FIELD OF THE INVENTION

[0001] The present invention relates to the field of manufacturing of aerospace parts. Particularly, the present invention relates to the field of additive manufacturing of aerospace parts.

[0002] More particularly, this invention relates to a turbine impeller and a method of manufacturing of turbine impeller in a jet engine.

BACKGROUND OF THE INVENTION

[0003] A turbine impeller plays an important role in the operation cycle of aero engines. It provides power to drive the compressor and accessories. It does this by extracting energy from the hot gases released from the combustion chamber and expanding them to a lower pressure and temperature. This process simply converts the heat energy to rotational energy. Traditionally, turbine impeller is made by investment casting followed by machining or electro- chemical machining or machining from a solid block (turning, milling, drilling, broaching, grinding, etc.).

[0004] These traditional manufacturing processes have the following drawbacks:

- Large machinery and enormous initial investments are required for these processes. Investment casting is labour intensive. It requires a very long production cycle time (the preparation of wax pattern and shell moulds requires much time and effort to ensure a quality product). Also, small changes in profile or geometry cannot be easily adopted.

Electro-chemical machining has environmentally harmful by products, very high power consumption and complicated tool design is involved.

Several different tools have to be used and applied correctly (straightforward face milling to 4-axis to 5-axis profiling) in a machining from a solid block.

[0005] Accordingly, there is a need for a method of manufacturing the turbine impeller.

OBJECTS OF THE INVENTION

[0006] It is an object of the invention to provide a turbine impeller. [0007] It is another object of the present invention to provide a manufacturing process which results in elimination of drawbacks of existing manufacturing methods as applied to making turbine impeller.

[0008] It is yet another object of the present invention to provide an additive manufacturing process which can produce desired shaped turbine impeller with precision and less material waste. [0009] It is still another object of the present invention to design turbine impeller in a single building block and in a single printing cycle, thereby eliminating excessive inventory which results in cost saving.

[00010] It is a further object of the present invention to provide an optimised support for holding the turbine impeller being printed and dissipating heat to surrounding.

SUMMARY OF THE INVENTION

[00011] Accordingly, the present invention provides a process for manufacturing of a turbine impeller; said process comprises additive manufacturing of turbine impeller. A tool-less manufacturing method of the present invention can produce a uniform turbine impeller in a short time with high precision. In one embodiment, said additive manufacturing comprises the following steps:

- providing metal powder as a raw material wherein the metal powder is selected from a group consisting of Nickel based alloy, Titanium alloys and Steel;

- providing a 3D printing device;

- spreading said metal powder layer by layer on a predetermined platform;

- selectively fusing said metal powder using at least one energy source at predetermined conditions to perform a printing operation to obtain a turbine impeller with a build platform;

- heat treating said turbine impeller with build platform in a furnace at a predetermined temperature followed by cooling to room temperature to obtain a heat treated turbine impeller with build platform;

- subjecting said heat treated turbine impeller with build platform to wire cutting operation to separate the turbine impeller from the build platform, followed by shot blasting to generate compressive residual stresses on the surfaces of the turbine impeller, and buffing operation to obtain the polished turbine impeller with pre-determined surface finish; and

- subjecting said polished turbine impeller central bore to broaching operation to achieve desired surface integrity, finish, and tolerance on the central bore.

[00012] In one embodiment, the process involves performing balancing operation to avoid vibrations which could cause catastrophic failure as well as noise and discomfort.

[00013] In one preferred embodiment, the process comprises a pre-step of printing a support having predetermined configuration meant for holding said turbine impeller and transferring heat from the part/s being 3D printed to the platform during printing operation, wherein said printing operation comprises spreading metal powder layer by layer on a predetermined platform followed by fusing said powder using at least one energy source at predetermined conditions.

[00014] In one aspect of the present invention, there is provided a turbine impeller (100) for a jet engine; said turbine impeller (100) comprises 3D printed turbine blades (10), turbine housing (20) and turbine hub (30), wherein said turbine hub (30) comprises a central bore (32) in which main power transmitting shaft of an engine is mounted.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

[00015] The invention will now be described in relation to the accompanying drawings, in which:

[00016] Figure 1 illustrates the typical turbine impeller printed by additive manufacturing method of the present invention; and

[00017] Figure 2 illustrates the flow chart of an invented process for turbine impeller manufacturing.

DETAILED DESCRIPTION

[00018] 3D printing, also known as additive manufacturing, refers to a process used to create a three-dimensional object in which layers of material are formed under computer control to create an object. Parts that are to be manufactured are made so by this process directly from digital model by using layer by layer material build-up approach. This tool-less manufacturing method can produce fully dense metallic parts in a short time period with high precision.

[00019] According to this invention, there is provided a turbine impeller and a manufacturing method for the same. Specifically, the present invention relates to the manufacturing of a turbine impeller for jet engines using a selective laser sintering process. The inventive step of this invention lies in the design and development of the turbine impeller and a manufacturing process to make the same.

[00020] In one aspect, the present invention provides turbine impeller (100) for a jet engine; said turbine impeller (100) comprises 3D printed turbine blades (10), turbine housing (20) and turbine hub (30), wherein said turbine hub (30) comprises a central bore (32) in which main power transmitting shaft of an engine is mounted.

[00021] Example embodiments will now be described more fully with reference to the accompanying drawings. The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. [00022] The following non-limiting figures illustrate the turbine impeller made in accordance with the present invention. [00023] Figure 1 illustrates the typical turbine impeller printed by additive manufacturing method of the present invention. This is referenced by numeral 100; and

[00024] Figure 2 illustrates the flow chart of an invented process for turbine impeller manufacturing.

[00025] In at least an embodiment of this invention, the turbine impeller comprising the above-mentioned feature/ features shown in drawings is designed and rendered using a rendering software which is then used as an input for the additive manufacturing process.

[00026] In accordance with another aspect, the present invention provides a process for manufacturing of turbine impeller. The process involves additive manufacturing of turbine impeller using IN718 (Inconel) as a raw material in the form of metal powder. The additive manufacturing according to the present invention involves the following steps:

[00027] In the first step, metal powder as a raw material and a 3D printing device is provided or kept ready. In the second step, the metal powder is spread layer by layer on a predetermined platform. Typically, the temperature of said platform is set in the range of 80 to 160 °C, preferably, at !20°C. [00028] Typically, the layer has a thickness in the range of 0.02 to 0.08 mm and a laser strip width in the range of 5 to 10 mm. Typically, the overlap between the layers is in the range of 0.10 to 0.15 mm. [00029] In one embodiment, the spreading comprises controlled deposition of the layers of metal powder. In one embodiment, the spreading comprises depositing layers of a metal powder sequentially one upon the other to form features. [00030] After spreading, the powder is selectively fused using at least one energy source at predetermined conditions to perform a printing operation to obtain a turbine impeller with a build platform. Typically, the energy source is selected from the group consisting of laser beam and electron beam. The energy source has a scanning speed of about 800 to 1400 mm/second and has power of 80 to 400 watt.

[00031] In the third step, the turbine impeller with a build platform is heated in a furnace at a predetermined temperature followed by cooling to room temperature to obtain heat treated turbine impeller with a build platform.

[00032] In one preferred embodiment, the heat treatment step involves the following sub- steps: [00033] Step a: annealing the turbine impeller with a build platform at a temperature ranging from 900 to 1200 °C for a period ranging from 30 minutes to 120 minutes in an inert Argon atmosphere followed by cooling to room temperature to obtain annealed turbine impeller with a build platform.

[00034] Step b: ageing the turbine impeller with a build platform by holding the parts at a temperature ranging from 700 to 800 °C for a time period ranging from 5 to 10 hours in an inert Argon atmosphere followed by cooling to a temperature ranging from 625 to 675 °C in 1 to 3 hours and holding at a temperature ranging from 625 to 675 °C for 6 to 10 hours in an inert Argon atmosphere to obtain aged turbine impeller with a build platform.

[00035] Step c: air cooling said parts with a build platform to room temperature to obtain a heat treated turbine impeller with build platform to obtain heat treated turbine impeller with a build platform.

[00036] In the fourth step, the heat treated turbine impeller is subjected to wire cutting operation to separate the turbine impeller from the platform to obtain separated turbine impeller.

[00037] In the fifth step, the separated turbine impeller is subjected to shot blasting to generate compressive residual stresses on the surfaces of the turbine impeller to obtain a shot blasted turbine impeller.

[00038] In the sixth step, a buffing operation is performed on the shot blasted turbine impeller to obtain the buffed turbine impeller with pre-determined surface finish. [00039] In the seventh step, the central bore of the buffed turbine impeller is subjected to broaching to obtain the desired surface integrity, finish, and tolerance. The output of this operation is a finished turbine impeller.

[00040] In one embodiment, the process involves a final step in which the finished turbine impeller is subjected to balancing operation to avoid vibrations. [00041] In accordance with a preferred embodiment of the present invention the process comprises a pre-step of printing a support having predetermined configuration meant for holding said turbine impeller and transferring heat from the part/s being 3D printed to the platform during printing operation, wherein said printing operation comprises spreading metal powder layer by layer on a predetermined platform followed by fusing said powder using at least one energy source at predetermined conditions.

[00042] The 3D printing or additive manufacturing process consists of making a part layer by layer. The required amount of a layer of powder is fused using an energy source. Each new layer of fused powder requires support from layer beneath it (formed previously). Turbine impeller have overhang or bridge thus, needs use of 3D printed support structures to ensure a successful print. The support structures are found to have both positive as well as negative effects on the 3D printing process. On the one hand the support structures help in transfer of heat, prevent extreme powder inclusion, support the overhanging part of the product and secures the part against detachment during the building process. On the other hand the support structure leads to waste of material, may affect the surface finish of the product and leads to requirement of post processing operations to remove it. Hence, it is found that the selection of type and geometry of support structure is critical for defect less manufacturing, ease of manufacturing and economic manufacturing. [00043] According to the present invention several types of supports which can be used during the 3D printing are tried. The type of support to be used is decided based on the quantity of material required for supports, heat dissipation of product to surrounding, geometry of model etc. Different types of supports which are tried include Block type, Line type, Point type, Web Type, Contour type, Gusset type, Hybrid type, Volume type etc. The support structure with different features like hatching, hatching teeth, fragmentation, borders, border teeth, perforations, gusset borders etc. are experimented. [00044] Based on the considerations and experimentations, during the manufacturing of the turbine impeller, the preferred type of supports used are combination of block support with hatching teeth and perforation type support, volume support and hybrid support. [00045] According to the invented process, the manufacturing process starts with a metal powder as raw material. The metal material (metal powder) includes but is not limited to Steel, Nickel based alloys (IN718, IN713C, IN625, etc.), Titanium alloy and the like. This powder is spread on a bed (which is its build platform), layer by layer, and selectively fused by using an energy source like a laser or an electron beam. After completion of the print, the part is transferred to a furnace, where heat treatment is conducted, according to pre- determined parameters, and required properties are achieved. Then, final heat-processed parts are separated from the build platform using a wire cutting operation. The final parts are then transferred to shot blasting to generate compressive residual stresses on the surface. Then buffing is carried out on the final parts to achieve the required surface finish. Finally, a broaching operation is conducted on the turbine impeller followed by balancing.

[00046] The turbine impeller manufacturing process is described, in detail, as below.

[00047] As shown in Figure 2, the manufacturing process, of the current invention, typically, involves the following steps: [00048] CAD Model generation:

Producing a digital model of the part (i.e. the turbine impeller) is the first step in the additive manufacturing process. A digital model is produced by using computer aided design, refer Figure 1. Then, this CAD model is converted into a Stereo lithography / Surface Tesselation Language / Standard Triangulation Language file (STL) which is used by further portions and processes of this invention. [00049] Additive Manufacturing program generation:

Once an STL file has been generated, the file is imported into a MAGICS MATERIALISE software. A MAGICS is used for defining part orientation and generating support. Then, STL file is sent to the slicer software for slicing. After slicing, the file is imported in EOSPRINT software. EOSPRINT software is used for assigning the build parameters and these further are optimized for CAD data. Then parameters like laser power, scanning speed, hatch distance and layer thickness are designed. Finally, the file is exported to the 3D printing machine for producing the part.

[00050] Additive Manufacturing or 3D printing:

Different types of materials can be used for manufacturing turbine impeller which include but are not limited to Steel, Nickel based alloys (IN718, IN713C, IN625, etc.), Titanium alloys and the like. Material is provided in the form of powder. Powder is spread on the build platform layer by layer with a layer thickness of 0.020 mm. During this activity, platform temperature is maintained at 120 °C throughout the process. After spreading each layer, powder is selectively fused by using a laser with a scanning speed of 1200 mm/Sec for parts and 500 mm/Sec for support in an Argon environment. The output of this process is a turbine impeller with a build platform. In one embodiment, the impeller is made using IN718 material. The summary of parameters used to produce the turbine impeller in additive manufacturing is mentioned in table 1. Table 1

[00051] Heat treatment:

Heat treatment is carried out on the turbine impeller with build platform to achieve the mechanical properties and de-stress the parts. Firstly, turbine impeller with build platform is solution annealed. The turbine impeller with build platform is solution treated at 1065 °C for one hour in an inert Argon atmosphere, followed by air cooling to room temperature. The second heat treatment is ageing. In this treatment, parts are held at 760 °C for ten hours in an inert Argon atmosphere, after that it is furnace cooled to 650 °C in two hours and then held at 650 °C for eight hours in an inert Argon atmosphere. Finally, the turbine impeller with build platform is air cooled to the room temperature. The above heat treatment is performed for IN718. The various materials can be utilized to manufacture the impeller which include but are not limited to Steel, Nickel based alloys (IN718, IN625, IN 713C etc.), Titanium alloys and the like. The mechanical properties achieved after heat treatment for IN 718 are summarised in table 2. The below provided properties and values are illustrative and not considered as limitation to scope of the present invention. The output of this step is a heat treated turbine impeller with build platform.

Table 2

[00052] Wire cutting and support removal:

The heat treated turbine impeller with build platform is separated from the build platform using wire cutting operation. Next, the supports formed during the 3D printing operation are machined off. The output of this step is a separated turbine impeller.

[00053] Shot blasting and Polishing

In this step, shot blasting is performed on the separated turbine impeller to generate compressive residual stresses on the surfaces of the turbine impeller, and buffing operation is carried out to obtain the turbine impeller with pre-determined surface finish. The output of this step is a buffed turbine impeller.

[00054] Post machining and balancing:

In this step, broaching operation is performed on the buffed turbine impeller to achieve desired surface integrity, finish, and tolerance at a central bore. Finally, balancing operation is performed on turbine impeller to avoid vibration which could cause catastrophic failure, as well as noise and discomfort. This produces the finished turbine impeller.

[00055] In accordance with another aspect of the present invention there is also provided turbine impeller made by the 3D printing method of the present invention. Said impeller is characterized by predetermined structural configuration and characteristics. [00056] In accordance with still another aspect of the present invention there is also provided a system for manufacturing turbine impeller by 3D printing method, said system comprises a 3D printing device and at least one support means. It is critical to design an optimized support which can be suitable for printing turbine impeller, as other type of support makes marks on surface of parts. In one embodiment, the support comprises teeth/grooves. The teeth/grooves enable easy removal of supports. Support height is optimised for better heat transfer (heat dissipation) between build platform and job at the time of part building. It also avoids distortion in the part. The amount of support required to build the part is based on the orientation of part. The optimized orientation is selected based on least amount of material required for support generation, minimum laser travel time for generating the support, support free critical areas of the component and height of support that dissipates better heat transfer to build platform from job. Based on above factors for optimized orientation of turbine impeller, the preferred type of supports used are combination of block support with hatching teeth and perforation type support, volume support and hybrid support and the height of supports is selected from the range of 10.88 to 2 . [00057] While this detailed description has disclosed certain specific embodiments for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.