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

Abstract

This invention relates to the field of aluminum alloy investment casting technology, and discloses a method for preparing a mold for aluminum alloy investment casting with a narrow internal cavity structure. The method includes designing a pre-reserved core structure for the mold, mold making, filling the mold cavity, mold assembly, shell fabrication, dewaxing, firing, pouring, cleaning, and inspection. This invention, through the design of the pre-reserved core structure and the design of the slurry composition, ensures the dimensional accuracy of the narrow internal cavity structure of the casting. Furthermore, during the pre-filling process of the mold cavity, α-gypsum powder, chromite sand, wood fiber, and glass fiber are mixed in proportion with solvents such as distilled water and silica sol, ensuring good reproducibility, thermal conductivity, permeability, fluidity, and strength of the slurry material. Vacuuming followed by drainage reduces bubble formation and improves the integrity of the mold. This method achieves high-quality and high-efficiency production of aluminum alloy castings with narrow internal cavities compared to traditional investment casting processes.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy investment casting technology, specifically relating to a method for preparing a mold for aluminum alloy investment casting with a narrow internal cavity structure. Background Technology

[0002] With intensifying market competition, the rapid development of metal 3D printing technology in the manufacturing of miniaturized and complex parts, and the continuous progress and cost reduction of die forging machining technology, traditional aluminum alloy structural parts are facing unprecedented challenges in the field of precision casting. This is especially true for aluminum alloy castings with small internal cavities and complex structures, such as micro-pump housings and precision sensor housings. These micro-components with high precision requirements are gradually becoming the focus of technological upgrades and business expansion in the aluminum alloy casting field.

[0003] The traditional manufacturing processes for this type of aluminum alloy casting with narrow internal cavities and pipe structures fall into three categories: 3D printing sand mold core casting, investment casting with plaster mold, and water-soluble salt core wax casting. The problems with using 3D printed sand mold core casting for this type of casting are: the surface of the inner cavity and pipes of the casting is rough, and there is a risk of local sand adhesion. During the operation of the whole machine, vibration can easily bring sand particles into the air passage and oil passage, reducing the service life of the whole machine. The problems with using investment casting with plaster mold precision casting are: plaster mold has poor thermal conductivity and is prone to moisture absorption. The inner cavity and pipes of the casting are prone to defects such as porosity and dense pores, resulting in a low pass rate of non-destructive testing. Air bubbles are prone to appear in the plaster mold during the manufacturing process, causing aluminum beads to form in the inner cavity and pipes of the casting, which are difficult to remove and reduce the yield of castings. The problems with using water-soluble salt core wax pressing precision casting for this type of casting are: water-soluble salt core is prone to moisture absorption, causing reactive porosity defects in the inner cavity and pipes of the casting, reducing the service life of the whole machine. On the other hand, the production cycle of 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 castings produced using the above manufacturing processes are subjected to fluorescent penetrant testing, the surface quality of the casting's internal cavity and pipes is difficult to meet the relevant standard requirements.

[0004] In recent years, with the deepening of the concepts of high quality, high efficiency, and low cost, traditional manufacturing processes have become increasingly inadequate to meet the diverse and comprehensive market demands for these products, whether in terms of high quality requirements, production cycles, or cost reduction and efficiency improvement. Furthermore, when using traditional silica sol ceramic mold precision casting processes to manufacture such products, unlike stainless steel or high-temperature alloy precision castings, it is difficult to clean the ceramic material from the internal cavities and channels of aluminum alloy precision castings with complex and narrow cavities and channels using alkaline explosion or chemical methods. On the other hand, due to the relatively low hardness of aluminum alloy, physical methods for cleaning the refractory materials in the internal cavities and channels can easily lead to product deformation and damage. Therefore, there is an urgent need to develop a method for preparing molds for aluminum alloy investment casting with narrow internal cavity structures to meet the current comprehensive market requirements for these products. Summary of the Invention

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

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for preparing a mold for aluminum alloy investment casting with a narrow internal cavity structure, comprising the following steps:

[0008] S1, Design the casting structure and reserve the core head portion;

[0009] S2, Model making based on the casting structure;

[0010] S3, Pre-filling of the model's inner cavity and pipes: Weigh the powder and solvent according to the proportion, mix the powder and solvent thoroughly, evacuate in a vacuum tank, and then pour the mixture into the inner cavity and pipes 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;

[0011] S4, after the casting is completed, it is allowed to dry on its own, and then the subsequent model tree assembly and module shell making work are carried out. After the shell making is completed, it is dewaxed and fired.

[0012] A further improvement of the present invention is that it also includes casting, cleaning and inspection of the mold shell. The specific method is as follows: the modified high-pressure water gun and sandblasting machine are used to clean the mold shell and refractory material residues attached to the casting and the inner cavity pipes. Then, an endoscope is used to inspect the inner cavity and pipes of the casting and to perform fluorescence penetration inspection and low magnification inspection.

[0013] A further improvement of the present invention is that, in step S2, the model is made using a wax model or 3D printing.

[0014] A further improvement of the present invention is that, in step S3, the component ratio of the powder and the solvent is as follows: chromite sand is 2.5% of the weight of α-gypsum powder, wood fiber is 0.75% of the weight of α-gypsum powder, glass fiber is 0.5% of the weight of α-gypsum powder, distilled water is 35% of the total weight of the powder, silica sol is 6% of the weight of distilled water, and n-octanol is 0.1% of the weight of distilled water.

[0015] A further improvement of the present invention is that the particle size of the chromite sand is 120 mesh.

[0016] A further improvement of the present invention is that, in step S3, the stirring time of the powder and solvent is 1-3 minutes, the vacuum degree of the vacuum tank is 10-20 kPa, and the vacuuming time is 1-3 minutes.

[0017] A further improvement of the present invention is that, in step S3, ribs are pre-embedded before the pre-filling of the model cavity and pipes, and the ribs are φ2~φ4 stainless steel wires.

[0018] A further improvement of the present invention is that, in step S4, the module is placed in a resistance furnace at room temperature, heated at a rate of 100~150℃ / h, held at 230~250℃ for 2~3h to remove the wax material from the module, and then heated to 750±10℃ and held for 2~3h before being cooled down in the furnace.

[0019] A further improvement of this invention is that the method is applicable to the preparation of aluminum alloy castings with a minimum internal cavity and pipe dimension X < 3.5 mm.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention provides a method for preparing a mold for investment casting of aluminum alloys with a narrow internal cavity structure. By designing the core head structure of the casting mold and the composition of the slurry, the method ensures the dimensional accuracy of the complex and narrow internal cavity structure of the casting. Furthermore, during the pre-pouring process of the mold's internal cavity and channels, powders such as α-gypsum powder, chromite sand, wood fiber, and glass fiber are mixed in proportion with solvents such as distilled water and silica sol. This ensures good reproducibility, thermal conductivity, permeability, flowability, and strength of the slurry material. After vacuuming in a vacuum chamber, the slurry is poured in, effectively reducing air bubble formation and improving the integrity of the mold. Following the traditional investment casting process, high-quality and high-efficiency production of aluminum alloy castings with narrow internal cavities is achieved. This invention simplifies the production process, reduces the production cycle, and improves production efficiency. Attached Figure Description

[0022] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components of the invention.

[0023] Figure 1 This is a schematic flowchart of the preparation method of the present invention;

[0024] Figure 2 This is a schematic diagram of the core head casting process of the present invention;

[0025] Figure 3 This is a schematic diagram of the aluminum alloy turbine casting structure in Embodiment 1 of the present invention.

[0026] The components are: 1. casting; 2. core; 3. core head; 4. turbine; 5. inner cavity. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0028] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0029] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0030] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0031] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0032] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0033] The present invention will now be described in further detail with reference to the accompanying drawings:

[0034] like Figure 1 As shown, the present invention provides a method for preparing a mold for aluminum alloy investment casting with a narrow internal cavity structure, comprising the following steps:

[0035] Step S1: Design the structure of the casting and reserve space for the core head process, such as... Figure 2 As shown, the structure of the chip head process is not limited to this; any structure that can play a positioning and limiting role is acceptable.

[0036] Step S2: Based on the casting structure, a model is made, using either a wax model or a 3D printed rapid prototyping model.

[0037] Step S3, Pre-filling of the model's inner cavity and pipes: Weigh the powder and solvent according to the ratio, mix the powder and solvent thoroughly, and then evacuate the mixture in a vacuum chamber with a vacuum degree of 10~20Kpa for 1~3 minutes to obtain a uniformly mixed pre-filling material. Then, use a guide rod to guide the uniformly mixed pre-filling material into the inner cavity and pipes 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.

[0038] The composition ratio of the powder and solvent is as follows: chromite sand is 2.5% of the weight of α-gypsum powder, wood fiber is 0.75% of the weight of α-gypsum powder, glass fiber is 0.5% of the weight of α-gypsum powder, distilled water is 35% of the total weight of the powder, silica sol is 6% of the weight of distilled water, and n-octanol is 0.1% of the weight of distilled water.

[0039] As a preferred option, the particle size of the chromite sand is 120 mesh.

[0040] It should be noted that before pre-filling the inner cavity and pipes of the model, it is necessary to pre-embed reinforcing ribs, which are φ2~φ4 stainless steel wires.

[0041] Step S4: After the pouring is completed, allow the module to air dry for more than 1 hour. Then proceed with the subsequent model tree assembly and module shell making. After the shell is made, put the module into the resistance furnace at room temperature and heat it at a rate of 100~150℃ / h. Hold it at 230~250℃ for 2~3 hours to remove the wax material from the module. Then heat it to 750±10℃ and hold it for 2~3 hours before cooling it down with the furnace.

[0042] Step S5: Pour, clean, and inspect the shell.

[0043] Specifically, the modified high-pressure water gun and sandblasting machine are used to clean the refractory material residue on the mold shell and inner cavity pipes of the casting. Then, an endoscope is used to inspect the inner cavity and pipes of the casting, and fluorescent penetrant testing and low-magnification inspection are carried out.

[0044] It should be noted that the high-pressure water gun and sandblasting machine used in this invention are both improved versions, specifically as follows:

[0045] By matching the screw-on thread specifications of the high-pressure water gun nozzle interface of the existing hydraulic shell cleaning machine and the nozzle interface of the sandblasting machine, the nozzles of the two post-cleaning equipment are modified. A stainless steel external thread adapter matching the screw-on thread of the high-pressure water gun nozzle interface and stainless steel pipes of different diameters with a wall thickness greater than 1mm are selected. Based on the internal cavity and pipe structure of the corresponding product, suitable stainless steel pipes are selected and adaptively bent and modified. These are then welded to the stainless steel external thread adapter and screwed into the high-pressure water gun nozzle interface of the hydraulic shell cleaning machine to clean the refractory materials of the casting's internal cavity and pipes. Considering that the bent sandblasting nozzle is prone to wear due to high-speed friction with sand particles during operation, an adaptively bent nozzle data model is designed based on the internal cavity and pipe structure of the corresponding product. An external thread adapter portion is reserved at the tail for machining. The K4169 high-temperature alloy scrap is used for casting using a 3D printing rapid prototyping mold + investment casting method. Subsequently, the external thread of the adapter is realized through machining and screwed into the sandblasting machine nozzle interface to achieve deep cleaning of the casting's internal cavity and pipes.

[0046] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0047] Example 1

[0048] This embodiment describes the fabrication of a certain type of aluminum alloy turbine casting with outline dimensions of 308×258×169mm and a minimum turbine cavity width of 2.7mm. The structure is shown below. Figure 3 As shown, it is difficult to achieve the required technical indicators such as surface roughness, dimensional accuracy, and metallurgical quality using traditional casting processes. The preparation steps are as follows:

[0049] Step 1: During the casting structure design stage, reserve space for the core head process;

[0050] Step 2: Model making, using 3D printing for rapid prototyping;

[0051] Step 3: Pre-filling of the model cavity and pipes. First, weigh 750g of α-gypsum powder, 18.8g of chromite sand, 5.6g of wood fiber and 3.8g of glass fiber and mix them thoroughly. Then weigh 263g of distilled water, 15.8g of silica sol and 0.25g of n-octanol. Pour the thoroughly mixed powder into the solvent and stir for 1 minute. Then, evacuate the vacuum in a vacuum chamber with a vacuum degree of 15Kpa for 1 minute. Then, use a flow guide to pour the mixture into the model cavity and pipes. Embed annealed φ3 stainless steel wire in the model cavity and pipes.

[0052] Step 4: After the filling process is completed and the model has been air-dried for 2 hours, proceed with the model assembly, coating, and shell making work according to the process requirements.

[0053] Step 5: Place the module into the resistance furnace at room temperature, heat it at a rate of 120±10℃ / h, hold it at 240±10℃ for 2h to remove the wax material from the module, then heat it to 750±10℃ and hold it for 2h before cooling it down in the furnace for later use.

[0054] Step 6: Cast the shell according to the process requirements;

[0055] Step 7: Use a high-pressure water gun with a modified nozzle to clean the residual gypsum refractory material adhering to the mold shell and inner cavity pipes of the casting. After cutting, use a sandblasting machine with a modified nozzle to perform surface treatment on the casting.

[0056] Step 8: Use an endoscope to inspect the inner cavity and pipes of the casting, and check that there are no defects such as porosity or slag inclusions on the surface of the casting, and that it meets the requirements of HB963 Class II.

[0057] Step 9: Inspect the surface of the casting for defects such as porosity, looseness, and slag inclusions by fluorescent penetrant testing, and confirm that it meets the requirements of HB963 Class II.

[0058] Step 10: Low magnification inspection: After heat treatment, the cross-section of the casting is dissected and inspected to find no defects such as porosity or slag porosity, and meets the requirements of HB963 Class II.

[0059] The batch of castings underwent surface inspection, fluorescence inspection, and low-magnification inspection. The surface quality and fluorescence inspection of the castings met the HB963 Class II casting standard. After heat treatment, the pinholes were inspected under low magnification and were found to be better than Grade 1, which met the HB963 Class II casting standard.

[0060] Many embodiments and applications beyond the examples provided will be apparent to those skilled in the art upon reading the foregoing description. Therefore, the scope of this teaching should not be determined by reference to the foregoing description, but rather by reference to the foregoing claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the applicant has not considered that subject matter as part of the disclosed inventive subject matter.

[0061] The above content provides a further detailed description of the present invention. It should not be construed that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection of the present invention as defined by the submitted claims.

Claims

1. A method for producing a mold for precision casting of an aluminum alloy with a narrow inner cavity structure, characterized by, Includes the following steps: S1, Design the casting structure and reserve the core head portion; S2, Model making based on the casting structure; S3, Pre-filling of the model's inner cavity and pipes: Weigh the powder and solvent according to the proportion, mix the powder and solvent thoroughly, evacuate in a vacuum tank, and then pour the mixture into the inner cavity and pipes 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 on its own, and then the subsequent model tree assembly and module shell making work are carried out. After the shell making is completed, it is dewaxed and fired. In step S3, the component ratio of the powder and solvent is as follows: chromite sand is 2.5% of the weight of α-gypsum powder, wood fiber is 0.75% of the weight of α-gypsum powder, glass fiber is 0.5% of the weight of α-gypsum powder, distilled water is 35% of the total weight of the powder, silica sol is 6% of the weight of distilled water, and n-octanol is 0.1% of the weight of distilled water.

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

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

4. The method for preparing a mold for aluminum alloy investment casting with a narrow internal cavity structure according to claim 1, characterized in that, The particle size of the chromite sand is 120 mesh.

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

6. The method for preparing a mold for investment casting of aluminum alloy with a narrow internal cavity structure according to claim 1, characterized in that, In step S3, ribs are pre-embedded before the pre-filling of the model cavity and pipes. The ribs are φ2~φ4 stainless steel wires.

7. The method for preparing a mold for aluminum alloy investment casting with a narrow internal cavity structure according to claim 1, characterized in that, In step S4, the module is placed into the resistance furnace at room temperature, heated at a rate of 100~150℃ / h, held at 230~250℃ for 2~3h to remove the wax material from the module, and then heated to 750±10℃ and held for 2~3h before cooling down with the furnace.

8. The method for preparing a mold for investment casting of aluminum alloy with a narrow internal cavity structure according to any one of claims 1 to 7, characterized in that, This method is applicable to the preparation of aluminum alloy castings with a minimum internal cavity and pipe dimension X < 3.5 mm.

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