Sustainability Dimensions to Abrasive Grits

2.10.1 Technological Dimension

Table 2.7 summarizes the most important grit characteristics in grinding technol­ogy. In general, the grit type is chosen with regard to the machined material and the grit size is defined by the desired workpiece quality. The individual performance profiles of the grit types can be visualized in radar charts [HELL11].

The abrasive material should be harder than the machined material. In general, corundum and CBN are used for long-chipping, ductile materials, whereas silicon carbide and diamond are used for short-chipping, brittle materials or titanium alloys [KLOC09, HELL11, LINK12b]. Superabrasives are chosen in particular for the higher precision or higher performance applications due to their low wear rate and ability to achieve close size tolerances [ROWE09, LINK12b]. The reactivity of diamond with transition metals such as nickel and iron limits the use of diamond to machine these metals, especially steels. However, there are some applications with ferrous materials where diamond is the tool material of choice, e. g. honing of cast iron [MARI07]. Diamond covers many applications formerly conducted by SiC [JUCH78].

The higher thermal conductivity of superabrasives compared to conventional abrasives can reduce grinding temperatures drastically [ROWE09, LINK12b]. For a specific application, the use of corundum could lead to unfavorable tensile stresses in the part surface layer, whereas CBN could produce favorable compressive stress [BRIN82, BRIN04b]. However, there is a common understanding that the surface finish is rougher with CBN grits than with conventional wheels [LINK12b]. It is believed that sharper and more pointed cutting edges lead to earlier chip formation and shallower initial depth [MALK08]. CBN grits have typically chip angles between -60° and -70° and have sharper cutting edges than conventional abrasives [FERL92, p. 31].