A precision die-casting method for non-ferrous metal parts of high-speed trains

Abstract

The application discloses a precision die-casting method for non-ferrous metal of high-speed train accessories, and aims to solve the technical problem of the internal porosity and oxidation inclusion caused by the spray jet gas rolling in the traditional high-pressure die-casting process, and further cause the insufficient fatigue performance and low reliability of the die-casting product; the method comprises the following steps: after the mold is closed, pre-vacuum extraction is performed to reduce the pressure of the mold cavity to below a preset threshold; the molten metal is accurately metered and injected into a pressure chamber; the injection punch fills and forms a continuous laminar flow front wave at a low speed to eliminate the spray jet phenomenon; when the metal liquid front reaches the gate position, a vacuum auxiliary system is triggered and switched to high-speed filling; then, pressure boosting and pressure maintaining solidification are performed, and the pressure maintaining parameters are dynamically adjusted according to the solidification process; finally, the mold is opened and the product is ejected; through the above scheme, the gas rolling mechanism can be eliminated from the source, the internal porosity is reduced, the structure is uniform and dense, the fatigue life, the thermal fatigue life and the comprehensive performance index of the die-casting product are significantly improved, the process window range is expanded, and the die-casting yield is improved.

Description

Technical Field

[0001] This invention relates to the technical field of metal material processing, and in particular to a precision die-casting method for non-ferrous metals used in high-speed train parts. Background Technology

[0002] As the core equipment of modern rail transit systems, the operational safety, passenger comfort, and long-term reliability of high-speed trains are closely related to the manufacturing quality of their key components. During high-speed operation, functional components such as car body structures, bogie assemblies, and electrical connections are continuously subjected to complex alternating loads, vibration stresses, and temperature cycles. This places extremely stringent requirements on the mechanical properties, dimensional accuracy, and microstructure uniformity of the component materials. Non-ferrous metals, especially aluminum alloys, magnesium alloys, and copper alloys with low density, high specific strength, excellent corrosion resistance, and outstanding formability, have become the irreplaceable preferred materials for key structural and functional components of high-speed trains.

[0003] Pressure casting, a highly efficient molten metal forming method that rapidly fills a precision cavity under high pressure and forms the metal, has gained widespread application and attention in the high-speed rail component manufacturing field due to its technological advantages in producing complex thin-walled components with high dimensional accuracy, good surface quality, excellent mechanical properties, and outstanding production efficiency. The core of pressure casting technology lies in using a pressure injection punch to drive the molten metal through a high-pressure filling and forming process. Its inherent process nature dictates that the filling speed and pressure parameters of the molten metal have a decisive impact on the final forming quality.

[0004] However, with the continuous increase in the operating speed and design life of high-speed trains, the structural complexity of high-speed rail components has significantly increased, the wall thickness difference has widened, and the requirements for internal quality have risen from the traditional "no major defects" to the level of "highly uniform and dense microstructure." Existing high-pressure die casting processes have revealed increasingly prominent technical bottlenecks in practical applications: while the high-pressure, high-speed filling method used in traditional high-pressure die casting processes can ensure complete filling of the molten metal, the molten metal, under the strong push of the injection punch, flows through the gating system at extremely high speeds and fills the mold cavity, making it prone to jetting and air entrapment. A large amount of air and oxide film are entrained into the molten metal, forming internal pores and inclusions that are difficult to remove. These microscopic defects can become the initiation source of fatigue cracks under subsequent complex stress conditions, severely weakening the fatigue life and structural reliability of the components. Simultaneously, during the high-speed filling process, the metal... The extremely rapid and uneven cooling rate of the liquid leads to a significant microstructure gradient within the die-cast parts. Significant differences exist in grain size, phase distribution, and second-phase morphology across different regions. This non-uniformity further exacerbates performance fluctuations under complex operating conditions, reducing dimensional stability and service life. Furthermore, traditional die-casting processes lack an effective dynamic feeding mechanism at the end of the filling stage. During solidification and shrinkage, the molten metal cannot receive sufficient replenishment, causing solidification defects such as shrinkage porosity and cavitation to concentrate in thick-walled areas, severely impacting the density and overall mechanical properties of the die-cast parts. These interconnected and mutually reinforcing technical deficiencies have created a difficult technical dilemma for traditional high-pressure die-casting methods in achieving the high reliability and long service life required for high-speed rail components.

[0005] The purpose of this invention is to provide a precision die-casting method for non-ferrous metals used in high-speed train parts, which can effectively solve the technical problems of internal porosity and oxide inclusions caused by spray jet air entrapment in traditional high-pressure die-casting processes, resulting in insufficient fatigue performance and low reliability of die-cast parts. Summary of the Invention

[0006] The purpose of this invention is to provide a precision die-casting method for non-ferrous metals used in high-speed train components, so as to overcome the shortcomings of the existing technology.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A precision die-casting method for non-ferrous metals used in high-speed train components includes the following specific steps: Step 1: Mold preparation and pre-vacuum extraction: After closing and locking the die-casting mold, the vacuum pump group is started to perform pre-vacuum extraction on the die-casting cavity, reducing the absolute pressure inside the cavity to below a preset vacuum threshold; Step 2: Quantitative pouring of molten metal: After precise measurement, the molten non-ferrous metal liquid is poured into the injection chamber of the die-casting machine; Step 3: Low-speed laminar flow filling: The injection punch is started, and low-speed laminar flow filling is performed at a preset first injection speed and first injection pressure, so that the molten metal forms a continuous laminar flow leading wave under the uniform push of the injection punch, eliminating the spray jet phenomenon in traditional die casting. Step 4: Vacuum Assisted Establishment and High-Speed ​​Filling Switching: When the laminar flow front of the molten metal is detected to reach the gate position, the vacuum assist system is triggered to start quickly, and the motion mode of the injection punch is switched to the preset second injection speed to complete the filling process of the die-casting cavity with molten metal; Step 5: Pressure Intensification and Holding Solidification: After the molten metal is filled, the pressure intensification and holding mode is switched to apply continuous high pressure to the solidifying molten metal, and the holding pressure parameters are dynamically adjusted according to the solidification process until the molten metal is completely solidified to form a die-cast product; Step 6: Mold Opening and Ejection: After the holding and solidification is completed, the cavity pressure is released and the mold is opened to eject the die-cast product, completing a complete die-casting process cycle.

[0008] Preferably, the first injection velocity and the first injection pressure in step 3 are set according to preset parameters. Under these velocity and pressure parameters, the molten metal is smoothly advanced along the sprue sleeve under the uniform push of the injection punch, forming a continuous laminar flow leading edge wave, completely eliminating the spray jet phenomenon in traditional die casting.

[0009] Preferably, the second injection speed in step 4 is higher than the first injection speed by a preset multiple. When the molten metal front reaches the gate position, the temperature sensor installed at the gate detects a temperature change signal. The temperature sensors installed at the gate and in various areas of the cavity are armored K-type thermocouples, with a high-temperature and high-pressure resistant nickel-based high-temperature alloy protective tube (grade GH3536, outer diameter 3mm, wall thickness 0.5mm, melting point ≥1300℃, pressure resistance ≥150MPa) sleeved on the probe. The installation structure is as follows: high-temperature sealant (temperature resistance ≥1200℃) is applied to the inner wall of the preset blind hole in the mold, and the thermocouple protective tube is embedded into the blind hole with an interference fit. The probe end is flush with or protrudes 0.1-0.2mm from the inner wall of the cavity. A 0.15mm gap is reserved at the bottom of the blind hole and filled with high thermal conductivity copper paste to ensure thermal response speed. The sealing method is: a double composite seal of "threaded interference fit + high-temperature ceramic glue" is used between the protective tube and the blind hole to prevent molten metal hydraulic fluid from seeping in. Signal transmission is as follows: The thermocouple leads are made of double-layer stainless steel braided shielded cable, which is led out through the mold clearance groove and connected to the signal isolation amplifier module via an aviation connector. This module is equipped with a low-pass filter circuit (cutoff frequency 200Hz) to eliminate mold closing impact and high-frequency electromagnetic interference from the hydraulic servo system. Reliability verification: Under continuous operating conditions of 80MPa holding pressure and 1100℃ molten metal flushing, the sensor's measurement accuracy remains within ±5℃, and the response time (from the arrival of the molten metal front to signal triggering) does not exceed 10ms, which meets the stability requirements of continuous batch production.

[0010] Alternatively, a time delay can be used as a backup judgment method. The die-casting machine control system issues dual commands: on the one hand, it sends an auxiliary output signal to trigger the external vacuum valve to open rapidly, so that the cavity vacuum level drops rapidly to below the preset target vacuum level within a preset response time; on the other hand, it switches the injection speed from the first injection speed to the second injection speed, entering the high-speed filling stage.

[0011] Preferably, for die casting of aluminum alloy materials, using AlSi9Cu3 aluminum alloy as the target, its liquidus temperature and solidus temperature are set according to preset temperature parameters. The AlSi9Cu3 aluminum alloy is heated to the preset temperature range, refined by slag removal, and then injected into the injection chamber through the die casting machine's quantitative system, with quantitative accuracy controlled within the allowable error range. The mold temperature is stabilized within the preset range. During the low-speed laminar flow filling stage, a preset first injection speed and first injection pressure are used, and this stage lasts for a preset time, with the molten metal front advancing to the gate position. After the vacuum assist system is activated, the cavity vacuum level rapidly decreases to the preset target vacuum level within a preset response time, and the second injection speed switches to the preset value. The boost pressure is rapidly increased to the preset target pressure, and the holding time is set to a preset range. When the cavity pressure sensor detects that the absolute pressure inside the cavity has dropped below the preset vacuum level, the pre-vacuum requirement is met.

[0012] Preferably, for die casting of magnesium alloy materials, using AZ91D magnesium alloy as the target, the liquidus temperature and solidus temperature are set according to preset temperature parameters. The magnesium alloy is heated to the preset temperature range, and a mixed protective atmosphere of sulfur hexafluoride and carbon dioxide is continuously introduced into the injection chamber. The ratio of sulfur hexafluoride to carbon dioxide is set according to a preset ratio, covering the surface of the molten metal in the injection chamber to prevent oxidation. During the low-speed laminar flow filling stage, a preset first injection speed and first injection pressure are used. Since the density of the magnesium alloy oxide film is close to that of the matrix, low-speed filling significantly reduces the risk of the oxide film being entrained into the molten metal. The vacuum valve opening delay time is set according to preset parameters, and the second injection speed is switched to a preset value. The boost pressure is set according to preset parameters, and the holding time is set according to a preset range. The target vacuum degree of the cavity does not exceed a preset threshold.

[0013] Preferably, for die casting of copper alloy materials, a copper-chromium-zirconium alloy of grade CuCr1Zr is used, and its liquidus temperature and solidus temperature are set according to preset temperature parameters. The copper alloy is heated to the preset temperature range under a nitrogen protective atmosphere, and after slag removal, it is injected into the injection chamber. Nitrogen protection is maintained throughout the casting process to prevent high-temperature oxidation. In the low-speed laminar flow filling stage, a preset first injection speed and first injection pressure are used. Due to the high viscosity of copper liquid, extremely low speed parameters are used to establish a stable laminar flow front, and this stage lasts for a preset time. The vacuum assist system is triggered by a dual determination method of gate temperature and time to prevent single sensor failure. The target vacuum degree of the cavity does not exceed a preset threshold, the vacuum valve opening delay time is set according to preset parameters, and the second injection speed is switched to a preset range. The cavity vacuum degree rapidly decreases to the preset target vacuum degree within a preset response time.

[0014] Preferably, step 5 involves dynamically adjusting the holding pressure parameters according to the solidification process. Specifically, this includes setting the holding pressure parameters in segments based on the wall thickness distribution characteristics of the die casting, applying higher holding pressure to the solidification stage corresponding to the thick-walled region. The segmented setting of the holding pressure includes the initial solidification feeding pressure, the middle solidification feeding pressure, and the late solidification feeding pressure, with the feeding pressure in the later stage being higher than the previous stage. Temperature sensors are installed in each area of ​​the cavity. Solidification begins when the temperature in the thin-walled region drops below the liquidus line. The solidification determination method is the same for the medium-thickness and thick-walled regions. A time-based backup determination serves as a contingency plan in case of abnormal temperature signals.

[0015] Preferably, during the solidification stage of the copper alloy, the pressurization pressure is rapidly increased to a preset target pressure. As the solidification process progresses, based on temperature sensor feedback, the feeding pressure is dynamically increased to a preset range when the thick-walled region enters the solidification shrinkage stage. The feeding pressure is the first preset value when the initial solidification temperature is higher than the preset temperature; the second preset value when the temperature is within the preset range during the middle solidification stage; and the third preset value when the temperature is lower than the preset temperature during the later solidification stage. This gradual pressurization strategy ensures sufficient liquid metal replenishment throughout the solidification shrinkage process. The total holding time is set within a preset range. The finished product is completed after heat treatment, solution treatment, and aging.

[0016] Preferably, the method also includes a process parameter matching method based on wall thickness distribution characteristics. Through pre-identification of wall thickness distribution characteristics and setting of zoned process parameters, the overall quality uniformity of complex structural components is achieved. The zone division method is as follows: based on the wall thickness distribution characteristics, the region is divided into thin-walled, medium-walled, and thick-walled regions. The process parameter matching rules are as follows: in the thin-walled region, the high-speed filling stage speed is increased according to a preset ratio, the feeding start timing is advanced according to a preset rule, the feeding pressure is set to a preset range, and the holding time is allocated according to a preset ratio; in the medium-walled region, standard parameters are used, the feeding pressure is set to a preset range, and the holding time is allocated according to a preset ratio; in the thick-walled region, the high-speed filling stage speed is increased according to a preset ratio, the feeding start timing is postponed according to a preset rule, the feeding pressure is set to a preset range, and the holding time is allocated according to a preset ratio.

[0017] Preferably, this method is suitable for precision die casting of high-speed train components. The non-ferrous metal is selected from aluminum alloy, magnesium alloy, or copper alloy. This method utilizes the multi-stage injection speed programmable control function of existing die casting machines to decouple the traditional single-speed high-pressure filling process into three controllable stages: low-speed laminar flow establishment, vacuum environment switching, and high-speed filling completion. No non-standard equipment needs to be added; the method of this invention can be realized simply by programming the process parameters.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Eliminate the root cause of air entrapment: By establishing a stable molten metal leading edge wave through the low-speed laminar flow filling stage, the air entrapment mechanism of spray jet, which is unavoidable in traditional die casting, is fundamentally eliminated, cutting off the formation path of internal pores from the source, and the internal porosity is significantly reduced. 2. Vacuum-assisted exhaust: After the laminar flow front is established, the vacuum-assisted system is started simultaneously to complete the high-speed filling stage in a stable vacuum environment, ensuring that even if a small amount of gas is generated during the filling process of a complex cavity, it can be extracted in time, and the target vacuum degree of the cavity is controlled within the preset range. 3. Uniform and dense structure: Solidification in a vacuum environment reduces the tendency of dissolved gas to precipitate. Combined with an optimized pressure-holding solidification process, a die-casting microstructure with fine grains, uniform structure, and high density is obtained, and the structure uniformity index reaches the preset level. 4. Significantly improved performance: The internal porosity is significantly reduced, and the fatigue life is greatly improved. Taking aluminum alloy as an example, the tensile strength reaches the preset performance index, and taking copper alloy as an example, the electrical conductivity reaches the preset performance index. The thermal fatigue life reaches the preset number of cycles, meeting the stringent requirements of high-speed train parts for high reliability and long service life. 5. Expanded process window: By using a time-separation strategy, the two mutually restrictive goals of filling integrity and internal quality in traditional processes are decoupled and realized, expanding the range of stable process window, achieving the preset range of die casting yield, and significantly improving the mechanical property dispersion coefficient. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall technical solution architecture of the precision die-casting method for non-ferrous metals used in high-speed train parts proposed in this invention. Figure 2 This is a schematic diagram of the core principle framework of the synergistic effect of low-speed laminar flow filling and vacuum-assisted exhaust in this invention; Figure 3 This is a schematic diagram of the dynamic adjustment framework for pressure holding parameters based on wall thickness distribution characteristics in this invention. Detailed Implementation

[0020] Example 1 To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0021] This invention proposes a precision die-casting method for non-ferrous metals based on low-speed laminar flow guidance and vacuum assistance. This method utilizes the multi-stage injection speed programmable control function of existing die-casting machines to decouple the molten metal filling process into multiple controllable stages. Through precise process parameter settings and timing control, it achieves coordinated control of low-speed laminar flow establishment, vacuum environment switching, and high-speed filling completion. The specific implementation of each step is described in detail below with specific technical solutions and implementation examples.

[0022] In step S1, after the die casting mold is closed and locked, a vacuum pump unit is started to pre-evacuate the die casting cavity, so that the absolute pressure in the cavity is reduced to below a preset vacuum degree threshold. The start of the vacuum pump unit is triggered by a drive signal sent from the die casting machine control system, which drives the vacuum pump motor to operate at the rated speed. The vacuum extraction pipeline is connected to the cavity flow channel through a cemented carbide sealing ring to ensure no gas leakage during the extraction process. A cavity pressure sensor monitors the pressure change in real time during the extraction process; the pressure sensor is a capacitive absolute pressure sensor with a measuring range of 0 to 101 kPa, an accuracy class of 0.5, and a resolution of 0.1 kPa. When the absolute pressure in the cavity drops below the preset vacuum degree threshold, the control system records the current pressure value, enters a standby state, and waits for the next instruction. The key parameters of the pre-evacuation stage include the target vacuum degree threshold, the extraction duration, and the operating power of the vacuum pump. For aluminum alloy die casting, the target vacuum degree threshold is set to ≤15 kPa, and the extraction duration is set to 60 seconds; for magnesium alloy die casting, the target vacuum degree threshold is set to ≤12 kPa, and the extraction duration is set to 55 seconds; for copper alloy die casting, the target vacuum degree threshold is set to ≤8 kPa, and the extraction duration is set to 90 seconds. The operating power of the vacuum pump is matched with the diameter of the extraction pipeline to ensure that the target vacuum degree is reached within the specified time.

[0023] In step S2, after accurately metering the molten non-ferrous metal liquid, it is poured into the injection chamber of the die casting machine. The melting of the metal liquid is carried out in a special melting furnace, which adopts medium-frequency induction heating, and the heating power is matched according to the mass of the metal liquid. The heating temperature range for aluminum alloy is 610°C to 630°C, for magnesium alloy is 580°C to 600°C, and for copper alloy is 1105°C to 1135°C. The temperature of the metal liquid is measured by an immersed thermocouple, with a temperature measurement accuracy of ±2°C and a temperature measurement response time of less than 1 second. Slag skimming and refining treatment are completed in the melting furnace. Degassing treatment is carried out by rotary degassing method or online degassing device, and inert gas argon or nitrogen is selected as the degassing medium. Quantitative pouring is realized by the quantitative system matched with the die casting machine, and the quantitative accuracy is controlled within ±1.5%. The metering principle of the quantitative system is that the pouring amount of the quantitative spoon is detected by a weighing sensor or a displacement sensor, and the detection signal is fed back to the control system for closed-loop control. The process of pouring into the injection chamber is carried out under a protective atmosphere. A mixed protective atmosphere of SF₆ and CO₂ is used for aluminum alloy and magnesium alloy, and a nitrogen protective atmosphere is used for copper alloy. The flow rate of the protective atmosphere is accurately controlled by a gas mass flow meter, with a flow control accuracy of ±2%.

[0024] In step S3, the injection plunger is activated to perform low-speed laminar flow filling at a preset first injection velocity and first injection pressure. This allows the molten metal to form a continuous laminar leading edge wave under the uniform propulsion of the injection plunger, eliminating the spray jet phenomenon. The first injection velocity ranges from 0.05 m / s to 0.5 m / s, and the first injection pressure ranges from 1 MPa to 3 MPa. Under these velocity and pressure parameters, the Reynolds number of the molten metal is controlled within the laminar flow range. The formula for calculating the Reynolds number is: Re = (ρvd) / μ Where ρ is the density of the molten metal, v is the injection velocity, d is the equivalent diameter of the gate, and μ is the dynamic viscosity of the molten metal. For AlSi9Cu3 aluminum alloy, the density ρ is 2.65 g / cm³, the dynamic viscosity μ is 1.2 × 10⁻³ Pa·s, and the equivalent diameter of the gate d is 10 mm. When the injection velocity v is 0.25 m / s, the Reynolds number Re is approximately 2200, which is lower than the critical Reynolds number of 2300, indicating that the molten metal is in a laminar flow state. Under the uniform propulsion of the injection punch, the molten metal smoothly advances along the gate sleeve, forming a stable laminar flow front wave in the gate region. The front-end shape of the laminar flow front wave is approximately parabolic, and the wavefront velocity is consistent with the injection punch velocity, without generating turbulence. The duration of the first injection stage is determined based on the distance from the gate to the cavity inlet. For typical high-speed train components, the distance from the gate to the cavity inlet is 50 mm to 100 mm, and the corresponding duration of the first injection stage is 0.3 seconds to 0.8 seconds. At this stage, the molten metal advances to the gate position, providing a stable initial filling state for subsequent stages.

[0025] In step S4, when the laminar flow front of the molten metal is detected to have reached the gate position, the vacuum-assisted system is triggered to start rapidly, and the motion mode of the injection punch is switched to the preset second injection speed to complete the filling process of the die-casting cavity with molten metal. The detection of the molten metal front reaching the gate position is determined by a temperature sensor at the gate. The temperature sensor is a type K thermocouple with a temperature range of 0℃ to 1300℃ and a response time of less than 50ms. When the molten metal front reaches the gate position, the temperature sensor detects a temperature change signal. The specific determination logic of the temperature change signal is as follows: the control system collects the thermocouple signal at the gate at a sampling frequency of ≥1000Hz. After removing high-frequency noise through digital low-pass filtering (cutoff frequency 100Hz), when the temperature rise rate (dT / dt) of three consecutive sampling cycles is greater than 15℃ / s and the amplitude is continuously higher than 2℃, it is determined that the molten metal front has effectively arrived, and a main trigger signal F_T is generated. Simultaneously, the control system dynamically calculates the backup time threshold based on the actual average velocity (v_real) of the first injection stage and the actual displacement (L) from the injection chamber to the gate: T_backup = L / v_real × 1.15. The arbitration rule for the dual-judgment logic is: the first condition met takes precedence; when F_T is valid, the temperature signal is prioritized; when only the time condition is met but the temperature signal is abnormal, forced triggering and alarm log recording are performed. A time delay is used as the backup judgment method, with the time delay set based on the duration of the first injection stage, typically 1.1 to 1.2 times the duration of the first injection stage. This dual-judgment mechanism ensures reliable triggering even when a single sensor fails. The trigger signal is output through the auxiliary output port of the die-casting machine control system, with a 24V DC switching signal type. Rapid opening of the vacuum auxiliary system is achieved through a solenoid valve drive circuit. The solenoid valve is a pilot-operated vacuum valve with a diameter matching the extraction pipeline. Upon receiving the trigger signal, the solenoid valve completes its opening action within 20ms, and the vacuum valve opening delay time is set to 20ms to 50ms. The cavity vacuum level rapidly decreases from a pre-vacuum state to the target vacuum level within 100ms to 150ms. For aluminum alloy die casting, the target vacuum level is set to ≤10kPa, and the vacuum level decrease response time is 150ms; for magnesium alloy die casting, the target vacuum level is set to ≤8kPa, and the vacuum level decrease response time is 120ms; for copper alloy die casting, the target vacuum level is set to ≤5kPa, and the vacuum level decrease response time is 100ms.The ratio of the second injection speed to the first injection speed is 10 to 25 times. For aluminum alloy die casting, the first injection speed is 0.25 m / s, and the second injection speed is 4.5 m / s, with a speed ratio of 18 times. For magnesium alloy die casting, the first injection speed is 0.18 m / s, and the second injection speed is 3.8 m / s, with a speed ratio of 21 times. For copper alloy die casting, the first injection speed is 0.08 m / s, and the second injection speed is 1.2 m / s, with a speed ratio of 15 times. During speed switching, the acceleration of the injection punch is precisely controlled by a servo proportional valve, and the acceleration setpoint ensures a smooth and shock-free switching process.

[0026] In step S5, after the molten metal is filled, the system switches to a pressurization and holding mode, applying continuous high pressure to the solidifying molten metal. The holding pressure parameters are dynamically adjusted according to the solidification process until the molten metal completely solidifies to form a die-cast product. The dynamic adjustment of the holding pressure parameters is achieved through a closed-loop control system of a built-in PLC in the die-casting machine. The control algorithm adopts an incremental PID combined with a feedforward compensation strategy. The pressure regulation mapping relationship is: ΔP = Kp·e + Ki·∫edt + Kd·(de / dt) + P_feedforward(T_wall), where e is the deviation between the real-time feedback value of the regional temperature sensor and the target solidification temperature, Kp, Ki, and Kd are the proportional coefficient (5-15), integral coefficient (0.1-0.5), and derivative coefficient (2-8), respectively, and P_feedforward is the basic feedforward compensation pressure obtained by looking up a table based on the local wall thickness of the casting. The priority arbitration rule for parallel signals from multiple regions is as follows: thin-walled regions respond first, and the compensation pressure is obtained immediately when the temperature drops to the liquidus line; thick-walled regions respond with a lag of 0.3-0.8 seconds, and if the temperature signal is delayed, the system automatically obtains the initial compensation pressure from the feedforward pressure lookup table. Pressure switching is controlled by a hydraulic proportional servo valve, which smoothly transitions within a 0.1-second control cycle to avoid abrupt changes.

[0027] The pressurization is achieved through a hydraulic system with a maximum working pressure of 80 MPa and a pressurization ratio of approximately 20:1 to 30:1. The initial pressurization pressure is set based on the characteristics of the metal material. For aluminum alloy die casting, the initial pressurization pressure is 35 MPa to 45 MPa; for magnesium alloy die casting, it is 30 MPa to 40 MPa; and for copper alloy die casting, it is 50 MPa to 60 MPa. The holding pressure parameters are dynamically adjusted according to the solidification process, which is determined by cavity temperature sensors. Multiple temperature sensors are installed in various areas of the cavity, and their placement is determined based on the wall thickness distribution of the die casting. Temperature sensors in thin-walled areas are placed at the minimum wall thickness, in medium-thickness areas at the middle of the wall thickness, and in thick-walled areas at the maximum wall thickness. Solidification begins when the temperature in thin-walled areas drops below the liquidus line; the solidification determination method is the same for medium-thickness and thick-walled areas. When the temperature in a specific region is detected to have entered the corresponding solidification stage, the control system automatically adjusts the corresponding feeding pressure for that region. The segmented setting of the holding pressure includes feeding pressure at the initial solidification stage, the middle solidification stage, and the late solidification stage. The initial solidification feeding pressure is used during the initial solidification stage (temperature above the solidus line +50°C); the middle solidification feeding pressure is used during the middle solidification stage (temperature within ±30°C of the solidus line); and the late solidification feeding pressure is used during the late solidification stage (temperature below the solidus line +20°C). The feeding pressure in each subsequent stage is higher than the previous stage, with a typical pressure increase gradient of 5 MPa to 10 MPa. For copper alloy die casting, a progressive pressure increase strategy is adopted: the initial solidification feeding pressure is 50 MPa, the middle solidification feeding pressure is 55 MPa, and the late solidification feeding pressure is 60 MPa. The holding time is determined based on the wall thickness and solidification characteristics of the die casting. For aluminum alloy die casting, the holding time is 8 to 12 seconds; for magnesium alloy die casting, it is 7 to 10 seconds; and for copper alloy die casting, it is 18 to 22 seconds. The holding time allocation is optimized according to the wall thickness distribution characteristics: the holding time in thin-walled areas accounts for 20% of the total holding time, the holding time in medium-thickness areas accounts for 35%, and the holding time in thick-walled areas accounts for 45%.

[0028] In step S6, after pressure holding and solidification are completed, the cavity pressure is released and the mold is opened to eject the die-cast part, completing one full die-casting process cycle. The cavity pressure is released via a hydraulic system pressure relief valve, with the pressure relief process lasting 2 to 3 seconds to ensure a smooth pressure drop to atmospheric pressure. The mold opening action is driven by a locking hydraulic cylinder, and the mold opening speed is set according to the structural characteristics of the die-cast part. After mold opening, the ejection device is activated, ejecting the die-cast part from the mold cavity. The ejection device is hydraulically driven, with an ejection speed of 10 mm / s to 30 mm / s, and the ejection stroke is determined according to the mold structure. After ejection, the die-cast part is removed by a part-removing robot or manually and transferred to the post-processing stage.

[0029] Hereinafter, the application of the method of the present invention in the precision die-casting of aluminum alloy brackets for high-speed train bogies will be described in detail with reference to specific application examples.

[0030] The aluminum alloy bracket for high-speed train bogies is a key load-bearing component connecting the car body and the bogie, and its structural characteristics are as follows: the wall thickness of the mounting flange area is 15mm to 25mm, the wall thickness of the functional rib plate area is 3mm to 5mm, and the wall thickness of the shell wall thickness area is 5mm to 10mm. This part is die-cast from aluminum alloy of grade AlSi9Cu3, the liquidus temperature of the material is 571°C, and the solidus temperature is 521°C.

[0031] In the mold preparation stage, the die-casting mold for the bogie aluminum alloy bracket is installed on a horizontal cold chamber die-casting machine, and the mold is closed and locked. The mold adopts a 3-point angular pin side core-pulling structure, and the parting surface is arranged at the maximum projection contour of the part. Start the mold temperature control system, and control the mold temperature to be stable within the range of 180°C to 220°C through the mold temperature controller. The mold temperature controller adopts heat-conducting oil circulation heating, the heating power is 24kW, and the temperature control accuracy is ±3°C. The mold temperature is measured by an embedded thermocouple, the temperature measuring points are arranged on the working surfaces of the moving mold and the fixed mold, and the measurement accuracy is ±1°C.

[0032] In the pre-vacuum extraction stage, the cavity is pre-evacuated by the vacuum tank system equipped with the die-casting machine. The volume of the vacuum tank is 50L, and the pumping speed of the vacuum pump is 180m³ / h. After the vacuum pump has been running for 60 seconds, the absolute pressure in the cavity is detected by the cavity pressure sensor to drop to 12kPa, which meets the pre-vacuum requirement. The cavity pressure sensor is installed at the vacuum valve seat of the mold, the sensor signal is transmitted to the control system through a shielded cable, and the signal transmission delay is less than 5ms.

[0033] In the molten metal pouring stage, the AlSi9Cu3 aluminum alloy is heated to 620±10°C in a resistance melting furnace. The melting process is protected by nitrogen coverage, and the melting time is 2 hours to 3 hours. The slag skimming and refining treatment is carried out with hexachloroethane refiner, the refining temperature is 630°C to 640°C, and the refining time is 5 minutes to 8 minutes. After slag skimming, front-furnace chemical inspection is carried out, and quantitative pouring is performed after the chemical composition is qualified. The molten aluminum is injected into the shot chamber through the quantitative system of the die-casting machine, the quantitative accuracy is controlled within ±1.5%, and the quantitative weight is 1.8kg to 2.2kg.

[0034] In the low-speed laminar flow filling stage, the injection plunger is activated. The first injection stage uses preset low-speed parameters: injection speed of 0.25 m / s and injection pressure of 2 MPa to 3 MPa. At this speed, the molten metal is smoothly advanced along the sprue sleeve under the uniform propulsion of the injection plunger. The inner diameter of the sprue sleeve is 50 mm, the gate length is 30 mm, and the gate cross-section is circular. When the molten metal flows through the gate, a stable laminar flow front wave is formed due to the sudden change in the flow cross-section. The leading edge of this laminar flow front wave has a smooth parabolic shape with no turbulent disturbances, completely eliminating the spray jet phenomenon in traditional die casting. The advancing speed of the molten metal front is consistent with the speed of the injection plunger, and the Reynolds number of the molten metal front in laminar flow is approximately 2200, which is within the stable laminar flow range. The first injection stage lasts for approximately 0.8 seconds, during which the molten metal front advances to the gate position.

[0035] During the vacuum-assisted setup and speed switching phase, when the molten metal front reaches the gate position, the K-type thermocouple installed at the gate detects a temperature jump signal. After amplification and filtering, the temperature jump signal is used to determine if the temperature change exceeds 15°C. Simultaneously, the time recorded by the internal timer of the control system is compared with a preset value. When both the temperature jump signal and the time condition are met, it is determined that the molten metal front has reached the gate position. The die-casting machine control system issues dual commands: on the one hand, it outputs a 24V DC switching signal through the auxiliary output port, triggering the external vacuum valve to open rapidly, causing the cavity vacuum level to drop rapidly from 12kPa to 7kPa within 150ms; on the other hand, the injection speed switches from 0.25m / s to 4.5m / s, entering the high-speed filling phase. Since a large amount of residual gas has been removed from the cavity at this time, the molten metal fills the cavity at a high speed under vacuum. The filling pressure during the high-speed filling phase is 35MPa to 45MPa, and the filling time is approximately 0.05 seconds to 0.08 seconds.

[0036] During the pressure-increasing, holding, and solidification stage, after the molten metal is filled, the die-casting machine automatically switches to the third injection stage, rapidly increasing the pressure to 40 MPa. The pressure-increasing process is achieved through a hydraulic system, with a response time of less than 100 ms. During the holding pressure process, the holding pressure parameters are dynamically adjusted according to the solidification progress. Temperature sensors located in various areas of the mold cavity monitor the molten metal temperature changes in real time. When the temperature in the thin-walled area drops below 571℃ (liquidity line), solidification is determined to have begun in the thin-walled area; similarly, when the temperature in the thick-walled area drops below 571℃, solidification is determined to have begun in the thick-walled area. Based on the solidification progress determination, the control system automatically adjusts the feeding pressure. The holding pressure time is set to 10 seconds, with the last 5 seconds of holding pressure representing a pressure reduction phase, gradually decreasing the pressure from 40 MPa to 10 MPa to prepare for mold opening.

[0037] During the mold opening and ejection stage, after pressure holding and solidification, the hydraulic system's pressure relief valve opens, and the cavity pressure is gradually released to atmospheric pressure within 2 seconds. The mold locking hydraulic cylinder retracts, separating the moving mold from the fixed mold. The mold opening process is divided into two stages: the first stage is slow mold opening, with an opening speed of 5mm / s to 10mm / s and an opening stroke of 20mm to 30mm, used to overcome unlocking resistance; the second stage is rapid mold opening, with an opening speed of 30mm / s to 50mm / s and an opening stroke of 200mm to 300mm. After the moving mold is fully opened, the ejection device is activated, ejecting the die-cast product from the moving mold cavity. The ejection speed is 15mm / s to 25mm / s, and the ejection pressure is 3MPa to 5MPa. After ejection, the die-cast product is transferred to post-processing steps for edge trimming, punching, heat treatment, etc.

[0038] Test results show that the aluminum alloy bracket for high-speed train bogies die-cast using the method of this invention has an internal porosity of 0.3%, lower than the technical requirement of 1.0%; an average grain size of 32μm, better than the technical requirement of 40μm; a microstructure uniformity index of 0.85, meeting the technical requirement of 0.80; a tensile strength of 285MPa, exceeding the technical requirement of 240MPa; and a fatigue life test result of 5×10⁻⁶. 6 All cycles passed under the load without failure.

[0039] Example 2 This embodiment describes the application of the method of the present invention in the precision die casting of magnesium alloy motor housings for high-speed trains. Magnesium alloys, with their advantages of low density, high specific strength, and good vibration damping performance, are widely used in the manufacture of high-speed train motor housings. However, the die casting process of magnesium alloys presents technical challenges such as a strong tendency for oxidation and combustion, a narrow solidification range, and rapid heat loss. The present invention effectively overcomes these technical challenges through targeted process parameter setting and timing control, achieving high-quality precision die casting of magnesium alloy motor housings.

[0040] In step S1, the magnesium alloy die-casting mold for the motor housing is installed on the die-casting machine and the mold is closed and locked. The motor housing mold adopts a 4-point inclined guide post side core-pulling structure, and the mold material is H13 hot work mold steel with a hardness of HRC44 to 48. The mold temperature control system uses an oil temperature controller, and the mold temperature is stabilized within the range of 160℃ to 200℃. The target vacuum level for the pre-vacuum extraction stage is set to ≤12kPa, and the extraction duration is set to 55 seconds. The pressure change during the extraction process is monitored in real time by a cavity pressure sensor to ensure that the absolute pressure inside the cavity drops below 12kPa.

[0041] In step S2, molten metal is quantitatively poured using magnesium alloy of grade AZ91D. The liquidus temperature of AZ91D magnesium alloy is 595℃, and the solidus temperature is 470℃. The magnesium alloy is smelted in a dedicated magnesium alloy smelting furnace, with the smelting temperature controlled within the range of 590±10℃. A protective atmosphere of mixed SF6 and CO2 is used during the smelting process, with a volume mixing ratio of SF6 to CO2 of 1:99 to 2:98, and a total flow rate of 3L / min to 5L / min. The protective atmosphere covers the surface of the molten metal in the injection chamber, effectively preventing the magnesium melt from oxidizing and burning. Slag removal and refining are performed using a flux refining method, with a refining temperature of 600℃ to 610℃ and a refining time of 5 to 8 minutes. Quantitative pouring is achieved through the die-casting machine's quantitative system, with a quantitative accuracy controlled within ±1.5%, and a quantitative weight of 1.2kg to 1.5kg.

[0042] In step S3, the injection plunger is activated for low-speed laminar flow filling. The first injection velocity is set to 0.18 m / s, and the first injection pressure is set to 1.5 MPa to 2.5 MPa. For AZ91D magnesium alloy, the density ρ is 1.74 g / cm³, and the dynamic viscosity μ is 1.0 × 10⁻³ Pa·s. When the injection velocity v is 0.18 m / s, the Reynolds number Re is approximately 3150, slightly higher than the critical Reynolds number. However, through the coordinated control of pressure parameters, the molten metal can still maintain a stable flow state without significant spray jet phenomenon. Since the density of the magnesium alloy oxide film is close to that of the matrix, under traditional high-speed filling conditions, the oxide film is easily entrained into the molten metal, forming inclusion defects. This invention significantly reduces the risk of the oxide film being entrained into the molten metal through low-speed laminar flow filling. The duration of the low-speed laminar flow filling stage is approximately 1.0 to 1.2 seconds, during which the leading edge of the molten metal advances to the gate position.

[0043] In step S4, when the molten metal front reaches the gate position, the vacuum-assisted system is rapidly activated, and the injection speed is switched to the second injection speed. The triggering method uses a temperature sensor at the gate to detect temperature changes, with the determination condition being a temperature change greater than 15°C or a time frame of 1.2 seconds. Because magnesium alloy solidifies quickly, the vacuum valve opening delay time is set to 25ms to 35ms, resulting in a faster response time than aluminum alloy die casting. The cavity vacuum level rapidly decreases from 12kPa to below 8kPa within 120ms. The second injection speed is set to 3.8m / s, 21 times the first injection speed. During speed switching, the acceleration of the injection punch is precisely controlled by a servo proportional valve to ensure a smooth and shock-free switching process.

[0044] In step S5, after the molten metal is filled, the system switches to a pressurization and holding mode. The initial pressurization pressure is set to 30 MPa to 40 MPa. The solidification shrinkage rate of magnesium alloy is approximately 3.8% to 4.2%, requiring appropriate feeding pressure for compensation. During the holding process, the holding pressure parameters are dynamically adjusted according to the solidification progress. Temperature sensors located in the thin-walled, medium-walled, and thick-walled regions of the mold cavity monitor the molten metal temperature changes in real time. The solidification determination temperature for the thin-walled region is 595℃ (AZ91D liquidus), and the solidification determination temperature for the thick-walled region is the solidus +30℃. When the temperature of a specific region enters the corresponding solidification stage, the control system automatically adjusts the feeding pressure for that region. The holding time is set to 7 to 10 seconds, adjusted appropriately according to the wall thickness.

[0045] In step S6, after the pressure holding and solidification are completed, the cavity pressure is released and the mold is opened to eject the motor housing product. The ejection speed is 12 mm / s to 20 mm / s, and the ejection pressure is 2.5 MPa to 4 MPa.

[0046] Key process control points include: the temperature of the molten metal is monitored by infrared thermography before pouring, with a temperature range of 580℃ to 600℃ and a measurement accuracy of ±3℃; the flow rate of the protective atmosphere is monitored in real time by a gas mass flow meter to ensure that it covers the liquid surface without generating turbulence; the vacuum level is monitored in real time by a vacuum sensor, and the judgment criterion is that the cavity pressure ≤8kPa before continuing; the speed switching timing is determined by both the temperature change of the gate thermocouple and the time backup, and is triggered when the temperature change is >15℃ or the time reaches 1.2s.

[0047] The test results show that the high-speed train motor housing die-cast using the method of this invention has an internal porosity of 0.4%, which is lower than the technical requirement of 0.8%; no visible inclusions were found in the oxide inclusion test; the tensile strength is 252 MPa, which exceeds the technical requirement of 230 MPa; the elongation is 6.8%, which meets the technical requirement of 5%; and the die-casting yield is 97.2%, which exceeds the technical requirement of 95%.

[0048] Example 3 This embodiment describes the application of the method of the present invention in the precision die casting of copper-based pantograph sliding plate components for high-speed trains. Copper-chromium-zirconium alloy (CuCr1Zr) is an ideal material for pantograph sliding plates on high-speed trains due to its high strength, high hardness, excellent electrical and thermal conductivity, and wear resistance. However, copper alloy die casting presents technical challenges such as high melting point, poor fluidity, large solidification shrinkage, and severe oxidation at high temperatures. The present invention effectively overcomes these technical challenges through targeted optimization of process parameters and a progressive pressure-feeding strategy.

[0049] In step S1, the pantograph sliding plate die-casting mold is installed on a copper alloy die-casting machine, and the mold is closed and locked. The copper alloy die-casting mold adopts an integral structure, and the mold material is tungsten-based hot-work mold steel with a hardness of HRC46 to 50, exhibiting excellent high-temperature wear resistance. Preheating is achieved through the mold temperature control oil circuit, with the moving mold temperature controlled at 180℃ to 200℃ and the fixed mold temperature controlled at 220℃ to 250℃. After preheating, the vacuum system is activated to pre-evacuate the cavity, and the cavity pressure is reduced to below 6 kPa after 90 seconds. Due to the sensitivity of copper alloy to oxidation at high temperatures, the pre-vacuum extraction requirements are more stringent, with the target vacuum level set at ≤8 kPa.

[0050] In step S2, a quantitative casting of molten metal is performed using a copper-chromium-zirconium alloy with the grade CuCr1Zr. The liquidus temperature of the CuCr1Zr alloy is 1080℃, and the solidus temperature is 1020℃. The copper alloy is smelted in an induction melting furnace, with the heating temperature controlled within the range of 1120±15℃. A nitrogen protective atmosphere is introduced throughout the smelting process to prevent high-temperature oxidation of the molten copper. Slag removal is performed using a phosphate-based flux at a slag removal temperature of 1080℃ to 1100℃. Quantitative casting is achieved through a die-casting machine's quantitative system, with a quantitative accuracy controlled within ±1.0%, and a quantitative weight of 0.8kg to 1.2kg.

[0051] In step S3, the injection plunger is activated for low-speed laminar flow filling. The first injection speed is set to 0.08 m / s, and the first injection pressure is set to 1 MPa to 2 MPa. Due to the high viscosity of molten copper (dynamic viscosity is approximately 4.0 × 10⁻³ Pa·s), a lower injection speed is required to establish a stable laminar flow front. For CuCr1Zr copper alloy, the density ρ is 8.9 g / cm³. When the injection speed v is 0.08 m / s, the Reynolds number Re is approximately 1800, which is lower than the critical Reynolds number, and the molten metal is in a stable laminar flow state. The low-speed laminar flow filling stage lasts for approximately 1.5 seconds. Under the uniform push of the injection plunger, the molten metal front advances along the sprue sleeve in an extremely stable state, forming a stable laminar flow front wave.

[0052] In step S4, when the leading edge of the molten metal reaches the gate position, the vacuum assist system is rapidly activated, and the injection speed is switched to the second injection speed. The triggering method employs a dual-determination approach based on gate temperature and time to prevent single sensor failure. When the temperature sensor detects a sudden temperature change signal and the time reaches a preset value (dual-determination condition), a trigger signal is output. The vacuum valve opening delay time is set to 20ms to 30ms for faster response to match the rapid solidification characteristics of molten copper. The cavity vacuum level rapidly decreases from 6kPa to below 2.5kPa within 100ms. The second injection speed is set to 1.0m / s to 1.2m / s, which is 12.5 to 15 times the first injection speed.

[0053] In step S5, after the molten metal is filled, the system switches to a pressurization and holding mode. The initial pressurization pressure is rapidly increased to 50 MPa. Since the solidification shrinkage rate of the copper alloy is approximately 5.2%, a higher feeding pressure is required for compensation. This embodiment employs a progressive pressurization and feeding strategy, dynamically adjusting the holding pressure parameters according to the solidification process. In the early stage of solidification (temperature above the solidus line +50°C, i.e., >1070°C), the feeding pressure is set to 50 MPa; in the middle stage of solidification (temperature within ±30°C of the solidus line, i.e., 990°C to 1050°C), the feeding pressure is increased to 55 MPa; and in the later stage of solidification (temperature below the solidus line +20°C, i.e., <1040°C), the feeding pressure is further increased to 60 MPa. The temperature sensor feedback signal is transmitted to the control system in real time, and the control system automatically adjusts the feeding pressure value according to temperature changes. The total holding time is set to 18 to 22 seconds to ensure sufficient feeding to compensate for the narrow solidification range of the copper alloy.

[0054] In step S6, after pressure holding and solidification, the mold is opened and the product is ejected. The product is then subjected to heat treatment (solution treatment + aging) to complete the process. The heat treatment process parameters are as follows: solution treatment temperature 920℃ to 940℃, holding time 2 hours, water quenching; aging treatment temperature 480℃ to 500℃, holding time 4 hours, air cooling.

[0055] Test results show that the copper-based pantograph sliding plate of the high-speed train, die-cast using the method of this invention, has an internal porosity of 0.25%, lower than the technical requirement of 0.8%; a density of 99.2%, exceeding the technical requirement of 98%; an electrical conductivity of 78.5% IACS, exceeding the technical requirement of 75% IACS; a tensile strength of 435 MPa, exceeding the technical requirement of 400 MPa; a wear resistance of 0.08 mm / 100 km, better than the technical requirement of 0.15 mm / 100 km; and a thermal fatigue life of 7.2 × 10⁻⁶. 4 This time, exceeding the technical requirement of 5×10 4 Second-rate.

[0056] Example 4 This embodiment describes the general application of a process parameter matching method based on wall thickness distribution characteristics in the precision die casting of complex structural components for high-speed trains. High-speed train components have complex structures and significant differences in wall thickness. Taking the traction motor end cover as an example, its typical wall thickness distribution is: 15mm to 25mm in the mounting flange area, 3mm to 5mm in the functional rib area, and 5mm to 10mm in the shell wall area. This invention achieves overall quality uniformity for complex structural components through pre-identification of wall thickness characteristics and setting of zoned process parameters.

[0057] The wall thickness distribution feature identification method includes the following steps: First, obtain the structural model of the die casting through 3D scanning or design drawings, identify and record the wall thickness distribution of each region, and form a wall thickness distribution map. The wall thickness distribution map is established using a gridding method, dividing the die casting surface into several feature regions, and the average wall thickness value of each feature region is taken. Second, based on the wall thickness value, the feature regions are divided into thin-walled regions (1.5mm to 3mm), medium-walled regions (5mm to 10mm), and thick-walled regions (15mm to 25mm). The solidification characteristics of the thin-walled region are rapid solidification, with a solidification time of 0.5 seconds to 1.2 seconds, and the process challenges are difficult filling and easy cold shuts; the solidification characteristics of the medium-walled region are medium-speed solidification, with a solidification time of 2 seconds to 4 seconds, and the process challenge is controlling the uniformity of the microstructure; the solidification characteristics of the thick-walled region are slow solidification, with a solidification time of 6 seconds to 12 seconds, and the process challenges are the risk of shrinkage porosity and shrinkage cavities.

[0058] The matching rules for process parameters and wall thickness are set as follows: For thin-walled areas, the high-speed filling stage speed is increased by 5% to 15%, the feeding start time is advanced (thin walls solidify first), the feeding pressure is set to 30MPa to 35MPa, and the holding time is allocated to 20% of the total holding time; For medium-thickness areas, the high-speed filling stage speed uses standard parameters, the feeding start time is moderate, the feeding pressure is set to 38MPa to 42MPa, and the holding time is allocated to 35% of the total holding time; For thick-walled areas, the high-speed filling stage speed is increased by 10% to 20%, the feeding start time is delayed (thick walls solidify later), the feeding pressure is set to 48MPa to 55MPa, and the holding time is allocated to 45% of the total holding time.

[0059] Process parameter programming is achieved through the die-casting machine control system. The injection speed curve and the feeding pressure curve are programmed according to the aforementioned matching rules to form a timing control sequence. During injection, the control system automatically switches process parameter segments based on trigger conditions. The trigger conditions are obtained by installing temperature sensors in the thin-walled, medium-walled, and thick-walled regions of the cavity, with the sensors positioned at the geometric center of each region. When the temperature sensor detects that the temperature has dropped below the liquidus line, solidification in that region is determined to have begun. A time backup mechanism serves as a contingency plan in case of abnormal temperature signals. This is achieved by timing the process using an internal timer within the die-casting machine. When the timer reaches a preset value, a corresponding action is triggered.

[0060] The comparison of implementation results shows that after adopting the process parameter matching method based on wall thickness distribution characteristics, the thin-wall filling integrity improved from 92% to 99.5%, an improvement of +7.5%; the internal porosity decreased from 1.8% to 0.25%, an improvement of -86%; the shrinkage porosity grade in the thick-walled area improved from level 3 to level 1, an improvement of 2 levels; the microstructure uniformity index improved from 0.62 to 0.89, an improvement of +44%; the mechanical property dispersion coefficient decreased from 12% to 4%, an improvement of -67%; and the die-casting yield improved from 91% to 98.5%, an improvement of +7.5%.

[0061] The universality of the method was verified on various high-speed train components, including brake caliper brackets (wall thickness distribution from 2mm to 18mm), door hinge seats (wall thickness distribution from 3mm to 20mm), current collector bases (wall thickness distribution from 2.5mm to 15mm), and air conditioning fan impellers (wall thickness distribution from 1mm to 8mm). The verification results showed that after adopting this method, the internal porosity of various complex structural components was significantly reduced to 0.3%, 0.28%, 0.35%, and 0.22%, respectively, all of which are superior to the internal porosity levels of traditional processes.

[0062] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the scope of protection of the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely exemplary and not restrictive. Various equivalent substitutions, modifications, or alterations made by those skilled in the art based on the teachings of the present invention without departing from the spirit or principles thereof should be covered within the scope of the claims of the present invention.

Claims

1. A precision die-casting method for non-ferrous metals used in high-speed train components, characterized in that, Includes the following steps: Step 1, Mold Preparation and Pre-vacuum Extraction: After closing and locking the die-casting mold, start the vacuum pump unit to perform pre-vacuum extraction on the die-casting cavity, so that the absolute pressure in the cavity is reduced to below the preset vacuum threshold. For aluminum alloy materials, the target vacuum degree is ≤15kPa and the extraction duration is 60s. For magnesium alloy materials, the target vacuum degree is ≤12kPa and the extraction duration is 55s. For copper alloy materials, the target vacuum level is ≤8kPa and the extraction duration is 90s. Step 2, Quantitative Casting of Molten Metal: After precise metering, the molten non-ferrous metal liquid is poured into the injection chamber of the die-casting machine. For aluminum alloys, the heating temperature of the injection chamber and mold is 620±10℃, with a metering accuracy of ±1.5%. For magnesium alloys, the heating temperature is 580-600℃, and the protective atmosphere is a mixture of SF6 and CO2. For copper alloys, the heating temperature is 1105-1135℃, and the protective atmosphere is nitrogen, with a metering accuracy of ±1.0%. Step 3, Low-speed laminar flow filling: Start the injection punch and perform low-speed laminar flow filling at the preset first injection speed and first injection pressure. This allows the molten metal to form a continuous laminar flow leading edge wave under the uniform push of the injection punch, eliminating the spray jet phenomenon. For aluminum alloys, the first injection speed is 0.05-0.5 m / s and the first injection pressure is 1-3 MPa; for magnesium alloys, the first injection speed is 0.05-0.3 m / s and the first injection pressure is 1-2.5 MPa; for copper alloys, the first injection speed is 0.03-0.15 m / s and the first injection pressure is 1-2 MPa. Step 4, Vacuum Assist Establishment and High-Speed ​​Filling Switch: When the laminar flow front of the molten metal reaches the gate position, the vacuum assist system is triggered to start rapidly. At the same time, the motion mode of the injection punch is switched to the preset second injection speed. The ratio of the second injection speed to the first injection speed is 10-25 times, completing the filling process of the die-casting cavity with molten metal. For aluminum alloys, the second injection speed is 4.5-5.5 m / s; for magnesium alloys, it is 3.5-4.5 m / s; for copper alloys, it is 1.0-1.5 m / s. The cavity vacuum degree is ≤10 kPa for aluminum alloys, ≤8 kPa for magnesium alloys, and ≤5 kPa for copper alloys. The vacuum degree decrease response time is ≤150 ms for aluminum alloys, ≤120 ms for magnesium alloys, and ≤100 ms for copper alloys. Step 5, Pressure Intensification and Holding Solidification: After the molten metal is filled, switch to pressure intensification and holding mode to apply continuous high pressure to the solidifying molten metal, and dynamically adjust the holding pressure parameters according to the solidification process until the molten metal is completely solidified to form a die-cast product. Step 6, mold opening and ejection: After the pressure holding and solidification are completed, the cavity pressure is released and the mold is opened to eject the die-cast product, completing a complete die-casting process cycle; In step 5, the pressure holding parameters are dynamically adjusted according to the solidification process. Specifically, the pressure holding parameters are set in segments according to the wall thickness distribution characteristics of the die casting. Higher pressure holding is applied in the solidification stage corresponding to the thick wall area. The segmented setting of the pressure holding is the feeding pressure in the early solidification stage, the feeding pressure in the middle solidification stage, and the feeding pressure in the late solidification stage. The feeding pressure in the later stage is higher than that in the previous stage. Temperature sensors are installed in each area of ​​the cavity. When the temperature in the thin wall area drops below the liquidus line, it is determined that solidification has started. The solidification determination method is the same for the medium wall thickness area and the thick wall area. The time backup determination is used as a backup plan when the temperature signal is abnormal. The process parameter matching rules are as follows: In the high-speed filling stage of the thin-walled region, the speed is increased according to the preset ratio, the feeding start time is advanced according to the preset rules, the feeding pressure is set to the preset range, and the holding time is allocated according to the preset ratio; in the medium-thickness region, standard parameters are used, the feeding pressure is set to the preset range, and the holding time is allocated according to the preset ratio; in the high-speed filling stage of the thick-walled region, the speed is increased according to the preset ratio, the feeding start time is postponed according to the preset rules, the feeding pressure is set to the preset range, and the holding time is allocated according to the preset ratio.

2. The method according to claim 1, characterized in that: In step 3, the first injection speed and the first injection pressure are set according to preset parameters. The molten metal is smoothly advanced along the sprue sleeve under the uniform push of the injection punch, forming a continuous laminar flow leading edge wave and eliminating the spray jet phenomenon.

3. The method according to claim 1, characterized in that: In step 4, the second injection speed is higher than the first injection speed according to a preset multiple. When the front edge of the molten metal reaches the gate position, the temperature sensor installed at the gate detects a temperature change signal, or a time delay is used as a backup judgment method. The die-casting machine control system issues dual commands: on the one hand, it issues an auxiliary output signal to trigger the external vacuum valve to open quickly, so that the cavity vacuum level drops rapidly to below the preset target vacuum level within a preset response time. On the other hand, the injection speed is switched from the first injection speed to the second injection speed, entering the high-speed filling stage.

4. The method according to claim 1, characterized in that: For die casting of aluminum alloy materials, taking AlSi9Cu3 aluminum alloy as the object, the aluminum alloy is heated to a preset temperature range, and after slag removal and refining, it is injected into the injection chamber through the quantitative system of the die casting machine. The mold temperature is stabilized within a preset range. During the low-speed laminar flow filling stage, a preset first injection speed and a preset first injection pressure are used. After the metal liquid front advances to the gate position, the vacuum auxiliary system is activated, and the cavity vacuum degree drops rapidly to the preset target vacuum degree within a preset response time. The second injection speed is switched to a preset value, and the boost pressure is rapidly increased to the preset target pressure. The holding time is set to a preset range.

5. The method according to claim 1, characterized in that: For die casting of magnesium alloy materials, taking AZ91D magnesium alloy as the object, the magnesium alloy is heated to a preset temperature range. The injection chamber is circulated with a mixed protective atmosphere of sulfur hexafluoride and carbon dioxide throughout the process. The ratio of sulfur hexafluoride to carbon dioxide is set according to a preset ratio to cover the surface of the molten metal in the injection chamber to prevent oxidation. In the low-speed laminar flow filling stage, a preset first injection speed and a preset first injection pressure are used. Since the density of the magnesium alloy oxide film is close to that of the matrix, low-speed filling reduces the risk of the oxide film being drawn into the molten metal. The vacuum assist system uses a preset vacuum valve opening delay time. The second injection speed is switched to a preset value. The boost pressure is set according to preset parameters. The holding time is set according to a preset range. The target vacuum degree of the cavity does not exceed a preset threshold.

6. The method according to claim 1, characterized in that: For die casting of copper alloy materials, taking CuCrZr copper-chromium-zirconium alloy as the object, the copper alloy is heated to a preset temperature range under a nitrogen protective atmosphere, and after slag removal, it is injected into the injection chamber. Nitrogen protection is introduced throughout the casting process to prevent high-temperature oxidation. In the low-speed laminar flow filling stage, a preset first injection speed and first injection pressure are used. Due to the high viscosity of copper liquid, extremely low speed parameters are used to establish a stable laminar flow front. This stage lasts for a preset time. The vacuum auxiliary system is triggered by a dual judgment method of gate temperature and time to prevent single sensor failure. The target vacuum degree of the cavity does not exceed a preset threshold. The vacuum valve opening delay time is set according to preset parameters. The second injection speed is switched to a preset range.

7. The method according to claim 1, characterized in that: For the solidification stage of copper alloys, the pressurization pressure is rapidly increased to the preset target pressure. As the solidification process progresses, based on the feedback from the temperature sensor, when the thick-walled area enters the solidification shrinkage stage, the feeding pressure is dynamically increased to the preset range. When the initial solidification temperature is higher than the preset temperature, the feeding pressure is the preset first value. When the temperature in the middle of solidification is within the preset range, the feeding pressure is the preset second value. When the temperature in the later stage of solidification is lower than the preset temperature, the feeding pressure is the preset third value. The gradual pressurization strategy ensures that sufficient liquid metal is replenished throughout the solidification shrinkage process. The total holding time is set to the preset range. The product is completed after heat treatment, solution treatment, and aging.

8. The method according to claim 1, characterized in that: It also includes a process parameter matching method based on wall thickness distribution characteristics. By identifying wall thickness distribution characteristics in advance and setting process parameters for different zones, the overall quality of complex structural parts can be made uniform. The zone division method is as follows: based on the wall thickness distribution characteristics, it is divided into thin-walled areas, medium-walled areas and thick-walled areas.

9. The method according to any one of claims 1 to 8, characterized in that: This method is suitable for precision die casting of high-speed train parts. The non-ferrous metals are selected from aluminum alloys, magnesium alloys or copper alloys. The method utilizes the multi-stage injection speed programmable control function of the existing die casting machine to decouple the molten metal filling process into three controllable stages: low-speed laminar flow establishment, vacuum environment switching and high-speed filling completion. No non-standard equipment needs to be added. It can be achieved simply by programming the process parameters.

Images