Hong Jun Xu

Fabrication of Monolayer Brazed Diamond Tools with Optimum Grain Distribution

A new generational manufacturing technology for diamond tools on brazing process cooperated with optimum distribution of grains is put forward in this paper. Monolayer brazed diamond tools with optimum grain distribution are manufactured and their machining performance is investigated through experiments. The testing results show that this series of diamond tools are certain to have super outstanding machining performance, which provides an innovative technology for manufacturing new generation of superbrasive tools.

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.

Form and Distribution Characterization of Reaction Products at the Brazing Interface Between Ni-Cr Alloy and Diamond

In order to reveal the size, number, form and distribution characterization of resultant at the brazing diamond interface using Ni-Cr alloy, vacuum furnace brazing was carried out. SEM-EDS microanalyses have shown that during brazing the chromium present in the alloy segregated preferentially to the surface of the diamond to form a chromium-rich reaction product. X-ray diffraction revealed that the wetting and bonding behaviour on diamond surface by molten Ni-Cr alloy is realized through Cr3C2 and Cr7C3 which are produced by interaction between Cr atoms of Ni-Cr alloy and C atoms of diamond surface at elevated temperatures. Furthermore, the size, number, form and distribution characterization of Cr3C2 and Cr7C3 were discovered and the brazing mechanism for diamond was illuminated. Introduction Much attention has been paid to brazed diamond tools, among which mono-layer tools are born and come into practical use as a new tool. In mono-layer tools, the size, number, form and distribution characterization of resultant at the brazing interface are key factors to determine the adhesion performance and service life. The main bonding method used for brazing diamond is to utilize alloy containing Cr, Ti, Mo, Zr or V, which are all carbide-forming metals, as brazing materials, and then to braze diamond on a metal substrate in vacuum or inert atmosphere. Many papers have reported on the performance evaluation of cutting or grinding tools by machining test, but few have been found to discuss the form and distribution characterization of resultant at the brazing diamond interface. Therefore the basic objective of the present work was the study on the form and distribution characterization of resultant at the brazing diamond interface using Ni-Cr alloy during vacuum furnace brazing. Experimental Procedure Ni-Cr alloy with a suitable composition was used for brazing purpose. The said alloy was applied on the top surface of the steel, followed by sprinkling of diamond grits on it. The brazing was carried out under vacuum atmosphere at moderate temperature. Results and Discussion The appearance of brazing diamond observed by SEM was shown in Fig.1. The result illustrated that diamond grits were effectively wetted and protrusion height of grit could reach more than 2/3 of its size. SEM-EDS microanalyses (Fig.2) have shown that the chromium present in the alloy segregated during brazing towards the diamond surface, most probably to form chromium carbide. The thermodynamic data presented in Table 1 clearly indicate a high chemical stability of chromium carbide than that of diamond. Therefore under the prevalent brazing condition the formation of chromium carbide at the interface is quite expected. Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 151-153 doi:10.4028/www.scientific.net/KEM.259-260.151

Microstructure and Performance of Porous Ni-Cr Alloy Bonded Diamond Grinding Wheel

Although the porous metal bonded diamond grinding wheel, which has recently been developed, had an excellent grinding performance for hard-brittle materials, its applications were only in precision grinding in past study. A new method for fabricating the new porous metal bonded diamond grinding wheel by Ni-Cr alloy as bond and vacuum loose powder sintering was proposed in this paper. The morphology of cross section of the segments and microstructure of interface between diamond grits and bond were analyzed. The wetting mechanism between Ni-Cr alloy bond and diamond is reacting wetting. Machining performance experiments about grinding ratio and surface roughness have been carried out. The testing results show that the porous Ni-Cr alloy bonded diamond grinding wheel has certainly fine machining performance in high grinding force occasion, and the maximal grinding ratio and best surface roughness were 6660 and 1.08 m, respectively.

Machining Performance of Brazed Diamond Wire Saw with Optimum Grain Distribution

A kind of new monolayer brazed diamond wire saw with both chemical bonding at the interface between diamond grits and brazing alloy and optimum grits distribution was made. And a machining performance comparative experiment was carried out between the sintered diamond saw from Italy and the brazed one mentioned above. The sawn material is marble with middle hardness. The testing results show that the wire saw with a brazed bonding diamond grid can achieve two to three times the working efficiency of conventional sintered diamond saw, and the corresponding service life can do 3~4 times. Furthermore, the grits of the brazed diamond wire fail mainly in micro fracture modes other than pull-out ones of the sintered diamond saw grits, indicating the strong retention of brazing alloy to the diamond grits. Almost no grits pulling out for brazed diamond wire saw is the key factor of its longer service life, and the optimum distribution and micro fracture of the brazed diamond wire grits raise the machining efficiency.

Measurement Technique of Grinding Wheel Topography Based on Binocular Stereo Vision

Measurement of the grinding wheel topography and its change in machining process is important for revealing the grinding principle of high-temperature brazed mono-layer super-abrasive grinding wheel. A new approach of measuring grinding wheel topography based on binocular stereovision is presented. Firstly, the binocular images are achieved while the optical axes of the two cameras are parallel, and a corner reflection function algorithm is applied to detect corners. Secondly, in order to get matching corners, optimal matching template is obtained by matching curves. The experimental results show that the sequential similarity matching operation with optimal template has advantages of high accuracy, and less error matching. Finally, the height of the corners is obtained by calculating their parallax on left and right image, and the height error is less than 5%.

Laser Brazing of Diamond Grits with a Ni-Based Brazing Alloy

Brazing diamond grits onto steel substrate using a Ni-based filler alloy was carried out by laser beam in an argon atmosphere. The microstructure of the interfacial region among the Diamond grits, the filler layer and the steel substrate, were investigated by means of scanning electron microscopes (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Meanwhile, the formation mechanism of carbide layers was discussed. All the results indicated that the active element chromium in the Ni-based alloy concentrated preferentially to the surface of the grits to form a chromium-rich layer, and the hard joint between the alloy and the steel substrate is established through a cross-diffusion of iron and Ni-based alloy.

Performance of Brazed Diamond Wheel in Grinding Cemented Carbide

A kind of brazed monolayer diamond grinding wheel was developed with a relatively regular distribution of grains on the wheel surface. Grinding performances of this kind of brazed wheel in the surface grinding of cemented carbide were studied. The experiment results show that the grinding forces ratio becomes higher with the increasing of the maximum undeformed chip thickness and the specific energy falls with the material removal rate during grinding cemented carbide process. Under certain grinding conditions, the material was removed almost through plastic deformation and good surface quality is gained. Furthermore, the grits of the brazed diamond grinding wheel fail mainly in attritious wear modes other than pull-out ones in conventional electroplated and sintered diamond tools, which indicates that the strong retention of brazing alloy to the diamond grits and longer service life of this kind of wheel.

The Cooling Effects of Cryogenic Pneumatic Mist Jet Impinging in Grinding of Titanium Alloy

Grinding is inherently characterized by high specific energy requirements, a high grinding zone temperature. Many methods have been employed in grinding high grinding zone temperature. But all have their shortfalls, both in cooling environmental pollution. Here a new high efficiency cooling technology—cryogenic mist jet impinging (CPMJI) cooling technology is offered. In this technology, coolant is carried by high-pressure cryogenic air (–20°C) and reaches the machining form of mist jet to enhance heat transfer in machining zone. This paper mainly cooling effects of CPMJI in surface grinding, compared with grinding with compressed flood cooling. CPMJI seems to have better effects than other cooling methods.

Induction Brazing Diamond Grinding Wheel with Ni-Cr Filler Alloy

An experimental study on induction brazing diamond grinding wheel with Ni-Cr filler alloy was carried out. Brazing trial was conducted at the temperature range of 1020-1080 oC and the brazing time were 10, 20, 30 and 40 seconds in a flowing argon environment with a flow rate of 5000cm3/min. The scanning electron microscopic (SEM) results indicate that good wetting existed between the brazing alloy and diamond. The element distribution of C, Cr, Si and Ni were examined by energy dispersive spectrometer (EDS), the results demonstrated an intermediate layer rich in the chromium formed between the filler metal and diamond. Kinds of compounds formed in the interface were detected by means of x-ray diffraction (XRD), and the graphitization of the brazed diamond grits was determined by Raman spectroscopy. The monolayer induction brazing diamond grinding wheels were used in grinding of nature granite, experimental results show that induction brazing wheels performed better than vacuum brazing diamond wheels, and no pullout of diamond grits or peeling of the filler metal layer took place.