Semi-solid Die Casting Process Research Articles

Structure Optimization of Semi-Solid Die Cast Steering Knuckle and its Experiment Verification

Steering knuckles are vital functional and structural components in automotive suspension systems, requiring high strength, high ductility, and complex shapes. In this study, an aluminum alloy knuckle with the semi-solid die casting process was developed to replace the conventional steel components. This research aims to optimize product design based on both structural simulation and casting process simulation to avoid defects and to meet mechanical requirements. Furthermore, the optimal design solutions need to be verified through the filling experiments and defect analysis. The results show that the removal of support rib located in the thick area of the shock absorber mounting arm is helpful to avoid the rewelding defects in the filling frontier of the SSM melt. Besides, the position of the steering rod is of medium thickness, and two ribs from different directions come together to support that area. Rewelding defects were detected when two ribs come together. To avoid rewelding defects in local areas of steering rod position, the ribs were reduced to uniform wall thickness. Thus, the local flow state was modified and the SSM melt was reinforced shear action. Ultimately, by controlling all the processes of the SSM die casting process, the high performance of aluminum knuckle was successfully developed.

Study on microstructure and thermal conductivity of semi-solid die casting aluminum alloy

In order to improve the comprehensive properties of casting aluminum, and to fulfill the requirements of forming thin wall fins for communication products, mechanical stirring was employed to prepare the semi-solid aluminum alloy AlSi8. communication products were produced by the semi-solid die casting process. The microstructure and mechanical and thermal properties were studied. The test results show that the microstructure of semi-solid die-casting samples changes from dendrite to globular microstructure, and the average tensile strength, elongation and thermal conductivity are 220MPa, 7% and 170 W/(m*K), respectively, which is significantly higher than that of the common die-casting samples. It was proved that the semi-solid die casting technology can be used in actual production and improve the products quality.

Effects of Process Parameters on Shrinkage Porosity in 357 Semi-Solid Die Casting Parts

The shrinkage porosity that was caused by the insufficient feeding during solidification, was a common defect in the semi-solid die casting process. This defect decreased significantly the mechanical properties of the casting. In order to avoid the shrinkage porosity in casting, the die design, slug preparation and die casting process were carefully considered. In this study, a designed mold was used to make the sequential solidification of the slug. The process parameters, including intensification pressure, die temperature and biscuit thickness of the casting, were studied to show their influence on shrinkage porosity defects. The experimental results show that the high intensification pressure, high die temperature and long biscuit can be beneficial to obtain castings with no shrinkage porosity.

Multiphase modelling of the transient flow for Sn-15Pb and 357.0 alloys in semi-solid die casting process

Abstract The transient flow behavior of the semi-solid slurries for Sn-15Pb and 357.0 alloys during die casting process is investigated by experimental and numerical methods. A model for the transient-state three-dimensional multiphase flow based on the kinetic theory of granular flow is developed. This model is applied to investigate the distribution of solid concentration, flow state, pressure variation of the semi-solid slurry in the die casting process. The three important aspects of the multiphase flow, flow regime, particle-particle interaction and particle-liquid interaction, are interpreted according to the characteristic of the system. The model is verified by partial filling and in-situ observation experiments. Then it is applied for the phase segregation study of an elbow cavity encountered in practice. Results indicate that the 3D multiphase model can depict the flow characteristics of the semi-solid slurry very well. The inner arc side of the elbow cavity is easier to have liquid phase segregation than the outer arc side for the lower velocity gradients of the solid and liquid phases.

Experimental and simulation study for rewelding defects during the flow process of Semi-solid die casting

Semi-solid die casting process due to its advantages of compact process, high performance and low cost is widely applied in automobile, communication and other industries for the preparation with high performance aluminum alloy castings. Compared with liquid metal melt, the filling behavior is laminar flow for semi-solid metal melt with higher apparent viscosity. In the process of semi-solid die casting, the semi-solid metal melt from different directions came together, it will lead to “rewelding” defects if with insufficient fusion or uneven slurry state. In this paper, the formation reasons and forms of flow “rewelding” defects are analyzed. By numerical simulation and experimental analysis, the flow state of semi-solid metal melt at the junction of filling frontier is represented, and the state of “rewelding” defect is characterized. The effect of eliminating defects is analyzed by modifying the mold structure, such as redesigning overflow and venting systems at the confluence position. The results show that the microstructure of the “rewelding” defects in the confluence position of the semi-solid metal melts is the segregati12on of solid and liquid phase, gas, oxidation inclusions and other defects. Different semi-solid die casting process will affect the flow state and defect size at the location of different semi-solid metal melt coming together. By means of the process control and the mold structure optimization, “rewelding ” defects can be removed from the product cavity. The aluminum alloy semi-solid die-casting products with high performance are obtained finally.

Floating Behavior of Entrapped Gas in Semi-Solid Metal

Semi-solid die casting technology has great advantages at defects control and has been successfully used to produce high quality aluminum alloy components for several years. In this process, semi-solid metal with high apparent viscosity and low plunger velocity are used to avoid surface turbulence which is the main source of entrapped gas in conventional die casting processes. But, entrapped gas still has other sources, such as melting, pouring, surface flooding and confluence weld. Solution heat treatment is always used to strengthen semi-solid die castings. The entrapped gas leads to blister defects, which directly decreases the acceptance rate of semi-solid die castings. So, the entrapped gas is still a serious issue in semi-solid die casting process. We studied the floating behavior of entrapped gas bubble in semi-solid metal. Two floating models were established for gas bubbles with different sizes. These models were used to analyze the possibility of entrapped gas escaping from semi-solid metal in casting practice. The results showed that entrapped gas from feed billet could not escape from the semi-solid metal in the casting process of impeller, which was proved by experiment results. These results emphasized the importance of clean melt and semi-solid metal. Some advices were given at last for avoiding or removing the entrapped gas in semi-solid die casting process.

Development of Semi-Solid Die Casting Process Technology for Aluminium Alloy Clamp

Compared with traditional liquid and solid processing methods, semi-solid die casting process can apparently overcome shrinkage cavity and porosity defects in castings and high deformation resistance and high residual stress shortcomings in forging parts. Semi-solid die casting process with advantages such as high efficiency and low cost, will become the optimal process for high quality automobile parts. In this study, using the clamp as an example, the author introduced product structure optimization and die design for semi-solid die-casting process of aluminum alloy in a new product development.The Computer Aided Engineering technology was applied to the product structure optimization according to the stress analysis. The optimal mold structure, including cavity layout, gating system, overflow and vent systems, were confirmed based on the die design criteria for traditional die casting, combining with the characteristics of semi-solid forming and the simulation results. The semi-solid aluminum alloy clamp parts with excellent performances were finally developed successfully by means of product structure optimization, die design, parameters optimization of die casting process, and the mechanical properties test of products.The existing parts were optimized to make them more suitable for semi-solid die casting processing. In addition, a reasonable die design specially for semi solid processing was an important guarantee for a successful semi solid product applied in industry. Computer numerical simulation was applied in product structure design for semi-solid die casting, die design, die-casting process optimization and other aspects, to shorten the development cycle of new product, reduce cost and improve efficiency.

Model-based cost estimates for selecting a die casting process

ABSTRACTSemisolid die casting (SSDC) is a newly developed technology to improve the quality of products and to reduce the costs of liquid die casting process. We assessed the gas-induced semisolid process (GISS), which generates a semisolid metal for die casting, in this comparison of the costs per unit between a traditional liquid die casting process and the semisolid die casting process. A process-based costing model (PBCM) was created to estimate the production costs. In principle, the PBCM consists of three submodels: process model, operation model, and financial model. This study indicates that three main factors, namely cycle time, rate of waste, and die life, affected the unit production costs. The production cost estimates decreased by approximately 13% when the process was switched from a liquid to a semisolid one.

Numerical Analysis of Semi-Solid Die-Casting Automobile Part Based on the Thermo-Visco-Plastic Constitutive Relation

Thermal simulation compression tests were performed on semi-solid billet in order to observe and investigate the behavior of 6061 aluminum alloys while varying the processing parameters such as apparent viscosity, the shear rate and the temperature. Specimens of 6061 aluminum alloys were characterized with their semi-solid behavior during partial melting and holding in the semi-solid state. Furthermore, the constitutive equation of semi-solid 6061 aluminum alloys was investigated. Moreover, the tests allow the apparent viscosity and shear rate of the alloys to be determined as a function of the solid volume fraction and strain rate together with the geometry behavior of the specimen. Utilizing these parameters, semi-solid die casting process of 6061 aluminum alloys could be simulated by the change of the solid volume fractions.

Semisolid Die-Casting Process of Mg-20Al-0.8Zn Magnesium Alloy

Based on microstructure evolution of Mg-20Al-0.8Zn magnesium alloys realized by semisolid isothermal heat-treatment (SSIT), we obtained the non-dendrite or spherical grains microstructure under the suitable technological parameters that isothermal temperature is 495 °C and holding time is 120 min. With the help of special experimental equipment, the semisolid die-casting process has been studied and the specimens have been analyzed. The effects of different parameters as injection speed and pressure on tensile strength, elongation rate, hardness, etc have been investigated. The results indicate that tensile strength was improved along with increasing injection speed and pressure. However, excessive speed will involve gas, which formed defects and reduced the mechanical properties. When the injection pressure is 40MPa and injection speed is 4m/s, the tensile strength and elongation rate can reach maximal 220MPa and 5.63% respectively. Its fracture mechanism was intercrystalline cracking.

Simulation of semisolid diecasting process of four-way valve of HPb59-1 alloy for air-conditioner

There exist many problems in producing four-way valve of HPb59-1 alloy for an air-conditioner by traditional solid state hot forging, i.e. larger forming loads, lower material utilization, larger subsequent machining allowance and nonuniform microstructure. For this reason, based on the orthogonal test, the semisolid diecasting process of a certain type of four-way valve was simulated with FLOW-3D. The simulation results show that the optimized process parameters are: the pouring temperature of 897.25 °C, the shot velocity of 2.0 m/s and the preheated die temperature of 260 °C. The simulation results demonstrate that the cavity can be filled smoothly and completely, the surface defects are small, the temperature field and the pressure field are uniform, and the casting quality is satisfactory. The effectiveness and availability of applying this technology are well verified by the numerical simulation.

Parameters Optimization of Semisolid Diecasting Process for Air-Conditioner’s Triple Valve in HPb59-1 Alloy

The disadvantages of air-conditioner’s triple valve in HPb59-1 alloy processed by traditional solid state hot forging, such as larger forming loads, lower material utilization, larger subsequent machining allowance, nonuniform microstructure, are put forward. However, semisolid diecasting forming which can overcome the above shortcomings is a fascinating technology. The process paremeters which had a larger influence on filling ability of semisolid slurry and casting quality, such as pouring temperature, shot velocity and preheated temperature of the die, were chosen. Furthermore, based on orthogonal test, the semisolid diecasting process of a certain type triple valve was simulated with FLOW-3D. According to the analysis of temperature field, pressure field and surface defect concentration, the optimal process parameters such as pouring temperature 897.25 °C, shot velocity 1.5 m/s and preheated temperature of the die 260 °C, were obtained, and the effectiveness of the technology was well demonstrated by numerical simulation.

Microstructure and mechanical properties of AZ91D alloy prepared by a semi-solid diecasting process

Abstract Semi-solid processing has been combined with die-casting for the magnesium alloy AZ91D. The microstructure of the semi-solid diecast AZ91D has been examined by optical microscopy and scanning electron microscopy. No pores were visible under optical microscopy, indicating a very low porosity. Mechanical properties of the semi-solid diecast AZ91D alloy have also been tested. High ultimate tensile strength and elongation have been achieved due to the low porosity and the fine microstructure. The fracture surfaces have been investigated by scanning electron microscopy in order to reveal the fracture mechanism. A typical inter-granular fracture surface was observed, indicating that the alloy fails in a brittle manner. The vertical-section microstructure of the fractured sample has indicated that the crack mainly propagates along the grain boundaries through the brittle fracture of the eutectic phase or the interface decohesion of the primary Mg phase and the eutectic phases.

Numerical integration design process to development of suspension parts by semi-solid die casting process

In recent years in the automobile industry, it has been necessary to reduce the weight of automobile parts. To solve this problem, lower arm parts have been fabricated with the aluminum alloy metal by semi-solid die casting as substitutes for steel arm parts. Aluminum alloy parts can reduce the weight of automobiles, but the mechanical properties of aluminum alloy parts are inferior to those of steel parts. In order to substitute aluminum alloys parts for steel arm parts, simulations of strength and fatigue have to be performed, before changing to new model designs. The die design for the semi-solid die casting of the arm part has to be considered according to defects from air porosities, impurities and filling errors. In this study, the filling and solidification processes were simulated in order to propose the optimal die design.

The effect of the gate shape on the microstructural characteristic of the grain size of Al–Si alloy in the semi-solid die casting process

Semi-solid forming is an attractive process for fabricating sound, weight-reduced automotive parts. Therefore, in this work, die systems of varied gate shape, gate width, and gate thickness were designed to investigate the filling characteristics of semi-solid material with a controlled solid fraction. When semi-solid materials with controlled solid fraction of 50% filled inside die cavity, the causes of liquid segregation according to the separation phenomena of solid particles and liquid materials were investigated. The parts were characterized for eutectic segregation, a segregation band, cracks and shrinkage hole on the part surface. It was found that all these defects could be solved by the selection of the optimal casting speed and selection of gate shape when the semi-solid material with a controlled solid fraction completely filled the die cavity. The correlation between liquid segregation and a gate system has been synthetically investigated with experimental results and theoretical results. The hardness in the primary α zone and the eutectics microstructural zone were measured by nano indentation. The relationship between liquid segregation and hardness was also investigated.

Effects of die shape and injection conditions proposed with numerical integration design on liquid segregation and mechanical properties in semi-solid die casting process

To solve the problem of reducing the weight of automobiles for the improvement of fuel efficiency and the protection of the environment, aluminum alloy parts have been substituted for steel parts. However, aluminum-alloy parts have inferior mechanical properties to those of steel parts. To improve the mechanical properties of aluminum-alloy parts, the semi-solid die casting process is used in the manufacture of automobile components. Semi-solid die casting has a different die structure from those of general die casting and squeeze casting. Because the oxide skin is produced during the reheating process will cause defects when it fills the die cavity, in semi-solid die casting the most important factors are the filling velocity, the area of the gate, and the position, size, the number of overflow. In this paper, a theoretically-proposed die structure for semi-solid die casting is verified by experiments, and the mechanical properties of the resultant parts are also presented.

The effect of injection velocity on liquid segregation and mechanical properties in arm part fabricated by semi-solid die casting process

Semi-solid die casting of Al alloy is suitable for complicated large parts of near net shape without defect and excellent mechanical properties in comparison with conventional casting process. Die design for the product with high quality in semi-solid die casting is required to prevent micro porosity, inflow of oxidized substances, and liquid segregation. Therefore, shape and size of runner, position and size of overflow and air vent, and arrangement of heating line are very important. Micro porosity, unfilled phenomena, turbulent flow, and liquid segregation occurs during semi-solid die casting. To prevent these phenomena, defect analysis of product according to the change of injection velocity is carried out and optimal injection velocity for high quality product is proposed and simulated. Also, the measurement of mechanical properties according to various injection velocity and heat treatment condition is performed.

비대칭 다단 두께 변화를 고려한 결정입 제어 반용융 알루미늄 소재의 캐스팅에서 사출속도가 액상편석에 미치는 영향

Recently, in the field of automobile industry, to solve the problem of reducing the weight of automobile for the improvement of fuel efficiency and the protection of environment, the aluminum alloy parts have been substituted for the steel parts. However, the aluminum alloy does not have as good mechanical property as the steel part. To improve the mechanical property, the semi-solid die casting process is performed to make automobile parts. In the fabrication of semisolid material the control of the liquid segregation is very important to improve the material properties of aluminum alloy. In the present paper we examine the influence of the liquid segregation by the injection conditions in the semi-solid die casting has been investigated.

게이트 형상이 결정립 제어 소재의 미세조직에 미치는 영향

In the semi-solid die casting process, an important thing is the flow behavior of semi-solid materials. The flow patterns of the semi-solid material can make the defects during die filling. To control the flow patterns is very important and difficult. In this paper, the flow behavior of the semi-solid A356 alloy material during die filing at various die gate shapes has been observed with the grain size controlled material. The effect of the gate shape on the die filling characteristics was investigated. The filling tests in each plunger stroke were experimented, and also simulated on the semi-solid material die casting process by MAGMAsoft. According to the filling tests and computer simulation, the effect of the gate shape on liquid segregation has been investigated.

Semi-solid die casting process with three steps die system

In automobile suspension part, knuckle as functional component is very complex shape and required high strength. To manufacture the high strength component like knuckle with semi-solid die casting process, there are required reheating condition, casting plan, die design, injection condition, defect analysis and measurement of mechanical properties.In this study, aluminum knuckle with semi-solid die casting process was developed to replace the conventional steel components. Semi-solid die casting was established to lead the laminar flow and pressure transfer to the end point of product and to avoid oxide skin and shrinkage porosity. Three steps die system was made up two-step moving die and biscuit cutting system. And that was suitable for center-positioned gate and designed to hold the similar filling length and applying pressure. Aluminum knuckle component made by three steps die system designed by casting simulation. Also, injection condition was established to remove oxide skin and liquid segregation. After controlled above process parameters, tensile strength, yield strength, elongation and microstructure were investigated to verify the real automobile applicability.