US20200376758A1 - System for additively manufacturing composite structure - Google Patents

Abstract

An additive manufacturing system is disclosed for use in fabricating a structure. The additive manufacturing system may include a support, and a print head configured to wet a continuous reinforcement with a liquid matrix and discharge the wetted continuous reinforcement. The print head may be operatively connected to and moveable by the support during discharge. The additive manufacturing system may also include a matrix control mechanism configured to selectively adjust an amount of matrix on the continuous reinforcement being discharged from the print head.

Description

RELATED APPLICATION
• This application is based on and claims the benefit of priority from U.S. Provisional Application No. 62/853,610 that was filed on May 28, 2019, the contents of which are expressly incorporated herein by reference.
TECHNICAL FIELD
• The present disclosure relates generally to a manufacturing system and, more particularly, to a system for additively manufacturing composite structures.
BACKGROUND
• 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 head-mounted 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. Pat. No. 9,511,543 that issued to Tyler on Dec. 6, 2016 (“the '543 patent”).
• Although CF3D® provides for increased strength, compared to manufacturing processes that do not utilize continuous fiber reinforcement, improvements can be made to the structure and/or operation of existing systems. For example, Applicant has found that greater control over an amount of the matrix wetting the reinforcement can improve properties (e.g., strength, stiffness, weight, etc.) of the resulting structure. The disclosed additive manufacturing system is uniquely configured to provide these improvements and/or to address other issues of the prior art.
SUMMARY
• In one aspect, the present disclosure is directed to an additive manufacturing system. The additive manufacturing system may include a support, and a print head configured to wet a continuous reinforcement with a liquid matrix and discharge the wetted continuous reinforcement. The print head may be operatively connected to and moveable by the support during discharge. The additive manufacturing system may also include a matrix control mechanism configured to selectively adjust an amount of matrix on the continuous reinforcement being discharged from the print head.
• In another aspect, the present disclosure is directed to a method of additively manufacturing a structure. The method may include wetting a continuous reinforcement with a liquid matrix inside of a print head, and discharging the wetted continuous reinforcement through an outlet of the print head. The method may also include moving the print head during discharging, and selectively adjusting an amount of matrix on the continuous reinforcement being discharged from the print head.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a diagrammatic illustration of an exemplary disclosed additive manufacturing system; and
• FIGS. 2 and 3, are isometric, diagrammatic of exemplary disclosed portions of the system ofFIG. 1.
DETAILED DESCRIPTION
• FIG. 1 illustrates an exemplary system10, which may be used to manufacture acomposite structure12 having any desired shape. System10 may include asupport14 and a deposition head (“head”)16.Head16 may be coupled to and moved bysupport14. In the disclosed embodiment ofFIG. 1,support14 is a robotic arm capable of movinghead16 in multiple directions during fabrication ofstructure12.Support14 may alternatively embody a gantry (e.g., an overhead-bridge or single-post gantry) or a hybrid gantry/arm also capable of movinghead16 in multiple directions during fabrication ofstructure12. Althoughsupport14 is shown as being capable of 6-axis movements, it is contemplated thatsupport14 may be capable of movinghead16 in a different manner (e.g., along and/or around a greater or lesser number of axes). In some embodiments, a drive may mechanically couplehead16 to support14, and include components that cooperate to move portions of and/or supply power or materials tohead16.
• Head16 may be configured to receive or otherwise contain a matrix (shown as M). The matrix may include any types or combinations of materials (e.g., a liquid resin, such as a zero-volatile organic compound resin, a powdered metal, etc.) that are curable. Exemplary resins include thermosets, single- or multi-part epoxy resins, polyester resins, cationic epoxies, acrylated epoxies, urethanes, esters, thermoplastics, photopolymers, polyepoxides, thiols, alkenes, thiol-enes, and more. In one embodiment, the matrix insidehead16 may be pressurized (e.g., positively and/or negatively), for example by an external device (e.g., by an extruder, a pump, etc.—not shown) that is fluidly connected tohead16 via a corresponding conduit (not shown). In another embodiment, however, the pressure may be generated completely inside ofhead16 by a similar type of device. In yet other embodiments, the matrix may be gravity-fed into and/or throughhead16. For example, the matrix may be fed intohead16, and pushed or pulled out ofhead16 along with one or more continuous reinforcements (shown as R). In some instances, the matrix insidehead16 may need to be kept cool and/or dark in order to inhibit premature curing or otherwise obtain a desired rate of curing after discharge. In other instances, the matrix may need to be kept warm and/or illuminated for similar reasons. In either situation,head16 may be specially configured (e.g., insulated, temperature-controlled, shielded, etc.) to provide for these needs.
• The matrix may be used to at least partially coat any number of continuous reinforcements (e.g., separate fibers, tows, rovings, socks, and/or sheets of continuous material) and, together with the reinforcements, make up a portion (e.g., a wall) ofcomposite structure12. The reinforcements may be stored within or otherwise passed throughhead16. When multiple reinforcements are simultaneously used, the reinforcements may be of the same material composition and have the same sizing and cross-sectional shape (e.g., circular, square, rectangular, etc.), or a different material composition with different sizing and/or cross-sectional shapes. The reinforcements may include, for example, carbon fibers, vegetable fibers, wood fibers, mineral fibers, glass fibers, plastic fibers, metallic fibers, optical fibers (e.g., tubes), etc. It should be noted that the term “reinforcement” is meant to encompass both structural and non-structural (e.g., functional) types of continuous materials that are at least partially encased in the matrix discharging fromhead16.
• The reinforcements may be at least partially coated with the matrix while the reinforcements are insidehead16, while the reinforcements are being passed tohead16, and/or while the reinforcements are discharging fromhead16. The matrix, dry (e.g., unimpregnated) reinforcements, and/or reinforcements that are already exposed to the matrix (e.g., pre-impregnated reinforcements) may be transported intohead16 in any manner apparent to one skilled in the art. In some embodiments, a filler material (e.g., chopped fibers, nano particles or tubes, etc.) and/or additives (e.g., thermal initiators, UV initiators, etc.) may be mixed with the matrix before and/or after the matrix coats the continuous reinforcements.
• One or more cure enhancers (e.g., a UV light, an ultrasonic emitter, a laser, a heater, a catalyst dispenser, etc.)18 may be mounted proximate (e.g., within, on, and/or adjacent)head16 and configured to enhance a cure rate and/or quality of the matrix as it is discharged fromhead16.Cure enhancer18 may be controlled to selectively expose portions ofstructure12 to energy (e.g., UV light, electromagnetic radiation, vibrations, heat, a chemical catalyst, etc.) during material discharge and the formation ofstructure12. The energy may trigger a chemical reaction to occur within the matrix, increase a rate of the chemical reaction, sinter the matrix, harden the matrix, solidify the matrix, polymerize the matrix, or otherwise cause the matrix to cure as it discharges fromhead16. The amount of energy produced bycure enhancer18 may be sufficient to cure the matrix beforestructure12 axially grows more than a predetermined length away fromhead16. In one embodiment,structure12 is at least partially (e.g., completely) cured before the axial growth length becomes equal to an external diameter of the matrix-coated reinforcement.
• The matrix and/or reinforcement may be discharged together fromhead16 via any number of different modes of operation. In a first example mode of operation, the matrix and/or reinforcement are extruded (e.g., pushed under pressure and/or mechanical force) fromhead16 ashead16 is moved bysupport14 to create features ofstructure12. In a second example mode of operation, at least the reinforcement is pulled fromhead16, such that a tensile stress is created in the reinforcement during discharge. In this second mode of operation, the matrix may cling to the reinforcement and thereby also be pulled fromhead16 along with the reinforcement, and/or the matrix may be discharged fromhead16 under pressure along with the pulled reinforcement. In the second mode of operation, where the reinforcement is being pulled fromhead16, the resulting tension in the reinforcement may increase a strength of structure12 (e.g., by aligning the reinforcements, inhibiting buckling, equally loading the reinforcements, etc.) after curing of the matrix, while also allowing for a greater length ofunsupported structure12 to have a straighter trajectory. That is, the tension in the reinforcement remaining after curing of the matrix may act against the force of gravity (e.g., directly and/or indirectly by creating moments that oppose gravity) to provide support forstructure12.
• The reinforcement may be pulled fromhead16 as a result ofhead16 being moved bysupport14 away from an anchor point (e.g., a print bed, an existing surface ofstructure12, a fixture, etc.)20. For example, at the start of structure formation, a length of matrix-impregnated reinforcement may be pulled and/or pushed fromhead16, deposited against anchor point20, and at least partially cured, such that the discharged material adheres (or is otherwise coupled) to the anchor point. Thereafter,head16 may be moved away from anchor point20, and the relative movement may cause the reinforcement to be pulled fromhead16. As will be explained in more detail below, the movement of reinforcement throughhead16 may be selectively assisted via one or more internal feed mechanisms, if desired. However, the discharge rate of reinforcement fromhead16 may primarily be the result of relative movement betweenhead16 and anchor point20, such that tension is created within the reinforcement. As discussed above, anchor point20 could be moved away fromhead16 instead of or in addition tohead16 being moved away from anchor point20.
• Head16 may include, among other things, anoutlet26 and amatrix reservoir24 located upstream ofoutlet26. In one example,outlet26 is a single-channel outlet configured to discharge composite material having a generally circular, tubular, or rectangular cross-section. The configuration ofhead16, however, may allowoutlet26 to be swapped out for another outlet that discharges multiple channels of composite material having the same or different shapes (e.g., a flat or sheet-like cross-section, a multi-track cross-section, etc.). Fibers, tubes, and/or other reinforcements may pass through matrix reservoir24 (e.g., through one or more internal wetting mechanisms located inside of reservoir24) and be wetted (e.g., at least partially coated, encased, and/or fully saturated) with matrix prior to discharge.
• Outlet26 may take different forms. In one example, a guide or nozzle may located downstream ofmatrix reservoir24, and a compactor (e.g., a wheel, a shoe, a wiper, etc.) may trail the nozzle (e.g., relative to a normal travel direction ofhead16 during material discharge) and function to compact the material discharging from the nozzle. It is contemplated that either of the nozzle or the compactor may function as a tool center point (TCP) ofhead16, to affix the matrix-wetted reinforcement(s) at a desired location prior to and/or during curing when exposed to energy by cure enhancer(s)18. It is also contemplated that the nozzle may omitted, in some embodiments, andoutlet26 may simply include the compactor located at a discharge opening of any associated wetting mechanism(s).
• One or more controllers22 may be provided and communicatively coupled withsupport14 andhead16. Each controller22 may embody a single processor or multiple processors that are programmed and/or otherwise configured to control an operation of system10. Controller22 may include one or more general or special purpose processors or microprocessors. Controller22 may further include or be associated with a memory for storing data such as, for example, design limits, performance characteristics, operational instructions, tool paths, and corresponding parameters of each component of system10. Various other known circuits may be associated with controller22, including power supply circuitry, signal-conditioning circuitry, solenoid driver circuitry, communication circuitry, and other appropriate circuitry. Moreover, controller22 may be capable of communicating with other components of system10 via wired and/or wireless transmission.
• One or more maps may be stored within the memory of controller22 and used during fabrication ofstructure12. Each of these maps may include a collection of data in the form of lookup tables, graphs, and/or equations. In the disclosed embodiment, the maps may be used by controller22 to determine movements ofhead16 required to produce desired geometry (e.g., size, shape, material composition, performance parameters, and/or contour) ofstructure12, and to regulate operation of cure enhancer(s)18 and/or other related components in coordination with the movements.
• It may be important, in some applications, to control an amount of matrix wetting the reinforcement. For example, some application may require a particular matrix-to-reinforcement ratio. In another example, a greater amount of matrix may be required at a particular location (e.g., along a particular side) of the reinforcement than at another side.FIGS. 2 and 3 illustrate ways to control (e.g., limit and/or steer) the amount of matrix clinging to the reinforcement.
• One way to control an amount of matrix wetting the reinforcement is associated with controlling a tilt angle ofoutlet26 relative to a trajectory of the reinforcement passing therethrough (e.g., an upstream and/or downstream trajectory). For example, it has been determined that a tilt angle α ofoutlet26 relative to the trajectory of the reinforcement (represented by an arrow98) can be selectively adjusted to effect at least one of (e.g., both of) a total amount of matrix being discharged and a location of the matrix relative on the reinforcement. As shown inFIGS. 2 and 3, the closer that the tilt angle α ofoutlet26 is to the discharge direction (e.g., as α approaches zero), the greater the amount of matrix may be discharged together with the reinforcement. The reduction of matrix associated with a greater tilt angle α may be caused by alip100 at a distal end ofoutlet26 pressing against the matrix-wetted reinforcement with a greater pressure. This pressure forces some of the matrix away (e.g., scrapes and/or pushes the matrix away) from the reinforcement at the engagement location. The forced-away matrix may move through the reinforcement towards an opposing side and/or up intooutlet26. In addition, the closer that the tilt angle α ofoutlet26 is to the discharge direction, the more equally dispersed the matrix may be around the reinforcement. For example, asoutlet26 is tilted away from the discharge direction, only an inside portion of the reinforcement may be scrapped bylip100, thereby generating an unequal distribution of the resin (e.g., the portion of thereinforcement engaging lip100 may have less matrix than an opposite side of the reinforcement). In some embodiments, the tilt angle may be regulated to additionally control wetting of the interior of the reinforcement (e.g., by pushing matrix from the outside of the reinforcement towards the center).
• The tilt angle ofoutlet26 may be regulated by controller22 via support14 (referring toFIG. 1). For example,head16 may be tilted bysupport14 relative to structure12, such thatoutlet26 is placed at a desired angle α corresponding to a desired amount and/or distribution of the matrix. Controller22 may selectively command tilting ofsupport14 based on a desired amount and/or distribution of matrix at a particular location (e.g., distance along the reinforcement and/or coordinates on structure12). This command may be determined, at least in part, by referencing the particular location with one or more desired ratios and/or corresponding angles stored in memory.
• FIG. 2 illustrates an additionalmatrix control mechanism102 that may be used to regulate the amount of matrix allowed to cling to the outside of the reinforcement. It is contemplated thatmechanism102 may be used as an exit ofmatrix reservoir24 and/or an entrance ofoutlet26, as desired. It is also contemplated thatmechanism102 may be used together with active tilt-control ofoutlet26 or alone, if desired.
• Mechanism102 may include, among other things, acompliant valve104 that at least partially (e.g., completely) surrounds the reinforcement passing throughhead16, and anactuator106 that functions to selectively deformvalve104. In the disclosed embodiment,actuator106 includes a threaded male base108 located at one side ofvalve104, a threaded female cap110 located at an opposing side ofvalve104, and amotor112 that is operatively connected to one of base108 and cap110. In response to a command from controller22,motor112 may cause the connected base108 and/or cap110 to rotate (e.g., and thread together by a greater amount) and move axially closer together, thereby compressingcompliant valve104. This compression may causevalve104 to deform radially inward and reduce an open cross-sectional area through which the reinforcement may pass. In this manner, an amount of restriction placed on the reinforcement (and thereby the amount of matrix allowed to remain on the reinforcement) may be actively controlled.
• In one example,valve104 has a generally conical shape and a tip of the conical shape pinches down on the reinforcement during rotation of base108 and/or cap110. It is contemplated that a flexible tube (not shown) could pass through thevalve104 and function as a guide for the reinforcement, if desired. In this embodiment, inward deformation ofvalve104 may result in pinching of the tube and subsequently pinching of the reinforcement. It is also contemplated thatvalve104 could have a shape other than conical (e.g., frustoconical, cylindrical, etc.), which may facilitate a more gradual application of pressure (e.g., less of a point-pinch).
• It is contemplated that in addition to or in place ofactuator106, a pneumatic and/or hydraulic bladder could be used (e.g., around and/or inside of resilient valve104) to variably restrict passage of the reinforcement throughmechanism102. For example, the bladder could be selectively filled with a pressurized medium, causing restriction to occur.
INDUSTRIAL APPLICABILITY
• The disclosed system may be used to manufacture composite structures having any desired cross-sectional shape and length. The composite structures may include any number of different fibers of the same or different types and of the same or different diameters, and any number of different matrixes of the same or different makeup. Operation of system10 will now be described in detail.
• At a start of a manufacturing event, information regarding a desiredstructure12 may be loaded into system10 (e.g., into controller22 that is responsible for regulating operations ofsupport14 and/or head16). This information may include, among other things, a size (e.g., diameter, wall thickness, length, etc.), a contour (e.g., a trajectories, surface normal, etc.), surface features (e.g., ridge size, location, thickness, length; flange size, location, thickness, length; etc.), connection geometry (e.g., locations and sizes of couplings, tees, splices, etc.), reinforcement selection, matrix selection, desired matrix ratios and/or distributions, discharge locations, severing locations, curing specifications, compaction specifications, etc. It should be noted that this information may alternatively or additionally be loaded into system10 at different times and/or continuously during the manufacturing event, if desired. Based on the component information, one or more different reinforcements and/or matrix materials may be installed and/or continuously supplied into system10.
• To install the reinforcements, individual fibers, tows, and/or ribbons may be passed throughmatrix reservoir24 and outlet26 (e.g., through features of the nozzle, and under the compactor). In some embodiments, the reinforcements may also need to be connected to a pulling machine (not shown) and/or to a mounting fixture (e.g., to the anchor point). Installation of the matrix material may include filling head16 (e.g., reservoir24) and/or coupling of an extruder (not shown) tohead16.
• The component information may then be used to control operation of system10. For example, the in-situ wetted reinforcements may be pulled and/or pushed fromoutlet26 ofhead16 assupport14 selectively moves (e.g., based on known kinematics ofsupport14 and/or known geometry of structure12), such that the resultingstructure12 is fabricated as desired.
• Operating parameters ofsupport14, cure enhancer(s)18, matrix control mechanism103, and/or other components of system10 may be adjusted in real time during material discharge to provide for desired bonding, strength, tension, geometry, and other characteristics ofstructure12. Oncestructure12 has grown to a desired length,structure12 may be severed from system10.
• It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system. 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.

Claims (20)

What is claimed is:

1 . An additive manufacturing system, comprising:

a support;

a print head configured to wet a continuous reinforcement with a liquid matrix and discharge the wetted continuous reinforcement, the print head being operatively connected to and moveable by the support during discharge; and

a matrix control mechanism configured to selectively adjust an amount of matrix on the continuous reinforcement being discharged from the print head.

2. The additive manufacturing system ofclaim 1, wherein the matrix control mechanism is disposed at least partially around the wetted continuous reinforcement at a location inside of the print head.

3. The additive manufacturing system ofclaim 2, wherein:

the matrix control mechanism includes a compliant valve having an opening through which the wetted continuous reinforcement passes; and

an area of the opening is adjustable.

4. The additive manufacturing system ofclaim 3, wherein the compliant valve further includes an actuator configured to deform the compliant valve and cause the opening to close.

5. The additive manufacturing system ofclaim 4, wherein the actuator includes:

a base located at a first side of the compliant valve;

a cap located at a second side of the compliant valve and configured to engage the base; and

a motor configured to adjust engagement of the cap with the base.

6. The additive manufacturing system ofclaim 2, further including a controller in communication with the support and the matrix control mechanism, the controller being programmed to selectively cause the support to tilt the print head relative to a trajectory of the wetted continuous reinforcement through the print head based on a desired amount of matrix on the continuous reinforcement at discharge.

7. The additive manufacturing system ofclaim 6, wherein the desired amount is a desired ratio of matrix-to-continuous reinforcement.

8. The additive manufacturing system ofclaim 6, wherein the desired amount is a distribution of the liquid matrix on the continuous reinforcement.

9. The additive manufacturing system ofclaim 6, wherein:

the print head includes an outlet through which the wetted continuous reinforcement finally passes during discharge; and

tilting of the print head causes a lip of the outlet to at least one of push matrix from a first side of the continuous reinforcement towards a second side of the continuous reinforcement and scrape matrix away from the continuous reinforcement.

10. The additive manufacturing system ofclaim 1, wherein the matrix control mechanism includes a controller in communication with the support and programmed to selectively cause the support to tilt the print head relative to a trajectory of the wetted continuous reinforcement through the print head based on a desired amount of matrix on the continuous reinforcement at discharge.

11. The additive manufacturing system ofclaim 10, wherein the desired amount is a desired ratio of matrix-to-continuous reinforcement.

12. The additive manufacturing system ofclaim 10, wherein the desired amount is a distribution of the liquid matrix on the continuous reinforcement.

13. The additive manufacturing system ofclaim 10, wherein:

the print head includes an outlet through which the wetted continuous reinforcement finally passes during discharge; and

tilting of the print head causes a lip of the outlet to at least one of push matrix from a first side of the continuous reinforcement towards a second side of the continuous reinforcement and scrape matrix away from the continuous reinforcement.

14. A method of fabricating a composite structure, comprising:

wetting a continuous reinforcement with a liquid matrix inside of a print head;

discharging the wetted continuous reinforcement through an outlet of the print head;

moving the print head during discharging; and

selectively adjusting an amount of matrix on the continuous reinforcement being discharged from the print head.

15. The method ofclaim 14, wherein selectively adjusting the amount of matrix includes adjusting an opening area of the outlet.

16. The method ofclaim 15, wherein adjusting an opening area includes deforming a compliant valve located around the continuous reinforcement.

17. The method ofclaim 14, wherein selectively adjusting the amount of matrix includes tilting the print head relative to a trajectory of the wetted continuous reinforcement through the print head.

18. The method ofclaim 14, wherein selectively adjusting the amount of matrix includes selectively adjusting the amount of matrix based on a desired amount of matrix on the continuous reinforcement at discharge.

19. The method ofclaim 18, wherein the desired amount is a desired ratio of matrix-to-continuous reinforcement.

20. The method ofclaim 18, wherein the desired amount is a distribution of the liquid matrix on the continuous reinforcement.

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