多组元金属粉末选择性激光烧结数值模拟及试验研究

1、南京航空航天大学硕士学位论文 i 摘 要 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

2、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。 关键词：快速原型，选择性激光烧结，ANSYS，数值模拟，温度场，应力场 多组元金属粉末选择性激光烧结数值模拟及试验研究 ii ABSTRACT As an important branch of Rapid prototyping (RP), Selective Laser Sintering (SLS) is attractive to many researchers in manufacturing for its wide use of m etal, polymer, ceramic and other powder in the sintering. However, “ balling” , warping and cracking problems associ

3、ated 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

4、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 distri

5、bution 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

6、 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 i nduced 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. 南京航空航天大学硕士学位论文 iii A multi- component metal powder system mixed by pure Ni, pre- alloyed CuSn and additive Cu

7、P powder was developed for the exclusive use of SLS. Through a series of SLS experiments, some required- shaped laser sintered parts with sound densification are obtained. The experimental results show a good agreement with the corresponding simulating results. The scanning electron microscope (SEM) results show that the sintered structure was consisted of the partially melted Ni and the rapid solidified CuSn, with the bonding mechanism of this process being liquid phase sintering (LPS). Key Wor

8、ds: Rapid prototyping (RP), Selective laser sintering (SLS), ANSYS, Numerical simulation, Temperature field, Stress field 承诺书 本人郑重声明：所呈交的学位论文，是本人在导师指导下，独立进行研究工作所取得的成果。 尽我所知，除文中已经注明引用的内容外， 本学位论文的研究成果不包含任何他人享有著作权的内容。 对本论文所涉及的研究工作做出贡献的其他个人和集体， 均已在文中以明确方式标明。 本人授权南京航空航天大学可以有权保留送交论文的复印件， 允许论文被查阅和借阅， 可以将学位论文的全部或部分内容编入有关数据库进行检索，可以采用影印、缩印或其他复制手段保存论文。 （保密的学位论文在解密后适用本承诺书） 作者签名： 日 期： 南京航空航天大学硕士学位论文 vii 图表清单 图清单 图 1.1 CAD 系统与 RP 系统间的数据传输 3 图 1.2 选择性激光烧结工艺原理示意图 3 图 1.3 粉床传热示意图 9 图 1.4 粉末颗粒间热传导示意图 10 图 1.5 烧结件“ 球化” 现象 11 图 1.6 典型翘曲实物图 11 图 1.7 典型开裂实物图

《多组元金属粉末选择性激光烧结数值模拟及试验研究》由会员豆浆分享，可在线阅读，更多相关《多组元金属粉末选择性激光烧结数值模拟及试验研究》请在金锄头文库上搜索。