JP2001150047A - Machine method with pre-bending and pushing axes process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a machining method with pre-bending and pushing axes process with which materials are machined with pushing axes process in a prescribed bending shape while suppressing cracks in materials. SOLUTION: When a metal tube P, which is machined in a pre-bending process, is laid in a metal mold with a cavity of the bending shape and is machined with pre-bending and pushing axes process, the metal tube P is machined with pre-bending process so that a bending neutral axis O' of the pre-bent metal tube P can be located inside a bending neutral axis O, which is obtained in a shape after molding. This method delays the timing that the outer surface of the pre-bent metal tube P comes into contact with the inner surface 7 located on the outside of the metal mold 1, and allows entire, homogeneous deformation for a longer period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-bending axle pressing method using a pre-bent metal pipe as a raw material among pipe axle pressing methods also called hydroforming method or hydraulic bulging method. Things.

[0002]

2. Description of the Related Art Using a metal tube as a raw material, to expand the middle of the raw material in the longitudinal direction, or to manufacture parts having a bulge portion in the middle of the raw material, such as a g-shape, a human shape, and a Y-shape. Conventionally, an axial pressing method is known. In this method, for example, as shown in FIG. 4, a metal tube as a material is set inside a molding die 2 having a flute-shaped hollow portion 1, and both ends of the metal tube are provided with a shaft press fitting 4 having a hydraulic pressure supply hole 3. A metal pipe as a material is set inside a molding die 2 having a human-shaped cavity 1 as shown in FIG. 5, and a hydraulic pressure supply hole 3 is provided at both ends. This is a method in which the shaft is pressed by the shaft pressing fitting 4. The end face of the metal tube is axially pushed while a hydraulic pressure is applied to the inside thereof, and the hollow portion 1 of the molding die 2 is pressed.
Plastically deforms along the shape of.

In many cases, however, it is often desired to form a bulge not only in a straight pipe but also in a curved pipe. Since the straight pipe cannot be bent by the axial pressing method, it is practical to add a bending step before and after the axial pressing in such a case. However, at present, there is no established technique for performing bending after performing axial pressing. Therefore, a method of pre-bending a material in advance and axially pressing the material is exclusively used. The most typical pre-bending axial pressing method is shown in FIG.
This is to expand the pre-bent metal tube shown in FIG. 7 into a flute shape, or to form a branch tube into the pre-bent metal tube shown in FIG. In these cases, the pre-bending of the material is performed so as to match the shape obtained by molding.

[0004] However, bending is one of the most severe processes for a material, and the material usually reaches almost a limit deformation amount only by pre-bending. Therefore, when the axial pressing is performed, if the processing conditions are not properly set, the material is broken during the axial pressing. Therefore, conventionally, it has relied on costly methods such as changing the material to a higher quality material, or heating the pre-bent material once to release the strain and then axially press work.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides a pre-bent metal pipe which can be axially pressed to a predetermined bent shape while suppressing cracks in the material. This was made to provide a bending axial pressing method.

[0006]

In order to solve the above-mentioned problems, a pre-bending axial pressing method according to the present invention sets a pre-bent metal tube in a molding die, and When shaping the end face while applying hydraulic pressure inside to form a predetermined bent shape, the neutral axis of the bend is located closer to the center of curvature than the neutral axis of the bent shape obtained by molding. It is characterized by using a pre-bent metal tube.

[0007] It is preferable to use a metal pipe that has been pre-bent in an arc shape, and it is preferable that the shape obtained by molding bend in an arc shape. In this case, the radius of curvature R of the bending of the shape obtained by molding
The radius of curvature of the pre-bent metal tube is 1.05R
It is preferably set to 1.251.25 R.

As described above, in the prebending axial pressing method of the present invention, when performing the axial pressing, the conventional method in which the axis of the shape after the processing and the axis of the prebended material are substantially coincident with each other. An empirical rule has been modified so that the axis of the pre-bent material takes a shape closer to a straight line. Since there is a material dynamic theory which is hard to find at first glance, it will be described in detail below with embodiments of the present invention.

[0009]

FIG. 1 is a cross-sectional view showing an embodiment of an expanded pipe pre-bending axial pressing method according to the present invention. The final shape obtained by the molding, that is, the shape of the hollow portion 1 of the molding die 2 is a fleshy mushroom shape having a narrow tube portion 6 at both ends and a central portion 5 expanded, and has a bending radius R and a bending angle θ. It has a mushroom shape.

Conventionally, when a pre-bending axial pressing process is performed on such a shape, as shown in FIG. 6, the narrow tube portion 6 has the same bending radius R and bending angle θ as the shape obtained by molding.
A pre-bent metal pipe P having substantially the same diameter as the radius of the pre-bent metal pipe P was set in the molding die 2 to perform the axial pressing. That is, the pre-bent metal pipe P and the neutral axis of the bending in the final shape were exactly coincident.

During the axial pressing, a hydraulic pressure is applied to the inside of the pre-bent metal pipe P, and the pre-bent metal pipe P is pushed from the inside to the outside by this internal pressure. The force F is represented by F = internal pressure × surface area. However, since the inside and outside of the pre-bent metal pipe P have different surface areas and the outside surface area is larger, the entire pre-bent metal pipe P is pushed outward accordingly. That is, the pre-bent metal pipe P shown in FIG. 6 is deformed so as to approach the outer inner surface 7 of the molding die 2 by receiving a force F in the normal direction at the center of the bent portion by the internal pressure. As a result,
The outer surface of the pre-bent metal tube P comes into contact with the outer inner surface 7 of the molding die 2 very early in the axial pressing process, and the frictional force generated thereby prevents further deformation of the contact portion. The expansion deformation is performed in a narrow portion. This is one reason that the pre-bent metal pipe P is easily broken in the pre-bending axial pressing.

[0012] In the present invention, on the other hand, larger than R (bend radius of the resulting shape by molding) bend radius of the molding die 2 the pre-bent metal pipe P of the bending radius R ^{`as</sup> shown in FIG. 1, the pre bending is moved inward closer to the center of curvature than the neutral axis O of the bending of the resulting shape by molding a <sup>`neutral} axis O of the bending of the metal tube P, it is as close to the inside of the inner surface 8 of the molding die 2. When an internal pressure is applied to the pre-bent metal tube P from this state, the pre-bent metal tube P is deformed so as to approach the outer inner surface 7 of the molding die 2 as described above.
Amount corresponding pre-bent metal pipe P to a neutral axis O ^`are moved from the first to the inside of the bend of the can prevented from contacting the outside of the inner surface 7 of the molding die 2 in an early stage. As a result, it is possible to have a longer uniform deformation time for a longer time than in the past, and the crack can be delayed accordingly.

If the number of bends is one, the bending angle θ cannot be changed. However, in the case of a continuous bending shape as shown in FIG. 2, the bending angle θ can be reduced. In Figure 5, so as to vary smoothly curvature at coupling point 9 of the bending, molding die bending radii R1 and R2 is greater than pre-bent radius R1 ^{`and R2,</sup> and the adoption, and the molding die bending angle θ1 and θ
We have adopted the pre-bent angle θ1 <sup>`and θ2,} narrower than 2.

[0016] In the case of axial pressing to a shape having a bulge outside the bend as shown in FIG. 6, the effect of improving the pre-bend shape cannot be expected in the previous two examples. The reason is that the deformation of the pre-bent metal tube P is difficult to lock because the frictional force due to the bulging deformation is not so large because the bulging portion is present in the molding die 2. Nevertheless, the effect on the inward swelling increases. Although there is no alternative to changing the bending radius R in the shaft pressing system only of bulging, it is also possible to adjust the bending radius and the bending angle by using a pre-bent metal pipe P having a smaller diameter. .

[0015] Figure 2 is a an example, using the pre-bent metal pipe P of smaller diameter than the inner diameter of the forming die 2, and to increase the pre-bent radius R ^`as possible. If the diameter of the pre-bent metal pipe P is too small, it is necessary to expand the pipe rather than the diameter. Therefore, it is important to design in consideration of the balance. Empirically, this balance can be ensured in a range where the bending radius is 1.05R or more and 1.25R or less with respect to the bending radius R of the shape obtained by molding. The balance is also an important examination item in the expansion type axial pushing system shown in FIG.

Until now, the description has been made on the premise that the pre-bend of the pre-bent metal pipe P is a circular arc. However, if a free-bend metal pipe can be directly manufactured in the future, the pre-bend shape of the pre-bend metal pipe P will be positive. It is not necessary to limit to arcs. The final shape may of course have a free bending axis. Hereinafter, an example in which the workability of the pre-bending shaft pressing method of the present invention and the conventional pre-bending shaft pressing method is compared will be described.

[0017]

(Embodiment 1) The pre-bending axial pressing method of the present invention was carried out by the working system shown in FIG. The final shape obtained by molding is an expanded portion having a bent shape of R100 mm × θ90 ° having a diameter of 40.0 mm and both ends having a diameter of 35.00 mm.
The shape is a straight narrow tube of 0 mm. The tube expansion already starts from a straight pipe-shaped position. The metal pipe used in the processing method according to the present invention has a diameter of 35.0 mm x a wall thickness of 0.8 mm, and is 30K.
A Grade carbon steel, have been subjected to pre-bent working of R ^{`120mm</sup> × θ90 °. Since <sup>R`} > R, the bending neutral axis of the steel pipe is deviated more inward than the bending neutral axis of the cavity of the molding die. As a result, according to the processing method of the present invention, when the conventional processing method is used, the steel pipe having the same material and the bending axis coincides with that of the molding die is broken before obtaining the final shape. The steel pipe stuck well to the molding die, and the final shape could be accurately obtained.

(Embodiment 2) FIG. 2 shows that R1 = 100 mm × θ.
A bent shape portion of 1 = 40 degrees and a bent shape portion of R2 = 80 mm × θ2 = 50 degrees are connected at an expanded portion having a diameter of 60.0 mm, and both ends thereof are straight narrow tube portions having a diameter of 56.0 mm. This is a shaft pushing system for obtaining the final shape. The tube expansion already starts from a straight pipe-shaped position. The metal pipe used in the processing method according to the present invention has a diameter of 56.0 mm and a wall thickness of 1.2.
mm is a 30K-grade carbon steel pipe, R1 ^{`=</sup> 120mm × θ
The pre-bending process is performed at 1 ′ = 36 degrees and R2 ′ = 100 mm × θ2 ′ = 42 degrees. However, the axis of the steel pipe at the connecting point 9 coincides with that of the molding die. R1 <sup>`} > R1
And R2 ′> R2, and θ1 ′ <θ1 and θ
Since 2 ′ <θ2, the neutral axis of the bending of the steel pipe is deviated more inward than the neutral axis of the bending of the molding die. As a result, according to the processing method of the present invention, the steel pipe according to the present invention has The final shape was obtained with good accuracy by adhering to the molding die.

[0019]

As described above, according to the present invention, the strain state generated by the pre-bending process is made milder by devising a pre-bending design method, and the pre-bending shape is reduced in the axial pressing process. The shape is such that the distortion is dispersed as a whole, so that a pipe expansion or bulging process having a bent shape, which was impossible in the past, has become possible at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an axial pressing method according to the present invention for forming a bent mushroom mold using a pre-bent metal tube.

FIG. 2 is a cross-sectional view showing a bending axis of a forming die and a bending axis of a metal pipe in the shaft pressing method according to the present invention for forming a two-type bent connected mushroom mold.

FIG. 3 is a cross-sectional view showing an axial pressing method according to the present invention for forming a bent branch bulging die using a pre-bent metal tube.

FIG. 4 is a perspective view showing a conventional pipe expansion type axial pressing method.

FIG. 5 is a perspective view showing a conventional bulging-type axial pressing method.

FIG. 6 is a cross-sectional view showing a conventional axial pressing method of forming a bent mushroom mold using a pre-bent metal tube.

FIG. 7 is a cross-sectional view showing a conventional axial pressing method for forming a bent branch bulging die using a pre-bent metal pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cavity part 2 Molding die 3 Hydraulic pressure supply hole 4 Axle press fitting 5 Central part (expansion range in expansion pipe pushing method) 6 Narrow tube part (non-expansion range in expansion pipe pushing method) 7 Outside molding die 8 Inside surface of molding die 9 Bending continuous contact

Claims (4)

[Claims] 1. A pre-bent metal tube is set in a molding die, and the end surface is axially pressed while applying a hydraulic pressure to the inside of the metal tube to form a predetermined bent shape. A pre-bent shaft pressing method using a metal tube pre-bent so that the neutral axis of the bend is located closer to the center of curvature than the neutral axis of the bent shape. 2. The method according to claim 1, wherein a metal pipe pre-bent in an arc shape is used. 3. The method according to claim 2, wherein the bending of the shape obtained by molding is a circular arc. 4. The radius of curvature of a pre-bent metal tube is defined by the radius of curvature R of the shape obtained by molding.
4. The pre-bending axial pressing method according to claim 3, wherein the value is 1.05R to 1.25R.