Method for casting hollow casting at high pressure

Abstract

The invention discloses a method for casting a hollow casting at high pressure. The method comprises the following steps: manufacturing a hollow aluminum tube into a required shape; ceramic particles are guided into the aluminum pipe and vibrated to be compacted, the two ends of the aluminum pipe are sealed, and a mold core is obtained; the mold core is put into a die-casting mold, aluminum alloy melt is pressed into the die-casting mold for die-casting forming, demolding and cooling are conducted after solidification, and a casting is obtained; and removing seals at the two ends of the aluminum pipe of the mold core, and blowing out all the ceramic particles in the aluminum pipe to obtain the hollow casting. The mold core disclosed by the invention has the advantages of good strength, easiness in operation, no pollution, low cost and wide application range.

Description

Technical Field

[0001] The invention relates to the technical field of casting, and more particularly to a method for high-pressure casting of a hollow casting. Background Art

[0002] High-pressure casting is a casting method that fills liquid metal into a cavity composed of a metal mold at a high speed under high pressure and solidifies it under high pressure. The pressure inside the cavity commonly used in high-pressure casting is 40-120MPa, and the metal filling speed is 25-80m / s. Therefore, high pressure and high speed are the fundamental differences between high-pressure casting and other pressure casting methods, and are also important features. At present, high-pressure casting is mainly used for zinc alloys, aluminum alloys, copper alloys and magnesium alloys. In the output of die castings, aluminum alloy die castings account for the largest proportion, which is 30% to 50%; followed by zinc alloy die castings; copper alloy die castings account for 1% to 2%. The largest application of die castings is in the automobile and tractor manufacturing industries, followed by instrument manufacturing and electronic instrument industry, and then agricultural machinery, defense industry, computer, medical equipment and other manufacturing industries.

[0003] The advantages of high-pressure casting include: 1. High productivity, easy to achieve mechanization and automation, and can produce thin-walled castings with complex shapes; 2. High dimensional accuracy of castings and low surface roughness. The dimensional tolerance grade of die castings can reach CT3~CT6, and the surface roughness is generally Ra0.8~3.2μm; 3. Parts can be embedded in die castings, which not only saves precious materials and machining hours, but also replaces the assembly process of parts, which can save the assembly process and simplify the manufacturing process. The disadvantages of high-pressure casting include: 1. The liquid metal filling speed is high during die casting, and it is difficult to completely remove the gas in the mold cavity. The casting is prone to defects such as pores, cracks, and oxidation disasters. Therefore, die castings cannot usually be subjected to long-term solid solution heat treatment; 2. The structure of the die casting mold is complex, the manufacturing cycle is long, and the cost is high, which is not suitable for small-batch casting production; 3. The die casting machine is expensive and the investment is large. Due to the limitations of the die clamping force and die size of the die casting machine, the cost of producing large die castings will increase significantly; 4. The types of alloys are limited, and non-ferrous alloys with low melting points such as zinc, magnesium, and copper are not suitable. In recent years, high technology has been applied to the field of die casting. For example, a three-level injection mechanism is used to control pressure, injection speed, and gas in the mold. Develop special die casting processes, such as vacuum die casting, directional air entrainment die casting, and oxygenated die casting. Apply computer control technology to effectively remove pores and improve the density of castings. At the same time, new mold materials and new heat treatment processes are developed to extend the life of the die.

[0004] Due to the high pressure in the die casting cavity, the general sand core has low strength and cannot work. In order to manufacture hollow castings, soluble salt cores, ceramic cores and low melting point metal cores have been successfully developed in recent years. The ceramic core has high strength, but its preparation process is complicated and costly, and the post-casting cleaning process has a certain corrosive effect on the casting. The water-soluble salt core has good surface quality and dimensional accuracy, high strength and hardness, and excellent water-soluble disintegration, which has made the water-soluble salt core have a large development in the core for die casting in recent years, but the salt core is also prone to corrosion and will cause environmental problems after dissolving in water. Especially when manufacturing small channels, the core is brittle and the strength is still insufficient. The low melting point metal core can be recycled, but it needs pre-forming and surface treatment, and the process is relatively complicated. In particular, once the surface treatment is not perfect, the material of the metal core will react with aluminum. Therefore, developing a core preparation method with good strength, easy operation, no pollution, low cost, environmental protection and wide application range is a technical problem that needs to be solved in the current high-pressure casting manufacturing of hollow parts. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a method for high pressure casting hollow castings.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The present invention discloses a method for high pressure casting of a hollow casting, comprising the following steps:

[0008] Step 1: Make the hollow aluminum tube into the required shape. The specific method is to bend and connect hollow aluminum tubes of different or same thickness into the required shape.

[0009] Step 2: Introduce ceramic particles into the aluminum tube and vibrate to compact it, seal both ends of the aluminum tube to obtain a core;

[0010] Step 3: placing the core into a die-casting mold, pressing aluminum alloy melt into the die-casting mold for die-casting, demolding and cooling after solidification to obtain a casting;

[0011] Step 4: Remove the seals at both ends of the aluminum tube of the core, blow compressed air into the aluminum tube of the core through the pipe fittings, blow out the ceramic particles in the aluminum tube to form a clean channel, and leave the aluminum tube body in the casting to complete the cleaning of the casting core and obtain a hollow casting.

[0012] Furthermore, the function of the aluminum tube is to form a channel and to resist a part of the pressure during the die casting process, and to become a part of the casting after die casting. Therefore, the inner diameter of the aluminum tube can be consistent or inconsistent, and can also be a special-shaped tube. The core can be composed of one aluminum tube or several aluminum tubes connected. However, the inside of the aluminum tube needs to be connected to form a connected whole. This allows the next step of operation. The material of the aluminum tube can be the same as the casting material, or pure aluminum tube can be used. The choice of aluminum tube wall thickness can be changed according to the size of the casting, but in principle it should not be greater than 1 mm.

[0013] Furthermore, the role of the ceramic particles is to generate back pressure in the aluminum tube to resist the deformation caused by the external pressure generated during the filling process. The ceramic material is preferably in granular or coarse powder form, and its size varies according to the diameter of the aluminum tube. For aluminum tubes with a diameter greater than 10 mm, the particle size is controlled between 25 and 100 meshes, and for aluminum tubes with a diameter less than or equal to 10 mm, the particle size is controlled between 75 and 150 meshes. The material of the ceramic particles can be selected from one or more of alumina, silicon dioxide, boron nitride, and boron carbide.

[0014] Furthermore, in step 3, the core needs to be preheated before use, and the preheating temperature is 100°C to 250°C. This is used to compensate for the shrinkage of subsequent castings.

[0015] Furthermore, in step three, the aluminum tube core should have at least one supporting fixing point to ensure the accurate position of the core, and the die casting adopts hot chamber high pressure casting, cold chamber high pressure casting, extrusion casting or semi-solid casting.

[0016] Furthermore, the pipe in step 4 is a flexible air pipe with a diameter smaller than the inner diameter of the aluminum tube. The air pipe needs to be constantly adjusted in the aluminum tube so that the pressure and flow on the ceramic surface are large enough to allow the ceramic particles to flow out smoothly.

[0017] Furthermore, the order of step 1 and step 2 can be interchanged. The ceramic particles can be first loaded into the aluminum tube or aluminum cavity and then transformed into a core with a desired structure, or the aluminum tube can be first made into a shape with a desired structure and then the ceramic particles can be added.

[0018] The beneficial effects of the present invention are: 1. The composite structure of the core can take into account both strength and toughness, and will not deform or break when the high-speed and high-pressure metal liquid is filled into the mold. The interior of the core is filled with loose and dry ceramic particles without any adhesive. Therefore, the core structure is rigid on the outside and flexible on the inside, and precise and complex shapes can be manufactured; 2. The aluminum tube outside the core is nested in the casting after casting, which can not only accurately control the size and distribution, but also improve the corrosion resistance due to the characteristics of the aluminum tube; 3. The aluminum tube on the surface of the core has excellent moisture absorption resistance and has a comparable volume shrinkage rate to that of cast aluminum alloy. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] Example 1

[0021] A method for high-pressure casting of hollow castings is used for casting hollow castings of electric vehicle motor shells. The hollow structure is a cooling channel in the shape of a 6 mm cylindrical spring distributed along the axial direction of the motor shell.

[0022] Select a pure aluminum tube with an inner diameter of 6 mm and a wall thickness of 0.5 mm, cut the aluminum tube to the required length, then fill the tube with 100 / 150 mesh silica particles, gently shake it to compact it, and then seal and clean both ends of the aluminum tube.

[0023] The sealed aluminum tube is bent into a cylindrical spring shape to form a core.

[0024] Install the die-casting mold on the 1200-ton die-casting machine and preheat the die-casting mold to 180°C with high-pressure hot water. Preheat the prepared core to 100°C and install it into the die-casting mold of the die-casting machine, then close the mold. Then, the pre-melted and degassed A380 alloy melt at a temperature of 700°C is controlled to enter the die-casting mold cavity at a speed of 35m / s, solidify at a pressure of 60MPa for 35 seconds, demold after cooling, take out the casting, and cool the casting to room temperature.

[0025] Place the cooled casting on a workbench, cut off the seals at both ends of the aluminum tube, and then fix the pre-prepared flexible tube with an inner diameter of 1.5 mm and a wall thickness of 0.5 mm on a fixture at the end of the aluminum tube and allow the flexible tube to move axially. Align the flexible tube with the aluminum tube, turn on the compressed air, and adjust the pressure to 6 bar. The air will hit the silica particles in the aluminum tube and blow the silica particles out. Then slowly insert the flexible tube deep into the aluminum tube until all the silica particles in the aluminum tube are blown out. Then you get an electric vehicle motor housing casting with a cooling water channel.

[0026] Example 2

[0027] A method for high-pressure casting hollow castings is used for casting irregular inner hollow pressure castings, wherein the hollow structure is an irregular and curved mixture of cylinders and ellipses, with a main diameter of 26 mm and some 14 to 18 mm cylinders.

[0028] Select 6013 aluminum alloy tubes with different inner diameters but the same wall thickness of 0.8 mm, cut the different aluminum tubes into the required length, and then weld the different aluminum tubes into the required cavity shape. Then fill the cavity with 50 / 100 mesh alumina particles, gently vibrate to compact, and then seal and clean both ends of the aluminum cavity.

[0029] The sealed aluminum cavity is shaped to form a core.

[0030] Install the die casting mold on the 1000-ton die casting machine. Preheat the die casting mold to 150°C with high-pressure hot water. Preheat the prepared core to 250°C and install it into the die casting mold of the die casting machine, then close the mold. Then, control the melt of the pre-melted and degassed A380 alloy at a temperature of 700°C to enter the die casting mold cavity at a speed of 35m / s, and solidify it at a pressure of 60MPa for 30 seconds. After cooling, demold and take out the casting, and cool the casting to room temperature.

[0031] Place the cooled casting on a workbench, cut off the seals at both ends of the core, and then fix the pre-prepared flexible tube with an inner diameter of 2.5 mm and a wall thickness of 0.5 mm on a fixture at the end of the aluminum tube and allow the flexible tube to move axially. Align the flexible tube with the aluminum tube, turn on the compressed air, and adjust the pressure to 6 bar. The air will hit the aluminum oxide particles in the aluminum tube and blow out the ceramic particles. Then slowly insert the flexible tube deep into the aluminum tube until the aluminum oxide particles in the aluminum tube are blown dry and quiet. Then you get a die casting with an internal cavity.

[0032] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for high pressure casting of hollow castings, characterized in that: The following steps are involved: Step 1: Make the hollow aluminum tube into the desired shape; Step 2: Introduce ceramic particles into the aluminum tube and vibrate to compact it, seal both ends of the aluminum tube to obtain a core; Step 3: placing the core into a die-casting mold, pressing aluminum alloy melt into the die-casting mold for die-casting, demolding and cooling after solidification to obtain a casting; Step 4: Remove the seals at both ends of the aluminum tube of the core, blow compressed air into the aluminum tube of the core through the pipe fitting, blow out all the ceramic particles in the aluminum tube, and leave the aluminum tube in the casting to obtain a hollow casting.

2. A method for high pressure casting hollow casting according to claim 1, characterized in that: The core is formed by connecting a plurality of aluminum tubes, and the plurality of aluminum tubes are internally connected.

3. A method for high pressure casting hollow casting according to claim 1, characterized in that: The wall thickness of the aluminum tube is not more than 1 mm.

4. A method for high pressure casting of hollow castings according to claim 1, characterized in that: The diameter of the aluminum tube is greater than 10 mm, and the diameter of the ceramic particles is 25 to 100 mesh.

5. A method for high pressure casting of hollow castings according to claim 1, characterized in that: The diameter of the aluminum tube is less than or equal to 10 mm, and the diameter of the ceramic particles is 75 to 150 mesh.

6. A method for high pressure casting of hollow castings according to claim 1, characterized in that: The material of the ceramic particles is one or more of aluminum oxide, silicon dioxide, boron nitride or boron carbide.

7. A method for high pressure casting of hollow castings according to claim 1, characterized in that: In step three, the die casting adopts hot chamber high pressure casting, cold chamber high pressure casting, squeeze casting or semi-solid casting.

8. The method for high pressure casting of hollow castings according to claim 1, characterized in that: In step 4, the pipe fitting is a flexible air pipe with a diameter smaller than the inner diameter of the aluminum tube.

9. A method for high pressure casting of hollow castings according to claim 1, characterized in that: In step three, the core is preheated before being placed in the die-casting mold, and the preheating temperature is 100°C to 250°C.