【作者】 孙明宇；

【导师】 姜世杰；

【作者基本信息】 东北大学 ， 机械工程（专业学位）， 2021， 硕士

【摘要】 熔丝成型(Fused filament fabrication,FFF)技术作为快速成型技术之一,具有成本低廉、制造简单、几乎无设计限制等优点,被广泛地应用在汽车、航空航天、医疗、电子等各个重要领域。然而,逐层累加的成型方式致使FFF产品普遍存在气孔、夹杂、层间分离等缺陷问题,导致其动力学性能远逊于传统加工方式生产的工件,严重阻碍了该技术的进一步发展。随着工作环境越来越严苛,尤其是在动态循环载荷的作用下,亟需对FFF产品进行更为实际的动力学分析以准确判定和预测成型零件的稳定性和可靠性,因此,开展FFF薄板结构的动力学特性及其改进研究具有重要的科学意义。本文通过对普通和利用振动加工的FFF薄板分别展开实验和理论研究,以确定FFF薄板动力学特性的准确预估方法以及利用振动加工对其进行改进的可行性和有效性。具体分为以下四个部分:(1)以FFF薄板为研究对象,实验研究了不同过程参数对FFF薄板动力学特性的影响规律。具体包括:利用D-FORCE V2FFF设备制备了不同过程参数(打印速度、挤出温度和填充率)作用下的薄板样件;然后通过自主搭建的模态实验系统,获取了薄板样件的固有特性和振动响应;通过对比分析不同样件的动力学特性参数,揭示了不同过程参数的影响规律。实验结果表明,随着打印速度、挤出温度的降低或填充率的增加,FFF薄板的固有频率增加、振动响应降低,动力学性能得到提升。(2)对FFF薄板动力学特性进行了解析研究。具体包括:考虑FFF薄板的分层和正交各向异性等特点,基于正交多项式法对FFF薄板进行了解析研究;通过Rayleigh-Ritz法、频域振动方程以及半功率带宽法分别求解了 FFF薄板的固有特性、振动响应以及阻尼比,进而提出了理论分析FFF薄板动力学特性的具体流程;将理论分析结果与上述实验结果进行了对比,验证了解析模型的正确性;此外,针对该解析模型完成了敏感性分析,确定了材料参数(弹性模量、泊松比和密度)对FFF薄板动力学特性的影响规律。(3)提出了利用振动改善FFF薄板动力学特性的方法,并实验研究了不同形式振动(不同频率或幅值)对FFF薄板动力学特性参数的影响规律。针对普通D-FORCE V2 FFF设备进行了改装研究,搭建了振动式FFF系统;然后利用该系统制备了不同形式振动加工的FFF薄板样件,并完成了模态实验确定了其固有特性和振动响应等参数;通过对比分析不同形式振动加工的FFF样件的实验结果,揭示了不同振动频率或幅值对FFF薄板的固有特性、振动响应和阻尼比等动力学特性参数的影响规律。实验结果表明,利用振动加工可以提高FFF薄板的动力学性能,且随着振动频率或幅值的增加,FFF薄板的动力学性能可得到进一步提升。(4)完成了利用振动加工的FFF薄板动力学特性的解析研究,阐明了改进机理。以利用振动加工的FFF薄板为研究对象,创建了动力学解析模型,并完成了利用不同形式(不同频率或幅值)振动加工的FFF薄板动力学特性参数的理论辨识;将理论分析与实验结果进行对比,验证了该解析模型的正确性,并进一步确定了不同振动频率或幅值对FFF薄板的固有特性和振动响应等动力学特性参数的影响规律,阐明了利用振动改善FFF薄板动力学特性参数的机理。本文完成了 FFF薄板动力学特性的解析和实验研究,确定了利用振动改善FFF薄板动力学特性新方法的可行性,并阐明了相应机理。相关的研究成果可以为FFF技术的进一步发展提供理论参考和技术支持。更多还原

【Abstract】 As one of the rapid prototyping technologies,the fused filament fabrication(FFF)technology has the advantages of low cost,simple manufacturing process,and almost no design restrictions.It is widely used in aviation,aerospace,medical and other important fields.However,due to the defects of the fused forming process,such as the internal voids of the FFF parts and the absence of interlayer pressure caused by layer-by-layer accumulation,the dynamic characteristics of the FFF parts is far inferior to the traditional processing parts,which seriously hinders the further development of FFF technology.As the working environment becomes more and more severe,especially under the action of dynamic cyclic load,it is urgent to conduct a more realistic dynamic analysis of FFF parts to accurately determine and predict the stability and reliability of FFF parts.Therefore,it is of great scientific significance to carry out the study on the dynamic characteristics and improvement of the FFF thin plate structure.This paper conducts experimental and theoretical study on ordinary and vibration-processed FFF plates respectively,to determine the feasibility and effectiveness of using vibration processing to improve the dynamic characteristics of FFF thin plates.This study is mainly classified to four chapters:(1)Taking the polylactic acid(PLA)material FFF plate as the research object,the influence of different process parameters on the dynamic characteristics was tested,including the plates with different process parameters(printing speed,extruder temperature and filling rate)were prepared by D-FORCE V2 equipment.Then through the self-built modal experiment system,the natural frequency and resonant response of the FFF thin plate were obtained through the identification parameter,the influence of different process parameters on the dynamic characteristics of the FFF plate was studied through experiments.Experimental results show that with the decrease of printing speed,extruder temperature or increase of filling rate,the natural frequency of the FFF plate increases,the resonant response decreases,and the dynamic performance is improved.(2)The dynamic characteristics of the FFF plate were analyzed analytically.Considering the property of lamination and orthogonal anisotropy,the FFF plate was theoretically modeled based on the orthogonal polynomial method.Then,the dynamic characteristics of the FFF plate were worked out by Ritz method,and the resonant response of any point in the fused plate was analyzed by using the frequency domain vibration equation,the damping ratio was analyzed by the half-power bandwidth method.Besides,a specific process for theoretical analysis of the dynamic characteristics of the FFF thin plate was proposed.The comparison between theoretical analysis and the above experimental results verifies the correctness of the analysis model.Sensitivity analysis was completed for the analytical model,and the influence of material parameters(elastic modulus,Poisson’s ratio and density)on the dynamic characteristics of the FFF plate was determined.(3)It was proposed to use vibration to improve the dynamic characteristics of the FFF plate,and the influence of different forms of vibration on the FFF plate was studied through experiments.Refitting the ordinary D-FORCE V2 FFF equipment was carried out,and a vibrating FFF system was built;then the FFF plates of different forms of vibration processing were prepared by the system,and the modal experiment was completed to determine its inherent characteristics and resonant response.By comparing and analyzing the experimental results of FFF plates built with different forms of vibration(different frequencies or amplitudes),the influence of different vibration frequencies or amplitudes on the inherent characteristics,resonant response and damping ratio of the FFF plate was determined.Experimental results show that the use of vibration processing can improve the dynamic characteristics of the FFF plate,and with the increase of the vibration frequency or amplitude,the dynamic characteristics of the FFF plate can be further improved.(4)Completed the analytical study of the dynamic characteristics of FFF plates built with vibration,and clarified the improvement mechanism.Taking the FFF plate built with vibration as the research object,a dynamic analysis model was created,and the theoretical identification of the dynamic characteristics of the FFF plate built with different forms(different frequencies or amplitudes)of vibration was completed.The theoretical analysis was compared with the experimental results to verify the correctness of the analytical model,and further determine the influence of different vibration frequencies or amplitudes on the inherent characteristics and vibration responses of the FFF plate.The mechanism of using vibration to improve the dynamic characteristic parameters of the FFF plate was clarified.This paper has completed the analytical and experimental study of the dynamic characteristics of the FFF plate,determined the feasibility of using vibration to improve the dynamic characteristics of the FFF plate,and clarified the corresponding mechanism.Related research results can provide theoretical reference and technical support for the further development of FFF technology.更多还原