Mapping ductile-to-fragile transition and the effect of tool nose radius in diamond turning of single-crystal silicon

Abstract

Although it has long been known that tools with more negative rake angles allow the ductile regime to be achieved when machining monocrystalline silicon; little has been discussed about the tool-material interaction in terms of the microgeometric contact of the tool tip at this interface. In this paper, the tool rake angle was varied in order to change the undeformed chip thickness value once the tool cutting radius, formed in front of the tool rake face, changes when the tool rake angle becomes more negative. Based on the statistical design of the experiment applied to cutting tests, a map relating values of transition pressure and different crystallographic directions is built to assist in determining machining conditions with a ductile response within a wider spectrum based on tool rake angle under different machining conditions. The results obtained allowed to answer questions under which machining conditions and tool geometry account for better surface finishes, lower machining forces, and lower residual stresses. The response surfaces generated provided answers capable of establishing under which cutting radii yielded more ductile mode material removal and avoided a brittle response, related to anisotropic response due to change in the crystallographic direction. Finally, we used the brittle-to-ductile transition map to determine a more suitable machining condition to diamond turn Fresnel lenses in single crystal silicon.