Study On Lightweight Complex Structure TPU Components And Its Mechanical Properties By FDM And Microcellular Foaming

Thermoplastic polyurethane(TPU)is a type of thermoplastic elastomer that not only has the characteristics of traditional cross-linked rubber,but also can be used for thermoplastic processing.TPU has high elasticity and resilience,high strength and toughness,excellent biocompatibility,chemical resistance and wear resistance,and has become one of the most widely used polymer materials,and has broad application prospects in automotive,medical,construction,footwear,wire and cable industries.The traditional thermal processing methods of TPU include injection molding,hot pressing,extrusion and calendering,etc.However,it is difficult to easily manufacture products with complex structures or unique structures by these methods,which limits the use of TPU to some extent.As a growing additive manufacturing technology,3D printing technology has the significant advantages of rapid prototyping without the need for molds,allowing the printing of lightweight and complex products that are difficult to achieve by other manufacturing methods.Among them,the most widely used 3D-printing technology is fused deposition modeling(FDM),which is simple to operate,easy to maintain and significantly reduces the time of product research and production.Therefore,the emergence of emerging 3D printing technology can combine the advantages of 3D printing with the flexibility of TPU to meet the needs of more users.Supercritical carbon dioxide foaming(ScCO2)is a green,safe and non-toxic physical foam molding technology,which can produce foam with large expansion rate by rapid pressure release foaming.Based on the broad market prospect and excellent performance,TPU is the most promising candidate for the preparation of lightweight and highly elastic structural products.Cyclic compression is an important indicator to characterize the mechanical properties of foam such as elasticity,but there is a lack of systematic research on the properties of elasticity and other factors such as cell morphology.In addition,although there are many studies on 3D printing and microcellular foaming,there is little literature to study the foaming behavior and mechanical properties of foams obtained by using 3D printed blanks and subsequent microcellular foaming.In view of the above shortcomings,this paper mainly conducts the following research.First of all,this paper used the modeling software UG for 3D solid modeling to design the required samples of two different structures(corrugated structure and honeycomb structure).After the 3D model was created,it was converted to STL format for layering by the slicing software.Then import the model data with the set parameters into the 3D printer,and during this process,appropriate printing parameters can be set in order to prepare structural parts with excellent performance.Using 3D printing technology,the material was printed layer by layer according to a set program,and the desired TPU structural parts can be obtained in the end.Secondly,using supercritical CO2 as the foaming agent,TPU foam with adjustable cell structure was prepared by autoclave foaming method.The cell morphology of the foam was observed and analyzed by scanning electron microscope,and the effects of changing foaming conditions on the expansion ratio,cell size,cell density and overall porosity of the TPU foam were also studied.Studies have shown that the expansion ratio of foam is significantly affected by temperature and pressure.The optimal foaming temperature of the foam is about 155℃.With the increase of temperature,the foaming ratio of the cells and the size of the cells first increase and then decrease.However,the effect of foaming pressure on the cells shows a monotonous change,and the increase of foaming pressure will increase the foaming ratio and decrease the size of the cells.The porosity is used to characterize the overall change of structural parts before and after foaming.The results show that the foam porosity increased significantly after foaming,indicating that microcellular foaming gives TPU excellent porous structure.Finally,the single-variable method was used to study the compressive mechanical properties of the prepared two kinds of foam structures,and to explore the effect of each parameter on the cyclic compressive properties of the foams.The results show that the foam structure exhibits different compression properties in different compression directions.The effect of cell size on the compressive properties of the foam is not significant.When the range of cell size changes is large,the compressive mechanical properties of the foam become better with the increase of cell size,but when the cell size is not much different,the change pattern of mechanical properties and resilience of foam is not obvious.The foaming ratio has a significant effect on the cyclic compression performance of the TPU foam structure.With the increase of the foaming ratio,the resilience performance of the foam increases significantly,but the mechanical properties decrease significantly.Foams with larger expansion ratios show lower energy loss coefficients,but at the same time,their maximum stress,compressive stress and Young’s modulus are also lower.As the filling density increases,the support of TPU foam parts increases and the energy loss also increases.With the increase of the number of honeycomb edges,the elasticity of the foam becomes better and the energy loss decreases.Through the above research,this paper prepared TPU foams with different cell morphologies by changing the foaming temperature and pressure,and analyzed the cell morphologies,thereby realizing the controllability of the TPU foam structure.And two different types of TPU structural foams were prepared,and the effects of loading direction,cell size,foaming ratio and filling density on the foam compressibility were systematically studied by single-variable method.This study provides an important reference for the preparation of TPU foams with high elasticity and low energy consumption,and ultimately provides valuable theoretical guidance for strengthening the combination of 3D printing and microcellular foaming technologies.