Surface Integrity And Cutting Parameters Optimization In Side Milling Of Titanium Alloy Based On Specific Cutting Energy

Titanium alloy has a very broad development prospect in the field of aviation and aerospace because of its outstanding performance characteristics such as high strength and fatigue resistance.Titanium alloy structural parts in side cutting process have poor stiffness,high amount of material removed and excellent surface quality requirements.Nevertheless,titanium alloy is usually considered to be a difficult-to-machine metal material,which often suffers from poor surface quality,inefficient machining efficiency,and extensive energy consumption in the machining process,making it difficult to satisfy production processing.In this thesis,the specific cutting energy calculation model in two-step milling of titanium alloy was established with Ti-6Al-4V,the effect of variations in machining parameters on the milling force and specific cutting energy of titanium alloy was investigated.The change of surface integrity with varying machining parameters and their interrelationship with specific cutting energy were revealed.Finally,the process parameters were optimized in two-step side milling of titanium alloy.The empirical model and mechanical model of milling force of carbide end mill were established,and the two models were verified and analyzed by milling experiments.The results show that the prediction error of the main cutting force of the empirical exponential formula is range from 4.19%to 10.0%,and the error of the simulation model is between 5.56%and 15.8%,which can be better used for the prediction of cutting force and parameter optimization,and a theoretical basis has been laid for further research into the effect of cutting parameters on the basic law of milling forces.Through the two-step titanium alloy milling experiments,a specific cutting energy model was established,and the impacted law of milling parameters,material removal rate and undeformed chip thickness on the specific cutting energy was studied.The results show that the milling force in the first cutting step increases significantly with the increasing of feed and radial depth of cut;the second cutting step is affected by the change of milling parameters in the first cutting step.Non-linear inverse relationship between material removal rate and cutting ratio of titanium alloy machining.When the value of the un-deformed chip thickness gradually increases,the side effect enhances,then the specific cutting energy tend to rise.The value of specific cutting energy gradually decreases as the feed per tooth and radial depth of cut increase.An increase in the cutting speed results in a larger value for the cutting specific energy,indicating an increase in the energy consumed.The effect of changing cutting parameters in the two-step side milling experiment on the machined surface roughness and micro-hardness was analyzed,and the correlation between the specific cutting energy of milling and the machined surface integrity was revealed.The results show that the variation of feed per tooth has the most obvious influence on the surface roughness and the radial depth of cut is the smallest.The effect of milling speed,feed per tooth and radial depth of cut on the degree of hardening of the machined surface has a similar pattern,with the increase of surface layer depth,it shows a trend of hardening-softening-reaching the sub-peak of hardening-stabilizing.The specific cutting energy is inversely proportional to the surface roughness,proportional to the degree of machining hardening,and proportional to the residual stress.The milling parameters were optimized with material removal rate,cutting specific performance and surface roughness as optimization objectives by means of a NSGA-II.The results show that the selection of larger feed per tooth,axial depth of cut,and radial depth of cut is beneficial in improving the machining efficiency and reducing energy consumption in the first cutting step.The selection of larger cutting speed can improve the surface quality of the second cutting step,which is an important guidance for the optimization of cutting parameters.