Study On Process Optimization For Directional Internal-cooling Milling Of Nickel-based Superalloy

Nickel-based superalloys are widely applied in the aerospace,aerospace and marine industries,owing to its high strength,excellent corrosion resistance and good fatigue resistance.However,nickel-based superalloys have poor milling performance.During milling processes,a large amount of heat generates on the tool-chip interface,resulting in surface burns and cracks on the workpiece,which limited the surface integrity.Under traditional flood cooling condition,the cutting fluid always have small flow rate,low pressure and poor cooling effect.Furthermore,it is difficult to penetrate accurately into the tool-chip interface to remove the milling heat,which limits the processing quality and efficiency.Consequently,exploring of new cooling technologies to strengthen the heat transfer efficiency has a great significance for improving the milling efficiency and quality of nickel-based superalloy parts.The directional internal-cooling technology injects cutting fluid to the milling area through outlets of flow channel inside the tool.Since the relative position of the outlets and the tool remains unchanged,the cutting fluid can be directed and continuously sprayed to the tool-chip interface even if the tool rotates at a high speed.Thus,the adverse effects of tool movement and workpiece shape on the heat transfer of cutting fluid are weakened.Due to the small size of the outlets,the coolant speed is easier to improve,which could generates better cooling,lubrication and flushing effects.In this paper,numerical simulations and experimental methods were used to study the directional internal-cooling milling of GH4169 superalloy,and the milling parameters were optimized based on the fatigue characteristics.The main research contents of this paper are as follows:(1)A computational fluid dynamics simulation model of directional internal-cooling milling was established.The influence of cutting fluid pressure and spindle speed on outlet velocity and outlet pressure were investigated.(2)Based on the flow field simulations,the heat transfer coefficients of cutting fluid when directional internal-cooling milling were calculated,and the finite element model of directional internal-cooling milling of GH4169 superalloy was established.The influences of cutting speed,depth of cut,feed per tooth and cutting fluid pressure on milling temperature,milling stresses and milling force were analyzed.(3)The experimental platform of directional internal-cooling milling was set up,and milling experiments of GH4169 superalloy were carried out.The effects of milling parameters and cooling methods on milling temperature,surface roughness,surface residual stress and surface morphology were studied.The finite element simulation results were verified.(4)Adopting the central composite circumscribed design approach,the optimization study of directional internal-cooling milling parameters of GH4169 superalloy was carried out based on the surface roughness and surface residual stresses.The prediction model of surface roughness and surface residual stresses were established.The milling parameters were optimized and verified to improve the performance and fatigue life of nickel-based superalloys.