Study On Key Technology Of FDM Additive Manufacturing For Fiber Reinforced Heat Resistant Resin Composites

Heat-resistant resin has more excellent thermal properties than ordinary resins,which has very broad application prospect in aerospace,electronics,automotive,chemical and other fields.The lightweight and high performance characteristics of heat-resistant resin are more prominent especially after combining with fiber.Moreover,fused deposition molding(FDM)applied to fiber/resin composites can solve the problems of complex processing,long production cycle and difficult fabrication of complex parts of traditional fiber/resin composites.In this paper,a typical heat-resistant resin of PEEK was selected as the research object.However,PEEK has many technical bottlenecks used in FDM-3D printing due to its characteristics of high melting temperature and difficulty in forming,such as the manufacturing capacity of FDM-3D printing equipment,continuous fiber laying and path planning process,molding process control,and the fiber/resin interface combination,etc.To solve these problems,firstly,based on the characteristics of FDM-3D printing heat-resistant resin and continuous fiber,the FDM-3D printing nozzle and continuous fiber cutting mechanism were designed,the FDM-3D printer and process planning software of continuous fiber/heat-resistant resin composites were also developed.Secondly,study on FDM-3D printing short/continuous fiber reinforced heat resistant resin PEEK was carried out.The control strategy on mechanical properties and porosity was put forward.The multi-scale mechanism of FDM-3D printing process on the porosity of printed parts from microscale to macroscale was revealed.A prediction model for its mechanical properties was proposed and verified.Finally,aiming at the problems of poor toughness and weak interlayer bonding performance of FDM-3D printed fiber/heat-resistant resin composites,the corresponding toughening and reinforcing strategies were proposed.The fiber/heat-resistant resin composite components with low porosity and high strength were prepared.This study can provide a flexible manufacturing method for fiber/heat-resistant resin composites,which has good theoretical significance and practical engineering value.The main research contents are as follows:The preparation process of FDM-3D printed short fiber/PEEK composites was carried out.CF/PEEK and GF/PEEK composite filaments with fiber content of 5wt%-15wt%were prepared.The micromorphology,porosity and thermal properties of composite filaments were analyzed.Experimental research on FDM-3D printing composite filaments with different composition was carried out.CF/PEEK filament with fiber content of 5wt%was selected according to the mechanical properties,porosity and surface quality.The effects of nozzle temperature,plateform temperature,printing speed and layer thickness on tensile strength,flexural strength and impact strength of 5wt%CF/PEEK were studied using response surface method.The effect of process parameters and their interaction on mechanical properties was analyzed.The optimal FDM-3D printing parameters were determined by using multi-objective optimization method:the nozzle temperature of 419℃,the plateform temperature of 277℃,the printing speed of 5mm/s,and the layer thickness of 0.1mm.The comprehensive mechanical properties of FDM-3D printed 5wt%CF/PEEK are the best with tensile strength of 96.8MPa,flexural strength of 167.9MPa,and impact strength of 38.2kJ/m2.The preparation process of FDM-3D printed continuous fiber/PEEK composites was carried out.FDM-3D printing prototype Fibresin200 and continuous fiber cutting mechanism were designed.Considering the continuous fiber cutting scene,cutting instructions and path planning,the slicing software was developed,which can meet the requirements of FDM-3D printing continuous fiber/heat-resistant resin.In order to verify the printing capacity of the equipment,the experiments under different FDM-3D printing parameters and fiber laying process parameters were carried out.The FDM-3D printing parameters were optimized based on the tensile and interlaminar shear properties of continuous fiber/PEEK composites.With a nozzle temperature of 295℃,plateform temperature of 240℃,and printing speed of 3mm/s,the effects of fiber layers,co-contour added turns,filling angle and filling density on mical properties and fracture failure mechanism were explored.Forming mechanism and property prediction of FDM-3D printed fiber/PEEK composites were studied.The differences between FDM-3D printing and traditional injection molding on fiber/PEEK composites were analyzed.A prediction model of mechanical properties considering porosity was proposed.The uncertainty of microstructure changes caused by FDM-3D printing parameters was explained.The functional relationship between the process parameters and the intra-bead/inter-bead porosities was obtained using RSM.A mathematical model of the relationship between process parameters,microstructure and mechanical properties was established.Based on multi-scale mechanical analysis from microscale to macroscale,the tensile modulus prediction of FDM-3D printed fiber/PEEK composites was realized.The reliability of the model was verified by a series of experiments.Toughening and strengthening methods for FDM-3D printed fiber/PEEK composites were studied.Aiming at the defect of FDM-3D printed short fiber/PEEK composites with poor toughness,a method of single-nozzle FDM-3D printing gradient composite based on welding filament was proposed.The multi-material gradient FDM-3D printing were realized using short fiber/PEEK composites with fiber content of 5wt%and PEEK,which not only ensures good interlayer bonding performance,but also increases the elongation at break by 150%.Based on the advantages of welding filament FDM-3D printing,the gradient design of composition and structure on the transition interface was proposed.The comprehensive mechanical properties of the gradient composites prepared by PEEK and 15wt%short fiber/PEEK were improved by 12%.The toughening and strengthening mechanism of FDM-3D printed short fiber/continuous fiber heat-resistant resin composites by heat treatment process was revealed.The heat treatment temperature and time were optimized,and the optimal heat treatment process parameters were 250℃-6h.The ILSS of short fiber/PEEK and continuous fiber/PEEK increased by 16%and 85%respectively compared with untreated samples.