Currently, the vacuum brazed methods for diamond tools is becoming a hotspot technology. However, this method is confined to the single layer tools. By contrast, the impregnation technology is immature for the multi-layer diamond tools; studies on the vacuum brazed method developed since 1980s, compared with the developed countries, domestic vacuum brazed technology started late, studying scope and depth are still far behind. As a result, it progresses rather slowly. This article concentrates on the technical characteristics of diamond granulation fixing and clearance for debris in using, and analyzes the diamond abrasive fixing technology of the metal bonded diamond grinding wheels. In addition, it analyzes the current situation of the vacuum brazed technology in diamond grinding wheel, and points out the technological problems and solutions for vacuum brazed diamond grinding wheel.
According to the different manufacturing methods, the metal bonded diamond tools can be divided into following 3 categories: Powder metallurgy hot-pressing sintered diamond tools, electroplated diamond tools and vacuum brazed diamond tools.
(1), Powder metallurgy hot-pressing sintered diamond tools.
diamond is the abrasive for the bond for the powder metallurgy hot-pressing sintered diamond tools. And the metal powder is the bond for this method. By the powder metallurgy method, through the material mixing, granulation making, pressing, sintering and the necessary post-dressing.
The products have already been serialized, standardized, various and completed in specifications, and stable in product quality. Part of the products are competitive in global market. Powder metallurgy hot-pressing sintered diamond tools merged first among the diamond tools. And it is of the widest varieties, the largest quantity and widest applications. And the sales volume of the products accounts for above 80% metal bonded diamond tools.
Though diamond tools produced by this method have been applied widespread in many industries and achieved considerable economic benefit. However, the diamond fixing technology always exist major deficiencies. The availability of diamond is around 10%, which gives rise to the huge waste of the diamond. It is because the diamond grains exist in metal matrix in the form of mechanic coating, and the holding force of the metal bond to diamond grains is weak. So there are much particular weariness, fall-off and residual diamond. And thus the practical efficiency of diamond is low, and the diamond material waste is huge.
Over the years, in order to improve the bonding strength of the metal bond to diamond grains, many experts have made great efforts. Except for the surface modification of diamond( surface metallization and surface morphology change etc) to increase the holding force of metal bond to diamond, which acquires some effects. There is no great technological breakthrough in adding some suitable active element, such as Ti、Cr、In、Zr to reinforce the metal bond. In the academic world, it it widely believed that the enhancement mechanism of metal bond can be achieved through forming the carbide between the diamond surface and metal bond. As the transitional layer, the carbide can increase wetting ability and capillary action of metal bond to diamond surface, and thus achieve the combination of chemical and metallurgy.
Actually, in the process of hot-pressing sintering, in order to protect the diamond grains from graphitization, the use quality of the diamond will be affected. Its sintering temperature can not reach the melting temperature of these active elements, as a result, the carbide can not form, causing the active elements can not reach the theoretical effect. Diamond grains have been clamped in the metal bond, and do not happen the so-called chemical metallurgical reactions. So, this kind of tool can only rely on mechanical package to fix diamond abrasive, and the holding force for diamond is very limited in use.
Through the observation of using condition of powder metallurgy hot-pressing sintering diamond tools, it can be found that the chip space is formed in the process of operation, and rely on the regrinding from materials scraps of processed . The chip space of diamond grains has undergone a process from nil to existence, so in the period of validity, the average chip space of the diamond granulations is very small. Therefore, during use, it is frequent that scraps block, burn and cut workpieces.
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