Study On The Formation Mechanism And Compensation Method Of Dimensional Error Of Fused Deposition Modeling Parts

With the advantages of simple equipment,low cost,fast molding speed and wide range of molding materials,FDM technology is widely used in the fields of automotive,medical,architecture,entertainment,electronics and education for conceptual modeling,functional prototyping,manufacturing,and finally used for parts manufacturing and trimming.However,the size changes caused by the thermal expansion and cold shrinkage of printing materials seriously affect the forming precision of the parts.This paper aims at the problem of size shrinkage of cylindrical parts during FDM molding,using numerical simulation as a research method,starting from the temperature field and stress field of FDM forming process,revealed the size shrinkage law and mechanism of cylindrical parts during molding and cooling.The effects of different process parameters on the size shrinkage of cylindrical parts were studied,and the size error compensation mathematical model of the cylindrical parts was established to provide guidance for improving the forming precision of the cylindrical parts.In present study,based on the process characteristics of the dynamic accumulation of the molten filament in the FDM forming process and the complex changes in temperature field and stress field,reasonable assumptions for the forming process were provided,a thermodynamic coupling simulation model for the FDM forming process was established based on the basic theory of thermal simulation,the dynamic loading method of nozzle scanning path,initial conditions and convection heat transfer boundary conditions were set using APDL language and birth-and-death element technology,and the algorithm design of thermal-mechanical coupling simulation analysis was completed.Based on the APDL command flow,the thermal-mechanical coupling simulation of the FDM forming and cooling process of the cylindrical part was completed.The change of the temperature gradient in the temperature field and the equivalent stress in the stress field was analyzed,and the internal mechanism of the size shrinkage of the cylindrical part was revealed.The simulation results show that the radial temperature gradient distribution of the cylindrical parts is very uneven and the equivalent stress is high.While the axial temperature gradient distribution is relatively uniform,and the equivalent stress is lower than the radial one.The difference between radial and axial temperature gradients results in large radial shrinkage and small axial deformation in the cylindrical parts.The simulation results are basically consistent with the test results.A single factor experiment method was used to study the effect of process parameters on the dimensional accuracy of FDM shaped cylindrical parts based on the simulation results.The main process parameters that affect FDM molding accuracy,i.e.layer thickness,printing speed,and nozzle temperature at different levels were selected to carry out thermomechanical coupled finite element simulation.Through comparing the temperature gradient,equivalent stress,and maximum deformation at the end of the molding and after cooling,it was found that the dimensional accuracy of the cylindrical parts can be effectively improved by choosing lager layer thickness,printing speed,and lower nozzle temperature.The effect of structural parameters(inner diameter,wall thickness,and filling rate)of cylindrical parts on the size shrinkage was studied by means of a full-factor test design method.According to the size error measurement data obtained from the test program,response surface diagrams of structural parameters to size error were drawn,based on which the influence of different structural parameters on the size shrinkage of cylindrical parts was analyzed,and size error compensation models for cylindrical parts were established,which have important practical value and guiding significance for improving the dimensional accuracy of FDM molded thin-wall parts.