JPH0379094B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a flange by making the middle of a metal tube protrude in the radial direction, and particularly relates to a method for preventing the occurrence of cracks in the inner wall of the flange.

2. Description of the Related Art Conventionally, a flexible joint structure as shown in FIG. 7 is known as a flexible joint structure for connecting separately piped exhaust pipes to the engine side and the vehicle body side of an automobile, for example. That is, an engine-side exhaust pipe a has a radially projecting flange a ₁ formed at its connection end, and a vehicle body-side exhaust pipe has a flare b ₁ formed at its connection end corresponding to the exhaust pipe a. b is fitted through a seal ring c, and fastening flanges d, welded to the outer peripheries of exhaust pipes a and b, respectively.
By tightening e with bolt f and nut g, and with spring h... biased in the tightening direction, both exhaust pipes a and b are connected without gas leakage while absorbing vibrations. be.

And flange a ₁ of the engine side exhaust pipe a
To form the flange, first insert a bulging molding tool into the part of the exhaust pipe a to be flange-formed, and insert the bulging molding tool into the part of the exhaust pipe a.
By rotating eccentrically with respect to the axis of the exhaust pipe a while pressing against the inner circumference, the inner wall of the exhaust pipe a is expanded in the radial direction to form a bulge (beading process) (for example, (see Publication No. 57-9537), and then pressurizes the exhaust pipe a in the axial direction of the exhaust pipe a to make the bulged portion protrude in the radial direction (flange processing) to form a flange _a1 . A method has been adopted to do so.

However, in the conventional flange forming method described above, as shown in _{FIG .}
There was a problem that deep cracks were generated on the inner wall of the flange A1 due to the "processing overhang" that occurs during the flanging process, and the flange _A1 could be damaged during use due to these cracks becoming a starting point.

Therefore, the present invention was made in view of this point, and it was discovered that if the bending R of the inner wall of the bent part of the flange of the exhaust pipe is made to be a certain value or more, cracks will not occur. The object of the present invention is to provide a method for forming a flange on a metal pipe such as a pipe without causing cracks.

In order to achieve this object, the structure of the method of the present invention is a method of forming a flange by protruding the middle of a metal tube in the radial direction. By rotating the metal tube, the inner wall of the metal tube is expanded in the radial direction to form a bulge, and then a ring-shaped spring with a reduced diameter is inserted into the metal tube up to the bulge using a spring insertion tool. A ring-shaped spring is elastically fitted to the inner wall of the bulge of the metal tube, and the metal tube is further pressurized in the axial direction of the metal tube to cause the bulge to protrude in the radial direction. The ring-shaped spring expands as it protrudes, forming a flange in which the ring-shaped spring is inserted into the inner wall of the distal end of the bulging portion of the metal tube, and the bending process at the flange is performed by fitting the ring-shaped spring. This is to ensure that the bending R of the inner wall of the section exceeds a specific value.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

1 to 5 show an embodiment in which the method of the present invention is applied to forming a radially projecting flange at one end of a thin-walled circular exhaust pipe. First, as shown in FIG. 1, one end of a thin circular straight pipe 1 for an exhaust pipe, which has been previously cut to a predetermined length in a cutting process and from which burrs on the cut surface have been removed in a burring process, is placed in a clamp 2. Twist and bite. The clamp 2 is divided into upper and lower halves in FIG. 1, each of which is connected to a holder (not shown). It is designed to hold and remove the tube 1.

Next, with the straight pipe 1 held by the clamp 2, a bulging tool 3 is inserted into the straight pipe 1, as shown in FIG. 1, to bulge the middle of the straight pipe 1 in the radial direction. The expansion molding tool 3 has a shaft portion 3 held by a chuck 4.
a and a disc-shaped molded part 3b formed at the tip of the shaft part 3a, and the shaft center of the chuck 4 is aligned with the straight pipe 1 by the operation of a hydraulic cylinder (not shown) disposed in the chuck 4. It rotates eccentrically with respect to the axis, and by gradually increasing the amount of eccentricity, the inner wall of the straight pipe 1 is expanded in the radial direction to form a bulge 5 having a V-shaped cross section (beading process). ) is a thing. Furthermore, reference numeral 2a is a slide portion provided on the clamp 2 facing the bulging portion 5 and capable of sliding in the radial direction (vertical direction), and a spring ( (not shown) is compressed, and as the bulge 5 of the straight pipe 1 is formed, it moves radially outward while pressing the bulge 5 to improve the formability of the tip of the bulge 5. It is something that enhances.

After performing the beading process, as shown in FIG. 2, a spring insertion tool 6 for inserting a ring-shaped spring 7 into the straight pipe 1 instead of the chuck 4 is placed opposite to one end of the straight pipe 1. do. The spring insertion tool 6 is fitted into a cylindrical spring guide 6a having an inner diameter equal to the inner diameter of the straight pipe 1, and is slidably inserted in the axial direction from the rear end (right end in FIG. 2) of the spring guide 6a. A ring-shaped spring 7 with a reduced diameter is loaded into the spring guide 6a. The ring-shaped spring 7 is made by winding a spring wire with a circular cross section of radius r into a ring shape, and the length of the coil is one turn at the end of the flange process (when the ring-shaped spring 7 is expanded), which will be described later. The length is set not to exceed.

Thereafter, as shown in FIG. 3, after the front end of the spring insertion tool 6 is brought into contact with the end of the straight pipe 1, the ring-shaped spring 7 is inserted into the straight pipe 1 by protruding the rod 6b forward. The ring-shaped spring 7 is inserted up to the bulge 5 and elastically fitted to the inner wall of the bulge 5 of the straight pipe 1 (spring wire pushing step).

When the spring wire pushing process is completed, instead of the clamp 2, a die 8 divided into upper and lower halves is fixed to the holder as shown in FIG. At the same time, the straight pipe 1 is held at the end of the straight pipe 1.
A punch 9 for forming a flange on the swollen portion 5 is fitted. The punch 9 includes a straight pipe 1 from the bulging portion 5 of the straight pipe 1.
A fitting hole 9a is provided in the outer peripheral surface extending to the end of the tube, and a centering jig 10 that fits into the straight pipe 1 is provided at the axial center of the fitting hole 9a.

In this state, by pressing the punch 9 to the left, the straight pipe 1 is pressurized in the axial direction of the straight pipe 1, thereby buckling the bulging portion 5 and causing it to protrude in the radial direction. At this time, as the bulging part 5 protrudes, the ring-shaped spring fitted to the inner wall of the bulging part 5 expands, and further pressurization of the punch 9 progresses and the rear end surface of the die 8 and the punch 9
When the bulging portion 5 is pressed from the front and back by the front end surface and is completely flanged, the ring-shaped spring 7 is formed within the inner wall of the bent portion 11a on the outer periphery of the flange 11, as shown in FIG. The flange 11 is molded in the sandwiched state. (Flanging process). Note that 12 is a support member that fits into the other end of the straight pipe 1 and supports the straight pipe 1.

Here, the inner wall of the bent portion 11a of the flange 11 formed in the flanging process is bent in accordance with the wire radius r of the ring-shaped spring 7, so that the bending R of the inner wall is equal to or less than r. There isn't.

Therefore, the flange 11 formed in this way has the above-mentioned r set to a specific value, for example, 0.5 to 1.0 mm.
By setting this, cracks do not occur on the inner wall of the bent portion 11a of the flange 11, and therefore, damage to the flange 11 during use of the exhaust pipe can be prevented.

Further, since the ring-shaped spring 7 is inserted into the inner wall of the bent portion 11a, the ring-shaped spring 7 allows the flange 11 to have a good outer diameter shape.
can be molded.

In the above embodiment, the ring-shaped spring 7 is formed of a wire having a circular cross section with a radius r, but for example, as shown in FIG. It is also possible to use a ring-shaped spring 7' made of a wire having a ring shape.

Further, in the above embodiment, the present invention is applied to a thin circular exhaust pipe, but it goes without saying that the present invention can be widely applied to other metal pipes.

As explained above, according to the flange forming method of the present invention, the inner wall of a metal tube is expanded in the radial direction to form a bulge, a ring-shaped spring is then inserted into the bulge, and then a metal By pressurizing the tube in the axial direction, the bulge is made to protrude in the radial direction, and a ring-shaped spring is inserted into the inner wall of the tip of the bulge to form a flange.
It is possible to ensure that the bending R of the inner wall of the bending part of the flange exceeds a certain value, thereby preventing cracks from occurring in the inner wall, and thus making it possible to form a highly durable flange on a metal pipe. It is something.

[Brief explanation of drawings]

1 to 4 show the molding process of an embodiment of the present invention, FIG. 1 is a sectional view showing the beading process, FIG. 2 is a sectional view showing the state before the spring wire pushing process, and FIG. 3 is a sectional view showing the state before the spring wire pushing process. 4 is a sectional view showing the state after the spring wire pushing process, FIG. 4 is a sectional view showing the flanging process, FIG. 5 is an enlarged sectional view of the formed flange, and FIG. 6 is a modified example of the ring-shaped spring. 7 is a sectional view showing a conventional flexible joint structure, and FIG. 8 is an enlarged sectional view of the flange portion. DESCRIPTION OF SYMBOLS 1... Straight pipe, 3... Expansion forming tool, 5... Expansion part, 6...
Spring insertion tool, 7, 7'...ring-shaped spring, 11...flange, 11a...bending part.

Claims (1)

[Claims] 1 A method of forming a flange by protruding the middle of a metal tube in the radial direction, first inserting a bulge forming tool into the metal tube and rotating the bulge forming tool to radially extend the inner wall of the metal tube. The ring-shaped spring is pushed wide to form a bulge, and then the ring-shaped spring with its diameter reduced is inserted into the metal tube up to the bulge with a spring insertion tool to place the ring-shaped spring on the inner wall of the bulge of the metal tube. The metal tube is elastically fitted, and the metal tube is pressurized in the axial direction of the metal tube to cause the bulge to protrude in the radial direction, and as the bulge protrudes, the ring-shaped spring expands, causing the metal tube to expand. A metal tube flange forming method characterized by forming a flange with a ring-shaped spring inserted into the inner wall of the tip of the protrusion.