JPH0866728A - Hydraulic forming press and method thereof - Google Patents

Abstract

PURPOSE: To prevent cracking in a deep drawn part by dividing a main hydraulic chamber and a sub hydraulic chamber with a floating holder, pressing a work with an upper punch in the main hydraulic chamber and forming a slit on a work with a slit blade in the sub hydraulic chamber. CONSTITUTION: A work W is placed on a lower die 3, depressed and fixed by a blank holder 9. A liquid is filled in a main hydraulic chamber 5 and a sub hydraulic chamber 17. When an upper punch 13 is lowered, the work W is pressed against the upper punch 13 by the hydraulic pressure of the main chamber 5 and press-formed. The work W is further lowered and held between a working holder 19 and the flat part 13F of the upper punch 13. The hydraulic pressure of the sub hydraulic chamber 17 is reduced so that the upper punch 13 is further lowered. A slit is formed on the work W with a slit blade 39 provided inside the sub hydraulic chamber 17. The upper punch 13 is still further lowered, and press-forming is completed. Since a material is supplied from the sub hydraulic chamber 17 side to the deep drawing part on the main hydraulic chamber 5 side in the manner of expanding the slit, deep drawing is made possible for more than the elongation percentage of the work W.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic pressure for forming a work by imitating the work by applying a hydraulic pressure such as water pressure or hydraulic pressure to the work and pressing the work against a forming die (punch). The present invention relates to a molding apparatus and a hydraulic molding method. More specifically, it has a void such as a large hole or window inside,
Further, the present invention relates to a hydraulic forming apparatus and a forming method suitable for forming a molded product having a deep drawing portion having a work elongation rate or more.

[0002]

2. Description of the Related Art As a prior art example according to the present invention, there is, for example, JP-A-63-13626. In this precedent,
After placing the doughnut-shaped work on the die having the pillar portion in the center and the ring-shaped die hole on the outer periphery thereof,
The work is pressed and fixed on the die by a restraint plate provided inside the annular punch that is inserted into and removed from the ring-shaped die hole and a donut-shaped blank holder arranged outside the annular punch, and then the annular punch. When the workpiece is formed by engaging with the ring-shaped die hole, the holding force of the restraining plate and the holding force of the donut-shaped blank holder are appropriately controlled to control the inside and outside, and The lip skin is molded by controlling the flow of the material.

[0003]

In the structure of the above-mentioned prior art, since the hole is machined in the central portion before forming the work, a cutting die for cutting the hole and a cutting operation are required, and an extra work is required. There is a problem that mold cost and man-hours are required.

Further, since the restraint plate is arranged inside the annular punch, there is a problem that the die structure is complicated, the punch strength is lowered, and the die cost is increased.

Further, in the structure of the prior art, it is difficult to make the material flow from inside and outside uniform, and a trimming step is required in the next step.

[0006]

The present invention has been made in view of the conventional problems as described above, and a hydraulic forming apparatus according to the present invention is a lower mold having a work supporting surface for supporting a work at an upper portion thereof. The die is provided with a main hydraulic chamber that applies a hydraulic pressure to the work over its entire surface, and a floating holder that comes into contact with the work to partition the main hydraulic chamber into a main hydraulic chamber and a sub hydraulic chamber is provided. It is installed in the main hydraulic chamber so that it can move up and down and can be pressed and urged upward, and an upper die punch that can press the workpiece into the main hydraulic chamber against the hydraulic pressure in the main hydraulic chamber is moved up and down. A slit cutting blade, which is movably provided, holds the work by the floating holder and the upper die punch, and then gives a slit to the work, is provided in the sub-hydraulic chamber.

Further, the hydraulic forming apparatus is provided with a sensor for detecting the contact pressure between the floating holder and the work.

Further, in the hydraulic forming apparatus, the floating holder is provided with a seal portion on the contact surface which comes into contact with the work.

Further, in the hydraulic forming apparatus, the slit cutting edge is formed in an arc shape near both ends, and the end portions are directed inward.

In the molding method according to the present invention, a lower die having a work supporting surface for supporting a work is provided with a main hydraulic chamber for applying a hydraulic pressure to the work, and the main die is brought into contact with the work. Then, a floating holder, which is capable of partitioning the main hydraulic chamber into a main hydraulic chamber and a sub hydraulic chamber, is provided in the main hydraulic chamber so as to be vertically movable and upwardly biased, and An upper die punch that presses the work toward the main fluid pressure chamber against the fluid pressure in the fluid pressure chamber is provided movably up and down, and the work is clamped by the floating holder and the upper die punch, and then the work is slit. In a sub-hydraulic chamber before forming a slit by the slit cutting blade in a hydraulic forming method for forming a workpiece by a hydraulic forming device provided with a slit cutting blade in the sub-hydraulic chamber Depressurize and above Further boosting the hydraulic pressure of the primary liquid within the chamber after decompression of the liquid pressure internal a hydroforming method of performing molding with allowed rise to flow to the primary liquid chamber side of the secondary liquid chamber side workpiece.

[0011]

As apparent from the above construction, in the present invention, the lower die having the work supporting surface for supporting the work at the upper portion is provided with the main hydraulic chamber for applying the hydraulic pressure to the whole work. , A floating holder that divides the main fluid pressure chamber into a main fluid pressure chamber and a sub fluid pressure chamber by contacting the work is provided in the main fluid pressure chamber so as to be movable up and down, and can be biased upward. It is provided in. Then, when the upper die punch is lowered to press the work against the hydraulic pressure in the main hydraulic chamber toward the main hydraulic chamber, a part of the work is held by the floating holder and the upper punch. The hydraulic chamber is divided into a sub hydraulic chamber surrounded by the floating holder.

As described above, after the sub hydraulic chamber is partitioned from the main hydraulic chamber, a slit is formed in the work by the slit cutting blade provided in the sub hydraulic chamber.

After that, when the upper die punch is further lowered or the hydraulic pressure in the main hydraulic chamber is raised, the work is strongly pressed against the upper die punch, and the work is formed following the upper die punch.

As described above, when the work is crimped to the upper die punch to perform the forming process, since the slit is formed in the work in the sub-hydraulic chamber, the flow of the material occurs so as to enlarge the slit. Even if there is a deep drawing portion larger than the work elongation, it is possible to prevent the material from flowing from the sub-hydraulic chamber side to the deep drawing portion and to prevent the deep drawing portion from cracking or the like. It is a thing.

As described above, it is desirable to reduce the hydraulic pressure in the sub-hydraulic chamber in advance before forming slits on the work by the slit cutting blade. In this way, by preliminarily reducing the pressure in the sub-hydraulic chamber, it is possible to prevent a reduction in processing accuracy due to the high-pressure liquid escaping from the slit to the space between the workpiece and the upper die punch when the slit is formed.

Further, in the present invention, since the sensor for detecting the contact pressure between the floating holder and the work is provided, the sealed state between the main hydraulic chamber and the sub hydraulic chamber is surely performed. After that, it becomes possible to reduce the pressure in the sub-hydraulic chamber, prevent the liquid from flowing into the sub-hydraulic chamber from the main hydraulic chamber, and reliably prevent the liquid from leaking. In other words, it is possible to prevent the hydraulic pressure in the main hydraulic chamber from decreasing.

Further, in the present invention, since the floating holder is provided with the seal portion on the contact surface which comes into contact with the workpiece, the main hydraulic chamber and the sub hydraulic chamber can be reliably sealed. It is a thing.

Further, in the present invention, since the slit cutting edge is formed in an arc shape near both ends and the ends are directed inward, the fracture of the work from the ends of the slit formed in the work. Even when the work progresses, the breakage does not progress to the outer product portion side, and a new problem due to the formation of the slit in the work does not occur.

In the molding method of the present invention, the hydraulic pressure in the sub-hydraulic chamber in which the slit cutting blade is disposed is reduced before the slit is formed in the work by the slit cutting blade, and then the hydraulic pressure in the main hydraulic chamber is set. When performing the forming process by further increasing the pressure, the forming process is performed by allowing the material flow from the sub-hydraulic chamber side to the main hydraulic chamber side so as to enlarge the slit formed in the work. Even if there is a deep drawing portion larger than the elongation rate of the work, the material is replenished from the sub-hydraulic chamber side to the deep drawing portion, which effectively causes the occurrence of cracks in the deep drawing portion. It can be prevented.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a hydraulic forming apparatus 1 according to the present embodiment is equipped with a lower die 3 supported by a bolster 2 in a press machine (the entire structure is not shown). A work supporting surface 3F that supports a plate-shaped work W is provided on the upper portion of the die 3. The lower die 3 is provided with a main hydraulic chamber 5 that applies a hydraulic pressure to the work W entirely. The work supporting surface 3F is provided with a seal 7 for preventing liquid from leaking from the work.

Above the lower die 3, the work W is
A blank holder 9 which can press and fix the peripheral edge portion of the blank holder to the work supporting surface 3F of the lower die 3 is provided so as to be vertically movable. The blank holder 9 is vertically movable in a press machine (the entire structure is not shown). It is attached to the outer ram 11.

In addition, above the lower die 3, a workpiece W whose peripheral portion is pressed and fixed to the work supporting surface 3F of the lower die 3 by the blank holder 9 is placed in the main hydraulic chamber 5. An upper die punch 13 is provided which presses the main hydraulic chamber 5 against the hydraulic pressure. The upper die punch 13 is attached to an inner ram 15 which is located inside the outer ram 11 and is vertically movable.

The lower surface of the upper die punch 13 is formed as a forming surface for forming the work W, and a forming die portion 13D for deep drawing is provided on a part of the forming surface so as to largely protrude from the flat surface portion 13F. I am doing it. The intersection 13C between the molding die 13D and the flat surface 13F is formed into an arcuate curved surface.

This embodiment exemplifies a hydraulic forming apparatus for forming a window frame integrated type door inner (full door inner) A as shown in FIG.
3D corresponds to a portion for molding the door portion B, and the flat portion 13F
Is a portion corresponding to the window portion C. And the intersection 13
C corresponds to the opening D between the door B and the window C.

The window inner door type inner door A is shown as a mere example of a molded product in order to facilitate understanding, and can be molded by the hydraulic molding apparatus according to this embodiment. It does not limit the product.

As already understood, the portion of the work W corresponding to the flat surface portion 13F of the upper die punch 13 is a scrap portion which is cut and separated from the molded product and discarded after the work is molded.

Now, referring again to FIG. 1, when the work W is pressed down by the upper die punch 13 into the main hydraulic chamber 5 of the lower die 3, the workpiece W is brought into contact with the work W when forming. Further, an annular floating holder 19 that is partitionable in the main hydraulic pressure chamber 5 into the main hydraulic pressure chamber 5 and the sub hydraulic pressure chamber 17 is provided so as to be vertically movable and upwardly biased.

The floating holder 19 is arranged corresponding to the plane portion 13F of the upper die punch 13.
In other words, the floating holder 19 is arranged at a position corresponding to a portion to be scrapped after the work W is formed.

On the contact surface where the floating holder 19 contacts the work W, a seal member 2 is provided as a seal portion.
1 is provided. In this embodiment, the seal member 21
As an example, a structure in which a general sealing material is provided has been described, but the structure of the sealing portion may be a labyrinth seal-like sealing structure in which a circumferential groove is formed in multiple layers on the contact surface.

The floating holder 19 is vertically movably fitted in an annular groove 23 formed in the bottom portion 5B of the main hydraulic chamber 5, and the annular groove 23 is formed at a plurality of locations on the lower surface of the floating holder 19. The upper end portions of a plurality of support pins 25 penetrating the bolster 2 in a vertically movable manner are integrally connected to each other.

The lower end portion of each support pin 25 has a bolster 2
Is supported by a support plate 27 that is vertically movable at a lower position of the support pin 25, and the contact pressure between the work W and the contact surface of the floating holder 19 is provided between the lower end of each support pin 25 and the support plate 27. A sensor 29 composed of a load cell is provided to detect this.

The support plate 27 is supported by a vertically movable piston rod 33P of an appropriate number of fluid pressure cylinders 33 mounted on the cylinder mount 31. The fluid pressure cylinder 33 has a function of pressing and biasing the floating holder 19 in an upward direction, and is composed of, for example, a fluid pressure cylinder such as an air cylinder or a hydraulic cylinder. It is desirable to be able to adjust the fluid pressure so that the pressure bias can be adjusted.

The floating holder 19 is the work W.
To reduce the hydraulic pressure in the sub-hydraulic chamber 17 inside the floating holder 19 when the contact pressure reaches a predetermined value, the sub-hydraulic chamber 17 is provided with a relief valve 35 for electromagnetic control. It is connected. The relief valve 35 is a relief valve whose set pressure is controllable, and when the detected value of each sensor 29 is input to the control device 37 and the average value reaches the set value, the set pressure is set in advance. It is controlled.

The floating holder 19 holds the work W between the flat portion 13F of the upper die punch 13 and a slit is formed in the work W after the hydraulic pressure in the auxiliary hydraulic chamber 17 is reduced. Slitting blade 39 for cutting
Are arranged in the sub-hydraulic chamber 17.

The slit cutting blade 39 forms a slit in the scrap portion of the work W, and the flat surface portion 13F of the upper die punch 13 corresponding to the slit cutting blade 39.
The cutting edge biting groove 13G is formed in the.

As shown in FIG. 2, the slit cutting blade 39
Around the both ends of the arc-shaped portion 39R is formed, and both end portions 39E are directed inwardly away from the annular floating holder 19.

A hydraulic pressure supply unit 41 including, for example, a hydraulic pump, a check valve, a relief valve, etc. is connected to the main hydraulic chamber 5.

In the above structure, after the work W is placed and positioned on the work supporting surface 3F of the lower die 3,
First, lower the outer ram 11 to lower the blank holder 9
(Step S1 in FIG. 7).

When the blank holder 9 descends and presses and fixes the work W on the work supporting surface 3F of the lower die 3, the plate pressing force of the blank holder 9 gradually increases (step S2). Then, when the plate pressing force becomes equal to or more than a predetermined value (step S3), the liquid is supplied into the main hydraulic chamber 5 of the lower die 3, and the liquid is spread over the auxiliary hydraulic chamber 17 surrounded by the floating holder 19. Is filled (step S
4, S5).

Whether or not the plate pressing force has reached a predetermined value can be determined by detecting the hydraulic pressure of a hydraulic cylinder (not shown) for moving the outer ram 11 up and down by a pressure sensor. is there. Whether or not the main hydraulic chamber 5 and the sub hydraulic chamber 17 are filled with liquid is determined by detecting whether or not the hydraulic pressure in the main hydraulic chamber 5 has reached a predetermined hydraulic pressure, or This can be detected by presetting the relief valve 35 to operate at a predetermined pressure and detecting whether or not the liquid has flowed out from the relief valve 35.

As described above, when the liquid is supplied into the main hydraulic chamber 5 and the hydraulic pressure is P1 (see FIG. 6), the inner ram 15 is lowered to move the upper die punch 13 at the top dead center a _0. It is lowered (step S6). The hydraulic pressure Pm in the main hydraulic chamber 5 and the hydraulic pressure P _s in the auxiliary hydraulic chamber 17 are at a constant pressure P ₁ until the upper die punch 13 descends and contacts the work W at the position a ₁ . Step S7).

After the upper die punch 13 contacts the work W,
When the upper die punch 13 is further lowered against the hydraulic pressure in the main hydraulic chamber 5, the hydraulic pressure in the main hydraulic chamber 5 is gradually increased, and the workpiece W is moved upward by the hydraulic pressure acting on the workpiece W. It is pressed against the punch 13 and the molding process is started. (Step S8).

When the forming process of the work W is started as described above and the lowering of the upper die punch 13 progresses to reach the position a ₂ , the hydraulic pressure rises to P ₂ , and as shown in FIG. The work W contacts the floating holder 19 which has been raised by 33 (step S9).

When the work W is in contact with the floating holder 19 as described above, a part of the work W is sandwiched between the floating holder 19 and the flat surface portion 13F of the upper die punch 13. Then, the main hydraulic chamber 5 is partitioned from the auxiliary hydraulic chamber 17 surrounded by the floating holder 19 so as to be disconnected from the communication.

After the work W comes into contact with the floating holder 19 as described above, when the upper die punch 13 is further lowered, the floating holder 19 and the upper die punch 13 are moved.
The holding force by the flat surface portion 13F, in other words, the contact pressure (pressing force) between the floating holder 19 and the work W gradually increases (step S10).

The contact pressure (sealing force) is measured by the sensor 2
9, the controller 37 determines whether or not the detected value by each sensor 29 has reached the set value (step S11). When the detected value from each sensor 29 becomes equal to the set value, the controller 37 Outputs a control signal to the relief valve 35 (step S12), and the set value of the relief valve 35 is lowered to the initial pressure P ₁ .
The hydraulic pressure in the sub hydraulic chamber 17 drops to the pressure P ₁ (steps S13, 14).

After the pressure in the sub-hydraulic chamber 17 has dropped to P ₁ , the upper die punch 13 is further lowered against the fluid pressure cylinder 33 (step S15). Rises to P ₃ and the upper punch 13 descends to the position a ₃ , so that the slit cutting blade 39 provided in the sub-hydraulic chamber 17 relatively rises, and slit cutting is performed as shown in FIG. A slit is formed in the work W by the blade 39 (step S16).

When the upper die punch 13 is further lowered after forming the slit in the workpiece W, the hydraulic pressure in the main hydraulic chamber 5 is further increased, and the workpiece W is crossed at the intersection 13 of the upper die punches 13.
The work W is pressed by C and is formed in a mode in which the work W is in close contact with the upper die punch 13 (step S17). Then, the upper die punch 13 is positioned at the bottom dead center a ₄ , the hydraulic pressure in the main hydraulic chamber 5 is maintained at the maximum pressure P ₄ for a predetermined time, and then the workpiece W is formed by returning to the top dead center. Ends (step S18).

When a slit is formed in the work W by the slit cutting blade 39 as described above, the hydraulic pressure in the sub-hydraulic chamber 17 is lowered to P ₁ , so that the upper die punch 13 and the work W are separated from the slit. The liquid does not leak into the space.

Further, since the floating holder 19 and the work W are securely sealed with a predetermined contact pressure, the high-pressure liquid in the main hydraulic chamber 5 leaks to the sub hydraulic chamber 17 side. Therefore, the hydraulic pressure in the main hydraulic chamber 5 can be maintained at a high pressure.

Since the slit cutting blade 39 is formed in an arc-shaped portion 39R near both ends and the end portion 39E is directed inwardly away from the floating holder 19, the slit formed in the work W is formed. The slit does not reach the product part even if the product gradually expands and grows.

After the slit is formed in the work W as described above, when the hydraulic pressure in the main hydraulic chamber 5 is gradually increased and the work W is pressed and brought into close contact with the intersection 13C of the upper die punch 13, the slit is enlarged. As described above, since the material flows from the side of the sub-hydraulic chamber 17 to the side of the main hydraulic chamber 5 to replenish the material, the vicinity of the intersection 13C is a deep drawing portion having a larger elongation rate than the work W. Even if there is, the molding process can be performed without causing a crack or the like at the intersection 13C.

Therefore, in the prior art, since the opening D portion of the above-described window frame integrated door inner A is a deep-drawing portion, it sometimes caused cracks. However, according to the present embodiment, cracks occur. It can be easily molded without any occurrence.

By the way, the present invention is not limited to the above-mentioned embodiment, but can be carried out in other modes by making appropriate changes.

For example, in order to urge the floating holder 19 upward, it is possible to use a coil spring or a gas spring instead of the fluid pressure cylinder 33.

Further, as a structure in which the slits are formed in the work W and the hydraulic pressure in the main hydraulic chamber 5 is increased to press the work W against the upper die punch 13, the upper die punch 13 is used.
It is also possible to adopt a configuration in which a higher-pressure working fluid is supplied from the hydraulic pressure supply unit 41, instead of the configuration for lowering.

[0057]

As can be understood from the above description of the embodiments, in the present invention, the lower die provided with the work supporting surface for supporting the work on the upper surface thereof applies the hydraulic pressure to the work entirely. A main hydraulic pressure chamber is provided, and a floating holder that divides the main hydraulic pressure chamber into a main hydraulic pressure chamber and a sub hydraulic pressure chamber by contacting a workpiece is vertically movable. Moreover, it is provided so that it can be pressed and biased upward. Then, when the upper die punch is lowered to press the work against the hydraulic pressure in the main hydraulic chamber toward the main hydraulic chamber, a part of the work is held by the floating holder and the upper punch. The hydraulic chamber is divided into a sub hydraulic chamber surrounded by the floating holder.

As described above, after the sub hydraulic chamber is partitioned from the main hydraulic chamber, the slit is formed in the work by the slit cutting blade provided in the sub hydraulic chamber.

After that, when the upper die punch is further lowered or the hydraulic pressure in the main hydraulic chamber is raised, the work is strongly pressed against the upper die punch, and is shaped in accordance with the upper die punch.

As described above, when the work is crimped to the upper die punch to perform the forming process, since the slit is formed in the work in the sub-hydraulic chamber, the flow of the material occurs so as to enlarge the slit. Even if there is a deep drawing portion larger than the work elongation, it is possible to prevent the material from flowing from the sub-hydraulic chamber side to the deep drawing portion and to prevent the deep drawing portion from cracking or the like. It is a thing.

As described above, before the slit is formed on the work by the slit cutting blade, the hydraulic pressure in the auxiliary hydraulic chamber is reduced in advance. As described above, by preliminarily reducing the pressure in the sub-hydraulic chamber, it is possible to prevent a reduction in processing accuracy due to the high-pressure liquid escaping from the slit to the space between the work and the upper die punch when the slit is formed.

Further, in the present invention, since the sensor for detecting the contact pressure between the floating holder and the work is provided, the sealed state between the main hydraulic chamber and the sub hydraulic chamber is surely performed. After that, it becomes possible to reduce the pressure in the sub-hydraulic chamber, prevent the liquid from flowing into the sub-hydraulic chamber from the main hydraulic chamber, and reliably prevent the liquid from leaking. That is, it is possible to prevent a decrease in the hydraulic pressure in the main hydraulic chamber.

Further, in the present invention, since the floating holder is provided with the seal portion on the contact surface which comes into contact with the work, the main hydraulic chamber and the sub hydraulic chamber can be reliably sealed. It is a thing.

Further, in the present invention, since the slit cutting edge is formed in an arc shape near both ends and the ends are directed inward, the fracture of the work from the end of the slit formed in the work. Even when the work progresses, the breakage does not progress to the outer product portion side, and a new problem due to the formation of the slit in the work does not occur.

In the molding method of the present invention, the hydraulic pressure in the sub-hydraulic chamber in which the slit cutting blade is arranged is reduced before the slit is formed in the work by the slit cutting blade, and then the hydraulic pressure in the main hydraulic chamber is set. When performing the forming process by further raising the, the forming process is performed by causing the material flow from the sub-hydraulic chamber side to the main hydraulic chamber side so as to enlarge the slit formed in the work. Even if there is a deep drawing portion larger than the elongation rate of the work, the material is replenished from the sub-hydraulic chamber side to the deep drawing portion, which effectively causes the occurrence of cracks in the deep drawing portion. It can be prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing a main part of a hydraulic forming apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view of a lower die according to this embodiment.

FIG. 3 is an explanatory diagram of a main part showing a state of a processing process according to the present embodiment.

FIG. 4 is an explanatory diagram of a main part showing a state of a processing process according to the present embodiment.

FIG. 5 is an explanatory diagram of a main part showing a state of a processing process according to the present embodiment.

FIG. 6 is an explanatory diagram showing the relationship between the slide position of the upper die punch and the pressure change in the main hydraulic chamber and the sub hydraulic chamber.

FIG. 7 is a flowchart of the operation.

FIG. 8 is a perspective explanatory view of an example of a window frame-integrated door inner as a molded product.

[Explanation of symbols]

 3 Lower die 5 Main hydraulic chamber 9 Blank holder 13 Upper die punch 17 Sub hydraulic chamber 19 Floating holder 29 Sensor 33 Fluid cylinder 39 Slit cutting blade

Claims (5)

[Claims] 1. A main die pressure chamber for applying a hydraulic pressure to the work is provided in a lower die having a work supporting surface on the top for supporting the work, and the main hydraulic pressure is brought into contact with the work. A floating holder, which can divide the chamber into a main hydraulic chamber and a sub hydraulic chamber, is provided in the main hydraulic chamber so as to be movable up and down and urged upward, so that the pressure in the main hydraulic chamber can be adjusted. An upper die punch that presses the work against the main hydraulic chamber is provided so as to be movable up and down, and a slit cutting blade that gives a slit to the work after the work is clamped by the floating holder and the upper die punch. A hydraulic forming device provided in the sub-hydraulic chamber. 2. The hydraulic forming apparatus according to claim 1, further comprising a sensor that detects a contact pressure between the floating holder and the work. 3. The hydraulic forming apparatus according to claim 1, wherein the floating holder is provided with a seal portion on a contact surface that comes into contact with the work. 4. The hydraulic forming apparatus according to claim 1, wherein the slit cutting edge is formed in an arc shape near both ends, and the ends are directed inward. . 5. A main die pressure chamber for applying a hydraulic pressure to the work is provided on a lower die having a work supporting surface on the upper side for supporting the work, and the main hydraulic pressure is brought into contact with the work. A floating holder, which is capable of partitioning the chamber into a main hydraulic chamber and a sub hydraulic chamber, is provided in the main hydraulic chamber so as to be movable up and down and urged upward, and the hydraulic pressure in the main hydraulic chamber is set. Slit cutting blade for providing a slit to the work after the work is clamped by the floating holder and the upper die punch by providing an upper die punch that is capable of vertically pushing the workpiece against the main hydraulic chamber against Is a hydraulic forming method of forming a work by a hydraulic forming apparatus provided in the sub-hydraulic chamber, and performing decompression in the sub-hydraulic chamber before forming slits by the slit cutting blade, and Main fluid pressure after depressurization in sub-hydraulic pressure A hydraulic forming method, wherein the hydraulic pressure in the chamber is further raised to cause a material flow to the main hydraulic chamber side in the work on the side of the sub hydraulic chamber, and the forming process is performed.