阅读说明：本技术 一种预制棒锥头的加工装置及加工方法 (Processing device and processing method for prefabricated rod conical head ) 是由 崔东明 孔明 伍淑坚 于 2019-10-08 设计创作，主要内容包括：本发明公开了一种预制棒锥头的加工装置及加工方法,该加工装置包括安装板、上夹具、下夹具、加热机构、第一驱动设备和第二驱动设备；上夹具组设于安装板上且用于夹持预制棒顶部；下夹具可移动地组设于安装板上,且位于所述上夹具下方,并用于夹持或松开预制棒底部；加热机构具有一加热区,所述加热区用于收容并加热预制棒；第一驱动设备组设于安装板上,且与所述下夹具连接,并用于驱动所述下夹具靠近或远离所述上夹具；第二驱动设备与安装板相连,并用于驱动安装板升降。本发明解决了采用重力掉锥方式造成锥头形状与尺寸难以统一的问题。(The invention discloses a processing device and a processing method of a prefabricated rod conical head, wherein the processing device comprises an installation plate, an upper clamp, a lower clamp, a heating mechanism, a first driving device and a second driving device; the upper clamp group is arranged on the mounting plate and used for clamping the top of the prefabricated rod; the lower clamp is movably assembled on the mounting plate, is positioned below the upper clamp and is used for clamping or loosening the bottom of the prefabricated rod; the heating mechanism is provided with a heating zone which is used for accommodating and heating the preform; the first driving equipment group is arranged on the mounting plate, is connected with the lower clamp and is used for driving the lower clamp to be close to or far away from the upper clamp; the second driving device is connected with the mounting plate and used for driving the mounting plate to lift. The invention solves the problem that the shape and the size of the cone head are difficult to unify due to the adoption of a gravity cone falling mode.)

1. A preform rod taper head processing device is characterized by comprising:

a mounting plate (1);

the upper clamp (2) is arranged on the mounting plate (1) and is used for clamping the top of the prefabricated rod (8);

the lower clamp (3) is movably assembled on the mounting plate (1), is positioned below the upper clamp (2), and is used for clamping or loosening the bottom of the prefabricated rod (8);

a heating mechanism (4) having a heating zone for accommodating and heating the preform (8);

the first driving device (5) is assembled on the mounting plate (1), is connected with the lower clamp (3) and is used for driving the lower clamp (3) to be close to or far away from the upper clamp (2);

and the second driving device (6) is connected with the mounting plate (1) and is used for driving the mounting plate (1) to lift.

2. The apparatus for processing a preform rod end according to claim 1, wherein the lower jig (3) comprises:

a chuck (30);

and a plurality of jaws (31) movably assembled on the chuck (30), the plurality of jaws (31) being capable of approaching each other and gripping the preform (8) or moving away from each other and releasing the preform (8).

3. The apparatus for processing a taper head of a preform according to claim 1, wherein: and the upper clamp (2) is provided with a vacuumizing tool (7) for vacuumizing the sleeve (81).

4. The apparatus for processing a taper head of a preform according to claim 1, wherein: the displacement sensor is arranged on the mounting plate (1), the upper clamp (2) or the lower clamp (3), and is used for measuring the distance of the lower clamp (3) moving in the vertical direction relative to the upper clamp (2) and displaying the distance through display equipment.

5. A method for processing a preform taper head is characterized by comprising the following steps:

providing a preform tap processing apparatus according to claim 1;

vertically clamping a prefabricated rod (8) on the upper clamp (2) and the lower clamp (3) to enable the bottom end of a core rod (83) to be located in the heating zone, wherein the prefabricated rod (8) comprises an upper auxiliary sleeve (80), a sleeve (81), a lower auxiliary sleeve (82) and the core rod (83) located in the sleeve (81), wherein the upper auxiliary sleeve, the sleeve (81) and the lower auxiliary sleeve are sequentially connected from top to bottom;

heating the mandrel (83) by the heating mechanism (4) for a preset time;

the lower clamp (3) loosens the lower auxiliary sleeve (82) and drives the lower clamp (3) to descend to a preset position;

continuing heating, clamping the lower auxiliary sleeve (82) by the lower clamp (3) when the lower auxiliary sleeve (82) falls down onto the lower clamp (3), and performing a tapering process to form a tapered part;

and cutting the cone part to obtain a cone head.

6. A method for processing a preform taper head is characterized by comprising the following steps:

providing a sleeve assembly comprising an upper sub-sleeve (80), a sleeve (81) and a lower sub-sleeve (82) connected in sequence from top to bottom, and a preform nose processing apparatus according to claim 3;

inserting a core rod (83) into the sleeve (81), and clamping an upper auxiliary sleeve (80) and a lower auxiliary sleeve (82) on the upper clamp (2) and the lower clamp (3), respectively, so that the core rod (83) is partially positioned in the heating zone;

the sleeve (81) is vacuumized through the vacuumizing tool (7);

starting the heating mechanism (4), and melting the core rod (83) and the sleeve (81) into a solid rod to obtain a prefabricated rod (8);

heating the bottom end of the core rod (83) for a preset time;

the lower clamp (3) loosens the lower auxiliary sleeve (82) and drives the lower clamp (3) to descend to a preset position;

continuing heating by the heating mechanism (4), clamping the lower auxiliary sleeve (82) by the lower clamp (3) when the lower auxiliary sleeve (82) falls onto the lower clamp (3), and performing a tapering process to form a tapered part;

and cutting the cone part to obtain a cone head.

7. The method of processing a taper head of a preform according to claim 6, wherein: and heating the bottom end of the mandrel (83) for a preset time by adopting the residual heat of the heating mechanism (4).

8. The method for processing a tapered end of a preform according to claim 5 or 6, wherein the tapering process comprises the steps of:

driving the lower clamp (3) to descend at a first preset speed through the first driving device (5), and driving the lower clamp (3) to descend at a second preset speed through the first driving device (5) for a second preset distance when the first preset distance is reached, so as to finish cone drawing;

wherein the first preset speed is less than the second preset speed.

9. The method for processing a tapered end of a preform according to claim 8, wherein the tapering process further comprises the steps of:

driving the mounting plate (1) to ascend by a third preset distance at a third preset speed through a second driving device (6); the second driving device (6) drives the mounting plate (1) to ascend and the first driving device (5) drives the lower clamp (3) to descend simultaneously;

and the third preset speed is less than or equal to the first preset speed.

10. The method of fabricating a taper head of a preform according to claim 5 or 6, further comprising the steps of, before cutting the taper portion: after cooling in the heating zone for a period of time, the mounting plate (1) is driven by the second driving device (6) to move downwards until the cone is positioned outside the heating zone, and natural cooling is carried out.

Technical Field

The invention relates to the technical field of optical fiber perform processing, in particular to a processing device and a processing method of a preform taper head.

Background

The drawing length of the single optical fiber preform is improved, the optical fiber production efficiency can be effectively improved, and the manufacturing cost is reduced. Thus, optical fiber preforms are gradually being developed in larger dimensions, and the drawable length of a single rod has reached thousands of kilometers.

For the manufacturing technology of large-size optical fiber preforms, a two-step manufacturing process is mainly adopted, namely, a core rod with a certain refractive index profile and a certain geometric size is prepared, and then a cladding with a certain thickness is coated. Among many outer cladding manufacturing processes, the sleeving method (RIC) easily produces a large-sized optical fiber preform having stable optical parameters since the sleeve is not limited in size and has a uniform geometric size. In CN101328012A, a method for manufacturing a large-sized optical fiber preform by a high-efficiency and low-cost fusion-shrink tube process is introduced.

Before drawing the optical fiber preform, the starting part needs to be processed in advance to manufacture a streamline conical head, so that the subsequent optical fiber drawing operation is facilitated.

Most manufacturers adopt a cone head processing mode of high-temperature cone falling, namely, the processed part is melted at high temperature and gradually thinned by falling under the action of gravity to form a cone. The processing mode is affected by the gravity of the lower cone part, so that the length and the shape of the cone head of each prefabricated rod are difficult to unify, the loss of the prefabricated rod is more, and the waste of the prefabricated rod is caused.

Patent document CN103739193A describes a method for welding the remaining cone of the drawn wire to the preform to form a cone, which can reduce the waste of the preform, but involves multiple cutting and welding operations, and the process is complicated, and has high requirements for the remaining cone.

Patent document CN105271702A describes a method of heating and softening the front section of a preform to form a V-shaped groove, and then horizontally tapering the preform after butt-jointing a quartz rod with the preform. Although the method can effectively reduce the taper loss, the operation difficulty is high, and the unification of the length and the shape of the taper head is difficult to ensure.

Especially for large-sized sleeve preforms, the conventional cone head processing methods have the problems of difficult operation and low efficiency due to large size, heavy weight, and long time for heating, softening and cooling, and therefore, a new cone head processing method needs to be developed.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a device and a method for processing a prefabricated rod conical head, which solve the problem that the conical head shape and size are difficult to unify due to the adoption of a gravity conical dropping mode.

In order to achieve the above purposes, the technical scheme adopted by the invention is as follows:

a preform rod taper head processing apparatus, comprising:

mounting a plate;

the upper clamp is arranged on the mounting plate and used for clamping the top of the prefabricated rod;

the lower clamp is movably assembled on the mounting plate, is positioned below the upper clamp and is used for clamping or loosening the bottom of the prefabricated rod;

the heating mechanism is provided with a heating zone, and the heating zone is used for accommodating and heating the preform;

the first driving device is arranged on the mounting plate, connected with the lower clamp and used for driving the lower clamp to be close to or far away from the upper clamp;

and the second driving device is connected with the mounting plate and is used for driving the mounting plate to lift.

Further, the lower jig includes:

a chuck;

and a plurality of jaws movably assembled on the chuck, the plurality of jaws being capable of approaching each other and gripping the preform or moving away from each other and releasing the preform.

Further, the upper clamp is provided with a vacuumizing tool for vacuumizing the sleeve.

Further, a displacement sensor is arranged on the mounting plate, the upper clamp or the lower clamp, and is used for measuring the distance of the lower clamp moving in the vertical direction relative to the upper clamp and displaying the distance through a display device.

The invention also provides a processing method of the prefabricated rod conical head, which comprises the following steps:

providing a preform rod end processing device as described above;

vertically clamping a prefabricated rod on the upper clamp and the lower clamp to enable the bottom end of the mandrel to be located in the heating area, wherein the prefabricated rod comprises an upper auxiliary sleeve, a sleeve and a lower auxiliary sleeve which are sequentially connected from top to bottom and the mandrel located in the sleeve;

heating the core rod to a preset time through the heating mechanism;

the lower clamp loosens the lower auxiliary sleeve and drives the lower clamp to descend to a preset position;

continuing heating, when the lower auxiliary sleeve falls onto a lower clamp, clamping the lower auxiliary sleeve through the lower clamp, and performing a tapering process to form a tapered part;

and cutting the cone part to obtain a cone head.

The invention also provides a processing method of the prefabricated rod conical head, which comprises the following steps:

providing a sleeve assembly and a processing device of the preform taper head, wherein the sleeve assembly comprises an upper auxiliary sleeve, a sleeve and a lower auxiliary sleeve which are sequentially connected from top to bottom;

inserting a core rod into the sleeve, and clamping an upper auxiliary sleeve and a lower auxiliary sleeve on the upper clamp and the lower clamp respectively to enable the core rod to be partially positioned in the heating zone;

vacuumizing the sleeve through the vacuumizing tool;

starting the heating mechanism, and melting the core rod and the sleeve into a solid rod to obtain a prefabricated rod;

heating the bottom end of the core rod for a preset time;

the lower clamp loosens the lower auxiliary sleeve and drives the lower clamp to descend to a preset position;

continuously heating by the heating mechanism, clamping the lower auxiliary sleeve by the lower clamp when the lower auxiliary sleeve falls onto the lower clamp, and performing a tapering process to form a tapered part;

and cutting the cone part to obtain a cone head.

Further, the bottom end of the mandrel is heated to a preset time, and the residual temperature of the heating mechanism is adopted for heating.

Further, the tapering process comprises the following steps:

driving the lower clamp to descend at a first preset speed through first driving equipment until the lower clamp descends for a second preset distance at a second preset speed through the first driving equipment, and finishing tapering;

wherein the first preset speed is less than the second preset speed.

Further, the tapering process further comprises the following steps:

driving the mounting plate to ascend by a third preset distance at a third preset speed through second driving equipment; the second driving device drives the mounting plate to ascend and the first driving device drives the lower clamp to descend simultaneously;

and the third preset speed is less than or equal to the first preset speed.

Further, before cutting the taper, the method further comprises the following steps: after cooling in the heating area for a period of time, the mounting plate is driven by the second driving device to move downwards until the cone part is positioned outside the heating area, and natural cooling is performed.

Compared with the prior art, the invention has the advantages that:

the invention controls the first driving device and the second driving device to carry out cone drawing, standardizes the cone drawing operation, and is easier to realize the unification of the shape and the size of the cone head under the condition of unchanged process parameters, thereby solving the problem that the shape and the size of the cone head are difficult to unify due to the adoption of the cone drawing mode which is manually uncontrollable, namely gravity cone falling.

Drawings

FIG. 1 is a first schematic view of a preform taper head processing apparatus according to an embodiment of the present invention;

FIG. 2 is a second schematic view of a preform taper head processing apparatus according to an embodiment of the present invention;

fig. 3 is a schematic view of a taper portion of a preform according to an embodiment of the present invention.

In the figure: 1. mounting a plate; 2. an upper clamp; 3. a lower clamp; 30. a chuck; 31. a claw; 32. a through hole; 4. a heating mechanism; 5. a first driving device; 6. a second driving device; 7. vacuumizing the tool; 8. performing a rod; 80. an upper auxiliary sleeve; 81. a sleeve; 82. a lower auxiliary sleeve; 83. and (4) a core rod.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

Referring to fig. 1 and 2, a first embodiment of the present invention provides a preform rod nose processing apparatus, which includes a mounting plate 1, an upper jig 2, a lower jig 3, a heating mechanism 4, a first driving device 5 and a second driving device 6; wherein:

the upper clamp 2 is arranged on the mounting plate 1 and used for clamping the top of the prefabricated rod 8;

the lower clamp 3 is used for clamping or loosening the bottom of the prefabricated rod 8, and the lower clamp 3 is movably assembled on the mounting plate 1, is positioned below the upper clamp 2 and is arranged opposite to the upper clamp 2;

the heating mechanism 4 is provided with a heating zone for accommodating and heating the preform 8;

the first driving device 5 is arranged on the mounting plate 1, connected with the lower clamp 3 and used for driving the lower clamp 3 to be close to or far away from the upper clamp 2;

the second driving device 6 is connected with the mounting plate 1 and is used for driving the mounting plate 1 to lift, thereby driving the upper clamp 2, the lower clamp 3 and the first driving device 5 to lift integrally.

The processing device provided by the embodiment, when in use, vertically clamp the prefabricated stick 8 between the upper clamp 2 and the lower clamp 3, heat the processing position of the prefabricated stick 8 for a period of time through the heating mechanism 4, then loosen the lower clamp 3, and drive the lower clamp 3 to descend to be separated from the prefabricated stick 8 through the first driving device 5, and keep a certain vertical distance, when the lower part of the processing position of the prefabricated stick 8 is softened and falls down onto the lower clamp 3 under the action of gravity, clamp the lower part at the moment, and carry out the tapering operation through the first driving device 5 and the second driving device 6, so as to obtain the conical head. The processing device performs tapering by controlling the first driving device 5 and the second driving device 6, standardizes tapering operation, and is easier to realize the unification of the shape and the size of the conical head under the condition of unchanged technological parameters, thereby solving the problem that the shape and the size of the conical head are difficult to unify due to the adoption of a manually uncontrollable tapering mode of gravity tapering; and moreover, the taper drawing mode is adopted, and the taper drawing loss can be obviously reduced in a gravity taper falling mode.

Referring to fig. 1 and 2, a second embodiment of the present invention provides an apparatus for processing a taper head of a preform, which is different from the first embodiment in that: the lower chuck 3 includes a chuck 30 and a plurality of jaws 31 movably assembled to the chuck 30, and the plurality of jaws 31 can approach each other and grip the preform 8 or move away from each other and release the preform 8.

The mounting plate 1, the upper clamp 2 or the lower clamp 3 is provided with a displacement sensor (not shown in the figure) which is used for measuring the distance of the lower clamp 3 moving in the vertical direction relative to the upper clamp 2 and displaying the distance through a display device.

Referring to fig. 1 and 2, a third embodiment of the present invention provides an apparatus for processing a taper head of a preform, which is different from the first embodiment in that: the lower clamp 3 includes a chuck 30 and a plurality of jaws 31 movably assembled on the chuck 30, the chuck 30 having a through hole 32, the plurality of jaws 31 being capable of approaching the through hole 32 and gripping the preform 8 or departing from the through hole 32 and releasing the preform 8; the upper clamp 2 is provided with a vacuumizing tool 7 for vacuumizing the sleeve 81, and the vacuumizing tool 7 further has cooling and sealing functions, and adopts the existing equipment, which is not described herein.

This embodiment sets up evacuation frock 7 and through-hole 32, and its meaning lies in: when the conical head of the traditional large-size sleeve preform is processed, after the melting and shrinking are finished, the large-size sleeve preform is naturally cooled to a low temperature on melting and shrinking equipment, the process generally needs more than several hours, and then the large-size sleeve preform is taken down from the melting equipment by using hoisting equipment; then cutting off the lower auxiliary sleeve by using a cutting machine, and cleaning the cut part; then the material is sent to cone falling equipment, the material is hoisted to the cone falling equipment by using hoisting equipment, the temperature is raised, the cone is dropped, the material is hoisted and taken down after being cooled, the processing of the cone head is finished, the process is tedious and time-consuming, and the process is difficult to operate due to multiple hoisting and carrying; and this embodiment, collect melt shrink and draw awl in an organic whole, the processingequipment that this embodiment provided is equipped with evacuation frock 7, accomplish through this processingequipment and melt shrink and form jumbo size sleeve pipe prefabricated stick after, directly carry out the cone head processing on this processingequipment, obvious easy operation, the process is simplified, can draw the awl to hot prefabricated stick moreover, perhaps heat through the waste heat of heating mechanism, and not heat refrigerated prefabricated stick, consequently, the heating is consuming time short, draws awl efficiently, has reduced the energy consumption simultaneously.

Referring to fig. 1 to 3, a fourth embodiment of the present invention provides a method for processing a taper head of a preform, including the steps of:

s1: providing a preform taper head processing apparatus of the first embodiment;

s2: providing a prefabricated rod 8, wherein the diameter of the prefabricated rod is D, the prefabricated rod 8 comprises an upper auxiliary sleeve 80, a sleeve 81, a lower auxiliary sleeve 82 and a mandrel 83 positioned in the sleeve 81, the upper auxiliary sleeve 80, the sleeve 81, the lower auxiliary sleeve 82 and the mandrel 83 are sequentially connected from top to bottom, the prefabricated rod 8 is vertically arranged, the upper auxiliary sleeve 80 and the lower auxiliary sleeve 82 are respectively clamped on the upper clamp 2 and the lower clamp 3, the bottom end of the mandrel 83 is used as a conical head processing position, and the bottom end of the mandrel 83 is positioned in;

s3: starting the heating mechanism 4, heating the mandrel 83 to a preset time through the heating mechanism 4, wherein the preset time is set according to the actual situation, the step is used for preheating the machining position of the conical head, and the lower auxiliary sleeve 82 is not softened to be capable of falling;

s4: the lower clamp 3 loosens the lower auxiliary sleeve 82 and drives the lower clamp 3 to descend to a preset position, at the preset position, the lower clamp 3 is completely separated from the lower auxiliary sleeve 82, and a vertical distance exists, wherein the specific vertical distance is set according to actual conditions, in the embodiment, the lower clamp 3 is separated from the lower auxiliary sleeve 82 and keeps a vertical distance of 10-20 mm;

s5: continuing to heat, in the embodiment, rapidly heating the heating mechanism 4 to 1900-2200 ℃ within 15-30 min, keeping the heating state, gradually melting and softening the conical head processing position at a high temperature, clamping the lower auxiliary sleeve 82 through the lower clamp 3 when the lower auxiliary sleeve 82 falls to contact the upper surface of the lower clamp 3 under the action of gravity, and performing a tapering process to form a conical part;

s6: after cooling for a period of time in the heating area, the mounting plate 1 is driven to move downwards through the second driving device 6, so that the preform 8 integrally moves downwards to the position where the cone part is located outside the heating area, natural cooling is performed, and the position where the diameter d of the cone part is 20-30 mm is cut through a glass cutter, so that a streamline cone head with a specific size and a specific shape is obtained.

Referring to fig. 1 to 3, a fifth embodiment of the present invention provides a method for processing a preform taper head, including the steps of:

s1: providing a sleeve assembly and a preform taper head processing apparatus of claim 3, the sleeve assembly comprising an upper sub-sleeve 80, a sleeve 81 and a lower sub-sleeve 82 connected in this order from top to bottom;

s2: inserting a core rod 83 into the sleeve 81, and clamping the upper auxiliary sleeve 80 and the lower auxiliary sleeve 82 on the upper jig 2 and the lower jig 3, respectively, so that the core rod 83 is partially positioned in the heating zone;

s3: arranging a sealing element from the through hole 32, sealing the bottom of the lower auxiliary sleeve 82, and vacuumizing the sleeve 81 through a vacuumizing tool 7 with cooling and sealing functions;

s4: starting the heating mechanism 4, and melting the core rod 83 and the sleeve 81 to form a large-size sleeve solid rod from the position 30-50 mm below the top end of the lower auxiliary sleeve 82 by adopting a regionalized sintering technology at 1900-2200 ℃ to obtain a preform 8, wherein the diameter of the preform is D, such as 150-200 mm;

s5: the bottom end of the mandrel 83 is used as a conical head processing position, the residual temperature of the heating mechanism 4 is adopted to heat the bottom end of the mandrel 83 to the preset time, the residual temperature of the heating mechanism 4 for melting and preparing the preform rod 8 is fully utilized, the energy consumption is reduced, the overall production efficiency is improved, the length of the preset time is set according to the actual situation, the step is used for preheating the conical head processing position, and the lower auxiliary sleeve 82 is not softened to fall at the moment; the preform preparation and the tapering are carried out on the same apparatus as used in this example, and therefore, the preset time in this example is generally shorter than that in the fourth example,

s6: the lower clamp 3 loosens the lower auxiliary sleeve 82 and drives the lower clamp 3 to descend to a preset position, at the preset position, the lower clamp 3 is completely separated from the lower auxiliary sleeve 82, and a vertical distance exists, wherein the specific vertical distance is set according to actual conditions, in the embodiment, the lower clamp 3 is separated from the lower auxiliary sleeve 82 and keeps a vertical distance of 10-20 mm;

s7: heating is continuously carried out through the heating mechanism 4, in the embodiment, the heating mechanism 4 is rapidly heated to 1900-2200 ℃ within 15-30 min and is kept in a heating state, the conical head processing position is gradually melted and softened at high temperature, when the lower auxiliary sleeve 82 falls to contact the upper surface of the lower clamp 3 under the action of gravity, the lower clamp 3 clamps the lower auxiliary sleeve 82, and a tapering process is carried out to form a conical part;

s8: after cooling for a period of time in the heating area, the mounting plate 1 is driven to move downwards through the second driving device 6, so that the preform 8 integrally moves downwards to the position where the cone part is located outside the heating area, natural cooling is performed, and the position where the diameter d of the cone part is 20-30 mm is cut through a glass cutter, so that a streamline cone head with a specific size and a specific shape is obtained.

Referring to fig. 1 and 2, a sixth embodiment of the present invention provides a method for processing a taper head of a preform, which is different from the fourth or fifth embodiment in that: the tapering process comprises the following steps: driving the lower clamp 3 to descend at a first preset speed through the first driving device 5 until the first preset distance, driving the lower clamp 3 to descend at a second preset speed through the first driving device 5 for a second preset distance, and closing the heating mechanism 4 to finish tapering; wherein the first preset speed is less than the second preset speed. In this embodiment, the first predetermined speed is 50-100mm/min, the second predetermined speed is 200-.

The first driving device 5 drives the lower clamp 3 to descend in two stages, and the reasons are as follows: when tapering is started, the diameter of the preform 8 is still large, the viscosity of the molten part is large, the stretching tension is large, stretching needs to be performed at a first slower preset speed, after the diameter of the stretched part is reduced, the required stretching tension is small, and tapering forming can be performed at a second faster preset speed.

The tapering process further comprises the following steps: driving the mounting plate 1 to ascend by a third preset distance at a third preset speed through the second driving device 6; the second driving device 6 drives the mounting plate 1 to ascend and the first driving device 5 drives the lower clamp 3 to descend simultaneously; and the third preset speed is less than or equal to the first preset speed. In the embodiment, the third preset speed is 25-50mm/min, the third preset distance is 20-40mm,

the second driving device 6 drives the mounting plate 1 to ascend to lift the preform 8 upward by a certain height, and this process is performed simultaneously with the first driving device 5 driving the lower jig 3 to descend because: because the tapering operation time is short, if not simultaneously performed, melting of the surface layer of the preform 8 at a high temperature may cause a downward flow to cause local coarsening, and the preform 8 moves upward as a whole in order to change the heating position of the preform, thereby reducing the tapering loss.

The present invention is not limited to the above-described embodiments, and it will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the principle of the present invention, and such modifications and improvements are also considered to be within the scope of the present invention. Those not described in detail in this specification are within the skill of the art.