Residual Stress Control in Mid-infrared Laser Rounding of Glass Plate Edges by Reciprocal Scanning Assist Laser Irradiation

Abstract

Light absorption depth of glasses in a mid-infrared wavelength of 2.8 μm is the same scale as thickness of glass plates used in flat panel displays. Such an absorption property allows relatively uniform heating in the thickness direction of glass plates when a mid-infrared laser is irradiated vertically to the glass plate surface. Therefore, the mid-infrared laser is convenient for edge rounding of complex shape glass plates. Application of the mid-infrared laser to the edge finishing process has been developed. However, residual tensile stress in rounded edges which weakens final products has been a problem to be solved. Simultaneous assist laser irradiation with the mid-infrared laser rounding is a candidate solution because of its controllability of residual stress. In this study, residual stress control has been examined by high-frequency reciprocal scanning assist laser irradiation. In addition, relationship between residual stress and assist heating width has been investigated by numerically and experimentally. Existence of an optimum assist heating width which minimize residual stress was confirmed. Both increase and decrease in assist heating width from the optimum width increased residual stress.