Ductile grinding of tungsten carbide applying standard CNC machines
A process analysis
Ductile mode grinding is a finishing process usually being applied to generate molds in brittle materials (e.g. tungsten carbide) to be used for precision glass molding (PGM). To that aim, ultra-precision machineries (UPM) are applied controlling depth of cut not to exceed a critical value, hcu,crit (e.g. 160 nm for tungsten carbide). Recent process analyses of the ductile mode grinding process of brittle materials have demonstrated that the critical indentation depth hcu,crit, that determines the transition from brittle mode to ductile mode removal, can significantly be shifted to higher values by adjusting process parameters such as the type of coolant and its pH value: e.g. for tungsten carbide up to 1600 nm and for BK7 glass up to 350 nm depth  Consequently, this paper reports on two experimental feasibility studies to extend the process window of ductile mode grinding of brittle materials. Applying ductile process parameter sets featuring values of the critical depth of cut larger than 1 micron depth two processes were experimentally analyzed that are up to now not applicable in industrial production environments: a) single point diamond turning (SPDT) of BK7 glass applying UPM machineries and b) ductile grinding of tungsten carbide molds applying standard CNC grinding machines featuring lower tool positioning accuracies than UPM. Experimental data of both tests will be presented demonstrating that by controlling and adjusting ductile process parameters only, it is possible to extend its process window into regimes that are today not yet machinable.