【作者】 路家斌；

【导师】 阎秋生；

【作者基本信息】 广东工业大学 ， 机械制造及其自动化， 2011， 博士

【摘要】 随着微机电系统的应用和进一步发展,微尺寸零件的需求迅速增加,硬脆材料微结构的精细加工要求越来越高,微细加工技术是硬脆材料微结构微细加工的关键。作为一种智能材料,电磁流变液综合了电流变液和磁流变液的优点,在电场和磁场同时作用时,能够产生“协同效应”,造成屈服应力高于单独电场和磁场作用下的屈服应力甚至其总和。本文基于电流变抛光和磁流变抛光原理,提出了电磁流变协同效应微磨头加工方法,研制了相应的试验加工装置,采用定点加工方法试验研究了工艺参数的影响,建立了微磨头中固相粒子(包括分散粒子和磨粒)的受力模型和材料去除模型,深入研究了电磁流变协同效应微磨头加工的电磁耦合协同作用机理。基于电磁流变协同效应的微磨头加工方法,是将磨料混入电磁流变液形成抛光液,以导电和导磁材料制作锥形工具,在锥形工具和工件之间形成高压电场和磁场,在电磁耦合场作用下锥形工具端部形成电磁流变效应微磨头,利用电磁流变液的“协同效应”来控制电磁流变效应微磨头的性能,实现硬脆材料的高效抛光和微量去除。针对绝缘性较差的水基电流变液无法形成稳定电流变效应的问题,深入分析了电流变效应的形成机理,提出了隔离电极的电流变效应加工方法和装置,改进后的电流变效应微磨头加工装置能形成良好的电流变效应,具有较好的加工效果。根据电磁流变协同效应微磨头加工原理,研制了电磁流变协同效应微磨头加工试验装置,可以实现电场与磁场不同方向叠加以及对硬脆材料工件的定点加工和轨迹加工,满足加工试验要求。采用电磁流变协同效应微磨头定点加工方式对玻璃材料进行了试验研究。随外场强度增大、加工时间延长、初始间隙减小,电磁流变协同效应微磨头的去除能力增强,工具速度对加工效果的影响取决于微磨头切削速度和离心力的共同作用。电磁流变抛光工作液中混入的磨粒对电磁流变效应微磨头的链串结构有显著影响,磨料种类、粒度和浓度等均影响到电磁流变效应微磨头的性能及材料去除能力。磨粒的添加能显著提高材料去除效率,但磨粒浓度增大到一定程度后,材料去除量的增速趋缓。在材料去除效率方面,磨粒的硬度起着关键因素,磨粒硬度越大,材料去除效率越高,但硬度较小的磨料可以得到粗糙度较小的加工表面,磨料的粒度和密度会影响微磨头链串结构稳定性,最佳的磨料粒度和密度需要根据电、磁场强度和分散粒子的大小来优化。基于固相粒子的极化理论,推导了电磁流变液中固相粒子之间的电、磁场作用力计算公式,利用Ansys软件进行了电、磁场分布情况仿真,采用叠加法建立了固相粒子在电磁流变协同效应微磨头中的受力模型,在此基础上,建立了工件表面的抛光压力计算模型和材料去除模型。根据材料去除模型计算出的轮廓与定点加工试验得到的工件加工截面轮廓曲线形状一致,证明了建立的材料去除模型的正确性。通过电磁场耦合状态下的加工试验和微磨头中固相粒子链串间作用力的计算,改进了电磁流变协同效应微磨头中固相粒子在工具旋转时的受力模型,揭示了电磁耦合协同加工作用机理和微磨头的形成机理。在电磁流变协同效应微磨头加工中,微磨头中固相粒子在电磁场耦合场中受电场力、磁场力以及洛伦兹力产生的自旋力偶的共同作用维持链串的动态稳定性,其中电场力和磁场力维持固相粒子链串结构的稳定性,自旋力偶产生的固相粒子的原位振动会影响链串结构的稳定。但固相粒子的原位振动对材料去除具有双重作用,一方面原位振动会对工件表面产生冲击,对材料去除有很大的促进作用,另一方面若链串固相粒子间连接力较弱或自旋力偶较大时,会对链串造成破坏,降低了材料去除能力。当电、磁场力相近并与自旋力偶相匹配时,电磁流变效应微磨头加工有很好的协同作用效果。为进一步验证电磁流变协同效应微磨头加工的电磁耦合协同作用机理,进行了工具旋转和工作台旋转两种加工模式的正交试验对比。在工具旋转加工模式下,由于磁场中存在移动的电流变效应偶极子而产生洛伦兹力,在洛伦兹力产生的自旋力偶的作用下固相粒子链串会发生原位振动,促进了材料去除,相比于工作台旋转加工模式材料去除深度明显较大。电磁场耦合方式对电磁流变协同效应微磨头加工的加工效率有决定性影响,在本文试验条件下,高电场电压、低励磁电压条件下具有较好的电磁流变协同效应。更多还原

【Abstract】 With the development of the micro electro mechanical systems (MEMS) technology, the demand for micro apparatuses made of hard brittle materials, which have miniature size, complex shape and high surface quality, is increasing. Micromachining is the key supporting technology that has to be developed to meet the increasing accuracy requirements of product miniaturization and industrial realization of nanotechnology. As a new type of smart materials, the electro-magneto-rheological (EMR) fluid combines the characteristics of both the electrorheological (ER) fluid and the magnetorheological (MR) fluid, and exhibits not only the ER effect but also the MR effect under the applied fields. In particular, the EMR fluid can produce a synergistic effect under an electro-magnetically coupled field, which exhibits that the shearing stress of the EMR fluid can be increased more than the combination of the shearing stresses under the electric or magnetic field.Based on the machining principles of ER finishing and MR finishing, an EMR synergistic effect-based tiny-grinding wheel finishing (EMR finishing) method is presented. In the EMR finishing, the EMR fluid dispersed with micron-sized finishing abrasives is used as a polishing fluid to form a flexible EMR tiny-grinding wheel at the end of the cone-shaped tool when an electro-magnetically coupled field is applied, and the machining performance of the EMR tiny-grinding wheel can be controlled effectively by using the EMR synergistic effect. The EMR finishing can employed to polish the surface or machine the microstructure of brittle materials with a high efficiency.To solve the problem that the water-based ER fluid with poor insulating property cannot form a stable ER effect, the mechanism of ER effect is investigated thoroughly, and a noval ER polishing method, where the electrode and the ER fluid is separated by insulating materials, is presented. Using the impoved ER polishing device, the water-based ER fluid can form a stable ER effect and a good machining effect can be obtained. Based on the principle of the EMR finishing, the experimental equipment of the EMR finishing is developed to machine the workpiece under the paralled or cross combination of the electric and magnetic fields.Experiments of the EMR finishing are conducted to study the influences of some parameters on the polishing effect of the glass workpiece at a fixed-point machining mode. With the increase of the applied field intensity, the extension of the machining time and the decrease of the machining gap, the removal ability of the EMR tiny-grinding wheel will enhance. Influence of the rotational speed of the tool on material removal depends on the combined action of the cutting speed and the centrifugal force of the EMR tiny-grinding wheel. The presence of the abrasives can enhance the efficiency of material removal remarkably, however, too much diamond abrasives have little effect on the increase of the polishing performance of the EMR tiny-grinding wheel. The hardness of the abrasives determines the material removal ability of the EMR tiny-grinding wheel. The greater the abrasive hardness, the higher the material removal efficiency. The grain size and density of the abrasives directly influence the structure of the EMR particle chains and then change the efficiency of material removal. The optimum size and density of the abrasives should be chosen according to the field strength, the centrifugal force of the abrasives and the grain size of the dispersed particles.The distribution of the electric and magnetic field is simulated using Ansys software. According to the dipole model of particle energy interaction, the formulae of the field attraction forces between the EMR particles (including the dispersed particles and the abrasives) are derived, and the mechanical model of the EMR particle in the EMR tiny-grinding wheel is put forward. Furthermore, the distribution model of the polishing pressure and the material removal model are established. The real profiles of the machined surface at a fixed-point machining mode confirm the material removal model of the EMR finishing.The improved mechanical model of the EMR particle in the rotational EMR tiny-grinding wheel is established on the basis of the experimental results under the different electro-magnetically coupled fields and the calculating results of mutual particle interactions. This model clarifies the synergistic effect mechanism of electro-magnetically coupled field and the formation mechanism of the EMR tiny-grinding wheel. During the EMR finishing, the combined effect of the electric force, the magnetic force and the spin couple generated by the Lorentz force determines the stability of the EMR particle chains, the electric force and the magnetic force sustain the stability of the EMR particle chains, whereas in situ vibration of the EMR particles generated by the spin couple will affect the stability of the chains. In situ vibration of the EMR particles has two effects on the material removal performance of the EMR tiny-grinding wheel. On the one hand, in situ vibration of the EMR particles will impact regularly on the workpiece surface and promote material removal. On the other hand, in situ vibration will break the particle chains and reduce material removal when the interaction force of the particle chains is weak or the spin couple is large. When the electric force and the magnetic force are close in the value and match the spin couple, a good synergistic effect of the EMR finishing can be achieved. Results of orthogonal tests of two rotational modes further confirm the synergistic effect mechanism of electro-magnetically coupled field. At the rotational tool mode, the rotational motion of the EMR polarized particles in the magnetic field will generate the Lorentz force and the spin couple, and the EMR particles will vibrate in situ due to the effect of the spin couple, then material removal will increase. The couple mode of electric and magnetic field has a significant influence on the machining efficiency of the EMR finishing, and there is a good synergistic effect of the EMR finishing in the condition of high voltage of electric field and low excitation voltage of magnetic field.更多还原