Browsing by Subject "shrinkage"

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DETERMINATION AND COMPENSATION OF THE SHRINKAGE BEHAVIOR OF CYLINDRICAL ELEMENTS IN THE FDM PROCESS
(University of Texas at Austin, 2023) Koers, T.; Magyar, B.
Fused Deposition Modeling (FDM) is an additive manufacturing process to produce complex thermoplastic geometries layer by layer. The filament is melted in a nozzle, iteratively deposited, and then cools down. Due to the solidification process, the deposited filament strands deviate from their intended position due to shrinkage, resulting in significant geometric deviations in the final part. In terms of dimensional accuracy, there is a need for optimization, especially for local curved geometries in relation to the global part with higher nominal dimensions. The aim of this study is to investigate the size and shape deviations for cylindrical FDM elements and to compensate the expected deformations by using an in-house software with adaptive scaling factors in the x-y plane. Previous studies mainly focus on simple, non-curved objects, this study also considers the influence of curvature and global as well as local deviations on the final part.
Development of Direct SLS Processing for Production of Cermet Composite Turbine Sealing Components- Part II
(1996) Fuesting, T.; Brown, L.; Das, S.; Harlan, N.; Lee, G.; Beaman, J.J.; Bourell, D.L.; Barlow, J.W.; Sargent, K.
An Investigation of Build Orientation on Shrinkage in Sintered Bioceramic Parts Fabricated by Vat Photopolymerization
(University of Texas at Austin, 2017) Aduba, Donald C. Jr.; Feller, Keyton D.; Williams, Christopher B.
In this work, a vat photopolymerization (VP) additive manufacturing process fabricated bioceramic cuboids at different build orientations to investigate their effects on post-sintering shrinkage and associated physical properties. A suspension of β-tricalcium phosphate (TCP) in Autodesk PR 57 commercial photopolymer resin and dimethyl sulfoxide (DMSO) solvent was used to shape green parts. Thermal treatment removed polymer from the green shape before sintering TCP at 1300 ◦C at 5 ◦C/min. Part morphology, dimensional shrinkage, and mass loss after sintering were evaluated. Part dimensions parallel to the build direction exhibited greater shrinkage compared to the other two dimensions. Mass loss was independent of build orientation. This paper is the first to investigate the relationship between build orientation and post-sintering shrinkage of bioceramic structures shaped by VP. In this work, an understanding of printing ceramic suspensions, and accounting for dimensional ceramic part shrinkage with respect to build orientation is gained to help guide print parameter selection to improve part fidelity and performance.
A Method for Measuring Powder Bed Density in Binder Jet Additive Manufacturing Process and the Powder Feedstock Characteristics Influencing the Powder Bed Density
(University of Texas at Austin, 2016) Elliott, A.M.; Nandwana, P.; Siddel, D.; Compton, B.G.
Powder bed additive manufacturing involves layer-by-layer spreading of powders before melting, sintering or binding them. Traditionally apparent and tapped density measurements have been carried out to get an estimate of the powder bed density. Powder bed density is especially important in the case of binder-jet additive manufacturing where sintering is carried out as one of the steps to achieve full densification. During densification, shrinkage occurs. The extent of shrinkage depends upon the powder bed density. Thus, it is important to understand the role of powder feedstock on controlling the powder bed density. In the present paper, we have developed a technique to measure the powder bed density. We also used different powder feedstock materials to understand the role of powder size distribution and morphology on the powder bed density. The detailed results are presented.
On the Half-Cauchy Prior for a Global Scale Parameter
(2012) Polson, Nicholas G.; Scott, James G.; Scott, James G.
This paper argues that the half-Cauchy distribution should replace the inverse-Gamma distribution as a default prior for a top-level scale parameter in Bayesian hierarchical models, at least for cases where a proper prior is necessary. Our arguments involve a blend of Bayesian and frequentist reasoning, and are intended to complement the case made by Gelman (2006) in support of folded-t priors. First, we generalize the half-Cauchy prior to the wider class of hypergeometric inverted-beta priors. We derive expressions for posterior moments and marginal densities when these priors are used for a top-level normal variance in a Bayesian hierarchical model. We go on to prove a proposition that, together with the results for moments and marginals, allows us to characterize the frequentist risk of the Bayes estimators under all global-shrinkage priors in the class. These results, in turn, allow us to study the frequentist properties of the half-Cauchy prior versus a wide class of alternatives. The half-Cauchy occupies a sensible middle ground within this class: it performs well near the origin, but does not lead to drastic compromises in other parts of the parameter space. This provides an alternative, classical justification for the routine use of this prior. We also consider situations where the underlying mean vector is sparse, where we argue that the usual conjugate choice of an inverse-gamma prior is particularly inappropriate, and can severely distort inference. Finally, we summarize some open issues in the specification of default priors for scale terms in hierarchical models.
Selective Laser of a Copper-PMMA System
(1991) Badrinarayan, B.; Barlow, J.W.
The Selective Laser Sintering process was used to manufacture green copper parts from a copper-polymer mixture. PMMA was used as the polymer binder for the metal. The green part was fired in a furnace under reducing conditions to obtain a pure metal part. The metal-polymer system and the conditions used to make parts are described in this paper. The effect of laser parameters and particle sizes on part density are also discussed. Keywords: laser sintering, copper, polymer, part density, dwell time, shrinkage.