A thermomechanical analysis leading to a novel flank face design providing longer tool lives for tools used in the drilling of Inconel 718

Abstract

Inconel 718 is a versatile material due to its excellent properties. However, machining and in particular drilling of Inconel 718 present great challenges for the tools. In order to increase process reliability and tool life, a novel modification for the applied drilling tools was developed. It consists of a flank face retraction behind the cutting edge which is created by grinding. While regular drilling tools feature a continuous flank face on the tool tip, the retraction provides a minimized frictional surface between the tool tip and the bore hole ground. Furthermore, computational fluid dynamics simulations have shown that the created vacuous volume behind the cutting edge becomes filled with cutting fluid during the drilling process. The described effects result in longer tool lives which could be shown in experimental investigations. This paper presents the conducted experiments in which both the occurring mechanical and thermal loads were examined in order to determine the radius-dependent thermomechanical loads along the cutting edge. The results have shown that an increase in either cutting speed or feed result in significantly higher temperatures at the cutting edge corners while temperatures at the inner diameter of the tool remained almost constant. At the same time, a rise in feed leads to notably higher mechanical loads along the whole cutting edge. In addition, reference tool life tests were conducted using standard tools and under variation of the cutting values. The resulting tool wear as well as the tool-workpiece contact zones were investigated in detail. The gathered findings were then used to develop a flank face modification whose sufficient thermomechanical stability was ensured by FEM simulations. Afterwards, the new tool design was applied to drilling tools and then validated in field tests. The results show that a considerably higher drilling distance as well as lower tool wear and thus a longer tool life could be achieved with the modified drills.