A coaxial bimodal in-situ material extrusion 3D printing interlayer reinforcement method

Abstract

The present application relates to the technical field of additive manufacturing, and relates to a coaxial dual-state in-situ material extrusion 3D printing interlayer reinforcement method, which comprises the following steps: (1) data processing, (2) reading data and dividing a printing area, the printing area is divided into two types of outer wall and internal filling, (3) adjusting printing parameters to obtain a coaxial dual-state process control method, (4) automatically adjusting printing strategies and process parameters according to the printing area and printing materials: when the program identifies that the printing area is an outer wall, normal printing process parameters are kept unchanged; when the program identifies that the printing area is internal filling, the coaxial dual-state process control method is applied for printing. The coaxial dual-state in-situ material extrusion 3D printing method provided by the present application can effectively improve the material extrusion interlayer strength without additional integrated components and additional control systems, and has the advantages of simplicity, high efficiency and no directional restriction.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and more specifically, to a method for interlayer reinforcement in coaxial dual-state in-situ material extrusion 3D printing. Background Technology

[0002] Material extrusion 3D printing is a low-cost and effective method for manufacturing complex structural parts, enabling the integrated molding of components. However, as a material manufacturing method that "accumulates layer by layer", the weak interlayer bonding strength is one of the main technical challenges for the industrial application of this technology.

[0003] Currently, common methods for improving interlayer bond strength in extrusion molding include material modification and additional hardware devices. Material modification mainly refers to increasing interlayer bond strength by utilizing the reaction between organic additives and the polymer matrix or by introducing amorphous polymer blends. However, material synthesis is expensive and the improvement in interlayer strength is limited. Physical aids include laser preheating and roll pressing; however, both suffer from directional issues. The laser preheating position and roller position must remain constant relative to the nozzle. When the angle between the laser preheating direction and the nozzle movement direction changes, the preheating or extrusion effect on the printed area cannot be effectively achieved. Roll pressing has a significant impact on the dimensional accuracy of the parts. Furthermore, current physical aid methods often require the integration of multiple components and additional control systems, increasing costs. Therefore, ensuring printing accuracy while simply, efficiently, and cost-effectively improving interlayer strength is a pressing technical challenge. Summary of the Invention

[0004] To address the problems existing in the background technology, this invention proposes a coaxial dual-state in-situ material extrusion 3D printing interlayer reinforcement method. This method does not require modification of the printing material, does not have directionality issues, does not require the integration of multiple components, and does not require the introduction of an additional control system. It can achieve a significant improvement in interlayer bonding strength simply and efficiently while ensuring printing accuracy.

[0005] The technical solution of the present invention to solve the above problems is:

[0006] This invention proposes a method for interlayer reinforcement in coaxial dual-state in-situ material extrusion 3D printing, characterized by the following steps:

[0007] (1) Data processing.

[0008] (2) Read the data and divide the printing area into two categories: outer wall (WALL) and inner fill (FILL).

[0009] (3) Adjusting printing parameters to obtain coaxial dual-state process control method: By changing the wire feeding speed and heating temperature, the outer part of the wire is in a molten state while the inner part is in an incompletely molten state when the wire is extruded. The outer molten state ensures that the wires between layers can bond together, while the inner incompletely molten state, due to its structural stability and high rigidity, can increase the extrusion pressure when the material is extruded from the nozzle, making the bonding interface more closely contacted and improving the interlayer bonding strength.

[0010] (4) Automatically adjust printing strategy and process parameters according to printing area and printing material: When the program recognizes that the printing area is the outer wall, the normal printing process parameters remain unchanged; when the program recognizes that the printing area is the inner filling, the coaxial dual-state process control method is applied for printing.

[0011] The above method ensures the printing accuracy of the outer wall while increasing the interlayer strength of the internal filling.

[0012] Furthermore, in step (1), the data processing specifically involves importing the established 3D model into the slicing software to obtain printing data.

[0013] Furthermore, in step (2), the data is read to divide the printing area. The printing data in step (1) is divided into two categories: outer wall and internal filling.

[0014] Furthermore, in step (3), the method of making the outside of the filament molten while the inside is incompletely molten is specifically as follows:

[0015] (3.1) During the printing process, the filament feeding speed is gradually increased, so that the outer surface of the filament melts when it is extruded, while the inside is not completely melted;

[0016] (3.2) If the surface temperature of the extruded filament is insufficient, increase the heating temperature of the print head and return to step (3.1);

[0017] (3.3) Repeat steps (3.1) and (3.2) until the external melting temperature of the filament is high enough to allow the molecular chains at the interlayer to fully diffuse across the interface and the internal incomplete melting stiffness is large enough to efficiently transmit force; interlayer bonding is the combined result of temperature and force. The interface temperature affects the interlayer molecular chains' ability to diffuse across the interface, and the pressure affects the tightness of the bonding interface contact.

[0018] Furthermore, it also includes step (3.4): printing the parts at a suitable speed based on the printing line width requirements and the filament feeding speed and nozzle temperature determined in step (3.3) above. The formula for determining the printing speed is:

[0019]

[0020] In the formula: W is the line width, in mm; D is the wire diameter, in mm; H is the printing layer height, in mm; V f The wire feeding speed is expressed in mm·s. -1 V p Printing speed, unit mm·s -1 The filament diameter D is typically 1.75mm, therefore, when determining the printing layer height H, printing linewidth W, and filament feed speed V... f Then, the corresponding printing speed can be determined by this formula.

[0021] Advantages of this invention:

[0022] This invention proposes a low-stress, high-entropy alloy design method for additive manufacturing based on lattice mismatch. This method identifies the printing area and automatically adjusts the printing strategy and process parameters. During the printing of the outer wall area, it maintains normal printing accuracy. During the printing of the internal filling area, by controlling the filament feed speed and nozzle temperature, the filament melts externally but not completely internally during extrusion. Therefore, a glassy / highly elastic state with a certain stiffness exists within the filament throughout the entire extrusion process. Compared to traditional fully molten extrusion methods, this method increases the extrusion pressure of the filament, allowing the extruded material to fuse more tightly with the previous layer, thereby improving interlayer bonding strength. Traditional extrusion molding is fully molten extrusion, resulting in poor melt stiffness and easy shape changes under stress. This means a prolonged material response time, and the melt cannot transmit force accurately and promptly. Therefore, the extrusion pressure at the nozzle is significantly reduced relative to the driving force provided by the filament feed drive wheel. In contrast, molecules or atoms in the non-fully molten state (glassy / highly elastic state) typically exist in a fixed, ordered arrangement. This orderliness endows them with high structural stability and high stiffness. When transmitting force, they can directly transmit force from one end to the other, enabling direct and effective force transmission. This increases the extrusion pressure at the material extrusion nozzle, allowing the freshly extruded material to be pressed more tightly together with the previous layer, thereby improving the interlayer bonding strength. Attached Figure Description

[0023] Figure 1 A schematic diagram illustrating the principle of interlayer reinforcement in coaxial dual-state in-situ material extrusion 3D printing;

[0024] Figure 2 An adaptive printing flowchart for an interlayer reinforcement method in coaxial dual-state in-situ material extrusion 3D printing;

[0025] Figure 3 The effect of coaxial dual-state material extrusion on the cross-section of polyetheretherketone (PEEK) 3D printed filaments. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The coaxial dual-state in-situ material extrusion 3D printing interlayer reinforcement method proposed in this invention is as follows:

[0028] (1) Data processing: Import the established STL format 3D model into slicing software such as Cura to obtain gcode data.

[0029] (2) Reading data and dividing the printing area: Read the gcode format data after slicing, identify the printing area marker codes (TYPE:WALL-OUTER / INNER, TYPE:FILL) in the data, and divide the printing area into outer wall and inner filling areas. The process is as follows: Figure 2 As shown.

[0030] (3) Adjusting printing parameters to obtain a coaxial dual-state process control method. Taking the polymer polyether ether ketone as an example, its crystallinity and color characterize the melting degree of the filament. By changing the filament feeding speed and heating temperature, the filament is made to be in a molten state on the outside and in an incompletely molten state on the inside when it is extruded. The molten state on the outside ensures that the filament between the layers can be bonded, while the incompletely molten state on the inside can increase the extrusion pressure when the material is extruded from the nozzle due to its structural stability and high rigidity, so that the bonding interface is more closely contacted and the interlayer bonding strength is improved.

[0031] (4) Automatically adjust printing strategy and process parameters based on the printing area. When the program identifies the printing area as the outer wall, it keeps the normal printing process parameters unchanged to ensure that the printing accuracy remains unchanged; when the program identifies the printing area as the inner filling, it adopts the coaxial dual-state process control method to appropriately increase the filament feeding speed and nozzle temperature.

[0032] Specifically, in step (3), see Figure 1 The coaxial dual-state process control method is as follows:

[0033] (3.1) During the printing process, the filament feeding speed is gradually increased so that the outer surface of the filament melts when it is extruded, and the inside is in a partially melted state. The filament melts from the outside to the inside inside the nozzle. Therefore, the time the filament stays in the heating channel can be shortened by increasing the filament feeding speed, so that the outside of the filament melts while the inside does not melt completely.

[0034] (3.2) If the surface temperature of the extruded filament is insufficient, increase the heating temperature of the print head and return to step (3.1); because increasing the filament feeding speed will cause the surface temperature of the filament to drop during extrusion. When the surface temperature of the extruded filament drops to a level that cannot raise the interface temperature above the glass transition temperature, the molecular chains at the interlayer cannot diffuse across the interface, that is, the interlayer filaments cannot bond together, so it is necessary to increase the heating temperature.

[0035] (3.3) Repeat steps (3.1) and (3.2) until the external melting temperature of the filament is high enough to allow the molecular chains at the interlayer to fully diffuse across the interface and the internal non-fully molten stiffness is large enough to efficiently transmit force; interlayer bonding is a combination of temperature and force. The interface temperature affects the interlayer molecular chains' ability to diffuse across the interface, and the pressure affects the tightness of the bonding interface contact.

[0036] (3.4) Print the parts at a suitable speed based on the required line width and the wire feed speed and nozzle temperature determined in step (3.3). The formula for determining the printing speed is:

[0037]

[0038] In the formula: W is the line width, in mm; D is the wire diameter, in mm; H is the printing layer height, in mm; V f The wire feeding speed is expressed in mm·s. -1 V p Printing speed, unit mm·s -1 The filament diameter D is typically 1.75mm, therefore, when determining the printing layer height H, printing linewidth W, and filament feed speed V... f Then, the corresponding printing speed can be determined by this formula.

[0039] In this invention, coaxial dual-state refers to changing the melting state of the filament inside the heating channel through process control, so that the inside of the filament is in a partially molten state (glassy / highly elastic state) while the outside is molten during extrusion. The internal stiffness is used to transmit force in a timely and effective manner, thereby increasing the extrusion pressure of the filament and achieving high-strength bonding between layers. In-situ extrusion refers to automatically adjusting the printing strategy according to the printed outer wall / internal filling area. The printing accuracy of the outer wall area needs to be ensured, while the interlayer strength needs to be increased in the internal filling area. The process method of this invention is simple, efficient, and can significantly improve the interlayer bonding strength of the printed parts.

[0040] This paper proposes a coaxial dual-state in-situ material extrusion 3D printing interlayer reinforcement method. This method significantly increases the filament feed speed during printing, resulting in an external molten state and an internal incompletely molten state during filament extrusion. The external molten state ensures adhesion between layers (molecular chain diffusion across the interface), while the internal incompletely molten state increases the extrusion pressure, thereby improving interlayer bonding strength. The coaxial dual-state interlayer reinforcement process specifically includes the following steps:

[0041] (1) During the printing process, by adjusting the filament feeding speed, the filament becomes solid inside when it is extruded. The filament melts from the outside to the inside inside the nozzle. Therefore, by controlling the filament feeding speed, the outside of the filament can be melted while the inside is not completely melted. The coaxial dual-state principle and process flow are as follows: Figure 2 As shown.

[0042] (2) If the surface temperature of the extruded filament is insufficient, increase the heating temperature of the printhead so that the surface temperature of the extruded filament reaches at least above the glass transition temperature of the filament material, and return to step (1). In order to make the interior of the extruded filament in a partially molten state, a higher filament feeding speed is required. However, increasing the filament feeding speed will cause the surface temperature of the filament to drop during extrusion. When the surface temperature of the extruded filament drops to a level that prevents the interface temperature from rising above the glass transition temperature, the molecular chains at the interlayer cannot diffuse across the interface, that is, the interlayer filaments cannot bond together. Therefore, it is necessary to increase the heating temperature.

[0043] (3) Repeat the above steps until the external melting temperature of the filament during extrusion is greater than or equal to the glass transition temperature of the filament material, so that the molecular chains at the interlayer can fully diffuse across the interface and the internal solid stiffness is large enough to efficiently transfer force. Interlayer bonding is a combined result of temperature and force. The interface temperature affects the interlayer molecular chains' ability to diffuse across the interface, and the pressure affects the tightness of the bonding interface.

[0044] (4) Establish a coaxial dual-state process parameter library for each material based on the requirements of temperature and wire feeding speed for coaxial dual-state process. The coaxial dual-state process parameter library includes the name of the printing material, the nozzle heating temperature and wire feeding speed that meet the requirements of coaxial dual-state printing.

[0045] The invention will be further understood from the following illustrative examples.

[0046] Example 1

[0047] This example uses polyetheretherketone (PEEK) as the 3D printing material and enhances the interlayer strength of PEEK 3D printing through a coaxial dual-state in-situ material extrusion process.

[0048] A 1.2mm diameter chromium-zirconium copper nozzle was used to print standard tensile specimens along the Z-axis, based on the testing standard GB / T 1040.1-2018, "Determination of Tensile Properties of Plastics". The nozzle temperature was set to 500℃, the layer thickness to 0.3mm, and the line width to 2mm, determined by the wire cross-section. Figure 3 It is observed that the coaxial dual-state structure appears when the wire feed speed reaches 12 mm / s. With further increases in wire feed speed, the incompletely melted region not only gradually increases in area but also shows a gradual upward trend in the vertical direction. Mechanical property testing results show that the interlayer tensile strength of the coaxial dual-state in-situ material extrusion tensile specimens increases with increasing wire feed speed. When the wire feed speed is increased to a certain threshold, the interlayer tensile strength remains unchanged; further increases in wire feed speed result in poor wire ejection. Experimental results indicate that coaxial dual-state in-situ material extrusion can effectively increase the interlayer bonding strength of 3D printing.

[0049] In summary, this invention proposes a process method to improve the interlayer bonding strength of 3D printing by utilizing the incompletely molten state (glassy / highly elastic state) of the filament itself for efficient force transfer. This process method differs from the traditional method of fully melting the filament before extrusion. Instead, during extrusion, the outer layer is in a molten state while the inner layer is in an incompletely molten state. The outer molten state ensures that the filaments between layers can bond together, while the inner incompletely molten state can increase the extrusion pressure of the filament, resulting in a tighter contact at the bonding interface, thereby improving the interlayer bonding strength.

[0050] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related system fields, are similarly included within the scope of protection of the present invention.

Claims

1. A method for interlayer reinforcement in coaxial dual-state in-situ material extrusion 3D printing, characterized in that, Includes the following steps: (1) Data processing; (2) Read the data and divide the printing area into two categories: outer wall and internal filling; (3) Adjusting printing parameters to obtain coaxial dual-state process control method: By coordinating the change of filament feeding speed and heating temperature, the filament is actively extruded to form and maintain a coaxial dual-state structure in which the outside is in a molten state and the inside is in an incompletely molten state. The incompletely molten state is a glassy state or a high-elastic state. The molten state of the outside ensures that the filaments between the layers can be bonded, while the incompletely molten state of the inside can increase the extrusion pressure when the material is extruded from the nozzle due to its structural stability and high rigidity, so that the bonding interface is in closer contact, thereby improving the interlayer bonding strength. The filament material is polyetheretherketone. (4) Automatically adjust printing strategy and process parameters based on the printing area: When the program recognizes that the printing area is the outer wall, keep the original printing process parameters unchanged; When the program detects that the printing area is filled internally, it applies the coaxial dual-state process control method for printing.

2. The method for interlayer reinforcement in coaxial dual-state in-situ material extrusion 3D printing according to claim 1, characterized in that: In step (1), the data processing specifically involves importing the established 3D model into the slicing software to obtain printing data.

3. The method for interlayer reinforcement in coaxial dual-state in-situ material extrusion 3D printing according to claim 2, characterized in that: In step (2), the data is read and the printing area is divided. The printing data in step (1) is divided into two categories: outer wall and internal filling.

4. The method for interlayer reinforcement in coaxial dual-state in-situ material extrusion 3D printing according to claim 3, characterized in that: In step (3), the method for adjusting printing parameters to obtain coaxial dual-state process control is as follows: (3.1) During the printing process, the filament feeding speed is gradually increased so that the outer surface of the filament melts when it is extruded, while the inside is not completely melted. The filament melts from the outside to the inside inside the nozzle. Therefore, by increasing the filament feeding speed, the time the filament stays in the heating channel is shortened, so that the outside of the filament melts while the inside is not completely melted. (3.2) If the surface temperature of the extruded filament is insufficient, increase the heating temperature of the print head and return to step (3.1); because increasing the filament feeding speed will cause the surface temperature of the filament to drop during extrusion. When the surface temperature of the extruded filament drops to a level that cannot raise the interface temperature above the glass transition temperature, the molecular chains at the interlayer cannot diffuse across the interface, that is, the interlayer filaments cannot bond together, so it is necessary to increase the heating temperature. (3.3) Repeat steps (3.1) and (3.2) until the external melting temperature is high enough during the extrusion of the filament so that the molecular chains at the interlayer can fully diffuse across the interface and the internal incomplete melting stiffness is large enough to transmit force efficiently. Interlayer bonding is a combined result of temperature and force. Interface temperature affects the cross-interface diffusion ability of molecular chains between layers, while pressure affects the tightness of the bonding interface contact.

5. The method for interlayer reinforcement in coaxial dual-state in-situ material extrusion 3D printing according to claim 4, characterized in that: It also includes step (3.4): Based on the printing line width requirements and the filament feeding speed and nozzle temperature determined in step (3.3) above, a suitable speed is matched for printing the parts. The formula for determining the printing speed is: ， In the formula: W is the line width, in mm; D The diameter of the wire is in mm. H This refers to the print layer height, in mm. V f The wire feeding speed is expressed in mm·s. -1 ; V p Printing speed, unit mm·s -1 Wire diameter D The thickness is typically 1.75mm, therefore, when determining the printing layer height... H Print line width W With wire feeding speed V f Then, the corresponding printing speed is determined by this formula.

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