Cooling Selection for High-Speed Milling
Cooling selection is an integral part of high speed machining (HSM), and is one of the key factors influencing cutting temperatures, cutting speed and tool life when machining. With regard to cooling, there are a number of methods and systems available; each with their own advantages and disadvantages. This article intends to provide an overview of the common cooling methods used in the practice of HSM, including the lubrication methods, flood coolants and mist coolants.
Lubrication Methods
This type of cooling is often referred to as “dry” machining; as it does not require the use of flood or mist coolants. With regard to cutting, the lubrication methods include cutting fluids which are applied directly onto the cutting tool, grease or oil baths as well as paste lubricants.
Cutting Fluids
Cutting fluids are often used in HSM to reduce the negative effects of high cutting velocities, including excessive temperatures and friction. They can also provide chip evacuation, reduce wear, and increase tool life. Cutting fluids are either mineral oils, or emulsifiable oils which form an emulsion when mixed with water. Both types can be used in HSM but with certain restrictions, such as the limitations of water-soluble minerals oils with regards to coolant pressure and tool overhang.
Grease and Oil Baths
These lubrication methods are used in HSM and involve the use of either liquid or oil baths. Liquid baths are typically made up of lubricants such as cutting fluids or oils and can be used for both cutting and cooling purposes. Oil baths offer an added advantage over liquid baths in that the oil is spread over an entire machine, eliminating the need for localized coolant applications. Grease baths are also used in HSM, but are less common than either of the other lubrication methods.
Paste Lubricants
Paste lubricants are used in HSM and offer a similar advantage to oil and grease baths in that they are applied to an entire machine and can reduce the need for localized coolant application. However, paste lubricants also have the added benefit of being able to adhere to the cutting edge, reducing heat transfer and improving tool life.
Flood Coolants
Flood coolants are high pressure coolants that consist of a combination of emulsifiable oils and water. They are used in HSM when a high volume of coolant needs to be applied to the part being machined in order to remove the chips effectively. Flood coolants are typically applied through a nozzle or spray bar that is positioned directly above the part being machined.
Mist Coolants
Mist coolants are a similar type of coolant to flood coolants; however, they are used when a high volume of coolant is not necessary. Mist coolants are applied through a spray nozzle that is positioned directly above the part being machined and can provide both cooling and lubrication.
The choice of cooling method for HSM is dependent on the specific application and its associated requirements. It is important to consider the specific machining requirements such as cutting speed and depth of cut, the type of material being machined, and the desired outcome of the machining process when selecting the coolant method. It is also important to remember that improper selection of coolant can result in decreased tool life and reduced accuracy of the machined part.
