Comparative Study of the Drilling Operation in Duplex Stainless Steels with Drills of Two and Three Cutting Edges

Abstract

The three cutting edge drills are not the most common drills, nevertheless, are characterized by superior stability, excellent precision and finishing, due to the intersection of three cutting edges at one point. In general, stainless steels are considered as difficult to machine materials due to their tendency to work harden, their toughness and relatively low conductivity, leading to poor surface finish, poor chip breaking and built-up-edge formation. In the case of duplex stainless grades, the high strength, and the very good corrosion resistance, only compared with austenitic steels, make these materials as an alternative to the austenitic stainless steels, with superior mechanical properties. In this study, the performance of the drills with two and three cutting edges were evaluated in the drilling of duplex stainless steels, when low-pressure external cooling or high-pressure internal cooling were applied. Whether used drills of two or three cutting edges, the most important factor to increase the number of holes made, is the use of high-pressure internal cooling, in detriment of external low-pressure external cooling. The drills of three cutting edges have better results in roughness and dimensional tolerance of the holes. However, these drills proved to be more fragile and more sensitive to the cutting parameters. The use of three cutting edges drills is recommended for situations where hole quality is more important, while two cutting edges drills is recommended for situations where productivity is the main objective.