The mirror-turning of aluminum alloy workpieces and other non-ferrous metals and their alloy workpieces with single crystal diamond turning tools or polycrystalline diamond turning tools not only achieves a very smooth and smooth surface, but also has a long service life. The advantage is that other turning tools can't match. However, it is difficult to form complex-shaped cutters such as end mills, drills, and taps with single crystal diamond and polycrystalline diamond. The only way to apply diamond to a complex shape tool is to apply a diamond film coating to the complex tool surface using gas phase synthesis (or vapor deposition).
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1 Coating principle of diamond film coating The coating principle of diamond film coating is to use hydrocarbon gas (such as methane) as the main raw material and hydrogen as the carrier fluid to form diamond film coating on complex tool surface by plasma CVD. . The methods for providing plasma include a direct current discharge method, a microwave method, a hot filament method, etc. In industrial applications, a microwave method and a hot filament method are mainly used. In the plasma state, the carbon atoms of the hydrocarbon gas are converted into SP3 bonded diamond, SP bonds or SP2 bonded DLC and graphite. After the DLC and graphite are removed by the carrier gas hydrogen, only high-quality diamond is deposited on the surface of the substrate. The base material of the diamond coated tool needs to have sufficient strength. At present, cemented carbide is used as the base material, and high speed steel and die steel cannot be used as the base material of the diamond coating.
When manufacturing diamond coated carbide tools, the pre-coating of the tool is very important. Since the presence of cobalt in the cemented carbide affects the formation of diamond, the cobalt in the surface of the cemented carbide substrate is removed prior to coating. When the diamond coating is applied, the coating element and the cemented carbide matrix element do not diffuse from each other. In order to prevent the coating from being weakly bonded to the substrate, the surface of the substrate must be treated to have a certain uneven surface. The pretreatment process continues until the diamond is completely nucleated. The quality of the diamond film coating depends almost entirely on the quality of the pre-coating treatment. The thickness of the tip coating of the diamond coated carbide end mill is about 10 μm.
2 Development of ultrafine crystal diamond coating technology
The diamond coating coated by the conventional vapor deposition method has a grain size of about 10 μm, so the surface of the coating is rough and cannot be used for high-precision processing. The diamond crystal formed by the vapor deposition method is a crystal grain of a previously processed crystal nucleus and grows into a crystal grain of a coating thickness. Therefore, if the coating thickness is small, a fine grained coating can be formed. However, the diamond coating itself needs to have the necessary strength, so it is desirable that the coating thickness be 10 μm or more. Ultrafine grained diamond coatings can be obtained by appropriate combination of pre-coating and plasma process conditions.
3 Cutting performance of ultra-fine grain diamond coated tools (1) Diamond coated end mills In the past, diamond coated end mills were only used for graphite machining. Machining aluminum alloys with diamond-coated tools can give full play to their excellent cutting performance. However, due to the rough surface of the ordinary grain diamond coating, it is difficult to obtain an excellent machined surface when the ultra-hard aluminum is milled according to the cutting conditions of Table 1. The ultra-fine grain diamond-coated end mill can obtain an excellent machined surface. A similar machined surface can also be obtained with an uncoated end mill.
Table 1 Cutting conditions of aluminum alloy Cutting tool: φ6mm2 blade carbide end mill Workpiece material: A7075 super hard aluminum Cutting speed: 9400m/min (12700r/min)
Feed rate: 1270mm/min (0.05mm/tooth)
Cutting depth: AD=10mm; RD=0.1mm
Cutting fluid: Floating coolant If the crystal grain diameter of diamond is large, aluminum will adhere to the gap between the crystal grains due to frictional extrusion, which shortens the life of the tool and makes it difficult to perform dry cutting. If ultra-fine grain diamond-coated end mills are used, dry sticking can be avoided and dry cutting can be achieved with long tool life.
When the ADC12 aluminum die-casting part was cut according to the conditions in Table 2, when the ordinary grain-grain diamond-coated end mill cuts 3.5m, the aluminum chips block the chip flute and cannot continue cutting; and the ultra-fine grain diamond coated end mill is used for processing. At 8.75m, only minimal aluminum adhesion is visible and cutting can continue.
Table 2 Cutting conditions of aluminum die castings Cutting tool: φ10mm2 edge carbide end mills Workpiece materials: ADC12 aluminum die castings Cutting speed: 300m/min
Feeding speed: 1000mm/min (0.05mm/tooth)
Cutting depth: AD=8mm; RD=2.5mm
Cutting fluid: air-cooled Due to the ultrafine graining, the toughness of the diamond coating itself is improved. When the aluminum die-casting parts were processed under the conditions of Table 2, when the ordinary grain-grained diamond end mill was used to process 1108 m, the blade edge arc-coated coating peeled off to reach the wear state of the service life; and the ultrafine grain diamond coating was used. When the milling cutter is processed at 1108 m, the cutting edge is not damaged. The above results demonstrate the advantages of ultra-fine grain diamond coated end mills, expand the range of materials to be processed, and explore their appropriate uses.
Machining of metal matrix composites (MMC) with R5 diamond coated ball end mills (circumferential speed: 8000/min, feed: 2000 mm/min, depth of cut: AD = 1 mm, pf = 0.5 mm; dry cutting) Example: MMC (SiC20%-Al) is an aluminum alloy containing a large amount of ceramic hard particles in an aluminum matrix. These hard particles accelerate the wear of the tool tip and are ultra-difficult-cut aluminum composite materials. After cutting with a universal TiAlN coated end mill for about 20m, the tool tip wears extremely much and cannot continue cutting. When the ultra-fine grain diamond coated end mill is used for cutting more than 200m, the wear of the tool tip is very slight.
An example of milling an electrode for electric discharge machining using an end mill coated with an ultrafine grain diamond coated circular insert on a F2139 cutter body: after cutting for 39 minutes with a conventional end mill, the cutting edge is broken to reach a service life; In contrast, ultra-fine grain diamond coated end mills have a service life of 400 minutes.
As a new material, Fiber Reinforced Plastic (FRP) is a difficult-to-machine material containing a large amount of ceramic or glass fiber in a resin matrix. Like MMC, FRP can hardly be machined with ordinary tools. Milling of glass fiber reinforced (20%) plastic with end mills, milling with 3.8 m with high speed steel end mills, long service life due to excessive wear of the cutting edge; milling with ultrafine grain diamond coated end mills 11.4 After m, the tip wear is still very slight.
(2) Diamond coated drill bit It is well known that drilling is difficult to dissipate heat, so a large amount of coolant must be used for drilling. In recent years, in order to improve the environmental protection of cutting, it is necessary to use dry cutting and minimum mass lubrication (Minimum Quantity Lubrication, MQL) cutting technology. At present, PVD coated tools for dry and MQL hole processing of steel have been industrialized. However, due to the high affinity of aluminum and tool materials, it is more difficult to achieve aluminum dry and MQL drilling. Especially in the dry hole processing of high silicon aluminum alloy, the drill bit is often blocked by aluminum chips. Short life. Even DLC coated drill bits with low-silicon aluminum alloys that prevent sticking of the knife are difficult to handle dry drilling or MQL drilling of high-silicon aluminum alloys.
Example of dry-type (air-cooled) cutting of ADC12 aluminum die-casting holes with DLC coated drill bits and ultra-fine grain diamond coated drills according to the conditions listed in Table 3: DLC coated drills for 450 holes, due to aluminum filings The drill hole can be blocked and the drilling process cannot be continued; while the ultra-fine grain diamond coated drill bit has no sticking to the knife after 3600 holes, it can continue drilling, showing great advantages.
Table 3 Dry hole machining conditions for aluminum die castings Cutting tool: φ6mm carbide drill bit Workpiece material: ADC12 aluminum die casting Cutting speed: 96m/min
Feed rate: 0.12mm/rev
Cutting depth: 18mm
Cutting fluid: air-cooled under dry air-cooled drilling and MQL drilling conditions (except for cutting fluid, other processing conditions are the same as in Table 3), uncoated drill bit, ordinary grain diamond coated drill bit and ultrafine grain diamond Comparison of cutting life of coated drill bit ADC12 aluminum parts: Under air-cooled conditions, when the uncoated drill bit is machined to 94 holes, the bit breaks due to chipping; however, under MQL conditions, the bit life is extended to 447 hole. Tool life testing was also performed with conventional grain diamond coated drill bits and ultrafine grain diamond coated drill bits under air-cooled and MQL conditions. Ordinary die drills are broken when drilled to 731 holes under air-cooled conditions, and are broken when drilled to 2160 holes under MQL conditions. The cause of the break is the sticking knife and the chipping. Ultra-fine-grain drills drilled to 3,080 holes in air-cooled conditions and 9216 holes in MQL conditions, reaching service life due to drill-edge chipping. It can be seen that the ultrafine grain diamond coated carbide drill is suitable for dry cutting of aluminum alloy.
When a conventional grain diamond coated drill bit is drilled to 2000 holes under MQL conditions, aluminum flakes are adhered to one side of the drill groove, and then 160 holes are processed, that is, when the total of 2160 holes are broken, the drill bit is broken due to the plugging. The ultra-fine grain diamond coated drill bit is serviced to 3,080 holes under air-cooled conditions, and the life is reached due to the cutting edge of the drill tip. A small amount of aluminum scrap is stuck on the bottom of the drill groove, and the drill tip collapses due to chip biting. blade. The ultra-fine grain diamond coated drill bit was drilled to a life of 9216 holes under MQL conditions, and the drill bit reached the service life, but no stickiness was observed. It can be seen that the combined application of ultrafine grain diamond coating and MQL can significantly improve the service life of the drill bit.
(3) Diamond coated tap tap is a processing tool that forms a female thread on the inner hole surface. The shape of the cutting edge is more complicated than that of the end mill and the drill bit. It cannot be made of polycrystalline diamond. It can only be represented by diamond coating. Sexual tools. Tapping of alumina fiber reinforced plastic (FRP) (tool: OTTM3×0.6; workpiece material: FRP (containing 15% alumina fiber); cutting speed: 500/min) Test results show: uncoated cemented carbide Taps are almost impossible to tap; ultrafine grain diamond coated taps can tap 500 holes. Tapping processing of aluminum alloy composite (MMC) (machine tool: vertical CNC tapping center; tool: M4×0.8 diamond coated tap; workpiece material: MMC (including 30% SiC); cutting speed: 4m/min; Bottom hole: φ3.4×12mm blind hole; tapping depth: 8mm; water-soluble cutting fluid) test results show that when ultra-fine grain diamond coating tap taps to 464 threaded holes, it will reach service life due to large wear The life of a conventional grain diamond coated tap is less than half of that of an ultrafine grain tap due to peeling of the coating.
4 Recoating of diamond coating In order to save the cost of the tool, after the general coating tool is used for the set life, the remaining coating can be removed by grinding and then recoated. However, for diamond coated tools, it is difficult to remove the coating with a diamond wheel, the efficiency is very low, and the quality after recoating is also problematic. Therefore, it is desirable to remove the diamond coating and then re-grind it. For this purpose, a method of plasma burning to remove diamond has been developed, and the tool can be generally reground and recoated by this process. However, if the plasma conditions are not well controlled, excessive combustion can cause melt damage to the cemented carbide substrate, while insufficient combustion can result in residual coating. According to the conditions in Table 4, the comparison of tool life when milling aluminum die-casting parts with 3R cemented carbide ball end mills shows that after removing the diamond coating by appropriate plasma conditions, the performance of the recoated tool is comparable to that of the new tool.
Table 4 Machining conditions for milling aluminum die castings Cutting tool: 3R cemented carbide ball end mill Workpiece material: ADC aluminum die casting Cutting speed: 376m/min (20000/min)
Feed rate: 3500mm/min (0.09mm/tooth)
Cutting depth: 0.3mm axial, periodic feed 1.2mm
Cutting fluid: The new technology of air-cooled diamond coating grain ultra-fine refinement has greatly expanded the application range of cutting tools, making workpiece materials such as aluminum alloy and copper alloy that could not be processed in the past become machinable, and the tool life is greatly improved. The extension greatly reduces the types and quantities of cutting tools necessary for production at the processing site. New materials such as MMC and FRP have excellent characteristics such as light weight and high strength, but processing is very difficult, so the popularity of the application is slightly slower. The emergence of ultra-fine grain diamond coated tools will definitely make a significant contribution to the material revolution in the future.
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The latest development trend of ultra-fine grain diamond coated tools
Abstract The single-crystal diamond turning tool or polycrystalline diamond turning tool mirror-turning aluminum alloy workpieces and other non-ferrous metals and their alloy workpieces can not only obtain a very smooth and smooth surface, but also have a long service life. Its advantage is unmatched by other turning tools. but...