Metal Cutting Lubrication 101

What is cutting fluid?

Cutting fluid is used in metal cutting operations to manage heat. Managing heat while cutting provides improved surface finish and longer tool life. Different types of cutting fluids exist, each with a different purpose. Some cutting fluids are coolants - these are designed to remove heat from the cutting process and cool by quenching heat. Some cutting fluids are lubricants - these are designed to prevent heat by reducing friction through lubrication. MQL cutting fluids are lubricants.

A general term sometimes used for cutting fluids is metal working fluids, or MWF. Both coolants and lubricants are available in many different types or formulations of cutting fluid, depending on the material being cut. Different fluids might be specified, for example, for processing aluminum, steel, stainless steel, or titanium.

Unist offers MQL oil in three different variations for general machining, specifically for aluminum, and specifically for ferrous materials. The ferrous material fluid includes an extreme pressure additive that is activated with the higher cutting temperatures generated when cutting tougher materials. Some MQL fluids are designed to evaporate and leave no residue, while others might require a small amount of clean up after the fact. Any clean up, however, is minimal compared to when using flood coolant, as most of the MQL oil applied is consumed by the process.

For ferrous & non-ferrous metals
For aluminum & stainless steel
Includes extreme pressure additive

MQL vs Flood Coolant

There is a basic difference between the chief purpose of lubricant and the purpose of coolant: lubricants reduce the amount of heat generated, coolants remove the heat that is generated. Flood coolant is often easier to implement in a machining process and is the widely accepted method.

Machining clean with MQL - Reduce friction and avoid heat - neatly apply ounces of lubricant per shift with no fluid cleanup or disposal
Machining with coolant - Cool down hot tools and work - flood with gallons of coolant - recirculate/treat fluid, clean up fluid mess, pay for disposal.

However, flood coolant can involve many other costs due to shorter equipment life and headaches of disposal, spills, and more. It may be more difficult to implement MQL, but the potential savings down the line are more than worth it. Imagine using a few ounces of cutting oil per shift vs. gallons of coolant per hour with no extra recirculation equipment and nothing to dispose of!

As an added benefit, MQL is more environmentally friendly than flood coolant. This is due to the natural, bio-based origins of MQL oils versus the coolants that are used in flood coolant systems. MQL is a near-dry process, so both chips and finished products come out dry and clean.


MQL System Installation

The vast majority of new machines and used machines are set up for flood coolant from the factory. This is true of most machining centers, mills, lathes, and even standard bandsaws. Due to this, MQL systems must be retrofitted onto existing machines. This takes more attention and effort to set up the system, but pays off quickly.

For someone who is coming from flood coolant and moving to MQL, the first step is defining the specific operation and lubrication needs of that machine operation. Once we have this info, we can make a recommendation for the specific systems and products you'll need for your process. We will work with you to define the kind of automation or level of control you need. We will help you determine the type of nozzles for your process and how to mount it and route tubing through the machine. Also we can guide you on how to mount system enclosures and how to wire in control signals.

MQL System Start Up

Once installed, the system is ready to start up. Typically, compressed air needs to be turned on, the reservoir needs to be filled, and the pumps and output lines need to be primed. We can provide suggested starting points for the output rate settings, but to optimize your savings, you'll need to make some adjustments as required. It is possible that you might need to tweak the speeds and feeds of your process as the sweet spot might not be exactly the same as flood coolant. This can even lead to decreased part cycle times as speeds increase.

We offer initial MQL system set up assistance and provide service for all of our MQL products. Our MQL systems allow control over how much oil is dispensed, along with control over atomization air flow rate. These settings can change based on what metal you're cutting, and what tools you are using. Often, our customers are initially impressed with how little cutting oil their new MQL system utilizes. Their enthusiasm only increases when they see dramatic improvement in tool life. Once they begin refining their MQL system settings and pursuing the "sweet spot" for their application, they soon realize that with the proper settings, they are able to increase speeds and feeds and therefore productivity. Dramatically extended tool life and significant fluid savings are common themes with our MQL system customers' stories.

MQL System Maintenance & Cleaning

MQL is a neat process and does not require intensive cleanup. Oftentimes, no cleaning is required before secondary processing of machined parts. Work areas stay clean and as an added bonus, you no longer have to deal with the cost and hassles associated with coolant maintenance and disposal. With MQL, the spills, overspray, pooling, and health concerns associated with flood coolant are things of the past.

What are Polar Properties or Polar Additives in MQL Lubricant?

The combination of polar properties and surface tension help fluid adhere to and wet out on surfaces. When water is dropped on a piece of clean glass, and it wells up as a bead, because the water sticks together with high surface tension. Coolube dropped on the same glass will tend to spread out more evenly due to low surface tension and the polar nature of the molecules that help it align into an even coating. It wants to arrange itself into positive and negative ends. This is referred to wetting, and how well a fluid wets out influences how well it lubricates. The surface being cut needs to be uniformly coated to ensure proper lubrication. At a microscopic level, the material being cut slides along the surface of the cutting tool until it bends enough to break off. You want the lubricant to be covering the whole surface for the best heat reduction.

Environmental impact of metal cutting fluid

The environmental impact of a metal working fluid can depend on its formulation. Some chemicals break down naturally, while others are not biodegradable. High quality MQL oils are completely made of natural products and are biodegradable. Also, when used properly, there is almost no excess fluid to dispose of. Spent flood coolant has to be collected and contained, and since it constitutes toxic waste, its disposal is regulated. This is a sometimes overlooked indirect cost associated with machining with flood coolant.

Non-toxic metal cutting lubricant

Unist Coolube oils are all plant based. Respiration issues and dermatitis issues that arise from breathing in flood coolant or coming into contact with it are avoided when using MQL.

Minimizing coolant & cutting fluid waste

With MQL, there are no disposal costs that come from having to take a tank out and empty and haul off. The spill kits, chemistry management, testing, filtering, and disposal associated with flood coolant can all be avoided when using MQL. You might end up with a very slight film of oil on a finished part, but overall your shop will be much cleaner.