| The production model of individual units and small batch sizes has become a trend in modern production systems. In the face of increasingly diversified and personalized demands of plastic products, the traditional injection process requires multistage molds in order to satisfy the complex structure of the products, resulting in large energy and raw material wastages. However, the use of 3D printing technology to produce plastic products has advantages of being able to process complex-structure products, near net forming, no mold, digital design and manufacturing.In this paper, the evolution history and main technical classification of polymer materials 3D printing technology was summarized, and the application and development trend of polymer materials 3D printing technology was analyzed. Besides, the limitations of lessing material consumption and low building speed of the existing fused deposition modeling was clarified. Based on this, a new method of fused deposition modeling was proposed, and the name is melt differential 3D printing.In the forming mechanism research, the basic concept of melt differential 3D pringting was clarified firstly. The corresponding theoretical models and control methods were studied from the aspects of the melt differential extrusion and regional differential filling, and the feasibility of melt micro-droplets stacking forming was analyzed.Secondly, based on the analysis of process and kinetics of melt differential extrusion, the melt flow rates are affercted by pressure-gradient flow generated by back pressure in valve cavity and shear flow generated by the movement of valve needle. Besides, the influence of process parameters on melt extrusion flow rates was analyzed by means of numerical simulation.In view of the problem of warping deformation in the processing large scale plastic products, the feasibility of reducing the warping deformation by means of regional differential filling was analyzed. Besides, the influence of the size of cells for regional differential filling and the number of print head on the temperature field and stress field of processing products was analyzed, in order to improve the problem of thermo-stress distortion.In the experimental study, melt differential 3D printing devices was designed and manufactured firstly. The device was divided into electromagnetic and pneumatic type based on the different driving model,and the device was analyzed by the range of materials melting, extrusion on-demand, stacking forming and control system. The device lay the foundation of following experiment study.Secondly, based on the analysis of the feasibility of melt micro-droplets stacking forming, the diameter dimension and uniformity of micro-droplets were studied respectively, and the influence of process parameters on diameter of droplets were analyzed correspondingly. Besides, the experiment of micro-droplets stacking forming was conducted with PP and PLA, in order to analyse the influence of material properties on forming accuracy.In order to verify the advantages of the new device in the process of soft and brittle materials products, the experiment was carried out with TPU elastomer and CNT/PLA conductive composite. Besides, the influence of process parameters on the properties of the products was analyzed.The experiment of large-scale industrial differential 3D printing wad carried out. The original design was optimized with adding the double step extrusion device, and the theoretical analysis of stacking forming was analyzed. The quantitative experimental on flow rates, filament width,strength and accurary of products were carried out. Besides, the large plastic mold used in casting was processed and analyzed.In conclusion, this study proposed a new forming method of melt differential 3D printing, and the related research on the forming mechanism,process, device and application were studied, which laid the foundation for rapid processing the large plastic products. |
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