U.S. patent application number 17/738044 was filed with the patent office on 2022-08-18 for sheet material, mold, and methods of making and using the sheet material and mold.
This patent application is currently assigned to RigidCore Group LLC. The applicant listed for this patent is RigidCore Group LLC. Invention is credited to Robert J. Bingham.
Application Number | 20220259857 17/738044 |
Document ID | / |
Family ID | |
Filed Date | 2022-08-18 |
United States Patent
Application |
20220259857 |
Kind Code |
A1 |
Bingham; Robert J. |
August 18, 2022 |
Sheet Material, Mold, and Methods of Making and Using the Sheet
Material and Mold
Abstract
A one-piece component comprising a tetrahedral-octahedral
honeycomb lattice is disclosed herein, along with a mold, a system
and methods of making the component. A one-piece component
comprising a truncated tetrahedral-octahedral honeycomb lattice
also is disclosed, along with corresponding molds, systems and
methods.
Inventors: |
Bingham; Robert J.; (Canton,
CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RigidCore Group LLC |
Hartford |
CT |
US |
|
|
Assignee: |
RigidCore Group LLC
Hartford
CT
|
Appl. No.: |
17/738044 |
Filed: |
May 6, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16311430 |
Dec 19, 2018 |
11365543 |
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PCT/US2018/028801 |
Apr 23, 2018 |
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17738044 |
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62489060 |
Apr 24, 2017 |
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International
Class: |
E04C 2/36 20060101
E04C002/36; B32B 27/08 20060101 B32B027/08; B32B 3/12 20060101
B32B003/12; B33Y 80/00 20060101 B33Y080/00; B29C 33/00 20060101
B29C033/00; B29C 45/04 20060101 B29C045/04; B29C 43/22 20060101
B29C043/22; B29C 45/37 20060101 B29C045/37; B29C 33/42 20060101
B29C033/42; E04C 2/32 20060101 E04C002/32 |
Claims
1. A one-piece component comprising a tetrahedral-octahedral
honeycomb lattice.
2. The one-piece component of claim 1, wherein the component is
isotropic.
3. The one-piece component of claim 1, wherein the component is
quasi-isotropic.
4. The one-piece component of claim 1, wherein the component
comprises substantially flat, parallel first and second faces.
5. The one-piece component of claim 1, wherein the component
comprises curved, generally parallel first and second faces.
6. A structure comprising the one-piece component of claim 1.
7. The structure of claim 6, comprising at least one of a floor, a
ceiling, a wall, a door and a compartment of at least one of a
building, a vehicle, an aircraft, a watercraft, a train, or a cover
of at least one of a floor, a ceiling, a wall, a door and a
compartment of at least one of a building, a vehicle, an aircraft,
a watercraft, a train.
8. The structure of claim 6, comprising at least one of a turbine
blade, a pallet, a shipping container and a roadside fixture.
9. A one-piece component comprising a truncated
tetrahedral-octahedral honeycomb lattice.
10. The one-piece component of claim 9, wherein the component is
isotropic.
11. The one-piece component of claim 9, wherein the component is
quasi-isotropic.
12. The one-piece component of claim 9, wherein the component
comprises substantially flat, parallel first and second faces.
13. The one-piece component of claim 9, wherein the component
comprises curved, generally parallel first and second faces.
14. The one-piece component of claim 9, wherein at least some of
the tetrahedral portions of the tetrahedral-octahedral honeycomb
lattice are truncated.
15. The one-piece component of claim 9, wherein at least some of
the octahedral portions of the tetrahedral-octahedral honeycomb
lattice are truncated.
16. The one-piece component of claim 9, wherein at least some of
the tetrahedral portions and at least some of the octahedral
portions of the tetrahedral-octahedral honeycomb lattice are
truncated.
17. The one-piece component of claim 9, wherein substantially all
of the tetrahedral portions and octahedral portions of the
tetrahedral-octahedral honeycomb lattice are truncated.
18. A structure comprising the one-piece component of claim 9.
19. The structure of claim 18, comprising at least one of a floor,
a ceiling, a wall, a door and a compartment of at least one of a
building, a vehicle, and aircraft, a watercraft and a train, or a
cover for a portion of at least one of a floor, a ceiling, a wall,
a door and a compartment of at least one of a building, a vehicle,
and aircraft, a watercraft and a train.
20. The structure of claim 18, comprising at least one of a turbine
blade, a pallet, a shipping container and a roadside fixture.
Description
BACKGROUND
[0001] While many core producers have been aware of the isotropic
strength properties inherent in a Tetrahedral-Octahedral Honeycomb
Lattice-based core material, most of the manufacturing processes
proposed/employed to date involve molding a top and bottom sheet of
material with tetrahedral elements and bonding them together to
create a multi-piece core/lattice. U.S. Pat. Nos. 3,642,566 and
3,689,345 disclose known processes that involve connecting two
sheets to form a core material. This approach runs the risk of core
failure due to delamination and is difficult and expensive to
manufacture. Alternatively, filament winding has been proposed, as
is described in U.S. Pat. Nos. 3,657,059 and 3,645,833, but this
too is time consuming and expensive. Further efforts to produce
isotropic core material are described in U.S. Pat. No. 4,020,205,
which describes manufacturing the core material by bending
continuous strips of ribbon having lateral offset sections to form
triangular sides and occluded dihedral angles of alternating
tetrahedrons and octahedrons.
[0002] The interest in and use of lightweight composite materials
has steadily grown over the last 40 years driven by the need to
reduce weight in a range of structural products used by the marine,
aerospace and transportation industries, among others. Common core
materials used in composites include foam, aluminum honeycomb,
Nomex honeycomb, balsa wood, and plywood among others. While each
of these core materials has satisfied the needs of various
applications, there remains a need for a lightweight, isotropic or
quasi-isotropic, inherently rigid, core material that can be molded
at low cost and in high volume.
SUMMARY
[0003] One embodiment described herein is a one-piece component
comprising a tetrahedral-octahedral honeycomb lattice.
[0004] Another embodiment is a one-piece component comprising a
truncated tetrahedral-octahedral honeycomb lattice. Yet another
embodiment is a structure that includes a one-piece component
comprising a tetrahedral-octahedral honeycomb lattice and/or a
truncated tetrahedral-octahedral honeycomb lattice.
[0005] A further embodiment is a mold configured to form a
one-piece component comprising a tetrahedral-octahedral honeycomb
lattice and/or a truncated tetrahedral-octahedral honeycomb
lattice. In embodiments, the mold includes a first portion with a
base having a first set of tetrahedral and inclined pyramidal
protrusions formed thereon, and a second portion with a base having
a second set of tetrahedral and inclined pyramidal protrusions
formed thereon, wherein the first and second sets of tetrahedral
and pyramidal protrusions are complementary, and wherein the
inclined pyramidal protrusions comprise a rectangular first surface
portion and triangular second, third and fourth surface portions.
In embodiments, during use, the rectangular first surface portion
of each inclined pyramidal protrusion formed on the first portion
of the mold is adjacent to and in contact with a rectangular first
surface portion of an inclined pyramidal protrusion formed on the
second portion of the mold. In embodiments, the first and second
portions of the mold are configured to separate in opposite
diagonal directions that are parallel to the plane of the
rectangular first surface portions of the inclined pyramidal
protrusions.
[0006] Yet another embodiment is an apparatus comprising a first
portion with a base having a first set of tetrahedral and inclined
pyramidal protrusions formed thereon, and a second portion with a
base having a second set of tetrahedral and pyramidal protrusions
formed thereon, wherein the first and second sets of tetrahedral
and pyramidal protrusions are complementary and positioned adjacent
to one another, forming a lattice-shaped void therebetween, and
wherein the inclined pyramidal protrusions comprise a rectangular
first surface portion and triangular second, third and fourth
surface portions.
[0007] A further embodiment is a method of making a component,
comprising obtaining a mold comprising the apparatus described in
the previous paragraph, filling the mold with a liquid or molten
moldable material, allowing the moldable material to solidify to
form the component, and removing the component from the mold. In
embodiments, the moldable material comprises at least one of a
thermoplastic polymer and a thermoset polymer. In embodiments, the
component is post-treated.
[0008] Another embodiment is a method of forming a component
comprising a tetrahedral-octahedral honeycomb lattice or a
truncated tetrahedral-octahedral honeycomb lattice using additive
manufacturing. In embodiments, the component is post-treated. A
further embodiment is a tetrahedral-octahedral honeycomb lattice or
a truncated tetrahedral-octahedral honeycomb lattice formed by
additive manufacturing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a perspective view of a sheet according to a
first embodiment.
[0010] FIGS. 2A-2D show symmetric side views of the sheet of FIG.
1.
[0011] FIGS. 2E-2G show asymmetric side views of the sheet of FIG.
1.
[0012] FIG. 3 is a top plan view of the sheet of FIG. 1.
[0013] FIG. 4 shows a perspective view of a sheet in accordance
with a second embodiment, having a truncated tetrahedral
configuration.
[0014] FIG. 5A-5B show symmetric side views of the sheet of FIG.
4.
[0015] FIGS. 5C-5D show asymmetric side views of the sheet of FIG.
4.
[0016] FIG. 5E is a side perspective view of the sheet of FIG.
4.
[0017] FIG. 6 is a top plan view of the sheet of FIG. 4.
[0018] FIG. 7A is a perspective view of a prototype of a first
embodiment of two halves of a mold for forming a sheet, the halves
being positioned next to one another in a perpendicular
arrangement.
[0019] FIG. 7B shows the mold of FIG. 7A in a closed position.
[0020] FIG. 7C shows the mold of FIG. 7A in a closed position with
slats showing the spaces where sheet material fills the mold.
[0021] FIG. 7D shows the mold of FIG. 7A in a partially open
position.
[0022] FIG. 7E shows the mold of FIG. 7A in an open position.
[0023] FIG. 7F is a top view of a mold half showing the relative
alignment of the tetrahedral and pyramidal portions.
[0024] FIG. 8 is a schematic side sectional view of two mold halves
similar to that shown in FIG. 7 with a molded sheet
therebetween.
[0025] FIG. 9 is a schematic side sectional view showing diagonally
upward movement of the first mold section in order to remove the
sheet.
[0026] FIG. 10 is a schematic side sectional view showing the
angled direction of ejection of the sheet from the second mold
half.
[0027] FIG. 11 is a schematic side section view showing movement of
the lower mold section away from the molded sheet.
[0028] FIG. 12A is a schematic side sectional view showing
simultaneous movement of the two mold halves away from the
sheet.
[0029] FIG. 12B is a schematic side view of a mold with vertical
pulls for forming the sheet of FIG. 1.
[0030] FIG. 13 is a schematic side view of two mold halves of a
vertical pull mold for forming a sheet of truncated configuration
with a sheet molded therebetween.
[0031] FIG. 14 is a schematic side view showing upward movement of
the second mold half in order to remove the sheet.
[0032] FIG. 15 is a schematic side view showing the vertical
direction of ejection of the sheet from the second mold half.
[0033] FIG. 16 is a schematic side view showing movement of the
first mold section away from the sheet.
[0034] FIG. 17 is a schematic side sectional view showing
simultaneous movement of the two mold halves away from the
sheet.
[0035] FIG. 18 is a top view of an embodiment of sheet material
having closed sides.
[0036] FIG. 19 is a table showing simulation data for non-truncated
and truncated sandwich core material.
[0037] FIG. 20 is a table showing simulation data, including beam
load and shear load data for non-truncated and truncated sandwich
core material.
DETAILED DESCRIPTION
[0038] The embodiments described herein demonstrate a mold design
that makes it possible to directly mold a tetrahedral-octahedral
honeycomb lattice for use in commercial applications. Methods of
making the product and the resulting product also are
described.
[0039] In some cases, the product is a one-piece core or sheet
comprising a lattice of material (including but not limited to a
thermoplastic resin, thermoset material, thermoplastic elastomer,
carbon fiber, metals, including but not limited to aluminum, steel,
cardboard, rubber, concrete or any other material suitable for
applications requiring an engineered structure) where the lattice
is comprised of intersecting rows of parallel slats of material
oriented along 3 distinct and intersecting sets of parallel planes,
such that any 3 of the slat planes which are not parallel intersect
to form an equilateral, regular tetrahedron. Non-limiting examples
of suitable thermoplastic materials include polymers such as
polyethylenes, polypropylenes, polyvinyl chlorides, nylons, ABS,
polylactic acid, acrylics, polycarbonates, polystyrenes,
polyethers, polyphenylenes, as well as copolymers and terpolymers
of the same. Non-limiting examples of suitable thermoset materials
include polymers such as natural and synthetic rubber, vinyl
esters, polyesters, thermosetting acrylic resins, polyurethanes and
epoxies. Non-limiting examples of suitable thermoplastic elastomers
include olefinic thermoplastic elastomers, styrene block
copolymers, thermoplastic copolyesters, and thermoplastic
polyamides. Fillers and other additives can be included with the
polymeric materials. The polymeric material can be a foam, and can
molded using structural foam molding or another suitable
technique.
[0040] The adjacent parallel slats are separated by a constant
distance, xo, where xo is the same for all of the adjacent parallel
slats oriented across all 3 distinct sets of parallel planes. For a
top view, see FIG. 3 below.
Definitions
[0041] Platonic Solid: A polyhedron constructed of congruent,
regular polygonal faces. The same number of faces must meet at each
vertex of the faces of the polyhedron. The regular congruent
tetrahedron and the regular congruent octahedron are both Platonic
solids.
[0042] Regular Convex Tetrahedron (RCT): A platonic solid having 4
regular triangular faces.
[0043] Irregular Tetrahedron: A tetrahedron with 4 triangular
faces, at least one of which is not an equilateral triangle. An
irregular tetrahedron has six edges and four vertices.
[0044] Regular Convex Octahedron (RCO): A platonic solid having 8
regular triangular faces.
[0045] Irregular Octahedron: An octahedron with 8 triangular faces,
at least one of which is not an equilateral triangle. An irregular
octahedron has twelve edges and six vertices.
[0046] Pyramid: One half of an RCO comprised of a square base and 4
of the 8 regular triangular faces of the RCO defining the sides.
Two pyramids with adjoining square bases form an RCO.
[0047] Tessellation: A pattern of shapes that fit perfectly
together (mathisfun.com). A tessellation of tetrahedrons and
octahedrons can be formed by alternating the octahedrons with
tetrahedrons in successive offsetting rows where half of the
tetrahedrons have their vertices pointed downward and half have
their vertices pointing upward. The faces of the tetrahedrons and
octahedrons form multiple parallel linear faces across the
tessellation oriented in only 3 of the non-horizontal directions
corresponding to the three non-base faces of any/all of the
tetrahedrons. These parallel linear faces define slats that make up
the lattice that is molded to become the final
Tetrahedral-Octahedral Honeycomb lattice core material.
[0048] Tetrahedral-Octahedral Honeycomb: A tessellation of RCT and
RCO where the faces are congruent. The focus of this document is a
3-dimensional, single layered tessellation of RCT and RCO.
[0049] Tetrahedral--Octahedral Honeycomb Lattice: The space falling
between the RCO and RCT in a Tetrahedral-Octahedral tessellation.
This is the space into which material is injected to mold the
Tetrahedral-Octahedral Honeycomb lattice. Alternatively, it is the
space left void to form a lattice when the objective is to create a
lattice of space for uniformly disbursing liquids, gases or other
flowing materials.
[0050] Dihedral Angle: The angle between two intersecting planes.
The dihedral angle of a regular convex tetrahedron or a regular
convex octahedron is the interior angle between two adjacent face
planes. The dihedral angle of a regular convex tetrahedron is 70.53
degrees. The dihedral angle of a regular convex octahedron is
109.47 degrees. The dihedral angle of a right regular pyramid
between the square base and a triangular side is 54.735
degrees.
[0051] Isotropic: Exhibiting properties with the same values when
measured along axes in all directions (Merriam Webster); in
physics, an object or substance having a physical property that has
the same value when measured in different directions (Oxford
Dictionaries).
[0052] One-piece: Formed as a unitary component in a molding
process, without requiring lamination or adhesion of two or more
sub-parts.
[0053] Sheet: A three-dimensional lattice with planar or curved top
and bottom faces.
[0054] The product comprises a one-piece Tetrahedral-Octahedral
Honeycomb Lattice Core, because the negative space between the
intersecting slats comprising the lattice are alternating rows of
tetrahedra and octahedra. The rows of tetrahedra alternate between
being pointed upwards and pointed downwards. These alternating rows
of tetrahedra and octahedra form a tetrahedral-octahedral
tessellation as the width of the lattice slats converges on 0.
Conversely, as the space between the platonic solids forming the
tetrahedral-octahedral tessellation is expanded, material can be
injected or otherwise inserted into the space to form a
Tetrahedral-Octahedral Honeycomb Lattice. The Lattice that is
formed makes a highly desirable, quasi-isotropic, rigid core
material. Importantly, the core geometry is inherently rigid,
independent of being sandwiched between surface and base layers in
a laminate structure. So as a result, it can enhance the rigidity
of a composite laminate when used as a core, versus other core
materials structured around alternative geometries.
[0055] The strength of the core, for any given material, is a
function of the spacing between the slats and the width of the
slats themselves, in addition to the material from which the core
is made. The height of the core is primarily a function of the
distance between the slats (xo). That said, by shaving or
truncating the top and bottom of the lattice structure, the lattice
height can be reduced and weight removed. By increasing the width
of the slats, the loss of strength due to truncation can be
compensated for, albeit while adding additional weight. If
truncated, the negative space of the lattice forms alternating
truncated tetrahedra and octahedra. By varying the core material,
the width of the slats, the distance between slats, the size of the
tetrahedrons and octahedrons, and the degree of truncation, the
dimensions of the core can be adapted to the unique rigidity,
height, weight and other engineering needs of each manufactured
application.
[0056] Truncation provides other benefits as well: It can reduce
the pressures required to mold the core; and it can provide
additional surface area for bonding when the core is used in
laminates.
[0057] By virtue of being one piece, the lattice also can serve as
a delivery vehicle for liquids, gases, and other molecular and
atomic particles if the lattice is defined by a vacuum or gas or
permeable substance constrained by the aforementioned tessellation
of truncated or non-truncated tetrahedra and octahedral elements.
While in the manufacturing of a core, material would in most
instances be removed from the negative space, in applications such
as a delivery vehicle, material can be introduced into the negative
space, leaving the core area available to disperse the substance
being delivered. In essence, one would "mold" the mold, and
assemble the two halves leaving the lattice as the empty space.
[0058] In other applications the core can be formed and then the
negative space can be filled with a different material with
complementary properties. For example, the core can be made of a
rigid, solid material and foam can be injected into the negative
space to provide insulation to a refrigerated space. Alternatively,
the foam can be molded to resemble the two halves of the mold and
then the two halves can be assembled around the lattice.
[0059] In some embodiments, the tetrahedral and/or octahedral
shapes (non-truncated or truncated) may be irregular in order to
provide for efficient molding and/or mold release. In some
embodiments, the tetrahedral and/or octahedral shapes
(non-truncated or truncated) may be irregular in order to provide
for desired lattice wall thicknesses, and/or to enhance or
compensate for properties of the material or materials used to form
the lattice, and/or to introduce a curvature.
Methods
[0060] Another embodiment described herein is an elegant and low
cost method of producing a Tetrahedral-Octahedral Honeycomb
lattice. The method employs an appropriately designed injection
mold or compression mold (casting). The core, sheet, or other
structure can be manufactured in any moldable material (plastic,
aluminum, steel, or concrete, for example) which would make a
desirable lattice core structure.
[0061] One embodiment is a method of producing a core, sheet or
other material that involves truncating the top and bottom of the
structure to open up the peaks of the tetrahedral and octahedral
elements. This provides more surface area for bonding laminated
sheets of material and reduces the pressure required to mold the
lattice. It also reduces the weight of the lattice and provides a
means of adjusting the height. The manufacturing process of the
modified lattice is, in many respects, the same as the original
core-lattice structure.
[0062] The product described herein can be used in place of
conventional honeycomb material. While a hexagonal honeycomb
laminate handles compressive forces well, the geometry of hexagonal
honeycomb does not handle shear and a variety of other forces well.
To compensate, a variety of materials have been employed to produce
the hexagonal honeycomb structure (for example aluminum and Kevlar)
to compensate for these shortcomings. Also, a variety of sheet
materials have been laminated to honeycomb cores to improve the
composite structures' performance under the anticipated conditions
of use. The result has been an increase in manufacturing complexity
and cost.
[0063] Furthermore, low-margin, cost sensitive applications that
could benefit from the high strength to weight ratio of a
honeycomb-type core material have been precluded from using
conventional honeycomb technology due to cost considerations. A
principal objective of the method described herein is to
manufacture a core material which possesses inherent
quasi-isotropic or isotropic properties, and/or enhanced
performance properties including tension, compression, shear,
bending and torsional rigidity. But unlike prior known
manufacturing techniques, the embodiments described herein seek to
produce this core material directly, in one piece, and at a
substantially reduced cost.
[0064] The mold to produce the lattice fills the voids in the
lattice while leaving space for the resin or other structural
material to flow and harden into lattice. Filling the Regular
Convex Tetrahedral voids is straightforward. The top and bottom
mold components simply need to have offsetting parallel rows of RCT
with the triangular base of the RCT built into the mold base and
top, and one side of all of the RCT in the row aligned along a
common plane. It is noted that the planes of alignment of the sides
of the RCT are at an angle to the base or top of the lattice equal
to the dihedral angle of an RCT (70.53 degrees).
[0065] The method of filling the octahedral voids which alternate
with the RCT in the tetrahedral rows of the lattice is non-trivial
but elegant. Note that the RCO alternating with the RCT have a face
which is also aligned along the common plane of the tetrahedral
faces in the same row. The disclosed embodiments are based on the
fact that an RCO is composed of two Pyramids (see definition above)
with Pyramids' adjacent square bases aligned on a diagonal plane.
As noted in the definitions above, the triangular sides of the
Pyramids are congruent to the faces of the RCT. As a result, when
the 2 sides of the mold are released at an angle equal to the
diagonal orientation of the square bases of the Pyramids, the
void-filling Pyramids can be removed from the top and bottom of the
RCO leaving the lattice.
[0066] In another method, the tetrahedral-octahedral honeycomb
lattice is printed using an additive manufacturing process. When
this technique is used, in embodiments, post-treatment and or
fiber-reinforcement techniques are employed to ensure that the
resulting product exhibits quasi-isotropic or isotropic
qualities.
[0067] Referring to the drawings, FIG. 1 shows a perspective view
of a sheet 10 according to a first embodiment. The sheet is three
dimensional. FIGS. 2A-2G show other views of the sheet of FIG. 1.
The sheet has substantially isotropic properties due to its
geometry. FIG. 3 shows a top plan view of the sheet. The bottom
plan view looks generally the same as the top plan view.
[0068] FIGS. 4-6 illustrate a second embodiment of a sheet 110 in
which the tetrahedral and octahedral portions are truncated along
the opposite first and second faces. It is noted that in other
embodiments, one face has truncated tetrahedrons and/or octahedrons
while the other face does not. Furthermore, in embodiments, there
may be truncation of only some of the tetrahedral portions and/or
octahedral portions within a single sheet. In certain embodiments,
some of the tetrahedral portions are truncated while other
tetrahedral portions are not truncated. In certain cases, some of
the octahedral portions are truncated while other octahedral
portions are not truncated. In some embodiments, some or all of the
tetrahedral portions are truncated while the octahedral portions
are not truncated. In certain embodiments, some or all of the
octahedral portions are truncated while the tetrahedral portions
are not truncated.
[0069] FIGS. 7A-7E show perspective views of a first mold section
220 and a second mold section 221 that can be used to mold the
sheet shown in FIGS. 1-3. The first mold section 220 has a series
of aligned tetrahedrons 222. In between the tetrahedrons 222, a
series of aligned regular square pyramids 224 are positioned. Each
pyramid 224 is positioned sideways, with the base 226 of the square
pyramid extending at an angle relative to a horizontal plane. In
FIG. 7A, the top mold half 221 is disposed vertically to show the
inner side. The top mold half 221 include a plurality of aligned
regular square pyramids 234, each with a base 236. The tetrahedrons
232 on the top mold half 221 can be seen in FIG. 7B. FIG. 7B shows
the mold of FIG. 7A in a closed position. The space between the
protrusions on the top mold half and bottom mold half are filled
with moldable material in order to form the lattice. FIG. 7C shows
the mold in a closed position with slats showing the spaces where
sheet material fills the mold. The square bases of the pyramids on
the top mold half are in contact with the square bases of the
pyramids on the bottom mold half, and the combination of the upper
and lower pyramid pairs forms the octahedral spaces in the
lattices.
[0070] FIG. 7D shows the mold of FIG. 7A in a partially open
position. As can be seen, the direction of pull is parallel to the
plane of the pyramid bases. FIG. 7E shows the mold of FIG. 7A in an
open position.
[0071] FIG. 8 shows a schematic view of a closed mold during
molding. The first mold section 320 has alternating tetrahedrons
322 and inclined pyramids 324 (pyramids that are positioned
sideways, with one triangular face parallel to the length of the
first mold section 320, and the square base 326 of the pyramid
extending diagonally upward relative to the length of the first
mold section 320), as can be seen in FIGS. 7A-7D. The second mold
section 321 also includes a plurality of alternating tetrahedrons
332 and inclined pyramids 334. The second mold section 321 is
configured to be complementary in order that, substantially
throughout the mold, a base 326 of the inclined pyramid 324 is in
substantially complete contact with a base 336 of the inclined
pyramid 334 with no space therebetween, such that an octahedral
void is created during molding. Thus, the material used to form the
sheet 310 is prevented from moving between the two rectangular
bases of each pyramid 324 and its complementary pyramid 334 during
molding.
[0072] Movement of the mold parts and the molded sheet can be seen
in FIGS. 9-12. To remove a molded sheet 310, one or both mold
sections are moved, and the direction of movement is at an angle
relative to the plane of the sheet 310. As is shown in FIGS. 9, 11
and 12, the mold sections are removed in directions that are
parallel to the bases of the base-to-base pyramids that define the
octahedral portion of the mold when the mold is in a closed
position. For a right regular pyramid, the dihedral angle between
the plane of the square base and the plane of a triangular side is
54.735 degrees. This is half of the dihedral angle of a regular
convex octahedron, which as indicated above, is 109.47 degrees.
(Stated in general terms, because one triangular side of the
regular square pyramid is coplanar with the mold base, the square
base that is defined by each of the two pyramidal shapes that form
one octahedron is angled relative to the plane of the mold base.)
The upward and sideward direction that the second mold section 321
is moved when the mold is opened is about 35.3 degrees away from a
vertical direction, and about 54.7 degrees away from a horizontal
direction. Similarly, if the first mold section 320 is moved in a
downward and sideward direction, as in the embodiment shown in FIG.
11, the first mold section 320 is moved in a direction that is
about 35.3 degrees away from a vertical direction and about 54.7
degrees away from a horizontal direction. In the configuration
shown in FIG. 12A, the second mold section 321 moves in a "left"
sideward direction and the first mold section 320 moves in a
"right" sideward direction. As is sometimes the case in molding
operations, the line of draw can be slightly different from a
direct line of draw in order to facilitate removal of the molded
piece.
[0073] For cases in which both mold sections are moved away from
the sheet, the second mold section 321 can be removed first (FIG.
9), the first mold section 320 can be removed first (FIG. 11), or
both mold sections can be removed at the same time (FIG. 12A, and
also FIG. 12B, which shows first mold section 370 and second mold
section 371). For cases in which one mold section is removed and
the mold includes a sheet ejector (see, for example, FIG. 10, which
includes retractable ejector pins 344), the sheet is ejected in
generally the same angular direction as the movement of the mold
section that is first removed. As is shown in FIG. 10, if the
second (upper) mold section 321 is removed first, in the direction
shown in FIG. 9, the sheet 310 can be ejected from the first
(lower) mold section 320 in a direction generally parallel to the
direction of movement of the second mold section 321.
[0074] In embodiments, the second mold section can be moved,
before, after, or at the same time as the movement of the first
mold section. Furthermore, in some cases, (see FIG. 11), if the
first mold section 320 is moved away from the sheet, the sheet 310
will drop from the second mold section 321 due to gravity. In other
embodiments, after the first (lower) mold section 320 is moved away
from the sheet 310, the sheet is ejected from the second (upper)
mold section 321 in a direction parallel to the angular movement of
the first mold section 320 using a suitable ejection technique.
[0075] FIGS. 12A and 12B show simultaneous movement of the upper
and lower mold sections away from the molded sheet. FIG. 12A shows
an embodiment in which the sheet is positioned horizontally during
molding. FIG. 12B shows an embodiment in which the sheet is
positioned at an angle during molding, with the direction of pull
of the upper mold half being vertically up and the direction of
pull of the lower mold half being vertically down.
[0076] FIGS. 13-17 show a mold that is generally similar that that
of FIGS. 7-12 except that the tetrahedral and/or octahedral
portions of the mold are truncated, and the mold has vertical pulls
such that the sheet is angled during molding. Movement of the first
mold section 420, the second mold section 421 and the sheets 410
are similar to the movements described above in connection with
FIGS. 7-11, except that the planes of molded sheets are positioned
at an angle relative to a horizontal plane. More specifically, FIG.
13 shows closed mold sections 420 and 421. FIG. 14 shows the upward
movement of second mold section 421. FIG. 15 shows upward movement
of the sheet off of first mold section 420. FIG. 16 shows downward
movement of first mold section 520. FIG. 17 shows downward movement
of first mold section 620 and upward movement of second mold
section 621.
[0077] FIG. 18 depicts a top view of an embodiment of sheet
material 210 having closed sides around the perimeter of the
four-sided lattice.
[0078] In embodiments, the lattice is post-treated to impart
desired characteristics. Non-limiting examples of post-treatment
techniques include coating, impregnating, compressing, curing,
post-curing, heating, cooling, wetting, abrading, solvent
treatment, washing, rinsing, grinding, irradiating, sintering,
bending and/or sterilizing.
A Method of Making a Mold
[0079] In the description of the technique for molding a single
piece tetrahedral-octahedral honeycomb core structure, the focus
was on the individual elements of the negative space comprising the
mold (the tetrahedra and pyramid-pairs forming the octahedra). In
embodiments, the actual machining of the mold is much more elegant.
In one embodiment, given a block of aluminum, steel or other
material from which the mold-halves are to be machined, the removal
of material is along 4 sets of parallel planes, 3 of which are
defined by the non-horizontal sides of the tetrahedra (relative to
the sheet plane), and one which is defined by the base plane of the
pyramids which form 1/2 of the octahedra (see FIG. 7F). The base
plane of the pyramids and one of the planes of the tetrahedra run
along a common axis, albeit at different angles which intersect at
the base of a given mold-half. As can be seen in FIG. 7F, the space
between these two planes forms a wedge which eventually is machined
out in its entirety to make room for the top half of the mold. The
width of the material removed along the parallel planes defined by
the tetrahedra corresponds to the desired width of the lattice
comprising the honeycomb.
[0080] These machined cuts form 1/2 of the mold. If this is the
bottom half of the mold, then the top half is a mirror image of the
bottom half and is machined the same way. Details on mold material
insertion/injection and end-product extraction will vary depending
upon the materials and methods of the application. Details on the
construction of the sides of the mold also will vary depending upon
the materials and methods of the application being manufactured. In
embodiments, machining is performed with a router.
[0081] In other embodiments, the top and bottom halves of the mold
can be made using additive manufacturing.
[0082] Additive Manufacturing
[0083] Recent advances in software technology have enabled the
manufacture of a variety of product designs through the use of
additive manufacturing. ISO/ASTM52900-15 defines seven categories
of additive manufacturing processes as being examples of 3D
printing, namely Binder Jetting, Directed Energy Deposition,
Material Extrusion, Material Jetting, Powder Bed Fusion, Sheet
Lamination and Vat Photopolymerization. The sheet material and core
material described above can be made using additive manufacturing.
In embodiments, the additive manufacturing technique that is used
produces the material as a one-piece component. That is, no
lamination, soldering or welding is required of two or more
separate parts. In some cases, the production driver used in
additive manufacturing is organized around the tetrahedral and
octahedral elements, in order that the additive manufacturing
device can "print" the sheet material around separate octahedral
and tetrahedral elements.
[0084] If vat polymerization is used, the liquid or molten polymer
is irradiated, often using UV light, to convert that liquid or
molten material into a solid. If stereolithography is used, a
stereolithographic machine converts the liquid or molten plastic
into a solid.
[0085] Polymeric materials used in 3D printing include a variety of
thermoplastic and thermoset materials, and composites incorporating
fillers, including carbon or metallic materials.
[0086] In some cases, the sheet material is fabricated using a 3D
printer that uses fused filaments. In embodiments, the 3D printed
sheet material is post-treated to further improve its tensile
strength, such as by coating the sheet material with a coating
applied by spraying, dipping or the like. In embodiments, the
material used in additive manufacturing is a fiber-reinforced
polymer, thereby imparting additional strength, including favorable
tensile strength and stiffness, to the final product.
[0087] Non-limiting examples of polymers that can be used in 3D
printing include acrylonitrile butadiene styrene (ABS) and
polylactic acid (PLA). These polymers can be fiber reinforced, with
carbon fibers or another suitable type of fiber.
[0088] One embodiment disclosed herein is a lightweight, strong
sheet material formed by additive manufacturing. In embodiments,
the sheet material is carbon-reinforced material in order to impart
favorable stiffness and tensile strength to the sheet material
while making it lightweight. In some cases, the build direction of
the material, i.e., the direction in which the nozzle moves when
forming each layer, is parallel to the direction in which the
greatest tensile strength is desired, thereby reducing the
likelihood of breakage.
[0089] 3D printed thermoset polymers can be cured during
manufacture by photopolymerization, such as with UV light, or can
be post-cured, such as by heating.
[0090] In embodiments, the 3D printed sheet material is
post-processed using a suitable solvent, such as acetone or methyl
ethyl ketone. The solvent can be used to smooth the sheet material
or hold pieces together. In vacuum treatment, heat is applied to
evaporate the solvent so that it interacts with the surfaces of the
sheet material in a closed container.
[0091] In embodiments, internal tetrahedral and octahedral supports
are used during printing to support "overhanging" features of the
sheet material, such as diagonal walls. These supports may have the
configuration of the mold halves shown in the photographs included
herein.
[0092] Other types of post-treatment include application of a
strengthening thin layer of a polymeric coating composition, as
well as the types of post-treatments described above.
EXAMPLES
Example 1
[0093] Simulations were conducted to determine physical properties
of tetrahedral-octahedral honeycomb lattice formed from
polycarbonate with an aluminum skin on the top and bottom surfaces.
The samples had a length of 3 inches, a width of 8 inches, and a
total thickness of 0.468-0.500 inches including the skin. Some of
the samples had truncated tetrahedral-octahedral honeycomb lattice.
The sample dimensions and the finite element analysis test results
for Beam Load and Shear Load simulations are shown on FIGS. 19 and
20 below. "Cell thk (in)" indicates cell wall thickness in
inches.
[0094] Beam loading test were conducted as per MIL-C-7438. Shear
loading tests were conducted as per ASTM C-273. Cell size was
measured along one side of the triangles from the wall centers, as
viewed from the top of the lattice.
Prophetic Example 2
[0095] Tetrahedral-octahedral honeycomb core samples measuring 1
foot by 1 foot by 1/2 inch with a wall thickness of about 0.045
inch are made from aluminum. The lattice optionally can be
sandwiched between two aluminum skin sheets.
Prophetic Example 3
[0096] Tetrahedral-octahedral honeycomb core samples measuring 1
foot by 1 foot by 1/2 inch with a wall thickness of about 0.045
inch are made from stainless steel. The lattice optionally can be
sandwiched between two aluminum skin sheets.
Prophetic Example 4
[0097] Tetrahedral-octahedral honeycomb core samples measuring 9
inches by 9 inches by 3/4 inch with a wall thickness of about 0.045
inch are made from aramid fiber. The lattice optionally can be
sandwiched between two aluminum skin sheets.
Prophetic Example 5
[0098] Tetrahedral-octahedral honeycomb core samples measuring 2
foot by 1 foot by 1/2 inch with a wall thickness of about 0.045
inch are made from Kevlar or Nomex aramid fiber. The lattice
optionally can be sandwiched between two aluminum skin sheets.
Prophetic Example 6
[0099] Tetrahedral-octahedral honeycomb core samples measuring 2
foot by 1 foot by 1/2 inch with a wall thickness of about 0.045
inch are made from polypropylene. The lattice optionally can be
sandwiched between two aluminum or stainless steel skin sheets.
Applications of the Tetrahedral--Octahedral Honeycomb Lattice
[0100] The lattice can be useful anywhere a lightweight,
quasi-isotropic structural core material/laminate would be
beneficial, including, but not limited to, the following: [0101] 1)
Aerospace: Airplane Flooring, Bulkheads, Engine Turbine Blades,
Hull [0102] 2) Trucking: Trailer siding, Refrigerated Trailer
siding, Flooring, Doors [0103] 3) Building and Construction: Doors,
Garage Doors, Walls, Concrete Cinderblocks [0104] 4) Shipping:
Pallets, Corrugated Cardboard, Shipping Containers [0105] 5)
Marine: Bulkheads, Doors, Flooring, Hull [0106] 6) Solar
Panels--Backing Material Supporting Solar Receiver [0107] 7)
Decorative--Lightweight, Rigid, Decorative Panel [0108] 8) Wind
Energy--Wind Turbines [0109] 9) FEMA Trailers--Sides of lightweight
FEMA Housing [0110] 10) Recreational Vehicles--Sides of Superlight
RVs [0111] 11) Ballistic Protection--Ballistic Protection Panels
for Military Vehicles [0112] 12) Unmanned Undersea
Vehicles--Bulkheads, Hull, Flooring, Doors, [0113] 13) Rail--Floor,
Bulkhead, Doors, Decorative Panels [0114] 14) Automotive--Ballistic
Protection, Crash Panels, Floor Panels [0115] 15) Highway--Crash
Barrels, Sign Backing [0116] 16) Advertising--Billboards [0117] 17)
Other--Flat Panel TV, Lightweight Drywall Alternative, Alternative
to Plywood, Stealth Benefits, Acoustic Dampening, Support for
insulation integrated into voids [0118] 18) Dissipation of material
like drugs through the lattice if the lattice area is left void and
the mold structure is left in place to form the lattice-void. In
this application, one would "mold" the two halves of the mold and
then assemble the two halves to form the final product.
[0119] A number of alternatives, modifications, variations, or
improvements therein may be subsequently made by those skilled in
the art, which are also intended to be encompassed by the following
claims.
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