Ladle-less single chamber directional solidification vacuum casting furnace with 3D printed components

Abstract

A ladle-less vacuum casting furnace can include a melt pour cup configured to directly melt a charge, a susceptor configured to heat the melt pour cup, and a mold cavity, formed by additive manufacturing, configured to receive the melted charge, where the vacuum casting furnace does not have a ladle. The susceptor can have a barrel part and at least one dome shaped part. The at least one mold cavity is lowered out of the furnace with the assistance of a nickel isolation shutter with a ceramic shield. A method casting in a ladle-less vacuum casting furnace includes placing a metal charge in the melt pour cup, heating the metal charge with the susceptor to form a melt, and pouring the melt into the at least one mold cavity, the pouring being performed without a ladle, and lowering the mold cavity out of the furnace to solidify the workpiece.

Description

LADLE-LESS SINGLE CHAMBER DIRECTIONAL SOLIDIFICATION VACUUM CASTINGFURNACE WITH 3D PRINTED COMPONENTSThis application claims priority of provisional application no. 63 / 615,702 and provisional application no. 63 / 615,708, both filed on December 28, 2023, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0001] Embodiments are generally related to a single chamber directional solidification vacuum casting furnace with a ladle-less pour utilizing 3D printing technology and novel susceptor geometry.BACKGROUND

[0002] The production of high strength and thermally resistant single crystalline (SX), directional solidification (DS) and epitaxial solidification (ES) workpieces, such as turbine blades for aerospace applications, has traditionally been performed using methods where the metal alloy is melted before being molded into the workpiece.

[0003] One example is the Bridgman process. The Bridgman technique involves slow cooling of a molten material by moving its container from a hot zone into a cold one. To facilitate the crystal growth, the end of the container where a crystal starts to grow may be elongated, and a seed crystal can be placed at that end. Presence of the seed crystal requires precise temperature control at the interface, and in many cases crystal growth is done without a seed crystal. In the original Bridgman technique, the cold zone is the outside of the furnace, and thus the temperature gradient is not well defined.

[0004] The Bridgman technique uses a “hot” and “cold” zone to create a temperature difference within a furnace as shown in FIG. 1. The hot zone 10 is kept at a temperature above the melting point of the material 20. With superalloys, the metal is molten in aseparate crucible (not shown). Once the metal is at the correct temperature, and the mold 30 is at the correct temperature, the molten metal is poured into the mold. A pouring method like the Bridgeman technique requires a separate procedure of melting the metal before it is poured. The mold has a predefined shape which is the desired shape of the end-use component. The precursor material is a melt in the hot zone 10 and translated into the cold zone 50 by motion. The material solidifies 40 as it moves through the temperature gradient in the furnace. The Bridgman method can be performed in vertical configurations.

[0005] A modified Bridgman method, known as the Bridgman-Stockbarger technique, has two well controlled temperature zones, which is achieved by employing two separate furnaces with a baffle in-between. Some variants of the Bridgman and Bridgman- Stockbarger techniques include rotation of the container and horizontal arrangement of the furnace / s. The important considerations during the crystal growth are the mold material, temperature of the hot zone, temperature gradient, and cooling rate. The container should have minimal reactivity with the sample and withstand the temperature and ambient environment during the growth.

[0006] The production of advanced superalloy components for applications in aerospace, power generation, automotive, biomedical, chemical or recreational uses is accomplished in a vacuum precision casting furnace. Conventional processing produces castings having equiaxed, or randomly orientated grain structures. Using the principles of the ‘lost wax’ process, a ceramic mold is prepared and heated prior to casting. A measured quantity of pre-alloyed metal is then rapidly re-melted and poured into the mold under vacuum.

[0007] Directionally solidified (DS) and single-crystal (SX) castings are required for use in aerospace and industrial gas turbine applications due to their improved mechanical properties at very high operating temperatures. Furnaces to cast these components contain features to control the solidification process in the casting. Most production VPIC furnaces are of the semi-continuous variety due to the ladle. In this case, the furnace has two chambers isolated by a large vacuum valve. One chamber contains the melting coil and crucible assembly and the other is used as a mold loading and unloading chamber.

[0008] These conventional DS furnaces are suitable for high volume production using large molds (18” to 32” in diameter) made via a conventional shell process. These furnaces require high capital investments typically over three (3) million dollars excluding theinvestment required for building infrastructures. Also, conventional DS furnaces have slow turn-around times and thus require a long lead time to produce a finished part.

[0009] To reduce the initial capital investment for low volume production, the furnace architecture and operation need to be modified. There is accordingly a need for DS vacuum casting furnaces with novel design and architecture that leads to a simplified system.BRIEF SUMMARY

[0010] The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[0011] It is, therefore, one aspect of the disclosed embodiments pertains to a vacuum casting furnace that includes a melt pour cup configured to directly melt a charge, a susceptor configured to heat the melt pour cup; at least one mold cavity configured to receive the melted charge, the at least one mold cavity and the melt pour cup being a single piece formed by 3D printing, and a pin sealing an opening between the melt pour cup and the at least one mold cavity, where the vacuum casting furnace does not have a ladle.

[0012] In the disclosure, the pin, the at least one mold cavity and the melt pour cup being a single piece formed by 3D printing, or the pin, the at least one mold cavity and the melt pour cup being a single ceramic piece formed by 3D printing. An isolation shutter may be configured to block a lower end of the susceptor once the at least one mold cavity is completely out of the furnace, with the isolation shutter being formed from a ceramic material. The susceptor may be formed from graphite. The disclosure can further include an argon purge system configured to cool down the at least one mold cavity upon completion of a withdrawal cycle, and the melt stopper mechanism, i.e., a pin, designed to seal a mold pour cup-opening, is either fixed or made from a melt able material. If fixed, the pin may be ceramic. Induction coils are configured to heat the susceptor.

[0013] In the disclosure, melt pour cup and the at least one mold cavity may be madefrom the same ceramic, thereby promoting fitting the melt pour cup and the at least one mold cavity together. Multiple thermocouples are installed in the susceptor, and each thermocouple is fitted in a boron nitride plug fitted into the susceptor. The furnace may also have an argon urge system and a ram configured to lower the mold. There additionally may be a 3D printed chill plate on which the at least one mold cavity rests; and a chill spool near the chill plate. The susceptor may include a first bottom part, the bottom part having a shape of a hollow cylinder, and a first top part over the first bottom part, the first top part having a shape of a downward sloping cone or a dome. The first top part has the dome shape, and a surface area of the susceptor is approximately equivalent to a cylinder of a same height. The first top part has the cone shape, and a surface area of the susceptor can be modulated by varying a length of the cone to a length of the first bottom part. A third part under the first bottom part, the third part having a shape of an upward sloping cone.

[0014] The disclosure, in part, pertains to a method of casting a metal workpiece, that includes placing a metal charge in the melt pour cup of the vacuum casting furnace of the disclosure; heating the metal charge in the melt pour cup with the susceptor until the metal charge forms a melt; pouring the melt into the at least one mold cavity, the pouring being performed without a ladle; and lowering the at least one mold cavity out of the furnace to solidify the workpiece.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying figures, in which like reference numerals refer to identical or functionally similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein.

[0016] FIG. 1 depicts a Bridgeman apparatus for the manufacture for a SX part.

[0017] FIG. 2 is a drawing of a directional solidification vacuum casting furnace.

[0018] FIG. 3 is a drawing of a single chamber directional solidification (DS) vacuum furnace with a ladle-less pour in accordance with an embodiment of the disclosure.

[0019] FIG. 3A is an outer view and a cut-away view of the interior mechanism of the melt chamber according to an embodiment of the disclosure.

[0020] FIG. 3B shows view of the chill plate of an embodiment of the disclosure compared to a conventional chill plate.

[0021] FIG. 4 is drawing showing the design of a double wall of the furnace in accordance with an embodiment of the disclosure.

[0022] FIG. 5 is drawing showing configurations of the fixed stopper and pour cup of ladle-less pour in accordance with an embodiment of the disclosure.

[0023] FIG. 5B is drawing showing configurations of melt able stopper and pour cup of ladle-less pour in accordance with an embodiment of the disclosure.

[0024] FIG. 5C shows a mold configuration in accordance with an embodiment of the disclosure.

[0025] FIG. 5D shows a vacuum casting susceptor canister in accordance with an embodiment of the disclosure.

[0026] FIG. 6 is drawing showing general design of the heating system in accordance with an embodiment of the disclosure.

[0027] FIG. 7 is drawing showing details of mold cooling in accordance with an embodiment of the disclosure.

[0028] FIG. 8 is drawing showing control elements of the furnace in accordance with an embodiment of the disclosure.

[0029] FIG. 9 is a cross sectional view of a ladle-less DS vacuum furnace in accordancewith an embodiment of the disclosure.

[0030] FIG. 10 is a cross sectional diagram of a ladle-less DS furnace in accordance with another embodiment of the disclosure.

[0031] FIG. 11 is a cross sectional diagram of a ladle-less DS furnace in accordance with another embodiment of the disclosure.

[0032] FIG. 12 is a cross-sectional diagram of a ladle-less DS furnace in accordance with another embodiment of the disclosure.

[0033] FIG. 13 is a graph of surface area as a function of cone height furnace in accordance with an embodiment of the disclosure.

[0034] FIG. 14 is a diagram of a method of operating the furnace in accordance with an embodiment of the disclosure.

[0035] FIG. 15A is a photomicrograph of a section of cast part showing a linear orientation of the grain structure in accordance with an embodiment of the disclosure.

[0036] FIG. 15B is a photomicrograph showing an overhead view of the grain structure of the cast part in accordance with an embodiment of the disclosure.DETAILED DESCRIPTION

[0037] The particular values and configurations discussed in the following non-limiting examples can be varied and are cited merely to illustrate one or more embodiments and are not intended to limit the scope thereof.

[0038] Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments are shown. The embodiments disclosed herein can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art. Like numbers refer to like elements throughout.Definitions

[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprise" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0040] Throughout the specification and claims, terms may have nuanced meanings suggested or implied in context beyond an explicitly stated meaning. Likewise, the phrase “in one embodiment” as used herein does not necessarily refer to the same embodiment and the phrase “in another embodiment” as used herein does not necessarily refer to a different embodiment. It is intended, for example, that claimed subject matter include combinations of example embodiments in whole or in part.

[0041] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0042] It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

[0043] It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

[0044] The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

[0045] As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0046] The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinationsthereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAG, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.Furnaces

[0047] Conventional DS furnaces are suitable for high volume production using large molds (18” to 32” in diameter) made via a conventional shell process. Theses furnaces require high capital investments typically over three (3) million dollars excluding the investment required for building infrastructure. This leaves the lower volume projects requiring DS components waiting in line for months or years and costing a premium compared to high production parts.

[0048] A typical directional solidification vacuum casting furnace is shown in FIG. 2. This type of furnace 200 is suitable for high volume production using large molds (18” to 32” in diameter) made via a conventional shell process. The furnace includes a vacuum chamber 210 which contains a separate container or ladle 220 in which the metal or alloy is melted before the molten metal is poured into a mold 230. An elevator apparatus 240 can move the mold 230 from the hot zone into the cool zone in order to solidify the workpiece. A vacuum pump 250 keeps the vacuum chamber under a vacuum in order to inhibit the formation of non-metal oxides in the workpiece, which can weaken the workpiece and cause failure under the high temperatures and stresses to which nickel alloy parts are subject.

[0049] In Investment casting production, there are large vacuum furnaces that need large “tree” structures to load and cast multiple parts in one shot. Due to the size of these “tree” systems they get constructed across several steps as individual bodies, and over the course they get assembled into one large structure. These get loaded into the furnace and one casts multiple bodies simultaneously. These furnaces are very large and require significant facility resources to run. To counter this, there are more and more needs to have castings with faster timelines and at lower quantity. With the process of the conventionalart, there is a 12-18-month lead time before receiving castings. With the technology of the disclosure, one obtains castings and iterations in 6-8 weeks or even a few days.

[0050] Leveraging 3D printing produces ceramic molds, and these molds are designed to interface directly with the casting furnace and are fully unlocking the design freedom and material performance to load and cast metal parts in a ceramic mold that is fully 3D printed. These single body molds are made up of a: pour cup, cast body, structural support to hold the part, grain selector, and ladle-less pour stopper. In another embodiment, the stopper is a separate piece unless it is soluble in the melt. That is, the stopper is not necessarily integral to the mold.

[0051] The casting furnace is designed in such a way to ingest the 3D printed ceramic mold, and interface directly with the ladle-less pour stopper. Once the alloy charge is placed into the pour cup on the mold, the mold gets loaded into the furnace, the pour stopper is armed with the mold, the furnace closes, vacuum is pulled on the whole vessel, and a temperature ramp leverages a custom tuned susceptor design that ensures full heat penetration into the mold. Once the desired temperature of molten the alloy is achieved, one then increments down the elevator that the mold is placed on, that triggers the pour stopper and allows the molten alloy to flow into the cast body of the printed mold. There is an immediate cooling ramp part of the procedure so that the alloy is allowed to densify in the 3D printed ceramic mold, once cooled the mold is pulled from the furnace and processed off to get to the metal casted part

[0052] A smaller furnace can be optimized to small batches of parts would reduce the space, initial investment cost, and energy requirements for a DS furnace. Conventional furnaces also typically require separate heating components and chambers for the molten feed metal and the mold. Combining these sections further reduces cost and footprint.

[0053] In an embodiment, a DS furnace is formed from of a single vacuum chamber where both the mold and charge are loaded. The charge is placed into a separate section of the mold, referred to as the pour cup, and heated past its melting point while simultaneously preheating the mold. The charge is allowed to flow into the rest of the mold after melting and reaching sufficient superheat. This may be done by a stopper mechanism or a non-reactive metallic pin that can dissolve into the melt and not appreciably alter the charge chemistry. In one aspect, the at least one mold cavity and the melt pour cup are asingle piece formed by 3D printing. After releasing the charge into the mold, a mechanical axis (ram) lowers the mold out of the heating region at a controlled rate to encourage directional solidification in the part.

[0054] After the mold reaches the bottom of travel, the heater is turned off and argon is flooded into the chamber to cool the mold and pressurize the chamber to ambient atmospheric levels. The mold is then removed from the furnace by moving the filled mold back to the position where it was loaded.

[0055] To help faster melting of the charge in the ladle-less casting method, heat flux to the alloy charge needs to be increased by more direct radiation. This is true for the technology of ladle-less directional solidification (DS) vacuum furnaces, where the lack of a moving zone result in the loss of a degree of freedom. This can be accomplished by utilizing a susceptor having a cylindrical body with conical top and bottom sections.

[0056] More efficient casting can be achieved with a single chamber directional solidification vacuum casting furnace with a ladle-less pour, such as is shown in an embodiment of the disclosure depicted in FIG. 3.

[0057] Referring to FIG. 3, melt chamber 300 includes a ladle-less melt reactor 302 that is actively cooled by a double wall 304. The reactor includes a melt pour or charge cup 306 configured to directly melt the charge in the melt pour cup using a “ladle-less pour.” Heat is supplied by a susceptor 308 driven by induction coil 310. A melt or stopper mechanism 312 is designed to seal the mold pour cup-opening 316 where melt enters the at least one mold cavity 318. In this embodiment, the melt or pour stopper mechanism 312 is fixed and attached to the chamber with rod 314. The melt pour or charge cup 306 rests on a chill plate 334 which serves to help chill the charge cup and preserve any seed crystal, if present.

[0058] In an embodiment, an argon purge system 324 is introduced to cool down the mold upon completion of the withdrawal cycle. Therefore, the mold can be off-loaded from the furnace as with mold elevator or “ram” 326 as quickly as possible and without any safety concern.

[0059] The “ram” 326 is a moving platform that raises and lowers the mold at a controlled rate between process stages. It includes a servo motor 328 mounted below the vacuum chamber, a mechanical coupling 330 that passes through the chamber floor, a ball-screwassembly 332 that’s rotated by the motor through the coupling, a linear shaft 334 that supports the chill plate 316. The chill plate supports and cools the bottom of the mold, and a support frame 322 that provides horizontal and torsional support to the linear shaft. Most furnaces used in industry rely on hydraulic controls for moving the ram or platform; this design required more rapid movement for initial pull of the stopper which is better supplied by a servomotor and ball-screw combination.

[0060] FIG. 3A is an outer view and a cut-away view of the interior mechanism of the melt chamber according to an embodiment of the disclosure. The melt or pour stopper mechanism 312 is fixed and attached to the chamber with rod 314, which together form a pour stopper with the stopper mechanism being nestled in a charge cup 315. The charge cup 315 leads to the cast body 317, into which the molten charge is poured. A stand or base 319 supports the cast body. In an embodiment the pour stopper, rod cast body and stand are a single piece formed by 3D printing. In this embodiment the pour stopper is formed from a material or metal that has the same or similar melting point is the metal charge, and upon heating the pour stopper melts to admit the molten metal into the cast body. In another embodiment, the pour stopper and rod are a single piece, which may be 3D printed, which has a higher melting point than the metal charge. When the metal charge forms a melt upon heating, the rod and pour stopper can be raised to permit the molten metal into the mold or cast body. An area around casting mold filled with custom designed / 3D printed filler material 321 to optimize casting solidification profile for components within mold. All the component parts shown in FIG. 3A may be 3D printed.

[0061] FIG. 3B shows view of the chill plate 334 of an embodiment of the disclosure compared to a conventional chill plate 336. The conventional chill plate 336 is based on a shell and tube heat exchanger. The chill plate 334 of the disclosure is formed by additive manufacturing, i.e., 3D printing to form a single unified construction. The chill plate can have cooling fluid circulating inside. Alternately the chill plate can be electrically cooled using a Peltier.

[0062] 3D printing or additive manufacturing (AM) may be used to manufacture components of the apparatus of the disclosure. Seven AM technologies are defined by, ISO ASTM 52900. These include binder jetting (BJT) which produces parts by selectively depositing a binding agent over a powder bed. BJT uses the same powder-spreadingmethods as powder bed fusion (PBF). However, unlike PBF, a liquid binding agent bonds parts instead of a laser and / or beam. With Directed Energy Deposition (DED), powder or wire is pushed through a nozzle and melted by an intensely focused energy source (usually a laser) at the point of deposition. The molten material is incorporated into the energy flow, melting and depositing at the same time. Powder bed fusion (PBF) uses an energy force to selectively melt or sinter powdered material. A large bed of powdered material is heated to just below its melting point and spread over the build platform in a fine layer. The energy source (usually a laser or electron beam) is then directed across the powder’s surface, which bonds the powder, forming a thin layer of combined material.

[0063] Induction heating can be utilized in vacuum furnaces since a heat transfer medium (such as air, hydrogen, nitrogen, or argon) isn’t necessary to heat the metal charge. For a smaller chamber, as in an embodiment, induction heating also reduces the insulation and space required for the heating elements in the chamber.

[0064] In an embodiment of the disclosure, an indirect induction heating method is optimal since the heater must heat both the charge and mold simultaneously. This is formed from of the induction coil 310 and conductive susceptor 308. The Induction coil heats the susceptor to a temperature slightly exceeding that of the desired metal and mold temperatures. This can be further optimized by customizing the coil design to heat the upper section of the susceptor more than the bottom or vice versa depending on the sensitivity of the alloy and the makeup of the ceramic in the mold.

[0065] In an embodiment, the susceptor 308 is formed from graphite. However, the susceptor can also be formed from other materials such as aluminum, carbon steel, copper stainless steel, silicon carbide or molybdenum. However, susceptors are often made from graphite because it is highly resistive and very machinable and a range of temperatures up to 3,000°C (5,430°F). The susceptor can be made in the form of a crucible, disk, tube, a layer in the material, or whatever form best suites the application.

[0066] In an embodiment, an isolation shutter 320 is made of heat resistant alloy (preferably nickel based alloys) with ceramic shield / coating to block the susceptor lower end once the mold is totally out of the furnace. This will allow the heat transfer from the susceptor to the chamber to be significantly reduced during mold cooldown operation.

[0067] These alloys may be HASTELLOY, HAYNES or INCONEL alloys that may containFe, Mo and Cr. HASTELLOY Alloy X contains Ni 47.5, Cr 21.8, Fe 18.5, and Mo 9.0 in wt %. INCONEL Alloy 625 contains Ni 61.0, Cr 21.5 Mo 9.0, Nb+Ta 3.6 by Wt%. INCONEL Alloy 718 contains Ni 52.5, Cr 19.0 Fe 18.5 Mo 3.0 Nb+Ta 3.6 by wt %. INCONEL Alloy 600 contains Ni 52.5, Cr 19.0 Fe 18.5 Mo 3.0 Nb+Ta 3.6 by wt %. INCONEL Alloy 601 contains Ni 61 Cr 23 C 0.10 Mn 1 .0 Al 1 .4 Fe balance S 0.015 Si 0.5 by wt %. INCONEL Alloy 800H / HT contains Fe base, Ni 32, Cr 21 , Mn 1 .5, Ti-AI strengthened by wt %.

[0068] The isolation shutter 320 also has a ceramic shield. The material of this shield may be carbides such as HfC, TaC, NbC, TiC, SiC, VC or ZrC. Nitride ceramics include HfN, TiN, ZrN, TaN, NbN and VN. The ceramics can also include borides. The properties of high temperature ceramics can be seen in Table 1 .Table 1 . Crystal structures, densities and melting points of high temperature ceramics.

[0069] Additional applicable ceramics include silica and alumina. Silica is formed fromsilicon and oxygen and has the general formula:where 0 < x < 2. The family includes orthosilicate, metasilicate and pyrosilicate. Alumina ceamics are based on AI2O3 and It occurs naturally in its crystalline polymorphic phase a- AI2O3 as the mineral corundum. Hybrid ceramics can be made from both silica and aluminum as (SiC HAhOs). Mullite is formed from (3Al2O3*2SiO2). There are also magnesium silicates and alkaline earth silicates.

[0070] DS furnaces require parts to be at elevated temperatures for significant periods of time. This leads to two requirements: Active cooling of the chamber walls and an inert or vacuum atmosphere. The chamber is actively cooled by means of a double wall that is sealed internally and allows the flow of a cooling medium between the walls. Water or other coolant is pumped through ports in the outer wall and recirculated through a chiller to remove heat generated during the casting process. Typically the lid or door of the chamber is cooled in a similar manner.

[0071] The design 400 of the double wall 304 can be seen in the diagram in FIG. 4. The double wall 304, 410 is sealed internally and allows the flow of a cooling medium 420 between the walls. Water or other coolant is pumped through ports 430a, 430b in the outer wall and recirculated through a chiller 440 to remove heat generated during the casting process. Typically the lid or door 450 of the chamber is cooled in a similar manner. The coolant can be pumped directly inside the double wall. Optionally, cooling coils 460 can be installed the double wall, through which the coolant is circulated.

[0072] Active cooling is provided to other components inside of the chamber as well. These include but are not limited to the chill plate, chill spool, and induction coil (if using induction heating). Copper tubing is the preferred material for cooling components, but stainless-steel tubing or braided hose may be used for areas that aren’t being directly heated.

[0073] Configurations of the stopper and pour cup of ladle-less pour can be seen in FIG. 5. FIG. 5A shows a stopper 510, corresponding to the stopper 312 of FIG. 3, the bottom of which is inserted into an opening 520 and acts as stopper of mold cup 530. In operation themold cup is charged with metal ingots 540. The ingots are heated until they melt. Then the mold cup and mold are lowered while the stopper remains stationary. As the mold cup is lowered the molten metal pours through the opening and into the mold 550. In this configuration the stopper and the mold cup are formed of the same material, which may be a ceramic material, to assure a good fit of the stopper into the mold cup.

[0074] The configuration shown in FIG. 5B has similar elements as in FIG. 5A. In this configuration, the stopper 560 is not held stationary by an arm extending outside of the pour cup. In this embodiment, the stopper may be shortened to be completely inside the pour cup, and it is made out of the same or similar material as the metal charge. When the mold cup is heated both the charge and stopper melt, and the molten material flows into the mold. Differential heating can provide an option where the metal charge melts before the stopper. That is, the stopper may be designed to melt at a temperature above the melting point of the charge so as to modulate the melt viscosity as it enters the mold.

[0075] FIG. 5C shows a mold configuration in accordance with an embodiment of the disclosure. In this embodiment a raw material cavity 565 connects to a mold cavity 570 via a throttle point 575. Seeds, if present, can be found at the bottom 580 of the mold cavity. The mold packing area 585 around the casting mold is filled with custom designed 3D printed filler material to optimize the casting solidification profile for components within the mold. In contrast, in the conventional art, the ladle acts as a funnel. The mold of the disclosure has no ladle and thus has a simplified design.

[0076] FIG. 5D shows a vacuum casting susceptor canister in accordance with an embodiment of the disclosure. The canister includes a vacuum port 590, a threaded lid 592 and dovetail guides 594. The canister provides optimized / reduced vacuum volume to match the core / shell mold. Exchangeable canisters reduces the need for a large vacuum chamber. Pulling a vacuum can be done in separate station, this reducing production time. The dovetail guide / chill plate interface increases cooling efficacy. The canister can be formed from a compatible material for 3D printing fabrication.

[0077] For this type of furnace, an indirect induction heating method is optimal since the heater must heat both the charge and mold simultaneously. This includes an induction coil and conductive susceptor. The Induction coil heats the susceptor to a temperature slightly exceeding the desired metal and mold temperatures. This can be further optimized bycustomizing the coil design to heat the upper section of the susceptor more than the bottom or vice versa depending on the sensitivity of the alloy and the makeup of the ceramic in the mold.

[0078] In contrast, typical casting furnaces heat the mold and the metal charge separately, this furnace uses a common heating chamber with the charge pre-loaded in the mold. The melt must be released to enter the mold at the appropriate time when both mold preheat and metal “superheat” have been achieved. This may be achieved with the “ladleless” pour method of the disclosure which may be a mechanical stopper that is removed to allow premelted material to enter the mold or a dissolvable plug of inert material that will diffuse into the molten charge over time once sufficient superheat has been achieved and allow flow through the recess where the solid plug was.

[0079] The general design of the heating system can be seen in the cross sectional views and top views shown in FIG. 6. For this type of furnace, an indirect induction heating method is optimal since the heater must heat both the charge and mold simultaneously. This includes an induction coil 610 and conductive susceptor 620. The Induction coil is designed to heat the susceptor to a temperature slightly exceeding the desired metal and mold temperatures. This can be further optimized by customizing the coil design to heat the upper section of the susceptor more than the bottom or vice versa depending on the sensitivity of the alloy and the makeup of the ceramic in the mold.

[0080] The susceptor 620 is a ring of graphite or other electrically conductive material that heats when energized by the induction coil. Its inner diameter must be large enough to allow a mold and chill plate to travel through with a slight gap. Its thickness should be such that it can store heat to prevent temperature fluctuations during the heating and holding cycles. It’s thermally insulated from the induction coil by a set of high temperature insulation shields 630 around the perimeter and top. The top insulation section 630a protects the chamber and equipment from radiant heat escape from the mold and melt as well as the susceptor itself. The susceptor should be monitored for temperature in multiple places both radially and along the height to prevent overheating of the mold and melt. The temperature is monitored using thermocouples 640 in the susceptor. Each thermocouple is mounted in a boron nitride plug 660.

[0081] The coil is a simple multi-turn round coil that wraps around the susceptorinsulation. Chilled water is pumped through the coil to maximize induction efficiency and prevent damage to the coil. It’s coated in an epoxy paint 650 designed to minimize arcing between turns of the coil and mounting hardware in a vacuum environment.

[0082] In the disclosure, the graphite susceptor may be divided in two sections (second generation), and the shape of the susceptor top section is changed to a conical shape. Other shapes like a dome can also be utilized. By introducing this modification, radiation view angle between the alloy charge and susceptor is changed and consequently, more heat radiates directly to the charge and hence results in faster melting. In addition, more uniform temperature profile and sharper temperature gradient can be obtained which both help to optimize the DS solidification process for complex part geometries.

[0083] There are many advantages to the susceptor and furnace of the disclosure. There is a potential solution to accelerate melting alloy charge and eliminate the need for induction melting. Competitive differentiation increases versus comparable technologies. The technology of the disclosure lowers the cost of manufacturing of the DS furnace by eliminating the need for induction melting. The furnace and susceptor of the disclosure is technically very feasible, and easy to implement.

[0084] Details of mold cooling are shown in FIG. 7. During the process of moving the mold through the heated susceptor, the bottom of the mold and part must be cooled below the solidification temperature of the molten metal to ensure that the grain growth of the metal proceed from the base of the casting to the top. Directly below the susceptor base insulation is a “chill spool” 710 formed from a fabricated copper “spool” that is actively cooled by an attached copper coil with chill water pumped through. As the mold is lowered through the chill spool, heat is extracted by means of radiation and transferred to the chill water by conduction through the spool.

[0085] To prevent heating of the mold as it fully exits the susceptor, a heat shield 720 may be installed. In this embodiment the heat shield is below the chill spool, but it can be to the side of the chill spool in an alternative embodiment. This heat shield 720 is an actively cooled metal plate that is actuated by mechanical means between the bottom opening of the chill spool and the top of the mold. This prevents radiative heating of the top of the mold after it exits the chill spool. This feature also protects components in the chamber below the chill spool from overheating due to overexposure from the radiant heat of the susceptor.

[0086] The pouring mechanism design of the disclosure is a unique departure from the conventional art. Typical casting furnaces heat the mold and the metal charge separately, this furnace uses a common heating chamber with the charge pre-loaded in the mold. The melt must be released to enter the mold at the appropriate time when both mold preheat and metal “superheat” have been achieved. This may be achieved with a “ladle-less” pour method which may be a mechanical stopper that is removed to allow premelted material to enter the mold or a dissolvable plug of inert material that will diffuse into the molten charge over time once sufficient superheat has been achieved and allow flow through the recess where the solid plug was.

[0087] Melting a metal charge for casting in the same chamber as the mold is heated greatly decreases the complexity and cost of a vacuum furnace. This is enabled by use of a mechanical or chemical plug that may be removed when the charge reaches sufficient superheat to fill the mold cavity and solidify at the desired rate.

[0088] In contrast to the ladle-less casting of the disclosure, traditional ladle casting requires heating a volume of metal in a separate vessel (ladle or crucible) with a separate heating element than the mold, after which the ladle is moved over the mold and metal is released to fall into the pour cup of the mold. This is done by tipping the ladle or opening a trapdoor in the bottom of the ladle. Integrating the metal charge into the mold eliminates the ladle and separate heating source for the ladle / crucible.

[0089] Active cooling is provided to other components inside of the chamber as well. These include but are not limited to the chill plate, chill spool, and induction coil (if using induction heating). Copper tubing is the preferred material for cooling components, but stainless-steel tubing or braided hose may be used for areas that aren’t being directly heated.Controls and Safety Considerations

[0090] The controls system in this furnace design manages component cooling, susceptor heating, and atmosphere management.

[0091] Referring to FIG. 8, in the system 800, component cooling is provided by a chiller 802 that pushes coolant through a manifold 804 where both inlet and outlet flow of each chill circuit 806 is monitored. Pressure is kept constant for each chill circuit, but flow isregulated by means of pressure regulators 808 and / or control valves 810 that balance flow as needed to each circuit. Flow rates and pressure at the inlet and outlet of each circuit are compared to determine if there is a leak or blockage and shut down the heating system when there’s an issue. Mass flow controllers (not shown) can also be utilized.

[0092] Susceptor heating must be well controlled to ensure the correct temperature ramp rate and thermal gradient. If the mold is heated too quickly it could result in cracking and escape of molten material into the chamber. If it heats too slowly, the melt could be held at a melting temperature long enough to evaporate lower melting point elements, resulting in a cast component that isn’t within chemistry requirements.

[0093] Temperature monitoring is done by means of multiple thermocouples 640 placed at various heights and positions in the susceptor 620, as was shown in FIG. 6. Depending on the coil and susceptor design, there may be a significant temperature gradient from the bottom of the susceptor to the top. Placing thermocouples throughout the susceptor provides tighter temperature control and over temperature protection. The thermocouples are housed in machined boron nitride plugs 660 that thread into the susceptor. These plugs provide high thermal conductivity and physical protection to the thermocouples.

[0094] A thermocouple can be incorporated into a well in a fixed ceramic stopper to directly measure the melt temperature. A high temperature k-type thermocouple can measure up to 1370 °C or 2498 °F. Other high temperature thermocouple Probes are designed for use in extreme temperatures, up to 2315°C (4200°F). These probes utilize either Platinum / Rhodium (types R, S, or B) or Tungsten / Rhenium (types G, C, or D) elements.

[0095] Temperature control is provided by varying the field intensity of the induction coil based on a programmed PID response based on ramped temperature inputs from the controller and feedback from the thermocouples.

[0096] Atmosphere management involves monitoring gas pressure and temperature in the chamber 812 as well as introducing argon 814 to assist in cooling and repressurization. A vacuum pump 816 continuously removes gas from the chamber during the casting process. At least one gauge 818 monitors pressure, temperature and gas composition. Prior to heating, the oxygen level in the chamber must be within a certain range to ensure safety and that the molten material doesn’t form oxides or have other detrimental reactions.During casting operation, argon may be bled into the chamber to precipitate evaporated metal and ensure that the vacuum pump has a minimum gas flow for operation. Argon is purged or flooded into the chamber after the casting process is complete and the mold has cooled sufficiently to ensure full metal solidification and minimal part distortion. This argon flood continues until the susceptor has reached safe temperature levels and the pressure inside the chamber is equal to atmospheric pressure.

[0097] Having chilled water circuits in an enclosed space with high temperature components allows for the possibility of steam generation in the vessel if a leak were to happen. The hazards of this are largely mitigated by constantly pulling vacuum on the chamber which should evacuate steam as it’s generated. The flow in vs out differential triggers an emergency shutdown that disables the induction coil. A burst-disc is also furnished a backup if these systems aren’t sufficient to prevent pressure buildup.

[0098] The combination of the isolation shutter with the argon purge system produces unexpected advantages. This combination helps furnace to operate in a production environment without safety and throughputs concerns.

[0099] FIG. 9 is a cross sectional view of a ladle-less DS vacuum furnace in accordance with an embodiment of the disclosure. In FIG. 9 the cylindrical shaped furnace has walls 905 that may be made from quartz. Outside the walls 905 are induction coils 910 which are connected to an induction heating power source 915. Inside of the walls is a susceptor 920 that may be made from graphite. In this embodiment the susceptor 920 has a single zone in the form of a hollow cylinder. Inside of the susceptor is a metal ingot 925 resting on a basin 930. Below the basin is a mold 935 into which the molten metal flows after the ingot is melted by the furnace. The mold may rest on a pedestal 940 which may be attached to a ram configured to lower the mold out of the furnace. The basin, mold and pedestal may be made from materials highly resistant to heat, such as silicon carbide, molybdenum, graphite, stainless steels and other conductive materials. The basin, mold and pedestal may be formed as a single piece by 3D printing. In the furnaces of the disclosure there are no ladles to pour molten metal or elevators to move the mold through different heat zones, thereby resulting in a simplified and more cost effective design. In an embodiment, the induction coils my not be present, and any device capable of providing electromagnetic energy may be used to heat the susceptor. This susceptor can also be used in the ladle-less furnace shown, for example, in FIGs. 3 and 5 and the associated text.

[0100] FIG. 10 is a cross-sectional diagram of a ladle-less DS furnace 1000 in accordance with another embodiment of the disclosure. This embodiment has many of the components shown in the embodiment of FIG. 9. However, in this embodiment the susceptor 1020 is divided into a first bottom zone 1022 and a second top zone 1024 located over the bottom zone. The first bottom zone 1022 is a hollow cylinder, on top of which is the second top zone 1024, which is in the shape of a cone or a downward facing ramp. FIG. 10 also shows a top wall 1045 and a view port 1050 through which the ingot may optionally extend.

[0101] FIG. 11 is a cross sectional diagram of a ladle-less DS furnace in accordance with another embodiment of the disclosure. The furnace depicted in FIG. 1 1 has many of the features of FIG. 10. In this embodiment, the furnace 1100 has a susceptor 1 120 that is divided into three zones: a central cylindrical zone 1123, a top zone 1 124 that is in the shape of a downwardly sloping ramp or cone, and a bottom zone 1125 in the shape of an upwardly sloping cone or ramp. The induction coils are also divided into three zones allowing for differential heating: a central zone 1 160, a lower zone 1161 and an upper zone 1 162. An additional feature is a ram or elevator 1 170 configured to lower the mold from the furnace into a cooling zone.

[0102] That is, this susceptor design features a horizontally split susceptor 1 120 with a typical annular cylinder geometry at the base and a sloped down facing ramp 1124 in the top section. The bottom section could also have an upward facing ramp 1125 to direct energy away from the base which is actively cooled. Thickening the top section also provides more thermal mass to soak the heat from the induction coil 1162. This allows for smaller temperature swings during the heating process and less chance of overheating the melt.

[0103] The differing shapes of the first zone and the second and third zones provide different surface areas radiating heat onto the workpiece, i.e., the metal ingot. The cylindrical part has a surface area calculated as:A = 2irrh + 2nr2where A is the area, r is the radius and h is the height of the cylinder.

[0104] In contrast, the surface area of a cone is calculated as:A = TTr(r + (h2+ r2)1 / 2) where A is the area, r is the radius at the bottom of the cone and h is the height of the cone.

[0105] In an example, when the susceptor is a one piece cylinder (no cone) with a height of 100 cm and a radius of 10 cm, the surface area is 6,912 cm2. In contrast, in an embodiment in which the cylindrical bottom part of the susceptor is 80 cm in height, the cylindrical top part of the susceptor is 20 cm in height, and the radius is 10 cm, the Area is calculated as 5,655 (cylinder) + 1 ,017 (cone) = 6,672 cm2. In this embodiment, the surface area cylinder / cone is 96.5 % of that of the cylinder. If inches instead of cm are used, the figures would be the same. Comparison of some cylinder / cone geometries are set forth in Table 2.Table 2. Surface Area of Cylinder / Cone Susceptors (cm2or inches2).

[0106] FIG. 12 is a cross-sectional diagram of a ladle-less DS furnace 1200 in accordance with another embodiment of the disclosure. This embodiment has many of the components shown in the embodiments of FIG. 9 and FIG. 10. However, in this embodiment the susceptor 1220 is divided into a first bottom zone 1222 and a second top zone 1224 located over the bottom zone. The first bottom zone 1222 is a hollow cylinder, on top of which is the second top zone 1224, which is in the shape of a dome. A dome or cone-like structure may also be present under the first bottom zone 1222.

[0107] In this embodiment the surface area of the dome can be calculated as:A = 2irrh, where A is the surface area, r is the radius at the bottom of the dome, and h is the height ofthe dome.

[0108] In an example of this embodiment, when the susceptor is a one piece cylinder (no dome) with a height of 100 cm and a radius of 10 cm, the surface area is 6912 cm2. In contrast, in an embodiment in which the cylindrical bottom part of the susceptor is 80 cm in height, the dome-shaped top part of the susceptor is 20 cm in height, and the radius is 10 cm, the Area is calculated as 5655 (cylinder) + 1257 (cone) = 6912 cm2. In this embodiment, the surface area cylinder / cone is 96.5 % of that of the cylinder. If inches instead of cm are used, the figures would be the same. Comparison of some cylinder / cone geometries are set forth in Table 3.Table 3. Surface Area of Cylinder / Dome Susceptors (cm2or inches2).

[0109] As can be seen, when the upper part of the susceptor is a dome, the surface area of the susceptor stays about the same as compared to the surface area of the embodiment where the susceptor is only cylinder shaped. In contrast, the surface area change when the top of the susceptor is a cone or downward ramp can be seen in FIG. 13, which is a graph of surface area as a function of cone height furnace in accordance with an embodiment of the disclosure. As can be seen, the surface area can be modulated to an extent by varying the length of the cone.

[0110] However, it should be noted that the magnitude of the radiant flux is not determined by the surface area of the susceptor. When the susceptor has a cone or dome shape portion, parts of the susceptor are closer to the workpiece than in the cylindrical section. In the embodiments of the disclosure, the radiant flux can be modulated to a muchhigher degree than when the susceptor is only cylindrical in shape.

[0111] Moreover, Magnetic flux control, i.e., modification of the magnetic field distribution and intensity may be accomplished by variation of shape and positioning of the induction heating coil turns, by insertion of the non-magnetic shields or the magnetic templates that may be all called the magnetic controllers. Each method of magnetic control has its own advantages.

[0112] Splitting the susceptor allows for preinstalling the mold and stopper then installing the upper section whose inside diameter is reduced and may collide with the mold if lowered from the top. The susceptor could be manufactured in one piece if the mold was removable from the bottom of the furnace instead. Thermocouples are installed in both the upper and lower sections to manage process control.

[0113] Splitting the susceptor into more than two segments or matching the contours of the susceptor to geometry and / or functional zones of the mold would allow for more uniform heating of the mold initially though it could result in inconsistencies during the drawing cycle.

[0114] In order to measure and modulate the heat flux, thermocouples are installed in the susceptor, as can be seen in FIG. 6 (previously discussed), which shows a susceptor cut (cross-sectional) section 620 with thermocouple mounting holes. The top section 625 is angled for better radiation coupling to the charge, where the bottom section is the typical design for induction susceptors. The top section has at least one hole 630 configured for a thermocouple. The bottom section 635 has at least one hole 640 configured for a thermocouple.

[0115] The susceptor configurations depicted in FIGs. 9 to 12 can also be used in the ladle-less furnace shown, for example, in FIGs. 3 and 5 and the associated text.Operation of the Furnace

[0116] The operation of the furnace is diagrammed in FIG. 14.

[0117] In step 1402 the stopper is installed in the mold. The stopper may be a fixed ceramic stopper or the melt able metal stopper. In step 1404 the pour cup is charged with metal, the mold and metal charge are placed inside the furnace, and then secured 1406. In step 1408 the furnace is closed and the mold is moved into the starting position. In step1410 the furnace chamber is sealed and a vacuum is pulled to the desired level. At step 1412 the temperature is ramped up to casting temperature and hold at that temperature to ensure mold and metal reach the temperature. Step 1414 is the ladle-less pour where, if the stopper is fixed, the mold is pulled or, alternately, if the stopper is melt able, held at temperature longer to ensure that the stopper has fully melted. The melt thus pours from the melt cup into the mold.

[0118] After the mold is filled with molten metal, in step 1416, the mold is moved through the chill spool at a prescribed rate for directional solidification. In step 1418, when the mold is below the chill spool, the shield is closed off and mold is rapidly drawn to the bottom positon. The mold and susceptor are cooled in step 1420. Next, in step 1422, argon is flooded into the chamber until the internal pressure reaches that of the outside atmosphere. Purge valves are opened so that air enters the chamber and argon is let in, in step 1424. In step 1426 air is allowed to reach safe levels in the chamber. The mold is moved to an unloading position in step 1428. Finally, in step 1430, the chamber is opened and the mold is removed.

[0119] In operation, the melt pour cup is charged with a metal ingot. The metal ingot may be a nickel alloy ingot, which can be Ni-Cr-Fe-based (e.g., INCONELS), Ni-Mo-Fe- based (e.g., HASTELLOY A and B), and Ni-Cr-Mo-Fe-based (e.g., HASTELLOY C and HASTELLOY X). The ingot is melted with heat supplied from the susceptor under an inert atmosphere such as argon. The molten metal is then poured (without a ladle) into the mold through the melt stopper mechanism. The melt is solidified by lowering the mold with the isolation shutter in conjunction with the argon purge system, thus reducing the heat input into the melt chamber.

[0120] Results for the casting technology of the disclosure can be seen in FIGs. 15A and 15B. FIG. 15A is a photomicrograph of a section of cast part showing a linear orientation of the grain structure. FIG. 15B is a photomicrograph showing an overhead view of the grain structure of the cast part. The process of the disclosure thus produces very uniform parts for critical applications such as turbine blades and other parts designed to operate at high temperatures.

[0121] The ladle-less furnace and novel susceptor of the disclosure yields may advantages. These advantages include lowering cost of manufacturing of the DS furnace,pairing 3D printed shell process with the casting process for low volume production, competitive differentiation vs comparable technologies. The technology of the disclosure is technically very feasible and easy to implement. The ladle-less furnace and novel susceptor of the disclosure has advantages that include single piece flow, core / shell compatibility, a vacuum casting canister, is modular, is scalable, has multiple heating source capabilities, has multiple quenching capabilities, and is automation ready.

[0122] All of the compositions and / or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and / or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:1 . A vacuum casting furnace, comprising: a melt pour cup configured to directly melt a charge; a susceptor configured to heat the melt pour cup; and at least one mold cavity configured to receive the melted charge, the at least one mold cavity and the melt pour cup being a single piece formed by 3D printing; and a pin sealing an opening between the melt pour cup and the at least one mold cavity; wherein the vacuum casting furnace does not have a ladle.

2. The vacuum casting furnace of claim 1 , wherein the pin, the at least one mold cavity and the melt pour cup comprise a single piece formed by 3D printing.

3. The vacuum casting furnace of claim 1 , further comprising: an isolation shutter configured to block a lower end of the susceptor once the at least one mold cavity is completely out of the furnace.

4. The vacuum casting furnace of claim 3, wherein the isolation shutter is formed from a ceramic material.

5. The vacuum casting furnace of claim 1 , wherein the susceptor is formed from graphite.

6. The vacuum casting furnace of claim 1 , further comprising: an argon purge system configured to cool down the at least one mold cavity upon completion of a withdrawal cycle.

7. The vacuum casting furnace of claim 1 , further comprising: induction coils configured to heat the susceptor.

8. The vacuum casting furnace of claim 1 , wherein the pin is fixed to the furnace.

9. The vacuum casting furnace of claim 1 , wherein the pin is configured to melt at a temperature of the molten charge.

10. The vacuum casting furnace of claim 1 , wherein the pin is made from ceramic.1 1 . The vacuum casting furnace of claim 1 , wherein the melt pour cup and the at least one mold cavity are made from the same ceramic, thereby promoting fitting the melt pour cup and the at least one mold cavity together.

12. The vacuum casting furnace of claim 1 , wherein a plurality of thermocouples are installed in the susceptor, and each thermocouple is fitted in a boron nitride plug fitted into the susceptor.

13. The vacuum casting furnace of claim 1 , further comprising: an argon purge system.

14. The vacuum casting furnace of claim 1 , further comprising: a ram configured to lower the mold.

15. The vacuum casting furnace of claim 1 , further comprising: a 3D printed chill plate on which the at least one mold cavity rests; and a chill spool near the chill plate.

16. The vacuum casting furnace of claim 1 , wherein the susceptor comprises: a first bottom part, the bottom part having a shape of a hollow cylinder; and a first top part over the first bottom part, the first top part having a shape of a downward sloping cone or a dome.

17. The vacuum casting furnace of claim 16, wherein the first top part has the dome shape, and a surface area of the susceptor is approximately equivalent to a cylinder of a same height.

18. The vacuum casting furnace of claim 16, wherein the first top part has the cone shape, and a surface area of the susceptor can be modulated by varying a length of the cone to a length of the first bottom part.

19. The vacuum casting furnace of claim 16, further comprising a third part under the first bottom part, the third part having a shape of an upward sloping cone.

20. A method of casting a metal workpiece, comprising: placing a metal charge in the melt pour cup of the vacuum casting furnace of claim 1 ; heating the metal charge in the melt pour cup with the susceptor until the metal charge forms a melt; pouring the melt into the at least one mold cavity, the pouring being performed without a ladle; and lowering the at least one mold cavity out of the furnace to solidify the workpiece.

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