Influence of single diamond wire sawing of photovoltaic monocrystalline silicon on the feed force, surface roughness and micro-crack depth

Abstract

To gain an in-depth understanding of the influence of diamond wire sawing of monocrystalline silicon on the feed force and wafer quality, experiments with a single diamond wire in the form of a loop were performed. The cutting parameters of wire cutting speed, feed rate and wire tension were varied. The feed force was monitored and surface roughness of the specimen was measured. The micro-crack depth was determined using an image processing. The results show that cutting conditions of higher feed rate and higher wire tension increased the feed force by 78% and 20%, respectively, since for chip removal these conditions is required a higher force per grain. On increasing the wire cutting speed, the feed force reduced by 66% due to a decrease in penetration depth of the grains. Based on an analytical model, it was evidenced that volume of material removed per wire length has a significant effect on feed force. The variation of the feed rate and wire cutting speed had a greater effect on surface roughness Ra and Rq, with a minor effect on Rz. With a higher feed rate the micro-crack depth increased, whereas it was reduced on increasing the wire cutting speed. A strong correlation between sawn surface and subsurface damage was found, indicating that the micro-crack depth is around 1.37 times higher than Rz value. The combination of a lower feed rate and lower wire tension with higher wire cutting speed resulted in lower feed force, smoother surface and shallower micro-crack depth.