Browsing by Subject "Consistency"
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Item Development of a feedforward laser control system for improving component consistency in Selective Laser Sintering(2019-06-18) Phillips, Timothy Bryce; Beaman, Joseph J.; Milner, Thomas; Crawford, Richard; Seepersad, Carolyn; Fish, ScottSelective Laser Sintering makes up a significant portion of the polymer additive manufacturing market and is often the process of choice for structurally significant polymer components. With its expanding market, especially among end-use components, comes a growing need for improving reproducibility. Components built using Selective Laser Sintering display a large range among their mechanical properties and it has been shown that the thermal history of the building process has a strong influence over these variations. Temperature fluctuations of just a few degrees can mean the difference between scrapped parts or those with excellent mechanical and dimensional properties. This dissertation will introduce a novel method of reducing temperature and mechanical variations among parts. Physical simulations and empirical measurements of laser-polymer interaction are evaluated and used to guide development of an advanced laser power controller. The feedforward control system developed uses thermal imagery and dynamic surrogate modeling to systematically modulate laser energy impinging on the polymer surface to homogenize post-sintering temperatures. Results from thermal and mechanical tests will be presented, showing the laser control system is capable of reducing standard deviations by up to 57% for post-sintering temperature and 45% for ultimate flexural strength.Item Mixtures of triangular densities with applications to Bayesian mode regressions(2014-08) Ho, Chi-San; Damien, Paul, 1960-The main focus of this thesis is to develop full parametric and semiparametric Bayesian inference for data arising from triangular distributions. A natural consequence of working with such distributions is it allows one to consider regression models where the response variable is now the mode of the data distribution. A new family of nonparametric prior distributions is developed for a certain class of convex densities of particular relevance to mode regressions. Triangular distributions arise in several contexts such as geosciences, econometrics, finance, health care management, sociology, reliability engineering, decision and risk analysis, etc. In many fields, experts, typically, have a reasonable idea about the range and most likely values that define a data distribution. Eliciting these quantities is thus, generally, easier than eliciting moments of other commonly known distributions. Using simulated and actual data, applications of triangular distributions, with and without mode regressions, in some of the aforementioned areas are tackled.