铝合金挤压铸造过程微观孔洞形成的建模与仿真

基于挤压铸造过程微观孔洞的形成机理,建立了模拟铝合金挤压铸造过程微观孔洞的数学模型.该模型考虑了传热、凝固收缩、补缩流动、压力传递、氢(H)的再分配等因素,通过计算凝固收缩导致的补缩流动与压力降低,以及挤压过程的压力传递,获得挤压铸造过程糊状区的压力分布,结合微观孔洞形成条件及H的守恒方程,计算微观孔洞的体积分数.对不...     

Effect of vibration on seepage feeding during low-pressure casting of ZL205A alloy

Appropriate vibration can promote the feeding capacity of gravity casting, but the effect of vibration on the feeding of low-pressure casting is not clear. The effect of vibration on the seepage feeding of ZL205A alloy was investigated by vibration casting experiment and physical simulation. The aqueous solution of sodium carboxymethyl cellulose(CMC) with the same rheological characteristic of metal melt was used. The results show that vibration can improve the feeding capacity and reduce shrinkage defects of ZL205A alloy in lowpressure casting. The orthogonal physical simulation experiments indicate that vibration with low frequency and great exerted force can significantly improve the seepage velocity of non-Newtonian fluid with solid particles in porous medium. The seepage phenomenon in CMC solution shows that vibration can change the structure of accumulated particles at the seepage entrance, and thus open the blocked feeding channel. The numerical simulation of one-dimensional semisolid fluid seepage reveals that vibration can form a wave field in the porous medium, which can reduce the adhesion force between fluid and capillary wall and destroy the boundary layer of fluid, and thus promote the seepage velocity.     

γ—TiAl增压涡轮熔模铸造过程数值模拟研究

根据熔模型壳离心浇注的铸造工艺特点，建立了γ－TiAl增压涡轮凝固传热过程的数值模型，推导了离心压力下γ－TiAl金属间化合物的凝固收缩和补缩过程数学模型，模拟计算了γ－TiAl增压涡轮铸件的温度场和收缩缺陷，结果表明，模型能可靠计算γ－TiAl增压涡轮铸件凝固过程的温度分布和准确预测铸件的收缩缺陷，数值模拟结果与实验结果吻合良好，数值模拟结果证实了前期工作所提出的进一步减少及消除收缩缺陷的优化工艺措施的合理性。     

低压铸造下凝固过程缩孔缩松的预测方法研究

基于铸件铸型的传热学基础,详细研究了低压铸造下铸件缩孔缩松缺陷的形态,考虑到低压铸造补缩具有重力补缩和压力补缩双重性质的规律,以及压力对临界固相率的影响,提出了一种新的预测低压铸造下缩孔缩松预测的方法,并建立了数学模型.该预测技术基于中北大学特种液态成形技术研究中心所开发的EasyCast软件进行研究,并集成到该软件中.最后将模拟结果与实验结果进行对比,显示该模型能够较好地表现低压铸件的缩孔缩松.     

铝镁合金消失模铸造技术研究及应用新进展

阐述了铝镁合金消失模铸造技术的现状,重点介绍了铝镁合金消失模铸造在浇注充型、振动凝固、压力凝固、壳型铸造等技术研究方面的新进展。作者认为,消失模铸造铝镁合金,必须重点解决针孔、缩松等缺陷,提高液态合金的充型能力和铸件的力学性能。     

机械振动对纯Al晶粒细化及凝固收缩的影响

研究了振动场对纯Al晶粒细化和凝固收缩的影响，并着重进行理论分析。实验结果表明：振动能明显细化晶粒，改善收缩。随着振动的加强，纯Al中心的等轴晶区逐渐增大，边缘部位的柱状晶区逐渐减小，当振击力达到81．87N时整个试样端面全部变为等轴晶。理论分析认为：振动引起的强烈冲击和搅拌作用使金属液产生晶粒游离、增殖、快速冷却是晶粒细化和收缩改善的根本原因。     

Modeling of shrinkage defects during solidification of long and short freezing materials

The aim of the model presented in this paper is to capture the difference in solidification behavior of long and short freezing materials. The shrinkage defects in short freezing materials tends to be internal, as porosity, while in long freezing materials these defects tend to be external in the form of surface depressions. To achieve this, a pressure drop based 3D feeding flow model has been developed to evaluate shrinkage defects for casting alloys. A continuum formulation is used to describe the transport of mass, energy and momentum. It is assumed that during solidification the driving force for flow is shrinkage. A Darcy type source term has been included in the momentum equation to account for flow resistance in the mushy zone. A VOF free surface model has been used to describe shrinkage defects, i.e., external surface depressions and internal shrinkage porosities, while ensuring mass conservation. The model is used to calculate the shrinkage in a simple casting. The results shows internal and outside shrinkage defects depending on the freezing range of the metal. Short freezing range results mainly in internal shrinkage whereas the long freezing range results in external shrinkage. The expected shrinkage features are well described by the present model.     

结晶器振动系统机电液协同仿真技术研究

连铸机铸坯质量的好坏与结晶器振动系统的工作性能关系密切,应用ADAMS建立了结晶器振动系统刚柔耦合机械模型,并在MATLAB中根据机械电气液压的关系,搭建了控制框图,利用软件之间的接口建立了结晶器振动系统协同仿真模型,并对正弦和非正弦信号下的结晶器动态响应进行了分析,该方法可以为冶金机电液设备的设计与优化提供理论指导。根据现场测试的数据,对振动系统刚柔耦合机械模型进行了验证,结果表明所建立的模型是正确的。     

挤压铸造凝固过程热-力耦合模拟 Ⅰ.数学模型及求解方法

开发了模拟挤压铸造凝固过程中铸件温度、应力及形状变化的有限元模型.该模型包括了凝固过程中潜热的释放和体积收缩效应、界面传热和变形的相互作用以及凝固壳在冲头压力下的变形等.应力场模拟中采用热弹粘塑性本构模型描述凝固壳的变形,并对液相和糊状区进行了特殊处理.利用接触算法处理铸件与模具界面,并且采用一种特殊的迭代法来模拟冲头的运动.该模型可以用来研究模具设计和工艺参数(如模具温度及冲头压力等)对铸件质量的影响.     

压力对ADC12铝合金超低速压铸件组织及力学性能的影响

采用光学显微镜、扫描电镜、X射线衍射和能谱等显微分析技术,结合力学性能检测,研究超低速压铸条件下压力对ADC12铝合金铸件组织及力学性能的影响。试验结果表明,在超低速试验条件下,持压时间越长、增压延时时间越短,铸件性能越好;铸造压力导致初生α-相形态发生变化,但铸造压力有最佳值,压力较小时,增大铸造压力可使α-相细化,铸件性能升高,过大的铸造压力将导致α-相粗大,使铸件性能下降;在无增压条件下,仅采用较大的压射压力也可使α-相组织细小,获得较好的力学性能。     

ZL205A铝合金线状偏析的形成机理及判据(英文)

采用实验和数值模拟方法,对ZL205A铝合金筒形壳体铸件在低压铸造时出现的线状偏析的形成机理及预测模型进行研究。利用数值模拟技术对该铸件在凝固期间的传热进行分析,通过大量实际低压铸造获得ZL205A合金铸件中产生的线状偏析信息、铸件低压铸造过程的温度场以及线状偏析形成部位凝固参数的变化规律,提出了ZL205A合金低压铸造过程线状偏析的形成机理和判据。研究表明,ZL205A合金铸件的线状偏析是由于铸件在凝固后期,浇注系统尚能进行补缩,此时铸件局部形成热裂,高浓度的溶质在补缩压力的作用下对该热裂填充而最终在该部位形成线状偏析。根据分析得出形成机理,得到消除线状偏析的工艺控制方法。采用线状偏析判据对其它铸件的线状偏析进行模拟预测,预测结果与实际浇注结果的对比表明,该判据能够较为准确地预测ZL205A合金筒形壳体铸件的线状偏析位置。     

Numerical simulation and optimization of shell mould casting process for leaf spring bracket

Although the shell mould casting process has a wide range of application in many fields,the prediction of casting defects is still a problem.In the present work,a typical leaf spring bracket casting of ZG310-570 was fabricated by shell mold casting.The finite element model and ProCAST software were utilized for simulating the filling and solidification processes of the casting;and the formation mechanism of the gas pore,and shrinkage porosity defects were analyzed.The results indicate that the gas pore and shrinkage porosity defects are formed due to air entrapment,insufficient feeding and non-sequential solidification.Subsequently,through changing the position of risers,adding a connecting channel between the risers,and setting blind risers at the U-shaped brackets,an optimized gating and feeding system was established to improve the quality of the casting.After optimization,the gas pore and shrinkage porosity defects of the leaf spring bracket casting are effectively eliminated.The experiment results with the optimized casting process are in good agreement with the numerical simulation,which verifies the validity of the finite element model in the shell mould casting.     

挤压铸造ZA27合金大高径比铸件

通常挤压铸造仅适用于高径比小于3.5的铸件,研究大高径比铸件的挤压铸造将扩大这种先进铸造技术的应用范围.用试验和计算机模拟的方法,研究了高径比为7的ZA27合金铸件的力学性能、凝固过程中铸件内的温度、压力以及缩松的分布.结果表明,增加挤压铸造的压力不能有效地减少大高径比铸件的缩松缺陷;合理控制浇注温度和铸型预热温度能有效地消除大高径比铸件内的缩松,获得力学性能高且均匀的铸件.     

THERMOMECHANICAL MODELING OF SOLIDIFICATION PROCESS OF SQUEEZE CASTING I. Mathematic Model and Solution Methodology

开发了模拟挤压铸造凝固过程中铸件温度、应力及形状变化的有限元模型. 该模型包括了凝固过程中潜热的释放和体积收缩效应、界面传热和变形的相互作用以及凝固壳在冲头压力下的变形等. 应力场模拟中采用热弹粘塑性本构模型描述凝固壳的变形, 并对液相和糊状区进行了特殊处理. 利用接触算法处理铸件与模具界面, 并且采用一种特殊的迭代法来模拟冲头的运动. 该模型可以用来研究模具设计和工艺参数(如模具温度及冲头压力等)对铸件质量的影响.     

基于数值模拟的大型薄壁铝合金件差压铸造工艺设计

将传统工艺和现代计算机模拟技术相结合,利用View Cast软件对薄壁铝合金筒体铸件凝固过程进行了分析,通过凝固过程时间分布预测了缩孔缩松产生的位置。采用加设缝隙式内浇道和增大冒口尺寸的方法对初始铸造工艺方案进行了优化。再次模拟表明,改进后的方案合理可行,铸件实现了充分补缩和顺序凝固,消除了缩孔（松）等缺陷。     

Reduction of shrinkage porosities in aluminum alloy castings by external pressure fluctuation under gravity field

A novel method to improve the feeding capacity of ZL205 A alloy castings by pressure fluctuation during its solidification process under gravity field was proposed. The experiments were done in the graphite mould by applying the fluctuation pressure at the top of the riser. Results of the X-ray inspection of castings and simulations of flow velocity of alloy melt and temperature field show that the new method can effectively improve the feeding capacity and significantly reduce the shrinkage in the castings. The mechanism of improving the feeding capacity by pressure fluctuation is that the fluctuating pressure can make the ZL205 A alloy melt form a vibration wave in the melt. The vibration wave can intensify the convection of the melt, and therefore, break down the barrage from the feeding channel which forms during the solidification process of the ZL205 A alloy, improving the feeding capacity.     

镁合金压铸件收缩缺陷分析及对策

对音箱面板镁合金压铸件出现的收缩缺陷进行了检测分析，认为表面裂痕和内部裂纹产生的原因是由于压铸喷射填充状态下的分层充填以及凝固收缩的不同时性所引起的，轴线缩松涉及到不同壁厚铸件的补缩特点及持压时间。提出了防止和消除镁合金压铸件缺陷的思路和措施。     

水压机下横梁铸造工艺模拟分析

采用三维绘图软件绘制了水压机下横梁的实体模型,并设计和制定了其浇注系统及工艺参数.运用ProCAST软件对铸件及其浇冒系统进行有限元网格划分,并模拟分析了充型和凝固过程,结合铸件不同位置的温度与时间曲线分析表明,浇冒系统能实现金属液的平稳充型、铸件的顺序凝固与补缩.铸件的超声和磁粉等无损检验结果表明,工艺方案设计合理,铸件没有缩孔、缩松和表面气孔、夹杂等缺陷.     

凸式冲头挤压铸造中比压的数值模拟分析

作为挤压铸造中的一个重要参数,比压严重影响铸件的组织和性能。利用有限元法对凸式冲头挤压铸造进行了热力耦合数值模拟,分析了A356合金铸件比压与显微组织和力学性能的关系,得到了经济的临界比压。结果发现,随着比压增大,缩孔、缩松缺陷逐步减少,直至基本消失。进一步加大比压后,变化不明显,反而增加了模具的负担。随着比压增大,组织晶粒逐步细化,达到120MPa时,晶粒尺寸减小了8%,另外,二次枝晶间距缩小了12.5%,但当比压继续增大之后,没有出现继续细化,反而有粗化的趋势。     

Numerical simulation and optimization of Al alloy cylinder body by low pressure die casting

Shrinkage defects can be formed easily at critical location during low pressure die casting （LPDC） of aluminum alloy cylinder body. It has harmful effect on the products. Mold filling and solidification process of a cylinder body was simulated by using of Z-CAST software. The casting method was improved based on the simulation results. In order to create effective feeding passage, the structure of casting was modified by changing the location of strengthening ribs at the bottom, without causing any adverse effect on the part＇s performance. Inserting copper billet at suitable location of the die is a valid way to create suitable solidification sequence that is beneficial to the feeding. Using these methods, the shrinkage defect was completely eliminated at the critical location.