熔融沉积快速成型喷头有限元辅助设计

对两种典型结构熔融沉积快速成型喷头中材料的压力场和速度场进行了有限元分析和实验验证.结果表明,外置喷嘴出口压力骤降,出丝阻力增大;喷嘴外置式喷头由于融化罐与喷嘴材料流动速度矢量的极度不一致,材料补充不及时,导致断丝现象;一体化喷头融化罐内材料流动速度矢量和喷嘴出丝方向一致,保证出丝顺畅.     

薄层复合材料的抗平头冲击特性研究

采用圆柱平头型冲头(直径为25mm)在一定的冲击速度范围内冲击薄层复合材料(厚度:1.50～2.50mm),利用加速度传感器分析复合材料冲击背面的应力动态变化情况,研究了影响复合材料抗平头冲击能力的因素和复合材料的冲击损伤过程。结果表明:影响复合材料抗平头冲击能力的主要因素是纤维织物本身特性、纤维含量和界面强度;冲击能量阀值决定复合材料冲击损伤模式和能量吸收过程;增加复合材料的刚性,提高复合材料的冲击变形范围可充分发挥吸能垫的作用。     

并联贮罐出液受堵问题分析及数值模拟

针对某加注系统在某任务过程中两台贮罐并联供液时其中一台发生出液受堵问题,为避免再次发生类似问题,建立系统物理模型,通过流体动力学连续方程和动能方程进行分析计算,找出了导致问题产生的主要原因。利用FLUENT仿真软件对两罐汇流区域进行数值模拟和结果分析,验证了并联贮罐出液受堵问题发生的根本原因,提出了针对性措施。     

浮动块硬盘磁头抛光机的运动学分析

通过对抛光盘摩擦驱动力矩和导轮阻力矩等影响因素的仿真分析计算,研究了各因素与抛光机运动学行为的关系。结果表明,转速比是主要的运动学行为,导轮的滚动摩擦系数和偏心距对抛光机转速比的影响比较大,偏心距需要和其它抛光因素协调选择。     

Experimental study on drilling basalt with self-vibratory drilling head

Based on the goal of improving the rock breaking ability when drilling asteroid rock samples under limited energy conditions, this paper proposes a method of drilling rock using self-vibratory drilling head and develops a small self-vibratory drilling head for drilling rock. In order to analyze the dynamic characteristics of drilling rock with self-vibratory drilling head, a rock model hypothesis that the rock consists of a series of micro-segment uniform continuous media is put forward. Base on the hypothesis, the model of drilling rock is constructed, the stability lobes diagram of self-vibratory drilling head drilling basalt is plotted, and the energy mechanism of drilling rock system with self-vibratory drilling head is discussed. The comparison tests of drilling basalt by three kinds of self-vibratory drilling head with different spring stiffness and the conventional method are carried out. The rotational speed is a variable in the comparative tests. The test results show that under the specific rotational speed and spring stiffness, self-excited vibration is produced in self-vibratory drilling head drilling basalt. When self-excited vibration drilling is conducted, although the amplitude fluctuation range of the drilling thrust force is wider than that of conventional drilling, the average drilling thrust force is smaller than the conventional drilling. The amplitude of drilling thrust force increases with an increase in spring stiffness. The method of drilling rock by self-vibratory drilling head is proved to be a potential method for viable drilling of asteroid rock samples.     

某磁头抛光技术

根据硬盘磁头加工的特点,分析了抛光机的运动学特性及抛光盘、抛光液、磨粒在抛光过程中的摩擦学行为等对磁头表面质量的影响。     

深孔变深拉槽工具头及拉槽刀的设计分析

本文就小孔径变深槽加工，所需要的拉槽工具头及拉槽刀进行设计分析并验证。     

Influence mechanism of machining angles on force induced error and their selection in five axis bullnose end milling

In the machining of complicated surfaces, the cutters with large length/diameter ratios are used widely and the deformation of the machining system is one of the principal error sources. During the process planning stage, the cutting direction angle, the cutter lead and tilt angles are usually optimized to minimize the force induced error. It may lead to a low machining efficiency for bullnose end mills, as the material removal rates are different largely for different machining angles. In this paper, the influence mechanism of the machining angles on the force induced error is studied based on the models of the instantaneous cutting force when the cutter flute traveling through the cutting contact point and the stiffness of the machining system. In order to evaluate the machining angles, the force induced error/efficiency indicator (FEI) is defined as the division of the force induced error and the equal volume sphere of the removed material. FEI is dimensionless, with the lower FEI, the lower force induced error and the higher machining efficiency. For optimal selection of the machining angles, the critical FEI is calculated with the constraint of force induced error and the desired material removal rate, and the critical FEI separate the set of the machining angles into two subsets. After the feed rate scheduling process, the machining angles in the optimal subset would have higher machining accuracy and efficiency, while the machining angles in the other subset have lower machining accuracy and efficiency. Through the machining experiment of five axis machining and freeform surface machining, the effectiveness and superiority of the proposed FEI method is verified with a bullnose end mill, which can improve the machining efficiency with the constraint of force induced error.     

A review of chatter vibration research in milling

Chatter is a self-excited vibration of parts in machining systems. It is widely present across a range of cutting processes, and has an impact upon both efficiency and quality in production processing. A great deal of research has been dedicated to the development of technologies that are able to predict and detect chatter. The purpose of these technologies is to facilitate the avoidance of chatter during cutting processes, which leads to better surface precision, higher productivity, and longer tool life. This paper summarizes the current state of the art in research regarding the problems of how to arrive at stable chatter prediction, chatter identification, and chatter control/suppression, with a focus on milling processes. Particular focus is placed on the theoretical relationship between cutting chatter and process damping, tool runout, and gyroscopic effect, as well as the importance of this for chatter prediction. The paper concludes with some reflections regarding possible directions for future research in this field.     

爆震发动机超声速进气道的非定常耦合流场数值研究

采用带化学反应的非定常数值仿真方法,对爆震发动机(PDE)内进气道、燃烧室、尾喷管的耦合流场进行了分析,并着重研究了爆震压力波及其反射波对超声速进气道内流动结构的非定常干扰过程,对比了3种进气道/燃烧室耦合方式下进气道流动特性的差异.结果表明:通过在燃烧室内填充以化学恰当比预混的燃料和氧化剂,数值仿真可获得稳定自持的爆震波.在爆震波压强作用下所产生的结尾波系和反射激波会发生耦合干扰作用,它们在流道内的运动传播影响了结尾波系的前传幅度.通过对比不同进气道/燃烧室耦合方式的流场特征发现:采用突扩式进气道/燃烧室连接段可利用燃烧室头部固壁的阻碍以及其对爆震高压波的反射作用将大部分的压缩气体存储于燃烧室内,进而减弱进气道与燃烧室之间的耦合干扰作用,对提高进气道的工作稳定性有利.另外,内凹式燃烧室头部段的引入还为压缩气体提供了额外的存储空间,故可以进一步缓冲爆震高压,提高进气道的稳定工作裕度.