Page:Advanced Automation for Space Missions.djvu/361

 accomplishedindustrial robots, although actual patusing tern formation remains largely manual. In permanent die casting, the Nike sports shoe subsidiary in Massachusetts produces tapes for its N/C electrical discharge machining apparatus which drives the tool to form the dies automatically from drawings of the shoe's sole constructed using the plant's CAD/CAM system. On the whole, however, the formation of patterns and disposable molds (especially green sand casting molds) has remained manual; only equipment for lifting and turning the flasks has come into widespread use. Robots have been employed to unload hot parts from die casting machines as well as place the (hot) castings into trimming dies. Almost all automation of casting has been in high-volume applications where one standard shape is produced ten thousand times per year or more. High-volume production is not likely to be the general mode of space manufacturing, which will probably call for small lot, intermittent production. Methods of performing automatic casting, especially using disposable molds, and doing this efficiently in low or zero-gravity conditions are required. Elimination of molds using containerless forming techniques should also be investigated and, if successful, will significantly reduce the high capital costs of forming molds and dies. The problems of heat removal and control of the rate of cooling to control grain size in the castings requires both sensor development to sense the internal temperatures and new heat dissipation technologies. Powder processing has been somewhat automated on Earth, but has not been used extensively due to the tremendous costs associated with purifying and maintaining a nonoxidizing environment for manufacturing. This environment is available in space and on the lunar surface. But, as in the case of casting, powder processing uses dies to form parts. Again, the study of containerless forming techniques may be fruitful, with powder processing alleviating some of the heat dissipation problem, since sintering temperatures are lower than those required for casting. The applicability of powder formation via liquefaction and spraying should be assessed. Grinding and milling must also be examined, since the cold welding phenomenon between similar pure metals may be turned to advantage if it can be used to facilitate coalescence of the metals without sintering or melting. Intensive study of this effect is best performed in space, as pure powders are extremely difficult to prepare and maintain on Earth. Cold welding also has important implications for machining and lubrication. Machining, or chip formation processes, are the usual finishing operations. These have been extensively automated, but significant problems with heat dissipation and cold welding may be encountered in space if the tools are run in a vacuum. The primary cause of tool wear is the temperature generated at the tool/chip interface. Removal of this heat through the use of cutting fluids will be difficult because all terrestrially used fluids are either petrolemn or water-based two commodities expensive in space and difficult to control in a zero-g environment. Cold welding will decrease chip forming in two ways -first, by the formation of built-up edge on the tool face (although temperature and pressure may still be the determinants of this effect), and second, by the reattachment of the pure metal chips to the cut or uncut surface or machine table by vacuum welding. Use of lasers to finish may eliminate many of these problems and thus may be of tremendous utility, especially if casting or powder techniques can be expected to produce high-tolerance parts. The use of ultra-high speed machining in which most of the heat of cutting is carried away by the molten chip could also be a partial solution, and also the use of ceramic tool bits and cast basalt tables. (See also appendix 5F.) Assembly requires robotic/teleoperator vision and end effectors which are smart, self-preserving, and dexterous. Accuracy of placement to 0.001 in. and repeatability to 0.0005 in. is desirable for electronics assembly. Fastening technologies, including nonvolatile adhesives, cold welding, mechanical fasteners, and welding all require special adaptation to the space environment. Control of a large-scale space manufacturing system demands the use of a distributed, hierarchical, machine intelligent information system. Material handling tasks require automated, mobile robots/teleoperators. In support of these activities, vision and high-capacity arms, multi-arm coordination, and dexterous end-effectors must be developed. For inventory control, an automated storage and retrieval system well suited to the space environment is needed. The ability to gauge and measure products (quality control) benefits from automated inspection, but a general-purpose machine-intelligent high -resolution vision module is necessary for quality control of complex products.

6.4.2 Materials Processing and Utilization While it is expected that the orbiting space manufacturing experiment station initially will be supplied with differentiated raw feedstock for further processing, some interesting experiments in systems operations and materials extraction are possible and should be vigorously pursued. One such experiment could be a project to build one reasonably complex machine tool using a minimum of human intervention and equipment. Two logical candidates emerge. The first is a milling, grinding, or melting device that could be used to reduce Shuttle external tanks to feed stock for further parts building or experiments. This project would allow experimentation in material separation and processing using a well-defined and limited input source which can be obtained at relatively low cost whenever the Space Shuttle carries a volume-limited rather than a weight-restricted load. Such a large-scale experiment could be used as an "extra-laboratory" verification of extraction, manipulation aswellaspro andcontrolmechanizations, vidingrelativelyeasyaccessto puremetalpowdersfor