Note: Descriptions are shown in the official language in which they were submitted.
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DIFFUSION BONDING
[0001]
BACKGROUND
[0002] The present disclosure concerns improvements in or relating to
diffusion
bonding.
[0003] It is known to use isostatic pressure techniques to diffusion bond
metal
components together. Diffusion bonding occurs when two mating surfaces are
pressed
together under temperature, time and pressure conditions that allow
interchange of
atoms across the interface. It is necessary that the surfaces to be joined are
clean and
that the variables of temperature, pressure and time are closely controlled,
so that the
necessary interchange of atoms may be achieved. lsostatic pressing is the
application
of high pressure gas (e.g. argon) at high temperature within a pressure vessel
to the
components to be joined. Gas pressure is applied isostatically so that there
are minimal
or no changes to the geometry of the components being joined. This diffusion
bonding
process requires the efficient sealing of the components, and conventionally,
this has
been accomplished outside the pressure vessel in a preliminary step. However,
the
seal between the components after this preliminary step is fragile, and great
care has to
be taken in moving the joined components to the apparatus where the diffusion
bonding
process is to be carried out.
[0004] Further, as it relates to parts for the impact protection of jet
engine fan blades,
such parts are exposed to potential impacts from birds and other foreign
objects
specifically during takeoff where the parts are under the most severe stress
while at the
same time being the most susceptible to impacts. Conventionally, the parts
were
constructed as one-piece. However, the one-piece part is costly to
manufacture. Two-
piece parts having a welded joint and/or a bonded joint via a conventional
diffusion
bonding process could not withstand the impacts associated with the use of the
parts.
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The raw material required to make a one-piece part is costly and is double the
cost of a
two-piece part. This along with the amount of machining required to generate
the
internal and external surfaces is tremendous. Most of the machining time
required is to
produce the internal surfaces and specifically an internal nose radii due to
the depth of
cut and the small size of the internal nose radii and therefore the need to
use small
cutting tools.
[0005]
The present disclosure provides a process of diffusion bonding which
overcomes certain difficulties with the prior art methods while providing
better and more
advantageous overall results.
SUMMARY OF THE INVENTION
[0006]
In accordance with one non-limiting aspect of the present disclosure, a
method of bonding a part for use in jet engine fan blade protection is
provided.
Although the invention is particularly directed to diffusion bonding of one or
more aircraft
engine parts and will be described with particular reference thereto, it will
be
appreciated the diffusion bonding process can be used to bond materials
together to
form parts for other types of devices (e.g., automotive parts, military
components,
spacecraft components, etc.). The part for use in a jet engine fan blade
includes a first
component and a second component diffusion bonded to the first component. The
first
component is configured as a pressure side component and includes a first
primary
bond land surface. The second component is configured as a suction side
component
and includes a second mating bond land surface. A mandrel is provided. The
mandrel
includes a first surface having a contour that mates with at least a portion
of the first
component and a second surface having a contour that mates with at least a
portion of
the second component. The first and second components are positioned on the
mandrel so that the first bond land surface and the second bond land surface
are in
mating abutment.
The first component is releasably connected to the second
component. The connected first and second components together with the mandrel
are
positioned in a die assembly. The die assembly including a first die, a second
die and a
plurality of fastening members for releasably securing the first die to the
second die.
The first and second dies are formed of a first material having a first
coefficient of
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thermal expansion. The fastening members are formed of a second material
having a
second smaller coefficient of thermal expansion. The die assembly is placed in
a
vacuum furnace or other type of heating arrangement for a diffusion bonding
cycle. The
heating arrangement is evacuated. For example, the heating arrangement is
first
purged with argon gas to displace any atmospheric contamination and then the
heating
arrangement is evacuated to a predetermined vacuum level. The temperature of
the
heating arrangement is increased to a predetermined temperature. Uniform
pressure is
applied across an interface between the first and second bond land surfaces of
the first
and second components. The vacuum level, temperature and pressure is
maintained
within the furnace for a predetermined period of time. The die assembly
including the
diffusion bonded first and second components is removed from the furnace.
[0007] In accordance with another non-limiting aspect of the present
disclosure, a
diffusion bonding die assembly for diffusion bonding a first component having
a
nonplanar first bond land surface to a second component having a nonplanar
second
bond land surface is provided. The diffusion bonding die assembly comprises a
mandrel, an upper die and a lower die. The mandrel is configured to releasably
hold the
first and second components. The first bond land surface and the second bond
land
surface are in mating abutment when loaded on the mandrel. The upper die
includes
an upper surface and a lower surface. The lower surface includes a first
portion
configured to engage the mandrel and a second portion configured to mate with
one of
the first and second components. The lower die includes an upper surface and a
lower
surface. The upper surface includes a first portion configured to engage the
mandrel
and a second portion configured to mate with one of the first and second
components.
A flexible pressure container is at least partially disposed between one of
the upper and
lower dies and one of the first and second bond land surfaces of the first and
second
components. A plurality of fastening members secures the upper die to the
lower die
and holds the diffusion bonding die assembly together during a diffusion
bonding cycle.
The plurality of fasteners is configured to limit expansion of the upper and
lower dies
during the diffusion bonding cycle.
[0008] In accordance with yet another non-limiting aspect of the present
disclosure,
a method of diffusion bonding comprises providing a first component and a
second
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component. The first component includes a first bond land surface having a
wave-like
conformation. The second component includes a second bond land surface having
a
wave-like conformation. The mating first and second bond land surfaces to be
diffusion
bonded are prepared to a predetermined condition such that diffusion bonding
across
an interface between the surfaces is possible. The first component to the
second
component are connected so that the first and second bond land surfaces are in
mating
abutment. A diffusion bonding die assembly configured to releasably secure the
connected components therein is provided. The die assembly includes a first
die, a
second die and a plurality of fastening members for releasably securing the
first die to
the second die. The die assembly is coated with a release agent along with
specifically
identified critical areas of the first and second components. The first and
second
components with the first and second bond land surfaces in mating abutment are
placed
in the die assembly. The die assembly is placed in a vacuum furnace or other
type of
heating arrangement for a diffusion bonding cycle. The heating arrangement is
evacuated and the temperature of the heating arrangement is increased to a
first
temperature. The first temperature is maintained for a predetermined period of
time.
The temperature of the heating arrangement is increased to a second
temperature,
which is maintained for a predetermined period of time. A first pressure is
applied at the
second temperature across the interface of the first and second components for
a
predetermined period of time. The applied pressure is increased to a second
pressure.
The second pressure is applied at the second temperature across the interface
of the
first and second components for a predetermined period of time. The applied
pressure
is decreased to a third pressure. The third pressure is applied at the second
temperature across the interface of the first and second components for a
predetermined period of time.
The temperature of the heating arrangement is
decreased to a third temperature. The die assembly including the diffusion
bonded first
and second components is removed from the heating arrangement.
[0009]
In accordance with yet another non-limiting aspect of the present disclosure,
a part formed by diffusion bonding comprises a first component and a second
component. The first component includes a first, bond land surface, a second
surface
offset from the first surface via a connecting, arcuate wall, and a third
surface opposite
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the first and second surfaces. The second component includes a first surface
and a
second surface. A section of the second surface forms a second, bond land
surface
which is bonded to the first, bond land surface of the first component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIGURE 1 is a side elevational view of a non-limiting part including
a first
component and a second component bonded to the first component in accordance
to
the diffusion bonding process of the present disclosure.
[0011] FIGURE 2 is a side elevational view of the first component of the
part of
FIGURE 1.
[0012] FIGURE 3 is a top perspective view of the first component of FIGURE
2.
[0013] FIGURE 4 is a cross-sectional view of the first component of FIGURE
2 taken
generally along lines 4-4 of FIGURE 2.
[0014] FIGURE 5 is a partially enlarged view of FIGURE 4.
[0015] FIGURE 6 is a side elevational view of the second component of the
part of
FIGURE 1.
[0016] FIGURE 7 is a cross-sectional view of the second component of FIGURE
6
taken generally along lines 7-7 of FIGURE 6.
[0017] FIGURE 8 is a side elevational view of the first component of the
part of
FIGURE 1 illustrating a non-limiting bond land surface.
[0018] FIGURE 9 is a side elevational view of the second component of the
part of
FIGURE 1 illustrating a non-limiting bond land surface.
[0019] FIGURE 10 is a front perspective view of a mandrel having the first
and
second components positioned thereon.
[0020] FIGURE 11 is a partially enlarged view of FIGURE 10.
[0021] FIGURE 12 is a side cross-sectional view of FIGURE 10.
[0022] FIGURE 13 is an exploded front perspective view of a non-limiting
diffusion
bonding die assembly for forming the part of FIGURE 1 including a first die, a
second
die, a pressure bag, and the mandrel and first and second components of FIGURE
10.
[0023] FIGURE 14 is a front perspective view of the diffusion bonding die
assembly
of FIGURE 13 is an assembled condition.
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[0024] FIGURE 15 is a cross-sectional view of the diffusion bonding die
assembly of
FIGURE 13 taken generally along lines 1 5-1 5 of FIGURE 13.
[0025] FIGURE 16 is a partially enlarged view of FIGURE 15.
[0026] FIGURE 17 is a cross-sectional view of the diffusion bonding die
assembly of
FIGURE 13 taken generally along lines 17-17 of FIGURE 13.
[0027] FIGURE 18 is a partially enlarged view of FIGURE 17.
[0028] FIGURE 19 is a front perspective view of the first and second dies
and the
mandrel in a post diffusion bonding inspection condition.
[0029] FIGURE 20 is a side perspective view of the part of FIGURE 1.
[0030] FIGURE 21 is a cross-sectional view of the part of FIGURE 20.
[0031] FIGURE 22 is an enlarged partial view of FIGURE 21.
[0032] FIGURE 23 is a chart summary of a non-limiting diffusion bonding
process
according to the present disclosure.
DETAILED DESCRIPTION
[0033] It should, of course, be understood that the description and
drawings herein
are merely illustrative and that various modifications and changes can be made
in the
structures disclosed without departing from the present disclosure. It will
also be
appreciated that the various identified components for the diffusion bonding
process
disclosed herein are merely terms of art and should not be deemed to limit the
present
disclosure.
[0034] Further, it should be appreciated that the component materials
disclosed
herein are by way of example only. The component materials can further include
not
only elementary metals but metal alloys per se and alloys of metals with
ceramic
material. The materials may be in the form of sintered powder, a casting,
sheet, plate or
a forging.
[0035] Referring now to the drawings, wherein like numerals refer to like
parts
throughout the several views, FIGURE 1 illustrates a non-limiting example of a
part 100
to be manufactured via a diffusion bonding process according to the present
disclosure.
The example should not be construed as limiting as the example is useful in
understanding and practicing the diffusion bonding process described herein.
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[0036] A general overview of the diffusion bonding process is first
provided. The part
100 is manufactured in two separate components, to wit, a first, pressure side
component 102 that is bonded to a second, suction side component 104 at a bond
joint
110. As can be appreciated, part 100 can be formed of more than two
components;
however, this is not required. The first component 102 can be manufactured
from AMS
4911 plate stock (approximately .375 in. thick) that is rough machined, hot
formed and
then machine finished in preparation for diffusion bonding. The second
component 104
can be manufactured from AMS 4911 sheet stock (approximately .040 in. thick)
that is
machine finished as a flat pattern and then hot formed. As can be appreciated,
one or
both of the components can be formed of different materials and/or have
different
thicknesses.
[0037] As is well known, AMS 4911 is a titanium alloy which is heat
treatable and
combines excellent strength and corrosion resistance. AMS 4911 is widely used
in the
aircraft industry in a variety of turbine (i.e., turbine discs) and "hot"
structural
applications. It is generally employed in applications up to 750 F (400 C).
[0038] In preparation for the diffusion bonding process, the two components
102,
104 are typically cleaned, connected together and then loaded into a diffusion
bonding
die assembly 106 according to the present disclosure (FIGURES 13 and 14). The
diffusion bonding die assembly 106 is then placed in a heating arrangement
such as a
vacuum furnace and a diffusion bonding cycle is run at preset parameters.
After
bonding, metallographic samples can be taken and evaluated for bond integrity;
however, this is not required. The part 100 can also, or alternatively, be
ultrasonically
inspected; however, this is not required. After ultrasonic inspection, the
part is typically
finished machined and manually dressed to meet predetermined visual
requirements.
Again, the part 100 is by way of example only. It should be appreciated that
parts
having alternative materials, shapes and/or sizes can be manufactured via the
diffusion
bonding process described herein.
[0039] The first and second components 102, 104 of the part 100 will now be
described in greater detail. With reference to FIGURES 2-5, the first
component 102
comprises a first elongated member 112 having a wave-like or ribbon-like
conformation.
Particularly, as shown in FIGURE 3, as the elongated member twists from a
first end
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portion 114 to a second end portion 116, the elongated member curving along
two
opposed diameters. The elongated member includes a first or primary bond land
surface 120, a second surface 122 offset from the bond land surface via a wall
126, and
a third surface 128 opposite the first and second surfaces. A plurality of
spaced apart
tabs 130 can extend from the first surface. As shown in FIGURE 4, the first
and third
surfaces together 120, 128 define a first section 134 of the elongated member
and the
second and third surfaces together 122, 128 define a second section 136 of the
elongated member. The first section 134 increases in thickness as it
transitions into the
second section 136; however, this is not required. The second section
decreases in
thickness as it extends at an acute angle from the first section. As noted in
FIGURE 1,
the first component 102 has a varying thickness.
[00401 With reference to FIGURES 4 and 5, the wall 126 connects the first
surface
120 and the second surface 122. The wall includes an arcuate surface 140
having a
first end 142 that connects to the second surface and a second end 144 that
connects
to a ramp 150. The ramp has a generally triangular shape, an end portion of
the ramp
being slightly offset from the first surface.
[0041] With reference to FIGURES 6 and 7, the second component 104
comprises a
second elongated member 160 having a wave-like or ribbon-like conformation,
which
twists from a first end portion 166 to a second end portion 168. The second
elongated
member includes a first surface 162 and a second surface 164. A section 170 of
the
second surface at least partially defines a second mating bond land surface
that is
bonded to the first, bond land surface 120. Similar to the first elongated
member, a
plurality of spaced apart tabs 172 can extend from the bonding surface section
170. As
noted in FIGURE 1, the second component 104 includes a first section 174
having a
constant thickness and a second, transitioning section having a decreasing
thickness;
however, this is not required.
[0042] In preparation for the diffusion bonding process, and as indicated
above, the
first and second components 102, 104 are cleaned and the mating surfaces of
the first
and second components are prepared to a predetermined smoothness (e.g., a
smoothness of about 1 micron or better). The components 102, 104 are then
connected and loaded into the diffusion bonding die assembly 106. To
facilitate the
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cleaning and any subsequent inspection, and as shown in FIGURES 8 and 9, the
first
and second components include at least one hole 180, 182 which allows the
first and
second components to be hung to avoid contact with foreign surfaces. As can be
appreciated, this inclusion of one or more holes in the components is not
required.
[0043]
With reference to FIGURES 10-12, a mandrel 200 is provided to ensure the
proper connecting of the first component 102 to the second component 104. The
mandrel includes a base 202 and an arm 204 extending from the base. The arm is
generally triangular in shape and includes a first surface 205, a second
surface 206 and
an arcuate end portion 208. As can be appreciated, the arm 204 can have other
shapes. The first and second surfaces have contours which mate with the ribbon-
like
contours of the respective first and second components 102, 104. The end
portion 208
has a contour which mates with the arcuate surface 140 of the wall 126. This
allows the
first component 102 to be releasably positioned on the mandrel. At least one
pin 210
extends outwardly from a lower portion of the second surface 206 of the arm
204. The
at least one pin allows the second component to be releasably placed on the
mandrel.
As shown, two pins are provided; however, a greater or lesser number of pins
can be
used. The pins are located a predetermined distance from the end portion 208
so that
once the second component 104 is positioned on the pins 210, the tabs 172 can
be
aligned with the tabs 130 (see FIGURE 11). Once aligned, the tabs 130, 172 are
held
together by suitable fastening means, such as, but not limited to, small C-
clamps (not
shown). The mandrel 200 and clamped first and second components 102, 104 are
then
placed in an argon chamber (not shown) wherein the tabs 130, 172 can be tack
welded
together. Although, it should be appreciated that the first and second
components can
be connected via additional or alternative means. In that instance, the tabs
130, 172
are not required. The mandrel and connected first and second components are
then
quickly placed in the diffusion bonding die assembly 106 to ensure that the
bonding
surfaces remain clean.
[0044]
As shown in FIGURES 13 and 14, the diffusion bonding die assembly 106
comprises a first die 220 and a second die 222. The second die includes a
surface 230
having a configuration which can mate with one of the first and second
components
102, 104. The first die includes a surface 232 which can conform to the other
of the first
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and second components. For example, the surfaces 230, 232 can have a wave-like
or
ribbon-like conformation; however, surfaces 230, 232 can have other or
additional
shapes. In the depicted embodiment, surface 230 protrudes at least partially
from the
second die and engages the second component 104. Surface 232 protrudes at
least
partially from the first die and engages the first component 102. The first
die 220
includes a plurality of spaced apart cutouts 250 located on opposed sides 252,
254 of
the die. A wall 256 of the first die includes a plurality of spaced apart
shelves 258 which
extend outwardly from the wall 256. The cutouts 250 extend through the shelves
258.
Similarly, the second die 222 includes a plurality of spaced apart cutouts 260
located on
opposed sides 262, 264 of the die. A wall 270 of the second die 222 includes a
plurality
of spaced apart shelves 272 which extend outwardly from the wall 270. The
cutouts
260 extend through the shelves 272. In an assembled position (FIGURE 14), the
wall
256 is parallel to the wall 270; however, this is not required. The first and
second dies
220, 222 can be formed of a HH2 casting, which is a 309 stainless steel that
has a high
carbon content; however, other materials can be used.
[0045] As shown in FIGURES 15 and 16, in an assembled position, the mandrel
200
is securely positioned between the first and second dies 220, 222.
Particularly, the
mandrel 200 includes first and second opposed grooves 274 and 276,
respectively.
Each groove extends the length of the mandrel base 202; although, this is not
required.
The first and second grooves 274, 276 are configured to receive first and
second
projections 280, 282 located on the respective first and second dies 220, 222.
Spacing
is provided between portions of the base 202 and the first and second dies. As
shown
in FIGURES 17 and 18, the mandrel 200 further includes first and second
recesses 288,
290, respectively. The recesses are located in an offset region 292 of the
mandrel base
and are generally normal to the first and second grooves 274, 276. The first
and
second recesses 288, 290 are configured to receive first and second tabs 294,
296
located on the respective first and second dies 220, 222. Each tab extends
inwardly
from a respective offset region 300, 302 of each die 220, 222. Further, the
surface 232
of the first die 220 includes an offset portion 304. At least a portion of the
pressure bag
340 is disposed in the offset portion for bond transition.
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[0046] With reference again to FIGURE 14, in the assembled position, the
cutouts
250 are aligned with the cutouts 260 and corresponding cutouts 310 located on
the
base 202 of the mandrel 200. The cutouts are dimensioned to receive fastening
member or pins 320. As shown, each pin can be generally dumbbell-shaped;
although,
this is not required. The pin includes and a shaft 322 and caps 324, 326
located on
ends of the shaft. The shaft is cylindrically shaped and the caps are
rectangularly
shaped; although, this is not required. As shown, sixteen pins are provided,
eight for
each side of each first and second die 220, 222. Although, it should be
appreciated that
more or less than sixteen pins can be used to secure the diffusion bonding die
assembly 106. Each pin can be stamped with its own unique number and
correlates
with a cutout location stamped on the die assembly 106. Additionally, the pins
can be
marked with a letter of the alphabet that associates them with a specific die.
Each pin
has a predetermined length, the length of the pin being dependent on it
location on the
die.
[0047] The pins can be formed from a Haynes 230 alloy; however, other
materials
can be used. As is well known, Haynes 230 alloy is a nickel-chromium-tungsten-
molybdenum alloy that combines excellent high temperature strength,
outstanding
resistance to oxidizing environments up to 2100 F (1149 C) for prolonged
exposures,
premier resistance to nitriding environments, and excellent long-term thermal
stability. It
is readily fabricated and formed, and is castable. Other attractive features
include lower
thermal expansion characteristics than most high-temperature alloys, and a
pronounced
resistance to grain coarsening with prolonged exposure to high-temperatures.
[0048] As illustrated in FIGURE 13, a pressure container or bag 340 is
positioned
between one of the first and second dies 220, 222 and one of the first and
second
components 102, 104 positioned on the mandrel 200 for applying a uniform
pressure
between the one of the first and second dies and one of the first and second
components during the diffusion bonding process. The pressure bag is made of a
flexible sheet of material, such as, but not limited to, a sheet of 309
stainless steel, so
that the pressure bag can conform to the shape of one of the first and second
components located on the mandrel 200. This is desirable because the twisting,
ribbon-
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like shape of each part component 102, 104 makes it difficult for the first
and second
components to be simply pressed in a conventional die.
[0049]
In the depicted embodiment of FIGURE 13, the pressure bag is disposed
between the surface 232 of the first die 220 and the second component 104
located on
the mandrel 200. One of the first die and the mandrel can include means for
proper
positioning of the pressure bag thereon. For example, the first die can
include locating
pins (not shown) which engage corresponding holes (not shown) located on the
pressure bag. The pressure bag 340 defines a chamber (not shown) for receiving
a gas
from a remote source via a gas line 342 connected to the pressure bag. In this
embodiment, compressed argon gas is released from a storage tank at
approximately
200 PSI to approximately 250 PSI; although, alternative gases and pressures
are
contemplated. The argon gas flows through a hose and into the pressure bag
line 342.
The line can be regulated by a digital pressure gage (not shown) that can be
monitored
by the operator. The argon gas dew point can be periodically monitored (e.g.,
monthly,
etc.) to determine that moisture content generally does not to exceed about -
76 F.
[0050]
As it relates to the complementary materials for the first and second dies
220,
222 and the pins 320, the HH2 material compared to the Haynes 230 alloy
provides a
small but significant difference in the coefficients of thermal expansion
between the two
materials.
It should be appreciated by one skilled in the art that alternative
complementary metal or metal alloys are contemplated so long as differing
coefficients
of thermal expansion exists between the alternative materials. As is well
known,
coefficients of thermal expansion of a material are complicated and can vary
dramatically as the actual temperature varies, but defines the relationship of
the change
in size of a material as the temperature of the material changes. A
coefficient of thermal
expansion is the fractional increase in length per unit rise in temperature.
It can be
defined at a precise temperature or over a temperature range. Thermal
expansion is an
important considerations in design, and are often overlooked. As will be
appreciated by
one skilled in the art, the coefficient of thermal expansion for the HH2
material is slightly
higher than that of Haynes 230 alloy. Thus, the first and second dies 220, 222
will
expand slightly more than the pins 320 upon exposure to a temperature
exceeding the
annealing temperatures of both materials. In use, as the temperature in the
furnace
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increases, the first and second dies 220, 222 will start to expand. This
expansion will
be limited by the pins 320, which are expanding at a slower rate.
Additionally, because
the pins 320 can have differing lengths, the length of the pins can further
limit the
expansion of the first and second dies. The difference in expansion between
the first
and second dies and pins transfers pressure to the pressure bag 340, which, in
turn,
provides a uniform load to the bond land surfaces 120, 170 of the first and
second
components 102, 104. Further, the increase of temperature in the furnace will
increase
the pressure within the pressure bag 340, which, in turn, increases the
pressure
between the first and second dies 220, 222 and the first and second components
102,
104.
[0051] Non-expandable thermocouples 344 can be located in at least one of
the first
and second dies 220, 222 for monitoring temperature. The thermocouples are
generally
used for up to thirty bond cycles and can be calibrated to special limits.
Usage of the
thermocouples can be controlled by system accuracy tests performed at about
1500 F
to a maximum deviation of 4 F ( 0.4%) to maximum 5 F or up to the thirty
bond
cycles, whichever occurs first.
[0052] With reference to FIGURES 20-21, the part 100, after the diffusion
bonding
process and the connected tabs 130 and 172 are carefully removed from the
part,
includes a bond area 370. The bond area can be ultrasonically inspected to
ensure
proper connection between the bond land surface 120 of first component 102 and
the
section 170 of the second surface 164 of second component 104. The external
surfaces of the part can then be cleaned and finished.
[0053] With reference to FIGURE 23, a summary of the diffusion bonding
process
according to the present disclosure is provided. As indicated previously, the
first
component 102 can be manufactured from AMS 4911 plate stock (approximately
.375
in. thick) that is rough machined, hot formed and then machine finished in
preparation
for diffusion bonding. The second component 104 can be manufactured from AMS
4911 sheet stock (e.g., .040 in. thick) that is machine finished as a flat
pattern and then
hot formed.
[0054] In preparation for the diffusion bonding process, the two components
102,
104 are cleaned, connected together and loaded into the diffusion bonding die
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assembly 106. In order to chemically clean the first and second components,
the
halves can be placed on cleaning racks made of 316 stainless steel. Up to four
separate processing tanks can be utilized for the cleaning, namely, an
alkaline cleaner
tank, a chemical clean etch tank, a city rinse tank and/or a deionize rinse
tank. The
parameters of each of the tanks are provided below. The maximum time between
cleaning and diffusion bonding is generally eight (8) hours or less.
ALKALINE CLEANER CHEM-CLEAN ETCH
CITY RINSE TANK ' DEIONIZE RINSE ;
TANK TANK TANK
1
Solution Components Solution Components at Solution Components - I Solution
Components -
! at start up: start up: I 100% City Water 100% Deionized
water
Water = 48" = 745 gals 35 +/- 5% Nitric (HNO3) Operating Conditions -
Operating Conditions -
= 17.8" = 278 gals Temperature - As Temperature - As
8-10 oz./gal Turco received in city line; received in
city line
Vitro-Kleene = 500 lbs 3 +/- 1%
Hydrofluoric through DI unit;
(1 1/4 drum) (HF) = 1.5" = 24 gals Agitation - Air or Spray Agitation
- Spray
rinse when activated; when activated
Operating Conditions - Remainder Water =
Temperature - 160 F- 31.6" = 493 gals No contaminants -
such Control limits -
, 200 F; as rust particles if Conductivity -
<10
Air Agitation Operating Conditions - overflow tank
umhos (which = 6ppm
1 Temperature - RT to NaCI); Total
Dissolved
Frequency Analysis - 120 F max; Air
Agitation Control limits -Chlorine Solids (TDS) -10 ppm
Once per week content - 2.0 ppm max.; max
Frequency Analysis - Total Dissolved
Spec limit - Vitro- Twice weekly
Kleene 7-12 oz/gal Solids (TDS) - 750 ppm
Spec limit- HNO3(30- max.; Chlorides - 30
Target limits - Vitro- 40%); *HF (6% Max); j ppm max
Kleene 8-10oz/gal Etch rate .0015-.005
I/S/H
Target limits - HNO3(31-
39%); Etch rate .0019-
.0046 I/S/H
*Note: Acid tanks - shall
be controlled by etch
rate. Process may
continue if etch rate is
= within limits and HF is
= below minimum limit
[0055]
The first and second dies 220, 222 are inspected to ensure die flatness and
parallelism. The length of each pin 320 is typically measured for accuracy.
The
contours of each die 220, 222 and the mandrel 200 can be inspected after every
10th
bond cycle; however, inspections can occur after more or less numbers of bond
cycles.
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WO 2009/039282 PCT/US2008/076865
The second die can be divided into multiple sections (e.g. 3, 4, 5, 6
sections, etc.) and
compared to certain die parameters. Data regarding the die can be collected
and
stored electronically to be monitored. This data collection can serve as a
trouble
shooting tool relative to part quality. The pressure bag 340 can be pressure
tested prior
to every bond cycle to confirm that the pressure bag will hold pressure (e.g..
50 psi with
argon gas) and that there are no leaks. With reference to FIGURE 19, the
diffusion
bonding die assembly 106 and mandrel can be inspected after one or more
cycles.
Particularly, the first and second dies 220, 222 and the mandrel 200 are
generally
assembled without the pressure bag 340 to verify that a gap 306 surrounding
the first
and second dies and mandrel does not exceed a maximum gap of approximately
0.010
inches.
[0056] The furnace is also periodically checked. For example, furnace burn
outs can
be performed weekly at about 2000 F for one hour. Furnace leak rates meeting
less
than or equal to about 3 microns or less per hour are performed weekly.
Furnace
temperature uniformity surveys to about 15 F are performed quarterly. System
accuracy tests are performed monthly to about 0.5% to maximum about 5 F (this
includes control thermocouples and load thermocouples). Instrumentation
calibrations
are performed quarterly to about 2 F readable within about 1 F.
[0057] Prior to diffusion bonding, the following items generally are
verified: 1) that a
scheduled burnout has been performed; 2) that the scheduled leak rate has been
performed and is less than or equal to a predetermined amount per hour; 3)
that
there is sufficient gas for delivery to the pressure bag 340 during a bond
cycle; and 4)
that the first and second dies 220, 222 are clean and free of any
oils/grease/cutting
fluid residue, etc. If the diffusion bonding die assembly 106 is not clean,
the diffusion
bonding die should be burned out at about 1800 F for about 1 hour, furnace
cool to
about 1000'F maximum and gas fan quench; 5) that the first and second dies
220,
222 and mandrel 200 and pressure bag 340 are clean from any previous bond
cycle
(i.e., have been scotch-brited smooth), with no remaining solids, residue or
raised
material on the surfaces. The surfaces must be dry.
[0058] To assemble the diffusion bonding die assembly 106 for a diffusion
bonding
cycle, the operator should wear clean lint free gloves. The mandrel 200, first
and
CA 02699952 2010-03-16
WO 2009/039282 PCT/US2008/076865
second dies 220, 222 and the pressure bag 340 can be coated with a release
agent,
such as a boron nitride spray. Specifically identified critical areas of the
first and second
components are also coated with the release agent. The release agent is
typically used
when diffusion bonding titanium components. The part 100 is loaded onto the
mandrel
200 and the mandrel is placed on the second die 222 as described above making
sure
that the connected tabs 130, 172 of the part 100 are seated properly into the
second
die. The pressure bag 340 is placed at least partially over the part and
secured on the
first die. The pins 320 are then secured to the diffusion bonding die assembly
106,
noting that the pins can be numbered and correlated with a numbered position
on the
first die 220. The pressure bag 340 is inflated with gas and held to verify
that the
pressure bag maintains adequate pressure. The diffusion bonding die assembly
106
including mandrel 200 and part 100 are then loaded into a vacuum furnace in a
predetermined orientation (i.e., 45 front right to back left). The gas
pressure valves are
left open to prevent pressure build up in the pressure bag until soak point.
The
furnace's pyrometry system is controlled per set requirements. The furnace is
first
purged with argon gas to displace any atmospheric contamination and then the
furnace
is evacuated to a predetermined vacuum level. Multiple bonding dies may be run
in one
furnace load depending on the size of the vacuum furnace being used.
[0059] The diffusion bonding cycle of the present disclosure is typically
run to the
following preset parameters; although, it should be appreciated that the
exemplary
parameters can vary.
FURNACE LOAD
EQUIPMENT: VACUUM BONDING PRESS
MATL SPEC: AMS 4911 MAX. STK. THK.: 0.300" (Ref Only)
APPROX. PART SIZE: 6" x 42" (Die Size 10" x 1' x 3.5')
ATMOSPHERE (DURING RAMP): 5 x 10-4 Torr Max.
ATMOSPHERE (DURING SAOK): 5 x 10 4 Torr Max.
Controller Set Point May Be Set Within 10 Deg. F. Higher Or Lower Than The
Soak Temps To Bring
The TC Spread Within The Evenly Distributed Range.
Pump Furnace Down To 5 3 microns Then Backfill With Argon And Turn On Fan
Twice At Start Of
= Cycle
1st Ramp Rate: 20 F./ Min Max.
1 st Soak Temp: 1500 50 Deg. F.
15t Soak Time: Equalize TC's to 20
As Cycle Temp Increases Verify That There Is No Pressure In The Pressure Bag
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2rd Ramp Rate: 5 F./ Min. Max.
2nd Soak Temp: 1700 15 Deg. F.
td Soak Time: Hold 1 50-1 70 Minutes
Once load reaches soak temp pressurize to 100 10 psi for 50-60 minutes,
increase to 200 10 psi for
next 50-60 minutes, then decrease to 150 10 psi for remaining cycle. Release
pressure after end of
cycle.
3rd Ramp Rate: Furnace Cool
3rd Soak Temp: 1200 Deg. F.
3rd Soak Time: N/A
¨fh
4 Ramp Rate: N/A
4th Soak Temp: N/A
4th Soak Time: N/A
. GAS FAN COOL USING ARGON ATMOSPHERE TO A MAX. TEMP. OF 300 DEG. F.
FURNACE LOAD
EQUIPMENT: VACUUM BONDING PRESS
MAT'L SPEC: AMS 4911 MAX. STK. THK.: 0.300" (Ref Only)
APPROX. PART SIZE: 6" x 42" (Die Size 10" x 1' x 3.5')
ATMOSPHERE (DURING RAMP): 5 x 10-4 Torr Max.
ATMOSPHERE (DURING SAOK): 5 x 10-4 Torr Max.
Controller Set Point May Be Set Within 10 Deg. F. Higher Or Lower Than The
Soak Temps To Bring
The TC Spread Within The Evenly Distributed Range.
1 Pump Furnace Down To 5 3 microns Then Backfill With Argon And Turn On Fan
Twice At Start Of
Cycle
1st Ramp Rate: 20 F./ Min. Max.
1st Soak Temp: 1500 20 Deg. F.
1st Soak Time: E. ualize TC's to 20
As Cycle Temp Increases Verify That There Is No Pressure In The Pressure Bag
2nd Ramp Rate: 5 F./ Min. Max.
2'd Soak Temp: 1700 15 Deg. F.
2nd Soak Time: Hold 1 50-1 70 Minutes
Once load reaches soak temp pressurize to 100 10 psi for 50-60 minutes,
increase to 250 10 psi for
next 50-60 minutes, then decrease to 200 10 psi for remaining cycle. Release
pressure after end of
cycle.
3rd Ramp Rate: Furnace Cool
3rd Soak Temp: 1000 Deg. F.
3" Soak Time: N/A
4th Ramp Rate: N/A
4th Soak Temp: N/A
4th Soak Time: N/A
GAS FAN COOL USING ARGON ATMOSPHERE TO A MAX. TEMP. OF 300 DEG. F.
[0060] After bonding, metallographic samples are taken and evaluated for
bond
integrity. The part 100 can also be ultrasonically inspected. For example, the
bond are
370 can be inspected using a pulse-echo L-wave mode. The bond area is
inspected
17
CA 02699952 2012-10-31
with the ultrasonic beam generally normal to the part surface (e.g. about 1
degree)
and focused at the bond joint. Laboratory testing can be performed directly
from
samples obtained from excess trim areas of each diffusion bonded part. After
ultrasonic
inspection, the part is then finished machined, cleaned and manually dressed
to meet
predetermined visual requirements. Again, the part 100 is by way of example
only. It
should be appreciated that parts having alternative shapes and sizes can be
manufactured via the diffusion bonding process described herein.
[0061] As is
evident from the foregoing, the diffusion bond die assembly 106 is
unique for several reasons. The die can operate at up to about 1720 F. The die
material can be cast HH2 which has a slightly higher carbon content than
standard cast
309 stainless steel. The mechanical, uniform load that is applied to the bond
land at
temperature can be produced using a 309 stainless steel pressure bag 340. This
allows
this type of tool to be run in almost any standard vacuum furnace with only
slight
modification for plumbing for the pressure bag. The first and second dies 220,
222 can
be held together at temperature using pins 320 made of Haynes 230 alloy. This
material
can be used because it has a slightly lower coefficient of thermal expansion
in
comparison to HH2 die material. As shown in FIGURE 16, this allows the die to
be put
together loose and then become tight at a temperature when the load is place
on the
bond land.
[0062] While
embodiments of the invention have been described in the detailed
description, the scope of the claims should not be limited by the preferred
embodiments
set forth in the examples, but should be given the broadest interpretation
consistent with
the description as a whole.
18
