| 4D printing is an additive manufacturing technology.Through the active design of materials or structures,the shape,performance and function of components can achieve controllable changes in time and space.Subversive manufacturing technology has become a research hotspot for scholars at home and abroad.In recent years,researchers mostly use temperature driving,electric driving and other driving forms as the main research ideas of external stress conditions,so that components can get the"intelligent"effect of deformation,denaturation or function change.However,when these intelligent components produce the expected performance changes,they cannot avoid the interference of the external environment on themselves.In other words,the component requires the outside world to produce responsive changes to its direct contact.Therefore,the components have strict requirements on the environment of driving deformation,which also restricts the application range of smart materials.In this paper,the external stress condition for deformation of smart materials is magnetic drive,which can avoid direct contact between the intelligent component and the driving source.By adjusting the driving source to generate periodic changes of the magnetic field,thus achieving controllable deformation of intelligent components,the effect of"intelligence"is achieved.This article uses the additive manufacturing technology of selective laser sintering(SLS),according to the selected new type of magnetic composite material system.The parameter process is optimized,the experimental steps are formulated in detail,and the expected results are obtained,which can generate a controllable deformation of the external magnetic shaped parts.This subject's research on the magnetic composite system is mainly divided into two directions:the microscopic structural characteristics and macroscopic evolution law of deformation performance.The specific research content and results are as follows:(1)Thermoplastic polyurethane(TPU)powder and neodymium iron boron(NdFeB)powder were selected as the composite matrix of laser selective sintering.The initial temperature of pre-laying is 115?,the time interval of pre-laying is 20 s,and the thickness of the powder bed is 2.4 mm,this set of parameters keeps the forming process stable.For 20%,30%,and 40%gradient composite powders,the print temperatures are set to 125?,128?,and 130?,respectively.After each group finished printing,they all obtained shaped parts that meet the expected effect,and the shaped parts also maintained basic mechanical strength.(2)The microstructure characteristics of shaped parts are studied.By studying the particle size of the composite material,the evolution law of particle size of composite powder is obtained,and judge the performance of the experimental results at different particle sizes in the formed parts.In the analysis of the results,the average particle size of NdFeB powder was the smallest among all samples,which is 34.8?m.The average particle size of 20%,30%,and40%NdFeB composite powders are 79.2?m,64.1?m,and 60.7?m,respectively.The average particle size decreases with the increase of NdFeB content,and less than 100?m,can get better printing results.The morphological characteristics using scanning electron microscope were observed to obtain the powder mixing.Mechanical mixing is suitable for the material system,which can achieve the expected properties of the material after forming;Using infrared spectroscopy and X-ray diffraction analysis,the composition of each part in the material system was speculated,mainly Fe_xNd_y,Fe_xO_y,C and other compounds.The main elements such as Fe,C,and O have not changed significantly.The evolution of chemical groups before and after forming is mainly the stretching vibration of C-C,N-H,C=O and the bending vibration of C-N-H.It is determined that the material SLS process is the bonding behavior of the material itself,eliminating the possibility of chemical reactions.The properties of the shaped parts maintain the corresponding functions of the two different component materials.(3)The properties of the shaped parts are studied,and the deformation laws of the shaped parts are revealed from the two physical characterization methods of mechanics and magnetism.Through the tensile test,the stress-strain curves of the three experimental samples were obtained.After comparative analysis,when the NdFeB content in the shaped part was30%,the shaped part had the largest strain with the value of 87%,and the stress reached 2.8MPa.The ultimate stress of the 20%NdFeB composite part is the largest,reaching 3.0 MPa,and the strain is less than 75%.The stress and strain of the 40%NdFeB composite part are the smallest,1.9 MPa and 66%,respectively.After magnetization,the magnetic properties were analyzed.The magnetization of the molded parts continues to increase with the increase of the content of NdFeB.The magnetization values of 20%,30%,and 40%NdFeB molded parts are1.4 m T,2.5 m T,and 5.0 m T,respectively,which are positively correlated in general.The magnetic properties of 40%NdFeB composite parts are the best,when the strength of the magnetic field given by the outside is large,and the deformation amount exceeds 1.2 mm.The magnetic properties of the shaped parts are also related to many factors,and changing various environmental variables will have a relevant effect on the deformation of the shaped parts.In this paper,magnetic composite materials were prepared,and the combination of magnetic materials and laser-selective sintering results in a 4D printed component driven by magnetic drive.It supplements the material system for the research and manufacture of magnetic intelligent components for 4D printing,and studies the microstructure and macroscopic characterization of the material system from various aspects. |
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