TOWARDS A PHYSICAL COMPREHENSION OF MATERIAL STRENGTHENING FACTORS DURING MACRO TO MICRO-SCALE MILLING

Abstract

Present work highlights the importance of material strain rate hardening characteristics as an influential factor in increasing material strength, as uncut chip thickness decreases from macro to micro-level dimensions during down-cut milling process. It has been found for a strain rate dependent material (A2024-T351) that rake face-chip contact length increases nonlinearly when tool approaches to micro-level of uncut chip thickness. This suggests higher energy consumption due to frictional interaction at tool-chip interface, resulting in higher specific cutting energy. In addition, results depict that increase in cutting speeds are attributed to increased rake face-chip contact lengths. Furthermore, to analyze the contribution of the strain gradient hardening on size effect phenomenon during micro cutting operations, modified Johnson-Cook material model (strain gradient-based approach) of the equivalent stress has been formulated in ABAQUS®/EXPLICIT via its user subroutine VUMAT. The results put forward the significance of strain gradient hardening to fully capture the size effect phenomenon du-ring micro cutting operations, at high cutting speeds for a strain rate dependent material. Finally, milling experiments have been performed to validate the numerical model in terms of specific cutting energy and chip morphology.

http://dx.doi.org/10.5755/j01.mech.17.1.210