# Experimental Study on ELID Grinding of Silicon Nitride Ceramics for G5 Class Bearing Balls
## 5 Conclusions  
The ceramic silicon nitride specimens for ceramic bearing balls were prepared, and ELID grinding experiments were conducted to compare and analyze the influence of material properties and grinding conditions on the quality of the ground surface.  
The results of ground surface morphology analysis revealed the following:  
1. Diamond abrasives exhibited smooth cutting surfaces due to ductile mode machining, where the traces of abrasive passing through were faithfully transferred onto the machined surface.
2. For the diamond abrasives at lower grit sizes (#325 and #1200), the ground surface exhibited distinct peaks and valleys compared to the cBN ground surface, indicating a higher proportion of ductile mode fractured surface than brittle mode.
3. At a higher grit size (#2000), the ground surface showed almost no evidence of brittle mode fractured surface, resulting in a smoother ground surface compared to cBN. Surface roughness comparison analysis yielded the following conclusions:  
1. It has been confirmed that an increase in the DOC led to an increase in surface roughness under the same grinding conditions.
2. The analysis of surface roughness based on different grit sizes revealed that the #325 cBN abrasive showed a superior ground surface compared to the diamond abrasive, #1200 showed no significant difference between the two abrasives, and #2000 showed a significantly superior surface when ground with the diamond abrasive compared to cBN.
3. Based on the comparison between material properties and surface roughness, it was observed that higher fracture toughness and flexural strength were correlated with superior surface roughness. Ground surface morphology analysis visually confirmed the cutting performance of diamond and cBN abrasives on silicon nitride ceramics.  
Figure 12: Comparison of surface roughness and flexural strength by specimen.  
It has been confirmed that the material characteristics and grinding parameters affect the surface roughness of silicon nitride ceramics during the grinding process through surface morphology and surface roughness analysis after ELID grinding experiments. Expanding the applicability of results derived from this experiment, through surface roughness comparison analysis, it was observed that in the roughing process, using low-grit-size cBN wheels such as #325 at deeper depths of cut can increase grinding efficiency while enhancing the quality of the ground surface. On the other hand, in the finishing process, using high-grit-size diamond wheels such as #2000 allows for the achievement of nanosurfaces, providing a more efficient and effective approach for high-efficiency machining and nanosurface fabrication. The surface ground with the #2000 wheel is at a level that can satisfy the required surface roughness, 0.014 um or less in G5 class bearing balls.  
Conceptualization, T.-S.K.; methodology, T.-S.K.; validation, T.-S.K. and H.-N.K.; specimens fabrication and material testing, H.-N.K. and J.-W.K.; experimentation and measurement, S.-M.L. and T.-S.K.; data curation, S.-M.L. and T.-S.K.; writing--original draft preparation, T.-S.K.; writing--review and editing, S.-M.L. and T.-S.K.; visualization, T.-S.K.; supervision, T.-S.K.; project administration, T.-S.K.; funding acquisition, J.-W.K. All authors have read and agreed to the published version of the manuscript. This research was funded by the Korea Institute of Material Science, grant number PNK8830.  
Not applicable.  
The authors declare no conflict of interest.