A vacuum die casting system, a high-vacuum die casting method, and their applications

Abstract

This invention discloses a vacuum die-casting system, a high-vacuum die-casting method, and their applications. The vacuum die-casting system includes a horizontal die-casting machine, a die-casting mold, a vacuum pump, a vacuum tank, a filter, a hydraulic vacuum valve, a vacuum valve controller, a displacement acquisition device, and a displacement grating. The high-vacuum die-casting method sequentially includes melting aluminum alloy liquid, evacuating the vacuum tank, preheating the mold, spraying a release agent, closing and locking the mold, low-speed injection, evacuating the mold cavity, high-speed injection, pressure holding and cooling, mold opening, and part removal. This invention, through scientific design of the vacuum die-casting system and optimization of the vacuum die-casting process, shortens the response time of the hydraulic vacuum valve to 35ms and increases the vacuum degree of the mold cavity to 50mbar, achieving high-vacuum die-casting molding, improving the density, mechanical properties, and dimensional accuracy of the die-cast parts, and reducing the equipment failure rate. This invention also discloses the application of the described vacuum die-casting system and method in large and complex aluminum alloy die-cast parts for new energy vehicles.

Description

Technical Field

[0001] This invention belongs to the field of die casting technology, specifically relating to a vacuum die casting system, a high-vacuum die casting method, and their applications. Background Technology

[0002] Die casting is a molding technology that uses high-speed, high-pressure hydraulic injection of aluminum alloy into a mold cavity for cooling and solidification to obtain die-cast parts. Die casting technology has high production efficiency and is widely used in automobiles, motorcycles, electronics, and machinery. In conventional die casting production, molten aluminum alloy fills the mold cavity at high speed in a jet-like manner. Because the gas in the injection chamber and mold cavity cannot escape in time, gas is trapped in the die casting, reducing its density and mechanical properties. It also makes the die casting unsuitable for heat treatment because heat treatment would cause the trapped gas to expand, leading to deformation and surface bubbles in the die casting.

[0003] Vacuum die casting involves first evacuating the gas from the injection chamber and mold cavity using a vacuum pump, then hydraulically injecting aluminum alloy into the mold cavity under high speed and pressure. Vacuum die casting avoids the entrapment of gas during the liquid aluminum alloy filling process, improving the density and mechanical properties of the die casting. This allows for further improvement of the mechanical properties through heat treatment, and prevents deformation and surface bubbles in the die casting.

[0004] With the rapid development of new energy vehicles, integrated die casting technology has also developed rapidly. Integrated die casting involves die casting multiple chassis components into a single part in one go. Currently, integrated die casting parts under development include the front engine compartment, rear floor, and battery tray for electric vehicles. Compared to traditional automotive manufacturing technologies, integrated die casting significantly reduces the number of body parts and welding points, simplifies the automotive manufacturing process, greatly improves production efficiency, reduces manufacturing costs, lightens body weight, and promotes the development of lightweight vehicles.

[0005] Integrated die-cast parts are characterized by their large size and complex structure. To meet the requirements of integrated die casting, higher demands are placed on both the vacuum die casting system and the vacuum die casting process. Firstly, due to the larger mold cavity space, a more powerful vacuum die casting system is needed to achieve the high vacuum level. Secondly, suitable aluminum alloys and vacuum die casting processes are also required for integrated die casting. However, existing vacuum die casting systems and methods still suffer from problems such as low mold cavity vacuum, high equipment failure rate, and low mechanical properties and yield of die-cast parts. Therefore, existing vacuum die casting systems and methods still require improvement and development. Summary of the Invention

[0006] In response to the problems and shortcomings mentioned in the background art, this invention provides a vacuum die casting system, a high-vacuum die casting method, and its application. By scientifically designing the vacuum die casting system and optimizing the vacuum die casting process, the response speed of the hydraulic vacuum valve and the vacuum degree of the mold cavity are improved, thereby increasing the density, mechanical properties, dimensional accuracy, and yield of the die castings, reducing the equipment failure rate, and meeting the integrated die casting requirements of large and complex aluminum alloy body structural parts for new energy vehicles.

[0007] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0008] The first aspect of this invention provides a vacuum die-casting system, characterized by comprising a horizontal die-casting machine, a die-casting mold, a vacuum pump, a vacuum tank, a filter, a hydraulic vacuum valve, a vacuum valve controller, a displacement collector, and a displacement grating. The horizontal die-casting machine is equipped with a fixed mold plate, a moving mold plate, an injection chamber, an injection rod, an injection punch, and a gating gate. The die-casting mold includes a fixed module and a moving module. The fixed module is mounted on the fixed mold plate of the horizontal die-casting machine, and the moving module is mounted on the moving mold plate of the horizontal die-casting machine. A mold core is respectively disposed inside the fixed module and the moving module. The fixed module is equipped with an inner sprue, and the moving module is equipped with an ejector device. After the fixed module and the moving module are closed, an inner sprue, a mold cavity, and an exhaust channel are formed. The hydraulic vacuum valve is installed between the fixed module and the moving module and is connected to the exhaust channel. The hydraulic vacuum valve is connected to a filter, a vacuum tank, and a vacuum pump through a pipeline. The hydraulic vacuum valve is connected to a vacuum valve controller and a displacement collector through a cable. The displacement grating is installed on the injection rod of the horizontal die-casting machine and is located below the displacement collector. The position of the injection rod is sensed by the displacement grating and the displacement collector.

[0009] Preferably, the number of exhaust channels is 4-6, and the number of hydraulic vacuum valves is the same as the number of exhaust channels. Gas from the mold cavity and injection chamber is discharged into the vacuum tank through exhaust pipes, creating a vacuum negative pressure in the mold cavity. Due to the large size of the integrated die-cast part, the space of the mold cavity and injection chamber is also large. In order to expel gas from the mold cavity and injection chamber into the vacuum tank more quickly, existing technologies typically set exhaust channels separately in the mold cavity and injection chamber. This method results in a complex structure and is difficult to implement. To ensure a high vacuum negative pressure in the mold cavity, this invention enhances the discharge of gas from the mold cavity by increasing the number of exhaust channels directly connected to the mold cavity. A greater number of exhaust channels is more conducive to the discharge of gas from the mold cavity, but too many exhaust channels also lead to layout difficulties and increased costs. Therefore, the preferred number of exhaust channels is 4-6, and the corresponding number of hydraulic vacuum valves is the same as the number of exhaust channels. Preferably, the exhaust channels are located on top of the mold closing surface, but they can also be located on the front or back of the mold closing surface, depending on the shape characteristics of the die-cast part and ease of layout.

[0010] Preferably, the response time of the hydraulic vacuum valve when opening and closing does not exceed 35ms. Vacuuming of the mold cavity is controlled by opening and closing the hydraulic vacuum valve, and the time from the opening of the valve to its closing significantly affects the vacuum level of the mold cavity. Existing conventional vacuum die casting typically uses solenoid valves for control. While easy to implement, the response time of solenoid valves is usually over 150ms. This long response time firstly easily leads to molten aluminum alloy entering the solenoid valve and causing blockage, resulting in a high equipment failure rate. Secondly, the long response time shortens the vacuuming time, leading to insufficient vacuum in the mold cavity. To solve this problem, this invention uses a hydraulic vacuum valve for control, utilizing a displacement sensor and displacement grating to sense the position of the injection rod, and then controlling the opening and closing of the hydraulic vacuum valve through a vacuum valve controller. This reduces the response time of the hydraulic vacuum valve to less than 35ms. The fast response of the hydraulic vacuum valve firstly prevents molten aluminum alloy from entering and causing blockage, reducing the equipment failure rate. Secondly, it allows for more time for vacuuming, ensuring a high vacuum in the mold cavity.

[0011] Preferably, the volume of the vacuum tank is not less than 5 cubic meters. Vacuuming the mold cavity involves extracting gas from the mold cavity and injection chamber into the vacuum tank, creating a vacuum negative pressure within the mold cavity. Therefore, the effectiveness of vacuuming the mold cavity is closely related to the volume of the vacuum tank. Conventional vacuum tanks for vacuum die casting typically have a volume of only 0.5-2 cubic meters. Due to the large size of integrated die-cast parts, the space in the mold cavity and injection chamber is also large. To achieve a vacuum level of 50 mbar in the mold cavity, a larger vacuum tank than that used in conventional vacuum die casting is required; otherwise, it is impossible to achieve a vacuum level of 50 mbar in the mold cavity.

[0012] A second aspect of the present invention provides a high-vacuum die-casting method, which employs the aforementioned vacuum die-casting system and is characterized by comprising the following steps in sequence:

[0013] Step 1: Melt and prepare aluminum alloy liquid and refine and purify the aluminum alloy liquid, and then control the temperature of the aluminum alloy liquid at 680-690℃;

[0014] Step 2: Start the vacuum pump to evacuate the vacuum tank and preheat the die-casting mold core;

[0015] Step 3: Spray release agent onto the mold core of the die-casting mold, and then start the horizontal die-casting machine to push the moving template to close the mold;

[0016] Step 4: Inject the molten aluminum alloy into the injection chamber through the pouring port, and start the injection rod of the horizontal die casting machine to push the molten aluminum alloy forward;

[0017] Step 5: After the injection punch moves past the sprue, open the hydraulic vacuum valve and allow the gas in the mold cavity to be discharged into the vacuum tank through the exhaust channel;

[0018] Step 6: After the injection punch reaches the fast injection position, close the hydraulic vacuum valve, and the injection rod continues to push the aluminum alloy liquid forward to fill the mold cavity at high speed;

[0019] Step 7: Hold the pressure to allow the molten aluminum alloy to cool and solidify, then open the die-casting mold, remove the die-casting part, and obtain a high-vacuum die-casting part.

[0020] Preferably, the aluminum alloy liquid in step one is composed of the following components by mass percentage: Si 8.6-9.1%, Zn 1.62-1.67%, Fe 0.7-0.8%, Cr 0.43-0.48%, Zr 0.18-0.23%, Ce 0.15-0.19%, with the balance being Al and other unavoidable impurity elements, wherein the content of each individual impurity element is ≤0.05%, and the total content of other impurity elements is ≤0.2%.

[0021] Integrated die casting requires aluminum alloys to possess excellent filling capabilities and superior mechanical properties in their non-heat-treated state. Specifically, silicon (Si) enhances the fluidity of the molten aluminum alloy and improves the strength and hardness of the die casting. Zn strengthens the die casting through solid solution treatment, further enhancing its strength and hardness. Fe facilitates demolding and also enhances the die casting's strength and hardness. Cr refines the modified iron-rich phase, further increasing the die casting's strength and hardness. Zr refines the grain structure of the die casting, improving its uniformity and plasticity. Ce refines the modified eutectic silicon phase, improving the die casting's strength and plasticity. It is crucial to note that the elemental composition and their mass percentages in the aluminum alloy are a scientifically determined combination; only when both the elemental composition and content are simultaneously satisfied can the desired effect be achieved.

[0022] Preferably, the refining and purification gas in step one is nitrogen with a purity of ≥99.99%, and the refining solvent consists of the following components by mass percentage: 36.12% AlCl3, 28.37% LiF, 21.69% CuCO3, and 13.82% Ce(NO3)3. The amount of refining flux is 0.2-0.3% of the weight of the aluminum alloy liquid, and the refining and purification time is 15-20 minutes.

[0023] Inevitably, molten aluminum alloys contain inclusions and gases. The main inclusion is alumina, and the main gas is hydrogen. These inclusions and gases reduce the density and mechanical properties of die-cast aluminum alloy parts, making vacuum die-casting impossible. The refining and purification effect is closely related to the composition of the flux. Existing fluxes are composed of chloride and fluoride salts of alkali metals such as Na, K, and Ca. These fluxes increase the alkali metal content in the aluminum alloy, thereby reducing the strength, plasticity, and fatigue resistance of the die-cast parts, increasing the risk of premature fracture failure in automotive components. To address this problem, this invention develops a high-efficiency flux free of alkali metals. AlCl3 has a very low melting and boiling point, sublimating into bubbles in high-temperature molten aluminum alloys. These bubbles can adsorb and remove inclusions and hydrogen from the molten aluminum alloy, thus purifying it. LiF forms molten salts in high-temperature molten aluminum alloys, dissolving and adsorbing inclusions such as alumina, promoting the separation of inclusions from the molten aluminum alloy, and improving the purification effect of the flux. CuCO3 decomposes into CO2 bubbles in molten aluminum alloy, which can adsorb and carry away inclusions and hydrogen, thus purifying the alloy. The decomposed Cu can replenish the Cu content of the molten aluminum alloy, improving the strength of the die-cast aluminum alloy parts. Ce(NO3)3, as a heating agent, decomposes and releases a large amount of heat, accelerating the melting of the flux, improving the fluidity of the molten aluminum alloy, accelerating the flotation of inclusions and hydrogen, and enhancing the purification effect. The decomposed NO and NO2 bubbles also play a purifying role, and the decomposed Ce can refine the modified eutectic silicon, improving the strength and plasticity of the die-cast aluminum alloy parts.

[0024] Preferably, after starting the vacuum pump to evacuate the vacuum tank in step two, the vacuum level of the vacuum tank is not less than 10 mbar.

[0025] Vacuuming the mold cavity involves extracting gas from the mold cavity and injection chamber into a vacuum tank, creating a negative pressure vacuum within the mold cavity. Therefore, the effectiveness of vacuuming the mold cavity depends not only on the volume of the vacuum tank but also on the vacuum level achieved within it. Due to the large size of integrated die-cast parts, the mold cavity and injection chamber are also large; the vacuum level in the vacuum tank after evacuation must not be lower than 10 mbar, otherwise, it will be impossible to achieve a vacuum level of 50 mbar in the mold cavity.

[0026] Preferably, the preheating of the die-casting mold core in step two is to preheat the mold core to 280-300℃.

[0027] Preheating of the mold core is achieved using a mold temperature controller. The preheating temperature of the mold core is crucial for the smooth filling of the mold cavity by the molten aluminum alloy and for obtaining a highly dense aluminum alloy die casting. Due to the large size, complex structure, and thin wall thickness of integrated die castings, the requirements for the preheating temperature of the mold core are more stringent. If the preheating temperature of the mold core is too low, the molten aluminum alloy will cool and solidify too quickly, failing to completely fill the mold cavity and resulting in a poorly filled aluminum alloy die casting. On the other hand, if the preheating temperature of the mold core is too high, it will increase the cooling and solidification time, easily causing shrinkage defects in the aluminum alloy die casting, reducing the density and mechanical properties of the aluminum alloy die casting, and prolonging the holding time, thus reducing production efficiency.

[0028] Preferably, the time for spraying the mold release agent onto the die-casting mold core in step three is 5-8 seconds. The mold release agent consists of the following components by mass percentage: 11.65% methyl hydroxy silicone oil, 5.62% synthetic vegetable ester, 5.23% sodium alkylbenzene sulfonate, 4.58% ethanol, 3.41% sodium hexametaphosphate, 3.65% dibutyltin dilaurate, 0.84% ​​pentachloronitrobenzene, and the remainder is deionized water.

[0029] The function of a release agent is to form a uniform thin film on the surface of the mold core of a high-temperature die-casting mold, providing lubrication and demolding, improving the surface quality of the die-casting, and extending the mold life. Due to the large size and high performance requirements of integrated die-casting parts, the quality requirements for release agents are also higher. Existing release agents still suffer from problems such as difficulty in demolding, severe carbon buildup, slow evaporation, and impact on the vacuum level of the mold cavity and the density of the die-casting. To solve these problems, this invention has developed a release agent with superior overall performance suitable for integrated die-casting. Methyl hydroxy silicone oil possesses excellent thermal stability, electrical insulation, and lubricity, forming a uniform thin film on the mold surface and reducing the adhesion between the die-casting and the mold. Synthetic plant esters primarily suppress oil seepage and increase the surface gloss of the die-casting. Ethanol primarily increases the high-temperature volatility of the release agent, accelerates the drying of the die-casting mold, prevents moisture residue from reducing the vacuum level of the mold cavity, and improves the density of the die-casting. Sodium alkylbenzene sulfonate primarily promotes the uniform dispersion of methyl hydroxy silicone oil and other components in water, forming a stable emulsion, making the release agent easier to spray evenly. The main function of dibutyltin dilaurate is to improve the stability of the release agent and prevent the degradation or inactivation of the active ingredient. The main function of pentachloronitrobenzene is to inhibit the growth of microorganisms and extend the service life of the release agent.

[0030] Preferably, the clamping force when starting the horizontal die-casting machine and pushing the moving template to close the mold in step three is 7000-16000kN.

[0031] Clamping force is the clamping force applied between the stationary and moving modules of the die-casting mold by a horizontal die-casting machine. This clamping force is primarily achieved through the horizontal die-casting machine and its function is to prevent the moving mold block from moving and opening the mold when molten aluminum alloy fills the mold cavity at high speed and pressure. The determination of the clamping force is closely related to the size and weight of the die-casting part; the larger and heavier the die-casting part, the greater the clamping force required. Since the integrated die-casting of the front engine compartment, rear floor, and battery tray of electric vehicles are all large-size, high-mass die-casting parts, the molten aluminum alloy fills the mold cavity at a faster speed and higher pressure. To ensure successful filling, the clamping force for the front engine compartment is typically 70,000 kN, the rear floor typically requires 120,000 kN, and the battery tray typically requires 160,000 kN.

[0032] Preferably, in step four, when the injection rod of the horizontal die-casting machine is started to push the molten aluminum alloy forward, the moving speed of the injection rod is 0.08-0.12 m / s.

[0033] The speed of the injection rod as it propels the molten aluminum alloy into the ingate must be strictly controlled. If the speed is too slow, the temperature of the molten aluminum alloy in the injection chamber will drop too much, making it difficult to fill the mold cavity. However, the speed cannot be too fast either. Excessive speed will first cause the molten aluminum alloy in the injection chamber to tumble, entraining gas and slag, resulting in porosity and inclusions in the die casting, making it impossible to obtain a high-density and high-strength aluminum alloy die casting. Secondly, it will reduce the time for vacuuming the mold cavity. This is because the vacuum tank evacuates the mold cavity from the moment the injection plunger passes the gating gate until it reaches the fast injection position. If the injection rod moves too fast during this distance, it will reduce the vacuum tank's evacuation time, making it difficult to achieve a high vacuum level in the mold cavity.

[0034] Preferably, in step six, when the injection rod continues to push the aluminum alloy liquid forward to complete the filling of the mold cavity, the moving speed of the injection rod is 8-10 m / s, and the pressure of the injection rod is 50-60 MPa.

[0035] The basic principle of die casting is to propel molten aluminum alloy into the mold cavity at high speed using an injection rod. Because one-piece die castings are characterized by large size, complex structure, and thin walls, the injection rod needs to propel the molten aluminum alloy into the mold cavity at an even faster speed to achieve rapid filling. If the injection rod moves too slowly, the molten aluminum alloy will fill the mold cavity slowly, causing it to cool and solidify prematurely, failing to completely fill the cavity and resulting in an aluminum alloy die casting with a complete shape and dimensions. Of course, it's also impossible to increase the injection speed of the injection rod indefinitely; otherwise, the tonnage and power of the die casting machine would need to be increased exponentially, leading to a sharp rise in costs.

[0036] Preferably, the pressure holding step seven refers to maintaining the clamping force for 35-45 seconds after the aluminum alloy liquid has finished filling the mold cavity, so that the aluminum alloy liquid in the mold cavity can be completely cooled and solidified into solid aluminum alloy parts.

[0037] The holding time is closely related to the pouring temperature of the molten aluminum alloy, the filling speed, and the size and wall thickness of the die casting. Lower pouring temperatures, slower filling speeds, or smaller die castings with thinner walls allow for a shorter holding time; conversely, longer holding times are necessary. Because integrated die castings are large, structurally complex, and have thicker walls in some areas, a longer holding time is required to ensure the molten aluminum alloy completely cools and solidifies into a solid die casting within the mold cavity.

[0038] The third aspect of this invention provides the application of the vacuum die-casting system and high-vacuum die-casting method, characterized in that the vacuum die-casting system and high-vacuum die-casting method are applied to large and complex aluminum alloy structural parts of new energy vehicles, such as aluminum alloy front engine compartments, aluminum alloy rear floors, and aluminum alloy battery trays.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) This invention directly senses the position of the injection rod by using a displacement acquisition device and a displacement grating, and improves the response speed of the hydraulic vacuum valve by controlling the opening and closing of the hydraulic vacuum valve through a vacuum valve controller. The response time of the hydraulic vacuum valve is less than 35ms, which provides more time for vacuuming the mold cavity. At the same time, it effectively prevents aluminum alloy liquid from entering the vacuum valve, preventing equipment failure and significantly reducing the equipment failure rate. In addition, by increasing the number of exhaust channels and increasing the volume of the vacuum tank, the gas in the mold cavity is discharged more quickly, providing the equipment conditions for high vacuum die casting of large and complex aluminum alloy automotive structural parts.

[0041] (2) This invention optimizes the vacuum die casting process by developing aluminum alloy materials, refined flux and release agent suitable for integrated die casting, ensuring that the mold cavity obtains a high vacuum, with the vacuum degree of the mold cavity reaching 50mbar, realizing the integrated high vacuum die casting of large and complex aluminum alloy automotive structural parts, and improving the density of die castings and the product qualification rate.

[0042] (3) By optimizing the vacuum die casting system and vacuum die casting process, this invention achieves high vacuum die casting of large and complex aluminum alloy structural parts such as the front engine compartment, rear floor and battery tray of electric vehicles, which greatly improves the mechanical properties of the die castings. The tensile strength of the die castings is greater than 330MPa, the yield strength is greater than 260MPa and the elongation after fracture is greater than 10%. It has the dual advantages of high strength and good plasticity, which meets the needs of the lightweight development of electric vehicles. Attached Figure Description

[0043] Figure 1This is a schematic diagram of the vacuum die-casting system of the present invention;

[0044] Among them, 10-horizontal die casting part, 20-die casting mold, 31-vacuum pump, 32-vacuum tank, 33-filter, 34-hydraulic vacuum valve, 35-vacuum valve controller, 36-displacement collector, 37-displacement grating, 38-pipe, 39-cable, 11-fixed template, 12-moving template, 13-injection chamber, 14-injection rod, 15-injection punch, 16-sprue, 21-fixed module, 22-moving module, 23-mold core, 24-inner runner, 25-ejection device, 26-inner gate, 27-mold cavity, 28-venting channel. Detailed Implementation

[0045] like Figure 1 As shown, the vacuum die-casting system includes a horizontal die-casting machine 10, a die-casting mold 20, a vacuum pump 31, a vacuum tank 32, a filter 33, a hydraulic vacuum valve 34, a vacuum valve controller 35, a displacement collector 36, and a displacement grating 37. The horizontal die-casting machine 10 is equipped with a fixed template 11, a moving template 12, an injection chamber 13, an injection rod 14, an injection punch 15, and a pouring gate 16. The die-casting mold 20 includes a fixed module 21 and a moving module 22. The fixed module 21 is mounted on the fixed template 11 of the horizontal die-casting machine 10, and the moving module 22 is mounted on the moving template 12 of the horizontal die-casting machine 10. A mold core 23 is respectively provided inside the fixed module 21 and the moving module 22. The fixed module 21 is equipped with... The machine has an ingate 24, and the moving module 22 is equipped with an ejector 25. After the fixed module 21 and the moving module 22 are closed, an ingate 26, a mold cavity 27, and an exhaust channel 28 are formed. A hydraulic vacuum valve 34 is installed between the fixed module 11 and the moving module 22 and is connected to the exhaust channel 28. The hydraulic vacuum valve 34 is connected to a filter 33, a vacuum tank 32, and a vacuum pump 31 through a pipe 38. The hydraulic vacuum valve 34 is connected to a vacuum valve controller 35 and a displacement collector 36 through a cable 39. A displacement grating 37 is installed on the injection rod 14 of the horizontal die-casting machine 10 and is located below the displacement collector 36. The position of the injection rod 14 is sensed by the displacement grating 37 and the displacement collector 36. Preferably, the number of exhaust channels 28 is 4-6, and the number of hydraulic vacuum valves 34 is the same as the number of exhaust channels 28. Preferably, the response time of the opening and closing of the hydraulic vacuum valve 34 does not exceed 35ms. Preferably, the volume of the vacuum tank 32 is not less than 5 cubic meters.

[0046] Example 1:

[0047] The vacuum die-casting system described above is used to integrally die-cast the aluminum alloy front engine compartment of an electric vehicle. It has four exhaust channels, a 35ms response time for opening and closing the hydraulic vacuum valves, and a vacuum tank volume of 5 cubic meters. The high-vacuum die-casting method includes the following steps:

[0048] Step 1: Melt and prepare the aluminum alloy liquid and refine and purify it. Then, control the temperature of the aluminum alloy liquid at 685℃. The aluminum alloy liquid is composed of the following components by mass percentage: Si 8.92%, Zn 1.65%, Fe 0.73%, Cr 0.46%, Zr 0.19%, Ce 0.17%, with the balance being Al and other unavoidable impurity elements. The content of each other impurity element is ≤0.05%, and the total content of other impurity elements is ≤0.2%. The gas used for refining and purification is nitrogen with a purity of 99.99%. The refining solvent is composed of the following components by mass percentage: 36.12% AlCl3, 28.37% LiF, 21.69% CuCO3, 13.82% Ce(NO3)3. The amount of refining flux is 0.25% of the weight of the aluminum alloy liquid, and the refining and purification time is 18 minutes.

[0049] Step 2: Start the vacuum pump to evacuate the vacuum tank to a vacuum level of 10 mbar, and preheat the die-casting mold core to 290°C.

[0050] Step 3: Spray the mold release agent onto the die-casting mold core for 6 seconds, then start the horizontal die-casting machine to push the moving template to close the mold. The clamping force is 7000kN. The mold release agent consists of the following components by mass percentage: 11.65% methyl hydroxy silicone oil, 5.62% synthetic vegetable ester, 5.23% sodium alkylbenzene sulfonate, 4.58% ethanol, 3.41% sodium hexametaphosphate, 3.65% dibutyltin dilaurate, 0.84% ​​pentachloronitrobenzene, and the remainder is deionized water.

[0051] Step 4: Inject the molten aluminum alloy into the injection chamber through the pouring port, and start the injection rod of the horizontal die casting machine to push the molten aluminum alloy forward at a speed of 0.09 m / s;

[0052] Step 5: After the injection punch moves past the sprue, open the hydraulic vacuum valve and allow the gas in the mold cavity to be discharged into the vacuum tank through the exhaust channel;

[0053] Step 6: After the injection punch reaches the fast injection position, close the hydraulic vacuum valve, and the injection rod continues to push the aluminum alloy liquid forward at high speed to fill the mold cavity at a pressure of 55 MPa and a speed of 9 m / s.

[0054] Step 7: Hold the pressure for 40 seconds to allow the aluminum alloy liquid to cool and solidify. Then open the die-casting mold, remove the die-casting part, and obtain a high-vacuum die-casting part that can be used in the aluminum alloy front engine compartment of electric vehicles.

[0055] Example 2:

[0056] The vacuum die-casting system described above is used to integrally die-cast the aluminum alloy rear floor of an electric vehicle. It has five exhaust channels, a 35ms response time for opening and closing the hydraulic vacuum valves, and a vacuum tank volume of 6 cubic meters. The high-vacuum die-casting method includes the following steps:

[0057] Step 1: Melt and prepare the aluminum alloy liquid and refine and purify it. Then, control the temperature of the aluminum alloy liquid at 680℃. The aluminum alloy liquid is composed of the following components by mass percentage: Si 9.1%, Zn 1.62%, Fe 0.8%, Cr 0.43%, Zr 0.23%, Ce 0.15%, with the balance being Al and other unavoidable impurity elements. The content of each other impurity element is ≤0.05%, and the total content of other impurity elements is ≤0.2%. The gas used for refining and purification is nitrogen with a purity of 99.99%. The refining solvent is composed of the following components by mass percentage: 36.12% AlCl3, 28.37% LiF, 21.69% CuCO3, and 13.82% Ce(NO3)3. The amount of refining flux is 0.2% of the weight of the aluminum alloy liquid, and the refining and purification time is 15 minutes.

[0058] Step 2: Start the vacuum pump to evacuate the vacuum tank to a vacuum level of 10 mbar, and preheat the die-casting mold core to 280°C.

[0059] Step 3: Spray the mold release agent onto the die-casting mold core for 5 seconds, then start the horizontal die-casting machine to push the moving template to close the mold. The clamping force is 12000kN. The mold release agent consists of the following components by mass percentage: 11.65% methyl hydroxy silicone oil, 5.62% synthetic vegetable ester, 5.23% sodium alkylbenzene sulfonate, 4.58% ethanol, 3.41% sodium hexametaphosphate, 3.65% dibutyltin dilaurate, 0.84% ​​pentachloronitrobenzene, and the remainder is deionized water.

[0060] Step 4: Inject the molten aluminum alloy into the injection chamber through the pouring port, and start the injection rod of the horizontal die casting machine to push the molten aluminum alloy forward at a speed of 0.12 m / s;

[0061] Step 5: After the injection punch moves past the sprue, open the hydraulic vacuum valve and allow the gas in the mold cavity to be discharged into the vacuum tank through the exhaust channel;

[0062] Step 6: After the injection punch reaches the fast injection position, close the hydraulic vacuum valve, and the injection rod continues to push the aluminum alloy liquid forward at high speed to fill the mold cavity at a pressure of 50 MPa and 10 m / s.

[0063] Step 7: Hold the pressure for 35 seconds to allow the molten aluminum alloy to cool and solidify. Then open the die-casting mold, remove the die-casting part, and obtain a high-vacuum die-casting part that can be applied to the aluminum alloy rear floor of electric vehicles.

[0064] Example 3:

[0065] The vacuum die-casting system described above is used to integrally die-cast an aluminum alloy battery tray for an electric vehicle. It has six exhaust channels, a 35ms response time for opening and closing the hydraulic vacuum valves, and a vacuum tank volume of 7 cubic meters. The high-vacuum die-casting method includes the following steps:

[0066] Step 1: Melt and prepare the aluminum alloy liquid and refine and purify it. Then, control the temperature of the aluminum alloy liquid at 690℃. The aluminum alloy liquid is composed of the following components by mass percentage: Si 8.6%, Zn 1.67%, Fe 0.7%, Cr 0.48%, Zr 0.18%, Ce 0.19%, with the balance being Al and other unavoidable impurity elements. The content of each other impurity element is ≤0.05%, and the total content of other impurity elements is ≤0.2%. The gas used for refining and purification is nitrogen with a purity of 99.99%. The refining solvent is composed of the following components by mass percentage: 36.12% AlCl3, 28.37% LiF, 21.69% CuCO3, and 13.82% Ce(NO3)3. The amount of refining flux is 0.3% of the weight of the aluminum alloy liquid, and the refining and purification time is 20 minutes.

[0067] Step 2: Start the vacuum pump to evacuate the vacuum tank to a vacuum level of 10 mbar, and preheat the die-casting mold core to 300°C.

[0068] Step 3: Spray the mold release agent onto the die-casting mold core for 8 seconds, then start the horizontal die-casting machine to push the moving template to close the mold. The clamping force is 16000kN. The mold release agent consists of the following components by mass percentage: 11.65% methyl hydroxy silicone oil, 5.62% synthetic vegetable ester, 5.23% sodium alkylbenzene sulfonate, 4.58% ethanol, 3.41% sodium hexametaphosphate, 3.65% dibutyltin dilaurate, 0.84% ​​pentachloronitrobenzene, and the remainder is deionized water.

[0069] Step 4: Inject the molten aluminum alloy into the injection chamber through the pouring port, and start the injection rod of the horizontal die casting machine to push the molten aluminum alloy forward at a speed of 0.08 m / s;

[0070] Step 5: After the injection punch moves past the sprue, open the hydraulic vacuum valve and allow the gas in the mold cavity to be discharged into the vacuum tank through the exhaust channel;

[0071] Step 6: After the injection punch reaches the fast injection position, close the hydraulic vacuum valve, and the injection rod continues to push the aluminum alloy liquid forward at high speed to fill the mold cavity at a pressure of 60 MPa and 8 m / s.

[0072] Step 7: Hold the pressure for 45 seconds to allow the molten aluminum alloy to cool and solidify. Then open the die-casting mold, remove the die-casting part, and obtain a high-vacuum die-casting part that can be used in aluminum alloy battery trays for electric vehicles.

[0073] Comparative Example 1:

[0074] The comparative vacuum die-casting system and method are the same as those in Example 1, except that the vacuum die-casting system does not use a hydraulic vacuum valve, but instead uses a traditional solenoid valve to control the exhaust channel to evacuate the mold cavity.

[0075] Comparative Example 2:

[0076] The comparative vacuum die-casting system and method are the same as those in Example 1, except that in step two, the vacuum pump is started to evacuate the vacuum tank to a vacuum level of 50 mbar.

[0077] Comparative Example 3:

[0078] The vacuum die casting system and method in this comparative example are the same as those in Example 1, except that in step one, the alkali-free metal refining flux developed in this invention is not used, but a traditional alkali-containing metal flux is used to refine and purify the aluminum alloy liquid.

[0079] Comparative Example 4:

[0080] The comparative vacuum die casting system and method are the same as those in Example 1, except that in step three, the mold release agent developed in this invention is not used, but an existing mold release agent is used to spray the mold core.

[0081] Comparative Example 5:

[0082] The comparative vacuum die casting system and method are the same as those in Example 1, except that in step four, the injection rod moves the molten aluminum alloy forward at a rate of 0.2 m / s.

[0083] Verification example:

[0084] Samples were taken from the aluminum alloy die castings obtained in Examples 1-3 and Comparative Examples 1-5, and processed into tensile specimens according to the national standard GB T 228.1-2010 "Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Method". The specimens were subjected to room temperature tensile testing on an electronic tensile testing machine to detect the tensile strength, yield strength, and elongation after fracture of the aluminum alloy die castings. The results are shown in Table 1. The vacuum degree of the mold cavity during the vacuum die casting process in Examples 1-3 and Comparative Examples 1-5 was tested according to the vacuum degree detection method given in the literature (Vacuum Degree Detection in Vacuum Die Casting [J]. Railway Locomotive and Rolling Stock Worker, 1997, (7): 25-27). The results are shown in Table 1. As can be seen from Table 1, the tensile strength of the aluminum alloy vacuum die castings obtained in Examples 1-3 is greater than 330 MPa, the yield strength is greater than 260 MPa, and the elongation after fracture is greater than 10%. The average vacuum degree of the mold cavity during the vacuum die casting process reached 50 mbar. Comparative Example 1 uses a traditional solenoid valve to control the exhaust channel for vacuuming the mold cavity. The slow response of the solenoid valve shortens the vacuuming time. Comparative Example 2 suffers from a vacuum tank with a vacuum level below 10 mbar. Comparative Example 3 uses a traditional alkali-containing metal flux for refining and purifying the aluminum alloy melt. Comparative Example 4 uses an existing release agent to coat the mold core. Comparative Example 5 shows that the injection rod in step four moves the aluminum alloy melt forward too quickly, resulting in poor vacuum levels in the mold cavity during vacuum die casting in Comparative Examples 1-5, leading to poor mechanical properties of the aluminum alloy die castings. The comparison shows that the technical solution of this invention can improve the vacuum level within the mold cavity during vacuum die casting, achieving high-vacuum die casting and significantly improving the mechanical properties of the aluminum alloy die castings.

[0085] Table 1. Room temperature tensile mechanical properties and mold cavity vacuum degree of aluminum alloy die castings in the examples.

[0086]

[0087] This invention has been described by way of embodiments, but does not constitute a limitation thereof. Other variations of the disclosed embodiments, which are readily apparent to those skilled in the art, should fall within the scope of the claims of this invention, with reference to the description of this invention.

Claims

1. A high-vacuum die casting method, wherein the vacuum die casting system used in the method includes a horizontal die casting machine, a die casting mold, a vacuum pump, a vacuum tank, a filter, a hydraulic vacuum valve, a vacuum valve controller, a displacement collector, and a displacement grating. The horizontal die casting machine is equipped with a fixed mold plate, a moving mold plate, an injection chamber, an injection rod, an injection punch, and a gating gate. The die casting mold includes a fixed module and a moving module. The fixed module is mounted on the fixed mold plate of the horizontal die casting machine, and the moving module is mounted on the moving mold plate of the horizontal die casting machine. A mold core is respectively provided inside the fixed module and the moving module. The fixed module is provided with an internal gating system, and the moving module is provided with an ejector device. After the block and moving module are molded together, an inner gate, mold cavity, and venting channel are formed. The hydraulic vacuum valve is installed between the stationary module and the moving module and connected to the venting channel. The hydraulic vacuum valve is connected to a filter, vacuum tank, and vacuum pump through pipes. The hydraulic vacuum valve is connected to a vacuum valve controller and a displacement acquisition device through cables. The displacement grating is set on the injection rod of the horizontal die-casting machine and located below the displacement acquisition device. The position of the injection rod is sensed by the displacement grating and the displacement acquisition device. The number of venting channels is 4-6, and the number of hydraulic vacuum valves is the same as the number of venting channels. The response time of the opening and closing of the hydraulic vacuum valve does not exceed 35 ms. The volume of the vacuum tank is not less than 5 cubic meters. The characteristic of this design is that... The steps are as follows: Step 1: Melt and prepare aluminum alloy liquid and refine and purify the aluminum alloy liquid, and then control the temperature of the aluminum alloy liquid at 680-690℃; Step 2: Start the vacuum pump to evacuate the vacuum tank, ensuring the vacuum level is not less than 10 mbar, and preheat the die-casting mold core to 280-300℃. Step 3: Spray release agent onto the mold core of the die-casting mold for 5-8 seconds, then start the horizontal die-casting machine to push the moving template to close the mold. The clamping force is 7000-16000 kN. Step 4: Inject the molten aluminum alloy into the injection chamber through the pouring port, and start the injection rod of the horizontal die casting machine to push the molten aluminum alloy forward; Step 5: After the injection punch moves past the sprue, open the hydraulic vacuum valve and allow the gas in the mold cavity to be discharged into the vacuum tank through the exhaust channel; Step 6: After the injection punch reaches the fast injection position, close the hydraulic vacuum valve, and the injection rod continues to push the aluminum alloy liquid forward to fill the mold cavity at high speed; Step 7: Hold the pressure for 35-45 seconds to allow the aluminum alloy liquid to cool and solidify, then open the die-casting mold, remove the die-casting part, and obtain a high-vacuum die-casting part; The aluminum alloy liquid described in step one is composed of the following components by mass percentage: Si 8.6-9.1%, Zn 1.62-1.67%, Fe 0.7-0.8%, Cr 0.43-0.48%, Zr 0.18-0.23%, Ce 0.15-0.19%, with the balance being Al and other unavoidable impurity elements, where the content of each individual impurity element is ≤0.05% and the total amount of other impurity elements is ≤0.2%. The refining and purification gas mentioned in step one is nitrogen with a purity of ≥99.99%. The refining flux is composed of the following components by mass percentage: 36.12% AlCl3, 28.37% LiF, 21.69% CuCO3, and 13.82% Ce(NO3)3. The amount of refining flux is 0.2-0.3% of the weight of the aluminum alloy liquid, and the refining and purification time is 15-20 minutes. The release agent described in step three consists of the following components by mass percentage: 11.65% methyl hydroxy silicone oil, 5.62% synthetic vegetable ester, 5.23% sodium alkylbenzene sulfonate, 4.58% ethanol, 3.41% sodium hexametaphosphate, 3.65% dibutyltin dilaurate, 0.84% ​​pentachloronitrobenzene, and the remainder is deionized water.

2. The high-vacuum die-casting method according to claim 1, characterized in that, In step four, when the injection rod of the horizontal die-casting machine is started to push the molten aluminum alloy forward, the moving speed of the injection rod is 0.08-0.12 m / s.

3. The high-vacuum die-casting method according to claim 1, characterized in that, In step six, as the injection rod continues to push the molten aluminum alloy forward to complete the filling of the mold cavity, the moving speed of the injection rod is 8-10 m / s, and the pressure of the injection rod is 50-60 MPa.

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