JP2002143938A - Method and apparatus for expanding and forming pipe body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for expanding and forming a pipe body which is formed in one stroke using a general purpose press. SOLUTION: After filling up liquid 10 inside the pipe body 2, by further injecting the liquid 10 into the inside while compressing the pipe body 2 in the axial direction, the middle part 2b is expanded with axial force and hidraulic pressure with both end parts 2a of the pipe body 2 left in the size of a base stock. Next, by pressing the middle part 2b expanded with the liquid sealed inside the pipe body 2 from the outside, the pipe body is formed into a desired shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for expanding a pipe in which a central portion is expanded and formed into a desired shape while keeping both ends of the pipe at the same material size.

[0002]

2. Description of the Related Art As shown in FIG. 9, a dead axle case 1 used for a truck or the like is an axle case other than a drive axle in a tandem axle vehicle, and both end portions 1a have a round cross section and a central portion 1b is enlarged. It has a hollow structure with a square cross section. The dead axle case 1 usually includes two parts (parts formed by press-forming the central part of the case 1 into a U-shaped cross section and both end parts having a semi-circular cross section). It is manufactured by welding it against each other. The plate thickness is 10 to 12 mm and the length is 1.5
Many are ~ 1.8m.

Recently, the dead axle case 1 is shown in FIG.
Attempts have been made to form by a hydroforming method as shown in FIG. In this method, first, as shown in FIG. 7A, a round pipe body 2 is set in upper and lower split dies 3, 4 (die). These split molds 3 and 4
In order not to open during the processing of the hydroform, it is clamped between the upper base 5 and the lower base 6 with a force of 7000 tons or more as described later. This clamping force indicates the capability of the hydroforming device. Then, axial force punches 7, 7 for applying a compressive force in the axial direction by an axial force cylinder (not shown) are set at both ends of the pipe body 2. An injection passage 9 for injecting the liquid pressurized by the high-pressure pump 8 into the inside of the pipe body 2 is formed in the axial force punch 7. The axial force punch 7 also has a function of sealing the opening at the end face of the pipe body 2 so that the liquid 10 filled therein does not leak.

By controlling the axial force applied to the pipe body 2 by the axial force punch 7 and the hydraulic pressure in the pipe body 2 by the high-pressure pump 8, as shown in FIG. The central portion is expanded while keeping the size of the material, and pressed against the inner surfaces of the split dies 3 and 4 to form the dead axle case 1 shown in FIG. According to this method, the molded hydroformed product (dead axle case 1)
Since there is no welded portion, the strength is advantageous, and the thickness can be made thinner than that of a conventional welded product, which leads to weight reduction and cost reduction.

[0005]

However, in the above-mentioned hydroforming method, since it takes time to increase the liquid pressure inside the pipe body 2, the molding tact is basically slow. Further, the high-pressure pump 8 for supplying pressure is expensive.

In order to accurately transfer the shape of the central portion 1b of the hydroform product (dead axle case 1) to the shape of the inner surfaces of the split dies 3 and 4, the hydraulic pressure in the pipe body 2 must be extremely high. The central portion of the expanding pipe body 2 must be strongly pressed against the inner surfaces of the split molds 3 and 4. For this reason, the clamping force is increased, and a hydroforming device having a large capacity is required.

In particular, when a dead axle case 1 as shown in FIG. 9 is formed, as shown in FIG. 8, the central portion of the pipe 2 needs to be formed from a round shape into a small corner of a round shape. Must be pressed strongly against the corners of the inner surfaces of the split dies 3 and 4, and the thickness of the pipe body 2 (10 to 12 mm) is also thick. It needs to be raised. Therefore, a mold clamping force of 7000 tons or more is required.

[0008] Such a hydroforming apparatus having a large clamping force (capacity) is very expensive and has a limited demand. When the cost of the hydroforming device is compared with that of the press machine, the hydroforming device has the same capacity (the clamping force of the hydroforming device and the press load of the pressing machine), and is 1.5 to 2 times as expensive as the pressing machine.
In addition, a typical hydroforming apparatus has a class of 3500 tons in many cases, and a large-sized apparatus generally has 5000 tons.

On the other hand, when the dead axle case 1 is formed by hydroforming, as described above, 7000
Although an apparatus of more than ton is required, there are very few products originally suitable for hydroforming, and much less product types that need to be formed by a very large apparatus of more than 7,000 ton. It is sufficient that the operation load is satisfied as a dedicated device only for the dead axle case, but if there is not such a quantity, the operation rate of the device becomes worse, which leads to an increase in product cost.

An object of the present invention, which has been made in view of the above circumstances, is to provide a method and an apparatus for expanding a pipe, which can be formed in one stroke by using a general-purpose press machine.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, a method for expanding a pipe body according to the present invention comprises the steps of: filling a pipe body with a liquid; compressing the pipe body in an axial direction; The central part is expanded by axial force and liquid pressure while the both ends of the pipe body are kept in the raw material dimensions, and then the central part expanded while the liquid is sealed inside the pipe body is removed by injecting the liquid into the pipe body. It is designed to be pressed from one side and formed into a desired shape.

Further, a pipe is horizontally disposed between an upper table and a lower table of the press apparatus, and both ends of the pipe are interposed between a pair of holders which are horizontally adjacent to each other in conjunction with the proximity of the upper table and the lower table. While holding and sealing, the pipe body sandwiched between the holders is compressed in the axial direction by bringing the upper table and the lower table close to each other while the pipe body is filled with the liquid, and at the same time, contracted by the proximity of the upper table and the lower table. The liquid discharged from the piston-cylinder mechanism is guided inside the pipe body, and the central part is expanded by the axial force and the liquid pressure while the both ends of the pipe body are made the material dimensions, and then the pipe body is inserted into the pipe body. With the liquid enclosed, the upper and lower bases are further brought close to each other, and the dies attached to the upper and lower bases are pressed against the central part of the expanded pipe body to form.

According to these methods, a round pipe body as a raw material can be formed into a dead axle case having a square cross section at the center while keeping both ends of the raw material diameter.

[0014] The pipe expansion apparatus for pipes according to the present invention is an apparatus for expanding pipes for forming a pipe into a desired shape by expanding a central portion of the pipe body while keeping both ends of the pipe as raw materials. A pair of holders provided between an upper base and a lower base of the press device and horizontally adjacent to each other in conjunction with their proximity, a pipe body whose both ends are sealed and held between these holders, A piston-cylinder mechanism that is provided between the lower base and pressurizes the liquid in accordance with their proximity, and a pressurizing pipe that guides the liquid pressurized by the piston-cylinder mechanism into the inside of the pipe body sealed by the holder. When,
A mold that is attached to the upper base and the lower base, respectively, and presses and forms the central part of the pipe expanded by the axial force and the hydraulic pressure while keeping the both ends at the material dimensions in accordance with the proximity of the upper base and the lower base. It is provided with.

Further, a cam mechanism may be provided between the upper table and the lower table of the press device and moves the pair of holders in the horizontal direction in conjunction with their proximity.

According to these devices, it is possible to form a dead axle case in which a round pipe body as a raw material has a square cross-section at the center while keeping both ends of the raw material diameter.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the accompanying drawings.

The pipe expanding apparatus shown in FIGS. 1 to 3 is for forming the dead axle case 1 shown in FIG. As shown in FIG.
Between the 2 (punch) and the lower table 13 (bed), there is provided a pair of holders 14 and 14 which approach in the horizontal direction in conjunction with the proximity of the upper table 12 and the lower table 13. These holders 14, which hold the round pipe body 2 as a material, engage with a groove 15 formed in the lower base 13 and move in the horizontal direction.

Each of the holders 14 has a straight hole 16 formed into an inner diameter where the outer diameter of the pipe body 2 just fits, and a tapered portion 1c of the dead axle case 1 shown in FIG. Transferred tapered hole 1
And 7. The straight holes 16 hold the openings at both ends of the pipe body 2 in a liquid-tight manner as described later.
Each of the holders 14 is adapted to approach in the horizontal direction with the approach of the upper table 12 and the lower table 13 by the cam mechanism 18.

The cam mechanism 18 has a first inclined surface portion 18 formed on the side surface of each of the holders 14, 14 so as to form an upper pot.
a, and a second die formed on the upper mold 19 provided on the upper base 12 so as to spread downward in accordance with the first inclined surface portion 18a.
The holders 14 and 14 are brought close to each other by the proximity of the upper table 12 and the lower table 13 as shown in FIG. The adjacent holders 14 and 14 abut against the side surface 20a of the lower mold 20 provided on the lower base 13, and the proximity is regulated. That is, the side surface 20a of the lower mold 20 serves as a stopper.

Between the upper table 12 and the lower table 13, there is provided a piston / cylinder mechanism 21 for pressurizing the liquid 10 in accordance with their proximity. Piston / cylinder mechanism 21
Is a cylinder 22 provided on the lower base 13, a block 23 provided on the upper base 12, a piston 24 pressed downward by the block 23, and a liquid pressurized by the piston 24 received and lowered in the cylinder 22. 10 (water, oil, etc.).

Between the cylinder 22 and the holder 14, the liquid 10 pressurized due to the proximity of the upper table 12 and the lower table 13
Is provided in the pipe body 2 sealed by the holder 14. A relief pipe 26 is connected to the pressurizing pipe 25, and a relief valve 27 is provided in the relief pipe 26. Relief valve 27
Regulates the hydraulic pressure inside the pipe body 2 to a predetermined relief pressure.

According to this configuration, when the upper base 12 shown in FIG.
Due to the axial force of the holders 14 and 14 which are horizontally adjacent to each other and the hydraulic pressure of the liquid 10 injected from the piston / cylinder mechanism 21, the straight holes 16 of the holder 14 are formed.
The central portion 2b is held at both ends 2a held in
Is expanded from the circular cross section shown in FIG. 3 (a) to the elliptical cross section shown in FIG. 3 (b).

At this time, the capacity and number of the piston / cylinder mechanism 21 for injecting the liquid 10 into the inside of the hype body 2 are determined by the internal volume of the pipe body 2 as a material and the dead axle case 1 as a finished product. Any number may be used. Then, as shown in FIG. 3 (b), the central portion 2b of the pipe body 2 expanded into an ellipse is pressed by the upper mold 19 and the lower mold 20 provided on the upper base 12 and the lower base 13, respectively.
The finished product (dead axle case 1) shown in FIG. 9 is formed into a square shape at the central portion 1b.

The lower mold 20 is shown in FIGS. 1, 2 and 3 (a),
As shown in FIGS. 9 (b) and 9 (c), the finished product (dead axle case 1) shown in FIG. 9 has a square groove-like concave portion 20a to which the square lower surface and both side surfaces of the central portion 1b are transferred. As shown in FIG. 2, both end edges of the concave portion 20a are formed so as to be smoothly connected to the opening of the tapered hole 17 of the holder 14 when the holder 14 comes into contact with the side surface 20a (stopper) of the lower mold 20. Have been.

On the other hand, the upper mold 19 is
0a has a convex portion 19a fitted from above. Convex part 19a
The upper surface shape of the central portion 1b of the completed product (dead axle case 1) shown in FIG. As shown in FIG. 2, the lower end edge of the convex portion 19 is completed when the operation of approaching the upper base 12 to the lower base 13 is completed, that is, the press is operated to the bottom dead center, and the holders 14 and 14 20a (stopper), the taper hole 17 of the holder 14
Is formed so as to be smoothly connected to the opening.

As shown in FIG. 1, the inside of the pipe 2 sandwiched between the holders 14 and 14 is previously filled with a liquid 10 (water, oil, etc.) in the state shown in FIG. Is installed. The filling pipe 28 is connected to a liquid tank (not shown) and a pressure pump, and is provided with an on-off valve 29.

A method for expanding a pipe using the above-structured apparatus for expanding a pipe will be described.

First, as shown in FIG. 1, a round pipe 2 as a raw material is sandwiched between a pair of holders 14 and 14. This holding is realized by moving the upper base 12 further upward than the position shown in FIG. 1 and further separating the holders 14 and 14 along the groove 15 formed in the lower base 13. next,
The inside of the pipe 2 is filled with the liquid 10 (water, oil, etc.) via the filling pipe 28, and when the inside of the pipe 2 is filled with the liquid 10, the on-off valve 29 is closed, and the inside of the pipe 2 is filled with the liquid. 10 is closed.

Then, the upper table 12 (ram) is brought close to the lower table 13 (bed). Then, the respective holders 14 and 14 are brought close to each other by the cam mechanism 18 and the piston
The pressurized liquid 10 generated by the cylinder mechanism 21 is injected into the pipe body 2 through the pressurized pipe 25. At this time, when the holders 14 that move in the axial direction start to strongly hit the open end of the pipe 2, the open end is sealed, and the liquid 10 is completely sealed inside the pipe 2. Therefore, thereafter, the internal hydraulic pressure of the pipe body 2 increases as the upper table 12 approaches the lower table 13.

Then, the deformation of the pipe body 2 starts due to the rise of the liquid pressure inside the pipe body 2 and the axial force by the holders 14 and 14. More specifically, the pipe body 2 has only the central portion 2b housed in the square groove-shaped concave portion 20b of the lower mold 20 while the both end portions 2a inserted into the straight holes 16 of the holder 14 remain the material dimensions (material diameter). However, as shown in FIG. 3 (b), the material gradually expands and expands to an elliptical cross section as the pressure increases from the material state (circular cross section) of FIG. 3 (a).

The pressure required for this deformation depends on the diameter, wall thickness, material strength and the like of the pipe body 2. Therefore, if the predetermined pressure value P1 is previously obtained by an experiment, calculation, or the like, and the predetermined pressure value P1 is set to the relief pressure of the relief valve 27, the central portion 2a of the pipe body 2 is moved to the position shown in FIG.
3 can be expanded and expanded to a desired state (the state shown in FIG. 3B) without excessive expansion.

In this embodiment, the high pressure pump 8 (expensive) as shown in FIG. The liquid 10 is injected into the pipe body 2 from the piston / cylinder mechanism 21 by the lowering of the upper base 12, and the pipe body 2 is compressed in the axial direction by the holders 14 and 14 adjacent to each other to reduce the internal volume. This is because the internal pressure of the body 2 is increasing. Then, the internal pressure of the pipe body 2 is limited to the predetermined pressure value P1 by the relief valve 27.

After that, the upper table 12 is brought closer to the lower table 13. Then, as shown in FIG. 3 (b), the projection 19a of the upper mold 19 is placed on the upper part of the central portion 2b of the pipe 2 deformed into an elliptical cross section in the square groove-shaped recess 20b of the lower mold 20.
Then, as shown in FIG. 3 (c), the central portion 2b of the pipe body 2 deformed into an elliptical cross section while the liquid 10 is sealed inside the pipe body 2 It is pressed (rest-like) by the mold 20 and formed into a square shape of the central portion 1b of the completed product (dead axle case 1) shown in FIG.

Here, as shown in FIG.
Center portion 2 of the pipe body in which the convex portion 19a is expanded in an elliptical cross section.
The timing of contact with the upper part of b is such that the pipe body central portion 2b expanded into an elliptical cross-section is appropriately formed into a predetermined angular cross-sectional shape at the bottom dead center of the press as shown in FIG. 3 (c).
It is predetermined in consideration of the amount of axial compression of the pipe body 2 according to the angles of the inclined surfaces 18a and 18b of the cam mechanism 18, and the like.

Thereafter, as the lowering of the upper table 12 to the lower table 13 progresses, the pipe body central portion 2b expanded to have an elliptical cross section.
The work (hereinafter, referred to as a work) is pressed (restrike) by the upper mold 19 and the lower mold 20 in a state where the liquid 10 is sealed therein, and is compressed in the axial direction by the holders 14 and 14 adjacent to each other. By being pressed against the inner surface of the concave portion 20b of the mold 20 and the lower surface of the convex portion 19a of the upper mold 19, the radius of the corner is reduced and the corner is deformed into a square cross section.

The hydraulic pressure in the work 2b at the time of this restric- tion is determined by the pressing force of the upper and lower dies 19, 20 and the pressure of the holder 1.
As long as the pressure P2 is such that the workpiece 2b does not buckle as shown in FIG.
As shown in FIG. 3B, the pressure P1 when expanding and expanding the pipe body 2 (material) shown in FIG. Therefore, at this time, if the relief pressure of the relief valve 27 is changed from P1 to P2, the press load can be suppressed accordingly.

It should be noted that, even if the liquid pressure in the work 2b at the time of restriking is higher than the required minimum pressure P2, there is no problem in molding. Therefore, the relief valve 27 is switched from P1 to P2 by 2
Instead of the step control, one-step control of only P1 may be performed. In addition, at the time of this restriking, the work 2b in the portion facing the tapered hole 17 in the holder 14 is also expanded and expanded and pressed against the tapered hole 17, and its shape is transferred.

As a result, the pipe body 2 (material) shown in FIG.
Makes the holder 1
2, the portion facing the tapered hole 17 is deformed into a tapered shape, and the central portion 2b facing the upper and lower dies 19 and 20 while the both end portions 2a inserted into the straight holes 16 of FIG. Is deformed into a tube having an enlarged diameter and is formed into a dead axle case 1 (completed product) shown in FIG.

Here, in the forming by the hydroform shown in FIG. 7, the pipe body 2 is expanded by the internal liquid pressure by the high-pressure pump 8 and the axial force by the axial force punches 7, 7 to form the upper and lower split dies 3, 4. While a high internal pressure is required because it is pressed against the inner surface and molded, the method according to the present embodiment requires:
After the pipe body 2 is expanded and expanded to some extent by the internal hydraulic pressure of the piston / cylinder mechanism 21 and the axial force of the holders 14, 14, the work 2b is pressed by the upper and lower dies 19, 20 while the liquid is sealed inside. It does not require high pressure because it is restriated.

That is, the dead axle case 1 shown in FIG. 9 (plate thickness: 10 to 12 mm, length: 1.
5 to 1.8 m), the hydroforming method shown in FIG. 7 requires a clamping force of 7000 tons or more as described above, but the method according to the present embodiment requires 400 tons or more.
A press load of about 0 ton is sufficient. Therefore, the construction method according to the present embodiment is a general-purpose press machine (4000 ton class).
It can be realized by using

That is, if a 4000 ton class press machine is owned, the upper die 1 shown in FIG. 1 is placed on the upper base 12 (ram) and lower base 13 (bed) of the press machine.
9, the lower mold 20, the holders 14, 14, the piston cylinder mechanism 21 and the like need only be attached, and it is not necessary to newly invest in equipment. Therefore, this embodiment can be realized at extremely low cost.

Even if a press machine is newly introduced, it can be purchased at a cost of about 1/2 or less of the hydroforming apparatus as described above. In addition, since it is a general-purpose press, it can be used for press molding of products other than the dead axle case 1. Compared with a dedicated hydroforming device, the production volume of the dead axle case does not need to be at least, and there is no need to worry about a decrease in the operation rate of the device. .

In the method according to the present embodiment, molding can be performed by making the press device make one stroke. That is,
With the lowering of the upper table 12 to the lower table 13, the cam mechanism 18 brings the holders 14 and 14 close to each other to apply axial force to the pipe body 2, and the piston / cylinder mechanism 21 pressurizes the liquid 10. The internal pressure is increased by being injected into the inside of the pipe body 2, whereby the central portion 2 b of the expanded and expanded pipe body 2 is provided on the upper base 12 and the lower base 13 in the mold 1.
Since the pressing is performed by the components 9 and 20, the rest alike molding is performed, the dead axle case 1 is automatically molded from the pipe body 2 by one stroke of the press device.

In the method according to the present embodiment, the molding tact is much faster than in the hydroform method shown in FIG. 7, and the productivity is improved. As mentioned in the previous paragraph,
A cam mechanism 18, a piston / cylinder mechanism 21, and dies 19 and 20 are provided between the lower base 13 and the lower base 13, and these are operated in conjunction with each other as the upper base 12 is lowered to the lower base 13. Therefore, the pipe body 2
This is because the hydraulic pressure inside the inside quickly increases.

FIG. 5 shows another embodiment of the present invention.

As shown, this embodiment is different from the previous embodiment only in that the relief valve 27 shown in FIGS. 1 and 2 is replaced with an accumulator 30, and the other configuration is the same as that of the previous embodiment. ing. The accumulator 30 also adjusts the pressure (fluid pressure) in the pipe body 2 to P1, P2
And can be set. This embodiment has the same operation and effect as the previous embodiment.

FIG. 6 shows still another embodiment.

As shown, this embodiment stops the filling pipe 28 shown in FIG. 1 and FIG.
The only difference from the first embodiment is that a liquid tank 31 for filling the liquid inside is provided on the lower base 13. According to this configuration, as shown in FIG.
When the pipe 2 is set in the liquid tank 31
Since the pipe 10 is immersed in the liquid, the inside of the pipe body 2 is filled with the liquid 10. Note that the relief valve 26 in FIG. 6 may be replaced with the accumulator 30 in FIG.

[0050]

As described above, according to the method and apparatus for expanding a pipe according to the present invention, the following effects can be obtained. (1) A product similar to that manufactured by a hydroforming device using a general-purpose press device can be manufactured. (2) It can be formed by a press machine with a capacity (press load) smaller than the capacity (clamping force) of the hydroform machine. (3) Molding tact is faster than hydroform.

[Brief description of the drawings]

FIG. 1 is a sectional side view of a pipe expanding apparatus for a pipe body according to an embodiment of the present invention before operation.

FIG. 2 is a side cross-sectional view after the operation of the pipe expanding apparatus.

FIG. 3 is a cross-sectional view showing an operation state of the pipe expanding apparatus.

FIG. 4 is a cross-sectional view showing a state in which the work has buckled because the internal pressure is too low.

5 is a side view of an apparatus for expanding and expanding a pipe body according to another embodiment of the present invention. FIG. 5 (a) shows a state before operation, and FIG. 5 (b) shows a state after operation.

FIG. 6 is a side view of an apparatus for expanding a pipe body according to still another embodiment of the present invention. FIG.
(b) shows the state after operation.

FIG. 7 is an explanatory view showing a conventional hydroforming method, in which FIG. 7 (a) shows a state before operation and FIG. 7 (b) shows a state after operation.

FIG. 8 is a sectional view taken along the line VII-VII of FIG. 7;

FIG. 9 is a perspective view of a dead axle case as a pipe body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Dead axle case 2 Pipe 2a Both ends 2b Central part 10 Liquid 11 Pressing device 12 Upper base 13 Lower base 14 Holder 18 Cam mechanism 19 Upper mold 20 Lower mold 21 Piston / cylinder mechanism 25 Pressurized piping

Claims (6)

[Claims] After filling the inside of a pipe body with a liquid, a liquid is injected into the pipe body while compressing the pipe body in an axial direction. The pipe body is expanded by axial force and liquid pressure, and then, the liquid is sealed inside the pipe body, and the expanded central part is pressed from the outside to form the pipe body into a desired shape. Tube expansion method. 2. A pipe body is horizontally arranged between an upper base and a lower base of a press device, and both ends of the pipe body are interposed between a pair of holders horizontally adjacent to each other in conjunction with the proximity of the upper base and the lower base. While holding and sealing, the pipe body sandwiched between the holders is compressed in the axial direction by bringing the upper table and the lower table close to each other while the pipe body is filled with the liquid, and at the same time, contracted by the proximity of the upper table and the lower table. The liquid discharged from the piston-cylinder mechanism is guided inside the pipe body, and the central part is expanded by the axial force and the liquid pressure while the both ends of the pipe body are made the material dimensions, and then the pipe body is inserted into the pipe body. Expanding the pipe body characterized in that the upper and lower bases are further brought close to each other while the liquid is sealed, and the dies attached to the upper and lower bases are pressed against the center of the expanded pipe body. Method. 3. A method according to claim 1 or 2, wherein a round pipe body as a raw material is formed into a dead axle case having a square cross section at the center while keeping both ends of the raw material diameter. A method for expanding a pipe body. 4. A pipe-expansion forming apparatus for forming a pipe into a desired shape by expanding a central portion while keeping both end portions of the pipe at a material size, provided between an upper base and a lower base of a press device. A pair of holders approaching in the horizontal direction in conjunction with the proximity, a pipe body whose both ends are sealed and held between the holders, and a pipe body provided between the upper base and the lower base, A piston-cylinder mechanism that pressurizes the liquid, a pressurized pipe that guides the liquid pressurized by the piston-cylinder mechanism into a pipe body sealed with the holder, and attached to the upper base and the lower base, respectively. A pipe which is provided with a mold for pressing and forming a central portion of a pipe body expanded by axial force and hydraulic pressure while keeping both end portions of the material size in accordance with the proximity of the upper base and the lower base. Body tube forming equipment. 5. The pipe expanding device according to claim 4, further comprising a cam mechanism provided between the upper and lower bases of the press device, the cam mechanism moving the pair of holders in the horizontal direction in conjunction with their proximity. Molding equipment. 6. A dead axle case in which a round pipe body as a raw material is formed into a square cross section at a center portion while keeping the both ends of the raw material diameter by the apparatus according to claim 4 or 5. Pipe expansion device for pipes.