U.S. patent application number 11/536337 was filed with the patent office on 2007-07-12 for apparatus and method for performing welding at elevated temperature.
This patent application is currently assigned to General Electric Company. Invention is credited to James Walter JR. Caddell, Robert Dale Lawrence.
Application Number | 20070158321 11/536337 |
Document ID | / |
Family ID | 32325978 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070158321 |
Kind Code |
A1 |
Caddell; James Walter JR. ;
et al. |
July 12, 2007 |
Apparatus and Method for Performing Welding at Elevated
Temperature
Abstract
A welding apparatus includes a workpiece housing having a window
therethrough and having a welding access therethrough for a welder
to an interior of the workpiece housing. The workpiece housing is
metallic with a heat insulation on an internal surface thereof. A
lamp heat source is directed through the window and at the
workpiece in the interior of the workpiece housing. A gas source
delivers a controllable flow of a shielding gas to the interior of
the workpiece housing. A temperature sensor senses a temperature of
the workpiece within the interior of the workpiece housing. A
feedback controller controls the power to the lamp heat source
responsive to the temperature of the workpiece. To perform welding,
the workpiece is placed into the interior of workpiece housing to
have its temperature sensed by the temperature sensor, and the gas
source is operated to envelope the workpiece in the shielding
gas.
Inventors: |
Caddell; James Walter JR.;
(Milford, OH) ; Lawrence; Robert Dale;
(Hammerville, OH) |
Correspondence
Address: |
MCNEES, WALLACE & NURICK LLC
100 PINE STREET
PO BOX 1166
HARRISBURG
PA
17108-1166
US
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
32325978 |
Appl. No.: |
11/536337 |
Filed: |
September 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10318764 |
Dec 13, 2002 |
7137544 |
|
|
11536337 |
Sep 28, 2006 |
|
|
|
Current U.S.
Class: |
219/137R |
Current CPC
Class: |
B23K 9/16 20130101; Y02T
50/6765 20180501; B23P 6/002 20130101; F01D 5/005 20130101; Y02T
50/671 20130101; Y02T 50/60 20130101; Y02T 50/67 20130101; B23K
9/235 20130101 |
Class at
Publication: |
219/137.00R |
International
Class: |
B23K 33/00 20060101
B23K033/00 |
Claims
1. Apparatus for performing welding on a workpiece at elevated
temperature, comprising: a workpiece housing having a window
therethrough and having a welding access therethrough for a welder
to an interior of the workpiece housing, wherein the interior of
the workpiece housing is sized to receive the workpiece therein,
and wherein the workpiece housing is metallic with a heat
insulation on an internal surface thereof; a lamp heat source
directed through the window and at the workpiece in the interior of
the workpiece housing; a gas source that delivers a controllable
flow of a shielding gas to the interior of the workpiece housing; a
temperature sensor that senses a temperature of the workpiece
within the interior of the workpiece housing; and a feedback
controller having a setpoint input and an input responsive to the
temperature sensor, wherein the feedback controller controls the
power to the lamp heat source responsive to the temperature of the
workpiece.
2. The apparatus of claim 1, wherein the workpiece housing is made
of a stainless steel.
3. The apparatus of claim 1, wherein the workpiece housing has a
wall having an interior shape that is curved in its corners to
avoid dead gas spaces in the corners.
4. The apparatus of claim 1, wherein the workpiece housing has a
removable top cover that provides the welding access.
5. The apparatus of claim 1, wherein the heat insulation is a
ceramic thermal barrier coating.
6. The apparatus of claim 1, wherein the window is made of
quartz.
7. The apparatus of claim 1, wherein the lamp heat source comprises
at least two quartz lamps, and a cooled lamp housing in which the
quartz lamps are received.
8. The apparatus of claim 1, wherein the lamp heat source comprises
a lamp having a lamp output beam, and a support upon which the lamp
is supported, wherein the support is adjustable to establish an
angle of incidence of the lamp output beam upon the workpiece and a
distance of the lamp from the workpiece.
9. The apparatus of claim 1, wherein the temperature sensor is
selected from the group consisting of a pyrometer and a
thermocouple.
10. The apparatus of claim 1, wherein the gas source comprises a
gas distribution structure in a bottom of the workpiece
housing.
11. (canceled)
12. (canceled)
13. (canceled)
14. A method for welding a workpiece at elevated temperature,
comprising the steps of furnishing the workpiece; furnishing a
welding apparatus comprising: a workpiece housing having a window
therethrough and having a welding access therethrough for a welder
to an interior of the workpiece housing, wherein the interior of
the workpiece housing is sized to receive the workpiece therein,
and wherein the workpiece housing is metallic with a heat
insulation on an internal surface thereof; a lamp heat source
directed through the window and at the workpiece in the interior of
the workpiece housing; a gas source that delivers a controllable
flow of a shielding gas to the interior of the workpiece housing; a
temperature sensor that senses a temperature of the workpiece
within the interior of the workpiece housing; a feedback controller
having a setpoint input and an input responsive to the temperature
sensor, wherein the feedback controller controls the power to the
lamp heat source responsive to the temperature of the workpiece;
and a welder that may be positioned to weld the workpiece through
the welding access; placing the workpiece into the interior of the
workpiece housing so as to have its temperature sensed by the
temperature sensor; operating the gas source to envelope the
workpiece in the shielding gas; heating the workpiece by powering
the lamp heat source responsive to the setpoint input and to the
temperature of the workpiece; and welding the workpiece using the
welder.
15. The method of claim 14, wherein the step of furnishing the
workpiece includes the step of furnishing a component of a gas
turbine engine as the workpiece.
16. The method of claim 14, wherein the step of heating includes
the step of performing a pre-welding heat treatment of the
workpiece prior to the step of welding.
17. The method of claim 14, wherein the step of heating includes
the step of maintaining the workpiece at a welding temperature
during the step of welding.
18. The method of claim 14, wherein the step of heating includes
the step of performing a post-welding heat treatment of the
workpiece after the step of welding.
19. The apparatus of claim 1, wherein the window is in a side of
the workpiece housing and the welding access is through a top of
the workpiece housing.
20. The apparatus of claim 1, further including: a welder having
access to the interior of the workpiece housing through the welding
access.
Description
[0001] This invention relates to the welding of articles, wherein
the articles are maintained at elevated temperature during the
welding operation, and more particularly to the weld repair of
superalloy components of gas turbine engines at elevated
temperature.
BACKGROUND OF THE INVENTION
[0002] In an aircraft gas turbine (jet) engine, air is drawn into
the front of the engine, compressed by a shaft-mounted compressor,
and mixed with fuel. The mixture is burned, and the hot combustion
gases are passed through a turbine mounted on the same shaft. The
flow of combustion gas turns the turbine by impingement against an
airfoil section of the turbine blades and vanes, which turns the
shaft and provides power to the compressor. The hot exhaust gases
flow from the back of the engine, driving it and the aircraft
forward.
[0003] In the most common approach, the turbine blades are cast
from nickel-base superalloys. In service, the turbine blades are
subjected to extremely aggressive conditions of elevated
temperature and harsh environment. It is not uncommon that some of
the airfoil, particularly the portion near the tip, of the turbine
blade is lost during service by a combination of erosion,
corrosion, and oxidation damage. As the tip is removed, gas leakage
around the turbine blade and thence around the turbine increases so
that the efficiency of the gas turbine engine decreases.
[0004] Because gas turbine blades are expensive to produce as
new-make articles, whenever possible the damaged turbine blades are
repaired rather than scrapped. The repair involves adding new
material to the tip or other damaged portion of the turbine blade
by welding. In the welding operation, the same material of the
turbine blade (or a different material in some cases) is melted
onto the damaged area and then allowed to solidify to build up the
damaged portion and return it to its permitted dimensional
range.
[0005] Some of the nickel-base superalloys used in turbine blades
are subject to embrittlement and cracking when the welding
operation is conducted with the portion of the turbine blade
adjacent to the welded region at a relatively low temperature. To
accomplish the welding of these alloys, a process termed Superalloy
Welding at Elevated Temperature (SWET) has been developed. As
described in U.S. Pat. Nos. 5,897,801 and 6,124,568, whose
disclosures are incorporated by reference, the SWET process
involves preheating the portion of the turbine blade adjacent to
the welding region to an elevated welding temperature prior to
welding and maintaining the turbine blade at the welding
temperature during the welding operation. The welding is performed
in a controlled-atmosphere glove box or similar enclosure to avoid
undue oxidation of the turbine blade. Before the welding operation,
there may be a separate pre-welding heat treatment, and after the
welding operation there may be a separate post-welding heat
treatment.
[0006] The SWET welding process has been successfully applied to
the weld repair of turbine blades and other superalloy components.
However, the repair is relatively slow. It also requires that the
welding operator control a number of different facets of the
welding operation at once. Although the operators are highly
skilled, performing the welding operation may overtax their
abilities, and in some cases the welding cannot be accomplished
successfully. Accordingly, there is a need for an improved approach
to the welding of materials at elevated temperatures. The present
invention fulfills this need, and further provides related
advantages.
SUMMARY OF THE INVENTION
[0007] The present approach provides an apparatus and method for
performing welding operations on a workpiece at elevated
temperatures. The approach allows the workpiece to be maintained at
the proper elevated welding temperature with good precision, and
also allows pre-welding and post-welding heat treatments to be
performed with precise temperature and time control, and in a
precisely controlled inert gas environment. All of the heat
treating and welding is performed in a single apparatus, without
the need to move the workpiece between different facilities. The
workpiece may be heated much more rapidly and evenly than with
prior elevated-temperature welding apparatus. The longevity of the
heat source is improved. One embodiment of the apparatus is
self-contained except for the welding equipment.
[0008] An apparatus for performing welding on a workpiece at
elevated temperature comprises a workpiece housing having a window
therethrough and having a welding access therethrough for a welder
to an interior of the workpiece housing. The interior of the
workpiece housing is sized to receive the workpiece therein. The
workpiece housing is metallic with a heat insulation, preferably a
ceramic thermal barrier coating, on an internal surface thereof.
The apparatus includes a lamp heat source directed through the
window and at the workpiece in the interior of the workpiece
housing, a gas source that delivers a controllable flow of a
shielding gas to the interior of the workpiece housing, and a
temperature sensor that senses a temperature of the workpiece
within the interior of the workpiece housing. A feedback controller
has a setpoint input and an input responsive to the temperature
sensor, and the feedback controller controls the power to the lamp
heat source responsive to the temperature of the workpiece.
[0009] The workpiece may be of any operable type that requires
elevated-temperature welding. A workpiece of most interest is a gas
turbine component made of a nickel-base superalloy, such as a gas
turbine blade.
[0010] The workpiece housing may be made of any operable material,
but a stainless steel such as a 300-series stainless steel is
preferred. The workpiece housing preferably has a wall having an
interior shape that is curved in its corners to avoid dead gas
spaces in the corners. The workpiece housing preferably has a
removable insulated top cover that provides the welding access. The
window is typically made of quartz.
[0011] The lamp heat source comprises at least two quartz lamps,
and preferably at least four quartz lamps. There is desirably a
cooled lamp housing in which the quartz lamps are received. The
lamps are preferably supported on a support that is adjustable to
establish an angle of incidence of the lamp output beam upon the
workpiece and a distance of the lamp from the workpiece.
[0012] The temperature sensor is desirably a non-contacting
pyrometer or a contacting thermocouple.
[0013] The gas source preferably includes a gas distribution
structure in a bottom of the workpiece housing, to ensure that the
shield-gas flow is evenly distributed.
[0014] A method for welding a workpiece at elevated temperature
comprises the steps of furnishing the workpiece and furnishing a
welding apparatus of the type discussed herein, and a welder that
may be positioned to weld the workpiece through the welding access.
The method includes placing the workpiece into the interior of the
workpiece housing so as to have its temperature sensed by the
temperature sensor, operating the gas source to envelop the
workpiece in the shielding gas, heating the workpiece by powering
the lamp heat source responsive to the setpoint input and to the
measured temperature of the workpiece, and welding the workpiece
using the welder.
[0015] The step of heating may include steps of performing a
pre-welding heat treatment of the workpiece prior to the step of
welding, and/or performing a post-welding heat treatment of the
workpiece after the step of welding, as well as maintaining the
workpiece at a welding temperature during the step of welding.
[0016] The present approach provides a convenient approach for
performing superalloy welding at elevated temperature (SWET)
welding. The size of the workpiece housing may be scaled to
accommodate one or more workpieces at a time. The number and
positioning of the heating lamps may also be optimized to the
nature of the workpiece(s) and the precise treatment to be
performed. Heat treatments may be employed in addition to the basic
temperature control at the welding temperature. The present
approach reduces the ancillary duties of the welding operator,
allowing the welding operator to concentrate on the welding
operation.
[0017] The present approach also may be used for brazing. Thus, as
used herein, the term "welding" encompasses brazing as well as
repair welding of individual workpieces and multi-piece joining
welding of two or more workpieces.
[0018] The present approach produces substantially better
controllability and reproducibility in the welding operation than
prior approaches, leading to a high-quality welded article. The
present approach also significantly improves repair/manufacturing
operations in regard to efficiency and workflow. In prior
approaches, the workpiece was pre-welding heat treated in a
separate heat-treating facility that was sometimes in another
building or even at another site, moved into the SWET-welding
facility, heated to the welding temperature and welded, cooled,
moved to the separate heat-treating facility, and then post-welding
heat treated. This process could require several days to complete,
considering the need to move the workpieces to the heat treating
facility, accumulate furnace loads of workpieces to be heat
treated, wait for an available furnace, perform the actual heat
treating, and return the workpieces to the welding facility. In the
present approach, the pre-welding heat treatment, welding, and
post-welding heat treatment are accomplished in a single facility
in a continuous manner. The welding apparatus may be placed at a
convenient location in the repair facility to allow a smooth flow
of workpieces from pre-welding operations such as cleaning, to the
welding facility, and then to post-welding operations such as final
coating. The efficiency of the repair process is thereby improved
and the costs reduced.
[0019] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings, which illustrate, by way of example, the principles of
the invention. The scope of the invention is not, however, limited
to this preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a perspective view of a welding workpiece in the
form of a turbine blade;
[0021] FIG. 2 is a schematic view of a welding apparatus and a
welder, with the workpiece housing in side sectional view;
[0022] FIG. 3 is a schematic top view of the workpiece housing of
FIG. 2;
[0023] FIG. 4 is an enlarged sectional view of the wall of the
workpiece housing, taken on line 4-4 of FIG. 2;
[0024] FIG. 5 is a schematic side view of an embodiment of the
welding apparatus;
[0025] FIG. 6 is a block flow diagram of an approach for performing
the welding operation; and
[0026] FIG. 7 is a schematic temperature-time diagram for the
welding operation.
DETAILED DESCRIPTION OF THE INVENTION
[0027] FIG. 1 depicts a welding workpiece 20 in the form of a gas
turbine blade 22 which has preferably previously been in service,
or which may be a new-make article. The gas turbine blade 22 has an
airfoil 24 against which the flow of hot combustion gas impinges
during service operation, a downwardly extending shank 26, and an
attachment in the form of a dovetail 28 which attaches the gas
turbine blade 22 to a gas turbine disk (not shown) of the gas
turbine engine. A platform 30 extends transversely outwardly at a
location between the airfoil 24, on the one hand, and the shank 26
and dovetail 28, on the other. There may be one or more internal
cooling passages extending through the interior of the gas turbine
blade 22, ending in openings 32.
[0028] The airfoil 24 of the gas turbine blade 22 may be described
as having a root 34 and a tip 36. If the length of the airfoil 24
between the root 34 and the tip 36 is shorter than the minimum
acceptable dimension, either due to removal material during service
or an undersize newly made article, the airfoil 24 may be
lengthened by welding additional material onto the tip 36. The
present approach is described in relation to such an addition of
material onto the tip 36 of the airfoil 24 of the gas turbine blade
22, as that is a preferred application. Other types of workpieces
20 of particular interest are high-pressure-turbine nozzles
(vanes), low-pressure-turbine nozzles (vanes), and shrouds.
However, the present approach is limited to these types of
workpieces, and may be applied in relation to any operable
workpiece 20.
[0029] The preferred embodiment is utilized in relation to the gas
turbine blade 22 which has previously been in service, and that
embodiment will be described although the invention may be used as
well in relation to newly made articles. The gas turbine blade 22,
which has previously been in service, was manufactured as a
new-make gas turbine blade, and then used in aircraft-engine
service at least once. During service, the gas turbine blade 22 was
subjected to conditions which degrade its structure. Specifically,
a portion of the tip 36 of the gas turbine blade 22 was burned away
so that its shape and dimensions change, other portions may be
burned and damaged, and coatings are pitted or burned. Because the
gas turbine blade 22 is an expensive article, it is preferred that
relatively minor damage be repaired, rather than scrapping the gas
turbine blade 22. The present approach is provided to repair,
refurbish, and rejuvenate the gas turbine blade 22 so that it may
be returned to service. Such repair, refurbishment, and
rejuvenation is an important function which improves the economic
viability of aircraft gas turbine engines by returning
otherwise-unusable gas turbine blades 22 to subsequent service
after appropriate processing.
[0030] The entire gas turbine blade 20 is preferably made of a
nickel-base superalloy. A nickel-base alloy has more nickel by
weight percent than any other element, and a nickel-base superalloy
is a nickel-base alloy that is strengthened by gamma-prime phase or
a related phase. The nickel-base superalloys of interest are
susceptible to embrittlement and cracking when welded without
heating the workpiece, as described in U.S. Pat. No. 5,897,801.
Examples of nickel-base superalloys with which the present
invention may be used include Rene.TM. 80, having a nominal
composition in weight percent of about 14.0 percent chromium, about
9.5 percent cobalt, about 4.0 percent molybdenum, about 4.0 percent
tungsten, about 3.0 percent aluminum, about 5.0 percent titanium,
about 0.17 percent carbon, about 0.015 percent boron, about 0.03
percent zirconium, balance nickel and minor elements; Rene.TM. N5,
having a nominal composition in weight percent of about 7.5 percent
cobalt, about 7.0 percent chromium, about 1.5 percent molybdenum,
about 5 percent tungsten, about 3 percent rhenium, about 6.5
percent tantalum, about 6.2 percent aluminum, about 0.15 percent
hafnium, about 0.05 percent carbon, about 0.004 percent boron,
about 0.01 percent yttrium, balance nickel and minor elements; and
Rene.TM. 142, having a nominal composition in weight percent of
about 12.0 percent cobalt, about 6.8 percent chromium, about 1.5
percent molybdenum, about 4.9 percent tungsten, about 2.8 percent
rhenium, about 6.35 percent tantalum, about 6.15 percent aluminum,
about 1.5 percent hafnium, about 0.12 percent carbon, about 0.015
percent boron, balance nickel and minor elements. The present
approach is operable with other alloys as well, and the use of the
invention is not limited to those listed above.
[0031] FIG. 2 schematically depicts an apparatus 50 for performing
welding on the workpiece 20 at elevated temperature. The apparatus
50 includes a workpiece housing 52 that is preferably made of a
metal such as a 300-series stainless steel. An interior 54 of the
workpiece housing 52 is sized to receive the workpiece 20 therein
and to permit the use of the proper combination of exterior heating
lamps to heat the workpiece. The workpiece housing is sized to
receive three workpieces 20 in the illustrated embodiment, see FIG.
3.
[0032] As seen in the top view of FIG. 3, the illustrated workpiece
housing 52 is generally rectangular. The workpiece housing 52 may
have any operable shape and size that is most suited to the
processing of a particular workpiece. For example, the workpiece
housing may be hexagonal or octagonal in top view. The workpiece
housing 52 has an interior shape of its wall 56 that preferably is
curved in the corners 58 to avoid dead gas spaces in the corners in
relation to the flow of the shielding gas, as will be discussed
subsequently. The workpiece housing 52 has a removable top cover
60, preferably made of the same material, that provides a welding
access 62 through the open top of the workpiece housing 52 for a
welder 63 to the interior 54 of the workpiece housing 52. The top
cover 60 of the illustrated three-workpiece embodiment is
preferably formed as two half-covers that each cover half of the
welding access 62, so that half of the interior 54 of the welding
housing 52 is accessible while the other half remains enclosed so
as to retain heat in the interior 54.
[0033] As seen in FIG. 4, the wall 56 preferably has heat
insulation 64 on an internal surface 66 thereof. The heat
insulation 64 aids in reducing heat loss from the workpiece 20 and
more generally from the interior 54 of the workpiece housing 52.
Due to the use of the heat insulation 64, the interior of the
workpiece housing 52 and the workpiece 20 therein may be heated
much more rapidly than possible in the absence of the heat
insulation 64. The heat insulation 64 is preferably a ceramic
thermal barrier coating 68 made of a material such as
yttria-stabilized zirconia (YSZ), applied directly to the internal
surface 66 or with a bond coat therebetween. YSZ is zirconia with
typically about 2-12 weight percent, preferably about 6-8 percent,
yttria added to stabilize the zirconia against phase changes. The
ceramic thermal barrier coating is preferably applied by air plasma
spray (APS). The preferred ceramic thermal barrier coating 68 is at
least about 0.015 inch thick to provide sufficient insulation, but
not more than about 0.030 inch thick so that the ceramic thermal
barrier coating 68 does not flake and spall off as a result of
thermal cycling the workpiece housing 52 during repeated welding
operations. Optionally but preferably, a thin layer about
0.001-0.005 inch thick of a bond coat such as a NiCrAl material is
applied to the interior surface 66 before the ceramic thermal
barrier coating 68 is applied, to aid in its adhesion to the
interior surface 66 of the wall 56. The ceramic thermal barrier
coating 68 conforms to the shape of the interior surface 66,
including the curved corners 58, providing excellent thermal
insulation for the walls 56 of the workpiece housing 52. The top
cover 60 may have the ceramic thermal barrier coating 68 applied to
its interior surface. More preferably, the flat top cover 60 is
insulated on its inner surface with a flat ceramic tile.
[0034] The workpiece housing 52 has a window 70 therethrough. In
the preferred embodiment, there are two windows 70 on opposite
sides of the workpiece housing 52, but there may be other windows
as well. The window or windows 70 are preferably made of quartz so
as to be transparent to light and also to resist the elevated
temperatures that are experienced by the workpiece housing 52.
There may be any combination of number and size of windows 70
required to provide heating access for particular-shaped workpieces
20. For example, there may be windows through all of the walls 56,
to heat the workpieces on all sides if required. Additionally, the
top cover 60 may have a window therein, or the top cover may have
an opening therethrough (without a window) to provide access for a
top lamp. A virtue of the present approach, as compared with
alternative heating techniques such as resistance furnaces and
induction heating, is that the heating may be made very rapid but
also precisely tailored for each type, shape, configuration, and
number of workpieces.
[0035] A lamp heat source 72 is located outside of the workpiece
housing 52. The lamp heat source 72 has a lamp output beam 74
directed through the window 70 (or through the welding access) and
at the workpiece 20 in the interior 54 of the workpiece housing 52.
There is preferably a lamp heat source 72 associated with each of
the windows 70, so that in the embodiment of FIG. 2 there would be
two lamp heat sources 72, only shown directed through the
right-hand window 70 and the other (not shown) directed through the
left-hand window 70. Each lamp heat source 72 includes at least
one, and preferably at least two, quartz lamps 76 (only one of
which is visible in the view of FIG. 2). The quartz lamps 76 (also
termed quartz halogen lamps) are available commercially in a 2000
watt size, so that in the preferred embodiment of FIG. 2 there are
two quartz lamps 76 associated with each of the two lamp heat
sources 72, for a total of 8000 watts of available heating power
directed toward the workpiece 20 as the lamp output beams 74. This
high power level allows the workpiece 20 to be heated rapidly when
desired. There may be other combinations of lamp heat sources, and
in an alternative design being developed for another type of
workpiece, there is a further lamp heat source directed through an
opening in the top cover 60. Thus, the combination of lamp heat
sources may be precisely tailored to provide the optimum heating
for the type of workpiece that is to be welded.
[0036] The quartz lamps 76 are preferably received in a cooled lamp
housing 78. A flow of a coolant, preferably water, is controllably
circulated through the lamp housing 78 by a water pump/radiator 80.
The illustrated form of the water cooling structure is a
closed-loop recirculating cooling system, so that external water
source and drain connections are not required. However, a
non-recirculating water flow system may be used as well. A flow of
pressurized shop air may also be provided to cool the bulb of the
lamp 76. The cooling of the lamp housing 78 cools the quartz lamp
76 and the pressurized air flow, if any, cools the lamp bulb,
thereby prolonging the service life of the lamp 76. Additionally, a
flow of cooling air may be provided to move heat away from the
operator of the welding facility, and to blow or draw any fumes
away from the operator.
[0037] The lamp housing 78 and thence the lamp(s) 76 are supported
on a support 82. The support 82 is preferably adjustable to
establish an angle of incidence of each of the lamp output beams 74
upon the workpiece 20, and also to establish a distance of the lamp
76 from the workpiece 20. In the embodiment of FIG. 2, the lamp
housing 78 and thence the lamp(s) 76 are slidably supported on the
support 82 to establish the distance of the lamp 76 from the
workpiece 20, and may be fixed in place at a selected sliding
location. The support 82 is pivoted at the end closest to the
workpiece housing 52, and the remote end is supported on an
adjustable arm 84 that may be moved to cause the support 82, and
thence the lamp housing 78 and the lamp(s) 76 to be pivoted about
the pivot point to adjust the angle of incidence of the lamp output
beam 74 onto the workpiece 20. Adjusting the lamp(s) 76 in this
manner helps to optimize the power input to, and thence the heating
of, the workpiece or workpieces 20. Typically it is not necessary
to uniformly heat the entire workpiece 20. Instead it is sufficient
that the portion of the workpiece 20 adjacent to the region to be
welded (e.g., the tip 36 in the illustrated embodiment) is
controllably heated.
[0038] The welding operation is performed in an inert gas shielding
atmosphere, such as an argon atmosphere, to prevent oxidation of
the workpiece 20. To supply the inert shielding gas, a controllable
gas source 86 delivers a controllable flow of the inert shielding
gas to the interior 54 of the workpiece housing 52. The gas source
86 includes a gas supply 88 and a controllable valve 90 that meters
the shielding gas from the gas supply 88 to the interior 54 of the
workpiece housing 52. Experience with a prototype unit has shown
that the shielding gas must be carefully introduced into the
interior 54 of the workpiece housing 52 to ensure that the entire
workpiece 20, or the multiple workpieces 20 where present, are
fully enveloped in the shielding gas. To ensure the full
envelopment, the shielding gas is introduced through a plenum 92
that delivers the shielding gas over the entire area of a gas
distribution plate 94 that forms the bottom of the workpiece
housing 52. The entire face of the gas distribution plate 94 has a
plurality of holes 96 therethrough that spread the shielding gas
over the entire bottom area of the workpiece housing 52. A mass of
steel wool 98 is placed into the plenum 92 below the gas
distribution plate 94 to further diffuse the flow of the shielding
gas. Once the shielding gas is introduced into the interior 54 of
the workpiece housing 52, the rounded corners 58 help to ensure
that there are no stagnated gas volumes within the interior 54 of
the workpiece housing 52. The shielding gas escapes through the
welding access 62 at the top of the workpiece housing 52. The flow
of the shielding gas is desirably controlled to be of high volume
and low pressure. If too low a flow of shielding gas is used, air
may diffuse into the interior 54 of the workpiece housing 52 and
oxidize the workpiece at elevated temperature. If too high a flow
of shielding gas is used, there may be turbulence that draws air
into the interior 54, with the same disadvantageous results.
[0039] A temperature sensor 100 senses a temperature of the
workpiece 20 within the interior 54 of the workpiece housing 52.
Multiple temperature sensors 100 may be used for each workpiece 20
if desired, but typically a single temperature sensor 100 for each
workpiece 20 is sufficient. The temperature sensor 100 is
preferably either a noncontacting pyrometer or, as illustrated, a
contacting thermocouple 102, or both may be used. The temperature
sensor 100 provides a real-time measurement of the temperature of
the workpiece 20 in a vicinity of the region to be welded. The lamp
heat source 72 and the welder 63, when operating, provide the heat
inputs to the workpiece 20. Heat is lost from the workpiece 20
through the walls 56 and top cover 60 of the workpiece housing 52
by conduction, radiation, and heating of the flow of the shielding
gas, and, when the top cover 60 is removed in whole or in part,
through the welding access 62. The temperature sensor 100 provides
a measurement of the actual temperature of the workpiece 20.
[0040] A feedback controller 104 has a setpoint input 106 and an
input responsive to the temperature sensor 100. The feedback
controller 104 controls the power to the lamp heat source 72, and
thence the heating power delivered to the workpiece 20 from this
source, by controlling its lamp power supply 108, responsive to the
temperature of the workpiece measured by the temperature sensor 100
and to the setpoint input 106. Although schematically illustrated
as a manual control, the setpoint input 106 usually also includes a
pre-programmed temperature profile selected to bring the workpiece
20 to a desired welding temperature (and perform pre-welding heat
treatments and post-welding heat treatments as desired), and
maintain it at the welding temperature so that the welding of the
workpiece 20 may be accomplished. The feedback controller 104 also
desirably has control outputs to the water pump/radiator 80 and to
the valve 90 of the controllable gas source 86. These control
outputs may be simple on/off controls to ensure that these
functions are operating, or they may be selected to control the
magnitude of the water flow and gas flow, respectively.
[0041] FIG. 5 illustrates a preferred form of the apparatus 50. The
apparatus 50 as described above is built into a table 110 with a
control panel 112 readily accessible to the operator. The various
elements 80, 88, 104, 108, and others (and the interconnections,
not shown in FIG. 5) are built into the table 110. The table 110
may be furnished with wheels so that it may be readily moved about.
The apparatus 50 in this form is fully self-contained except for a
power input, and sources of air and inert gas. The air and/or inert
gas sources may be provided in bottled form and carried on the
table 110, so that only a power input is required. This form of the
apparatus 50 thus is readily moved to convenient locations in a
factory setting.
[0042] A method for welding the workpiece 20 at elevated
temperature is depicted in block diagram form in FIG. 6. The method
includes furnishing the workpiece or workpieces 20, step 120, and
furnishing the welding apparatus 50, such as that illustrated in
FIG. 2 and/or FIG. 5, step 122. The workpiece 20 is preferably a
component of a gas turbine engine, such as the gas turbine blade 22
illustrated in FIG. 1. The workpiece 20 is placed into and
positioned within the interior 54 of the workpiece housing 52 so
that it may be heated by the lamp output beams 74 and have its
temperature sensed by the temperature sensor 100, step 124. The
workpiece 20 is supported as necessary by tooling or supports.
[0043] The gas source 86 is controllably operated to envelope the
workpiece in the shielding gas, step 126. Simultaneously, it is
preferred that the water pump/radiator 80 be operated to cool the
lamp housing 78 and the lamp 76. The operation of the controllable
gas source 86 and the controllable water pump/radiator 80 (and any
air cooling systems) is preferably controlled by the controller
104, to avoid the chance that an operator will forget to turn them
on or have to be concerned with their proper service levels.
[0044] A heating/welding cycle is performed, step 128. In this
cycle, the workpiece 20 is heated by powering the lamp heat source
72 responsive to the setpoint input 106 and to the temperature of
the workpiece 20 as measured by the temperature sensor 100, step
130, and the workpiece 20 is welded using the welder 63, step 132.
The heating step 130 and the welding step 132 are usually performed
with both sequential and simultaneous substeps, and FIG. 7
illustrates a typical operating cycle. The workpiece is initially
at room temperature, numeral 140, and is initially heated at a
controllable heating rate, numeral 142. There may be an optional
pre-welding heat treatment of the workpiece 20 prior to the step of
welding, numeral 144. A typical pre-welding heat treatment requires
the workpiece 20 to be maintained at a pre-welding temperature for
a pre-welding time. The workpiece 20 is thereafter further heated
at a controllable heating rate, numeral 146, to the welding
temperature and maintained at that temperature for a period of time
sufficient to perform the weld repair, numeral 148. After the
welding step 132 is complete, the workpiece 20 is cooled back to
room temperature at controllable rates, numerals 150 and 154. There
may be an optional post-welding heat treatment, numeral 152, that
is performed between the cooling segments 150 and 154, typically
requiring that the workpiece 20 be held at a post-welding
heat-treatment temperature for a post-welding heat-treatment period
of time. The temperature profile, including the temperatures,
times, heating rates, and cooling rates of steps 142-154, is
readily controlled by the feedback controller 104, with a manual
interrupt provided to allow step 148 to extend for as long a time
as required so that the welding operation may be completed. The use
of the lamp heat source 72 and the well-insulated workpiece housing
52 allow the temperature profile to be readily and precisely
controlled. The specific parameters of the temperature profile of
FIG. 7 are selected according to the specific type of workpiece 20
and its material of construction, and are known in the art or will
be developed for various types of workpieces.
[0045] The present approach has been reduced to practice with a
prototype apparatus 50 as shown in FIG. 2, and has been operated
using the approach of FIG. 6 and a temperature profile such as that
shown in FIG. 7.
[0046] Although a particular embodiment of the invention has been
described in detail for purposes of illustration, various
modifications and enhancements may be made without departing from
the spirit and scope of the invention. Accordingly, the invention
is not to be limited except as by the appended claims.
* * * * *