Abstract
A cut-away or restricted contact tool for turning operations has been proposed and successfully employed to improve the machinability of an 18%Mn-18%Cr manganese steel (HB=241). Both chip contact length on the rake face and chip flow direction can be uniquely determined by the energy method after Usui and others, when the restricted length is assumed to be proportional to the real feed in the direction of chip flow. The optimum restricted length is found to be 1.25 times as large as the real feed, which is slightly wider than that of the two-dimensional cut-away tool. The predicted cutting force, cutting temperature and tool wear are all in good agreement with experiment. The restriction of the contact length reduces cutting force and heat generation on the shear plane and at the tool-chip interface, leading to a decrease in tool temperature. As a result, crater wear on the rake face of a P20 grade carbide tool is lessened by 10 % compared with the dry turning of such a high-hardness metal using a natural contact tool.
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