JP2002028734A - Hydroform process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydroform process capable of achieving the hydroform without generating any cracks even when the internal shape of a die is not uniform. SOLUTION: When the internal shape of the die 1 is non-uniform, the imbalance of the local expansion ratio determined by the contact condition of an inner surface of the die with tube stock 2 in a seamed condition is mitigated by moving a split surface 8 of the die 1 to the side of the higher local expansion ratio. The local expansion ratio is determined as the ratio dB/dA of the non- contact circumferential length dA of the tube stock held by contact points between the tube stock 2 and the die 1 to the inner circumferential length of the die corresponding thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydroforming method using a metal tube.

[0002]

2. Description of the Related Art There has been known a hydroforming method in which an end face of a material tube set in a mold is axially pushed while applying liquid pressure to the inner surface. In this working method, the material pipe is first set inside a split mold, and after being clamped, axial pressing is performed while applying liquid pressure to the inner surface of the material pipe with an axial pressing tool.

Conventionally, a mold for hydroforming is usually divided at the center, and even if there is a rare case where the divided surface is biased, it is unavoidably deformed due to a product shape such as piercing holes. It was. However, when the inner surface shape of the mold 1 with the divided surface at the center of the mold is uneven vertically as shown in FIG. 3, for example, a material pipe 2 having a circular cross section is set therein and hydroforming is performed by a standard method. At the lower corners.

[0004] The theoretical elucidation of the hydroforming process has just begun, and the cause of cracking has not been completely elucidated. It is considered that cracks occur. Originally, three-dimensional distortion should be adopted as the degree of deformation, but since measurement and calculation are extremely difficult, the concept of expansion ratio has been recently used for simplicity. The pipe expansion ratio is a value defined as a ratio B / A of the total circumference A of the material pipe in a certain cross section and the total inner circumference B of the mold (that is, the product circumference) corresponding thereto. The critical expansion ratio is a value defined as an elongation ratio Bc / Ac until a raw material tube having a circumferential length Ac uniformly expands in the circumferential direction to reach a circumferential length Bc at which one of the circumferences breaks. . That is, recently, design has been performed so that B / A is not larger than Bc / Ac.

However, in the example shown in FIG. 3, cracks may occur even though the expansion ratio is smaller than the limit expansion ratio, and no effective preventive measures have been found so far. .

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned conventional problems and to complete hydroforming without cracking even when the inner surface of the mold is uneven. It was done to provide a way to do that.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention sets a material pipe in a split mold, clamps the material, and applies a liquid pressure to the inner surface of the material pipe. In the hydroforming method of axial pressing, the use of a mold whose divided surface has been moved from the center of the mold allows the imbalance of the local expansion rate determined by the contact state between the mold inner surface and the material pipe when the mold is clamped. Is alleviated. The local pipe expansion ratio is defined as a ratio dB / d between the uncontacted peripheral length dA on the material pipe sandwiched between the contact points between the material pipe and the mold and the corresponding mold inner peripheral length dB.
It is preferable to use the value defined as A.

Before describing the embodiment of the present invention, a new concept, local expansion ratio, will be described. It is a fact that hydroforming has been known through lubrication and the like that processing proceeds while a material tube contacts a mold, and when the contact state changes, the workability also changes. However, the conventional design guideline of the expansion ratio cannot consider the contact state between the material pipe and the die, so it must be said that this point has a fatal defect. This is simply because it is difficult to take into account the contact situation. Therefore, in the present invention, instead of directly considering the contact state, the contact state is considered by using the new concept of local pipe expansion rate and by considering the width, length, or shape of the non-contact portion generated by the contact. It was to be.

For example, in the case of FIG. 3, the material pipe 2 and the mold 1 are connected to four contact points 11, 12, 1 by performing mold clamping.
If the contact occurs at 3, 14, even if the lubricant is used successfully, the frictional force at the contact position becomes considerably large.
It is reasonable to consider that the contact position on the material tube does not move during the processing after mold clamping. Therefore, in the area surrounded by such a contact point, the deformation during processing is completed within that area,
No material is supplied from outside the range, and no material is supplied to other ranges. Therefore, the pipe expansion ratios (the uncontacted circumference dA on the material pipe and the corresponding inner circumference of the mold) are considered locally between 11-12 and 11-14 and between 12-13 and 13-14. The ratio to the length dB (dB / dA) is calculated and used as the local tube expansion rate.

In this example, dA and d above the center
The local expansion rate is relatively small because B is close, but the local expansion rate is clearly large because dB is large on the lower side. As a result, when hydroforming is performed from the mold-clamped state in FIG. 3, the material pipe 2 may be slightly expanded in sections 11-12 and 11-14.
In the section (1), the material pipe 2 must be greatly expanded before reaching the inner surface of the mold 1, so that the supply of the material becomes insufficient and cracks occur. As described above, since the portion where the local expansion ratio is large in the mold-clamped state is likely to be a source of cracks, the present invention seeks to equalize the local expansion ratio by a new idea of reviewing the mold division position. It was done.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a view showing a first embodiment of the present invention.
The upper mold 5 is provided with an inclined portion 7 on the inner surface thereof. Although the material pipe 2 is a vertically elongated steel pipe, if the mold is normally clamped as a center split type, the local pipe expansion rate becomes unbalanced as described in FIG. .

Therefore, as shown in FIG. 1, in this embodiment, the dividing surface 8 of the mold 1 is moved to the lower side where the local expansion ratio is large. First, in the state of FIG. 1A, three of the contact points 11, 12, 13, and 14 between the material pipe 2 and the mold 1 are on the upper mold 5 side, and the contact point on the lower mold 6 side is 13 Only one point.

As a result, the contact points 11, 1 on the upper mold 5 side
In the section sandwiched between 2 and 14, the material pipe 2 is restrained by frictional force, and the distance between each contact point is constant.
As shown in FIG. 1B, the material pipe 2 does not deform much even when the mold clamping proceeds. However, since the distance between the contact points changes on the lower mold 6 side, the lower part of the material pipe 2 is deformed toward both outer sides, and in the state C where the mold clamping is completed, the lower mold 6
The contact area with the contact is greatly expanded.

In the state of FIG. 1C, the contact points 15, 1
The local expansion ratio between the sections 6 is considerably smaller than that in the case of FIG. 3, and there is no longer a risk of cracking even if the hydroforming process in which axial pressing is performed while applying liquid pressure to the inner surface of the material pipe is started. As described above, in the first embodiment, by moving the divided surface 8 of the mold 1 to the lower side where the local expansion ratio is large, the imbalance of the local expansion ratio at the time of completion of the mold clamping is reduced, and the occurrence of cracks is reduced. Can be prevented.

(Second Embodiment) FIG. 2 is a view showing a second embodiment of the present invention. In this embodiment, the mold 1 is of a split type comprising an upper mold 5 and a lower mold 6, and an R portion 9 is provided on a left inner surface of the upper mold 5 and a right inner surface of the lower mold 6. Have been. The material pipe 2 is a slightly vertically long steel pipe. In this case, the contact point between the material 2 and the mold is indicated by A in FIG.
As shown in the figure, there are four points of 11, 12, 13, and 14,
In the sections 11-14 and 12-13 on the side where the R portion 9 is located, the local pipe expansion rate is small, but the local pipe expansion rate in the other sections is large. Becomes unbalanced and sections 11-12, 13-14
May crack in

Therefore, in this embodiment, the divided surface 8 of the mold 1 is moved to the upper right and lower left where the local expansion ratio is large. As a result, between the contact points 11 and 14 and between 12 and 13 which are in contact with the same mold, the material 2 is locked, and the material 2 is hardly deformed as described above. However, since the distance between the contact points 11-12 and 13-14 becomes smaller as the mold clamping progresses, the upper right and lower left sides of the material pipe project outward as shown in FIGS. 2B and 2C.

In the state of C, the contact points 11-12, 1
Since the local pipe expansion ratio between 3 and 14 is small, even if the hydroforming process in which axial pressing is performed while applying liquid pressure to the inner surface of the material pipe is started, there is no longer a risk of cracking. As described above, in the second embodiment, the dividing surface 8 of the mold 1 is used.
Is moved to the upper right side and the lower left side where the local pipe expansion rate is large, the imbalance of the local pipe expansion rate at the time of completion of the mold clamping can be alleviated, and the occurrence of cracks can be prevented.

[0018]

As described above, according to the present invention, even when the inner surface shape of the mold is uneven, a new method of moving the divided surface from the center of the mold in accordance with the distribution of the local pipe expansion ratio is provided. It has succeeded in alleviating the imbalance in the local pipe expansion rate when the mold is clamped, and preventing the occurrence of cracks during the hydroforming process. ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to shape | mold the shape which could not be shape | molded conventionally, and there exists an advantage that a defect generation rate can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention,
A shows a state before mold clamping is started, B shows a state during mold clamping, and C shows a state at the time of mold clamping completion.

FIG. 2 is a sectional view showing a second embodiment of the present invention,
A shows a state before mold clamping is started, B shows a state during mold clamping, and C shows a state at the time of mold clamping completion.

FIG. 3 is a cross-sectional view showing a conventional technique, wherein A shows a state before mold clamping is started, and C shows a state when mold clamping is completed.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 material pipe 5 upper mold 6 lower mold 7 inclined section 8 division surface 9 R section 11 contact point 12 contact point 13 contact point 14 contact point 15 contact point 16 contact point

Claims (2)

[Claims] 1. A material tube is set inside a split mold,
In the hydroforming method in which the mold is clamped and the inner surface of the material tube is axially pushed while applying liquid pressure, the mold inner surface and the material tube when the mold is clamped are used by using a mold whose divided surface is moved from the center of the mold. A hydroforming method characterized by alleviating an imbalance in a local pipe expansion rate determined by a contact state with a pipe. 2. The local expansion ratio is a ratio dB / dA between a non-contacting perimeter dA on the raw pipe sandwiched between contact points of the raw pipe and the die and a corresponding inner peripheral length dB of the die. The hydroforming method according to claim 1, wherein a value defined as