Composite wire, 3D printed part and preparation method and application thereof

Abstract

The present application belongs to the technical field of composite materials, and particularly relates to a composite wire, a 3D printed part and a preparation method and application thereof. The present application successfully prepares a composite material with fibers oriented in the plane by using short fiber felt and thermoplastic polymer sheet through layering and hot pressing technology. Then, the composite wire with the fiber length direction basically same as the wire length direction is further prepared through heating and softening rolling process. In the 3D printing process, the fibers are oriented again by using the extrusion effect of the nozzle and the optimized printing process, and finally the 3D printed part with high fiber orientation degree and excellent mechanical properties is obtained. The preparation process of the 3D printed part not only effectively plays the original performance of the fiber, but also makes the 3D printed part exhibit more excellent mechanical properties. In addition, the preparation process of the composite wire is simple and efficient, and the requirement for equipment is low, which provides strong support for meeting the application requirements in multiple fields.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology. More specifically, it relates to a composite filament, a 3D printed part, its preparation method, and its application. Background Technology

[0002] Short fiber reinforced thermoplastic polymer composites, with their advantages of high strength, high modulus, excellent designability and processability, have been widely used in aerospace, rail transportation, electronics, and medical devices. The emergence of 3D printing technology has brought new expansions to the application fields of short fiber reinforced thermoplastic polymer composites. In particular, fused deposition modeling (FDM) technology, due to its simplicity, ease of operation, and low cost, has become one of the most commonly used 3D printing methods for manufacturing short fiber reinforced thermoplastic polymer composites. FDM not only enables moldless manufacturing of composite parts but also allows for the rapid production of customized and structurally complex parts. However, the mechanical properties of 3D-printed short fiber reinforced thermoplastic polymer composites are mainly affected by the fiber content, distribution, and orientation in the composite material. When the fiber content is the same, improving the fiber orientation can further enhance the mechanical properties of the composite material.

[0003] To investigate the impact of fiber orientation on the mechanical properties of composite materials, researchers have conducted related studies. Tekinalp et al. (Highly oriented carbon fiber-polymer composites via additive manufacturing) pointed out that by melt-blending chopped carbon fibers with ABS resin and then extruding them, composite filaments for FDM printing were obtained. During FDM printing, they found that the fibers would undergo a certain degree of orientation along the printing path, but compared with composites prepared by hot pressing, the improvement in tensile strength and modulus was not significant. Furthermore, the fibers broke due to high shear forces during mixing and extrusion, resulting in shortening and reducing the mechanical properties of the composite. Yan et al. (3D short fibre orientation for universal structures and geometries in material extrusion additive manufacturing) explored fiber orientation in FDM printed structures and geometries in detail. They found that in the thickness direction of the printed filament, the fiber orientation in the middle region was more inclined towards the Z-axis. Simultaneously, increasing the extrusion width and height led to a decrease in fiber orientation, and the intersections and corners of the printed filaments had lower fiber orientation than the straight sections. Yang et al. (Biotribological properties of 3D printed high-oriented short carbon fiber reinforced polymer composites for artificial joints) prepared composite filaments for FDM printing by mixing short carbon fibers with polyetheretherketone (PEEK) and extruding them using a twin-screw extruder. They utilized the shear stress generated during nozzle extrusion of the molten filament to orient the fibers, thus preparing short carbon fiber reinforced PEEK composites with a certain degree of orientation. However, when the fiber content was 20 wt%, although the compressive strength and elastic modulus increased by 15% and 33% respectively, they were still far below the theoretical predictions, indicating that the degree of fiber orientation in this study was still relatively low. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the prior art in the preparation of short fiber reinforced thermoplastic polymer composites with fiber orientation, such as the fiber being subjected to high shear force and breaking during the mixing and extrusion process, and the difficulty in making the short fibers tend to be oriented in the same direction during the printing process after the wire is prepared by mixing and extrusion, which limits the improvement of the mechanical properties of the composite material. The present invention provides a method for preparing composite wires.

[0005] Another object of the present invention is to provide a composite wire prepared by the above-described preparation method.

[0006] Another object of the present invention is to provide a method for preparing 3D printed parts.

[0007] Another objective of this invention is to protect the 3D printed parts prepared by the above-described preparation method.

[0008] Another object of the present invention is to provide the application of the above-mentioned composite filament or the above-mentioned 3D printed parts in the fields of aerospace, rail transportation, electronic products or medical devices.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution:

[0010] This invention protects a method for preparing a composite wire, comprising the following steps:

[0011] S1. Short fiber felt is laminated with thermoplastic polymer sheet and hot-pressed to obtain composite material;

[0012] S2. After cutting the composite material obtained in step S1 into strip composite materials, heat and soften them and roll them to obtain cylindrical composite wire rough product; continue to heat and soften and roll them to perform fiber orientation treatment on the obtained composite wire rough product so that the fiber length direction in the composite wire rough product is basically in the same direction as the wire length direction, and obtain the composite wire.

[0013] The inventors discovered that a fully impregnated composite material can be obtained by laminating short fiber felt and thermoplastic polymer sheets and then hot-pressing them. During the hot-pressing process, the thermoplastic polymer sheet melts into a liquid state upon heating. Subsequently, under vacuum and pressure, the liquid thermoplastic polymer sheet gradually permeates and impregnates the solid short fiber felt until the entire structure reaches a dense state without significant pores, signifying full impregnation of the composite material. This type of composite material offers advantages for subsequent wire processing because, compared to wires prepared by traditional shear mixing and extrusion methods, this method effectively maintains the integrity of the fiber network structure and significantly reduces the risk of fiber breakage during processing. This invention eliminates the shearing, mixing, and extrusion steps of traditional methods. The resulting composite material is cut into strips, then heated, softened, and rolled to obtain cylindrical composite wire roughs. Further heating, softening, and rolling are performed on the resulting composite wire roughs to induce fiber orientation. The original in-plane orientation of the fibers (fibers distributed in 360° within the plane) is adjusted so that the fiber length direction is essentially aligned with the wire length direction, exhibiting a clear axial alignment. In this process, the morphology and mechanical properties of the short fibers are fully preserved. The resulting composite wire not only avoids fiber breakage but also possesses a high degree of fiber orientation (observed under a microscope, at least 70% of the fiber length directions are parallel within the field of view, indicating high fiber orientation), thus improving the mechanical properties of the composite material. This invention's preparation method not only avoids the complex processes of shearing, mixing, and extrusion in existing technologies, reducing equipment requirements, but also produces composite wires with no fiber breakage and high fiber orientation. This not only improves the mechanical properties of the product but also greatly enhances the feasibility and economy of large-scale industrial production.

[0014] Further, in step S1, the method for preparing the short fiber felt includes the following steps:

[0015] Short fibers are fully dispersed in water and dried to obtain short fiber felt.

[0016] Furthermore, the thorough dispersion is ultrasonic dispersion.

[0017] Furthermore, the ultrasonic dispersion is performed twice.

[0018] Furthermore, the power of the first ultrasonic dispersion is 500–750 W. In the first ultrasonic dispersion, using higher ultrasonic power can induce the generation of larger cavitation bubbles around the fiber bundles formed by the short fibers in the solvent. When these cavitation bubbles rapidly collapse, they release strong shear forces, which facilitates the dispersion of the fiber bundles into individual short fiber materials.

[0019] Preferably, the duration of the first ultrasound is 1 to 10 minutes.

[0020] Preferably, the frequency of the first ultrasound is 20–30 kHz.

[0021] Furthermore, the power of the second ultrasonic dispersion is 80–200 W. In the second ultrasonic dispersion, conventional ultrasonic power is used to obtain a uniformly dispersed dispersion of the fiber material.

[0022] Preferably, the duration of the second ultrasound is 1 to 10 minutes.

[0023] Preferably, the frequency of the second ultrasound is 38–45 kHz.

[0024] Further, in step S1, the drying is filtration drying. Removing the solvent from the short fiber material dispersion by filtration allows the short fibers to form a fiber network structure due to entanglement and electrostatic forces, thus producing a short fiber felt. This short fiber felt exhibits excellent uniformity, large gaps, and good mechanical stability.

[0025] Further, in step S1, the short fiber felt includes one or more of polylactic acid short fiber felt, chopped carbon fiber felt, and chopped glass fiber felt.

[0026] Furthermore, in step S1, the thickness of the short fiber felt is 0.2 to 0.6 mm.

[0027] Further, in step S1, the thermoplastic polymer sheet is obtained by hot pressing thermoplastic polymer material slices.

[0028] Furthermore, the temperature of the hot pressing is 60–200°C.

[0029] Preferably, the hot pressing temperature is 70–150°C.

[0030] More preferably, the temperature of the hot pressing is 80–120°C.

[0031] Preferably, in step S1, the thickness of the thermoplastic polymer sheet is 0.2 to 1.0 mm.

[0032] Further, in step S1, the thermoplastic polymer sheet includes one or more of polycaprolactone sheet, polylactic acid sheet, and polypropylene sheet.

[0033] Furthermore, in step S1, the mass ratio of the short fiber felt to the thermoplastic polymer sheet is 1:(5-15). Within this range, the resulting composite material exhibits good mechanical properties.

[0034] Furthermore, in step S1, the mass ratio of the short fiber felt to the thermoplastic polymer sheet is 1:(6-12).

[0035] Preferably, in step S1, the mass ratio of the short fiber felt to the thermoplastic polymer sheet is 1:(7-10). Within this range, the resulting composite material exhibits superior mechanical properties.

[0036] Furthermore, in step S1, the lamination method is not specifically limited, as long as the thermoplastic polymer sheet is fully impregnated with the short fiber felt. It can be an alternating layer (e.g., ABABABA), a layering of multiple thermoplastic polymer sheets in contact with each other (e.g., ABAABA), or a layering of multiple short fiber felts in contact with each other (e.g., ABABBABA). "A" represents the thermoplastic polymer sheet, and "B" represents the short fiber felt.

[0037] Furthermore, in step S1, the conditions for hot-pressing composite are: pressure of 0.01–0.1 MPa, ambient vacuum of 0.02–0.1 MPa, temperature of 80–150 °C, and processing time of 0.5–10 h. Adjusting the hot-pressing composite conditions within this range results in composite materials with superior mechanical properties.

[0038] Furthermore, in step S1, the hot-pressing composite also includes a cooling step.

[0039] Furthermore, in step S1, the thickness of the composite material is 1 to 5 mm.

[0040] Furthermore, in step S2, the width of the strip-shaped composite material is 2.5 to 3.5 mm.

[0041] Furthermore, in step S2, the heating temperature is 50–150°C.

[0042] Furthermore, in step S2, the heating temperature is 50–100°C.

[0043] Furthermore, as a preferred method, in step S2, the rolling process involves placing the obtained strip-shaped composite material on a metal plate and using another metal plate to reciprocate roll-form the strip-shaped composite material.

[0044] Furthermore, in step S2, the rolling process also includes a stretching step.

[0045] Further, as a preferred method, in step S2, the fiber orientation treatment of the composite wire blank involves sequentially fixing cylindrical molds of different diameters to the front and rear edges of a metal plate. Then, the resulting composite wire blank is placed on the metal plate with the molds fixed in place. Next, another metal plate is used as a rolling tool to roll the composite wire blank. As the rolling process proceeds, the diameter of the composite wire gradually decreases as the mold diameter decreases, while the length of the composite wire gradually increases. During this process of changing force, the fiber length direction on the composite wire gradually adjusts along the extension direction of the wire's length at both ends until the fiber length direction is substantially the same as the wire length direction, thus completing the fiber orientation treatment and obtaining the composite wire.

[0046] Furthermore, in step S2, the fiber orientation process also includes a cooling and curing step.

[0047] Preferably, in step S2, the diameter of the composite wire is ≤1.8mm.

[0048] This invention protects the composite wires prepared by the above-described preparation method.

[0049] The composite wire prepared by this invention has the characteristics of high fiber orientation and no fiber breakage, exhibiting good mechanical stability and performance reliability in various environments, and has broad application potential in many fields.

[0050] This application protects a 3D printed part, the raw material of which includes the aforementioned composite filament.

[0051] Using the aforementioned composite filaments for 3D printing, 3D printed parts with high fiber orientation and excellent mechanical properties can be produced. These structural components can well meet the needs of various application fields, especially showing broad application potential in the medical and industrial 3D printing fields.

[0052] This application protects the method for preparing the above-mentioned 3D printed part, including the following steps:

[0053] The composite filaments were then 3D printed to produce 3D printed parts.

[0054] This invention uses composite filament with fiber length direction basically in the same direction as filament length direction as 3D printing consumable. Under appropriate printing process, the shear force applied by the 3D printing nozzle during extrusion is used to perform secondary orientation of the fibers in the filament, thereby successfully preparing 3D printed parts with high fiber orientation and significantly improved mechanical properties.

[0055] Furthermore, as a preferred method, the 3D printing equipment is a fused deposition modeling (FDM) printer.

[0056] Furthermore, the printing parameters of the FDM printer are as follows: the printer nozzle diameter is 0.6-2mm, the nozzle temperature is 100-200℃, the printing thickness is 0.45-1.5mm, the printing speed is 3-6mm / s, and the printing direction is the nozzle movement direction.

[0057] Furthermore, the 3D printer's feeding direction is along the length of the composite filament. This choice is limited by the printer's small feed port design, which restricts feeding to a single method along the length of the composite filament. In addition, since most fibers in the composite filament are pre-oriented along the filament's length, when these filaments pass through the 3D printer, not only is the original fiber orientation maintained, but unoriented fibers on the filament undergo secondary orientation, thereby further enhancing the overall fiber orientation in the printed part.

[0058] This application protects the use of the aforementioned composite filament or the aforementioned 3D printed parts in the fields of aerospace, rail transportation, electronic products, or medical devices.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] This invention utilizes short-fiber felt and thermoplastic polymer sheets, employing lamination and hot-pressing composite techniques to successfully prepare a composite material with in-plane fiber orientation. Subsequently, a composite filament with the fiber length direction substantially aligned with the filament length direction is further produced through a heating, softening, and rolling process. During the 3D printing process, the fibers are oriented again using the extrusion effect of the nozzle and an optimized printing process, ultimately yielding a 3D printed part with high fiber orientation and excellent mechanical properties. The fabrication process of the 3D printed part not only effectively utilizes the original properties of the fibers but also enables the 3D printed part to exhibit superior mechanical properties. Furthermore, the fabrication process of this composite filament is simple and efficient, with low equipment requirements, providing strong support for meeting the needs of multiple application fields. Attached Figure Description

[0061] Figure 1 This is a flowchart illustrating the preparation process of the composite wire obtained in Example 1.

[0062] Figure 2 The diagram shows the structure of the composite wire obtained in Example 1 (a), the SEM images of the composite wire obtained in Example 1 in the oblique section (b) and cross section (c), and the SEM images of the composite wire obtained in Comparative Example 1 in the oblique section (d) and cross section (e).

[0063] Figure 3 The images show SEM images of the composite wire obtained in Example 2 at the oblique section (a) and cross section (b), and SEM images of the composite wire obtained in Comparative Example 2 at the oblique section (c) and cross section (d).

[0064] Figure 4 SEM images of the 3D printed parts obtained in Example 1(a), Example 2(c), Comparative Example 1(b), and Comparative Example 2(d) in oblique sections. Detailed Implementation

[0065] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0066] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0067] Figure 2 (a) indicates Figure 2 Figure (a) in the middle; Figure 2 (b) indicates Figure 2 Figure (b) in the diagram is used as an example; the other figures are named similarly.

[0068] Example 1: Preparation of a composite filament and 3D printed part

[0069] 1. Preparation of a composite wire

[0070] S1. Preparation of polycaprolactone composite materials

[0071] S1-1: Mix 4.5 parts by weight of polylactic acid (PLA) short fibers and 1000 parts by weight of water in a beaker. First, place the ultrasonic probe of an ultrasonic disperser in the center of the beaker for the first ultrasonic treatment (frequency 20 kHz, power 600 W, time 6 min) to obtain a preliminary dispersion. Then, transfer the preliminary dispersion from the beaker to a square stainless steel container. Place the square stainless steel container in an ultrasonic cleaner and perform a second ultrasonic treatment under manual vibration (frequency 40 kHz, power 200 W, time 6 min) to obtain a PLA short fiber dispersion. Place a stainless steel filter screen on the PLA short fiber dispersion and use a syringe to extract the water above the stainless steel filter screen. Then, wash once with anhydrous ethanol and dry in a vacuum drying oven at 45℃ to obtain one PLA fiber felt. Prepare three more PLA fiber felts in the same way, resulting in four PLA fiber felts, each with a thickness of 0.3 mm.

[0072] S1-2: 100 parts by weight of polycaprolactone chips are hot-pressed into 6 polycaprolactone sheets at 90°C using a hot press, each sheet having a thickness of 0.5 mm.

[0073] S1-3: Cut both the polycaprolactone sheet and the polylactic acid fiber felt into the same size.

[0074] S1-4: Weigh the cut polycaprolactone sheets (6 sheets) and polylactic acid fiber felt (4 sheets). The ratio of the total mass of the polycaprolactone sheets to the total mass of the polylactic acid fiber felt is 89:11. Stack the polycaprolactone sheets and polylactic acid fiber felt (in the form of ABABAABABA, where A represents the polycaprolactone sheet and B represents the polylactic acid fiber felt) on a stainless steel lower plate. Then place a 5mm thick stainless steel upper plate and a 60kg weight on top (which, after conversion, is equivalent to a pressure of approximately 0.031MPa applied to the polycaprolactone sheets and polylactic acid fiber felt). Place the plate in a vacuum drying oven, evacuate to 0.1MPa, control the temperature at 120℃, heat and melt for 8 hours, and then remove and cool to obtain the polycaprolactone composite material. The stainless steel lower plate is also equipped with 3mm high pads at both ends to support the stainless steel upper plate during the heating and melting process, thereby controlling the thickness of the final polycaprolactone composite material to be 3mm.

[0075] S2. Preparation of composite wires

[0076] S2-1: Cut the polycaprolactone composite material obtained in step S1 into strips with a width of 3mm, place them on a metal plate at 50°C, and after the material softens, roll them back and forth using another metal plate at 50°C to obtain a rough polycaprolactone composite wire with a diameter of 3.4mm.

[0077] S2-2: Fix two metal rods with a diameter of 1.9 mm on the front and rear edges of a 50°C metal plate, and place the rough polycaprolactone composite wire obtained in step S2-1 on the aforementioned metal plate. Continue to use another 50°C metal plate to repeatedly roll the rough composite wire to obtain a semi-finished polycaprolactone composite wire with a diameter of 1.9 mm.

[0078] S2-3: Transfer the polycaprolactone composite wire semi-finished product obtained in step S2-2 to a metal plate at 25°C. Similarly, place two metal rods with a diameter of 1.75mm on the front and rear edges of the metal plate. Roll them back and forth using another metal plate at 25°C to make a composite wire with most of the fiber length direction in the same direction as the wire length direction and a diameter of 1.75mm.

[0079] The fabrication process flow chart and structural schematic diagram of the composite wire are as follows: Figure 1 and Figure 2As shown in (a), the specific steps include: first, heating and softening the strip-shaped composite material, followed by rolling to obtain a rough composite wire. Then, these rough wires undergo further rolling and elongation treatments until the final composite wire is formed. During this process, the wire gradually becomes thinner and longer; this change is equivalent to applying tension to both ends of the wire, therefore, the direction of force on each part of the wire is along the direction of wire elongation. Since the fibers are originally oriented in-plane 360° in the composite material, when the fiber length direction is inconsistent with the wire length direction, the fiber will deflect under the action of force. This process continues until the length direction of most of the fibers in the wire is consistent with the direction of force (i.e., the wire length direction), at which point the fiber orientation is complete.

[0080] 2.3D Printing Parts Preparation

[0081] The composite filament obtained in step 1 is placed into an FDM printer with a nozzle diameter of 0.8 mm, a nozzle temperature of 150 °C, a printing thickness of 0.6 mm, a printing speed of 4 mm / s, and a printing direction that is the same as the nozzle movement direction. A single-layer, single-strand composite filament is then printed.

[0082] Example 2: Preparation of a composite filament and 3D printed part

[0083] The difference from Example 1 is that in step S1-1 of the composite filament preparation, polylactic acid short fibers are replaced with an equal amount of chopped carbon fibers; in steps S2-1 and S2-2 of the composite filament preparation, the temperature of the metal plate is replaced from 50°C to 80°C; and in the preparation of the 3D printed part, the printing nozzle temperature is replaced from 150°C to 170°C.

[0084] The other steps and conditions are the same as in Example 1.

[0085] Example 3: Preparation of a composite filament and 3D printed part

[0086] The difference from Example 1 is that in the preparation of the 3D printed part, instead of printing a single layer of composite material filament, three layers of filament are printed, with the direction of each layer of filament alternating between 0° and 90°, and the interval between each filament is 1.2 mm, to obtain a porous composite material structure.

[0087] The other steps and conditions are the same as in Example 1.

[0088] Comparative Example 1: Preparation of a composite filament and 3D printed part

[0089] 1. Preparation of a composite wire

[0090] The difference from Example 1 lies in the fact that, in steps S1-4 of the composite wire preparation process, the hot-pressing composite of polycaprolactone sheets and polylactic acid short fiber felt is replaced by mechanical physical mixing in a mixer. Mechanical physical mixing involves two relatively rotating rotors clamping the material and drawing it into the roller gap. Under the extrusion and shearing action of the rotors, the material is divided into two parts after passing through the roller gap, returning to the top of the roller gap along the gap between the front and rear chamber walls and the rotors. During one revolution of the rotor flow, the material is subjected to shearing and friction to achieve mixing. In contrast, the twin-screw extruder used in the prior art uses the rotation and meshing of two screws to subject the material to intense shearing, extrusion, and mixing within the barrel. In both the mechanical mixing in the mixer and the processing in the twin-screw extruder, the fibers experience extrusion and shearing forces, leading to fiber breakage. Therefore, the composite wire prepared by first using mechanical mixing in a mixer and then by a heated rolling process is equivalent to the composite wire prepared by the twin-screw extruder used in the prior art. The specific preparation steps of the composite wire are as follows:

[0091] S1. Preparation of polycaprolactone composite materials

[0092] S1-1: Mix 4.5 parts by weight of polylactic acid (PLA) short fibers and 1000 parts by weight of water in a beaker. First, place the ultrasonic probe of an ultrasonic disperser in the center of the beaker for the first ultrasonic treatment (frequency 20 kHz, power 600 W, time 6 min) to obtain a preliminary dispersion. Then, transfer the preliminary dispersion from the beaker to a square stainless steel container. Place the square stainless steel container in an ultrasonic cleaner and perform a second ultrasonic treatment under manual vibration (frequency 40 kHz, power 200 W, time 6 min) to obtain a PLA short fiber dispersion. Place a stainless steel filter screen on the PLA short fiber dispersion and use a syringe to extract the water above the stainless steel filter screen. Then, wash once with anhydrous ethanol and dry in a vacuum drying oven at 45°C to obtain one PLA fiber felt. Prepare three more PLA fiber felts in the same way to obtain four PLA fiber felts.

[0093] S1-2: 100 parts by weight of polycaprolactone chips are hot-pressed into 6 polycaprolactone sheets at 90°C using a hot press, each sheet having a thickness of 0.5 mm.

[0094] S1-3: Cut both the polycaprolactone sheet and the polylactic acid fiber felt into the same size.

[0095] S1-4: Weigh the cut polycaprolactone sheets (6 sheets) and polylactic acid fiber felt (4 sheets). The ratio of the total mass of the polycaprolactone sheets to the total mass of the polylactic acid fiber felt is 89:11. Add both to a 120°C internal mixer for mechanical and physical mixing. After cooling, control the thickness of the final polycaprolactone composite material to be 3 mm.

[0096] S2. Preparation of composite wires

[0097] S2-1: Cut the polycaprolactone composite material obtained in step S1 into strips with a width of 3mm, place them on a metal plate at 50°C, and after the material softens, roll it back and forth using another metal plate at 50°C to obtain a rough polycaprolactone composite wire with a diameter of 3.4mm.

[0098] S2-2: Fix two metal rods with a diameter of 1.9 mm on the front and rear edges of a 50°C metal plate, and place the rough polycaprolactone composite wire obtained in step S2-1 on the aforementioned metal plate. Continue to use another 50°C metal plate to repeatedly roll the rough composite wire to obtain a semi-finished polycaprolactone composite wire with a diameter of 1.9 mm.

[0099] S2-3: Transfer the composite wire semi-finished product obtained in step S2-2 to a metal plate at 25°C. Similarly, place two metal rods with a diameter of 1.75mm on the upper and lower edges of the metal plate, and roll them back and forth using another metal plate at 25°C to obtain a composite wire finished product with a diameter of 1.75mm.

[0100] 2.3D Printing Parts Preparation

[0101] The composite filament obtained in step 1 is placed into an FDM printer with a nozzle diameter of 0.8 mm, a nozzle temperature of 150 °C, a printing thickness of 0.6 mm, a printing speed of 4 mm / s, and a printing direction that is the same as the nozzle movement direction. A single-layer, single-strand composite filament is then printed.

[0102] Comparative Example 2: Preparation of a Composite Wire and a 3D Printed Part

[0103] The difference from Example 2 is that, in steps S1-4 of the composite wire preparation, the hot-pressing method of combining polycaprolactone sheets and short carbon fiber felt is replaced by mechanical physical mixing in a mixer at 120°C. This operation is consistent with the mixing step using a mixer in Comparative Example 1.

[0104] The other steps and conditions are the same as in Example 2.

[0105] Comparative Example 3: Preparation of a Composite Wire and a 3D Printed Part

[0106] The difference from Example 3 is that the composite wire obtained in Example 3 is replaced with the composite wire obtained in Comparative Example 1.

[0107] The other steps and conditions are the same as in Example 3.

[0108] Characterization and performance testing of composite filaments and 3D printed parts in experimental examples

[0109] 1. SEM characterization of composite filaments and 3D printed parts

[0110] The composite filaments and 3D printed parts prepared in Examples 1-3 and Comparative Examples 1-3 were characterized using a scanning electron microscope (SU5000, Hitachi, Japan), and the results are shown in the figure. Figure 2 (b)~ Figure 2 (c) The oblique and cross sections of the composite wire obtained in Example 1 are shown respectively. It can be observed from the figures that a large number of fibers in the oblique section are oriented along the length of the wire, while correspondingly, a large number of fibers in the cross section are arranged perpendicularly. This indicates that most fibers in the composite wire obtained in Example 1 are axially aligned. In contrast, Figure 2 (d)~ Figure 2 (e) shows the oblique and cross sections of the composite wire obtained in Comparative Example 1. Since this composite wire was produced through mechanical mixing, fiber breakage occurred during the mixing process. Therefore, the fiber length direction on the oblique section is almost entirely oriented along the wire length direction. Correspondingly, only a small portion of the cross section is perpendicular to the wire length. This indicates that only a small portion of the fibers in the composite wire obtained in Comparative Example 1 are axially aligned. Similarly, Figure 3 (a)~ Figure 3 (b) shows the oblique and cross sections of the composite wire obtained in Example 2. The oblique section shows a large number of fibers oriented along the length of the wire, while the cross section shows a large number of fibers arranged vertically. This indicates that most of the fibers in the composite wire obtained in Example 2 are axially aligned. Figure 3 (c)~ Figure 3 (d) Corresponding to the oblique section and cross section of the composite wire obtained in Comparative Example 2, the fiber length direction on the oblique section is almost not oriented along the wire length direction. Correspondingly, only a small portion of the fibers on the cross section are perpendicular to the cross section. This indicates that only a small portion of the fibers in the composite wire obtained in Comparative Example 2 are axially aligned. Furthermore, Figure 4 (a) and Figure 4 (c) The oblique cross-sections of the 3D printed parts-composite filaments obtained in Examples 1 and 2 are shown respectively. It can be seen from the figures that the composite filaments obtained through hot-pressing, based on their original fiber orientation, are further enhanced by FDM printing in the printing direction (filament length direction) by the increased fiber orientation. Conversely, Figure 4 (b) and Figure 4 (d) Comparing the oblique sections of the 3D printed parts-composite filaments obtained in Comparative Example 1 and Comparative Example 2 respectively, these filaments are obtained by further 3D printing on the basis of composite wires prepared by mechanical and physical mixing. It can be seen that although a small number of fibers are oriented along the printing direction during the printing process, the overall orientation is not obvious.

[0111] 2. Mechanical property testing of 3D printed parts

[0112] (1) Experimental methods

[0113] Tensile properties were tested on the 3D printed parts prepared in Examples 1-3 and Comparative Examples 1-3 using an electronic universal testing machine (LE3104, Shanghai Lisheng Scientific Instruments Co., Ltd., China). The tensile rate was 50 mm / min, and the force sensing was 100 N. For Examples 1 and 2 and Comparative Examples 1 and 2, the test object was 3D printed part-composite material filaments. The purpose was to obtain the intrinsic property parameters of the material to make them universally applicable and comparable. The length of these filament samples was 45 mm, and the gauge length was 25 mm. After obtaining the force-displacement curves, they were converted into stress-strain curves, from which the yield strength and tensile modulus of the obtained 3D printed part-composite material filaments could be analyzed. For Example 3 and Comparative Example 3, the test object was a 3D printed part-composite material porous structure, that is, a finished product made of composite material according to a specific design and purpose. The aim was to evaluate the load-bearing capacity and deformation of the structure under actual use conditions. These structural specimens are 35 mm long, 5 mm wide, and 1.8 mm high. By obtaining force-displacement curves through testing, the maximum force and stiffness of the 3D printed composite porous structure can be determined. The test data are shown in Table 1.

[0114] (2) Experimental Results

[0115] Table 1. Statistical Table of Mechanical Properties Tested on 3D Printed Parts

[0116] Yield strength (MPa) Elastic modulus (MPa) Maximum force (N) Stiffness (N / m) Example 1 19.24±0.92 693.56±48.35 / / Example 2 58.35±2.32 2792.67±243.18 / / Example 3 / / 51.12±1.03 93.71±2.05 Comparative Example 1 16.40±0.53 461.18±15.83 / / Comparative Example 2 48.23±3.26 2030.48±65.86 / / Comparative Example 3 / / 42.16±0.87 69.08±3.93

[0117] Note: / indicates that this data has no practical meaning.

[0118] As can be seen from the data in Table 1, Examples 1 to 3 used composite materials with in-plane fiber orientation, and further prepared composite wires with fiber length direction and wire length direction basically in the same direction, and finally obtained 3D printed parts with high fiber orientation and excellent mechanical properties.

[0119] Compared to Comparative Examples 1 and 2, Examples 1 and 2 show that the 3D printed parts (composite material filaments) of Comparative Examples 1 and 2 experienced fiber breakage due to shear forces during the mixing of polycaprolactone sheets and polylactic acid short fibers / short carbon fibers in the internal mixer. Although these broken fibers exhibited some orientation during subsequent FDM printing, the orientation effect was poor. In contrast, the fibers in the composite materials of Examples 1 and 2 possessed inherent in-plane orientation, resulting in high fiber orientation when fabricated into composite filaments, which was further enhanced after FDM printing. Therefore, the 3D printed parts (composite material filaments) of Example 1 showed a significant improvement in yield strength (approximately 17.32%) compared to Comparative Example 1, and a substantial improvement in elastic modulus (approximately 50.39%). For the 3D printed parts (composite material filaments) of Example 2, compared to Comparative Example 2, the yield strength increased by approximately 20.98%, while the elastic modulus increased by approximately 37.54%.

[0120] Example 3 and Comparative Example 3 further reveal the impact of fiber orientation on the performance of 3D printed parts. In Comparative Example 3, due to fiber breakage occurring during the fabrication process of the composite material, the potential for increasing maximum force and stiffness in the final 3D printed part was weakened when these materials were further fabricated into composite filaments and used for 3D printing. In contrast, Example 3 used a composite material with a certain degree of in-plane orientation of the fibers, which resulted in a significant improvement of approximately 21.25% and 35.64% in maximum force and stiffness, respectively, compared to Comparative Example 3.

[0121] In summary, this invention successfully prepared a composite material with in-plane fiber orientation by using short fiber felt and thermoplastic polymer sheets as raw materials and employing lamination and hot-pressing composite techniques. Subsequently, a composite filament with the fiber length direction substantially aligned with the filament length direction was further produced through a heating softening and rolling process. During the 3D printing process, the fibers were oriented again using the extrusion effect of the nozzle and an optimized printing process, ultimately obtaining the 3D printed parts with high fiber orientation and excellent mechanical properties as shown in Examples 1-3. The fabrication process of the 3D printed parts not only effectively utilized the original properties of the fibers but also enabled the 3D printed parts to exhibit superior mechanical properties.

[0122] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite wire, characterized in that, Includes the following steps: S1. Short fiber felt is laminated with thermoplastic polymer sheet and hot-pressed to obtain composite material; S2. After cutting the composite material obtained in step S1 into strip composite materials, heat and soften them and roll them to obtain cylindrical composite wire rough product; continue to heat and soften and roll them to perform fiber orientation treatment on the obtained composite wire rough product so that the fiber length direction in the composite wire rough product is basically in the same direction as the wire length direction, and obtain the composite wire.

2. The preparation method according to claim 1, characterized in that, In step S1, the short fiber felt includes one or more of polylactic acid short fiber felt, chopped carbon fiber felt, and chopped glass fiber felt.

3. The preparation method according to claim 1, characterized in that, In step S1, the thermoplastic polymer sheet includes one or more of polycaprolactone sheet, polylactic acid sheet, and polypropylene sheet.

4. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of the short fiber felt to the thermoplastic polymer sheet is 1:(5~15).

5. The preparation method according to claim 1, characterized in that, In step S2, the diameter of the composite wire is ≤1.8mm.

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