BACKGROUND OF THE INVENTION

Low density/high strength materials are used in subsea industries in a wide variety of applications. The primary purpose of the materials is to lend buoyancy and/or thermal insulation to equipment and structures to reduce load and/or minimize heat loss. The material of choice for this purpose is epoxy and glass microsphere-based syntactic foam. The epoxy provides strength to withstand the extreme pressures subsea. The hollow glass microspheres provide buoyancy and insulative value.

This material and the processes used to manufacture and convert these materials into buoyant/insulative objects have remained essentially unchanged for over 50 years. The most common process consists of mixing epoxy resins with hollow glass microspheres (also known as microballoons), dispensing this mixture into molds or rotationally-molded plastic housings and then curing. In some cases, to increase buoyancy and/or insulative value further, larger hollow spheres (sometimes referred to as macrospheres) are added to the molds or housings and the syntactic foam is poured around them. In almost all cases, secondary

manufacturing processes are necessary to complete the objects.

Since the applications for these materials vary widely, innumerable sized and shaped forms must be created. Custom tooling must almost always be produced to cast the parts. This is an expense and also adds time to each project.

There are numerous drawbacks to this existing material and methodology which have yet to be overcome. A first drawback is that the bulk processing methodology relies on random arrangement of both microspheres and/or macrospheres (both of which contain a distribution of sizes) to create voids within the epoxy. As such, theoretical maximum packing of voids is never achieved. For example, an object with regularly- sized spheres, carefully packed, can achieve a void density of 74%. Maximum void density achieved by random packing of microspheres yields approximately 64%. With the addition of macrospheres to the syntactic foam, void density can be increased further but will never result in optimum sphere packing.

A second drawback is that the spheres are permitted to touch one another or have only a minimum thickness of epoxy between them. Ideally, there would be a carefully calculated thickness of epoxy between each void space to maximize composite strength and insulative value, and minimize density.

A third drawback is that random packing and batch processing technology allows for areas of castings to be void of epoxy. These spaces have microspheres or macrospheres that are not properly encapsulated in epoxy, resulting in weak sections in the objects.

Needs exist for improved subsea buoyancy and insulation materials and processes to meet the challenging demands of subsea applications.

SUMMARY OF THE INVENTION

The present invention relates to both a material construction and manufacturing method resulting in low density materials, especially for use as subsea buoyancy and insulation. The products are made by an additive manufacturing process, creating thin plural sequential layers of material while leaving voids of precisely controlled predetermined shapes, sizes and distribution, and with precisely controlled predetermined material thicknesses between the voids. Each sequential layer is produced as a liquid and then hardened, partially cured or fully cured. The resulting products provide optimized strength, buoyancy and insulative value with minimal material usage and density.

The present invention provides material with optimized void spaces created by additive manufacturing, such as 3D printing. The result is a low density material suitable for use in high pressure/force applications using a methodology of precisely arranging voids and precisely controlling material thicknesses around and between voids to minimize density whilst maximizing strength.

Material is selected and designed by beginning with the application' s geometric, pressure, density and/or insulative constraints. The solution is modeled in 3D CAD, and the void spaces are optimized. The strength of the result can be verified through finite element analysis (FEA). Upon completion of the design, the 3D CAD model is prepared for manufacturing. In the case of 3D printing, the material is printed layer by layer using the additive manufacturing process. The material is uniform or varied within the layers and/or within adjacent layers.

Optimization of void space is achieved through varying void size and shape, void placement, wall thickness between voids and external wall thicknesses in accordance with the requirements of a particular application.

In one embodiment, the voids are spheres, and the spheres are of varied sizes chosen for optimum packing, strength and/or insulative value. In another embodiment, the voids are oblate spheroids. Void shapes are unlimited and are based on the density, strength and/or insulative project requirements.

In one embodiment, the material is printed at atmospheric pressure. In other embodiments, the material incorporating the void volumes is printed in increased or reduced ambient pressures, the latter also being referred to herein as vacuum. In another embodiment, the void spaces may be filled with gases other than air which are present by filling the printer enclosure with selected, usually inert, gases.

In one embodiment the printed material is unitary. In another embodiment the void spaces are encapsulated by specific printed materials, and the balance of the printed material is a different material. In another embodiment an additional material is printed as an external shell. In another embodiment reinforcing materials, either printed or placed, are added to increase strength.

The invention provides the potential to supplant all instances of use of syntactic foam in subsea buoyancy and insulation material. An inherent value of the invention is the resultant material structure of precisely arranged predetermined voids in solid material. The material structure can be manufactured practically by using additive manufacturing processes. A low density material suitable for use in high pressure/force applications uses a methodology of precisely arranging predetermined voids and precisely controlling material thicknesses around and between the voids to minimize density while maximizing strength. A wide list of materials to print and materials to add includes as examples epoxy, vinyl esters, thermoplastics, polyurethanes, syntactic foam, styrenes, nanoparticles, glass fibers, carbon fibers, microspheres and natural fibers. Manufacturing process can also be performed under atmospheric pressure, increased or reduced pressure for controlling internal pressures in the voids and controlling air or gas content in the voids.

The invention provides strong low density objects with minimized density with maximized strength for use in high pressure/force applications. Objects have precisely controlled voids at predetermined locations and precisely controlled predetermined material thickness between the precisely controlled voids. The material is preferably a polymer containing fibers, nanoparticles, glass fibers, carbon fibers, microspheres, natural fibers, or combinations thereof. The polymer material is preferably a polymer such as: epoxy, vinyl, esters, thermoplastics, polyurethanes, syntactic foam, styrenes or combinations thereof. In one embodiment the polymer may be a solid polymer. The voids contain a gas or mixture of gases under atmospheric pressure, increased pressure or reduced pressure (the latter being also known as vacuum).

The gas is air, an inert gas or a low density gas.

In one form, the material is a first material, and the predetermined voids are surrounded by a second material between the first material and the voids. The first material and the second material are formed in thin plural sequential layers. The sequential layers of the first material and the second material are sequential layers deposited by an additive manufacturing process. The material is formed in thin plural sequential layers having predetermined material thickness between the predetermined locations of the voids.

A shell is formed around an outside of the material.

A new method forms a low density three-dimensional high pressure and force -resistant subsea buoyancy object by forming a material in additive layers around predetermined and precisely controlled sizes and positions of voids, while precisely controlling predetermined thicknesses of the material around and between the voids. The method uses an additive manufacturing process, such as three-dimensional printing. The method includes printing the material in an enclosure having a vacuum or a gas under a controlled pressure, wherein the voids contain the vacuum or the gas under the controlled pressure. In one method the material is a first material and a second material is deposited in the thin plural sequential layers between the first material and the predetermined voids, thereby forming surfaces of the second material surrounding the voids between the voids and the first material. An outer material layer is formed outside the first material around the object.

These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a cross-section of microspheres randomly mixed in an epoxy.

Figure 2 shows microspheres and macrospheres together in a casting as well as some loose macrospheres.

Figure 3 shows a cutaway of a plastic shell filled with foam and a mold containing syntactic foam.

Figure 4 shows an example of the invention in a cutaway of a printed part showing a solid material with different sized voids inside.

Figure 5 shows an example of the invention with a printed part that demonstrates naked voids and voids encapsulated by a material that is different from the primary solid material.

Figure 6 shows an example of a cutaway of a new printed part showing a solid material with different sized voids inside and a printed exterior shell of a secondary material.

Figure 7 is a schematic example of a part being printed.

DETAILED DESCRIPTION

Figure 1 is a microscopic image of a cross-section of microspheres 12 randomly mixed in epoxy 10. The image shows both the variation in size and shape of the microspheres 12, as well as the random packing of those spheres in the epoxy 10. Figure 2 shows macrospheres 14 of different sizes together with microsphere-filled foam in prior art syntactic foam casting 10 as well as some loose macrospheres 14. The image shows both the variation in size and shape of the macrospheres 14, as well as the random packing 16 of those spheres.

Figure 3 shows a cutaway of a plastic shell 30 filled with foam 32 and a mold 34 containing syntactic foam 32. In this image the objects are shown with syntactic foam 32 without macrospheres. The plastic housing has a fill port 31 through which the housing is filled. Once poured and cured, the object may undergo secondary operations (like drilling of mounting holes) before being ready for shipment. The mold shown 34 is typical. Molds are often made of wood or metal. The foam would be poured into open area of the mold and cured. After curing the foam 32 would be removed from the mold 34 and finished.

Figure 4 shows a cutaway of a printed part 40 of one embodiment of the invention, showing a solid material 42 with different sized voids 44 inside. The void sizes, shapes and placement and the thickness of the solid material 46 between the voids are determined prior to additive manufacturing and optimized to produce the best density/strength ratio for the application.

Figure 5 shows a printed part 50 of the invention that demonstrates naked voids 54 and voids 56 encapsulated by a material that is different from the primary solid material 52. A secondary material may be used to increase accuracy of void shape and size or to increase processing speeds by allowing the void shapes 56 to be printed precisely and the primary solid material 52 to be printed more rapidly.

Figure 6 shows a cutaway of a printed part 60 showing a solid material 62 with different sized voids 64 inside and a printed exterior shell 68 of a secondary material. Printing of an exterior shell creates a protective or decorative external surface and can eliminate the need for a secondary finishing process.

Figure 7 shows a part 50 being printed. The machine 70 includes components 72, 74 that allow for multiple axis movement of dispensing equipment 76 and/or printed part 50. The movements are computer controlled.

While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is defined in the following claims.