Investigation of surface properties in turn milling of particle-reinforced aluminium matrix composites using MCD-tipped tools

Abstract

Aluminium matrix composites (AMCs) consist of a comparably soft matrix alloy which is typically reinforced with at least one ceramic component such as fibres, whiskers, or particles. The additional ceramic components allow improved material properties but result in an increased tool wear in machining. Furthermore, the reinforcements lead to the generation of surface imperfections on the generated surface. The investigations aim for low roughness values, reduced surface imperfections, and strong compressive residual stresses. It is assumed that a combination of these properties benefits an improved fatigue behaviour. Turn milling experiments with single-edged monocrystalline diamond (MCD)-tipped tools are carried out to examine the influence of the cutting parameters and different clearance angles. The generated surfaces are evaluated considering roughness, porosity, and residual stress state. Additionally, the microstructure of the surface layer is analysed. In the investigated range, a cutting speed of 200 m/min, an axial feed of 1 mm, and a feed per tooth of 0.1 mm result in a reduced formation of surface imperfections. Moreover, using a tool with a clearance angle of 1° leads to smaller roughness values Rz and a lower valley void volume Vvv compared with a clearance angle of 5° for all combinations investigated. For all experiments, the generation of compressive residual stresses in the surface layer is observed. Higher absolute values of the compressive residual stresses are benefited by a reduced axial feed. EBSD analyses indicate that the grain structure in the surface layer is refined as a consequence of the cutting process. The research provides fundamentals in finishing of particle-reinforced AMCs by turn milling. A better understanding of the interaction between the cutting process and the surface properties is acquired.