Switching from flood lubricant/coolant to MQL

Controlling the heat generated when cutting tool meets workpiece is one of the challenges of machining. For years, the default has been to flood the work/tool interface with a coolant. This method works in that it reduces heat, but it comes with certain costs that many manufacturers may be overlooking. For most machining operations, Minimum Quantity Lubrication (MQL) can replace flood coolant and deliver a host of benefits.

Flood lubrication vs MQL: How do they differ?

Flood coolant
Flood coolant is aptly named in that one simply needs to flood the interface of the cutting tool and the workpiece with coolant. Coolant quenches the heat and allows a large portion of it to be carried away from the interface. In addition to heat reduction, flood coolant provides some lubrication and is good at chip evacuation. Coolant is not without its downsides however.

Coolant is messy. When low viscosity coolant meets a cutting tool spinning or moving at a high rate of speed, a large amount of coolant is thrown or splashed outward. This can result in coolant on surfaces that have nothing to do with machining and increased housekeeping costs and slip hazards. Coolant can also become atomized and can be harmful for workers lungs. Coolant produces a wet environment making skin contact unavoidable. Exposure can cause skin irritation and often mild to severe dermatitis when contact is prolonged and repeated.

Perhaps the most detrimental aspect of flood coolant is that, by its very nature, it results in standing liquid which can be infected with bacteria. This produces odors and necessitates extra equipment to test, treat, filter and circulate coolant in the hopes that bacterial contamination can be avoided. When coolant reaches the end of its lifecycle, it must be disposed of. In most cases, flood coolant's disposal is regulated and spent coolant is characterized as toxic waste. Coolant environmental impact should be considered when comparing it to MQL.

MQL (Minimum Quantity Lubrication)
Minimum Quantity Lubrication or MQL is a relatively new coolant alternative that takes a completely different approach to heat reduction. MQL is sometimes referred to as a near dry misting system, a spray mist cooling system, minimal lubrication, or simply a metal cutting mist system. With MQL, a very small amount of machining lubricant is delivered to the cutting tool / work piece interface in the form of an atomized spray. This lubricant creates a barrier of lubrication which reduces friction and therefore heat buildup. The quantity of lubricant used with MQL machining can vary but typically, a machining operation converted to MQL will use only a few ounces of lubricant per shift.

Switching to MQL means using significantly less fluid. This can add up into serious fluid savings but MQL's benefits don't end there. A quality MQL lubricant will reduce friction so well that big gains in tool life are often realized and efficiency increases. Because so little fluid is applied with MQL, there's no mess to contend with. Parts and equipment stay virtually dry leading to decreased maintenance and cleaning costs. With MQL, even the chips and swarf stay clean and dry - leading to increased profit from recycling.

Lastly, MQL stands as an environmentally-friendly alternative to flood oil lubrication. MQL lubricants are typically highly-refined plant-based oils. They are formulated from all natural, renewable material which is great for both the global and the shop environment and stands in stark contrast to coolant's environmental impact. MQL oils such as Unist's Coolube® are formulated from cosmetic-grade plant materials and are completely safe for workers' skin.

How to switch from flood to MQL?

Switching from flood oil lubrication to MQL is fairly straightforward but those who are used to machining with coolant may have to rethink their approach when it comes to Minimum Quantity Lubrication setup. With flood coolant, there are no real parameters to consider. If an adequate amount of coolant is reaching the cut, most machinists are satisfied. The simplicity of this approach makes coolant an appealing proposition. With MQL, the volume of lubricant applied and nozzle positioning are critical parameters. The large volume of flood coolant typically used causes many machinists who are new to MQL to adopt a "more is better" mentality. They tend to overapply lubricant which can undermine MQL's benefits and make for a frustrating experience. Perhaps the biggest challenge facing machinist looking to make the switch to MQL is the realization that MQL is a different process and involves a small, but impactful, learning curve. Machinists who realize that MQL is a different process and who make a small investment in familiarizing themselves with MQL up front will quickly start realizing its benefits.

The easiest and fastest way to make the switch from coolant to a minimum quantity lubrication setup is to get in touch with Unist. A friendly Unist team member will walk you through several considerations including:

  • Have you used MQL previously?
  • What type of machining operations are you performing (milling, drilling, tapping, etc.)?
  • What type of material are you machining/cutting?
  • What are your parameters (i.e.- machine type, blade size, hole depth, tap size, etc.)?
  • How do you want to actuate your MQL system?

How is an MQL system set up?

Once your new MQL system arrives, you'll install it on your equipment. Basic MQL system installation can be as simple as mounting your system, connecting to compressed air, filling the reservoir and positioning your nozzles. More complex installations for through-spindle applications will require additional components and configuration. Unist has everything needed for minimum quantity lubrication setup and can help guide you through the process.

System Mounting - Unist MQL systems can easily be mounted to machine surfaces with the included mounting flange using fasteners or optional magnetic mounts. Mounting considerations include mounting level and upright and mounting for easy access for operators. The physical distance between the mounting point and the tool/workpiece interface must be considered as well. Ensure there are no obstructions that may pinch or kink output or air feed tubing.

Connect to Air - Most Unist MQL systems are pneumatically powered. They require clean, dry, compressed air at 60-100 psi [4-7 bar], 25 SCFM [708 LPM] minimum.

Position Nozzles - To effectively do its job, the lubricant needs to get between the cutting edge and the work piece. With too little lubricant, friction is not reduced and heat builds up in the tool whereas using too much lubricant is wasteful and can lead to premature tool wear. The goal of MQL is to maintain a thin film of oil that lubricates the cutting interface. Some cutting applications will require multiple nozzles or unique configurations to ensure lubricant is uniformly applied during the cut. For details on actual nozzle positioning, reference your system's manual, the MQL Handbook or contact Unist for assistance.

Add fluid and prime system - Top your system's reservoir off with a high-quality lubricant suitable for MQL. Unist's Coolube® lubricant is formulated for use with MQL. It will never oxidize or cause dermatitis, is made from renewable plant-based materials and Unist customers who use Coolube exclusively in their Unist MQL systems enjoy a lifetime warranty on their system's pumps. To function properly, your Unist MQL system pumps must be primed. Follow the instructions in your system's manual to quickly and easily prime your system's pumps.

Adjust fluid and air rates - Adjusting the fluid and air rates of your MQL system is critical when optimizing your delivery of MQL lubricant for your application. Users who are new to Unist MQL systems should consult their systems' manuals and familiarize themselves with their system's adjustment points. The pulse generator is recommended as the primary fluid rate adjustment. The entire range of rates is contained in a single 360 degree rotation, so turning the knob a full turn will return the pulse generator to its initial rate. Adjust your pulse generator to initially operate at 10 pulses per minute. On atomizing pumps, the air metering screw will adjust how fine a spray is generated. Too little air will result in a pulsating and spitting spray. Too much air will create a fog of very fine mist. Adjust the air metering screw to the desired degree of atomization for the application.

How soon will you see the benefits of MQL?

You'll start realizing the benefits of MQL as soon as you start machining with it! The more familiar you become with MQL, the more you will refine your MQL settings and the more fully you will enjoy its benefits.

A properly set up MQL system will immediately produce these benefits:

  • Use less fluid - your system should use only a few ounces in an 8-hour shift
  • Longer tool life
  • Cleaner shops and work areas - if you're seeing fluid mess with MQL, you're applying way too much fluid!
  • Promote healthy workers - Coolube® is made from natural, plant-based materials
  • Dry chips - MQL produces clean chips with higher reycling profit