Machinability enhancement of stir cast Al-TiCp composites under cryogenic condition

The current research work makes an attempt to develop a methodology in order to produce high-quality Al-TiC_p composites by using systemized inert atmospheric stir casting facility. The quality of produced composites was characterized using microstructural, Energy-dispersive X-ray spectroscopy (EDX), and machinability studies. Atomized-Cryogenic-Liquid (ACL) spray machining technique was developed and used to enhance the machinability of composite. The results of microstructural analysis reveal that TiC_p refines Al grain structure to 50 times lesser than non-reinforced Al grains along the full length of the casting. Energy-dispersive X-ray analysis confirms that no metallic reaction takes place. Machining studies reveal that atomized cryogenic liquid-spray machining significantly improves the quality of machined surface and reduces the progressive wear occurring on tool during turning of Al-TiC_p composites in comparison with cryogenically chilled argon, wet, and dry machining conditions, respectively. The scientific methodology highlighted in this study helps to improve the productivity and reduces the manufacturing cost in various industrial applications.     

数据库系统原理课程中性能调优实验的设计与实践

论述了浙江大学计算机科学与技术学院采用数据库性能调优作为课程实验内容,分析讨论实验的过程、要求和内容安排等。性能调优是数据库系统应用开发的一项重要工作,具有实践性强、综合知识要求高等特点,非常适合于在探究型教学中作为实验内容。在本科生的数据库课程教学中进行了实践,取得了较好的效果。     

Optimization of multi-task turning operations under minimal tool waste consideration

Most of the literatures on machining economics problems tend to focus on single cutting operations. However, in reality most parts that need to be machined require more than one operation. In addition, machining technology has been developed to the point that a single computer numerical control (CNC) machine is capable of performing multiple operations, even simultaneously, employing multiple spindles and cutting tools. When several operations are performed on a CNC turning machine, various tools are required for the cutting operations. Determining the life of these cutting tools under different machining conditions is an arduous task for the operators. They usually replace the tools based on their experience or according to the specific cutting tool handbook. Frequent tool replacements may result in wasted tools and tool utilization, while infrequent tool replacements may result in poorly machined parts. In this study we propose a mathematical model in which several different turning operations (turning, drilling, and parting) with proper constraints are performed. The issue of tool replacement is taken into account in the proposed cutting model. In addition, an evolutionary strategy (ES)-based optimization approach is developed to optimize the cutting conditions of the multiple turning-related operations while taking into account the minimizing unit cost criteria under the economical tool replacement strategy.     

椭球面上螺纹的加工工艺分析

通过研究椭球面上螺纹的参数化编程与加工过程,利用F ANUC 0i Mate-TC数控系统提供的宏程序编程功能,编制出了具有通用性、适用性的椭球面上螺纹的数控加工程序。该技术使用简单,只需在主程序中对相关变量进行赋值即可完成所需椭球面上螺纹的加工,能有效地保证椭球上加工螺纹的准确性,提高产品的尺寸精度和表面质量。     

A parameter uniform B-spline collocation method for solving singularly perturbed turning point problem having twin boundary layers

A numerical scheme is proposed to solve singularly perturbed two-point boundary value problems with a turning point exhibiting twin boundary layers. The scheme comprises B-spline collocation method on a non-uniform mesh of Shishkin type. Asymptotic bounds are established for the derivative of the analytical solution of a turning point problem. The present method is boundary layer resolving as well as second-order accurate in the maximum norm. A brief analysis has been carried out to prove the uniform convergence with respect to the singular perturbation parameter ? by decomposing the solution into smooth and singular components. Some relevant numerical examples are also illustrated to verify computationally the theoretical aspects.     

变现闲置设备盘活闲置资产

文章就国有大型企业在改制及生产线改造过程中出现大量闲置设备的问题进行讨论,为使国有资产保值增值,本企业采取一种积极盘活闲置设备的有效办法,文章介绍了对设立企业设备管理基金、解决企业设备管理工作缺乏专项资金问题的具体做法.     

关于国标中剖视图内容不断完善的分析与建议

运用逻辑学关于“划分”、“概念间的关系”和“下定义”的有关原理,分析了近30年中国家标准中关于剖视图分类演变的进程,对剖视图的分类趋向科学性予以肯定,指出近代国标中关于剖视图分类存在的问题。在此基础上,阐明符合逻辑学的剖视图定义结构,并对剖视图标注中剖切符号的图示提出了改进建议。使得各类剖视图的定义更确切、科学,表达更方便、明了,绘图更容易。     

利用电流变液阻尼器改变切削系统特性的研究

为了进一步对先前研制的一种基于电流变液阻尼器的切削颤振抑制结构进行系统的研究,对其静态和动态特性进行了实验和理论研究。结果证明,这种结构可以显著改变车刀刀杆的固有频率、阻尼性能等动态特性和静态特性,在零电场下刀杆的静柔度约0.5μm/N,电场强度为1.5kV/mm时减小到约0.3μm/N,2kV/mm时减小到约0.2μm/N;在零电场时刀杆的加载和卸载曲线是大致重合的,近似一纯弹性体;而在电场强度为1.5kV/mm和2kV/mm时加载与卸载曲线包绕的面积都明显增大;刀杆的阻尼比在3kV/mm时为0.05127,而1.5kV/mm和0kV/mm时分别为0.02882和0.02163。动柔度曲线显示:随着电场强度的增大,结构的阻尼比增大,共振峰值减小。利用这种结构具有可控动态性能这一优点,可以在线对机床车削振动进行有效控制。     

河北省地下水降落漏斗修复

通过对河北省地下水超采状况分析,指出南水北调中线工程的尽快实施是降落漏斗修复的水源保障。农业节水、污水资源化和科学调蓄利用汛期雨洪资源是降落漏斗修复的主要途径。     

凸圆弧前刀面车刀微量切削机理

研究了凸圆弧前刀面车刀微量切削机理，实验证实了该刀具在微切深和小进给量的工作情况下，切削均匀而连续，在加工逆性材料时，可获得连续不断的丝状切削，且能获得较小的表面粗糙度。