A method for manufacturing a complex inner runner casting based on a foundry core

Abstract

The present application relates to the technical field of foundry mold design, solves the problems of insufficient strength, easy breakage, easy collapse, gas generation, difficult core removal, residual blockage and inability to reuse of the core of a complex internal runner casting under the traditional core preparation method, especially relates to a method for manufacturing a complex internal runner casting based on a foundry core, selects a thin-walled metal pipe with the same material as the base element of the casting and meeting the melting point matching requirement, fills the pipe with a flowable and reusable mixed medium, installs detachable ceramic sealing plugs at both ends of the pipe to form a core, installs the core to a mold and pours the casting, removes the sealing plugs after solidification, discharges the mixed medium for reuse, and obtains a casting with a complex internal runner structure. The present application can ensure the strength and stability of the core during installation, handling and pouring, has no organic and gas pollution, can efficiently remove and reuse the core after pouring, avoids residual blockage, and improves the casting quality, production efficiency, yield and green manufacturing level.

Description

Technical Field

[0001] This invention relates to the field of casting mold design technology, and in particular to a method for manufacturing complex internal flow channel castings based on casting cores, applicable to core design and preparation in the precision casting process of metal castings such as aluminum alloys, magnesium alloys, titanium alloys, high-temperature alloys and steel parts. Background Technology

[0002] Casting cores are crucial components in the casting process, used to form the internal cavities and flow channels of castings. They are widely used in precision casting and mold manufacturing. The performance of the core directly affects the dimensional accuracy, surface quality, and forming difficulty of the casting. With the increasing demand for castings with complex internal flow channels in industries such as aerospace, automotive, and energy, the importance of core design and manufacturing technology is becoming increasingly prominent.

[0003] Existing core preparation methods mainly include ceramic cores, resin sand cores, and 3D printed cores. While these methods have been applied to some extent in industrial production, significant problems remain. For example, during core handling and assembly, resin sand cores and 3D printed resin sand cores have relatively low overall strength, making them prone to breakage or deformation during handling or assembly, hindering the integrity and assembly stability of complex structures. During high-temperature casting, resin sand cores and 3D printed resin sand cores are prone to softening, disintegration, gas generation, and the production of organic matter and gaseous pollution at high temperatures. While ceramic cores and 3D printed ceramic cores possess some high-temperature resistance, they are brittle and still pose a risk of cracking or localized damage in complex flow channel structures. In the core removal stage after casting, ceramic, resin, and 3D printed cores all present difficulties in disassembly, easily leaving residues or clogging complex internal flow channels, increasing post-processing complexity. Furthermore, these cores are mostly disposable, impacting casting quality, production efficiency, yield, and the level of green manufacturing. These issues result in a technical bottleneck in core production when meeting the requirements for castings with complex internal flow channels. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a green method for manufacturing complex internal flow channel castings based on casting cores. It aims to solve technical problems encountered during the handling, installation, high-temperature casting, and subsequent removal of cores for complex internal flow channel castings, including insufficient strength, easy breakage, easy collapse, gas generation, gas pollution, difficulty in core removal, residual blockage, and difficulty in reusing core materials. Specifically, in the core preparation for the production of complex internal flow channel castings, existing ceramic cores and 3D-printed ceramic cores typically require dissolution with sodium hydroxide after casting, resulting in long removal cycles, low efficiency, and core fragility, making efficient core removal difficult. Resin sand cores and 3D-printed resin sand cores have low overall strength, are prone to breakage during handling and installation, easily generate gas during high-temperature casting, causing gas pollution, intruding into the casting and creating defects, and are prone to collapse and instability. They also suffer from difficulties in removal, low efficiency, and difficulty in reuse.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for manufacturing complex internal flow channel castings based on casting cores, the method comprising the following steps:

[0006] S1. Based on the casting material and casting conditions, select a thin-walled metal tube with the same material as the casting matrix element and that meets the melting point matching requirements. Its composition can introduce trace strengthening elements on the basis of the main elements to take into account both high-temperature strength and elongation. The wall thickness of the thin-walled metal tube is in the range of 0.08mm to 0.15mm and meets the length-diameter ratio-wall thickness matching control formula.

[0007] Furthermore, the main component of the thin-walled metal tube is the same as the base element material of the casting, and trace elements are allowed to improve the strength and elongation of the thin-walled metal tube during bending and casting, while maintaining melting point matching. When the main body of the casting is aluminum alloy, a material mainly composed of aluminum with trace amounts of Si, Mn, Ti, etc., is selected; when the main body of the casting is magnesium alloy, a material mainly composed of magnesium with trace amounts of Zn or Mn is selected; when the main body of the casting is titanium alloy, a material mainly composed of titanium with a small amount of Al or V is selected; when the main body of the casting is a high-temperature alloy, an alloy system material mainly composed of nickel is selected, and it may contain strengthening elements such as Cr, Al, Ti, etc.; when the main body of the casting is steel, low-carbon steel or micro-alloyed steel is selected. For other metals, metals with the same main elements and which may contain auxiliary trace elements to improve formability are selected.

[0008] Furthermore, the wall thickness of the thin-walled metal tube satisfies the aspect ratio-wall thickness matching control formula with respect to the tube length and outer diameter, ensuring rapid melting during casting without structural instability. The aspect ratio-wall thickness matching control formula is: ; in, The wall thickness of the thin-walled metal tube; respectively wall thickness The minimum and maximum values; The outer diameter of the thin-walled metal tube; The length of the thin-walled metal tube; The bending stability coefficient; This represents the maximum internal pressure of the filling medium at high temperatures. For thin-walled metallic materials, the allowable stress is... The thermal conductivity of thin-walled metals; This is the temperature difference between the molten metal temperature and the melting point of the thin-walled metal. The time required for a thin-walled metal to completely melt; The density of a thin-walled metal; It is the latent heat of fusion for thin-walled metals.

[0009] S2. The thin-walled metal tube is bent into a hollow structure corresponding to the complex flow channel inside the casting to form a core using a three-dimensional free bending process. The bending radius is controlled to be 2.5 to 5 times the outer diameter of the thin-walled metal tube.

[0010] S3. Fill the thin-walled metal tube with a reusable, flowable mixing medium, and control the surface roughness of the inner wall of the casting using a particle size-roughness coupling control formula.

[0011] Furthermore, the flowable mixing medium is one or more mixtures of silica sand, zircon sand, ferrochrome sand, boron nitride particles, metal powder, and ceramic particles that are separated and recovered after casting. The main particles of the flowable mixing medium are composed of silica sand, zircon sand, and ferrochrome sand mixed in a volume ratio, and the particle size of the main particles is 75–250 micrometers. Among them, the proportion of silica sand is 60%–80%, the proportion of zircon sand is 10%–25%, and the proportion of ferrochrome sand is 5%–15%. The flowable mixing medium also contains 5%–20% by volume high-temperature ceramic particles with a particle size of 1–5 μm or nanometers.

[0012] Furthermore, the particle diameter of the flowable mixing medium Surface roughness of the internal flow channel of the casting The particle size-roughness coupling control formula is satisfied, that is: ; Among them, the empirical coefficient The particle size is 0.01–0.03; the main particles have a particle size of 75–150 μm, and high-temperature ceramic particles with a particle size of 1–5 μm or nanometers are dispersed and added to them. This is to control the surface roughness of the internal flow channel through particle size distribution optimization, while improving the support performance and chilling ability of the flowable mixing medium, and ensuring the inner wall roughness of the hollow core of the casting. .

[0013] S4. Detachable ceramic sealing plugs are installed at both ends of the thin-walled metal tube. During installation, a high-temperature resistant adhesive is applied to the contact surface between the ceramic sealing plug and the tube end to achieve sealing and fixation, forming a core.

[0014] Furthermore, the outer end of the ceramic sealing plug is provided with a screw-out fitting groove, which allows the ceramic sealing plug to be disassembled by rotation; the center of the screw-out fitting groove is provided with a central blind threaded pull-out hole with a depth of 30% to 50% of the length of the ceramic sealing plug, so that a disassembly tool can be screwed in to pull it out; the edge of the screw-out fitting groove is provided with stress breaking grooves distributed radially, so that when it cannot be screwed out, the ceramic sealing plug can be broken by external force to remove it.

[0015] Furthermore, the ceramic sealing plug has a taper with a taper angle ranging from 2° to 6°, and the insertion depth accounts for 5% to 6% of the total length of the core. After insertion, the outer end face of the ceramic sealing plug remains flush with the end face of the thin-walled metal tube, thereby avoiding the need for mold slotting and enabling direct installation.

[0016] The screw-out groove at the outer end of the ceramic sealing plug can be designed to fit various screwdrivers, allowing for disassembly via rotation. A central blind threaded pull-out hole is located in the center of the screw-out groove, and stress-breaking grooves are radially distributed along the groove edge to facilitate removal by pulling and breaking the plug when it cannot be screwed out.

[0017] Furthermore, the unscrewing groove can be a slotted groove, a cross groove, a hexagonal groove, a plum blossom groove, or other polygonal grooves, so as to cooperate with the corresponding screwdriver tool, while ensuring that a blind thread pull hole can be machined in the center and a radial stress breaking groove can be machined on the edge.

[0018] S5. Make the mold, assemble the filled and sealed core into the preset position of the mold and close the mold to form a complete mold cavity.

[0019] S6. High-temperature molten metal matching the material of the thin-walled metal tube in the core is poured into the mold cavity, so that the thin-walled metal tube in the core melts at high temperature and fuses with the molten metal to meet the metallurgical bonding requirements.

[0020] Furthermore, after the high-temperature molten metal is cast, the thin-walled metal tube first melts completely and is uniformly fused with the molten metal. Then, a chilling layer is formed at the prototype core position. This chilling layer solidifies together with the surrounding molten metal to ensure the density of the casting and prevent inclusion defects.

[0021] Furthermore, the bonding between the thin-walled metal tube and the high-temperature molten metal after melting satisfies the metallurgical bonding criterion formula, namely: ; in, Indicates the degree of dilution and mixing at the interface; The thickness of the interdiffusion layer at the interface; The characteristic element concentration distribution of thin-walled metal tubes; This represents the nominal concentration of the element within the thin-walled metal tube. This represents the area fraction of interfacial oxide inclusions. and The control threshold is determined through experiments.

[0022] S7. After the casting cools, a chilling layer is formed in the original position of the thin-walled metal tube in the core and solidifies together with the casting matrix. After solidification, the seal is released by unscrewing the sealing plug or breaking its structure, allowing the flowable mixing medium to flow out naturally and be recycled, thus obtaining a casting with a complex internal flow channel structure.

[0023] By means of the above technical solution, the present invention provides a method for manufacturing complex internal flow channel castings based on casting cores, which has at least the following beneficial effects:

[0024] 1. The casting core method proposed in this invention ensures that the core possesses sufficient strength and stability during installation, handling, and high-temperature casting, without organic matter or gas pollution. Furthermore, it enables convenient core removal after casting, allowing the filling medium to be discharged and reused, simplifying subsequent processing. Simultaneously, this technology meets the forming requirements of complex hollow structural parts, improves the overall quality of castings, production efficiency, and yield, and enhances the level of green manufacturing.

[0025] 2. This invention uses a thin-walled metal tube as the core, whose material is compatible with the metal composition of the casting. It can be directly melted and fused with the casting metal during the casting process, without inclusions or impurities, ensuring the density and uniformity of the casting. It is suitable for precision casting of complex three-dimensional curvature internal channels, improving production efficiency and expanding the freedom of casting structure design. It avoids the problem of traditional resin cores easily generating gas, producing gas pollution and invading the casting to cause defects during high-temperature casting.

[0026] 3. This invention has high mechanical strength during mold assembly and handling, avoiding the problem of easy breakage of traditional ceramic or resin sand cores, improving process reliability, overcoming the problems of insufficient strength, easy breakage, and easy collapse of traditional cores, and after casting, the internal mixed medium can be allowed to flow out naturally by releasing the composite seal, completely solving the problems of difficult removal and low efficiency of traditional cores, avoiding residual blockage of complex internal flow channels, realizing the reuse of core materials, and simplifying the production process.

[0027] 4. This invention selects thin-walled metal tubes with compatible components and determines the matching relationship between melting point and casting temperature by combining the metallurgical bonding determination formula, ensuring that a good metallurgical bond is formed after melting, without segregation or gas contamination invading the casting, thus enhancing the overall performance of the casting.

[0028] 5. This invention adopts a three-dimensional free bending forming process and constrains the bending accuracy based on the structural stability judgment formula, so that the bending radius is controlled at 2.5-5 times the outer diameter of the thin-walled metal tube, ensuring the balance between the core forming quality and strength, and ensuring that instability or collapse does not occur during handling and high-temperature casting.

[0029] 6. This invention controls the particle size distribution of the mixed medium through a particle size-roughness coupling control formula, so that the surface roughness of the casting flow channel reaches Ra≤6.3μm, achieving low flow resistance and high precision, and improving the service performance of the parts.

[0030] 7. The present invention adopts a composite filling structure of ceramic particles and iron powder, which takes into account the structural stability at high temperature and the control of cooling rate. It also utilizes iron powder to enhance the local quenching effect, promote grain refinement, and improve the density and mechanical properties of the flow channel area.

[0031] 8. The composite sealing method of the present invention, which combines the plug with high-temperature resistant adhesive, ensures that the core does not leak during the high-temperature casting process. After cooling, the adhesive becomes brittle and the plug is easy to remove, thereby improving the core removal efficiency and preventing damage to the casting.

[0032] 9. This invention fuses the melting of thin-walled metal tubes with molten metal to form a chilling layer, thereby improving the grain refinement effect in the interface region, making the inner wall structure of the casting more compact, and significantly improving its overall performance. Attached Figure Description

[0033] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a flowchart of the casting core method in this invention; Figure 2 This is a schematic diagram of the thin-walled metal tube in this invention; Figure 3 This is a schematic diagram of the three-dimensional free bending process in this invention; Figure 4 This is a schematic diagram of the structure of the ceramic sealing plug in this invention; Figure 5 This is a schematic diagram of the diffusion fusion process of thin-walled metal tubes during the casting process of the present invention; Figure 6 This is a schematic diagram illustrating the process of chilled layer formation during the casting process of the present invention; Figure 7 This is a schematic diagram illustrating the principle of controlling the inner wall roughness of castings using a flowable mixing medium according to the present invention. Figure 8 The casting models of Embodiments 1 and 2 and Comparative Examples 1 and 2 of the present invention illustrate the core arrangement corresponding to the straight flow channel structure; Figure 9 The mold models of Embodiment 3 and Comparative Example 3 of the present invention illustrate the core arrangement corresponding to the spiral flow channel structure; Figure 10 The single-line detachable ceramic sealing plug used in Embodiment 1 of the present invention; Figure 11 The cross-shaped detachable ceramic sealing plug used in Embodiment 2 of the present invention; Figure 12 The hexagonal detachable ceramic sealing plug used in Embodiment 3 of the present invention. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. This will allow for a full understanding of how the present application uses technical means to solve technical problems and achieve technical effects, and to facilitate its implementation.

[0035] Example 1 This embodiment uses a straight-path flow channel of an A356 aluminum alloy casting as an example, and prepares the core using the casting core method of this invention. A pure aluminum thin-walled tube with an outer diameter of 4mm and a wall thickness of 0.10mm is selected, and the plug size is precisely matched with the inner diameter of the tube. A high-precision CNC three-dimensional tube bending machine is used to process the core along a straight path at room temperature, with the bending radius controlled within three times the tube diameter. A flowable mixed medium consisting mainly of 70% silica sand, 20% zircon sand, and 10% chromium iron sand is filled into the thin-walled tube. The main particle size is 75-150μm, and 10% alumina micro-powder with a particle size of 1-5μm is dispersed and added. The filling volume accounts for 95% of the tube cavity volume. Detachable ceramic sealing plugs are installed at both ends of the thin-walled tube. The outer end of the sealing plug has a cross-shaped screw-out groove, the middle has a central blind thread pull-out hole, and the groove edge has a stress-breaking groove along the radial direction. The contact surface is coated with high-temperature resistant adhesive to form the core. The core is assembled into the preset position in the mold, and after the mold is closed, A356 aluminum alloy molten metal is poured at 680℃. After the casting cools, the sealing plug is unscrewed, and the flowable mixing medium is discharged naturally, forming a straight internal flow channel.

[0036] Example 2 This embodiment uses a straight-path flow channel of an A356 aluminum alloy casting as an example, and prepares the core using the casting core method of this invention. A pure aluminum thin-walled tube with an outer diameter of 4mm and a wall thickness of 0.10mm is selected, and the plug size is precisely matched with the inner diameter of the tube. A high-precision CNC three-dimensional tube bending machine is used to process the core along a straight path at room temperature, with the bending radius controlled within three times the tube diameter. A flowable mixed medium consisting mainly of 75% silica sand, 15% zircon sand, and 10% chromium iron sand is filled into the thin-walled tube. The main particle size is 200-250μm, and 5% by volume of boron nitride micropowder with a particle size of 1-5μm is dispersed and added, filling 95% of the tube cavity volume. Detachable ceramic sealing plugs are installed at both ends of the thin-walled tube. The outer end of the sealing plug has a slotted groove, the middle has a central blind thread pull-out hole, and the edge of the groove has a stress-breaking groove along the radial direction. The contact surface is coated with high-temperature resistant adhesive to form the core. The core is assembled into the preset position in the mold, and after the mold is closed, A356 aluminum alloy molten metal is poured at 680℃. After the casting cools, the sealing plug is unscrewed, and the flowable mixing medium is discharged naturally, forming a straight internal flow channel.

[0037] Example 3 This embodiment uses a Ti-6Al-4V titanium alloy casting spiral flow channel as an example, and prepares the core using the casting core method of this invention. A pure titanium thin-walled tube with an outer diameter of 4 mm and a wall thickness of 0.15 mm is selected, and the plug is precisely fitted to the inner diameter of the tube. A high-precision CNC three-dimensional tube bending machine is used to process the core along a spiral path at room temperature, with a pitch of 25 mm and a bending radius controlled to be 4 times the tube diameter, resulting in a wrinkle-free cross-section. The thin-walled tube is filled with a flowable mixed medium consisting mainly of 65% silica sand, 20% zircon sand, and 15% chromium iron sand. The main particle size is 100–150 μm, and 15% alumina micropowder (1–5 μm by volume) is dispersed and added, filling 92% of the tube cavity volume. Detachable ceramic sealing plugs are installed at both ends of the thin-walled tube. The outer end of the sealing plug has a hexagonal screw-out groove, the center has a central blind thread pull-out hole, and the groove edge has a stress-breaking groove along the radial direction. The contact surface is coated with high-temperature resistant adhesive to form the core. The core is assembled into the preset position in the mold, and after the mold is closed, the Ti-6Al-4V alloy melt is poured at 1650℃. After the casting cools, the sealing plug is unscrewed or broken, allowing the flowing mixing medium to drain naturally, forming a spiral internal flow channel.

[0038] Comparative Example 1 This comparative example uses a straight-path flow channel in an A356 aluminum alloy casting as an example, and employs the traditional phenolic resin sand core method to prepare the core. Silica sand with a particle size of 100–200 μm is selected, phenolic resin binder is added, and the core is hardened using a cold box process to prepare a straight-path core. After demolding, the core is placed in the preset position in the mold, and after mold closing, the molten A356 aluminum alloy is poured at 680℃.

[0039] Comparative Example 2 This comparative example uses a straight-path flow channel in an A356 aluminum alloy casting as an example, and employs the traditional phenolic resin sand core method to prepare the core. Silica sand with a particle size of 200–250 μm is selected, phenolic resin binder is added, and the core is formed through a thermosetting process to prepare a straight-path core. After demolding, the core is placed in the preset position in the mold, and after mold closing, the molten A356 aluminum alloy is poured at 680℃.

[0040] Comparative Example 3 This comparative example uses a spiral flow channel in a Ti-6Al-4V titanium alloy casting as an example, employing the traditional water glass sand core method to prepare the core. Silica sand with a particle size of 100–150 μm is selected, water glass binder is added, and the core is formed using a carbon dioxide hardening process. After demolding, the core is assembled into the preset position in the mold, and after mold closing, the Ti-6Al-4V alloy melt is cast at 1650℃.

[0041] Experimental Example This embodiment is based on the castings prepared in Embodiments 1, 2, and 3 above, as well as Comparative Examples 1, 2, and 3. The effects were measured and verified using an electronic universal testing machine, as detailed below: Taking the straight-path flow channel of the A356 aluminum alloy casting prepared in Example 1 as an example, the flexural strength was determined by a three-point bending test. A 1kN electronic universal testing machine was used to apply a constant loading rate of 5mm / min to the core along its longest straight segment at room temperature, and the moment of fracture was recorded. The completeness of medium discharge was determined by removing the pipe seal after the casting had completely solidified, collecting and weighing the discharged flowable mixed medium, and calculating the discharge ratio by weight. The surface finish of the inner flow channel was measured using a laser scanning micrometer, with the measurement location selected at key sections of the straight path. The content of inclusions or impurities was detected by metallographic analysis and microscopic X-ray imaging, recording residual non-metallic substances within the metal matrix. The porosity of the flow channel edge was obtained by industrial CT scanning to acquire the three-dimensional structure of the flow channel region, and calculated based on the volume fraction statistical porosity ratio. The dimensional deviation of the inner flow channel was detected using a coordinate measuring machine, and the actual measured values ​​were compared with the design CAD data to obtain the dimensional deviation. The composition spectrum of the same thickness section of the thin-walled tube before and after melting was determined by optical emission spectroscopy, recording the changes in elemental diffusion in the tube.

[0042] Taking the straight-path flow channel of the A356 aluminum alloy casting prepared in Example 2 as an example, the flexural strength was determined by a three-point bending test. A 1kN electronic universal testing machine was used to apply a constant loading rate of 5mm / min to the core along its longest straight segment at room temperature, and the moment of fracture was recorded. The completeness of medium discharge was determined by removing the pipe seal after the casting had completely solidified, collecting and weighing the discharged flowable mixed medium, and calculating the discharge ratio by weight. The surface finish of the inner flow channel was measured using a laser scanning micrometer, with the measurement location selected at key sections of the straight path. The content of inclusions or impurities was detected by metallographic analysis and microscopic X-ray imaging, recording residual non-metallic substances within the metal matrix. The porosity of the flow channel edge was obtained by industrial CT scanning to acquire the three-dimensional structure of the flow channel region, and calculated based on the volume fraction statistical porosity ratio. The dimensional deviation of the inner flow channel was detected using a coordinate measuring machine, and the actual measured values ​​were compared with the design CAD data to obtain the dimensional deviation. The composition spectrum of the same thickness section of the thin-walled tube before and after melting was determined by optical emission spectroscopy, recording the changes in elemental diffusion in the tube.

[0043] Taking the spiral path flow channel of the Ti-6Al-4V titanium alloy casting prepared in Example 3 as an example, the flexural strength was determined by a three-point bending test. A 2kN high-precision electronic universal testing machine was used to apply a load to the spiral path core at a constant loading rate of 5mm / min at room temperature, and the breaking moment was recorded. The completeness of medium discharge was determined by removing the pipe seal after the casting had completely solidified, collecting and weighing the discharged flowable mixed medium, and calculating the discharge ratio by weight. The surface finish of the inner flow channel was measured using a non-contact laser scanning micrometer to measure the Ra value, with the measurement location selected from key sections of the spiral path. The content of inclusions or impurities was detected by X-ray fluoroscopy combined with metallographic analysis, recording the residual non-metallic substances in the metal matrix. The porosity of the flow channel edge was obtained by industrial CT scanning to acquire the three-dimensional structure of the flow channel area, and the porosity ratio was calculated based on the volume fraction. The dimensional deviation of the inner flow channel was detected using a coordinate measuring machine, and the actual measured values ​​were compared with the design CAD data to obtain the dimensional deviation. The composition spectrum of the same thickness section of the thin-walled tube before and after melting was determined by optical emission spectroscopy, recording the changes in elemental diffusion in the tube.

[0044] Taking the straight-path flow channel of the A356 aluminum alloy casting prepared in Comparative Example 1 as an example, a straight-path inner flow channel core was used, and the flowable mixing medium particles were 50-70 mesh phenolic resin coated sand. Flexural strength was determined by a three-point bending test using a 1kN electronic universal testing machine. At room temperature, a constant loading rate of 5mm / min was applied to the core along its longest straight segment, and the moment of fracture was recorded. The completeness of medium discharge was determined by removing the pipe seal after complete solidification of the casting, collecting and weighing the discharged flowable mixing medium, and calculating the discharge ratio by weight. The surface finish of the inner flow channel was measured using a laser scanning micrometer, with the measurement location selected at key sections of the straight path. Inclusion or impurity content was detected by metallographic analysis and microscopic X-ray imaging, recording residual non-metallic substances within the metal matrix. The porosity of the flow channel edge was calculated by obtaining the three-dimensional structure of the flow channel region using industrial CT scanning and statistically analyzing the porosity percentage based on volume fraction. The dimensional deviation of the internal flow channel is detected using a coordinate measuring machine, and the actual measured values ​​are compared with the design CAD data to obtain the dimensional deviation.

[0045] Taking the straight-path flow channel of the A356 aluminum alloy casting prepared in Comparative Example 2 as an example, a straight-path inner flow channel core was used, and the flowable mixing medium particles were 1000μm coarse particles after pickling or coating. Flexural strength was determined by a three-point bending test using a 1kN electronic universal testing machine. At room temperature, a constant loading rate of 5mm / min was applied to the core along its longest straight segment, and the moment of fracture was recorded. The completeness of medium discharge was determined by removing the pipe seal after complete solidification of the casting, collecting and weighing the discharged flowable mixing medium, and calculating the discharge ratio by weight. The surface finish of the inner flow channel was measured using a laser scanning micrometer, with the measurement location selected at a key section of the straight path. Inclusion or impurity content was detected by metallographic analysis and microscopic X-ray imaging, recording residual non-metallic substances within the metal matrix. The porosity of the flow channel edge was calculated by obtaining the three-dimensional structure of the flow channel region using industrial CT scanning and statistically analyzing the porosity percentage based on volume fraction. The dimensional deviation of the internal flow channel is detected using a coordinate measuring machine, and the actual measured values ​​are compared with the design CAD data to obtain the dimensional deviation.

[0046] Taking the spiral path flow channel of the Ti-6Al-4V titanium alloy casting prepared in Comparative Example 3 as an example, a spiral path resin sand core was used, with a sand particle size of 50–70 mesh and phenolic resin binder added for curing. Flexural strength was determined by a three-point bending test using a 2kN high-precision electronic universal testing machine. A constant loading rate of 5mm / min was applied to the spiral path core at room temperature, and the breaking moment was recorded. The completeness of medium discharge was determined by removing the pipe seal after complete solidification of the casting, collecting and weighing the discharged flowable mixed medium, and calculating the discharge ratio by weight. The surface finish of the inner flow channel was measured using a non-contact laser scanning micrometer, with the measurement location selected at key sections of the spiral path. Inclusion or impurity content was detected by X-ray fluoroscopy combined with metallographic analysis, recording residual non-metallic substances within the metal matrix. The porosity of the flow channel edge was calculated by obtaining the three-dimensional structure of the flow channel region using industrial CT scanning and statistically analyzing the porosity percentage based on volume fraction. The dimensional deviation of the internal flow channel is detected using a coordinate measuring machine, and the actual measured values ​​are compared with the design CAD data to obtain the dimensional deviation.

[0047] Table 1. Influence of sand particle size on the surface roughness of the inner flow channel

[0048]

[0049] Table 2. Component diffusion results before and after melting of thin-walled tubes

[0050]

[0051] Table 3 Overall Performance Comparison

[0052]

[0053] As shown in Table 1, different flowable mixing media particle sizes significantly affect the surface roughness of the inner flow channel. In Example 1, when the filling particle size was 75–150 μm, the surface roughness of the inner flow channel was controlled within the range of 6–7 μm. In Example 2, when the particle size was 200–250 μm, the roughness was 7–8 μm. In Example 3, the spiral flow channel with a particle size of 100–150 μm had a roughness of 6–8 μm, and the overall surface quality remained excellent. In Comparative Example 1, phenolic resin sand with a particle size of 100–200 μm was used, and the surface roughness was between 20 and 25 μm. In Comparative Example 2, phenolic resin sand with a particle size of 200–250 μm was used, and the roughness further increased to 28–32 μm. The spiral flow channel with a water glass sand core in Comparative Example 3 had the highest roughness, reaching 35–40 μm. This difference indicates that Examples 1 to 3, through the combination of thin-walled metal tubes and inorganic particle gradation, effectively improved the surface quality of the flow channel, which is significantly better than the traditional organic or inorganic resin sand core method used in Comparative Examples 1 to 3. This avoids surface roughness and defects caused by binder carbonization or sintering. At the same time, since no resin-based organic binder is introduced, the adverse effects of gases generated by high-temperature decomposition on the surface quality of the flow channel are reduced.

[0054] As shown in Table 2, the metallurgical diffusion effect of the thin-walled tube after high-temperature casting is significant. In Example 1, the aluminum content increased from 90.2% to 95.6% after melting, while the elemental changes in Comparative Examples 1 and 2 were minimal, almost retaining their original state, indicating that the traditional core in the comparative examples did not participate in the metallurgical process. In Example 2, the titanium content increased from 91.0% to 96.2%, and the proportions of aluminum and vanadium decreased, showing that the thin-walled titanium tube completely melted and bonded with the base metal after high-temperature casting, while Comparative Example 3 did not exhibit this effect. This significant difference in elemental diffusion indicates that Examples 1 and 2 not only achieved rapid core melting but also improved the local compositional distribution of the casting during flow channel formation, creating a reinforced chilling zone and enhancing the density and mechanical properties of the microstructure, far superior to the resin sand cores used in Comparative Examples 1 to 3.

[0055] As can be seen from Table 3, there are significant differences in core flexural strength, media discharge rate, and casting quality between the examples and comparative examples. The flexural strength of Example 1 reaches 6 N·m, while that of Examples 2 and 3 reaches 5.5 N·m and 7 N·m, respectively. However, the strengths of Comparative Examples 1 to 3 are only between 2.5 and 3.0 N·m, which is clearly insufficient to guarantee the molding stability of complex paths.

[0056] Regarding discharge rates, Examples 1 and 3 both achieved 99%, Example 2 achieved 98%, and the residual amount was controlled within 1%. In contrast, Comparative Example 1 had a discharge rate of 65%, Comparative Example 2 had a rate of 50%, and Comparative Example 3 had the lowest rate at only 30%, with residual amounts ranging from 15% to 35%. Furthermore, Comparative Example 3 showed significant flow channel blockage. In terms of surface finish and dimensional accuracy, the flow channel surface roughness of Examples 1 to 3 was less than 10 μm, and the dimensional deviation was controlled within ±0.5 mm. In contrast, the dimensional deviation of the comparative examples ranged from ±1.5 mm to ±3.0 mm, indicating a significant decrease in surface quality. Simultaneously, the inclusion content of the examples was less than 0.5%, while the comparative examples generally reached 3% to 5%. Further analysis of the flow channel porosity data reveals that the porosity of Examples 1 to 3 was controlled within the range of 0.6% to 0.75%, while that of Comparative Examples 1 to 3 reached approximately 1% to 3.5%, significantly higher. This indicates that traditional resin sand cores are prone to gas generation during high-temperature casting due to the thermal decomposition of organic binders, which then enters the casting, leading to porosity defects and gas pollution. Furthermore, a comparison of resin usage shows that Comparative Examples 1 and 2 used approximately 1.5% to 2.0% resin, a typical consumable binder system. Examples 1 to 3, however, did not use resin binders, allowing the filling medium to be directly discharged and reused, thus reducing material consumption while maintaining molding performance. These results demonstrate that Examples 1 to 3, by employing thin-walled metal tubes and high-temperature stable inorganic media, achieved high-strength, controllable melting, and efficient green core removal, significantly superior to the traditional cores used in Comparative Examples 1 to 3.

[0057] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0058] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Since the above embodiments are substantially similar to the method embodiments, their descriptions are relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0059] The above embodiments provide a detailed description of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for manufacturing complex internal flow channel castings based on casting cores, characterized in that, The method includes the following steps: S1. Based on the casting material and casting conditions, select a thin-walled metal tube that is the same as the base material of the casting and meets the requirements for fusion in terms of melting point matching. The wall thickness of the thin-walled metal tube is in the range of 0.08mm to 0.15mm and meets the length-to-diameter ratio – wall thickness matching control formula. S2. The thin-walled metal tube is bent into a hollow structure corresponding to the complex flow channel inside the casting to form a core using a three-dimensional free bending process. The bending radius is controlled to be 2.5 to 5 times the outer diameter of the thin-walled metal tube. S3. Fill the thin-walled metal tube with a reusable flowable mixing medium and control the surface roughness of the inner wall of the casting by a particle size-roughness coupling control formula. S4. Detachable ceramic sealing plugs are installed at both ends of the thin-walled metal tube. During installation, a high-temperature resistant adhesive is applied to the contact surface between the ceramic sealing plug and the tube end to achieve sealing and fixation, forming a core. S5. Make the mold, assemble the filled and sealed core into the preset position of the mold and close the mold to form a complete mold cavity; S6. High-temperature molten metal matching the material of the thin-walled metal tube in the core is poured into the mold cavity, so that the thin-walled metal tube in the core melts at high temperature and fuses with the molten metal to meet the metallurgical bonding judgment requirements. S7. After the casting cools, a chilling layer is formed in the original position of the thin-walled metal tube in the core and solidifies together with the casting matrix. After solidification, the seal is released by unscrewing the sealing plug or breaking its structure, allowing the flowable mixing medium to flow out naturally and be recycled, thus obtaining a casting with a complex internal flow channel structure.

2. The method according to claim 1, characterized in that, The main components of the thin-walled metal tube are the same as those of the casting matrix, and trace elements are allowed to be present while maintaining melting point matching in order to improve the strength and elongation of the thin-walled metal tube during bending and casting. When the main body of the casting is aluminum alloy, a material with aluminum as the main component and trace amounts of elements including Si, Mn and Ti should be selected. When the main body of the casting is a magnesium alloy, a material with magnesium as the main component and added Zn or Mn should be selected. When the main body of the casting is a titanium alloy, a material that is mainly titanium and contains Al or V should be selected. When the main body of the casting is a high-temperature alloy, a nickel-based alloy system material is selected, which also contains strengthening elements including Cr, Al, and Ti. When the main body of the casting is made of steel, low-carbon steel or micro-alloyed steel should be selected.

3. The method according to claim 1 or 2, characterized in that, The wall thickness of the thin-walled metal tube satisfies the length-to-diameter ratio-wall thickness matching control formula with respect to the tube length and outer diameter, so as to ensure rapid melting and no structural instability during the casting process. The formula for controlling the aspect ratio-wall thickness matching is: ； in, The wall thickness of the thin-walled metal tube; respectively wall thickness The minimum and maximum values; The outer diameter of the thin-walled metal tube; The length of the thin-walled metal tube; The bending stability coefficient; This represents the maximum internal pressure of the filling medium at high temperatures. For thin-walled metallic materials, the allowable stress is... The thermal conductivity of thin-walled metals; This is the temperature difference between the molten metal temperature and the melting point of the thin-walled metal. The time required for a thin-walled metal to completely melt; The density of a thin-walled metal; It is the latent heat of fusion for thin-walled metals.

4. The method according to claim 1, characterized in that, The flowable mixing medium is one or more of the following: silica sand, zircon sand, ferrochrome sand, boron nitride particles, metal powder, and ceramic particles, which are separated and recovered after casting.

5. The method according to claim 4, characterized in that, The main particles of the flowable mixing medium are composed of silica sand, zircon sand and chromium iron sand mixed in a volume ratio, and the particle size of the main particles is 75 to 250 micrometers. Of these, silica sand accounts for 60% to 80%, zircon sand accounts for 10% to 25%, and chromite sand accounts for 5% to 15%. The flowable mixing medium also contains high-temperature ceramic particles with a volume ratio of 5% to 20% and a particle size of 1–5 μm or nanometers.

6. The method according to claim 1, 4, or 5, characterized in that, The particle diameter of the flowable mixing medium Surface roughness of the internal flow channel of the casting The particle size-roughness coupling control formula is satisfied, that is: ； Among them, the empirical coefficient Take values ​​between 0.01 and 0.03; The main particles have a particle size of 75–150 μm, and high-temperature ceramic particles with a particle size of 1–5 μm or nanometers are dispersed within them. This is to optimize the particle size distribution and control the surface roughness of the internal flow channels, while simultaneously improving the support performance and chilling capacity of the flowable mixing medium, ensuring the inner wall roughness of the hollow core formed in the casting. .

7. The method according to claim 1, characterized in that, The outer end of the ceramic sealing plug is provided with a screw-out fitting groove, and the middle part of the screw-out fitting groove is provided with a central blind thread pull-out hole with a depth of 30% to 50% of the length of the ceramic sealing plug; The edge of the screw-out fitting groove is radially distributed with stress breaking grooves so that when it cannot be screwed out, the ceramic sealing plug can be broken by external force to remove it.

8. The method according to claim 1 or 7, characterized in that, The ceramic sealing plug has a taper with a taper angle ranging from 2° to 6°. The insertion depth accounts for 5% to 6% of the total length of the core, and after insertion, the outer end face of the ceramic sealing plug remains flush with the end face of the thin-walled metal tube.

9. The method according to claim 1, characterized in that, After the high-temperature molten metal is cast, the thin-walled metal tube first melts completely and fuses uniformly with the molten metal. Then, a chilling layer is formed at the prototype core position. This chilling layer solidifies together with the surrounding molten metal to achieve the density of the casting and prevent inclusion defects.

10. The method according to claim 1 or 9, characterized in that, The bonding between the thin-walled metal tube and the high-temperature molten metal after melting satisfies the metallurgical bonding determination formula, namely: ； in, Indicates the degree of dilution and mixing at the interface; The thickness of the interdiffusion layer at the interface; The characteristic element concentration distribution of thin-walled metal tubes; This represents the nominal concentration of the element within the thin-walled metal tube. This represents the area fraction of interfacial oxide inclusions. and The control threshold is determined through experiments.

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