Fiber-reinforced composite 3D printer and printing method

Abstract

This invention relates to the field of 3D printing technology, and discloses a fiber-reinforced composite material 3D printer and printing method. The method utilizes an interlayer pressing device to heat / cool the currently deposited filament bundle under a preset interlayer pressing force, promoting interlayer fusion and improving interlayer bonding strength. It also eliminates the thermal history during filament cooling, controls the crystallization behavior, grain size, and distribution of the polymer in the printed filament, and improves the microscopic uniformity of the printed composite material. The inter-pass pressing device hot-presses and shapes the sides and top surfaces of the currently deposited filament bundle, while simultaneously performing secondary hot-pressing on the adjacent printed layer's deposited filament bundles. This allows the resin in the currently deposited filament bundle and the adjacent printed layer's deposited filament bundles to melt and flow, filling the inter-pass gaps between adjacent printed layers and improving inter-pass bonding strength.

Description

Technical Field

[0001] This invention relates to the field of 3D printing technology, and discloses a fiber-reinforced composite material 3D printer and printing method. Background Technology

[0002] Fiber-reinforced composite 3D printing technology is a process that manufactures composite parts by layering fibers and resin filaments. Compared to traditional composite material processes such as compression molding and pultrusion, fiber-reinforced composite 3D printing technology has advantages such as strong designability, no mold dependence, and suitability for manufacturing complex structures. In particular, fiber-reinforced thermoplastic resin composites have advantages over traditional thermosetting materials, including high heat resistance, good toughness, high flexural strength, good interlaminar shear properties, low water absorption, and reusability. Therefore, it has significant application value in advanced manufacturing fields such as aerospace, shipbuilding, and automotive.

[0003] However, due to material properties and printing processes, the performance of fiber-reinforced thermoplastic composites produced by 3D printing is generally weak. Many researchers both domestically and internationally have made considerable efforts to improve the performance of 3D printed fiber composites, mostly by improving fused deposition modeling (FDM) 3D printing nozzles. However, these efforts have not comprehensively considered the multiple factors affecting performance, resulting in no substantial improvement in the strength of the printed parts. In particular, problems such as insufficient interlayer performance and poor interlayer bonding significantly limit its application and development in the field of 3D printing. Summary of the Invention

[0004] The purpose of this invention is to provide a fiber-reinforced composite material 3D printer and printing method, which can improve the interlayer bonding strength and inter-layer bonding strength of the printed product.

[0005] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows:

[0006] A fiber-reinforced composite material 3D printer, comprising:

[0007] A printhead, comprising a heat insulation shell and a throat tube, wherein the throat tube is disposed within the heat insulation shell and is used to provide an extrusion channel for the printing filament, and the heat insulation shell is provided with a rotating component;

[0008] An interlayer pressing device includes a fixed base, an interlayer pressing drive assembly, an interlayer pressing force sensor, and an interlayer pressing nozzle assembly. The fixed base is installed inside a heat-insulating housing. The interlayer pressing drive assembly is fixed to the fixed base, and its actuator is connected to the interlayer pressing force sensor. The interlayer pressing force sensor is connected to the interlayer pressing nozzle assembly. The interlayer pressing nozzle assembly is used to heat, melt, and cool the current deposited filament bundle and the adjacent printed layer deposited filament bundle, and, driven by the interlayer pressing drive assembly, performs hot pressing on the current deposited filament bundle with a preset interlayer pressing force.

[0009] An inter-pass pressing device includes a connecting rod, a lateral pressing rod, and an inter-pass hot pressing part. One end of the connecting rod is fixed to the rotating component, and the other end is connected to the lateral pressing rod. The inter-pass hot pressing part is mounted on the lateral pressing rod. The end of the lateral pressing rod is used to move with the print head during the printing process and to hot press and shape the side of the current deposited filament bundle at a first preset pressing temperature and a preset pressing interval. The inter-pass hot pressing part is used to move synchronously with the lateral pressing rod and to hot press and shape the upper surfaces of the current deposited filament bundle and the previous deposited filament bundle at a second preset pressing temperature and a preset pressing height.

[0010] Furthermore, the interlayer ironing device also includes an equalizing plate; the equalizing plate includes an upper equalizing plate and a lower equalizing plate respectively connected to the upper and lower ends of the interlayer ironing force sensor, the upper equalizing plate is connected to the actuator of the interlayer ironing drive assembly, the lower equalizing plate is connected to the interlayer ironing nozzle assembly, and a heat insulation plate is provided between the lower equalizing plate and the interlayer ironing nozzle assembly.

[0011] Furthermore, the interlayer pressing nozzle assembly includes:

[0012] A heating block, which is connected to the lower equalizing plate and located at the outlet end of the throat tube, is used to heat the printing filament in the throat tube;

[0013] A concentric circle stepped temperature control module is fixedly connected to the lower end of the heating block, and the throat is located at the center of the concentric circle stepped temperature control module. The concentric circle stepped temperature control module is used to apply a preset interlayer pressing force to the adjacent printed layer deposition filaments and the current deposition filament, and at the same time form a stepped temperature field to heat and cool the current deposition filament and the adjacent printed layer deposition filament.

[0014] Furthermore, a heat insulation plate is provided between the lower pressure equalizing plate and the heating block.

[0015] Furthermore, the concentric circle stepped temperature control module includes:

[0016] An iron-type high-temperature metal ring is provided, which surrounds the outside of the throat tube with the axis of the throat tube as the center. The iron-type high-temperature metal ring is used to heat the current deposition filament bundle and the adjacent printing layer deposition filament bundle at a first preset temperature.

[0017] The stepped temperature-controlled metal ring comprises several concentric metal rings with different diameters. All stepped temperature-controlled metal rings are arranged concentrically nested outside the iron-type high-temperature metal ring. The stepped temperature-controlled metal ring is used to form a preset temperature field with the temperature decreasing ring by ring from the inside to the outside, to control the temperature and cool the current deposition filament and the adjacent printed layer deposition filament, and to perform hot pressing on the current deposition filament.

[0018] A cooling metal ring is provided outside the outermost stepped temperature-controlled metal ring and is distributed in concentric circles. The cooling metal ring is used to cool the current deposition filament and the adjacent printed layer deposition filament at a second preset temperature.

[0019] A heat insulation ring is provided between the throat tube, the iron-type high-temperature metal ring, the stepped temperature-controlled metal ring, and the cooling metal ring, as well as between two adjacent stepped temperature-controlled metal rings.

[0020] Furthermore, the concentric stepped temperature control module also includes an additive dispensing channel, which is located between two adjacent heat insulation rings and is used to dispense additives to the current deposited filament bundle during the printing process.

[0021] A method for 3D printing fiber-reinforced composite materials, using the aforementioned fiber-reinforced composite material 3D printer, includes the following steps:

[0022] The printing parameters of the interlayer pressing device and the inter-pass pressing device are determined. The printing parameters include the optimal preset interlayer pressing force of the concentric circle stepped temperature control module, the temperature of the iron-type high-temperature metal ring, the stepped temperature control metal ring, and the cooling metal ring in the concentric circle stepped temperature control module, and the inter-pass pressing temperature and pressing distance of the inter-pass pressing device.

[0023] Based on the preset printing path and preset layer thickness of the target printed part, the fiber-reinforced composite material 3D printer starts printing to obtain the target printed part.

[0024] Furthermore, the method for determining the optimal preset interlayer pressing force of the concentric circle stepped temperature control module includes:

[0025] Based on the material coefficient of the printing filament, the interlayer shear strength of the finished product obtained by the printing filament under the comparative molding process, the comparative molding process coefficient, the preset printing line width, and the radial contact length between the concentric circle stepped temperature control module and the printing filament, the theoretical maximum preset interlayer pressing force of the concentric circle stepped temperature control module is calculated.

[0026] Within the range of zero to the theoretical maximum preset interlayer pressing force, several preset interlayer pressing force test values ​​are selected according to preset step sizes. The fiber-reinforced composite material 3D printer is used to prepare interlayer shear samples corresponding to each preset interlayer pressing force test value and test the interlayer shear strength. The preset interlayer pressing force corresponding to the highest interlayer shear strength is selected as the optimal preset interlayer pressing force.

[0027] Furthermore, the theoretical maximum preset interlayer pressing force of the concentric circle stepped temperature control module is calculated using the following formula:

[0028] ;

[0029] in, This is the theoretical maximum preset interlayer pressing force; The material coefficient of the printing filament; Interlaminar shear strength of the finished product obtained by printing filament under comparative molding process; To compare molding process coefficients; Preset print line width; The contact length between the concentric circle stepped temperature control module and the printing wire along the radial direction is denoted as .

[0030] Compared with the prior art, the beneficial effects of this invention are:

[0031] This invention utilizes an interlayer pressing device to heat / cool the currently deposited filament bundle under a preset interlayer pressing force. This promotes interlayer fusion and improves interlayer bonding strength, eliminates thermal history during filament cooling, controls the crystallization behavior, grain size, and distribution of the polymer in the printed filament, and improves the microscopic uniformity of the printed composite material. The invention also uses an inter-pass pressing device to hot-press and shape the sides and top surface of the currently deposited filament bundle, while simultaneously performing secondary hot-pressing on the adjacent printed layer's deposited filament bundles. This allows the resin in both the currently and adjacent printed layer bundles to melt and flow, filling the inter-pass gaps between adjacent printed layers and improving inter-pass bonding strength. Through the synergistic effect of the interlayer and inter-pass pressing devices, this invention enhances both the interlayer and inter-pass bonding strength of the printed product, improving its overall performance. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the fiber-reinforced composite material 3D printer structure in the embodiment;

[0033] Figure 2 This is a schematic diagram of the interlayer pressing device of the printer in the embodiment;

[0034] Figure 3 This is a schematic diagram of the concentric circle stepped temperature control module in the embodiment;

[0035] Figure 4 This is a bottom view of the concentric circle stepped temperature control module in the embodiment;

[0036] Figure 5 This is a schematic diagram of the three areas of the concentric circle stepped temperature control module in the embodiment;

[0037] Figure 6 This is a schematic diagram illustrating how the concentric circle stepped temperature control module performs secondary heating on the adjacent printed layer deposition filaments of the current deposition filament in the embodiment.

[0038] Figure 7 This is a schematic diagram of the concentric circle stepped temperature control module with additive dispensing channels in the embodiment.

[0039] Figure 8 This is a schematic diagram of the interpass pressing and ironing device in the embodiment;

[0040] Figure 9 This is a schematic diagram of the inter-pass pressing device performing hot pressing and shaping on the current deposited filament bundle in the embodiment;

[0041] Figure 10 This is a flowchart of a 3D printing method for fiber-reinforced composite materials in the embodiment, in which interlayer and interpass pressing can be applied;

[0042] Among them, 11-heat insulation shell, 12-throat, 21-fixed seat, 22-interlayer pressing drive assembly, 23-interlayer pressing force sensor, 241-heating block, 242-concentric circle stepped temperature control module, 243-iron-type high-temperature metal ring, 244-step temperature control metal ring, 245-cooling metal ring, 246-heat insulation ring, 247-additive dispensing channel, 248-heating device, 249-temperature measuring device, 251-upper pressure equalizing plate, 252-lower pressure equalizing plate, 26-heat insulation plate, 31-connecting rod, 32-lateral pressing rod, 33-interlayer hot pressing part, 34-rotating component, 4-filament feeding mechanism, 5-substrate. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings. However, this should not be construed as limiting the scope of the above-described subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0044] See Figures 1 to 9This invention provides a fiber-reinforced composite material 3D printer, comprising:

[0045] The printhead includes a heat insulation shell 11 and a throat 12. The throat 12 is disposed inside the heat insulation shell 11 and is used to provide an extrusion channel for the printing filament. The heat insulation shell 11 is provided with a rotating component 34.

[0046] An interlayer pressing device includes a fixed base 21, an interlayer pressing drive assembly 22, an interlayer pressing force sensor 23, and an interlayer pressing nozzle assembly. The fixed base 21 is installed inside a heat-insulating housing 11. The interlayer pressing drive assembly 22 is fixed to the fixed base 21, and the actuator of the interlayer pressing drive assembly 22 is connected to the interlayer pressing force sensor 23. The interlayer pressing force sensor 23 is connected to the interlayer pressing nozzle assembly. The interlayer pressing nozzle assembly is used to heat, melt, and cool the current deposited filament and the adjacent printed layer deposited filament, and, driven by the interlayer pressing drive assembly 22, performs hot pressing on the current deposited filament with a preset interlayer pressing force.

[0047] An inter-pass pressing device includes a connecting rod 31, a lateral pressing rod 32, and an inter-pass hot pressing part 33. One end of the connecting rod 31 is fixed to the rotating component 34, and the other end is connected to the lateral pressing rod 32. The inter-pass hot pressing part 33 is mounted on the lateral pressing rod 32. The end of the lateral pressing rod 32 is used to move with the print head during the printing process and to hot press and shape the side of the current deposited filament bundle at a first preset pressing temperature and a preset pressing interval. The inter-pass hot pressing part 33 is used to move synchronously with the lateral pressing rod 32 and to hot press and shape the upper surfaces of the current deposited filament bundle and the previous deposited filament bundle at a second preset pressing temperature and a preset pressing height.

[0048] This invention utilizes an interlayer pressing device to heat / cool the currently deposited filament bundle under a preset interlayer pressing force. This promotes interlayer fusion and improves interlayer bonding strength, eliminates thermal history during filament cooling, controls the crystallization behavior, grain size, and distribution of the polymer in the printed filament, and improves the microscopic uniformity of the printed composite material. The invention also uses an inter-pass pressing device to hot-press and shape the sides and top surface of the currently deposited filament bundle, while simultaneously applying a secondary hot-press to the previous deposited filament bundle. This promotes the flow and fusion of the current and previous deposited filament bundles, filling the inter-pass gaps and improving inter-pass bonding strength. Through the synergistic effect of the interlayer and inter-pass pressing devices, this invention enhances both the interlayer and inter-pass bonding strength of the printed product, thereby improving its overall performance.

[0049] In some embodiments, see Figure 1 and Figure 2 The printhead also includes a filament feeding mechanism 4, which is installed inside the heat insulation housing 11. The filament feeding mechanism 4 can consist of two filament feeding gears. By rotating the filament feeding gears, the two filament feeding gears drive the printing filament to move downward along the throat tube 12, thereby achieving filament feeding. Moreover, the filament feeding mechanism 4 and its supporting motor and other components are all at a certain distance from the heating elements in the printhead, and heat insulation protection is added as needed.

[0050] In some embodiments, see Figure 1 and Figure 2 The interlayer pressing drive assembly 22 of the interlayer pressing device can adopt a motor screw structure or a hydraulic cylinder driven structure capable of linear reciprocating motion. One end of the interlayer pressing drive assembly 22 is fixed on the fixed base 21. The actuator of the interlayer pressing drive assembly 22 is connected to the upper pressure equalizing plate 251, the lower pressure equalizing plate 252 is connected to the upper side of the interlayer pressing force sensor 23, and the lower side of the interlayer pressing force sensor 23 is connected to the lower pressure equalizing plate 252. The lower pressure equalizing plate 252 is then connected to the interlayer pressing nozzle assembly through the heat insulation plate 26. During the printing process, the interlayer pressing nozzle assembly is used to heat the printing filament to be extruded and the currently deposited filament in the throat 12, and to perform secondary heating on the surface of the uppermost adjacent printed layer deposited filament at the throat 12 outlet. At the same time, it heats the extruded printing filament, i.e., the currently deposited filament, at the throat 12 outlet and performs hot pressing in the interlayer direction to promote interlayer fusion and improve interlayer bonding strength.

[0051] It should be noted that, see Figure 1 and Figure 2 The heat insulation plate 26 is made of heat insulation material with certain rigidity and strength. During the printing process, if the actual preset interlayer pressing force of the interlayer pressing device on the current deposited filament bundle is less than the safety threshold, the heat insulation plate 26 remains stable, playing a role in heat insulation and force transmission. When the actual preset interlayer pressing force of the interlayer pressing device on the current deposited filament bundle exceeds the safety threshold, the heat insulation plate 26 is crushed and broken, unloading the preset interlayer pressing force. This prevents excessive pressing force from damaging other structures of the print head under abnormal conditions such as failure of the pressing force adjustment module, thus acting as a fuse. The safety threshold is set as a multiple of the preset interlayer pressing force, for example, the safety threshold is set to 1.2 times the preset interlayer pressing force. This multiple can be set as needed.

[0052] In some embodiments, see Figure 3 and Figure 4The interlayer pressing nozzle assembly includes a heating block 241 and a concentric stepped temperature control module 242. The heating block 241 is fixedly connected to the heat insulation plate 26 and is located at the outlet end of the throat tube 12, used to heat the printing filament to be extruded in the throat tube 12 to a molten state. The concentric stepped temperature control module 242 is fixed to the lower end of the heating block 241, and the throat tube 12 is located at the center of the concentric stepped temperature control module 242.

[0053] During the printing process, the interlayer pressing device of the present invention applies a preset interlayer pressing force to the current deposited filament bundle and performs hot pressing. The reaction force of the preset interlayer pressing force is transmitted sequentially through the concentric stepped temperature control module 242, the heating block 241, and the heat insulation plate 26 to the interlayer pressing force sensor 23, thereby enabling real-time monitoring of the preset interlayer pressing force. During the printing process, the printhead control device controls the interlayer pressing drive assembly 22 to adjust the height of the interlayer pressing nozzle assembly in real time according to the real-time changes in the preset interlayer pressing force measurement value. When the preset interlayer pressing force detection value is greater than the set value, the interlayer pressing drive assembly 22 drives the interlayer pressing nozzle assembly to move slightly upward, reducing the preset interlayer pressing force to the set value. When the preset interlayer pressing force detection value is less than the set value, the interlayer pressing drive assembly 22 drives the interlayer pressing nozzle assembly to move slightly downward, increasing the preset interlayer pressing force to the set value. It should be noted that the throat tube 12 is fixed in the print head, and the outer wall of the throat tube 12 is provided with a heat insulation layer. The part of the lower end of the throat tube 12 corresponding to the heating block 241 is not provided with a heat insulation layer. There are gaps between the upper pressure equalizing plate 251, the lower pressure equalizing plate 252, the heat insulation plate 26, the heating block 241, and the concentric circle stepped temperature control module 242 and the throat tube 12. At the same time, there are also gaps between the upper pressure equalizing plate 251, the lower pressure equalizing plate 252, the heat insulation plate 26 and the heat insulation shell 11. This ensures that under the drive of the interlayer pressing drive component 22, the upper pressure equalizing plate 251, the lower pressure equalizing plate 252, the heat insulation plate 26, the heating block 241 and the concentric circle stepped temperature control module 242 can move up and down, so as to realize the adjustment of the hot pressing force applied to the current deposited filament bundle and the preset interlayer pressing force.

[0054] The concentric ring stepped temperature control module 242 includes multiple layers of concentric rings. Centered on the axis of the throat tube 12, from the inside out, it includes an iron-type high-temperature metal ring 243, a stepped temperature control metal ring 244, and a cooling metal ring 245. A heat insulation ring 246 is provided between adjacent metal rings to prevent mutual interference between different heating zones. Furthermore, the widths of the iron-type high-temperature metal ring 243, the stepped temperature control metal ring 244, and the cooling metal ring 245 can be set according to the material properties of the printing filament and experience. Figure 4 As shown.

[0055] The iron-type high-temperature metal ring 243 surrounds the outside of the throat tube 12 and has an independent heating device 248 and a temperature measuring device 249. During the printing process, the first preset temperature of the iron-type high-temperature metal ring 243 is set to the melting point of the printing filament, which is used to heat the current deposited filament bundle extruded from the throat tube 12, maintain its molten state, and reheat the adjacent printing layer deposited filament bundles adjacent to the current deposited filament bundle to the molten state. During the printing process, the iron-type high-temperature metal ring 243 applies a preset interlayer pressing force to the current deposited filament bundle, causing the molten current deposited filament bundle and the adjacent printing layer deposited filament bundles to begin to fuse.

[0056] Several stepped temperature-controlled metal rings 244 are provided, all with different diameters and arranged concentrically. All stepped temperature-controlled metal rings 244 are located outside the iron-type high-temperature metal ring 243. Each stepped temperature-controlled metal ring 244 is equipped with an independent heating device 248 and a temperature measuring device 249. The stepped temperature-controlled metal ring 244 with the smallest diameter and adjacent to the iron-type high-temperature metal ring 243 is the inner ring, and the stepped temperature-controlled metal ring 244 with the largest diameter and adjacent to the cooling metal ring 245 is the outer ring. The temperature of all stepped temperature-controlled metal rings 244 gradually decreases from the inside to the outside, forming a preset temperature field with a temperature gradient. This ensures that the current deposition filament and the adjacent adjacent deposition filaments in the molten state during the printing process can be gradually cooled according to the preset temperature field, thereby regulating the grain size and uniformity of the crystalline resin inside the adjacent deposition filaments and the current deposition filament, controlling the forming quality and internal stress distribution of the printed layer, and further fusing the current deposition filament and the adjacent adjacent deposition filaments. The highest temperature of the preset temperature field is lower than the melting point of the printing filament, and the lowest temperature of the preset temperature field is higher than the glass transition temperature of the printing filament. The temperature difference between two adjacent stepped temperature-controlled metal rings 244 is set according to the material properties of the printing filament.

[0057] The cooling metal ring 245 is located outside the outermost ring of the stepped temperature-controlled metal ring 244. It performs stepped temperature-controlled cooling of the current deposited filament bundle and the adjacent printed layer deposited filament bundle at a second preset temperature. The cooling metal ring 245 is equipped with a cooling device and a temperature measuring device 249. The cooling device and the temperature measuring device 249 ensure that the temperature of the cooling metal ring 245 is set 80°C lower than the glass transition temperature of the printed filament. This allows the fused current deposited filament bundle and the adjacent printed layer deposited filament bundle to quickly pass through the glass transition temperature region during the cooling process, avoiding problems such as stress concentration, deformation, or cracking inside the printed layer filament bundle due to improper cooling speed.

[0058] It should be noted that, since the size of the concentric circle stepped temperature control module 242 is larger than the linewidth of the current deposited filament bundle, and the concentric circle stepped temperature control module 242 only acts on the current deposited filament bundle locally, i.e., the rear side of the concentric circle stepped temperature control module 242, during the printing process, the front side of the concentric circle stepped temperature control module 242 can preheat the upper surface of the adjacent printed layer deposited filament bundle before the filament bundle is deposited. As the print head moves forward, after the current deposited filament bundle is deposited on the adjacent printed layer deposited filament bundle, under the hot pressing action of the concentric circle stepped temperature control module 242, the current deposited filament bundle and the adjacent printed layer deposited filament bundle are fused together, thereby improving the interlayer bonding strength.

[0059] It should be noted that the heating device 248 can be a resistance heating device, induction heating device, etc.; the cooling device can be a water cooling device, radiant cooling device, etc. The temperature measuring device 249 can be a thermocouple or other non-contact temperature measuring device, such as infrared thermometry. Figure 3 In the structure shown, the heating device 248 uses resistance heating, and the temperature measuring device 249 uses a thermocouple.

[0060] It should be noted that the lower surface of the concentric circle stepped temperature control module 242 that contacts the current deposition filament bundle needs to be polished using a mirror polishing process, with a surface roughness not exceeding 0.2 μm, to reduce the friction between the current deposition filament bundle and the concentric circle stepped temperature control module 242.

[0061] In some embodiments, see Figure 7 The concentric circle stepped temperature control module 242 is also provided with an additive dispensing channel 247, see [link / reference]. Figure 6 The additive dispensing channel 247 can be made of heat-insulating material into a hollow dispensing ring. The upper end of the dispensing ring is connected to an external additive adding device through a pipe, and the lower end of the dispensing ring is an open end. Depending on the printing requirements, during the printing process, additives can be dispensed onto the surface of the current deposited filament and adjacent printed layer deposited filaments through the dispensing ring. The additives include functional powders, auxiliary slurries, etc. The additive dispensing channel 247 can be positioned at any location between the iron-type high-temperature metal ring 243, the stepped temperature-controlled metal ring 244, and the cooling metal ring 245, depending on the printing requirements. For example, the additive dispensing channel 247 can be positioned between the iron-type high-temperature metal ring 243 and the first stepped temperature-controlled metal ring 244. The number of additive dispensing channels 247 can also be set according to the printing requirements.

[0062] In some embodiments, see Figure 1 , Figure 8 and Figure 9The rotating component 34 can be a rotating disk mounted on the heat insulation housing 11. Driven by a motor and gears, as the print head travels along a preset path, the rotating component 34 rotates around the axis of the print head, causing the lateral pressing rod 32 and the inter-pass hot pressing part to rotate circumferentially around the print head. This adjusts the distance between the axis of the lateral pressing rod 32 and the axis of the current deposited filament bundle, i.e., the pressing gap, ensuring that the pressing gap remains constant. (See [reference]). Figure 1 and Figure 8 The current deposition filament axis refers to the position where half the width of the current deposition filament is located.

[0063] In some embodiments, see Figure 1 , Figure 8 and Figure 9 The inter-pass pressing device includes a connecting rod 31, a lateral pressing rod 32, and an inter-pass hot pressing unit 33. One end of the connecting rod 31 is fixed to the rotating component 34, and the other end is provided with a connecting cylinder. The lateral pressing rod 32 is inserted into the connecting cylinder, and the connecting cylinder is provided with an actuating wheel for driving the lateral pressing rod 32 to rise and fall, so that the lateral pressing rod 32 can move up and down as needed, avoiding interference between the lateral pressing rod 32 and the filaments deposited in adjacent printing layers when it rotates in a circle following the rotating component 34. Moreover, the connecting rod 31 is a telescopic rod, for example, an electric push rod is installed on the connecting rod 31. According to the follow-up needs of the hot pressing assembly, the connecting rod 31 can extend and retract radially along the rotating component 34, and drive the lateral pressing rod 32 to move synchronously, thereby adjusting the distance between the axis of the lateral pressing rod 32 and the axis of the print head.

[0064] In some embodiments, a high-temperature resistant ceramic heating rod and a temperature-sensing thermocouple are installed inside the lateral pressing rod 32 to achieve heating and temperature sensing and adjustment functions. The lateral pressing rod 32 is made of high thermal conductivity brass to ensure uniform heat transfer. The working section at the end of the lateral pressing rod 32 is polished to reduce the surface roughness to within Ra4, thereby reducing the friction between the lateral pressing rod 32 and the molten current deposited filament bundle. During the printing process, the working section at the end of the lateral pressing rod 32 contacts the side of the current deposited filament bundle, heating the side of the current deposited filament bundle at a first preset pressing temperature. Through a preset pressing interval, the working section at the end of the lateral pressing rod 32 applies lateral pressure to the side of the current deposited filament bundle, hot-pressing and shaping the side of the current deposited filament bundle, transforming the originally nearly elliptical side of the current deposited filament bundle into a nearly vertical plane, thereby increasing the contact area between the passes and improving the bonding strength between the passes. During printing, the preset pressing distance can be adjusted by rotating the rotating component 34, thereby adjusting the pressing force of the lateral pressing rod 32. Moreover, with the rotation of the rotating component 34 and the on-demand extension and retraction adjustment of the connecting rod 31, the lateral pressing rod 32 can always maintain lateral contact and compression with the current deposited filament bundle at the preset pressing distance during the printing process, realizing accompanying hot pressing in various printing paths such as straight lines and corners.

[0065] In some embodiments, the inter-pass hot pressing ironing section 33 is a flat, circular plate-shaped structure. The diameter of the inter-pass hot pressing ironing section 33 is at least larger than the width of the currently deposited filament bundle. The inter-pass hot pressing ironing section 33 is made of high thermal conductivity brass to ensure uniform heat transfer. The lower surface of the inter-pass hot pressing ironing section 33 is polished to reduce the surface roughness to within Ra4, thereby reducing the friction between the inter-pass hot pressing ironing section 33 and the molten current deposited filament bundle. The inter-pass hot pressing ironing section 33 is equipped with a high-temperature resistant ceramic heating rod and a temperature-measuring thermocouple, which can heat the upper surfaces of the current deposited filament bundle and the previous deposited filament bundle at a second preset pressing temperature. The preset pressing height is set to the printing layer thickness, which is the distance between the lower surface of the inter-pass hot pressing ironing section 33 and the adjacent printed layer deposited filament bundle. When the lateral pressing rod 32 hot presses and shapes the side of the current deposited filament bundle, the lower surface of the inter-pass hot pressing part 33 constrains the flow direction of the current deposited filament bundle, causing the current deposited filament bundle to flow and merge with the next deposited filament bundle, while simultaneously achieving surface shaping.

[0066] Because the raw material filament for continuous fiber 3D printing has a circular cross-section, currently common continuous fiber 3D printing devices only use a printing nozzle to hot-press and shape the filament from its upper surface. This causes the circular cross-section continuous fiber filament to deform into a near-elliptical cross-section under the hot-pressing action on the upper surface and deposited on the forming platform. A large gap exists between two adjacent near-elliptical cross-section filaments, preventing them from fitting tightly together, resulting in a small contact area between the channels and ultimately low bonding strength. In this invention, the inter-channel hot-pressing iron 33 and the lateral pressing iron 32 work together to hot-press and shape the currently deposited filament bundle. The extrusion action causes the molten current deposited filament bundle to flow and fuse with the previous deposited filament bundle, filling the inter-channel gap between the current and previous deposited filament bundles, increasing the contact area between the printed channels, and enhancing the inter-channel bonding strength of continuous fiber 3D printing.

[0067] It should be noted that the inter-pass hot pressing ironing part 33 is mounted on the lateral pressing ironing rod 32. The inter-pass hot pressing ironing part 33 is provided with an actuating wheel that contacts the lateral pressing ironing rod 32, so as to drive the inter-pass hot pressing ironing part 33 to move up and down along the lateral pressing ironing rod 32, thereby realizing the adjustment of the preset pressing height of the inter-pass hot pressing ironing part 33. The preset pressing height refers to the distance between the lower surface of the inter-pass hot pressing ironing part 33 and the adjacent printed layer deposited filament bundle.

[0068] In some embodiments, the fiber-reinforced composite material 3D printer also includes a substrate 5 serving as a forming platform. The substrate 5 is supported by a base, and its normal direction is rigidly constrained. The number of bases is set as needed, and heaters can be installed on the bases to heat the substrate 5 to a suitable printing temperature during printing. During printing, molten printing filament is deposited on the substrate 5, and then printed layer by layer to finally obtain the target printed part. It should be noted that the substrate 5 is only rigidly (e.g., bolted) or flexibly (e.g., magnetically or vacuum-adhesive) fixed to the base in the central area. Other areas of the substrate 5 are only supported by the base, allowing the substrate 5 to expand and contract freely in the plane, avoiding unevenness of the substrate 5 due to heating or cooling.

[0069] This invention takes continuous carbon fiber reinforced polyaryletherketone (CF / PAEK) printing filament as an example, and uses a fiber-reinforced composite material 3D printer to print the target part, to further illustrate the fiber-reinforced composite material 3D printing method of this invention, specifically including the following steps:

[0070] Step 1: Determine the printing parameters of the interlayer ironing device and the inter-pass ironing device. These printing parameters include the optimal preset interlayer ironing force of the concentric circle stepped temperature control module 242, the temperatures of the iron-type high-temperature metal ring 243, the stepped temperature control metal ring 244, and the cooling metal ring 245 in the concentric circle stepped temperature control module 242, and the inter-pass ironing temperature and ironing spacing of the inter-pass ironing device. Specifically, this includes:

[0071] Step 1.1: First, weigh an appropriate amount of CF / PAEK printing filament and place it in a crucible. Use a differential scanning calorimeter (DSC) to test the enthalpy change of the system during the heating and cooling process of the CF / PAEK printing filament. During the cooling process, select several temperature points at intervals near the temperature corresponding to the resin solidification peak to conduct isothermal crystallization tests. Obtain the relationship curve between the system enthalpy and time, i.e., the thermal analysis test curve, and record the time corresponding to the peak value.

[0072] Then, a certain length of CF / PAEK printing filament was cut, heated to its melting point, and quickly placed under a polarizing microscope (POM) equipped with a hot stage to observe its isothermal crystallization process. The crystallization time and grain size of the filament at the corresponding temperature were recorded simultaneously.

[0073] Finally, the optimal isothermal crystallization temperature and crystallization time of the CF / PAEK printing filament were determined using differential scanning calorimetry (DSC) and polarized light microscopy (POM). The optimal isothermal crystallization temperature of the CF / PAEK printing filament includes the glass transition temperature and melting point obtained from DSC testing.

[0074] Step 1.2: Based on the optimal isothermal crystallization temperature and crystallization time of the CF / PAEK printing filament, set the temperatures of the iron-type high-temperature metal ring 243, the stepped temperature-controlled metal ring 244, and the cooling metal ring 245. The first preset temperature of the iron-type high-temperature metal ring 243 is set to the melting point of the CF / PAEK printing filament. The preset temperature field of the stepped temperature-controlled metal ring 244 corresponds to the temperature range from the glass transition temperature to the melting point of the CF / PAEK printing filament. The number of stepped temperature-controlled metal rings 244 and the temperature difference between two adjacent stepped temperature-controlled metal rings 244 are set empirically. The second preset temperature of the cooling metal ring 245 is set to 80°C below the glass transition temperature of the CF / PAEK printing filament.

[0075] Step 1.3: Determine the printing speed of the iron-type high-temperature metal ring 243, the cooling metal ring 245, and each stepped temperature-controlled metal ring 244. The calculation formula is as follows:

[0076] ;

[0077] in: The printing speed of the iron-type high-temperature metal ring 243, the cooling metal ring 245, and the temperature-controlled metal ring 244 of each step; The widths of the iron-type high-temperature metal ring 243, the cooling metal ring 245, and each stepped temperature-controlled metal ring 244; The temperatures of the iron-type high-temperature metal ring 243, the cooling metal ring 245, and the temperature-controlled metal ring 244 at each step are specified. For printing filament at temperature The ratio of temperature to crystallization rate; given a type of printing filament material, observe the printing filament at a constant temperature using a polarizing microscope (POM). The crystallization behavior under the given conditions was analyzed to obtain the crystallization rate, and then the ratio was calculated. .

[0078] Finally, the minimum speed among the printing speeds of the iron-type high-temperature metal ring 243, the cooling metal ring 245, and each stepped temperature-controlled metal ring 244 is selected as the printing speed of the print head. This invention considers the size and temperature of each metal ring, as well as the ratio of temperature to crystallization rate of the printing filament at the corresponding temperature, when determining the printing speed of the print head. This ensures that the printing speed of the print head matches the residence time of each metal ring on the CF / PAEK filament during the printing process, avoiding printing defects caused by excessively fast or slow printing speeds, such as insufficient or excessive melting of the filament. This ensures that the printed continuous fiber-reinforced composite material has a uniform structure and excellent performance. Simultaneously, by selecting the minimum printing speed among the various metal rings as the printing speed of the print head, the stability and reliability of the printing process are ensured, improving print quality.

[0079] Step 1.4: Using traditional molding as a comparative molding process, and carbon fiber reinforced polyaryletherketone (CF / PAEK) filaments as raw materials, the interlaminar shear strength of the carbon fiber reinforced polyaryletherketone composite material prepared by traditional molding process is measured. The pressure is 50 MPa; compared with the molding process coefficient The value is 0.8; the material coefficient of the CF / PAEK printing filament. The value is 0.5; preset print line width. The value is 1mm; the radial contact length between the concentric circle stepped temperature control module 242 and the printing filament is... If the value is 8mm, then by formula... Calculate the theoretical maximum preset interlayer ironing force of the concentric circle stepped temperature control module 242 It is 160N. In the formula... middle, This is the material coefficient of the printing filament. The specific value is determined based on the material viscosity. For high melt viscosity materials such as PAEK (viscosity > 350 Pa·s), the value is more specific. The value ranges from 0.4 to 1, for low melt viscosity materials such as PLA (viscosity ≤ 350 Pa·s). The value range is 0.01 to 0.4; To determine the interlaminar shear strength of the printed filament under the comparative molding process, data was obtained through interlaminar shear strength testing. To compare the molding process coefficients, values ​​are determined based on experience. If the compared molding process is a standard compression molding process, then... The value range is 0.8~3; if the comparison molding process is a conventional winding process, then The value range is 0.3 to 1.2; Preset print line width; The contact length between the concentric circle stepped temperature control module 242 and the printing line along the radial direction is obtained by measurement.

[0080] Then, with a step size of 10N, within the range of 0~160N, 16 preset interlayer pressing force test values ​​were selected starting from 10N. Using the fiber-reinforced composite material 3D printer, interlayer shear samples corresponding to each preset interlayer pressing force test value were prepared, and the interlayer shear strength was tested. The preset interlayer pressing force corresponding to the highest interlayer shear strength was selected as the optimal preset interlayer pressing force. Statistical data showed that within the theoretical maximum preset interlayer pressing force range of 10N~160N, the interlayer shear strength exhibited a trend of first increasing and then decreasing. Furthermore, the sample with the highest interlayer shear strength was observed when the theoretical maximum preset interlayer pressing force was 120N; therefore, 120N was set as the optimal preset interlayer pressing force.

[0081] Step 1.5: Take 1.5 times the optimal preset interlayer pressing force as the safety threshold for activating the overload protection of the heat insulation plate 26, and calculate and select heat insulation material of appropriate strength to make the heat insulation plate 26 according to the safety threshold; and determine whether the additive dispensing channel 247 is open according to the requirements of the printing material system of the target printed part. If the additive dispensing channel 247 needs to be opened, the additive to be mixed in needs to be determined.

[0082] Step 1.6: Based on the resin matrix type of the CF / PAEK printing filament, select and set the heating temperatures of the lateral pressing rod 32 and the inter-pass hot pressing section 33. Specifically, to ensure that the resin of the printing filament is fully melted and to avoid thermal decomposition of the resin, the range of the first preset pressing temperature of the lateral pressing rod 32 and the second preset pressing temperature of the inter-pass hot pressing section 33 is set to the melting point of the printing filament ±30℃. Since the polyetheretherketone (PAEK) resin component of the carbon fiber reinforced polyaryletherketone (PAEK) filament has a melting point of 370℃ and a thermal decomposition temperature of 490℃, the first preset pressing temperature of the lateral pressing rod 32 and the second preset pressing temperature of the inter-pass hot pressing section 33 are set to 400℃.

[0083] Step 1.6: Conduct process experiments to determine the preset ironing spacing b. Specific steps include:

[0084] (1) Calculate the ideal ironing spacing. The cross-section of the carbon fiber reinforced polyaryletherketone (PAEK) filament is a circle with a diameter of 0.5 mm. The preset printing layer thickness of the target printed part is 0.2 mm. The radius of the lateral ironing rod 32 is 1 mm. Therefore, the ideal ironing spacing = filament cross-sectional area ÷ preset printing layer thickness ÷ 2 + radius of lateral ironing rod 32 ≈ 1.5 mm.

[0085] (2) Determine the upper limit of the preset ironing spacing through process experiments. Print a 300mm long straight line using carbon fiber reinforced polyaryletherketone (PAEK) filament with a layer thickness of 0.2mm. After printing, set a measuring point every 10mm along the 300mm straight line, for a total of 30 measuring points. Use a vernier caliper to measure the width of the printed filament at each measuring point, i.e., the width of the printed layer. Then calculate the average value of the measured width of the printed layer at each measuring point, i.e., the line width, which is approximately 1.2mm. Then calculate the upper limit of the preset ironing spacing = line width ÷ 2 + radius of the lateral ironing rod 32 = 1.6mm.

[0086] (3) Determine the lower limit of the preset ironing distance through process experiments. Using the ideal ironing distance as the maximum value, a test gradient matrix of different ironing distances is generated by decreasing step by step with a fixed step size. Specifically, the ideal ironing distance is 1.5mm, and the step size is set to 0.05mm, so the test gradient matrix is ​​1.45mm, 1.4mm, 1.35mm, 1.3mm, 1.25mm, 1.2mm, 1.15mm, 1.1mm, 1.05mm, and 1.0mm. According to the above ironing distance matrix, start the 3D printing equipment to print samples. During the printing process, observe the accumulation of residual resin on the lateral ironing rod 32 and record the ironing distance when printing cannot be completed due to excessive resin extrusion at the beginning. When the ironing distance is 1.15mm, the resin accumulation on the outer contour of the sample occurs due to excessive residual resin on the lateral ironing rod 32, resulting in a large deviation between the sample size accuracy and the preset value. Therefore, the previous set of 1.2mm is taken as the lower limit of the preset ironing distance. Therefore, in this embodiment, the preset ironing distance can be selected from 1.2 to 1.6 mm, and is set to 1.4 mm. It should be noted that the preset ironing distance can be within the upper and lower limits of the ironing distance; the smaller the preset ironing distance, the stronger the ironing effect.

[0087] Step Two: Based on the preset printing path and preset layer thickness of the target printed part, input the above parameters and other relevant parameters into the 3D printer's control program, and after reading the given printing path code, perform continuous fiber 3D printing additive manufacturing of composite materials to obtain the target printed part. During the process of the print head moving along the preset path, the CF / PAEK filament first melts in the printing nozzle (temperature set to 400℃) and is deposited onto the printing platform. The deposited filament, i.e., the current deposited filament bundle, first passes through the high-temperature region (temperature set to 380℃) formed by the iron-shaped high-temperature metal ring 243 in the concentric stepped temperature control module 242. Figure 5 In region 1, downward pressure is applied to the current deposition filament via the concentric stepped temperature control module 242, ensuring good interlayer adhesion between the current deposition filament and the printing platform or the underlying deposition filament; simultaneously, as Figure 6 As shown, the previous deposited filament adjacent to the current deposited filament is also within the coverage area of ​​the high-temperature region, enabling secondary heating and melting of the adjacent deposited filament. This improves the interaction force between the previous and current deposited filaments, enhancing the inter-pass bonding strength of the printed product. Then, as the print head moves forward, the current deposited filament enters the second-step temperature segment formed by the stepped temperature control molding module, as shown... Figure 5In region 2, isothermal crystallization occurs under a preset temperature field. Under similar temperature and pressure, the PAEK resin grains grow at a similar rate, resulting in printed products with uniform grain size. Finally, the deposited filament bundle passes through a third-step temperature band formed by the cooling metal ring 245, as shown... Figure 5 In region 3, the microstructure of the PAEK resin is rapidly cooled and fixed. At the same time, cooling under pressure can alleviate the degree of thermal deformation, thus preparing CF / PAEK composite material printed products.

[0088] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fiber-reinforced composite material 3D printer, characterized in that, include: The print head includes a heat insulation shell (11) and a throat (12). The throat (12) is disposed inside the heat insulation shell (11) and is used to provide an extrusion channel for the printing filament. The heat insulation shell (11) is provided with a rotating part (34). An interlayer pressing device includes a fixed base (21), an interlayer pressing drive assembly (22), an interlayer pressing force sensor (23), an interlayer pressing nozzle assembly, and a pressure equalizing plate. The fixed base (21) is installed inside a heat insulation housing (11). The interlayer pressing drive assembly (22) is fixed to the fixed base (21), and the actuator of the interlayer pressing drive assembly (22) is connected to the interlayer pressing force sensor (23). The interlayer pressing force sensor (23) is connected to the interlayer pressing nozzle assembly, which is used to press the current deposited filament and adjacent printed filaments. The deposited filament bundle is heated, melted, and cooled, and then hot-pressed with a preset interlayer pressing force under the drive of the interlayer pressing drive assembly (22). The pressure equalization plate includes an upper pressure equalization plate (251) and a lower pressure equalization plate (252) connected to the upper and lower ends of the interlayer pressing force sensor (23). The upper pressure equalization plate (251) is connected to the actuator of the interlayer pressing drive assembly (22), and the lower pressure equalization plate (252) is connected to the interlayer pressing nozzle assembly. A heat insulation plate (26) is provided between the lower pressure equalization plate (252) and the interlayer pressing nozzle assembly. An inter-pass pressing device includes a connecting rod (31), a lateral pressing rod (32), and an inter-pass hot pressing part (33). One end of the connecting rod (31) is fixed to the rotating part (34), and the other end is connected to the lateral pressing rod (32). The inter-pass hot pressing part (33) is installed on the lateral pressing rod (32). The end of the lateral pressing rod (32) is used to move with the print head during the printing process and to hot press and shape the side of the current deposited filament bundle with a first preset pressing temperature and a preset pressing spacing. The inter-pass hot pressing part (33) is used to move synchronously with the lateral pressing rod (32) and to hot press and shape the upper surface of the current deposited filament bundle and the previous deposited filament bundle with a second preset pressing temperature and a preset pressing height. The interlayer pressing nozzle assembly includes: Heating block (241), which is connected to the lower equalizing plate (252) and located at the outlet end of the throat tube (12), is used to heat the printing filament in the throat tube (12); A concentric circle stepped temperature control module (242) is fixedly connected to the lower end of the heating block (241), and the throat tube (12) is located at the center of the concentric circle stepped temperature control module (242). The concentric circle stepped temperature control module (242) is used to apply a preset interlayer pressing force to the adjacent printing layer deposition filaments and the current deposition filaments, and at the same time form a stepped temperature field to heat and cool the current deposition filaments and the adjacent printing layer deposition filaments.

2. The fiber-reinforced composite material 3D printer according to claim 1, characterized in that, A heat insulation plate (26) is provided between the lower pressure equalizing plate (252) and the heating block (241).

3. The fiber-reinforced composite material 3D printer according to claim 2, characterized in that, The concentric circle stepped temperature control module (242) includes: An iron-type high-temperature metal ring (243) is used to heat the current deposition filament and the adjacent printing layer deposition filament at a first preset temperature. A stepped temperature-controlled metal ring (244) is provided, comprising several concentric metal rings with different diameters. All stepped temperature-controlled metal rings (244) are arranged concentrically outside the iron-type high-temperature metal ring (243). The stepped temperature-controlled metal ring (244) is used to form a preset temperature field with the temperature decreasing ring by ring from the inside to the outside, to control the temperature and cool the current deposition filament and the adjacent printing layer deposition filament, and to perform hot pressing on the current deposition filament. Cooling metal ring (245) is located outside the outermost stepped temperature-controlled metal ring (244) and is distributed in a concentric circle. The cooling metal ring (245) is used to cool the current deposition filament and the adjacent printed layer deposition filament at a second preset temperature. A heat insulation ring (246) is disposed between the throat (12), the iron-type high-temperature metal ring (243), the stepped temperature-controlled metal ring (244), the cooling metal ring (245), and between two adjacent stepped temperature-controlled metal rings (244).

4. The fiber-reinforced composite material 3D printer according to claim 3, characterized in that, The concentric stepped temperature control module (242) also includes an additive dispensing channel (247), which is located between two adjacent heat insulation rings (246) and is used to dispense additives to the current deposited filament bundle during the printing process.

5. A method for 3D printing fiber-reinforced composite materials, implemented using the fiber-reinforced composite material 3D printer according to any one of claims 1-4, characterized in that, Includes the following steps: The printing parameters of the interlayer pressing device and the inter-pass pressing device are determined. The printing parameters include the optimal preset interlayer pressing force of the concentric circle stepped temperature control module (242), the temperature of the iron-type high temperature metal ring (243), the stepped temperature control metal ring (244), and the cooling metal ring (245) in the concentric circle stepped temperature control module (242), and the inter-pass pressing temperature and pressing distance of the inter-pass pressing device. Based on the preset printing path and preset layer thickness of the target printed part, the fiber-reinforced composite material 3D printer starts printing to obtain the target printed part.

6. The 3D printing method for fiber-reinforced composite materials according to claim 5, characterized in that, The optimal preset interlayer pressing force determination method of the concentric circle stepped temperature control module (242) includes: Based on the material coefficient of the printing filament, the interlayer shear strength of the finished product obtained by the printing filament under the comparative molding process, the comparative molding process coefficient, the preset printing line width, and the contact length of the concentric circle stepped temperature control module (242) with the printing filament in the radial direction, the theoretical maximum preset interlayer pressing force of the concentric circle stepped temperature control module (242) is calculated. Within the range of zero to the theoretical maximum preset interlayer pressing force, several preset interlayer pressing force test values ​​are selected according to preset step sizes. The interlayer shear sample corresponding to each preset interlayer pressing force test value is prepared using the fiber-reinforced composite material 3D printer, and the interlayer shear strength is tested. The preset interlayer pressing force corresponding to the highest interlayer shear strength is selected as the optimal preset interlayer pressing force.

7. The 3D printing method for fiber-reinforced composite materials according to claim 6, characterized in that, The theoretical maximum preset interlayer pressing force of the concentric circle stepped temperature control module (242) is calculated using the following formula: ； in, This is the theoretical maximum preset interlayer pressing force; The material coefficient of the printing filament; Interlaminar shear strength of the finished product obtained by printing filament under comparative molding process; To compare molding process coefficients; Preset print line width; The contact length between the concentric stepped temperature control module (242) and the printing wire in the radial direction is given.

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