Patent Application
20150050179
The present invention relates to the fields of solid freeform fabrication, three-dimensional printing, and micro-molding.
The following patent application has a relationship to the current application:
Patent application (WO2011055347) describes the using a chip device for deformation of ferrofluids and includes using the chip device for micro-molding.
The present invention comprises a method directed to curing molding materials (30) (such as polymers, plastics, metals, ceramics) against the shape and flow of a mold comprising a combination of ferrofluid substrate (10) and non-magnetic fluid substrate (10) that takes place within the space of a magnetic system (30). The ferrofluid substrate is a fluid that aligns in the direction of a magnetic field, which can be applied to the ferrofluid substrate by the surrounding magnetic system. A non-magnetic fluid substrate may be further used within the space of the magnetic system to shape the ferrofluid substrate in the presence of a magnetic field, by means of acting as a barrier and/or a guide. The non-magnetic substrate may also function as a surface against which the curing molding material can mold, such as in areas where the presence ferrofluid substrate is non desirable, such as planar surfaces adjacent to ferrofluidic substrate features.
The shape and flow of the ferrofluid substrate can be manipulated by magnetic fields around the ferrofluid substrate. Ferrofluid is a man made material. The dynamics and attributes of ferrofluid are an active area of academic study and have been since the material was first made in 1963. The most-well known application of ferrofluid is in artistic sculptures, but ferrofluid has found particular application an actuating material, whereby it enables switches, sensors and pumps in mechanical systems. The magnetic fields in turn can be organized by the magnetic system. A ‘magnetic system’ refers to a system comprised of magnets, such as permanent and/or electromagnets, and metallic materials in a two or three dimensional configuration around a central space where the molding material is contacted against the mold, that are affected by magnetic fields, such that the metallic materials may orient a particular way in the presence of a magnetic field. The magnetic system configuration may be arranged such that the field lines of the magnet serve as the basic map for the flow direction of the ferrofluid substrate. The shape may be narrowed and refined, or “guided”, by the metallic materials within the central space that are aligned with the magnets. The metallic materials may additionally dam or bridge flow between magnets, allowing for a more diverse range of patterns and shapes to be achieved by the magnets. The metallic materials may serve as a focus for the magnetic field lines; those produced by the magnets alone have directionality but not singularity, and the metallic elements may provide for shapes and flow, such as individual lines on the order of microns, to be singular features. Similarly, placing a bend on the gauge wire may allow the ferrofluid to follow the path of the bent wire. Metallic elements, such as a gauge wire, can additionally create a ‘bridge’ to allow for flow between two or more magnets. Introducing a ferrofluid substrate at a first weaker magnet, the ferrofluid substrate can flow toward a stronger second magnet, following the path of the metallic element, moving from the weaker to the stronger magnet. Likewise repulsive field effects can be introduced in the magnetic system, such as placing a metallic element tangentially between two magnets (north pole to north pole), and allowing the field lines to repel in the direction of the metallic element. Magnets can also be placed in a three-dimensional system. For example, ferrofluid substrate placed between two cylindrical magnets will create an hourglass shape. Placing a metallic material, such as a wire, between these can elongate the hourglass shape but allow the ferrofluid substrate to maintain continuity. In another configuration, the ferrofluid substrate can be held to a surface by one magnet, and by placing another in proximity can create arcs and wave-like shapes that can then be molded.
By manipulating magnetic field lines and densities via the magnetic system, the ferrofluid substrate can be moved dynamically and formed into a specific shape. Once the ferrofluid substrate has taken the desired shape, a curing material (in fluid or powder form) can be introduced within the central space of the magnetic system and molded against the specific shape of the ferrofluid substrate. “Curing materials” are those such as photopolymers, powder metals, ceramics, or any used in current three-dimensional printing techniques.
The interaction of the curing materials and ferrofluid substrate can be viewed as analogous to three different processes, a) where the ferrofluid substrate may be a direct mold cavity, b) where the ferrofluid substrate may be a resist, and c) where the ferrofluid substrate may be in a dynamic state. In the case of (a) for static configurations, the use of powdered metals are of particular import in terms of improving the art.
The ferrofluid substrate can also be used as a heat transport mechanism for induction heating via varying magnetic fields. The curing method (40) and interaction with the ferrofluid substrate will change according to the curing material used. A photopolymer requires a (typically) ultraviolet light source, which limits the system to those that need the curing material to ‘see’ the light source. A powdered metal requires heat, which allows for a greater variety of molding shapes, but alters the specifications for the ferrofluid substrate so that it does not evaporate. The ferrofluid substrate's shape can also be further changed dynamically during the curing step to further impact the final shape of the cured mold. The present method permits fast three-dimensional molding in a programmable fashion.
The present invention provides a method comprising engaging a ferrofluid substrate material with a magnetic system and a molding material. The method of the present invention comprises utilizing a magnetic system to manipulate within a central space a first shape of a ferrofluid substrate and introducing a molding material to form a mold against the first shape of the ferrofluid substrate. The method may further comprise additionally altering the shape of the ferrofluid substrate by adjusting the magnetic system after the molding material has been introduced or as the molding material cures. The magnetic system comprises a two or three-dimensional system of metallic, magnetic (permanent and/or electromagnets) elements, which map a ferrofluid substrate, whereby the system can direct the shape and flow of the ferrofluid substrate through the resulting magnetic field lines. The present invention may use a ferrofluid substrate as part of a molding surface that allows for shapes beyond static configurations, such as features created by fluid flow and complex features that result from the application of ferrofluid substrate in multi-dimensional magnetic system. The materials and curing method (40) may be variables within the process and those skilled in the art will appreciate that the specific configurations of the materials and associated curing method may vary based on the molding material being used. The magnetic system provides a tool to direct magnetic field lines and ferrofluid flow.
A mold may be created against which a molding material may be contacted and shaped around. The mold comprises a ferrofluid substrate and a non-magnetic material, such as a non-magnetic metal, paramagnetic material, or a polymer. A ferrofluid, as is known in the art, refers to a material comprised of magnetic particles, surfactant and carrier fluid. The carrier fluid can be hydrophobic, hydrophilic, or any fluid which can carry a surfactant. Ferrofluids have been used in a variety of industries such as components in sensors, liquid seals, switches, loudspeakers, solenoids, dampers, drug delivery, ink-jet printing, and sink-float material separator systems. Ferrofluid is a stable substance comprised of colloidal nanoparticulate magnetite or iron oxide (or other magnetic materials) coated with surfactant such as oleic acid, citric acid, soy lecithin, tetramethlyammonium hydroxide, and in suspension in a carrier fluid. The versatility of the carrier substance, which can be oil, water or diester, provides a wide berth of possibilities for interactions with molding substances. (See, Williams, A. M., 2008. The Hydrodynamics of Ferrofluid Aggregates. Virginia Polytechnic Institute and State University, Blacksburg, Va.).Error! Reference source not found. When in the presence of a magnetic field, the fluid shifts in order to align itself along the magnetic field lines, as is similarly seen with iron filings around a magnet. However, the surface tension of the ferrofluid cannot typically hold the full circular contour of a magnetic field. This effect is most dramatically witnessed when the magnetic field is normal to the ferrofluid, and the ferrofluid in turn resolves itself into cone like structures, the size and shape of which are determined by the strength of the magnetic field in that location.
The behavior of the ferrofluids is referred to as ‘instability,’ and the behavior can be variously described by normal field, labyrinthine, Rayleigh-Taylor and Kelvin-Helmholtz instabilities. (See, Bacri, J. C. and D. Salin. Instability of ferrofluid magnetic drops under magnetic field. Journal de Physique-Lettres. No. 17, pp. 650, 1982).Error! Reference source not found. These behaviors do not correlate directly to a magnetic field, as the behavior is additionally dependent on whether the applied magnetic field has been present and is now decreasing. (See, Mayer, D. Future of electrotechnics: Ferrofluids. Advances in Electrical and Electronic Engineering. Pp. 9 and Dickstein, A. J., S. Erramilli, R. E. Goldstein, D. P. Jackson and S. A. Langer. Labyrinthine Pattern Formation in Magnetic Fluids. Science, New Series, Vole. 261, No. 5124, Aug. 20, 1993, 1012-1015) The normal field, or Rosenweig instability, occurs when a magnetic field is applied normally to the ferrofluid surface. This instability has different states, as the peaks of the ferrofluid shift from hexagonal to square with increasing field strength. The ferrofluid is further more sensitive to the magnetic field when then field is increasing than when it is decreasing in strength. (See, Buzduga, C., V. Vlad, C. Ciufudean. Experimenting the Stability of Ferrofluids. Mathematical Models in Engineering and Computer Science Conference Paper, 2013, pp. 80). The effect of a step-function change versus gradual change of the magnetic field strength may also influence the shape and the growth of peaks; one magnetic field does not necessarily provide one equivalent ferrofluid shape, and the method of producing that field is of equal importance in operating the magnetic system.
Relationships between the peak profile and radius of curvature of the fluid with respect to the magnetic field intensity, the peak density as a function of magnetic field intensity (see, Strek, T. Chapter 28, Finite element simulation of heat transfer in ferrofluid. Modelling and Simulation. Pp. 533. I-Tech Education and Publishing, June 2008), the transfer of heat through ferrofluids (see, Brullot, W., N. K. Reddy, J. Wouters, V. K. Valev, B. Goderis, J. Vermant, T. Verbiest. Versatile ferrofluids based on polyethylene glycol coated iron oxide nanoparticles. Journal of Magnetism and Magnetic Materials, 324, 2012, 1919-1925), the stability, dynamics of feature formation, variations in composition and resulting effects, saturation of magnetic particles with respect to viscosity and magnetization (see, Zelazo, R. E. and J. R. Melcher. Dynamics and stability of ferrofluids: surface interactions. Journal of Fluid Mechanics, 1969, Vol 39, part 1, pp. 1-24 and Webster, J. R., M. A. Burns, D. T. Burke and C. H. Mastrangelo. An inexpensive plastic technology for microfabricated capillary electrophoresis chips. Micro Total Analysis Systems '98. 1998, pp. 249-252): all of these have been investigated in academic literature and are understood in the art.
The ferrofluid substrate may be immiscible or exhibit reduced miscibility with the molding material and therefore the two will not intrinsically homogenize together. Immiscibility of the molding material with the ferrofluid substrate allows for the mold to form. Selecting immiscible materials is known in the art, such as using hydrophobic materials with hydrophilic materials or polarized materials with non-polar materials. For example, a molding material may be a hydrophilic material (such as Sartomer 399), or a hydrophobic material, such as functionalized Sartomer 351, or partially hydrophilic (such as Sartomer 351 LV). In instances that use powdered materials for a curing material, the magnetized ferrofluid substrate may be denser than the powdered curing material. In instances where the molding material is hydrophilic, the carrier fluid of the ferrofluid substrate may be a hydrophobic material (such as synthetic oil, an animal oil or a vegetable oil), or can be hydrophobic; water itself may be used as a carrier fluid. Non-magnetic fluid material used in the substrate may be miscible or immiscible with the molding material depending on the desired shape outcome.
The carrier fluid of the ferrofluid substrate may comprise a hydrophobic material such as oil or a hydrophilic material (such as water). The choice of carrier fluid may affect the miscibility of the ferrofluid substrate with the molding material. Those skilled in the art will appreciate that reduced miscibility with the molding material may allow for better or improved molding. Those skilled in the art will also appreciate that the choice of carrier fluid may additionally allow for varying temperature ranges within the ferrofluid substrate during the curing process of the molding material. For example, a three-dimensional printer using a high powered 200 watt Yb-fiber optic laser to melt a 20 micron layer of stainless steel will raise the temperature of the steel to approximately 1500° C.; the temperature to achieve fusion is lower than bulk metals because the material is in powder form. Typical stainless steels have a specific heat of around 500 J/kg*K; that is, 500 joules of energy to raise a kilogram of stainless steel by one degree. Water is 4.187 kJ/kg*K, over eight times that of stainless less, which means that it takes longer to heat than stainless steel. The melting temperatures of the two substances, 100° C. versus 1500° C., dictates that to maintain the shape of the ferrofluid substrate three primary courses can be followed: one uses a depth of ferrofluid substrate that can absorb the energy transfer from the melted stainless steel; a flow rate of ferrofluid substrate that carries the energy downstream; a non-magnetic fluid placed in a thin layer above the ferrofluid substrate and used as a thermal shield/sacrificial layer.
For powdered metals with ferrous material in the powder, the ferrofluid substrate can be rapidly alternated to induce heating of the molding material. The fluid flow of the ferrofluid fluid may then be continuous, and accordingly prevent overheating. A few degrees prior to achieving melting temperature, the alternating field may be stopped to allow the ferrofluid substrate to take the final required shape, thus allowing the metal to be molded accordingly.
The present invention also provides for contacting a molding material against a mold comprising a combination of ferrofluid substrate and non-magnetic substrate. The non-magnetic substrate can interact with the ferrofluid substrate in either a miscible or immiscible manner. Immiscible non-magnetic substrates serve a similar function to the ferrofluid substrate, i.e. a surface which serves as a mold cavity. Miscible non-magnetic substrates may interact with the molding material to alter the final shape outcome and change surface characteristics. For example, once the ferrofluid substrate is aligned with the magnetic field, a non-magnetic immiscible fluid may be placed adjacent to the ferrofluid substrate to alter the shape of the ferrofluid substrate. The non-magnetic fluid may also be in place prior to the application of the ferrofluid substrate, and the ferrofluid substrate may a) move around an immiscible fluid and/or b) move through a miscible fluid.
The present invention provides for contacting a molding material against a mold, such as a combination of ferrofluid substrate and non-magnetic substrate. The molding material may a solid or a liquid. The molding material may have reduced miscibility with the ferrofluid substrate. The molding material may be immiscible with the ferrofluid substrate. The molding material may be a photopolymer, such as Sartomer 399, SU8, PMMA, PDMS, Sartomer 351. As is known in the art, a photopolymer may cure following exposure to particular wavelengths of light. As is known in the art, the wavelength required to cure the photopolymer is dependent on the selected photopolymer. Photopoymers, such as sartomer 351 HP, use ultraviolet wavelengths to cure between 300-380 nm, SU-8 cures at 365 nm, PMMA cures at 248 nm. The penetration depth and cure time of the photopolymer are also dependent on the photopolymer selected.
The molding material may further be a solid, such as powder, including powdered metals (such as 304 stainless steel, ferritic steel, cobalt alloys, copper alloys, inconcel; others are available commercially in powdered form and any alloy can accordingly be used). Powdered metals are known in the art and may be the same as those used by Solid Freeform Fabrication processes. As is also understood within the art, powdered metals may be cured by laser application, radiative heat or other similarly known methods.
The ferrofluid substrate may be shaped based on the presence of magnetic particles within the ferrofluid substrate reacting to a surrounding magnetic system. The mold may be held in a desired shape through the use of a magnetic field applied by the magnetic system to the ferrofluid substrate. The magnetic particles within the ferrofluid substrate will attempt to align in the direction of the applied magnetic field lines and according to the field density applied. The resulting shape of the ferrofluid substrate therefore depends on the direction and intensity of the applied magnetic fields from the surrounding magnetic system. The magnetic field strength may be limited by the magnet used (permanent or electromagnet) and by the physical distance between each magnet and the ferrofluid substrate. Controlling these factors is a known in the art of magnetic control (See, e.g., Paul, C. R. and S. A. Nasar, Introduction to Electromagnetic Fields, McGraw-Hill, 1982 and Hanselman, D. C., Brushless Permanent-Magnet Motor Design, McGraw-Hill, 1994).
The ability to shape the mold also can be affected by the surface tension of the ferrofluid substrate and the volume of the ferrofluid substrate. The surface tension is a result of the carrier fluid and the strength of the magnetic field within the ferrofluid substrate. Selecting for lower surface tension allows the ferrofluid substrate to create finer features. The volume of the ferrofluid substrate may further change the resulting shape of the ferrofluid. For example, when placed in proximity to a normal magnetic field (the Rosenweig instability), the ferrofluid substrate may form conical peaks. Small changes in volume may effectively change the strength of the magnetic field, thereby allowing the base of the resulting peaks to range from spherical to square to hexagonal. (See, Buzduga, C., V. Vlad, C. Ciufudean. Experimenting the Stability of Ferrofluids. Mathematical Models in Engineering and Computer Science Conference Paper, 2013, pp. 80). Using a three-dimensional configuration, such as that shown in
Upon exposure to a magnetic field, the apparent viscosity of the ferrofluid substrate may change. Those skilled in the art will appreciate that the higher the intensity magnetic field allows for a more viscous ferrofluid substrate. Increased viscosity aids in molding because the fluid becomes effectively gel-like, creating a stronger force against which to mold.
The present invention also provides for a magnetic system to surround the molding material in a central space. The magnetic system configuration may be arranged such that the field lines of the magnet serve as the basic map for the flow direction of the ferrofluid substrate. The shape may be narrowed and refined, or “guided”, by the metallic materials that may be present within the central space that align with the magnets as a magnetic field is applied. The metallic materials may further additionally dam or bridge flow between magnets of the magnetic system, allowing for a more diverse range of patterns and shapes to be achieved by the magnets. The metallic materials within the central space may also serve as a focus for the magnetic field lines; those produced by the magnets alone have directionality but not singularity, and the intermediary metallic elements assist to provide for shapes and flow, such as individual lines on the order of microns, to be singular features. For example, placing a gauge wire on a magnet, aligned with the direction of the magnetic field, and covered by a metallic shim will create a single line of ferrofluid; placing a bend on the magnet wire will allow the ferrofluid to follow the path of the bent wire. Without the gauge wire, the ferrofluid substrate would spread directionally in line with the magnetic field lines, creating multiple parallel lines along the magnet, but not a singular feature. Metallic elements within the central space, such as a gauge wire, can additionally create a ‘bridge’ to allow for flow between two magnets. For example, by placing a metal wire or razor between two magnets, one of greater strength than the other, and introducing the ferrofluid substrate to the weaker magnet, the ferrofluid substrate can flow between the magnets, following the path of the metallic element, moving from the weaker to the stronger magnet. Likewise repulsive field effects can be introduced within the magnetic system, such as placing a metallic element tangentially between two magnets (north pole to north pole), and allowing the field lines to repel in the direction of the metallic element. Magnets can also be arranged in a three-dimensional systems. For example, ferrofluid substrate placed between two cylindrical magnets will create an hourglass shape. Placing a wire between these can elongate the hourglass shape but allow the ferrofluid substrate to maintain continuity. In another configuration, the ferrofluid substrate can be held to a surface by one magnet, and by placing another in proximity can create arcs and wave-like shapes that can be molded.
The present invention also relates to for dynamic, flowing molds. The use of magnetism can provide for highly directed flow, allowing dynamic flow systems to be molded, such as that seen with highly controlled micro jet manufacturing. When ferrofluid substrate is constantly input into the system, the flow of the ferrofluid is directed by the magnetic system in place. For example, placing a ferrofluid substrate bath against two magnets with opposing poles in proximity to one another, the ferrofluid substrate will be pulled to the location with the highest field density, i.e., between the two magnets. A continuous input of ferrofluid substrate away from the location between the magnets, but still within the magnetic field, may therefore flow to that central location. Putting uncured or partially cured molding material on the ferrofluid substrate and curing that material as the ferrofluid substrate flows may allow those flow lines to be molded. In another example, a curing material volume is set within a central space within the magnetic system that allows ferrofluid substrate to flow through the curing material. The material is cured as the ferrofluid flows between the magnets and through the curing material, thereby creating a mold that has a channel. Those familiar with the fluidic systems art can appreciate that the flow created can take many forms, dependent on the flow factors (e.g., rate, volume etc.) applied.
The magnetic system may use any combination of ‘magnetic foci’, metallic elements and ‘guiding’ magnets. The field lines of magnets are at various locations straight and curved, and these lines may interact, either via attraction or repulsion, with other magnets present within the magnetic system. Manipulation of these field lines requires taking the natural direction of the field within a particular magnet and applying how it will interact with other magnets and metallic elements within a defined proximity, properties that are understood by those skilled in the art. The mold shape may be defined by the organization of the surrounding magnets such that the flow, shape and behavior of the ferrofluid substrate can be predicted. The ferrofluid substrate may then flow and/or align according to the direction and density of the field lines, and the field lines can become singular or complex features with the addition of metallic elements within the magnetic system.
The magnetic foci are permanent and electro-magnets that create a generalized field intensity to influence the ferrofluid substrate. Metallic elements, such as paramagnets and non-magnetic materials, can be placed in proximity to magnetic foci to allow the mold to form a specific shape.
Guiding magnets may also be used within the magnetic system to direct flow of the ferrofluid substrate.
Accordingly, these three elements of the magnetic system can be used in conjunction with one another to achieve the desired molding shape.
The present invention provides for a molding material to be applied to the ferrofluid substrate within a central space of the magnetic system. The moldable material should have a low miscibility with the ferrofluid substrate to prevent or reduce mixing with the ferrofluid substrate. The molding material may be introduced to the ferrofluid substrate as a solid or as a fluid. The fluid-state molding materials are applied volumetrically according to the curing limitations for the molding material (penetration depth of curing energy). For example, using ultraviolet light to cure Sartomer 399, several millimeters of photopolymer can be molded without layering, whereas SU8 and other photopolymers have penetration depths limited to hundreds of microns. Powdered materials can be applied using a more layered approach, the volume again dependent on the curing requirements. If induction or ovens are used to heat the powder, higher volumes of powder can be fused at one time. Using lasers, as three-dimensional printers typically do, layers of up to 20 microns are typically fused at a time, although the penetration depth of lasers in typical systems suggest a maximum of 500 microns. Curing using a directed radiative source may impose volumetric limits because the wavelength applied may be absorbed within a given distance. The specific distance may depend on the curing material's absorption of light.
Curing the molding material may require exposure to high temperatures. To prevent heating of the ferrofluid substrate when high heat is applied to the molding material, a fluidic thermal shield can be used, the carrier fluid can be used to absorb the heat, or the depth of the applied molding material on the ferrofluid can be equal or greater than that of the radiative heating method to prevent penetration to the ferrofluid layer.
The present invention can further use plastics or ceramics as the molding material to be cured, where the application of these materials is in liquid or powder form and parallels the considerations for photopolymer and metals.
The interaction between the molding material and the ferrofluid substrate may be analogous to three known behaviors.
Once applied, the molding material can be cured so as to create a mold. As is known to those skilled in the art, the process of curing the molding material is dependent upon the molding material used, as well as other parameters such as the volume of the final mold to be created. For example, a photopolymer requires curing by exposure to ultraviolet light; using melted plastics or metals requires curing by cooling; using powdered metals requires curing by the addition of heat. The resulting molded material can also additionally be cured by drying and baking.
Optionally, a further step in the method of the present invention may involve a wash of the remaining ferrofluid substrate, which remains in fluid form, enabling mold release, from the surface of the cured material. The wash used can be water or other chemicals that do not serve as a solvent for the molding material, such as water and acetone. Cleaning may enabled by the immiscibility of the molding material and the ferrofluid substrate. Excess material can additionally be removed by the application of magnets to pull the remaining fluid from the surface of the molded material.
The foregoing descriptions of various embodiments provide illustration of the inventive concepts. The descriptions are not intended to be exhaustive or to limit the disclosed invention to the precise form disclosed. Modifications or variations are also possible in light of the above teachings. The embodiments described above were chosen to provide the best application to thereby enable one of ordinary skill in the art to utilize the inventions in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention. Further, the disclosure of all patents, patent application and non-patent literature discussed herein is to be considered incorporated by reference in their entirety.
This application claims priority to U.S. Provisional Patent Applications 61/866,757, filed Aug. 16, 2013, all of which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61866757 | Aug 2013 | US |
