Design and manufacturing criteria and optimization modeling method of sand mold conformal cooling structure

Abstract

The present invention provides sand mold conformal cooling structure design and manufacturing criteria and optimization modeling methods. It uses droplet jet 3D printing technology to manufacture internal pipes that are consistent with the changes in the sand mold / core. It proposes a sand mold internal pipe design and manufacturing criterion and internal pipe optimization criterion, and optimizes the rationality of the pipe layout through mold flow analysis. It uses cooling / heating media to quickly regulate the temperature in the internal pipes, thereby effectively controlling the solidification sequence of the casting. The present invention proposes sand mold internal pipe design and optimization modeling criteria, which have strong control over the surface temperature of the casting, can achieve rapid and uniform cooling of complex special-shaped castings, thereby reducing structural defects inside the castings and achieving short-process casting of high-quality castings. The present invention is simple to operate and has a fast manufacturing process. It is suitable for the rapid production and quality control of castings with complex curved surfaces.

Description

Technical Field

[0001] The present invention relates to the field of internal piping design optimization in a sand mold design method, and in particular to a sand mold conformal cooling structure design and manufacturing criterion and an optimization modeling method. Background Art

[0002] Over 80% of products in the foundry industry are produced using sand casting, making it a widely used process. However, the traditional sand casting process currently suffers from slow cooling. This is particularly true during the cooling and solidification of large, special-shaped castings. This often leads to defects such as coarse grains, segregation, cracks, and shrinkage feeding difficulties caused by a disrupted solidification sequence, and the ability to precisely control complex castings is limited.

[0003] To meet the growing demand for high-precision, high-quality, and highly complex products in the automotive, shipbuilding, medical device, and intelligent manufacturing sectors, more and more products are being designed with complex, sophisticated, and unique shapes to meet the diverse needs of these fields. These castings have complex geometric surfaces, large variations in curvature, and uneven cooling, which often lead to deformation, warping, and cracking, seriously affecting casting production quality and efficiency.

[0004] To address these challenges, traditional sand casting typically uses materials and processes with strong heat storage capabilities, such as chilled iron, chromite sand, and metal molds, to enhance the cooling process by dissipating heat. However, this approach not only increases production costs and increases operational complexity, but also fails to fully meet the requirements for enhanced cooling using heat storage materials. In sand casting, the use of cooling devices to dissipate heat at specific locations within the mold is a common practice.

[0005] Traditional sand molds mostly use linear cooling channels, mainly because linear cooling channels are easy to form and can meet the cooling requirements of simple castings. Traditional cooling pipes are mostly processed into straight lines by drilling. The different distances from the water channel to the mold cavity make it difficult for the sand mold to obtain a uniform temperature distribution, which leads to inconsistent cooling and shrinkage in various parts of the casting, resulting in the existence of residual stress, warping, deformation or cracking of the product. There are also processes that use pre-buried cooling pipes in the mold as a heat exchange device to enhance the cooling of the casting, but this method lacks manufacturing flexibility and cannot quickly respond to complex and diverse product shape requirements. In essence, it uses mold recasting to cast sand molds, and it is also impossible to quickly produce small batches of highly variable castings through digitalization. Summary of the Invention

[0006] To solve the above problems, the present invention discloses the design and manufacturing criteria and optimization modeling method of the sand mold conformal cooling structure, which compensates for the problem of uneven temperature distribution of the casting in the sand mold and prevents deformation, warping, cracking and other problems caused by uneven cooling of the casting. It uses 3D printing technology to simplify the manufacturing process and make the design of the internal pipeline more conformal, effectively shortening the heat exchange cycle and improving the molding quality of the product.

[0007] In order to achieve the above invention purpose, the present invention adopts the following technical solutions:

[0008] Sand mold conformal cooling structure design and manufacturing criteria and optimization modeling method, the method includes the following steps:

[0009] Step 1: Determine the geometric features of the casting and divide the corresponding sand mold cavity and core areas according to 3D drawing software;

[0010] Step 2: Divide the cavity and core into sub-units based on the surfaces of the sand mold cavity and core, and design an internal pipe cooling system that matches each sub-unit according to the sand mold internal pipe design and manufacturing guidelines;

[0011] Step 3: Assemble the pipelines of each sub-region surface, and adjust the structure of the combined pipelines according to the internal pipeline optimization criteria to obtain the overall conformal internal pipeline layout of the sand mold;

[0012] Step 4: After simulation mold flow analysis, structural adjustments are made to ultimately achieve the optimal layout of the sand mold's internal piping design;

[0013] Step 5: Slice the designed conformal cooling structure in layers and import it into a digital sand mold 3D printer. Lay the molding sand as needed based on the cross-sectional information of each layer to form a sand mold with internal pipes.

[0014] Step 6: After printing, the entire sand mold is passed through the pipeline with cooling / heating gas medium to regulate the temperature distribution of the casting in the cavity, reduce casting defects, and facilitate sand falling.

[0015] Furthermore, the inner pipeline design criterion is through the formula To calculate the cooling gas flow rate and thus determine the pipe diameter, where V refers to the flow rate of the required cooling medium, c p is the specific heat capacity of the cooling medium, ρ is the density of the cooling medium, T out is the outlet temperature of the cooling medium, T in is the inlet temperature of the cooling medium; according to the above calculation V value, V≤5.0×10 -3 m 3 / min, the pipe diameter is set to be less than 5mm; V≤15.0×10 -3 m 3 / min, the pipe diameter is set to 8mm; V>15.0×10 -3 m 3 / min, the pipe diameter is set to 12-20mm.

[0016] Furthermore, the internal pipeline design criteria can be divided into various styles such as straight-through, circular, multi-stage, cross, spiral, and jet according to the different surface features of the sand mold and the core. These styles cooperate with each other to form the internal pipeline circuit of the sand mold.

[0017] Furthermore, the inner pipe design criteria are based on a method for generating a conformal cooling pipe topology structure with equidistant sections. By generating different water channel centerline topologies between adjacent sections, such as "serial single helix", "serial double helix", "parallel stepped" and other types, conformal cooling water channels in a specified area are generated. The diameter of the inner pipe, the distance between adjacent pipes, and the distance between the cooling pipe and the cavity wall surface are key factors in the design of the cooling system. The wall thickness of the inner pipe is 2mm to 4mm, and the geometric shape formed by the conformal cooling pipe layout is consistent with the geometric shape of the casting surface, and always uniformly covers the entire casting at a certain distance (5mm to 10mm).

[0018] Furthermore, the internal pipeline design criteria include a cold gap design method; the cold gap design method refers to leaving a gap of 0.5 to 2 mm in the design of the assembly dimensions between sand molds or between sand blocks that are assembled together at room temperature or in a cold state of a general sand mold, to compensate for the expansion generated when high-speed compressed gas passes through the internal pipeline and the thermal stress and thermal deformation caused by the sand mold casting process.

[0019] Furthermore, the pipes within the sand mold can be used for rapid cooling and heating. During cooling, low-temperature gaseous media such as low-temperature CO2, nitrogen, and compressed dry air can be passed through; during heating, hot water vapor can be passed through. The gaseous media pressure must be ≥0.6 MPa. There are two ways to set up the heating and cooling pipes: one is to set them up independently, with the heating medium passing through the heating pipe during heating and the cooling medium passing through the cooling pipe during cooling; the other is to share the heating and cooling pipes as a single set. The pipe inlet must be located above the outlet to prevent residual media from damaging the sand mold.

[0020] Furthermore, the internal pipeline optimization criteria include airflow pulsation optimization and internal pipeline structure vibration optimization standards. The airflow pulsation optimization refers to suppressing the pulsation of the gas medium by adding an orifice plate at the pipeline connection. The orifice plate is the place where the pipeline diameter changes. Generally, to suppress airflow pulsation, the aperture ratio of the orifice plate is It is set in the range of 0.4 to 0.6, where D1 is the diameter of the upstream pipeline of the orifice plate along the airflow direction, and D2 is the diameter of the downstream pipeline of the orifice plate; the internal pipeline structure vibration optimization standard is that the pressure drop in the pipeline must be less than 0.25% of the absolute average pressure of the pipeline.

[0021] Furthermore, the simulation mold flow analysis indicators include pouring fluidity, heat transfer effect, and sand mold deformation. On simulation platforms such as Moldflow and Procast, if the casting volume shrinkage is ≤2%, the melt flow front temperature difference is ≤15°C, the inlet and outlet coolant temperature difference is greater than 20°C, the cast iron surface temperature difference is less than 200°C, the cast aluminum surface temperature difference is less than 100°C, the sand mold tensile strength is greater than 1MPa, the casting cooling time is reduced by more than 30%, and the total deformation is reduced by more than 50%, the internal piping design is considered to meet the requirements.

[0022] Beneficial effects of the present invention:

[0023] 1. The present invention incorporates internal sand mold piping that adapts to the contours of the casting. Compared to traditional sand mold cooling methods, this conformal internal piping is more than just a straight line; its distance from the mold cavity surface is consistent, resulting in uniform temperature distribution in the sand mold cavity. Furthermore, the present invention's internal sand mold piping can be used for rapid cooling and heating, flexibly adapting to different sand molds and casting conditions. This invention achieves efficient and uniform cooling of castings, eliminating defects such as warping and deformation, while also shortening the casting cycle, improving production efficiency, and enhancing enterprise competitiveness, demonstrating its strong applicability.

[0024] 2. This invention uses 3D printing technology to manufacture sand molds with internal pipes. Traditional machining often fails to produce complex conformal cooling channels. 3D printing is insensitive to the geometric characteristics of the manufactured parts, making it an ideal choice for manufacturing complex structures such as lattice structures and conformal cooling pipes. It not only simplifies the design and manufacturing process, but also makes the cooling pipe design more conformable. Furthermore, after printing, no heat treatment is required; the part is directly connected to a gas medium for temperature control, resulting in a simple process and high overall manufacturing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the sand mold cross-type internal pipeline design of the present invention.

[0026] Figure 2 It is the sand mold jetting inner pipeline design of the present invention.

[0027] Figure 3 This is the "U"-shaped cooling / heating pipeline layout of the present invention.

[0028] Figure 4 This is a diagram of the conformal inner piping used in the present invention.

[0029] Figure 5This is a comparison diagram of the series and parallel structures of the present invention. The left picture is the series structure and the right picture is the parallel structure.

[0030] Figure 6 This is a schematic diagram of embodiment 1 of the present invention.

[0031] Figure 7 This is a schematic diagram of embodiment 2 of the present invention.

[0032] Figure numerals: 1, sand mold; 2, runner; 3, gate; 4, serial liquid inlet; 5, serial liquid outlet; 6, compartment casting; 7, serial conformal internal pipeline; 8, parallel liquid inlet; 9, parallel conformal internal pipeline; 10, outlet switch casting; 11, parallel liquid outlet. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, and the terms "inward" and "outward" refer to directions toward or away from the geometric center of a particular component, respectively.

[0034] Example 1:

[0035] Traditional sand molds generally use pre-buried chillers or machined cooling pipes to control temperature. Due to the limitations of the processing method, they can only be limited to simple cooling control at individual hot spots and hot nodes. The internal pipe design method proposed in this invention is as follows Figures 1 to 3 For sand molds with thinner walls and smaller sizes, a Figure 1 Cross-type internal pipe shown; for sand molds corresponding to slender castings, use Figure 2 The jet-type inner pipe design shown in the figure, the gas medium flows from the inner pipe to the end, then sprays out like a jet, and flows back to the inner pipe from the outer pipe. It is the most effective cooling method for slender sand molds / sand cores. In order to make the sand mold temperature cycle between high and low temperatures quickly, the common heating and cooling inner pipe layout is as follows Figure 3 The U-shaped cooling / heating piping layout shown is arranged along the sand mold's surface. The piping is shared by both steam and cooling gas. During heating, water vapor is introduced to heat the sand mold cavity, while during cooling, vaporized dry ice, liquid nitrogen, or other media is introduced to cool the sand mold. When cooling after heating or heating after cooling, compressed air is used to blow out the steam or condensed water in the piping to avoid affecting cooling or heating efficiency.

[0036] Traditional cooling lines are complex to design and manufacture because they are constrained by various factors (such as accommodating ejector pins and screws), and the use of numerous water plugs and rubber rings, as well as machining and assembly errors, can easily lead to coolant leaks. Furthermore, the varying distances between the horizontal and vertical cooling lines and the sand mold cavity can easily lead to uneven cooling and warping of the casting. In conformal cooling, the conformal cooling lines are evenly attached to the mold cavity, providing greater control over the surface temperature and enabling rapid and uniform cooling of complex castings.

[0037] The specific steps include:

[0038] Step 1: Determine the geometric characteristics of the casting. In this example, the casting to be cast is a cabin of a certain type, made of aluminum alloy. Design a corresponding sand mold 1 based on the geometric dimensions of the three-dimensional model of the cabin 6. The sand mold 1 includes a gate 3, a runner 2, and a cavity for the cabin 6.

[0039] Step 2: Based on the characteristics of each surface of the compartment casting, the spiral design method, as specified in the sand mold internal piping design guidelines, was employed. The internal piping design for this sand mold consists of two parts: external and internal cavity piping. The external cavity piping consists of circular pipes of equal diameter, with the spacing between the pipes increasing from the bottom to the top of the casting. This design ensures a more uniform flow of cooling medium through each external pipe, resulting in better cooling and significantly alleviating the "air pockets" and "weld marks" observed during filling analysis. The internal cavity piping is a single, spiraling, conformal pipe. The diameter of the circular pipe decreases layer by layer as the spiral rises. The large-diameter circular pipe in the bottom ring cools the convex edge of the casting, where the highest temperature is concentrated during the pouring process. Therefore, the water inlet of the pipe is also located on the side of the internal cavity pipe. Due to the convex cylindrical fastening structure inside the cavity, the upper layer of piping is cooled using smaller-diameter pipes that decrease in diameter layer by layer. The calculated V value is >15.0×10 -3 m 3 / min, the inner pipe diameter is set to 15mm. The inner pipe wall thickness is 2mm, and it always uniformly covers the entire cabin casting at a certain distance of 6mm.

[0040] Step 3: Combine the cavity external pipeline and the cavity internal pipeline to form a series single spiral conformal cooling internal pipeline. The geometric shape formed by the layout of the series conformal internal pipeline 7 is consistent with the geometric shape of the casting surface, such as Figure 4As shown in the left figure, there is one outlet 5 and one inlet 4, no branching pipes, and the coolant velocity is balanced throughout the entire circuit, resulting in effective cooling and relatively even heat dissipation. The mold is assembled, integrated, and modified within the cavity, with overlapping pipes removed. A 1mm gap is left in the assembly dimensions to compensate for the expansion caused by high-speed compressed gas flowing through the internal pipes and the thermal stress and deformation caused by the sand casting process. If the sand mold is parted, orifice plates are installed between the sand blocks or between the sand molds to balance the pulsating impact of the airflow, ensuring optimal working conditions for the internal pipe system.

[0041] Step 4: Conducting mold flow simulation analysis using the Moldflow simulation platform, we first optimized the potentially excessive length of the series conformal internal pipe 7 circuit, reduced the coolant pressure drop, and controlled the coolant temperature rise in the second half of internal pipe 7. The inlet and outlet coolant temperature difference was controlled to >30°C, the casting surface temperature difference to <100°C, and the sand mold tensile strength to >1 MPa. Using Procast software, since the casting material is aluminum alloy, the casting surface temperature difference was controlled to <80°C, the casting volume shrinkage was ≤2%, and the melt flow front temperature difference was ≤15°C. This reduced the casting cooling time by over 30%, and the total deformation by over 50%.

[0042] Step 5: The 3D-printed sand mold with the conformal cooling structure designed is sliced ​​and layered, and the sliced ​​results are imported into the digital sand 3D printer. The molding sand and internal piping areas are identified and marked in each layer of sand slice. The digital sand 3D printer lays the molding sand as needed based on the cross-sectional information of each layer. The molding sand is made of silica sand, pre-mixed with 0.2% resin curing agent, and the adhesive used in the molding sand is phenolic resin. The printed sand mold includes the internal piping.

[0043] Step 6: After printing, the entire sand mold 1 does not need heat treatment. By passing cooling / heating gas medium through the pipeline, the temperature distribution of the casting in the mold cavity can be controlled, thereby reducing casting defects and facilitating sand removal.

[0044] Example 2:

[0045] The specific steps include:

[0046] Step 1: Determine the geometric characteristics of the casting. The casting to be cast in this embodiment is a certain type of water outlet switch made of gray cast iron. Design a corresponding sand mold model based on the geometric dimensions of the three-dimensional model of the water outlet switch casting 10;

[0047] Step 2: Since the water outlet switch casting includes complex surface features and a large curvature variation, the inner pipe center line is generated by the automatic generation algorithm of the CAD software in the second embodiment. The topological connection structure of the inner pipe center line is a parallel topology, and a parallel conformal inner pipe 9 is generated, as shown in FIG. Figure 7 As shown. 5.0×10 -3 m 3 / min<V≤15.0×10 -3 m 3 / min, the inner pipe diameter is set to 6mm or 8mm, the pipe wall thickness is 4mm, the parallel stepped inner pipe 9 layout forms a geometric shape consistent with the geometric shape of the casting surface, and always uniformly covers the entire outlet switch casting 10 at a certain distance of 5mm.

[0048] Step 3: The geometry of the parallel conformal cooling inner pipe 7 layout is consistent with the geometry of the casting surface, such as Figure 5 As shown in the figure on the right, the entire circuit of this structure has a parallel outlet 11 and a parallel inlet 9, with multiple branches. The circuit is relatively short and the coolant pressure drop is relatively small, which can ensure sufficient coolant flow rate and a smaller coolant temperature difference than the series topology structure.

[0049] Step 4: Optimize the structural parameters of the parallel conformal internal pipe 9 in the sand mold using the dynamic structure-thermal coupling module of the finite element analysis platform. Optimize the inconsistent flow velocities of the various branches of the parallel conformal internal pipe 9, maintain consistent mold cavity temperature, minimize warping of the outlet switch casting 10, maintain the inlet and outlet coolant temperature difference >40°C, the casting surface temperature difference <150°C, and maintain the sand mold tensile strength >1.2MPa.

[0050] Step 5: Slice the 3D-printed sand mold with the conformal cooling structure and import the sliced ​​results into the digital sand 3D printer. The digital sand 3D printer lays the sand as needed based on the cross-sectional information of each layer. The sand is made of chromite sand, pre-mixed with 0.24% resin curing agent, and the adhesive used is phenolic resin. The inkjet printhead sprays the phenolic resin adhesive as needed based on the cross-sectional information of the current layer of the sand mold, forming the sand mold and the parallel internal pipeline 9.

[0051] Step 6: After printing, the entire sand mold does not need to be heat treated. The metal pipeline is directly connected to low-temperature compressed dry air with a temperature of less than -10°C, so that the temperature of the outlet switch casting 10 in the mold cavity is evenly distributed, reducing casting defects.

[0052] The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above-mentioned embodiment, but also include technical solutions composed of any combination of the above technical features.

Claims

1. Design and manufacturing criteria and optimization modeling method of sand mold conformal cooling structure, characterized by: The method comprises the following steps: Step 1: Determine the geometric features of the casting and divide the corresponding sand mold cavity and core areas according to 3D drawing software; Step 2: Divide the cavity and core into sub-units based on the surfaces of the sand mold cavity and core, and design an internal pipe cooling system that matches each sub-unit according to the sand mold internal pipe design and manufacturing guidelines; Step 3: Assemble the pipelines of each sub-region surface, and adjust the structure of the combined pipelines according to the internal pipeline optimization criteria to obtain the overall conformal internal pipeline layout of the sand mold; The optimization criteria for the internal pipeline include airflow pulsation optimization and internal pipeline structure vibration optimization standards; the airflow pulsation optimization refers to suppressing the pulsation of the gas medium by adding an orifice plate at the pipeline connection. The orifice plate is the place where the pipeline diameter changes. In order to suppress the airflow pulsation, the aperture ratio of the orifice plate is Set in the range of 0.4 to 0.6, D1 is the diameter of the upstream pipeline of the orifice plate in the airflow direction, and D2 is the diameter of the downstream pipeline of the orifice plate; the internal pipeline structure vibration optimization standard is that the pressure drop in the pipeline must be less than 0.25% of the absolute average pressure of the pipeline; Step 4: After simulation mold flow analysis, structural adjustments are made to ultimately achieve the optimal layout of the sand mold's internal piping design; Step 5: Slice the designed conformal cooling structure in layers and import it into a digital sand mold 3D printer. Lay the molding sand as needed based on the cross-sectional information of each layer to form a sand mold with internal pipes. Step 6: After printing, the entire sand mold is passed through the pipeline with cooling / heating gas medium to regulate the temperature distribution of the casting in the cavity, reduce casting defects, and facilitate sand falling.

2. The sand mold conformal cooling structure design and manufacturing criteria and optimization modeling method according to claim 1 is characterized in that: The internal piping design and manufacturing criteria are as follows: To calculate the cooling gas flow rate and determine the pipe diameter, V Refers to the flow rate of the required cooling medium, c p is the specific heat capacity of the cooling medium, is the density of the cooling medium, is the outlet temperature of the cooling medium, is the inlet temperature of the cooling medium; according to the calculated V value, V ≤5.0×10 -3 m 3 / min, the pipe diameter is set to less than 5mm; V ≤15.0×10 -3 m 3 / min, the pipe diameter is set to 8mm; V >15.0×10 - 3 m 3 / min, the pipe diameter is set to 12~20mm.

3. The sand mold conformal cooling structure design and manufacturing criteria and optimization modeling method according to claim 1 is characterized in that: The internal pipeline design and manufacturing guidelines are divided into multiple styles such as straight-through, circular, multi-stage, cross, spiral, and jet according to the different surface features of the sand mold and core. These styles cooperate with each other to form the internal pipeline circuit of the sand mold.

4. The sand mold conformal cooling structure design and manufacturing criteria and optimization modeling method according to claim 1 is characterized in that: The internal pipeline design and manufacturing criteria are based on a conformal cooling water channel topology generation method with equidistant sections, by generating different water channel centerline topologies between adjacent sections.

5. The sand mold conformal cooling structure design and manufacturing criteria and optimization modeling method according to claim 4 is characterized in that: Generate multiple types of conformal cooling channels in a specified area, including serial single helix, serial double helix, or parallel stepped types. The diameter of the inner pipe, the distance between adjacent pipes, and the distance between the cooling pipe and the cavity wall surface are key factors in cooling system design. The inner pipe wall thickness is 2mm to 4mm. The geometry formed by the conformal cooling pipe layout is consistent with the geometry of the casting surface and always uniformly covers the entire casting at a certain distance of 5mm to 10mm.

6. The sand mold conformal cooling structure design and manufacturing criteria and optimization modeling method according to claim 1 is characterized in that: The internal pipeline design and manufacturing guidelines include a cold gap design method; the cold gap design method refers to leaving a gap of 0.5 to 2 mm in the design of the assembly dimensions between sand molds or between sand blocks that are assembled in a general sand mold at room temperature or a frozen sand mold in a cold state, to compensate for the expansion generated when high-speed compressed gas passes through the internal pipeline and the thermal stress and thermal deformation caused by the sand mold casting process.

7. The sand mold conformal cooling structure design and manufacturing criteria and optimization modeling method according to claim 1 is characterized in that: The pipeline inside the sand mold can be used for rapid cooling and heating; the pressure of the gas medium needs to be ≥0.6MPa; there are two ways to set up the heating and cooling pipelines. One is to set them independently, that is, heating medium is introduced into the heating pipeline during heating and cooling medium is introduced into the cooling pipeline during cooling; the other is to share the heating and cooling pipelines as the same group of pipelines; the pipeline inlet must be set above the outlet to prevent medium residue from damaging the sand mold.

8. The sand mold conformal cooling structure design and manufacturing criteria and optimization modeling method according to claim 7 is characterized in that: During cooling, low-temperature gas medium is passed, such as low-temperature CO2, nitrogen and compressed dry air; during heating, hot water vapor can be passed.

9. The sand mold conformal cooling structure design and manufacturing criteria and optimization modeling method according to claim 1 is characterized in that: The simulation mold flow analysis indicators include pouring fluidity, heat transfer effect and sand mold deformation; in the Moldflow and Procast simulation platforms, the volume shrinkage of the casting is ≤2%, the temperature difference of the melt flow front is ≤15°C, the temperature difference of the inlet and outlet coolant is >20°C, the surface temperature difference of cast iron is <200°C, the temperature difference of cast aluminum is <100°C, the tensile strength of the sand mold is >1MPa, the cooling time of the casting is reduced by more than 30%, and the total deformation is reduced by more than 50%. If the above indicators are met, it is considered that the internal piping design meets the requirements.

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