CRYOGENIC MACHINING OF KEVLAR COMPOSITES

Abstract

Previous attempts to machine Kevlar aramid fibre reinforced plastics (KFRP) with conventional cutting tools have proven to be extremely difficult. This has somewhat restricted the material's usage, often negating the advantages of its high strength to weight ratio and fatigue tolerance. The present paper describes a novel technique of machining KFRP under cryogenic conditions with remarkable results compared to those obtained at ambient temperatures. The investigation carried out with turning operation shows dramatic improvement of the tool performance and surface quality. The effects of various machining parameters such as workpiece temperature, cutting speed and tool geometry on the machinability of KFRP are presented and analyzed. It appears that care is necessary to judge the tool life as the typical tool wear growth and surface finish or cutting force may produce contradictory results. It is also suggested that, for KFRP, surface finish of the machined workpiece is a very good criterion to determine the tool life. To aid the understanding of the machining mechanics, a microscopic investigation of the cutting zone while actually machining a testpiece at ambient and cryogenic temperatures is also reported.