FIELD OF INVENTION
The present invention relates to a method of making wax pattern die for manufacturing hollow blade nozzle of gas turbine by investment casting. More particularly the invention relates to the development of wax pattern die for making gas turbine hollow blade nozzle where the die is manufactured with ceramic core inside for making the hollow blade portion for internal cooling.
BACKGROUND OF THE INVENTION AND PRIOR ARTS
The patent search has been carried out on this subject, but the complete information related to this invention is not directly available. The following patents (W02015017111A1, US20150037602A1, JP5662818B2, JP 2015016477A, US 20150017007A, JP 5561/33B2, US- 20130236318, US20130108448A1, JP5080720BL etc..) related to the present invention were checked and found discrete information either related to Investment casting process or gas turbine blade design. But there is no mention of a method, to develop a wax pattern die for producing Gas Turbine hollow buckets using Investment Casting.

OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a method of making wax pattern die for manufacturing hollow blade nozzle of gas turbine by investment casting, which is capable of producing a wax pattern die with consideration of shrinkage allowances during casting process to meet the requirement of profile accuracies.
Another object of the invention is to propose a method of making wax pattern die for manufacturing hollow blade nozzle of gas turbine by investment casting, which is able to make provision to add edges to both side of the hollow blade nozzle in a single cast, which can be used later for machining of blade roots, to fix in the casing.
A further object of the invention is to propose a method of making wax pattern die for manufacturing hollow blade nozzle of gas turbine by investment casting, which is capable of incorporating support system for accurately placing the ceramic core for creating the hollow portion of the nozzle.
A still another object of the invention is to propose a method of making wax pattern die for manufacturing hollow blade nozzle of gas turbine by investment casting, which can provide a guidance system for easy opening and closing of the two cavities of the die.

A still further object of the invention is to propose a method of making wax pattern die for manufacturing hollow blade nozzle of gas turbine by investment casting, which provides a locking system for accurately aligning and firmly holding the two cavities of the die.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig 1: shows a two cavity wax pattern die for producing hollow blade nozzle.
Fig 2: shows the same two cavity wax pattern die showing the cylindrical locking pins (13,14,15).
Fig 3: shows the same two cavity wax pattern die showing the locating holes (16,17, 18)
Fig 4: shows photography of solid model of hollow nozzle. Fig 5: shows photography of single casting of hollow blade. Fig 6: shows photograph of wax pattern of Hollow nozzle.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The hollow nozzles used in Gas Turbine are subjected to high inlet temperature, of the order of 1060°C. These blades are designed with very intricate & narrow serpentine passages, inside the blade, which are necessary for cooling of the blades

during GT operation. Since the materials used for these blades are heat resistant alloys like Nickel/Cobalt based Superalloys, which are difficult to machine, it is very much essential to adopt Investment Casting Process for manufacturing these blades. Investment Casting Process is also inevitable to achieve the complex internal cooling passages inside the blades.
For investment casting process, the foremost requirement is the design and manufacture of Wax Pattern press moulds, which decide the final form of the inner as well as the outer shapes of the blade. Once the Dies are machined, Wax Patterns are manufactured through injection moulding process.
The aerofoil sections of suction side and pressure side of the nozzle are to be maintained within the specified tolerances and also edges at both sides are to be provided to the nozzle in a single cast for making the roots. This invention establishes a method to design and develop the wax pattern die for the Gas Turbine hollow nozzle by considering shrinkage allowances.
By considering the above conditions, a two cavity die is designed for producing the hollow blade nozzle. The suction side and pressure side of the nozzle are machined on left hand cavity (1) and right hand cavity (2) respectively. The root portion of the

nozzle is provided on both the sides with additional blocks (3, 4, 5 and 6). To form one cavity for the nozzle the three blocks (1, 3 and 4) are fixed to an angular plate (7) and firmly tightened with the help of bolts. The other side of the cavity is formed with the blocks (2, 5, and 6) and these blocks are fixed to a plate (8) and tightened with the help of bolts.
Since the shape of the hollow nozzle has got the shape of the root shroud, which is cylindrical in nature, the die parts are to be designed in the same way, to retract the pattern after injection. For which proper guide way is to be provided in the base plate (9) of the die assembly. A slot with a defined curvature (10) is machined to accommodate the curvature on blade profiles. On this curvature slot, both cavities of the die are moved with the help of angle plates (7, 8). These angle plates (7, 8) consist of a step to sit in the curvature slot (10) and move in the same radius. The curvature slot (10) works as a guidance system for cavities of the die, in such a way that, when both cavities are closed by moving on this guide way, the curvatures required for suction and pressure side of the bucket are achieved.
The important aspect of this Die is the support system for location of the Ceramic Core inside the Die assembly while poring of wax material. For achieving this, at the root area one locating pin was given to locate the core at the root. And also at

the trailing edge (11) and tip side (12), locating surfaces were provided, to match the extra portion of the Ceramic Core. These features enable the ceramic core to sit properly in the wax.pattern and enable to achieve serpentine cooling of the bucket.
To have accurate alignment and firm locking of the two cavities, cylindrical locking pins (13, 14, and 15) setup has been arranged. The locating holes (16, 17 and 18) are machined on other cavity. These pins are located into the holes and form a good locking mechanism to withstand casting pressures. Core points on the die are machined to enable accurate placement of ceramic core in the die for making the hollow portion of the nozzle.

WE CLAIM
1. A method of making wax pattern die for manufacturing hollow blade
nozzle of gas turbine by investment casting comprising;
designing a two cavity die to produce hollow blade nozzle, where suction side of the nozzle to be machined on left hand cavity (1) and pressure side of the nozzle to be machined on right hand cavity (2);
providing the root portion of the nozzle on both sides with additional
blocks (3,4, 5 and 6);
fixing and firmly tightening three blocks (1, 3 and 4) to an angular plate
(7) with bolts to form one cavity for the nozzle;
fixing and firmly tightening three blocks (2, 5 and 6) to an angular plate
(8) with bolts to form other side cavity;
machining a slot (10) with a defined curvature on a base plate (9) of the die assembly to accommodate the curvature on blade profiles to facilitate the movement of the two cavities of the die by the angle plates (7, 8), the said angle plates consisting of step to sit in the curvature slot (10) and to move in the same radius; wherein,

ceramic core is located at the root area by a locating pin at trailing edge (11) and tip side (12) to match the extra portion of the ceramic core wherein cylindrical locking pins (13, 14 and 15) are disposed to have accurate alignment and firm locking of two cavities, when the locating holes (16, 17 and 18) are machined on other cavity so that pins are located into the holes and form a good locking mechanism to withstand casting pressures.