JP6361902B2 - Press molding method and manufacturing method of press molded parts - Google Patents

Description

  When applying a high strength material to a complex shape part such as an automobile frame part, the present invention sets the part shape of the previous process before reaching the final part shape when pressing the part in a plurality of steps. The present invention relates to a press molding method in which press molding is performed using the part shape of the previous process, and a press molded component manufacturing method using the same.

  In recent years, in the automobile field, the use of high-strength materials is increasing from the viewpoints of weight reduction for improving fuel economy in response to environmental problems, or improvement of collision safety performance. On the other hand, since high-strength materials are susceptible to cracking during press molding due to a decrease in ductility, development of materials with good ductility and development of countermeasure technologies during press processing are being promoted.

  One of the crack countermeasure technologies is hot pressing (see Patent Document 1). In this technique, a steel sheet is heated and pressed in a softened state to improve formability at the time of forming, and then strengthened by quenching by mold cooling.

  In addition, a technique has been proposed in which cracks are generated by pressing a plurality of processes on a complex-shaped part that is cracked when pressed in one process, thereby suppressing the generation of cracks (see Patent Documents 2 and 3). ).

Special table 2014-520961 gazette Japanese Patent No. 5614514 International Publication No. 2014/106932

  However, the hot press requires special equipment, is slow in production speed, and has problems in terms of cost and productivity. On the other hand, the improvement of formability due to multiple processes is largely due to the experience of engineers in setting the part shape of the previous process before reaching the final part shape, and the shape setting method of the previous process has not been established, and the shape setting It is hard to say that efficiency is being improved.

  Therefore, the present invention establishes a shape setting method for the previous process and efficiently sets the part shape for the previous process and simplifies the pressing process of the final process to solve the above problems. An object is to provide a method of pressing without cracking.

The press molding method of the present invention that advantageously solves the above problems sets the shape of the press molded product of the previous process from the development intermediate shape obtained in the middle of developing the final part shape of the press molded part having a drawn shape,
Press-molding the pre-processed press-molded product into the set pre-processed press-molded product shape ,
Next, a part of the press-formed product of the previous process is press-formed into the final part shape,
Thereafter, the remaining portion is press-molded into the final part shape .

In the press molding method of the present invention, the press molding of the previous step from the development middle shape obtained while opening the flange part of the final part shape of the press molded part having a hat-shaped cross-sectional shape as the drawing shape in the outward direction of the part. arbitrariness preferred to as setting the goods shape.

And the manufacturing method of the press-molded part of the present invention is a press-molding method of the present invention described above, and press-molds the press-molded product of the previous process into the press-molded product shape of the set previous process,
The pre-processed press-molded product is press-molded into the final part shape.

  When molding complex shaped parts in a single process, high strength materials have a lower ductility, so strains often lead to cracking. For this reason, multiple processes are used to disperse the strain and form it. In the past, attempts have been made to improve the performance. Since cracks occur when the material is stretched, in the present invention, the shape is set so that the cross-sectional line length does not substantially change when forming from the previous process shape to the final part shape. That is, by setting the pre-process shape from the development intermediate shape obtained during the development of the final part shape, the press-formed product shape of the pre-process having substantially the same cross-section line length as the final part shape is set.

  The set shape of the press-molded product in the previous process is based on the shape obtained in the process of developing the final part shape, so by pressing a part and closing the cross-sectional shape to the final shape, Since the entire shape of the press-formed product is formed toward the final part shape, it is possible to simplify the press work in the final process.

  In other words, the present invention is a technique for improving the formability by forming a plurality of processes when pressing a complicated part shape. From the shape obtained in the process of developing the final part shape, Accordingly, it is possible to efficiently set the shape of the press-formed product in the previous process in which cracking is unlikely to occur.

  In addition, the present invention uses a simple press process in which a part of the shape of the press-formed product in the previous process is closed because there is no substantial change in the cross-sectional line length between the shape of the press-formed product in the previous process and the shape of the final part. Thus, it is possible to perform press molding that brings the shape of the press-formed product in the previous process closer to the final part shape without fear of cracking.

(A), (b), and (c) are a blank shape before press molding in an embodiment of the press molding method of the present invention and an embodiment of a method of manufacturing a press molded part of the present invention using the same. It is the perspective view seen from the back side slanting side of the part which shows a process press molded product shape and a final part shape, respectively with a rough line. (A) And (b) is the side view which shows the final part shape press-molded with the press molding method of the said embodiment, and the perspective view seen from the front side diagonal side of the component. (A) And (b) is a side view which shows the final part shape, and sectional drawing which shows the cross-sectional shape of the linear part, (c) And (d) is the expansion | deployment in the middle of expand | deploying the said final part shape It is sectional drawing which shows the cross-sectional shape of the side view which shows the press-formed product shape of the pre-process set from the halfway shape, and the linear part. It is a disassembled perspective view which shows the structure of the drawing die which draw-forms the press-molded product shape of the previous process set from the said halfway shape from a rectangular blank by planar view. It is the perspective view seen from the back side slant side of a part which shows the part with a large board thickness reduction rate especially the case where it shape | molds from a blank in 1 process, and a small part. It is a disassembled perspective view which shows the structure of the press-molding die of the preliminary | backup process which forms the linear part of the press-molded product of the said front process into the last part shape. (A) is a side view showing the shape of the press-molded product in the previous process, the shape of the press-molded product in the preliminary process, and the final part shape, and (b), (c) and (d) are (a) It is sectional drawing which each follows the AA line in FIG.), A BB line, and CC line.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, FIG. 1 (a), FIG. 1 (b) and FIG. 1 (c) show one embodiment of the press molding method of the present invention and one embodiment of the manufacturing method of the press molded part of the present invention using the same. It is the perspective view seen from the back side slanting side of the part which shows the blank shape before press molding in, the pre-process press-formed product shape, and the last part shape in a rough line, respectively.

  In the press molding method of this embodiment and the press molded part manufacturing method of this embodiment using the same, for example, a hat-shaped cross section as a complex-shaped part that has been conventionally prone to cracking in a high-tensile steel plate as a high-strength material. In order to improve the yield by reducing the frequency of occurrence of cracks in the drawing of shaped automotive frame parts, as shown in FIGS. 1 (a)-(c) The press-formed product 2 of the previous process is drawn from the rectangular flat blank 1 and the final part 3 is press-formed from the press-formed product 2 of the previous process.

  2 (a) and 2 (b) are final part shapes that are press-molded by the press-molding method and press-molded part manufacturing method of the above embodiment (indicated by the same reference numerals as the final part for easy understanding). FIG. 3 is a side view showing a part 3 and a perspective view of the component as viewed from an oblique front side. The final part shape 3 includes a linear portion 3a, a curved portion 3b that is connected to the linear portion 3a and curved toward the opening side, and a rising portion 3c that is connected to the curved portion 3b and rises with respect to the linear portion 3a. And a flange portion 3d located on both sides of the opening, and has a hat-shaped cross-sectional shape over the entire length, and an angle formed between the linear portion 3a and the rising portion 3c is, for example, approximately It is 140 °.

  3 (a) and 3 (b) are a side view showing the final part shape 3 and a cross-sectional view showing the cross-sectional shape of the linear part thereof, and FIG. 3 (c) and FIG. FIG. 3 is a side view showing a pre-processed press-formed part shape set from a development intermediate shape in the middle of developing a part shape 3, and a cross-sectional view showing a cross-sectional shape of a linear portion thereof. When the final part shape 3 to be shown is press-molded, in the press molding method of this embodiment, the flange part 3d of the final part shape 3 is obtained while being developed in the part outer direction (left and right direction in FIG. 3B). In consideration of the shape of the blank and the like from the shape in the middle of the development, a pre-processed press-formed product shape 2 shown in FIGS. 3C and 3D is set.

  The shape of the press-formed product in the previous process (indicated by the same reference numerals as the press-formed product in the previous process for easy understanding) 2 is also connected to the linear portion 2a and the linear portion 2a and curved to the opening side. It has a bent hat 2b, a raised portion 2c that is connected to the bent portion 2b and rises with respect to the linear portion 2a, and flange portions 2d that are positioned on both sides of the opening. The angle formed by the straight portion 2a and the rising portion 2c is, for example, approximately 130 °. In the final part shape 3, the angle formed between the bottom and the side wall is, for example, approximately 90 °, whereas in the press-formed product shape 2 in the previous process, the angle formed between the bottom and the side wall is, for example, approximately 130 °. .

  FIG. 4 is an exploded perspective view showing the structure of a drawing mold for drawing a press-formed product shape of a previous process set from the shape in the middle of development from a rectangular blank in plan view. In this drawing mold, a rectangular blank 1 in a plan view is held between a die 4 and a blank holder 5 while being bent, and is pressed against a punch 6 by a die 4 as indicated by an arrow P1, and extends substantially over the entire length. A shallow groove shape with a hat-shaped cross section is formed, and the center portion is drawn into a press-formed product shape 2 of the previous process in which the center portion is curved in the opening direction of the groove.

  FIG. 5 is a back view of a part showing a part having a large thickness reduction rate and a part having a small thickness reduction rate of the final part shape 3 when formed from a blank in one step, obtained by FEM (Finite Element Method) analysis for press forming. FIG. 5 is a perspective view seen from the side oblique side, for example, when the final part shape 3 is drawn with a drawing die from a 2.0 mm thick plate made of a high-tensile steel plate of 590 MPa class, and the wrinkles of the blank holder 5 When the pressing force was set to 75 tons and the friction coefficient was set to 0.15, the thickness reduction rate of the region TR1 on the bottom back surface of the curved portion 3b The maximum was approximately 20%, and cracks occurred in this region TR1. Further, the thickness of the boundary region TR2 between the side wall portions and the flange portion of the curved portion 3b is increased, and the increase rate is approximately 17%, and wrinkles are generated in this region TR2. On the other hand, for the case of drawing the press-formed product shape 2 of the previous process from the plate material having a thickness of 2.0 mm made of a high-tensile steel plate of, for example, 590 MPa class with the above drawing mold, When FEM analysis was performed in advance with 75 tons and a friction coefficient set to 0.15, and the degree of reduction in thickness of each part was examined, the rate of reduction in thickness in the region TR1 on the bottom rear surface of the curved portion 2b was maximized. Although it was about 17%, it was a grade which does not lead to a crack.

  The blank mesh size was 2 mm. The element used was a shell element. The FEM analysis was performed by static implicit method using LS-DYNA ver971, which is also a commercially available CAE program.

  FIG. 6 is an exploded perspective view showing the structure of a pre-process press mold that forms the linear portion 2a of the press-formed product 2 of the previous process into a final shape without using a blank holder. This pre-process press mold includes a die portion as indicated by an arrow P2 in a state where the linear portion 2a of the press-molded product 2 of the pre-process is placed on the punch 8 with the opening facing downward and positioned by a positioning member (not shown). 7 is lowered and the linear part 2a is sandwiched between the punches 8 to form a foam, and the cross-sectional shape of the linear part 2a is closed to form the linear part 3a of the final part shape 3. In addition, the press-molding die for the preliminary process is not limited to the foam-molding die, and a draw-molding die that holds the wrinkles with a blank holder may be used.

  According to the press molding of this preliminary process, since the material of both side walls of the curved portion 2b of the press-molded product 2 of the previous process moves inward in the radial direction of the curved portion, the circumferential length is left, As shown by the arrow L in FIG. 6, the bending angle of the curved portion 2 b decreases, and the entire press-formed product shape 2 in the previous process is formed toward the final part shape 3, and is close to the final part shape 3. Since the shape of the press-formed product in the preliminary process described later (indicated by the same reference numeral as that of the press-molded product in the preliminary process for ease of understanding) is 3 ', the press process in the final process can be simplified. As for the preliminary press forming, FEM analysis was conducted in advance to examine the plate thickness reduction rate of each part. As a result, the maximum plate thickness reduction rate was found at the portion where the linear portion 2a and the curved portion 2b were connected. However, the reduction rate was only about 2.5%, and there was no concern about the occurrence of cracks.

  FIG. 7A shows a pre-processed press molded product shape 2 (indicated by a solid line), a preliminary process press molded product shape 3 ′ (indicated by a one-dot chain line), and a final part shape 3 (indicated by a two-dot chain line). 7 (b), FIG. 7 (c) and FIG. 7 (d) are the AA, BB and CC lines in FIG. 7 (a). It is sectional drawing which each follows a line. As shown in FIG. 7, the pre-processed press-molded product shape 2 becomes a pre-processed press-molded product shape 3 ′ in the preliminary-process foam molding. As shown in d), the linear part where the CC line is located coincides with the final part shape 3, and as shown in FIG. 7C, the curved part where the BB line is located is almost the final part shape. Matches 3.

  Then, as shown in FIGS. 7A and 7B, only the rising portion where the line AA is located is quite close to the final part shape 3, but the opening of the side wall part and the flange part is still the final part shape 3. Although this is larger than this, the shape deviation of this degree can be sufficiently corrected by the restric process. In addition, since this modification hardly changes the line length of the material, there is no fear of new cracks.

  Therefore, according to the press molding method and the method of manufacturing a press molded part of this embodiment, a high-strength steel sheet as a high-strength material, for example, for a car having a hat-shaped cross-section as a complex-shaped part that has been easily cracked in the past. When drawing a frame part in multiple steps, the pre-press shape 2 is set from the shape obtained in the process of developing the final part shape 3. The product shape 2 can be set efficiently, and the yield in actual press molding can be improved.

  Moreover, according to the press molding method and the press molded part manufacturing method of this embodiment, there is no substantial change in the cross-sectional line length between the press molded product shape 2 and the final part shape 3 in the previous process. By using a simple press process that closes the linear portion that is a part of the press-formed product shape 2, press forming that brings the press-formed product shape 2 from the previous process closer to the final part shape 3 without fear of cracking is performed. Can do.

  Thus, according to the press molding method and the press molded part manufacturing method of the present invention, the shape of the press molded product of the previous process is set from the development intermediate shape obtained during the development of the final part shape of the press molded part having the drawn shape. Since the pre-processed press-molded product is press-molded into the set pre-processed press-molded product shape, it is possible to efficiently set the pre-processed press-molded product shape that is less prone to cracking and has high strength. Even when a metal plate material is used, the yield at the time of press forming can be improved.

1 Blank 2 Press-formed product of the previous process (Press-formed product shape of the previous process)
2a Linear part 2b Curved part 2c Raising part 2d Flange part 3 Final part (final part shape)
3a Linear part 3b Curved part 3c Raising part 3d Flange part 3 'Preliminary press-molded product (preliminary press-molded product shape)
4 Die 5 Blank holder 6 Punch 7 Die 8 Punch

Claims (3)

Set the shape of the press-molded product of the previous process from the shape in the middle of development obtained during the development of the final part shape of the press-formed part having the drawing shape,
Press-molding the pre-processed press-molded product into the set pre-processed press-molded product shape ,
Next, a part of the press-formed product of the previous process is press-formed into the final part shape,
Thereafter, the remaining part is press-molded into the final part shape .   The press-formed product shape of the previous process is set from the development intermediate shape obtained while opening the flange portion of the final part shape of the press-formed part having a hat-shaped cross-sectional shape as the drawing shape, The press molding method according to claim 1. 3. The press molding method according to claim 1 or 2 , wherein the pre-processed press-molded product is press-molded into the set pre-processed press-molded product shape, and the pre-processed press-molded product is pressed into the final part shape. A method for producing a press-molded part, comprising molding.

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