Polycrystalline diamond PCD material is a super-hard composite material that is firmly combined with a cemented carbide substrate by a thin polycrystalline diamond layer under high pressure high temperature (HPHT) conditions, such as the materials in our PCD product range.
PCD, as the layer of the cutting edge of the tools, it has high hardness, high wear resistance, and high thermal hardness.
Cemented carbide, as the supporting base of the PCD composite material, it has high strength, a certain amount of impact toughness and thermal conductivity, and small thermal expansion coefficient, so using this composite superhard material as a tool material has the following advantages.
1) improve tool durability
2) improve the processing quality of the work-pieces to be processed
3) to cut high hardness work-pieces
4) to process special non-ferrous metals
5) cost-effective
The performance of the cutting tools made of polycrystalline diamond PCD is much higher than that of cemented carbide, ceramics, and even natural diamond tools in cutting applications. However, whether the superiority of the material itself can be exerted in practical application depends on the processing level of the tool, the rationality of the selection of the geometric angle of the tool and the correct method of use. Only by mastering the tool manufacturing and use technology can we better solve the difficult problems in machining.
Machining of PCD Tools
The processing of the PCD blade mainly includes the steps of cutting the PCD blank, welding the blade, and sharpening the blade. The PCD composite disc is cut into various shapes and the blades are brazed on the tool body, then the PCD tip is sharpened and ground to required radius. The surface of the PCD tool requires a grinding and polishing method, and the PCD surface is ground into a mirror surface (Ra≤50mm) to ensure that the generation of built-up edge is minimized and the chips can be discharged smoothly. In general, the polycrystalline diamond PCD layer has already been ground to a polished surface (the PCD blanks we supplied to manufacturers are mirror polished), so the tool manufacturers can directly use the PCD blanks without a further polishing of the PCD layer.
I ) Cutting of PCD blanks
Due to the high hardness and high wear resistance of PCD composite material, special processing technology must be adopted. At present, the processing of PCD blank mainly adopts several processing methods such as wire electric discharge machining (EDM), laser machining, ultrasonic machining, and high-pressure water jet.
Among the above processing methods, EDM has a better result, the presence of the metal bond in the PCD layer makes it possible to EDM the PCD composite blank, so the consistent electrical conductivity is a key factor when we producing the PCD blanks, as a result, we will suggest our customers the suitable quality grade of our PCD blanks for their applications if EDM is required.
The efficiency and surface quality of EDM PCD blanks are affected by factors such as cutting speed, PCD layer particle size, PCD layer thickness and electrode quality, among which the reasonable selection of cutting speed is very important. Experiments show that increasing the cutting speed will reduce the quality of the machined surface, while too low cutting speed will cause the phenomenon of “arching wire” and reduce the cutting efficiency. Increasing the thickness of the PCD layer also reduces the cutting speed.
II) Welding of PCD tips
The combination of PCD blade and cutter body is mostly by brazing the PCD tips on the cemented carbide substrate, in addition to the mechanical clamping and bonding methods. The welding methods mainly include laser welding, vacuum brazing, high frequency induction brazing, etc.
At present, high-frequency induction heating brazing with low investment and low cost is widely used in PCD blade welding. During the blade welding process, 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. Due to the poor heat resistance of the PCD material itself, the welding temperature should not exceed 700 ℃, and welding time should not be too long, but it must achieve a certain welding strength.
The effective welding area of most PCD blanks is below 10 square millimeter, so the welding strength must be guaranteed to be above 120MPa (shear strength). Practice has proved that the silver content in the solder should not be less than 40%, in order to meet the requirements of low temperature and high strength at the same time.
The surface before welding should be subjected to ultrasonic or other purification treatment, and carefully cleaned to remove surface oil, oxidation and other impurities that affect the welding strength. Carefully slow cooling after soldering to reduce PCD delamination due to excessive thermal stress.
(III) Grinding of PCD tips
The high hardness of polycrystalline diamond makes its material removal rate extremely low (even only one ten thousandth of the removal rate of cemented carbide).
At present, the sharpening process of PCD tools mainly uses resin bonded diamond grinding wheels for grinding. Since the grinding between the grinding wheel abrasive and the PCD layer is the interaction between two materials with similar hardness, the grinding law is more complicated. For coarse-grained, low-speed grinding wheels, the use of water-soluble coolant can improve the grinding efficiency and grinding accuracy of the PCD layer.
The choice of wheel bond should depend on the type of grinder and processing conditions. Since the electrical discharge grinding technology (EDG) is almost unaffected by the hardness of the ground work piece, the use of EDG technology to grind PCD tools has great advantages. The grinding of certain complex-shaped PCD cutting tools, such as woodworking blades, also has a huge demand for this flexible grinding process. With the continuous development of EDM grinding technology, EDG technology will become a main development direction of PCD grinding. Like the grinding and polishing process of PCD material, the sharpening technology of PCD tools can also use a combination of the above two technical processes, that is, electric discharge grinding (EDG) is used first, and then resin bond grinding is used.
It is worth noting that the final sharpening of the PCD tool is carried out on a dedicated diamond wheel tool grinder.
For more information and the specific inquiry on our PCD blanks material, please contact us to find the technical support.