Page:Advanced Automation for Space Missions.djvu/188


 * Required consumables - Air, water, or other pressure-producing agents are needed for cold, friction, and roll welding. Explosion welding uses explosive sheets with TNT, ammonium nitrate, amatol, and others. Ultrasonic welding requires a transmission medium for sound waves.
 * Production energy - Vacuum (cold) welding requires only a very light pressure. Ultrasonic welders are rated at up to 25 kW (Schwartz, 1979).
 * Preparation steps - Materials to be cold welded under vacuum need only be appropriately positioned for application of modest pressure, though the exact preparation steps for a vacuum welding machine are unknown. Explosion welding involves placing an explosive sheet on the workpieces. Friction and inertia welding require a driving system, hydraulic cylinder, bearing, bearing enclosure, etc. Ultrasonic welding utilizes a rigid anvil, a welding tip consisting of a piezoelectric crystal and a transducer with horn, and a force-application mechanism. Parts alignment is a crucial step in all joining processes.
 * Automation/teleoperation potential - Most, if not all, of these techniques should readily be automatable.
 * People roles - None, other than original design.
 * R&amp;D required - Cold welding has the highest appeal as a simple joining process. A system of applying small pressures without accidentally contact welding the machine to the workpiece must be devised. One simple method is a vise made of insulated metal parts (teflon- or oxide-coated). More must be learned about cold-welding properties of various materials.
 * Qualitative Tukey Ratio - Seems likely to be extremely good for cold welding. Closely related forms such as friction, inertia and roll welding should also exhibit satisfactory Tukey Ratios, since only small pressures need be applied. Forge and diffusion welding require heat as well (and hence, seem superfluous), but can probably exhibit favorable ratios with some modification. The ratio for ultrasonic welding appears relatively poor.

4E.1.5 Electronic welding

Electronic welding methods encompass forms of electron-beam, laser, induction, and high-frequency resistance welding. The following is the SMF suitability assessment:


 * Make other equipment - A basic joining process is needed. (Note: A number of these techniques, particularly the laser, can be used for many other options.)
 * Production rates - Lindberg (1977) cites a figure of 16 m/hr (50 ft/hr) for a high-power continuous-wave solid-state laser. The estimate by Schwartz (1979) is much higher: 50 to 80 m/hr (150 to 250 ft/hr). Electron-beam welders can produce up to 1800 small parts per hour in a partial vacuum (Schwartz, 1979) or up to 200 mm2/sec of welding (Houldcroft, 1977). Induction welding production rates are given as 6.5 m/min (20 ft/min) of 20 cm (8 in.) pipe (Phillips, 1963) and 3.1 m/min (122 in./min) of tube welding for typical machines (Lindberg, 1977). High-frequency resistance methods can weld seams at 50 m/min (150 ft/min) with 60% efficiency (Schwartz, 1979).
 * Required consumables - Flashlamps for solid-state lasers have a lifetime of 104 to 105 shots. Gas lasers may use a variety of gases including CO2/H2/N2, argon, krypton, neon, xenon, and others. Electron-beam filaments last 2 to 1000 hr depending on filament type. High-frequency resistance welding contacts are good for roughly 6,000 to 130,000 m (50,000 to 400,000 ft) of welding before they must be replaced (Schwartz, 1979).
 * Production energy - Lasers require up to 15 to 20 kW (Lindberg, 1977; Schwartz, 1979). Schwartz notes that gas lasers are inefficient (less than 0.1%) relative to solid-state lasers (up to 10% efficiency). Electron-beam welders draw 6 to 75 kW, with voltages in the 15 to 200 kV range. The American Welding Society (Phillips, 1963) estimates 1 to 600 kW output power for induction welding - as much as 1 MW may be needed in some cases. Energy requirements for high-frequency resistance welding are much lower than other resistance techniques due to increased resistivity at higher (400 kHz) frequencies (Lindberg, 1977; Schwartz, 1979). Schwartz claims that the most powerful high-frequency resistance welding machines in terrestrial use draw 150 kW, though many require only 1 to 50 kW.
 * Preparation steps - A solid-state laser is comprised of a rod, laser cavity, precision-ground mirrors, flashlamp, cooling system, focusing optics, and power supply. In recent years ruby rods have been increasingly replaced by Nd:YAG rods (Schwartz, 1979). Flashlamps usually are xenon- or krypton-filled (Lindberg, 1977). Gas lasers do not need rods and flashlamps of such exotic composition, but instead require gas and a heat exchanger. Electron-beam welders need a sophisticated variant of the cathode-ray tube, a very high voltage power supply, and preferably a vacuum environment. Induction welding units are characterized by a large coil at low frequencies, a high-power oscillator circuit at high frequencies,