工程陶瓷材料磨削加工技术

概述了近年来国内外工程陶瓷磨削加工技术的研究进展，对高速深切磨削、超声波辅助磨削、激光预热辅助磨削、延性域磨削、在线电解修锐、电解间隙修锐磨削等几种典型的磨削加工技术的特点及最新进展进行了分析评述；提出了非导电陶瓷双电极同步伺服跟踪电火花磨削加工工艺，并介绍了其磨削加工特点及关键技术，最后指出了今后的发展及研究方向。     

名词解释

<正>电解电火花机械磨削电解电火花机械磨削方法的技术关键是使用外圈上均匀分布着8~16个导电区的特制树脂结合剂砂轮,在特殊导电砂轮和被加工零件之间施加25~30V的直流电压,并注入具有导电性的低浓度电解液作为磨削液,使砂轮在进行机械磨削的同时,还通过电脉冲进行电解、电火花加工。对于非导电材料,在磨削区附近设置了电极,甚至以喷嘴作为电极,通过电解液形成电解和放电回路。在电解电火花机械磨削加工过程     

非导电工程陶瓷电火花单脉冲放电加工实验研究

提出了一种非导电工程陶瓷电火花磨削新工艺，为了对该工艺的加工机理有更清楚的了解，在非导电工程陶瓷工件表面进行了片电极尖端单脉冲放电的实验，测量了放电间隙大小并分析了其变化规律，给出了放电蚀除坑的形状，研究了各种参数对放电蚀除坑大小的影响关系，根据放电后电极的形状，分析叮放电的极性效应和放电通道的状态。     

绝缘及弱导电工程陶瓷电火花铣磨复合加工技术及机理研究

工程陶瓷因具有优良的力、热、声、电及化学等性能,被日益广泛地应用于机械、电子、冶金、化工、地质钻探、航空航天和核工业等领域中,并带来了巨大的社会和经济效益。随着用途的日益广泛和深入,对工程陶瓷构件的加工精度、加工效率和表面质量等要求也越来越高。然而,现有的工程陶瓷加工技术存在效率低、成本高、难以满足高精度和高表面质量的加工要求等问题。对于导电性能较好(电阻率低于100.cm)的工程陶瓷可以直接采用电火花线切割、电火花成型加工、电火花磨削和电火花铣削等加工工艺,其加工成本高、效率低等问题得到了一定的解决;而绝缘和弱导电工程陶瓷直接进行电     

非电参数对非导电工程陶瓷电火花磨削效果的影响

开发了一种新的非导电工程陶瓷电火花磨削工艺,对不导电的A1203工程陶瓷进行了加工实验研究,给出了一些非电参数对材料去除率和工件表面粗糙度的影响规律,并进行了理论分析.结果表明,非电参数在该加工工艺中起到举足轻重的作用,设置合理可以大大提高材料去除率,并能改善工件表面质量.     

电火花机械复合磨削反应烧结SiC陶瓷的表面特征

研究了基于电火花机械复合磨削技术加工的反应烧结碳化硅(RB-SiC)陶瓷的表面特征。用电火花机械复合磨削(EDDG)、电火花磨削(EDG)以及普通磨削(CG)三种方法加工RB-SiC陶瓷,并采用激光共聚焦显微镜和扫描电子显微镜对加工后的SiC陶瓷的表面粗糙度、表面形貌及微观裂纹进行测量和对比试验,获得了RB-SiC陶瓷的EDDG加工特性。实验显示:EDDG加工的RB-SiC陶瓷的表面粗糙度优于EDG加工的表面粗糙度,为0.214 9μm,但比CG加工的表面粗糙度0.195 6μm略差。对加工后的SiC陶瓷表面形貌观察显示,传统磨削加工后的表面存在明显划痕,EDG加工表面主要由放电凹坑组成,而EDDG加工表面同时存在放电凹坑和磨削划痕;另外,传统磨削表面也存在磨削裂纹和晶界裂纹,但EDG加工后的表面只存在热裂纹,而EDDG加工后的表面存在磨削裂纹和热裂纹,不过热裂纹可以用金刚石磨粒磨削去除。对比实验显示RB-SiC陶瓷的EDDG加工与EDG和CG加工获得了不同的表面特征。     

基于正交试验分析的电火花放电磨削聚晶立方氮化硼复合片工艺

聚晶立方氮化硼(PCBN)材料具有高温抗热性和高硬度,是干式车削硬态材料的最佳选择,在黑色金属加工领域得到越来越广泛的采用。目前,电火花放电磨削加工是应用广泛的聚晶立方氮化硼焊接刀具加工方法之一。以GE公司PCBN复合片8200作为试样材料,采用正交试验法,在超硬刀具电火花磨削加工机床上加工PCBN复合片,结合扫描电镜观测、粗糙度仪测试,选取电极旋转线速度、峰值电流、脉冲宽度作为主要工艺参数,以材料去除量、电极损耗作为加工效率的评价指标,以样品加工表面粗糙度、变质层厚度作为加工质量评价指标,分析电火花放电磨削加工PCBN材料的工艺。试验结果表明:当电极旋转线速度60m/min、峰值电流2A、脉冲宽度20μs时,PCBN的去除量为1.1mm~3,电极损耗为3.2mm~3,PCBN样品加工面的表面粗糙度达到R_a0.8μm,变质层厚度为12μm,得到比较满意的加工效果。     

基于正交试验的电火花加工工艺效果试验分析

通过正交试验分析,探讨电火花成形加工中影响加工效果的主要因素,阐述了脉冲峰值电流、脉冲宽度及脉冲间 隔等对加工速度、加工表面粗糙度及工具电极损耗的影响关系,对解决电火花加工实践中工艺参数优化问题具有一定的 理论和实践意义。     

硬质合金电火花加工性能的试验研究

通过试验研究硬质合金的电火花加工中脉冲宽度、峰值电流等电参数对加工速度、电极损耗、加工表面粗糙度的影响规律,得出结论:脉冲宽度和峰值电流必须在一个合适的范围内才能得到较好的加工效果。     

混粉电火花加工Ti-6Al-4V钛合金表面强化研究

以石墨为工具电极,在精密电火花成型机床上进行混粉电火花加工,对Ti-6Al-4V钛合金表面进行强化处理。利用TR200手持式粗糙度仪对传统电火花加工和混粉电火花加工的表面进行粗糙度的测量,并利用SEM、XRD等研究混粉电火花加工参数对加工表面层的影响。在MMU-10G型摩擦磨损试验机上对基体表面、普通电火花加工工件及磁力搅拌混粉电火花加工工件表面进行摩擦磨损试验。磁力搅拌混粉电火花加工使得工件表面的粗糙度降低且随着峰值电流和脉冲宽度的增大而增大,提高了工件表面质量。随着峰值电流和脉冲宽度的增大强化层越均匀、致密性越好且强化层越厚。工件表面还生成了TiC硬质合金相使工件表面耐磨性得到提高,工件表面性能显著改善。混粉电火花加工后工件表面得到强化。     

Diamond face grinding of WC-Co composite with spark assistance: Experimental study and parameter optimization

Electro-discharge machining (EDM) characteristics of tungsten carbide-cobalt composite are accompanied by a number of problems such as the presence of resolidified layer, large tool wear rate and thermal cracks. Use of combination of conventional grinding and EDM (a new hybrid feature) has potential to overcome these problems. This article presents the face grinding of tungsten carbide-cobalt composite (WC-Co) with electrical spark discharge incorporated within face of wheel and flat surface of cylindrical workpiece. A face grinding setup for electro- discharge diamond grinding (EDDG) process is developed. The effect of input parameters such as wheel speed, current, pulse on-time and duty factor on output parameters such as material removal rate (MRR), wheel wear rate (WWR) and average surface roughness (ASR), are investigated. The present study shows that MRR increases with increase in current and wheel speed while it decreases with increase in pulse on-time for higher pulse on-time (above 100 μs). The most significant factor has been found as wheel speed affecting the robustness of electro- discharge diamond face grinding (EDDFG) process.     

ELECTRIC DISCHARGE MILLING AND MECHANICAL GRINDING COMPOUND MACHINING OF SILICON CARBIDE CERAMIC

Silicon carbide (SiC) ceramics have been widely used in modern industry. However, the manufacture of SiC ceramics is not an efficient process. This paper proposes a new technology of machining SiC ceramics with electrical discharge milling and mechanical grinding compound method. The compound process employs the pulse generator used in electrical discharge machining, and uses a water-based emulsion as the machining fluid. It is able to effectively machine a large surface area on SiC ceramics with a good surface quality. In this paper, the effects of pulse duration, pulse interval, peak voltage, peak current and feed rate of the workpiece on the process performance parameters, such as material removal rate, relative electrode wear ratio and surface roughness, have been investigated. A L₂₅ orthogonal array based on Taguchi method is adopted, and the experimental data are statistically evaluated by analysis of variance and stepwise regression. The significant machining parameters, the optimal combination levels of machining parameters, and the mathematical models associated with the process performance are obtained. In addition, the workpiece surface microstructure is examined with a scanning electron microscope and an energy dispersive spectrometer.     

A study of mirror-like grinding of fine ceramics with in-process electrolytic dressing

Fine ceramics have the properties of high hardness, chemical inertness, high thermal resistance and low electrical conductivity, but, because of high hardness and brittleness, they are very difficult to machine. Therefore, a superabrasive diamond wheel is used for mirror-like grinding of this material. In this study, an in-process electrolytic dressing system for carrying out mirror-like surface grinding was constructed. Using this system the grinding force for fine ceramics was reduced. This work shows that the application of electrolytic dressing is beneficial in obtaining a mirror-like surface when grinding fine ceramics.     

Slotted-electrical discharge diamond cut-off grinding of Al/SiC/B4C hybrid metal matrix composite

Advanced manufacturing industries need materials with high strength and low weight in the fields of advanced engineering, such as automobiles and aeronautics. Metal matrix composites (MMCs) are one of the advanced engineering materials that meet the above requirements. To enhance the properties of MMCs, researchers added an additional phase of reinforcements into single reinforced MMCs; such developed MMCs are known as hybrid MMCs. The additional phase of reinforcements enhances the properties of MMCs, but simultaneously leads to rapid tool wear and poor machinability. This study developed an innovative hybrid machining process (HMP) consisting of electrical discharge grinding and diamond grinding in such a way that both the processes occur alternately with equal intervals due to the rotation of a slotted abrasive grinding wheel. The performance of the hybrid process was tested on an Al/SiC_p/B₄C_p work-piece in cut-off grinding mode. The experiments were conducted on an electrical discharge machining machine, which consists of a separate attachment on a vertical column to rotate the wheel. Pulse current, pulse on-time, pulse off-time, wheel RPM, and abrasive grit number were taken as input parameters while material removal rate (MRR) and average surface roughness were taken as output parameters. Result were shown that the HMP gives higher MRR with better surface finish as compared to the constituent processes. Pulse current ranging from 3 A to 21 A, pulse on-time ranging from 30 μs to 200 μs, and pulse off-time ranging from 15 μs to 90 μs were also found to be more suitable for higher MRR, and a wheel RPM at 1300 RPM was more suitable for higher MRR with better surface finish.     

ELECTRICAL DISCHARGE DIAMOND GRINDING OF HIGH SPEED STEEL

A combination of two machining processes (i.e., a hybrid process) has a potential to improve process performance. This paper reports on experimental investigation of the electrical discharge diamond grinding process that combines mechanical grinding with electrical discharge machining. In this process, the workpiece is simultaneously subjected to heating, by electrical sparks bridging the gap between the metallic wheel bonding material and the work, and abrasion by diamond grains. The effect of current, voltage, pulse-on-time and duty factor on the grinding forces and the material removal rate while machining high speed steel workpiece, are investigated. The spark discharges facilitate grinding by thermally softening the work material in the grinding zone, and consequently decreasing the nromal force. It is observed that the material removal rate increases with an increase in current and pulse on-time, while it decreases with an increase in voltage and duty factor. These independent parameters are also found to significantly influence the grinding forces.     

HIGH SPEED AND HIGH MATERIAL REMOVAL RATE GRINDING OF CERAMICS USING THE VITREOUS BOND CBN WHEEL

High-speed (up to 127 m/s) and high material removal rate grinding experiments were conducted using a vitreous bond cubic boron nitride (CBN) wheel to investigate the effects of material removal rate, wheel speed, dwell time and truing speed ratio on cylindrical grinding of silicon nitride and zirconia. Experimental results show that operating the grinding wheel at a high surface speed can reduce grinding forces, enable high material removal rates, and achieve a higher grinding ratio (G-ratio). The material removal rate was increased to 9.6 and 7.6 mm³/s/mm for zirconia and silicon nitride, respectively, to explore the advantage of using high wheel speeds for cost-effective, high-material-removal-rate grinding of ceramics. Models for specific grinding force vs. the specific material removal rate and G-ratio vs. grinding wheel surface speed were developed based on the experimental results. Overall, this study showed that high grinding wheel surface speed is beneficial to the grinding of ceramics.     

Optimizing machining parameters of silicon carbide ceramics with ED milling and mechanical grinding combined process

A novel combined process of machining silicon carbide (SiC) ceramics with electrical discharge milling and mechanical grinding is presented. The process is able to effectively machine a large surface area on SiC ceramics with a good surface quality. The effect of tool polarity on the process performance has been investigated. The effects of peak current, peak voltage, pulse on-time and pulse off-time on the material removal rate (MRR), electrode wear ratio (EWR), and surface roughness (SR) have been investigated with Taguchi experimental design. The mathematical models for the MRR, EWR, and SR have been established with the stepwise regression method. The experiment results show that the MRR, EWR, and SR can reach 46.2543 mm³/min, 20.7176%, and 0.0340 µm, respectively, with each optimal combination level of machining parameters.     

激光与电火花复合修整粗粒度弧形金刚石砂轮试验研究

因受到激光高斯光束特性的影响,辐照在砂轮表面上的光斑大小和激光能量都跟随修整路径变化,难以实现高精度的弧形金刚石砂轮的修整,为此,提出采用激光粗修整和电火花精修整的复合修整方法。先用激光修整高效去除多余磨料层来得到弧形轮廓,再用一高精度弧形电极匹配该轮廓进行电火花修整,得到较高精度的弧形砂轮。在粒度为120的金刚石砂轮上试验修整半径为13 mm的弧形轮廓,最终修整出的弧形轮廓半径为13.006 mm,轮廓误差PV值为10.90 μm。最后,通过磨削氧化铝陶瓷验证了砂轮修整效果。检测磨削工件的弧形轮廓拟合半径为13.012 mm,轮廓误差PV值为11.33 μm。     

IN SITU TRUING/DRESSING OF DIAMOND WHEEL FOR PRECISION GRINDING

An application for achieving on-machine truing/dressing and monitoring of diamond wheel is dealt with in dry grinding. A dry electrical discharge （ED） assisted truing and dressing method is adopted in preparation of diamond grinding wheels. Effective and precise truing/dressing of a diamond wheel is carried out on a CNC curve grinding machine by utilizing an ED assisted diamond dresser. The dressed wheel is monitored online by a CCD vision system. It detects the topography changes of a wheel surface. The wear condition is evaluated by analyzing the edge deviation of a wheel image. The benefits of the proposed methods are confirmed by the grinding experiments. The designed truing/dressing device has high material removal rate, low dresser wear, and hence guarantees a desired wheel surface. Real-time monitoring of the wheel profile facilitates determining the optimum dressing amount, dressing interval, and the compensation error.