Wear mechanisms of uncoated and coated carbide tools when machining Ti6Al4V using LN2 and cooled N2

Abstract

One of the main challenges of the manufacturing industry is to optimise the cutting tool life in order to increase both the process productivity and the product surface quality in machining operations. Several innovative strategies were developed and tested as function of both the workpiece material and the peculiar machining operation, being the most interesting in case of difficult-to-cut alloys, the use of low-temperature cutting fluids that would be able to inhibit the thermally activated wear mechanisms responsible of the cutting edge geometrical alterations. In this context, the aim of the paper is to investigate the effect of cryogenic cooling technologies based on the use of liquid nitrogen (LN2) and gaseous nitrogen (N2) cooled at − 100 °C on the tool wear when using uncoated and coated cemented carbide inserts in semi-finishing turning of the Ti6Al4V titanium alloy. Four commercially available insert grades commonly used in machining difficult-to-cut alloys were tested using the cutting parameters recommended by the tool manufacturer. The investigation combined scanning electron microscopy and optical profiler analyses to efficiently define and quantify the main tool wear mechanisms. The study proved that the innovative technology based on cooled N2, regardless of the adopted insert grade, determined the best results in terms of tool life improvement since it simultaneously inhibited the cratering phenomenon onto the tool rake face and produced the lowest flank wear with respect to both the dry cutting, wet strategy, and LN2 cooling cases. It was also proved that the best results were obtained for the uncoated insert when using cooled N2.