Machining behaviour of green gelcast ceramics

Green gelcast alumina samples containing binder and samples prepared in bisque fired conditions were subjected to three machining operations—drilling, grinding and milling. Forces were measured during grinding and milling. Drilling of binder-containing samples indicated rapid wear of HSS tools while carbide tools could be used without significant wear. Bisque fired samples required lower force for grinding. Tangential and normal forces during grinding increased rapidly with successive passes due to clogging of the wheel. Increase in forces was much more rapid for binder-containing samples and for higher depth of cut. The rise in grinding force with increase in binder content correlated with the observed increase in Vickers hardness number of the green samples. During milling the tangential force increased with slight wearing of the tool. Material removal during grinding was in the form of large binder-powder aggregates for binder-containing samples, in smaller powder particle clusters for bisque fired samples. During milling of binder-containing samples, the material came out in the form of long chips.