Design and simulation optimization method for integrated forming equipment of magnesium alloy rear floor component of new energy automobile

Abstract

The invention discloses a design and simulation optimization method for magnesium alloy rear floor component integrated forming equipment of a new energy automobile, and relates to a design and simulation optimization method for magnesium alloy component integrated forming equipment. The method aims at solving the technical problems that in the magnesium alloy integrated die casting process, an isolated liquid phase area is easily formed in a thick and large area, feeding is difficult, and shrinkage porosity and shrinkage cavities are formed. The method comprises the following steps: constructing a three-dimensional model of a casting and die-casting equipment, and carrying out finite element mesh local refinement on a thin wall and a key feature region; setting magnesium alloy special thermophysical parameters and multi-field coupling simulation boundary conditions; and an orthogonal test method or a response curved surface method is adopted to carry out multi-target collaborative optimization on key process parameters such as the mold temperature, the injection speed and the boost pressure. According to the method, the mold filling stability of the magnesium alloy melt is remarkably improved, the internal defect volume of a casting is greatly reduced, and the mechanical property and the size precision of the integrated floor are effectively improved.

Description

TECHNICAL FIELD

[0001] The application relates to a magnesium alloy component integrated forming equipment design and simulation optimization method. BACKGROUND

[0002] Under the background of the double carbon strategy and the new energy vehicle development policy, in order to develop green manufacturing, reduce environmental pollution and save energy, the integrated die casting technology of new energy vehicles emerges as the times require. Compared with the traditional production process, the integrated die casting technology has the advantages of high production efficiency, low production cost and high material recovery rate. The development of integrated die casting technology helps new energy vehicles to become more energy-saving and environmentally-friendly transportation tools. At present, the production process of the main material aluminum alloy of the integrated component of new energy vehicles is mature, in order to further improve the lightweight level of the vehicle body, using magnesium alloy with higher specific strength, lighter quality and better fluidity to replace aluminum alloy is a new direction for the future development of new energy vehicles. In the process of magnesium alloy integrated die casting, due to the characteristics of complex shape, large size, large wall thickness difference and long filling process of the casting, isolated liquid phase zones are easily formed in the thick area of the rear floor, and it is difficult to compensate and form shrinkage and shrinkage holes. The traditional process cannot meet the needs of magnesium alloy component production. Combined with the differences between magnesium alloy and aluminum alloy, the equipment for producing aluminum alloy components, including the structure of the mold overflow system, the structure of the temperature control system, the control parameters and the production process parameters, need to be optimized. SUMMARY

[0003] The application aims to solve the technical problem that isolated liquid phase zones are easily formed in the thick area in the process of magnesium alloy integrated die casting, and it is difficult to compensate and form shrinkage and shrinkage holes, and provides a new energy vehicle magnesium alloy rear floor component integrated forming equipment design and simulation optimization method.

[0004] The new energy vehicle magnesium alloy rear floor component integrated forming equipment design and simulation optimization method of the application is carried out according to the following steps:

[0005] Step 1, build a system three-dimensional geometric model and an overflow system: according to the size, shape and hot spot of the magnesium alloy thin-walled casting in the casting process, a digital three-dimensional geometric model of the new energy vehicle magnesium alloy rear floor casting and the mold is established by using UG / NX or CATIA software; the projection area of the new energy vehicle magnesium alloy rear floor casting is about 2.7m 2 ~2.9m 2 , the minimum wall thickness is 2.5mm~2.8mm, and the longest flow channel is 1.4~1.5m;

[0006] The mold comprises a venting system, a gating system and a temperature control system; the venting system is composed of a venting system and an overflow system; in view of the characteristics of the high ingate speed of 60 m / s to 80 m / s and easy gas entrapment of the magnesium alloy melt during mold filling, the principle of "downstream slag collection and end strong venting" is followed, the venting system is arranged at the converging area of the melt during mold filling at the end of the rear floor longitudinal beam, the end of the shock tower and the center of the rear cross beam, specifically, 4 groups of high vacuum stop valve interfaces and 6 wave-shaped venting plates are arranged; the depth of the venting channel is controlled to be 0.15 mm to 0.2 mm, and the total cross-sectional area of the venting channel is designed to be 15% to 20% of the total cross-sectional area of the ingate to ensure that more than 90% of the gas in the cavity can be effectively discharged within the extremely short filling time of 0.01 s to 0.015 s;

[0007] The layout of the overflow system is arranged according to the cold dirty metal liquid and the oxide skin at the front end of mold filling, and 7 overflow channels are arranged along the periphery of the casting profile, including 3 inverted T-shaped overflow channels and 4 standard overflow channels, which are mainly located at the end of the forming flow channel of the thin-walled large surface and the far end of the impact area opposite to the ingate, so as to solve the cold segregation defect and the vortex gas entrapment problem; the inverted T-shaped overflow channel arranged in the impact area is more effective in collecting slag and reducing backflow; the volume of each standard overflow channel is designed to be 15 cm 3 ~20 cm 3 , and the total overflow amount is controlled to be 15% to 20% of the weight of the casting; the size of the overflow port is determined according to the solidification characteristics of the magnesium alloy, the thickness of the overflow port is 0.8 mm to 1.2 mm, and the length is 15 mm to 20 mm, which can effectively avoid the premature solidification of the metal liquid before the overflow channel is filled, so as to ensure the smoothness of the slag removal channel;

[0008] Step two, non-uniform meshing of the mold and casting: the three-dimensional model obtained in step one is imported into finite element analysis software (such as ProCAST or HyperMesh), and a non-uniform discretization strategy is adopted for the characteristics of large size and ultra-thin wall coexisting in the casting. Differentiated grid density and grid size are applied to the thin-wall forming area and thick-node area respectively; local grid refinement is performed at the key fluid impact areas such as the ingate inlet, flow channel turning point, overflow groove neck and reinforcement dense intersection, and the surface grid size is set to 0.8mm~1.5mm to accurately capture the micro-turbulent flow characteristics and locate the hot spot position; in the large-area flat area of the rear floor and non-critical die frame parts, the surface grid size is relaxed to 4mm~9mm; in order to solve the convergence difficulty problem caused by too large grid size difference, gradual grid is adopted, and transition grid layer is set between the encrypted area and sparse area to control the adjacent layer grid size growth of 10%~20% to realize the smooth connection from high-density fine area to low-density sparse area; finally, tetrahedral mesh is generated to ensure that at least 2-3 layers of units are distributed at the minimum wall thickness of 2.5mm, and the total number of global body mesh is controlled between 65 million and 95 million units, which avoids the overload calculation caused by global encryption and ensures the high fidelity of key physical field simulation;

[0009] Step three, thermal-physical parameter and boundary condition definition: based on the Scheil non-equilibrium solidification model in ProCAST simulation software, the model of magnesium alloy material is established in the finite element analysis software, and the parameters are determined by analysis and test. The solid-liquid line temperature interval is set to 477℃~613℃; the process boundary conditions are set: the pouring temperature is set to 690℃~720℃, the initial preheating temperature of the mold is set to 180℃~220℃, and the liquid material enters the pressure chamber and stays for 2s; the staged injection parameters are set: the slow injection speed is 0.4m / s~1m / s, then the acceleration is increased to 5 ~6.5m / s 2 of fast injection speed to complete rapid filling; at the end of filling, 30~40MPa of boost pressure is applied at the front end of the piston to realize forced solidification shrinkage; the interfacial heat transfer coefficient is set: a dynamic model coupled with time-temperature is adopted, and the heat transfer coefficient of the filling interface is set to 1000~2000 W / (m 2 ·K) in the initial stage of static and filling, and set to 10000~12000 W / (m 2 ·K) in the holding stage to simulate the rapid cooling effect;

[0010] Step four, multi-field coupling simulation and equipment structure optimization: numerical simulation of filling and solidification process is carried out, in the integrated die casting filling process, the magnesium alloy melt is regarded as an incompressible fluid, its flow obeys the conservation of mass and momentum, and the two equation turbulence model is used to describe the turbulence; according to step three, numerical simulation of filling and solidification process is carried out, based on temperature field, solidification field, shrinkage hole distribution and gas entrapment cloud picture, the high gas entrapment area under high speed filling and the isolated liquid phase area (hot spot) in solidification process are accurately positioned; accordingly, a vacuum-extrusion composite equipment is constructed, including integrating vacuum interface in gas entrapment area and deploying local extrusion compression mechanism with integrated pressure-displacement double closed loop feedback sensor in isolated liquid phase area (such as shock tower mounting seat);

[0011] Step five, structure design of vacuum-extrusion composite equipment: according to the simulation results of step four, the mold structure described in step one is designed; according to the gas entrapment cloud picture of step four, high vacuum degree stop valve interface is set in the gas entrapment area to improve the vacuum degree; according to the shrinkage hole cloud picture of step four, local extrusion compression mechanism is set in isolated liquid phase area away from ingate and with large wall thickness, including thick hot spot parts of shock tower mounting seat and rear longitudinal beam connection; when the target hot spot center alloy solid phase fraction reaches 30%~40% paste interval, start the active compression program; the extrusion pin is smoothly pressed in at a speed of 5~15mm / s, a local specific pressure of 90~120MPa is applied, the compression stroke depth is set to 8~12mm to fully compensate for the solidification volume shrinkage, and the pressure maintaining time is set to 5s~8s until the temperature of the area completely drops below the solidus, so as to eliminate shrinkage and porosity by forced compression on the basis of eliminating pores by vacuum, and realize the densification forming of key functional areas of the casting;

[0012] Step six, partition layout optimization of mold temperature control system: according to the temperature field simulation results of step four, the mold cavity surface is divided into thermal topology partitions, and the thin wall supercooling area prone to cold shut defects and the thick superheating area prone to hot spot shrinkage are identified; on this basis, a set of block type, multi-loop real-time dynamic closed loop temperature control system is designed; the temperature control system uses heat conducting oil as heat exchange medium, sets the heating temperature interval to 220℃~260℃, the oil pressure in the pipeline is 17bar, and the flow is set to 35~50L / min; the cooling system is set in the superheating area, and 10℃~15℃ industrial softened water is used as strong cooling medium; the cooling system water supply pressure is 0.2bar, and the single pipe flow is controlled at 12~18L / min to realize local rapid cooling; the whole temperature control system integrates PID intelligent temperature control algorithm, dynamically adjusts the medium flow and temperature of each partition according to the real-time temperature data feedback by the thermocouple in the mold, ensures the overall thermal balance of the mold, strictly follows the sequential solidification thermodynamics requirements of magnesium alloy, and eliminates the shrinkage and cold shut hazards at the microstructure level;

[0013] Step 7: Multi-objective collaborative optimization of key process parameters: Select slow injection speed, fast injection speed, pouring temperature, and mold preheating temperature as key process factors; construct L... 16 (4 4 Standard orthogonal experimental matrix or response surface experimental design; with minimizing the orifice volume and air entrainment as the control objectives, use genetic algorithm or particle swarm algorithm to perform global iterative optimization in multidimensional parameter space to obtain Pareto optimal solution set and determine the optimal process parameter window;

[0014] Step 8: Real-time Feedback-Based Closed-Loop Control Molding Verification: Molding experiments are conducted according to the optimal process parameters obtained in Step 7. Based on the simulation results in Step 7, the maximum expansion force is 8000~8200 tons. A safety factor of 1.15~1.2 is introduced, and a large die-casting island with a clamping force of 10000 tons is selected as the physical carrier. In the molding verification stage, a closed-loop feedback control system based on high-frequency sampling is constructed. Using an inertial rotation sensor and a pressure sensor integrated on the local piston device with a response frequency of 1000Hz, the real-time collected data is dynamically compared with the ideal process curve set in the simulation. When the actual pressure value exceeds the set target value, the control system will drive the electro-hydraulic servo valve to adjust the hydraulic oil flow and dynamically modify the extrusion speed and holding pressure within a response time of 10ms~15ms. In the holding pressure stage, by real-time compensation of a constant specific pressure of 30~35MPa, the pressure fluctuation range is controlled within 0.5MPa, thereby achieving active closure and precise control of internal shrinkage defects.

[0015] The method of this invention includes: constructing a high-precision three-dimensional model of the casting and die-casting equipment system (including temperature control pipelines), and locally refining the finite element mesh for thin-walled and key feature areas; setting specific thermophysical parameters for magnesium alloys and multi-field coupled simulation boundary conditions; identifying high-incidence areas of air entrapment and hot spots through flow simulation, and constructing a vacuum-assisted and local extrusion composite system accordingly; using orthogonal experimental design or response surface methodology to perform multi-objective collaborative optimization of key process parameters such as mold temperature, injection speed, and pressurization pressure; performing actual die-casting based on the optimal equipment structure and process parameter window, and implementing piston closed-loop control extrusion based on real-time feedback during the solidification stage. This invention, through the synergistic effect of vacuum drainage and local forced feeding, combined with precise real-time control of piston movement, significantly improves the filling stability of the magnesium alloy melt, greatly reduces the volume of internal defects in the casting, and effectively improves the mechanical properties and dimensional accuracy of the integrated floor. Attached Figure Description

[0016] Figure 1 This is a simulation diagram of the mold fixing process in step one of Experiment 1;

[0017] Figure 2 This is a simulation diagram of the moving mold in step one of experiment one;

[0018] Figure 3 The image shows a front view of the flow channel layout simulation for the temperature control system in step six of Experiment 1. The red line represents the oil heating pipe, and the blue line represents the water cooling pipe.

[0019] Figure 4 for Figure 3 A schematic diagram of the back of the structure within the yellow box; the blue area represents the water-cooling pipes.

[0020] Figure 5 This is a simulated schematic diagram of the inverted T-shaped overflow channel in step one of the experiment.

[0021] Figure 6 The simulated front view of the exhaust channel of the rear wave plate of the longitudinal beam in step one of Experiment 1;

[0022] Figure 7 for Figure 6 Top view;

[0023] Figure 8 This is a simulated front view of the exhaust duct of the rear wave plate of the wheel arch in step two of Experiment 1;

[0024] Figure 9 and Figure 10 First physical photograph of the magnesium alloy rear floor casting prepared for step eight of Experiment 1;

[0025] picture Figure 10 A second physical photograph of the magnesium alloy rear floor casting prepared for step eight of Experiment 1. Detailed Implementation

[0026] Specific Implementation Method 1: This implementation method is a design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles, specifically carried out according to the following steps:

[0027] Step 1: Constructing the System's 3D Geometric Model and Overflow System: Based on the dimensions and shape of the magnesium alloy thin-walled casting and the hot spots during the casting process, a digital 3D geometric model of the new energy vehicle magnesium alloy rear floor casting and mold is created using UG / NX or CATIA software; the projected area of ​​the new energy vehicle magnesium alloy rear floor casting is approximately 2.7m². 2 ~2.9m 2 The minimum wall thickness is 2.5mm~2.8mm, and the longest flow channel is 1.4~1.5m;

[0028] Step 2: Non-uniform mesh generation for the mold and casting: Import the 3D model obtained in Step 1 into the finite element analysis software. A non-uniform discretization strategy is adopted to address the characteristics of the casting's large size and ultra-thin walls. Different mesh densities and sizes are applied to the thin-walled forming area and the thick node area, respectively. Local mesh refinement is performed at critical fluid impact areas such as the inlet of the ingate, the flow channel turning point, the overflow groove neck, and the densely intersecting reinforcing ribs. The surface mesh size is set to 0.8mm~1.5mm to accurately capture microscopic turbulence characteristics and locate hot spots. In the large flat area of ​​the rear floor and non-critical mold frame parts, the surface mesh... The mesh size was increased to 4mm~9mm. To address the convergence difficulties that might be caused by excessive mesh size differences, a gradient mesh was adopted, with a transition mesh layer set between the dense and sparse regions. The mesh size of adjacent layers was controlled to increase by 10%~20% to achieve a smooth transition from the high-density fine region to the low-density sparse region. Finally, a tetrahedral volume mesh was generated, ensuring that at least 2-3 layers of elements were distributed at the minimum wall thickness of 2.5mm, and the total number of elements in the global volume mesh was controlled between 65 million and 95 million. This avoided the overload computation caused by global refinement and ensured the high fidelity of the simulation of key physical fields.

[0029] Step 3: Definition of Thermophysical Parameters and Boundary Conditions: Based on the Scheil non-equilibrium solidification model in ProCAST simulation software, a model of the magnesium alloy material was established in finite element analysis software. Parameters were determined through analysis and testing, and the solid-liquid phase temperature range was set to 477℃~613℃. Process boundary conditions were set as follows: casting temperature was set to 690℃~720℃, initial mold preheating temperature was set to 180℃~220℃, and the liquid material was allowed to stand in the pressure chamber for 2 seconds. Staged injection parameters were set: slow injection speed was 0.4m / s~1m / s, followed by 400m / s. 2 The acceleration is increased to a fast injection speed of 5m / s to 6.5m / s to complete rapid filling; at the end of filling, a pressure of 30 to 40MPa is applied to the front end of the piston to achieve forced solidification and feeding.

[0030] Step 4: Multi-field coupling simulation and equipment structure optimization: Numerical simulation of the filling and solidification process is performed according to Step 3. Based on the temperature field, solidification field, shrinkage cavity distribution, and gas entrapment cloud map, the high-incidence area of ​​gas entrapment under high-speed filling and the isolated liquid phase area during the solidification process are accurately located. Based on this, a vacuum-extrusion composite equipment is constructed, including integrating a vacuum interface in the gas entrapment area and deploying a local extrusion and feeding mechanism with integrated pressure-displacement dual closed-loop feedback sensors in the isolated liquid phase area.

[0031] Step 5: Vacuum-Extrusion Composite Equipment Structural Design: Based on the simulation results of Step 4, the mold structure described in Step 1 is optimized in a directional manner; based on the gas entrapment cloud map of Step 4, a high vacuum shut-off valve interface is set in the gas entrapment convergence area to improve the vacuum level; based on the shrinkage cloud map of Step 4, a local extrusion and feeding mechanism is set in the isolated liquid phase area far from the ingate and with a large wall thickness, specifically including the thick hot section at the connection between the shock absorber tower mounting base and the rear longitudinal beam.

[0032] Step Six: Optimization of the Die Temperature Control System Zoning Layout: Based on the temperature field simulation results from Step Four, the die cavity surface is divided into thermal topology zones to identify thin-walled undercooled areas prone to cold shut defects and thick, overheated areas that tend to form thermal shrinkage cavities. On this basis, a segmented, multi-loop, real-time dynamic closed-loop temperature control system is designed. This system uses heat transfer oil as the heat exchange medium, with a heating temperature range of 220℃~260℃, an oil pressure of 17 bar, and a flow rate of 35~50 L / min. A cooling system is installed in the overheated area, using industrial softened water at 10℃~15℃ as the strong cooling medium. The cooling system has a water supply pressure of 0.2 bar and a single-pipe flow rate controlled at 12~18 L / min to achieve localized rapid cooling.

[0033] Step 7: Multi-objective collaborative optimization of key process parameters: Select slow injection speed, fast injection speed, pouring temperature, and mold preheating temperature as key process factors; construct L... 16 (4 4 Standard orthogonal experimental matrix or response surface experimental design; with minimizing the orifice volume and air entrainment as the control objectives, use genetic algorithm or particle swarm algorithm to perform global iterative optimization in multidimensional parameter space to obtain Pareto optimal solution set and determine the optimal process parameter window;

[0034] Step 8: Real-time feedback-based closed-loop control forming verification: Actual production is carried out based on the optimized equipment and process parameters; High-frequency sensors integrated on the extrusion device are used to collect displacement and pressure data of the extrusion piston in real time at a 1ms cycle; The collected data is dynamically compared with the ideal P~t and S~t process curves set in the simulation; When the deviation is detected to exceed the threshold (such as displacement deviation > 0.1mm), the control system drives the electro-hydraulic servo valve to adjust the hydraulic oil flow and opening within 10~15ms, dynamically corrects the extrusion action, and realizes closed-loop control.

[0035] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the mold described in step one includes an overflow system, a gating system, and a temperature control system. The overflow system consists of an venting system and an overflow system. For the magnesium alloy molten metal filling process, where the ingate velocity reaches 60m / s to 80m / s, an venting system is installed at the end of the rear floor longitudinal beam, the end of the shock absorber tower, and the center of the rear crossbeam, where the molten metal converges. Specifically, this involves configuring four sets of high-vacuum shut-off valve interfaces and six corrugated venting plates. The venting channel depth is controlled at 0.15mm to 0.2mm, and the total cross-sectional area of ​​the venting channel is designed to be 15% to 20% of the total cross-sectional area of ​​the ingate to ensure that over 90% of the gas in the cavity can be effectively discharged within the extremely short filling time of 0.01s to 0.015s. Everything else is the same as in Specific Implementation Method One.

[0036] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the overflow system layout described in step one is designed to accommodate the cold molten metal and oxide scale at the front of the mold filling. A total of seven overflow channels are arranged along the perimeter of the casting outline, including three inverted T-shaped overflow channels and four standard overflow channels. These are primarily located at the ends of the forming runners on thin-walled, large surfaces and at the far end of the impact area directly opposite the ingate, to address cold shut defects and vortex entrapment issues. The inverted T-shaped overflow channels in the impact area more effectively collect slag and reduce entrapment. Each standard overflow channel is designed with a volume of 15 cm³. 3 ~20cm 3 The total overflow flow is controlled at 15%~20% of the casting weight; the overflow port size is determined according to the solidification characteristics of magnesium alloy, with an overflow port thickness of 0.8mm~1.2mm and a length of 15mm~20mm, which can effectively prevent the molten metal from solidifying and blocking the channel before filling the overflow tank, thereby ensuring the unobstructed flow of the slag discharge channel. Other aspects are the same as in specific implementation method one or two.

[0037] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step two, the thickness of the rear floor is 2.5mm to 3mm, and a surface mesh of 0.8mm to 1.1mm is used, with a volume mesh number of 10 million to 15 million. Everything else is the same as in Specific Implementation Methods One to Three.

[0038] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that: in step two, the wheel cover uses a 1.2~1.4mm surface mesh with a volume mesh count of 21 million~35 million; the longitudinal beam uses a 1.5~1.8mm surface mesh with a volume mesh count of 22 million~36 million. Everything else is the same as in Specific Implementation Method Four.

[0039] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that step three also includes setting the interface heat transfer coefficient: using a dynamic model that couples changes with time and temperature, the heat transfer coefficient of the filling interface is set to 1000~2000 W / (m²) during the static and initial filling stages. 2 ·K), the pressure holding stage is set to 10000~12000W / (m 2 A high value of K is used to simulate the quenching effect. Everything else is the same as in Specific Implementation Method Five.

[0040] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that: in step five, when the solid fraction of the alloy at the center of the target hot spot reaches a pasty range of 30%~40%, the active feeding program is initiated; the extrusion pin is smoothly pressed in at a speed of 5~15mm / s, applying a local specific pressure of 90~120MPa, setting the feeding stroke depth to 8~12mm to fully compensate for the volume shrinkage of the solidified solid, and maintaining the pressure holding time for 5s~8s until the temperature in this area completely drops below the solidus line. Thus, based on the elimination of porosity in vacuum, forced feeding is used to eliminate shrinkage cavities, achieving the densification of the key functional areas of the casting. Everything else is the same as in Specific Implementation Method Six.

[0041] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that: in step six, the entire temperature control system integrates a PID intelligent temperature control algorithm. Based on real-time temperature data fed back from the thermocouples inside the mold, it dynamically adjusts the medium flow rate and temperature of each zone, ensuring that the overall thermal balance of the mold strictly follows the sequential solidification thermodynamic requirements of magnesium alloys, thereby eliminating shrinkage porosity and cold shut-off risks at the microstructural level. Everything else is the same as in Specific Implementation Method Seven.

[0042] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that: in step eight, molding experiments are conducted according to the optimal process parameters obtained in step seven. Based on the simulation results in step seven, the maximum expansion force is 8000~8200 tons. A safety factor of 1.15~1.2 is introduced, and a large die-casting island with a clamping force of 10000 tons is selected as the physical carrier. Everything else is the same as in Specific Implementation Method Eight.

[0043] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that: In step eight, during the molding verification stage, a closed-loop feedback control system based on high-frequency sampling is constructed. Utilizing an inertial rotation sensor and a pressure sensor integrated on the local piston device, with a response frequency of 1000Hz, the real-time collected data is dynamically compared with the ideal process curve set in the simulation. When the actual pressure value exceeds the set target value, the control system will drive the electro-hydraulic servo valve to adjust the hydraulic oil flow and dynamically modify the extrusion speed and holding pressure within a response time of 10ms~15ms. During the holding pressure stage, by real-time compensation of a constant specific pressure of 30~35MPa, the pressure fluctuation range is controlled within 0.5MPa, thereby achieving precise control of internal shrinkage defects. Everything else is the same as in Specific Implementation Method Nine.

[0044] The invention was verified using the following experiments:

[0045] Experiment 1: This experiment demonstrates the design and simulation optimization method for an integrated molding equipment for magnesium alloy rear floor components in new energy vehicles. The verification object is the rear floor of a certain new energy vehicle model, with external dimensions of 1850mm × 1550mm × 450mm and a projected area of ​​2.8m². 2 The average wall thickness is 3mm, and the material is magnesium alloy. The specific steps are as follows:

[0046] Step 1: Constructing the system's three-dimensional geometric model and overflow system: Based on the size, shape, and hot spots of the magnesium alloy thin-walled casting during the casting process, a digital three-dimensional geometric model of the new energy vehicle magnesium alloy rear floor casting and mold is established using UG software; the minimum wall thickness of the new energy vehicle magnesium alloy rear floor casting is 2.5mm, and the longest flow channel is 1.5m.

[0047] The mold includes an overflow system, a gating system, and a temperature control system. The overflow system consists of an exhaust system and an overflow system. Considering the high inlet gate velocity (60m / s~80m / s) and easy air entrapment characteristics of magnesium alloy melt filling, following the principle of "co-current slag collection and strong end-point exhaust," an exhaust system is installed at the melt filling convergence area at the end of the rear floor longitudinal beam, the end of the shock absorber tower, and the center of the rear cross beam. Specifically, it is equipped with 4 sets of high-vacuum shut-off valve interfaces and 6 corrugated exhaust plates. The exhaust channel depth is controlled at 0.18mm, and the total cross-sectional area of ​​the exhaust channel is designed to be 18% of the total cross-sectional area of ​​the inlet gate to ensure that more than 90% of the gas in the cavity can be effectively discharged within the extremely short filling time of 0.01s~0.015s.

[0048] The overflow system is designed to accommodate the cold molten metal and oxide scale at the front of the mold filling process. Seven overflow channels are arranged along the perimeter of the casting, including three inverted T-shaped channels and four standard overflow channels. These are strategically located at the ends of the forming runners on thin-walled, large surfaces and at the far end of the impact zone directly opposite the ingate, to address cold shut defects and vortex entrapment issues. The inverted T-shaped overflow channels in the impact zone more effectively collect slag and reduce entrapment. Each standard overflow channel has a volume of 15 cm³. 3 The total overflow is controlled at 15% of the casting weight; the overflow port size is determined according to the solidification characteristics of magnesium alloy, with an overflow port thickness of 0.8mm and a length of 15mm, which can effectively prevent the molten metal from solidifying and blocking the channel before filling the overflow tank, thereby ensuring the smooth flow of the slag discharge channel.

[0049] Step 2: Non-uniform mesh generation for the mold and casting: Import the 3D model obtained in Step 1 into the finite element analysis software (ProCAST). A non-uniform discretization strategy is adopted to address the characteristics of the casting's large size and ultra-thin walls. Different mesh densities and sizes are applied to the thin-walled forming area and the thick node area, respectively. Local mesh refinement is performed in key fluid impact areas such as the inlet of the ingate, the runner turning point, the overflow neck, and the densely intersecting reinforcing ribs. The surface mesh size is set to 1mm to accurately capture microscopic turbulence characteristics and hot spot locations. In the large flat area of ​​the rear floor and non-critical mold frame parts, the surface mesh size is widened to 5mm. To address the convergence difficulties that may be caused by excessive mesh size differences... A gradient mesh is used, with a transition mesh layer set between the dense and sparse regions. The mesh size of adjacent layers is controlled to increase by 15% to achieve a smooth transition from the high-density fine region to the low-density sparse region. Finally, a tetrahedral volume mesh is generated, and the total number of volume meshes in the whole domain is controlled at 85 million elements. Compared with the whole domain fine mesh (about 150 million elements), the computational efficiency is improved by 40%. This avoids the overload computation caused by the whole domain refinement and ensures the high fidelity of the simulation of key physics fields. In step two, the rear floor uses a 1mm surface mesh with 15 million volume meshes; the wheel cover uses a 1.4mm surface mesh with 35 million volume meshes; and the longitudinal beam uses a 1.8mm surface mesh with 35 million volume meshes.

[0050] Step 3: Definition of Thermophysical Parameters and Boundary Conditions: Based on the Scheil non-equilibrium solidification model in ProCAST simulation software, a model of the magnesium alloy material was established in finite element analysis software. Parameters were determined through analysis and testing, and the solid-liquid phase temperature range was set to 477℃~613℃. Process boundary conditions were set as follows: casting temperature was set to 690℃~720℃, initial mold preheating temperature was set to 180℃~220℃, and the liquid material was allowed to stand in the pressure chamber for 2 seconds. Staged injection parameters were set: slow injection speed was 0.4m / s~1m / s, followed by 400m / s. 2The acceleration is increased to a fast injection velocity of 5~6.5 m / s to complete rapid filling; at the end of filling, a booster pressure of 40 MPa is applied to the piston front end to achieve forced solidification and feeding; the interface heat transfer coefficient is set: a dynamic model that varies with time and temperature is adopted, and the heat transfer coefficient of the filling interface is set to 2000 W / (m²) during the static and initial filling stages. 2 ·K), the holding pressure stage is set to 12000 W / (m 2 High values ​​of K) are used to simulate the rapid cooling effect;

[0051] Step 4: Multi-field Coupled Simulation and Equipment Structure Optimization: Numerical simulation of the filling and solidification process is performed. In the integrated die casting filling process, the magnesium alloy melt is regarded as an incompressible fluid, and its flow obeys the laws of mass conservation and momentum conservation. A two-equation turbulence model is used to describe the turbulence. According to the numerical simulation of the filling and solidification process described in Step 3, based on the temperature field, solidification field, shrinkage cavity, and gas entrapment cloud map, the high-incidence area of ​​gas entrapment under high-speed filling and the isolated liquid phase area (hot spot) in the solidification process are accurately located. Based on this, a "vacuum-extrusion composite equipment" is constructed: a vacuum interface is integrated in the gas entrapment area, and a local extrusion and feeding mechanism with integrated pressure-displacement dual closed-loop feedback sensors is deployed in the isolated liquid phase area (such as the shock absorber tower mounting base).

[0052] Step 5: Vacuum-Extrusion Composite Equipment Structure Design: Based on the simulation results of Step 4, the mold structure described in Step 1 is optimized in a directional manner. According to the gas entrapment cloud map of Step 4, a high-vacuum shut-off valve interface is set in the gas entrapment convergence area to improve the vacuum level. According to the shrinkage cavity cloud map of Step 4, in the isolated liquid phase area far from the ingate and with a large wall thickness, specifically including the thick hot section at the connection between the shock absorber tower mounting base and the rear longitudinal beam, a local extrusion pin (16mm in diameter) is set. When the alloy solid fraction at the center of the target hot section reaches a pasty area of ​​35%, the active feeding program is started. The extrusion pin is pressed in smoothly at a pushing speed of 15mm / s, applying a local specific pressure of 100MPa. The feeding stroke depth is set to 10mm to fully compensate for the solidification volume shrinkage, and the holding pressure is maintained for 5s~8s until the temperature in this area completely drops below the solidus line. Thus, based on the elimination of porosity in vacuum, the shrinkage cavity is eliminated by forced feeding, achieving the densification of the key functional areas of the casting.

[0053] Step Six: Optimization of the Die Temperature Control System Zoning Layout: Based on the temperature field simulation results in Step Four, the die cavity surface is divided into thermal topology zones to identify thin-walled undercooled zones prone to cold shut defects and thick, overheated zones that tend to form thermal shrinkage cavities. On this basis, a segmented, multi-loop real-time dynamic closed-loop temperature control system is designed. The temperature control system uses heat transfer oil as the heat exchange medium, sets the heating temperature range to 240℃, the oil pressure in the pipeline to 17 bar, and the flow rate to 50 L / min. A cooling system is installed in the overheated area, using 15℃ industrial softened water as the strong cooling medium. The cooling system's water supply pressure is 0.2 bar, and the single-pipe flow rate is controlled at 12 L / min to achieve localized rapid cooling. The entire temperature control system integrates a PID intelligent temperature control algorithm, dynamically adjusting the medium flow rate and temperature of each zone based on real-time temperature data fed back by thermocouples inside the die. This ensures that the overall thermal balance of the die strictly follows the sequential solidification thermodynamic requirements of magnesium alloys, thereby eliminating shrinkage porosity and cold shut defects at the microstructural level.

[0054] Step 7: Multi-objective collaborative optimization of key process parameters: Select slow injection speed, fast injection speed, pouring temperature, and mold preheating temperature as key process factors; construct L... 16 (4 4 The standard orthogonal experimental matrix is ​​shown in Tables 1 and 2 below. With minimizing the orifice volume and air entrainment as the control objectives, the genetic algorithm or particle swarm optimization algorithm is used to perform global iterative optimization in the multidimensional parameter space to obtain the Pareto optimal solution set and determine the optimal process parameter window.

[0055] Table 1. Factors and Levels of Orthogonal Experiments

[0056]

[0057] Table 2 Orthogonal Experimental Design Table (Four Factors, Four Levels)

[0058]

[0059] The optimal combination of process parameters was determined by range analysis and genetic algorithm optimization: casting temperature 690℃, mold temperature 180℃, fast injection speed 6m / s, and slow injection speed 0.4m / s.

[0060] Step 8: Real-time feedback-based closed-loop control forming verification: A 00000T die-casting machine was used for production verification. During the 5th batch of production, the closed-loop control system detected that the extrusion pin displacement lagged behind the preset curve by 0.15mm (indicating high resistance and slightly faster solidification). The system automatically increased the driving pressure by 5% to ensure proper extrusion.

[0061] Experimental Results Analysis: The magnesium alloy rear floor casting produced after optimizing the process using the method in Experiment 1 ( Figure 9 andFigure 10 The surface is smooth and free of cold shut defects.

[0062] Testing showed that the average air entrapment porosity of castings produced using the first test method was reduced to below 0.5%, the damping tower section was completely dense, the tensile strength of the main body reached 245MPa, the yield strength was 160MPa, the elongation was 8.5%, and the first-pass yield was increased to over 92%.

[0063] Comparative Example 1: Traditional die casting process, using the same casting model and materials as Experiment 1, but with the following process design: Overflow system: only a conventional slag bag is set, no vacuum valve is installed; mesh division uses a globally uniform 3mm volume grid with 20 million cells. Temperature control system uses constant water cooling, without zoned oil heating. Feeding method relies solely on gate budget feeding, without local extrusion devices. Control method uses open-loop control, with parameters set but not adjusted during the process. As a result, large shrinkage cavities with a diameter >3mm exist at the root of the damping tower, and there is obvious cold shut at the end of the flow channel.

[0064] Comparative Example 2: The optimized process was partially improved upon in Comparative Example 1: the number of overflow channels was increased, but a vacuum exhaust system was not introduced. The mesh generation used a standard uniform mesh size of 2mm without partitioning, resulting in insufficient mesh layers at thin-walled sections and a computation time as long as 30 hours. The feeding method added local extrusion pins, but a fixed time delay was used for triggering, without adjustment based on real-time solid phase fraction. Results: Compared to Comparative Example 1, shrinkage porosity was improved, but insufficient mesh accuracy led to a deviation in hot spot positioning, causing the extrusion pin position to become 5mm from the hot spot center, resulting in decreased feeding efficiency.

Claims

1. A design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles, characterized in that... The method is performed according to the following steps: Step 1: Constructing the System's 3D Geometric Model and Overflow System: Based on the dimensions and shape of the magnesium alloy thin-walled casting and the hot spots during the casting process, a digital 3D geometric model of the new energy vehicle magnesium alloy rear floor casting and mold is created using UG / NX or CATIA software; the projected area of ​​the new energy vehicle magnesium alloy rear floor casting is approximately 2.7m². 2 ~2.9m 2 The minimum wall thickness is 2.5mm~2.8mm, and the longest flow channel is 1.4m~1.5m; Step 2: Non-uniform mesh generation for the mold and casting: Import the 3D model obtained in Step 1 into the finite element analysis software. A non-uniform discretization strategy is adopted to address the characteristics of the casting's large size and ultra-thin walls. Different mesh densities and sizes are applied to the thin-walled forming area and the thick node area, respectively. Local mesh refinement is performed at critical fluid impact areas such as the inlet of the ingate, the flow channel turning point, the overflow groove neck, and the densely intersecting reinforcing ribs. The surface mesh size is set to 0.8mm~1.5mm to accurately capture microscopic turbulence characteristics and locate hot spots. In the large flat area of ​​the rear floor and non-critical mold frame parts, the surface mesh... The mesh size was increased to 4mm~9mm. To address the convergence difficulties that might be caused by excessive mesh size differences, a gradient mesh was adopted, with a transition mesh layer set between the dense and sparse regions. The mesh size of adjacent layers was controlled to increase by 10%~20% to achieve a smooth transition from the high-density fine region to the low-density sparse region. Finally, a tetrahedral volume mesh was generated, ensuring that at least 2-3 layers of elements were distributed at the minimum wall thickness of 2.5mm, and the total number of elements in the global volume mesh was controlled between 65 million and 95 million. This avoided the overload computation caused by global refinement and ensured the high fidelity of the simulation of key physical fields. Step 3: Definition of Thermophysical Parameters and Boundary Conditions: Based on the Scheil non-equilibrium solidification model in ProCAST simulation software, a model of the magnesium alloy material was established in finite element analysis software. Parameters were determined through analysis and testing, and the solid-liquid phase temperature range was set to 477℃~613℃. Process boundary conditions were set as follows: casting temperature was set to 690℃~720℃, initial mold preheating temperature was set to 180℃~220℃, and the liquid material was allowed to stand in the pressure chamber for 2 seconds. Staged injection parameters were set: slow injection speed was 0.4m / s~1m / s, followed by 400m / s. 2 The acceleration is increased to a fast injection speed of 5m / s to 6.5m / s to complete rapid filling; at the end of filling, a boost pressure of 30MPa to 40MPa is applied to the front end of the piston to achieve forced shrinkage; Step 4: Multi-field coupling simulation and equipment structure optimization: Based on the numerical simulation of the filling and solidification process described in Step 3, the high-incidence area of ​​air entrapment under high-speed filling and the isolated liquid phase area during the solidification process are accurately located based on the temperature field, solidification field, shrinkage cavity distribution, and air entrapment cloud map. Based on this, a vacuum-extrusion composite equipment is constructed, including a vacuum interface integrated in the air entrapment area and a local extrusion and feeding mechanism with pressure-displacement dual closed-loop feedback sensors deployed in the isolated liquid phase area. Step 5, Vacuum-Extrusion Composite Equipment Structural Design: Based on the simulation results of Step 4, the mold structure described in Step 1 is optimized in a directional manner; based on the gas entrapment cloud map of Step 4, a high vacuum shut-off valve interface is set in the gas entrapment convergence area to improve the vacuum level; based on the shrinkage cloud map of Step 4, a local extrusion and feeding mechanism is set in the isolated liquid phase area far from the ingate and with a large wall thickness, specifically including the thick hot section at the connection between the shock absorber tower mounting base and the rear longitudinal beam. Step Six: Optimization of the Die Temperature Control System Zoning Layout: Based on the temperature field simulation results from Step Four, the die cavity surface is divided into thermal topology zones to identify thin-walled undercooled areas prone to cold shut defects and thick, overheated areas that tend to form thermal shrinkage cavities. On this basis, a segmented, multi-loop, real-time dynamic closed-loop temperature control system is designed. The temperature control system uses heat transfer oil as the heat exchange medium, with a heating temperature range of 220℃~260℃, an oil pressure of 17 bar in the pipeline, and a flow rate of 35L / min~50L / min. A cooling system is installed in the overheated area, using industrial softened water at 10℃~15℃ as the strong cooling medium. The cooling system has a water supply pressure of 0.2 bar and a single-pipe flow rate controlled at 12L / min~18L / min to achieve localized rapid cooling. Step 7: Multi-objective collaborative optimization of key process parameters: Select slow injection speed, fast injection speed, pouring temperature, and mold preheating temperature as key process factors; construct L... 16 (4 4 Standard orthogonal experimental matrix or response surface experimental design; with minimizing the orifice volume and air entrainment as the control objectives, use genetic algorithm or particle swarm algorithm to perform global iterative optimization in multidimensional parameter space to obtain Pareto optimal solution set and determine the optimal process parameter window; Step 8: Real-time feedback-based closed-loop control forming verification: Actual production based on optimized equipment and process parameters; The high-frequency sensor integrated on the extrusion device is used to collect displacement and pressure data of the extrusion piston in real time with a period of 1ms. The collected data is dynamically compared with the ideal P~t and S~t process curves set in the simulation. When the deviation exceeds the threshold (such as displacement deviation > 0.1mm), the control system drives the electro-hydraulic servo valve to adjust the hydraulic oil flow and opening within 10~15ms, dynamically corrects the extrusion action, and realizes closed-loop control.

2. The design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles according to claim 1, characterized in that... The mold described in step one includes an overflow system, a gating system, and a temperature control system. The overflow system consists of an venting system and an overflow system. For magnesium alloy molten metal filling at ingate speeds as high as 60m / s to 80m / s, an venting system is installed at the molten metal converging areas at the ends of the rear floor longitudinal beams, the ends of the shock absorber towers, and the center of the rear crossbeams. Specifically, this involves configuring four sets of high-vacuum shut-off valve interfaces and six corrugated venting plates. The venting channel depth is controlled at 0.15mm to 0.2mm, and the total cross-sectional area of ​​the venting channel is designed to be 15% to 20% of the total cross-sectional area of ​​the ingate to ensure that over 90% of the gas in the cavity can be effectively discharged within the extremely short filling time of 0.01s to 0.015s.

3. The design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles according to claim 2, characterized in that... The overflow system described in step one includes seven overflow channels arranged around the perimeter of the casting to collect the cold molten metal and oxide scale from the front of the mold filling process. These include three inverted T-shaped overflow channels and four standard overflow channels. The channels are primarily located at the ends of the thin-walled, large-area forming runner and at the far end of the impact zone directly opposite the ingate, to address cold shut defects and vortex entrapment issues. The inverted T-shaped overflow channels in the impact zone more effectively collect slag and reduce entrapment. Each standard overflow channel is designed with a volume of 15 cm³. 3 ~20cm 3 The total overflow flow is controlled at 15% to 20% of the casting weight; the overflow port size is determined according to the solidification characteristics of magnesium alloy, with an overflow port thickness of 0.8mm to 1.2mm and a length of 15mm to 20mm, which can effectively prevent the molten metal from solidifying and blocking the channel before filling the overflow tank, thereby ensuring the smooth flow of the slag discharge channel.

4. The design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles according to claim 1, characterized in that... In step two, the thickness of the floor is 2.5mm to 3mm and it uses a surface mesh of 0.8mm to 1.1mm, with a volume mesh of 10 million to 15 million.

5. The design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles according to claim 4, characterized in that... In step two, the wheel cover uses a 1.2mm~1.4mm surface mesh with a volume mesh count of 21 million~35 million; the longitudinal beam uses a 1.5mm~1.8mm surface mesh with a volume mesh count of 22 million~36 million.

6. The design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles according to claim 1, characterized in that... Step three also includes setting the interface heat transfer coefficient: using a dynamic model that couples time and temperature, the heat transfer coefficient of the filling interface is set to 1000~2000 W / (m²) during the static and initial filling stages. 2 ·K), the pressure holding stage is set to 10000~12000W / (m 2 The high value of K was used to simulate the rapid cooling effect.

7. The design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles according to claim 1, characterized in that... In step five, when the solid fraction of the alloy at the center of the target hot spot reaches a paste-like range of 30% to 40%, the active feeding program is initiated. The extrusion pin is pressed in smoothly at a speed of 5 mm / s to 15 mm / s, applying a local specific pressure of 90 MPa to 120 MPa. The feeding stroke depth is set to 8 mm to 12 mm to fully compensate for the volume shrinkage of the solidified solids. The pressure is maintained for 5 to 8 seconds until the temperature in this area completely drops below the solidus line. Thus, based on the elimination of porosity in the vacuum, forced feeding is used to eliminate shrinkage cavities, achieving the densification of the key functional areas of the casting.

8. The design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles according to claim 1, characterized in that... The temperature control system in step six integrates a PID intelligent temperature control algorithm, which dynamically adjusts the medium flow and temperature of each zone based on real-time temperature data fed back by thermocouples inside the mold. This ensures that the overall thermal balance of the mold strictly follows the thermodynamic requirements of the sequential solidification of magnesium alloy, thereby eliminating the hidden dangers of shrinkage porosity and cold shut at the microstructure level.

9. The design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles according to claim 1, characterized in that... In step eight, a molding experiment is conducted according to the optimal process parameters obtained in step seven. Based on the simulation results in step seven, the maximum expansion force is 8000t~8200t. Combined with a safety factor of 1.15~1.2, a large die-casting island with a clamping force of 10000 tons is selected as the physical carrier.

10. The design and simulation optimization method for an integrated forming equipment for magnesium alloy rear floor components of new energy vehicles according to claim 9, characterized in that... In step eight, during the molding verification stage, a closed-loop feedback control system based on high-frequency sampling is constructed. Utilizing an inertial rotation sensor and a pressure sensor integrated on the local piston device, with a response frequency of 1000Hz, the real-time collected data is dynamically compared with the ideal process curve set in the simulation. When the actual pressure value exceeds the set target value, the control system will drive the electro-hydraulic servo valve to adjust the hydraulic oil flow and dynamically modify the extrusion speed and holding pressure within a response time of 10ms~15ms. During the holding pressure stage, by real-time compensation of a constant specific pressure of 30MPa~35MPa, the pressure fluctuation range is controlled within 0.5MPa, thereby achieving precise control of internal shrinkage defects.

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