Part-scale thermal simulation of laser powder bed fusion using graph theory: Effect of thermal history on porosity, microstructure evolution, and recoater crash
Part-scale thermal simulation of laser powder bed fusion using graph theory: Effect of thermal history on porosity, microstructure evolution, and recoater crash
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DOI：
10.1016/j.matdes.2021.109685
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发表时间：
2021-03
影响因子：
8.4
通讯作者：
R. Yavari;Z. Smoqi;A. Riensche;Ben Bevans;Humaun Kobir;H. Mendoza;Hyeyun Song;K. Cole;Prahalada K. Rao
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文献类型：
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作者：
R. Yavari;Z. Smoqi;A. Riensche;Ben Bevans;Humaun Kobir;H. Mendoza;Hyeyun Song;K. Cole;Prahalada K. Rao
激光粉末床熔合（LPBF）过程中缺陷的形成受工件温度场的时空分布（热历史）影响。因此，为了防止裂纹的形成，需要快速和准确的模型，可以预测作为零件形状和加工参数的函数的热历史。在以前的工作中，基于图论的热建模方法被用来预测LPBF部件的热历史，所需的时间少于基于有限元的模型的20%，误差在实验测量的10%以内。目前的工作过渡到使用的图论方法预测缺陷的形成。本文的目的是：（1）应用图论方法预测几个具有不同几何形状但全部构建在单个构建板上的LPBF部件的热历史：（2）将图论热模型与使用原位红外相机进行的实验温度测量进行比较;（3）将从图论方法得到的热历史预测与LPBF部件中的裂纹形成相关联。为了实现这些目标，在开放式架构LPBF平台上同时构建了包含五种不同形状的十五种不同Inconel 718零件（构建时间为9.5小时）。第二，LPBF机器配备有原位红外摄像机，以捕获每个部件在沉积时的逐层表面温度。第三，每个部分的热历史预测与图论的方法，并对实验温度测量模型预测进行评估。第四，在某些测试部分的孔隙度进行了定量与X射线计算机断层扫描，其微观结构的特点是与光学和扫描电子显微镜。结果表明，零件的形状对热历史有显着影响，从而影响构建故障（重涂机崩溃）的发生，孔隙的类型和严重程度，以及微观结构的形态。图论方法正确地预测了导致LPBF在构建时间的一小部分内形成裂纹的热历史趋势-均方根预测误差小于20 °C，计算时间约为5分钟。图论方法有可能作为一种快速的基于物理的方法来指导零件设计和确定合适的工艺参数，以代替昂贵和耗时的经验试错优化，为LPBF从业者服务。
Flaw formation in laser powder bed fusion (LPBF) is influenced by the spatiotemporal temperature distribution – thermal history – of the part during the process. Therefore, to prevent flaw formation there is a need for fast and accurate models that can predict the thermal history as a function of the part shape and processing parameters. In previous work, a thermal modeling approach based on graph theory was used to predict the thermal history in LPBF parts in less-than 20% of the time required by finite element-based models with error within 10% of experimental measurements. The present work transitions toward the use of the graph theory approach for predicting flaw formation. The objectives of this paper are to: (1) apply the graph theory approach for predicting the thermal history of several LPBF parts that have different geometries but were all built together on a single build plate; (2) compare the graph theory thermal model with experimental temperature measurements made using an in-situ infrared camera; and (3) relate the thermal history predictions obtained from the graph theory approach to flaw formation in LPBF parts. In pursuit of these objectives, fifteen different Inconel 718 parts encompassing five different shapes were built simultaneously on an open architecture LPBF platform (build time 9.5 h). Second, the LPBF machine was instrumented with an in-situ infrared camera to capture the layer-wise surface temperature of each part as it was being deposited. Third, the thermal history for each part was predicted with the graph theory approach, and the model predictions were assessed against experimental temperature measurements. Fourth, the porosity in certain test parts was quantified with X-ray computed tomography, and their microstructure was characterized with optical and scanning electron microscopy. The results show that the shape of the part has a significant effect on the thermal history, and thereby influences the occurrence of build failures (recoater crash), type and severity of porosity, and morphology of the microstructure. The graph theory approach correctly predicted the thermal history trends that lead to flaw formation in LPBF within a fraction of the build time – the root mean squared prediction error was less-than 20 °C, and computation time was approximately 5 min. The graph theory method has the potential to serve LPBF practitioners as a rapid physics-based approach to guide part design and identify suitable processing parameters in place of expensive and time-consuming empirical trial-and-error optimization.