Self-sharpening Behavior Of Single-layer Brazed Polycrystalline CBN Grinding Wheels

Polycrystalline CBN (PCBN for short) grains are multicrystalline CBN grains that are synthesizedby using the microcrystalline CBN particles and AlN ceramic binder material under high pressure andhigh temperature. PCBN grains could generate sequentially micro-fracture behavior to recover thegrain sharpness in the grinding process, which is called as the grain self-sharpening effect. Theself-sharpening behavior could ensure the sharp cutting edges and good wear resistance of the brazedabrasive tools. However, due to the insufficient investigation on self-sharpening behavior of PCBNgrains, the application of these abrasive tools is significantly limited.In the present investigation, the monolayer brazed grinding wheels were fabricated using PCBNgrains. The main goal is to correlate fractal theory, fracture behavior and the brazed PCBN wheeltopography for a further understanding of the self-sharpening mechanism effects on the performanceof wheel during high speed grinding. The results obtained could contribute to fulfilling the goodgrinding potential and the application of PCBN grains.The main work is summarized as follows:(1) The fractal analysis of wear topography of PCBN grain was conducted by means of theconstruction of micro fracture of grain in grinding process. The results obtained show that the fractaldimension of the grain wear topography formed due to micro-fracture takes a value of2.04019whileformed due to abrasion wear takes a value of2.03609.(2) The single grain grinding test block was developed in order to clarify the wear characteristics ofthe grain cutting edges in the process of high speed grinding of nickel superalloy GH4169. Based onthe reconstructed model, the fracture behavior and the self-sharpening mechanism of PCBN grainwere investigated. The results indicate that there is a close relationship between fractal dimension Dsand abrasion wear flat percentage Ag.(3) Comparative experiments were carried out between brazed wheels with multicrystalline CBNgrains and that with monocrystalline CBN grains during high speed grinding of GH4169. The wheeltopography was analyzed using statistical method. The results obtained demonstrate that differentwear characteristics of brazed wheel correspond to specific values in fractal dimension. That is,average fractal dimension for multicrystalline CBN wheel topography formed due to abrasive wear is2.04673, and formed due to micro-fracture is2.05140. In contrast, average fractal dimension formonocrystalline CBN wheel topography formed due to abrasive wear is2.04161, formed due to micro-fracture is2.04560and formed due to large micro-facture is2.04331. The effect ofself-sharpening on grinding force and force ratio was finally studied. The brazed wheel withmulticrystalline CBN grains exhibits better grinding performance than that with monocrystalline CBNgrains.