A casting process for thin-walled aluminum alloy castings

Abstract

The application discloses a casting process of a thin-wall aluminum alloy casting, and belongs to the casting technical field. The main casting process is as follows: a special wax mold group tree process is designed according to the structural characteristics of the aluminum alloy thin-wall casting; a silica sol precision casting ceramic mold shell is prepared; the silica sol precision casting ceramic mold shell is placed into a sand box; a piper resin sand is used to bury the box; a casting mold box is formed; a resin sand direct sprue box is prepared; then, the hardened casting mold box and the resin sand direct sprue box are preheated at low temperature; the box is closed; the composite casting mold after the box is closed is moved into a differential pressure casting device; the differential pressure casting device is sealed and locked; differential pressure casting parameters are set; and then, differential pressure casting is carried out. The aluminum alloy thin-wall casting prepared by using the casting process has good internal quality and has no defects such as porosity, shrinkage cavity and pinhole.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal casting technology, specifically a casting process for thin-walled aluminum alloy castings. Background Technology

[0002] With the rapid development of the aviation and aerospace industry, aluminum alloy castings are being used more and more widely in the aviation and aerospace fields due to their advantages such as low price, light weight and easy recycling. Currently, aluminum alloy castings are typically produced using sand casting or precision casting. However, in actual production, we have found that using these single casting methods to prepare thin-walled aluminum alloy castings, especially those with high requirements for dimensional accuracy and internal quality, can lead to quality problems. For example, while sand casting offers good process operability and allows for relatively inexpensive optimization of the gating system design and chill settings, it is susceptible to the effects of low cavity temperature and poor molten metal flow on thin-walled aluminum alloy castings. This makes it difficult to guarantee filling quality and can easily result in defects such as incomplete filling, surface cold shuts, and pinholes. To address these issues, existing technologies often employ low-pressure casting or differential pressure casting for thin-walled aluminum alloy castings. However, due to the inherent quality of the sand mold, excessive pressure can easily lead to deformation, sand adhesion, and poor surface roughness in the produced castings. Therefore, most differential pressure castings currently use a pressure setting of (1.3-1.5)P. 充 Among them, P 充 For filling pressure, P 充 =μρgH, where H represents the distance (m) from the surface of the molten metal in the crucible to the top of the casting at the end of the filling process; ρ represents the density of the molten metal (kg / m³). 3 g represents gravitational acceleration (m / s²). 2 μ represents the filling resistance coefficient, which ranges from 1.2 to 1.5, with the lower limit for low resistance and the upper limit for high resistance. Although the mold shell of precision casting has high strength, heat resistance and surface finish, it can ensure rapid filling of the casting under high temperature preheating of the mold shell and obtain castings with accurate dimensions and smooth surface. However, due to the high temperature of the mold shell (generally, the mold shell temperature needs to reach above 350℃ when precision casting of aluminum alloy), the solidification speed of aluminum alloy is slow, which can easily cause defects such as pinholes and shrinkage porosity in the casting. In addition, the minimum wall thickness of the casting needs to be above 3.5mm. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a casting process for thin-walled aluminum alloy castings. The thin-walled aluminum alloy castings prepared using this casting process have good internal quality and are free from defects such as porosity, shrinkage cavities, and pinholes.

[0004] To achieve the above objectives, the specific solution adopted by the present invention is as follows:

[0005] A casting process for a thin-walled aluminum alloy casting mainly includes the following steps:

[0006] S1. Fabricate a silica sol precision-cast ceramic mold shell;

[0007] S2. Place the obtained silica sol precision-cast ceramic shell on the molding plate with the sprue facing down, place the sand box, put in Piper resin sand to embed the mold box and create the casting box.

[0008] S3. Construct a resin sand direct casting channel box;

[0009] S4. The hardened mold box and resin sand direct gating box are preheated at low temperature and then closed to obtain a composite mold.

[0010] S5. Place the aluminum alloy ingot in a melting furnace for melting. After melting, the aluminum alloy liquid is refined, degassed, and modified. Finally, the treated alloy liquid is poured into a crucible.

[0011] S6. Install the composite mold and the crucible (after melting) into the upper and lower tanks of the differential pressure casting device, respectively. After sealing, pour the molten aluminum alloy from the crucible into the composite mold to perform the entire process of differential pressure casting, including liquid raising, filling, pressurizing, holding, and depressurizing, thus obtaining a dense casting. After filling, the gas is discharged through the exhaust pipe of the upper tank, causing the pressure inside the upper tank to drop by (1.6-2.25)P. 充 And maintain pressure for a period of time; P 充 Indicates the pressure during filling;

[0012] S7. After depressurization is complete, open the upper tank and lift out the casting.

[0013] As a preferred option, the specific steps for fabricating the silica sol precision-cast ceramic shell in step S1 are as follows:

[0014] S11. Press the medium-temperature wax mold and gating system, and weld the wax mold and gating system together according to the assembly welding process to obtain the wax mold assembly;

[0015] S12. Place the wax model in the surface slurry and coat it. After removing it, sprinkle 50-100 mesh white corundum sand and then dry it. Repeat this process 2-3 times to obtain the surface layer of the shell on the model. The filler in the surface slurry is 270-320 mesh white corundum powder, and the binder is silica sol. The mass ratio of filler to binder is 3:1.

[0016] S13. The module with the surface layer coated is subjected to 4-5 layers of back layer slurry coating, sanding and drying treatment to obtain the back layer of the shell; wherein, the filler in the back layer slurry is 270-320 mesh mullite powder, the binder is silica sol, and the mass ratio of filler to binder is 2:1.

[0017] S14. Dewaxing is performed using a steam dewaxing kettle, followed by calcination, cleaning, and drying to obtain a silica sol precision-cast ceramic shell.

[0018] As a preferred option, in step S12, the drying temperature is 24-26℃, the humidity is controlled at 60-70%, and the drying time is not less than 8 hours.

[0019] As a preferred embodiment, in step S13, after the first application of the backing slurry, the sand sprinkled is 40-70 mesh mullite; after each subsequent application of the backing slurry, the sand sprinkled is 10-30 mesh mullite.

[0020] As a preferred option, in step S13, the drying process is carried out at a temperature of 24-26℃, a humidity of 50-60%, a wind speed of ≤6m / s, and a drying time of not less than 6 hours.

[0021] As a preferred embodiment, in step S4, the preheating temperature is 100±10℃ and the heat preservation time is 3h.

[0022] As a preferred option, in step S5, the melting temperature is 710±30℃; the refining and degassing is carried out by using a rotary jet degasser to degas the aluminum alloy liquid, and the refining time is not less than 20 minutes; the modification treatment is carried out by using a modifier to modify the aluminum alloy liquid, stirring for 3-5 minutes until it is completely dissolved, and letting it stand for not less than 15 minutes.

[0023] As a preferred embodiment, the differential pressure casting apparatus includes:

[0024] The lower tank is used to place the crucible, and the lower tank is provided with a lower air inlet pipe and a lower air outlet pipe;

[0025] An intermediate partition is placed on the open end face of the lower tank body; the intermediate partition is used to place the composite mold.

[0026] The upper tank body is covered by the composite casting mold, and the upper tank body is provided with an upper air inlet pipe and an upper exhaust pipe;

[0027] A riser pipe, used to guide the molten aluminum alloy in the crucible into the composite mold;

[0028] A locking assembly for locking the upper tank and the lower tank together.

[0029] As a preferred option, the specific process of differential pressure casting in step S6 is as follows:

[0030] S61. Gas is introduced through the upper air inlet pipe of the upper tank and the lower air inlet pipe of the lower tank, and a system pressure of 500-600 kPa is simultaneously formed in the upper and lower tanks.

[0031] S62. Stop venting to the upper and lower tanks, and discharge the gas through the upper exhaust pipe of the upper tank to reduce the pressure in the upper tank to 470-585 kPa. The aluminum alloy liquid rises into the riser pipe at a pouring temperature of 710±10℃ with a rising pressure of 15-30 kPa and a rising speed of 0.5-1.1 m / s.

[0032] S63. Continue to discharge gas through the upper exhaust pipe of the upper tank, so that the pressure inside the upper tank drops to 450-565 kPa, and the aluminum alloy liquid rises to the top of the cavity at a filling pressure of 20-40 kPa and a filling speed of 0.6-1.4 m / s.

[0033] S64. Gas is discharged again through the upper exhaust pipe of the upper tank, reducing the pressure inside the upper tank to 418-533 kPa. The aluminum alloy liquid is held under a solidification and crystallization pressurization pressure of 32-88 kPa for 450 seconds to form a dense casting.

[0034] S65. After the pressure holding is completed, the upper and lower tanks are depressurized simultaneously.

[0035] The casting process for thin-walled aluminum alloy castings provided by this invention has the following beneficial effects:

[0036] First, the casting process of this invention utilizes a precision-cast silica sol ceramic mold shell combined with Piper resin sand molding, and is completed using a differential pressure casting method. 1) This invention employs differential pressure casting, which makes filling easier, reducing incomplete filling. Furthermore, the casting process is carried out under pressure, which is beneficial for casting shrinkage compensation and reduces defects such as shrinkage porosity, shrinkage cavities, and pinholes. 2) The mold shell in this invention does not require preheating to a high temperature (below 120℃), and preheating is even unnecessary if the cavity is kept dry, enabling rapid filling and faster solidification of the molten metal, reducing defects such as pinholes and shrinkage porosity. More importantly, repeated verification has shown that the thinnest wall thickness of cast aluminum alloy parts can reach below 2.0mm. 3) Compared to traditional sand mold differential pressure casting cavities, the pre-cast silica sol precision-cast ceramic shell has high strength and good surface quality, and the pressure boosting pressure is set to (1.6-2.25)P. 充 It can still guarantee the strength of the mold shell, with no sand adhesion or deformation, while the maximum pressure boosting pressure of traditional differential pressure casting can only reach 1.5P. 充 This ensures the dimensional accuracy and surface finish of the castings, and reduces the risk of sand adhesion and deformation that are common in differential pressure casting.

[0037] Secondly, the aluminum alloy thin-walled parts produced by the casting process of this invention not only ensure the dimensional accuracy and surface finish of the castings, but also ensure the pouring and filling capacity, and have good internal quality without defects such as porosity, shrinkage cavities and pinholes, which greatly improves the yield of aluminum alloy thin-walled castings and significantly reduces production costs. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the differential pressure casting device in this invention.

[0039] Illustration markings: 1. Upper tank, 2. Casting mold box, 3. Silica sol precision casting ceramic shell, 4. Cavity, 5. Upper exhaust pipe, 6. Upper air inlet pipe, 7. Resin sand direct casting channel box, 8. Locking assembly, 9. Middle partition plate, 10. Lower exhaust pipe, 11. Lower air inlet pipe, 12. Crucible, 13. Aluminum alloy liquid, 14. Lifting pipe, 15. Lower tank. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0041] This invention designs a dedicated wax pattern assembly process based on the structural characteristics of thin-walled aluminum alloy castings. A silica sol precision-cast ceramic shell 3 is fabricated, placed inside a sand box, and embedded in it using Piper resin sand to create a casting mold box 2. A resin sand direct gating box 7 is then fabricated. The hardened casting mold box 2 and resin sand direct gating box 7 are then preheated at low temperature and assembled. The assembled composite mold is then transferred to a differential pressure casting device, sealed and locked, and after setting the differential pressure casting parameters, differential pressure casting is performed. Please refer to [reference needed]. Figure 1 The differential pressure casting apparatus used in this invention includes a lower tank 15, an intermediate partition 9, an upper tank 1, a liquid riser 14, and a locking assembly 8. The lower tank 15 is used to hold a crucible 12 and is equipped with a lower air inlet pipe 11 and a lower exhaust pipe 10. The intermediate partition 9 is placed on the open end face of the lower tank 15 and is used to hold a composite mold. The upper tank 1 covers the outside of the composite mold and is equipped with an upper air inlet pipe 6 and an upper exhaust pipe 5. The liquid riser 14 is used to guide the molten aluminum alloy 13 from the crucible 12 into the composite mold. The locking assembly 8 is used to lock the upper tank 1 and the lower tank 15 together.

[0042] Among them, the locking component 8 can be a locking ring.

[0043] The casting process for thin-walled aluminum alloy castings is described in detail below.

[0044] A casting process for a thin-walled aluminum alloy casting mainly includes the following steps:

[0045] S1. Fabricate a silica sol precision-cast ceramic mold shell;

[0046] S11. Press the medium-temperature wax mold and gating system, and weld the wax mold and gating system together according to the assembly welding process to obtain the wax mold assembly;

[0047] S12. Place the wax model in the surface slurry and coat it. After removing it, sprinkle 50-100 mesh white corundum sand and then dry it. Repeat this process 2-3 times to obtain the surface layer of the shell on the model. The filler in the surface slurry is 270-320 mesh white corundum powder, and the binder is silica sol. The mass ratio of filler to binder is 3:1.

[0048] S13. The module with the top layer coating is subjected to 4-5 applications of back layer slurry, sanding, and drying to obtain the back layer of the shell. The back layer slurry contains 270-320 mesh mullite powder as filler and silica sol as binder, with a filler to binder mass ratio of 2:1. After the first application of the back layer slurry, 40-70 mesh mullite is sprinkled; after each subsequent application of the back layer slurry, 10-30 mesh mullite is sprinkled.

[0049] S14. Dewaxing is performed using a steam dewaxing kettle, followed by calcination (calcination temperature 980-1050℃), cleaning and drying to obtain silica sol precision casting ceramic shell 3.

[0050] S2. Place the obtained silica sol precision-cast ceramic shell 3 on the molding plate with the direct sprue facing down, place the sand box, put in Piper resin sand to embed the box for molding, and make the casting box 2.

[0051] S3. Construct resin sand direct casting channel box 7;

[0052] S4. The hardened casting mold box 2 and resin sand direct pouring box 7 are subjected to low temperature preheating treatment at 100±10℃ and kept at the temperature for 3 hours. Then, the mold box is closed to obtain a composite casting mold.

[0053] S5. Place the aluminum alloy ingot in a melting furnace for melting. After melting, the aluminum alloy liquid is refined, degassed, and modified. Finally, the treated alloy liquid is poured into crucible 12.

[0054] The melting temperature is 710±30℃; the refining and degassing process uses a rotary jet degasser to degas the aluminum alloy liquid, and the refining time is not less than 20 minutes; the modification treatment uses a modifier to modify the aluminum alloy liquid, and stirs for 3-5 minutes until it is completely dissolved, and then lets it stand for not less than 15 minutes.

[0055] S6. The composite mold and the crucible 12, which has completed the melting step, are respectively installed into the upper and lower tanks 1 and 15 of the differential pressure casting device. After sealing, the molten aluminum alloy 13 in the crucible 12 is injected into the composite mold to carry out the entire process of differential pressure casting, including liquid raising, mold filling, pressurization, pressure holding, and pressure release, thus obtaining a dense casting. After filling, the gas is discharged through the upper exhaust pipe 5, causing the pressure in the upper tank 1 to drop by (1.6-2.25)P. 充 And maintain pressure for a period of time; P 充 Indicates the pressure during filling;

[0056] S61. Gas is introduced into the upper tank 1 and the lower tank 15 through the upper air inlet pipe 6 and the lower air inlet pipe 11 respectively, so that a system pressure of 500-600 kPa is simultaneously formed in the upper and lower tanks 1 and 15.

[0057] S62. Stop venting to the upper and lower tanks 1 and 15. Reduce the pressure in the upper tank 1 to 470-585 kPa through the upper exhaust pipe 5. The aluminum alloy liquid 13 rises to the riser pipe 14 at a pouring temperature of 710±30℃ with a rising pressure of 15-30 kPa and a rising speed of 0.5-1.1 m / s.

[0058] S63. Continue to discharge gas through the upper exhaust pipe 5 of the upper tank 1, so that the pressure inside the upper tank 1 drops to 450-565 kPa. The aluminum alloy liquid 13 rises to the top of the cavity 4 of the composite mold at a filling pressure of 20-40 kPa and a filling speed of 0.6-1.4 m / s. S64. Discharge gas again through the upper exhaust pipe 5 of the upper tank 1, so that the pressure inside the upper tank drops to 418-533 kPa. The aluminum alloy liquid 13 is held under a solidification and crystallization pressurization pressure of 32-88 kPa for 450 s to form a dense casting.

[0059] S65. After the pressure holding is completed, the upper and lower tanks 1 and 15 are depressurized simultaneously.

[0060] S7. After depressurization is complete, open the upper tank 1 and lift out the casting.

[0061] The casting process and the properties of the prepared castings are described below with reference to specific embodiments.

[0062] Example 1

[0063] First, the casting is 800mm high, with an outer wall thickness of 3.5mm and an inner cavity rib plate wall thickness of 2.0mm; the composition of the aluminum alloy casting and the content of each component are detailed in Table 1.

[0064] Table 1 Composition of the casting in this embodiment

[0065]

[0066] A casting process for a thin-walled aluminum alloy casting, comprising the following steps:

[0067] 1) Press the medium-temperature wax mold and gating system, and weld the wax mold and gating system together according to the assembly welding process to obtain the wax mold assembly;

[0068] 2) Place the wax model in the surface slurry and coat it. After removing it, sprinkle 50-100 mesh white corundum sand, and then perform drying treatment (temperature 24-26℃, humidity controlled at 60-70%, drying time not less than 8 hours). Repeat twice to obtain the surface layer of the shell on the model. The filler in the surface slurry is 270-320 mesh white corundum powder, and the binder is silica sol. The mass ratio of filler to binder is 3:1.

[0069] 3) The module with the top layer coating is subjected to four applications of back layer slurry, sanding, and drying treatment (drying temperature 24-26℃, humidity 50-60%, wind speed ≤6m / s, drying time not less than 6 hours) to obtain the back layer of the shell; the filler in the back layer slurry is 270-320 mesh mullite powder, the binder is silica sol, and the mass ratio of filler to binder is 2:1; after the first application of back layer slurry, the sanding material is 40-70 mesh mullite; after each subsequent application of back layer slurry, the sanding material is 10-30 mesh mullite.

[0070] 4) Dewaxing is performed using a steam dewaxing kettle, followed by calcination at 1000℃, cleaning, and drying to obtain silica sol precision casting ceramic shell 3;

[0071] 5) Transfer the silica sol precision-cast ceramic shell 3 to the sand casting workshop for embedded box molding. Place the silica sol precision-cast ceramic shell 3 with the sprue facing down on the molding plate fixed position, place the sand box, put in Piper resin sand for embedded box molding, and make the casting mold box 2.

[0072] 6) Construct the resin sand direct casting channel box;

[0073] 7) The hardened mold box 2 and resin sand direct gating box 7 are preheated at low temperature using a bogie furnace at 100±10℃ for 3 hours; then the mold box 7 and the mold box 2 are assembled from bottom to top to form a composite mold.

[0074] 8) Place the aluminum alloy ingot in a melting furnace for melting. After melting, refine, degas, and modify the molten aluminum alloy. Finally, pour the treated molten alloy into crucible 12.

[0075] Specifically, the melting temperature is 710±30℃; the refining and degassing process involves using a rotary jet degasser to degas the molten aluminum alloy for a refining time of not less than 20 minutes; the modification treatment involves using a modifier to modify the molten aluminum alloy and stirring for 3-5 minutes until it is completely dissolved, then letting it stand for not less than 15 minutes.

[0076] 9) When the temperature of the aluminum alloy liquid meets 700±10℃, cover the crucible 12 with the middle partition plate 9 and lock it with the locking ring. Move the composite mold to the middle partition plate 9, align the resin sand direct pouring box 7 with the liquid riser pipe 14 and seal the joint surface with the asbestos ring. Lock the entire composite sand mold on the middle partition plate 9 with a chain and a tensioner.

[0077] 10) Gas is introduced through the upper air inlet pipe 5 of the upper tank 1 and the lower air inlet pipe 11 of the lower tank 15, so that a system pressure of 550 kPa is simultaneously formed in the upper and lower tanks 1 and 15.

[0078] 11) Stop venting to the upper and lower tanks 1 and 15. Reduce the pressure inside the upper tank 1 to 528 kPa through the upper exhaust pipe 5 of the upper tank 1. The aluminum alloy liquid 13 rises to the riser pipe 14 at a rising pressure of 22 kPa and a rising speed of 0.78 m / s at a casting temperature of 710°C.

[0079] 12) Continue to discharge gas through the upper exhaust pipe 5 of the upper tank 1, so that the pressure in the upper tank 1 drops to 500KPa, and the aluminum alloy liquid 13 enters the cavity 4 at a filling pressure of 28KPa and a filling speed of 0.9m / s until it fills to the top of the cavity 4.

[0080] 13) Gas is discharged again through the upper exhaust pipe 5 of the upper tank 1, so that the pressure inside the upper tank 1 drops to 438KPa. The aluminum alloy liquid 13 is held under the solidification and crystallization pressure of 62Kpa for 450s to form a dense casting.

[0081] 14) After the pressure holding is completed, the upper and lower tanks 1 and 15 are depressurized at the same time. After the pressure is depressurized, the upper tank 1 is opened and the casting is lifted out.

[0082] Example 2

[0083] First, the casting is 750mm high and has an outer diameter of... The outer wall thickness is 7mm; the composition and content of each component of the aluminum alloy casting are detailed in Table 2.

[0084] Table 2 Composition table of castings in this embodiment

[0085]

[0086] A casting process for a thin-walled aluminum alloy casting, comprising the following steps:

[0087] 1) Press the medium-temperature wax mold and gating system, and weld the wax mold and gating system together according to the assembly welding process to obtain the wax mold assembly;

[0088] 2) Place the wax model in the surface slurry (the filler in the surface slurry is 270-320 mesh white corundum powder, the binder is silica sol, and the mass ratio of filler to binder is 3:1) and coat it. After removing it, sprinkle 50-100 mesh white corundum sand, and then perform drying treatment (temperature is 24-26℃, humidity is controlled at 60-70%, drying time is 10 hours). Repeat twice to obtain the surface layer of the shell on the model.

[0089] 3) The module with the top layer coating is subjected to four applications of back layer slurry, sanding, and drying treatment (drying temperature 24-26℃, humidity 50-60%, wind speed ≤6m / s, drying time 6 hours) to obtain the back layer of the shell; the filler in the back layer slurry is 270-320 mesh mullite powder, the binder is silica sol, and the mass ratio of filler to binder is 2:1; after the first application of back layer slurry, the sanding material is 40-70 mesh mullite; after the remaining three applications of back layer slurry, the sanding material is 10-30 mesh mullite;

[0090] 4) Dewaxing is performed using a steam dewaxing kettle, followed by calcination at 1050℃, cleaning, and drying to obtain silica sol precision casting ceramic shell 3;

[0091] 5) Transfer the silica sol precision-cast ceramic shell 3 to the sand casting workshop for embedded box molding. Place the silica sol precision-cast ceramic shell 3 with the sprue facing down on the molding plate fixed position, place the sand box, put in Piper resin sand for embedded box molding, and make the casting mold box 2.

[0092] 6) Construct the resin sand direct casting channel box;

[0093] 7) The hardened mold box 2 and resin sand direct gating box 7 are preheated at low temperature using a bogie furnace at 100±10℃ for 3 hours; then the mold box 7 and the mold box 2 are assembled from bottom to top to form a composite mold.

[0094] 8) Place the aluminum alloy ingot in a melting furnace for melting. After melting, the aluminum alloy liquid is refined, degassed, and modified. Finally, the treated alloy liquid is poured into crucible 12. Specifically, the melting temperature is 700℃. The refining and degasing are carried out by using a rotary jet degaussing machine to degause the aluminum alloy liquid for 25 minutes. The modification treatment is carried out by using a modifier to modify the aluminum alloy liquid and stirring for 5 minutes until it is completely dissolved, and then letting it stand for 20 minutes.

[0095] 9) When the temperature of the aluminum alloy liquid meets 700±10℃, cover the crucible 12 with the middle partition plate 9 and lock it with the locking ring. Move the composite mold to the middle partition plate 9, align the resin sand direct pouring box 7 with the liquid riser pipe 14 and seal the joint surface with the asbestos ring. Lock the entire composite sand mold on the middle partition plate 9 with a chain and a tensioner.

[0096] 10) Gas is introduced through the upper air inlet pipe 5 of the upper tank 1 and the lower air inlet pipe 11 of the lower tank 15, so that a system pressure of 550 kPa is simultaneously formed in the upper and lower tanks 1 and 15.

[0097] 11) Stop venting to the upper and lower tanks 1 and 15. Reduce the pressure inside the upper tank 1 to 526 kPa through the upper exhaust pipe 5 of the upper tank 1. The aluminum alloy liquid 13 rises to the riser pipe 14 at a rising pressure of 24 kPa and a rising speed of 0.8 m / s at a casting temperature of 710°C.

[0098] 12) Continue to discharge gas through the upper exhaust pipe 5 of the upper tank 1, so that the pressure inside the upper tank 1 drops to 500KPa, and the aluminum alloy liquid 13 enters the cavity 4 at a filling pressure of 26KPa and a filling speed of 0.78m / s until it fills to the top of the cavity 4.

[0099] 13) Gas is discharged again through the upper exhaust pipe 5 of the upper tank 1, so that the pressure inside the upper tank 1 drops to 442KPa. The aluminum alloy liquid 13 is held under the solidification and crystallization pressure of 58Kpa for 450s to form a dense casting.

[0100] 14) After the pressure holding is completed, the upper and lower tanks 1 and 15 are depressurized at the same time. After the pressure is depressurized, the upper tank 1 is opened and the casting is lifted out.

[0101] Comparative Example 1

[0102] The only difference between Comparative Example 1 and Example 1 is that: 1) In step 5), 50-80 quartz sand is used for the buried box molding; 2) In step 13), the gas is discharged again through the upper exhaust pipe 5 of the upper tank 1, so that the pressure in the upper tank 1 drops to 458KPa, and the aluminum alloy liquid is held under the solidification and crystallization pressure of 42Kpa for 450s.

[0103] Comparative Example 2

[0104] The only difference between Comparative Example 2 and Example 2 is that: 1) In step 5), 50-80 quartz sand is used for the buried box molding; 2) In step 13), the gas is discharged again through the upper exhaust pipe 5 of the upper tank 1, so that the pressure in the upper tank 1 drops to 458KPa, and the aluminum alloy liquid is held under the solidification and crystallization pressurization pressure of 39Kpa (26*1.5) for 450s.

[0105] The performance test results of the castings prepared in Examples 1-2 and Comparative Examples 1-2 are detailed in Table 3.

[0106] Table 3. Performance test results of castings prepared in Examples 1-2 and Comparative Examples 1-2

[0107]

[0108] As shown in Table 3, the aluminum alloy thin-walled castings prepared using the casting process of the present invention have superior dimensional accuracy and surface finish, as well as good internal quality, free from defects such as porosity, shrinkage cavities, and pinholes. Furthermore, the overall mechanical properties of the products can be significantly improved, greatly increasing the yield of aluminum alloy thin-walled castings.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A casting process for thin-walled aluminum alloy castings, characterized in that, The main steps include the following: S1. Fabricate a silica sol precision-cast ceramic mold shell; S2. Place the obtained silica sol precision-cast ceramic shell on the molding plate with the sprue facing down, place the sand box, put in Piper resin sand to embed the mold box and create the casting box. S3. Construct a resin sand direct casting channel box; S4. The hardened mold box and resin sand direct gating box are preheated at low temperature and then closed to obtain a composite mold. S5. Place the aluminum alloy ingot in a melting furnace for melting. After melting, the aluminum alloy liquid is refined, degassed, and modified. Finally, the treated alloy liquid is poured into a crucible. S6. Install the composite mold and the crucible (after melting) into the upper and lower tanks of the differential pressure casting device, respectively. After sealing, pour the molten aluminum alloy from the crucible into the composite mold to perform the entire process of differential pressure casting, including liquid raising, filling, pressurizing, holding, and depressurizing, thus obtaining a dense casting. After filling, the gas is discharged through the exhaust pipe of the upper tank, causing the pressure inside the upper tank to drop by (1.6-2.25)P. 充 And maintain pressure for a period of time; P 充 Indicates the pressure during filling; S7. After depressurization is complete, open the upper tank and lift out the casting. In step S6, the specific process of differential pressure casting is as follows: S61. Gas is introduced through the upper air inlet pipe of the upper tank and the lower air inlet pipe of the lower tank, and a system pressure of 500~600Kpa is simultaneously formed in the upper and lower tanks. S62. Stop venting to the upper and lower tanks, and discharge the gas through the upper exhaust pipe of the upper tank to reduce the pressure in the upper tank to 470~585KPa. The aluminum alloy liquid rises into the riser pipe at a pouring temperature of 710±30℃ with a rising pressure of 15~30Kpa and a rising speed of 0.5~1.1m / s. S63. Continue to discharge gas through the upper exhaust pipe of the upper tank, so that the pressure inside the upper tank drops to 450~565KPa, and the aluminum alloy liquid rises to the top of the cavity at a filling pressure of 20~40KPa and a filling speed of 0.6~1.4m / s. S64. Gas is discharged again through the upper exhaust pipe of the upper tank, reducing the pressure inside the upper tank to 418~533KPa. The aluminum alloy liquid is held under the solidification and crystallization pressure of 32-88Kpa for 450s to form a dense casting. S65. After the pressure holding is completed, the upper and lower tanks are depressurized simultaneously.

2. The casting process for a thin-walled aluminum alloy casting according to claim 1, characterized in that, In step S1, the specific steps for fabricating the silica sol precision-cast ceramic shell are as follows: S11. Press the medium-temperature wax mold and gating system, and weld the wax mold and gating system together according to the assembly welding process to obtain the wax mold assembly; S12. Place the wax model in the surface slurry and coat it. After removing it, sprinkle 50-100 mesh white corundum sand and then dry it. Repeat this process 2-3 times to obtain the surface layer of the shell on the model. The filler in the surface slurry is 270-320 mesh white corundum powder, and the binder is silica sol. The mass ratio of filler to binder is 3:

1. S13. The module with the top layer is coated with back layer slurry 4-5 times, then sanded and dried to obtain the back layer of the shell; wherein, the filler in the back layer slurry is 270-320 mesh mullite powder, the binder is silica sol, and the mass ratio of filler to binder is 2:

1. S14. Dewaxing is performed using a steam dewaxing kettle, followed by calcination, cleaning, and drying to obtain a silica sol precision-cast ceramic shell.

3. The casting process for a thin-walled aluminum alloy casting according to claim 2, characterized in that, In step S12, the drying temperature is 24-26℃, the humidity is controlled at 60-70%, and the drying time is not less than 8 hours.

4. The casting process for a thin-walled aluminum alloy casting according to claim 2, characterized in that, In step S13, after the first application of the backing slurry, the sand sprinkled is 40-70 mesh mullite; after each subsequent application of the backing slurry, the sand sprinkled is 10-30 mesh mullite.

5. The casting process for a thin-walled aluminum alloy casting according to claim 2, characterized in that, In step S13, the drying process is carried out at a temperature of 24-26℃, a humidity of 50-60%, a wind speed of ≤6m / s, and a drying time of not less than 6 hours.

6. The casting process for a thin-walled aluminum alloy casting according to claim 1, characterized in that, In step S4, the preheating temperature is 100±10℃ and the holding time is 3h.

7. The casting process for a thin-walled aluminum alloy casting according to claim 1, characterized in that, In step S5, the melting temperature is 710±30℃; the refining and degassing process involves using a rotary jet degasser to degas the aluminum alloy liquid, with a refining time of not less than 20 minutes; the modification treatment involves using a modifier to modify the aluminum alloy liquid, stirring for 3-5 minutes until it is completely dissolved, and then letting it stand for not less than 15 minutes.

8. The casting process for a thin-walled aluminum alloy casting according to claim 1, characterized in that, The differential pressure casting apparatus includes: The lower tank is used to place the crucible, and the lower tank is provided with a lower air inlet pipe and a lower air outlet pipe; An intermediate partition is placed on the open end face of the lower tank body; the intermediate partition is used to place the composite mold. The upper tank body is covered by the composite casting mold, and the upper tank body is provided with an upper air inlet pipe and an upper exhaust pipe; A riser pipe, used to guide the molten aluminum alloy in the crucible into the composite mold; A locking assembly for locking the upper tank and the lower tank together.

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