Research On High Temperature-Selective Laser Sintering Of High-Performance Engineering Plastics

High-performance engineering plastics,such as Polyetheretherketone(PEEK),have the advantages of lightweight,high strength and corrosion resistance.Therefore,they have been widely used for the manufacturing of key components in the national strategic fields.However,the traditional manufacturing method has low degree of design freedom and difficulty for the integrated manufacturing of complex structures.As an important branch of Additive Manufacturing(AM)technologies,Selective Laser Sintering(SLS)is of significant advantages for integrated forming of complex structural components.However,the current domestic SLS equipment has low preheating temperature and can only be used for the forming of polymers with low melting points.Warpage deformation is very easy to occur when forming high-performance polymers,which has become an important factor limiting the development of SLS technology in our country.Therefore,in this thesis,the research of High Temperature-Selective Laser Sintering(HT-SLS)with 400 ? preheating temperature is carried out to form high-performance polymers,but the following problems are faced,(1)High temperature equipment:HT-SLS equipment shall meet the requirements of high temperature and its field uniformity in the processing chamber,and provide effective thermal protection for optical system;(2)Powder material:the powder material suitable for HT-SLS needs to meet the requirements of high temperature fluidity,sintering window and other indicators at the same time;(3)Forming mechanism:the understanding of dynamic crystallization behavior during HT-SLS is important for controlling the performance reproducibility and stability,but there is no relevant mechanism research.For the problems above,the following research works are carried out:(1)The HT-SLS equipment with independent temperature control function is constructed.By redesigning the individual-spaced powder feeding and processing chambers,the independent preheating and temperature uniformity control of both chambers can be effectively realized.The processing platform is 125×125×400 mm³and the maximum preheating temperature can reach 400?.The design of height difference and partial overlap between chambers solves the problem of powder transportation and heat dissipation.Morefover,the thermal protection and cooling system with stacked layers is designed to make the optical layouts work in an appropriate temperature range;(2)The PEEK powder material suitable for HT-SLS is prepared by means of high-temperature infrared radiation pre-spreading method.The prepared PEEK powder presents a uniform powder morphology,significantly reduced BET area,spherical trend and wide sintering window 27.26 ?.After the further modification by hexamethyl-disilazane aerosil SiO₂,the Angle of Repose(Ao R)of PEEK powder can be reduced to 31.74°,and the bulk density can be raised to 0.454 g·cm^-3,which can satisfy the requirements of HT-SLS for high temperature fluidity,sintering window and bulk density;(3)Based on the processing and microstructure research of Polycaprolactam(PA6),the research on the forming mechanism of PEEK is carried out.The quasi-isothermal and dynamic non-isothermal crystallization processes involved in HT-SLS are analyzed from the perspective of crystallization kinetics.The sensitivity mechanism of PEEK to the crystallization promotion of Cold Powder Coating(CPC)is found,and the effective processing temperature of 330?is determined through the extrapolated halftime analysis of Hoffman-Lauritzen theory.The maximum tensile strength of PEEK can reach 85.14±4.62 MPa,which presents characteristic radial pattern morphology,as well as more extended benzene planar subunit and cell volume.Based on the research of high temperature equipment,powder material and forming mechanism,the complex structural parts of PEEK are formed,including minimal surface lattice structures and the assembly parts of intervertebral fusion cage.This research will provide theoretical support and effective technical means for additive manufacturing of high-performance polymer parts with complex structures.