KR20130008511A - Investment casting utilizing flexible wax pattern tool - Google Patents

Abstract

An investment casting process is disclosed in which the wax pattern tool 44 is flexible to facilitate removal of the tool from the casting wax pattern 52 even when the casting shape may require multiple traction planes. The flexible tool can include a flexible insert 42 precisely indexed in the peripheral coffin mold 40, thereby enclosing the ceramic core 10. The positioning pin 106 may extend from the flexible tool to make a flexible contact with the core prior to the wax injection step. The surface of the final wax pattern may include a processing topography 36 that has been replicated through the flexible surface from the master tool 12. The flexible tool can surround thermally conductive or magnetic particles 92 or other active devices 96 such as sensors or vibrators operable during wax injection.

Description

Investment casting using flexible wax pattern tool {INVESTMENT CASTING UTILIZING FLEXIBLE WAX PATTERN TOOL}

Cross Reference of Related Application

This application claims the benefit of the December 8, 2009 application date of US Provisional Patent Application No. 61 / 267,519 (Representative Document No. 2009P22785US), which is incorporated herein by reference in its entirety.

Field of invention

FIELD OF THE INVENTION The present invention relates generally to the field of investment casting, and more particularly to the use of flexible tools or molds for forming wax patterns as part of an investment casting process.

Investment casting is one of the oldest known metal forming processes dating back thousands of years when it was first used to manufacture detailed handicrafts from metals such as copper, bronze and gold. Industrial investment casting became more common in the 1940s, when World War II increased demand for precisely dimensioned parts formed from specialized metal alloys. Currently, investment casting is commonly used in the aerospace and power industries to manufacture gas turbines such as blades or vanes with complex airfoil shapes and internal cooling passage shapes.

The manufacture of an investment casting gas turbine blade or vane has an outer ceramic shell having an inner surface corresponding to the airfoil shape and one or more ceramic cores located in the outer ceramic shell corresponding to the internal cooling passages to be formed in the airfoil. This involves making a ceramic casting vessel. The molten alloy is introduced into the ceramic casting vessel and then cooled to harden. The outer ceramic sheath and ceramic core (s) are then removed by mechanical or chemical means to expose the cast blades or vanes having hollow internal cooling passages in the shape of the outer airfoil and of the ceramic core (s).

The ceramic core for injection casting first processes the desired core shape into mating core mold halves formed of high strength hardened mechanical steel, and then joins the mold halves to form an injection volume corresponding to the desired core shape, It is produced by vacuum injection of a ceramic molding material into an injection volume. The molding material is a mixture of ceramic powder and binder material. Once the ceramic molding material is cured to a green state, the mold halves are separated to release the green state ceramic core. The fragile green state core is then heat treated to remove the binder and sinter the ceramic powder together to produce a material that can withstand the temperature requirements needed to survive casting of the molten alloy. The complete ceramic casting vessel places the ceramic core in two joined halves of another precision machined hardened steel mold (called wax pattern mold or wax pattern tool) that forms an injection volume corresponding to the desired airfoil shape, and then the ceramic. It is formed by vacuum injection of molten wax into the wax pattern mold around the core. Once the wax has cured, the mold halves are separated and removed to reveal a ceramic core surrounded inside the wax pattern, which wax pattern now corresponds to the airfoil shape. The outer surface of the wax pattern is then coated with a ceramic mold material by, for example, a dipping process to form a ceramic shell around the core / wax pattern. Upon sintering of the skin and the resulting removal of the wax, the finished ceramic casting vessel is available to receive the molten alloy in the investment casting process as described above.

It is also known to insert a positioning wire or pin into the wax pattern before coating the wax pattern with the ceramic mold material. The positioning wires are inserted through the wax until they only make light contact with the enclosed ceramic cores, causing further insertion of the wires to end before causing damage to the fragile ceramic core material. A portion of the wire extends beyond the wax surface and is subsequently enclosed within the surrounding ceramic mold material. The positioning wire functions to provide mechanical support to the core during subsequent molten metal injection steps once the wax is removed. The wire material, typically platinum, is melted after it is injected into the finished ceramic casting mold so that it is melted and integrated into the final cast product.

Known investment casting processes are expensive and time consuming, and the development of new blade or vane designs typically requires months and hundreds of thousands of dollars to complete. Moreover, design choices are limited by process limitations in the manufacture of ceramic cores and wax patterns. The metal forming industry recognized these limitations and developed at least some incremental improvements, such as an improved process for casting airfoil trailing edge cooling channels described in US Pat. No. 7,438,527. Incremental enhancements have been suggested in the field of investment casting technology, but the inventors have found that the industry continues to increase combustion temperatures and improve gas turbine hot gas path component size in many fields, for example to improve combustion efficiency. It is recognized that as levels rise, the next generation of gas turbine engines continues to face fundamental limitations that can significantly inhibit component design for planned advances.

The present invention is part of an entirely new aspect for investment casting. As described and claimed herein, the flexible wax pattern mold can be formed as a hybrid tool with a flexible insert in a coffin mold. The flexible insert facilitates removal of the wax pattern tool from the cast wax pattern by modifying the flexible insert around the casting feature, which may require multiple traction planes for hard tooling. Flexible inserts can be cast from master tools that are processed from relatively low cost, low hardness materials such as aluminum or mild steel.

Some desired surface topography is so fine that they cannot survive on the surface of the wax during subsequent handling and ceramic shell forming steps. In this embodiment, the ceramic insert can be used with a flexible wax pattern mold. The ceramic insert can be formed to include the desired complex surface topography. The ceramic insert forms a portion of the surface that is disposed within the flexible wax pattern and forms a wax injection volume. After wax injection and solidification, the ceramic insert remains attached to the wax pattern when the flexible wax pattern mold is removed. Thereafter, a ceramic sheath is formed around the wax pattern and its attached insert, for example by an immersion process as described above, and the insert becomes an integral part of the ceramic sheath upon combustion.

Ceramic inserts disposed in flexible wax pattern molds may also be used to form surface open passageways in subsequent cast metal portions, such as, for example, trailing edge cooling holes for gas turbine blades. In this embodiment, the ceramic insert may include protrusions that correspond to the desired shape of the cooling holes. The protrusion may extend to be in contact with the ceramic core, thereby extending the cooling channel in a subsequent casting that extends from the hollow inner portion of the blade (formed by the ceramic core) to the blade surface (formed by the inner surface of the ceramic sheath). Form. The distal end of the protrusion can be formed with features that match the cooperative features formed on the ceramic core. Mechanical contact between the core and the ceramic insert protrusions serves to precisely position the ceramic core in the flexible wax pattern mold and also to mechanically support the ceramic core during subsequent wax and metal injection steps.

The flexible insert of the wax pattern mold can be formed to include an alignment feature that allows the insert to be precisely positioned relative to the surrounding coffin mold, which alignment feature then inserts against the ceramic core enclosed for the wax injection step. Any feature formed on the insert can be precisely positioned.

The molding material used to form the flexible mold or flexible mold insert may be injected into or inserted into a material or device that allows the flexible insert to be reacted in the desired manner, as broadly described herein as a flexible insert comprising a reaction element. Can be cast around. The reaction element may be a filler material that imparts the desired properties to the subsequent cured material. For example, if magnetic particles are used as filler, the cured flexible insert will respond to magnetic energy. This property can be useful for securing flexible inserts in the surrounding coffin mold when the coffin mold is formed to include permanent magnets or electromagnets. If a thermally conductive or insulating material is used as the filler, heat transfer through the flexible insert can be more conveniently controlled during its use.

Another type of reaction element that can be embedded in a flexible mold or insert when formed is an active device. Such active devices include temperature sensors, pressure sensors, mechanical vibrators, heating or cooling devices or other devices that may be useful when a flexible insert is used during the subsequent wax injection process.

Positioning pins (wires) can be used with the flexible wax pattern to mechanically support the ceramic core surrounded during metal casting, and importantly they can be positioned relative to the ceramic core prior to the wax injection step. The specified pin support element is located in the recess of the surface of the flexible insert, thereby precisely positioning the pin relative to the ceramic core prior to wax injection. This allows pins to support the core during wax injection and also allows pins to be positioned more precisely than in conventional processes where pins are required to be inserted through pre-cast wax patterns. As a result, damage to fragile ceramic cores is reduced and process yield is increased.

Possible techniques utilized in the present invention are all assigned to US Pat. Nos. 7,141,812, 7,410,606 and 7,411,204, assigned to Mikro Systems, Inc., Charlottesville, VA, and incorporated herein by reference. Described in This technique is called Tomo Lithographic Molding Technology (hereinafter referred to as "Tomo Process") and involves the use of a metal foil stack laminate mold to produce a flexible induction mold, followed by component parts. Used to cast The component design is first embodied in a digital model, then sliced digitally, and metal foils are formed corresponding to each slice using photolithography or other precision material removal processes. The inherent precision of the two-dimensional material removal process, combined with the designer's ability to control the thickness of the various slices in the third dimension, provides some degree of three-dimensional manufacturing tolerance precision that was not previously available using standard mold processing processes. to provide. The foils are laminated together to form a lamination mold for receiving a suitable flexible molding material. The term “flexible” is used herein to refer to a material such as room temperature vulcanized (RTV) silicone rubber or a mold that is curved and stretched to a degree that facilitates removal of the mold from a structure molded therein but not rigid. It is used to refer to other materials that can be used to form a "flexible mold" that can be made. Moreover, the terms “flexible mold” and “flexible tool” can be used herein to include a flexible liner or insert included in a rigid coffin mold as well as a freestanding flexible structure. The components are then cast directly into the flexible mold. The flexibility of the mold material allows casting of component features with protruding undercuts and reverse cross-section tapers due to the ability of the flexible mold material to deform around the feature as the casting is towed away from the mold.

Collectively, these improvements form new aspects for investment casting that overcome many of the conventional limitations, in particular the limitations of the wax pattern portion of the investment casting process, as described in more detail below.

The invention is explained in detail in the following detailed description with reference to the drawings.
1 is a view of a conventional ceramic core.
2A and 2B illustrate steps for manufacturing wax pattern tooling for an investment casting process.
3 shows a spacer positioned between a ceramic core and a flexible wax pattern mold to position and support the core during wax injection.
4A-4H illustrate stages of an investment casting process in which a processing surface topography is cast directly into a metal surface.
FIG. 5 is a diagram of a first wax pattern surface resulting from Tomo-process flexible tooling. FIG.
FIG. 6 is a view of the second wax pattern surface generated from the Tomo-Process flexible tooling. FIG.
7 is a view of a wax pattern surface with a protruding surface pattern.
8A-8C show wax surfaces derived from a single master tool subjected to progressive grit blasting.
9A-9C illustrate steps for manufacturing a machined surface in an investment casting.
10A and 10B illustrate wax pattern tool inserts used to form open surface passages in a cast metal portion.
FIG. 11 is a partial cross-sectional view of a flexible wax injection mold insert comprising magnets and reactive (magnetic) particles attached to a coffin mold. FIG.
12 is a partial cross-sectional view of a flexible wax injection mold insert positioned in a coffin mold where the liner encapsulates the active device.
13A-13E illustrate the use of core positioning wire with a flexible mold insert where the wire is positioned relative to the core prior to the wax injection step.
FIG. 14 shows an insert with a comb design. FIG.

As part of an investment casting process, such as can be used to cast gas turbine blades or other components with complex internal cooling passages, a ceramic core is formed that can form the shape of the internal cooling passages. 1 is a diagram of one such ceramic core 10 that may be formed by any known process.

Once the ceramic core is manufactured, the next step in the investment casting process is to use the core as part of a wax pattern tool to cast wax around the core to form the final outer surface shape of the casting blade or other casting. Conventional wax pattern tooling designs are particularly complex and expensive when multiple pulling planes are required for the removal of tooling from the wax pattern or casting due to the shape of the part. The present invention is a novel approach to wax pattern tooling that reduces tool manufacturing time and costs with the small fraction required for traditional wax pattern tooling, and also provides improved ability to result in greater component design flexibility and higher casting yield. To provide. Simple low cost aluminum or mild steel (or other easily processed material, collectively referred to as soft metal) master tooling is used in place of conventional expensive machine tool steel tooling. The derived flexible wax pattern mold (tool) is then made from the master mold using a low pressure injection process. FIG. 2A shows a section of a master tool 12 formed of a soft metal, such as machined aluminum, containing a flexible mold material 14 to manufacture one side 16a of the flexible wax pattern tool 16 and FIG. And the other side 16b of the flexible wax pattern tool 16 is manufactured in a similar manner. The flexible wax pattern tool may be entirely formed of a flexible mold material or may take the hybrid form of a flexible mold insert (or liner) for use with the solid coffin molds illustrated and described below. Two assembled sides of the flexible wax pattern tool are shown in FIG. 2B showing the placement of the ceramic core into the injection cavity 18 formed between the flexible mold sides.

The master tool in the embodiment of FIGS. 2A and 2B forms a positioning feature 22, for example in the form of a flexible positioning pin, which is formed integrally with the flexible inner surface 24 of the mold abutting the core. It can be formed to accommodate one or more precision inserts 20 used. If required to form improved areas of high definition detail, including, for example, machined surface roughness, which facilitates adhesion of the coating to be applied to the post-cast metal part as described more fully below, precision inserts of various shapes are required for the master tool. It can be used in any area of. Inserts can be formed using a Tomo process, stereo lithography, direct metal fabrication, or other high definition processes. The hybrid surface 26 (machining aluminum surface and precision insert surface) of the master tooling is then replicated within the flexible inner surface of the wax injection mold that duplicates the details of the master tool.

The positioning feature shown in FIG. 2B has a high mechanical history and extends from the body of the flexible mold to make soft contact with the ceramic core, thereby ensuring proper positioning of the core within the flexible wax pattern mold. The positioning feature provides some degree of compliance at the core / molded interface 28 while providing mechanical support for the core during wax injection. Conventional tooling is known to have metal pins in violent contact with the core, but such violent contact often causes damage to the ceramic core, which is relatively fragile during mold closure. The flexible features described herein provide some degree of tolerance, which translates into a higher yield of acceptable portions due to the reduced chance of damage to the core. The degree of flexibility of the positioning features may vary, but may be more flexible than the core surface they contact so that they may be deformed by the core without causing damage to the ceramic core material. In contrast, conventional positioning pins are more rigid than the core material and they cannot be deformed by the core without causing damage to the ceramic core material. Advantageously, the positioning features do not need to be located in parallel traction planes due to the flexible nature of the mold material, which allows these positioning features to be curved to facilitate removal.

In another embodiment, shown in FIG. 3, a flexible pin or spacer 30 that is not integral to the flexible mold can be positioned between the core and the flexible mold to position the core and provide mechanical support to the core. . Such non-integral spacers may be formed of foam or wax or any material capable of bonding to the ceramic core without causing damage to the core. The spacers may be held in place with adhesive 32 and / or inserted into openings 34 formed in the flexible mold. The spacer may be designed to burn out during shell hardening after wax injection or may be pulled out of the wax pattern prior to skin formation. Alternatively, the spacer may be formed of a ceramic casting material, may be collected and held by a wax pattern and then coated and integrally coated with a ceramic sheath material that is subsequently applied. In casting a molten metal alloy, the collected ceramic spacers will function to form surface open passages in the cast metal portion. In any of these options, the flexibility of the spacer itself, as well as the flexible inner surface of the flexible mold, functions to provide some degree of flexible support to the core during the wax injection step.

The foregoing embodiments for making wax pattern tooling are properly compared to known conventional processes, as summarized in Table 1 below.

The prior art
characteristic The
characteristic The prior art
ability The
ability Hard Precision Tooling Soft precision tooling Linear extraction only Curved Extraction Capability Single sectional towing plane Multi Section Traction Plane Hard Pin Positions Core in Hard Tool Flexible mold expander positions core in flexible mold Hard tooling of the core interface Soft tooling of core interfaces Limited cores for tooling interfaces provide low certainty of core position Less rigid areas of the core can be located at the soft tooling interface. More control over core position Inflexible tool set,
High cost to fix Low cost modular modification possible Rigid mold cavity,
Precision Linear Tool Separation Flexible mold cavity,
Nonlinear Mold Separation

4A-4H illustrate stages of an investment casting process in which the processing surface topography 36 is cast directly into the metal surface 38. In FIG. 4A, two halves of the coffin mold (die) 40 are shown, each comprising a flexible mold insert (liner) 42a, 42b having an exposed surface comprising the desired surface topography. do. Flexible inserts can be manufactured directly from a master mold formed by a Tomo process or by another precision process. 4B shows the cast coffin mold halves that are assembled together as a flexible wax pattern tool 44 around the ceramic core, thereby forming an injection cavity 18 that conforms to the desired shape of the subsequent cast metal portion 46. have. The end of the ceramic core, known as core print 48, extends to make contact with the coffin mold to support the core against the coffin mold and the flexible mold insert. The injection cavity is then filled with wax 50 using an injection process as shown in FIG. 4C. After the wax has cured, the tool is removed to reveal the wax pattern 52 shown in FIG. 4D with the desired topography on its outer surface. The wax pattern is then coated (covered) with a ceramic material using techniques known in the art to form the wax-filled ceramic casting vessel 54 shown in FIG. 4E. The wax is then removed, for example by heating, to produce the casting vessel 56 shown in FIG. 4F. Molten metal alloy 58 is then cast into the casting vessel as shown in FIG. 4G, and the ceramic casting vessel is destructively removed to allow internal cavity 60 on its surface 38 as shown in FIG. 4H. And component part 46 having integrally molded machined surface topography 36.

The flexible mold insert of FIG. 4A can be derived directly from the Tomo process master mold, as described in US Pat. Nos. 7,141,812, 7,410,606 and 7,411,204, cited. Alternatively, a Tomo process mold or other precision master mold may be used to form one or more intermediate molds, wherein the intermediate mold (s) are subjected to additional process steps to modify and further improve the surface topography. In one embodiment, a metal foil master tomo process mold is used to cast the first flexible mold, and the first flexible mold is used to cast the fibrous material intermediate mold. The intermediate mold is then grit blasted to expose a portion of the fiber to the surface of the mold. The second flexible mold is then cast into the intermediate mold, which will duplicate the shape of the exposed fiber as part of its surface topography. The second flexible mold is then used for the coffin die of FIG. 4A.

In its simplest form, flexible tooling is generally used to create tough features in the surface of the wax pattern that can be concave into the surface of the wax. Typically, these features can be relatively small angles and shallow profiles with the purpose of creating high angle steps at the edges to create interlocking shapes and increase the surface area of the interface with the upper coating. Hexagonal structures or honeycomb structures can be used. FIG. 5 shows one such surface 62 which proved to be robust at the surface of the wax pattern using the steps described above. The surface in this wax pattern creates a honeycomb surface that is feasible in investment casting to create a periodically rough surface (in macroscopic range) that produces a high interlock and increased surface area for bonding integrity with the upper coating layer. . Additional benefits can also be obtained from increased intermittent coating thicknesses across the surface.

Additional surface machining can lead to greater surface area increases and interlocking as shown in FIG. 6, where the edges of the hexagonal shape are chamfered to form a gear-cog type layer 64. Form. Although typical surface feature depths are produced and appear to be effective at both 0.38 mm and 0.66 mm, these depths do not represent optimization and are not intended to be limiting. In regions of high surface angularity (eg, leading edge or trailing edge of an airfoil or airfoil / platform intersection), pattern projections from the surface may be advantageous. Such protrusions can be made from second generation flexible molds (ie, flexible mold replicas from flexible mold masters). 7 illustrates an example of a raised wax surface pattern 66 produced by this mold technique. The protruding mold can be processed to create an undercut in the surface, thereby increasing the degree of mechanical interlocking with the coating. This is useful in the high stress region of the coating. It is noted that undercuts may also be created in the pressed surface features.

Master tooling may include grit blasting or sanding or the generation of laser induced micro pot marks on the surface or the addition of a second phase material bonded to the surface of the master tool by an adhesive such as epoxy, for example. It can be further modified by non-Tomo surface modification techniques. Such materials can include, but are not limited to, silicon carbide particles or chopped fibers that can be applied to a surface with a random or predetermined pattern. Surface modification techniques or second phase materials can be used to form the surface of the flexible mold tool and create a random surface array on the surface of the tool that can potentially be replicated from the second generation flexible mold tool. By way of example, FIGS. 8A-8C illustrate wax pattern surfaces 68, 70, 72 generated from master tools that are gradually modified with varying degrees of hybridized surfaces to create unique micro surface features. In this case, the master tool was gradually grit blasted, and the basic tomo process shape gradually eroded, creating a more rounded structure as it progressed from surface 68 to surface 72, but still the basic shape of the tomo process features. Holds. This hybridization, in combination with the ability of the Tomo process to create concave or protruding machined surfaces, represents a significant flexibility of the process for producing a wide range of machined surfaces in as-cast parts. Advantageously the process of the present invention allows for the replication of the grit blasted master tool surface through the creation of multiple casts of flexible inserts cast into the grit blasted master tool without additional real grit blasting, thus ensuring accurate inter-part replication do. Since the process is the same for all the final surfaces derived from the master tool, once the desired master tool surface is created, it is not effectively sensitive to the surface modification process.

9A-9C illustrate another embodiment for creating a machining surface in an investment casting that is too vulnerable at the wax patterning stage for the desired surface finish to efficiently transition into the sheath coating 74. Such surfaces can be those that can create fragile protrusions in the wax pattern that can typically be easily damaged during handling and skin coating. In this embodiment, consumable ceramic insert 76 may be formed in a tomo process or otherwise to have the desired surface topography 36. The consumable insert forms part of the flexible wax injection mold 16 as shown in FIG. 9A, but is detached from the mold as shown in FIG. 9B and the wax pattern 52 upon removal of the mold from the cast wax pattern. Stay with). When the wax pattern is sheathed and the sheath 74 is heat treated, the insert remains as part of the sheath structure forming the outer cavity wall 78 for the casting vessel 56 as shown in FIG. 9C. The inner surface of the insert includes the desired topography of the final metal surface of the casting, and this detail is retained in a more robust form by an alternative method of transferring the topography through wax. This process can be used to retain details of the surface that may be damaged in the wax pattern due to fragility. This process provides for itself modularity when additional fastening is required for exposed airfoil areas, such as the leading and trailing edges of the airfoil, for example. Such ceramic inserts may be partially heat treated prior to application to the wax injection tool.

10A and 10B illustrate another use of consumable insert 80 for forming surface opening passages in the final cast metal portion, such as may be useful for forming trailing edge cooling passages in gas turbine blades, for example. Doing. The insert can be made of silica, ceramic, or quartz material, which is designed to fit within a cooperating recess 82 such as a slot or opening in the flexible wax pattern mold 16. The insert, flexible wax pattern mold and the core 10 can all be formed with appropriate precision, for example by a tomo process, such that the protruding legs 84 of the insert abut the core, as shown in FIG. 10A. Or mate with cooperating openings 86 in the core to create a mechanical interface therebetween. The mechanical interface may be a butt joint or recessed joint or other cooperative shape. The insert remains in the wax pattern 52 after the flexible wax pattern mold has been removed, as shown in FIG. 10B, and is integral with the skin (not shown) during the subsequent skin forming process. The protruding legs of the insert create a passage in the cast metal portion between the inner passage formed by the core and the outer surface of the portion formed by the shell inner surface, which also provide mechanical support for the core during the wax and metal injection step. By forming a flexible wax pattern mold insert by a precision process such as the Tomo process, we now produce blade trailing edge cooling passages with shapes, angles, aspect ratios, tapers, spirals, etc. that were not previously possible in the prior art. It is possible to do One example is a non-linear cooling channel formed by the insert 80 of FIGS. 10A and 10B. Advantageously, the insert comprises a portion 81 extending generally parallel to the surface of the component, thereby increasing the utility of the cooling channel. This type of shape cannot be obtained by standard post-casting processes. Each insert may form a single cooling channel, or alternatively, a plurality of cooling channels may be formed by insert 83 formed with a comb design as shown in FIG. 14.

11 shows a coffin mold 40 having a flexible mold insert 42 formed with cooperative alignment features to simplify the placement of the flexible mold insert into the coffin die and ensure proper alignment therebetween. An embodiment of the is shown. 11 illustrates the use of trapezoidal protrusions 88 on the surface of the insert and mirror image shaped grooves 90 on the surface of the coffin die, one skilled in the art will understand that any of a variety of cooperative shapes may be used. Could be. One of the advantages of using flexible molds is their low cost and interchangeability, and the use of such alignment features ensures that each of the multiple flexible mold inserts used with a single coffin die is properly positioned. Proper positioning of the flexible insert also ensures that the insert is properly indexed to the core when the core is supported from the coffin mold.

Various reaction elements can be enclosed in a flexible wax injection mold or mold insert. In one example, FIG. 11 illustrates the use of filler particles 92 as a reaction element in the mold material used to form flexible insert 42. The filler particles are mixed with the mold material prior to casting into the mold shape while the material is still in the liquid state. The particles can be any of a variety of materials or combinations of materials that jointly impart desired properties to the mold liner. For example, the particles can be selected to have the desired thermal conductivity properties, such as highly conductive to thermal energy, to increase the thermal conductivity of the insert. In other embodiments, the particles can be adiabatic. At least some of the filler particles of FIG. 11 may be magnetic and attracted to a magnet 94 mounted in a coffin die, thereby maintaining a flexible insert in its proper location within the coffin die. The magnet may be a permanent magnet or an electromagnet that makes it easier to release the insert from the coffin die when the electromagnet is de-energized. In another embodiment, the magnet is used in a master mold that is used to cast a flexible mold insert such that magnetic particles in the liquid mold material are attracted towards the magnet while the mold material is cured, whereby the magnet is in the region of the mold proximate the magnet. Resulting in a desirable distribution of particles.

12 illustrates the use of a reaction element, which is the active device 96 in the flexible insert 42. The active device is placed in a master mold (not shown) during casting of the mold material such that the device is surrounded within the mold material. The term “active device” is used herein to include any object or void other than the mold material that functions to enhance the utility of the mold during use of the flexible mold. Examples of active devices include sensors such as temperature or pressure sensors that can be used to monitor the casting process, actuators such as mechanical vibrators that can be used to facilitate the flow of casting material throughout the injection cavity, and temperatures during the casting process. Temperature control devices such as, but not limited to, fluidic channels or resistance heaters for the passage of heating or cooling fluids that can be used to regulate. The active device may be connected to an associative system 98 such as an electronic circuit or fluid system located outside of the mold material, or the device may be isolated within the mold material and may be connected to a telecommunication signal such as an interrogation RF signal or acoustic energy. You can respond.

As described in the 'Background Art' section above, it is conventionally known to insert platinum wires (or fins) into the wax pattern to make contact with the embedded ceramic core. This procedure is unreliable because the insertion of platinum wires that are too deep can cause damage to the ceramic core and the damage can remain undetected until after the metal part has been cast, thus failing post-casting inspection. Moreover, conventional platinum wire does not provide support for the core during the wax injection step because it is not placed in place until after the wax has been cast. The present invention utilizes the use of such positioning wires or pins with flexible wax pattern molds to provide some degree of flexibility in the support provided by the wires and also to allow the wires to be positioned relative to the ceramic core prior to wax injection. Consider. 13A-13E illustrate one embodiment of how this can be accomplished.

Flexible insert 42 is formed with a surface recess 100 for receiving a removable support element, such as disk 102, as shown in FIG. 13A. The support elements may have other shapes in other embodiments. In one embodiment, flexible inserts and discs may be formed of the same material to ensure chemical and thermal expansion suitability. The disk is formed with a hole or opening 104 for receiving a positioning pin 106, such as a known platinum positioning wire. Those skilled in the art will appreciate that there may be many such disks and wires associated with inserts for supports of a particular ceramic core design. The flexible mold may be formed with a bottom flexible insert (not shown) and a top flexible insert (not shown). The wires, disks and inserts are preassembled, and then the ceramic core 10 is placed in a flexible mold to make light contact with the top surface of the wires. In the horizontal embodiment shown, the bottom insert forms the bed on which the core is placed, and then the top insert (not shown) is lowered over the core to form a flexible mold. Moderate finger pressure may be applied to preload the core evenly on the wire. The diameter of the hole formed in the disk may be 0.005 to 0.010 inch (0.127 to 0.254 mm) smaller than the diameter of the wire in one embodiment, thereby providing a moderate resistance to the movement of the wire through the disk, whereby the core material This allows the wire to extend into or through the disc to any extent necessary to support the core without causing damage to the core. In embodiments where a single flexible insert design is used with multiple core designs, blank discs (ie, holes 104) for areas where there is a recess in the insert but no wire is needed to support a particular core design. This none] may be provided.

The positioning wire is placed in place to make light contact with the core prior to the wax injection step, thereby overcoming the conventional problem of proper positioning of the wire through the cast wax pattern and also providing some degree of mechanical support to the core during wax injection. It will be understood from FIG. 13A to provide. Wax 108 is then injected as shown in FIG. 13B, and once the wax has solidified, the flexible insert and positioning disk are removed as shown in FIG. 13C to reveal the wax pattern 52 and wax Leave portions 110 of each wire extending beyond surface 112. Since each wire can be positioned to be generally perpendicular to the surface of the core at that location, there may be multiple pull planes required for removal of the flexible insert from the wire. The tapered shape of the disk and its cooperative recess in the flexible insert facilitate the removal of the insert from a plurality of positioning pins that can be used for a particular core. It will be appreciated that a positioning disk may not be needed for embodiments in which the wires in each mold half are all generally parallel to each other. In this embodiment, each wire may be received in each hole formed directly in the flexible insert.

A ceramic skin coating 74 is then formed on the wax pattern by a known dipping process to enclose the protrusion of the wire as shown in FIG. 13D, and the wax is then pre-positioned as shown in FIG. 13E. It is removed to reveal the finished ceramic casting vessel 56 that includes the core support wire.

The investment casting aspect described above represents a new business model for the casting industry. Conventional business models have used very expensive, long lead time rigorous tooling to produce multiple ceramic casting vessels (and subsequent cast metal parts) from a single master tool with fast injection and hardening times. In contrast, the novel embodiments disclosed herein utilize lower cost, faster manufacturing less stringent master tools and intermediate flexible molds derived from master tools to produce ceramic casting containers with much slower injection and curing times. . Thus, the novel casting aspect enables the creation of the first ceramic casting vessel (and subsequent manufactured cast metal parts) much faster and cheaper than conventional methods, and thus can be advantageously applied for rapid prototyping and development testing. have. Many different circular designs can be made relatively easily from a single master tool by using interchangeable inserts for the design features to be altered. Moreover, the novel aspect can be effectively applied in solid state manufacturing applications since many of the same intermediate flexible molds can be cast from a single master tool, thereby still maintaining significant cost advantages over the prior art while still maintaining a significant cost advantage over the prior art. Multiple ceramic casting vessels can be manufactured in parallel to matching or exceeding manufacturing capabilities. The time and cost savings of aspects of the present invention not only reduce the cost and effort of manufacturing the master tool, but also the specific post-metal casting steps that are conventionally required to make certain design features such as trailing edge cooling holes or surface roughness. Exclusions are included because these features can be cast directly into the metal parts using the novel aspects disclosed herein while the prior art requires post-casting treatment. The present invention offers the potential for improved yield of acceptable parts since it reduces the risk of placement of locating wires for fragile ceramic cores, and allows the core to have more mechanical compliance than is possible with conventional hard tooling. Being supported in a wax injection mold also offers the potential for higher wax injection pressures without damaging the ceramic core. The present invention not only produces high precision parts via flexible molds, but also enables inter-part precision to an extent not obtainable in conventional flex mold processes. Finally, aspects of the present invention provide these cost and manufacturing advantages while at the same time enabling the casting of design features that did not exist within the capabilities of the prior art, thereby allowing component designers to achieve the next generation of gas turbine design goals for the first time. It enables the manufacture of the hardware features needed to make them.

While various embodiments of the invention have been shown and described herein, it will be apparent that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions may be made without departing from the invention.

10: ceramic core 12: master tool
14: flexible mold material 16: flexible wax pattern tool
18: Injection cavity 20: Precision insert
28: core / mold interface 30: flexible pin or spacer
32: adhesive 34: opening
36: surface topography 38: metal part surface
40: coffin mold 46: subsequent cast metal part
50: wax 52: wax pattern
54, 56: casting container 60: cavity

Claims (29)

A tool for forming a wax pattern as part of an investment casting process,
Coffin mold,
A core disposed in the coffin mold and supported in place therewith;
A feature including a feature to be replicated in wax during the wax injection step of the investment casting process, and a flexible liner indexed to the coffin mold to position the feature at a known position relative to the core during the wax injection step.
The tool of claim 1, wherein the feature comprises a flexible positioning element integrally formed with the flexible liner and brought into contact with the core to support the core during the wax injection step.
The tool of claim 1, wherein the feature includes an insert comprising a non-linear leg extending to contact the core.
4. The tool of claim 3, wherein the insert includes a leg extending to contact the core to support the core during the wax injection step.
The tool of claim 1, wherein the feature includes a pin extending to contact the core to support the core during the wax injection step.
The method of claim 5,
A recess formed in the inner surface of the flexible liner, and
Further comprising a support element disposed in said recess,
The pin passes through an opening in the support element and extends towards the core.
A tool for forming a wax pattern as part of an investment casting process,
A tool body comprising a flexible inner surface defining a desired outer surface shape of the wax pattern;
A core disposed within the tool body and forming a portion of the wax pattern after a wax injection step,
A positioning element disposed between the core and the tool body and supported by the flexible inner surface to provide flexible support for the core during the wax injection step.
8. The tool of claim 7, wherein the positioning element is integrally formed with the flexible inner surface of the tool body.
8. The tool of claim 7, wherein the positioning element is attached to the flexible inner surface of the tool body with an adhesive.
The method of claim 7, wherein
A recess formed in the flexible inner surface of the tool body,
The positioning element is disposed in the recess and extends beyond the flexible inner surface towards the core.
8. The tool of claim 7, wherein the positioning element comprises a spacer that can be pulled out of the wax pattern prior to a subsequent ceramic shell forming step or burned off during a subsequent ceramic shell curing step.
8. The tool of claim 7, wherein the positioning element comprises a ceramic material that can be collected and retained by the wax pattern after the wax injection step and then integral with the subsequently applied ceramic shell material.
The method of claim 7, wherein the positioning element is
A support element disposed in a recess formed in the flexible inner surface of the tool body, and
And a pin passing through the opening in the support element and extending towards the core.
8. The tool body of claim 7, wherein the tool body is
Coffin mold, and
A flexible insert comprising a flexible inner surface disposed within the coffin mold, and
A cooperative indexing feature formed on the coffin mold and the flexible insert to position the flexible insert within the coffin mold at a known relative position.
8. The tool body of claim 7, wherein the tool body is
Coffin mold, and
A flexible insert comprising a flexible inner surface disposed within said coffin mold,
And a reaction element disposed within the flexible member.
16. The thermal conductivity of claim 15, wherein the reactive element is of a thermal conductivity different from the coefficient of thermal conductivity of the sensor, actuator, temperature control element, magnet, particles reacting to magnetic energy, and the flexible material of the flexible member surrounding the particle. A tool comprising one of a group of particles representing coefficients.
8. The tool body of claim 7, wherein the tool body is
Coffin mould,
A flexible insert defining a flexible inner surface disposed within the coffin mold, and
A tool comprising a precision ceramic insert disposed in the recess of the flexible inner surface.
A tool for forming a wax pattern as part of an investment casting process,
A tool body comprising a flexible member defining a desired outer surface shape of the wax pattern;
A core disposed within the tool body and forming a portion of the wax pattern after a wax injection step,
Means for supporting the core in the tool body;
A tool comprising a reaction element disposed within the flexible member.
19. The method of claim 18,
The reaction element comprises a sensor, an actuator, a temperature control element, a magnet, particles reacting to magnetic energy, and particles exhibiting a coefficient of thermal conductivity different from the coefficient of thermal conductivity of the flexible material of the flexible member surrounding the particle. Tool containing one of the groups.
19. The device of claim 18, wherein the means for supporting the core in the tool body is disposed between the core and the tool body and supported by the flexible member to provide flexible support for the core during the wax injection step. Tool containing positioning elements to be.
19. The apparatus of claim 18 wherein the means for supporting the core in the tool body is
A support element disposed in a recess formed in the flexible member of the tool body, and
And a pin passing through the opening in the support element and extending towards the core.
Positioning a ceramic core in a wax injection mold comprising a flexible member having an inner surface defining a desired outer surface shape of the wax pattern to be formed in the mold;
Supporting a ceramic core from the flexible member to form a wax pattern while injecting wax into the wax injection mold around the ceramic core.
23. The investment casting of claim 22 further comprising forming a flexible member to include a protrusion extending from the inner surface toward the core to contact the core to provide support to the core during a wax injection step. Way.
24. The method of claim 23, further comprising forming a protrusion to be integral with the flexible member inner surface.
The method of claim 22,
Forming a recess in the inner surface of the flexible member,
Inserting a spacer in the recess extending toward and contacting the core to provide support to the core during a wax injection step, and
And removing the spacers after the wax injection step.
The method of claim 22,
Forming a recess in the inner surface of the flexible member,
Inserting a ceramic insert into the recess extending toward and contacting the core to provide support to the core during a wax injection step,
Solidifying the injected wax to form a wax pattern in the wax injection mold,
Removing the wax injection mold while retaining the ceramic insert having the wax pattern, and
And forming a ceramic sheath structure comprising a ceramic insert around the wax pattern.
The method of claim 22,
Forming a recess in the inner surface of the flexible member,
Inserting a support element comprising an opening in the recess,
Inserting a pin in the opening extending toward the core to contact the core to provide support to the core during a wax injection step,
Solidifying the injected wax to form a wax pattern in the wax injection mold,
Removing the wax injection mold from the wax pattern and removing the support element from the pin while retaining the pin in the wax pattern, the portion of the pin subsequently extending away from the core past the wax pattern; and
Forming a ceramic sheath structure around the wax pattern and surrounding the extension of the pin.
23. The method of claim 22, wherein the inner surface forms a machined surface topography for the outer surface shape.
The method of claim 22,
Prior to wax injection, attaching an insert to the inner surface of the flexible member, wherein the insert comprises processing topography on its surface in close proximity to the core,
Removing the flexible member from the wax pattern after wax injection while retaining the insert in the wax, and
Coating the wax pattern and insert with a ceramic material to form a ceramic casting vessel.

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