【作者】 郑书友；

【导师】 徐西鹏；

【作者基本信息】 华侨大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 旋转超声加工是集传统超声加工与磨粒磨削加工为一体的复合加工,是加工硬脆性材料的一种有效方法,具有良好的应用前景。然而,通过大量文献的阅读及实际的调查研究发现,国内目前还没有生产完善的旋转超声加工机床,超声加工的技术也远远滞后于发达国家的水平。本文试图对旋转超声加工机床的研制做些工作,设计、制作出结构合理、易于操作、性能优良、生产效率高适宜于孔、面加工的大功率旋转超声加工机床。在此基础上开展相关实验研究,探索旋转超声加工在石材加工上的优势及工具磨损实验研究。论文主要内容概括如下:1.利用通用的电子元器件,设计适用于本文要求的1000W超声波电源。根据不同加工需要,电源应具备频率跟踪功能、功率可调及阻抗匹配等特性。2.依据一维振动理论模型和机-电等效理论,综合考虑各环节因素,设计适用于本文需要的三明治式压电陶瓷换能器;从换能器谐振工作点附近导纳特性出发,分析和比较了换能器串并联匹配的特点和效果;利用阻抗分析仪对设计换能器主要参数进行测试,结果显示各项参数满足设计指标,谐振频率偏离设计值仅0.8%,圆满完成本文换能器的设计。3.采用理论解析法近似求解阶梯形变幅杆的尺寸大小。借助ANSYS有限元分析对变幅杆进行了模态分析,通过对比计算确定了本文设计变幅杆的最优过渡圆弧和变幅杆位移节面的位置,确立了较为准确的法兰盘的加工位置,从而最大可能降低超声振动系统与机床的连接部分声耦合对超声振动系统的影响。将优化设计的尺寸加工的变幅杆与换能器组装成整个超声振子进行阻抗分析,数据显示优化设计的超声振子谐振频率与换能器谐振频率相当一致,其误差仅为0.2%。4.针对目前超声加工多数局限于陶瓷材料小孔加工的现状,选择典型的石材作为工件进行包括游离磨料非旋转超声、游离磨料旋转超声和固结磨料旋转超声大截面加工实验研究。目前国内外从事旋转超声加工研究所用的工具均为电镀或者粉末冶金烧结的金刚石工具,但其磨损大,寿命短。众所周知,钎焊金刚石工具能在结合界面上实现化学冶金结合,具有高出露度的特点,可以提供更大的容屑空间,减小加工过程中工具、磨屑和工件的摩擦。但目前还没有利用钎焊工具进行旋转超声加工的报道,而且对于工具端面的形状对加工过程的影响,也少见报到。为此,从工具材料的选择,断续和连续环面工具基体的设计和优化,钎焊金刚石工具的制备等方面开展工作,为实验的进行做好准备。5.在以上工作的基础上,重点研究旋转超声机床的设计。对于其中的关键技术问题,给予详细的分析与设计。解决了机床高速旋转条件下的电能换向问题;研制了气动恒力进给工作台;通过直流电机和电源的选择,设计了符合本机床要求的调速器,实现旋转超声振动系统的高速、平稳运转。考虑操作的便利及安全性,设计分离的电箱柜。6.在完成以上各项工作的情况下,对选择的石材工件进行不同输入参数下的三种大截面超声加工实验,统计材料去除率的大小,观察工件加工表面质量。通过加工过程中静压力及扭矩变化的监控,和光学显微镜对工件加工形貌和工具磨损的观察、统计,可以全面认识和分析超声加工过程,了解各加工参数对加工过程的影响,揭示工具磨损的机理。7.在游离磨料非旋转超声加工实验的研究中,对于实验的工具、工件材料和25μm的超声振幅输入条件下,实验结果显示,静压力F0=6 0N时,材料的去除率最大。固定静压力F0=6 0N不变,材料的去除率随着工具振幅的增大而增大,于此同时,表面粗糙度也使之增加,加工表面质量下降。8.在游离磨料旋转超声加工中,由于主轴转速的引入,材料的去除率较普通超声有了大幅度的增加。但是,对于较大截面的游离磨料旋转超声加工,主轴的旋转速度不宜过大,否则由于旋转离心力的作用,会导致加工区域的磨粒分布不均,影响材料的去除能力。与游离磨料非旋转超声加工不同的是,游离磨料旋转超声加工中,就工件的振幅对材料的去除率来说,并不是振幅越大越好,而是有个最佳振幅值,本实验中振幅为30μm左右。对于扭矩的测量和分析发现,扭矩随着转速的增大而增大,随着振幅的增大而降低。9.在钎焊金刚石断续工具的旋转超声加工实验中发现,材料的去除率随着主轴旋转速度和振幅的提高,都有了大幅度的增加。同样条件下,断续工具的材料去除能力是连续工具2.5倍以上,而且其寿命得以大大提高。对于扭矩的测量和分析发现,断续工具加工过程中的扭矩较连续工具有显著的降低。10.在钎焊金刚石的旋转超声加工中,金刚石磨粒的磨损形式表现为完整、微破、宏破、断裂和磨平五种形式。对于不同的工具条件,磨粒磨损过程存在很大差异,各种磨损形式的比例有所差异。对于连续截面工具,加工开始后的一段时间内,磨粒以破碎和断裂形式快速磨损。而断续钎焊工具,在起始阶段的加工过程很平稳,金刚石的磨损缓慢,在加工的后期,工具的磨损以磨平居多。更多还原

【Abstract】 Rotary ultrasonic machining is a hybrid machining process which combines the material removal mechanisms of conventional ultrasonic machining (CUSM) and diamond grinding. It is not limited by the electrical or chemical characteristics of the workpiece materials. Thus it has been proved to be a promising and cost-effective machining method for hard and brittle materials, such as engineering ceramic, glass, stone, which has been widely used in many fields such as electronics, metallurgy, chemistry industry, machine, energy power, aviation and space flight.However, referenced from a variety of literature and the actual investigation, marketability and perfect rotary ultrasonic machining equipment had been in oversea market for many years ago. But at present, we cannot find one with our Chinese Independent property right, it in turn, compared with developed country, we have a poor level at the technology of rotary ultrasonic machining.This article attempts to carry out series of work on the design and development of rotary ultrasonic equipment, beared with the characteristic of reasonable configuration, operating convenience, perfect performance, high efficiency and low cost. It can be suitable in the hole and face processing with a level of high power and spindle rotary speed. Based on this foundation, serials experiment will be carried out to reveal the materials removal principle and the attrition of diamond tool during rotary ultrasonic processing on stone materials.The main work of this thesis can be summarized as following:1. To design an ultrasonic power supply with 1000 watts power. In order to be suitable with different working status, the power supply should have the function of automatic frequency tracking, power adjusting and also impedance matching.2. Based on the theory of one-dimensional vibration and the method of mechanical-electrical equivalent, a sandwich type of piezoelectricity ceramic transducer was developed. From the point of basic principle of matching and the equivalent circuit near resonance frequency of piezoelectricity transducer, resonance characteristic of serial and parallel matching have been analyzed. The main parameters of designed transducer wear tested by an impedance analyzer, results revealed they were well accorded with the design target, it just has a 0.8% error between the testing resonance frequency with the theoretical one.3. Stepped horn was theoretically calculated. In virtue of Finite Element Analysis, desired natural frequency and vibration model of the horn was analyzed, giving the optimal transition circular radius and the displacement nodal point. So the acoustical couplings energy will remarkably decreased between the whole ultrasonic oscillator and the engine bed through the flange setted up form the accurate nodal point. The main parameters of the whole ultrasonic oscillator wear tested, results revealed they were well accorded with the design target, it just has a 0.2% error between the testing resonance frequency with the theoretical one.4. At present, ultrasonic machining experiments study were mainly limited to the little hole machining of ceramics. As a comparison, a typical kind of stone material was selected to conduct the large scale cross-section ultrasonic experiments, including the Non-rotary Ultrasonic Machining with free Abrasives (NRUSM), Rotary Ultrasonic Machining with free Abrasives (RUSM) and Rotary Ultrasonic Machining with fixed Abrasives (RUM). In the case of diamond tool utilized in the rotary ultrasonic processing, electroplating coating and powder metallurgy diamond tool were primary selected, but they have the drawbacks of the high tool were and low tool life. As is known, the brazing of monolayer of diamond tool possesses of the high protrusion height and strong bonding force between grits and substrate. It provides more swarf storage spaces to decrease the tribology among swarf, workpiece and tools. But, there were no reports on the rotary ultrasonic processing with brazing diamond tool, and few reports on the influence of tool end shape to ultrasonic processing. From these points of view, variety of work has been done on the choice of tool material, analyzing and optimizing design of tool matrix and fabrication of diamond tool at circumstance of vacuum status, which will make good preparations for the conduction of experiments.5. Based on the above work, critical attention was focus on the detailed design and analysis of the whole engine bed. Electrical energy transmission between the ultrasonic power supply and the spindle at a high speed level has been solved; Constant pneumatic force feed-up work table was developed. Proper Direct Current Power Supply and Direct Current Motor were selected to design the velocity modulation system, which can actualize the ultrasonic spindle system work steadily.6. Based on completion of the above works, three kinds of large scale cross-section ultrasonic experiment were carried out to the selected workpiece. The influences of different input parameters on the material removal rate and surface quality of the workpiece were studied. Constant static force and torque were tested during the process, at the same time, the topography of the diamond tool and workpiece were observed with a digital microscope, which will give a good explanation of the tool wear mechanism.7. In NRUSM experiments, as for the maximum MRR, there exists an optimal static load, namely 60 Newton, at the given condition of tool and its 25μm amplitude. Under the machining condition of constant 60 Newton static load, MRR increases along with the amplitude increasing, and also the value of surface roughness Ra increases.8. In RUSM experiments, because of the introducing of spindle rotary speed, MRR has a dramatically increases compared with the NRUSM experiment. But there exists a proper speed range of about 100-150 rpm for the giving tool. As for the maximum MRR, there exists an optimal amplitude 30μm in RUSM. Torque increases along with the increase of rotary speed, and decreases along with the tool amplitude increases. 9. In RUM experiments with brazing diamond tool, MRR has a notable increase with the improvement of rotary speed and amplitude. MRR with the intermittent matrix diamond tool is 2.5 times that of with continuous one. Moreover, its life has improved dramatically. Compared with the continuous matrix diamond tool, intermittent one has a lower torque.10. As for the tool wear mechanisms in RUM, wear form of diamond grit can be divided into five different kinds, that is whole crystal, micro fracture, macro fracture, fracture and polishing. The process of diamond wear has a big difference according to the different kind of tool. To continuous one, it has a large proportion of macro fracture and fracture diamond grits at the beginning of the process. But to intermittent one, it has a steady process of diamond grits wear at the earlier period. Polishing wear diamond grits will be in the highest flight at the later period.更多还原