Preparation method of casting mold with narrow inner cavity structure for aluminum alloy investment precision casting

Abstract

The invention relates to the technical field of aluminum alloy investment precision casting, and discloses a preparation method of an aluminum alloy investment precision casting mold with a narrow inner cavity structure, and the preparation method comprises the steps of model reserved core head structure design, model manufacturing, model inner cavity casting, module manufacturing, shell manufacturing, dewaxing, roasting, pouring, cleaning and checking. Through the design of the reserved core head structure of the model and the design of the casting slurry components, on one hand, the mold position size precision of the narrow inner cavity structure of the casting is guaranteed; on the other hand, in the pre-filling process of the inner cavity of the model, powder such as alpha gypsum powder, chromite sand, wood fibers and glass fibers and solvents such as distilled water and silica sol are mixed in proportion, so that good replicability, heat conductivity, air permeability, flowability and strength of the filling material are ensured, drainage filling is performed after vacuumizing, bubbles are reduced, and the service life of the filling material is prolonged. And the integrity of the casting mold is improved. And through a traditional investment precision casting process, high-quality and high-efficiency production of the aluminum alloy casting with the narrow and small inner cavity is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy investment casting, and in particular relates to a method for preparing a casting mold with a narrow inner cavity structure for aluminum alloy investment casting. Background Art

[0002] With the intensification of market competition, the rapid development of metal 3D printing technology in the manufacture of miniaturized and complex parts, and the continuous improvement and cost reduction of die forging machining technology, traditional aluminum alloy structural parts are facing unprecedented challenges in the field of precision casting. In particular, for aluminum alloy castings with small inner cavity and pipeline size and complex structure, such as micro pump housing, precision sensor housing, etc., these micro components with high precision requirements are gradually becoming the focus of technology upgrading and business expansion in the field of aluminum alloy casting.

[0003] The traditional manufacturing processes for this type of aluminum alloy castings with narrow inner cavities and pipe structures are the following three categories: 3D printing sand mold core casting, investment gypsum mold precision casting, and water-soluble salt core wax pressure precision casting. The problems with using 3D printed sand mold core assembly to cast this type of casting are: the inner cavity and pipe surface of the casting are rough, and there is a risk of local sand sticking. When the whole machine is in working condition, sand particles are easily brought into the airway and oil circuit due to vibration, which reduces the working service time of the whole machine; the problems with using investment wax gypsum mold precision casting this type of casting are: the gypsum mold has poor thermal conductivity and is easy to absorb moisture. The inner cavity and pipe of the casting are prone to looseness and dense holes, and the qualified rate of non-destructive testing is low. Bubbles are prone to appear in the gypsum mold during the manufacturing process, resulting in aluminum beans in the inner cavity and pipe of the casting, which are difficult to remove, reducing the casting yield; the problems with using water-soluble salt core wax pressing precision casting this type of casting are: the water-soluble salt core is easy to absorb moisture, resulting in reactive porosity defects in the inner cavity and pipe of the casting, reducing the working service time of the whole machine. On the other hand, the production cycle of the water-soluble salt core is long, and there is a risk of core breakage during the wax pressing process. X-ray inspection is required for each piece, which extends the production cycle. When the castings produced by the above manufacturing process are subjected to fluorescent penetrant inspection, the quality of the casting inner cavity and the pipeline surface is difficult to meet the relevant standard requirements.

[0004] In recent years, with the deepening of the concept of high quality, high efficiency and low cost, such traditional manufacturing processes have been difficult to meet the market's comprehensive requirements for such products in terms of high quality requirements, production and manufacturing cycle, or cost reduction and efficiency improvement. When using the traditional silica sol ceramic shell precision casting process to produce such products, for aluminum alloy precision castings with relatively complex narrow cavities and pipes, unlike stainless steel and high-temperature alloy precision castings, alkali explosion or chemical methods are not used to clean the ceramic materials in the inner cavity and pipes; on the other hand, due to the low hardness of aluminum alloy materials, physical methods are used to clean the inner cavity and pipe refractory materials, which can easily cause deformation and damage to the product. Therefore, there is an urgent need to develop a casting preparation method for aluminum alloy investment casting with a narrow inner cavity structure to meet the current market's comprehensive requirements for such products in many aspects. Summary of the invention

[0005] The object of the present invention is to overcome the above-mentioned problems and provide a method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure, so as to improve the overall surface roughness, dimensional accuracy, overall surface quality and overall shell cleaning difficulty of aluminum alloy castings with narrow inner cavities and pipelines, shorten the production cycle and reduce production costs.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: The present invention provides a method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure, comprising the following steps: S1, design the casting structure and reserve the core head part; S2, making models according to the casting structure; S3, pre-filling the inner cavity and pipeline of the model: weighing powder and solvent in proportion, fully mixing the powder and solvent, evacuating the vacuum tank, and then draining and filling the inner cavity and pipeline of the model; the powder includes α-gypsum powder, chromite sand, wood fiber and glass fiber; the solvent includes distilled water, silica sol and n-octanol; S4, after the casting is completed, it is allowed to dry by itself, and then the subsequent model tree assembly and module shell making work are carried out. After the shell making is completed, dewaxing and baking are carried out.

[0007] A further improvement of the present invention is that it also includes pouring, cleaning and inspecting the mold shell. The specific method is: using a modified high-pressure water gun and sandblasting machine to clean the mold shell and the refractory material residues attached to the casting and the inner cavity pipeline, and then using an endoscope to inspect the inner cavity and pipeline of the casting, and performing fluorescent penetration inspection and low-magnification inspection.

[0008] A further improvement of the present invention is that in step S2, the model is made by wax pressing or 3D printing.

[0009] A further improvement of the present invention is that in step S3, the component ratios of the powder and the solvent are: chromite ore is 2.5% of the weight of the α-gypsum powder, wood fiber is 0.75% of the weight of the α-gypsum powder, glass fiber is 0.5% of the weight of the α-gypsum powder, distilled water is 35% of the total weight of the powder, silica sol is 6% of the weight of the distilled water, and n-octanol is 0.1% of the weight of the distilled water.

[0010] A further improvement of the present invention is that the particle size of the chromite ore sand is 120 meshes.

[0011] A further improvement of the present invention is that in step S3, the stirring time of the powder and the solvent is 1 to 3 minutes, the vacuum degree of the vacuum tank is 10 to 20 KPa, and the vacuuming time is 1 to 3 minutes.

[0012] A further improvement of the present invention is that in the step S3, reinforcements are pre-embedded before pre-casting the inner cavity and the pipeline of the model, and the reinforcements are φ2~φ4 stainless steel wires.

[0013] A further improvement of the present invention is that in step S4, the module is placed in a resistance furnace at room temperature, the temperature is increased at a rate of 100-150°C / h, the temperature is kept at 230-250°C for 2-3h, the module wax is removed, the temperature is increased to 750±10°C, the temperature is kept for 2-3h, and the temperature is decreased with the furnace.

[0014] A further improvement of the present invention is that the method is suitable for preparing aluminum alloy castings with a minimum inner cavity and pipeline size X less than 3.5 mm.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing a casting mold for aluminum alloy investment casting with a narrow inner cavity structure. By designing the core head part structure reserved in the casting model and designing the casting slurry components, on the one hand, the mold position dimensional accuracy of the complex and narrow inner cavity structure of the casting is guaranteed; on the other hand, in the process of pre-casting the inner cavity and pipeline of the model, α-gypsum powder, chromite sand, wood fiber, glass fiber and other powders, as well as solvents such as distilled water and silica sol are mixed in proportion to ensure good reproducibility, thermal conductivity, air permeability, fluidity and strength of the casting material. After vacuuming in a vacuum tank, the material is drained and poured, which effectively reduces the generation of bubbles and improves the integrity of the casting mold. After that, the traditional investment casting process is used to achieve high-quality and high-efficiency production of aluminum alloy castings with a narrow inner cavity structure. The preparation method of the present invention simplifies the production process, reduces the production cycle, and improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings described herein are only for explanation purposes and are not intended to limit the scope of the present invention in any way. In addition, the shapes and proportional dimensions of the various components in the drawings are only schematic, used to help understand the present invention, and are not intended to specifically limit the shapes and proportional dimensions of the various components of the present invention.

[0017] Figure 1 It is a schematic diagram of the process of the preparation method of the present invention; Figure 2 It is a structural schematic diagram of the core head process of the casting of the present invention; Figure 3 This is a schematic diagram of the structure of the aluminum alloy turbine casting according to Example 1 of the present invention.

[0018] Among them: 1. Casting; 2. Core; 3. Core head; 4. Turbine; 5. Inner cavity. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0022] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0023] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0024] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings: like Figure 1 As shown, the present invention provides a method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure, comprising the following steps: Step S1, structural design of the casting and reserve the core head process part, such as Figure 2 As shown, the structure of the core head process part is not limited to this, as long as it can play a positioning and limiting role; Step S2, making a model according to the casting structure, wherein a wax pressing model or a 3D printing rapid prototyping model is used; Step S3, pre-filling the inner cavity and pipeline of the model: weighing powder and solvent in proportion, fully stirring and mixing the powder and solvent, and then evacuating the mixture in a vacuum tank with a vacuum degree of 10-20 KPa for 1-3 minutes to obtain a uniformly mixed pre-filled material, and then using a drainage rod to drain the uniformly mixed pre-filled material into the inner cavity and pipeline of the model; the powder includes α-gypsum powder, chromite sand, wood fiber and glass fiber; the solvent includes distilled water, silica sol and n-octanol; The component ratios of powder and solvent are as follows: chromite ore accounts for 2.5% of the weight of α-gypsum powder, wood fiber accounts for 0.75% of the weight of α-gypsum powder, glass fiber accounts for 0.5% of the weight of α-gypsum powder, distilled water accounts for 35% of the total weight of powder, silica sol accounts for 6% of the weight of distilled water, and n-octanol accounts for 0.1% of the weight of distilled water.

[0026] As a preferred embodiment, the particle size of the chromite ore is 120 mesh.

[0027] It should be noted that before the inner cavity and pipeline of the model are pre-cast, reinforcements need to be pre-embedded, and the reinforcements are φ2~φ4 stainless steel wires.

[0028] Step S4, after the casting is completed, the self-drying time is greater than 1 hour, and then the subsequent model assembly and module shell making work are carried out. After the shell making is completed, the module is loaded into the resistance furnace at room temperature, and the temperature is increased at a rate of 100-150℃ / h. After being kept at 230-250℃ for 2-3 hours, the module wax material is removed, and the temperature is increased to 750±10℃ and kept for 2-3 hours, and then the temperature is reduced with the furnace.

[0029] Step S5, pouring, cleaning and inspecting the shell; Specifically, modified high-pressure water guns and sandblasting machines are used to clean the mold shell and inner pipe refractory material residues attached to the casting, and then an endoscope is used to inspect the inner cavity and pipes of the casting, and fluorescent penetration inspection and low-magnification inspection are carried out.

[0030] It should be noted that the high-pressure water gun and sandblasting machine used in the present invention are improved, and the specific improvements are as follows: By matching the screw thread specifications of the existing hydraulic shell cleaning machine high-pressure water gun nozzle interface and the sandblasting machine nozzle interface, the nozzles of the two post-cleaning equipment are modified; a stainless steel external thread conversion joint that matches the screw thread of the high-pressure water gun nozzle interface and stainless steel pipes of different diameters with a wall thickness greater than 1 mm are selected, and a stainless steel pipe of suitable specifications is selected according to the inner cavity and pipeline structure of the corresponding product and adaptively bent and modified, and it is fastened to the stainless steel external thread conversion joint by welding, and screwed into the hydraulic shell cleaning machine high-pressure water gun nozzle interface to realize the cleaning of the refractory materials of the casting inner cavity and pipeline; considering that the bent sandblasting nozzle rubs against the sand particles at high speed during work and is a vulnerable part, an adaptively bent nozzle data model is designed according to the inner cavity and pipeline structure of the corresponding product, and the outer thread conversion joint part is reserved at the tail for mechanical processing, and the K4169 high-temperature alloy waste is used for casting by the method of 3D printing rapid prototyping mold + investment casting, and then the outer thread of the conversion joint is completed by mechanical processing, and it is screwed to the sandblasting machine nozzle interface to realize the deep cleaning of the casting inner cavity and pipeline.

[0031] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0032] Example 1 This example is to prepare a certain type of aluminum alloy turbine casting, whose outline dimensions are: 308×258×169mm, the narrowest dimension of the turbine cavity is 2.7mm, and the structure is shown in FIG. Figure 3 As shown, it is difficult to achieve the technical indicators such as surface roughness, dimensional accuracy, and metallurgical quality using traditional casting processes. The preparation steps are as follows: Step 1: In the casting structure design stage, reserve the core head process part; Step 2: Model making, using 3D printing to quickly prototype the model; Step 3: Pre-filling the inner cavity and pipeline of the model, first weigh 750g of α-gypsum powder, 18.8g of chromite sand, 5.6g of wood fiber and 3.8g of glass fiber, and stir them thoroughly. Then weigh 263g of solvent distilled water, 15.8g of silica sol and 0.25g of n-octanol. Pour the fully mixed powder into the solvent and stir it thoroughly for 1min. Then, evacuate the vacuum tank with a vacuum degree of 15Kpa for 1min, and then use a drainage rod to drain and pour into the inner cavity and pipeline of the model. The inner cavity and pipeline of the model are pre-buried with annealed φ3 stainless steel wire. Step 4: After the casting is completed and the casting is allowed to dry for 2 hours, the model assembly, coating and shell making work are carried out according to the process requirements; Step 5: Place the module into a resistance furnace at room temperature, heat it up at a rate of 120±10℃ / h, keep it at 240±10℃ for 2h, remove the module wax, heat it up to 750±10℃ and keep it for 2h, cool it down with the furnace and set it aside; Step 6: Cast the shell according to the process requirements; Step 7: Use a high-pressure water gun with a modified nozzle to clean the mold shell and the inner cavity pipeline gypsum refractory material residue attached to the casting, and use a sandblasting machine with a modified nozzle to perform surface treatment on the casting after cutting; Step 8: Use an endoscope to inspect the inner cavity and pipeline of the casting to check whether there are defects such as pores and slag inclusions on the surface of the casting, which meets the requirements of HB963 Class II; Step 9: Use fluorescent penetrant inspection to check if there are defects such as pores, looseness, slag inclusions, etc. on the casting surface, which meets the requirements of HB963 Class II; Step 10: Low-power inspection: After heat treatment, the casting is dissected and inspected to see if there are defects such as pores and slag pores in the cross section, which meets the requirements of HB963 Class II.

[0033] This batch of castings has undergone surface inspection, fluorescent inspection and low-power inspection. The surface quality and fluorescent inspection of the castings meet the HB963 Class II casting standards. After heat treatment and low-power inspection, the pinhole degree is better than level 1, which meets the HB963 Class II casting standards.

[0034] Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the preceding claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended to be a disclaimer of such subject matter, nor should it be considered that the applicants did not consider such subject matter to be part of the disclosed inventive subject matter.

[0035] The above content is a further detailed description of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, they can also make several simple deductions or substitutions, which should be regarded as belonging to the protection scope of the present invention determined by the submitted claims.

Claims

1. A method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure, characterized in that: The following steps are involved: S1, design the casting structure and reserve the core head part; S2, making models according to the casting structure; S3, pre-filling the inner cavity and pipeline of the model: weighing powder and solvent in proportion, fully mixing the powder and solvent, evacuating the vacuum tank, and then draining and filling the inner cavity and pipeline of the model; the powder includes α-gypsum powder, chromite sand, wood fiber and glass fiber; the solvent includes distilled water, silica sol and n-octanol; S4, after the pouring is completed, it is allowed to dry by itself, and then the subsequent model tree assembly and module shell making work are carried out. After the shell making is completed, dewaxing and baking are carried out.

2. The method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure according to claim 1, characterized in that: It also includes pouring, cleaning and inspection of the mold shell. The specific method is: use a modified high-pressure water gun and sandblasting machine to clean the mold shell and inner cavity pipeline refractory material residues attached to the casting, and then use an endoscope to inspect the inner cavity and pipeline of the casting, and perform fluorescent penetration inspection and low-magnification inspection.

3. The method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure according to claim 1, characterized in that: In step S2, the model is made by wax molding or 3D printing.

4. The method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure according to claim 1, characterized in that: In step S3, the component ratios of the powder and the solvent are: chromite ore accounts for 2.5% of the weight of the α-gypsum powder, wood fiber accounts for 0.75% of the weight of the α-gypsum powder, glass fiber accounts for 0.5% of the weight of the α-gypsum powder, distilled water accounts for 35% of the total weight of the powder, silica sol accounts for 6% of the weight of the distilled water, and n-octanol accounts for 0.1% of the weight of the distilled water.

5. The method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure according to claim 4, characterized in that: The particle size of the chromite ore is 120 meshes.

6. The method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure according to claim 1, characterized in that: In step S3, the stirring time of the powder and the solvent is 1-3 min, the vacuum degree of the vacuum tank is 10-20 KPa, and the vacuuming time is 1-3 min.

7. The method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure according to claim 1, characterized in that: In the step S3, reinforcements are embedded before the inner cavity and pipeline of the model are pre-cast, and the reinforcements are φ2~φ4 stainless steel wires.

8. The method for preparing a mold for aluminum alloy investment casting with a narrow inner cavity structure according to claim 1, characterized in that: In step S4, the module is placed in a resistance furnace at room temperature, heated at a rate of 100-150°C / h, kept at 230-250°C for 2-3h, and after removing the module wax, the temperature is raised to 750±10°C and kept for 2-3h, and then cooled with the furnace.

9. The method for preparing an aluminum alloy investment casting mold with a narrow inner cavity structure according to any one of claims 1 to 8, characterized in that: The method is suitable for preparing aluminum alloy castings with a minimum inner cavity and pipeline size X less than 3.5 mm.

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