JP4757820B2 - Multi-stage press forming method with excellent shape freezing - Google Patents

Description

  In the present invention, for example, in a specific in-plane direction as shown in FIG. 1 (in FIG. 1 (a), if the plane including the flange surfaces 11 and 12 on both sides is the X plane, an arbitrary plane in the X plane can be obtained. Direction, in FIG. 1 (b), if the plane including the ridge lines 15 and 16 on both sides is the X plane, it will be an arbitrary direction in the X plane) Reduces dimensional accuracy defects such as torsion A and B that usually occur after mold release and camber (longitudinal deviation from the normal (designed) product shape) in press-formed products of metal parts having a cross section. The present invention relates to a press molding method for obtaining a product having a precise shape.

  When a metal part having a hat-shaped cross section having a shape curved in a specific in-plane direction is manufactured by press molding, a tensile stress 1 (plus) in the longitudinal direction on the inner flange surface 11 of the curved portion shown in FIG. Force), and a compressive stress 2 (force represented by minus) in the longitudinal direction is generated on the outer flange surface 12 of the curved portion. In this way, internal stresses having different signs are generated inside and outside the curve, which gives a twist moment to the channel cross-section and causes twist A. Further, in the molding of a U-shaped section curved in a specific in-plane direction shown in FIG. 1B, a tensile stress 3 (force represented by plus) in the longitudinal direction is generated on the vertical wall surface 13 inside the curved portion. Then, a compressive stress 4 (force represented by minus) in the longitudinal direction is generated on the vertical wall surface 14 outside the curved portion. In this case as well, a twisting moment is generated in the channel cross section, causing twist B. It is known that the direction and amount of twisting varies depending on the degree of stress generated and the remaining amount of flange.

In the conventional technique, the amount of spring back is estimated, and the mold shape is corrected in advance, or as described in Non-Patent Document 1, non-uniform residual stress is added by adding a plate excess absorbing bead to the shrinkage deformed portion. For example, a method of obtaining a molded product having a desired shape by reducing the above is used. However, in the former, a material with a large spring back such as a high-strength steel plate or an aluminum alloy plate inevitably has a large expected amount, and as a result, a desired product shape cannot be obtained, or what is required by trial and error until it is obtained. There are also problems in terms of cost and construction period because it may be necessary to modify the mold once. In the latter case, man-hours and costs for adjusting the depth of the beads to be added to the shape are required, and the bead shape remains as a product shape. In particular, a component that receives a load at the time of a collision has a problem that the bead is a starting point for buckling the component, which may reduce the collision safety of the vehicle itself and cannot be applied for general purposes.
Press Form Difficulty Handbook 2nd edition, 222 pages (Nikkan Kogyo Shimbun)

  In view of the above-mentioned problems, the present invention is a regular shape that is curved in a specific in-plane direction with a U-shaped or hat-shaped cross section with high accuracy without adjusting the mold shape and in a predetermined part shape. It is possible to obtain a metal member (a press-formed product) having a (designed shape).

In order to solve the problem, the gist of the present invention is as follows.
(1) A method of forming a metal member having a U-shaped or hat-shaped cross section and having a curved shape in a longitudinal plane, and among a plurality of curved portions formed on the metal member For at least one bend,
In the first molding step, an intermediate product having a smaller radius of curvature than the product shape is molded, and in the second molding step, a radius of curvature larger than the curvature radius in the first molding step is formed. A multi-stage press molding method excellent in shape freezing property, wherein the molding step and the second molding step are molded without changing the radius of curvature of the mold, and the entire molded product is made into a product shape or a substantially product shape.
(2) When the line length of the ridge line in the longitudinal direction of the shape change portion in the product shape and the intermediate product shape is L [mm], L ′ [mm]
1 <L '/ L <1.1
The multi-stage press molding method having excellent shape freezing property according to (1), wherein the intermediate product is molded so as to satisfy the following conditions.
(3) The shape freezing property according to (1) or (2), wherein the first molding step is draw molding or foam molding, and the second molding step is a wrist-like process for molding into a product shape. Multi-stage press molding method with excellent resistance.
(4) The first molding step and the second molding step are draw molding or foam molding, and include a wrist-like process for molding into a product shape after the second molding step (1) or ( 2) The multistage press molding method which is excellent in the shape freezing property of description.

  In the present invention, the substantially product shape is 1 when the line length of the ridge line in the longitudinal direction of the shape change portion in the product shape and the shape of the molded product after the second molding step is L [mm] and Ls [mm]. It means satisfying the condition of <Ls / L <1.2. Of the plurality of curved portions formed on the metal member, at least one curved portion refers to a part or all of one or both of the curved inner side and outer side of the metallic member.

  According to the present invention, a regular shape curved in a specific in-plane direction (in terms of design) with a U-shaped or hat-shaped cross section with high accuracy without adjusting the mold shape and with a predetermined part shape. ) Metal member (press-molded product).

  Examples of the present invention will be described below.

  In a metal part having a U-shaped or hat-shaped cross section curved in a specific in-plane direction, the flange surfaces 11 and 12 (see FIG. 1A) and the vertical wall surfaces 13 and 14 (see FIG. 1A) 1 (b)), longitudinal stresses having different signs are generated, and the stresses are released to generate springback due to twists A and B as shown in FIGS. 1 (a) and 1 (b). In order to suppress the spring back in the final product as much as possible, the tensile stress and the compressive stress in the longitudinal direction at the corresponding part (the curved part of the flange surfaces 11 and 12 or the curved part of the vertical wall surfaces 13 and 14) at the end of the final molding. However, it is sufficient that the shape rigidity is sufficiently small. The reason why the tensile stress is increased in the longitudinal direction on the inner flange surface 11 and the longitudinal wall surface 13 is that the material is stretched in the longitudinal direction as the material flows in, and the outer flange on the curve. The reason why the compressive stress is increased in the longitudinal direction on the surface 12 and the longitudinal wall surface 14 is that the material is contracted in a flange-shaped manner in which the material is contracted in the longitudinal direction as the material flows.

  As a result of research on a molding method that sufficiently reduces the tensile stress or compressive stress in the longitudinal direction, the curvature radius of the intermediate product is determined to be the final product in the first molding process for at least one of the plurality of curved portions. In the second molding step, it is molded as a radius of curvature larger than the curvature radius of the intermediate product obtained in the first molding step, and the remaining portion is formed in the first molding step. This is achieved by forming the entire molded product into the shape of the final product (product shape) or a shape closer to the final product (substantially product shape). (Invention according to (1) above).

  In the first molding process, if the curvature radius of the curved part of the molded product is molded in a shape smaller than that of the final product, the material inside the curve will be Is compressed in the longitudinal direction along with the inflow, the tensile stress generated in the first molding step and the compressive stress generated in the second molding step cancel each other, and the longitudinal stress approaches zero. Similarly, on the outer side of the curve, the material is pulled in the longitudinal direction along with the inflow in the second molding process, the compressive stress generated in the first molding process and the tensile stress generated in the second molding process cancel each other, and the stress in the longitudinal direction is zero. Get closer to. Thereby, it can suppress that a springback etc. generate | occur | produce by the stress which generate | occur | produced in the product, and can improve the precision of a product shape.

  Further, the radius of curvature of the curved portion in the intermediate product shape may be made smaller than the radius of curvature of the curved portion in the product shape. On the other hand, when the radius of curvature of the curved portion of the intermediate product is too small, FIG. As described above, the amount of change (L′−L) in the length of the ridge line in the longitudinal direction of the shape changing portion 5 of the curved portion becomes too large, causing wrinkles during the second molding step or leaving marks on the molded product. End up. Therefore, even when the radius of curvature of the curved portion in the intermediate product shape is reduced, the line lengths of the product shape and the ridge line in the longitudinal direction of the shape changing portion 5 in the intermediate product shape are L [mm] and L ′ [mm]. Then, it is desirable to set within the range of 1 <L ′ / L <1.1, more preferably within the range of 1 <L ′ / L <1.05 (the invention according to (2) above).

  As the process of forming the intermediate product, if the first forming process is draw (draw-bending) forming or foam forming, and the second forming process is a wrist-like process for forming into a product shape, the first forming process is performed. (Invention according to (3) above).

  In addition, when the first molding process is a first-stage draw molding or foam molding and the second molding process is a second-stage draw molding or foam molding to form a product shape or a substantially product shape, the first molding process The intermediate molding process may be used, and when there is a wrist-like process that molds the product after the second molding process, the second molding process is molded into a substantially product shape as the intermediate molding process. (Invention according to (4) above). The molding step here refers to a step of forming into a product-shaped outer shape, and refers to a step that does not include a step for punching or cutting, such as punching (piercing) and outer cutting (trim). That is, a process such as punching may be appropriately performed according to the product shape.

  In the case of molding an intermediate product, the molding height does not have to be molded up to the height of the product shape, but it is preferable that an intermediate product having a height of half or more of the product shape is molded.

  If the ridge line between the intermediate product shape and the curved part of the product shape is large, the intermediate product may not easily fit into the mold in the second molding process, or the shape may be displaced. It is desirable to use a positioning device such as a jig.

  When the curvature radius of the curved inner portion is reduced as the intermediate product shape and the ridge line shift becomes large, it becomes difficult to fit into the lower die (punch) 10 in the second molding step as shown by the dotted line in FIG. Therefore, it is desirable to use a second-stage drawing process in which the intermediate product 8 is gripped by the wrinkle presser (holder) 9 and the upper die (die) 7 and then molded. Also, when the curvature radius of the curved outer portion is reduced as an intermediate product shape and the ridge line shift amount increases, the lower mold (punch) 10 is formed in the second molding step as shown by the dotted line in FIG. Since it fits, the re-striking process of forming with the upper die (die) 7 without using the wrinkle presser (holder) is sufficient. However, it is desirable to use a pin or a guide for positioning the intermediate product.

  FIG. 4 shows the product shape studied in the present invention. The steel plate uses a 980 MPa grade steel plate having a thickness of 1.2 mm, the height of the hat-shaped cross section (distance between the surface of the ceiling portion 17 and the surfaces of the flanges 11 and 12) H is 40 mm, and the width W1 of the ceiling portion 17 is A member having 60 mm, a length L1 of 500 mm, a width W2 of each flange 11 and 12 of 20 mm, a curvature radius of 300 mm of the curved inner portion 21 and a curvature radius of 360 mm of the curved outer portion 22 was formed. As a comparative example, in one-step molding using a mold having a shape corresponding to the product shape, 40 ton of wrinkle holding load is applied as a molding condition, and draw molding is performed, and a cross section at both ends of the obtained molded product is measured with a shape measuring machine. did. When the angle (deviation amount) of the ceiling portion 17 when the cross sections at both ends of the molded product are overlapped is evaluated as a twist angle, the shape after the first molding step (the shape of the product obtained in the comparative example) is 2.5. A twist of ° occurred.

  FIG. 5 is a diagram for explaining the change of the radius of curvature of the intermediate product and the product shape implemented in the present invention. Here, FIG. 5 is a view of the product (or intermediate product) shown in FIG. 4 as viewed from above, and the flanges 11 and 12 are omitted.

  Fig.5 (a) is an example which changed the curvature radius about all the curved outer sides 22 by the 1st shaping | molding process. That is, as shown by the dotted line in FIG. 5A, the first molding step is performed so that the curvature radius of the curved outer portion 22 in the intermediate product is smaller than the curvature radius of the curved outer portion 22 in the product. . Specifically, in the first molding step, the curved outer portion 22 was draw-molded with a radius of curvature of 60, 160, 260 mm, and in the second molding step, the curved outer portion 22 was foam-molded with a radius of curvature of 360 mm. The remaining portion (the portion excluding the curved outer portion 22) is not changed in the radius of curvature of the mold in the first molding step and the second molding step, that is, the curvature radius of the curved inner portion 21 is set to 300 mm. 22 and the straight portions located on both sides of the curved inner portion 21 have an infinite radius of curvature (straight line), and the rest-like process is performed in which the entire molded product is made into the final product shape in the second molding process.

  FIG. 5B is an example in which the radius of curvature is changed for all of the curved inner side 21 in the first molding step. That is, as shown by the dotted line in FIG. 5B, the first molding step is performed such that the curvature radius of the curved inner portion 21 in the intermediate product is smaller than the curvature radius of the curved inner portion 21 in the product. . Specifically, in the first molding step, the radius of curvature of the curved inner portion 21 was set to 50, 100, and 200 mm, and in the second molding step, the radius of curvature of the curved inner portion 21 was set to 300 mm. Further, the remaining portion (the portion excluding the curved inner portion 21) is not changed in the radius of curvature of the mold in the first molding step and the second molding step, that is, the curvature radius of the curved outer portion 22 is set to 360 mm. The straight portions located on both sides of 21 and the curved outer portion 22 have an infinite radius of curvature (straight line), and the rest-like process is performed in which the entire molded product is the final product shape in the second molding process.

  FIG. 5C is an example in which the curvature radius is changed for all of the curved inner portion 21 and the curved outer portion 22 in the first molding step. That is, as shown by the dotted line in FIG. 5C, the curvature radii of the curved inner portion 21 and the curved outer portion 22 in the intermediate product are smaller than the curvature radii of the curved inner portion 21 and the curved outer portion 22 in the product. In addition, the first molding step is performed. Specifically, in the first molding step, the curvature radius of the curved inner portion 21 is 50, 100, 200 mm, and the curvature radius of the curved outer portion 22 is 60, 160, 260 mm. Draw molding was performed with a curvature radius of 300 mm and a curvature radius of the curved outer portion 22 of 60, 160, 260 mm. Further, the remaining portions (portions other than the curved inner portion 21 and the curved outer portion 22) are not changed in the radius of curvature of the mold in the first molding step and the second molding step, that is, the curved inner portion 21 and the curved outer portion 22. The straight part located on both sides of the product was formed into a substantially product shape with the curvature radius being infinite (straight line). After that, as a final molding step (third molding step), a foam shape was formed with a curvature radius of the curved inner portion 21 of 300 mm and a curvature radius of the curved outer portion 22 of 360 mm, and a re-striking step was performed to obtain a product shape.

  Table 1 shows the experimental conditions and the shape measurement results. The twist angle is the angle (deviation amount) of the ceiling portion 17 when the cross sections at both ends of the product obtained in the molding process described above are overlapped, and the twist angle of 0.5 ° or less is ◎, 0.5 to 1.0. The case where the angle was greater than 1.0 ° and the case where the angle was greater than 1.0 ° was evaluated as x. As for the surface properties of the final product, a case where the width of the scratch that causes wrinkles was 5 mm or more was evaluated as △, a case where the width of the scratch was as small as less than 5 mm, or a thing that could not be visually confirmed was evaluated as ◯. .

  FIG. 6 shows the product shape studied in the present invention. In this product, the height of the hat-shaped cross section increases from one end side to the other end side, and the width of the ceiling portion 17 increases from one end side to the other end side. Further, the widths of the flanges 11 and 12 change from the both end sides toward the intermediate portion. Furthermore, this product has two curved inner portions 21 and two curved outer portions 22.

  The steel plate is a 980 MPa grade steel plate having a thickness of 1.2 mm. The maximum height Hmax of the hat-shaped cross section is 40 mm, the maximum width W3 of the ceiling portion 17 is 80 mm, the length L2 is 525 mm, and the flanges 11 and 12 are the maximum. A member having a large W4 of 30 mm, a curvature radius of 300 mm of the curved inner portion 21 and a curvature radius of 360 mm of the curved outer portion 22 was formed. As a comparative example, in one-stage draw molding using a mold having a shape corresponding to the product shape, molding is performed by applying a wrinkle holding load of 40 ton as a molding condition, and the cross section at both ends of the obtained molded product is copied with a shape measuring machine. It was measured. When the angle of the ceiling portion 17 when the cross sections at both ends of the molded product (final product) are overlapped is evaluated as the twist angle, the shape after the first molding step (the shape of the product obtained in the comparative example) is 1.5. A twist of ° occurred.

  FIG. 7 is a diagram for explaining changes in the radius of curvature of the intermediate product shape and the product shape implemented in the present invention. Here, FIG. 7 is a view when the product (or intermediate product) shown in FIG. 6 is viewed from above, and the flanges 11 and 12 are omitted.

  In Fig.7 (a), the curvature radius was changed about the whole curved inner part 21 (2 places) at the 1st shaping | molding process. That is, as shown by a dotted line in FIG. 7A, the first molding step is performed so that the curvature radius of the curved inner portion 21 in the intermediate product is smaller than the curvature radius of the curved inner portion 21 in the product. . Specifically, the radius of curvature of the curved inner portion 21 was set to 50, 100, and 200 mm in the first molding step, and the curvature radius of the curved inner portion 21 was set to 300 mm in the second molding step. Further, the remaining portion (the portion excluding the curved inner portion 21) is not changed in the radius of curvature of the mold in the first molding step and the second molding step, that is, the curvature radius of the curved outer portion is set to 360 mm, and other straight portions The radius of curvature was infinite (straight line), and the entire molded product was made the final product shape in the second molding step.

  FIG.7 (b) changed the curvature radius about all the curved outer side parts 22 (2 places) at the 1st shaping | molding process. That is, as shown by a dotted line in FIG. 7B, the first molding step is performed so that the curvature radius of the curved outer portion 22 in the intermediate product is smaller than the curvature radius of the curved outer portion 22 in the product. . Specifically, in the first molding step, draw molding was performed with the curvature radius of the curved outer portion 22 being 60, 160, 260 mm, and in the second molding step, foam molding was performed with the curvature radius of the curved outer portion 22 being 360 mm. The remaining portion (the portion excluding the curved outer portion 22) is not changed in the radius of curvature of the mold in the first molding step and the second molding step, that is, the curvature radius of the curved inner portion 21 is 300 mm, and other straight lines The part was subjected to a re-strike process in which the radius of curvature was infinite (straight line) and the entire molded product was made into the final product shape in the second molding process.

  FIG.7 (c) changed the curvature radius about all the curved inner side parts 21 and the curved outer side parts 22 (4 places) at the 1st shaping | molding process. That is, as shown by a dotted line in FIG. 7C, the curvature radii of the curved inner portion 21 and the curved outer portion 22 in the intermediate product are made smaller than the curvature radii of the curved inner portion 21 and the curved outer portion 22 in the product. In addition, the first molding step is performed. Specifically, in the first molding step, the radius of curvature of the curved inner portion 21 is 50, 100, 200 mm, and the radius of curvature of the curved outer portion 22 is 60, 160, 260 mm. The radius of curvature of 300 mm was set to 300 mm, and the radius of curvature of the curved outer portion 22 was set to 60, 160, and 260 mm. Further, the remaining portion (the portion excluding the curved outer portion 22 and the curved inner portion 21) does not change the radius of curvature of the mold in the first molding step and the second molding step, that is, the other straight portions have an infinite curvature radius. As a large (straight line), the entire molded product was molded into a substantially product shape. After that, as a final molding step (third molding step), a re-striking step was performed in which the radius of curvature of the curved inner portion 21 was 300 mm and the radius of curvature of the curved outer portion 22 was 360 mm to obtain a product shape.

  Table 2 shows the experimental conditions and the shape measurement results. Each twist is the angle of the ceiling of the cross section at both ends of the product obtained in the molding process described above, the twist angle is 0.5 ° or less, ◎, 0.5-1.5 ° is ○, 1.5 ° The case where it was large was also marked with x. As for the surface texture of the final product, a case where the width of the scratches causing wrinkles was 5 mm or more was evaluated as Δ, a case where the scratches were as small as less than 5 mm, or a case where the scratches could not be visually confirmed was evaluated as ◯.

  As described above, according to the present invention, the dimensional accuracy is improved as compared with the comparative example, and a hat-shaped cross-sectional component having excellent dimensional accuracy can be obtained. In addition, No. 1 of Example 1 was used. 2, 5 and 8, No. 2 in Example 2. 2, 5 and 8 are outside the scope of the present invention according to (2), but satisfy the requirements of the present invention according to (1), so that the twist in the longitudinal direction is significantly larger than that of the comparative example. It was possible to reduce it. It is sufficiently applicable to parts whose surface properties are not so important.

  In the first and second embodiments described above, a product having a hat-shaped cross section is molded. However, the same effect can be obtained when a product having a U-shaped cross section is molded.

The external view of the metal member which has a shape curved in the longitudinal direction with a hat-shaped or U-shaped cross section is shown. The top view of the intermediate product shape and product shape in this invention is shown. Sectional drawing of the 2nd shaping | molding process in this invention is shown. The product shape of Example 1 to which this invention is applied is shown. The intermediate product shape of Example 1 to which this invention is applied, and the top view of a product shape are shown. The product shape of Example 2 to which this invention is applied is shown. The intermediate product shape of Example 2 to which this invention is applied, and the top view of a product shape are shown.

Explanation of symbols

1 Tensile stress acting on the flange surface of the stretch flange 2 Compressive stress acting on the flange surface of the contraction flange 3 Tensile stress acting on the longitudinal wall surface of the stretch flange 4 Compressive stress acting on the longitudinal wall surface of the contraction flange 5 Change in shape of intermediate product and product shape Part 6 Edge line 7 of the shape change part of the intermediate product shape Upper die (die)
8 Molded product 9 Wrinkle presser (holder)
10 Lower mold (punch)
DESCRIPTION OF SYMBOLS 11 Flange surface 12 Flange surface 13 Vertical wall surface 14 Vertical wall surface 15 Edge line part 16 Edge line part 21 Curved inner side (curved inner side)
22 Curved outside (curved outside)
A Twist B Twist

Claims (4)

A method of forming a metal member having a U-shaped or hat-shaped cross section and a curved shape in a longitudinal plane,
Of the plurality of curved portions formed on the metal member, at least one curved portion,
In the first molding process, an intermediate product having a smaller radius of curvature than the product shape is molded,
In the second molding step, molding as a curvature radius larger than the curvature radius in the first molding step,
The remaining portion is molded without changing the radius of curvature of the mold in the first molding step and the second molding step, so that the entire molded product has a product shape or a substantially product shape. Multi-stage press molding method with excellent resistance. When the line length of the ridge line in the longitudinal direction of the shape change portion in the product shape and the intermediate product shape is L [mm] and L ′ [mm], respectively.
1 <L '/ L <1.1
The multistage press molding method with excellent shape freezing property according to claim 1, wherein the intermediate product is molded so as to satisfy the following conditions.   3. The multistage press molding excellent in shape freezing property according to claim 1 or 2, wherein the first molding step is draw molding or foam molding, and the second molding step is a wrist-like process for molding into a product shape. Method.   The said 1st shaping | molding process and said 2nd shaping | molding process are draw shaping | molding or foam shaping | molding, and have a re-like process which shape | molds in a product shape after said 2nd shaping | molding process. Multi-stage press molding method with excellent shape freezing properties.

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