Studies On Vitrified Bond And Molding Technology Of Diamond Abrasive Tools

Diamond was the hardest materials in nature, and it had very high strength andwearability, so it was made into abrasive tools to prosess other difficult-to-machinematerials, such as cemented carbide、polycrystalline diamond compacts、ceramicmaterials, etc. Diamond was bad stability and to be oxidized easily under hightemperature, its crystal was damaged, so that grinding performance of abrasive toolsreduced greatly.Therefore, we developed new diamond grinding tool as a research focusof grinding industries.At present, the commonly bond varieties of diamond abrasive tools had resin、vitrified and metal. Vitrified bond diamond abrasive tools had very good applicationprospect because of its incomparable advantages with them, such as high processingefficiency, shape holding capacity, good rigidity, low cost process, etc. Vitrified bond ofdiamond abrasive tools should have low melting point、high strength and low heatexpansion coefficient to match lower the sintering, energy conservation, as well as acertain strength characteristics at low sintered temperature. Molding process of diamondabrasive tools had always been a weak link in industry of super rigid materials, and itwas neglected by people. The green body prepared by cold isostatic pressing had highdensity and uniformity, cold isostatic pressing could solve structure defects ofnon-uniform microstructure and flaws in the process of traditional forming process, so itprovided a immeasurable role to ensure further processing. Therefore, the objectives ofthis article were to look for vitrified bond of low melting temperature、high strength andlow thermal expansion coefficient, and explore effect on properties of vitrified bonddiamond abrasive tools by cold isostatic pressing.This paper studied effect of additives on properties and structure of vitrified bond used in diamond abrasive tools. Three vitrified bonds were made, namely bond No.1byusing tribasic base R2O-Al2O3-B2O3-SiO2as basic vitrified bond, bond No.2by addingappropriate alkali metal oxide MgO、ZnO and fluoride CaF2in the bond No.1, and bondNo.3by adding appropriate rare-earth metal oxide CeO2in the bond No.2. Meanwhilethe vitrified bond was used above. the paper studied effect of cold isostatic pressing、formula and sintering process on properties of vitrified bond diamond abrasive tools, toselect better property of formula and sintering process through comprehensive analysis,D45W5grinding wheel prepared by unidirection pressing、bidirectional pressing andcold isostatic pressing respectively, to do simulated grinding test and analyzsystematically effect of molding process factors on grinding properties of wheel.The study result showed that: with the increase of the alkali earth metal ratio invitrified bond, mechanical properties of vitrified bond significantly improved, meltingtemperature significantly reduced, and the thermal expansion coefficient reduced from6.61×10-6/℃to5.37×10-6/℃, adding appropriate alkali metal compounds MgO、ZnO、CaF2and rare-earth metal oxide CeO2into basic vitrified bond, the bond had got betterwettablility for diamond at sintering temperature, and it combined well with diamondabrasives to improved the strength of the bond, the samples of diamond abrasive toolswere prepared with the above mentioned bonds, the bending strength and rockwellhardness of diamond abrasive tools made of NO.3were significantly higher thandiamond abrasive tools made of the other two vitrified bonds; Volume density ofsamples increased with the raise of cold isostatic forming pressure in100~260MParange, when the forming pressure was220MPa, it reached to2.34g/cm3, and thentended to be constant, or16.4%and15.8%higher than that of the samples byunidirection pressing and bidirectional pressing respectively. As cold isostatic formingpressure rose, the volumetric shrinkage of samples unsintered increased, the shrinkageof samples sintered fluctuated around0.18%, but the bending strength of samplessintered were firstly increased and then decreased, when the forming pressure was180MPa, it reached to93.48MPa, or60.7%and42.5%higher than that of the samplesby unidirection pressing and bidirectional pressing respectively; As vitrified bondcontent rose from23%to35%, bending strength and grinding ratio of sintered samplesby CIP were increased graduarally, when vitrified bond content reached35%, the sample foamed, and its bending strength declined, as diamond content rose from40%to60%, bending strength of sintered samples by CIP increased slowly, but the change wasvery small, its grinding ratio increased firstly then tended to be stable, diamond grit sizedecreased in140/170~270/325, bending strength of sintered samples by CIP increasedfirstly and then decreased, its grinding ratio had trended downwards; Wheel by CIPground different workpieces, grinding ratio and grinding efficiency of wheel werehigher, surface roughness of workpieces were lower, and scratches were shallow andequally distributed.