消失模铸造充型速度和流动前沿温度的数值模拟研究

采用数值模拟方法,通过模拟板形灰铸铁件的消失模铸造充型过程,分析了各种工艺因素对充型过程中金属液前沿的流动速度和温度的影响规律.结果表明,液态金属充型速度随浇注温度、负压度和涂层透气性的增大而增大,随模样密度和涂层厚度的增大而减小;金属液流动前沿温度随模样密度和涂层厚度的增大而下降,而随负压度的增大而提高.     

消失模铸造滑体铸件的数值模拟

采用数值模拟方法研究了模样密度和浇注温度对消失模铸造灰铸铁滑体铸件充型及凝固过程的影响,并与实际生产进行了对比。模拟结果表明,提高浇注温度和降低模样密度,铸件的充型速度增加,同时高的浇注温度也会使模样与金属液间的气膜压力增加,这会使模样的退让速度与液态金属的前进速度达到动态平衡。较高的浇注温度和较低的模样密度使缩孔的形成倾向变小。     

消失模铸造金属液流动前沿气隙中气体压力的研究

利用基础理论计算出消失模铸造正常浇注时金属液流动前沿气隙中压力P膜随直浇道的面积S直与液态金属在其内部的流速ν直的乘积、浇注温度T膜、模型的密度ρ模、涂层厚度H的增大而增大;随真空度P真、铸件的水平周长S、透气性K的增加而减小,并通过生产实践加以验证.     

消失模负压铸造液流前沿气膜厚度与其放热系数的关系

为寻求更通用简洁的消失模负压铸造液态金属流动前沿气膜厚度“δ”,运用传热学原理及函数的线性化方法,找到了适用于平衡充型状态及非平衡充型状态“δ”的计算方法：δ与气膜面积A、液态金属的浇注温度T金呈正比,与在直浇道的横截面积S直、在其中的液态金属的流速V直、气化单位质量消失模的吸热量WQ和消失模的密度ρ模呈反比。     

镁合金真空低压消失模铸造的技术特征与实践

详细介绍了镁合金在真空低压消失模铸造下的技术特征.试验研究表明真空低压消失模铸造的流动性受充型气体的流量与压力、浇注温度、涂层厚度、泡沫密度、真空度等多方面的因素影响;在低充型速度和低真空度的条件下,液态镁合金在真空低压消失模铸造过程中的充型形貌均呈现以内浇道为中心的拱形层状推进流动,如充型速度加快,金属液流动前沿拱形形貌更加突出,而真空度增加会出现明显的"附壁效应";与重力消失模铸造比较,真空低压消失模铸造镁合金铸件凝固更呈现"同时凝固"特征;由于快速充型、压力下凝固,镁合金真空低压消失模铸造零件的铸态抗拉强度(σb=180.8MPa)、屈服强度(σ0.2=113.2 MPa)、伸长率(δ=4.4%),高于重力消失模铸造、树脂砂真空型铸造的铸态性能,达到了金属型铸造的铸态性能,经热处理达到了压力铸造镁合金的性能范围.浇注实践表明,真空低压消失模铸造对液态镁合金,具有良好的抗氧化保护能力、优良的浇注充型性能和力学性能,可铸造出高精度的、薄壁复杂的镁合金消失模铸件.     

可控气压下镁合金消失模铸造工艺参数的研究

研究了模样密度、涂层厚度、浇注温度、真空度等工艺参数对可控气压下镁合金消失模铸造时液态金属的充填形态和充型速度的影响,以及充型速度与充型形态之间的关系.结果表明:在可控气压下镁合金消失模铸造过程中,液态镁合金呈拱形平稳向前推进,并随着泡沫模样密度的降低、涂层厚度的减小、浇注温度和真空度的提高,充型速度提高.各因素对充型速度的影响效果由大到小的顺序是:泡沫模样密度→涂层厚度→浇注温度→真空度.通过分析实验数据,建立了可控气压下镁合金消失模铸造的充型速度的非线性数学模型.     

不同浇注方式对消失模铸造充型的影响

运用ProCAST软件研究了铝合金铸件的消失模铸造充型过程,考察了不同浇注方式对铸件消失模铸造过程的影响。研究表明,底注式浇注系统的充型相对平稳,是一种比较好的消失模铸造浇注系统方案。浇注系统、浇注速度和界面气隙压力对消失模铸造的充型有很大影响。     

静压节流器微孔气膜参数测量装置设计与试验

研制一种节流器气膜场多路热工参数同时测量的自动化装置,阐述机械装置、硬件电路和软件程序的设计原理与实现。采用气膜厚度调节和气膜压力承载分离设计原理的机械结构以及基于Cortex-M4F内核的STM32F407主控芯片的电控系统和上下位机共同操作的软件程序组合的测量装置,具有自动化程度大、测量精度高等优点。在气膜厚度为6和10μm以及供气压力为0.3、0.5和0.8MPa的实验条件下进行测试,得到双U形平面静压节流器的气膜场温度和压力参数分布。分析得出:在供气压力和气膜厚度增大过程中,双U形节流器气膜场温度值均呈现减小趋势,气膜场压力值分别呈现增加和减小趋势;在供气压力和气膜厚度保持不变的情况下,双U形节流器气膜场在节流槽处产生温度骤降现象,在越过节流槽处产生压力骤降现象。     

铝合金真空低压消失模壳型铸造工艺参数研究

研究了铝合金真空低压消失模壳型铸造工艺参数与铸件充型能力、内部质量的关系。结果表明,铸件的充型能力与浇注温度、充气流量、真空度、充气压力成正比;相比真空度和充气压力,充气流量与浇注温度对铸件充型能力的影响更为显著。工艺参数对薄壁铸件充型能力的影响要大于厚壁铸件;铸件孔隙率随浇注温度的提高先降低后升高,随着充气流量、充气压力、真空度的增大而降低,而密度则随各工艺参数的增大而增大。真空低压消失模壳型优化的工艺参数:浇注温度为720~750℃,充气流量为12~19m3/h,真空度为-0.03~-0.04MPa,充气压力为0.03~0.04MPa。     

镁合金真空低压消失模铸造的技术特征与实践

介绍了镁合金在真空低压消失模铸造下的技术特征。研究表明：真空低压消失模铸造的流动性受充型气体的流量与压力、浇注温度、涂层厚度、泡沫密度、真空度等多方面的因素影响；在低充型速度和低真空度的条件下，液态镁合金在真空低压消失模铸造过程中的充型形貌均呈现以内浇道为中心的拱形层状推进流动，如充型速度加快金属液流动前沿拱形形貌更加突出。而真空度增加会出现明显的“附壁效应”；与重力消失模铸造比较，真空低压消失模铸造镁合金铸件凝固更呈现“同时凝固”特征；由于快速充型、压力下凝固，镁合金真空低压消失模铸造零件的铸态抗拉强度（σh=180．8MPa）、屈服强度（σ0.2=113．2MPa）、伸长率（δ=4．4％），高于重力消失模铸造、树脂砂空型铸造的铸态性能，达到了金属型铸造的铸态性能，经热处理达到了压铸镁合金的性能范围。浇注实践表明，真空低压消失模铸造对液态镁合金，具有良好的抗氧化保护能力、优良的浇注充型性能和力学性能，可铸造出高精度的、薄壁复杂的镁合金消失模铸件，是一种极有潜力和优势的镁（铝）合金精密铸造技术。     

Numerical simulation of heat transfer and fluid flow of molten metal in MMA–St copolymer lost foam casting process

In this study, a computational fluid dynamics (CFD) code was developed to calculate the filling pattern using volume of fluid (VOF) algorithm with donor–acceptor method for free surface simulation. This algorithm has been modified to include the pressure of the gas produced from foam degradation. For this purpose a heat transfer model and 2D foam degradation model were developed. In heat transfer model, radiation and conduction between foam and molten metal; and convection between gas and molten metal were considered. In order to evaluate the results of simulation, a bench scale casting apparatus was assembled and the casting was conducted in a transparent mold. The effect of several parameters such as coating thickness, foam density and vacuum level on the gap temperature, gap pressure and filling speed was studied with the developed software. It was found that the simulated results are in good agreement with experimental results.     

Simulation of mould filling in lost foam casting process

In this investigation, an algorithm was developed to calculate the gas pressure at the melt/foam interface (gap) owing to degraded foam during mould filling in the lost foam casting process (LFC). The effect of back-pressure on mould filling was modelled using a new experimental function by the addition of a three-dimensional volume of fluid (3D-VOF) function. The molten flow and free surface were simulated using the solution algorithm-VOF (SOLA-VOF) numerical technique. To simulate the three-dimensional incompressible flow in the LFC, the pressure boundary conditions, heat transfer and foam gas pressure effect were modified. Finally, in order to verify the computational results of simulation, a thin plate of grey iron was poured into a transparent foam mould. The mould filling process was recorded using a 16 mm high-speed camera, then images were analysed frame-by-frame to obtain foam depolymerisation and gap volume during mould filling. The comparison of experimental and numerical results in the LFC filling sequence showed good agreement, which confirms the accuracy of the model. IJCMR/447     

消失模铸造充型过程气隙压力的研究

设计了一种新的气隙压力测试方法，连续测试了浇注过程中的气隙压力。结果表明，随浇注时间增加，气隙中的压力逐渐增大，而气隙尺寸减小，金属充型速度减小，气隙压力受浇注温度、真空度和模样密度等多种因素影响，其中真空度影响最大。     

不同排气塞数量下的泡沫模样的射料充填数值模拟

建立了欧拉/拉格朗日离散颗粒模型,采用数值模拟方法,研究消失模铸造泡沫珠粒射料充填过程中稠密气/固两相流动的流体动力特性。泡沫珠粒的运动与气相压力分布密切相关,泡沫珠粒充填过程中在排气塞附近区域形成型腔内外压力差,是珠粒充填的动力。在其他条件相同时,对3种不同排气条件下的射料充填过程进行了数值模拟,结果表明,排气不畅时射料充填过程持续时间最长,易在型腔内的高压区出现充填不密实的现象。     

Numerical simulation of mould filling process for pressure plate and valve handle in LFC

In lost foam casting (LFC),the distribution of polymer beads during the bead filling process is not uniform,and the collision between polymer beads determines the distribution of two-phase flow of gas and solid.The interaction between the gas and solid phases reveals as coupling effect of the force that gas exerts on particles or vice versa,or that among particles.The gas-solid flow in filling process is nonlinearity,which makes the coupling effect an essential point to carry out a simulation properly.Therefore,information of each particle's motion is important for acquiring the law of filling process.In bead filling process,compressed air is pressed into mold cavity,and discharged from gas vent,creating a pressure difference between outer and inner space near the gas vent.This pressure difference directly changes the spatial distribution and motion trace of gas and solid phases.In this paper,Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) are employed to simulate the fluid dynamic character based on Newton's Third Law of Motion.The simulation results of some casting products such as pressure plate and valve handle are compared with the result obtained from practical experiment in order to test the feasibility of DEM.The comparison shows that this DEM method can be a very promising tool in the mould filling simulation of beads' movement.     

Numerical simulation and analysis of mould filling process in lost foam casting

In lost foam casting （LFC） the foam pattern is the key criterion, and the filling process is crucial to ensure the high quality of the foam pattern. Filling which lacks uniformity and denseness will cause various defects and affect the surface quality of the casting. The influential factors of the filling process are realized in this research. Optimization of the filling process, enhancement of efficiency, decrease of waste, etc., are obtained by the numerical simulation of the filling process using a computer. The equations governing the dense gas-solid two-phase flow are established, and the physical significance of each equation is discussed. The Euler/Lagrange numerical model is used to simulate the fluid dynamic characteristics of the dense two-phase flow during the mould filling process in lost foam casting. The experiments and numerical results showed that this method can be a very promising tool in the mould filling simulation of beads＇ movement.     

基于欧拉-拉格朗日模型的射料过程的数值模拟

针对消失模铸造中的泡沫颗粒射料充填过程，建立了基于欧拉一拉格朗日模型的气一固两相流的数学模型，并利用商业流体软件对泡沫颗粒顶部射料以及侧向射料充填过程进行了数值模拟。数值模拟结果与物理模拟结果对比表明，模拟的结果与实际情况基本上是一致的。     

3 D SIMULATION OF FLUID FLOW IN LOST FOAM PROCESS

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镁合金消失模铸造液模气隙尺寸的数值模拟

消失模铸造中充型的平稳性非常重要,充型越均匀铸件质量越好。使用SOLA-VOF计算方法模拟了镁合金在消失模铸造中的充型过程,计算了金属液和泡沫模样之间的气隙距离。结果表明液模气隙在充型过程中逐渐减小并趋向恒定值。。