Precise design of high-throughput heat transfer parameters and low-stress manufacturing method for frozen sand molds

Abstract

The present invention provides a method for accurately designing high-throughput heat transfer parameters and manufacturing low-stress frozen sand molds. The present invention takes multi-material complex structure frozen sand molds as the research object, divides the overall frozen sand mold into multiple different sub-molds, and determines the thermal physical parameter requirements of each sub-mold by analyzing the casting and solidification performance requirements of the casting. By utilizing the multi-parameter free matching of different molding sand types, water content and freezing temperature, different thermal physical parameters of each sub-mold are achieved, thereby improving the stability of the overall casting metal liquid solidification process, reducing the generation of defects such as shrinkage and shrinkage cavities during low-temperature pouring, and reducing the generation of internal stress in the casting process through the balanced solidification technology of complex castings. The invention has high engineering application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of sand casting, and in particular relates to a method for accurately designing high-throughput heat transfer parameters and manufacturing a frozen sand mold with low stress. Background Art

[0002] Sand mold freezing casting technology is a new green casting technology, in which frozen sand mold molding uses water as a binder instead of the resin binder in traditional sand casting. It is frozen with the molding sand material at low temperature and a casting with a certain strength is obtained through various methods such as mold turning, cutting and printing. The final formed casting is obtained by pouring under normal pressure or negative pressure. No polluting waste gas is generated during the pouring process. The small amount of water binder in the sand mold evaporates when heated, and the sand mold naturally collapses. At the same time, the molding sand can be directly recycled.

[0003] During the pouring process of frozen sand castings, due to the differences in the casting structure, the amount of molten metal poured in different parts is different. During the cooling process of the casting, the heat dissipation speed of each part is different, which can easily cause excessive stress in the casting and casting defects. Under the currently commonly used single sand mold and fixed thermophysical parameter system, it is difficult to meet the pouring quality requirements of complex structure castings. At present, some high-end equipment basic castings with high precision retention requirements need to break through the frozen sand mold high-throughput thermophysical parameter precise design and low stress manufacturing technology, and improve the heat and mass transfer conditions of the casting process from the aspects of material matching and structural design. Summary of the Invention

[0004] In response to the shortcomings of the above-mentioned existing technologies, a method for precise design of high-throughput heat transfer parameters and low-stress manufacturing of frozen sand molds is provided. This method can achieve precise mold design of multiple physical property parameters of complex structure castings, and solve the quality defects caused by different heat dissipation in different parts during casting.

[0005] The technical solution adopted by the present invention comprises the following steps:

[0006] The precise design of high-throughput heat transfer parameters and low-stress manufacturing method for frozen sand molds specifically include the following steps:

[0007] Step 1: Perform pouring performance simulation calculation based on the input complex casting model to obtain important parameters such as the temperature field and flow field distribution of each part, and obtain the cooling and heat dissipation diagram of each part of the complex casting.

[0008] Step 2: Determine the corresponding casting model based on the casting model. Use the calculated casting cooling and heat dissipation diagram to design the casting model in blocks. Each casting part is shaped separately. Select different molding sand types, freezing temperatures, and water contents as the basic variables for the comprehensive performance changes of the casting part. Among them, different molding sand types represent differences in heat transfer coefficients, different freezing temperatures represent differences in pouring supercooling, and different water contents represent differences in air permeability. The physical parameter performance design is performed according to the following equation:

[0009] P = αA + βB + γC;

[0010] Among them, P is the comprehensive performance of casting mold parting, A is the type of molding sand, B is the freezing temperature, C is the water content of the sand mold, and α, β and γ are the corresponding proportional coefficients.

[0011] Step 3: Sand mixing and molding are performed on different block design models of the casting to obtain the casting mold.

[0012] Step 4: Wrap the mold with thermal insulation film and assemble it to obtain a precisely designed mold with different physical parameters.

[0013] Preferably, the casting is a complex structure casting, and different parts have different cooling and heat dissipation during pouring.

[0014] Preferably, the number of mold blocks and the method of segmentation are determined according to the distribution of the casting simulation solidification temperature field, and the number of blocks is determined by the proportion of unsolidified parts in the initial solidification stage of the casting.

[0015] Preferably, the casting mold is a cantilevered structure, and the cantilevered structure is precisely designed according to the number of blocks.

[0016] Preferably, the types of molding sand include silica sand, chromite sand, zircon sand, olivine sand, magnesia sand, corundum sand, ilmenite sand and bauxite sand.

[0017] Preferably, the freezing temperature of the sand mold is between -196°C and -10°C.

[0018] Preferably, the water content of the sand mold is between 2 wt.% and 8 wt.%.

[0019] Preferably, the thermal insulation film material is thermal insulation material such as aerogel thermal insulation film, expanded graphite film and polyethylene honeycomb film.

[0020] Preferably, the physical parameter performance design includes selecting different combinations of molding sand types, water binder addition amounts and freezing temperatures for casting molds at different positions.

[0021] Preferably, the physical parameter performance design includes selecting different types of molding sand, water binder addition amounts and freezing temperatures for casting molds at different positions, and freely combining them to obtain a precise combination that promotes balanced solidification of various parts of the casting. The multi-parameter database is integrated to automatically match the model combination scheme according to the casting shape, material and modulus requirements to achieve a balanced solidification process of complex castings.

[0022] Preferably, the frozen sand mold is obtained by mold forming, CNC machining or 3D printing.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. The present invention realizes the precise design of thermophysical parameters such as heat transfer coefficient, air permeability and supercooling degree of different casting parts by combining different types of molding sand, amount of water binder added and freezing temperature of the casting mold, so that the casting can be cooled more evenly after pouring and the generation of internal stress can be reduced.

[0025] 2. The present invention determines the number of frozen sand mold blocks through pouring simulation, which can realize high-density casting mold parting modeling, assembly and high-throughput thermal physical property parameter design, making the temperature transition between different areas smoother.

[0026] 3. The present invention uses a heat-insulating film to block the temperature transfer in the contact area of ​​the mold parts during assembly, thereby achieving stability of the performance of each parting mold after mold assembly.

[0027] 4. The present invention greatly improves the pouring and cooling performance of traditional block molding through the precise design of the thermal physical property parameters of the frozen sand mold, and has practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a process flow chart of the present invention.

[0029] Figure 2 It is a schematic diagram of assembling the casting and the integral casting mold of the present invention.

[0030] Figure 3 It is a schematic diagram of the solidification temperature field distribution of the casting.

[0031] List of reference numerals:

[0032] Among them, 1-sand block one; 2-sand block two; 3-sand block three; 4-sand block four; 5-sand block five; 6-sand block six; 7-sand block seven; 8-sand block eight; 9-sand block nine; 10-casting; 11-solidified part; 12-unsolidified part. 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] like Figure 1-Figure 2 As shown, this embodiment provides a method for accurately designing high-throughput heat transfer parameters and manufacturing frozen sand molds with low stress, including the following specific steps:

[0035] Step 1: Simulate the aluminum alloy casting performance based on the impeller casting model to obtain the cooling and heat dissipation diagram of each part of the casting. Figure 3 As shown, it can be seen that during the cooling process, the unsolidified part 12 has a large amount of molten metal accumulation and a slow solidification speed, which is prone to excessive internal stress. Therefore, when forming a frozen sand mold, chromite sand with better heat dissipation performance is selected as the molding material for the sand mold close to the solidified part 12.

[0036] Step 2: Determine the corresponding casting model based on the casting model, and use the calculated casting cooling diagram to design the casting model in blocks. There are 9 sub-types in total, and each casting sub-type is shaped separately. Figure 2 It can be seen that the structural information of the mold after block division is selected. Different types of molding sand, freezing temperature and water content are selected as the basic variables for the comprehensive performance change of frozen sand mold. Among them, different types of molding sand represent the difference in heat transfer coefficient, different freezing temperature represents the difference in pouring supercooling, and different water content represents the difference in permeability. According to the calculation results of step 1 and Figure 2 Comprehensive analysis of the block design shows that sand block No. 5 is located in the center of the casting. Due to the presence of unsolidified areas, internal stress is generated between the solidified and unsolidified areas, which can easily cause solidification defects. Therefore, chromite sand with good heat dissipation performance is selected for sand block 5 to increase the cooling and solidification speed of the center of the casting. Silica sand is selected as the molding material for the other 8 sand blocks. The physical parameter performance design is carried out according to the following equations:

[0037] P = αA + βB + γC;

[0038] Among them, P is the comprehensive performance of molding sand, A is the type of molding sand, B is the freezing temperature, C is the water content of the sand mold, and α, β and γ are the corresponding proportional coefficients.

[0039] Step 3: Sand mixing and molding are performed on different block design models of the casting to obtain the casting mold.

[0040] Step 4: Wrap the 9 molds separately with aerogel insulation films, and assemble them to obtain molds with precisely designed physical parameters.

[0041] In this embodiment, the number of mold blocks and the method of segmentation are determined according to the distribution of the casting simulation solidification temperature field, and the number of blocks is determined by the proportion of unsolidified parts in the initial solidification stage of the casting.

[0042] In this embodiment, the casting mold is a cantilevered structure, and a precise cantilevered structure design is performed according to the number of blocks.

[0043] In this embodiment, the types of molding sand are silica sand and chromite sand.

[0044] In this embodiment, the freezing temperature of the chromite sand mold is -90°C to ensure the strength of the casting cavity and the pouring supercooling degree. The freezing temperature of the silica sand mold is -30°C. The water content of the chromite sand mold is 6wt.%, and the water content of the silica sand mold is 4wt.%.

[0045] In this embodiment, the thermal insulation film material is an aerogel thermal insulation film.

[0046] 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. Precise design of high-throughput heat transfer parameters and low-stress manufacturing method for frozen sand molds, characterized by: The following steps are involved: Step 1: Perform pouring performance simulation calculation based on the input casting model to obtain the cooling and heat dissipation diagram of each part of the casting; Step 2: Determine the corresponding casting model based on the casting model. Use the calculated casting cooling and heat dissipation diagram to design the casting model in blocks. Each casting part is shaped separately. Select different molding sand types, freezing temperatures, and water contents as the basic variables for the comprehensive performance changes of the casting part. Among them, different molding sand types represent differences in heat transfer coefficients, different freezing temperatures represent differences in supercooling during the pouring process, and different water contents represent differences in air permeability. The physical parameter performance design is performed according to the following equation: P = αA + βB + γC; Among them, P is the comprehensive performance of the casting mold, A is the type of molding sand, B is the freezing temperature, C is the water content of the sand mold, and α, β and γ are the corresponding proportional coefficients; Step 3: Sand mixing and shaping of different block design models of the casting to obtain the parting model of the casting; Step 4: Wrap the mold with insulation film and assemble it to obtain a precisely designed mold with different physical parameters; the insulation film material is aerogel insulation film, expanded graphite film or polyethylene honeycomb film insulation material to prevent heat conduction between the sand blocks.

2. The method for accurately designing high-throughput heat transfer parameters and manufacturing frozen sand molds with low stress according to claim 1, characterized in that: When the casting is a complex structure casting, the cooling and heat dissipation of different parts are very different during pouring. It is necessary to calculate the P value of each part of the casting according to the casting solidification to obtain a P value matrix of multiple model combinations.

3. The method for high-throughput heat transfer parameter precision design and low-stress manufacturing of frozen sand molds according to claim 1, characterized in that: The number of mold blocks and the subdivision method are determined according to the pouring simulation solidification temperature field and the distribution of hot spots. Where the temperature field and hot spots are higher, a material combination with better thermal physical parameters is used. The number of blocks is determined by the proportion of unsolidified parts in the initial solidification stage of the casting.

4. The method for accurately designing high-throughput heat transfer parameters and manufacturing frozen sand molds with low stress according to claim 1, characterized in that: The casting mold is a joint structure, and its joint structure includes a geometric structure or an interface fusion joint method. The geometric joint structure includes a truncated cone, a cylindrical or an irregular structure. The interface fusion joint structure includes a low-temperature freezing bonding and a resin glue bonding method. The precise joint structure design is performed according to the number of blocks.

5. The method for precise design of high-throughput heat transfer parameters and low-stress manufacturing of frozen sand molds according to claim 1, characterized in that: The types of molding sand include silica sand, chromite sand, zircon sand, olivine sand, magnesia sand, corundum sand, ilmenite sand and bauxite sand, and the precise sand material required by the model is obtained according to the multi-model design criteria.

6. The method for accurately designing high-throughput heat transfer parameters and manufacturing low-stress frozen sand molds according to claim 1, characterized in that: The freezing temperature of the sand mold is between -196°C and -10°C, and the precise temperature required by the model is obtained according to the multi-model design criteria.

7. The method for accurately designing high-throughput heat transfer parameters and manufacturing frozen sand molds with low stress according to claim 1, characterized in that: The water content of the sand mold is between 2wt.% and 8wt.%, and the precise water content required by the model is obtained according to the multi-model design principle.

8. The method for accurately designing high-throughput heat transfer parameters and manufacturing low-stress frozen sand molds according to claim 1, characterized in that: The casting mold is obtained by mold forming, CNC machining or 3D printing.

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