Solid freeform fabrication

Researchers at Austin have been working on technologies termed solid freeform fabrication (SFF) or, as reported in the popular press, desktop manufacturing, rapid prototyping, and layered manufacturing. Such processes have the potential to produce accurate, structurally sound 3-D renditions of objects designed with computers and manufactured directly from a CAD database, without part-specific tooling or human intervention, and to make them available to the user in minutes or hours. The benefits include greatly reduced prototyping cost and design time and reliability to achieve, in one operation, shapes that would otherwise require multiple operations or in some cases be impossible to produce with standard techniques. Automated manufacturing technologies in general are well suited to large production numbers, but ill suited to low-volume runs. In the latter case, the components are too few to adequately amortize the cost of part-specific tooling; instead, they are typically made by hand at much greater unit cost and longer completion times. Nor is it a completely desirable low-volume option to interface CAD systems with numerically controlled (NC) machining centers-in essence, computer controlled material removal systems-because so much human intervention is involved in producing NC programs and setting up and supervising NC systems. In fact, the low-volume production arena is exactly where SFF slashes cost and time to completion     

Bed-Shear Stress Characteristics of a Simple, Prismatic, Rectangular Channel

This paper examines the use of data obtained from large eddy simulations in exploring the instantaneous characteristics of boundary shear stress. The probability density functions (PDF) of the shear stress are shown to be non-Gaussian, whereas the PDF of the shear force per unit length is found to be approximately Gaussian. Conditional sampling is used in order to provide an insight into the average behavior of an extreme shear stress event. Finally, proper orthogonal decomposition illustrates that the behavior of the shear stress is complex and cannot necessarily be attributed to a single major flow event.     

A demonstration of melt rate control during VAR of “Cracked” electrodes

A particularly challenging problem associated with vacuum arc remelting occurs when trying to maintain accurate control of electrode melt rate as the melt zone passes through a transverse crack in the electrode. As the melt zone approaches the crack, poor heat conduction across the crack drives the local temperature in the electrode tip above its steady-state value, causing the controller to cut back on melting current in response to an increase in melting efficiency. The difficulty arises when the melt zone passes through the crack and encounters the relatively cold metal on the other side, giving rise to an abrupt drop in melt rate. This extremely dynamic melting situation is very difficult to handle using standard load-cell based melt rate control, resulting in large melt rate excursions. We have designed and tested a new generation melt rate controller that is capable of controlling melt rate through crack events. The controller is designed around an accurate dynamic melting model that uses four process variables: electrode tip thermal boundary layer, electrode gap, electrode mass and melting efficiency. Tests, jointly sponsored by the Specialty Metals Processing Consortium and Sandia National Laboratories, were performed at Carpenter Technology Corporation wherein two 0.43 m diameter Pyromet® 718 electrodes were melted into 0.51 m diameter ingots. Each electrode was cut approximately halfway through its diameter with an abrasive saw to simulate an electrode crack. Relatively accurate melt rate control through the cuts was demonstrated despite the observation of severe arc disturbances and loss of electrode gap control. Subsequent to remelting, one ingot was sectioned in the “as cast” condition, whereas the other was forged to 0.20 m diameter billet. Macrostructural characterization showed solidification white spots in regions affected by the cut in the electrode.     

Effect of intravenous immunoglobulin G on natural killer cell cytotoxicity in vitro in women with recurrent spontaneous abortion

Intravenous immunoglobulin (IVIg) has been used to treat women with recurrent spontaneous abortion (RSA), particularly for women with elevated natural killer (NK) cells. We investigated the effect of IVIg on peripheral blood NK cell activity in vitro in women with RSA. 51Cr-release assays using K562 in the presence of varying concentrations of IVIg were performed using PBL from 16 women with RSA. Antibody dependent cellular cytotoxicity (ADCC) was evaluated using Daudi cells. Effectors and targets were preincubated with IVIg. Binding of IVIg to K562 and Daudi was evaluated by flow cytometry. The effect of K562 absorbed IVIg on NK activity was compared to that of non-absorbed IVIg. NK cytotoxicity and ADCC in the presence of F(ab')2 fragments were compared with those in the presence of intact IVIg. IVIg produced a significant, dose dependent inhibition of NK activity in vitro. Inhibition of NK activity occurred when effectors but not targets were preincubated with IVIg. IVIg binds to K562 and Daudi. IVIg increased ADCC when targets but not effectors were incubated with IVIg. K562 absorbed IVIg produced more inhibition of NK cytotoxicity than non-absorbed IVIg. Suppression of NK cytotoxicity by F(ab')2 was as effective as that of IVIg. However, F(ab')2 did not increase ADCC. IVIg effectively reduces peripheral blood NK cytotoxicity in vitro. Inhibition of NK cytotoxicity is mediated at the effector cell level through the antigen binding portion of the immunoglobulins. Women with RSA and elevated NK cells may benefit from IVIg treatment.     

Direct SLS Processing for Production of Cermet Composite Turbine Sealing Components

This paper presents the development to date of Selective Laser Sintering (SLS) technologies for production of cermet composite turbine sealing components, the particular application being an abrasive blade tip. The component chosen for the application is an integral part of the low pressure turbine in a. IHPTET (Integrated High Performance Turbine Engine Technology) demonstrator engine. Both indirect and direct SLS techniques are being developed. Initial trials and process development involved the use of fugitive polymeric binders. Sequential refinements were performed to develop a binderless direct SLS process. Results from mechanical testing indicate that acceptable microstructure and properties are attainable by SLS with substantial cost savings as compared to the currently employed production method. This is the first instance of direct Solid Freeform Fabrication (SIT) method applied to a functional component.     

V-ATPase upregulation during early pregnancy: a possible link to establishment of an inflammatory response during preimplantation period of pregnancy

Various mechanisms exist to prevent a potentially deleterious maternal immune response that results in compromising survival of semiallogeneic fetus. In pregnancy, there is a necessary early preimplantation inflammatory stage followed by a postimplantation anti-inflammatory stage. Thus, there is a biphasic 'immune response' observed during the course of pregnancy. We provide the evidence that capacitation of sperm induced the expression of a2 isoform of V-ATPase (ATP6V0A2 referred to as a2V), leukemia inhibitory factor (Lif), Il1b, and Tnf in the sperm. Capacitated sperm also released cleaved N-terminal domain of a2V-ATPase (a2NTD), which upregulates the gene expression of Lif, Il1b, Tnf, and monocyte chemotactic protein-1 (Ccl2 (Mcp1)) in the uterus. Unfertilized eggs had low a2V expression, but after fertilization, the expression of a2V increased in zygotes. This increased level of a2V expression was maintained in preimplantation embryos. Seminal plasma was necessary for upregulation of a2V expression in preimplantation embryos, as mating with seminal vesicle-deficient males failed to elicit an increase in a2V expression in preimplantation embryos. The infiltration of macrophages into the uterus was significantly increased after insemination of both sperm and seminal plasma during the preimplantation period of pregnancy. This dynamic infiltration into the uterus corresponded with the uterine a2V expression through the induction of Ccl2 expression. Furthermore, the polarization ratio of M1:M2 (pro-inflammatory/anti-inflammatory) macrophages in the uterus fluctuated from a ratio of 1.60 (day 1) to 1.45 (day 4) when female mice were inseminated with both sperm and seminal plasma. These data provide evidence that exposure to semen may initiate an inflammatory milieu by inducing a2V and cytokine/chemokine expression, which triggers the influx of macrophages into the preimplantation uterus during the onset of pregnancy and ultimately leads to successful pregnancy outcome.     

Differential binding of Nocardia asteroides in the murine lung and brain suggests multiple ligands on the nocardial surface

The adherence of Nocardia asteroides in the murine brain and lungs was determined. Virulent strains had increased adherence in the brain and lungs, whereas less virulent strains bound in either the brain or lungs. Nocardiae that attached apically penetrated host cells. Multiple receptors on the nocardial surface may be involved in this differential attachment and penetration.     

Development of a poly(methyl methacrylate-co-n-butyl methacrylate) copolymer binder system

Low molecular weight poly(methylmethacrylate) and poly(methylmethacrylate-co-n-butylmethacrylate) emulsion-based polymers are developed for use as fugitive binders of high temperature powders to be used with the rapid prototyping method known as selective laser sintering. Kinetics of the homopolymerization of methylmethacrylate and n-butyl-methacrylate are found to deviate from Smith-Ewart Type II predictions. Reactivity ratios for the monomer pair are determined and indicate the pair to yield random copolymers. Molecular weight was controlled by the addition of chain transfer agents. Several transfer agents were studied and one, iso-octyl-3-mercaptopropionate, was selected for use with emulsion polymerizations. Glass transition temperatures of the homopolymers and copolymers were studied. © 1994 John Wiley & Sons, Inc.     

Titanium castings using laser-scanned data and selective laser-sintered zirconia molds

Titanium casting molds, made of stabilized and unstabilized zirconium oxide, were created using a combination of selective laser sintering (SLS) and colloidal infiltration. The mold material system was chosen for its thermal shock resistance and low reactivity with molten titanium. The starting material, stabilized zirconia powder mixed with a copolymer binder, was laser sintered into the desired green shape. The binder was removed during pyrolysis and replaced by unstabilized zirconia. As infiltrant weight gain increased, the density, flexural strength, and surface roughness improved to levels adequate for titanium casting trials. A half-scale casting mold for the ball of a human femur bone was produced from laser-scanned data and cast with Ti-6Al-4V alloy. The castings exhibited an as-cast surface roughness (R _a ) of 8 μm and a typical microstructure. This work demonstrates a feasible method of producing complex titanium castings for one-of-a-kind and custom components without the necessity of part-specific tooling or wax patterns.