Page:Advanced Automation for Space Missions.djvu/177



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.

(a) Forging

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.

(b) Rolling

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.