Binder Jetting: A microstructural perspective
Author/s: Sergi Bafaluy Ojea
Director/s: María Teresa Pérez Prado and Federico Sket
Defence Date: 22/09/2023
Ph.D. Awarding Institution: Universidad Carlos III de Madrid
Abstract
The investigations carried out in this work aimed to accomplish the objectives cited in the Chapter 3. Therefore, the general conclusions are divided to address each proposed goal. 1. Develop automated characterization methods that allow for metrics subtraction and comparison between BJ green parts:
• The lack of green part microstructural characterization in BJ 3D printing pointed towards the development of image treatment algorithms for SEM and OM micrographs and XCT volumes allowing the subtraction of relevant metrics for understanding BJ processes.
• These algorithms were not only developed, but also employed in several studies, which proved their high sensitivity to a variety of BJ parameters, printed geometries, or sintering conditions.
• The extracted metrics presented a high correlation with relevant process parameters, exhibiting a great potential for process predictability at different stages. 2. Contribute to the existing knowledge of BJ printing process through the addition of a deep characterization of green parts and their respective sintered parts outcome:
• The Chapter 5 explored the relationship of BJ part with some printing parameters already available in the literature. However, the addition of a new perspective combining commonly seen characterization with the microstructural readings of the green parts allowed to get new insights into BJ printing mechanisms. 3. Investigate the impact of part geometry, size, and features on the resulting microstructure:
• Part geometry was found to significantly influence the microstructural observations. A relationship was established between a variety of geometrical features and the resulting microstructural metrics.
• The geometrical influences exploration emphasized the need for adaptative print modes that consider the previously mentioned relationships. 4. Advance in the understanding of the surface defects relationship with the printing recipe and its link to posterior machinability:
• OM microstructural metrics were developed to characterize porosity gradients in BJ sintered parts.
• Several process parameters were found to promote or hinder the formation of porosity in the sintered state.
An optimization of these parameters was proposed.
• The resulting variability of porosity metrics within the part also evidences the need for adaptative print modes the optimize porosity locally.