A model for the contact conditions at the chip-tool interface in machining

A high-speed photographic study has been made of the chip-tool interface and its evolution when cutting pure metals with optically transparent sapphire tools. The use of a high speed camera in conjunction with an optical microscope has enabled details of the interface, including the velocity field along the interface, to be resolved at high spatial and temporal resolution while cutting at speeds between 1 mm/sec and 2000 mm/sec. The results show the chip-tool contact along this interface to be composed of four distinct regions: a region of stagnation at the cutting edge, a region of retardation adjoining the stagnation region, a region of sliding beyond the retardation region, followed by a region of metal transfer or "sticking" that is located furthest away from the cutting edge alongside the boundary of the contact. The chip and tool appear to be in intimate contact over the stagnation, retardation, and sliding regions, with sliding occurring at the interface over much of this zone of intimate contact. These observations have provided direct experimental evidence for a model of the contact conditions proposed by Enahoro and Oxley based on analytical considerations. Cutting experiments with non-oxide tools such as aluminum and high speed steel suggest that this description conditions is equally applicable to tool materials other than sapphire.