Empirical Study of the Effect of Cutting Tool Geometry and Coating Type on Machinability of Nodular Cast Iron in the Nigerian Foundry and Machining Industry

Nodular cast iron is extensively used in the production of automotive and industrial machinery components by Nigerian foundries serving the Nnewi and Lagos manufacturing clusters, and its machinability characteristics critically determine the productivity and tooling costs of subsequent machining operations at small and medium-scale machine shops. This study empirically investigates the influence of cutting tool geometry, specifically nose radius and relief angle, and coating type on the machinability of nodular cast iron grade 500-7 produced at a foundry in Onitsha, Anambra State. A factorial experiment was designed using three nose radii of 0.4, 0.8, and 1.2 millimetres, two relief angles of 6 and 11 degrees, and three carbide insert coating types comprising uncoated, TiN-coated, and TiAlN-coated inserts, with cutting speed and feed rate held constant at values representative of current practice. Machinability responses measured included surface roughness, cutting force in three axes, tool flank wear after 60 minutes of cutting, and chip morphology. Analysis of variance identified coating type and nose radius as the most significant factors influencing surface roughness and tool wear respectively. TiAlN-coated inserts produced the lowest flank wear of 0.12 millimetres after 60 minutes, compared to 0.31 millimetres for uncoated carbide. Surface roughness was minimised at a nose radius of 0.8 millimetres, achieving Ra of 0.96 micrometres under optimised conditions. Specific cutting energy and chip curl characteristics correlated with graphite nodule distribution in the cast iron microstructure. Keywords: machinability, nodular cast iron, cutting tool coating, tool geometry, surface roughness.