JP2005095909A - Press forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a press forming method by which cracks, wrinkles and failure in shape freezing property are simply avoided without correcting a die and changing materials. <P>SOLUTION: In the press forming method by which a die for press forming on which a plurality of distance blocks 5 are mounted is used, one or more of the distance blocks are replaced with variable height blocks 6 and the height of the variable height block is changed by fluid pressure during press forming. A hydraulic liner is preferably used for the variable height block. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to thin steel plate press forming used in the manufacture of automobiles, home appliances, etc., and avoids cracks, wrinkles and shape freezing defects, which are typical actual press forming defects, at low cost without mold correction. The present invention relates to a press molding method.

In the field of manufacturing automobile parts and home appliances, thin steel plates are press-formed, and various press defects appear in actual press forming. . In order to avoid this crack without upgrading the material, measures are usually taken to increase the bending radius and optimize the shape by correcting the mold, but there is a concern that correcting the mold will require a large amount of man-hours and costs. . Therefore, conventionally, methods for avoiding cracks without correcting the mold have been studied. As such a method, for example, a method of applying ultrasonic vibration as described in Non-Patent Document 1 or Non-Patent Document 2 or a method of vibrating a blank holder as described in Patent Document 1 is known. It has been.
JP 7-47432 A Plasticity and processing vol.23, No.256, (1982), 458 Plasticity and processing vol.35, No.403, (1994), 977

  However, any of the above conventional methods has a problem that the entire blank holder is integrally displaced, requiring large-scale equipment, and once the mold is completed, it is not easy to mount. In addition, in the above conventional method, there are cases where cracking can be solved only by improving the lubricating oil performance, but it may not be possible to solve the problem of the site where cracks and wrinkles coexist, and the shape freezing property is improved. Had the problem of not contributing.

  In view of the above-described problems of the prior art, the present invention provides press molding that can easily avoid defects in cracking, wrinkles, and shape freezing among molding defects of difficult-to-mold parts without mold correction or material change. It aims to provide a method.

  The present inventors have intensively studied to achieve the above object, and as a result, by changing the wrinkle holding force at a specific position of the mold according to the molding stroke and the number of moldings, molding conditions in which wrinkles and cracks do not occur. The scope of the present invention has been found to be expanded, and further studies have been made based on this finding to make the present invention.

  That is, the present invention provides a press molding method using a press molding die equipped with a plurality of distance blocks, wherein one or two or more of the distance blocks can be changed in height at any timing by fluid pressure. A press molding method characterized in that the height variable block is replaced with a variable height block, and the height of the height variable block is changed during press molding. In the present invention, a hydraulic liner can be preferably used for the height variable block whose height can be changed by the fluid pressure.

  According to the present invention, one or more of the distance blocks are replaced with a height variable block whose height can be changed at any timing by fluid pressure (hydraulic pressure, pneumatic pressure, etc.), and the height of the height variable block is changed. By changing the thickness by pressurizing during press molding, cracks, wrinkles, and shape freezing defects can be easily avoided without modifying the mold or changing materials. It is possible to easily and inexpensively avoid molding defects of difficult-to-mold parts that are likely to occur when manufacturing by actual press molding, and it is also possible to reduce the grade of the material.

The inventors of the present invention have examined the preferred implementation conditions of the present invention for improving the drawability by using an actual molding tester. As a result, the crack / wrinkle coexisting site (the site where both cracks and wrinkles are likely to occur) It was confirmed that the drawability was greatly improved by increasing the height of one or more blocks in the latter half of the press molding from those close to. Here, the latter term refers to the remaining steps after digesting 20 to 90% of all the steps from the start to the end of press molding.
That is, in the present invention, in order to improve the drawability, for example, as shown in FIG. 1, the distance block 5 in the vicinity of the crack / wrinkle coexistence site (the crack merged site 8 and the merged site with the wrinkle risk site 7). At least one (or two or more) may be replaced with a variable height block 6, and the height of the variable height block 6 is preferably set in a pattern as shown in FIG. It is preferable to increase in the latter stage of press molding. In FIG. 1 (the same applies to FIG. 3 described later), 1 is a punch, 2 is a die 3 is a blank holder that restrains the peripheral edge of the molding material M, and these constitute a press molding die. . The distance block 5 or the variable height block 6 is mounted between the die 2 and the blank holder 3.

  Furthermore, the present inventors examined suitable implementation conditions of the present invention for improving the shape freezing property. The shape freezing property can be evaluated by the difficulty of warping at the vertical wall, which is a problem especially during press forming of high-strength steel sheets, and this warpage is reproduced by a press forming test with a hat-shaped cross-sectional shape as the forming shape. it can. By proceeding with the above examination by such a press molding test, as a result, by reducing the height of one or more blocks from those close to the warpage occurrence site (site where warpage is likely to occur) in the later stage of press molding, It was confirmed that the amount of warpage could be greatly reduced. Here, the term “late stage” refers to the remaining process in which 60 to 95% of the entire process from the start to the end of press molding is digested.

  That is, in the present invention, in order to improve the shape freezing property, for example, as shown in FIG. 3, at least one (two or more) of the distance blocks 5 in the vicinity of the warp occurrence site (warp amount measurement site 9) may be used. Is replaced with a variable height block 6, and the height of the variable height block 6 is preferably decreased later in the press molding, preferably in a pattern as shown in FIG. .

  Note that the height variable block configured to control the height by hydraulic pressure as illustrated in FIGS. 1 and 3 is referred to as a hydraulic liner. In the present invention, it is preferable to use a hydraulic liner as the variable height block in terms of control response.

A cold-rolled steel sheet having the sheet thickness and mechanical properties shown in Table 1 (yield point YP, tensile strength TS, elongation El, n value, r value) was used as a test material, and formed by a molding production test of difficult-to-form parts. Excess amount (Press forming condition value range (formable region) that does not cause cracking and wrinkling) was examined. Here, YP, TS, El were obtained by JIS No. 5 tensile test, and n value was flow at 10% and 20% deformation. The r value was obtained from the plate width at the time of 15% deformation, the lubricant was rust-preventive oil, and both sides were applied at 1.5 g / m ^2. The outline of the test is shown in FIG. 2 shows the results in Table 2. As is apparent from the results shown in Table 2, when the block height is changed according to the present invention as compared with the case where the block height is constant, cracks and wrinkles are observed. The moldable area with no cracking has been greatly expanded, and improvement in moldability has been recognized.

A cold-rolled steel sheet having the sheet thickness and mechanical properties (yield point YP, tensile strength TS, elongation El, n value, r value) shown in Table 3 was used as a test material, and a hat-shaped cross-section shaped product was manufactured and tested. Then, the amount of warp of the vertical wall was examined. Here, YP, TS, and El are obtained by a JIS No. 5 tensile test, the n value is obtained from the flow stress at the time of 5% and 10% deformation, and the r value is obtained from the plate width at the time of 10% deformation. The lubricant was rust-preventing oil, and 1.5 g / m ^{2 on} both sides was applied. The outline of the test is shown in FIG. 3, the molding conditions are shown in FIG. 4, and the results are shown in FIG. As is clear from the results shown in FIG. 5, when the block height is changed according to the present invention, the warpage amount (evaluated by the warpage curvature) is remarkably reduced as compared with the case where the block height is constant. As a result, improvement in formability was recognized.

  INDUSTRIAL APPLICABILITY The present invention can be used in any industry that includes a thin steel plate press forming process as at least a part of a part manufacturing process.

It is a schematic diagram (a: side view, b: plan view) showing an outline of the test in Example 1. It is a change pattern figure of the block height which shows the molding conditions of the example of an invention in Example 1. FIG. It is a schematic diagram (a: side view, b: plan view) showing the outline of the test in Example 2. It is a change pattern figure of the block height which shows the molding conditions of the invention example in Example 2. FIG. 10 is a graph showing the effect of reducing the amount of warping according to the invention example in Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Punch 2 Die 3 Blank holder 4 Hydraulic source 5 Distance block 6 Height variable block 7 Wrinkle danger part 8 Crack danger part 9 Warp amount measurement part M Molding material

Claims (2)

  In a press molding method using a press molding die equipped with a plurality of distance blocks, one or more of the distance blocks are replaced with a height variable block whose height can be changed by fluid pressure. A press molding method, wherein the height of the variable block is changed during press molding.   2. The press forming method according to claim 1, wherein the height variable block whose height can be changed by the fluid pressure is a hydraulic liner.

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