Coaxial double-state in-situ material extrusion 3D printing interlayer enhancement method

Abstract

The invention relates to the technical field of additive manufacturing, in particular to a coaxial two-state in-situ material extrusion 3D printing interlayer enhancement method which comprises the steps of (1) data processing, (2) data reading and printing area dividing, dividing the printing area into an outer wall filling type and an inner filling type, and (3) adjusting printing parameters to obtain a coaxial two-state process control method. (4) a printing strategy and process parameters are automatically adjusted according to the printing area and the printing material, and when the program recognizes that the printing area is the outer wall, the normal printing process parameters are kept unchanged; and when the program recognizes that the printing area is internally filled, a coaxial double-state process control method is used for printing. According to the coaxial two-state in-situ material extrusion 3D printing method, on the premise of not additionally integrating parts and not additionally introducing a control system, the material extrusion interlayer strength can be effectively improved, and the coaxial two-state in-situ material extrusion 3D printing method has the advantages of being simple, efficient, free of directional limitation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a coaxial dual-state in-situ material extrusion 3D printing interlayer reinforcement method. Background Art

[0002] Material extrusion 3D printing is a low-cost and effective method for manufacturing complex structural parts. It can achieve integrated forming of components. However, as a "layer-by-layer accumulation" material manufacturing method, weak interlayer bonding strength is one of the main technical difficulties for this technology to be applied in industry.

[0003] At present, the common methods to improve the interlayer bonding strength of material extrusion molding are material modification and additional hardware devices. Material modification mainly refers to the use of the reaction between organic additives and polymer matrix or the introduction of amorphous polymer blending to increase the interlayer bonding strength, but the material synthesis cost is expensive and the interlayer strength improvement is limited. Physical assistance includes laser preheating and roller pressing assistance, but both have directional problems. The laser preheating position and the roller position must remain unchanged with the nozzle. When the angle between the preheating direction of the laser preheater and the movement direction of the nozzle changes, it cannot have a good preheating effect or extrusion effect on the printed area; roller pressing assistance has a great impact on the dimensional accuracy of the parts. In addition, current physical assistance methods often require the integration of multiple components and require additional control systems, resulting in increased costs. Therefore, it is a technical problem that needs to be solved urgently to improve the interlayer strength in a simple, efficient and low-cost manner while ensuring printing accuracy. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned background technology, the present invention proposes a coaxial dual-state in-situ material extrusion 3D printing interlayer reinforcement method, which does not require modification of the printing material, does not have directional problems, does not require the integration of multiple components, and does not require the introduction of additional control systems. It can simply and efficiently achieve a significant improvement in the interlayer bonding strength while ensuring printing accuracy.

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

[0006] The present invention proposes a method for coaxial dual-state in-situ material extrusion 3D printing interlayer reinforcement method, which is special in that it includes 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 filling (FILL).

[0009] (3) The coaxial dual-state process control method is obtained by adjusting the printing parameters: by changing the wire feeding speed and the heating temperature, the outside of the wire is in a molten state and the inside is in an incompletely molten state during extrusion. The molten state on the outside ensures that the wire between 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, making the bonding interface more closely contacted and improving the interlayer bonding strength.

[0010] (4) Automatically adjust the printing strategy and process parameters according to the printing area and printing material: When the program recognizes that the printing area is the outer wall, keep the normal printing process parameters unchanged; when the program recognizes that the printing area is internal 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 strength of the internal filling layers.

[0012] Furthermore, in the step (1), the data processing specifically includes: importing the established three-dimensional model into the slicing software to obtain printing data.

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

[0014] Furthermore, in the step (3), the method of making the outer part of the wire material molten and the inner part in an incompletely molten state is specifically as follows:

[0015] (3.1) During the printing process, the wire feeding speed is gradually increased so that the outer surface of the wire is melted during extrusion, and 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 the above steps (3.1) and (3.2) until the external molten state temperature of the wire is high enough during extrusion so that the molecular chains between layers can fully diffuse across the interface and the internal incomplete molten state stiffness is large enough to efficiently transmit force; the interlayer bonding is the combined result of temperature and force, the interface temperature affects the cross-interface diffusion ability of the molecular chains between layers, and the pressure affects the tightness of the bonding interface contact.

[0018] Furthermore, the method further includes step (3.4): printing parts at a suitable speed according to the printing line width requirement and the wire feeding speed and nozzle temperature determined in the above step (3.3). The formula for determining the printing speed is:

[0019]

[0020] Where: W is the line width, in mm; D is the wire diameter, in mm; H is the print layer height, in mm; V f is the wire feeding speed, in mm·s -1 ; V p Printing speed, in mm·s -1 ; The wire diameter D is usually 1.75mm, so when determining the print layer height H, print line width W and wire feeding speed V f Then, the corresponding printing speed can be determined by this formula.

[0021] Advantages of the present invention:

[0022] The present invention proposes a design method for additive manufacturing of low-stress high-entropy alloys based on lattice mismatch. The method identifies the printing area and automatically adjusts the printing strategy and process parameters. When printing the outer wall area, the printing accuracy is maintained and the printing is normal. During the printing of the internal filling area, the wire material is melted on the outside and not completely melted on the inside by adjusting the wire feeding speed and the nozzle temperature. Therefore, there is a glassy state / high elastic state with a certain rigidity inside the wire material during the entire extrusion process. Compared with the traditional full-melt extrusion method, the method increases the extrusion pressure of the wire material, so that the newly extruded material is pressed more tightly together when it is fused with the material of the previous layer, thereby improving the interlayer bonding strength. Traditional extrusion molding is all fully molten extrusion, the melt has poor rigidity, and it is easy to change its shape when it is subjected to force, which means that the material's response time to force is prolonged, and the melt cannot transmit force in a timely and accurate manner. Therefore, the extrusion pressure when the material is extruded from the nozzle has been greatly weakened relative to the driving force provided by the wire feeding drive wheel. Molecules or atoms that are not completely molten (glassy state / high elastic state) usually exist in a fixed and orderly arrangement. This orderliness gives them a high degree of structural stability and high rigidity. When transmitting force, they can directly transmit force from one end to the other end, and can directly and effectively transmit force, that is, they can increase the extrusion pressure when the material is extruded from the nozzle, so that the newly extruded material is pressed more tightly together with the material of the previous layer when it is fused, thereby improving the interlayer bonding strength. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0024] Figure 2 An adaptive printing flow chart for the interlayer reinforcement method of 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 3D printing filament. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work 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 drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work 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 by the present 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) Read data and divide the printing area: Read the sliced ​​Gcode format data, identify the printing area mark code (TYPE: WALL-OUTER / INNER, TYPE: FILL) in the data, and divide the printing area into the outer wall and the internal filling area. The process is as follows: Figure 2 shown.

[0030] (3) The coaxial dual-state process control method is obtained by adjusting the printing parameters. Taking the polymer polyetheretherketone as an example, the degree of melting of the wire is characterized by its crystallinity and color. By changing the wire feeding speed and heating temperature, the wire is extruded so that the outside is molten and the inside is in an incompletely molten state. The molten state on the outside ensures that the wire layers can be bonded together, 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, making the bonding interface more closely contacted and improving the interlayer bonding strength.

[0031] (4) Automatically adjust the printing strategy and process parameters according to the printing area. When the program recognizes that the printing area is the outer wall, the normal printing process parameters are kept unchanged to ensure the printing accuracy; when the program recognizes that the printing area is internal filling, the coaxial dual-state process control method is used to appropriately increase the wire feeding speed and nozzle temperature.

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

[0033] (3.1) During the printing process, the wire feeding speed is gradually increased so that the outer surface of the wire melts during extrusion and the inside of the wire is not completely molten. The wire melts from the outside to the inside of the nozzle. Therefore, the time the wire stays in the heating flow channel can be shortened by increasing the wire feeding speed, so that the outside of the wire melts but the inside is not completely melted.

[0034] (3.2) If the surface temperature of the extruded wire is insufficient, increase the heating temperature of the print head and return to step (3.1); because increasing the wire feeding speed will cause the surface temperature of the wire to drop during extrusion. When the surface temperature of the extruded wire drops to a point where the interface temperature cannot rise above the glass transition temperature, the molecular chains between the layers cannot diffuse across the interface, that is, the wires between the layers cannot bond, so the heating temperature needs to be increased.

[0035] (3.3) Repeat the above steps (3.1) and (3.2) until the external molten temperature of the wire is high enough during extrusion so that the molecular chains between layers can fully diffuse across the interface and the internal non-completely molten stiffness is large enough to efficiently transmit force; the interlayer bonding is the combined result of temperature and force, the interface temperature affects the cross-interface diffusion ability of the molecular chains between layers, and the pressure affects the tightness of the bonding interface contact.

[0036] (3.4) Print parts at an appropriate speed based on the printing line width requirements and the wire feeding speed and nozzle temperature determined in the above step (3.3). The formula for determining the printing speed is:

[0037]

[0038] Where: W is the line width, in mm; D is the wire diameter, in mm; H is the print layer height, in mm; V f is the wire feeding speed, in mm·s -1 ; V p Printing speed, in mm·s -1 The wire diameter D is usually 1.75 mm, so when determining the print layer height H, print line width W and wire feeding speed V f Then, the corresponding printing speed can be determined by this formula.

[0039] In the present invention, coaxial dual-state refers to changing the melting state of the wire inside the heating flow channel through process control, so that the inside of the wire is in an incompletely molten state (glassy state / high elastic state) while the outside is molten during extrusion, and the internal stiffness is used to timely and effectively transmit the force to increase the wire extrusion pressure and achieve 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 outer wall area needs to ensure printing accuracy, and the internal filling area needs to increase the interlayer strength; the process method of the present invention is simple and efficient and can greatly improve the interlayer bonding strength of the printed part.

[0040] This paper proposes a coaxial dual-state in-situ material extrusion 3D printing interlayer reinforcement method. This method greatly increases the wire feeding speed during the printing process so that the wire is molten on the outside and incompletely molten on the inside during extrusion. The molten state on the outside ensures that the wire between layers can be bonded (molecular chains diffuse across the interface), while the incompletely molten state on the inside can increase the extrusion pressure of the wire, thereby improving the interlayer bonding strength. The coaxial dual-state interlayer reinforcement process method specifically includes the following steps:

[0041] (1) During the printing process, the wire feeding speed is adjusted so that the wire is solid inside when it is extruded. The wire melts from the outside to the inside of the nozzle. Therefore, the wire feeding speed can be controlled so that the outside of the wire melts but the inside is not completely melted. The coaxial dual-state principle and process flow are as follows: Figure 2 shown.

[0042] (2) If the surface temperature of the extruded wire is insufficient, the heating temperature of the print head is increased so that the surface temperature of the extruded wire reaches at least above the glass transition temperature of the wire material, and the process returns to step (1). In order to make the inside of the extruded wire in a non-completely molten state, a higher wire feeding speed is required. However, increasing the wire feeding speed will cause the surface temperature of the wire to drop during extrusion. When the surface temperature of the extruded wire drops to a point where the interface temperature cannot rise above the glass transition temperature, the molecular chains between the layers cannot diffuse across the interface, that is, the interlayer wires cannot bond, and thus the heating temperature needs to be increased.

[0043] (3) Repeat the above steps until the external molten state temperature of the wire material during extrusion is ≥ the glass transition temperature of the wire material, so that the molecular chains between the layers can fully diffuse across the interface and the internal solid stiffness is large enough to efficiently transmit force. The interlayer bonding is the combined result of temperature and force. The interface temperature affects the cross-interface diffusion ability of the molecular chains between the layers, and the pressure affects the tightness of the bonding interface contact.

[0044] (4) A coaxial dual-state process parameter library for each material is established based on the requirements of the coaxial dual-state process for temperature and wire feeding speed. 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 present invention will be further understood from the following illustrative examples.

[0046] Example 1

[0047] In this example, polyetheretherketone (PEEK) is used as the 3D printing material, and the interlayer strength of the PEEK 3D printing is enhanced through a coaxial dual-state in-situ material extrusion process.

[0048] A 1.2mm chrome-zirconium-copper nozzle was used to print a standard tensile test piece along the Z direction based on the test standard "GB / T 1040.1-2018 Determination of tensile properties of plastics". The nozzle temperature was set to 500°C, the layer thickness was set to 0.3mm, the line width was set to 2mm, and the wire cross section was set to 1.5mm. Figure 3 It can be seen that the coaxial dual-state structure appears when the wire feeding speed reaches 12mm / s. With the further increase of the wire feeding speed, the non-completely melted area not only gradually increases in area, but also shows a trend of gradually moving upward in the vertical direction. The mechanical properties test results show that the interlayer tensile strength of the coaxial dual-state in-situ material extrusion tensile specimen increases with the increase of the wire feeding speed. When the wire feeding speed is increased to a certain threshold, the interlayer tensile strength of the specimen remains unchanged. Further increase of the wire feeding speed will cause the phenomenon of poor wire spouting. The experimental results show that coaxial dual-state in-situ material extrusion can effectively increase the interlayer bonding strength of 3D printing.

[0049] In summary, the present invention proposes a process method for improving the interlayer bonding strength of 3D printing by utilizing the incompletely molten state (glassy state / highly elastic state) of the wire itself to efficiently transmit force. This process method is different from the traditional method of fully melting the wire and then extruding it. Instead, the outside is in a molten state and the inside is in a incompletely molten state during extrusion. The molten state on the outside ensures that the wire between layers can be bonded, while the incompletely molten state on the inside can increase the extrusion pressure of the wire, making the bonding interface more closely contacted, thereby improving the interlayer bonding strength.

[0050] The above descriptions are merely embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related system fields, are also included in the protection scope of the present invention.

Claims

1. A coaxial dual-state in-situ material extrusion 3D printing interlayer reinforcement method, characterized in that: The following steps are involved: (1) Data processing; (2) Reading data to divide the printing area, and dividing the printing area into two categories: outer wall and internal filling; (3) The coaxial dual-state process control method is obtained by adjusting the printing parameters: by changing the wire feeding speed and the heating temperature, the outer part of the wire is in a molten state and the inner part is in an incompletely molten state during extrusion. The molten state of the outer part ensures that the wires between the layers can be bonded, while the incompletely molten state of the inner part can increase the extrusion pressure when the material is extruded from the nozzle due to its structural stability and high rigidity, making the bonding interface more closely contacted and improving the interlayer bonding strength; (4) Automatically adjust the printing strategy and process parameters according to the printing area: When the program recognizes that the printing area is the outer wall, the original printing process parameters remain unchanged; When the program recognizes that the printing area is internal filling, the coaxial dual-state process control method is applied for printing.

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

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

4. The method for improving interlayer strength of 3D printing by coaxial dual-state in-situ material extrusion according to claim 3, characterized in that: In the step (3), the coaxial dual-state process control method is obtained by adjusting the printing parameters: (3.1) During the printing process, the wire feeding speed is gradually increased so that the outer surface of the wire melts when it is extruded, but the inside is not completely melted. The wire melts from the outside to the inside of the nozzle, so the time the wire stays in the heating flow channel can be shortened by increasing the wire feeding speed, so that the outside of the wire melts but the inside is not completely melted. (3.2) If the surface temperature of the extruded wire is insufficient, increase the heating temperature of the print head and return to step (3.1); because increasing the wire feeding speed will cause the surface temperature of the wire to drop during extrusion. When the surface temperature of the extruded wire drops to a point where the interface temperature cannot rise above the glass transition temperature, the molecular chains between the layers cannot diffuse across the interface, that is, the interlayer wires cannot bond, so the heating temperature needs to be increased; (3.3) Repeat the above steps (3.1) and (3.2) until the temperature of the external molten state is high enough during wire extrusion so that the molecular chains between the layers can fully diffuse across the interface and the rigidity of the internal incomplete molten state is large enough to efficiently transmit force; Interlayer bonding is the combined result of temperature and force. The interface temperature affects the cross-interface diffusion ability of the interlayer molecular chains, and the pressure affects the tightness of the bonding interface contact.

5. The method for improving interlayer strength of 3D printing by coaxial dual-state in-situ material extrusion according to claim 4, characterized in that: The method further includes step (3.4): printing the part at a suitable speed according to the printing line width requirement and the wire feeding speed and nozzle temperature determined in the above step (3.3). The formula for determining the printing speed is: Where: W is the line width, in mm; D is the wire diameter, in mm; H is the print layer height, in mm; V f is the wire feeding speed, in mm·s -1 ; V p Printing speed, in mm·s -1 ; The wire diameter D is usually 1.75 mm, so when determining the print layer height H, print line width W and wire feeding speed V f Then, the corresponding printing speed can be determined by this formula.

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