复杂零件粉末注射成形多相流动过程三维数值模拟

将金属粉末注射成形充模过程视为粉末、粘结剂和空气的三相流动过程,给出了金属粉末注射成形充模多相流动的控制方程。根据钳口复杂模腔的铁粉注射成形实际参数确定了充模多相流动控制方程的初边界条件,基于CFX计算流体力学软件对钳口铁粉注射成形充模多相流动过程实现了三维数值模拟。给出了钳口铁粉注射成形充模多相流动中固相粉末的速度流线图,分析了模腔中温度场和压力场分布的瞬态情况,以及模腔中不同位置的温度和压力随时间变化的曲线;分析了钳口铁粉注射成形充模多相流动过程中不同时刻粉末体积分数的分布情况。数值模拟结果可用于分析注射成形过程中产生粉末粘结剂两相分离和成形坯密度分布不均的原因,数值模拟为研究注射成形产品缺陷产生的原因提供了直观分析方法。     

基于ANSYS的硬质合金MIM充模数值模拟

以流体力学和热力学理论为基础，结合金属注射成形的特点，建立了其充模流动过程中的控制方程、初始条件和边界条件，并以硬质合金材料为例，采用大型有限元软件ANSYS进行了计算数值模拟，求解了流体前沿、温度场、压力场，同时结合实验分析了金属注射成形过程中的几种常见缺陷的产生条件。模拟结果表明：当采用中间浇口、模温60℃、料温160℃、体积流速在40cm^3／s～70cm^3／s的范围内进行注射可以得到良好的硬质合金Ⅰ型拉伸试样预成形坯。该结论与实验结果一致。     

粉末注射成形充模流动过程模壁凝固层增长的计算与模拟

应用微流边界层理论从微观上阐述了粉末注射成形充模过程模壁凝固层的存在性,分析了PIM模壁凝固层的结构,它包含微流边界层,其厚度远远小于L．Prandtl边界层的厚度,说明假设在PIM充模流动过程中无滑移边界条件是合理的。根据L．Prandtl边界层厚度的计算方法和微流边界层的定义,建立了计算PIM浇道模壁凝固层厚度的数学模型,数值模拟结果说明所给数学模型较好地描述浇道模壁凝固层的增长情况。利用该模型可以方便地预测浇道模壁凝固层厚度的增长,为优化影响制品质量的工艺参数提供了理论依据。     

复杂零件金属注射成形3D充模模拟

以实际生产的支持块为例,结合3D技术,模拟了注射成形喂料在复杂几何模腔中的流动情况.基于ANSYS提供的Z-Buffer切片模型空间观测方式,预测了实际制品缺陷产生的部位并分析了缺陷形成机理.最后依据模拟结果,推荐在实际生产中采用INLET4位置浇口进行注射生产,实验表明制得的支持块无缺陷,产品通过了有关部门的验收,证明了充模流动3D模拟的可行性和准确性.     

水辅助注射成型充模过程的数值模拟研究

基于Hele-Shaw流动模型,采用广义牛顿流体本构方程,建立了三维薄壁塑件的水辅助注射成型充模过程数学模型,采用有限元/有限差分/控制体积法数值求解。对薄壁平板塑件的水辅助注射成型充模过程进行了模拟,模拟得到的熔体前沿位置与前人实验结果吻合较好,浇口处压力变化、水的厚度分布及平均温度分布合理,验证了所建立的模型和采用的数值模拟方法的有效性。     

粉末注射成形两相流动三维数值模拟及粉末与粘结剂的分离

分析齿轮零件粉末注射成形(PIM)实验成形坯密度分布以及成品容易出现飞边和塌陷的位置特点。根据粉末注射成形技术工艺过程的特点给出PIM的双流体模型及初边界条件,基于计算流体力学软件CFX对I型拉伸试样和齿轮零件的PIM两相流动过程进行三维数值模拟。根据数值模拟结果,对PIM充模流动过程中粉末和粘结剂两相速度的变化曲线进行对比分析,证实I型拉伸试样和齿轮零件的PIM充模过程中多个位置发生过不同程度的粉末与粘结剂两相分离现象。对模腔中多个不同结点处发生粉末与粘结剂两项分离的现象进行分析比较。结果表明:PIM充模过程中位于远离浇口狭窄模腔内的点容易产生两相分离现象,粉末与粘结剂两相分离现象只发生在相应位置被充填初期的一段时间内,且不同位置发生的两相分离持续时间也不同。     

金属粉末注射成形充模流动过程模拟的数学模型探讨

在流体动力学理论的基础上,结合对金属粉末注射成形充模流动过程流变特性机理的分析,建立了关于连续介质模型和两相流模型的动力学方程,为进一步对MIM充模流动过程进行数值模拟奠定了理论基础。     

充模流动计算机模拟在硬质合金MIM中的应用

预测了金属注射成形过程中常见缺陷的产生 :比较了选择不同浇口对注射拉伸试样质量的影响。结果表明 :通过充模流动量计算机模拟预测在某种注射工艺条件下部分常见注射缺陷的产生 ,能够更好地指导硬质合金注射工艺参数的选择 ;选择中心浇口可以降低注射压力 ,但是采用测面浇口的注射坯比采用中心浇口的注射坯件温度和压力分布都要均匀。因为注射时温度和压力分布的不够均匀是导致注射坯缺陷和降低最终产品质量的直接原因之一 ,所以为了进一步减少硬质合金注射坯的缺陷和提高最终产品的性能 ,注射时应该采用侧面浇口。     

硬质合金I型拉伸试样计算机充模模拟应用分析

以硬质合金I型拉伸试样为例,模拟了PIM喂料在普通几何模腔的流动情况,讨论了注射速度、注射温度、浇口位置等主要工艺参数对熔体充模过程的影响,预测注射成形过程中部分常见缺陷产生的条件。分析表明:当采用侧面浇口、模温300K、注射温度420K、体积流速61cm3/s的注射参数进行注射可以得到良好的硬质合金I型拉伸试样预成形坯。     

注射模充模过程CAE技术I理论与算法

在分析充模流动机理基础上 ,从粘性流体力学的质量、动量和能量方程出发 ,针对塑料注射成型特点 ,经过量纲分析和引入合理而必要的假设 ,建立了描述塑料注射成型充模流动过程的数学模型 ,重点讨论了注射模充填阶段数值分析的方法。     

气辅共注射成型充填过程数值模拟中的移动界面追踪技术

气辅共注射成型工艺的充填过程中存在多个移动界面。为能对充填过程进行有效的模拟,针对凝固层界面、表层熔体前沿、内层熔体前沿和气体穿透前沿推进的特点,采用不同的方法实现其追踪。模拟结果与实验结果比较表明,该方法简单有效,能够较准确地预测内层熔体前沿的位置,而要更准确地预测气体穿透前沿的位置,还要进一步考虑注气延迟时间和保压冷却阶段气体在熔体中的“二次穿透”。     

Numerical simulation of tungsten alloy in powder injection molding process

The flow behavior of feedstock for the tungsten alloy powder in the mold cavity was approximately described using Hele-Shaw flow model. The math model consisting of momentum equation, consecutive equation and thermo-conduction equation for describing the injection process was established. The equations are solved by the finite element/finite difference hybrid method that means dispersing the feedstock model with finite element method, resolving the model along the depth with finite difference methgd, and tracking the movable boundary with control volume method, then the pressure equation and energy equation can be resolved in turn. The numerical simulation of the injection process and the identification of the process parameters were realized by the Moldflow software. The results indicate that there is low temperature gradient in the cavity while the pressure and shear rate gradient are high at high flow rate. The selection of the flow rate is affected by the structure of the gate. The shear rate and the pressure near the gate can be decreased by properly widening the dimension of the gate. There is a good agreement between the process parameters obtained by the numerical simulation and the actual ones.     

矩形薄板共注射成型的芯层熔体前缘充破模拟研究

采用Moldflow Plastics Insight软件中的Co_injection模块,对矩形薄板的形状和浇口位置的变化进行数值模拟分析,揭示了薄板长度、宽度及浇口位置对芯层熔体前缘充破的影响。结果表明进料方向平行于熔体流动方向的浇口位置利于芯层体积分数(N)的提高;制品宽度的减小,长宽比增大,N值总体趋势变大,但制品的长度存在一个最佳值。     

工艺参数对金属粉末共注射成形芯层熔体形貌的影响

分别以316L(40%,体积分数)、316L(60%)为芯、壳层喂料,研究工艺参数如壳层熔体温度、壳层注射速度和延迟时间对粉末共注射芯层熔体形貌的影响;分析工艺参数对金属共注射芯层形貌影响的流变学机理。结果表明:芯层熔体前沿呈蘑菇状;固定芯层熔体温度,随着壳层熔体温度的升高,芯层穿透深度从148 mm减小到136 mm,最大穿透宽度从133 mm增加到139 mm;随壳层注射速度的增加,芯层穿透深度从148 mm减小到143 mm,而芯层穿透宽度的变化规律不明显;随着芯层熔体延迟时间的增大,芯层穿透深度从146 mm增加到154 mm,穿透宽度从118 mm增加到136 mm。     

Numerical simulation for thermal flow filling process of casting

The solution algorithm （SOLA） method was used to solve the velocity and pressure field of the thermal flow filling process, and the volume of fluid （VOF） method for the flee surface problem. Since the ＂donor-acceptor＂ rule often results in the free interface vague, the explicit difference method was adopted, and a method describing the flee surface state at 0〈F〈 1 was proposed to deal with this problem. In order to raise the computation efficiency, such algorithms were investigated and invalidated as： 1） internal and external area separation simplification algorithm; 2） the reducing necessary search area method. With the improved algorithms, the filling processes of the valve cover castings with gravity cast and an up cylinder block casting with low-pressure cast were simulated, the simulation results are believable and the computation efficiency is greatly improved. The SOLA-VOF model and its difference method for thermal fluid flow filling process were introduced.     

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.     

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.