Research On Feed Control System And Application Of Electrical Discharge Milling For Engineering Ceramics

Due to the characteristics of high hardness, high strength, poor electrical conductivity and high abrasion resistance, the engineering ceramics were very difficult to shaping machinability. The electrical discharge machining(EDM) was a effectively process methods. Compared the metal material machined by EDM and the engingeering ceramics machined by the same, the gap which producted the valid discharge of the latter was more narrow, and the no-load and arc which were invalid even harmful state were more easy turn up. How to stably and efficiently control the the engingeering ceramics EDM is a hard issue all the time. The theoretical studies and the experimental analysis methods were applied in the paper to study the feed control system and application of the engineering ceramics EDM milling. The discharge gap sensing circuits and the gap state identification methods were depthly studied. The feed control methods and the driver circuit were designed base on the gap state identification. The special intelligent power supply for engineering ceramics was studied. A series of experiment were done base on this. And the reason of tool wear which used to process the engineering ceramics was studied. The issue of processing parameter optimization was studied, too.The feed control system of the engineering ceramics EDM milling was studied in the first. The main controller were confirmed which composed by PC and Single Chip Microcomputer (SCM). Part of control software were made based on the Windows XP operating system . The detection method of discharge for engineering ceramics EDM milling was studied. Three methods for the gap state identifying was put to use, including the identification method based the gap voltage falling edge, the method based on the trained WNN data base and the method based on the low frequency coefficient of gap voltage wavelet decomposition. The great identification result were acquired through the experiment. Before the identification the gap state using the low frequency coefficient of wavelet decomposition, the gap signal was de-noised by the different wavelet de-nosing method. The de-noised results were compared when the gap signal de-noised by the different wavelet functions.The PD feed controller was designed on the base of the the gap identification result. The mixed H₂ /H_∞control criterion was adopted to effective control the uncertain disturbance induced by the particles which spalled form the work piece and the electrode because of the woekpiece corrosion removing and electrode wear. The suitable algorithm was used to ensure the PD controller parameters k pand k d under the optimum condition.The mechanism of spark erosion for the engineering ceramics was studied. Based on this, the special power supply was designed. The PC and SCM were used to control the pulse on-time, pulse off-time, current of the power supply. The gap voltage detection circuit was designed. The gap current detection circuit using Hall element was designed, too. The gap voltage and current signal were sampled to the controller formed the closed-loop control. And a certain intelligent special power supply for engineering ceramics EDM milling was formed.The SiC ceramics EDM milling test was carried used the two different control system, the control system designed as above and the control system come from the NH250 EDM machine. The result of SiC ceramics machining were relative analysised when the pulse on-time, pulse off-time, current and voltage of the power supply were varied. The machining result include the materical remove rate of workpiece(MRR), the roughness concentration of workpiece(Ra) and the wear rate of the electrode(EWR). The processed results proved the better machining result of the control system designed in the paper with the higher MRR and the lower EWR.The reasons of the EWR were studied when the SiC ceramics was EDM milling. The relationship between the EWR and the equivalent carbon on the electrode surface was analysised by the scanning electron microscope and energy spectrum analysis. And relationship function was concluded using the test data. The relationship between the slope of the gap current rising edge and the EWR was acquired by the test, too. And the curve of the process time and the EWR was got. The Curves between the EWR and the pulse on-time, off-time, peak current, peak voltage were anlysised intensively. The related coefficient of every factor as noted above was got by the correlation analysis. A quadratical polynomial regression equation was obtained to fit the experimental data used regression analysis. The compensation method of electrode base on this of the feed control system was provided.