Vacuum die-casting system, high-vacuum die-casting method and application

Abstract

The invention discloses a vacuum die-casting system, a high-vacuum die-casting method and application. The vacuum die-casting system comprises a horizontal die-casting machine, a die-casting die, a vacuum pump, a vacuum tank, a filter, a hydraulic vacuum valve, a vacuum valve controller, a displacement collector and a displacement grating. The high-vacuum die-casting method sequentially comprises the steps of smelting molten aluminum alloy, vacuumizing a vacuum tank, preheating a die, spraying a release agent, closing and locking the die, carrying out low-speed injection, vacuumizing a die cavity, carrying out high-speed injection, maintaining pressure and cooling, opening the die and taking a part. By scientifically designing the vacuum die-casting system and optimizing the vacuum die-casting process, the response time of the hydraulic vacuum valve is shortened to 35 ms, the vacuum degree of the die cavity is improved to 50 mbar, high-vacuum die-casting forming is achieved, the density, mechanical property and size precision of die castings are improved, and the equipment failure rate is reduced. The invention further discloses application of the vacuum die casting system and method to large complex aluminum alloy die castings of new energy automobiles.

Description

Technical Field

[0001] The present invention belongs to the technical field of die casting, and in particular relates to a vacuum die casting system and a high vacuum die casting method and applications. Background Art

[0002] Die casting is a molding technology that involves hydraulically injecting aluminum alloy into a mold cavity at high speed and high pressure, followed by cooling and solidification to produce die-cast parts. Die casting technology boasts high production efficiency and is widely used in the automotive, motorcycle, electronic, and mechanical equipment industries. In conventional die-casting production, the aluminum alloy liquid is injected into the mold cavity at high speed. Because the gas in the injection chamber and mold cavity has no time to escape, it can become entrapped in the die-cast part, reducing its density and mechanical properties. It also renders the die-cast part unsuitable for heat treatment, as heat treatment causes the entrapped gas to expand, leading to deformation and surface bubbles.

[0003] Vacuum die-casting uses a vacuum pump to evacuate the air from the injection chamber and mold cavity before hydraulically injecting the aluminum alloy into the mold cavity at high speed and high pressure. This prevents the entrapment of air during mold filling, improving the density and mechanical properties of the die-casting. This allows the die-casting to undergo heat treatment to further enhance its mechanical properties and prevent deformation and surface bubbles.

[0004] With the rapid development of new energy vehicles, integrated die-casting technology has seen rapid growth. Integrated die-casting combines multiple vehicle body and chassis components into a single component. Currently under development are integrated die-cast parts, including electric vehicle front cabins, rear floors, and battery trays. Compared to traditional automotive manufacturing techniques, integrated die-casting significantly reduces the number of body parts and weld points, simplifying the manufacturing process. This can significantly improve production efficiency, reduce manufacturing costs, and reduce vehicle weight, ultimately promoting the development of lightweight vehicles.

[0005] Integrated die-casting parts are large in size and complex in structure. To meet these requirements, higher demands are placed on both the vacuum die-casting system and the process. First, due to the larger mold cavity space, achieving a high vacuum level requires a more powerful vacuum die-casting system. Second, aluminum alloys and vacuum die-casting processes suitable for integrated die-casting are also required. However, existing vacuum die-casting systems and methods still face challenges such as low mold cavity vacuum, high equipment failure rates, poor mechanical properties of die-casting parts, and low pass rates. 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 technology, the present invention provides a vacuum die-casting system and a high-vacuum die-casting method and application. By scientifically designing the vacuum die-casting system, optimizing the vacuum die-casting process, improving the response speed of the hydraulic vacuum valve and the vacuum degree of the mold cavity, improving the density, mechanical properties, dimensional accuracy and pass rate of the die-casting parts, reducing the equipment failure rate, and meeting the integrated die-casting needs of large and complex aluminum alloy body structural parts of new energy vehicles.

[0007] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows:

[0008] The first aspect of the present invention provides a vacuum die-casting system, which is 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, wherein the horizontal die-casting machine is provided with a fixed platen, a movable platen, an injection chamber, an injection rod, an injection punch and a pouring gate, and the die-casting mold comprises a fixed module and a movable module, wherein the fixed module is mounted on the fixed platen of the horizontal die-casting machine, and the movable module is mounted on the movable platen of the horizontal die-casting machine, and a mold core is respectively provided inside the fixed module and the movable module. The fixed module is provided with an inner gate, and the movable module is provided with an ejection device. After the fixed module and the movable module are molded together, an inner gate, a mold cavity and an exhaust channel are formed. The hydraulic vacuum valve is installed between the fixed module and the movable module and connected to the exhaust channel. The hydraulic vacuum valve is connected to the filter, vacuum tank and vacuum pump through a pipeline. The hydraulic vacuum valve is connected to the vacuum valve controller and the displacement collector through a cable. The displacement grating is provided on the shot rod of the horizontal die-casting machine and is located below the displacement collector. The position of the shot 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 exhausted into a vacuum tank through exhaust ducts, creating a vacuum negative pressure in the mold cavity. Due to the large size of the integrated die-casting, the mold cavity and injection chamber also have a large space. In order to more quickly exhaust gas from the mold cavity and injection chamber into the vacuum tank, the prior art typically installs exhaust channels in the mold cavity and injection chamber separately. This approach results in a complex structure and is difficult to implement. To ensure a high vacuum negative pressure in the mold cavity, the present invention enhances the exhaust 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 facilitates the exhaust 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. The exhaust channels are preferably located above the die-casting surface, but can also be located in front of or behind the die-casting surface. The specific location should be determined based on the shape characteristics of the die-casting and the ease of layout.

[0010] Preferably, the hydraulic vacuum valve has a response time of no more than 35ms when opening and closing. Vacuuming the mold cavity is controlled by opening and closing the hydraulic vacuum valve. The time from the start of vacuuming to the end of vacuuming has a significant impact on the vacuum level of the mold cavity. Conventional vacuum die-casting typically uses a solenoid valve for control. While easy to implement, the solenoid valve's response time is typically over 150ms. This long response time can easily lead to aluminum alloy liquid entering the solenoid valve, causing blockage and a high equipment failure rate. Secondly, the long response time shortens the vacuuming time, resulting in insufficient vacuum in the mold cavity. To address this issue, the present invention employs a hydraulic vacuum valve for control, utilizes a displacement collector and a displacement grating to sense the position of the shot rod, and then controls 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 hydraulic vacuum valve's fast response prevents aluminum alloy liquid from entering the hydraulic vacuum valve, causing blockage and reducing equipment failure rates. Secondly, it provides a longer vacuuming time, ensuring a high vacuum in the mold cavity.

[0011] Preferably, the volume of the vacuum tank is not less than 5 cubic meters. The mold cavity is evacuated by extracting the gas in the mold cavity and the injection chamber into the vacuum tank through the vacuum tank, so that the mold cavity forms a vacuum negative pressure. Therefore, the effect of evacuating the mold cavity is also closely related to the volume of the vacuum tank. The volume of a conventional vacuum tank for vacuum die-casting is usually only 0.5-2 cubic meters. Due to the large size of the integrated die-casting, the space in the mold cavity and the injection chamber is also large. In order to make the vacuum degree of the mold cavity reach 50mbar, a vacuum tank with a larger volume than the vacuum tank used for conventional vacuum die-casting is required, otherwise the vacuum degree of the mold cavity cannot reach 50mbar.

[0012] A second aspect of the present invention provides a high vacuum die-casting method, which adopts the above-mentioned 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, 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 core of the die-casting mold;

[0015] Step 3: Spray the mold core of the die-casting mold with a release agent, then start the horizontal die-casting machine to push the dynamic mold plate to close the mold;

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

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

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

[0019] Step 7: Maintain pressure to allow the aluminum alloy liquid to cool and solidify, then open the die-casting mold, take out the die-casting, and obtain a high vacuum die-casting.

[0020] Preferably, the aluminum alloy liquid in step 1 is composed of the following components in mass percentage: Si 8.6-9.1%, Zn 1.62-1.67%, Fe 0.7-0.8%, Cr 0.43-0.48%, Zr0.18-0.23%, Ce 0.15-0.19%, and the balance is Al and other unavoidable impurity elements, the individual content of other impurity elements is ≤0.05%, and the total amount of other impurity elements is ≤0.2%.

[0021] Integrated die-casting requires that the aluminum alloy has excellent filling capacity and excellent mechanical properties in the non-heat-treated state. Among them, the role of Si is to enhance the fluidity of the aluminum alloy liquid and improve the strength and hardness of the die-casting. The role of Zn is to enhance the strength and hardness of the die-casting through solid solution strengthening. The role of Fe is conducive to the demolding of the die-casting, while enhancing the strength and hardness of the die-casting. The role of Cr is to refine the metamorphic iron-rich phase and enhance the strength and hardness of the die-casting. The role of Zr is to refine the grain structure of the die-casting and improve the structural uniformity and plasticity of the die-casting. The role of Ce is to refine the metamorphic eutectic silicon phase and improve the strength and plasticity of the die-casting. It should be pointed out in particular that the elemental composition and mass percentage of the aluminum alloy are a scientific combination. The expected effect can only be achieved when the elemental composition and content are met at the same time.

[0022] Preferably, the refining and purification gas in step 1 is nitrogen with a purity of ≥99.99%, and the refining solvent is composed of the following components in percentage by mass: 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] Aluminum alloy liquid inevitably contains inclusions and gases. The inclusions are mainly aluminum oxide, and the gases are mainly hydrogen. The inclusions and gases will reduce the density and mechanical properties of aluminum alloy die castings, and the effect of vacuum die casting cannot be achieved. The effect of refining and purification is closely related to the composition of the flux. Existing fluxes are all composed of chloride and fluoride salts of alkali metals such as Na, K, and Ca. This type of flux will cause the alkali metal content in the aluminum alloy to increase, thereby reducing the strength, plasticity and fatigue resistance of the die castings, and causing the risk of premature fracture and failure of automotive parts. In order to solve this problem, the present invention has developed a high-efficiency flux that does not contain alkali metals, wherein the melting point and boiling point of AlCl3 are very low. It sublimates into bubbles in high-temperature aluminum alloy liquid, which can absorb and take away slag inclusions and hydrogen in the aluminum alloy liquid, playing a purifying role. LiF forms molten salt in high-temperature aluminum alloy liquid, which can dissolve and adsorb slag inclusions such as aluminum oxide, promote the separation of slag inclusions from the aluminum alloy liquid, and improve the purification effect of the flux. CuCO3 decomposes into CO2 bubbles in the aluminum alloy liquid, which absorb and remove slag inclusions and hydrogen from the aluminum alloy liquid, thus purifying it. The decomposed Cu replenishes the Cu content of the aluminum alloy liquid, improving the strength of aluminum alloy die-castings. Ce(NO3)3, as a heat-generating agent, decomposes and releases a large amount of heat, accelerating the dissolution of the flux, improving the fluidity of the aluminum alloy liquid, and accelerating the floating of inclusions and hydrogen, thus enhancing the purification effect. The decomposed NO and NO2 bubbles also play a purifying role. The decomposed Ce can refine the modified eutectic silicon, improving the strength and plasticity of aluminum alloy die-castings.

[0024] Preferably, in step 2, after the vacuum pump is started to evacuate the vacuum tank, the vacuum degree of the vacuum tank is not less than 10 mbar.

[0025] Evacuating the mold cavity involves extracting the air from the mold cavity and injection chamber into a vacuum tank, creating a negative pressure in the mold cavity. Therefore, the effectiveness of vacuuming the mold cavity is closely related not only to the volume of the vacuum tank but also to its vacuum level. Due to the large size of integrated die-cast parts, the mold cavity and injection chamber spaces are also large, so the vacuum level in the vacuum tank must be no less than 10 mbar after evacuation; otherwise, the mold cavity vacuum level cannot reach 50 mbar.

[0026] Preferably, the step 2 of preheating the core of the die-casting mold is to preheat the core to 280-300°C.

[0027] The mold core is preheated using a mold temperature controller. The preheat temperature of the mold core is crucial to whether the aluminum alloy liquid can smoothly fill the mold cavity and whether a high-density aluminum alloy die-casting can be obtained. Due to the large size, complex structure and thin wall thickness of integrated die-castings, the preheat temperature requirements for the mold core are more stringent. If the mold core preheat temperature is too low, the aluminum alloy liquid will cool and solidify too quickly and will not be able to completely fill the mold cavity, and it will not be possible to obtain a fully filled aluminum alloy die-casting. If the mold core preheat temperature is too high, it will increase the cooling and solidification time, which is likely to cause shrinkage defects in the aluminum alloy die-casting, reduce the density and mechanical properties of the aluminum alloy die-casting, and prolong the pressure holding time, thereby reducing production efficiency.

[0028] Preferably, the time for spraying the release agent on the core of the die-casting mold in step three is 5-8 seconds, and the release agent is composed of the following components in mass percentage: 11.65% methylhydroxy silicone oil, 5.62% synthetic plant ester, 5.23% sodium alkylbenzene sulfonate, 4.58% ethanol, 3.41% sodium hexametaphosphate, 3.65% dibutyltin dilaurate, 0.84% pentachloronitrobenzene, and the rest is deionized water.

[0029] The function of a mold release agent is to form a uniform film on the core surface of a high-temperature die-casting mold, providing lubrication and mold release, improving the surface quality of the die-casting and extending the life of the mold. Due to the large size and high performance requirements of integrated die-castings, the quality of the mold release agent is also highly demanding. However, existing mold release agents still suffer from problems such as difficulty in demolding, severe carbon deposits, slow volatilization, and poor mold cavity vacuum and die-casting density. To address these issues, the present invention has developed a mold release agent with superior overall performance suitable for integrated die-casting. Methylhydroxy silicone oil, in particular, exhibits excellent thermal stability, electrical insulation, and lubricity, forming a uniform film on the mold surface and reducing adhesion between the die-casting and the mold. Synthetic plant esters primarily inhibit oil bleeding and increase the surface gloss of the die-casting. Ethanol primarily increases the high-temperature volatility of the mold release agent, accelerating the drying of the die-casting mold, preventing residual moisture from reducing the mold cavity vacuum, and improving the die-casting density. Sodium alkylbenzene sulfonate primarily promotes the uniform dispersion of methylhydroxy silicone oil and other ingredients in water, forming a stable emulsion that facilitates even spray application of the mold release agent. The main function of dibutyltin dilaurate is to improve the stability of the release agent and prevent the degradation or failure of the active ingredients. The main function of pentachloronitrobenzene is to inhibit the growth of microorganisms and extend the service life of the release agent.

[0030] Preferably, in step three, when the horizontal die-casting machine is started to push the movable die plate to close the mold, the clamping force is 7000-16000 kN.

[0031] The clamping force is the clamping force applied between the fixed and movable die blocks of the die-casting mold by a horizontal die-casting machine. The clamping force is mainly achieved by the horizontal die-casting machine. Its function is to prevent the movable die of the die-casting mold from moving and opening the mold when the aluminum alloy liquid fills the mold cavity at high speed and high pressure. The determination of the clamping force is closely related to the size and weight of the die-casting part. The larger the size and the heavier the weight of the die-casting part, the greater the clamping force required. Since the front cabin, rear floor and battery tray of the integrated die-cast electric vehicle are all large-sized and large-mass die-cast parts, the aluminum alloy liquid fills the mold cavity faster and with greater pressure. In order to ensure that the mold cavity can be filled, the clamping force of the front cabin is usually required to be 70,000kN, the clamping force of the rear floor is usually required to be 120,000kN, and the clamping force of the battery tray is usually required to be 160,000kN.

[0032] Preferably, in step 4, when the horizontal die-casting machine's shot rod is started to push the aluminum alloy liquid forward, the moving speed of the shot rod is 0.08-0.12 m / s.

[0033] The speed of the shot rod as it pushes the aluminum alloy liquid toward the ingate must be strictly controlled. If the shot rod moves too slowly, the temperature of the aluminum alloy liquid in the shot chamber will drop too much, making it difficult to fill the mold cavity. However, the shot rod's movement speed cannot be too fast either. First, too fast a speed will cause the aluminum alloy liquid in the shot chamber to roll over and entrain gas and slag, resulting in air pores and slag inclusions within the die-casting, making it impossible to obtain highly dense and high-strength aluminum alloy die-castings. Second, it will reduce the time it takes to evacuate the mold cavity. This is because the vacuum tank evacuates the mold cavity from the time the shot rod's punch moves across the sprue to the time the punch reaches the fast-shot position. If the shot rod moves too quickly during this distance, the vacuum tank's evacuation time will be reduced, making it difficult to achieve a high vacuum in the mold cavity.

[0034] Preferably, in step six, when the injection rod continues to push the aluminum alloy liquid forward to complete 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 use the shot rod to push the aluminum alloy liquid to fill the mold cavity in the form of a high-speed jet. Due to the large size, complex structure and thin wall thickness of the integrated die-casting parts, in order to quickly fill the mold cavity with the aluminum alloy liquid, the shot rod needs to push the aluminum alloy liquid to fill the mold cavity at a faster speed. If the shot rod moves too slowly, the speed at which the aluminum alloy liquid fills the mold cavity will also be slow, causing the aluminum alloy liquid to cool and solidify prematurely and fail to completely fill the mold cavity, thus failing to obtain an aluminum alloy die-casting with a complete shape and size. Of course, it is impossible to increase the speed of the shot rod indefinitely. Otherwise, the tonnage and power of the die-casting machine will need to be increased exponentially, resulting in a sharp increase in costs.

[0036] Preferably, the pressure maintenance in step seven means that the clamping force is maintained for 35-45 seconds after the aluminum alloy liquid completes filling the mold cavity, so that the aluminum alloy liquid in the mold cavity is completely cooled and solidified into a solid aluminum alloy component.

[0037] The holding time is closely related to the aluminum alloy liquid's pouring temperature, filling speed, and the size and wall thickness of the die-casting. If the aluminum alloy liquid's pouring temperature is low, the filling speed is slow, or the die-casting is small and thin-walled, the holding time can be shortened; conversely, it needs to be extended. Because integrated die-castings are large and complex, with thicker walls in some areas, the holding time must be appropriately extended to ensure the aluminum alloy liquid completely cools and solidifies within the mold cavity into a solid die-casting.

[0038] The third aspect of the present invention provides the application of the vacuum die-casting system and the high vacuum die-casting method, which is characterized in that the vacuum die-casting system and the 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 compartment, aluminum alloy rear floor, and aluminum alloy battery tray.

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

[0040] (1) The present invention uses a displacement collector and a displacement grating to directly sense the position of the injection rod, and opens and closes the hydraulic vacuum valve through a vacuum valve controller, thereby improving the response speed of the hydraulic vacuum valve. 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. At the same time, by increasing the number of exhaust channels and the volume of the vacuum tank, the exhaust of gas in the mold cavity is accelerated, providing equipment conditions for high-vacuum die-casting of large and complex aluminum alloy automotive structural parts;

[0041] (2) The present invention develops aluminum alloy materials, refined fluxes, and release agents suitable for integrated die casting, optimizes the vacuum die casting process, ensures high vacuum in the die cavity, and achieves a vacuum degree of 50 mbar, thereby achieving integrated high-vacuum die casting of large and complex aluminum alloy automotive structural parts, thereby improving the density of die castings and the product qualification rate;

[0042] (3) The present invention realizes high vacuum die-casting of large and complex aluminum alloy structural parts such as the front cabin, rear floor and battery tray of electric vehicles by optimizing the vacuum die-casting system and vacuum die-casting process, which greatly improves the mechanical properties of the die-cast parts. The tensile strength of the die-cast parts 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, meeting the development needs of lightweight electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1Schematic diagram of the structure of the vacuum die-casting system of the present invention;

[0044] Among them, 10-horizontal die casting, 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-pipeline, 39-cable, 11-fixed plate, 12-moving plate, 13-injection chamber, 14-injection rod, 15-injection punch, 16-pouring gate, 21-fixed module, 22-moving module, 23-mold core, 24-ingate, 25-ejection device, 26-ingate, 27-mold cavity, 28-exhaust channel. DETAILED DESCRIPTION

[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 provided with a fixed plate 11, a movable plate 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 movable module 22. The fixed module 21 is installed on the fixed plate 11 of the horizontal die-casting machine 10, and the movable module 22 is installed on the movable plate 12 of the horizontal die-casting machine 10. The fixed module 21 and the movable module 22 are respectively provided with a mold core 23. The fixed module 21 is provided with a mold core 23. The die block 22 is provided with an ingate 24. The movable die block 22 is equipped with an ejector device 25. When the fixed die block 21 and the movable die block 22 are joined, an ingate 26, a mold cavity 27, and an exhaust channel 28 are formed. A hydraulic vacuum valve 34 is installed between the fixed die block 11 and the movable die block 22 and 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 via a pipe 38. The hydraulic vacuum valve 34 is connected to a vacuum valve controller 35 and a displacement collector 36 via a cable 39. A displacement grating 37 is installed on the shot rod 14 of the horizontal die-casting machine 10 and located below the displacement collector 36. The displacement grating 37 and the displacement collector 36 sense the position of the shot rod 14. 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 for opening and closing the hydraulic vacuum valve 34 does not exceed 35 ms. Preferably, the volume of the vacuum tank 32 is no less than 5 cubic meters.

[0046] Example 1:

[0047] The vacuum die-casting system is used to integrally die-cast an aluminum alloy front engine compartment of an electric vehicle. The number of exhaust channels is 4, the response time of opening and closing the hydraulic vacuum valve is 35ms, and the volume of the vacuum tank is 5 cubic meters. The high vacuum die-casting method includes the following steps in sequence:

[0048] Step 1: smelting and preparing aluminum alloy liquid and refining and purifying the aluminum alloy liquid, then controlling the temperature of the aluminum alloy liquid at 685°C, the aluminum alloy liquid is composed of the following components in mass percentage: Si 8.92%, Zn 1.65%, Fe 0.73%, Cr0.46%, Zr 0.19%, Ce 0.17%, the balance is Al and other inevitable impurity elements, the individual content of other impurity elements is ≤0.05%, and the total amount of other impurity elements is ≤0.2%, the refining and purification gas is nitrogen with a purity of 99.99%, the refining solvent is composed of the following components in 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 degree of 10 mbar, and preheat the core of the die-casting mold to 290°C;

[0050] Step 3: Spray a mold release agent onto the core of the die-casting mold for 6 seconds, then start the horizontal die-casting machine to push the dynamic die plate to close the mold with a clamping force of 7000 kN. The mold release agent is composed of the following components by mass percentage: 11.65% methylhydroxy silicone oil, 5.62% synthetic plant 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: Pour the aluminum alloy liquid into the injection chamber through the pouring port, start the injection rod of the horizontal die casting machine and push the aluminum alloy liquid forward at a speed of 0.09 m / s;

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

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

[0054] Step 7: Maintain pressure for 40 seconds to allow the aluminum alloy liquid to cool and solidify, then open the die-casting mold and take out the die-casting part to 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 is used to integrally die-cast an aluminum alloy rear floor of an electric vehicle. The number of exhaust channels is 5, the response time of opening and closing the hydraulic vacuum valve is 35ms, and the volume of the vacuum tank is 6 cubic meters. The high vacuum die-casting method includes the following steps in sequence:

[0057] Step 1: smelting and preparing aluminum alloy liquid and refining and purifying the aluminum alloy liquid, then controlling the temperature of the aluminum alloy liquid at 680°C, the aluminum alloy liquid is composed of the following components in mass percentage: Si 9.1%, Zn 1.62%, Fe 0.8%, Cr0.43%, Zr 0.23%, Ce 0.15%, and the balance is Al and other inevitable impurity elements, the individual content of other impurity elements is ≤0.05%, and the total amount of other impurity elements is ≤0.2%, the refining and purification gas is nitrogen with a purity of 99.99%, and the refining solvent is composed of the following components in 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 degree of 10 mbar, and preheat the core of the die-casting mold to 280°C;

[0059] Step 3: Spray a mold release agent on the core of the die-casting mold for 5 seconds, then start the horizontal die-casting machine to push the dynamic mold plate to close the mold with a clamping force of 12,000 kN. The mold release agent is composed of the following components by mass percentage: 11.65% methylhydroxy silicone oil, 5.62% synthetic plant 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: Pour the aluminum alloy liquid into the injection chamber through the pouring gate, start the injection rod of the horizontal die casting machine to push the aluminum alloy liquid forward at a speed of 0.12 m / s;

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

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

[0063] Step 7: Maintain pressure for 35 seconds to allow the aluminum alloy liquid to cool and solidify, then open the die-casting mold and take out the die-casting part to obtain a high-vacuum die-casting part that can be used for the aluminum alloy rear floor of electric vehicles.

[0064] Example 3:

[0065] The vacuum die-casting system is used to integrally die-cast an aluminum alloy battery tray for an electric vehicle. The number of exhaust channels is 6, the response time of the hydraulic vacuum valve when opening and closing is 35ms, and the volume of the vacuum tank is 7 cubic meters. The high vacuum die-casting method includes the following steps in sequence:

[0066] Step 1: smelting and preparing aluminum alloy liquid and refining and purifying the aluminum alloy liquid, then controlling the temperature of the aluminum alloy liquid at 690°C, the aluminum alloy liquid is composed of the following components in mass percentage: Si 8.6%, Zn 1.67%, Fe 0.7%, Cr0.48%, Zr 0.18%, Ce 0.19%, the balance is Al and other inevitable impurity elements, the individual content of other impurity elements is ≤0.05%, and the total amount of other impurity elements is ≤0.2%, the refining and purification gas is nitrogen with a purity of 99.99%, the refining solvent is composed of the following components in mass percentage: 36.12% AlCl3, 28.37% LiF, 21.69% CuCO3, 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 degree of 10 mbar, and preheat the core of the die-casting mold to 300°C;

[0068] Step 3: Spray a mold release agent onto the core of the die-casting mold for 8 seconds, then start the horizontal die-casting machine to push the dynamic die plate to close the mold with a clamping force of 16,000 kN. The mold release agent is composed of the following components by mass percentage: 11.65% methylhydroxy silicone oil, 5.62% synthetic plant 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: Pour the aluminum alloy liquid into the injection chamber through the pouring gate, start the injection rod of the horizontal die casting machine to push the aluminum alloy liquid forward at a speed of 0.08 m / s;

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

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

[0072] Step 7: Maintain pressure for 45 seconds to allow the aluminum alloy liquid to cool and solidify, then open the die-casting mold and take out the die-casting to obtain a high-vacuum die-casting that can be used in aluminum alloy battery trays for electric vehicles.

[0073] Comparative Example 1:

[0074] The vacuum die-casting system and vacuum die-casting method of this comparative example are the same as those of 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 vacuum the mold cavity.

[0075] Comparative Example 2:

[0076] The vacuum die-casting system and vacuum die-casting method of this comparative example are the same as those of Example 1, except that in step 2, the vacuum pump is started to evacuate the vacuum tank so that the vacuum degree in the vacuum tank is 50 mbar.

[0077] Comparative Example 3:

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

[0079] Comparative Example 4:

[0080] The vacuum die-casting system and vacuum die-casting method of this comparative example are the same as those of Example 1, except that in step 3, the mold release agent developed by the present invention is not used, but the existing mold release agent is used to spray the mold core.

[0081] Comparative Example 5:

[0082] The vacuum die-casting system and vacuum die-casting method of this comparative example are the same as those of Example 1, except that in step 4, the speed at which the shot rod pushes the aluminum alloy liquid forward is 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 "Tensile testing of metallic materials - Part 1: Room temperature test methods". The specimens were stretched at room temperature on an electronic tensile testing machine to test the tensile strength, yield strength, and elongation of the aluminum alloy die castings. The results are shown in Table 1. The vacuum degree of the die cavity during the vacuum die casting process of Examples 1-3 and Comparative Examples 1-5 was tested according to the vacuum degree testing method for vacuum die casting given in the literature (Vacuum degree testing in vacuum die casting [J]. Railway Locomotive and Rolling Stock Workers, 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 was greater than 330 MPa, the yield strength was greater than 260 MPa, and the elongation was greater than 10%. The vacuum degree of the die cavity during the vacuum die casting process reached an average of 50 mbar. In Comparative Example 1, the vacuum degree of the mold cavity in the vacuum die-casting process of Comparative Examples 1-5 is poor due to the slow response speed of the solenoid valve, the vacuum time is shortened, the vacuum tank vacuum in Comparative Example 2 is less than 10mbar, the aluminum alloy liquid is refined and purified by the traditional alkali metal flux in Comparative Example 3, the existing mold release agent is used to spray the mold core, and the speed of the injection rod in step 4 of Comparative Example 5 pushing the aluminum alloy liquid forward is too fast. As a result, the vacuum degree of the mold cavity in the vacuum die-casting process of Comparative Examples 1-5 is poor, and the mechanical properties of the aluminum alloy die-casting are also poor. By comparison, it can be seen that the technical solution of the present invention can improve the vacuum degree in the mold cavity during the vacuum die-casting process, achieve high vacuum die-casting, and significantly improve the mechanical properties of the aluminum alloy die-casting.

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

[0086]

[0087] The present invention is described through embodiments, but does not constitute a limitation of the present invention. With reference to the description of the present invention, other changes to the disclosed embodiments are easy for professionals in this field to think of, and such changes should fall within the scope defined by the claims of the present invention.

Claims

1. A vacuum die-casting system, characterized in that: The invention comprises 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 provided with a fixed platen, a movable platen, an injection chamber, a shot rod, an injection punch and a pouring gate. The die-casting mold comprises a fixed module and a movable module. The fixed module is installed on the fixed platen of the horizontal die-casting machine, and the movable module is installed on the movable platen of the horizontal die-casting machine. A mold core is respectively provided inside the fixed module and the movable module. An ingate is provided on the fixed module, and an ejection device is provided on the movable module. When the fixed module and the movable module are combined, an ingate, a mold cavity and an exhaust channel are formed. The hydraulic vacuum valve is installed between the fixed module and the movable module and connected to the exhaust channel. The hydraulic vacuum valve is connected to the filter, the vacuum tank and the vacuum pump through a pipeline. The hydraulic vacuum valve is connected to the vacuum valve controller and the displacement collector through a cable. The displacement grating is provided on the shot rod of the horizontal die-casting machine and is located below the displacement collector. The position of the shot rod is sensed by the displacement grating and the displacement collector.

2. The vacuum die-casting system according to claim 1, characterized in that: The number of the exhaust channels is 4-6, and the number of the hydraulic vacuum valves is the same as the number of the exhaust channels.

3. The vacuum die-casting system according to claim 1, characterized in that: The response time of the hydraulic vacuum valve when opening and closing does not exceed 35ms.

4. The vacuum die-casting system according to claim 1, characterized in that: The volume of the vacuum tank is not less than 5 cubic meters.

5. A high vacuum die-casting method, which adopts the vacuum die-casting system according to any one of claims 1 to 4, characterized in that: The following steps are included in sequence: Step 1: Melt and prepare aluminum alloy liquid and refine and purify the aluminum alloy liquid, then control the temperature of the aluminum alloy liquid at 680-690℃; Step 2: Start the vacuum pump to evacuate the vacuum tank so that the vacuum degree of the vacuum tank is not less than 10mbar, and preheat the core of the die-casting mold to 280-300℃; Step 3: Spray the mold release agent on the core of the die-casting mold for 5-8 seconds, then start the horizontal die-casting machine to push the dynamic mold plate to close the mold, with a clamping force of 7000-16000kN; Step 4: Pour the aluminum alloy liquid into the injection chamber through the pouring gate, and start the injection rod of the horizontal die casting machine to push the aluminum alloy liquid forward; Step 5: After the injection punch moves past the pouring gate, open the hydraulic vacuum valve and exhaust the gas in the mold cavity into the vacuum tank through the exhaust channel; Step 6: When the injection punch reaches the fast injection position, the hydraulic vacuum valve is closed, and the injection rod continues to push the aluminum alloy liquid forward to fill the mold cavity at high speed; Step 7: Maintain pressure for 35-45 seconds to allow the aluminum alloy liquid to cool and solidify, then open the die-casting mold, take out the die-casting, and obtain a high vacuum die-casting.

6. The high vacuum die casting method according to claim 5, characterized in that: The aluminum alloy liquid in step 1 is composed of the following components in mass percentage: Composition: 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%, the balance is Al and other unavoidable impurity elements, the content of each impurity element is ≤0.05%, and the total amount of other impurity elements is ≤0.2%.

7. The high vacuum die casting method according to claim 5, characterized in that: The refining and purification gas in step 1 is nitrogen with a purity of ≥99.99%, and the refining solvent is composed of the following components in 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.

8. The high vacuum die casting method according to claim 5, characterized in that: Step 3: The release agent is composed of the following components in percentage by mass: 11.65% methylhydroxy silicone oil, 5.62% synthetic plant ester, 5.23% sodium alkylbenzene sulfonate, 4.58% ethanol, 3.41% sodium hexametaphosphate, 3.65% dibutyltin dilaurate, 0.84% pentachloronitrobenzene, and the rest is deionized water.

9. The high vacuum die casting method according to claim 5, characterized in that: When the horizontal die-casting machine is started in step 4 to push the aluminum alloy liquid forward, the moving speed of the injection rod is 0.08-0.12 m / s.

10. The high vacuum die casting method according to claim 5, characterized in that: In step 6, 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.

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