FIELD OF THE INVENTION
The present invention relates to an improved three-piece wax pattern die to
produce a gas turbine bucket in an investment casting process.
BACKGROUND OF THE INVENTION
The patent search has been carried out on this subject and the following
patents (WO2017009216A1, EP1759788B1, WO2016174344A1,
US20160318816A1, EP3065896A1, EP1866110B1, EP1813366B1,
WO2015017111A1, US20150037602A1, JP2015016477A, US20150017007A,
JP5561733B2, US20130236318, US20130108448A1, JP5080720BL) related to
the present invention were identified. However, these prior art provide
discrete information either related to Investment casting process or gas
turbine blade design, but there is no mention of a method of making three
piece wax pattern die for manufacturing gas turbine bucket using
investment casting. The problems associated with the process recognized that
the aerofoil sections of suction side and pressure side of the blade are to be
maintained within specified tolerances and also rear edge to be provided to
the blade in a single cast for making the roots. Further, shrinkage allowances
to be catered for during the casting process.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved three-piece
wax pattern die to produce in an investment casting process a gas turbine
bucket.
Another object of the invention is to propose an improved three-piece wax
pattern die to produce in an investment casting process a gas turbine bucket,
which is enabled to add edges to both sides of the bucket in a single cast, the

edges subsequently allowing machining of the blade roots including fixing the
blades in the casings.
A still another object of the invention is to propose an improved three-piece
wax pattern die to produce in an investment casting process a gas turbine
bucket, which caters for the shrinkage allowances during casting to maintain
profile accurse of the blades.
A further object of the invention is to propose an improved three-piece wax
pattern die to produce in an investment casting process a gas turbine bucket,
which employs a guidance means to easy opening and closing of the two
cavities in the die.
A still further object of the invention is to propose an improved three-piece
wax pattern die to produce in an investment casting process a gas turbine
bucket, which incorporates a locking means to accurately and firmly hold the
two cavities of the die.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved three-piece wax pattern die to
produce in an investment casting process a gas turbine bucket, the bucket
consisting of suction side and pressure side profiles, root and shroud
portions, the bucket being bifurcated on its parting plane and shroud portions
(4,12) is asymmetrical, the die having cylindrical slots (10); locating pins
(11); a clamping means (6,13) to hold and lock the concave and convex
(8,9); die components at least one guide plate (14) attached to the die
cavities; and a locking guide plate (16) to lock the shroud (4,12) to the part
of the die; wherein the guide plates (14) having identical curvatures of a
base plate slot (1,3,5), wherein the locking guide plate (16) is construct ed
to

withstand the casting pressure and accurately maintain the alignment of the
die components, and wherein the shroud portion (4,12) is provided as a
separate piece and added to the die components (2,7,15).
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is a view of a Gas Turbine Bucket
Figure 2 is a view of the Die Assembly for Gas Turbine Bucket.
Figure 3 is a view of concave, convex and Shroud side portion of the die
Figure 4 is a view of the base Plate of clamping Fixture & Guide plates for
moving in the slots.
Figure 5 is a view of the Die Side Plates, Locking Plate & Dies used during
cooling of wax pattern.
DETAILED DESCRIPTION OF THE INVENTION
The buckets used in gas turbine are subjected to high inlet temperature.
Since the materials used for these blades are of heat resistant alloys like
Nickel/Cobalt based super alloys, which are difficult to machine, it is very
much essential to adopt Investment Casting Process for manufacturing
these blades.
By considering the above conditions, the wax pattern die is designed using
two cavity method by adopting a 3D model of the gas turbine bucket as
reference (1). The bucket consists of suction side and pressure side profiles,
Root and shroud portions. However, shrinkage allowance has been
considered while producing the bucket, since industrial wax is being used as
the pattern material. The bucket (1) is bifurcated on its parting plane. The
two halves of the blade are projected on two cavities of the Die. The shroud
portion (4&12) of the blade is attached separately as it is not symmetrical.

For proper alignment and locking (16) of the die components for example,
cylindrical slots (10) and locating pins (11) are incorporated. The shroud
portion (4, 12) is not symmetrical. Hence, it is produced as a separate piece
and added to the die (2, 7 & 15) components.
A clamping means (6) is designed for firmly holding and locking (3 & 16)) the
die components. Since the shape of the bucket at root and shroud in
cylindrical form, the die parts have been designed in the same way, to retract
the wax pattern after injection. For this a slot (13) with defined curvature has
been created in the base plate (5). The guide plates (14) are fixed to the die
cavities.
The guide plates (14) have the same curvature of the slot (5 & 13). The
convex (9) and concave (8) die components are fixed with these guide plates
(14) in to the slot, so that they can be opened easily after wax injection and
pattern can be easily removed. The Locking guide plate (16) is used to lock
the shroud (4 & 12) part of the die. The other components used in locking
fixture (3) are shown in die assembly for the gas turbine bucket.
After the wax pattern is removed from the die, it should be allowed to cool.
During this cooling process, the shape may get distorted. To avoid this, the
guide dies (17) are designed, wherein the wax pattern is kept and allowed to
cool.

WE CLAIM :
1. An improved three-piece wax pattern die to produce in an investment
casting process a gas turbine bucket, the bucket consisting of suction
side and pressure side profiles, root and shroud portions, the bucket
being bifurcated on its parting plane and shroud portions (4,12) is
asymmetrical, the die having cylindrical slots (10); locating pins (11); a
clamping means (6,13) to hold and lock the concave and convex (8,9);
die components at least one guide plate (14) attached to the die
cavities; and a locking guide plate (16) to lock the shroud (4, 12) to
the part of the die; wherein the guide plates (14) having identical
curvatures of a base plate slot (1,3,5), wherein the locking guide plate
(16) is construct ed to withstand the casting pressure and accurately
maintain the alignment of the die components, and wherein the
shroud portion (4,12) is provided as a separate piece and added to
the die components (2,7,15).