Casting mold, method for manufacturing the mold, and casting method

Abstract

The present invention relates to the field of casting, and more specifically to a casting mold (1), which includes at least one molding cavity (2) and a pair of supply arms. The molding cavity (2) extends along a horizontal axis (X) from a first end (2a) to a second end (2b), and the first pair of supply arms includes a first supply arm (3) that extends in a substantially vertical direction and is connected to the first end (2a) of the first molding cavity (2), and a second supply arm (4) that is substantially parallel to the first supply arm (3) and is connected to the second end (2b) of the first molding cavity (2). The present invention also relates to a method for manufacturing a mold (1) and a casting method using the mold (1).

Description

Field of the Invention

[0001] The present invention relates to the field of metal casting. In this context, the meaning of "metal" is pure metals and metal alloys. Prior Art

[0002] For known casting methods, which include pouring liquid metal into a forming cavity through a gate leading to one end of the forming cavity and then cooling and solidifying the metal in the forming cavity in at least one step before demolding and solidifying the metal, defects may be encountered, especially during the manufacture of components with particularly thin parts (such as the trailing edge of a turbine engine blade). In fact, during the cooling of the metal in the mold, the different shrinkage rates of the metal and the mold material can generate mechanical stresses until defects, especially cracks, appear in the solidified metal.

[0003] In particular, when the component to be formed has a central part that is narrower compared to its ends, as is typically the case for a turbine engine blade that extends along the main axis from the blade root to the blade tip, the mold can hold these ends during the cooling and shrinkage of the solidified metal. This then creates tensions in the component that can generate cracks and local recrystallization, especially in the transition region between the ends and the central part of the component. Between the end connected to the gate and the opposite closed end, this phenomenon can be further exacerbated by the temperature gradient along the forming cavity. Summary of the Invention

[0004] The present invention seeks to remedy these drawbacks by proposing a casting mold that will allow reducing the crack and recrystallization phenomena that occur due to the internal tensions resulting from the difference in the thermal shrinkage rates of the metal and the mold during the cooling of the metal in the mold.

[0005] To this end, according to a first aspect, the mold may include at least one first forming cavity extending from a first end to a second end along a horizontal main axis, and a first pair of feeder arms. The first feeder arm of the first pair of feeder arms may be oriented and connected to the first end of the first forming cavity together with the main axis in a substantially vertical direction, while the main axis of the second feeder arm of the first pair of feeder arms may be substantially parallel to the first feeder arm and connected to the second end of the first forming cavity. The mold may be constructed such that any cross-section of the first and second feeder arms of the first pair of feeder arms perpendicular to the vertical axis has a larger area compared to any cross-section of the forming cavity perpendicular to the horizontal axis.

[0006] Since a feeder arm is arranged at each end of the forming cavity, the thermal contraction of the metal in these feeder arms will cause them to bend towards each other, which will allow the forces generated by the thermal contraction of the metal in the first forming cavity to be balanced, thus avoiding cracks and recrystallized grains that could weaken the formed part. Due to the change in the cross-sectional area of the forming cavity and the feeder arms, starting from the core of the first forming cavity with the smallest cross-section, the solidification of the metal can propagate through the cross-section with an increasing area in this direction through the two feeder arms to avoid pipe defects caused by shrinkage in the die cavity.

[0007] According to a second aspect, the die may include docking heads that connect the first and second ends of the first forming cavity to the corresponding feeder arms of the first pair of feeder arms. Each docking head has a cross-section perpendicular to the horizontal axis, the area of which is larger than any cross-section of the first forming cavity perpendicular to the horizontal axis, but smaller than any cross-section of the first and second feeder arms of the first pair of feeder arms perpendicular to the vertical axis. In addition, in the same sense, the first and second feeder arms of the first pair of feeder arms may have cross-sections perpendicular to the vertical axis, the area of which increases upward along the vertical axis.

[0008] According to a third aspect, in order to allow multiple parts to be formed simultaneously in the same die, the die may include a first row of forming cavities, which includes the first forming cavity. Each forming cavity in the first row of forming cavities extends from a first end to a corresponding second end along a corresponding horizontal axis. The first end of each forming cavity in the first row of forming cavities is connected to the first feeder arm of the first pair of feeder arms, and the second end of each forming cavity in the first row of forming cavities is connected to the second feeder arm of the first pair of feeder arms. Thus, the parts can be formed in each forming cavity in the first row of forming cavities between the feeder arms of the first pair of feeder arms. In addition, in order to avoid pipe cracks, the die may be constructed such that any cross-section of the first and second feeder arms of the first pair of feeder arms perpendicular to the vertical axis is larger than any cross-section of each of the first plurality of forming cavities perpendicular to the corresponding horizontal axis.

[0009] In addition, in order to allow even more parts to be formed simultaneously in the same die, the die may include at least one second row of forming cavities and a second pair of feeder arms. Each forming cavity in the second row of forming cavities extends from a first end to a corresponding second end along a corresponding horizontal axis. The first end of each forming cavity in the second row of forming cavities is connected to the first feeder arm of the second pair of feeder arms, and the second end of each forming cavity in the second row of forming cavities is connected to the second feeder arm of the second pair of feeder arms. In addition, in order to avoid pipe defects in the parts formed in the second row of forming cavities, the die may be constructed such that any cross-section of the first and second feeder arms of the second pair of feeder arms perpendicular to the vertical axis is also larger than any cross-section of each of the forming cavities in the second row of forming cavities perpendicular to the corresponding horizontal axis.

[0010] According to a fourth aspect, in order to ensure feeding the molding cavity with liquid metal during the pouring process, the upper end of the feeder arm can be connected to a gate, for example, through a channel for feeding liquid metal.

[0011] According to a fifth aspect, at least the first molding cavity can be configured to mold a turbine engine blade that extends along a horizontal axis from the blade tip to the blade root. Here, "turbine engine" refers to any machine in which energy transfer can occur between a fluid flow and at least one blade device (such as a compressor, pump, turbine, propeller, or even a combination of at least two of them). In order to transfer this energy between the blade device and the rotating shaft, the blade generally forms part of a rotor, which includes a lug and a plurality of blades, and each blade extends radially from the blade root to the blade tip along a respective radial direction with respect to the rotating axis of the lug. These blades are subjected to particularly high mechanical and thermal forces, and particularly at their trailing edges, they can have a particularly thin material thickness. In this field, it is particularly desirable to avoid any local defects, such as cracks, piping, or recrystallization.

[0012] According to a sixth aspect, the mold can be configured as a shell mold. A "shell mold" refers to a mold formed by refractory material particles bonded by a slurry baked around the molding cavity of the mold. The mold can particularly be formed by a plurality of stacked layers, and each stacked layer includes particles bonded by a slurry.

[0013] A seventh aspect of the present invention relates to a method for producing such a mold, including the following steps: dipping a non-permanent pattern into a slurry, dusting the non-permanent pattern with refractory material particles after impregnation to form a layer of refractory material particles coated with the slurry, removing the non-permanent pattern from the shell formed by the refractory material particles coated with the slurry, and baking the shell.

[0014] An eighth aspect of the present invention relates to a casting method, including the following steps: pouring liquid metal into such a casting mold, cooling and solidifying the metal in the mold, and demolding the solidified metal. In addition, the method can further include a step of preheating the mold in an oven before the pouring step, and holding the mold in the oven before and during the pouring step. However, it is also conceivable to perform the preheating step in a first oven and the pouring step in a second oven different from the first oven. Description of the Drawings

[0015] After reading the following detailed description of an embodiment shown by way of non-limiting examples, the present invention will be better understood, and its advantages will become more obvious. This specification refers to the accompanying drawings, in which:

[0016] Figure 1 A Figure 1 A is a first cross-sectional view of a casting mold according to an aspect of the present invention.

[0017] Figure 1 B Figure 1 B is a cross-sectional view taken perpendicular to the plane IB-IB Figure 1 of

[0018] Figure 2 A Figure 2 A is a side view of a cluster of non-permanent patterns of a mold for forming Figure 1 A and 1B,

[0019] Figure 2 B Figure 2 B is Figure 2 a front view of the A cluster,

[0020] Figure 3 A Figure 3 A shows the impregnation step in the mold manufacturing method starting from the cluster of Figure 2 A and 2B, Figure 1 for the mold of A and 1B,

[0021] Figure 3 B Figure 3 B shows the dust removal step in the mold manufacturing method starting from the cluster of Figure 2 A and 2B, Figure 1 for the mold of A and 1B,

[0022] Figure 3 C Figure 3 C shows the baking step in the mold manufacturing method starting from the cluster of Figure 2 A and 2B, Figure 1 for the mold of A and 1B,

[0023] Figure 4 A Figure 4 A shows the preheating step in the casting method using the mold of Figure 1 A and 1B,

[0024] Figure 4 B Figure 4 B shows the pouring step in the casting method using the mold of Figure 1 A and 1B,

[0025] Figure 4 C Figure 4 C illustrates the cooling step in the casting method using the mold of Figure 1 A and 1B,

[0026] Figure 4 D Figure 4 D illustrates the demolding step in the casting method using the mold of Figure 1 A and 1B, and

[0027] Figure 5Figure 5 Shows in detail the propagation of two solidified fronts starting from the central region of the molding cavities of the molds of Figure 1 A and 1B. DETAILED DESCRIPTION

[0028] Figure 1 A and 1B illustrate a casting mold 1 according to an embodiment of the present invention. As can be seen from these figures, the mold 1 of the "shell mold" type may include a plurality of molding cavities 2. Each of these molding cavities 2 can extend along a first horizontal axis X from a first end 2a to a second end 2b in such a way that the first horizontal axis X forms its main axis and is formed to mold a turbine engine blade extending from the blade tip to the blade root along the first horizontal axis X. However, the technical teachings of the present invention are also applicable to the casting of other types of components.

[0029] The mold 1 may also include several pairs of feeder arms, each of which may include a first feeder arm 3 and a second feeder arm 4. Each of these feeder arms 3, 4 can be oriented in the direction of an axis Z that is substantially perpendicular to the respective main axis. Each pair of feeder arms 3, 4 can be associated with a row of molding cavities 2 that are offset from each other perpendicularly. Thus, in each row of molding cavities 2, the first end 2a of each molding cavity 2 can be connected to the first feeder arm 3 of the corresponding pair of feeder arms 3, 4 through a first docking head 5, and the second end 2b of each molding cavity 2 can be connected to the second feeder arm 4 of the corresponding pair of feeder arms 3, 4 through a second docking head 6. These pairs of feeder arms 3, 4 can be laterally offset from each other in the direction of a second horizontal axis Y that is substantially perpendicular to the first horizontal axis X. The molding cavities 2 can also be arranged in several rows, densely occupying the volume of the mold 1. When the molding cavities 2 are configured to form turbine engine blades, the first and second docking heads 5, 6 can correspond to the blade root and blade tip beads, respectively.

[0030] As shown, the top of the mold 1 may have a funnel-shaped feeder 7, which is connected to the top of each pair of feeder arms 3, 4 through a network of feeder channels 8.

[0031] To avoid piping defects, the Heuvers circle method described, for example, by R. Wlodawer in Directional Solidification of Steel Castings, Pergamon Press, 1966, can be employed in such a way that the area A of any cross-section Sb of the first and second feeder arms 3, 4 of each pair that is perpendicular to the vertical axis Z b is greater than the area A of any cross-section S of the corresponding row of molding cavities 2 that is perpendicular to the first horizontal axis X c . In addition, each docking head 5, 6 may have a cross-section St that is perpendicular to the horizontal axis X, and its area A tGreater than the area A of any cross-section S of the corresponding shaping cavity 2 perpendicular to the horizontal axis X c thereof c , but less than the area A of any cross-section S of the corresponding feeder arms 3, 4 of the first pair of feeder arms perpendicular to the vertical axis Z b thereof b . Furthermore, each feeder arm 3, 4 may have a cross-section Sb, the area A b of which increases upwards along the vertical axis. As Figure 1 shown in A, this can be obtained with a divergence angle α of, for example, 5 to 15° between the opposite edges of the feeder arms 3, 4. Thus, as Figure 5 shown, the metal solidification that can be triggered within each shaping cavity 2 where the cross-section is narrowest will be able to extend up to the feeder arms 3, 4 with two opposite and continuously increasing solidification fronts 10, 11, thus avoiding possible pipe defects due to shrinkage of the die shaping cavity.

[0032] Moreover, in order to limit the stress transmitted by the die 1 to the metal solidifying in the shaping cavity 2 at the locations where the metal is thinnest (e.g., the trailing edge of a turbine engine blade), it is conceivable that these walls of the die 1 are thinner at these locations compared to other locations of the die 1.

[0033] The first step of the manufacturing method of the die 1 may be to create a non-permanent cluster 21 containing a plurality of patterns 22, as Figure 2 shown in A and 2B. The parts of the cluster 21 for forming hollow volumes in the die 1, such as the patterns 22 for forming the shaping cavities 2, the vertical arms 23 for forming the feeder arms 3, 4, the cone 24 for forming the gate 7, and the connection 25 connecting the cone 24 and the feeder arms 3, 4 to form the feeder channels 8, may be formed of a material with a low melting temperature (such as wax or molding resin). When considering the production of a large number of parts, these elements can be manufactured in particular by spraying wax or molding resin into a permanent die. In the illustrated embodiment for producing turbine engine blades, the patterns 22 show such blades oriented horizontally.

[0034] The non-permanent cluster 21 may also include refractory elements to ensure its structural integrity, such as drop devices (not shown). These drop devices may be positioned on the sides to release space below the gate 7 to accommodate additional shaping cavities 2, but it is also possible to consider only having a single refractory drop device, for example, positioned centrally below the cone 24.

[0035] In order to produce the die 1 starting from the non-permanent cluster 21, the cluster 21 can be continued to be immersed in a slurry B, as Figure 3 shown in A, and then dusted with refractory sand S (i.e., particles of refractory material), as Figure 3As shown in B. The materials for the slurry B and the refractory sand, as well as the determination of the particle size of the refractory sand S, can be, for example, those disclosed in French Patent Application Publications FR 2 870 147 A1 and FR 2870 148 A1. Thus, the slurry B can, for example, contain particles of ceramic materials, especially in powder form, with a mineral colloidal binder, and possibly adjuvants depending on the rheology required for the slurry, while the refractory sand S can also be ceramic. Among the ceramic materials that can be considered for the slurry B and / or the refractory sand S are alumina, mullite, and zircon. The colloidal mineral binder can be, for example, an aqueous colloidal mineral solution, such as colloidal silica. The adjuvants can include wetting agents, diluents, and / or structure modifiers. These immersion and dust removal steps can be repeated several times, possibly using different slurries B and refractory sands S, until the desired thickness of the sand shell C impregnated with the slurry is formed around the cluster 21. This thickness can be adapted to different positions of the mold, for example, by locally restricting certain dust removal.

[0036] Then, for example, the cluster 21 coated with the shell C can be heated in an autoclave 200 to a temperature between 160 and 180 °C and a pressure of 1 MPa to melt and remove from the interior of the shell the low melting temperature materials of the cluster 21. Then, in a baking step at a higher temperature (for example, 900 to 1200 °C), the slurry B can be cured, thereby consolidating the refractory sand S to form the refractory wall of the mold 1, as Figure 3 shown in C.

[0037] In the casting method using the mold 1, before continuing to pour the liquid metal into the mold 1, the step of preheating the mold 1 can be continued, as Figure 4 shown in A. In this step, after the mold 1 is introduced into the oven 100, the mold 1 can be heated in the oven 100, which can reach a first temperature T1. Then, without removing the mold 1 from the oven 100, while maintaining the oven 100 at the first temperature T1, the liquid metal M can be continued to be poured into the mold 1, as Figure 4as shown in B, in order to fill the hollow volume of the mold 1, in particular its molding cavity 2. The metal can be poured into the mold at a second temperature T2 that is greater than the first temperature T1. However, the temperature difference ΔT between the second temperature T2 and the first temperature T1 can be limited, for example, not exceeding 170 °C, or 100 °C, or even 80 °C. Thus, if the metal is, for example, a nickel-based equiaxed alloy of the René 77 type with a solidus temperature of 1240 °C and a liquidus temperature of 1340 °C, the second temperature T2 can be, for example, 1450 °C, and then the first temperature T1 is 1350 °C, where the difference ΔT is not greater than 170 °C. Thus, the excessive thermal shock of the molten metal poured into the mold 1 thereby reduces the risk of premature and unintentional solidification of the metal in the narrowest channels of the mold 2, resulting in solidification that may cause blockages and local defects in the component. The pouring of the liquid metal is carried out rapidly and is thus completed in a time t v which v can be, for example, approximately 2 seconds, or even one second.

[0038] In Figure 4 the following step shown in C, the mold 1 can still be maintained in the oven 100 for the first cooling and solidification step of the metal M in the mold 1, where, for example, the cooling rate dT / dt of the oven 100 can be controlled and limited to at most approximately 7 °C / min. This upper limit of the cooling rate also allows the forces exerted on the metal to be limited by the thermal shrinkage difference between the mold 1 and the cooling metal. However, a greater thermal shrinkage of the metal M compared to the thermal shrinkage of the refractory walls of the mold 1 will result in Figure 4 the bending of the metal in the feeder arms 3, 4 as shown by the dashed line in C, which bending will exert compressive stresses on the metal M in the molding cavity 2 in order to at least partially balance the tensile stresses caused by the thermal shrinkage of the metal M in the molding cavity 2. Thus, force concentration can be avoided, which force concentration would interfere with the crystallization of the metal and result in weaknesses in the components produced by this casting method.

[0039] In the illustrated embodiment, since the René 77 type alloy is a polycrystalline equiaxed alloy, the metal will form during its solidification a plurality of grains of generally the same size of about 1 mm, but more or less randomly oriented.

[0040] When the oven 100 has been sufficiently cooled until it reaches a third temperature T3, for example, between 800 °C and 900 °C, the mold 1 can be removed from the oven 100 so that it continues to cool naturally after being placed under an insulating bell surrounded by a refractory fabric until the step of breaking the casing as shown in Figure 4 D, where the mold is broken to remove the solidified metal therefrom, including the turbine engine blade 100 thus formed, and then subsequent steps of cutting and finishing can be carried out on the solidified metal.

[0041] Although the present invention has been described with reference to a specific exemplary embodiment, it is apparent that various modifications and changes can be made to the example without departing from the general scope of the invention as defined by the claims. Therefore, the specification and drawings should be considered illustrative rather than restrictive.

Claims

1. A casting mold (1), at least comprising: a first forming cavity (2) that extends along a horizontal axis (X) from a first end (2a) to a second end (2b), a first pair of feeder arms, the feeder arms comprising: a first feeder arm (3) that extends in a generally perpendicular direction and is connected to the first end (2a) of the first forming cavity (2), and a second feeder arm (4) that is generally parallel to the first feeder arm (3) and is connected to the second end (2b) of the first forming cavity (2), wherein the casting mold (1) is characterized in that any cross-section (Sb) of the first and second feeder arms (3, 4) of the first pair of feeder arms perpendicular to the vertical axis (Z) has a larger area than any cross-section (Sc) of the first forming cavity (2) perpendicular to the horizontal axis (X).

2. The casting mold (1) according to claim 1, comprising docking heads (5, 6) that connect the first and second ends (2a, 2b) of the first forming cavity (2) to the respective feeder arms (3, 4) of the first pair of feeder arms, each of the docking heads (5, 6) having a cross-section (St) perpendicular to the horizontal axis (X), the area of which cross-section (St) is larger than any cross-section (Sc) of the first forming cavity (2) perpendicular to the horizontal axis (X), but smaller than any cross-section (Sb) of the first and second feeder arms (3, 4) of the first pair of feeder arms perpendicular to the vertical axis (Z).

3. The casting mold (1) according to claim 1, wherein, the first and second feeder arms (3, 4) of the first pair of feeder arms have a cross-section (St) perpendicular to the vertical axis (Z), the area of which cross-section (St) increases upward along the vertical axis (Z).

4. The casting mold (1) according to claim 1, comprising a first row of forming cavities (2), the first row of forming cavities (2) including the first forming cavity (2), each forming cavity (2) of the first row of forming cavities (2) extending along a respective horizontal axis (X) from a first end (2a) to a respective second end (2b), the first end (2a) of each forming cavity (2) of the first row of forming cavities (2) being connected to the first feeder arm (3) of the first pair of feeder arms, and the second end (2b) of each forming cavity (2) of the first row of forming cavities (2) being connected to the second feeder arm (4) of the first pair of feeder arms.

5. The casting mold (1) according to claim 4 includes at least a second row of molding cavities (2) and a second pair of feeder arms. Each molding cavity (2) in the second row of molding cavities (2) extends from a first end (2a) to a corresponding second end (2b) along a respective horizontal axis (X). The first end (2a) of each molding cavity (2) in the second row of molding cavities (2) is connected to the first feeder arm (3) of the second pair of feeder arms, and the second end (2b) of each molding cavity (2) in the second row of molding cavities (2) is connected to the second feeder arm (4) of the second pair of feeder arms.

6. The casting mold (1) according to claim 1, wherein, the upper end of the feeder arm is connected to a feeder (7).

7. The casting mold (1) according to claim 1, wherein, the first molding cavity (2) is configured to form a turbine engine blade extending from a blade tip to a blade root along a horizontal axis (X).

8. The casting mold (1) according to claim 1 is configured as a shell mold.

9. A method for manufacturing the casting mold (1) according to claim 8, comprising the following steps: immersing a non-permanent pattern (22) in a slurry; after impregnation, sprinkling refractory material particles on the non-permanent pattern (22) to form a layer of refractory material particles coated with slurry; removing the non-permanent pattern (22) from the shell formed by the refractory material particles coated with slurry; and baking the shell.

10. A casting method, comprising the following steps: pouring liquid metal into the casting mold (1) according to claim 1; cooling and solidifying the metal in the casting mold (1); and demolding the solidified metal.

11. The casting method according to claim 10 includes a step of preheating the casting mold (1) in an oven (100) before the pouring step, wherein, the mold is held in the oven (100) before and during the pouring step.

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