Fundamental Research On Process Of High-performance Additive Manufacturing For Continuous Fiber Reinforced Composites

Continuous fiber reinforced polymer composites present wide potential applications in aerospace,automobiles,ships and other fields,mainly due to the advantages of high strength,light weight together with excellent fatigue and corrosion resistance.Additive manufacturing technology is a threedimensional rapid free forming manufacturing technology,which can realize the integrated rapid forming of complex components.Using additive manufacturing technology to fabricate continuous fiber composites can give full play to the performance advantages of composites and the forming advantages of additive manufacturing,which can satisfy the development needs towards lightweight,precise shape control,short cycle,high performance,high precision and integrated manufacturing.However,several technical bottlenecks including difficult impregnation,weak interface bonding,poor interlayer performance and low precision in the manufacturing of continuous fiber reinforced plastics are existed.Through the combination of theoretical analysis,experimental investigation and simulation research,the present paper systematically analyzed the forming mechanism of continuous carbon fiber reinforced PEEK composites(CCF/PEEK)additive manufacturing.Besides,several fundamental processes including filament fabrication,additive manufacturing and laser-assisted preheating were investigated,and corresponding manufacturing equipments were developed.The specific research contents are list as follows:(1)In order to promote the impregnation behavior of the continuous carbon fiber bundles in the high-viscosity thermoplastic resin,the melting impregnation and interface bonding mechanism was analyzed.The melting impregnation model based on bending channel was established and the influencing mechanism of different processing parameters were explored.The results indicated that wedge-shaped area between the curved channel wall and the fiber bundles can form local melting pressure and promote the resin to penetrate into the fiber bundles.With the increase of melting viscosity and traction speed,the melting pressure was improved while the impreganation distance decreased.Based on the mechanical testing and microscopic characterization,the mechanical performance and failure modes of the filaments were investigated.It was found that as the mould temperature increased and traction speed decreased,the thermal stability and tensile strength of the filaments were gradually improved,and the internal dry fiber and pore defects were reduced.(2)To idnetify the influencing mechanism of processing parameters on the performance,the theoretical model of continuous fiber reinforced composites additive manufacturing was establised,and the remelting impregnation,thermo-mechanical coupling deformation and interlayer adhesion mechanism were analyzed.Based on the quadratic rotationorthogonal combination design,the regression prediction model was established to identify the effect of processing parameters.The results showed that tensile strength of the printed CCF/PEEK composites was enhanced with the increase of nozzle temperature and bed temperature together with decrease of layer thickness and printing speed.The experimental results indicated that the regression model was accurate and the optimized parameters were reliable.The failure modes of the fractured surface were analyzed,and the failure mechanisms were revealed with both strong interface failure and weak interface failure.The strong interface failure included filament fracture and fiber fracture,while weak interface failure contained inter-channel crack,filament pull-out,interlayer crack,fiber pull-out and inner pores under tensile load.Furthermore,the equipment for continuous fiber additive manufacturing was constructed,and the high-performance additive manufacturing method under the multiple thermo-mechanical coupling effect was obtained.(3)To improve the interlaminar performance,a laser-assisted preheating method based on infrared temperature measurement and feedback was proposed in this paper.The finite element model was established to investigate temperature distribution and analyze the temperature variation progess.The simulation results demonstrated that the maximum temperature and heat affected zones gradually increased with the increase of preheating temperature and the decrease of printing speed.Based on the full-factoral experimental design,the effects of different processing parameters on the interlaminar strength and failure modes were investigated.It was concluded that the interlaminar strength of laser preheated CCF/PEEK composites was significantly improved with up to 157%improvement than that of unpreheated samples.With the increase of preheating temperature and printing speed,the interlaminar strength first increased and then decreased.Through the analysis of cross-section morphology,the interlayer strengthening mechanism was revealed,which demonstrated that the application of laser can realize the preheating of surface resin,internal fiber impregnation and pore filling between layers,thus improving the interlayer adhesion and shear strength.(4)Aiming at improving the forming accuracy of printed parts,the adaptive slicing algorithm based on size error compensation was established and the effectiveness of the slicing algorithm was verified.It was found that this method can improve the dimensional accuracy and surface quality of formed specimens.The theoretical model of warpage deformation was established and the mechanism of restraining warpage deformation was analyzed.It was shown that decreasing layer thickness and increasing ambient temperature and fiber content can reduce warpage deformation.With the characterization of surface morphology for the fabricated specimens,it was concluded that increasing nozzle temperature together with reducing printing speed and interlayer thickness reduced the surface roughness and improved surface quality.The results in this paper effectively solved the key technical problems of difficult impregnation,weak interface bonding,poor interlayer performance and low precision of formed parts.The gained results and conclusions promoted the development of continuous fiber reinforced additive manufacturing technology,which presented important guiding significance for the low cost,short cycle and integrated forming and manufacturing of complex composite components in aerospace and other fields.