WO2025217022A1

WO2025217022A1 - Continuous fiber reinforced photo sensitive polymer 3d printing

Info

Publication number: WO2025217022A1
Application number: PCT/US2025/023385
Authority: WO
Inventors: Guoying DONG; Yuanrui WANG
Original assignee: University of Colorado System; University of Colorado Colorado Springs
Current assignee: University of Colorado System; University of Colorado Colorado Springs
Priority date: 2024-04-08
Filing date: 2025-04-07
Publication date: 2025-10-16
Anticipated expiration: 2026-10-08

Abstract

Hybrid 3D printing systems and methods that can embed continuous fibers in photosensitive resins to produce a dense, high surface quality, fiber reinforced component, including complex shapes. The system includes a nozzle system having a resin container and a fiber path therethrough, the nozzle system having an outlet for resin and a continuous fiber, and at least three light sources spaced around and each in close proximity to the outlet, with each of the at least three light sources independently controllable. In use, the light source behind the nozzle, when the nozzle is moving, is activated to cure the photosensitive resin. The continuous fiber can be a pre-impregnated, high density fiber bundle (e.g., 6K, 12K).

Description

CONTINUOUS FIBER REINFORCED PHOTO SENSITIVE POLYMER 3D PRINTING

CROSS-REFERENCE

[0001] This application claims priority to U.S. provisional application no. 63/631,063 filed April 8, 2024, the entire disclosure of which is incorporated herein by reference for all purposes.

TECHNICAL FIELD

[0002] This disclosure is directed to fiber reinforced, UV curable three-dimensional structures and methods of making.

BACKGROUND

[0003] Additively manufactured fiber reinforced composites can be classified into continuous fiber and short fiber composites. Three-dimensional (3D) printing of polymer composites with nanoparticles (e.g., carbon black, carbon nanotubes) and short fibers has been demonstrated using various printing methods including powder bed printing, stereolithography, digital light processing, and inkjet. However, the direct incorporation of continuous fiber is challenging for these processes.

[0004] Recently, the challenges in additive manufacturing (AM) of continuous fiber reinforced composites have been overcome by several processes including fused deposition modeling (FDM) and direct ink writing (DIW). Currently, continuous fibers are blended with thermoplastics or thermoset precursors before the manufacturing process. FDM employs a thermoplastic filament to feed into the heated printing nozzle and extrude the molten material onto a deposition bed with a pre-programmed printing path in a layer-by-layer manner. Continuous fiber is extruded from another nozzle to deposit the fiber on the matrix material. Overall however, the FDM-based methods are limited to printing thermoplastic composites, which do not typically possess the stiffness and strength for high-performance applications. Different from FDM, DIW deposits the continuous fiber coated with a reactive thermoset rein on a platform after which it is immediately cured by thermal or ultraviolet sources to form structures.

[0005] There does exist a DIW 3D printer for photo-curable epoxy composites. The printer head has a syringe for resin storage, a deposition nozzle, a feeder for continuous fiber, and an ultraviolet (UV) lamp for photo-polymerization. The feeder connects to the syringe through a one-way valve, which prevents the liquid resin from entering the feeder. In the meantime, the one-way valve provides considerable friction to the fiber extrusion. Therefore, the deposited composite filaments are required to be fully cured upon UV irradiation before the printer head advances. However, instead of printing a fully dense composite part, this printer, and DIW can only add fibers to the surface of existing parts, resulting in a rough finishing quality.

SUMMARY

[0006] The present disclosure describes an approach to printing continuous fibers, providing a hybrid AM printer that integrates a digital light processing (DLP) process with the digital ink writing (DIW) process to embed continuous fibers in photopolymers. The hybrid system includes at least three light sources proximate a fiber nozzle, allowing curing of a photosensitive resin on the fiber after having been expelled from the nozzle. Also described is an approach to pre-impregnating fiber bundles prior to printing.

[0007] In one particular implementation, this disclosure provides a system including a resin source and a light source operably located in relation to the resin source to irradiate a photosensitive resin in the resin source, a nozzle system having a resin container and a fiber path therethrough, the nozzle system having an outlet for resin and a continuous fiber, with the nozzle system moveable relative to the resin source in all of an X-direction, a Y-direction, and a Z- direction, and at least three light sources spaced around and each in close proximity to the outlet of the nozzle system, with each of the at least three light sources independently controllable.

[0008] In another particular implementation, this disclosure provides a method of forming a fiber-reinforced part, the method including forming a base part by a digital light processing (DLP) method, applying a continuous fiber on the base part by a direct ink writing (DIW) process including at least three individually controllable light sources proximate an outlet of a photosensitive resin and fiber nozzle, and curing the applied fiber with a light source on a backside of the outlet.

[0009] In another particular implementation, this disclosure provides a method of forming a fiber-reinforced part, the method including forming a base part by curing resin in a resin bath, applying a photosensitive resin and a continuous fiber on the base part from a nozzle system moving in a first direction, and curing the photosensitive resin and continuous fiber with a first light source proximate an outlet from the nozzle system, and applying additional photosensitive resin and additional continuous fiber on the base part from the nozzle system moving in a second direction different than the first direction, and curing the additional photosensitive resin and additional continuous fiber with a second light source proximate an outlet from the nozzle system.

[001 OJ In another particular implementation, this disclosure provides a resin- impregnated fiber bundle formed by coating an uncoated fiber bundle with a resin, at least partially curing the coated fiber bundle, coating the partially cured coated fiber bundle with a second resin, and partially cured second coated fiber bundle. The cross-sectional shape of the fiber bundle can be altered prior to the second cure. The fiber bundle may have, e.g., 6,000 (6K) fibers, 12,000 fibers (12K), or more. The impregnated fiber bundles can be used in any of the fiber printing processes described herein.

[0011] These and other aspects of the technology described herein will be apparent after consideration of the Detailed Description and Figures herein. It is to be understood, however, that the scope of the claimed subject matter shall be determined by the claims as issued and not by whether given subject matter addresses any or all issues noted in the Background or includes any features or aspects recited in the Summary.

BRIEF DESCRIPTION OF THE FIGURES

[0012] FIG. 1 is a schematic diagram of a hybrid polymeric printing system.

[0013] FIG. 2 is a schematic diagram of a nozzle for use with the system of FIG. 1, the nozzle shown in top view and in side view.

[0014] FIG. 3 A is schematic diagram of a first step in a fiber printing method; FIG. 3B is a second step in the method; FIG. 3C is a third step in the method; and FIG. 3D is a fourth step in the method.

[0015] FIG. 4A is a schematic diagram of a fiber pre-impregnation system; FIG. 4B is another schematic diagram of the fiber pre-impregnation system.

[0016] FIG. 5 is photomicrograph of a part formed by a system and method described herein.

[0017] FIG. 6 is a photomicrograph of two parts formed by a system and method described herein. DETAILED DESCRIPTION

[0018] As indicated above, described herein is a hybrid 3D printing system and methods that can embed continuous fibers in photosensitive resins to produce dense, high surface quality, fiber reinforced components, including those having complex shapes. The printing system includes a fiber deposition arrangement that expands the manufacturing freedom of continuous fibers. Also described is a system and methods that can resin-impregnate large bundles of fiber for use with the printing system.

[0019] Structures/products made via continuous fiber-reinforced polymers (CFRPs) have superior combinations of stiffness, strength, and light weight and CFRPs are leading contenders in various applications ranging from aerospace to ground transportation. Compared to conventional composite manufacturing methods, additive manufacturing (AM) allows for the moldless fabrication of complex structures with tailored fiber distribution and orientation. Various functions can be readily incorporated by printing with functional fibers. The substantially promoted design freedom and low manufacturing cost per part make AM ideal for rapid prototyping and composite product development. However, existing AM methods have several limitations related to fabrication of CFRPs. For example, CFRP structures made by fused deposition modeling (FDM) processes have internal pores and gaps that can dramatically decrease the stiffness and strength of the product; this is because it is difficult to plan the path of the nozzle to fill the gaps between fiber filaments.

[0020] Furthermore, in AM processes, the reinforcing fiber can only be deposited in the X-Y plane, which means that the product is vulnerable to the load in the z-direction. Although direct ink writing (DIW) and automated fiber placement processes can place the fiber out-of- plane, fibers are often deposited on the outer surface instead of being embedded into the product. Digital light processing (DLP) can fabricate products with high-quality short fiber reinforced polymers, but DLP cannot accommodate continuous fibers in the printing process. Therefore, it is challenging to embed out-of-plane fibers in fully dense CFRPs using existing AM processes.

[0021] Photopolymer, also referred to as photosensitive polymer/resin and photocurable polymer/resin, has been widely used in DLP AM processes and can potentially be used as the matrix material to 3D print CFRPs without pores and gaps. However, the traditional DLP process cannot print photopolymers with continuous fibers. [0022] To provide 3D printing of continuous fiber in the DLP process, the present disclosure describes a hybrid AM printing system that integrates the DLP process with a DIW process to embed continuous fibers in photopolymers; particularly, the DLP process is used to fabricate the matrix material and the DIW process deposits the fiber into the cured photosensitive resin. By combining the two processes, the DLP process fills any gaps left after the fiber deposition by the DIW process. In addition, the DIW process can deposit the fiber on curved surfaces and the photosensitive resin can be cured by DLP after the fiber deposition, which enables producing a product having the fiber embedded out-of-plane in the matrix material. In such a manner, the hybrid AM system leverages the capabilities of DLP and DIW processes to overcome the current limitations and fabricate CFRPs with high dimensional accuracy and excellent mechanical performance.

[0023] In the following description, reference is made to the accompanying drawing that forms a part hereof and in which is shown by way of illustration at least one specific implementation. The following description provides additional specific implementations. It is to be understood that other implementations are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the examples, including the figures, provided below. In some instances, a reference numeral may have an associated sub-label consisting of a lower-case letter to denote one of multiple similar components. When reference is made to a reference numeral without specification of a sub-label, the reference is intended to refer to all such multiple similar components.

[0024] A general structure of a hybrid system is shown in FIG. 1 as system 100, the system 100 being a combination or hybrid of a DLP subsystem 110 and a DIW subsystem 120. The DLP subsystem 110 includes a UV light source 112, a build plate 114 mounted on a Z- movement mechanism 116 (e.g., a threaded frame), and a first resin source 118 (e.g., a tank) receiving the build plate 114. This DLP subsystem 110 works as a DLP printer to 3D print photopolymer layer by layer in the resin tank 118. The DIW subsystem 120 has a nozzle 122 operably connected to a fiber source 124, the nozzle 122 mounted on an X-Y movement mechanism 126 (e.g., a frame). The fiber may be any suitable fiber, such as carbon, basalt, aramid (e.g., Kevlar), glass, metal, and may be a monofilament or formed from multiple bundled, fiber strands (e.g., IK, 3K, 6K, 12K); bundled fibers may be pre-impregnated with a resin prior to use. The nozzle 122 includes an interior volume for receiving a volume of a second resin therein.

[0025] The first resin and the second resin are photosensitive resins, meaning, that their curing is at least initiated by UV or visible light, and may include various additives such as initiators or curing agents. The resins may be chemically different or chemically the same. Even if chemically the same, the first resin and the second resin may have different viscosities and/or have different inert additives.

[0026] A process for producing a fiber-reinforce three-dimensional part by using this hybrid system 100 is summarized in the following steps:

1. The build plate 114 moves down to the resin tank 118 (in the Z-direction) and is submerged in the resin.

2. The UV light 112 turns on to at least partially cure at least one layer of resin.

3. The build plate 114 moves up (in the Z-direction) to the nozzle 122, removing the build plate 114 from the resin in the tank 118; in some instances, the nozzle 122 may make physical contact with the resin present on the build plate 114.

4. The nozzle 122 moves in the X-Y plane to deposit resin-coated fiber in a desired pattern on the cured resin layer on the build plate 114.

5. After depositing the fiber, the nozzle 122 separates from the build plate 114, by either the nozzle 122 moving away in the X-Y plane or the building plate 114 moving in the Z- direction.

6. Steps 1-5 are repeated as desired to complete the printing and deposition of the fiber.

7. The build plate 114, with the deposited fiber thereon, lowers into the resin in the tank 118, thereby flooding the deposited fiber with the resin.

8. The UV light 112 turns on cure the resin over and around the deposited fiber.

[0027] Typical DLP systems have several common, detrimental issues. For example, during the deposition of resin-coated fibers, the resin may oxidize, which causes difficulty for the DLP printing of the next fiber layer. Because of the oxidation or for other reasons, adhesion between the fiber and the resin substrate may be weak, and may not be enough to fix the fiber on the substrate. Additionally, the viscosity of the resin significantly affects the deposition of the fiber, including producing a non-uniform coating of the fiber. Still further, as the resin cures, it can clog the tip of the nozzle.

[0028] The system 100 has overcome these issues by utilizing the nozzle 122 and its corresponding set-up. A detailed structure of a nozzle is shown in FIG. 2, as nozzle system 200, both in top view and side view; in the side view, a build plate 214 is also seen.

[0029] The nozzle system 200 includes a container 202, such as a syringe, having an interior volume for receiving an amount of resin (e.g., photopolymerizable polymer). The container 202 has an outlet 204 through which the resin can flow. The container 202 may be designed to receive and dispense a batch of resin (a set volume of resin) or the container 202 may be configured to receive resin (e.g., continuously) during the printing process, e.g., as resin is dispensed through the outlet 204.

[0030] The container 202 includes an inlet 206 for receiving an extended length of fiber (commonly known as continuous fiber) into the container interior; the continuous fiber may be provided, for example, from a spool. The fiber passes through the resin so that, upon movement of the fiber through the interior, the fiber and resin exit the container 202, simultaneously, via the outlet 204. The speed of the fiber and/or the volume flow of the resin can be adjusted to obtain a desired fiber to resin ratio. The fiber may be deposited at a speed of, for example, 100 mm per minute to 400 mm per minute. Further, the diameter of the outlet 204 can be selected to obtain a desired fiber to resin ratio.

[0031] Proximate the outlet 204 are at least three UV lights or light sources 210, shown as lights 210a, 210b, 210c; in other embodiments, four or more light sources 210 are present. Any light source that emits UV light or UV radiation may be suitable for use with the system 200. The UV light source 210 may be, for example, an LED, a deuterium lamp, or a laser. Examples of suitable UV lasers include a cerium laser, excimer laser, argon laser, free electron laser, and ion laser. The light source 210 may provide a wavelength of about 10 to 400 nm, including UV-A, UV-B, UV-C, N-UV, M-UV, F-UV, E-UV, and V-UV. Depending on the particular resin used, the light source may have a longer wavelength than UV, in the visible or near-infrared spectral region. For many resins, a UV wavelength of about 405 nm (e.g., 390 nm to 420 nm) is suitable.

[0032] Each UV light source 210 is positioned proximate the outlet 204 to provide UV light or radiation to the exiting resin. Each UV light source 210 may be operably connected to an optical (e.g., glass) fiber 212 that guides the UV light to the region proximate the outlet 204; any suitable light fiber may be used.

[0033] The light from UV light sources 210 are equally and/or evenly positioned around the outlet 204, best seen in the top view of FIG. 2. By having the UV light sources 210, or the ends of an optical fiber, positioned equidistant around the outlet 204, at least one of the light sources 210 will be behind (downstream), or close to behind, the outlet 204 no matter which X-Y direction the nozzle system 200 moves.

[0034] In use, the light source 210 behind the outlet 204 (based on the direction of movement of the outlet 204) is activated to cure the resin after the resin and fiber have exited the outlet 204. In the top view in FIG. 2, light source 210a is activated and light sources 210b, 210c are off, due to the direction of movement of the nozzle outlet 204. If a light 210 were to be activated and resin cured in front (upstream) of the nozzle outlet 204, the cured resin could collide with the nozzle and break the fiber. Depending on the direction of movement, the back or downstream side of the nozzle outlet 204 may be between two adjacent light sources 210; in such a situation, both light sources 210 can be activated.

[0035] The light sources 210 can be controlled manually or be integrated into an electronic control system (not depicted) to adjust the on/off of the light sources 210, each being controlled individually; this same control system can control the movement of the container 202 and nozzle outlet 204. The light intensity and/or pulse duration (particularly when the light source 210 is a laser) can also be adjusted individually. The intensity of the light sources can be adjusted to obtain a desired cure to maintain good adhesion between the resin-coated fiber from the nozzle system 200 and the resin on the build plate.

[0036] As indicated above, during use the light sources 210 are switched on and off according to the direction of movement of the nozzle outlet 204. Depending on the positioning of the light sources 210 and the movement direction of the nozzle outlet 204, two or more light sources 210 may be active (on) simultaneously. For example, when two light sources 210 are activated and the back of the nozzle outlet 204 is directly between the two, each source 210 may be less than 100% intensity, e.g., at 80%. In another example, when the back of the nozzle outlet 204 is unequally between two light sources 210, the two sources 210 may have different intensities (e.g., 50% and 90%). [0037] As shown above in FIG. 1, the hybrid 3D printing system 100 includes the DLP subsystem 110 and the DIW subsystem 120. Additional details regarding a system such as the system 100 are shown in FIGS. 3A through 3D as a system 300, as is use of the system 300 in a step-wise manner.

[0038] In FIG. 3A, a resin tank 302, a build plate 304, and a light source 306, such as a projector, are shown as part of the system 300; these features are part of a DLP subsystem. The build plate 304 is moveable along a Z-axis (in a Z-direction) via a frame, e.g., by a motor.

[0039] Also part of the system 300, shown in FIG. 3B, is a nozzle system 310 similar to the nozzle system 200 of FIG. 2, mounted on a frame and moveable in an X-direction and a Y- direction, e.g., by motors. The nozzle system 310 includes a container with a volume for retaining resin therein, an inlet into the container for an extended length of fiber, and an outlet from the container for the fiber and the resin. Surrounding the nozzle system 310 are at least three UV light sources, with their light output in close proximity to the output of the container.

[0040] An example manufacturing process using this system 300 is summarized in the following steps:

1. During a DLP printing, the nozzle system 310 is not in close proximity to the resin tank 302, but is spaced sufficiently far from the DLP light source 306 to inhibit UV from the light source 306 from affecting any resin in the nozzle system 310. The DLP light source 306 is activated to cure a portion of the liquid resin present in the tank 302, layer by layer, on the build plate 304, as shown in FIG. 3 A. The cured part shown in FIG. 3 A has a dogbone shape.

2. After curing an amount of resin in the tank 302, the DLP light source 306 is turned off. The build plate 304 is moved up (e.g., out from the resin in the tank 302) and the nozzle system 310 is moved into position above the raised build plate 304. Continuous fiber, coated with resin from the container, is deposited by the nozzle system 310 onto the part formed in step 1 while the nozzle system 310 is moving in the X- and/or Y-directions, as desired to obtain the desired part, and as shown in FIG. 3B. The UV light source(s), positioned on the backside of the nozzle outlet as it moves, cures the resin around the fiber on the part. In FIG. 3B, the fiber is deposited in the X-direction, longitudinally on the dogbone. Multiple passes of the fiber, offset in the Y-direction, can be made, with the appropriate downstream light source(s) curing the resin after being printed. 3. After the fiber deposition is complete, the nozzle system 310 is moved away from the deposited fiber and the build plate 304 is moved down into the resin tank 302 to allow the resin to flood the printed part. The DLP light source 306 is turned on again, irradiating the fiber-containing dogbone shape. The resin from the tank 302 fills the gaps between the deposited fibers and the light source 306 cures the new layer of resin between and over the fibers, as shown in FIG. 3C. Thus, the fiber is embedded into the cured resin part.

4. As shown in FIG. 3D, the fiber-depositing step (FIG. 3B) and the irradiating step

(FIG. 3C) are repeated until the desired number of layers (arranged in the Z-direction) is printed.

[0041] As indicate above, the fiber may be any suitable fiber, such as carbon, basalt, aramid (e.g., Kevlar), glass, metal, and may be a monofilament or formed from multiple bundled, fiber strands. The advantage of printing fiber bundles, such as 6K and 12K, is that it can offer significant time efficiency, as an example, a single 12K fiber bundle contains the equivalent fiber content of twelve IK bundles. To facilitate printing with bundles, the fiber bundles can be preimpregnated with a resin prior to use. Pre-impregnation of bundled fibers with resin prior to the nozzle system allows more complete coating of the individual fibers with resin, resulting in a more dense and less porous part. FIGS. 4A and 4B show a system for pre-impregnating fiber bundles. A pre-impregnation process using this system involves multiple resin impregnation and curing steps to improve resin penetration and bonding into a bundle of fibers.

[0042] FIGS. 4A and 4B shows the same system 400 in different orientations; thus, FIG. 4A is labeled as system 400a and FIG. 4B is labeled as system 400b.

[0043] The system 400 has a first resin bath 402a, 402b, a first curing station 404a, 404b, a second resin bath 406a, 406b, and a second curing station 408a, 408b. Each system 400 has a source of bundled fiber 410a, 410b, shown as a spool of bundled fiber. The system 400 has a fiber path from the fiber source 410 that sequentially passes through the first bath 402, the first curing station 404, the second bath 406, and then the second curing station 408.

[0044] The resin baths 402, 406 have a volume for receiving a volume of resin therein. As the fiber bundle passes through the baths 402, 406, the resin envelopes and adheres to the surfaces of the fibers. The resin in the two baths 402, 406 may be the same or may be different, and may be UV-curable or initiated resins or thermally-curable or initiated resins. The curing stations 404, 408 are configured for at least partially curing the resin in the immediately upstream bath 402, 406; that is, for example, when the first bath 402 has UV-curable resin therein, the first curing station 404 produces UV light or radiation.

[0045] When the curing stations 404, 408 utilize UV lights, as shown in FIGS. 4A and 4B, the stations are UV light source or stations. In other designs, the curing stations 404, 408 may be thermal sources providing elevated temperatures, depending on the resin composition.

[0046] The particular system 400 is configured to alter the shape of the fiber bundle as it progresses from the fiber source 410 to the second curing station 408. Typically, as the bundle leaves the fiber source 410, it has a generally circular cross-sectional shape. Before the resin- coated fiber enters the first curing station 404 after the first bath 402, the bundle is relatively flat. This may be accomplished before, within, or after the first resin bath 402. For example, the bundle may be flattened by combs or striations on any of the rollers of the bath 402 or by an individual comb not associated with a roller. Alternately, the resin coated fiber bundle (after the resin bath 402) may be flatted by combs or the like at the inlet to the first curing station 404. By providing a relatively flat orientation of the bundle as it enters the first curing station 404, the probability that the fibers are consistently cured (partially cured) is increased, the surface area of the fibers exposed to the resin in the second bath 408 is maximized, and overall the flat orientation allows more fibers within the bundle to be impregnated and partially cured.

[0047] The system 400 also includes a condenser 420a, 420b that forms the flattened, partially cured bundle into a dense bundle having a generally circular cross-sectional shape. In the particular system 400, the condenser 420 is downstream of the second bath 406 and upstream of the second curing station 408. The condenser 420 may be a syringe, a device as simple as an aperture through a plate, or any other element that can shape the continuously moving fiber into a generally circular form. The circular cross-sectional shape is more suitable for DIW printing than a flattened or irregular shape.

[0048] An example pre-impregnation process using this system 400 is summarized in the following steps:

1 . In a first step, bundled fibers are drawn from a spool 410 through an initial resin bath 402 and then through a flat curing chamber 404 equipped with 30 UV lights arranged in two sets, 15 lights above and 15 lights below the chamber. Each light in this chamber 404 operates at 10.2V and 13.2mA, providing controlled partial curing. 2. After the initial curing stage, the now-coated and partially cured fibers are drawn through a second resin bath 406 for re-impregnation, followed by reshaping via a needle and nozzle mechanism from a flat to a round cross-section. The intermediate or partial curing achieved in the first chamber 404 affect this reshaping step, as insufficient curing leads to structural instability while over-curing prevents the fiber bundle from conforming to the desired rounded shape.

3. After the reshaping, the rounded bundles are drawn through a second curing chamber 408. Here, the fibers undergo a second curing step using 12V and 20mA per light, with nine lights in total. After this second curing step, the resin on the rounded bundle is semi- or partially-cured, which provides better adhesion to subsequent processing steps in a hybrid 3D printing system.

[0049] The method above describes one example process using a pre-impregnation system such as the system 400. The described process settings can be adjusted and refined to account for the size of the fiber bundle; thicker bundles require slower movement speeds. Example speeds for different fiber bundles are 5mm/s (for 3K), 4mm/s (for 6K), and 3mm/s (for 12K) to obtain sufficient exposure time in each curing chamber. This adjustment compensates for the increased volume of resin required to penetrate the bundle and ensures consistent partial and full curing.

[0050] The resins used in the hybrid 3D printing and the pre-impregnation processes described above can be any suitable polymer or resin that at least partially cures via UV radiation; such polymers or resins are referred to as photosensitive polymers/resins, photocurable polymers/resins, or photopolymers. Non-limiting examples of suitable polymers/resins includes phenolics (e.g., bisphenol A), acylates (e.g., methylacrylate, dimethylacryate), and acrylics. One particular suitable material is a blend of bisphenol A ethlyxlate dimethyacryalte and 4- acryloymorpholine. The resin, either in the nozzle or in the tank, may include a UV initiator. One particular suitable initiator is 2-benzuyl-2-dimethylamino-l-(4-morpholinophenyl)-butanone-l (available as Irgacure® 369 photoinitiator). The resins, in the nozzle or in the tank, may be 100% solids or may be water-based or solvent-based.

[0051] As indicated above for the pre-impregnation of the fiber bundles, the impregnation polymer may be thermally cured or initiated rather than UV cured or initiated. [0052] Any of the resins can be modified to affect the viscosity and/or curing rate. The viscosity of the resin in the nozzle system plays an integral part in proper coating of the fiber to obtain good encapsulation of the coated fiber in the resin bath. If the viscosity is too low in the nozzle, the resin can flow out of the nozzle too quickly, even uncontrollably. If the viscosity is too high, the fiber may not be uniformly coated by the resin as the fiber passes out from the nozzle outlet. The fiber optimally bonds to the build plate or to the existing part when there is a continuous, even coating of resin on it.

[0053] The viscosity can be modified by adjusting the amount of solvent in the resin. Additionally or alternately, a filler (e.g., particulate filler) can be added to the resin, e.g., the resin in the nozzle system, to adjust and control the viscosity. The viscosity of the resin in the nozzle system can be less than, the same as, or greater than the viscosity of the resin in the tank, depending on the desired process parameter. The resin in the tank should, however, be sufficiently mobile to allow it to flood the fibers and the part when submerged therein. In many processes, the viscosity of the resin in the tank is less than the viscosity of the resin in the nozzle. The viscosity of the resin for the pre-impregnation may be high or low, although in many processes the viscosity for the pre-impregnation is similar to that of the tank resin.

[0054] A suitable particulate filler to add to the resin in the nozzle system is a ceramic powder, such as an aluminum-based powder; other suitable powders include metals, talc, glass, polymeric beads. The filler is typically nanometer size, e.g., about 50 nm, to facilitate homogeneous dispersion throughout the resin and maintain its suspension. A white or light colored powder reflects light, allowing easier control of the curing conditions of the resin, including increasing the reaction time. A suitable amount of powder to add to the resin is about 5-10%, by weight, of the resin, in some embodiments about 8%.

[0055] In one example, the resin in the nozzle system has a viscosity of about 795 cps, whereas the resin in the tank has a viscosity of about 125 cps. The pre-impregnation resin has a viscosity of about 125 cps.

[0056] A sample part made by a manufacturing system described above, and including ceramic powder filler, is shown in FIG. 5 as part 500. The fiber, present as straight, essentially parallel fibers, is thoroughly embedded in the resin. In other embodiments, the fiber may be laid in a non-straight pattern (in the X-Y directions), such as arcs, polygons (triangles, squares, etc.), circles, or irregular shapes. FIG. 6 shows two sample parts made by a manufacturing system described above, shown as part 600 A and part 600B. The part 600 A has a fiber deposited in a circular path and a fiber deposited in a rectangle or square. The part 600B has a fiber deposited in a triangular path and one deposited in a pentagonal path. Additionally, the fiber may be laid on a non-planar (curved) Z-direction surface.

[0057] The hybrid 3D printing systems and methods described above integrate features from a DLP subsystem and a DIW subsystem and further include multiple, precisely positioned light sources for curing the resin encasing the continuous fiber as it is deposited or printed. The light sources, particularly their position around the fiber-positioning nozzle and their individual controllability, enable the simultaneous deposition of fibers with liquid resin. Because of the multiple light sources and their individual control, the fiber can be successfully deposited in any direction without having to manipulate (e.g., rotate) the orientation of the nozzle or the base plate.

[0058] The hybrid 3D printing systems and methods described herein can embed continuous fibers in photo-sensitive resins, with the resin filling the gaps between fibers to provide a low or no porosity part. The systems and methods expand the manufacturing freedom of continuous fibers, including printing continuous fiber reinforced resin with complex shapes. This process also has the potential to print conductive fibers to fabricate electronics.

[0059] From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

[0060] Although the technology has been described in language that is specific to certain structures and materials, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific structures and materials described. Rather, the specific aspects are described as forms of implementing the claimed invention. Because many embodiments of the invention can be practiced without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

[0061] Various features and details have been provided in the multiple designs described above. It is to be understood that any features or details of one system or method may be utilized for any other system or method, unless contrary to the construction or configuration. Any variations may be made. [0062] The above specification and examples provide a complete description of the structure and use of exemplary implementations of the invention. The above description provides specific implementations. It is to be understood that other implementations are contemplated and may be made without departing from the scope or spirit of the present disclosure. The above detailed description, therefore, is not to be taken in a limiting sense. While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the examples provided.

[0063] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties are to be understood as being modified by the term “about,” whether or not the term “about” is immediately present. Accordingly, unless indicated to the contrary, the numerical parameters set forth are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

[0064] As used herein, the singular forms “a”, “an”, and “the” encompass implementations having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

Claims

WHAT IS CLAIMED IS:

1. A system comprising: a resin source and a light source operably located in relation to the resin source to irradiate a resin in the resin source; a nozzle system having a resin container and a fiber path therethrough, the nozzle system having an outlet for resin and a continuous fiber; the nozzle system moveable relative to the resin source in all of an X-direction, a Y- direction, and a Z-direction; and at least three light sources spaced around and each in close proximity to the outlet, with each of the at least three light sources independently controllable.

2. The system of claim 1, wherein each of the three light sources includes a light guide.

3. The system of claim 1, wherein the resin source is movable in the Z-direction and the nozzle system is moveable in the X-direction and the Y-direction.

4. The system of claim 1, wherein the light source and the at least three light sources each have a UV component.

5. The system of claim 1, wherein the at least three light sources are evenly spaced around the outlet.

6. The system of claim 1 further comprising a pre-impregnation system for preimpregnating the continuous fiber, the pre-impregnation system comprising a first resin bath, a fiber flattener, a first curing station, a second resin bath, a fiber condenser, and a second curing station.

7. A method of forming a fiber-reinforced part, the method comprising: forming a base part by a digital light processing (DLP) method; applying a continuous fiber on the base part by a direct ink writing (DIW) process including at least three individually controllable light sources proximate an outlet of a resin and fiber nozzle; and curing the applied fiber with a light source on a backside of the outlet.

8. The method of claim 7, further comprising, after curing the applied fiber, submersing the cured applied fiber to flood the fiber, and curing the flooded fiber.

9. The method of claim 8, further comprising, after curing the flooded fiber, applying additional fiber on the base part by the DIW process, curing the applied additional fiber, and submersing to flood the fiber and curing the flooded fiber.

10. The method of claim 7, wherein curing the applied fiber with a light source on a backside of the outlet includes having two light sources activated.

11. The method of claim 10, wherein the two light sources are activated at different intensities.

12. The method of claim 7 further comprising pre-impregnating a continuous fiber bundle with a bath resin and partially curing the bath resin, and applying the pre-impregnated continuous fiber bundle on the base part by the direct ink writing (DIW) process.

13. The method of claim 12, wherein pre-impregnating the continuous fiber bundle comprises: applying the bath resin to the fiber bundle; flattening the fiber bundle; partially curing the bath resin on the flattened fiber bundle; applying a second bath resin to the partially cured flattened fiber bundle; reshaping the partially cured flattened fiber bundle; and partially curing the second bath resin on the reshaped fiber bundle.

14. The method of claim 13, wherein flattening the fiber bundle is done before applying the bath resin to the fiber bundle.

15. The method of claim 13, wherein reshaping the partially cured flattened fiber bundle is done before applying the second bath resin.

16. A method of forming a fiber-reinforced part, the method comprising: forming a base part by curing resin in a resin bath; applying a resin and a continuous fiber on the base part from a nozzle system moving in a first direction, and curing the resin and continuous fiber with a first light source proximate an outlet from the nozzle system; and applying additional resin and additional continuous fiber on the base part from the nozzle system moving in a second direction different than the first direction, and curing the additional resin and additional continuous fiber with a second light source proximate an outlet from the nozzle system.

17. The method of claim 16, wherein the first light source is behind the nozzle when moving in the first direction, and the second light source is behind the nozzle when moving in the second direction.

18. The method of claim 16, further comprising applying yet additional resin and yet additional continuous fiber on the base part from the nozzle system moving in a third direction different than the first direction and the second direction, and curing the yet additional resin and yet additional continuous fiber with a third light source proximate an outlet from the nozzle system.

19. The method of claim 18, wherein curing the additional resin and additional continuous fiber with the second light source comprises curing the additional resin and additional continuous fiber with the second light source and another light source.

20. The method of claim 19, wherein the another light source is the first light source or the third light source.

21. The method of claim 16, further comprising submersing the base part, continuous fiber and additional continuous fiber in the resin bath and curing.

22. The method of claim 16, wherein applying a resin and a continuous fiber comprises applying a resin including a nanometer powder therein.