Surface Integrity Of Nickel-based Super-alloy Inconel 718 In High-efficiently Cutting Process

Nickel-based superalloys have been widely used in aerospace engines and nuclear industry, owing to their superior performance such as high thermal stability, high resistance to corrosion, mechanical and thermal shock, mechanical and thermal fatigue, creep and erosion at elevated temperature over 650℃. The superior performance of nickel-based superalloys make them typical difficult-to-machining materials. The poor machining performance of this kind of materials cause high cutting force and poor surface quality, as a result, resulting in low efficiency and high cutting cost. Fatigue life and safety performance of a machined component strongly depends on its surface condition. Effective surface integrity control strategy can ensure better reliability and longer service life of parts. Therefore, it is necessary to study on the surface integrity of machined parts, so as to improve the level of the machining technology for difficult-to-machining materials.Based on the above analyses about the present situation of the processing of nickel-based superalloy, nickel-based superalloy Inconel 718 is chose to study. In view of the actual problems in the fatigue failure of the aircraft, almost all of the fatigue damage is concentrated on the surface or near the surface of the parts. Investigation of the key problems that seriously limit the surface integrity of Inconel 718 in high-efficiently cutting process. The effect of nose radius on cutting force is presented, and a cutting force model is proposed. Surface integrity is an important evaluation indicator of surface quality, such as cutting force, coated materials, geometry of cutting tool and machining parameters. The effects of nose radii and coated materials on surface integrity are also discussed. Based on orthogonal analysis, the effects of cutting parameters on surface integrity evaluation index: residual stress, surface roughness, depth of wok hardening layer are presented, and the regression models for surface integrity evaluation index are put forward. The following is the main research contents:Firstly, a novel method for cutting force prediction with taking account of the effect of nose radius by analyzing the dynamic uncut chip is proposed. Based on the detail analysis of cutting geometry the contact region of tool and workpiece is also accurately described for the dynamic uncut chip thickness. At the same time, a cutting experiment is carried out to verify the accuracy of the cutting force model with variable cutting force coefficients.Secondly, surface integrity is an important evaluation indicator of surface quality, and the surface integrity of machining Inconel 718 with new coated cemented carbide cutting tools is studied. Investigation of the effects of nose radius, coated materials on surface integrity is compared. A finite element model is proposed to explain the difference of residual stress under different cutting conditions. A laser scanning confocal microscope is used providing the image of surface topography. The test of microhardness is carried out on a durometer for detail research on work hardening. The cutting conditions are optimized to improve the surface integrity and to achieve the purpose of efficient processing by comparative analysis.Finally, based on the orthogonal analysis method the effects of cutting process parameters on surface integrity index: residual stress and surface roughness, depth of work hardening layer depth are studied. In order to determine the significant impact of cutting parameters on axial residual stress σx, radial residual stress σx, surface roughness Ra and depth of the work hardening layer Dh is also discussed. The empirical models for the axial residual stress σx, the radial residual stress σx, the surface roughness Ra and the depth of the work hardening layer Dh are established and the effectiveness of these models are validated. The optimization of cutting parameters is realized by orthogonal analysis, and the regression empirical models are established to provide theoretical guidance for the actual cutting process.