Dry cutting process application
The key to the success of the dry cutting process is to find a way to replace cooling and lubrication. At present, there are two successful dry cutting methods: high speed dry cutting and low temperature cold cutting.
First, high speed dry cutting and low temperature cold air cutting
High-speed dry cutting method This processing method uses a high cutting speed for cutting without the action of cooling or lubricating oil. Dry cutting must use the appropriate cutting conditions. First, use a high cutting speed to minimize the contact time between the tool and the workpiece, and then use compressed air or other similar methods to remove the chips to control the temperature of the working area. With the extensive use of CNC technology, the rigidity and dynamic performance of machine tools are constantly improving, and it is not difficult to increase the cutting speed of machine tools. Practice has shown that when the cutting parameters are set correctly, 80% of the heat generated by cutting can be carried away by the chips.
High-speed dry cutting has strict requirements for the knife: 1 The tool should have excellent high temperature resistance and can work without cutting fluid. New types of cutting materials such as cemented carbide, polycrystalline ceramics and CBN are the materials of choice for dry cutting tools; 2 the coefficient of friction between the chips and the tool should be as small as possible (the most effective method is the surface coating of the tool), supplemented by Good chip removal structure and reduced heat accumulation; 3 dry cutting tools should also have higher strength and impact toughness than wet cutting tools.
Low-temperature cold-air cutting This cutting method is a processing method in which cold air of -10 to -100 ° C and very small amount of vegetable oil are used instead of cooling and lubricating oil cooling. It was first proposed by Yokokawa Kazuhiko of Meiji University in Japan. It has been found that in the metal cutting process, if only a very small amount of vegetable oil with good lubricating effect and unoxidized is supplied to the processing point, the processing point will lose lubricity due to high temperature. If cold air (-10~-100°C) is supplied to the processing point, the high temperature of the processing point can be prevented and the above situation can be avoided. The cutting performance is greatly improved during cold air cutting. Tests have shown that cold air cutting and grinding are more than twice as efficient in performance as oil cutting and grinding. Comparison of cutting performance with and without vegetable oil cutting agent and cold air. It can be seen that the use of cold air cutting is better than the use of plants, and the cutting performance of the tool is further enhanced when cold air is used together with trace vegetable oil. Cutting conditions during the test: workpiece diameter: f92~f98mm, cutting speed: 45.1~48.0m/min, feed: 0.5mm, cutting tool: tool nose radius R0.4, equivalent to SKH4 high speed steel, no re-grinding blade.
▲ No precision lubricating oil, no cold air processing; - Precision lubricating oil, no cold air; ◠Precision lubricating oil, cold air; ◆ No precision lubricating oil, -16.7 °C cold air, no vegetable oil cutting agent and cold air cutting Performance When using strong cold air with very low temperature, to prevent oil from freezing and losing lubricity, apply a small amount of vegetable oil to the surface of the tool before processing, and then supply strong cold air to the processing point. That is to say, if the strong cold air is mixed with the oil agent, the effect will be better. The use of trace vegetable oils not only reduces cutting energy, but also eliminates rusting of the workpiece.
Second, the application of dry cutting in the field of gear processing
The new carbide coating method and the use of CNC machines have led to a new trend in the manufacture of cylindrical gears: high-speed cutting of carbide-free tools without cooling. If the process parameters are optimally set, the machining time is short and the tool life is longer. Japan's Mitsubishi Corporation, the US Gleason Corporation, etc. have carried out fruitful research in this regard.
Japan's Mitsubishi Corporation introduced the world's first dry hobbing system. It uses a cutting speed that is twice the traditional hobbing speed and can reach 200m/min. Dry hobbing has special requirements for the hob. Mitsubishi's special dry hob is made of MACH7 high speed steel and the surface is coated with A special coating that helps to dissipate heat and reduce tool loss, extending its life to five times the normal wet cut. This system is ideal for processing automotive final drive gears, large load gears, automotive pinions and planetary gears, reducing production costs by at least 40%.
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