Freezing sand mold high-flux heat transfer parameter accurate design and low-stress manufacturing method

Abstract

The invention provides a freezing sand mold high-flux heat transfer parameter accurate design and low-stress manufacturing method, which takes a multi-material complex structure freezing sand mold as a research object, divides the whole freezing sand mold into a plurality of different parting blocks, and determines the thermophysical property parameter requirements of each parting block by analyzing the pouring solidification performance requirements of a casting, so as to obtain the high-flux heat transfer parameter accurate design and low-stress manufacturing method of the freezing sand mold. Different thermophysical parameters of each parting are realized by utilizing a multi-parameter free ratio of different molding sand types, water content and freezing temperature, the stability of an integral casting metal liquid solidification process is improved, the defects of shrinkage porosity, shrinkage cavity and the like in a low-temperature pouring process are reduced, the internal stress in the casting process is reduced through a balanced solidification technology of a complex casting, and the casting quality is improved. And the method has very high engineering application value.

Description

Technical Field

[0001] The 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 low-stress frozen sand molds. Background Art

[0002] Sand mold freezing casting technology is a new type of 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 pouring amount of molten metal in different parts is different, and the heat dissipation speed of each part is different during the cooling process of the casting, which can easily cause excessive internal 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, for some high-end equipment basic castings with high precision retention requirements, it is necessary 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 view of the deficiencies of the above-mentioned prior art, a method for precise design of high-throughput heat transfer parameters and low-stress manufacturing of frozen sand molds is provided. This method can realize precise mold design of multiple physical property parameters of complex structure castings and solve the quality defect problem 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 of frozen sand molds specifically include the following steps:

[0007] Step 1: Perform a simulation calculation of the pouring performance based on the input complex casting model, 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: According to the casting model, the corresponding casting model is inversely obtained, and the casting model is designed in blocks using the calculated casting cooling and heat dissipation diagram. Each casting part is modeled separately, and different types of molding sand, freezing temperature and water content are selected as the basic variables for the comprehensive performance change of the casting part. Among them, different types of molding sand represent the difference in heat transfer coefficient, different freezing temperatures represent the difference in pouring supercooling, and different water contents represent the difference in permeability. The physical parameter performance design is carried out according to the following equation:

[0009] P = αA + βB + γC;

[0010] Among them, P is the comprehensive performance of 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.

[0011] Step 3: Mix sand and shape 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 casting of a complex structure, and cooling and heat dissipation in different parts are different during pouring.

[0014] Preferably, the number of mold blocks and the segmentation method 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 fitting structure, and a precise fitting structure design is performed 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 2wt.% and 8wt.%.

[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 mold partings 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 for free combination, obtaining a precise combination that promotes balanced solidification of various parts of the casting, integrating a multi-parameter database, and automatically matching a 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 thermal physical parameters such as heat transfer coefficient, air permeability and supercooling degree of different casting parts by combining different types of molding sand, water binder addition amount and freezing temperature of 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, can realize high-density casting mold parting modeling, assembly and high-throughput thermal physical property parameter design, and make the temperature transition of 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 the stability of each mold parting performance after mold assembly.

[0027] 4. The present invention greatly improves the pouring and cooling performance of traditional block molding by accurately designing 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 is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the accompanying drawings, and the words "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0034] like Figure 1-Figure 2 As shown, this embodiment provides a method for accurately designing high-throughput heat transfer parameters of frozen sand molds and manufacturing low-stress molds, including the following specific steps:

[0035] Step 1: According to the impeller casting model, simulate and calculate the aluminum alloy casting performance 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 and a slow solidification speed, which is prone to excessive internal stress. Therefore, when the frozen sand mold is formed, the sand mold close to the solidified part 12 selects chromite sand with better heat dissipation performance as the molding material.

[0036] Step 2: Determine the corresponding casting model based on the casting model, and use the calculated casting cooling and heat dissipation diagram to design the casting model in blocks. There are 9 sub-types in total, and each casting sub-type is modeled 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 According to the comprehensive analysis of the block design, sand block No. 5 is located in the center of the casting. Due to the existence of unsolidified parts, internal stress is generated between the solidified area and the unsolidified area, which is very likely to 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, and 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: Mix sand and shape 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 segmentation method 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 fitting structure, and a precise fitting 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 scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical schemes 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 in that: The following steps are involved: Step 1: Perform a simulation calculation of the pouring performance based on the input casting model to obtain the cooling and heat dissipation diagram of each part of the casting; Step 2: According to the casting model, the corresponding casting model is inversely calculated, and the casting model is divided into blocks for design using the calculated casting cooling and heat dissipation diagram. Each casting part is individually shaped, and different types of molding sand, freezing temperature and water content are selected as the basic variables for the comprehensive performance change of the casting part. Among them, different types of molding sand represent the difference in heat transfer coefficient, different freezing temperatures represent the difference in supercooling during the pouring process, and different water contents represent the difference 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: Mix sand and shape different block design models of the casting to obtain a parting model of the casting; Step 4: Wrap the mold with thermal insulation film and assemble it to obtain a precisely designed mold with different physical parameters.

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 the P value matrix of the multi-model combination.

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 segmentation method are determined according to the pouring simulation solidification temperature field and the distribution of thermal nodes. A material combination with better thermal physical parameters is used in places with higher temperature fields and thermal nodes. The number of blocks is determined by the proportion of unsolidified parts in the initial solidification stage of the casting.

4. 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 casting mold is a fitting structure, and its fitting structure includes a geometric structure or an interface fusion fitting method. The geometric fitting structure includes a truncated cone, a cylindrical or a special-shaped structure. The interface fusion fitting structure includes a low-temperature freezing bonding and a resin glue bonding method. The precise fitting structure design is performed according to the number of blocks.

5. 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 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 high-throughput heat transfer parameter precision design and low-stress manufacturing of 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 high-throughput heat transfer parameter precision design and low-stress manufacturing of frozen sand molds 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 criteria.

8. 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 thermal insulation film material is an aerogel thermal insulation film, an expanded graphite film or a polyethylene honeycomb film thermal insulation material, which prevents heat conduction between the sand blocks.

9. 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 frozen sand mold is obtained by mold turning, CNC machining or 3D printing.

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