JP2001062522A - Double tube hydroform processing method - Google Patents

Abstract

(57) [Summary] Hydroform processing in which a pipe is put into a mold, a divided mold is clamped, and then an internal pressure and a pushing force in the axial direction of the pipe are applied to the inside of the pipe to form a predetermined shape. In the method, there is provided a processing method for obtaining a molded article having a double pipe structure having a predetermined gap between an outer pipe and an inner pipe after molding. SOLUTION: After mounting a double pipe in a mold smaller than the final product shape and clamping the mold, an outer tube 1 and an inner tube 2 are subjected to axial pressing and simultaneously a pressure is applied inside the inner tube to form a final product. By molding to a shape smaller than the shape, then replacing the molded product in the mold of the final product shape, applying axial pressing only to the outer tube, and simultaneously applying the same pressure to the gap between the inner tube and the inner and outer tubes, Only the outer tube is deformed to obtain a product with a gap between the inner and outer tubes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hydroforming double pipes used for manufacturing exhaust pipes and the like for automobile parts.

[0002]

2. Description of the Related Art In recent years, hydroforming technology has attracted attention in the automotive field as one of the means of cost reduction and weight reduction by reducing the number of parts, and has been adopted in actual vehicles in Europe and the United States for several years, and in Japan. Application to actual vehicles also started in May this year. In the field of automobiles, especially in the field of exhaust systems such as manifolds, the effect of reducing the number of parts is significant, and each company is actively adopting hydroforming technology. On the other hand, in recent years, examples of using a double pipe as a pipe material for an exhaust system have been increasing for the purpose of noise prevention and the like, but at present, it is not possible to integrally process a plurality of parts by a hydroforming process on the double pipe. That is, a Monaka structure in which two press steel plates are welded to a portion corresponding to an outer pipe is adopted in a T joint or the like which is divided frequently at a portion where it is divided into two forks and joined by welding or a flange, and a T joint or the like which is divided into two forks. It is common. In the case of a double pipe T-joint, there is an example in which an expansion pipe shrink-fit type corrosion resistant double pipe developed for oil plant piping is formed by cold bulge forming (the original form of today's hydroforming). Process Vol.3,547 (1990)).

[0003]

As described above, in a single pipe, a plurality of parts can be integrally formed by hydroforming, and the number of parts can be reduced. However, in a double pipe used for an exhaust system, a hydroform is used. Since it cannot be processed, the number of parts cannot be reduced, and labor and cost for welding and the like are required. In particular, T-joints and the like cannot be manufactured unless they have a Monaka structure, and have significant disadvantages in terms of cost and efficiency. In addition, in the above example where a T-joint is formed by a cold bulge from an expansion pipe shrink-fit type double pipe for oil plant piping introduced above, the inner pipe and the outer pipe are in close contact with each other. There is also a disadvantage that it cannot be directly applied to an exhaust double pipe having a gap between the inner and outer pipes.

[0004] The present invention has been made to solve the above-mentioned conventional problems, and it is possible to obtain a molded article having a double-pipe structure having a predetermined gap between an outer pipe and an inner pipe after molding. An object of the present invention is to provide a hydroforming method.

[0005]

In order to solve the above-mentioned problems, the present invention invents a method for hydroforming a double pipe and obtaining a molded article having a gap between an inner pipe and an outer pipe after the processing. That is, the gist of the present invention is to attach a double pipe to a mold smaller than the final product shape, clamp the mold, apply axial pressing to the outer pipe and the inner pipe, and simultaneously apply pressure to the inside of the inner pipe. To form an intermediate molded product smaller than the final product shape, and then replace the intermediate molded product in the mold of the final product shape, apply axial pressing only to the outer tube, and simultaneously apply the same gap between the inner tube and the inner and outer tubes. By applying the pressure of
This is a hydroforming method characterized in that only the outer tube is deformed to obtain a product having a gap between the inner and outer tubes.

[0006]

FIG. 1 shows a working example of a T-joint in which a branch pipe is bulged from the center of a double pipe. The details of the present invention will be described using this working example. First, the inner pipe 2 having an outer diameter smaller than the inner diameter of the outer pipe 1 is inserted into the outer pipe 1, and is attached to the lower mold 4 for the primary hydroform in a double pipe state. Upper mold 3 for primary hydroforms formed in the middle
And close the mold. At this time, the dies 3 and 4 are formed into dies having a shape smaller than the final product shape (step).

Next, the axially pushing cylinder heads 5 and 6 are pushed in from both tube ends, and the outer tube 1 and the inner tube 2 are simultaneously axially pushed. At that time, a fluid such as water is filled into the interior 9 of the inner pipe 2 through the nozzle hole 8 formed in the one cylinder head 5 at the same time, and a pressure is applied. Due to this axial pushing and pressure load (primary hydroform), the outer pipe 1 and the inner pipe 2 swell into the branch hole 7 of the upper mold 3 in a tightly contacted state, and the branch of the double pipe as an intermediate molded product. A tube is formed (step).

[0008] The intermediate molded product formed in the above process is once taken out of the mold, mounted on other final hydroforming dies 10, 11, and clamped. At this time, mold 1
The molds 0 and 11 are formed into a mold having a final product shape (process).

Next, the cylinder pushing cylinder heads 12 and 13 are pushed in from both pipe ends, and the axial pushing is loaded. Circular grooves 17, 18 are provided at the tips of the cylinder heads 12, 13 so that the inner sides are equal to the inner diameter of the inner tube 2, so that the tips of the cylinder heads 12, 13 slide into the inner tube 2 when the shaft is pushed. It has a simple structure. With this structure, the inner pipe 2
Is not axially pushed, and only the outer tube 1 can be subjected to axial pushing. Simultaneously with the axial pushing, a fluid such as water, nitrogen gas or the like is filled into the interior 9 of the inner pipe 2 through a nozzle hole 15 formed in one cylinder head 12, and through a nozzle hole 16 branched from the nozzle hole 15. The gap 19 between the outer pipe 1 and the inner pipe 2 is filled with a fluid such as water or nitrogen gas, and the same pressure is applied to both.

In the illustrated embodiment, the nozzle holes 15 and 16 have a branched structure. However, independent nozzles may be used, and the pressure medium does not need to be the same as long as the pressure is the same. Water 9 and gap 19
For example, a nitrogen gas or the like which can be easily injected into a narrow place may be used. However, in that case, the inner pipe 2 and the cylinder heads 12, 1
It is necessary to devise an O-ring or the like between them and 3 so that different pressure media are not mixed. Furthermore, in order to make it easier to inject the pressure medium into the boundary surface between the outer tube 1 and the inner tube 2, a part of the boundary surface between the outer tube 1 and the inner tube 2 at the injection-side tube end is formed after forming into an intermediate molded product. Alternatively, the outer tube 1 and the inner tube 2 are prepared before the first hydroform for forming the intermediate molded product.
A small steel plate or the like may be partially sandwiched in the gap, and the steel plate may be removed before being mounted on the final hydroform mold.

When the injection into the boundary surface is devised as described above, since the inner surface shape of the inner tube 2 is not a perfect circle,
The cross-sectional shape of the tip of the sliding portion of the inner tube inner surface of the axle-pressing cylinder head 12 must be matched to the shape of the intermediate molded product, and the structure must return to a perfect circle as the axle-press and slide. Due to this axial pushing and pressure load (final hydroform), only the outer tube 1 is deformed, and the outer tube is expanded by the space of the gap 14 between the outer tube 1 and the molds 10 and 11, and finally the outer tube 1 A double pipe T-joint with a gap 19 between the inner pipes 2 is obtained as a final product (step). Although a gap 19 is finally left at the pipe ends of the outer pipe 1 and the inner pipe 2, rattling can be prevented by filling the gap 19 with steel wool or the like as necessary.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A working example of a double pipe T-joint according to the present invention will be described below.・ Base tube: Outer tube… Steel tube with outer diameter 60.5mm × sheet thickness 1.6mm Inner tube… Stainless steel tube with outer diameter 57.0mm × sheet thickness 0.8mm ・ Intermediate molded product: outer tube… 60.5mm outer diameter Branch pipe outer diameter 60.5 mm, branch pipe height 58 mm Inner pipe: mother pipe outer diameter 57.3 mm, branch pipe outer diameter 57.3 mm, branch pipe height 56.4 mm Molding conditions: pressure inside the inner pipe: 50 MPa (Hydraulic pressure) Axial pushing amount of outer tube and inner tube: 50 mm on both sides ・ Final shape: outer tube: outer diameter of main pipe 65 mm, outer diameter of branch pipe 65 mm, height of branch pipe 60 mm inner pipe: outer diameter of main pipe 57.3 mm Branch pipe outer diameter 57.3 mm, branch pipe height 56.4 mm Gap: uniformly 2-3 mm Molding conditions: pressure inside the inner pipe: 20 MPa (water pressure) Pressure between the outer pipe and the inner pipe: 20 MPa (nitrogen Gas) Axial pushing amount of outer tube: 10 mm on both sides

[0013]

According to the present invention, it has become possible to hydroform double fittings of an automobile exhaust system, which has been disadvantageous in terms of cost and efficiency due to the conventional welding structure of Monaka or the like. Costs can be reduced.
Further, it is possible to integrate not only the joint part but also the parts conventionally divided into a plurality of parts, and it is expected that the cost and efficiency of the exhaust system-related parts can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a hydroforming method according to the present invention.

[Explanation of symbols]

1 Outer pipe 2 Inner pipe 3 Upper mold for primary hydroform 4 Lower mold for primary hydroform 5 Axial cylinder head for primary hydroform (with nozzle hole) 6 Axial cylinder head for primary hydroform (without nozzle hole) 7 Primary Hydroform Branch Hole 8 Primary Hydroform Nozzle Hole 9 Inner Tube Inside 10 Upper Mold for Final Hydroform 11 Lower Mold for Final Hydroform 12 Axial Cylinder Head for Final Hydroform (with Nozzle Hole) 13 Final Axial cylinder head for hydroforming (no nozzle hole) 14 Gap between mold for final hydroforming and outer tube 15 Nozzle hole for filling inner tube of final hydroform 16 Nozzle hole for filling gap between inner and outer tubes of final hydroforming 17 Final hydro Groove for pipe slide in foam 18 The gap between the hydroforming the tube sliding groove 19 outer and inner tubes

Claims (1)

[Claims] 1. The final product shape is obtained by mounting the double tube in a mold smaller than the final product shape and clamping the mold, then applying axial pressing to the outer tube and the inner tube and simultaneously applying pressure to the inside of the inner tube. Forming into a smaller intermediate molded product, then replacing the intermediate molded product in the final product shape mold, applying axial pressing only to the outer tube, and simultaneously applying the same pressure to the gap between the inner tube and the inner and outer tubes The method according to claim 1, wherein only the outer tube is deformed to obtain a product having a gap between the inner and outer tubes.