Coaxial extrusion printhead with core material switching, printing method, and printed products

Abstract

This invention relates to a coaxial extrusion printing nozzle and printing method with rapid core material switching, as well as printed products. The nozzle body includes a nozzle body comprising a housing forming structure and a core forming structure. The housing forming structure includes a housing material flow channel located within the nozzle body. The core forming structure has at least two material partitions between the outlet ends of adjacent core material flow channels. This invention controls the extrusion of material through air pressure, enabling the printing of a wide range of materials. The coaxial structure with a housing provides mechanical reinforcement between heterogeneous materials. Printing is achieved by controlling the air pressure system to slice and plan paths based on a multi-material 3D digital model. The printing nozzle is controlled to extrude material as needed during its movement. Through the encoded extrusion and layering of materials, a functional multi-material device is ultimately formed.

Description

Technical Field

[0001] This invention relates to the field of 3D printing nozzle technology, and in particular to a coaxial extrusion printing nozzle with rapid core material switching, a printing method, and printed products. Background Technology

[0002] Additive manufacturing technology has been widely applied in aerospace, biomedicine, and automotive manufacturing. As the performance requirements of high-end equipment continue to increase, additive manufacturing urgently needs to break through from single-material structures to multi-material structures, realizing the manufacturing of composite materials, functionally graded materials, and heterogeneous materials.

[0003] In traditional 3D printing technology, materials are often extruded through a single inlet and a single outlet, resulting in a limited variety of printed materials and restricting the diversity of product performance and form. Some research has explored multi-material 3D printing using multiple single extrusion systems, but this process is cumbersome and prone to errors. Currently, the main multi-material printing method involves designing a nozzle with multiple inlets that converge to a single outlet. This allows for the organic combination of different types of materials within the 3D printing system, achieving combinations of different properties and enabling more diverse product design and manufacturing.

[0004] However, stable and continuous additive manufacturing using multiple materials requires excellent bonding strength between the materials, and material parameters such as high viscosity and shear thinning must meet the requirements of 3D printing. In reality, however, the materials used in multi-material additive manufacturing often cannot simultaneously meet the requirements of high bonding strength between heterogeneous materials and good printing parameters. This often necessitates modifying existing materials, increasing the complexity of the process. Summary of the Invention

[0005] In response to the shortcomings of the existing production technology, the applicant provides a coaxial extrusion printing nozzle with a reasonable structure and a rapid switching of core material, as well as a printing method and printed products. This nozzle and printing method can control the extrusion of materials by air pressure frequency to achieve a multi-material linear structure with a rapidly switching core material enclosed by a shaft shell, so as to realize the manufacturing of some three-dimensional structures with multiple materials and functions.

[0006] The technical solution adopted in this invention is as follows:

[0007] A coaxial extrusion printing nozzle with rapid core material switching includes a nozzle body, wherein the nozzle body includes a housing forming structure and a core forming structure.

[0008] The housing molding structure includes a housing material flow channel located inside the nozzle body, with a housing material inlet and a housing material outlet at each end.

[0009] The core forming structure has at least two locations, each including a core material flow channel located within the nozzle body, a core material inlet located at both ends of the core material flow channel, and a core material outlet.

[0010] A material partition is installed between the outlet ends of adjacent shaft core material channels.

[0011] As a further improvement to the above technical solution:

[0012] After the core material flows through the material partition, it flows out through the core material outlet.

[0013] According to the material flow direction, shaft housing material flow channels are divided into single flow channels near the inflow end and circumferential flow channels near the outflow end.

[0014] The annular output position of the circumferential flow channel of the housing material is connected to the housing material chamber, which contracts toward the housing material outlet end of the nozzle body.

[0015] The outlet of the shaft core material flow channel is led to the shaft housing material outlet, and an axial distance of 0.3-0.4mm is reserved between the two.

[0016] The core material flow channel includes a first core material flow channel and a second core material flow channel. The first and second core material flow channels are introduced into the nozzle body from the side wall of the nozzle body. The material baffle is located between the outlet direction of the first core material flow channel and the outlet direction of the second core material flow channel.

[0017] A method for designing a coaxial extrusion printhead with rapid core material switching includes the following steps:

[0018] Based on the characteristics of the flow channel and the principle that incompressible fluids have equal volumes, the ideal state during the core material switching process is that the volume V of the common cavity of the core is... m The volume V0 at the end of a single shaft-core flow channel is equal to the volume of the nozzle. Based on the model, the following parameters are given: nozzle diameter D0 = 0.8 mm, semi-circular baffle R0 = 0.3 mm, distance from the end to the outlet H = 1.0 mm, diameter of the circular end section D = 1.6 mm, and nozzle length L = 0.7 mm.

[0019] (1)

[0020] (2)

[0021] K= (3)

[0022] (4)

[0023] As a further improvement to the above technical solution:

[0024] Substituting into the model, we get:

[0025] V m =0.352mm 3 V0 = 0.327 mm 3 ,

[0026] Therefore, K = 1.08, Δ = 0.08, and K is the ratio of volumes.

[0027] A product printed by a coaxial extrusion printhead with a rapidly switchable core material includes a housing and a core encased within the housing, wherein the viscosity of the housing is greater than that of the core.

[0028] As a further improvement to the above technical solution:

[0029] The extrusion process is pneumatically operated. Fluent is used to perform numerical simulation of the material flow inside the nozzle, and the interference effect of the reserved air pressure on the core material during the switching process is analyzed.

[0030] The core material is SE1700 silicone, and its viscosity satisfies the Herschel-bulkley equation, taking into account laminar flow and VOF models.

[0031] Continuity equation:

[0032] (1)

[0033] Momentum equation:

[0034] (2)

[0035] Phase equations of the VOF model:

[0036] (3)

[0037] Interface power source item:

[0038] (4)

[0039] The middle item on the right side of the interface force source term represents curvature. Combining interfacial tension, these two can be expressed as the pressure difference across the interface. ,

[0040] The fluid velocity is in m / s;

[0041] Fluid density, kg / m³;

[0042] Pressure, Pa;

[0043] The acceleration due to gravity is expressed in m / s².

[0044] It refers to the viscosity of the fluid material. ;

[0045] For the interface force source item, ;

[0046] It is the phase volume fraction;

[0047] Surface tension, N / m;

[0048] denoted as , where is the curvature of the liquid phase interface, 1 / m.

[0049] The viscosity requirement for the shaft housing is that it can be set immediately after extrusion.

[0050] The product's printing extrusion frequency is less than or equal to 50Hz, and the reserved air pressure range for core material switching is 70-73KPa.

[0051] The beneficial effects of this invention are as follows:

[0052] The coaxial extrusion 3D printing nozzle of the present invention has a rapid core material switching function, which can print a wide range of materials, namely lower viscosity materials. At the same time, the coaxial structure with a shaft shell can achieve mechanical reinforcement between heterogeneous materials. The printing process is controlled by the air pressure system to slice and plan the path according to the multi-material 3D digital model. The printing nozzle is controlled to extrude the printed material according to the requirements during the movement. Through the layering of material codes, a functional physical model is finally formed.

[0053] The 3D printing nozzle of this invention can effectively print a multi-material structure of a shaft core wrapped in a shaft shell, and can continuously and stably extrude materials to manufacture multi-material three-dimensional structures with specific functions.

[0054] The multi-material printing method used in the 3D printing nozzle of this invention can expand the range of printing materials compared with existing multi-material 3D printing methods, and at the same time has the effect of mechanical reinforcement of heterogeneous materials.

[0055] This invention provides a material partition to prevent different materials in different flow channels from being squeezed into another flow channel, ensuring a clear boundary between the subsequently extruded materials. The material partition is recessed inside the printhead to provide a buffer distance for the two materials to come into close contact before complete extrusion. Since the material partition has a certain thickness, extending it directly to the outlet end could result in loose adhesion and gaps between the two different core materials. Therefore, in this invention, the material partition is positioned at the innermost part of the outlet, and the wall between the core material flow channel and the shell material chamber is located at the end of the partition and between the main outlet. This allows the extruded materials to gradually come together, resulting in a finished product containing multiple core materials and one layer of shell material during final extrusion.

[0056] This invention can obtain extruded products with different contents by controlling the extrusion pressure in the flow channels of different core materials. In actual use, it can not only provide extruded materials with a variety of contents, but also use the support of the external shaft shell to limit the internal core material, so that the source of the core material is not limited to a certain viscosity range, thus increasing the scope of application. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the printhead structure of the present invention.

[0058] Figure 2 This is a cross-sectional view of the printhead of the present invention.

[0059] Figure 3 This is a schematic diagram of the internal flow direction of the printhead of the present invention.

[0060] Figure 4 This is a partial cross-section of the printing nozzle of the present invention, showing the material flow direction.

[0061] Figure 5 This is a cross-sectional view of the print head of the present invention from another direction.

[0062] Figure 6 for Figure 5 A schematic diagram of the internal material flow direction in the mid-section view.

[0063] Figure 7-1 This is a schematic diagram of the assembly structure of the printing nozzle and the cartridge in this invention.

[0064] Figure 7-2 This is a schematic diagram of the printing system process.

[0065] Figure 8 This is a schematic diagram of the printed product of the present invention.

[0066] Figure 9This is a schematic diagram of the extrusion pressure pulse of the nozzle material.

[0067] Figure 10-1 , Figure 10-2 This is a simulation diagram of the present invention.

[0068] The components are: 1. Shaft housing material inlet; 2. Shaft housing material single flow channel; 3. Threaded interface; 4. Shaft core material first inlet; 5. Shaft core material first flow channel; 6. Shaft core material outlet; 7. Shaft housing material outlet; 8. Shaft housing material chamber; 9. Shaft core material second flow channel; 10. Material partition; 11. Shaft core material second inlet; 12. Shaft housing material circumferential flow channel; 13. Material cylinder. Detailed Implementation

[0069] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0070] like Figures 1-8 As shown, the coaxial extrusion printing nozzle with rapid core material switching in this embodiment includes a nozzle body, which comprises a housing forming structure and a core forming structure.

[0071] The housing molding structure includes a housing material flow channel located inside the nozzle body, with a housing material inlet and a housing material outlet at each end.

[0072] The core forming structure has at least two locations, each including a core material flow channel located inside the nozzle body, a core material inlet located at both ends of the core material flow channel, and a core material outlet 6.

[0073] A material partition 10 is provided between the outlet ends of adjacent shaft core material channels.

[0074] After the core material flows through the material partition 10, it flows out through the core material outlet 6.

[0075] According to the material flow direction, the shaft housing material flow channel is divided into a single flow channel 2 near the inflow end and a circumferential flow channel 12 near the outflow end.

[0076] The annular output position of the circumferential flow channel 12 of the housing material is connected to the housing material chamber 8, and the housing material chamber 8 contracts toward the housing material outlet 7 of the nozzle body.

[0077] The outlet of the shaft core material flow channel is led to the shaft housing material outlet 7, and an axial distance of 0.3-0.4mm is reserved between them.

[0078] The core material flow channel includes a first core material flow channel 5 and a second core material flow channel 9. The first core material flow channel 5 and the second core material flow channel 9 are introduced into the nozzle body from the side wall of the nozzle body. The material partition 10 is located between the outlet direction of the first core material flow channel 5 and the outlet direction of the second core material flow channel 9.

[0079] The method for designing a coaxial extrusion printing nozzle with rapid core material switching in this embodiment includes the following steps:

[0080] Based on the characteristics of the flow channel and the principle that incompressible fluids have equal volumes, the ideal state during the core material switching process is that the volume V of the common cavity of the core is... m The volume V0 at the end of a single shaft-core flow channel is equal to the volume of the nozzle. Based on the model, the following parameters are given: nozzle diameter D0 = 0.8 mm, semi-circular baffle R0 = 0.3 mm, distance from the end to the outlet H = 1.0 mm, diameter of the circular end section D = 1.6 mm, and nozzle length L = 0.7 mm.

[0081] (1)

[0082] (2)

[0083] K= (3)

[0084] (4)

[0085] Substituting into the model, we get:

[0086] V m =0.352mm 3 V0 = 0.327 mm 3 ,

[0087] Therefore, K = 1.08, Δ = 0.08, and K is the ratio of volumes.

[0088] Compared to positive pressure operation driven by a syringe pump, the main advantages of pneumatic operation are faster start-up time and near-instantaneous switching between inks. For pneumatic extrusion, ink rheology, printhead internal channels, and flow pressure must be designed to prevent ink from one channel from interacting with ink in adjacent channels.

[0089] In one embodiment of the present invention, the extrusion process is pneumatically operated; fluid numerical simulation of the material flow inside the nozzle is performed using Fluent to analyze the interference effect of the reserved air pressure on the core material during the switching process.

[0090] The core material is SE1700 silicone, a non-Newtonian fluid. The viscosity of the core material satisfies the Herschel-bulkley equation, primarily considering laminar flow and the VOF (volume of fluid) model.

[0091] Continuity equation:

[0092] (1)

[0093] Momentum equation:

[0094] (2)

[0095] Phase equations of the VOF model:

[0096] (3)

[0097] Interface power source item:

[0098] (4)

[0099] The middle item on the right side of the interface force source term represents curvature. Combining interfacial tension, these two can be expressed as the pressure difference across the interface. ,

[0100] The fluid velocity is in m / s;

[0101] Fluid density, kg / m³;

[0102] Pressure, Pa;

[0103] The acceleration due to gravity is expressed in m / s².

[0104] It refers to the viscosity of the fluid material. ;

[0105] For the interface force source item, ;

[0106] It is the phase volume fraction;

[0107] Surface tension, N / m;

[0108] denoted as , where is the curvature of the liquid phase interface, 1 / m.

[0109] The nozzle parameters were optimized through simulation, primarily by optimizing the reserved air pressure, to minimize interference between the two core materials during extrusion. As shown in Figure 10, the simulation revealed that the interference was minimized when the reserved air pressure for core material switching was 71.6 kPa.

[0110] The product printed by the coaxial extrusion printhead with rapid core material switching in this embodiment includes a shaft housing and a core encased in the shaft housing. The viscosity of the shaft housing is greater than that of the core.

[0111] The viscosity requirement for the shaft housing is that it can be set immediately after extrusion.

[0112] The product's printing extrusion frequency is less than or equal to 50Hz.

[0113] The specific structure and principle of this invention are as follows:

[0114] like Figures 1-2 The 3D nozzle shown includes a housing material inlet 1, a housing material flow channel, a Luer thread interface 3, a shaft core material inlet 4, a shaft core material flow channel 5, a shaft core material outlet 6, a housing material outlet 7, a housing material chamber 8, a shaft core material second flow channel 9, a material partition 10, a shaft core material second inlet 11, and a housing material flow channel.

[0115] like Figures 3-4 The diagram shows the flow direction of the housing material and the core material in the corresponding flow channels.

[0116] In one embodiment of the present invention, three material cylinders 13 are connected to the print head, namely a shaft housing material cylinder 13 and two shaft core material cylinders 13. Three different materials are prepared and loaded into the syringe. The material cylinders 13 are connected to the print head through the Luer thread interface 3. The shaft housing material and the shaft core material are extruded into the inlet by air pressure, and enter the chamber for supplying the shaft housing material through the shaft housing feed channel, thereby encapsulating the shaft core material and extruding it.

[0117] The first core material is extruded under air pressure control. Core material one flows through core material one channel 5 and reaches material partition 10 to prevent it from entering the adjacent core material two channel. The partition effectively avoids material interference during material switching, allowing it to be smoothly extruded from the core nozzle. Core material two flows through core material two channel 9 and reaches material partition 10. At this time, the housing material is extruded after passing through the housing material channel and housing material chamber 8. The simultaneous extrusion of the housing material and the core material forms a coaxial structure.

[0118] During printing, the print head is connected to three cartridges 13, each filled with a different material. The control system transmits the corresponding core material extrusion signal by sending signals to a pneumatic switch. The housing material is continuously and stably extruded throughout the printing process. The core material is driven by a set of rapidly circulating pneumatic solenoid valves to achieve high-frequency switching of the core material, with a maximum frequency of 50Hz. The core material is extruded on demand along the printing path using edited G-code for the multi-material coaxial 3D printing path.

[0119] For example, when the extrusion pressure in a core material flow channel is 0, the core material is not extruded. Core materials with extrusion pressure in other flow channels continue to be extruded. After the core material moves to the material baffle, it is axially guided by the material baffle and flows to the inner position of the housing material chamber 8, where it is wrapped and extruded by the housing material.

[0120] By using a 3D printing motion platform to stack layers, a specific multi-material three-dimensional structure is ultimately formed.

[0121] In one embodiment of the present invention, the printing nozzle is capable of extruding a 1.8mm thick housing structure and a 0.8mm thick core structure. The height difference between the core nozzle and the housing nozzle is 0.6mm, wherein the included angle of the feed channels for the dual materials of the core is 38°.

[0122] The material baffle is 0.6mm thick, and the height difference between the material baffle and the core nozzle is 0.37mm, which effectively prevents material interference during core material switching. By controlling the extrusion frequency of the core structure, with a maximum extrusion frequency of 50Hz, rapid switching of core materials can be achieved.

[0123] During extrusion, refer to Figure 9 The upper line represents the pressure pulse at inlet 11 of the second core material, and the lower line represents the pressure pulse at inlet 4 of the first core material. This pulse pattern illustrates the change in air pressure pulses during material switching in the multi-material nozzle, primarily to demonstrate the technical characteristic of the core material being extruded on demand. Air pressure control is mainly to ensure smooth material extrusion without causing material interference, which is ultimately reflected in the printed structure.

[0124] The shaft shell in this invention has a self-supporting effect, allowing for continuous and stable printing of shaft core materials with low viscosity or even liquids, thereby expanding the range of materials for direct writing. Simultaneously, the shaft shell encapsulates the heterogeneous shaft core material, providing mechanical reinforcement and solving the problem of poor adhesion or low bonding strength at the interface of heterogeneous materials during multi-material additive manufacturing, which affects the overall mechanical properties of the product.

[0125] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims. Within the scope of protection of the present invention, any form of modification may be made.

Claims

1. A design method for a coaxial extrusion 3D printing nozzle with rapid core material switching function, wherein the extrusion of the core material is controlled by air pressure frequency to achieve a multi-material line structure with rapid core material switching function enclosed by a shaft shell, characterized in that: The coaxial extrusion 3D printing nozzle includes a nozzle body, which includes a housing forming structure and a core forming structure. The housing forming structure includes a housing material flow channel located inside the nozzle body. The two ends of the housing material flow channel are a housing material inlet and a housing material outlet, respectively. The core forming structure has at least two locations. Each core forming structure includes a core material flow channel located inside the nozzle body, a core material inlet located at both ends of the core material flow channel, and a core material outlet. A material partition (10) is provided between the outlet ends of adjacent core material flow channels. The core material flow channel includes a first core material flow channel (5) and a second core material flow channel (9). The first core material flow channel (5) and the second core material flow channel (9) are introduced into the nozzle body from the side wall of the nozzle body. The material partition (10) is located between the outlet direction of the first core material flow channel (5) and the outlet direction of the second core material flow channel. After the core material flows through the material partition (10), it flows out through the core material outlet (6); According to the material flow direction, the shaft housing material flow channel is divided into a single flow channel (2) near the inflow end and a circumferential flow channel (12) near the outflow end. The annular output position of the circumferential flow channel (12) of the housing material is connected to the housing material chamber (8), and the housing material chamber (8) contracts toward the housing material outlet (7) of the nozzle body. The outlet of the shaft core material flow channel is led to the shaft housing material outlet (7), and an axial distance is reserved between the shaft core material outlet (7) and the shaft housing material outlet (7); Its design method includes the following steps: Based on the characteristics of the flow channel and the principle that incompressible fluids have equal volumes, the ideal state during the core material switching process is that the volume V of the common cavity of the core is... m The volume V0 at the end of a single shaft-core flow channel is equal to that of the other two. Based on the model, the following parameters are given: shaft-core nozzle diameter D0 = 0.8 mm, semi-circular baffle R0 = 0.3 mm, end distance from outlet H = 1.0 mm, end cross-sectional diameter D = 1.6 mm, and shaft-core nozzle length L = 0.7 mm. (1) (2) K= (3) (4) When the dimensionless constant The smaller the nozzle, the faster the switching speed. Substituting this into the model, we get: V m =0.352mm 3 ,V0=0.327mm 3 , Therefore, K = 1.

08. =0.08, where K is the volume ratio.

2. A coaxial extrusion 3D printing nozzle obtained by the design method according to claim 1.

3. A printing method using the coaxial extrusion 3D printing nozzle as described in claim 2, characterized in that: The extrusion process is pneumatically operated, and the reserved air pressure for switching core materials is 70-73 kPa.

4. The printed product obtained by the printing method according to claim 3, characterized in that: It includes a shaft housing and a shaft core encased within the shaft housing. The viscosity of the shaft housing is greater than that of the shaft core, and the viscosity of the shaft housing is required to be set immediately after extrusion.

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