METHOD AND MATERIAL FOR ADDITIVE MANUFACTURING Related Applications

[0001] This application is based on and claims the benefit of priority from United States Provisional Application Nos. 62/526,448 and 62/611,922 that wer filed on June 29, 2018 and 12/29/17, respectively, the contents of both of which are expressly incorporated herein by reference.

Technical Field

[0002] The present disclosure relates generally to additive manufacturing and, more particularly, to a method and material for additive manufacturing.

Background

[0003] Continuous fiber 3D printing (a.k.a., CF3D™) involves the use of continuous fibers embedded within a matrix discharging from a moveable print head. The matrix can be a traditional thermoplastic, a powdered metal, a liquid resin (e.g., a UV curable and/or two-part resin), or a combination of any of these and other known matrixes. Upon exiting the print head, a cure enhancer (e.g., a UV light, an ultrasonic emitter, a heat source, a catalyst supply, etc.) is activated to initiate and/or complete curing of the matrix. This curing occurs almost immediately, allowing for unsupported structures to be fabricated in free space. When fibers, particularly continuous fibers, are embedded within the structure, a strength of the structure may be multiplied beyond the matrix-dependent strength. An example of this technology is disclosed in U.S. Patent 9,511,543 that issued to Tyler on December 6, 2016 ("the '543 patent").

[0004] Although CF3D™ provides for increased strength, compared to manufacturing processes that do not utilize continuous fiber reinforcement, it may still be possible for the resulting structure to crack or break when exposed to excessive loading. The cracking or breaking may be difficult to detect, and a resulting strength of the structure may be reduced. The disclosed method and material are directed to addressing these issues and/or other problems of the prior art. Summary

[0005] In one aspect, the present disclosure is directed to an additively manufactured structure. The additively manufacture structure includes at least one continuous reinforcement, and a healing matrix associated with the at least one continuous reinforcement. Wherein a cure energy is applied to the at least one continuous reinforcement at a time of failure, the healing matrix is caused to cure and shore up the at least one continuous reinforcement.

[0006] In another aspect, the present disclosure is directed to another additively manufactured structure. The additively manufactured structure may include at least one continuous reinforcement, and a healing matrix at least partially filling the at least one continuous reinforcement. When the healing matrix may breaches from the at least one continuous reinforcement at a time of failure, the healing matrix at least partially coats the at least one continuous reinforcement and cures.

[0007] In yet another aspect, the present disclosure is directed to a method of additive manufacturing. The method may include simultaneously discharging from a print head structural reinforcements and healing reinforcements that are at least partially coated with a structural matrix. The healing reinforcements may contain a healing matrix. The method may also include directing cure energy toward the structural matrix discharging from the print head, and moving the print head during discharging to create a three-dimensional structure.

Brief Description of the Drawings

[0008] Fig. 1 is a diagrammatic illustration of an exemplary disclosed manufacturing system; and

[0009] Figs. 2 and 3 are diagrammatic illustrations of an exemplary material that may be utilized with the manufacturing system of Fig. 1.

Detailed Description

[0010] Fig. 1 illustrates an exemplary system 10, which may be used to continuously manufacture a composite structure 12 having any desired cross-sectional shape (e.g., circular, ellipsoidal, polygonal, etc.). System 10 may include at least a support 14 and a print head ("head") 16. Head 16 may be coupled to and moved by support 14. In the disclosed embodiment of Fig. 1, support 14 is a robotic arm capable of moving head 16 in multiple directions during fabrication of structure 12, such that a resulting longitudinal axis of structure 12 is three- dimensional. It is contemplated, however, that support 14 could alternatively be an overhead gantry or a hybrid gantry/arm also capable of moving head 16 in multiple directions during fabrication of structure 12. Although support 14 is shown as being capable of multi-axis movements, it is contemplated that any other type of support 14 capable of moving head 16 in the same or in a different manner could also be utilized, if desired. In some embodiments, a drive may mechanically couple head 16 to support 14 and may include components that cooperate to move and/or supply power or materials to head 16.

[0011] Head 16 may be configured to receive or otherwise contain a matrix. The matrix may include any type of material (e.g., a liquid resin, such as a zero-volatile organic compound resin; a powdered metal; etc.) that is curable. Exemplary matrixes include thermosets, single- or multipart epoxy resins, polyester resins, cationic epoxies, acrylated epoxies, urethanes, esters, thermoplastics, photopolymers, polyepoxides, thiols, alkenes, thiol-enes, reversible resins (e.g., Triazolinedione, a covalent- adaptable network, a spatioselective reversible resin, etc.) and more. In one embodiment, the matrix inside head 16 may be pressurized, for example by an external device (e.g., an extruder or another type of pump - not shown) that is fluidly connected to head 16 via a corresponding conduit (not shown). In another embodiment, however, the matrix pressure may be generated completely inside of head 16 by a similar type of device. In yet other embodiments, the matrix may be gravity-fed through and/or mixed within head 16. In some instances, the matrix inside head 16 may need to be kept cool and/or dark to inhibit premature curing; while in other instances, the matrix may need to be kept warm for similar reasons. In either situation, head 16 may be specially configured (e.g., insulated, chilled, and/or warmed) to provide for these needs.

[0012] The matrix may be used to coat, encase, or otherwise at least partially surround any number of continuous reinforcements (e.g., separate fibers, tows, rovings, ribbons, and/or sheets of material) and, together with the reinforcements, make up at least a portion (e.g., a wall) of composite structure 12. The reinforcements may be stored within (e.g., on separate internal spools - not shown) or otherwise passed through head 16 (e.g., fed from external spools). When multiple reinforcements are simultaneously used, the reinforcements may be of the same type and have the same diameter and cross-sectional shape (e.g., circular, square, flat, hollow, solid, etc.), or of a different type with different diameters and/or cross-sectional shapes. The reinforcements may include, for example, carbon fibers, vegetable fibers, wood fibers, mineral fibers, glass fibers, metallic wires, optical tubes, etc. It should be noted that the term "reinforcement" is meant to encompass both structural and non-structural types of continuous materials that can be at least partially encased in the matrix discharging from head 16.

[0013] The reinforcements may be exposed to (e.g., coated with) the matrix while the reinforcements are inside head 16, while the reinforcements are being passed to head 16 (e.g., as a prepreg material), and/or while the reinforcements are discharging from head 16, as desired. The matrix, dry reinforcements, and/or reinforcements that are already exposed to the matrix (e.g., wetted reinforcements) may be transported into head 16 in any manner apparent to one skilled in the art.

[0014] The matrix and reinforcement may be discharged from a nozzle 18 of head 16 via at least two different modes of operation. In a first mode of operation, the matrix and reinforcement are extruded (e.g., pushed under pressure and/or mechanical force) from nozzle 18, as head 16 is moved by support 14 to create the 3-dimensional shape of structure 12. In a second mode of operation, at least the reinforcement is pulled from nozzle 18, such that a tensile stress is created in the reinforcement during discharge. In this mode of operation, the matrix may cling to the reinforcement and thereby also be pulled from nozzle 18 along with the reinforcement, and/or the matrix may be discharged from nozzle 18 under pressure along with the pulled reinforcement. In the second mode of operation, where the matrix is being pulled from nozzle 18, the resulting tension in the reinforcement may increase a strength of structure 12, while also allowing for a greater length of unsupported material to have a straighter trajectory (i.e., the tension may act against the force of gravity to provide free-standing support for structure 12).

[0015] The reinforcement may be pulled from nozzle 18 as a result of head 16 moving away from an anchor point 20. In particular, at the start of structure-formation, a length of matrix- impregnated reinforcement may be pulled and/or pushed from nozzle 18, deposited onto a stationary anchor point 20, and cured, such that the discharged material adheres to anchor point 20. Thereafter, head 16 may be moved away from anchor point 20, and the relative movement may cause additional reinforcement to be pulled from nozzle 18. It should be noted that the movement of the reinforcement through head 16 could be assisted (e.g., via internal feed mechanisms), if desired. However, the discharge rate of the reinforcement from nozzle 18 may primarily be the result of relative movement between head 16 and anchor point 20, such that tension is created within the reinforcement.

[0016] Nozzle 18 may be fluidly connected to a matrix reservoir 22. Although matrix reservoir 22 is shown as being at least partially inside of head 16, it should be noted that matrix reservoir 22 could alternatively be located separately upstream of head 16. Nozzle 18 may be a generally cylindrical component having an upstream or base end in communication with matrix reservoir 22, a downstream or tip end, and one or more axially oriented passages that extend from the base end to the tip end.

[0017] Any number of reinforcements (represented as R in Fig. 2) may be passed axially through reservoir 22 where at least some matrix- wetting occurs (matrix represented as M in Figs. 2 and 3), and discharged from head 16 via nozzle 18. One or more orifices may be located at the tip end of nozzle 18 to accommodate passage of the matrix-wetted reinforcements. In the disclosed embodiment, a single generally circular orifice is utilized. It is contemplated, however, that multiple circular orifices could be used. In addition, orifices of another shape (e.g., a rectangular shape) may allow for printing of ribbons and/or sheets.

[0018] One or more cure enhancers (e.g., one or more light sources, ultrasonic emitters, lasers, heaters, catalyst dispensers, microwave generators, etc.) 26 may be mounted proximate head 16 (e.g., at a trailing side of nozzle 18) and configured to enhance a cure rate and/or quality of the matrix as it is discharged from nozzle 18. Cure enhancer 26 may be controlled to selectively expose internal and/or external surfaces of structure 12 to cure energy (e.g., light energy, electromagnetic radiation, vibrations, heat, a chemical catalyst or hardener, etc.) during the formation of structure 12. The cure energy may increase a rate of chemical reaction occurring within the matrix, sinter the material, harden the material, or otherwise cause the material to cure as it discharges from nozzle 18.

[0019] A controller 28 may be provided and communicatively coupled with support 14, head 16, and any number and type of cure enhancers 26. Controller 28 may embody a single processor or multiple processors that include a means for controlling an operation of system 10. Controller 28 may include one or more general- or special-purpose processors or microprocessors. Controller 28 may further include or be associated with a memory for storing data such as, for example, design limits, performance characteristics, operational instructions, matrix characteristics, reinforcement characteristics, characteristics of structure 12, and corresponding parameters of each component of system 10. Various other known circuits may be associated with controller 28, including power supply circuitry, signal-conditioning circuitry, solenoid/motor driver circuitry, communication circuitry, and other appropriate circuitry. Moreover, controller 28 may be capable of communicating with other components of system 10 via wired and/or wireless transmission.

[0020] One or more maps may be stored in the memory of controller 28 and used during fabrication of structure 12. Each of these maps may include a collection of data in the form of models, lookup tables, graphs, and/or equations. In the disclosed embodiment, the maps are used by controller 28 to determine desired characteristics of cure enhancers 26, the associated matrix, and/or the associated reinforcements at different locations within structure 12. The characteristics may include, among others, a type, quantity, and/or configuration of reinforcement and/or matrix to be discharged at a particular location within structure 12, and/or an amount, intensity, shape, and/or location of desired curing. Controller 28 may then correlate operation of support 14 (e.g., the location and/or orientation of head 16) and/or the discharge of material from head 16 (a type of material, desired performance of the material, cross-linking requirements of the material, a discharge rate, etc.) with the operation of cure enhancers 26, such that structure 12 is produced in a desired manner.

[0021] Fig. 2 illustrates an exemplary structure 12 manufactured by system 10 to have a self- healing property. Structure 12, of this embodiment, may include multiple types of continuous reinforcements, including at least structural-type reinforcements Rs and healing-type reinforcements R _H . Both types of reinforcements may be at least partially coated with a structural matrix Ms, used together, and in some embodiments, interwoven. The structural-type reinforcements Rs may be generally solid and fabricated from any material having properties that contribute to a desired performance of structure 12. The healing-type reinforcements R _H may be hollow, generally more brittle and/or smaller than the structural-type reinforcements Rs, and at least partially filled (and pressurized in some instances) with a healing matrix M _H . When structure 12 is exposed to extreme conditions (e.g., excessive loading, excessive cycling, temperature extremes, etc.), the healing type of reinforcements R _H may crack, break, or otherwise rupture before or at the same time that mechanical damage occurs within the structural- type reinforcements Rs. The healing matrix MH may be curable upon breaching through the associated healing-type reinforcements RH and being exposed to the environment (e.g., to the surrounding heat, humidity, light, chemical, etc.) surrounding it. The healing matrix MH may be designed to then flow and at least partially surround or coat the reinforcements within the damaged area to shore it up and/or repair the damage.

[0022] It is contemplated that structure 12 may be fabricated to have a different amount or ratio of healing-type reinforcements RH in some areas than in other areas. For example, in an area that is known to damage/wear excessively, a tighter vascular network of healing-type reinforcements RH may be used for greater healing capabilities.

[0023] In some embodiments, the healing-type reinforcements RH may be vein-like and classified into two different types. This first type may have a base matrix stored therein, while the second type may have a catalyst or a hardener stored therein. A volume or quantity ratio of the catalyst matrix to the base matrix within structure 12 may be about (e.g., +/-10% of) 1.8 to 1.9:1. The two types of healing reinforcements RH may be deposited adjacent each other, twisted or woven together, and/or one-inside-the other.

[0024] In one embodiment, both parts of a two-part healing matrix MH may be provided separately inside of a single type of healing reinforcement RH, without allowing the parts to mix. For example, the healing matrix MH may be provided in the form of capsules 90 (e.g., base matrix capsules 90A and/or catalyst or hardener capsules 90B). When exposed to the extreme conditions described above, a desired ratio of base matrix and/or hardener capsules 90 may burst at the damage location, mix, and cure in the surrounding environment. It should be noted that both parts of the matrix may be provided as capsules 90, or only one part as capsules 90 within a surrounding bath of the other part.

[0025] In another embodiment, only one of the base or catalyst components of the healing matrix MH may be located inside of the healing reinforcements R¾ while the other of the base or catalyst components may already be located on an outer surface of the healing reinforcements RH- For example, the healing reinforcements RH may be coated with one of the components (e.g., as a pre-preg material) and also filled with the other component (as a liquid bath or as capsules).

[0026] The healing reinforcements RH may be filled and/or coated with the healing matrix MH at any time during or after the formation of structure 12. For example, the healing reinforcements RH may be pre-filled with the healing matrix MH before entering head 16 to be coated with the structural matrix Ms. Alternatively, the healing matrix MH may be pressurized and forced into the healing reinforcements RH at the same time that the healing reinforcements RH are passing through head 16 and being coated by the structural matrix Ms. Finally, it is contemplated that the hollow tubes of the healing reinforcements RH may be connected to a source (not shown) of pressurized healing matrix MH after structure 12 is formed (e.g., once to fill the healing reinforcements RH or continuously during operational use of structure 12 to maintain a desired pressure).

[0027] Fig. 3 illustrates another exemplary structure 12 manufactured by system 10 to have self-healing properties. Structure 12 of this embodiment may also include multiple types of continuous reinforcements, including at least structural-type reinforcements Rs and healing-type reinforcements RH. Both types of reinforcements may be at least partially coated with a matrix material that is capable of healing. The structural-type reinforcements Rs may be solid and fabricated from any material having properties that contribute to a desired performance of structure 12. In this embodiment, the healing-type reinforcements RH may be configured to selectively activate the healing matrix material, for example after a minimum level of damage has occurred. In one embodiment, the healing-type reinforcements RH include electrodes (or another type of electrical conductors) 92 that are configured to generate heat within the healing matrix when energized. In another embodiment, the healing-type reinforcements RH include fiber optics 94 configured to conduct light into the healing matrix.

[0028] When structure 12 is exposed to extreme conditions, the healing matrix surrounding both the structure and healing types of reinforcements Rs, RH may begin to fail (e.g., deform, degrade, crack, etc.). This may occur before mechanical damage occurs within the structural- type reinforcements Rs. In some embodiments, the fiber optic of healing reinforcement RH 94 may crack, break, or otherwise rupture at the same time that the healing matrix begins to fail.

[0029] In response to the failing of the matrix material, the healing-type reinforcements RH may be selectively energized to direct heat and/or light into the surrounding healing type of matrix material. For example, in response to a detected change in resistance and/or capacitance with electrodes 92 (and/or within an electrically conductive particles or other filler placed inside the matrix) corresponding with strain, an associated structural controller may cause a current to be passed through electrodes 92, thereby generating heat that is conducted into the matrix material. In another example, in response to the cracking, breaking, or rupturing of fiber optics 94, light being conducted through fiber optics 94 may leak out at the failure location and pass into the matrix material. The heat and/or light energy may be sufficient to cause the matrix material to soften and/or liquify temporarily. Thereafter, the heat and/or light energy may be terminated, allowing the matrix material to re-harden and solidify. By this method, the failure (e.g., the deformation or crack) in the matrix material may be healed. It is contemplated that this process may be implemented more than once (e.g., via multi-phase healing), if desired. For example, different sources of heat and/or light may be selectively activated at different times and/or to different degrees, such that repairs may be made multiple times at the same locations.

[0030] The healing matrix of the Fig. 3 embodiment may include polymer networks having cross-linking strands that undergo reversible rearrangement when exposed to the heat and/or light described above. For example, the healing matrix may include Triazolinedione, a covalent- adaptable network, a spatioselective reversible resin, etc. When softened and/or liquified, the matrix material may flow to a lower-pressure area within structure 12 (e.g., into the failed area), causing a relaxation of any existing stress. Thereafter, the material may harden and shore up the failed area.

Industrial Applicability

[0031] The disclosed system and print head may be used to continuously manufacture composite structures having any desired cross-sectional size, shape, length, density, and/or strength. The composite structures may be fabricated from any number of different reinforcements of the same or different types, diameters, shapes, configurations, and consists, each coated with a variety of matrixes. In addition, the fabrication method and composite material may allow for in-situ repairs to be automatically made to the structure as soon as damage occurs. Operation of system 10 will now be described in detail.

[0032] At a start of a manufacturing event, information regarding a desired structure 12 may be loaded into system 10 (e.g., into controller 28 that is responsible for regulating operations of support 14 and/or head 16). This information may include, among other things, a size (e.g., diameter, wall thickness, length, etc.), a contour (e.g., a trajectory), surface features (e.g., ridge size, location, thickness, length; flange size, location, thickness, length; etc.) and finishes, connection geometry (e.g., locations and sizes of couplings, tees, splices, etc.), location-specific matrix stipulations, location-specific reinforcement stipulations, etc. It should be noted that this information may alternatively or additionally be loaded into system 10 at different times and/or continuously during the manufacturing event, if desired. Based on the component information, one or more different reinforcements and/or matrixes may be selectively installed and/or continuously supplied into system 10.

[0033] Installation of the reinforcements may be performed by passing the reinforcements down through matrix reservoir 22, and then threading the reinforcements through nozzle 18. Installation of the matrix may include filling reservoir 22 within head 16 and/or coupling of an extruder or external bath (not shown) to head 16. Head 16 may then be moved by support 14 under the regulation of controller 28 to cause matrix-coated reinforcements to be placed against or on a corresponding stationary anchor point 20. Cure enhancers 26 within head 16 may then be selectively activated to cause hardening of the matrix surrounding the reinforcements, thereby bonding the reinforcements to anchor point 20.

[0034] The component information may then be used to control operation of system 10. For example, the reinforcements may be pulled and/or pushed from nozzle 18 (along with the matrix), while support 14 selectively moves head 16 in a desired manner during curing, such that an axis of the resulting structure 12 follows a desired trajectory (e.g., a free-space, unsupported, 3-D trajectory). Once structure 12 has grown to a desired size and/or length, structure 12 may be disconnected (e.g., severed) from head 16 in any desired manner.

[0035] As described above, some or all of the reinforcements printed into structure 12 may be at least partially filled or otherwise coated with a healing matrix MH. When damage of structure 12 occurs, the healing matrix MH may be activated to shore up the damage site. For example, different parts of the healing matrix MH may flow around the damaged reinforcements, be mixed together and/or exposed to a cure energy, and then harden in place. When this occurs, the healing matrix MH becomes the structure matrix Ms, binding the reinforcements to each other.

[0036] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system, method, material, and print head. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system, method, material, and print head. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.