Process Optimization In High-efficiency Turning Inconel 718

Nickel-based alloys especially Inconel 718 play an important role in the field of high-temperature alloys, which are widely used in jet aero-engines and gas turbines. Due to the combination of poor thermal conductivity, low elastic modulus and high chemical activation, Inconel 718 belongs to one of the difficult-to-cut materials. Cutting process of Inconel 718 is characterized by the high cutting force, high cutting temperature, severe work-hardening and rapid tool wear. In addition, the geometrical characteristics of the integrated structure parts result in higher material removal volume, longer machining time, and higher costs. Therefore, the contradiction between increasing machining demand and poor machining performance has been one of the bottlenecks blocking the development of aerospace industry. In this paper, high-efficiency turning process on Inconel 718 is systematically investigated, and the main researches are summarized as followed.A series of experiments were conducted on the CA6140 lathe to investigate the cutting forces in turning Inconel 718 with SECO coated carbide tools. It was indicated that the tangential force was the largest cutting force component, followed by the radial force and the axial force. Cutting forces increased almost linearly with the feed rate and the depth of cut. The effect of cutting speed on cutting force was more complex, and the cutting speed was the most dominant factor affecting the cutting forces, followed by the feed rate and the depth of cut.The effect of cutting parameters on surface roughness was investigated. The results showed that the surface roughness increased with the increase of cutting parameters. By means of X-ray radiation diffraction method, the influence of cutting parameters on residual stress was investigated. Plastic protruding was generated on the machined surface due to the mechanical and thermal stress in the cutting processes, which resulted in the tensile residual stress on the machined surface.The effect of cutting parameters on chip morphology was studied. One important feature in turning Inconel 718 was the formation of periodic saw-tooth chips. Under different combinations of cutting parameters, the morphology of chip changed from continuous to saw-tooth. The saw-tooth chip generated in the turning processes caused the fluctuation of the cutting forces with high frequency, and the relationship between the frequency of saw-tooth chip formation and cutting forces was studied in this paper.The wear modes and wear mechanisms of coated carbide tool in turning Inconel 718 under the wetting conditions were experimentally studied by means of scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results showed that the main wear modes of the cutting tools were flank wear, groove wear and flake wear. The wear mechanisms mainly included adhesive wear, abrasive wear, oxidation wear, etc. The relationship between tool wear and cutting time was plotted. The effect of tool wear on the surface roughness and saw-tooth chip was also studied.In this research, chip morphology, cutting forces, surface roughness, residual stresses and tool wear were deeply investigated in high-efficiency turning Inconel 718, which has a very important theoretical and practical significance to improve the manufacturing level of Nickel-based alloys and development of aerospace industry.This research is supported by the National Key Science & Technology Specific Projects "milling-lathe machining center" (2009ZX04001-032).