Design and manufacturing integrated forming method for face and back sand composite frozen sand mold

Abstract

The invention provides a face and back sand composite frozen sand mold designing and manufacturing integrated forming method, which comprises the following steps of: designing and processing three-dimensional models of an upper mold and a lower mold according to the size of a casting, manufacturing a frozen sand mold according to the size of the casting, putting large-mesh molding sand mixed with resin and a curing agent and the frozen sand mold into the mold, and molding the large-mesh molding sand and the frozen sand mold; and full filling is conducted through shaking and extruding, and standing is conducted till fixed forming is achieved. And after forming, opening the upper model, removing waste sand, taking out a sand mold, putting the sand mold into a box, filling the periphery with small-mesh molding sand for fixing, and then carrying out metal solution anti-gravity casting forming. According to the method, a complex high-quality casting can be manufactured, a cavity mold is manufactured by combining freezing mold manufacturing and a resin sand mold, sand mold manufacturing with fixed filling of a surface sand mold and back sand molding sand with a certain thickness is achieved, and green, high-performance and high-precision development of sand mold manufacturing is promoted.

Description

Technical Field

[0001] The invention belongs to the field of frozen sand mold forming, relates to the field of sand mold green casting, and particularly to an integrated forming method for designing and manufacturing a face-back sand composite frozen sand mold. Background Art

[0002] Frozen sand technology is an advanced casting process that has developed significantly in recent years. This technology freezes the sand mold to an extremely low temperature, thereby improving the hardness and stability of the sand mold and significantly reducing the deformation and defects of the casting. Its main advantages include: improving the dimensional accuracy and surface quality of the casting, reducing the scrap rate generated during the casting process, improving the working environment, and reducing the labor intensity of workers. In addition, frozen sand technology is particularly outstanding in casting complex shapes and thin-walled parts, and is widely used in fields with high precision requirements such as automobiles, aerospace and machinery manufacturing.

[0003] In sand casting, face sand and back sand each play an important role. Face sand is the sand layer that directly contacts the molten metal. Its main function is to provide a smooth casting surface, high temperature resistance and good metal corrosion resistance, thereby improving the surface quality of the casting. Back sand is filled outside the face sand to provide structural support and shape retention, mainly playing the role of reducing costs and improving the overall strength and stability of the sand mold. The combination of face sand and back sand can not only ensure the surface quality of the casting, but also effectively control production costs, reduce material waste, and improve production efficiency. In the process of sand mold 3D printing, the application of face sand and back sand faces some unique difficulties. Face sand needs to have high fire resistance and excellent metal corrosion resistance, while also ensuring high precision of the printing layer to ensure the surface quality of the casting, which puts high demands on material selection and printing technology. Back sand needs to provide sufficient structural support during the printing process to prevent deformation of the sand mold, while also taking into account cost control and selecting suitable and cost-effective materials. Therefore, the coordination of face sand and back sand in 3D printing is crucial, which is necessary to ensure the surface quality of the casting and maintain the stability and economy of the overall sand mold, which requires continuous optimization and innovation in material science, printing technology and cost control. At the same time, the "Hollow Printing Method for Composite Manufacturing of Frozen Sand Mold and Resin Sand Mold" with patent application number "CN202210210944.6" cannot achieve high-flexibility sand mold manufacturing of face sand and back sand. Therefore, the manufacturing of complex and high-quality sand molds still needs further research. Summary of the invention

[0004] In order to solve the above problems, the present invention discloses an integrated forming method for designing and manufacturing a composite frozen sand mold with face and back sand, and the specific steps are as follows: Step 1: Design the upper and lower mold 3D models according to certain requirements based on the casting 3D model, and process the upper and lower molds; Step 2: Make a cavity mold of the same size according to the three-dimensional model of the casting; Step 3: Put the molding sand mixed with a certain proportion of resin and curing agent into the lower mold according to a certain volume, put in the frozen sand mold, fill the lower mold with the molding sand, cover the upper mold and add the molding sand, fill it completely by shaking and squeezing, and let it stand until the molding sand is fixed; Step 4: Open the upper model, remove the scattered waste sand, and take out the formed sand mold; Step 5: Place the formed sand mold into a box, fill it with sand all around, and perform counter-gravity casting.

[0005] Furthermore, the design principle of the upper and lower molds is to put the frozen sand mold into the mold and then fill the mold with a certain thickness of molding sand. The specific thickness needs to be determined based on the strength analysis of the resin sand mold. The smaller the thickness within the allowable range, the better. Furthermore, the thickness of the sand mold in different areas can be set according to the casting requirements to adjust the cooling rate of the metal solution in the mold cavity to achieve gradient forming or joint forming. Furthermore, the upper and lower molds can be made of paraffin, plastic, or rubber, which are easy to demold and do not react with the resin and curing agent in the molding sand. The integrally formed cavity mold needs to collapse after heating and be reusable without pollution. Therefore, it can be formed by freezing and cutting of water-containing molding sand, metal powder, or freeze printing, or it can be formed by wax mold; Furthermore, the molding sand used in the molding sand has a mesh number of 200 mesh or more as the surface sand, and the contents of the resin and the curing agent are 2.2wt.‰ and 2.5wt.‰; Furthermore, the mesh size of the filling sand is 50-100 mesh, which acts as backing sand and support; Furthermore, when designing the upper and lower models, the thickness can be determined according to the force distribution in different areas. The thickness is thicker in the direction below the gravity, and the minimum layer thickness is not less than 1 cm. Furthermore, after the upper and lower models are molded together, hot air is continuously introduced into the runner, and negative pressure is extracted at the riser to perform rapid forming and reduce the moisture contained in the resin sand mold; Furthermore, after the formed sand mold is taken out, it is first heated and cured to remove the moisture or wax in the resin sand mold, thereby further improving the strength of the resin sand mold; Furthermore, the riser and the runner of the frozen sand mold are in direct contact with the upper and lower molds, and corresponding grooves and bosses are provided in the upper and lower molds and the frozen sand mold to accurately fix the model; Furthermore, if there are concave or convex areas around the casting, filling the molding sand from bottom to top will result in some areas of the molding sand not being filled. Based on the concave or convex areas in this direction, multiple channels can be set up to fill the upper side with different directions as the gravity direction, so as to further improve the integrity of the resin sand mold; Furthermore, during the molding sand filling process, different areas can be filled with molding sand of different materials to further improve the controllability of casting performance; the molding sand can be filled with multiple materials, chromite sand can be added to one area to improve heat dissipation performance, and another area can be filled with molding sand with large particle size to improve air permeability.

[0006] Furthermore, the molding sand filling needs to be carried out in a low temperature environment, and the frozen sand mold needs to ensure a certain strength so as not to be destroyed and not to collapse when the temperature rises; Furthermore, if mass production is carried out, specific molds can be used, such as wooden molds, metal molds, etc., but the resin sand mold needs to be formed separately in two upper and lower models; Furthermore, the backing sand is filled in the same way as the forming sand to ensure that the resin sand mold is completely fixed; Furthermore, during the manufacturing process of the cavity mold, the moisture content of the frozen sand mold is 3-5%, and the mesh size of the molding sand is above 200 meshes.

[0007] After adopting the above technical solution, the beneficial effects of the present invention are: 1. This method can produce frozen sand molds of complex parts by cryo-cutting or cryo-printing, which is green and environmentally friendly and can recycle waste sand; 2. This method realizes the requirements for the surface sand and back sand of the sand mold during the sand casting process, and can produce complex and high-quality castings; 3. This method combines frozen sand mold making and resin sand mold manufacturing to manufacture cavity molds, thereby realizing the manufacturing of face sand molds with a certain thickness and the filling of back sand molds with fixed sand, which is suitable for casting high-performance and high-precision castings, and promotes the development of sand mold manufacturing towards green, high-performance and high-precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a process flow chart of the integrated forming method of designing and manufacturing the composite frozen sand mold with face and back sand; Figure 2 It is a schematic diagram of the lower mold in the integrated forming method of designing and manufacturing the composite frozen sand mold with face and back sand; Figure 3 It is a schematic diagram of the upper mold in the integrated forming method of designing and manufacturing the composite frozen sand mold with face and back sand; Figure 4 It is a schematic diagram of the mold after the mold is closed in the integrated forming method of designing and manufacturing the composite frozen sand mold with face and back sand; Figure 5It is a schematic diagram of the face sand and back sand in the integrated forming method of the face sand and back sand composite frozen sand mold design and manufacturing;

[0009] Figure 6 The present invention is a schematic diagram of filling the concave or convex area with molding sand in the integrated forming method of designing and manufacturing the surface-covered sand composite frozen sand mold. DETAILED DESCRIPTION

[0010] 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.

[0011] like Figure 1-6 As shown in the figure, it is difficult to achieve accurate control of the thickness and area of ​​the face sand in some current face and back sand forming sand molds. Figure 1 For a wheel hub casting, the casting surface accuracy Ra5.0~8.5μm is required, and green and environmentally friendly production is required as much as possible. Therefore, the upper and lower mold 3D models are designed according to certain requirements based on the casting 3D model, and the upper and lower plastic molds are processed, among which; the same size 200 mesh molding sand and cavity frozen sand mold with a water content of 3.5% are manufactured according to the casting 3D model. The thickness of the casting in the vertical direction is 10mm, so the thickness of the sand in the filling area is 5mm; put the 200-mesh molding sand mixed with 2.2wt.‰ resin and 2.5wt.‰ curing agent into the lower model, put in the frozen sand mold, fill the lower model with the molding sand, cover the upper model and add the molding sand, fill it completely by shaking and squeezing, and let it stand for 24 hours in a zero-degree environment until the molding sand is fixed; open the upper model, remove the scattered waste sand, take out the formed sand mold, put the sand mold into a 500-degree oven for further heating to remove excess moisture; put the formed sand mold into a box, fill it with 50-100 mesh molding sand all around, and perform anti-gravity casting. After forming, the surface accuracy of the casting reaches Ra6.0mm, and there is less pollution.

[0012] 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. An integrated forming method for designing and manufacturing a composite frozen sand mold with face and back sand, characterized in that: The specific steps are as follows: Step 1: Design the upper and lower mold 3D models according to the requirements based on the casting 3D model, and process the upper and lower molds; Step 2: Make a cavity mold of the same size according to the three-dimensional model of the casting; Step 3: Put the molding sand mixed with resin and curing agent into the lower model, then put in the frozen sand mold, fill the lower model with the molding sand, cover the upper model, add molding sand between the frozen sand mold and the mold, fill it completely by shaking and squeezing, and let it stand until the molding sand is fixed and formed; Step 4: Open the upper model, remove the scattered waste sand, and take out the formed sand mold; Step 5: Place the formed sand mold into a box, fill it with sand all around, and perform counter-gravity casting.

2. The method for designing and manufacturing an integrated forming method for a composite frozen sand mold with face and back sand according to claim 1, characterized in that: The design principle of the upper and lower molds is to put the frozen sand mold in and then fill the molding sand in the mold. The specific thickness needs to be determined based on the strength analysis of the resin sand mold. The smaller the thickness is within the allowable range, the better. Furthermore, the thickness of the sand mold in different areas can be set according to the casting requirements to adjust the cooling rate of the metal solution in the mold cavity to achieve gradient forming or common forming.

3. The method for designing and manufacturing an integrated forming method for a composite frozen sand mold with face and back sand according to claim 1, characterized in that: The upper and lower molds are made of paraffin, plastic or rubber; the integrally formed cavity mold is formed by freezing water-containing molding sand or metal powder and then cutting or freezing printing, or by wax molding.

4. The method for designing and manufacturing an integrated forming method for a composite frozen sand mold with face and back sand according to claim 1, characterized in that: The molding sand used in the forming molding sand has a mesh number of 200 or more as the surface sand, and the contents of resin and curing agent are 2.2wt.‰ and 2.5wt.‰; the mesh number of the filling molding sand is 50~100 mesh, which acts as back sand and support; during the manufacturing process of the cavity mold, the moisture content of the frozen sand mold is 3wt.%~5wt.%, and the mesh number of the molding sand is above 200 mesh.

5. The method for designing and manufacturing an integrated forming method for a composite frozen sand mold with face and back sand according to claim 1, characterized in that: When designing the upper and lower models, the thickness can be determined based on the force distribution in different areas. The thickness is thicker below the gravity direction, and the minimum layer thickness is not less than 1 cm.

6. The method for designing and manufacturing an integrated forming method for a composite frozen sand mold with face and back sand according to claim 1, characterized in that: After the upper and lower models are closed, hot air is continuously introduced into the gate, and negative pressure is extracted at the riser; After the formed sand mold is taken out, it is first heated and cured to remove moisture or wax in the resin sand mold.

7. The method for designing and manufacturing an integrated forming method for a composite frozen sand mold with face and back sand according to claim 1, characterized in that: The riser and runner of the frozen sand mold are in direct contact with the upper and lower molds. At the same time, corresponding grooves and bosses are set in the upper and lower molds and the frozen sand mold to accurately fix the model.

8. The method for designing and manufacturing an integrated forming method for a composite frozen sand mold with face and back sand according to claim 1, characterized in that: If there are recessed or convex areas around the casting, filling the molding sand from bottom to top will result in some areas not being filled with molding sand. Based on the recessed or convex areas in this direction, multiple channels are set up, and different directions are used as the gravity direction for filling upward; the back sand is filled in the same way as the molding sand to ensure that the resin sand mold is completely fixed.

9. The method for integrated design and manufacturing of face-back sand composite frozen sand molds according to claim 1, characterized in that: When mass production is carried out, a mold is used to make a resin sand mold. When the resin sand mold is used, the upper and lower models need to be formed separately.

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