Machining Mechanism And Experimental Investigation On High-efficiency Machining Of Nickel-based Super-alloy Inconel 718

High-efficiency machining is the goal in the process of metal cutting, also the important direction of manufacture technology. Nickel-based super-alloy are widely used in the aerospace engine, e.g. compressor discs, turbine discs, integral impeller blades, casing and other high-temperature engine parts for its high strength, high corrosion resistance, excellent fatigue properties and thermal stability at high temperature. However, the poor machining performance of this kind of material results in low processing efficiency and high cutting cost. That's mainly for the lack of understanding on cutting processing mechanism, to be specific, First, the weak accumulation of processing technology makes the machining process tends to select conservative parameters to reduce the unseen risk. Second, the restriction on the development of cutting tool material and unreasonable process cutting parameters lead to severe tool wear in machining of nickel-base super alloy, which is the most direct factor of low efficiency. Furthermore, the sharp rise of cutting force and temperature that caused by the work hardening as well as the sub-surface microstructure changes, restricts the development and application of advanced machining technology.Based on the developing status and technical difficulties, this paper investigate the key problems that limit the high-efficiency machining technology, such as cutting force, cutting temperature, tool wear and surface integrity. The high efficiency machining methods are given by establish series of prediction model with cutting experiments. Around the cutting theory in high-efficiency machining, the works are carried out as follows:A novel method for cutting force prediction with round cutting inserts by considering the dynamic uncut chip is proposed. The round ceramic cutting inserts are preferred as the cutting tool by the comparative cutting experiments with PVD cutting inserts. Then, the contact region of tool and workpiece discretized for the dynamic uncut chip thickness based on the detail analysis of cutting geometry. The variation of cutting force coefficients under different cutting conditions are fitted by cutting experiments. According to the mechanical cutting force model, the accurate cutting force prediction of whole inserts can be realized.The notch wear prediction model is presented by considering the tool and workpiece contact geometry. Ceramic cutting tool is more and more widely used for its excellent performance in high speed machining, investigate its quantitative wear model can give advice to the chosen of cutting parameters and machining conditions. The experimental results indicate that notch wear and flank wear are the main failure modes of ceramic cutting tools during high speed machining of Inconel 718. The assumption that hardened layer beneath the workpiece surface caused by previous cutting is the main causation of notch wear is proposed. Based on this hypothesis, a new quantitative prediction model is established and cutting results verify the proposed model.A new cutting model is developed to predict the plunge milling force based on the more precise plunge milling geometry analysis compared to point/flank milling operation. In this model, the step of cut as well as radial cutting width is taken into account for chip thickness calculation. Frequency domain method is employed to estimate the stability of the machining process. Based on the prediction of the cutting force and milling stability, a strategy to optimize the cutting parameters of plunge milling process is presented. Cutting tests of Inconel 718 with double inserts are conducted to validate the developed cutting force and cutting parameters optimization models.Based on the hypothesis for the heat flux distribution shape at the tool-workpiece interface to be an isosceles trapezoid, a temperature calculation model for the workpiece in flank milling operation has been constructed. It has been found that in the premise of surface quality guarantee, the material removal rate can be improved by elevating the feed rate and milling speed, enhancing the number of tool teethes, or moderately improving the tool helix angle.The detail analysis of the influences of cutting parameters on surface integrity is given in this study. The coupling of mechanical and thermal in the process of machining Inconel 718 can change the surface integrity, which affects the fatigue life of the components and reduces the service performance. Measurements results indicate that assisted machining methods can improve the surface integrity by reduce workpiece surface roughness, residual stress and work hardening depth.