Process Monitoring and Defect Detection of Additive Manufacturing Using Inline Coherent Imaging

With applications ranging from aerospace to biomedicine, additive manufacturing (AM) has been revolutionizing the manufacturing industry. The ability of additive techniques, such as selective laser melting (SLM), to create fully functional, geometrically complex, and unique parts out of high strength materials is of great interest. Unfortunately, despite numerous advantages afforded by this technology, its widespread adoption is hindered by a lack of on-line, real time feedback control and quality assurance techniques. In this thesis, inline coherent imaging (ICI), a broadband, spatially coherent imaging technique, is used to observe the SLM process in 15 - 45 $\mu m$ 316L stainless steel. Imaging of both single and multilayer builds is performed at a rate of 200 $kHz$, with a resolution of tens of microns, and a high dynamic range rendering it impervious to blinding from the process beam. This allows imaging before, during, and after laser processing to observe changes in the morphology and stability of the melt. Galvanometer-based scanning of the imaging beam relative to the process beam during the creation of single tracks is used to gain a unique perspective of the SLM process that has been so far unobservable by other monitoring techniques. Single track processing is also used to investigate the possibility of a preliminary feedback control parameter based on the process beam power, through imaging with both coaxial and 100 $\mu m$ offset alignment with respect to the process beam. The 100 $\mu m$ offset improved imaging by increasing the number of bright A-lines (i.e. with signal greater than the 10 $dB$ noise floor) by 300\%. The overlap between adjacent tracks in a single layer is imaged to detect characteristic fault signatures. Full multilayer builds are carried out and the resultant ICI images are used to detect defects in the finished part and improve upon the initial design of the build system. Damage to the recoater blade is assessed using powder layer scans acquired during a 3D build. The ability of ICI to monitor SLM processes at such high rates with high resolution offers extraordinary potential for future advances in on-line feedback control of additive manufacturing.

RE-MEANING THE SACRED: COLONIAL DAMAGE AND INDIGENOUS COSMOLOGIES

Indigenous ways of knowing are dependent on an inheriting process both amongst humans and between human and non-human being. These multi-relationships cross material and immaterial borders as sites of knowledge production. This manuscript will interrogate how three particular Indigenous cosmological relationships have been purposefully re-meaninged by colonial institutions: 1) How Anishinaabe and Haudenosaunee origin stories have been abstracted into a distinctive epistemological versus ontological site; 2) How Anishnaabe spirit worlds are impacted by colonial relations, and how state institutions benefit from the re-meaning of these worlds; and 3) How Indigenous sovereignty in Canada is imagined from a statist perspective, and how these polices have re-meaninged the sacred relationships within a cosmological understanding of Haudenosaunee governance. The re-meaning of sacredly-held Indigenous relationships is both accelerated by, and contributes to, a practice of reducing upon Indigenous and non-human societies. Throughout expressions of colonialism on Indigenous territories (the academy, the state, Indian policy), Indigenous knowledge is consistently either dismissed or appropriated. This reduction of Indigenous knowledge continues to bolster functions of the state as related to the elimination of the “Indian Problem” via reducing the “Indian” to an adaptive subject.