Research On 3D Printing Preparation Method Of Variable Stiffness Components Based On Low Melting Point Alloy

Variable-stiffness material can perceive and recognize external stimulation,then convert its own stiffness.The stiffness of the component made by variable stiffness changes at the corresponding position under the stimulation of temperature,electricity,light,etc.Materials with controllable stiffness are widely used in medicine,soft robot,civil engineering,aerospace and other fields.However,most of the main implementation methods of variable stiffness function need external work,resulting in complex and huge structure.Furthermore,there are small variation range,slow response and large mechanical loss.Low melting point alloy(LMPA)maintain strong mechanical at the temperature below its melting point(30-300 °C).When the temperature is higher than its melting point,the mechanical properties change significantly.Utilizing the low melting point characteristics of LMPA and 3D printing,LMPA is compounded with polymer materials or through coaxial extrusion is proposed.Finally,the integrated printing and molding of LMPA variable stiffness components are achieved.In this paper,the function of variable stiffness is realized by the solidliquid phase conversion of LMPA.Based on the basic principle of melt deposition manufacturing(FDM)process,polylactic acid(PLA)/LMPA composites was prepared by single screw extrusion mechanism.The printed product is analyzed from the observation of micro morphology and the characterization of mechanical properties.In additional,from the perspective of printing equipment,a manufacturing method of 3D coaxial printing with thermoplastic material wrapped LMPA is proposed.The 3D coaxial printing preparation technology of LMPA variable stiffness components is studied from three aspects: equipment construction,product characterization and numerical simulation.The main research contents are as follows:(1)A manufacturing method of composites wire rod based on PLA and LMPA is proposed.The function of variable stiffness controlled by temperature is studied.The mechanical properties of printed product are characterized.The reason of the rigid practices changes the mechanical properties is analyzed by the observation of micro morphology.The method of variable stiffness through solid-fluid transformation of LMPA is verified.(2)The control system,heating system and feeding system of coaxial extrusion equipment is designed.The 3D coaxial printing equipment is successfully built finally.The 3D coaxial printing of thermoplastic and LMPA is simulated by hydrodynamics.The temperature,stress,movement condition in the nozzle is studied.The optimum printing parameters of material forming are analyzed.Theoretical basis and reference for 3D coaxial printing experiment is provided.(3)The common FDM printing materials extruded coaxially with LMPA are displayed.The best forming and printing parameters of coaxial extrusion are explored through experiments.The effect of printing parameters on PA/LMPA 3D coaxial printing quality is further explored with examples.(4)The application scenario of variable stiffness structure with 3D coaxial printing is studied.The mechanical properties and fundamental frequency are measured under different temperature.Which open up new direction for further research.