Effect of resultant force direction in machining of single crystal (100)Ge

On-axis single point diamond turning experiments were conducted on (100)Ge to investigate the relation between the direction of the resultant force and the surface topography. This was done by measuring cutting and thrust forces for feedrates ranging from 0.3 μm/rev to 12 μm/rev. The geometrical relation between the resultant force, slip systems and fracture systems was investigated using the Schmid factor Sf and the fracture factor Ff. Their ratio [SfFf]* was used to identify the cutting directions that were more favorable for slip and fracture. The surface topography, measured by AFM, corresponded with the [SfFf]* prediction. Three regimes were identified on (100)Ge depending on the resultant force angle f. When φ < 40°, fracture is predicted for cutting directions along <110>. When 40° < φ < 55, fracture is predicted for cutting directions along both <100> and <110>. When φ > 55°, fracture is predicted for cutting directions along <100>. The study of [SfFf]* for the Ge lattice indicates that fracture is the most favorable when the force is aligned with the <110> and <111> direction families. This study shows that the slip and fracture systems can be used in machining of Ge in order to suppress fracture and favor shear deformation.