Composite wire rod, 3D printed piece and preparation method and application of 3D printed piece

Abstract

The invention belongs to the technical field of composite materials, and particularly relates to a composite wire, a 3D printed piece and a preparation method and application of the 3D printed piece. According to the invention, the short fiber felt and the thermoplastic polymer sheet are adopted, and the composite material with orientation in the fiber plane is successfully prepared through a laminating and hot-pressing compounding technology. And then, a composite wire with the fiber length direction basically the same as the wire length direction is further prepared through a heating, softening and rolling process. In the 3D printing process, the extrusion effect of the spray head and the optimized printing technology are utilized, the fibers are oriented again, and finally a 3D printed piece with the high fiber orientation degree and the excellent mechanical property is obtained. The preparation process of the 3D printed piece not only effectively exerts the original performance of the fiber, but also enables the 3D printed piece to show more excellent mechanical properties. In addition, the preparation process of the composite wire is simple, convenient and efficient, the requirement for equipment is low, and powerful support is provided for meeting application requirements in multiple fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and more specifically, relates to a composite wire, a 3D printed part, and a preparation method and application thereof. Background Art

[0002] Short fiber reinforced thermoplastic polymer composites have been widely used in aerospace, rail transportation, electronic products, medical devices and other fields due to their advantages of high strength, high modulus, excellent designability and processability. The emergence of 3D printing technology has brought new developments to the application of short fiber reinforced thermoplastic polymer composites. In particular, fused deposition modeling (FDM) technology has become one of the most commonly used 3D printing methods for manufacturing short fiber reinforced thermoplastic polymer composites due to its simplicity, easy operation and low cost. FDM not only realizes mold-free manufacturing of composite workpieces, but also can quickly produce customized and complex workpieces. 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. When the fiber content is the same, improving the fiber orientation can further improve the mechanical properties of the composite.

[0003] In order to study the effect of fiber orientation on the mechanical properties of composite materials, researchers have conducted relevant explorations. Tekinalp et al. (Highly oriented carbon fiber-polymer composites via additive manufacturing) pointed out that short-cut carbon fibers were melt-blended with ABS resin and then extruded to produce composite wires for FDM printing. During the FDM printing process, they found that the fibers would be oriented to a certain extent along the printing path, but the improvement in tensile strength and modulus was not significant compared with the composites prepared by hot pressing. In addition, the fibers broke due to high-intensity shear forces during mixing and extrusion, resulting in shortening of length 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 the fiber orientation in FDM printed structures and geometries in detail. They found that in the thickness direction of the printed filaments, the fiber direction in the middle area tended to be more oriented along the Z axis. At the same time, increasing the extrusion width and height would lead to a decrease in fiber orientation, and the intersection and corner parts of the printed filaments had a lower fiber orientation than the straight part. Yang et al. (Biotribological properties of 3D printed high-oriented short carbon fiber reinforced polymer composites for artificial joints) mixed short carbon fibers with polyetheretherketone and prepared composite wires for FDM printing through a twin-screw extruder. They used the shear stress generated by the molten wire during the nozzle extrusion process to orient the fibers and prepared short carbon fiber reinforced polyetheretherketone composites with a certain orientation. However, when the fiber content was 20wt%, its compressive strength and elastic modulus increased by 15% and 33% respectively, but 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 that during the mixing and extrusion process of preparing short fiber reinforced thermoplastic polymer composites with fiber orientation, the fibers are subjected to high-intensity shear force and break, and the printing process after the wire is prepared by mixed extrusion makes it difficult to orient the short fibers in the same direction, thereby limiting the improvement of the mechanical properties of the composite material, and a method for preparing a composite wire is provided.

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

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

[0007] Another object of the present invention is to protect the 3D printed part prepared by the above preparation method.

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

[0009] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

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

[0011] S1. Laminating the short fiber felt and the thermoplastic polymer sheet, hot pressing and compounding to obtain a composite material;

[0012] S2. Cut the composite material obtained in step S1 into strip-shaped composite materials, heat and soften them, and roll-form them to obtain a cylindrical composite wire crude product; continue heating and softening rolling, and perform fiber orientation treatment on the obtained composite wire crude product so that the fiber length direction in the composite wire crude product is basically the same as the wire length direction, thereby obtaining the composite wire.

[0013] The inventors have discovered that by stacking short fiber felt and thermoplastic polymer sheets and hot pressing them together, a fully impregnated composite material can be obtained. During the hot pressing process, the thermoplastic polymer sheet melts into a liquid state after being heated. Subsequently, the liquid thermoplastic polymer sheet gradually penetrates and infiltrates the solid short fiber felt under the action of vacuum and pressure until the entire structure reaches a tight state with no obvious pores, indicating that the composite material is fully impregnated. This type of composite material provides advantages for subsequent wire processing, because compared with wires prepared by traditional shear mixing and extrusion methods, this method can effectively maintain the integrity of the fiber network structure and significantly reduce the risk of fiber breakage during processing. The present invention abandons the shear mixing and extrusion steps of the traditional method, cuts the obtained composite material into strip composite materials, heats and softens them, rolls them to obtain cylindrical composite wire crude products, continues to heat and soften and rolls them, and further performs fiber orientation treatment on the obtained composite wire crude products. The original in-plane orientation of the fibers in the composite wire crude products (the fiber direction is distributed in the plane at 360°) is adjusted to be basically in the same direction as the length direction of the fiber and the length direction of the wire, showing an obvious axial arrangement. In this process, the morphology and mechanical properties of the short fibers are completely retained, and the composite wire finally obtained not only avoids the problem of fiber breakage, but also has a high degree of fiber orientation (observing the fiber length direction in the composite wire through a microscope, at least 70% of the fiber length direction in the field of view is in a parallel arrangement state, that is, a high fiber orientation degree), which can improve the mechanical properties of the composite material. The preparation method of the present invention not only avoids the complex process steps of shear mixing, extrusion, etc. in the prior art, reduces the demand for equipment, but also prepares composite wires with no fiber breakage and high fiber orientation. This not only improves the mechanical properties of the product, but also greatly improves the feasibility and economy of large-scale industrial production.

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

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

[0016] Furthermore, the sufficient 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, the use of a higher ultrasonic power can promote the generation of larger cavitation bubbles around the fiber bundles formed by the short fibers in the solvent. When these cavitation bubbles burst quickly, they will release strong shear force, which is conducive to dispersing the fiber bundles into single short fiber materials.

[0019] Preferably, the first ultrasound treatment lasts for 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 fiber material dispersion.

[0022] Preferably, the second ultrasound treatment lasts for 1 to 10 minutes.

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

[0024] Furthermore, in step S1, the drying is filtration drying. By removing the solvent in the short fiber material dispersion by filtration, the short fiber materials can form a fiber network structure due to mutual entanglement and electrostatic force, thereby forming a short fiber mat. This short fiber mat has excellent uniformity, large gaps and good mechanical stability.

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

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

[0027] Furthermore, 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 temperature of the hot pressing 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 0.2-1.0 mm.

[0032] Furthermore, in step S1, the thermoplastic polymer sheet includes one or more of a polycaprolactone sheet, a polylactic acid sheet, and a 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 obtained composite material can exhibit 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 mechanical properties of the obtained composite material are more excellent.

[0036] Furthermore, in step S1, the stacking method does not need to be specifically limited, as long as the thermoplastic polymer sheet can fully infiltrate the short fiber mat. It can be stacked alternately (such as ABABABA), or multiple thermoplastic polymer sheets can be stacked in contact with each other (such as ABAABA) or multiple short fiber mats can be stacked in contact with each other (such as ABABBABA). "A" represents a thermoplastic polymer sheet, and "B" represents a short fiber mat.

[0037] Furthermore, in step S1, the conditions for hot pressing and laminating are: pressure of 0.01-0.1 MPa, environmental vacuum of 0.02-0.1 MPa, temperature of 80-150° C., and processing time of 0.5-10 h. By regulating the conditions for hot pressing and laminating within this range, the mechanical properties of the obtained composite material are more excellent.

[0038] Furthermore, in step S1, the hot pressing compounding further 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 2.5-3.5 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 method is to place the obtained strip-shaped composite material on a metal plate, and use another metal plate to reciprocatingly roll-form the strip-shaped composite material.

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

[0045] Further, as a preferred method, in step S2, the fiber orientation treatment of the composite wire crude product is performed by fixing cylindrical molds of different diameters on the front and rear edges of a metal plate in sequence. Subsequently, the resulting composite wire crude product is placed on the metal plate on which the mold has been fixed. Next, another metal plate is used as a rolling tool to perform a rolling operation on the composite wire crude product. As the rolling process proceeds, due to the continuous reduction in the diameter of the mold, the diameter of the composite wire will gradually decrease accordingly, and at the same time, the length of the composite wire will gradually increase. In the process of this force change, the fiber length direction on the composite wire will gradually adjust along the extension direction of the length of the two ends of the wire until the fiber length direction is basically in the same direction as the wire length direction, thereby completing the fiber orientation treatment, and obtaining the composite wire.

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

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

[0048] The present invention protects the composite wire material prepared by the above preparation method.

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

[0050] The present application protects a 3D printed part, the raw material of which includes the above-mentioned composite wire.

[0051] 3D printing with the above composite wire can produce 3D printed parts with high fiber orientation and excellent mechanical properties. These structural parts can well meet the needs of various application fields, especially in the fields of medical and industrial 3D printing, showing wide application potential.

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

[0053] The composite wire is 3D printed to obtain a 3D printed part.

[0054] The present invention adopts a composite wire with a fiber length direction that is basically in the same direction as the wire length direction as a 3D printing consumable. Under a suitable printing process, the shear force applied by the 3D printing nozzle during the extrusion process is used to perform secondary orientation on the fibers in the wire, thereby successfully preparing a 3D printed part with a high fiber orientation degree and significantly improved mechanical properties.

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

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

[0057] Furthermore, the feeding direction of the 3D printer is the length direction of the composite wire. This choice is limited by the small feed port design of the printer, which makes the printer feed port only able to feed in a single way along the length direction of the composite wire. In addition, since the length direction of most of the fibers in the composite wire is already along the length direction of the wire in advance, when these wires are 3D printed, not only the original fiber orientation is maintained, but also the fibers that have not been oriented on the wire are prompted to undergo secondary orientation, thereby further enhancing the overall orientation of the fibers in the print.

[0058] This application protects the application of the above-mentioned composite wire or the above-mentioned 3D printed part 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] The present invention adopts short fiber felt and thermoplastic polymer sheet, and successfully prepares a composite material with fiber plane orientation through lamination and hot pressing composite technology. Subsequently, a composite wire whose fiber length direction is basically the same as the wire length direction is further prepared through a heating softening rolling process. During the 3D printing process, the fibers are oriented again by utilizing the extrusion effect of the nozzle and the optimized printing process, and finally a 3D printed part with high fiber orientation and excellent mechanical properties is obtained. The preparation process of the 3D printed part not only effectively exerts the original performance of the fiber, but also enables the 3D printed part to exhibit more outstanding mechanical properties. In addition, the preparation process of the composite wire is simple and efficient, with low equipment requirements, which provides strong support for meeting the application needs in multiple fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a flow chart for preparing the composite wire obtained in Example 1.

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

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

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

[0065] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

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

[0067] Figure 2 (a) indicates Figure 2 Figure (a) in the figure; Figure 2 (b) indicates Figure 2 The naming of other figures is similar to that of Figure (b).

[0068] Example 1 Preparation of a composite wire and 3D printed parts

[0069] 1. Preparation of a composite wire

[0070] S1. Preparation of polycaprolactone composites

[0071] S1-1: 4.5 parts by mass of polylactic acid staple fibers and 1000 parts by mass of water were added to a beaker and mixed. The ultrasonic probe of the ultrasonic disperser was first placed in the middle of the beaker, and the first ultrasonic treatment (frequency of 20kHz, power of 600W, time of 6min) was performed to obtain a preliminary dispersion, and then the preliminary dispersion in the beaker was transferred to a square stainless steel container, and the square stainless steel container was placed in an ultrasonic cleaning machine, and the second ultrasonic treatment (frequency of 40kHz, power of 200W, time of 6min) was performed under manual oscillation to obtain a polylactic acid staple fiber dispersion, and then a stainless steel filter was placed on the polylactic acid staple fiber dispersion, and the water above the stainless steel filter was extracted with a syringe, and then washed once with anhydrous ethanol, and then placed in a 45°C vacuum drying oven to dry, to obtain a polylactic acid fiber felt. Three more polylactic acid fiber felts were prepared in the same way, that is, 4 polylactic acid fiber felts were obtained, each with a thickness of 0.3mm.

[0072] S1-2: 100 parts by mass of polycaprolactone chips were heat-pressed in a heat press at 90° C. to form 6 polycaprolactone sheets, each with a thickness of 0.5 mm.

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

[0074] S1-4: Weigh the mass of 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 the polylactic acid fiber felt (the stacking form is ABABAABABA, A represents the polycaprolactone sheet, and B represents the polylactic acid fiber felt) on the stainless steel lower plate, and then place a 5mm thick stainless steel upper plate and a 60kg weight (after conversion, it is equivalent to a pressure of about 0.031MPa applied to the polycaprolactone sheet and the polylactic acid fiber felt), put them in a vacuum drying oven, evacuate to 0.1MPa, control the temperature at 120°C, heat and melt for 8h, then take out and cool to obtain a polycaprolactone composite material; wherein, gaskets with a height of 3mm are also provided at both ends of the stainless steel lower plate to support the stainless steel upper plate during the heating and melting process, so as to control the thickness of the final polycaprolactone composite material to be 3mm.

[0075] S2. Preparation of composite wire

[0076] S2-1: Cut the polycaprolactone composite material obtained in the above step S1 into strip-shaped composite materials with a width of 3 mm, place them on a metal plate at 50°C, and after the material is softened, reciprocately roll it using another metal plate at 50°C to obtain a polycaprolactone composite wire rough product with a diameter of 3.4 mm.

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

[0078] S2-3: The polycaprolactone composite wire semi-finished product obtained in step S2-2 is transferred to a metal plate at 25°C, and two metal round rods with a diameter of 1.75 mm are fixed on the front and rear edges of the metal plate. Another metal plate at 25°C is used to reciprocately roll the semi-finished polycaprolactone composite wire to form a composite wire with a diameter of 1.75 mm and a fiber length direction that is in the same direction as the wire length direction.

[0079] The preparation flow chart and structural schematic diagram of the composite wire are shown in Figure 1 and Figure 2As shown in (a), the specific steps include: first, heating and softening the strip composite material, and then rolling it to obtain a rough composite wire product. Then, these rough products are further rolled and stretched until the final composite wire is formed. In this process, the wire gradually becomes thinner and longer. This change is equivalent to applying tension to both ends of the wire to drive it. Therefore, the force direction of each part of the wire is along the direction of the wire lengthening. Since the fibers are originally oriented 360° in the plane in the composite material, when the fiber length direction is inconsistent with the wire length direction, the fibers will be deflected under the action of force. This process continues until the length direction of most of the fibers in the wire is consistent with the force direction (that is, the wire length direction), and the fiber orientation is completed.

[0080] 2. Preparation of 3D printed parts

[0081] Put the composite wire obtained in step 1 into the FDM printer, the printer nozzle diameter is 0.8mm, the printing nozzle temperature is 150℃, the printing thickness is 0.6mm, the printing speed is 4mm / s, the printing direction is the nozzle movement direction, and a single layer and single composite material filament is printed.

[0082] Example 2 Preparation of a composite wire and 3D printed parts

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

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

[0085] Example 3 Preparation of a composite wire and 3D printed parts

[0086] The difference from Example 1 is that in the preparation of the 3D printed part, the printing of a single layer of a single composite material filament is changed to printing three layers of filaments, the direction of each layer of filaments alternates at 0° / 90°, and the interval between each filament is 1.2 mm, so as to obtain a composite porous structure part.

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

[0088] Comparative Example 1 Preparation of a composite wire and 3D printed parts

[0089] 1. Preparation of a composite wire

[0090] The difference from Example 1 is that in the preparation step S1-4 of the composite wire, the hot-pressing composite method of the polycaprolactone sheet and the polylactic acid staple fiber felt is replaced by mechanical physical mixing in an internal mixer. The mechanical physical mixing is to clamp the material into the roller gap by two relatively rotating rotors. Under the extrusion and shearing action of the rotors, the material is divided into two parts after passing through the roller gap, and then returns to the top of the roller gap along the gap between the front and rear chamber walls and the rotors. During the flow of the rotor, the material is subjected to shear and friction everywhere to achieve mixing, while the twin-screw extruder used in the prior art is to subject the material to strong shear, extrusion and mixing in the barrel through the rotation and meshing of the two screws. During the mechanical mixing in the internal mixer and the processing of the twin-screw extruder, the fibers will experience extrusion and shearing forces, which will lead to fiber breakage. That is, the composite material is first prepared by mechanical mixing in an internal mixer, and then the composite wire prepared by the heating 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 composites

[0092] S1-1: 4.5 parts by mass of polylactic acid staple fibers and 1000 parts by mass of water are added to a beaker and mixed. First, the ultrasonic probe of the ultrasonic disperser is placed in the middle of the beaker, and the first ultrasonic treatment (frequency is 20kHz, power is 600W, and time is 6min) is performed to obtain a preliminary dispersion liquid, and then the preliminary dispersion liquid in the beaker is transferred to a square stainless steel container, and the square stainless steel container is placed in an ultrasonic cleaning machine, and a second ultrasonic treatment (frequency is 40kHz, power is 200W, and time is 6min) is performed under manual oscillation to obtain a polylactic acid staple fiber dispersion liquid, and then a stainless steel filter is placed on the polylactic acid staple fiber dispersion liquid, and the water above the stainless steel filter is extracted with a syringe, and then washed once with anhydrous ethanol, and then placed in a 45°C vacuum drying oven to dry, to obtain a polylactic acid fiber felt. Prepare 3 more polylactic acid fiber felts in the same way, that is, 4 polylactic acid fiber felts are obtained.

[0093] S1-2: 100 parts by mass of polycaprolactone chips were heat-pressed in a heat press at 90° C. to form 6 polycaprolactone sheets, each with a thickness of 0.5 mm.

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

[0095] S1-4: Weigh the mass of 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 being 89:11; add the two into a 120°C internal mixer for mechanical and physical mixing, and after cooling, control the thickness of the final polycaprolactone composite material to be 3 mm.

[0096] S2. Preparation of composite wire

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

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

[0099] S2-3: The semi-finished composite wire obtained in step S2-2 is transferred to a metal plate at 25°C, and two metal round bars with a diameter of 1.75 mm are placed on the upper and lower edges of the metal plate. Another metal plate at 25°C is used to reciprocately roll the semi-finished composite wire to obtain a finished composite wire with a diameter of 1.75 mm.

[0100] 2. Preparation of 3D printed parts

[0101] Put the composite wire obtained in step 1 into the FDM printer, the printer nozzle diameter is 0.8mm, the printing nozzle temperature is 150℃, the printing thickness is 0.6mm, the printing speed is 4mm / s, the printing direction is the nozzle movement direction, and a single layer and single composite material filament is printed.

[0102] Comparative Example 2 Preparation of a composite wire and 3D printed parts

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

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

[0105] Comparative Example 3 Preparation of a composite wire and 3D printed parts

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

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

[0108] Experimental example: Characterization and performance testing of composite wire and 3D printed parts

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

[0110] The composite wires and 3D printed parts prepared in Examples 1 to 3 and Comparative Examples 1 to 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) shows the oblique section and cross section of the composite wire obtained in Example 1. It can be observed from the figure that a large number of fibers on the oblique section are oriented along the length direction of the wire. Correspondingly, a large number of fibers on the cross section are arranged in a vertical state, which indicates that most of the fibers in the composite wire obtained in Example 1 are arranged axially. In contrast, Figure 2 (d)~ Figure 2 (e) shows the oblique section and cross section of the composite wire obtained in Comparative Example 1. Since the composite wire is made by mechanical physical mixing, the fibers are broken during the mixing process. Therefore, the fiber length direction on the oblique section is almost not oriented along the length direction of the wire. Accordingly, only a small part of the cross section is perpendicular to the cross section, which indicates that only a small part of the fibers in the composite wire obtained in Comparative Example 1 are arranged axially. Similarly, Figure 3 (a)~ Figure 3 (b) shows the oblique section and cross section of the composite wire obtained in Example 2, respectively. On the oblique section, a large number of fibers are oriented along the length direction of the wire. Correspondingly, on the cross section, a large number of fibers are arranged vertically, which indicates that most of the fibers in the composite wire obtained in Example 2 are arranged axially. Figure 3 (c)~ Figure 3 (d) corresponds to the oblique section and cross section of the composite wire obtained in Example 2, respectively. The fiber length direction on the oblique section is almost not oriented along the length direction of the wire. Correspondingly, only a small part of the fibers on the cross section are perpendicular to the cross section, which indicates that only a small part of the fibers in the composite wire obtained in Example 2 are axially arranged. Further, Figure 4 (a) and Figure 4 (c) shows the oblique cross-sections of the 3D printed parts-composite filaments obtained in Example 1 and Example 2, respectively. It can be seen from the figure that the composite wire obtained by hot pressing has the original fiber orientation. After FDM printing, the orientation of the fibers in the printing direction (the length direction of the wire) is further enhanced. On the contrary, Figure 4 (b) and Figure 4 (d) The oblique cross-sections of the 3D printed composite filaments obtained in comparative example 1 and comparative example 2, respectively. These filaments are obtained by further 3D printing on the basis of the composite wires prepared by mechanical and physical mixing. It can be seen that although a small amount of fibers are oriented along the printing direction in the length direction during the printing process, this orientation is not obvious as a whole.

[0111] 2. Mechanical properties test of 3D printed parts

[0112] (1) Experimental methods

[0113] The 3D printed parts prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to tensile performance tests using an electronic universal testing machine (LE3104, Shanghai Lishi Scientific Instrument Co., Ltd., China), with a tensile rate of 50 mm / min and a force sensor of 100 N. For Examples 1 and 2 and Comparative Examples 1 and 2, the test objects were 3D printed parts-composite filaments, the purpose of which was to obtain the intrinsic performance parameters of the material so that it had universal applicability and comparability. The length of these filament samples was 45 mm and the gauge length was 25 mm. After the force-displacement curve was obtained by testing, it was converted into a stress-strain curve, from which the yield strength and tensile elastic modulus of the obtained 3D printed parts-composite filaments could be analyzed. For Example 3 and Comparative Example 3, the test objects were 3D printed parts-composite porous structures, i.e. finished products made of composite materials according to specific designs and uses, which were intended to evaluate the bearing capacity and deformation of the structural parts under actual use conditions. The length of these structural specimens is 35 mm, the width is 5 mm, and the height is 1.8 mm. The force-displacement curve is obtained through testing, from which the maximum force and stiffness of the 3D printed component-composite porous structural component can be obtained. The test data are shown in Table 1.

[0114] (2) Experimental results

[0115] Table 1 Mechanical properties test statistics of 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 the data has no practical significance.

[0118] From the data in Table 1, it can be seen that Examples 1 to 3 use composite materials with fiber orientation in the plane, and on this basis further prepare composite wires with the fiber length direction and the wire length direction being basically in the same direction, and finally obtain 3D printed parts with high fiber orientation and excellent mechanical properties.

[0119] Compared with Comparative Examples 1 to 2, the 3D printed parts (composite filaments) of Comparative Examples 1 to 2, when the polycaprolactone sheet and the polylactic acid short fiber / short carbon fiber are mixed in the internal mixer, the fibers are broken due to the shear force. Although these broken fibers show a certain orientation in the subsequent FDM printing process, the orientation effect is poor. In contrast, the fibers in the composite materials of Examples 1 to 2 have a certain in-plane orientation, which makes them have a higher fiber orientation when prepared into composite wires. After FDM printing, these orientations are further enhanced. Therefore, the 3D printed parts (composite filaments) of Example 1 have a greater improvement in yield strength than Comparative Example 1, which is about 17.32%; at the same time, the elastic modulus has also been greatly improved, reaching about 50.39%. For the 3D printed parts (composite filaments) of Example 2, compared with Comparative Example 2, its yield strength is increased by about 20.98%, while its elastic modulus is increased by about 37.54%.

[0120] Example 3 and Comparative Example 3 further reveal the effect of fiber orientation on the performance of 3D printed parts. In Comparative Example 3, since fiber breakage has occurred in the composite material during the preparation process, when these materials are further prepared into composite wires and used for 3D printing, the potential for improving the maximum force and stiffness of the final 3D printed parts is weakened. In contrast, Example 3 uses a composite material with a certain in-plane orientation of the fibers, which enables its 3D printed parts (composite porous structures) to achieve a significant improvement of about 21.25% and 35.64% in maximum force and stiffness, respectively, compared with Comparative Example 3.

[0121] In summary, the present invention uses short fiber felt and thermoplastic polymer sheets as raw materials, and utilizes lamination and hot pressing composite technology to successfully prepare a composite material with fiber in-plane orientation. Subsequently, a composite wire having the fiber length direction substantially in the same direction as the wire length direction is further prepared through a heating and softening rolling process. During the 3D printing process, the fibers are oriented again by utilizing the extrusion effect of the nozzle and the optimized printing process, and finally 3D printed parts with high fiber orientation and excellent mechanical properties in Examples 1 to 3 are obtained. The preparation process of 3D printed parts not only effectively exerts the original properties of the fibers, but also enables the 3D printed parts to exhibit better mechanical properties.

[0122] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a composite wire, characterized in that: The following steps are involved: S1. Laminating the short fiber felt and the thermoplastic polymer sheet, hot pressing and compounding to obtain a composite material; S2. Cut the composite material obtained in step S1 into strip-shaped composite materials, heat and soften them, and roll-form them to obtain a cylindrical composite wire crude product; continue heating and softening rolling, and perform fiber orientation treatment on the obtained composite wire crude product so that the fiber length direction in the composite wire crude product is basically the same as the wire length direction, thereby obtaining the composite wire.

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

3. The preparation method according to claim 1, characterized in that: In step S1, the thermoplastic polymer sheet includes one or more of a polycaprolactone sheet, a polylactic acid sheet, and a 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 ≤1.8 mm.

6. The composite wire prepared by the preparation method according to any one of claims 1 to 5.

7. A 3D printed part, characterized in that: The raw material of the 3D printed part includes the composite wire material according to claim 6.

8. The method for preparing a 3D printed part according to claim 7, characterized in that: The following steps are involved: The composite wire material according to claim 6 is 3D printed to obtain a 3D printed part.

9. The preparation method according to claim 8, characterized in that: The printing thickness of the 3D printing is 0.45 to 1.5 mm.

10. Application of the composite wire material according to claim 6 or the 3D printed part according to claim 7 in the fields of aerospace, rail transportation, electronic products or medical devices.

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