Abstract
Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle cutting. In this research, cutting characteristics in nanometric cutting of BK7 and fused silica glasses, including machined surface morphology, surface roughness, cutting force and specific cutting energy, were investigated with nanometric plunge-cutting experiments. The same cutting speed of 300 mm/min was used in the experiments with single-crystal diamond tool. CUCT was determined according to the mentioned cutting characteristics. The results revealed that 320 nm was found as the CUCT in BK7 cutting and 50 nm was determined as the size effect of undeformed chip thickness. A high-quality machined surface could be obtained with the undeformed chip thickness between 50 and 320 nm at ductile cutting stage. Moreover, no CUCT was identified in fused silica cutting with the current cutting conditions, and brittle-fracture mechanism was confirmed as the predominant chip-separation mode throughout the nanometric cutting operation.
Highlights
Precision optical components, made of hard-brittle materials such as ceramics and glasses, always require high-quality surface with good edge and crack-free zone
Where dc is critical undeformed chip thickness (CUCT), E is the Young’s modulus, H is the nano-hardness, KIC is the fracture toughness of mode I, and is a dimensionless material constant determined by the cutting conditions. was estimated as 0.15 for brittle materials derived by Bifano [10] in precision grinding tests
The crack proves the occurrence of brittle fracture in the cutting process. This stage was defined as ductile cutting and CUCT could be determined as
Summary
Made of hard-brittle materials such as ceramics and glasses, always require high-quality surface with good edge and crack-free zone. These hard and brittle characteristics would cause micro-fractures and micro-cracks during ultra-precision cutting process. Arif et al [15] established a predictive model regarding CUCT estimation for ductile-brittle transition, and validated the applicability in machining of single crystal silicon and BK7 glass. These studies have shown that CUCT exhibited consistent relation with the nature of work materials and machining conditions including cutting parameters and tool geometries. Several aspects including surface roughness, cutting-force generation and specific cutting energy were precisely investigated aiming to clarify the ductile-brittle transition point and the material removal regime during ductile and brittle cutting
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