AN EXPERIMENTAL STUDY OF ORTHOGONAL MACHINING OF GLASS

An experimental study of machining glass with a geometrically defined cutting tool is presented. Orthogonal cutting conditions are employed to permit a focus on the fundamental modes of chip and surface formation. Analysis of the machined surfaces under an optical microscope identifies four regimes that are distinctly different with respect to either chip formation or surface formation. For a very small target uncut chip thickness, one on the order of the cutting edge radius, pure rubbing of the edge with no chip formation is observed. Edge rubbing imparts light scuffmarks on the machined surface giving it a frosted appearance. At a larger uncut chip thickness, ductile-mode chip formation occurs ahead of the cutting edge and a scuffed surface remains after the subsequent rubbing of the edge across the freshly machined surface. A further increase in uncut chip thickness maintains a ductile-mode of chip formation, but surface damage initiates in the form of surface cracks that grow down into the machined surface and ahead of the tool. The transition to this machining mode is highly dependent on rake angle. Increasing the uncut chip thickness further causes brittle spalling of chips leaving half-clamshell shaped divots on the surface. This experimental identification of the machining modes and their dependence on uncut chip thickness and rake angle supports the use of geometrically defined cutting tools to machine glass in a rough-semi-finish-finish machining strategy as is traditionally employed for machining metals.