Minimal Lubrication Machining (MQL Machining) and Its Applications
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Improve the processing of the environment
In the task of improving the on-site processing environment at the workshop, it is also crucial to create a work environment that ensures the physical and mental health of workers while increasing productivity and reducing costs.
Many machining enterprises have problems with noise, dust, and the use of cutting fluids that cause harm to workers' health, and the misty particles of cooling fluids pose the greatest threat to workers' health. Nowadays, due to the increasing application of high-speed processing equipment and the heavy use of powerful cutting fluids in the process of continuously increasing productivity, the problem of environmental pollution is more serious and costs are increasing. These problems have received more attention from people.
In order to effectively solve the above problems, people tried to adopt a dry machining method for cutting, but due to dry cutting, the tool life is short, the surface finish of the workpiece is poor, the workpiece is hot-deformed, and the risk of handling iron chips under a high temperature is likely to occur. Many problems, such as the generation of large amounts of dust, eventually failed to be successfully applied in large quantities. As a result, people began to pay attention to other more environmentally friendly processing methods or approaches to near-dry processing, such as the use of vegetable oil cutting fluid harmless to the human body for processing, or the use of micro-supply cutting fluid processing methods. The latter is the "MQL processing" method that has received much attention, namely, the micro-lubrication process, also called "spray processing" or "semi-dry processing."
MQL processing is a processing method developed based on the ultimate goal of improving the environment, using only a small amount of cutting fluid, which greatly affects the service life of the tool. But in many occasions, using MQL processing is not only more environmentally friendly, but also can achieve the ideal cutting results. At the same time, the service life of the tool can still reach satisfactory results. Then, MQL processing is a suitable processing option.
Range of applicable MQL processing
1. High-speed processing at high temperatures
When high-speed processing is performed at temperatures higher than the normal processing temperature (700 to 800°C), the use of a cutting fluid will reduce the service life of the tool. In this case, MQL machining may be considered. In terms of tool life, although dry cutting is more advantageous, MQL processing should be considered when solving other problems caused by high temperatures and obtaining a certain surface finish.
As we all know, the use of cutting fluid in the machining process is usually conducive to cutting, but in the general high-speed machining of steel parts, the cutting edge of the tool will produce a high temperature close to 900 ~ 1000 °C, if the supply of cutting fluid, cutting fluid inside Moisture will not be instantaneously vaporized until it reaches the edge of the high-temperature state, and the cooling effect will be lost. Even if the cutting fluid occasionally reaches the cutting edge, it will cause thermal shock to the blade and generate heat to the blade. This also affects the service life of the tool. This phenomenon also occurs frequently during low-speed machining of materials such as high-temperature alloys, which are prone to heat generation, and it is more advantageous to adopt the MQL processing method in this case.
2. Workpiece processing with large heat difference
Under normal circumstances, when dry turning or milling of workpieces with large thermal difference, dry cutting can be used generally, because in the process of intermittent cutting, the use of cutting fluid will aggravate the blade temperature change, easy to cause the tool to crack, Dry cutting can avoid this problem, but the dry cutting process often brings phenomena such as thermal deformation and poor surface finish. Obviously, MQL processing is more favorable.
3. Deep hole machining on small diameter workpieces
When deep hole machining is performed on small diameter workpieces, MQL machining can achieve the best results. In the past, this kind of deep-hole machining generally used cemented carbide gun drills or high-speed steel drills. Usually, the cutting speed of steel is 25 to 60 m/min, and the feed per revolution is 0.05 to 0.08 mm. Therefore, it is necessary to perform intermittent cutting. The production efficiency is very low, and the chip removal capability is poor due to insufficient speed of the machine tool or low cutting fluid pressure (0.5 to 1 MPa) and insufficient rigidity of the drill bit. Of course, now, with the increase in the spindle speed of the machine tool, the cutting speed can reach 100m/min or more when using a carbide drill, and the supply pressure of the cutting fluid has also increased to a high pressure state of 5 to 8 MPa, and chip removal has become easy. .
In the case of small, deep hole drilling, if a carbide drill with an internal construction of an MQL supply system is used, proper cooling during machining will facilitate cutting. At the same time, the appropriate size of cutting iron will be generated in high pressure fogging. The chip is discharged under the effect of the chip, so it can be processed very efficiently without intermittent cutting.
In the case of slender drills under normal circumstances, not only is the lack of rigidity of the tool detrimental to chip evacuation, the narrow chip flutes are also not conducive to rapid chip evacuation and squeezing occurs, resulting in increased torque and tool fracture. Drills used for MQL machining should have excellent rigidity in terms of structure. In addition, the cutting edge design should greatly reduce the cutting resistance. At the same time, in order to facilitate chip removal, the chip flutes should be smoothed.
Of course, carbide cutting tools should maintain a very balanced flutes spacing and rigidity. In this case, the drill bit manufactured is used for MQL machining, the cutting speed can reach 80-150m/min, the feed per revolution can reach 0.15-0.2mm, and there is no need for intermittent processing. This not only extends the service life of the tool, but also significantly increases the production efficiency.
Conclusion
In summary, MQL machining is established for the purpose of improving the working environment. Compared with the traditional machining methods using cutting fluids, there is a certain gap in tool life. Therefore, it is also used in milling and turning operations. It failed to show obvious advantages, but in the deep-hole processing and other aspects, MQL processing has a very good processing effect, and more environmentally friendly and economical, therefore, its scope of use will continue to expand.