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efect. Tey allow a rapid response to change in settings and contain the dispersion of aerosol better than the external systems. However, they sometimes require special tooling, machine or spindle modifcations and, overall, require higher investments. One- and two-channel systems are two basic through- the-tool methods available for mixing the air and lubricant before delivering them at the point of cut. Especially for external systems, the position of the nozzle to the tool and point of cut (such as angle and distance) ofer opportunity for optimization. Te position will play a role in how well the surface of the tool is covered with fuid and lubricated. Te pressure, fow and aerosol mix are the other factors that will regulate tool coverage and lubrication. While MQL uses oil in most cases, TechSolve is devel- oping a system that can use water-based fuids as well. Tis system is efcient for cutting difcult materials such as titanium and Inconel alloys, which present challenges because they do not conduct heat well. One of the disad- vantages of oil is that it has an insulation property, tending to hold heat in. However, it lubricates better than water- based fuids, reducing the friction force, and therefore reducing heat in that way. In some difcult to cut materials, though, the importance of cooling may outweigh that of lubrication, so water-based fuids may be preferred. If a shop already works with oil, there should be no reason to change to water-based fuids for the purposes of MQL. But fuids for MQL are engineered diferently than those used in food-coolant applications. Te properties of these dedicated fuids are designed to optimize adhesion to the tool and evaporation. Tese characteristics are signifcant to the efectiveness of the process. Although these special fuids are generally more expensive than standard metalworking oils, so much less is consumed that the initial expense can be recovered. Characteristics Te efectiveness of MQL can vary from one application to another, and the proper characteristics can be debated. Clearly, only a small amount of fuid is being delivered through the system, but specifcally how much may be dependent on a number of factors. Most commonly, MQL systems distribute between 5 and 80 ml/hour, but values as low as 0.2 ml/hour and as high as 500 ml/hour (or even higher in rare cases) have been reported. Droplet size can be as small as 0.1 micron and as large as 50 microns. Typically, smaller droplets are preferred to allow a good aerosol mix and delivery. Aerosol pressure is also important and can be adjusted to optimize the machining performance. For typical MQL systems using shop air, pressures between 4 and 10 bars have been reported in literature; however, the range varies as a function of technology. For the more sophisticated systems, the balance between pressure and fow will be adjusted depending on the nozzle shape and size and the process being assisted. MQL is more process sensitive than flood cooling. Finding the "sweet spot" can lead to a significant increase in efficiency and savings. Therefore, some optimization for the cutting parameters may be in order at times. In other cases, the sweet spot is fairly large and superimposes over the flood fluid workzone. In these latter cases, switching between MQL and flood may be an easy process. Why MQL? Te concept of MQL is not new. Studies and trials with mist-coolant applications go back more than two :: MQL is sometimes considered only as a beneft in milling applications, but with the right parameters, it can be efectively applied in many turning operations as well. MQL technology was developed to address many of the inconveniences and concerns posed by food fuid systems. METALWORKING FLUIDS 40 PRODUCTION MACHINING :: MAY 2016