CN115740371A - Casting process of thin-wall aluminum alloy casting - Google Patents

Abstract

The invention discloses a casting process of a thin-wall aluminum alloy casting, which belongs to the technical field of casting, and mainly comprises the steps of designing a special wax module tree process according to the structural characteristics of the aluminum alloy thin-wall casting, manufacturing a silica sol precision casting ceramic shell, putting the silica sol precision casting ceramic shell into a sand box, embedding the sand box with a filler resin, manufacturing a casting box, manufacturing a resin sand sprue box, preheating the hardened casting box and the resin sand sprue box at low temperature, assembling the boxes, moving the assembled composite casting mold into a differential pressure casting device, sealing, locking, setting differential pressure casting parameters, and performing differential pressure casting. The aluminum alloy thin-wall casting prepared by the casting process has good internal quality and does not have the defects of looseness, shrinkage cavities, pinholes and the like.

Description

Casting process of thin-wall aluminum alloy casting

Technical Field

The invention relates to the technical field of casting of non-ferrous metal castings, in particular to a casting process of a thin-wall aluminum alloy casting.

Background

With the rapid development of the aviation and aerospace industries, aluminum alloy castings are more and more widely applied to the aviation and aerospace fields due to the advantages of low price, light weight, easiness in recovery and the like. At present, sand casting or precision casting is generally adopted as a casting method of aluminum alloy castings, but in actual production, the fact that when the thin-wall aluminum alloy castings, especially the thin-wall aluminum alloy castings with high dimensional precision and internal quality requirements, are prepared by adopting the single casting method is found to have quality problems, for example, although sand casting has good process operability, cheaper process optimization can be carried out on the design of a casting head system and the arrangement of a chill, for the thin-wall aluminum alloy castings, sand casting is easily influenced by low cavity temperature and poor metal liquid fluidity, the filling quality is difficult to guarantee, and the easy occurrence of the problem is easily causedThe casting has the defects of insufficient casting, surface cold shut, pinholes and the like, in order to solve the problems of insufficient casting, cold shut and pinholes, low-pressure casting or differential pressure casting is usually adopted for casting thin-wall aluminum alloy castings in the prior art, but the problems of deformation, sand adhesion and poor surface roughness of the produced castings are easily caused by the influence of the quality of a sand mold and once the pressurizing pressure is set to be too high, so that most of the pressurizing pressure in differential pressure casting is set to be (1.3-1.5) P _{Charging (CN)} (ii) a Wherein, P _{Charging (CN)} For filling pressure, P _{Charging device} H represents the distance (m) from the liquid level of the crucible to the top end of the casting at the end of filling; ρ represents the density (kg/m) of molten metal ³ ) (ii) a g represents the acceleration of gravity (m/s) ² ) (ii) a Mu represents the filling resistance coefficient, the value is 1.2-1.5, the lower limit is taken for small resistance, and the upper limit is taken for large resistance; although the precision casting mold shell has high strength, heat resistance and surface smoothness, the casting can be well ensured to be quickly filled under the condition of preheating the mold shell at high temperature, and the casting with accurate size and smooth surface can be obtained, because the mold shell temperature is higher (the mold shell temperature needs to reach more than 350 ℃ in the process of casting aluminum alloy precision casting), the defects of casting pinholes, shrinkage porosity and the like are easily caused because the solidification speed of the aluminum alloy is slow, and the wall thickness of the minimum casting cast part needs to be more than 3.5 mm.

Disclosure of Invention

In order to solve the defects in the prior art, the invention provides a casting process of a thin-wall aluminum alloy casting, and the aluminum alloy thin-wall casting prepared by the casting process has good internal quality and does not have the defects of looseness, shrinkage cavities, pinholes and the like.

In order to achieve the purpose, the invention adopts the specific scheme that:

a casting process of a thin-wall aluminum alloy casting mainly comprises the following steps:

s1, manufacturing a silica sol precision casting ceramic shell;

s2, placing the obtained silica sol precision casting ceramic shell on a moulding flat plate in a state that a sprue is downward, placing a sand box, and placing general resin sand for embedding and moulding to form a casting mould box;

s3, manufacturing a resin sand straight pouring channel box;

s4, preheating the hardened casting box and the resin sand straight pouring channel box at a low temperature, and closing the box to obtain a composite casting mold;

s5, placing the aluminum alloy ingot in a smelting furnace for smelting, and refining, degassing and modifying aluminum alloy liquid after smelting; finally, injecting the treated alloy liquid into a crucible;

s6, respectively installing the composite casting mold and the crucible which finishes the smelting step into an upper tank body and a lower tank body of a differential pressure casting device, and injecting aluminum alloy liquid in the crucible into the composite casting mold after sealing to carry out the whole process of liquid lifting, mold filling, pressurization, pressure maintaining and pressure relief of differential pressure casting, so as to obtain a casting with compact structure; wherein, after the filling is finished, the gas is discharged through the exhaust pipe of the upper tank body, so that the pressure in the upper tank body is reduced by (1.6-2.25) P _{Charging (CN)} And maintaining the pressure for a period of time; p _{Charging device} Indicating the pressure at the time of filling;

and S7, after pressure relief is finished, opening the upper tank body, and lifting out the casting.

Preferably, in step S1, the specific steps of manufacturing the silica sol precision-cast ceramic shell are as follows:

s11, pressing a medium-temperature wax mold and a casting head system, and performing assembly welding on the wax mold and the casting head system according to an assembly welding process to obtain a wax mold set;

s12, placing the wax mould set in the surface layer slurry for hanging coating, after the wax mould set is taken out, scattering 50-100 meshes of white corundum sand, then drying, and repeating for 2-3 times to obtain a surface layer of the shell on the mould set; wherein, the filler in the surface layer slurry is 270-320 meshes of white corundum powder, the binder is silica sol, and the mass ratio of the filler to the binder is 3;

s13, carrying out coating and hanging, sanding and drying treatment on the back layer slurry for 4-5 times on the module coated with the surface layer to obtain the back layer of the shell; wherein, the filler in the back layer slurry is 270-320 meshes of mullite sand powder, the binder is silica sol, and the mass ratio of the filler to the binder is 2;

s14, dewaxing by using a steam dewaxing kettle, and then roasting, cleaning and airing to obtain the silica sol precision casting ceramic shell.

Preferably, in step S12, the temperature during drying treatment is 24-26 deg.C, the humidity is controlled at 60-70%, and the drying time is not less than 8 hr.

Preferably, in step S13, after the first coating of the back layer slurry, the sand material is sprinkled to be 40-70 mesh mullite sand; after the other times of coating the back layer slurry, the sand material is 10-30 meshes of mullite sand.

Preferably, in step S13, the temperature is 24-26 deg.C, humidity is 50-60%, wind speed is less than or equal to 6m/S, and air drying time is not less than 6 hr.

Preferably, in step S4, the preheating temperature is 100 +/-10 ℃, and the holding time is 3h.

Preferably, in the step S5, the smelting temperature is 710 +/-30 ℃; refining degassing is to carry out degassing on the aluminum alloy liquid by adopting a rotary blowing degassing machine, and the refining time is not less than 20min; the modification treatment is to adopt modifier to modify the aluminum alloy liquid, stir for 3-5min until all aluminum alloy liquid is dissolved, and stand for no less than 15min.

Preferably, the differential pressure casting apparatus includes:

the lower tank body is used for placing a crucible, and a lower air inlet pipe and a lower air outlet pipe are arranged on the lower tank body;

the middle partition plate is arranged on the opening end face of the lower tank body; the middle partition plate is used for placing a composite casting mold;

the upper tank body covers the outer part of the composite casting mold, and an upper air inlet pipe and an upper air outlet pipe are arranged on the upper tank body;

the liquid lifting pipe is used for guiding the aluminum alloy liquid in the crucible into the composite casting mold;

and the locking assembly is used for locking the upper tank body and the lower tank body.

Preferably, in step S6, the differential pressure casting specifically comprises the following steps:

s61, introducing gas through an upper gas inlet pipe of the upper tank body and a lower gas inlet pipe of the lower tank body, and synchronously forming system pressure of 500-600 Kpa in the upper tank body and the lower tank body;

s62, stopping ventilating the upper tank body and the lower tank body, discharging gas through an upper exhaust pipe of the upper tank body, reducing the pressure in the upper tank body to 470-585 KPa, and raising the aluminum alloy liquid into a liquid lifting pipe at the casting temperature of 710 +/-10 ℃ at the liquid lifting pressure of 15-30 KPa and the liquid lifting speed of 0.5-1.1 m/S;

s63, continuously exhausting gas through an upper exhaust pipe of the upper tank body, reducing the pressure in the upper tank body to 450-565 KPa, and raising the mold filling pressure of the aluminum alloy liquid to the top of the cavity at the mold filling speed of 0.6-1.4 m/S and the mold filling pressure of 20-40 KPa;

s64, exhausting gas through an upper exhaust pipe of the upper tank body again to reduce the pressure in the upper tank body to 418-533 KPa, and maintaining the pressure of the aluminum alloy liquid for 450S under the solidification crystallization pressurization pressure of 32-88KPa to form a casting with a compact structure;

s65, after the pressure maintaining is finished, the upper tank body and the lower tank body are simultaneously decompressed.

The casting process of the thin-wall aluminum alloy casting provided by the invention has the following beneficial effects:

firstly, the casting process is completed by matching a precision casting silica sol ceramic mould shell with a general resin sand model and by adopting a counter-pressure casting mode, 1) the counter-pressure casting process is more easily filled to reduce the phenomenon of insufficient casting, and the casting process is carried out under pressure, so that the casting feeding is facilitated, and the defects of shrinkage porosity, shrinkage cavity, pinholes and the like are reduced; 2) The formwork in the invention can realize rapid filling without preheating at a high temperature (below 120 ℃) even under the condition of ensuring the drying of a cavity, the solidification of molten metal is quicker, the generation of defects such as pinholes, shrinkage porosity and the like is reduced, and more importantly, the thinnest wall thickness of a cast aluminum alloy casting can reach below 2.0mm through repeated verification; 3) Compared with the traditional sand differential pressure casting cavity, the prefabricated silica sol precision casting ceramic shell has high strength and good surface quality, and the pressurizing pressure is set to (1.6-2.25) P _{Charging device} Can still ensure the strength of the mould shell without sand sticking and deformation, and the highest pressurizing pressure of the traditional differential pressure casting can only reach 1.5P _{Charging (CN)} The size precision and the surface smoothness of the casting are ensured, and the risk of sand dipping and deformation easily caused by differential pressure pouring is reduced.

Secondly, the aluminum alloy thin-wall part produced by adopting the casting process of the invention not only ensures the size precision and the surface smoothness of the casting, but also can well ensure the pouring and filling capacity, has good internal quality and does not have the defects of looseness, shrinkage holes, pinholes and the like, greatly improves the yield of the aluminum alloy thin-wall casting and greatly reduces the production cost.

Drawings

FIG. 1 is a schematic view showing the construction of a differential pressure casting apparatus according to the present invention.

The graphic symbols are: 1. the device comprises an upper tank body, 2 a casting box, 3 a silica sol precision casting ceramic shell, 4 a cavity, 5 an upper exhaust pipe, 6 an upper exhaust pipe, 7 a resin sand sprue box, 8 a locking assembly, 9 a middle partition plate, 10 a lower exhaust pipe, 11 a lower intake pipe, 12 a crucible, 13 aluminum alloy liquid, 14 a riser pipe, 15 and a lower tank body.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to specific embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, belong to the scope of the present invention.

The invention designs a special wax module tree process according to the structural characteristics of an aluminum alloy thin-wall casting, manufactures a silica sol precision casting ceramic shell 3, puts the silica sol precision casting ceramic shell 3 into a sand box, buries the box with Papu resin sand, manufactures a casting box 2, manufactures a resin sand sprue box 7, then preheats the hardened casting box 2 and the resin sand sprue box 7 at low temperature, closes the box, moves the closed composite casting mould into a differential pressure casting device, seals and locks, and carries out differential pressure casting after setting differential pressure casting parameters. Referring to fig. 1, the counter-pressure casting apparatus used in the present invention includes a lower tank 15, a middle partition 9, an upper tank 1, a lift pipe 14 and a locking assembly 8, wherein the lower tank 15 is used for placing a crucible 12, and the lower tank 15 is provided with a lower inlet pipe 11 and a lower outlet pipe 10; the middle partition plate 9 is arranged on the opening end face of the lower tank body 15; the middle partition plate 9 is used for placing a composite casting mold; the upper tank body 1 covers the outside of the composite casting mold, and an upper air inlet pipe 6 and an upper air outlet pipe 5 are arranged on the upper tank body 1; the liquid lifting pipe 14 is used for introducing the aluminum alloy liquid 13 in the crucible 12 into the composite casting mold; the locking assembly 8 is used for locking the upper tank 1 and the lower tank 15.

Wherein, locking assembly 8 can choose the locking ring.

The casting process of the aluminum alloy thin-wall casting is explained in detail below.

A casting process of a thin-wall aluminum alloy casting mainly comprises the following steps:

s1, manufacturing a silica sol precision casting ceramic shell;

s11, pressing a medium-temperature wax mold and a casting head system, and performing assembly welding on the wax mold and the casting head system according to an assembly welding process to obtain a wax mold set;

s12, placing the wax mould set in the surface layer slurry for hanging coating, after the wax mould set is taken out, scattering 50-100 meshes of white corundum sand, then drying, and repeating for 2-3 times to obtain a surface layer of the shell on the mould set; wherein, the filler in the surface layer slurry is 270-320 meshes of white corundum powder, the binder is silica sol, and the mass ratio of the filler to the binder is 3;

s13, coating and hanging the back layer slurry, sanding and drying the module coated with the surface layer for 4-5 times to obtain the back layer of the shell; wherein the filler in the back layer slurry is 270-320 meshes of mullite sand powder, the binder is silica sol, and the mass ratio of the filler to the binder is 2; after the first coating of the back layer slurry, the sand material is 40-70 meshes of mullite sand; after the other coating back layer slurry, the sand material is 10-30 meshes mullite sand;

s14, dewaxing by using a steam dewaxing kettle, then roasting (the roasting temperature is 980-1050 ℃), cleaning and airing to obtain a silica sol precision casting ceramic shell 3;

s2, placing the obtained silica sol precision casting ceramic shell 3 on a moulding flat plate in a sprue-downward state, placing a sand box, placing common resin sand for embedding and moulding, and moulding a casting mould box 2;

s3, manufacturing a resin sand straight pouring channel box 7;

s4, performing low-temperature preheating treatment at 100 +/-10 ℃ on the hardened casting box 2 and the resin sand sprue box 7, preserving heat for 3 hours, and then performing box closing treatment to obtain a composite casting mold;

s5, placing the aluminum alloy ingot in a smelting furnace for smelting, and refining, degassing and modifying aluminum alloy liquid after smelting; finally, the processed alloy liquid is injected into the crucible 12;

the smelting temperature is 710 +/-30 ℃; the refining degassing is to carry out degassing on the aluminum alloy liquid by adopting a rotary blowing degassing machine, and the refining time is not less than 20min; modifying by using modifier, stirring for 3-5min until the aluminum alloy is completely dissolved, and standing for no less than 15min;

s6, respectively installing the composite casting mold and the crucible 12 which finishes the smelting step into an upper tank body 1 and a lower tank body 15 of a differential pressure casting device, sealing, and injecting the aluminum alloy liquid 13 in the crucible 12 into the composite casting mold to carry out the whole processes of liquid lifting, mold filling, pressurization, pressure maintaining and pressure relief of differential pressure casting, thereby obtaining a casting with compact structure; wherein, after the mold filling is finished, the pressure in the upper tank body 1 is reduced (1.6-2.25) by discharging gas through the upper exhaust pipe 5 _{Charging device} And maintaining the pressure for a period of time; p _{Charging device} Indicating the pressure at the time of filling;

s61, respectively introducing gas into the upper tank body 1 and the lower tank body 15 through the upper gas inlet pipe 6 and the lower gas inlet pipe 11, and synchronously forming system pressure of 500-600 Kpa in the upper tank body 1 and the lower tank body 15;

s62, stopping ventilation to the upper tank body 1 and the lower tank body 15, reducing the pressure in the upper tank body 1 to 470-585 KPa through the upper exhaust pipe 5, and raising the aluminum alloy liquid 13 into a lift pipe 14 at the casting temperature of 710 +/-30 ℃ at the lift pressure of 15-30 KPa and the lift speed of 0.5-1.1 m/S;

s63, continuously exhausting gas through the upper exhaust pipe 5 of the upper tank body 1 to reduce the pressure in the upper tank body 1 to 450-565 KPa, and raising the mold filling pressure of the aluminum alloy liquid 13 to the top of the cavity 4 of the composite casting mold at 20-40 KPa and the mold filling speed of 0.6-1.4 m/S; s64, discharging gas through the upper exhaust pipe 5 of the upper tank body 1 again to reduce the pressure in the upper tank body to 418-533 KPa, and maintaining the pressure of the aluminum alloy liquid 13 for 450S under the solidification crystallization pressurization pressure of 32-88KPa to form a casting with a compact structure;

s65, after the pressure maintaining is finished, the upper tank body 1 and the lower tank body 15 are simultaneously decompressed.

And S7, after pressure relief is finished, opening the upper tank body 1, and lifting out the casting.

The casting process and the properties of the prepared castings are explained below with reference to specific examples.

Example 1

Firstly, the height of a casting is 800mm, the external wall thickness is 3.5mm, and the wall thickness of an inner cavity rib plate is 2.0mm; the composition of the aluminum alloy castings and the contents of the components are detailed in table 1.

TABLE 1 composition Table of cast article in this example

A casting process of an aluminum alloy thin-wall casting comprises the following steps:

1) Pressing the medium-temperature wax mold and the casting head system, and assembling and welding the wax mold and the casting head system according to an assembling and welding process to obtain a wax mold group;

2) Placing the wax mould set in the surface layer slurry for coating in a hanging way, after taking out, scattering 50-100 meshes of white corundum sand, then carrying out drying treatment (the temperature is 24-26 ℃, the humidity is controlled at 60-70%, the drying time is not less than 8 hours), and repeating for 2 times to obtain the surface layer of the shell on the mould set; wherein, the filler in the surface layer slurry is 270-320 meshes of white corundum powder, the binder is silica sol, and the mass ratio of the filler to the binder is 3;

3) Coating and hanging the back layer slurry, sanding and drying the module coated with the surface layer for 4 times (the temperature is 24-26 ℃, the humidity is 50-60%, the wind speed is less than or equal to 6m/s, and the air drying time is not less than 6 hours during the drying treatment), so as to obtain the back layer of the shell; wherein, the filler in the back layer slurry is 270-320 meshes of mullite sand powder, the binder is silica sol, and the mass ratio of the filler to the binder is 2; after the first coating of the back layer slurry, the sand material is 40-70 meshes of mullite sand; after the other times of coating the back layer slurry, the sand material is 10-30 meshes of mullite sand;

4) Dewaxing by using a steam dewaxing kettle, and then roasting, cleaning and airing at 1000 ℃ to prepare a silica sol precision casting ceramic shell 3;

5) Transferring the silica sol precision casting ceramic shell 3 to a sand casting workshop for embedding and molding, placing a sprue of the silica sol precision casting ceramic shell 3 downwards at a fixed position of a molding flat plate, placing a sand box, placing common resin sand for embedding and molding, and manufacturing a casting molding box 2;

6) Manufacturing a resin sand sprue box 7;

7) Preheating the hardened casting box 2 and the resin sand sprue box 7 at low temperature by adopting a trolley furnace, keeping the temperature at 100 +/-10 ℃ for 3 hours; then assembling and assembling the mold from bottom to top according to the sequence of the resin sand sprue box 7 and the casting mold box 2 to obtain a composite casting mold;

8) Placing the aluminum alloy ingot in a smelting furnace for smelting, and refining, degassing and modifying aluminum alloy liquid after smelting; finally, the processed alloy liquid is injected into the crucible 12;

in detail, the smelting temperature is 710 +/-30 ℃; the refining degassing is to carry out degassing on the aluminum alloy liquid by adopting a rotary blowing degassing machine, and the refining time is not less than 20min; modifying by using modifier, stirring for 3-5min until the aluminum alloy is completely dissolved, and standing for no less than 15min;

9) When the temperature of the aluminum alloy liquid meets 700 +/-10 ℃, covering a middle partition plate 9 on a crucible 12, locking by using a locking ring, moving the composite casting mold to the middle partition plate 9, aligning a resin sand sprue box 7 to a liquid lifting pipe 14, sealing a joint surface by using an asbestos ring, and locking the whole composite sand mold on the middle partition plate 9 by using a chain tightener;

10 Introducing gas through an upper gas inlet pipe 5 of the upper tank body 1 and a lower gas inlet pipe 11 of the lower tank body 15, and synchronously forming system pressure of 550Kpa in the upper tank body 1 and the lower tank body 15;

11 Stopping introducing air into the upper and lower tank bodies 1 and 15, reducing the pressure in the upper tank body 1 to 528KPa through the upper exhaust pipe 5 of the upper tank body 1, and raising the liquid aluminum alloy 13 into the liquid lifting pipe 14 at the liquid lifting pressure of 22KPa and the liquid lifting speed of 0.78m/s at the pouring temperature of 710 ℃;

12 Continuously exhausting gas through an upper exhaust pipe 5 of the upper tank body 1 to reduce the pressure in the upper tank body 1 to 500KPa, and feeding aluminum alloy liquid 13 into the cavity 4 to the top of the cavity 4 at the mold filling pressure of 28KPa and the mold filling speed of 0.9 m/s;

13 And) discharging gas again through the upper exhaust pipe 5 of the upper tank body 1 to reduce the pressure in the upper tank body 1 to 438KPa, and maintaining the pressure of the aluminum alloy liquid 13 for 450s under the solidification crystallization pressurization pressure of 62KPa to form a casting with a compact structure;

14 And (4) after pressure maintaining is finished, simultaneously releasing the pressure of the upper tank body 1 and the lower tank body 15, opening the upper tank body 1 after pressure releasing is finished, and lifting out the casting.

Example 2

First, the casting is 750mm high and has an outer diameter

The external wall thickness is 7mm; the components and the contents of the components of the aluminum alloy casting are detailed in table 2.

Table 2 composition table of casting in this example

A casting process of an aluminum alloy thin-wall casting comprises the following steps:

1) Pressing the medium-temperature wax mold and the casting head system, and assembling and welding the wax mold and the casting head system according to an assembling and welding process to obtain a wax mold group;

2) Placing the wax mould set in surface layer slurry (the filler in the surface layer slurry is 270-320 meshes of white corundum powder, the binder is silica sol, and the mass ratio of the filler to the binder is 3);

3) Coating back layer slurry, sanding and drying the module coated with the surface layer for 4 times (the temperature is 24-26 ℃, the humidity is 50-60%, the wind speed is less than or equal to 6m/s, and the air drying time is 6 hours) to obtain the back layer of the shell; wherein, the filler in the back layer slurry is 270-320 meshes of mullite sand powder, the binder is silica sol, and the mass ratio of the filler to the binder is 2; after the first coating of the back layer slurry, the sand material is 40-70 meshes of mullite sand; after the coating of the back layer slurry for the rest 3 times, the sand material is 10-30 meshes of mullite sand;

4) Dewaxing by using a steam dewaxing kettle, and then carrying out baking at 1050 ℃, cleaning and airing treatment to obtain a silica sol precision casting ceramic shell 3;

5) Transferring the silica sol precision casting ceramic shell 3 to a sand casting workshop for embedding and molding, placing a sprue of the silica sol precision casting ceramic shell 3 downwards at a fixed position of a molding flat plate, placing a sand box, placing common resin sand for embedding and molding, and manufacturing a casting mold box 2;

6) Manufacturing a resin sand straight pouring channel box 7;

7) Preheating the hardened casting box 2 and the resin sand sprue box 7 at low temperature by adopting a trolley furnace, keeping the temperature at 100 +/-10 ℃ for 3 hours; then assembling and assembling the mold from bottom to top according to the sequence of the resin sand sprue box 7 and the casting mold box 2 to obtain a composite casting mold;

8) Placing the aluminum alloy ingot in a smelting furnace for smelting, and refining, degassing and modifying aluminum alloy liquid after smelting; finally, the processed alloy liquid is injected into the crucible 12; in detail, the smelting temperature is 700 ℃; refining degassing is to perform degassing on the aluminum alloy liquid by adopting a rotary blowing degassing machine, wherein the refining time is 25min; modifying by using modifier, stirring for 5min until all aluminum alloy liquid is dissolved, and standing for 20min;

9) When the temperature of the aluminum alloy liquid meets 700 +/-10 ℃, covering a middle partition plate 9 on a crucible 12, locking by using a locking ring, moving the composite casting mold to the middle partition plate 9, aligning a resin sand sprue box 7 to a liquid lifting pipe 14, sealing a joint surface by using an asbestos ring, and locking the whole composite sand mold on the middle partition plate 9 by using a chain tightener;

10 Introducing gas through an upper gas inlet pipe 5 of the upper tank body 1 and a lower gas inlet pipe 11 of the lower tank body 15, and synchronously forming system pressure of 550Kpa in the upper tank body 1 and the lower tank body 15;

11 Stopping introducing air into the upper and lower tank bodies 1,15, reducing the pressure in the upper tank body 1 to 526KPa through the upper exhaust pipe 5 of the upper tank body 1, and raising the molten aluminum alloy 13 into the lift pipe 14 at a lift pressure of 24KPa and a lift speed of 0.8m/s at a casting temperature of 710 ℃;

12 Continuously exhausting gas through an upper exhaust pipe 5 of the upper tank body 1 to reduce the pressure in the upper tank body 1 to 500KPa, and feeding aluminum alloy liquid 13 into the cavity 4 at the mold filling pressure of 26KPa and the mold filling speed of 0.78m/s until the mold is filled to the top of the cavity 4;

13 B), discharging gas through an upper exhaust pipe 5 of the upper tank body 1 again to reduce the pressure in the upper tank body 1 to 442KPa, and maintaining the pressure of the aluminum alloy liquid 13 for 450s under the solidification crystallization pressurization pressure of 58KPa to form a casting with compact structure;

14 And (4) after pressure maintaining is finished, simultaneously releasing the pressure of the upper tank body 1 and the lower tank body 15, opening the upper tank body 1 after pressure releasing is finished, and lifting out the casting.

Comparative example 1

Comparative example 1 differs from example 1 only in that: 1) In the step 5), 50-80 quartz sand is adopted for carrying out embedded molding; 2) And step 13), the gas is exhausted again through the upper exhaust pipe 5 of the upper tank body 1, so that the pressure in the upper tank body 1 is reduced to 458KPa, and the pressure of the aluminum alloy liquid is maintained for 450s under the solidification crystallization pressurization pressure of 42 KPa.

Comparative example 2

Comparative example 2 differs from example 2 only in that: 1) In the step 5), 50-80 quartz sand is adopted for carrying out embedded molding; 2) And step 13), the gas is discharged again through the upper vent pipe 5 of the upper tank 1, the pressure in the upper tank 1 is reduced to 458KPa, and the pressure of the aluminum alloy liquid is maintained for 450s at the solidification crystallization pressurization pressure of 39KPa (26 × 1.5).

The results of the performance tests on the castings prepared in examples 1-2 and comparative examples 1-2 are detailed in Table 3.

TABLE 3 results of the property test of the castings prepared in examples 1-2 and comparative examples 1-2

As can be seen from Table 3, the aluminum alloy thin-wall casting prepared by the casting process of the invention has the advantages of excellent dimensional accuracy and surface finish, good internal quality, no defects of looseness, shrinkage cavities, pinholes and the like, and can greatly improve the overall mechanical properties of the product and the yield of the aluminum alloy thin-wall casting.

The foregoing is merely a preferred embodiment of the invention and is not to be construed as limiting the invention in any way. All equivalent changes and modifications made according to the spirit of the present invention should be covered in the protection scope of the present invention.

Claims (9)

1. The casting process of the thin-wall aluminum alloy casting is characterized by mainly comprising the following steps of:

s1, manufacturing a silica sol precision casting ceramic shell;

s2, placing the obtained silica sol precision casting ceramic shell on a moulding flat plate in a state that a sprue is downward, placing a sand box, placing common resin sand for embedding and moulding, and moulding a casting mould box;

s3, manufacturing a resin sand straight pouring channel box;

s4, preheating the hardened casting box and the resin sand straight pouring channel box at a low temperature, and closing the box to obtain a composite casting mold;

s5, placing the aluminum alloy ingot into a smelting furnace for smelting, and refining, degassing and modifying aluminum alloy liquid after smelting; finally, injecting the treated alloy liquid into a crucible;

s6, respectively installing the composite casting mold and the crucible which finishes the smelting step into an upper tank body and a lower tank body of a differential pressure casting device, sealing, and injecting aluminum alloy liquid in the crucible into the composite casting mold to carry out the whole processes of liquid lifting, mold filling, pressurization, pressure maintaining and pressure relief of differential pressure casting, so as to obtain a casting with compact tissue; wherein, after the filling is finished, the gas is exhausted through the exhaust pipe of the upper tank body, so that the pressure in the upper tank body is reduced by (1.6-2.25) P _{Charging device} And maintaining the pressure for a period of time; p _{Charging device} Indicating the pressure at the time of filling;

and S7, after pressure relief is finished, opening the upper tank body, and lifting out the casting.

2. A casting process of a thin-wall aluminum alloy casting according to claim 1, wherein in the step S1, the specific steps of manufacturing the silica sol precision casting ceramic shell are as follows:

s11, pressing a medium-temperature wax mold and a casting head system, and performing assembly welding on the wax mold and the casting head system according to an assembly welding process to obtain a wax mold set;

s12, placing the wax mould set in the surface layer slurry for hanging coating, after the wax mould set is taken out, scattering 50-100 meshes of white corundum sand, then drying, and repeating for 2-3 times to obtain a surface layer of the shell on the mould set; wherein, the filler in the surface layer slurry is 270-320 meshes of white corundum powder, the binder is silica sol, and the mass ratio of the filler to the binder is 3;

s13, coating the back layer slurry on the surface layer coated module for 4-5 times, sanding and drying to obtain the back layer of the shell; wherein, the filler in the back layer slurry is 270-320 meshes of mullite sand powder, the binder is silica sol, and the mass ratio of the filler to the binder is 2;

s14, dewaxing by using a steam dewaxing kettle, and then roasting, cleaning and airing to obtain the silica sol precision casting ceramic shell.

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

4. A casting process of a thin-walled aluminum alloy casting according to claim 2, wherein in step S13, after the first application of the backing layer slurry, the sand is 40-70 mesh mullite sand; after the other times of coating the back layer slurry, the sand material is 10-30 meshes of mullite sand.

5. A casting process of a thin-wall aluminum alloy casting according to claim 2, wherein in the step S13, the temperature is 24-26 ℃, the humidity is 50-60%, the wind speed is less than or equal to 6m/S, and the air drying time is not less than 6 hours.

6. A casting process of a thin-walled aluminum alloy casting according to claim 1, wherein in step S4, the preheating temperature is 100 +/-10 ℃ and the holding time is 3 hours.

7. A casting process of a thin-wall aluminum alloy casting according to claim 1, wherein in the step S5, the melting temperature is 710 ± 30 ℃; the refining degassing is to carry out degassing on the aluminum alloy liquid by adopting a rotary blowing degassing machine, and the refining time is not less than 20min; the modification treatment is to modify the aluminum alloy liquid by using modifier, stir for 3-5min until all aluminum alloy liquid is dissolved, and stand for no less than 15min.

8. A casting process of a thin-walled aluminum alloy casting according to claim 1, wherein the counter-pressure casting apparatus comprises:

the lower tank body is used for placing a crucible, and a lower air inlet pipe and a lower air outlet pipe are arranged on the lower tank body;

the middle partition plate is arranged on the opening end face of the lower tank body; the middle partition plate is used for placing the composite casting mold;

the upper tank body covers the outside of the composite casting mold, and an upper air inlet pipe and an upper air outlet pipe are arranged on the upper tank body;

a riser tube for introducing the aluminum alloy liquid in the crucible into the composite casting mold;

and the locking assembly is used for locking the upper tank body and the lower tank body.

9. The casting process of the thin-wall aluminum alloy casting, according to the claim 8, is characterized in that in the step S6, the differential pressure casting is carried out by the following specific processes:

s61, introducing gas through an upper gas inlet pipe of the upper tank body and a lower gas inlet pipe of the lower tank body, and synchronously forming system pressure of 500 to 600Kpa in the upper tank body and the lower tank body;

s62, stopping ventilating the upper tank body and the lower tank body, discharging gas through an upper exhaust pipe of the upper tank body, reducing the pressure in the upper tank body to 470 to 585KPa, and raising the liquid aluminum alloy liquid into a liquid lifting pipe at the pouring temperature of 710 +/-30 ℃ at the liquid lifting pressure of 15 to 30KPa and the liquid lifting speed of 0.5 to 1.1m/S;

s63, continuously exhausting gas through an upper exhaust pipe of the upper tank body, reducing the pressure in the upper tank body to 450 to 565KPa, and increasing the filling pressure of the aluminum alloy liquid to 40KPa and the filling speed of 0.6 to 1.4m/S to the top of the cavity;

s64, exhausting gas through an upper exhaust pipe of the upper tank body again to reduce the pressure in the upper tank body to 418 to 533KPa, and maintaining the pressure of an aluminum alloy liquid for 450S under the solidification crystallization pressurization pressure of 32 to 88KPa to form a casting with a compact structure;

s65, after the pressure maintaining is finished, the upper tank body and the lower tank body are simultaneously decompressed.

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