工艺参数对固体自由成型工艺中陶瓷膏体挤出过程的影响

基于陶瓷膏体挤出的固体自由成型(SFF)技术是复杂陶瓷零件制造技术的重要发展方向,膏体挤出过程的控制对SFF陶瓷零件制作工艺至关重要.研究了挤出速度和挤出口尺寸对水基膏体挤出过程的影响,结果表明:挤出压力随挤出速度和挤出口长度的增加而增大,挤出体液相含量在速度较低时偏离初始值,发生了液相迁移现象;挤出压力图和液相迁移的发生存在一定的关系;在挤出速度为0.15 mm/s,挤出头长度和直径分别为12～18 mm和1mm的情况下,膏体挤出过程不发生液相迁移现象,可用于陶瓷零件的SFF制造工艺.     

An investigation of fracture criteria for predicting surface fracture in paste extrusion

In the extrusion of pastes, fractures may be found on the surface of product. Such fractures compromise strength and are often unacceptable aesthetically. Here some theoretical criteria for predicting the onset of surface fracture, using the elastic–plastic finite element method are evaluated and the success of these criteria in predicting recent observations is assessed. Two criteria based on stress fields successfully predicted an increase in the depth of fracture cracks with extrusion ratio. However these criteria, which are dependent on the deforming zone stresses and extrudate residual stresses, respectively, do not successfully predict the increase in fracture with increasing die entry angle observed experimentally. Three criteria based on ductile fracture are also investigated and difficulties associated with their accurate evaluation in extrusion problems highlighted. However, all three successfully predict the increase in fracture with increasing die entry angle. In considering the effect of extrusion ratio on surface fracture, two of these criteria should be at least qualitatively correct while for the third this is unlikely.     

Improvement of mechanical properties of Al6061 extrudate by die cooling with N2 gas during hot extrusion

In this study, the mechanical properties of the extrudate are improved by correcting the defects such as abnormal grain growth (AGG). Die cooling with N₂ gas is conducted to control the extrusion temperature during the hot extrusion of Al6061 in order to obtain fine grains of the extrudate. Computational fluid dynamics (CFD) is conducted to evaluate the effect of die cooling with N₂ gas and to determine the relationship between AGG and the extrusion temperature. The optimal cooling channel with a high cooling effect is designed by using the design of experiment (DOE) method, and thermo-mechanical analysis is performed to predict the extrusion temperature. A hot extrusion experiment is also carried out to measure the extrusion temperature and to observe the microstructure of the extrudate. The extrusion temperature predicted from the thermo mechanical analysis is found to be in good agreement with the measured extrusion temperature. The process condition required to reduce the AGG is determined on the basis of the distribution of the evolved microstructure in the hot extrusion experiment. The results confirm the relationship between the distribution of AGG and the mechanical properties of the extrudate. It is confirmed that the mechanical properties of Al6061 can be improved by the application of die cooling with N₂ gas during the hot extrusion process.     

无源MEMS压力开关的设计与制备

为了克服传统机械式和电子式压力开关的体积大、制作工艺复杂以及不易与后续电路集成等缺点,论文采用具有金属引线台阶覆盖能力的玻璃浆料封装技术进行了无源MEMS压力开关的设计和制备。设计的无源MEMS压力开关的整体结构方案主要包括硅盖板上的压力敏感膜、硅岛、上电极和微阻挡凸台以及玻璃基底上的玻璃浆料和下电极。通过仿真优化了压力敏感膜、硅岛和上下电极的关键尺寸。经过三次湿法腐蚀工艺流程制得了双阻挡凸台、硅岛和感压膜片。通过玻璃浆料热压工艺将硅盖片、玻璃基底和金属引线三者键合成一体,工艺结果显示双阻挡凸台的高度和感压膜片的厚度很好地控制在8μm和50μm,而且经测试,MEMS压力开关的阈值压力为125kPa。     

出口压力容器制造的检验控制

介绍ASME U、U2标准证书对出口压力容器产品质量控制要求及实施方法,重点介绍焊接工艺流程图以及过程控制表的制作要点。     

Micro fabrication using electro deposition and ultrasonic acoustic liquid manipulation

We report improvement of the acoustic liquid manipulation (ALM) assisted electroplating process for micro fabrication. We refined the process and were able to achieve a plated dot size of 0.031 inches, using highly backed ultrasonic transducers. This potential tool-less fabrication (TLF) technique will reduce the need for masking and can be used for rapid prototyping of microstructures. We report the plating of copper on steel plates. An ion-depleted layer is formed at the cathode when the electroplating process starts, thus forming a natural mask. A fine stream of fresh electrolyte formed by acoustic streaming by an ultrasonic transducer is directed to refresh the ion-depleted layer at the cathode. This causes the plating process to continue at a localized point. The thickness of the plating increases with time. The process can be automated by mounting the transducer assembly on a three dimensional control system. This will enable rapid fabrication of three dimensional micro structures and shapes by the direct writing method.     

连续挤压机成型压力的实验研究

连续挤压生产过程中,压实轮压下量是一个至关重要的参数.压下量过大会加剧设备的磨损,降低使用寿命;压下量过小会导致"闷车现象".连续挤压机成型压力直接反映出压下量的大小.提出用应变电测法测量连续挤压机压实轮的压下力,以替代当前采用的理论计算法,对进行的连续挤压机挤压过程数值模拟有很好的指导意义.     

薄膜生产线挤出压力自校正预测控制

挤出机压力控制是薄膜生产线中非常重要的一个环节,挤出压力的稳定与否直接导致薄膜产品的质量.针对实际生产中挤出机压力复杂的非线性特性,提出了一种基于自校正预测的快速控制算法.根据生产线的实际情况,系统进行周期递推参数辨识,最终完成对挤出压力的准确和快速的控制.实际运行结果表明了该方法的有效性和优越性.     

Factors influencing the durability of chrome plate

The bores of many cannon tubes are electroplated with chromium. This is done to provide better resistance to erosion and wear and in the case of naval guns to provide corrosion resistance as well. The resistance of chrome plate to erosion and wear is so good that there is little or no wear of the bore until the chromium begins to spall off the steel substrate. In the present research the effects of various factors on the durability of the plate were investigated using a geared roller test machine. It was found that the important stress is the shear stress in the plane normal to the direction of rolling rather than the maximum shear stress; this corresponds to the maximum shear strain. This result has application to the subcase fatigue or “case crushing” failure of case-hardened gears. The failure on repeated loading was found to be in the substrate steel immediately below the interface rather than at the interface itself. The durability of the plated surface decreased by about half as its thickness was increased from 0.15 to 0.41 mm although most or all of this can be attributed to the increased shear stress near the interface for the thicker electroplates. It was also found that residual compressive stress in the substrate steel had a great effect on durability; even the mild residual compressive stress introduced into the steel surface by sand blasting before plating increased durability many-fold. Finally it was found that a bainite microstructure rather than the usual tempered martensite caused a significant decrease in durability.     

钬激光碎石术中结石位移的影响因素

为了减小钬激光碎石术中结石产生的位移,研究了钬激光脉冲峰值功率、激光烧灼尺寸和工作距离对于结石位移的影响。分析了影响结石位移的因素,搭建了一个体外模型装置以此来模拟输尿管内钬激光碎石的过程,实验使用0.25 g的正方体石膏模型来代替人体结石,钬激光功率选择12 W(0.6 J×20 Hz,0.8 J×15 Hz,1.2 J×10 Hz)和20 W(0.8 J×25 Hz、1.0 J×20 Hz、2.0 J×10 Hz),脉冲持续时间为200μs和800μs,光纤使用272μm以及550μm,工作距离从0~5 mm。最后,将体外模型置于水中,在室温进行实验。实验结果表明,结石位移随着脉冲峰值功率的增大而增大;较长的脉冲持续时间可以减小16.95%~27.27%的结石位移;272μm的光纤相比于550μm的光纤能够减少35.59%~54.17%的结石位移;增大工作距离可以减小结石位移,同时降低消融效率,但当结石模型与光纤顶端接触时,会产生吸附挣扎的现象。上述结论为改进国产钬激光器设计以及钬激光参数精细化设置提供了参考,对于临床手术有借鉴意义。     

手性E型胆甾相液晶薄膜的制备与偏振特性研究

制作出一种厚度为30μm的手性E型胆甾相液晶薄膜,通过原子力显微镜测试显示其螺距为364nm。使用He-Ne激光对其出射光的偏振特性及左右圆偏振光透射特性进行测试,结果表明手性E型胆甾相液晶表现出较强的左圆偏振光透射特性,其左右圆偏振光透射比为1∶0.4。     

On the stress distribution in prestressed extrusion dies under non-uniform distribution of internal pressure

Cold extrusion die stress distribution is normally calculated on the assumption that there is a uniform distribution of internal pressure, e.g. by application of the Lamé equations. With FE-analysis this assumption can be overcome by the introduction of arbitrary boundary conditions. However, as little information existed about realistic distribution of radial and axial stresses in container and die this possibility was not used very much. Only after a recent investigation of Bay [1] into friction and pressure distribution in forward extrusion an FE-calculation of stresses in a prestressed extrusion die under non-uniform distribution of radial pressure seemed to be promising. The results show very clearly that no negative effects on the stress state—e.g. increase of stress peaks—may be expected in case of combined continuous decrease of radial pressure in the container and discontinuous increase at the die entry.     

影响毛细管电泳分离生物大分子的因素

目前毛细管电泳在分离方面的应用越来越广泛,但重复性一直是制约其应用的主要问题。随着毛细管电泳技术的发展,影响毛细管电泳结果的因素也发生着变化。本文对影响毛细管电泳分离生物大分子的因素进行综述,希望对使用毛细管电泳的使用者者有所帮助。     

The influence of temperature and preheating time in extrudate quality of solid-state recycled aluminum

Recovering waste metal without the need for remelting in solid-state recycling of metal chips can create green production. The overall process of solid-state recycling should be run at the lowest possible cost to remain competitive. High temperature and prolonged preheating time for billet’s homogenization in hot extrusion to consolidate the chips conflicts with the aim of minimizing energy usage. Therefore, optimizing the effect of preheating temperature and time prior to hot extrusion is important. This study investigates the effects of preheating temperature and preheating time on the extrudates’ quality. Milling chips of AA6061 were cold compacted and hot extruded through a flat-face die using preheating temperatures of 400, 500, and 550 °C for 1–6 h of preheating time. The mechanical and physical properties and microstructure of the extruded profiles were compared. The results revealed that higher acceptable strength and ductility were obtained at 500 °C with 2 h of preheating time. On top of that, temperature increase was the main criterion that results in the highest tensile strength; nevertheless, it was subjected to trade-off in ductility. The profile extruded at 500 and 550 °C had gained a close tensile strength. The study includes the prediction of the chip’s welding quality through the damage evolution on the extrudate’s structure. It was implemented with the help of DEFORMTM 3D finite element method (FEM) software, and the normalized Cockcroft and Latham (C & L) fracture criterion was chosen. The results of the simulations were compared and validated by the experimental results.     

Factors influencing the wearing out of a sniper bore

This article shows the influence of the physical-mechanical, chemical, and geometric factors on the wearing out of the bore of sniping weapons. The complex interconnection of the surface failure process parameters is shown.     

分布式光纤测温系统分辨率影响因素研究

应用分布式光纤测温系统对船舶电力系统进行在线监测时,由于船舶电缆的特殊运行环境,对测温系统的空间分辨 率和温度分辨率提出了更高的要求,而在基于拉曼散射双路解调的分布式光纤测温系统中,系统的空间分辨率、温度分辨 率、时间分辨率和测温距离相互制约。 为设计满足船舶电力系统在线监测需求的测温系统,分析了系统空间分辨率的影响 因素,并在此基础上建立了基于光时域反射技术的分布式光纤测温系统的等效模型,分析了不同影响因素之间的主次关系; 基于拉曼散射光强度公式推导出了准确性更高的系统温度分辨率影响模型;在此基础上得到了空间分辨率、温度分辨率、时 间分辨率和测温距离之间的相互影响公式,为分布式光纤测温系统的性能指标设计提供了参考,在测温距离较短时,通过进 一步增大累加次数和减小泵浦光脉宽,可在保证空间分辨率和时间分辨率的条件下提高空间分辨率。 搭建实验平台对所提 出的方法进行验证,通过调节累加次数和脉冲宽度在 500 m 的测温距离达到了温度分辨率 0. 65℃ 、空间分辨率 1 m、时间分 辨率 1 s 的分辨率指标。     

冷冲压钢球组合模具过盈组装挤压力的计算

依据材料的塑性变形原理,详细地计算了组合模具装配时所需要的挤压力大小,进而阐述了验算有关丝杠螺母副设计时参数选择正确与否所遵循的原理。     

工程化光纤光栅液体压力传感器的研制

液体压力是流体压力管道结构的重要荷载,传统的液体压力传感装置无法满足长期监测对其稳定性与耐久性的要求.基于双光纤光栅感知原理,针对某重点工程项目的环境条件,设计开发出了一种满足工程应用需求的液体压力传感装置,给出了详细的理论分析,并通过大量的标定试验分析了该装置的传感特性,理论与实验数据吻合很好,相差小于3％.根据随机抽取的100个传感器的标定数据,采用统计分析方法得到了该类传感器的各性能指标:测量范围0～2.5 MPa,分辨率＜0.4％F·S,迟滞＜2.4％F·S,重复性＜2.3％F·S,线性度＜2.1％F·S,总精度＜4％F·S,结果表明该传感器具有温度自补偿、线性度和重复性好、精度较高等优点,适合压力管道结构液体压力测试,具有良好的应用前景满足实际工程需要.