Research On Freeform Fabrication Of Polymer Melt Based On Micro-droplet Jetting

The freeform fabrication technology has the characteristics of low cost,short manufacturing period,wide forming materials,etc,which can meet the requirements of the future manufacturing industry in terms of flexibility,efficiency and energy saving,and attracts extensive attention by various fields.Micro-droplet jetting freeform fabrication is an important modern advanced manufacturing technology,represents the development trend of freeform fabrication technology,and has a broad application prospects.It separates forming material to small uniform droplets by jets,then the complex geometric model is formed on the substrate with point by point deposition.The technique has made significant progress in the jetting forming of low-viscosity fluids such as molten and water-soluble polymers,but encounters difficulties in the jetting forming of high-viscosity such as polymer melt.In this paper,exploratory research for polymer melt micro-droplet jetting freeform fabrication has been conducted,the main work is as follows:1.As the viscosity of polymer melt is higher,in order to improve the driving power,the mechanical jet was used.Analysis concluded that the mechanical jet has two working modes:impact and pressure,then the influence of inertia force,viscous force and surface tension on the droplet jetting process was analyzed qualitatively.The simulation model was established,then the droplet jetting process in impact mode and pressure mode were simulated respectively,the results show that necking,liquid line elongation and fracture occured during the droplet jetting process.The effects of process parameters,physical parameters and structural parameters on the droplet jetting performance were analyzed in detail,and then the main structural parameters of the mechanical jet were given.2.The structure design of the hydraulic powered mechanical jet was carried out,and the movement characteristics of the stricker in the nozzle was emphatically analyzed.It can be seen from the analysis that the jet can work in two modes by adjusting the relevant parameters.The pressure control subsystem,temperature control subsystem,motion control subsystem,etc,were designed with the jet as the core,and the whole construction of the micro－droplet jetting freeform fabrication experimental device was completed.3.On the basis of the experimental device,the micro-droplet jetting experiment was carried.The results show that the jet can generate uniform droplets by setting the process parameters reasonably.The effect of each process parameter on the droplet volume was obtained by single-factor and multi-factor analysis of the two working modes of the jet respectively.Finally,the combination of the process parameters with the smallest volume of the droplet was given.4.The deposition morphology of micro-droplet was analyzed from the geometrical point of view,and the effect of parameters on the morphology of micro-droplet was investigated with the curing angle as the evaluation index.The optimal droplet deposition interval and line deposition interval are analyzed and calculated,and then the three-dimensional solid forming experiments were carried out,the forming samples are analyzed from the aspects of forming dimensional accuracy and density,which provided a means of evaluation for the forming quality.