Materials removal and energy dissipation during sawing of polycarbonate and glass

A series of experiments on sawing plastic (PC) and glass (TaFD5) samples wa s conducted to verify the validity of the French-Preston law and also to st udy the environmental (air, water, decanol and cyclohexanol) effects on the sawing energy. Linear relations between cutting rate and sawing power were found using any liquid coolant, as predicted by the French-Preston law. Th e normal load and tangential force in sawing had a linear relation, as sugg ested by the law of kinetic friction, independent of speed or temperature i n the ranges studied. However, air is not a good coolant for sawing PC alth ough it is good for sawing glass. By blowing air on the PC sample at the cu tting interface and extrapolating to infinite air pressure, the French-Pres ton law was found to be obeyed. Using a coolant in sawing may cause extra e nergy dissipation, namely, the energy required to shear the fluid. The inve stigation shows that the extra energy dissipation is proportional to the vi scosity of the coolant so the sawing power required for PC was in the order of air, water, decanol and cyclohexanol. However, for sawing glass the cut ting efficiency (cutting rate per sawing power) is the highest in decanol, next in water and the lowest in air, just the opposite to the case of sawin g PC. In order to understand the difference between PC and glass the fractu re tough ness of TaFD5 was measured by the indentation method and the lowes t fracture toughness was found in decanol, next in water and the highest in air based on the lengths of indentation cracks. So it appears that the mat erial removal rate increases with decreasing of fracture toughness, but not exactly inversely proportional to it, as proposed by Buijs and Houten. Sin ce the glass removal rate is strongly dependent on the fracture toughness, it suggests that sawing of glass takes place by a process of microscopic fr acture. On the other hand, the mechanism for sawing PC appears to be plasti c deformation or ductile tearing. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.