An adjustable back pressure pneumatic extrusion 3D printing nozzle, apparatus and method of printing

Abstract

The application discloses a kind of adjustable back force pneumatic extrusion type 3D printing nozzle, equipment and printing method, belong to 3D printing technical field.Printing nozzle includes the printing nozzle fixed plate installed on 3D printer moving shaft;Printing nozzle fixed plate is fixed with back extraction device, material pipe adapter and material pipe fixed frame;Back extraction device includes air inlet, air passage, air flow regulating plate, back extraction regulating knob, air passage control valve, exhaust port;Air passage control valve can control the switching of back extraction and normal printing state in printing process;Back extraction regulating knob can adjust the strength of back extraction material in printing process.The application can provide back extraction function in printing process, which can effectively ensure the cleaning of printing process, avoid the accumulation of residues in the nozzle to cause pollution, while avoiding material waste;Reduce the material accumulation in printing process, provide more accurate and consistent printing results;Meanwhile, the adjustable back extraction force makes the printing nozzle compatible with a wider range of printable material viscosity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of 3D printing, and more particularly, relates to a pneumatic extrusion type 3D printing nozzle with adjustable back-pulling force, a device and a printing method. BACKGROUND

[0002] Printing technology around semi-solid materials in molten state, gel state, etc. has become an excellent technical method for manufacturing flexible electronic circuits and biological tissues due to the advantages of high throughput, low cost and ability to manufacture complex structures. The extrusion type nozzle used by such 3D printers is crucial and is a key component for achieving printing effect and completing printing. For a pneumatic extrusion type nozzle, during the 3D printing process, the gas source is usually a high-pressure cylinder or an air compressor, which continuously provides positive air pressure and cannot generate negative pressure or immediately generate negative pressure, making it difficult to achieve back-pulling control of materials when the printing action stops. Therefore, the printing process is prone to collapse and material accumulation, making it difficult to ensure the continuity and high fidelity of the complex curvature structure of the formed object, causing pollution due to the accumulation of residues in the nozzle, affecting the printing quality, and also causing a certain degree of waste of printing materials. SUMMARY

[0003] In view of the defects of the prior art, the present application aims to provide a pneumatic extrusion type 3D printing nozzle with adjustable back-pulling force, a device and a printing method, which aims to achieve fine control of semi-solid materials during the printing process, reduce or eliminate residues of printing materials around the nozzle or printing area, and improve the accuracy and precision of printing.

[0004] To achieve the above-mentioned purpose, the present application provides a pneumatic extrusion type 3D printing nozzle with adjustable back-pulling force, which comprises a printing nozzle fixing plate that can be installed on a moving shaft of a 3D printer; a back-pulling device, a tube adapter and a tube fixing frame are fixed on the printing nozzle fixing plate; the back-pulling device comprises an air inlet, a back-pulling adjustment knob, an airflow adjustment plate, an air duct, an air duct control valve, an air outlet and a silencer valve; the air inlet is connected to a high-pressure gas source for continuously providing positive air pressure; the back-pulling adjustment knob can manually adjust the force of back-pulling materials during the printing process; the airflow adjustment plate can change the airflow speed by adjusting the angle, thereby adjusting the back-pulling force of the device, so that the device can print printing materials with a larger viscosity range; the air duct control valve can control the switching between the back-pulling and normal printing states of the printing nozzle; the air outlet is used for discharging gas in the back-pulling state of the device; the tube adapter is connected to the back-pulling device at the upper part, and after being connected to the tube at the lower part, the lower part can be embedded in the clamping groove of the upper part to complete the fixation, and the air duct of the back-pulling device is communicated with the tube through the tube adapter; the tube fixing frame is arranged below the printing nozzle fixing plate, and the assembled tube can be fixed by being embedded in the fixing frame.

[0005] Further, the airway control valve comprises a spring, a permanent magnet valve and an electromagnetic coil. When the electromagnetic coil is in an energized state, an electromagnetic effect is generated, and the magnetic field generated by setting the current direction of the electromagnetic coil is of the same polarity as the contact surface of the permanent magnet valve, thereby generating a repulsive magnetic field and pushing the permanent magnet valve to the airway side wall cavity, so that the airway is communicated with the exhaust port and the exhaust port is opened. When the electromagnetic coil is in a non-energized state, the spring pushes the permanent magnet valve back into the airway, and the exhaust port is closed.

[0006] Further, the back-pumping device comprises an airflow adjusting plate, a narrow-throat airway, a material dropping airway and an exhaust airway. The positive pressure airflow enters the back-pumping device from the air inlet of the back-pumping device; in the closed state of the airway control valve, the airway is in a closed state, the airflow enters the material dropping airway through the airway, and a positive pressure is generated on the material in the material pipe, so that the material is extruded from the lower part of the material pipe for printing; in the open state of the airway control valve, the airflow first passes through the narrow-throat airway, then passes through the airflow adjusting plate, and finally is discharged from the exhaust port.

[0007] According to Bernoulli's principle, the mechanical energy of the fluid is conserved, and the sum of the kinetic energy, pressure potential energy and potential energy of the airflow is a constant for any point in the current airway.

[0008] P+1 / 2ρv 2 +ρgh=C

[0009] Wherein, P is the pressure of the gas (Pascal), ρ is the density of the gas (kg / m 3 ), v represents the speed of the fluid (m / s), g represents the acceleration of gravity (m / s 2 ), and h represents the height of the fluid (m). In the fluid system, the gravity of the gas can be ignored, and the potential energy of the gas flow has little effect, so the equation can be simplified as

[0010] P+1 / 2ρv 2 =C

[0011] It can be deduced that the faster the gas flow rate is, the smaller the pressure is; the slower the flow rate is, the greater the pressure is.

[0012] According to the continuity equation, the flow rates of each cross section are equal. The flow rate is equal to the flow rate multiplied by the cross-sectional area of the pipeline, and it can be deduced that the flow rate is small in the place with large cross-sectional area, and the flow rate is large in the place with small cross-sectional area.

[0013] According to the above two principles, when the airflow passes through the narrow-throat airway, the airflow speed increases and the pressure decreases; the high-speed gas enters the exhaust airway from the narrow-throat airway, and a negative pressure area is formed around the airflow, the negative pressure of the material dropping airway port causes the material pipe to generate a negative pressure, and then the material is back-pumped into the material pipe, thereby realizing the back-pumping effect.

[0014] The airflow adjusting plate can change the airflow speed according to the angle change of the airflow adjusting plate. The front edge close to the airflow direction is designed as a horizontal upper surface, the front edge to the front middle part of the lower surface is raised, the raised part to the rear edge is narrowed, and the front and rear angle radians are processed to reduce the additional resistance influence on the airflow. According to the Bernoulli principle, the strength of the back-pulling force can be adjusted by adjusting the speed of the airflow above the material falling airway opening. The rear part of the airflow adjusting plate is located above the material falling airway opening, and the angle of the raised part of the airflow adjusting plate can be changed to change the airway width above the material falling airway opening, so as to adjust the airflow speed. When the upper surface plane of the airflow adjusting plate is horizontal to the airflow direction, the back-pulling adjustment strength is the minimum value, the change of the airflow speed by the airflow adjusting plate is the minimum, and the back-pulling force of the back-pulling device under the current gas pressure provided by the gas source is basically not affected. When the tail end plane of the lower surface of the airflow adjusting plate is horizontal to the airflow direction, the back-pulling adjustment strength is the maximum value, the airway at the material falling airway opening is narrowed, the airflow speed is accelerated, the negative pressure formed by the airflow is improved, and the back-pulling force of the back-pulling device is increased.

[0015] Further, the back-pulling adjustment knob is connected with the airflow adjusting plate, a certain rotation damping force is set for the knob to improve the adjustment accuracy, the knob is rotated within the selected range of the airflow adjusting plate to control the back-pulling strength of the equipment, and the back-pulling strength is set according to the viscosity of the material to be printed each time.

[0016] As preferred, the viscosity range of the printing material suitable for the printing nozzle is 2 to 30 Pa·s.

[0017] As preferred, the vacuum degree range adjustable by the airflow adjusting plate is 45 to 130 kPa.

[0018] As preferred, the back-pulling adjustment knob sets the adjustable range according to the viscosity range of the printing material suitable for the printing nozzle, scale lines are arranged around the knob, the scale value range is 2-30 Pa·s, and the adjustable vacuum degree range of the internal airflow adjusting plate corresponding to the scale value is 45-130 kPa.

[0019] The application also provides a 3D printing device, which comprises a rack, a printing platform and a nozzle transmission device, and further comprises the printing nozzle.

[0020] The nozzle transmission device is installed in the rack.

[0021] The printing nozzle is installed in the nozzle transmission device and moves parallel to the printing platform under the drive of the nozzle transmission device.

[0022] The application also provides a 3D printing method, which adopts the printing nozzle and comprises the following steps.

[0023] Step S1: inject the printing material into the material pipe, continuously provide positive air pressure to the air passage from the air inlet, and adjust the back-drawing knob according to the viscosity characteristics of the material;

[0024] Step S2: in the normal printing state, the positive pressure airflow enters the back-drawing device from the air inlet, the air passage control valve is in the closed state, the air passage is in the closed state, the airflow enters the material falling air passage through the air passage, generates positive pressure on the printing material in the material pipe, and then extrudes the printing material from the lower part of the material pipe for printing;

[0025] Step S3: in the back-drawing state, the air passage control valve is in the open state, the airflow first passes through the narrow throat air passage, then passes through the airflow adjusting plate, and finally is discharged from the exhaust port; when the airflow enters the exhaust passage from the narrow throat air passage, a negative pressure area is formed around the airflow, a negative pressure is generated on the printing material in the material pipe through the material falling air passage, and then the material is back-drawn into the material pipe, so that the material back-drawing effect is achieved;

[0026] Step S4: close the air passage control valve when returning to the normal printing stage, the electromagnetic coil is not electrified, loses magnetism, and the spring pops the permanent magnet valve back into the air passage, and the exhaust port is closed;

[0027] Step S5: repeat the steps S2-S4 process until the printing is completed.

[0028] Through the above technical scheme conceived by the present application, compared with the prior art, the following advantages can be achieved

[0029] Advantages:

[0030] (1) The pneumatic back-drawing device of the present application can quickly recover excess material when the printing nozzle stops moving, keep the printing area clean and tidy, and avoid cross contamination affecting the functionality of the formed part.

[0031] (2) When the 3D printer is printing a model with high curvature and multiple curvatures, the printing speed is reduced at the transition angle of the curved part, which is prone to material accumulation, resulting in poor forming effect. The present application can reduce the accumulation of materials during printing, improve the quality and precision of 3D printing, and ensure the fidelity of the formed part.

[0032] (3) The back-drawing adjustment knob of the present application can adjust the back-drawing force according to the viscosity characteristics of the printing material, and can adapt to a wider range of printing materials. Only a simple rotation angle is needed to achieve the purpose of adjustment, and the device has low cost and is easy to use. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a perspective structural schematic diagram of the appearance of the pneumatic extrusion type 3D printing nozzle with adjustable back-drawing force.

[0034] Figure 2 It is a sectional view structural schematic diagram of the main body of the pneumatic extrusion type printing nozzle.

[0035] Figure 3 Schematic diagram of gas flow for a pneumatic extrusion type printing nozzle body in a retraction state;

[0036] Figure 4 Schematic diagram of gas flow for a pneumatic extrusion type printing nozzle body in an extrusion state.

[0037] Fig. 1 is a retraction device; Fig. 11 is a retraction adjusting knob; Fig. 12 is a gas passage control valve; Fig. 121 is a spring; Fig. 122 is a permanent magnet valve; Fig. 123 is an electromagnetic coil; Fig. 13 is a muffler valve; Fig. 14 is an exhaust port; Fig. 15 is an air inlet; Fig. 16 is a material pipe adapter; Fig. 17 is a gas passage; Fig. 171 is a narrow-throat gas passage; Fig. 172 is a material dropping gas passage; Fig. 173 is an exhaust passage; Fig. 18 is a gas flow adjusting plate; Fig. 2 is a printing nozzle fixing plate; Fig. 21 is a material pipe fixing frame; Fig. 3 is a material pipe. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0039] The present application provides a pneumatic extrusion type 3D printing nozzle with adjustable retraction force, as shown in the whole structure, which includes a retraction device 1, a printing nozzle fixing plate 2 and a material pipe fixing frame 21. The external visible part of the retraction device 1 includes a retraction adjusting knob 11, a gas passage control valve 12, a muffler valve 13, an exhaust port 14, an air inlet 15 and a material pipe adapter 16; as shown in the internal visible part of the retraction device 1, it includes a gas passage control valve 12 and a gas passage 17; the gas passage control valve 12 includes a spring 121, a permanent magnet valve 122 and an electromagnetic coil 123; the gas passage 17 includes an exhaust port 14, an air inlet 15, a narrow-throat gas passage 171, a material dropping gas passage 172, an exhaust passage 173 and a gas flow adjusting plate 18. Figure 1 Figure 2 The gas passage control valve 12 can generate an electromagnetic field when energized, and the direction of the magnetic field generated by the energized direction is opposite to the direction of the magnetic field of the permanent magnet valve 121, and at the same time cooperates with the spring 121 to control the opening and closing of the exhaust port 14.

[0040] The gas passage control valve 12 can generate an electromagnetic field when energized, and the direction of the magnetic field generated by the energized direction is opposite to the direction of the magnetic field of the permanent magnet valve 121, and at the same time cooperates with the spring 121 to control the opening and closing of the exhaust port 14.

[0041] ​The back-pulling adjustment knob 11 is connected with the airflow adjustment plate 18, and the angle of the airflow adjustment plate 18 can be changed by rotating the back-pulling adjustment knob 11 outside the device, so as to adjust the back-pulling degree of the device. The airflow adjustment plate 18 changes the airflow speed by changing the angle itself. When the upper plane of the airflow adjustment plate 18 is horizontal to the airflow direction, the back-pulling adjustment is the minimum value, the airflow speed change of the airflow adjustment plate 18 is the minimum, and the back-pulling degree of the back-pulling device 1 under the current gas pressure provided by the gas source is basically not affected, as shown in state C; when the lower plane of the airflow adjustment plate 18 is horizontal to the airflow direction, the back-pulling adjustment is the maximum value, the gas channel at the opening of the material falling gas channel 172 is narrowed, the airflow speed is accelerated, the negative pressure formed by the airflow is improved, and the back-pulling degree of the back-pulling device 1 is increased, as shown in state D. Figure 3 Figure 3

[0042] The specific implementation steps of the printing nozzle are as follows:

[0043] Step S1: The printing material is injected into the material pipe 3, and the lower part of the feeding pipe conversion head 16 is fixed by being inserted into the clamping groove of the upper part, and the pipe body is clamped on the material pipe fixing frame 21; the air inlet 15 is connected with a high-pressure gas cylinder or an air compressor, and the gas source switch is opened to continuously provide positive pressure; the back-pulling adjustment knob 11 is rotated according to the viscosity characteristics of the material.

[0044] Step S2: Start printing. In the normal printing stage, the positive pressure airflow enters the back-pulling device 1 from the air inlet 15 of the back-pulling device 1, the air channel control valve 12 is in the closed state, the air channel 17 is in the closed state, the airflow enters the material falling gas channel 172 through the air channel 17, and the positive pressure is generated on the semi-solid material in the material pipe 3, so as to extrude the material from the lower part of the material pipe 3 for printing, as shown in state B. Figure 4

[0045] Step S3: The back-pulling function of the printing nozzle is needed when the printing is paused, the printing nozzle is moved to a new position, or a high-curvature structure part is encountered. In this state, the control program opens the air channel control valve 12, first makes the electromagnetic coil 123 in the energized state, and then generates an electromagnetic effect. The magnetic field generated by the current direction of the electromagnetic coil 123 is the same polarity as the contact surface of the permanent magnet valve 122, so as to generate magnetic field repulsion, push and squeeze the permanent magnet valve 122 into the upper cavity, and open the exhaust port 14, as shown in state A. The airflow first passes through the narrow-throat air channel 171, then passes through the airflow adjustment plate 18, and finally is discharged from the exhaust port 14; the high-speed gas enters the exhaust channel 173 from the narrow-throat air channel 171, and a negative pressure area is formed around the airflow, so as to generate negative pressure on the material in the material pipe 3 through the material falling gas channel 172, and then the material is back-pulled into the material pipe 3, so as to achieve the material back-pulling effect, as shown in state A. Figure 2 Figure 3

[0046] ​​​​​Step S4: Close the airway control valve 12 when returning to the normal printing stage, the electromagnetic coil 123 is not powered, loses magnetism, and the spring 121 pushes the permanent magnet valve 122 back into the airway, and the exhaust port 14 is closed, as shown in Figure 2 State B;

[0047] Step S5: Repeat steps S2-S4 until the printing is completed and the printed shaped part is moved to the post-processing.

[0048] Example One:

[0049] The adjustable back-pulling force pneumatic extrusion type 3D printing nozzle provided by the application can be applied to the field of biological 3D printing. The general process is to first print a tubular structure by sacrificing material, then print biological material containing cells to cover it, and finally reduce the temperature to pull out the liquefied sacrificial material to form a pipeline structure. The main purpose of the sacrificial material is to be sacrificed, consumed or removed after completing a specific task or achieving a specific requirement. In combination with the description of the above general steps, the specific example steps are as follows:

[0050] Step S1`: In this embodiment, 35wt / vol% polyether F127 is selected as the sacrificial material, which is in a gel state at about 25°C and becomes liquid below 4°C. The viscosity of the sacrificial material at room temperature 25°C is about 18Pa·s, the nozzle size is 100μm, and the required back-pulling force is 88kPa. According to this value, the back-pulling adjustment knob 11 is set to the back-pulling force. The sacrificial material is injected into the material pipe 3 and fixed; the air inlet 15 is connected with the air pipe to continuously provide positive air pressure;

[0051] Step S2`: Start printing. In the normal printing stage, the airway control valve 12 is in the closed state, the positive pressure of the positive air pressure on the biological material in the material pipe 3 further extrudes the biological material from the bottom of the material pipe 3; when the back-pulling function of the printing nozzle is needed, the program automatically controls the airway control valve 12 to open, and the vacuum area generated by the high-speed gas pulls the biological material in the material pipe 3 back into the material pipe 3 through the material falling airway 172, thereby achieving the material back-pulling effect; when returning to the normal printing stage, the airway control valve 12 is closed, and the normal printing state is restored to continue printing. Repeat this process to complete the printing of the sacrificial material part;

[0052] Step S3`: Select the cell-containing biomaterial printing consisting of 7.5 wt / vol% gelatin and 10 mg / mL fibrinogen. Replace the biomaterial-filled tube with the sacrificial material tube, and install it on the tube holder 21. The viscosity of the biomaterial at room temperature 25°C is about 8 Pa·s, the nozzle size is 311 μm, and the required backpressure is 63 kPa. The viscosity of the printing material changes, so the backpressure is set by rotating the backpressure adjustment knob 11 according to the current material viscosity. Complete the printing of the biomaterial part according to the process of step S2` of this embodiment;

[0053] Step S4`: After completing the printing of the biological tissue, move the printed and shaped biological tissue into the incubator.

[0054] Embodiment Two:

[0055] The adjustable backpressure pneumatic extrusion type 3D printing nozzle provided by the present application is suitable for the manufacturing of flexible electronic circuits and devices, and completes the circuit printing on a soft substrate through a direct writing technology. In combination with the above description, the specific implementation steps are as follows:

[0056] Step S1``: In this embodiment, AgTPU conductive ink prepared by adding silver Ag to thermoplastic polyurethane TPU is selected as the printing material. The material viscosity at room temperature 25°C is about 43 Pa·s, the nozzle size is 150 μm, the required backpressure is 127 kPa, and the backpressure is set by rotating the backpressure adjustment knob 11 according to this value. The printing material is injected into the tube 3 and fixed; the gas inlet 15 is connected to the air pipe to continuously provide positive air pressure;

[0057] Step S2``: Start the circuit printing. Extrude the printing material according to the path set by the model to the soft substrate, and connect each electronic component on the soft substrate. Complete the printing according to the process of step S2` of embodiment one;

[0058] Step S3``: After completing the printing, solidify the printed and shaped part at 80°C for 2 hours to complete the manufacturing of the entire circuit assembly.

[0059] The adjustable backpressure extrusion type 3D printing nozzle provided by the present application can keep the printing process clean, avoid material dripping or overflowing to cause pollution, reduce the material accumulation during the printing process, provide more accurate and consistent printing results, and improve the shaping fidelity. At the same time, the adjustable backpressure makes the printing nozzle have a wider range of printable materials.

[0060] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A pneumatic extrusion 3D printing nozzle with adjustable backdraft force, characterized in that: It includes a print head fixing plate mounted on a movable axis of a 3D printer; a retraction device, a material pipe adapter and a material pipe fixing frame are fixed on the print head fixing plate; The backdraft device includes an air inlet, an airway, an airflow adjustment plate, a backdraft adjustment knob, an airway control valve, and an exhaust port; One end of the air inlet is connected to an external high-pressure air source, and the other end is connected to one end of the air duct for continuously providing positive air pressure to the air duct; the backflow adjustment knob is located on the outside of the backflow device and is connected to the airflow adjustment plate, and the airflow adjustment plate is located in the air duct, and the airflow adjustment plate is driven by rotating the backflow adjustment knob to adjust the angle of the airflow adjustment plate to change the airflow speed, thereby adjusting the backflow force of the print head; the upper surface of the airflow adjustment plate is horizontal, and the front edge of the lower surface is convex to the front middle, and the convex part is narrowed to the rear edge, where the front edge is close to the airflow direction; when the upper surface plane of the airflow adjustment plate is in a horizontal state with the airflow direction, the backflow adjustment is at the minimum value, and when the airflow adjustment knob is turned on, the backflow adjustment is at the minimum value. When the tail end plane of the lower surface of the section plate is in a horizontal state with the direction of the airflow, the retraction is adjusted to the maximum value; the airway control valve is connected to the other end of the airway, and is used to control the printing nozzle to switch between the retraction state and the normal printing state; the exhaust port is connected to the airway control valve, and is used to exhaust gas in the retraction state; the airway includes a narrow throat airway, a blanking airway, and an exhaust port. When the airway control valve is closed, the airflow enters the blanking airway through the narrow throat airway, generates positive pressure on the material in the material pipe, and then squeezes the material out from the bottom of the material pipe for printing; when the airway control valve is open, the airflow first passes through the narrow throat airway, then passes through the airflow adjustment plate, and finally is discharged from the exhaust port; The material pipe adapter has an upper portion connected to the withdrawal device and a lower portion connected to the material pipe, and the air passage of the withdrawal device is connected to the air passage of the material pipe through the material pipe adapter; The material pipe fixing frame is arranged in the middle and lower part of the print head fixing plate and is used to fix the assembled material pipe.

2. The 3D printing nozzle according to claim 1, characterized in that: The airway control valve includes a spring, a permanent magnet valve, and an electromagnetic coil. One end of the spring is fixed, and the other end is connected to the permanent magnet valve, located on one side of the airway. The electromagnetic coil is arranged on the other side of the airway. The electromagnetic coil is used to generate an electromagnetic effect when powered on, generating a magnetic field repulsion with the permanent magnet valve, pushing the permanent magnet valve into the cavity on the side wall of the airway, so that the airway is connected to the exhaust port, opening the exhaust port, and the airway control valve is in an open state. In the non-powered state, the spring bounces the permanent magnet valve back into the airway, closing the exhaust port, and the airway control valve is in the closed state.

3. The 3D printing nozzle according to claim 1, characterized in that: It also includes a muffler valve located at the exhaust port and used to reduce noise generated when gas passes through the exhaust port.

4. The 3D printing nozzle according to claim 1, characterized in that: The upper portion of the material pipe adapter is provided with a clamping groove for fixing the lower portion of the material pipe adapter after docking with the material pipe.

5. A 3D printing device, comprising a frame, a printing platform and a nozzle transmission device, characterized in that: Also includes a print head according to any one of claims 1 to 4, wherein: The nozzle transmission device is installed in the frame; The printing nozzle is installed on the nozzle transmission device and moves parallel to the printing platform under the drive of the nozzle transmission device.

6. A 3D printing method, using the printing head according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step S1: Inject printing material into the material tube, and continuously provide positive air pressure to the airway through the air inlet; adjust the retraction adjustment knob according to the viscosity characteristics of the material; Step S2: In the normal printing state, positive pressure air flows from the air inlet into the retraction device, the airway control valve is in a closed state, the airway is in a sealed state, and the airflow passes through the airway into the blanking airway, generating positive pressure on the printing material in the material tube, thereby squeezing the printing material out from the bottom of the material tube for printing; Step S3: In the retraction state, the airway control valve is open, and the airflow first passes through the narrow throat airway, then passes through the airflow adjustment plate, and finally is discharged from the exhaust port. When the airflow enters the exhaust duct from the narrow throat airway, a negative pressure area is formed around the airflow, and negative pressure is generated on the printing material in the material pipe through the blanking airway, thereby retracting the material into the material pipe, achieving the material retraction effect. Step S4: When returning to the normal printing stage, the airway control valve is closed, the electromagnetic coil is not energized, and loses its magnetism, the spring bounces the permanent magnet valve back into the airway, and the exhaust port is closed; Step S5: Repeat steps S2-S4 until printing is completed.

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