FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules, 2003
Complete Specification
(See section 10 and rule 13)
A Metal Injection Moulding Process And An Apparatus For Making Distortion Free Integral Turbine Blade
1. Bharat Forge Limited
An Indian company registered under the Indian Companies Act, 1956. Mundhwa, Pune - 411036, Maharashtra, India
2. INMET TECHNOLOGY SOLUTIONS PRIVATE LIMITED
An Indian company registered under the Indian Companies Act, 1956. Plot no. G-31, MIDC, Jejuri - 412303, Maharashtra, India
The following specification particularly describes the invention and the manner in which it is to be performed.

Field Of Invention
The present invention relates to manufacturing of turbocharger components. Particularly, the present invention relates to a turbine blade of locomotive turbocharger and a method of manufacturing an integral turbine blade. More particularly, the present invention relates to manufacturing of integral turbine blade of locomotive turbocharger using Metal Injection Moulding (MIM).
Background Of Invention
Diesel engines typically used in locomotive applications include a turbocharger. In an internal combustion engine, like the diesel engine or petrol engine, the air is aspirated in the piston cylinder assembly where it is mixed with fuel and then combusted to produce power. The air gets aspirated inside the engine cylinder under atmospheric pressure where it fills up the void created by the moving piston. The performance of any IC engine can be increased by introducing air inside the piston under high pressure. Due to this more mass of air enters the combustion zone, due to which more fuel can also be inserted and thus, during combustion more power is produced from the same engine.
The task of inserting air under high pressure in the combustion chamber is done using a turbocharger. The turbocharger has two main sections, a turbine section and a compressor section. The turbocharger normally uses the energy of the exhaust gases coming out of the engine. The exhaust gases are allowed to flow over the turbine section of the turbocharger. The exhaust gases, which have a high

temperature and are under high pressure, expand in the turbine section while losing velocity, and in turn rotate the turbine section. The rotational motion is transferred to the compressor section which compresses the intake air of the engine and supplies it to the combustion chamber under high pressure.
The turbine blade is a key component of the turbocharger in locomotive engines. The turbocharger generates energy to power a compressor with the help of hot exhaust gases. Turbine blades are made of two parts, namely a blade aerofoil section and a blade fir-tree base. Traditionally, turbine blades are manufactured by investment casting followed by finish machining and/or electrochemical machining. Another conventional manufacturing method is to machine a turbine blade directly from a solid block through carving route. MIM has also been used for the manufacturing of turbine blade for turbocharger. But, in that case the turbine blade is produced in two parts. The blade and root are made separately and then welded together. Manufacturing integral turbine blade has its own challenges which have been described in following section.
These traditional manufacturing processes have following drawbacks:
1. Investment casting route:
i. The desired surface finish cannot be achieved on aerofoil profile of turbine blade by investment casting itself. Thus, additional subsequent finishing operations are required to achieve the desired surface finish.

ii. The turbine blades, so produced, require subsequent side and fir-tree grinding operations on the blade fir-tree base after investment casting, for which additional machining allowances have to be provided at the investment casting stage.
iii. The turbine blade produced by investment casting have casting defects like blow holes, surface cracks etc.
iv. Electro-chemical machining is used as finishing operation to achieve the desired surface finish after investment casting, however, this increases the cost of the product.
2. Machining from solid block Route:
i. Several type of cutting tools and machining operations are required (face
milling to 4 to 5-axis profile milling) to produce an aerofoil profile from a
solid block. ii. Large amount of material volume has to be removed from the solid block,
resulting in material wastage, excess power utilization and cutting tools
consumption.
3. Metal Injection Moulding of the turbine blade;
i. In an integral turbine blade, made using MIM, debinding time required for blade and blade fir-tree base is different due to differences in thickness of blade and blade fir-tree base. The blade of lesser thickness requires shorter time for debinding as compared to blade fir-tree base. Traditional methods

of debinding like solvent or thermal debinding are not capable of debinding the thicker section and results into cracking and distortion of blade-fir tree having size greater than 10 mm thickness. ii. After the MIM process, post-MIM processes are required to achieve required surface finish and accuracy. Processes like machining or electro chemical machining is done after MIM. iii. The complex shape of the blade profile and the sudden change in section from the blade fir-tree base to the blade, leads to the distortion and cracking during the debinding and sintering process. In conventional process, the distortion and cracking is compensated by providing allowance throughout the blade profile and by increasing joint area between thick and thin section (i.e., between blade and blade fir-tree base), which is then machined off after the MIM process to achieve required finish and profile accuracy.
The nature of probable defects occurring during conventional MIM route are shown in Table 1
Table 1

Sr. No. Defects Description
1 Voids A void is a cavity or packet inside the integral turbine blade. It originates from the shrinkage of the material or the trapping of gas in the cavity.
2 Cracks A crack is caused by improper debinding operation as well as stress concentration at particular location during shrinkage of the material during sintering operation.
3 Warping
and
distortion The Warping and distortion occurs due to fast heating rate during sintering and improper setters used during sintering operation.

Accordingly, it is required to provide a manufacturing method which can overcome the above stated drawbacks of conventional manufacturing methods.
Objects Of Invention
Some of the objects of the present invention, which at least one embodiment
herein satisfies, are now disclosed.
It is an object of the present invention to produce an integral turbine blade using Metal Injection Moulding (MIM).
It is another object of the present invention to produce an integral turbine blade using Metal Injection Moulding (MIM) which eliminates the requirement of finish machining operations for blade.
It is further object of the present invention to produce an integral turbine blade using Metal Injection Moulding (MIM) which eliminates the requirement of machining allowances for blade.
It is yet another object of the present invention to produce an integral turbine blade with desired accuracy and surface finish.

It is still another object of the present invention to produce an integral turbine blade without any distortion in the final product.
Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
Brief Description Of Drawings
The following non-limiting figures illustrate the integral turbine blade made in
accordance with preferred embodiments of the present invention.
Figure 1 illustrates the perspective views of typical integral turbine blade
Figure 2 illustrates the flow chart for method of manufacturing of an integral
turbine blade in accordance with one implementation of the present invention
Figure 3 illustrates the part-specific ceramic stager/setter in accordance with one
implementation of the present invention
Figure 4 illustrates two injection moulds in mating position in accordance with
one implementation of the present invention
Figure 5a illustrates first mould of metal injection molding apparatus used in
manufacturing of integral turbine blade in accordance with one implementation of
the present invention
Figure 5b illustrates second mould of metal injection molding apparatus used in
manufacturing of integral turbine blade in accordance with one implementation of
the present invention

List Of Parts:
Integral Turbine blade - 100 Convex mould - 300B
Aerofoil Profile - 80 Blade concave impression - 55a
Blade - 10 25 Blade convex impression - 55b
Convex Profile of blade - 75 Fir-tree base concave side
Concave Profile of blade - 15 impression - 60a
Blade hub or blade fir-tree base - Fir-tree base convex side
20 impression - 60b
Blade hub radius - 25 30 Cooling channels in concave
Blade root surface- 30 mould - 65a
Fir-tree profile - 35 Cooling channels in convex mould
Part-specific ceramic stager - 200 - 65b
Support profile of blade - 40 Oil in and out openings for
Support profile of Blade hub or 35 concave moulds - 85a and 90a
blade fir-tree base - 45 Oil in and out openings for convex
Injection mould - 300 moulds -85b and 90b
Integral Turbine blade impression Drilled opening in concave mould
- 70 - 50a
Blade impression - 70a 40 Drilled opening in convex mould -
Fir-tree base impression - 70b 50b
Concave mould - 300A

Summary Of The Invention
In accordance with the present invention, a Metal Injection Moulding (MIM) process is disclosed for the manufacturing of an integral turbine blade (100). In particular, the invention provides for a Metal Injection Moulding (MIM) process for manufacturing of integral turbine blades (100) such that it eliminates many of the post MIM processes such as precise electro-chemical machining, etc. The moulds (300) used in this MIM process are designed and manufactured to produce a void free integral turbine blade (100). Further these moulds (300) also assist in achieving required blade profile/shape (80) with a surface roughness of less than Ra 0.8 µm. The mould design eliminates subsequent processes for achieving the desired surface finish. Common defects like distortion and cracking, which occurs in integral turbine blade (100) manufactured by conventional manufacturing processes, are eliminated by using specially designed part-specific ceramic stager/setter (200) during debinding and sintering steps of the present invention along with optimising the parameters like sintering temperature and sintering pressure.
The MIM process for producing said integral turbine blade (100) comprises the steps of selection of feedstock, its characterisation and inspection followed by moulding a green integral
turbine blade using a designed mould (300), debinding the green integral turbine
blade for primary binder removal which converts green integral turbine blade to
brown integral turbine blade using a specially designed stager/setter (200) and
finally sintering of the brown integral turbine blade using the specially designed

stager/setter (200) in controlled atmosphere to produce fully dense metallic integral turbine blade.
Description of the invention
The present invention is focused on eliminating the stated drawbacks/limitations of conventional manufacturing processes of integral turbine blade (100). This is achieved by providing a manufacturing method for integral turbine blade (100) which is defects (distortion, void, cracks, warp etc.) free, within controlled tolerances and free from post MIM machining processes. The present invention provides a Metal Injection Moulding Process as a manufacturing method for integral turbine blade (100).
Accordingly the present invention provides the MIM process using specifically designed moulds (300), setter/stager (200), and parameters like temperature, pressure etc. during the moulding, debinding and sintering steps.
In an embodiment of present invention, there is provided an integral turbine blade (100), as shown in Figure 1, of a turbocharger locomotive engine; said integral turbine blade (100) comprises a blade (10), aerofoil profile (80), blade hub or blade fir-tree base (20), blade hub radius (25), blade root surface (30), convex profile of blade (75), concave profile of blade (15) and blade fir-tree profile (35). Various views of typical integral turbine blade (100) with the above stated features are shown in Figure 1.

In one aspect of present invention, manufacturing method for integral turbine blade involves sequential steps. These steps are described in detail with the help of Figure 2, as below.
1. Feedstock selection, characterization and inspection:
In this step, selection of feedstock is carried out based on characterization and inspection of raw material. Feedstock is made of powdered metal and binders. Characterization and inspection of feedstock involves confirming properties of raw material like chemical composition, sintered density, shrinkage factor and mechanical properties after sintering. The raw material is selected from a group consisting of Nickel based alloys, Titanium based alloys, Aluminium alloys and Iron based alloys (steels). The material is selected based on the working conditions of the final part. The final part i.e. integral turbine blade (100) can be used in hot or cold section of a turbocharger. Depending upon the working condition, the raw material can be selected from above mentioned material group. In one embodiment, a nickel based alloy is chosen for the manufacturing of the integral turbine blade which can be used in hot section of turbocharger.
2. Injection moulding / Green integral turbine blade manufacturing:
The feedstock (i.e. Nickel Based Alloy) received, after having been characterized and inspected, is fed into the machine feedstock hopper.

Following this the designed Injection moulds (300), as shown in Figure 4, are loaded and connections to mould’s cooling channels (65a and 65b), as shown in Figure 5a and 5b, are carried out.
After reaching a nozzle temperature of around 180 to 220 °C, feedstock is injected into a cavity of injection moulds (300). The cavity (70) of injection moulds (300) corresponds to the shape of the blade and blade hub of integral turbine blade. During moulding, optimized parameters such as injection pressure (ranging from 1300 to 1700 Bar), injection flow/speed (ranging from 32 to 40 cm3/sec) and holding pressure (ranging from 1300 to 1700 Bar) are used to get defect-free green integral turbine blade. After completion of injection, green integral turbine blades are allowed to cool for 10-30 seconds in mould. During cooling, oil is not present in cooling channels (65a, 65b) i.e. said oil in said cooling channels (65a and 65b) is drained out before carrying out cooling. The output of this stage is a green integral turbine blade which is sent for the next operation of debinding.
The injection moulding stage takes approximately 1 to 2 minutes.
3. Debinding of Green integral turbine blade:
In this step, the green integral turbine blade is subjected to debinding operation. Catalytic debinding method is used in this process step. It controls distortion in the integral turbine blade along with precise weight loss in both thick (i.e.,

blade hub) (20) and thin (i.e., blade) (10) sections of the integral turbine blade. Precise weight loss means weight loss achieved greater than 7.5% weight of integral turbine blade. In this step, the green integral turbine blade is staged on a specially designed ceramic stager/setter (200), shown in Figure 3.
The use of stager (200) in this process step gives following benefits:
1. Stager (200) provides support during the debinding process,
2. It helps to avoid damage to the green integral turbine blade during the integral turbine blade movement to sintering operation and,
3. It helps to avoid distortion in the green integral turbine blade.
Nitric Acid of 98% concentration is used as a catalyst in this catalytic debinding process. This step is carried out in a debinding oven under controlled atmosphere and temperature. In this treatment, the green integral turbine blade is held at temperature ranging from 110 ºC - 150 ºC for around 4 to 8 hrs. The Nitric acid is stored in a tank outside debinding oven. It is supplied in to the oven by means of an acid pump in mist form. The Nitric Acid reacts with primary binders to form Formaldehyde gas which is subsequently pushed outside the oven and burnt by burner system. The debinding reaction goes deep inside the integral turbine blade. The binder on surface reacts first and gets vaporized. The debinding reaction continues till all primary binder in the integral turbine blades is removed. This process produces a porous integral turbine blade, which is called brown integral turbine blade, due to removal of

binder from the green integral turbine blade. This debinding process produces thick section like blade hub or blade fir-tree base (20) and thin section like blade aerofoil profile (80) integrally. The brown integral turbine blade is not removed from the stager/setter (200) after completion of the process.
The debinding process is carried out for approximately 10-12 hours depending on the size and geometry of the green integral turbine blade.
4. Sintering of brown integral turbine blade:
Sintering process is carried out on the brown integral turbine blade in inert atmosphere in a sintering furnace. After the debinding process, brown integral turbine blade, placed on specially designed ceramic stager/setter (200), is loaded into the sintering furnace. Ceramic stager/setter (200) is designed by considering shrinkage factor for Nickel Based Alloy feedstock material during sintering. The stager/setter (200) is designed/manufactured such that it supports either entire convex profile of blade (75) or entire concave profile of blade (15) during sintering. It also supports entire fir-tree profile (35) or part of fir-tree profile (35) during sintering. In one embodiment, the stager/setter (200) is manufactured from Al2O3 ceramic material.
In the sintering process, the heating of brown integral turbine blade along with stager/setter (200) starts from ambient temperature with the rate of 2 °C/min till it reached 450 °C. Then the brown integral turbine blade is soaked for 45

minutes at this temperature. After 45 mins, the brown integral turbine blade is further heated till it reaches 600°C with the rate of 3 °C/min, then the brown integral turbine blade is soaked for 60 minutes at this temperature. During this step, remaining primary and secondary binders burn out. After 60 mins, the brown integral turbine blade is further heated till it reaches 1050 °C with the rate of 4 °C/min and the brown integral turbine blade is soaked for 45 minutes at this temperature. After 45 mins, the brown integral turbine blade is further heated till it reaches 1295 °C with the rate of 5 °C/min, then the brown integral turbine blade is soaked for 150 minutes at this temperature. After 150 mins, the brown integral turbine blade is cooled to 200 °C by the rate of 5 °C/min. During above steps, the partial pressure is maintained at 400 millibar. After reaching 200°C, brown integral turbine blade is further cooled to 70 °C with 5 °C/min rate of cooling while maintaining partial pressure at 865 millibar. This sintering process is carried out on the brown integral turbine blade in argon atmosphere in a sintering furnace. The output of this stage is a fully dense metallic integral turbine blade called a sintered integral turbine blade.
The sintering process is carried out for approximately 15-20 hours depending on the size and geometry of the brown integral turbine blade. The output of this process is fully dense metallic integral turbine blade.
5. Grinding of Fir-Tree Profile

In this step, the fir-tree profile of fully dense metallic integral turbine blade is grinded to achieve specified surface finish. Any suitable grinding machine can be used depending upon the size and shape of fully dense metallic integral turbine blade. The output of this step is grinded integral turbine blade. This process step is optional.
6. Cleaning
In this final step, the grinded integral turbine blade is cleaned to obtain final finished product i.e. integral turbine blade (100).
Stager/Setter
In another aspect of the present invention, a ceramic stager/setter (200), as shown in Figure 3, is used during debinding and sintering process to avoid distortion and to maintain surface finish of integral turbine blade (100). It is designed by considering shrinkage factor of material during sintering and the profile of the stager/setter (200) is made such that almost all of its area is in contact with integral turbine blade profile (80) during both debinding and sintering process. The stager/setter (200) is made from ceramic material. In one embodiment of present invention, the stager/setter (200) is manufactured in Al2O3 ceramic material.
There is provided a part-specific ceramic stager/setter (200), as shown in Figure 3; said part-specific ceramic stager (200) comprises of support profile for blade (40)

which supports either entire convex profile of blade (75) or entire concave profile of blade (15) and support profile for blade hub or blade fir-tree base (45) which supports entire fir-tree profile (35) or part of fir-tree profile (35).
In an exemplary embodiment of present invention, setter/stager (200) for integral turbine blade comprises: support profile for blade (40) for supporting entire concave profile of blade (15) and support profile for blade hub or blade fir-tree base (45) for supporting part of fir-tree profile (35). The Figure 3 illustrate the setter/stager having support profile for blade (40) for supporting entire concave profile of blade (15) and support profile for blade hub or blade fir-tree base (45) for supporting part of fir-tree profile (35).
Injection moulds (300)
In accordance with another aspect of present invention, Injection moulds (300), as shown in Figure 4, are provided for Injection moulding or green integral turbine blade manufacturing from selected feedstock. The injection mould (300) has two parts/moulds i.e. a first mould (300A) and a second mould (300B). These moulds are designed by considering shrinkage factor of integral turbine blade’s material. These moulds are such that when the first mould (300A) and second mould (300B) are assembled together, the enclosed cavity has a shape which corresponds to the shape of blade (10) and blade hub or blade fir-tree base (20). Cavity surfaces of the moulds have the impressions of concave (15) and convex profiles (75) of blade along with the impressions of blade fir-tree base (20). These mould

impressions are called concave (55a) and convex (55b) impressions. Convex (55b) and concave (55a) impression of moulds corresponds to convex profile of blade (75) and concave profile of blade (15) respectively. When the first mould (300A) and second mould (300B) are assembled together, the enclosed cavity formed by the concave (55a) and convex (55b) impressions of moulds is referred to as blade profile impression (70a). Similarly, when the first mould (300A) and second mould (300B) are assembled together, the enclosed cavity formed by impressions of blade fir-tree base (20) collectively is referred to as fir-tree base impression (70b). Blade profile impression corresponds to a shape and profile of blade (10). Fir-tree base impression corresponds to the shape and profile of blade hub or blade fir-tree base (20). The blade profile impression (70a) and fir-tree base impression (70b) are collectively referred to as integral turbine blade impression (70). Further, both, blade profile impression (70a) and fir-tree base impression (70b) together corresponds to the shape and profile of blade (10) and blade hub or blade fir-tree base (20) to be manufactured as green integral turbine blade at the injection moulding stage. The dimensional accuracy of the all impressions of mould cavity (70) is maintained within ± 20 micron and finishing i.e. polishing operation is conducted on mould to achieve mirror surface finish. Along with cavities, these moulds have cooling channels (65a and 65b). These cooling channels (65a and 65b) are either made by machining or additive manufacturing method followed by finish machining operations in moulds (300a and 300b). The positions, size and shape of cooling channels (65a and 65b) in the moulds (300) are decided based on required surface properties and allowed distortion in integral

turbine blade (100). In one embodiment, the shape of cooling channels (65a and 65b) used in moulds (300a and 300b) of present invention is cylindrical. In the present invention, the cooling channels (65a and 65b) are placed around impressions (70). Oil is used as a cooling media which is passed through the cooling channels (65a and 65b) during the injection process. Oil of required temperature flows through the cooling channels (65a and 65b) to maintain mould’s temperature during the injection operation. It helps in preventing defects like voids, cracks, distortion and warpage in green integral turbine blades during the injection moulding. After completion of the injection, integral turbine blades are allowed to cool for certain period of time in the mould. While cooling, there is no oil flow in cooling channels (65a and 65b). Cooling connections (hose pipes) are used to circulate the hot oil from mould to mould temperature control unit. Mould temperature control unit is used to heat oil to a desired temperature before the oil is supplied to the mould.
In another exemplary embodiment of present invention, the injection mould (300) comprises: blade profile impression (70a) and fir-tree base impression (70b). The blade profile impression (70a) corresponds to concave (15) and convex (75) profiles of blade and fir-tree base impression (70b) corresponds to blade hub or blade fir-tree base (20). Figure 4 illustrates an injection mould (300) comprising concave mould (300A) and convex mould (300B), in accordance with one implementation of the present invention. Figure 5a illustrates the concave mould (300A) and Figure 5b illustrates the convex mould (300B) separately. The

injection mould (300) is used to manufacture green integral turbine blade (100) from feedstock. In the illustrated implementation, cavity surfaces of the concave mould (300A) have the concave impression (55a) and the blade fir-tree base impression (60a), while the convex mould (300B) have convex impression (55b) and blade fir-tree base impression (60b). The concave (55a) and convex (55b) impressions are collectively referred to as blade profile impression (70a) and the blade fir-tree base impressions (60a and 60b) are collectively referred to as fir-tree base impression (70b). The concave impression (55a) of mould (300a) and convex impression (55b) of convex mould (300B) corresponds to convex profile of blade (75) and concave profile of blade (15) respectively. Blade profile impression (70a) corresponds to the shape and profile of blade (10). Fir-tree base impression (70b) corresponds to the shape and profile of blade hub or blade fir-tree base (20). Both, blade profile impression (70a) and fir-tree base impression (70b) together correspond to the shape and profile of blade (10) and blade hub or blade fir-tree base (20) to be manufactured as green integral turbine blade at the injection moulding stage. Along with cavities, these moulds have cooling channels (65a and 65b). Concave mould (300A) and convex mould (300B) comprises cooling channels (65a and 65b) around impression (55a, 55b, 60a and 60b) through which oil of required temperature flows and maintains desired mould temperature during injection operation and prevents defects like voids, cracks, distortion and warpage in green integral turbine blades. The cooling channels have two openings, oil in and oil out openings (85a, 85b and 90a, 90b) and drilling opening (50a and 50b). The drilling openings (50a and 50b) are closed by any closing means like plugs.

The physical properties (proof stress, ultimate tensile strength and elongation) of the integral turbine blade (100) obtained by proposed/invented manufacturing process is ensured by producing a dog bone tensile specimens as per ISO 2740 standard in the form of type B from as-received feedstock material and testing the dog bone tensile specimen. The dog bone specimen is made using the present method of manufacturing of the integral turbine blade (100) and it is made and treated along with integral turbine blade (100) at every stage. Mechanical testing is done on dog bone tensile specimens as per ISO 6892-1 with method A i.e. strain rate control method. The tests are performed on MTS-250 kN testing machine with wedge grips.
The accuracy of profile (80) of integral turbine blade (100) is measured on CMM. The profile accuracy achieved should fall within tolerance of + 0.2 mm.
In at least an embodiment of this invention, the integral turbine blade (100) comprising these above-mentioned features is designed and rendered using a rendering software which is then used as an input for making moulds (300A and 300B).
According to manufacturing process of the present invention, a three dimensional object is created in six subsequent steps viz. Feedstock selection, characterization and inspection, injection moulding, debinding of green integral turbine blade to

convert it into the brown integral turbine blade, sintering of brown integral turbine blade to produce fully dense metallic integral turbine blade having density 7.8 g/cm3, fir-tree grinding and cleaning. The three dimensional object is an integral turbine blade (100).
According to this invention, there is provided a method of metal injection moulding for making integral turbine blades (100).
It is evident from the foregoing discussion that the invention has a number of embodiments.
In the preferred embodiment, a metal injection moulding process for distortion free integral turbine blade (100) is disclosed. The said process comprises the steps of:
a. characterising, inspecting and providing feedstock;
b. feeding the feedstock into a feedstock hopper
c. moulding the feedstock in an injection mould (300) to produce a
defects-free green integral turbine blade,
d. cooling said green integral turbine blade for 10-30 seconds in said
injection mould (300),
e. debinding in a debinding oven the green integral turbine blade staged
on a stager to produce a brown integral turbine blade
f. sintering in a sintering furnace the brown integral turbine blade staged

on said stager by step-by-step heating and soaking, and cooling at variable heating and cooling rates and under variable pressure to produce fully dense turbine blade
g. fir-tree grinding the fully dense turbine blade to produce fir-tree-grinded integral turbine blade
h. cleaning the fir-tree-grinded integral turbine blade to produce distortion free integral turbine blade.
In another embodiment, in step c, after reaching a temperature of around 180 to 220 °C for the injection nozzle, moulding is carried out at an injection pressure ranging from 1300 to 1700 bar, an injection flow/speed ranging from 32 to 40 cm3/sec, and holding pressure ranging from 1300 to 1700 bar.
In a further embodiment, the injection mould (300) is provided with cooling channels (65) that carry oil of temperature in the range of 40 - 150°C.
In a still further embodiment, the oil in the cooling channels (65a and 65b) is drained out before carrying out said step d of cooling.
In yet another embodiment of the method, the step e is carried out using a catalytic debinding method.
In a further embodiment, 98% concentrated Nitric acid is used as catalyst in said

step e.
In an embodiment of the method, step e is carried out in a debinding oven at a temperature ranging from 110 ºC - 150 ºC for a period between 4 to 8 hrs., more particularly, at a temperature between 115 - 125 °C.
In a further embodiment of the method, Nitric acid is stored in tank outside said debinding oven and supplied in a mist form to said debinding oven by means of an acid pump.
In a still further embodiment, during said step e, said green integral turbine blade is staged on stager such that the area supported by support profile for blade of stager is 100% same as said concave or convex blade profile.
In another embodiment, in said step f, said brown integral turbine blade is sintered in an inert atmosphere in a sintering furnace.
In another embodiment, the said brown integral turbine blade is not removed from the said stager/setter after completion of step e of debinding and the said brown integral turbine blade staged on said stager along with said stager is transferred to step f of sintering.

In another embodiment, during said step f of sintering, said brown integral turbine blade is staged on stager such that the area supported by support profile for blade of stager is 100% same as said concave or convex blade profile.
In a further embodiment, said stager used in step e of debinding and step f of sintering is made of Al2O3 ceramic material.
In a still further embodiment, in step f of sintering, said step-by-step heating and soaking of said brown integral turbine blade starts from ambient temperature at a rate of 2 °C/min till a temperature of 450 °C, following which said brown integral turbine blade is soaked for 45 minutes, which is followed by the following stages of heating and soaking and cooling:
- heating to 600 °C at a rate of 3 °C/min followed by soaking for 60 minutes, followed by;
- heating to 1050 °C at a rate of 4 °C/min followed by soaking for 45 minutes, followed by;
- heating to 1295 °C at a rate of 5 °C/min followed by soaking for 150 minutes, followed by;
- cooling said brown integral turbine blade to 200 °Cat a cooling rate of 5 °C/min;
wherein said heating, soaking, and cooling steps are carried out at a pressure of 400 millibar, and wherein said cooled brown integral turbine blade is further cooled to 70 °C under a pressure of 865 millibar and at a

cooling rate of 5 °C/min.
The invention also discloses an apparatus for making for distortion free integral turbine blade, characterised in that said apparatus comprising a feedstock hopper, an injection mould (300), a stager/setter (200), a debinding oven, a sintering furnace, a grinding station, and a cleaning station.
In an embodiment of the apparatus as disclosed here, the mould has cooling channels (65) to carry oil, and wherein said mould has a first mould (300A) and a second mould (300B), wherein the first mould (300A) and second mould (300B) are in mating position, the enclosed cavity has a shape which corresponds to the shape of blade (10) and blade hub or blade fir-tree base (20).
In another embodiment of the apparatus, the mould cavity has a blade profile impression (70a) formed by a concave (55a) and convex (55b) impression, and fir-tree base impression (70b), said blade profile impression (70a) and said fir-tree base impression (70b) are collectively referred to as integral turbine blade impression (70).
In yet another embodiment of the apparatus, the dimensional accuracy of the all impressions of injection mould cavity (70) is maintained within ± 20 micron and finishing i.e. polishing operation is conducted on mould impressions (70) to achieve mirror surface finish.

In yet another embodiment of the apparatus, the cooling channels are positioned around said impressions and they have a cylindrical cross-section.
In a still further embodiment of the apparatus, said stagers comprises of support profile for blade (40) which supports either entire convex profile of blade (75) or entire concave profile of blade (15) and support profile for blade hub or blade fir-tree base (45) which supports entire fir-tree profile (35) or part of fir-tree profile (35).
In another embodiment of the apparatus, said debinding oven and said sintering furnace carry out debinding of said green integral turbine blade staged on stager (200) and sintering of said brown integral turbine blade staged on stager (200) respectively. The details of the stages have been provided earlier.
In a final embodiment of the apparatus, said mould is provided with a mould temperature control unit for heating said oil to a temperature between 40 - 150°C.
Example of invention
A nickel based alloy, IN713C is chosen for the manufacturing of the integral
turbine blade which can be used in hot section of a turbocharger.
1. Feedstock selection, characterization and inspection:

Catalytic feedstock of IN713C is selected as catalytic debinding process has been selected in order to overcome the problem faced during debinding due to change in section from blade to blade fir-tree base. In this step, characterization and inspection of IN713C feedstock is carried out, following which the inspected IN713C feedstock is sent to the moulding process. Metal powder of 20 to 40 µm size is used in the feedstock. 2. Injection Moulding / Green Integral Turbine Blade Manufacturing:
The catalytic feedstock of IN713C received after having been characterized and inspected is fed into the machine feedstock hopper, following which the designed injection moulds (300) loading and connection to mould’s cooling channels (65a and 65b) is carried out.
The Injection moulds (300) are designed by considering shrinkage factor of 1.1555 for IN713C material. The mould is made in two parts (300A and 300B) using machining process and has cavities of integral turbine blade (100) in air hardened grade 2 tool steel with optimised cooling channels (65a, 65b) of 6 mm internal diameter. The dimensional accuracy of the all mould impressions is maintained within ± 20 micron and finishing i.e. polishing operation is conducted on mould to achieve mirror surface finish. The dimensional accuracy and surface finish of mould ensure the desired surface finish on integral turbine blade. The cooling channels (65a, 65b) are formed by drilling operation in mould around part cavity/part profile. Oil at 140°C is passed through the cooling channels (65a, 65b) to maintain mould temperature up to

120°C during injection operation. This prevents defects in green integral turbine blades. Mould temperature control unit is used to heat the oil in the temperature range of 40 – 150 °C which is then supplied to moulds on machine through cooling connections.
After reaching a nozzle temperature of around 180 to 220 °C, moulding is carried out to produce green integral turbine blade along with dog bone specimens. During moulding, injection pressure (ranging from 1300 to 1700 Bar), injection flow/speed (ranging from 32 to 40 cm3/sec) and holding pressure (ranging from 1300 to 1700 bar) are used to get defect-free green integral turbine blade. After completion of injection, green integral turbine blades are allowed to cool for 10-30 seconds in mould. During cooling, oil is not present in cooling channels (65a, 65b) i.e. said oil in said cooling channels (65a and 65b) is drained out before carrying out cooling. The output of this stage is a green integral turbine blade which is sent for the next operation of debinding. The weight of green integral turbine blade (moulded) is 28.5121 gm. The injection moulding stage takes approximately 1 to 2 minutes.
3. Debinding of Green Integral Turbine Blade:
Catalytic debinding method is used in this process. In this step, the green integral turbine blade is staged on specially designed ceramic stager/setter (200). Ceramic stager/setter is designed by considering shrinkage factor of 1.1555 for IN713C material during sintering. The stager/setter (200) is

manufactured in Al2O3 ceramic material. The specially designed stager/setter (200) is designed/manufactured such that it supports entire concave profile of blade (15) during debinding. It also supports part of fir-tree profile (35) during debinding.
Nitric acid of 98% concentration is used as catalyst in this catalytic debinding process. This step is carried out in debinding oven with controlled atmosphere and temperature. In this treatment, the green integral turbine blade is held at temperature ranging from 115 ºC - 125 ºC in nitrogen atmosphere for around 4 to 8 hrs. The Nitric acid is stored in tank outside debinding oven. It is supplied in to oven by means of acid pump in mist form. The nitric acid reacts with primary binders to form formaldehyde gas which is subsequently pushed outside the oven and burnt by burner system. The debinding reaction goes deep inside integral turbine blade. The binder on surface reacts first and gets vaporized. The debinding reaction continues till all primary binder in the integral turbine blades gets removed. This process produces a porous integral turbine blade, which is called brown integral turbine blade, due to removal of binder from green integral turbine blade. This debinding process produces thick section like blade hub or blade fir-tree base (20) and thin section like blade aerofoil profile (80) integrally. The brown integral turbine blade is kept placed on the stager/setter (200).

The weight of brown integral turbine blade is 26.2535 gm and weight loss of 7.9215% is achieved. This debinding process assists in achieving the desired surface finish.
4. Sintering of brown integral turbine blade:
In this step, sintering process is carried out on the brown integral turbine blade in argon atmosphere in a sintering furnace. In this step, staged brown integral turbine blade placed on specially designed ceramic stager/setter (200) is loaded into the sintering furnace. The stager/setter (200) is designed/manufactured such that it supports entire concave profile of blade (15) during sintering. It also supports part of fir-tree profile (35) during sintering. The stager/setter is manufactured in Al2O3 ceramic material.
Sintering of the brown integral turbine blade is performed while staged on the stager (200) in a sintering furnace by step by step heating at variable heating rate, soaking at different soaking time & temperature and cooling at variable cooling rates and under variable pressure to produce fully dense integral turbine blade. In this process, the heating of brown integral turbine blade made of IN713C material along with stager/setter (200) starts from ambient temperature with the rate of 2°C/min till it reached 450°C. Then the brown integral turbine blade is soaked for 45 minutes at this temperature. After 45 mins, the brown integral turbine blade is further heated till it reaches 600°C with the rate of 3°C/min, then the brown integral turbine blade is

soaked for 60 minutes at this temperature. During this step, remaining primary binder and secondary binder burn out. After 60 mins, the brown integral turbine blade is further heated till it reaches 1050°C with the rate of 4°C/min and the brown integral turbine blade is soaked for 45 minutes at this temperature. After 45 mins, the brown integral turbine blade is further heated till it reaches 1295°C with the rate of 5°C/min, then the brown integral turbine blade is soaked for 150 minutes at this temperature. After 150 mins, the brown integral turbine blade is cooled to 200°C at the rate of 5°C/min. During above steps, the partial pressure is maintained at 400 millibar. After reaching 200°C, brown integral turbine blade is further cooled to 70°C with 5°C/min rate of cooling while maintaining partial pressure at 865 millibar. This sintering process is carried out on the brown integral turbine blade in argon atmosphere in a sintering furnace.
The output of this stage is a fully dense metallic integral turbine blade called a sintered integral turbine blade. The weight of sintered integral turbine blade is 26.091 gm and total weight loss of 8.491 % is achieved. The sintering process is carried out for approximately 15-20 hours.
5. Grinding of Fir-Tree Profile
In this step, the fir-tree profile of sintered brown integral turbine blade or full dense metallic integral turbine blade is grinded. The output of this step is fir-tree-grinded integral turbine blade.

6. Cleaning
In this final step, the fir-tree-grinded integral turbine blade is cleaned. The output of this process step is final finished product i.e. integral turbine blade (100).
The integral turbine blades were inspected and observed to be free from defects like cracks, voids and distortion. The desired surface finish of 0.6 Ra is achieved. The density achieved on integral turbine blade is 7.723 g/cm3. The dog bone specimens were tested for mechanical properties at room temperature. The proof strength of 790 – 820 MPa and UTS of 1020 – 1220 MPa is obtained.
The drawbacks of the conventional manufacturing process are overcome in the
invented process as follows: i. Dense product: Use of the designed MIM process produces integral turbine blades (100) with very good consolidation. This overcomes the problem of investment casting and MIM process defects like voids, blow holes etc. ii. Integral turbine blade: Due to the use of catalytic debinding as debinding process, the turbine blade can be manufactured integrally. The catalytic debinding process allows precise debinding of the thinner aerofoil blade section (10) as well as the thicker root section (20). This overcomes the drawbacks of the prior art MIM processes where the turbine blade had to be made in two parts.

iii. Post MIM processes: The post MIM process of welding is avoided by producing an integral turbine blade (100). Further, the use of specially designed stager/setter (200) helps in avoiding the distortion of integral turbine blade (100). The correct selection of feedstock and parameters used during the MIM process helps achieve the required surface finish and accuracy in the integral turbine blade and hence, helps in avoiding the post MIM processes like machining or electro chemical machining.
Specially designed ceramic stager/setter (200), mould (300), catalytic debinding process and optimized sintering process parameters plays key role in achieving distortion free integral turbine blade and desired surface finish. It has eliminated further aerofoil profile (80) finish.
It is evident that the invention has a number of embodiments.
In a preferred embodiment, the invention disclosed a metal injection moulding process for distortion free integral turbine blade. The process has the following steps:
a. characterising, inspecting and providing feedstock;
b. feeding the feedstock into a feedstock hopper
c. moulding the feedstock in an injection mould (300) to produce a
defects-free green integral turbine blade,
d. cooling said green integral turbine blade for 10-30 seconds in said

injection mould,
e. debinding the green integral turbine blade staged on stager (200) in a
debinding oven to produce a brown integral turbine blade
f. sintering the brown integral turbine blade staged on stager in a
sintering furnace (200) by step-by-step heating at variable heating
rate, soaking at different soaking temperature & time, and cooling at
variable cooling rates and under variable pressure to produce fully
dense integral turbine blade
g. fir-tree grinding the fully dense integral turbine blade to produce fir-
tree-grinded integral turbine blade
h. cleaning the fir-tree-grinded integral turbine blade to produce distortion free integral turbine blade.
In another embodiment of the process, in the aforementioned step c, after reaching a temperature of around 180 to 220 °C for the injection nozzle, moulding is carried out at an injection pressure ranging from 1300 to 1700 bar, an injection flow/speed ranging from 32 to 40 cm3/sec, and holding pressure ranging from 1300 to 1700 bar.
In another embodiment of the process, the injection mould is provided with cooling channels (65a and 65b) that carry oil of temperature in the range of 40 – 150 ºC, wherein the said oil in said cooling channels (65a and 65b) is drained out before carrying out said the aforementioned step d of cooling.

In yet another embodiment of the process, the aforementioned step e is carried out using a catalytic debinding method; wherein said catalytic debinding method of said step e is carried out in a debinding oven at a temperature ranging from 110 ºC - 150 ºC for a period between 4 to 8 hrs, more particularly, at a temperature between 115 - 125 °C; wherein Nitric acid of 98% concentration is used as catalyst in said catalytic debinding method of said step e; wherein said Nitric acid is stored in tank outside said debinding oven and supplied in a mist form to said debinding oven by means of an acid pump.
In a further embodiment, during the aforementioned step e, said green integral turbine blade staged on stager (200) such that the area supported by support profile for blade (40) of stager (200) is 100% same as either concave (15) or convex (75) blade profile.
In a still further embodiment, in the aforementioned step f, said brown integral turbine blade is staged on stager (200) such that the area supported by support profile for blade (40) of stager (200) is 100% same as either concave (15) or convex (75) blade profile.
In a yet further embodiment of the process, said stager (200) used in said step e of debinding and said step f of sintering, is made of Al2O3 ceramic material.

In another embodiment of the process, in said step f of sintering of said brown integral turbine blade staged on stager (200) is carried out in an inert atmosphere in a sintering furnace; wherein said step-by-step heating and soaking of said brown integral turbine blade staged on stager (200) starts from ambient temperature at a rate of 2 °C/min till a temperature of 450 °C, following which said brown integral turbine blade is soaked for 45 minutes, which is followed by the following stages of heating and soaking and cooling:
- heating to 600 °C at a rate of 3 °C/min followed by soaking for 60 minutes, followed by;
- heating to 1050 °C at a rate of 4 °C/min followed by soaking for 45 minutes, followed by;
- heating to 1295 °C at a rate of 5 °C/min followed by soaking for 150 minutes, followed by;
- cooling said brown integral turbine blade to 200 °C at a cooling rate of 5 °C/min;
wherein said heating, soaking and cooling steps are carried out at a pressure of 400 millibar, and wherein said cooled brown integral turbine blade is further cooled to 70 °C under a pressure of 865 millibar and at a cooling rate of 5 °C/min.
In yet another embodiment of the process, said brown integral turbine blade is not removed from the said stager/setter (200) after completion of step e of debinding and the said brown integral turbine blade staged on said stager (200) along with

said stager (200) is transferred to step f of sintering.
In still another preferred embodiment of the invention, an apparatus is disclosed for making for distortion free integral turbine blade (100). The apparatus comprises a feedstock hopper, an injection mould (300), a stager (200), a debinding oven, a sintering furnace, a grinding station, and a cleaning station.
In an embodiment of the apparatus, said injection mould (300) has cooling channels (65a and 65b) to carry oil, and wherein said mould has a first mould (300A) and a second mould (300B), wherein when the first mould (300A) and second mould (300B) are in assembled condition, the enclosed cavity has a shape which corresponds to the shape of blade (10) and blade hub or blade fir-tree base (20).
In a further embodiment of the apparatus, said cavity of said injection mould (300) has a blade profile impression (70a) formed by a concave (55a) and convex (55b) impression, and fir-tree base impression (70b), said blade profile impression (70a) and said fir-tree base impression (70b) are collectively referred to as integral turbine blade impression (70).
In a still further embodiment of the apparatus, said cooling channels (65a and 65b) of said injection mould (300) are positioned around said impressions (70) and they have a cylindrical cross-section.

In a yet further embodiment of the apparatus, said stager (200) comprises of support profile for blade (40) which supports either entire convex profile of blade (75) or entire concave profile of blade (15) and support profile for blade hub or blade fir-tree base (45) which supports entire fir-tree profile (35) or part of fir-tree profile (35).
In another embodiment of the apparatus, said debinding oven and said sintering furnace carry out debinding of said green integral turbine blade staged on stager (200) and sintering of said brown integral turbine blade staged on stager (200) as claimed in claim 1 respectively.
In a final embodiment of the apparatus, said injection mould (300) is provided with a mould temperature control unit for heating said oil to a temperature between 40 - 150°C.
While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.

We claim:
1. A metal injection moulding process for making distortion free integral
turbine blade (100), characterised in that said process comprises the steps
of:
a. characterising, inspecting and providing feedstock;
b. feeding the feedstock into a feedstock hopper
c. moulding the feedstock in an injection mould (300) to produce a
defects-free green integral turbine blade,
d. cooling said green integral turbine blade for 10-30 seconds in said
injection mould,
e. debinding the green integral turbine blade staged on a stager (200) in a
debinding oven to produce a brown integral turbine blade
f. sintering the brown integral turbine blade staged on the stager (200)
in a sintering furnace by step-by-step heating with variable heating
rates, soaking at different temperatures & times, and cooling at
variable cooling rates and under variable pressure to produce fully
dense integral turbine blade
g. fir-tree grinding the fully dense integral turbine blade to produce fir-
tree-grinded integral turbine blade
h. cleaning the fir-tree-grinded integral turbine blade to produce distortion free integral turbine blade (100).
2. The metal injection moulding process as claimed in claim 1 wherein in
step c, after reaching a temperature of around 180 to 220 °C for the

injection nozzle, moulding is carried out at an injection pressure ranging from 1300 to 1700 bar, an injection flow/speed ranging from 32 to 40 cm3/sec, and holding pressure ranging from 1300 to 1700 bar.
3. The metal injection moulding process as claimed in claim 2, wherein said injection mould is provided with cooling channels (65a and 65b) that carry oil of temperature in the range of 40 - 150 °C, wherein the said oil in said cooling channels (65a and 65b) is drained out before carrying out said step d of cooling
4. The metal injection moulding process as claimed in claim 1, wherein said step e is carried out using a catalytic debinding method; wherein said catalytic debinding method of said step e is carried out in a debinding oven at a temperature ranging from 110 ºC - 150 ºC for a period between 4 to 8 hrs, more particularly, at a temperature between 115 - 125 °C; wherein Nitric acid of 98% concentration is used as catalyst in said catalytic debinding method of said step e; wherein said Nitric acid is stored in tank outside said debinding oven and supplied in a mist form to said debinding oven by means of an acid pump.
5. The metal injection moulding process as claimed in claims 1, wherein during said step e, said green integral turbine blade staged on the stager (200) such that the area supported by support profile for blade (40) of stager (200) is 100% same as either concave (15) or convex (75) blade profile.
6. The metal injection moulding process as claimed in claims 1, wherein in

said step f, said brown integral turbine blade is staged on stager (200) such that the area supported by support profile for blade (40) of stager (200) is 100% same as either concave (15) or convex (75) blade profile.
7. The metal injection moulding process as claimed in claims 1 to 6, wherein said stager (200) used in said step e of debinding and said step f of sintering, is made of Al2O3 ceramic material.
8. The metal injection moulding process as claimed in claims 1 to 7, wherein in said step f of sintering of said brown integral turbine blade staged on stager (200) is carried out in an inert atmosphere in a sintering furnace; wherein said step-by-step heating and soaking of said brown integral turbine blade staged on stager (200) starts from ambient temperature at a rate of 2 °C/min till a temperature of 450 °C, following which said brown integral turbine blade is soaked for 45 minutes, which is followed by the following stages of heating, soaking and cooling:

- heating to 600 °C at a rate of 3 °C/min followed by soaking for 60 minutes, followed by;
- heating to 1050 °C at a rate of 4 °C/min followed by soaking for 45 minutes, followed by;
- heating to 1295 °C at a rate of 5 °C/min followed by soaking for 150 minutes, followed by;
- cooling said brown integral turbine blade to 200 °C at a cooling rate of 5 °C/min;
wherein said heating, soaking, and cooling steps are carried out at a

pressure of 400 millibar, and wherein said cooled brown integral turbine blade is further cooled to 70 ℃ under a pressure of 865 millibar and at a cooling rate of 5 ℃/min.
9. The metal injection moulding process as claimed in claims 1 to 8, wherein the said brown integral turbine blade is not removed from the said stager/setter (200) after completion of step e of debinding and the said brown integral turbine blade staged on said stager (200) along with said stager (200) is transferred to step f of sintering.
10. The metal injection moulding process as claimed in claims 1 to 9, wherein said feedstock is selected from a nickel based alloy, preferably IN713C.
11. An apparatus for making for distortion free integral turbine blade (100), characterised in that said apparatus comprising a feedstock hopper, an injection mould (300), a stager (200), a debinding oven, a sintering furnace, a grinding station, and a cleaning station.
12. The apparatus as claimed in claim 11, wherein said injection mould (300) has cooling channels (65a and 65b) to carry oil, and wherein said mould (300) has a first mould (300A) and a second mould (300B), wherein when the first mould (300A) and second mould (300B) are in mating position, the enclosed cavity has a shape which corresponds to the shape of blade (10) and blade hub or blade fir-tree base (20).
13. The apparatus as claimed in claim 11 and 12, wherein said cavity of said injection mould (300) has a blade profile impression (70a) formed by a concave (55a) and convex (55b) impression, and fir-tree base impression

(70b), said blade profile impression (70a) and said fir-tree base impression (70b) are collectively referred to as integral turbine blade impression (70).
14. The apparatus as claimed in claim 11to 13, wherein the dimensional accuracy of the all impressions of injection mould cavity (70) is maintained within ± 20 micron and finishing i.e. polishing operation is conducted on mould impressions (70) to achieve mirror surface finish.
15. The apparatus as claimed in claims 11 to 14, wherein said cooling channels (65a and 65b) of said injection mould (300) are positioned around said impressions (70) and they have a cylindrical cross-section.
16. The apparatus as claimed in claims 11 to 15, wherein said stager (200) comprises of support profile for blade (40) which supports either entire convex profile of blade (75) or entire concave profile of blade (15) and support profile for blade hub or blade fir-tree base (45) which supports entire fir-tree profile (35) or part of fir-tree profile (35).
17. The apparatus as claimed in claims 11 to 16, said debinding oven and said sintering furnace carry out debinding of said green integral turbine blade staged on stager (200) and sintering of said brown integral turbine blade staged on stager (200) as claimed in claim 1 respectively.
18. The apparatus as claimed in claim 11 to 17, wherein said injection mould (300) is provided with a mould temperature control unit for heating said oil to a temperature between 40 - 150°C.