Research On Integrated Manufacturing Of Functionally Graded Materials-Structures Based On Multi-Material 3D Printing And Constrained Sacrificial Layer

With the development of science and technology,people have put forward more stringent requirements on the performance of materials.Polymer-based functional gradient materials not only excellent processing characteristics,but also the advantages of light weight,good corrosion resistance,good fatigue resistance and high safety performance.They have been widely used in aerospace,mechanical engineering,biomedical,flexible products and many other fields.In order to solve the deficiencies and limitations of the existing polymer-based functionally graded materials and structures in the manufacturing process of consistency,interlayer bonding,precise shape control,and universality(high viscosity material system,low viscosity material system).In this paper,a new method of integrated manufacturing of functionally graded materials-structure based on multi-material 3D printing and constrained sacrificial layer is proposed.The construction of experimental platform,study on process parameters,preparation of typical experimental samples,and testing of their properties for analysis and research,the specific work is as follows:(1)An integrated manufacturing technology of functionally graded materials-structures based on multi-material 3D printing and constrained sacrificial layer was proposed,its principle is:firstly,a layer of constrained sacrificial structure is prepared with the constrained sacrificial printing nozzle(FDM Technology),and then the gradient material is printed with passive hybrid printing nozzle in the constrained sacrificial layer,and the layer is cured.After that,the next layer is printed,and the shape is sequentially formed until the entire functionally graded structure is completed.By changing the feeding speed of the feeding module,the continuous gradient change of the material is realized.The innovation points are as follows:the constraint sacrificial layer structure is introduced to solve the problem of poor printing accuracy,stability and consistency.The interlayer bonding strength and continuous gradient performance of functionally graded parts can be improved by introducing a two-step curing strategy with the aid of constrained sacrifice layer.(2)The experimental platform was designed and built.The influence of the printing layer thickness on the functionally graded materials was explored.It was found that the functionally graded materials layer with good surface finish could be printed when the constraint sacrificial printing layer thickness was equal to the functionally graded materials printing layer thickness,and the printing speed was equal to the discharge speed for functionally graded materials.The effects of printing parameters(extrusion speed,printing speed,line spacing)on the thickness of printing layer were studied,and the following rules were obtained by studying printing process parameters:whether it is printing low-viscosity material system(UV Curable Resin),or printing high-viscosity material system(PDMS),the printing speed or line spacing gradually increases,the printing layer thickness gradually decreases.With the increase of extrusion speed,the printing layer thickness gradually increases.The delivery delay problem of the material mixing ratio was studied,and the total delay volume was optimized by testing the mass flow rate of the discharge port.(3)A simulation study on homogeneous UV Curable Resin insulators and gradient material insulators shows that the electric field distribution of dielectric functionally graded insulators is optimal,which is more suitable for high-voltage environments.The UV Curable Resin/Graphene dielectric functionally gradient insulators with low viscosity material system are prepared by using the technique,and their electrical properties were tested.The experimental results show that the dielectric constant gradually increases with the increase of the graphene content.Meanwhile,due to the enhancement of the interface polarization,the loss factor also gradually increases.With the increase of Graphene content,the number of internal carriers in the dielectric functional gradient structure increases,which leads to the decrease of resistivity.Compared with the homogeneous insulation,the surface flashover strength gradually increases with the increase of Graphene content under AC or DC voltage when gradient insulation is used,and the improvement amplitude is more than 14%.(4)Two post-processing methods of stress and displacement are used for finite element analysis to explore the unique advantages of the functionally graded structure,and determine the optimal thickness of the printing layer.The PDMS/Al₂O₃ variable stiffness functionally gradient three-dimensional structure of the high-viscosity material system is prepared by this technology.The micro composition of two different gradient sections was analyzed,the results show that the change curve of the mass fraction of Al element is basically the same,and presents a continuous linear change with the gradient change of three-dimensional structure.The hardness gradually increases with the change of Al₂O₃ content,and the side with the highest content has doubled than a single PDMS material.In conclusion,the integrated manufacturing of functionally graded material-structure based on multi-material 3D printing and constraint sacrificial layer has the advantages of high universality,accurate control of the printing shape,high consistency,and excellent interlayer bonding performance.