Jacek K Kaminski

Investigation of tool wear mechanisms in CGI machining

In this study, the tool wear, including wear mechanisms on coated cemented carbide inserts were investigated in the turning of Compacted Graphite Iron (CGI) materials with varying nodularity. The results showed that increasing nodularity, in the range of 5-62%, affects wear at moderate and high cutting speeds without having the same impact at lower cutting speeds. A small difference in nodularity, in the lower range, such as an increase from 5% to 20%, has a more significant impact on wear than an increase from 20% to 62%.

Machinability of compacted graphite iron (CGI) and flake graphite iron (FGI) with coated carbide

Compacted graphite iron (CGI) has an important role in manufacturing of new generation engines. Better strength of CGI, as compared to flake graphite iron (FGI), allows CGI engine to perform at higher peak pressure, higher fuel efficiency and lower emission rate. However, the machinability of CGI is as poor as compared to FGI. The machinability of CGI is an area that needs to be studied in a better way to cut the production cost of the engine. It is a well known fact that the as-cast engine block has varying microstructure and mechanical properties due to different cooling rates at different locations of such a geometrically complex component. This has highlighted the need for studying machinability as a function of microstructural and mechanical properties so that the machining process could be optimised. For this reason, machinability of 18 different types of CGI materials along with two FGI materials has been studied, in terms of cutting force and tool life, in a turning operation in this work.

An experimental investigation of temperature and machinability in turning of compacted graphite irons

The life and the performance of an insert in metal cutting are mainly dependent on the heat that is generated in the contact zones on the tool rake face with chips and on the flank face with the transient and machined surfaces. According to tool life standard, the wear on the flank face is usually taken as a decision for tool life. This occurs because of contact stresses, temperature and friction between tool workpiece contacts. Hence, knowledge of temperature on the flank face becomes important. The temperature on the flank face has been measured in this work for different CGI materials having different microstructure and physical properties in a turning operation. It has been seen that there is no significant difference of flank temperature, while machining different CGI materials having hardness from (140 to 236 HBW). For temperature measurement, special inserts integrated with gold-platinum thermocouple on the flank face were used. It has been noticed that the materials having 31% resultant cutting force difference and six to eight times tool life difference have almost same temperature on the flank face measured at different distances from the edge line of the insert.

Microstructure characterization of white layer formed by hard turning and wire electric discharge machining in high carbon steel (AISI 52100)

White layers, formed during hard turning and wire electric discharge machining, were characterized by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Different cutting speeds and flank wear were utilized in order to obtain different thermally and/or plastically deformed white layer. Since the white layer after wire electric discharge machining is mainly thermally induced, it was used as a reference structure. In the investigation, both bainitic and martensitic structures were studied. With a constant flank wear of 0.175 mm the thickness of the white layer increased from 1.5 μm to 3 μm as the cutting speed was increased. In both processes the white layer were characterized by nanosized grains and surface tensile residual stresses. M3C carbides were observed in the hard turned white layer, indicating that the time and temperature needed for completely dissolving the carbides were not reached during cutting. For both materials the white layers formed by wire electric discharge machining consisted of ~ 30 vol. % of retained austenite. Observation regarding the volume fraction of the retained austenite in the white layer formed by hard turning for martensitic material showed an increase in the volume fraction of retained austenite from ~ 2 - 3 vol. % to ~ 6 vol. %, while this observation was not seen in the white layer formed in the bainitic material.

An Experimental Investigation of the Influence of Cutting Edge Geometry on the Machinability of Compacted Graphite Iron

Compacted graphite iron (CGI) is considered as the potential replacement of flake graphite iron (FGI) for the manufacturing of new generation high power diesel engines. Use of CGI, that have higher strength and stiffness as compared to FGI, allows engine to perform at higher peak pressure with higher fuel efficiency and lower emission rate. However, not only for its potential, CGI is of an area of interest in metal cutting research because of its poor machinability as compared to that of FGI. The higher strength of CGI causes a faster tool wear rate in continuous machining operation even in low cutting speed as compared to that for FGI. This study investigated the influence of cutting edge geometry at different cutting parameters on the machinability of CGI in terms of tool life, cutting force and surface roughness and integrity in internal turning operation under wet condition. It has been seen that the cutting edge radius has significant effect on tool life and cutting forces. The results can be used to select optimum cutting tool geometry for continuous machining of CGI.