Material removal mechanism and microstructure fabrication of GDP during micro-milling

Abstract

Glow discharge polymer (GDP) material is essential for target ball fabrication in inertial confinement fusion applications. Fine microstructures (∼several tens-hundreds of micros) machining on the GDP surface is required for directing the high-power laser. The machinability and material removal mechanism of the GDP are critical to achieve high surface quality, remaining an unsolved challenge. This study investigated cutting mechanisms of the GDP based on feed per tooth and inclination angle in micro ball-end milling. Chip formation modes and machined surface morphologies as well as their generation mechanism were studied. Three types of chips (i.e., chip clusters, bulk/node chips, banded chips) were formed when the forming force of compression shifts to shear. Thermal effect and plastic flow promote a smooth surface under the squeezing effect of the tool cutting edge. The different ratios of feed rate to tool line velocity caused the micro pits and feed marks on the machined surface with the viscoelasticity of polymer material. By analyzing the cutting force, specific cutting force and machined surface roughness, together with the chip modes and surface morphologies, a transition of cutting modes from ploughing to ploughing-shearing coexistence and then to shearing were revealed. Finally, micro-dimpled structures were machined for validating the influence of the reveled material removal mechanism for fabrication of microstructures. The presented findings are of great significance for the application of micro-cutting processes in future engineering fabrication of microstructures on the GDP target ball.