Fresamento frontal de ferros fundidos de alta resistência

Abstract

In recent years, the automotive industry has sought to implement in the production line engines with higher combustion chamber pressures, therefore, more efficient and less polluting, in order to remain competitive in the market. For this purpose, they try to use lighter engines with smaller wall thicknesses, thus conquering a space in the industrial scenario, aiming the global competition. Due to its mechanical and thermal properties, gray cast iron is used in the manufacturing of blocks and heads of combustion engines, as they possess characteristics such as low manufacturing cost and good machinability mainly because of the large amount of free graphite in its microstructure, good damping and dimensional stability, which become fundamental in the application of these materials in automotive parts. However, this material has lower mechanical strength than some other types of cast irons, such as the Compacted Graphite Iron (CGI). One way to improve the performance of gray cast iron engines is to increase its mechanical strength. The present work aims to evaluate the machinability of high strength gray cast iron FC 300 grade (FC300(Mo+RG)), with graphite refinement and alloyed with molybdenum, for application in cylinder heads, in comparison with materials already used for this purpose: gray cast iron FC 250 (FC250), gray cast iron FC 300 alloyed with molybdenum (FC300(Mo)) and compacted graphite iron FV 450 (CGI). The machinability was evaluated by tool life trials in the dry face milling process, an operation frequently used in the manufacturing of cylinder heads, with two carbide tool geometries, and the surface roughness was also measured. Two levels of cutting speeds (vc) = 230 and 350 (m/min) and feed rates (fz) = 0,1 e 0,2 (mm/tooth) were used. The depth of cut was kept constant at (ap) = 1 (mm). Among the evaluated materials, the FC300(Mo+RG) cast iron presented the worse machinability indexes, as a result of its higher mechanical strength and hardness. As for the surface finishing, at the beginning of the tool life tests (without considering the wear of the tool), at the highest cutting speed, presented the best results, but at the lowest cutting speed the worst.