SECTION 3.8
Choosing the Perfect Coolant: There Are No Easy Answers

Of course, there are more aspects to coolants than those presented here. There are no real secrets or off-the-shelf recommendations for a perfect coolant. The coolant that is excellent for broaching high-alloy steel may be very poor for broaching stainless, and vice versa. The action of a cutting fluid in reducing friction depends entirely upon the chemical properties involved, and the fluid must be tailored and adjusted with the correct amount and types of additives. Too weak a reaction and the lubricating film may not form. Too strong a reaction, and both the tool and the work piece may be chemically attacked and worn down.

At low cutting speeds, cutting fluids vary greatly in their ability to reduce chip-to-tool face friction. However, at faster cutting speeds, there is less time for fluid penetration, less time to react, and therefore, less friction-reducing ability. Good cooling and wetting abilities are much more important at faster speeds since the time for chemical reactions to form adsorbed films is measured in milliseconds.