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.     

Manufacturing of complex-shaped ceramic components by micropowder injection molding

The micropowder injection molding process (microPIM) offers a large-scale fabrication technology for metal/ceramic microstructures. Current R + D efforts focus on increasing the degree of complexity of the 3D microparts molded rendering it necessary to implement novel tools and demolding methods. The increase in the degree of complexity was demonstrated by a dispenser screw. Progress included the adaptation of the untwisting technique known from plastic injection molding to PIM green compacts. This allowed for a burr-free demolding in spite of the backcuts of the screw design.     

陶瓷微板热隔离气体传感器阵列热干扰分析

热干扰特性是影响微热板气体传感器阵列热结构设计的重要因素之一。为探讨微热板阵列传感器单元之间的热力学特性关系,设计并制备了具有独立式加热功能的热隔离结构4单元微热板气体阵列,传感器阵列单元由Al N陶瓷衬底、Pt膜电极组成,为提高加热效率,阵列单元中间加热区采用激光微加工刻蚀热隔离通孔设计,与边缘形成微梁连接结构。利用有限元法对传感器阵列结构进行了热干扰仿真分析,验证了热隔离结构设计的合理性。给出了4种热干扰测试模式,并进行了热干扰特性测试分析,给出了4单元之间的热干扰规律曲线,得出传感器单元功耗300m W时最大干扰温度达169.6℃,最小热干扰温度84.7℃。热隔离通孔设计可有效降低传感器单元热传导损耗,热干扰分析对微热板传感器阵列的热结构设计具有重要意义。     

TT12／90HSE新型全电动微型注射成型机

不久前，Hewaco注射成型技术有限公司在Fakuama博览会上推出了MTT12／90HSE新型全电动微型注射成型机。该公司与Kobelin模具制造有限公司合作共同开发出这种机型，该机特别适用于加工精密医用部件用的特殊材料——聚醚醚酮（PEEK）。尤其是采用该机加工能保持稳定的质量。     

粉末注射成形过程中熔体前沿速度优化

在粉末注射成形中,喂料熔体中的聚合物在充模阶段由于非均匀的熔体前沿速度将导致坯件非均匀收缩、坯件密度变小和翘曲变形.基于充填过程数值模拟提出实现在粉末注射成形过程中的注射速率优化方法,以获得均匀熔体前沿速度从而减少喂料中聚合物非均匀收缩以实现提高成形坯件密度.通过模拟熔体前沿面积变化曲线的与螺杆行程的关系,确定分级注射点;结合分级注射点对应的注射量与螺杆注射位置的对应关系,导出一个简化的分级注射参数.由模拟和实验表明,该方法能获得较为均匀的熔体前沿速度,熔体前沿速度的标准方差从优化前14.6 cm/s下降到优化后的42cm/s;生坯平均密度由从优化前5.34g/cm3提高到优化后的5.54g/cm3,生坯样本方差由从优化前0.235g/cm3下降到优化后的0.0823g/cm3.     

Bending strength analysis of micro WC-shaft manufactured by micro electro-discharge machining

Micro electro-discharge machining (micro-EDM) is a critical technology to fabricate high aspect ratio 3D micro-components. However, the surfaces of micro-components manufactured by micro-EDM will exhibit micro-cracks to produce notch effects, and lead to stress concentrate and reduction of fatigue strength. This paper performs micro-bending tests to investigate the influence of various roughness and size on the bending fracture strength of micro WC-shafts manufactured by micro-EDM. The experimental results indicate that the surface roughness, axial surface area, volume, and length of the specimen will affect its bending fracture strength. For specimens with the same size, the mean bending fracture strength decreases as the surface roughness increases, and the bending fracture probability of the specimens also increases (roughness effect). For specimens with the same roughness, reducing the length or axial surface area will increase the mean bending fracture strength, and reduces the bending fracture probability (size effect).     

Effects of machined cavity texture on ejection force in micro injection molding

The friction force developed in the demolding phase of the micro injection molding process is mainly determined by mold surface finish, which affects the tribological phenomena occurring at the polymer–tool interface. In this work, the effects on the ejection force of two cavity surfaces machined with different technologies (viz. micro milling and micro electro discharge machining), but with similar value of Ra, were investigated. The relations between different surface topography parameters and the ejection force were then analyzed, in order to identify the parameters that most appropriately describe the friction at the polymer–tool interface. The experimental results showed the strong interactions between the mold surface texture and the micro injection molding process parameters that promote the replication, such as mold temperature and holding pressure. The different machining technologies generated two mold textures that have a similar value of Ra, but their influence on friction can be properly described only using several other surface topography parameters.     

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.     

陶瓷微板热隔离半导体气体传感器阵列设计与实现

具有高浓度、挥发性、强氧化性的液氯、氮氧化物等危化品泄露、爆炸的安全检测一直是一个难点问题,要求检测传感器具有较宽量程和抗腐蚀设计。基于Al N陶瓷的微热板半导体气体传感器阵列设计,采用耐腐蚀的Al N陶瓷为衬底,物理化学性能稳定的Pt膜作为信号和加热器电极,经杂化修饰的In-Nb复合半导体氧化物为敏感材料,结合柔性光刻剥离工艺和激光微加工工艺,制备了陶瓷微板热隔离气体传感器阵列。为验证传感器阵列热结构设计的合理性,进行了有限元热仿真分析,优化了设计结构。经静态气敏测试分析,传感器阵列对浓度体积比500×10~(-6)的Cl_2和100×10~(-6)的NO_2两种气体的气敏响应时间分别为30 s和60 s左右,灵敏度最高分别为275倍和4倍,且在0~500×10~(-6)和0~100×10~(-6)检测范围均具有良好的气敏特性,对Cl_2等高浓度宽量程危化品气体检测具有良好的应用前景。     

Inhomogeneity of CoCrW powder products manufactured by SLM technology

Journal of Mechanical Science and Technology - The article deals with selective laser melting process using CoCrW powder. Our aim was to identify the influence of product position on the building...     

Fracture strength analysis of micro WC-shaft manufactured by micro-electro-discharge machining

Micro-electro-discharge machining (micro-EDM) is a potential micro-manufacturing technology. However, the surfaces of micro-components manufactured by micro-EDM will exhibit micro-cracks and micro-craters, and then micro-cracks and micro-craters will produce notch effects leading to stress concentration and reduction of fatigue strength. In particular, the roughness and size of tiny components strongly affect the strength of micro-scale components. Therefore, this study performs micro-tensile tests for micro-shaft specimens of various roughness and size to investigate the influence of roughness and size on the fracture strength of micro WC-shafts manufactured by micro-EDM. Experimental results indicate that the surface roughness, axial surface area, volume, and length of the specimen affect its fracture strength. For specimens of the same size, the mean fracture strength decreases as the surface roughness increases, and the fracture probability of the specimens also increases (roughness effect). For specimens with the same diameter and roughness, increasing the length, volume or axial surface area reduces the mean fracture strength, and increases the fracture probability (size effect).     

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.     

Mechanical etching of micro pockets by powder blasting

The main objective of this research is to develop a mechanical etching technique to produce micro mould dies having micro pockets of hundreds of μm. A powder blasting technique is applied to stainless steel plates based on predefined process conditions. This paper describes the performance of a powder blasting technique and the effect of the number of nozzle scanning times and the stand-off distance of the nozzle on the depth and width of pockets. Required blasting and measurement steps are performed to extract the relationships between given process parameters and machined results. Experimental results show that increasing the number of nozzle scanning times and decreasing the stand-off distance of the nozzle increase the depth and width of machined pockets. Increase of the width of the pockets results from mask film wear. The results of this research can be a fundamental basis to produce more accurate and smaller micro pockets using the powder blasting process .     

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.     

注塑机常见故障及维修方法

故障的判断和处理是注塑机维修工作的核心,该文详细阐述了注塑机的检修方法、并从常见故障的初步检查、确定故障、找出故障级、找出故障元器件、更换元器件五个方面总结出排除故障行之有效的处理方法.     

Densification behaviour of ceramic powder

A three-dimensional compaction device has been developed to carry out compaction of a ceramic powder. The details of the device, which provides compaction with various stress ratios, are described. A densification criterion for the powder is proposed; this is similar to that for the case for metal powders, but the role of the hydrostatic stress component appears to be different. Stress-strain rate relations are then derived using the concept of plastic potential; experimental results show that the normality of the strain rate vector to the surface which corresponds to the criterion almost holds.     

Moldflow在键盘面板成型中的应用

分析了键盘面板的结构特点,使用Moldflow软件对注塑件的成型过程进行CAE分析,确定浇口数量及位置,并预测可能出现的翘曲、气孔和熔接痕等缺陷.结果表明,通过CAE模拟计算,可有效地消除产品设计、模具设计及产品制造成型过程中可能出现的不足,取代传统的反复试模、修模等过程,从而降低产品制造成本,缩短产品开发周期.     

Warpage phenomenon of thin-wall injection molding

This study investigates warpage of electronic dictionary battery covers fabricated using thin-wall injection molding as a replacement for conventional insert molding. The primary concern is the molding window in thin-wall injection molding for acrylonitrile?Cbutadiene styrene (ABS) and polycarbonate (PC)+ABS plastics. Finally, the process parameters for thin-wall injection molding that eliminate warpage of electronic dictionary battery covers are identified. Experimental results demonstrate that the area of the molding window for ABS exceeds that for PC+ABS. Analysis of the molding window reveals that ABS is more appropriate than PC+ABS for battery covers. Low melt temperature, high injection speed, and high packing pressure eliminate battery cover warpage. Melt temperature is the most important process parameter for eliminating warpage when using both ABS and PC+ABS.