UCLA

Big data plays an important role in the fourth industrial revolution, which requires engineersand computers to fully utilize data to make smart decisions to optimize industrial processes. In the additive manufacturing (AM) industry, laser powder bed fusion (LPBF) and direct metal laser solidification (DMLS) have been receiving increasing interest in research because of their outstanding performance in producing mechanical parts with ultra-high precision and variable geometries. However, due to the thermal and mechanical complexity of these processes, printing failures are often encountered, resulting in defective parts and even destructive damage to the printing platform. For example, heating anomalies can result in thermal and mechanical stress on the building part and eventually lead to physical problems such as keyholing and lack of fusion. Many of the aforementioned process errors occur during the layer-to-layer printing process, which makes in-situ process monitoring and quality control extremely important. Although in-situ sensors are extensively developed to investigate and record information from the real-time printing process, the lack of efficient in-situ defect detection techniques specialized for AM processes makes real-time process monitoring and data analysis extremely difficult. Therefore, to help process engineers analyze sensor information and efficiently filter monitoring data for transport and storage, machine learning and data processing algorithms are often implemented. These algorithms integrate the functionality of automated data processing, transferring, and analytics. In particular, sensor data often takes the form of images, and thus, a prominent approach to conducting image analytics is through the use of convolutional neural networks (CNN). Nevertheless, the industrial utilization of machine learning methods often encounters problems such as limited and biased training datasets. Hence, simulation methods, such as the finite-element method (FEM), are used to augment and improve the training of the deep learning process monitoring algorithm. Motivated by the above considerations, this dissertation presents the use of machine learning techniques in process monitoring, data analytics, and data transfer for additive manufacturing processes. The background, motivation, and organization of this dissertation are first presented in the Introduction chapter. Then, the use of FEM to model and replicate in-situ sensor data is presented, followed by the use of machine learning techniques to conduct real-time process monitoring trained from a mixture of experimental and replicated sensor image data. In particular, a cross-validation algorithm is developed through the exploitation of different sensor advantages and is integrated into the machine learning-assisted process monitoring algorithm. Next, an application of machine learning (ML) to non-image sensor data is presented as a neural network model that is developed to estimate in-situ powder thickness to account for recoater arm interactions. Subsequently, an integrated AM smart manufacturing framework is proposed which connects the different manufacturing hierarchies, particularly at the local machine, factory, and cloud level. Finally, in addition to the AM industry, the use of machine learning, specifically neural networks, in model predictive control (MPC) for dynamic nonlinear processes is reviewed and discussed.