The cutting of polymers

Abstract

The variation in the cutting behaviour of two polymers (Kematal and Perspex) as conditions are varied is described. Subject to the proviso that the Merchant shear plane angle is not greater than 45°, cutting force component data are shown to obey theoretical relations derived to account for the cutting behaviour of metals. The transition from brittle to ductile chip formation can be assessed (a) visually (b) in terms of the cutting force variation and (c) in terms of the change in the proportion of the shear zone which is subject to tensile stress; results obtained by each of these assessments are shown to be substantially in agreement. Utilizing the observations, made inter alia, by Banerjee and Palmer, that during discontinuous chip formation, chip material moves up the rake face by a series of “sticks” and “slips”, a hypothesis is proposed wherein it is suggested that such a motion of chip material occurs not solely during discontinuous chip formation but that it occurs during all forms of chip formation and, in particular, during continuous chip formation. In this way the existence of rugosities on the upper side of continuous chips is explained and deductions from this hypothesis are verified using experimental data.