The main function of cutting fluid is to achieve chip removal, cooling and lubrication between the tool and the workpiece material. When applied correctly, cutting fluids will 

maximize throughput and improve machining security, tool performance and part quality.

In some cases, machining without coolant (dry machining) may provide environmental and cost benefits. Contact your Sandvik Coromant expert to choose the best tool, 

geometry and grade for dry machining.

Many applications require coolant to ensure tolerances, surface quality and machinability. Since coolant is required, it should be put to optimal use to maximize its true 

potential.

Coolant has many different aspects that are important to the cutting process:

coolant medium

coolant outlet

coolant pressure

coolant medium

There are many different coolant media that can be used when turning:

Emulsions, which are oil-water mixtures (5-10% oil in water) are the most common coolant medium

Oil, some machine tools use oil instead of emulsion

Compressed air, used for chip evacuation but does not dissipate heat well

MQL (minimum quantity lubrication) - compressed air containing the minimum amount of oil required for lubrication

Cryogenic refrigerant, maximum cooling effect is achieved using this liquefied gas as coolant

Emulsions, oils and compressed air can be applied through coolant channels in turning tools. When we refer to coolants in general, we are referring to the use of emulsions 

or oils for cooling. MQL and cryogenic refrigerants require specialized equipment.

coolant outlet

Most modern turning tools are designed with through-the-tool coolant, and many of them actually provide both high-precision upper and lower coolant. Coolant outlets in 

the tool may be of the following types, providing different benefits to your machining:

With high-precision coolant, or high-precision overhead coolant, a nozzle (or similar component) directs a jet of coolant directly against the cutting area on the rake face. 

Reduce temperatures and improve chip control. Can be used with high coolant pressure to improve chip breaking performance

Lower coolant, a jet of coolant acting on the flank surface, can effectively dissipate heat from the blade, thereby extending tool life

Conventional coolant outlets, in most cases adjustable nozzles with a larger outlet diameter than high-precision coolant nozzles. Used to move coolant through the insert 

and part during machining (might be considered traditional cooling). These tools cannot be used with high pressure coolant

High precision coolant

Modern turning tools are equipped with nozzles that deliver high-precision coolant directly to the cutting area on the rake face, thereby controlling chip breaking and 

ensuring safe machining. To optimize machine tool capabilities, further extend tool life and improve chip formation, coolant flow and velocity can be fine-tuned by changing 

the nozzle diameter.

High-precision coolant starts to have a positive impact at lower coolant pressures, however, the higher the pressure, the more demanding materials can be machined 

successfully.

With high-precision coolant, you'll get improved chip control, longer tool life, better machining security and higher productivity.

Failure to use high-precision coolant can lead to chip blockage problems, resulting in machine downtime, emergency repair services, greater tool wear and poor surface 

quality.

Coolant below

The most modern turning concepts also use subsurface coolant. Coolant underneath controls heat in the cutting zone, resulting in longer tool life and predictable machining.

The lower coolant shows a noticeable effect at lower coolant pressures, but the higher the pressure, the greater the tool life extension we can see. Production can be 

increased by increasing cutting speed or feed.

Upper coolant or lower coolant? Or both?

If you are using a tool with overcoolant (precision coolant) and undercoolant, it may be advantageous to turn off the overcoolant during certain operations. This largely 

depends on the workpiece material being machined as well as the grades and cutting parameters used.

For thin-coated grades, such as the preferred PVD grade for ISO S materials, it is best to use both upper and lower coolant to provide thermal protection for the blade and 

avoid plastic deformation.

Coatings on thickly coated materials (such as the preferred CVD materials for ISO P and ISO K materials) have good thermal protection properties. In roughing to 

semi-finishing applications, these grades require only underlying coolant for optimal tool life. See blue chart and notes on ISO P below.

For thinner coating materials, such as the preferred CVD materials for ISO M materials, it is recommended to use both upper and lower coolant. However, if cratering wear 

occurs in an application, try using only the underlying coolant and compare tool life.

Coolant Recommendations for Steel Turning

Use coolant below to extend tool life

Use overcoolant (and undercoolant) when improved chip control is required, typically within the blue depth of cut (ap) and feed (fn) areas.

Outside of the blue zone, overlying coolant may cause slight wear on the cutting edge and increase crater wear. Crater wear can be difficult to assess, meaning unpredictable 

and shortened tool life. This is why it is recommended to use coolant below. (If coolant below is not available, use tools equipped with conventional coolant outlets)

coolant pressure

High-pressure coolant increases energy consumption, which needs to be considered from a sustainability and cost perspective. However, high-pressure coolant also 

improves productivity in different ways.

High pressure and high precision coolant

High coolant pressure in machine tools can work with nozzles to create high-velocity coolant jets that create hydraulic wedges. Coolant jets have 3 main functions:

More efficient cooling of the blade in the contact zone (A)

Forces chips to leave the blade surface quickly, thereby reducing blade wear (B)

Helps break chips into smaller pieces and expel them from the cutting area

Use the right pressure

7 - 10 bar (100 - 150 pounds per square inch)

High-precision coolant enables improved chip control and greater machining safety when machining steel and other common materials. This high precision allows you to 

increase cutting parameters while maintaining machining security.

70 - 80 bar (1000 - 1200 pounds per square inch)

At higher pressures, chip breaking can be improved. Better results can be achieved using geometries designed for high-precision coolants.

150-200 bar (2200-2900 pounds per square inch)

Demanding materials such as duplex stainless steels and high-temperature alloys require higher pressures. Use tool holders with high-precision coolant supply nozzles and 

special geometries for high-precision coolant.