Numerical simulation for permanent mold centrifugal cast TiAl exhaust valve

1INTRODUCTION Inthepastdecades,therehasbeenanenor mousincreaseintheresearchontitaniumalumin ides,inparticular,ontheTiAlcompounds[13].Thelowdensitycombinedwiththehigh strengthathightemperaturemaketitaniumaluminidealloy anexcellentcandidateforautomotiveexhaustvalve applications[47].ThekeytosuccessfulapplicationofTiAlexhaustvalvesisneitherthestrengthnor theductility,butalargeoutputandlowcostman ufacturingmethod[810].Numericalsimulationforthefillingandsolidi ficationofcastingshasbeenresearch…     

TiAl基合金排气阀立式离心铸造充型及凝固过程数值模拟

以N-S方程、连续性方程及Fourier导热方程为基础，结合离心力、重力及Coriolis力，在实验的基础上建立了立式离心铸造充型过程及凝固过程数学模型．并且依据此模型对TiAl基合金排气阀立式离心铸造过程温度场、流场及压力场进行了数值模拟．数值模拟结果表明，离心铸造的充型过程存在正向和反向两个充填过程，在入口处易出现卷气缺陷．凝固过程也存在正向和反向两个凝固顺序，在靠近先充填一侧易于形成偏轴线缩松缺陷．     

Ti-6Al-4V合金异形铸件离心力场下的充型与凝固

建立了离心力场下Ti-6Al-4V合金异形铸件充型及凝固过程的数学模型,通过引入附加项将离心力场模型化,采用流函数和涡函数代替描述方程中的压力项,并建立了数学模型的差分格式,总结了离心力场对Ti-6Al-4V合金异形铸件充型和凝固过程的影响规律.结果表明,在离心力场作用下,型腔内的流动由正向流动和反向流动两部分组成,初始温度分布的非对称性使凝固过程中的温度分布始终处于一种非对称状态,从而导致铸件的最后凝固区域与中心线发生偏离.     

离心场对钛合金铸造性能的影响

在立式离心场下和重力场下对石墨型钛合金铸件在铸造过程的充填及凝固情况进行研究.结果表明:在立式离心场下钛合金熔体的铸造性能好,其流动性和充填性得到很大改善;尤其对3 mm壁厚薄壁件,在重力场下由于充填阻力大于充填力,合金熔体无法完全充填铸型,而在离心场下可以实现全部充填,且最小壁厚可达到0.3 mm.此外,离心场下由于离心力和科氏力的共同作用,铸件的缺陷明显减少,且随铸型转速的增加而不断减小.     

Simulation of mold filling and solidification during centrifugal precision casting of Ti−6Al−4V alloy

A two-dimensional simulation model for melt flow and solidification in centrifugal precision casting has been developed based on experimental results on melt flow in a precision casting tree for Ti-6A1-4V alloy castparts. The amount of liquid alloy is intentionally adjusted to be less than that required for complete filling and is poured under a centrifugal force. The melt flows into mold cavities keeping contact with the vertical inside walls of the cavity in the anti-rotation side, and solidifies directionally by accumulating a solidified layer from the far end of the cavity to the gate according to the gradient of centrifugal force. The model reproduces melt flow observed in casting trials and directional solidification during centrifugal casting. In addition, it has been confirmed that the centrifugal force imposed on the melt enhances removal of defects caused by entrapment of gas bubbles or by solidification shrinkage and improves mechanical properties of the castparts. Formerly Graduate School of Iron and Steel Technology Pohang University of Science and Technology San 31 Hyoja-dong, Namku, Pohang 790-784, Korea     

钛合金离心精密铸造充型过程计算机模拟

建立了离心力场下铸造充型流动的数学模型 ,在自行研制的三维铸件充型 /凝固模拟软件 (CASM 3DforWin dows)基础上 ,研制开发了相应的离心力场铸造充型的计算机模拟软件。对钛合金薄壁铸件在重力场下及不同离心精密铸造工艺条件下的充型过程进行了实例模拟计算。计算结果表明 :在离心力场下金属液的薄壁充型能力比重力浇注强得多 ,而“拐头反充”式离心浇注方式是一种合理的离心力场下的铸造工艺方案     

Computer simulation for centrifugal mold filling of precision titanium castings

Computer simulation codes were developed based on a proposed mathematical model for centrifugal mold filling processes and previous computer software for 3D mold filling and solidification of castings (CASM-3D for Windows). Sample simulations were implemented for mold filling processes of precision titanium castings under gravity and different centrifugal casting techniques. The computation results show that the alloy melt has a much stronger mold filling ability for thin section castings under a centrifugal force field than that only under the gravity. A "return back" mold filling manner is showed to be a reasonable technique for centrifugal casting processes, especially for thin section precision castings.     

ZTC4钛合金机匣构件离心铸造过程的数值模拟

采用数值模拟方法,研究ZTC4合金机匣离心铸造的充型和凝固过程,分析了离心转速、浇注温度和铸型预热温度对熔体充填过程流动场、凝固过程温度场和应力场的影响,并预测了缺陷的分布.结果表明,随离心转速提高,熔体充型速度无明显变化,但柯氏力作用更加明显,铸型中熔体流股变细;熔体过热度低于30℃时,铸件出现明显的浇不足缺陷;铸型预热温度是影响铸件残余应力的主要因素,而离心转速和熔体过热度的影响次之;铸件最后凝固的较厚部位容易出现缩松、缩孔缺陷,且其位置与X射线检测结果较吻合.     

电磁离心凝固过程中宏观偏析的数值模拟

基于连续模型建立了非惯性坐标系下电磁离心凝固过程流动、传热、传质耦合数学模型．依此模型对Al-5％Cu合金进行了模拟计算．结果表明，电磁离心凝固过程中，电磁力使熔体的平均径向运动速度下降．熔体流动状态的改变使凝固合金外层的逆偏析减轻，凝固过程中两相区的负偏析也减轻．与普通离心铸造相比，电磁离心凝固可减轻铸件宏观偏析．模拟结果与实测铸件成分分布基本吻合，表明本数学模型较好地描述了电磁离心凝固过程．     

离心铸造钛合金熔体充型流动物理模拟相似理论及实验研究

借助相似物理模拟理论,研究离心铸造钛合金熔体充型流动物理模拟相似准则。并采用相似物理模拟的方法,研究离心力场下钛合金熔体充型流动过程中,熔体流动的变化规律。实验结果表明:离心力场下物理模拟钛合金熔体充型流动时,同时满足Cn准则和雷诺准则;模拟流体充型流动时,沿着横浇道后壁进行充型;流体的自由液面是以转轴为圆心的规则圆弧面;流体横截面面积随着旋转速度和充型长度的增加相应减小;转速越高,在同一时间内,充填速度和长度越小。     

Analysis of filling process of Ti6Al4V alloy melt poured in permanent mold during centrifugal casting process

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｉｔａｎｉｕｍａｌｌｏｙｓｈａｖｅａｔｔｒａｃｔｅｄａｇｒｅａｔｄｅａｌｏｆａｔ ｔｅｎｔｉｏｎｂｅｃａｕｓｅｏｆｔｈｅｉｒｐｏｔｅｎｔｉａｌａｔｔｒａｃｔｉｖｅｐｒｏｐｅｒｔｉｅｓｆｏｒｈｉｇｈ ｔｅｍｐｅｒａｔｕｒｅｓｔｒｕｃｔｕｒａｌｍａｔｅｒｉａｌｓ .Ａｔｔｈｅｓａｍｅｔｉｍｅ ,ｆｏｒｔｈｅｉｒｅｘｃｅｌｌｅｎｔｃｏｒｒｏｓｉｏｎ ,ｏｘｉｄａｔｉｏｎｒｅ ｓｉｓｔａｎｃｅａｎｄｌｏｗｄｅｎｓｉｔｙ ,Ｔｉ6Ａｌ4Ｖｂａｓｅｄａｌｌｏｙｓａｒｅｂｅｉｎｇａｐｐｌｉｅｄ…     

镁合金汽车下壳体充型和凝固过程数值模拟

对镁合金汽车下壳体铸件在液态和半固态条件下的充型凝固过程进行了数值模拟,并对两种状态下的零件在铸造过程中可能出现缺陷的位置进行了预测.结果表明,半固态合金熔体的充填有利于平稳充填型腔、型腔的气体能及时排出,减少了铸件的内部缺陷.同时,铸件的整体温度场相对均匀,有利于铸件内部的补缩和残余气体的排放,从而提高了铸件质量.     

数值模拟充填工艺参数对微结构零件充填深度的影响

微结构充填深度是具有高纵横比的微结构零件成形成功与否的关键之一.抽象出微结构零件的物理模型,分析影响微结构充填深度的充填工艺参数,分别在不同型腔压力、熔体温度和模具温度条件下,采用Moldflow MPI软件对其物理模型进行充填仿真分析.研究结果表明,模具温度对微结构充填深度影响最大,型腔压力和熔体温度对其影响不很显著.熔体到达型腔末端后还有部分熔体进入微结构,这是由于型腔压力突然剧增的缘故.     

Filling mode and regularity of vertical centrifugal casting process of titanium alloy in thin-walled cylinder cavity

The mold filling process of titanium alloy in a thin-walled cylinder cavity under vertical centrifugal casting process was studied by means of the hydraulic simulation experiments. Results show that the filling mode of the melt in the cylinder cavity varies with casting wall-thickness. When the casting wall-thickness is less than or equal to the thickness of the first layer during the filling process, the melts fill the cavity from the bottom to the top.When the casting wall-thickness is greater than the thickness of the first layer during the filling process, the melts first fill the largest radius parts of the cavity with a certain thickness of the first layer from the bottom to the top of the cavity, and then they fill the cavity from the larger radius part to the smaller radius part. The melt filling ability increases with the increment of the mold rotational speed and the pouring temperature. In another aspect, the melt filling ability rises with the decrement of the melt viscosity, and the melt with the better filling ability is prone to fill the cylinder cavity layer by layer.     

The high-quality precision casting of titanium alloys

A technique for the high-quality precision casting of titanium alloys has been developed that consists of the instantaneous dissociation of oxide at the metal-mold interface, followed by the rapid absorption and diffusion of the dissociated oxygen into the subsurface of the cast parts during solidification and cooling. In centrifugal casting trials using less molten alloy than required to completely fill the mold, the results suggest that the melt flowing in the mold cavities maintains contact with the vertical inside walls and directionally solidifies from the far end of the cavity to the gate, corresponding to the gradient in the centrifugal force on the horizontal plane. This force enhances the removal of defects, such as entrapped gas bubbles and solidification shrinkage. The results have enabled the development of a two-dimensional model to simulate melt flow during centrifugal casting. Author’s Note: Unless otherwise indicated, compositions are given in weight percent. Ken-ichiro Suzuki earned his Ph.D. at Tohoku University, Faculty of Engineering. He is currently a visiting professor at the Graduate School of Iron and Steel Technology at Pohang University of Science and Technology.     

TiAl基合金叶片吸铸成形缺陷的数值模拟

采用有限元软件ProCAST模拟TiAl基合金液在金属型真空吸铸成形铸造工艺中的充型凝固过程,分析在充型凝固过程中产生缺陷的原因,并进行了相关的实验验证。在模拟过程中发现铸件中确实存在模拟预测的缺陷,且缺陷主要集中在叶片隼部,在叶身部位出现少量的缩松缺陷,模拟和实际相吻合。     

立式离心场下钛合金熔体充填及凝固过程研究

研究立式离心场下不同铸造工艺参数对钛合金熔体的充填及凝固缺陷形成的影响。结果显示,立式离心场下得到的钛合金铸件质量优于重力场下的铸件。立式离心场下,合金熔体由于受离心力和科氏力的作用,沿着与旋转方向相对的型壁进行充填,且熔体的截面面积随充填长度的增加而逐渐减小,但是在内浇口处由于速度降低导致截面面积有所回升。此外,铸型的旋转方向,旋转半径及旋转速度直接影响铸件缺陷的形成。旋转方向直接影响合金熔体的充填顺序,进而影响合金熔体的凝固顺序及缺陷位置。实验结果显示,旋转半径及旋转速度的增加有利于减少铸件的缺陷体积。     

TiAl基合金叶片吸铸成形缺陷的数值模拟

采用有限元软件ProCAST模拟TiAl基合金液在金属型真空吸铸成形铸造工艺中的充型凝固过程,分析在充型凝固过程中产生缺陷的原因,并进行了相关的实验验证。在模拟过程中发现铸件中确实存在模拟预测的缺陷,且缺陷主要集中在叶片隼部,在叶身部位出现少量的缩松缺陷,模拟和实际相吻合。     

Ti-6-4合金熔体离心铸造过程中流态分析

针对金属型离心浇铸Ｔｉ６Ａｌ－４Ｖ（Ｔｉ－６－４）合金人工骨关节,对其充型过程进行了理论分析,得出了熔体离心充型过程中的层流判据以及熔体自由面仍的变化规律,结果表明,离心力场下,熔体充型时可保持的层流长度随转台转这的提高而减小;熔体自由表面将发生倾斜,最终趋于竖直,此外,讨论了离心力场下铸件内部卷入性气孔和偏中心线缩松的产生原因及分布规律。     

TiAl基合金连杆件底漏式真空吸铸数值模拟

利用ProCAST数值模拟技术对TiAl合金汽车发动机连杆铸件底漏式真空吸铸过程的充型过程、凝固过程、缩孔缩松缺陷形成进行了模拟。研究了底漏式真空吸铸的几个主要参数,如吸口直径、浇注温度、浇注速度,对连杆铸件充型凝固过程和缩孔、缩松缺陷的影响规律,得到了TiAl合金底漏式真空吸铸的优化工艺参数图。