基于FDM/FEM耦合的铸造热应力分析

使用华铸CAE铸造模拟软件模拟铸造过程的温度场,通过自主开发的温度转换模块,将华铸CAE计算的温度场结果转换为有限元温度载荷,并加载到ANSYS的有限元模型中,进行铸造热应力分析.使用ANSYS中的接触单元处理铸件与铸型之间力的相互作用,对典型应力框试件进行了热应力分析,并与自由收缩模型的计算结果进行了对比.结果表明,采用接触单元法的计算结果更为准确.     

铸件热应力模拟中铸件/型(芯)相互作用的研究进展

铸造过程热应力分析是当前铸件数值模拟领域的研究重点和热点之一.其中铸件/型(芯)之间的相互作用的处理直接影响铸件铸造过程热应力分析的准确性.介绍了国内外处理铸件/型(芯)热力相互作用的研究进展,接触单元法是三维复杂铸件应力模拟发展的趋势.文章还介绍了砂型材料高温力学性能的研究情况.     

基于典型曲面结构铸件凝固过程收缩量的模拟研究

为模拟铸造过程中铸件的受阻收缩问题,开发了基于ANSYS的铸造过程热应力双向耦合模拟系统。设定铸件材质以及铸型材质的物理参数随温度变化而变化,采用接触单元处理铸件-铸型间的相互作用,实现了温度场与应力场的耦合。通过模拟具有典型曲面结构的铸件,发现铸件在凝固过程中的收缩量不仅与铸件的材质有关,还与铸件的凝固速度成反比,凝固速度越快,铸件收缩量越小;凝固速度越慢,铸件收缩量越大。     

基于ANSYS的铸造过程热应力双向耦合模拟

为提高铸造过程温度场和应力场的模拟精度,开发了基于ANSYS的铸造过程热应力双向耦合模拟的FEM/FEM集成系统.系统使用接触单元处理铸件·铸型间的相互作用,采用一致的有限元网格模型模拟温度场和应力场,并实现了温度场-应力场的相互影响.最后使用该系统进行了应力框铸件的实例验算,模拟结果与实验结果吻合良好.     

EDM电极快速精铸有限元模拟研究

研究了EDM电极快速精铸凝固过程中铸型和铸件间的相互作用。利用接触单元法对铸型/铸件的边界进行处理,以及对半圆柱铸件在凝固中尺寸变化进行了模拟。从而为实际工艺过程补偿量大小的确定提供理论依据和指导。     

界面传热系数的反求计算

介绍了在镍铝青铜水玻璃砂型铸造中铸件-砂型界面传热系数的反求计算。首先对铸件、铸型的温度进行测量,然后通过ProCAST反求计算,得到了符合实际的传热系数。该方法可用于其它合金铸造过程中界面传热系数的确定。     

水轮机下环铸件凝固过程热应力模拟分析

采用数值模拟方法对水轮机下环铸件凝固过程中的应力场进行了模拟和分析。模拟中采用接触单元法处理铸件与砂芯之间力的作用,改进了传统的铸件/铸型边界条件处理方法。文中重点分析了下环凝固过程中准固相区的受力情况,根据准固相区受力特点建立了适当的热裂判据,对下环凝固过程热裂倾向性进行预测。实际生产结果与预测结果相符合。     

考虑界面传热系数时铸造凝固过程的缺陷预测

考虑了铸造凝固过程中铸件铸型的热胀冷缩速率的不同,导致铸件铸型之间产生细小空气间隙,使得铸件铸型之间的界面传热系数发生改变。采用三维绘图软件PROE对蜗轮毂进行三维建模,并通过有限元分析软件ANSYS在考虑到空气间隙存在的情况下对其进行铸造凝固过程的数值模拟,得到凝固过程中各时刻的温度场、温度梯度场、热应力场等的分布情况,预测了铸件可能出现缩孔缩松以及裂纹的部位,结果与实际生产结果相一致。     

界面热阻对镁合金砂型铸造过程温度分布的影响

采用直接差分法求解热传导方程,对AZ91镁合金砂型铸造过程进行模拟,研究了界面热阻对温度分布影响。结果表明:在AZ91镁合金砂型铸造过程中,随着铸件/铸型热阻的减小,铸件/铸型界面散热情况得到改善,拐角位置温度降低速率趋于相同,整个铸件从冒口区域和底座区域同时向内部区域凝固;随着铸件/空气热阻的增加,冒口位置温度降低速率减慢,冒口区域的优先凝固优势消失,整个铸件从冒口区域和底座区域同时向内部区域凝固。此外,铸型/空气热阻对AZ91镁合金砂型铸造过程的温度分布影响不明显。     

铸型和球铁铸件之间力的相互作用

刚性好,且不易变形的铸型,可大大减少球铁铸件的缩松。为了探讨铸型与铸件之间力的相互作用的计算方法,特使用专门仪器(图1)测量球铁收缩前的膨胀对型壁的压力。由于所用造型材料的热膨胀系数小,并加上水、空气冷却,从而排除了型腔的热膨胀影响。直径为100毫米的球形铸件,完全可以保汪铸件与型壁间产生最低的摩擦     

Effect of sand mold models on the simulated mold restraint force and the contraction of the casting during cooling in green sand molds

In this work, the JIS AD12.1 (almost the same as A383.1) aluminum alloy was cast in a green sand mold. The restraint force from the sand mold and the contraction of the casting were measured dynamically from the solidifying temperature to the shake-out temperature using a dedicated device. Then, FEM (Finite Element Method) thermal stress analyses of the experiment were performed. The analyses adopted four types of representative constitutive equations and the mechanical properties of the green sand mold, which were quoted from previous research articles. As verification, this study dynamically compared the simulated restraint force and the contraction of casting with measured results and examined which mechanical properties are important for expressing the restraint force of the sand mold. This verification is the first attempt in the world. As a result, the simulated restraint force was estimated to be over ten times as large as the measured result in each type of equation because the yield stress of the sand mold used in our experiment was lower than those quoted from previous studies. The yield stress measured by a uniaxial compression test was 1/20 of the quoted values. When the measured yield stress was adopted in the simulation, the simulated restraint force and contraction approached the measured results. The yield stress of the sand mold was a dominant factor in the restraint force simulated by the thermal stress analyses. The yield stress of the green sand mold used in the casting process should be measured to predict the residual stress using FEM thermal stress analyses.     

A verification of the thermal stress analysis,including the furan sand mold,used to predict the thermal stress in castings

The restraint exerted on a casting by a furan sand mold on the casting and the contraction of the casting during cooling was dynamically and simultaneously measured using a device that we developed. The measurements were compared during cooling with thermal stress analyses. The thermal stress analyses were based on the representative mechanical models for the furan sand mold, i.e., the elastic and elasto-plastic models used in previous studies. The comparison demonstrated that the elasto-plastic model simulates the restraint force more accurately than the elastic model. In the thermal stress analysis, it was important to describe the development of inelastic deformation and the fracture of the sand mold. However, the simulated restraint force was still twice as large as the measured force even in the elasto-plastic model. This error is most likely attributable to using the temperature-independent mechanical properties of the furan sand mold and the mechanical model of the casting alloy, which neglected the viscoplasticity at high temperature in the thermal stress analysis.     

树脂砂型(芯)热开裂及其铸件产生脉纹缺陷的理论判据的研究

本文应用弹性力学和传热学等理论导出了树脂砂型(芯)在铸造过程中的热应力和机械应力关于厚度方向的一维空间z和受热时间t的二元方程,据此提出了一种新颖的树脂砂型(芯)热开裂的理论判据,并首次建立了铸件产生脉纹缺陷的理论判据。文中对该热开裂理论判据进行了简化分析,结果表明:以前的一些判据只是该判据的特例或简化式。文章还根据所得的理论判据提出了防止砂型(芯)热开裂和铸件产生脉纹缺陷的措施。     

Dynamic measurements of the load on castings and the contraction of castings during cooling in sand molds

The load on flange castings in sand molds was gradually increased beginning from the end of the solidification process until the final cooling stage. The maximum tensile load on the flange castings in furan sand molds was larger than that of the flange castings in green sand molds. With the furan sand mold, permanent deformation in the flange castings occurred beginning from the end of the solidification process until reaching a temperature of approximately 250 °C. The mechanical interaction between the casting and the sand mold should be considered for more accurate stress calculations, particularly in furan sand molds.     

两种不同约束条件下发动机缸体铸件热应力场的数值模拟

采用FDM/FEM集成热应力分析系统(其中采用铸造之星FT-STAR进行温度场计算,ANSYS进行热应力场计算,采用FT-STRESS进行有限差分网格向有限元网格转换和有限差分/有限元温度载荷转换),对某厂柴油机发动机缸体铸件进行从浇注到冷却至室温全过程的温度场、热应力场数值模拟,得到冷却变形情况及残余应力分布,并研究比较了将气缸处砂芯考虑为部分刚性,和将砂芯考虑为完全退让性的两种不同约束模拟方案对计算结果的影响。前者应力值和变形值远远大于后者的结果。     

Development of a device for dynamical measurement of the load on casting and the contraction of the casting in a sand mold during cooling

To predict and control the residual stress present in sand castings manufactured via CAE (Computer Aided Engineering), the mechanical interaction between the casting and the sand mold during cooling must be determined experimentally. A device was developed in this study to determine the load on the casting caused by the resistance of the mold and the contraction of the casting during cooling. Our device consists of two modules that work simultaneously: a module containing a load cell, for measuring the load on the casting during cooling and a module containing an LVDT (Linear Variable Differential Transformer) for measuring the contraction of the casting during cooling. In performance verification testing, the device enabled the simultaneous measurement of the load on the sand casting and the contraction of the casting. This measurement was performed dynamically during the cooling process. Additionally, for the case where the contraction of the casting was hindered by the sand mold, the permanent deformation of the casting after shake out (which leads to residual stress in the casting) was successfully measured using our device.     

湿型砂造型和制芯过程数值模拟研究进展

造型是湿砂型铸造生产过程的核心环节,它的目标在于将松散的型砂紧实成为高紧实度的砂型.紧实度均匀、能抵抗金属液体冲击的合格砂型是保证铸件质量的关键因素之一.铸造技术的发展使得砂芯在铸造生产中的作用越来越大,被称为"精确砂型铸造"的组芯造型对砂芯的尺寸精度要求非常高.湿型砂造型和制芯过程的数值模拟可以预测砂型和砂芯质量,优化造型工艺,从而为生产高质量铸件提供重要保证.对湿型砂造型和制芯过程数值模拟的现状进行了分析,并提出了未来的发展方向.     

Thermal deformation of aluminum alloy casting materials for tire mold by numerical analysis

Thermal deformation of aluminum alloy casting materials for manufacturing the tire mold was numerically investigated.The AC7A and AC4C casting material was selected as casting material and the metal casting device was used in order to manufacture the mold product of automobile tire in the actual industrial field.The temperature distribution and the cooling time of casting materials were numerically calculated by finite element analysis (FEA).Also,the thermal deformation such as displacement and stress distribution was calculated from the temperature results.The thermal deformation was closely related to the temperature difference between the surface and inside of the casting.The numerical analysis results reveal that the thermal deformation of AC7A casting material is higher than that of AC4C casting material.Also,the thermal deformation results at the central part are larger than that on the side of casting because of the shrinkage caused by the cooling speed difference.