Additive Manufacturing System

A system is disclosed for additively manufacturing a structure. The system may have a support, and a print head operatively connected to and moveable by the support. The print head may include a first module configured to discharge a material, a second module configured to compact the material as it discharges from the first module, and a controller in communication with the second module. The controller may be configured to determine an as-discharged characteristic of the material, and to selectively adjust a force of the second module based on the as-discharged characteristic.

TECHNICAL FIELD

The present disclosure relates generally to a manufacturing system and, more particularly, to a system for additively manufacturing a structure.

BACKGROUND

Continuous fiber 3D printing (a.k.a., CF3D®) involves the use of continuous fibers embedded within material discharging from a moveable print head. A matrix is supplied to the print head and discharged (e.g., extruded and/or pultruded) along with one or more continuous fibers also passing through the same head at the same time. The matrix can be a traditional thermoplastic, a liquid thermoset (e.g., an energy-curable single- or multi-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, a laser, an ultrasonic emitter, a heat source, a catalyst supply, or another energy source) is activated to initiate, enhance, and/or complete curing or hardening of the matrix. This curing/hardening 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.

One application for continuous fibers coated with a matrix is disclosed in U.S. Pat. No. 4,137,354 that issued to Mayes, Jr. on Jan. 30, 1979 (“the '354 patent”). The '354 patent discloses a process for producing a ribbed structure known as an isogrid. The process includes laying filaments (e.g., fibers embedded with a matrix) around knurled metal pins in a repeating pattern to form interconnecting ribs that are attached to a skin. The ribs form an array of equilateral triangles, with the metal pins located at their vertexes. In one embodiment, the filaments are arranged in alternating pairs within each rib—one pair being parallel and one pair crossing. More specifically, a first filament of a first pair crosses from a left side of the rib to a right side and in so doing forms one side leg of each triangle. A second filament of the first pair crosses from the right side to the left side and in so doing forms the other side of each triangle. The two filaments cross at a center of the rib. A third filament of a second pair extends along the left side, while a fourth filament of the second pair extends along the right side. The first pair prevents separation of the rib, while the second pair increases an area moment of inertia of the rib. The structure is heated to cure the matrix after formation of the ribs.

Although the '354 patent may disclose a process that provides an isogrid structure suitable for some applications, the process and/or isogrid may be problematic in other applications. For example, the crossing filaments may create voids within the ribs that lower a performance of the structure. Further, the required use of the metal pins may increase a weight of the structure unnecessarily and/or limit a complexity of the rib structures. Additionally, the need to heat the structure after formation of the isogrid may limit a size of the structure and/or increase a cost of the process.

The disclosed print head and system are directed at addressing one or more of these issues and/or other problems of the prior art.

SUMMARY

In one aspect, this disclosure is directed towards a system for additively manufacturing a structure. The system may include a support, and a print head operatively connected to and moveable by the support. The print head may include a first module configured to discharge a material, a second module configured to compact the material as it discharges from the first module, and a controller in communication with the second module. The controller may be configured to determine an as-discharged characteristic of the material, and to selectively adjust a force of the second module based on the as-discharged characteristic.

In one aspect, this disclosure is directed towards a method of additively manufacturing a structure. The method may include discharging a material from a print head and moving the print head during discharging to form the object. The method may also include pressing a compactor against the material during discharging to compress the material, determining an as-discharged characteristic of the material, and selectively adjusting a force of the compactor toward the material based on the as-discharged characteristic.

DETAILED DESCRIPTION

The term “about” as used herein serves to reasonably encompass or describe minor variations in numerical values measured by instrumental analysis or as a result of sample handling. Such minor variations may be considered to be “within engineering tolerances” and in the order of plus or minus 0% to 10%, plus or minus 0% to 5%, or plus or minus 0% to 1% of the numerical values.

FIG.1illustrates an exemplary system10, which may be used to manufacture a composite structure12having any desired shape, size, configuration, and/or material composition. System10may include at least a support14and a head16. Head16may be coupled to and moveable by support14during discharge of a composite material (shown as C). In the disclosed embodiment ofFIG.1, support14is a robotic arm capable of moving head16in multiple directions during fabrication of structure12. Support14may alternatively embody a gantry (e.g., a floor gantry, an overhead or bridge gantry, a single-post gantry, etc.) or a hybrid gantry/arm also capable of moving head16in multiple directions during fabrication of structure12. Although support14is shown as being capable of moving head16about multiple (e.g., six) axes, it is contemplated that another type of support14capable of moving head16(and/or other tooling relative to head16) in the same or a different manner could also be utilized. In some embodiments, a drive or coupler18may mechanically join head16to support14and include components that cooperate to move portions of and/or supply power and/or materials to head16.

Head16may be configured to receive or otherwise contain a matrix (shown as M inFIG.2) that, together with a continuous reinforcement (shown as R inFIG.2), make up at least a portion of the composite material C discharging from head16. The matrix may include any type of material that is curable and/or hardenable (e.g., a liquid resin, such as a zero-volatile organic compound resin, a powdered metal, etc.). 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 inside head16may be pressurized, for example by an external device (e.g., by an extruder or another type of pump—not shown) that is fluidly connected to head16via a corresponding conduit (not shown). In another embodiment, however, the pressure may be generated completely inside of head16by a similar type of device. In yet other embodiments, the matrix may be gravity-fed into and/or through head16. For example, the matrix may be fed into head16and pushed or pulled out of head16along with one or more continuous reinforcements. In some instances, the matrix inside head16may benefit from being kept cool, dark, and/or pressurized (e.g., 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 light for similar reasons. In either situation, head16may be specially configured (e.g., insulated, temperature-controlled, shielded, pressurized, etc.) to provide for these needs.

The matrix may be used to coat any number of continuous reinforcements (e.g., separate fibers, tows, rovings, ribbons, socks, sheets and/or tapes of continuous material) and, together with the reinforcements, make up a portion (e.g., a wall, a floor, a ceiling, infill, support, etc.) of composite structure12. The reinforcements may be stored within (e.g., on one or more separate internal creels19) or otherwise passed through head16(e.g., fed from one or more external spools—not shown). 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, 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 are at least partially encased in the matrix discharging from head16.

The reinforcements may be exposed to (e.g., at least partially coated with) the matrix while the reinforcements are inside head16, while the reinforcements are being passed to head16, and/or while the reinforcements are discharging from head16. The matrix, dry reinforcements, and/or reinforcements that are already exposed to the matrix (e.g., pre-impregnated reinforcements) may be transported into head16in any manner apparent to one skilled in the art.

In some embodiments, a filler material may be mixed with the matrix before and/or after the matrix coats the continuous reinforcements. The filler material may be selected to adjust a characteristic of the matrix and/or resulting composite material.

As will be explained in more detail below, one or more enhancers (e.g., a UV light, an ultrasonic emitter, a laser, a heater, a catalyst dispenser, a fan, and/or another source of energy) may be mounted proximate (e.g., within, on, or adjacent) head16and configured to enhance a cure/hardening rate and/or quality of the matrix as it discharges from head16. The enhancer(s) may be controlled to selectively expose portions of structure12to the energy (e.g., to UV light, electromagnetic radiation, vibrations, heat, a chemical catalyst, etc.) during material discharge and the formation of structure12. 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, or otherwise cause the matrix to cure as it discharges from head16. The amount of energy produced by the enhancer(s) may be sufficient to cure/harden the matrix before structure12axially grows more than a predetermined length away from head16. In one embodiment, structure12is at least partially cured/hardened before the axial growth length becomes equal to an external diameter of the composite material C.

The matrix, filler, and/or reinforcement may be discharged from head16via one or more different modes of operation. In a first exemplary mode of operation, the matrix and/or reinforcement are extruded (e.g., pushed under pressure and/or mechanical force) from head16as head16is moved by support14to create the 3-dimensional trajectory within a longitudinal axis of the discharging material. In a second exemplary mode of operation, at least the reinforcement is pulled from head16, 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 head16along with the reinforcement, and/or the matrix may be discharged from head16under pressure along with the pulled reinforcement. In the second mode of operation, where the matrix is being pulled from head16with the reinforcement, the resulting tension in the reinforcement may increase a strength of structure12(e.g., by aligning the reinforcements, inhibiting buckling, distributing loading, etc.), while also allowing for a greater length of unsupported structure12to 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 for structure12.

The reinforcement may be pulled from head16as a result of head16being moved by support14away from an anchor (e.g., a print bed, a table, a floor, a wall, a surface of structure12, etc.). For example, at the start of structure formation, a length of matrix-impregnated reinforcement may be pulled and/or pushed from head16, deposited onto the anchor, and at least partially cured, such that the discharged material adheres (or is otherwise coupled) to the anchor. Thereafter, head16may be moved away from the anchor (e.g., via controlled regulation of support14), and the relative movement may cause the reinforcement to be pulled from head16. It should be noted that the movement of reinforcement through head16could be assisted (e.g., via one or more internal feed mechanisms), if desired. However, the discharge rate of reinforcement from head16may primarily be the result of relative movement between head16and the anchor, such that tension is created within the reinforcement. It is contemplated that the anchor could be moved away from head16instead of or in addition to head16being moved away from the anchor.

A controller20may be provided and communicatively coupled with support14, head16, and any number of the cure enhancer(s). Each controller20may embody a single processor or multiple processors that are specially programmed or otherwise configured via software and/or hardware to control an operation of system10. Controller20may 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 controller20, including power supply circuitry, signal-conditioning circuitry, solenoid driver circuitry, communication circuitry, and other appropriate circuitry. Moreover, controller20may be capable of communicating with other components of system10via wired and/or wireless transmission.

One or more maps may be stored in the memory of controller20and used by controller20during fabrication of structure12. Each of these maps may include a collection of data in the form of lookup tables, graphs, and/or equations. In the disclosed embodiment, controller20may be specially programmed to reference the maps and determine movements of head16required to produce the desired size, shape, and/or contour of structure12, and to responsively coordinate operation of support14, operation of the cure enhancer(s), and other components of head16.

An exemplary head16is disclosed in greater detail inFIG.2. As shown in this figure, any number of components of head16may be mounted to an upper plate24and/or a lower plate26. For example, a reinforcement supply module44and/or a matrix supply module46may be operatively connected to upper plate24, while a tensioning module48, a clamping module50, a wetting module52, a cutting module56, and/or a compacting/curing module58may be operatively mounted to lower plate(s)26. It should be noted that other modules and/or mounting arrangements may also be possible. As will be described in more detail below, the reinforcement may pay out from module44, pass through and be tension-regulated by module48, and be wetted with matrix (e.g., as supplied by module46) during discharge through module52. After discharge, the matrix-wetted reinforcement may be selectively severed via module56(e.g., while being clamped and held stationary by module50) and thereafter compacted and/or cured/hardened by module58.

In some embodiments, the mounting arrangement may also include an enclosure54configured to enclose and protect particular components of head16from inadvertent exposure to light, matrix, solvents, dust, and/or other environmental conditions that could reduce usage and/or a lifespan of these components. These components may include, among others, any number of conduits, valves, actuators, chillers, heaters, manifolds, wiring harnesses, sensors, drivers, controllers, input devices (e.g., buttons, switches, etc.), output devices (e.g., lights, speakers, etc.) and other similar components.

As shown inFIG.3, wetting module52may include an elongated (e.g., elongated in a direction of reinforcement motion through module52) base152having an inlet end154and an outlet end156, and a lid (not shown) that is pivotally or otherwise removably connected to base152via one or more (e.g., two) hinges160. A seal (not shown) may be disposed between base152and the lid, and any number of mechanisms (latches)162may connect the lid to base152at one or more locations (e.g., spaced apart at a side opposite hinges160). The lid may be configured to pivot or otherwise be moved from a closed or operational position to an open or servicing (e.g., threading/cleaning) position.

Base152and/or the lid may include one or more features for mounting module52to the rest of head16. These features may include, for example, bosses, holes, recesses, threaded bores and/or studs, dowels, etc. The number and locations of the mounting features may be selected based on a weight, size, material, and/or balance of module52.

As shown inFIG.3, base152may be configured to internally receive any number of nozzles168between inlet end154and outlet end156. In the disclosed embodiment, four nozzles168A,168B,168C and168D are disposed in series along a trajectory of the reinforcement passing through module52. It is contemplated, however, that a different number (e.g., a greater number or a lesser number) of nozzles168may be utilized, as desired. As will be explained in more detail below, nozzles168may function to limit an amount of matrix passing through module52with the reinforcement and/or to shape the reinforcement. In most instances, at least one entry nozzle168A and at least one exit nozzle168D should be employed to reduce undesired passage of matrix out of module52in upstream and downstream directions, respectively.

Nozzles168may divide the enclosure of module52into one or more chambers or sections. In the disclosed embodiment, nozzles168divide the enclosure into a main wetting chamber170(e.g., located between nozzles168B and168C), an upstream overflow chamber172(e.g., located between nozzles168A and168B), and a downstream overflow chamber174(e.g., located between nozzles168C and168D). As will be explained in more detail below, chamber170may be a primary location at which the reinforcement is intended to be wetted with matrix. While the reinforcement may additionally be wetted within each of the overflow chambers172and174, these overflow chambers172and174may primarily be intended as locations where excess resin can be collected and removed from module52. The collection and removal of excess resin from overflow chambers172and174may help to inhibit undesired leakage from module52at ends154,156.

Nozzles168may have different sizes and/or configurations that promote fiber wetting and resin retention under pressure. For example, nozzles168A,168B, and168C may be slightly larger than168D (e.g., have a larger internal cross-sectional area), in some applications. This may reduce tension on the reinforcement during pulling through main wetting chamber170, yet still ensure precise control over a fiber-volume-fraction (i.e., a ratio of fiber-to-matrix known as FVF) in the material discharging from module52. In another example, the nozzle(s)168located upstream of chamber170may have a shape that substantially matches an as-fabricated shape of the reinforcement (e.g., rectangular), while the nozzles168located downstream of chamber170may have a shape (e.g., circular or elliptical) designed to achieve a desired characteristic (enhanced steering and/or placement accuracy). It should be noted that circular or elliptical nozzles169may also be simpler and/or less expensive to manufacture with higher tolerances.

As shown inFIG.3, matrix may be pumped by module46into chamber170via an inlet port214. In some embodiments, module46may be selectively activated to pump matrix into chamber170based on a pressure detected by a sensor220in communication with chamber170. For example, when a pressure within chamber170drops below a low threshold pressure (e.g., about 0.25-0.35 psi or about 0.29 psi), controller20may generate a signal activating pumping of module46. Likewise, when a high threshold pressure (e.g., about 0.85-0.9 psi or about 0.87 psi) is reached within chamber170, controller20may stop sending the signal to module46. Pressure sensor220may be in communication with the matrix inside chamber170via a port219and be used to generate the above-described pressure signals.

Some of the matrix pumped into chamber170, due to a pressure differential between chamber170and chambers172and174, may leak upstream into chamber172(e.g., through and/or around nozzle168B) and/or downstream into chamber174(e.g., through and/or around nozzle168C). In addition, depending on an orientation of head16, gravity may force matrix from chamber170into chamber172and/or174. This excess matrix, if unaccounted for, may continue to leak in the same manner upstream and/or downstream through or around nozzles168A and/or168D and be lost into the environment.

To avoid waste, system contamination, and/or environmental spillage of the matrix, the excess matrix may be drained from chambers172,174via one or more outlet ports216. A low-pressure source224may connect with ports216to remove the excess matrix collected within chambers172,174. In some embodiments, the removed excess resin may be recirculated back into module52via one or more inlet ports218. In other embodiments, the removed excess resin may be discarded.

In some applications, a temperature of module52(e.g., of the matrix inside of module52) may be regulated for enhanced wetting and/or curing control. In these applications, a heater (e.g., a ceramic heating cartridge)182and a temperature sensor (e.g., a Resistance Temperature Detector—RTD)184may be utilized and placed at any desired location. In the disclosed example, heater182is located upstream of sensor184, such that the matrix is heated before passing by sensor184. The matrix may be heated to about 20-80° C. (e.g., 20-60° C.), depending on the application, the reinforcement being used, the matrix being used, and desired curing conditions. In general, a higher viscosity resin, a larger tow, and/or an opaquer reinforcement may require higher temperatures within module52. However, care should be taken to avoid exceeding a cure-triggering threshold inside of module52.

As discussed above, a cross-sectional area of nozzle168(particularly nozzle168D) may affect the FVF of the composite material C. For example, for a given cross-sectional area A of nozzle168D and a known cross-sectional area a of the reinforcement R, the FVF should theoretically be calculated as a/A. In demanding applications, the FVF could be 60% or higher, meaning that the area a consumes about 60% of the area A, allowing the remaining 40% of the area A to be consumed by the matrix M flowing therethrough.

However, it has been found that a pressure differential across nozzle168D may affect the FVF of the composite material discharging therethrough. For example, for the same cross-sectional areas a and A, a higher-pressure differential can result in a lower FVF. Similarly, for the same cross-sectional areas a and A, a lower-pressure differential can result in a higher FVF. This is because the higher-pressures cause the matrix to flow through the area (A-a) at a rate faster than the rate at which the reinforcements are traveling therethrough, thereby enriching the composite material with a greater amount of matrix (and inversely decreasing the fraction of reinforcement in the material). The opposite is also true, in regard to lower pressures.

The pressure differential across nozzle168D may be selectively modulated by controller20in multiple ways to adjust the FVF in real time (i.e., on the fly). For example, module46may be controlled to increase or decrease a pressure of the matrix supplied into primary chamber170(e.g., by supplying matrix at a faster or slower rate and/or directly adjusting a pressure of the matrix generated inside module46). This change in pressure may result in more (e.g., when the pressure is higher) or less (e.g., when the pressure is lower) material passing through nozzle168C into downstream overflow chamber174and a subsequent change in pressure at the upstream side of nozzle168D. Alternatively or additionally, source224may be regulated to remove the excess matrix from downstream overflow chamber174at a slower or faster rate, thereby raising or lowering the pressure at the upstream side of nozzle168D.

As shown inFIGS.4and5, modules56and58may be configured to move together relative to module52and the rest of head16. For example, a rail264may be affixed to lower plate26and oriented vertically relative to the perspective ofFIGS.4and5. In one embodiment, an axis of rail264may be generally parallel (e.g., collinear) with an axis of coupler18and/or a final rotation joint of support14(referring toFIG.1). Each of modules56and58may be connected to a common sled or carriage266that is configured to roll and/or slide along rail264in the vertical direction, and one or more (e.g., two) actuators268may be connected to translate carriage266and modules56,58together along rail264. In one embodiment, actuator(s)268are directly connected to a first end of carriage266, and modules56and58are separately connected to an opposing end of carriage266(e.g., module58may connect to carriage266via a bracket262). In this embodiment, operation of the dual actuators268are in opposition to each other (i.e., one functioning to exert extension forces and the other functioning to exert retraction forces) to provide for enhanced control over carriage motion. It is contemplated that actuators268may be mounted at the same side of carriage266(e.g., to reduce a moment acting on carriage266) or at opposing sides, as desired.

Actuator(s)268may be any type of actuators known in the art. In the disclosed example, actuators268are double-acting pneumatic cylinders. It is contemplated, however, that actuators268may or may not be cylinders, and/or actuated hydraulically, electronically, mechanically, and/or in any other manner.

During extension and retraction of actuator268, modules56and58may be moved away from or toward the material being extruded by head16. In some applications, it may be useful to know a location of modules56and/or58during this motion. For this reason, a sensor270may be positioned (e.g., mounted to plate26or actuator268) to detect the location. In the disclosed embodiment, sensor270is associated with actuator268and configured to detect a position of a portion of actuator268.

Module56may also be configured to selectively move relative to module58. For example, an additional actuator272may extend between carriage266and module56and be configured to selectively extend module56further in the axial direction of rail264.

An exemplary module58is illustrated inFIG.5. As shown in this figure, module58may be broken down into multiple (e.g., two, three, or more) subassemblies. These subassemblies may include a curing assembly320and a conditioning assembly322that leads curing assembly320. As will be explained in more detail below, each of these subassemblies may be connected to bracket262(e.g., via one or more locating pins and/or other fasteners) to form module58and move together to wipe, slide, and/or roller over; compact; and/or cure the material discharging from module52.

As shown inFIG.5, curing assembly320may include, among other things, an adapter324configured to hold at least two (e.g., two pairs of) oppositely arranged energy transmitters326. In the disclosed embodiment, transmitters326are light pipes that extend from one or more remote energy sources (e.g., light sources such as lasers, UV lights, etc.—not shown) to locations near the composite material being compacted by subassembly322. Transmitters326may be held within corresponding bores of adapter324via resilient members (e.g., o-rings) that contract during installation and expand into corresponding annular channels within the bores upon full insertion.

Conditioning assembly322may include one or more rolling compactors336and/or one or more sliding wipers338that are rotationally and/or pivotally mounted to compactor(s)336. In the disclosed embodiment, a single wiper338trails behind a single compactor336relative to a normal travel direction of head16. It should be noted, however, that this relationship could be reversed, one of these components may be deleted, one or both of these components may be duplicated, etc., if desired. Wiper338may be mounted to pivot about compactor336and is biased (e.g., via a spring—not shown) toward the material being discharged from head16. An outer surface of compactor336may be fabricated from a relatively harder and stiffer material than an outer surface of wiper338, allowing for compactor336to provide a primary or larger compacting force than wiper338and for wiper338to provide a primary wiping function of matrix function. This relationship could be reversed or annulled in some applications, if desired. It should be noted, however, that wiper338may still provide some compaction to the material passing thereby, and that compactor336may still provide some smoothing of the matrix, if desired. Wiper338, in addition to providing the matrix smoothing function and/or some compaction, may also shield the matrix from cure energy passing from transmitters326to the material being compacted/smoothed.

It should be noted that the described motion of wiper338could be different, if desired. For example, instead of a generally pivoting motion of wiper338about compactor336, wiper338could have a linear motion in a directional generally orthogonal to the underlying material, if desired. In this embodiment, wiper338may still be biased (e.g., via a spring—not shown) toward the material. It may also be possible for wiper338to have little or no motion, and for the biasing effect to be produced solely by a compressible material (e.g., foam or rubber) of wiper338.

The amount of compaction force applied by module58to the material discharging from module52may be dependent on several factors. These factors may include, for example, a resultant force F generated by actuators268in the material direction (i.e., downward direction shown inFIGS.4and5) that acts through compactor336on the material, and also an area A of the material being compacted by compactor336. For example, the compaction pressure may be calculated as the resultant force divided by the area (F/A).

In some applications, actuator(s)268may be actively controlled in real time to ensure that a desired and relatively constant (i.e., constant within engineering tolerances) pressure is applied to the material, regardless of any changes in the area A. For example, as the area A increases, actuator(s)268may be regulated to increase the resultant force F and thereby provide a constant compaction pressure to the material. Similarly, as the A decreases, actuator(s)268may be regulated to decrease the resultant force F.

The area A may change, for example, based on a change in reinforcement from a first reinforcement having a first tow width to a second reinforcement have a second tow width that is larger or smaller than the first tow width. In another example, the area A may change depending on whether the discharging material is isolated from other material and the only material being compacted or if the discharging material is being discharged adjacent previously discharged tows that will also be compacted together with the now-discharging material. Controller20may be configured to directly detect (e.g., via a sensor—not shown), calculate (e.g., based on a virtual model of structure12and/or a current path being discharged), and/or look up in the tables stored in memory, the area A and correspondingly adjust the resultant force F generated by actuators268, such that the discharging material is consistently experiencing the same level of compaction pressure.

For example, during discharge of a first path of material making up a portion of structure12, the area A may be small. In this instance, the force F may likewise be small (seeFIG.6—left most track), such that an actual pressure acting on the material is a desired pressure. During discharging of a second path of material adjacent the first path of material, compactor336may be axially long enough to span across both the first and second paths. Accordingly, the area of material being compacted by compactor336may be larger (e.g., doubled). In this situation, in order to achieve the same level of compaction pressure as originally applied to only the first path of material, the force generated by actuator(s)268may need to double. A further increase may be needed when subsequently discharging a third path of material adjacent the second, assuming that compactor336can simultaneously span across all three paths. As mentioned above, the area A may be detected (e.g., via a width sensor arranged in an axial direction of compactor336), assumed based on a number of paths having been generated and counted thus far, determined based on a virtual model of structure12and a known progress in fabrication, looked up in the table stored in memory, and/or determined in another manner known in the art.

In some applications, a spacing between adjacent discharge locations may be adjusted together with the compaction force (or alone for a given compaction force) to selectively adjust a height and/or a width of the tow resulting from compaction. For example, as shown inFIG.6, for a given dimension (e.g., diameter) of the tow discharging from module52(referring toFIGS.2and5) and for a given spacing d between adjacent tows (e.g., between lateral centers of adjacent as-discharged tows), compactor336of module58may compact the tows to a height H and a width w. As shown inFIG.7, for the same given diameter of the tow (and same material properties) and a greater spacing D between adjacent tows, compactor336may compact the tows using the same force to have a smaller height h and a greater width W. It should be noted that the relationship between the spacing, the height, and/or the width may not be linear, as the compaction force may result in a changing pressure as the resulting width (and corresponding compaction area) changes away from the as-discharged width.

Limits may be placed on acceptable tow spacing used to drive layer height and/or width. For example, a maximum spacing limit may be implemented that prevents gapping between adjacent tows after compaction. Similarly, a minimum spacing limit may be implemented that prevents significant overlapping between adjacent tows.

In some applications, a combination of force control and spacing control may be implemented to adjust layer height, path width, and/or other properties of individual paths and/or layers. For example, during discharge of a first tow, force alone may be used to set an initial desired height for the layer encompassing the first tow. Thereafter, the force may have less of an effect on layer height, whereas tow spacing between additional paths may be more influential.

FIG.8illustrates an exemplary structure12, which can be manufactured by system10(referring toFIG.1). In this embodiment, structure12is a partially hollow component known as a grid (e.g., an isogrid) or a structural panel (e.g., a sandwich-structure-panel or SSP). In general, the grid or panel is a thin structure (i.e., a structure having a height in a direction normal to a primary surface, wherein the height dimension is less than 50%, less than 25%, less than 10%, less than 5%, or less than 1% of the shorter of a length or a width dimension of the primary surface). As an isogrid or SSP, structure12may be formed from one or more skins400and any number of stiffening ribs402attached to and/or disposed between (e.g., sandwiched between) opposing skins400. In some embodiments, a spacing between ribs402may be left empty, while in other embodiments, the spacing may be at least partially filled with a low-density material (e.g., foam). Ribs402impart rigidity to panel(s)400, while the partially hollow nature of an isogrid or SSP (e.g., the empty or low-density spacing between ribs402) makes these components lightweight. Foam (or another low-density filler) within the space between ribs402may allow for improved support of panel(s)400, such that sagging does not occur within the space during fabrication and/or so that free-spacing printing is reduced. The foam may also improve an insulating (e.g., thermally and/or acoustically insulating) factor of structure12.

Skin400, while shown inFIG.8as generally planar, may have any desired (e.g., three-dimensional) contour. For example, each skin400may have a convex shape, a concave shape, a cylindrical shape, and/or a complex shape (e.g., a combination of multiple different planar and/or nonplanar shapes). The nonplanar contours may be achieved, for example, by printing skin400at least partially into free-space (e.g., without an intervening support, over or between ends of a contoured rib pattern, etc.) and/or into a corresponding mold. In addition, when adjacent skins400of the same structure12are spaced apart from each other by conjoined ribs402, skins400may be parallel/mirror images of each other or nonparallel and different, as desired. Each skin400may be a continuous or discontinuous surface (e.g., a surface with steps between heights, openings, etc.).

Ribs402may be bonded to skin(s)400and have a height that extends in a direction normal to the corresponding surface(s) of skin(s)400. The height of the extension may be generally consistent across an area of the panel(s)400or may be variable to accommodate non-planar and/or non-mirrored skin(s)400. It should be noted that, while the exemplary structure12illustrated inFIG.8includes ribs402arranged in a traditional triangular pattern (e.g., made of identical isosceles triangles connected to each other at their vertices) of an isogrid, ribs402could alternatively be arranged in a honeycomb pattern, a rectangular pattern, a cylindrical pattern, an elliptical pattern, another symmetric or non-symmetric geometric pattern, and/or a repeating or non-repeating combination of these closed-cell patterns, as desired. It is also contemplated that the pattern of ribs402may not be formed solely from closed cells, in some embodiments. That is, the pattern of ribs402could include some closed cells in combination with non-cellular formations (e.g., sinusoidal extensions, disconnected linear extensions, etc.) or only non-cellular formations, if desired.

In the example ofFIG.8, ribs402may have side walls that are perpendicular to the skin(s)400to which they are attached (e.g., having a neutral draft). In addition, a cross-section of ribs402(including their intersections—I) may remain substantially identical throughout the height direction. It should be noted, however, that other configurations may also be possible.

For example,FIG.9illustrates example ribs402having side walls that are not perpendicular (e.g., negative or positive draft). Similarly, structure12ofFIG.9has a cross-section that varies in relation to height away from skin400. This geometry and/or physical capability may improve strength of structure12and/or design flexibility.

As discussed above, ribs402may be made up of any combination of repeating or non-repeating geometric patterns. Depending on the pattern selected, each intersection I within the pattern may have a different number of legs extending therefrom. In the example of an isogrid having a repeating pattern of isosceles triangles (shown inFIG.8), each intersection I in the pattern is formed by 6 different triangles. In order to inhibit the intersections from building up to a greater thickness than the rest of ribs402, the legs of the 6 triangles that meet at each intersection should have a pattern that varies between layers.

In a first example shown inFIG.10, the legs of all of the triangles within every layer avoids a center C of the intersection I. As a result, a generally cylindrical void is created at the center C that can be filled with matrix and/or hardware (a boss, a fastener, a pin, a threaded insert, etc.) or left empty. The matrix may be used to transfer loads between the different legs, while the hardware may be used to connect structure12to another object. An opening at the center C may be used as a duct to transport materials through structure12. The legs of the triangles avoid the center C of the intersection I by deviating either to the left or right of the void. For example, the leg of a first triangle within a first layer408aof ribs402may deviate to the left, while the same leg of the same triangle with a second and overlapping layer408bmay deviate to the right. In this manner, although deposition of two layers of composite material along all of ribs402may result in 12 leg overlaps at each intersection I, the overlap locations may be distributed around the void and result in only a buildup at each overlap location that is equal in height to only two layers.

It should be noted that the generally cylindrical void at the center C in the embodiment ofFIG.10may be omitted, if desired. For example, the legs may lie immediately adjacent each other at the center (e.g., still deviating to one side of a center point, but with no space therebetween), such that no void exists.

While the configuration ofFIG.10may be fully symmetrical about the center C of the intersection I and inhibit undesired buildup, the configuration may also result in excessive porosity. That is, with the legs of each triangle being separated at the intersection I by the diameter of the void, triangularly shaped pores p may extend away from the void along the axial direction of each leg. This porosity, even when filled with excess matrix, may reduce a strength of structure12. In addition, the excess matrix may increase a weight of structure12.

FIG.11illustrates an alternative design, in which all overlapping legs within different layers of the same triangle deviate to one side of the center C (e.g., to the right). In this configuration, overlapping legs deviate to the same side by differing amounts, such that the legs are adjacent and do not lie directly on top of each other around the intersection I. The amount of deviation between corresponding legs of the same triangle that are within overlapping layers is only enough to place the legs next to each other without significant (e.g., without any) gapping therebetween. As can be seen inFIG.11, this arrangement may allow for elimination of the center void and/or of triangular spaced pores between the legs. This may increase a strength and/or reduce a weight of structure12.

It should be noted that, while symmetrical intersections I (e.g., intersections having substantially identical legs extending from a center, with equal angles therebetween) have been illustrated inFIGS.8-11and described above, the intersections need not be symmetrical. For example, as shown inFIG.18, the intersections I have different numbers of ribs402extending therefrom and the angles between ribs402are different. Ribs402can be straight or curved and lie within a plane or extend into three dimensions. Ribs402may also have different thicknesses and/or heights within the same structure12.

An isogrid and/or SSP-type structure12may be fabricated using system10in multiple different ways. For example, a first skin400of structure12may be fabricated (e.g., discharged from head16against a flat or contoured print surface, compacted, and at least partially cured) first; ribs402may then be fabricated against the first skin400; and then, in some applications, an additional second skin400may be fabricated against ribs402at a side opposite the first skin400(e.g., by extending through free-space over the extending portions of ribs402). Alternatively, ribs402may be fabricated first, followed by fabrication of the first and/or second skins400. In some applications, curing of the different parts of structure12may be only partially completed (e.g., left in a green or semi-green state that holds its shape), such that the entire structure12is thereafter through-cured together as a monolithic structure. As will be explained in more detail below, in some applications, only portions of a particular skin400may be fabricated, followed by portions of ribs402, and then additional portions of the same skin400. It is contemplated that the materials used to fabricate panel(s)400may be the same or different from the materials used to fabricate ribs402.

In one application, formation of a skin400within structure12may include discharge of multiple adjacent paths404of composite material (i.e., continuous reinforcement(s) R at least partially coated with matrix M) within one or more overlapping layers406. For example,FIG.12, shows a single skin400fabricated from first and second overlapping layers406aand406b, each consisting of multiple adjacent paths404of composite material. It should be noted that skin400may include any number of layers406, and that the paths404within each of the layers406may have any trajectory and be the same or different. Paths404may be immediately adjacent to each other (i.e., without significant spacing therebetween) or include intentional gaps therebetween, as desired. In some embodiments, that number of layers406and/or trajectories of paths404within the respective layers may be selected such that skin400has general consistent performance parameters (e.g., isotropic or quasi-isotropic stiffness, strength, etc.) in each direction within skin400. In other embodiments, however, the number of layers406and/or the trajectories of paths404within layers406may be selected to provide anisotropic performance parameters within skin400.

As shown inFIG.13, after formation of skin400, any number of layers (e.g., a first layer408aand a second layer408b) of composite material may be deposited against an exposed surface of skin400to form ribs402, along borders of the associated geometric pattern(s). It is contemplated that each layer408of ribs402may be the same (e.g., lie partially or entirely on top of each other) or different (e.g., cross over, but not lie directly on top of each other). After a desired number of layers408have been deposited, formation of structure12as a grid (isotropic or anisotropic grid) may be complete. However, if a sandwich type panel is desired, the same or a similar process depicted inFIG.12may be repeated to form a substantially identical or different second skin400at a side of ribs402opposite the first panel. As discussed above, it is contemplated that ribs402could alternatively be formed first, after which one or two skins400could be formed at the sides of ribs402, if desired.

It is contemplated that only a portion (e.g., only one or more layers406—referring toFIG.14) of skin400may be formed prior to formation of some or all (e.g., one or more layers408) of ribs402, followed by additional formation (e.g., completion) of skin400, in some embodiments. For example, after formation of at least one layer (e.g., a base layer406a) of skin400and at least one layer408of ribs402on top of base layer406a, an additional layer (e.g., layer406b) of skin400may be formed. In the embodiment ofFIG.14, the additional layer406bof skin400may be formed from the open-side of structure12and placed immediately adjacent other layers406of the same skin400. For example, the additional layer406bmay be discharged into the empty space(s) within and/or between the geometric shapes of ribs402(e.g., inside of each triangle) and against the previously discharged base layer406a. In the example ofFIG.14, the additional layer406bmay be interrupted by ribs402, such that multiple separate discontinuous sections410make up layer406b. In this example, each section410may be the same (e.g., have a same number/spacing/trajectories of paths404) or different to provide different performance characteristics across an area of skin400. In other words, skin400may have different thicknesses (e.g., thinner) adjacent and (e.g., thicker) between ribs402.

In another example shown only in cross-section inFIG.15, the additional layer(s)406bmay be continuous and extend over at least a portion (e.g., one or more layers408) of ribs402. In this example, the additional layer(s)406may function as intermediate locking mechanisms to help bond ribs402to skin400.

As mentioned above, ribs402may have geometry that varies in the height direction. For example, a particular rib402may have a base or “noodle region”500adjacent skin400that is wider than a distal portion away from skin400. The cross-section of rib402may gradually taper or step inward from region500toward the distal portion, as desired. In some embodiments having opposing skins400separated by ribs402, one or more of ribs402may include dual noodle regions (e.g., one region500located at each skin400) separated from each other by a thinner middle region. In addition, the geometry of a particular rib402may vary along a length of the rib. For example, the noodle region(s) and/or middle region may become thicker (e.g., wider in a direction parallel with the surface of skin400) at intersections I to provide a greater load-carrying capacity.

In an additional example illustrated inFIG.16, only particular path(s)406b-1of particular layer(s)406bmay extend over some portions or all of particular layer(s)408of rib402, while the remaining path(s)406b-2of the same layer(s)406bmay be truncated at ribs402. In a final example illustrated inFIG.17, one or more paths406of one or more layers may extend into and form a portion or all of ribs408. This integral formation may increase a bond strength between skin400and ribs402.

It is contemplated that the reinforcements utilized for each portion of skin400may be selected to provide for a particular functional characteristic corresponding to its use. For example, the reinforcement used as the outer layer of skin400may be fabricated from a first material (e.g., carbon) and provide a first functional characteristic (e.g., UV resistance); the reinforcement used as a locking layer may be fabricated from a second material (e.g., SiC) and provide a second functional characteristic (e.g., hardness); a third reinforcement used as the inner layer of may be fabricated from a third material (e.g., glass) and provide a third functional characteristic (e.g., corrosion resistance); and a fourth reinforcement used to form ribs402may be fabricated from a fourth material (e.g., Kevlar) and provide a fourth functional characteristic (e.g., flexibility).

In some applications, an insert600of another material (e.g., a different composite material and/or a non-composite material) may be used in conjunction with the composite material discharged by head16during fabrication of structure12. Insert600may provide a harder, stronger, more wear-resistant point of attachment that can be used to assemble components to structure12and/or to assembly structure12to another structure. As shown in the embodiment ofFIG.18, insert600may be shaped to fit within a pre-fabricated pocket602of structure12. In some applications, insert600may be bonded into the pocket (e.g., with matrix or another adhesive). In other applications, the composite material making up ribs402may be deposited around insert600and cured to lock insert600in place.

In some embodiments, mechanical interference (e.g., with or without adhesive bonding) may be used to retain insert600in place relative to structure12. An exemplary process for implementing mechanical bonding of insert600into structure12is illustrated inFIGS.19,20, and21. As shown inFIG.19, pocket602may first be formed to have an end supporting surface604and at least one side wall606that extends from surface604in a direction generally perpendicular to surface604. In the disclosed embodiment, surface604extends only around a periphery of pocket602and includes an open center that allows access to a center portion (e.g., an open bore, a threaded interface, etc.) of insert600. It is contemplated, however, that surface604could be a solid surface that completely blocks off one side of insert600, if desired. Side wall(s)606may extend a distance about equal to a thickness of insert600, such that an upper surface of structure12and an upper surface of insert600are generally co-planar immediately after insertion of insert600into pocket602. Additional adhesive (e.g., adhesive in addition to the matrix used to form pocket602) may be applied to surface604and/or side wall(s)606in preparation for receiving insert600).

After placement (e.g., manual placement or automatic placement performed by another machine) of insert600into pocket602(seeFIG.20), fabrication of structure12may be complete. However, in some applications, additional composite material may be discharged from head16to mechanically lock insert600in place. For example,FIG.21illustrates at least a border608formed around an upper surface of insert600that is connected to structure12. In one example, border608is identical to surface604(referring toFIG.19) other than location at an opposing side of insert600. It is contemplated, however, that border608could completely cover the upper surface of insert600, if desired. Border608may be integral to a layer of structure12, such that border608is flush with the upper surface of structure12. Alternatively, boarder608could extend past the upper surface of structure12(e.g., as an extra feature added to structure12).

INDUSTRIAL APPLICABILITY

The disclosed system and print head may be used to manufacture composite structures having any desired cross-sectional size, shape, length, density, and/or strength. The composite structures may include any number of different reinforcements of the same or different types, diameters, shapes, configurations, and consists, each coated with a common matrix. Operation of system10will now be described in detail with reference toFIGS.1-21.

At a start of a manufacturing event, information regarding a desired structure12may be loaded into system10(e.g., into controller20that is responsible for regulating operations of support14and/or head16). This information may include, among other things, a size (e.g., diameter, wall thickness, length, etc.), a shape, 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 couplers, tees, splices, etc.), location-specific matrix stipulations, location-specific reinforcement stipulations, compaction requirements, curing requirements, etc. It should be noted that this information may alternatively or additionally be loaded into system10at 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 loaded into head16. For example, one or more supplies of reinforcement may be loaded onto creel19(referring toFIG.2) of module44, and one or more cartridges of matrix may be placed into module46.

The reinforcements may then be threaded through head16prior to start of the manufacturing event. Threading may include passing the reinforcement from module44around redirects of module48and through module50. The reinforcement may then be threaded through module52and wetted with matrix. Module52may then extend to place the wetted reinforcement under module58. Module58may thereafter press the wetted reinforcement against an underlying layer. After threading is complete, head16may be ready to discharge matrix-coated reinforcements.

At a start of a discharging event, any available cure sources may be activated to direct cure energy to the discharging material. Module50may be deactivated to release the reinforcement, and head16may be moved away from a point of anchor to cause the reinforcement to be pulled out of head16and at least partially cured. This may continue until discharge is complete and/or until head16must move to another location without discharging material during the move.

During discharge of the wetted reinforcements from head16, module58may roll and/or slide over the reinforcements. A pressure may be applied against the reinforcements, thereby compacting and/or wiping the material. The material may be exposed to cure energy during discharge from head16and during compacting, such that at least a portion of the material is cured and hardened enough to remain tacked to the underlying layer and/or to maintain its discharged shape and location. In some embodiments, a majority (e.g., all) of the matrix may be cured by exposure to the energy.

It should be noted that the amount of cure energy generated by module58may be variable. For example, the energy could be generated at levels that are related to other parameters (e.g., travel speed) of head16. For instance, as the travel speed of head16increases and the discharge rate of reinforcement from head16proportionally increases, the amount of energy generated by module58and directed toward the discharging material may likewise increase. This may allow a consistent unit of energy to be received by the matrix coating the reinforcement under a range of conditions. It is also possible that a greater unit of energy may be received during particular conditions (e.g., during anchoring, during free-space printing, at particular geometric locations of structure12, etc.), if desired.

The component information may be used to control operation of system10. For example, the reinforcements may be discharged from head16(along with the matrix), while support14selectively moves head16in a desired manner during curing, such that an axis of the resulting structure12follows a desired trajectory (e.g., a free-space, unsupported, 3-D trajectory). In addition, modules46and52may be carefully regulated by controller20such that the reinforcement is wetted with a precise and desired amount of the matrix.

During payout of matrix-wetted reinforcement from head16, modules44and48may together function to maintain a desired level of tension within the reinforcement. It should be noted that the level of tension could be variable, in some applications. For example, the tension level could be lower during anchoring and/or shortly thereafter to inhibit pulling of the reinforcement during a time when adhesion may be lower. The tension level could be reduced in preparation for severing and/or during a time between material discharge. Higher levels of tension may be desirable during free-space printing to increase stability in the discharged material. Other reasons for varying the tension levels may also be possible.

At completion of a discharging event, module58may be selectively activated to sever the reinforcement.