Effect of increased mechanical strength on the machinability of graphite cast irons in face milling

Abstract

Due to the low cost and high vibration damping capacity, gray cast irons are commonly used in machine tool bases, in addition to applications with noise restrictions, such as engine blocks, housings, and brakes. The matrix's graphite, sul des, and ferrite/pearlite ratio are some of the most important parameters governing the machinability of the gray cast irons. This work aims to evaluate the machinability of high-resistance gray cast irons of the FC 300 grade, in two versions, with the addition of molybdenum (FC 300 (Mo) ) and with re ned graphite and addition of molybdenum (FC 300 (Mo+RG) ), for use in cylinder heads and engines blocks, compared to materials that have been used for this purpose, gray cast iron FC 250 and the compacted graphite cast iron FV450. The face milling process was chosen for the tests, as it is widely used in manufacturing cylinder heads and engine blocks. Uncoated cemented carbide tools with tangential rhomboid geometry were used in the experiments. Analysis of tool life and wear mechanisms and machined surfaces' quality (Ra roughness parameter) where the output variables are considered. The materials were characterized according to the cementite interlayer spacing and microhardness of the perlite matrix, the number of eutectic cells, and the distribution of manganese sul de inclusions, with those characterizations being correlated with the machinability results. The cutting speed and feed were varied, and the dry condition was used. Among the gray cast irons investigated, the FC 300 (Mo+RG) presented worse machinability rates because of its greater mechanical resistance and hardness. Regarding the surface nish, at the beginning of the tool life tests (without considering tool wear) and employing the highest cutting speed, the FC 300 (Mo+RG) showed the best results, but at the lowest cutting speed, the worst.