CN111229852A

CN111229852A - Extrusion die, device and method for realizing bidirectional extrusion forming process

Info

Publication number: CN111229852A
Application number: CN202010120265.0A
Authority: CN
Inventors: 喻俊荃; 赵国群; 朱传宝; 林建国
Original assignee: Kaiweisi Lightweight Intelligent Manufacturing Research Institute Heze Co Ltd
Current assignee: Kaiweisi Lightweight Intelligent Manufacturing Research Institute Heze Co Ltd
Priority date: 2020-02-26
Filing date: 2020-02-26
Publication date: 2020-06-05
Anticipated expiration: 2040-02-26
Also published as: WO2021169513A1; CN111229852B

Abstract

The invention discloses an extrusion die, a device and a method for realizing a bidirectional extrusion forming process, and relates to the field of dies, wherein the device comprises an extruder central beam, a first extrusion cylinder, a second extrusion cylinder, a push-pull rod and an extrusion die for realizing the bidirectional extrusion forming process, the push-pull rod is fixedly connected with a male die, a first extrusion cylinder inlet and a second extrusion cylinder inlet are respectively formed in a first side surface and a second side surface of the extruder central beam, when the extrusion die for realizing the bidirectional extrusion forming process enters an inlet and an outlet of the die, the first extrusion cylinder penetrates through the first extrusion cylinder inlet and is in mutual contact with the first side surface of the male die, and the second extrusion cylinder penetrates through the second extrusion cylinder inlet and is in mutual contact with the second side surface of the male die. The invention can solve the problems of die disassembly and assembly, feeding, bidirectional extrusion action, discard shearing and the like in the conventional bidirectional extrusion process.

Description

Extrusion die, device and method for realizing bidirectional extrusion forming process

Technical Field

The invention relates to the field of dies, in particular to an extrusion die, an extrusion device and an extrusion method for realizing a bidirectional extrusion forming process.

Background

The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.

The bi-directional extrusion process is a novel extrusion forming process for applying pressure to a material from two directions, so that a velocity gradient is generated in the material to drive the material to be integrally bent, and thus an extruded product bent along the length direction is obtained. By the process, metal and non-metal profiles which are curved in the length direction and have variable curvature can be manufactured. The main advantages of manufacturing curved profiles by means of a bi-directional extrusion process include: (1) the forming defects of bending resilience, wrinkling, section deformation, cracking and the like commonly existing in the traditional cold-bending forming process can be reduced or even eliminated, so that the bending forming limit of the material is remarkably improved, and the method is particularly suitable for bending forming of materials and structures which are difficult to bend; (2) the microstructure of the material can be obviously improved, and the mechanical property of the section bar is enhanced; (3) the extrusion-bending one-step forming is realized, the curvature of the bent section can be dynamically regulated and controlled in the length direction of the section, and the manufacturing process flow of the bent section is greatly shortened.

The inventor finds that in the field of metal extrusion, the extrusion machines generally used at present mainly adopt forward extrusion, backward extrusion, forward-repeat co-extrusion and the like, but the extrusion methods only apply pressure to the billet from one direction, and the extruded profile product is a profile which is straight along the length direction. These extruders may be referred to as conventional extruders. The conventional extruder cannot achieve bidirectional extrusion. The die matched with the traditional extruder can be called as a traditional extrusion die, and mainly comprises a flow guide die for extruding a solid profile and a flow dividing extrusion die for extruding a hollow profile. A characteristic of conventional dies is that the material enters from one direction and flows out along the die orifice of the extrusion die parallel to that direction, so that an extruded profile is obtained that is straight along the length. The inventors have found that no special extruder and extrusion die suitable for bi-directional extrusion processes have been available. The problems of structural design, quick disassembly and assembly, automatic feeding, realization of bidirectional extrusion action, discard shearing and the like of the bidirectional extrusion die are main problems for realizing the bidirectional extrusion process.

Disclosure of Invention

Aiming at the vacancy of the prior art, the invention aims to provide an extrusion die, a device and a method for realizing a bidirectional extrusion forming process, and the device can solve the problems of die disassembly and assembly, feeding, bidirectional extrusion action, discard shearing and the like in the conventional bidirectional extrusion forming process.

In order to achieve the purpose, the invention is realized by the following technical scheme:

in a first aspect, an embodiment of the present invention provides an extrusion die for implementing a bidirectional extrusion molding process, including a male die and a female die that are matched with each other, wherein one side surface of the male die can be matched with the female die; the male die is provided with a T-shaped or star-shaped channel, the T-shaped or star-shaped channel forms an opening on the surface of the male die, two opposite openings of the T-shaped or star-shaped channel are feeding openings, and openings outside the two opposite openings of the T-shaped or star-shaped channel are discharging openings; the female die is provided with a through hole, and after the male die and the female die are installed in a matched mode, the discharge hole of the male die is coaxial with the through hole of the female die.

With reference to the first aspect, an embodiment of the present invention provides a first possible implementation manner of the first aspect, where axes of two material inlets of the male dies are on the same straight line, and are at right angles to an axis of a material outlet.

With reference to the first aspect, the embodiments of the present invention provide a second possible implementation manner of the first aspect, and after the male mold and the female mold are installed in a matching manner, a cavity is formed on the periphery of the mold core, and the cavity is used for welding.

In a second aspect, an embodiment of the present invention further provides an extrusion apparatus for implementing a bidirectional extrusion molding process, including a central beam of an extruder, a first extrusion container, a second extrusion container, a push-pull rod, and an extrusion mold for implementing a bidirectional extrusion molding process as described in the first aspect, where the push-pull rod is fixedly connected to a male mold, a first side surface and a second side surface of the central beam of the extruder are respectively provided with a first extrusion container inlet and a second extrusion container inlet, a front side surface of the central beam of the extruder is provided with a mold inlet and a mold outlet, and a rear side surface of the central beam of the extruder is provided with a bent profile outlet.

In combination with the second aspect, the embodiments of the present invention provide a first possible implementation manner of the second aspect, where a first side of the central cross beam of the extruder is connected to a first container cross beam through a connecting rod, a second side of the central cross beam of the extruder is connected to a second container cross beam through a connecting rod, the first container is connected to the first container cross beam, and the second container is connected to the second container cross beam.

In combination with the second aspect, the embodiments of the present invention provide a second possible implementation manner of the second aspect, wherein the die inlet and the die outlet form a cavity in a central beam of the extruder, and the cavity is communicated with the first extrusion container inlet, the second extrusion container inlet and the curved profile outlet simultaneously; the upper surface and the lower surface of the cavity are both provided with sliding chutes.

In a third aspect, an embodiment of the present invention provides an extrusion method for implementing a bidirectional extrusion forming process, where the extrusion method is used in an extrusion apparatus for implementing a bidirectional extrusion forming process as described in the second aspect, and includes the following steps:

the male die and the female die are installed in a matched mode and pushed in from the die inlet and the die outlet of the central beam of the extruder along the sliding groove through the push-pull rod, and the push-pull rod applies pressure to the extrusion die to enable the female die and the male die to be locked mutually;

respectively placing two extruded bars into a first extrusion container and a second extrusion container, applying pressure to a central beam on a first extrusion container beam and a second extrusion container beam to enable the first extrusion container beam and the second extrusion container beam to move towards the central beam of the extrusion machine, and respectively attaching the first extrusion container and the second extrusion container to two surfaces of a male die so that the extrusion containers and the die are locked with each other;

respectively applying loads to the extruded bars in the first extrusion cylinder and the second extrusion cylinder to enable the extruded bars to move towards a central cross beam of the extruder;

extruding a bar stock to gradually enter two inlets of the male die, then carrying out solid-state welding in a cavity at the periphery of the die core, and flowing out from a space between the female die and the male die working belt to form a hollow section; in this step, a variable-curvature hollow profile, which is bidirectionally curved in length, can be obtained by regulating the extrusion speed of the extruded rod.

And after the blank in the extrusion container is extruded to a preset length, the first extrusion container cross beam and the second extrusion container cross beam are retracted, the shearing device enters from the die inlet of the central cross beam of the extrusion machine, and the pressure residue is sheared.

The beneficial effects of the above-mentioned embodiment of the present invention are as follows:

1) in the extrusion die for realizing the bidirectional extrusion forming process, the novel structural form of double material inlets and a side material outlet is adopted, and the axis of the double material inlets is vertical to the axis of the material outlet. This particular design has three main advantages: the material flow rate of each material inlet is controlled independently, so that the bending curvature of the section obtained after the materials respectively entering the welding cavity from the two material inlets are welded and flow out of the extrusion die working belt is effectively controlled; secondly, the material entering the cavity of the extrusion die from the feeding port deflects by 90 degrees in the flow direction, and the material is subjected to strong shearing deformation in the deflection process, so that the material is favorable for obtaining good welding quality, and can have fine grains and special textures, thereby remarkably improving the performance of the extruded bent section; and thirdly, the male die and the female die are easy to assemble, position, disassemble and replace.

2) In the extrusion device for realizing the bidirectional extrusion forming process, the novel central beam structure of the extruder is used, so that the mounting, fixing and dismounting of the bidirectional extrusion die are realized. Through the novel combined structure form of the central beam of the extruder, the first extrusion container and the second extrusion container, automatic feeding and pressure trimming in the bidirectional extrusion process are realized, frequent removal of the extrusion containers and the extrusion dies is avoided, and the production efficiency is improved. By adopting the form that the first extrusion container and the second extrusion container are locked with the two sides of the fixed male die, the male die can be effectively prevented from deforming, and the stress condition of the die is improved. The extrusion device not only realizes bidirectional extrusion action, but also has compact structure, easy automation, convenient operation, high production efficiency and wide application range.

3) In the extrusion method for realizing the bidirectional extrusion forming process provided by the embodiment of the invention, bidirectional bending of the bent section is realized, and the variable-curvature section with a plurality of bending sections along the length direction of the section can be manufactured. The types of the bent section include wire, bar, pipe, special-shaped solid section and various hollow sections. The important functions of die disassembly and assembly, automatic feeding, bidirectional extrusion, pressure residue shearing and the like are realized.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

Figure 1 is a three-dimensional exploded view of the present invention according to one or more embodiments,

figure 2 is an assembled cross-sectional view of the present invention according to one or more embodiments,

figure 3 is a three-dimensional view of an extruder center beam according to one or more embodiments of the present invention,

figure 4 is a cross-sectional view of a mold according to one or more embodiments of the invention,

FIG. 5 is a schematic representation of a final product shape according to one or more embodiments of the present disclosure.

In the figure: 1. the extrusion machine comprises an extrusion machine central beam, 2 parts of a first extrusion container beam, 3 parts of a second extrusion container beam, 4 parts of a connecting rod, 5 parts of a first extrusion container, 6 parts of a second extrusion container, 7 parts of a female die, 8 parts of a male die, 9 parts of a hydraulic push-pull rod, 3-001 parts of a first extrusion container inlet, 3-002 parts of a second extrusion container inlet, 3-003 parts of a bent profile outlet, 3-004 parts of a die inlet and a die outlet, 3-005 parts of a chute, 4-001 parts of a first die inlet, 4-002 parts of a second die inlet, 4-003 parts of a welding chamber, 4-004 parts of a die core, 4-005 parts of a male die working zone, 4-006 parts of a female die working zone.

The spacing or dimensions between each other are exaggerated to show the location of the various parts, and the illustration is for illustrative purposes only.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an", and/or "the" are intended to include the plural forms as well, unless the invention expressly state otherwise, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof;

for convenience of description, the words "up", "down", "left" and "right" in the present invention, if any, merely indicate correspondence with up, down, left and right directions of the drawings themselves, and do not limit the structure, but merely facilitate the description of the invention and simplify the description, rather than indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the invention.

The terms "mounted", "connected", "fixed", and the like in the present invention are to be understood in a broad sense, and may be, for example, fixedly connected, detachably connected, or integrated; the two components can be connected mechanically or electrically, directly or indirectly through an intermediate medium, or connected internally or in an interaction relationship, and the terms used in the present invention should be understood as having specific meanings to those skilled in the art.

As described in the background, there are many advantages to bi-extrusion processes, but no dedicated extruder and extrusion die have been developed for bi-extrusion processes. The problems of structural design, quick disassembly and assembly, automatic feeding, realization of bidirectional extrusion action, discard shearing and the like of the bidirectional extrusion die are main problems for realizing the bidirectional extrusion process. In order to solve the technical problems, the invention provides an extrusion die, an extrusion device and an extrusion method for realizing a bidirectional extrusion forming process.

Example 1

In a typical embodiment of the present invention, please refer to fig. 4, this embodiment discloses an extrusion die for implementing a bidirectional extrusion forming process, which includes a male die 8 and a female die 7, wherein the male die 8 is matched with the female die 7;

the female die 7 is provided with an opening as a discharge hole, a working band is arranged at the opening, and the shape of the opening is consistent with the shape of the cross section of the outer surface of the hollow section product.

The male die 8 is provided with two feeding ports and a discharging port, the two feeding ports are respectively located on a first side face and a second side face of the male die 8, the first side face and the second side face of the male die 8 are two opposite side faces of the male die 8, the discharging port is located on a third side face, the third side face is located between the first side face and the second side face, and the axes of the two feeding ports are on the same straight line and perpendicular to the axis of the discharging port.

It can be understood that the first side, the second side and the third side of the male die 8 in this embodiment are all components forming the outer surface of the male die 8, and a T-shaped or star-shaped channel is formed between two feeding ports and one discharging port; when the axes of the two feeding ports of the male die are on the same straight line and are at right angles with the axis of the discharge port, a T-shaped channel is formed between the two feeding ports and one discharge port; when the axes of the two feeding ports of the male die are positioned on different straight lines, a star-shaped channel is formed between the two feeding ports and one discharging port.

The male die 8 is also provided with a die core 4-004, the die core 4-004 is provided with a working band 4-005, and the shape of the working band is consistent with the shape of the section of the inner surface of the hollow section product. It will be appreciated that in this embodiment the extruded profile is a hollow profile and therefore has a mandrel 4-004.

It will be understood that the work belt is a section of the aluminum extrusion die adjacent to the die opening for ensuring the shape, size and surface quality of the extruded product, and is not a specific component.

Referring to fig. 4, after the female die 7 and the male die 8 are assembled, there is a cavity around the core 4-004, which is the weld chamber 4-003.

Example 2

In a typical embodiment of the present invention, as shown in fig. 1, this embodiment discloses an extrusion apparatus for implementing a bidirectional extrusion forming process, which includes an extruder central beam 1, an extrusion container beam 2, an extrusion container beam 3, a connecting rod 4, a first extrusion container 5, a second extrusion container 6, a hydraulic push-pull rod 9, and a bidirectional extrusion die disclosed in embodiment 1. In the structure shown in fig. 1, the central beam 1 of the extruder is located at the central position, the left side and the right side of the central beam are respectively provided with a container beam and a container, and the central beam 1 of the extruder is connected with the container beams at the left side and the right side of the central beam through connecting rods 4.

That is, the two sides of the central beam 1 of the extruder are respectively connected with the

beams

2 and 3 of the first extrusion container 5 and the second extrusion container 6 through the connecting rods 4, and the

beams

2 and 3 of the first extrusion container 5 and the second extrusion container 6 can reciprocate along the connecting rods 4, so that the

beams

2 and 3 of the first extrusion container 5 and the second extrusion container 6 can be close to or far away from the central beam 1 of the extruder.

The inner side of the cross beam 2 of the first extrusion container 5 is provided with the first extrusion container 5, the inner side of the cross beam 3 of the second extrusion container 6 is provided with the second extrusion container 6, one side of the central cross beam 1 of the extruding machine, which is close to the cross beam 2 of the first extrusion container 5, is provided with a first extrusion container inlet 3-001, and one side of the central cross beam 1 of the extruding machine, which is close to the cross beam 3 of the second extrusion container 6, is provided with a second extrusion container inlet 3-002.

In this embodiment, the number of links 4 is 4.

It will be appreciated that, in space, the extruder center beam 1, the container beam 2, the container 1 and the container 2 are positioned on the same straight line at the radial centers.

It can be understood that the central beam 1 of the extruder, the female die 7, the male die 8 and the hydraulic push-pull rod 9 are positioned on a straight line in the space. The axis of the hydraulic push-pull rod 9 is perpendicular to the axis of the connecting rod 4.

The extruder central beam 1 has a curved profile outlet 3-003 in addition to the first and second barrel inlets 3-001 and 3-002; referring to fig. 3, in the front-back direction of the central beam 1 of the extruder, the front side surface of the extruder is provided with a die inlet/outlet 3-004, the die inlet/outlet 3-004 is simultaneously communicated with a first extrusion container inlet 3-001, a second extrusion container inlet 3-002 and a bent profile outlet 3-003, in fig. 3, the die inlet/outlet 3-004 inwards forms a cavity in the central beam 1 of the extruder, and the cavity is simultaneously communicated with the first extrusion container inlet 3-001, the second extrusion container inlet 3-002 and the bent profile outlet 3-003; the upper surface and the lower surface of the cavity are both provided with chutes 3-005; meanwhile, a first side surface of the central beam 1 of the extruding machine is also provided with a chute 3-005, and the chute 3-005 passes through an inlet and an outlet 3-004 of the die.

It will be appreciated that the extruder central beam 1 has eight openings for connecting four connecting rods 4 in addition to the first barrel inlet 3-001, the second barrel inlet 3-002 and the curved profile outlet 3-003.

The radial center of the first container inlet 3-001 is collinear with the radial center of the first container 5 and the radial center of the second container inlet 3-002 is collinear with the radial center of the second container 6.

The diameter of the first container inlet 3-001 is larger than the diameter of the outer surface of the first container 5; the diameter of the secondary container inlets 3-002 is greater than the diameter of the outer surface of the secondary container 6.

In space, the outlet 3-003 of the bent section bar is coaxial with the inlet 3-004 of the die, the inlet 3-001 of the first extrusion container is coaxial with the inlet 3-002 of the second extrusion container, and the axial lines of the outlet 3-003 of the bent section bar and the inlet 3-004 of the die are vertical to the axial lines of the inlet 3-001 of the first extrusion container and the inlet 3-002 of the second extrusion container.

The size of the outlet 3-003 of the bent section is larger than that of a discharge hole on the female die 7;

the size of the mold inlet and outlet 3-004 is larger than the external dimensions of the female mold 7 and the male mold 8.

Example 3

In a typical embodiment of the present invention, example 3 provides an extrusion method for implementing a bi-directional extrusion process, which employs the extrusion apparatus for implementing a bi-directional extrusion process as disclosed in example 2, and comprises the following steps:

before the bidirectional extrusion, the female die 7 and the male die 8 are connected together by connecting and positioning parts thereon and are pushed in from the die inlet of the central beam 1 of the extruder along the chutes 3-005 by a hydraulic push-pull rod 9. The hydraulic push-pull rod 9 applies certain pressure to the extrusion die to lock the female die 7 and the male die 8 mutually;

two extruded bars are respectively placed into a first extrusion container 5 and a second extrusion container 6 through a feeding mechanism, then a beam 2 of the first extrusion container 5 and a beam 3 of the second extrusion container 6 both move towards a central beam 1 of the extrusion machine through a certain hydraulic transmission mechanism, so that the first extrusion container 5 and the second extrusion container 6 are respectively attached to two surfaces of a male die 8, and a certain force is applied to enable the extrusion containers and the dies to be locked with each other;

respectively applying loads to the bars in the two extrusion cylinders to enable the bars to move towards a central cross beam 1 of the extruder; at the moment, the material gradually enters two inlets of the male die 8, then solid welding is carried out in a welding chamber 4-003, and the material flows out from between the working belt of the female die 7 and the working belt of the male die 8 to form a hollow section;

by controlling the extrusion speed of the material in the two barrels, a hollow profile with a variable curvature curve in length can be obtained, as shown in fig. 5.

When the blank in the extrusion container is extruded to a preset length, the

extrusion container beams

1 and 2 are retracted under the action of a hydraulic transmission mechanism, a shearing device enters from the die inlet of the central beam 1 of the extrusion machine, and the excess pressure is sheared.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An extrusion die for realizing a bidirectional extrusion forming process is characterized by comprising a male die and a female die which are matched, wherein one side surface of the male die can be matched with the female die; the male die is provided with a T-shaped or star-shaped channel, the T-shaped or star-shaped channel forms an opening on the surface of the male die, two opposite openings of the T-shaped or star-shaped channel are feeding openings, and openings except the two opposite openings of the T-shaped or star-shaped channel are discharging openings; the female die is provided with a through hole, and after the male die and the female die are installed in a matched mode, the discharge hole of the male die is coaxial with the through hole of the female die.

2. The extrusion die for realizing the bidirectional extrusion forming process as recited in claim 1, wherein the axes of the two feeding ports of the male die are on the same straight line and form a right angle with the axis of the discharging port.

3. The extrusion die for carrying out the bi-directional extrusion process as recited in claim 1, wherein the male die has a core, and the core terminates in a working band.

4. An extrusion die for performing a bi-directional extrusion process as recited in claim 1, wherein the core has a cavity at a periphery thereof for welding when the male die is mated with the female die.

5. An extrusion device for realizing a bidirectional extrusion molding process, which is characterized by comprising a central beam of an extruder, a first extrusion cylinder, a second extrusion cylinder, a push-pull rod and the extrusion die for realizing the bidirectional extrusion molding process as claimed in any one of claims 1 to 4, wherein the push-pull rod is fixedly connected with a male die, the first side surface and the second side surface of the central beam of the extruder are respectively provided with a first extrusion cylinder inlet and a second extrusion cylinder inlet, the front side surface of the central beam of the extruder is provided with a die inlet and a die outlet, the rear side surface of the central beam of the extruder is provided with a bent profile outlet, after the extrusion die for realizing the bidirectional extrusion forming process enters the inlet and the outlet of the die, the first extrusion container passes through the inlet of the extrusion container of the first extrusion container and is in contact with the first side surface of the male die, and the second extrusion container passes through the inlet of the extrusion container of the second extrusion container and is in contact with the second side surface of the male die.

6. An extrusion apparatus for performing a bi-directional extrusion process as recited in claim 5 wherein said extruder center beam is connected on a first side to a first barrel beam by a connecting rod and on a second side to a second barrel beam by a connecting rod, said first barrel being connected to the first barrel beam and said second barrel being connected to the second barrel beam.

7. An extrusion apparatus for performing a bi-directional extrusion process as recited in claim 5 wherein said die inlet and outlet define a cavity in a central beam of the extruder, the cavity communicating with the first container inlet, the second container inlet and the curved profile outlet; the upper surface and the lower surface of the cavity are both provided with sliding chutes.

8. The extrusion apparatus for performing a bi-directional extrusion process as recited in claim 5 wherein the diameter of the inlet of the first container is greater than the diameter of the outer surface of the first container; the diameter of the inlet of the second extrusion container is larger than the diameter of the outer surface of the second extrusion container; the size of the outlet of the bent section is larger than that of the discharge hole of the female die; the size of the inlet and the outlet of the die is larger than the external dimensions of the female die and the male die.

9. An extrusion apparatus for performing a bi-directional extrusion process as recited in claim 5 wherein said curved profile outlet and said die access are coaxial, said first container inlet and said second container inlet are coaxial, and the axis of said curved profile outlet and said die access are perpendicular to the axis of said first container inlet and said second container inlet.

10. An extrusion method for realizing a bidirectional extrusion molding process, which is characterized by using the extrusion device for realizing the bidirectional extrusion molding process according to any one of claims 5 to 9, and comprises the following steps:

extruding a bar stock to gradually enter two inlets of the male die, then carrying out solid-state welding in a cavity at the periphery of the die core, and flowing out from a space between the female die and the male die working belt to form a hollow section; in the step, the hollow section with the length being bidirectionally-variable-curvature bent can be obtained by regulating and controlling the extrusion speed of the extruded bar;