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就固-液-孔隙系统的流变学特性而言,粉末注射成形与液相烧结具有同样特点.粉末注射成形起始于1930年代,而金属粉末的液相烧结大体上也可溯源于同一时代.这2种工艺都对粘度和固体含量与温度的关系高度敏感,但都有所不同.因此,提出了一个包括应变速率、颗粒大小、固体含量等因素及颗粒结合程度的模型.在液相烧结中.固体在液体中的溶解度通过颗粒结合影响与时间相关的粘度.同样,在粉末注射成形中,长聚合物的缠结影响与时间相关的粘度.粉末注射成形与液相烧结二者的相似之处,在于都能够将流变学特性模型用于计算机模拟. 相似文献
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钛及钛合金兼具低比重、高比强度、优异的生物相容性和良好的耐腐蚀性,在航空航天、生物医疗、化工、汽车等领域有极大的应用潜力。钛及钛合金金属粉末注射成形技术(metal injection molding,MIM)能够实现中小型复杂形状钛产品的大批量、低成本制备,对于推动钛及钛合金产品的生产及应用具有重要意义。本文介绍了金属粉末注射成形钛及钛合金的特点及优势,从粉末原料、黏结剂体系、粉末注射成形、脱黏和烧结等方面综述了钛及钛合金金属粉末注射成形技术的研究进展,并针对目前存在的主要问题,分析了金属粉末注射成形钛及钛合金的研究方向及发展前景。 相似文献
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金属粉末注射成形复杂模腔计算机充模模拟研究 总被引:1,自引:0,他引:1
利用有限元分析软件ANSYS,对金属粉末注射成形计算机复杂模腔充模过程进行了模拟,模拟结果与Cro—cher等用商业软件Polymold算出的结果相似,证明了所建模型和分析计算方法的可行性。同时通过分析模拟结果中流体前沿、压力场和温度场的分布,预测了部分常见注射缺陷产生的条件,讨论了如何利用模拟结果指导注射工艺参数的选择,展示了其实用前景。 相似文献
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《粉末冶金学》2013,56(4):274-277
AbstractA homogeneous powder and binder distribution in the green body in powder injection moulding (PIM) is important. In the present study, the mould filling model of PIM has been developed, based on the multiphase fluid theory, viscosity model of feedstock and powder-binder drag force model. The particle Reynolds number is influenced by the particle size and density, resulting in the different drag force between powder and binder. Furthermore, the varied velocity of binder and powder will be obtained with numerical calculation of the continuity equations, leading to the change of green body homogeneity. CFX was used to simulate the mould filling in PIM. The results showed that the homogeneity of green bodies was relative to the filling patterns, which varied with different powder densities. The powders were not suitable for PIM when the particle size was bigger than 20 μm, and the fine powders were beneficial to improve the homogeneity. 相似文献
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粉末注射成形(PIM)是集塑料成形与传统粉末冶金工艺优势而产生的一种新型零部件近净成形技术。叙述了粉末注射成形的优点和有待解决的难题,利用模拟软件可以有效地避免或减少PIM各个阶段的缺陷,重点介绍了国内外在PIM喂料充模模拟技术上已经取得的成果和待解决的问题,依据目前的PIM喂料充模模拟研究现状,对PIM模拟的发展进行了展望,认为以Burracuda软件为基础的粉末颗粒模拟研究将成为PIM喂料充模模拟的主要发展趋势,并为粉末注射成形喂料模拟技术的进一步发展提供参考。 相似文献
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《粉末冶金学》2013,56(3):208-212
AbstractThe Fe–48 at.-%Al powder used for powder injection moulding (PIM) was prepared by mechanical alloying in a high energy planetary ball mill and subsequent vacuum annealing. The effects of stearic acid (SA) as the process control agent on powder characteristics were investigated using X-ray diffractometer, laser particle size analysis and scanning electron microscopy. The dependence of solvent debinding efficiency of PIM feedstock on the powder characteristics was also studied. The results indicate that a low SA content for ball milling helps to prepare near spherical, coarse powder particles that exhibit good solvent debinding efficiency. On the contrary, a high SA content leads to thin layered, small particles with poor PIM solvent debinding efficiency. An intermediate SA content such as 1 wt-% makes the ball milled powder combine the advantageous characteristics for PIM process. 相似文献
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AbstractThe conventional powder metallurgy (PM) approach of compaction and sintering has been used extensively in the fabrication of tungsten alloys and composite hardmetals based on WC-Co. In fact, these are some of the earliest known materials to have been fabricated by the PM route. The last 15-20 years have seen the emergence of a new shaping technique of powder injection moulding (PIM) which can shape such tungsten metal alloys and composites into complex near net shaped components. The PIM process starts with the mixing of an organic binder with the desired powders in the form of a homogeneous mixture, known as a feedstock. The feedstock, like plastics, can be moulded into near net shapes from which the organic part is removed and then the material can be sintered to almost theoretical density. This produces complex, near net shaped parts that have properties that are comparable to that of the press and sintered materials. This paper will provide a brief overview of the use of PIM in tungsten based alloys and composites and discuss some of the applications of these materials. 相似文献
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注射成形钨合金用新型粘结剂的研究 总被引:7,自引:0,他引:7
针对形状异常复杂的大钨环和大直径(≥20.00mm)的钨棒在注射成形中存在的问题。综合利用了蜡基粘结剂与油基粘结剂的优点,研究制备一种多组元油 蜡塑料体系改性粘结剂OP3010。研究对比了该种粘结剂与传统蜡基粘结剂和油基粘结剂对注射料流变性、热性能及注射坯脱脂的影响。由此种新型粘结剂组成的注射料具有流变性好、注射工艺稳定、注射压坯强度高、注射温度范围宽、易于脱模等特点,可以成功制备无缺陷的大钨环、大钨棒弹芯材料的注射坯。该粘结剂在溶剂脱脂时脱除速度快,粘结剂脱除量大,可达74%左右。而且脱脂后的毛坯强度高、不变形。可成功实现大钨棒和钨环的脱脂,并制备综合力学性能高的散弹和弹芯材料。 相似文献
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《粉末冶金学》2013,56(3):236-240
AbstractViscosity, specific heat and thermal conductivity of the standard feedstock of 316L stainless steel have been measured under the typical conditions of a real powder injection moulding (PIM) process. The viscosity was measured in a wide range of shear rates at four different temperatures. The experimental viscosity data were fitted into the Carreau-Yasuda model. Both specific heat and thermal conductivity were measured in the temperature range that overlaps the recommended processing range for the studied feedstock. It has been shown that at high cooling rates the transition temperature of the binder material is shifted towards lower temperatures. Tabulated values of thermal conductivity and specific heat for the studied feedstock are presented. The obtained data can be used for numerical simulation of the powder injection moulding process. 相似文献
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Steel samples taken from ladles or tundishes during the steel making process can be of significant importance when monitoring the inclusion size and distribution. In order to preserve the original size and distributions of inclusions in the extracted samples, it is important to avoid their collisions and coagulations inside samplers during filling. Thus, it is necessary to investigate the flow during a sampling process to make sure that this is minimized. In addition, it is important to study the turbulence characteristics, since it is known to influence the inclusion growth. This study presents mathematical modelling of sampler filling using water as a media and experimental results for verification. The study focuses on a lollipop‐shaped sampler since it is one of the most common in the industry. The sampler is filled from an inlet pin located at the bottom centre of the main body. In addition, two different turbulence models, the realizable k‐ε model and Wilcox k‐ω model, were used to study the flow pattern in the sampler. The predictions were compared to experimental results obtained by Particle Image Velocimetry (PIV) measurements. It was found that the flow field predictions using the Wilcox k‐ω model agreed best with the flow field obtained by PIV measurements. Furthermore, it was illustrated that the Wilcox k‐ω model can be used for predictions of the different flow regions as well as the positions of the centres of vortexes which are located near the free surface. Thus, it is concluded that the Wilcox k‐ω model can be used in the future to predict the filling of steel samplers. 相似文献
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MA Sandberg BS Pawlyk J Dan B Arnaud TP Dryja EL Berson 《Canadian Metallurgical Quarterly》1998,116(7):867-872
The potential of liquisolid systems to improve the dissolution properties of water-insoluble agents was investigated using hydrocortisone as the model medication. The in vitro release patterns of this very slightly water-soluble corticosteroid, formulated in directly compressed tablets and liquisolid compacts, were studied at different dissolution conditions. The new formulation technique of liquisolid compacts was used to convert liquid medications such as solutions or suspensions of hydrocortisone in propylene glycol, a nonvolatile liquid vehicle, into acceptably flowing and compressible powders by blending with selective powder excipients. Several liquisolid tablet formulations were prepared using a new mathematical model to calculate the appropriate quantities of powder and liquid ingredients required to produce acceptably flowing and compressible admixtures. Due to their increased wetting properties and surface of drug available for dissolution, liquisolid compacts demonstrated significantly higher drug release rates than those of conventionally made, directly compressed tablets containing micronized hydrocortisone. The in vitro drug dissolution rates of liquisolid tablets were found to be consistent and independent of the volume of dissolution medium used, in contrast to the plain tablets which exhibited declining drug release patterns with decreasing dissolution volumes. It has been also shown that the fraction of molecularly dispersed drug in the liquid medication of liquisolid systems is directly proportional to their hydrocortisone dissolution rates. 相似文献