JP4799812B2 - Tailored tube hydroforming method - Google Patents

Description

  The present invention is used for manufacturing exhaust system parts, suspension system parts, body parts, etc. for automobiles. A tailored tube in which metal pipes having different plate thicknesses and materials are connected is placed in a mold, and the mold is molded. The present invention relates to a hydroform processing method and a molded product that are molded into a predetermined shape by applying an internal pressure and a pushing force in the tube axis direction into the tailored tube after tightening.

  In recent years, hydroform technology has been attracting attention in the automobile field as one of the means for reducing costs and reducing weight by reducing the number of parts, and it has been applied to actual vehicles in Japan since 1999. Since then, the number of applicable parts for hydroforming has increased year by year, and the market size has greatly expanded.

  On the other hand, from the viewpoint of weight reduction, tailored blank technology has become widespread in press parts. The tailored blank is a combination of a plurality of metal plates having different thicknesses and materials. That is, since a necessary plate thickness is arranged at a necessary location, it is attracting attention as a very effective technique for reducing the weight of automobile parts.

Two technologies aimed at reducing the weight, that is, hydroforming and tailored blanks are combined to form hydroforming with tailored tubes. As conventional techniques in this field, as in Patent Document 1 and Patent Document 2, specific examples of automobile parts incorporating a hydroform part using a tailored tube, and hydroform properties as in Patent Document 3 are used. There are examples of excellent tailored tube inventions.
Japanese Patent Laid-Open No. 2001-321843 JP 2002-53069 A Japanese Patent Laid-Open No. 2003-211234

The most difficult thing in hydroforming is the balance between the internal pressure inside the pipe (hereinafter referred to as internal pressure) and the amount of pushing in the axial direction of the pipe (hereinafter referred to as axial pushing amount). FIG. 1 shows an example of a load path at the time of hydroforming in a normal uniform thickness / material pipe (hereinafter referred to as a single pipe) which is not a tailored tube. In this way, even a single pipe shows a complicated load path, and not only the final internal pressure and the axial push amount but also the path along the way is very important. For example, if the internal pressure in the middle is too high ((a) in the figure), the tube may rupture in the middle of molding, or wrinkles may remain if the pressure in the middle is too low ((c) in the same figure). This proper load path naturally depends on the tube thickness and material characteristics.
Therefore, in the case of tailored tubes having different plate thicknesses and materials, the load path becomes more difficult. For example, if molding is performed with a load path suitable for the material on the high strength side, the pressure is too high for the material on the low strength side, so that it tends to burst in the middle. In addition, as shown in FIG. 2, when molding is performed with a load path suitable for the material 1 on the low strength side, bursting in the middle can be prevented. 2 occurs. Thereafter, even if molding is continued, buckling remains at the joint (FIG. 2).

As described above, tailored tubes are much harder to hydroform than single tubes, and currently have a shape that does not increase the enlargement ratio (= (maximum circumference-minimum circumference) / minimum circumference x 100). Designing. Alternatively, the difference in strength between materials (specifically, the difference between the tensile strength of the material on the high strength side × the thickness value and the tensile strength of the material on the low strength side × the thickness value) is reduced. Is set. However, the advantages of the original tailored tube and hydroform cannot be fully utilized, and the effect of weight reduction will be diminished.
The expansion rate is an index indicating the expansion rate for each region after molding, and is an index different from the tube expansion rate obtained from the raw tube diameter before molding and the product diameter after molding.

  As described above, the present invention is a hydrofoam processing method capable of processing a hydrofoam molded article having a large enlargement ratio with a tailored tube having a large strength difference between materials, which was conventionally impossible to mold, and the processing method An object of the present invention is to provide a hydroform molded article having a large expansion ratio and a large difference in strength between materials.

In order to solve the problem, the gist of the present invention is as follows.
(1) A first metal tube having a tensile strength TS ₁ [MPa] and a plate thickness t ₁ [mm] and a second metal tube having a tensile strength TS ₂ [MPa] and a plate thickness t ₂ [mm] A cylindrical tailored tube arrayed in series in the axial direction and welded is clamped to a mold having a substantially rectangular cross section with a space between inner flat portions smaller than the outer diameter of the tailored tube. In the hydroform processing method in which the tube side surface is in linear contact with the inner flat portion of the mold in the tailored tube axial direction, and the tailored tube is loaded with the internal pressure and the pushing force in the tube axis direction, the tensile strength × the plate After expanding the low strength metal tube by applying axial push from the tube end of the low strength metal tube while the pressure is increased to a pressure that only the low strength metal tube of small thickness expands, High-strength metal with high strength x thickness Hydroforming method tailored tubes, characterized in that for tube expansion the metal pipe of the high-strength side by loading the axial pressing from the pipe end.

  According to the present invention, it is possible to perform a hydroforming process with a large expansion ratio using a tailored tube having a large strength difference between materials that could not be formed by a conventional hydroforming. This can contribute to the effect of reducing the weight of the automobile parts as described at the beginning.

  FIG. 3 shows an example of hydroforming when the tailored tube 4 in which the high-strength material 1 and the low-strength material 2 are joined by the welded portion 3 is expanded to a rectangular cross section. However, the term “strength” here means the tensile strength of the material × the thickness of the material, and the higher one is the material on the high strength side and the lower one is the material on the low strength side. The details of the present invention will be described using this example.

  In hydroforming, the pressure is increased with almost no axial push amount (press the tube so that the water inside the tube does not leak), but the internal pressure at that time is when the material 2 on the low strength side is a single tube. Set to a suitable pressure (a). This is to prevent the material 2 on the low strength side from bursting.

Next, the shaft is pushed in this state. Usually, in the case of a single pipe, axial push is applied to both pipe ends, but here the axial push is applied only to the pipe end of the material 2 on the low strength side. As the axial push is applied, the material 2 on the low strength side is expanded and gradually formed into a shape along the mold, that is, a rectangular cross section in this example (b).
And it axially pushes to the target axial pushing amount of the material 2 on the low strength side. During this time, the material 1 on the high-strength side is not axially pushed, and the internal pressure is also low for the material 1, so that almost no tube expansion is performed, and buckling that enters the material 2 does not occur (c ).

  Thereafter, the internal pressure is increased, and the pressure at that time is set to a pressure suitable when the high-strength material 1 is a single pipe. At this time, the material 2 on the low-strength side has progressed considerably in tube expansion, and since the restraint of the mold is large, it is difficult to burst even when the pressure is increased (d).

  In this state, only the pipe end of the material 1 on the high strength side is axially pushed. As the axial push is applied, the material 1 on the high strength side is now expanded and gradually formed into a rectangular cross section. Finally, the shaft is pushed to the target push amount of the material 1 on the high strength side. In the process so far, both materials are expanded, and a good shape with no buckling at the joint is obtained (e).

  Finally, if necessary, only boosting is performed without pushing the shaft. This is a process of sharpening the corner R, and is often used for ordinary single-tube hydroforms. Thus, a tailored-tube hydroform molded product that does not rupture during molding and does not leave any buckling or wrinkles is completed (f).

  In the above load path, it is easy to understand, and the internal pressure during pressing of each shaft is constant. However, depending on the part shape and material, it may be better to change the internal pressure during axial pushing even in single-tube hydroforming to prevent rupture and buckling during molding. In that case, as shown in FIG. 4, the internal pressure during the axial pushing may be changed based on the load path in the single pipe of each material.

  By the above-described method, the ratio of the tensile strength of the high strength side metal tube to the thickness of the metal tube on the low strength side × the plate thickness × the ratio of the plate thickness is 1.2 or more and the cross-sectional shape is 15% or more. It is possible to obtain a tailored tube hydroform molded product having the same.

Examples of the present invention are shown below.
The outer diameter of the tailored tube used as the raw tube was 63.5 mm, and the total length was 490 mm. The material on the high strength side was a steel pipe having a tensile strength of 330 MPa and a thickness of 1.4 mm, and the material on the low strength side was a steel pipe having a tensile strength of 330 MPa and a thickness of 1.0 mm. The mold used for the hydroform has a shape that expands into a rectangular cross section as shown in FIG. 5A, and the enlargement ratio (= (maximum circumference−minimum circumference) / minimum circumference × 100) is 54%. . For the shape of this part only, the minimum circumference is 63.5φ at both ends, which matches the outer diameter of the tube, so that the tube expansion ratio (= (maximum product circumference-tube circumference) Length) / perimeter of the tube × 100) is 54% which is the same as the enlargement ratio. Even with hydroforms that are currently mass-produced with a single pipe, the pipe expansion rate is at most about 40%, so this shape can be said to be a considerably large level of pipe expansion rate.

  The processing load path is as shown in FIG. 5B. First, the pressure was increased to 12 MPa in accordance with the condition of the thin material (1.0 mm), and only the tube end on the thin wall side was axially pushed to 30 mm. However, in the latter half of the axial pushing, the pressure was slightly increased to 14 MPa. After completing the axial push on the thin wall side, pressurize only the tube end on the thick wall side after increasing the pressure to 17 MPa according to the conditions of the thick material (1.4 mm), and push the shaft at the same 30 mm position as the thin wall side. Stopped. Finally, the inner pressure was increased to 37 MPa with both pipe ends fixed, thereby completing the molding.

  As shown in FIG.5 (c), it turns out that the favorable molded product without processing defects, such as wrinkles, is obtained with this hydrofoam processing method. That is, by this method, a hydroformed molded article having a magnification ratio of 54% (peripheral length of tube end portion = 199.4 mm, peripheral length of rectangular cross section = 306.6 mm) was obtained with a tailored tube having a strength ratio of 1.4.

The explanatory view of the general load course in single pipe hydroforming is shown. Explanatory drawing of the processing defect which generate | occur | produces when the load path | route of a single-tube hydroform is applied to a tailored tube is shown. The explanatory view of the hydroforming processing method of the tailored tube by the example of the present invention is shown. Of the hydroformed processing methods for tailored tubes according to the present invention, an example in which the control of the internal pressure is complicated will be described. An explanatory view of an example of the present invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... High-strength side material 2 ... Low-strength side material 3 ... Welded part 4 ... Tailored tube

Claims (1)

A first metal tube with a tensile strength TS ₁ [MPa] and a plate thickness t ₁ [mm] and a second metal tube with a tensile strength TS ₂ [MPa] and a plate thickness t ₂ [mm] are in the axial direction. The cylindrical tailored tubes arranged in series and welded in series are clamped into a mold having a substantially rectangular cross section with a space between the inner plane portions smaller than the outer diameter of the tailored tube, so that the side surface of the tailored tube is In the hydroform processing method in which the inner flat surface of the mold is linearly contacted in the axial direction of the tailored tube, and the internal pressure and the pressing force in the axial direction of the tube are loaded on the tailored tube, the tensile strength × the plate thickness is small In a state where only the low-strength side metal tube is expanded to a pressure that expands, the axial strength is applied from the tube end of the low-strength side metal tube to expand the low-strength side metal tube, and then the tensile strength × Metal pipe on the high strength side with large plate thickness Hydroforming method tailored tubes, characterized in that for tube expansion the metal pipe of the high-strength side by loading the axial pressing from.

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