• additive
• additive manufacturing
• in situ
• laser
• manufacturing
• monitoring
• state of the art

Additive manufacturing (AM) of metal alloys is a relatively novel manufacturing technology that have attracted a lot of attention, eventually becoming one of the most important current research topic. Due to its many advantages, AM is believed to become a disruptive technology across multiple industries such as automobile, aerospace, and biomedical.
The present study is organized as to firstly provide a description of the state of the art of Additive Manufacturing: the different techniques will be presented and compared. Moreover, the thesis will focus on the current challenges that are holding AM back from reaching its full potential, such as the lack of a strong monitoring system in order to ensure quality assurance (QA) of the final part. Several in-situ diagnostic methodologies are listed but just the few that are currently being actively used for production will be thoroughly explained.
A catalogue of the most common defects found in additively manufactured parts is thoroughly presented and the effect of defect on the quality of the final part is evaluated. Further studies will be necessary in order to establish acceptance criteria i.e. establish limits for specific defect types, sizes and distribution.
Moreover, currently, the lack of a Non Destructive Evaluation (NDE) procedure standard makes arbitrary and complicate post processing evaluation of the part. Therefore, possible NDE methods will be listed as well as each capability to detect critical and unique L-PBF planar flaw types like Lack Of Fusion, cross layer and trapped powder. Probability of Detection methods will also be presented for CT scanning.
Therefore, a real manufacturing scenario is presented along with the steps that were carried out in order to shed light on the process parameters that lead to a failure of the design requirements of the part. A powder bed machine, EOS 290, was used to built the part along with the post process monitoring system OT that represented a useful tool to extract important information about the process. A Root Cause Analysis is the problem solving method used to identify the root cause of the process faults that lead to the formation of defects in the microstructure of the final part. Every possible root cause was singularly investigated by means of the Design of Experiments approach. Further analysis must be carried out once the results from the post processing will be disclosed.
The final part of the thesis will be focused on the process to determine the suitability of Aluminum alloy 6061 for Additive Manufacturing by Direct Metal Deposition. Indeed, as a consequence of being a novel manufacturing technology, lack of standards is currently a major drawback in every step of the additive manufacturing process. The procedure of creating a Standard is very complicated, time consuming and very expensive. In this thesis, the evaluation of a non weldable alloy, like Al6061, processed by Direct Metal Laser Deposition will be presented at different process parameters. The characteristic of Al6061 are presented along with the effect of the laser on the phase transformations and microstructure changes. Different laser parameters such as laser speed, laser powder, gas flow rate, controlled atmosphere, etc. are taken into account. Optical microscope and Scanning Electron Microscopy are used to evaluate the microstructure of the final product whereas Energy-dispersive X-ray spectroscopy is used to evaluate the chemical composition.