Study On Cutting Performance Evaluation And Constitutive Model Of Superalloy GH4169

Superalloy GH4169 is a typical kind of difficult-to-cut material. In order to reduce its application cost and enhance its service performance, study on cutting performance of superalloy GH4169 was conducted to improve its machinability and machining induced surface quality. Tool life and tool failure mechanism of face milling of GH4169 were analyzed, based on which a new method to evaluate the machinability of difficult-to-cut materials was established. Effect of cutting parameters on machining induced surface integrity and their further influence on fatigue life of the machined workpiece were investigated. A new constitutive model of GH4169, considering the coupling effect between thermal and mechanical loads, was built and then applied in FEM simulation. Tool life, tool failure mechanism and machining induced surface integrity of machining GH4169 under dry, wet and cryogenic conditions were studied.Tool life and tool failure mechanism of face milling of GH4169 at a wide range of cutting speed were analyzed, based on which a new method to evaluate the machinability of difficult-to-cut materials was established. The tool life decreased dramatically with an increase in the cutting speed. At a low cutting speed, the tool failure mode was flank wear, and the wear mechanism was typical abrasive wear. With an increase of cutting speed, the tool failure mode turned from wear to tipping. Crack was induced by both mechanical and thermal shock at a moderate cutting speed, while at a high cutting speed, the thermal shock became a leading reason. Two concepts of the sensitivity index of tool life to cutting speed and the critical speed when the tool failure mode changed from wear to tipping were proposed to evaluate the machinability of difficult-to-cut materials. A higher sensitivity index of tool life to cutting speed indicated worse machinability, and a lower critical speed when the tool failure mode changed from wear to tipping also showed a worse machinability. Based on this evaluation method, the machinability of four kinds of superalloys was evaluated, and they could be ranked in such an order as GH605<GH4169<GH4033<GH2132.Effect of cutting parameters on machining induced surface integrity and their further influence on fatigue life of the machined workpiece were investigated. Within the chosen cutting parameters range, the cutting speed barely affected the surface roughness, and with an increase of cutting speed, the surface roughness decreased firstly and then increased, while the surface roughness increased with the increasing cutting speed. The depth of hardening layer was less than 20?m, and the surface hardness increased with the increasing cutting speed and feed rate. There was tensile residual stress on the machined surface, and the cutting speed had no regular influence on it, while increasing feed rate could improve the tensile residual stress. During the three-point bending fatigue life experiments, all the fractures were multisource fractures, and all the cracks initiated from the very surface. The cutting speed was not an influence factor on the fatigue life, but the feed rate could affect the fatigue life via the surface roughness. Higher surface roughness resulting from higher feed rate could result in a higher stress concentration factor, leading to a lower fatigue life. The working hardening under the present experimental conditions was not remarkable enough to produce an effect on the fatigue life. Besides, the tensile residual stress could reduce the fatigue life, but the relaxation of residual stress during fatigue experiment reduced its effect. A new constitutive model of GH4169, considering the coupling effect between thermal and mechanical loads, was built and then applied in FEM simulation. Dynamic behavior of Inconel 718 at a high strain rate of 5000-11000s'1 and an elevated temperature of 500-800? was obtained using SHPB (Split Hopkinson Pressure Bar) test. Strain rate strengthening and softening effect were both found, and they were temperature dependent, but no rule was found. Thermal softening was not affected by the strain rate. A modified Johnson-Cook model was established, and it was verified by experiment. Effect of cutting edge radius on cutting force, cutting zone temperature field and strain rate field was investigated via FEM simulation using the new constitutive model. When the cutting edge radius increased, the shear effect decreased while the ploughing effect increased, resulting in a higher cutting force and larger primary deformation zone and third deformation zone, which could increase the high cutting temperature area.Tool life, tool failure mechanism and machining induced surface integrity of machining GH4169 under dry, wet and cryogenic conditions were studied. During face turning of GH4169, wet machining and cryogenic machining could significantly improve the tool life than dry machining. The tool wear mechanism were abrasive wear and adhesive wear for dry machining and wet machining, but for cryogenic machining, flow direction of chip and serration on the chip were the main causes of the notch wear. As for face milling of GH4169, wet machining and cryogenic machining could prolohg the tool life because they could suppress diffusive wear and oxidative wear, whereas cryogenic machining may lead to thermal crack. During face turning of GH4169, wet machining and cryogenic machining were detrimental for surface roughness under low cutting speed. On the contrary, they could benefit it at a high cutting speed. There was softening affect in turning, and high cutting speed could aggravate it, but cryogonic machining could suppress it. With an increase of cutting speed, the tensile residual stress increased under dry turning, and the compressive residual stress turned to tensile residual stress under wet turning, while under cryogenic turning, the residual stress could remain a compressive status.