Centrifugal casting of an Al-12Si-2Mg/Al2O3-particulate MMC. Part II: Evaluation of soundness and structure

A technique for the preparation of an MMC using centrifugal casting has been developed and tested for its feasibility in preparing Al-12Si-2Mg/Al₂O₃- particulate composites. The process is evaluated by observing the structure, measuring the homogeneity in the distribution of the ceramic particles, the porosity type and distribution, and by analysing the metal/ceramic interface for possible reactions.

The different processing conditions applied are: rotational frequency 16, 22.7 and 33.3 Hz (960, 1360 and 2000 rpm), Al₂O₃ particle size 30, 47, 60 and 89 μn, melt superheat 20, 100 and 150°C, specimen radius of rotation from 145 to 180 mm.

Because the ceramic particles are close packed, a uniform particle distribution with no agglomeration is obtained, and the interparticle distance depends only on the alumina particle size. The metal/ceramic interface was sharp with no reaction. Microporosity is observed in some locations due to incomplete infiltration between the alumina particles. Increasing rotational speed, particle size, superheat, and radius of rotation help to decrease the microporosity. The macrostructure along the composite length showed columnar grains followed by equiaxed grains. The type and size of the structure depend mainly on the composition of the matrix and not on the presence of the alumina particles.     

塑料异型材挤出模具CAPP系统的开发研究

通过对塑料异型材挤出模具产品的归纳与整理，实现了其结构的标准化，并在此基础上构建了塑料异型材挤出模具CAPP系统框架，实现了挤出模具零件工艺设计的自动化、规范化。     

基于实时监控的金属结合剂金刚石微粉砂轮电火花精密整形

采用金属结合剂超微细粒度超硬磨料砂轮实现硬脆材料的ELID(Electrolytic In—process Dressing在线电解修整)精密与超精密磨削是一项加工新技术。金属结合剂砂轮具有很高的强度、硬度及良好的耐磨性,但修整困难。与普通磨削砂轮不同,金属结合剂金刚石微粉砂轮的修整分为整形和修锐两个阶段。本文开发了基于组态软件LabVIEW的数据采集系统,研究了基于实时监控的金属结合剂金刚石微粉砂轮电火花精密整形技术。结果表明砂轮旋转周期中的放电电流曲线是否呈现局部放电特征可以作为新设定电参数是否具有加工能力的判据。砂轮整形过程中的放电电流曲线是否达到平滑,即是否出现周圈放电现象可以作为其是否还具有整形能力的判据。对于圆跳小于10μa砂轮精密整形来说,仅靠观察火花状况实施进给难以避免空载、拉弧甚至短路现象。通过整形电流波形的实时监控不仅可以方便地获取有效加工电规准,而且很容易避免极间短路现象、鉴别非正常工作状态。金属结合剂微粉砂轮的整形精度和效率不仅与电规准有关,而且受到电极形状、工作液的绝缘性能及最小进给量值的影响。实验表明以电解液作为工作液、采用平面电极,选定合适的电规准,W10微粉金刚石砂轮最终的整形精度可达到圆跳小于2μm、锥度误差在1μm以内,平均整形效率约0．95μm／min。     

四角螺母级进模设计

针对零件需多次拉伸、冲孔、翻边、倒角、切边弯曲等工序 ,成功地设计和制造了1副级进模 ,合理地选用了模具材料,满足了四角螺母大批量生产的要求 ,可为类似零件的成形提供参考。     

漏斗式自动送料弯曲模设计

介绍了在通用冲床上使用的漏斗式自动送料弯曲模的结构形式、工作过程和设计要点。该模具采用漏斗式半自动送料装置,用于弯制各种V形、U形和弓形工件,适合大批量生产。     

熔座夹切口成形模设计及改进

介绍了熔座夹零件成形模由多副模具到1副模具的设计改进过程及其结构、模具工作过程和主要模具零件的设计 ,并提出了模具设计及制造时应注意的事项。该模具提高了生产效率和工件质量 ,有较好的经济效益。     

电机铁芯冲片模冲槽废料回跳问题分析与解决

分析了电机铁芯冲片上嵌线槽在高速冲制过程中废料回弹的原因 ,并从凸、凹模结构形式及润滑油的使用等方面介绍了解决废料回弹的方法。     

翅片模开条子模结构的优化设计

针对翅片模开条子模制造周期长、拆卸不便、片形不容易调整、精度很难保证等问题 ,通过对原模具结构的探讨与分析 ,设计出1副结构合理、拆卸方便、尺寸位置精度很好保证、开条刀间隙很容易调整的开条子模 ,解决了原模具存在的问题     

定、转子冲片级进模维护要领及常见故障的排除

通过对电机定、转子片级进冲模结构形式的分类、凸模、凹模常见的固定方式的介绍，阐述了电机定、转子片级进冲模模具在日常使用中的维护和保养要领。重点介绍了凸模、凹模的更换程序，卸料板的安装程序，以及模具在使用中常见故障原因的分析和排除方法。     

Microstructure Transformation in the Welding Heat Affected Zone of 800MPa Grade Ultra Fine Structured Steel

The transformation behavior and microstructure development in the heat affected zone (HAZ) of 800MPa grade ultra fine structured steel was investigated. It was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates, with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the .fast cooling regime. At relatively high cooling rates, which corresponded to low heat inputs, the hardness o.f the simulated HAZ was above that of the base metal. When the cooling rate was below 9℃/s, the welding HAZ would have an obvious softening. The analysis of transformation rates in continuous cooling processes was completed by numerical differential method. The result indicated that the microstructure transformation rate o.f the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time t8/5 is longer than 7s.