Effect of tool coatings on the performance of small-diameter drills in drilling deep holes with higher cutting speed

Machining with higher cutting speeds is one of the most welcome advances in metal cutting today, since it is, among other benefits, associated with a significant reduction in process time. However, certain prerequisites are inevitable in order to make a particular process using certain cutting tools eligible for realising higher cutting speeds, because the rise in cutting speed is usually associated with increased cutting temperatures, very often resulting in a substantial decrease in tool life. This paper investigates the extent to which tool coatings can enable small diameter Co-HSS twist drills to achieve a satisfactory performance in deep-hole drilling of carbon steel using minimum quantity lubrication. It is shown that tool coatings that combine a high hot-hardness with a smooth surface are very important in order to ensure a satisfactory tool life of the Co-HSS twist drills employed with higher cutting speeds.