall / flange molding portion 13b in the process from the start of molding to the first bottom dead center. It is intended to provide a difference in the amount of penetration between the inner edge and the outer edge. This makes it possible to make a difference in the amount of strain returned in the process from the time of clamping to the second bottom dead center.

Since the action and effect of the press molding method of the present invention have been verified by conducting a press molding experiment, this will be described below.
As shown in FIGS. 4 and 5, the target shape of the press-molded molded product 51 is a shape curved along the longitudinal direction having a hat cross section, a length of 1000 mm, a cross section height of 30 mm, and a punch bottom. The width of 51a is 20 mm, the width of the curved inner flange portion 51e and the curved outer flange portion 51f is 25 mm, and the longitudinal curvature radius of curvature at the center of the width of the shape is 1000 mm. As the blank 69, a steel plate having a thickness of 1.2 mm and a tensile strength of 980 MPa class was used. A 1000 tonf hydraulic press was used as the press.

As an example of the present invention, using the press forming apparatus 1 shown in FIG. 1, a punch gap G between the upper punch 7 and the lower punch 5, an inner vertical wall / flange forming portion 13a, and an outer vertical wall / flange forming portion 13b are used. the height (die gap g ₁ and g ₂₎ were set separately.
On the other hand, as a comparative example, the relative movement distance h was changed by using the press molding apparatus 59 shown in FIG. 14 and using the method of Patent Document 1. A pad was used in both the comparative example and the example of the present invention, and the pad pressure was 50 tonf.

The evaluation of the molded product 51 was performed by comparing the bending amount Δy shown in FIG. 6 with the twist amount Δθ shown in FIG.
The amount of bending Δy was measured by the following method. First, the shape of the molded product 51 was measured with a three-dimensional shape measuring device. After that, the measurement shape data is aligned on the CAD software so that the curved portion in the center of the longitudinal direction matches the design shape, and then the Y coordinate difference between the measurement shape data and the design shape data at the component end (bending amount Δy, figure). 6) was calculated, and this bending amount Δy was used as an index of bending deformation due to springback.

The amount of bending Δy is that if it is positive, it bends and deforms in the direction in which the curvature of curvature of the part increases (the radius of curvature decreases), and if it is negative, it bends and deforms in the direction in which the curvature of curvature decreases (the radius of curvature increases). Means that. And if the absolute value is small, it means that the amount of springback is small.

On the other hand, the twist amount Δθ was measured by the following method.
Similar to the method for measuring the bending amount Δy, after aligning the measurement shape data so that the curved portion in the center of the longitudinal direction matches the design shape, the cross-sectional shapes of the center and the end of the curved portion are extracted as shown in FIG. did. The extracted cross-sectional shape is as shown in the schematic view of FIG. The angle formed by the punch bottom portion of the measurement shape and the punch bottom portion of the design shape (rotation angle due to springback) is measured with the direction of the rotation angle in FIG. 7 as positive, and the punch bottom rotation angle θ _C at the center of the curved portion is obtained. , The twist amount was calculated as Δθ = θ _E − θ _C from the punch bottom rotation angle θ _{E at the end.}

In Example 1 of the present invention, when the punch gap G is 10 mm, the die gap g ₁ of the inner vertical wall / flange forming portion 13a is 17 mm, and the die gap g ₂ of the outer vertical wall / flange forming portion 13b is 15 mm, the bending amount Δy Both the twist amount Δθ and the twist amount Δθ could be set to a value close to zero.
In Inventive Example 2, a case where the molded in the same height of the vertical wall flange molding portion 13, the inner vertical wall flange forming portion 13a, the die gap g _1, g of the outer vertical wall flange forming portion 13b _The results of measuring the bending amount Δy and the twist amount Δθ by changing 2 from 2.5 mm to 25 mm at the same time (and changing the punch gap G at the same time) are shown in FIG. It is plotted and shown. In Example 2 of the present invention, when the die gap g ₁ = g ₂ = 11.8 mm, the bending amount Δy becomes almost zero, and when the die gap g ₁ = g ₂ = 18.2 mm, the twist amount Δθ becomes almost zero. It was.
Further, as a conventional example, when the integrated die 53 shown in FIG. 11 is used, that is, when the relative movement distance h = 0 mm, the bending amount Δy = 7.3 mm and the twisting amount Δθ = 6.0 °, and the present invention example 1 and the present invention It was significantly lower than that of Invention Example 2.

As can be seen from this embodiment, in the method of the present invention, in addition to setting the punch gap G, the die gaps g ₁ and g ₂ of the inner vertical wall / flange forming portion 13a and the outer vertical wall / flange forming portion 13b are set. Each can be set independently, and it is possible to search for and set operating conditions such that both the bending amount and the twisting amount are close to zero. It is also possible to search for and set operating conditions so that only the bending amount and the twisting amount are close to zero with the same device.

1 Press molding device 3 Die 5 Lower punch 7 Upper punch 9 Upper punch support mechanism 11 Pad 13 Vertical wall / flange molding part 13a Inner vertical wall / flange molding part 13b Outer vertical wall / flange molding part 15 Upper die holder 17 Pad pressing mechanism 19 Vertical wall / flange molding part support mechanism 19a Inner vertical wall / flange molding part support mechanism 19b Outer vertical wall / flange molding part support mechanism 21 Pad pressing mechanism accommodating part 23 Vertical wall lower molding part 25 Flange molding part 27 Cavity part 29 Communication Groove 31 Support member 33 Stopper 35 Support device <molded product>
51 Molded product 51a Punch bottom 51b Vertical wall (curved inside)
51c Vertical wall (curved outside)
51d Groove shape part 51e Curved inner flange part 51f Curved outer flange part <Conventional example>
53 Die 55 Punch 57 Press forming die 59 Press forming device 61 Die 63 Flange forming die 65 Support mechanism 67 Punch 69 Blank 69a Inner end 69b Outer end 71 Pad <symbol>
G Punch gap g Die gap g ₁ Inner vertical wall / flange molded part die gap g ₂ Outer vertical wall / flange molded part die gap h Relative movement distance

Claims (3)

Molding consisting of a punch bottom and a pair of vertical wall portions continuous from both sides of the punch bottom, having a groove-shaped portion extending in the longitudinal direction, and having a flange portion curved in the longitudinal direction on at least one of the vertical wall portions. A press molding device that molds a product into a target shape.
A punch bottom forming portion for forming the punch bottom portion, a die having vertical wall / flange forming portions arranged on both sides of the punch bottom forming portion for forming the vertical wall portion and the flange portion, and a die.
A lower punch that forms the lower part of the vertical wall portion and the flange portion in cooperation with the die, and
An upper punch that is provided so as to be detachable (separate and contactable) from the lower punch in the height direction and that forms the bottom of the punch and the upper part of the vertical wall in cooperation with the die.
It is provided with an upper punch support mechanism that is installed in the lower punch and supports the upper punch so that the punch gap between the upper punch and the lower punch can be adjusted.
A press molding apparatus characterized in that the vertical wall / flange molding portions on both sides of the punch bottom molding portion are configured so that their heights can be changed independently of each other. A target having a groove-shaped portion composed of a punch bottom portion and a pair of vertical wall portions continuous from both sides of the punch bottom portion and extending in the longitudinal direction, and having a flange portion curved along the longitudinal direction on at least one of the vertical wall portions. A press molding method for molding a molded product having a shape using the press molding apparatus according to claim 1.
The upper punch is supported by providing a predetermined punch gap with respect to the lower punch, and the die is placed on the lower punch side with one and the other of the vertical wall / flange molded portion having the same height or different heights. And the pre-molding step of molding the upper part of the vertical wall portion by the die and the upper punch.
By further moving the die to the lower punch side, the upper punch is pressed against the lower punch so that there is no punch gap, and the vertical wall portion and the flange portion are formed into the target shape by the die and the lower punch. A press molding method characterized by comprising a molding step after molding. The molded product having a target shape having a groove-shaped portion extending in the longitudinal direction and having a flange portion curved along the longitudinal direction on at least one of a pair of vertical wall portions forming the groove-shaped portion is described in claim 1. It is a press molding method that molds using the press molding equipment of
With the upper punch supported by providing a predetermined punch gap with respect to the lower punch, the die is moved to the lower punch side, and the vertical wall / flange forming portion is placed between the flange forming portion of the lower punch. The first molding step of forming a predetermined die gap and
A second molding step of pressing the upper punch into the lower punch so that the lower punch does not have the punch gap by further moving the die to the lower punch side.
A third molding step of molding into the target shape by further moving the vertical wall / flange molding portion to the flange molding portion side so that there is no die gap is provided.
The height of the vertical wall / flange molded portion that can be changed in the first molding step is adjusted so that the die gap formed in the first molding step differs between one and the other of the vertical wall / flange molded portion. A press molding method characterized by

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