JP2002346664A - Method for flaring edge of metal tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently flaring the diameter of the end of a metal tube made to a stainless steel or a high tension steel of high yield strength and work hardening coefficient, while preventing buckling. SOLUTION: Upon flaring the diameter of a pipe by pushing a punch 2 from the end of a metal pipe 1, the punch 2 is such that the taper angle θ is set at the range from 15 to 30 degrees with the length L of the cylindrical part ranging from 5 to 40 mm. The tube being flared is grasped with a metal tube- grasping die 3 having a tapered part 6, the taper angle of which is set to be the same as that of the punch, and the punch 2 is pushed therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for expanding a pipe at an end of the pipe while preventing buckling.

[0002]

2. Description of the Related Art The method of pushing a punch into the end of a metal pipe and expanding the pipe is a method commonly used for ordinary steel. However, the method used for ordinary steel has a high yield strength and a large work hardening index. When applied to stainless steel or high tensile steel, buckling is likely to occur. Therefore, JP-A-61-
Japanese Patent Application Laid-Open No. 296918 discloses a method in which a pipe end is flared in advance, and a mandrel is press-fitted from the pipe end in a state where the flared portion is sandwiched by clamp members to expand the pipe while preventing buckling. I have. But with this method,
The tube cannot be expanded to an outside diameter larger than the flare processed part, and the expansion ratio is small and inefficient.

[0003]

SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem, and is intended to solve the problem of the end of a metal pipe made of stainless steel or high tensile steel having a high proof stress and a large work hardening index. To efficiently expand the pipe while preventing buckling from occurring.

[0004]

In order to achieve the object, the method for expanding the end of a metal tube according to the present invention has a taper angle of 15 to 3 when a punch is pushed in from the end of the metal tube to expand the tube.
A metal tube gripping type having a punch set to a range of 0 degrees and a tapered portion having the same taper angle as the taper angle of the punch is used. It is preferable to use a punch having a punch cylinder length of 5 to 40 mm. Furthermore, when performing tube expansion in a plurality of steps, a punch having a short punch cylinder length is used in the first half of the process, and a flat expansion having a small deformation such as flatness can be obtained by using a punch having a long punch cylinder in the final process. it can.

[0005]

Generally, it is known that the buckling load of a pipe depends on the cross-sectional area of the pipe and the proof stress and tensile strength of the pipe. If the outer diameter of the pipe is increased by expanding the pipe, the cross-sectional area of the pipe is also increased, and buckling becomes difficult. On the other hand, if the outer diameter is increased by expanding the pipe, the contact area between the punch and the pipe is increased, so that the frictional resistance is increased. In addition, the expanded pipe is work-hardened and the axial load in the pipe is increased. FIG. 1 shows a conventional pipe expansion method.
As described above, the load in the pipe axial direction generated at the time of expanding the pipe with the increase in frictional resistance gradually increases, and the load concentrates on the raw pipe portion at the boundary with the grip portion, so that buckling 5 is likely to occur. In the present invention, as shown in FIG. 2, by using a metal tube gripping mold 3 having a tapered portion 6 provided with the same taper angle θ as the taper angle θ of the punch, when expanding in a plurality of steps,
Even if it is going to cause buckling in the tube part in the second step and thereafter, the expanded pipe taper part formed in the previous step becomes a mode in which the tapered part of the holding type is supported from behind, reducing the load applied to the pipe part, Buckling will be prevented.

In order to prevent buckling during pipe expansion, it is effective to optimize the shape of the punch as well as to reduce frictional resistance by applying a lubricating oil or applying a ceramic coating to the punch. Factors that affect the axial load during pipe expansion include the frictional resistance between the pipe and the surface of the punch taper, the axial component of the bending and deformation (expansion) of the pipe depending on the punch taper angle, and the force after expansion. Three factors of frictional resistance with the surface of the punch cylinder due to springback are considered.

The inventors of the present invention have examined various shapes of the punch, and found that the frictional resistance with the punch taper portion surface increases as the punch taper decreases, because the contact area between the tube and the punch increases. It is known that the higher the viscosity of the ceramic coating or the lubricating oil on the punch, the better the slip resistance and the smaller the friction resistance, but the rate is limited to some extent. It was found that the axial component of the force for bending and deforming (expanding) the pipe becomes a compressive load in the pipe axis direction as the punch taper angle increases, and increases. FIG. 3 shows that the present inventors used SUS4 with a metal tube gripper and a punch having various taper angles.
The punch taper angle θ when the end of a 36L steel pipe (outer diameter 25.4 mm x wall thickness 0.8 mm) is expanded at an expansion ratio of 34%.
And the relationship between the load in the pipe axis direction. From this result, a curve relation having a local minimum value near the taper angle of 20 degrees is obtained. To suppress buckling in the first step, the taper angle θ should be 15 to 3
It turns out that it is necessary to set it to 0 degree. Ideally, it is preferable to be about 20 degrees.

[0008] The frictional resistance of the surface of the punch cylinder due to the springback after the expansion of the tube increases as the length L of the punch cylinder increases. Stainless steel and high-tensile steel, which have higher proof strength than ordinary steel, have a greater springback, and the length of the punch cylinder greatly affects the axial load. When the present inventors expanded the pipe by changing the length L of the punch cylinder,
Although the axial load becomes smaller as the length of the punch cylindrical portion is shorter, the shorter the length is, the more likely it is to bend and it is difficult to make a stable expansion, so the minimum length was set to 5 mm. In addition, it was confirmed that buckling did not occur if it was 40 mm or less.

As described above, the shorter the cylindrical length L of the punch, the smaller the axial load at the time of expanding the tube and the less likely it is for buckling to occur. Expand using a punch with a short cylinder length,
When only the last tube expansion step is performed using a punch having a cylindrical portion length of 30 to 40 mm, a tube expansion portion having a good final finished state can be obtained. In addition, when the pipe expansion is performed in a plurality of steps, as described above, the expanded taper part formed in the previous step is held by the gripping taper part from behind, and the load applied to the raw pipe part is reduced. Therefore, molding can be performed with a molding pressure exceeding the buckling load of the raw tube after the second step.

[0010]

EXAMPLE 1 As a test material, a SUS304 tube made by high frequency welding and having an outer diameter of 25.4 mm, a wall thickness of 0.8 mm and a length of 350 mm was used. The expansion pipe punch has a taper angle θ of 7 degrees to 7 degrees.
In the range of 0 degrees, use a punch cylinder having a length L of 40 mm, and a diameter of up to 34 mm, 42 mm and 52 mm.
Coaxial expansion was performed in the process. The lubricating oil has a viscosity of 60m
Press oil of m ² / S was used. Table 1 shows the results. In the table, φ indicates the outer diameter in units of mm. As can be seen from Table 1, the punch taper angle θ is 15 to 3 in the process of expanding the pipe so that the mold contacts the expanded taper portion.
Test No. 0 using a 0 degree punch. Only 3 to 6 could expand to an outer diameter of 52 mm without buckling.

[0011]

Example 2 As a test material, a SUS304 pipe made by high frequency welding and having an outer diameter of 25.4 mm, a wall thickness of 0.8 mm and a length of 350 mm was used. The expansion pipe punch has a taper angle θ of 7 degrees to 7 degrees.
Using a punch cylinder having a cylinder length L of 0 to 70 mm at 0 °, coaxial expansion to an outer diameter of 34.0 mm was performed in one step. In all the tests, a metal tube gripping type having a taper angle equal to the punch taper angle was used. Table 2 shows the results. The punch cylinder length L of the present invention is 5 to 40 mm, and the taper angle θ is 15 to
In the range of 30 degrees, buckling and bending of the tube did not occur, and no abnormality was observed. However, when the punch cylinder length L was 0 mm, buckling did not occur due to the expansion, but the expanded portion was bent and the shape was poor. Also, when the taper angle θ is large, the expanded portion tends to be easily bent.

[0013]

Example 3 As a test material, a SUS304 tube made by high frequency welding and having an outer diameter of 25.4 mm, a wall thickness of 0.8 mm and a length of 350 mm was used. The expansion pipe punch has a taper angle θ of 15 degrees,
Punch cylinder lengths L of 10 mm and 30 mm were used, and coaxial expansion to an outer diameter of 52.0 mm was performed in three steps. In all the tests, a metal tube gripping type having a taper angle of 15 ° and a taper angle of a punch was used. In each step shown in Table 3, the length L of each punch cylinder is
The tube was expanded using a punch having.

[0015]

The test No. Test No. 41 is a test of a normal pipe expanding operation in which the punch cylinder length L is 50 mm. Reference numeral 42 denotes an attempt to expand the tube under efficient conditions without causing buckling as much as possible. Further, the test No. Reference numeral 43 is used to select a condition that does not cause buckling and finally does not cause deformation such as flatness. FIG. 4 shows the load applied in the tube axis direction in each step. Any test No. It can be seen that the tube was expanded in the second step at a pressure exceeding the buckling load of the tube.

The outer diameter of each section shown in FIG. 5 was measured at a position 10 mm from the end of each expanded tube, and the oblateness (%) was determined.
Was evaluated as (outer diameter of AB section−outer diameter of CD section) / average outer diameter after tube expansion × 100. Test No. No. 41 required a high deformation pressure because a punch having a long punch cylindrical portion was used, but deformation such as flatness was small, and the flatness ratio was as good as 0.1%. On the other hand, Test No. 42
Uses a punch with a short punch cylinder length, so the frictional resistance due to the springback force is small. As a result, the tube can be expanded with a relatively low deformation pressure, but flattening occurs, and the flatness is 1.2%. It was big. Then, in the final step, a test N using a punch having a long punch cylindrical portion length was performed.
o. 43, test No. The flat deformation was smaller than that of the sample of No. 42, and the flattening ratio was as good as 0.2%.

[0018]

As described above, according to the present invention, when the punch is pushed in from the end of the metal tube to expand the tube, the taper angle θ is set in the range of 15 to 30 degrees, and the length L of the cylindrical portion is reduced. Using a punch having a diameter of 5 to 40 mm, the pipe to be expanded is gripped with a metal pipe gripping type having a tapered portion having the same taper angle as the taper angle of the punch, and the punch is pressed in, whereby a high yield strength is obtained. The end of a metal pipe made of stainless steel or high-tensile steel having a large hardening index could be efficiently expanded without causing buckling and without causing bending or deformation such as flattening. Therefore, it is possible to provide the most suitable technology for the field in which the end of the stainless steel pipe is expanded and used, such as a fuel supply pipe for automobile fuel injection.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a conventional coaxial expansion method using a gripping die without a tapered portion.

FIG. 2 is a conceptual view of the present invention showing a method of coaxial expansion using a gripping mold having a tapered portion having the same taper angle as the punch taper angle.

FIG. 3 SUS436L with a tapered punch
The end of a steel pipe (outer diameter 25.4 mm x wall thickness 0.8 mm) is 34
Graph showing the relationship between the punch taper angle and the pipe axial load when the pipe is expanded at a% expansion rate

[Fig. 4] SUS by changing the combination of punch cylinder length L
Graph showing the relationship between the punch outer diameter and the axial load when the end of 304 steel pipe (outer diameter 25.4 mm x wall thickness 0.8 mm) is expanded.

FIG. 5 is a diagram showing a cross section of an outer diameter measured.

[Explanation of symbols]

1: Tube 2: Punch 3: Grab type
4: Stopper 5: Buckling 6: Grip type taper part θ: Taper angle L: Length of cylindrical part of punch

Claims (3)

[Claims] 1. A punch having a taper angle set in a range of 15 to 30 degrees when a punch is pushed in from a pipe end of a metal pipe to expand the pipe, and a taper portion having the same taper angle as that of the punch. A method for expanding a pipe end of a metal pipe, comprising using a metal pipe gripping type. 2. The method according to claim 1, wherein a punch having a punch cylindrical portion length of 5 to 40 mm is used. 3. The metal pipe tube according to claim 2, wherein when expanding the pipes in a plurality of steps, a punch having a short punch cylinder length is used in the first half step, and a punch having a long punch cylinder length is used in the final step. End expansion method.