No abstract

Grey cast iron (GCI) is the most common material used in diesel engineCompact graphite iron is a material with intermediary properties between grey cast iron (GCI) and ductile cast iron (Sahm et al., 2002). Like in the GCI, the graphite particles in the CGI are flat, long, randomly oriented and interconnected. In the ductile iron they are in form of nodules (Warrick et al., 1999). However, as it can be seen in Fig. 1(b), the "worms" (as the graphite particles in the CGI are called) have something in common with the nodules of the ductile iron ( Fig. 1(a)), since both are much smaller than the graphite lamellas of the GCI (Fig. 1(c)). On the other hand, the morphology of CGI graphites is compact and with rounded tips, what makes the nucleation and growth of cracks more difficult than in the GCI. The sharp and lamellar graphites of the GCI with smooth surfaces (Fig. 1(c)) make this material more fragile than the other two (Löhe, 2005).The CGI alloys have good properties of mechanical strength, ductility, toughness, thermal shocks, damping and heat conductivity (Mocellin et al., 2004). These properties are better for the CGI part functioning, but make its machinability worse than the machinability of GCI.Compared with GCI, the CGI presents some advantages like reduction of the wall thickness of the parts for a same load, reduction of the safety factor due to a smaller variation of the cast properties, reduction of the fragile fractures during manufacturing, assembly and service due to its higher ductility and strength (Dawson, 1999).Compared with ductile cast iron, it can be said that with CGI it is easier to produce complex cast parts and the residual stresses are smaller due to the higher heat conductivity (what also helps to increase cutting tool life). Moreover, it presents smaller Young modulus and better machinability (Guesser, 2004). Milling of CGI engine blocksBesides the worm graphite particles, a certain percentage of spheroidal graphite nodules is also present in the CGI. As the nodularity increases, the material strenght also increases making the forces needed to cut the material higher. Moreover, with the nodularity growth, the heat conductivity decreases, decreasing machinabilty even more (Dawson, 2002).A factor that makes the engine blocks even more difficult to be machined is the great number of interruptions on the surface. Special care has to be taken in the mill cutter choice, because very positive tools reduce cutting force, but may generate tool life relatively lower when compared to the cutters with negative geometry, due to their small impact resistance.As the tool wears, workpiece surface roughness and flatness error increase. Besides tool wear, other important factors to obtain J. of the Braz. Soc. of Mech. Sci. & Eng.

Compacted Graphite Iron (CGI) is a good option for the manufacturing of engine blocks

No 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.