Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C21/00—Flasks; Accessories therefor
  • B22C21/12—Accessories
  • B22C21/14—Accessories for reinforcing or securing moulding materials or cores, e.g. gaggers, chaplets, pins, bars
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C7/00—Patterns; Manufacture thereof so far as not provided for in other classes
  • B22C7/02—Lost patterns
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/02—Sand moulds or like moulds for shaped castings
  • B22C9/04—Use of lost patterns
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/12—Treating moulds or cores, e.g. drying, hardening
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/22—Moulds for peculiarly-shaped castings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
  • B22D27/045—Directionally solidified castings

Definitions

• the present invention relates to the field of metal parts, such as turbomachine blades obtained by casting metal in a shell mold and is directed to a method of manufacturing these parts with columnar or monocrystalline directed solidification.
• the process for manufacturing metal parts by lost-wax foundry comprises a succession of steps recalled below.
• Models of the parts to be manufactured are first elaborated in wax or in another temporary material. If necessary the models are gathered in a cluster around a central drum also in wax.
• a shell of ceramic material is then formed on the models, thus assembled, by successive dipping in slip of suitable composition comprising particles of ceramic materials suspended in a liquid, alternated with dusting refractory sand.
• the wax model is then removed while consolidating by heating the shell mold thus formed.
• the next step is to cast a metal alloy, especially a nickel superalloy, melt in the shell mold and then cool the parts obtained so as to direct the solidification according to the desired crystalline structure. After solidification, the shell is removed by shaking to extract the pieces. Finally, the finishing steps are carried out to eliminate excess material.
• the cooling and solidification step is therefore controlled. Since the solidification of the metal alloy is the transition from the liquid phase to the solid phase, the directed solidification consists of advancing the growth of "seeds" in the molten metal bath in a given direction, avoiding the appearance of seeds. new by controlling the thermal gradient and the solidification rate. Directed solidification may be columnar or monocrystalline. Columnar directed solidification consists of orienting all grain boundaries in the same direction so that they do not contribute to the propagation of cracks. Monocrystalline direct solidification consists of completely removing the grain boundaries.
• the monocrystalline directed solidification further comprises the interposition between the molding and the cooled sole, either of a baffle or grain selector, or of a monocrystalline seed; the thermal gradient and the rate of solidification are controlled in such a way that no new seeds are created before solidification front. The result is a monocrystalline casting after cooling.
• weights are used, in order to eliminate the porosity defects in end zones of parts to manufacture.
• surplus volumes are expected when wax models are made, which are placed against the zones of the parts which are likely to have porosity defects after solidification.
• the weights are the reserves of solidified metal that fill the extra volumes in the shell. The porosity defects, when they occur, are then displaced in the flyweights and are no longer located in the parts manufactured themselves. Then, once the metal solidified and cooled, the weights are removed during a part finishing operation, for example by machining, by cutting or by grinding.
• the ceramic cores for the turbomachine blades comprise, according to a known method of manufacture, two bearing surfaces or lugs, one at each longitudinal end.
• the models are prepared in such a way that embedding or anchoring of the ceramic core is defined at the region of the foot of the core in the upper part of the mold. Indeed according to this technique the nucleus and the model in wax are mounted foot up and the top down. Thus after the ceramic molding operations, the formed ceramic shell blocks the core in this area.
• the molten metal fills the impression released by the wax that has been removed beforehand. The molten metal occupies the space between the core and the wall of the carapace.
• the solidification is then operated by drawing up and down the hearth of the furnace on which is placed the shell, the solidification progresses from the starter in which several metal grains solidify then successively in the top of the blade, the blade and the foot.
• the core is then held at both ends and is forced into compression. It follows a deformation of the core by buckling.
• the core no longer respects its theoretical position and defects may appear on the part: thicknesses of metal wall may not be respected, or the core under the effect of the constraints of the two embeddings at both ends perforates the metal wall of dawn by buckling. In both cases the part must be scrapped.
• the positioning of the embedding at the onset of solidification has the disadvantage of disturbing the nascent solidification front with the risk of generating parasitic grains or disorientation.
• there is in the case of the single crystal a risk of failure to glue up the rising edges on either side of the embedding zone.
• the invention therefore relates to a method of manufacturing a part that overcomes the problems presented above.
• the process for the production by lost-wax casting of a nickel-alloy metal part with a columnar or monocrystalline structure with at least one elongated cavity, comprising the following steps of producing a a wax model of the part with a ceramic core corresponding to said cavity, the ceramic core having a first holding surface at one longitudinal end and a second holding surface at the opposite end,
• the mold comprising a base and the first range of the core being on the side of the base,
• the core is secured to the shell mold by means of anchoring between the first bearing of the core and the wall of the mold, the second bearing of the core being retained in the mold by a holding means sliding on the wall of the mold.
• the solution of the invention avoids deformation of the core during the progression of the directed solidification because the core is not retained by anchoring at both ends. It is thus not put in compression by the constraints which would result from the difference of the coefficients of expansion between the mold and the core. There is also no risk of parasitic grain generation or defects in the main grain.
• the solution of the invention also ensures the position of the core during the entire phase of manufacture of the piece: from the wax model to the casting and the solidification of the piece.
• the anchoring means comprises a rod, more particularly refractory ceramic, for example alumina, passing through the first litter and the wall of the mold.
• the ceramic rod is of small diameter of the order of one millimeter. The rod passes through the wax model and the core which were previously drilled to a diameter slightly greater than that of the rod to prevent stresses being generated at this level.
• the sliding holding means is formed by a space formed between the bearing surface and the wall of the mold, this space is obtained by means of a film of expansion varnish deposited on the surface of the bearing surface. realization of the model. This is then removed during the mold dewaxing operation.
• This is for example a nail varnish type material to obtain thicknesses of a few hundredths of a millimeter per layer.
• a varnish suitable for this application includes solvents, resin, nitrocellulose and plasticizers.
• a varnish such as "Thixotropic base” marketed under the trade name: "Peggy Sage Nail Polish All Formulas" can be used in the process of the present invention.
• This film is more precisely interposed between the second surface and the wall of the mold. It is applied, before the formation of the carapace mold, on the surfaces of the second reach which are parallel to the direction of the progression of the cooling; that is to say in the case of a mobile hearth, parallel to the direction of draft of the movable hearth.
• This film of varnish is preferably thin in the order of 3 to 5 hundredths of a millimeter. Its purpose is to avoid, on the one hand, that the wall of the mold comes to stick to the core in this zone and, on the other hand, to create a free space, after dewaxing, of small thickness allowing the longitudinal guidance of the second bearing relative to mold and avoiding the mold to exert stress on the core.
• the surfaces of the second span which are not parallel to the axis of the progression of solidification, axis of pull, are initially covered by a wax deposit so as to provide, after dewaxing, a space between said surfaces of the second range and the wall of the mold.
• This space prevents, during molten metal casting, the contact between the wall of the shell and the second range of the core, and prevents stressing of the core in this area during solidification.
• the thickness of this wax deposit is of the order of millimeter for pieces having a length of 100 to 200 mm or about 1% of the length of the piece.
• the process allows the simultaneous manufacture of several pieces.
• the models of said parts are in this case gathered in a cluster inside a carapace mold.
• the method is applicable to the manufacture of at least one metal part with a columnar structure, a means of germination of the crystalline structure being formed between the mold and the hearth of the furnace.
• the method applies to the manufacture of at least one piece with a monocrystalline structure, a grain selector being formed between the germination element and the mold.
• the invention applies in particular to the manufacture of a turbomachine blade, the first scope being in line with the top of the blade of the blade, the second scope being in the extension of the root of the blade.
• the method advantageously uses an oven whose sole is vertically movable between a hot zone where the metal is melted is a cold zone of solidification of the metal, the sole being itself cooled.
• FIG. 1 represents a turbomachine blade that can be obtained according to the method of the invention
• Figure 2 schematically shows a ceramic core for turbomachine blade
• Figure 3 shows the core of Figure 2 seen in profile.
• Figure 4 schematically shows a wax model with the core of Figure 2;
• Figure 5 shows the carapace mold seen in longitudinal section through the core
• Figure 6 shows an example of a furnace for directed solidification of cast metal in a shell mold
• Figure 7 is an enlarged view of the upper end of the shell mold shown in Figure 5.
• the present invention relates to a method of manufacturing metal parts made of nickel-based alloy, which, by suitable directional solidification, makes it possible to obtain a columnar or monocrystalline crystalline structure.
• the invention relates more particularly to the manufacture of turbomachine blades such as that shown in Figure 1; a blade 1 comprises a blade 2, a foot 5 allowing its attachment to a turbine disk, and a vertex 7 with a bead if appropriate. Due to the operating temperatures of the turbomachine, the blades are provided with an internal cooling circuit traversed by a cooling fluid, generally air. A platform 6 between the foot and the blade constitutes a portion of the radially inner wall of the gas stream.
• the piece shown here is a moving blade but the invention also applies to a dispenser or to any other piece having a core.
• Figures 2 and 3 show schematically a simplified shaped core, ceramic, used to spare the internal cavities of a turbomachine blade.
• the elongated core 10 comprises a branch or a plurality of branches 1 1 separated by spaces 12 for, after the casting of the metal, forming the partitions between the cavities; in the example shown, the core comprises two branches 1 1 separated by a space 12.
• the core is extended by a span or lug 14 whose function is to maintain the core during the manufacture of the part but which does not does not necessarily correspond to a part of the room, once it is completed.
• the core includes a second span 16 for also maintaining the core during the manufacturing steps. It is observed in Figure 3 that the core as shown is relatively thin in relation to its length. It is understood that the more the core is fine compared to its more sensitive length it will be buckling.
• FIG. 4 shows schematically this model 20 in wax with the core 10 in dashed lines.
• the model extends at a first end 24 in the extension of the blade so as to cover the bearing surface 14 and at the opposite end 26, at the level of the foot.
• a portion 16A of the scope 16 is not covered with wax.
• This portion 16A comprises surfaces parallel to the axis of the core and is coated with a varnish whose function is explained below.
• the models are usually clustered together to make multiple parts simultaneously.
• the models are for example arranged in a drum parallel to a vertical central cylinder and held by the ends.
• the lower part is mounted on an element intended to ensure the germination of the crystalline structure.
• the next step is to form a shell mold around the model or models.
• the assembly is soaked in slips so as to deposit in successive layers the refractory ceramic particles.
• the mold is finally consolidated by heating and the wax removed by the dewaxing operation.
• FIG. 5 shows diagrammatically, in longitudinal section, the arrangement of the invention between the core 10 and the shell 30 at the level of a single model 20.
• the first surface 14 is held in the mold 30 by a refractory ceramic rod 40, which passes through it and extends into the wall of the mold 30 being embedded therein.
• the rod 40 has been put in place before the shell mold is made, after the model has been drilled at the level of the bearing surface 14.
• the hole is of diameter slightly greater than that of the stem so that it is not created. constraints between the rod and the bearing and that the rod ensures correct positioning of the core in the model.
• the second bearing 16 opposite to the first, is initially coated with a layer of varnish 17 on the portion 16A of the core which is not covered with wax and which after constitution of the shell mold comes into direct contact with the inner wall of the mold. After dewaxing the mold, as seen in FIG. 5, the layer having disappeared leaves a free space between the bearing surface 16 of the core and the wall of the shell mold. Reference 17 designates this free space left by the varnish layer. This space 17 is thin, 3 to 5 hundredths of a millimeter. It forms a sliding support means of the second bearing 16 on the wall of the shell 30.
• the surfaces - here the horizontal surface 16B - which are not parallel to the axis of the progression of the solidification are initially covered by a deposit of wax 18.
• This deposit of wax leaves after dewaxing a free space, likewise reference 18, which prevents the scope 16 of the core from coming into contact with the wall of the shell when the core expands, thereby avoiding the stressing of the core.
• the thickness of this wax deposit is of the order of one millimeter for pieces having a length of 100 to 200 mm or about 1% of the length of the piece.
• the core is not likely to flare up and the initial wall thicknesses of the part between the mold wall and the core are retained.
• FIG. 5 shows, in section along the part, the shell mold 30 and the core 10 inside the mold with the branches 1 1, the bearing surfaces 14 and 16.
• the section of the core is made according to the line VV of FIG. FIG. 4.
• the volume 30 'corresponds to the wax of the model or, after solidification of the shell, to the space between the wall of the mold and the core to be filled by the metal.
• the rod 40 passes through the first bearing 14; it is long enough to be anchored in the walls of the shell mold 30. In this way, the core 10 is positioned inside the shell mold 30.
• the mold is placed on the floor of a furnace equipped for directed solidification.
• a furnace equipped for directed solidification.
• Such an oven 100 is shown in Figure 6. It shows an enclosure 101 provided with heating elements 102.
• An orifice 103 The molten metal supply unit communicates with a crucible 104 which contains the molten metal charge and which, when tilted, fills the shell mold 30 disposed on the hearth 105 of the furnace.
• the sole is movable vertically, see the arrow, and is cooled by the circulation of water in a circuit 106 internal to its tray.
• the mold rests with its base on the cooled sole.
• the lower part of the mold is opened on the sole by means of a germination member.
• the method of manufacture comprises pouring the molten metal from crucible 104 directly into the mold 30 which is maintained at a temperature sufficient to retain the molten metal, by means of heating 102 of the chamber 101 and where it fills the voids 30 'between the core 10 and the wall of the mold 30.
• the metal solidifies forming a crystalline structure that spreads from below upwards.
• Sole 105 is cooled continuously and gradually descended from the heated enclosure. In the case of a monocrystalline structure a grain selector is interposed between germination and solidification as is known per se.
• the core is held by anchoring the first bearing 14 in the only lower zone of initialization of the solidification.
• the core is free to expand differentially in the direction of its length relative to the carapace 30 because at the opposite end of the first scope, the second bearing 16 is guided along the wall of the mold thanks to the free space 17 left by the layer of varnish, eliminated during the dewaxing of the mold.
• the surfaces of the second span 16 - here the horizontal surface 16B - which are not parallel to the axis of the progression of the solidification, thanks to the free space 18 formed by the wax deposit do not come into contact with the wall of the carapace. This prevents the stressing of the core.
• the thickness of this space corresponding to the wax deposit is of the order of one millimeter for pieces having a length of 100 to 200 mm or about 1% of the length of the piece.
• the mold is broken and the parts that are directed to the finishing shop are extracted.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

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Citations (3)

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• 2013
  • 2013-01-17 FR FR1350424A patent/FR3000910B1/fr active Active
• 2014
  • 2014-01-13 BR BR112015016771A patent/BR112015016771B1/pt active IP Right Grant
  • 2014-01-13 CN CN201480004729.4A patent/CN104918731B/zh active Active
  • 2014-01-13 US US14/760,559 patent/US10717128B2/en active Active
  • 2014-01-13 WO PCT/FR2014/050061 patent/WO2014111648A1/fr not_active Ceased
  • 2014-01-13 CA CA2897680A patent/CA2897680C/fr active Active
  • 2014-01-13 JP JP2015553146A patent/JP6342427B2/ja active Active
  • 2014-01-13 RU RU2015128268A patent/RU2652526C2/ru active
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