Patent Description:
Parts and other objects may be manufactured using various manufacturing techniques depending on the performance requirements of the parts and the availability of manufacturing equipment. An additive manufacturing technique that may be used to build objects is fused filament fabrication (FFF), in which a filament is heated and deposited as beads onto a substrate in successive build layers to form the object. The filament is typically formed of a thermoplastic, polycarbonate, or other similarly configured material. Filament based additive manufacturing, such as FFF, may introduce voids between adjacent beads that reduce inter-layer strength, thereby resulting in an object with reduced structural strength.

<CIT>, in its Abstract, states an electromagnetic wave-induced heating of carbon nanotubes filled (or coated) polymer composites for enhancing inter-bead diffusive bonding of fused filament fabricated parts. The technique incorporates electromagnetic wave absorbing nanomaterials (carbon nanotubes) onto the surface or throughout the volume of 3D printer polymer filament to increase the inter-bead bond strength following a post electromagnetic wave irradiation treatment and/or in-situ focused electromagnetic beam during printing.

In accordance with one aspect of the present disclosure, a coated filament for use in an additive manufacturing process according to claim <NUM> is provided.

In accordance with another aspect of the present disclosure, a method of fabricating a coated filament for use in an additive manufacturing process according to claim <NUM> is provided.

In accordance with a further aspect of the present disclosure, a method of fabricating an object by fused filament fabrication according to claim <NUM> is provided.

The novel features believed characteristic of the illustrative examples are set forth in the appended claims. The illustrative examples, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of illustrative examples of the present disclosure when read in conjunction with the accompanying drawings, wherein:.

The following detailed description is directed to technologies for fused filament fabrication using electromagnetic susceptible polymer coatings for strengthening. In some implementations, various portions of an object may be strengthened using electromagnetic radiation. In some examples, a portion of an object needing increased strength is determined and an amount or duration of electromagnetic radiation is applied.

References are made to the accompanying figures that form a part hereof, and which are shown by way of illustration, specific examples, or examples. Like numerals represent like elements through the several figures.

"Fused Filament Fabrication" (FFF) is an additive manufacturing technology used for building up successive layers of material to form products and, for example, three-dimensional products, prototypes, or models. The process can be rapid for quick prototyping and manufacturing to build layer after layer of molten material to create a model, product, or the like.

As used herein, the term "filament" refers to feedstock used in an additive manufacturing process that has a slender, threadlike shape.

Turning now to the figures, <FIG> illustrates a process of converting a polymer filament <NUM> to a coated filament <NUM> that can be used in an additive manufacturing process to build an object having improved structural integrity. Specifically, the polymer filament <NUM> is uncoiled off of a first spool <NUM> as it is pulled through a reservoir <NUM> that holds a liquid coating <NUM>. Accordingly, as the polymer filament <NUM> exits the reservoir <NUM>, it is coated with the liquid coating <NUM>. When the liquid coating <NUM> subsequently dries, the coated filament <NUM> includes a base polymer layer <NUM> (formed by the polymer filament <NUM>) and a coating polymer layer <NUM> surrounding the base polymer layer <NUM>. The coated filament <NUM> then may be collected and coiled onto a second spool <NUM> for use in an additive manufacturing process. In this example, rotation of the first and the second spools <NUM>, <NUM> is controlled so that the rate at which the polymer filament <NUM> is uncoiled off of the first spool <NUM> is substantially the same as the rate at which the coated filament <NUM> is coiled onto the second spool <NUM>. The materials used to form the base polymer layer <NUM> and the coating polymer layer <NUM> of the coated filament <NUM> permit selective heating during a filament-based additive manufacturing process, thereby promoting inter-filament chain diffusion and bonding so that the resulting build object has improved structural integrity. As discussed in greater detail below, the materials used for the base polymer layer <NUM> and the coating polymer layer <NUM> may be selected based on relative responsiveness to dielectric heating, as well as proximity of melting points.

Regarding responsiveness to dielectric heating, materials used in the coated filament <NUM> may be selected so that the coating polymer layer <NUM> is more susceptible to heating in response to electromagnetic radiation than the base polymer layer <NUM>. A property known as dielectric loss factor (which is also known as the dissipation factor and is represented by the symbol tan δ) quantifies a material's ability to dissipate applied electromagnetic energy in the form of heat. A material with a higher dielectric loss factor will heat up more in response to an applied electromagnetic field than a material with a lower dielectric loss factor. To focus heating at the external surface of the coated filament <NUM>, the coating polymer layer <NUM> is formed of a coating polymer material having a higher dielectric loss factor than a base polymer material used for the base polymer layer <NUM>. In some examples, the coating polymer material has a tan δ value at least about <NUM> times the tan δ value of the base polymer material. Additionally or alternatively, the base polymer material has a tan δ value less than. <NUM> and the coating polymer material may have a tan δ greater than.

The coated filament <NUM> further may use materials for the base polymer layer <NUM> and the coating polymer layer <NUM> that have similar melting points, which improves strength of the build object formed by layers of coated filament deposited during the additive manufacturing process. As noted above, the coating polymer material has a higher dielectric loss factor, and therefore generates heat directly in response to the application of electromagnetic energy. The base polymer material may be selected so that it has a melting point that is proximate to that of the coating polymer material, so that heating of the coating polymer layer <NUM> by the electromagnetic energy will, in turn, heat at least an outer portion of the base polymer layer <NUM>. This indirect heating of the base polymer layer <NUM> causes the base polymer layer <NUM> to remain in the softened and/or molten state for a longer period of time, thereby promoting increased diffusion and bonding between adjacent beads of coated filament <NUM> after they are deposited on the substrate. The melting points of the base polymer material and the coating polymer material permit formation of a solid and liquid morphology. In some examples, the base polymer material has a first melting point, the coating polymer material has a second melting point, and the first melting point of the base polymer material is within <NUM> degrees Celsius of the of the second melting point of the coating polymer material.

Materials with melting points within about <NUM> degrees, or about <NUM> degrees, or about <NUM> degrees Celsius have been found to generate sufficient heat to prolong the molten state of the base polymer layer <NUM> to promote diffusion and bonding between adjacent beads of coated filament <NUM> deposited and heated during additive manufacturing.

The materials selected for the base polymer layer <NUM> and the coating polymer layer <NUM> further may have compatible solubility parameters, further promoting bonding between adjacent beads and build layers of coated filament <NUM> when used in the additive manufacturing process. For example, the coating polymer material may be immiscible with the base polymer material to prevent phase separation and promote fusion of the base polymer layers of adjacent beads of deposited coated filament <NUM> during additive manufacturing. According to the disclosure as claimed herein, the base polymer material has a first solubility parameter, the coating polymer material has a second solubility parameter, and the second solubility parameter is within about <NUM> (J/cc)<NUM> (or (J/cm<NUM>)<NUM>) of the first solubility parameter. Materials with solubility parameters within about <NUM> (J/cc)<NUM> (or (J/cm<NUM>)<NUM>), or about <NUM> (J/cc)<NUM> (or (J/cm<NUM>)<NUM>), or about <NUM> (J/cc)<NUM> (or (J/cm<NUM>)<NUM>) of each other have been found to advantageously promote intermixing when heated during the additive manufacturing process.

In view of the foregoing considerations, suitable base polymer materials include polyethylene, polyethylene terephthalate, polypropylene, polyamides, polyetheretherketone, polyphenylene sulphide, polyetherimide, polystyrene, acrylonitrile/butadiene/styrene, polyacrylates, polyacrylonitrile, polycarbonate, or any mixture thereof.

Suitable coating polymer materials include polyvinyl alcohol, polyvinylidene fluoride, polyurethane, polyamide imide, polyamide, polyvinyl chloride, acrylic, cellulose esters, or mixtures thereof. Other examples of suitable coating polymer materials include materials and solvents that contain -OH, -NH, C=O, -N=O functional groups with a high dielectric loss factor. Further examples of suitable coating polymer materials include polyacrylonitrile (tan δ=. <NUM> at <NUM>), polyethylene glycol, or mixtures thereof. In some examples, the coating polymer material is particularly responsive to electromagnetic energy in a specific frequency range, such as microwave energy in the GHz range.

TABLE <NUM> compares the dielectric loss factors, melting points, and solubility parameters for a specific example in which the coating polymer material is polyvinyl alcohol and the base polymer material is Ultem™ <NUM> (polyetherimide):.

In this example, the use of Ultem™ <NUM> (polyetherimide) as the base polymer material and polyvinyl alcohol as the coating polymer material is advantageous because polyvinyl alcohol has a high dielectric loss factor (tan δ=<NUM> in the MHz-GHz frequency range), relative to Ultem™ <NUM> (tan δ=<NUM> in the MHz-GHz frequency range), the melting points of the two materials are <NUM> degrees Celsius apart, and the solubility parameters are close, indicating compatibility.

In addition to chemical characteristics, the base polymer layer <NUM> and the coating polymer layer <NUM> further may have physical characteristics that indicate suitability promoting fusion, bonding, and intermixing. For example, the base polymer layer <NUM> may have a thickness within a range of about <NUM> to about <NUM> millimeters, or within a range of about <NUM> to about <NUM> millimeters, or within a range of about <NUM> to about <NUM> millimeters. The coating polymer layer <NUM> may have a thickness within a range of about <NUM> micron to about <NUM>,<NUM> microns, or within a range of about <NUM> microns to about <NUM> microns, or within a range of about <NUM> microns to about <NUM> microns. Additionally, the liquid coating <NUM> may be characterized as having a viscosity of from about <NUM> to about <NUM> Pascal-seconds (Pa. s), or from about <NUM> to about <NUM> Pa. s, or from about <NUM> to about <NUM> Pa.

<FIG> illustrates an object formed by a conventional FFF technique. One embodiment of FFF is an additive manufacturing technique (the FFF technique and the following components used to manufacture object <NUM> are not shown) in which a filament on a spool is fed into an extruder. The extruder uses a torque and a pinch system to feed and retract the filament in precise amounts to a heater block. The heater block melts the filament to a molten state, and the heated filament is extruded out of a nozzle at a smaller diameter and deposited on a substrate or work plate. During a typical FFF process, multiple build layers are deposited on top of each other to form a three-dimensional object.

Specifically with reference to <FIG>, the object <NUM> is manufactured through the successive deposition of beads of adjacent beads of the uncoated filament <NUM> until the object <NUM> is complete. For example, the object <NUM> of <FIG> is made of three build layers, and each build layer includes four beads of the uncoated filament <NUM>. The beads of uncoated filament <NUM> deposited in this example on substrate <NUM> result in seams between adjacent beads. Due to the properties of conventional uncoated polymer filaments, when a first bead is deposited it cools and is no longer in a fully molten state when a subsequent, adjacent bead of uncoated filament is deposited. Because the previously deposited bead is at least partially hardened, voids <NUM> form between adjacent beads of uncoated filament <NUM> within a given build layer, and between adjacent build layers, which weaken the object <NUM>.

As best shown in <FIG>, the coated filament <NUM> according to this disclosure includes both the base polymer layer <NUM> and the coating polymer layer <NUM>. As noted above, materials used for the base polymer layer <NUM> and the coating polymer layer <NUM> are selected so that diffusion and bonding is promoting between adjacent beads and build layers, thereby eliminating the voids <NUM>. In one example, the coated filament <NUM> is manufactured using the process outlined in <FIG>. It should be noted, however, that the presently disclosed subject matter is not limited to any particular manufacturing method. In some examples, the coated filament <NUM> may be a filament used in additive manufacturing machines, such as machines utilizing FFF, or other commonly used additive manufacturing techniques.

<FIG> illustrates an example of a system <NUM> for fabricating an object using the coated filament <NUM> by FFF and applying electromagnetic radiation as discussed below. The coated filament <NUM>, having the base polymer layer <NUM> and the coating polymer layer <NUM>, is fed into a nozzle <NUM>. The nozzle <NUM> heats the coated filament <NUM>, turning it into a molten state before extruding it from the nozzle <NUM> and depositing it as a first bead <NUM> onto a substrate <NUM>. The substrate <NUM>, in one non-limiting example, is a work station. The substrate <NUM> may be heated to prevent any filament from hardening and sticking onto the substrate <NUM>.

The nozzle <NUM> heats the coated filament <NUM> to a molten state at a temperature of from about <NUM> to about <NUM> degrees Celsius, or from about <NUM> to about <NUM> degrees Celsius, or from about <NUM> to about <NUM> degrees Celsius. The coated filament <NUM> is then deposited on the substrate <NUM> at a speed of from about <NUM> to about <NUM>/second, or from about <NUM> to about <NUM>/second, or from about <NUM> to about <NUM>/second.

After the first bead <NUM> is deposited, subsequent beads are formed on the substrate <NUM>, as best shown in <FIG>. The number of beads per build layer, and the number of build layers, is dependent on the specific object to be fabricated and the chosen additive manufacturing technique. No matter what technique is utilized, the use of the coated filament <NUM> strengthens the bonds between adjacent beads and build layers. For example, <FIG> depicts a cross-sectional front view of adjacent deposited beads <NUM>, which includes the first bead <NUM> and a second bead <NUM> of the coated filament <NUM>. Each bead of the deposited pair of beads <NUM> is formed from the coated filament <NUM>, extruded from the nozzle <NUM>, and deposited onto the substrate <NUM>, and includes the base polymer layer <NUM> and the coating polymer layer <NUM>. In order to strengthen the bond between the first and second beads <NUM>, <NUM>, electromagnetic radiation <NUM> is applied to an interface area <NUM> between the beads <NUM>, <NUM>. In one non-limiting example, the interface area <NUM> is the area located between the first and second beads <NUM>, <NUM>, but in other examples, the interface area <NUM> is the area between two build layers. In further non-limiting implementations, the electromagnetic radiation <NUM> is applied to the entire object (such as object <NUM> illustrated in <FIG>) and not just to the area between adjacent beads. In this example, since the base polymer material has a lower dielectric loss factor than the coating polymer material, electromagnetic radiation only heats the coating polymer layer <NUM> and not the base polymer layer <NUM> of each bead.

In one non-limiting example, the electromagnetic radiation <NUM> is applied from a heating source <NUM>. In this example, the heating source <NUM> directs the electromagnetic radiation to the interface area <NUM> of the object, or the entire object itself, as well as controls the duration during which the electromagnetic radiation <NUM> is applied, in order to strengthen localized areas of the object or the entire object. For example, the electromagnetic radiation <NUM> can be applied at the interface area <NUM> to further heat and fuse the base polymer layers <NUM> of adjacent beads. Further, the electromagnetic radiation <NUM>, in one example, can be microwaves having frequencies in a range between <NUM> and <NUM>. In this example, the coating polymer material has a high dielectric loss factor and is susceptible to microwave radiation, and thus dielectric heating. In a further non-limiting example, the electromagnetic radiation <NUM> is continuously applied as the coated filament <NUM> is deposited. In another example, the electromagnetic radiation <NUM> is selectively applied between adjacent, deposited beads.

Since the coating polymer material has a higher dielectric loss factor, and the base polymer material has a lower dielectric loss factor, a frequency of the electromagnetic radiation may be selected so that only the coating polymer layer <NUM> is melted directly in response to the electromagnetic radiation. Additionally, the base polymer material may have a melting point near that of the coating polymer material, so that the base polymer layer <NUM> at least partially melts in response to heating of the coating polymer layer <NUM>. Thus, the coating polymer layer <NUM> will directly melt and the base polymer layer <NUM> will indirectly melt in response to the electromagnetic radiation <NUM>. In other examples, the electromagnetic radiation <NUM> may directly heat both the coating polymer layer <NUM> and the base polymer layer <NUM>. In either case, melted portions of the base polymer layer <NUM> in adjacent beads may fuse together, further preventing formation of voids between adjacent beads and promoting structural integrity of the object built.

As the coating polymer material and the base polymer material have compatible solubility parameters (see the non-limiting example in Table <NUM>), melting of both the coating polymer layer <NUM> and the base polymer layer <NUM> creates a homogenous mixture, and therefore no phase separation occurs when the melted layer subsequently cool and harden.

<FIG> illustrates the first and second beads <NUM>, <NUM> of the coated filament <NUM> fused together subsequent to melting by the electromagnetic radiation <NUM>, to form a fused pair of beads <NUM>. In this figure, the electromagnetic radiation <NUM> has heated the coating polymer layers <NUM> of the first and second beads <NUM>, <NUM>, which in turn melted at least portions of the base polymer layers <NUM>.

<FIG> illustrates an object <NUM> formed using the coated filament <NUM> in an additive manufacturing technique. In this example, the object <NUM> was fabricated by placing beads <NUM> of coated filament <NUM> onto the substrate <NUM>. Specifically, <FIG> shows three build layers <NUM>, with each build layer <NUM> including four beads <NUM>. Further, in this example, electromagnetic radiation <NUM> was applied into order to fuse the base polymer layer <NUM> and the coating polymer layer <NUM> of adjacent beads of the coated filament <NUM>. The resulting object <NUM> has no voids between beads <NUM> or build layers <NUM>.

Claim 1:
A coated filament (<NUM>) for use in an additive manufacturing process, the coated filament (<NUM>) comprising:
a base polymer layer (<NUM>) formed of a base polymer material having a first dielectric loss factor; and
a coating polymer layer (<NUM>) surrounding the base polymer layer (<NUM>) and formed of a coating polymer material having a second dielectric loss factor, wherein the second dielectric loss factor of the coating polymer material is greater than the first dielectric loss factor of the base polymer material,
wherein the base polymer material has a first solubility parameter, the coating polymer material has a second solubility parameter, characterized in that the second solubility parameter is within about <NUM> (J/cm<NUM>)<NUM> of the first solubility parameter.