Patent Description:
Typical sandwich structures are used for high stiffness/low weight applications consisting of face sheets, core, and fastener hard points. The different materials are joined by an adhesive, which is the weakest point and labor intensive.

<NPL>, discloses a flexural support technique for a primary mirror of a telescope, the mirror comprising a front face, bearing the reflective surface, which is supported by a network of ribs.

<CIT> discloses a sandwich structure including a first skin, a second skin, a first hinge member, and a second hinge member. The first hinge member is movably coupled to the first skin at a first skin joint. The second hinge member is movably coupled to the second skin at a second skin joint. The first hinge member and the second member are movably coupled to one another at a member joint located between the first and second skin joint. The joints may be rigid or flexible.

A sandwich structure has an internal lattice with hard points.

A sandwich structure has an additively-manufactured lattice structure that includes hard points.

According to an aspect of the invention, a sandwich structure comprising: a pair of face plates; and a lattice structure between the face plates; wherein the lattice structure includes stiffened hard points that are stiffer than surrounding regions of the lattice structure; wherein the hard points are located at junctions between the lattice structure and one of the face plates; wherein the hard points provide anchor points for fasteners, to mechanically couple the sandwich structure to one or more other objects; wherein the hard points function as nut plates that are configured to receive threaded fasteners; and wherein the hard points have integrally-formed internally-threaded holes.

According to an embodiment of any paragraph(s) of this summary, the lattice structure is additively manufactured as a unitary piece.

According to an embodiment of any paragraph(s) of this summary, at least one of the face plates is also additively manufactured as part of the unitary piece that includes the lattice structure.

According to an embodiment of any paragraph(s) of this summary, the lattice structure and at least one of the face plates are made of the same material.

According to an embodiment of any paragraph(s) of this summary, the lattice structure includes ribs.

According to an embodiment of any paragraph(s) of this summary, some of the ribs are stiffer than other of the ribs.

According to an embodiment of any paragraph(s) of this summary, some of the ribs are made of different material(s) than other of the ribs.

According to an embodiment of any paragraph(s) of this summary, some of the ribs are thicker than other of the ribs.

According to an embodiment of any paragraph(s) of this summary, the lattice structure includes ribs, at least some of which are hollow ribs.

According to an embodiment of any paragraph(s) of this summary, the lattice structure includes ribs angled at multiple non-perpendicular angles to major surfaces of the face plates.

According to another aspect of the invention, a method of making a sandwich structure, the method comprising: manufacturing a lattice structure of the sandwich structure; wherein the lattice structure is between face plates of the sandwich structure; and the lattice structure includes stiffened hard points that are stiffer than surrounding regions of the lattice structure; wherein the hard points are located at junctions between the lattice structure and one of the face plates; wherein the hard points provide anchor points for fasteners, to mechanically couple the sandwich structure to one or more other objects; wherein the hard points function as nut plates that are configured to receive threaded fasteners; and wherein the hard points have integrally-formed internally-threaded holes.

According to an embodiment of any paragraph(s) of this summary, the manufacturing of the lattice structure is additive manufacturing.

According to an embodiment, the lattice structure includes ribs extending between the face plates.

According to an embodiment of any paragraph(s) of this summary, the ribs intersect with the stiffened hard points.

To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.

A sandwich structure includes two face plates, with a lattice structure between the plates, and with hard points at selected locations. The face plates, and the lattice structure with its hard points, may all be made as a single continuous piece by an additive manufacturing process. The hard points may be strengthened and/or stiffened areas of the lattice that may be used for connecting fasteners, or for other purposes. The hard points may be located at the junction between the lattice and one of the faces, and may be a locally thickened portion on one of the faces, for example being a cylindrical or parallelepiped protrusion out from the face. The hard points may serve the purpose of a built-in nut plate, such as themselves containing threaded holes, or by having a threaded inserts put into holes or recesses in the hard points.

The lattice may have ribs that are all substantially the same. Alternatively some of the ribs may have different materials, different thicknesses, and/or different configurations than other of the ribs. Stronger and/or stiffer ribs, and/or additional ribs, may be used in areas where the lattice carries higher loads. Some or all of the ribs may be hollow.

<FIG> show a sandwich structure <NUM> that includes a pair of face plates <NUM> and <NUM>, and a lattice structure <NUM> between the plates <NUM> and <NUM>. The lattice structure <NUM> includes a series of ribs or struts <NUM> that are angled relative to one another, and that extend between the plates <NUM> and <NUM>. The ribs <NUM> may intersect with one another, and may be in any of a variety of configurations. The ribs <NUM> of the lattice structure <NUM> may be considered to be a truss, providing support between the face plates <NUM> and <NUM>, while still having considerable empty space between and around the ribs <NUM>. This provides a structural member that is light weight, yet of considerable strength and/or stiffness, able to bear and withstand loads.

The lattice structure <NUM> may be a periodic structure, with a configuration that repeats in directions parallel to the plates <NUM> and <NUM>. In some embodiments, there may be portions of the lattice structure <NUM> that divert from the period structure in number, characteristics, or configuration of ribs <NUM>.

The lattice structure <NUM> includes hard points <NUM>. The hard points <NUM> are strengthened and/or stiffened points of the lattice <NUM>, stronger and/or stiffer than adjoining portions of the lattice <NUM>. The hard points <NUM> may be at the junction between the lattice structure <NUM> and the face plate <NUM>, as shown in the illustrated embodiment.

The hard points <NUM> may be used for making connection to the structure <NUM>. For example the hard points <NUM> may be used as nut plates integrally built into (and part of) the lattice structure <NUM>. The hard points <NUM> may have integrally-formed internally-threaded holes in them for receiving fasteners or other suitable devices. With regard to threaded fasteners, the hard points <NUM> may have threaded holes, as is shown in the illustrated embodiment, or alternatively may have holes or recesses for receiving internally threaded inserts.

The hard points <NUM> may have any of a variety of shapes and thicknesses. For example the hard points <NUM> may have cylindrical and/or parallelepiped shapes, to give two non-limiting examples. The hard points <NUM> each may have a lateral extent (such as a diameter or length) that is greater than their height away from the adjoining face plate <NUM>, for example.

The hard points <NUM> may also be at locations that are built up or reinforced with additional material, such as the protrusions <NUM>, on an opposite side or major face of the plate <NUM> from where the hard points <NUM> are located.

The sandwich structure <NUM> may be made by an additive manufacturing process, as a single, unitary continuous piece. A suitable additive manufacturing method for making the sandwich structure <NUM> is laser powder bed fusion, in which laser energy is directed to selective portions of a powder bed to melt material that is then solidified, building up the sandwich structure <NUM> layer by layer. Other suitable additive manufacturing techniques may be employed, for example directed energy deposition using a laser with powder directed into the laser beam to build up material, or with extrusion and melting of a wire to build up material at desired locations. All of these methods may involve movement of some sort of energy source relative to a bed upon which the sandwich structure <NUM> is built.

The sandwich structure <NUM> may be made all of the same material, or may be made from multiple materials, with different material composition in different parts of the sandwich structure <NUM>. Materials may include metallic materials and/or non-metallic materials. Non-limiting examples of suitable metallic materials include metallic elements such aluminum, titanium, and copper, and metallic alloys such as nickel-chromium alloys marketed under the trademark INCONEL, and iron-nickel alloys marked as INVAR and SUPER-INVAR. Non-limiting example nonmetals include ceramic materials, and low-dielectric polymers.

The face plates <NUM> and <NUM> may be flat, as is shown in the illustrated embodiment of <FIG>. Alternatively the face plates <NUM> and <NUM> may be curved, or may have other non-flat configurations. In the illustrated embodiment the face plates <NUM> and <NUM> are shown as having uniform thickness, but alternatively there may be variations in thickness in one or both of the face plates <NUM> and <NUM>, for example to increase strength and/or stiffness when additional load needs to be supported.

Similarly, there may be variations in the material composition, thickness, and/or other characteristics of the ribs <NUM>. The ribs <NUM> may be stronger and/or stiffer in areas that receive more loading. The stronger and/or stiffer ribs of the ribs <NUM> may be thicker than other of the ribs <NUM>. Alternatively or in addition some or all of the ribs <NUM> may be hollow. Hollow ribs have the advantage of lighter weight.

The sandwich structure <NUM> has many advantageous characteristics. It is a lightweight structure that includes the self-supporting hard points <NUM> that (in some embodiments) are used for mounting. The mounting may involve mounting the structure <NUM> to other objects, and/or may involve mounting other objects onto the sandwich structure <NUM>. The sandwich structure <NUM> can have local reinforcement where needed and its manufacture requires no adhesive, joining, or wire electric discharge machining (EDM). If the sandwich structure <NUM> is all made of the same material it has isotropic properties, which gives it uniform growth or shrinkage from temperature changes. This is a significant advantage in situations where dimensional stability is important, such as for optical mirror supports or precision structures.

As noted above, the sandwich structure <NUM> may be optimized for stiffness and/or weight by having extra material in high-stress areas, and less material in low-stress areas. Also these benefits may be achieved by use of different materials in different parts of the structure.

The sandwich structure <NUM> may have reduced weight, reduced cost (in terms of analysis, manufacturing, touch labor, number of drawings, potential for scrap, additional steps such as heat treatments, and/or tooling required for complex shapes), reduced lead time, reduced part count, increased strength and/or stiffness, the ability to achieve configurations not achievable by prior manufacturing techniques, and/or isotropic properties that may lead to improved dimensional stability that is not possible with prior structures. Any combination of these advantageous may be achieved or achievable in any embodiment of the sandwich structure <NUM> described above.

The sandwich structure <NUM>, or variations of such structure, may be employed for a wide variety of purposes. The sandwich structure may be used as structural support, or as a mounting, such as for optical components. Other possible uses are as a radiation shield (against radio frequency (RF) radiation), a thermal shield, or as part of a heat exchanger.

<FIG> show another view of the configuration of the ribs or struts <NUM> in the lattice structure <NUM>. The ribs <NUM> are in a pattern at angles of <NUM> degrees from the direction perpendicular to the major surfaces of the face plates <NUM> and <NUM>, with the ribs <NUM> intersecting midway between the face plates <NUM> and <NUM>. This is only one example of an arrangement of the lattice structure <NUM>. Many other configurations are possible.

The parts of the sandwich structure <NUM> may have any of a variety of suitable dimensions. For example the ribs <NUM> may have diameters (or longest cross-sectional extents) of <NUM>-<NUM> (<NUM>-<NUM> inches), to give non-limiting examples. The face sheets <NUM> and <NUM> may also have a thickness of <NUM>-<NUM> (<NUM>-<NUM> inches), to give non-limiting examples. The structure <NUM> may have a length, width, and/or height of up to about <NUM> (<NUM> inches), with the above thicknesses appropriate for structures of such size. It may be possible to have larger structures, for example with dimensions up to <NUM> (<NUM> inches) or more, with correspondingly thicker face sheets <NUM> and <NUM>, and/or ribs <NUM>.

<FIG> show various alternate embodiments, some of which were mentioned above. The features of these alternate embodiments may be combined with those of other embodiments (including the embodiment shown in <FIG>) in any combination. In the descriptions that follow many details are omitted, being the same as or similar to those discussed above.

<FIG> show an alternate arrangement of ribs or struts, with a sandwich structure <NUM> having a lattice structure <NUM> between face plates <NUM> and <NUM>. Ribs or struts <NUM> of the lattice structure <NUM> are in a pyramidal pattern with the ribs <NUM> at an angle of <NUM> degrees from the direction perpendicular to the major surfaces of the face plates <NUM> and <NUM>. The ribs <NUM> extend directly between the face plates <NUM> and <NUM>.

The ribs <NUM> and <NUM> may have any of a variety of suitable cross-section shapes. For example the ribs <NUM> and <NUM> may be circular or elliptical.

<FIG> shows another variant, a sandwich structure <NUM> which has hard points <NUM> that have a parallelepiped shape, with internally-threaded inserts <NUM> in recesses or holes <NUM> in the hard points <NUM>. The inserts <NUM> allow the hard points <NUM> to receive threaded fasteners, with the hard points <NUM> functioning as nut plates.

<FIG> shows a sandwich structure <NUM> which has curved face plates <NUM> and <NUM>, between which is a lattice structure <NUM> with hard points <NUM>. As illustrated by <FIG>, the face plates of a sandwich structure may have a wide variety of suitable shapes, for example for conforming to an object or objects to which the sandwich structure is to be mechanically coupled.

<FIG> shows a further embodiment, a sandwich structure <NUM> which has a lattice structure <NUM> with hard points <NUM>, between face plates <NUM> and <NUM>. Unlike other embodiments, the face plates <NUM> and <NUM> have non-uniform thickness, for example being thicker in higher stress areas <NUM> and <NUM>.

<FIG> shows a sandwich structure <NUM> that illustrates several possible characteristics for making a lattice structure <NUM> more structurally robust in some local areas. Ribs <NUM> of the lattice structure <NUM> are between face plates <NUM> and <NUM>. Parts of the lattice <NUM> are stronger/weaker than other parts in order to tailor parts of the lattice structure <NUM> for handling different expected loads.

The ribs <NUM> include, for example, a first set of ribs <NUM> that have a different composition, being made of different material than other of the ribs <NUM>. The ribs <NUM> can also include a second set of ribs <NUM> that are thicker and thus stronger and/or stiffer than the first set of ribs <NUM>. As another example, a third set of ribs <NUM> are hollow, and are not as strong (stiff) as other ribs <NUM>, such as either the first or second sets of ribs <NUM>, <NUM>, but have the advantage of being lighter. Finally, an additional fourth set of ribs <NUM> is placed in a high-load area, providing additional strength and/or stiffness over that of the other parts of the lattice structure <NUM>. It will be appreciated that these features may be combined in the same region, in any combination, if desired.

Claim 1:
A sandwich structure (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a pair of face plates (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>); and
a lattice structure (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) between the face plates;
wherein the lattice structure includes stiffened hard points (<NUM>, <NUM>, <NUM>) that are stiffer than surrounding regions of the lattice structure;
wherein the hard points are located at junctions between the lattice structure and one of the face plates;
wherein the hard points provide anchor points for fasteners, to mechanically couple the sandwich structure to one or more other objects;
wherein the hard points function as nut plates that are configured to receive threaded fasteners; and
wherein the hard points have integrally-formed internally-threaded holes.