Cooling and lubrication technology in the hottest

2022-08-22
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Cooling and lubrication technology in high speed cutting

in the process of high speed cutting, the high temperature, high pressure and high frequency impact in the tool/tool friction contact area pose a severe test to the tool performance. Especially in high-speed cutting of difficult to machine materials with high hardness, high strength and high temperature resistance, sharp tool wear caused by high cutting temperature and friction is often an agreed factor that restricts the application of high-speed cutting. Therefore, good cooling and lubrication are the key conditions for high-speed cutting of difficult to machine materials. Although wet cutting has good cooling and lubrication performance, in high-speed cutting, it often increases the temperature change of the milling cutter edge in the cutting process, resulting in thermal fatigue, reducing the tool life and reliability, in addition to environmental pollution and other problems. Under the condition of not using cutting fluid, the machining efficiency of difficult to machine materials can be improved to a certain extent by optimizing the tool material and structure. However, the cooling, lubrication, chip removal and other functions of cutting fluid can not be compensated, which may seriously affect the machining quality, cutting efficiency and tool life. How to choose a reasonable and effective cooling and lubrication method to improve the tool/tool friction state and inhibit tool wear, so as to improve the machining quality and machining efficiency, is an important technical element that must be considered in the promotion and application of high-speed cutting technology

performance requirements of high-speed cutting on cutting medium

the cooling performance of cutting medium depends first on the properties of cutting medium itself, such as thermal conductivity, specific heat capacity, vaporization heat, vaporization speed, etc., and then on the action mode of cutting medium, such as injection flow, injection speed, injection angle, injection target distance and other factors. In terms of production technology, the cooling performance of gas medium is far lower than that of liquid medium, but high-speed cutting also needs to consider the thermal fatigue failure of tools caused by excessive cooling, and how to make the cutting medium enter the tool/chip/interface and the tool/tool interface for effective cooling. Generally, due to the entry of cutting media and strong thermal shock, tool wear tends to intensify in wet cutting. Therefore, dry and quasi dry cutting methods such as low-temperature air cooling and low-temperature micro lubrication are mostly used for high-speed cutting of difficult to machine materials

in most cases, the main purpose of using cutting medium is to use the antifriction and lubrication performance of the medium to improve the friction contact condition in the tool/workpiece contact area, so as to improve the service life of the tool. Figure 1 shows the diffusion distribution curve of the tool rake face when using WC Co cemented carbide for high-speed orthogonal cutting TC4 titanium alloy in terms of energy conservation, emission reduction and environmental protection under different heat transfer coefficients

the change of heat transfer coefficient has a certain effect on the average temperature of the tool rake face, but it has little effect on chip formation and the maximum temperature of the tool rake face (near the cutting edge). Therefore, the diffusion wear in the highest temperature area near the edge changes little, and the diffusion wear in the middle part decreases with the increase of heat transfer coefficient. At a distance from the cutting edge, the cutting temperature is relatively low, which has little effect on the diffusion wear of the tool. Figure 2 shows the simulation distribution curve of the diffusive wear rate of the rake face when WC Co cemented carbide is used for high-speed orthogonal cutting TC4 titanium alloy under different friction coefficient conditions. The cutting temperature at the distance from the cutting edge is the highest, which is located in the bonding contact window and is less affected by the change of friction coefficient. Therefore, the diffusive wear rate of the tool changes little near the cutting edge, However, with the increase of friction coefficient in the sliding contact window area, the cutting temperature increases significantly, so the tool diffusion wear rate is also larger. The comparison between Fig. 1 and Fig. 2 shows that the effect of improving lubrication performance on improving tool diffusion wear is more obvious than that of cooling

The problem of chip removal in high-speed cutting will have a certain impact on the cutting performance and machining surface quality of the tool. Therefore, high-speed cutting requires the cutting medium to have a certain chip removal effect. Generally, high-speed, high-pressure and large flow jet impact directly blows the chips away from the tool and processing area

the green performance of cutting media requires that the media be environmentally friendly and reduce the emission of pollutants. The main hazard to human body is inhalable particles in oil mist (PM10, aerodynamic diameter ≤ 10 μ M). Generally, the smaller the particle diameter, the deeper the part entering the human respiratory system, and the greater the harm to the human body. Generally, aerodynamic diameter ≥ 10 μ Most particles of M will be blocked outside the nasal cavity and will not enter the human body, and the diameter ≤ 10 μ M inhalable particles can enter the respiratory system smoothly and will deposit in the human body, causing long-term harm to human health. Therefore, for the cooling and lubrication mode that may produce oil mist, the medium composition, oil mist concentration and particle size must be controlled to avoid injury to the production site personnel. At present, mineral base oil has been banned as cutting medium oil in Europe

low temperature micro lubrication technology and its application

low temperature micro lubrication technology is a new cooling and lubrication technology for high-speed cutting, which organically combines low temperature air-cooled cutting technology with micro lubrication technology. It not only makes full use of the cooling effect of low temperature air, but also makes full use of the antifriction and lubrication effect of micro lubrication. When the low-temperature micro lubrication technology is used to assist cutting, the air, nitrogen or other gases are pre cooled to about -30 ℃ through the low-temperature refrigeration equipment, and then the low-temperature gas is passed through the micro lubrication device to form a low-temperature micro oil mist (oil gas) at the nozzle, which is continuously sprayed to the cutting area with high-pressure and high-speed industrial convergence, so as to realize the cooling and lubrication of the tool/worker contact area and improve the conditions of the cutting area. Low temperature micro lubrication cutting technology is a new advanced technology developed in the sense of real sustainable development by combining high-speed and efficient cutting technology with green processing from the perspective of high quality, high efficiency, economy and environmental protection, and this element does not contain metal lattice and insert material technology. The air quality test of cutting environment confirmed that the oil mist concentration in the low temperature MQL, normal temperature MQL and the external workplace of the machine tool under coolant pouring in the closed machining system was kept at a low level, reaching the safety standard. Low temperature MQL can effectively inhibit the atomization of lubricating oil and the generation rate of fine particle oil mist, which is more environmentally friendly and safe than normal temperature MQL

Figure 3 shows the change curve of tool tip wear with cutting time during high-speed turning Inconel718 under different cooling and lubrication conditions. It can be seen from the figure that the tool tip wear is the slowest when cutting at low temperature MQL, and the tool life at low temperature air cooling and low temperature MQL is 78% and 124% higher than that of dry cutting respectively. Figure 4 shows the surface roughness of kc5010 cemented carbide tool during high-speed turning Inconel718 under cooling and lubrication conditions. It can be seen that low-temperature MQL cutting can also reduce the surface roughness value of the workpiece

figure 5A shows the change curve of tool wear of titanium alloy in high-speed milling with milling time under different cooling and lubrication conditions. It can be seen from the figure that under the conditions of cutting parameters shown in the figure, -10 ℃ low-temperature air cooling and -20 ℃ low-temperature air cooling, the wear condition of the flank is slightly better than that of dry milling, while the application of low-temperature MQL can effectively improve the friction and lubrication condition of the tool/tool contact area and significantly improve the service life of the tool. Fig. 5B shows the effect of cooling and lubrication conditions on milling side roughness during high-speed milling of titanium alloy TC4. It can be seen from the figure that the surface roughness of low-temperature air cooling is equivalent to that of dry milling, and low-temperature MQL can significantly improve the machined surface roughness

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