Study on Numerical Simulation of Mold Filling and Heat Transfer in Die Casting Process

A 3-D mathematical model considering turbulence phenomena has been established based on a computational fluid dynamics technique, so called 3-D SOLA-VOF (Solution Algorithm-Volume of Fluid), to simulate the fluid flow of mold filling process of die casting. In addition, the mathematical model for simulating the heat transfer in die casting process has also been established. The computation program has been developed by the authors with the finite difference method (FDM) recently. As verification, the mold filling process of a S-shaped die casting has been simulated and the simulation results coincide with that of the benchmark test. Finally, as a practical application, the gating design of a motorcycle component was modified by the mold filling simulation and the dies design of another motorcycle component was optimized by the heat transfer simulation. All the optimized designs were verified by the production practice.

Development of vacuum die-casting process

The vacuum die-casting process,started 25 years ago in Japan,has been widely applied.This technology contributes very much to improvement of castings quality.The main factor causing the defects of die castings is the trapped air in the mold cavity,while the key technology of vacuum die-casting process is to avoid the trapped air effectively by evacuating the cavity before casting.At the same time,due to the shot speed and the casting pressure reduced in half,the service life of the die is prolonged and the productivity is enhanced,as well.Vacuum die-casting process is of great signif icance in improving the die castings quality and making up the shortcomings of super-high-speed shot casting.

Effects of process parameters on morphology and distribution of externally solidified crystals in microstructure of magnesium alloy die castings

During the cold-chamber high pressure die casting(HPDC) process, samples were produced to investigate the microstructure characteristics of AM60B magnesium alloy. Special attention was paid to the effects of process parameters on the morphology and distribution of externally solidified crystals(ESCs) in the microstructure of magnesium alloy die castings, such as slow shot phase plunger velocity, delay time of pouring and fast shot phase plunger velocity. On the basis of metallographic observation and quantitative statistics, it is concluded that a lower slow shot phase plunger velocity and a longer delay time of pouring both lead to an increment of the size and percentage of the ESCs, due to the fact that a longer holding time of the melt in the shot sleeve will cause a more severe loss of the superheat. The impingement of the melt flow on the ESCs is more intensive with a higher fast shot phase plunger velocity, in such case the ESCs reveal a more granular and roundish morphology and are dispersed throughout the cross section of the castings. Based on analysis of the filling and solidification processes of the melt during the HPDC process, reasonable explanations were proposed in terms of the nucleation, growth, remelting and fragmentation of the ESCs to interpret the effects of process parameters on the morphology and distribution of the ESCs in the microstructure of magnesium alloy die castings.

Neuro-Knowledge-Based Expert System (NKBES) for Optimal Scheming of Die Casting Process

We develop a neuro-knowledge-based expert system (NKBES) frame in this work. The system mainly concerns with decision of gating system and die casting machine based on a neuro-inference engine launched under the MATLAB software environment. For enhancement of reasoning agility, an error back-propagation neural network was applied. A rapidly convergent adaptive learning rate (ALR) and a momentum-based error back-propagation algorithm was used to conduct neuro-reasoning. The working effect of the system was compared to a conventional expert system that is based on a two-way (forward and backward) chaining inference mechanism. As the reference, the present paper provided the neural networks sum-squared error (S5E) and ALR vs iterative epoch curves of process planning case mentioned above. The study suggests that the neuro-modeling optimization application to die casting process design has good feasibility, and based on that a novel and effective intelligent expert system can be launched at low cost.

Heat Transfer between Casting and Die during High Pressure Die Casting Process of AM50 Alloy-Modeling and Experimental Results

A method based on die casting experiments and mathematic modeling is presented for the determination of the heat flow density （HFD） and interfacial heat transfer coefficient （IHTC） during the high pressure die casting （HPDC） process.Experiments were carried out using step shape casting and a commercial magnesium alloy,AM50.Temperature profiles were measured and recorded using thermocouples embedded inside the die. Based on these temperature readings,the HFD and IHTC were successfully determined and the calculation results show that the HFD and IHTC at the metal-die interface increases sharply right after the fast phase injection process until approaching their maximum values,after which their values decrease to a much lower level until the dies are opened.Different patterns of heat transfer behavior were found between the die and the casting at different thicknesses.The thinner the casting was,the more quickly the HFD and IHTC reached their steady states.Also,the values for both the HFD and IHTC values were different between die and casting at different thicknesses.

Finite element analysis for die casting parameters in high-pressure die casting process

The gating system and the overflow system were designed according to the casting structure during high pressure die casting(HPDC) process. The simulation was carried out by ProCAST software to visualize the injection chamber pre-crystallization and the flow of molten metal. The main work is to research four die casting process parameters, i.e. injection temperature, low-pressure velocity, high-and low-pressure velocity’s switching position, and high-pressure velocity. Experimental results show that the higher injection temperature and lowpressure velocity can mitigate the pre-crystallization of the injection chamber. However, when the low-pressure velocity exceeds 0.2 m·s-1, the air entrapment in the chamber occurs. Besides, when the high-pressure velocity is greater than 2.5 m·s-1, the overflow channel at the final filling position is covered by the liquid metal too early. Finally, the injection temperature of 650 °C, the low-pressure velocity of 0.2 m·s-1, the high-and low-pressure velocity’s switching position of 320 mm and the high-pressure velocity of 2 m·s-1 are obtained as the optimal parameters by the software simulation, which has been verified by actual production.

Microstructural characteristics of near-liquidus cast AZ91D alloy during semi-solid die casting

Near-liquidus cast ingot was reheated to semi-solid firstly, and then a bracket of motor was prepared by die casting the semi-solid ingot into mould. The microstructural characteristics of AZ91D alloy in these processes were investigated. In the process of near-liquidus casting, primary α-Mg grains tend to be rosette-like because of the increase of plentiful quasi-solid atom clusters in molten alloy with the decrease of pouring temperature. These rosette-like α-Mg grains in ingots fabricated by near-liquidus casting are fused off and refined into near-globular structure owing to the solute diffusion mechanism and the minimum surface energy mechanism during reheating. After semi-solid die-casting, α-Mg grains, located in biscuit, impact and connect with each other; α-Mg grains, located in inner gate, congregate together; while α-Mg grains, located in component, distribute uniformly and become into globularity or strip. Because the inner gate limits the flowing of semi-solid slurry, and the pressure acted on the semi-solid slurry decreases gradually along the filling direction of semi-solid slurry in cavity, microstructural segregation of unmelted α-Mg grains appears along this direction. Shrinkage holes in casting are caused by two different reasons. For biscuit, the shrinkage holes are caused by the blocked access of feeding liquid to the shrinkage zone for the agglomerated unmelted α-Mg grains. For component, the shrinkage holes are caused by the lack of feeding of liquid alloy.

Novel methodology for casting process optimization using Gaussian process regression and genetic algorithm

High pressure die casting (HPDC) is a versatile material processing method for mass-production of metal parts with complex geometries,and this method has been widely used in manufacturing various products of excellent dimensional accuracy and productivity. In order to ensure the quality of the components,a number of variables need to be properly set. A novel methodology for high pressure die casting process optimization was developed,validated and applied to selection of optimal parameters,which incorporate design of experiment (DOE),Gaussian process (GP) regression technique and genetic algorithms (GA). This new approach was applied to process optimization for cast magnesium alloy notebook shell. After being trained,using data generated by PROCAST (FEM-based simulation software),the GP model approximated well with the simulation by extracting useful information from the simulation results. With the help of MATLAB,the GP/GA based approach has achieved the optimum solution of die casting process condition settings.

Research and Applications of Semi-solid Processing

It has been more than ten years since the semi-solid processing (SSP) technique was put into commercial applications in the world. A lot of work on semi-solid metals (SSM) including their preparation, reheating and semi-solid forming has been done in China. In order to produce the high quality die-casting, a novel innovation that modifies the present machines based on the SSP technique was proposed. Semi-solid die-casting on modified casting machines can manufacture parts with more excellent quality than those produced by squeeze casting. It was found that the defects such as 'elephant foot' and 'periphery liquid metal loss' during reheating could be avoided through controlling the non-dendritic structure of billets and optimizing the reheating process. The processing parameters and mold designs of semi-solid die-casting are fairly different from those of liquid die-casting.

Continuous squeeze casting process by mass production

Squeeze casting has become the most competitive casting process in the automotive industry because of its many advantages over high pressure die casting (HPDC). Many squeeze casting R & D and small amount volume making have been implemented around the world, but the mass production control still exists problem. SPX Contech squeeze casting process P2000 successfully achieved the goal of mass production; it includes lower metal turbulence, less gas entrapment, minimum volumetric shrinkage, and thus less porosity. Like other casting processes, however, the quality of squeeze castings is still sensitive to process control and gate and runner design. Casting defects can form in both die-filling and metal solidification phases. The occurrence of casting defects is directly attributed to improper adjustment or lack of control of process parameters including metal filling velocity, temperature, dwell time, cooling pattern, casting design, and etc. This paper presents examples using P2000 techniques to improve part quality in the following areas: runner & gate design, casting & runner layout in the die, squeeze pin application, high thermal conductivity inserts, cooling/heating systems, spray & lubricant techniques, and part stress calculation from shrinkage or displacement prediction after stress relief.

An Industrial Perspective on Magnesium Alloy Wheels: A Process and Material Design

Light weights wheels improve vehicle performance with respect to road handling, cornering as well providing fuel economy and reduced greenhouse gas emissions. Aluminum wheels are currently used in many models and are produced usually by low pressure assisted gravity casting. Important property requirements are fatigue strength, pressure tightness, tensile strength, impact resistance, and corrosion resistance. Many attempts have been made to convert aluminum road wheels to magnesium. Race cars and some of the high end models (Porsche, Ferrari, etc.) have used magnesium wheels. These wheels have been gravity cast or forged. Viable corrosion protection systems have been developed and magnesium wheels have been used with success on these models. To use magnesium on more modest models is a challenge due to cost issues. Higher productivity casting processes or more cost effective coating systems need to be utilized. The project consists of selecting magnesium alloys for road wheels, examining the possible cost effective casting processes and corrosion protection systems, evaluating the cost per one wheel and comparing it to aluminum wheel costs. The wheels will also be compared with respect to fatigue and impact properties, pressure tightness, and corrosion.

基于正交试验的铝合金减速机壳体低压铸造工艺优化

利用数值模拟方法对铝合金蜗轮减速机壳体低压铸造过程进行分析,预测壳体中可能产生的缩松缩孔缺陷及位置分布,并分析其形成原因。在此基础上,通过改进冷却方案,并基于正交试验对工艺参数进行了多目标优化。得到的最优工艺参数为:浇注温度740℃、模具预热温度240℃、冷却水温度20℃。结果表明,优化后的壳体无缩松缩孔缺陷。通过生产试制和金相分析,验证了此优化工艺的可行性。

汽车车灯支架压铸工艺CAE分析及模具设计

分析了汽车车灯支架的结构特点,进行了压铸工艺设计,并应用ProCAST软件对该铝合金压铸件的充型过程、压铸模具热平衡和温度场进行了数值模拟分析,预测缺陷产生的位置及原因,根据预测结果对模具结构进行了优化。实际生产表明,采用优化后的模具设计方案提升了铸件质量。

铝合金后端盖压铸工艺优化及局部挤压设计

分析了铝合金后端盖铸件结构工艺性,根据压铸工艺经验公式设计了浇注系统。采用Flow-3D软件进行数值模拟,发现后端盖铸件悬置孔区域不能实现金属液顺序充填。根据数值模拟结果修改浇注系统设计并进行实际生产,铸件厚壁区域产生缩孔缺陷。针对厚壁区域设计局部挤压工艺,在其凝固过程中进行挤压补缩,消除了后端盖铸件悬置孔部位缩孔缺陷。

铝合金变速箱后壳压铸工艺设计与数值模拟优化

以某汽车变速箱后壳为研究对象,选择合适的压铸工艺参数并设计了浇注系统。应用MAGMAsoft软件对其充型过程、凝固过程进行数值模拟。结果表明,金属液充型过程平稳,但凝固时间顺序不合理,产生缩松缩孔缺陷。根据铸件凝固时间顺序添加冷却系统。通过对优化后的工艺方案进行数值模拟分析、产品试制,最终得到了合理可行的压铸工艺方案,提高了压铸件的产品质量。

车身真空高压压铸技术研究

铝合金真空高压压铸技术在汽车行业逐步得到应用,研究分析了真空高压压铸材料、工艺、产品及现阶段重点问题。概括了热处理和免热处理材料的物理特点、化学成分及机械性能;介绍了真空高压压铸工艺流程和产线、工艺设计、工艺参数、成形性能;分析了产品性能、厚度、尺寸、连接、维修、模具寿命现阶段的主要问题;总结了真空高压压铸技术的优势并展望其发展前景。

一种整体式齿轮箱铸造工艺及模具设计研究

针对一种整体式齿轮箱进行了铸造工艺设计、铸造CAE仿真及模具设计研究。通过合理地设计浇注系统、激冷冷铁和发热保温冒口等工艺措施,并采用预埋覆膜砂型芯、整体筋板抽活块等模具设计方案,成功开发了满足质量要求的整体式齿轮箱铸件。

基于数字化的压铸产品全流程质量管理

传统铸造工厂的质量管理针对产品全生命周期建立完整的质量检验标准,即建立与产品相对应的首检、巡检、尾检、抽检标准,这样的质量管理模式适用于生产节拍相对较慢的铸造工厂,但是压铸行业具备高精度、高效率、灵活性强的生产特点,如何高效、准确的进行产品质量管理成为了当前行业内的一大难点,本文基于数字化的压铸产品的全流程质量管理模式进行一个简单的分享。

铝合金支架零件压铸工艺研究

通过分析铝合金材料特性及其在压铸中的适用性,阐述了压铸工艺的基本原理和流程。重点从铝合金材料选择、压铸模具设计、工艺参数控制和后处理优化等方面,对铝合金支架零件压铸生产的关键工艺要点进行了系统研究。结果表明,优化铝合金材料成分和熔体质量,改进压铸模具的分型面设计、浇注系统布局和冷却水道参数,精确控制射速、射压、保压、温度等工艺参数,并采取合理的后处理措施,可显著提高铝合金支架零件的尺寸精度、表面质量和力学性能,实现压铸工艺的全面优化。