Machining Technology and PVD Coatings for Milling Thin Structural Parts of Inconel 718

Abstract

To improve the machining process of thin, susceptible structural components made of Inconel 718, the milling process for trochoide roughing and finishing was analyzed. In addition to the validation of cutting material, tool micro-geometry and the coolant supply, new PVD hard coatings including the coating post-processing were developed. These PVD coatings were used to modify the heat distribution during the cutting process and to improve the tool life. To reduce machining effort, in coating development micro-impact tests and vibrational wear tests at higher temperatures were used to identify trends with regard to the fatigue behavior of the coatings and the affinity for built-up edges. Optimized cutting results for both trochoide roughing and finishing can be reached by the combination of a carbide substrate with an average grain size of approx. 0.8 µm and a cobalt content of 10% as well as a cutting edge radius of the milling tools of about 8 µm. A suitable coolant and the effective coolant supply also have a very high influence on the tool life and the wear behavior of the milling tools. During machining tests, the convenient PVD coatings were also determined. Due to the longer tool life, a TiSiN-based coating shows the best results for rough milling. In finish milling processes, boron-containing coatings lead to reduced tool wear and the lowest surface roughness of the machined structural parts.