parameters for cost estimation. The Taylor tool life equation is VTnFm = k, where V is linear tool velocity across the workpiece (m/sec), T is tool life (sec), n and m are dimensionless empirical exponents (logarithmic slopes), F is tool bit-feed rate or relative speed of workpiece and cutting surfaces (m/sec or m/rev), and k is a constant determined by laboratory evaluation of various cutting materials. Machining time t is given by πLD/12VF, where L is length of cut (m) and D is tool diameter (m). Unfortunately, the special production environment includes low- to zero-g which precludes all shaving- or chip-generating processes unless tools are placed under an oxygen-rich atmosphere.
Clearly, novel techniques must be considered in manufacturing designs intended for nonterrestrial applications. For instance, thread rolling offers a solution to fastener production, electroforming appears suitable for thin-walled containers, and noncentrifugal basalt casting may prove useful in low- or zero-g and yield a more homogeneous product. Vacuum enhances the characteristics of some metals, e.g., cold rolling increases the tensile strength of steel and improves the ductility of chromium. Electrostatic fields may enhance bubble coalescence in metallurgical or rock-melt products.
Many areas of research and development are required to generate appropriate deformation options for an SMF. In deformation processes where oxidized metal surface coatings must be broken (e.g., impact forging, stretching, deep drawing, and shearing), the minimum amount of oxygen necessary to prevent cold welding must be determined. Specific surface poisoning requirements must be measured for specific metals. Thermal environment is also of critical significance. Deformation at temperatures below about 230 K must take proper account of metal embrittlement. Fracture propagation in very cold steel is a serious problem on Earth. Rate processes in metal deformation may be significant in a lunar factory. If an enclosed, slightly oxygenated automated factory bay is provided (perhaps adjacent to the shirtsleeve environment of a manned facility) there appears to be no severe energy constraint in keeping the bay area above 230 K. Temperature control could be achieved by electrical heaters or unidirectional heat pipes for factories sited, say, at the lunar poles (Green, 1978).
Additional research opportunities include:
- Remote sensing of nonterrestrial ore deposits
- Mass launch of materials to processing plants
- Commonality of magnetic impulse forming components with those of mass-launch equipment
- Quality control of ores by intelligent robots
- Optimum spun/cast basalt mixtures
- Tool-life evaluations including sintered and cast basalts
- Powder metallurgy using induction heating or admixed micron-sized raw native iron in lunar "soil" (abundance about 0.5%)
- Factory control strategies
- Factory configuration studies.
Further experimentation also is needed with metal/rock test pairs to determine wear, abrasion, and hardness characteristics after deformation under high-vacuum, low-oxygen conditions. The U.S. Bureau of Mines has done some research on certain aspects of this problem at their centers in Albany, Denver, and Twin Cities. Test equipment, procedures and key personnel pertinent to space and lunar manufacturing options are named in table 4.28.
The role played by humans in space operations will vary with the machine for some deformation processes. Optimum proportions of human and robot activities in lunar factories will doubtless evolve over a period of time, with major manned support expected in early phases of SMF operation, and far less, once production becomes routine. Almost all forming or shearing procedures can be automated either in feed or transfer operations. Indeed, present-day Unimate-series robots have proven especially suitable in such applications in terrestrial industry.
