US3029497A - Method of making turbine blades - Google Patents

Description

April 17, 1962 .1. H. NELSON 3,029,497

METHOD OF MAKING TURBINE BLADES Original Filed March 16, 1954 4 S eet -Sheet 1 Iivz a lia r' (/0121? H. Nelson A ril 17, 1962 J. H. NELSON 3,029,497

METHOD OF MAKING TURBINE BLADES Original Filed March 16, 1954 4 Sheets-Sheet 2 litre "7.2227? cfofm H Ne/aon uV/% H April 17, 1962 Y J. H. NELSON 3,029,497

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Original Fi l e d M a r C h l 6 l 9 54 3,629,497 METHGD GE MAKING TURBINE BLADEES John H. Nelson, Palos Park, ill, assignor to Krupp Forge Company, Chicago, Ill, a corporation of Illinois Griginal application Mar. 16, 1954, Ser. No. 416,525. Divided and this appiication Dec. 23, 1957, Ser. No. 713,076

1 Uiairn. (Cl. 29-156.S)

The present invention relates to improvements in the manufacture of turbine blades or buckets. The present application is a division of application Serial No. 416,525, filed March 16, 1954, now abandoned.

In the manufacture of the blades for combustion gas turbines by forging the blanks of the fairly expensive alloy, comprising high nickel content with chromium and iron, certain problems have been encountered which have been responsible for substantially increasing the cost of the blades.

Among these problems is that of die cost. Since the turbine blades must be formed to transverse curvature in the blade or airfoil section or portions thereof, and the airfoil sections must be disposed angularly relative to the root portion or sections of the blades, the forming dies require quite expensive shaping operations to pro vide the necessary complementary forming surfaces in the cooperating die elements. As heretofore constructed, such forming dies have been subject to failure due to cracking in the female or cavity die element, due to excessive wedging pressures incident to hammering of the blank by the male or punch die member.

Another problem of considerable importance has resided in the excessive amount of flash heretofore required on the blank being forged in order to afford shim between the die members to define proper spacing. Inasmuch as the material used for manufacture of turbine blades is costly, the waste incident to the excessive flash that must be trimmed from the forged blank has added materially to the cost of manufacture.

Accordingly, it is an important object of the present invention to improve the manufacture of turbine blades and substantially reduce the cost per blade unit.

Another object of the invention is to provide an im proved method of making turbine blades in which die stresses are substantially avoided and the useful life of the cooperating die members substantially prolonged.

Still another object of the invention is to improve the manufacture of turbine blades by substantially reducing the amount of flash incident to forging the blades and thereby effecting appreciable savings in material.

Other objects, features and advantages of the present invention will be readily apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a plan view of a turbine blade blank as it appears following finish forging and trimming off of flash;

FIGURE 2 is a plan View of a blank for making a turbine blade prior to forging the blade and root portions thereof to final shape;

FIGURE 3 is a bottom perspective view of a forging punch die member operable for shaping the blank of FIGURE 2;

FIGURE 4 is a female or cavity die member with which the die member of FIGURE 3 is cooperable,

FIGURE 5 is an end elevational view showing the die members of FIGURES 3 and 4 cooperatively related;

FIGURE 6 is a plan view of the blank after it has been forged in the complementary, cooperative forging dies of FIGURES 3, 4 and 5;

3,fi29,497 Patented Apr. 17, 1962 FIGURE 7 is a perspective view of a punch die operable for finish forging of the blank;

FIGURE 8 is a perspective view of the female die member cooperable with the male die punch of FIGURE 7;

FIGURE 9 is an end perspective view showing the die members of FIGURES 7 and 8 cooperatively related; and

FEGURE 10 is a fragmentary enlarged transverse vertical sectional view through the root cavity portion of the die assembly of FIGURE 9.

In FIGURE 1 is shown a forged turbine blade or bucket member 15 after completion of forging operations thereon and trimming away of flash, but before the blade member has been machined. At one end the blade member 15 has a root portion 17 which is adapted to be appropriately machined for assembly in locked relation upon a turbine rotor. The remainder of the blade member 15 comprises an airfoil section 18 of transversely concave-convex shape and angular disposition relative to the root section or portion 17, as is customary.

As a preliminary step, a billet of the alloy material is shaped as by forging to provide a more or less symmetrical blank B as shown in FIGURE 2 provided not only with a rudimentary enlarged root portion 17, and a rudimentary blade portion 18, but also a handling stem 19 which projects from the root 17' in the opposite direction from and preferably on the axis of the rudimentary blade extension 18'.

As to the second forging operation to which the blank is subjected, it is placed between and operated upon by a pair of forging die members 20 (FIG. 3) and 21 (FIG. 4) which cooperate (FIG. 5) to effect preliminary shaping of the root section 17 and the airfoil section 18 (FIG. 6). As an incident to this second forging operation, a limited amount of flash F is formed about the perimeter of the forged blank.

In order to enable the severe forging pressures to be applied by the male die member or punch 20- against the female die member 21 during the forging operations without danger of development of dangerous localized stresses that might cause cracking of the female die member, forging of the blade portion 18 of the blank is accomplished between forming surfaces on the die members which as nearly as practicable face toward one another in the direction of the axis of movement of the punch die member toward the female die member. Moreover, in order to avoid the need for excessive flash on the blank, the die members 24) and 21 are provided with means to positively maintain the die members in a preferred stroke limit. In addition, the die members are substantially locked in forging assembly to hold their relative location or position, but without any binding interaction. To this end, the punch or male die member 20 of the blocking die assembly is provided with a fiat downwardly facing surface 22 which in the assembly cooperates as a stroke-limiting stop against an upwardly facing complementary flat surface 23 on the female die member 21. Projecting in offset relation from the central portion of the male die face 22 and extending across the front to rear axis thereof is a punch projection 24 which in operation fits down into a complementary front to rear groove 25 in the sur face 23 of the female die member. The respective opposite longitudinal sides of the punch portion 24 are provided with inwardly tapered surfaces 27 which cooperate with complementary inwardly tapered side wall surfaces 28 defining the groove 25. In practice, the taper of the complementary surfaces 27 and 28 may be approximately 2 from the vertical. This affords a lead-in for the punch portion 24 and at the end of the forging stroke of the punch member 20, the tapered cooperating surfaces 27 and 28 afford a positive positioning lock for the die members cooperatively related to the opposing flat stop faces 22 and 23 to limit the extent of the forging stroke of the blocking die members, but without any binding action.

By providing differential radius so that spaced relation, as indicated at 29, will persist between the reentrant corner at the root of the punch portion 24 and the outside corner at juncture of the groove side walls 28 and the female die member surface 23, and a similar differential radius spaced relation 36 between the reentrant corners at the bottom of the side walls 28 and the leading end longitudinal corners of the punch member 24, interference with full cooperation of the stroke-limiting opposing surfaces and of the stroke-locking surfaces is avoided at the opposing juncture radii.

Within the the female die groove 25, and on and within the punch die portion 24, are formed the various cavities and shaped and contoured surfaces for blocking the blank B into the turbine blade form. To this end, the punch portion 24 has formed adjacent to one end thereof a cavity 31 complementary to and cooperative with a cavity 32 in the groove 25 for blocking out the root portion or section 17 of the blade blank. As best visualized in FIG. 5, the cavities 31 and 32 are formed on an axis which is substantially tilted to the plane of the cooperating faces 22 and 23 of the die members. Outwardly beyond the cavities 31 and 32 the blocking die members and 21 have respective transversely angular, but directly abuttingly opposing respective stop faces 33 and 34, respectively, having relatively offset portions joined by respective cooperating diagonal portions in line with the cavities 31 and 32 and provided with respective cooperating handling stem clearance grooves 35 and 37 opening outwardly from the coopcrating blade root cavities.

Extending inwardly beyond the punch nose cavity 31, longitudinally of the punch nose 24 and to the opposite end of the punch nose is a blade or airfoil contouring rib 38 which, in cooperation with the female die member 21 is adapted to operate with a complementary blade-forming cavity 39 in the groove and extending inwardly beyond the root-forming cavity 32. It will be observed from an inspection of FIGS. 3 and 4 that the transverse and longitudinal contouring of the forming rib 38 and the cavity 39 are such as to block out the rudimentary shape of the vane or airfoil section of the blade member.

For accommodating limited flash displacement laterally from the longitudinally aligned blade-forming surfaces of the die members 20 and 21, various flashaccommodating clearance recesses are formed in the die members. In the punch nose 24, shallow flash recesses 40 are provided at opposite sides of the root-forming cavity 31, and another such flash-receiving shallow recess 41 is provided substantially as an extension from the flash recess 40 at the upwardly inset face portion of the punch nose 24 for accommodating flash alongside the base portion of the turbine blade at juncture thereof with the root 17. On the female die member 21, are provided, at opposite sides of the root-forming cavity 32, shallow flash recesses 42 which cooperate with the corresponding flash recesses 48 on the punch nose. The flash recess 42 adjacent the inset portion of the stop surface 34 of the female die has an extension 43 into this stop surface. Entirely about the blade-forming cavity 39 is provided a shallow flash recess 44. Thus, While it is possible in practicing the method of the pres ent invention, with the aid of the blocking dies 2i} and 21, to provide the blank B with an amount of material which is close to the actual requirements, a small excess of material is desirable to assure proper flow and distribution of the material in forming the blade member and this slight excess of material is accommodated in the flash recesses of the die members and provides the minimum flash F. It may be pointed out that as a 4- matter of fact, by the present invention, due to the minimal flash allowance, up to three and one-half pounds of the expensive material are saved as compared with the prior method.

It will be observed that in blocking the blank B in the die assembly 20, 21, the major area of the blank residing in the blade-forming portion 13 is subjected to forging pressure between the opposing broad surfaces provided by the punch rib 38 and the die cavity 39, and the flash recesses 42, 43 and 44 and the opposing cooperative surfaces of the punch die member 20. Since these broad forming surfaces are directed generally axially with respect to the direction of the forging stroke, distribution of the hammer force is distributed over a large area of the female die block 21 without any such concentration of pressure along any given line as would tend to effect cleavage or cracking. This can be visualized not only from FIGS. 3 and 4, but also by inspection of FIG. 5 where several typical transverse positions along the mating die members 20 and 21 considered longitudinally of the punch nose 24 and the groove 25 have been depicted in dash outlines A, B and C taken generally in the planes of the lines A, B and C shown in FIG. 4.

Following the blocking operation, the partially formed turbine blade 15 is finish-forged between drop hammer forging dies 45 and 47 (FIGS. 7 to 10, inclusive). These dies are constructed similarly to and operate upon the same principle as the blocking dies 20 and 21. That is, the male and female finishing dies 45 and 47, respectively, are constructed to apply the forging pressure over relatively broad surfaces facing generally in the direction of the axis of the forging stroke, they rely upon stop surfaces to delimit the forging stroke, they have centering locks to assure proper registration of the dies, and the minimum flash is accommodated in appropriately disposed shallow recesses in the die members. To this end, the upper or male die member 45 has a preferably flat stop face 43 which opposes in stopping relation an upwardly facing flat stop face 49 on the lower or female die member 47. Projecting downwardly from the central portion of the male die face 48, and extending entirely thereacross from front to rear, is a punch nose 59 which is formed generally complementary to and fits down into a groove 51 extending entirely across the upper face 49 of the female die member 47 in a front to rear direction. Inwardly tapering longitudinal side surfaces 52 on the opposite sides of the punch nose cooperate with similarly tapering side wall surfaces 53 defining the groove 51.

For imparting the finish-forged shape to the blade blank, the punch nose 50 is provided with a root-shaping cavity 54 adjacent to one end cooperable with a rootshaping cavity 55 adjacent to the similar end of the female die member 47 within the groove 51. Outwardly of the respective root cavities 54 and 55 are provided respective opposing stroke-limiting surfaces 57 and 58 provided with respective complementary angular intermediate portions 59 and 60 having complementary matching stem clearance grooves 61 and 62 leading from the respective root cavities to the outside.

For finish-forging the blade portion 18 of the blade blank, the punch nose 50 is provided with a generally longitudinally extending forming rib 63 of proper longitudinal and transverse contour cooperable with a longitudinal cavity 64 formed in the female die groove 51.

For accommodating flash about the blade blank, the female die member 47 is provided at opposite sides of the inner end portion of the stem groove 62 with a shallow flash recess 65 arranged to match a shallow flash recess 67 located at opposite sides of the inner portion of the stern groove 61 of the punch nose 50 and running continuously onwardly at each side of the punch nose rib 63.

On comparison of FIGS. 5 and 9, it will be observed that the angularity of the blade portion 18 of the turbine blade member, relative to the transverse center line of the root i7, is substantially increased in the finish-forging operation. However, even though the forging surfaces of the female die member 47 are correspondingly more angular to the axis of the forging stroke, the surfaces are nevertheless still facing generally in the direction of the forging stroke axis and therefore the drop hammer force is distributed over a large area of the female die block and thus dissipated without localization in or along cleavage planes that might tend to cause cracking of the die. In FIG. 9 in order to better visualize the various angular relationships of the forging surfaces along the die assembly from front to rear, dashed in positions D, E and F have been shown which correspond generally to the locations indicated by the lines D, E and F applied to the punch nose portion 50 in FIG. 7.

In the operation of the finishing die assembly 45, 47, the tapering nose surfaces 52 and the female die surfaces 53 cooperate to assure centering and thus proper thrust of the punch die into mating relation within the depression in the female die member. In order to avoid any interference with proper cooperation of the stop surfaces of the die members, difierential radius clearance 68 is provided between the upper corners defining the groove 1 and the reentrant corners at the base of the punch nose 50. Similarly, differential radius clearance 69 is provided between the reentrant corner within the groove 51 and the outside longitudinal corners defining the punch nose 50.

Following the finishing forging in the dies 45, 47, the blank is trimmed to remove the flash and the handling stem 19 and then has the appearance shown in FIG. 1, ready for final machining for service installation in a turbine rotor.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

A method of forging turbine blades having a root portion and a blade portion extending therefrom in angular relation with respect to said root portion and in the general form of a twisted scoop-like generally concave airfoil section, the concavity of which diminishes from said root portion toward the end of said blade portion, the steps of rough forging a billet into a symmetrical blank having a root portion, a generally concave blade portion extending from said root portion and angularly disposed with respect to said root portion, with a handling stem extending from said root portion in an opposite direction from the blade portion, between stationary and axially movable forging surfaces primarily facing in the direction of axial movement of the movable forging surface, blocking the blade portion into a twisted scoop-like generally concave airfoil section, the concavity of which decreases toward the end of the blade portion and at the same time blocking the root portion into a rudimentary thickened and transversely elongated root section having its transverse axis angularly related with respect to the end of the blade portion of the airfoil section, between stationary and axially movable forging surfaces angularly disposed with respect to each other in accordance with the contour of the root portion and blade portion with the forging surfaces primarily facing each other in the general direction of axial movement of the movable forging surface and limiting the travel of the movable forging surfaces toward the stationary forging surfaces, and thereafter simultaneously finish forging the blank and root portions by further pressure thereon between additional stationary and movable forging surfaces limited in travel toward each other and traveling in the same angular relation as the forging surfaces for the blocking operation and primarily facing in the general direction of axial travel of the movable forging surfaces toward the stationary forging surfaces and thereby further emphasizing the airfoil section of the blade portion extending from the angular root portion to a thin relatively flat tip, and thereafter trimming the flash created by the foregoing forging operation from the blade and root portions and at the same time trimming off said handling stem.

References Qited in the file of this patent UNITED STATES PATENTS 379,730 Russell Mar. 20, 1888 1,748,364 Ray Feb. 25, 1930 1,841,920 Smith Jan. 19, 1932 1,996,014 Gladson Mar. 26, 1935 2,422,325 Wheelon June 17, 1947 2,503,630 Norton Apr. 11, 1950 2,593,139 Greenshields Apr. 15, 1952 2,716,270 Gibian Aug. 30, 1955 2,843,919 Garaventa et a1 July 22, 1958 FOREIGN PATENTS 2,329 England -1 1895 759,563 England Oct. 17, 1956

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