Investigation of material removal mechanisms of laser-structured Si3N4 via single diamond grit scratching

Abstract

Grinding hard-brittle materials like silicon nitride is faced with some challenges, including sub-surface damage, high tool wear, and low grinding efficiency. Ultrashort-pulse laser structuring of hard materials prior to the grinding process significantly reduces the cutting forces and temperature and increases the achievable material removal rate of the grinding process. These effects are partially due to controllable induced damages into the subsurface of the structured workpieces. However, the impacts of this surface structuring technique on the material removal mechanism of advanced ceramics, such as Si3N4, are not yet thoroughly investigated. The dominant material removal mechanism in grinding hard and brittle materials, such as silicon nitride (Si3N4), defines the surface integrity of the workpiece. For the first time, in-depth single diamond grit scratching experiments are carried out to investigate the changes in the dominant material removal mechanisms at various chip thicknesses by laser structuring of Si3N4. Two different structuring ratios (25% and 50%) were generated on sample surfaces by a femtosecond laser. The effects of laser structuring on material removal mechanism, pile-up area, area and width of the groove, grit path, normal and tangential forces, and specific cutting energy have been investigated. The results indicate that laser structuring considerably affects the reduction of depth ratio, normal (up to 89%) and tangential (up to 82%) forces, and specific cutting energy. The specific cutting energy of laser-structured Si3N4 workpieces converged to about 5 J/mm3, much lower than that of unstructured workpieces.

Defect-free grinding of silicon nitride at high material removal rate

“…Present methods of laser-assisted machining, which fracture weaken Si 3 N 4 prior to grinding and remain cracked after grinding, have shown MRR improvements on the order of 20–50 % [ 1 ] as compared to nonablated material. In this work, the MRR was 500 % higher compared to the nonablated sample (e.g., 0.027 mm3/mm sec vs 0.0054 mm3/mm sec).…”

“…Lasers are used to induce steep thermal gradients in Si 3 N 4 , resulting in surface and subsurface cracks. Grinding of fracture weakened Si 3 N 4 has been done at upwards of 50 % higher MRR [ 1 ]. There are, however, several issues with laser-assisted machining preventing its widespread adoption.…”