Study On Control System Of Wire Electrochemical Discharge Machining

With the rapid development of technology,hard and brittle materials,such as optical glass and engineering ceramics,have played an important role in modern high-tech fields,such as electronics,optics and aerospace.Hard and brittle materials have unique physical properties,like high hardness,high melting point and high brittleness.They also have the advantages of low conductivity,low coefficient of expansion,high wear-resistance and compatibility with organic materials while common metal materials normally have none of these properties.Therefore,it is well applied in many places.The electrochemical discharge machining method(ECDM)has great advantages in the micro-machining of hard and brittle materials.It does not require complicated equipment.And it has low processing cost and good processing flexibility with no mechanical force in the process.Good machining quality can be obtained by applying suitable processing conditions.Therefore,the mechanism and experimental study of wire-electrochemical discharge machining(WECDM)are carried out in this paper.Firstly,the process of gas film formation,discharge machining and the distribution of discharge energy of WECDM were analyzed.It is found that electrochemical discharge machining is like electrical discharge machining electrolyte and workpiece in gas.The single discharge heat transfer model is studied and simulated by ANSYS,and it is found that the actual discharge pits were smaller than the simulation result,because part of the energy is wasted on the electrolyte near the discharge channel.There are also many channels on the machined surface,which is because when the workpiece is mainly composed of and the electrolyte is alkaline,chemical reaction is also one of the main methods of material removal.Secondly,an experimental platform of WECDM was built with the force signal between electrode wire and workpiece as the feedback signal.And the model of force and displacement is established.The quartz material was processed by wetting liquid supply method on this experimental platform.The effects of different voltage types,feed speed and contact force on machining were studied.The micro-groove width was about 180 ? m,the surface is pretty well,and the overcutting phenomenon is reduced compared with the open-loop control feed mode.The practicability and stability of the feed-control method based on force signal feedback are verified.On the experimental platform,three stages of material removal were studied,the control strategy of "feed-static-back" and the control strategy using PID algorithm were put forward,and the velocity and force signals were collected and analyzed.By adjusting the PID parameters,a better control effect was achieved.Compared with the former algorithm,the velocity fluctuation range of the feed shaft using PID algorithm was smaller and the feed became more stable.And the experiments on the processing of quartz glass were carried out.The effects of open-loop control and the two closed-loop control strategies are compared.The machining efficiency decreases gradually with the increase of machining depth under the control strategy of "feed-static-back",and using PID algorithm,the machining efficiency did not decrease with the increase of depth.Moreover,the control strategy of PID algorithm can improve the machining efficiency and improve the quality of the machined surface.A fuzzy control system based on the closed-loop control was designed for WECDM.The force feedback signal and its changing rate were inputs.The fuzzy control rules were established according to the machining experiments,and speed,the output,was clarified using the area center method.The system was simulated by MATLAB.And the fuzzy control system was applied to the WECDM control system,and the micro-grooving experiments were carried out.Compared with the control strategy of PID algorithm,the fuzzy control system can effectively improve the overcut phenomenon on both sides of the microgroove.The width of the workpiece slot was about 160?m,and the machining efficiency was improved significantly.The practicability of the fuzzy control strategy in WECDM was verified.