2.8.1.5 Effect on Tool Production
High sintering temperatures over 1300 °C can occur in manufacturing of vitrified bonded tools. In particular, diamond features low thermal wear resistance in air, which forced manufacturers to develop special low-temperature sintered bonds and to apply inert atmospheres [LINK15].
Electric and magnetic properties are important for electro-plated bonds because they affect the deposition of the galvanic bond on grit and tool body [LINK15]. In particular, synthetic diamonds contain metallic inclusions, mostly of ferromagnetic character [YIN00]. For the tool manufacturing process, it is therefore necessary to separate between magnetic and non-magnetic grits.
2.8.1.6 Effect on Tool Performance
In the use phase of abrasive grits, the most important thermal properties are the thermal conductivity, the point of softening under load, and the melting point [KLOC05a, p. 34]. Thermal conductivity describes the material’s ability to level temperature differences. The grits will be loaded with a nearly punctiform heat source at the cutting edges during chip formation. With high thermal conductivity, the heat will distribute quickly along the grit volume.
For corundum, the temperature conductivity decreases rapidly with increasing temperature [KLOC05a, p. 34 f., COES71]. For high temperatures, it can be expected that the heat load concentrates more and more on the cutting edge leading to heat peaks. Thermal stresses inside the grit increase, being intensified by the simultaneously increasing thermal expansion coefficient. Thermal stress can occur between grit and bonding for strongly distinct thermal expansion coefficients [KLOC05a, p. 34 f.]. In synthesized diamonds, the thermal expansion of the metallic inclusions can induce grit fracture [MARI07].
High chemical resistance is desired for the grits when they interact with the air, cooling lubricant, or workpiece material. Chemical reactions could weaken the grit and need to be avoided also at higher pressures and temperatures [KLOC05a, p. 19].
2.8.2 Distribution of Characteristics Within Batch
Grit characteristics in a batch appear always in a range. A narrow distribution of characteristics allows a good predictability for the later tool performance [DYER79]. Abrasive layers should be homogeneous to have constant performance during lifetime and no imbalance during tool rotation. Grit density and grit size are related to the number of cutting edges in a bonded abrasive tool [YEGE86].