Research On Ultra-precision Grinding Of Hard And Brittle Material Si₃N₄ With Electrolytic In-process Dressing (ELID)

In this dissertation the author analyzed the present situations of ELID grindingtechnique and ED truing technique, and conducted the experimental research onelectro-discharge precision truing for cast iron-bonded diamond wheel andultra-precision grinding techniques for silicon nitride ceramic under the condition ofactive control of film state. The results have guidance meanings for ultra-precisionELID grinding of hard and brittle materials such as engineering ceramics, opticalglasses, hard alloys, etc. In the dissertation, accessorial equipments for ELID grinding had been designedand manufactured, and the configuration of ELID ultra-precision plane grindingsystem was carried out. To provide technical guarantee for precision truing ofmetal-bonded fine grain diamond wheel and for the study of grinding phenomenonand grinding features in the ELID grinding of silicon nitride, a real-time dataacquisition and analysis system was developed for the monitoring of electro-discharge(ED) truing and characteristic signals in the ELID grinding such as voltage, electriccurrent and grinding force.In the precision ED truing of metal-bonded fine grain diamond wheel, real-timemonitoring of working voltage and working current can not only make acquisition ofeffective electric specification and judgement criterion that electric specification hastruing capacity more simple and more convenient, but also avoid appearance ofno-load and short-circuit, and is helpful to elevate the efficiency and precision of finetruing. The key for the elevation of truing precision is the avoidance of short-circuitand the use of high insulation working liquid. In the dissertation, the radial run-outless than 1μm for diamond wheel has been obtained with plane electrodes under theelectric specification of 60 V and 20 μs: 20 μs while de-ionized water used as workingliquid, which provides an ideal tool technique for further experimental studies onELID precision and ultra-precision grinding.The equivalent model of electrolysis reaction circuit of ELID grinding systemwas established, and the film state characterized with the circuital current betweenelectrodes was proposed. Based on the analysis of ELID grinding principle, theconception of active control for the film state and the control strategies of intermittentelectrolyzing and intermittent grinding were proposed. The author has accomplishedeffective control for film state successfully and carried out experimental study on theELID precision and ultra-precision grinding of silicon nitride under the condition offilm state being actively controlled. Because of the limitation of equipments, thecontrol range of circuital current between electrodes was set too widely, resulting inlarge variation of film state in the control cycle. In experiments, the fluctuation rangeof grinding force under the condition of film state being actively controlled wasobviously larger than that in dynamic balance, but the low limits under theseconditions was approximately equal. The surface roughness of silicon nitrideworkpiece ground with film state being controlled was slightly larger than that indynamic balance, but there was no substantial difference.Material removal of ELID ultra-precision grinding is performed with compositemode of micro-grinding, lapping and polishing. The film state determines theprincipal removal mode of workpiece material and the proportion of different removalmode. The following technical means is very important to the ultra-precision ELIDgrinding: to select reasonable grain size;to uniform the organization of grindingwheel;to make fine truing and dynamic balancing for grinding wheel;to limit heatdeformation of grinding machine strictly, etc.