Turbomachine blade machining process

Background of the invention

The present invention relates to the general field of gas turbines for aircraft engines or helicopters and more particularly relates to a blade manufacturing process for minimizing stresses and its mass during its machining.

In a manner known per se, the blades are particularly complex parts whose manufacture according to a long and expensive foundry process proves tricky, in particular because of the manufacturing tolerances required.

A casting because of dimensional tolerances of the order of a millimeter and its surface condition is rarely a directly usable part. It must therefore at least partly be machined (typically on a CNC machining center), which requires the use of a geometric reference specific to this machining. However, to perform these machining operations, it is necessary to choose a part positioning system in the machining center that is optimal and ensure the accuracy required while allowing easy control. This positioning system must also respect the principle of isostatism, that is to say, it must allow to position unambiguously the room in space, usually at 6 points of support judiciously distributed, so especially to maximize the distance between them. These points of support that will remain once the machined part are in practice not punctual but small finite dimensions, however sufficient to get closer to the ideal punctual case. A device for holding a blade during the machining of its foot is disclosed in <patcit id="pcit0001" dnum="FR2956996"><text>FR 2956 996</text></patcit>.

However, mobile blades of turbines, for example, are generally small in size so that there is a difficulty in maximizing the distances between the fulcrums and all the more so that these important support points. non-zero generate an additional mass.

Obiet and summary of the invention

The main purpose of the present invention is thus to overcome such drawbacks by proposing a blade machining method which makes it possible to significantly reduce the concentrations of mechanical stresses while ensuring a gain in mass.

This object is achieved by a machining process in a three-dimensional machining center of a blade comprising an aerodynamic blade, a platform under the upstream and downstream parts of which are formed supports for a sealing liner, a foot dawn and a stilt interposed between said platform and said blade root, characterized in that said supports also constitute two points of support for a positioning system at 6 points of said blade in said three-dimensional machining center.

This combination of the support and fulcrum function makes it possible by limiting the mechanical stress concentrations on the blade to simplify the machining range and to obtain in addition the desired mass gain.

According to an advantageous arrangement, said support points are formed on the extrados side of said stilt.

Brief description of the drawings

Other features and advantages of the present invention will emerge from the description given below, with reference to the single appended figure which illustrates an embodiment having no limiting character.

Detailed description of embodiments

The single figure shows in elevation a turbine engine blade, for example a fan, a turbine or a compressor, fixed in a known manner on the periphery of a turbomachine rotor disk (not shown) and typically comprising a separate platform 12. from it by a stilt 14, a blade root 16 fir-shaped or dovetail being housed in a groove or corresponding cell (not shown) around the rotor disc.

The stilt 14 has a reduced thickness relative to the blade root 16 to cross the opening defined by the groove and allow the mechanical connection between the foot and the aerodynamic portion (or blade 18) of the blade. Under the platform are conventionally arranged, respectively upstream and downstream (with respect to the flow of air passing through the blades), supports 12A, 12B for a sealing jacket 20.

In order to allow the machining of such a blade, it is necessary to define reference faces which will be the starting faces for the dimensioning of the part and the points of support which will serve as a point of reference for this machining and for the subsequent control of the room. Conventionally these support points distributed around the workpiece are six in number and are part of a positioning system in 6 points for machining the workpiece in a three-dimensional machining center.

According to the invention, the lateral face of the stilt 14 on the extrados side is chosen as the reference face and the upstream and downstream supports of the sealing sleeve are also used as bearing points 22A, 22B for the positioning system at 6 points of the dawn in the three-dimensional machining center, the other four points of support being distributed on the other faces of the blade. With this configuration, these two support points are relatively close to the edge of the stilt maximizing the spacing between them. The stress concentrations resulting from the abundance of low value shelving already present at the base of the supports of the sealing liner 20 are thus not increased because of the combination of these shelves with those resulting from the supports and the overall mass of the lining. dawn is further reduced by the coincidence of the support and support functions combined at these two points.