【作者】 郑建新；

【导师】 徐家文；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 工程陶瓷由于其优良的物理力学性能在切削工具、汽车、航空航天及仪器仪表等诸多领域都有广泛的应用前景。但由于陶瓷材料同时具有高硬度、高脆性和低断裂韧性等特点,是典型的难加工材料。特别是陶瓷材料的成形加工是长期以来希望解决、而至今仍未解决好的难题。而使用陶瓷材料来制造发动机上某些关键零部件以提升发动机的性能,是当前发达国家的研究重点之一。本文为解决陶瓷整体叶轮的加工难题,研究探索一种类似于数控仿形侧铣加工的陶瓷叶片型面超声磨削加工技术,即陶瓷型面的数控展成蠕动进给超声磨削技术。主要研究内容包括:(1)对实验室原超声磨削型面加工机床进行改进以提升其性能,为后续试验提供可靠的试验平台。新增设了电机变频调速控制系统和磨轮驱动系统,并对超声振动系统进行了改进,以实现磨削过程平稳、磨轮定位准确且磨轮转速稳定可控。简要介绍了各单元的功能和设计过程。(2)对超声加工声学系统的关键部件——阶梯形变幅杆进行了仿真分析研究。考虑到一方面依理论设计的变幅杆其性能参数并不能完全满足试验要求,另一方面变幅杆在工程应用中存在的特殊结构(如过渡圆弧、匹配长度、法兰盘和螺纹孔等)会造成其性能参数的改变,而利用解析法难以对此求解。论文通过模态分析解决了这一难题,研究了过渡圆弧半径、匹配长度和连接部件等对阶梯形变幅杆谐振频率、位移节点和放大系数的影响规律,并根据模态分析结果设计了变幅杆。对实际变幅杆利用高频扫描激光测振系统进行了振动特性测试,实测结果与模态分析结果基本吻合,偏差在2.1%以内,表明模态分析结果可信。(3)对蠕动进给超声磨削加工技术基础理论进行了研究。首先分析了陶瓷材料延性域磨削加工的可行性,基于压痕断裂力学理论,探讨了陶瓷材料延性域超声磨削机理,并给出了延性域超声磨削的临界条件。然后从理论上分析了陶瓷材料蠕动进给超声磨削时去除材料所需的静载荷模型。该模型表明:当整个磨轮完全切入陶瓷材料后,在超声振动的作用下,将造成其磨削力降低,这将有利于陶瓷叶片型面数控展成蠕动进给超声磨削加工的顺利进行。通过分析单个磨粒的磨削参数,从理论上分析了利用小直径磨轮进行蠕动进给超声磨削的加工过程,给出了蠕动进给超声磨削加工过程中磨粒的最大磨削厚度、磨轮一转中磨粒的磨削弧长和扇形凹口高度的理论计算公式。(4)利用小直径磨轮进行了Al2O3陶瓷材料蠕动磨削试验,对比研究了超声和机械磨削中磨削参数对表面粗糙度和材料去除率的影响。采用小直径磨轮进行蠕动磨削时,超声磨削和机械磨削存在不同之处,从理论上给予了解释。深入研究表明,给工件施加一个附加的进给运动后,可以显著降低加工表面粗糙度值,而材料去除率都有所增大。当通过增大磨轮直径而提高磨削速度时,磨削结果更接近于通常磨削理论分析的情况。最后通过正交试验研究了磨削参数对加工表面粗糙度值和材料去除率的影响规律和显著程度。(5)基于平面超声磨削试验结果,进行了陶瓷叶片型面超声磨削基础工艺试验研究。构造了直纹面叶片型面数学模型,进行了加工误差分析,编制了数控加工程序并进行了基础工艺试验,首次在Al2O3陶瓷坯料上直接加工出完整的直纹面叶片型面。更多还原

【Abstract】 Ceramics has been found extensive promising application in many fields, such as cutting tool, automotive, aerospace and apparatus because of its superior physical and mechanical properties. But ceramics is considered to be typical hard-to-machine material for its high hardness, high brittleness and low fracture toughness. Especially the contour machining of ceramics is a difficult problem which is hoped to be solved for a long time while unresolved yet. It’s one of the key research issues for advanced countries to promote the performance of engine made of ceramics at present. This dissertation explores an ultrasonic grinding (USG) technology named NC-Contour Evolution Creep Feed Ultrasonic Grinding (NC-ECCFUSG) ceramic blade surface that similar to NC profiling flank milling so as to resolve the problem of machining ceramic integral wheel. The major research work includes:(1)The primary USG profile machine tool in our library is retrofitted to promote its performance so as to provide a reliable test-bed for the following experiments. A frequency control system is implied to control an inverter-fed motor and a grinding wheel driving system is designed, so as to obtain steady grinding process, install the grinding wheel accurately and make the rotating speed of the grinding wheel steady and controllable. And the ultrasonic vibration system is improved. Function of each unit and design process is introduced in brief.(2)Modal simulation analysis of the stepped horn, the key component of the USM acoustic system, is carried out. On the one hand, the performance parameters of the stepped horn designed according to the theory are not satisfied with the experiment requirement entirely and on the other hand, special structures of the horn in practice including radius of transitional circular are, matching length, flange and screw hole, etc. may lead to the change of its performance parameters, and which is difficult to be solved with analytical method. This problem is resolved through model analysis for the stepped horn. The influences of the radius of transitional circular arc, matching length and connected parts on the resonant frequency, displacement node and transformation ratio of the horn are studied through modal analysis. The stepped horn is designed based on the modal analysis results. Vibration characteristic test of the horn is carried out using method of measuring vibration system with high frequency scanning laser. The actual measuring result matches the modal analysis result approximately, and the discrepancy is less than 2.1%, which indicates that the modal analysis result is reliable.(3)Basic theoretical research on the creep feed USG technology is carried out. Firstly, feasibility of grinding ceramic in the ductile regime is analyzed, mechanism of USG ceramic in the ductile regime is discussed based on the theory of indentation fracture mechanics, and the critical condition of USG in the ductile regime is deduced. Secondly, the model of static load for the material removing in the process of creep feed USG ceramic is analyzed in theory. The model indicates that the grinding force will be reduced when the ultrasonic vibration is applied and the whole grinding wheel cuts into the ceramic, which is of advantage to NC-CECFUSG ceramic blade surface. The theoretic calculating expressions of the maximum grit depth of cut, the contact length in one rotation of the grinding wheel and the surface scallop height in the process of creep feed USG with small diameter grinding wheel are deduced through analyzing the grinding parameters of single grit in the grinding process.(4)Competitive experiments of creep feed ultrasonic face grinding ceramic using small diameter grinding wheel to study the influences of the grinding parameters on the surface roughness and material removal rate (MRR) in the grinding process with/without ultrasonic vibration are carried out to explore relative grinding parameters for the profile grinding. Difference exists in the process of creep feed grinding with/without ultrasonic vibration using small diameter grinding wheel, and which is explained in theory. Deeper research results indicate that the value of ground surface roughness will decrease obviously and MRR will increase a little when additional feed motion is applied to the workpiece. The grinding result is more close to the common theoretic result when increasing the grinding speed through increase the diameter of the grinding wheel. Finally, orthogonal experiments are carried out to study the influence law and prominence degree of the grinding parameters to the ground surface roughness and MRR.(5)Basic technological experimental research on the USG ceramic blade surface is carried out based on the experimental results of face grinding. The mathematical model of the blade with ruled surface is constructed, the machining error is analyzed, the NC machining program is written, the basic technological experiment is carried out and a set of Al2O3 ceramic integrated blades with ruled surface are machined for the first time.更多还原