A New Flank Face Design Leading to an Improved Process Performance when Drilling High-Temperature Nickel-Base Alloys

Abstract

In previous investigations, the concept of a modified flank face design with a retraction behind the cutting edge was developed. Based on fundamental investigations regarding the mechanical and thermal loads, combined with simulation-based analyses, a new design of the flank face has been created with the largest possible free volume behind the cutting edge while maintaining the mechanical stability required for the challenging machining of nickel-base alloys. This flank face modification allows a greater amount of cutting fluid to flow along the back of the cutting edge at higher velocities while at the same time creating the potential of a friction reduction between the tool tip and bore hole ground. The described concept was implemented on solid carbide twist drills which were then used to machine Inconel 718. The results show that, while tools equipped with a flank face retraction perform up to four times longer compared to standard tools, they tend to reach the end of tool life rather suddenly due to cutting edge chipping. This typically occurred when the maximum width of flank wear land equalled the width of the remaining cutting edge. Since then, further investigations have been carried out in order to refine the concept of the flank face modification. A new design was implemented with regard to a more effective cooling of the flank face, presumably caused by an improved cutting fluid flow velocity particularly at the cutting edge corners. Simulation-based findings, combined with experimental tests of the new prototypes, could reveal that the improved cutting fluid flow in the area of the cutting edges leads to significantly extended tool life and machining performance when drilling Inconel 718.