Finite Element Analysis of Machining Lightweight Syntactic Foams

Abstract

Aluminium alloys reinforced with hollow alumina microsphere syntactic foams possess superior physical and mechanical properties such as improved stiffness, peak compressive strength and total specific energy absorption. However, due to the inherent abrasive and brittle nature of the hollow alumina microspheres, syntactic foams bring two key machining issues in the form of poor machinability and surface integrity. This research focuses on understanding the physics behind chip formation during machining metal syntactic foams through development of a 2D finite element (FE) model which will enable to predict cutting forces using AdvantEdge FE software. To elucidate and explain the failure mechanisms in the form of hollow ceramic microsphere fracture and plastic deformation of the aluminium matrix which contributes to generation of cutting forces, a 2D ABAQUS/Explicit FE model is developed. Cutting tests were conducted on the aluminium syntactic foam with varying cutting velocity and undeformed chip thickness. Two different volume fractions (10% and 20%) with varying average hollow microsphere sizes were used in the validation trials. From the FE results, it is shown that the increase in cutting speed results in reduction of cutting force due to thermal softening of matrix alloy. However, the measured cutting force increase with increasing undeformed chip thickness is primarily due to increasing chip load. Increase in shear strength of the material is noticed with increasing volume fraction and finer hollow microsphere size which contributes to a higher magnitude of cutting force. A greater number of fractured hollow microspheres were involved in two-body and three-body tool abrasion on the rake face thereby increasing the cutting force. The finite element cutting force simulations is compared with the measured values for different cutting conditions. The AdvantEdge FE model shows comparable results with the validation experiments within an error of 15%.