Evaluation of heat transfer coefficients during upward and downward transient directional solidification of Al–Si alloys

Aluminum alloys with silicon as a major alloying element consist of a class of alloys which provides the most significant part of all shaped castings manufactured. This is mainly due to the outstanding effect of silicon in the improvement of casting characteristics, combined with other physical properties such as mechanical properties and corrosion resistance. In general, an optimum range of silicon content can be assigned to casting processes. For slow cooling rate processes (sand, plaster, investment), the range is 5 to 7 wt%; for permanent molds, 7 to 9%; and for die castings, 8 to 12%. Since most casting parts are produced considering there is no dominant heat flow direction during solidification, it seems to be adequate to examine both upward and downward growth directions to better understand foundry systems. The way the heat flows across the metal/mold interface strongly affects the evaluation of solidification and plays a remarkable role in the structural integrity of castings. Gravity or pressure die casting, continuous casting, and squeeze casting are some of the processes where product quality is more directly affected by the interfacial heat transfer conditions. Once information in this area is accurate, foundrymen can effectively optimize the design of their chilling systems to produce sound castings. The present work focuses on the determination and evaluation of transient heat transfer coefficients from the experimental cooling curves during solidification of Al 5, 7, and 9 wt% Si alloys. The method used is based on comparisons between experimental data and theoretical temperature profiles furnished by a numerical solidification model, which applies finite volume techniques. In other words, the resulting data were compared with a solution for the inverse heat conduction problem. The necessary solidification thermodynamic input data were obtained by coupling the software ThermoCalc Fortran interface with the solidification model. A comparison between upward and downward transient metal/mold heat transfer coefficients is conducted.     

Multidisciplinary shape optimization of ductile iron castings by considering local microstructure and material behaviour

During the casting process and solidification of ductile iron castings, a heterogeneous microstructure is formed throughout the casting. This distribution is strongly influenced by the item geometry and the process related factors, as chemical composition and local solidification conditions. Geometrical changes to the geometry of the casting thus alters the local mechanical behavior and properties, as well as the distribution of stresses and strains when the casting is subjected to load. In order to find an optimal geometry, e.g. with reduced weight and increased load-bearing capacity, this interdependency between geometry and local material behavior needs to be considered and integrated into the optimization method. In this contribution, recent developments in the multidisciplinary integration of casting process simulation, solidification and microstructure modelling, microstructure-based material characterization, finite element structural analyses with local material behavior and structural optimization techniques are presented and discussed. The effect and relevance of considering the local material behavior in shape optimization of ductile iron castings is discussed and evidenced by an industrial application. It is shown that by adopting a multidisciplinary optimization approach by integration of casting simulation and local material behavior into shape optimization, the potential of the casting process to obtain components with high performance and reliability can be enabled and utilized.     

Casting traceability with direct part marking using reconfigurable pin-type tooling based on paraffin–graphite actuators

Green sand moulding machines for cast iron foundries are presently unable to uniquely identify individual castings. An insert tool concept is developed and tested via incremental mock-up development. The tool is part of the pattern plate and changes shape between each moulding, thus giving each mould a unique ID by embossing a Data Matrix symbol into the sand. In the process of producing the mould, each casting can be given a unique (DPM), enabling part tracking throughout the casting's life cycle. Sand embossing is achieved with paraffin-actuated reconfigurable pin-type tooling under simulated processing conditions. The marker geometry limitations have been tested using static symbol patterns, both for sand embossing and actual casting marking. The marked castings have successfully been identified with decoding software. The study shows that the function of each element of this technology can be successfully applied within the foundry industry.     

板坯连铸凝固传热过程的有限元模拟

在建立板坯连铸凝固传热数学模型的基础上,采用有限元软件MSC Marc对国内某板坯连铸机的凝固过程进行模拟,并对其仿真结果进行分析.     

基于Pro/ENGINEER的铁路货车铸钢摇枕数值模拟

为实现铁路货车铸钢摇枕结构工艺性最优的目标,采用Pro/ENGINEER对摇枕铸造实体建模.选择ZCAST数据库中与铸件相近钢种的热物理参数对模型进行数值模拟.数值模拟计算结果显示出摇枕铸件各部位在浇注和凝固过程中的流场、速度场、温度场和时间场,预测铸件在生产过程中可能产生的缺陷.根据数值模拟结果对产品结构设计不合理的区域和工艺设计过程中存在的问题进行改进.实践表明结构和铸造工艺优化后所生产出的铸件质量满足铁路货车铸钢摇枕的要求.     

Restoring boundary conditions in the solidification of pure metals

The scope of the paper is an algorithm reconstructing the boundary conditions (heat flux and heat transfer coefficient) in the solidification of pure metals on the grounds of temperature measurements. For the verification of the algorithm experimental data derived in the course of the solidification of aluminum were used. An example of the application of the algorithm for designating the cooling conditions in continuous casting is provided, when the values of temperature at selected points on the boundary of the casting are known.     

铸造充型过程参数优选的两种方法比较

在实际铸造生产之前，利用计算机对整个铸造过程进行数值模拟，以及对浇注口位置和浇注速度等浇注过程的工艺参数进行优化计算，可以尽早发现可能产生的缺陷以及缺陷发生的位置，从而缩短设计周期，提高铸件质量，降低成本，本文比较了两类参数优选方法．方法一，利用铸造充型过程数值仿真软件，获得一些有关控制参数的数值实验结果；然后将数值实验结果作为样本数据，运用三次样每插值方法进行插值，获得输入参数(工艺参数)和输出值(充型结束时型腔内最高温度与最低温度之差)之间的函数关系；进而得到目标函数的最小值，即得到最合适的浇注过程中的工艺参数．方法二，使用数值实验数据对神经网络进行训练，再采用遗传算法对神经网络建立起的函数关系进行寻优，亦可得到最合适的工艺参数．使用两种方法得到的解基本一致，本文用较为成熟的方法一例证了有待探索的方法二．     

A genetic algorithm for optimizing gravity die casting’s heat transfer coefficients

Numerical simulation of solidification has improved our understanding of casting processes significantly over the last two decades. One of the most desirable features in the design of casting of high strength components is directional solidification. Generally, expertise from skilled foundry men is required during the design of casting-mould assembly interrogation in order to achieve a satisfactory thermal control, thus directional solidification. This process is not only costly, both financially and temporally to foundries, it also heavily rely on foundry men’s experiences. Our main aim in this project is to explore a novel and fully automated computer scheme that ties the geometric features of the casting with evolutionary algorithms to achieve thermal control. By extracting the medial axes of the casting geometry and correlate it with the interfacial heat transfer coefficient via evolutionary algorithm, we are able to perform non-exhaustive search of the optimized solution. Preliminary results from our computer experiments showed favourable results. In this paper, the focus is sharpened on the convergence and optimality of the developed GA.     

Case-based retrieval of 3-dimensional shapes for the design of metal castings

This paper describes research into retrieval based on 3-dimensional shapes for use in the metal casting industry. The purpose of the system is to advise a casting engineer on the design aspects of a new casting by reference to similar castings which have been prototyped and tested in the past. The key aspects of the system are the orientation of the shape within the mould, the positions of feeders and chills, and particular advice concerning special problems and solutions, and possible redesign. The main focus of this research is the effectiveness of similarity measures based on 3-dimensional shapes. The approach adopted here is to construct similarity measures based on a graphical representation deriving from a shape decomposition used extensively by experienced casting design engineers. The paper explains the graphical representation and discusses similarity measures based on it. Performance measures for the CBR system are given, and the results for trials of the system are presented. The competence of the current case-base is discussed, with reference to a representation of cases as points in an n-dimensional feature space, and its principal components visualization. A refinement of the case base is performed as a result of the competence analysis and the performance of the case-base before and after refinement is compared.     

Solidworks在铸造模型设计制造过程中的应用

长期以来,铸造用模的制造一直沿袭着零件图→铸造工艺图→模块设计放样→制造组合这一程序,制造周期长,成为新产品开发的瓶颈。我们应用计算机三维软件Solidworks将产品图纸转化为电子图形,然后结合铸造工艺参数直接编辑修正成放样图,实现了产品设计与模型制造交叉作业、相互验证,大大加快了模型制造的进度,提高了模型质量。     

Microcasting of Al bronze and a gold base alloy improved by plaster-bonded investment

Microcasting based on the investment casting process is a suitable method to shape various metals. It has mostly been used for parts in the millimeter and centimeter range made of precious alloys. A newly developed plaster-bonded investment allows to manufacture small structures in the micrometer range made of base alloys such as Al bronze. Compared to phosphate-bonded investments, the plaster-bonded investment can be easily removed from cast parts with very complicated microstructures without damaging or influencing the chemically reactive metal. Additionally, it was found that the new plaster-bonded investment significantly improves the casting of the gold base alloy Stabilor^® G, because the mold filling ability for structures in the submillimeter range was greatly facilitated at an even lower preheating temperature of the mold.     

Digital twin of functional gating system in 3D printed molds for sand casting using a neural network

Journal of Intelligent Manufacturing - The filling stage is a critical phenomenon in sand casting for making reliable castings. Latest research has demonstrated that for most liquid engineering...     

New approaches in microcasting: permanent mold casting and composite casting

For several years, microcasting was based on investment casting. New approaches are now the permanent mold casting and composite casting of micro parts. Casting was performed with aluminum bronze of the type CuAl₁₀Ni₅Fe₄. Permanent mold casting was commenced with steel mold inserts in a lost mold. The development of a band heater enabled the heating of permanent molds inside the casting machine. This shall ensure sufficient form filling of micro cavities. For permanent mold casting micro structured steel molds and graphite molds were used. Composite casting was investigated for surrounding a micro part by melt, and for pouring a metal melt into a micro structured part. In both cases different materials were combined. For metal–ceramic composite casting ZrO₂, Al₂O₃ or Si₃N₄ were used in connection with Al bronze. For metal–metal composite casting Al bronze was cast around steel. First results for both new approaches are presented.     

工业铸件缺陷无损检测技术的应用进展与展望

高端装备制造业是国民经济的支柱产业,是推动工业转型升级的引擎,发挥着举足轻重的作用.而铸造产业一直是人类现代生产生活中重要的、不可替代的产业,铸件产品既是工业制造产品,也是大型机械的组成部分.随着经济水平和工业自动化程度的不断提升,人们对于铸件的需求量呈指数爆炸式增长,铸件价值辐射到各行各业.与此同时,铸件在铸造、服役...     

利用神经网络控制连续浇铸过程中的热传导

In continuous casting, the cooling-solidification process must be based on the adaptation of heat transfer, which is directly connected to casting conditions such as casting speed, casting temperature, and cooling parameters. Most control schemes are based on the static relation between casting speed and water flow rate in each cooling zone; this constitutes an open loop that does not consider the dynamic surface temperature, which is an important parameter for the final slab quality. In steelmaking, the casting-speed changes affect the global heat transfer. An optimal operation requires an adjustment of the process control variables, i.e., global heat transfer. A learning neural network (NN) allows the identification and the control of a nonlinear heat transfer model in the continuous casting process. A heat transfer model was developed using the dynamic heat balance. A comparison between the experimental open loop results and those of the model simulation is considered. Following adaptation, the model is used for controlling the slab surface temperature in closed loop, using NN technology and PID controllers. The NN identification and control strategy gives a stable temperature closed loop control comparatively to the conventional PID.     

A level set based method for the optimization of cast part

A cast part is formed via casting process in which molten liquid is poured into and solidifies in a cavity enclosed by molds. Then, one obtains the cast part when the molds are removed. An important issue in the casting process is that a cast part should have a proper geometry so that the molds can actually be removed. Accordingly, in the optimization of a cast part one not only needs to optimize the performance of the cast part but also needs to ensure the cast part have a proper geometry. With these goals, a level set based method is proposed for the optimization of cast part. A molding condition and a performance condition on the design velocity are derived for the optimization. Numerical examples are provided in 2D and 3D.     

连铸二冷配水自适应动态优化控制

在常规连铸二冷配水控制方法的基础上,提出了自适应动态配水控制策略,建立了由基础自动控制、 软测量技术和智能控制技术相结合的二级动态配水控制系统．在控制系统中,建立了基于凝固传热理论的软测量模 型,用于实时预测铸坯表面温度;应用基于自整定神经元的多变量PID 控制算法,实现连铸二冷配水动态单元跟踪 控制,使铸坯表面温度保持在目标值范围内．仿真及应用结果表明了所建模型和控制算法的有效性,控制系统对拉 速扰动具有良好的目标温度跟随性能．     

双辊薄带连铸凝固过程的数值模拟与分析

建立双辊薄带连铸凝固数学模型,并利用有限元软件对薄带连铸凝固过程进行数值模拟. 通过比较和分析不同网格划分方法对计算结果的影响,为进一步研究薄带连铸凝固过程奠定基础.     

Design of particle-reinforced polyurethane mould materials for soft tooling process using evolutionary multi-objective optimization algorithms

Polyurethane is used for making mould in soft tooling (ST) process for producing wax/plastic components. These wax components are later used as pattern in investment casting process. Due to low thermal conductivity of polyurethane, cooling time in ST process is long. To reduce the cooling time, thermal conductive fillers are incorporated into polyurethane to make composite mould material. However, addition of fillers affects various properties of the ST process, such as stiffness of the mould box, rendering flow-ability of melt mould material, etc. In the present work, multi-objective optimization of various conflicting objectives (namely maximization of equivalent thermal conductivity, minimization of effective modulus of elasticity, and minimization of equivalent viscosity) of composite material are conducted using evolutionary algorithms (EAs) in order to design particle-reinforced polyurethane composites by finding the optimal values of design parameters. The design parameters include volume fraction of filler content, size and shape factor of filler particle, etc. The Pareto-optimal front is targeted by solving the corresponding multi-objective problem using the NSGA-II procedure. Then, suitable multi-criterion decision-making techniques are employed to select one or a small set of the optimal solution(s) of design parameter(s) based on the higher level information of the ST process for industrial applications. Finally, the experimental study with a typical real industrial application demonstrates that the obtained optimal design parameters significantly reduce the cooling time in soft tooling process keeping other processing advantages.