System and method for increasing the cooling rate of a metal sand cast during solidification

Abstract

A system and method for increasing the cooling rate of a metal sand cast part during solidification. The system includes a 3D printed manufactured sand mold defining a mold cavity, a coolant inlet port extending into the manufactured sand mold, a plurality of coolant channels surrounding a portion of the mold cavity, and a coolant outlet port in fluid communication with the coolant channels. The system also includes a coolant vapor extraction system having a collection manifold fluidly connected to the outlet port of the sand mold. Molten metal is poured into the mold cavity and liquid coolant is introduced into the sand mold. As the liquid coolant permeates through the sand mold, it changes state to a gas phase, thereby increasing the cooling rate of the cast part. The liquid coolant can be a coolant of liquid nitrogen.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to metal sand casting, and more particularly to a system and method for increasing the cooling rate of an aluminum sand cast during solidification. BACKGROUND

[0002] Sand casting is commonly used for casting aluminum automotive components, such as engine blocks and cylinder heads. In making a typical sand mold, sand is bound together and shaped to conform to a negative impression of the desired automotive component or workpiece. Molten aluminum is poured into the negative impression, also referred to as a mold cavity. Upon cooling and solidification, the cast aluminum component has the shape and geometry of the desired automotive component.

[0003] A typical sand mold is made from sand particles held together with organic or inorganic binders. After the poured aluminum has solidified and cooled to room temperature, the sand mold is opened to remove the cast component. The primary advantage of sand casting is the low cost of the sand mold and casting process. After casting, the sand can be recycled and reused. Sand casting is suitable for small volume and batch production of cast components with complex shapes. However, sand casting does not allow tight tolerances, and the mechanical properties of sand castings are relatively low due to a coarse grain structure, also referred to as microstructure, resulting from the low cooling rate during solidification.

[0004] In sand casting, the resulting microstructure of the cast aluminum component is typically coarse with large dendrite arm spacing (DAS) and high porosity due to the low cooling rate during solidification, as compared to the smaller DAS in metal mold casting, which has a higher cooling rate during solidification. As a result, the mechanical properties of sand castings, such as ductility, ultimate tensile strength (UTS), and fatigue strength, are typically lower than those of metal mold castings.

[0005] Therefore, while the current methods of aluminum sand cast components serve their intended purpose, there is a need for a system and method to increase the cooling rate of sand castings during solidification to improve the ductility, UTS, and fatigue strength of the cast aluminum components. SUMMARY

[0006] According to several aspects, a system for increasing the cooling rate of a metal sand casting during solidification is provided. The system includes a sand mold defining a mold cavity, a coolant channel surrounding a portion of the mold cavity, and a coolant inlet port fluidly connected to the coolant channel. The coolant inlet port is operable to receive a liquid phase coolant, and the coolant channel is operable to direct the coolant as it transitions from the liquid phase to a gas phase.

[0007] In additional aspects of the present disclosure, the coolant is a cryogenic liquid selected from the group consisting of argon gas, helium gas, and nitrogen gas.

[0008] In another aspect of the disclosure, the coolant is a refrigerant selected from the group consisting of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs).

[0009] In another aspect of the disclosure, the sand mold includes an interior mold surface defining a mold cavity, a first region between the interior mold surface and the coolant channel, wherein the first region includes a first permeability, and a second region between the coolant channel and an outer boundary of the sand mold, wherein the second region includes a second permeability. The first permeability is greater than the second permeability.

[0010] In another aspect of the disclosure, the sand mold further defines a coolant outlet port, wherein the coolant outlet port is at least one of (i) in indirect fluid communication with the coolant channel such that the gas phase permeates the sand mold before entering the coolant outlet port, and (ii) in direct fluid communication with the coolant channel.

[0011] In another aspect of the disclosure, the system further includes a coolant vapor extraction system having a vacuum pump configured to extract the gas phase of the coolant from the sand mold.

[0012] In another aspect of the disclosure, the sand mold includes an interior mold surface defining a mold cavity and a heat sink disposed in the sand mold between the coolant channel and the interior mold surface.

[0013] According to several aspects, a system for increasing a cooling rate of a metal sand cast is disclosed. The system includes a sand mold defining a mold cavity, and a coolant inlet port extending into the manufactured sand mold. The coolant inlet port is operable to receive a cryogenic liquid. The sand mold includes a permeability sufficient to cause the cryogenic liquid to transition into a gas phase while permeating through the manufactured sand mold.

[0014] In additional aspects of the disclosure, the sand mold includes a plurality of coolant channels surrounding a portion of the mold cavity. The coolant channels are in fluid connection with the coolant inlet port and are operable to contain the cryogenic liquid transitioning from a liquid phase to a gas phase.

[0015] In another aspect of the disclosure, the sand mold further includes a coolant outlet port in fluid communication with the coolant channel.

[0016] In another aspect of the disclosure, the system further includes a coolant vapor extraction system having a collection manifold in fluid connection with the outlet port of the sand mold.

[0017] In another aspect of the disclosure, the sand mold is manufactured with different sized sand grains by 3D printing.

[0018] According to aspects, a method of increasing a cooling rate of a metal sand cast is provided. The method includes pouring a molten metal into a mold cavity defined by a fabricated sand mold, introducing liquid nitrogen into the sand mold such that the liquid nitrogen transitions from a liquid phase to a gas phase as the nitrogen permeates through the sand mold, thereby increasing a cooling rate of the molten metal, and extracting the gas phase by applying a vacuum.

[0019] In additional aspects of the disclosure, the method further includes 3D printing the fabricated sand mold to define the mold cavity, a channel surrounding a portion of the mold cavity, an inlet port fluidly connected to the channel, and an outlet port fluidly connected to the channel.

[0020] The disclosure also includes the following aspects:

[0021] Aspect 1. A system for increasing a cooling rate of a metal sand cast, comprising:

[0022] a sand mold defining a mold cavity, a coolant channel surrounding a portion of the mold cavity, and a coolant inlet port fluidly connected to the coolant channel;

[0023] wherein the coolant inlet port is operable to receive a coolant in a liquid phase, and the coolant channel is operable to direct the coolant as the coolant transitions from the liquid phase to a gas phase.

[0024] Aspect 2. The system of Aspect 1, wherein the coolant is a cryogenic liquid selected from the group consisting of argon, helium, and nitrogen.

[0025] Aspect 3. The system of Aspect 1, wherein the coolant is liquid nitrogen.

[0026] Aspect 4. The system of Aspect 1, wherein the coolant is a refrigerant selected from the group consisting of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs).

[0027] Aspect 5. The system of Aspect 1, wherein the sand mold comprises:

[0028] an interior mold surface defining the mold cavity;

[0029] a first region between the interior mold surface and the coolant channel, wherein the first region comprises a first permeability; and

[0030] a second region between the coolant channel and an outer boundary of the sand mold, wherein the second region comprises a second permeability;

[0031] wherein the first permeability is greater than the second permeability.

[0032] Scheme 6. The system of Scheme 1, wherein the sand mold further defines a coolant outlet port, wherein the coolant outlet port is at least one of: (i) in indirect fluid communication with the coolant channel such that the gas phase permeates the sand mold before entering the coolant outlet port, and (ii) in direct fluid communication with the coolant channel.

[0033] Scheme 7. The system of Scheme 6, further comprising a coolant vapor extraction system having a vacuum pump configured to extract the gas phase of the coolant from the sand mold.

[0034] Scheme 8. The system of Scheme 7, wherein the coolant vapor extraction system comprises a vacuum pump and a manifold fluidly connected to the vacuum pump, wherein the manifold comprises a vacuum inlet fluidly connected to the outlet port of the sand mold.

[0035] Scheme 9. The system of Scheme 1, wherein the sand mold comprises:

[0036] an interior mold surface defining the mold cavity; and

[0037] a heat sink disposed in the sand mold between the coolant channel and the interior mold surface.

[0038] Scheme 10. The system of Scheme 1, wherein the coolant inlet port is positioned at a lower portion of the sand mold or an upper portion of the sand mold and the coolant outlet port is positioned within the sand mold.

[0039] Scheme 11. A system for increasing a cooling rate of a metal sand cast, comprising:

[0040] a sand mold defining a mold cavity and a coolant inlet port extending into the manufactured sand mold, wherein the coolant inlet port is operable to receive a cryogenic liquid; and

[0041] wherein the sand mold comprises a permeability sufficient to cause the cryogenic liquid to transition into a gas phase while permeating through the manufactured sand mold.

[0042] Scheme 12. The system of Scheme 11, wherein the sand mold comprises a plurality of coolant channels around a portion of the mold cavity, wherein the coolant channels are fluidly connected to the coolant inlet port and are operable to contain the cryogenic liquid transitioning from a liquid phase to a gas phase.

[0043] Scheme 13. The system of Scheme 12, wherein the sand mold further comprises a coolant gas outlet port in fluid communication with the coolant channels.

[0044] Scheme 14. The system of Scheme 13, further comprising a coolant vapor extraction system having a collection manifold fluidly connected to the coolant gas outlet port of the sand mold.

[0045] Scheme 15. The system of Scheme 14, wherein the sand mold is manufactured by 3D printing with different sized sand particles to define a first region having a first permeability and a second region having a second permeability, wherein the first permeability is greater than the second permeability.

[0046] Scheme 16. A method of increasing a cooling rate of a metal sand cast, comprising:

[0047] pouring a molten metal into a mold cavity defined by the manufactured sand mold; and

[0048] introducing liquid nitrogen into the manufactured sand mold such that as the liquid nitrogen permeates through the manufactured sand mold, the liquid nitrogen transitions from a liquid phase to a gas phase, thereby increasing a cooling rate of the molten metal.

[0049] Scheme 17. The method of Scheme 16, further comprising:

[0050] 3D printing the manufactured sand mold to define the mold cavity, a channel around a portion of the mold cavity, and an inlet port fluidly connected to the channel prior to pouring the molten metal;

[0051] wherein the inlet port is operable to receive the liquid nitrogen and the channel is operable to direct the liquid nitrogen as it transitions from the liquid phase to the gas phase.

[0052] Scheme 18. The method of Scheme 17, further comprising extracting the gas phase from the manufactured sand mold by applying a vacuum.

[0053] Scheme 19. The method of Scheme 18, wherein 3D printing the manufactured sand mold further comprises defining an outlet port fluidly connected to the channel; and further comprising applying a vacuum on the outlet port.

[0054] Scheme 20. The method of Scheme 19, wherein 3D printing the manufactured sand mold further comprises providing a heat sink between the channel and the mold cavity.

[0055] Other applicable fields will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0056] The drawings described herein are for purposes of illustration only and are not intended to limit the scope of the present disclosure in any way.

[0057] Figure 1 is a schematic diagram of a system for increasing the cooling rate of an aluminum sand cast during solidification according to a first exemplary embodiment;

[0058] Figure 2 is a schematic diagram of a system for increasing the cooling rate of an aluminum sand cast during solidification according to a second exemplary embodiment;

[0059] Figure 3 is a schematic diagram of a system for increasing the cooling rate of an aluminum sand cast during solidification according to another third exemplary embodiment;

[0060] Figure 4 is a schematic diagram of a system for increasing the cooling rate of an aluminum sand cast during solidification according to a fourth exemplary embodiment; and

[0061] Figure 5 is a block flow diagram of a method for increasing the cooling rate of an aluminum sand cast during solidification according to an exemplary embodiment. DETAILED DESCRIPTION

[0062] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. The illustrated embodiments are disclosed with reference to the drawings, wherein like numerals indicate corresponding parts throughout the several drawings. The drawings are not necessarily to scale and some features can be exaggerated in order to illustrate specific features. The specific structural and functional details disclosed are not intended to limit the scope of the disclosed concepts but merely to illustrate representative embodiments in accordance with the concepts disclosed.

[0063] The term "about" as used herein is known to those skilled in the art. Alternatively, the term "about" includes + / - 0.5% of the stated value. While examples have been described in detail, those skilled in the art who are familiar with the art to which the present disclosure relates will recognize various alternative designs and examples for practicing the disclosed method within the scope of the appended claims.

[0064] In sand casting, the resulting microstructure of cast aluminum parts is typically coarse with large dendrite arm spacing (DAS) due to the low cooling rate during solidification as compared to the smaller DAS in die casting. The DAS for sand castings is about 60 microns while the DAS for die castings is about 20 microns. The smaller DAS in die casting is due to the high cooling rate during solidification. Due to the larger DAS in sand casting, mechanical properties such as ductility, ultimate tensile strength (UTS), and fatigue strength of cast aluminum parts are typically lower than those of die castings. To limit the size of the DAS and minimize porosity in sand cast parts, methods and multiple exemplary embodiments of a system for increasing the cooling rate of aluminum sand castings during solidification are provided.

[0065] The methods and systems introduce a phase change liquid coolant into the sand mold, where as the coolant permeates through the sand mold, the state of the coolant changes from a liquid phase to a gas phase, thereby increasing the cooling rate of the casting during solidification. The sand mold defines a mold cavity for receiving a molten aluminum alloy suitable for forming a cast automotive part. During or after the molten aluminum is poured into the mold cavity, the coolant in a liquid phase is introduced into a flow channel defined through the sand mold. The liquid coolant gasifies, changes state from a liquid phase to a gas phase, and permeates through the sand mold, thereby increasing the cooling rate of the casting during the solidification phase of the casting process. The resulting gas phase is extracted from the sand mold to avoid or minimize gaseous porosity in the cast part.

[0066] The coolant can be a cryogenic liquid or refrigerant that is in a gas phase at an ambient temperature of about 25°C and a pressure of about 1 atmosphere (atm). Cryogenic liquids are defined as liquids with a boiling point below -150°C. Examples of cryogenic liquids include, but are not limited to, argon, helium, nitrogen, hydrogen, methane, oxygen, and mixtures thereof. Preferably, the cryogenic liquid is inert in both the liquid and gas phases, such as argon, helium, nitrogen, and mixtures thereof. Nitrogen is more preferable due to its abundance and low cost. Examples of refrigerants include, but are not limited to, chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs).

[0067] While aluminum casting alloys and cast automotive parts are used for descriptive purposes, the methods and multiple exemplary embodiments of the system can be used for most other metal casting alloys, such as iron, steel, magnesium, copper, zinc, and other alloys suitable for casting automotive and non-automotive parts.

[0068] Figures 1 to 4Four alternative embodiments of systems (system 100, system 200, system 300, system 400) for increasing the cooling rate of metal sand casting, such as aluminum sand casting, during solidification are shown. Each of the illustrated systems 100, 200, 300, 400 includes a metal flask 102 containing a manufactured sand mold 104 having an internal mold surface 106. The internal mold surface 106 includes protruding details and cavities to define a mold cavity 108 having a predetermined shape and geometry for forming the desired profile and features of a cast part. For example, such protruding details and cavities can form cylinder blocks, cylinder heads, and ports and other features of structural components. The manufactured sand mold 104 is typically formed from a refractory material, such as sand, and a suitable binder material to facilitate the mold cavity 108 retaining its predetermined shape and geometry.

[0069] While a metal flask 102 is shown in each of the four alternative embodiments of systems 100, 200, 300, 400, it should be understood that the metal flask 102 is not necessary for some manufactured sand molds 104. For example, for sand molds having chemical binders, the metal flask 102 can not be necessary as sand molds manufactured with chemical binders have sufficient strength to retain their structural integrity without the aid of a metal flask 102. Metal flasks 102 are typically used to house sand molds made from compressed bentonite clay bonded sand, also referred to as green sand.

[0070] In the illustrated example, the sand mold 104 defines a gating system 108 having a hopper 110, a sprue 112, a runner 114, and a riser 116. Molten metal, such as a molten aluminum casting alloy, is poured into the hopper 110 and directed through the sprue 112 to the runner 114. The runner 114, in turn, distributes the molten metal into the mold cavity 108. Most metals have a lower density as a liquid than as a solid, so the cast part can shrink as it cools. Excess molten metal fills the riser 116, which acts as a feeder during solidification to prevent the cast part from shrinking.

[0071] The manufactured sand mold 104 also defines a plurality of coolant channels 118, inlet ports 120A, 120B, 120C, 120D in direct fluid connection with the coolant channels 118, and at least one outlet port 122A, 122B, 122C, 122D operable to collect and transport gaseous coolant out of the sand mold 104. The outlet ports 122A, 122B, 122C, 122D can be in direct fluid connection with the coolant channels 118. The outlet ports 122A, 122B, 122C, 122D can also be spaced apart from the coolant channels 118, in which case coolant gas permeates through the sand mold 104 to the outlet ports 122A, 122B, 122C, 122D, or if an inert coolant is used, the coolant gas is allowed to vent to ambient atmosphere.

[0072] The coolant channels 118 are defined proximate to the mold cavity 108 such that heat from the molten metal is efficiently transferred to the coolant flowing through the coolant channels 118. As the coolant flows through the coolant channels 118 and permeates through the manufactured sand mold 104, the phase change of the coolant from liquid to gas increases the cooling rate of the casting during the solidification process.

[0073] The manufactured sand mold 104 can also include a first region 124 and a second region 126 having different permeabilities. The first region 124 is located between the coolant channels 118 and the mold cavity 108. The second region 126 is located between the coolant channels 118 and an outer boundary of the manufactured sand mold 104, such as a top surface 128 or the metal sand box 102. The first region 124 includes a first permeability that is greater than a second permeability of the second region 126. For example, the first permeability in the first region 124 is 10 -2 to 10 -3 cm / s, and the second permeability in the second region 126 is 10 -3 to 10 -5 cm / s. The difference in permeability can be achieved through additive manufacturing, such as by 3D printing the manufactured sand mold 104 using different sized sand grains.

[0074] The channels 118 for introducing liquid coolant into the sand mold 104 can also be manufactured through the use of 3D printing. 3D printing enables complex coolant channel shapes and routes that can be difficult or impossible to form with traditional sand casting, as well as variable permeability of the sand mold.

[0075] The timing of introducing liquid coolant into the sand mold 104 can be calculated based on a casting mold fill and solidification simulation. For example, to cast a part of a size approximating that of a typical engine block, there can be a mold fill time of about 15 to 30 seconds, followed by a solidification time of about 30 seconds to 600 seconds, depending on the mold geometry.

[0076] Referring to Figure 1 , the inlet port 120A is defined in the sand mold 104 below the mold cavity 108 relative to the direction of gravity. The outlet port 122A is defined in the sand mold 104 above the mold cavity 108. In this embodiment, system 100, the coolant in the liquid phase (also referred to as liquid coolant) flows from the bottom of the sand mold 104 into the coolant channel 118, and as the coolant flows through the coolant channel 118 and permeates through the sand mold 104 in an upward direction, the coolant in the liquid phase changes state to a gas phase (also referred to as coolant gas). The coolant gas is then collected by the outlet port 122A, which rises upward out of the sand mold 104. If the coolant is inert, such as helium or nitrogen, the coolant gas exiting the manufactured mold can be released to the ambient atmosphere.

[0077] Referring to Figure 2 , the inlet port 120B is defined in the sand mold 104 above the mold cavity 108 relative to the direction of gravity. The outlet port 122B is defined in the sand mold 104 from above the mold cavity 108 to the top surface 128 of the sand mold 104. In this embodiment, system 200, the liquid coolant flows under gravity from the top surface 128 of the manufactured sand mold 104 downward into the coolant channel 118, and as the coolant flows through the coolant channel 118 and permeates through the sand mold 104, the liquid coolant changes state to a gas phase. The coolant gas then rises out of the outlet port 122A or is released to the ambient atmosphere, if the coolant is inert.

[0078] Referring to Figure 3 and Figure 4 . Each of the systems 300 and 400 includes a coolant gas extraction system 150C, 150D. The coolant gas extraction system 150C, 150D includes a manifold 152C, 152D having at least one inlet 154C, 154D connectable to the at least one outlet port 122C, 122D and opposite outlets 156C, 156D connectable to a vacuum pump 158C, 158D. The manifold 152 includes a vacuum valve 160C, 160D positioned between the inlet 154C, 154D and the outlet 156C, 156D and a pressure gauge 162C, 162D positioned between the vacuum valve and the at least one inlet. The vacuum valve 160C, 160D is operable to control the amount of vacuum required.

[0079] Referring toFigure 3 Inlet port 120C is defined in sand mold 104 below mold cavity 108 relative to the direction of gravity. Outlet port 122C is also defined in sand mold 104 below mold cavity 108. Inlet 154C of coolant gas recovery system 150C is fluidly connected with outlet port 122C. In this embodiment, system 300, liquid coolant flows from the bottom of the manufactured sand mold 104 into coolant channel 118, which changes state from liquid to gas as the coolant flows through coolant channel 118 and permeates through sand mold 104. The coolant gas is then evacuated through outlet 122C under vacuum. Multiple heat sinks 130a, 130b, 130c (also referred to as cooling plates 130a, 130b, 130c) can be placed in predetermined locations at the interface of mold cavity 108 to further increase the cooling rate of the cast part at specific locations. Heat sinks 130a, 130b, 130c can be formed of any thermally conductive material such as aluminum and copper and coated with a refractory coating such as silica and mica.

[0080] Referring to Figure 4 Inlet port 120D is defined in sand mold 104 below mold cavity 108 relative to the direction of gravity. Outlet port 122D is defined in sand mold 104 from above mold cavity 108 to surface 128 of sand mold 104. In this embodiment, system 400, liquid coolant flows from the bottom of the manufactured sand mold 104 into coolant channel 118, which changes state from liquid to gas as the coolant flows through coolant channel 118 and permeates through sand mold 104 and enters outlet port under vacuum.

[0081] Figure 5 A block flow diagram illustrating a method of increasing the cooling rate of an aluminum sand cast during solidification is shown. The method begins in block 502, where a sand mold 104 is additively manufactured by 3D printing. An inorganic binder can be used during the 3D printing process to cause the manufactured sand mold 104 to retain its predetermined shape and geometry. Sand mold 104 defines a mold cavity 108, a gating system for filling mold cavity 108 with molten metal, and a plurality of coolant channels 118 surrounding mold cavity 108. Coolant channels 118 include an inlet port 120 and at least one outlet port 120. Sand mold 104 can include a first permeable region 124 between mold cavity 108 and coolant channels 118 and a second permeable region 126 between coolant channels 118 and an outer boundary 128 of sand mold 104. Various sizes of sand grains can be used for 3D printing to control the permeability of the different regions 124, 126.

[0082] Moving to block 504, the molten foundry alloy is poured into the mold cavity 108 through the gating system. At or shortly after pouring, liquid coolant is introduced into the coolant passages via the coolant inlet. As the coolant flows through the coolant channels 118 and permeates through the sand mold 104, the liquid coolant, such as liquid nitrogen, changes state from a liquid phase to a gas phase, thereby increasing the cooling rate of the metal casting during solidification. The timing of the liquid nitrogen introduction into the sand mold 104 can be calculated based on a casting mold fill and solidification simulation.

[0083] Moving to block 506, the exit gas phase of the coolant is collected or vented to ambient atmosphere by the exit port 122. The maximum gas pressure in the sand mold 104 adjacent to the mold surface is desirably about less than 0.1 atm difference compared to the local metal static pressure of the molten metal. A vacuum can be pulled to encourage the coolant gas to exit the sand mold 104 to prevent the gas phase from permeating into the mold cavity 108, which can potentially induce undesirable porosity in the cast part.

[0084] Moving to block 508, after the solidified casting cools to room temperature, the sand mold 104 is opened to remove the cast part, and the method 500 ends.

[0085] The above disclosed system and method for increasing the cooling rate of an aluminum sand cast part during solidification can be applied to any sand casting process, including but not limited to gravity pouring, low pressure casting processes, Cosworth, and electromagnetic (EM) pumps. The system and method increase the cooling rate of the metal sand cast part during solidification, thereby providing a refined microstructure and reduced casting defects to improve the cast part quality and performance.

[0086] The description of the present disclosure is merely exemplary in nature and variations that do not depart from the spirit and scope of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.

Claims

1. A system for increasing the cooling rate of metal sand castings, comprising: A sand mold, which defines a mold cavity, a coolant channel surrounding a portion of the mold cavity, and a coolant inlet port fluidly connected to the coolant channel; The coolant inlet port is operable to receive coolant in the liquid phase, and the coolant passage is operable to guide the coolant as it changes from the liquid phase to the gas phase. The sand mold includes: The internal mold surface that defines the mold cavity; A first region, located between the internal mold surface and the coolant channel, wherein the first region includes a first permeability; and A second region is located between the coolant channel and the outer boundary of the sand mold, wherein the second region includes a second permeability; The first permeability is greater than the second permeability.

2. The system of claim 1, wherein the coolant is a cryogenic liquid selected from the group consisting of argon, helium and nitrogen.

3. The system of claim 1, wherein the coolant is liquid nitrogen.

4. The system according to claim 1, wherein the coolant is a refrigerant selected from the group consisting of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs).

5. The system of claim 1, wherein the sand mold further defines a coolant outlet port, wherein the coolant outlet port is at least one of: (i) in indirect fluid communication with the coolant channel such that the gas phase permeates the sand mold before entering the coolant outlet port, and (ii) in direct fluid communication with the coolant channel.

6. The system of claim 5 further includes a coolant vapor extraction system having a vacuum pump configured to extract the vapor phase of the coolant from the sand mold.

7. The system of claim 6, wherein the coolant vapor extraction system comprises a vacuum pump and a manifold fluidly connected to the vacuum pump, wherein the manifold includes a vacuum inlet fluidly connected to the coolant outlet port of the sand mold.

8. The system according to claim 1, wherein, The sand mold includes a radiator disposed in the sand mold between the coolant channel and the surface of the inner mold.

9. The system according to claim 5, wherein, The coolant inlet port is located at the lower part of the sand mold or the upper part of the sand mold, and the coolant outlet port is located inside the sand mold.

10. A system for increasing the cooling rate of metal sand castings, comprising: A sand mold defining a mold cavity and a coolant inlet port extending into the manufactured sand mold, wherein the coolant inlet port is operable to receive a cryogenic liquid; and The sand mold possesses sufficient permeability to allow the cryogenic liquid to transform into a gaseous phase while permeating through the manufactured sand mold. The sand mold further includes a plurality of coolant channels surrounding a portion of the mold cavity, wherein the coolant channels are fluidly connected to the coolant inlet port and operable to contain the cryogenic liquid changing from a liquid phase to a gas phase, wherein the sand mold is manufactured by 3D printing with sand grains of different sizes to define a first region having a first permeability and a second region having a second permeability, wherein the first permeability is greater than the second permeability.

11. The system according to claim 10, wherein, The sand mold also includes a coolant gas outlet port that is in fluid communication with the coolant channel.

12. The system of claim 11 further includes a coolant vapor extraction system having a collection manifold fluidly connected to the coolant gas outlet port of the sand mold.

13. A method for increasing the cooling rate of a metal sand casting, comprising: Molten metal is poured into a cavity defined by a manufactured sand mold, wherein the manufactured sand mold is 3D printed before the molten metal is poured to define a first region having a first permeability and a second region having a second permeability, wherein the first permeability is greater than the second permeability; Liquid nitrogen is introduced into the manufactured sand mold, such that when the liquid nitrogen permeates through the manufactured sand mold, the liquid nitrogen changes from a liquid phase to a gas phase, thereby increasing the cooling rate of the molten metal.

14. The method according to claim 13, wherein, 3D printing the manufactured sand mold also includes defining the mold cavity, a channel surrounding a portion of the mold cavity, and an inlet port fluidly connected to the channel; The inlet port is operable to receive the liquid nitrogen, and the channel is operable to guide the liquid nitrogen as it changes from the liquid phase to the gas phase.

15. The method of claim 14, further comprising extracting the gas phase from the manufactured sand mold by applying a vacuum.

16. The method according to claim 15, wherein, 3D printing the manufactured sand mold further includes defining an outlet port that is fluidly connected to the channel; and also includes applying a vacuum to the outlet port.

17. The method according to claim 16, wherein, 3D printing the manufactured sand mold also includes placing a heat sink between the channel and the mold cavity.

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