Research On Uniform Metal Droplet Generation And Surface Topography Control In Metal Micro-droplet Deposition Manufacture

As a novel kind of rapid prototyping technology,metal micro-droplet deposition manufacture(MDDM)attracts more and more attentions at present.In the process,molten metal was ejceted from a nozzle to form uniform droplet.Then the droplet was deposited at certain location by coordinately controlling the droplet generation and substrate motion.Finally,theree dimensional structure was fabricated by depositing droplets sequently.Without expensive equipments,special mold and handling raw materials in manufacturing,the technique has lots advantages such as simple process,low cost of production and high performance of components.So it has great potential applications in directly fabricating metal components,printing flexible circuit and electronic package.However,the technique includes droplets ejection,solidification and other complex procedure,and the quality of component was effected by many factors such as droplet size,fusion state and overlap morphology.In order to develop the technique,droplet generation and surface quality optimization were needed to be studied.In present work,the effect of process parameters on droplet ejecting behavior was studied and a method for producing droplet smaller than the nozzle diameter was proposed.In order to improving the surface quality of component,a new approach aimed to the characterization of part surface topography was proposed and the evaluation indexes such as arithmetic average height and stratification angle were used to characterize the surface topography quantitatively.Surface topography models were developed to caculate the evaluation indexes and the effect of process parameters on surface quality was also studied.Based on the above research,appropriate parameters for fabricating component would be obtained.The main contents are listed as follow:The metal micro-droplet deposition manufacture system developed in this thesis involves metal melting subsystem,droplet generating and depositing subsystem,data acquisition subsystem.The droplet generator and heating equipment was improved for ejecting different metals.The data acqusition system was used for process parameter collecting and forming process monitoring.The experiment system laid a hardware foundation for studing the metal micro-droplet deposition manufacture.The pressure vibration in crucible in different conditions was measured and the control strategy was obtained.The effect of process parameters on droplet generation was studied by using experiment and simulation method.Based on the actual structure,a numerical model was proposed to study the effect of process parameters on droplet generation.According to the results,the range of parameters for generating uniform droplet was obtained.By analyzing the reason for which droplet smaller than nozzle diameter could not be generated by using the traditional pneumatic droplet generator,a new method for generating small droplet was proposed and a novel droplet generator was developed.The effect of structure parameters on droplet size was studied by using simulation method.Based on the simulation results,appropriate structure parameters were obtained and metal droplet smaller than nozzle diameter was produced.The research was useful for improving the component surface quality.Evaluation indexes for characterizing surface quality of component fabricated by MDDM were proposed for the first time.By studing the effect of droplet temperature and substrate temperature on droplet deposition shape,an arc model was developed to fit the deoplet deposition shape.Based on the arc model,models for characterizing the component surface topography were developed and the evaluation indexes could be predicted.Experiment were conducted to study the effect of scan step,offcet distance,droplet temperature,substrate temperature and other process parameters on surface quality.According to the results,appropriate parameters were obtained and components with fine surface quality were fabricated.The research was useful for promoting the application of the metal micro-droplet manufacture.