JPH06344028A - Method for shaping end of bent tube - Google Patents

Abstract

PURPOSE:To improve the roundness after shaping, to shorten the time required for process and to excellently make a bias of the process capability index. CONSTITUTION:This is the method to shape in order to improve the roundness by reducing dimensional tolerances of both inner and outer diameters of an end of a bent tube T. The bent tube T is fixed, the end of this bent tube T is forcibly inserted inside a diameter reduction correcting die 3, and corrected with diameter reducing. Then, the end of the tube T is taken out from the inside of the diameter reduction correcting die 4, an outer diameter regulating die 5 having a cavity with an inner diameter larger than the outer diameter of the diameter reducing part of the tube T is fit and covered around the end of the tube T. An enlarging correcting mandrel 4 is forcibly inserted inside the end of the tube T, the tube is enlarged and corrected, and the outer circumferential part is closely adjoined on the inner circumferential surface of cavity 5a of the outer diameter regulating die 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for shaping an end portion of a tube which is bent.

[0002]

2. Description of the Related Art For example, a branch pipe in an intake manifold of an automobile engine is made by bending a long tube and then cutting it. Therefore, the end portion of such a branch pipe has an elliptical shape, and the dimensional tolerance of the inner and outer diameters is about -0.5 to +0.2 mm in the major axis direction and about -0.8 to -0.2 mm in the minor axis direction. The roundness was inferior. Therefore, when brazing the end portion of the branch pipe while inserting it into the tubular portion formed on the flange for attachment to the plenum chamber or the cylinder head,
There is a risk that brazing will occur, resulting in defective brazing.

Therefore, conventionally, the roundness has been improved by reducing the dimensional tolerance between the inner and outer diameters of the end of the branch pipe as follows.

That is, a branch pipe is fixed, a split-expansion straightening die is inserted into the end of the branch pipe to expand the pipe without controlling the outer diameter, and then the inner diameter is regulated by upper and lower molds for straightening the pipe. The tube end was shaped by contracting the tube without doing this.

[0005]

In the conventional tube end shaping method, the dimensional tolerance between the inner and outer diameters is −0.
2 to +0.2 mm, -0.2 to +0.2 in minor axis direction
The roundness can be increased to about mm, but for that purpose, the tube expanding step and the tube contracting step must be repeated, and there is a problem that the step time is long, for example, about 60 seconds. Further, there is a problem that the deviation cpk of the process capability index is about 0.32 to 0.96, which is not sufficient. Further, recently, it has been required to further reduce the dimensional tolerances of the inner and outer diameters to further improve the roundness, but the conventional method has not been able to meet such demand.

An object of the present invention is to provide an end shaping method for a bending tube which solves the above problems.

[0007]

According to the method of shaping an end portion of a bent tube according to the present invention, the end portion of the bent tube is shaped in order to reduce the dimensional tolerance of the inner and outer diameters of the end portion of the bent tube to improve the roundness. The method is to fix the bent tube, forcibly insert the end of this tube into the diameter-reduction mold, correct the diameter, and then remove the end of the tube from the diameter-reduction mold. Then, an outer diameter control mold with a cavity having an inner diameter larger than the outer diameter of the reduced diameter portion of the tube is fitted around the end of this tube, and a tube expansion straightening mandrel is forcibly inserted into the end of the tube. Then, the tube is expanded and corrected, and the outer peripheral portion thereof is brought into close contact with the inner peripheral surface of the cavity of the outer diameter regulating type.

In the above, the diameter reducing step and the tube expanding step can be repeated, and in this case, the dimensional tolerances of the inner and outer diameters are further reduced and the roundness is improved.

[0009]

[Function] After the end of the bending tube is forcibly inserted into the diameter-reducing die to correct the diameter, the end of the tube is taken out of the diameter-reducing die, and then around the end of the tube. Fit an outer diameter control mold that has a cavity with an inner diameter larger than the outer diameter of the reduced diameter portion of the tube, and forcibly insert the tube expansion correction mandrel into the end of the tube to correct the tube expansion and Since the inner diameter of the cavity of the outer diameter regulating type is closely adhered, the circularity can be improved by making the dimensional tolerance between the inner and outer diameters -0.1 mm to +0.1 mm by a single operation. Further, by repeating the above work, it is possible to further reduce the dimensional tolerance of the inner and outer diameters and further improve the roundness.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In the following description, upper and lower sides and left and right sides of the drawing are referred to as upper and lower sides and left and right sides, respectively.

In FIG. 1, an apparatus used for carrying out the method of the present invention is arranged on the left side of the hugging die (1) for fixing the tube (T) by sandwiching the ends of the tube (T) from above and below. And a tool holding plate (2) which can move up and down with respect to the holding type (1) and can move up and down.

The tool holding plate (2) is provided with a diameter reducing straightening die (3), a pipe expanding straightening mandrel (4) having a circular cross section, and an outer diameter regulating die (5) at the time of pipe expanding. The diameter-reducing mold (3) is formed with a cavity (3a) having a circular cross section and an inner diameter slightly smaller than the outer diameter of the tube (T). The tube expansion straightening mandrel (4) is a tool holding plate below the diameter reduction straightening die (3).
It is fixedly provided at the right end of the rod (6) which is fixedly provided on (2) and extends to the right. Tube expansion mandrel
The outer diameter of (4) is equal to the inner diameter of the tube (T) after shaping. A mold support plate around the middle of the length of the rod (6)
(7) is fixedly installed. The through holes (7a) extending in the left and right direction are formed in the die support plate (7) on both upper and lower sides of the rod (6), and the die support rods (8) extending in the left and right direction are slid in the through holes (7a). It is threaded freely. Outer diameter regulation type
(5) is fixedly provided at the right end of the die support rod (8).
Between the die support plate (7) and the outer diameter regulation die (5), the die support rod
A coil spring (9) is arranged around (8). The outer diameter regulation type (5) has a cavity (5a) with a circular cross section having an inner diameter equal to the inner diameter of the shaped tube (T).
It is formed concentrically with (4) and penetrates in the left-right direction. The inner diameter of the cavity (5a) is larger than the inner diameter of the cavity (3a). Also, under normal conditions, the outer diameter regulation type
The right side of (5) is located to the right of the right end of the mandrel (4).

A method of forming an end portion of a bent tube using the above apparatus will be described with reference to FIGS. 2 and 3. First, the end portion of (T) that has been bent and cut at a predetermined position is fixed to the holding mold (1). Further, the tool holding plate (2) is moved so that the cavity (3a) of the diameter reducing type (3) is coaxial with the tube (T). In this state, bring the tool holding plate (2) close to the embracing die (1), and forcibly insert the end of the tube (T) into the cavity (3a) of the diameter-reducing die (3) to reduce the diameter. Correct (see Figure 2). Then, the tool holding plate
(2) is separated from the hugging mold (1), and the end of the tube (T) is taken out from the inside of the diameter-reducing mold (3). After that, the tool holding plate (2) is moved upward and the tube expansion straightening mandrel (4) is attached to the tube (T).
And make it come coaxially. Then, bring the tool holding plate (2) close to the hugging die (1), and attach the end of the tube (T) to the outer diameter regulating die.
Put it in the cavity (5a) of (5). If the tool holding plate (2) continues to approach the hugging die (1), the mandrel (4) will be delayed a little after the end of the tube (T) enters the cavity (5a).
Is forcibly inserted into the tube (T) and the specified length of the tube (T) is expanded and straightened, and the outer periphery of the tube (T) is the inner surface of the cavity (5a) of the outer diameter control type (5). (See Fig. 3). As a result, the dimensional tolerance of the inner diameter and the outer diameter of the end portion of the tube (T) is reduced, and the roundness is improved.

Next, specific examples of the present invention will be described.

A tube material made of JIS A6063 alloy was prepared. The outer diameter of this tube material is 38 mm, the dimensional tolerance is -0.1 to +0.1 mm, and the wall thickness is 2.0 mm. Then, the tube material was bent and then cut. The cut end has an elliptical shape, and the outer diameter has a dimensional tolerance of -0.5 to +0.2 mm in the major axis direction.
It was -0.8 to -0.2 mm in the minor axis direction. The end portion of the bent tube was shaped by reducing the diameter and expanding the tube as described above, and the dimensional tolerance of the outer diameter was set to −0.1 to +0.1 mm in both the major axis direction and the minor axis direction.
The time required for this step was 9.8 seconds, and the deviation cpk of the process capability index was 1.33 to 2.03.

[0016]

As described above, according to the method of shaping the end portion of the bending tube of the present invention, the roundness is improved by setting the dimensional tolerance of both the inner and outer diameters to -0.1 to +0.1 mm by one operation. Therefore, the time required for the process is shortened. Moreover, the deviation of the process capability index becomes excellent. Further, by repeating the above work, it is possible to further reduce the dimensional tolerance between the inner and outer diameters and further improve the roundness.

[Brief description of drawings]

FIG. 1 is a partially cutaway front view showing an apparatus used for carrying out the method of the present invention.

FIG. 2 is a partially cutaway front view showing a state in which an end portion of a tube is straightened.

FIG. 3 is a partially cutaway front view showing a state in which an end portion of a tube is straightened.

[Explanation of symbols]

 3 Reduced diameter type 4 Tube expansion straightened mandrel 5 Outer diameter restricted type 5a Cavity T tube

Claims (1)

[Claims] 1. A method of shaping a bent tube to reduce the dimensional tolerance of the inner and outer diameters of the end portion of the bent tube to improve the roundness, wherein the bent tube is fixed and After the end is forcibly inserted into the diameter-reducing mold to correct the diameter, the end of the tube is taken out of the diameter-reducing mold, and then around the end of the tube, outside the diameter-reducing part of the tube. Fit an outer diameter control mold that has a cavity with an inner diameter larger than the diameter, and forcibly insert a pipe expansion straightening mandrel into the end of the tube to correct the pipe expansion, and the outer peripheral part inside the outer diameter control mold cavity. A method for shaping an end portion of a bending tube, which is characterized in that it is closely attached to a peripheral surface.