Improvements of machinability of aerospace-grade Inconel alloys with ultrasonically assisted hybrid machining

Abstract

Aerospace-grade Ni-based alloys such as Inconel 718 and 625 are widely used in the airspace industry thanks to their excellent mechanical properties at high temperatures. However, these materials are classified as 'difficult-to-machine' because of their high shear strength, low thermal conductivity, tendency to work-harden and presence of carbide particles in their microstructure, which lead to rapid tool wear. Machining-induced residual stresses in a machined part is an important parameter which is assessed since it can be used to evaluate overall structural resilience of the component and its propensity to fatigue failure in-service. Ultrasonically assisted turning (UAT) is a hybrid machining technique, in which tool-workpiece contact conditions are altered by imposing ultrasonic vibration (typical frequency~20 kHz) on a tool's movement in a cutting process. Several studies demonstrated successfully the resulting improvements in cutting forces and surface topography. However, a thorough study of UATinduced residual stresses is missing. In this study, experimental results are presented for machining Inconel 718 and 625 using both conventional turning (CT) and UAT with different machining parameters to investigate the effect on cutting forces, surface roughness and residual stresses in the machined parts. The study indicates that UAT leads to significant cutting force reductions and improved surface roughness in comparison to CT for cutting speeds below a critical level. The residual stresses in machined workpiece show that UAT generates more compressive stresses when compared to those in CT. Thus, UAT demonstrates an overall improvement in machinability of Inconel alloys.

Improving machining stability of AISI-4140 with magnetic field

“…Experimental parameters have been determined using previous studies in the literature. 11,14,15,18,19 Technical characteristics of the modal analysis equipment are given in Table 4. Conventional and magnetic assisted turning operations were conducted, respectively.…”

Review of new developments in machining of aerospace materials

“…30. Frequency-amplitude graph showing discrete chips generation region during LF-VAD of Ti6Al4V [56] Ultrasonic VAM used in turning of Inconel 718 and 625 also leads to significant cutting force reductions, improved surface roughness, and generates more compressive stresses when compared to those in conventional turning [57].…”

Tool Wear Analysis during Ultrasonic Assisted Turning of Nimonic-90 under Dry and Wet Conditions

“…The CT does not show a significant difference in feed force under dry and wet conditions; however, the difference is noticeable in the UAT for both conditions. The UAT allows the cutting fluid to penetrate during the disengagement period, which reduces contact between tool and workpiece and ultimately reduces the feed force [32]. The approximate reductions in the feed force in UAT under dry conditions are 27%, 17%, and 13% compared to CT under dry, CT under wet and UAT under dry conditions, respectively.…”