Preparation method of sand mold forming mold shell for titanium alloy precision investment casting

Abstract

The invention provides a preparation method of a sand mold forming mold shell for titanium alloy precision investment casting, which comprises the following steps: S1, carrying out sand mold 3D printing on a three-dimensional sand mold to obtain a sand mold model; s2, a 3D printing spray gun is adopted for spraying the sand mold, the total spraying thickness is controlled to be 0.5-1 mm, low-temperature wax is adopted as a spraying raw material, and the model is K512; s3, a mold shell is prepared; s4, roasting and sand removal; the step S2 specifically comprises the following steps that S21, low-temperature wax is placed in a spray gun to be preheated, and the preheating temperature ranges from 50 DEG C to 60 DEG C; and S22, the temperature of the spray gun is increased to 60-120 DEG C, and a wax mold is sprayed on the sand mold. According to the preparation method, the 3D printing sand mold can replace a wax mold, and the problems of shrinkage deformation, shrinkage depression and the like of the wax mold are avoided; the spraying gun is used for spraying the 0.5-1 mm wax mould on the sand mould, the thickness is accurate and controllable, the sand mould model obtained by spraying the wax mould is smooth in surface and free of wax marks, the surface quality and the size precision of the titanium alloy casting can be effectively improved, manual finishing is not needed, and the manufacturing cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of mold shells for investment casting of titanium alloys. Specifically, it relates to a preparation method for a sand mold forming mold shell for precision investment casting of titanium alloys. Background Art

[0002] Investment precision casting, also known as lost-wax casting, is the most accurate forming method among all current casting methods and is the mainstream process for precision casting of titanium alloys. The production process of investment precision casting of titanium alloy castings has been basically formed, and most of its mold shells are prepared by applying multiple layers of coatings on the surface of wax patterns. However, due to the complex process of wax pattern preparation, it is necessary to select a suitable mold according to the part design and then inject and form it through a wax injection machine. This not only has a high mold cost, but also a long manufacturing cycle, high risk, and even cannot be manufactured. It is not advantageous for the production of small batches of less than a hundred pieces and complex thin-walled parts. Secondly, due to the insufficient strength of the wax pattern itself and the shrinkage of the wax liquid during filling and solidification, the wax pattern deforms and sinks, making it difficult to control the dimensions.

[0003] 3D printing additive manufacturing can directly additively manufacture wax patterns or other dissolvable investment patterns according to the three-dimensional design of parts, but the forming raw materials such as binders and powder materials restrict the low-cost application of 3D printed wax patterns or other dissolvable investment patterns. Further analysis shows that a method to give full play to the advantages of 3D printing additive manufacturing is to directly print the mold shell (casting mold). However, due to the extremely high high-temperature reaction activity of titanium, extremely high inertness requirements are imposed on the ceramic slurry to reduce the high-temperature reaction with the titanium liquid. However, there are problems such as high cost and difficult shell cleaning in the additive manufacturing of high-inertness mold shells. Chinese Patent (CN 114346166) reports a 3D printing sand mold precision casting mold shell preparation technology. This invention uses the high-temperature burning and dispersing characteristics of the sand mold and replaces the wax pattern with a 3D printed composite sand mold with wax to manufacture the precision casting mold shell. This method has a low cost and is easy to obtain a ceramic mold shell after roasting. However, the surface of the sand mold prepared by 3D printing is rough. Although the surface finish is improved by infiltrating molten wax in this report, the method of dipping the sand mold with wax will cause serious flow marks of the surface wax liquid, and the subsequent workload of surface trimming of the sand mold is large. It belongs to non-net-shape forming. This method not only has low forming dimensional accuracy but also poor stability. Summary of the Invention

[0004] In view of this, the present invention aims to propose a preparation method for a sand mold forming mold shell for precision investment casting of titanium alloys, so as to solve the problems in the prior art that the surface of the sand mold prepared by 3D printing is rough, the method of dipping the sand mold with wax will cause serious flow marks of the surface wax liquid, the subsequent workload of surface trimming of the sand mold is large, it belongs to non-net-shape forming, and this method not only has low forming dimensional accuracy but also poor stability.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] A preparation method of a sand mold forming shell for precision investment casting of titanium alloy, comprising the following steps:

[0007] S1: Perform 3D printing on the three-dimensional sand mold to obtain a sand mold model;

[0008] S2: Spray the sand mold using a 3D printing spray gun, with the total spraying thickness controlled within 0.5 - 1 mm, and the spraying raw material being low-temperature wax with the model number K512;

[0009] S3: Prepare the shell;

[0010] S4: Bake to remove the sand.

[0011] This setting can achieve the rapid preparation of the shell, with convenient operation, and the shell is used for preparing titanium alloy with high dimensional accuracy and good surface quality.

[0012] Further, in step S2, it specifically includes the following steps:

[0013] S21: Place the low-temperature wax in the spray gun for preheating, with the preheating temperature being 50 - 60 °C;

[0014] S22: Raise the temperature of the spray gun to 60 - 120 °C and spray a wax film on the sand mold.

[0015] This setting sprays a 0.5 - 1 mm wax film on the sand mold using a spray gun. The thickness of the sand mold is precisely controllable, and the sand mold model obtained by spraying the wax film has a smooth surface and no wax marks, which can effectively improve the surface quality and dimensional accuracy of titanium alloy castings, and there is no need for manual trimming, with low production costs.

[0016] Further, in step S22, it also includes the following:

[0017] S221: Adopt multi-pass spraying, with the spraying thickness for each pass being 0.06 - 0.1 mm.

[0018] This setting can improve the thickness uniformity of the sand mold film layer and the surface quality of titanium alloy castings.

[0019] Further, in step S3, it also includes the following steps:

[0020] S31: Apply the surface layer slurry, sprinkle sand, and dry the sand mold prepared in step S2;

[0021] S32: Apply the back layer slurry, sprinkle sand, and dry the model prepared in step S31.

[0022] This setting can improve the surface flatness, air permeability, strength, and accuracy of the shell, prevent crack generation, and thus improve the quality of titanium alloy castings.

[0023] Further, the surface layer slurry includes a surface layer binder, surface layer refractory powder, and JFC. The surface layer binder includes diluted silica sol, PVA solution, and acid-base regulator; the pH of the surface layer binder is 9-10.

[0024] Specifically, the mass ratio of the diluted silica sol to the PVA solution is 15-25:1. The mass fraction of SiO2 in the diluted silica sol is 15-20%, and the mass ratio of PVA in the PVA solution is 10-20%. The solvents of the diluted silica sol and the PVA solution are both deionized water.

[0025] In this setting, PVA can not only improve the adhesion between the diluted silica sol and the sand mold, but also improve the air permeability during subsequent sintering. Through the diluted silica colloidal solution, the strength of the mold shell is improved, thereby improving the quality of the titanium alloy castings cast using this mold shell.

[0026] Specifically, the preparation method of the surface layer slurry is as follows: Add the diluted silica sol to the PVA solution according to a certain mass ratio, start mechanical stirring, adjust the pH value to 9-10.5 with an acid-base regulator, then add the surface layer refractory powder, and disperse it at high speed by mechanical stirring for 60-120 min. Then add 0.03-0.1% (the weight ratio of JFC to the total of the surface layer binder and the surface layer refractory powder) of JFC to make a surface layer slurry with a viscosity of 6-10 s.

[0027] Specifically, the refractory powder is yttrium oxide powder or zirconium oxide powder, and the mass ratio of the surface layer binder to the surface layer refractory powder is 3.5:1-5.5:1.

[0028] Specifically, in the diluted silica sol, the pH is 9-10, the diameter of the SiO2 colloidal particles ≤ 6 nm, and the total mass ratio of the SiO2 colloidal particles to the diluted silica sol is 15-20%.

[0029] Specifically, the specific preparation steps of the diluted silica sol are as follows: Use ordinary silica sol, deionized water as the solvent, dilute the silica dioxide content to 15%-20%, add a pH value regulator to adjust the pH value to 9-10, and stir for about 24-48 h. Among them, the pH value regulator is NaOH solution and HCL solution, and the concentrations of the NaOH solution and the HCL solution are both 0.1-1 mol / L.

[0030] Further, in step S31, the sand spreading process uses yttrium oxide sand or zirconium oxide sand, with a mesh number of 60-120 mesh.

[0031] Further, in step S32, the sand spreading process uses back layer mullite sand, with a mesh number of 10-60 mesh.

[0032] Further, in step S31, the environmental humidity for drying is ≥75%, the drying temperature is 23 - 27°C, and the drying time is ≥12 h.

[0033] Further, in step S32, the environmental humidity for drying is ≥50%, the drying temperature is 23 - 27°C, and the drying time is ≥12 h.

[0034] Further, the back layer slurry is prepared by mixing mullite sand with a particle size of 200 - 300 mesh and silica sol with a SiO₂ mass fraction of 25% - 35% at a mass ratio of 4.5:1 - 6.5:1, and the viscosity of the back layer slurry is 6 - 15 s.

[0035] Further, 5 - 9 layers are prepared for the back layer.

[0036] Further, the roasting and sand removal in step S4 specifically means that without going through the dewaxing process, it is directly subjected to high-temperature roasting in a roasting furnace at a temperature of 900 - 1200°C for 120 - 180 min. The sand mold completely collapses and detaches at high temperature.

[0037] Compared with the prior art, the preparation method of the sand mold forming shell for titanium alloy investment casting described in the present invention has the following advantages:

[0038] (1) High dimensional accuracy: In the present invention, the 3D printed sand mold replaces the wax mold, avoiding problems such as shrinkage deformation and sink marks of the wax mold. By spraying a wax film with a thickness of 0.5 - 1 mm on the sand mold using a spray gun, the thickness is precisely controllable, and the sand mold model obtained by spraying the wax mold has a smooth surface and no wax marks, which can effectively improve the surface quality and dimensional accuracy of titanium alloy castings, and does not require manual trimming, with low production costs, giving full play to the advantages of 3D printing additive manufacturing in the field of investment casting;

[0039] (2) High surface quality: The present invention uses 3D printing to spray the wax film, avoiding flow marks and accumulation caused by dipping molten wax liquid. The surface of the sand mold with the deposited wax film does not require trimming. After sand removal and cleaning, the surface of the mold shell is smooth and pollution-free, with low surface roughness;

[0040] (3) Cost reduction and efficiency improvement: The present invention eliminates the mold processing cost and time for making wax molds in the traditional mode. For small-batch production of less than a hundred pieces or single-piece and small-quantity production, the production cost is greatly reduced and the production efficiency is improved;

[0041] (4) Convenient operation: The present invention reduces manual wax trimming operations, and the remaining operations are simple and do not contain complex technical processes;

[0042] (5) The shell mold obtained by the preparation method of the present invention is used for casting titanium alloy castings. The surface roughness of the titanium alloy castings can reach 3.1 - 3.2 μm, the dimensional accuracy can reach CT6 - CT7 levels of the GB / T 6414 standard, and the internal and external quality can meet the relevant requirements of Class II, Grade B and above castings of GJB 2896A - 2020. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is the 3D printing sand mold appearance diagram of Embodiment 1 of the present invention;

[0044] Figure 2 It is the 3D printing spray wax film sand mold appearance diagram of Embodiment 1 of the present invention;

[0045] Figure 3 It is the appearance quality of the cast blank of the castings poured in Embodiment 1 of the present invention;

[0046] Figure 4 It is the X-ray flaw detection internal quality diagram of the castings poured in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given with reference to the accompanying drawings.

[0048] Embodiment 1

[0049] The present invention provides a preparation method for a sand mold forming shell mold for precision investment casting of titanium alloy, including the following steps:

[0050] S1: First, design a three-dimensional sand mold; the sand mold structure diagram is as Figure 1 shown; reduce the single side of the three-dimensional sand mold model of the casting by 0.5 mm.

[0051] Secondly, design a riser; the shape of the riser is designed as a circle with few edges, which can reduce the dropping of impurities during the operation process; the size of the riser is designed to be not less than 15 mm and the height is not less than 5 mm; the position of the riser is generally designed above and on the side of the sand mold and at complex structures, which is convenient for cleaning during the sand removal process and plugging before pouring.

[0052] Then, perform 3D printing on the three-dimensional sand mold to obtain a sand mold model;

[0053] S2: Use a 3D printing spray gun to spray the sand mold, and control the total spraying thickness within 0.8 mm. The spraying raw material is low-temperature wax with the model number K512; the sand mold model obtained by spraying the wax film has a smooth surface and no wax marks.

[0054] Specifically, in step S2, it specifically includes the following steps:

[0055] S21: Place the low-temperature wax in a spray gun for preheating at a preheating temperature of 55 °C;

[0056] S22: Raise the temperature of the spray gun to 100 °C and spray a wax film on the sand mold.

[0057] Specifically, in step S22, the following is also included:

[0058] S221: Adopt multi-pass spraying, with the spraying thickness of each pass being 0.08 mm.

[0059] S3: Prepare a mold shell;

[0060] Specifically, in step S3, the following steps are also included:

[0061] S31: Apply a surface layer slurry, sprinkle sand, and dry the sand mold prepared in step S2;

[0062] S32: Apply a back layer slurry, sprinkle sand, and dry the model prepared in step S31.

[0063] Specifically, the preparation method of the surface layer slurry is as follows: Add the diluted silica sol with a SiO2 mass fraction of 15% to the PVA solution with a PVA mass fraction of 15% according to a mass ratio of 25:1. Start mechanical stirring, adjust the pH value to 9 with an acid-base regulator to obtain a surface layer binder. Then, add yttrium oxide powder according to a mass ratio of 1:3.5 and disperse it at high speed by mechanical stirring for 60 min. Then, add 0.03% (the weight ratio of JFC to the surface layer binder and yttrium oxide powder) of JFC to obtain the surface layer slurry.

[0064] Specifically, in the diluted silica sol, the pH is 9, and the diameter of the SiO2 colloidal particles is 3 - 5 nm.

[0065] Specifically, the specific preparation steps of the diluted silica sol are as follows: Use ordinary silica sol and deionized water as the solvent, dilute the silica dioxide content to 15%, add a pH value regulator to adjust the pH value to 9, and stir for 24 h. Among them, the pH value regulator is the NaOH solution and the HCL solution, and the concentrations of the NaOH solution and the HCL solution are both 0.1 mol / L.

[0066] Specifically, in step S31, the sand-sprinkling process uses yttrium oxide sand with a mesh number of 80.

[0067] Specifically, in step S32, the sand-sprinkling process uses back layer mullite sand with a mesh number of 40.

[0068] Specifically, in step S31, the drying is carried out in an environment with a humidity of 75%, a drying temperature of 23 °C, and a drying time of 24 h.

[0069] Specifically, in step S32, the environmental humidity for drying is 50%, the drying temperature is 23°C, and the drying time is 24 hours.

[0070] Specifically, the back layer slurry is prepared by mixing mullite powder with a particle size of 250 mesh and silica sol with a SiO2 mass fraction of 25% at a mass ratio of 5.5:1.

[0071] Specifically, the back layer is prepared in 7 layers.

[0072] Specifically, after preparing the mold shell, it is also necessary to polish the riser opening. Use a grinding wheel to polish the mold shell at the end face of the riser opening to expose the sand mold at that place.

[0073] S4: Roasting and sand removal.

[0074] The mold shell prepared in step S3 is directly subjected to high-temperature roasting in a roasting furnace at a temperature of 1100°C for 160 minutes without going through the dewaxing process. The sand mold completely collapses and detaches at high temperature.

[0075] Specifically, after roasting and sand removal, it is also necessary to clean the sand. Specifically, use a blower or compressed air, water washing, etc. to clean the mold shell from the opened riser opening.

[0076] Specifically, after cleaning the sand, the riser opening is also blocked. Specifically, use a graphite plug to block the riser opening. The diameter of the plug is slightly smaller than the size of the riser opening. During the blocking process, prevent impurities from falling in due to friction between the plug and the riser opening, and then use a vacuum cleaner to perform dust suction treatment inside the mold shell.

[0077] Example 2

[0078] The present invention provides a method for preparing a sand mold forming mold shell for precision investment casting of titanium alloy, including the following steps:

[0079] S1: First, design a three-dimensional sand mold; reduce the thickness of the three-dimensional sand mold model of the casting by 0.7 mm on one side.

[0080] Secondly, design the riser opening; the shape of the riser opening is designed as circular with few edges, which can reduce the falling of impurities during the operation process; the size of the riser opening is designed to be not less than 15 mm, and the height is not less than 5 mm; the position of the riser opening is generally designed above and on the side of the sand mold and at complex structures, which is convenient for cleaning during sand removal treatment and plugging before pouring.

[0081] Then, perform 3D printing on the three-dimensional sand mold to obtain a sand mold model. The sand mold structure diagram is as Figure 1 shown;

[0082] S2: Use a 3D printing spray gun to spray the sand mold. The total spraying thickness is controlled at 0.6 mm, and the spraying raw material is low-temperature wax, with the model number K512; as Figure 2As shown, the sand mold model obtained by spraying the wax mold has a smooth surface and no wax marks.

[0083] Specifically, in step S2, it specifically includes the following steps:

[0084] S21: Place the low-temperature wax in the spray gun for preheating, and the preheating temperature is 60°C;

[0085] S22: Raise the temperature of the spray gun to 110°C and spray a wax film on the sand mold.

[0086] Specifically, in step S22, it further includes the following:

[0087] S221: Adopt multi-pass spraying, and the spraying thickness per pass is 0.06 mm.

[0088] S3: Prepare the mold shell;

[0089] Specifically, in step S3, it further includes the following steps:

[0090] S31: Apply the surface layer slurry, sprinkle sand, and dry the sand mold prepared in step S2;

[0091] S32: Apply the back layer slurry, sprinkle sand, and dry the model prepared in step S31.

[0092] Specifically, the preparation method of the surface layer slurry is as follows: Add the diluted silica sol with a SiO2 mass fraction of 17% to the PVA solution with a PVA mass ratio of 12% according to a mass ratio of 20:1. Start mechanical stirring, and adjust the PH value to 9 with an acid-base regulator to obtain the surface layer binder. According to a mass ratio of 1:4.5, add the surface layer zirconia powder, and disperse it at high speed by mechanical stirring for 60 min. Then add 0.05% (the weight ratio of JFC to the total weight of the surface layer binder and zirconia powder) of JFC to obtain the surface layer slurry.

[0093] Specifically, in the diluted silica sol, the PH is 9, and the diameter of the SiO2 colloidal particles is 3 - 5 nm.

[0094] Specifically, the specific preparation steps of the diluted silica sol are as follows: Use ordinary silica sol, deionized water as the solvent, dilute the silica dioxide content to 17%, add a PH value regulator to adjust the PH value to 9, and stir for 24 h. Among them, the PH value regulator is the NaOH solution and the HCL solution, and the concentrations of the NaOH solution and the HCL solution are both 0.1 mol / L.

[0095] Specifically, in step S31, the sand sprinkling process uses zirconia sand with a mesh number of 90.

[0096] Specifically, in step S32, the sand sprinkling process uses back layer mullite sand with a mesh number of 40.

[0097] Specifically, in step S31, the environmental humidity for drying is 75%, the drying temperature is 25 °C, and the drying time is 24 h.

[0098] Specifically, in step S32, the environmental humidity for drying is 50%, the drying temperature is 25 °C, and the drying time is 24 h.

[0099] Specifically, the back layer slurry is prepared by mixing mullite powder with a particle size of 300 mesh and silica sol with a SiO2 mass fraction of 25% at a mass ratio of 4.5:1.

[0100] Specifically, the back layer is prepared in 9 layers.

[0101] Specifically, after the mold shell is prepared, it is also necessary to grind and clean the sand outlet. Use a grinding wheel to grind the mold shell at the end face of the sand cleaning port to expose the sand mold at that place.

[0102] S4: Roasting and sand removal.

[0103] The mold shell prepared in step S3 is directly subjected to high-temperature roasting in a roasting furnace at a temperature of 1000 °C for 120 min without going through the dewaxing process. The sand mold completely collapses and detaches at high temperature.

[0104] Specifically, after roasting and sand removal, it is also necessary to perform sand cleaning treatment. Specifically, use a blower or compressed air, water washing, etc. to clean the mold shell from the opened sand cleaning port.

[0105] Specifically, after sand cleaning treatment, the sand cleaning port is also blocked. Specifically, use a graphite plug to block the sand cleaning port. The diameter size of the plug is slightly smaller than the size of the sand cleaning port. During the blocking process, prevent the plug from rubbing against the sand cleaning port and causing impurities to fall in, and then use a vacuum cleaner to perform dust suction treatment inside the mold shell.

[0106] Specifically, this embodiment also provides a titanium alloy precision casting mold shell prepared by the above method, and its production of titanium alloy castings is as Figures 3 - 4 shown. The surface of the titanium alloy casting is smooth and there are no internal defects.

[0107] Example 3

[0108] The present invention provides a method for preparing a sand mold forming mold shell for titanium alloy investment casting, including the following steps:

[0109] S1: First, design a three-dimensional sand mold; reduce the single side of the three-dimensional sand mold model of the casting by 0.5 mm.

[0110] Secondly, design the riser; the shape of the riser is designed as circular with fewer edges, which can reduce the dropping of impurities during the operation process; the size of the riser is designed to be not less than 15 mm and the height is not less than 5 mm; the position of the riser is generally designed above and on the side of the sand mold and at complex structures, which is convenient for cleaning during the sand removal process and plugging before pouring.

[0111] Then, perform 3D printing on the three-dimensional sand mold to obtain a sand mold model. The structure diagram of the sand mold is as Figure 1 shown;

[0112] S2: Use a 3D printing spray gun to spray the sand mold. The total spraying thickness is controlled at 0.7 mm, and the spraying raw material is low-temperature wax with the model number K512.

[0113] Specifically, in step S2, it specifically includes the following steps:

[0114] S21: Place the low-temperature wax in the spray gun for preheating, and the preheating temperature is 70 °C.

[0115] S22: Raise the temperature of the spray gun to 90 °C and spray a wax film on the sand mold.

[0116] Specifically, in step S22, it also includes the following:

[0117] S221: Adopt multi-pass spraying, and the spraying thickness of each pass is 0.07 mm.

[0118] S3: Prepare the mold shell;

[0119] Specifically, in step S3, it also includes the following steps:

[0120] S31: Apply the surface layer slurry, sprinkle sand, and dry the sand mold prepared in step S2.

[0121] S32: Apply the back layer slurry, sprinkle sand, and dry the model prepared in step S31.

[0122] Specifically, the preparation method of the surface layer slurry is as follows: Add the diluted silica sol with a SiO2 mass fraction of 19% to the PVA solution with a PVA mass fraction of 15% according to a mass ratio of 20:1. Start mechanical stirring, and adjust the PH value to 9 with an acid-base regulator to obtain the surface layer binder. Then, add yttrium oxide powder according to a mass ratio of 1:5.5, and perform high-speed mechanical stirring and dispersion for 100 min. Then, add 0.07% (the weight ratio of JFC to the surface layer binder and yttrium oxide powder) of JFC to obtain the surface layer slurry.

[0123] Specifically, in the diluted silica sol, the PH is 9, and the diameter of the SiO2 colloidal particles is 3 - 5 nm.

[0124] Specifically, the specific preparation steps of the diluted silica sol are as follows: ordinary silica sol is used, deionized water is used as the solvent, the silica content is diluted to 19%, a pH regulator is added to adjust the pH value to 9, and stirring is carried out for 24 h. Among them, the pH regulator is a NaOH solution and an HCl solution, and the concentrations of the NaOH solution and the HCl solution are both 0.1 mol / L.

[0125] Specifically, in step S31, the sand spraying process uses yttrium oxide sand with a mesh number of 100.

[0126] Specifically, in step S32, the sand spraying process uses back layer mullite sand with a mesh number of 30.

[0127] Specifically, in step S31, the drying is carried out in an environment with a humidity of 75%, a drying temperature of 25 °C, and a drying time of 24 h.

[0128] Specifically, in step S32, the drying is carried out in an environment with a humidity of 50%, a drying temperature of 25 °C, and a drying time of 24 h.

[0129] Specifically, the back layer slurry is prepared by mixing mullite powder with a particle size of 250 mesh and silica sol with a SiO2 mass fraction of 25% according to a mass ratio of 5.5:1.

[0130] Specifically, the back layer is prepared in 7 layers.

[0131] Specifically, after the mold shell is prepared, it is also necessary to grind and clean the sand outlet. Use a grinding wheel to grind the mold shell at the end face of the sand cleaning port to expose the sand mold at that place.

[0132] S4: Roasting and sand removal.

[0133] The mold shell prepared in step S3 is directly subjected to high-temperature roasting in a roasting furnace at a temperature of 1100 °C for 160 min without going through the dewaxing process. The sand mold completely collapses and detaches at high temperature.

[0134] Specifically, after roasting and sand removal, it is also necessary to carry out sand cleaning treatment, specifically, use a blower or compressed air, water washing, etc. to clean the mold shell from the opened sand cleaning port.

[0135] Specifically, after the sand cleaning treatment, the sand cleaning port is blocked. Specifically, a graphite plug is used to block the sand cleaning port. The diameter size of the plug is slightly smaller than the size of the sand cleaning port. During the blocking process, prevent the plug from rubbing against the sand cleaning port and causing impurities to fall in, and then use a vacuum cleaner to carry out dust suction treatment inside the mold shell.

[0136] Comparative Example 1

[0137] The difference between this comparative example and Example 1 is that in step S2, the wax dipping liquid method is adopted.

[0138] The mold shells prepared in Examples 1 to 3 and Comparative Example 1 were cast with titanium alloy to obtain titanium alloy castings. The surface roughness of the castings and the dimensional accuracy under the GB / T 6414 standard were measured, and the measurement results are shown in Table 1 below.

[0139] Table 1

[0140]

[0141] It can be seen from Table 1 above that the mold shell obtained by spraying the wax film with a spray gun in the present invention, compared with the method of dipping in wax liquid, for the titanium alloy casting obtained by casting, the surface roughness of the casting is low and the dimensional accuracy of the casting is high. That is, the preparation method of the present invention is simple in operation, low in cost, and the titanium alloy casting obtained by casting has high dimensional accuracy and high surface quality.

[0142] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A method for preparing a sand mold shell for titanium alloy investment casting, characterized in that: The steps include: S1: Perform 3D printing on the three-dimensional sand mold to obtain a sand mold model; S2: Use a 3D printing spray gun to spray the sand mold, the total spray thickness is controlled at 0.5~1mm, and the spraying raw material is low-temperature wax, model K512; S3: preparing a mold shell; S4: roasting and desanding.

2. The preparation method according to claim 1, characterized in that: In step S2, the following steps are specifically included: S21: Preheat the low-temperature wax in a spray gun at a temperature of 50-60°C; S22: Raise the temperature of the spray gun to 60~120℃ and spray the wax film on the sand mold.

3. The preparation method according to claim 1, characterized in that: In step S22, the following is also included: S221: Multi-pass spraying is adopted, and the thickness of each spraying is 0.06~0.1mm.

4. The preparation method according to claim 1, characterized in that: In step S5, the following steps are also included: S31: coating the sand mold prepared in step S2 with a surface slurry, sprinkling sand, and drying; S32: Apply the backing slurry, sprinkle sand and dry the model made in step S31.

5. The preparation method according to claim 4, characterized in that: The surface layer slurry includes a surface layer binder, a surface layer refractory powder, and JFC. The surface layer binder includes diluted silica sol, PVA solution, and an acid-base regulator. The mass ratio of the diluted silica sol and the PVA solution is 15-25:1, the mass fraction of SiO2 in the diluted silica sol is 15-20%, and the mass ratio of PVA in the PVA solution is 10-20%.

6. The preparation method according to claim 5, characterized in that: The refractory powder is yttria powder or zirconium oxide powder, and the mass ratio of the surface layer binder to the surface layer refractory powder is 3.5:1-5.5:

1.

7. The preparation method according to claim 5, characterized in that: The preparation method of the surface layer slurry is specifically as follows: adding diluted silica sol to PVA solution, mechanically stirring, adjusting the pH value to 9-10.5 with an acid-base regulator, adding surface refractory powder, mechanically stirring and dispersing at high speed, and then adding JFC to prepare a surface layer slurry with a viscosity of 6-10s.

8. The preparation method according to claim 4, characterized in that: In step S31, the sand spreading process uses yttria sand or zirconium oxide sand with a mesh size of 60-120.

9. The preparation method according to claim 4, characterized in that: In step S31, the drying environment humidity is ≥75%, the drying temperature is 23-27°C, and the drying time is ≥12h.

10. The preparation method according to claim 4, characterized in that: The backing layer slurry is prepared by mixing mullite sand with a particle size of 200-300 meshes and silica sol with a SiO2 mass fraction of 25%-35% in a mass ratio of 4.5:1-6.5:1, and the viscosity of the backing layer slurry is 6-15s.

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