Research on the serrated chip in the milling of compacted graphite iron by cemented carbide tool

Abstract

The good physical and mechanical properties of compacted graphite iron (CGI) make it the ideal material for modern fuel-efficient diesel engine. However, it is difficult to be machined in comparison with gray cast iron (GCI). Serrated chip is a common phenomenon in the milling of CGI, and the formation of the serrated chip can influence the oscillation of the cutting force, fluctuation of the contact length, and roughness of the machined surface. This study investigated the chip formation process and the change of chip morphology in the milling process of CGI (GJV450) with an increase in the cutting speed and feed rate under normal and high cutting speed process. The results showed that the cutting chip changed from serrated-type to needle-type with an increase in the cutting speed. Although the cutting speed is far below the normal cutting speed range, continuous chip cannot be formed. For high cutting speed, increase in feed rate changed the chip type from serrated-type to needle-type. Both the cutting speed and feed rate influenced the serrated morphology sizes. Adiabatic shear zone cannot be found on the serrated chip, and brittle fracture surface was found on the upper side of the serrated chip side surface while the plastic fracture surface was found on the lower side of the side surface. The periodic brittle fracture theory can be used to explain the formation mechanism of the serrated chip during milling of CGI.