JP5808297B2 - Press forming method, press forming apparatus - Google Patents

Description

  The present invention relates to a press molding method and apparatus for bending a flat metal material into a U-shaped cross-sectional shape, and in particular, a press molding method and press molding apparatus for improving the dimensional accuracy of a shape after springback, and the press. The present invention relates to a press-molded product press-molded by a molding method and apparatus.

A frame provided on the lower surface of the floor plate of an automobile needs a sufficient strength to support an engine, a suspension, and the like. Furthermore, from the viewpoint of collision safety, the frame needs to be changed in strength and rigidity, such as a part that absorbs collision energy and a part that requires high rigidity for occupant protection.
In order to partially change the strength and rigidity in this way, for example, in a hat cross-sectional frame (hat cross-section component), a U-shaped cross-sectional shape is formed along the inner surface of the frame within the required length. The reinforcing material (a U-shaped cross-section component) is welded to increase the strength. Therefore, high cross-sectional accuracy is required for the hat cross-sectional component and the U-shaped cross-sectional component in order to bring the components into close contact with each other.

The above-mentioned hat cross-section parts and U-shaped cross-section parts support the center part in the width direction of a flat metal material with a punch from below, press against the punch with a pad from above, and lower the die to lower the width of the metal material. It is manufactured by press forming in which both side portions in the width direction of the metal material are pressed against the side surfaces of the punch while being pressed by pressing both side portions in the downward direction and bent.
However, in the press molding method as described above, since the shoulder portion R of the die is molded while sliding on the surface of the metal plate material, a so-called “ironing” process in which a passage resistance consisting of friction or the like is generated occurs. When taken out from the press die, the vertical wall portion is warped and a so-called spring back is generated which slightly spreads outward, and there is a problem that it is difficult to obtain the cross-sectional accuracy.

  In particular, in recent years, it has been desired to reduce the weight of automobiles, and it is necessary to ensure strength and rigidity while reducing the thickness of a metal plate material used for a frame. Therefore, a high-tensile steel plate has been adopted as a metal material, and the spring back tends to be further increased.

  Therefore, Patent Document 1 discloses an invention relating to a “press die” as a technique for preventing springback in press forming using a high-strength steel plate as described above. The “press die” described in Patent Document 1 is an inclination direction toward a punch by a cam driver while an upper bending blade (tip end of a die shoulder) provided on a suspension cam is in contact with a metal base plate during bending. The metal plate material can be bent into a hat cross-sectional shape without squeezing by bending the metal plate material and pressing it to the lower half.

JP 2005-254279 A

However, the technique of Patent Document 1 is such that when the die is brought into contact with the guide surface of the cam driver and moves obliquely toward the bottom dead center to bend the metal plate material, the upper bending blade (die Only the shoulder tip) is in contact with the metal plate material until the end of processing, and bending is performed with little slippage. Moreover, downward bending force is applied to the vertical wall of the metal plate material after bending. This is characterized by preventing the spring back by pressing, and the die shoulder tip and the metal plate material can always contact each other and the vertical wall portion can be pressed downward, i.e., the metal plate material It specializes in hat cross-section parts with flanges as well as walls.
For this reason, the U-shaped cross-section component without the flange portion, which is the subject of the present invention, cannot be bent while the tip of the die shoulder is in contact with the metal plate material, and can be pressed downward after bending. In addition, since it is not possible to prevent springback, it has been desired to develop a technology applicable to a U-shaped cross-section component.

  The present invention has been made to solve such a problem, and an object of the present invention is to reduce the spring back of the U-shaped cross-sectional component and improve the dimensional accuracy.

(1) A press molding method according to the present invention is a press molding method for bending a flat metal material into a U-shaped cross-sectional shape,
A pressing and bending step of bending the metal material by lowering a die while supporting the lower surface of the metal material with a punch and pressing the upper surface of the metal material with a pad, and after the pressing and bending step, the die And a bending process for bending the metal material by moving in a direction obliquely downward toward the punch,
The approach bending process at the time of the oblique downward movement after the die lowering is performed while the front end in the width direction of the metal material is in contact with the vertical wall of the die.

(2) Further, in the above-described (1), the close-bending step is performed while moving the vertical wall of the die relatively upward with respect to the front end in the width direction of the metal material. It is a feature.

(3) Further, in the above-described (1), in the shifting and bending step, the vertical wall of the die is not moved relative to the front end in the width direction of the metal material, or 2 mm in the vertical direction. It is characterized by performing the relative movement within the range.

(4) Moreover, it is a press-molded article characterized by being molded by the press-molding method according to any one of (1) to (3).

(5) A press molding apparatus according to the present invention is a press molding apparatus for bending a flat metal material into a U-shaped cross-sectional shape,
A punch that supports the lower surface of the metal material, a pad that presses the upper surface of the metal material supported by the punch, and a die that abuts against the metal material sandwiched between the punch and the pad and performs a bending process And a cam for changing the moving direction of the die into a direction approaching the punch obliquely below,
The die moves from the upper side to the lower side, and after contacting the cam, the die moves obliquely downward in a direction approaching the punch,
When the die contacts the cam and then moves to the bottom dead center, the inclination angle of the cam and the press start so that the front end in the width direction of the metal material contacts the vertical wall of the die. The horizontal distance of the die at time and bottom dead center is set.

(6) Further, in the above (5), when the die moves to the bottom dead center after contacting the cam, the vertical wall of the die is against the front end in the width direction of the metal material. The cam tilt angle and the horizontal distance of the die at the start of pressing and at the bottom dead center are set so as to move relatively upward.

(7) In the above (5), when the die moves to the bottom dead center after coming into contact with the cam, the vertical wall of the die is against the front end in the width direction of the metal material. The tilt angle of the cam and the horizontal distance of the die at the start of pressing and at the bottom dead center are set so that they do not move relative to each other or move relative to each other within 2 mm in the vertical direction. It is what.

  In the present invention, in a state where the lower surface of the metal material is supported by the punch and the upper surface of the metal material is pressed by the pad, the die is lowered to bend and form the metal material, and And then moving the die obliquely downward in a direction approaching the punch to bend and form the metal material, and the bending process at the time of obliquely downward movement after the die is lowered includes the metal material By carrying out while making the front-end | tip of the width direction contact the vertical wall of the said die | dye, a springback can be reduced and the dimensional accuracy of a U-shaped cross-section component can be improved.

It is an elevation view of the press molding apparatus concerning an embodiment of the invention. It is explanatory drawing explaining the press molding apparatus which concerns on embodiment of this invention, Comprising: It is explanatory drawing explaining operation | movement of die | dye. It is explanatory drawing explaining the press molding method which concerns on embodiment of this invention, Comprising: It is a figure explaining the state before the press molding start. It is explanatory drawing explaining the press molding method which concerns on embodiment of this invention, Comprising: It is a figure explaining the state in the middle of press molding. It is explanatory drawing explaining the press molding method which concerns on embodiment of this invention, Comprising: It is a figure explaining the state of a press bottom dead center. It is explanatory drawing explaining the definition of the springback amount in the press molding method which concerns on embodiment of this invention. It is explanatory drawing explaining the result of an example which carried out the press molding with the press molding method which concerns on embodiment of this invention, Comprising: It is a figure which shows the numerical analysis result of the amount of springbacks. It is a figure which shows the numerical-analysis result of the curvature change before and behind springback at the time of press-molding with the press-molding method concerning embodiment of this invention. It is explanatory drawing explaining the spring back and spring go in embodiment of this invention. It is the schematic which shows the positional relationship of the vertical wall of the die | dye during shaping | molding, and the metal material width direction front-end | tip in the press molding method which concerns on embodiment of this invention. In the press molding method according to the embodiment of the present invention, the positional relationship between the vertical wall of the die and the tip of the metal material at the start of bending (9d reaches the position Pb in FIG. 2) (FIG. 11 (a)), and It is a figure which shows the positional relationship (FIG.11 (b)) of the vertical wall of a die | dye in the bottom dead center (point in which 9d reached | attained Pc position of FIG. 2), and the metal raw material front-end | tip. It is explanatory drawing explaining the time change of the distance of die | dye shoulder front-end | tip and a metal raw material width direction front-end | tip in the press molding method which concerns on embodiment of this invention (lifting condition). It is explanatory drawing explaining the time change of the distance of die | dye shoulder front-end | tip and the metal raw material width direction front-end | tip in the press molding method which concerns on embodiment of this invention (push-down condition). It is explanatory drawing explaining the Example of this invention, Comprising: It is explanatory drawing explaining the result of press molding. It is explanatory drawing of the other aspect of the arrangement | positioning relationship between the die | dye and the metal raw material in the press molding apparatus which concerns on embodiment of this invention.

  A press molding apparatus according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the press forming apparatus 1 includes a punch 5 that supports the lower surface of the flat metal material 3, a pad 7 that presses the upper surface of the metal material 3 supported by the punch 5, and the punch 5 and the pad. 7 is provided with a die 9 in which the vertical wall portion comes into contact with the metal material 3 sandwiched by 7 and performs a bending process, and a cam 11 that changes the moving direction of the die 9 obliquely downward approaching the punch 5.

<Punch>
The punch 5 has a flat upper end surface 5a and a trapezoidal cross section in the longitudinal direction. The punch 5 supports the lower surface of the metal material 3 with the upper end surface 5a.

<Pad>
The pad 7 is disposed so as to face the upper end surface 5a of the punch 5 and can be moved up and down. If the pad 7 is lowered and pressed while the metal material 3 is placed on the upper end surface 5 a of the punch 5, the metal material 3 can be held.

<Cam>
The cams 11 are provided on both sides of the punch 5. The upper surface of the cam 11 is an inclined surface 11a that is inclined downward toward the punch 5 side. The inclination angle θ of the inclined surface 11a is set to a predetermined angle in consideration of the correlation with the standby distance D shown in FIG. That is, since the relative positional relationship in the press forming process between the width direction front end 3a of the metal material 3 and the vertical wall 9a of the die 9 is determined by the correlation between the inclination angle θ and the standby distance D described later, the die is lowered. In consideration of how this relative positional relationship is used in order for the width direction tip 3a of the metal material 3 to contact the vertical wall 9a of the die 9 when it is moved in an oblique direction and bent later. An angle θ is set. Details will be described later.

<Die>
The dies 9 are respectively provided above the left and right cams 11 and can be moved up and down and moved in the left-right direction in FIG. The die 9 has a vertical wall 9a, a horizontal portion 9b that continues in the horizontal direction from the lower end side of the vertical wall 9a, and an inclined portion 9c that continues to the horizontal portion 9b and is inclined obliquely upward. A corner portion at the boundary between the wall 9a and the horizontal portion 9b is a die shoulder portion 9d.
When the die 9 is lowered during press molding, the inclined portion 9c of the die 9 slides in contact with the inclined surface 11a of the cam 11, and the moving direction of the die 9 is inclined from the vertical direction by the cam 11. It is converted in a direction approaching the punch 5 below.

FIG. 2 illustrates the movement locus of the die shoulder 9d in the right die 9 from the start of press molding to the press bottom dead center.
As shown in FIG. 2, at the start of press molding, the die shoulder 9d has a predetermined distance from the punch 5 (the horizontal distance between the position Pa at the start of press molding of the die shoulder 9d and the position Pc at the bottom dead center. In the following description, this distance is referred to as “standby distance D.” (see position Pa in FIG. 2). When press molding is started and the die 9 is lowered, the die 9 is lowered by a predetermined distance in the vertical direction (see position Pb in FIG. 2). Thereafter, when the die 9 starts to slide on the inclined surface 11 a of the cam 11, the die shoulder portion 9 d moves linearly downward and approaches the punch 5. The inclination of this straight line is the same as the inclination angle θ of the cam 11. Thereafter, the die 9 reaches the bottom dead center, and the die shoulder 9d reaches the lowest position (see position Pc in FIG. 2).

A method for press-molding a rectangular metal material into a U-shaped cross-section using the press-forming apparatus 1 configured as described above will be described with reference to FIGS.
The metal material 3 has a flat plate shape extending in the direction perpendicular to the paper surface, and is sandwiched between the upper end surface 5a of the punch 5 and the pad 7 with the left and right sides in the figure as the width direction of the metal material 3 as shown in FIG. . At this time, the die 9 is positioned above the metal material 3 so as to have a predetermined standby distance D (see FIG. 2).
When the die 9 is lowered in the vertical direction (see the arrow in FIG. 3) in this state, the die 9 continues to descend in the vertical direction as it is, and the width direction front end 3a of the metal material 3 located below the die 9 becomes the die 9. The metal material 3 is pressed and bent by the punch shoulder 5b (press bending process). The width direction front end 3a of the metal material 3 does not necessarily need to contact the vertical wall 9a of the die 9 while the die 9 is vertically lowered. However, as shown in FIG. It is essential to contact the vertical wall portion 9a of the die 9.

After the pushing and bending step, as shown in FIG. 4, when the inclined surface 11a of the cam 11 and the inclined portion 9c of the die 9 come into contact with each other, the die 9 moves in a direction approaching the punch 5 (see the arrow in FIG. 4). Then, the metal material 3 is further bent and formed (close bending process). During the bending process, the width direction tip 3a of the metal material 3 is always in contact with the vertical wall 9a of the die 9, so that the metal material 3 is pressed in the width direction by the vertical wall 9a of the die 9, A bent portion 13 that slightly bulges outward is formed in a portion surrounded by a solid line circle in 4. The bent portion 13 has a shape bulging outward from the punch 5 during the bending, but at this time, a spring go component acting in the direction of canceling the springback component is accumulated in the bent portion 13 as a residual stress.
As described above, the inclination angle θ of the cam 11 and the waiting distance D of the die 9 are set so that the front end 3a in the width direction of the metal material 3 is in contact with the vertical wall 9a of the die 9 in the bending process. Yes.

Thereafter, as shown in FIG. 5, the die 9 reaches the bottom dead center, and the bending process ends. Through the push bending process and the bending process, a springback component is accumulated as a residual stress in a portion surrounded by a broken-line circle in FIGS.
As described above, the metal material 3 accumulates residual stress composed of two kinds of components, that is, a spring back component that generates spring back and a spring go component that generates spring go in the press forming process.
Then, by releasing the mold, the residual stress is released and shape deformation occurs, and the shape of the molded product is determined.

When the metal material is press-molded into a U-shaped cross-sectional shape by the press forming method as described above, the shape of the U-shaped cross-sectional component 15 after release is pressed at a standby distance D of 45 mm and an inclination angle θ of 20 degrees. A case where molding is performed will be described as an example.
6-8 is explanatory drawing explaining the shape of the U-shaped cross-section component 15. FIG.
As shown in FIG. 6 (see the thick solid line), the U-shaped cross-section component 15 has a ceiling portion 15a and a side portion 15b, and a shoulder portion 15c that is a corner portion formed by the ceiling portion 15a and the side portion 15b. ing. Since the U-shaped cross-section component 15 is symmetrical, FIG. 6 shows the right side of the center line.
As shown in FIG. 6, the vertical distance from the lower surface of the ceiling 15a of the U-shaped cross-section component 15 is L, the springback amount at the vertical distance L is S, and the vertical distance L and the springback amount S are FIG. 7 shows a graphical representation of the relationship.
As shown in FIG. 6, the spring back amount S refers to the surface on the punch 5 side of the U-shaped cross-section component 15 (shown by a two-dot chain line in FIG. 6) at the vertical distance L. The horizontal distance from the surface on the punch 5 side of the U-shaped cross-sectional component 15 (shown by a thick solid line in FIG. 6) after the spring back is defined.

As can be seen from FIG. 7, the slope of the graph suddenly increases until the vertical distance L is about 5 mm, but the slope of the graph gradually changes after about 5 mm, and the springback amount S decreases after about 30 mm. Yes.
When the springback amount S is differentiated twice, the curvature change before and after the springback can be obtained. FIG. 8 shows a graph obtained by calculating the curvature change from the springback amount S shown in FIG. In FIG. 8, the horizontal axis represents the vertical distance L (mm) from the lower surface of the ceiling portion 15a of the U-shaped cross-section component 15, and the vertical axis represents the change in curvature (1 / mm) before and after the springback.
A positive value for the change in curvature indicates that a springback occurs, and a negative value for the change in curvature indicates a phenomenon opposite to the springback, that is, a spring go.

As can be seen from FIG. 8, a springback occurs at the measurement position from the ceiling 15a to the lower end of the punch shoulder 5b (corresponding to the dotted line circle in FIG. 4), and the position up to 30 mm thereafter (in FIG. 4). Spring go is occurring in the circle corresponding to the solid line).
Thus, in the press-molded product molded by the press molding method of the present embodiment, a spring back component and a spring go component are generated by press molding, and the spring back is canceled by the spring go, thereby suppressing the spring back. ing.

Here, the meaning of canceling the springback by the spring go will be described in detail with reference to FIG.
FIG. 9 is a diagram for explaining a change in the shape of the U-shaped cross-section component 15 before and after mold release when a spring back or spring go occurs. The left side in the figure shows a state before mold release, and the right side in the figure shows mold release. The later state is shown.

As shown in the left figure of FIG. 9 (a), when the springback component is present in the portion surrounded by the dotted circle in the vicinity of the shoulder portion 15c before the mold release, after the mold release, FIG. 9 (a) As shown in the right figure, the shape changes in the direction of opening the opening of the U-shaped cross-section component 15 (spring back).
On the other hand, as shown in the left diagram of FIG. 9B, when the spring go component is present in the upper part of the side portion 15b (portion surrounded by a solid line circle) before release, (B) As shown in the right figure, the shape changes in the direction of closing the opening of the U-shaped cross-section component 15 (spring go).
Thus, the spring back and the spring go are deformations in opposite directions, and the spring back component and the spring go component are components that cancel each other.
Therefore, as shown in the left diagram of FIG. 9C, before release, both the springback component (portion surrounded by a dotted line circle) and the spring go component (portion surrounded by a solid line circle) exist, and the size is If they are almost the same, these components cancel each other after release, and the shape change becomes small as shown in FIG. 9C.

Next, it will be described under what conditions it is effective to perform press molding for canceling the springback component with the spring go component.
Since it is easier to control the spring go component than the spring back component, the conditions for controlling the spring go component will be described.
The spring go component is accumulated in the bent portion 13 generated in the metal material 3 shown in FIG. 4, and the condition that affects the formation of the bent portion 13 is the position of the tip 3a in the width direction of the metal material 3 in the press forming process. Since this is the relative position of the vertical wall 9a of the die 9, this will be described.

FIG. 10 is an enlarged view of the vicinity of the front end 3a in the width direction of the metal material 3 while the die 9 is descending (obliquely downward). As shown in FIG. 10, the distance in the direction along the vertical wall 9a of the die 9 from the width direction tip 3a of the metal material 3 to the die shoulder 9d is assumed to be X. X changes during the press working, but X at the start of the close bending (see FIG. 11A, when the die shoulder 9d is lowered to the position Pb in FIG. 2) is X _0, and at the end of the close bending (see FIG. 11 (b) see, the X point) of the die shoulder 9d reaches the lowermost position Pc in Fig 2, _{X 1.}

The distance X changes during press molding, and the mode of the change is determined according to the standby distance D and the inclination angle θ shown in FIG.
For example, FIG. 12 shows a change state of the distance X when the standby distance D is 45 mm and the inclination angle θ is 20 degrees. In FIG. 12, the vertical axis indicates the distance X (mm) between the tip of the die shoulder and the tip of the metal material, and the horizontal axis indicates the time from the start of the close bending to the end of the close bending.
The distance X varies from X ₀ (about 31.3 mm) to X ₁ (about 23.8 mm) along the curve shown in FIG. At this time, X ₀ −X ₁ = 7.5 mm> 0, and the die 9 is relatively upward when viewed from the width direction tip 3a of the metal material 3 (the width direction tip 3a of the metal material 3 and the die shoulder 9d). In the direction of approaching).
Here, when X ₀ -X ₁ > 0, that is, X ₀ > X ₁ , the die 9 is relatively upward when viewed from the width direction tip 3a of the metal material 3 (with the width direction tip 3a of the metal material 3). The die shoulder portion 9d moves in the direction in which the die shoulder portion 9d approaches. This condition is referred to as “lifting condition”.
In the case of the lifting condition, the die 9 moves relatively upward as viewed from the width direction tip 3a of the metal material 3, and the width direction tip 3a of the metal material 3 is rubbed upward. At this time, the frictional force generated between the width direction front end 3a of the metal material 3 and the vertical wall 9a of the die 9 acts in the direction of pushing up the metal material 3 toward the punch shoulder 5b. The amount of deflection generated in the metal material 3 becomes larger, and a spring go component is generated in the metal material 3.

As another example, FIG. 13 shows a change state of the distance X when the standby distance D is 15 mm and the inclination angle θ is 50 degrees.
In this case, the distance X changes from X ₀ (about 10.4 mm) to X ₁ (about 23.5 mm) along the curve shown in FIG. At this time, X ₀ −X ₁ = −13.1 mm <0, and the die 9 is relatively downward when viewed from the width direction tip 3a of the metal material 3 (the width direction tip 3a of the metal material 3 and the die shoulder portion). 9d is moving away).

Here, when X ₀ −X ₁ <0, that is, X ₀ <X ₁ , the die 9 is relatively downward when viewed from the width direction tip 3a of the metal material 3 (the width direction tip 3a of the metal material 3 is (The direction away from the die shoulder 9d). This condition is referred to as a “lowering condition”.
In the case of the lowering condition, the die 9 moves relatively downward as seen from the width direction tip 3a of the metal material 3, and the width direction tip 3a of the metal material 3 is rubbed downward. At this time, the bent portion 13 is formed in the same manner as in the lifting condition, but the amount of deflection is smaller than in the lifting condition.

In the press molding operation, there is a case where “scraping” in which the shavings of the metal material 3 due to sliding adhere to the press mold may occur. In this respect, if there is little change in the relative position between the position of the metal material 3 in the width direction front end 3a and the vertical wall 9a of the die 9 during the bending, the “mold galling” can be suppressed.
From such a point of view, a condition that X ₀ -X ₁ is in a predetermined value range (this condition is referred to as “neutral condition” in this specification), and as a specific example, −2 mm ≦ X ₀ -X _What is necessary is just to perform press molding under the condition of ₁ ≦ 2 mm.

  Thus, conditions can be selected by appropriately setting the standby distance D and the inclination angle θ, and press molding can be performed under optimum conditions. For example, if it is desired to increase the spring go component, it may be set so as to be a lift-up condition, and if it is desired to prevent the occurrence of mold squeezing, it may be set so as to be a neutral condition.

  As described above, in the present embodiment, the metal material 3 is bent by lowering the die 9 while supporting the lower surface of the metal material 3 with the punch 5 and pressing the upper surface of the metal material 3 with the pad 7. A pressing and bending step, and after the pressing and bending step, the die 9 is moved obliquely downward in a direction approaching the punch 5 to bend and form the metal material 3, and the die 9 is lowered obliquely after the die 9 is lowered. The bending process of moving to the metal material 3 is performed while bringing the width direction tip 3a of the metal material 3 into contact with the vertical wall 9a of the die 9, thereby bending the metal material 3 to generate a spring go component, and this spring go component Thus, the springback component can be reduced, and thereby the dimensional accuracy of the U-shaped cross-section component 15 can be improved.

In addition, by setting the standby distance D and the inclination angle θ to predetermined values as the lifting condition, the deflection amount of the deflection portion 13 can be increased, and the spring go component can be further increased. The back can be further reduced.
Moreover, if it is set as neutral conditions, generation | occurrence | production of type | mold galling can be prevented and it is preferable on operation.

In order to confirm the operational effects of the press molding method of the present invention, numerical analysis and press molding were performed with respect to the press molding of the U-shaped cross-section component 15, and the spring back was evaluated based on the results.
In this example, a high-tensile steel plate with a tensile strength of 980 MPa was used as the metal material 3. The initial shape of the metal material 3 was 400 mm long, 220 mm wide, and 2.0 mm thick. In the numerical analysis, a two-dimensional analysis was performed assuming a plane strain condition.

The springback amount S used for evaluation was defined in the same manner as in FIG. Here, the spring back amount S at the vertical distance L of 70 mm close to the width direction front end 3a of the metal material 3 after press forming is defined as “the spring back amount S at the front end”.
The waiting distance D was set to 15, 25, 35, and 45 mm, and the inclination angle θ was set to 20, 30, 40, and 50 degrees, and numerical analysis was performed on the conditions of all these combinations. Furthermore, press molding was performed using actual equipment under some conditions. Regarding the springback amount S, the result of press molding by the actual machine and the result of numerical calculation agreed well qualitatively. The results are shown in Table 1.

Each column in Table 1 is, in order from the leftmost column, No. (number), standby distance D, inclination angle θ, and X ₀ − which is the difference between X ₀ at the start of the close bending and X ₁ at the end of the close bending. X ₁ , the springback amount S at the tip, and remarks are shown.
In addition, as a conventional example, No. 10 is described as a result of simple bending in which the die 9 is lowered in the vertical direction without using the cam 11 and press molding is performed. In this case, the standby distance D corresponds to 0 mm.
Looking at Table 1, No. 3 and No. 4 are X ₀ -X ₁ > 0, which is a lifting condition. Further, Nos. ₁ , 2, and 5 to 9 are X ₀ -X ₁ <0, which is a close-down condition. No. 1, No. 2 and No. 5 are in the range of −2 mm ≦ X ₀ −X ₁ ≦ 2 mm and are neutral conditions.
The conditions described above with reference to FIG. 12 (standby distance D: 45 mm, inclination angle θ: 20 degrees) correspond to No. 4. Further, the condition described with reference to FIG. 13 (standby distance D: 15 mm, inclination angle θ: 50 degrees) corresponds to No. 6.

FIG. 14 is a plot of the relationship between X ₀ -X ₁ and the springback amount S at the tip for each of No. 1 to No. 9 in Table 1. In FIG. 14, the horizontal axis represents X ₀ -X ₁ (mm), and the vertical axis represents the tip spring back amount S (mm). Each plot is assigned a number corresponding to Table 1.
As shown in Table 1, in No. 10 with simple bending, in addition to the spring back due to the bending of the punch shoulder, a large spring back due to the distortion of the vertical wall is added by the die, and the spring back amount S at the tip is It became 3.5mm. On the other hand, in No. 1 to No. 9 subjected to bending according to the present invention, the amount of springback at the tip does not cause ironing distortion as compared with No. 10, and both are greatly improved. 3 and 4 are the most effective in reducing the spring back by adding a spring go that compresses the vertical wall.
From the above, it was proved that the present invention is effective in reducing the springback.

  Further, as shown in FIG. 14, in the lifting condition (No. 3 and No. 4), the springback amount S at the tip is significantly smaller than the other conditions. Even in the neutral conditions (No. 1, No. 2, and No. 5), the amount of spring back S at the tip is reduced, and in this embodiment, when it is desired to prevent both spring back and die scoring, No. 5 It can be seen that press molding should be performed under the conditions.

  In the description of the above embodiment, as shown in FIG. 3, the case where the width direction front end 3a of the metal material 3 projects outside the die shoulder portion 9d in the state before forming has been described. The present invention is not limited to this, and as shown in FIG. 15, the metal material 3 may have a width direction front end 3a inside the die shoulder portion 9d in a state before forming.

X, X ₀ , X ₁ Distance in the direction along the vertical wall 9 a of the die 9 from the width direction tip 3 a of the metal material 3 to the die shoulder 9 d θ Inclination angle D Standby distance Pa, Pb, Pc Position L Vertical direction distance S Springback amount 1 Press forming device 3 Metal material 3a Front end in width direction 5 Punch 5a Punch upper end surface 5b Punch shoulder 7 Pad 9 Die 9a Vertical wall 9b Horizontal portion 9c Inclined portion 9d Die shoulder 11 Cam 11a Inclined surface 13 Deflection 15 U-shaped cross-section parts 15a Ceiling part 15b Side part 15c Shoulder part

Claims (2)

A press molding method for bending a flat metal material into a U-shaped cross-sectional shape,
A pressing and bending step of bending the metal material by lowering a die while supporting the lower surface of the metal material with a punch and pressing the upper surface of the metal material with a pad, and after the pressing and bending step, the die And a bending process for bending the metal material by moving in a direction obliquely downward toward the punch,
The bending process at the time of the oblique downward movement after the lowering of the die is performed while bringing the front end of the metal material in the width direction into contact with the vertical wall of the die, and the vertical wall of the die with respect to the front end of the metal material in the width direction. The press molding method is characterized by being performed while moving relatively upward . A press molding apparatus for bending a flat metal material into a U-shaped cross-sectional shape,
A punch that supports the lower surface of the metal material, a pad that presses the upper surface of the metal material supported by the punch, and a die that abuts against the metal material sandwiched between the punch and the pad and performs a bending process And a cam for changing the moving direction of the die into a direction approaching the punch obliquely below,
The die moves from the upper side to the lower side, and after contacting the cam, the die moves obliquely downward in a direction approaching the punch,
When the die moves to the bottom dead center after contacting the cam, the front end in the width direction of the metal material is in contact with the vertical wall of the die, and the vertical wall of the die is made of the metal material. A press molding apparatus , wherein an inclination angle of the cam and a horizontal distance of the die at the start of pressing and at the bottom dead center are set so as to move relatively upward with respect to the front end in the width direction .

Images