【作者】 张立新；

【导师】 杨兆军；

【作者基本信息】 吉林大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 工程陶瓷材料具有耐高温、抗磨损、刚度高、热变形小等优良性能,但由于其硬度高、脆性大,难以对其进行切削加工,回转表面则更难加工。本文受线电极放电磨削加工中工件与电极之间相对运动关系的启发,提出了在线切割机上利用放电蚀除加工导电工程陶瓷回转表面的新型工艺方法。论文首先对数控快速走丝线切割机进行了改造,在机床上加装带动工件回转、并能传递加工电流的主轴装置,实现了对工程陶瓷回转表面的放电加工。在加工长径比较大的工件时,由于陶瓷材料的电阻率较高,随着放电加工部位的变化、放电能量将发生明显变化。本文从提高工件表面质量和加工稳定性的角度出发,创新提出了在线切割机床上加装回转表面自适应跟踪电极的方法。设计了一个安装在丝架上的在工件回转表面上滑动的辅助电极,辅助电极与电极丝的距离、亦即火花放电点的距离保持不变,使放电回路中工件的电阻值保持不变,放电能量均匀,进而保证工件表面加工质量均匀。同时辅助电极能适应工件直径变化并能自动越过阶梯轴阶梯,保持了对变径工件或阶梯回转工件的加工能力。对工程陶瓷回转表面线切割加工机理进行了研究。在理论分析的基础上,建立了线切割加工区域的有限元分析模型,用MSC.MARC有限元软件,对工程陶瓷回转表面线切割加工过程的温度场进行了数值模拟,得出了不同脉冲宽度和功率密度对放电凹坑形状和放电加工工件表面粗糙度的影响规律。通过单因素实验分析了主要放电参数和机械参数对加工工件表面质量的影响规律,采用正交多项式非线性回归设计,对线切割放电加工工程陶瓷回转表面的工艺参数进行了优化,提高了工件的表面质量,验证了线切割放电加工导电工程陶瓷回转表面新工艺的可行性。本文的研究工作,为工程陶瓷的加工提供了新型工艺方法,并且拓展了线切割加工机床的工艺范围,对促进工程陶瓷材料的应用具有重要意义。更多还原

【Abstract】 With the development of technology, the engineering materials are widely applied to the mechanical science, chemical technology and aviation technology. The traditional metal materials have already been more incompetent for the demand of the engineering application.The advanced ceramics have many good properties that the metals don’t have, such as the high hardness, high intensity, high wear resistance , high temperature resistance, low density, low thermal expansivity and low thermal conductivity. So the advanced ceramics have broad applications in modern engineering materials. Although the advanced ceramics have so many good properties, the sintered ceramic products are different from the metal powder products, its percentage reduction of size is more than 10%, and the latter is less than 0.2%. Because of the low dimensional accuracy of the ceramic products, it is very difficult to apply to the engineering. The control of dimensional makes more difficult for the complex shape products. So the sintered ceramic materials will need further process in many fields.At present, the process of ceramic include the Diamond Grinding, Superhard Cutting, Ultrasonic Machining, Laser Processing, Plasma Arc Cutting and High Pressure Water Jet Cutter. It is difficult to process the complex shape ceramic products because of the disadvantages and the limitations of various processing methods. Wire Electrical Discharge Grinding is an effective mean of the micro-axis parts processing. The mechanism of WEDG is basically the same as the technology of WEDM in essence. WEDM is a special processing method which has been widely used in the metal processing field. It achieves the technological breakthroughs that the material of high hardness can be processed the metal cutting tool of the soft materials. WEDM is an ideal processing method of the conductive engineering ceramic because it can achieve non-contact processing; the processing procedure cannot be affected by the mechanical stress; the residual stress of products doesn’t increase its mechanical property. The experiments show that WEDM can process the engineering ceramic materials of the resistivity of less than 100Ω·cm.The research on the WEDM of ceramic materials is based on the plane at home and abroad. The specialized WEDM can process the rotary surface; the equipment is limited to process the micro-axis with high expensive and low efficiency. A novel technology of Wire Electrical Discharge Machining rotary surface of engineering ceramic is presented in this paper. The common High-speed WEDM is advanced, and the current can be transmitted by the workpiece spindle machining device to achieve the engineering ceramic rotary surface. It is the key technology of improving the roughness of the machined surface that the discharge energy of pulse generator is micronized. The circuit of transistor pulse generator is analyzed in this paper, the experiments show that the discharge circuit between the anode and the negative pole can be changed by the change of the resistance. The method can decrease the discharge energy of single pulse and the roughness of machined surface. The vibratility of wire electrode would affect the roughness of the machined surface, so the shortening the length of wire electrode and the adding the limit apparent of wire electrode can be adopted in this paper. The methods can get higher surface quality.Following the worktable auto-feeding, the discharging station, the resistance between the discharging point and the sending end and the discharging parmeters are continous changing, because the resistance rate of long ceramics workpiece is bigger than metal material When it is being cut on the common high speed WEDM with the sprindle slewer, The changes results in the surface roughness of the cut ceramics workpiece uneven and the machining process unstable as well. A kind of self-adaptive tracking electode was designed innovative. The tracking electode installed on the wire shelf may slide on the rotary surface of workpiece, adapt the change of workpiece diameter and leapfrog the steps of step-shaft. So the resistance between the workpiece fixturing position and sending end and the peak current of the circuit cosist by wire,workpiece and tracking electode. In this paper, the structure design and the virtual prototype analysis were carried out. Firstly, the dimension of machine tool and the rotary equipment of principal axis were analyzed, the model of tracking-electrode is designed and dynamics simulation analysis of the processing procedure was presented by the ADAMS, The fact that tracking-electrode can meet the needs of the power is verified. The structural designs of tracking-electrode are done by the CATIA software. The whole tracking-electrode device was manufactured by the Aluminum Alloys, sliding electrode was done with graphite, the processing experiments were done by the presented equipment. The experiments show that the equipment with tracking-electrode can improve stability of the processing procedure and improve the surface quality of the workpiece.The processing mechanism of WEDM with rotary surface of engineering ceramic is researched. The processing mechanism are discussed from the following aspects, such as the WEDM discharge form of the engineering ceramics, the micro process of the materials removal, the process of distribution and conversion and the influencing factors of the materials removal.Based on the analysis of theory, the finite element models of the processing region is established using finite element analysis software MSC.MARC and the numerical simulation of temperature field for the WEDM process with the rotary surface of engineering ceramics are analyzed. The single-pulse discharge processing distribution of the temperature field is analyzed in the various power situations. The impact laws of various pulse-width and power density to the shape of the discharge pits and surface roughness. The theoretical basis of the engineering ceramics rotary surface characteristics of WEDM process is provided to the further study.Many experiments about the effect of discharging parameters to cutting surface roughness are carried out by the reformed WEDM device. The single factor experiments show that their function between the rotary surface roughness of engineering ceramic and main cutting parameters is nonlinear. So the regression experiment project of WEDM the rotary surface of B.C ceramics is designed by the orthogonal polynomial regression experiment method, about the surface roughness as experiment aim and the peak current, impulse width and workpiece speed as experimental factors. The optimum regression equation is obtained while the significant index is up to 99%. Based on this, the optimum technological parameters are determined to decrease the workpiece surface roughness under the paper’s experiment conditions. The better experimental result is achieved that the roughness value of Ra is equal to 0.75μm by using these optimum technological parameters ,and the results verifies the feasibility of the new technology on WEDM the rotary surface of engineering ceramics.更多还原