V-method precise resin sand mold casting process method suitable for gray iron or ductile iron

Abstract

The invention relates to the technical field of casting mold cooling capacity regulation and control and material-process collaborative optimization, in particular to a V-method precise resin sand mold casting process method suitable for gray iron or ductile iron. The invention relates to a V-method precise resin sand mold casting process suitable for gray iron or ductile iron, which comprises the following steps: firstly, preparing gradient function modified resin sand, mixing spherical reclaimed sand with various materials such as novolac epoxy resin, and carrying out multi-step stirring and surface modification treatment; an intelligent temperature control sand box is prepared, and then the steps of forming negative pressure curing, composite inoculation treatment, vacuum differential pressure pouring, intelligent cooling control and the like are carried out; in the process, special materials and structures such as a core-shell curing agent, a double-layer film and a core-spun yarn are used, and precise process control is achieved. According to the process, through material innovation and process optimization, the sand mold strength and stability are improved, and casting defects are reduced; the casting quality is improved through the precise temperature control and pouring mode, and the mechanical property is enhanced through composite inoculation; the method is environment-friendly and economical, reduces the cost, improves the yield and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of regulating the cooling capacity of casting molds and synergistic optimization of materials and processes, and specifically to a V-method precision resin sand mold casting process method applicable to gray iron or ductile iron. Background Art

[0002] Due to their good casting properties, mechanical properties, and cost advantages, gray iron and ductile iron are widely used in many fields such as automotive, machinery manufacturing, aerospace, etc. As an advanced sand casting process, V-method casting has the advantages of smooth casting surface, high dimensional accuracy, and reusable sand molds by compacting the sand mold under negative pressure, which can effectively reduce production costs and improve production efficiency. However, there are still many technical bottlenecks in the actual application of traditional V-method precision resin sand mold casting processes, making it difficult to meet the stringent requirements of modern manufacturing for high-quality castings.

[0003] Traditional resin sand mostly uses ordinary quartz sand and a single resin system. The sand grains have irregular shapes and rough surfaces, resulting in uneven compaction of the sand mold, and defects such as sand holes and air holes are likely to occur in the castings. At the same time, ordinary resins have poor thermal stability at high temperatures, are prone to thermal decomposition and volatilization, which not only pollutes the environment but also forms carbon deposits on the casting surface, affecting the quality of the castings. In addition, the existing curing agent system has low curing efficiency and difficult-to-control curing processes, resulting in insufficient strength of the sand mold, which is prone to collapse during the pouring process, affecting the forming accuracy of the castings.

[0004] The temperature control method of the sand box in traditional V-method casting is single and cannot perform precise temperature control according to the solidification requirements of different parts of the casting, resulting in inconsistent cooling rates of different parts of the casting, generating large thermal stresses, and easily causing defects such as casting deformation and cracks. Moreover, the traditional inoculation treatment method only uses a single inoculant and is difficult to simultaneously meet the requirements of gray iron and ductile iron for graphite morphology, grain refinement, etc., making the improvement of the mechanical properties of the castings limited. During the pouring process, the traditional atmospheric pressure pouring method easily entrains gases and inclusions into the molten iron, reducing the internal quality of the castings. In addition, there is a lack of effective control means during the casting cooling process, and it is impossible to precisely regulate the structure and properties of the castings.

[0005] With the development of modern manufacturing towards lightweight, precision, and high-performance directions, higher requirements are put forward for the quality and performance of gray iron and ductile iron castings. For example, in the casting of automotive engine blocks, the castings are required to have higher strength, wear resistance, and dimensional accuracy; in the aerospace field, more stringent requirements are placed on the lightweight and high-temperature resistance of the castings. Therefore, there is an urgent need to develop a new V-method precision resin sand mold casting process method applicable to gray iron or ductile iron. Through innovative material formulations and process designs, solve the technical problems existing in traditional processes, improve the quality and performance of castings, and meet the development needs of modern manufacturing. Summary of the Invention

[0006] (1) Technical problems to be solved Aiming at the deficiencies of the prior art, the present invention provides a V-method precision resin sand mold casting process method applicable to gray iron or ductile iron.

[0007] (2) Technical solutions A V-method precision resin sand mold casting process method applicable to gray iron or ductile iron, comprising the following steps: S1: Prepare gradient functional modified resin sand. Mix 85 - 95 parts by weight of spherical recycled sand, 5 - 8 parts of phenolic epoxy resin, 2 - 4 parts of nano-zirconia, 3 - 6 parts of core-shell structure composite curing agent, 1 - 2 parts of graphene nanosheets, and 0.5 - 1 part of carbon nanotubes; the core-shell structure composite curing agent uses hexamethylenetetramine as the core, and the outer layer is coated with organic sulfonic acid, with the mass ratio of p-toluenesulfonic acid to benzenesulfonic acid being 2:1, and a microcapsule structure of 20 - 50 μm is formed through interfacial polymerization; during sand mixing, first heat the spherical recycled sand to 90 - 110 °C, add nano-zirconia and graphene nanosheets, and stir at a high speed of 500 - 700 r / min for 15 - 20 minutes to form a mechanical alloying layer; then add silane coupling agent KH-560, accounting for 0.8 - 1.2% of the sand weight, and continue stirring for 8 - 12 minutes to graft the silane coupling agent onto the sand grain surface; finally, add phenolic epoxy resin, carbon nanotubes, and core-shell structure composite curing agent, and stir at 300 - 450 r / min for 25 - 35 minutes to obtain gradient functional modified resin sand; S2: Prepare an intelligent temperature-controlled sand box. Lay a phase change energy storage material layer with a thickness of 3 - 5 mm on the inner wall of the sand box, which is composed of a paraffin / expanded graphite composite with a mass ratio of 3:2 and a phase change temperature of 55 - 65 °C; install an electromagnetic induction heating coil on the outer side of the sand box, with a coil spacing of 5 - 8 mm and a power density of 1.5 - 2.5 kW / m²; S3: Molding and negative pressure curing. Fill the gradient functional modified resin sand into the intelligent temperature-controlled sand box, vibrate and compact it, with a vibration frequency of 40 - 60 Hz, an amplitude of 0.4 - 0.6 mm, and a compaction time of 4 - 6 minutes; cover with a double-layer composite film, the inner layer is a polyvinyl chloride film with a thickness of 0.1 - 0.15 mm, and the outer layer is an aluminum foil composite film with a thickness of 0.05 - 0.1 mm; start the air extraction system to make the negative pressure in the sand box reach 0.05 - 0.07 MPa, and at the same time turn on the electromagnetic induction heating to raise the temperature of the inner wall of the sand box to 120 - 140 °C and maintain it for 15 - 25 minutes to cause the resin to undergo a cross-linking curing reaction; S4: Composite inoculation treatment. Heat gray iron or ductile iron molten iron to 1450 - 1550 °C, and use the wire feeding method to add a composite inoculant cored wire into the molten iron. The outer layer of the cored wire is a low-carbon steel strip with an inner diameter of 8 - 12 mm, and the core consists of the following components: 70 - 80% ferrosilicon alloy, 5 - 10% nano calcium carbonate, 3 - 5% rare earth magnesium alloy, 2 - 4% boron nitride nanotubes, and the balance is silicon carbide whiskers. The addition amount is 0.3 - 0.6% of the weight of the molten iron, and the wire feeding speed is 1.5 - 2.5 m / s; S5: Vacuum differential pressure casting. Pour the treated molten iron into a holding furnace, and the holding temperature is 1380 - 1430 °C; Place the sand mold in a vacuum chamber to reduce the pressure in the vacuum chamber to 0.02 - 0.03 MPa; Adopt a bottom gating system, and make the molten iron fill the mold under the action of a pressure difference of 0.04 - 0.06 MPa through a differential pressure device, and the filling speed is 6 - 10 kg / s; S6: Intelligent cooling control. After casting is completed, use the temperature sensors installed in the sand mold to monitor the temperature of the casting in real time. When the temperature drops to 700 - 800 °C, start the air cooling system in the sand mold, and the wind speed is 3 - 5 m / s, so that the casting cools at a cooling rate of 15 - 25 °C / min to 350 - 450 °C; Then turn off the air cooling system and let the casting cool naturally to room temperature.

[0008] Preferably, it further includes that the particle size of the spherical recycled sand is 0.2 - 0.5 mm, the roundness coefficient ≥ 0.9, and the loss on ignition ≤ 0.3%, which is obtained by combined treatment of high-temperature roasting (850 - 950 °C) and mechanical regeneration.

[0009] Preferably, it further includes that the epoxy value of the phenolic epoxy resin is 0.4 - 0.5 eq / 100 g, and the softening point is 80 - 90 °C, which is prepared by reacting bisphenol A epoxy resin with linear phenolic resin under the action of a catalyst.

[0010] Preferably, it further includes that the particle size of the nano zirconia is 30 - 80 nm, the crystal form is a mixture of tetragonal phase and monoclinic phase with a mass ratio of 7:3, and the specific surface area is 60 - 100 m² / g.

[0011] Preferably, it further includes that the layer thickness of the graphene nanosheets is 3 - 8 nm, the sheet diameter is 5 - 15 μm, the carbon content ≥ 98%, which is prepared by the redox method and subjected to surface hydroxylation treatment, and the hydroxyl content is 2 - 5%.

[0012] Preferably, it further includes that in step S3, a breathable heat-insulating layer with a thickness of 0.5 - 1 mm is laid between the double-layer composite film and the sand mold, which is composed of ceramic fiber and aerogel, the porosity is 70 - 80%, and the thermal conductivity ≤ 0.03 W / (m·K).

[0013] Preferably, the preparation method of the composite inoculant cored wire in the step S4 is as follows: after mixing each component in proportion, it is pressed into a core rod by powder metallurgy method, and then wrapped with low-carbon steel strip and made by seam welding.

[0014] Preferably, the inner gates of the bottom gating system in the step S5 are arranged in a stepped manner, the distance between each layer of inner gates is 50 - 80 mm, and the cross-sectional area of the inner gates decreases layer by layer from bottom to top by 10 - 15%.

[0015] Preferably, the air ducts of the air cooling system in the step S6 are evenly distributed around the sand box, the distance between the air duct outlet and the casting surface is 80 - 120 mm, and temperature-adjustable electric heating wires are installed in the air ducts to adjust the cooling rate.

[0016] Preferably, it further includes that after the casting is cooled to room temperature, laser surface alloying treatment is carried out. A carbon dioxide laser is used, the laser power is 1.5 - 3 kW, the scanning speed is 5 - 10 mm / s, and an alloy layer with a thickness of 0.3 - 0.8 mm is cladded on the casting surface. The composition of the alloy layer by weight percentage is: Cr 15 - 20%, Ni 8 - 12%, Mo 3 - 5%, V 1 - 3%, and the balance is Fe.

[0017] (III) Beneficial technical effects Compared with the existing technology, the beneficial effects of the present invention are as follows: 1. By using gradient functional modified resin sand, spherical recycled sand combined with additives such as nano-zirconia and graphene nanosheets, through mechanical alloying and surface modification treatment, the surface properties of sand grains and the compactness of the sand mold are significantly improved, the strength of the sand mold is greatly increased, and casting defects such as sand holes and air holes are effectively reduced. The use of the core-shell structure composite curing agent realizes the controllable curing of the resin, shortens the curing time, and significantly improves the thermal stability of the cured sand mold, reducing the thermal decomposition and carbon deposition phenomena at high temperatures.

[0018] 2. The application of the intelligent temperature-controlled sand box, through the combination of phase change energy storage materials and electromagnetic induction heating, realizes the precise control of the sand box temperature, makes the cooling rate of each part of the casting uniform, greatly reduces the thermal stress, and effectively avoids the generation of casting deformation and cracks. The composite inoculation treatment uses a cored wire composed of a variety of high-performance additives, which can simultaneously meet the requirements of gray iron and ductile iron for graphite morphology and grain refinement, improve the tensile strength and hardness of the casting. The application of the vacuum differential pressure casting technology reduces the gas and inclusions involved in the molten iron during pouring, significantly improves the internal quality of the casting, and greatly reduces the defects of air holes and inclusions. The intelligent cooling control realizes the precise regulation of the casting cooling rate and can obtain ideal structures and properties according to different requirements of the casting.

[0019] 3. The process method of the present invention also has good environmental protection and economy. The use of spherical recycled sand improves the utilization rate of sand resources and reduces the exploitation of new sand; the application of the new resin and curing agent system reduces pollutant emissions. At the same time, this process improves the yield and quality of castings, reduces subsequent processing procedures, and lowers production costs, having broad application prospects and significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a process flow chart of the V-process precision resin sand mold casting method applicable to gray iron or ductile iron; Figure 2 is a bar chart comparing the room temperature compressive strength and high temperature compressive strength of the sand molds in the examples and comparative examples; Figure 3 is a line chart comparing the porosity of the castings and the proportion of the area of shrinkage and porosity defects in the castings in the examples and comparative examples; Figure 4 is a bar and line chart comparing the tensile strength and elongation rate of the castings in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0021] Example 1

[0022] Preparation of gradient functional modified resin sand

[0023] First, spherical recycled sand treated by combined high-temperature roasting (880 °C) and mechanical regeneration is selected, with a particle size of 0.3 mm, a roundness coefficient of 0.93, a loss on ignition of 0.25%, and a silica content of 96%. 90 parts of this spherical recycled sand are added to a heating type mixer and heated to 100 °C. Then, 3 parts of nano-zirconia (particle size 50 nm, mass ratio of tetragonal phase to monoclinic phase 7:3, specific surface area 80 m² / g) and 1.5 parts of graphene nanosheets (sheet thickness 5 nm, sheet diameter 10 μm) treated by surface hydroxylation (hydroxyl content 3%) are added, and stirred at a high speed of 600 r / min for 18 minutes to form a mechanical alloying layer on the surface of the sand grains through friction chemical reaction. Subsequently, 1% of the sand weight of silane coupling agent KH-560 is added and stirred for another 10 minutes to graft the silane coupling agent onto the surface of the sand grains. Then, 6 parts of phenolic epoxy resin (epoxy value 0.45 eq / 100 g, softening point 85 °C, prepared from bisphenol A epoxy resin and linear phenolic resin under the action of a catalyst), 1.2 parts of carbon nanotubes, and 5 parts of core-shell structure composite curing agent (using hexamethylenetetramine as the core and coated with an organic sulfonic acid with a mass ratio of p-toluenesulfonic acid to benzenesulfonic acid of 2:1 on the outer layer, forming a microcapsule structure with an average particle size of 30 μm through interfacial polymerization) are added in sequence, and stirred at a speed of 400 r / min for 30 minutes to mix evenly, thus preparing the gradient functional modified resin sand.

[0024] Preparation of intelligent temperature control sand box Apply a paraffin / expanded graphite composite phase change material with a thickness of 4 mm (mass ratio 3:2, phase change temperature 60 °C) evenly on the inner wall of the sand box. This material can absorb or release heat during the solidification process of the casting, playing a role in temperature buffering. Wind an electromagnetic induction heating coil with a spacing of 6 mm on the outer side of the sand box, and set the power density to 2 kW / m² for providing precise temperature control during the sand mold curing stage.

[0025] Molding and Negative Pressure Curing Fill the prepared modified resin sand into the intelligent temperature-controlled sand box, turn on the vibration compaction equipment, set the vibration frequency to 50 Hz, the amplitude to 0.5 mm, and the compaction time to 5 minutes to make the sand mold reach uniform compaction. After compaction, cover it with a polyvinyl chloride film with an inner layer thickness of 0.12 mm and an aluminum foil composite film with an outer layer thickness of 0.08 mm to form a sealed structure. Start the air extraction system to make the negative pressure in the sand box reach 0.06 MPa. At the same time, turn on the electromagnetic induction heating, raise the temperature of the inner wall of the sand box to 130 °C, and maintain it for 20 minutes to make the phenolic epoxy resin and the composite curing agent undergo a cross-linking curing reaction to form a sand mold with high strength and thermal stability.

[0026] Compound Inoculation Treatment Heat the ductile iron molten iron to 1500 °C in an intermediate frequency induction furnace. Feed the compound inoculant cored wire (the outer layer of the cored wire is a low-carbon steel strip with an inner diameter of 10 mm, and the core is composed of 75% ferrosilicon alloy (containing 75% Si), 8% nano calcium carbonate, 4% rare earth magnesium alloy, 3% boron nitride nanotubes, 5% silicon carbide whiskers, and the balance is iron) into the molten iron at a speed of 2 m / s through a wire feeder. The addition amount is 0.5% of the weight of the molten iron to fully inoculate the molten iron before pouring and improve the graphite morphology and grain structure.

[0027] Vacuum Differential Pressure Pouring Pour the treated molten iron into a holding furnace, and maintain the holding temperature at 1400 °C. Place the sand box in a vacuum chamber, start the vacuum pump to reduce the pressure in the vacuum chamber to 0.025 MPa. Adopt a bottom-gating stepped ingate (the cross-sectional area of the lower ingate is 15 cm², and the cross-sectional area of the upper ingate decreases by 12% in sequence). Through the differential pressure device, make the molten iron fill the mold smoothly at a speed of 8 kg / s under the action of a pressure difference of 0.05 MPa to ensure that gas and inclusions are less involved during the filling process of the molten iron.

[0028] Intelligent Cooling Control After pouring, monitor the temperature of the casting in real time through temperature sensors installed at different positions in the sand box. When the temperature of the casting drops to 750 °C, start the air-cooling system, set the wind speed to 4 m / s, and make the casting cool at a cooling rate of 20 °C / min to 400 °C. Then turn off the air-cooling system and let the casting cool naturally in the sand mold to room temperature. By precisely controlling the cooling rate, obtain the ideal casting structure and performance.

[0029] Example 2

[0030] Preparation of functionally gradient modified resin sand

[0031] Select 92 parts of spherical recycled sand treated in the same batch as in Example 1, with consistent indicators for each item. Add 2.5 parts of nano-zirconia and 1.2 parts of graphene nanosheets. In the same mixer, first stir at a speed of 620 r / min for 17 minutes, then add 0.9% of silane coupling agent KH-560 and stir for 9 minutes. Then add 5.5 parts of phenolic epoxy resin, 1 part of carbon nanotubes, and 4.5 parts of core-shell structure composite curing agent, and stir at a speed of 380 r / min for 32 minutes to obtain the modified resin sand.

[0032] Preparation of intelligent temperature control sand box Adjust the thickness of the phase change material layer on the inner wall of the sand box to 3.8 mm, set the spacing of the electromagnetic induction heating coils to 6.5 mm, and adjust the power density to 1.8 kW / m². Other structures are the same as those in Example 1.

[0033] Molding and negative pressure curing Fill the modified resin sand into the sand box, and adjust the vibration compaction parameters to a frequency of 48 Hz, an amplitude of 0.48 mm, and a compaction time of 4.5 minutes. Cover with a double-layer film, with the inner layer of polyvinyl chloride film being 0.11 mm thick and the outer layer of aluminum foil composite film being 0.07 mm thick. Evacuate to a negative pressure of 0.058 MPa, and use electromagnetic induction heating to raise the temperature of the inner wall of the sand box to 125 °C and maintain it for 22 minutes to complete curing.

[0034] Compound inoculation treatment Heat the gray iron molten iron to 1480 °C, and feed it into the compound inoculant cored wire at a speed of 1.8 m / s (the core component ratio is slightly adjusted to 72% ferrosilicon alloy, 9% nano-calcium carbonate, 3.5% rare earth magnesium alloy, 3.5% boron nitride nanotubes, 6% silicon carbide whiskers, and the balance is iron), and the addition amount is 0.45% of the weight of the molten iron.

[0035] Vacuum differential pressure casting The holding temperature of the molten iron is 1380 °C, the pressure in the vacuum chamber is reduced to 0.022 MPa, and a bottom-gating stepped ingate is used (the cross-sectional area of the lower ingate is 14 cm², and the upper layer decreases by 13%). Under a pressure difference of 0.045 MPa, cast at a speed of 7.5 kg / s.

[0036] Intelligent cooling control Start air cooling when the temperature of the casting drops to 760 °C, with a wind speed of 3.8 m / s. After cooling to 420 °C, cool naturally, and control the cooling speed at about 18 °C / min during the whole cooling process.

[0037] Example 3

[0038] Preparation of functionally gradient modified resin sand

[0039] Take 88 parts of spherical reclaimed sand, add 3.5 parts of nano-zirconia and 1.8 parts of graphene nanosheets. First, stir in a sand mixer at 580 r / min for 19 minutes, then add 1.1% of silane coupling agent KH-560 and stir for 11 minutes. Subsequently, add 6.5 parts of phenolic epoxy resin, 1.5 parts of carbon nanotubes, and 5.5 parts of core-shell structure composite curing agent, and stir at 420 r / min for 28 minutes to obtain modified resin sand.

[0040] Prepare an intelligent temperature-controlled sand box The thickness of the phase change material layer on the inner wall of the sand box is 3.5 mm, the power density of the electromagnetic induction heating coil is set at 2.2 kW / m², and the spacing is 5.5 mm.

[0041] Molding and negative pressure curing After the sand box is filled with sand, the vibration compaction frequency is 45 Hz, the amplitude is 0.45 mm, and the compaction time is 5.5 minutes. The inner layer of the double-layer film is a polyvinyl chloride film with a thickness of 0.13 mm, and the outer layer is an aluminum foil composite film with a thickness of 0.09 mm. Vacuum is pumped to 0.062 MPa, heated to 135 °C, and maintained for 18 minutes for curing.

[0042] Compound inoculation treatment Heat the ductile iron molten iron to 1520 °C, and feed it into the compound inoculant cored wire at a speed of 2.2 m / s (the content of rare earth magnesium alloy in the core is increased to 6%, and the proportion of other components is slightly adjusted), and the addition amount is 0.55% of the weight of the molten iron.

[0043] Vacuum differential pressure casting Keep the molten iron at 1420 °C, reduce the pressure in the vacuum chamber to 0.028 MPa, and use a bottom-gating stepped ingate (the cross-sectional area of the lower ingate is 16 cm², and the upper layer decreases by 10%). Cast at a speed of 8.5 kg / s under a pressure difference of 0.055 MPa.

[0044] Intelligent cooling control When the temperature of the casting drops to 780 °C, start air cooling with a wind speed of 3.5 m / s. After cooling to 380 °C, cool naturally, and control the cooling speed at about 22 °C / min.

[0045] Control group Adopt the traditional V-process casting technology, select ordinary 40-70 mesh quartz sand (mud content 0.8%, silica content 92%), add phenolic resin and a single hexamethylenetetramine curing agent according to the conventional ratio, and simply mix in a sand mixer. After the sand mold is compacted, only cover a single layer of ordinary plastic film with a thickness of 0.15 mm. The molten iron is poured under normal pressure, without compound inoculation treatment, and the casting is cooled in the natural environment after pouring, without any temperature control measures.

[0046] Performance test The performance comparison between Examples 1 to 3 and the comparative example shows that the new V-process casting technology significantly improves the quality of castings. The room-temperature compressive strength of the sand mold reaches 11.8 to 13.2 MPa, and the high-temperature compressive strength is 6.5 to 7.2 MPa, far higher than 7.5 and 3.2 MPa of the comparative example. The surface roughness of the casting is controlled at 6.5 to 7.2 microns, the porosity is only 1.0% to 1.5%, and the area ratio of shrinkage porosity defects is 0.6% to 1.2%, showing significant improvement compared with 12.3 microns, 5.8% and 4.5% of the comparative example. In terms of mechanical properties, the tensile strength reaches 405 to 435 MPa, the elongation is 2.5% to 3.0%, and the hardness is 178 to 192 HB, all of which are better than 320 MPa, 1.2% and 150 HB of the comparative example. These data indicate that the new process has made breakthrough progress in terms of sand mold strength, casting surface quality and mechanical properties.

[0047] The physical property comparison of the sand mold and the casting between the examples and the comparative example is shown in Table 1 below:

[0048] Conclusion: The room-temperature and high-temperature compressive strengths of the sand molds in Examples 1-3 are significantly higher than those of the comparative example. The casting surface has lower roughness, and the porosity and shrinkage porosity defect ratio are smaller, reflecting the optimization effect of the process of the present invention on the physical properties of the sand mold and the casting.

[0049] The mechanical property comparison of the castings between the examples and the comparative example is shown in Table 2 below:

[0050] Conclusion: The tensile strength, elongation and hardness of the castings in the three examples are better than those of the comparative example. Example 3 shows the best performance in all mechanical properties, indicating that the process of the present invention can effectively improve the mechanical properties of castings.

Claims

1. A V-process precision resin sand mold casting process method applicable to gray iron or ductile iron, characterized in that, It includes the following steps: S1: Prepare gradient functional modified resin sand by mixing spherical recycled sand, phenolic epoxy resin, nano-zirconia, core-shell structured composite curing agent, graphene nanosheets, and carbon nanotubes; the core-shell structured composite curing agent has hexamethylenetetramine as the core and is coated with organic sulfonic acid on the outer layer; during sand mixing, first heat the spherical recycled sand to 90 - 110 °C, add nano-zirconia and graphene nanosheets and stir; then add silane coupling agent KH-560 and continue stirring; finally, add phenolic epoxy resin, carbon nanotubes, and core-shell structured composite curing agent and stir to obtain gradient functional modified resin sand; S2: Prepare an intelligent temperature control sand box by laying a phase change energy storage material layer composed of paraffin / expanded graphite on the inner wall of the sand box; install an electromagnetic induction heating coil on the outer side of the sand box; S3: Molding and negative pressure curing, fill the gradient functional modified resin sand into the intelligent temperature control sand box, vibrate and compact it; cover it with a double-layer composite film; start the air extraction system, and at the same time turn on the electromagnetic induction heating to make the resin undergo a cross-linking curing reaction; S4: Composite inoculation treatment, heat gray iron or ductile iron molten iron to 1450 - 1550 °C, and use the wire feeding method to add a composite inoculant cored wire to the molten iron. The outer layer of the cored wire is made of low-carbon steel strip, and the core is composed of ferrosilicon alloy, nano-calcium carbonate, rare earth magnesium alloy, boron nitride nanotubes, and silicon carbide whiskers; S5: Vacuum differential pressure casting, pour the treated molten iron into a holding furnace; place the sand box in a vacuum chamber; adopt a bottom gating system, and make the molten iron fill the mold under the action of pressure difference through a differential pressure device; S6: Intelligent cooling control, after casting is completed, monitor the temperature of the casting in real time through a temperature sensor installed in the sand box. When the temperature drops to 700 - 800 °C, start the air cooling system in the sand box to cool the casting to 350 - 450 °C; then turn off the air cooling system and let the casting cool naturally to room temperature.

2. The vacuum precision resin sand mold casting process method applicable to gray iron or nodular iron according to claim 1, characterized in that, It also includes that the spherical recycled sand has a particle size of 0.2 - 0.5 mm, a roundness coefficient ≥ 0.9, a loss on ignition ≤ 0.3%, and is obtained through the combined treatment of high-temperature roasting and mechanical regeneration.

3. The V-process precision resin sand mold casting process method applicable to gray iron or ductile iron according to claim 1, characterized in that, It also includes that the phenolic epoxy resin has an epoxy value of 0.4 - 0.5 eq / 100 g and a softening point of 80 - 90 °C, and is prepared by reacting bisphenol A epoxy resin with linear phenolic resin under the action of a catalyst.

4. The V-process precision resin sand mold casting process method applicable to gray iron or ductile iron according to claim 1, characterized in that, It also includes that the nano-zirconia has a particle size of 30 - 80 nm, a crystal form that is a mixture of tetragonal and monoclinic phases with a mass ratio of 7:3, and a specific surface area of 60 - 100 m² / g.

5. The V-process precision resin sand mold casting process method applicable to gray iron or ductile iron according to claim 1, characterized in that, It also includes that the graphene nanosheets have a sheet thickness of 3 - 8 nm, a sheet diameter of 5 - 15 μm, a carbon content ≥ 98%, are prepared by the redox method and are surface hydroxylated with a hydroxyl content of 2 - 5%.

6. The V-process precision resin sand mold casting process method applicable to gray iron or nodular iron according to claim 1, characterized in that, It also includes that in step S3, a breathable heat insulation layer with a thickness of 0.5 - 1 mm composed of ceramic fiber and aerogel is laid between the double-layer composite film and the sand mold, with a porosity of 70 - 80% and a thermal conductivity ≤ 0.03 W / (m·K).

7. The vacuum precision resin sand mold casting process method applicable to gray iron or ductile iron according to claim 1, characterized in that, The preparation method of the composite inoculant cored wire in step S4 is: after mixing each component in proportion, press it into a core rod by powder metallurgy method, and then wrap it with a low-carbon steel strip and weld it by seam welding.

8. The V-process precision resin sand mold casting process method applicable to gray iron or ductile iron according to claim 1, characterized in that, In the S5 step, the ingates of the bottom gating system are arranged in a stepped manner, the spacing between each layer of ingates is 50 - 80 mm, and the cross-sectional area of the ingates decreases layer by layer from bottom to top by 10 - 15%.

9. The V-process precision resin sand mold casting process method applicable to gray iron or ductile iron according to claim 1, characterized in that, In the S6 step, the air ducts of the air cooling system are evenly distributed around the sand box, the distance between the air duct outlet and the casting surface is 80 - 120 mm, and temperature-adjustable electric heating wires are installed in the air ducts to adjust the cooling rate.

10. The V-process precision resin sand mold casting process method applicable to gray iron or ductile iron according to claim 1, characterized in that, It also includes that after the casting is cooled to room temperature, laser surface alloying treatment is carried out. A carbon dioxide laser is used, the laser power is 1.5 - 3 kW, the scanning speed is 5 - 10 mm / s, and an alloy layer with a thickness of 0.3 - 0.8 mm is cladded on the casting surface. The composition of the alloy layer by weight percentage is: Cr 15 - 20%, Ni 8 - 12%, Mo 3 - 5%, V 1 - 3%, and the balance is Fe.

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