3D printing method and system based on microwave heating

Abstract

The invention belongs to the field of 3D printing, and particularly relates to a 3D printing method which comprises the following steps: S1, arranging a powder layer; s2, wave-absorbing powder is sprayed to the printing area of the powder layer; s3, heating the wave absorbing powder by using a coaxial radiator; s4, the heated wave-absorbing powder connects the powder in the printing area to form a printing layer; s5, arranging the powder layer again; s6, wave-absorbing powder is sprayed to the printing area of the powder layer; s7, heating the wave-absorbing powder by using a coaxial radiator (2); s8, the powder in the printing area and the printing layer are connected through the wave-absorbing powder, and a new printing layer is formed; and S9, the steps from S5 to S8 are repeated until a finished product is printed. The invention provides a 3D printing method and system. The 3D printing method and system aim at solving the problem that an existing 3D printing method is low in efficiency.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing, specifically relating to a 3D printing method and system. Background Technology

[0002] 3D printing technology, a disruptive manufacturing technology that has gradually matured since the 1980s and triggered a global transformation in manufacturing, is characterized by its core feature: replacing the traditional material removal processing logic with material accumulation, thus completely reconstructing the forming path of three-dimensional objects. The core principle of this technology can be summarized as layered manufacturing, where each layer is stacked sequentially. First, computer-aided design software constructs a three-dimensional digital model of the target object. Then, specialized slicing software discretizes the model into a series of continuous two-dimensional thin layers. Finally, additive manufacturing equipment, based on the slicing data, deposits, melts, sinters, or solidifies the pre-set material layer by layer along a specific path, ultimately completing the construction of the three-dimensional entity. This process does not rely on molds, fixtures, or complex machining tools found in traditional manufacturing, achieving a direct conversion from digital model to physical entity. Its technological logic is fundamentally different from traditional subtractive manufacturing technologies such as cutting, drilling, milling, forging, and casting.

[0003] In the conventional 3D printing technology system, light-driven molding is one of the most widely used core technologies. Its energy source mainly includes lasers or infrared light, and its core principle is to achieve melting, sintering, or photopolymerization of the printed material through the directional transmission and focusing of light energy. However, the propagation characteristics of light energy in powder media have inherent limitations. This is mainly reflected in the fact that the energy density of light energy decreases exponentially with the propagation distance. If the powder layer thickness exceeds a critical value, the underlying material will not receive enough energy to achieve uniform melting or complete solidification, leading to serious defects such as poor interlayer bonding, excessive internal porosity, and decreased mechanical properties. To solve this problem, existing light-driven 3D printing equipment must strictly control the powder layer thickness within an extremely narrow range to ensure that light energy can completely penetrate the powder layer, achieving sufficient material reaction and densification. With thickness limitations, the overall 3D printing time increases significantly, resulting in lower efficiency. Summary of the Invention

[0004] This invention provides a 3D printing method and system, the purpose of which is to solve the problem of low efficiency in existing 3D printing methods.

[0005] To achieve the above objectives, the present invention provides a 3D printing method, comprising the following steps: S1, Set the powder layer; S2, spray microwave absorbing powder onto the printing area of ​​the powder layer; S3, heating the microwave-absorbing powder using a coaxial radiator; S4, the heated microwave-absorbing powder connects the powder in the printing area to form a printing layer.

[0006] This method involves spraying microwave-absorbing powder and heating it using a coaxial radiator. The heated powder binds together to form a printed layer. Due to the strong penetrating power of microwaves, the resulting printed layer is thicker than those formed by other existing printing methods, ultimately resulting in a shorter printing time and higher efficiency.

[0007] Preferably, in order to form a new printing layer and combine the printing layers to form a finished product, this solution also includes S5, setting a powder layer again; S6, spray microwave-absorbing powder onto the printing area of ​​the powder layer; S7, The microwave absorbing powder is heated using a coaxial radiator; S8, the absorbing powder connects the powder in the printing area and the printing layer to form a new printing layer; S9. Repeat steps S5 to S8 until the finished product is printed.

[0008] Preferably, in order to release the microwave absorbing powder onto the printing area of ​​the powder layer, this solution sprays the microwave absorbing powder onto the printing area of ​​the powder layer. By spraying the microwave absorbing powder, the microwave absorbing powder is released onto the powder layer.

[0009] Preferably, in order to uniformly heat different areas of the powder layer, the microwave absorbing powder in this solution is in a uniformly distributed state. Because the microwave absorbing powder is uniformly distributed in this solution, when the temperature of the microwave absorbing powder rises, the powder layer in each area is heated uniformly, resulting in a more uniform thickness of the printed layer.

[0010] A second aspect of the present invention discloses an apparatus using the above-described 3D printing method, comprising a coaxial radiator and a microwave device, wherein the coaxial radiator is connected to the microwave device and the coaxial radiator is used to heat microwave absorbing powder.

[0011] This solution uses a coaxial radiator to heat the microwave absorbing powder, raising its temperature, and then connects the powder layers to form a printing layer.

[0012] Preferably, to achieve more focused electric field and precise heating of the absorbing powder, ensuring printing accuracy, the coaxial radiator of this solution includes an internal guide, a dielectric, and an external guide. The internal guide is disposed inside the external guide, and the dielectric is disposed between the internal and external guides. The internal guide includes a heating end for heating, the diameter of which gradually increases towards the end of the heating end. The end face of the heating end is provided with a stepped structure, the stepped structure including at least two circular steps, and the circular steps are coaxially arranged.

[0013] In this design, the heating end achieves impedance matching and increases the electric field by gradually increasing its diameter. Then, a stepped structure is used to further focus the electric field, resulting in better heating of the absorbing powder by the coaxial radiator.

[0014] Preferably, to enable connection with the microwave device, this solution also includes a connector for the coaxial radiator, which connects to the microwave device via the connector. This solution achieves connection with the microwave device through the connector, ensuring microwave supply to the coaxial radiator.

[0015] Preferably, since the coaxial radiator is connected to an external microwave device via a connector, the external microwaves are easily affected when they enter through the connector. To address this issue, the internal conductor in this solution includes a connecting end for connection with the connector, the diameter of which gradually decreases towards its end. In this solution, the connecting end of the internal conductor mates with the connector; by reducing the diameter of the connecting end, impedance matching is achieved between the internal conductor and the connector, ensuring better heating performance.

[0016] Because the coaxial radiator connects to an external microwave device via a connector, the external microwaves are easily affected when they enter through the connector. To address this issue, the external conductor in this solution includes a connector end for connection to the connector, with the diameter of the connector end gradually decreasing towards its tip. In this solution, the connector end of the external conductor mates with the connector; by reducing the diameter of the connector end, impedance matching is achieved between the external conductor and the connector, ensuring better heating performance.

[0017] Preferably, to achieve the setting of the powder layer, this solution further includes a powder-applying device, which is used to set the powder layer. This solution sets the powder layer through a powder-applying structure, making it convenient to use.

[0018] To spray microwave absorbing powder onto the printing area of ​​the powder layer, this solution also includes a powder release device for spraying microwave absorbing powder onto the printing area of ​​the powder layer. This solution facilitates use by spraying microwave absorbing powder onto the printing area of ​​the powder layer using the powder release device.

[0019] In order to heat the absorbing powder in different areas, this solution also includes a moving mechanism, which is connected to the coaxial radiator and is used to drive the coaxial radiator to move.

[0020] This solution connects a moving mechanism to a coaxial radiator, which in turn moves the coaxial radiator. When different sized printing layers are needed, the coaxial radiator moves over the microwave-absorbing powder in different areas, heating the powder and ultimately forming printing layers of varying sizes.

[0021] Preferably, for greater automation, this solution also includes a controller, which is signal-connected to the powder application device, the powder release device, and the microwave device. The controller enables the powder application device, the powder release device, and the microwave device to work in coordination, avoiding interference.

[0022] The beneficial effects of this invention are as follows: First, this solution involves spraying microwave-absorbing powder and heating the powder using a coaxial radiator. The coaxial radiator heats the microwave-absorbing powder in an open environment, and the heat does not diffuse over a large area. The heated microwave-absorbing powder connects the powder layers to form a printed layer. Due to the strong penetrating power of microwaves, the resulting printed layer is thicker than those formed by other printing methods in the prior art, ultimately resulting in a shorter printing time and higher efficiency.

[0023] Secondly, microwaves have strong penetrating power. Therefore, in the process of creating a 3D model by heating absorbing powder with microwaves, the heating effect extends beyond the surface layer to the underlying layers, achieving volumetric heating of the entire model and solidifying a three-dimensional volume in a single operation. This overcomes the efficiency bottleneck of conventional 3D printing technology, which involves point-by-point scanning and layer-by-layer accumulation, and offers potential for rapid prototyping of large-sized parts. Furthermore, microwaves, with their strong penetrating power, can simultaneously heat both the newly formed printed layer and the solidified portion. This allows for more complete diffusion and fusion of materials at the molecular level, forming a denser and stronger interface. From a mechanical performance perspective, this strong interfacial bonding significantly improves the interlayer shear strength and tensile properties of 3D printed products, reduces anisotropy caused by incomplete interlayer fusion, and makes the parts approach the consistency of a single, integrally formed solid in terms of overall density and mechanical properties.

[0024] Third, compared to conventional 3D printing technologies that use infrared heating, the heat generated by infrared heating affects the entire printing space and is easily dissipated outwards, resulting in low energy utilization. In contrast, the microwave heating method used in this solution allows microwave energy to be absorbed by materials with specific dielectric losses (i.e., microwave-absorbing powder), resulting in higher energy utilization and reduced energy loss due to diffusion. Attached Figure Description

[0025] Figure 1 This is a flowchart of a 3D printing method.

[0026] Figure 2 This is a schematic diagram of a 3D printing system.

[0027] Figure 3 This is a cross-sectional view of a coaxial radiator.

[0028] Figure 4 This is a schematic diagram of the internal guide components.

[0029] Figure 5 The diagram shows a comparison of the electric field when the diameter remains unchanged and no stepped structure is set, and when the diameter of the heating end changes and a stepped structure is set.

[0030] Figure 6 This is a schematic diagram of the coaxial radiator printing the model.

[0031] The reference numerals in the attached drawings include: working plane 1, coaxial radiator 2, internal conductor 21, heating end 211, connecting end 212, stepped structure 213, external conductor 22, connector 23, microwave device 3, and moving mechanism 4. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0033] Example 1 The basic implementation examples are as follows: Figure 1 As shown, a 3D printing method includes the following steps.

[0034] S1, Spread a powder layer onto the working surface. The powder is made of a non-absorbent material, such as polyethylene or nylon. The powder is evenly distributed on the working surface. The powder layer can be applied using an existing powder application machine, or it can be applied manually.

[0035] S2, spray microwave-absorbing powder into the printing area of ​​the powder layer. The microwave-absorbing powder is also in a uniform state. The microwave-absorbing powder can be made of materials such as carbon nanotubes, carbon black, and Ketjen black. The printing area of ​​the powder layer is determined by the overall shape of the product. For example, if a rectangular base needs to be printed, then the printing area of ​​the powder layer will be rectangular.

[0036] S3: After spraying microwave-absorbing powder into the printing area, the coaxial radiator is positioned corresponding to the printing area. The coaxial radiator operates, thereby heating the microwave-absorbing powder in the printing area.

[0037] S4, the heated microwave-absorbing powder binds the powder in the printing area together, forming a printing layer.

[0038] S5, after the printed layer is formed, another powder layer is spread on the working surface. At this time, the powder layer covers both the newly formed printed layer and the previously set powder layer. The material of the powder layer in this step is the same as the powder layer material set in step S1, and the powder in the powder layer is in a uniform state.

[0039] S6, microwave absorbing powder is sprayed again onto the printing area of ​​the powder layer, and the microwave absorbing powder is also in a uniform state. The microwave absorbing powder is the same as that set in step S2. The position of the printing area is determined by the cross-sectional shape and overall outline of the finished product to be printed.

[0040] S7: After spraying microwave-absorbing powder into the printing area, the coaxial radiator is aligned with the printing area again. The coaxial radiator operates, causing the microwave-absorbing powder in the printing area to heat up.

[0041] S8, the heated absorbing powder connects with the powder in the printing area and the printing layer prepared in the previous step to form a new printing layer. Because the new printing layer is connected to the printing layer formed in the previous step and to the newly laid powder layer, the thickness of the new printing layer increases.

[0042] S9. Repeat steps S5 to S8 until the finished product is printed.

[0043] Example 2 This embodiment provides an apparatus for using the 3D printing method described in Embodiment 1, such as... Figures 2 to 6 As shown, it includes a working plane 1, a powder application device, a powder release device, a coaxial radiator 2, a moving mechanism 4, a microwave device 3, and a controller.

[0044] In this embodiment, the working plane 1 is used to set the powder layer and the microwave absorbing powder. The working plane 1 is a horizontal plane. The working plane 1 can be the surface of a workbench, or it can be the inner bottom of a container, with the inner bottom of the container serving as the working plane 1.

[0045] In this embodiment, the powder-spreading device is positioned above the working plane 1. The device primarily serves to spread powder onto the working plane 1. Specifically, it can be a powder-spreading machine, a technology that uses existing techniques to evenly spread the powder. The powder is made of a non-absorbent material, such as polyethylene or nylon. When the powder-spreading machine spreads the powder onto the working plane 1, the powder is evenly distributed. Simultaneously, the powder-spreading device can move above the working plane 1 (specifically, it can be powered by a robotic arm or other similar moving mechanisms found in existing technology). When powder spreading is required, the device moves above the working plane 1 and evenly spreads powder onto it. After powder spreading is complete, the device is removed from above the working plane 1, thus avoiding interference with the powder release device and the coaxial radiator 2.

[0046] The powder release device in this embodiment is used to release microwave-absorbing powder onto the powder layer. The release area of ​​the microwave-absorbing powder is the area to be printed. The microwave-absorbing powder can be materials such as carbon nanotubes, carbon black, and Ketjen black. The size of the printing area is specifically determined by the cross-sectional shape and overall form of the product. The powder release device can specifically be a nozzle, which is connected to a storage container through a pipe, allowing the nozzle to be supplied with microwave-absorbing powder. The nozzle can spray the microwave-absorbing powder onto the printing area of ​​the powder layer by spraying. The powder release device can move above the working plane 1 (specifically, it can be driven by a robotic arm or other similar moving mechanisms in the prior art). When it is necessary to spray microwave-absorbing powder, the powder release device moves above the working plane 1 and releases the microwave-absorbing powder onto the printing area of ​​the powder layer. After the microwave-absorbing powder is released, it is removed from above the working plane 1, thereby avoiding interference with the powder application device and the coaxial radiator 2.

[0047] It should be noted that, in this embodiment, the powder layer and microwave absorbing powder are preferably set using a powder application device and a powder release device. However, in some other embodiments, other methods can also be used to set the powder layer and microwave absorbing powder. For example, the powder layer and microwave absorbing powder can be set manually.

[0048] In this embodiment, the coaxial radiator 2 is used to microwave heat the absorbing powder. The electric field of the coaxial radiator 2 is more focused, which can accurately heat the absorbing material in an open scene, reduce microwave divergence, and achieve better heating effect.

[0049] like Figure 3 As shown, the coaxial radiator 2 specifically includes an internal conductor 21, a dielectric, an external conductor 22, and a connector 23. The internal conductor 21 has a cylindrical cross-section, and the external conductor 22 is also cylindrical. The internal conductor 21 is housed inside the external conductor 22, and the internal conductor 21 and the external conductor 22 are coaxially aligned. The dielectric is disposed between the internal conductor 21 and the external conductor 22, and the dielectric is preferably FR4. In this embodiment, the dominant mode of the guided wave in the coaxial radiator 2 is the TEM mode, which has low radiation loss and is not easily affected by external signals. The coaxial radiator 2 is connected to the microwave device via the connector 23 to ensure microwave feeding.

[0050] like Figure 4 and Figure 5As shown, the internal conductor 21 in this embodiment includes a heating end 211 and a connecting end 212, which are arranged opposite to each other. The connecting end 212 is in a mating connection with the connector 23, while the heating end 211 is used to heat the absorbing powder. To solve the problem that the electric field cannot be focused in a small area and the heating effect is poor, in this embodiment, the diameter of the heating end 211 of the internal conductor 21 gradually increases towards the end of the heating end 211, forming a frustum-shaped matching structure at the heating end 211. The matching structure is connected to the middle of the internal conductor 21. The main purpose of forming the frustum-shaped heating end 211 is to achieve a smooth transition region for impedance matching. The characteristic impedance of the heating end 211 changes slowly with length by continuously changing the radial dimension of the inner / outer conductors 22 (i.e., the diameter of the heating end 211 of the inner conductor 21 gradually increases, while the inner diameter of the outer conductor 22 remains unchanged). The frustum-shaped heating end 211 is a linear matching structure. Through continuous changes in its geometry, the boundary conditions of the electromagnetic field can be gradually altered, achieving impedance matching. Simultaneously, a stepped structure 213 is provided on the end face of the heating end 211. The stepped structure 213 includes at least two circular steps, preferably five or six. Each circular step is cylindrical, and all circular steps are coaxially aligned and coincide with the axis of the internal conductor 21. The diameter of each circular step gradually increases towards the end face of the heating end 211. The stepped structure 213 concentrates the electric field at the steps, achieving a focusing effect and improving the heating effect. Furthermore, to further focus the electric field, the external conductor 22 in this embodiment extends outwards, with its end extending towards the dielectric end, forming a ring-shaped port at the end of the coaxial radiator 2.

[0051] To enable connection with the microwave device 3, connector 23 in this embodiment is preferably an L29 connector. When the coaxial radiator 2 feeds a microwave signal through connector 23, reflection occurs due to the impedance mismatch between the internal conductor 21 and connector 23, causing energy loss. Therefore, in this embodiment, the diameter of the connection end 212 gradually decreases towards its end. The end of the connection end 212 connects to connector 23, and through this connection, the impedance at connector 23 gradually transitions to the impedance of the internal conductor 21, reducing energy loss. Similarly, to ensure impedance matching of the external conductor 22, the end of the external conductor 22 connected to connector 23 in this embodiment is called the connector end. The diameter of the connector end of the external conductor 22 gradually decreases towards its end, allowing the impedance at connector 23 to gradually transition to the impedance of the external conductor 22, further reducing energy loss.

[0052] It should be noted that: This embodiment provides a newly designed coaxial radiator 2, but in some other embodiments, other coaxial radiators 2 in the prior art can also be used, as long as it can achieve microwave heating of the absorbing powder. This embodiment does not impose any restrictions.

[0053] Because the coaxial radiator 2 is highly focused, it can only act on the absorbing powder at one location. Therefore, in order to enable the coaxial radiator 2 to act on the absorbing powder at different locations in the printing area, in this embodiment, the coaxial radiator 2 is connected to the moving mechanism 4. The moving mechanism 4 includes an X-axis moving module, a Y-axis moving module, and a Z-axis moving module. Two X-axis moving modules are provided, located on opposite sides of the working plane 1. Each X-axis moving module includes an X-axis mounting component and an X-axis linear moving module. The X-axis mounting component is mounted on the working plane 1 by welding or fasteners, and the X-axis linear moving module is mounted on the X-axis mounting component. The X-axis linear moving module includes a slider and a slide rail. The slide rail is mounted on the X-axis mounting component, and the slider is mounted on the slide rail. The slider can move along the slide rail, thereby driving the coaxial radiator 2 to move in the X-axis direction. Similarly, two Y-axis moving modules are provided, each connected to one of the two X-axis moving modules. A crossbeam is provided between the two Y-axis moving modules. The Y-axis moving module includes a Y-axis mounting component and a Y-axis linear moving module. The Y-axis mounting component is mounted on the slider of the X-axis moving module by welding or fasteners. The Y-axis linear moving module is mounted on the Y-axis mounting component and also includes a slider and a slide rail. The slide rail is mounted on the Y-axis mounting component, and the slider is mounted on the slide rail, allowing it to move along the slide rail, thereby driving the coaxial radiator 2 to move in the Y-axis direction. The Z-axis moving module is mounted on a crossbeam and includes a Z-axis mounting component and a Z-axis linear moving module. The Z-axis mounting component is mounted on the crossbeam by welding or fasteners, and the Z-axis linear moving module is mounted on the Z-axis mounting component. The Z-axis linear moving module also includes a slider and a slide rail. The slide rail is mounted on the Z-axis mounting component, and the slider is mounted on the slide rail, allowing it to move along the slide rail, thereby driving the coaxial radiator 2 to move in the Z-axis direction. The slider in the Z-axis linear moving module is connected to the coaxial radiator 2. The aforementioned slide rail and slider connection method can refer to existing linear sliding modules, and its movement power can be provided by a motor.

[0054] It is understood that, in this embodiment, the preferred moving mechanism 4 includes an X-axis moving module, a Y-axis moving module, and a Z-axis moving module, making the coaxial radiator 2 move more flexibly. However, in some other embodiments, the moving mechanism 4 may also include only one or any two of the X-axis moving module, Y-axis moving module, and Z-axis moving module. Furthermore, the moving mechanism 4 can be replaced by a robotic arm or other moving device.

[0055] In this embodiment, the powder application device, powder release device, microwave device 3, and moving mechanism 4 are all connected to the controller. The controller controls the powder application device, powder release device, microwave device 3, and moving mechanism 4 to work together. The controller can be a PLC control module, a microcontroller control module, or an industrial control computer module, etc., based on existing technology.

[0056] The following detailed explanation illustrates the specific implementation methods: The following describes the formation process of a printing layer. During 3D printing, the controller first controls the powder application device to apply powder to the working plane 1, thus creating a powder layer on the working plane 1. Next, the controller moves the powder application device away from the working plane 1 to avoid interference with subsequent steps. Then, the controller moves the powder release device above the powder layer, releasing microwave-absorbing powder into the printing area of ​​the powder layer. Next, the controller moves the powder release device away from the working plane 1 to avoid interference with subsequent steps. Then, the controller controls the moving mechanism 4 to move the coaxial radiator 2 above the microwave-absorbing powder. The coaxial radiator 2 operates, heating the microwave-absorbing powder, which then connects the powder layers to form the printing layer. Finally, the controller controls the moving mechanism 4 to move the coaxial radiator 2 away from the microwave-absorbing powder.

[0057] For example: Figure 6 As shown, when printing the SCU pattern, the microwave absorbing powder of the SCU pattern is heated by the coaxial radiator 2, and the microwave absorbing powder can form the SCU printing layer.

[0058] After a printing layer is formed, a new printing layer is formed on top of the existing printing layer through the above process. Multiple printing layers overlap each other, and finally, a 3D finished product is printed.

[0059] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method of 3D printing, characterized by: The method comprises the following steps S1, setting a powder layer; S2, spraying absorbing powder to the printing area of the powder layer; S3, heating the absorbing powder by using a coaxial radiator; S4, the heated absorbing powder connects the powder in the printing area to form a printing layer.

2. The 3D printing method according to claim 1, characterized in that: Further comprising S5, setting a powder layer again; S6, spraying absorbing powder to the printing area of the powder layer; S7, heating the absorbing powder by using a coaxial radiator; S8, the absorbing powder connects the powder in the printing area and the printing layer to form a new printing layer; S9, repeating the steps of S5 to S8 until the printing is completed.

3. The 3D printing method according to claim 1 or 2, characterized in that: The absorbing powder is sprayed to the printing area of the powder layer.

4. The 3D printing method according to claim 1 or 2, characterized in that: The absorbing powder is in a uniform distribution state.

5. An apparatus for use in the 3D printing method according to any one of claims 1 to 4, characterized in that: The coaxial radiator (2) is connected with the microwave device (3), and the coaxial radiator (2) is used for heating absorbing powder.

6. The 3D printing system of claim 5, wherein: The coaxial radiator (2) comprises an inner guide (21), a medium and an outer guide (22), the inner guide (21) is arranged inside the outer guide (22), and the medium is arranged between the inner guide (21) and the outer guide (22). The inner guide (21) comprises a heating end (211) for heating, the diameter of the heating end (211) gradually increases towards the end of the heating end (211), the end surface of the heating end (211) is provided with a stepped structure (213), the stepped structure (213) comprises at least two circular steps, and the circular steps are coaxially arranged.

7. The 3D printing system of claim 6, wherein: The coaxial radiator (2) is connected with the microwave device (3) through the joint (23).

8. The 3D printing system of claim 7, wherein: The inner guide (21) comprises a connecting end (212) for connecting with the joint (23), the diameter of the connecting end (212) gradually decreases towards the end of the connecting end (212); And / or; the outer guide (22) comprises a joint end for connecting with the joint (23), the diameter of the joint end gradually decreases towards the end of the joint end.

9. The 3D printing system of claim 5, wherein: Further comprising a powder setting device for setting a powder layer; And / or; further comprising a powder releasing device for spraying absorbing powder to the printing area of the powder layer; And / or; further comprising a moving mechanism (4) connected with the coaxial radiator (2), the moving mechanism (4) is used for driving the coaxial radiator (2) to move.

10. The 3D printing system according to any one of claims 5 to 9, characterized in that: Further comprising a controller, the controller is at least signal connected with the powder setting device, the powder releasing device and the microwave device (3).

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