Cutting Performance of Austenitic and Duplex Stainless Steels with Drills of Three Cutting Edges

Abstract

Austenitic and duplex stainless steels are considered be the best in corrosion resistance among different grades of stainless steels. Due to high strength, duplex stainless steels applications are increasingly as an alternative to the austenitic stainless steels. In this sense, the machining study of this materials is an important issue, in order to better understand the performance of the tools and the quality of the parts manufactured for high-demand industries. In this research, the machinability of both stainless steels was evaluated in the drilling operation, using drills with three cutting edges. This type of drill geometry is particularly useful when conventional solid carbide drills fail. The drill point of triple edge is very stable, demonstrating optimal positioning accuracy and better performance in deep bores. Using the same tool geometry, a comparative analysis of drilling performance on austenitic and duplex stainless steels was made. In experimental procedure, external low-pressure cooling or internal high-pressure cooling was applied alternatively. The cutting vibration, the tool wear, the roughness and the hole diameter accuracy were evaluated in the series of holes made. The obtained results show that the most important factor to increase the number of holes made is the use of high-pressure internal cooling. When external cooling is used, AISI 304 have a worse behaviour than duplex stainless steel, due to greater susceptibility to built-up-edge formation and work hardening. The tool deterioration is mainly non-uniform chipping for external cooling and flank wear for internal cooling.