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Polycrystalline diamond

2020-10-20 09:14:12

Polycrystalline diamond

 

Polycrystalline diamond (PCD) was produced in the 1970s by sintering with binder (cobalt, nickel and other metals) at 1,000 ~ 2,000 ℃ and about 50,000 ~ 100,000 atmospheric pressure using natural or synthetic diamond powder. It is usually produced with carbide layer joint together, PCD layer thickness of 0.3 ~ 1 mm, the total thickness of the PCD blanks about 2 ~ 8 mm, at present the maximum diameter of the PCD Blanks up to 90 mm. The directivity of single crystal diamond structure is very strong, which makes it has very high hardness. Polycrystalline diamond structure is a sintered body of fine grain diamond with different orientations, which shows isotropy, but its hardness and wear resistance are lower than that of single crystal diamond due to the addition of binder. But the hardness can also reach about 8 000Hv, more than 100 times higher than the hard alloy. Thermal conductivity is 1.5 ~ 9 times that of tungsten carbide, but also higher than PCBN and copper, so the heat can be quickly exported during processing. The friction coefficient is only 0.1 ~ 0.3, 1/4 of the carbide, and the cutting force is greatly reduced during machining. The thermal expansion coefficient is only 1/5 of the carbide, so the thermal deformation is very small and the machining precision is high. At the same time, it has a very low affinity for non-ferrous metals and non-metallic metals, so it is not easy for the chips to stick to the blade during the processing, resulting in the bonding damage of the blade, which is difficult to generate chip deposits, which can better ensure the surface quality of the processing.

 

PCD tool is mainly used for finishing, cutting depth is very small, is a micro cutting, so in the tool geometry structure, a small relief Angle, high quality surface of the back, in order to ensure a good workpieces surface.

 

EDG technology, which is almost unaffected by the hardness of the workpiece, will become a new direction of PCD tool grinding.

 

Endmill chip slot is polished, can be used for high speed cutting, chip removal friction is small, small cutting force, cutting power significantly reduced, stable cutting process, high tool life.

 

In the actual machining, the workpiece contour shape varies greatly, in order to meet the requirements of geometric and dimensional accuracy, technically, the tool center trajectory should be generated exactly according to the workpiece contour shape. For simple curves, numerical control system is relatively easy to realize, but for more complex shapes, the direct generation will make the calculation become very complex, the workload of the computer is also greatly increased. Therefore, in practical application, a small section of straight line or a small section of arc is often used for fitting to meet the accuracy requirements, and this fitting method is interpolation.

 

When machining threaded hole with interpolation method, high quality threaded hole can be obtained because the PCD edge does not produce burr. Even if there are transverse holes on the side of the screw hole, the subsequent cleaning procedure can be eliminated after processing with PCD thread milling cutter.

 

The machining quality of many precision holes in automobile engines, such as cylinder hole, transmission hole, crankshaft hole, piston pin hole and CAM shaft hole, including dimension accuracy, shape and position accuracy and surface physical and mechanical properties, affects the mechanical properties of components and even the whole of car

 

PCD precision boring and reamer tools play a very important role in aluminum alloy cylinder head, cylinder block, transmission hole and hole system machining. The coaxiality of these pore systems should be ≤0.02, and the cylindricity ≤0.01. Especially in a large number of production is always required to meet the stable quality standards, therefore, the quality and life of cutting tools is crucial.

 



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