MULTI-OBJECTIVE OPTIMIZATION OF WIRE ELECTRICAL DISCHARGE MACHINED ULTRA-THIN SILICON WAFERS USING RESPONSE SURFACE METHODOLOGY FOR SOLAR CELL APPLICATIONS

摘要

Recent investigations on the fabrication of ultra-thin silicon (Si) wafers using wire-electrical discharge machining (wire-EDM) were observed to possess some inherent limitations. This includes severe thermal damage, kerf-loss, and low slicing rate, which could be detrimental towards realizing actual practical applications. The extent of thermal damage, kerf-loss, and slicing rate largely depends on the process parameters such as open voltage (OV), servo voltage (SV), and pulse on-time (T_(on)). Therefore, choosing the optimal parameters that pertain to minimum thermal damage and kerf-loss while maintaining a higher slicing rate is the key to further excel in the fabrication of Si wafers using wire-EDM. Therefore, the present study is an effort to analyze and identify the optimal parameters that relate to the most effective Si slicing in wire-EDM. A central composite design (CCD) based response surface methodology (RSM) was used for optimizing the process parameters. The capability to slice Si wafers in wire-EDM was observed to be highly influenced by the discharge energy, which had a positive impact on the overall responses. The severity of thermal damages was observed to be mainly dominated by the variation in open voltage and T_(on) due to the high diffusion of thermal energy into the workpiece, which led to intense melting and subsequent re-solidification. The parametric optimization resulted in OV = 84.32 V, SV = 42.98 V and T_(on) = 0.62 μs as the most feasible parameter that relates to comparatively high slicing rate (0.65 mm/min), low kerf-loss (280 μm) and thermal damage (18 μm) for a given machine. In general, with a decrease in spark energy slicing rate and thermal damage decreases whereas, kerf-loss increases. When spark energy decreases by 83%, there is a nearly 55% decrease in slicing rate and thermal damage and a 10% increase in kerf-loss.