On Shear Instability in Machining a Nickel-Iron Base Superalloy

Abstract

The deformation in chips produced in machining a nickel-iron base superalloy (Inconel 718), at various speeds up to 213.5 m/min [700 surface feet per minute (SFPM)] has been investigated. In addition to slip, considerable twinning in the chips is observed at all speeds. Up to a cutting speed of about 30.5 m/min (100 SFPM), the chips formed are essentially continuous and ribbon-like, although deformation in the chip is inhomogeneous. At cutting speeds above 61 m/min (200 SFPM), shear-localized chips form. The longitudinal midsections of the chips show gross inhomogeneous deformation with shear localization between any two segments, and relatively low deformation within any individual segment. With an increase in speed the extent of contact between segments decreases rapidly, until a speed is reached where the individual segments become completely detached. The speed at which this occurs for other difficult-to-machine materials, such as AISI 4340, was found in an earlier study, to depend upon the metallurgical condition of the material and its hardness. Based on this study, the mechanism of chip formation when machining Inconel 718 is very similar to that reported earlier for machining both titanium alloys and hardened AISI 4340 steels at higher speeds. While the hcp crystal structure of titanium alloys in addition to titanium’s poor thermal properties (kρc) is believed to be partly responsible for the intense shear localization in that material, results with Inconel 718 (fcc) and AISI 4340 steel (bcc) indicate that the effect of structure on shear localization is not yet well understood.

Chip formation, cutting forces, and tool wear in turning of Zr-based bulk metallic glass

“…The serrated chip formation is similar to that of Ti and nickelbased alloys, which has the low thermal conductivity at about 7 and 10 W/m-K, respectively. Like the machined chip of Ti and nickel-based alloys, the shear localization (adiabatic shear band) in serrated BMG chip is due to the thermal instability of the low thermal conductivity work material during machining [12][13][14][15][16][17]. Comparing the serrated BMG chips in Fig.…”

Shear Localization: A Historical Overview

“…Shear instabilities have often been reported in investigations of machining and grinding metals. [40][41][42][43][44][45][46] They have also been advanced as a mechanism for material removal in solid particle erosion. [47][48][49][50][51][52][53][54][55] Shear bands in energetic materials have been identified as an important hot spot mechanism for their ignition.…”

An experimental study of tool wear and cutting force variation in the end milling of Inconel 718 with coated carbide inserts

“…Komanduri and Schroeder [6] investigated the shear instability and the deformation in chips produced in machining Inconel 718 at various speeds. Hanasaki et al [5] studied the tool wear in turning of a high nickel alloy with four representative coated tools, and reported that in using coated tools, the flank groove wear was reduced and the tool life was determined by the boundary wear instead of the flank groove wear.…”

“…Rapid tool wear in machining has long been recognised as a challenging problem. Hence careful machining practices are a must, and it is necessary to develop an efficient on-line tool condition monitoring method [5][6].…”