Page:Advanced Automation for Space Missions.djvu/187


 * R&amp;D required - Not a promising future line of inquiry.
 * Qualitative Tukey Ratio - Moderately poor. Some of the consumables, especially gases, are comparatively difficult to obtain in quantity from lunar soil.

4E.1.2 Oxyfuel welding

Included among the oxyfuel gas-welding techniques are oxyacetylene, methylacetylene propadiene (MAPP), airacetylene, oxyhydrogen, and pressure gas. The SMF suitability assessment produced the following results:


 * Make other equipment - Need a basic joining process.
 * Production rates - Estimates include 0.6 to 10 m/hr (2 to 30 ft/hr) (Romans and Simons, 1968), 1.6 to 5.4 mm2/sec (Houldcroft, 1977), and 0.3 to 0.6 kg/hr (Schey, 1977).
 * Required consumables - Main consumables are gases, especially acetylene and oxygen. Filler rods and flux may or may not be required (Houldcroft, 1977).
 * Production energy - Romans and Simons (1968) claim that vertical welding at a rate of 2-5 m/hr requires 70-500 liters/hr of acetylene gas at STP.
 * Preparation steps - Need gases in pressure tanks, a simple valve/regulator structure, gauges, hoses, torch and torch tip assemblies (Griffen et al., 1978). Surface preparation of workpieces requires a basic cleaning process. Jigs typically are used to hold the workpiece in the proper positions.
 * Production environment - Gases necessitate a pressurized environment.
 * Automation/teleoperation potential - Already automated in many terrestrial manufacturing applications (Phillips, 1963; Yankee, 1979).
 * People roles - Could conceivably be used by astronauts to perform quick, portable repair welding operations in a pressurized environment.
 * R&amp;D required - Not a promising future line of inquiry.
 * Qualitative Tukey Ratio - Very poor in the near-term due to heavy dependence on gases comprised of chemical elements having low lunar abundances (eg., acetylene, MAPP, hydrogen).

4E.1.3 Resistance welding

Resistance techniques include spot, projection, seam, flash butt, upset, and percussion welding. (High-frequency resistance welding is discussed as an electronic welding technology.) The assessment follows:


 * Make other equipment - Basic joining process is needed.
 * Production rates - Ranges from 16 to 107 mm2/sec are given by Houldcroft (1977) for resistance welding generally, and Romans and Simons (1968) estimate 1 to 4 m/min (36 to 144 in./min) for seam welding.
 * Required consumables - Air (gas) or water are necessary to provide high pressures, and water is needed for cooling. Substitutes can probably be found among available nonterrestrial materials.
 * Production energy - Considerable electrical energy is required, typically 1000 to 100,000 A at 2 to 20 V (Moore and Kibbey, 1965; Romans and Simons, 1968). Romans and Simons give a range of 1 to 140 W/hr per spot weld.
 * Preparation steps - Modest resistance welding machines require very large power supplies. Pressure-producing cylinders for larger equipment are somewhat complex, and sophisticated timing devices are necessary. However, little preparation of materials is needed, perhaps the key reason why resistance welding is so popular on Earth (Moore and Kibbey, 1965).
 * Production environment - Moore and Kibbey (1965) indicate that air must be supplied for operation of the electrodes, so a pressurized environment may be necessary.
 * Automation/teleoperation potential - These techniques have already been largely automated on Earth.
 * People roles - None required other than design.
 * R&amp;D required - Not a promising future line of inquiry.
 * Qualitative Tukey Ratio - Moore and Kibbey (1965) note that resistance welding electrodes are subjected to 10,800 A/cm2 at 410 MN/m2 (70,000 A/in.2 at 60,000 psi). It seems unlikely that lunar-abundant aluminum could even come close to replacing copper-bronze and copper-tungsten alloys used to make electrodes on Earth. Also, it is questionable whether aluminum could be incorporated in the massive high-current power transformers required. The Tukey Ratio appears quite poor in this case.

4E.1.4 Solid-state welding

Included within this category are ultrasonic, explosive, diffusion, friction, inertia, forge, vacuum (cold), and roll welding. The SMF assessment is as follows:


 * Make other equipment - Need a basic joining process.
 * Production rates - On thin materials, roller-seam ultrasonic welds can be produced at rates up to 10 m/min.