Molding Characteristic Research Of Molten Polymer Dripping On Demand

3D printing technology appeared its initial form in the mid-1990s. With the advances in information technology, this new manufacturing method which combines a variety of advanced manufacturing technology developed rapidly.3D printing has developed from fused deposition modeling mode to selecting laser sintering, three dimensional printing and gluing, Stereo lithigraphy apparatus, and so on. Droplet ejection 3D printing can achieve micro droplets that are generated and deposited precisely, which results in a more compact and uniform product micro structure when compared with traditional crafts. This subsequently results in better mechanical properties for the products. We are committed to the study of the technology for the generation of controllable and uniform droplets.Based on the previous research into droplet ejection mechanism, the microscopic process of molten polymer droplets forming was described in detail, mechanism of droplet deposition and stacking was theoretically deduced using the energy equation and the equilibrium equation, and the process parameters affecting the injection of polymer melt are obtained. A droplet ejecting device for molten polymer was designed, and the impact on how the different process parameters influence the molten droplet injection molding was analyzed through experiments. Finally, the process parameters were optimized, and the droplet ejection stability, ejecting device stability, and the accuracy of the product was improved.First, theoretical study on micro droplet injection mechanism of molten polymer was carried out. Jet velocity and viscous force which influence the maximum spreading diameter was obtained using the law of conservation of energy; The research started from a single molten polymer droplet to line deposition and surface deposition, finally got the influence of overlap on droplet array stack configuration, and got the process parameters which influence overlap, including jet frequency, nozzle movement speed, and droplet diameter. According to the staggered and warping phenomenon in 3D printing process, a simplified mechanical model was established, and the stress and strain in molding process was derived. Finally, it was concluded that the cause of the deformation is the uneven distribution of stress between layers, the parameter values that affect the distribution of stress and strain are obtained, such as the height of the layer, the deposition path and so on. The above analysis provides a theoretical basis for the study of the parameters of molten polymer droplet ejection device.Second, the polymer melt droplet ejection technology mechanism has been studied theoretically according the analysis of process parameters, the motor for driving the screw, the coupling, the heating coil etc. was selected for the desired process conditions. Three dimensional mobile platform and the screw was designed. Several different types of valve needles and nozzles were designed, and the micro plunger nozzle was selected. Optimize for the stability of the three dimensional mobile platform, the structure of the plasticizing unit and the needle driving unit of the first generation device, and the second generation device was designed, and the operating stability of the injection device, the injection precision of the droplet was improved.Third, the following four key technologies need to be solved in the process of achieving uniform and stable polymer melt, respectively, the size of droplet control, the separation between the adjacent droplets size control, continuous droplet control and droplet solidification morphology control. In view of the above key technologies, the influence of droplet deposition and the shape of stacked products on the droplet deposition and the shape of the stack in different process parameters were analyzed experimentally. The following conclusions are drawn:1. In order to form a single droplet, the polymer melt must depend on the drag and drop of the substrate.2. The shape of the droplet is affected by the screw speed, injection frequency, melt temperature, nozzle diameter and other parameters. The optimization of the parameters can improve the uniformity of micro droplet deposition of polymer melt.3. The optimized combination of the change of the movement speed, and the injection frequency and droplet diameter, can form the fused droplet line with high adhesion strength, which can improve the accuracy of droplet stacking. By adjusting the deposition path optimization droplet stacking process of heat distribution can effectively reduce the stack of heat distribution, and improve the warpage and the local collapse of the phenomenon.