FR2514072A1 - METHOD FOR MANUFACTURING A BLADE FOR A GAS TURBINE ENGINE - Google Patents

Abstract

PROCESS FOR MANUFACTURING A VANE, INCLUDING A BODY 20 WITH AN AERODYNAMIC PROFILE WHICH PRESENTS AN INTERNAL CAVITY 21. A GROOVE IS FORMED AT THE END OF THE TRAILING EDGE 23 OF WHICH THE WALLS 24A, 24B EXTEND DEPENDING ON THE LENGTH OF THIS END , AND WHICH IS SEPARATED FROM CAVITY 21 BY A PARTITION 25, AND THEN HOLES 26 CONNECTING CAVITY 21 TO THE GROOVE IN THIS PARTITION 25, HOLES 26 CONNECTING CAVITY 21 TO THE GROOVE. THE WALLS 24A, 24B CAN THEN BE PUSHED IN TO FORM A NARROW SLOT 22. APPLICATION IN PARTICULAR TO BLADES FOR A GAS TURBINE ENGINE.

Description

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  The present invention relates to a method of manufacturing a dawn

for gas turbine engine.

  Such vanes are known which comprise an aerodynamic body having a portion, known as the "trailing edge", in which the thickness of the body is gradually reduced to a free downstream end. It is also known to cool the trailing edge by air passing from a cavity in the body through holes

  which cross the trailing edge and open at the said end.

  Such an arrangement limits the possibility of reducing the width of the end of the trailing edge as much as aerodynamic reasons may require. On the other hand, this arrangement reinforces the need for said holes to have a great length-to-diameter ratio. This is because, for a given dimension of the cavity, if the average thickness of the trailing edge is to be reduced, the cavity must be located further from the free end. This in turn requires the holes to be deeper and causes manufacturing difficulties related to drilling holes

deep, small diameter.

  According to the invention, the method of manufacturing a gas turbine engine blade, which comprises an aerodynamic section body with an internal cavity comprises the following steps: a) producing at the leakage end of the body a groove Vant sidewalls extending along the length of said end, and a bottom wall defining a partition between the groove and the cavity, and b) producing holes in this bottom wall to connect the

cavity and groove.

  The method may include the step of pushing the walls towards each other, so as to produce at the free end of the walls a

  slot having a width less than the original width of the groove.

  The invention makes it possible to position the cavity relatively far from the end of the trailing edge, without this resulting in holes of undue depth. The invention also makes it possible to have a trailing edge end.

  narrower than in the case where the holes open at this end.

  The invention will now be described in detail by way of example,

  with reference to the accompanying drawings.

  FIG. 1 is a perspective view of a turbine rotor blade for a gas turbine engine. FIGS. 2 to 4 are cross sections through the blade of FIG. 1 at different stages of manufacture, FIGS. 4 being fragments represented on a larger scale,

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  Figure 5 is an elevational view corresponding to Figure 3.

  Referring to FIG. 1, it can be seen that the blade comprises a stem 18 made of fir, a platform 19 and a body 20 with an aerodynamic profile and which comprises a trailing edge 23 whose desired or final shape is represented in solid lines. A tear in the body was made to show a cavity 21 and a slot 22 formed in the free end 23a of the trailing edge for the exhaust of the cooling air from the cavity 21 to cool the trailing edge The cooling air is

  brought to the cavity by means not shown, but which are in themselves

  same well known and normally include channels crossing the

  root of dawn and communicating with a source of high pressure air.

  To ensure the aerodynamic profile of the blade, the trailing edge must be tapered and thin, the end 23a having a width W (FIG. 4) which must be as small as practical considerations, such as

mechanical resistance.

  As shown in FIGS. 2 to 5, the blade is first molded in the form of a blank 17a (FIG. 2), a core being provided in the mold to form the cavity 21. The mold for the blank is shaped in such a way to produce an aerodynamic section for the body 20 having substantially the desired shape, but to produce a trailing edge 23 X whose width WX is substantially greater than the width W. The blank 17a is then taken in a mohtage and produced in the trailing edge a groove 24 (FIGS. 3 and 5) A number of methods are available to produce the groove 24, but it is preferred to produce it by machining by electric discharge. It is seen in FIGS. 3 and 5 that the groove is relatively wide and consequentelelatively easy to produce, and that there remain two thin sidewalls 24a, 24b diverging from each other in the manner of a dovetail The groove is arranged so that its bottom wall, designated 25, forms a partition between the

groove and cavity 21.

  In a third stage of manufacture, holes 26 are drilled through the wall 25 to connect the groove 24 and the cavity 21. These holes extend along the line of camber C of the section of the blade, and the access to the wall 25 for the drilling operation is facilitated by the groove 24 o The holes are preferably drilled by machining by electric discharge,

  although there is obviously a series of other processes available.

  At a fourth stage of manufacture the diverging walls 24a, 24b are deformed and pushed towards each other, for example at the presses to close the groove 24 so that the ends of the walls form

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  between them the slot 22 The dimensions of the blank 17a and the groove 24 are chosen so that after this deformation the trailing edge 23 has

substantially the desired shape.

  The pressing operation is carried out by means of a pair of press tools 29, In an exemplary embodiment, a nickel-based alloy blade known under the designation IN 100 has been able to undergo the desired deformation at the temperature However, if necessary, the sketch can be

  be heated to the appropriate temperature to facilitate deformation.

  Preferably the groove is dimensioned so that the walls 24a, 24b are tapered and when the tools 29, 30 are applied, the walls flex so that the correct outer shape of the blade is obtained. calibration plate 28 (fig 4)

  is introduced to control the size of the slot 22.

  Note that special arrangements must be made at the ends of the slot 22 For this purpose, as shown in Figure 5, the end portion 31 of the groove 24, adjacent to the platform 19, has a gradually reduced width and ends at a distance D of the platform somewhat less than a distance E at which a rib of

  fitting 32, provided between the body 20 and the platform 19, joins the body.

  The final shape of the trailing edge 23 is shown in dashed lines.

  As also shown in FIG. 5, at the tip of the blade, the blank and the groove have portions 33 and 34, respectively, which have a progressively reduced width in order to facilitate obtaining the final shape.

represented in dashes.

  It may be necessary to finish the dawn manufacturing in different ways Thus it would probably be necessary to close the dawn tip with a brazed or welded bonnet 36 (Fig 1), and the aerodynamic surface itself may still require a finish Also the root 12 will probably have to be machined to its final dimensions and channels for

  cooling air will have to be drilled into this root.

  Thus the final dawn is produced with a narrow slot in a thin trailing edge without having to perform the difficult machining of the very narrow slot 22 In addition the small diameter holes 26 are drilled through a rather short piece of material solid, and from a convenient starting position close to the wall 25, so that they can be positioned accurately to make minimum all concentrations

  constraints caused by imprecise position of the holes.

  It should also be noted that the method according to the invention can also

  in this case the blank would be forged in the conventional manner to the section of FIG. 2, the cavity 21 being obtained by

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  electrochemical machining for example 7 and the steps described above

  would be applied to the forged blank.

  It is also understood that, although described with reference to a rotor blade, the invention is applicable to the manufacture of any rotor blade or stator requiring a split trailing edge for any reason

  (eg cooling or boundary layer control).

  It has been found that with a blade manufactured - according to the method according to the invention, the width W of the finished end of the trailing edge may be smaller than the corresponding width of a blade in which cooling holes The wall 24a on the concave or warmer side of the blade may be made shorter than the wall 24b, as shown in 24e (FIG. 4).

  still the effective width W and the thermal resistance of the wall 24 a.

  Pushing the walls 24a, 24b of the groove toward each other is desirable not only to allow the manufacture to begin with a groove large enough to provide access to the drilling of the holes, but also to ensure that the slit 22 flow rate is not greater than the combined flow section of the holes Section consideration is necessary to ensure that the individual detrimental flow rates form a common stream exiting the slit 22, and that the air is again accelerated after the diffusion that inevitably occurs at the

exit from the holes.

  The depth of the groove 24 and the divergence of the surfaces facing the walls 24a, 24b, depend on the distance between the cavity 21 and the end of the trailing edge Normally the depth of the groove does not exceed what is necessary to reduce any problem in drilling holes of a relatively long length The width of the groove is chosen to give access to the drilling tool In some cases it may be sufficient that the facing surfaces of the walls 24 a, 24 b, are parallel rather than divergent, as shown by a groove 27 (FIG. 3). It may then be possible not to push the walls towards each other, especially if one of the walls is shorter than the other, as mentioned above, and if the flow through the holes has a high speed, compared to the flow of gases on the outside of the blade When these facing surfaces are parallel the width WOX of the blank 17 a (Fig 2 ) is of course suitably reduced p relative to the case where these surfaces opposite are divergent.

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Claims (5)

REVENDI CATI ONS   A method of manufacturing a gas turbine engine blade, comprising an airfoil body having an internal cavity, characterized in that it comprises the following steps: a) forming at the trailing end of the body a groove having sidewalls extending along the length of said end, and a bottom wall defining a partition between the groove and the cavity, and b) drilling holes in said bottom wall to connect the cavity to the groove.   Method according to claim 1, characterized in that it further comprises the step of pushing the side walls of the groove towards each other so as to form at said end a slot whose width is   less than the original width of the groove.   3. Method according to claim 1, characterized in that the groove is formed so that the facing surfaces of said side walls diverge from said bottom wall to said end, and in that   the walls are then pushed towards each other to form at the said end   mente a slot whose width is less than the original width of the groove at said end.   4 Process according to claim 1, characterized in that the facing surfaces of said side walls are parallel between said   bottom wall and said end.   5. Dawn for gas turbine engine, characterized in that it is   obtained by the process according to any one of claims 1 to 4.