Machining and Tribological Characterisation of Uncoated and Coated Carbide Inserts while Turning Tungsten Heavy Alloy

Abstract

Tungsten heavy alloys are high density alloys containing 80 to 98 wt.% tungsten and the balance is a matrix made of relatively low melting elements such as copper, nickel and iron. These alloys are used as radiation shields, CG adjusters and also in armour piercing ammunition. Machining these alloys to close tolerances and finish leads to excessive tool wear, surface damage and hence proves to be a challenging task. This study focuses on turning operation carried out under dry and wet cutting conditions using three different commercially available cemented carbide inserts. Three different feed rates have been used at a constant depth of cut and cutting speed. The best possible cemented carbide tooling solution for machining tungsten heavy alloys has been determined based on the surface finish obtained, chip geometry, cutting forces, and machining temperature. The observations made during machining are correlated to the tribological behavior of the inserts and the alloy with the help of pin-on disc tests. Coated cemented carbide inserts provide surface roughness values lower than 1 µm under finish turning conditions. On the other hand, PVD coated inserts give consistently better results over different feed rates and are found to experience lower tool wear for the specific cutting conditions. Analytical tool wear model suggests better tool life for the PVD coated insert.