INVESTIGATION OF SURFACE FINISH ON ORTHOGONALLY MACHINED HEAT-TREATED NODULAR CAST IRON

ABSTRACT This study investigates the influence of annealing heat treatment temperature on the surface roughness characteristics of orthogonally machined nodular cast iron (NCI). NCI, known for its excellent mechanical properties, is widely used in various industries and the surface finish of machined components significantly impacts their performance and longevity. Annealing, a critical heat treatment process, is employed to modify the microstructure of NCI, enhancing its machinability. This research aims to establish the relationship between annealing temperature and the resulting surface roughness after orthogonal machining. The methodology involves annealing NCI samples under different temperatures (750°C - 950°C), followed by orthogonal machining using different cutting speeds (340rpm - 1400 rpm). Surface finish was then quantified using average surface roughness. The hardness and microstructural changes induced by annealing were respectively characterized using vicker hardness tester and metallographic techniques. The findings indicate that increasing the annealing temperature generally leads to improved surface finishes, with the optimal surface roughness of 2.62µm observed at 900°C. Cutting speed also significantly affects surface roughness, with higher speeds resulting in smoother surfaces up to a certain threshold. However, excessive cutting speeds can lead to increased roughness due to thermal effects, tool wear and machine vibration. The optimal combination of annealing temperature and cutting speed for achieving superior surface quality was identified as 900°C and 1150 rpm respectively, yielding an average surface roughness value of 2.62µm. It was further observed that the effect of annealing heat treatment is mostly to lower the hardness of metal so they can be machined at relative ease. The findings indicate that optimizing the annealing process can lead to significant improvements in the surface finish of orthogonally machined NCI components. This research provides valuable insights into the machinability of annealed NCI and offers practical guidelines for enhancing manufacturing processes, ultimately improving product quality and performance.