JP2007222906A - Multistage press-forming method excellent in shape freezing property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an accurate normal shape as it is a prescribed shape of parts without adjusting the shape of a die. <P>SOLUTION: This method is for forming a metallic member which has a U-shaped or a hat-shaped cross section and a shape curved in the height direction. In this multistage press-forming method, in a first forming stage, an embossment such as the condition of 1<L'/L<1.1 are formed on the web face when the line length in the longitudinal direction of a product is expressed by L [m] and the line length in the longitudinal direction of an intermediate article is expressed by L' [m] and, in the second stage, the intermediate article is formed into the product shape as performing so that the embossment disappears. It is preferable that the embossment is a plurality of convex-shaped projections which are intermittent in the longitudinal direction or projections which are continuous in the longitudinal direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention, for example, in a press-formed product of a metal member having a hat section curved in the height direction as shown in FIG. 1, reduces the displacement in the molding height direction that usually occurs after mold release, and has a precise shape. The present invention relates to a press molding method for obtaining the product.

  When a metal part having a hat-shaped cross section having a shape curved in the height direction is manufactured by press molding, the tensile stress in the longitudinal direction is released on the web surface 1 shown in FIG. 1, and as a result, the spring in the height direction is released. A back is produced and the dimensional accuracy deteriorates.

In the prior art, the mold shape is corrected in advance in anticipation of the amount of springback, or intermittent embossing is installed inside the web surface as disclosed in Patent Document 1, and this is bent. At the same time, a method of obtaining a predetermined shape by pressing to a predetermined dimension is employed. However, it is difficult to predict the amount of springback in the former, and there is a problem that cost and man-hours are required for shape correction because of a trial and error method. In the latter case, it is necessary to press the rib according to the amount of spring back, which requires man-hours and costs for adjusting the amount of pressing, and ribs or rib marks remain even after intermittent embossing pressing. Since it remained as a product shape, there was a problem that use on parts was limited. In addition, when the part shape is complicated, wrinkles may occur and there is a problem that it cannot be applied for general purposes.
JP 59-220215 A

  In view of the above-described problems, the present invention has a regular shape that is curved in the height direction with a U-shaped or hat-shaped cross section with high accuracy without adjusting the mold shape and with a predetermined part shape. It is possible to obtain a metal member.

  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 shape curved in the height direction, wherein an intermediate product in which embossing is provided on a web surface in a first forming step A multi-stage press molding method excellent in shape freezing property, characterized in that, in the second molding step, the product is molded into a product shape while pressing so as to eliminate the emboss.

  (2) In the first molding step, when the line length in the longitudinal direction of the product is L [m] and the line length in the longitudinal direction of the intermediate product is L ′ [m], 1 <L ′ / L <1.1 The multi-stage press molding method having excellent shape freezing property as described in (1) above, wherein an intermediate product is molded so as to satisfy the above conditions.

  (3) The multistage press molding method having excellent shape freezing property according to the above (1) or (2), wherein the emboss comprises a plurality of convex protrusions intermittent in the longitudinal direction of the intermediate product.

  (4) The multistage press molding method having excellent shape freezing property according to the above (1) or (2), wherein the embossment comprises convex protrusions continuous in the longitudinal direction of the intermediate product.

  According to the present invention, a metal member having a regular shape that is curved in the height direction with a U-shaped or hat-shaped cross section with high accuracy without adjusting the mold shape and with a predetermined part shape. Can be obtained.

  Examples of the present invention will be described below.

  In metal parts having a cross-section such as a hat shape curved in the height direction (Z direction in the figure), tensile stress acts in the longitudinal direction of the web surface (X direction in the figure) when molding with a mold, After release, this stress is released, and as shown in FIG. 2, the shape 4 in the longitudinal direction indicated by the dotted line (dotted line in FIG. 1) is compared to the regular product shape 3 (the portion corresponding to the dotted line 2 in FIG. 1). 2 is generated. In order to eliminate the spring back in the final product, it is sufficient that the tensile stress at the portion (web surface) at the end of the final molding is sufficiently small with respect to the shape rigidity of the metal part. In order to make the tensile stress of the web surface sufficiently small, in the first molding step, the line length in the longitudinal direction of the portion where the tensile stress acts is previously molded longer than the final product. In other words, the intermediate product is molded such that the line length in the longitudinal direction of the molded product (intermediate product) molded by the first molding process is longer than the line length in the longitudinal direction of the final product. And in the next process, it is achieved by forming into the shape of the final product. Specifically, it is effective to form an intermediate product provided with an emboss that is not in the product shape in the first molding step, and press the emboss in the second molding step. Since it can be molded while applying compressive stress by molding into a product shape while pressing so that embossing is eliminated in the second molding process, the tensile stress of the web surface generated in the first molding process is sufficiently small It becomes possible to do.

  Molded metal parts (final products) are usually used while being joined to other parts, as represented by automobile parts, and have a product shape based on the performance of the final product. There are many cases. For this reason, if the product shape changes, it may become difficult to assemble the final product due to interference with other parts, or the performance as a product may be deteriorated. The embossed shape is not left (the invention according to (1) above).

  Further, the embossing may be set so that the longitudinal line length is longer than the longitudinal line length of the product shape. On the other hand, when the line length is too long, the embossing in the second molding step is performed. After the pressing process, the emboss is not completely stretched and wrinkles, and the product shape changes. For this reason, the ratio of the line length L [m] in the longitudinal direction of the product to the line length L ′ [m] in the longitudinal direction of the intermediate product is preferably within the range of 1 <L ′ / L <1.1. It is desirable to set within the range of 1 <L ′ / L <1.05, more preferably 1 <L ′ / L <1.02 (the invention according to (2) above).

  Further, as the embossed shape, a plurality of embosses 7 may be provided intermittently as shown in FIG. 5 (the invention according to (3) above), but as shown in FIG. It is desirable to provide a convex emboss 5 (invention according to (4) above).

  When intermittently forming a plurality of embosses, the height of the embosses (the length in the Z direction in the figure) is preferably 10 mm or less from the viewpoint of ensuring flatness after the embossing is pressed. Further, the distance between adjacent embosses is 5 mm or more from the viewpoint of ensuring the flatness described above, and 50 mm or less from the viewpoint of uniformly relieving the tensile stress of the curved portion (web surface) generated during normal molding. preferable. Furthermore, when the line length in the longitudinal direction of the final product is L (m) and the line length in the longitudinal direction of the intermediate product having a plurality of embosses is L ′ (m), as in the invention according to (2), It is desirable to set within the range of 1 <L ′ / L <1.1, preferably 1 <L ′ / L <1.05, more preferably 1 <L ′ / L <1.02.

  Even if the embossed shape is concave, the same effect can be expected, but when L ′ and L are the same, the height of the embossed needs to be set high. And considering the influence on other dimensional accuracy, convex embossing with less shape change is preferable.

  In the invention according to the above (4), when continuous embossing is provided, the line length in the longitudinal direction of the embossing is 80 with respect to the line length of the bending portion of the product from the viewpoint of uniformly relaxing the tensile stress of the bending portion. % Or more is preferable. It goes without saying that the effects of the present invention can be obtained even if embossing is provided on the entire curved portion of the intermediate product (for example, 100% with respect to the line length of the curved portion of the product). Also, the line length in the width direction of the emboss is 70% or more with respect to the line length in the width direction (Y direction in the figure) of the web surface of the product from the viewpoint of uniformly relieving the tensile stress of the curved portion as described above. It is preferable to do. In order to suppress deterioration in dimensional accuracy due to material inflow from the web surface to the product vertical wall (a side wall located in the XZ plane and corresponding to the side wall 10c in FIG. 1) during embossing, The line length in the width direction of the intermediate product at each position in the direction is preferably 110% or less with respect to the line length in the width direction of the product shape.

  FIG. 1 shows the product shape studied in the present invention. The steel plate uses a 980 MPa class steel plate with a thickness of 1.6 mm, the hat-shaped cross section height (length in the Z direction of the product 10) 40 mm, the width of the ceiling portion 10a (length in the Y direction) 30 mm, the product A steel member (product) having a line length of 400 mm in the longitudinal direction (X direction) 10, a width of 20 mm of the flange 10 b, and a radius of curvature in the longitudinal direction (curvature radius of dotted line 2 shown in FIG. 1) of 1000 mm was formed. In the normal one-step molding as a comparative example, a tensile stress in the longitudinal direction is generated on the web surface 1, and this becomes a cause of occurrence of longitudinal warpage. Moreover, the cross-sectional shape of the product in the position shown by the dotted line part 2 in FIG. 1 and the cross-sectional shape of the product obtained after molding by the one-step molding method as a comparative example are shown in FIG. Compared to the regular product shape 3, the product shape 4 obtained by the molding method of the comparative example had a longitudinal warpage of 2.9 mm at both ends in the longitudinal direction (see No. 1 in Table 1).

  3 shows an intermediate product shape obtained after the first molding step according to the present invention, and a solid line portion 6 in FIG. 4 shows a cross-sectional shape in the longitudinal direction at the center in the width direction of the member (intermediate product) shown in FIG. It is. Reference numeral 5 denotes a convex emboss which is provided on the web surface and continues in the longitudinal direction. Both ends of the emboss are located 40 mm from both ends of the intermediate product, the total length of the emboss is 320 mm (80% of the length in the longitudinal direction of the intermediate product), and the width of the emboss is 26 mm (product width) The length was set to 87% with respect to 30 mm. Here, in the first molding step, a mold for molding the above-described intermediate product is used. This embossing is pressed so that the embossing is eliminated in the next second molding step (specifically, the height of the embossing is 0.2 mm or less), and is generated on the web surface in the first molding step. This eliminates or relaxes the tensile stress. Here, in the second molding step, a mold having a shape corresponding to the product shape is used. In the present invention, the molding process is performed step by step using the mold for the first molding process and the mold for the second molding process.

  In the experiment, the line length L ′ [m] in the longitudinal direction on the web surface after the first forming step (intermediate product) is changed with respect to the line length L [m] in the longitudinal direction of the web surface in the product shape. The shape was compared (see Table 1). The evaluation of the product was performed using the amount of longitudinal warpage and the generation of wrinkles on the web surface as evaluation items. Table 1 shows the experimental conditions and experimental results of Example 1 (see Nos. 2 to 5). The amount of longitudinal warpage is the amount of displacement in the press direction (Z direction in the figure) relative to the product shape (difference between the position of the specified product shape and the position of the product shape that is the subject of the experiment). A value larger than 0.2 mm and 0.5 mm or less was evaluated as ◯, and other values (larger than 0.5 m) were evaluated as x. In the evaluation of wrinkles, the height after emboss pressing was 0.2 mm or more, x, greater than 0, and less than 0.2 mm, ○, and those that could not be visually confirmed (height ≈ 0) were evaluated as ◎.

  As Example 2, the following experiment was performed with the same steel type and test piece size as in Example 1. FIG. 5 shows the shape of an intermediate product obtained after the first molding step according to Example 2, and the solid line portion 8 in FIG. 6 shows the longitudinal sectional shape at the center in the width direction of the member shown in FIG. Reference numeral 7 denotes a plurality of convex embosses intermittently formed in the longitudinal direction formed on the web surface. A plurality of embosses were intermittently arranged in a region between the positions of 40 mm from both ends of the intermediate product. The emboss width was fixed at 30 mm. As in Example 1, this embossing was pressed so that the embossing disappeared in the subsequent second molding step (specifically, the height of the embossing was 0.2 mm or less). In the experiment, the line shape L ′ [m] in the longitudinal direction on the web surface after the first forming step is changed with respect to the line length L [m] in the longitudinal direction of the web surface in the product shape, and the part shape is compared. went. Evaluation was carried out based on the same criteria as in Example 1 in terms of longitudinal warpage and wrinkles.

  The experimental conditions and results in Example 2 are shown in Table 1 (Nos. 6 to 9).

  By this invention, the dimensional accuracy improved from the comparative example, and the hat-shaped molded part excellent in dimensional accuracy was able to be obtained.

  Experiment No. 5 and 7 are out of the scope of the present invention according to (2), so the evaluation of wrinkles is “x”, but satisfies the requirements of the present invention according to (1). The warpage in the longitudinal direction could be reduced to 1/10 or less (<0.2 / 2.9) compared to the comparative example (No. 1).

The external view of the metal member which has a hat-shaped cross section and the shape curved in the height direction is shown. The cross-sectional shape of a regular product and the cross-sectional shape of a metal member obtained after forming by a conventional method are shown. The external view of the embossing after the 1st shaping | molding in this invention (the convex-shaped protrusion continuous in the longitudinal direction) is shown. The cross-sectional shape of the embossing after the first molding in the present invention (convex protrusions continuous in the longitudinal direction) is shown. The external view of the embossing after the 1st shaping | molding in this invention (the some convex-shaped protrusion interrupted in the longitudinal direction) is shown. The cross-sectional shape of the embossing (convex protrusion interrupted in the longitudinal direction) after the first molding in the present invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Web surface 2 Center position in the width direction on the web surface of a metal member 3 Longitudinal sectional shape 4 of a regular product Longitudinal sectional shape 5 after spring back of a metallic member in a conventional product Convex-shaped projections continuous in the longitudinal direction (Emboss)
6 Cross-sectional shape of intermediate product in which convex protrusions (embossing) continuous in the longitudinal direction are arranged 7 Plural protrusions (embossing) intermittent in the longitudinal direction
8 Cross-sectional shape of an intermediate product in which a plurality of protrusions (embosses) interrupted in the longitudinal direction are arranged 10 Product 10a Ceiling 10b Flange 10c Side wall

Claims (4)

A method of forming a metal member having a U-shaped or hat-shaped cross section and having a shape curved in the height direction,
In the first molding process, an intermediate product with embossing on the web surface is molded,
A multi-stage press molding method having excellent shape freezing property, wherein in the second molding step, the product is molded into a product shape while pressing so as to eliminate the emboss. In the first molding step, when the longitudinal length of the product is L [m], and the longitudinal length of the intermediate product is L ′ [m],
1 <L '/ L <1.1
The multistage press molding method having excellent shape freezing property according to claim 1, wherein the intermediate product is molded so as to satisfy the following conditions.   The multi-stage press molding method with excellent shape freezing property according to claim 1 or 2, wherein the emboss includes a plurality of convex protrusions intermittent in the longitudinal direction of the intermediate product. The multi-stage press molding method with excellent shape freezing property according to claim 1, wherein the emboss is formed of a convex protrusion continuous in the longitudinal direction of the intermediate product.

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