Aspects and embodiments disclosed herein are generally directed metal molds for casting to synthetic dry adhesive microstructures.
The gecko is known for its ability to climb smooth vertical walls and even to suspend itself inverted from smooth surfaces. This ability is derived from the presence of elastic hairs called setae that split into nanoscale structures called spatulae on the feet and toes of geckos. The abundance and proximity to the surface of these spatulae make it sufficient for van der Waals forces alone to provide the required adhesive strength for a gecko to climb smooth vertical walls. Researchers have been inspired to create synthetic structures, sometimes referred to as “gecko adhesive,” that mimic the natural adhesive properties of gecko feet.
In accordance with one aspect, there is provided a method of forming a metal mold for casting a micro-scale dry adhesive structure. The method comprises securing a master patch of material including a micro-scale dry adhesive structure on a plating fixture, electroforming the metal mold on the master patch of material, and removing the metal mold from the master patch of material and the plating fixture.
In some embodiments, the method further comprises depositing an adhesion layer on the micro-scale dry adhesive structure, and depositing a release layer on the adhesion layer prior to electroforming the metal mold on the master patch of material.
In some embodiments, the master patch of material is mounted to a backing substrate and the method comprises securing the backing substrate in a cavity of the plating fixture.
In some embodiments, the method further comprises depositing fillets on an interface area between the backing substrate and the plating fixture.
In some embodiments, the micro-scale dry adhesive structure includes an array of microwedges having center lines disposed at an angle of between about 30 degrees and about 70 degrees relative to a plane defined by bases of the microwedges. The microwedges in the array of microwedges may have leading edges disposed at an angle of between about 20 degrees and about 65 degrees relative to the plane defined by the bases of the microwedges. The microwedges in the array of microwedges may have trailing edges disposed at an angle of between about 35 degrees and about 85 degrees relative to the plane defined by the bases of the microwedges. The microwedges in the array of microwedges may have heights of between about 80 μm and about 120 μm and bases of between about 20 μm and about 40 μm. The microwedges in the array of microwedges may have lengths of between about 120 μm and about 160 μm.
In some embodiments, the method further comprises depositing a layer of release agent on a portion of the metal mold.
In accordance with another aspect, there is provided a method of forming a mold for casting a micro-scale dry adhesive structure. The method comprises forming an array of stubs on a metal block and cutting a negative form of an array of micro-wedges from the array of stubs.
In some embodiments, the method comprises cutting between about 5 μm and about 10 μm or between about 10 μm and about 20 μm of metal from sides of the stubs in the array of stubs to form the negative form of the array of micro-wedges.
In some embodiments, the method comprises cutting the negative form of the array of micro-wedges from the stubs with a fine finishing tool. The method may comprise cutting the negative form of the array of micro-wedges from the stubs with a diamond micromachining tool. Forming the array of stubs may include cutting recesses in the metal block with a micromachining tool other than the diamond micromachining tool.
In some embodiments, forming the array of stubs includes 3D printing the stubs on the metal block.
In accordance with another aspect, there is provided a metal mold for casting a micro-scale dry adhesive structure. The metal mold comprises a metal block including an upper surface and a negative pattern for an array of micro-scale dry adhesive structures defined in the upper surface, the upper surface at least partially coated with a release agent to reduce adhesion between the metal mold and a casting material for the micro-scale dry adhesive structure.
In some embodiments, the array of micro-scale structures includes an array of microwedges.
In some embodiments, the microwedges have heights of between about 80 μm and about 120 μm and bases of between about 20 μm and about 40 μm. The microwedges may have center lines disposed at an angle of between of between about 30 degrees and about 70 degrees relative to a plane defined by bases of the microwedges. The microwedges may have leading edges disposed at an angle of between about 20 degrees and about 65 degrees relative to the plane defined by the bases of the microwedges. The microwedges may have trailing edges disposed at an angle of between about 35 degrees and about 85 degrees relative to the plane defined by the bases of the microwedges.
In accordance with another aspect, there is provided a method of casting a micro-scale dry adhesive structure in a metal mold. The method comprises providing a metal mold including a negative pattern for the micro-scale dry adhesive structure in an upper surface of the metal mold, depositing a casting material on the negative pattern, and curing the casting material.
In some embodiments, the method further comprises at least partially coating the upper surface with a release agent to reduce adhesion between metal mold and the casting material.
In some embodiments, the negative pattern includes a negative pattern for an array of microwedges having center lines disposed at an angle of between of between about 30 degrees and about 70 degrees relative to a plane defined by bases of the microwedges. The negative pattern may include a negative pattern for the array of microwedges with leading edges disposed at an angle of between about 20 degrees and about 65 degrees relative to the plane defined by the bases of the microwedges. The negative pattern may include a negative pattern for the array of microwedges with trailing edges disposed at an angle of between about 35 degrees and about 85 degrees relative to the plane defined by the bases of the microwedges.
In some embodiments, the method further comprises forming the metal mold with an electroplating process.
In some embodiments, the method further comprises machining the negative pattern into the upper surface of the metal mold.
In accordance with another aspect, there is provided a method of forming a mold for casting a micro-scale dry adhesive structure. The method comprises cutting a negative pattern of micro-wedges from the metal block with a diamond micromachining tool.
The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
Aspects and embodiments disclosed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Aspects and embodiments disclosed herein are capable of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
Aspects and embodiments disclosed herein are generally directed to the formation of novel synthetic “dry adhesive” structures (the term dry adhesive comprising both adhesive and/or friction enhancing structures) and methods and apparatus for making same. Dry adhesive and/or friction enhancing structures disclosed herein may include micro-scale elements, for example, elements having characteristic dimensions of less than about 100 μm, and are thus referred to herein as micro-scale dry adhesive structures. An example of an embodiment of a micro-scale dry adhesive structure including a pattern of micro-elements is illustrated in
Embodiments of the micro-scale dry adhesive structures disclosed herein may be formed from a polymer, for example, polydimethylsiloxane (PDMS), other silicones, polyurethane, or another polymeric material. Specific examples of polyurethanes that embodiments of the adhesive structures disclosed herein may be formed include M-3160 A/B polyurethane and L-3560 A/B polyurethane, available from BJB Enterprises. In some embodiments, the material from which embodiments of the micro-scale dry adhesive structures disclosed herein may be formed exhibit a Shore A hardness of between about 40 and about 60.
In some embodiments, the microwedges 10 of the micro-scale dry adhesive structure 1 may include an adhesion and/or friction enhancing layer, for example, lips 20 as illustrated in
In some embodiments, the bases b of individual microwedges 10 may be spaced from one another, as illustrated in
In some embodiments, the micro-scale dry adhesive structure may be mounted on a rigid base substrate, for example, a substrate including layers of carbon fibers and plywood, and/or of a rigid polymer (in some embodiments, glass-reinforced) to provide the micro-scale dry adhesive structure with enhanced mechanical stiffness and/or to maintain the microwedges 10 in a substantially same plane.
In some embodiments, micro-scale dry adhesive structures as illustrated in
In accordance with aspects disclosed herein, a mold for casting micro-scale dry adhesive structures that is more durable than a polymer or epoxy mold may be formed from a metal or metal alloy. In some embodiments, the metal mold may be formed by electroforming, micromachining, or a combination of the two.
A process for electroforming a metal mold for casting micro-scale dry adhesive structures is illustrated beginning at
In other embodiments, where the micro-scale dry adhesive structure 1 is not mounted on a backing substrate 225, the micro-scale dry adhesive structure 1 may be directly adhered to a flat upper surface 240 of the plating fixture 230 using any of a variety of adhesives known in the art, for example, double-stick tapes (e.g., REVALPHA™ thermal release tape, Nitto Denko Corporation) or glues (e.g., Sil-Poxy® silicone rubber adhesive, Smooth-On Inc.). A roller including a rigid tube covered with a compliant layer, for example, neoprene may be used to apply the micro-scale dry adhesive structure 1 to the plating fixture 230, squeezing the micro-scale dry adhesive structure 1 as it is applied to the plating fixture 230 to minimize the formation of air bubbles between the micro-scale dry adhesive structure 1 and the plating fixture 230.
The plating fixture 230 may comprise steel or any other rigid, and optionally, conductive, material. In some embodiments, the backing 15 of the micro-scale dry adhesive structure 1 may extend above the upper surface 240 of the plating fixture 230, for example, by about 0.027 inches (about 0.06 cm) to set a uniform 0.027 inch recess into the finished metal mold to form the backing 15 of additional micro-scale dry adhesive structures 1 from the finished metal mold.
A fillet 245, for example, an epoxy fillet, may be formed at the interface 250 between side walls of the backing 15 of the micro-scale dry adhesive structure 1 and the plating fixture 230. The epoxy fillet 245 is used to fill any gaps that might be present between the micro-scale dry adhesive structure 1 and the cavity 235 of the plating fixture 230 to prevent metal from being electroformed in any such gaps and forming undesired features on an electroformed mold or that may make it difficult to release the completed electroformed mold from the plating fixture 230.
As illustrated in
A seed metal layer 260, for example, a layer of molybdenum or copper, is deposited onto the release layer 250 or micro-scale dry adhesive structure 1 (
The metal mold is then removed from the micro-scale dry adhesive structure 1 and plating fixture, resulting in a completed metal mold 270 (
In other embodiments, the metal mold 270 may be used as an injection mold insert. The metal mold 270 may be placed in an injection molding apparatus in an opposed position to a backing substrate 225. A polymer material may be injected into the space between the metal mold 27 and the backing substrate 225 to form a micro-scale dry adhesive structure mounted on a backing substrate 225 in a single injection molding operation.
In other embodiments, a metal mold 270 for casting micro-scale dry adhesive structures may be formed without the use of a pre-fabricated micro-scale dry adhesive structure by directly machining a metal block 275. For example, a metal block 275 may optionally be roughly machined by standard micromachining tools, for example, micro-milling bits made from tool steel or polycrystalline diamond stock (˜0.001″-0.010″ in diameter), to form an array of wedge stubs 280 with a desired orientation, wedge angle and pitch. In some embodiments, cutouts between adjacent wedges may have dimensions, for example widths, about 10 μm to about 20 μm less than the cutouts that will be used to mold microwedges in a finished mold. A diamond tool or other fine finishing tool (formed from, for example silicon carbide or tool steel) may be used to further process the metal block 275 to form finished microgrooves 285 and complete the metal mold 270 (
The metal mold 270 may be used for casting micro-scale dry adhesive structures. As illustrated in
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 62/090,265 titled “DURABLE MICRO/NANO MOLD FABRICATION TECHNIQUES” filed Dec. 10, 2014, which is incorporated herein by reference in its entirety for all purposes.
Filing Document | Filing Date | Country | Kind |
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PCT/US15/64798 | 12/9/2015 | WO | 00 |
Number | Date | Country | |
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62090265 | Dec 2014 | US |