MQL Fact and Fiction

Microlubrication techniques can improve the work environment and save money

hris Smrekar, product specialist for Unist Inc., talks with Modern Metals about common customer concerns and questions surrounding minimum quantity lubrication (MQL). What is MQL? It’s exactly what the name implies: a minute amount of a high-quality lubricant delivered to a cutting tool or workpiece to reduce friction. MQL can benefit sawing applications, dedicated tapping machines, drilling fixtures, beam drills and other machining processes.

Is MQL a hoax? How can less be more?

A: It’s not uncommon to meet resistance and confusion when discussing MQL. How can the tool survive without more fluid? But imagine jumping into a lake—you’re equally wet, no matter the size of the lake. Similarly, when applying lubrication to a cutting tool, there is a point when adequate lubrication is met and additional lubrication is just wasted. Field experience has shown that using too much oil can retain heat, reduce tool life, and create a substantial barrier between the cutting tool and workpiece, impeding a high-quality finish. When MQL is properly implemented with a high-quality lubricant, the lubricant creates a thin barrier, which reduces friction and therefore heat buildup. Additionally, tests have shown that materials can often be processed with higher speeds and feeds with MQL, compared with other lubrication methods.

How can MQL improve the shop environment?

A: It’s common knowledge that your flood coolant reservoir can house some pretty nasty bacteria. If you shouldn’t touch it, why would you want to breathe it? Vegetable-based cutting oils, such as Unist’s Coolube, are bio-based and are naturally removed from the lungs in days instead of the months required for petroleum-based fluids. In addition, the body’s removal method is different (expectoration versus absorption), and studies indicate bio-based fluids cause no long-term damage to lungs or skin. Additionally, because so little fluid is applied, there’s no mess to contend with. Parts and equipment stay virtually dry, leading to decreased maintenance and cleaning costs along with allowing operators to be tasked with more fulfilling work.

Although commonly referred to as a “mist system,” machining with MQL has been shown to produce fewer emissions than flood coolant. The German government performed a study that took emission measurements at the machine operator, machine panel and the extracted air, and the baseline measurement was done using flood coolants. The results showed MQL had less than half the airborne concentration of flood coolant in 95 percent of the tests.

Is MQL more expensive?

A: No. MQL has repeatedly proven to be a cost-effective investment. One example of this is a study from a global automaker. The company estimated that total cost of ownership with MQL, based on machine cost, downtime, maintenance, floor space, electricity usage, coolant management and related factors decreased by 13 percent. Availability of the machines was increased because the electronics on the machines last longer and have fewer nuisance faults; this reduced machine downtime by up to 40 percent. Metal chips could go straight to the recycler without secondary cleaning operations, and assembly could be moved closer to the machining cells, greatly reducing part travel throughout the facility.

Aren’t cutting oils messy?

A: When defining “messy,” we consider finished part cleanliness, lubrication in the work area and chip recyclability. With properly implemented MQL, users can expect virtually dry finished parts, chips, equipment and floors. The light residue of oil remaining on the part is barely noticeable and can aid in corrosion resistance and item separation. Lubrication in and around the work area is greatly reduced, considering the output differences between MQL and flood coolant—ounces compared to 64-plus gallons per shift. With dry chips, company management can sleep soundly knowing they’re going to fetch higher recycling returns and not have to deal with a cardboard chip gaylord container that’s crumbling.