ANNULAR GAS TURBINE ENGINE CASE AND METHOD OF MANUFACTURING
The method comprises flowforming at least one section of a preform and then adding at least one additional element on the at least one flowformed section.
The invention relates to an annular gas turbine engine case and a method of manufacturing the same.
BACKGROUNDAlthough 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.
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.
SUMMARYIn 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.
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.
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.
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.
Further details of these and other aspects will be apparent from the detailed description and figures included below.
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:
As schematically shown in
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.
The preform for the gas generator case may be obtained from any suitable process, such as deep drawing or stamping a cold rolled and annealed sheet. Where a stamped circular blank or flat plate is used, the blank is thicker than the thickest final portion of the case. The blank is preferably cold worked to introduce compressive stresses into the material. During the flowforimg process, material is displaced by shear force over the spinning mandrel to produce a variable thickness case. The central section 33 of the case is flowformed, preferably in one pass, using a two-roller flowforming machine (not shown). Preferably, a full anneal then follows to recrystallise the microstructure.
After forming/machining and assembly, the case is preferably also hardened-tempered to give the material its final properties, including obtaining the desired microstructure and hardness.
At least two different areas are provided, namely a containment area 42 having a first thickness and a non-containment area 44 having a second thickness less than the first thickness, to lower the overall weight. Accordingly, the first and second average thicknesses are different. The fan case is otherwise preferably smooth and continuous, with no abrupt changes or discontinuities in shape. Flanges 46 and 48 are provided, as discussed below.
A circular plate is preferably flowformed to a desired thickness(es). Preferably, suitable treatments to harden (e.g. by solid solution, etc.) and anneal the case are made after flowforming.
After flowforming, the flanges 46, 48 are provided by outwardly bending the two extremities of the flowformed shell using a suitable tool (not shown). In order to facilitate providing flanges on both ends of the same part, the fan case design includes a clearance gap “G” provided between diameter A (the outside diameter of the case 40 at the base of flange 46) and the outside diameter of the flange 48, in order to permit annular tooling T to fit over the rear flange 48 to support case 40 when bending front flange 46 into place. Thus, fan case 40 is provided within contraints on the diameters of the case at the base of flange 36 and the outside diameter of flange 38. Although not required or desired in this embodiment, flanged portions may alternately be welded to a flowformed portion of fan case 40. Referring to
Flowforming, however, can only generate axisymmetric shells or the like. Bosses, stiffeners or welding lips cannot be provided using these techniques. Furthermore, flanges cannot always be obtained, even after considering subsequent forming steps such as bending and rolling/necking. For these reasons, such details are preferably provided using other techniques, such as machined out of forged rings, and then attached to the flowformed shell, as will now be described.
Referring to
The above description is meant to be exemplary only, and one skilled in the art will recognize that other changes may also be made to the embodiments described without departing from the scope of the invention disclosed as defined by the appended claims. For instance, the present invention is not limited to gas generator case and fan case components exactly as illustrated herein. Also, the gas turbine engine shown in
Claims
1. 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.
2. The method as defined in claim 1, wherein the depositing is achieved by laser deposition and powder.
3. The method as defined in claim 1, further comprising:
- machining the at least one additional element formed by disposition.
4. The method as defined in claim 1, wherein the annular gas turbine engine case is a gas generator case.
5. The method as defined in claim 1, wherein the annular gas turbine engine case is a fan case.
6. 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.
7. The method as defined in claim 6, further comprising:
- machining the at least one additional element.
8. The method as defined in claim 6, wherein the annular gas turbine engine case is a gas generator case.
9. The method as defined in claim 6, wherein the annular gas turbine engine case is a fan case.
10. 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.
11. 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.
Type: Application
Filed: Oct 2, 2006
Publication Date: Apr 3, 2008
Inventors: Jean Savoie (Carignan), Daniel P. Turner (Montreal)
Application Number: 11/537,908
International Classification: F04D 29/44 (20060101);