| Due to its high electrical conductivity and high thermal conductivity,pure copper has been widely used in motor windings,radiators,heat exchangers and aircraft engines.While there are many difficulties in using traditional manufacturing methods for such complex parts,the development of additive manufacturing has made it easier to manufacture complex parts.Among additive manufacturing processes,selective laser melting stands out among additive manufacturing processes with its ability to rapidly produce components with complex geometries and high spatial resolution.Therefore,this paper takes pure copper as the research object,adopts the microscale selective laser melting forming method,and uses the process parameters to optimize the preparation of high-performance pure copper.The main contents include:(1)The characteristics of micro-scale selective laser melting of pure copper are analyzed.Due to the low absorptivity of pure copper powder to the laser in the infrared band,the insufficient energy of the molten material leads to a large number of pores in the formed parts,and the performance of the parts cannot meet the application requirements.The small spot diameter and powder particle size increase the surface area,which can effectively improve the energy density.microscale selective laser melting forming equipment with a spot diameter of 25μm was used to improve the energy density under the same parameters.Pure copper powder with a powder particle size of 5～25μm improved the absorption rate of the powder to infrared laser.The reasonable laser power range is 100～340W,and the scanning speed range is200～1600mm/s.(2)The powder bed model was established by discrete element method and the heat and mass transfer model of micro-scale laser selective melting single-pass forming process was established by fluid mechanics method.Using a high-speed camera to observe the melt pool,the reasons for the errors in the simulation and experiments were analyzed,and the correctness of the model was verified by a single-tracks experiment,the melt tracks width error is within 10%.In the heat and mass transfer model of microscale laser selective melting,the forming quality is characterized according to the continuity,width and uniform smoothness of the melt tracks.The power range is 220～280W,and the scanning speed range is 400～700mm/s.(3)First,on the premise of keeping the laser power and scanning speed unchanged,a single-factor variable test was carried out on the scanning distance.According to whether the melt tracks overlapped and whether the surface quality was good,it was determined that the reasonable scanning distance range should be greater than 50μm and less than 100μm.Then,the influence of various factors on the density of pure copper samples was analyzed by orthogonal experiments,and it was found that the laser power had the greatest influence on the density,and the best process parameters is: laser power 260 W,scanning speed 600mm/s,scanning spacing 70μm,Under this parameter,the density of pure copper samples can reach 98.8%.Finally,the mechanical properties of four kinds of specimens with optimal process parameters and heat treatment,low laser power and high laser power were tested.Under the optimal parameters,the Vickers hardness was 84HV0.05 and the tensile strength was 320 MPa.The surface morphology of the sample and the fracture morphology of the tensile part were observed,and the reasons why the tensile strength of the best parameter was better than other parameters were explained.The results of the thesis will provide process guidance for the forming and manufacturing of high-density,high-strength,and large-elongation pure copper complex structural parts. |
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