ABAQUS模拟粉末冲击压制冲模质量数值优化

采用有限元软件模拟金属粉末冲击压制过程时,由于计算量过大,所建立的模型颗粒数远低于实际粉末压制中的颗粒数,造成计算结果偏差过大,需要对冲模质量等相关参数进行优化。优化基于SHPB实验结果,通过ABAQUS对铝粉建立密排球堆积简化模型,有序增加模型横向与纵向颗粒数,确定仿真模型中冲模的质量,进而构建模拟中颗粒数与冲模相对质量之间关系,分别得到横向和纵向颗粒排数与冲模相对质量的关系;确立了粉末微观模拟压制中最常用的密排9堆积模型的冲模相对质量为0.093;通过与铜粉的冲击压实实验结果对比,验证所建立的模型颗粒数与冲模相对质量关系式在其他材料计算中也是适用的。     

Ti6Al4V粉末热等静压致密化的数值模拟

利用MSC.Marc对Ti6Al4V粉末热等静压致密化进行数值模拟,选用Shima屈服准则,分析了粉末在热等静压过程中颗粒的流动及整体致密化趋势。同时,通过热等静压试验,验证了数值模拟结果的准确性。模拟结果表明:粉末在致密化过程中先受热膨胀后收缩致密;除包套端盖与侧壁夹角处的粉末相对密度较低以外其他区域密度相差不大,部分区域已达全致密。试验表明:压坯的收缩量、相对密度分布与模拟结果基本一致。数值模拟结果合理可靠,可以为成形复杂钛合金构件提供参考。     

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。     

粉末注射成型过程的双流体数学模型

为了研究粉末注射成型(PIM)过程特有的偏析现象,提出了等效粉末的概念并引入粉末的拟流体假设;通过引用流体动力学的研究方法建立了PIM过程双流体模型基本控制方程,并对粉末、粘结剂相间作用的表达式及粉末与粘结剂的粘度关系进行了探讨;采用CFX软件分别基于双流体及单流体数学模型对PIM过程进行了数值模拟.结果表明:两者的模拟结果吻合较好,证明了双流体数学模型的可靠性.     

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。     

等离子体熔射粉末颗粒飞行特性研究

分别采用7速正六边形Lattice Boltzmann方法计算等离子体射流和随机算法计算颗粒运动,对等离子体射流中铁铬镍合金单个颗粒及颗粒群的热运动状态进行了较为详细的模拟研究,并采用芬兰Oseir公司热喷涂在线监测及诊断设备Spraywatch对不同电压下距射流出口200mm处颗粒平均速度和温度进行了实验测量。结果表明:模拟与实验符合较好,本模型计算速度比传统的方法快;颗粒直径大小、入口位置和运动轨迹决定颗粒的速度和温度变化,其他条件相同时,中心入射的大颗粒粉末可以比半径处入射的小颗粒粉末获得更高的速度和温度;通过计算得到了铁铬镍合金粉末颗粒在等离子体射流中稳定高速高温飞行的位置区间。     

人造石墨粉末选择性激光烧结成形工艺实验研究

将选择性激光烧结技术应用于人造石墨粉末成形,探索其回收循环再利用的可能性。研究了球形石墨粉末的加入量对人造石墨/酚醛树脂混合粉末流动性和堆积密度的影响,确定了石墨3D打印材料配方组成;研究了激光功率、扫描速度、扫描间距和分层厚度等工艺参数对石墨原型件的成形精度和抗弯强度的影响,确定了各工艺参数的取值范围;最后通过正交实验确定了最优工艺参数组合,并快速制备了复杂石墨功能件,验证了新工艺的可行性。     

以MSC.Marc为基的极片粉末轧制有限元模拟

粉末轧制工艺中的力学行为较难通过传统的数学模型综合准确地研究。但是基于有限元方法的数值模拟为研究粉末轧制过程中的力学特性提供了一种灵活高效的途径。在有限元方法中可以同时引入复杂的几何模型、材料本构模型和摩擦模型等多种信息,能够对轧制过程的材料流动及力能参数进行预测,可以更准确地综合研究粉末轧制的力学特性。     

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.     

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。     

基于粉末本构模型和多体力学仿真的模架集成式粉末成形设备的设计

研制出一种新型的低成本、小体积、高精度的专用模架集成式粉末成形设备。以MSC.Marc与MSC.Adams软件相结合提出基于数值模拟的1 MN压机设计方法,即根据粉末压制试验构建末材料流动应力本构模型;通过该模型在MSC.Marc软件数值计算出所设计压机压制过程的模冲载荷;在分析模架集成式粉末成形设备各个模板在压制工过程运动特点的基础上,建立多体运动学数学方程;将所得模冲载荷作为边界条件加载到对模架集成式粉末成形设备在压制过程的模拟仿真;并在MSC.Adams软件中分析各个模板在压制过程中力学状态,从中分析该设备在实际工况下的可靠性。研制出电液比例阀和光栅尺相结合的控制系统,实现对缸同时驱动,解决不同模板之间的动作协调的问题,所研制试验样机实现零件轴向压制精度为±0.02 mm。实际压制过程所得各模冲载荷与模拟结果相一致,从而验证粉末成形设备设计所采用的本构模型是准确的,基于数值模拟进行粉末成形设备设计的方法的正确性。     

Powder size measurement by acoustic emission

Acoustic emission was used to measure particle size properties of steel, cast iron, and alumina powders. Many powder samples with different weight and size distribution were prepared by sieving and their size distribution was measured by means of optical techniques. Acoustic emission measurements were carried out by dropping the powder on a metal plate to which an acoustic emission transducer was fixed, and results were expressed in terms of number of counts of four channels for data acquisition. The measurement set-up and procedure were original and never investigated before. Very good results were obtained for steel and cast iron samples, as measurement curves showed a clear linear trend as a function of the particle mean diameter and were vertically shifted in dependence of the sample weight. Alumina powders showed similar trends only for large particles and high weight differences.     

Simulation of microscopic shrinkage behaviour in sintering of powder compact

A method for simulating microscopic shrinkage behaviour of powder particles in sintering of a compact is proposed on the basis of the granular element method. In this method, the powder particles are modelled as many circular elements undergoing viscoplastic deformation due to surface tension during the sintering, and the microscopic shrinkage is calculated by equilibrating forces acting on the elements. The variation in shape of necks between the elements during the sintering is taken into consideration. Plane-strain shrinkage in sintering is calculated under regular and irregular dispositions of powder particles. In the regular disposition of powders having the same diameter, the obtained shrinkage behaviour is compared with the experimental one using glass rods and the calculated one by the viscoplastic finite-element simulation respectively. It is shown from the simulation of irregular disposition that the densification due to the sintering is accelerated by mixing powders having different diameters.     

纳米级金属粉改善润滑油摩擦性能的研究

在MPX200实验机上考察了粒径为20～30hm的铜粉和锡粉加入Q030润滑油后的摩擦性能,结果表明该铜粉能够提高Q030润滑油的极压性能,而将铜粉和锡粉一起加入该润滑油则效果更佳。     

光透过率法测量煤粉平均粒径

文中详细介绍了利用光透过率法测量煤粉颗粒比表面积平均直径的原理和测量装置，给出了实际测量数据，取得了与筛分法一致的结果，使用普通的光电测量装置，本法测量极限误差一般可小于２％ 。     

混粉电火花加工中粉末粒度特性及涡流分离器的仿真设计研究

利用自行研制的混粉电火花工作液处理系统对混粉电火花加工中粉末粒度对加工性能的影响进行分析与实验研究,证明粉末粒度越小加工效果越好。利用Solidworks的插件COSMOSFloWorks流体分析软件进行仿真试验,设计制造出适合于分离不同大小粉末颗粒的涡流分离器。从而能配合其他混粉工作液处理装置组成混粉工作液处理系统,得到优质的加工效果。     

不同压制工艺对粉末冶金制品性能影响的有限元模拟

利用MSC/MARC有限元分析软件对金属粉末压制过程进行模拟分析.采用基于更新拉格朗日方法的热-力耦合分析不同工艺条件(温度、摩擦条件和压制方式等)对压坯性能的影响规律,同时对压制过程中的力学特征(压制力、脱模力、侧压力和应力分布等)进行分析.结果显示,摩擦条件是影响压坯密度大小及分布的关键因素,通过采用双向压制方法可以有效地改善单向压制压坯密度分布不均、差值较大的现象.温度的提高有利于提高粉末颗粒的塑性变形能力,但效果不明显.另外,由于温度影响润滑剂润滑性能,因此在制定压制工艺时需考虑温度对压坯性能的影响.此外温度的提高、摩擦的降低均有利于降低压制力,提高压坯密度均匀性,改善压坯应力集中现象.     

Isostatic compaction of bimodal powder mixtures and composites

We study the effect of using a mixture of particles of two different sizes for the compaction of spherical metallic powders by discrete element method simulations (DEM). The study focuses on large size ratios (4 and 8) for which a wide range of volume fractions of large particles is investigated (from 0% to 80% volume). The bimodality of the powder is shown to affect all stages of powder compaction. The relative density of the powder when no significant load is applied (tap density) is a function of both the size ratio and the volume fraction of large particles. Furthermore, we show that bimodal compacts exhibit a stiffer response during isostatic plastic compaction compared to the monomodal case. The important practical application of a mixture of soft deformable particles (metallic) with hard particles (ceramic) is also studied. Following compaction, the unloading of the compact and the resulting tensile strength (green strength) are also shown to depend on the bimodality of the compact.     

EMO97上的粉末冶金高速钢刀具

文中介绍粉末冶金高速钢在欧、美发展的现状及在EMO97上展出的粉末冶金高速钢刀具。     

Powder sampling and characterization by digital image analysis

The knowledge and understanding of powder shape and size are essential to the improvement and control of several industrial processes. This paper describes an offline methodology used in the characterization of powder properties based on digital image analysis. The method provides a reliable sample preparation consisting of a mixing operation and a statistical test validation. A versatile digital image procedure is presented: image calibration, enhancing and clustering permit to automatically detect particles and retrieve 2D properties. Shadow casting is applied to achieve the third dimension. The method can deliver statistically significant size and shape information in a single measurement characterizing the salient parameters of powder. The potential of the proposed method is shown with its application to some industrial powders. As is suggested it fulfils the identified needs of product and process monitoring applications for technological/industrial manufacturing, for quality control and improvement purposes.