Heat is produced when energy is transferred from one object to another, creating a difference in temperature. In a car, for example, heat is created by friction that is produced as the pistons rub against the engine block. A car needs oil and coolant to run properly, because its engine is made up of metal components that rub together. This motion causes friction, and a by-product of friction is heat. If there was no coolant or lubricant in an engine, its parts would get hot and eventually the engine would overheat. The parts could even get hot enough to melt together, stopping the engine altogether.

Just like the car, heat in machining is created by friction that occurs when the machine’s internal components rub together, or when a workpiece is being machined. When machining a workpiece, heat is caused by several factors. These factors include cutting speed, feed rate, cutting method, workpiece material, cutting operation, and depth of cut. Some cutting fluids work better, depending on which machining operation is being performed.