Study On Preparation And Performance Of Vitrified Bond CBN Abrasive Tools

The vitrified bond CBN grinding wheels are widely used in grinding metal materials.High grinding efficiency,small grinding force,low grinding temperature,high precision,and easy dressing are their outstanding advantages.The key to preparing high-performance vitrified bond CBN grinding wheels is to further improve the wettability between vitrified bond and the CBN abrasive,control the porosity and pore distribution,form a homogeneous structure.First,the effect of Ti powder addition on the bending strength and phase composition of the vitrified bond was investigated.Then,the abrasive particles was micro-oxidized,the influence of this pretreatment on its microstructure and corresponding grinding tool's mechanical properties were investigated.Selecting Polymethylmethacrylate(PMMA)as pore former and analysing the effect of this operation on the bending strength and grinding performance of abrasive tools.Finally,the effects of cold isostatic pressing(CIP)on the mechanical properties and microstructure of abrasive tools were studied.X-ray diffractometer,nuclear magnetic resonance detector,thermogravimetric analyzer,Scanning electron microscope(SEM),electronic universal testing machine,still water and equal equipment were used to test and characterize the phase composition,CBN thermal properties,microstructure,bending resistance,density uniformity and other properties of samples.The result are as follows:(1)Different contents of Ti powder(wt%=0,2,4,6,8)were added to the binder.When increased the amount of Ti powder,the fluidity of the vitrified bond was improved,which showed that Ti powder addition is conducive to the densification of binder phase.Ti powder was oxidized to Ti_xO at sintering temperature of 660?,and participated in the formation of glass network in the form of[Ti O₄]tetrahedron.In a certain range,the increase of Ti powder content increased the strength of the vitrified bond significantly.(2)After the 950°C micro-oxidation treatment of CBN abrasive,the edges and corners of CBN surface became smooth,the bending strength of the abrasive tool increased by 5.2%,and the thermal shock resistance of CBN was also improved.(3)It is possible to control the level of porosity of grinding tools by changing the amount of PMMA.With the increase of PMMA content,the bending strength of the abrasive tool has declined.During the grinding process,the grinding wheel with 9vol.%of the pore former hardly appeared sticky chips,and its grinding efficiency was significantly better than that of the sample without PMMA.(4)For abrasive tools with 200%and 160%CBN concentrations,the increase in cold isostatic pressing could improve bending strength of tools by decreasing porosity,reducing crack initiation,shorting the binder bridge and increasing its cross-sectional area,improving the wettability between the CBN particles and vitrified binder phase.(5)When the samples pressed at 30 MPa under cold isostatic pressing,their variances of longitudinal and transverse density are 0.016 g²/cm⁶and 0.003 g²/cm⁶,which are smaller than unidirectional cold pressing(0.045 g²/cm⁶,0.022 g²/cm⁶)and bidirectional cold pressing(0.024 g²/cm⁶,0.015 g²/cm⁶).The cold isostatic pressing is helpful to obtain abrasive tools with uniform density.