Research On Equalizing Discharge And Synchronous Control Technology For Multi-Wire EDM Of Silicon Ingot

The development trend of silicon wafers needed for photovoltaic industry is large size, thin sheet and high productivity. It is difficult to realize the large size, high efficiency and super thin cutting by the traditional ID(Inner Diameter) and OD(Outer Diameter) slicing method. At present, widely used wire saw cutting has been difficult to meet the requirements of low cost, light damage and non pollution production due to the mechanical grinding force, and the top-grade wire cutting machine tools mainly rely on costly import. EDM is a kind of machining method using pulse electro erosion to remove material without macroscopic cutting force, which is very suitable for processing the brittle semiconductor material. But WEDM processing can only cut a single piece of silicon and the processing efficiency is far lower than that of wire saw. To improve slicing efficiency, in this paper a novel Multi-wire EDM machine for silicon ingot slicing is developed. Addressing the coupling problem of multi-wires, the technology of multi-electrode equalizing discharge and synchronous control is extended. Specific research is as follows.(1) On the basis of the structure analysis of wire saw cutting and WEDM, a kind of Multi-wire EDM with parallel discharge and adjustable electrode wire spacing was developed.And the main parts of multi-wire synchronous wire feeding mechanism were designed in detail.(2) Movement wire system with special broken wire protection circuitl was developed. And it can coordinate with the working fluid circulation system and feed servo control system.(3) Pulse power supply of Multi-wire EDM and fuzzy controller based on FPGA were designed.Multi-electrode parallel discharge closed loop control system based on sampling and feedback of multi-channel discharge state was established.(4) According to the coupling interference between a plurality of discharge electrode wire, the effects of multi-channel synchronous and asynchronous pulse discharge on the machining quality were compared and analyzed. MIMO fuzzy controller for pulse parameter adaptive adjustment was designed, and it realized multi-electrode synchronous equalizing discharge control.(5) The silicon ingot cutting test was carried out on the self developed Multi-wire EDM. The results show that compared with the traditional single-wire EDM and single electrode multi-wire EDM, the parallel multi discharge electrode wire cutting method put forward in this paper can significantly improve the processing efficiency while ensuring processing quality.