Machining of grey cast iron on CNC machines: problems, mathematical modeling

Abstract

This study provides a comprehensive analysis of the mechanical machining of gray cast iron (grade SCH20) on CNC lathes, focusing on surface roughness, microstructural changes, and optimization of technological parameters. The research involved the use of modern measurement tools to evaluate surface roughness (Ra), Vickers hardness (HV), and characteristics of graphite inclusions in the material's structure. The experiments revealed that increasing the cutting speed to 3000 rpm results in the formation of a cementite white zone in the cutting area, enhancing the surface hardness to 261.5 HV and improving wear resistance. In contrast, lower cutting speeds preserve the ferrite-pearlite structure with minimal changes to the graphite inclusions. Mathematical modeling, performed through regression analysis, identified key technological factors influencing surface roughness and microstructure. The number of graphite inclusions (Ng) was found to be the most significant factor, as confirmed by the Pareto chart. The developed mathematical model enables the prediction of surface roughness based on machining parameters and optimizes the machining process. The results demonstrate the possibility of purposefully controlling the microstructure and material properties during the machining of gray cast iron to produce surfaces with increased hardness and wear resistance. This is particularly relevant for manufacturing components operating under intense friction and heavy loads, such as gears and shafts. The proposed methods offer a cost-effective alternative to heat treatment while improving the quality of finished products.