Manufacturing by Solid Freeform Fabrication

The SFF/RP industry has grown steadily with the most significant gains made in the number of models produced per year – three million in the year 2000. Future growth is most likely to be in manufacturing applications of SFF where even a single application can double the number of models/parts produced annually. There are a number of factors or drivers which can motivate a manufacturing application of SFF either individually or in combination. These drivers include: i. avoid conventional tooling, ii. minimizing hand work, iii. mass customization, iv. geometric flexibility, v. local control of composition. The most intriguing of these drivers is that of mass customization – the manufacture of highly individual products, but on a mass scale. SFF offers the possibility of mass customization of components with complex 3D geometry. A prominent current example is that of Align Technology of Santa Clara, CA which produces unique plastic aligners for orthodontic applications. There already are manufacturing applications where the advantages offered by SFF are so compelling as to overcome any barriers. However, widespread impact of SFF on manufacturing will depend on overcoming several barriers. The essence of these barriers lies in the distinction between prototyping and manufacturing. Manufacturing applications are far more demanding in terms of build rate and associated cost, demands on dimensional control and tolerances, properties of materials, and ease of use and serviceability of equipment.Mechanical Engineerin

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

Production of Injection Molding Tooling with Conformal Cooling Channels using The Three Dimensional Printing Process

Three Dimensional Printing is a desktop manufacturing process in which powdered materials are deposited in layers and selectively joined with binder from an ink-jet style printhead. Unbound powder is removed upon process completion, leaving a three dimensional part. Stainless steel injection molding inserts have been created from metal powder with the 3DP process. The freedom to create internal geometry by the use of the 3D-Printing process allows for the fabrication of molds with complex internal cooling passages. Tooling was developed with cooling channels designed to be conformal to the molding cavity. A finite difference simulation was constructed to study conformal channel design. A direct comparison of the mold surface temperature during the injection cycle of a 3D Printed mold with conformal channels and a mold machined with conventional straight channels was completed. The conformal passages produced with the 3DP process provide the ability to accurately control the temperature of the molding cavity throughout the process cycle. Surface temperature measurements demonstrated that the inserts with conformal cooling channels exhibited a more uniform surface temperature than the inserts machined with straight channels. Issues such as powder removal and post processing of green parts with small cooling channels were investigated.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

Toward Manufacturing of Fine Components by 3D Printing 191

Solid Freeform Fabrication has earned its place in the industrial practice of prototyping and is beginning to have an impact in the fabrication of tooling. The next and perhaps greatest opportunity for SFF lies on the direct manufacture of components. This paper will present efforts directed toward the MANUFACTURE IN HIGH QUANTITY of small, precision components by 3D Printing. The primary focus is on ceramic and ceramic/metal components, although all metal components are envisioned as well. The production of small, fine-featured parts presents two opportunities for a new machine architecture. First, the powderbeds required for small parts are themselves small and lightweight. Thus, a machine can be designed where powderbeds move from the layer spreading station to the print station and back again. Multiple powder beds can be in play, taking full advantage of all stations of the machine. The second opportunity is to define the perimeter of the part using vector motions of a nozzle with the interior filled by raster scanning. Such an approach has the advantage that the boundary of the part will be defined as a smooth contour. Moving powderbeds and vector printing are combined in the linear shuttle-type machine for research purposes. Ultimately, a rotary machine is envisioned for high production.Mechanical Engineerin

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

Progress on Tooling by 3D Printing; Conformal Cooling, Dimensional Control, Surface Finish and Hardness

Three Dimensional Printing is being applied to the direct fabrication of tooling using metal powders. This paper presents progress updates in four areas: i) thermal management using conformal cooling and related work on enhanced heat transfer using surface textures, ii) data on dimensional control, iii) ) improvements in surface finish, and iv) harder tooling. Conformal cooling has demonstrated significantly improved performance in a production part geometry with simultaneous gains in production rate and part quality obtained as measured against conventional tooling. Surface textures printed on cooling channels have demonstrated 8X enhancement of heat transfer over smooth channels. A set of 18 tooling inserts was fabricated using hardenable stainless steel powder with a resultant tooling hardness of 25-30 Rockwell C. Harder alloy systems are being designed with the aid of computational thermodynamic tools which allow accurate prediction of the interaction of powder and binder. Significant improvements in surface finish were obtained using improved printing technology. Dimensional control of tools conformed well to the expected result of being dominated by control of shrinkage and being predictable to within ±.25%.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