Metal Parts Generation by Three Dimensional Printing

Mechanical Engineerin

Edge stabilized ribbon growth : a new method for the manufacture of photovoltaic substrates

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1983.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.Includes bibliographical references.by Emanuel M. Sachs.Ph.D

Modeling and Designing Components with Locally Controlled Composition

SFF processes have demonstrated the ability to produce parts with locally controlled composition. In the limit, processes such as 3D Printing,cancreate parts with composition control on thelength scaleiof 100 microns.ToexploitthispC)tential,~e\\ZJnethodsto rnod~l, exchange, and process parts.with local composition needtobe.deyeloped..... Anapproachtc) modeling a part's geometty,.topology, and composition will be presented.· This.approachis based on sUbdividing the solidmodel into sub-regions and associating analytic composition blending functions \\lith each region. These blending functions definethe composition throughout the model as mixtures ofthe primary materials available to·the SEF machine. Various design tools will also be presented, for example, specification of com~ositionasa function of the distance from the surface of a part. Finally,the role of design rules specifying maximum concentrations and concentration.gradients will be discussed.Mechanical Engineerin

Three Dimensional Printing of Tungsten Carbide-Cobalt Using a Cobalt Oxide Precursor

Tungsten Carbide 10 wt% Cobalt parts were formed by Slurry-based Three Dimensional Printing (3DPTM). The slurry contained a mixture of Tungsten Carbide and Cobalt Oxide powders, as well as dispersing and redispersing agents. The cobalt oxide is fully reduced to cobalt metal during the early stages of the sintering process. A new binder system, polyethylenimine, is described for use with powders with acidic surfaces, such as WC. Sintered densities approach the theoretical values for WC-10% Co, and the microstructures produced are similar to those of conventionally processed (press and sinter) materials. Up to four parts were produced in a single print run using a layer thickness of 25 Pm, with good dimensional agreement between them, and within the range of target dimensions after sintering.Mechanical Engineerin

3D printing metals like thermoplastics: Fused filament fabrication of metallic glasses

Whereas 3D printing of thermoplastics is highly advanced and can readily create complex geometries, 3D printing of metals is still challenging and limited. The origin of this asymmetry in technological maturity is the continuous softening of thermoplastics with temperature into a readily formable state, which is absent in conventional metals. Unlike conventional metals, bulk metallic glasses (BMGs) demonstrate a supercooled liquid region and continuous softening upon heating, analogous to thermoplastics. Here we demonstrate that, in extension of this analogy, BMGs are also amenable to extrusion-based 3D printing through fused filament fabrication (FFF). When utilizing the BMGs’ supercooled liquid behavior, 3D printing can be realized under similar conditions to those in thermoplastics. Fully dense and amorphous BMG parts are 3D printed in ambient environmental conditions resulting in high-strength metal parts. Due to the similarity between FFF of thermoplastics and BMGs, this method may leverage the technology infrastructure built by the thermoplastic FFF community to rapidly realize and proliferate accessible and practical printing of metals

Diffusion-Driven Looping Provides a Consistent Framework for Chromatin Organization

Chromatin folding inside the interphase nucleus of eukaryotic cells is done on multiple scales of length and time. Despite recent progress in understanding the folding motifs of chromatin, the higher-order structure still remains elusive. Various experimental studies reveal a tight connection between genome folding and function. Chromosomes fold into a confined subspace of the nucleus and form distinct territories. Chromatin looping seems to play a dominant role both in transcriptional regulation as well as in chromatin organization and has been assumed to be mediated by long-range interactions in many polymer models. However, it remains a crucial question which mechanisms are necessary to make two chromatin regions become co-located, i.e. have them in spatial proximity. We demonstrate that the formation of loops can be accomplished solely on the basis of diffusional motion. The probabilistic nature of temporary contacts mimics the effects of proteins, e.g. transcription factors, in the solvent. We establish testable quantitative predictions by deriving scale-independent measures for comparison to experimental data. In this Dynamic Loop (DL) model, the co-localization probability of distant elements is strongly increased compared to linear non-looping chains. The model correctly describes folding into a confined space as well as the experimentally observed cell-to-cell variation. Most importantly, at biological densities, model chromosomes occupy distinct territories showing less inter-chromosomal contacts than linear chains. Thus, dynamic diffusion-based looping, i.e. gene co-localization, provides a consistent framework for chromatin organization in eukaryotic interphase nuclei

The fractal globule as a model of chromatin architecture in the cell

The fractal globule is a compact polymer state that emerges during polymer condensation as a result of topological constraints which prevent one region of the chain from passing across another one. This long-lived intermediate state was introduced in 1988 (Grosberg et al. 1988) and has not been observed in experiments or simulations until recently (Lieberman-Aiden et al. 2009). Recent characterization of human chromatin using a novel chromosome conformational capture technique brought the fractal globule into the spotlight as a structural model of human chromosome on the scale of up to 10 Mb (Lieberman-Aiden et al. 2009). Here, we present the concept of the fractal globule, comparing it to other states of a polymer and focusing on its properties relevant for the biophysics of chromatin. We then discuss properties of the fractal globule that make it an attractive model for chromatin organization inside a cell. Next, we connect the fractal globule to recent studies that emphasize topological constraints as a primary factor driving formation of chromosomal territories. We discuss how theoretical predictions, made on the basis of the fractal globule model, can be tested experimentally. Finally, we discuss whether fractal globule architecture can be relevant for chromatin packing in other organisms such as yeast and bacteria

Three Dimensional Printing: Form, Materials, and Performance

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