Characterization of machinability of sintered steel foams having different porosities during drilling operations

Abstract

Steel foams are a new class of engineering materials with exceptional structure and properties. Foams produced by powder metallurgy generally have a near-net shape, however, sometimes machining operations may be required. The presence of porosity in steel foams significantly affects the cutting process and causes poor machinability. This study deals with the evaluation of the machinability of Cu-Ni-Mo-based steel foams having different porosity produced by powder metallurgy. High speed steel and carbide-tipped drills were used for the drilling. All tests were performed in dry condition with drill diameter of 3 mm. The drilling characteristics were evaluated in terms of the surface roughness, chip formation, drilling force, tool wear, microstructure and hardness change after drilling. The machinability was also evaluated by measuring average width of breakout and skewness values of the hole drilled. The results indicated that the increase of porosity negatively affected the drilling quality of high porous steels. Both drills broke the chips in powder form and produced discontinuous chips. High porous parts exhibited higher hardness change as compared to lower ones. The carbide drill showed acceptable drilling forces and surface quality. HSS drill is not suitable for drilling due to poor hole quality and high drill wear.