Cast iron blade with modified back edge geometry

Description

Background of the invention

[0001] The present invention relates to the general field of turbomachine turbine blades, and more particularly to as-cast turbine blades produced by the lost-wax casting technique.

[0002] As is well known, a turbomachine has a combustion chamber in which air and fuel are mixed before being burned. The gases from this combustion flow downstream of the combustion chamber and then power a high-pressure turbine and a low-pressure turbine. Each turbine has one or more rows of fixed blades (called distributors) alternating with one or more rows of moving blades (called runners), spaced circumferentially around the turbine rotor.

[0003] There figure 4Apartly illustrates a conventional distributor structure currently equipping many aircraft engines and comprising a plurality of fixed blades (e.g. US20150218962).

[0004] Each of these blades 10 comprises an aerodynamic profile or blade inserted between an external platform 14 uniting the blade tips and an internal platform 16 uniting the blade tips. Each blade has a leading edge 18 and a trailing edge 20 opposite each other and intrados 22 and extrados 24 walls extending radially between a blade tip and a blade tip in a blade elongation direction XX', which elongation direction is perpendicular to the longitudinal central axis (not shown) of the turbomachine.

[0005] There figure 4Billustrates a conventional hollow moving blade 30 for a gas turbine comprising an aerodynamic profile or blade having a leading edge 32 and a trailing edge 34 opposed to each other and connected by an intrados wall 36 and an extrados wall 38 extending radially between a blade root 40 and a blade tip 42 in the direction XX' of blade extension.

[0006] It is known that the trailing edge of such fixed or moving blades is a key dimensional characteristic for the aerodynamic performance of the turbine and engine. Therefore, to reduce engine fuel consumption, a known solution is to increase the turbine's aerodynamic performance by thinning the trailing edge of these blades.

[0007] Currently, turbine blades are primarily manufactured using the lost-wax casting technique. Given the desired thinness of the aerodynamic profile, this casting technique alone cannot produce blades with a fine trailing edge. Therefore, an additional polishing step is required to mechanically refine the trailing edge and thus thin it. Unfortunately, it has become apparent that this additional material removal step from the as-cast blade does not allow for maintaining the final shape of the aerodynamic profile and its dimensional tolerances. Indeed, polishing a thin surface generates heat and then local deformation of the aerodynamic profile, whose shape is no longer preserved, whether in terms of tangency or trailing edge radius. This, in turn, leads to a degradation of turbine performance, the opposite of what is desired. Subject matter and summary of the invention

[0008] The present invention therefore aims to overcome the disadvantages linked to the deformation of the trailing edge during the polishing of the trailing edge by proposing a modification of the blade manufacturing process by lost wax casting which does not generate dimensional non-conformities and allows the desired shape for the aerodynamic profile to be respected.

[0009] To this end, the invention relates to a rough casting of a turbomachine blade produced according to the lost-wax technique, the blade comprising a blade having a leading edge and a trailing edge opposite each other and connected by an intrados wall and an extrados wall extending between a blade root and a blade tip, characterized in that, in order to produce on said blade a thin trailing edge which is not deformed by a subsequent material removal operation, said rough casting of said blade comprises on an extrados wall and / or on an intrados wall of said blade intended to form respectively said extrados wall and / or said intrados wall of the blade, an excess casting extending from a trailing edge of said blade intended to form said trailing edge of the blade over a determined width in the direction of a leading edge of said blade intended to form said leading edge of the blade,with the exception of a reserved area extending in width along the chord length of the blade between said trailing edge of the blade and the casting overhang, and over at least part of the height of the blade.

[0010] Thus, by locally thickening the profile of the as-cast blade, the casting process proves to be more robust at the trailing edge and can therefore withstand subsequent material removal such as polishing without risk of blade deformation.

[0011] According to the envisaged embodiment, the said casting over-thickness is carried out over the entire height of the blade.

[0012] Preferably, said casting overthickness has a variable thickness which varies decreasingly over said determined width between a first value equal to zero and a second value between half and one time a desired thickness e for the blade and determined at a predetermined distance d from said trailing edge of the blade.

[0013] Advantageously, said first value is determined at the level of a first junction line, parallel to said trailing edge of the blade and constituting a line of tangency between said casting overthickness and said extrados wall of the blade, and said second value is determined at the level of a second junction line also parallel to the trailing edge of the blade and delimiting said reserved area.

[0014] Preferably, said casting overthickness joins said extrados wall of the blade at the level of a first edge along said line of tangency and at the level of second, third and fourth edges by sloping connections.

[0015] Advantageously, these sloping connections each have a slope between 20° and 50°.

[0016] Preferably, said line of tangency is parallel to said trailing edge and located at a distance from said trailing edge of the blade equal to 40 to 60% of a length L of the aubag rope.

[0017] The invention also relates to a method for manufacturing a turbomachine blade produced according to the lost-wax casting technique, the blade comprising a hollow blade having a leading edge and a trailing edge opposite each other and connected by an intrados wall and an extrados wall extending between a blade root and a blade tip, the method being characterized in that, to produce by casting a blade with a thin trailing edge, it comprises on the one hand a step comprising the production of a rough casting with a casting over-thickness of variable thickness at the level of an extrados wall and / or an intrados wall of said blade intended to form respectively said extrados wall and / or said intrados wall of the blade and extending from a trailing edge of said blade intended to form said trailing edge of the blade and towards a leading edge of the blade intended to form said leading edge of the blade,with the exception of a reserved area extending in width along the chord length of the blade between said trailing edge of the blade and the casting overhang, and on the other hand a subsequent material removal step from this casting overhang.

[0018] Preferably, the said casting over-thickness is carried out over all or part of the height of the blade.

[0019] Advantageously, the said material removal operation is a polishing.

[0020] The invention also relates to a turbomachine comprising a blade manufactured according to the aforementioned manufacturing process. Brief description of the drawings

[0021] Other features and advantages of the present invention will become apparent from the description given below, with reference to the accompanying drawings which illustrate an example of an embodiment without being limiting in any way and on which: there figure 1illustrates the aerodynamic profile of a turbine blade according to the invention, the figure 2 is a partial cross-sectional view of the dawn of the figure 1 at the trailing edge, the figure 3 is a partial elevation view of the dawn of the figure 1 at the level of the extrados wall, and the Figures 4A and 4B are perspective views of a portion of a prior art distributor showing a plurality of fixed blades and a moving prior art turbine blade, respectively. Detailed description of implementation methods

[0022] THE figures 1 and 2These represent an aerodynamic profile or blade of a rough casting intended to form a turbine blade, comprising a leading edge 18 and a trailing edge 20 opposite each other and connected by an intrados wall 22 and an extrados wall 24 extending between a blade root and a blade tip. For clarity in the following description, the elements of the rough casting bear the same numbers as those of the finished blade, to within a factor of 10. Thus, the leading edge of the finished blade 18 corresponds to a leading edge of the rough blade 180, the trailing edge of the finished blade 20 corresponds to a trailing edge of the rough blade 200, the intrados wall of the finished blade 22 corresponds to an intrados wall of the rough blade 220 and the extrados wall of the finished blade 24 corresponds to an extrados wall of the rough blade 240.

[0023] According to the invention, to enable the production of a thin trailing edge on the finished blade, i.e., one whose thickness measured 1 mm from the tip of this trailing edge is between 0.2 mm and 0.5 mm, it is proposed during the casting operation to locally thicken the aerodynamic profile of the as-cast blade, i.e., to add to this casting pattern a casting thickness 210 over a determined width of the intrados wall 220 and / or the extrados wall 240 extending from the trailing edge 200 towards the leading edge 180, with the exception, however, of a defined reserved area 250 adjacent to this trailing edge 200 and at least one radius of the trailing edge, but over all or part of the height of the blade, so that this trailing edge is not modified and therefore is not impacted, in particular not deformed by the material removal operation such as polishing which will follow this casting operation.In order not to penalize aerodynamic performance and to simplify tooling, the casting over-thickness is advantageously placed on the extrados wall of the raw 240 blade.

[0024] It should be noted that the 1mm value at the trailing edge tip is a predetermined threshold for measuring and adjusting the trailing edge thickness while maintaining a safety margin at this tip. Indeed, insufficiently controlled machining of the trailing edge could damage the tip and thus shorten the chord length. L of the blade, which would have a significant impact on aerodynamic performance.

[0025] This casting overstud 210, which is approximately rectangular in shape, has a variable thickness over the determined width, decreasing from a first value of zero (h = 0) present on the extrados wall 240 at the level of a first junction line 260 forming a first edge of this casting overstud, parallel to the trailing edge 200, to a second value between half and one time the thickness of the blade. edesired (0.4e <h< e), la surépaisseur de fonderie rejoignant la paroi extrados 240 par une liaison en pente 210a (idéalement comprise entre 20° et 50° de sorte à être suffisamment importante pour augmenter le bord de fuite sans nuire à l'injection de la cire et la coulabilité du métal) au niveau d'une seconde ligne de jonction 280 délimitant la zone réservée 250, également parallèle au bord de fuite 200 et formant un deuxième bord opposé au premier. Cela permet de rendre plus robuste l'opération de fonderie et l'opération de retrait matière est facilitée car le rayon du bord de fuite reste brut de fonderie. L'épaisseur désirée e de l'aube est définie à une distance d predetermined trailing edge 20 of this blade. Thus, as specified in the previous paragraph, taking for the distance d a value of 1 mm, for a thickness e For a desired trailing edge of 0.5 mm, a person skilled in the art will choose a casting over-thickness hbetween 0.2 mm and 0.5 mm.

[0026] If we consider L the rope length of the blade, then the first joining line 260 is preferably located at a distance from the trailing edge 200 equal to 40 to 60% of this length L Thus, a person skilled in the art would choose, for example, a distance of 10 mm to 15 mm for a rope length of 25 mm. Furthermore, to avoid any bump and obtain the desired zero thickness, this first joining line must form a line of tangency between the two tangent surfaces formed by the outer face of the casting overhang and the outer face of the extrados wall.

[0027] Similarly, the second joining line 280, defining the end of the reserved area 250, must be far enough from the trailing edge to avoid deformation of this edge, but also relatively close so as not to negatively impact the lost-wax casting process. Indeed, if this second joining line 280 is too close to the trailing edge 200, then the aerodynamic profile will be deformed during the material removal operation because the machined strip will be too close to this desired thin trailing edge. Positioning the second joining line too far from the trailing edge would be equivalent to creating this thin trailing edge directly from the casting, with the aforementioned drawbacks. Thus, a person skilled in the art will choose a distance between the trailing edge 200 and this second junction line 280 which should preferably be between 0.5 mm and 1 mm, that is to say of the order of 2 to 4 times the radius of the trailing edge which can be estimated at 0.25 mm for a thickness of 0.5 mm.

[0028] There figure 3 This illustrates more precisely the casting overhang 210 which extends over the extrados wall 240 of the rough blade, parallel to the trailing edge 200, between the first 260 and second 280 junction lines. In the perpendicular plane, along the height of the blade, this casting overhang also presents junctions with the extrados wall 240 forming third and fourth edges opposite each other and defining towards the blade tip a sloping joint 210b and towards the blade root a sloping joint 210c.

[0029] The manufacturing process for a turbine blade according to the invention, carried out using the lost-wax casting technique, does not differ from the conventional process in that it requires the creation of a wax model and a ceramic mold. The metal constituting the blade is poured in place of the wax previously placed in the mold, which is then liquefied by heating before the blade is removed from the mold. The only difference lies in the fabrication of the wax model, which therefore includes a casting overhang of variable thickness on the upper surface of the blade. This overhang is designed to facilitate the casting of a thin trailing edge (whose radius thus remains as cast) and is removed by a subsequent material removal operation such as polishing.

[0030] This modification of the aerodynamic profile of the as-cast blade by adding a casting over-thickness opens the way to a new industrialization process to obtain thin trailing edges with the lowest possible aerodynamic impact on this polishing operation.

Claims

1. A rough cast blading of a turbomachine blade produced according to the lost-wax casting technique, the blade (10) including an airfoil having a leading edge (18) and a trailing edge (20) opposite each other and connected by a pressure sidewall (22) and a suction sidewall (24) extending between a blade root and a blade tip, characterized in that, in order to produce on said blade a thin trailing edge which is not deformed by a subsequent material removal operation, said rough cast blading of said blade includes on a suction sidewall (240) and / or on a pressure sidewall (220) of said blading intended to respectively form said suction sidewall and / or said pressure sidewall of the blade, a casting allowance (210) extending from a trailing edge of said blading (200) intended to form said trailing edge of the blade over a determined width in the direction of a leading edge of said blading (180) intended to form said leading edge of the blade, except for a reserved area (250) extending in width according to the chord length of said blade between said trailing edge of the blading and the casting allowance (210) and over at least part of the height of the blading.

2. The rough cast blading according to claim 1, characterized in that said casting allowance is made over the entire height of the blading.

3. The rough cast blading according to claim 1 or 2, characterized in that said casting allowance has a variable thickness which decreasingly varies over said determined width between a first value equal to zero and a second value comprised between a half and once the thickness e desired for the blade and determined at a predetermined distance d from said trailing edge of the blade.

4. The rough cast blading according to claim 3, characterized in that said first value is determined at a first junction line (260), parallel to said trailing edge of the blading and constituting a line of tangency between said casting allowance and said suction sidewall of the blading, and said second value is determined at a second junction line (280) also parallel to the trailing edge of the blading and delimiting said reserved area.

5. The rough cast blading according to claim 4, characterized in that said casting allowance joins said suction sidewall of the blading at a first edge along the said line of tangency and at second, third and fourth edges.

6. The rough cast blading according to claim 5, characterized in that said sloping connections each include a slope comprised between 20° and 50°.

7. The rough cast blading according to any one of claims 1 to 6, characterized in that said line of tangency is parallel to said trailing edge of the blading and located at a distance from said trailing edge of the blading equal to 40 to 60% of a chord length L of the blading.

8. A method for manufacturing a turbomachine blade produced according to the lost-wax casting technique, the blade (10) including an airfoil having a leading edge (18) and a trailing edge (20) opposite each other and connected by a pressure sidewall (22) and a suction sidewall (24) extending between a blade root and a blade tip, the method being characterized in that, in order to produce by casting a blade with a thin trailing edge, it comprises on the one hand a step including the production of a rough cast blading with a casting allowance (210) of variable thickness at a suction sidewall (240) and / or a pressure sidewall (220) of said blading intended to form respectively said suction sidewall and / or said pressure sidewall of the blade and extending from a trailing edge of said blading (200) intended to form said trailing edge of the blade and in the direction of a leading edge (180) of said blading intended to form said leading edge of the blade, except for a reserved area (250) extending in width according to chord length between said trailing edge of the blading and the casting allowance (21) and on the other hand a step of subsequent material removal of this casting allowance.

9. The manufacturing method according to claim 8, characterized in that said casting allowance is made over all or part of the height of the blading.

10. The manufacturing method according to claim 8 or 9, characterized in that said material removal operation is a polishing.

11. A turbomachine including a blade manufactured according to the manufacturing method of claims 8 to 10.