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Polycrystalline diamond and cemented carbide sintered together to make polycrystalline diamond compact, cut into the desired shape, can be made into a variety of tools. However, due to its high hardness, high melting point, high resistivity and high wear resistance, it cannot be cut by traditional processing methods.

The cutting process of PDC is the first step of PDC blade processing. The integrity and surface quality of the cutting surface directly affect the efficiency of blade welding and the overall quality of PDC tool. At present, there are two main methods for cutting PDC, electric spark wire cutting and laser cutting. The following is a brief introduction to these two cutting methods.

1. WEDM

Since polycrystalline diamond is polymerized by diamond particles and conductive metal powder (such as Co), it is sintered on a cemented carbide substrate to become a polycrystalline diamond compact PDC. Electrical discharge machining is to realize the cutting of the workpiece material through the pulse discharge of the local area between the electrode wire and the workpiece, which is one of the commonly used methods of PCD cutting.

During EDM of PDC material, since diamond itself is not conductive, under the action of pulse voltage, the working fluid at the metal near the electrode first forms a discharge channel, and then spark discharge is generated in this part. The highly concentrated pulse discharge energy, strong discharge explosive force and instantaneous high temperature cause the metal in PCD material to melt, part of diamond to graphitize and oxidize, part of diamond to fall off, and this is repeated until the processing is completed.

It can be seen that the electrical machinability of PDC composite material mainly depends on the particle size of diamond and the content of conductive metal phase, such as diamond particle size is coarse, not easy to fall off, discharge electrode wire wear is large, and wire breakage is frequent. The conductive metal content in the composite sheet is large, the conductivity is good, and the cutting speed is fast.

WEDM polycrystalline diamond is mostly used to make machining tools, geological drill bits and wire drawing abrasives, these workpiece mold shapes are complex and changeable, forming with WEDM is one of the economically feasible ways.

2. laser cutting

The structure of PDC CNC laser cutting machine mainly includes machine frame, CNC table, Z-axis focusing system, laser bracket and other components.

The mechanism of laser processing polycrystalline diamond is: when laser cutting PDC, the laser emits a laser beam with extremely high energy density, which is irradiated on the surface of polycrystalline diamond, part of the light energy is absorbed by the surface and converted into heat energy, the temperature of the local area of the irradiated spot rises rapidly to tens of thousands of degrees, and the instantaneous high temperature makes the PDC melt rapidly and vaporize and form holes. At the same time, thermal diffusion also began, and then the material around the spot melted. As the laser energy continues to be absorbed, the steam in the pit expands, the pressure increases, the melt is ejected at high speed in the form of explosion, and the recoil pressure generated by the ejection forms a strong shock wave in the interior of the workpiece. In this way, polycrystalline diamond is etched away part of the material under the action of high temperature melting vaporization and shock wave, forming a slit, and finally cutting the PDC into the desired shape.

Of course, in the process of laser cutting, the laser parameters that play a decisive role are pulse width, maximum pulse power and average pulse power. There are many factors that affect the quality of cutting, for example, different laser wavelengths and lens focal distance will produce different spot sizes; The intensity and spot diameter of the laser beam determine the energy density on the surface of the workpiece; The material, surface state and laser wavelength of the workpiece determine the change of reflectivity and the absorption rate of input energy, as well as the surface temperature of the workpiece; the conductivity and thermal diffusivity of the workpiece affect, among other things, the transfer of heat within the workpiece.

Therefore, in the process of laser processing, it is necessary to optimize the process parameters of laser cutting through experiments.

When laser cutting PDC, the operator can observe the PDC laser cutting process in real time by observing the screen device, and can adjust the working state of the equipment in real time according to the cutting situation to avoid waste pieces and ensure the quality of cutting.

One of the advantages of laser cutting is that it is easy to integrate with the numerical control system, easy to realize the processing automation, and has better processing flexibility. Users only need to input PDC shape, spot diameter, cutting parameters and auxiliary functions into the numerical control system according to the specified graphics or data format, and the numerical control laser cutting automatic programming software system can automatically write a series of operations such as processing program sheets to process the workpiece, so that the processing process is fully automated, the processing accuracy and production efficiency are improved, and the stability of product quality is ensured, it can meet the requirements of large-scale industrial production in the future to a greater extent.

Although there are many researches on WEDM in China, when using WEDM to process PDC, the surface of PDC material will be damaged due to the difficulty of controlling the discharge intensity, which not only affects the quality of the cutting surface, increases the grinding margin of the tool, but also affects the life of the tool. Moreover, the speed of WEDM is much slower than that of laser cutting, and the effect is not ideal. In contrast, laser cutting is a non-contact processing, it has excellent characteristics in the processing of PCD materials, can process high-purity PCD materials (such as polycrystalline diamond film), processing deformation and thermal deformation are very small, and laser processing speed, high efficiency, is a more effective processing method. In particular, it shows its superiority in the processing of micro-porous and non-conductive superhard materials. It has the advantages of small cutting, high efficiency, small heat-affected zone, and no mechanical stress at the cutting edge. It is considered to be an ideal method for cutting PDC.

Reference: Research on Polycrystalline Diamond Composite CNC Laser Cutting Machine Tool, Ke Liang, Hui Xiangjun