Method for manufacturing a hollow structural metal casting

Abstract

This invention discloses a method for manufacturing hollow metal castings, belonging to the field of metal casting technology. The method includes: S1, creating a wax model core according to the shape of the hollow cavity of the casting; S2, coating the outer surface of the wax model with a high-temperature resistant inert powder slurry, which then solidifies to form a hard shell layer; S3, placing the wax model coated with the hard shell layer into a mold and pouring molten metal into it, causing the wax model to melt and flow out, obtaining a hollow hard shell core with a metal outer shell and a hard shell layer inside; S4, placing the hollow hard shell core as a prefabricated structural component into the outer mold of the final casting, pouring molten metal of the target material into it, causing partial remelting of the outer metal shell surface of the hard shell core, forming a molten-resolidified bonding zone at the interface with the subsequently poured molten metal. After cooling and solidification, the hard shell core connects to the main metal body to form a seamless, jointless integral structure, creating a hollow casting with a permanent hard shell layer inside. The hard shell layer is generated in situ during the casting process and remains on the inner wall of the hollow cavity, forming a heat dissipation functional layer. This invention solves the technical problems of traditional processes, such as the inability of the core to remain inside the casting as a structural skeleton and functional layer, the inability to form a heat dissipation functional layer in the inner cavity in one go, the inability to form complex inner cavity structures, and the inability to achieve both seamless integration and low-cost mass production. It is applicable to the manufacturing of hollow structural parts of various castable metals and alloys.

Description

Technical Field

[0001] This invention relates to the field of metal casting technology, specifically to a method for manufacturing hollow metal castings. This method is applicable to manufacturing various metal parts that simultaneously meet the requirements of lightweight, high strength load-bearing, rapid heat dissipation, integral molding, and no welding connections. Background Technology

[0002] Hollow metal castings, due to their internal cavities, can significantly reduce weight while maintaining structural strength. At the same time, the cavities can be used as heat dissipation channels or functional chambers, thus having a wide range of applications in fields such as motion machinery, load-bearing structures, heat dissipation devices, and power systems.

[0003] However, existing hollow casting methods have long failed to overcome the following fundamental technical contradictions: First, there is the contradiction between the disposable nature of the core and its permanent retention. Traditional investment casting, lost foam casting, and ceramic core precision casting all rely on disposable cores to form the hollow cavity inside the casting. After casting, the core must be removed through methods such as crushing, dissolving, or burning, and cannot be permanently retained inside the casting. This means that the production of each hollow casting requires a core that perfectly corresponds to the shape of the hollow cavity. The manufacturing cost of this core becomes the largest single item in the cost composition of hollow castings. In large-scale mass production scenarios, the repeated manufacturing cost of the core accumulates linearly and cannot be amortized through batch effects, resulting in a persistently high overall manufacturing cost for hollow castings.

[0004] Secondly, there is a contradiction between the internal cavity's function and the structural function. In traditional processes, after the core is removed, the casting's internal cavity is merely an exposed metal surface. This surface lacks the functional properties of heat conduction, heat dissipation, high-temperature resistance, and resistance to thermal deformation. If the internal cavity is required to possess these functions, it must be achieved through additional surface treatment processes (such as spraying, diffusion coating, bushing, etc.) after casting. This increases the number of processes, raises costs, and also leads to insufficient interfacial bonding strength between the coating layer and the substrate, making it prone to detachment during long-term use. Therefore, traditional processes cannot impart permanent heat dissipation and heat resistance functions to the internal cavity in a single casting process.

[0005] Third, there is a contradiction between the complexity of the internal cavity and the strength of the core. Traditional disposable core materials—whether ceramic, sand, or foam—have limited compressive strength. When castings with complex internal cavity structures such as mesh support ribs, diamond-shaped reinforcing ribs, and gradient channels are required, the core is highly susceptible to fracture, deformation, and collapse under the impact and static pressure of the molten metal, leading to the scrapping of the casting. Therefore, traditional processes can only produce hollow parts with relatively simple internal cavity structures and cannot achieve integrated molding of the internal load-bearing structure and the heat dissipation structure.

[0006] Fourth, the contradiction between integral molding and joint strength. To obtain complex internal cavity structures, some manufacturers adopt a process of separate casting followed by welding. However, welded joints are inherently weak areas in structural strength—the weld seam has inherent defects such as heat-affected zones, residual stress, and uneven microstructure. Under alternating loads, impact loads, and high-temperature conditions, the weld seam becomes the initiation source and propagation path of fatigue cracks, making the risk of structural failure far higher than that of integrally molded parts. However, traditional integral molding processes are constrained by the aforementioned core strength limitations, making it impossible to balance the complexity of the internal cavity with structural integrity.

[0007] Fifth, the contradiction between lightweighting and load-bearing strength. Traditional solid castings rely on material accumulation to meet load-bearing requirements, resulting in large weight, high rotational inertia, and high material costs. Traditional hollow designs, due to the inability to fabricate internal supporting ribs, suffer a significant decrease in overall stiffness and impact resistance, making them unsuitable for high-stress, high-speed, and heavy-load conditions. Therefore, the industry has long faced the dilemma of "being lightweight at the expense of strength, and being strong at the expense of lightweight."

[0008] In summary, existing hollow casting technologies cannot simultaneously achieve the following technical objectives: the core remains inside the casting as a structural skeleton; a permanent heat dissipation layer is formed in the inner cavity during the casting process; complex inner cavity support ribs and flow guiding structures can be fabricated; seamless integral molding is achieved; and overall manufacturing costs are controllable and suitable for large-scale mass production. These long-standing unresolved technical contradictions constitute the core problem that this invention aims to solve. Summary of the Invention

[0009] 1. Purpose of the invention The present invention aims to provide a method for manufacturing hollow metal castings to solve the technical problems existing in the prior art, such as the inability of the core to remain inside the casting to become a structural skeleton and functional layer, the inability to form a permanent heat dissipation functional layer in the inner cavity in one go, the inability to form complex inner cavity structures, and the inability to achieve both one-piece seamless molding and low-cost mass production.

[0010] 2. Technical Solution This invention provides a method for manufacturing a hollow metal casting, comprising the following steps: S1. Make the inner core of the wax model.

[0011] A wax core is made according to the required hollow cavity shape of the casting. The shape of the wax core is the reverse mold of the final hollow cavity of the casting. That is, the space occupied by the wax model is the hollow cavity space of the final casting.

[0012] The outer surface of the wax model core can be pre-machined with corresponding raised and recessed textures according to the internal structural requirements of the target casting. These textures correspond to the shapes of internal structures such as reinforcing ribs, supporting ribs, flow channels, and heat dissipation fins within the target casting. The wax model core is sealed at both ends to maintain its structural integrity during subsequent coating processes.

[0013] The interior of the wax model core can be pre-filled with high-temperature resistant inert powder according to process requirements. The function of this powder is to enhance the overall compressive strength of the wax model during subsequent casting and prevent deformation under the impact of molten metal. After the wax model melts, the filling powder can be partially or completely retained in the final hollow cavity, forming part of the heat dissipation functional layer.

[0014] The method for preparing the inner core of the wax model is not limited, and conventional methods such as wax injection molding, 3D printing of wax models, and hand carving of wax can be used.

[0015] S2, Wax coating cured.

[0016] A layer of high-temperature resistant inert powder slurry is uniformly coated onto the outer surface of the wax mold core prepared in S1. This slurry is composed of a mixture of high-temperature resistant inert powder and a binder, and has the characteristics of being coatable and forming a dense, hard shell after curing.

[0017] The coating method is not limited and can be conventional, such as brushing, dipping, or spraying. After coating, allow the slurry to cure by natural air drying or low-temperature drying, forming a dense, high-temperature resistant hard shell layer on the outer surface of the wax model.

[0018] The high-temperature resistant inert powder refers to a powdery substance that is chemically stable at the metal molten casting temperature, does not generate gas, does not expand, and does not react with the metal molten material. As an example and not a limitation, carbon-based powders (such as graphite powder) or ceramic-based powders (such as alumina ceramic powder) can be used. Any powdery substance possessing the above-mentioned characteristics of "high temperature resistance, inertness, non-gas generation, and non-expansion" can be used as the high-temperature resistant inert powder described in this step.

[0019] The binder refers to a substance that can bind powder into a shape at room temperature or low temperature. As an example and not a limitation, water glass or other conventional inorganic binders may be used.

[0020] The key function of the hard shell layer formed in S2 is that, in the subsequent core pre-casting in S3, the hard shell layer provides rigid support for the wax model, preventing the wax model from deforming under the impact of molten metal and static pressure; after the wax model melts due to heat, the hard shell layer does not disappear with the wax model, but remains on the inner wall of the formed hollow cavity, becoming a component of the inner cavity of the subsequent finished casting.

[0021] S3, Core precasting.

[0022] The wax model prepared in S2 with the hard shell layer coated is placed into the core prefabrication mold. The inner cavity shape of the core prefabrication mold corresponds to the outer contour shape of the target hollow hard shell core.

[0023] Molten metal is poured into the mold. The molten metal fills the space between the wax model and the inner wall of the mold cavity, encasing the wax model and its outer hard shell layer. After the molten metal solidifies and cools, it forms a metal shell that tightly wraps around the outside of the hard shell layer.

[0024] Under the high temperature of the molten metal, the inner core of the wax model melts, and the wax flows out from the pre-set wax outlet. The space occupied by the wax model is emptied, forming a hollow cavity enclosed by a hard shell layer. The hard shell layer remains on the inner wall of the hollow cavity, neither flowing away with the wax nor separating from the metal shell.

[0025] Thus, a hollow hard-shell core with an outer metal shell and an inner cavity containing a high-temperature resistant inert hard shell is obtained. This hollow hard-shell core is the core prefabricated structural component of this invention.

[0026] The molten metal poured into S3 is preferably the same as the target material of the final casting, or matches the target material of the final casting in terms of melting point, coefficient of thermal expansion, and metallurgical compatibility. This ensures that during the composite casting of the S4 body, the hard shell core and the body metal achieve sufficient remelting and bonding.

[0027] S4, composite casting of the main body.

[0028] The hollow hard-shell core prepared in S3 is used as a prefabricated structural component and placed into the outer mold of the final casting. The inner cavity shape of the outer mold corresponds to the outer contour shape of the final casting. The hollow hard-shell core is precisely fixed within the outer mold by a positioning structure to ensure that it does not shift during the casting process.

[0029] Molten metal of the target material is poured into the outer mold. The molten metal fills the entire space between the inner cavity of the outer mold and the outer wall of the hollow hard shell core, completely encasing the hollow hard shell core.

[0030] Under the action of high-temperature molten metal, the outer metal shell surface of the hollow hard-shell core partially remelts, forming a molten-resolidified bonding zone at the interface with the newly poured molten metal. After cooling and solidification, the hollow hard-shell core connects with the subsequently poured body metal to form a seamless, jointless integral structure. The hollow hard-shell core remains inside the casting, its metal shell portion fused with the body as one piece, and its inner hard-shell layer becomes the permanent functional inner wall of the hollow cavity of the casting.

[0031] Thus, a hollow metal casting with a solid outer shell and an inner cavity containing a high-temperature resistant inert hard shell was obtained.

[0032] 3. Core Process Principles The core principle of the manufacturing method described in this invention lies in transforming the traditional casting process's "discarded after single use" core into a prefabricated structural component that "remains inside the casting, serving as a structural skeleton and functional layer." This transformation is achieved through the synergistic combination of the following technical features: Firstly, the wax outer coating hard shell method. The hard shell layer is applied to the outer surface of the wax model, rather than being mixed into the interior. The wax model serves only as a temporary spacer; the hard shell layer is the functional layer that ultimately remains in the inner cavity. After the wax model melts and flows out, the hard shell layer sets on the inner cavity wall without any further treatment. During the casting process, the hard shell layer provides rigid support to prevent core deformation; in the finished casting, it provides heat conduction, forming a permanent heat dissipation layer within the inner cavity.

[0033] Secondly, a two-stage casting system. The purpose of the first-stage casting (S3) is to prepare a hollow hard-shell core with a functional internal cavity. The purpose of the second-stage casting (S4) is to embed this hard-shell core as a structural component into the final casting body. The two-stage casting works in synergy to realize the manufacturing logic of "prefabricated structural component → embedded into the body → fused together".

[0034] Third, interfacial remelting bonding. In S4, the outer metal of the pre-cast hard shell core undergoes partial surface remelting under the action of high-temperature molten metal, forming a molten-resolidified bonding zone at the interface with the subsequently poured molten metal. This bonding zone is formed by the mutual diffusion and mixing of the two metals in the liquid state followed by solidification. There are no discontinuous areas such as welds or fusion lines between the metals on both sides of the bonding zone, and the connection strength is the same as the strength of the metal body.

[0035] Fourth, the internal cavity functional layer is generated in situ. The hard shell layer is coated and formed in S2, exposed to the internal cavity in S3 as the wax pattern melts, and retained in S4 as the hard shell core is embedded in the body. Throughout the process, the hard shell layer remains in situ, requiring no transfer, no secondary processing, and no post-processing, and can serve as a permanent heat dissipation functional layer for the internal cavity of the finished casting.

[0036] 4. Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: I. Completely solves the technical challenge of core retention. Through the "wax-coated hard shell method combined with two-stage casting," the traditional disposable core is transformed into a structural framework and functional layer retained within the casting. The core is no longer a consumable material but an integral part of the product itself. This transformation fundamentally eliminates the problem of linear cost accumulation from repeated core manufacturing in traditional processes, while simultaneously providing the internal cavity with permanent structural support and functional characteristics.

[0037] Second, a one-step forming process for the internal cavity heat dissipation functional layer was achieved. The inert hard shell layer formed by S2 remains on the inner wall of the hollow cavity, utilizing its high thermal conductivity, high heat dissipation, and high temperature resistance to constitute the standard internal cavity heat dissipation layer. This functional layer is generated in situ during the casting process, requiring no post-processing. It is firmly bonded to the substrate, does not detach or peel off, and remains indefinitely. The heat dissipation efficiency and resistance to thermal deformation are significantly superior to the traditional method of exposing the inner cavity metal surface.

[0038] Third, it resolves the contradiction between complex internal cavity structures and core strength. The hard shell layer formed by the wax outer coating provides rigid support for the wax model, preventing deformation under the impact of molten metal and static pressure. Complex internal cavity structures such as mesh support ribs, diamond-shaped reinforcing ribs, and gradient flow channels can all be fabricated without being limited by the strength of the core material.

[0039] Fourth, it achieves seamless integral casting, completely eliminating weak points in welding. During the S4 composite casting process, the surface of the outer metal shell is partially remelted, forming a molten-resolidified bonding zone with the subsequently poured molten metal. After cooling, it is connected as a whole, eliminating inherent defects such as welds, heat-affected zones, residual stress, and uneven microstructure found in traditional split welding processes. The overall structure of the casting is continuous, the stress distribution is uniform, and the impact resistance, fatigue resistance, and torsional resistance are significantly improved.

[0040] Fifth, it balances lightweight and high strength. By eliminating a large amount of unnecessary solid metal material through a hollow design, the weight is significantly reduced; however, through the internal mesh support structure and the dense crystalline structure of the pre-cast inner core, stiffness and load-bearing capacity are increased without sacrificing them. This achieves the structural goal of "reducing weight without sacrificing strength, and hollow without weakening."

[0041] VI. Overall manufacturing costs are controllable, making it suitable for large-scale mass production. The process only adds one composite casting step, and the operation logic is compatible with existing casting production lines, requiring no new large-scale equipment. Wax molds are recyclable and reusable, resulting in a slight increase in process costs. However, the material cost savings through the hollow design far outweigh the increased costs of the process, leading to a significant overall manufacturing cost advantage. Hard-shell cores can be prefabricated and stockpiled in batches, ensuring that subsequent mass production efficiency is not constrained by the core preparation cycle.

[0042] VII. Universal material compatibility, no size limitations, and wide range of applications. This method is applicable to all types of castable metals and alloys, including aluminum alloys, cast iron, cast steel, copper alloys, magnesium alloys, and titanium alloys. It is not limited by the size, shape, or purpose of the casting and can cover all categories of needs, including lightweight moving parts, heavy-duty pressure-bearing structural parts, heat dissipation functional parts, and critical parts for extreme working conditions. Attached Figure Description Figure 1 A schematic diagram illustrating the overall structure of the casting process; Figure 2 Overall schematic diagram of the completed casting process; Figure 3 Schematic diagram of wax core and high-temperature inert coating material; Figure 4 Schematic diagram of high-temperature resistant inert material integrated with outer metal shell; Figure 5 Schematic diagram of the wax core; Figure 6 Schematic diagram of the cross-section of the completed casting body.

[0043] Explanation of reference numerals in the attached figures; 1. Wax mold inner core; 2. High-temperature resistant inert coating; 3. Cast the inner core of the main body; 4. Casting body; 5. High temperature resistant material. Detailed Implementation To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] Example 1: Hollow Structure Aluminum Alloy Wheel This embodiment provides a method for manufacturing a hollow aluminum alloy wheel hub.

[0045] S1: The inner core of the wax model is made according to the required hollow cavity shape of the wheel hub. The outer surface of the wax model is pre-machined with a diamond-shaped mesh support rib texture, with a texture depth of 3 to 5 mm and a rib spacing of 20 to 30 mm. The two ends of the wax model are closed. The interior of the wax model is pre-filled with graphite powder to enhance its compressive strength during casting.

[0046] S2: Apply a layer of slurry made of alumina ceramic powder and water glass evenly to the outer surface of the wax model, with a coating thickness of 2 to 3 mm. Allow it to air dry naturally for 24 hours to form a dense, high-temperature resistant hard shell.

[0047] S3: Place the wax model, coated with a hard shell and filled with graphite powder, into the core pre-made mold, and pour in molten A356 aluminum alloy at a casting temperature of 700 to 720 degrees Celsius. After the aluminum alloy solidifies, the wax model melts due to heat and flows out from the wax outlet, forming a hollow hard shell core with an alumina ceramic hard shell. The graphite powder remains in the hollow cavity, forming a heat dissipation functional layer together with the hard shell layer.

[0048] S4: Place the hollow hard-shell core into the outer mold of the wheel hub, precisely fitting the core head with the mold's positioning hole. Pour in molten A356 aluminum alloy at a casting temperature of 700 to 720 degrees Celsius. Under the action of the high-temperature molten metal, the outer metal surface of the hard-shell core partially remelts, forming a molten-resolidified bonding zone at the interface with the newly poured molten metal. After cooling and solidification, the hard-shell core and the wheel hub body become a single unit, forming a hollow aluminum alloy wheel hub with a solid outer shell, a heat-dissipating hard shell inside, and diamond-shaped mesh support ribs inside.

[0049] Example 2: Hollow Cast Iron Brake Disc This embodiment provides a method for manufacturing a hollow cast iron brake disc.

[0050] S1: The inner core of the wax model is made according to the required hollow cavity and internal gradient guide channel shape of the brake disc. The outer surface of the wax model is machined with a textured surface of the gradient channel, and the cross-section of the channel gradually expands from the inside to the outside. The two ends of the wax model are closed.

[0051] S2: A slurry composed of graphite powder and water glass is uniformly dipped into the outer surface of the wax model, with a coating thickness of 1.5 to 2.5 mm. The wax model is then dried at a low temperature to form a dense, high-temperature resistant hard shell.

[0052] S3: Place the wax model with the hardened shell into the core pre-made mold, and pour in HT250 cast iron molten metal at a casting temperature of 1320 to 1350 degrees Celsius. After the cast iron solidifies, the wax model melts and flows out, forming a hollow hardened core with a graphite hard shell inside.

[0053] S4: Place the hollow hard shell core into the outer mold of the brake disc, and pour in HT250 cast iron molten metal at a casting temperature of 1320 to 1350 degrees Celsius. Under the action of the high-temperature molten metal, the outer metal surface of the hard shell core partially remelts, forming a molten-resolidified bonding zone at the interface with the subsequently poured molten metal. After cooling and solidification, the hard shell core and the brake disc body are connected as a whole, forming a hollow cast iron brake disc with a solid outer shell, a graphite heat dissipation hard shell in the inner cavity, and gradually changing flow channels inside.

[0054] Example 3: Hollow Structure Cast Steel Engine Housing This embodiment provides a method for manufacturing a hollow cast steel engine housing.

[0055] S1: Create the inner core of the wax model according to the required shape of the hollow cooling cavity in the engine housing. Machin the curved texture of the water-cooling cavity onto the outer surface of the wax model. Seal both ends of the wax model.

[0056] S2: A slurry composed of alumina ceramic powder and water glass is evenly sprayed onto the outer surface of the wax model, with a coating thickness of 2 to 4 mm. The mixture is then dried at a low temperature to form a dense, high-temperature resistant hard shell.

[0057] S3: Place the wax model with the hardened shell into the core pre-made mold, and pour in ZG35 cast steel liquid at a casting temperature of 1550 to 1580 degrees Celsius. After the cast steel liquid solidifies, the wax model melts and flows out due to the heat, forming a hollow hard-shell core with an alumina ceramic hard shell inside.

[0058] S4: Place the hollow hard shell core into the outer mold of the engine housing, and pour in ZG35 cast steel molten material at a casting temperature of 1550 to 1580 degrees Celsius. Under the action of the high-temperature molten metal, the outer metal surface of the hard shell core partially remelts, forming a molten-resolidified bonding zone at the interface with the subsequently poured molten metal. After cooling and solidification, the hard shell core connects with the housing body to form a whole, forming a hollow cast steel engine housing that is solid on the outside and hollow on the inside, with a heat dissipation hard shell in the inner cavity and a water-cooled cavity inside.

[0059] Example 4: Hollow titanium alloy aerospace structural component This embodiment provides a method for manufacturing hollow titanium alloy structural components.

[0060] S1: Fabricate the inner core of the wax model according to the required hollow cavity and internal mesh support rib shape of the structural component. The wax model is closed at both ends.

[0061] S2: Apply a uniform layer of a slurry made of alumina ceramic powder and water glass to the outer surface of the wax model, with a coating thickness of 1 to 2 mm. Dry at low temperature.

[0062] S3: Place the wax model with the hardened shell into the core pre-made mold, and pour in Ti6Al4V titanium alloy liquid at a casting temperature of 1680 to 1720 degrees Celsius. After the titanium alloy liquid solidifies, the wax model melts and flows out due to the heat, forming a hollow hard-shell core with an alumina ceramic hard shell inside.

[0063] S4: Place the hollow hard shell core into the outer mold of the structural component, and pour in Ti6Al4V titanium alloy liquid at a casting temperature of 1680 to 1720 degrees Celsius. Under the action of the high-temperature molten metal, the outer metal surface of the hard shell core partially remelts, forming a molten-resolidified bonding zone at the interface with the subsequently poured molten metal. After cooling and solidification, the hard shell core connects with the body to form a whole, forming a hollow titanium alloy structural component with a solid outer shell, a heat dissipation hard shell in the inner cavity, and a mesh-like support rib inside.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing a hollow metal casting, characterized in that, Includes the following steps: S1. Making the wax mold core: Make a wax core according to the shape of the hollow cavity required for the casting; S2. Wax outer coating curing: A layer of high-temperature resistant inert powder slurry is uniformly coated on the outer surface of the wax mold core prepared in S1. The slurry is made of high-temperature resistant inert powder and binder. After curing, a dense and high-temperature resistant hard shell layer is formed on the outer surface of the wax mold. S3. Core Precasting: The wax model prepared in S2 with a hard shell layer is placed into the core precast mold. Molten metal is poured into the mold, and the molten metal fills the space between the wax model and the inner wall of the mold cavity. After the molten metal solidifies and cools, it forms a metal shell that tightly wraps around the outside of the hard shell layer. Under the high temperature of the molten metal, the inner core of the wax model melts and the wax flows out from the pre-set wax discharge port. The space occupied by the wax model is emptied, forming a hollow cavity surrounded by the hard shell layer. Thus, a hollow hard shell core with a metal shell on the outside and a high temperature resistant inert hard shell layer in the inner cavity is obtained. S4. Composite Casting of the Whole Body: The hollow hard shell core prepared in S3 is used as a prefabricated structural component and placed into the outer mold of the final casting. Molten metal of the target material is poured into the outer mold, and the molten metal fills the entire space between the inner cavity of the outer mold and the outer wall of the hollow hard shell core. Under the action of the high-temperature molten metal, the surface of the outer metal shell of the hollow hard shell core undergoes partial remelting, forming a molten-resolidified bonding zone with the newly poured molten metal at the interface. After cooling and solidification, the hollow hard shell core and the subsequently poured body metal are connected to form an integral structure without welds or joints. The hollow hard shell core remains inside the casting, and its inner hard shell layer becomes the permanent functional inner wall of the hollow cavity of the casting.

2. The method according to claim 1, characterized in that, The high-temperature resistant inert powder mentioned in S2 refers to a powdery substance that is chemically stable at the metal molten casting temperature, does not produce gas, does not expand, and does not react with the metal molten material, and is at least one of carbon-based powder or ceramic-based powder.

3. The method according to claim 2, characterized in that, The carbon-based powder is graphite powder, and the ceramic-based powder is alumina ceramic powder.

4. The method according to claim 1, characterized in that, The adhesive mentioned in S2 is water glass.

5. The method according to claim 1, characterized in that, The molten metal material poured in S3 is the same as the target material poured in S4, or matches the target material of the final casting in terms of melting point, coefficient of thermal expansion, and metallurgical compatibility.

6. The method according to claim 1, characterized in that, The outer surface of the wax mold core described in S1 is pre-processed with a raised texture according to the internal structural requirements of the target casting. The raised texture corresponds to at least one of the structural shapes of the reinforcing ribs, supporting ribs, and flow channels inside the final casting.

7. The method according to claim 1, characterized in that, The interior of the wax mold core described in S1 is pre-filled with high-temperature resistant inert powder. After the wax mold melts when heated, some or all of the powder remains in the final hollow cavity, forming part of the heat dissipation functional layer.

8. The method according to claim 1, characterized in that, The molten-resolidified bonding zone described in S4 is formed by the partial remelting of the outer wall of the outer metal shell under the action of the molten metal in the composite casting of the body, and the cooling and solidification together with the newly poured molten metal. The bonding strength formed by this bonding method is the same as the strength of the metal body. There are no discontinuous areas such as welds, fusion lines, or interface layers between the metals on both sides of the bonding zone.

9. The method according to any one of claims 1 to 8, characterized in that, The hard shell layer formed in S2 remains in place throughout the entire casting process of S3 and S4, requiring no transfer, secondary processing, or post-processing, serving as a permanent heat dissipation functional layer for the inner cavity of the finished casting.

10. The method according to any one of claims 1 to 8, characterized in that, The molten metal is any one of aluminum alloy, cast iron, cast steel, copper alloy, magnesium alloy, and titanium alloy.

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