熔融沉积成型过程温度场和应力场研究

发布时间：2018-02-14 19:55

本文关键词： 熔融沉积成型生死单元翘曲变形应力场温度场　出处：《昆明理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：熔融沉积是近几十年发展起来的一种重要的快速成型制造技术,在药物医疗、产品设计与开发,模具制造与设计,艺术创作中应用广泛。熔融沉积成型技术中,由于冷却固化的丝材与高温丝材粘结的工艺特点,使得沉积层之间产生较大温度梯度。导致热塑性丝材因冷却收缩不一致而产生内应力。应力会导致制件翘曲变形,开裂,影响制件的精度和质量。因此,本文基于简化假设建立应力翘曲变形模型。结合工艺,采用ANSYS对成型过程中的温度场和应力场进行数值分析,并进行温度测量实验。实现理论,数值模拟,实验的相互印证。这不仅具有重要的理论意义,还具有重要的应用价值。本文主要研究内容为以下几点:(1)本文首先对喷头温度场进行了数值模拟,结果表明喷头为稳态温度场,喷出熔融丝材的温度为一恒定值。确定了熔融沉积成型瞬态温度场的热源载荷类型。(2)建立了熔融成型过程数值模拟有限模型,分析了 ABS材料属性和本构关系。运用APDL语言和生死单元技术对扫描路径进行设计,对载荷和边界条件的加载方式进行了设置。使得数值模拟过程能实现材料沉积,热源移动,边界变化。与真实加工过程相一致。(3)从分子角度分析了丝材粘结机制,研究了应力和翘曲产生原因以及界面温度对应力的影响。基于内应力产生机理,建立了简化的应力模型和翘曲变形模型,定量地分析出界面温度和其他因素对应力和翘曲变形的影响。为复杂的温度场和应力场分析以及工艺分析提供了方向。(4)在5mm/s,10mm/s,15mm/s扫描速度下对熔融沉积过程的温度场进行数值模拟,结果表明了沉积过程中成型件温度场一般分布规律。沉积层上节点的温度曲线变化呈现一定规律性,并受到成型室温度、制件大小、沉积速度,对流换热等工艺参数的影响。其中保证这些工艺参数都合理的情况下,扫描速度越慢,界面温度越高。在温度场分析的基础上,基于热弹塑性理论进行应力场耦合分析,分析了应力场分布特点。得到了在不同扫描速度下制件应力的大小,扫描速度越慢,应力越小。再结合温度场结果,与应力模型相互印证。(5)最后,设计了熔融沉积成型过程测温实验方案。测量了喷头工作时的温度值。利用数据采集系统,在不同扫描速度下,采集了沉积过程中第一层中央位置温度变化数据。并将实测结果处理后与模拟温度曲线进行对比,实验与模拟结果相符合。
[Abstract]:Melt deposition is an important rapid prototyping technology developed in recent decades. It is widely used in medicine, product design and development, mold manufacture and design, art creation. Due to the process characteristics of bonding between the cooling and solidified wire and the high temperature wire, there is a large temperature gradient between the deposited layers, which leads to the internal stress of the thermoplastic wire due to the inconsistency of cooling and shrinkage. The stress will lead to the warping and cracking of the workpiece. Therefore, based on the simplified hypothesis, the stress warping model is established. Combined with the process, the temperature field and stress field in the molding process are analyzed numerically by ANSYS, and the temperature measurement experiments are carried out to realize the theory. Numerical simulation, experimental verification, not only has important theoretical significance, but also has important application value. The main contents of this paper are as follows: 1) the temperature field of nozzle is numerically simulated in this paper. The results show that the nozzle is a steady temperature field and the temperature of the fused wire is a constant value. The heat source load type of the transient temperature field of the melt deposition molding is determined. The finite model of numerical simulation of the melt forming process is established. The properties and constitutive relations of ABS materials are analyzed. The scanning path is designed by using APDL language and birth and death element technology, and the loading modes of load and boundary conditions are set up. The process of numerical simulation can realize material deposition and heat source movement. Boundary change. Consistent with the true processing process, the bonding mechanism of the wire is analyzed from the molecular perspective, and the causes of stress and warpage are studied, as well as the influence of interfacial temperature on the stress. A simplified stress model and a warpage model are established. The effects of interfacial temperature and other factors on stress and warpage deformation are quantitatively analyzed. The results show that the temperature field of the forming parts is generally distributed in the deposition process, and the temperature curve of the nodes on the deposit layer shows a certain regularity, and is affected by the temperature of the molding chamber, the size of the parts, and the deposition rate. The effect of the process parameters, such as convection heat transfer, on the condition that these parameters are reasonable, the slower the scanning speed is, the higher the interface temperature is. Based on the analysis of temperature field, the stress field coupling analysis is carried out based on thermoelastic-plastic theory. The characteristics of stress field distribution are analyzed. The size of the stress of the workpiece is obtained at different scanning speeds. The slower the scanning speed, the smaller the stress. Finally, combining the results of temperature field with the stress model, the results are verified with the stress model. The experimental scheme of temperature measurement in melt deposition molding process was designed. The temperature value of nozzle was measured. The data acquisition system was used to measure the temperature at different scanning velocities. The temperature variation data of the first layer in the process of deposition are collected and the measured results are compared with the simulated temperature curves. The experimental results are in good agreement with the simulation results.
【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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