论文标题:多组元金属粉末选择性激光烧结数值模拟及试验研究
Numerical and Experimental Investigations on Selective Laser Sintering of Multi-component Metal Powder
论文作者
论文导师 沈以赴,论文学位 硕士,论文专业 材料学
论文单位 南京航空航天大学,点击次数 139,论文页数 118页File Size2781K
2006-03-01论文网 http://www.lw23.com/lunwen_493740422/
Rapid prototyping (RP); Selective laser sintering (SLS); ANSYS; Numerical simulation; Temperature field; Stress field
选择性激光烧结技术(SLS)是快速原型技术(RP)中的一个重要分支,以其选材广泛受到重视。但是,直接用金属粉末激光烧结金属零件还存在一定的不足之处,其中烧结件“球化”、翘曲和开裂现象是制约金属粉末选择性激光烧结应用的主要障碍。因此,本文针对Ni-Cu基多组元混合粉末选择性激光烧结温度和应力应变的变化规律和特点开展了系统深入的数值分析和试验研究。 利用ANSYS有限元软件,建立了Ni-CuSn多组元混合粉末选择性激光烧结过程三维瞬态温度场分析模型。在考虑了相变潜热、对流和随温度变化的热物性参数下,使用APDL参数化语言实现了高斯热源的施加和热源按一定速率的移动。将分析结果与试验结果对比表明,“球化”效应与温度的分布有很大的关系,通过改变工艺参数优化温度场可以有效降低烧结件“球化”效应。 基于温度场的计算结果,采用热力耦合方法,建立了Ni-CuSn多组元混合粉末选择性激光烧结过程应力应变场分析模型。利用“生死”单元技术,模拟了烧结材料由粉末态转变为高温液态继而转变为连续实体的过程。结果表明,优化烧结件结构,提高预热温度,精选基板等措施可以有效避免由应力导致的烧结件翘曲和开裂等现象。 对添加了CuP作为添加剂的Ni-CuSn多组元混合粉末进行了烧结试验研究,获得的结果与数值模拟结果较为吻合。通过扫描电镜对烧结样品分析发现,烧结件的显微组织为微熔Ni颗粒和CuSn快速凝固的混合组织,其成形机制为液相烧结。
As an important branch of Rapid prototyping (RP), Selective Laser Sintering (SLS) is attractive to many researchers in manufacturing for its wide use of metal, polymer, ceramic and other powder in the sintering. However,“balling”, warping and cracking problems associated with metallic SLS have presented serious obstacles that restrict the more extensive applications of SLS technique. To alleviate the defects in metallic SLS, numerical and experimental studies were carried out detailed on the features of temperature field as well as thermal elastic-plastic stress and strain during metallic SLS process. By using the ANSYS software, a finite element model which simulates a real SLS process of a multi-component Ni-CuSn metal powder system was established to calculate the 3D transient temperature field. In the model, the latent heat, convection and temperature-dependent thermal properties were taken into account. A moving Gaussian laser beam was simulated using the ANSYS parametric design language. Comparisons were made between the numerical and experimental results. The results show that, the distribution of temperature during laser sintering process has a great effect on“balling”phenomena of the laser sintered metal part. Optimizing the distribution of temperature, which can be realized by changing laser processing parameters, is an effective way to decrease the“balling”effects. Based on the results of temperature field, a finite element model for analyzing the stress field in SLS process of a multi-component metal powder system was established by using an indirect thermal-mechanical coupling method. A successive transformation of the sintering material from powder morphology to high-temperature liquid phase and, afterwards, to continuous solids was simulated by using a“birth and death”element technique of the ANSYS software. The analysis results show that, the warping and cracking of sintered part which is induced by thermal stress can be efficiently alleviated by optimizing the geometrical structure of the part to be built, enhancing the pre-heating temperature, and well choosing the building substrate.
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