Numerical Simulation of Shrinkage Cavity Formation in Spheroidal Graphite Iron Castings Based on Micro Modeling

A micro-modeling method (MM) for the quantitative prediction of the shrinkage cavity formation in SGiron castings is proposed. The mathematical models describing the volume changes during the solidification ofspheroidal graphite cast iron are established based on the models of solidification kinetics. The shrinkage cavityformation of T-shaped SG iron castings is calculated with MM method. The calculated results are compared with theexperimental results. It is shown that the predicted size, shape and distribution of shrinkage cavity by MM methodare in good agreement with the measured results.

Optimized DISA system parameters of a thin-wall malleable iron pipe casting by numerical simulation

The filling and solidification of a malleable iron pipe casting manufactured by DISA casting mold line with different design parameters were calculated by using software MAGMASOFT. Then the shrinkage porosity was predicted by thermal criterion. Based on the simulation results, the influences of the runner ratio and feeder position on the porosity were discussed. The results show that synchronization of injection can be significantly influenced by the size of downsprue section, and an de-sign structure of DISA gating system was used to solve the problem of flow imbalance in the filling procegs. At the same time, the riser was designed on the hotspot for feeding shrinkage. At last, the optimizated gating system and feeding system were ac-complished to eliminate shrinkage porosity.

Confluence and cold shut computation based on time field in casting simulation

Numerical simulation technology has been widely used in the foundry industry to analyze and improve casting processes.During the casting filling process,many filling-related defects form easily at the confluences of liquid metal streams.The main filling-related defects are cold shut defects.To calculate the positions of casting defects,the characteristics of liquid metal confluences were analyzed.The flow front of liquid metal was captured by the volume-of-fluid algorithm to obtain a time field,which was used to calculate the time derivatives of the liquid front position and the confluences of liquid metal streams.To distinguish small confluences from the main confluences,the concept of confluent scale was developed,which was used to filter the small confluences based on a threshold.The calculation process was demonstrated through the post-processing of numerical simulation.A "W" shaped casting and a steering wheel casting were calculated to validate the accuracy of the method developed in this study.The positions of cold shut defects were predicted by calculating the confluences of liquid metal streams.The method was proved to be practical by comparing the calculation results with the positions of cold shut defects in an end cover casting.The computation of confluences and cold shut defects can improve the analysis efficiency and provide assurance for the optimization of a casting process plan.

Numerical simulation and analysis of mould filling process in lost foam casting

In lost foam casting(LFC)the foam pattern is the key criterion,and the filling process is crucialto ensure the high quality of the foam pattern.Filling which lacks uniformity and denseness will cause variousdefects and affect the surface quality of the casting.The influential factors of the filling process are realized in thisresearch.Optimization of the filling process,enhancement of efficiency,decrease of waste,etc.,are obtained bythe numerical simulation of the filling process using a computer.The equations governing the dense gas-solid two-phase flow are established,and the physical significanceof each equation is discussed.The Euler/Lagrange numerical model is used to simulate the fluid dynamiccharacteristics of the dense two-phase flow during the mould filling process in lost foam casting.The experimentsand numerical results showed that this method can be a very promising tool in the mould filling simulation of beads’movement.

Shrinkage Behaviour of Spheroidal Graphite Cast Iron in Green and Dry Sand Molds for the Benchmarking of Solidification Simulation

The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus, mold type (green or dry) and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroids graphite cast iron castings were discussed. Finally, two regression equations relating these variables to the formation of shrinkage porosity were derived based upon the orthogonal experiments conducted.

3-D Finite-Element Numerical Simulation of Centrifugal Induction Electrosalg Casting Solidification Process

A 3-D finite-element numerical simulation model of temperature field for CIESC casting solidification process was developed with the aid of ANSYS software and a series of corresponding experiments were made. The results showed that the good agreement was obtained between the numerical simulation and the experiments. Based on the numerical simulation results, the characteristics of temperature distribution in the castings during CIESC solidification process were analyzed and summarized. According to the G/R-1/2 method and numerical simulation results, there is no any shrinkage defect in the CIESC casting and structure or casting is fine and compact.

Optimization of investment casting process for K477 superalloy aero-engine turbine nozzle by simulation and experiment

In order to reduce the shrinkage porosity of nickel-based superalloy castings in the investment casting process,the effects of different gating systems on mold filling,solidification process,and prediction of shrinkage porosity of aero-engine turbine nozzle castings were investigated by simulation and experimental methods.Results show that the design of the vertical runner would cause greater turbulence of the melt in the riser during the mold filling process,and the outer runner is not necessary.With the decrease in number of runners,the hot spot moves down towards the casting,and the shrinkage and porosity defects are formed in the casting below the riser.In the original designs,a certain tendency of shrinkage and porosity defect is found in the vanes,inner rings,and outer rings of the castings by both simulation prediction and experiment.Finally,based on the processing optimization,the aero-engine turbine nozzle casting with no shrinkage and porosity defects is obtained.

Modeling and simulation of 3D thermal stresses of large-sized castings in solidification processes

When heavy machines and large scaled receiver system of communication equipment are manufactured, it always needs to produce large-sized steel castings, aluminum castings and etc. Some defects of hot cracking by thermal stress often appear during solidification process as these castings are produced, which results in failure of castings. Therefore predicting the effects of technological parameters for production of castings on the thermal stress during solidification process becomes an important means. In this paper, the mathematical models have been established and numerical calculation of temperature fields by using finite difference method (FDM) and then thermal stress fields by using finite element method (FEM) during solidification process of castings have been carried out. The technological parameters of production have been optimized by the results of calculation and the defects of hot cracking have been eliminated. Modeling and simulation of 3D thermal stress during solidification processes of large-sized castings provided a scientific basis, which promoted further development of advanced manufacturing technique.

Finite element simulation of real cavity closure in cast Ti6Al4V alloy during hot isostatic pressing

The healing behavior of shrinkage cavity inside the cast Ti6Al4V alloy during hot isostatic pressing(HIP)was investigated experimentally by interrupted hot isostatic pressing tests.The X-ray micro computed tomography was used to record the morphology changes before and after hot isostatic pressing.The two-dimensional geometry obtained by the microCT scan was used in simulation to study the evolution of the real shrinkage cavity during hot isostatic pressing.Shrinkage cavities,shrinkage porosity and small gas pores can be effectively eliminated under proper HIP conditions.The two-dimensional morphology in the simulation results agrees well with the experimental results.This study reveals that plastic deformation,creep and diffusion are the main mechanisms of cavity closure during hot isostatic pressing.In addition,the simplified elliptical pores with aspect ratios at different positions were used to replace the real pores to further study the factors affecting the position of dimples after HIP by simulation.It is found that the position of the dimples mainly depends on the aspect ratio of the elliptical pore and the distance between the pore surface and the external surface of the geometric model.

Eliminating shrinkage defects and improving mechanical performance of large thin-walled ZL205A alloy castings by coupling travelling magnetic fields with sequential solidification

ZL205 A alloys with large thin-walled shape were continuously processed by coupling travelling magnetic fields(TMF)with sequential solidification,to eliminate the shrinkage defects and optimize the mechanical performance.Through experiments and simulations,the parameter optimization of TMF and the influence on feeding behavior,microstructure and properties were systematically studied.The results indicate that the magnetic force maximizes at the excitation current of 20 A and frequency of 200 Hz under the experimental conditions of this study,and increases from center to side-walls,which is more convenient to process thin-walled castings.TMF can break secondary dendritic arm and dendrites overlaps,widen feeding channels,prolong the feeding time,optimize the feeding paths,eliminate shrinkage defects and improve properties.Specifically,for as-cast state,TMF with excitation current of 20 A increases ultimate tensile strength,elongation and micro-hardness from 186 MPa,7.3%and 82.1 kg/mm^(2) to 221 MPa,11.7%and 100.5 kg/mm^(2),decreases porosity from 1.71%to 0.22%,and alters brittle fracture to ductile fracture.

Impact analysis of casting parts considering shrinkage cavity defect

Shrinkage cavity may be detrimental to mechanical performances of casting parts.As a consequence,design engineers often use overly large safety factors in many designs due to insufficient understanding of quantitative effects of shrinkage cavity defects.In this paper,process of Al alloy wheel impact test was computationally analyzed for both the wheel models with and without shrinkage cavity defects.Based on shrinkage cavity data obtained from industrial CT (Computerized Tomography),the shrinkage cavity defects were modeled with SSM (Shape Simplification Method),which reconstructs shrinkage cavity defects to hollow spheroid primitives.After the impact simulation was conducted,the results show that under impact test condition,the wheel considering shrinkage cavity defects may fracture while the sound-assumed wheel may not.

A Mathematical Model for Predicting Shrinkage Defect of Ductile Iron Castings

The shrinkage defect of a ductile iron casting is attributed to the volume variations occurring in solidification, which consist of liquid contraction, solidification shrinkage, graphitization expansion, and mold cavity enlargement. Based on this understanding, a mathematical model for predicting the shrinkage defect of the casting is developed, in which the volume variations of the casting in soli- dification are numerically simulated, especially, the mold cavity enlargement is quantitatively calculated. Moreover, the reliability of the model is verified in production and experiment.

To develop a quantitative method for predicting shrinkage porosity in squeeze casting

In order to secure high strength and high elongation of suspension parts,it is critical to predict shrinkage porosity quantitatively.A new simulation method for quantitative prediction of shrinkage porosity when replenishing molten metal has been proposed for squeeze casting process.To examine the accuracy of the calculation model,the proposed method was applied to a plate model.

Influence of random shrinkage porosity on equivalent elastic modulus of casting： A statistical and numerical approach

Shrinkage porosity is a type of random distribution defects and exists in most large castings. Different from the periodic symmetry defects or certain distribution defects, shrinkage porosity presents a random "cloud-like" configuration, which brings difficulties in quantifying the effective performance of defected casting. In this paper, the influences of random shrinkage porosity on the equivalent elastic modulus of QT400-18 casting were studied by a numerical statistics approach. An improved random algorithm was applied into the lattice model to simulate the "cloud-like" morphology of shrinkage porosity. Then, a large number of numerical samples containing random levels of shrinkage were generated by the proposed algorithm. The stress concentration factor and equivalent elastic modulus of these numerical samples were calculated. Based on a statistical approach, the effects of shrinkage porosity's distribution characteristics, such as area fraction, shape, and relative location on the casting's equivalent mechanical properties were discussed respectively. It is shown that the approach with randomly distributed defects has better predictive capabilities than traditional methods. The following conclusions can be drawn from the statistical simulations:(1) the effective modulus decreases remarkably if the shrinkage porosity percent is greater than 1.5%;(2) the average Stress Concentration Factor(SCF) produced by shrinkage porosity is about 2.0;(3) the defect's length across the loading direction plays a more important role in the effective modulus than the length along the loading direction;(4) the surface defect perpendicular to loading direction reduces the mean modulus about 1.5% more than a defect of other position.

基于AnyCasting排气歧管砂型铸造数值模拟及试验研究

用砂型铸造生产的排气歧管汇聚多个支管,内外表面有极复杂的曲面,这对生产工艺提出很高要求,若工艺不当,会在浇注过程中产生缩松、缩孔、卷气、冷隔、夹渣等缺陷。运用AnyCasting铸造模拟软件对试制产品进行流场和温度场分析,基于分析结果预测铸件中存在的缺陷种类、位置和大小。理论分析与试验结果基本吻合,通过分析缺陷情况实施相应工艺优化,将缺陷影响降至最小程度,从而得到满意铸件。

Numerical Simulation on Inclusion and Bubble Entrapment in Solidified Shell in Model Experiment and in Mold of Continuous Caster With DC Magnetic Field

A model experiment investigating entrapment of inclusions and bubbles on the solidified shell was performed using molten steel,and the conditions for inclusion and bubble entrapment and mechanism of entrapment were studied. The results were applied to the flow behavior in the casting mold of a continuous caster.At the solid-liquid interface, entrapment of inclusions is greatly reduced by the existence of a low velocity flow,e.g.,0.05m/s.The above-mentioned interfacial flow velocity dependency of inclusion entrapment is considered to be largely influenced by changes in the thickness of the concentration boundary layer,which depend on the interfacial flow velocity.Specifically,bubbles and inclusions which enter the concentration boundary layer are drawn to the solid-liquid interface by a suction force which is several orders larger than the Saffman's force.In addition to the above-mentioned suction force,the so-called cleaning effect is determined by fluid-dynamic forces such as drag force,etc.which act on particles,and furthermore,by resident time of particles at the solid-liquid interface,which depends on the solidification rate.In a FC mold with a 2-stage electromagnetic brake,flotation of bubbles entrained in the jet flow from the nozzle is accelerated with the large DC magnetic field.This is attributed to the braking effect of the DC field on the nozzle jet and the upward flow by the buoyancy of the bubbles.As a result,the interfacial flow velocity can be normalized by increasing the strength of the magnetic field,and entrapment of large bubbles and inclusions can be reduced.

AnyCasting模拟软件在汽车零件铸造工艺设计中的应用

以发动机缸体、轮毂为例，介绍了AnyCaSting软件分别在高压、低压铸造工艺中的应用，针对不同铸造工艺汽车零部件充型和凝固过程中产生的常见缺陷进行了预测分析。通过软件的后处理模块，能直观地观察铸造生产过程中气体包卷、缩孔等缺陷的分布，对铸造缺陷进行准确的预测，从而有利于铸造工艺改进，并节约试制成本，提高产品质量。

基于AnyCasting的磨辊辊皮铸造模拟与工艺优化

针对磨辊辊皮铸造过程中易出现缩孔等缺陷问题,运用AnyCasting软件对其充型、凝固过程进行模拟。首先,分析铸件金属液的凝固规律,预测缩孔缺陷产生的部位;其次,通过在型腔底部下方增设冷铁,对初始铸造工艺进行优化。结果表明,上移缩孔在冒口中的位置可有效防止在铸件上发生缩孔。按此工艺生产的辊皮铸件无缩孔、组织致密且硬度高。

AnyCasting虚拟仿真在砂型铸造中的应用及缺陷分析

基于AnyCasting虚拟仿真软件,论述了实践教学案例侧枕模型模拟预测砂型铸造过程中填充和凝固的顺序以及可能存在的缺陷。经过AnyPRE前处理、AnySOLVER计算求解和AnyPOST后处理,观察分析充型时间、凝固时间、温度、压力、卷气、水平涡流等。通过结果合并功能发现二维或三维的凝固缺陷,并对缺陷进行分析解决方案。

基于AnyCasting的减速器下箱体铸造模拟及工艺优化

使用UG建立减速器下箱体三维模型。在原有铸造工艺的基础上利用AnyCasting软件模拟了减速器下箱体的充型和凝固过程。根据模拟结果分析了铸件的温度场和缺陷分布。结果表明,在原工艺方案下会出现缩松、缩孔等铸造缺陷。通过增大冒口尺寸以及添加冷铁等工艺优化,可以消除铸件内部缺陷的产生,为类似下箱体的实际生产起到了一定的指导作用。