Eliminating white layer and enhancing surface integrity by gas cooling in the hard turning of aisi d steels using cbn inserts

Abstract

Of late, hard turning has established itself as an innovative and cost newlineeffective machining solution, due to its ability to facilitate precise machining newlinefor super hardened steels beyond 45HRC. Also, it has the capability to produce newlineintricate profiles in a single machining set-up with dry or near dry condition. newlineHard turning has also emerged a viable alternative to the traditional grinding. newlineBecause, it is possible to produce parts with very high dimensional accuracy, newlinegeometrical tolerance and surface finish without the application of coolant. newlineBut, it has been accomplished only with the modern machine tools and newlinesuperior cutting tools. Obviously, coated and uncoated CBN inserts have newlineproven to be the technologically feasible tool material for the hard turning. newlineHowever, parts produced by the hard turning process are found to newlinebe affected by adverse surface pattern known as White Layer . Besides, it newlineproduces parts with poor surface reliability properties such as extremely newlineincreased microhardness, severely affected microstructure, widely varied newlinechemical compositional changes and unbearably reduced surface finish. In newlinefact, the White Layer is a hard and brittle featureless layer. Also, it has been newlineobserved at the machined surfaces by several researchers. Moreover, it has newlinebeen studied that, the excessive tool wear and extreme cutting temperature are newlineconsidered to be the root causes for the White Layer formation. It is also newlinerevealed that, the white layer occurs due to the following three vital newlinemechanisms such as (i) SPD (ii) Phase-transformations (iii) Surface reactions newline newline