Computational modeling of free abrasive machining in wiresaw slicing

Wiresaw, the modern version of woodcutter's saw, is finding extensive applications in slicing of large diameter (up to 300 mm) semiconductor wafers. The objective of this dissertation is to build a computational model in hydrodynamics and fracture mechanics to further our understanding for the wiresaw slicing process.;In a typical wiresaw slicing process, the material removal is accomplished by using an abrasive-carrying slurry. This slurry is carried by the wire into the cutting zone. This generates a three body abrasion environment, wherein the abrasives are free to move in between the axially translating wire and the ingot. This is the so-called Free Abrasive Machining (FAM) process, or float machining process.;The general observation from this study is that the film thickness is greater than the typical size of the abrasives. This means that the wire does not directly press the abrasives against the surface being machined. A model is then proposed to explain cutting action of 'floating abrasives'. As per this model the hydrodynamic shear causes the abrasives to roll, whereas the hydrodynamic pressure causes it to indent onto the surface. Material removal is thus accomplished by these abrasives in the rolling-indenting process.;As a first approximation, we model material removal by pure indentation of abrasives. One should use the smallest angle abrasive which would cause transverse cracking. For silicon this boils down to conical abrasive particles of 105° included angle.;A model for wiresaw slicing is proposed to integrate EHD interaction and indentation cracking. This model predicts qualitatively the variation of material removal rate (MRR) with various wire-saw operating parameters. So in last stages of this research we generated a scheme to model chipping by rolling-indenting abrasives.;Under reasonable assumptions and limitations, the model proposed in this dissertation provides a prediction on the variation of MRR with various operating parameters for the highly complex wiresaw slicing process. It provides pointers to optimum operation of the wiresaw. (Abstract shortened by UMI.)...