粉末注射成形过程计算机数值模拟

分析了粉末注射成形过程计算机数值模拟的意义、研究现状、所取得的成果及存在的问题，提出了将分形和混沌理论引入粉末注射成形过程的研究。建立颗粒模型、两相流模型，采用多重网格等新的数值方法进行过程模拟来解决这些问题的设想。     

粉末注射成形充模过程特有边界层效应的数值模拟

基于粉末-粘结剂的双流体模型,利用CFX软件粉末口射成形(PIM)对充模过程中粘结剂的分布变化进行了模拟计算.结果表明:在注射坯的表面薄层内粘结剂含量多于在注射坯中的平均值,且表面薄层内粘结剂体积分数由表到里逐渐下降,证实了PIM特有边界层效应的存在.随着注射温度由420 K升高到440 K,PIM特有的边界层效应变明显;随着入口的喂料流量由60cm3·s-1增加到80 am3·s-1,这种效应反而略有减轻.试验结果与模拟结果基本一致,表明了双流体模型用于PIM研究的可靠性.     

基于数值模拟的粉末注射成形模具结构优化设计

在粉注射成形过程中,模具结构的设计合理与否对成形质量和效率都有决定性影响.在基于数值模拟的基础上导出了粉末注射模具的浇注系统优化设计模型,并在MODEFLOW软件模拟和工艺实验中得到验证.结果表明优化后的模具在锁模力和成形周期方面都明显下降,生坯成形密度明显提高且密度方差明显减小,同时有效减少了试模次数,提高成形效率.     

[成形过程仿真优化与集成计算材料工程]注射成形熔体喷射的三维模拟及消除对策研究

为了探寻塑料注射成形过程中熔体喷射的消除对策,采用高精度离散格式追踪熔体流动前沿,基于有限体积法离散控制方程,发展了三维数值算法。与实验结果对比发现：所发展算法能有效模拟壁厚为4 mm的长方体型腔内的两种喷射演化模式以及厚壁型腔内的熔体喷射及其演化过程;小壁厚型腔内熔体的屈曲呈二维折叠演化,厚壁型腔内熔体的屈曲呈三维缠绕演化;重力对厚壁型腔内的喷射演化产生影响。通过增大剪切速率即改变熔体流动速度大小或者流动方向能有效消除或抑制喷射现象,并且用两个数值算例论证了该观点。     

注射成形熔体喷射的三维模拟及消除对策研究

为了探寻塑料注射成形过程中熔体喷射的消除对策,采用高精度离散格式追踪熔体流动前沿,基于有限体积法离散控制方程,发展了三维数值算法。与实验结果对比发现:所发展算法能有效模拟壁厚为4 mm的长方体型腔内的两种喷射演化模式以及厚壁型腔内的熔体喷射及其演化过程;小壁厚型腔内熔体的屈曲呈二维折叠演化,厚壁型腔内熔体的屈曲呈三维缠绕演化;重力对厚壁型腔内的喷射演化产生影响。通过增大剪切速率即改变熔体流动速度大小或者流动方向能有效消除或抑制喷射现象,并且用两个数值算例论证了该观点。     

粉末注射成形材料微波烧结过程的有限元模拟

基于传统电阻加热烧结过程的建模与模拟,通过对粉末注射成形材料微波烧结过程的机理分析,结合电磁场、热力学以及连续介质力学原理,确定了微波烧结全过程的数学模型和模拟方法;通过建立合理的力学模型和控制方程,采用COMSOL Multi-physics软件模拟微波烧结过程,并将模拟结果与试验结果进行了对比。结果表明:氧化锆粉末成形件在微波烧结初始阶段加热缓慢,当温度升至400℃之后,成形件内部温度持续急剧升高;当加热至1 360℃时,烧结件的相对密度高达92%,可满足粉末烧结工艺要求;建立的数学模型能有效模拟微波烧结过程中粉末成形材料内部的电场、温度场分布以及密度的衍化过程。     

粉末注射成形技术及其应用

介绍了粉末成形新技术的原理、特点和应用。对PIM制件的工艺性和质量进行了评价为成形方法的选择提供了参考。     

粉末流动温压过程中粉末堆积数值模拟与优化

基于离散元法,综合考虑重力、接触力、阻尼、摩擦、范德华力等多种作用力的影响,建立了粉末流动温压过程中粉末堆积的数学模型,对相同材料不同粒径的二元颗粒粉末和相同粒径不同材料的二元粉末颗粒的混粉过程进行了研究。通过实验研究和数值模拟的结合,得到了一个不同数量比的二元堆积的密度规律:在大小粒子直径比为10,当小粒子是大粒子数量的300倍时,获得的最大堆积密度为0.824。通过实验验证了相同粒径不同密度的二元粉末颗粒的填充模拟过程,得到了一致的实验结果。研究结果有效地验证了离散元数学模型的正确性及相关数值模拟的实用性。     

金属(陶瓷)粉末注射成形技术及应用

介绍金属 (陶瓷 )粉末注射成形技术的主要工艺过程 ,分析其工艺的特点及其在零部件制造方面所具有的技术优势及应用     

钛合金粉末成形技术及数值模拟研究

对TC4粉末压制成形过程中温度和压力对压胚密度的影响进行研究。同时,研究了不同压制条件对压胚密度分布的影响。结果表明,粉体成形过程中模壁摩擦导致了相对密度分布的不同;通过对圆柱体试样压制过程的模拟验证表明,样品沿挤压轴方向上密度分布不均匀,与有限元分析结果一致。     

Computing gas/melt free interface of gas-assisted injection molding

A solution was put forward to predicate the flow pattern of gas penetration in gas-assisted injection molding. The differential equations that governed the flow field and gas/melt free-interface evolution were analyzed and discretized by Galerkin finite element method, and the free interface was located by the volume of fluid method. The gas was assumed as a fluid phase of constant density and viscosity instead of being simply treated as boundary conditions. The non-Newtonian property of polymer melt was characterized by Carreau model with four parameters. As a case study, different kinds of gas channel were modeled. The gas/melt free interface was captured. The gas front velocity and the pressure of gas/melt front were also computed. The edge shape of gas channel was discussed, which are helpful for the design of gas-assisted injection molding.     

注塑机前模板的拓扑与参数优化设计

以浙江某注塑机厂BT2200V-Ⅱ的前模板为对象,借助于ANSYS有限元软件对前模板进行拓扑优化,寻找模板的最优结构形式;并通过将参数优化,确定前模型的实际结构尺寸.最后对优化前后的模板进行了有限元对比分析,检验了优化模板结构的合理性和可用性.     

Mold surface roughness effects on cavity filling of polymer melt in micro injection molding

Micro injection molding presents many challenges in the injection-molding community. When the dimensions of the part (and thus the cavity of the mold) are small, micro-scale factors such as mold surface roughness may play an important role in the filling of polymer melt. This paper investigates the effects of mold surface roughness on cavity filling of polymer melt in micro injection molding. A disk insert, which has two halves with different surface roughness but with the same roughness mean lines, was used in the investigations. The ratio of flow area of the rougher half with the total flow area of the molded part is used to evaluate the significance of surface roughness effect. The experimental results revealed that mold surface roughness does resist the cavity filling of polymer melt in micro injection molding. For the limited range of injection rate investigated, it is not significant on the surface roughness effects. The increase of mold temperature will decrease surface roughness effects. The change of melt temperature within the range allowed by the process is insignificant for surface roughness effects.     

Small-hole arrays of ceramic material manufactured by micro powder injection molding

Ceramic substrate with three kinds of small-hole arrays (the minimum diameter is 400?μm) was manufactured by micro powder injection molding. The homogeneity, thermal, and rheological properties of the feedstock was characterized by means of SEM, Archimedes method, TGA, DSC, and capillary rheometer, respectively. The feedstock has good uniformity and the viscosity of feedstock accords with the pseudo-plastic behavior which is suitable for micro powder injection molding. The test results also show that the linear shrinkage of small holes is lower than the substrate which is important to mold design and size contraction of the sample. Moreover, the porosity of the sintered substrate is lower than that of the thin wall between two neighborhood small holes. Good surface roughness of the sintered samples is obtained by using sub-micron ZrO₂ powder which is even lower than molded surface. The relative density and hardness of the ceramic substrate with small-hole arrays sintered under 1,500°C for 2?h is 98.3% and 13.68?GPa, respectively.     

基于流动模拟技术的注塑成型工艺参数优化

利用Pro／E建立了15寸电脑显示器前壳简化3D模型，并用Mold Plastics Insight(MPL)软件对该制品的注塑成型过程进行流动、保压、冷却和翘曲模拟分析，优化工艺参数。然后，针对塑件材料的注射温度和模具温度的选用范围进行分组模拟，得到几组较优的工艺参数组合，并以翘曲变形量为参考标准，获得合理的工艺参数组合。     

基于遗传算法的注塑机肘杆机构优化设计

遗传算法对于多参数系统优化设计具有较好的鲁棒性。针对注塑机肘杆机构优化设计的问题,通过对注塑机单肘杆合模装置的运动分析,建立了数学模型。以肘杆机构长度最小为目标,利用遗传算法进行了优化设计,并与常规设计方法进行了比较。研究结果表明,基于遗传算法的优化设计体现出了明显的优化效果,具有一定的实际应用价值。     

Studies on size accuracy of microgear wheels produced by powder injection molding of zirconia feedstocks

Two-component micropowder injection molding allows two different materials and, hence, two different functions to be integrated in one microdevice. This requires both components to be matched precisely. Therefore, high dimensional accuracy is essential in the successful development of a two-component micropart. This paper is about studies of the accuracy of the diameters of the inner hole of a gear wheel to be used as the first component of a shaft-to-collar connection. Diameters were measured in two defined directions, oriented 90° relative to each other. Items discussed are the size accuracy of green bodies and sintered specimens as well as the effects of different gating concepts. Sometimes, the inner hole is eccentric, depending on the gating concept employed. It was shown that a point-shaped gate can exert pressure on the feedstock nearby, thus causing deformation and reducing the diameter in these areas compared to the diameter in areas far from the gating system. The results also show that the eccentricity of the inner hole after sintering differs from that measured on green bodies, which is an indication of anisotropy in sintering. Moreover, the types of powder were seen to have an effect.     

红外菲涅尔透镜的注射超声辅助成型优化

为了提升聚合物红外菲涅尔透镜的光学性能,以其表面微沟槽的成型质量为目标,提出了一种高效的注射超声辅助成型方法,并对工艺参数进行了综合质量优化。首先分析了超声振动对聚合物的加热和加压效应,设计了一套一模两腔的对比试验模具;接着以红外菲涅尔透镜的调制传递函数MTF和齿形平均高度h为优化质量目标,设计了四步骤的多目标优化流程,通过试验设计、基于BP神经网络的质量目标与注射工艺参数关系建模、基于NSGA-Ⅱ的多目标优化和试验验证进行工艺参数的综合优化。实验结果表明:该多目标优化流程具有很高的精度,MTF和h的平均预测误差MPE分别为4.16%和3.32%;注射超声辅助成型的菲涅尔透镜微沟槽具有更高的复制质量,其齿沟槽平均高度h增加了15.6%,且h值的波动量随着h值的增大而增大,MTF值受齿高h均匀性的影响大于齿高h对其的影响。     

Determination of the flow stress and thermal properties of ceramic powder feedstock in ceramic injection molding

To simulate numerically the material behavior of a ceramic powder feedstock that consist of a two-phase mixture of zirconia powder and polymer binder, a material model is needed that incorporates the change in volume fraction and temperature dependency of viscosity. Heat transfer occurs between the feedstock and the mold during ceramic injection molding (CIM). The feedstock is heavily influenced by thermal properties such as thermal conductivity and specific heat. In this study, three models are proposed to explain the material and thermal properties: a rigid-plastic flow stress model that is dependent on volume fraction and viscosity, a thermal conductivity model, and a specific heat model as a function of temperature. The material parameters in each model are obtained by using the optimization method. Error functions are defined as the differences between the experimental measurements and numerical simulation results. The parameters are determined by minimizing the error functions. The confirmation simulation for each model is conducted by applying cases that are not directly used in the optimization. The results of the confirmation simulation tend to follow the experimental results well, with correlation coefficients exceeding 0.92. The numerical simulation of the CIM process with the determined parameters is compared with the flow behavior of an actual CIM process. Simulation results, such as flow pattern and direction, are in good agreement with the measured feedstock behavior. Therefore, the method for determining the material parameters of the proposed models is feasible.