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  Annular gas turbine engine case and method of manufacturingThe Patent Description & Claims data below is from USPTO Patent Application 20080080974. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001]The invention relates to an annular gas turbine engine case and a method of manufacturing the same. BACKGROUND [0002]Although unlikely, it is possible that during operation of a gas turbine engine a rotating airfoil can fail by separating from the hub or disc and being released in a radial direction. A surrounding containment structure is designed to capture the released airfoil and prevent it from leaving the engine, in either the radial or axial direction. The containment structure must be strong, and for airborne applications, lightweight. It is also desirable, of course, to provide components as cost effectively as possible. A turbofan fan case is one example of an airfoil containment structure, and a compressor or gas generator case is another example. In addition to performing a containment function, a gas generator case is also a pressure vessel. [0003]Traditionally, a fan case is manufactured by machining a forging, but this wastes much material, and requires several steps, and therefore time. Traditionally, a gas generator case is machined out of two or three forged or sheet metal rings, provided to meet the various thickness requirements and design intents, then these rings are welded together. However, the weld joint(s) must to be located in a region away from the fragment trajectory of the impeller blade, since weld lines are not desired in containment sections of components. All these steps are time consuming and therefore increase lead-time. It is desirable to provide improved ways for manufacturing annular gas turbine engine cases in effort to reduce lead-time and manufacturing costs. SUMMARY [0004]In one aspect, the present concept provides a method of manufacturing an annular gas turbine engine case comprising: flowforming at least one section of the preform; and forming at least one additional element on the at least one flowformed section by depositing material onto the flowformed section. [0005]In another aspect, the present concept provides a method of manufacturing an annular gas turbine engine case comprising: flowforming at least one section of the preform; and then adding at least one additional element on the at least one flowformed section by brazing. [0006]In another aspect, the present concept provides an annular gas turbine engine case, comprising: at least one flowformed section; and at least one additional element added to the at least one section by laser deposition. [0007]In another aspect, the present concept provides an annular gas turbine engine case, comprising: at least one flowformed section; and at least one additional element added to the at least one section by brazing. [0008]Further details of these and other aspects will be apparent from the detailed description and figures included below. BRIEF DESCRIPTION OF THE FIGURES [0009]For a better understanding and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying figures, in which: [0010]FIG. 1 schematically shows a generic turbofan gas turbine engine to illustrate an example of a general environment in which annular gas turbine engine cases can be used; [0011]FIGS. 2a and 2b schematically illustrate the principles of flowforming; [0012]FIG. 3a is a side view of an example of a gas generator case and 3b is a cross-section view of a portion of a gas generator case; [0013]FIG. 4a is a cross-section view of a portion an example of a fan case, and [0014]FIG. 4b is an enlarged portion of an example of a fan case; and [0015]FIGS. 5a and 5b are cross-section views of portions of example cases. DETAILED DESCRIPTION [0016]FIG. 1 illustrates a turbofan gas turbine engine 10 of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan 12 through which ambient air is propelled, a fan case 13 surrounding the fan, a multistage compressor 14 for pressurizing the air, a combustor 16 in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, a gas generator case 17 surrounding at least a portion of compressor 14 and combustor 16, and a turbine section 18 for extracting energy from the combustion gases. Fan case 13 and gas generator case 17 are preferably manufactured using flowforming techniques, as will be described further below. [0017]As schematically shown in FIGS. 2a and 2b, flowforming generally involves applying a compressive force using rollers 20 on the outside diameter of a rotating preform 22 (also called a blank) mounted on a rotating mandrel 24. The preform 22 is forced to flow along the mandrel 24, for instance using a set of two to four rollers 20 that move along the length of the rotating perform 22, forcing it to match the shape of the mandrel 24. The process extrudes and therefore thins or reduces the cross-sectional area of the wall thickness of the rotating perform 22, which is engineered to produce a cylindrical, conical or contoured hollow shape. The thickness of the finished part is determined by the gap that is maintained between the mandrel 24 and the rollers 20 during the process, and therefore the final thickness of the part may be controlled. This gap can be changed or remain constant anywhere along the length of the part, to thereby change or maintain part thickness, as desired. [0018]FIGS. 3a and 3b show an example of a flowformed gas generator case 30. The case includes a rear flange portion 32, a central flowformed section 33 and a front flange portion 36. Central flowformed section 33 includes a containment portion 35 and a gas generator portion 37. As will be appreciated, the limitations of flowforming are such that the gas generator case 30 cannot be flowformed in its entirety as a single piece. Therefore, rear flange portion 32 and front flange portion 36 are joined by welds 39 to central flowformed section 33. The thickness of the central flowformed section 33 varies along the central section 33, from an area of increased thickness corresponding to containment portion 35, decreasing smoothly to a smaller thickness corresponding to a gas generator portion 37. More material is thus provided where needed for containment, and less material where not required for the pressure vessel portions. The thickness of gas generator portion 37 is designed to handle the high pressure compressor exit pressure (so-called "P3" pressure, whereas the thicker portion of containment portion 35 is sized to contain any high energy fragments from the compressor impeller blades in addition handling P3 pressure. Central flowformed section 33 has a generally conical or cylindrical shape, to facilitate mandrel removal after flowforming. The case 30 includes An example material is ferritic/martensitic stainless steel SS410. [0019]A traditional way to provide a gas generator case is to machine the case out of two or three forged rings sized to meet the various thickness requirements, an then weld these rings together. Using flowforming reduces the costs significantly and reduces the number of welds, which are undesirable in high temperature and high pressure environments. Since only a section of the gas generator case 30 of this design could be flowformed, the rear flange portion 32 may be provided, for example, by outwardly bending the perform using a press, or by machining rear flange portion 32 from a ring, etc. Also, an non-axisymmetric detail 34 was later joined at the bottom of the flowformed section using a suitable method, such as welding. Continue reading... Full patent description for Annular gas turbine engine case and method of manufacturing Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Annular gas turbine engine case and method of manufacturing patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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