Research On Multi-physics Simulation Analysis Of Multi-wire EDM Of Semiconductor Material

For photovoltaic cells based on silicon wafers,the feedstock and cutting costs of crystalline silicon account for the largest portion of their total manufacturing cost.Wire cut Electrical Discharge Machining(WEDM)is a kind of machining method using pulse electro erosion to remove material.The workability is independent of the mechanical properties of the material such as hardness and brittleness.It is only related to the thermal properties of the material.Therefore,WEDM is very suitable for processing brittle and hard semiconductor materials.The process of WEDM is very complicated,involving multiple physical fields such as electric field,magnetic field,flow field,temperature field and stress field,accompanied by heat transfer,mass transfer and momentum transfer.It is very difficult to measure the relevant data of various physical fields directly through experiments.In the circumstances,it is important to study the influence of multi-physical fields on processing stability and processing quality by finite element method to achieve high efficiency,high quality and low slicing loss.In this paper,four physical fields including flow,heat,magnetism and force in the Multi-wire cut EDM(MWEDM)process are taken as objects.The effects of processing parameters on processing quality,processing efficiency and kerf width were analyzed by finite element analysis software called COMSOL Multiphysics and continuous pulse discharge experiments.The main research contents are as follows:(1)Two kinds of liquid supply methods were studied in terms of their influence on the inter-electrode flow field of the MWEDM.The three-dimensional inter-electrode flow field model of MWEDM was established.The effects of spraying pressure and wire-electrode traveling speed on inter-electrode flow field were also investigated by using the finite element method.(2)On the basis of considering the phase transformation of the workpiece,the thermal erosion process of the semiconductor material during the single pulse discharge was studied.The effects of discharge current and pulse width on pit size,material erosion rate and workpiece surface roughness were analyzed.(3)The theoretical model of the wire electrode vibration during the continuous pulse discharge process of MWEDM was established.The influence of different processing parameters on the transverse vibration amplitude of the wire electrode was analyzed by the thermo-magnetic-structure coupling simulation.(4)The erosion model of semiconductor material and the vibration model of wire electrode were tested by continuous pulse discharge experiments.The results show that the prediction accuracy of surface roughness and processing rate of the erosion model of semiconductor material is 90% and 95% respectively,and the prediction accuracy of wire vibration model for kerf width is 93%.