Flexible fabricating punches up productivity Essay

“Every American manufacturer must reduce production costs to
stay alive in today’s fierce world market. One way is by embracing
FMS technology,” says William F Iacoe, director of manufacturing,
Electronic Products Div, Onan Corp, Minneapolis, MN.
“Unfortunately, yesterday’s hardware justification
methods–direct labor or material reduction–direct labor or material
reduction–can’t be applied to FMS.

“A flexible manufacturing system can produce parts with almost
no setup cost. That’s where to look. When you eliminate
time-consuming and labor-intensive setups, you begin to realize the vast
potential for FMS productivity.”

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Onan, a subsidiary of McGraw-Edison, manufactures portable and
stationary electric generator sets, diesel and gasoline engines,
alternators…they’re heavy-duty metalworkers and they practice
what they preach. The firm recently purchased a $2.5-million FMS for
fabricating from Trumpf America Inc, Farmington, CT. The turnkey system will automate Onan’s entire sheet-metal part production, and might
be the most comprehensive fabrication FMS installed in the US.

Sophisticated subsystems

The entire FMS is comprised of many integrated subsystems, Figures
1 and 2. The automatic storage and retrieval subsystem (AS/RS), for
example, has a rack consisting of 51 material bins, each capable of
holding 6600 lb of sheet or plate stacked to a height of 6-1/2″ and
serviced by a stacker crane. A second rack can be added for future

Herehs how the FMS operates.

A guided transfer cart delivers pallets of raw material to an
automatic sheet loader. A thickness sensor and double-sheet detector
ensure correct single-sheet transfer.

A vacuum-cup lifter transports a sheet of work material to the
machine tool, a Trumatic 180 Laserpress that combines punching and
contouring with laser cutting (800 W Co.sub.2.; both pulsing and
continuous wave). The machine handles up to 1/4″-thick sheets.

The press features X-axis stop-pin location and four clamps for
Y-axis registration. Electronic sensors ensure overall material
registration prior to processing.

Unlike conventional turret punch presses, the FMS is serviced by a
robot toolchanger. The three-axis programmable robot has a
double-ended, rotary, axial gripper. The end effector removes a
preloaded tool cartridge from the press, rotates, and inserts a new
cartridge. While the machine punches and laser cuts, the robot returns
the used tool to its appropriate location in the storage towers, then
selects the next tool.

the rotary tool towers are designed to allow many tools in a
limited space, and minimize the locations programmed for the robot. Each
of the 10 circular levels in a tower holds 10 tools.

Whiel three towers provide the necessary number of preloaded tool
cartridges for continuous automated production, up to four towers may be
specified. Using a new Multitool unit (i.e., a single cartridge
carrying up to four tools), the system has capacity for 1600 tools.

Finished parts up to 8″ X 16″ enter a programmable drop
chute adjacent to the laser cutting head and are directed to a
small-parts sorter. A linear shuttle, with six bins, sorts part-size

Larger parts are picked up by an unloading device that has 72
densely arranged suction cups individually programmed to conform to hole
patterns and sheet size. Under program control, these parts are
conveyed to one of nine sorting pallets in two shuttle carts. Long
strips of offal are sorted into bins at the front of the carts and may
be used in other progressive-die operations, thereby optimizing
raw-material use.

Finally, forklifts remove filled pallets, transporting them either
to storage or other manufacturing areas. According to Trumpf,
wire-guided vehicles or other transport systems can be incorporated here
to fully automate the FMS.

Onan’s Iacoe emphasizes, “Delivery of the system
culminated nearly two years of effort. Our manufacturing engineers
surveyed leading equipment manufacturers on three continents, visiting
numerous installations, before selecting Trumpf. In effect, we formed a
partnership with them to do something in sheet-metal FMS that
hasn’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 that
automatically generates nested parts on sheets in two modes–one for
ongoing production, the other for exceptions that need expediting. The
DNC continuously monitors inventory, tooling (e.g., hit count and
regrind status), and work in progress.

The DNC system is hardware-independent, which allows any compatible
computer to be incorporated. In Onan’s case, the brain is a DEC
VAX-750, multitasking, multiuser, 32-bit speed demon.

DNC begins with input concerning tooling inventory in the towers
and material in the storage and retrieval system, incoming order
information, and part definition supplied by a Computervision CAD/CAM system. Tool-path information can be accepted in three formats: APT
source code, an APT-CL document, or actual NC code. This data enters a
System Planner software module, which performs nesting calculations that
consider burden and penalties for breaking a lot run, and prepares both
suspended and ready-to-execute job lists.

A System Schduler software module groups jobs according to priority
and efficiency. For instance, when feasible, jobs calling for the same
gage material are grouped sequentially, rather than separated by jobs
requiring different material gages.

Jobs are run by an execution Controller software module that
interfaces with a graphics monitor and an exception handler (one of the
first implementations of a shop-floor expert system). The EC
manipulates all operations of the AS/RS, the laser press, sheet loader
and unloader, part sorter, and robot tool-changing system.

Initial production is scheduled this month. Over 1000 part numbers
already are programmed for the system, with full production expected by
the end of the first quarter (approximately 5000 total part numbers).

For more information about flexible-fabricating technology, circle


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