Research On Material Removal And Parameter Optimization In Micro Milling SiCp/Al Composites

Not only owing to the superior properties such as high specific strength and modulus,high temperature resistance,high wear resistance,high fatigue resistance,low thermal expansion,good dimensional stability,but also easy batch manufacturing ability and low cost,SiC particle reinforced aluminum matrix composites(SiCp/Al)are being commonly utilized in various industries,such as aerospace and automotive industries.However,because of the different material characteristics of the matrix phase and the reinforcement phase,machining process of the composites is difficult,machining mechanism is complex,and there are many surface defects in the machined surface,which seriously restrict the wide application of the composites in precision field.In this paper,micro milling process is used for precision machining the SiCp/Al composites,and a research on the material remove mechanism,surface defect formation mechanism,milling force model and analysis,surface quality,and surface defect supression method during the micro-milling process is done to select and optimize suitable cutting parameters.It will be significant and helpful for the further broad application of this material.To investigate the effect of heterogeneity properties on material removal and surface defects,a micromechanics finite element model,with single particle integrated with the brittle cracking model,is built,and then the cutting mechanisms under different tool-particle interaction locations and cutting speeds conditions are simulated.The simulation results show that when tool cuts the upper part of the particle,the particle fractures and is cut through,and the main surface defect is crack;with the increasing of the cutting speeds,the fracture degree decreases and surface defect is reduced.However,when the tool cuts the lower part of the particle and the cutting speed is small,the particle is pull out and surface defect is big pit;as the speeds increases,the failure of the particle is changed from pullout to fracture,and the surface defect is also changed to crack.In a word,a big cutting speed can be beneficial to material removal and weaken surface defects.Milling force has a great effect on the material removal and surface generation.Based on the research of material removal mechanism of SiCp/Al composites,considering the plough force caused by the size effect of matrix and fracture force caused by the removal of particles,a predictive force model in micro milling the SiCp/Al composites is established and verified.And then,the influences of cutting parameters on milling forces are investigated.Meanwhile,the contribution of the particle fracture force is also investigated.It is found that the fracture force plays a noteworthy effect on resultant force,and its proportion is about 20-30%.To evaluate the surface microtopography of the machined SiCp/Al composite surface by micro milling process,the three dimensional surface roughness(arithmetic mean roughness and RMS roughness)and surface fractal dimension are used.By single factor experiments and orthogonal experiments,the influences of cutting parameters on machined surface are investigated.Meanwhile,the relationship between surface roughness and fractal dimension is analyzed.Finally,to obtain smallest surface roughness and biggest fractal dimension,the cutting parameters are optimized by a multi-objective genetic algorithm.On the basis of above research,according to the removal ways of the two phases,a method restraining the surface defects of SiCp/Al composites during micro milling process is deduced,which can weaken the size effect of matrix,realize the ductile regime machining of particle and restrain the cracks caused by particle fracture.The suitable value range of the feed per tooth is obtained by this method,and then is optimized according to the influences of tool parameters(diameter,edge radius,corner radius,and relief angle)and material parameter(particle size)on it.Besides,in order to design and select suitable tool,the relationship among tool diameter,corner radius and cutting edge radius are established.Micro milling experiments are used for verification.This method can reduce experiment dependence,save cost and time and be flexible for machining of other composites.It provides evidence for parameters selection in micro milling to further improve surface quality of SiCp/Al composites,and will be of great importance in precision machining composites.