| Nowadays,semiconductor materials represented by silicon materials are increasingly used in the fields of integrated circuits,aerospace,automotive,solar energy and national defense.The surface quality,processing accuracy and smoothness of silicon crystal are increasingly demanded in many fields.The common processing methods of silicon crystal have been applied,but silicon crystals are easy to collapse and fracture because of the mechanical stress during processing.Wire cut electrical discharge machining(WEDM)technology is very suitable for hard and brittle materials such as silicon crystals because it generates no macroscopic stress between the electrode wire and the workpiece.However,due to the bulk resistance and contact barrier of silicon crystal,the servo control system fails to effectively identify the working state of the process,and the feed speed can not respond to the changes of the working state in real time when using traditional WEDM machine tools to process silicon crystal,so the processing quality and cutting efficiency are not ideal.In order to solve this problem,this paper focuses on the design of servo control system and new Pulse Power Source according to the previous research on discharge probability detection.In this paper,the discharge characteristics of silicon crystal were experimentally investigated,and the relationships between discharge probability,feed speed and pulse width were obtained.The WEDM servo control system for silicon crystal based on discharge probability detection and a new constant discharge probability pulse power source were designed and built.The feasibility of servo system and power source system was verified by a series of technological experiments.The process parameters were optimized through experiments,the processing quality and cutting efficiency of silicon crystal were improved.The main contents of this paper are as follows:(1)The discharge characteristics of silicon crystal were systematically studied on the single pulse discharge platform.The significant differences in discharge characteristics between silicon crystals and metal materials were compared.The basic concept and sampling method of discharge probability were obtained by theoretical analysis and experimental data,which provides experimental basis for the optimization of discharge probability sampling circuit.(2)The discharge probability was sampled during silicon crystal cutting by ordinary WEDM machine.The relationships between discharge probability,feed speed and pulse width were explored through a series of experiments.The conclusion is that discharge probability is positively correlated with feed speed and negatively correlated with pulse width,which provides theoretical and experimental basis for the design of servo control system and power source system.(3)Taking ARM as the control core,the servo control system of the existing machine tool was designed and reformed: the hardware modules of the system were designed and built,the PID algorithm of the feed speed was optimized according to the relationship between the feed speed and discharge probability,the interpolation algorithm was reprogrammed and optimized,and the upper computer was designed to track the real-time processing state.The construction of the servo control system was done.(4)A control method based on pulse width PID regulation was proposed.A new pulse width PID constant discharge probability pulse power source was designed and built.The hardware modules of each part of the power source are designed,and the algorithm of the pulse width PID control was designed to complete the design and construction of the new constant discharge probability pulse power source.(5)The feasibility and superiority of the new servo control system and the new constant discharge probability pulse power source were verified by experiments,and the process parameters were optimized.Finally,the stable,automatic and efficient processing of silicon crystal was realized. |
PDF Full Text Request