it is needed in the fabrication sector. A general flowchart of the entire automated parts fabrication process appears in figure 5.17.
5F.5 Parts Fabrication: State-of-the-Art
In the operation of any general-purpose fabrication machine (mill, lathe, laser machining system, casting robot, there are seven distinct functions which must be performed either manually or automatically, according to Cook (1975):
- Move the proper workpiece to the machine,
- Load the workpiece onto the machine and affix it rigidly and accurately,
- Select the proper tool and insert it into the machine,
- Establish and set machine operating speeds and other conditions of operation,
- Control machine motion, enabling the tool to execute the desired function,
- Sequence different tools, conditions, and motions until all operations possible on that machine are complete, and
- Unload the part from the machine.
Traditionally all seven operations were performed by the human operator. The development of numerical-control (N/C) machining relieved human operators of the need to manually perform step (5), and automatic tool-changing systems supplanted step (3). Although most modern computer-controlled machining systems have "a finite number of tool-storage locations - 24, 48, or 60 tools, for example - the number that could be built into a system runs into the thousands" (Gettleman, 1979). If the seed is comprised of about 1000 different kinds of parts, each requiring a template pattern for the casting robot, Gettleman's estimate for N/C machine tooling makes plausible the satisfaction of this requirement by extensions of current technology. Adaptive control of N/C machine tools, with sensors that measure workpiece and tool dimensions, tool application forces, vibration and sound, temperatures, and feed rates to optimize production have already been developed (Nitzan and Rosen, 1976) but will require further improvements to achieve the kind of generalized capability required for a lunar SRS.
The next logical developmental step is the design of a completely computer-managed integrated parts manufacturing system. Cook (1975) describes such a system developed and built by Sunstrand Corporation. One version in operation at the Ingersoll-Rand Company is used primarily for fabricating hoists and winches, while another at the Caterpillar Tractor Company is used for making heavy transmission casing parts (Barash, 1976). As of 1975 there were about ten similar systems in operation in the U.S., Japan, Germany, and the U.S.S.R. (Barash, 1975).
The Ingersoll-Rand system consists of six NIC tools - two 5-axis milling machines, two 4-axis milling machines, and two 4-axis drills - arranged around a looped transfer system as shown in figure 5.42. Machining operations include milling, turning, boring, tapping, and drilling, all under the control of an IBM 360/30 central computer. At any given time about 200 tools are in automatic toolchanging carousels, available for selection by the computer, although about 500 are generally available in the system. The computer can simultaneously direct the fabrication of as many as 16 different kinds of parts of totally different design which are either being machined, waiting in queue to be machined, or are in the transfer loop. The entire system is capable of manufacturing about 500 completely different parts. During each 12-hr shift the system is run by three human operators and one supervisor. It is calculated that to achieve the same output using manual labor would require about 30 machines and 30 operators. Finally, the circular pallets used to present parts to each control station have maximum dimensions which fit inside a 1-m cube, exactly the scale discussed earlier in connection with the casting robot.
Another major advance is the variable-mission manufacturing system developed by Cincinnati Milacron Inc. This system not only has the general character of computer managed parts manufacture seen in other systems but also provides for the processing of low-volume parts at higher rates than those which can be achieved with more conventional N/C machines. For instance, an ingenious five-axis "manufacturing center" automatically changes clusters of tools mounted on a single head so that a number of operations can be performed simultaneously by means of a novel scheme of handling workpieces from above, the Cincinnati Milacron system provides efficient management of coolants and chips, together with easy access for inspection and servicing (Cook, 1975).
The Japanese have been most aggressive in pursuing the "total automation" concept. During 1973 through 1976 their Ministry of International Trade and Industry (MITI) supported a survey and design study entitled "Methodology for Unmanned Manufacturing" (MUM) which forecast some rather ambitious goals. The MUM factory was to be operated by a 10-man crew, 24 hr/day, and replace a conventional factory of about 750 workers. The factory will be capable of turning out about 2000 different parts at the rate of 30 different parts (in batches of about 1-25) per day, which will be inspected and assembled to produce about 50 different complex machine components such as spindle and turret heads, gear boxes, etc. Machining cells, based on the principle of group technology, will be controlled by a hierarchy of minicomputers and microcomputers, and will receive workpieces via an automated transfer system. Each machine cell will be equipped with inspection and diagnostic systems to monitor such useful
