Manufacturing & Prototyping

Improvements in Rapid Prototyping

Molecular structures would be tailored to obtain superior structural properties.Several improvements have been proposed for the fabrication process known as "rapid prototyping." In this process, a model or prototype of a solid object is built up by controlled ejection of molten polymeric material through programmed orifices to form patterned layers. The second layer is deposited on top of the first layer, the third layer is deposited on top of the second layer, and so forth, until the stack of layers reaches the desired final thickness and shape.

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Correlation Spectrometers for Detecting Fires in Aircraft

Products of early stages of com- bustion would be detected with sensitivity and selectivity. Compact, lightweight, sensitive correlation spectrometers for detecting gaseous byproducts of the onset of fire are under devel- opment. These spec- trometers would be installed in aircraft, where early detection of fire could enable crews to respond with timely fire-suppression actions. Correlation spectroscopy involves measurements of absorption spectra of chemical species of interest but is not the same as classic absorption spectroscopy, which has been used for decades for detecting airborne chemicals. Classic absorption spectroscopy involves steadystate techniques that are not suited for rapid detection of compounds of immediate interest that may be present along with other compounds that are not of immediate interest.

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Automated Apparatus for Welding to Seal Pyrotechnic Devices

An automated, remotely controllable apparatus has been developed for resistance welding for hermetic sealing of pyrotechnic devices, as a substitute for special-purpose welding equip- ment that is no longer commercially available. Hermetic sealing of a pyrotechnic device involves a sequence of closely spaced, precise, spot welds made with low heat to minimize the potential of ignition. For safety, the welding must be performed under remote control. The apparatus includes a rotary table with a chuck, in which is mounted a fixture that holds the pyrotechnic device to be welded. The rotary table is programmed to step through appropriate angular increments (e.g., 360° in 1° increments). After each increment, a switch is closed to actuate a solenoid valve to extend a pneumatic cylinder to drive a welding head toward the pyrotechnic device. A spring-loaded electrode in the welding head is forced into contact with the pyrotechnic device with increasing force until a switch closes at a preset contact force, triggering a pulse of welding current through the welding electrode and workpiece with a return path through the welding fixture. The welding head is then retracted, the rotary table steps through the next increment, and the foregoing process is repeated.

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Lithographic Fabrication of Mesoscale Electromagnet Coils

Fabrication should be faster and cheaper than in conventional winding. A partly lithographic method of fabrication is being developed to enable the economical mass production of mesoscale electrically conductive coils for miniature electro- magnets, solenoids, electric motors, and the like. This or a similar method is needed to overcome the limitations of prior techniques:

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Improved Attachment in a Hybrid Inflatable Pressure Vessel

Care is taken to distribute loads and maintain desired shapes.Some modifications that could be made, separately or together, have been conceived as improvements of the generic design of a structure of the type described in “Hybrid Inflatable Pressure Vessel” (MSC-23024/92), NASA Tech Briefs, Vol. 28, No. 4 (April 2004), page 44. To recapitulate: The vessel is a hybrid that comprises an inflatable shell attached to a rigid structure. The inflatable shell is, itself, a hybrid that comprises (1) a pressure bladder restrained against expansion by (2) a restraint layer that comprises a web of straps made from high-strength polymeric fabrics. The present improvements are intended to overcome deficiencies in those aspects of the original design that pertain to attachment of the inflatable shell to the rigid structure. In a typical intended application, such attachment(s) would be made at one or more window or hatch frames to incorporate the windows or hatches as integral parts of the overall vessel.

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Electrostatic Separator for Beneficiation of Lunar Soil

Process complexity may be significantly reduced.A charge separator has been constructed for use in a lunar environment that will allow for separation of minerals from lunar soil. Any future lunar base and habitat must be constructed from strong, dense materials to provide for thermal and radiation protection. It has been proposed that lunar soil may meet this need, and sintering of full-scale bricks has been accomplished using lunar simulant. In the present experiments, whole lunar dust as received was used. The approach taken here was that beneficiation of ores into an industrial feedstock grade may be more efficient. Refinement or enrichment of specific minerals in the soil before it is chemically processed may be more desirable as it would reduce the size and energy requirements necessary to produce the virgin material, and it may significantly reduce the process complexity. The principle is that minerals of different composition and work function will charge differently when tribocharged against different materials, and hence be separated in an electric field. The charge separator is constructed of two parallel copper plates separated by a variable distance in a vacuumcompatible box. The top and bottom of the box are designed so that the separation and angle between the plates can be varied. The box has a removable front plate for access, and each plate is connected to a high-voltage, vacuumcompatible connector that connects to feedthroughs in a vacuum chamber. Each plate is respectively powered by positive and negative high-voltage regulated DC power modules. Tribocharged dust is fed into the top through a small hole, where it is subjected to an intense electric field generated between the plates. Positively charged particles will be attracted to the negative plate, while negatively charged particles will be attracted to the positive plate. Dust collected on each plate and on filter paper in the collection box at the bottom of the plates can then be weighed to determine the mass-fraction separation. Because this device is meant for use in a lunar environment, much higher voltages can be used where there is no gas breakdown. Special care was taken in the design of the high-voltage connections to the separator plates. Pure copper plates and other materials were chosen for their low outgassing properties. Modeling of particle trajectories within the plates showed that for the Q/M (charge to mass ratio) measurements of the charged particles in vacuum, a smaller, more compact separator can be used on the Moon compared to the same device on Earth. Another advantage of this design is that, in the lower gravity environment of the Moon, particles will spend more time falling between the plates. Again, a smaller device and higher voltages can use this advantage to increase the efficiency of the lunar soil beneficiation process. This work was done by Jacqueline Quinn, and Ellen Arens of NASA Kennedy Space Center, Steve Trigwell of ASRC Aerospace, and James Captain of the University of Central Florida. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Manufacturing & Prototyping category. KSC-13007

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Bonded Invar Clip Removal Using Foil Heaters

A new process uses local heating and temperature monitoring to soften the adhesive under Invar clips enough that they can be removed without damaging the composite underneath or other nearby bonds. Two 1×1 in. (≈2.5×2.5 cm), 10-W/in.2 (≈1.6-W/cm2), 80-ohm resistive foil Kapton foil heaters, with pressure-sensitive acrylic adhesive backing, are wired in parallel to a 50-V, 1-A limited power supply. At 1 A, 40 W are applied to the heater pair. The temperature is monitored in the clip radius and inside the tube, using a dual thermocouple readout. Several layers of aluminum foil are used to speed the heat up, allowing clips to be removed in less than five minutes. The very local heating via the foil heaters allows good access for clip removal and protects all underlying and adjacent materials.

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