Study On The Surface Integrity In High Speed Milling SiCp/Al Composites Under Liquid Nitrogen Cryogenic Condition

As an excellent cooling medium,liquid nitrogen has an extremely low temperature(-196?)and the liquid-gas phase nitrogen conversion leads to the generation of large amounts of gas phase nitrogen,which not only acts as a chip breaking but also forms boundary films to provide a lubricating effect.In order to achieve efficient,high precision and pollution-free machining of SiCp/Al composites,this paper applies liquid nitrogen cryogenic cooling technology to the machining process and investigates the surface integrity of SiCp/Al composite materials after high-speed milling under liquid nitrogen cryogenic condition.Firstly,the milling experiments of SiCp/Al composite are carried out by using polycrystalline diamond tools with different tool geometry parameters under liquid nitrogen cryogenic assisted cooling condition,and the surface roughness and tool wear are used as indicators to optimize the tool geometrical parameters.Single-factor test using the preferred tool under liquid nitrogen cryogenic condition,the variation of surface roughness with different milling parameters is analysed.Based on the surface three-dimensional topography of machined specimen,the variation of surface defects with milling parameters is analyzed.Secondly,based on the response surface methodology and combined with the central composite experimental data under liquid nitrogen cryogenic assisted cooling condition,the mathematical model of surface roughness is established.To ensure model fitting degree,the model is validated using surface roughness test data.In order to explore the main effects of factors in the linear and interaction effects of the milling parameters under liquid nitrogen cryogenic milling conditions,the significance of the model regression coefficients is analysed.The response surface diagram of interaction between factors is drawn.Then,microhardness tester is used to test the work hardening of the finished specimens.The variation pattern of machining hardening with different milling parameters under liquid nitrogen cryogenic assisted cooling condition is analysed.Using the microhardness test data and based on GRNN neural networks,mathematical model of work hardening is constructed.Finally,simplified two-dimensional milling model with separately defined properties for the base material and the particle material is developed.The influence of reinforcement SiC particles and milling parameters on the distribution of residual stress in the workpiece is explored.In addition,the residual stress on the surface of the specimen after milling under liquid nitrogen cryogenic condition is examined by X-ray diffractometry.The pattern of residual stress variation with milling parameters is explored.To ensure the accuracy of the simulation,the test data and simulation values are verified against each other.