Influence of distribution and size of graphite particle on the machinability of nodular cast iron

Abstract

Nodular cast iron (NCI), also known as particulate metal matrix composites (PMMCs), is extensively utilized in the manufacturing of pistons for high-power engines. However, poor machinability is a significant problem due to the inherent microstructural inhomogeneity of the NCI. Therefore, this study aims to investigate influence of graphite particle distribution and size on the machinability of NCI. Microstructure of NCI is experimentally examined and quantitatively analyzed, and NCI is treated as a three-phase composite (i.e., matrix-interface-graphite particles). Graphite particles are considered as a plastic material, and debonding of interfaces is taken into account. Based on average particle size and volume fraction of graphite nodules, four microstructural models with different particle sizes and distributions are discussed, and turning experiments are conducted to validate simulation results. The findings reveal that graphite particles of different sizes and distributions affect stress–strain distribution in the cutting region of the material. As the distance between the graphite particles and the cutting tool increases, their influence on the stress–strain distribution becomes less significant. Furthermore, random distribution of graphite particles is more likely to result in complex crack initiation and expansion, leading to more pronounced serrated chips. The distribution of graphite particles has a more significant impact on the stability of cutting forces compared to the particle size. Both experiments and simulation results show that cavities and burrs are appeared along the cutting path because of graphite nodules, which reduces the surface quality and affects the subsequent use of the parts. On the one hand, the present work provides guidance for the finite element modelling of NCI, which is helpful to improve the precision of cutting simulation. On the other hand, by integrating advanced manufacturing technology to regulate the microstructure and cutting parameter of NCI, the present study can provide data basis and numerical analysis support for improving the machinability of NCI.