Evaluation of the tool wear in the turning process of INCONEL 718 using PCD tools

Abstract

The use of nickel-based alloys (superalloys) has an ever-growing demand because of the combination of mechanical properties and corrosion resistance even at relatively high temperatures. Those same properties, however, increase the challenge to increase the cost-benefit of the machining operations. Nickel superalloys are usually machined using coated cemented carbide inserts at relatively lower cutting speeds or ceramic inserts at higher cutting speeds. The use of PCD tools, despite widespread at the machining process of titanium alloys, regarding the machining of nickel-based alloys has almost no research data, especially for Inconel. This happens mostly because of the alloys’ iron content leading to graphitization of the diamond at the tool. This paper presents a study about the viability of PCD tools in the turning process of Inconel 718 in finishing conditions. The machinability was assessed under different tool rake angles, cutting speeds, feed rates, and minimum lubrication flow rates. The results were compared regarding the specific cutting pressure, average workpiece profile roughness, tool wear and wear mechanisms observed through electronic microscopy. The results indicate that the rake angle did not have a statistically significant influence for the evaluated machining conditions and the feed rate was the most significant parameter, as it is linked with the specific cutting pressure and workpiece roughness. Adhered material seemed to have protected the rake surface from attrition, which reduced the amount of wear particles that promote abrasion of the flank surface. However, the increase in MQL flow seems to destabilize the adhered material and promote more severe wear. Overall, microchipping and adhesion were the most important wear mechanisms.