Transient stress-induced tool wear mechanisms and adhesive layer formation in single-point diamond fly-cutting of KDP crystals

KDP crystals are essential for high-energy laser systems due to their unique optical properties, yet their brittleness and stress sensitivity present challenges for ultra-precision machining. Single-point diamond fly-cutting (SPDF) is preferred for high-accuracy machining of large KDP components, but tool wear remains a critical issue due to transient impact forces generated with each tool-crystal contact. While most research has focused on steady-state conditions, the effects of transient impacts on tool wear and surface quality are often overlooked. This study addresses this gap by developing and validating a novel tool wear model that includes dynamic interactions between the diamond tool and KDP crystals. Models for cutting forces and stress distributions under both steady-state and transient conditions were established, followed by a tool cutting edge wear model that incorporates these effects. Results show that maximum transient stresses reach 3.28 GPa at the separation point between the rake face and cutting edge, while stresses on the cutting edge itself reach 1.46 GPa. These elevated stress levels lead to tool wear rates in SPDF that are 2.46 times higher than those under steady-state conditions in turning. Additionally, progressive tool wear and an adhesive layer in SPDF increase surface roughness, producing deeper, irregular scratches beyond typical feed marks. The adhesive layer forms through chemical adsorption onto oxygen-containing groups on the worn tool surface, with hydrogen bonding within the chips. These insights support optimizing machining parameters to enhance tool longevity and surface quality in KDP crystal applications.