Advanced Automation for Space Missions/Appendix 4D
Appendix 4D Review Of Deformation In Manufacturing
Deformation involves the production of metal parts from ingots, billets, sheets, and other feedstock. Metal is forced to assume new shapes by the application of large mechanical forces to the material while it is either hot or cold. The purpose of this mechanical working is twofold: first, to bring the feedstock into a desired shape, and second, to alter the structure and properties of the metal in a favorable manner (e.g., strengthening, redistribution of impurities).
4D.1 Deformation Techniques
A number of major deformation techniques are described below with emphasis on currently automated techniques, followed by an overview of deformation criteria in space manufacturing applications.
The deformation of metal into specific shapes includes a family of impact or pressure techniques known as forging. Basic forging processes are smith or hammer forging, drop forging, press forgin8, machine or upset forging, and roll forging. Special forging processes include ring rolling, orbital forging or rotaforming, no-draft forging, high-energy-rate forming, cored forging, wedge rolling, and incremental forging.
Unimate and Prab industrial robots are already employed in many commercial forge shops. For example, the 2000A Unimate is currently used to feed billets through a two-cavity die-forging press to be formed into raw differential side gears (Unimation, 1979). A more sophisticated robot, the 4000A three-axis Unimate, is used to transfer hot (~1400 K) diesel engine crankshafts from a forging press into a twister (fig. 4.27). The Unimate used in this operation has a 512-step memory, rotary-motion mirror imaging, and memory-sequence control with one base and one subroutine (Unimation, 1979). Forging systems involving gas, steam, or hydraulic drives are excluded from consideration in space or lunar factories since, in general, any system susceptible to fluid leakage is of lower developmental priority for space operations than other processes with similar capabilities.
The energy required for single-drop forging is a function of the mass and velocity of the ram, exclusive of energy to rough form or to heat the parts for the forge. This assumes only a single pass and not the usual progressive steps to create a metal form from one die impression to the next. One modification to be considered in gravity-fall (drop) forging on the Moon is mass enhancement by sintered iron weights, possibly coupled with electromagnetic acceleration (only electrical energy is needed for lunar factory forging processes). Impact forging by electromagnetically driven opposing die sets may produce still closer parts tolerances than drop forging.
Forging operations, from raw precut feedstock to ejected forging, likely can be completely automated on the Moon.
Space manufacturing applications of rolling mills have been considered by Miller and Smith (1979). Automated stop-go operations for the rolling mill, slicer, striater, trimmers, welders, and winders in figure 4.28 readily may be visualized. It is important to note that aluminum is the resource considered and ribbon is the processed form. Lunar aluminum-rich mineral recovery, extraction, and processing make good sense since beam builders in Earth orbital space already have been designed for aluminum ribbon feedstock.
Two types of rolling mills can manufacture ribbon from aluminum alloy slabs prepared from lunar anorthosite. The first or regular type of mill consists of a series of rolling stands with lead-in roughing rollers and finishing rollers at the end. Input slabs travel through one stand after another and are reduced in thickness at each stand. Each stand rolls the slab once. High production rates result. A second option is the reversing mill. Slabs are routed back and forth through the same stand several times and are reduced in thickness during each pass. This requires a mill with movable rolls able to continually tighten the gap as slabs grow thinner. Although reversing mills have lower production rates and are more complicated than regular rolling mills, they are more versatile and require fewer machines. Expected yearly aluminum production at the SMF designed by Miller and Smith (1979) is minimal by normal rolling mill standards, so low-mass reversing mills are sufficient for the present reference SMF.
Input slabs can be hot-rolled or cold-rolled. However, if a cold aluminum alloy slab is rolled to more than 120% of its input length, cracks appear in the material. To avoid this problem, slabs are annealed between passes or are rolled hot throughout the process. (The final rolling pass should be done cold to improve the structural properties of the output.) Miller and Smith (1979) chose to hot-roll the input slabs, which, therefore, either travel directly from the continuous caster to the rolling mill without cooling or are taken from intermediate storage and preheated before insertion into the mill. Aluminum alloy slabs elongate roughly by a factor of 11 as they are squeezed from a thickness of 2 cm down to 1.77 mm. Rolling also widens the slabs from 70 to 73.5 cm, the width required for structural member ribbon. Input slab length is arbitrary and often is determined merely by handling convenience, though slabs usually are at least as long as they are wide. An 80-cm-long slab produces about 8.8 m of ribbon.
(c) Special Forming Operations
The following forming operations are considered as a group with respect to robotics applications and lunar factory criteria: conventional stretching, conventional drawing (involving nine suboperations) and deep drawing, swaging, spinning, and bending.
Stretching is a cold-forming process in which sheet metal is wrapped around an upward-moving form block. Conventional drawing involves pressing a flat metal blank into a male die while stretching the blank to force it to conform to the shape of a male die or punch. Shallow drawing is defined as a deformation cup no deeper than half its diameter with little thinning of the metal, whereas, deep drawing produces a cup whose depth may exceed its diameter with more pronounced wall thinning. Swaging is a cold-forging process in which an impact or compressive force causes metal to flow in a predetermined direction. Spinning is a forming technique for plastically deforming a rapidly rotating flat disk against a rotating male contour. Cold spinning is used for thin sheets of metal. Hot-spinning of heavier sheets up to 150 mm thick can produce axisymmetric (shell) shapes. Finally, bending is the plastic deformation of metals about a linear axis with little or no change in the surface area.
Robotics applications and space manufacturing options for these types of deformation processes are minimal, especially under vacuum conditions. If there is no oxidized film on the metal, the workpiece and die may contact weld, causing the machine to seize.
In the extrusion process, either at high or low temperatures, metal is compressively forced through a suitably shaped die to form a product with reduced cross-section - like squeezing toothpaste from a tube. Lead, copper, aluminum, magnesium, and their many alloys are commonly employed, and hydrostatic extrusion using high-pressure fluids into the die makes possible similar processing of relatively brittle materials such as molybdenum, beryllium, and tungsten. Steel is relatively difficult to extrude because of its high-yield strength and its tendency to weld to die walls. Extrusion by pressurizing solid metals shares with other deformation processes problems of cold welding. However, the degree of such welding decreases if markedly dissimilar metals are in contact. The vacuum environment may enhance ductility for some extruded metals.
In one variant of the basic extrusion process, melts are drawn through dies to produce threads. The use of basalt in preparing spun products is well known (Kopecky and Voldan, 1965; Subramanian et al., 1975, 1979) and has numerous lunar applications (see table 4.16). A variation of the technique is the use of centrifugal force to spin the extruded threads (Mackenzie and Claridge, 1979).
In commercial spun basalt processes, molten basalt is drawn through a platinum-rhodium bushing and the final fiber blasted by a tangential gas or steam jet in the air cone as shown in figure 4.7. Fibers also may be produced without the air cone by direct pulling of a winding reel. For example, work done by Subramanian et al. (1975) showed that molten basalt flowing from a 3-mm hole in a graphite crucible, yielded fibers by simple mechanical pulling (table 4.26). The crude fibers created using this procedure were nonuniform, measured about 150 um diam, and contained many nodules - a poor product compared with air cone output. Assuming the air/steam cone can be eliminated from basalt spinning operations, a step-by-step Unimate-automatable sequence is suggested in table 4.27.
|Temperature at bottom of bushing, K||Fiber size, um||Tensile strength,|
aAverage of only five specimens.
As yet no research has been performed either on vacuum or lunar basalt fiber drawing. Molten basalt on the Moon has very low viscosity which may possibly be controlled, if necessary, by additives. At present it remains unknown whether mechanical spinning of raw lunar basalts is possible or if the vacuum environment will yield a thinner, more uniform product. Still, extrusion of viscous rock melts to produce spun products appears promising and as indicated in table 4.27 is likely amenable to automation in space-manufacturing applications.
Shearing is the mechanical cutting of sheet or plate materials using two straight cutting blades, without chip formation, burning or melting (DeCarmo, 1979). If the shearing blades have curved edges like punches or dies the process is given another name (e.g., blanking, piercing, notching, shaving, trimming, dinking, and so on as noted in table 4.17.)
Shearing already has been automated in many industries. For instance, the Chambersburg Engineering Company has incorporated a 2000B Unimate into a trimming operation performed on the output of an impact forging system. The robot moves 1400 K platters from the forge to hot trimmers, sensing, via hand tooling interlocks, that it has properly grasped the platter. An infrared detector checks parts for correct working temperatures, and the robot rejects all platters for which either grasp or temperature requirements are not met (Unimation, 1979).
Despite its tremendous utility on Earth, shearing appears less desirable than other options for space manufacturing because of the problems of cold welding and shearing tool wear. Also, ceramic and silicate forms cannot be processed by conventional shearing techniques. The most attractive alternative may be laser-beam cutting, piercing, punching, notching, and lancing. Yankee (1979) has reviewed laser-beam machining (LBM) generally, and additional data are provided in section 4.3.1. The application of LBM techniques to metals for shearing operations is an established technology, whereas laser beam cutting of basalt and basalt products is not well-documented.
4D.2 Deformation Criteria and Research Options for Space Manufacturing
In general, deformation processes that do not require gas or liquid drives but emphasize electrical or electromagnetic mechanical power sources appear more practical for space manufacturing applications. Processes yielding thin-walled or ribbon forms such as reversible rolling or electroforming appear favorable. The mass/production ratio argues against heavy forges and in favor of roller technology, an approach which also should improve the quality of output in high-vacuum manufacturing environments. Deformation processes involving forming or shearing typically consume little material (except for fluid-driven devices). On the Moon, the optimum near-term design philosophy is to develop automated systems powered exclusively by electric and magnetic forces.
In order to make tool products, versatile semiautomated machines are initially required for the terrestrial demonstration program Tool life and machining time must be assessed in view of the extraterrestrial conditions anticipated. For example, Ostwald (1974) has reviewed these 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.
|Friction and Abrasion Wear|
|Erosive-wear testing facility||Albany Metallurgy Research Center
John E. Kelley, 420-5896
|A 12-specimen erosion test apparatus built at AMRC uses an S.S. White Airbrasive model-H unit to propel 27 um AI2O3 particles against specimens at temperatures UP to 1,000°C in selected atmospheres and at selected impingement angles. Relative erosion is determined by comparing material loss of a target with that of a "standard" specimen.|
|Friction and rubbing-wear test facility||Albany Metallurgy Research Center
John E. Kelley, 420-5896
|A Falex-6 friction and wear machine built by Faville-LeVally Corp. is used to measure abrasion wear, adhesive wear, and coefficient of friction of solid materials. Pin-on-disc and ring-on-ring tests can be made, wet or dry, with or without abrasive particles, in either cyclic or continuous rubbing modes, under variable and controllable conditions of speed, load, atmosphere,and temperature to 260°C (500°F).|
|Friction and wear||Twin Cities Mining Research Center
D. R. Tweeton, 725-3468
|The Dow Coming Alpha LWF-1 friction- and wear-testing machine can measure sliding friction of metal/metal or metal/mineral test pairs in air or environmental fluid.|
|Impact-abrasion tester||Albany Metallurgy Research Center
John E. Kelley, 420-5896
|An impact machine with variable speed and thrust is used to repeatedly impact test specimens tangentially against a rough material such as sandstone to determine the impact-abrasion wear rate.|
|Simulated-service ball-valve tester||Albany Metallurgy Research Center
John E. Kelley, 420-5896
|Ball valves fitted with experimental parts such as balls and seats can be tested for wear by automatic cyclic operation. During each cycle a differential pressure up to 2100 Pa at 430°C (650°F) is applied, then relieved, across the valve, and abrasive solids are passed back and forth through the valve by operating the tester in the manner of an hourglass. Parts wear is monitored by recording the rate of gas leakage across, say, the ball and seat each time the differential pressure is applied. Damaged parts are removed and examined both macro- and microscopically.|
|Hardness and Scratch Analysis|
|Microhardness||Twin Cities Mining Research Center
George A. Savanick, 7254543
|The Zeiss microindentation hardness tester is capable of measuring the microhardness of selected microscopic areas on solid surfaces. A Knoop diamond is pressed into the solid and the diamond-shaped impression thus formed is measured under high magnification (500-1,500X)with a special eyepiece. The optical system is equipped with a Nomarski differential interference contrast capability which enhances image contrast.|
|Schmidt hardness||Twin Cities Mining Research Center
W. A. Olsson, R. E. Thill, 725-4580
|Soil test Schmidt hardness hammer and Shore scleroscope hardness tester for determining the hardness properties of a material.|
|Scratch analysis||Twin Cities Mining Research Center
Robert J. Willard, 7254573
|Hilger and Watts fine-scratch microscope, model TM-52, for use in measuring widths and depth (in inches) of scratches on rock and mineral materials. Moderate experience in scratch measurements, can provide scratch analyses on a limited number of samples of any solid, translucent or opaque material.|
|Shore hardness||Denver Mining Research Center
R. Gerlick, 234-3765
|Shore hardness tester to determine hardness of rock and other materials.|
|Rock drilling and cutting, core preparation||Denver Mining Research Center
H. C. Farley, E. B. Wimer, 234-3755
|Trained staff and equipment available to take core from small samples and prepare it for testing, cutting, grinding, etc.|
|Rock cutting and handling||Twin Cities Mining Research Center
R. L. Schmidt, 725-3455
|Trained staff and equipment are available to conduct small- or large-scale experiments in the laboratory or field. Instrument drilling equipment includes a 2-boom jumbo with drifters, airleg drills, a diesel-powered diamond drill, and a truck-mounted rotary drill. Small- and large-scale linear rock-cutting apparatus are also available with thrust capabilities to 14 tons. The laboratory is equipped with service equipment for handling up to 7-ton rock blocks.|
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