MQL: 5 Key Factors

MQL (Minimum Quantity Lubrication) offers some serious benefits to those who make the switch from flood coolant. Reducing the amount of fluid used and the amount of fluid-related equipment required can affect your bottom line. Improving tool life and operational efficiencies can increase your profits, and adopting an environmentally-friendly MQL system is a big plus for both your shop and the global environment.

But jumping from traditional flood cooling to MQL requires a change in mindset. This can be a stumbling block for some who make the switch. The ‘more is better’ methodology of coolant does not translate well into the new MQL mentality. MQL is a process-sensitive approach to metalworking lubrication and requires a bit more planning and consideration than using flood coolant. Luckily, the basic considerations required for a successful MQL implementation make for a short list.

There are five key controllable items you must consider when implementing MQL:

  1. Lubricant – Be sure to choose a high-quality, plant-based MQL lubricant such as Unist’s Coolube. The polar nature of these plant-based lubricants make them especially good at adhering to metal surfaces and creating a friction-reducing boundary layer. Beware of lesser lubricants which are not as highly refined as Coolube and which can oxidize on your cutting tools, forming a layer which can reduce the tool’s effectiveness and is virtually impossible to remove. Many lubricants, which appear to be great bargains initially, may end up gumming up your tools or not lubricating well due to their high levels of impurities.
  2. Quantity – Success with MQL relies in large part on finding the correct amount of lubricant to deliver for each unique process. With coolant, as long as sufficient amounts of coolant are sloshed over the cutting zone (and onto equipment and floors), relative success is likely. WIth MQL, the amount of lubricant delivered to the cutting zone is critical and varies from application to application. Face milling aluminum will have a different ‘lubricant sweet spot’ than drilling steel, which is different from sawing titanium. Fortunately, the amount of lubricant delivered to the cutting zone is easily controlled with a quality MQL applicator.
  3. Nozzle position/Oil-hole size – When using external nozzles with MQL, the position of those nozzles is critical. In most cases, the recommended distance for the nozzle from the tool is 4″ or less. When cutting in multiple directions or with large tools/blades, MQL may require multiple nozzles to ensure that critical tool areas are properly lubricated. (add image from tim’s presentation). In through-tool applications the oil hole size and location determines how much air – and thus lubricant – can flow to the cut. Positioning is important in both cases.
  4. Tooling choice – Some tool types do produce better results with MQL. Multi-layer tools often increase MQL’s effectiveness when working some metals, for example, TiAIN often gives good results on steels. Tool geometries also play a role. Geometries designed to decrease the cutting temperature and break chips help in the absence of coolant flow. With carbide tools, tool surface can be polished to decrease friction and heat.
  5. Speeds/Feeds – the optimum speed/feed for MQL may not be just what it is with flood coolant. In general, a bigger chip is better with MQL, so many have had success increasing the feed rate.

As with any process, systematically working to improve the results can lead to dramatic results. Hopefully this list helps you as you look at adopting or improving your MQL processes.

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