There are many different types of coolant readily available in the market, each with different properties and purposes. To determine which coolant is the right one for your application, your machine, and your workpiece is often a difficult task with the minefield of technical data and opinions. Amidst all of this it is easy to lose sight of what the actual purpose of a coolant when working with metals.
Firstly, what is a metal working coolant?
Metal working fluids is a term that covers a wide range of products, from neat oils to soluble oils to industrial gear or slide-way oils. Metal cutting coolants are oils or synthetic formulations that are water miscible or soluble.
Metal working applications that need coolants include: cutting, drilling, turning, milling, threading, broaching, grinding, lapping and much more.
Coolants are used to achieve 4 main objectives when working with metals. These are cooling, washing, lubricating, and protecting.
Cooling
The primary objective of most metal working fluids is obviously cooling, hence why it is commonly called coolant. Heat is generated by the friction caused when the cutting tip or tool impacts the work piece.
The heat generated can reach excessive temperatures and depending on the application, the metal, and the working conditions, this can be up to 1000° C. This heat has obvious consequences causing premature wear, fracturing and or deforming of the tooling and the workpiece.
A common problem in machining especially ferrous metals is if too much heat is created, the workpiece can get harder (similar result from heat treatment) and make it more difficult to machine. It must also be noted that tooling, work holders, bearings and seals are potentially adversely impacted by the heat generated in the machining process. Applying coolant directly to the cutting area combats the heat and reduces the impacts of it.
Washing
Coolants need to clean swarf away from the cutting area.
The process of metal cutting creates chips or swarf, and these need to be carried away from the cutting tip. Swarf is typically harder material than the work piece, as heat is transferred to it during the cutting process. If the chips come in-between the cutting edge and the workpiece it will cause the cutting edge to wear prematurely. Clearing these chips away allows the tool to do the work it needs to do.
Lubricating
Lubricating is debatably more important than cooling and washing especially when machining non-ferrous metals.
This does not need too much explaining - but when you lubricate anything, the purpose is to reduce friction. So, to achieve good tool life, a coolant must lubricate the cutting tip as it reduces friction, and therefore heat build-up, which assists in increasing tool life.
Lubrication is commonly achieved in a coolant with oil, however, technology is changing and newly developed polymers and EP additives are now replacing oil as the most common used lubricant. It also must be noted that if we were to only use water it would evaporate at the cutting edge due the high heat and therefore provide nothing in between the cutting edge and the workpiece. The lubricant is normally resistant to very high temperatures so it will remain on the cutting edge in high temperatures and keep reducing the friction.
Protecting
Cooling and washing is important but not all that is required, otherwise we could just use water in our machining applications. The machining of ferrous metals is very common and ferrous metals are very prone to oxidation and therefore rusting. But it is not only the workpieces that rust, a coolant must also protect the machine, the tooling, and other equipment used nearby from corrosion.
If a coolant achieves these 4 objectives, the user will find that they will increase their tool life, protect their machinery investments and ultimately save time and money.
