Observation of shear plane instability during microgrinding of plastic metals

The abnormal loads placed on the metal chip during the first encounter with the cutting tool manifest themselves as an unpredictable curl that forces the chip to distance itself from the surface of the rake face. Frictional interactions between a metal chip and the rake face of a virgin cutting tool reveal the complex nature of initial chip formation and shear plane instabilities during the first few seconds of intimate contact. The variation of the load causes a shear plane instability that is directly observed using a high-speed camera and a specially designed machining apparatus. As the variation of load progresses, the chip tends to curl away from the tool with varying radii until the apparently curved shear plane becomes linear. The results of initial chip formation demonstrate a very complex interaction between metal chip and rake face of the tool and the resulting development of the shear plane and its effect on chip formation.