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FUNIKE -Professional Cubic Boron Nitride, Synthetic Diamond Superhard Abrasive, Superhard Tool, Superhard Tool Manufacturer Stock Code: 831378

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Future technology trends for cutting tools in superhard materials

Summary:
Superhard materials such as diamond and cubic boron nitride are commonly used in high-speed machining processes and difficult-to-cut materials. This paper discusses and analyzes three aspects of superhard materials. First, PCBN is used for high-speed milling of cast iron to make it hard, heat conductive, and difficult to react with iron materials. Thermal cracks caused by thermal gradients during high-speed milling are one of the technical difficulties. Second, diamond-plated tools were used to drill carbon fiber reinforced plastic (CFRP). CFRP materials are used in aircraft fuselage, main structure and component preparation. The carbon fiber in CFRP has high hardness, so it is suitable to process with diamond-coated carbide tools. Finally, the direct milling of cemented carbide by BL-PCD (binder-free nano-polycrystalline diamond) tools in the mold preparation process is also discussed.
Keywords : CBN diamond plating nano-polycrystalline diamond high-speed milling CFRP
1 Introduction:
Cemented carbide was first developed and invented by the Germans in 1926. Cemented carbide tools have gradually been transformed into coated carbide tools, becoming one of the most important cutting tools for more than 80 years. PCD and PCBN are also more important tools. This paper discusses three novel technologies for superhard materials, a new PCBN grade for high-speed machining of cast iron, diamond-coated carbide for drilling CFRP, and BL-PCD face milling for direct milling of carbide.
2. CBN for high speed milling of cast iron
Cubic boron nitride (CBN) has high hardness, good thermal conductivity, and does not easily react with ferrous materials, and its performance is second only to diamond. Polycrystalline cubic boron nitride (PCBN) is made by sintering CBN particles with a ceramic binder; PCBN facilitates the transformation of hardened steel processing from grinding to cutting. PCBN cutting tools produced by Sumitomo Electric Hardmetal can significantly improve production efficiency and reduce costs in the finishing and semi-finishing processes of ferrous materials such as cast iron. On the other hand, PCBN is applied to the high-efficiency and high-precision machining of cast iron due to its high strength and good thermal conductivity. For example, the surface processing of engine blocks and oil pumps is usually done with PCBN cutting tools. This paper mainly discusses the milling of cast iron with new PCBN tools.
There are two types of PCBN sintered bodies: one is to bond CBN particles to a binder; the other is to use a small amount of binder material to bond CBN particles together. The former has good abrasion resistance and is cut with hardened steel; otherwise, it has a high CBN content and good thermal conductivity, and is used for cast iron processing, heat-resistant alloys and PM parts. The BN7000 is classified as the latter.
Figure 1 shows the new PCBN grade BN7000 cutter. The CBN content of BN7000 is higher than other traditional PCBN grade tools, with high strength, good toughness, high hardness and good thermal conductivity. Figure 2 shows the microstructure and properties of the BN7000. With a sintering pressure higher than the commonly used 5GPa, the CBN content increased from 90 vol% to 93vol%. In order to reduce the abrasive wear of the binder, the binding amount of the BN7000 sintered body was reduced by 30%. The accelerated reaction of CBN particles during the sintering process improves the composition of the binder, thereby making the binding strength of the binder much greater than that of traditional binders.
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In order to compare the similarities and differences between BN7000 and traditional grades in terms of heat-resistant cracking resistance, the experiment uses FMU4100R milling cutter and SNEW1203ADTR cutting tool to perform milling experiments on two cast iron discs (length, width and height: 150 * 100 * 25mm; hardness HB200-300), such as As shown in Figure 3: Vc = 1500m / min, f = 0.2mm'rev, ap = 0.3mm, without coolant. Figure 4 is a comparison chart after processing. The thermal cracks appearing on the BN7000 cutting edge are significantly less than the traditional grades, and the heat crack resistance is significantly improved.
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Using the new PCBN grade BN7000 to process cast iron can achieve efficient cutting and maintain long tool life. BN7000 has a high CBN content, high hardness, and good thermal conductivity. It is suitable for processing difficult-to-cut materials, which plays an important role in reducing cutting costs and achieving high-precision and efficient cutting.
3. Diamond plating tools for CFRP processing
A suitable combination of the matrix and the reinforcing material to form a controllable mechanical feature is a feature of the composite material. Carbon fiber reinforced plastic (CFRP) is widely used in industrial machinery such as automobiles, helicopters, medical equipment and railway vehicles due to its superior tensile strength, specific humidity, and corrosion resistance. In addition, CFRP material is a basic structural material in the aerospace field, which can reduce the weight of the aircraft fuselage, thereby improving fuel efficiency and saving maintenance costs.
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In the field of aerospace, diamond-plated tools are used for processing related to CFRP materials. Figure 5 is Sumitomo diamond plated drill for precision drilling of CFRP materials. Due to the axial force applied along the fiberboard stacking layer, CFRP materials are prone to delamination when drilling, as shown in Figures 6 and 7. With the intensification of cutting tool wear and debris sticking to the cutting edge, the drilling resistance during drilling also gradually increases, and the CFRP material is excessively heated, which reduces the strength. In order to solve this problem, it is unavoidable to apply it to diamond plated drills.
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Figure 8 shows the structure of a diamond plated drill. There are three changes in the apex angle from the center of the drill to the edge. This reduces the axial force of the outer edge of the drill during drilling and minimizes the delamination of CFRP material. The optimization between the spiral angle and the groove shape design, the cutting edge has three apex angles and the length has been shortened; this design allows the temperature during drilling of deep holes to be controlled so as not to be too high.
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Figure 9 shows the surface of a diamond-coated film. By improving the microstructure of diamond and optimizing the plating pretreatment technology, the problem that the diamond-plated film and the hard substrate are difficult to combine together is solved. Figure 10 shows an SDC drill for CRFP drilling. The quality of the holes produced is precise, without delamination and uncut fibers. Diamond coating has good abrasion resistance, which improves tool life and achieves stable drilling.
4 Direct milling of cemented carbide
In the mold preparation process, in order to improve the accuracy of the mold, direct milling is usually performed on the end face milling of the coated carbide. As manufacturers' requirements for mold hardness increase, the emergence of polycrystalline diamond (PCD) tools, diamond-coated carbide tools and single crystal diamond (SCD) tools can be used for direct milling of hard materials.
For direct milling of hard alloy molds, the hardness of traditional PCD tools is not enough to meet their requirements; the strength of SCD is not enough, and the sharpness of PCD and diamond-plated tools is not enough. Therefore, binder-free nano-polycrystalline diamond (BL-PCD) came into being. BL-PCD has higher hardness than PCD and SCD and better sharpness than PCD and diamond plating. It is suitable for direct milling of hard alloy molds, especially for finishing.
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Figure 11 shows the microstructures of BL-PCD and conventional PCD. Under ultra-high temperature and high pressure conditions, nano-graphite is directly converted into binder-free nano-diamond. The BL-PCD synthesized in this study is firmly bonded together, and the diameter of the diamond particles is about 10 nm.
Figure 12 shows the hardness comparison of BL-PCD. Conventional PCD contains binder Co with a hardness of about 40-60 GPa; SCD has a hardness of about 60-120 GPa.
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Figure 13 shows BL-PCD ball end milling, single cutting edge, ball radius R is 0.5mm; BL-PCD is brazed on a carbide shank.
Figure 14 shows one of the results of a direct milling experiment with cemented carbide. The purpose of this test is to study how BL-PCD face milling can produce fine surface roughness. The material of the workpiece is ultra-fine-grained cemented carbide, HRA92.5, and WC particle size is 0.5 μm. BL-PCD face milling is used for fine machining; diamond plated face milling is used for rough and semi-fine machining. In this experiment, the spindle speed is N = 4000, the feed rate is Vf = 120mm / min, the cutting depth is ap = 0.003mm, and the total time for fine milling is 150 minutes. The surface roughness of the workpiece is 8nm at the concave center and 7nm at 45 °. Cutting edge damage is slight, and the side wear is only 4 μm, without chipping and serious damage.
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Figure 15 shows another experimental result of direct milling. The purpose of this experiment is to study the efficient milling process in the actual production of cemented carbide molds. The workpiece material is fine-grained cemented carbide A1, 91.4HRA, and the WC particle size is 0.7 μm. The spindle speed is 4000, the cutting depth ap = 5μm, the feed speed Vf = 800mm / min, and the total grinding time is 38 minutes. The experimental results show that the workpiece has good overall surface quality, with Ra below 15nm.
5 Conclusion
This paper discusses three aspects of superhard materials, with the following conclusions:
(1) The new PCBN grade BN7000 has high strength, good toughness, and good thermal conductivity. The CBN content can be increased from 90vol% to 93vol%. Realized high-speed milling of cast iron, Vc = 1500m / min.
(2) Developed SDC diamond plated drill for CFRP material for fine drilling. In the case of CFRP drilling, the occurrence of delaminated and uncut fibers was reduced. The optimized diamond film structure plating and coating pretreatment achieves an increase in tool life, which is much better than traditional tools.
(3) BL-PCD (binder-free nano-polycrystalline diamond) tool was developed by using ultra-high pressure technology in experiments. The hardness and toughness are higher than those of SCD, and the cutting edge is higher than that of traditional PCD tools. BL-PCD ball end face milling can be used in direct milling of hard alloy molds to achieve better surface roughness, less than 10nm. ( Compilation: China Superhard Materials Network )