PCD Tool Welding

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PCD superhard tool is a tool made of superhard material PCD (polycrystalline diamond) and tool matrix by special technology.
The characteristics of PCD tools:
High hardness, high compressive strength, good thermal conductivity, good wear resistance.
PCD Tool Main Indicators:
1. The hardness of PCD can reach 8000HV, which is 8-12 times of that of cemented carbide.
2. The thermal conductivity of PCD is 700W/mK, which is 1.5-9 times higher than that of cemented carbide, even higher than that of PCBN and copper, so the heat transfer of PCD tools is rapid.
3. The friction coefficient of PCD is generally only 0.1-0.3 (the friction coefficient of cemented carbide is 0.4-1), so the cutting force of PCD cutter can be significantly reduced.
4. The thermal expansion coefficient of PCD is only 0.9 x 10 ^ – 6 to 1.18 x 10 ^ – 6, which is only 1/5 of that of cemented carbide. Therefore, the thermal deformation of PCD tools is small and the processing accuracy is high.
5. The affinity between PCD tools and non-ferrous and non-metallic materials is very small, and the chips are not easy to adhere to the tool tips to form chip tumors during processing.
PCD tool manufacturing process:
PCD tool manufacturing process includes two stages:
1. Manufacture of PCD Composites: PCD Composites are sintered by natural or synthetic diamond powder and binder (including cobalt, nickel and other metals) in a certain proportion at high temperature (1000-2000 C) and high pressure (500000-100000 atmospheric pressure). In the sintering process, due to the addition of binder, a bonding bridge with TiC, SiC, Fe, Co and Ni as the main components is formed between diamond crystals. Diamond crystals are embedded in the framework of the bonding bridge in the form of covalent bonds. Usually the composite sheet is made into a disc with fixed diameter and thickness, and the sintered composite sheet needs grinding and polishing and other corresponding physical and chemical treatment.
2. PCD blade processing: PCD blade processing mainly includes the cutting of composite blade, blade welding, blade grinding and other steps.

PCD Tool Cutting Technology
Because PCD composite has high hardness and wear resistance, special processing technology must be adopted. At present, WEDM, laser processing, ultrasonic processing, high-pressure water jet and other processing methods are mainly used to process PCD composite, and the effect of EDM is better.
The combination bridge in PCD makes EDM composite possible. Under the condition of working fluid, the working fluid near the electrode metal forms discharge channel by using pulse voltage, and produces partial discharge spark. The instantaneous high temperature can make polycrystalline diamond melt and fall off, thus forming the required triangular, rectangular or square tool head blank.
The efficiency and surface quality of EDM PCD composites are affected by cutting speed, particle size, thickness and electrode quality. The reasonable selection of cutting speed is very important. Experiments show that increasing cutting speed will reduce the surface quality, while too low cutting speed will cause “arch wire” phenomenon and reduce cutting efficiency. Increasing the thickness of PCD blade also reduces the cutting speed.

PCD Tool Welding Technology
In addition to mechanical clamping and bonding methods, the bonding mode of PCD composite sheet and tool body is mostly to press PCD composite sheet on cemented carbide matrix by brazing. The main welding methods are laser welding, vacuum diffusion welding, vacuum brazing, high frequency induction brazing and so on. At present, high frequency induction heating brazing with low investment and low cost has been widely used in PCD blade welding. In the process of blade welding, the selection of welding temperature, flux and welding alloy will directly affect the performance of the tool after welding. In the welding process, the control of welding temperature is very important. If the welding temperature is too low, the welding strength is not enough. If the welding temperature is too high, PCD is easy to graphitize, and may lead to “over-burning”, which affects the bonding of PCD composite sheet and cemented carbide matrix. In the actual processing, the welding temperature can be controlled according to the holding time and the depth of reddening of PCD (generally less than 700 C). In foreign countries, automatic welding technology is often used for high frequency welding, which has high welding efficiency and good quality, and can realize continuous production. In China, manual welding is mostly used, and the production efficiency is low, and the quality is not ideal.

PCD/PCBN Vacuum Brazing Furnace

 

PCD Tool Grinding Technology
The high hardness of PCD makes its material removal rate very low (even only one thousandth of that of cemented carbide). At present, the PCD tool grinding process mainly uses ceramic bonded diamond grinding wheel for grinding. Because grinding between grinding wheel abrasives and PCD is the interaction between two materials with similar hardness, its grinding law is more complex. For high grain size and low speed grinding wheels, the grinding efficiency and precision of PCD can be improved by using water-soluble coolant. The choice of grinding wheel binder depends on the type of grinder and processing conditions. Because EDG technology is hardly affected by the hardness of the grinded workpiece, EDG technology has great advantages in grinding PCD. The grinding of some PCD tools with complex shapes (such as woodworking tools) also has a great demand for this flexible grinding process. With the continuous development of EDG technology, EDG technology will become a major development direction of PCD grinding.