Elasto-Hydrodynamic Interaction in the Free Abrasive Wafer Slicing Using a Wiresaw: Modeling and Finite Element Analysis

Abstract

Free abrasive machining (FAM) process associated with the wiresaw wafer slicing involves a three body abrasion environment. During the process, the cutting action is caused by fine abrasives freely dispersed in the slurry, which get trapped between an axially moving taut wire and the ingot being sliced. In this paper a model is proposed wherein the entry of abrasives into the cutting zone is governed by elasto-hydrodynamic (EHD) interaction between the slurry and the wire. An EHD film is formed by the abrasive carrying viscous slurry, squeezed between the wire and the ingot. This phenomenon is analyzed here using the finite element method. The analysis of such an interaction involves coupling of the basic Reynold’s equation of hydrodynamics with the elasticity equation of wire. Newton–Raphson algorithm is used to formulate and solve this basic coupling. The finite element discretization of the resulting nonlinear equation is carried out using Galerkin’s method of weighted residuals. Basic hydrodynamic interaction model and the incorporation of the entry level impact pressure into the inlet boundary conditions are the two novel features introduced in this work. The analysis yields film thickness profile and pressure distribution as a function of wire speed, slurry viscosity, and slicing conditions. A perusal of results suggests that the wiresawing occurs under “floating” machining condition. The minimum film thickness is greater than the average abrasive size. This is practically very important since the wiresaw is used to slice fragile semiconductor wafers with severe requirements on the surface finish. The possible mechanism by which a floating abrasive can cause material removal is also touched upon in this work. Material removal rate has been modeled based on energy considerations. [S0742-4787(00)00702-5]