Ductile‐Regime Machining of Germanium and Silicon

TLDR

The ductile regime enables optical‑quality finishes on brittle germanium and silicon by controlling the transition from plastic flow to fracture along the tool nose. The study used single‑point diamond turning with an interrupted‑cutting test and a new model to experimentally determine the critical‑depth parameter and its dependence on tool geometry and clearance angle. Despite operating in the ductile regime, a substantial portion of material removal still occurs by fracture because of the complex interaction between tool geometry, machining parameters, and material response.

Abstract

Precision machining of germanium and silicon was studied using single‐point diamond turning. Special attention was directed to the so‐called ductile regime wherein optical quality surface finishes can be machined directly on brittle materials. A novel interrupted‐cutting test and a new model of the machining process were used to measure a critical‐depth parameter experimentally. This parameter governs the transition from plastic flow to fracture along the tool nose. The critical‐depth parameter can be used to provide physical insight into the effect of various machining parameters such as tool rake angle or tool clearnace angle. Because of a complex interplay between tool geometry, machining parameters, and material response, a large fraction of material removal occurs by fracture even when ductile‐regime conditions are achieved.