Papers by Keyword: Brittle Mode

Abstract: Monocrystal sapphire ground surfaces obtained by ductile mode and brittle mode are analyzed in this paper. A two dimension (2D) fractal properties of different ground surfaces are calculated and analyzed by a box-counting fractal method. The results show that the fractal dimension (FD) in parallel grinding direction can imply the material removal mode, especially for the surfaces with a similar roughness Ra obtained in different material removal modes. The ground surface obtained in ductile mode has much higher FD in the parallel direction than that in brittle mode. For the surface with high FD in parallel direction, its profile is more exquisite and surface quality is better. For the surface with a small FD in the parallel direction, a deeper crack and more pronounced defects occur. On the other hand, the profile FD distributions can reflect the anisotropic features of monocrystal sapphire ground surfaces. Therefore, the fractal analysis method has the potential to reveal precisely and comprehensively the ground surface characteristics of monocrystal sapphire.

Abstract: There is a demand for high-efficiency and high surface integrity grinding of fused silica. Ductile grinding is an ideal method for producing a mirror finished surface on hard and brittle materials to significantly decrease polishing time. However, the fused silica is still difficult to ductile grind because of its high brittleness. A creep feed taper grinding method was applied to investigate the relationship between maximum grit depth of cut and surface integrity of fused silica. Ductile mode grinding was achieved on fused silica. When the depth of cut exceeds the critical wheel depth of cut, the surface suddenly changes from the ductile mode to the brittle mode. At the same ratio of wheel speed and table speed, the critical wheel depth of cut is noticeably increased by increasing the wheel speed which caused an increase in the temperature at the interface of grains and workpiece. The depth of subsurface damage (SSD) was investigated by polishing the ground surface. The experiment results show that the depth of SSD is deepest in transition mode and stables in brittle mode.

Abstract: Fused silica is an important material for optics of ultraviolet laser transmission. It is difficult to be ground in ductile mode because of a high brittleness. In this paper, ductile mode grinding was achieved by a taper grinding method when the initial surface was a polished surface. However, when the initial surface was an unpolished surface, ductile mode grinding could not be realized because of the existence of surface and subsurface damages. The damages on the ground fused silica surface were repaired by CO2 laser irradiation with optimal laser power and scanning velocity. The optimal parameters were determined by studying the viscosity of fused silica and etching depth of laser irradiated groove. Besides laser processing parameters, surface roughness of laser irradiated surface is also greatly influenced by the initial surface roughness.