【作者】 陈春沐；

【导师】 唐勇军；

【作者基本信息】 广东工业大学 ， 机械制造及其自动化， 2012， 硕士

【摘要】 随着现代科技和现代工业的发展,高速度、高精度、耐高压、耐高温、小型化的产品被越来越多的应用于各个领域。其所用硬脆性难加工材料如硬质合金、钛合金、淬硬钢、工程陶瓷、光学玻璃、硅晶体、宝石、刚玉等,由于材料本身机械加工性能差、传统方法的加工效率低、质量差、成本高,极大的限制了此类材料的推广和应用。旋转超声加工不依赖于材料的导电性,热物理作用小,可有效避免热损伤和微细龟裂的产生,故旋转超声加工技术在陶瓷、硅等硬脆材料加工方面有着得天独厚的优势。超声振动系统主要由超声变幅杆、工具头和换能器组成。可以将超声电源输出地高频震荡电压转换成高频的机械振动,从而对工件进行加工。目前,旋转超声加工材料去除机理还没有定论,其原因是工具做高频振动(>16KHz),工具振幅太小(<100μm),无法直接观测到材料的去除过程。因此有限元仿真的方法成为解决这一问题的有效手段。旋转超声加工通孔时,出口处经常出现崩边现象,严重影响工件加工质量。崩边原因是工具与工件直接接触,在加工最后阶段,由于孔内工件剩余材料很少,加之工件底部支撑位置在孔的外侧,因此在孔内径周围容易产生较大的应力集中,从而断裂产生崩边。为了预测裂纹的扩展方向,找出影响裂纹方向的因素,本文首次将扩展有限元理论引入超声加工中,对加工中裂纹生长的方向进行模拟。本文的主要研究内容有以下几个方面：1、根据变截面杆的一维振动理论,对换能器、变幅杆和工具的尺寸进行设计,总结了一套完整的设计公式；对设计的超声振动系统进行模态分析,并对工具磨损、工具直径变化对超声振动系统谐振频率的影响进行分析；最后对超声振动系统的制造,总结一套装配流程。2、着重讨论加工过程中材料去除的理论模型,包括锤击(在超声振动冲击下的压痕和碎裂)、磨蚀(切削工具的旋转运动可以模型化为磨削过程)和抛磨(或撕扯)作用(由超声振动和工具旋转运动的同时作用产生的)。运用动力学有限元软件LS-DYNA分别建立了单颗立方体和球型磨粒旋转振动冲击工件的模型对单颗磨粒旋转加工工件的过程进行仿真。仿真以最大主应力为断裂准则,应用生死单元的方法获得了工件被加工后的材料去除情况以及表面应力分布。3、首次提出将扩展有限元(XFEM)理论应用于旋转韶声加工裂纹预测领域。详细介绍了XFEM理论,并模拟了陶瓷试件三点弯曲试验中裂纹的扩展,得到与实相吻合的结果。根据实际加工参数,对在陶瓷工件上旋转超声加工通孔出现的出口崩边现象进行了模拟,将得到的裂纹扩展形貌和实际加工结果对比。4、针对实际旋转超声加工过程中出现的入口崩边现象设计实验,获得了减少崩边现象的加工工艺参数。更多还原

【Abstract】 As the development of modern industrial and scientific experiments, industry products with high precision, high pressure and temperature resistance and small-scaled are more and more applied in various fields. Because the materials of these products such as carbide, stainless steel, engineering ceramics, optical glass and crystal are hard to be processed and coast too much, so the application of hard brittle are limited. does not depend on the conductivity of the material, and generates only a few heats, so thermal damage and micro-cracking is avoided. Therefore, Ultrasonic machining has uniquely advantages in hard brittle materials machining.Ultrasonic vibration system is mainly composed of ultrasonic transducer, ultrasonic horn and tool. It can convert the high-frequency oscillatory voltage into high frequency mechanical vibration to process the work piece.At present, the material removal mechanism of rotary ultrasonic vibrate machining (RUM) has not being a conclusion. Because vibrate frequency of the tool is too high (>16KHz), and the amplitude of the tool are too small that people can not directly observe the material removal process. Therefore, the finite element simulation method becomes an effective means to solve this problem.When using rotary ultrasonic machining processing a through-hole, there always being an edge chipping in the export. The reason is that tool directly contacts work piece, and when the remaining material in the hole is few, and coupled with the support position of work piece is near the bottom of the hole, there always be a big stress concentration around the edge of internal diameter. To predict the crack propagation direction and identify the factors that will affect the crack direction, this paper for the first time applies extended finite element method (XFEM) to rotary ultrasonic vibration machining in order to predict the crack propagation direction.The main contents of this paper are as follows,1、According to one-dimensional vibration theory of variable cross-section bar, the dimension of rotary ultrasonic vibration system is designed, and a set of calculation formula is summarized. Then the model of RUM system designed by the above mentioned dimension is model analyzed. The effects of resonant frequency caused by tool wear and tool diameter change are analyzed.2、Theoretical model of material removal include impact, abrasion and torn is focused. LS-DYNA finite element software is used to imitate the processing of RUM. The simulation follows the max principal stress fracture criterion. The surface stress distribution is get.3、This paper for the first time applies extended finite element method (XFEM) to rotary ultrasonic vibration machining in order to predict the crack propagation direction. Crack propagation of three-point bending test imitated and get the result coincide with the actual. Edge-chipping appeared in ultrasonic machining through-hole is simulated using XFEM, and get the crack direction coincide with the actual very well.4、According to the phenomenon of edge-chipping in RUM, an experiment is designed to investigate parameters to reduce edge-chipping.更多还原