[0001] The present invention relates to a Fan Blade and its manufacturing method. Particularly, the present invention relates to a metal fan blade for aero-engine and its manufacturing through hot forging route.

Background of invention

[0002] Airplanes use aero engines for their propulsion. The aero engines are broadly divided as propeller based aero engines and turbine based aero engines. Now a days, almost all the airplanes use turbine based propulsion system for their flight.

[0003] The turbine based aero engines, also called jet engines, are also divided as turbo fan engines and turbo jet engines. The turbo jet engines use a compressor to compress air which is then mixed with fuel and burned. The burned mixture is then passed through a turbine which extracts the required mechanical energy from the high pressure - high velocity gas and rest is passed through a nozzle to get the required thrust. [0004] In the turbofan engine, a big propeller fan is connected in front of l the engine. This fan serves the dual purpose of sucking in the required amount of air as well as producing some thrust similar to propeller driven engines. Moreover, a certain proportion of the air sucked in by this fan is passed through compressor, fuel injection, fuel burning, turbine and then jet propulsion. Thus, the turbofan engine is a combination of propeller driven engine and turbo jet engine.

[0005] The fan as described above used in the turbo fan engine is very large in size and is made of many fan blades. These fan blades have to undergo very strenuous working conditions in terms of stresses generated in them, temperature variations due to change in altitude etc. Further, it is required that the fan blades provides desired properties against the impact of foreign objects as well as provide resistance against cracking from nicks and dents. Typically, these fan blades are made of titanium alloys due to its good strength, corrosion resistance and very high strength to weight ratio.

[0006] The present invention particularly addresses the problem associated with known methods of manufacturing the fan blade. Conventionally, the fan blades are made using hot forging of the titanium alloy. The hot forging process typically consists of multiple preforming operations to gather material for the fan blade root. Next, this preform has to undergo flattening, twisting, blocker and then finisher. Due to the use of 4 or more steps in making the fan blade, the cycle time of manufacturing is very large. Moreover, between each operation the material has to be cooled and re-heated. This increases the energy cost associated with the process and also the carbon foot print of the manufacturing cycle. Further, the rejection chances are higher which make the process costly.

[0007] Still further, in the earlier design and method, pre-form could not be located properly on flattener die thus material flow and thereby forging operation is affected. [0008] Accordingly, it is desired to provide an arrangement and a method for manufacturing fan blade which can resolve the drawbacks mentioned hereinabove.

Objects of the invention:

[0009] It is an object of the present invention to provide a forging method for manufacturing a fan blade.

[0010] It is another object of the present invention to provide a forging process design to reduce the number of steps required for manufacturing a fan blade which reduces the cycle time and improves material flow.

[0011] It is still another object of the present invention to provide a die arrangement which is capable of performing flattening and twisting operation simultaneously.

[0012] It is yet another object of the present invention to provide a die with a means to hold the pre-form to avoid displacement of pre-form while performing the forging operation.

[0013] It is a further object of the present invention to provide a forged titanium based fan blade of desired strength and characteristics.

[0014] These and other objects, features and advantages will be readily apparent upon consideration of the following detailed description of the invention in conjunction with the accompanying drawings.

Brief Description of Drawings:

[0015] Fig. 1 and 2 illustrates a forging apparatus 10, in accordance with one implementation of the present invention. [0016] Fig. 3 illustrates an arrangement of the top die and the bottom die, in accordance with one implementation of the present invention.

[0017] Fig. 4 illustrates a method of manufacturing the fan blade, in accordance with one implementation of the present invention. Description of the invention:

[0018] As mentioned previously, conventional forging techniques for manufacturing fan blades are less effective due to many factors. One of the reasons is big change in the section size of a part of the fan blade from root area to the blade area. Moreover, the change in section size is abrupt which further increases the difficulty. Another reason is the presence of twists/ contours present in the fan blade. Yet another reason is the thin section at aerofoil portion of the fan blade that increases forging load & reduces material ability to flow, thus increasing complexity in forging technique.

[0019] In order to overcome the first difficulty, multiple operations are performed such as upsetting operation in 2-3 stages followed by flattening operation. Further, to overcome the second difficulty, twisting operation is performed after the flattening operation. Thereafter, blocker and finisher operations are also performed for getting the final shape. Another challenge faced during performing the aforementioned operations is maintaining the position of the flattened product on the twister die because of the die's contoured inner surface (slanting die surface). As a result, the preform may tend to slip from its position. As a result, conventional forging techniques are costly as well as time consuming. Moreover, occurrence of errors is far greater owing to more number of steps involved in manufacturing. As a result, more number of steps increases the chances of high defect rate and, as a result, higher rejections. It is also realized that the conventional process is also not very stable due to complicated shape of the fan blade. Therefore, the conventional forging technique is also not very reliable method of manufacturing fan blades. [0020] The present invention relates to an improved forging technique that overcomes the limitations of the conventionally known forging techniques. Forging techniques based on the present invention do away additional step associated with the conventional forging techniques and the complete forging operation can be performed in fewer steps. [0021] According to an aspect, the present invention relates to a newly designed preform of predetermined shape and size. Preform can be formed using an extrusion process. A shape of said preform is chosen to reduce the number of operations to be performed during the forging technique. [0022] In accordance with another aspect of the present invention there are provided buster dies which are adapted to perform twisting and flattening simultaneously, said die comprises plunging locators. Said plunging locators are adapted for robust and consistent location of extruded pre-form on buster dies.

[0023] According to another aspect, the present invention also relates to a forging apparatus for performing forging. The apparatus is designed to accommodate the preform of predetermined size such that forging operation can be performed in minimum steps with minimum errors. The apparatus may include a top die and a bottom die where each die includes at least one locator or plunger that facilitates in placing the predetermined shaped preform in the apparatus. In addition, the locators also ensure that the preform remains in its predetermined position while forging is performed. As a result, during forging, the preform does not slip or jump from its position thereby reducing errors, that otherwise would have occurred if the preform slips from its position. [0024] These and other advantages of the present invention would be described in a greater detail in conjunction with the following figures. It should be noted that the description and figures merely illustrate the principles of the present invention.

[0025] Fig. 1 and 2 illustrates a forging apparatus 10, in accordance with one implementation of the present invention. Fig. 1 illustrates the forging apparatus before forging operation is performed (dies in open condition) while Fig. 2 illustrates the forging apparatus after forging operation is performed (dies in closed condition). The forging apparatus can be used to manufacture a fan blade 12 from a preform 14 of predetermined shape. The size and shape of the preform 14 is kept so as to reduce time consumed in the forging operation. Moreover, unlike the conventional preform that has continuous cylindrical shape, the preform 14 based on the present invention has long cylindrical snout followed by a tapered region and a thickened portion towards the right side as shown in Fig. 1. Further, the preform can be formed by extrusion process. The manner by which the forging apparatus works would be explained in subsequent embodiments.

[0026] According to an aspect, the forging apparatus 10 may include a top die 22 and bottom die 24. The top die may be mounted on an upper cassette 32 and the bottom die 24 may be mounted on a lower cassette 34. In the illustrated implementation, inner surfaces of the top die 22 and the bottom die 24 have one type of impressions (22-1, 24-1) collected referred to as first impression. In addition, the top die 22 and the bottom die 24 have another type of impressions (22-2, 24-2) collectively referred to as second impression. Further, both the impressions correspond to a shape and profile of the fan blade 12 to be manufactured. In an example, the first impression is used for the buster operation while the second impression is used for the finisher operation. When the dies are closed, the inner surface of buster impression forms a rough shape of fan blade having volume greater than the volume of fan blade. Similarly, when the die is closed, the inner surface of finisher impression forms a cavity whose volume is equal to the volume of the fan blade 12 and shape also matches with that of fan blade. The structural details of the top die and the bottom die would be explained with respect to Fig. 3 later.

[0027] Referring back to Fig. 1, the top die 22 is provided with a first pair of plungers 26 while the bottom die 24 is provided with a second pair of plungers 28 in the buster impression. Further, both set of plungers are spring loaded (not shown) and can retract into their respective holes in the dies in which the set of plungers are installed. In addition, the plungers are supported inside the dies by Bakelite 30. In the illustrated implementation, the plungers are so installed inside the die such that the plungers do not cause any errors when forging operation is performed. The purpose of the plungers is to hold the preform 14 inside the die so that the preform does not slip or moves from its intended location inside the cavity during the buster operation. Another purpose of the plungers is to retract back into the die when the die is closed. Fig. 1 shows the plungers holding the preform 14 and protruding from the inner surfaces of both the die. Fig. 2 shows closed dies in which the plungers have moved into the die so that no portion of the plunger protrudes into the cavity. Therefore, the plungers do not take up any volume of the cavity and hence, during forging, preform 14 can be reshaped to occupy maximum volume of the cavity. Moreover, a surface of the plunger which makes contact with the preform 14 also has contours, such that when the plungers retract, the surface falls in line with the inner surface of the cavity.

[0028] Fig. 2 illustrates an arrangement of the top die 22 and the bottom die 24, in accordance with one implementation of the present invention. As mentioned previously, inner surfaces of the top die 22 and the bottom die 24 corresponds to the contours of the fan blade 12. Further, the inner surfaces of both the buster impression are formed so as to facilitate both the flattening operation and the twisting operation. In the illustrated implementation, portions of the inner surface of the top die 22 and the bottom die 24 have slopes that facilitates in performing twisting operation inside the die. Further, portions that are less sloped facilitates in performing flattening operation. Since both the operations are performed inside the die at the same time, the total number of steps to be performed during forging operations is reduced from 'more than 4'to '3 or less' [0029] Fig. 4 illustrates a method of manufacturing the fan blade 12, in accordance with one implementation of the present invention. The method begins with an extrusion process in which material, by which the fan blade 12 will be manufactured, is extruded to form a preform of predetermined shape. This step is followed by a buster operation, where rough shape of fan blade 12 is made from the preform by forging. Thereafter, the rough shape of fan blade 12 formed in the previous step is further processed to give the final shape in the finisher die (with some excess flash) and finally a trimming operation is performed to obtain the final product.

[0030] In accordance with another aspect of the present invention there is also provided a forged titanium based fan blade of desired /predetermined strength and characteristics obtained by the process of the present invention. [0031] According to the illustrated aspect following steps are performed: a) providing a titanium billet of pre-determined size; b) heating said billet at a temperature ranging from 900 to 960 C to obtain a heated billet; c) extruding said heated billet to obtain an extruded piece of pre- determined size and shape; d) cooling said piece to room temperature; e) heating said cooled piece at a temperature of about 900 to 960°C; f) subjecting said heated piece to flattening and twisting simultaneously using buster dies to obtain a flat and twisted piece; g) cooling said piece to room temperature followed by heating at a temperature of about 900 to 960°C; and h) subjecting said piece to finishing, trimming and padding operations to obtain a fan blade.

[0032] In accordance with the present invention, said method characterized in that said flattening and twisting of piece is carried out in a single buster die having pre-determined configuration as explained herein above, wherein said die is provided with at least one pair of plungers.

[0033] Technical Advancement and Economic Significance: a) The present invention reduces the number of forging steps required to achieve the final shape of the complex part. b) The present invention provides an arrangement for proper positioning of the preform on the dies. c) The present invention provides a preform of unique shape obtained using an extrusion process which gives precise distribution of the material in the preform. d) The die used in the present invention is adapted to confer a shape to the extruded preform which is similar to the shape obtained by two successive operations of flattening and twisting (used conventionally).

[0034] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0035] The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

[0036] Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

[0037] The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

[0038] While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure.

[0039] These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.