• Straight oils are generally considered to be versatile and can be made up of mineral, vegetable or animal oils. Straight oils are not diluted and are usually used in heavy-duty machining processes. Extreme pressure additives are often used to formulate straight oils to enhance performance.
• Synthetic fluids contain such synthetic base stocks as esters or polyalphaolefins and are used to continually wet the workpiece to prevent mist and smoke, particularly during the grinding process. A significant drawback of synthetic fluids, though, is that they are not as capable of preventing corrosion and can be harsh on the tool over time.
• Emulsifiable or soluble oils are designed to be used as both coolants and lubricants, particularly for cutting and grinding applications. These oils inhibit welding between the cutting tools and the workpiece while also preventing tool wear. Soluble oils contain pure mineral oils (about 40%-70% of the total formulation) as well as emulsifiers.
• Semi-synthetic fluids contain anywhere from 5%-30% mineral oil and are diluted with 30%-50% water. Semi-synthetic fluids often contain high concentrations of additives and are designed to cool and lubricate. They are typically used in all metal cutting processes.

Some of the most common additives used in metalworking fluids are corrosion inhibitors, such as calcium sulfonate, boric acid, fatty acid soaps and amines; extreme pressure additives, like chlorinated paraffins and phosphorous derivatives; anti-mist agents, such as polyisobutylene polymers; emulsifiers, like triethanolamine and salts of fatty acids; dispersants; and odorants. 

Any metalworking fluid that contains any amount of water will incorporate some type of biocide, which is generally considered an additive as well, because water is conducive to the growth of microorganisms. The presence of microorganisms can result in health and safety hazards, separation of emulsions, creation of sediments, formation of biofilms and metal corrosion, among other things. 

Processes

There are a number of processes used to manufacture metal products. Milling operations typically employ soluble coolants and lubricants Turning uses a straight oil or soluble coolant. Most grinding operations use soluble oils. Heading and stamping use soluble, neat and synthetic oils. Casting requires a water-based die lubricant. Drawing uses a soluble, wax-based or soap-based lubricant, as well as straight oils.