“Every American manufacturer must reduce production costs tostay alive in today’s fierce world market. One way is by embracingFMS technology,” says William F Iacoe, director of manufacturing,Electronic Products Div, Onan Corp, Minneapolis, MN.”Unfortunately, yesterday’s hardware justificationmethods–direct labor or material reduction–direct labor or materialreduction–can’t be applied to FMS. “A flexible manufacturing system can produce parts with almostno setup cost. That’s where to look. When you eliminatetime-consuming and labor-intensive setups, you begin to realize the vastpotential for FMS productivity.
” Onan, a subsidiary of McGraw-Edison, manufactures portable andstationary electric generator sets, diesel and gasoline engines,alternators…
they’re heavy-duty metalworkers and they practicewhat they preach. The firm recently purchased a $2.5-million FMS forfabricating from Trumpf America Inc, Farmington, CT. The turnkey system will automate Onan’s entire sheet-metal part production, and mightbe the most comprehensive fabrication FMS installed in the US. Sophisticated subsystems The entire FMS is comprised of many integrated subsystems, Figures1 and 2.
The automatic storage and retrieval subsystem (AS/RS), forexample, has a rack consisting of 51 material bins, each capable ofholding 6600 lb of sheet or plate stacked to a height of 6-1/2″ andserviced by a stacker crane. A second rack can be added for futureexpansion. Herehs how the FMS operates. A guided transfer cart delivers pallets of raw material to anautomatic sheet loader. A thickness sensor and double-sheet detectorensure correct single-sheet transfer. A vacuum-cup lifter transports a sheet of work material to themachine tool, a Trumatic 180 Laserpress that combines punching andcontouring with laser cutting (800 W Co.sub.
2.; both pulsing andcontinuous wave). The machine handles up to 1/4″-thick sheets. The press features X-axis stop-pin location and four clamps forY-axis registration. Electronic sensors ensure overall materialregistration prior to processing. Unlike conventional turret punch presses, the FMS is serviced by arobot toolchanger.
The three-axis programmable robot has adouble-ended, rotary, axial gripper. The end effector removes apreloaded tool cartridge from the press, rotates, and inserts a newcartridge. While the machine punches and laser cuts, the robot returnsthe used tool to its appropriate location in the storage towers, thenselects the next tool. the rotary tool towers are designed to allow many tools in alimited space, and minimize the locations programmed for the robot. Eachof the 10 circular levels in a tower holds 10 tools.
Whiel three towers provide the necessary number of preloaded toolcartridges for continuous automated production, up to four towers may bespecified. Using a new Multitool unit (i.e., a single cartridgecarrying up to four tools), the system has capacity for 1600 tools. Finished parts up to 8″ X 16″ enter a programmable dropchute adjacent to the laser cutting head and are directed to asmall-parts sorter. A linear shuttle, with six bins, sorts part-sizecategories. Larger parts are picked up by an unloading device that has 72densely arranged suction cups individually programmed to conform to holepatterns and sheet size. Under program control, these parts areconveyed to one of nine sorting pallets in two shuttle carts.
Longstrips of offal are sorted into bins at the front of the carts and maybe used in other progressive-die operations, thereby optimizingraw-material use. Finally, forklifts remove filled pallets, transporting them eitherto storage or other manufacturing areas. According to Trumpf,wire-guided vehicles or other transport systems can be incorporated hereto fully automate the FMS. Onan’s Iacoe emphasizes, “Delivery of the systemculminated nearly two years of effort. Our manufacturing engineerssurveyed leading equipment manufacturers on three continents, visitingnumerous installations, before selecting Trumpf. In effect, we formed apartnership with them to do something in sheet-metal FMS thathasn’t been done before in this country.” System smarts DNC synchronizes and controls all activity in the FMS, Figure 3.
Production at Onan is being converted into a queuing process thatautomatically generates nested parts on sheets in two modes–one forongoing production, the other for exceptions that need expediting. TheDNC continuously monitors inventory, tooling (e.g.
, hit count andregrind status), and work in progress. The DNC system is hardware-independent, which allows any compatiblecomputer to be incorporated. In Onan’s case, the brain is a DECVAX-750, multitasking, multiuser, 32-bit speed demon. DNC begins with input concerning tooling inventory in the towersand material in the storage and retrieval system, incoming orderinformation, and part definition supplied by a Computervision CAD/CAM system. Tool-path information can be accepted in three formats: APTsource code, an APT-CL document, or actual NC code. This data enters aSystem Planner software module, which performs nesting calculations thatconsider burden and penalties for breaking a lot run, and prepares bothsuspended and ready-to-execute job lists.
A System Schduler software module groups jobs according to priorityand efficiency. For instance, when feasible, jobs calling for the samegage material are grouped sequentially, rather than separated by jobsrequiring different material gages. Jobs are run by an execution Controller software module thatinterfaces with a graphics monitor and an exception handler (one of thefirst implementations of a shop-floor expert system).
The ECmanipulates all operations of the AS/RS, the laser press, sheet loaderand unloader, part sorter, and robot tool-changing system. Initial production is scheduled this month. Over 1000 part numbersalready are programmed for the system, with full production expected bythe end of the first quarter (approximately 5000 total part numbers). For more information about flexible-fabricating technology, circleE62.