An experimental study of orthogonal machining of glass

An experimental study of machining glass with a geometrically defined cutti ng 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 surf ace formation. For a very small target uncut chip thickness, one on the ord er of the cutting edge radius, pure rubbing of the edge with no chip format ion is observed. Edge rubbing imparts light scuffmarks on the machined surf ace giving it a frosted appearance. At a larger uncut chip thickness, ducti le-mode chip formation occurs ahead of the cutting edge and a scuffed surfa ce remains after the subsequent rubbing of the edge across the freshly mach ined surface. A further increase in uncut chip thickness maintains a ductil e-mode of chip formation, but surface damage initiates in the form of surfa ce cracks that grow down into the machined surface and ahead of the tool. T he transition to this machining mode is highly dependent on rake angle. Inc reasing the uncut chip thickness further causes brittle spalling of chips l eaving half-clamshell shaped divots on the surface. This experimental ident ification of the machining modes and their dependence on uncut chip thickne ss and rake angle supports the use of geometrically defined cutting tools t o machine glass in a rough-semifinish-finish machining strategy as is tradi tionally employed for machining metals.