Undeformed chip thickness may be smaller than sharpness radius of a cutting edge at small feed rate when workpieces are cut by a finishing tool with a large round corner. Therefore, in finish cut, sharpness of a cutting edge has to be taken into consideration in cutting process. The purpose of this study is to find mechanism of cutting force occurrence at smaller undeformed chip thickness than sharpness radius of a cutting edge. In this study, effect of sharpness of a cutting edge on cutting force and its effect on burnishing force were investigated in orthogonal cutting process. Furthermore, contact length between a tool flank face and a workpiece during cutting was measured in order to consider the relation between the burnishing force and the contact length. As a result, principal conclusions reached were as follows. The following parameters were in inverse proportion to the nth power of undeformed chip thickness normalized by sharpness radius of a cutting edge: ( i ) cutting forces per unit area of chip section, (ii) specific burnishing force defined as burning force divided by undeformed chip thickness and width of cut, and ( iii ) specific burnishing length defined as burnishing length divided by undeformed chip thickness.
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