Diamond tools have excellent adaptability in processing applications of non-ferrous metals and wear-resistant materials.
Among the tool materials, diamond is the hardest. Under suitable processing conditions, diamond has a longer service life than high-speed steels, hard alloys, ceramics, and polycrystalline cubic boron nitride. It also has deficiencies that generally do not apply to the processing of ferrous materials. However, diamonds are often the most effective tools for processing materials such as aluminum and graphite in high-speed mass production.
When using diamond tools, users have two options: one is polycrystalline diamond (PCD) and the other is newer chemical vapor deposition (CVD) diamond.
Performance has long proven that polycrystalline diamond has the hardness, strength, and abrasion resistance of natural diamond, but there is no natural diamond-to-breakage sensitivity. It is formed by polymerizing synthetic diamond particles under high temperature and high pressure. During the process, the polycrystalline particles are integrally bonded to a cemented carbide substrate at the same time to improve mechanical strength and impact resistance.
According to GE's Super Abrasives Division, PCD is very suitable for high-speed cutting of aluminum, and is particularly suitable for applications where good surface roughness is essential. It also exhibits excellent performance when processing high wear-resistant materials. In general, PCD is recommended for cutting high-silicon aluminum alloys and also for the processing of brass, copper, bronze, and carbides. The procedures used include cars, rakes, profiling, grooving, milling and hole machining.
Due to the chemical interaction between diamond and iron, PCD is generally not suitable for processing ferrous materials. But it can deal with the processing of bimetallic materials, including the combination of aluminum and cast iron. For example: An auto parts supplier uses a 305 mm diameter tool-clamp face milling cutter when machining aluminum and cast iron bimetallic cylinder blocks. The tip radius is 2.36 mm with a light knife, the cutting speed is 304.8 m/min, and the feed rate is 0.10. Mm/tooth, depth of cut 5mm, after machining up to 5000 cylinders, the blade needs to be indexed once.
GE's application planning manager believes that the application of PCD has been driven by the mass production of the industry, mainly the automotive industry, which is increasingly improving the processing speed of aluminum parts. At the same time, automakers are evaluating composites using metal substrates for weight reduction and cost reduction that require PCD processing. He said: "This kind of material cannot be processed with carbide tools."
The polycrystalline product production manager said that although PCD's development achievements have given people a very deep impression, GE's Super Abrasives Department has continued to work in order to further improve its anti-wear properties.
PCD tools bring many benefits to the process in terms of application area and production efficiency. Although diamond is the hardest among existing materials, its material properties and toughness issues still need further study. One factor that improves the toughness of the PCD is that cobalt is added into the random, non-aligned diamond grains. In addition, the cemented carbide substrate can also provide mechanical support for the diamond abrasive layer, thereby increasing the impact resistance and facilitating brazing in tool manufacture.
Another benefit of PCD is that the existing range of various grades already meets the needs of any non-ferrous metal processing application. In general, fine-grained diamond is used in applications where the wear resistance of the material to be processed is low and surface roughness requirements are very high; medium-grain diamond is generally used as a general grade for machining; coarse-grained diamond is used for roughing and special anti-wear. Materials, but the surface roughness is not high.
A new member of the Diamond family, Chemical Vapor Deposition (CVD) diamond, is a highly abrasive pure diamond material that does not contain a binder. Diamond deposition is divided into two forms: one is a thick film diamond, deposited as a monolithic, individual sheet, and then cut to the desired size; the other is a thin film diamond deposited on a carbide insert or rotary tool.
To date, the most promising use of CVD diamond is the processing of graphite. However, Norton Diamond Film Co., Ltd. is selling CVD diamonds for various applications for the processing of non-ferrous metals, plastics and composites. Norton's application technology manager believes that CVD diamond is suitable for almost all non-ferrous metals. Good results are being obtained in the processing of interrupted cutting of high-silicon aluminum alloys and the preparation of pre-sintered cemented carbide, brass, copper and carbon fiber materials. Norton also believes that CVD diamonds can compete with PCDs when processing a wide range of aluminum alloy materials, including 6061 and others.
Norton's application technology manager also believes that the main advantage of CVD diamond compared to PCD is the quality of the cutting edge. Although CVD is also polycrystalline, it does not contain a cobalt binder and is pure diamond, so the cutting edge is continuous. This allows higher cutting speeds and better surface roughness because the tool does not heat up. He also believes that BUE does not pose a problem for CVD diamond.
According to Norton, CVD diamond has 50% higher thermal conductivity than PCD. The reason for this is that the CVD inserts are monolithic diamonds, which can lead to heat immediately. The heat conduction of the PCD blade is to pass through the cobalt-diamond composite, and the thermal conductivity is poor.
CVD diamond also has a low coefficient of friction. Both cemented carbide and PCD bond the workpiece material, and CVD diamond is not sticky. At the same time, the low coefficient of friction also enables CVD diamond tools to withstand large cutting loads, making cutting faster and more efficient.
CVD diamonds exhibit thermal and chemical stability in use. However, PCD and cemented carbide are affected by binders containing metal components in this respect. Put CVD diamond into the **, nothing will happen. However, if the PCD diamond is put in, the acid will eat the cobalt binder. This means that CVD diamond can withstand the attack of certain materials in the production of acid, such as phenolic resin, urethane rubber, carbonated carbonate and so on.
Although all forms of diamond, including PCD, react chemically with some components of ferrous metals or superalloys at high temperatures, diamonds are known to be chemically inert to most materials. Because PCD and cemented carbide contain a cobalt binder, chemical stability degradation occurs when the cutting temperature is high. CVD diamond does not contain binders and it avoids this phenomenon. In addition, CVD diamond has good lubricity and thermal conductivity, making it a key advantage for use in high speed and dry cutting.
The last advantage of CVD diamond is that it maintains high hardness and wear resistance even at high cutting temperatures. Nagy, application technology manager at Norton, pointed out: "Because there is no soft cobalt coated with diamond, the hardness of the blade is uniform."
Bright prospects GE Superabrasives and Norton DiamondFilm believe that at present, many production sites do not take full advantage of diamonds. The reason is that the speed and torque of many machine tools are not enough to ensure the efficient operation of tools.
In addition to the mechanical problems, there is a difficult problem that is to convince people in the production plant not to just stare at the initial price of diamond (PCD or CVD diamond), but to see the cost savings and performance improvements it brings. benefit. You can make diamonds run at higher speeds than conventional tools (depending on machine performance) to increase throughput. At the same time, there are fewer tool changes. Assuming that diamond is 50 to 100 times longer than carbide, you don't have to stop it often.
