Machine learning approaches to manufacturing and materials: Applications to semi-supervised, unbalanced and heterogeneous data problems
The objective of this thesis is to use machine learning and deep learning techniques for the quality assurance of metal casting processes. Metal casting can be defined as a process in which liquid metal is poured into a mold of a desired shape and allowed to solidify. The process is completed after ejection of the final solidified component, also known as a casting, out of the mold. There may be undesired irregularities in the metal casting process known as casting defects. Among the defects that are found, porosity is considered to be a major defect, which is difficult to detect, until the end of the manufacturing cycle. When there are small voids, holes or pockets found within the metal, porosity defect occurs. It is important to control and alleviate porosity below certain permissible thresholds, depending on the product that is being manufactured. If the foundry process can be modeled using machine learning approaches, to predict the state of the casting prior to completion of the casting process, it would save the foundry the inspection and testing of the casting, which requires specific attention of the staff and expensive machinery for testing. Moreover, if the casting fails the quality test, then it would be rendered useless. This is one of the major issues for the foundries today. The main aim of this project, is to make predictions about the quality of metal cast components. We determine whether under certain given conditions and parameters, a cast component would pass or fail the quality test. Although this thesis focuses on porosity defects, machine learning and deep learning techniques can be used to model any other kinds of defects such as shrinkage defects, metal pouring defects or any metallurgical defects. The other important objective is to identify the most important parameters in this casting process, that are responsible for the porosity control and ultimately the quality of the cast component. The challenges faced during the data analysis while dealing with a small sized, unbalanced, heterogeneous and semi-supervised dataset, such as this one, are also covered. We compare the results obtained using different machine learning techniques in terms of F1 score, precision and recall, among other metrics, on unseen test data post cross validation. Finally, the conclusions and scope for the future work are also discussed.