Research On Servo Control And Processing Technology Of Wire-cut Electrical Discharge Machining Of Silicon Crystals

Nowadays,with the rapid development of science and technology,the importance of information and energy is self-evident.As a result,semiconductor materials,especially silicon crystal,are widely applied in microelectronics industry,emerging photovoltaic industry and many other fields,this also puts forward more requirements for the processing monocrystalline silicon such as the efficiency,machining quality.In consideration of the hard and brittle characteristics of silicon crystal,this paper studies the control of wire electrical discharge machining(WEDM)which is not subject to the physical and mechanical properties of the workpiece,and for WEDM has no macroscopic mechanical cutting force,it is suitable for the machining of silicon crystal.In the existing research,the mechanism and characteristics of the EDM for semiconductor materials have been relatively studied to theoretical basis.However,the domestic high-speed reciprocating wire cutting machine on the market is mainly used for cutting metal materials,and the discharge characteristic of semiconductor materials is different from the metal,so the control system is unable to accurately distinguish the processing state in process,servo feed speed cannot response to processing in real-time,resulting in processing quality and efficiency is difficult to meet the requirements.Thus it can be known the most challenging technical difficulty is servo control system.In order to solve the above problems,this paper presents a new sampling method based on discharge probability detection,then design and build the crystal silicon WEDM servo control system,After the system was built,the process verification experiments were carried out to improve the cutting efficiency and quality of silicon crystal.The main contents of this paper were as follows:(1)Using traditional machine tool for basic experimental research to find out differences of discharge characteristic between silicon crystal and metal mater ials,and analysing of the limitations of existing systems,proposing the servo control based on the discharge probability detection according to discharge characteristics of the silicon crystal.(2)Having des igned and built a micro operation platform for single pulse discharge experiments,to study on single pulse erosion of silicon crystal under different discharge parameters.And with theoretical analys is to improve the efficiency and quality of silicon crystal processing: applying the discharge probability detection method to improve the utilization rate of pulse,using the discharge parameters of small pulse width and large discharge current.(3)Transformation of servo control system of existing machine tool: taking FPGA as the core control unit and carry on the function design of each module of the system,improving pulse power supply,designing the discharge probability detection circuit,high frequency pulse signal drive circuit,servo feed control circuit and making PCB board,complete the control system based on discharge probability detection and PID servo feed.(4)Debugging and improving the control system program,using Labview to design the upper computer control interface to achieve the setting of discharge parameters,real-time tracking display and monitoring discharge processing state.(5)Experiments with new servo control system based on discharge probability detection,the results show that the new servo system can realize stable discharge machining for silicon crystal compared to the traditional system.By analyzing the processing effects of different target probability,pulse parameters and discharge energy,the machining parameters of high cutting efficiency and quality are summarized.