Vacuum sealed FDM 3D printer for preparing optical fiber preform

Abstract

The vacuum sealing FDM 3D printer comprises a printer body and a vacuum cover, the printer body is arranged on the inner wall of the vacuum cover, a sealing door used for blocking an in-out window is hinged to the surface of the vacuum cover, and the periphery of the outer surface of the sealing door is fixedly connected with a sealing ring and a rubber expansion ring. The surface of the sealing door is fixedly connected with an inflating assembly for inflating the rubber expansion ring, the left side of the vacuum cover is fixedly connected with a cold trap, a vacuum pump and a control panel, an air inlet pipe of the cold trap extends into the vacuum cover, and an exhaust pipe of the cold trap is fixedly communicated with an air inlet pipe of the vacuum pump. The vacuum cover is arranged outside the printer body, a printing area is isolated from the external environment in the printing process, the rubber expansion ring is inflated through the inflating assembly, air leakage of the sealing door is effectively avoided, the sealing performance of the sealing door is guaranteed, and the internal uniformity and surface flatness of a printed optical fiber preform are improved.

Description

Technical Field

[0001] The invention relates to the technical field of 3D printers, in particular to a vacuum sealed FDM 3D printer for preparing optical fiber preform rods. Background Art

[0002] 3D printing technology has been widely used in various engineering fields because it can print 3D structures of various shapes, especially applying 3D printing technology to optical devices. For example, using 3D printing technology to print optical fiber preforms can not only obtain preforms of various structures, but also effectively reduce costs and improve manufacturing efficiency.

[0003] The working principle of existing FDM 3D printers is to heat and melt the plastic filament, and then drive the extruder through a motor to extrude the molten plastic. The extruded molten plastic is ejected from the extruder head and deposited on the printing platform to form the first layer. Subsequently, the print head moves along a predetermined path, extruding and depositing the next layer of plastic, stacking layer by layer to form the entire 3D printed part.

[0004] If FDM 3D printing of optical fiber preforms is performed in a vacuum environment, air interference can be reduced, and the formation of bubbles can be greatly reduced, thereby improving the optical performance of the optical fiber preforms; the vacuum environment can also remove impurities and moisture in the material, improve the purity of the optical fiber preforms, and ensure the stability of the optical fiber performance; the molten state of the polymer in a vacuum is more stable, making the bonding between layers tighter, and improving the mechanical strength of the optical fiber preforms; the heat conduction in a vacuum environment is more controllable, which helps to maintain temperature stability during the printing process and reduce the impact of thermal stress. Combined with the above factors, the vacuum environment can significantly improve the overall performance and reliability of FDM 3D printed polymer optical fiber preforms.

[0005] Since the FDM 3D printers currently on the market all work in a normal atmospheric environment, during the process of printing optical fiber preforms, bubbles in the air are easily captured, resulting in internal defects in the preforms and affecting the optical properties of the optical fiber; impurities and moisture in the external environment are easily mixed into the material, which will reduce the purity of the optical fiber preform, thereby affecting the performance of the subsequently drawn optical fiber; the bonding between the layers is not tight enough, resulting in insufficient mechanical strength of the optical fiber and easy breakage; during high-temperature printing, the material reacts with oxygen to cause oxidation, which will affect the performance and life of the optical fiber preform; and temperature fluctuations may cause thermal stress in the material during the cooling process, affecting the shape and strength of the optical fiber preform. Interference from the external environment will also lead to reduced printing accuracy and affect the size and consistency of the optical fiber. These shortcomings affect the overall performance of the optical fiber preform and limit its scope of application.

[0006] Moreover, a certain amount of fine particles will be generated during the FDM printing of optical fiber preforms. These particles will pollute the air quality of the printing environment. Some printing materials will also release some harmful gases when melted, which may cause potential harm to the health of operators and the environment. Therefore, we need a vacuum-sealed FDM 3D printer. Summary of the invention

[0007] The object of the present invention is to provide a vacuum sealed FDM 3D printer for preparing optical fiber preform rods to solve the problems raised in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A vacuum sealed FDM 3D printer for preparing optical fiber preforms comprises a printer body and a vacuum cover, wherein the printer body is arranged inside the vacuum cover, a printing platform is arranged at the bottom of the vacuum cover, an access window is opened on the surface of the vacuum cover and a sealing door is hingedly connected to block the access window, a cold trap, a vacuum pump and a control panel are respectively installed on the outer side of the vacuum cover, and an air inlet pipe of the cold trap extends to the inside of the vacuum cover, an exhaust pipe of the cold trap is fixedly connected to an air inlet pipe of a vacuum pump, and an exhaust pipe of the vacuum pump is located outside the vacuum cover.

[0010] A vacuum-sealed FDM 3D printer for preparing optical fiber preform rods is characterized in that: a sealing ring and a rubber expansion ring are installed along the edges of the outer surface of a sealing door, the mating surface of the access window and the sealing door is a step surface, an annular groove corresponding to the rubber expansion ring is provided at the root of the step, an air pumping assembly for inflating the rubber expansion ring is connected to the outer side of the sealing door, a locking mechanism of the air pumping assembly is provided on the side of the access window, the locking mechanism includes a threaded sleeve and a threaded column, and the threaded column is connected to the air pumping assembly.

[0011] Preferably, the inflation assembly includes a U-shaped support frame, an airbag, a first spring, a reset disk, a pressing disk, a movable rod, a connecting plate and an air pipe, the U-shaped support frame and the airbag are both fixedly connected to the surface of the sealing door, the first spring is fixedly connected to the inner wall of the airbag, the reset disk is fixedly connected to the end of the first spring away from the airbag, the movable rod is slidably connected to the surface of the U-shaped support frame, the pressing disk is fixedly connected to the end of the movable rod, one end of the air pipe is fixedly connected to the interior of the airbag, and the other end of the air pipe is fixedly connected to the interior of the rubber expansion ring; a connecting plate is fixed to the upper end of the movable rod, the connecting plate extends to above the threaded sleeve, and a threaded column is inserted at the far end of the connecting plate.

[0012] Preferably, there are two cold traps, and the exhaust pipe of one cold trap is fixedly connected to the air inlet pipe of the other cold trap via a flange.

[0013] Preferably, the inner wall of the vacuum cover is fixedly connected with a first temperature sensor and a pressure sensor respectively.

[0014] Preferably, the printer body includes a melt extrusion mechanism and a nozzle mechanism, the nozzle mechanism is arranged on the lower surface of the melt extrusion mechanism, the nozzle mechanism includes a feed pipe, a positioning ball head, a ball head cover and a plurality of discharge nozzles with different nozzle hole sizes, the upper end of the feed pipe is fixedly connected to the discharge port of the melt extrusion mechanism, the lower end of the feed pipe is fixedly connected to the positioning ball head, the ball head cover is rotatably connected to the outer surface of the positioning ball head, the surface of the ball head cover is fixedly connected with a plurality of docking tubes in an annular array, a circular passage is opened inside the positioning ball head to connect the feed pipe and the docking tube to each other, and the discharge nozzle is threadedly connected to the end of the docking tube.

[0015] Preferably, a groove is provided on the surface of the positioning ball head, and a plurality of slots are provided on the surface of the ball head cover. A second spring and a limit baffle are fixedly connected to the inner wall of the groove, a toggle plate is fixedly connected to the end of the second spring, a block is fixedly connected to the end of the toggle plate, and the block is slidably connected to the limit baffle, and the slot can fit with the block.

[0016] Preferably, the number of the slots, the butt joints and the discharge nozzles are the same, and the slots are distributed on the surface of the ball head cover in a ring array.

[0017] Preferably, a heating ring and a second temperature sensor are built into the interior of the positioning ball head, and the heating ring surrounds the outside of the circular passage.

[0018] Preferably, a ventilation pipe is provided on the surface of the vacuum cover, and a solenoid valve is provided on the surface of the ventilation pipe.

[0019] Preferably, the printing platform includes a temperature-controlled support plate, four ordinary telescopic rods and an electric telescopic rod, the upper ends of the ordinary telescopic rods are fixedly connected to the four corners of the lower surface of the temperature-controlled support plate, the upper ends of the electric telescopic rods are fixedly connected to the center of the lower surface of the temperature-controlled support plate, and the lower ends of the ordinary telescopic rods and the electric telescopic rods are fixedly connected to the bottom of the vacuum cover, and an electric heating plate and a third temperature sensor are built into the temperature-controlled support plate.

[0020] Beneficial Effects

[0021] The present invention provides a vacuum sealed FDM 3D printer for preparing optical fiber preform, which has the following beneficial effects:

[0022] 1. The vacuum-sealed FDM 3D printer for preparing optical fiber preforms, by arranging a vacuum cover outside the printer body, realizes the isolation of the printing area from the external environment during the printing process, and by arranging a sealing door, the sealing door can be closed by threaded connection of a threaded column and a threaded sleeve, and after the sealing door is closed, the rubber expansion ring is inflated by an air pump assembly, so that the rubber expansion ring can be expanded, so that the rubber expansion ring is pressed against the annular groove, thereby effectively avoiding air leakage of the sealing door, ensuring the sealing performance of the sealing door, and effectively avoiding the influence of impurities and oxygen in the air on the quality of the printed optical fiber preform. At the same time, the vacuum environment is also helpful to reduce the air remaining in the material when entering the printing nozzle, thereby improving the internal uniformity and surface flatness of the printed optical fiber preform, and improving the use effect.

[0023] 2. The vacuum-sealed FDM 3D printer for preparing optical fiber preform rods is provided with a cold trap and a vacuum pump. During the printing process, the vacuum cover is connected to the cold trap, and the vacuum pump is connected to the cold trap. The vacuum pump is used to evacuate air outward. During the printing process, the cold trap can be used to effectively capture the harmful gases generated, prevent pollution of the printing environment, and is suitable for printing toxic materials.

[0024] 3. The vacuum-sealed FDM 3D printer for preparing optical fiber preform rods, when it is necessary to switch the discharge nozzle, the second spring can be compressed by pushing the toggle plate upward, and the toggle plate will drive the card block away from the card slot, and then the ball head cover can be rotated to quickly switch the discharge nozzle, thereby providing convenience for printing work. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the overall three-dimensional structure of a vacuum-sealed FDM 3D printer for preparing optical fiber preforms proposed by the present invention;

[0026] Figure 2 This is a schematic diagram of a top-down cross-sectional structure of a vacuum-sealed FDM 3D printer for preparing an optical fiber preform proposed by the present invention;

[0027] Figure 3 A vacuum sealed FDM 3D printer for preparing optical fiber preform rods proposed by the present invention Figure 2 A is a schematic diagram of the enlarged structure;

[0028] Figure 4 A schematic diagram of the three-dimensional structure of a sealing door of a vacuum-sealed FDM 3D printer for preparing optical fiber preforms proposed by the present invention;

[0029] Figure 5 A schematic cross-sectional view of a vacuum cover of a vacuum-sealed FDM 3D printer for preparing an optical fiber preform proposed by the present invention;

[0030] Figure 6 This is a schematic cross-sectional structural diagram of a nozzle mechanism of a vacuum-sealed FDM 3D printer for preparing an optical fiber preform proposed by the present invention;

[0031] Figure 7 A schematic diagram of the three-dimensional structure of a nozzle mechanism of a vacuum-sealed FDM 3D printer for preparing an optical fiber preform proposed by the present invention;

[0032] Figure 8 This is a schematic cross-sectional structure diagram of a temperature control support plate of a vacuum sealed FDM 3D printer for preparing optical fiber preforms proposed by the present invention.

[0033] In the figure: 1. Printer body; 2. Vacuum cover; 3. Printing platform; 4. Inlet and outlet window; 5. Sealing door; 6. Sealing ring; 7. Rubber expansion ring; 8. Annular groove; 9. Inflating assembly; 10. Threaded sleeve; 11. Threaded column; 12. Limiting plate; 13. Knob; 14. Cold trap; 15. Vacuum pump; 16. Control panel; 17. U-shaped support frame; 18. Air bag; 19. First spring; 20. Reset plate; 21. Press plate; 22. Movable rod; 23. Connecting plate; 24. Air pipe; 25. A temperature sensor; 26. A pressure sensor; 27. A melt extrusion mechanism; 28. A nozzle mechanism; 29. ​​A feed pipe; 30. A positioning ball head; 31. A ball head cover; 32. A discharge nozzle; 33. A butt joint; 34. A circular passage; 35. A card slot; 36. A second spring; 37. A limit baffle; 38. A toggle plate; 39. A card block; 40. A heating ring; 41. A second temperature sensor; 42. A vent pipe; 43. A temperature control support plate; 44. An electric telescopic rod; 45. An electric heating plate; 46. A third temperature sensor. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1, please refer to Figure 1-8The present invention provides a technical solution: a vacuum sealed FDM 3D printer for preparing optical fiber preform, comprising a printer body 1 and a vacuum cover 2, the printer body 1 is arranged on the inner wall of the vacuum cover 2, a printing platform 3 is arranged on the bottom of the vacuum cover 2, an inlet and outlet window 4 is provided on the surface of the vacuum cover 2, a sealing door 5 for blocking the inlet and outlet window 4 is hinged on the surface of the vacuum cover 2, a sealing ring 6 and a rubber expansion ring 7 are fixedly connected to the outer surface of the sealing door 5, an annular groove 8 corresponding to the rubber expansion ring 7 is provided on the inner wall of the inlet and outlet window 4, an air pumping component 9 for inflating the rubber expansion ring 7 is fixedly connected to the surface of the sealing door 5, and a vacuum seal is formed on the inner wall of the inlet and outlet window 4. A threaded sleeve 10 is fixedly connected to the surface of the vacuum cover 2, and a threaded column 11 that can be threadedly connected to the threaded sleeve 10 is inserted at the end of the inflation component 9. The outer surface of the threaded column 11 is rotatably connected to a limit disk 12, and the end of the threaded column 11 is fixedly connected to a knob 13. A cold trap 14, a vacuum pump 15 and a control panel 16 are fixedly connected to the left side of the vacuum cover 2, and the air inlet pipe of the cold trap 14 extends to the inside of the vacuum cover 2, and the exhaust pipe of the cold trap 14 is fixedly connected to the air inlet pipe of the vacuum pump 15, and the exhaust pipe of the vacuum pump 15 is located outside the vacuum cover 2.

[0036] By arranging a vacuum cover 2 outside the printer body 1, the printing area is isolated from the external environment during the printing process. By arranging a sealing door 5 and threadedly connecting the threaded column 11 with the threaded sleeve 10, the sealing door 5 can be closed. After the sealing door 5 is closed, the rubber expansion ring 7 is inflated by the air pump component 9, which can expand the rubber expansion ring 7 and make the rubber expansion ring 7 press against the annular groove 8, thereby effectively avoiding air leakage of the sealing door 5 and ensuring the sealing performance of the sealing door 5, thereby effectively avoiding the influence of impurities and oxygen in the air on the quality of the printed optical fiber preform. At the same time, the vacuum environment also helps to reduce the air remaining in the material when it enters the printing nozzle, thereby improving the internal uniformity and surface flatness of the printed optical fiber preform and improving the use effect.

[0037] By setting up the cold trap 14 and the vacuum pump 15, during the printing process, the vacuum hood 2 is connected with the cold trap 14, and the vacuum pump 15 is connected with the cold trap 14. The vacuum pump 15 is used to evacuate air outwards. During the printing process, the cold trap 14 can be used to effectively capture the harmful gases generated to prevent pollution of the printing environment, and is suitable for printing of toxic materials. In addition, the cold trap 14 can also maintain the temperature stability of the printing environment by lowering the temperature inside the vacuum hood 2, thereby improving the printing quality.

[0038] The inflation assembly 9 includes a U-shaped support frame 17, an airbag 18, a first spring 19, a reset plate 20, a pressing plate 21, a movable rod 22, a connecting plate 23 and an air pipe 24. The U-shaped support frame 17 and the airbag 18 are both fixedly connected to the surface of the sealing door 5, the first spring 19 is fixedly connected to the inner wall of the airbag 18, the reset plate 20 is fixedly connected to the end of the first spring 19 away from the airbag 18, the movable rod 22 is slidably connected to the surface of the U-shaped support frame 17, the pressing plate 21 is fixedly connected to the end of the movable rod 22, the connecting plate 23 is fixedly connected to the end of the movable rod 22 away from the pressing plate 21, and the threaded column 11 is inserted on the surface of the connecting plate 23, one end of the air pipe 24 is fixedly connected to the inside of the airbag 18, and the other end of the air pipe 24 is fixedly connected to the inside of the rubber expansion ring 7. After inflation, the threaded sleeve 10 and the threaded column 11 can be used to lock the position of the connecting plate 23 and the movable rod 22.

[0039] When closing the sealing door 5, the threaded column 11 can be driven to rotate by rotating the knob 13. The threaded connection between the threaded column 11 and the threaded sleeve 10 can make the limit plate 12 press the connecting plate 23, so that the movable rod 22 drives the pressing plate 21 to squeeze the airbag 18, so that the airbag 18 and the first spring 19 are compressed, and the air in the airbag 18 is squeezed into the rubber expansion ring 7 through the air supply pipe 24, thereby realizing the expansion of the rubber expansion ring 7.

[0040] When the sealing door 5 needs to be opened, the threaded column 11 can be disengaged from the threaded sleeve 10 by rotating the knob 13 in the opposite direction, and the pressing plate 21 will also move away from the airbag 18. Under the elastic force of the first spring 19, the reset plate 20 will lift the airbag 18, and the air in the rubber expansion ring 7 will be sucked into the airbag 18, thereby expanding the airbag 18 and shrinking the rubber expansion ring 7.

[0041] There are two cold traps 14 , wherein the exhaust pipe of one cold trap 14 and the intake pipe of another cold trap 14 are fixedly connected via a flange. By arranging two cold traps 14 in series, the treatment effect of harmful gases in the vacuum cover 2 can be effectively improved.

[0042] The inner wall of the vacuum cover 2 is fixedly connected with a first temperature sensor 25 and a pressure sensor 26 . The first temperature sensor 25 can monitor the temperature inside the vacuum cover 2 , and the pressure sensor 26 can monitor the air pressure inside the vacuum cover 2 .

[0043] The printer body 1 includes a melt extrusion mechanism 27 and a nozzle mechanism 28. The nozzle mechanism 28 is arranged on the lower surface of the melt extrusion mechanism 27. The nozzle mechanism 28 includes a feed pipe 29, a positioning ball head 30, a ball head cover 31 and a plurality of discharge nozzles 32 with different nozzle hole sizes. The upper end of the feed pipe 29 is fixedly connected to the discharge port of the melt extrusion mechanism 27, the lower end of the feed pipe 29 is fixedly connected to the positioning ball head 30, the ball head cover 31 is rotatably connected to the outer surface of the positioning ball head 30, the surface of the ball head cover 31 is fixedly connected with a plurality of docking tubes 33 in an annular array, the interior of the positioning ball head 30 is provided with a circular passage 34 that connects the feed pipe 29 and the docking tube 33 to each other, and the discharge nozzle 32 is threadedly connected to the end of the docking tube 33.

[0044] A groove is provided on the surface of the positioning ball head 30, and a plurality of slots 35 are provided on the surface of the ball head cover 31. A second spring 36 and a limit baffle 37 are fixedly connected to the inner wall of the groove. A toggle plate 38 is fixedly connected to the end of the second spring 36. A block 39 is fixedly connected to the end of the toggle plate 38. The block 39 is slidably connected to the limit baffle 37, and the slot 35 can fit with the block 39.

[0045] The number of the slots 35 , the butt joints 33 and the discharge nozzles 32 is the same, and the slots 35 are distributed on the surface of the ball head cover 31 in a ring array.

[0046] When it is necessary to switch the discharge nozzle 32, the second spring 36 can be compressed by pushing the toggle plate 38 upwards, and the toggle plate 38 will drive the block 39 away from the slot 35. Then, by rotating the ball head cover 31, the discharge nozzle 32 can be quickly switched, thereby providing convenience for the printing work. By setting the slot 35, the second spring 36, the limiting baffle 37, the toggle plate 38 and the block 39, the elastic force of the second spring 36 is utilized, and the limiting baffle 37 is cooperated to limit the block 39, so that the block 39 can be stuck in the slot 35, so that the ball head cover 31 and the discharge nozzle 32 can be fixed.

[0047] A heating ring 40 and a second temperature sensor 41 are built into the interior of the positioning ball head 30, and the heating ring 40 surrounds the outside of the circular passage 34. By setting the heating ring 40, the material passing through the circular passage 34 can be heated. The second temperature sensor 41 can be used to monitor the temperature of the material discharged from the discharge nozzle 32, and the first temperature sensor 25 can be used to monitor the temperature inside the vacuum cover 2. In this way, the printing parameters can be adjusted in time according to the actual situation during the printing process to ensure printing quality and efficiency.

[0048] A ventilation pipe 42 is provided on the surface of the vacuum cover 2, and a solenoid valve is provided on the surface of the ventilation pipe 42. When the sealing door 5 needs to be opened, the solenoid valve on the surface of the ventilation pipe 42 is opened through the control panel 16, so that outside air can enter the vacuum cover 2, and the air pressure inside and outside is consistent, thereby facilitating the opening of the sealing door 5.

[0049] Example 2, please refer to Figure 1-8 , including embodiment 1, and on the basis of embodiment 1, the present invention provides a technical solution: the printing platform 3 includes a temperature control support plate 43, four ordinary telescopic rods and an electric telescopic rod 44, the upper ends of the ordinary telescopic rods are fixedly connected to the four corners of the lower surface of the temperature control support plate 43, the upper ends of the electric telescopic rods 44 are fixedly connected to the center of the lower surface of the temperature control support plate 43, and the lower ends of the ordinary telescopic rods and the electric telescopic rods 44 are fixedly connected to the bottom of the vacuum cover 2, and the temperature control support plate 43 is internally provided with an electric heating plate 45 and a third temperature sensor 46. By setting the electric heating plate 45, the temperature control support plate 43 can be heated, and by setting the third temperature sensor 46, the temperature of the temperature control support plate 43 can be monitored.

[0050] When printing, the printer body 1 can move left and right, forward and backward, and at the same time use the electric telescopic rod 44 to extend and retract, and cooperate with the ordinary telescopic rod for support, so that the height of the temperature control support plate 43 can be adjusted. The melt extrusion mechanism 27 will squeeze the material into the discharge pipe 29, and the material will pass through the circular passage 34 and the docking pipe 33, and finally be discharged from the discharge nozzle 32, so that printing can be carried out.

[0051] In the drawings of the embodiments disclosed in the present invention, only the structures related to the embodiments disclosed in the present invention are involved, and other structures can refer to the general design. In the case of no conflict, the same embodiment and different embodiments of the present invention can be combined with each other;

[0052] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A vacuum sealed FDM 3D printer for preparing optical fiber preform, comprising a printer body (1) and a vacuum cover (2), characterized in that: The printer body (1) is arranged inside a vacuum cover (2), a printing platform (3) is arranged at the bottom of the vacuum cover (2), an inlet and outlet window (4) is opened on the surface of the vacuum cover (2) and a sealing door (5) is hingedly connected to block the inlet and outlet window (4), a cold trap (14), a vacuum pump (15) and a control panel (16) are respectively installed on the outer side of the vacuum cover (2), and an air inlet pipe of the cold trap (14) extends into the interior of the vacuum cover (2), an exhaust pipe of the cold trap (14) is fixedly connected to an air inlet pipe of the vacuum pump (15), and an exhaust pipe of the vacuum pump (15) is located outside the vacuum cover (2).

2. A vacuum sealed FDM 3D printer for preparing optical fiber preform, characterized in that: The outer surface of the sealing door (5) is provided with a sealing ring (6) and a rubber expansion ring (7) along the peripheral edges thereof; the mating surface of the access window (4) and the sealing door (5) is a stepped surface; an annular groove (8) corresponding to the rubber expansion ring (7) is provided at the root of the stepped surface; an air pumping assembly (9) for inflating the rubber expansion ring (7) is connected to the outer side of the sealing door (5); a locking mechanism of the air pumping assembly (9) is provided on the side of the access window (4); the locking mechanism comprises a threaded sleeve (10) and a threaded column (11); and the threaded column (11) is connected to the air pumping assembly (9).

3. A vacuum sealed FDM 3D printer for preparing optical fiber preform according to claim 2, characterized in that: The inflating assembly (9) comprises a U-shaped support frame (17), an air bag (18), a first spring (19), a reset plate (20), a pressing plate (21), a movable rod (22), a connecting plate (23) and an air delivery pipe (24); the U-shaped support frame (17) and the air bag (18) are both fixedly connected to the surface of the sealing door (5); the first spring (19) is fixedly connected to the inner wall of the air bag (18); the reset plate (20) is fixedly connected to the first spring (19) away from the air bag (18); At one end, a movable rod (22) is slidably connected to the surface of the U-shaped support frame (17), a pressing plate (21) is fixedly connected to the end of the movable rod (22), one end of the air supply pipe (24) is fixedly connected to the inside of the air bag (18), and the other end of the air supply pipe (24) is fixedly connected to the inside of the rubber expansion ring (7); a connecting plate (23) is fixed to the upper end of the movable rod (22), the connecting plate (23) extends to the top of the threaded sleeve (10), and a threaded column (11) is inserted at the far end of the connecting plate (23).

4. A vacuum sealed FDM 3D printer for preparing optical fiber preform according to claim 1, characterized in that: There are two cold traps (14), the exhaust pipe of one cold trap (14) and the intake pipe of another cold trap (14) are fixedly connected via a flange, and the inner wall of the vacuum cover (2) is respectively fixedly connected with a first temperature sensor (25) and a pressure sensor (26).

5. A vacuum sealed FDM 3D printer for preparing optical fiber preform according to claim 1, characterized in that: The printer body (1) comprises a melt extrusion mechanism (27) and a nozzle mechanism (28). The nozzle mechanism (28) is arranged on the lower surface of the melt extrusion mechanism (27). The nozzle mechanism (28) comprises a feed pipe (29), a positioning ball head (30), a ball head cover (31) and a plurality of discharge nozzles (32) with different nozzle hole sizes. The upper end of the feed pipe (29) is fixedly connected to the discharge port of the melt extrusion mechanism (27). The lower end of the feed pipe (29) is fixedly connected to the positioning ball head (30). The ball head cover (31) is rotatably connected to the outer surface of the positioning ball head (30). The surface of the ball head cover (31) is fixedly connected to a plurality of butt joint pipes (33) in an annular array. A circular passage (34) is provided inside the positioning ball head (30) to connect the feed pipe (29) and the butt joint pipe (33). The discharge nozzle (32) is threadedly connected to the end of the butt joint pipe (33).

6. A vacuum sealed FDM 3D printer for preparing optical fiber preform according to claim 5, characterized in that: A groove is provided on the surface of the positioning ball head (30), a plurality of slots (35) are provided on the surface of the ball head cover (31), a second spring (36) and a limit baffle (37) are fixedly connected to the inner wall of the groove, a toggle plate (38) is fixedly connected to the end of the second spring (36), a block (39) is fixedly connected to the end of the toggle plate (38), and the block (39) is slidably connected to the limit baffle (37), and the slot (35) can fit with the block (39).

7. A vacuum sealed FDM 3D printer for preparing optical fiber preform according to claim 6, characterized in that: The numbers of the clamping grooves (35), the butt joint pipes (33) and the discharge nozzles (32) are the same, and the clamping grooves (35) are distributed on the surface of the ball head cover (31) in a ring array.

8. A vacuum sealed FDM 3D printer for preparing optical fiber preform according to claim 7, characterized in that: A heating ring (40) and a second temperature sensor (41) are built into the interior of the positioning ball head (30), and the heating ring (40) surrounds the outside of the circular passage (34).

9. A vacuum sealed FDM 3D printer for preparing an optical fiber preform according to any one of claims 1 to 8, characterized in that: A vent pipe (42) is arranged on the surface of the vacuum cover (2), and a solenoid valve is arranged on the surface of the vent pipe (42).

10. A vacuum sealed FDM 3D printer for preparing optical fiber preform according to any one of claims 1 to 8, characterized in that: The printing platform (3) comprises a temperature control support plate (43), four common telescopic rods and an electric telescopic rod (44), wherein the upper ends of the common telescopic rods are fixedly connected to the four corners of the lower surface of the temperature control support plate (43), the upper ends of the electric telescopic rods (44) are fixedly connected to the center of the lower surface of the temperature control support plate (43), and the lower ends of the common telescopic rods and the electric telescopic rods (44) are fixedly connected to the bottom of the vacuum cover (2), and the temperature control support plate (43) is internally provided with an electric heating plate (45) and a third temperature sensor (46).

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