Patent Application
20150183164
The present invention relates to a rapid non-contact energy transfer for additive manufacturing driven high intensity electromagnetic fields.
Additive manufacturing may be used to quickly and efficiently manufacture complex three-dimensional components layer-by-layer, effectively forming complex components. Such additive manufacturing may be accomplished using polymers, alloys, powders, wires, or similar feed stock materials that transition from a liquid or granular state to a cured, solid component.
Polymer-based additive manufacturing is presently accomplished by several technologies that rely on feeding polymer materials through a nozzle that is precisely located over a preheated polymer substrate. Parts are manufactured by the deposition of new layers of materials above the previously deposited layers. Unlike rapid prototyping processes, additive manufacturing is intended to produce a functional component constructed with materials that have strength and properties relevant to engineering applications. On the contrary, rapid prototyping processes typically produce exemplary models that are not production ready.
Heating of the feed or filler material in the nozzle in additive manufacturing is generally accomplished by direct contact between a polymer feed stock and a heating element, typically a resistively heated metal cylinder at elevated temperatures. Likewise, in additive manufacturing, unlike rapid prototyping, the entire component under construction is typically maintained at an elevated temperature in a chamber or furnace until the build is complete. Keeping previously deposited layers at elevated temperature improves the adhesion between the component and newly deposited material while minimizing macroscopic distortion. There are inherent limitations to this technology that prevent higher deposition rates, out of furnace printing and control of microstructural defects (such as pores).
In addition, existing additive manufacturing processes, including polymer extrusion based deposition for additive manufacturing (PeD), typically exhibit a thermal lag associated with heating a deposition nozzle. Typical PeD systems obtain thermal stability by maintaining a massive resistive heater at a constant temperature resulting in slow response. This makes accurate control of the flow control difficult and prevents the building of advanced structures that require transient deposition rates and frequent interruptions in flow (in a mechanism analogous to image generation in an ink jet printer).
Magneto-thermal conversion is the conversion of electromagnetic energy into thermal energy. In ferromagnetic magnetic materials, a principle mechanism underlying magneto-thermal conversion is related to externally induced disturbances in the magnetic structure and how strongly the materials resist these disturbances. The dissipated electromagnetic energy is the product of these two and can be transformed into thermal energy among other forms. Therefore the external field should be sufficient to induce disturbances in the magnetic structure while the magnetic material should provide sufficient resistance to dissipate energy yet not resist so strongly that the external fields cannot induce disturbances. It is therefore desired to match the magnetic response of a material with the correct amplitude and frequency of electromagnetic energy. In soft magnetic materials, there is a minimal energetic barrier to either rotate the moment within a domain, or nucleate a reversed domain and move the resulting domain as opposed to hard magnetic materials that resist such disturbances. The energy product associated with magnetic materials is a function of the coercivity, remnant magnetization and magnetic anisotropy. In general, materials with coercivity ≧1000 Oe can be classified as hard ferromagnets. Soft ferromagnets have lower coercivity, and good soft ferromagnets have coercivity <1 Oe. Intermediate materials having a coercivity >1 Oe and <1000 Oe are useful in applications where a magnetic hysteresis losses are required in applications such as, for example, transformation of electromagnetic energy into thermal energy, also known as magneto-thermal conversion
One motivation for the subject invention is to increase the sensitivity and controllability of the flow of polymer, both of which translate to increased build rates. This is accomplished, in part, by reducing the weight of the liquefier and increasing the thermal response time between the power supply and liquefier. The subject invention enables high fidelity control of deposition rates with a non-contact heating technology that can be used to quickly heat a low thermal mass deposition nozzle, materials within a deposition nozzle, locally heat specific locations of the build and/or uniformly heat the build out of the furnace.
In addition, removal of joule heating will significantly separate the position dependent heat source from the extruder which impacts part quality. In this manner, a part may be manufactured in accordance with the invention in large scale applications and without reliance on an oven or controlled environment for the build. Further, this technology may be used as a means to apply targeted heating of the polymer material through the build or locally to active manufacturing surface locations. This is accomplished by applying high intensity electromagnetic energy, for instance, transient high flux alternating magnetic fields, to the previous layers polymer materials.
Further, the polymer feed materials may be tuned by doping the polymer feed stock with specific magnetically active materials, microscale particles, and/or nano particles. As a result, custom feed materials may be employed depending on the desired characteristics of the build, for instance, carbon fiber may be added to the feed material to tailor conductive properties and thus rapidly and uniformly heat the feed material, when desired.
Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings.
The present invention provides a non-contact heating technology that can be used to quickly heat materials within a deposition nozzle, locally heat specific locations of a deposition modeling build and/or uniformly heat the build outside of a furnace or similarly controlled environment. As a result, the weight and size of the liquefier is reduced and sensitivity and controllability of polymer flow is improved, resulting in increased build rates. According to a preferred embodiment, the subject method and apparatus employs high intensity electromagnetic energy, for instance, transient high flux alternating magnetic fields, to polymer working materials resulting in a highly controllable additive manufacturing process.
Although not required, the subject invention may be used in connection with large scale polymer added manufacturing such as the schematic shown in
According to a preferred embodiment of the invention, a method of additive manufacturing includes the steps of providing an apparatus for additive manufacturing, for instance the gantry system shown in
A schematic of a deposition nozzle 80 used in such a system is shown in
Accordingly, as shown in
The coil 120 is preferably an induction heating coil wherein a desired number of turns of the coil 120 are used to introduce inductance into the nozzle 80 thereby producing a desired and controllable heating. Alternatively, a series of coils may be positioned around or with respect to the nozzle 80 to provide the desired heating. According to a preferred embodiment of this invention, the nozzle 80 is directly coupled to the power supply, i.e., the electro-magnetic energy source. The thermal link to the nozzle 80 may thus be quickly and controllably decoupled by decoupling the power supply from the nozzle 80. In this manner, heat control may be precisely administered to the nozzle 80.
The coil 120 may be insulated, for instance, with a TEFLON coating and is preferably tightly wrapped with respect to the barrel 85 or a conductive coating arranged around the barrel 85. According to one preferred embodiment of this invention, the coil 120 is arranged with non-uniform spacing. The printing tip 100 having non-uniform spacing may include an arrangement wherein the coil 120 is tighter at a distal end of the barrel 85.
According to one preferred embodiment, the electro-magnetic heating element, particularly the coil 120, is maintained at a lower temperature than material guide, or barrel 85. The printing nozzle 80 may further include a heat exchanger (not shown), primarily for cooling, positioned with respect to at least one of the tip 100 and the barrel 85 to provide a desired cooling to one or both respective components. In this manner, the deposition of material may be precisely controlled so as to avoid and excess or absence of material deposition in the desired locations. The heat exchanger may circulate at least one of helium and nitrogen to provide the desired cooling to the nozzle 80, more specifically to the tip 100 and/or the barrel 85 of the nozzle 80.
The nozzle 80 preferably produces a time varying, high flux, frequency sweeping, alternating magnetic field in the vicinity of the nozzle 80 so that (i) the time varying magnetic field penetrates into and is coupled by the magnetically susceptible working material to induce transient magnetic domains resulting in heating of the magnetically active components; and/or (ii) the transient magnetic field penetrates into and is coupled by the electrically conductive working material to generate an induced, annular current that causes direct electrical resistive heating of the material.
As described above,
According to a preferred embodiment of this invention, heating efficiency and energy transfer dynamics are tunable in this magneto-dynamic approach by tailoring the magnetic and/or the conductive properties of the polymer feed material. This is accomplished by compounding the polymer feed stock with specific magnetically active materials, microscale particles, nano particles, and/or carbon fiber. As a result, a portfolio of tuned polymer feed materials may be employed depending on the desired characteristics of the build.
As described, the polymeric working material is preferably tuned by matching a magnetic response of the working material to an electromagnetic wave. This is preferably accomplished by compounding or doping the working material with magnetically active microscale and/or nano particles to adjust a heating efficiency of the magnetic field. The polymeric working material preferably comprises a thermoplastic or thermosetting polymer, such as a nylon or epoxy. Suitable doping agents may include at least one of iron oxide, manganese borate, nano particles, and/or carbon fiber. Suitable nano particles may include at least one of Ho0.06Fe2.94O4 and Gd0.06Fe2.94O4.
According to a preferred embodiment of the invention, the polymeric working material comprises 90-99% a polymer matrix and 1-10% doping agent and more preferably 95-99% a polymer matrix and 1-5% doping agent.
In addition,
Specifically,
While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be prepared therein without departing from the scope of the inventions defined by the appended claims.
This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
