Conventional casting generally involves pouring liquid metal into a sacrificial mold made from low-cost, consumable materials. The sacrificial mold materials have melting points higher than the liquid metal and are effectively chemically inert for the duration of a single casting process. This casting process is regularly used to produce low-cost, relatively simplistic parts using manual sand casting and to produce high-cost, relatively complex aerospace parts (e.g. blades and vanes) using lost wax investment casting. Although the cost per mold is relatively low, the molds are destroyed during each casting and require reproduction for subsequent castings.
Die casting generally involves pouring liquid metal into a durable metal mold made from two precision-machined dies. Contrary to conventional casting processes, die casting processes aim to rapidly mass-produce cast parts without reproducing and preparing sacrificial molds. Commonly, this process is used to cast low melting metals (e.g. aluminum and copper). Die casting is also used to cast high melting alloys (e.g. nickel alloys). However, in such processes the die life is further limited.
Contrary to conventional casting and die casting processes in which the solidification process is largely uncontrolled (i.e. solidification is omnidirectional), directional solidification processes control the location and rate of solidification to form unidirectional grain structures within the solidified metal. In its simplest form, directional solidification of a casting is achieved by progressively depowering heating elements, thereby cooling the casting from one end of the mold to the other. Continuous casting is another form of directional solidification in which liquid metal is poured into a vertically-oriented, water-cooled copper mold. Typically, the copper molds have a cylindrical, square or I-beam cross section and an open-ended bottom. As liquid metal flows through the mold, the metal along the water-cooled surfaces of the mold solidifies and, as the remainder of the metal cools, this process forms long, continuous billets of cast metal. In its most advanced form, directional solidification casting is practiced in conjunction with the investment casting process to form single crystal cast parts. In this process, a mold full of liquid metal is cooled from one end by a water-cooled plate. As the mold and water-cooled plate are slowly moved from a hot zone to a cool zone in the direction of the water-cooled plate, the liquid material solidifies and forms columns of crystal or single crystal in the direction of withdrawal.
In each casting process, a core can be suspended within the mold to form a hollow cavity. However, when conventional casting or directional investment casting processes are used, the core becomes encapsulated in the solidified material. To remove the core and thereby expose the hollow cavity, a chemical leaching or heating process is used to chemically remove or burn the core. The chemical leaching and/or baking processes destroy the core. When a die casting process is used, the core is susceptible to damage when the cast part is removed from the mold. Moreover, when a continuous casting process is used, the cores are fixed and thus, the castings are limited to fixed cross-sections. Therefore, a need exists for an improved casting process that utilizes reusable cores to improve manufacturing time and reduce manufacturing expense.
A method of manufacturing includes providing a casting assembly, providing a material having solid, transition, and liquid phases, heating the material to form the liquid phase, supplying the material to the casting assembly, cooling the material, monitoring the solidification of the material from the liquid phase through the transition phase, and moving one of the casting mold or the reusable core in a first direction relative to the other when a substantial portion of the reusable core contacts the transition phase. The casting assembly comprises a casting mold and a reusable core inserted within the casting mold.
A method of manufacturing a die-cast component includes providing a casting assembly, providing a material having solid, transition, and liquid phases, and heating the material to for the liquid phase. The casting assembly comprises a permanent casting mold having first and second halves that mate along a plane and a core plate rotatably mounted relative to the permanent casting mold. The core plate has an axis of rotation parallel to the plane and defines a plurality of passages extending therethrough. The method further includes supplying the material to the casting assembly through the plurality of passages of the core plate and controlling the solidification of the material such that the core plate is positioned substantially within the transition phase. The material has a solid phase when the material temperature is less than or equal to the solidus temperature. The material has a transition phase when the material temperature is between the solidus and liquidus temperatures. The material has a liquid phase when the material temperature is greater than or equal to the liquidus temperature.
The present invention relates to casting apparatuses and processes, and in particular, to casting apparatuses and processes that couple precision movement with one or more durable, non-wettable cores.
Generally, method 10a includes steps 12, 14, 16, 18, 20, 22, 24a, 26, and 28. Step 12 involves providing a casting assembly. The casting assembly includes, at a minimum, a casting mold to define the exterior features of the cast component and a durable, non-wettable core to define the interior features (i.e. one or more hollow cavities) of the cast component. To establish the cast component geometry, the core is positioned relative to the casting mold. Step 14 involves providing a material characterized by solid, transition, and liquid phases. The boundaries between each phase are marked by a solidus temperature and a liquidus temperature of the material. The material takes a solid phase when the material temperature is less than or equal to the solidus temperature and takes a liquid phase when the material temperature is greater than or equal to the liquidus temperature. Between the solidus and liquidus temperatures, the material forms a transition phase characterized by a viscous fluid relative to the material in the liquid phase. Following step 14, the material is prepared for casting by heating it until the material is substantially in the liquid phase. Heating the material prior to casting is accomplished by one or more methods well known in the art (e.g., using a combustion or induction furnace). Once the material forms a liquid phase, it is delivered to the casting assembly in step 18. The material is poured into the casting assembly, thus filling at least a portion of the casting assembly. Next, step 20 involves cooling the material in the region adjacent the core. In particular, the material is cooled near a portion of the core used to form internal hollow cavities within the cast component and is not necessarily the entire core. While the material is cooling, its material temperature approaches the liquidus temperature. During this time, various process parameters are monitored to evaluate the solidification process in step 22. Among the monitored process parameters are the material temperature in the region adjacent to the core, the bulk material temperature, the temperature of the casting mold, the furnace temperature, and other environmental parameters such as ambient temperature and the like. Once the material bounding the core enters the transition phase and the viscosity of the material is sufficient to support the hollow cavities within the material, one of the casting mold and the core is held stationary while the other is moved in a direction relative to the other in step 24a. In some embodiments, the casting mold is heated in order to reduce a rate of solidification. If the component is fully formed in step 26, the cast component is removed from the casting mold in step 28. However, if the component is not fully formed (i.e. additional hollow cavities are required), steps 18 through 24a are repeated until the cast component is fully formed and removed in step 28. Moreover, repeating steps 18 through 24a (or alternatively 24b as described below) occurs when material is periodically supplied to the casting assembly in order to better control the solidification rate of the material.
Alternatively,
For the core to be successfully implemented in methods 10a and 10b, the core is designed to withstand multiple casting cycles without replacement. A core withstanding only a few casting cycles is sufficiently durable if the manufacturing costs (e.g., material cost, manufacturing time, labor) are reduced by eliminating chemical leaching and/or baking steps associated with sacrificial cores. To attain core durability, the core is constructed from one or more materials that produce a non-wettable surface (i.e. a surface that inhibits the ability of a liquid to wet or cover the surface). Additionally, the core material has thermal shock resistance and erosion resistance sufficient to enable the core to survive multiple casting cycles that produce cast components within manufacturing tolerances. For example, melting metals such as tin, zinc, copper, and aluminum as well as the alloys associated with such materials requires core materials with lower temperature resistance than the core materials used for melting iron and nickel base alloys. In some embodiments, the core is constructed from silicide or ternary intermetallic metals (e.g., MAX phase materials) with appropriate ceramic coatings for casting higher temperature materials such as iron and nickel base alloys. Typically, ceramic coatings include alumina and yittra-stabilized zirconia based coatings. In other embodiments used for manufacturing relatively thin cast components, thin metallic sheets with thermal barrier and/or environmental coatings are used to create thin cast components that are not achievable with brittle materials.
Movement of the core and/or the casting mold is a repeated motion or pattern of motion used to define the desired shape of the cast component. Depending on the motion of the core and/or casting mold, voids, porosity, foam structures, and lattice structures are created. Such motion can be controlled remotely or with embedded digital motors and/or actuators.
Typically, the casting material is a metal (e.g., aluminum, carbon steel, and nickel and associated alloys). However, methods 10a and 10b can be applied to other materials such as organic and inorganic salts, paraffin wax, plastics, or food items such as confectionary sugar syrup or gelatins. When such nonmetal materials are used, the resulting cast component (i.e. foam, lattice, cored material) can be used for cosmetic reasons.
As will be appreciated by those skilled in the art, methods 10a and/or 10b apply to conventional casting, die-casting, and directional solidification casting processes as will be described in greater detail below. Although the following casting molds and cores will be described in the following embodiments with a particular geometry, it is understood that other geometries can be implemented so long as the geometries are compatible with methods 10a and/or 10b as described generally above.
To form a cast component, material 42 is melted and poured into casting assembly 38 in accordance with method 10a. After material 42 conforms to the surfaces of core 30 and mold 40, casting assembly 38 is placed in a cooling environment. Omnidirectional heat loss from material 42 through casting assembly 38 causes material 42, initially in a liquid phase, to form a transition phase. Portions of material 42 adjacent to mold 40 but that is not contacting mold 30 can solidify. When the remaining portions of material 42 adjacent to core 30 are relatively viscous (i.e., form transition phase), core 30 is removed.
Prior to removal, structures 34 and 36 are retracted relative to structure 32 of core 30 as depicted in
To form a cast component, material 78 is supplied to casting assembly 54. In some embodiments, material 78 fills the interior volume of casting assembly 54 defined by casting mold 72 and core 58. In other embodiments, material 78 is fed to casting assembly 54 at an average feed rate. In such embodiments, the feed rate can be characterized by periodically supplying material 78 to casting assembly 54 to better control the solidification of material 78 in casting assembly 54.
Chill plate 76 is configured to cool material 78 to promote solidification of material 78 while side mold 74 is insulated and/or heated to prevent premature solidification of material 78. In some embodiments, chill plate 76 is a water-cooled metal plate (e.g., a water-cooled copper plate). This arrangement of casting mold 72 causes material 78 to solidify adjacent to chill plate 76 while material 78 remains in a liquid or transition phase elsewhere within casting mold 72. Thus, material 78 forms solid phase 78a, transition phase 78b, and liquid phase 78c, in sequential order, extending from a region adjacent chill plate 76.
Referring now to
To form a cast component, material 104 is supplied to casting assembly 82. In some embodiments, material 104 fills the interior volume of casting assembly 82 defined by casting mold 87 and core 86. In other embodiments, material 104 is fed to casting assembly 82 at an average feed rate. In such embodiments, the feed rate can be characterized by periodically supplying material 104 to casting assembly 82 to better control the solidification of material 104 in casting assembly 82. Material 104 forms solid phase 104a, transition phase 104b, and liquid phase 104c as a result of chill plate 102 cooling material 104 from an end of casting mold 87. In any embodiment, spokes 90 are shaped (e.g., tapered) such that material 104 readily flows along spokes 90 and through volute 92.
In a process similar to the directional casting process described in
The following are non-exclusive descriptions of possible embodiments of the present invention.
A method of manufacturing includes providing a casting assembly, providing a material having solid, transition, and liquid phases, heating the material to form the liquid phase, supplying the material to the casting assembly, cooling the material, monitoring the solidification of the material from the liquid phase through the transition phase, and moving one of the casting mold or the reusable core in a first direction relative to the other when a substantial portion of the reusable core contacts the transition phase. The casting assembly comprises a casting mold and a reusable core inserted within the casting mold. The material has a solid phase at a temperature less than or equal to the solidus temperature. The material has a transition phase at a temperature between the solidus and liquidus temperatures. The material has a liquid phase at a temperature greater than or equal to the liquidus temperature.
The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
A further embodiment of the foregoing method, wherein the reusable core can move relative to the casting mold.
A further embodiment of any of the foregoing methods can further include removing the reusable core from the casting mold. The viscosity of the material adjacent to the reusable core at a time immediately preceding the removal of the core can be sufficient to form one or more hollow cavities within the material.
A further embodiment of any of the foregoing methods can further include heating the casting assembly during the removal of the core to reduce a rate of solidification of the material.
A further embodiment of any of the foregoing methods, wherein the reusable core can further comprise a first structure that extends into the casting mold along a central axis and a second structure attached to the first structure such that the second structure is movable relative to the first structure in a direction substantially perpendicular to the central axis.
A further embodiment of any of the foregoing methods, wherein the reusable core can further comprise a protrusion extending from the second structure configured to form a hollow cavity within the material, wherein a distal end of the protrusion can be tapered.
A further embodiment of any of the foregoing methods wherein the casting mold can move relative to the reusable core, and wherein during the solidification of the material, a substantial portion of the reusable core can be immersed in the transition phase.
A further embodiment of any of the foregoing methods, wherein the casting mold can move from a first zone having a first temperature sufficient to form the liquid phase to a second zone having a second temperature sufficient to form a solid phase.
A further embodiment of any of the foregoing methods, wherein the casting assembly can further comprise a plate forming an end of the casting mold configured to cool the material.
A further embodiment of any of the foregoing methods can further include forming a unidirectional crystalline structure within the material.
A further embodiment of any of the foregoing methods can further include forming a passage extending through at least a portion of the material, wherein the passage can be formed by the relative movement of the casting mold to the reusable core.
A further embodiment of any of the foregoing methods, wherein the reusable core can comprise a shaft extending in the casting mold along a central axis, a plate having a first face affixed to the shaft and a second face opposite the first face, and a plurality of protrusions extending from the second face, each protrusion having a tapered distal end.
A further embodiment of any of the foregoing methods, wherein the reusable core can comprise a hollow shaft extending in the casting mold along a central axis, a plurality of spokes affixed to an outer surface of the hollow shaft that extend outward from and generally perpendicular to the axis, and a volute affixed to the outer surface of the hollow shaft and the plurality of spokes, wherein the volute extends in a circumferential direction about the axis.
A further embodiment of any of the foregoing methods can further include moving the reusable core in a second direction relative to the casting mold, wherein the second direction is different from the first direction.
A further embodiment of any of the foregoing methods, wherein the second direction can be substantially perpendicular to the first direction.
A further embodiment of any of the foregoing methods can further include forming a first plurality of cavities and a second plurality of cavities within the material, wherein the second plurality of cavities can be offset from the first plurality of cavities.
A further embodiment of any of the foregoing methods, wherein the material can be periodically supplied to the casting assembly.
A method of manufacturing a die-cast component includes providing a casting assembly, providing a material having solid, transition, and liquid phases, and heating the material to for the liquid phase. The casting assembly comprises a permanent casting mold having first and second halves that mate along a plane and a core plate rotatably mounted relative to the permanent casting mold. The core plate has an axis of rotation parallel to the plane and defines a plurality of passages extending therethrough. The method further includes supplying the material to the casting assembly through the plurality of passages of the core plate and controlling the solidification of the material such that the core plate is positioned substantially within the transition phase. The material has a solid phase at a temperature less than or equal to the solidus temperature. The material has a transition phase at a temperature between the solidus and liquidus temperatures. The material has a liquid phase at a temperature greater than or equal to the liquidus temperature.
The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
A further embodiment of any of the foregoing methods can further include oscillating the core plate about the axis to form porosity within the material.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.