JP2002045922A - Hydroforming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method to hydroform a tube stock of a round cross section to a square cross section without developing a crack at a corner part. SOLUTION: The tube stock 2 having a round cross section is set into a split type die 1 having an inner face of a square cross sectional shape, in the case of conducting hydroforming, the tube stock 2 is preformed to narrow/long in a die clamping direction and is set to be pressed in die clamping. By this method, the tube stock 2 is bulged toward corner parts of the die 1 in the case of completing die clamping, thus, a crack in hydroforming is prevented.

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 material pipe, and more particularly to a method for hydroforming a material pipe having a round cross section into a product having a square cross section. Things.

[0002]

2. Description of the Related Art Hydroforming is a method in which a material tube set inside a mold is expanded by axially pressing while applying liquid pressure to the inside of the material tube, and formed into a shape conforming to the internal shape of the mold. It is. In this processing method, the material tube is first set inside a split mold, and after clamping, the shaft pressing tool is applied to the end of the tube, and the shaft is pressed while applying liquid pressure to the inner surface of the material tube.

[0003] However, many of the product shapes required in this hydroforming process are square in cross section, while the material pipes used are often round in cross section. Not easy. For example, as shown in FIG. 6, if the cross-sectional shape of the mold 1 is a square and the cross-sectional shape of the raw material tube 2 is a circle inscribed therein, even if the raw material tube 2 is hydroformed to a square shape, In many cases, cracks occur at the corners, and it is not easy to form the final shape. The reason is,
This is considered to be because the degree of deformation when the material is deformed to the corner 3 of the mold 1 exceeds the limit degree of deformation of the material tube 2.

In view of the above, conventionally, a required degree of deformation has been reduced by forming a large corner R on the corner 3 of the mold 1, lubrication of the contact surface between the mold 1 and the material pipe 2 has been devised, Various devices have been devised, such as making the device more easily deformable. However, there is a limit to the approach from the lubrication surface, and the change of the angle R and the material itself are often limited by the product specifications, so that there is also a limit. Therefore, conventionally, it has been extremely difficult to hydroform a round material tube until it becomes square in cross section.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and hydroforms a round-shaped material tube until it becomes square in cross-section without causing cracks in the corners. It was done to provide a way to do that.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a material pipe having a round cross section inside a split mold having an inner cross section having a square cross section. In the hydroforming method, which is set, clamped, and axially pressed while applying liquid pressure to the inner surface of the material tube, it is characterized by using a material tube that is elongated and pre-processed in the mold clamping direction so that it is pressed at the time of mold clamping. Is what you do. In addition,
It is preferable that the cross-sectional shape of the pre-processed material pipe is elliptical, and that the circumference of the pre-processed material pipe is equal to the inner circumference of the mold corresponding to the position. Is preferred.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in more detail with reference to embodiments. As shown in FIG. 1, in the present invention, the material pipe 2 having a circular cross section is pre-processed to be elongated vertically so that the cross section becomes elliptical in the previous step, and
Is set in a split mold 1 as shown in FIG. Mold 1
Has a square cross-sectional shape on the inner surface, and in this embodiment, has a square cross-sectional shape with one side L in the mold clamping state. The material tube 2 is set in the mold 1 such that the major axis a of the pre-processed ellipse coincides with the mold clamping direction.

The material pipe 2 is pre-processed so that the length of the major axis a is longer than L so as to be pressed at the time of mold clamping. The present invention has no effect unless the pre-processed material pipe 2 has a certain degree of ellipse, and if it is too elliptical, it induces buckling when closing the mold. Generally, a large effect can be expected when the ellipticity (ratio of major axis / edge diameter) is in the range of 1.2 to 2.0.

When the mold clamping is started from this state, the top portion 4 of the material tube 2 is pressed, and at the same time, the material tube 2 gradually expands in the lateral direction and comes into contact with the inner side walls on both sides of the mold 1. However, if the top portion 4 of the material tube 2 is further pressed by the mold clamping, the material tube 2 cannot be further deformed in the lateral direction, and is still restrained by the frictional force at the top portion 4 and the contact points 5 on both sides. As shown in FIG. 4, the mold 1 is gradually bent toward the corner 3 of the mold 1. FIG. 3 shows a state in which the mold clamping is completed.
It is assumed that the length of the major axis a of the raw material tube 2 at the time of pre-processing is determined so that the mold clamping is completed in the state described above.

[0010] When the mold clamping is completed in this manner, the blank 2 is then axially pushed by a shaft pressing tool while applying liquid pressure to the inner surface thereof by a conventional method, and subjected to hydroforming until it conforms to the internal shape of the mold 1. You. During the hydroforming, the deformation starts from the mold clamping state A in FIG. On the other hand, if the material pipe 2 remains circular, the length of contact with the upper, lower, left and right inner surfaces of the mold 1 increases with clamping as shown in FIG. 5, but the middle part thereof is relatively flat. The state is maintained, and the deformation of the hydroforming process starts from the mold clamping state B in FIG.

The local expansion rate at the start of the hydroforming process (the ratio Y / X of the peripheral length X of the non-contact portion of the material pipe sandwiched between the contact points and the corresponding peripheral length Y of the inner surface of the mold). In the mold clamping state B in FIG. 5, the local expansion ratio was calculated to be 1.22 by focusing only on the non-contact portion, whereas the mold clamping state B in FIG. In the state A, it was 1.18 because there was almost no non-contact portion.

In general, the critical expansion ratio of carbon steel pipe is 1.2.
In many cases, the hydroform from the state B based on the conventional method causes cracking, whereas the hydroform from the state A according to the present invention successfully completes the molding. Can be done. For reference, for a circular material tube cross-section (C in FIG. 6 or FIG. 5) that can be fitted in a mold in advance, 1/4 circumference =
2πL / 4 = 1.57L and 1/4 inner circumference of the mold =
Since it is 2L, the local expansion rate is 2L / 1.57L = 1.
27, which is out of the question.

As described above, according to the present invention, the material tube 2 which is elongated in the mold clamping direction so as to be pressed at the time of mold clamping is used, and the material tube 2 is directed toward the corner 3 of the mold 1 when the mold clamping is completed. If 2 is overhanged, the local pipe expansion rate at the start of hydroforming can be made smaller than before. As a result, it is possible to reliably prevent the occurrence of cracks during the hydroforming process.

Note that the concept of the local expansion ratio used here is newly proposed by the present inventor,
This is a design concept that has not existed in the past in that it considers the expansion ratio of only a local section sandwiched between the contact points between the mold and the material pipe.

[0015]

As described above, the hydroforming method according to the present invention uses a material pipe that is pre-elongated in the mold clamping direction so as to be pressed at the time of mold clamping.
At the time of completion of the mold clamping, the material pipe is made to protrude toward the corner of the mold, thereby making it possible to prevent the occurrence of cracks during the hydroforming process. For this reason, there is an advantage that it is possible to mold even a square product shape which could not be processed conventionally.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a pre-processing step of a material pipe.

FIG. 2 is a sectional view showing a state in which a pre-processed material tube is set in a mold.

FIG. 3 is a cross-sectional view showing a clamped state.

FIG. 4 is a diagram showing a deformed state of a material tube at a corner of a mold.

FIG. 5 is a diagram showing a deformed state at a corner of a mold when the material pipe has a circular cross section or a cross section close to a circular shape.

FIG. 6 is a sectional view showing a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Material tube 3 Corner part 4 Top part 5 Side contact point

Claims (3)

[Claims] 1. A material tube having a round cross-sectional shape is set inside a split mold having an inner surface having a square cross-sectional shape, the mold is clamped, and a shaft is formed while applying liquid pressure to the inner surface of the material tube. In a hydroforming method for pressing, a material pipe which is elongated and pre-processed in a mold clamping direction so as to be pressed at the time of mold clamping is used. 2. The hydroforming method according to claim 1, wherein the cross section of the pre-processed material pipe is elliptical. 3. The hydroforming method according to claim 1, wherein a peripheral length of the pre-processed material tube is equal to an inner peripheral length of a mold corresponding to the position.