Technical status of brazed diamond tools
At present, brazing diamond tools has become a hot technology, but only limited to single-layer tools, for multi-layer realization of "impregnation" is not mature. Foreign brazing technology research began in the late 1980s, but because of the complexity of the work is still in the experimental stage, its application is limited to single-layer tools; domestic brazing technology research started late, compared with developed countries, the breadth and depth of research is far from enough, so the progress is very slow. In this paper, the metal The technical characteristics of bonded diamond tools for consolidating diamond abrasives and the characteristics of the chip-holding space of diamond abrasives during operation are expounded. The present situation of brazing method for diamond tools is analyzed, and the technical problems and solutions for brazing diamond tools are pointed out.
1 metal bonded diamond tools
According to different fabrication methods, metal bonded diamond tools can be divided into three categories: powder metallurgy hot-pressing sintered diamond tools, electroplated diamond tools and brazed diamond tools.
1.1 hot pressing diamond tools for powder metallurgy
Powder metallurgy hot-pressing sintered diamond tool is a kind of diamond tool product, which is made of diamond as cutting and grinding material, metal powder as binder, powder metallurgy method, through mixing, granulating, pressing molding, sintering and necessary finishing.
Products have formed a series, standardization, complete varieties and specifications, product quality is stable, some products in the international market has a certain competitiveness. Powder metallurgy hot-pressing sintered diamond tools are the earliest of all kinds of diamond products, but also the largest variety, the largest amount of use, the most widely used category, its product sales account for more than 80% of the total metal bonded diamond tools.
Although the diamond tools produced by this method have been widely used in various industries and achieved remarkable economic benefits, the technology of consolidating diamond abrasives has always been seriously inadequate. The effective utilization rate of diamond is about 10%, resulting in a great waste of diamond abrasive resources. The diamond abrasives mainly exist in the metal matrix in the form of mechanical encapsulation. The metal binder has not strong ability to control the diamond abrasives. The abnormal wear, shedding and residual diamonds are more in the process of using diamond tools. The actual utilization rate of diamond is lower, and the waste of diamond raw materials is larger.
Over the years, experts in the industry have done a lot of work to improve the ability of metal bond to control diamond. In addition to the surface modification of diamond (surface metallization, surface morphology changes, etc.) to enhance the metal bond on the control of diamond abrasive has a certain effect, by directly in the metal bond. There is no great technological breakthrough in adding active elements such as Ti (Ti), Cr (Cr), In (In), Zr (Zirconium) to strengthen metal bonds. It is generally believed that the enhancement mechanism of metal bond is to form a layer of metal carbide between the diamond surface and the bond, and to improve the wettability and capillarity of the bond on the diamond surface by using the carbide as the transition layer.
In fact, in order to protect diamond abrasives from graphitization and affect the quality of diamond, the sintering temperature of diamond can not reach the melting temperature of these active elements and carbides can not be formed during hot-pressing sintering, so that the active elements can not play an ideal role in theory. Diamond abrasives are mechanically trapped in metal binders and there is no so-called chemical metallurgical reaction. Therefore, this kind of tool only depends on the mechanical encapsulation form to fix the diamond abrasive, in the use process of diamond control is limited.
Observing the usage of a large number of powder metallurgy hot-pressing sintered diamond tools, it is found that the chip-holding space of diamond abrasives is formed in the running process and is obtained by the anti-grinding of the waste materials. The chip-holding space of diamond abrasives is a process from nothing to something, so the effective use time of diamond abrasives is limited. The average value of chip space is very small, so it often happens that the scraps of processing materials are blocked and the workpiece is burned and scratched in the process of using.
1.2 electroplated diamond tools
Electroplated diamond tool is a kind of product which is made by electroplating a layer of diamond firmly embedded in the metal substrate through the process of metal electrodeposition. This kind of products have the characteristics of high efficiency and high grinding precision. The main products are formed grinding and precision machining tools. The products are also widely used in geological exploration, stone, machinery, automobile and national defense industries.
Although various kinds of diamond tools produced by this method have been widely used in certain industries and obtained certain economic benefits, the technology of consolidated diamond abrasive grain itself also has serious shortcomings. The effective utilization rate of diamond is about 20%. The main performance is that the metal binder has not strong ability to control diamond abrasives, diamond abrasives are only embedded in the coated metal by mechanical embedding.
The method of electroplating is that Ni or Ni-Co or Ni-Co-Mn and other metal ions precipitate, enter and bury on the surface of cathode diamond and substrate, and the next electroplating layer is deposited in turn. After repeated deposition to a certain thickness, the semi-finished product is removed from the electroplating solution for subsequent processing, such as sanding and thickening, and finally the electroplating diamond worker is obtained. It is. During the whole production process, no chemical reaction occurred in diamond. Therefore, such tools only rely on mechanical encapsulation to fix the diamond abrasive, the use of diamond in the process of control is also limited, once the electrodeposit is worn to half the height of the abrasive, diamond abrasive will fall off naturally.
Observing a large number of electroplated diamond tools, it is found that about 2/3 of diamond abrasives are deposited in the electroplated metal layer, so the chip space of diamond abrasives is basically fixed and relatively small, so there will still be blockage and burns of processing material scraps in the use process. Scratch the workpiece phenomenon.
1.3 brazing diamond tools
Brazing diamond tool is a kind of tool product which solders a layer of diamond firmly on the metal substrate through brazing and metal solder melting process. This kind of product has the characteristics of high efficiency, long service life of single diamond particle and high grinding precision. The main products cover all coarse and medium-coarse grain electroplated diamond tools and some hot-pressed diamond tools.
In order to avoid the problems of low holding force, small chip space, low exposure height and easy shedding caused by traditional manufacturing methods, and to make greater use of the advantages of single-layer diamond tools, brazing technology has been applied to the field of diamond tools manufacturing since 2000 and has been developed rapidly. Brazing technology, as a new manufacturing method of diamond tools, has attracted wide attention at home and abroad. Different from other soldering methods, the solder alloy melting temperature is lower than the base metal melting temperature, and the soldering temperature is lower than the base metal solid line but higher than the solder liquid line. For diamond, the brazing temperature is smaller than that of diamond. During brazing, the brazing filler metal wets, capillarizes, fills, spreads and encapsulates diamond abrasives tightly on the surface of diamond, and forms chemical metallurgical bonding between diamond and brazing alloy in the form of carbide. Diamond tools manufactured by brazing method have higher bonding strength and cutting edge height, sharpness and cutting performance, fixed chip space and relatively large, especially suitable for high-speed and high-efficiency grinding, machining of difficult-to-machine materials and precision machining. In recent years, high temperature brazing of single layer diamond tools has become a research and development hotspot of research institutions and manufacturers at home and abroad.