A lightweight aluminum alloy casting low-pressure forming device and operating process

Abstract

The present invention discloses a low-pressure forming device and operation process for lightweight aluminum alloy castings, including a holding furnace installed on a lifting base and equipped with a riser pipe, a clamping cylinder installed on a bracket, an upper mold installed at the lower end of the clamping cylinder, a lower mold arranged below the upper mold, a connecting pipe adapted to the output end of an air compressor arranged on the outer wall of the holding furnace, a pressure relief pipe also arranged on the holding furnace, and further including a gas rapid filling unit. By setting the gas rapid filling unit, a large amount of nitrogen can be rapidly filled into the furnace, reducing the inflation time and greatly improving the working efficiency of the low-pressure casting machine. Moreover, by discharging the nitrogen in the furnace to the hollow pipe for the first time, the gas rapid filling unit can be reused. At the same time, the gravity of a heavy object is used to squeeze the nitrogen to maintain the furnace pressure within a set constant pressure range, which is also applicable even for different liquid levels of the aluminum alloy melt in the furnace.

Description

Technical Field

[0001] The present invention relates to the technical field of low-pressure casting of aluminum alloys, and particularly relates to a low-pressure forming device and operation process for lightweight aluminum alloy castings. Background Art

[0002] When lightweight aluminum alloy castings are made, a low-pressure casting machine is generally used for casting. The low-pressure casting machine includes upper and lower molds, a holding furnace with a riser tube, and an air compressor for adding inert gas (generally nitrogen) into the holding furnace. When the low-pressure casting machine works, nitrogen is first filled into the holding furnace by the air compressor. When the air pressure in the furnace reaches a certain value, the molten aluminum alloy solution begins to rise and enters the mold. After the mold cavity is filled, pressure is applied (which can make the liquid aluminum alloy fill the mold cavity more fully, reduce defects such as pores and looseness inside the casting, thereby improving the density and overall quality of the casting. Applying pressure helps the liquid metal form a denser structure during solidification, which is particularly important for castings that require high strength and good mechanical properties), and after the pressure is applied to the set value, pressure holding is carried out. After the casting in the mold is cooled and solidified by the cooling system in the mold, pressure relief treatment is carried out (pressure relief is carried out through the pressure relief pipeline on the holding furnace), so that the aluminum alloy solution in the riser tube flows back into the holding furnace.

[0003] For the existing low-pressure casting machine, affected by factors such as the exhaust volume of the air compressor, the size of the holding furnace, and the amount of aluminum alloy melt in the holding furnace, in the process of filling nitrogen into the holding furnace by the air compressor and making the aluminum alloy melt in the riser tube start to rise, conventionally, it takes at least not less than 3 minutes. For a larger holding furnace with less aluminum alloy melt, it takes more than ten minutes or even longer, seriously affecting the working efficiency of the entire low-pressure casting machine. Therefore, the present application provides a low-pressure forming device and operation process for lightweight aluminum alloy castings to meet the requirements. Summary of the Invention

[0004] The purpose of the present application is to provide a low-pressure forming device and operation process for lightweight aluminum alloy castings to solve the technical problems raised in the above background.

[0005] To achieve the above object, the present application provides the following technical solutions: A low-pressure forming device for lightweight aluminum alloy castings, comprising a holding furnace installed on a lifting base and equipped with a lifting pipe, a clamping cylinder installed on a bracket, an upper mold installed at the lower end of the clamping cylinder, a lower mold arranged below the upper mold, a connecting pipe adapted to the output end of an air compressor arranged on the outer wall of the holding furnace, a pressure relief pipe also arranged on the holding furnace, and further comprising a gas rapid filling unit. Before aluminum alloy casting, inert gas can be rapidly filled into the holding furnace, so that the air pressure in the holding furnace is rapidly maintained within a constant range, and within this range, the aluminum alloy solution in the lifting pipe does not rise.

[0006] As a preferred implementation manner in this embodiment, the gas rapid filling unit includes a hollow tube with an open upper end and a closed lower end, and a heavy object slidably installed in the inner cavity of the hollow tube;

[0007] An elastic sealing sleeve is arranged on the outer wall of the heavy object, and the outer wall of the elastic sealing sleeve is in sliding contact with the inner wall of the hollow tube;

[0008] A plurality of main pipes are arranged on the outer wall of the hollow tube, and electric valves are arranged on each of the plurality of main pipes. The air outlet ends of the plurality of main pipes are hermetically docked with corresponding branch pipes at the upper end of the holding furnace, and the plurality of branch pipes communicate with the inner cavity of the holding furnace;

[0009] A pressure sensor is further arranged in the inner cavity of the air outlet of the main pipe, and both the pressure sensor and the electric valve are electrically connected to a controller.

[0010] As a preferred implementation manner in this embodiment, a pressure relief unit is further included to prevent the heavy object from being ejected out of the hollow tube by air pressure, and at the same time prevent the air pressure in the holding furnace from not being maintained within a constant range when the hollow tube injects gas into the holding furnace subsequently.

[0011] As a preferred implementation manner in this embodiment, the pressure relief unit includes an exhaust pipe penetrating through the heavy object and a mounting bracket installed at the upper end of the hollow tube and provided with a toothed rod;

[0012] A ball valve is installed on the exhaust pipe, and a driving gear ring is installed on the outer wall of the handwheel of the ball valve, and the toothed rod is correspondingly arranged with the driving gear ring;

[0013] A limiting protrusion is arranged on the outer wall of the elastic sealing sleeve, and a limiting chute adapted to the limiting protrusion is arranged in the inner cavity of the hollow tube.

[0014] As a preferred implementation manner in this embodiment, a variable resistance unit is further included, which can automatically change the resistance between the heavy object and the inner wall of the hollow tube according to the magnitude of the air pressure, and the resistance is proportional to the air pressure.

[0015] As a preferred implementation manner in this embodiment, the variable resistance unit includes an extrusion cavity provided inside the heavy object, and the air inlet end of the extrusion cavity is sealed by an elastic diaphragm.

[0016] As a preferred implementation manner in this embodiment, a plurality of arc-shaped extrusion rods are arranged in a circle in the extrusion cavity, an extrusion plate installed at the upper end of the elastic diaphragm, and a plurality of movable rods rotatably arranged in the extrusion cavity through pin shafts;

[0017] A plurality of mounting plates are slidably arranged on the extrusion plate through sliders, the lower end of the movable rod is rotatably connected to the corresponding mounting plate, the upper end of the movable rod is slidably abutted against the end of the corresponding abutting rod, and the abutting rod is fixedly installed on the corresponding arc-shaped extrusion rod;

[0018] The outer end of the arc-shaped extrusion rod contacts the inner wall of the elastic sealing sleeve;

[0019] The pin shaft is located above the middle of the movable rod.

[0020] An operation process of a low-pressure forming device for lightweight aluminum alloy castings includes the following steps.

[0021] S1: Inflation. First, open the electric valve 9, and quickly squeeze the nitrogen in the hollow tube 10 into the holding furnace 2 through the gravity of the heavy object 11, and maintain the air pressure in the furnace within a set constant pressure range. Subsequently, precise pressurization is performed by the air compressor.

[0022] S2: Nitrogen reflux. When the casting in the cavity is solidified and the holding furnace 2 performs the first pressure relief, open the electric valve 9, so that the nitrogen in the holding furnace 2 enters the hollow tube 10, and finally maintain the air pressure in the furnace within the set constant pressure range.

[0023] S3: When performing subsequent pressure relief, directly perform pressure relief through the pressure relief pipeline on the holding furnace 2.

[0024] In summary, the technical effects and advantages of the present invention:

[0025] The structure of the present invention is reasonable. A gas rapid filling unit is provided, which can quickly fill a large amount of nitrogen into the furnace, reduce the inflation time, and greatly improve the working efficiency of the low-pressure casting machine. And by relieving the pressure of the nitrogen in the furnace to the hollow tube for the first time, the gas rapid filling unit can be reused. At the same time, the gravity of the heavy object is used to squeeze nitrogen to maintain the air pressure in the furnace within the set constant pressure range, which is also applicable even for different liquid levels of the aluminum alloy melt in the furnace.

[0026] In the present invention, a pressure relief unit is provided to prevent the heavy object from being pushed out of the hollow tube by the air pressure, and also to prevent the air pressure in the holding furnace from being unable to be maintained within a constant range when the hollow tube subsequently injects gas into the holding furnace.

[0027] In the present invention, a variable resistance unit is provided to prevent the heavy object from moving too fast, thereby causing severe friction of the elastic sealing sleeve, resulting in tooth collapse and requiring long-term stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0030] Figure 2 for Figure 1 Schematic diagram of the structure of the gas rapid filling unit;

[0031] Figure 3 for Figure 2 Schematic diagram of the medium and heavy object structure;

[0032] Figure 4 for Figure 3 Schematic diagram of the structure of medium and heavy objects viewed from above;

[0033] Figure 5 for Figure 4 Schematic diagram of the cross-sectional structure of a medium-heavy object;

[0034] Figure 6 for Figure 5 Enlarged structural diagram at point A in the middle

[0035] Figure 7 for Figure 2 Schematic diagram of the partial cross-section structure of the middle main pipe.

[0036] In the figure: 1. Lifting base; 2. Holding furnace; 3. Lower mold; 4. Upper mold; 5. Bracket; 6. Opening and closing cylinder; 7. Branch pipe; 8. Main pipe; 9. Electric valve; 10. Hollow pipe; 11. Weight; 12. Elastic sealing sleeve; 13. Limiting protrusion; 14. Exhaust pipe; 15. Ball valve; 16. Drive gear ring; 17. Mounting frame; 18. Gear rod; 19. Elastic diaphragm; 20. Extrusion chamber; 21. Arc-shaped extrusion rod; 22. Resistance rod; 23. Movable rod; 24. Extrusion plate; 25. Mounting plate; 26. Pin; 27. Slider; 28. Air pressure sensor; 29. Limiting slide rod. Detailed implementation manners

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] Embodiment: Refer to Figure 1 A low-pressure forming device for lightweight aluminum alloy castings as shown, which includes a holding furnace 2 installed on a lifting base 1 and having a liquid-riser pipe, a clamping cylinder 6 installed on a bracket 5, an upper mold 4 installed at the lower end of the clamping cylinder 6, a lower mold 3 arranged below the upper mold 4, a connecting pipe adapted to the output end of an air compressor is arranged on the outer wall of the holding furnace 2, a pressure relief pipe is also arranged on the holding furnace 2, and further includes a gas rapid filling unit. Before aluminum alloy casting, inert gas can be rapidly filled into the holding furnace 2, so that the air pressure in the holding furnace 2 can be rapidly maintained within a constant range, and within this range, the aluminum alloy solution in the liquid-riser pipe does not rise.

[0039] As a preferred implementation manner in this embodiment, as Figures 1-4 and Figure 7 shown, the gas rapid filling unit includes a hollow tube 10 with an open upper end and a closed lower end, and a heavy object 11 slidably installed in the inner cavity of the hollow tube 10;

[0040] An elastic sealing sleeve 12 is arranged on the outer wall of the heavy object 11, and the outer wall of the elastic sealing sleeve 12 is slidably abutted against the inner wall of the hollow tube 10;

[0041] A plurality of main pipes 8 are arranged on the outer wall of the hollow tube 10, and electric valves 9 are arranged on all the main pipes 8. The air outlet ends of the plurality of main pipes 8 are hermetically butted with corresponding branch pipes 7 at the upper end of the holding furnace 2, and the plurality of branch pipes 7 communicate with the inner cavity of the holding furnace 2;

[0042] It further includes a pressure sensor 28 arranged in the inner cavity of the air outlet of the main pipe 8, and both the pressure sensor 28 and the electric valve 9 are electrically connected to a controller.

[0043] Before the casting in the holding furnace 2 starts, the inside of the holding furnace 2 is in an atmospheric pressure state. At this time, all the electric valves 9 can be opened through the controller. At this time, the nitrogen gas stored inside the hollow tube 10 is transported into the holding furnace 2 by the gravity of the heavy object 11. Due to the gravity of the heavy object 11, the air pressure inside the holding furnace 2 is squeezed and maintained within a set constant pressure range (when the air pressure inside the furnace is within this constant pressure range, there is no flow of the molten metal in the riser tube). The air pressure inside the furnace is detected by the pressure sensor 28. When the inside of the furnace stabilizes within the set constant pressure range, the controller controls the electric valve 9 to close. After that, the air compressor precisely pressurizes the inside of the furnace, causing the molten metal in the riser tube to rise and enter the cavity for casting, and then pressurization (the air pressure inside the furnace increases significantly compared to before) and pressure holding are carried out. When performing the first pressure relief, to ensure that the nitrogen gas can return to the hollow tube 10 for subsequent use, the electric valve 9 can be controlled to open at this time, enabling the nitrogen gas inside the furnace to enter the hollow tube 10 and lift the heavy object 11 upward by a certain height and then remain stable. At this time, the air pressure in the hollow tube 10 is balanced with that inside the furnace. When the air pressure sensor 28 detects that the air pressure inside the furnace stabilizes within the set constant pressure range, the electric valve 9 is controlled to close. At this time, the aluminum alloy molten metal in the riser tube flows back into the furnace. When performing the second pressure relief later, the automatic pressure relief pipeline on the holding furnace 2 can be directly used for pressure relief. The air pressure inside the furnace after this pressure relief is maintained within the set constant pressure range (it is not necessary to use the gravity of the heavy object 11 to squeeze the nitrogen gas in the hollow tube 10 to inflate the furnace). That is, each holding furnace 2 only needs to use the gravity of the heavy object 11 to send the nitrogen gas in the hollow tube 10 into the furnace at the beginning, which can quickly fill a large amount of nitrogen gas into the furnace, reduce the inflation time, and greatly improve the working efficiency of the low-pressure casting machine. Moreover, by relieving the nitrogen gas pressure inside the furnace to the hollow tube 10 for the first time, the gas filling unit can be reused. At the same time, the gravity of the heavy object 11 is used to squeeze the nitrogen gas to maintain the air pressure inside the furnace to reach the set constant pressure range, which is also applicable even for different liquid levels of the aluminum alloy molten metal inside the furnace.

[0044] It should be noted that: First, an air inlet pipe with a one-way inflation head is provided on the hollow tube 10 to facilitate the inflation of nitrogen gas into the hollow tube 10; Second, the gravity of the heavy object 11 can be increased or decreased as needed to adjust the constant pressure range inside the furnace; Third, the set constant pressure range should be less than the air pressure inside the furnace when the molten metal in the riser tube rises. Because the gravity of the heavy object 11 cannot make the molten metal in the riser tube flow at a constant speed, and the uniform injection of the molten metal into the cavity is beneficial to improving the mechanical properties of the casting. Therefore, only the gravity of the heavy object 11 is used to make the air pressure inside the furnace reach the set constant pressure range, and then the air compressor system is used for precise adjustment of the air pressure; Fourth, an elastic sealing ring is provided at the upper end of the branch pipe 7. The holding furnace 2 is lifted by the lifting base 1 to make the pipe orifice of the branch pipe 7 contact with that of the main pipe 8 to form a seal.

[0045] As a preferred implementation scheme in this embodiment, it also includes a pressure relief unit to prevent the heavy object 11 from being pushed out of the hollow tube 10 by air pressure, and also to prevent the subsequent hollow tube 10 from injecting gas into the insulation furnace 2, causing the air pressure in the insulation furnace 2 to be unable to be maintained within a constant range.

[0046] At the beginning, when the pressure in the furnace is relieved for the first time and the liquid level of the melt in the furnace is very low, since there is a pressurization stage before the pressure relief, the air pressure at this time is higher than the set range and the amount of nitrogen in the furnace is also large. After the pressure relief, it is easy to cause the heavy object 11 to be lifted to a very high height or even out of the hollow tube 10. Therefore, a pressure relief unit is set to allow the excess nitrogen in the hollow tube 10 to be discharged.

[0047] As a preferred implementation in this embodiment, Figure 3 As shown, the pressure relief unit includes an exhaust pipe 14 provided through the weight 11 and a mounting bracket 17 mounted on the upper end of the hollow tube 10 and having a gear rod 18;

[0048] A ball valve 15 is installed on the exhaust pipe 14, and a drive gear ring 16 is installed on the outer wall of the hand-cranked wheel of the ball valve 15, and a gear rod 18 is provided corresponding to the drive gear ring 16;

[0049] A limiting protrusion 13 is provided on the outer wall of the elastic sealing sleeve 12 , and a limiting sliding groove adapted to the limiting protrusion 13 is provided in the inner cavity of the hollow tube 10 .

[0050] During the first pressure relief, under the action of the gas pressure in the furnace, the weight 11 rises. As the weight 11 rises, the driving gear ring 16 on the ball valve 15 arranged thereon engages with the gear rod 18, and the passage of the exhaust pipe 14 is opened. The nitrogen in the hollow tube 10 is discharged from the exhaust pipe 14 until the hollow tube 10 and the gas pressure in the furnace reach a balance within the set constant pressure range.

[0051] It should be noted that the function of the limiting protrusion 13 is to prevent the weight 11 from rotating when moving upward or downward, so as to prevent the positions of the driving gear ring 16 and the gear rod 18 from changing and failing to engage with each other.

[0052] As a preferred implementation in this embodiment, a variable resistance unit is also included, which can automatically change the resistance between the weight 11 and the inner wall of the hollow tube 10 according to the size of the air pressure, and the resistance is proportional to the air pressure.

[0053] When starting to fill nitrogen into the furnace, the heavy object 11 moves downward in the hollow tube 10. First, it undergoes an accelerating motion with a continuously decreasing acceleration. When the speed reaches the maximum, it then undergoes a decelerating motion until it stops. At this time, due to the excessive air pressure below, that is, the air pressure is greater than the sum of the weight of the heavy object 11 and the frictional resistance it receives, the heavy object 11 will move upward for a certain distance. This process repeats up and down until the heavy object 11 stabilizes and the air pressure in the furnace becomes stable. When relieving pressure, the heavy object 11 moves upward in the hollow tube 10. The heavy object 11 first undergoes an accelerating motion with a continuously decreasing acceleration. When the speed reaches the maximum, it then undergoes a decelerating motion until the speed becomes zero, and then the heavy object will move downward for a certain distance and then recover. When the heavy object 11 moves upward or downward, it is likely to cause the moving speed to be too fast. An excessive moving speed will cause the elastic sealing sleeve 12 and the hollow tube 10 to form relatively intense friction, affecting the service life of the elastic sealing sleeve 12. Moreover, an excessive moving speed is likely to cause the driving gear ring 16 and the gear rod 18 to collide violently, easily resulting in the phenomenon of tooth breakage. At the same time, it also makes the heavy object 11 take a relatively long time to achieve stability (at this time, the air pressure inside the tube and in the furnace is within the set constant pressure range).

[0054] As a preferred implementation manner in this embodiment, as Figure 4 and Figure 5 shown, the variable resistance unit includes an extrusion cavity 20 provided inside the heavy object 11, and the air inlet end of the extrusion cavity 20 is sealed by an elastic diaphragm 19.

[0055] During inflation, when the electric valve 9 is suddenly opened, the air pressure inside the hollow tube 10 rapidly decreases. When the heavy object 11 starts to move downward, the extrusion force acting on the elastic diaphragm 19 suddenly decreases, that is, the resistance to the downward movement of the heavy object 11 decreases. As the heavy object moves downward, the air pressure inside the hollow tube 10 becomes greater and greater, and the extrusion force acting on the elastic diaphragm 19 becomes greater and greater, causing the elastic diaphragm 19 to be more concave. The extrusion cavity 20 is squeezed, causing part of the elastic sealing sleeve 12 (the part whose inner wall is directly located inside the extrusion cavity 20) to expand outward and form an extrusion with the inner wall of the hollow tube 10, thereby slowly increasing the resistance received by the heavy object and finally reducing the moving speed of the heavy object 11 to avoid the moving speed of the heavy object 11 from being too fast. During pressure relief, when the electric valve 9 is suddenly opened, the air pressure in the furnace rapidly enters the hollow tube 10, and the air pressure inside the hollow tube 10 rapidly increases. At this time, the extrusion force acting on the elastic diaphragm 19 becomes greater, and the resistance to the upward movement of the heavy object 11 becomes greater. As the heavy object 11 moves upward, the air pressure inside the hollow tube 10 becomes lower and lower, and the extrusion force acting on the elastic diaphragm 19 becomes smaller and smaller, and the resistance received by the heavy object 11 becomes smaller and smaller, effectively avoiding the moving speed of the heavy object 11 from being too fast.

[0056] As a preferred implementation manner in this embodiment, as Figures 4-6As shown, a plurality of arc-shaped extrusion rods 21 are arranged in a circle in the extrusion cavity 20, an extrusion plate 24 mounted on the upper end of the elastic diaphragm 19, and a plurality of movable rods 23 rotatably arranged in the extrusion cavity 20 through a pin shaft 26;

[0057] A plurality of mounting plates 25 are slidably arranged on the extrusion plate 24 through sliders 27. The lower ends of the movable rods 23 are rotatably connected to the corresponding mounting plates 25. The upper ends of the movable rods 23 are slidably abutted against the ends of the corresponding abutting rods 22. The abutting rods 22 are fixedly mounted on the corresponding arc-shaped extrusion rods 21;

[0058] The outer ends of the arc-shaped extrusion rods 21 are in contact with the inner wall of the elastic seal sleeve 12;

[0059] The pin shaft 26 is located above the middle of the movable rod 23.

[0060] When the elastic diaphragm 19 is squeezed, the lower ends of the plurality of movable rods 23 will rotate counterclockwise, thereby squeezing and abutting against the abutting rods 22, and finally causing the arc-shaped extrusion rods 21 to squeeze the elastic seal sleeve 12. During the whole process, the mounting plates 25 always slide on the extrusion plate 24. Since the pin shaft 26 and the movable rod 23 cooperate to form a labor-saving lever, the variable resistance unit can achieve a good variable resistance effect and effectively prevent the problem of the excessive movement speed of the heavy object 11.

[0061] It should be noted that, first, both ends of the extrusion plate 24 are provided with limit slide rods 29, and the ends of the two limit slide rods 29 away from the extrusion plate 24 are slidably arranged in the chutes provided on the inner wall of the extrusion cavity 20, so that the extrusion plate 24 moves along the vertical direction, which can make the forces on the respective movable rods 23 balanced, is beneficial to smoothly reduce the speed, and at the same time prevents serious wear of a certain part of the elastic seal sleeve and affects its service life; second, limit cavities adapted to the arc-shaped extrusion rods 21 and the abutting rods 22 are respectively arranged in the extrusion cavity 20.

[0062] An operation process of a lightweight aluminum alloy casting low-pressure forming device includes the following steps

[0063] S1: Inflation. First, open the electric valve 9. Through the gravity of the heavy object 11, the nitrogen in the hollow tube 10 is quickly squeezed and sent to the heat preservation furnace 2, and the air pressure in the furnace is maintained within a set constant pressure range. Subsequently, precise pressurization is carried out by an air compressor;

[0064] S2: Nitrogen reflux. When the casting in the mold cavity is solidified and the heat preservation furnace 2 performs the first pressure relief, open the electric valve 9, so that the nitrogen in the heat preservation furnace 2 enters the hollow tube 10, and finally the air pressure in the furnace is maintained within the set constant pressure range

[0065] S3: When performing subsequent pressure relief, the pressure relief can be directly carried out through the pressure relief pipeline on the heat preservation furnace 2.

[0066] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A low-pressure forming device for lightweight aluminum alloy castings, comprising a holding furnace (2) installed on a lifting base (1) and equipped with a lifting pipe, a clamping cylinder (6) installed on a bracket (5), an upper mold (4) installed at the lower end of the clamping cylinder (6), a lower mold (3) arranged below the upper mold (4), a connecting pipe adapted to the output end of an air compressor is arranged on the outer wall of the holding furnace (2), and a pressure relief pipe is further arranged on the holding furnace (2), characterized in that: It further includes a gas rapid filling unit, which can rapidly fill inert gas into the holding furnace (2) before aluminum alloy casting, so that the air pressure in the holding furnace (2) is rapidly maintained within a constant range, and within this range, the aluminum alloy solution in the riser pipe does not rise; The gas rapid filling unit includes a hollow tube (10) with an open upper end and a closed lower end, and a heavy object (11) slidably installed in the inner cavity of the hollow tube (10); An elastic sealing sleeve (12) is arranged on the outer wall of the heavy object (11), and the outer wall of the elastic sealing sleeve (12) is in sliding contact with the inner wall of the hollow tube (10); A plurality of main pipes (8) are arranged on the outer wall of the hollow tube (10), and electric valves (9) are arranged on each of the plurality of main pipes (8). The air outlet ends of the plurality of main pipes (8) are hermetically docked with the corresponding branch pipes (7) at the upper end of the holding furnace (2), and the plurality of branch pipes (7) communicate with the inner cavity of the holding furnace (2); It further includes a pressure sensor (28) arranged in the inner cavity of the air outlet of the main pipe (8), and both the pressure sensor (28) and the electric valve (9) are electrically connected to a controller; It further includes a pressure relief unit to prevent the heavy object (11) from being ejected out of the hollow tube (10) by air pressure, and at the same time prevent the air pressure in the holding furnace (2) from not being maintained within a constant range when the hollow tube (10) injects gas into the holding furnace (2) subsequently; The pressure relief unit includes an exhaust pipe (14) penetrating through the heavy object (11) and a mounting frame (17) installed at the upper end of the hollow tube (10) and provided with a rack (18); A ball valve (15) is installed on the exhaust pipe (14), and a driving gear ring (16) is installed on the outer wall of the handwheel of the ball valve (15), and the rack (18) is arranged corresponding to the driving gear ring (16); A limiting protrusion (13) is arranged on the outer wall of the elastic sealing sleeve (12), and a limiting sliding groove adapted to the limiting protrusion (13) is arranged in the inner cavity of the hollow tube (10).

2. The low-pressure molding device for lightweight aluminum alloy castings according to claim 1, wherein: It further includes a variable resistance unit, which can automatically change the resistance between the heavy object (11) and the inner wall of the hollow tube (10) according to the magnitude of the air pressure, and the resistance is proportional to the air pressure.

3. A low-pressure forming device for lightweight aluminum alloy castings according to claim 2, characterized in that: The variable resistance unit includes an extrusion cavity (20) arranged inside the heavy object (11), and the air inlet end of the extrusion cavity (20) is sealed by an elastic diaphragm (19).

4. A low-pressure forming device for lightweight aluminum alloy castings according to claim 3, characterized in that: A plurality of arc-shaped extrusion rods (21) are arranged in a circular pattern in the extrusion cavity (20), an extrusion plate (24) installed at the upper end of the elastic diaphragm (19), and a plurality of movable rods (23) rotatably arranged in the extrusion cavity (20) through pin shafts (26); A plurality of mounting plates (25) are slidably arranged on the extrusion plate (24) through sliders (27). The lower ends of the movable rods (23) are rotatably connected to the corresponding mounting plates (25), the upper ends of the movable rods (23) are in sliding contact with the ends of the corresponding abutting rods (22), and the abutting rods (22) are fixedly installed on the corresponding arc-shaped extrusion rods (21); The outer end of the arc-shaped extrusion rod (21) contacts the inner wall of the elastic sealing sleeve (12); The pin shaft (26) is located above the middle of the movable rod (23).

5. The operating process of a low-pressure molding device for lightweight aluminum alloy castings according to any one of claims 1-4, characterized in that: The method includes the following steps: S1: Inflation. First, open the electric valve (9), and use the gravity of the heavy object (11) to quickly squeeze the nitrogen in the hollow tube (10) into the heat preservation furnace (2), and maintain the air pressure in the furnace within a set constant pressure range. Subsequently, precise pressurization is carried out by the air compressor; S2: Nitrogen reflux. When the casting in the cavity is solidified and the heat preservation furnace (2) undergoes the first pressure relief, open the electric valve (9) so that the nitrogen in the heat preservation furnace (2) enters the hollow tube (10), and finally maintain the air pressure in the furnace within the set constant pressure range; S3: When subsequent pressure relief is required, pressure relief can be directly carried out through the pressure relief pipeline on the heat preservation furnace (2).

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