Low-pressure Casting Process Research Articles

Multi-Objective Optimization of The Low-Pressure Casting of Large-Size Aluminum Alloy Wheels through a Systematic Optimization Idea.

The process parameters in the low-pressure casting of large-size aluminum alloy wheels are systematically optimized in this work using numerical casting simulation, response surface methodology (RSM), and genetic algorithm (NSGA-II). A nonlinear input-output relationship was established based on the Box-Behnken experimental design (BBD) for the crucial casting parameters (pouring temperature, mold temperature, holding pressure, holding time), and response indicators (defect volume fraction, spokes large plane mean secondary dendrite spacing (SDAS)), and a mathematical model was developed by regression analysis. The Isight 2017 Design Gateway and NSGA-II algorithm were used to increase the population and look for the best overall solution for the casting parameters. The significance and predictive power of the model were assessed using ANOVA. Casting numerical simulation was used to confirm the best option. To accomplish systematic optimization in its low-pressure casting process, the mold cooling process parameters were adjusted following the local solidification rate. The results showed that the mathematical model was reliable. The optimal solutions were a pouring temperature of 703 °C, mold temperature of 409 °C, holding pressure of 1086 mb, and holding time of 249 s. The mold cooling process was further optimized, and the sequence solidification of the optimal solution was realized under the optimized cooling process. Finally, the wheel hub was manufactured on a trial basis. The X-ray detection, mechanical property analysis, and metallographic observation showed that the wheel hub had no X-ray defects and its mechanical properties were well strengthened. The effectiveness of the system optimization process scheme was verified.

Optimization of residual stress in low-pressure casting of ZL205A alloys

ZL205A alloys are prone to generate serious residual stress due to the long solidification intervals and multi-phase composition. In this study, the low-pressure casting process for ZL205A alloy hemisphere shell casting was investigated and continuously optimized. In the initial process, the knockout time, pouring temperature, preheating temperature of the sand mould, dwelling pressure, and filling rate were 3 h, 710 °C, 30 °C, 65 kPa, and 0.33 kPa·s−1, respectively. Macroscopic properties and microstructural features were simulated using a combination of ProCAST and Thermal-Calc software. Additionally, a series of experimental procedures, including EBSD, SEM, EDS, and XRD tests, were conducted to investigate the formation, morphology, and distribution of the microstructure. Current findings demonstrate that during the solidification process, the maximum temperature difference exceeds 220 °C, the maximum undercooling reaches 49.56 °C, and the maximum effective stress peaks at 301.7 MPa. The residual stress ranges from 20 to 200 MPa. Furthermore, there is no significant texture and preferred grain orientation during nucleation and solidification, and the structure field exhibits an equiaxed crystal but inhomogeneous pattern. Moreover, the finer and more homogeneous the grains and the smaller the deviation in grain orientation, the lower the residual stress. Specifically, two analytical models are developed: one between the casting parameters and the residual stress, and another between the shrinkage defects and the casting parameters. The lowest residual stress is achieved when the knockout time, pouring temperature, preheating temperature of the sand mould, dwelling pressure, and filling rate are 6 h, 725 °C, 250 °C, 95 kPa, and 1.67 kPa·s−1 respectively.

Research on the low-pressure casting process of a double suction impeller in 304 austenitic stainless steel with high performance and thin-wall complex structure

The manufacturing of thin-wall complex castings using pressure-assisted casting is one of the most significant challenges for structural applications requiring excellent mechanical properties and fuel. In this paper, efforts have been made to manufacture thin-wall complex structure casting using high-temperature alloys with high strength. Low pressure casting forming process was used to manufacture a double suction impeller in 304 austenitic stainless steel with a thin-wall complex structure. By combining 3D printed sand mold with an optimized low-pressure casting process, a double suction impeller with a thin-wall thickness of 3mm was successfully prepared. The prepared double suction impeller showed structural integrity, smooth surface, and compact structure. The filling and solidification process of the 304 austenitic stainless-steel melts were analyzed using casting simulation software. The casting had an excellent mechanical property with a tensile strength of 595 MPa, yield strength of 265 MPa, and elongation of 48%. Results show that the improved low-pressure casting processes could be applied to the production of thin-wall complex structure parts during high-temperature casting processes. The results are of great significance to the casting of high-temperature alloys.

Microstructure and mechanical properties of LPSC AZ91-Sb magnesium alloy

ABSTRACT Microstructures and mechanical properties of AZ91-Sb magnesium alloy fabricated by low-pressure shell casting (LPSC) process in different conditions were investigated. The as-cast alloy exhibited a good internal quality and denser structure. The microstructure of α-Mg phases displayed dendritic feature and fine isolated β-Mg17Al12 particles phases uniformly distributed in the matrix. After the solution treatment at 415°C for 12 h, almost β-Mg17Al12 phases dissolved into the matrix. After ageing treatment at 200°C for 14 h, the LPSC alloy attained the peak hardness with restrained age-hardening kinetics. The discontinuous precipitates initiated at the grain boundaries and then continuous precipitates occurred in the grain interior. The LPSC alloy exhibits higher mechanical properties in both as-cast and heat-treated alloys compared with the gravity casting (GC) process alloy.

Key Analysis of Design and Numerical Simulation for Aluminum Alloy Impeller Low-pressure Casting Mold

It is of great practical value to complete the low-pressure casting of aluminum alloy impeller in the current development of low-pressure casting process. In the research, it is necessary to focus on factory realization and use low-pressure casting to produce aluminum alloy impellers, so that impeller castings with compact structure and meeting performance requirements can be obtained. Compared with other casting methods, low-pressure casting itself, as a precision casting method, can be cast on the metal solution with lower pressure in the application process. The castings can be filled and solidified under certain pressure, and the castings with compact structure can be obtained. In the research, Pro / Engineer is used to design the low-pressure casting mold for aluminum alloy impeller, and MAGMASOFT is used to carry out the filling and solidification process of aluminum alloy impeller. Through numerical simulation, we can accurately predict the defects of impeller castings, and optimize the mold scheme and pressure-time parameters according to the prediction results.

Effects of different holding pressures on the microstructure and mechanical properties of Al-5.9Zn-2.2Mg-1.8Cu alloy

In this study, a low-pressure casting process was used to examine the influence of the holding pressure on the Al–5.9Zn–2.2Mg–1.8Cu alloy. The study aimed to refine the grain structure and optimize the microstructural homogeneity and mechanical properties of the alloy. The phase composition, microstructure, chemical composition, and fracture morphology of the alloy were determined using optical microscopy, SEM, inductively coupled plasma spectroscopy, and XRD. As the holding pressure increased, the theoretical crystallisation temperature of the alloy increased, which increased the degree of undercooling during solidification and the effective number of nuclei, resulting in grain refinement. In addition, increase in the holding pressure strengthened the feeding ability of the alloy melt and reduced the occurrence of shrinkage porosity defects. When the optimal pressure was exceeded, the nucleation rate as well as the denseness of the alloy decreases. When the holding pressure was 0.035 MPa, the grain refining effect was the best and the microstructure was the most uniform. The yield strength, tensile strength, and elongation of the alloy reached the maximum values of 264.6 MPa, 290.8 MPa, and 7.7%, respectively. When the holding pressure was >0.035 MPa, the structure was not further refined; in contrast, the grains were larger, and the mechanical properties were inferior.

Simulation and optimization of low pressure casting process forAlSi9Mg gearbox shell

Simulation and optimization of low pressure casting process forAlSi9Mg gearbox shell

Casting defects and microstructure distribution characteristics of aluminum alloy cylinder head with complex structure

Due to the complex structure of the large cylinder head, it is prone to produce uncontrolled casting defects and uneven microstructure distribution. In order to predict the porosity defects and secondary dendrite arm spacing (SDAS) in the as-cast cylinder head, the low pressure casting process of aluminum alloy cylinder head was simulated. Moreover, to verify the accuracy of the simulation results, microscopic observations were performed, in which the simulation results are reasonably matching with that of experiment results. Both simulation and experiment results demonstrate that porosity defects mainly exist in thick walls as well as thick-thin wall junctions. In addition, the top plate presents the finest microstructure, while the microstructure of the force wall is the coarsest. Additionally, the correlation of casting parameters with porosity defects and microstructure was discussed, suggesting that increasing the cooling rate could partially reduce porosity defects. Furthermore, the finding that decreasing the cooling rate can reduce the SDAS of the casting, resulting in a dense microstructure, was drawn. Besides, it has been concluded that regular shapes and thin walls are advantageous for both reducing porosity defects and obtaining uniform microstructures. This provides an effective approach for predicting the casting defects and microstructure of large complex structural castings through numerical simulation. In addition, a quantitative understanding of the casting parameters, complex structure-microstructure relationship for cast aluminum alloys will allow better determination of process parameters based on microstructure and properties requirements of complex components.

Low pressure casting effect to tensile strength of aluminium

The air in the mould cavity is pushed out by liquid metal when the liquid metal entered mould cavity. In green sand-casting process, the air passes through the pores in the mould. Permanent mould doesn’t have pores and the air released from the mould cavity only through air outlet. Low pressure on mould cavity make liquid metal easier and faster filling the mould cavity, and make casting process can be done at lower temperature, the main focus of this research is about effect of pouring temperature on the low-pressure casting process to tensile strength and porosity of the aluminium. The casting process carried out at 750, 800 and 850°C. Aluminium smelting uses electric furnace and the mould used is a metal mould with a pressure of 0.33 atm. The casting process on aluminium at low pressure (-0.33 atm) and at a temperature of 750 °C produces the highest tensile strength compared to aluminium casting at 800 and 850 °C. The increasing pouring temperature increasing porosity of aluminium is from 1.86% at 750 °C to 4.03% at 850 °C.

Numerical Simulation of Latent Heat of Solidification for Low Pressure Casting of Aluminum Alloy Wheels

In this paper, aiming at focusses on many problems existing in the mathematical model of temperature change in the low-pressure casting solidification process of aluminum alloy wheel hub, there is a big gap between the simulation and the actual temperature change, which affects the research on the solidification defects of the wheel hub. In order to study the solidification behavior of aluminum alloy hub in low-pressure casting process, the mathematical model describing the temperature change in the process of casting solidification is established by using different solidification latent heat methods. through finite element simulation and experiment, the temperature change in the process of aluminum alloy (A356) solidification is obtained to compare the difference between the temperature change described by different mathematical models, simulation and experiment. The results show that the temperature numerical model of "the temperature compensation heat capacity method" proposed in this paper is most consistent with the simulation temperature change during the solidification process of the aluminum alloy wheel in the simulation mold, which lays a good theoretical foundation for the study of the low-pressure casting process of the aluminum alloy wheel hub.

Accurate Simulation of Complex Temperature Field in Counter-Pressure Casting Process Using A356 Aluminum Alloy

Automobile steering knuckle is an important part of the steering system, which is subjected to significant impacts and loads during its operation. Generally, cast aluminum steering knuckles are usually produced using some type of enhanced low-pressure casting process, like counter-pressure casting. Compared with aluminum forging and sand cast ductile iron, it can improve the production speed and achieve the adequate casting quality. In this study, various methodologies such as dynamic thermomechanical analysis, differential scanning calorimetry, and the laser flash method were employed to study the thermophysical properties of AlSi7Mg0.3. Further, the physical model of a counter-pressure casting system with an aluminum interior was established based on the combination of the tested and the theoretical properties of aluminum; this was achieved with the consideration of the presence of other factors including rapid solidification. The temperature field of the system was computed and verified by thermocouples at six different points during the tooling and the shrinkage simulation. It was observed that the plot shape of the computed temperatures and that of the simulated ones correlated; further, the difference between the peaks and the valleys was controlled to be 3% on an average, with the maximum variation of 7% at only one point. Moreover, all the predicted shrinkages were verified by the casting. This study provides a solid foundation for facilitating the simulation of the morphologies of the microstructure.

Geometrical effects on filling dynamics in low pressure casting of light alloys

In aluminum low-pressure sand casting process, filling oscillations are observed when the metal front reaches a section change in a part. The effect of geometry on the filling oscillations is primary considered experimentally, including both mold cavity and filling system geometries. To highlight the geometric parameters impacting the oscillations, the pressurized melt flow is secondly studied numerically and analytically. A new analytical model of oscillation is developed to quantitatively predict the oscillations. It links the resulting filling velocity to both the low-pressure casting parameters and the mold cavity geometry. Considering oxides inclusion criterion from casting literature, new rules to avoid bi-films defects are recommended for making reliable low-pressure castings.

Research on design and technology of aluminium alloy conductor low pressure casting die

Basic principles of aluminium alloy conductor low pressure casting are introduced in the paper. Casting die design and casting system are respectively introduced aiming at the low-pressure casting process of aluminium alloy conductor, the influence of cylindrical riser tube and cone riser tube on liquid rising pressure and liquid rising stability in liquid rising process are analysed in details. It is concluded that the liquid rising pressure for liquid rising process is relatively low during selection of cone liquid rising, and liquid rising process of cone riser tube is more stable. Therefore, cone riser tube is more suitable for liquid rising process of aluminium alloy conductor low pressure casting than cylindrical riser tube. Low pressure casting technological parameters of aluminium alloy conductors are summarized through analysis on low pressure casting technology, thereby providing reference for low pressure casting technique of aluminium alloy conductors.

Mastering of the Filling Stage in Low Pressure Sand Casting Process

In Low Pressure Casting (LPC), the counter gravity filling at low velocity and the protective gas atmosphere above the metal can potentially reduce gas and oxides entrapment in the metal. However, the relationship between the imposed gas pressure evolution and the melt filling dynamics cannot be analytically determined as it is geometry-dependent. This issue is the missing link to master and automate the filling step in LPC process. In this work, the filling dynamics is numerically investigated for different mold geometries and pressure ramps. The simulation, carried out using ANSYS Fluent® simulation software, is combined with an analytical model. As the results are quantitatively predictive of the filling flow, it permits to develop a numerical study, considering different sudden or progressive section changes and pressure ramps. The impact of the different process parameters on the flow dynamics is analyzed, particularly the transition smoothing impact.

Similitude analysis on flow characteristics of water, A356 and AM50 alloys during LPC process

The present work endeavours to map mold filling characteristics of water to real melts of A356 aluminium alloy and AM50 magnesium alloy during low pressure casting process (LPC). The analogy of dynamic similitude has been applied on a benchmarked computational fluid dynamics (CFD) based simulation model developed for tracking fluid free surfaces. Scaling factors for A356 and AM50 melts with respect to water are calculated by equating the non-dimensional numbers deduced from forces acting on the fluids. Buckingham's Pi theorem is used to verify the derived scaling equations. The mold filling time for water in the benchmarked simulation model and for real alloy melts in the scaled computational models is compared for different inlet pressure regimes. The proposed analogy is verified using variations occurring in velocity scaling factors for the melts during mold filling.

Formation Mechanism of Surface Crack in Low Pressure Casting of A360 Alloy

A surface crack defect is normally found in low pressure castings of Al alloy with a sudden contraction structure. To further understand the formation mechanism of the defect, the mold filling process is simulated by a two-phase flow model. The experimental results indicate that the main reason for the defect deformation is the mismatching between the height of liquid surface in the mold and pressure in the crucible. In the case of filling, a sudden contraction structure with an area ratio smaller than 0.5 is obtained, and the velocity of the liquid front increases dramatically with the influence of inertia. Meanwhile, the pressurizing speed in the crucible remains unchanged, resulting in the pressure not being able to support the height of the liquid level. Then the liquid metal flows back to the crucible and forms a relatively thin layer solidification shell on the mold wall. With the increasing pressure in the crucible, the liquid level rises again, engulfing the shell and leading to a surface crack. As the filling velocity is characterized by the damping oscillations, surface cracks will form at different heights. The results shed light on designing a suitable pressurizing speed for the low pressure casting process.

Investigating surface roughness of ZE41 magnesium alloy cast by low-pressure sand casting process

The sand mold 3D printing technologies enable the manufacturing of molds with great dimensional accuracy. However, the roughness of as-cast components is higher when cast in a 3D printed mold rather than in a traditional sand mold. Coating the inner cavity is an efficient solution but can be costly and, in the narrowest cavities, not achievable. Finding a procedure to reduce the as-cast roughness without coating would ease the casting procedures. In the present work, surface analysis of ZE41 magnesium alloy is presented after being cast in 3D printed furan sand molds without coating using the low-pressure casting process. The molten metal temperature was measured during casting at different positions along the cast cavity. The as-cast surface roughness was correlated to the molten metal temperature and solid fraction at the time of contact against the sand mold surface.

Numerical simulation and experimental validation of free surface flows during low pressure casting process

The present work analyzes the free surface flow characteristics during mold filling in a low pressure casting process (LPC) through water model experiments and numerical simulations. The flow patterns visualized through the water analog experiments using different input pressure sequences have been verified with numerical simulation results for the entire LPC process. The benchmarked numerical model has been further used to study the impact of different in-gate shapes on fluid free surface behavior inside the mold cavity. The mold filling and solidification simulation is then carried out using magnesium alloy as liquid for the same geometry and the same input pressure profile to highlight the effect of thermo physical properties of actual melts on the free surface flow behavior.

Computer Simulation of Low Pressure Casting Process Using Flow 3D<sup>TM</sup>

The calibre of low pressure casting (LPC) process in meeting the demands for improved quality and aesthetics for thin walled components has been widely accepted in casting industries. In spite of numerous advantages, the process is still being used very less to its potential. The basic reason has been the difficulty in determining various processing parameters associated which can be circumvented effectively by numerical simulation. In the present work, the commercial CFD code FLOW 3DTM, has been used to simulate the mould filling and solidification during the LPC process.

Effect of Heat Treatment on Microstructures and Mechanical Properties of A356 Alloy by Low Pressure Casting

Automobile wheel of A356 alloy was cast by low pressure casting process. The effect of heat treatment process on microstructures and mechanical properties of A356 alloy cast was discussed. The results indicated that optimal parameters of heat treatment process for A356 alloy included solution temperature of 535°Cand holding time of 4.5hours, aging temperature of 145°Cand holding time of 4hours. Ultimate strength of A356 is 270MPa and elongation rate is 10%. Meanwhile, the microstructure has been apparently improved. The eutectic silicon particle became more spheroidal and distributed uniformly in matrix.