Yan Jie "Beyond Dream" Drilling CFRP Material Aircraft Parts Processing
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The assembly of the aircraft body mainly relies on fasteners (rivets), etc., and therefore requires a large number of drilling operations. In view of the CFRP characteristics, Yan Jie mainly uses the diamond-sintered body (PCD) and cemented carbide sintered "Visi-Drill" VN-DTD shape for drilling.
1. "Beyond Dreams"
The "Dream" drill is a spiral groove machined on a cemented carbide substrate and filled with sintered diamond powder and sintered integrally under high temperature and high pressure conditions. Because it is sintered with sintered diamond and hard alloy, the "Dream" drill has the following features:
(1) There is no fear of desoldering. The conventional sintered diamond drill bit is welded, and the welded portion is easily welded due to the friction of the chip, so that chip clogging and jamming are likely to occur, so the life and surface roughness are caused. Degree has a certain impact. The "Dream" drill is sintered by injecting sintered diamond into the cemented carbide matrix, so there is no trouble with welding. Especially in high-speed, ultra-high-speed machining, there is no common worry about the loss of soldering out of conventional PCD tools.
(2) Long life and high precision Since the cutting edge is made of sintered diamond, it can greatly extend the life compared with the carbide drill and the diamond coated drill. Sintered diamond has excellent adhesion resistance, so it can be stable to good surface roughness and aperture accuracy.
(3) Small diameter can be made. Since the drill bit is sintered from sintered diamond and hard alloy, the minimum diameter can be 0.4mm, and the rigidity of the cemented carbide support part of the welded diamond drill bit does not occur. Happening.
(4) Spiral blade sintered diamond is sintered as a whole, and the sintered diamond is made into the same spiral blade as the cemented carbide drill. The sintered diamond blade has a 30° helix angle on the outer circumference, and the sharpness is excellent. Compared with the welded sintered diamond drill bit, it has a large helix angle to prevent the hole from collapsing and raising.
(5) Difficult to machine materials can be drilled CFRP, metal matrix composites (MMC), graphite, carbon materials, hard alloys, etc. From the characteristics of these materials, the life of cemented carbide drills is extremely short. In contrast, the "Dream" drill chip base is a sintered diamond material with a low resistance edge with a large helix angle, so a stable long life can be achieved for such materials. Especially in the CFRP processing, the fiber cutting ability is strong, the axial resistance value is small, and the delamination can be suppressed.
(6) The true re-grinding can be carried out in the same way as the cemented carbide drill bit, and the re-grinding can be carried out in the range of the sintered diamond layer, and the economy is good.
And unlike diamond-coated drill bits, re-grinding does not change the outer diameter of the drill bit, and the geometry of the re-grinding bit does not change, so the processing performance is also very stable, and there will be no re-grinding geometry after welding diamond drill bits. The problem of shape change.
2. Processing examples
(1) Step drill type "Beyond Dream" Drill Figure 3 shows the machining example of the aircraft fuselage parts. The "Beyond Dream" drill has a chamfering edge f 4.8mm × f 10mm, the cutting speed is 275m / min, the speed is 18 000r /min, the feed amount is 1 140 mm/min, and the through hole of 15 mm is processed with the back knife amount being 0.064 mm/r. Since the fastener orifices need to be machined with a tapered chamfer at the same time, a chamfering blade is added to the "Dream" drill. In this case, the life of the drill bit is judged by the degree of outlet stratification, which is about 1,000 holes. The burrs and fiber collapse of the chamfered portion of the hole did not occur, and the quality of the entire processed part was very good. In addition, the bit must be re-grind at the same time as the drill tip edge and the sintered diamond chamfer blade portion.
(2) CFRP+ aluminum alloy (A7075) stacking processing Fig. 4 shows the lamination processing case of the wing part CFRP (2.5mm) + aluminum alloy material (2.5mm), using the "Bi Meng" drill VN-DTD-040 Processing parameters: cutting speed 126m / min, machine speed 10 000r / min, feed rate 500mm / min, back knife amount 0.05mm / r. In the past, welded sintered diamond drill bits were used to machine such holes. Although the sintered diamond drill bit has a spiral groove, since the sintered diamond plate is welded at the cutting edge, the cutting edge has no helix angle. In the processing, the life of the tool is usually determined by the burr at the exit of the aluminum alloy material. The conventional welded sintered diamond bit produces burrs after processing about 1 000 holes, reaching the life limit. In addition, due to the welding, the strength of the tool is insufficient, and the sintered diamond portion is prone to chipping, and a stable tool life cannot be obtained. The chipping of the sintered diamond portion also causes re-grinding and the processing cost increases. "Better than dream" drilling good sharpness can effectively inhibit the occurrence of burrs, the life can be extended to 2 times, about 2,000 holes. In addition, the "Bi Meng" drill is integrally sintered, and the cutting edge has superior strength to prevent chipping, so the true re-grinding can be carried out. It is because of long life and regrind, so the processing cost can be reduced to welding. 1/3 of the diamond drill bit.
When the stacking process is performed, depending on the cooling condition, the first plate is often processed and the second plate is processed. When the workpiece is slightly moved, the drill bit may be damaged. At this time, it is most important to effectively fix the parts. In addition, grinding the outer diameter of the drill body a few millimeters from the head is also a good way to prevent the drill bit from breaking when the parts are shaken.
3. Precautions for use
Since the cutting edge is a hard and brittle sintered diamond, the machining system needs to be more rigid than when using a cemented carbide drill bit. Highly rigid machine tools are recommended for high rigidity clamping of workpieces.
The above mainly describes the hole machining of CFRP material aircraft parts. This material has overwhelming specific strength and superior corrosion resistance compared with metal materials, so the proportion of the materials used in other fields will gradually increase in the future. There are still many issues related to the cost and quality of the material processing, but we firmly believe that "Beyond Dream" drilling as one of the solutions will definitely make a valuable contribution to the aerospace industry.
