Research On 3D Printing And Forming Technology Of Metal Powder

Metal 3D printing technology is the most cutting-edge and potential technology in the field of 3D printing,and it is an important direction of additive manufacturing technology development.Currently,metal 3D printing methods include selective laser sintering(SLS),laser selective melting(SLM)and electron beam melting(EBM),etc.,which directly melt and deposit metal powders with high energy sources such as laser/electron beam.However,the equipment is expensive and the metal powder materials are limited.Aiming at the shortcomings of existing metal 3D printing,this paper proposes a pneumatic extrusion direct writing metal powder 3D printing technology that combines metal injection molding technology and FDM technology.This technology has the advantages of low cost,low requirements for printing conditions,strong adaptability of metal powder and reusable metal powder.The research content of this topic includes preparation of metal slurry,construction and improvement of 3D printing equipment,3D printing and molding of metal slurry,degreasing and sintering process of metal body and application of copper sample in electrocatalytic reduction of CO2.The primary content and research production are as belows:(1)In this paper,copper powder is selected as the experimental material,and PVA aqueous solution with a mass fraction of 10%is selected as the binder.Through theoretical calculation and comparative experiment,when the mass ratio of copper powder and PVA aqueous solution is 9:1,the extruded slurry is uniform and smooth with the best molding effect,and the content of copper powder is the largest.At this time,the slurry density is 4.386g/cm3,and the viscosity is 421 Pa-s,which provides a theoretical basis for the other metal slurry.(2)The influence of process parameters such as printing speed,extrusion pressure,printing layer height and printing spacing on the molding accuracy and surface quality was studied through experiments.The test shows that the slurry extrusion stacking is uniform when the printing speed is 15mm/s and the extrusion pressure is 30psi.When the printing layer height is 80%of the diameter of the nozzle,that is,0.4mm,the surface precision is high,and the bonding between layers is tight.When the printing spacing is 0.5mm,the bond between adjacent two filament materials is close and the forming precision is high.(3)First,the rough steps of degreasing were determined by thermogravimetric analysis of the printing body.The influence of degreasing temperature and holding time on the degreasing quality was studied through the experiment,and the optimal degreasing process was determined.The degreasing samples with good morphology and no defects were obtained,and the final degreasing rate was 95.6%.The degreasing effect was confirmed by SEM observation and XRD experiment.The effects of sintering temperature,heating rate and holding time on the sintering quality and properties of the samples were studied experimentally.Thus,the optimum sintering process was determined:sintering temperature is 880?,the heating rate of 5?/min,heat preservation time is 2h.Finally,samples with good shape and uniform size shrinkage can be obtained,its density is 6.954 g/cm3,hardness is 85.7 HV,tensile strength is 115.413 MPa,size shrinkage rate is about 11%.(4)The porous copper electrode sheet was prepared by 3D printing process and used as a catalyst in the electro-catalytic reduction of CO2.Its electrochemical properties were tested by means of potentiostatic electrolysis,and the Current density and the Faraday efficiency were compared with that of the copper electrode obtained by electrodeposition.The experimental results indicate that the Faraday efficiency of copper sheet of electrodeposition,copper of 3D printing and porous copper sheet of 3D printing are basic same,but the current density of copper sheet of 3D printing is 60.7mA/cm2,about 6 times that of copper sheet of electrodeposition,and the current density of porous copper sheet of 3D printing is 69 mA/cm2,about 7 times that of copper sheet of electrodeposition,which suggesting that 3D printing on CO2 reduction catalytic application has great prospects.