Method for fabricating integrally bladed rotors

A method and apparatus are disclosed which are useful for fabricating integrally bladed rotors. In particular, the method and apparatus are used to increase the twist of the blades on the rotor from a first degree of twist to a second degree of twist under superplastic forming conditions. The apparatus is constructed and arranged such that the method can be carried out at ambient atmospheric conditions. A key feature of the invention is that the blade twisting dies are present in the blade heating zone only when the dies contact the blade. When the dies are not in contact with the blades, they are at ambient conditions where oxidation is at a minimum.

BEST MODE FOR CARRYING OUT THE INVENTION 
This invention is described in terms of the fabrication of an integrally 
bladed rotor, and in particular, in terms of an apparatus and method for 
the superplastic forming of blades which extend from the rim of the rotor, 
to change the degree of blade twist. However, it will be apparent from the 
following description that the invention is also useful in hot working 
other disk-shaped components which have appendages which extend radially 
outwardly from the component rim. 
Referring to FIG. 1, an integrally bladed rotor 10 is shown as comprising a 
central hub section 12, a rim 14 at the outer periphery of the hub 12, and 
blades 16 which are spaced apart from each other about the circumference 
of the rim 14 and extend radially outwardly from the rim 14. The blades 16 
are integral with the rim 14, either because the central portion of the 
rotor 10 and the blades 16 were forged from the same starting stock of 
material, or because the blades 16 were bonded to the rim 14 in a separate 
fabrication step. The rotor 10 includes a bore 11 through which the rotor 
axis 52 extends. 
With respect to the following description of this invention, the blades 16 
of the rotor 10 have a first degree of twist, fabricated, for example, 
according to the technique described in the above-mentioned patent to 
Walker et al. Use of the present invention imparts a second degree of 
twist to the blades 16. 
The blade twisting apparatus 15 includes a rotor support structure 18 (see 
FIG. 2) which is secured to a horizontal support table 20. The support 
structure 18 includes a pair of vertical posts 22 which are fixedly 
secured to each other by the crossbar 26 and to the table 20. The posts 22 
pass through cylinders 24, and the cylinders 24 are slidable on the posts 
22. Attached to the crossbars 28 is a bearing carrying support plate 29 
which cooperates with attachment fixture 30 and retaining ring 31 for 
fixedly securing the rotor 10 in the vertical plane to the crossbars 28 
and therefore to the support structure 18. See FIG. 3A. In particular, a 
spindle 33 rotates on bearings carried by the plate 29; the spindle 33 has 
an outside diameter which approximates the inside diameter of the rotor 
bore 11, and passes through the bore 11 when the rotor 10 is secured to 
the support structure 18. The attachment fixture 30 is threaded onto the 
end of the spindle 33, over the retaining ring 31. 
Referring also to FIGS. 3A and 3B, the blade twisting apparatus 15 includes 
dies 32, 34 which move between a first die position (shown in FIG. 3A) to 
twist the blade 16 to the desired degree of twist and a second die 
position (shown in FIG. 3B). The dies 32, 34 have contact surfaces which 
cooperate to form a cavity having a shape corresponding to a blade having 
the desired degree of twist. One of the dies has a surface for contacting 
the suction (concave) side of the blade 16, and the other die has a 
surface for contacting the pressure (convex) side of the blade 16. Each 
die 32, 34 is moved between the first and second die positions and along a 
die axis 50 which is related to the particular blade geometry. The dies 
32, 34 are moved by hydraulic actuators 36, 38; hoses 37 carry hydraulic 
fluid from a source (not shown) to the actuators 36, 38. Hoses 39 carry 
coolant fluid from a source (not shown) to the dies 32, 34; the fluid 
moves through passages within the dies 32, 34 to maintain the dies at a 
relatively low temperature during the twisting operation. Also, the cool 
dies act as a buffer to isolate the actuators 36, 38 from the heat 
produced during the twisting operation. 
The path of die movement is governed by the wedge shaped die guides 40, 41. 
The guides 40, 41 rest upon guide support 42 which is secured to the table 
20. Each die 32, 34 has a trapezoidal shaped root section 44, and the root 
surfaces 46 slidingly mate with the wedge shaped surfaces 48 of the guides 
40, 41 and with the surface 49 of the guide support 42. 
As best shown in FIGS. 3A and 3B, the rotor 10 is fixedly secured to the 
support structure 18, and between the dies 32, 34 and their respective die 
guides 40, 41. To allow the rotor 10 to rotate about its axis 52 
(discussed in more detail below), the guides 40, 41 are axially separated 
from each other by a distance W at least equal to the width of the blade 
16. 
This invention is particularly useful in the superplastic forming of blades 
of an integrally bladed rotor. In order to accomplish such forming, the 
blade 16 to be twisted must be heated to a temperature within the rotor 
alloy superplastic temperature range. The term "superplastic forming 
temperature range" is the temperature within which the rotor becomes 
superplastic, but below the temperature at which significant grain growth 
occurs. While this temperature range depends on the particular alloy from 
which the rotor is fabricated, for an alloy such as IN100, the 
superplastic forming temperature range is between about 985.degree. C. and 
1,095.degree. C. (between about 1,800.degree. F. and 2,000.degree. F.) Of 
course, the rotor must have the required fine grained microstructure 
necessary for superplastic forming See, for example, the aforementioned 
patent to Moore and Athey. For IN1OO, a grain size within the range of 
ASTM 12.5-13.5 (about 4.7-3.3 microns) is preferred. As shown in the 
Figures, the forming apparatus 15 includes heaters 56, 58 which are 
constructed and arranged for raising the temperature of at least one blade 
16 to a temperature within the alloy superplastic forming temperature 
range, and to raise the temperature of the portion of the rim 14 from 
which the blade 16 extends to a temperature approximately equal to the 
blade temperature. It is necessary to heat both the blade 16 and the rim 
14 to prevent the rim 14 from acting as a heat sink during the forming 
operation; heating the hub portion 12 of the rotor 10 does not seem to be 
necessary. 
Preferably, the heaters 56, 58 are disposed directly adjacent to the rotor 
10, and are as close to the blade to be twisted as possible In such a 
construction, the heaters 56, 58 produce a local and well-defined heating 
zone which surrounds the blade 16. Most preferably, and as shown in FIG. 
1, the heaters 56, 58 surround a circumferential sector of the rotor 10 so 
as to simultaneously heat several adjacent blades. When the apparatus is 
used to twist each blade of the rotor, this heater configuration greatly 
reduces the overall time necessary to heat the blades to within their 
superplastic forming temperature range. The temperature of the rotor blade 
16 being twisted is monitored by conventional techniques, such as by using 
thermocouples, thermographic paint, or optical pyrometers. 
A passageway 60, 62 extends along the die axis 50 through each heater 56, 
58, respectively, and is sized to allow each blade forming die 32, 34 to 
move through its heater, in and out of the heating zone, between the first 
and second die positions. The passageways 60, 62 are large enough to 
permit the dies 32, 34 to move along the die axis 50, but are also as 
small as is practical, to limit the escape of heat from the heating zone. 
During operation of the blade twisting apparatus 15, the dies 32, 34 are 
kept within the heating zone no longer than the time necessary to twist 
the blade 16 to the second degree of twist. Owing to the superplastic 
condition of the rotor blade 16, the time necessary to twist the blade is 
short. During the twisting operation, the dies are heated, but not to a 
temperature sufficient to do damage to the dies due to the coolant which 
passes through them. At the conclusion of the twisting operation, the 
hydraulic units 36, 38 remove the dies 32, 34 from the heating zone, and 
place them in the second die position where they rest at ambient 
conditions. As a result of the movement of the dies 32, 34 between the 
first and second die positions, and the minimal input of heat to the dies 
during the twisting operation, a protective gas atmosphere to protect the 
dies from oxidation is not necessary. 
The blade forming apparatus 15 includes means (not shown) for automatically 
rotating the rotor 10 about its axis 52 at the completion of each blade 
twisting operation, and while the dies 32, 34 are in the second die 
position. In other words, after a blade "N" in circumferential position 
"n" is twisted, the rotor is indexed to bring blade "N+1" into position 
"n+1" and into alignment with the dies 32, 34. Preferably, blade "N+1" is 
circumferentially adjacent to blade "N", to take advantage of the blade 
preheating described above. At the completion of each blade twisting 
operation, the rotor 10 is again rotated until each blade 16 has been 
twisted, or until the required blades have been twisted. 
FIG. 1 shows the preferred construction for the heaters 56, 58 which 
radiantly heat the blade 16 in a heating zone: The heaters 56, 58 are 
axially spaced apart and the passages 60, 62 allow for the axial movement 
of the blade forming dies 32, 34 between the first and second die 
positions. In an alternate embodiment of this invention shown in FIGS. 4A 
and 4B, the blade 16 is heated by an induction coil 64, similar to the 
manner described by Athey and Moore in commonly assigned U.S. Pat. No. 
3,741,821, which is incorporated by reference. The coil moves between a 
first coil position (FIG. 4A) and a second coil position (FIG. 4B). In the 
second coil position, the coil 64 surrounds the blade 16 and creates a 
heating zone which raises the temperature of the blade 16 to within the 
superplastic forming temperature range, while the blade forming dies 32, 
34 are in the second die position. Once the desired forming temperature 
has been reached, the coil 64 is moved radially outwardly by the coil 
moving apparatus 66 to the first coil position, and the blade forming dies 
32, 34 move to the first die position to contact and twist the heated 
blade 16. After the blade 16 has been twisted, dies 32, 34 are 
automatically moved back to the second die position, the rotor 10 is 
indexed to its next position, and the coil 64 is moved back into the 
second coil position to heat the next blade. The process continues along 
the liner discussed above. 
After all of the rotor blades 16 have been twisted, the support apparatus 
18 (and the rotor attached thereto) is moved vertically upward, sliding on 
the posts 22. Such movement removes the rotor 10 from the vicinity of the 
heaters 56, 58, and the rotor 10 can then be easily removed from the 
structure 18. 
While FIG. 1 shows the blade forming apparatus 15 as comprising only one 
pair of blade forming dies 32, 34 and one pair of radiant heaters 56, 58, 
the apparatus 15 may include several pairs of dies and heaters so that 
more than one blade 16 would be formed at any one time. In this regard, 
the invention contemplates several heating and forming stations disposed 
approximately circumferentially about the rotor 10. Such stations would 
each be characterized by the features discussed above, and in particular, 
by means for moving the forming dies into and out of contact with a heated 
blade such that the dies are not continuously in the heating zone. 
This invention can also be used for repair and manufacturing-type forming 
operations. For example, if one or more of the rotor blades becomes 
damaged, or inspection reveals that one or more blades is not within the 
required twist tolerances, the invention can be used to retwist such blade 
or blades. 
The invention apparatus and method was used in the fabrication of an 
integrally bladed rotor made of the superalloy designated IN100. IN100 is 
a widely used nickel base superalloy having a composition, by weight 
percent, of 8-11Cr, 13-17Co, 2-4Mo, 4.5-5Ti, 5-6Al, 10-11Al+Ti, 
0.15-0.20C, 0.01-0.02B, 0.7-1.2V, 0.03-0.09Zr, balance Ni and incidental 
impurities. In the first step of the overall rotor fabrication process, 
superplastic forming techniques similar to those described in commonly 
assigned U.S. Pat. No. 4,150,557 to Walker et al were used to form a 
powder metallurgy 
to a near net shape rotor having a diameter of about 61 cm (24 in.). The 
rotor had 70 blades which were about 6.4 cm (2.5 in.) in length. The 
distance from the blade leading edge to the blade trailing edge was about 
3.8 cm (1.5 in.) and the maximum thickness of each blade was about 0.8 cm 
(0.3 in.). Microstructural evaluation of the rotor after the initial 
forming operation revealed that it had a fine grain size of about ASTM 
12-13.5 (about 3.3-5.6 microns). To accommodate differences between the 
coefficient of thermal expansion between the forming dies and the rotor 
blades, and to account for tooling tolerances, an envelope of between 0.1 
and 0.2 cm (between about 0.04 and 0.08 in.) was present around each 
blade. The envelope was greater near the root portion of the blade; the 
envelope was removed (as described below) after the twisting operation. 
The rotor was assembled into an apparatus substantially corresponding with 
that shown in FIGS. 1 and 2, where the blades were radiantly heated and 
then contacted by TZM molybdenum dies coated with a thin layer of boron 
nitride. The blades were sequentially heated to a forming temperature of 
about 1,040.degree. C. (1,900.degree. F.), which is within the preferred 
superplastic forming temperature range for IN100. After each blade reached 
its desired forming temperature, the blade forming dies were moved from 
outside the heating zone to a position where they contacted and twisted 
the heated blade. The blades were twisted about 26.degree. about their 
stacking line, at a rate sufficient to accomplish approximately three to 
five degrees of twist per second. After the blade had been twisted to the 
desired degree of twist, the dies were moved out of the heating zone. The 
rotor was indexed into position to twist the circumferentially adjacent 
blade, and the process repeated. The movement of the dies and rotation of 
the rotor was coordinated by conventional software. After twisting several 
blades in this fashion, the rotor was inspected. No cracks were located in 
the formed blades, and the blades had the desired degree of twist. 
The rotor was then heat treated to optimize the superalloy properties. The 
heat treatment cycle was conducted under inert gas atmosphere conditions, 
and was as follows: Heat to about 1,100.degree. C. .+-.8.degree. C. (about 
2,065.degree. F. .+-.15.degree. F.) for 120-140 minutes and oil quench; 
then heat to about 870.degree. C. .+-.8.degree. C. (1,600.degree. F. 
.+-.15.degree. F.) for 35-45 minutes and cool to below about 370.degree. 
C. (700.degree. F.) at a rate equivalent to air cool; then heat to about 
980.degree. C. .+-.8.degree. C. (1,800.degree. F. .+-.15.degree. F.) for 
40-55 minutes and cool to below 370.degree. C. (700.degree. F.) at a rate 
equivalent to air cool; then heat to about 650.degree. C. .+-.8.degree. C. 
(1,200.degree. F. .+-.15.degree. F.) for 24 hours and cool to below 
370.degree. C. (700.degree. F.); then heat to about 760.degree. C. 
.+-.8.degree. C. (1,400.degree. F. .+-.15.degree. F.) for 4 hours and air 
cool to below 370.degree. C. (700.degree. F.). 
The rotor was then ultrasonically inspected using conventional techniques, 
which revealed no internal defects. After inspection, the blades were 
electrochemically machined to their final dimensions, to remove the 
envelope which was present prior to the twisting operation. Machining 
techniques such as those disclosed in U.S. Pat. No. 4,663,011 to Hinman 
were used. Following a final machining operation of other details on the 
rotor, and another inspection, the rotor was ready for installation and 
use in a gas turbine engine. 
This invention is useful in the superplastic forming of other alloys 
besides besides IN100, for example, the nickel based alloys commonly known 
as modified IN100, IN 718, Waspaloy, Astroloy, Udimet 500, Rene 95, 
Inconel X, Inconel 625 and AF2-1DA. Components made of titanium base 
alloys such as Ti-8-1-1, Ti-6-2-4-6 and Ti-6-4 can also be fabricated 
using the methods and apparatus of this invention. Integrally bladed 
rotors are not the only components which can be made according to this 
invention; other components will be apparent to those skilled in the art. 
Although this invention has been shown and described with respect to 
detailed embodiments thereof, it will be understood by those skilled in 
the art that various changes in form and detail may be made without 
departing from the spirit and scope of the claimed invention. For example, 
while the invention is particularly adapted for superplastic forming, it 
can also be used for more conventional hot forming operations.