U.S. patent application number 12/029287 was filed with the patent office on 2008-06-19 for assembly for fabricating large dimension bonds using reactive multilayer joining.
This patent application is currently assigned to REACTIVE NANOTECHNOLOGIES, INC. Invention is credited to Michael V. Brown, Alan Duckham, Ellen M. Heian, Omar M. Knio, Jesse E. Newson, Timothy Ryan Rude, Jai S. Subramanian.
Application Number | 20080145695 12/029287 |
Document ID | / |
Family ID | 37069104 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080145695 |
Kind Code |
A1 |
Duckham; Alan ; et
al. |
June 19, 2008 |
Assembly For Fabricating Large Dimension Bonds Using Reactive
Multilayer Joining
Abstract
An assembly for joining component bodies of material over
bonding regions of large dimensions including a plurality of
substantially contiguous sheets of reactive composite materials
between the bodies and adjacent sheets of fusible material. The
contiguous sheets of the reactive composite material are
operatively connected by an ignitable bridging material so that an
igniting reaction in one sheet will cause an igniting reaction in
the other. An application of uniform pressure and an ignition of
one or more of the contiguous sheets of reactive composite material
causes an exothermic thermal reaction to propagate through the
bonding region, fusing any adjacent sheets of fusible material and
forming a bond between the component bodies.
Inventors: |
Duckham; Alan; (Baltimore,
MD) ; Newson; Jesse E.; (Cockeysville, MD) ;
Brown; Michael V.; (Timonium, MD) ; Rude; Timothy
Ryan; (Baltimore, MD) ; Knio; Omar M.;
(Timonium, MD) ; Heian; Ellen M.; (Cockeysville,
MD) ; Subramanian; Jai S.; (Lutherville-Timonium,
MD) |
Correspondence
Address: |
POLSTER, LIEDER, WOODRUFF & LUCCHESI
12412 POWERSCOURT DRIVE SUITE 200
ST. LOUIS
MO
63131-3615
US
|
Assignee: |
REACTIVE NANOTECHNOLOGIES,
INC
Hunt Valley
MD
|
Family ID: |
37069104 |
Appl. No.: |
12/029287 |
Filed: |
February 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11393055 |
Mar 30, 2006 |
7354659 |
|
|
12029287 |
|
|
|
|
60666179 |
Mar 30, 2005 |
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Current U.S.
Class: |
428/686 |
Current CPC
Class: |
Y10T 428/12438 20150115;
B23K 20/165 20130101; Y10T 428/12472 20150115; C06B 45/12 20130101;
Y10T 428/12222 20150115; B23K 1/0006 20130101; B23K 20/00 20130101;
B32B 15/01 20130101; Y10T 428/31678 20150401; Y10T 428/31504
20150401; Y10T 428/12986 20150115; Y10T 156/10 20150115; H05K
3/3494 20130101 |
Class at
Publication: |
428/686 |
International
Class: |
B23K 35/22 20060101
B23K035/22 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] The United States government has certain rights in this
invention pursuant to NSF Award DMI-034972.
Claims
1. An assembly comprising at least two adjacent sheets of reactive
composite material interconnected by at least one coupling
means.
2. The assembly of claim 1 wherein said coupling means is a
structural support tab.
3. The assembly of claim 2 wherein said structural support tab
consists of a fusible material.
4. The assembly of claim 1 wherein said coupling means is a bond
between contiguous edges of said adjacent sheets of reactive
composite material.
5. The assembly of claim 4 wherein said bond is formed by an
organic adhesive.
6. The assembly of claim 4 wherein said bond contains a fusible
material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of, and claims
priority from, U.S. patent application Ser. No. 11/393,055 filed on
Mar. 30, 2006, which in turn is related to, and claims priority
from, U.S. Provisional Patent Application Ser. No. 60/666,179 filed
on Mar. 30, 2005, both of which are herein incorporated by
reference.
BACKGROUND OF THE INVENTION
[0003] This invention relates to the joining of bodies of material
over bonding regions of large dimension using reactive composite
materials such as reactive multilayer foils.
[0004] Reactive composite joining, such as shown in U.S. Pat. No.
6,534,194 B2 to Weihs et al and in U.S. Pat. No. 6,736,942 to Weihs
et al. is a particularly advantageous process for soldering,
welding, or brazing materials at room temperature. The process
involves sandwiching a reactive composite material (RCM) between
two layers of a fusible material. The RCM and the fusible material
are then disposed between the two components to be joined, and the
RCM is ignited. A self-propagating reaction is initiated within the
RCM which results in a rapid rise in temperature within the RCM.
The heat released by the reaction melts the adjacent fusible
material layers, and upon cooling, the fusible material bonds the
two components together.
[0005] Alternatively, depending upon the composition of the two
components, the layers of fusible material are not used, and the
reactive composite material is placed directly between the two
components. Thermal energy released by ignition of the RCM melts
material from the adjacent component surfaces and consequently
joins the components.
[0006] Turning to FIG. 1, an arrangement 9 for performing the
process of reactive composite joining of two components 10A and 10B
is illustrated. A sheet or layer of reactive composite material 12
is disposed between two sheets or layers of fusible material 14A
and 14B which, in turn, are sandwiched between the mating surfaces
(not visible) of the components 10A and 10B. The sandwiched
assembly is then pressed together, as symbolized by vise 16, and
the reactive composite is ignited, as by match 18. The reaction
propagates rapidly through the RCM 12, melting fusible layers 14A
and 14B. The melted layers cool, joining the components 10A and 10B
together. The RCM 12 is typically reactive multilayer foil, and the
fusible materials 14A and 14B are typically solders or brazes.
[0007] The process of joining the two components 10A and 10B occurs
more rapidly with a reactive composite joining process than with
conventional joining techniques such as those which utilize
furnaces or torches. Thus, significant gains in productivity can be
achieved. In addition, with the very localized heating associated
with the reactive composite joining process, temperature sensitive
components, as well as dissimilar materials such as metals and
ceramics, can be soldered or brazed without thermal damage.
Fine-grained metals can be soldered or brazed together using a
reactive composite joining process without grain growth, and bulk
amorphous materials can be welded together with only a local
excursion from room temperature, producing a high strength bond
while minimizing crystallization.
[0008] The reactive composite materials 12 used in reactive
composite joining process are typically nanostructured materials
such as described in U.S. Pat. No. 6,534,194 B2 Weihs et al. The
reactive composite materials 12 are typically fabricated by vapor
depositing hundreds of nano-scale layers which alternate between
elements having large, negative heats of mixing, such as nickel and
aluminum. Recent developments have shown that it is possible to
carefully control both the heat of the reaction as well as the
reaction velocity by varying the thicknesses of the alternating
layers. It has also been shown that the heats of reaction can be
controlled by modifying the foil composition, or by low-temperature
annealing of the reactive multi-layers after their fabrication. It
is further known that alternative methods for fabricating
nanostructured reactive multilayers include mechanical
processing.
[0009] Two key advantages achieved by the use of reactive composite
materials for joining components are speed and the localization of
heat to the joint area. The increased speed and localization are
advantageous over conventional soldering or brazing methods,
particularly for applications involving temperature-sensitive
components or components with a large difference in coefficient of
thermal expansion, such as occur in metal/ceramic bonding. In
conventional welding or brazing, temperature-sensitive components
can be destroyed or damaged during the process. Residual thermal
stress in the components may necessitate costly and time-consuming
operations, such as subsequent anneals or heat treatments. In
contrast, joining with reactive composites subjects the components
to little heat and produces only a very local rise in temperature.
Generally, only the adjacent fusible layers and the adjoining
surfaces of the components are heated substantially. Thus, the risk
of thermal damage to the components is minimized. In addition,
reactive composite joining is fast and results in cost-effective,
strong, and thermally conductive joints.
[0010] While conventional reactive composite joining works well in
joining components over lengths less than about four inches and
areas less than about 16 square inches, joining over larger lengths
and areas presents particular challenges. It has been observed that
for optimal joining it is advantageous that the surfaces to be
joined be heated as uniformly, and as simultaneously, as possible.
When the lengths and areas become larger, it is increasingly
difficult to maintain the desired reaction simultaneity and
uniformity from a single ignition point. In addition, larger
joining region dimensions can exceed those of easily fabricated
RCM's, requiring multiple pieces of reactive foil to cover the
joint surface area. Even though the joining reaction spreads
rapidly through the RCM, not every part of a large surface area
joint area may be molten at the same time, possibly resulting in
poor bonding between the components. Moreover, increasing the
surface area to be joined presents increasingly stringent
requirements for the uniform application of pressure to the
components during the joining process.
[0011] Accordingly, it would be advantageous to provide a reactive
composite joining process for use in joining components over
surface areas which are larger than the size of a single sheet of
reactive composite material, and which result in a strong and
relatively uniform bond between the component materials.
BRIEF SUMMARY OF THE INVENTION
[0012] Briefly stated, the present invention provides a method for
joining bodies of component material over regions of large
dimensions by disposing a plurality of substantially contiguous RCM
sheets between the component material bodies. Each of the
substantially contiguous RCM sheets is coupled to at least one
adjacent RCM sheet by a bridging material capable of transferring
an energetic reaction from one sheet to another. An ignition
reaction is initiated in one or more of the RCM sheets and enabled
to spread through all remaining sheets via the bridging material,
resulting in rapid localized heating of materials adjacent the
sheets, which form a bond between the bodies of component material
upon cooling.
[0013] In an embodiment of the present invention, a plurality of
substantially contiguous RCM sheets disposed between component
material bodies to be joined over a region of large dimension are
coupled together by a bridging material. The bridging material may
be in the form of a reactive foil, wire, layer, powder, or other
material which is capable of conveying an ignition reaction from
one sheet to another, either directly or by thermal conduction. The
bridging material is reactive in response to an ignition of a first
RCM sheet to ignite a second RCM sheet.
[0014] In an alternate embodiment of the present invention, a
plurality of substantially contiguous RCM sheets disposed between
component material bodies to be joined over a region of large
dimension are coupled together by structural support tabs of
fusible material to enable easy assembly, transport, and
positioning of the multiple RCM sheets between the component bodies
to be joined.
[0015] In a variation of the present invention, a plurality of
substantially contiguous RCM sheets are disposed between component
material bodies to be joined over a region of large dimensions,
directly adjacent surfaces of the component material bodies to be
joined.
[0016] In an alternate embodiment of the present invention, a
plurality of substantially contiguous RCM sheets are disposed
between component material bodies to be joined over a region of
large dimensions. Sheets of fusible material such as solder or
braze are disposed in proximity to the RCM sheets and to the
component material bodies. The fusible material sheets can overlie,
underlie, or sandwich the sheets of reactive composite materials.
The fusible material sheets can be continuous across the boundaries
of the contiguous RCM sheets, and may optionally function as
connecting material to hold RCM sheets together.
[0017] A method of the present invention for joining bodies of
component material over regions of large dimension disposes at
least one RCM sheet between the component material bodies. An
ignition reaction is initiated at a plurality of ignition points
disposed about the RCM sheet, resulting in rapid localized heating
of materials adjacent the sheets which form a bond between the
bodies of component material upon cooling.
[0018] A variation of the method of the present invention for
joining bodies of component material over regions of large
dimension disposes at least one RCM sheet between the component
material bodies. At least one spacer plate is positioned between an
external pressure source and the component bodies. Pressure is
applied to the arrangement from the external pressure source,
urging the component bodies towards each other to control the
formation of a bond between the component bodies following
initiation of an ignition reaction in the RCM sheets. The ignition
reaction within the RCM sheets results in rapid localized heating
of materials adjacent the sheets, which form a bond between the
bodies of component material upon cooling.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0019] The advantages, nature and various additional features of
the invention will appear more fully upon consideration of the
illustrative embodiments now to be described in detail in
connection with the accompanying drawings. In the drawings:
[0020] FIG. 1 schematically illustrates a prior art arrangement for
performing conventional reactive composite joining of two
components;
[0021] FIG. 2 is a block diagram representing the steps involved in
joining two bodies by a large dimension joint in accordance with
the invention;
[0022] FIG. 3 is a top plan view of a plurality of contiguous
reactive composite material sheets operatively connected by
structural support tabs and ignition bridges within the bonding
region for the formation of a large area bond between two component
bodies;
[0023] FIG. 4 is a top plan view of a plurality of contiguous
reactive composite material sheets operatively connected by
structural support tabs within the bonding region and ignition
bridges external to the bonding region, for the formation of a
large area bond between two component bodies;
[0024] FIG. 5 schematically illustrates several contiguous reactive
composite material sheets operatively connected by ignition bridges
external to the bonding region for the propagation of an ignition
reaction from sheet to sheet;
[0025] FIG. 6 is a cross sectional view of a pair of contiguous
reactive composite material sheets sandwiched between two layers of
a fusible material;
[0026] FIG. 7 is a block diagram representing an arrangement of
components and layers for practicing a joining method of the
present invention;
[0027] FIG. 8 illustrates an exemplary arrangement for
simultaneously igniting a plurality of reactive composite material
sheets during formation of a bonding joint in accordance with a
method of the present invention;
[0028] FIG. 9 is a top-plan acoustic image of a large dimension
joint formed in accordance with a method of the present
invention;
[0029] FIG. 10 is a top-plan acoustic image of a large dimension
joint formed in accordance with an a method of the present
invention, illustrating edge voids;
[0030] FIG. 11 is a top-plan acoustic image of a large dimension
joint formed in accordance with an optimized loading bonding method
of the present invention;
[0031] FIG. 12 illustrates an exemplary arrangement of contiguous
reactive composite material sheets, fusible material support tabs,
ignition bridges, and ignition points;
[0032] FIG. 13 is a top-plan acoustic image of a large dimension
joint resulting from the arrangement illustrated in FIG. 12;
[0033] FIG. 14 illustrates an exemplary arrangement of contiguous
reactive composite material sheets, fusible material support tabs,
ignition bridges, and ignition points;
[0034] FIG. 15 is a top-plan acoustic image of a large dimension
joint resulting from the arrangement illustrated in FIG. 14;
[0035] FIG. 16 is a block diagram representing a first exemplary
arrangement of components and layers for practicing a joining
method of the present invention; and
[0036] FIG. 17 is a block diagram representing a second exemplary
arrangement of components and layers for practicing a joining
method of the present invention.
[0037] Corresponding reference numerals indicate corresponding
parts throughout the several figures of the drawings. It is to be
understood that the drawings are for illustrating the concepts of
the invention and are not to scale.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] The following detailed description illustrates the invention
by way of example and not by way of limitation. The description
enables one skilled in the art to make and use the invention, and
describes several embodiments, adaptations, variations,
alternatives, and uses of the invention, including what is
presently believed to be the best mode of carrying out the
invention.
[0039] As used herein, the phrase "large dimension" is used to
describe a joint or bonding region and is understood to mean a
joint or bonding region having either an area or length which
exceeds the area or length of a single sheet of reactive composite
material utilized in the joining processes, which is sufficiently
large enough that a single propagation wave front from an ignition
reaction within a sheet of reactive composite material fails to
achieve desired bond characteristics throughout the bonding region,
or which exhibits a loading variation between the center and the
edges of the joint or bonding region. For example, an area of at
least 16.0 sq. inches or a length of at least 4.0 inches is
considered to be a large dimension when utilizing a sheet of
reactive composite material having an area of less than 16.0 sq.
inches and a longest dimension of less than 4.0 inches.
[0040] As used herein, the phrase "reactive composite material" or
"RCM" is understood by those of ordinary skill in the art to refer
to structures, such as reactive multilayer foils, comprising two or
more phases of materials spaced in a controlled fashion such that,
upon appropriate excitation or exothermic reaction initiation, the
materials undergo an exothermic chemical reaction which spreads
throughout the composite material structure. These exothermic
reactions may be initiated by electrical resistance heating,
inductive heating, laser pulses, microwave energy, or ultrasonic
agitation of the reactive composite material at one or more
ignition points.
[0041] Referring to the drawings, FIG. 2 illustrates a generalized
flow diagram of the steps involved in joining together two
component bodies 10A and 10B over a joint or bonding region having
a large dimension (large area or large length), using at least two
contiguous sheets 12 of reactive composite material. Initially, as
shown in block A, two component bodies 10A and 10B to be joined
over substantially conforming large dimension mating surfaces are
provided. The two component bodies 10A and 10B may be coated in
advance with one or more layers of a fusible material 14A and 14B,
such as a solder or braze alloy, or one or more sheets of the
fusible material 14A and 14B may be placed between the component
bodies 10A and 10B. The component bodies 10A and 10B may comprise
the same type of materials, such as brass, or may be of different
types of materials, such as nickel and brass, aluminum and
titanium, boron carbide and steel, boron carbide and copper,
silicon carbide and aluminum, and a tungsten-titanium alloy and a
copper-chromium alloy.
[0042] Next, as shown in Block B, two or more sheets 12 of reactive
composite material in a substantially contiguous arrangement are
disposed between the mating surfaces of the two component bodies
10A and 10B. As used herein, the term "contiguous" is understood by
those of ordinary skill in the art to mean that any adjacent edges
of the sheets 12 of reactive composite material are arranged as
close together as necessary to form a substantially void-free bond
and at least sufficiently close together such that adjacent sheets
12 of reactive composite material can be operatively connected
together into a single assembly. Contiguous RCM sheets do not need
to be in physical contact with each other.
[0043] To operatively connect adjacent RCM sheets 12, a number of
structurally supporting bridges or tabs 20 are formed between the
sheets 12 (as shown in FIGS. 3 and 4). The bridges or tabs may be
formed from either a fusible material 20 which will form part of
the bond between the component bodies 10A and 10B, or may be formed
from reactive material 22 which is capable of conveying an ignition
reaction between adjacent sheets of RCM. Using the bridges or tabs
20, 22, two or more adjacent RCM sheets 12 are secured together in
an assembly 24 in such a way as to maintain the relative positions
to each other during assembly, transport, and positioning between
the matching surfaces of the component bodies 10A and 10B in the
large dimension bonding region.
[0044] A structural support bridge or tab 20 can be in any one of
several forms to secure contiguous RCM sheets 12 together in the
assembly 24. In one exemplary embodiment, the structural support
bridges or tabs 20 are in the form of a soft metal or fusible
material sheet, for instance indium, which is cold-pressed or
rolled onto the RCM sheets 12.
[0045] An ignition bridge or tab 22 formed from a reactive material
is preferably selected such that it will either ignite or conduct
thermal energy between the adjacent sheets 12 to enable a reaction
initiated in a first sheet 12A to continue via the bridge or tab to
the adjacent sheet 12B. The configuration of an ignition bridge or
tab 22 can be in any one of several forms to assist propagation of
reaction between contiguous RCM sheets 12. For example, the
ignition bridge or tab 22 can be in the form of a reactive
multilayer foil, similar or identical to that used for the RCM
sheets 12, or a thin wire that contains regions or layers of
materials with a large negative heat of mixing. These
configurations of the ignition bridges or tabs 22 can be attached
to one or both contiguous sheets 12 with a small amount of glue or
with a small piece of fusible solder. In addition to conveying an
initiated reaction, ignition bridges or tabs 22 may be structural
in nature, i.e. providing structural support to an arrangement of
sheets 12 of RCM, or may be non-structurally supporting in nature,
For example, a non-structurally supporting ignitable bridge 22 can
be in the form of a loose or compact powder mixture of materials
with a large negative heat of mixing.
[0046] Advantageously, the various forms of both bridges and tabs
20, 22 are small in comparison to the size of the RCM sheets 12,
and do not interfere with the flow of any fusible material present
in the bonding region, or with the flatness of the component body
mating surfaces during the joining process.
[0047] Turning to FIG. 3, an exemplary arrangement of a plurality
of contiguous RCM sheets 12 are shown arranged and connected by
solder assembly tabs 20 and ignitable bridges 22 to form a reactive
composite material sheet assembly 24 covering a large area bonding
region 26 between two component bodies (not shown). In the
arrangement shown in FIG. 3, both the solder assembly tabs 20 and
the ignitable bridges 22 are contained within the large area
bonding region 26. The arrows arranged about the periphery of the
assembly 24 indicate a plurality of ignition or reaction initiation
points associated with the assembly 24.
[0048] FIG. 4 illustrates a second exemplary arrangement of a
plurality of contiguous RCM sheets 12 arranged and connected by
solder assembly tabs 20 and ignitable bridges 22 to form a reactive
composite material sheet assembly 24 covering a large area bonding
region 26 between two component bodies (not shown). In the
arrangement shown in FIG. 4, the solder assembly tabs 20 are
contained within the large area bonding region 26, while the
ignitable bridges 22 are disposed outside the large area bonding
region 26. By disposing the ignitable bridges 22 outside of the
large bonding region 26, the ignitable bridges 22 may be attached
to the sheets 12 of the assembly 24 with tape or other means that
would not be possible within the large area bonding region. The
bridges may thus be used for securing the sheets 12 within the
assembly 24, as well as for ignition of the bonding reactions, as
is indicated by the arrows arranged about the periphery of the
assembly 24 to indicate a plurality of ignition or reaction
initiation points.
[0049] Within a large area bonding region 26, the solder tabs 20
may be secured to the sheets 12 of the assembly 24 by pressing or
with a minimal amount of glue. If it is undesirable to use a solder
material for the tabs 20 which differs from the solder material
used as a fusible material within the joint, due to concerns about
alloying, small tabs of the desired solder could be glued to the
reactive sheets, preferably minimizing the amount of glue.
[0050] FIG. 5 illustrates a third exemplary arrangement of a
plurality of contiguous RCM sheets 12 arranged and connected by
solder assembly tabs 20 and ignitable bridges 22 to form an RCM
sheet assembly 24 covering a large linear dimensioned bonding
region 30 between two component bodies (not shown). The ignitable
bridges 22 may be attached to the reactive sheets 12 with glue or
small pieces of solder material if they are disposed inside a joint
region, or with adhesive tape if they are disposed outside a joint
region.
[0051] Those of ordinary skill in the art will recognize that the
number of RCM sheets 12 comprising the various assemblies 24 shown
in FIGS. 3, 4, and 5 may be varied depending upon the size and
configuration of the large area bonding region 26 or large linear
dimensioned bonding region 30. Preferably, RCM sheets 12 are
arranged within the assemblies 24 such that the gaps G between
adjacent sheets 12 are as far to the interior of the bonding region
as possible, particularly gaps G which are parallel to the edges of
the bonding region. Similarly, it will be recognized that the
placement and number of tabs 20 and ignition bridges 22 may be
varied depending upon the particular application and geometry of
the assembly 24, provided that the assembly 24 is secured in a
stable configuration during placement in the bonding region, and
that reactions can propagate between the sheets 12 of the assembly
24 in a generally rapid and uniform manner.
[0052] In lieu of assembly tabs 20, an assembly 24 of two or more
RCM sheets 12 with ignition bridges 22 may be packaged as shown in
FIG. 6 between layers 32A and 32B of a fusible material, such as a
solder or a braze. Such packaging allows the fusible material
layers 32A and 32B and the assembly 24 of RCM sheets 12 to be
handled as a unit, aiding in placement within a bonding region. The
RCM sheets 12 may be bonded to the fusible material layers 32A and
32B by rolling, pressing, or other suitable means to ensure that
the packaging remains structurally secure.
[0053] Once the assembly 24 is formed, with or without fusible
layers 32A and 32B, it is disposed within the bonding region 26
between the components 10A and 10B to be joined. As shown in Block
C of FIG. 2, the components 10A and 10B to be joined are pressed
together to provide a generally uniform pressure over the bonding
region 26. A variety of devices and techniques may be utilized to
achieve the generally uniform pressure between components 10A and
10B over the bonding region 26, for example, hydraulic or mechanic
presses. As is shown in FIG. 7, the components 10A and 10B may be
disposed with suitable spacers 34 between a pair of press platens
36A and 36B. The selection of the spacers 34, and their effect on
the resulting bond formed within the bonding region 26 are
described below in further detail. An optional compliant layer 38,
such as a rubber sheet, may be placed in the component arrangement
between one component 10A or 10B and an adjacent press platen to
accommodate any imperfections on the outside surfaces of the
components 10A and 10B and the surfaces of the press platens 36A
and 36B during the joining process. Pressure is exerted on the
press platens 36A and 36B by any suitable means, such as by a
hydraulic press with automatic pressure control.
[0054] The final step, shown in Block D of FIG. 2, is to ignite the
RCM sheets 12 comprising the assembly 24. When bonding large areas,
it is advantageous to symmetrically ignite the RCM sheets 12 at
multiple points about the peripheral edge of the assembly 24, such
as illustrated by the ignition point arrows in FIGS. 3 and 4.
Interior sheets 12 which do not have edges outside the bonding
region 26 are then ignited by the propagation of the reaction
across the ignition bridges 22 within the assembly 24 as discussed
previously. Simultaneous ignition of the sheets 12 in an assembly
24 can be conveniently effected by simultaneous application of an
electrical impulse, such as shown in FIG. 8, or by laser impulse,
induction, microwave radiation, or ultrasonic energy.
[0055] Those of ordinary skill in the art will recognize that a
variety of devices which are capable of simultaneous delivery of
ignition energy to the ignition points may be used. For example, an
electrical circuit consisting of a capacitor and a switch
associated with each ignition point may be employed. All the
switches are controlled by a master switch, such that the
capacitors charge and discharge simultaneously. An electrical pulse
travels from the capacitors, through the switches to the ignition
points on the RCM sheets 12, and to an electrical ground through
the press platens 36A and 36B, igniting the sheets 12 within the
assembly 24 and ultimately forming the bond between components 10A
and 10B. Alternatively, a single large capacitor and switch may be
connected to all the ignition points in parallel, such that energy
is discharged to all ignition points about the assembly 24
simultaneously from the capacitor to ignite each sheet 12.
[0056] During the bonding process, it is known that non-uniform
load distribution between the component bodies 10A and 10B will
result in poor quality bonds with the presence of air gaps (voids)
following the ignition of the sheets 12 within the assembly 24.
Uneven load distribution typically results when the press platens
36A and 36B of the loading mechanism are significantly oversized or
undersized compared to the size of the bonding region 26. This
problem may be exacerbated when one or both of the components 10A
and 10B to be joined are relatively thin. In the case where the
press platens 36A and 36B are oversized relative to the size of the
bonding region 26, the resulting pressure near the peripheral edges
of the bonding region 26 is greater than the pressure near the
center of the bonding region 26, and thus voids may form near the
center of the bonding region 26. This is illustrated by the white
regions visible near the center of the top-plan ultrasonic acoustic
image or C-scan of a bonding region 26 shown in FIG. 9.
[0057] Conversely, in the case where the press platens 36A and 36B
are undersized relative to the bonding region 26, the pressure near
the center of the bonding region is greater than the pressure near
the peripheral edges of the bonding region 26, and thus voids may
appear about the peripheral edge as is shown by the white regions
visible about the peripheral edges of the top-plan ultrasonic
acoustic image or C-scan of a bonding region 26 shown in FIG.
10.
[0058] In order to distribute the load from the press platens 36A
and 36B in a uniform manner to the bonding region 26, one or more
spacer plates 34 sized to match the bonding region 26 are placed
between the components 10A, 10B, and the platen or platens 36A,
36B. The ideal thickness for the spacer plate or plates 34 may be
determined by a sequential process, in which a test bond is
initially formed without the use of any spacer plate or plates 34.
The resulting bond between components 10A and 10B is evaluated to
identify the presence of voids. For applications where the press
platens 36A and 36B are larger than the bonding region 26, the bond
quality may be characterized by a ratio of voided area in the
center quarter of the bonding region 26 to the total area of the
bonding region. To reduce the voided area, spacer plates 34 of
increasingly greater thickness are employed in additional bonding
test procedures between components 10A and 10B until the desired
ratio of voided areas to bonding region area is achieved for a
bonding procedure. Preferably, the thickness of the spacer plates
34 is doubled between each bonding test procedure until the desired
ratio is achieved.
[0059] The procedure may be modified for large area joining
applications where none or only a limited number of edge voids can
be tolerated. For these applications the percentage of edge voids,
defined as the ratio of voided area in the outer quarter of the
bonding region 26 to the total joining area, may be tracked as
described above. If the process of doubling the spacer plate
thickness results in an acceptable percentage of center voids and
no edge voids, then the optimal spacer plate thickness has been
derived. If on the other hand, the process results in an acceptable
percentage of center voids, but some percentage of edge voids are
detected, then the spacer plate thickness should be reduced to the
average thickness of the present and previous spacer plate
thicknesses. This process is repeated until a spacer plate 34
having a determined thickness results in the minimum amount of
center voids and the desired amount of edge voids. This is
illustrated by the small white region near the center and the
general lack of any white regions visible near the peripheral edges
of the top-plan ultrasonic acoustic image or C-scan of a bonding
region 26 shown in FIG. 11.
[0060] For applications where the press platens 36A and 36B are
undersized relative to the bonding region 26, the bond quality may
be characterized by a ratio of voided area in the outer quarter of
the bonding region 26 to the total area of the bonding region. To
reduce the voided area, spacer plates 34 of increasingly greater
thickness are employed in additional bonding test procedures
between components 10A and 10B until the desired ratio of voided
areas to bonding region area is achieved for the bonding procedure.
Preferably, the thickness of the spacer plates 34 is doubled
between each bonding test procedure until the desired ratio is
achieved.
[0061] The methods of the present invention for joining component
bodies 10A and 10B over a large dimension bonding region 26 are
further illustrated by the following six examples.
Example 1
[0062] In this example, reactive or ignition bridges 22 and
assembly tabs 20 were disposed on an assembly 24 inside the
peripheral edges of a bonding region 26 as is illustrated in FIG.
3. As shown in the general arrangement of FIG. 7, the various
components were assembled between press platens 36A and 36B, with
the bonding region 26 to be formed between a nickel disk component
10A (0.2 in. thick) and a brass disk component 10B (0.6 in. thick).
The bonding region 26 was circular, with an outer diameter of 17.7
in. and an area of 246 sq. inches. Layers of fusible material 32A
and 32B, such as tin-lead solder, were pre-applied to the nickel
and brass bodies 10A and 10B. To provide coverage for the bonding
region 26, a total of sixteen RCM sheets 12 (Ni--Al, 80 .mu.m
thick, reaction velocity 7 m/s) were pre-assembled as an assembly
24 as shown in FIG. 3, by pressing a total of twelve indium solder
tabs 20 across the gaps G. To ensure reaction propagation across
the gaps G, six reactive foil ignition bridges 22 were attached
across gaps G within the bonding region 26. Small pieces of indium
solder were additionally used to affix the reactive foil ignition
bridges 22 to the RCM sheets 12.
[0063] The brass disk 10B was placed on a flat surface with the
pre-applied layer of tin-lead solder 32B facing upwards. The
portions of the assembly 24 were positioned adjacent to each other
with a minimum separation gap G on top of the brass disk 10B so
that they completely covered the bond region 26. The nickel disk
10A was placed above the reactive multilayer foil with the
pre-applied layer of tin-lead solder 32A facing down, in contact
with the RCM sheets 12 (Ni--Al, 80 .mu.m thick, reaction velocity 7
m/s) in the assembly 24. An aluminum spacer plate 34 0.75 inches
thick, with a diameter of 17.7 inches, was positioned above and
aligned with the nickel disk 10A. The spacer thickness was
previously determined using the process described above, by making
several joints with different sized spacer plates. A thin layer of
hard rubber 38, with a matching surface area, was placed above the
aluminum spacer plate 34 to accommodate any imperfections on the
outside surfaces of the brass and nickel disks 10A and 10B, and the
surfaces of the platens of the press 36A, 36B used to apply a load
during joining. The entire arrangement was transferred to a
hydraulic press, where a load of 107,000 lbs was applied to the
arrangement. The sheets 12 of the assembly 24 were then ignited
electrically, simultaneously at twelve ignition points around the
circumference identified by the arrows in FIG. 3, resulting in the
bonding of the component bodies 10A and 10B to each other.
Example 2
[0064] In this example, assembly tabs 20 were disposed on an
assembly 24 inside the peripheral edges of a bonding region 26,
while the reactive or ignition bridges 22 were disposed outside the
peripheral edges of the bonding region 26, as is illustrated in
FIG. 4. As shown in the general arrangement of FIG. 7, the various
components were assembled between press platens 36A and 36B, with
the bonding region 26 to be formed between a nickel disk component
10A (0.2 in. thick) and a brass disk component 10B (0.6 in. thick).
The bonding region 26 was circular, with an outer diameter of 17.7
in. and an area of 246 sq. inches. As with Example 1, above, layers
of fusible material 32A and 32B, such as tin-lead solder, were
pre-applied to the nickel and brass bodies 10A and 10B. To provide
coverage for the bonding region 26, a total of eight RCM sheets 12
were pre-assembled as an assembly 24 as shown in FIG. 4, by
pressing a total of three indium solder tabs 20 across the gaps G.
To ensure reaction propagation across the gaps G, eight reactive
foil ignition bridges 22 were attached across gaps G outside the
bonding region 26. Small pieces of high temperature tape
(Kapton.RTM.) were used to provide adhesion between the ignition
bridges 22 and the RCM sheets 12, and to further serve the purpose
of providing structural support to the assembly 24.
[0065] Next, the brass disk 10B was placed on a flat surface with
the pre-applied layer of tin-lead solder 32B facing upwards. The
portions of the assembly 24 were positioned adjacent to each other
with a minimum separation gap on top of the brass disk 10B so that
they completely covered the bond region 26. The nickel disk 10A was
placed above the reactive multilayer foil with the pre-applied
layer of tin-lead solder 32A facing down, in contact with the RCM
sheets 12 in the assembly 24. An aluminum spacer plate 34 0.75
inches thick, with a diameter of 17.7 inches, was positioned above
and aligned with the nickel disk 10A. The spacer thickness was
previously determined using the process described above, by making
several joints with different sized spacer plates. A thin layer of
hard rubber 38, with matching surface area, was placed above the
aluminum spacer plate 34 to accommodate any imperfections on the
outside surfaces of the brass and nickel disks 10A and 10B, and the
surfaces of the platens of the press 36A, 36B used to apply a load
during joining. The entire arrangement was transferred to a
hydraulic press, where a load of 107,000 lbs was applied to the
arrangement. The sheets 12 of the assembly 24 were then ignited
electrically, simultaneously at sixteen ignition points around the
circumference identified by the arrows in FIG. 4, resulting in the
bonding of the component bodies 10A and 10B to each other.
Example 3
[0066] In this example, assembly tabs 20 and ignition bridges 22
were disposed on an assembly 24, both inside and outside of the
peripheral edges of a bonding region 26, as is illustrated in FIG.
12. Component bodies 10A and 10B consisting of a 0.3'' thick copper
alloy disk (10A) and a 0.5'' thick copper alloy disk (10B) were
arranged with the assembly 24 in the bonding region 26, according
to the general arrangement shown in FIG. 7. The bonding region 26
was circular, with a diameter of 13 inches and an area of 133 sq.
inches. Tin-lead solder was used as the fusible material layers 32A
and 32B. Nine RCM sheets 12 were pre-assembled in the assembly
arrangement 24 shown in FIG. 12 by pressing four indium solder tabs
20 across sheet gaps G. To ensure reaction propagation across the
sheet gaps G, ten reactive ignition bridges 22 were attached at
critical boundaries, two within the bonding region 26 and eight
outside the bonding region 26. The various components were arranged
as shown in FIG. 7 with the 0.5'' copper disk 10B at the bottom,
but with no optional spacer plate 34 below it, then the assembly 24
was positioned within the bonding region 26, and then the 0.3''
copper disk 10A placed on top. An aluminum spacer plate 34 was
positioned above, and aligned with, the 0.3'' thick copper disk
10A. A thin layer of stiff foam, with a matching surface area
dimension served as the compliant layer 78. The entire arrangement
was transferred to a hydraulic press and a load of 57,850 lbs was
applied to the assembly 24 by the press. The RCM sheets 12 were
ignited electrically, simultaneously at twelve points evenly spaced
around the circumference, as indicated by the arrows in FIG. 12, to
initiate the bond forming reaction.
[0067] The resulting joined assembly was ultrasonically
(acoustically) scanned to determine the quality of the bond. A
representative acoustic scan is shown in FIG. 13, with areas of
poor bond quality including trapped air, know as voids, displayed
as bright white regions adjacent the peripheral edge of the bonding
region 26. The void content, measured as a percentage of the total
bond area, is less than 1%, indicating a high quality bond. Dark
lines in FIG. 13 indicate cracks or gaps between individual sheets
of reactive composite material that have been filled in by molten
solder during the joining process. The non-straight dark lines are
due to cracking of individual sheets of the reactive composite
material which occurs during joining due to volume contraction of
the sheets as they react. The filled gaps between individual pieces
of reactive multilayer foil are straight lines and reveal the
pattern of individual sheets of the reactive composite material
that were pre-assembled into the assembly 24 prior to joining.
Example 4
[0068] In this example, an assembly 24 of RCM sheets 12 is arranged
with assembly tabs 20 disposed within a square bonding region 26,
and with ignition bridges 22 outside of the peripheral edges of the
square bonding region 26, as is illustrated in FIG. 14. The
components 10A and 10B to be bonded consist of a square plate 10A
of aluminum 0.5'' thick and a square plate 10B of
titanium-aluminum-vanadium alloy 0.5'' thick. The bonding region 26
defines a square with sides 12 inches long and an area of 144 sq.
inches. A tin-silver solder was used to provide fusible layers 32A
and 32B on the two component bodies 10A, 10B. Six equal sized RCM
sheets 12 were pre-assembled in the pattern shown in FIG. 14 by
pressing two indium solder tabs 20 across gaps G between the sheets
12. To ensure reaction propagation across the gaps G, six reactive
multilayer foil ignition bridges 22 were attached at critical
boundaries outside the bonding region 26. As shown in the general
arrangement of FIG. 7, a square spacer plate 34 of aluminum, 0.5
inches thick with 12 inch sides was placed on a flat surface. The
titanium alloy component body 10B, reactive multilayer foil
assembly 24, and aluminum component body 10A were then placed on
top of the spacer plate 34. A second square aluminum spacer plate
34 of the same dimension as the first spacer plate, was positioned
above, and aligned with, the aluminum component body 10A. A thin
layer of hard rubber disposed above the second spacer plate 34
served as a compliant layer 38. The entire assembled arrangement
was transferred to a hydraulic press and a load of 62,640 lbs was
applied to the assembled arrangement by the press platens 36A and
36B. The RCM sheets 12 were ignited electrically, simultaneously at
ten points evenly spaced around the circumference, indicated by
arrows in FIG. 14, resulting in a bonding reaction between the
component bodies 10A and 10B.
[0069] The resulting joint between the component bodies 10A and 10B
was ultrasonically scanned to determine the quality of the bond. An
acoustic scan is shown in FIG. 15. The void content, measured as a
percentage of the total bond area, is less than 1%, indicating a
high quality bond. The dark horizontal and vertical lines in FIG.
15 indicate gaps between individual RCM sheets 12 that have been
filled by molten solder during the joining process. Thus from the
ultrasonic C-scan it can clearly be observed that six sheets of
reactive composite material effectively joined the two component
bodies 10A and 10B.
Example 5
[0070] In this example, an assembly 24 of RCM sheets 12 was
utilized to simultaneously join a set of discrete component tiles
40A-40F to a single base component body 42, as shown schematically
in FIG. 16. Each of the discrete component tiles 40A-40F is
composed of boron carbide (B.sub.4C), and has dimensions of 6.25
inches long by 6 inches wide, by 0.25 inches thick. The single base
component body 42 comprises a copper plate having overall
dimensions of 26.25 inches long by 7.25 inches wide by 0.31 inches
thick. The bonding region 26 has a rectangular configuration, with
a length of 25 inches, a width of 6 inches, and an area of 150 sq.
inches. Layers of tin-silver solder pre-applied to the copper plate
42 and to each boron carbide tile 40A-40F act as fusible material
layers 32A and 32B. Six RCM sheets 12 were pre-assembled into an
assembly 24 by taping ten reactive multilayer foil ignition bridges
22 across gaps between the sheets 12 outside of the bonding region
26, as shown in FIG. 5, increasing the probability of simultaneous
ignition of all the sheets 12. The copper plate 42 was placed on a
flat surface with the layer of tin-silver solder 32B facing
upwards. The assembly 24 was positioned on top of the copper plate
42 so that it completely covered the bonding region 26. Each boron
carbide tile 40A-40F was placed above the assembly 24 in the
desired configuration, with the layers of tin-silver solder 32A
facing down, in contact with the sheets 12 of the assembly 24. In
the present example, the boron carbide tiles 40A-40F were
positioned end to end, in contact with each other and aligned with
the rectangular bonding region 26, as shown in FIG. 16. A compliant
layer 38 consisting of a thin layer of hard rubber, matching the
configuration of the bonding region 26, was placed above the boron
carbide tiles 40A-40F. An aluminum spacer plate 34 was positioned
above the compliant layer 38, and aligned with the bonding region
26. The entire arrangement was transferred to a hydraulic press,
and a load of 65,250 lbs was applied to the arrangement by the
press platens 36A and 36B. The RCM sheets 12 were ignited
electrically, simultaneously at twelve evenly spaced points
corresponding to each of the ignition bridges 22 and one at each
end of the assembly 24, resulting in a bonding reaction between the
copper plate 42 and the boron carbide tiles 40A-40F.
Example 6
[0071] In this example, an assembly 24 of RCM sheets 12 was
utilized to bond two curved component bodies 44A and 44B over
matching non-planar (curved) surfaces, as illustrated in FIG. 17.
Specifically, a component body 44A comprising a curved sheet of
steel having a thickness of 0.015 inches was bonded to a component
body 44B comprising a curved boron carbide tile. The bonding region
was not restricted to a regular shape, and had a surface area of
approximately 111 sq. inches. Fusible layers 32A and 32B of
tin-silver solder were pre-applied to the sheet steel and to the
boron carbide tile. Six RCM sheets 12 were pre-assembled into an
assembly 24 by taping six reactive multilayer foil ignition bridges
22 across gaps G outside of the irregular curved bonding region 26
and pressing two indium solder tabs across gaps G inside of the
bonding region 26. The boron carbide tile was placed on a
form-fitting mold 46 with the fusible layer 32B of tin-silver
solder facing upwards. The form-fitting mold 46 was lined with a
compliant layer 38 of rubber to accommodate surface imperfections.
A free-standing fusible layer 48, consisting of a
silver-tin-titanium solder (S-Bond.RTM. 220) comprising four pieces
each 3 inches wide, was positioned over the boron carbide tile 44B.
The RCM assembly 24 was then positioned on top of the free-standing
fusible layer 48 so that it completely covered the irregular curved
bonding region 26. The steel sheet 44A was next placed above the
assembly 24 with the fusible layer 32A of tin-silver solder facing
down, in contact with the RCM sheets 12. A matching form fitting
mold 50 was positioned above the steel sheet 44A, and the entire
assembly was transferred to a hydraulic press. A load of 32,000 lbs
was applied to the assembly by the press platens 36A and 36B, and
the reactive composite material was ignited electrically,
simultaneously at ten points evenly spaced around the peripheral
edges of the bonding region 26 to initiate the bonding reaction
throughout the curved irregular bonding region.
[0072] As various changes could be made in the above constructions
and procedures without departing from the scope of the invention,
it is intended that all matter contained in the above description
or shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
* * * * *