Evaluation of Cutting Forces During Single Pass Microtrenching of Poly (Methyl Methacrylate)

Research was conducted to evaluate a microtrenching process to create microchannels on the surface of poly (methyl methacrylate) (PMMA) for applications in tissue engineering. Experiments with a trenching tool included an exaggerated cutting edge radius (48 μm) to study the impact of a highly negative effective rake angle on forces during single pass microtrenching at subradius cutting conditions. During microtrenching, forces were measured by dynamometer and compared to a finite element (FE) model using an elastic-perfectly plastic material model for an undeformed chip thickness from 9 to 64 μm. During experiments, cutting was first observed when the ratio of undeformed chip thickness to cutting edge radius was 0.33. Measured and predicted values of thrust force exceeded cutting force up to an undeformed chip thickness equivalent to the cutting edge radius. The FE model predicted a linear trend in cutting force with feed (r = 0.99) and was substantiated by linear regression of experimental data (r = 0.99). However, at lower values of feed the model overestimated force, with a maximum difference of 42% at a feed of 22 μm. Thrust force was also predicted to be linear (r = 0.99), but at greater feed the experiments indicated a nonlinear decline in thrust force, resulting in a maximum difference of 27% at 64 μm. Finally, an analysis of nodal velocity plots from the FE model revealed a material stagnation zone developed along the cutting edge, rising from the workpiece surface in proportion to feed and then remaining fixed at 63 deg (stagnation angle) for all feeds greater than 35 μm. While the application of an elastic-perfectly plastic material model for PMMA was sufficient to predict microtrenching forces by the FE method, differences between predicted and measured thrust forces at greater undeformed chip thickness implies a more complex rheological model may add value.