A casting system design and preparation method of a thin-wall casting

Abstract

The present application belongs to the field of high-temperature alloy thin-wall casting, and particularly relates to a thin-wall casting pouring system design and preparation method. According to theoretical formula, the relationship between the cooling speed of the thin-wall casting, the solidification time and the dendrite spacing size is calculated, and in combination with the distribution relationship of the size of the thin-wall casting and the original wax type pouring process defects such as micro-cracks, the bottom of the pouring cup in the optimized pouring system is a plate-shaped straight runner arranged along the vertical direction, the side surface of the straight runner is vertically arranged with an inner runner, one end of the inner runner is connected with the straight runner, and the other end of the inner runner is connected with the casting. By optimizing the structure of the pouring system and the preparation process parameters of the casting, the solidification sequence of the casting is improved, the generation tendency of the thermal stress is greatly reduced, and the thermal cracks distributed at the size mutation section can be effectively reduced, which helps to improve the qualified rate of the casting. The present application is suitable for the preparation of thin-wall castings, can significantly improve the quality of the castings, greatly improve the qualified rate, and has significant economic benefits.

Description

Technical fields:

[0001] This invention belongs to the field of high-temperature alloy thin-walled casting, specifically relating to the design and preparation method of a casting system for thin-walled castings. Background technology:

[0002] Aero engines are a crucial indicator of advanced manufacturing development and comprehensive national strength. High-temperature alloys, as irreplaceable materials in the manufacture of high-temperature hot-end components such as aero-engines, space engines, and gas turbines, account for approximately 40% of the materials used in engines. They are primarily used in high-temperature combustion chambers, turbines, and compressor hot-end components. Additionally, they are used in load-bearing casings, rings, and exhaust nozzles. Therefore, the performance and selection of high-temperature alloy materials are key factors determining the performance of aero engines.

[0003] With the rapid development of my country's aerospace and shipbuilding industries, the application of large-scale, lightweight, and complex high-temperature alloy components is becoming increasingly widespread. Based on this, large thin-walled high-temperature alloy structural components (generally composed of several individual thin-walled casting units of varying sizes and shapes, with an external area typically around 100 cm²) are increasingly being developed. 2 The above (its wall thickness is generally only about 1mm) is widely used in the aerospace engineering field due to its excellent heat dissipation capacity and light weight.

[0004] Thin-walled castings, with their smaller temperature gradients in structural design, reduce thermal stress and have thus gradually become a major component of the floating wall structures in advanced European and American aero-engine combustors. These floating wall structures are assembled from thin-walled castings of varying sizes and shapes; these castings are ultra-thin, high-temperature alloy miniature castings with complex structures. Their casting process is extremely complex, and deformation control requirements are very stringent.

[0005] Because the mold wall is extremely thin, the solidification sequence of the thin-walled section and the thicker sections of the studs connected to it is difficult to control, and special phenomena such as thin-wall remelting may even occur due to the release of latent heat in the thicker sections. Given the complexity of the casting structure and the requirements for its size and shape, integral investment casting is the only feasible process adopted by leading international aero-engine manufacturers. Furthermore, due to the special dimensions of the thin-walled casting and the presence of many abrupt cross-sections in its structure, in addition to the susceptibility to quality defects such as cold shuts, shrinkage cavities, and porosity during solidification, microcracks are easily generated at these abrupt cross-sections under the influence of thermal stress during casting. Summary of the Invention:

[0006] To address the shortcomings and deficiencies of existing technologies, the present invention aims to provide a casting system design and preparation method for thin-walled castings. Through reasonable module design optimization, while ensuring that thin-walled castings are free from quality defects such as shrinkage cavities and porosity, the solidification sequence and thermal stress generation of the castings are improved, and the generation of microcracks in thin-walled castings is reduced, thereby increasing the casting qualification rate, which has significant economic implications.

[0007] The technical solution of this invention is:

[0008] A method for designing a gating system for thin-walled castings. The optimized gating system mainly includes a pouring cup, a sprue, and an ingate. The bottom of the pouring cup is a vertically arranged plate-shaped sprue. The ingate is vertically arranged on the side of the sprue. One end of the ingate is connected to the sprue, and the other end is connected to the casting. The design basis of the gating system is as follows:

[0009] First, based on the length of the thin-walled casting, select the number of ingates n = 4 to 6;

[0010] Second, determine the size range of the ingate based on the casting dimensions. The contact surface dimensions between the ingate and the casting should satisfy the following relationship:

[0011] a2=(5~8)b (1)

[0012] b2=(10~25)b (2)

[0013] c2=(0.5~1)c (3)

[0014] Where a2 and c2 are the length and width of the contact surface between the ingate and the casting, respectively, in mm; b2 is the thickness of the ingate, in mm; b and c are the thickness and width of the casting, respectively, in mm.

[0015] Third, the dimensions of the sprue should be designed to meet the following relationship:

[0016] a1=(0.6~1.1)a (4)

[0017] b1 = (2~3)a2 (5)

[0018] Where a1 and b1 are the length and thickness of the sprue (plate-shaped), respectively, a is the length of the casting, and a′2 is the length of the contact surface between the ingate and the sprue, all in mm;

[0019] Fourth, the design of the ingate location: To ensure the uniformity of the heat radiation effect of the sprue on the thin-walled casting during solidification, the center of the casting in both length and width should coincide with the center of the sprue. Simultaneously, in the length direction, the distance between two adjacent ingates on the sprue, from the center outwards, should satisfy the following relationship:

[0020] e1∶e2∶e3=1∶(0.6~1)∶(0.4~1) (6)

[0021] Where e1, e2, and e3 are the distances between the 1st, 2nd, and 3rd adjacent ingates from the center outwards along the length direction of the sprue, respectively, in mm.

[0022] In the second aspect of the design method for the casting system of the thin-walled casting, in order to ensure the filling speed during the casting process, based on the principle of equal flow rate, that is:

[0023] Q = SV (7)

[0024] Where Q is the flow rate of the molten metal, in mm. 3 / s; S is the cross-sectional area of ​​the gating system, in mm. 2 V represents the flow rate of the molten metal, in mm / s.

[0025] According to the above formula, reducing the cross-sectional area of ​​the gating system increases the flow rate of the molten metal. The ingate in the casting system adopts a wedge-shaped design, and its dimensions must meet the following relationship:

[0026] S′2=(2~4)S2 (8)

[0027] a′2≥a2 (9)

[0028] c′2≥c2 (10)

[0029] Where S2 and S′2 are the cross-sectional areas of the ingate in contact with the casting and the sprue, respectively, in mm. 2 a′2 and c′2 are the length and width of the contact surface between the ingate and the sprue, respectively, in mm.

[0030] In the second item of the design method for the casting system of the thin-walled casting, b2 is the shortest thickness of the ingate for a thin-walled casting with a certain curvature.

[0031] In the third section of the design method for the casting system of the thin-walled casting, when designing the width of the sprue, in order to ensure complete pouring, it is necessary to calculate the minimum remaining pressure head height, which must satisfy the following relationship:

[0032]

[0033] Where c1 is the width of the sprue, c is the width of the casting, b′2 is the maximum value of different sprue thicknesses in mm; α is the pressure angle, which ranges from 10° to 14°.

[0034] The casting system design method for the thin-walled casting involves creating a cutout in the sprue between the ingates as needed. The length a3 of the cutout should not exceed the corresponding ingate distance. The minimum width of the sprue after cutting out the cutout is calculated based on the corresponding flow rate formula, i.e.:

[0035] Q≤2S3V (12)

[0036] S3=c3b1 (13)

[0037]

[0038] B1 = 1.25 + 0.25x (15)

[0039] Where Q is the flow rate of molten metal in the casting system, in mm. 3 / s; S3 is the cross-sectional area at the bottom of the cutout location, in mm. 3 V is the flow velocity of molten metal at the bottom of the cutout position, in mm / s; c3 is the width of the bottom of the cutout position, in mm; b1 is the thickness of the sprue, in mm; g is the acceleration due to gravity; B1 is the energy loss factor; x is the number of 90° bends in the sprue, x takes the value 1, and B1 takes the value 1.5.

[0040] The aforementioned method for designing the casting system for thin-walled castings involves hollowing out the sprues between all the ingates, or hollowing out the sprues between some of the ingates near the center.

[0041] The aforementioned method for designing a gating system for thin-walled castings involves adding shims at the contact points between the ingate and the casting, as needed. This shim-based approach locally thickens the casting, thereby reducing the equivalent stress on the casting. The shim dimensions should satisfy the following relationship:

[0042] a4 = a2 + (1 ~ 3) (16)

[0043] b4 = (0.5 ~ 1.5)b (17)

[0044] c4 = c2 + (1 ~ 5) (18)

[0045] Where a4, b4, and c4 are the length, thickness, and width of the gasket, a2 and c2 are the length and width of the contact surface between the ingate and the casting, and b is the thickness of the casting, all in mm.

[0046] A method for preparing a thin-walled casting, characterized by comprising the following steps: a method for designing the casting system for the thin-walled casting;

[0047] (1) Wax pattern pressing: using molds to press wax patterns of thin-walled castings;

[0048] (2) Wax model finishing: Finish the wax model, clean up the burrs and flash, and repair defects such as chipped corners, cold shuts, cracks and air bubbles.

[0049] (3) Module optimization design: smaller size sprue and ingate wax molds are used, and the sprue between the ingates is hollowed out;

[0050] (4) Wax pattern assembly: Weld the wax pattern of the casting and the gating firmly, and add a shim at the contact point between the ingate and the casting;

[0051] (5) Shell preparation: Dip different surface layer slurries onto the assembled wax mold to prepare a multi-layer shell;

[0052] (6) Dewaxing treatment: After the shell is prepared and dried, dewaxing treatment is carried out;

[0053] (7) Shell firing: The shell is fired after dewaxing;

[0054] (8) Casting: Thin-walled castings are cast using a vacuum induction furnace.

[0055] (9) Cooling of castings: After the castings are poured, they should be placed for no less than 5 minutes before being taken out of the furnace. A layer of cotton should be wrapped around the outer surface of the mold shell to prevent the cooling rate from being too fast.

[0056] In the preparation method of the thin-walled casting, steps (7)-(8) include the shell baking and casting pouring processes:

[0057] 1) Shell firing temperature: 1075±30℃;

[0058] 2) Pouring temperature: 1520±30℃;

[0059] 3) Pouring speed: Pouring shall be completed within no more than 3 seconds;

[0060] 4) The gas pressure of the vacuum induction furnace is less than 10. -1 Pa.

[0061] The design concept of this invention is:

[0062] To address the problems of low yield and low production efficiency caused by numerous microcracks in thin-walled castings produced by traditional gating systems and preparation methods, this paper proposes a gating system design and preparation method for thin-walled castings. By optimizing the casting module, gating system design, and casting process, the solidification sequence and rate of thin-walled castings are improved, thereby reducing the tendency for thermal stress to form during cooling and effectively preventing the formation of thermal cracks at abrupt dimensional changes in thin-walled castings. This significantly improves the yield and production efficiency of thin-walled casting products.

[0063] The advantages and beneficial effects of this invention are:

[0064] 1. Based on theoretical formulas, the relationship between cooling rate, solidification time, and dendrite spacing of thin-walled castings is calculated. Combining the dimensions of thin-walled castings with the distribution of defects such as microcracks in the original wax pattern casting process, this invention proposes a new casting system design and preparation method for thin-walled castings. This includes the design of casting modules, gating systems, and casting processes. By optimizing the casting system structure and casting preparation process parameters, the solidification sequence of castings is improved, the tendency to generate thermal stress is significantly reduced, and thermal cracks distributed at the abrupt change in size section are effectively reduced, which helps to improve the casting qualification rate.

[0065] 2. This invention is applicable to the preparation of thin-walled castings, which can significantly improve the quality of castings, greatly increase the pass rate, and generate significant economic benefits. Attached image description:

[0066] Figures 1-3 Schematic diagrams from different angles show the optimized design of the gating system for thin-walled castings. In the diagram, 1 represents the gating system (11 pouring cup, 12 sprue, 13 ingate), 2 represents the casting, 3 represents the spacer, and 4 represents the cutout. Detailed implementation method:

[0067] During the solidification process of castings, the alloy first solidifies along the dendrite trunk. Therefore, the size of the secondary dendrite spacing directly affects the formation of defects such as shrinkage cavities and porosity in the casting. The secondary dendrite spacing λ2 (in meters) is related to the cooling rate GR (in kJ / s) and the local solidification time t. f The unit is seconds (s). It satisfies the following relationship:

[0068] λ2=a(t f ) 1 / 3 =b(GR) -1 / 3 (19)

[0069]

[0070] b = a(ΔT′) 1 / 3 (twenty one)

[0071] Where Γ is the Gibbs-Thomson coefficient, in K·m; D is the diffusion coefficient in the liquid phase, in m. 2 / s;C1 m Often equals C e C e denoted as eutectic concentration in the alloy, in wt.%; C0 as original concentration, in wt.%; m as mass, in g; k as equilibrium distribution coefficient; ΔT′ as temperature difference between dendrite tip and root, in K.

[0072] As can be seen from the above formula, under the condition that the external conditions are determined, a and b are constants related to the material itself.

[0073] According to equation (19), when the cooling rate of a thin-walled casting increases, its local solidification time will decrease, and the secondary dendrite spacing will also decrease. Therefore, when designing a wax pattern, optimization and improvement can be made based on the original wax pattern to appropriately increase the solidification rate in order to improve the internal quality of the thin-walled casting. At the same time, because the thin-walled casting is smaller in size, it is more susceptible to thermal stress during solidification, that is, cracks are more likely to occur near the contact position between the thin-walled casting and the ingate.

[0074] In its implementation, this invention has made several optimizations and improvements to the original mold, proposing a new design and preparation method for a casting system for thin-walled castings. For example... Figures 1-3 As shown, the optimized casting system 1 mainly includes a pouring cup 11, a sprue 12, and an ingate 13. The bottom of the pouring cup 11 is a vertically arranged plate-shaped sprue 12. The ingate 13 is vertically arranged on the side of the sprue 12. One end of the ingate 13 is connected to the sprue 12, and the other end is connected to the casting 2. A shim 3 is provided at the connection between the ingate 13 and the casting 2 as needed. Holes 4 are created in the sprue 12 between some of the ingates 13 as needed. The design basis of the casting system 1 is as follows:

[0075] (1) Based on the length of the thin-walled casting, select an appropriate number of ingates, n, which is generally between 4 and 6;

[0076] (2) Determine the range of guillotine dimensions based on the casting dimensions. The dimensions of the contact surface between the guillotine and the casting should satisfy the following relationship:

[0077] a2=(5~8)b (1)

[0078] b2=(10~25)b (2)

[0079] c2=(0.5~1)c (3)

[0080] Where a2 and c2 are the length and width of the contact surface between the ingate and the casting, respectively, in mm; b2 is the thickness of the ingate, in mm; b and c are the thickness and width of the casting, respectively, in mm.

[0081] To ensure the filling speed during the casting process, based on the principle of equal flow rate, that is:

[0082] Q = SV (4)

[0083] Where Q is the flow rate of the molten metal, in mm. 3 / S; S is the cross-sectional area of ​​the gating system, in mm. 2 V represents the flow rate of the molten metal, in mm / s.

[0084] As shown in the above formula, reducing the cross-sectional area of ​​the gating system can increase the flow rate of the molten metal. Therefore, the ingate in the casting system of this invention adopts a wedge-shaped design, and the dimensions must meet the following relationship:

[0085] S2=(2~4)S2 (5)

[0086] a′2≥a2 (6)

[0087] c′2≥c2 (7)

[0088] Among them, S2 、S′2 represents the cross-sectional area of ​​the ingate in contact with the casting and the sprue, respectively, in mm². 2 a′2 and c′2 are the length and width of the contact surface between the ingate and the sprue, respectively, in mm.

[0089] For thin-walled castings with a certain curvature, the dimensions of the castings mentioned above are all linear dimensions. At the same time, the thickness of the ingate at different locations should be flexibly matched according to the relationship between the dimensions of the casting and the sprue. The calculated b2 in the above formula is the shortest thickness of the ingate.

[0090] (3) Design of sprue dimensions. The design of sprue dimensions should satisfy the following relationship:

[0091] a1=(0.6~1.1)a (8)

[0092] b1=(2~3)a′2 (9)

[0093] Where a1 and b1 are the length and thickness of the sprue (plate-shaped), respectively, a is the length of the casting, and a′2 is the length of the contact surface between the ingate and the sprue, all in mm.

[0094] When designing the width of the sprue, the minimum remaining head height must be calculated to ensure complete pouring. This requires satisfying the following relationship:

[0095]

[0096] Where c1 is the width of the sprue, c is the width of the casting, and b′2 is the maximum value of different sprue thicknesses, in mm. α is the pressure angle, typically 10° to 14°.

[0097] (4) Ingate location design. To ensure the uniformity of the heat radiation effect of the sprue on the thin-walled casting during solidification, the center position of the casting in the assembly pattern should coincide with the center position of the sprue in both length and width. At the same time, in the length direction, the distance between two adjacent ingates on the sprue should meet the following relationship from the center outward:

[0098] e1∶e2∶e3=1∶(0.6~1)∶(0.4~1) (11)

[0099] Where e1, e2, and e3 are the distances between the 1st, 2nd, and 3rd adjacent ingates from the center outwards along the length direction of the sprue, respectively, in mm.

[0100] (5) Compared to the dimensions of thin-walled castings, the sprue dimensions are larger, resulting in significant heat radiation during solidification. The larger temperature gradient not only affects the solidification rate of the casting but also easily leads to greater stress concentration. Therefore, the sprues between the ingates can be completely hollowed out as needed. The length a3 of the hollowed-out section should not exceed the corresponding ingate distance. The minimum width of the hollowed-out sprue is calculated according to the corresponding flow rate formula, i.e.:

[0101] Q≤2S3V (12)

[0102] S3=c3b1 (13)

[0103]

[0104] B1 = 1.25 + 0.25x (15)

[0105] Where Q is the flow rate of molten metal in the casting system, in mm. 3 / s; S3 is the cross-sectional area at the bottom of the cutout location, in mm. 3 V is the flow velocity of molten metal at the bottom of the hollowed-out position, in mm / s; c3 is the width of the bottom of the hollowed-out position, in mm; b1 is the thickness of the sprue, in mm; g is the acceleration due to gravity; B1 is the energy loss factor; x is the number of 90° bends in the sprue. In the casting system of this invention, x is 1 and B1 is 1.5.

[0106] (6) Add shims at the contact point between the ingate and the casting. As mentioned earlier, the dimensions of the casting differ significantly from those of the sprue. During solidification, large shrinkage stresses are easily generated at the contact point between the ingate and the casting. Simultaneously, due to the small thickness of the casting, microcracks are easily formed. To avoid this, shims can be added to locally thicken the casting, thereby reducing the equivalent stress on the casting. The dimensions of the shims should satisfy the following relationship:

[0107] a4 = a2 + (1 ~ 3) (16)

[0108] b4 = (0.5 ~ 1.5)b (17)

[0109] c4 = c2 + (1 ~ 5) (18)

[0110] Where a4, b4, and c4 are the length, thickness, and width of the gasket, a2 and c2 are the length and width of the contact surface between the ingate and the casting, and b is the thickness of the casting, all in mm.

[0111] A multi-layered shell is prepared based on the pressed wax mold. After preheating for an appropriate time, vacuum casting is carried out in a vacuum induction melting furnace.

[0112] This invention proposes a casting system design and preparation method for thin-walled castings, comprising the following steps:

[0113] (1) Wax mold pressing: using molds to press wax molds of thin-walled castings.

[0114] (2) Wax model repair: Use appropriate tools to repair the wax model, clean up the burrs and flash, and repair defects such as chipped corners, cold shuts, cracks, and bubbles.

[0115] (3) Module optimization design: smaller size sprue and ingate wax molds are used, and the sprue between the ingates is hollowed out.

[0116] (4) Wax pattern assembly: Weld the wax pattern of the casting and the gating firmly, and add a shim of appropriate size at the contact point between the ingate and the casting.

[0117] (5) Shell preparation: Dip different surface slurries into the assembled wax mold to prepare a multi-layer shell with a shell thickness of about 8mm.

[0118] (6) Dewaxing treatment: After the shell is prepared and dried, dewaxing treatment is carried out.

[0119] (7) Shell firing: The shell is fired after dewaxing.

[0120] (8) Casting: Thin-walled castings are cast using a vacuum induction furnace.

[0121] Secondary firing of the mold shell and casting process for thin-walled parts (gas pressure in the vacuum induction furnace is less than 10). -1 Pa):

[0122] 1) Shell firing temperature: (1075±30)℃;

[0123] 2) Pouring temperature: (1520±30)℃;

[0124] 3) Pouring speed: Pouring shall be completed within 3 seconds.

[0125] (9) Cooling of castings: After the castings are poured, they can be taken out of the furnace after being left for no less than 5 minutes. The outer shell of the mold is wrapped with a layer of cotton to prevent the cooling rate from being too fast.

[0126] The present invention will be further described in detail below through embodiments.

[0127] Example 1

[0128] The master alloy grade used for smelting thin-walled castings is M951, and the weight of the casting material is 5.2 kg.

[0129] The wax model design and shell preparation for the thin-walled casting are carried out according to steps (1) to (7) above. The dimensions of the designed gating system are as follows:

[0130] Table 1 Design parameters for castings and gating systems

[0131]

[0132] Thin-walled castings are poured according to steps (8) to (9) above. Parameters for the secondary firing of the mold shell and the pouring process of thin-walled castings:

[0133] 1) Shell firing temperature: 1075℃;

[0134] 2) Pouring temperature: 15-15℃;

[0135] 3) Pouring speed: Pouring is completed in 3 seconds;

[0136] 4) Casting settling time: 5 minutes.

[0137] The results show that, according to nondestructive testing, the number of internal defects in the thin-walled castings obtained by the method of this invention is significantly reduced, the number of cracks that were originally concentrated at the contact point between the ingate and the casting is significantly reduced, and the casting pass rate is increased from 43% to over 65%, which is a significant improvement.

Claims

1. A method for designing a casting system for thin-walled castings, characterized in that, The optimized casting system mainly includes a pouring cup, a sprue, and an ingate. The bottom of the pouring cup is a vertically arranged plate-shaped sprue. The ingate is vertically arranged on the side of the sprue. One end of the ingate is connected to the sprue, and the other end is connected to the casting. The design basis of the casting system is as follows: First, based on the length of the thin-walled casting, select the number of ingates n=4~6; Second, determine the size range of the ingate based on the casting dimensions. The contact surface dimensions between the ingate and the casting should satisfy the following relationship: （1） （2） （3） Where a2 and c2 are the length and width of the contact surface between the ingate and the casting, respectively, in mm; b2 is the thickness of the ingate, in mm; b and c are the thickness and width of the casting, respectively, in mm. Third, the dimensions of the sprue should be designed to meet the following relationship: （4） （5） Where a1 and b1 are the length and thickness of the plate-shaped sprue, respectively, a is the length of the casting, and a'2 is the length of the contact surface between the ingate and the sprue, all in mm; Fourth, the design of the ingate location: To ensure the uniformity of the heat radiation effect of the sprue on the thin-walled casting during solidification, the center of the casting in both length and width should coincide with the center of the sprue. Simultaneously, in the length direction, the distance between two adjacent ingates on the sprue, from the center outwards, should satisfy the following relationship: （6） Where e1, e2, and e3 are the distances between the 1st, 2nd, and 3rd adjacent ingates from the center outwards along the length direction of the sprue, respectively, in mm.

2. The method for designing a casting system for thin-walled castings according to claim 1, characterized in that, In the second item, in order to ensure the filling speed during the casting process, according to the principle of equal flow rate, that is: （7） Where Q is the flow rate of the molten metal, in mm. 3 / s; S is the cross-sectional area of ​​the gating system, in mm. 2 V represents the flow rate of the molten metal, in mm / s. According to the above formula, reducing the cross-sectional area of ​​the gating system increases the flow rate of the molten metal. The ingate in the casting system adopts a wedge-shaped design, and its dimensions must meet the following relationship: （8） （9） （10） Where S2 and S'2 are the cross-sectional areas of the ingate in contact with the casting and the sprue, respectively, in mm. 2 a'2 and c'2 are the length and width of the contact surface between the ingate and the sprue, respectively, in mm.

3. The method for designing a casting system for thin-walled castings according to claim 1, characterized in that, In the second item, for thin-walled castings with a certain curvature, b2 is the shortest thickness of the ingate.

4. The method for designing a casting system for thin-walled castings according to claim 1, characterized in that, In the third section, when designing the width of the sprue, in order to ensure complete pouring, the minimum remaining pressure head height needs to be calculated, which means the following relationship must be satisfied: （11） Where c1 is the width of the sprue, c is the width of the casting, b'2 is the maximum value of different sprue thicknesses, in mm; α is the pressure angle, which ranges from 10° to 14°.

5. The method for designing a casting system for thin-walled castings according to claim 1, characterized in that, A cutout is made in the sprue between the ingates, and the length a3 of the cutout should not exceed the corresponding distance between the ingates; the minimum width of the sprue after the cutout is calculated according to the corresponding flow rate formula, that is: （12） （13） （14） （15） Where Q is the flow rate of molten metal in the casting system, in mm. 3 / s; S3 is the cross-sectional area at the bottom of the cutout location, in mm. 3 V is the flow velocity of molten metal at the bottom of the cutout position, in mm / s; c3 is the width of the bottom of the cutout position, in mm; b1 is the thickness of the sprue, in mm; g is the acceleration due to gravity; c1 is the width of the sprue; B1 is the energy loss factor; x is the number of 90° bends in the sprue, with x taking the value of 1 and B1 taking the value of 1.

5.

6. The method for designing a casting system for thin-walled castings according to claim 5, characterized in that, Cut out the sprues between all the ingates, or cut out the sprues between some of the ingates near the middle.

7. The method for designing a casting system for thin-walled castings according to claim 1, characterized in that, A shim is added at the contact point between the ingate and the casting to locally thicken the casting and reduce the equivalent stress on it. The dimensions of the shim should meet the following relationship: （16） （17） （18） Where a4, b4, and c4 are the length, thickness, and width of the gasket, a2 and c2 are the length and width of the contact surface between the ingate and the casting, and b is the thickness of the casting, all in mm.

8. A method for preparing a thin-walled casting using a casting system designed according to the casting system design method for thin-walled castings as described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Wax pattern pressing: using molds to press wax patterns of thin-walled castings; (2) Wax model finishing: Finish the wax model, clean up the burrs and flash, and repair defects such as chipped corners, cold shuts, cracks and air bubbles. (3) Module optimization design: smaller size sprue and ingate wax molds are used, and the sprue between the ingates is hollowed out; (4) Wax pattern assembly: Weld the wax pattern of the casting and the gating firmly, and add a gasket at the contact point between the gating and the casting; (5) Shell preparation: Dip different surface layer slurries into the assembled wax mold to prepare a multi-layer shell; (6) Dewaxing: After the shell is prepared and dried, dewaxing is performed; (7) Shell firing: The shell is fired after dewaxing; (8) Casting: Thin-walled castings are cast using a vacuum induction furnace; (9) Cooling of castings: After the castings are poured, they should be placed for no less than 5 minutes before being taken out of the furnace. A layer of cotton should be wrapped around the outer surface of the mold shell to prevent the cooling rate from being too fast.

9. The method for preparing a thin-walled casting according to claim 8, characterized in that, In steps (7)-(8), the shell baking and casting process is as follows: 1) Firing temperature of the mold shell: 1075±30℃; 2) Pouring temperature: 1520±30℃; 3) Pouring speed: Pouring shall be completed within no more than 3 seconds; 4) The gas pressure of the vacuum induction furnace is less than 10. -1 Pa.

Images