Experiment Study Of EDM Milling Servo Control System For Semiconductor Silicon

Semiconductor silicon materials,with their special optical and physical properties,are used more and more widely in the field of high-energy diffraction crystals.However,as a typical hard and brittle material,when the semiconductor silicon is processed by the traditional machining method,the mechanical force may cause crushing and cracking on the machined surface.The material removing of EDM,not restricted to the hardness and brittleness of the workpiece,is based on electric erosion phenomenon and suitable for processing semiconductor silicon material.By the use of standard shaped electrode,such as rods,tubes,plates and frames,the aimed cavity can be machined with the multi-axis CNC servo control in EDM milling process.In this paper,the different processing characteristics of semiconductor and metal materials are firstly analyzed,and a servo control system for semiconductor silicon is set up.Then the form of electrode wear is studied,and the electrode wear compensation based on discharged pulse counting is established.Finally,the influence of working solution properties on processing efficiency and electrode wear is studied,and glycerol working solution is proposed and tested experimentally.The specific research contents of this paper are as follows:(1)Developed EDM milling experimental system based on discharged pulse possibility detection.Analyzed the difference of processing characteristics between silicon and metal,designed the feedback signal detecting circuit and ARM micro-controller based servo control system;designed the pulse power supply suitable for semiconductor EDM machining and solved the power dissipation problem;realized the accurately returnable point-by-point interpolation algorithm.(2)Established electrode wear compensation system based on discharged pulse counting and studied the influence of milling routine to machining accuracy.It shows that the electrode wear form and rate of different directions ranges,axial feed losses are mainly concentrated on the terminal face,and smaller the milling thickness is,the radial feed losses are more concentrated on the terminal face.The terminal face losses is more conductive to compensate than the radial surface losses.(3)Solved the problems occur in silicon EDM machining,include passivation with dielectric water solution and carbon deposition with spark oil,analyzed and tested the influence of conductivity,and the composition of working solution on the processing performance.Studies shows that the decrease of conductivity can increase the discharge gap,which could improve machining stability.And the carbonaceous working solution can decompose carbon under the instantaneous hightemperature generated by the discharge to enhance the coating effect on the electrode to reduce the electrode wear.However,if the carbon content is too high to be expelled in time,it will produce carbon deposition and reduce the machining efficiency.(4)Proposed the glycerol working solution and experimentally tested the influence of its concentration to the working efficiency and electrode wear,it shows that the better concentration is20%~30%.Compared the performance with dielectric water under certain conditions,machining in glycerol working solution can be more stable which the best duty ratio is 1:7,much better than 1:21 of dielectric water;and higher pulse voltage,reach to 210 V can be used than the 180 V in dielectric water.All of this may improve the machining efficiency more than 3 times.