Changes of cutting performance under different workpiece removal volume during normal speed and high speed milling of compacted graphite iron

Abstract

Compacted graphite iron (CGI) possesses good mechanical properties and thermal properties in comparison to gray cast iron (GCI) and spherical graphite spheroidal cast iron (SGI). However, the machinability of CGI is poor, and the cutting tool wear is very fast during the machining of CGI, which can lead to the changes of the cutting force and the machined surface integrity. The present study investigates the influence of workpiece material removal volume (Q) on the cutting tool wear, cutting force, machined surface roughness, and morphology under normal (V = 134 m/min) and high cutting speed process (V = 800 m/min). The result shows that Q had a more obvious effect on the value of cutting forces when the cutting speed was 800/min, while the effect was slight when the cutting speed was 134 m/min. However, the effect of Q on the direction of the resultant cutting force was small, and the direction of the resultant cutting force was more likely to be affected by the increase of cutting speed. The effect of Q on the machined surface roughness Ra and Rz was different between normal and high cutting speed process. Dark and bright areas can be found on the machined surfaces obtained under the normal speed cutting process, and the ratio of dark area to total area P can be used as a parameter to measure the machined surface quality. The flank wear of the cutting tool used for normal speed cutting process can be divided into brighter cemented carbide region and darker coating wear region due to the low wear rate, while only the brighter cemented carbide wear region was found on the tool used for high cutting speed process. Cracks could be found on the cutting tool used for both normal cutting speed process and high cutting speed process. However, the crack propagation appeared faster under high cutting speed process, chipping was formed near the crack. The depth and width of the crater wear under normal cutting speed process were larger than that under high cutting speed process.