Numerical Simulation of Temperature Field and Thermal Stress in ZTA(p)/HCCI Composites During Solidification ProcessEI北大核心CSCD

As advanced wear-resistant materials, it is important to promote the process and application of high chromium cast iron (HCCI) matrix composite reinforced by zirconia toughened alumina ceramic particles (ZTA(p)/HCCI composite). For the purpose of wider applications of this kind of composite, it is urgent to optimize the process parameters of casting process for it. Based on the finite element software the temperature field and thermal stress in ZTA(p)/HCCI composite during casting process were simulated. The temperature fields of castings are investigated using the uniform initial temperature and the non-uniform initial temperature at the beginning of solidification. It is more appropriate to the actual situation at the end of mold filling process when the initial temperature of solidification is considered as an unstable temperature field. The influence from performs with different honeycomb shapes is considered in the calculations of temperature fields of castings. In this work, the thermo-elastic plastic model was used to accurately describe the thermal stress in the castings with different honeycomb shapes of preforms, and the results indicate that the thermal stress in them decreases with the increase of edge number of holes in preforms. Finally, the hot crack in castings is predicted and the shakeout process is optimized. It is concluded that the simulated results are in good agreement with the experimental results.     

铸钢件凝固过程三维位移场数值模拟研究

在开发铸钢件凝固过程三维位移场数值模拟有限元程序时 ,对准固态区间用粘弹塑性模型 ,固相线以下用弹塑性模型的本构关系 ;用初应变法计算温度载荷 ;用增量变刚度法求解位移场。对实际铸钢件凝固过程的位移场进行计算 ,模拟结果与理论分析一致 ,本研究工作是进一步模拟分析应力场和进行热裂预测的基础     

基于微机的铸件凝固过程应力数值模拟及工程应用

开发了基于微机平台的FDM／FEM集成应力分析系统，对复杂大型铸件的凝固过程热应力进行三维数值模拟；比较了鼓风机机壳在两种不同工艺方案中的残余应力，并且分析了对水轮机长轴头的热裂倾向。     

铸件热应力及热裂的数值模拟研究

铸件在铸造凝固过程中热应力场及热裂的数值模拟在实际的生产实践中起着十分重要的作用。本文综合国内外对铸造凝固过程中热应力及热裂数值模拟研究的现状，结合中北大学铸造工程研究中心的实际情况，指出了今后的研究方向和重点：建立适合铸造过程应力场数值模拟的模型，采用有限元软件ANSYS实现铸件热应力场的模拟分析，并计算残余应力。     

Application of 3-D numerical simulation software SRIFCAST to produce ductile iron castings

1. IntroductionSince the 1960's, there have been 3 progressive periodsfor modeling and simulation of the technological processof castings. In 1988, 3-D temperature fields were calculatedsuccessfully during the solidification process of steelcastings in many countries [1-4]. In 1995, 3-D velocityfields calculations of metal flow in mold filling were alsoachieved by advanced researchers [5-8]. From 1990 untilnow, the new task has been to model and simulate themicrostructure and morphology of cr…     

大型铸件成形过程数值模拟及工艺优化

用工程湍流模式计算大型铸件充型凝固过程三维速度场、温度场时,对提高模拟计算精度和效率进行了探讨。应用新的计算方法对大型不锈钢和合金铸铁件进行数值模拟,优化其铸造工艺。     

不锈钢焊接凝固裂纹温度场的数值模拟

进行不钢焊接凝固裂纹温度场分析与数据模拟。首先将电弧民辐射状对称并呈高斯分布的二维热流作用于工件表面,解决了电弧产热问题;其次,通过液淬法测试金属的固相分数随温度变化率,得到了凝固热放率;最皇采用增大热传导系数的方法,考虑了熔池内流体流动对整个温度场的影响。在此基础上,建立了二维焊接凝固裂纹温度场计算模型。此外,采用有限元方法计算了二维焊接凝固纹温度场,并研究了焊接规范参数及材料的热物理性能对 影     

薄板坯连铸结晶器内钢液凝固行为的研究

针对薄板坯连铸漏斗型结晶器内凝固过程,采用热弹塑性有限元法,考虑铸坯与铜板的接触状态,建立了热力耦合模型。模拟分析了铸坯经过结晶器过程中坯壳内的温度场和应力场,得到了凝固坯壳形成过程的传热和变形规律。模拟结果表明：铸坯角部温度高于宽面和窄面中心温度并出现两个平台期;两个弧线段交界区域出现应力峰值,是铸坯裂纹敏感区。该结果为漏斗型结晶器形状的设计、结晶器锥度的优化以及提高连铸坯质量提供理论依据和技术基础。     

Thermomechanical analysis of multi-bead pulsed laser powder deposition of a nickel-based superalloy

In laser powder deposition (LPD) repair of nickel-based turbine blades, hot cracking is the most common defect. The cracking has been found to be associated with thermal stress concentration and low-melting constituents on the grain boundaries. For directionally solidified and single-crystal blades, a positive correlation is established between cracking and the “stray grain” formation. Control of the deposit molten pool shape has been proposed as an effective method to limit the stray grains. However, in multi-bead, multi-layer LPD with a pulsed laser, due to a much more complex bead geometry, appearance of stray grains seems to be random. To obtain insight into cracking and stray grain formation during multi-bead LPD process on nickel-based superalloys, a 3-D transient finite element (FE) model has been developed and a thermomechanical analysis is performed. Time-dependent temperature and thermal strain fields have been predicted. The developed thermal model has been applied to predict and analyze the distribution of thermal stress concentration and the tendency of stray grain formation. The reliability and accuracy of the model are verified experimentally by the measured temperature field profile and the observation of microstructure.     

铝合金石膏型精密铸件凝固过程数值模拟与实验验证

应用自行开发的铸件充型及凝固模拟系统,对铝合金石膏型精密铸件的凝固过程进行了数值模拟。采用自行设计制备的多通道自动测温装置,对所模拟的铸件进行现场测温。为了提高模拟精度,对铸件铸型热物性参数进行了实测,并采用最小二乘法进行拟合。通过计算机模拟预测了铸件的缩孔区,分析了铸件缺陷产生的原因,提出了合理的工艺方案,消除了铸件内缩孔的发生。实验验证的结果表明,数值模拟结果与测试值拟合较好     

Ni3Al基合金薄壁件精铸工艺对热裂缺陷的影响及其数值模拟

研究了精铸工艺参数对Ni3Al基合金薄壁件热裂缺陷的影响,并运用铸造模拟软件对精铸过程的温度场、应力场进行了模拟,分析了薄壁精铸件热裂产生的机理。研究结果表明,铸件充型的先后顺序是薄壁型零件产生热裂缺陷的主要因素,优化浇注系统并改进浇注工艺参数能消除热裂缺陷的发生,从而提高薄壁件的铸造质量。     

The mechanism of hot crack formation in Ti-6Al-4V during cold crucible continuous casting

Hot crack is one of common defects in castings, which often results in failure of castings. This work studies the formation of hot crack during cold crucible continuous casting by means of experiments and theoretical analysis. The results show that hot crack occurs on the surface and in the circumference of ingots, where the solidified shell and the solidification front meet each other. The tendency of hot cracking decreases with the increase of withdrawal velocities in some extent. The hot crack is caused mainly by the friction force between the shell and the crucible inner wall, and it takes place when the stress resulting from friction exceeds the tensile strength of the shell. The factors of μ_m, η_t, η_s and η_m, affecting hot cracks are analyzed and verified. In order to decrease the tendency of hot cracks, technical parameters should be optimized by decreasing μ_m, η_t, η_s and η_m.     

起始铸造速度对AA7050合金半连续铸锭应力分布的影响

通过温度场、流场和应力场的三场耦合,对某铝业公司AA7050铝合金铸锭在半连铸过程中3种不同起始铸造速度下的应力、应变分布进行了数值模拟研究。结果显示,铸锭心部呈现很大的三轴拉应力,表面则呈现明显的压应力。根据在糊状区环向和径向的应力、应变分量较大,而轴向应力、应变分量较小,可以预计热裂纹倾向平行于轴向分布,不太可能发生垂直于轴向的热裂纹。铸造时在起始铸造阶段有必要采用小的铸造速度,以降低糊状区的热应力、应变,减小开裂倾向。     

铸件计算机凝固模拟的现状、发展与前景

计算机凝固模拟已经取得令人注目的成就，可以协助设计人员改进工艺设计，提高铸件质量。但是凝固模拟软件需要在铸件凝固的物理模型，计算机数值计算，铸件的三维成形，初始条件和边界条件确定，热物性数据的测量，铸件缺陷的预测及显示等多方面进行改进以更大程度上满足铸造生产的实际需要。在未来很长时期内，凝固模拟作为一个有力的工具，仍然需要有实际铸造工艺设计经验的专家使用才能发挥其作用与潜力。另一方面，铸造生产厂家必须严格生产过程控制，正确使用凝固模拟软件，加强对技术人员的培训和不断积累使用凝固模拟软件的经验，这是生产高质量铸件的需要，也是成功应用凝固模拟软件的重要条件。     

Continuous squeeze casting process by mass production

S queeze casting has been widely used for automotive struc tural parts because it offers a vast material selection from aluminum and magnesium alloys. In comparison with low pressure die casting, squeeze casting also overcomes many fluidity problems and thus it can use both hypereutectic and hypoeutectic alloys such as 319, 383 and 390. Squeeze casting can also apply “spot solidification” technology in addition to directional solidification method. The shortcoming of directional solidificati…     

Using finite difference method to simulate casting thermal stress

Thermal stress simulation can provide a scientific reference to eliminate defects such as crack,residual stress centralization and deformation etc., caused by thermal stress during casting solidification. To study the thermal stress distribution during casting process, a unilateral thermal-stress coupling model was employed to simulate 3D casting stress using Finite Difference Method (FDM), namely all the traditional thermal-elastic-plastic equations are numerically and differentially discrete. A FDM/FDM numerical simulation system was developed to analyze temperature and stress fields during casting solidification process. Two practical verifications were carried out, and the results from simulation basically coincided with practical cases. The results indicated that the FDM/FDM stress simulation system can be used to simulate the formation of residual stress, and to predict the occurrence of hot tearing. Because heat transfer and stress analysis are all based on FDM, they can use the same FD model, which can avoid the matching process between different models, and hence reduce temperature-load transferring errors. This approach makes the simulation of fluid flow, heat transfer and stress analysis unify into one single model.     

大型蒸汽轮机高压缸铸件的铸造工艺

介绍了蒸汽轮机高压缸铸件的结构特点和技术条件,分析了其技术难点,确定了分型面和工艺参数,设计了浇冒口系统,利用MAGMA软件对铸件的凝固及充型过程进行了模拟,优化了铸造工艺方案。工艺验证结果表明,高压缸管孔的壁厚均匀,铸件的组织致密,无缩松,性能可满足顾客要求,达到了降低生产制造成本,提高铸件质量的目的。     

铝合金铸件凝固过程效应力数值模拟

通过铝硅合金准固态力学行为和流变性能的测试，获得了该合金铸件凝固过程应力应变本构方程。并在此基础上开发了考虑材料高温力学性能，分析三维轴对称铸件凝固过程热粘弹塑性问题的热应力模拟程序，对带热节铝硅合金铸件的计算表明，计算结果与实验结果吻合较好。     

钢液导热系数对大型钢锭凝固过程的影响

数值模拟是提高大型钢锭质量、优化浇铸工艺、降低实验费用和帮助缺陷诊断分析的重要手段之一.模拟结果是否可靠很大程度上取决于数学模型假设是否合理,合金热物性参数和边界条件的设置是否准确等因素.利用ProCAST铸造模拟软件,分析了钢液导热系数对钢锭充型和凝固过程中的温度分布、凝固时间和缩孔、疏松的影响规律.结果表明,导热系数的提高显著缩短钢锭整体凝固时间,增加钢锭中心产生缺陷的可能性,因此有必要在模拟计算之前准确测量该物性参数.另外,对于在同一模具中浇铸具有不同物性参数的各类合金,该结果为了解其凝固规律提供了参考.     

铝合金拐臂盒件铸造工艺优化

铝合金拐臂盒铸件轴孔处容易产生缩松缺陷,对此进行了原因分析和工艺改进。依据铸造凝固理论结合实际生产经验,采用不同热导率的金属材料的冷铁及增加工艺补贴等方法,对铸造工艺进行优化。优化后经过X光无损检测及机加工验证,成功解决了轴孔处缩松的铸造缺陷。