Research On Additive Manufacturing Of High Performance Thermoplastic Polyimide And Its Composites

3D printing technology is used for rapid processing and manufacturing,which can produce parts with complex geometric shapes according to computer design.Due to the inherent limitations of the mechanical properties and functions in3D-printed pure polymer parts,it is necessary to develop high-performance printable polymer composites.3D printing offers many advantages in the manufacture of composite materials,including high precision,low cost and customized complex shapes.The 3D printing technology of thermoplastic polyimide composites and the mechanical,electrical and thermal properties of thermoplastic polyimide composites parts are studied.The potential applications of thermoplastic polyimide composites in biomedical,electronic and aerospace engineering are reviewed in this paper.The manufacturing methods and properties of thermoplastic polyimide(TPI)composites reinforced by particles,fibers and nano-materials are introduced.These researches are pointed out to promote future research that is the development of 3D printing materials and 3D printing equipment.Thermoplastic polyimide(TPI)has a narrow processing temperature range,high viscosity,and high viscous flow temperature(Tf).These properties lead to difficulties in 3D printing and traditional forming with TPI owing to deformation caused by thermal stress,stratification,and other problems.In this paper,a high-temperature 3D printer was developed,and 1.75mm thermoplastic polyimide3D-printed filaments was successfully prepared.The thermal stability of TPI raw materials and 3D printing filaments were analyzed in this study.Relationships between the T_f of the 3D printing filament and the starting printing temperature were studied.The influence of the 3D printing temperature on the interlayer bonding force of a 3D printed part was studied.The appropriate printing temperature range of TPI3D printing was found to be 320-340°C.When the printing temperature was 335°C,the interlayer bonding force was 344.5 N.When the printing temperature was 340°C,the interlayer bonding force decreased to 260.5 N.Manufacturing difficulties,poor strength and foaming result from the high temperature that is used in thermoplastic polyimide(TPI)3D printing and the high viscosity and water absorption by the TPI.To overcome these difficulties,the water absorption of pure TPI 3D printed filaments and short-fiber TPI composites were analyzed.The relationship between the drying time of pure TPI 3D printed filaments and the tensile strength of 3D printed specimens was studied.The effects of 3D printing speeds,layer thicknesses and filling rates on the tensile strength of the 3D printed parts were studied employed pure TPI,original continuous carbon fiber reinforced TPI(OCC)and separated continuous carbon fiber reinforced TPI(SCC).The mechanical properties of the continuous-carbon-fiber reinforced TPI were tested on TPI 3D printed samples with or without continuous fiber reinforcement.The SCC improved the success rate of the continuous-carbon-fiber reinforced TPI by 3D printing and enhanced the interfacial bonding strength between the continuous carbon fiber and the TPI matrix.The tensile strength of the continuous carbon fiber reinforced TPI was 158%higher than that of the OCC.A strong bonding surface formed between the continuous carbon fiber and the TPI plastic matrix.The tensile and bending strengths of the the SCC samples were 214%and 167%higher than those of pure TPI.Existing aerospace metal parts or structural parts have the problems of finite elasticity,large mass,difficult manufacture of complex parts,expensive equipment,narrow range of shielding and electrostatic regulation.This study analyzed the tensile and bending properties of pure TPI 3D printing specimens printed by the nozzles with different diameters.The effects of different carbon nanotube(CNT)contents on the thermal and electrical properties of carbon nanotube composites were investigated.The relationship between the electrical conductivity,tensile properties,bending properties,resistivity and cyclic bending deformation of 3D printed specimens with different carbon nanotube contents was studied.Compared with the 0.4 mm nozzle,the tensile and bending strength of pure TPI specimen printed by a 0.8 mm nozzle were increased by 40%and 20%,respectively.In order to ensure the excellent mechanical and electrical properties of 3D printed composites,3%wt thermoplastic polyimide-carbon nanotubes(TPI-CNTs)composites with appropriate tensile and bending strength were used to print the characteristic structure,and then the relationship between the deformation and conductive resistance was studied.