Characterisation of wear resistance of natural and synthetic diamond tools during single point diamond turning

Achievable cutting distance of a diamond tool during turning is finite and is a limiting factor in the size of component that can be turned. This limit is particularly problematic when attempting to turn brittle materials, such as those used in infra-red optics. Natural diamond tools have been used for this application. However natural diamond introduces problems: the gems can contain possible contamination with a range of impurities and strong residual stresses from formation. Cutting distance is therefore inconsistent when using natural diamond. Industry is keen to increase possible cutting distance and to increase the consistency of cutting distance. One possible solution is synthetic diamond materials. New CVD single crystal synthetic diamonds possess high purity and consistent growth conditions and therefore have the potential to be a superior tool-material that provides longer achievable cutting distance and extremely consistent cutting behaviour. This new material is compared against natural and HPHT synthetic diamonds in machining tests against silicon workpieces in a selection of tool-orientations. Aluminium workpieces are machined with MCC and natural diamond tools to assess the performance of the new material against this commonly diamond turned material. While analysing the results from these cutting trials the failure modes of diamond tools were examined closely, resulting in discovering the existence of two separate failure modes and the development of a new wear-model. Natural diamond tools were carefully tested using a range of techniques hoping to find a root cause of the wide variability seen. FTIR offered a strong clue as to the defect within natural diamond tools that leads to occasional high cutting life.