Experimental and simulation study of material removal behavior in ultra-precision turning of magnesium aluminate spinel (MgAl₂O₄)

Ultra-precision turning is one of the effective process methods to machine magnesium aluminate spinel with high efficiency and low damage. The influences of turning parameters and material microstructure on material removal behavior in ultra-precision turning of magnesium aluminate spinel (MgAl₂O₄) were investigated through experiment and simulation. A finite element method (FEM) model was developed to understand the effect of tool rake angle, cutting depth and cutting speed on the machined surface. Simulation results were verified experimentally by micro-groove cutting test. A negative rake angle tool can improve the plasticity of spinel and increase the ductile-brittle transition depth. However, the compressive stress field generated by the negative rake face brings the risk of more serious damage. Reducing cutting depth can suppress cracks. Elevating the cutting speed within a certain range does not deteriorate the surface quality and can increase the material removal rate. The anisotropy of spinel grains at micro-scale is of a great influence on the material behavior, leading to a non-uniform surface topography. In order to obtain a high-quality machined surface, the undeformed chip thickness must be smaller than the ductile-brittle transition depth of the most brittle grain. Experimental and simulation results suggest an optimized combination of turning parameters for a smooth surface by ultra-precision turning to achieve low-damage ultra-precision turning of polycrystalline hard and brittle materials.