Study On Tool Wear In The Turning Of Laser Additively Manufactured Nickel-Based Superalloys

Laser additive manufacturing technology is widely used in marine environment,aerospace and other fields.However,the products manufactured by laser additive manufacturing technology have low surface accuracy and poor surface roughness,which are difficult to be directly used.Therefore,it is still necessary to carry out cutting processing.In this paper,laser additively manufactured nickel-based superalloys were used as the research objects,mainly studied the characteristics,cutting force,cutting temperature,cutting vibration and tool wear of laser additively manufactured nickel-based superalloys.The cutting law and tool wear form of workpiece material were explained from the perspective of experiment and simulation.The multi-objective parameter optimization of turning laser additively manufactured nickel-based superalloys was carried out by genetic algorithm.The laser additively manufactured nickel-based superalloys were tested and analyzed from the aspects of geometry,metallographic structure,density,thermal conductivity,microhardness and phase composition of the sample,and compared with the traditional wrought nickel-based alloys.The results indicated that the surface of laser additively manufactured nickel-based superalloys was rough,the internal structure was uneven（equiaxial crystal and columnar crystal distribution）and pore crack existed,which reduced the mechanical properties of the material.The density of the material was low（density is 8.1577 g/cm³）,and the microhardness of the material(412HV_0.2)was smaller than that of wrought nickel-based alloys.The thermal conductivity of laser additively manufactured nickel-based superalloys was 24.7 W/（m·K）at300℃,which was higher than that of wrought nickel-based alloys.The precision turning experiments of laser additively manufactured nickel-based superalloys were carried out by using cemented carbide,coated cemented carbide and CBN cutting tools respectively,and compared with traditional wrought nickel-based alloys,the influence of different cutting tools on the cutting rule of laser additively manufactured nickel-based superalloys was studied.The results showed that the chips of laser additively manufactured nickel-based superalloys was irregular and continuous,and the chips was easy to curl,while the chips of wrought nickel-based alloys were spiral and easy to control.In addition,due to high cutting temperature and large cutting deformation,all chips had serrated edges.The cutting force,cutting temperature and cutting vibration of laser additively manufactured nickel-based superalloys were smaller than those of wrought nickel-based alloys.Cemented carbide tool and CBN tool had short life and fast wear.The coated cemented carbide tool had three wear stages:early rapid wear,middle stable wear and late severe wear,and had a long service life.The wear morphologies of cemented carbide tools were mainly crater wear and flank wear;the wear morphologies of coated cemented carbide tools mainly included crater wear on rake face,flank wear,coating spalling and nose breakage;the wear morphologies of CBN tool were mainly edge breakage and groove wear.The main wear mechanisms were abrasive wear,adhesive wear,oxidation wear,coating spalling and fatigue crack.The surface roughness of Ni based alloys machined by each tools could meet the requirements of finish machining,but it was greatly affected by the tool materials.From the perspective of tool life,the coated carbide tools were the most suitable tools for cutting laser additively manufactured nickel-based superalloys.Aiming at the cutting simulation of laser additively manufactured nickel-based superalloys,the Johnson cook constitutive model parameters of laser additively manufactured nickel-based superalloys were obtained by quasi-static compression experiment and dynamic Hopkinson pressure bar experiment.The two-dimensional and three-dimensional cutting simulation models were established by deform cutting simulation software.The changing rules of saw tooth shape of chips,cutting force,and tool wear are studied.The results showed that the chip had serrated edge at different cutting speed,and the cutting force increased with the increasing of cutting speed.Tool wear increased with the increasing of cutting time and cutting speed.Comparing the simulation results with the experimental results,the maximum error of cutting force was 17.4%,and the chips and tool wear morphologies were more consistent,which could ensure the accuracy of the simulation model.The multi-objective cutting parameters optimization of laser additively manufactured nickel-based superalloys was carried out by using genetic algorithm.The cutting parameters were taken as the optimization variables,and the cutting force,tool wear,material removal rate and surface roughness were taken as the optimization objectives.The optimal parameters were obtained by applying different weights to each optimization index,and verified by simulation and optimization results,The maximum error between optimization results and simulation results was 7.3%,which showed that the optimization model was reasonable.