Titanium will play an increasingly important role in the future (especially in the aerospace industry) due to its own material properties. Titanium has the characteristics of high strength, good toughness, low thermal conductivity and special corrosion resistance. As carbon fiber (CFU) is used in a large amount as aerospace component materials, the application of titanium components has also increased. This is because when titanium metal is used in combination with CFK, the electrochemical potential difference between the two is higher than that of lead metal and CFK. The potential difference between them is low. In the future, more and more structural components will be made of titanium, which puts demands on the process design of the cutting process. It is necessary to provide an efficient milling tool that can adapt to titanium metal processing.
In order to improve the efficiency of milling, in addition to the macro-geometry design of the tool, it is one of the ways to change the design parameters of the micro-geometry. Here, the cutting edge passivation process which plays an important role in improving the cutting efficiency is first mentioned. According to people's current understanding, the use of cutting edge cutting tools is beneficial to improve cutting efficiency when processing titanium. The test results presented below show that although titanium has such material properties, it can also improve the cutting efficiency by appropriately changing the design parameters of the tool micro-geometry.
Cutting edge passivation technology with high reproducibility
The way in which the cutting edge of the tool is passivated is usually brush, shot peening, barrel polishing, and the like. This paper introduces a newer edge passivation process - magnetic precision trimming technology. The two magnetic heads are filled with a squeegee medium mixed with magnetic particles, the two magnetic heads are rotated at different speeds, and the processed tool is placed between the two magnetic heads, and is rotated in a fluid filled with the scraping medium, and the medium is rotative to the cutter. The edge, back, front and edge are flushed. This method can also be used to process PVD coated tools.
Since the geometry of the cutting edge is not completely symmetrical, the degree of passivation is not uniform. In order to clearly describe the geometry of any one of the cutting edges, the following parameters are used: the front segment Sγ, the rear segment Sα, the segment ratio K, and the radius spacing Δr. Previous studies have shown that the passivation of the cutting edge has a great influence on the cutting efficiency of the tool. After further research, it is found that the cutting edge of the tool passes through the asymmetric uniform passivation process, and its cutting performance is better than that of the symmetric uniform passivation process.
The adjustment parameters of the technology for tool edge passivation include: tool rotation direction; head rotation direction; tool rotation speed; head rotation speed; two head spacing; processing time; position of the tool between the heads; immersion depth; Media size.
The head spacing and passivation processing time have a great influence on the processing effect. Prolonging the passivation treatment time, the degree of passivation of the cutting edge is increased, but the degree of increase is decreasing. Therefore, in order to further increase the amount of passivation, it takes more time and materials.
If the edge passivation processing time is constant, the smaller the pitch between the two heads, the larger the edge passivation amount. This is because when the pitch is reduced, the scraping medium can be more and more firmly adsorbed when the spacing is larger. On the cutting edge surface, when the cutter and the magnetic head rotate, the higher medium adsorption force will exert a large pressure on the cutting edge, so that the cutting edge surface material can obtain a better scraping effect.
Cutting edge passivation improves tool durability
From the tool passivated by the cutting edge (such as a solid carbide milling cutter with 4 cutting edges, diameter D = 16mm, helix angle λ = 40°, rake angle γ = 12°, radial relief angle α = The microscopic shape of 10°) clearly shows that after the cutting edge of the tool is precisely trimmed, the surface of the edge is polished, except that the cutting edge is passivated.
With a passivated tool, the service life can be increased by 70% when machining with conventional cutting parameters. The greater the amount of edge passivation, the better the wear resistance of the tool. When the tool is not passivated, the cutting edge will be worn due to minor damage, and this phenomenon rarely occurs on the tool that passes through the passivation process because it is in the cutting process. A large amount of pressure is created on the cutting edge and some bond is formed on the passivated blade, making the blade stronger and less prone to wear.
After the tool is passivated, the cutting performance of the cutting edge is more stable, which is especially important for improving the processing efficiency of titanium metal. Since the cutting edge can be effectively avoided, the distribution and process of tool wear are very uniform and stable, and the safety and reliability of the cutting process are greatly improved.
In the case of the maximum amount of edge passivation, the test data for increasing the feed per tooth indicates that the tool is durable when the feed per tooth is fz=0.06mm, which is double the normal cutting condition. The highest degree. The test was stopped when the cutting amount reached vw=2300 cm3. Since the cutting stroke of each cutting edge is reduced, the tool durability at fz=0.06 mm is much higher than that at fz=0.03 mm.
In order to process the same amount of material, it is necessary to reduce the speed of the tool. When the cutting thickness is larger than the segment Sα behind the cutting edge of the tool, the tool wear condition can also be improved. However, continuing to increase the amount of tooth feed will cause an increase in the mechanical load of the machine tool, resulting in increased wear and a reduction in the amount of cutting. In addition, the passivation process can reduce the chattering caused by the cutting process, and even if the cutting parameters are selected for cutting, the durability of the tool can be guaranteed.
After passivation of the cutting edge, the tool wears very evenly during use, at which point a bond is formed in front of and behind the tool.
When the feed rate is large, the cutting edge does not appear to be significantly damaged. For further testing, the feed per tooth was increased to fz = 0.15 mm and the depth of cut was reduced to ap = 5 mm. When the depth of cut is large, the cutting force is also increased correspondingly, resulting in damage to the tool. When the feed rate is also large and the cutting depth is ap=16mm, chattering will occur during the cutting process, causing damage to the tool and damage to the machine tool spindle.
summary
The edge passivation treatment has a great influence on tool wear and machining efficiency. Circular cutting edges such as milling cutters and rotationally symmetrical cutters can be passivated by magnetic precision trimming technology. The front, back and cutting edges of the tool are also polished at the same time, which is very advantageous for avoiding bonding. When the tool is passivated by the cutting edge, the durability of the titanium metal can be increased by about 70% according to the conventional cutting parameters, and the feed per tooth can be significantly improved. Tests have shown that when the feed per tooth fz = 0.06 mm, the cutting state of the tool is optimal, and no slight damage is observed on the cutting edge of the tool.
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