Vacuum brazed diamond cutter

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Polycrystalline diamond, or PCD for short, is sintered from many fine single crystals at high temperatures and pressures. The grains in the polycrystals are arranged in disorder, and their hardness and wear resistance are relatively close in all directions. At the same time, they have good fracture toughness. Therefore, different shapes can be made according to different conditions of use.

In order to give full play to the performance of PCD, polycrystalline diamond thin layer and cemented carbide matrix are sintered together to form a composite, which is polycrystalline diamond composite sheet PDC (Polycrytalline Diamond Composite).

Polycrystalline diamond and composite sheets have been widely used in manufacturing metal cutting tools, petroleum drills, geological drilling bits, stone processing tools and so on. Because of the low brazing temperature allowed by PCD and PDC and the poor brazing ability of tungsten carbide and other materials, the brazing ability of these products is not good, but brazing is one of the key technologies for manufacturing such products and tools. The main problems of PCD and PDC brazing are wettability, brazing seam strength and brazing temperature.

Because the materials of diamond sintered bodies (cutter head, PCD and PDC) in diamond tools are very different, even the same formula of the same manufacturer is changed, which brings great difficulties to the selection of filler metals and fluxes. The brazing ability of different batches of cutters often varies greatly.

The brazing surface of PDC is tungsten carbide cemented carbide, and the brazing property of YG cemented carbide is good, but the brazing wettability of PDC is worse than that of cemented carbide due to the limitation of brazing temperature. PCD and cutter often contain hard brazing metals such as Cr, Ti and Pb, and their brazing wettability is not good.

Because the sintering temperature of the cutter is only tens of degrees higher than that of brazing, and the porosity of the cutter is relatively high, the interaction between brazing filler metal and the cutter is very significant during brazing. The results show that in less than 20 seconds of brazing time, the filler metal can penetrate into 8-12 mm inside the cutter due to capillary action, while Sn, Pb, Zn and other low melting point metals in the cutter can diffuse into the brazing seam from 5-8 mm inside the cutter.

Carbon powder added in cutter and residual carbon in graphite die have adverse effects on brazing process.

In the industrial production of diamond tools, the main methods of connecting the diamond cutter to the steel substrate are as follows: deposition, integral hot pressing and sintering, mechanical mosaic or welding in separate fabrication.

Diamond deposition technology rose in the 1980s, and has been applied in optics, acoustics, electronic technology, heat conduction, mechanical cutting tools and other fields, but the application of small-sized saw blades is still in the stage of technological development.

Integral hot pressing sintering is generally used to manufacture small size saw blades. Its technological characteristics are that the matrix metal is directly sintered on the steel substrate. Due to the great difference of linear expansion coefficient between steel matrix and matrix material, thermal stress occurs during cooling process after sintering. This part of internal stress is superimposed on shear stress during the use of saw blade, which affects the service life of saw blade.

The machine mosaic method of split manufacturing is mainly applied to machine tools and various dies.

Brazing is the most widely used process in diamond tool manufacturing. Because the diamond cutter is produced by powder metallurgy, the brazing characteristics of this kind of tool are similar to those of cemented carbide. Brazing of single crystal diamond is mainly carried out in vacuum.

Due to the limited temperature resistance of diamond under atmospheric conditions, the use of lower brazing temperature is a remarkable feature of diamond tools.

In fact, the brazing of diamond cutter and matrix is the brazing of steel and powder metallurgy matrix. The composition, structure and structure of matrix bottom layer are the key factors affecting the brazing performance. Titanium, chromium, lead, zirconium and 663 bronze powders in the base material have adverse effects on brazing.

Single layer diamond tools have the advantages of high cutting efficiency and long service life. Single layer diamond tools can be manufactured by brazing single crystal diamond in vacuum brazing furnace.

Brazing of PCD and PDC is equivalent to brazing of YG cemented carbide, but vacuum brazing temperature should be controlled in the range of 720-760 degrees Celsius or more.