Simulation And Experiment Study Of Additive Manufacturing Employing Pneumatic Injection Of Iron Powder Slurry

Additive manufacturing has reached a breakthrough in the field of metal manufacturing,which has been proved to be a fast,flexible,short cycle process for forming complex metal components.Considering research situation at home and abroad of powder slurry additive manufacturing,the theory of pneumatic and the experience in powder metallurgy,this paper studies on the pneumatic injection forming process of iron powder slurry by means of simulation and experiment.By the advantages of low-cost operating equipment,no any inert-gas protection and no high-energy beam,the forming process widen the range of material,which has a good prospect of application in the field of metal manufacturing.Aimed to prepare iron powder slurry distributed evenly and stably,many factors which include proportion of monomers and crosslinking agents,the amount of the dispersant and milling time are optimized based on methylolacrylamide system.Experimental results show that iron powder slurry has non-Newtonian fluid’s dynamic characteristics;the viscosity of the feedstock grow continually with increase of milling time,the amount of the dispersant WinSperse 4060 and solid volume fraction;the sensitivity of viscosity to shear strain rate increases at low shear rate.The parameters for viscosity model including Bird-Carreau model,power-law model,H-B model are calculated by using the Stepwise linearization and least square method.The rheology constitutive equation of iron powder slurry is established by analyzing the results of model fitting.On the basis of the establishment of fluid dynamic characteristic equation in the flow field inside the nozzle,numerical simulation of the fluid flow condition was provided with finite element method by POLYFLOW.Analysis of the simulation result attests that the distribution of the fluid flow and exit velocity was affected by the entrance pressure,diameter and length of the needle.Distinct extrusion swell in conical needle with different structural factor is analyzed by reconstructing the meshon the free surface flow.The stable and controllable forming platform on which the iron powder slurry is injected pneumatically is designed and made.Based on three kinds of deposited line width models established,the width of deposited line varied by injection pressure,platform speed,nozzle structure parameters are studied.To guarantee effective combination between layers and the quality of the part,the change rule of the forming affected by layer level,delay time and the amount of accumulated layer is researched.The causes of forming defects such as collapse,fracture and pore in the forming part are analyzed.By means of experiment,suitable condition of drying,degreasing and sintering are set.The forming part is characterized by the mass ratio,shrinkage rate,density and microstructure.Thus the process has been proved to achieve the additive manufacturing using pneumatic injection of iron powder slurry.