JP2005324219A - Hollow parts forming die, hollow parts manufacturing method, and hollow parts - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hollow parts of high accuracy having a complicated shape in the axial direction to provide required functions at required portions. <P>SOLUTION: Cavities 28, 40 of twisted polygonal sectional shape are formed, and the cavities 28, 40 are sectioned by die section faces 38, 42 arranged not to generate any negative angle in the opening/closing direction of a die with respect to a hollow parts 100. A hollow stock material 100 is set in the cavities 28, 40, and the shapes of the cavities 28, 40 are transferred to the hollow stock material by the hydroforming to obtain the hollow parts of high accuracy having a twisted portion of the polygonal sectional shape. The thickness of the hollow parts can be reduced to < 1 mm, and the weight of the parts can be reduced very easily. Further, the wall thickness can be unified. Steel can also be used, and limitation of the material selection is eliminated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for manufacturing a hollow part whose cross-sectional shape changes for each part.

  In recent years, functional hollow parts, in which the cross-sectional shape is changed for each part in order to give a necessary part a necessary function to a strength member of an automobile (for example, aiming to improve shock absorption). Is being used. As the manufacturing method, there are an extrusion method (for example, see Patent Document 1) and a hydroform method (for example, see Patent Document 2).

JP 2000-25648 A ([Claim 1], [FIG. 1]) Japanese Patent Laid-Open No. 2001-301843 (Claim 1 and FIG. 1)

However, according to the conventional extrusion molding method, usable materials are limited to extruded materials such as aluminum and magnesium, and steel materials having the greatest demand cannot be used as the materials. In addition, there is a drawback that the degree of freedom of the shape in the axial direction is low and an optimum shape for carrying a necessary function cannot be given. Furthermore, it has been extremely difficult to suppress variations in sheet thickness for each part of the product.
On the other hand, the conventional hydrofoam method has a drawback that the degree of freedom in the shape of the product in the axial direction is low and an optimum shape for carrying a necessary function cannot be provided.
As other manufacturing methods, a casting method or a method of obtaining a necessary product shape by welding a press-molded product can be considered, but it is difficult to avoid post-processing by the casting method and it is difficult to reduce the thickness of the 1 mm range Therefore, there is a problem that it is extremely difficult to reduce the weight of the parts. In addition, in the technique of welding a press-formed product, it is difficult to obtain a complicated shape in the axial direction, and it is easy to cause deterioration of component accuracy due to springback for each mated component, thermal distortion of welding, and There is a drawback that it is necessary to provide a welding flange for each mating part.

    The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-precision hollow part having a complicated shape in the axial direction so that a necessary part has a necessary function. There is.

In order to solve the above-mentioned problems, a mold for forming a hollow part according to the present invention is a mold for hydroforming a hollow part having a twisted portion having a polygonal cross-sectional shape, and has a twisted polygonal cross-section. A cavity having a shape is formed, and the dividing surface is arranged so as not to cause a negative angle in the opening / closing direction of the mold with respect to the hollow part in the cavity.
According to the present invention, a hollow part having a twisted portion having a polygonal cross-sectional shape can be obtained by setting a hollow material in a cavity and transferring the cavity shape to the hollow material by hydroforming. In addition, since the mold dividing surface is arranged so as not to cause a negative angle in the mold opening / closing direction with respect to the hollow part in the cavity, the mold opening and opening can be performed without adopting a complicated slide structure for the mold. Product release is possible.

Further, in the present invention, the mold is composed of a plurality of mold units that are continuous in the axial direction, and a twisted polygonal cross-sectional shape of the cavity is formed across the plurality of mold units, The torsion angles of the torsional polygonal cross-sectional cavities that the mold unit takes over are limited to a range that does not cause a negative angle in the mold opening and closing direction.
With this configuration, it is possible to give the necessary twisted polygonal cross-sectional shape to the cavity of the hydroforming die without adopting a complicated slide structure in the die.
Further, the mold unit is provided with a mold dividing surface that displaces the position in the opening and closing direction of the mold, following the twist of the cavity having a twisted polygonal cross-sectional shape for each of the mold units. The twisted polygonal cross-sectional shape required for the cavity can be given without adopting a complicated slide structure in the mold.

Further, in the present invention, the twist angle of the twisted polygonal cross-sectional shape of the cavity each of the mold units is responsible for is 360 / n ° at the maximum when the polygonal cross-section of the cavity is a regular n-square shape. To do.
With this configuration, a cavity for hydroforming a hollow part having a regular n-gonal twisted polygonal cross-section can be formed in the mold.

As another example of the present invention, the twist angle of the twisted polygonal cross-sectional shape of the cavity that each of the mold units is responsible for is a regular n-gonal polygonal cross-section, and a fillet is formed at the corner. In some cases, the maximum value is 360 / n °.
With this configuration, a cavity for hydroforming a hollow part having a twisted polygonal cross-sectional shape part in which the polygonal cross section of the cavity has a regular n-gonal shape and a fillet is formed at the corner part is formed in the mold. can do.

As yet another example, the twist angle of the torsional polygonal cross-sectional shape of the cavity each of the mold unit takes is maximum when the polygonal cross-section of the cavity is a regular n-gonal shape and its corners are chamfered. It is assumed that 360 / 2n °.
With this configuration, a cavity for hydroforming a hollow part having a twisted polygonal cross-sectional shape portion in which the twisted polygonal cross section of the cavity has a regular n-gonal shape and a chamfered corner is provided in the mold. Can be configured.

The plurality of mold units may be formed integrally, and the plurality of mold units are formed separately and integrated by a fastening member. Also good.
In any case, a mold having a cavity having a necessary twisted polygonal cross-sectional shape can be configured.

In addition, a method for manufacturing a hollow part according to the present invention for solving the above-described problem is a method for manufacturing a hollow part having a twisted portion having a polygonal cross-sectional shape, and a cavity having a twisted polygonal cross-sectional shape is formed. In addition, a hollow material is set in a pair of molds that are arranged so that the mold split surface does not cause a negative angle in the mold opening and closing direction with respect to the product in the cavity, and the cavity shape is hollowed by hydroforming. It is characterized by being transferred to a material.
According to the present invention, a hollow part having a twisted portion having a twisted polygonal cross-sectional shape can be formed by hydroforming.

  Furthermore, a hollow part according to the present invention for solving the above-mentioned problem is formed with a cavity having a twisted polygonal cross-sectional shape, and the mold dividing surface is a negative angle with respect to the product in the cavity in the opening / closing direction of the mold. The hollow material is set in a pair of molds arranged so as not to cause the cavities, and the cavity shape is transferred to the hollow material by hydroforming and molded.

  Since this invention was comprised in this way, it becomes possible to provide the highly accurate hollow part which has a complicated shape of an axial direction for giving a required function to a required site | part.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a hollow part molding die 20 according to an embodiment of the present invention, and a hollow material 100 set in the molding die 20. The molding die 20 is a hydroforming die, and includes an upper die 22 and a lower die 24. As shown in FIG. 2A, the hydroforming process is performed by first setting the hollow material 100 on the mold 20 and applying the hydraulic pressure P to the hollow material 100 while the shaft pressing force F is applied to the shaft pressing force F. To load. Then, the hollow material 100 is deformed in accordance with the shape of the cavity 28 of the mold 20 as shown in FIG. 2B, and finally the cavity of the mold 20 is shown in FIG. 2C. The shape of 28 is transferred to the hollow material 100. In many cases, the hollow material 100 is obtained by subjecting a metal tube to bending processing called pre-forming or crushing processing. In addition, the material of the hollow raw material 100 used in the embodiment of the present invention is not limited by the material unlike the case of extrusion molding, and a metal steel pipe or the like can be used.

Here, based on the lower mold | type 24 shown in FIG. 3, the metal mold | die 20 which concerns on embodiment of this invention is demonstrated in detail. The upper die 22 has the same configuration as that of the lower die 24, and is not shown.
A cavity 28 having a necessary twisted polygonal cross-sectional shape is formed in the lower mold 24 (upper mold 22). The lower mold 24 (upper mold 22) is composed of a plurality of mold units 30 that are continuous in the axial direction. In addition, the twisted polygonal cross-sectional shape of the cavity 28 is formed across the plurality of mold units 30 (30A, 30B), and a part 28A of the cavity that each mold unit 30A, 30B having the length L receives, The twist angle of 28B is limited to an angle that does not cause a negative angle in the opening and closing direction of the mold (described later). In the example of FIGS. 1 to 3, the mold units 30 </ b> A and 30 </ b> B are integrally formed. In addition, end units 32 and 34 having a cylindrical cavity for maintaining the diameter of the hollow material 100 are integrally formed before and after the mold units 30A and 30B.

  4A and 4C show the sectional shapes of the end sections I and III of the mold unit 30A, and FIG. 4B shows the sectional shape of the middle section II of the mold unit 30A. Is shown. The cross-sectional shape of the mold unit 36A corresponding to the upper mold 22 is also shown. As apparent from FIGS. 4A to 4C, the mold unit 30A has a mold part whose position is displaced in the opening and closing direction of the mold following the twist of the polygonal sectional shape of the cavity portion 28A. A surface 38 is provided. Similarly, with respect to the corresponding upper mold unit 36A, the part 40A of the cavity of the mold unit 36A is displaced in the mold opening / closing direction following the twist of the polygonal cross-sectional shape. 42 is provided. Then, as is apparent from the cross-sectional shapes of the end sections I and III of the mold unit 30A shown in FIGS. 4A and 4C, a part 28A of the cavity that each mold unit 30A and 36A receives, In 40A, a negative angle in the opening and closing direction of the mold does not occur over the entire length.

By the way, in the example of FIG. 3, FIG. 4, the twist polygonal cross-sectional shape of the cavity 28 is a regular square, and the fillet is formed in the corner | angular part. In such a case, the negative angle in the mold opening / closing direction does not occur when the torsion angles of the cavity portions 28A and 28B respectively handled by the mold units 30A and 30B are 360 / n ° at the maximum. It will be a thing.
Therefore, in the example shown in the figure, the twist angle is 360 ° / 4 = 90 °, and as shown in FIG. 5 (a), the corner of the square cross section of the square with the fillet formed (encircled in the figure) It is understood that even if the portion is rotated from 0 ° to 90 ° as shown in FIG. 5B, no negative angle in the mold opening / closing direction is generated in the cavity portions 28A and 40A.
In the case of the mold 20 shown in FIGS. 1 to 4, by using two of the two mold units 30A and 30B, as shown in FIG. Overall, a twist angle of 180 ° is obtained.

  It should be noted that the twist angle of the twisted polygonal cross-sectional shape of the cavity each mold unit is responsible for is a case where the twisted polygonal cross-section of the cavity is a regular n-gonal shape and no fillet is formed at the corner. When the maximum is 360 / n °, a negative angle in the opening and closing direction of the mold does not occur.

The above conditions also apply to other polygonal sections as they are. For example, in the case of a cavity with a triangular section, the twist angle of the cavity that each mold unit takes is 360/3 = 120 ° at the maximum, In the case of a pentagonal cross section, the maximum twist angle of the cavity that each mold unit takes is 360/5 = 72 °. Further, if the twist angle for each mold unit is 360 / n ° or less, a negative angle in the opening / closing direction of the mold does not occur. Therefore, if necessary, the twist angle for each square mold unit is within this range. It is also possible to decide freely.
Further, even when an irregular n-gonal cross section is adopted for the cavity, the twist angle of the twisted polygonal cross-sectional shape of each cavity that each mold unit handles is 360 / n ° at the maximum, similarly to the regular n-square shape. .

  On the other hand, as shown in FIG. 6 (a), when the polygonal cross section of the cavity is a quadrangle and the corners are chamfered, the twist angle of the twisted polygonal cross-sectional shape of each cavity that each mold unit takes care of. Is 360/2 n ° at the maximum, that is, 360 / (2 × 4) = 45 ° at the maximum. The reason for this is that, as shown in FIG. 6 (a), the corners (portions enclosed by circles in the figure) of the rectangular cavity cross-section that has been chamfered are 0 ° to 0 ° as shown in FIG. 6 (b). This is because when the rotation angle is 90 °, a negative angle in the mold opening / closing direction is generated in the cavities 28A and 40A when the rotation angle exceeds 45 °. Accordingly, the twists of 45 ° to 90 ° are shared by the portions 28B and 40B of the cavities of the adjacent mold units.

  By the way, the plurality of mold units may be integrally formed as shown in FIG. 3, and the mold units 30A and 30B and the end units 32 and 34 are separated from each other as shown in FIG. It is good also as forming them in a body and integrating them with fastening members, such as volt | bolt 44 and nut 46. FIG. Further, as shown in FIG. 8, if four mold units 30 </ b> A to 30 </ b> D are used, the cavity 28 having a square cross-sectional shape can obtain a twist angle of 360 ° as a whole. Furthermore, as shown in FIG. 9, if seven mold units 30A to 30G having cavities having a regular octagonal cross section are used, the twist angle of 360/8 × 7 = 315 ° is obtained as a whole cavity. Can be obtained. Therefore, the twisted hollow part 102 hydroformed by such a mold becomes a twisted hollow part having a regular octagonal cross section having a twist angle of 315 °.

According to the embodiment of the present invention having the above-described configuration, the following operational effects can be obtained. First, a hollow part molding die 20 according to an embodiment of the present invention is a mold for hydroforming a hollow part having a polygonal cross-sectional twisted portion, and has a twisted polygonal cross-sectional shape. , And the mold dividing surfaces 38 and 42 are arranged so as not to form a negative angle in the mold opening / closing direction with respect to the hollow part 100 in the cavities 28 and 40. The hollow material 100 is set in the cavities 28 and 40, and the shape of the cavities 28 and 40 is transferred to the hollow material by hydroforming, so that a highly accurate hollow part having a twisted portion having a polygonal cross-sectional shape (see FIG. 9). See twisted hollow part 102). The mold can be opened and the product can be released without adopting a complicated slide structure for the mold. Moreover, it is possible to reduce the thickness of the hollow part to less than 1 mm, and it is very easy to reduce the weight of the part. In addition, the thickness of the hollow part can be made uniform. Furthermore, it is possible to use steel, and there is no restriction on material selection.
Therefore, it is possible to manufacture a complex shape in the axial direction called a twisted polygonal cross-sectional shape without causing variations in the thickness of the product and without being restricted by the material. Can be provided.

Further, in the embodiment of the present invention, the mold 20 is constituted by a plurality of mold units 30 (30A, 30B,...) That are continuous in the axial direction, and the cavity 28 extends across the plurality of mold units 30. A twisted polygonal cross-sectional shape is formed, and the twist angle of the twisted polygonal cross-sectional shape that each mold unit 30 receives is determined by the twist angle of the cavity 28A, 28B,. It is limited to a range that does not cause a negative angle in the mold opening and closing direction. Therefore, it is possible to give the necessary twisted polygonal cross-sectional shape to the cavities 28 and 40 of the hydroforming die 20 without adopting a complicated slide structure in the die.
Further, as shown in FIGS. 3 and 4, the mold unit 30 includes mold dividing surfaces 38 and 42 that displace the position in the opening and closing direction of the mold following the twist of the polygonal cross-sectional shape of the cavity 40. Thus, the twisted polygonal cross-sectional shape necessary for the cavities 28 and 40 can be provided without adopting a complicated slide structure in the mold 20.

Note that the twist angle of the twisted polygonal cross-sectional shape of the cavity that each mold unit 30 handles is such that when the polygonal cross-section of the cavity 28 is a regular n-gonal shape, and fillets are formed at the corners of the regular n-gonal shape. When the angle is 360 / n ° at the maximum, it is possible to prevent a negative angle in the opening / closing direction of the mold 30 from being generated in a part of the cavity of each mold unit 30.
On the other hand, when the polygonal cross section of the cavity is a regular n-gon and the corner is chamfered, the twist angle of the twisted polygonal cross-sectional shape of each cavity of each mold unit is 360 / 2n at the maximum. By setting the angle, it is possible to prevent a negative angle in the opening / closing direction of the mold 20 from occurring in a part of the cavity of each mold unit 30.

  Further, the plurality of mold units 30 may be integrally formed as shown in FIG. 3, and the plurality of mold units 30A, 30B, 32, and 34 are separated from each other as shown in FIG. It may be formed on the body and integrated with the fastening members 44 and 46. In any case, the mold 20 including the cavities 28 and 40 having a necessary twisted polygonal cross-sectional shape can be configured.

  The cavities 28 and 40 having a twisted polygonal cross-section are formed, and the mold dividing surfaces 38 and 42 are arranged so as not to cause a negative angle in the opening and closing direction of the mold with respect to the products in the cavities 28 and 40. The hollow material 100 is set in a pair of molds 22 and 24, and the shape of the cavities 28 and 40 is transferred to the hollow material 100 by hydroforming, thereby providing a complex shape in the axial direction called a twisted polygonal cross-sectional shape. It is possible to manufacture the hollow part without causing variations in the plate thickness of the product and without being restricted by the material.

10 to 18 show examples of the shape of a hollow part having at least one twisted polygonal cross-sectional shape portion that can be formed by the hydroforming method according to the embodiment of the present invention. First, the twisted hollow part 104 shown in FIG. 10 is obtained by integrally forming a twisted polygonal cross-sectional shape portion 104a, a polygonal portion 104b that is a non-twisted portion, and a cylindrical shape 104c. This twisted hollow part 104 is hydroformed by a mold in which a plurality of mold units having a cavity having a twisted polygonal cross-sectional shape and an end unit having a twisted polygonal cross-sectional shape and a cylindrical shape are combined. It is.
In addition, the twisted hollow part 106 shown in FIG. 11 is obtained by reversing the twist direction of the twisted polygonal cross section in the middle, and uses a mold in which mold units having different twist directions are combined, and is denoted by reference numeral 106a. The range and the range indicated by reference numeral 106b are integrally formed.

Further, the twisted hollow part 108 shown in FIG. 12 is different in material, plate thickness, and the like between the range indicated by reference numeral 108a and the range indicated by reference numeral 108b. This twisted hollow part 108 is formed by using a tailored tube by a so-called tailored blank method (a characteristic of a single material can be partially changed by joining different steel plates) to a hollow material. Can be obtained.
Further, the twisted hollow part 110 shown in FIG. 13 has a different twist pitch in the range indicated by reference numeral 110a and the range indicated by reference numeral 110b. The mold for forming the twisted hollow part 110 is a combination of mold units having different twist pitches.
Further, the twisted hollow part 112 shown in FIG. 14 is obtained by integrally molding a twisted polygonal cross-sectional shape part 112a and a polygonal part 112b which is a non-twisted part. In addition, about the cavity shape for shape | molding the gradual change part 112c which connects both, you may provide in the die unit for shape | molding the twist polygonal cross-sectional shape part 112a, and the end for shape | molding the polygon part 112b It may be provided in the unit.

Further, the twisted hollow part 114 shown in FIG. 15 has a cross-sectional area indicated by a reference numeral 114a and a cross-sectional area indicated by a reference numeral 114b that are different from each other and are connected by a polygonal cross-section 114c. And the hollow material used for this twisted hollow part 114 may be a metal tube that has been subjected to preliminary processing such as contraction or expansion, like the hollow material 101 shown in FIG. It is good also as using the thing of the state which does not give preliminary processing like the hollow raw material 100 shown in FIG.16 (b).
Further, FIG. 17 shows a side member 116 of an automobile in which a twisted portion 116a having a polygonal cross section is integrally formed. The side member 116 can freely control the shock absorbing performance at the twisted portion 116a. FIG. 18 shows a twisted crush box 118 formed of steel. The crush box 118 is able to absorb the force F freely by compressing and deforming so as to reduce the twist pitch upon receiving the axial force F. Such a crash box 118 is a part having a shape that cannot be obtained by conventional extrusion molding.

It is a perspective view which shows the metal mold | die for hydroforming of the hollow part which concerns on embodiment of this invention, and the hollow raw material set to the said metal mold | die. It is a schematic diagram which shows the process sequence by the metal mold | die for hydroforming shown in FIG. 1, (a) shows an initial stage, (b) shows an intermediate process, (c) shows a final process. It is a perspective view which shows the lower mold | type of the metal mold | die for a hydroforming process shown in FIG. FIGS. 1 to 3 show the cross-sectional shapes of the respective parts of the mold unit shown in FIGS. 1 to 3, wherein (a) is a cross-sectional view taken along the plane I in FIG. 3, (b) is a cross-sectional view taken along the line II in FIG. It is sectional drawing in the III surface of FIG. (A) is a sectional view of the cavity of the mold unit shown in FIG. 3, and (b) is a rotation of the corner of the cavity section shown in (a) (the part surrounded by a circle in the figure) from 0 ° to 90 °. It is a figure which shows the displacement of the parting surface between. (A) is a cross-sectional view of an example of chamfering the corner of the cavity section of the mold unit shown in FIG. 3, and (b) is a corner of the cavity section shown in (a) (encircled in the figure). It is a figure which shows the displacement of the parting surface while rotating a part) to 0 degree-90 degrees. FIG. 4 is a perspective view showing an example in which each lower mold unit shown in FIG. 3 is formed separately and integrated by a fastening member. It is a disassembled perspective view which shows the example of the lower mold | type using four mold units based on embodiment of this invention. It is a perspective view which shows the lower mold | die using the seven metal mold | die units provided with the cavity which has a regular octagonal cross-sectional shape based on Embodiment of this invention, and the twist hollow part hydroformed by it. It is an example of the shape of the hollow component which concerns on embodiment of this invention. It is an example of the shape of the hollow component which concerns on embodiment of this invention. It is an example of the shape of the hollow component which concerns on embodiment of this invention. It is an example of the shape of the hollow component which concerns on embodiment of this invention. It is an example of the shape of the hollow component which concerns on embodiment of this invention. It is an example of the shape of the hollow component which concerns on embodiment of this invention. Both (a) and (b) show a hollow material for forming the hollow part shown in FIG. It is a perspective view which shows the side member of the motor vehicle which integrally molded the twist part of polygonal cross-sectional shape based on embodiment of this invention. It is a schematic diagram which shows before and after deformation | transformation of the twist shape crush box shape | molded with the steel materials based on embodiment of this invention.

Explanation of symbols

20: Mold for molding, 22: Upper mold, 24: Lower mold, 26: Shaft push, 28, 40: Cavity, 30, 36: Mold unit, 32, 34: End unit, 38, 42: Mold split Surface, 44: bolt, 46: nut, 100: hollow material, 102: twisted hollow part

Claims (10)

A mold for hydroforming a hollow part having a twisted portion having a polygonal cross-sectional shape,
A hollow part characterized in that a cavity having a twisted polygonal cross-sectional shape is formed, and the mold splitting surface is arranged so as not to form a negative angle in the opening and closing direction of the mold with respect to the hollow part in the cavity. Mold for molding. Consists of a plurality of mold units continuous in the axial direction, and a twisted polygonal cross-sectional shape of the cavity is formed across the plurality of mold units, and a twisted polygonal cross-sectional shape that each mold unit takes over 2. The mold for molding a hollow part according to claim 1, wherein the twist angle of each of the cavities is limited to a range in which a negative angle in the opening and closing direction of the mold does not occur. 3. The molding of a hollow part according to claim 2, wherein each mold unit is provided with a parting surface that displaces the position in the opening and closing direction of the mold following the twist of the cavity having a twisted polygonal cross section. Mold. The twist angle of the twisted polygonal cross-sectional shape of the cavity each of the mold units is handled is 360 / n ° at the maximum when the polygonal cross-section of the cavity is a regular n-gonal shape. Or 3. A mold for molding hollow parts according to 3. The twist angle of the torsional polygonal cross-sectional shape of the cavity each of the mold unit takes is 360 / n ° at the maximum when the polygonal cross-section of the cavity is a regular n-gonal shape and a fillet is formed at the corner. 4. A mold for molding a hollow part according to claim 2, wherein the mold is used for molding a hollow part. The twist angle of the torsional polygonal cross-sectional shape of the cavity each of the mold unit takes is 360 / 2n ° at the maximum when the polygonal cross-section of the cavity is a regular n-gonal shape and its corners are chamfered. 4. A mold for molding a hollow part according to claim 2, wherein the mold is used for molding a hollow part. The mold for molding a hollow part according to any one of claims 1 to 6, wherein all of the plurality of mold units are integrally formed. The mold for molding a hollow part according to any one of claims 1 to 7, wherein each of the plurality of mold units is formed separately and integrated by a fastening member. . A method of manufacturing a hollow part having a twisted portion having a polygonal cross-sectional shape,
A hollow material is set in a pair of molds in which a cavity with a twisted polygonal cross-section is formed and the mold splitting surface is arranged so as not to create a negative angle in the mold opening / closing direction with respect to the product in the cavity And a method for producing a hollow part, wherein the cavity shape is transferred to a hollow material by hydroforming. A hollow material is set in a pair of molds in which a cavity with a twisted polygonal cross-section is formed and the mold splitting surface is arranged so as not to create a negative angle in the mold opening / closing direction with respect to the product in the cavity The hollow part is formed by transferring the cavity shape to a hollow material by hydroforming.

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