Failure mechanisms and cutting characteristics of brazed single diamond grains

Abstract

The knowledge about the cutting characteristics and the critical loading of brazed diamonds is essential for a safe and economic application of engineered grinding tools. Scratch tests were performed with single grains. The experiments were conducted with standard polyhedral diamond grains of different sizes, ranging from 300 to 850 μm, brazed with an Ag-Cu-based and a Cu-Sn-based active filler alloy onto a steel pin. Two failure mechanisms were revealed, namely “grain pullout” and “grain fracture”. Large grits mainly fail by grain fracture, whereas the smaller ones were mostly pulled out. This trend is supported by a simple mechanical model. The critical values, i.e. cutting force/scratch area, for grain fracture and grain pullout show a decrease with bigger grit size. Scratches are also analysed in terms of cutting characteristics. The dependency of the cutting and the normal force on the scratch area can be described by a power law with powers ranging between about 0.2 and 0.7, respectively. The measured cutting forces strongly depend on the rake angle, which was tested for −19.5° and −35.3°.