A Study on Surface Integrity of Nickel Based Superalloy Inconel 718 under Robotic Belt Grinding

Author:Wang Jun Wei

Supervisor:chen xiao qi xu ji jin


Degree Year:2018





As a precision forming technology,grinding has attracted more and more attention.The traditional manual grinding is unable to meet the high-quality and high-efficiency modern industrial needs due to its shortcomings such as poor controllability.With the implementation of Industry 4.0 and China Manufacturing 2025,the robotic belt grinding has become an inevitable development trend.Nickel-based superalloy Inconel 718 is widely used in the field of aerospace,oil and natural gas because of its excellent serviceability,which puts higher requirements on its surface integrity.Grinding quality includes grinding accuracy and surface integrity.Surface integrity is often overlooked in traditional manual grinding,but has a significant impact on the serviceability of the material.Therefore,this paper designed and developed a robotic belt grinding system for Inconel 718 and improved its surface integrity and serviceability through controlling the grinding parameters.The effects of grinding process parameters on the surface integrity(surface burnout,roughness,residual stress,structural domain size,microhardness and microstructure)of the alloy were systematically studied.A comprehensive multi-index surface integrity prediction model was established.The mechanism of electrochemical corrosion of the grinding surface was discussed.This study provides effective theoretical support and experimental basis for the development and application of robotic belt grinding technology.The main research contents and results are as follows:(1)A robotic belt grinding system was built and the relationship between grinding parameters and main indicators of surface integrity was analyzed.Studies have shown that the surface of specimens will be obviously burnt when the measured grinding surface temperature is higher than 580 °C.As the grinding force increases,the surface roughness increases,and the residual stress tends to change from compressive stress to tensile stress.At grinding force of 178 kPa and belt speed of 31 m/s,the surface of Inconel 718 not only achieved a large compressive residual stress(about 355 MPa)but also obtained the smallest surface roughness.At the same time,the surface microhardness was increased by about 15% compared to the base metal.The surface integrity of the sample is improved because continuous partial dynamic recrystallization occurs during grinding process.(2)Based on the sound features,an Optimally Pruned Extreme Learning Machine(OP-ELM)model is established to estimate the belt wear conditions..The temperature prediction model during the grinding process was established based on the heat source method,and the heat generation and conduction mechanism during grinding process was further analyzed.The variation of the surface temperature during the grinding process was obtained.which was used to predict and control the surface burning during the grinding process.Based on the linear weighting function,a novel surface integrity optimization prediction model is proposed.The model comprehensively evaluates several factors of surface integrity.(3)Experiments were carried out on the surface residual stress of Inconel 718 under robotic belt grinding.A predictive model of residual stress of grinding specimens was established based on the combination of adaptive neuro-fuzzy inference system(ANFIS)and particle swarm optimization(PSO).The prediction of surface residual stress and maximum residual stress on the grinding surface were realized.Compared with the test results,the obtained MSE is less than 735.85,the RMSE is less than 27.13,the EM is less than 4.26,and the ESD is less than 26.94.It can be seen that the method can predict the residual stress and the maximum residual stress on the grinding surface quickly and accurately.It lays a foundation for the control of the residual stress on the grinding surface and the improvement of residual stress state of the alloy surface.(4)The corrosion performance of the ground surface was analyzed systematically.The main influencing factors of the ground surface corrosion performance including grinding process,surface roughness and residual stress were discussed.Studies have shown that the electrochemical corrosion of Inconel 718 ground by the robotic belt grinding system proceeds from oxide film defect occurrence and Nb-rich region formation,to corrosion product generation.Then the corrosion products shed into the electrolyte due to the dissolution of the boundary,leaving a large number of corrosion pits.As the abrasive grain size decreases,the roughness of the ground surface decreases,and the surface compressive residual stress increases,and the corrosion resistance of the ground specimen surface is effectively improved.The smaller roughness reduces the surface area involved in the corrosion process,suppressing the generation of corrosion products.The compressive residual stress hinders the peeling of the corrosion products.