JP2003290844A - Hydroforming method superior in formability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a machining method capable of producing a formed article that needs machining harder than conventional in hydroforming. <P>SOLUTION: The hydroforming method in which an axial thrust and hydraulic pressure are imparted to a metallic tube is characterized by the way of using the metallic tube. In the formula defined in (1),εratio=εaxis/ε circumfrence...(1), where ε axis = axial thrust [mm]/length of tube expansion part in axial direction [mm], and where ε circumference=(circumference of maximum tube expansion part in die [mm] - circumference of tube stock [mm])/circumference of tube stock [mm]; when the ε ratio is in the deformation region of 0.3 or below, a metallic tube is used in which γ value in the tube axial direction is larger than γ value in the tube circumferential direction; and when the ε ratio is in the deformation region of 0.3 or above, a metallic tube is used in which γvalue in the tube circumferential direction is larger than γ value in the tube axial direction. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of mounting a metal pipe such as a steel pipe, an aluminum pipe, or a titanium pipe in a mold and applying an internal pressure to the pipe at the same time in the axial direction of the pipe. The present invention relates to a hydroform molding method for processing into a predetermined shape while pushing. 2. Description of the Related Art In automobile parts and the like, products in which metal pipes such as steel pipes are manufactured by hydroforming are beginning to be used. Here, the hydroform molding means that the metal tube 1 is put into the dies 4 and 5 and the liquid 9 is introduced into the metal tube 1 through the liquid introduction hole 8 and the internal pressure is increased as shown in the example of the expansion mold shown in FIG. This is a method of forming a predetermined shape while applying a compressive load in the tube axis direction with the pushing cylinders 6 and 7 from both sides and pushing. The obtained molded article 3 is lightweight and can be molded into a complicated shape. As shown in FIG. 2, the metal tube 1 is manufactured by forming a metal plate 2 into a tubular shape and welding a butt portion, and a seamless tube is also used. [0003] Generally, a soft material,
It is known that a material having a high n value and a material having a high r value exhibit high workability. In hydroforming, it is known that the anisotropy of the r value of the pipe affects the workability. As a technique using this in-plane anisotropy, Japanese Patent Application Laid-Open No. H10-175027 discloses a metal pipe which obtains high workability by increasing the r value in the tube axis direction than the r value in the tube circumferential direction. [0004] In the prior art, in order to obtain high workability, a metal pipe having an r value in the pipe axis direction higher than the r value in the pipe circumferential direction is used. However, the influence of in-plane anisotropy originally changes depending on whether or not axial pressing can be sufficiently performed when hydroform molding is performed. For this reason, a metal pipe in which the r value in the pipe axis direction is higher than the r value in the pipe circumferential direction does not always show high formability by hydroforming. An object of the present invention is to provide a hydroform processing method that enables more severe processing than before. [0005] In order to achieve the above object, the gist of the present invention is to provide a hydroforming method for applying axial pressing and liquid pressure to a metal pipe by the following formula (1). When the defined ε-ratio is a deformation region of 0.3 or less, use a metal pipe whose r-value in the tube axis direction is larger than the r-value in the tube circumferential direction, and when the ε-ratio is a deformation region of 0.3 or more. And a hydroforming method excellent in formability, characterized by using a metal pipe having an r value in the pipe circumferential direction larger than the r value in the pipe axis direction. ε ratio = ε axis / ε circumference ... (1) where ε axis = axial pushing amount [mm] / axial length of expanded part [mm] ε circumference = (maximum expanded part of mold) Perimeter [mm] −perimeter of base tube [mm]) / perimeter of base tube [mm] In the present invention, the axial length of the expanded portion refers to the length of the base tube set in a mold at the start of molding. Defined as the length of the central axis of the raw tube at the point where the mold and the entire circumference are not in contact at the time when it was performed, and the perimeter of the maximum expanded part of the mold is the normal direction of the mold's pipe axis direction. Is defined as the maximum perimeter of the section to be formed. Hereinafter, the present invention will be described in detail.
As shown in FIG. 1, the diameter r1 of the expanded portion is 140 mm, and the axial length L1 of the expanded portion is 100 mm. The metal pipe and the metal pipe whose r value in the pipe axis direction is larger than the r value in the pipe circumferential direction are set so that the axial pushing amount is 1 mm to 60 mm so that the ε ratio takes various values between 0 and 0.5. Hydroform molding was performed with various changes. Here, the shaping is performed by pressing the shaft by 1 mm and then pressing the shaft by a predetermined amount at a constant holding pressure.
Thereafter, the pressure was increased to 1000 bar in a machining path, and the pipe expansion rate at the time when the raw pipe burst was measured. In addition, since the optimal processing conditions differ for each material characteristic, the test was performed on 11 different paths in which the holding pressure at the time of pressing the shaft was changed in the range of 170 bar to 370 bar in increments of 20 bar. The value was taken as the maximum expansion ratio. From this test result, when the ε ratio is in the deformed region of 0.3 or more, use a metal pipe having an r value in the circumferential direction of the tube larger than the r value in the tube axis direction. It has been found that the maximum pipe expansion ratio is increased by using a metal pipe whose r value is larger than the r value in the pipe circumferential direction. A cold-rolled steel sheet is manufactured by cold-rolling a hot-rolled sheet and then annealing. Usually, the r-value in the direction perpendicular to the rolling direction (C direction) is smaller than the r value in the rolling direction (L direction). Is high. Therefore, when such a cold-rolled steel sheet is formed into a tubular shape as shown in FIG. 2, the sheet is taken out so that the rolling direction (L direction) is the pipe circumferential direction (the direction of rθ). A metal pipe having an r value larger than the r value in the tube axis direction can be manufactured. In addition, a metal pipe whose r value in the tube axis direction is larger than r value in the tube circumferential direction can be manufactured by taking a plate so that the rolling direction (L direction) is in the tube axis direction (rφ direction). . A steel plate having a thickness of 2.3 mm (STCE specified in JIS G3141) is formed into a tube as shown in FIG. 2 and welded to produce a steel pipe having an outer diameter of 63.5 mm and a length of 430 mm. The metal tube 1 is cut out and has a diameter D of an expanded portion as shown in FIG.
A molding test was carried out using a simple expansion mold having a length of 140 mm and a length L1 of 100 mm in the axial direction of the expanded portion. Steel sheet, using what r values in the rolling direction r value (L direction) (r _L) is perpendicular to and rolling direction is 1.2 (C direction) (r _c) is 2.2 , L direction is the tube axis direction,
A steel pipe A having a large circumferential r value (rθ) and a steel pipe B having a large axial r value (rφ) were manufactured with the C direction as the pipe axis direction. Molding is performed by pressing the shaft by 1 mm, then pressing the shaft by a predetermined amount at a constant holding pressure, and then 1000 bar.
The pipe expansion rate was measured at the time when the pipe bursted. Since the optimum processing conditions are different for each material characteristic, eleven paths were tested for each of the A and B steel pipes in which the holding pressure at the time of axial pressing was changed from 170 bar to 370 bar in steps of 20 bar. The value at the time when the pipe was expanded the most was defined as the maximum expansion rate. In addition, the axial pushing amount is 60 mm when the ε ratio is 0.3 or more and 0.3 mm.
The following two levels of 20 mm were performed. When the axial pushing amount is 60 mm, the ε ratio is as follows. ε ratio = ε axis / ε circumference = (axial pushing amount / axial length of expanded part) / ｛(perimeter of maximum expanded part of mold [mm]-peripheral length of base tube [mm]) / base tube Perimeter of｝ = (60/100) / {(π · 140−π · 63.5) / (π · 63.5)} = 0.50 Similarly, when the axial pushing amount is 20 mm, the ε ratio Is as follows. ε ratio = (20/100) / {(π · 140−π · 63.5) / (π · 63.5)} = 0.17 As shown in Table 1, the ε ratio is 0.3
In the above-described forming with a shaft pushing amount of 60 mm, the steel pipe A in which the r value (rθ) in the pipe circumferential direction is larger than the r value (rφ) in the pipe axis direction.
In the case of the above, the maximum pipe expansion ratio was large, and excellent workability was obtained. In the case of forming with a shaft pushing amount of 20 mm where the ε ratio is 0.3 or less, the steel pipe B having a larger r value (rφ) in the pipe axis direction than the r value (rθ) in the pipe circumferential direction has a larger maximum expansion ratio and is excellent. Workability was obtained. [Table 1] According to the working method of the present invention, a metal pipe having an in-plane anisotropy of an optimum r value is used in hydroforming according to the balance between the axial pushing amount and the expansion ratio. It is possible to manufacture molded products that require more severe processing than before.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing an example of a hydroforming method according to the present invention. FIG. 2 is a perspective view showing a production example of a metal tube used in the present invention. [Explanation of Signs] 1 Metal tube 2 Metal plate 3 Molded product 4,5 Die 6,7 Cylinder 8 Liquid introduction hole 9 Liquid

Claims (1)

Claims 1. In a hydroforming method for applying axial pressure and hydraulic pressure to a metal tube, when the ε ratio defined by the following equation (1) is a deformation region of 0.3 or less, the tube is A metal pipe having an r value in the axial direction larger than the r value in the circumferential direction is used, and the ε ratio is 0.3.
In the above deformation region, the r value in the pipe circumferential direction is r in the pipe axis direction.
A hydroforming method excellent in formability, characterized by using a metal tube having a larger value. ε ratio = ε axis / ε circumference ... (1) where ε axis = axial pushing amount [mm] / axial length of expanded part [mm] ε circumference = (maximum expanded part of mold) Perimeter [mm]-tube circumference [mm]) / tube circumference [mm]