基于双流体模型的粉末压制过程气体流动特性仿真研究

利用实验方法很难获得粉体内部气流轨迹和压力分布的详细信息,因此仿真技术是研究粉末压制的重要手段之一。针对粉体床内部在压制过程中的气体流场变化,采用基于双流体模型的二维多相流CFD软件Fluent对粉体床内的气流进行模拟。通过研究压制过程中初期、中期和末期3个时间点的气体体积分布和速度分布,发现压制速度是粉末压制非常重要的因素。由于粉床中的气体主要聚集在靠近压头的上层,因此提出在压头表面设计排气孔,有助于粉末中的空气流出,提高砖坯质量。     

循环负荷与选粉效率实验设计与研究

针对由球磨机和配套选粉机组成的典型闭路粉磨系统,分析了循环负荷与选粉效率对粉磨过程以及粉磨效果的影响。在理论分析的基础上,以水泥粉磨为对象,研究设计了一种分析和确定闭路粉磨系统最佳循环负荷与选粉效率的实验方法。通过模拟闭路粉磨系统的粉磨流程,探索典型闭路粉磨系统循环负荷与选粉效率的最佳工艺参数,并根据实验结果,提出了此类粉磨系统循环负荷与选粉效率的最佳取值范围。为此类球磨粉磨系统循环负荷与选粉效率的参数优化提供了实验方法与数据基础。     

粉末冶金压制过程装粉状态自动监测系统

要模式识别与时间序列分析理论基础上，针对粉末冶金压制过程开发出模具装粉状态自动监测系统，为保证粉末冶金生产的优质高效进行，提供了一条新的途径。     

粉末冶金件的精整方法

粉末冶金产品在脱模及烧结过程中都伴有体积膨胀,同时装粉量的准确度、装粉是否均匀及铁粉混合的均匀度都会对成品件的尺寸产生影响。文中针对这种情况,介绍了一种对粉末冶金产品进行精整的方法,一次压制后,合格率达90％以上,不合格产品经二次压制后,合格率接近100％。     

基于双“8”字型光纤谐振环的全光纤三端口Interleaver

为改善全光纤三端口Interleaver的输出特性,提出了一种基于双“8”字型光纤谐振环的对称结构三端口全光纤Interleaver.该谐振环由一个一字型3×3单模光纤耦合器和两个2×2单模光纤耦合器组成双“8”字型作为输入耦合器,而一个品字型3×3单模光纤耦合器作为输出耦合器.理论和实验分析了该波长交错器的输出特性,结果表明:与两级级联马赫-曾德尔干涉仪型(TCMZI)全光纤三端口Interleaver相比,其输出波形通带更加平坦,通带和阻带加宽,信道间功率旁瓣降低了约24 dB.通过实验用光纤熔融拉锥法制作了该器件,结果显示实验结果与理论分析吻合得很好,实验样品的信道间旁瓣值小于-30 dB,信道隔离度大于30 dB.     

金属粉末零件压制过程有限元模拟的研究

论述粉末压制过程的建模理论，建立屈服准则中静水应力影响因子与粉末压坯密度之间的动态关系式。在此基础上，运用有限元方法对回转类粉末压制零件进行计算机模拟，结果印证理论分析，并与实验结果相符。     

侧向槽粉末制品压制成型工艺

叙述了YAN79Z-B型模架全自动干粉成型液压机压制工艺的设计，在压制粉末冶金侧向槽过程中，阴模与浮动冲上升到设定位置，送粉器前移对阴模腔内充满粉料后，上冲下行到阴模内向下压制时，利用阴模与浮动冲的同步浮动，压制到终了位置产品成型，然后阴模拉下，浮动冲微升推出产品，实现了侧向槽产品国产化，自动化生产。     

多级离心泵叶轮口环磨损监测方法研究

采用计算流体动力学理论对多级离心泵整机流场进行了建模,分析了多级离心泵口环间隙对整机流场的影响,得到了多级离心泵效率随口环磨损变化的曲线,引入了轴向振动指标,将效率与轴向振动相结合,提出一种口环磨损量实时监测评估方法。建立了多级离心泵实验台,将实验结果与模拟结果相对比,验证了所提出方法的可行性。通过实验分析了口环磨损故障与叶轮腐蚀以及堵塞故障的特点,排除了叶轮腐蚀及堵塞对口环磨损实时监测的影响,完善了所提出方法。     

钼与石墨的瞬间液相扩散焊

借助瞬间液相扩散焊接技术,分别以铬-镍粉、铬-镍-铜压制薄片、锆-镍-钛粉作中间层,于1 650℃下真空保温1 h对钼和石墨进行焊接,对焊接接头进行了剪切试验和微观形貌观察、成分分析.结果表明:钼和石墨在添加以上三种中间层后均可实现焊合,接头有一定强度;其中以锆-镍-钛粉作中间层时所得接头的抗剪强度最大,超过了石墨的抗...     

平台罗经方位环结构实验模态参数识别

平台罗经是惯性导航系统中的一种精密复杂的导航仪器,平台罗经的核心部件方位环的动态特性直接决定着惯性仪表的工作精度和可靠性,模态分析是研究机械系统动态特性的主要方法之一。在概述了实验模态分析理论的基础上,建立了某型号平台方位环结构的实验模型,对方位环进行了实验模态分析。通过对实验结果与有限元计算结果比较,验证了有限元计算结果较为准确。     

高效高精度火工品压药控制技术

针对传统压药控制技术中电气比例阀对气液增力缸冲压力控制的不稳定和精度不高的问题,提出了改进方法。在传统压药工艺控制系统基础上,通过软件PID控制算法,实现高精度压药控制,并通过改进PID控制方式,可克服PID控制过程中稳定周期过长的缺点,从而实现压药控制的稳定性和高效率。     

多层模板粉末压制设备的研制

为了生产密度均匀、无裂纹的多台面粉末冶金零件，设计和制造了用于成形多台面复杂粉末冶金零件的多层模板粉末压制设备，并根据压制工艺要求设计了适用于该压制设备的控制系统。采用集成油缸驱动多层模架，多层模冲均能单独控制，可满足多台面复杂粉末冶金零件压坯的压制动作要求，改善了压坯的密度均匀性，避免产生裂纹。     

Densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing

Densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing was investigated. Hot isostatic pressing was carried out for a bundle of copper-coated tungsten fibers in copper powder. Due to tungsten-fibers and copper coating layers, the densification rate of a tungsten-fiber-reinforced copper powder compact was slower than that of pure copper powder. The constitutive equations by McMeeking and co-workers and by Abouaf and co-workers were implemented into a finite element program (ABAQUS) to analyze densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing. Finite element calculations were compared with experimental results for the variation of relative density with time for copper powder compacts during hot isostatic pressing. Density distributions in copper powder compacts were also investigated by comparing experimental results with finite element calculations.     

Creep densification of copper powder compact

Densification of metal powder under high temperature processing was investigated. Experimental data were obtained for copper powder under hot isostatic pressing, hot pressing and uniaxial creep compression. Theoretical calculations from the constitutive models by McMeeking and co-workers were compared with the experimental data. The agreements between experimental data and theoretical calculations are reasonably good when hydrostatic stress is dominant, but not as good when deviatoric stress increases.     

Effect of friction between powder and a mandrel on densification of iron powder during cold isostatic pressing

The effects of friction between the powder and the mandrel on densification behavior of metal powder were investigated under cold isostatic pressing. The friction coefficients between the powder and the mandrels with different surface roughness were determined from the relationship between the compaction pressure and the ejection pressure of the mandrel from powder compacts. The elastoplastic constitutive equations based on the yield function of Shima and Oyane were implemented into a finite element program (ABAQUS) to simulate compaction responses of metal powders during cold isostatic pressing. Finite element results were compared with experimental data for pure iron powder under cold isostatic pressing.     

Densification of mixed metal powder at high temperature

Densification behaviors of mixed metal powder under high temperature were investigated. Experimental data of mixed copper and tool steel powder with various volume fractions of Cu powder were obtained under hot isostatic pressing and hot pressing. By mixing the creep potentials of McMeeking and co-workers and of Abouaf and co-workers originally for pure powder, the mixed creep potentials with various volume fractions of Cu powder were employed in the constitutive models. The constitutive equations were implemented into a finite element program (ABAQUS) to compare with experimental data for densification of mixed powder under hot isostatic pressing and hot pressing. Finite element calculations by using the creep potentials of Abouaf and co-workers agreed reasonably well with experimental data, however, those by the model of McMeeking and co-workers underestimate experimental data as observed in the case of pure metal powders.     

Near net shape processing of a sintered alumina component: adjustment of pressing parameters through finite element simulation

Near net shape forming of alumina powder by cold die pressing and pressureless sintering was investigated. From experimental data of triaxial compression test of alumina powder, a hyperbolic cap model with a critical state line was proposed for densification of alumina powder at room temperature. For pressureless sintering, the phenomenological model for densification and viscous behavior of alumina powder proposed by Kim and co-workers was used. The constitutive models were implemented into a finite element program (ABAQUS) to simulate densification of alumina powder under cold die pressing and pressureless sintering. Finite element results were compared with experimental data for density distribution and deformation of an alumina powder compact under cold die pressing and pressureless sintering. New conditions of compaction were then proposed to reduce the distortion of the sintered part.     

CALCULATION AND EXPERIMENTAL INVESTIGATION OF ELECTRIC FIELDS INDUCED BY ELECTRODES IN ELECTROSTATIC CHARGED POWDER SPRAYING TECHNIQUE

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高长径比粉末冶金零件成形过程的数值模拟

针对粉末冶金法生产高长径比产品尺寸变形大和产品精度低等问题,提出分段成形控制工艺。通过ABAQUS进行数值分析,采用更新的Lagrange方式和大变形弹塑性理论从Mises应力、节点位移、径向最远端密度分布方面进行对比,结果表明,该方法可有效提高密度分布均匀性,显著减小零件双向成形腰部尺寸偏小问题。与现有高长径比产品生产工艺进行对比,节省原材料并简化后续加工工艺。