SURFACE ABUSE ASSOCIATED WITH FINISH TURNING OF GRAY CAST-IRON WITH CERAMIC TOOLS

Machining trials were carried out on a G-17 cast iron using round and square-shaped pure oxide (less than or equal to 99 vol. % Al2O3 + less than or equal to 1 vol. % ZrO2), mixed oxide (70 vol. % Al2O9 + 30 vo l % TiC) and silicon coarbide whisker-reinforced (75 vol. % Al2O3 + 25 vol. % SiC) ceramic tools in order to study the extent of damage on t he machined surfaces. G-17 is a BS 1452 (1977) designation and equival ent to ANSI/ASTM A48-83 grade 40 designation. The test results show th at the round-shaped ceramic tools produced better surface finish and l ess damage than square inserts under the cutting conditions investigat ed due to their increased nose radius, which increased the tool-workpi ece contact area during machining. The surface finish deteriorates wit h prolonged machining and an increase in the depth of cut. The hardnes s values of the surface layer-were generally above the average hardnes s value of the base material due to the hardening of the surface layer as a result of the high pressure, compressive stress and temperatures generated at the cutting edge during machining. A higher rate of hard ening was observed when, machining with the mixed oxide and SiC whiske r-reinforced ceramic tools due, perhaps, to the relatively high temper atures generated al the higher cutting speed (500 m/min.) used.