JP3459004B2 - Press molding method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a press molding method and apparatus for suppressing springback and the like due to residual stress of a material after pressing.

[0002]

2. Description of the Related Art In recent years, in order to reduce the weight and strength of automobile body frames and the like, press forming using high tensile strength and high strength steel sheets has been carried out.

In Japanese Utility Model Laid-Open No. 6-5724, spring back is suppressed by increasing the holding force of the press material to suppress the material flow of the press material and imparting a large tensile force to the press material in the latter stage of molding. The technology to do is proposed.

Japanese Patent Laid-Open No. 11-290951 discloses that in a punch forming process, while pressing a press material, a corrugated portion (bead) is formed on the pressing surface to increase the tension of the vertical wall portion and spring back. A technique for suppressing this has been proposed.

[0005]

However, as in the above-mentioned prior art, by suppressing the material flow in the latter stage of molding or forming beads, the bending radius of the material is small when the bending radius of the material in the initial stage of molding is small. Since the difference in residual stress between the inner side and the inner side of the bend cannot be reduced, the spring back cannot be sufficiently suppressed particularly in the press forming of the high strength steel plate.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to reduce the residual stress difference between the outer side of bending and the inner side of bending of a raw material to improve the shape retention after press forming. It is an object of the present invention to provide a press molding method and apparatus that can be improved.

[0007]

In order to solve the above-mentioned problems and to achieve the object, a press forming method of the present invention comprises a punch part having receiving parts arranged to face each other in order to press a material. , Using a die part that is provided so as to be able to move back and forth in the punch part direction and a blank part that is arranged to face the die part, and press the die part while pressing the material between the die part and the blank part. In a press forming method for forming a material into a desired final shape by lowering the material relative to the above, the material is formed into a final shape.
Before reaching the latter stage of molding, the die part and blank part
Press the material with and to put the die part into the punch part.
While lowering relative to the die, move the die part
The punch part is moved forward by moving the punch part toward the punch part.
The bending radius of the material due to
The material is stretched in a larger size, and the material is pressed into the final shape in the final stage, while further pressing the material.
The die part is lowered relative to the punch part.
And a step portion formed at each end portion of the die portion on the punch portion side and the blank portion side, and a protrusion formed at a corner portion of the blank portion facing the step portion by advancing together. And the side wall of the material is tensioned while the material is prevented from flowing into the punch section.

[0008]

[0009]

The press-forming apparatus of the present invention comprises a punch section having receiving sections arranged to face each other to press the material, a die section provided so as to be movable back and forth in the punch section direction, and the die section. A press including a blank portion arranged to face each other, and pressing the raw material between the die portion and the blank portion to lower the die portion relative to the punch portion to form the raw material into a desired final shape. In the molding machine, the die part is aligned with the punch part.
Die driving means for advancing the die part in the direction of the punch part while descending relative thereto, and an inclined surface provided on the die driving means and formed on the rear surface part of the die part to press the inclined surface. And a cam for advancing the die part toward the punch part while sliding the die, and the die driving means reaches the latter stage of forming the material into a final shape.
Before, press the material between the die part and the blank part.
At least, the die part is relatively moved with respect to the punch part.
While lowering, move the die part toward the punch part.
By moving it forward, the punch bends the material
In the condition that the bending radius is larger than the bending radius of the material in the final shape
Late stage of forming by stretching the material and forming the material into the final shape
In, by further lowering the die part in the punch part direction and moving it forward while further pinching the material, a step part formed at each end part of the die part on the punch part side and the blank part side. , The protrusions formed at the corners of the blank portion are fitted so as to face the stepped portion, and tension is applied to the side wall portion of the blank material while preventing the raw material from flowing into the punch portion side. .

[0011]

Further, preferably, the cam is supported by a supporting means of a holder for pressing the material in cooperation with the die part, the cam moves in synchronization with the die part and the holder in the initial stage of molding, and the latter stage in the latter stage of molding. The inclined surface is slid to move the die part forward in the punch part direction relative to the holder.

[0013]

As described above, according to the invention of claim 1 , the raw material is formed into the final shape in the latter half of the forming.
Bending the material to the outer side by applying tension to
After press molding, reduce the residual stress difference between the inner sides.
The shape retention property of can be improved more effectively. Also, the final form
When forming into a shape, the material from the material holding part to the punch part side
Applying tension to the material with the material flow blocked
As a result, tension can be reliably applied .

[0014]

[0015]

According to the invention of claim 2, the die part is panned.
By providing the die drive means for moving the die part forward in the direction of the punch part while lowering it relative to the punch part, the bending radius of the material at the punch shoulder part at the initial stage of forming can be It can be press-formed to be larger than the latter stage of forming into a shape. Further, the die driving means is provided with a cam that pushes the inclined surface formed on the rear surface portion of the die portion and slides the inclined surface while advancing the die portion toward the punch portion. It is possible to perform press forming so that the bending radius of the material at the punch shoulder portion in the initial stage of forming becomes larger than that in the latter stage of forming in the final shape.

[0017]

According to the third aspect of the present invention, the cam is supported by the supporting means of the holder for pressing the material in cooperation with the die part, and the cam moves in synchronization with the die part and the holder at the initial stage of molding,
In the latter stage of molding, by sliding the inclined surface and advancing the die part relatively to the holder in the punch part direction, the die part can be advanced with a simple structure.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing the main part of the press molding apparatus of this embodiment.

As shown in FIG. 1, in the press molding apparatus of this embodiment, an upper mold 1 which is a movable mold and a lower mold 1 which is a fixed mold are used.
It is configured to move in the direction of descending or rising relative to 1.

The upper die 1 is provided with a punch receiving portion 2 which receives the punch portion 12 of the lower die 11, and a die portion 3 which is provided in the direction of the punch portion 12 so as to be movable back and forth within a predetermined movable range X.

The lower die 11 presses the material W with the punch receiving portion 2 at a position facing the punch receiving portion 2 of the upper die 1 so as to be surrounded by the lower die 11.
2 is fixed, and a blank portion 13 that clamps the material W by the die portion 3 is supported by the blank holder 14 at a position facing the die portion 3 of the upper die 1.

The blank holder 14 is a cushion pin 1.
5 is movably supported in the vertical direction, and the blank portion 13 is urged upward without being pressed by the die portion 3 and upwardly of the cushion pin 15 while being pressed by the die portion 3. It moves downward against the urging force of.

A die driving cam 16 for advancing the die portion 3 toward the punch portion 12 is fixed to the support plate 17 on the lower die 11 as the upper die 1 approaches the lower die 11. The gas spring 18 urges the gas spring 18 upward with a predetermined pressure.

The support plate 17 is a die driving cam 16
The blank holder 1 is pressed by the die portion 3 through the blank portion 13 and abutted against the blank holder 14 that descends while being pressed by a predetermined pressure (two-dot chain line in FIG. 1).
4 is also urged upward by the gas spring 18 at a predetermined pressure. That is, the support plate 17 is the gas spring 1
The urging force of 8 defines the lowering limit of the die driving cam 16 and the blank holder 14.

The die driving cam 16 is a cam surface 16a that presses an inclined surface 3a which is inclined downward (downward in the drawing) toward the punch portion 12 formed on the rear surface of the die portion 3.
have. The cam surface 16a is formed as an inclined surface that inclines upward in the direction opposite to the punch portion 12 (upward to the right in the drawing), and when the die portion 3 descends, slides on the inclined surface 3a while punching the die portion 3. Advance in the direction of section 12. This allows the die unit 3 to move back and forth with a simple structure including the die unit 3 and the die drive cam 16.

In the lower part of the die part 3 on the punch part 12 side,
The lower step portion 3b and the upper step portion 3c, which are formed stepwise, are formed, and when the die portion 3 advances to the full movable range (at the end of press molding), the lower step portion 3b is replaced by the blank portion 1.
3 is fitted to the protrusion 13a formed at the corresponding position,
The upper step portion 3c is configured to fit into a corner portion 12a formed at a corresponding position of the punch portion 12.

The die portion 3 is lowered to bend the material W at the bending radius R at the shoulder portion 12b of the punch portion 12 and is advanced in the direction of the punch portion 12 to bend at the shoulder portion 12b of the punch portion 12. As will be described later, the radius R is set such that the bending radius in the initial stage of forming is larger than that in the latter stage of forming. [Press Molding Step] Next, a press molding step using the press molding apparatus of this embodiment will be described.

FIG. 2 shows the positional relationship between the die, punch and blank in the initial molding state, FIG. 3 shows the positional relationship between the die, punch and blank in the middle stage of molding, and FIG. 4 shows the die and punch in the latter stage of molding. The positional relationship between the blank portion and the blank portion is shown.

At the initial stage of forming shown in FIG. 2, the flat plate material W is projected onto the punch 12 and the blank 13 while the punch 12 and the projection 13a of the blank 13 are arranged at substantially the same height. It is thrown in on the part 13a (FIG. 2 (a)), and the die part 3 is lowered to clamp it with the blank part 13 (FIG. 2 (b)). In this state, the die part 3 does not move forward, the punch part 12 is at a position relatively elevated with respect to the blank part 13, and the material W is stretched while the punch part 1 is being stretched.
It is bent with a bending radius R1 by the shoulder portion 12b of No. 2.

In the middle stage of molding shown in FIG. 3, the die part 3 is advanced in the direction of the punch part 12 and lowered, and the punch part 12 is in a position further raised relative to the blank part 13. While the material W is further extended, it is bent by the shoulder portion 12b of the punch portion 12 so that the bending radius R2 becomes smaller (R1> R2).

In the latter stage of molding shown in FIG. 4 (FIG. 4 (a)),
The die portion 3 is further advanced and lowered in the direction of the punch portion 12, and the lower step portion 3b of the die portion 3 and the blank portion 1 are
The protrusions 13a of No. 3 start to be fitted, and the shoulder 12b of the punch 12 bends the bending radius R3 to a smaller value (R1>R2> R3). This fitting causes the material to flow into the punch 12 side. The side wall portion of the material is stretched in a state where the (stretch) is blocked to apply tension. And finally,
The upper surface portion of the punch portion 12 and the lower surface portion of the punch receiving portion 2, the side wall portion of the die portion 3 and the side wall portion of the punch portion 12 are in contact with each other, and the lower step portion 3b, the protrusion portion 13a of the blank portion 13, and the upper step portion. The material W is squeezed into the final shape and press-formed by fitting 3c into the corners 12a of the punch 12 respectively (FIG. 4B).

The material W has, for example, a tensile strength of 340 to 340.
A high-strength steel plate of about 780 MPa, which is a vehicle body frame (for example, front frame or side frame)
Is pressed as.

As a modified example of the press forming apparatus according to the present embodiment, as shown in FIG. 5, the upper step portion 3c of FIG. 1 is eliminated and only the lower step portion 3b is provided, and the lower step portion 3b is replaced by the punch portion 12.
By extending in the direction of
And the corners 12a of the punch 12 may be fitted together. [Press Forming Result] FIG. 6 is a diagram illustrating a method for measuring the side wall warpage and the springback of the press material formed by using the press forming apparatus according to the present embodiment. FIG. 7: is a figure explaining the measuring method of the twist of the press raw material shape | molded using the press molding apparatus of this embodiment. FIG. 8 is a diagram showing the amount of side wall warpage measured by the measuring method shown in FIG. FIG. 9 is a diagram showing a springback amount measured by the measuring method shown in FIG. FIG. 10 shows FIG.
It is a figure which shows the twist amount measured by the measuring method shown in FIG.

In FIG. 6, the side wall warpage amount 1 / ρ (1 / mm) of the press materials W1 and W2 is a plurality of predetermined intervals (for example, 50 mm) between the side wall of the punch section 12 and the side wall of the press material. It is represented by the reciprocal of the curvature ρ measured at three points at intervals.

In FIG. 6, the springback amount Δθ (degrees) of the press materials W1 and W2 is the shoulder 1 of the punch section 12.
It is expressed as the amount of change of the portion of the press material corresponding to the shoulder portion with respect to 2b (design angle).

In FIG. 7, the twist amount ΔD (mm) of the press materials W1 and W2 is measured at two points where the upper surface of the punch 12 and the portion of the press material corresponding to the upper surface are separated by a predetermined distance. The result is expressed as the difference between H1 and H2.

As a result of the above measurement, the press material W1
Is formed by using the die portion 3 having the upper and lower step portions 3b and 3c shown in this embodiment, and the press material W2 is formed by the die portion 3 having only the lower step portion 3b as a modified example.

As shown in the measurement results of FIG. 8, the side wall warp amount 1 / ρ of the press materials W1 and W2 has a tensile strength of 30.
It is within the optimum range for materials of 0 to 780 MPa, and it is possible to reduce the amount of side wall warpage and improve the shape retention after press molding as compared with conventional drawing.

Further, as shown in the measurement results of FIG. 9, the springback amount Δθ of the press materials W1 and W2 is a material having a tensile strength of 300 to 780 MPa, which is smaller than that of the conventional draw forming. It can be reduced to improve the shape retention after press molding. In order to further suppress the springback amount, the shoulder portion 12b of the punch portion 12 may be raised to overbend as shown by the dotted line in FIG.

Further, as shown in the measurement result of FIG. 10, the twist amount ΔD of the press materials W1 and W2 has a tensile strength of 3
With a material of from 00 to 780 MPa, the amount of twist can be reduced and shape retention after press molding can be improved compared to conventional drawing. In order to further suppress the amount of twist, a corrugated portion (bead) may be provided on the material near the shoulder portion of the punch portion 12.

Further, regarding the formability of the press materials W1 and W2, breakage did not occur in the materials having a tensile strength of 300 to 780 MPa, and good results were obtained as compared with the conventional draw forming. [Operation and Effect of Press Forming] FIG. 11 is a diagram showing a residual stress in the side wall portion P of FIG. 6 which is a press material formed by using the press forming apparatus of this embodiment.
FIG. 12 is a diagram showing a residual stress corresponding to the side wall portion P of FIG. 6, which is a press material formed by using the conventional press forming apparatus.

In the press molding of this embodiment, the die portion 3
Moves toward the punch portion 12, the bending radius R1 of the material of the punch shoulder portion 12b at the initial stage of forming shown in FIG.
However, the bending radius R3 of the material at the latter stage of molding to form the final shape
And the lower step portion 3b of the die portion 3 and the protrusion 13a of the blank portion 13 are fitted to each other in the latter stage of molding shown in FIG. Since tension is applied to the side wall portion 12b of the material in the blocked state, as shown in FIG. 11, the residual stress difference between the outer bending side Wa and the inner bending side Wb of the material is reduced, or the stress direction is changed. It can be oriented in one direction and the shape retention after press molding can be improved.

The residual stress difference between the outer bending side Wa and the inner bending side Wb of the material is caused by the material being bent at the punch shoulder portion 12b and then extended (bent back). In conventional press molding, the die part 3
Does not advance in the direction of the punch portion 12, the bending radius R of the material of the punch shoulder portion 12b becomes small from the initial stage of forming, and the material flows (extends) to the punch portion side in the latter stage of forming.
Therefore, as shown in FIG. 12, the bending outer side Wa of the material is
The difference in residual stress between the inner side of the bend Wb and the inner side of the bend Wb is large, or the direction of the stress is in the opposite direction, and the bending moment acts on the side with the larger stress to cause warpage.

The present invention can be applied to a modified or modified version of the above embodiment without departing from the spirit of the present invention.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a main part of a press molding apparatus of this embodiment.

FIG. 2 is a diagram showing a positional relationship between a die part, a punch part and a blank part in an initial state of molding.

FIG. 3 is a diagram showing a positional relationship among a die part, a punch part and a blank part in a middle stage of molding.

FIG. 4 is a diagram showing a positional relationship among a die part, a punch part, and a blank part in a later stage of molding.

FIG. 5 is a cross-sectional view showing a main part of a press molding apparatus of a modified example.

FIG. 6 is a diagram illustrating a method for measuring a side wall warp and a springback of a press material formed by using the press forming apparatus according to the present embodiment.

FIG. 7 is a diagram illustrating a method for measuring twist of a press material formed by using the press forming apparatus according to the present embodiment.

8 is a diagram showing the amount of side wall warpage measured by the measuring method shown in FIG.

9 is a diagram showing a springback amount measured by the measuring method shown in FIG.

10 is a diagram showing the amount of twist measured by the measuring method shown in FIG.

11 is a view showing a residual stress in a side wall portion P of FIG. 6, which is a press material formed by using the press forming apparatus of the present embodiment.

FIG. 12 is a view showing a residual stress at a position corresponding to the side wall portion P of FIG. 6, which is a press material formed by using a conventional press forming apparatus.

[Explanation of symbols]

1 ... Upper mold 2 Punch receiver 3 ... Dice part 11 ... Lower mold 12 ... Punch part 13 ... Blank part 14 ... Blank holder 15 ... Cushion pin 16 ... Die drive cam 17 ... Support plate 18 ... Gas spring

Claims (3)

(57) [Claims] 1. A punch part having receiving parts arranged to face a material for press working, a die part provided so as to be movable back and forth in the punch part direction, and a blank part arranged to face the die part. using the door, in the press molding method for molding the die unit while nipped material between the die portion and the blank portion in the desired final shape of the material by lowered relative said punch portion, the material Before it reaches the final stage of molding
, Press the material between the die part and the blank part,
Lower the die part relative to the punch part
While moving the die part forward in the direction of the punch part,
The bending radius of the material by the punch
Stretch the material so that it is larger than the bending radius of the material in its final shape.
Bridge, in the molding late shaping the material into a final shape, further
While pressing the material, place the die part against the punch part.
And lower it relatively and move it forward.
Ri, mating with the punch portion and the blank portion side step portion formed at each end of the said die portion, and a protruding portion formed on the corners of the blank portion to face the stepped portion Then, the press molding method is characterized in that tension is applied to the side wall of the material while the material is prevented from flowing into the punch section. 2. A punch part having receiving parts arranged to face a material for press working, a die part provided so as to be movable back and forth in the punch part direction, and a blank part arranged to face the die part. with the door, in the press molding apparatus for molding the die unit while nipped material between the die portion and the blank portion in the desired final shape of the material by lowered relative said punch portion, said die Part relative to the punch part
While, the die driving means for advancing the die part in the punch part direction, and the die driving means, which is provided in the die driving part, presses the inclined surface formed on the rear surface part of the die portion, while sliding the inclined surface, And a cam for advancing the die part toward the punch part, wherein the die driving means forms the raw material into a final shape.
Before reaching the latter stage of molding, the die part and blank part
Material tighten assay nip, the die portion in the punch unit in a
While lowering relative to the die, move the die part
The punch part is moved forward by moving the punch part toward the punch part.
The bending radius of the material due to
The material is stretched in a larger size, and the material is formed into the final shape.
While pressing the material , lower the die part toward the punch part.
By descending and moving forward , a step portion formed at each end of the die portion on the punch portion side and the blank portion side and a corner portion of the blank portion facing the step portion are formed. The press forming apparatus is characterized in that a tension is applied to a side wall portion of the raw material in a state where the raw material is prevented from flowing into the punch portion side by engaging with the protruding portion. 3. The cam is supported by supporting means of a holder that presses a material in cooperation with the die part, moves in synchronization with the die part and the holder at the initial stage of molding, and the inclination at the latter stage of molding. The press molding apparatus according to claim 2, wherein the surface of the die is slid to advance the die portion in the punch portion direction relative to the holder.