A study of crack generation at loading/unloading process in wheel cleaving (Circular/half-penny crack generation mechanisms)

Abstract

Wheel cleaving is one of the dividing methods of glass substrates, and is widely used in industrial scenes like manufacturing of flat panel displays. However, the crack generation mechanisms are not fully understood and therefore, the processing conditions are determined empirically. In this study, we observed crack generation behaviors during loading/unloading processes of toothed wheels by using highspeed imaging system. Finite element method (FEM) analysis of stress distribution in glass substrates were also carried out. As a result, two types of vertical cracks (circular and half-penny cracks) were observed just below the scribing wheel. Depending on the wheel shapes and applied load, the generation behavior of these cracks varied. Numerical results suggested that the crack generation behavior was determined by whether the tensile stress field was distributed up to the glass surface where some defects existed formed by wheel contact. This means low-height tooth and high applied load conditions produce a compressive stress field at the vicinity of glass surface, and the vertical crack generation is suppressed. To obtain a smooth cleaved surface, the half-penny crack generation during loading process is essential. For this purpose, precise control of indentation depth by optimizing wheel shape (tooth length, height and span) and applied load is necessary.