熔融沉积成型过程传热研究及其数值模拟

发布时间：2018-07-11 16:19

本文选题：熔融沉积成型 + 热传导方程组　；参考：《昆明理工大学》2017年硕士论文

【摘要】：熔融沉积成型(FDM)技术是近几十年来在国内外应用逐渐广泛的一种快速原型制造技术,可以较好地适应制造领域竞争的全球化,用户需求的个性化和多样化,降低生产成本,提高生产效率,快速响应市场的变化需求。熔融沉积成型技术是基于离散/堆积原理,由二维截面逐层成型三维实体,易产生阶梯效应,产生翘曲变形等缺陷。成型过程中温度场的变化情况与应力场及应变场等直接相关,对翘曲变形等缺陷有重要影响,成型过程的传热分析是非常有必要的。成型过程中,表面换热系数是传热分析研究的一个必不可少的边界条件。目前,对熔融沉积成型过程中表面换热系数的研究较为匮乏,而不准确的换热系数严重地影响传热过程的分析研究,进而严重地影响各种缺陷的分析研究。熔融沉积成型过程中表面换热系数的研究已经势在必行。本文基于热力学第一定律和能量守恒定律以及其他相关理论,对熔融沉积成型过程传热问题进行分析研究,建立了相关的数学模型,基于有限差分法和传热学等相关理论,考虑了材料热物理性能参数变化以及内热源和性态转变潜热的影响,推导出熔融沉积成型过程的传热控制方程组。本文对传热控制方程组进行有限差分格式替代,结合非线性迭代估算原理,提出了熔融沉积成型过程表面换热系数的反问题求解思路,利用MATLAB软件编写出熔融沉积成型过程表面换热系数的反求程序,求解出表面换热系数随时间和温度的变化规律,以及有限差分划分不同节点处温度随时间的变化值。在成型实验过程中,利用温度采集系统测出成型件一些节点位置的温度值,通过比对验证与反求程序中相同节点处温度计算值与实测值之间的关系,得出反求程序的合理性和有效性。本文通过对熔融沉积过程成型特点的分析,提出合理假设,建立有限元模型,对熔融沉积成型过程进行传热分析。利用ANSYS有限元分析软件中“生死单元”技术,结合成型实验过程中实际的扫描方式和扫描速度,通过APDL参数化设计语言进行编程,并将求解得到的表面换热系数作为边界条件代入,求解出模型的温度场变化情况,不同时刻的温度梯度分布图,以及不同节点处温度随时间变化情况,对应力场和应变场等提供了一定的理论依据。模拟结果与实际情况较为相符,表明所求表面换热系数有效。
[Abstract]:Fused deposition molding (FDM) is a kind of rapid prototyping technology which has been widely used in recent decades. It can adapt to the globalization of manufacturing competition, the individuation and diversification of user demand, and reduce the production cost. Improve production efficiency and respond quickly to changing market demands. The melt deposition technology is based on the discrete / stacking principle. The 3D solid is formed by two dimensional cross section layer by layer. It is easy to produce step effect and warp deformation and so on. The variation of temperature field is directly related to the stress field and strain field, and has an important effect on the warping and deformation. It is necessary to analyze the heat transfer during the molding process. The surface heat transfer coefficient is an essential boundary condition for heat transfer analysis. At present, the study of surface heat transfer coefficient in the process of melt deposition molding is relatively scarce, but the inaccurate heat transfer coefficient seriously affects the analysis and research of heat transfer process, and then seriously affects the analysis and study of various defects. It is imperative to study the surface heat transfer coefficient in the process of melt deposition forming. Based on the first law of thermodynamics, the law of conservation of energy and other relevant theories, this paper analyzes and studies the heat transfer in the process of melt deposition molding, and establishes the relevant mathematical model, which is based on the theory of finite difference method and heat transfer, etc. The heat transfer control equations of the melt deposition molding process are derived considering the change of the material thermal physical properties parameters and the effects of the internal heat source and the latent heat transfer of the property state. In this paper, the finite difference scheme is used to replace the heat transfer control equations. Combining with the nonlinear iterative estimation principle, the inverse problem of surface heat transfer coefficient in the process of melt deposition molding is proposed. The inverse program of surface heat transfer coefficient in melt deposition molding process is compiled by using MATLAB software. The variation law of surface heat transfer coefficient with time and temperature and the variation value of temperature with time at different nodes are solved. In the process of forming experiment, the temperature values of some nodes are measured by the temperature acquisition system, and the relationship between the calculated and measured values at the same node in the program is verified by comparison. The rationality and validity of the reverse procedure are obtained. Based on the analysis of the forming characteristics of the melt deposition process, a reasonable hypothesis is put forward and a finite element model is established to analyze the heat transfer of the melt deposition forming process. Using the technology of "birth and death element" in ANSYS finite element analysis software, combined with the actual scanning mode and scanning speed in the process of forming experiment, the programming is carried out by APDL parameterized design language. The calculated surface heat transfer coefficient is used as boundary condition to calculate the temperature field of the model, the temperature gradient distribution at different time, and the temperature variation at different nodes with time. The corresponding force field and strain field provide some theoretical basis. The simulation results are in good agreement with the actual situation and show that the calculated surface heat transfer coefficient is effective.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH16

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