The Gap Analysis And Control For Wire Electrical Discharge Machining Process Of Monocrystalline Silicon

Monocrystalline silicon is a kind of important semiconductor material,due to its good features such as resistance to high temperature and radiation,it is widely used in large scale integrated circuit manufacturing,microelectronics components,solar cells and other industries,which becomes an important and indispensable material of the industry,national defense,aerospace and other fields.However,monocrystalline silicon is a typical hard brittle material,which has the characteristics of high hardness and high brittleness.It is difficult to use the traditional machining methods because the mechanical force is easy to cause fracture and collapse.As its non-contact machining characteristic,there is no mechanical stress,wire electrical discharge machining(WEDM)is very suitable for hard and brittle materials.The size of the WEDM discharge gap has an important influence on the interelectrode discharge status,and the interelectrode discharge status directly affects the stability of machining process and material cutting efficiency.Therefore,it is of great practical significance to control the WEDM discharge gap.In this paper,a control model of monocrystalline silicon WEDM process between the interelectrode gap average current and the feedrate is established by the method of system identification,and a controller is designed to adjust the feedrate online to make the gap average current kept constant to obtain a stable discharge gap through the process.Finally,some experiments are conducted to test the performance of the controller.Since the discharge gap in the kerf during the WEDM process cannot be obtained directly,the mathematical model of the gap average current and the discharge gap is established,therefore the discharge gap can be fed back through the gap average current.Based on the analysis of the waveform of gap voltage and gap current during the monocrystalline silicon WEDM process,it is confirmed that there are three kinds of gap discharge status in the process.The influence of feedrate on the processing quality as well as the breaking of wire electrode during the process are analyzed,and the necessity of controlling the discharge gap is illustrated.The order of the discharge gap control system model is identified by the determinant ratio method.The forgetting factor recursive least square method with forgetting factor of 0.98 is determined by MATLAB simulation results as the method of online parameter identification.The difference equation model of the interelectrode gap average current and the feedrate is established.A minimum variance self-tuning controller for monocrystalline silicon WEDM discharge gap control is designed,then it is simulated by MATLAB,and the results show that the designed controller has a good tracking performance.The hardware platform of the discharge gap control system as well as the control algorithm program and the application program are completed.The experimental results show that the controller has a good practical control effect.Compared with the constant feedrate,the machining process with controller is more stable,and the machining quality is relatively improved,while the cutting efficiency is improved significantly.