Cubic Boron Nitride Grits Research Articles

Effect of laser power on morphology, microstructure and mechanical properties of CBN abrasive block prepared by two-step laser cladding

The preparation of cubic boron nitride (CBN) grinding tools using laser cladding has the advantages of strong bonding, short time consumption and customizable abrasive arrangement. In this paper, a two-step laser cladding method was used to prepare CBN abrasive blocks with the aim of reducing laser damage to CBN grits during the laser cladding process. The cross-sectional morphology of CBN abrasive blocks under different laser power conditions was characterized, and the relationship among laser power, preparation method, and forming quality of Cu–Sn–Ti/CBN cladding layer was investigated. Then, the microstructure at the Cu–Sn–Ti/CBN interface under different laser power conditions was characterized, and the main phase compositions at the Cu–Sn–Ti/CBN interface were analyzed. Finally, the grinding tests were carried out on CBN abrasive blocks. The results show that as the laser power increases from 250 W to 400 W, the fracture ratio of CBN grits increases dramatically from 4.3 % to 17.3 %. TiN, TiB2, and TiB compounds are all detected at the Cu–Sn–Ti/CBN interface under different laser power conditions. The mass loss of the TC4 wheel caused by the CBN abrasive block initially increases and then decreases as the laser power increases from 250 W to 400 W. The CBN abrasive block has the optimum material removal performance at the laser power of 300 W using two-step laser cladding. The results provide a theoretical basis for the preparation of high-performance CBN grinding tools using laser cladding.

Finite element investigation on the evolution of wear and stresses in brazed CBN grits during grinding

Finite element method (FEM) is a power tool to predict the stress distribution in the cubic boron nitride (CBN) grits, which are difficult to accurately characterize with the experimental methods due to rather small grit size of 100–400 μm. In this work, modeling techniques on the coupling effects of brazing-induced stresses and grinding-induced stresses in the brazed CBN grits are investigated by applying FEM code ABAQUS in order to understand the grit fracture wear. The stress evolution in the bottom surface, in the top surface, and in the tensile side of the CBN grits is discussed for six sequential wear stages. Results obtained reveal that, with the wear advance of the grit and bond, the effect of the grinding force on the resultant stresses is generally weak in the grit bottom surface, while the corresponding effect of the brazing-induced stresses is significant. Large magnitude of resultant stresses ranging from −754 to −1243 MPa is formed in the grit vertex region, which is the primary factor for grit micro-fracture during grinding. Meanwhile, large brazing-induced tensile stresses are usually obtained in the grit-bond junction region, which is the vital factor for grit macro-fracture in grinding.

Development of a Thin CBN Grinding-Tool by Compound Process

This study presents a compound process combining composite electroforming with wire Electrical Discharge Machining (w-EDM) for developing a thin cubic boron nitride (CBN) grinding-tool. A precisely designed set-up in which a small compound depositing tank providing effectual convection of a compound electroplating solution to help fabricate a CBN grinding-blank is presented. A funneled entrance design for converging CBN grits in the working tank and creating a depositing effect on the substrate is employed and proposed. Considerable micro CBN abrasives are evenly embedded into the nickel-based coating layer, which offers enough abrasives for grinding-edge. Subsequently, the coated grinding-blank is trued and dressed by using w-EDM to form a multiple thin CBN grinding-tool. Experimental results indicate that the electroforming process can create a Ni-based CBN layer of high-integrity under current density of 2 ASD and concentration of 8.6 g/l CBN grits. Moreover, the CBN grinding-edge of 10 μm in thickness (each edge) can be achieved.

Fundamental Technology and Properties Research of Brazing CBN Grinding Wheels

In order to produce new generation monolayer brazing CBN(cubic boron nitride) grinding wheels, an active filler alloys(Ag-Cu-Ti) were tested in vacuum furnace. The results show that Ag-Cu-Ti alloy exhibits good wetting and bonding toward as CBN grits. SEMEDS microanalyses have shown that during brazing Ti in Ag-Cu-Ti alloy segregated preferentially to the surface of the CBN to form a Ti-rich reaction produce. X-ray diffraction reveals that the wetting and bonding behaviour on CBN surface by Ag-Cu-Ti alloy melt is realized through TiN and TiB2 which is produced by interaction between Ti atoms of Ag-Cu-Ti alloy and N or B atoms of CBN surface.

Microstructure characteristics of CBN/steel joints brazed with TiB2 modified active filler

The joint of cubic boron nitride (CBN) grits to 0·45%C steel were obtained by using TiB2 modified Ag–Cu–Ti active filler at the brazing temperature of 920°C for the holding time of 5 min. The microstructure characteristics of the brazing interface were detected by means of optical microscope, scanning electron microscope, energy dispersion spectrometer, X-ray diffraction and microhardness measuring equipment as well. It has been found that the microstructure of Ag–Cu–Ti filler layer is significantly refined by TiB2 particles. The almost well proportioned distribution of TiB2 particles in the filler layer is realised. Negative influence of TiB2 particles has not occurred on the chemical reaction of CBN particles and the filler at elevated temperatures. Reliable joining of CBN grits to 0·45%C steel is accomplished dependent on the resultant reaction products at the brazing interface.

Brazed CBN Grinding Wheel with Ag-Base Filler Alloy

In this paper, the disadvantages of the current CBN (Cubic Boron Nitride) grinding wheels were firstly introduced briefly, for indicating that it was very urgent and important to develop new kinds of grinding wheels with excellent performance to replace the conventional wheels. Then high temperature brazing experiments of monolayer CBN wheels with Ag-Cu-Ti filler alloy were carried out. The result shows that the filler alloy has good wetting capability towards CBN grits. The results of scanning electron microscope (SEM) and energy dispersion spectrometer (EDS), as well X-ray diffraction (XRD) analysis show that, just because during brazing titanium atoms in filler alloys segregated preferentially to the surface of the CBN to form Ti-nitride or Ti-boride layer by reaction between titanium atoms and nitride and boron atoms at elevated temperature, strong chemical joining was formed in the interface between CBN grits and filler alloys. Finally, the contrastive grinding experiments were performed between the monolayer brazed CBN grinding wheels and the electroplated ones. The results show that the brazed wheels have more excellent performance than the latter.

On brazing of cubic boron nitride abrasive crystals to steel substrate with alloys containing Cr or Ti

An investigation has been carried out to gain information about the capabilities of some filler alloys for direct brazing of CBN (cubic boron nitride) grits to a steel substrate. It has been found that a Ni-Cr alloy, known for effective diamond brazing, failed to show satisfactory wetting and bonding characteristics towards CBN under the same brazing conditions as that of diamond. The situation could not be improved either by increasing the wt% of Cr or the brazing temperature. Also, prolongation of the brazing time did not show any significant change. It was further revealed that a Ag-Cu-Ti alloy, which is well established for the brazing of diamond and ceramics, exhibited good wetting and bonding towards CBN at moderate temperature. Based on the thermodynamic properties of various materials, characteristic properties of elements of group IV B to VI B and the physical observations made during the investigation, it is suggested that the transition elements of group IV B, such as Ti or Zr, are preferred to transition elements of group VI B, such as Cr, as an activator to promote the wetting characteristics of the braze alloy towards CBN, which is far more chemically stable than diamond.

Current Trends in CBN Grinding Technology

Although the superior grinding performance of cubic boron nitride (CBN) abrasive is well documented, its more widespread utilization in industry has been limited to some extent by technological problems, as well as cost. The demand for more efficient grinding techniques has prompted increased research activity to advance CBN grinding technology and thereby more fully realize the apparent potential of this superabrasive. The present paper reviews the current trends in the development of CBN grinding technology. The unique properties of CBN and its peculiar grinding behavior are discussed, which provides a basis for identifying the process limitations and the prospects for more effective utilization of CBN abrasives. The most promising new developments appear to be in vitreous bonded wheels, pre-grinding wheel preparation methods, polycrystalline CBN grits, more powerful and stiffer machine tools, and special purpose machines combining multiple grinding operations