Growth of tool wear in turning of Ti-6Al-4V alloy under cryogenic cooling

Abstract

Titanium alloys are readily machinable provided the cutting velocity is in the range of 30–60 m/min. To achieve higher productivity, if the cutting velocity is enhanced to 60–120 m/min and beyond, rapid tool wear takes place diminishing the available tool life. Tool wear in machining of titanium alloys is mainly due to high cutting zone temperature localised in the vicinity of the cutting edge and enhanced chemical reactivity of titanium with the tool material. Cryogenic cooling with its excellent cooling abilities and environmental friendliness is being investigated to control cutting zone temperature in machining of such alloys. In the present investigation, the tool wear and tool life of uncoated carbide cutting tool inserts in machining of Ti-6Al-4V alloy have been studied under dry, wet and cryogenic cooling environments. A substantial improvement in tool life was obtained under cryogenic cooling compared to dry and wet machining in all the machining trials undertaken. The scanning electron microscope (SEM) investigation of the used cutting tool inserts revealed adherent depositions of the titanium chip material on the inserts under all machining environments. Other than adhesion–dissolution–diffusion wear, attrition, micro and macro fracturing of the cutting edge and depression of the cutting edge also contributed significantly in rapid tool wear, especially at higher cutting velocities.