Metallurgical and machining performance aspects of cryotreated tungsten carbide micro-end mill cutters

Abstract

Demand for miniaturized parts with tight geometrical tolerances and superior surface finish has been increasing. Development of micromachining processes has enabled adaptation of miniaturized parts and products in mechanical systems. Machining at the microscale level has supplementary challenges like high cutting forces, reduced tool life, and damaged machined surfaces. Catastrophic failure of microtools is notable problem, if tool deflection increases significantly. Therefore, incorporating tool life improvement measures are essential to minimize tool replacement cost and also to achieve efficient cutting at micro-level. Cryotreatment imparts better physical properties to cutting tools. In the present work, effects of different cryogenic treatment parameters on micro tungsten carbide-cobalt (WC-Co) end mill cutters and its performance while machining Ti-6Al-4V have been investigated. The metallurgical changes imparted to cutting tool by cryotreatment are studied via micro-hardness test along with EDS, SEM and XRD methods. It is found that all cryotreated tools have higher hardness compared to untreated tools. Additional η (eta) carbide formation has been clearly observed for the tools soaked for 24 h, moreover a variation in other phase of WC is also observed for different set of cryotreatment. Machining process is significantly affected by the low thermal conductivity of Ti-6Al-4V. In case of untreated micro-milling tool, abrasive wear is dominant, whereas built-up-edge affected the performance of cryotreated tools at shallow cryotreatment temperatures for 8–16 h soaking time. Deep cryotreated tool (at 24 h soaking time) performed better in terms of cutting force and surface roughness due to retainment of sharp cutting edge.