Injection formed hydrid airfoil

Abstract: A hybrid gas turbine engine airfoil is made by forming a metal airfoil (12) with a pocket (16) in one side thereof. The pocket is covered by a caul (22). An elastomeric fluid (24) is injected into the pocket and cured therein for bonding thereto. The caul is removed from the airfoil to expose the cured elastomer conforming to the aerodynamic profile thereof.

Description: The present invention relates generally to gas turbine engines, and, more specifically, to airfoil manufacture therefor. A turbofan gas turbine engine includes a fan having a row of fan blades extending outwardly from a supporting rotor disk. The fan is powered by a turbine which extracts energy from combustion gases generated in a core engine for producing thrust to power an aircraft in flight. Minimizing engine weight for an aircraft application is a primary design objective. However, weight reduction is itself limited by the requirement to maintain component strength under the various loads experienced during operation. For example, the fan blades are relatively large and generate significant centrifugal force during rotor operation. The blades must be designed to withstand both centrifugally induced loads and stress as well as aerodynamic loads as ambient air is pressurized for generating propulsion thrust. Maximum fan blade size is limited by the high strength materials available for the manufacture thereof, and the associated cost of manufacture. All-metal fan blades, such as titanium, have high strength yet are expensive to manufacture. All-metal fan blades are also relatively heavy which correspondingly increases the size and strength requirements of the supporting dovetails thereof and rotor disk. Composite fan blades, such as shown in EP 0764763, formed of high strength graphite fibers in a carbon matrix enjoy high strength at reduced weight over all-metal fan blades. However, composite fan blades are expensive to manufacture, and must be specifically configured to provide directional strength for enjoying a suitable useful life. Hybrid fan blades are being developed for reducing weight while providing suitable strength. A typical hybrid blade has a metal body, such as titanium, with weight reducing pockets preferentially formed in one side thereof. The pockets are filled with a suitable elastomer to complete the required aerodynamic contour of the airfoil portion of the blade for acceptable aerodynamic performance. The metal portion of the blade provides the required strength, with metal being removed in the pockets for removing weight without compromising overall strength of the blade. One manner of making hybrid blades includes machining the desired pockets in the pre-formed or pre-forged airfoil as its contours are machined. Elastomer in the form of a paste or putty is positioned in the respective pockets. And, a pair of contoured forming tools or dies are disposed on opposite sides of the blade for pressing the elastomer in the pockets to undergo curing. However, this manufacturing process is complex and expensive, and is not practical for producing hybrid blades in large quantities. Accordingly, it is desired to provide an improved method of making hybrid gas turbine engine airfoils at reduced cost. According to the invention, there is provided a method of making a hybrid gas turbine engine airfoil comprising: forming a metal airfoil with a pocket in a first side thereof; covering the pocket with a caul; injecting an elastomeric fluid into said pocket; and curing the fluid in the pocket for bonding thereto. The airfoil first side may have a varying contour; the caul may have a complementary contour; and the caul may be registered with the airfoil to match said complementary contours thereof. The method may further comprise sealing the caul to the airfoil atop the pocket; injecting the fluid under pressure into the pockets; and bleeding air from the pocket as the fluid displaces the air in the pocket. The airfoil may be formed with a plurality of the pockets in the first side thereof; and the fluid may be injected in turn into the pockets. The airfoil may be formed with recessed ribs between adjacent ones of the pockets; the caul may be contoured to provide a gap atop the ribs; and the fluid may be injected in one of the pockets to flow through the gap to fill an adjoining one of the pockets. The fluid may be injected through the caul at a single site and fills all the pockets in turn. The pressure of the fluid may be maintained after the pocket is filled therewith until the fluid is cured. The fluid may be injected at one end of the caul, and the air is bled at an opposite end of the caul. The method may further comprise limiting back pressure of the fluid in the pocket to limit distortion of the caul. The invention will now be described in greater detail, by way of example, with reference to the drawings, in which:- The invention, in accordance with preferred and exemplary embodiments, together with further objects and advantages thereof, is more particularly described in the following detailed description taken in conjunction with the accompanying drawings in which: Figure 1 is an elevational view of a gas turbine engine airfoil and complementary caul used in the manufacture thereof in accordance with an exemplary embodiment of the present invention. Figure 2 is a flowchart representation of an exemplary method for making the hybrid airfoil illustrated in Figure 1 with a cooperating caul. Figure 3 is a radial sectional view through the airfoil and cooperating caul illustrated in Figure 2 and taken along line 3-3. Figure 4 is an isometric view of the finished airfoil including cured elastomer in the several pockets thereof. Illustrated in Figure 1 is an exemplary gas turbine engine fan blade 10 in an intermediate form of manufacture. The blade 10 includes an airfoil 12, and an integral dovetail 14 which may have any conventional profile for use in a turbofan gas turbine engine. The airfoil and dovetail may be initially formed as a unitary forging of a suitable high strength metal, such as titanium. The metal airfoil 12 has suitably formed therein one or more recesses or pockets 16 extending into a first, or pressure side 18 of the airfoil. Six exemplary pockets 16 are shown in this embodiment and may be conventionally machined in the initially solid airfoil. The opposite, second side 20 of the airfoil is continuous metal and defines an aerodynamically smooth suction side of the airfoil. The airfoil extends radially along its span from a root near the dovetail to its radially outer tip, and axially between opposite leading and trailing edges in a conventional configuration. The airfoil typically twists around the span axis from its root to tip, and has changing camber therebetween as required for maximizing aerodynamic efficiency. Accordingly, the airfoil has relatively complex three dimensional (3D) contour which varies from root to tip and between the leading and trailing edges, with the blade first and second sides 18,10 being configured for their pressure and suction side functions. As shown in Figure 1, a caul 22 is configured for covering the airfoil first side 18, and thereby cover the several pockets 16. The caul 22 may be formed of a composite material such as carbon fiber in an epoxy matrix for providing sufficient strength and stiffness, with a complementary contour on the inboard surface which engages the airfoil first side 18. Since the airfoil first side 18 has a varying contour from root to tip and between the leading and trailing edges, the caul 22 has a complementary contour to closely match and engage the airfoil first side 18. As shown in Figure 2, an uncured elastomer 24 in the form of a viscous fluid or liquid is suitably injected into the pockets 16 for filling thereof. In this way, the individual pockets are filled with the elastomeric fluid 24, which may then be suitably cured in the pockets 16 for bonding thereto. The caul 22 may then be removed to expose the so-formed hybrid blade. In the exemplary embodiment illustrated in Figure 2, the elastomeric fluid 24 is provided in any conventional manner as specified by the manufacturer for the specific elastomer desired. For example, the elastomer may be in the preferred form of polyurethane rubber which is provided in an initial liquid form which is heated to a suitable temperature and undergoes suitable deaeration, and is mixed with a corresponding curative agent which has been heated to a suitable temperature, in metered portions thereof. The elastomeric fluid and curative are mixed together and then injected into the pockets for curing therein. The entire hybrid blade and conforming caul 22 are preferably heated to a common temperature prior to injection of the heated elastomeric fluid 24 therein. Upon filling the several pockets of the airfoil, the so filled airfoil is maintained at the common temperature of the blade and caul for initial curing. The blade may then be conventionally post-cured at suitable elevated temperature for completing the curing process as required for the particular elastomeric material used. Since both the airfoil 12 and the caul 22 have complementary varying 3D contours, the caul is preferably registered or aligned with the airfoil to match the complementary contours thereof. This may be effected by providing registration tabs 26 integrally formed at selected locations around the perimeter of the caul for laterally engaging respective edges of the airfoil, as illustrated for example in Figures 2 and 3. Two of the registration tabs 26 may be spaced apart along the leading edge of the airfoil, with a third registration tab being disposed at the tip of the airfoil near its trailing edge. In this way, the caul may be quickly and accurately applied atop the airfoil by abutting the respective registration tabs along the corresponding edges of the airfoil. As shown in Figures 1 and 3, the caul 22 preferably includes a perimeter seal 28 in the exemplary form of a O-ring mounted in a corresponding recess or seat in the engaging surface of the caul. The seal follows the perimeter of the caul around the one or more pockets being filled with elastomer. In this way, the caul 22 may be sealed to the airfoil first side 18 atop the corresponding pockets 16. As shown in Figures 2 and 3, the caul preferably also includes a perimeter frame 30, which may be a separate component or integrally formed with the caul itself, that provides a locally stiff or rigid region around the caul upon which a plurality of suitable clamps, designated by the letter C, may be applied for clamping the caul to the airfoil around the perimeter thereof. In this way, the caul is clamped to the airfoil, with the seal 28 being clamped to the airfoil first side for maintaining a seal therewith. The elastomeric fluid 24 may then be injected under suitable pressure into the pockets 16. Since the pockets 16 initially have air therein, the caul 22 is preferably configured for bleeding air from the pockets as the elastomeric fluid displaces the air in the pockets. This may be effected by providing a plurality of bleed or weep holes 32 in the form of recessed slots at the tip of the caul as illustrated in Figures 1 and 2. The bleed holes 32 interrupt the perimeter seal 28 and permit the escape of air as the elastomeric fluid 24 is injected into the pockets. As indicated above, the airfoil 12 is preferably formed with a plurality of the pockets 16 in the first side thereof. And, the elastomeric fluid 24 is preferably injected in turn into the pockets to ensure escape of all air therein. This may be accomplished with a single injection site, or multiple injection sites. As shown in Figures 1 and 3, the airfoil 12 is preferably formed with recessed lands or ribs 34 between adjacent ones of the pockets 16. The caul 22 is preferably contoured to provide a gap 36 atop the ribs 34. The engaging surface of the caul 32 is therefore configured to define the final profile or surface of the airfoil first side 18 upon final injection of the elastomer. As the elastomeric fluid 24 is injected into the one of the pockets 16 as illustrated in Figure 3 it is permitted to flow through the several gaps 36 to fill the adjoining pockets in turn. As the pockets are filled, the air contained therein is discharged through the bleed holes 32 as illustrated in Figure 2 until some of the elastomer fluid itself is bled therethrough upon complete filling of the several pockets. In the preferred embodiment illustrated in Figure 2, the elastomeric fluid 24 is injected through the caul 22 at a single site at one end of the caul, and fills all of the pockets 16 in turn. As the fluid travels from pocket to pocket through the respective gaps 36, air is bled from the opposite end of the caul to ensure complete evacuation of air from the several pockets and complete filling thereof with the elastomeric fluid. As shown in Figures 2 and 3, the caul includes an integral inlet tube or port 38 suitably located at one end of one of the pockets 16 to be filled. The inlet tube 38 is suitably joined to the injection apparatus for receiving the elastomeric fluid under suitable pressure. Since the elastomeric fluid 24 is initially viscous in the exemplary consistency of syrup, sufficient pressure must be provided for injecting the fluid through the caul and from pocket to pocket through the small gaps 36 therebetween. The pressure of the elastomeric fluid is preferably maintained after all the pockets are filled until the fluid is suitably cured to ensure complete filling of the several pockets. The caul 22, itself should therefore have suitable structural rigidity for withstanding the developed pressure during fluid injection without unacceptable distortion of the caul which would increase the profile thickness of the elastomer in the pockets. In the preferred embodiment, the back pressure exerted by the caul on the fluid being injected is preferably limited to in turn limit distortion of the caul 22 itself. Back pressure reduction may be controlled by using a suitable number of the bleed holes 32 with suitably large flow areas, as well as by providing suitably sized gaps 36 for reducing pressure losses along the flowpath of the fluid being injected through the caul. Upon removal of the caul 22 and final curing of the elastomer, the resulting blade 10 enjoys a smooth aerodynamic profile as illustrated in Figure 4. The cured elastomer 24 fills all of the pockets 16 and is bonded thereto flush to the airfoil first side 18 for completing the aerodynamic contour thereof. The caul 22 may be reused to manufacture subsequent fan blades in series production. Hybrid airfoils including metal bodies with elastomeric pockets may be readily formed at significantly reduced cost using the injection process according to the present invention. The process may also be used for other types of hybrid airfoils in a gas turbine engine such as stator vanes or outlet guide vanes.

Claims: A method of making a hybrid gas turbine engine airfoil comprising: forming a metal airfoil (12) with a pocket (16) in a first side (18) thereof; covering said pocket with a caul (22); injecting an elastomeric fluid (24) into said pocket; and curing said fluid in said pocket for bonding thereto. A method according to claim 1, wherein: said airfoil first side (18) has a varying contour; said caul (22) has a complementary contour; and said caul (22) is registered with said airfoil to match said complementary contour thereof. A method according to claim 1, or 2 further comprising: sealing said caul (22) to said airfoil atop said pocket; injecting said fluid (24) under pressure into said pocket; and bleeding air from said pocket(s) as said fluid displaces said air in said pocket. A method according to claim 3 wherein: said airfoil (12) is formed with a plurality of said pockets (16) in said first side (18) thereof; and said fluid (24) is injected in turn into said pockets. A method according to claim 4 wherein: said airfoil (12) is formed with recessed ribs (34) between adjacent ones of said pockets (16); said caul (22) is contoured to provide a gap (36) atop said ribs (34); and said fluid is injected in one of said pockets to flow through said gap to fill an adjoining one of said pockets. A method according to claim 5, wherein said fluid (24) is injected through said caul (22) at a single site at one end of said caul, and fills all said pockets in turn as said air is bled at an opposite end of said caul.

Inventors: BEGOVICH JOSEPH THOMAS JR, EVANS CHARLES RICHARD, WARD DOUGLAS DUANE, BEGOVICH, JOSEPH THOMAS, JR., EVANS, CHARLES RICHARD, WARD, DOUGLAS DUANE
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 2000
Main classification: B29C70
IPC codes: B29C70, F01D5, F04D29, B29C45, F02C7