Experimental and numerical studies on ductile regime machining of silicon carbide and silicon nitride
Ceramic materials such as silicon carbide and silicon nitride are hard and brittle. Conventional grinding or machining of these materials is by brittle fracture which leaves microcracks and pits on the surface after grinding. For quality surface finish, these materials require further finishing operations such as lapping and polishing. These finishing processes can be avoided if the ceramic materials can be machined similar to metals in the ductile regime. Recent machining studies on brittle materials such as silicon and germanium have shown that ductile regime machining using a single point diamond tool can produce a mirror-like finish provided various machining parameters such as the feed, cutting speed, depth of cut, cutting edge radius and tool rake angle are properly controlled so that the material deforms plastically during machining. The main objective of the present work is to study this type of machining in detail for the ceramic materials, silicon carbide and silicon nitride using experimental and numerical tools. Scratching and diamond turning experiments are carried out to understand the effect of various parameters that influence ductile regime machining of silicon carbide. Edge machining experiments are also carried out on silicon nitride to identify the possible mechanisms that cause diamond tool wear and their dependence on various machining parameters. Numerical modeling of machining of silicon carbide is carried out to study the possibility of phase transformation during machining by considering the initial stages of machining prior to material separation as a nanoindentation problem. Conditions conducive to phase transformations are determined from these studies. Assuming phase transformations, orthogonal cutting simulations of SiC are also carried out using the finite element analysis tool ABAQUS/Explicit for various cutting parameters. The studies show that the hydrostatic pressures reach values in excess of the hardness values of the material during machining which supports the hypothesis on ductile regime machining via a High Pressure Phase Transformation (HPPT).