Preparation Of Vitrified Bond For CBN Grinding Tools

Vitrified bond cBN grinding tools have advantages of strong grinding force, not burning the workpiece with a high-speed processing, durable and dressing easily. It is the ideal high-speed, high efficiency and high precision grinding tools, especially there are unparalleled advantages in the processing of ferrous metals and their alloys.Therefore, it is of great significance to study the vitrified bond of high performance cBN grinding tools.In this paper, on the basis of SiO2-Al2O3-B2O3-R2O-RO system,the effects of the molar ratio of (Na2O+Li2O) to SiO2, which defined as (Na2O+Li2O)/SiO2, on the structure and properties of the vitrified bond were studied by means of FTIR, XRD,SEM,hardness,thermal expansion coefficient and bending strength analysis. The effects of the addition of MgF2, ?-spodumene and AIN on the mechanical properties,thermal expansion coefficient, phase and microstructure of the basic vitrified bond were studied. The effects of the (Na2O+Li2O)/SiO2 of vitrified bond,particle size of cBN abrasive and the addition of MgF2 on the porosity, microstructure, bending strength and grinding performance of cBN grinding tools were also investigated.The results show that (Na2O+Li2O)/SiO2 of vitrified bond affected its melting degree, the combination of [SiO4], [BO3] and [BO4], as well as the content of glass phase. The refractoriness of the vitrified bond decreased with the increasing of value of (Na2O+Li2O)/SiO2. When the value of (Na2O+Li2O)/SiO2 is 0.12, the bending strength of the vitrified bond sintered at 680 ? for 2 h was the highest, which reached 152 MPa. With the increasing of (Na2O+Li2O)/SiO2, the optimum sintering temperature and the bending strength of the vitrified bond sintered samples decreased gradually. The microhardness tend to decreasing correspongdingly and thermal expansion coefficient tend to rising correspongdingly, but it will be affected by the phase composition and microstructure of the sintered samples.The thermal expansion coefficient of the vitrified bond sintered samples decreased gradually with the increasing addition of AIN, but there are little effect with the addition of ?-spodumene and MgF2. The addition of AlN and ?-spodumene reduces the bending strength of the sintered samples, while the addition of MgF2 increase it. When the MgF2 content is 8 wt%, the bending strength reaches the maximum value of 153 MPa, increased by 10% compared to that without the addition of MgF2. The (Na2O+Li2O)/SiO2 of vitrified bond has a great influence on the bending strength, porosity and grinding performance of cBN grinding tools.When (Na2O+Li2O)/SiO2 increased from 0.12 through 0.16 to 0.20, the maximum bending strength and porosity of cBN grinding tools were decreased to 77, 70, 60 MPa, 19.78, 15.94 and 12.14 %, respectively. When (Na2O+Li2O)/SiO2 is 0.16, the grinding performance of cBN grinding tool is the best. The bending strength and grinding performance of the cBN grindings tools become worse with the increasing of particle size of cBN grinding tools used. After adding 8 wt% MgF2 to the vitrified bond with the (Na2O+Li2O)/SiO2 of 0.12, the porosity of the cBN grinding tools was increased, the bending strength was slightly decreased, and the grinding performance was slightly improved.