This study has focused on analyzing the impact of material characteristics and grinding conditions on the surface roughness in ELID grinding of ceramic materials intended for bearing balls. The main research objective was to examine the feasibility of achieving the required surface roughness for G5 class bearing balls through a high-efficiency and high-precision ELID grinding process. Three types of silicon nitride specimens and two types of grinding wheels with cBN and diamond abrasives were prepared for the experiments. An HP (high-pressure) specimen was fabricated through high-temperature and high-pressure sintering at 1700 °C for 2 h, containing a composition of Y₂O₃ and MgO in Si₃N₄, while GPS 1hr and GPS 6hr specimens were prepared using gas-pressure sintering for 1 h and 6 h, respectively. From the experimental results, it has been confirmed through surface morphology and surface roughness analysis that material characteristics and grinding parameters affect the surface roughness of silicon nitride ceramics during the grinding process. The surface ground with a #2000 diamond wheel is at a level that can satisfy the required surface roughness, 0.014 um or less in G5 class bearing balls. Based on the analysis of surface morphology and roughness in grinding processes, the #325 cBN wheel exhibited excellent performance in rough grinding, while the #2000 diamond wheel demonstrated highly effective surface finishing performance, indicating that the combination of these two abrasives can be effectively utilized for high-efficiency and high-precision nanosurface machining of silicon nitride ceramics.

Silicon nitride (Si₃N₄) is used for high-speed rotating bearings in machine tools, aircraft, and turbo pumps due to its excellent material properties such as high-temperature strength, hardness, and fracture toughness. Grinding with fixed abrasives enables high shape accuracy and high efficiency in machining brittle materials. However, it is difficult to completely remove surface damage, which limits its use in products requiring a nano surface. These defects also result in reduced reliability and shortened lifespan. Magnetic-assisted polishing (MAP) is a technology that can achieve a fine surface by using a mixture of iron powder and abrasives, but it requires a lot of time due to the low material removal rate (MRR). Therefore, this study developed a hybrid processing technology using a metal-bonded grinding wheel and a slurry with hard abrasives for the high precision of silicon nitride ceramic ball bearings. Experiments were conducted in order to compare and analyze the surface roughness and material removal rate. Through MAP, using a grinding wheel with low grit (#325), high-efficiency machining performance was confirmed with a maximum material removal rate of 1.193 mg/min. In MAP, using a grinding wheel with high grit (#2000), a nano-level surface roughness of 6.5 nm Ra was achieved.

Chemically vapor-deposited silicon carbide (CVD-SiC) is a high-performance material that possesses excellent mechanical, chemical, and electrical properties, making it highly promising for components in the semiconductor, aerospace, and automotive industries. However, its inherent hardness and brittleness present significant challenges to precision machining, thereby hindering the commercialization of reliable, high-precision parts. Therefore, the application of CVD-SiC in fields that require ultra-precision shaping and nanometric surface finishing necessitates the exploration of machining methods specifically tailored to the material’s unique characteristics. This paper presents a comprehensive review of CVD-SiC machining—from traditional mechanical approaches to advanced hybrid and high-energy techniques—aimed at overcoming machining limitations from its material properties and achieving high-efficiency and nanometric-quality machining. The study discusses various grinding tools designed for superior surface finishing and efficient material removal, as well as machining techniques that utilize micro-scale removal mechanisms for ductile regime machining. Looking ahead, the integration of AI-based process optimization with enhanced machining methods is expected to fully exploit the superior properties of CVD-SiC and broaden its industrial application as a high-performance material.

Chemical Vapor Deposition Silicon Carbide (CVD-SiC) is a suitable material for satellite-borne optical payloads, such as space observation mirrors, owing to its exceptional mechanical and chemical properties, superior optical characteristics, and robust resistance to space radiation. However, its inherent high hardness and brittleness present substantial machining challenges, necessitating systematic selection of processing parameters tailored to the specific functional objectives of each grinding process. This study aims to quantitatively derive optimal machining conditions across the process stages of Electrolytic In-Process Dressing (ELID) grinding for CVD-SiC mirrors. ELID grinding experiments were conducted through three sequential phases: coarse grinding, medium finishing, and finishing/ultra-finishing. Based on the surface roughness and material removal rates, a Multi-Criteria Decision Making (MCDM) evaluation utilizing the Faire Un Choix Adéquat (FUCA) method was performed. Hybrid weights were synthesized by applying the Bonferroni operator to weights derived from various techniques, including EQUAL, RS, ROC, and MEREC. The proposed approach determined the optimal machining conditions that align with the specific technical goals of each process stage. These findings suggest that the FUCA-based MCDM evaluation integrated with Bonferroni fusion weights offers a useful approach for identifying optimal CVD-SiC ELID grinding conditions among those tested.