Method for manufacturing at least one metal turbine engine part

Abstract

A method of fabricating at least one metal part for a turbine engine, the method including the steps of casting a metal alloy by centrifuging into a permanent metal mold for making a blank; obtaining a cast blank of elongate shape and of section that is circular or polygonal; and machining the blank to make the part.

Claims

1. A method of fabricating a turbine engine blade for a turbine engine, the method comprising: a) casting a metal alloy by centrifuging into a permanent metal mold for making a blank, the permanent metal mold rotating about an axis during the casting; b) obtaining a cast blank of elongate shape and of section that is circular or polygonal; and c) machining the blank to make the turbine engine blade by removing material of the blank to reveal all exterior features of the turbine engine blade, wherein the metal alloy is TiAl-based, wherein the permanent metal mold includes a plurality of housings extending radially from the axis and being regularly spaced around the axis, wherein the cast blank is initially in a form of a wheel including a plurality of radial blanks in which radially inner ends of the radial blanks are secured to a common central hub, and wherein the blank obtained in step b) is tubular, with at least one turbine engine blade being machined from a thickness of a tubular wall of the blank.

2. A method according to claim 1, wherein the metal alloy is TiAl 48-2-2.

3. A method according to claim 1, wherein step a) comprises melting an ingot into a cooled metal crucible and pouring the metal melted into a centrifuged permanent mold.

4. A method according to claim 1, wherein the number of turbine engine blades machined from the blank is greater than six.

5. A method according to claim 1, wherein the blank obtained in step b) is obtained by separating the blank from the wheel having the plurality of radial blanks secured at the radially inner ends thereof to the common central hub by machining.

6. A method according to claim 1, wherein each of the housings of the plurality of housings is cylindrical.

7. A method according to claim 1, wherein the blank obtained in step b) is subjected to heat treatment prior to machining step c).

8. A method according to claim 7, wherein said heat treatment includes a step of hot isostatic compression.

9. A method of fabricating a turbine engine blade for a turbine engine, the method comprising: a) casting a metal alloy by centrifuging into a permanent metal mold for making a blank, the permanent metal mold rotating about an axis during the casting; b) obtaining a cast blank of elongate shape and of section that is circular or polygonal; and c) machining the blank to make the turbine engine blade by removing material of the blank to reveal all exterior features of the turbine engine blade, wherein the metal alloy is TiAl-based, wherein the permanent metal mold includes a plurality of housings extending radially from the axis and being regularly spaced around the axis, wherein the cast blank is initially in a form of a wheel including a plurality of radial blanks in which radially inner ends of the radial blanks are secured to a common central hub, wherein the turbine engine blade includes a dovetail attachment at a first end and a platform with a sealing element at a second end, and wherein the blank obtained in step b) is tubular, with at least one turbine engine blade being machined from a thickness of a tubular wall of the blank.

10. A method according to claim 9, wherein each of the housings of the plurality of housings is cylindrical.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Other advantages and characteristics of the invention appear on reading the following description made by way of non-limiting example and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic flow chart showing the various successive steps in an implementation of the method of the invention;

(3) FIG. 2 shows a device for melting, casting, or molding blanks;

(4) FIGS. 3 and 4 are a diagrammatic side view and a diagrammatic end view of a solid cylindrical bar in which a turbine engine blade is to be machined;

(5) FIG. 5 is a diagrammatic perspective view of a hollow cylindrical bar of the invention from which turbine engine blades are to be machined; and

(6) FIG. 6 is a diagrammatic view in perspective and in axial section of the bar of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 is a flow chart showing the various successive steps in an implementation of the method of the invention.

(8) The method comprises a first step 1 of fabricating at least one ingot, e.g. out of a gamma-TiAl type alloy, preferably of TiAl 48-2-2 type. TiAl 48-2-2 comprises 48% aluminum, 2% chromium, and 2% niobium (atomic percent).

(9) The ingot may be made by a method of the vacuum arc remelting (VAR) type or of the plasma arc melting (PAM) type.

(10) Thereafter, the method has a step 2 of remelting the ingot by the VAR method in a metal crucible and of pouring it into a centrifuged permanent mold. This step is described in detail with reference to FIG. 2.

(11) This figure shows a device 10 for fabricating blanks 11, e.g. in the form of cylindrical bars, by successive operations of melting, casting, and molding.

(12) The device 10 comprises a closed and leaktight enclosure 12 in which a partial vacuum is established. The ingot 13 made of metal alloy, e.g. based on TiAl, is fastened to one end of an electrode 14 that is connected to one terminal of an electricity source having its other terminal connected to a crucible 15 housed in the enclosure 12. In order to melt the ingot 13, the electrode 14 is moved over the crucible 15 with small-amplitude reciprocating movements. When the ingot 13 comes close to the crucible 15, electric arcs form between the crucible 15 and the ingot 13, thereby causing the ingot 13 to melt and drop into the bottom of the crucible 15 (VAR: vacuum arc remelting). When the ingot 13 has been completely melted, the molten metal alloy in the crucible 15 is poured into the permanent mold 16 made of metal.

(13) The mold 16 enables the alloy to be cast by centrifuging. For this purpose, the mold 16 is set into rotation about an axis A, the mold 16 having a plurality of cylindrical housings 17 that extend radially around the axis A and that are regularly spaced apart around the axis A. The centrifugal force generated by rotating the mold 16 forces the molten alloy to penetrate into the housings 17 and fill them.

(14) After cooling, the mold 16 is opened and the rough casting is extracted. The casting is in the form of a wheel having a plurality of radial blanks 11 secured via their radially inner ends to a common central hub.

(15) Each blank 11 is in the form of a solid cylinder and may be separated from the hub and from the other blanks 11 by machining (step 3 in FIG. 1), and thereafter it may be subjected to heat treatment (step 4 in FIG. 1).

(16) The heat treatment applied may in particular be that described in U.S. Pat. No. 5,609,698 and it may include a heat treatment step in preparation for hot isostatic compression, during which the blank 11 is subjected to a temperature lying in the range 1900 F. to 2100 F. for a duration lying in the range 5 h to 50 h, then a step of hot isostatic compression at 2200 F., followed by an additional step during which the blank is subjected to a temperature in the range 1850 C. to 2200 F.

(17) After the blank 11 has been subjected to heat treatment it is machined (step 5 in FIG. 1) in order to form at least one blade 18.

(18) FIGS. 3 and 4 show in particular the situation in which a single blade 18 is machined from a blank.

(19) Naturally, it is also possible, for example, to machine three, four, five, or even six blades 18 from a single blank 11.

(20) It should be observed that it is also possible to obtain blanks 11 that are tubular in shape. For this purpose, a cylindrical core 19 (represented diagrammatically by a dashed line in FIG. 2) may be mounted coaxially inside each of the housings 17.

(21) FIGS. 5 and 6 thus show a blank 11 in the form of a bar of hollow cylindrical shape.

(22) In a particular implementation of the invention, the bar has a length or axial dimension lying in the range 10 centimeters (cm) to 50 cm, an outside diameter lying in the range 5 cm to 20 cm, an inside diameter lying in the range 4 cm to 10 cm, and a radial thickness lying in the range 1 cm to 10 cm.

(23) As can be seen in FIGS. 5 and 6, the tubular blank 11 is machined to make ten rotor blades 18, each blade 18 having an airfoil with its ends connected to platforms. The blades 18 are machined from the thickness of the wall of the tubular blank 11, over angular sectors 20 of the blank 11 that are arranged side by side, each being of an elongate shape extending substantially parallel to the longitudinal axis X of the blank (the sectors 20 are defined by dashed lines in FIG. 6).

(24) The wall of the blank 11 may be of thickness that varies along the longitudinal axis X (cf. FIG. 6).

(25) At the end of machining, the blades are inspected (step 6 in FIG. 1) using non-destructive inspection methods (radio, penetrant inspection, dimensional checking).