JP2001355765A - Hydroform metal pipe and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal pipe with an excellent hydroforming property and a manufacturing method thereof. SOLUTION: A metal pipe of which a pipe ordinary temperature aging index (RIAIp) shown by formula (1) is not more than 40 MPa is used as a hydroform metal pipe and a metal band of which a plate ordinary temperature aging index (RIAI) is not more than 40 MPa is prepared to manufacture a metal pipe. Pipe ordinary temperature aging index (RIAIp; MPa)=Ypaged (30 deg.C#×yield strength after aging-processing at ordinary temperature for one month; MPa)-YP(yield strength of original pipe; MPa) (1) plate ordinary temperature aging index (RIAI; MPa)=Fsaged (10% previous distortion+30 deg.C×floating stress after aging-processing at ordinary temperature for one month)-FS(floating stress at the time of 10% previous distortion) (2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to underbody parts, such as suspension arms, which are hydroformed into a predetermined automobile part shape by applying internal pressure to a pipe in a mold;
The present invention relates to a metal tube used for a closed-section automobile structural component such as a chassis component, a body component, and a frame structural component.

[0002]

2. Description of the Related Art A technique for processing a metal pipe into a closed cross-section automobile part shape by hydroforming requires less welding margin than a technique for processing a metal sheet pressed product, so that a lightweight and highly rigid part can be obtained. There are features. As a technique for processing a metal tube into an automobile part shape by hydroforming, for example, Japanese Patent Publication No. 5-55209 discloses a technique for forming a frame member having a box-shaped cross section.

[0003]

However, the technology of processing a metal pipe into a closed cross-section automobile part shape by hydroforming is limited in the cross-sectional circumferential length of the pipe by the peripheral length of the pipe and the deformability of the pipe. Therefore, it cannot be applied to a part having a part whose circumferential length is largely different in the longitudinal direction, and a design in which the circumferential length exceeds 5% of the raw pipe is also performed by the method disclosed in Japanese Patent Publication No. 5-55209. In such a case, there was a problem that defects such as cracks occurred.

[0004] The present invention has been made in view of the material of the hydroform material in order to solve the above-mentioned problems at the time of overhang in the circumferential direction, and provides a steel pipe excellent in hydroformability and a method of manufacturing the same. The purpose is to do.

[0005]

Means for Solving the Problems The present inventors examined the effects of the mechanical properties of a metal tube and a metal band as a material thereof on hydroform workability by examining the metal components having different chemical compositions and manufacturing conditions. A metal tube was manufactured using a metal strip as a material, and a study was conducted. The thickness of the metal strip is 0.8-6mm
Then, a metal tube having an outer diameter of 22 to 254 mm is manufactured using the metal band as a material, a tensile test piece is collected from the metal band and the metal tube, and the room temperature aging index of the metal tube is expressed by the formula (1). The aging index was determined by equation (2).

[0006] The normal temperature aging index (RTAIp; MPa) of a metal tube = YPaged (Yield strength of pipe after normal temperature aging treatment at 30 ° C x 1 month; MPa)-YP (yield strength of raw pipe; MPa) 1) Sheet metal room temperature aging index (RTAI; MPa) = FSaged (10% prestrain + 30 ° C. × flow stress after normal temperature aging treatment for 1 month) -FS (flow stress at 10% prestrain) -(2) Next, the hydroform workability of the metal pipe was evaluated by a bulge test. FIG. 1 schematically shows an apparatus used for a hydraulic bulge test. The test apparatus comprises a mold moving mechanism, an axial compression force loading mechanism, a hydraulic pressure generating mechanism and a computer 9 for controlling them. In the case of a free bulge test, the internal pressure is applied to the raw tube 1 by a hydraulic pump 8, a pressure amplifier 7, a pressure gauge. The load is applied via the shaft compressors 3a and 3b by the hydraulic pressure generating mechanism 6.

In the case of the mold bulge test, the molds 2a, 2b
After the raw tube 1 is inserted into the tube, an internal pressure is applied to form the tube. Shaft compressor 3
The displacement amounts of a and 3b are taken into a computer 9 by a displacement meter 4a and 4b, the displacement amount of a molding die 2a by a displacement meter 5, and the internal pressure is taken into a computer 9 by a pressure gauge 6 and used for control.

The details of the hydraulic bulge test are described in the preprints 98153, "Hide-Following Deformation Characteristics of ERW Steel Pipes for Automobiles", 1998-5 p1.
49, Proceedings of the 1999 Spring Lecture on Plastic Working p237
It is described in "Examination of trial production of deformed section material by preforming continuous molding".

As a result, it has been found that when the room-temperature aging index of a metal band or a metal tube is within a certain range, the hydroformability of the metal tube is excellent, and the present invention is based on these findings. It was done. That is, the present invention provides: Ambient temperature aging index (RTAIp) of metal tube is 40MP
(a) a metal tube for hydroforming, characterized in that: However, tube normal temperature aging index (RTAIp; MPa) = Y
1. Paged (Yield strength of pipe after aging treatment at room temperature of 30 ° C. × 1 month; MPa) −YP (Yield strength of raw pipe; MPa) A method for producing a metal tube for hydroforming, characterized by producing a metal band having a plate room temperature aging index (RTAI) of 40 MPa or less. However, the sheet room temperature aging index (RTA
I; MPa) = FSaged (10% pre-strain + 30 ° C. × flow stress after aging treatment at room temperature for one month) −FS (flow stress at 10% pre-strain)

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a metal tube having a room temperature aging index (RTAIp) of 40 MPa or less is used as a metal tube for hydroforming. Room temperature aging index (R
When TAIp) is set to 40 MPa or less, an excellent rate of increase in breaking limit circumferential length can be obtained in a hydraulic free bulge test and a mold bulge test.

FIG. 2 and FIG. 3 show the relationship between the tube room temperature aging index (RTAIp) of a metal tube and the rate of increase of the breaking limit circumference in a hydraulic free bulge test. The hydraulic free bulge test shows the hydroformability in a deformed state where the raw tube is not in contact with the mold. The deformation part length 2D (D: pipe outer diameter), axial compression Evaluation was made under two conditions of no (FIG. 2) and with (FIG. 3). Here, the axial compression force was set to be such that the stress ratio of the tubular body (axial stress / circumferential stress) = 0. Ambient temperature aging index (RTAIp) of metal tube is 40MP
In the case of a or less, an excellent peripheral length increase rate of 22% or more under the condition without axial compression and 40% or more under the condition with axial compression can be obtained.

FIG. 4 and FIG. 5 show the relationship between the tube room temperature aging index (RTAIp) of a metal tube and the rate of increase of the critical limit circumferential length in a hydraulic bulge test. The mold bulge test shows the hydroformability when the mold is constrained. A mold bulge test is performed inside a mold having a rectangular cross-sectional shape with an aspect ratio of 2: 1. No axial compression (FIG. 4) and presence (FIG. 5) ) Were evaluated based on the rate of increase in the limit of circumferential length under the two conditions. Here, the axial compression force is set to the maximum value that does not cause buckling. Metal room temperature aging index (RTAI)
When p) is 40 MPa or less, 1
An excellent peripheral length increase rate of 0% or more and 14% or more under axial compression is obtained.

Furthermore, in the present invention, the room temperature aging index (RTA)
I) Pipes a metal strip having a pressure of 40 MPa or less to produce a metal pipe for hydroforming. When the plate room temperature aging index (RTAI) of the metal strip is set to 40 MPa or less, an excellent rate of increase in the breaking limit perimeter of the manufactured metal pipe is obtained in the hydraulic free bulge test and the mold bulge test.

FIGS. 6 and 7 show the relationship between the plate room temperature aging index (RTAI) of the metal strip used for manufacturing the metal pipe and the rate of increase of the critical limit circumferential length in the hydraulic free bulge test. FIG. 6 shows a case without an axial compression force, and FIG. 7 shows a case with an axial compression force.

When the RTAI of the metal band is 40 MPa or less, 20% or more without axial compression, and 3 with axial compression force.
An excellent circumference increase rate of 6% or more is obtained.

FIGS. 8 and 9 show the relationship between the plate room temperature aging index (RTAI) of the metal strip used in the manufacture of the metal pipe and the rate of increase of the critical limit circumferential length in the hydraulic bulge test. FIG. 8 shows the case without the axial compression force, and FIG. 9 shows the case with the axial compression force.

When the metal strip has an RTAI of 40 MPa or less, an excellent peripheral length increase rate of 8% or more without axial compression and 12% or more with axial compression can be obtained.

The metal tube for hydroforming according to the present invention and the metal tube for hydroforming manufactured according to the present invention may be hydroformed after being preformed by bending, pressing, hydroforming, swaging, etc. A lubricating oil may be applied to the tube surface or a lubricating film may be formed to obtain the amount. As a seam joining method for forming a pipe from a steel strip, electric resistance welding, laser welding, TIG welding, forging, and the like can be used. The material of the metal tube is not particularly limited, such as a steel tube, a surface-treated steel tube, a stainless steel tube, an aluminum tube, and a magnesium tube.

[0019]

Next, the steel pipe of the present invention will be specifically described. C: 0.05 to 0.15% by mass, Mn: 0.4 to mass
Hot rolled steel strip obtained by hot rolling and pickling a steel slab containing 1.3% at a finishing temperature of 840 ° C, or 750 ° C after cold rolling at a cold pressure rate of 75% after hot rolling pickling. The cold-rolled steel strip and the hot-dip galvanized steel strip annealed in the above were roll-formed into a tube and then welded to obtain a welded steel pipe under the condition of a width reduction ratio of 4%. The width reduction ratio is determined by the following equation. Width drawing = {[slit width｝-π ([outer diameter]-[plate thickness])} / π
([Outer diameter] − [plate thickness]) × (100%) The strength, TS, pipe normal temperature aging index and RTAIp of the steel pipe thus obtained are evaluated according to JIS No. 11 and JIS No. 12, and their hydroformability is evaluated. Was evaluated by a hydraulic free bulge test and a mold bulge test.

The results are shown in Table 1. The tube of the present invention having a room temperature aging index RTAIp of 40 MPa or less.
The metal tubes for hydroforming of Nos. 1 to 6 have a circumferential increase rate of 22% or more in the hydraulic free bulge II test without axial compression,
44% or more with axial compression, Perimeter increase rate in mold bulge II test is 10% or more without axial compression, 14% with axial compression
As described above, high hydroformability was obtained.

On the other hand, when the RTAIp exceeds 40 MPa, N
o. The metal pipes for hydroforming 7 to 12 have a circumference increase rate of less than 22% without axial compression in a hydraulic free bulge test, less than 44% with axial compression, and a circumferential increase rate of no axial compression in a mold bulge test. Less than 10%, 14 with axial compression
%, Hydroforming properties required for overhanging in the circumferential direction could not be obtained.

[0022]

[Table 1]

Table 2 shows examples of the conditions of the original plate and the hydroformability. The room temperature aging index according to the present invention, RTAI is 40
No. MPa or less. The metal tube for hydroforming using a steel strip of 13 to 18 as a base plate has a circumferential increase rate of 20% or more without axial compression in a hydraulic free bulge test, 36% or more with axial compression, and a circumferential length in a mold bulge test. High hydroforming properties with an increase rate of 8% or more without axial compression and 12% or more with axial compression are obtained.

On the other hand, when the RTAIp exceeds 40 MPa, N
o. The metal tube for hydroforming using a steel strip of 19 to 24 as a base plate has a circumferential length increase rate of less than 20% without axial compression in a hydraulic free bulge test, less than 36% with axial compression, and a circumferential increase rate in a mold bulge II test. When the rate of increase in length is less than 8% without axial compression and less than 12% with axial compression, hydroforming properties required for overhanging in the circumferential direction cannot be obtained.

The evaluation of the room-temperature aging index of pipes and plates is based on the Hundy equation (Hundy, B. et al.) From the viewpoint of quick evaluation.
B. J .; Iron & SteelInst. , 178
(1954) p. It is also possible to evaluate under the conditions for promoting the equivalent aging time as described in 34-38).

The embodiments described above are for explaining the present invention, and do not limit the present invention in any way.

[0027]

[Table 2]

[0028]

As described above, according to the present invention, undercarriage parts such as suspension arms, chassis parts, and body parts are hydroformed into a predetermined automobile part shape by applying internal pressure to a pipe in a mold. Also, in a closed-section automobile structural part such as a frame structural part, cracking or partial decrease in wall thickness when extending in the circumferential direction is avoided, and a molded product requiring more severe processing than before can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus used for a hydraulic bulge test.

FIG. 2: RTAIp (Metal tube normal temperature aging index; MP
The figure which shows the relationship between a) and the breaking limit circumference increase rate in a hydraulic free bulge test (no axial compression force).

FIG. 3 RTAIp (tube room temperature aging index of metal tube; MP
The figure which shows the relationship between a) and the breaking limit circumference increase rate in a hydraulic free bulge test (with axial compression force).

FIG. 4: RTAIp (tube room temperature aging index of metal tube; MP
The figure which shows the relationship between a) and the breaking limit perimeter increase rate in a hydraulic bulge test (no axial compression force).

FIG. 5: RTAIp (medium room temperature aging index of metal tube; MP
The figure which shows the relationship between a) and the breakage perimeter increase rate in a hydraulic bulge test (with axial compression force).

FIG. 6 is a graph showing the relationship between the RTAI of a metal band as a material (sheet room temperature aging index; MPa) and the rate of increase in the critical circumferential length at break in a hydraulic free bulge test (no axial compression force).

FIG. 7 is a graph showing the relationship between the RTAI of a metal band as a raw material (sheet room temperature aging index of the metal band; MPa) and a breaking limit circumferential length increase rate in a hydraulic free bulge test (with axial compression force).

FIG. 8 is a diagram showing the relationship between the RTAI of a metal band as a material (plate room temperature aging index; MPa) and the rate of increase in the critical limit circumferential length in a hydraulic bulge test (no axial compression force).

FIG. 9 is a diagram showing the relationship between the RTAI of a metal band as a material (plate room temperature aging index; MPa) and the rate of increase in the critical limit circumferential length in a hydraulic bulge test (with axial compression force).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Material, 2a, 2b ... Mold, 3a, 3b ... Shaft compression device, 4a, 4b ... Displacement meter for shaft compression devices. 5: Displacement gauge for molding 6: Pressure gauge 7: Pressure amplifier 8: Hydraulic pump 9: Computer for control

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoshi Uei 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Kunikazu Tomita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun F-term in Honko Co., Ltd. (reference) 3H111 AA01 BA02 BA34 DA26 DB19

Claims (2)

[Claims] 1. A pipe normal temperature aging index (RTAIp) of 40 M
A metal tube for hydroforming, characterized by being at most Pa. However, the tube normal temperature aging index (RTAIp; MPa) =
YPaged (Yield strength of tube after aging treatment at room temperature of 30 ° C. × 1 month; MPa) −YP (Yield strength of raw tube; MPa) 2. A normal temperature aging index (RTAI) of 40MP.
A method for producing a metal tube for hydroforming, characterized by producing a metal band having a diameter of not more than a. However, the sheet normal temperature aging index (RTAI; MPa) = FSaged (10% pre-strain + 30)
° C × 1 month flow stress after normal temperature aging treatment)-FS (10
% Pre-strain flow stress)