US2762114A - Method of making sheet metal turbine bucket - Google Patents

Description

Sept. 11, 1956 G. C. STEINHAUER METHOD OF MAKING SHEET METAL TURBINE BUCKET Filed Aug. 28, 1951 3nventor 5w C'JZ zkkzw Gttornegs United States 1 METHOD OF MAENG SHEET IVIETAL BUCKET George C. Steinhauer, Danville, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application August 28, 1951, Serial No. 243,950

1 Claim. (Cl. 29-1563) This invention relates to blading of a type specially suited for use in elastic fluid machines such as gas turbine engines and the like, and is directed to an improved construction for and the manufacture of folded sheet metal blades having an integrally formed foot or base thereon.

The invention is particularly adapted to the manufacture of integrally footed blading for use in the rotors of axial flow compressors and turbines. Such blading elements do not admit of simplicity of manufacture as they are of complex form, having oppositely curved faces that may be tapered and/or twisted from the tip to the base of the blade and may have complicated foot or root structures thereon.

Among the numerous methods proposed for the manufacture of footed blades have been various forging, machining, and rolling processes, all of which involve the use of heavy, expensive, and complicated machinery. From the standpoint of simplicity and economy of manu facture the impeller elements formed in accordance with these processes do not afford the advantages presented by sheet metal blading. Moreover, hollow blades are better adapted to cooling and may be lighter than solid blades.

Several methods for manufacturing sheet metal blades have been proposed heretofore, including that of fabricating a blade from several parts. This method has not been entirely satisfactory in view of the numerous production difficulties encountered and the inherent weakness.

of the blades formed in accordance therewith. Another method proposed has been that of folding a blade blank at the leading edge thereof. Although this method eliminates one or more of the parts, it is not well adapted to the formation of blades of complex shape and meets with the additional difficulty of unduly stressing the blade material by folding on a sharp radius at the edge thereof.

Accordingly, it is the general object of the present invention to provide an improved construction of, and process for the manufacture of, folded sheet metal blades with an integrally formed foot thereon.

Another object is to provide a satisfactory, inexpensive high-production method of manufacturing folded sheet metal blades of low unit cost.

The present invention is directed toward an improved construction of and the manufacture of a sheet metal blade formed from a single elongated strip of metal that is folded back about the central portion thereof in a a recess in the central portion of the blank for the base of the blade, forming the contour curvatures for the blade faces in each end of the blank, folding the blank back about the central portion thereof to bring the blade face edge portions thereof together, and uniting the edges of said blank along the forward and trailing edges of the faces of the blade.

Among the advantages of the invention is the fact that the curved surfaces of the blade and the base thereof are integrally formed from a single elongated strip of sheet metal stock. Another is the fact that the blade is not stressed because it is folded about the base where a generous radius is available instead of about the leading or trailing edge thereof. A further advantage is that the blade may be readily formed with complex curved surfaces that may be tapered and twisted.

These and other objects, features and advantages of the invention will appear more fully to those skilled in the art from the following detailed description and drawings of the preferred embodiment of the invention, where- Fig. 1 is an axonometric view of a prepared blank from which the blade is formed;

Fig. 2 illustrates the step of forming the base attachment recess and blade face offset in the blank of Fig. 1;

Fig. 3 illustrates the step of tapering each end of the blank of Fig. 1 after the first forming operation;

Fig. 4 illustrates the step of forming the contour curvature of the blade faces including the rough contour of the base attachment;

Fig. 5 is an axonometric view of an insert that is placed in the base attachment recess prior to folding of the blade about the base thereof;

Fig. 6 is a view along the leading edge of a folded sheet metal compressor blade constructed in accordance with the invention, and

Fig. 7 is a sectional view taken along the plane 77 of Fig. 6 to illustrate the cross-sectional shape of the blade thereof.

By way of introduction it may be advisable to refer first to Figs. 6 and 7 which illustrate a compressor rotor blade which has been constructed in accordance with the process of the invention. The blade 10 comprises a light hollow blade portion 12 and an integral foot portion 14 which is adapted for mounting in a mating slot in a turbine rotor or the like. As shown by Fig. 7, the blade portion 12 is of an airfoil form in cross-section with one convex side or face 16 and one concave side or face 18. The blade is tapered along its length from the tip 20 to the top of the foot portion 14 thereof and may also be twisted along its length, as illustrated. The process of the invention is readily adapted to the formation of blades of twisted section as will be brought out in the description of the process of the invention.

The foot portion 14 is of the well-known serrated dovetail or fir-tree type commonly employed for the roots of turbine buckets. The invention can, of course, be applied to the formation of other types of blade roots. A core or filler block 22 is inserted and may be welded or brazed in the base of the blade to reinforce the base and thus facilitate securing the base of the blade in its mating slot.

It will be noted that the blade face ofisets 24, 24' are integrally formed with the blade portions 12 and base portion 14 of the blade, thereby providing a structurally improved blade. Also, the base portion is of continuous unbroken contour formation in the sense that it is nowhere split or interrupted about the base of the blade, a feature that contributes substantially to insuring maximum blade strength. Of further interest is the fact that the blade is folded smoothly without creasing on a generous radius about its base, thereby eliminating undesirable stresses occasioned by folding the blade about a Patented Sept. 11, 1956 3 narrow radius at the leading edge thereof as proposed heretofore.

Turning now to the preferred embodiment of the process of the invention, the blade is formed from a single flat rectangular elongated metal strip 26 as illustrated in Fig. l. The base portion 14 of the blade is formed from the central portion 28 of the blank between the dotted lines XX indicated thereon While the blade faces are formed from the terminal portions 30, 30' on opposite sides of the central portion of the blank. The blank may be prepared in any of a number of ways known to those skilled in the art as by blanking or trimming, for example, from strip or sheet stock. The original stock may be rolled by a hot rolling operation from a strip or block of metal to the desired thickness of the blank desired. For greater blade strength the grain flow of the metal should preferably be parallel to the length of the blank.

Fig. illustrates the first forming operation which involv'e's forming the base attachment or foot section recess 32 in the blank of Fig. l. The extended vertical sections 24, 24' of the recess 32 act as the blade face oflsets for the base portion 14 of the blade as illustrated in Fig. 6. The forming operation may be accomplished in various ways as by pressing the blank of Fig. 1 between suitably formed dies in a hydraulic press or by striking the blank in a rough die. if desired, the blanking and rough forming operations could be performed simultaneously.

Following the forming operation, the portions 36, 36 of the blank of Fig. 2 are tapered toward the ends as shown in Fig. 3 so as to thicken the metal in the lower region of the blade portion 12 relative to the thickness at the tip of the blade for purposes of increasing blade strength. The tapering operation is preferably performed by hot rolling to avoid excessive working of the metal. After the tapering operation the ends of the blade will be longer than the desired length of the finished blade.

The next operation, illustrated by Fig. 4, entails forging the contour curvature of the blade faces in the tape'red portions of the blank of Fig. 3. This step may be accomplished with forging dies having the desired curvature of the blade faces so that when the ends 38, 30' of the blank are brought together, the curved surfaces will mate into an airfoil shape or a dished or crescent shape as required. Any desired degree of taper or twist may be imparted to the blade faces 'by employment of appropriately shaped forging dies. The process is thus readily adapted to the formation of twistedand tapered blades and is capable of forming such blades with a reasonable degree of accuracy.

The rough serrated contour of the base attachment 32 can be forged simultaneously with the forging of the blade face contours with a single set of forging dies if desired. The bottom of the base attachment and the diagonal sides thereof are formed from the central flat portion forming a non-corrugated floor 3-4 and the corrugated side portions 36, 36, respectively, of the forged recess 32 of the blank of Fig. 4.

The fin or flash (not shown) formed around the edges of the blank of Fig. 4 during the forging operation is then trimmed in a trimming die, for example, and the ends of the blade cut to the desired length. The blank is then pickled or vapor blasted and inspected.

Prior to the next operation, the tiller block 22 of Fig. 5, which can be a cast metal insert having a shape that conforms to the contour of the base portion 14 of the finished blade, is inserted in the base attachment recess of the blank of Fig. 4. The filler block serves several purposes including that of facilitating bending of the blank and improving the rigidity of the base attachment recess and the strength of the base portion of the blade.

The next major operation in the formation of the blade is that of folding or bending the blank about the blade attachment recess 32 containing the filler block 22 so as to bring the curved blade face terminal portions thereof and the base portion'weldejd around the filler insert 22.

This is followed by grinding of the welds and polishing the blade portion to obtain the desired edge contour. If ar b se P tion, ma be ound 9r t wise accurately finished to the desired base contour. The blade portion may be restruck for more precise dimensioning.

It will thus be seen that the invention provides a simple and inexpensive construction for an integrally footed blade or bucket element, the manufacture of which does not require the use of complicated machinery or skilled operators. The invention is not limited to the particular blade face and foot contours shown and may be readily applied within forging limitations to the formation of any shape of blade.

Although a preferred embodiment of the process of the invention has been described and illustrated, numerous other variations, modifications and applications within the scope thereof will be apparent to those skilled in the art to which it appertains.

I claim:

A process for forming a turbine bucket comprising an integrally formed blade portion, a planar platform portion, and a substantially triangular shaped foot portion having a fir-tree filler block inserted therein from a fiat, elongated blank of material having an intermediate por-' tion and terminal portions on the opposite sides of the intermediate portion and a triangular filler block hav* ing serrated sides, which method comprises the steps of laterally ofisetting the intermediate portion of the blank from the plane of the blank to form a recess of uniform depth having a pair of spaced parallel walls joining the terminal portions of the blank with a floor portion of the recess parallel to the plane of the terminal portions, form ing the blade face contour in the terminal portions of the blank and corrugating the floor of said recess transversely of the blank on each side of a central portion of the floor to form a pair of spaced corrugated portions thefein, placing the said filler block on the central portion of the floor of the recess and smoothly folding the blank about the central portion of the floor of the recess and around the filler block to bring the terminal portions of the blank in face-to face relation to form the said blade portion of the bucket and to bend the said walls of the recess with respect to the corrugated floor portions to decrease the angle therebetween and thus form the said planar platform portion, and the said base portion, the latter having serrated sides formed by the spaced corrugated portions 'of the floor of the recess, and uniting the adjacent edges of the blade face terminal portions to form the leading edge and the trailing edge of the bucket.

References Cited in the file of this patent UNITED STATES PATENTS 412,278 Lee Oct. 3, 1 89 814,804 Raieau Mar. 13, 1906 881,409 Jude Mar. 10, 1903 953,568 Westinghouse Mar. 29, 1910 994,166 Kienast Tune 6, l9ll 1,530,249 Eveleth a. Mar. 17, 1925 1,829,179 Back on. 27, 1931 1,913,459 Skillinan et 1. i June 13,193

(Other refe ences as following page) 5 UNITED STATES PATENTS Smith July 9, 1935 Litchfield June 2, 1936 McKee Nov. 11, 1941 Chilton Jan. 9, 1951 6 Oestrich et a1. July 3, 1951 Atkinson Oct. 7, 1952 Sollinger Oct. 23, 1953 FOREIGN PATENTS Germany May 21, 1930

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