Research On Fused Deposition Modeling Simulation And Welding Property For PVDF

Fused deposition modeling(FDM)is a printing process in which fuses are interlaced layer by layer to form three-dimensional network structural parts,including extrusion section,air section and deposition section.Polymer interfacial bonding is realized through diffusion and entanglement of molecular chains in the process of melt printing,that is,adjacent fuses contact with each other to form the bonding interface,so the bonding of fuses in the process of FDM molding depends on the interface temperature history.Finite element method was used to simulate the forming process of FDM,and the change of temperature field in FDM forming was analyzed quantitatively,which provided theoretical basis for improving the bonding performance of the parts.At present,the simulation research mainly simulates a certain process in FDM forming,but lacks the whole process system research.In addition,the mechanical properties of printed parts are determined by the interface bond strength,which is directly related to the temperature history of the interface and is determined by the printing parameters and the properties of the material itself.Therefore,it is very important to study the influence of various process parameters on the temperature field and bond properties of the parts.Polyvinylidene fluoride(PVDF)has been used in the melting printing of functional devices due to its excellent dielectric properties,excellent machining properties and mechanical properties.However,due to the poor thermal conductivity of PVDF,in the printing process,the parts are easy to warpage due to uneven heat dissipation,which affects the mechanical properties.In this research,multi-walled carbon nanotubes(MWCNT)were used to improve the thermal conductivity of PVDF,and the whole FDM process was simulated by ANSYS to study the temperature field in the whole forming process(extrusion section,air section and deposition section),and analyze the influence of different process parameters and MWCNT content on the temperature field.Based on the temperature field simulation results,the bonding strength and tensile strength of the parts were predicted,which provided theoretical guidance for improving the mechanical properties of the printed parts.Firstly,based on the material properties and constitutive equation of PVDF,the fluid model of extrusion section and the temperature field model of air section in FDM were established.The temperature field model of sedimentary section was established by using the life-and-death unit technology and APDL(parameterized programming language).The average temperature of the melt at the nozzle outlet was taken as the initial temperature condition of the air section,and the average temperature when the melt was deposited on the bottom plate was taken as the initial temperature condition of the deposition section to realize the simulation of the whole FDM forming process.Secondly,the effects of nozzle temperature,nozzle diameter,printing speed and MWCNT content on the simulation results of extrusion,air and deposition sections were studied based on the simulation model of FDM forming process.The results show that the melt can only melt completely when the nozzle temperature is higher than 230?.Increasing the nozzle temperature,reducing the printing speed and selecting the nozzle with small aperture can improve the overall temperature of the parts,the temperature field distribution is more uniform,and the effective bonding time is increased,which is conducive to the improvement of the bonding performance of the parts.In addition,after adding MWCNT,the thermal conductivity of PVDF is improved,the temperature field distribution of the parts is more uniform,and the warping problem is solved.With the increase of MWCNT content,the effective bonding time decreases first and then increases,and the bonding performance of printed parts improves.Finally,based on the theory of polymer welding and polymer rheology,and combined with the simulation results of interface temperature history under different forming conditions,the strength of welding interface and printed parts under different printing parameters were predicted,and the model was applied to MWCNT/PVDF composites.The effects of different printing parameters and MWCNT content on the bonding properties were studied theoretically and experimentally.The model can be used to predict the strength of printed parts of different materials and provide reference for selecting the best printing parameters of different materials and improving the bond strength of printed parts in the actual printing process.