Manufacturing & Prototyping

Fabrication of an Integrated Photonic Waveguide Joint in Micromachined Silicon

This technology could be used in any MEMS or micromachined structure that requires multiple levels of topography.

Goddard Space Flight Center, Greenbelt, Maryland

High-aspect-ratio silicon structures are necessary components in many MEMS (microelectromechanical systems). Aspect ratio is defined as the ratio of the height of the structure to its lateral width. The structures are typically fabricated through bulk micromachining steps such as deep reactive ion etching. In some cases, multiple levels of high-aspect-ratio structures are required. For instance, one may want to etch completely through a silicon wafer to thermally isolate a bolometer or provide waveguide coupling to an antenna defined on an insulating membrane, and at the same time have integrated high-topology structures required for microwave coupling or filtering. Definition of the structures typically uses photolithographic technology. But for high-aspect-ratio structures, spin cast resist becomes difficult to incorporate due to the non-uniform thickness of the resist around tall structures. One can cast very thick layers of photoresist, but this limits the minimum feature size, and additionally, very thick layers of photoresist are difficult to work with due to solvent release and moisture that can cause the resist to crack or swell. For electromagnetic reasons, the structures would preferably be made from conductive material such as metal or degeneratively doped silicon. The objective of this work was to incorporate multiple levels of conductive high-aspectratio structures with standard micromachining processes.

Posted in: Briefs, Manufacturing & Prototyping, Electromagnetic compatibility, Waveguides, Fabrication, Silicon alloys
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Very Large Inflatable Antenna Structures

This methodology enables production of very large, but lightweight, structures in space.

Future space exploration past Earth orbit has a significant need for manufacturing in space beyond simple assembly of prefabricated parts. The next generation of very large aperture antennas will exceed the size achievable with conventional folding mesh technologies and new concepts are needed to support football-field-size structures. Technologies to address the problem have been developed using the formation of polyurethanes in a vacuum environment. Large inflatable structures can be stabilized by the formation of polyurethane foams of controlled density. For use in a vacuum environment, the availability of oligomeric precursors is important. Low-molecular-weight components would immediately evaporate, changing the stoichiometry of the reaction and potentially contaminate a space environment, but high-molecular-weight precursors have a much more limited range of properties.

Posted in: Briefs, Manufacturing & Prototyping, Antennas, Packaging, Foams, Materials properties
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Method for Fabricating Metallic Panels with Deep Stiffener Sections

This method is a rapid, more environmentally friendly, cost-effective process.

This innovation integrates existing highperformance metallic materials and manufacturing technologies (all of which are now certified and used to produce thinner stiffened panels for launch vehicle structures) in a novel manner to allow fabrication of more structurally efficient panels with stiffeners that are substantially deeper than existing plate stock materials.

Posted in: Briefs, Manufacturing & Prototyping, Fabrication, Metallurgy, Launch vehicles
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Robust, High-Temperature Containment Cartridges for Microgravity

Other potential applications include chemical processing, heat pipes, power generation equipment, nuclear components, and automotive.

Robust, high-temperature containment cartridges are needed for processing materials science experiments in microgravity. In general, the refractory metals (Nb, Ta, Mo, W, Re) possess the chemical inertness and high melting temperatures desired. Of these materials, niobium and tantalum alloys have been the materials of choice due to their low ductile to brittle transition temperatures, which allow deep-draw forming into cylindrical shapes. The high cost of tantalum and niobium, along with the desire for cartridges resistant to molten zinc and usable to 1,500 °C, demonstrates the need for alternative cartridge materials. Two candidate materials are molybdenum and tungsten alloys. Both have high melting temperatures and cost an order of magnitude less than tantalum and niobium.

Posted in: Briefs, Manufacturing & Prototyping, Containers, Refractory materials, Test equipment and instrumentation, Spacecraft
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Method for Insertion of Carbon Fiber Through the Thickness of Dense Dry Fiber Preform

Heat shields for re-entry vehicles, and jet engine exhaust components are two potential applications.

Ames Research Center, Moffett Field, California

Creation of a structural joint for a heat shield for extreme entry environments requires structural fibers penetrating through the thickness of the shield at joint locations. The structural fibers must be made of carbon to withstand extremely high temperatures, i.e. 2000 ºC. Carbon fibers, due to their relatively high modulus (stiffness), are easily damaged and broken when handled by a conventional sewing machine. Special coatings such as nylon are required to increase the durability of the fiber to enable its use in a sewing or tufting process.

Posted in: Briefs, Manufacturing & Prototyping, Coatings, colorants, and finishes, Fibers, Materials properties
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Edge-Bonded Shims

Edge-bonded shims reduce assembly time and require less inventory storage space.

SPIROL International Corp., Danielson, Connecticut

Precision shims are used as compensators to absorb tolerances between mating components. They significantly reduce manufacturing costs by eliminating the need for each component to be precision-machined in order to achieve the proper fit and function of the total assembly. During the assembly process, shims provide adjustment to compensate for accumulated tolerances that significantly reduces the need for re-machining and assembly time. Additionally, shims are commonly used to preserve the faces between mating components, cutting down the required machining time during rebuilds/retrofitting.

Posted in: Briefs, Manufacturing & Prototyping, Assembling, Machining processes, Parts
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Precision Detector Conductance Definition via Ballistic Thermal Transport

This innovation could be applied in the development of bolometric detector array sensors.

Goddard Space Flight Center, Greenbelt, Maryland

The characteristics of a thermal detector, such as sensitivity, response time, and saturation power (or energy resolution), are functions of the thermal conductance of the detector to its cryogenic environment. The thermal conductance is specified to achieve a tradeoff among the highest sensitivity, allowed response time, and the desired saturation energy or power budget for the particular application. It is essential to achieve the design thermal conductance (within an acceptable variance) after a thermal detector has been fabricated. Otherwise, the detector will fail to achieve its desired functionality. In addition, the formation of a multi-pixel imaging array becomes difficult and costly when the design thermal conductance is not achieved with high post-fabrication yield.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Sensors, Imaging and visualization, Conductivity, Thermal testing
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Thermal Spraying of Coatings Using Resonant Pulsed Combustion

This is a high-volume, high-velocity surface deposition of protective metallic and other coatings on surfaces.

John H. Glenn Research Center, Cleveland, Ohio

Thermal spray coating is not a new process. There are different techniques utilized that depend on the objective function of the coating, the environment to which the coated piece will be subjected, and the coating material used. In any application, quality is ultimately measured by how well the coating material adheres to the sprayed surface. This, in turn, is controlled by the velocity at which the coating material impinges on the substrate, the size of the molten coating particles, and the degree to which the coating material is prevented from chemically reacting while in a molten state.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Spraying, Coatings, colorants, and finishes
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Plasma Treatments to Assist Fluid Manipulation in Microgravity

Altering the surface energy of container walls permits anchoring of fluids within the container.

Lyndon B. Johnson Space Center, Houston, Texas

A recent innovation has made manipulation of hazardous laboratory reagents in microgravity easier, thus enabling even more scientific research to be performed on the International Space Station (ISS). Prior to this innovation, moving fluids from container to container was performed only under conditions of redundant and physically separate layers of containment. This design paradigm restricts access to — and direct manipulation of — fluids in microgravity conditions.

Posted in: Briefs, Manufacturing & Prototyping, Waste management, Hazardous materials, Spacecraft
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Stencil-less Jet Printing for PCB Assembly

Solder paste inkjet is an inline, solder-mask printing technology that enables 3D printing of different thicknesses of solder paste for prototype PCBs.

Imagineering Inc., Elk Grove Village, Illinois

For many years, stencil printing has been the standard method of depositing solder paste on surface mount assembly printed circuit boards (PCBs). It has provided a durable method of applying solder paste, but there were always difficulties that significantly slowed down a change from one product to another in the assembly operation, and added cost. A significant challenge in newer, smaller electronics assembly is the huge difference in size among components. Therefore, trying to apply the right amount of solder paste for each component with one stencil is difficult. The biggest problem is how to produce quick-turn prototypes without disrupting series production that is already running in the line. Product changeover requires time-consuming tweaks to the stencil printing process, while unnecessarily shutting down an expensive assembly line to change the product. The inability of the stencil’s technology to vary solder paste volume by part, on the run, remains the biggest impact on the soldering quality.

Posted in: Briefs, Manufacturing & Prototyping, Computer software and hardware, Production, Welding
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